Multi-path Signal Receiver with Parallel Matched Filter for
The W-CDMA Systems
SHIGENORI TANI†, CINDY BERNADETH TJITROSOEWARNO, †ATSUSHI FUKASAWA†
TOMOKO KASHIMA††, and YUMI TAKIZAWA††,
Graduate School of Science and Technology,
1-33 Yayoi-cho, Inage-ku, Chiba-shi,
Chiba 263-8522, JAPAN
Institute of Statistical Mathematics
Ministry of Education, Science and Technology
4-6-7 Minami Azabu, Minato-ku,
Tokyo 106-8569, JAPAN
Abstract: - The basic structure of the W-CDMA system is investigated first in this paper together with its
characteristics which have been provided previously by the authors. The advantages of the W-CDMA are wide
spreading and coherent detection with a pilot channel. The pilot channel is optimized to give the best
performance of Bit Error Rate. New structure of W-CDMA receiver is then studied to increase transmission data
rate and capacity of mobile communications. This structure, with parallel matched filter, has been proposed for
synchronization and demodulation under multipath environments. Parallel matched filter is configured by analog
MOS LSI instead of conventional digital components. The power consumption and dimension of the LSI are
reduced by the combination of system and hardware approaches.
Keyword: - Synchronization, Pilot signal, Matched filter, W-CDMA, Mobile communications.
was proved to be advantageous for high-speed data
1 Introduction transmission.
DS-CDMA system provides high-speed data
transmission over radio channels. Due to multipath
propagation and Doppler effect, it is important to
establish accurate synchronization. It is also
necessary to perform demodulation without
distortion, as rapid phase rotation exists in radio
Pilot signal is transmitted continuously together
with data signal in this system. Accurate initial
acquisition and precise tracking is achieved by
continuous pilot transmission (pilot channel).
Estimation and compensation of phase rotation is
achieved effectively with high resolution using
continuous pilot signal. And highly improved
demodulation of received data is also provided using
the received pilot signal ~.
This paper describes characteristic evaluation of
the W-CDMA system~ and a novel
configuration of analog matched filters to realize
compact system with low power consumption. The
coherent demodulation using continuous pilot signal
Channel Coding SS Modulation
2 System Configuration Ψ1 Ψ2 Φ
2.1 Transmitter I(t)
The transmitter in the reverse or the forward link is Traffic
FEC QPSK Mod
shown in Fig.1. Q(t)
Data signal is fed to I and Q-channels of QPSK Signaling
modulator. The pilot signal is fed to I-channel only.
They are fed to QPSK modulator. The pilot signal is (a)
composed of Walsh-0 and PN codes. I and Q Channel Coding SS Modulation
components of data signal are composed of Walsh-1 Other channel
and PN codes.
TPC Ψi Φ
In this system, pilot signal transmitted
continuously via a pilot channel merged in the I- Traffic FEC MUX
channel of data channels. QPSK mod
2.2 Receiver Other channel
The receiver in the reverse or forward link is shown
in Fig.2. One correlator is provided for (b)
synchronization with long correlation of 8-16 bit-
data-length. Acquisition and tracking are achieved Fig.1 Transmitter of (a) reverse link and (b) forward link.
precisely using continuous pilot signal. The other
correlator is provided for coherent demodulation with
short-term correlation of 1-bit-data-length based on
phase estimation and compensation using the vectors
u and v (see Appendix).
2.3 Spreading codes Fast initial acquisition of cell synchronization is
The PN code is provided by multiplication of Walsh- provided together with precise tracking of path
0 and PN code, which is an alternate repeated synchronization using pilot signal and parallel
sequence. Walsh-0 is equal to 1. Data signal is spread matched filter. For cell synchronization, a single
by multiplication of Walsh-1 and PN code, so that sample point and correlation of 8-bit-data-span are
data and pilot signal become orthogonal each other. used. For path synchronization, 4 points over
The PN code, fed to I-component, becomes sampling over 1 chip is used to get precise resolution.
orthogonal to the code fed to I and Q components of An analog matched filter system is considered for
data in Fig.1. correlation calculation of received and the pilot signal
The detection of PN code for synchronization is to provide compact and low power receiver.
conducted independently to PN code, fed to I and Q Estimation and compensation of phase rotation with
components in Fig.1. highly improved demodulation of received traffic
Spreading ratio is assumed to be 64. One code is data have been achieved by utilizing received pilot
composed of 64 chips. Available orthogonal codes signal.
Matched Filter Data I
Power Peak Path u,v Path
Q(t) Detector Detector Decoder Calculator Combiner
for Q Data Q
PN Walsh SIR SIR
Generator Generator Combiner
Fig.2 Receiver with correlation system and vector combiner for multipath components.
3.1 System parameters 3.3 Demodulation
Chip rate 4.096 Mchip/sec 3.3.1 Correlation length for pilot detection
Symbol rate 64 Ksymbol/sec Fig. 4 shows the result of BER vs correlation length
Data modulation QPSK under the condition of frequency difference related to
Spreading modulation Direct Sequence phase rotation under single path condition.
Spreading factor 64 Correlation lengths of 8-32 bits are found to be
Spreading code Walsh Code (Channelization) appropriate correlation length.
PN Code (Scrambling code) E+00
Frame length 20 msec
3.2 Initial acquisition 900H z
Fig.3 shows the characteristics of acquisition. The deal
vertical axis shows acquisition success rate vs Ec/N0. E-01
Success rate is defined as the ratio of times of
acquisition being successful in total trial times. Ec
and N0 are the chip power and the noise power per 1
Hz. Fig.3 (a) and (b) show the results of correlation
length of 8bits and 16 bits respectively. Frequency E-02
1 2 4 8 16 32 64 128
variation in the notation of each figure shows the ate sym
C orrel Length（ bol）
difference between local oscillator frequency of Fig. 4 Correlation length vs BER.
transmitter and receiver, which causes phase rotation.
It is found that the appropriate correlation length is 8
3.3.2 Power level of pilot signal
bits because of large frequency deviation 0 – 3kHz in Fig. 5 shows the results of BER vs the power level of
the initial phase of operation. pilot signal relative to that of data signal. The pilot
0% level was set to 6 dB lower than the signal level.
Aqusition Sucess Rate
0% 1kH z E+00
0% 3kH z
-30 -27 -24 -21 -18 -15 -12
-20 -14 -10 -8 -6 -4 -3 -2 -1 0
l gnal dB
Level of P iot S i （ ）
Fig. 5 Pilot signal level vs BER
3.3.3 Doppler shift
Fig. 6 shows the result of BER vs Eb/N0 under the
condition of Doppler shift at the point of frequency
varied from 150 to 250Hz.
It is found that the frequency variation up to 40
Hz/s is found sufficient in BER characteristics.
Fig 3 Characteristics of acquisition.
number of segments to be combined. Time length for
each segment is 5 msec (for 4 segments) and 2.5
msec (for 8 segments).
1. 0H z
0 1 2 3 4 5 6 7 8 9 10
Fig.6 BER characteristics
3.4 Multipath combining
Fig. 7 shows the result of BER vs Eb/N0 of 1-3 path
Characteristics of total system are found sufficient
for high-speed data transmission.
Fig. 8 Characteristics of Initial Acquisition with Parallel
Matched Filters (PMF)
(a) 4 PMF (4 segments; 5 msec/segment)
(b) 8 PMF (8 segments; 2.5 msec/segment)
Fig. 7 BER vs Eb/N0 of 1-3 path combiner
4.2 LSI chip design
In this study, neuron MOS LSI is utilized for
4 Parallel Matched filter system synchronization. It provides analog product of input
4.1 Parallel MF configuration and embedded data at each element. This system
An appropriate correlation length is required for realizes low power consumption as it avoids a lot of
reliable initial acquisition. It is found that the numerical multiplications.
minimum length L must be 8 bits. L = 64 chips x 8 The basic configuration of correlation system is
bits = 512 chips. To get suitable dimension of LSI shown in Fig.9. The matched filter is a FIR with
chip, a parallel matched filter is designed by dividing waiting (replica) code as its input and received input
total L into several segments M . signal as its tap coefficients. Peak detector selects a
Total code length of the pilot signal is set to be maximum peak by using threshold and comparison. It
20msec. The time length of each section of matched also provides the timing information of each
filter is 20ms/M. The summation of correlation value multipath component.
of each section is done for enhancing of For high resolution of synchronization for cell
characteristics of acquisition. search, correlation length of 8 bits (= 64chips x 8
The characteristics of success rate of parallel bits) is assumed. For fine resolution of
matched filters of 4 and 8 segments are shown in synchronization for path synchronization, 4 sample
Fig.8a and 8b. The parameters in these figures show points over a single chip of code waveform is
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Fig.9 Configuration of Parallel Matched Filter (in case of 4
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held constantly during this iteration. Appendix
Acknowledgement Estimation and compensation of radio
The authors express sincere gratitude to Prof. Tadashi propagation characteristics
Shibata; Assistant Professor; Toshihiko Yamazaki, Transmitted signal Tx(t) is given by
and, graduate student Tomoyuki Nakayama with Tx(t) = d(t)(t) + (t)
Tokyo University for their collaboration. d: data signal, (t): PN code, Walsh code (i ≠ 0).
Received signal Rx(t) is given by
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