愛総研・研究報告 創 刊 号 平 成11年
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69Masahichi Kishi tラNaruhikoSugiura t
，
Hiroaki Kuraoka:tラ MasahiroOhba t岸 政 七 ラ
杉浦徳彦ラ倉岡宏明ラ
大 羽 勝 弘
t
Aichi Institute ofTechnologyラ ToyotaヲAichiヲ470-0356JAP A N愛知工業大学総合技術研究所ラ豊田市
主DENSOCORPORATIONラKariya
，
Aichiラ448-8661JAPANデ ン ソ 一 通 信 技 術 第
3
部ラ刈谷市
Abstrαct: As well known， CDMA possesses such αdvαntαgesαs high capαcity， low powe1't1'ansmission，α!nd system jlexibility， but it is cont;γαrdicto1'Y suffe1'ed from
b1'oαdband occupαncy ofwαsting戸nitefiヤequency1'esource owing to innocent
spectrum sp1'eαding. Narrowing f1'equency bαndwidth occupied over propαgα託on
channels is eαge1'to efficiently develop the high cαpαci砂digitaltransmissionαs
one of the most imp俳 句rntkey technologies p1'omising e.i
汀
.ectivef1'equency usage.Nαrr1'owingfiヤequencybandwidth both of the p1'imαη1αnd secondαηv modulations
hαs been keenly discussed in these yeα!1's to1'eαlize high cαpαcityωld speed
d
す
CDMA.Thephαse continuity primary DQPSK， which hαsαrl1'eady repo1'ted inVTC98αs the
f
i
1'st solution fo1'2 Mbps/ 8 Mcps diffCDMA， is1'etrieved he1'e torealize the higher reliαrbilii勺)andfiヤequencyefficiency 2 Mbps/4 Mcps diffCDMA. Vi1'tuα1 se
g
r
r
.
‘ent interleα!ving is successfully discussed in this pαrper to1'educechip ratingαs one of the important solutions fo1'effective frequency usαge without
int1'oducing any problem in system1'eliαbilityαnd complexity‘ Both continuous phαse primαη) modulα!tion and continuous chip shapingα!reαIso enhαnced in this proposing 2Mbps/4Mcps diffCDMA.
愛知工業大学総合技術研究所研究報告，創刊号ヲ平成11年ョVol.1，Mar.1999 70 As CDMA being as known well given by the direct product of primary modulat四 ing PSK and spread spectrum code， the CDMA transmission capacity is nominally defined by the PSK capacity multiplied by the number of spreading spectrum code in the secondary. modulation. And the frequency bandwidth of the CDMA is， therefore
，
defined by the convolution ofthe and the spread spectrum code bandwidth. Because of the Walsh function being adopted to span the code space in addition to the primary PSK modulationラ the CDMA is seemed to inherit robustness from both Walsh code and PSK genius during fading propagation. BER vs. CNR is shown in fig.l for2 Mbps/ 8 Mcps CDMA of employing QPSK as the primary modulation measured ai王er propagation through such two-ray Rayleigh fading environment as10 dB DUR with0.5 micro-sec delay spread. As clearly shown in fig.l， the transmission quality is catas -trophically degraded if bandwidth being restricted beyond the Nyquist chip limit， i.e.1 Hzlchip， where it becomes to be remarkable PSK Narrowing frequency bandwidth occu -pied over propagation channels is eager to efficiently develop the high capacity digital transmission as one of the most impo抗ant key technologies promising effective frequency usage. Typical CDル1Ais desired to communicate up to 2 Mbps with using less than 4 Mcps through 4 MHz frequency bandwidth. On the otherhandヲ thena汀owfrequency band limited
signals are easily suffered from BER degradation over poor channels， especially damaged by additional frequency expan -sion where meg-order high capacity communications from high speed running vehicles. IMT2000
1
.
INTRODUCTION
'3qu副er_Nyq凶sf一一一 'Nyquist_limif --_. 'doubled_Nyquist'一一 -'quadrupled_Nyquisf-一一 fading degradation through multi圃raypropagation environment. On the other hand， the multi-ray fading robustness is also cat出trophicallyimproved in BER meanings by expanding frequency from the limit to quadrupled Nyquist After expanding the transmission bandwidth beyond the doubled limit， 10 20 dB 10 、U A、
t、
‘
、
¥
;
Y
I
¥
ι ¥、 札 、
、 柏 、
i I t-、
、
uh い ¥ 、 ¥ h h一
1 1 1 -Y 入 ぃ ‘ 弘 、 支 え ー10。
-20 0.1 0.01 0.001 M 凶 凶 白 BER occupancy doubled or chip limit. CDMA CNR， Fig.l BER VS. CNR of CDMA， limited within Nyquist chip limit， doubled， or quardrupled bandwidth， through two ray Rayleigh fading environment of DUR=l OdB with0.5 micro second d巴layspread.Application Virtual Segrnent Interleaving to High Speed Land Mobile diflCDMA 71
saturates to the characteristics of the
doubled limit.
2
.
HIGH
FREQUENCY
EFFI-CIENCY MODULATIONS IN
diffCDMA
2
.
1
.
Phasese Continuity in thePrimary Modulation ReducingCDMA bandwidth is impor・ tant for promising efficient 企equency usage in realizing such high reliability in narrow bandwidth出 合eespace propaga -tion with base of prevention both from fading bandwidth expansion and spectrum distortion through multi圃raypropagation. PSK phase is illustrated in fig.2. As shown by dotted lines
，
the existing PSK is given by square topped waves to maintain a unique value over the whole duration of every symbol to cause a jump at every fringe in proportion to the ph邸edifference 172 3172 侃世証明吐x>l md:明吐Xll αh 往冒頭enCIIヨtim Fig.2 I1lustrative time response of continuous phase among the adjacent symbols. If there exists no jump around a11 fringes， PSK modulated waves are obviously vanished frequency bandwidth to zero with victim of losing transmission ability. It is，
therefore，
necess釘γto maintain individual phase value at every symbol center， but is sufficient to keep the sarne value in neighbors at the center in order to transmit information with phase difference. ltbecomes to be possible to reduce the occupied bandwidth where the rapid variation is suppressed to yield continuous phase PSK of the primary modulation in CDMA systems. Phase continuity is facilitated as shown in fig.2 出 solid curve by substituting smoothing function 泊 the transient duration spanning over adjacent symbols. The白nction touches current and next symbol phase values at the合ontand tai1 ends with Oth order contact，
respectively，
and varies with the steepest gradient just at the center of the transient durat
:
ion， i.e. at the fringe. For exarnple， the following eq.l is matched to the above phase smoothing function. p(t)= Pc + A pS(t) 4・ ・ A 、 、 . ， ， ， J ' z ‘ 、 位re E F J b ωa
T
吻 v m H 限 切 砂 '品川涜 n F J 町 四 J ・ ! O E F Lu-nh-仰 げ 側 、E ， 〆 . ， ， B J 噌 ' b S 1 4 t t q ' c mnmum ρ ぃ v ' h H F 内 川 v v ' ' 吋 A -﹄ J m M一
n m G α 寸 e 治 p ν c 司 A M 剛 仇p
'
畑 出 & 恥 一 一 P -u v ' -A r p -、 J ' ' 凡m
R
a
m
v
間
)
=
ド
(
1
+
;
引
っ
;
l
g
T
(2) where，72 愛知工業大学総合技術研究所研究報告，創刊号，平成11年，Vol.1，Mar.1999 ら=tlmodT'川 柳bold;仰 がon.(3) Effect of Phase Continuity Both lower and upper eight side lobes are shown in fig.3 after averaging instanta -neous spec仕umsover pl町alsymbols. The solid and dotted curves show the compari -son between the ensemble spectrum of phase continuous and discontinuous PSK
，
respectively. When the transient duration is set to a quarter symbol， power levels are suppressed through phase co国inuity processing by 3.87 and 19.36 dB at the force and eighth harmonics. lt is adequate to assume that all the spectrum except main lobe are interference rather than田mecessary component in communication system， because of the alias being leak:ed into inside企omthe outside and of remarkable distortion being occurred at band edges where企equency bandwidth being limited. ln paradoxically。
m 切 羽 出 回 ) R E E Hち 主
的
イ刃 Fig3Fr司班町陪戸ae∞ロ脚im同 制1悼館田由1KllS 副 daor訪問工sPSKPJ.澗 S同 組m speak:ing for ph回ediscontinuous existing PSK and/or CD恥1A which employing existing PSK as the primary modulation， the phase continuous PSK is able to improve robustness of合equencyexpansion by this harmonic power reduction in high speed running vehicle communications through multi-ray propagation environment.2.2.CONT悶UOSCHIP SHAPING IN
THE SECONDARY MODULATION
CDMA being defined by convolution of the primary PSK modulation and spreading code spectrum， reduction of the secondary modulation bandwidth is also discussed here as the important problem in addition to phase continuous PSK. Typical code waves are illustrated in fig.4.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 cause a jump at every企ingein proportion to the chip value difference between adjacent chips. lf no jumps exist at around all chip fringes， the secon -d鉱ymodulated signal is obviously reduced frequency occupied bandwidth to arbitrary single PSK with victim of losing code space spanning ability. Itis，
however，
necess釘y to maintain individual code value at every chip center， but is sufficient to 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. Itbecomes to be possible to reduce the occupied bandwidth73 Application Virtual Segment Int巴rleavingto High Speed Land Mobile di妊CDMA next chip current chip Oth contact where the rapid variation is suppressed yield smooth chip wave in secondary modulation. Continuous chip shaping is facilitated as shown in fig.4as solid curve by substituting similar smoothing function the continuous ph出e primary modulation over newly introducing the to to time Oth contact
一
transient duration iτo
+r Fig.4Illustrative time response of continuous chip. d，j"J (叫品 "'...."'Il'~ 一[1) -∞ ℃ 、E
コ ﹂ ぢ 主 的 ﹂ O B C 仏 21.1 --;0 -~i)伊 ¥11 -xW transient duration spanning over a時jacentchips. Th巴smoothingfunction touches current and next chips at the with Oth contact， respectively， and varies with the steepest gradient just幻 thecenter of the transient duration， i咽e.at every orderEffect of Continuous Chip Shapi
n
.
g ends and tai1 front fringe. 2W 4W &W HW frU[IJGllt.T. N }， llUl~t !illlI( 仁官、レーtlluじ む 伺tnuo..Jてユ ーーー一 れ り ! ∞司、E
コ ﹂ 討 。 立 的 ﹂ ω 言 。ι
2(1 1 1 ( l -2W ihl Fig. 5 Frequency response comparison bet'A悦nじolltinu曲。
uschip sh品pingand discontinuoLls chip wavピpower spectrum， (a) chip continuous and (b) chip discutinuou札 I t ! a! 2\\十~\\' fiW X¥¥ I 'r"'llIel)(')'_NytjtiiSI lim!1 -+W -()W 一 ~O -gW Figures 5a and 5b show the en岡 田mble-averaged spectrum of continuous and discontinuous chip shaping， respectively. If the transient duration is expanded to th巴wholechip duration， the side lobes are efficient1y reduced by 3.69， 13.75ラand24.59 dB at the secondラ thirdラ and forth harmonics. The side lobe reduction effect is observed by more than 30 dB the eighth harmonics with comparing those of discontinuous chip shaping. The continuos chip shaping is recognized to reduce the excessive bandwidth expansion occurred during th巴 secondary modulation with the victim of increasing the transient time domain for varying the chip value. Otherwise， ifthe chip shaping transient duration is too long beyond a priori 会2W 」町 6W at74 愛知工業大学総合技術研究所研究報告，創刊号，平成11年，VoI.1，Mar.1999
optimum value， the subjective domain is
restricted within undetectable limitation for
unifoI1I).ly defining chip value.
3.CDMA
明11THVIRTUAL
SEGMENT INTERLEA
VING
3
.1
.
Concept of Virtual SegmentInte.rleaving The virtual segment interleaving estab -lishes a novel solution for efficient frequency usage without introducing any contradictions between phase continuity primary modulation and continuous chip shaping in the secondary modulation. The transmission reliability is improved with proportion to the subjective symbol chip number given by a product of effective segment/symbol and chip/segment numbers because of the random noise being aver -aged among the plural subjective segment. Here， the segment means the duration of given length compact Walsh code. A compact Walsh is described by distinguishing from spatiality in code using if and only if all the code of given length Walsh is used for DS/SS. For example， 32 out of 128 Walsh code is devoted to DS/SS as a single segment scheme， it is equivalent to 4 segments of compact 32 Walsh code in spanning code space meanings. Or回 thogonality stands over any 32 chips current symbol successively located in multi segment compact Walsh code because of recursive structure as follows.
I
~N12 ~N12I
~" N=
-11
1
1 I~NI2 ~N121 here，
~N is N length~alsh βmctioη.(
4
)
The j raw of 4 segment N length Walsh，
W} isラtherefore，described in the following style.
K
=
l
w
j
w
j
w
d
w
d
l
j三N (5) Equations(5) is summing up by using larger Walsh as follows， 1 N L 牝 lN陀
f Nh
一 一 F J W (6) On the other hand， equations(5) is also decomposed into smal1er Walsh asヲ死
二
[
巧
i
尾町吸町玖巧
2九
]
I~~/ ，ザ j 斗
Here，附
/={A
L A円
，
else (7) Finally，W
}
is decomposed into order 1i
剛 tsymbol 叫 輔 ー ー 一 一 一 一 一 ‘ ー Fundamental Segment Virtiual Segment time Fig.6 Virtual SegmentInterleavingApplication Virtual Segment lnterleaving to High Spe巴dLand Mobile di狂CDMA 75 scholar form as follows.
眠
=
[
w
/
玖
J夙
J.
.
玖
J眠
J所
i]=
[
1
1101...1101
1/0
]
Here， ~ I~ι ザ j=1
wljペ
l
g
i
v
e
n
l
i
k
e
LSB 01
jラe
l
s
e
3.2.仁田定
α
疋IRYζON阻GRA百ONOFV~葺
The system configuration of the CD恥1A
with proposing VSI is illustrated in fig.7 as
significant functional block diagrams. As
shown in fig. 7a for the transmission
module of diffCD恥1A-VSI， the circuitry
→日明+
Any successive a quarter length ofWj gives mutually orthogonal vector with each other for every valuej. Therefore， we can inp凶2 settle virtual segments on the chip stream of scrambling for the fundamental seg -ments with overlaying on these 4 funda -m巴ntalsegments as shown in fig.6. Cross-correlation of the random noise among these 4 fundamental and 3 virtual segments is r巴asonablysmallless than half unity. Here， the fundamental segment 0 or 1 Is consists of 32 chips from 0 to 31 or from 32 to 63 chip of the inner symbol chip stream. Andヲthevirtual segment 0 or ] is consists of 32 chips from 16 to 47 or from 48 to 79 chip of the inner symbol chip， and so on. In the case of phase continuity transient duration being given by a quarter symbol， the fundamental segment 0 and 3 are damaged in the front-half and tail-half 16 chips over the transient duration， respectively. Otherwise，
the 2 segments of ( 司 the fundamental segment from 1 and 2， and 防( all virtual segments from 0 to 2 are left as the effective segments for estimating r巴ceivingsignals to improve the transmis -sion reliability. Fig.7 Block diagram of continuous chip shaping CDMA， m speech channel transmission mod-ule (a)， and m' speech channel receiving mod-ule (b).76 愛知工業大学総合技術研究所研究報告，創刊号，平成11年，Vol.l，Mぽ.1999 skeleton is same to those of diffむDMA. CS is a continuous chip shaping circuit deMOD interpolated between specむum spreading code generator CG and the secondary modulator SS for every transmission channel. ECC is pre・fixedto the primary
C
G
modulator MOD to yield double error correction BCH (63，
51) code along加 individual bit string. That is，
two ECC will be employed for each spectrum spreading code if the prima:ηmodulation is per-deMOD formed as QPSK. Here， mark MOD，L
， or BPF means the primary PSK modulator， adder or band-pass filter， respectively. And， the total mimber of transmission channels IS宜1. Circuit topology of the receiving moduleC
凶C
K
ofthe diffCDMA-VSI is same as shown in
自g. 5b to the receiving module of
diffCDMA with exception of virtual
segment interleaving circuit
，
VSI.MarkRX， SYN， CNT， CG， DEC， or deECC
means the receiving unit， s戸lchronization detector， con仕01signal recovery circuit， the primary demodulator， spectrum de -spreading code generator
，
decision circuit，
or double eηor correction decoding circuit for BCH (63，51) code， respectively. Circui甘yconfiguration is shown in fig.8 in details for VSI function block. The product of demodulated signal，
i(t) or q(t)，
and deDS/SS code is accumulated in the double buffers，
ACUM，
in corresponding to the fundamental and virtual segments. In fig.7， ma:rk SEL， D恥1PX，CNT， or DMPL is selector， chip counter， or de・multiplexer， which are consist of the double buffer. Here， the total receiving speech channel ism' ρ ト V TLi n H UD
E
C
Fig.8 Block diagram ofVirtual SegmentInterleaving with deSS.o
a
民福
o
a
。、衣=みBo
a
o
c
民oa
G包。
2 3 4 5 6 7 在日担也 Fig.9 BER vs. segment at CNR=・3dB.Application Virtual Segment Interleaving to High Speed Land Mobile di狂CDMA 77 In general speaking， the transmission channel number m is required to be larger 也anreceiving speech channel m'， even if the maximum transmission capacity is achieved in the case of m being equal to m' . In fact
，
control and synchronization canγ through these redundant m-m' channels both in cdmaOne and W cdmaOne，
or carry by redundant time slot shared by time compression to yield equivalent redun -dancy both on time and企equencyspace in Wide CDMA，
in which m is at a glance nearly equal to m'. Fortunately， a novel CDMA system， named by diffCDMA， has successfully excluded redundancy of the channel or time slot as previously reported. This diffCDMA is categorized into an enhanced system of WcdmaOne企om甘ansmissionand signaling points of views.百lemaximal transmission capacity is given by 1.66Mbps where BCH (63，51) ECC being adopt， the bandwidth is restricted within 4 恥任Izoverなansmission channel， and chip rate is 4Mcps if 4 funda -mental segments being employed in every symbol.4
.
SIMULATION RESULTS
The VSI is able to improve transmission reliability without introducing any circuitry complexity at sending module and slight victim of adding double buffer at receiving module. The subjective segments for detecting symbol value is consequently reduced after introducing phase co凶inuity in the prima叩 modulation. That is， the stronger the segments neighbor to the symbol fringe are damaged from the ph出e distortion for continuity， the smaller the random noise being averaged in small segments around at symbol center. Figure 9 shows the relation between BER vs. segments number at receiving level of CNR=-3dB. While the segmentnumber changes企omzero to 7
，
the BERshows a trade開off as showing virtual segment interleaving effect at around 4 like a priori expectation. If segment number is expanded to 7
，
a few segments are dam-aged from ph邸econtinuity. On the other hand，
if one segment is employed，
the BER is degraded合omweakness in smoothing random noise induced during propagation over poor radio channe1.Simulation results are shown in fig.l0 to improve two・ray Rayleigh fading robustness by vanishing any bit eηors via employing continuous chip shaping，
ph邸econtinuous QPSK，
and BCH (63，
51) ECC at CNR=10.0dB if communications being carried合om 10 km/h walking pedesなians.BER is null at CNR=15.2dB if合om 100 kmIh running vehicles，
or at CNR=17.5 dB iffrom 1，
000 kmIh flying aircraft through the urban environment mentioned in the above. In discussing diffCDMA， 64 bits are simulta -neously caηied through 32 code channels，
BER is observed to be null in EblNo meanings at・8.0dBfor pedestrian，
at 2.8dB for vehic1es， or 0.5dB for aircraft after compensation by 1010g64， respectively.CONCLUSION
The newly proposing diffCDMA with virtual segment interleaving has been successfully discussed in this paper with emphasis both on realizing bullet train and aircraft 1.6 Mbps CDMA communication78 愛知工業大学総合技術研究所研究報告，創刊号，平成 11年，Vol.l，Mar.1999 system. The diffCDMA-VSI is able to put high capacity and high speed CDMA communication on the developing stages with einploying such novel techniques出 continuous chip shaping， phase continuous primary modulations， virtual segment interleaving， and BCH double e汀or correction.
l
HR 'Airc胞11'一一 'Ve凶dぜ一一 'Pedeslria目 -白 'Ped.wilhouIECC'一一 Q任Dl -1) 咽回目 n u A n υ 噌 M I 1)。
Fig.l0 BER VS. CNR response comparison among aircraft， vehicle， and p巴destria ncommuni-cation of double error correctionl.6Mbps/ 4.096MHz diffCDMA through two-ray Rayleigh environment with 0.5 micro sec -ond delay spread 1)C
M
，
c
I
ヨ
REFERENCES (1) Masahichi Kishi， Kuixi Yinヲ Hiroshi Iwata， and Yuiaka Amano， Considera -tion on System Capability Characteris -tics of Portable 2Mbps /8Mcps CDlvfA with Phase Continuous QPSK， IEEE VTC'98， Proc. Vo.12ラpp.924・928.May 1998， Ottawa， Canada (2) Masahichi Kishi，
and Takashi Kunoラ Application of the An吟 ticReceivingand PSK-DOE to the 16QAM and its
Chαracteristics on Poor Radio
Chan-nels， lEEE VTC'96ヲAtlant，aGA USA，
Proc.Vol
ム
pp.998四1002ヲApr.1996(3) Masahichi Kishi， and Takao
Inoue， A Proposal of PSK-DOE
and its BER Characteristics， IEEE
VTC'96， Atlanta， GA USA，
Proc.Vo.12ラpp.795-799， Apr.1996
L[)
(4) Masahichi Kishi， Norihiro
Hattori， and Kenzo Urabe，
Application of the Short Tim巴DFT
Correlαtor 10 the RAKE receiver
for DS/SS Communicαtion System
αnd Its BER Improvement E
j
J
ectちIEEE PIMRC'95ラToronto，Canada，
Proc.Vol.1，pp. 208-212ヲSep.1995 (5) Masahichi Kishiラ Envelope Detection in Strict Senseαnd its Application to Syllα'bic Companders， IEEE VTC'94， Stockholm， Sweden， Proc.Vo.13ラpp. 1704・1708ヲJune1994 (6)Masahichi Kishi， High Cαpαdty to Defereni抗α!llyDetected π/4 shifted DQPSK with Nαrrrowing Occupied Bαnm申idth b αsed on Short Time DFT， IEEE VTC'93， Secaucus， NJ USAラProc. pp.384・387，May 1993 (受付平成11年3月20日)
