WI-LAN Inc. v. Alcatel-Lucent USA Inc. et al

Filing 492

RESPONSE to Motion re 481 MOTION for New Trial CONCERNING THE NON-INFRINGEMENT OF CERTAIN CLAIMS OF U.S. PATENT NOS. 6,088,326; 6,222,819; 6,195,327 AND 6,381,211 filed by Alcatel-Lucent USA Inc., Ericsson Inc., Exedea INC., HTC America, Inc., HTC Corporation, Sony Mobile Communications (USA) Inc., Sony Mobile Communications AB, Telefonaktiebolaget LM Ericsson. (Attachments: # 1 Exhibit A: Markman Transcript, # 2 Exhibit B: Trial Transcript, # 3 Exhibit C: Trial Transcript, # 4 Exhibit D: Trial Transcript, # 5 Exhibit E: Trial Transcript, # 6 Exhibit F: PX 1, # 7 Exhibit G: PX 2, # 8 Exhibit H: PX 3, # 9 Text of Proposed Order)(Heinlen, James)

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EXHIBIT F 111111111111111111111111111111111111111111111111111111111111111111111111111· US006088326A United States Patent Lys~jko [11] et al. [54] Inventors: Martin Lysejko, Bagshot, United Kingdom; Paul F. Struhsaker, Plano, Tex. [73] Assignee: Airspan Cummunicatiuns Corporation, Wilmington, Del. 6,088,326 Date of Patent: Jul. 11, 2000 PROCESSING DATA TRANSMITTED AND RECEIVED OVER A WIRELESS LINK CONNECTING A CENTRAL TERMINAL AND A SUBSCRIDER TERMINAL OF A WIRELESS TELECOMMUNICATIONS SYSTEM [75] Patent Number: [45] [19] f21l Filed: [30] Nov. 26, 1997 Foreign Application Priority Data Dec. 20, 199n [51] l52j [58] [GR] 7 United Kingdom ................... 902()507 H04J 11/00; H04J 13/00; II04D 7/216 U.S. CJ ........................... 370/209; 370/342; 370/345; 370/441; 370/442; 370/479 Field of Search ..................................... 370/328, 329, 370/330, 335, 336, 337, 340, 341, 342, 343,345,347,441,442,465,468,479, 498, 203, 208, 209 Int. Cl. .............. .. ...... .... . .. References Cited [56] U.S. PA1ENT DOCUMENTS 4,688,210 8/1987 Eizenhoffer eta!. ................... 370/342 4,799,252 1/1989 Eizenhoffer et a!. ................... 370/342 5,373,502 12/1994 Turban ...................................... 370/18 5,592,469 li1997 Szabo .... ... .. .... .... ... ......... ... .... .. 370/342 6,005,854 12/1999 Xu et al. ................................. 370/335 FOREIGN PATENT DOCUMENTS 0652650 5/1995 European PaL Off. .. ........ H04L 1/00 United Kingdom .. ....... .... H04Q 7/32 WTPO .. ............................ H04N 1 /00 WIPO .. ........................... H04J 13/00 WIPO .. .. .. ...... ...... ... .... .. .. .. H04J 3/22 Primary Examiner-Ricky Ngo Attorney, Agent, or Firm-Baker Botts L.L.P. ABSTRACT l57J Appl. No .: 08/979,408 [22] 0730356 9/1996 2301744 12/1996 9::114590 7/'1993 9315573 8/1993 9523464 8/1995 The present invention provides a transmission controller and method for processing data items to be transmitted over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being employed for transmitting data items pertaining to a plurality of wireless links. The transmission controller comprises an orthogonal code generator for providing an orthogonal code from a set of 'm' orthogonal codes used to create 'm' orthogonal channels within the single frequency channel, and a first encoder for combining a data item to be transmitted on the single frequency channel with said orthogonal code from the orthogonal code generator, the orthogonal code determining the orthogonal channel over which the data item ·is transmitted, whereby data items pertaining to diiTen:nt wireless links may be transmitted simultaneously within different orthogonal channels of said single frequency channeL Further, the transmission controller comprises a IDM encoder arranged to apply time division multiplexing (TDM) techniques to the data item in order to insert the data item within a time slot of the orthogonal channel, whereby a plurality of data items relating to difl::erent wireless links may be transmitted within the same orthogonal channel during a predetermined frame period. The invention also provides a reception controller and method for processing data items received over a wireless link. 15 Claims, 1li Orawing Sheets European Pat. Off..... ...... H04B 7i26 113 126 140 1.38 136 1.34 132 130 PLAINTIFF'S TRIAL EXHIBIT 6:10-CV-521-LED PX-1 exhibitsticker.com 142 BPF PA BPF \J\~xo; EXHqT t1..' 'l () I \) Rich Germosen, CSR, CSR-R, RPR, CRR WIL-0009775 U.S. Patent Jul. 11, 2000 6,088,326 Sheet 1 of 16 FIG. 1 ,c2A 20 ~ DO D FIG. 2 WIL-0009776 U.S. Patent 6,088,326 Sheet 2 of 16 Jul. 11, 2000 52 42 44 46 i 10 46 FIG. 3 46 46 55 60 / " 62 L------------------------J 66 FIG. 3A \ 68 \ I RFU I AN I t 42 70 \ MC 74 ; 72 ; I TU I sc : ~ 46 f.-. 55 47 WIL-0009777 U.S. Patent Jul. 11, 2000 N I .......... + N :c :::!! 1.(') N ,.,-) "'<t" N N Sheet 3 of 16 6,088,326 2281.75--------------------2278.25--------------------2274.75--------------------2271.25--------------------2267.75--------------------2264.25 ---------------·-----2260.75 F12 2257.25-,--------c F11 2253.75FlO!=' 2250.25 F9 en 0 2246.75 F8 12243.25F7 ........... 0 2239.75 F6 ~ 2236.25F5 S 2232.75 F4 ~ 2229.25 F3 g 2225.75 F2 2222.25 F1 2218.75--------------------2215.25--------------------2211.75---------------··----2208.25--------------------2204.75--------------------N ::c ~ ~.{")______________________ N II N ~ 0 en _o N :r: :::!! N I .......... + N :c ~ 1.(') N cri 1.0 D N 2106. 75----------------·----21 03.25---------------------2099.75--------------------2096.25 ----------------·--·--2092.75--------------------2089.25--------------------2085.75 F12 2082.25 F11 2078.75 F10 ..-. 2075.25 F9 o 2071.75 F8 8 2068.25----F7 t;; 2064.75 F6 ._. 2061.25---------tF5 ~ 2057.75 F4 0: 2054.25-F3 :::> 2050.75F2 2047.25 F1 2043.75--------------------2040.25--------------------2036.75--------------------2033.25--------------------2029.75--------------------- WIL-0009778 U.S. Patent Jul. 11, 2000 6,088,326 Sheet 4 of 16 FS1 ~ FS2 14t------ 2-80Km == FS3 ~ ----~ @y1o FIG. SA FS1 ~ FS2 - - - - - - 2-BOKm == FS3 ~ -----.-1 '' \ ' \ \, S3 '§r-~-~-------- Sl / ,, / I S2 I I I I I FIG. 5B WIL-0009779 ~ r.F1 . 93 85 83 ~ 95 ~ ~ ~ 2.56Mbits/s In 3.5MHz Multiple User Channel Multiple User Channel = 160Kbits/s ~ ~ 0 80 J \ I BASEBAND I 86 SIGNAL(1) BASEBAND lr96 SIGNAL(1) 87 __j_ I BASEBAND SIGNAL(N) 1 ~ ~ t"" N c c 0 rJ:, ::r WALSH CODE SPREAD(N) ~ ~ l""f' til -. 0 SON ( 160K?its/s 94N 1 External Interference 96N Other Cell interference I ~ 0\ 88 0 Q1 ur J t fc: QO U:J J l lr 90 J C:\ 0 ~ FIG. 6 ~ ~ w N 0'\ ~ 6 0 r 0 CD --.,J 00 0 ~ . 113 \Jl ~ OVERLAY CODE HYBRID [±11----i~ 2 WIRE 1/F ~SEERR~~~ H R=1/2. K=7 ~ GENERATOR CONVOLUTIONAL ENCODER CODEC ~ 118 116 r---\ I ) \ I) I ~ = ~ 0/A ~ 102 100 104 106 ~ 11 a 108 ~ ~ 112-.J RW CODE N 0 GENERATOR 0 0 PN CODE 114-1 GENERATOR 126 en 124 =- ~ ~ t""'!' 0'\ 0 ~ ~ TX ANTENNA I 140 \ 138 134 132 130 I _n_ <] BPF 142 136 PA POWER CONTROL <JHJlH<J BPF FIG. 128 @ II MIXER 7A 0"-. 122 MODULATOR 120 \_ LPF 0'\ .... 0 00 00 ~ N 0\ ~ r 6 0 0 <0 ~ ~ ~ . . rJJ 113 ~ CONVOLUTIONAL ENCODER 105 103 109 TDM ENCODER I • I I I OVERHEAD INSERTION ~ OVERLAY CODE GENERATOR ~ ~ 118 = ~ 116 D/A R:::: 1/2, K=7 ~ 1~ 1 108 ~ 110 ~ ~ N 0 112 ---j RW CODE 0 GENERATOR 0 PN CODE 114_.-r I GENERATOR r:fJ 1'1C ILU =-' 124 ('C ('C f""t- -..l 0 ~ ~ 0'\ TX ANTENNA 140 1 "'ZO IJU Jl <J BPF 142 PA 136 POWER CONTROL 134 132 130 <JHI1H<J BPF FIG. 7B 128 1®1 MIXER 122 MODULATOR 120 \__ 0', LPF 0 00 QQ ~ N 0'\ ~ r 6 0 0 <0 --.,j co N ~ ~ RX ANTENNA BPF LNA BPF 150~_{\_ 152 [> 154 ® [> _[\_ 158 156 170 MIXER LNA LPF IQ DE -MODULATOR ~ """""' re A/D = """""' 168 166 164 \_ 1-0 ~ ~ :1--1. 162 192 190 2 WIRE 1/F 188 184 [±]H~ HYBRID 183 182 r 160 N 0 0 0 180 179 TOM OVERHEAD EXTRACTION DECODER ~ ~ !"'t- oe; R=1/2, K=7 0 -. VITERBI CO DEC DECODER CALL CONTROL f-- 181 OVERLAY CODE GENERATOR ! 185 172 -1 FIG. BA r.r.. =- 187 RW CODE GENERATOR PN CODE 174 --1 GENERATOR 1--1. 0\ 0'\ .... 0 00 00 w N 0'\ ~ 6 0 r 0 <D -...) 00 (...) d . en . RX ANTENNA BPF 150~Jl 152 LNA [> 154 BPF MIXER LNA _}\_ 158 156 ~ ~ ® [> ~ LPF IQ DE -MODULATOR 166 164 (t> \_ = ~ 168 ~ i 162 F- SYNTHESIZER I )ooool )ooool \ 160 N 0 0 0 182 \,_ 191 189 179 \ ,.1'\nnr• ATnn l..Vr\r\C.U\1 Ur\ 1 178 VITERBI DECODER 172 ~ GENERATOR FIG. BE f""l- \0 0 ~ i---1. 0\ OVERLAY CODE GENERATOR RW CODE 380 ::::r ("p A/D R=l/2, K=7 181 ENGINE w fe OVERHEAD EXTRACTION DA 180 PN CODE 174 ~ GENERATOR 170 0'\ ..... 0 00 00 ~ N 0"\ ~ 6 0 r ~ -.._) (X) ~ ~ r;n COMA RW SPACE ~ ~ ~ ~ RW1 RW2 RW3 RW4 RWS RW6 RW7 RW8 RW9 RW10 RW11 RW12 RW13 RW14 RW15 O a a a oQQ 0 Q Q Q Q Q Q Q Q Q Q Q a a Q Q Q Q Q Q Q Q Q Q QQ Q Q a a L 12 3 4 1234 1234 12 3 4 , 23 4 , 23 4 12 3 4 123 4 12 3 4 123 4 12 3 4 12 34 12 3 4 1 Q Q Q Q Q Q Q Q Q Q Q Q QQ QO L 1 ~ 125.00us 40kb/s 10kb/s 10kb/s FIG. 9A RW2 RWJ RW4 RW5 RW6 ~ ~ N 0 r:.r. ~ =:::" RWB RW9 RW10 RW11 RW12 RW13 TIME F1-T4/1 Fl-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 Fl-14/1 Fl-14/1 F1-T4/1 F1-T4/1 F1-T4/1 F1-T4/1 RW1 F- 0 0 CDMA RW SPACE RW7 RW14 ("e ("e !""!' RW15 0 F1-T4/2 F1-T4/2 Fl-T4/2 F1-T4/2 Fl-T4/2 F1-T4/2 F1-T4/2 F1-T4/2 F1-14/2 F1-T4/2 F1-T4/2 F1-T4/2 F1-T4/2 Q Fl-14/3 Fl-14/3 F1-T4/3 F1-T4/3 F1-T4/3 F1-T4/3 Fl-14/3 F1-T4/3 F1-T4/3 F1-T4/3 Fl-14/3 Fl -:14/3 F1-T4/3 1 ~ c 0 I l = ~ TIME j re l 1 31.25us -. )--< 0'\ 62.50us 93.75us Fl-14/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 F1-T4/4 125.00us 40kb/s FIG. 9B 40kb/s 10kb/s "" ~ 0 00 00 w N "" ~ 6 0 r 0 (0 ---1 (X) Ul U.S. Patent F1 6,088,326 Sheet 11 of 16 Jul. 11, 2000 F1 /~ H2 H1 Hn / 1\ Q3 ' \ 02 Qn Q1 Ln L1 Fl"G. 1 Ql ()4 I I L2 I I L3 L4 20 10 y_ 202 UPLINK 2~ DOWNLINK CENTRAL TERMINAL cs PC 204 214 SUBSCRIBER TERMINAL F'IG. 11 220 PN CODE ~JE SEQUENCE 222-1 212 DOWNLINK 216 R/W CODE OVERLAY CODE FIG. 12 FRAME INFORMATION WIL-0009786 U.S. Patent (!) Jul. 11, 2000 l 6,088,326 Sheet 12 of 16 OH --------------------------~ 01 (II) OH 02 03 I 0 25us 50 us 75us FIG. 04 125us 100us 13A (I) ~~_ _ _ _ _ _ __ _ _ _ _ ___, oH (11) I OH/0 81 81 81 81 I OH I B1 81 I 81 I 81 I D I 82 I 82 I 82 I 82 (IV) IOH I811 811 811 811 011 B2j 821821821 OH I831831831831 D2jB41 841841841 (!II) 25us 0 50 us FIG. (1) ! (II) I~....__ _ FA_w (Ill) cs FAW 125us 100us 75us 13B PC CH.!D OMC _...._ __ _.....__P_c_ cs _...._ _ c_H._ID_~ FAW CS1 PC1 OMC1 CH.ID CS2 PC2 OMC2 FAW CS3 PC3 OMC3 CH.ID* CS4 PC4 OMC4 FIG. 14A WIL-0009787 U.S. Patent (I) cs FAW I FAW cs (Ill) I FAW cs (IV) I FAW cs PC [) D PC (II) 6,088,.326 Sheet 13 of 16 Jul. 11, 2000 OMC/D PC I= OMC~ PC I- ] ] [~:H.ID I UNUS~ I UNUSED I UNUSED] OMC 1 Oms lms 3ms 2ms F.! G. 4ms t4B TOTAL TRAFFIC CHANNEL ·----------------~·~ INTERFERENCE LIMITED TRAFFIC CHANNEL POOL +--------------------------------~·~ ~--LT_c__~___ __~j__ n_c Ao~rc.~j_____s._rc____~__ P_rc_] LTC FTC AOTC AITC BTC PTC = LOCKED TRAFFIC CHANNEL = FREE TRAFFIC CHANNEL = ACCESS OUTGOING TRAFFIC CHANNEL = ACCESS INCOMI~IG TRAFFIC CHANNEL = BUSY TRAFFIC CHANNEL = PRIORITY TRAFFIC CHANNEL FIG. 1 {J WIL-0009788 d . LOCKED CHANNELS TURNED OFF RW1 RW2 RW3 TIME RW4 RWS RW6 Fl-14/1 l Fl RW7 RWB RW9 RW10 RW11 Fl-T4/1 F1-T4/1 FIXED ASSIGNMENT LINKS, 160kb/s FIG. rJ). RW12 RW13 RW14 RW15 F1-T4/1 Fl-12/1 F1-T2/1 F1-T2/1 Fl-12/1 F1-14/2 Fl-14/2 F1-14/2 F1-T4/3 F1-T4/3 F1-T4/3 F1-T4/3 F1-T4/3 ... Fl-12/2 F1-T2/2 Fl-14/4 F1-T4/4 F1-T4/4 Fl-T4/4 F1-T4/4 Fl . ~ COMA RW SPACE F1 F1-T4/2 Q F1-T4/3 1 0 31.25us L 1 ~ ~ = ~ 62.50us 93.75us Fl-14/4 125.00us 40kb/s 15A ~ ~ 1Okb/s ~ =: :-1-< -.:-" l.'-J C> C> 0 COMA RW SPACE RW1 RW2 RWJ RW4 RW5 RW7 RW6 RWB RW9 RW10 RW11 ~ RW13 RW12 RW14 RW15 O TIME ,.... l F1 a F1 ·0 oa 1 .· ..· .. 4 1 2 .... Q aL a 4 12 3 H :_: Q H QQ H :. 1 4 1 34 1 (t> (t> !""!" H H 1 2 Fl L 1 L :1 L 1 FIXED ASSIGNMENT LINKS, l60kb/s 0 tO -.._] tO -. 0\ FREE Ln SLOTS AVAILABLE FOR UPLINK ACQUISITION 125.00us FREE Ln SLOTS AVAILABLE 80kb/s FOR UPLINK ACQUISITION FIG. ()) .+;;.. 0 1-< UPLINK ACQUISITION, 10kb/s ~ 6 0 1-< .. L---....L..----'-__,.;,;~~~_._~......,-4-'-.....~-o~~~.....L,;,(.J...J.-L...L....._~;.;.J,._~--L-~---L.~;.;.;..;..;.;.;~-~-...J r en PRIORITY UPLINK ACQUISITION, 1 Okb/s 15B 0'\ 0 ~ ~ ~ N 0'\ ~ 370 302 MANAGEMENT SYSTEM 380 I ~ ~ ~ = 365 DA ENGINE I "'C ----.. r-~----------- 390. 'i'"J. I I I . ~ DYNAMIC POOL SIZING ~ 'G • Ii' .L . .L -1 I F- 7 ~ ~ N 0 0 0 ,.,.. ...,_. :::-' (t) ("C 336 ~ )-1. Ul -. 0 )-1. 0\ 0", ..... 0 00 ~ ~-----------~~-======~~--- w N 0\ ~ 6 0 r 0 (!) "'-! (!) 0 U.S. Patent 6,088,326 Sheet 16 of 16 Jul. 11, 2000 0 (I) (Ill) FIG. 18 58 ct=J 10 I I 405 @-20 SERVICE DOMAIN CONTROLLER 400 10 FIG. 19A 420 -- I • 435 r \ MESSAGE DECODER ) ( ( _)_ CHANNEL SELECTION CONTROLLER 465 425"""-. 445 ; \ RADIO SUBSYSTEM 440 470 \ 4~ 460 LL . ..... --- r 455 450 \ 336 430 FIG. CALL CONTROL 19B WIL-0009791 o,OR8,326 1 2 PROCESSING DATA TRANSMITTED AND RECEIVED OVER A WIRELESS LINK CONNECTING A CENTRAL TERMINAL AND A SUBSCRIBER TERMINAL OF A WIRELJESS TELECOMMUNICATIONS SYSTEM communications system, and as it is desirable for neighbouring cells to use different frequency channels so as to reduce interference, the demand cannot be met by merely adding more modem shelves to each central terminal. SUMMARY OF TI-lE INVENTION TECHNICAL FIELD OF THE INVENTION According to the present invention, there is provided a transmission controller for processing data items to be transmitted over a wireless tink connecting a central termi10 nal and a subscriber terminal of a wireless telecommunications system, a single frequency channel being employed for transmitting data items pertaining to a plurality of wireless links, the transmission controller comprising: an orthogonal BACKGROUND OF THE INVENTION code generator for providing an orthogonal code from a set 15 A wirdess telecommunications system has been proposed of ·'m' orthogonal codes used to create 'm' orthogonal channels within the single frequency channel; a first 1;ncoder in which a geographical area is divided in to cells, each cell having one or more central terminals (CTs) for communifor combining a data item to be transmitted on the single frequency channel with said orthogonal code from the cating over wireless links with a number of subscriber orthogonal code generator, the orthogonal code determining terminals (S'ls) in the cell. These wireless links are estab20 lished over pr~determined frequency channels, a frequency the orthogonal channel over which the data item is channel typically consisting of one frequency for uplink transmitted, whereby data items pertaining to different wiresignals from a subscriber terminal to the central terminal, less links may be transmitted simultaneously within different and another frequency for downlink signals from the central orthogonal channels of said single frequency channel; and a terminal to the subscriber terminal. TDM encoder arranged to apply time division multiplexing 25 (TDM) techniques to the data item in order to insert the data Due to bandwidth constraints, it is not practical for each item \vithin a time slot of the orthogonal channel, wherehy individual subscriber terminal to have its own dedicated a plurality of data items relating to different wireless links frequency channel for communicating with the central termay be transmitted within the same orthogonal channel minal. Hence, techniques need to be applied to enable data items relating to different wireless links to be passed over the 30 during a predetermined frame period. same frequency channel without interfering with each other. Viewed from a second aspect, the present invention In current wireless telecommunications systems, this can be provides a reception controller for processing data items achieved through the use of a 'Code Division Multiple received over a wireless link connecting a central terminal Access' (CDMA) technique. One way to implement CDMA and a subscriber terminal of a wireless telecommunications is through the application of a set of orthogonal codes to the 35 system, a single frequency channel being employed for data items to be transmitted on a particular frequency transmitting data items pertaining to a plurality of wireless channel, data items relating to different wireless links being links, and 'm' orthogonal channels being provided within the combined with different orthogonal codes from the set. A single frequency channel, the receiver controller comprissuitable set of orthogonal codes is a "Rademacher-Walsh" ing: an orthogonal code generator for providing an orthogo(RW) set of sixteen 16-bit codes. Orthogonal codes have the nal code from a set of 'm' orthogonal codes used to create 40 property that, when perfectly aligned, all codes crosssaid 'm' orthogonal channels within the single frequency correlate to zero, thus making it possible to decode a signal channel; a first decoder for applying, to signals received on to which one orthogonal code has been applied while the single frequency channel, the orthogonal code provided cancelling interference from signals to which different by the orthogonal code generator, in order to isolate data orthogonal codes have been applied. items transmitted within the corresponding orthogonal chan45 nel; and a TDM decoder arranged to extract a data item from Signals to which an orthogonal code has been applied can a predetermined time slot within said orthogonal channel, a be considered as being transmitted over a corresponding plurality of data items relating to different wireless links orthogonal channel within a particular frequency charmel. being transmitted within the same orthogonal channel during Hence, considering the example of a set of 16 RW codes, 16 orthogonal channels can be created within a single fre- 50 a predetermined frame period. quency channel, and hence up to sixteen separate commuBy using TDM techniques in addition to the known set of nication signals (corresponding to sixteen separate wireless orthogonal codes, it is possible for selected orthogonal links) can be transmitted simultaneously over the single channels to be subdivided in the time dimension. For frequency channel if different RW codes are applied to each example, if TDM is used to divide one frame period in to communication signal. 55 four subframes, and each orthogonal channel is subject to the TDM technique, then up to 64 separate communication It is known to provide a number of modem shelves within signals can be transmitted on the sixteen orthogona] chanone central terminal, and for each modem shelf to employ a nels during one frame period, albeit at a quarter of the rate different frequency channel. Hence, if a central terminal has that the communication signals could be transmitted if the four modem shelves, and the set of 16 RW codes is employed for each frequency channel, one central terminal 60 TOM technique was not used. would be able to support wireless links with up to 60 Such an approach has the advantage that it preserves subscriber terminals simultaneously. compatibility with current hardware and software equipment However, as more subscribers subscribe to the wireless which use the set of orthogonal codes, but which do not tdecummunicatiuns ne!wurk, it is becoming desirablt: tu ~upport tht u~t uf TDM ttdmiyue::;. By designating '.;trtain support more and more subscriber terminals from each 65 orthogonal channels as channels for which TDM is not used, central terminal. There are only a limited number of frethe current equipment can communicate over those channels quency channels that can be allocated to the wireless telewithout any changes being required to the equipment. The present invention relates in general to wireless telecommunications systems and more particularly to techniques for processing data transmitted and received over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications system. WIL-0009792 6,0RR,326 4 3 In preferred embodiments, the transnuss1on controller further comprises: an overlay code generator for providing an overlay code from a first set of 'n' overlay codes which are orthogonal to each other; and a second encoder, selectively operable instead of the TDM encoder, to apply the overlay code from the overlay code generator to said data item, whereby 'n' data items pertaining to different wireless links may be transmitted simultaneously within the same orthogonal channeL Similarly, the reception controller may further comprise: an overlay code generator for providing an overlay code from a first set of 'n' overlay codes which are orthogonal to each other, the set of 'n' overlay codes enabling 'n' data items pertaining to different wireless links to be transmitted simultaneously within the same orthogonal channel; and a second decoder, selectively operable instead of the TDM decoder, to apply to the data items of the orthogonal channel, the overlay code from the overlay code generator so as to isolate a particular data item transmitted using that overlay code. By such an approach, data items transmitted within certain orthogonal channels can be encoded using TDM techniques whilst data items transmitted within other orthogonal channels can be encoded using overlay codes, the reception controllers including the necessary decoders to decode either type of encoded data item. A preferred arrangement, where certain orthogonal channels are subject to TDM techniques whilst others are subject to overlay codes, will be discussed in more detail later. The orthogonal code generator may be arranged to generate orthogonal codes 'on the fly' using predetermined algorithms. However, alternatively, the orthogonal code generator may be provided as a storage arranged to store the set of orthogonal codes. Appropriate orthogonal codes can then he read out to the encoder or decoder from the storage as required. In preferred embodiments, the set of orthogonal codes comprise a set of Rademacher-Walsh (RW) codes, in preferred embodiments the set comprising a 16x16 matrix of RW codes. The transmission controller in accordance with the present invention may be provided within the central terminal of a wireless telecommunications system. In preferred embodiments, the central terminal would further comprise channelisation means for determining which of the orthogonal channels will be subject to TDM techniques, and for transmitting that information to a plurality of subscriber terminals within the wireless telecommunications system. This is useful since, for example, certain orthogonal channels can hence be designated as being reserved for communications with STs that do not incoqJOrate the features necessary to support TDM techniques, and which hence require the full orthogonal channel for the whole frame period. In preferred embodiments, the channelisation means also determines, for those orthogonal channels subject to TDM techniques, how many time slots will be provided within each orthogonal channel. This gives a great deal of flexibility in how channels are used, since some can be subdivided in the time dimension whilst others are not, and those which are subdivided can be subdivided differently to yield differing numbers of time slots per frame period. For instance, if an orthogonal channel operates at 160 kb/s, and [our Lime slots are provided within that orthogonal channel in order to carry data items pertaining to four different wireless links during one frame period, then each ST receiving data from said orthogonal channel will receive data at a rate of 40 kb/s (since each ST will only read a quarter of the data transmitted on the orthogonal channel during each frame period). If, alternatively, two time slots are provided within the orthogonal channel, then data items pertaining to only two different wireless links will be transmitted per frame period, and the two STs receiving data will do so at a rate of 80 kb/s (since each ST will read half of the data transmitted on the orthogonal channel during one frame period). This flexihil10 ity is useful, since for some communications, eg. fax, a rate of 40 kb/s may not be acceptable, and hence the use of four time slots would not be suitable. In preferred embodiments, a number of said orthogonal channels are designated as traffic channels for the transmis15 sion of data items relating to communication content, and the TDM encoder is employed to apply time division multiplexing (TDM) techniques to data items to be sent over a traffic channel from said central terminal to said subscriber terminal. The use of this CDMA!fDM hybrid approach for zo downlink traffic channels retains the benefit of CDMA access, i.e. interference is reduced when traffic is reduced, and also reduces receiver dynamic range requirements. However, a first of the orthogonal channels is preferably reserved for the transmission of signals relating to the 25 acquisition of wireless links, and the second encoder is used instead of the TDM encoder to enable overlay codes to be applied to data items to be sent within said first orthogonal channel from the central terminal to one of said subscriber 30 ~er:~e~a~~~ ;::~~Yfoar ~~~~;n~!1~~:i~~t~~:i~~: 1:~e~~~:l~ f~ 1 the control of calls, and the second encoder is used instead of the TDM encoder to enable overlay codes to be applied to data items to be sent within said second orthogonal channel from the central terminal to one of said subscriber 35 terminals. In preferred embodiments, at least one of the subscriber terminals of a \vireless telecommunications system comprises a reception controller in accordance with the present invention. However, for transmission of data from sub40 scriber terminals, it is preferable for the ST to have a transmission controller which employs overlay codes for all types of orthogonal channels, whether they be traffic channels or otherwise. On these uplink channels, the pure CDMA approach using overlay codes eliminates the need to time 45 synchronise STs to a TDM frame reference, and reduces the peak power handling requirements in the ST RF transmit chain. Viewed from a third aspect, the present invention provides so a wireless telecommunications system comprising a central terminal and a plurality of subscriber terminals, wherein the central terminal comprises a transmission controller in accordance with the present invention, and at least one of the subscriber terminal comprises a reception controller in 55 accordance with the present invention. Viewed from a fourth aspect, the present invention provides a method of processing data items to be transmitted over a wireless link connecting a central terminal and a subscriber terminal of a wireless telecommunications 60 system, a single frequency channel being employed for transmitdng data items pertaining to a plurality of wireless links, the method comprising the steps of: (a) providing an orthogonal code from a set of 'm' orthogonal codes used to create 'm' orthogonal charmels within the sirrgk frequency 65 channel; (b) combining a data item to be transmitted on the single frequency channel with said orthogonal code, the orthogonal code determining the orthogonal channel over WIL-0009793 6,0RR,326 5 6 which the data item is transmitted, whereby data items FIG.10 illustrates the CDMAchannel hierarchy in accorpertaining to different wireless links may be transmitted dance with preferred embodiments of the present invention; simultaneously within different orthogonal channels of said FIG. 11 is a schematic diagram illustrating downlink and single frequency channel; and (c) applying time division uplink communication paths for the wireless telecommunimultiplexing (TDM) techniques to the data item in order to cations system; insert the data item within a time slot of the orthogonal FIG.l2 is a schematic diagram illustrating the makeup of channel, whereby a plurality of data items relating to difa downlink signal transmitted by the central terminal; ferent wireless links may be transmitted within the same FIGS. 13A and 13B illustrate the structure of the frames orthogonal channel during a predetermined frame period. of information sent over the downlink and uplink paths; Viewed from a fifth aspect, the present invention provides 10 FIGS. 14A and 14B illustrate the overhead frame struca method of processing data items received over a wireless ture for the downlink and uplink paths; link connecting a central terminal and a subscriber terminal FIGS. 15Aand 15B illustrate typical downlink and uplink of a wireless telecommunications system, a single frequency channel structures that might occur in a loaded system in channel being employed for transmitting data items pertaining to a plurality of wireless links, and 'm' orthogonal 15 accordance with preferred embodiments of the present invention; channels being provided within the single frequency channel, the method comprising the steps of: (a) providing FIG. 16 illustrates how the available traffic channels are an orthogonal code from a set of 'm' orthogonal codes used classified in preferred embodiments of the present invention; to create said 'm' orthogonal channels within the single FIG. 17 illustrates the elements used by the central frequency channel; (b) applying, to signals received on the zo terminal to perform interference limiting; single freq11ency channel, the orthogonal code in order to FIG. 18 illustrates possible antenna configurations that isolate data items transmitted vvithin the corresponding can be employed in a wireless telecommunications system in orthogonal channel; and (c) extracting a data item from a accordance with the preferred embodiment of the present predetermined time slot within said orthogonal channel, a invention; and plurality of data items relating to different wireless links 25 FIGS. 19A and 19B illustrate how channel switching is being transmitted within the same orthogonal channel during facilitated in preferred embodiments of the present invena predetermined frame period. By using TDM techniques in tion . addition to the known set of orthogonal codes, it is possible for selected orthogonal channels to be subdivided in the time DETAILED DESCRIPTION OF THE dimension, thereby making it possible to support more 30 INVENTION wireless links on one frequency channel. FlfG. 1l is a schematic overview of an example of a BRIEF DESCRIPTION OF THE INVENTION wireless telecommunications system. The telecommunications system includes one or more service areas 12, 14 and An embodiment of the invention will be described hereinafter, by way of example only, with reference to the 35 ll6, each of which is served by a respective central terminal (CT) 10 which establishes a radio link with subscriber accompanying drawings in which like reference signs are terminals (S1) 20 within the area concerned. The area which used for like features and in which: is covered by a central terminal10 can vary. For example, FIG. 1 is a schematic overview of an example of a in a rural area with a low density of subscribers, a service wireless telecommunications system in which an example of 40 area 12 could cover an area with a radius of 15-20 Km. A the present invention is included; service area 14 in an urban environment where is there is a FIG. 2 is a schematic representation of a premises; FIGS. high density of subscriber terminals 20 might only cover an 2A and 2B are schematic illustrations of an example of a area with a radius of tht order of 100 m. In a suburban area subscriber terminal of the telecommunications system of with an intermediate density of subscriber terminals, a FIG.1; service area 16 might cover an area with a radius of the order FIG. 3 is a schematic illustration of an example of a 45 of 1 Km. It will be appreciated that the area covered by a central terminal of the telecommunications system of FIG. particular central terminal10 can be chosen to suit the local 1; requirements of expected or achtal subscriber density, local FIG. 3A is a schematic illustration of a modem shelf of a geographic considerations, etc., and is not limited to the central terminal of the telecommunications system of FIG. 50 examples illustrated in FIG.l. Moreover, the coverage need 1; not be, and typically will not be circular in extent clue to FIG. 4 is an illustration of an example of a frequency plan antenna design considerations, geographical factors, buildfor the telecommunications system of FIG. 1; ings and so on, which will affect the distribution of transFIGS. 5A and 5B are schematic diagrams illustrating mitted signals. possible configurations for cells for the telecommunications The central terminals :n.o fur respective service areas 12, 55 system of FIG. 1; ll4, 16 can be connected to each other by means of links 13, FIG. 6 is a schematic diagram illustrating aspects of a 15 and 17 which interface, for example, with a public code division multiplex system for the telecommunications switched telephone network (PSTN) 18. The links can system of FIG. 1; include conventional telecommunications technology using FIGS. 7A and 7B are schematic diagrams illustrating 60 copper wires, optical fibres, satellites, microwaves, etc. signal transmission processing stages for the telecommuniThe wireless telecommunications system of FIG. 1 is cations system of FIG. 1; based on providing fixed microwave links between subFIGS. SA and 8B are schematic diagrams illustrating scriber terminals 20 at fixed locations within a service area signal reception processing stages for the telecommunica(t:.g.,. 12, 14, 16) amltht: <.:entral termina110 Lor Lhal ~.ervi<.:<; tions system of FIG. 1; 65 area. Each subscriber terminal 20 can be provided with a FIGS. 9A and 9B are diagrams :illustrating the uplink and permanent fixed access link to its central terminallO, but in preferred embodiments demand-based access is provided, so downlink delivery methods when the system :is fully loaded; WIL-0009794 6,0R8,326 7 8 central terminal10. Tbe site controller 56 can be connected that the number of subscribers which can be supported exceeds the number of available wireless links. The manner to each modem shelf of the central terminal 10 via, for example, RS232 connections 55. The site controller 56 can in which demand-based access is implemented will be then provide support functions such as the localisation of discussed in detail later. faults, alarms and status and the configuring of the central FIGS. 2A and 2B illustrate an example of a configuration terminal 10. A site controller 56 will typically support a for a subscriber terminal 20 for the telecommunications single central terminal 10, although a plurality of site system of FIG. 1. FIG. 2 includes a schematic representation controllers 56 could be networked for supporting a plurality of customer premises 22. A customer radio unit (CRU) 24 is of central terminals mounted on the customer's premises. The customer radio unit 24 includes a fiat panel antenna or the like 23. The 10 As an alternative to the RS232 connections 55, which extend to a site controller 56, data connections such as an customer radio unit is mounted at a location on the customX.25 links 57 (shown with dashed lines in FIG. 3) could er's premises, or on a mast, etc., and in an orientation such instead be provided from a pad 228 to a switching node 60 that the fiat panel antenna 23 within the customer radio unit of an element manager (EM) 58. An element manager 58 can 24 faces in the direction 26 of the central terminal10 for the support a number of distributed central terminals 10 conservice area in which the customer radio unit 24 is located. The customer radio unit 24 is connected via a drop line 28 15 nectcd by respective connections to the switching node 60. The element manager 58 enables a potentially large number to a power supply unit (PSU) 30 within the customer's (e.g., up to, or more than 1000) of central terminals 10 to be premises. The power supply unit 30 is connected to the local integrated into a management network. The element manpower supply for providing power to the customer radio unit ager 58 is based around a powerful workstation 62 and can 24 and a network terminal unit (NTU) 32. The customer 20 include a number of computer terminals 64 for network radio unit 24 is also connected via the power supply unit 30 engineers and control personneL to the network terminal unit 32, which in turn is connected FIG. 3A illustrates various parts of a modem shelf 46. A to telecommunications equipment in the customer's transmit/receive RF unit (RFU-for example implemented premises, for example to one or more telephones 34, facon a card in the modem shel±) 66 generates the modulated simile machines 36 and computers 38. The telecommunica- 25 transmit RF signals at medium power levels and recovers tions equipment is represented as heing within a single and amplifies the baseband RF signals for the subscriber customer's premises. However, this need not be the case, as terminals. The RF unit 66 is connected to an analogue card the subscriber termina120 preferably supports either a single (AN) 68 which performs A-DID-A conversions, baseband or a dual line, so that two subscriber lines could be supported filtering and the vector summation of 15 transmitted signals by a single subscriber terminal 20. The subscriber terminal 30 from the modem cards (MCs) 70. The analogue unit 68 is 20 can also be arranged to support analogue and digital connected to a number of (typically 1-8) modem cards 70. telecommunications, for example analogue communications The modem cards perform the baseband signal processing of at 16, 32 or 64 kbits/sec or digital communications in the transmit and receive signals to/from the subscriber accordance with the ISDN BRA standard. terminals 20. This may include Y2 rate convolution coding FIG. 3 is a schematic illustration of an example of a 35 and x16 spreading with "Code Division Multiplexed central terminal of the telecommunications system of FIG. 1. Access" (CDMA) codes on the transmit signals, and synThe common equipment rack 40 comprises a number of chronisation recovery, de-spreading and error correction on equipment shelves 42, 44, 46, including a RF Combiner and the receive signals. Each modem card 70 in the present power amp shelf (RFC) 42, a Power Supply shelf (PS) 44 example has two modems, and in preferred embodiments and a number of (in this example four) Modem Shelves 40 there are eight modem cards per shelf, and so sixteen (MS) 46. The RF combiner shelf 42 allows the modem modems per shelf. However, in order to incorporate redunshelves 46 to operate in paralleL If 'n' modem shelves are dancy so that a modem may be substituted in a subscriber provided, then the RF combiner shelf 42 combines and link -when a fault occurs, only 15 modems on a single amplifies the power of 'n' transmit signals, each transmit modem shelf 46 are generally used. The 16th modem is then signal being from a respective one of the 'n' modem shelves, 45 used as a spare which can be switched in if a failure of one and amplifies and splits received signals 'n' way so that of the other 15 modems occurs. The modem cards 70 are separate signals may be passed to the respective modem connected to the tributary unit (TU) 74 which terminates the shelves. The power supply shelf 44 provides a connection to connection to the host public switched telephone network 18 the local power supply and fusing for the various compo(e.g., via one of the lines 47) and handles the signalling of nents in the common equipment rack 40. A bidirectional so telephony information to the subscriber terminals via one of connection extends between the RF combiner shelf 42 and 15 of the 16 modems. the main central terminal antenna 52, such as an omnidiThe wireless telecommunications between a central terrectional antenna, mounted on a central terminal mast 50. minal 10 and the subscriber terminals 20 could operate on This example of a central terminal10 is connected via a various frequencies. FIG. 4 illustrates one possible example point-to-point microwave link to a location where an inter- 55 of the frequencies which could be used. In the present face to the public switched telephone network 18, shown example, the wireless telecommunication system is intended schematically in FIG. 1, is made. As mentioned above, other to operate in the 1.5-2.5 GHz Band. In particular the present types of connections (e.g., copper wires or optical fibres) can example is intended to operate in the Band defined by ITU-R be used to link the central terminal10 to the public switched (CCIR) Recommendation F.701 (2025-2110 MHz, telephone network 18. In this example the modem shelves 60 2200-2290 MHz). FIG. 4 illustrates the frequencies used for are connected via lines 47 to a microwave terminal (MT) 48. the uplink from the subscriber terminals 20 to the central A microwave link 49 extends from the microwave terminal terminal10 and for the downlink from the central terminal 48 to a point-to-point microwave antenna 54 mounted on the 10 to the subscriber terminals 20. It will be noted that 12 mast 50 for a host connection to the public switched teleuplink aml12 downlink radio channels o[ 3.5 MHz each are phone network 18. 65 provided centred about 2155 MHz. The spacing between the A personal computer, workstation or the like can be receive and transmit channels exceeds the required miniprovided as a site controller (SC) 56 for supporting the mum spacing of 70 MHz. WIL-0009795 6,0R8,326 10 9 In the present example, each modem shelf supports 1 increased three fold, while still providing permanent fixed frequency channel (i.e. one uplink frequency plus the coraccess for each subscriber terminal 20. responding downlink frequency). Currently, in a wireless Arrangements such as those in FIGS. SA and SB can help telecommunications system as described above, CDMA reduce interference, but in order to ensure that cells operencoding is used to support up to 15 subscriber links on one ating on the same frequency don't inadvertently decode each frequency channel (one subscriber link on each modem). others data, a seven cell repeat pattern is used such that for Hence, if a central terminal has four modem shelves, it can a cell operating on a given frequency, all six adjacent cells support 60 (15x4) subscriber links (i.e. 60 STs can be operating on the same frequency are allocated a unique connected to one C:T). However, it is becoming desirable for pseudo random noise (PN) code. The use of PN codes will more than 60 STs to be supported from one central terminal, 10 be discussed in more detail later. The use of different PN and, in preferred embodiments of the present invention, codes prevents nearby cells operating on the same frequency enhancements to the COMA encoding technique are profrom inadvertently decoding each others data. vided to increase the number of subscriber links that can be .As mentioned above, CDMA techniques can be used in a supported by a central terminal. Both CDMA encoding, and fixed assignment arrangement (ie. one where each ST is the enhancements made to the CDMA encoding in accor- 15 assigned to a particular modem on a modem shelf) to enable dance with preferred embodiments, will be discussed in each channd fn:qutncy to support 15 subscriber links. FIG. more detail later. 6 gives a schematic overview of CDMA encoding and Typically, the radio traffic from a particular central terdecoding. minallO will extend into the area covered by a neighbouring In order to encode a CDMA signal, base band signals, for central termina110. 'lb avoid, or at least to reduce interfer- 20 example the user signals for each respective subscriber link, ence problems caused by adjoining areas, only a limited are encoded at 80-SON into a 160 ksymbols/sec baseband number of the available frequencies will be used by any signal where tach symbol represents 2 data bits (see, for given central terminal 10. example the signal represented at 81). This signal is then spread by a factor of 16 using a spreading function 82-82N FIG. SA illustrates one cellular type arrangement of the frequencies to mitigate interference problems between adja- 25 to generate signals at an effective chip rate of 2.56 Msymbols/sec in 3.5 MHz. The spreading function involves cent central terminals 10. In the arrangement illustrated in applying a PN code (that is specified on a per CT basis) to FIG. SA, the hatch lines for the cells 76 illustrate a frequency the signal, and also applying a Rademacher-Walsh (RW) set (FS) for the cells. By selecting three frequency sets (e.g., code which ensures that the signals for respective subscriber where: FS1=F1, F4, F7, FlO; FS2=F2, F5, F8, Fll; FS3=F3, F6, F9, F12), and arranging that immediately adjacent cells 30 terminals will be orthogonal to each other. Once this spreading function has been applied, the signals for respective do not use the same frequency set (see, for example, the subscriber links are then combined at step 84 and converted arrangement shown in FIG. SA), it is possible to provide an to radio frequency (RF) to give multiple user channel signals array of fixed assignment omnidirectional cells where inter(e.g. 85) for transmission from the transmitting antenna 86. ference between nearby cells can be reduced. The transmitDuring transmission, a transmitted signal will be subter power of each central terminal10 is preferably set such 35 that transmissions do not extend as far as the nearest cell jected to interference sources 88, including external interwhich is using the same frequency set. Thus, in accordance ference 89 and interference from other channels 90. Accordingly, by the time the CDMAsignal is received at the with the arrangement illustrated in .FIG. SA, each central receiving antenna 91, the multiple user channel signals may terminallO can use the four frequency pairs (for the uplink and downlink, respectively) within its cell, each modem 40 be distorted as is represented at 93. shelf in the central terminal 10 being associated with a In order to decode the signals for a given subscriber link respective RF channel (channel frequency pair). from the received multiple user channel, a Walsh correlator 94-94N ust:s the samt: RV( and PN codes lhat wt:re ust:d for FIG. 5B illustrates a cellular type arrangement employing sectored cells to mitigate problems between adjacent central 45 the encoding for each subscriber link to extract a signal (e.g, as represented at 95) for the respective received baseband terminals 10. As with FIG. SA, the different type of hatch signal 96-96N. It will be noted that the received signal will lines in FIG. 5B illustrate different frequency sets. As in include some residual noise. However, unwanted noise can FIG. SA, FIG. SB represents three frequency sets (e.g., be removed using a low pass filter and signal processing. where: FS1=F1, F4, F7, FlO; FS2=F2, F5, F8, Fll; FS3=F3, F6, F9, F12). Howevt:r, in FIG. SB the cdls are st:ctored by 50 Tht: kty to CDMA i& the application of lhe RW codes, using a sectored central terminal (SCT) 13 which includes these being a mathematical set of sequences that have the three central terminals 10, one for each sector S1, S2 and S3, function of "orthonormality". In other words, if any RW with the transmissions for each of the three central terminals code is multiplied by any other RW code, the results are zero. A set of 16 RW codes that may be used is illustrated in 10 being directed to the appropriate sector among S1, S2 and S3. This enables he number of subscribers per cell to be Table 1 below: TABLE 1 RWO RW1 KW2 RW3 RW4 RWS RW6 RW7 RW8 RW9 -1 1 -1 1 -1 1 -1 1 -1 -1 -1 1 -1 -1 1 -] -1 1 1 -1 -1 -1 -1 -1 1 -1 -1 1 -1 -1 1 -1 -1 -1 -1 -1 1 1 1 -1 -1 1 -1 1 -1 -1 -1 1 -1 -1 -1 -1 1 1 -1 -1 -1 1 1 -1 1 1 -1 -1 -1 -1 -1 1 -1 1 -1 -1 -1 -1 -1 -1 1 -1 -1 1 -1 1 -1 -1 -1 -1 -1 1 1 -1 -1 1 -1 -1 1 -1 1 1 -1 -1 -1 1 1 -1 -1 1 -1 1 -1 1 -1 WIL-0009796 6,0R8,326 12 11 TABLE 1-continued RW10 RW11 RW12 RW13 RW14 RW15 1 -l -1 -1 1 -1 -" -J. -1 1 1 -1 -1 -1 1 -1 -1 -1 1 -1 -1 1 -1 -1 -1 -1 -1 1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 1 -1 l 1 1 -1 1 -1 -1 -J -1 -1 1 -1 1 -1 -1 1 1 -1 1 -1 1 -1 1 -1 -1 -1 -1 1 10 Overlay codes are used extensively to provide variable rate uplink traffic channels. Overlay codes will also be used to implemerrt downlink control channels, these control channels being discussed in more detail later. However, as 15 mentioned earlier, a different approach is taken for providing flexible channelisations on the dmvnlink traffic channel paths. Downlink traffic channels will operate in high rate, 160 kb/s, mode, with lower data rates of 80 and 40 kb/s being supported by 'Time Division Multiplexing' (IDM) 20 the available bandvvi.dth. In preferred embodiments, TDM timeslot bit numbering will follow the CCITT G.732 convention with bits transmitted in the sequence bit 1, bit 2 ... bit 8. Byte orientation is specified per channel as either most significant bit (MSB) 25 first, least significant bit (LSB) first or N/A The provision of a hybrid CD1tiA!TDM approach for downlink traffic channels retains the benefits of CDMA access, ie. interference is reduced when traffic is reduced. Further, use of TDM ensures that the CDMA signal is 30 limited to a256 'Quadrature Amplitude Modulation' (QAM) constellation which reduces receiver dynamic range requirements. QAM constellations will be familiar to those skilled in the art. On the uplink channels, the pure CDMA approach using 35 overlay codes eliminates the need to time synchronise STs to a TDM frame reference. This has the advantage ofelimi160 kbis Full rate (F1) nating TDM delays and the 'guard time' in between TDM 80 kb/s Half rate (H1, H2) Quarter rate (Q1, Q2. Q3, Q4) 40 kbis frames. Another benefit is reduced peak power handling 10 kbis Low rate (Ll, L2, L3, L4), for uplink acquisition requirements in the ST RF transmit chain which would 40 otherwise be needed when transmitting bursty TDM data. High dynamic range requirement is restricted to the CT In preferred embodiments, the manner in which these receiver. channelisations are provided differs for the downlink (CT to The manner in which the transmitted and received signals ST) and uplink (ST to CT) communication paths. This is because it has been realised that different performance 45 are processed in accordance with preferred embodiments of the present invention will be described with refe.rence to requirements exist for the downlink and uplink paths. On the FIGS. 7 and 8. FIG. 7A is a schematic diagram illustrating downlink all signals emanate from a single source, namely signal transmission processing stages as configured in a the central terminal, and hence the signals will be synchrosubscriber tcrminal20 in the telecommunications system of nised. However, on the uplink path, the signals will emanate from a number of independent STs, and hence the signals so FIG. 1. In FIG. 7A, an analogue signal from a telephone is passed via an interface such as two-wire interface 102 to a will not be synchronised. hybrid audio processing circuit 104 and then via a codec 106 Given the above considerations, in preferred to produce a digital signal into which an overhead channel embodiments, on the uplink path fu11 rate (160 kh/s) operaincluding control information is inserted at 108. If the tion is implemented using the basic set of RW codes discussed earlier, but half and quarter rates are achieved 55 subscriber terminal supports a number of telephones or other telecommunications equipment, then elements 102, 104 and through the use of 'Overlay Codes' which comprise RW 106 may be repeated for each piece of telecommunications coded high rate symbol patterns that are transmitted for each equipment. intermediate rate data symbol. For half rate operation, two At the output of overhead insertion circuit 108, the signal 2-bit overlay codes are provide, whilst for quarter rate operation, four 4-bit overlay codes are provided. When 60 wi11 have a bit rate of either 160, RO or 40 kbits/s, depending on which channel has been selected for transmission of the generating a signal for transmission, one of the overlay signal. codes, where appropriate, is applied to the signal in addition The resulting signal is then processed by a convolutional to the appropriate RW code. When the signal is received, encoder 110 to produce lwo signals with tht: same bil rale as then at the CDMA demodulator the incomirrg signal is multiplied by the channel's PN, RW and Overlay codes. The 65 the input signal (collectively, these signals will have a symbol rate of 160, 80 or 40 KS/s). Next, the signals are correlator integration period is set to match the lerrgth of the passed to a spreader 111 where, if a reduced bit rate channel Overlay code. TI1e above set of RW codes are orthogonal codes that allow the multiple user signals to be transmitted and received on the same frequency at the same time. Once the bit stream is orthogonally isolated using the RW codes, the signals for respective subscriber links do not interfere with each other. Since RW codes are orthogonal, when perfectly aligned all codes have zero cross-correlation, thus making it possible to decode a signal while cancelling interference from users operating on other RW codes. In preferred embodiments of the present invention, it is desired to provide the central terminal with the ability to support more than 15 subscriber links on each channel frequency, and to achieve this the above set of 16 RW codes has been enhanced. In order to maintain compatibility with former products using the 16 RW codes, it was desirable that any enhancements should retain the same set o[ 16 RW codes. TI1e manner in which the enhancement-s have been implemented provides flexibility in the way the frequency channels are configured, with certain configurations allowing a greater number of subscriber links to be supported, but at a lower gross bit rate. In preferred embodiments, a channel can be selected to operate with the following gross bit rates: WIL-0009797 6,0R8,326 13 14 bas been selected, an appropriate overlay code provided by code generator providing appropriate overlay codes to the overlay code generator 113 is applied to the signals. At the spreader 111. The overlay code generator will be controlled output of the spreader 111, the signals will be at 160 KS/s so as to produce the desired overlay code, in preferred irrespective of the bit rate of the input signal since the embodiments, this control coming from the DAengine (to be discussed in more detail later). overlay code will have increased the symbol rate by the necessary amount. FIG. SA is a schematic diagram illustrating the signal reception processing stages as configured in a subscriber The signals output from spreader 111 are passed to a tcrminal20 in the telecommunications system of FIG. 1. In spreader 116 where the Rademacher-Walsh and PN codes are applied to the signals by a RW code generator 112 and FIG. SA, signals received at a receiving antenna 150 are PN Code generator 114, respectively. The resulting signals, 10 passed via a band pass filter 152 before being amplified in a low noise amplifier 154. The output of the amplifier 154 is at 2.56 MC/s (2.56 Mega chips per second, where a chip is then passed via a further band pass filter 156 before being the smallest data element in a spread sequence) are passed further amplified by a further low noise amplifier 158. The via a digital to analogue converter 118. The digital to output of the amplifier 158 is then passed to a mixer 164 analogue converter 118 shapes the digital samples into an analogue wavdorm and provides a stage of baseband power 15 where it is mixed with a signal generated by a voltage controlled oscillator 162 which is responsive to a synthesizer control. The signals are then passed to a low pass filter 120 160. The output of the mixer 164 is then passed via the T/Q to be modulated in a modulator 122. The modulated signal de-modulator 166 and a low pass filter 168 before being from the modulator 122 is mixed with a signal generated by passed to an analogue to digital converter 170. The digital a voltage controlled oscillator 126 which is responsive to a synthesizer 160. The output of the mixer 128 is then 20 output of the A;D converter 170 at 2.56 MC/s is then passed to a correlator 178, to which the same Rademacher-Walsh amplified in a low noise amplifier 130 before being passed and PN codes used during transmission are applied by a RW via a band pass filter 132. The output of the band pass iilter code generator 172 (corresponding to the RW code genera132 is further amplified in a further low noise amplifier 134, tor 112) and a PN code generator 174 (corresponding to PN before being passed to power control circuitry 136. The output of the power control circuitry is further amplified in 25 code generator 114), respectively. The output of the correlator 178, at 160 KS/s, is then applied to correlator 179, a power amplifier 13S before being passed via a further hand where any overlay code used at the transmission stage to pass filter 140 and transmitted from the transmission antenna encode the signal is applied to the signal by overlay code 142. generator 181. The elements 170, 172, 174, 178, 179 and FIG. 7B is a schematic diagram illustrating signal transmission processing stages as configured in a central terminal 30 181 form a CDMA demodulator. The output from the CDMA demodulator (at correlator 179) is then at a rate of 10 in the telecommunications system of FIG. 1. As will be either 160, 80 or 40 KS/s, depending on the overlay code apparent, the central terminal is configured to perform applied by correlator 179. similar signal transmission processing to the subscriber The output from correlator 179 is then a]pplied to a Viterbi terminal 20 illustrated in FIG. 7A, but does not include elements 100, 102, 104 and 106 associated with telecom- 35 decoder 180. The output of the Viterbi decoder 180 is then passed to an overhead extractor 182 for extracting the munications equipment. Further, the central terminal overhead channel information. If the signal relates to call includes a TDM encoder 105 for performing time division data, then the output of the overhead extractor 182 is then multiplexing where required. The central terminal will have passed through TDM decoder 183 to extract the call data a network interface over which incoming calls destined for a subscriber terminal are received. When an incoming call is 40 from the particular time slot in which it was inserted by the CT TDM encoder 105. Then, the call data is passed via a received, the central terminal will contact the subscriber codec 184 and a hybrid circuit 188 to an interface such as terminal to which the call is directed and arrange a suitable two wire interface 190, where the resulting analogue signals channel over which the incoming call can be established are passed to a telephone 192. As mentioned earlier in with the subscriber terminal (in preferred embodiments, this is done using the call control channel discussed in more 45 connection with the ST transmission processing stages, elements 184, 188, 190 may be repeated for each piece of detail later). The channel established for the call will dett:rtelecommunications equipment 192 at the ST. mine the time slot to be used for call data passed from the If the data output by the overhead extraction circuit 182 CT to the STand the TDM encoder 105 will be supplied \Vith is data on a downlink control channels, then instead of this information. Hence, when incoming call data is passed from the so passing that data to a piece of telecommunications equipment, it is passed via switch 187 to a call control logic network interface to the TDM encoder 105 over line 103, the 185, where that data is interpreted by the ST. TDM encoder will apply appropriate TDM encoding to At the subscriber terminal 20, a stage of automatic gain enable the data to be inserted in the appropriate time slot. control is incorporated at the IF stage. The control signal is From then on, the processing of the signal is the same as the e4uivalent processing performed in the ST and described 55 derived from the digital portion of the COMA receiver using with reference to FIG. 7A, the overlay code generator the output of a signal quality estimator. producing a single overlay code of value '1' so that the FIG. SB illustrates the signal reception processing stages signal output from spreader 111 is the same as the signal as configured in a central terminal 10 in the telecommuniinput to the spreader 111. cations system ofFIG.l. As will be apparent from the figure, As mentioned earlier, in preferred embodiments, overlay 60 the signal processing stages between the RX antenna 150 and the overhead extraction circuit 182 are the as those codes, rather than TDM, are used to implement downlink within the ST discussed in connection with FIG. SA control channels, and data relating to such chmmels is passed However, in the case of the CT, call data output from the from a demand assignment engine (to be discussed in more uverht:ad extraction circuit is passed over line 189 to the detail later) over line 107 through switch 109 lo the overhead insertion circuit 108, thereby bypassing the TOM encoder 65 network interface within the CT, whilst control channel data is passed via switch 191 to the DA engine 380 for process105. The processing of the signal is then the same as the ing. The DA engine is discussed in more detail later. equivalent processing performed in the ST, with the overlay WIL-0009798 6,0R8,326 16 15 scriber terminal 20. A downlink communication path is established from transmitter 200 in central terminal 10 to receiver 202 in subscriber terminal 20. An uplink communication path is established from transmitter 204 in subscriber terminal 20 to receiver 206 in central terminal 10. Once the downlink and the uplink communication paths have been established in wireless telecommunication system 1, telephone communication may occur between a user 208, 210 of subscriber terminal 20 and a user serviced through 10 central terminal10 over a downlink signa1212 and an uplink signal214. Downlink signal212 is transmitted by transmitTABLE 2 ter 200 of central terminal 10 and received by receiver 202 STTx. of suhscriher terminal 20. Uplink signal 214 is transmitted power by transmitter 204 of subscriber terminal20 and received by Net Channel relative C:orrelator Rate designa- to Fl-U integration Acquisition 15 receiver 206 of central terminallO. Receiver 206 and transmitter 200 within central terminal tion Overlay Code (kb/s) (dB) period (us) overlay 10 are synchronized to each other with respect to time and -Fl-U 160 6.25 L1 1 phase, and aligned as to information boundaries. In order to 80 -Hl-U -3 1 12.5 L1 establish the downlink communication path, receiver 202 in 80 -H2-U -3 1 -1 12.5 L3 ·Ql-U -6 40 1 25 L1 20 subscriber terminal20 should be synchronized to transmitter -Q2-U -6 -1 40 25 1 -1 L2 200 in central terminal10. Synchronization occurs by per-Q3-U -6 40 1 -1 -1 25 L3 forming an acquisition mode function and a tracking mode -Q4-U -G 40 1 -1 -1 25 L4 function on downlink signal212. Initially, transmitter 200 of c~::ntral t~::rminal10 transmits downlink signal 212. FIG. 12 In preferred embodiments, a 10 kb/s acquisition mode is 25 shows the contents of downlink signal 212. A frame inforprovided which uses concatenated overlays to form an mation signal 218 is combined with an overlay code 217 acquisition overlay; this is illustrated in table 3 below: where appropriate, and the resultant signal219 is combined Overlay codes and channelisation plans are selected to ensure signal orthogonality-i.e. in a properly synchronised system, the contribution of all channels except the channel being demodulated sum to zero over the correlator integration period. Further, uplink power is controlled to maintain constant energy per bit. The exception to this is Low rate which will be transmitted at the same power as a Quarter rate signal. Table 2 below illustrates the overlay codes used for full, half and quarter rate operations: TABLE 3 Acquisition overlay Ll-U L2-U 13-U IA-U Equivalent high rate pattern 1 1 -1 -1 -1 1 -1 -1 -1 1 1 1 -1 -1 -1 -1 1 -1 -1 1 1 -1 -1 -1 -1 1 -1 -1 1 -1 -1 -1 1 -1 -1 -1 FIGS. 9A and 9B are diagrams illustrating the uplink and downlink delivery methods, respectively, when the system is fully loaded, and illustrate the difference hetween the use of overlay codes illustrated in FIG. 9A and the use of IDM as illustratt:d in FIG. 9B. When using overlay codes, an RW code is split in the RW space domain to allow up to four sub channels to operate at the same time. In contrast, when using TDM, an RW code is split in the time domain, to allow up to four signals to be sent using one RW code, but at dille rent times during the 125 us frame. As illustrated in FIGS. 9A and 9R, the last two RW codes, RW14 and RW15, are not used for data traffic in preferred embodiments, since they are reservt:cl for call control and acquisition functions; this will be discussed in more detail later. The CDMAchannel hierarchy is as illustrated in FIG. 10. Using this hierarchy, the following CDMA chan:nelisations are possible: Fl with a code sequence signal 216 for central terminal 10 to produce the downlink 212. Code sequence signal 216 is 40 derived from a com hi nation of a pseudo-random noise code signal 220 and a Rademacher-Walsh code signal 222. Downlink signal 212 is receivtd at receiver 202 of subscriber terminal20. Receiver 202 compares its phase and code sequence to a phase and code sequence within code 45 sequence signal 216 of downlink signal 212. Central tenninal 10 is considered to have a master code sequence and subscriber terminal 20 is considered to have a slave code sequence. Receiver 202 incrementally adjusts the phase of its slave code sequence to recognize a match to master code 50 sequence and place receiver 202 of subscriber terminal 20 in phase with transmitter 200 of central terminal10. The slave code sequence of receiver 202 is not initially synchronized to the master code sequence of transmitter 200 and central terminal10 due to the path delay between central terminal 55 10 and subscriber terminal 20. This path delay is caused by Hl+H2 the geographical separation between subscriber terminal 20 H1+03+Q4 and central terminal 10 and other environmental and techH2+Ql+Q2 nical factors affecting wireless transmission. After acquiring and initiating tracking on the central 01+02+03+04 Having discussed how the CDMA codes are enhanced to 60 terminal10 master code sequence of code sequence signal enable flexible channelisations to be achieved, whereby the 216 within downlink signal212, receiver 202 enters a frame bit rates can be lowered to enable more subscriber links to alignment mode in order to establish the downlink commube managed per channel frequency, a general overview of nication path. Receiver 202 analyzes frame information how the downlink aml uplink paths art: tstablisht:cl will be within frame information signal218 of downlink signal 212 provided with reference to FIGS. 11 and 12. 65 to identify a beginning of frame position for downlink signal FIG. 11 is a block diagram of downlink and uplink 212. Since receiver 202 does not know at what point in the communication paths between central terminal10 and subdata stream of downlink signal 212 it has received WIL-0009799 o,mm,326 17 18 information, receiver 202 must search for the beginning of frame position in order to be able to process information received from transmitter 200 of central terminal 10. Once receiver 202 has identified one further beginning of frame position, the downlink communication path has been established from transmitter 200 of central terminallO to receiver 202 of subscriber terminal 20. The structure of the radio frames of information sent over the downlink and uplink paths will now be discussed with reference to FIGS. 13 and 14. In FIGS. 13 and 14, the following terms are used: Bn Customer payload, lx32 to 2x64 Kb/s Dn Signalling Channel, 2 to 16 kb/s OH Radio Overhead Channel 16 kb/s Traffic Mode 10 kb/s Acquisition/Standby Mode munication paths and a path from the central terminal to the subscriber terminal on which the communication protocol which operates on the modem shelf between the shelf controller and the modem cards also extends. The OMC/D signal is a combination of the OMC signal and a signalling signal (D), whilst the Ch.ID signal is used to uniquely identify an RW channel, this Ch.ID signal being used by the subscriber terminal to ensure that the correct channel has been acquired. 10 In preferred embodiments, the subscriber terminal will receive downlink traffic channel data at a rate of 160 kb/s. Depending on the B-channel rate, the ST will be allocated an appropriate share of the radio overhead. The following TDM mappings are created: TABLE 4 Ralt Channd (kb/s) designation 1GO -Fl-0-Tl/1 80 -Fl-D-T2/l ~0 -F1-JJ--T2/2 40 40 40 40 -F1-D-T4/2 -F1-D-T4/3 -F1-D-T4/4 -F1~D-T4/1 Bearer cs Bl, B2, B3, B4 CS1, CS3 Bl, B2 CSl, CS3 H3, .1:54 CS2, CS4 Bl CS1 B2 CS2 CS3 B3 B4 CS4 Overhead rate PC OMC PCl, PC3 PCl, PC3 PC2, PC4 PC1 PC2 PC3 PC4 OMCl, OMC3 4 OMCl, OMC3 4 ms OMC2, OMC4 4 ms OMC1 OMC2 OMC3 OMC4 8 8 8 8 IllS ms ms ms ms Both FIGS. 13A and 13B show a 125 us subframe format, In the above chart, the scheme used to identify a channel which is repeated throughout an entire radio frame, a frame is as follows. Rate code 'F1' indicates full rate, 160 kb 'D' typically lasting for 4 milliseconds (ms). FIG. 13A illustrates 35 indicates that the channel is a downlink channel, and 'Tn/t' the radio frame structures that are used in preferred embodiindicates that the channel is time division multiplexed ments for the downlink path. Subframe (i) in FIG. 13A between STs, 'n' indicating the total number of TDM shows the radio frame structure used for low rate, 10 Kb/s, time:slots, and 't' indicating the selected traffic timeslot. acquisition mode (Ln-D) during which only the overhead All ST's operating on a traffic channel will receive channel is transmitted. Suhframe (ii) in FIG. 13A shows the D-channel information at the 16 kb/s rate. The D-channcl radio frame structure employed for the call control channel 40 protocol includes an address field to specify which ST is to operating in quarter rate, 40 Kb/s, mode (Qn-D) , whilst process the contents of the message. subframe (iii) of FIG. 13A illustrates the radio frame strucThe channel structure was illustrated earlier in FIGS. 9A ture used for trilffic cbilnnels operilting in full rate, 160 kb/s, and 9B. In preferred embodiments, the channel structure is mode (F1-D). flexible but comprises: Similarly, sub frame (i) of FIG. 13B shows the radio frame 45 At least one Link Acquisition Channel (LAC) structure used for the uplink path when operating in low rate At least one Call Control Channel (CCC) acquisition or call control mode (Ln-U). Sub-frames (ii) to Typically one Priority Traffic Channels (PTC) (iv) show the radio frame structure used for traffic channels \Vhen operating in quarter rate mode (Qn-U), half rate mode 1 to 13 Traffic Channels (TC) The manner in which the channelisation is provided (Hn-U), and full rate mode (Fl-U), respectively. 50 Considering now the overhead channel in more detail, ensures that former fixed assignment arrangements using the FIGS. 14A and 14B show the overhead frame structure set of 16 RW codes discussed earlier are still supported, as employed for various data rates. The overhead channel may we11 as demand access services that are available when using include a number of fields-a frame alignment word (PAW), a system in accordance with the preferred embodiment. a code synchronization signal (CS), a power control signal ss FIGS. 15A and 15B illustrate typical downlink and uplink (PC), an operations and maintenance channel signal (OM C), channel structures that might occur in a loaded system in a mi.'l:ed OMC/D-Channel (HDLC) signal (OMC/D), a chanaccordance with preferred embodiments of the present nel identifier byte (Ch.ID), and some unused fields. invention. As illustrated in FIG. 15A, on the downlink path, The frame alignment word identifies the beginning of some signals may be at 160 kb!s and utilise an entire RW frame position for its corresponding frame of information. 60 channel. An example of such signals would be those sent The code synchronization signal provides information to over fixed assignment links to products which do not support control synchronization of transmitter 204 in subscriber the CDMA enhancements provided by systems in accorterminal20 to receiver 206 in central termina110. The power dance with preferred embodiments of the present invention, cunlrol signal pruvidt:s infunnaliun lu L:unlrul transmitting as illu:siraltu fur RW1 <mu RW2 in FIG. 15A. Al!trnalivdy, power of transmitter 204 in subscriber terminal 20. The 65 a user may have authority to utilise a whole RW channel, for operations and maintenance channel signal provides status example when sending a fax, as illustrated by RW12 in FIG. information with respect to the downlink and uplink com15A. WI L-0009800 6,0R8,326 19 20 As .illustrated by RW5 to RWll, TDM can be used on the (iii) In the event of a CT restart, invite STs to attempt downlink traffic channels to enable more than one CT to ST uplink warm start. A reduction in net entry time of a communication to take place on the same RW channel factor of 4 could be achieved. This mechanism would during each frame. Further, as illustrated for RW3 and RW4, need to be safeguarded against possible deterioration of in preferred embodiments, certain channels can be locked to uplink warm start parameters-i.e. it should only be limit interference from other nearby cells, as will be disallowed provided no CT RF related parameters have cussed in more detail later. been modified. The CT would need to broadcast an ID Similar channelisations can be achieved for the uplink to allow an ST to validate that the uplink warm start paths, hut as illustrated in FIG. 15R, overlay codes are used parameters were valid for this C::T. instead of TDM to enable more than one ST to CT com- 10 (iv) ST n:start-tht CT will ktt:p copies of tht: ST warm munication to take place on the same RW channel during start parameters so that a cold ST may have warm start each frame (as shown in FIG. 15B for RW5 to RWll). It parameters downloaded in the invitation to acquire and should be noted that, in both FIGS. 15A and 15B, the then be instructed to warm start. channels RW14 and RW15 are reserved as a call control Following Net Entry, all STs listen to the CCC. This channel and an link acquisition channel, respectively, and 15 channel broadcasts management and call control informaoverlay codes are employed on these channels, irrespective tion via a 32 kb/s HDLC channel. In order to maintain of whether the path is a downlink or an uplink path. These management communication, the CT polls each ST in two channels will be discussed in more detail below. sequence. Each poll comprises a broadcast invitation for an Acquisition/net entry will take place via the Link Acquiaddressed ST to acquire the CCC Uplink followed by an sition Channd (LAC). Following power-up an ST will zo exchange of management information (authentication, ST automatically attempt downlink acquisition of the LAC on a alarm update, warm start parameters, downlink radio perpre-determined 'home' RF channel. The LAC downlink formance data etc.). channel (eg. RW15 in preferred embodiments) will operate A Management Poll may fail for one of the following at 10 kb/s, full single user power. Downlink acquisition will reasons: be simultaneous for all STs. 25 (i) The ST is or has been powered down. An EM alarm Each CT Modem Shelf will maintain a database holding may be tlagged if this persists and the database for that the serial numbers of all STs that could possibly be supST should be marked cold. The Net Entry process will ported by that CT. The state of each ST will recorded with follow. top level states as follows: (ii) The ST is either making a call or in the process of 30 cold making a call. The poll cycle rna y be suspended and idle management communications effected on the appropriate traffic channel. call_in_proogress When a Management Poll fails it should be followed up Transition states will also be defined. An ST is considered cold if the ST is newly provisioned, the CT has lost 35 by a number of faster polls until either the ST responds or it is marked cold. The CCC is required to transmit all copies management communications with the ST or the CT has of the invitations to acquire the LAC so that an ST can be been power cycled. Over the LAC, the CT broadcasts forcetl to acquire the LAC uplink. individual ST serial numbers and offers an invitation to Traffic Channel Uplink Acquisition Procedure acquire the LAC uplink. Cold uplink acquisition will be The basic acquisition process from the ST side is as carried out on the Link Acquisition Channel at low rate. The 40 follows; CTwill invite specific ST's to cold start via the management channel. (i) Switch the downlink (receiver) circuitry to 10 kh/s rate, and select the appropriate Traffic Channel RW and Assuming an uplink channel is available, the appropriate acquisition overlay will be selected, and acquisition will be Overlay codes. Acquisition of the TC downlink is limited to achieving frame alignment. initiated. s 4 'Rapid' downlink RW channel switching may be sup(ii) The downlink PC/CS channel will be decoded to ported at rates other than Ln-D. Rapid means that coherent create a busy/idle tlag. lf PC/CS reports busy, then this demodulation is maintained, and only convolutional decodmeans that another ST is using that traffic channel and ing and frame synchronisation processes need be repeated. the ST aborts the acquisition process. On acquisition, managc:mt:nt information will bt 50 (iii) Switch uplink to 10 kb/s rate, and select the approexchanged. The ST will be authenticated and allocated a priate Traffic Channel RW and Overlay codes. Enable short ST_identifier (between 12 and 16 bits) which will be the ST transmitter at a level of nominal full rate power used for subsequent addressing. The ST uplink will operate minus 18 dB. While PC/CS reports idle the ST will for long enough for the uplink to be parametised by the ST continue uplink fast codesearch, stepping the uplink in terms of code phase and transmit power. These parameters 55 powc:r ltvd by +2 dB at the c:nd of each search. The will be used by the ST for subsequent warm start acquisiuplink should acquire at nominal full rate power minus tions and will also be held by the CT to allow the CT to force 6 dB. Uplink acquisition is aborted if maximum transa cold ST to warm start. On successful completion of net mit level is reached and PC/CS continues to report idle. entry, the ST will be placed in the idle state and instructed (iv) PC/CS reports busy. At this point the ST may have to cease uplink communications and move to the Call 60 genuinely acquired the traffic channel, or instead may Control Channel (CCC) (RW14 in preferred embodiments). be observing PC/CS go busy because another ST has The time taken for net entry to be achieved can be acquired the traffic channel. The ST is sent an authenmonitored, and the following techniques can be used to tication request and responds with it's ST_identifer. decrease net entry time if desired: Tht: CT grants uplink access by returning tht (i) Prioritise so that high GOS (Grade Of Service) users 65 ST_identifier. The ST aborts the acquisition process if are offered net entry first. the returned ST_identifier is not recognised (i.e. is not the ST_identifer that it sent). This authentication pro(ii) Convert Traffic Channels to LACs. WIL-0009801 o,ORR,326 21 22 ~ess arbitrates between two STs contending for outgo(vi) The ST may be unable to acquire a TC by tbe time the mg access and it also keeps STs from acquiring TCs call setup timer expires. The ST may in such cases that have been reserved from incoming access. c.ease attempting outgoing access and generate congestiOn tone. Incoming Call Outgoing Priority Call A number of TCs will be reserved for incoming calls, and It is recognised that the random access protocol used to incoming call processing is as follows: setup normal outgoing calls could lead to blocking. In (i) Check the CT database-if the ST is in the call in preferred embodiments, access to a largely non-blocking progress state the call is rejected. - Priority Traffic Channel will be allowed. Priority calling is (ii) Check that an uplink TC ~f the required bandwidth is complicated because the ST must: available. If there is bandwidth then a TC is reserved. 10 (i) Capture and decode dialed digits. (iii) An incoming call setup message is broadcast over the (ii) Rt:gt:neratt: digits wht:n a bloc..:king condition occurs. CCC to inform the addressed ST of the incomincr call (iii) Allow transparent network access in a non-blockina and specify the TC on which to receive the call. If no · condition. "" TC is available but the CT forms part of a Service (iv) Categorise all outgoing calls as priority or normal so Domain, then the incoming call setup message is sent 15 that normal calls are dropped in favor of priority calls. with a null TC otht:rwise the c.;all is rt:jt:c.:led. St:rvic.;e 1be priority call procedure in preferred embodiments is as domains will be discussed in more detail later. The follows: incoming call setup message is repeated a number of (:i) The CT will p11blish Directory Numbers (DNs) for a times. number of emergency services over the CCC. (iv) The ST attempts uplink acquisition. The ST listens to 20 (ili) The ST will attempt uplink access according to the the downlink and keeps trying for uplink acquisition normal algorithms. If the outgoing access is successful until tht: CT s~:::nds a mt:ssagt: to tht: ST to rdurn the ST then the customer is able to dial as normal. All dialed to the CCC. The ST will also run a timer to return it digits are check against the emergency DN list so that back to the CCC in the event of an incoming call failing calls may be categorised normal or priority at the CT. 25 to complete. (iii) J[f congt:slion tone is returned Lhe c.;ustornt:r is allowt:d (v) On successful uplink acquisition, the CT authenticates to dial the emergency number into the ST. If the ST · the ST. detects an emergency DN sequence then uplink access (vi) Rate switching is originated from the CT modem. A via the Priority Traffic Channel (PTC) is attempted. command is sent via the PC/CS to switch the downlink 30 (iv) On PTC acquisition, the ST relays the dialed digit to the required bandwidth. The ST returns the rate sequence to the CT for dialling into the PSTN. switch command via the uplink PC/CS. The link is now (iv) The CT converts the PTC to a TC and reallocates of the required bandwidth. another TC to become the PTC, dropping a normal call Outgoing Call in progress if necessary. Outgoing calls are supported by allowing slotted random 35 Interference Limiting (Pool Sizing) access to the TC uplinks. The outgoing call processing is as Across a large scale deployment of cells, optimum capacfollows: ity is achieved by minimising radio traffic while maintaining (i) The CT publishes a 'free list' of available Traffic an acceptable grade of service. Lowest possible radio traffic Channels and Priority Traffic Channels with their respective bandwidths. This list is published periodi- 40 results in improved 'carrier to interference' (C./I) ratios for users within the cell of interest and to co-channel users in cally (in preferred embodiments, every 500 ms) and is nearby cells. The C/I ratio is a measure (usually expressed used to mark uplink access slots. in dB) of how high above interference the transmitted signal (ii) An off-hook condition is detected by the ST. The ST needs to be to be decoded effectively. In preferred starts a call setup timer. · embodiments, the central terminal is provided with the (iii) The ST waits for the next free list to be received over 45 ability to trade traffic for C;I, thereby allowing network the CCC. If Lhe Fret: list is t:mply the outu-oinu- c.;all is planning to be carried out less rigidly. This fe.ature can be blocked. The ST will generate a ·congesti;'n to~e. realist:d by a system using CDMA as in prt:ferred embodi(iv) If the Free list has available channels, the ST picks a ments of the present invention, and is a benefit that CDMA channel from the free list at random. The algorithm that offers over TDMA and FDMA systems. the ST uses to pick a channel will need to be specified 50 In preferred embodiments, the CT will control the number in the free list. For example, the ST may be required to of Traffic Channels to minimise access noise. TCs will be always choose from a pool of minimum bandwidth classified as: channels so that high bandwidth channels remain avail(i} Busy-carrying traffic; able for high GOS users. Alternatively the ST may be (ii) Access, Incoming (Access_ln)-reserved for :incomallowt:d to choost any channd rt:gardkss of bandwidth 55 ing access; for minimum blocking. In preferred embodiments, STs (iii) Access, Outgoing (Access_Out)-reserved for outwill not choose low bandwidth channels and negotiate going access-such TCs appear on the Free list; the rate up. (iv) Priority-reserwd for priority outgoing acc..:t:ss-suc.;h (v) The ST attempts uplink acquisition on the specified TCs appear in the Free list; TC, this process having been described earlier. If 60 (v) Free-available for any purpose; and acquisition is successful then the outgoing call is pro(vi) Locked-not available due to interference limiting. cessed. Otherwise the ST returns to the CCC and waits This classification scheme is illustrated in FIG. 16. The for the next available free list. To avoid a number of STs CT will allocate traffic on the following basis: rt:pelilivdy attempting Lo acquire the same TC, and blocking each other, a suitable protocol can be 65 (i) The CT will monitor incoming and outgoing call employed to govern how individual STs will act upon setup-times and convert Access TCs from Free TCs in receipt of the free list. order to achieve a required grade of service. WIL-0009802 6,088,326 23 24 (ii) When a call is setup, an Access TC is converted to a Busy TC. If a Free TC is available, it is converted to a new Access TC. H there are no Free TCs then the Access TC is lost until a call clears. (iii) When a call clears the Busy TC is converted to a Free TC. If a previous call setup resulted in a lost Access TC then the Busy TC is converted back into an Access TC. (iv) When the PTC is accessed, a new PTC is created by converting a Free, Access or Busy (normal call) TC. (v) The CTwill monitor the Busy TC downlink and uplink soft error counts in an attempt to establish link quality. If the CT records a lower than average soft error count and long call setup times are being recorded, a Locked TC may be converted to a Free TC. Conversely, if the C:T records a higher than average soft error count, a Free or Access TC may be converted to a Locked TC. FIG. 17 illustrates how the central terminal performs the above interference limiting function. When incoming call data arrives at a central terminal modem 320, encoder 325 encodes the data for transmission over the wireless link 300 to the subscriber terminal 20. At the subscriber terminal 20 the decoder 326 decodes the data, and passes the decoded user data over line 328 to the subscriber telecommunications equipment. As the decoder 326 decodes the data, it is able to establish a bit error rate (BER) estimate 330 associated with the signal transmission over the wireless link 300, which can be passed to the multiplexer 332 for combining with other signals, such as those from a call control function 336 or user data on line 338, before being passed to an encoder 334. Here, the BER estimate is encoded and passed on the OMC channel over the wireless link 310 to the decoder 340 within the central terminal modem 320. Once decoded by the decoder 340, the signal passes to the multiplexer 345, where the BER estimate from the subscriber terminal is detected and passed over line 355 to the dynamic pool sizing function 360. Further, as at the subscriber terminal20, the decoder 340 within the central terminal modem 320 is able to establish a bit error rate estimate 350 associated with the signal transmission over the wireless link 310. This BER estimate 350 is al~o passed over line 355 to the dynamic pool sizing function 360. The dynamic pool sizing function 360 is provided on the CT modern shelf 302, and receives BER estimates from each of the modems on that shelf indicated by the lines entering the bottom of the dynamic pool sizing function 360. . In ad.dition to BER estimates, grade of service (GOS) data IS obtamed from two sources. Firstly, at each subscriber terminal 20, the call control function 336 will note bow readily it is able to establish traffic channels for transmittinoand receiving data, and from this can provide a GOS estimate to the multiplexer 332 for encoding by the encoder 334 for subsequent transmission over the wireless link 310 to the central terminal modern 320. Here, the GOS estimate is decoded by decoder 340, passed through multiplexer 345, and then the GOS estimate is passed over line 355 to the dynamic pool sizing function 360. Additionally, incoming call information to the central terminal, other than call information from the subscriber terminals 20 connected to the central terminal, is provided over the concentrated network interface 390 to the DA engine 380. The DA engine 380 includes a call control function, similar to the call control function 336 in each of the subscriber terminals 20, for each of the modems on the modem shelf. Hence, in a similar fashion to the call control function 336 at the subscriber tem1inals 20, the call control functions within the DA engine 380 are also able to provide GOS estimates for incoming calls, and r.hese GOS estimates are passed over line 395 to the dynamic pool sizing function 360. At set up, the management system 370 within the element manager will have connected to the central terminal and provided the dynamic pool sizing function 360 withi~ the modem shelf with data identifvino- a BER o-oal a GOS goal and a pool size limit (i.e. the n~1mber of ch~nn~ls that can b~ used for data traffic). The dynamic pool sizing function 360 then compares this data from the management system with the actual BER, actual GOS, and the actual pool size information that it receives. A suitable algorithm can be provided within the dynamic pool sizing function 360 to determi~e, based on this information, whether pool sizing is appropnate. For example, if the actual bit error rate exceeds the BER goal provided by the management system 370, then the dynamic pool sizing function 360 may be arranged to send a pool sizing request to the demand assignment encine 10 15 380. 20 25 30 35 40 45 so 55 60 65 b The demand assignment engine 380 provides modern enable signals over lines 400 to each of the modems on the CT modem shelf. If the dynamic pool sizing function 360 has requested that the DA engine 380 perform pool sizing, then the DA engine 380 can disable one or more of the modems, this causing the interference, and hence the actual BER, to be n:duced. Apart from being used for interference limiting, the DA engine is also responsible, in preferred embodiments, for providing the encoders 325 with instructions on which set of overlay codes or how many TDM slots to he used for signals to be transmitted to the STs 20. The dynamic pool sizing function can store the BER and GOS information received in the storage 365, and periodically may pass that data to the management system 370 for analysis. Further, if the system is unable to attain the BER or GOS goal with the allocated pool size, the dynamic pool sizing function can be arranged to raise an alarm to the management system. The receipt of this alarm will indicate to personnel using the management system that manual intervention may be required to remedy the situation, eg by the provision of more central terminal hardware to support the ST.<>. The CDMA approach used in preferred embodiments exhibits the property that the removal of any of the orthogonal channels (by disabling the modem) will improve the resistance of the other channels to interference. Hence, a suitable approach for the demand assignment engine 380, upon receipt of pool sizing request from the dynamic pool sizing function 360, is to disable the modem that has the least traffic passing through it. RF Channel Switching In preferred embodiments, it has been realised that if an ST is allowed to operate from more than one CT Modern Shelf/RI' Channel then the following benefits may be realised: (i) Fault tolerance-should a CT Modem Shelf subsystem fault occur, an ST may switch to an alternative frequency for service. (ii) Call blocking-an ST denied servkt: from one CT shelf may choose to switch to an alternative frequency for service. (iii) Traffic load balancing-the Element Manager may on the basis of call blocking statistics choose to move STs between CT shelves. (iv) Frequency diversity-in the presence of channel selective fading (slow rnultipath) an ST may operate on the frequency channel offering highest signal strength and lowest soft error count. WIL-0009803 6,mm,326 25 26 RF channel switching is only possible where there are two typically switch to a different CT, since some errors e),"Peor more co-located cr shelves serving the same geographirienced by one CT shelf may also affect other shelves within cal area on different RF frequency channels within the same the same CT, and so for fault tolerance (described in more RF band. A deployment that meets this criterion may be detail below), it is preferable for the ST to switch to a configured as a 'Service Domain'. Possible deployment separate CT. scenarios are illustrated in FIG. 18. FIG. 18(i) shows an Database consistency across CT shelves is preferably arrangement where omni antennae arc used to provide the supported through the service domain controller 400. Dataentire cell with four frequency channels, eg Fl, F4, F7, FlO. base consistency needs to be real-time so that an ST entering FIG. lR(ii) shows an arrangement where sectored antennae the network is allowed full Service Domain access immeare used to provide six separate sectors within a cell, each 10 diately (the Service Domain message is broadcast to all STs, sector being covered by two frequency channels. FIG. 18(iii) and so a new ST will expect access across the full Service shows an alternative arrangement where three sectored Domain). antennae are used to divide the cell in to three sectors, each Incoming access via backup CTs requires some f-unction sector being covered by a separate frequency channel, and to be provided to broadcast duplicate incoming call setup then an omni antenna is used to provide an 'umbrella' 15 messages to all CT.o:; that form a Service Domain. Preferably coverage for the entire cell, this coverage employing a this is handled by the service domain controller 40(]1, which frequency channel different to the three frequency channels forwards incoming call setup messages to each CT operating used by the sectored antennae. in the service domain. All CTs will allocate Access_In For the system to work effectively, the STs must be able Traffic Channels and relay the incoming call setup message to switch channels quickly, and fast channel switching 20 via the Call Control Channel. On successful uplink access, necessitates that CT shelf synchronisation be provided at the one CT will respond to the service domain controller with a following levels: call accepted message, the other CTs will eventually respond with call setup failed messages. Outgoing access via a (i) CDMA PN code. This preserves uplink code phase backup CT is similar to normal outgoing access. across RF channels during warm start; and .Another job which can be performed by the service (ii) RF carrier frequency. This eliminates the need for the 25 domain controller is to assist the element manager 58 in coarse frequency search on a downlink RF channel reconfiguring equipment in the event of a fault. For example, switch. if one CT is taken out of commission because of a fault, a On installation, an ST will be programmed with an RF different CT can be brought 'on-line', and the service channel and PN code, these codes specifying the ST' s initial home channel. 30 domain controller can provide that new CT with the necessary information ahout the other CTs in the service domain. The manner in which channel switching is facilitated in FIG. 19B illustrates those clements of the subscriber preferred embodiments will be described with reference to terminal used to implement RF channel switching. The radio FIGS. 19A and 19B. A service domain controller 400 is subsystem 420, which incorporates the transmission and preferably provided to act as an interface between the exchange connected to the service domain controller over 35 reception signal processing stages, will pass any data received on the call control channel over line 425 to the path 405 and a number of central terminals 10 connected to message decoder 430. If the decoder 430 determines that the the service domain controller over paths 410. The central data on the call control channel forms a service domain terminals connected to the service domain controller form a message, then this is passed over line 435 to the channel 'service domain' of central terminals that may be used by a 40 selection controller 440, where the information within the subscriber terminal 20 for handling communications. service domain message is stored in storage 445. In preferred embodiments, the service domain controller Similarly, if the message decoder identifies the data as a 400 is used to provide each CT 10 with appropriate infor'free list' identifying the available traffic channels on a mation about the other CTs within the service domain. Each particular RF frequency, then this data is passed to the call CT can then broadcast a 'Service Domain' message comprising a list of RF frequencies and CT Identifiers that form 45 control function 336 and the channel selection controHer 440 over path 450. The call control function 336 stores the free a Service Domain to be used by the ST.o:; for subsequent RF list in the storage 445 for subsequent use by the call control switching functions. The ST then stores this information for function 336 and the channel selection controller 440. future reference when establishing a link with one of the If the message decoder 430 determines that the data forms CTs. It is preferable for each CT to broadcast the ~ervice domain message since an ST may be listening to any of the so an incoming call setup message, then that information is supplied over line 455 to the call control function 336 and CT..;; at the time that the message is broadcast. the channel selection controller 440 for processing. The Each CT database will hold an entry for every ST located incoming call setup message will typically specify a TC on within the Service Domain. Each database entry describes the current frequency channel which should be used to how the CT views it's relationship with the STand may be ss access the incoming call, and the channel selection controlmarked as: ler will attempt to establish a link on that TC. The channel (i) Primary service provider-the CT is the ST's home seleetion controller will in such cases instruct the radio channel. All management communication with an ST is sub-system 420 over line 465 to use the current frequency via it's home CT. channel to establish the required link. If, on the other hand, (ii) Supplying backup service-the CT is providing ser- 60 the traffic channel specified in the call setup message is vice to the ST. 'null', the channel selection controller has the option to (iii) Available for backup service-the CT will provide change RF frequency using the information stored in storage service to the ST if required. 445 about the other CT.<; in the service domain. It should be noted Lhal lht: ST nt:t:d nol ~witl:h to an To t:nablt: !ht: channd ~dtl:tion controlkr 440 to rt:ct:ivt: entirely different CT, but can instead switch to a different CT 65 information about the status of links, a link operating status shelf (and hence different RF frequency channel) within the signal can be supplied over line 470 from the radio subsame CT. However, in preferred embodiments, the ST will system. This signal will give an indication of the radio link WIL-0009804 6,0RR,32o 27 28 (iv) When the call clears, the ST downlink preferably quality, and may be a simple 'OK' or 'faikd' indication, or alternatively may include e:ll..1:ra information such as BER switches back to the home CT. RF Channel Switching for Traffic Load Balancing values for the link. This information can be used by the Traffic load balancing is, in preferred embodiments, prochannel selection controller to determine whether a particuvided by static configuration via the EM 58. Call blocking lar frequency channel should be used or not. and setup time statistics may be forvvarded to the EM where To enable the call control function to specify a specific an operator may decide to move an ST to another RF Access-Out channel for outgoing calls, a line 460 is prochannel. vided between the call control function 336 and the channel selection controller 440. The call control function 336 may RF Channel Switching for Frequency Diversity choose an access-out channel from the free list in storage Frequency diversity is, in preferred embodiments, pro10 vided by static configuration via the EM 58. Radio link 445, and instruct the channel selection controller over line statistics may be forwarded to the EM where an operator 460 to attempt acquisition of that channel. may decide to move an ST to another RF channel. The following examples indicate how the above described structure may be used to perform channel switching in Although a particular embodiment has been described particular circumstances. herein, it will he appreciated that the invention is not limited 15 thereto and that many modifications and additions thereto RF Channel Switching for Fault Tolerance Should one RF channel su.lier complete loss of downlink, may be made within the scope of the invention. For example, the following process takes place in preferred embodiments: various combinations of the features of the following dependent claims could he made with the features of the indepen(i) The ST will attempt downlink re-acquisition for a dent claims without departing from the scope of the present period of time, say 20 seconds. (ii) If acquisition fails, the channel selection controller zo invenLion. What is claimed is: 440 of the ST will select the next available channel 1. A transmission controller for processing data items to from the Service Domain information in storage 445 be transmitted over a wireless link connecting a central and attempt downlink acquisition. terminal and a subscriber terminal of a wireless telecoi:nThis process will be repeated until a downlink signal is 25 munications system, a single frequency channel being acquired. employed for transmitting data items pertaining to a plural(iii) Once a backup RF channel is located, the ST will ity of wireless links, the transmission controller comprising: 'camp' on the Call Control Channel and may subsean orthogonal code generator for providing an orthogonal quently be granted traffic access. code from a set of 'm' orthogonal codes used to create (iv) If the CT fault persists, the EM 58 may use the service 'm' orthogonal channels within the single frequency 30 domain controller 400 to reconfigure the Service channel; Domain so that the functioning CT shelves become a first encoder for combining a data item to be transmitted primary service providers for the pool of 'homeless' on the single freq11ency channel with said orthogonal STs. code from the orthogonal code generator, the orthogoA fault that docs not result in complete loss of downlink nal code determining the orthogonal channel over signal will not result in RF channel switching 'en mass'. 35 which the data item is transmitted, whereby data items Rather, a fault may result in excessive or total call blocking, pertaining to different wireless links may be transmitted simultaneously within different orthogonal channels of as discussed below. said single frequency channel; and RF Channel Switching for Call Blocking a TDM encoder arranged to apply time division multiIf Incoming access traffic channels are being blocked, the plexing (TDM) techniques to the data item in order to following process is employed in preferred embodiments: 40 insert the data item within a time slot of the orthogonal (i) The call setup message sent over the Call Control channel, whereby a plurality of data items relating to Channel will specify a TC on which to access the call. different wireless links may be transmitted within the (ii) In the cas~;; of incoming a<.:cess b~;;ing blocked, the CT same orthogonal channel during a predetermined frame will specify a null TC. The channel selection controller 45 period. 440 of the ST will in such cases switch to the next RF 2. A transmission controller as claimed in claim 1, further channel from the Service Domain information in storcomprising: age 445 and monitor the Call Control Channel. an overlay code generator for providing an overlay code (iii) If the ST receives a call setup message with a valid from a first set of 'n' overlay codes which are orthogoTC, th~;;n the call is processed as normaL nal to each other; and 50 (iv) When the call clears, the ST downlink preferably a second encoder, selectively operable instead of the TDM switches back to the home CT. encoder, to apply the overlay code from the overlay If Outgoing access traffic channels are being blocked, the code generator to said data item, whereby 'n' data items following process is employed in preferred embodiments: pertaining to different wireless links may be transmitted (i) The ST registers an off-hook. The Pree List in storage 55 simultaneously within the same orthogonal channel. 445 is checked and if a traffic channel is available, then 3. A transmission controller as claimed in claim 1, the call control f1mction 336 asserts a channel request wherein the orthogonal code generator is a storage arranged on line 460 to the channel selection controller 440 and to store the set of orthogonal codes. normal uplink access is attempted. 4. A transmission controller as claimed in claim 1, (ii) If the Free List shows no Access_Out channels are 60 wherein the set of orthogonal codes comprise a set of Rademacher-Walsh (RW) codes. available on the current frequency channel, then the channel selection controller will be used to switch the 5. A central terminal of a wireless telecommunications ST to the next RF channel in the Service Domain, system, comprising a transmis.<>ion controller having: whereupon the ST will wait for the next f<ree List. an orthogonal code generator [or providing an orthogonal code from a set of 'm' orthogonal codes used to create (iii) When the ST finds a Free List with an available 65 'm' orthogonal channels within the single frequency Access_Out channel, then uplink access is attempted channel; and the call is processed as normal. WI L-0009805 o,mm,326 29 30 a first encoder for combining a data item to be transmitted code from the orthogonal code generator, the orthogoon the single frequency channel with said orthogonal nal code determining the orthogonal channel over code from the orthogonal code generator, the orthogowhich the data item is transmitted, whereby data items nal code determining the orthogonal channel over pertaining to different wireless links may be transmitted which the data item is transmitted, whereby data items simultaneously within different orthogonal channels of pertaining to different wireless links may be transmitted said single frequency channel; and simultaneously within different orthogonal channels of a TOM encoder arranged to apply time division multisaid single frequency channel; plexing (TOM) techniques to the data item in order to a TDM encoder arranged to apply time division multiinsert the data item within a time slot of the orthogonal plexing (TOM) techniques to the data item in order to 10 channel, whereby a plurality of data items relating to insert the data item within a time slot of the orthogonal different wireless links may be transmitted within the channel, whereby a plurality of data items relating to same orthogonal channel during a predetermined frame different wireless links may be transmitted within the period; same orthogonal channel during a predetermined frame period; an overlay code generator for providing an overlay code from a first set of 'n' overlay codes which are orthogoan overlay code generator for providing an overlay code 15 nal to each other; from a first set of 'n' overlay codes which are orthogonal to each other; a second encoder, selectively operable instead of the TOM a second encoder, selectively operable instead of the TOM encoder, to apply the overlay code from the overlay encoder, to apply the overlay code from the overlay code generator to said data item, whereby 'n' data items 20 code generator to said data item, whereby 'n' data items pertaining to different wireless links may be transmitted pertaining to different wireless links may be transmitted simultaneously within the same orthogonal channel, simultaneously within the same orthogonal channel, wherein the orthogonal code generator is a storage wherein the orthogonal code generator is a storage arranged to store the set of orthogonal codes and arranged to store the set of orthogonal codes and wherein the set of orthogonal codes comprise a set of wherein the set of orthogonal codes comprise a set of 25 Rademacher-Walsh (RW) codes; Rademacher-Walsh (RW) codes. and wherein at least one subscriber terminal comprises a 6. A central terminal as claimed in claim 5, further reception controller having: comprising channelisation means for determining which of an orthogonal code generator for providing an orthogothe orthogonal channels will be subject to TOM techniques, nal code from a set of 'm' orthogonal codes llsed to and for transmitting that information to a plurality of sub- 30 scriber terminals within the wireless telecommunications create said 'm' orthogonal channels within the single system. frequency channel; 7. A central terminal as claimed in claim 6, wherein the a first decoder for applying, to signals received on channelisation means also determines, for those orthogonal the single frequency channel, the orthogonal code provided by the orthogonal code generator, in channels subject to TOM techniq11es, how many time slots 35 order to isolate data items transmitted within the will be provided within each orthogonal channel. 8. A central terminal as claimed in claim 7, wherein a corresponding orthogonal channel; and number of said orthogonal channels are designated as traffic a TOM decoder arranged to extract a data item from a channels for the transmission of data items relating to predetermined time slot within said orthogonal channel, a plurality of data items relating to different communication content, and the TOM encoder is employed 40 to apply time division multiplexing (TOM) techniques to wireless links being transmitted within the same data items to be sent over a traffic channel from said central orthogonal channel during a predetermined frame period; terminal to said subscriber terminal. 9. A central terminal as claimed in claim 5, wherein a first an overlay code generator for providing an overlay of the orthogonal channels is reserved for the transmission 45 code from a first set of 'n' overlay codes which are of signals relating to the; acquisition of wireless links, and orthogonal to each other, the set of 'n' ovt:rlay codes enabling 'n' data items pertaining to different wirethe second encoder is used instead of the TOM encoder to enable overlay codes to be applied to data items to be sent less links to be transmitted simultaneously within the \>,ritbin said first orthogonal channel from the central terminal same orthogonal channel; to one of said subscriber terminals. a second decoder, selectively operable instead of the 50 10. A central terminal as claimed in claim 5, wherein a TOM decoder, to apply to the data items of the second of the orthogonal channels is reserved for the transorthogonal channel, the overlay code from the overmission of signals relating to the control of calls, and the lay code generator so as to isolate a particular data second encoder is used instead of the TDM encoder to item transmitted using that overlay code, wherein the enable overlay codes to be applied to data items to be sent 55 orthogonal code generator is a storage arranged to within said second orthogonal channel from the central store the set of orthogonal codes and wherein the set terminal to one of said subscriber terminals. of orthogonal codes comprise a set of Rademacher11. A wireless telecommunications system comprising a Walsh (RW) codes. central terminal and a plurality of subscriber terminals, 12. A method of processing data items to be transmitted wherein the central terminal comprises a transmission con- 60 over a wireless link connecting a central terminal and a troller having: subscriber terminal of a wireless telecommunications system, a single frequency channel being employed for an orthogonal code generator for providing an orthogonal transmitting data items pertaining to a plurality of wireless code from a set of 'm' orthogonal codes used to create links,. the method comprising steps of: 'm' orthogonal channels within the single frequency channel; 65 providing an orthogonal code from a set of 'm' orthogonal a first encoder for combining a data item to be transmitted codes used to create 'm' orthogonal channels within the single frequency channel; on the single frequency channel with said orthogonal WI L-0009806 6,088,326 31 32 comb.in.ing a data item to be transmitted on the s.ingle applying the overlay code to said data item, whereby 'n' data items pertaining to different wireless links may be frequency channel with said orthogonal code, the transmitted simultaneously within the same orthogonal orthogonal code determining the orthogonal channel channel. over which the data item is transmitted, whereby data 14. A method as claimed in claim 12, further comprising items pertaining to different wireless links may be steps of: transmitted simultaneously within different orthogonal determining which of the orthogonal channels will be channels of said single frequency channel; and subject to TDM techniques; and applying time division multiplexing (TDM) techniques to transmitting that information to a plurality of subscriber the data item in order to insert the data item within a terminals within the wireless telecommunications syslime slot of the orthogonal channel, whereby a plurality 10 tem. of data items relating to different wireless links may be 15. A method as claimed in claim 14, further comprising transmitted within the same orthogonal channel during a step of: a predetermined frame period. determining, for those orthogonal channels subject to 13. A method as claimed in claim 12, wherein said TDM techniques, how many time slots will be provided applying step is selectively replaced by steps of: 15 within each orthogonal channel. providing an overlay code from a first set of 'n' overlay codes which are orthogonal to each other; and * * * * WIL-0009807

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