占有帯域幅4MHzチャンネル上における連続チップ波形整形技術を適用した1.6Mbps/4Mcps差分CDMAの伝送特性

愛総研・研究報告 第2号 平 成12年

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Masahichi

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shi 岸 政 七 Abstract: From the frequency削 ageefficiency points of view， the novel d

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Rayleigh j舟adi昭n!genvironment α伺'sp戸OωO俳rand nαrrow 4MHz bandwidth radio chα仰nnel戸jor1.6Mbps transmission via 4Mcps to be error free by employing both continuous chijフshaping加directspectrum scrambling and BCl{j何3，51)double error correction code 9

1

.

INTRODUCTION

Itis important to improve high capacity and high四speedtransmission of such CDMA featured with low power transmission， high reliability， and system flexibility. This CDMA is strongly eager to be developed邸 the third or so-called the forth generation CDMA in serving high speed links more than meg-bps among high speed running land vehicle through urban multi-ray propagation environment.As CDMA being well known as given by the direct product of primary modulating PSK and spread spectrum code， the CDMA transmission capacity is nominally defined by the PSK capacity multiplied by the spreading spectrum code number. And the企equency bandwidth of the CDMA is， therefore， defined by the convolution of the PSK and the spread spectrum code bandwidth. 愛知工業大学総合技術研究所(豊田市) Because of the Walsh白nction being adopted to span the code space in addition to the primary PSK modulation， the CDMA is seemed to be inherited robustness from both Walsh code and PSK genius during fading propagation.

10 愛知工業大学総合技術研究所研究報告，第2号，平成12年，Vo.l2， Mar.2000 BER vs. CNR is shown in fig.l for CD恥iAof employing QPSK as the primary modulation measured a1王er propagation through such two-ray Rayleigh fading environment as 10 dB DUR with 0.5 micro-sec delay spread. As clearly shown in fig.l， the 仕 組smission quality is catastrophically degraded ifbandwidth being restricted beyon.d the Nyquist chip limitラi.e. Hzlchip， where it becomes to be remarkable in fading degradation through multi-ray propagation environment.On the other hand， the multi-ray fading robustness is also catas仕ophically improved in BER meanings by expanding企equencyoccupancy 企omthe limit to doubled 2 Hzlchip and quadrupled 4Hzlchip. After expanding the CDMA仕a.nsmissionbandwidth beyond the doubled 2Hzlchip， BER is saturated to the characteristics for the doubled bandwidth. Being depended on symbol speedヲ CDMA bandwidth is especially extended beyond the Nyquist limit by switching its chip value at every chip fringe. In factラeven if it reduces transmission capacity to the unique single PSK， the secondary modulation vanishes itself bandwidth to zero to match the PSK bandwidth in the case of every spectrum spreading code being set to be unique in every chip. However， it is possible to reduce CDMA bandwidth close to the Nyquist chip limit with decreasing varying 珂 u昌ter_Nyq画r一一 'Nyqu陥Ui同首r 一一-'doubled_Nyq国sf. -gradient by continuous shaping at every chip fringe. 0.1 0.01 0.001 -20 -1日 ' 司uadn.耳pi回一Nyqu訟f一一

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10 20 Eb!隙0，d除

Fig.l BER vs.Eb庁、~o of CDMA， limited within Nyquist chip

limit， doubled， or quardrupled bandwidth， through two ray Rayleigh fading environment of DUR=lOdB with 0.5 micro second delay spread

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the continuous chip shaping spreading code is employed in the secondary modulation of CDMA over a given limited frequency bandwidth， this CDMA is expected to transmit high capacity in Fig.l BER vs. Eb/No of CDMA， limited within Nyquist chip limit， doubled， or quardrupled bandwidth， through two ray Rayleigh fading environment of DUR=lO dB with 0.5 micro second delay spread

Transmission Characteristics ofthe1.6Mbps/4Mcps di妊CDMAwith Continuous Chip Shaping 11 formation in such high reliability shown in fig.l as the c出eof doubled bandwidth. From the frequency usage efficiency points of view， the novel CDMA with continuous chip shaping is proposed in this paper to achieve such high reliability as shown in企eespace propagation.

2

.

CONTINUOUS CHIP SHAPING

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Concept of Conti盟 国os Chip

Shaping Reducing CDMA bandwidth is not only effective for日nitefrequency resources but also promising solution for realizing such high reliability in given bandwidth出 free space with base of prevention both from fading bandwidth expansion and spectrum distortion through multi-ray propagation. CD恥1Abeing defined by convolution of the primary PSK modulation and spreading code chip value next chip Oth contact steepest gradient spectrum， reduction of the secondary modulation bandwidth is also discussed here as the important problem in addition to phase continuous PSK previously reported in VTC'98. Typical code waves are illustrated in fig.2. As shown by dotted lines， the existing code wave is given by square topped signal to maintain a unique value within the whole duration of every chip to c加 sea jump at every fringe in proportion to the chip value difference between adjacent chips. If there exist no jumps around all chip fringes， CDMA modulated signal is obviously reduced frequency occupied bandwidth to arbitrary single PSK with victim of losing code space spanning ability. It is， however， necessary to maintain individual code value at every chip center， but is su百icientto keep the same value in neighbors at the center in order to spread the spectrum of the primary modulating PSK along its individual code axis. It becomes to be possible to reduce the occupied bandwidth where the rapid variation is suppressed to yield smooth chip wave in the secondary modulation. δ-τ δ+1: time Continuous chip shaping is facilitated as shown in fig.2 as solid curve by substituting smoothing Oth contact transient duration 2τ

Fig.2Illustrative time response of continuous chip function over newly introducing transient duration spanning over adjacent chip企inges. The former is the cu汀entand the later is the next chip. The smoothing

12 愛知工業大学総合技術研究所研究報告，第2号，平成12年，Vo1.2， Mar.2000

。

ー10 'chip_Cm誼:inu由民s'一一一 .2{) 30 -40 -50 ・.204串1792153e128G102ヰ768-512-256 0 256 512 76810:241280153617922044 (a)

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-10 'chip_disCo晴tinuous'一一一 -20 ー30 -40 -50 -204817921536128Gl02牛76日司5百2-256 0 256 512 76810241280官5361792204 (b) Fig.3Frequency response comparison between contrnuous chip shap血g (a) and discontinuous chip wave power spec仕出n(b) 白nction touches current and next chips at the front and tail ends with Oth order contact， respectivelyラ and varies with the steepest gradient just幻 the center of the transient duration， i.e. at every fringe. For example， w(t) given by following eq.l 1S matched to the above chip smoothing function. here， w(t)= Wc + d.wS(t) (1)

w

C is the - P LHH P し V 4 g b n ' p ν ρ しV W H L 叫 U G c v Aw =WC回 wn' Wn is the next chip

Transmission Characteristics ofthe1.6Mbps/4Mcps di宜CDMAwith Continuous Chip Shaping 13

2.2 Bandwidth Reduction Effect 01 Continuous Chip Shsping

Both lower and upper eight side lobes are shown in fig.3 as averaged instantaneous spectrum at plural symbols fringes. Figs.3a and 3b show the ensemble averaged spectrum of continuous chip shaping and chip discontinuous existing CDMAヲ respectively. If the transient durationラれ isset to be same to the chip durationラ δ，the side lobes are efficiently reduced by 3.69ラ 13.75，and 24.59 dB at the second， third， and forth harmonics. The side lobe reduction effect is observed by more than 30 dB at eighth harmonics. Itis adequate to the assumption to de日neall the spectrum except main lobe are interference rather than unnecessary component in communication systemラ becauseof the alias being leaked into inside from the outside and of remarkable distortion being occurred at band edges IF frequency bandwidth being limited. Itrequires so widely value， S(t)おsucha function given by ¥ 、 l i l t -/ 尉

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ratio (2) exp組 ded bandwidth up to doubled bandwidth as shown in白g.3in order to suppress the interference energy of the chip discontinuous CDMA to the equal level of the continuos chip shaping. In paradoxically speaking for the existing CD恥tlAwhich employs the chip discontinuous in the secondary modulation， the newly proposing continuous chip shaping CDMA is able to reduce the bandwidth to improve fading or frequency selective fading robustness by this frequency reduction effect in the multi-ray propagation envlronment.

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14 愛知工業大学総合技術研究所研究報告，第2号，平成12年，Vo1.2， Mar.2000 2.3 Circuitry Configuration of Contimu:TU.s Cb.ip Shaping τhe continuous chip shaping is realized by merely prefixing the chip continuity module with exception of the continuous chip shaping CS組 derror correction coding circuits ECC. The CS is inte中olatedbetween spectrum circuit shown in日g.4ato the secondary modulator of existing CDMA. In this figureラ the smoothing function of eq.2 is stored in a ROM， which is marked with SMO， to read out by modulus

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time base as shown fig.4b. The register REG latches the output at the tail-end of the transient duration and keeps the holding value within the following chip durationラand

the mark MUL or Adder means a multiplier or an adder， respectively.

3. CD時宣A WITH CON'fINUOUS CHIP SHAPING 3.1 Syst母 臨 む011.釘g悶ration The system configuration of the CD恥1Awith continu -ous chip shaping is illustrated in fig. 5 as significant functional block diagrams. As shown in日g.5a for the continuous chip shaping CDMA transmission moduleラ the circuitry skeleton is almost the same to the existing CDMA transmission

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Transmission Characteristics ofthe1.6Mbps/4Mcps diffCDMA with Continuous Chip Shaping 15 spreading code generator CG and the secondary modulator SS for every transmission channel. The ECC is pre-fixed to the primary modulator to yield double e汀orcorrection BCH (63，51) code along to individual bit string， if bit grouping scheme S of fig.6 being adopted. That is，

two ECC will be employed for each spectrum spreading code if the primary modulation is performed as In general speaking， the transmission channel number m is required to be larger than receiving speech channel m九evenif the maximum transmission capacity is achieved in the c出eof m being equal to m'. In factラ controland synchronization ca汀y through these redundant m-m' channels both in cdmaOne and W cdmaOne， or ca汀yby

redundant time slot shared by time QPSK.HereラmarkMOD， 1:， or BPF means the primary PSK modulator， adder or band-pass filter， respectively. Andラthetotal number of transmission channels ISm. Circuit topology of the receiving module of the continuous chip shaping CD恥1A is almost the same as shown in 白g. 5b to the existing CDMA receiving module. Mark RX， SYNラ CNT，deSS， CG， or DEC

means the receiving unit， syncbronization detector， control signal recovery circuit， the prim紅y demodulator， de凶spread spectrum circuit， spectrum de-spreading code generator， or decision circuit， respectively. The deECC is attached to the tail end of the decision circuit DEC to coηect the double e汀ors within 63 bits block along the individual bit string. Here， the total receiving speech channel is 町l'. d四ialG池 @ ⑧ 層調嘩1)I I t 量 @ 電骨 量liHHil6ltei⑧ 事l' 量骨.~G 量 重骨量 @ 311

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16 _{愛知工業大学総合技術研究所研究報告，第2号，平成12年，Vo.12， Mar.2000} compression to yield equivalent redundancy both on time and企'equencyspace in Wide CDMA， in which m is at a glance i1early equa1to mヘ Fortunately， a novel CDMA system， named by di旺CDMA，has beena1ready reported in previous VTC98 to perfectly exclude redundancy of the channel or time slot. This diffCDMA is categorized into an e曲anced system of W cdmaOne from transmission and signaling points of views， and is also characterized on such tech -nologies田 di能rential coding and post de-spreading spectrum ana1ytic receiving to be verified by 2Mbps仕 組smissionability within 5MHz bandwidth even through multi-ray fading environment. 3.2 Signal Scheme The ロlaximum transmission capacity of di茸CDMAwith ECC is achieved by simultaneously employing all of the 32 speech channels of 32kHz symbol rate QP8K回 theprimary modulation. 80 long as the dif配DMA being facilitated in CDMA with phase continuous QP8K to exclude any redundancy， the spread spectrum code length is enough to be 32， because of 仕 組smission m being equa1 to receiving channel number m'， and of receiving channel number m' being sufficiently 32. 1

。

-1 employed. Grouping 8 means the c出eof 12 redundant bits of BCH ECC being interpolated after every 51 information bits. Individualれ'"10BCH (63，51) block codes are simultaneously adopted恒toevery spectrum spreading codea10ng time bases. Grouping B is rather simple to adopt BCH with somewhat loss in transmission e由cient， where 12 redundant bits are interpolated after every 50 information bits. Every shortened BCH (62，50) is employed for every DS/88 code along to time axis. The resulting grouping P is performed along to D8/S8 code axis. That is， shortened BCH (62，50) is also convenient to in仕oduceinto diffCDお1A，because one of 32 code channels being devoted to so-called con甘ollingsignal. The maximal transmission capacity is

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pvala ，姐Ia Figure 6 shows 3 kind bit mapping schemes where ECC being Fig.7 Rr， elaatnidons仕 組hip bsieetnt dweenu srautbijoenct， ive2 tZ"im， e dion tmaihne， continuous chip shaped waves

Transmission Characteristics ofthe1.6Mbps!4Mcps di宜CDMAwith Continuous Chip Shaping ₁₇ given by 1.66Mbps where grouping S being adopt in the prosing diffCDMA as discussed in the followings. Where the bandwidth is restricted within 4 MHz over transmission channel， and chip rate is 4Mcps if 4 fundamental segments being employed in every symbol. 4. SIMULATION R.ESULTS

4，1 ContioUll.ous Chip Shaping Effed

Excessive bandwidth expansion is caused in the secondary modulation of DS/SS from the chip discontinuity at every chip fringe. The continuos chip shaping is able to reduce this excessive 合equency expansion as discussed in the above with the victim of increasing the transient time domain for varying the chip value. The subjective domain for detecting chip value is consequently reduced as shown in fig.7.τhat is， the longer the transient duration being set to 0.314 decrease the frequency bandwidthラ the shorter the subjective domain being restricted. Figure 8 shows the relation between BER vs. subjective 0313 domain at receiving level of CNR=づdB， in which the horizontal axis means su吋ective domain ratio， r/

d

.

Here，

d

is chip lengthヲandr is half of the transient duration at tail and 企ontchip ends. 0.312 0 the BER shows a trade0宜 as showing continuous chip shaping e:ffect at around r=3/8 like a priori expectation. If the transient duration is expanded to whole chip durationラthesubjective domain is vanished. On the other handラifno subjective domain 1S 己mployed，the BER is degraded from the excessive frequency expansion during the secondary modulation.

4.2 BERI臨 prove醐entEffed

The BER improvement e:ffect of continuous chip shaping di:ffCDMA is verified as shown in fig.9 through computer simulation. Simulations are performed under following conditions. All 1.66 Mbps signals are carried by 4.096恥1cps on 4.096恥任fz frequency bandwidth at the 2GHz domain from 300知lIhbullet trains passing through such urban environment as two-ray Rayleigh 'EbNo=.5dB'イ ト ー 2 4 6 8 10 12 14 16 subjeclive domain dura嗣on While the subjective domain ratio changes from zero to unity， Fig

，8 ECC bit map comparison among typical grouping

respectively. Such compensations as RAKE receiving and power control faciHtated in the di宜CDMA， exc1uded from simulations to continuous chip shaping effect clear. CNR are measured on the maximum transmission capacity of 1.66Mbps when all the 32 code being employed. Simulation results are shown in白g.9to improve two-ray Rayleigh fading robustness by vanishing any bit e打orsvia employing continuous chip shaping， phase continuous QPSK， 阻 dBCH (63，51) ECC at CNR=lO.OdB communications from are easily which make are the 愛知工業大学総合技術研究所研究報告，第2号，平成12年，Vo1.2， Mar.2000 fading of DUR= lOdB with 0.5 micro second delay spread. The all codes of 321ength Walsh sequence are employed to span 32 code space. The BCH (63，51) ECC is employed to coηect double e町orswithin 63bit block.as grouping S along individual string of 32k symbol/second. transient duration ratio， r/δis set to be a The 18 bit quarter. Therefore， fdT and Doppler shift are set to be 0.015 and 0.3 ppm in the all simulations， if being km/h 'Aircr畠，11 圃一-'Vetお1ぜ 一 -V組 制ir畠[1' . 'Ped， withoutECC固一一四 10 c o n a -F 1 4 S L n_、 u ' E E A e ， u 吋 m n y carried walking BER is

。

.1 at CNR=15.2dB iffrom 100 km/h running vehicles， or at CNR=17.5 dB if from 1，000km/h f1ying aircraft through the urban environment mentioned in the above. discussing diffCDお1A，64 bits are simultaneously caηied through 32 code channelsラ BER is observed to be zero in Eb/No meanings 圃8.0dBfor pedestrian， at 2.8dB for vehicIes， 0.5dB for aircraft after In at 引¥ 司¥目、司 : 1 . . 、

。

.{)1 0.0001 ・20 O.叩1 or compensation by 1 0l0g64ラ respectively， 30 40 CN円.dB fig.9 BER vs. CNR response comparison among aircraft， vehicle， and pedes仕iancommunication of double e町or correction 1.6恥1bps/4.096恥任IzdiffCDMA through two ray Rayleigh environment with 0.5 micro second delay spread 20 10

。

.10

Transmission Characteristics ofthe1.6Mbps/4Mcps di妊CD恥1Awith Continuous Chip Shaping 19

CONCLUSION

The newly proposing diffCDMA with continuous chip shaping has been successfully discussed in this paper with emphasis both on realizing bullet train and aircra氏 1.6 Mbps CDMA communication system. The diffCDMA is able to put high capacity and high speed CDMA communication on the developing stages with employing such novel techniques as continuous chip shaping， phase continuous primary modulations， and BCH double eηor correction. REFERENCES (l)Masahichi Kishi， Kuixi Yin， Hiroshi Iwata， and Yutaka Amano， Consideration on System Capability Characteristics

0

1

Portable 2Mbps / 8Mcps CDλμ with Phase Continuous QPSK， IEEE VTC98， Proc.Vo.21， pp.924・928. May 1998， Ottawa， Canada (2) Masahichi Kishi， and Takashi Kuno， Application

0

1

the A

聞

か

tic Receiving and PSK-DOE的 the 16QAM and its

Characteristics on Poor Radio Channels，

IEEE VTC96， Atlanta， GA USA， Proc. Vo.21， pp.998-1002， Apr.1996

(3)恥1asahichi Kishi， and Takashi Kuno， Application

0

1

the An

ゆ

tic Receiving

and PSK-DOE to the 16QAM and its Characteristics on Poor Radio Channelsラ

IEEE VTC96ラ Atlanta，GA USA，

Proc.Vo1.2， pp.998・1002ヲApr.1996

(4) Masahichi Kishi， and Takao Inoue， A

Proposal

0

1

PSK-DOE and its BER Characteristics， IEEE VTC96， Atlant，a GA USA， Proc.VoL2， pp.795-799， Apr.1996 (5)恥1asahichiKishiラNorihiroHattori， and Ke由。 Urabe，Application

0

1

the Short Time DFT Correlator to the RAKE receiver lor DS/SS Communication System and Its BER Improvement E

.

f

f

ect，

IEEE PIMRC95， Toronto， Canada， Proc.Vol.1，pp.208・212，Sep.1995 (6)恥1asahichiKishi， Envelope Detection in Strict Sense and its Application to Syllabic Companders， IEEE VTC 94， Stoc闘101m， Sweden， Proc.九To.13，pp. 1704-1708， June 1994 (7) Masahichi Kishiラ High Capacity to Dそferential

か

Detectedsh

i

.

f

t

ed DQPSK with Narrowing Occupied Bandwidth based on Short Time DFT， IEEE VTC 93ラ Secaucusラ NJ USAヲ Proc.pp.384・387， May 1993 (受付平成12年3月18日)