5282222 method and apparatus for multipl

8/8/2019 5282222 Method and Apparatus for Multipl

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US005282222AUnited States Patent 1191 11 11 Patent Number: 5,282,222Fattouche et d. [45] Date of Patent: Jan. 25, 1994[54] METHOD AND APPARATUS FORMULTIPLE ACCESS BETWEEN

TRANSCEIVERS N W IRELESSCOMMUNICATIONS USING OFDMSPREAD SPECTRUM[76] Inventors: Mich el Fattouche, 156 Haw kwoo dBlvd. N.W., Calgary, Alberta,Canada, T3G 2T2; Hatim Zlgloul,402 - 1st Avenue, N.E., Ca lgary ,Alberta, Canada, T2E OB4[21] Ap pl. No.: 861,725[22] Filed: Mu. 31,1992[51] ht. Cl.5 ........................................ H04K 1/00[52] US. CI. ........................................... 375/1; 380/34[58] Field of Scuch ..............................380/34; 375/1;364/724.01, 827[561 References Cited

U.S. PAT EN T DOCUM ENTS4,601,005 7/1986 Kilvington .4,623,980 11/1986 Vary .................................... 364/7244,893,266 1/1990 Deem .4,914,699 4/1990 Dunn ct al. ......................... 375/1 X5,034,911 7/1991 Rachels .5,063,560 11/1991 Ycrbury ct al. .................... 375/1 X5,089,982 2/1992 Grm et al. .5,151,919 9/1992 Dent ........................................375/1

OTHER PUBLICATIONSReduction of M ultipath F ading Effects in Single Vari-able Modulations, M. A. Poletti and R. G. Vaughan,ISSPA 90 Signal Processing T heories, Im plementationsand Applications, Gold Coast, Australia 27-31 Aug.,1990, 672-676.OFDM for Data Communication over Mobile RadioFM Chan nels; Part 11: Performance Improv emen t1 byE . F. Casas and C. Leung, Department of ElectricalEngineering University of British Columbia, Vancou-ver, B.C., Canada V6T 1WS.OFDM for Data Communication Over Mobile RadioF M Channels-Part I: Analysis and Experimental Re-sults, Edua rdo F. Casas and Cyril Leung, IE E E Trans-actions on Co mm unications, vol. 39, No. 5, May 1991,pp. 783-793.Performance of an RCPC-Coded OFDM-based Digi-

tal Audio Broadcasting (DAB) System, P. Hoeher, J.Hagenauer, E. Offer, Ch. Rapp, H. Schulze, Globe-com P1, CH298&1/91/0000-0040, pp. 00 40 dW 6.T he Multitone Channel, Irving Kalet, IE E E Transac-tions on C omm unications, vol. 37, No. 2, Feb. 1989, pp.119-124.Optimized Decision Feedback Equalization versusOptimized Orthogonal Frequency Division Multiplexingfor High-Speed Da ta Transmission Ov er the LocalCable Network, N ikolaos A. Zervos and Irving m e t ,CH2655-9/89/0000-1989 IE EE, p. 1080-1085.

(List continued on next page.)Primary Examiner-Tod R. Swa nnAttorney, Agent, or Finn-Daniel L. DawesA method for allowing a number of wireless transceiv-ers o exchange information (data, voice or video) witheach other. A first frame of information is multiplexedover a number of wideband frquency bands at a fmttransceiver, and the information transmitted to a secondtransceiver. T1.e informatio n is received an d processedat th e second transceiver. T he information is differen-tially encoded using phase shift keying. In addition,after a pre-selected time interval, the first transceivermay transmit again. During the preselected time inter-val, the second transceiver may exchange informationwith another transceiver in a time duplex fashion. Theprocessing of the signal at the second transceiver mayinclude estimating the phase differential of the transmit-ted signal and predistorting the transmitted signal. Atransceiver includes an encoder for encoding informa-tion, a wideband frequency division multiplexer formultiplexing the information onto w ideband frequencyvoice channels, and a local oscillator for upconvertingthe multiplexed information. The apparatus may in-clude a processor for applying a Fourier transform tothe multiplexed information to bring the informationinto the time domain for transmission.

12 Claim, 23 Dmwing Sheets01I


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5,282,222Pane 2

OTHER PUBLICATIONSAdvanced Groupband Data Modem Using Orthogo-nally Multiplexed QAM Technique, B otaro Horosaki,Satoshi Hasegawa, and Akio Sabato, IEEE Transac-tions on Com munications, vol. COM-34, No. 6, Jun.1986, pp. 587-592.A 19.2 Kb ps voiceband data mode m based on orthogo-nally multiplexed QAM techniques B. Hirosaki, A.Yoshida, 0. Tanaka, S. Hasegawa, K. Inoue and K.Watanabe , CH2175-8/85/-1, IE EE , pp.661-665.Analysis and Simulation of a Digital Mobiie ChannelUsing Orthogonal Frequency Division Multiplexing,Leonard J. Cimini, Jr., IE E E Transactions on Comm u-nications vol. Com-33, No. 7, Jul., 1985, pp. 665-675.An Orthogonally Multiplexed QAM System Using theDiscrete Fourier Transform, Botaro Huosaki, IEEETransactions on Comm unica tions, vol. Corn-29, No. 7,Jul. 1981, pp. 982-989.An Analysis of Autom atic Equalizers for Orthogona llyMultiplexed QAM Systems Botaro Hirosaki, IEEE

Transactions on Com mu nication s, vol. Corn-28, No. 1,Jan. 1980, pp. 73-83.An Improved Method for Digital SSB-FDM Modula-tion and Demodulation, Rikio Mamta and AtsushiTomozawa, IEEE Transactions on Communications,vol. Com-26, No. 5, May 1978.Da ta Transm ission by Frequency-Division Multiplex-ing Using the Discrete F ourier T ransform, S. B. W ein-stein and Paul M. E bert, I E E E Transactions on Corn-mu nication Techno logy, vol. Corn-19, No. 5, Oct.,1971, pp. 628-634.Per formance of an E f f~ c i i t arallel Data TransmissionSystem, Burton R. Saltzberg, IEEE Transactions onCom munication Technology vol. Com-15, No. 6, Dec.,1967, pp. 805-81 1.A Theoretical Study of Performance of an OrthogonalMultiplexing Data Transmission Scheme, Robert W.Chang, Richard A. Gibby, IE E E Transactions on Com -munication Technology, vol. Corn-16, No. 4, Aug.,1968, pp., 529-540.Synthesis of Band-Limited Ortho gona l Signals for Mul-tichannel Data Transmission by R obert W. Chang, Th eBell System Technical Journal, Dec. 1966, pp.1775-1796.


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U.S. Patent Jan. 25,1994 Sheet 1of 23


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U.S. Patent Jan. 25,1994 Sheet 2 of 23


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1 frame> .

Fig. 3a

1 frame

Fig.3b

1 framee 52 PS * p~39.152 s + 2.8488sTotal# of frames = 252

Fig. 3c


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U.S. Patent Jan. 25, 1994 Sheet 4 of 23


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U,S, Patent Jan. 25,1994 Sheet 5 of 23


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Repeat right & Leftw~thout verlapfollowed by a raisedcosine window(last2 blocks in processor)

Repeat right & leftwith overlapfollowed by arectangular window(last2 bkxks inde-processor)


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U.S. Patent Jan. 25, 1994

s Ia-m== 25E ca-m-- 3a z s-25V-3 E5sscn

r

4;kI =.s? c5 g 25 aTo"

Sheet 10 of 23


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at each frequencyand calculate theamplitude and phase

Calculateai 2 tCalculate Calculate

P= w,(n) - ( ~ ( n ) A w (n))I N =C [w ,(n)- (o(n) - Ao n))]

tCalculate

t

I use 1 I Use I

d

Fig. 7b

Calculate Calculateo (n) + A G (n) o n) - Ao (n)1 I

o n) + Aw (n)to demodulate

Calculate the ideal phase GI+ (n)based on the quadrant ofo n) + Ao n)

w (n) Aw (n)to demodulate

Calculate the ideal phase GI, (n)based on the quadrant ofo n) - Ao n) .I I


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U.S. Patent Jan. 25,1994 Sheet 12 of 23 5,282,222

Fig. 8a

Fig. 8b Fig.&


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U.S. Patent Jan. 25, 1994 Sheet 13 of 23 5,282,222


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US, atent Jan. 25,1994 Sheet 15 of 23


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Frame Duration-

1 frameLd555 =I1180sKHzd{

1 frame

1 frame

Fig. 11c


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U.S.Patent Jan. 25,1994 Sheet 17 of 23


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US, atent Jan. 25, 1994 Sheet 20 of 23


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Repeat right & Leftw~thout verlapfollowed by a raisedcosine window(lad2 b b c b n procelrsor) Flg. 14c

Repeat right & leftwith overlapfollowed by arectangular window(last 2 blocks in de-processor)


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Estimate Group Delay o(n)

Fig. 15

N01Hilbert la'(n)l Estimate mg(n)Polarity Pe,~ransform of m(n)A

A'(n)-A'(n- 1A'@)

128 b estimate "("1fromDeprocessor

ArithmeticOperation-.


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5,282,2221 2cochannel interference and little or no intersymbol in-METHOD AND APPARATUS FO R MULTIPLE terference.ACCESS BETWEE N TRANSCEIVERS IN The new access technique can ffer up to 38tima th eWIRELESS COMMU NICATIONS USING OFDM capacity of analog FM. t includes in one aspect wide-SPREAD SPECTRUM 5 band orthogona l frequency division multiplexing of theinformation to be exchanged, and may include slowF I E L D O F T H E I N V E N T IO N Frequency Hopping 0.he technique is imple-This nvention relates to v oice and data transmission mented using Digital Signal Processors @SP) replac-in wireless communications, and particularly between ing conventional analog devices. Th e system operatesfixed and portable transmitters and receivers. 10 with relatively small cells. In other aspects, dynamic

CLAIM TO COPYRIGHT channel allocation and voice activation may be used toimprove the capacity of the system.A portion of the disclosure of this patent document Advantages of the present invention include:contains material which is subject to copyright protec- 1. It can be used indoors as well as outd oors using thetion. Th e copyright ow ner has no objection to the fac- l5 same transceivers. If da ta is to be exchanged, as op-simile reproduction by anyone of the patent document, posed to voice, the transceiver preferably contains anas it appears in the Patent and Trademark O fic e patent estimator to allow pre-distortion and post-distortionfile or records, but otherwise reserves all copyright of the transmitted signal.rights whatsoever. Software for carrying out some of 2. Th e system, as compared with prior art systems omitsthe method described in this patent document has been 20 the clock or c-er recovery, automa tic gain cont rolfiled w ith th e Patent and T radem ark Office in the form or passband limiter, power am plze r, an equalizer orof a microfiche and includes 55 frames including a title an interleaverdeinterleaver, and therefore has lowframe. complexity.BA CK G RO UN D A N D S U M MA RY O F TH E 3. Th e system offers good spee ch quality, as well as owINVENTION 25 probabilities of dropped and blocked calls. It is robustagainst Doppler and multipath shifts. It is also robustThis patent document presents a new multiple access against both impulse noise and narrowband interfer-technique for Personal Communication Networks ence.(PCN). communication networks are net- 4. The system is flexible, such that at the expense ofworks that allow individuals and equipment to ex- 30 increased complexity of the DSP receiver it canbechange information with each other anywhere at any- applied noncontiguous bands. ms istime through data Or video' PCN in- plished by dividing a 100 MHz (in of the exem-clude a num ber of transceivers, each capable of trans-mitting and receiving information (voice, data o r video) plary em bodiments described here) band in to severalin the form of electromagnetic signals. T he transceivers 35 subbands each accommodating an integer number ofmay be fu ed o r portable, and may be identical or one o rmore of them may be more complex. 5. Th e system offers low frame delay (less than 26.2 msThe system must allow the transceivers to access in the embodiment describedeach other to enable the exchange of infomation. When here). Th e transceiver requires low average transmit-there are a number of transceivers, multiple access, that 40 ted power (of the order of Z0 pW in the exemplaryis, access by more than one transceiver to another trans- cellular embodiment described here) which meanscciver, must be allowed. pow er saving as well as enhanced biological safety.One of the constraints of designing a PCN is that a 6. T he system offers UP to a 38 fold increase in capacitytransceiver, o r portable radio unit, must be small in size. over the North American Advanced M obile PhoneThe smaller the unit, the better for portability. The 45 System (AMPS) which uses analog frequency modu-small size of the units means only small and light-w eight lation-power sources be used. If the po rtable is to be used Operation of the system in accorda nce with the tech-for any length of time, it must therefore consum e mini- niques descr ibed in th is disc losure may permit ~ m ~ l i -

ma1 power. ance with technical requirements for spread spectrumAlso, to allow use of the radio frequency spectrum 50 systems.without obtaining a license in ~ o r t h merica, the sys- There is therefore disclosed in one aspect of the in-tern must use a spread spectrum and satisfy federal r e p - vention a method for allowing a number of wirelesshtions. In part, these regulations impose limits on the transceivers to exchange information (data, voice orpower and the frequency spread of the signals ex- video) with each other. In the method, a fmt frame ofchanged k t w m he transceivers. An object of an as- 55 inform ation is multiplexed ove r a num ber of frequencypect of this invention is to satisfy those requirem ents. bands at a first transceiver, and the informa tion trans-Also, transceivers talk to each other over a fued mitted to a second transceiver. In a cellular implementa-bandwidth. B ecause of the limited availability of the R F tion, the second transceiver may be a base station withspectrum, the system must be bandwidth efficient yet at capacity to exchange information with several otherthe same time maintain high quality exchange of infor- 60 transceivers. The information is received and proc e3s dmation at al l times in one of the most hostile channels at the second transceiver. T he frequency bands areknown in comm unication. T he new multiple access selected to occupy a wideband and are preferably con-technique proposed here addresses all these issues. tiguous, with the informatio n being differentially en-The new access technique has a low Bit Er ror Proba- coded using phase shift keying.bility (BER) as well asa low probability of drop ped and 65 A signal may the n be sent from the sec ond trans-blocked calls. This is due to the fact that the access ceiver to the first transceiver and de-processed at thetechnique is robust against multipath , Do pple r shifts, first transceiver. In addition, after a preselected timeimpulse noise and narrowband interference. It hasa low interval, the first transceiver transmits again. During


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5,282,2223 4the preselected time interval, the second transceiver FIG . 7a is a schematic showing the structure andmay exchange information with another transceiver in a function of the channel estimator in FIG. 56;time duplex fashion. FIG. 76 s a flow chart showing the operation of theTh e processing of the signal at the second transceiver channel estimator of FI GS . Sb and 7a;ma include estim ating the ph ase differential of the tran s- 5 FIGS. &, 8b and 8c are respectively schem atics ofmitted signal and predistorting the transmitted signal. 126,63 and 7 cell reuse patterns;The time intervals used by the transceivers may be FIGS. 9a and 9b are schematics showing transmitassigned so that a plurality of time intervals are made protocols according to one aspect of the invention;available t o the first transceiver for each time interval FIG. 10 s a schematic showing the use of the avail-made available to th e second transceiver while the fvst 10 able frequencies according to another aspect of thetransceiver is transmitting , and for a plurality of time invention for use with local area network applications;intervals to be made available to the second transceiver FIG . lla is a schematic showing an idealized pulsefor each time interval made available to the fust trans- for transmission over a local network system;ceiver otherwise. Frequencies may also beborrowed by FIG . 118 s a schematic showing a m odified versionone base station from an adjacent base station. Thus if 15 of the pulse shown in FIG. lla;one base station has available a fust Set of frequencies, FIG. llc a schematic showing a f urth er modifiedand ano ther a second set of distinct frequencies, then a version of the pulse shown in FIG . llo;portion of the frequ encies in the first set may be empo- FIG. 12 s a schematic showing a preferred protocolrarily re-assigned to the second base station. for local area network communication;In an im plementation of the invention for a local area 20 FIG. 1% is a block diagram showing the structurenetwork, each transceiver may bemade identical except and function of an embodiment of the transmitter of afor its address. local area network transceiver according to the inven-Apparatus for carryingdout the m ethod of the invention;tion is also described here. The basic apparatus is a FIG. 136 is a block diagram showing the structuretransceiver w hich will include an encoder for encoding 25 function of an embodiment of a further local areainformation, a wideband frequency division multiplexer network transceiver according to the invention;for multiplexing the information onto wideband fre- FIG. 1 3 ~s a block diagram showing the structurequency vo ice channels, and a local oscillator for upcon- and function of an embodiment of the receiver ofa localverting the multiplexed information. Th e apparatus may area network transceiver according to the invention;include a processor for applying a Fo urier transform t o 30 FIG. is a flow diagram showing the function ofthe multiplexed information to bring the information the processor in either of FIGS. 1% or 13b;into the time domain for transmission. F I G . 146 is a schematic showing the function of theBRIEF DESCRIPTIONOF THE DRAWINGS deprocessor in either of FIG S. 13b or 13c;FIG. 14c s a schematic further illustrating the opera-The re will now be described a preferred em bodiment 35 tion of the processor deprocessor shown in FIGS.of the invention, with reference to the drawings, by an d 14b; ndway of illustration, in w hich like numerals denote like FIG. is a =hematic showing the structure andelements and in which: function of the channel estimator in F IG. 13b.FIGS. laand lb are schem atics of a prior art receiverand transmitter respectively; 40 DE T A I L E D DE S C RI PT ION O F P R E F E R R E DFIG. 2 s a schematic showing the use of the available EMBODIMENTSfrequencies according to one aspect of the invention for Introductionuse with cellular applications;FIG. 3a s a schematic showing an idealized pulse for Th e benefits of the invention can be readily appreci-transmission over a cellular svstem: 45 ated with reference to FIG. 1,which show s a prior art. ,FIG. 3b s a schematic showing a modified version of transmitterheceiver configuration for a portable unit.the pulse shown in FIG . 3a; Th e transmitter includes a vocoder 110, n interleaverFIG. 3c is a schematic showing a further modified 112, modulator 114, filter 116, ocal oscillator 118,version of the pulse shown in FIG . 3a; power amplifier (PA) 120 and antenna 122. The re-

FIG. 4 s a schem atic showing an exemplary protocol 50 ceiver includes an LNA 124, a local oscillator 126, afor cellular communication; filter 128, utomatic gain control (AGC) 130 with anFIG. Sa is a block diagram showing th e structure and associated passband hardlimiter not separately shown,function of an embo dimen t of the transmitter of a cellu- carrier recovery 132, ampler 134, lock recovery 136,lar portable in accordance with the invention; adaptive (or fued) equalizer 138, demodulator 140,FIG. Sb s a block diagram showing the structure and 55 deinterleaver 142 and decoder 144. With implementa-function of an embodiment of the transmitter and re- tion of the present invention, several of the blocksceiver of a cellular base station in accordance with the shown in FIG . 1 are not required. These are the inter-invention; leaver 112, einterleaver 142, ower amplifier WJ,au-F I G . Sc is a block diagram showing the structure and tomatic gain control 130 with passband hard-limiter,function of an embodiment of the receiver of a cellular 60 clock recovery 136 and carrier recovery 132, nd theportable in accordance with the invention; equalizer 138. It will now be explained how the pro-FIG. 6a s a flow diagram showing the function of the posed system obtains the omission of these blocks with-processor in either of FIGS . 5a or 5b; out impairing the quality and capacity of the system.FIG. 66 s a schematic showing the function of the In this disclosure there will be described tw o systemsdeprocessor in either of FIG S. Sb or 5c; 65 as examples of the implementation of the invention. Th eFIG. 6c is a schematic further illustrating the opera- system described first here will apply to a cellular sys-tion of the processor and deprocessor shown in FIG S. tem with a number of portable transceivers and base60 and 6b; stations (BS). Then will be described a local area net-


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5,282,2225 6work implementation. A local area network will typi- is duration of on e time domain sample and x is any realcally be a system of equal transceivers. Th e invention value, the shift is equal to 2aAfxT. Hence, 7 causes amay also be implemented with com binations of cellular shift in th e phase difference between adjacent symbolsand local area networks, or t o a system with a number of value 2 q / K 1 since T is equal to I/(KlAf). By dou-of equal transceivers and a master or controlling trans- 5 bling the number of symbols from K1 to 2K1 the shift inceiver. "Equal" as used here means that the transceivers the phase difference is reduced by half from 2ax/ X1 tohave m ore o r less the same processing equipment and ?rx/Kl. Thus, the effect of the clock erro r on the BERprocessing capabilities. The system described here is is reduced by increasing K.primarily for the exchange of voice information. (2) When there is relative motion between the trans-Link set-UPand terminatio n protocols betwee n trans- 10 mitting transceiver and the receiving transceiver, aceivers, and the equipment required t o implement them, Doppler shift occurs with a maximum absolute valueare well understood in the art as as the basic strut- (V /h ( where V is the relative velocity between the tw oture of radio transceivers that may be used to im plement transceivers and A is the of the travellingthe invention. Hence these elements are not described wave correspondingto the carrier fc(i.e. f,ishere. W hat is described here are the novel operational, 15 the frequency corresponding to the middle point in thefunctional and structural elements that constitute the frame). Sucha Doppler shift causes a sampling ininvention. the frequency domain of the same amount, or cquiva-Cellular Implementation of Wideband M odulation lently, it causes a samp ling err or of V/(hAf) relative to

T he present invention proposes in one embodiment a 20 one symbol sample. Thus, the effect of the Dopp ler shiftwideband modulation scheme for exchange of informa- On the BER is reduced by increasing Af'tion betwee n transceivers such as portables and base (3) When a the in thestations. transmitter and the one in the receiver occurs with aWideband in this patent docum ent is described in the value f& it causes a sampling error in the frequencycontext of Wideband-Ofihogonal Frequency Domain 25 domain of the % me amount, o r equivalently, it causes aModulation (W-OFDM or wideband OFDM). In sampling error of fdA f relative t o one symbol sample.OF DM , the entire available bandwidth B is divided into Thus9 the effect on the BER of the frequency offseta number of points K, where adjacent points are =pa- between the LO in transmitter and the one in the re-rated by a frequency band Af, that is B=KA f. Th e K ceiver is reduced by increasing Af.points are grouped into a frame of K1points and tw o tail 30 In summ ary, O FD M with a K and a Af large enoughslots of K2 points each, s o that K =K I+ 2K2. Th e frame to be able to achieve a specific throughput and largecarries the information intended for transmission under enough to be able to avoid using either a clock or athe form of multilevel differential phase shift keying camer recovery device without substantially affecting(MDPS K) symbols or differential quadrature amplitude the BER is referred to here as Wideband-OFDM . As anmodulated (DQAM) symbols. Thus each point in the 35 example, let us assume that MDPSK is used in anframe corresponds to one information symbol. Th e tw o OF DM system with the number M of levels, with atail slots act as guard bands to ensure that the out-of- carrier frequency fc, with a raised cosine pulse of roll-band signal is below a certain powe r level. Fo r example, off P, with the LO at the receiver having a frequencywhen a pulse P(f) is selected for pulse shaping and the offset forelative to the L O at the transmitter (so that theout-of-band signal has t o be ydB or less relative to the frequency offset between the carrier frequencies in thein-band signal, K2 is selected suc h that first and second transceivers of the multiplexed infor-mation is fo), with a given maximum expected clock2O.loglolP(f)/F(O) I+ for fZKzAf. error 7= xT at the rece ivi~ gransceiver, whe re T is th eduration of one time domain sample, and with a maxi-When the pulse is a pulse with a P q5 mum expected relative velocity V between the trans-and when the number of levels each can take is ceivers. Thus, in order to ensure that the out-of-bandM, the bit rate is equal to Kllog2M/(8t+(l +P)/Af) signal is ydB or less relative to the in-band signal and towhere (I +P)/Af is the duration of the frame and 6t is be to avoid using either a clock or a carrier recov-the guard time required to take into account the delayof arrival and the delay spread due t o multipath. In this ery device without substantially affecting the BE R wecase, the bandwidth eficiency, which is defined as th e haveratio between the bit rate and the bandwidth, is equal to: Find the Af 9one symbol sample, which does not substantially

log~M/((l+B+8tAfK1+2Kfll)) affect th e BER . This can be done using the followingrules:In wideband-OFDM, both K and Af are selected 55sufficiently large to achieve a high throughp ut as w ell When 0.2SBS0.3, A f =7.W)%as to reduce the effects on the BE R of the clock error,the D oppler shift and the frequency offset between the Whm 0.3SBS0.4, A f =10.0%L O in the transmitter and the one in the receiver. T o Whm O.4iSBS0.5,~f = 12.5%sho w what is meant by "K and Af are selected suffi- 60ciently large", consider th e effect of increasing K and When 0.5SBS0.6, ~f IS.^%Af on (1) the clock error, (2) the Doppler shift and (3)the frequency offset between the L O in the transmitter 2. Find Af such that:and the L O in the receiver.(1) When a clock error at a transceiver of value T 65 V/(Mf)+fJAfiAfoccurs in the time domain, it causes a shift in the phasedifference between adjacent symbols in the frequency 3. Find K2 such thatdomain of value 2aAfr. W hen 7 is equal to X T where T


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5,282,22272O.loglolP(f)/P(O) Id for fZK2uf 8to ensure a transmission delay to allow one transceiverto communicate with other transceivers at the same4. Find K1 such that time, but must not be so long that the delay becomesZUX/P~


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5,282,2229 10frquency hopped into a new vc slot within the same low, the transmitted power is increased and if the aver-(frequency domain) frame. This frequency hopping is age power is too high, the transmitted power is de-ordered by the BS which is constantly monitoring the creased. The power controller 525 may also be used inchannel frequency response. Monitoring techniques, as frquency hopping to monitor the average power of thewell as frequency hopping, are known in the art, and 5 received frequency and determine when frequencynot described here further. When an unacceptable hopping need take place.speech degradation is first noticed by the BS a proba- FIG. Sc corresponds to step4, nd shows the receivertion period is initiated and maintained for at least 10 of the portable, which is the same as the receiver in thecycles 6.e. 10X 13.104 ms) unless speech degradation BS except it does not include an estimator or r powerhas cursed. In other words, the probation period is 10 controller. These are not required in the portable on theterminated i f s F h degradation has ceased.Frequency assumption that the BS will carry out the phase estima-hopping is then ordered at the end of the probation tion and the power control. However, if desired, theperiod. The period of 10 cycles is long enough to indi- portable may include these functions.the portable stationarit~ nd is short enough to FIGS. 6u, b and 6, llustrate the function and struc-a o w s F h interpolation between unacceptable 15 ture of the processor and the deprocessor respectivelyspeech frames*hence maintaining goodsFhuality. in the transmitter and receiver. Software for modellingAs known in the art, the BS ensures that no collisions the function of the processor in a general purposetake place betwem hopping portables. auter has been filed with the Patent and Trademark

Digital Signal Processing bfice as frames 3 to 26 of the microfiche appendix and20 for modelling the function of the deprocessor has beenThe transmitter/receiver block diagrams correspond-filedwith the Patat and Trademad as framesing to the protocol in FIG. 4 are shown in FIGS. So,56 2741 of the microfiche appendix.and Sf' to step in the protocol FIG. Q shows that the prOceSsor s a DSP -Imen-described above- Speech is provided a vocoder tation of an RC pulse shaping filter with a 20% roll-off,where the speech is digitized and coded to create bits of 25 followed by an Fourier transform.The proces-information. The bits are provided to the modulator 512which turns them into D8PSK symbols, with three bits sor first inverse Fourier transforms the 4096 D8PSKper symbol. The D8PSK symbols are then processed in modulated symbols output from the modulator. Thethe processor 514which is described in more detail in transformed are then as a group soFIG. 6u.The output from the processor is then filtered 30 that the total number of is trip1ed, with three

in low pass filter 516,upconverted to RF frequencies consecutive groups each consisting of the m6 rans-using local 518 transmitted by antenna formed symbols. The triplication of the signal is illus-520.Figure Sb corresponds to steps 2 and 3. trated in FIG. k,where the symbols are shown as first

In FIG. 56, he received signal at the base station is delayed and added together. Next, as shown in FIGS.filtered in a bandpass filter 522, nd down converted by 35 and 6~ he three groups are by a Raisedmixing with the output of a local oscillator 524.ne Cosine window with a roll-off of 0.2 centered in theaverage power of the downcoverted signal is monitored th e three groups- In other the proces-by a power controller 525 that adjusts the average sor takes D8PSK pulse shapes them andpower to the specifications required by the sampler526. invqseourier transforms hem.On he hand* heThe adjusted downconverted bits are then sampled in 40 de~rocesmr ndoes what the processor did, i.e. it re-sampler 526 to produce bits of information. The bits are move the pulse shaping* then Fourier transforms thethen processed in fie deprocessor ~ a ,escribed in received signal to obtain the original D8PSK symbols.more detail in FIG. An estimate of the phase differ- The first two blocks in FIG. 6b are ~h i l a ro the secondential of the received signal is taken in the channel esti- two blocks in FIG. Q except for two differences. Themator 530, as described in more detail in relation to 45 tWO differences are as ~ O ~ ~ O W S .n the first block of theFIG. 7a nd 78below, and the estimated phase differen- d e ~ r m s o r yhe repeated groups of symbols are Par-tial is supplied to a decoder-demodulator532 o correct tially overlapped as shown in FIG-k on the fight handthe received bits. The estimated phase differential s also side. In the second block, a rectangular window is usedsupplied to a pre-distorter 534 n the transmitter. At the instead of the Raised Cosine. In the preferred h ~ l e -transmitter in the Base Station, the same blocks are 50 mentation, the blocks are repeated three times but otherincorporated as in the portable transmitter except that a ~ ~ ~ b e r sf repetition may be used.pre-distorter is used to alter the phase of the D8PSK FIGS. Q, and 6, how that the DSP blocks usedsymbols to make the channel appear Gaussian (ideal) as in the processor are identical to the ones used in theopposed to a fading channel. The predistorter 534 re- depr-sor, except for a small change in the two trans-ceives a signal corresponding to the estimated phase 55 forms and a small change in the shapes of the two win-differential of the channel. On the (believed reasonable) dows. Thus the same hardware canbe used by both theassumption that the channel is reciprocal, the signal processor and the deprocessor.being transmitted is predistorted with the estimated FIG. 7a shows a block diagram of an example of aphrrsc differential so that the received signal at the por- preferred channel estimator, and FIG. 76 is a flow charttable with which the BS is communicating will be cor- 60 showing the operation of the phase estimator. Each ofrected for any phase distortion over the channel. The the steps is camed out in a computing means that mayadvantage of rendering the channel Gaussian is a large be a special purpose computer or a general purposesaving in the power required to achieve an acceptable computer programmed to carry out the digid signalBER. The initial power control 525 also sends a signal processing described here, as for example with the soft-to the pre-distorter 534 o adjust the transmitted power 65 ware that has been filed with the Patent and Trademarkto an appropriate signal level for the sampler526 in the Ofice as frames 42-55 of the microfiche appendix.portable's receiver depending on the average power of Other methods of estimating the channel may be usedthe received signal. Thus if the average power is too that obtain an estimate of the channel group delay or


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5,282,22211 12phase differential of the transm itted symbols. How ever, N = x I o{o(n)-Ao(n)} I are calculated. If P< N , thena preferred implem entation is described here. o(n) + Ao(n) is used to corre ct th e signal, and if not thenThe first block in FIG. 7a estimates the envelope o(n)-Ao(n) is used t o correct the signal.A(n) for n= 1, .. 096 of the (frequency domain) Fo r simplicity of the estimator, the determination ofsamples transmitted over the fading channel as outpu t 5 the sign need only be carried out for phase differentialsfrom the deprocessor. Th e estimate A1(n) is the square- greater than a predetermined threshold. This will be inroot of the sum of the squares of the quadrature (Q) and the vicinity of a fade and may be accomplished by seg- .inphase @ samples output from the de ~r oc es so r hich Denting the data record into a segment in which themay be filtered in t~ ~ o r d a n c eith known technique s phase differential is larger than a selected threshold andbefore Or after estimation of the envelope. The second 10 setting the remainder of the data record to zero. Thisblock performs the operation: computation may be carried out w ith a simple discrimi-Aln(~'(t))= A'(t)) = A'(n) - '(n - ))/A1(n), for n=2, nation circuit or equivalent computing means in the. . . ,4096, where A'(n) is the estim ate of A(n). Th e thirdblock performs a Hilbert transform operationHIAln(A1(t))] on the result of the second block.HIAln(A1(t))] is an estimate of IAo(n)l for n= 2, .4096, where Ao(n) is the phase differe ntial of the trans-mitted signal ( o is the phase of the signal). T he H ilberttransform is preferably carried out by taking the dis-crete fast Fourier transform of the data record, multi-plying the positive frequency spectrum of the transformby -i (square root -I), and the negative frequencyspectrum of the transform by i, and taking the inversediscrete fast Fourier transform. The result is a set ofsymbols representing an estimate of the phase differen-tial of the received signal, as determined from its sam-pled am plitude envelope.Instead of a Hilbert transform, a different estimationmay be made to estimate the phase differential. In thiscase, firstly, after the electromagnetic signal has beensampled, a series of data fram es of a number of consec u-tive amplitude samples (A(t)) of the electromagneticsignal are constructed. The se data frames are then seg-mented in to segments [tl,t2], where th e amplitude of theelectromagnetic signal is at least a predetermined num-ber of dB less than its running mean, for example, 1WB .T he following calculation is then applied to these seg-ments of the amplitude samples:where tl= t-t m in, tmin is the time in [tl, t2] when A(t)reaches its minimum, t is the tim e from the beginning ofthe segm ent, and to s the time from the instant the am-plitude of the electromagnetic signal reaches its mini-mum during the segment until the amplitude reachesdouble its minimum during the segment. In otherwords, the phase differential may be calculated from

estimator.Th e bias S o of the channel group delay is estimatedby averaging Ao'(n) ove r n for n= 1, . 4096 whereAol(n) is the measured value of Ao(n). The estimatesA1(n) and A ol(n) are used directly in th e predistortionfilter in FIG . Sb, while the estimates Ao(n) and 6 0 ofthe unbiased channel group delay and of the bias of thechannel group delay respectively are used in the de-modulator.The complexity of the processor-deprocessorchan-nel estimator is displayed in Table 11. Complexity ismeasured in Mega Instructions Per Second (MIPS)where one instruction is defined as one complex addi-tion, one com plex multiplication and a storage of onecomplex number. It does not include overhead.The complexity of the processor-deprocessorchan-nel estimator in the BS is computed from th e complex-ity of the Inverse Fast Fourier Transform (IFFT)/Fas tFourier Transform (FlT)/Hilbert Transform. Th ecomplex ity is 4 0 9 6 ~ 2 ~ 4 ~ 2 1 / 1 3 . 1 0 4s for the BS.Fo r the portable, it is computed from the com plexity ofthe FFT AF FT per vc: (32x5+64+128+256+512+1024+2048+4096)2/13.104 ms for the

portable with a 6.18 Kbps vocoder. Such a complexityassumes that the A /D converter operates at 100 MHzwith 12 bit precision. As seen in Table 11, the portablehas smaller complexity due to the fact that the portabletransmits/rec eives one vc in 13.104 ms and the BS trans-mits/receives up t o 21 X N v c in 13.104 ms.Reducing Analog Complexity

Comparing FIG . 1 prior art) and FIG. 5, it will beseen that several conven tional blocks are not used in thepresent invention , namely the interleaver-deinterleaver,the Pow er Am plifier (PA), both the clock and the car-rier recovery, both the AGC with its associated Pass-band hard limiter, as well as the equalizer.F rom the BS ~ o i n t f view, the interleaver-deinter-

LC&)= -w(to2+ .3. leaver is not required since the signal is predistortedbefore transmission forcing the received samples to beT he polarity of A o(n) is extracted using the last block independent. From the portable point of view, the inter-show- in FIG. 7a. Th e estimate so calculated does not 55 leaver-deinterleaver is not required as a separate entityprovide the sign of the differential. This may be deter- from the vocoder due to th e fact that the channel ismined by known techniques, for example by adding the highly frequency selective, hence the interleaving/dein-phase differential to and subtracting the phase differen- terleaving can be applied implicitly in the vocoder o vertial from the received phase (tan-1 (QA)) and taking one vc, without a need for a separate time domain inter-the sign to be positive if the addition results in the 60 leaver/deinterlea ver. Thi s eliminates excess speech de-smaller Euclidean distance to the expected value and lays associated with interleaving/deinterleaving be-negative if the subtraction results in the smaller Euclid- tween frames.ean distance to the expected value. T he PA is not required since the cells can have, asEquiva lently, for each sample n, the ideal phase clos- show n later, a radius of up to at least 250 m outdoorsest to o(n)+Ao(n) is determined and labelled o+(n), 65 and 30 m indoors, if the transmitted power is up to 6and the ideal phase closest to o(n)-Ao(n) is deter- dBm. Such a powe r can be generated by the Localmined and labelled o-(n). Th e tw o sums P = Oscillator (LO) without a need for a PA. It is importantxIo+(n)-{o(n)+do(n))I and to avoid using a PA since D OF D M generates a time


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domain signal with non constant envelope. A power the BS over one vc slot is (6 dBm - 0logloN dB) whileefficient class C PA cannot be used without distorting the signal power transmitted by the portable over onethe signal. A class A PA can be used at the expense of vc slot is0 Bm. Also, since the noise power over a 100power efficiency. MHz band is -94 dBm, it is (-94 dBm - OlogloN dB)A clock recovery device is not required since a sam- 5 over one vc. A typical noise figure at the receiver is 7pling error in the time domain is equivalent to a phase dB. The penalty for not using a matched filter in theshift in the frequency domain. The phase shift is a linear receiver is 1 dB. Combining together the above figuresfunction of frequency. It contributes to the bias in the provides the portable with an (92 dB - path loss in dB)channel group delay. Such a biascanbe easily estimated received signal to noise ratio (SNR), while it providesand removed as mentioned previously by averaging 10 the BS with an (86 dB +lOlogloN dB - path loss ino'(n) over n in the frquency domain. Such an estimate dB) received SNR.is accurate as long as the sampling error is less than 0.2 For a path loss of 75 dB, the radius of the urban cellps or equivalently less than 20 samples (since in this can be 250 m while it can be 30 m for the indoor cell.case, the corresponding phase shift is less than n),and as Such a path loss provides the portable with a 17 dBlong as the number of points in one vc is large enough 15 received SNR, while it provides the BS with an (1 1 dBas it is here. + 1OlogloN dB) received SNR. From the portableA carrier recovery device is not required since a point of view, the channel can be modeled approxi-carrier offset in the time domain is equivalent to a sam- mately as an ideal AWGN channel, hence the 17 dBpling error in the frquency domain. For the chosen RC received SNR results in a 2X 10-3 BER. On the otherpulse, a sampling error of up to 10% of the duration of 20 hand, the channel can be pessimistically modeled as aone pulse is acceptable. Rayleigh fading channel from the BS point of view. TheThis implies that a frequency offset of up to 2.414 corresponding BER are displayed in Table 111 whichIUIz is acceptable regardless whether it is due to camer shows that the achieved BER is S4x10-3. A BERoffset as low as 1part in a million, i.e. as low as 1 KHz S 10-2 is acceptable for voice.per 1 GHz. When a camer frequency higher than 2.414 25GHz is required, one can decrease in FIG. 2 the number Cell Pattern Reuseof points per 100 MHz or one can use an RC pulse with From Table I, the number of Full Duplex voice chm-a rolloff larger than 20%. nels (FDvc) that can be transmitted/received per frameNeither an AGC nor a Passband hard-limiter are is 136 over 100 MHz, for a 6.18 Kbps vocoder. If therequired since the level of the received power may be 30 bandwidth is halved to 50 MHz, the number of FDvccontrolled constantly. This is achieved as follows: The per frame is reduced to 68, the noise floor is reduced byportable transmits a frame. The BS receives the frame 3 dB and the number of full duplex frames that a BScanand predistorts a frame intended for transmission ac- transmit/receive is doubled to 42, leaving the framecordingly, assuming that the channel is reciprocal and duration, the number of frames per 13.104 ms and thestationary over 520 ps. This includes controlling the 35 processor/deprocessor complexity unchanged.transmitted power according to the received power. Reducing the available bandwidth directly affects theThe BS transmits the predistorted frame and simulta- cell pattern reuse. This can be explained as follows,neously orders the portable to control its power. The assuming that we are required to offer a minimum oforder is conveyed using the control symbol in the vc 136 FDvc per cell, that the vocoder rate is 6.18 Kbpsslot (See table I). The degree of power control may be 40 and that the cell radius is fixed at 250 m outdoors and 30determined using the power controller 525, and the m indoors. For a 100 MHz band, we assign one frameinstruction for the inclusion of a power control symbol per cell and offer 136 FDvc per cell. In this case, hein the vc may be sent from the power controller 525 to cell pattern reuse consists of 126 cells as shown inFIG.the predistorter 534. & which displays a seven layer structure. For a 50MHzOne advantage of wideband modulation over nar- 45 band, we assign two frames per cell and offer 136 FDvcrowband modulation is that the wideband signal does per cell, hence reducing our cell pattern reuse to a 63not experience short term fading the same way the cell pattern as shown in FIG. 8b which displays a fivenarrowband one does. The wideband signal is mainly layer structure. If the available bandwidth is as low asaffected by shadowing and other long term effects 5.86 MHz, we have 8 vc per frame. Hence we have towhich vary slowly and are easily monitored from one M assign 18 frames per cell in order to offer the minimumframe to the other as long as the same vc slot is used by required number of FDvc per cell. This reduces the a l lthe portable to transmit and receive (i.e. as long as TDD pattern reuse to as low as a 7 cell pattern as shown inis employed). FIG. 8c which displays a two layer structure.Finally, conventional equalization, whether it is lin- In FIGS. 8a b and c, a shaded area is shown aroundear or nonlinear, is not required simply because there is 55 the center of the pattern, indicating 19, 38 and 126 fulllittle or no ISI. Also, from the portable point of view, duplex frames that the central BS can ransmit/receiveeach received vc is predistorted by the BS. Hence, the respectively. Tables IVa, b and c show the number ofchannelcanbe modeled approximately asan ideal mem- cell layers in each cell pattern reuse, the coverage areaoryless Additive White Noise Gaussian (AWGN) chan- in Krn2 of the pattern reuse for both the indoor and thenel, assuming channel reciprocity and stationarity over 60 urban environments, as well as the carrier to interfer-520 p . From the BS point of view, since the received ence ratio (CIR) in dB, for the 100 MHz, 50 MHz andsignal is not predistorted by the portable prior transmis- 5.96 MHz bands, respectively. In all cases, the CIR ission, the channel estimator is used to reduce the effect large enough to sustain a toll quality speech.of the channel group delay.

65 Transmission/Reception ProtocolSmaller cells Since the number of FDvc a portable can transmit/-As mentioned previously, the LO generates a 6 dBm receive is one, while the number of FDvc a BS canaverage power, hence the signal power transmitted by transmit/receive is much larger asshown in Table V for


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each of the three vocoder rates, we have chosen the adjacent cell. It canuse the original channel as long asfollowing transmission/reception protocol: the level of CIR is acceptable. If on the other hand, a1. The portable transmits a frame over a vc. portable wants to initiate a call in cell Y where all preas-2. Seven adjacent BS receive the frame from the porta- signed channels are used, BS Y can borrow a channelble. 5 from an adjacent cell up to a limit of 64 channels per3. One BS transmits to the portable, depending for ex- cell.ample on the strength of the received signal by each The main advantage of DCA over Fixed Channelof the BS. Allocation (FCA) is the increase in traffic handlingThe control of this protocol may use any of several capability For FCA, a 7 cell pattern each with a preas-known techniques. For example, the commonly used 10 signed 144 Fdvc cancarry a total traffic of 880.81 Er-technique is to have the portable monitor the channel lang at 0.01 Blocking Probability (BP). For DCA, a 7and determine which of several base stations it isclosest cell pattern consists of 6 cells each with 80 FDvc thatto. It can then order the nearest BS to communicate can carry a total traffic of 392.17 Erlang, combinedwithwith it. Another technique is to use a master control one cell with 528 FDvc that can carry 501.74 Erlang.which receives information about the strength of the 15 The total trafiic is therefore 893.91 Erlang. This in-signal on the channel used by the portable and controls crease appears to be marginal (1.5%). However, ifthe BS accordingly. Such techniques in themselves are 501.74 Erlang are actually offered to one cell in theknown and do not form part of the invention. FCA system (with 14 FDvc/cell), while the six othwSuch a protocol has several advantages. For instance, cells carry 392.17/6=65.36 Erlang per cell, the BP atthe location of the portable canbedetermined with high 20 that busy cell 0.714 while it is negligible at the six otheraccuracy based on the received vc at the seven adjacent cells. The total blocked traffic (i.e. lost traffic) in the

BS. Locating the portable can assist in the BS hand-off. FCA system is then equal toA BS hand-off and a portable hand-off do not necessar- ( 6~65 .36~ 0 .0 +X0.714X501.24) 358.24 Erlang. Thisily occur simultaneously, contrary to other prior art represents a 0.4 average BP. If the DCA is allowed suchsystems. In the present invention, when a portable 25 a loss, its traffic handling capacity would increase toroams from one cell X to an adjacent cell Y, a new vc 1768.04 Erlang which represents a 100% increase inis not required immediately. What is required is a BS traffk handling capacity over the FCA system, orhand-off, meaning that BS Y (associated with cell Y) equivalently a 160% increase in the number of availablemust initiate transmission to the portable over the same FDvc. The DCA system thus represents a marked im-vc, while the BS X (associated with cell X) must termi- 30 provement over the FCA system.nate its transmission to the portable.A BS hand-off occurs without the knowledge of the Voice Activationportable and can occur several times before a portable Voice activation is controlled by the BS according tohand-off is required. A portable hand-off is required techniques known in the art. At any instant during aonly when the CIR is below a certain level. In this case, 35 conversation between a BS and a portable, there arethe Mobile Telephone Switching Office (not shown) four possibilities:calls for a portable hand-off in accordance with known 1. BS talks while the portable listens.procedures. Reducing the portable hand-off rate re- 2. BS listens while the portable talks.duces the probability of dropped calls. This is because a 3. BS and portable talk simultaneously.dropped call occurs either because the portable hand- 40 4. BS and portable listen simultaneously.off is not successful or because there are no available The BS controls the voice activation procedure bychannels in cell Y. allocating in cases 1, 3 and 4 three slots (frames 1.1, 1.2The present invention allows the use of post-detec- and 1.3) to the BS and one slot the portable (frame 1)tion diversity at the BS, and the use of dynamic channel every four slots as shown in FIG. 9a. Likewise up to 21allocation (DCA). 45 portables may communicate with the base station in likefashion.Dynamic Channel Allocation In case 2, on receiving a signal from the portable, theDCA is made possible by each BS having capability BS allocates three slots (frames 1.1, 1.2 and 1.3) to theto transmit/receive more than the number of FDvc portable and one slot (frame 1) to the BS every fourallocated to its cell, namely seven times the number of 50 slots as shown in FIG. 9b. Likewise, up to 21 otherFDvc for a 5.86 MHz band and up to twenty-one times portables may communicate with the base station in likethe number of FDvc for a 100 MHz as well as a 50 MHz fashion. Consequently, instead of transmitting two fullband. The DCA protocol simply consists of borrowing duplex voice frames over four slots as in FIG. 4, voiceas many FDvc as needed from the adjacent cells, up to activation allows us to transmit three full duplex voicea certain limit. The limit for the case when we employ 55 frames over four slots. Hence, voice activation providesa 6.18 Kbps vocoder, a 5.86 MHz band and 18 frames a 50% increase in the number of available FDvc at theper cell is obtained as follows. The cell reuse pattern expense of increasing DSP complexity.consists of 7 cells. Each cell is preassigned 144 FDvc.Assuming that at peak hours, 75 FDvc are used on the Capacityaverage and 5 FDvc are reserved at all times, then we 60 The capacity of Code Division Multiple Accessare left with 64 idle channels which represent the limit (CDMA) may be defined as the number of half duplexon the number of FDvc one can borrow from the cell. voice channels (HDvc) effectively available over a 1.25One should distinguish between the limit on the chan- MHz band per cell. Based on such a definition, Table 1Vnels borrowed and the S i t on the nonpreassigned displays the capacity of analog FM and of the presentchannels a BS can use. For instance, if a call originates 65 system with a 6.18 Kbps vocoder, 5.86 MHz band, 1in cell X and the portable roams into an adjacent cell Y frame per cell and DCA. As shown in Table IV, hewhere no preassigned cells are available, BS Y does not capacity of analog FM is 6 HDvcA.25 MHz/cell whileneed to borrow immediately a new channel from an for the present system it is 150 HDvd1.25 MHz/cell.


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The 6.25 MHz band w n s G o f 5 .86 MHz plus two tail sampler 826 o produ ce bits of information. T he bits areslots. Wh en voice activation is used, the capacity of the then processed in th e d eprocessor 828, described inpresent system is increased by 1.5 tim es to 225 mo re detail in FI G . 14b.An estimate of the phase differ-HD vc/l.25 MHz/cell, a 38 fold increase over analog ential is taken in the channel estimator 830, as describedFM. 5 in more detail in relation to FIG. above, and the esti-mated phase differential is supplied to a decoder/-Local Area Networks demodulator 832 o correct the received bits. T he esti-The invention may also be applied to produce a 48 mated phase differential is also supplied to a pre-dis-Mbps wireless LAN , w hich also satisfies the technical torter 834 in the transmitter. At the transmitter in therequirements for spread spectrum. 10 Base Station, the sam e blocks are incorporated as in theFo r wireless LA N, wideband differential orthogonal portable transmitter except that a pre-distorter isused ofrequency division multiplexingis again employed. T he alter the envelope and phase of the D8P SK symbols toL A N will incorporate a plurality of transceivers, all make the channel appear Gaussian (ideal) as opposed tomore or less equal in terms of processing complexity, a fading channel. The initial power control 825 alsoand possibly with identical components except for ad- 15 sends a signal to the pre-distorter 834 to adjust the trans-dresses. mitted power to an appropriate signal level for theT o implement wideband modulation for a LA N, a 26 sampler 826 in the first transceiver. I t will be apprcci-MH z band is divided into 128 points, as shown in FI G . ated that a predistorter will be included in the first10, lus two tail slots of 1.48 MHz each within the 26 transceiver's transmitter but that it will not be operable,MHz and. Adjacent points are separated by 180 ICHz 20 except when the first transceiver is operating as a baseand each point, as w ith the application described above station.for a portab le-base station, represents a D8PSK symbol. FIG . 13c shows the functional blocks of the reu iv erT he transmitter components will be the same as shown of the first transceiver, which is the same as the re ui ve rin F IG . Sb, with suitable modifications as described in in the second transceiver except it does not includemthe following, and will include an encoder. T he outp ut 25 estimator. Th e processor is illustrated in FI G. 14u andbits from the encoder are mapped onto the D8PSK 14c and the deprocessor in FIG. 14b and 14c.Th e pro-symbols. cessor frrst inverse Fourier transforms the 128 D8PSKTh e frame duration for the symbols is illustrated in symbols output from the modulator. Th e transformedFIG. 11. A rectangular time dom ain window corre- symbols are then triplicated as a group so that the totalsponding to a RC fr qu en cy domain pulse has a 5.55 ps 30 number of sam ples is tripled (see the left side of FI G .duration, and includes a 25% roll-off and excess frame k),with t h r n consecutive groups each consisting ofduration of 0.26 ps, making a total 7.2 p s duration fo r the 128 transform ed symbols. Next, the three groups arethe frame. windowed by a Raised Cosine window w ith a roll-off ofFo r such a w ireless local area netw ork (LAN), in 0.25 centered in the middle of the three groups. In otherwhich the transceivers are equal, the T i e Division 35 words, the processor takes D8PSK symbols in, pulseDuplex protocol is as illustrated in FIG. 12 (assuming shapes them and inverse Fourier transforms them. Onthere are at least a pair of transceivers): the other hand, the deprocessor undoes what the pro-1. A first transceiver transmits a signal (frame 0) ve r cessor did, i.e. it remov es the pulse shaping, then Fou -the entire frame. rier transforms the received signal to obtain the original2. A second transceiver re ceives the signal from the first 40 D8PSK symbols. The first two blocks in FIG. 14b ar etransceiver and processes (analyzes) it. similar to the second tw o blocks in FIG . 14u except for3. Based on the received signal, the second transceiver tw o differences as follows. In the first block show n inpredistorts and transmits nine frames (frames 1-9) o FIG. 146, he repeated groups of symbols are pa rt dl ythe first transceiver immediately. overlapped, as shown in FIG . 14c. n the second block,Eac h transceiver has transmitter components similar 45 a rectangular window is used instead of the Raisedto those illustrated in FIG . Sb, with suitable modifica- Cosine to produce 128 output samples corresponding totions to the internal structure to allow the use of the the 416 input samples.particular frequency band and frame duration em- T he phase estimator is the same as that shown in FI G.ployed. 7, except that there ar e only 128 input samples, and theTh e transmitter/receiver functional and structural 50 same description applies.block diagrams are shown in FIG S. 130,13b nd 13c or For both the L A N and cellular networks, the presentthe exchange of data. Dat a is provided to an encoder system is designed to operate as a spread spectrum sys-810where the data is digitized and coded to create bits tem preferably over such bands asare permitted, whichof information. Th e bits are provided to t he modulator at present are the 902-928 MH z band, 2.4-2.4835812which turns them into D8 PSK symbols, with three 55 GH z and 5.725-5.85 MHz. The ca me r fr qu en cy inbits per symbol. Th e D8PSK symbols are then pro- the local oscillator show n in FIG S. Sa, b and c will thenccssed in the processor 814which is described in more be 915 MH z in the case of the 902-928 MH z band, anddetail in FIG. 14u. Th e output from the processor is the frq ue nci es used for modulation will be centered onthen filtered in low pass filter 816, pxmverted to RF this carrier frequency.frq uen cie s using loc'al oscillator 818 &d transmitted by 60antenna 820.

- -Alternative Embodiments

In FIG. 136, the received signal at the base station is A person skilled in the ar t could make immaterialfiltered in a bandpass filter 822, nd down converted by modifications to the invention described and claimed inmixing with the output of a local oscillator 824. T he this patent without departing from the essence of theaverage power of the dow ncoverted signal is monitored 65 invention.by an initial power c ontrol 825 hat adjusts the average For example, a system may consist of one or morepowe r to the specifications required by the sampler 826. central controllers (comparable to the Base Stations inT he adjusted dow nw nver ted signal is then sampled in the exem plary cellular system described) and som e


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5,282,22219 20slave units (comparable to the portables). The slave unit 5. The transceiver of claim 4 in which the powerexecutes the commands it receives from the central controller is also connected to the pre-distorter forcontroller. The commands may be requesting the slave controlling the power of the signal to be transmitted.unit to transmit a receive acknowledge, a status code or 6.The transceiver of claim1 urther including: meansinfomation that the slave has a-s to. The cornand 5 to modify the received signal with one or both of themay also be to relay the command or the information to estimated amplitude and phax differential respectively.another slave unit. 7. A method for allowing a number of wireless trans-

We claim: ceiver to exchange frames of information, the method1.A transceiver including a transmitter for transmit- comprising the stepsting electromagnetic ignals and a receiver for receiving 10 multiplexing a fmt frame of information over a num-electromagnetic signals having amplitude and phase ber of frequencies within a frequency band at a firsttransceiver to produce multiplexed information;differential characteristics, the transmitter comprising: processing the multiplexed at thean encoder for encoding information; transceiver,a wideband frequency division multiplexer or multi- transmittingthe processed information to a secondplexing the information onto wideband frequency transceiver using a carrier frequency fc;channels; receiving the processed information at the seconda low pass filter; transceiver; and8 local oscillator for up~onverting he multiplexed processing the processed infomation at the secondinformation for transmission; 20 transceiver during a f a t ime interval;a Processor for applying a fourier transform to the in which the frequency band is formed from a first set

multiplexed information to bring the information of K1 points and a pair of tall slots each having K2into the time domain for transmission; points, each of the points being separated by afurther including, in the receiver of the transceiver; frequency range of Af, the second transceiver hasaa bandpass fdter for filtering the received electromag- 25 maximum expected clock error xT, where T is thenetic signals; duration of one time domain sample, the informa-a local oscillator for downconverting the received tion is multiplexed over a numberM of levels, andelectromagnetic signals to produce output; K1 selected such that 2~x/Kl


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UNITED STATES PATENT AND TRADEMARKOFFICECERTIFICATE O F CORRECTION

PATENTNO. : 5,282,222DATED : January 25,1994INVENTOR(S) : M. Fattouche et al.

Page 1 of 1

It is certified that error appears in the above-identified patent and that said Letters Patent ishereby corrected as shown below:

Column 19,Line 14, "or" should read -- for --Line 21, "fourier" should read --Fourier --Line 24, "transceiver;" should read -- transceiver: --

Column 20,Line 8, "transceiver" should read -- transceivers --Line 14, L'trans~eiver,"hould read -- transceiver; --Line 22, "tall slots" should read -- tail slots --Line 42, "of of the" should read -- of fo, the --Line 44, "+oflAfJ" should read -- +folAfl --

Signed and Sealed thisEighteenth Day of September, 200 1

Attest:

NICHOLAS P.GODICIAttes ting m c e r Acting Director of the United States Patent and Trademark m c e

5282222 method and apparatus for multipl

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