Vol.26 No.6 JOURNAL OF ELECTRONICS (CHINA) November 2009
PDA DETECTOR FOR DS-CDMA COOPERATIVE SYSTEM
1
Mei Zhonghui Meng Qingmin Li Xiaofei Wu Lenan
*
(College of Telecommunication and Information Engineering, Nanjing University of Posts and Telecommunica-
tions, Nanjing 210003, China)
*
(College of Information Science Engineering, Southeast University, Nanjing 210096, China)
Abstract This paper considers the uplink of a cooperative Code-Division Multiple-Access (CDMA)
system where parts of mobile nodes serve as source nodes while the others serve as relay nodes at any
instant in time. When the non-orthogonal spreading codes are adopted, Multiple Access Interference
(MAI) will exist at both the relay nodes and the base node, causing diversity gain to diminish. To
mitigate MAI and exploit full advantages of cooperation, the Probabilistic Data Association (PDA) is
developed at the relay nodes and the base node. Simulation results demonstrate that some performance
gains can be obtained by the PDA detector over the Minimum Mean Square Error (MMSE) detector at
high Signal-to-Noise Ratio (SNR) and conversely at low SNR.
Key words Cooperative communication; Multiuser detection; Probabilistic Data Association (PDA);
Code-Division Multiple-Access (CDMA)
CLC index TN911.23
DOI 10.1007/s11767-008-0157-x
I. Introduction
More recently, researchers begin to consider the
multiuser cooperative communication system in
non-orthogonal conditions, especially the coopera-
tive Code-Division Multiple-Access (CDMA) net-
works which employ non-orthogonal spreading
waveforms. However, for such cooperative CDMA
networks, Multiple Access Interference (MAI) will
exist both of the relay nodes and the base node,
causing the cooperative diversity to diminish. To
deal with this issue, Ref. [1] considers to employ the
Minimum Mean-Square-Error (MMSE) detector at
both the relay nodes and the base node to mitigate
MAI, and provides performance analysis of the
given detection strategy in terms of the Sig-
nal-to-Interference plus Noise Ratio (SINR) and
the Bit Error Rate (BER). Ref. [2] develops the
relay-assisted decorrelating multiuser detector to
1
Manuscript received date: December 24, 2008; revised
date: September 24, 2009.
Supported by the National Natural Science Foundation of
China (No. 60772061), Science Foundation of Nanjing
University of Posts and Telecommunications (No.
NY207132), and the Postdoctoral Research Programs (No.
0801054B).
Communication author: Mei Zhonghui, born in 1976, male,
Ph.D. Box 179, Nanjing University of Posts and Tele-
communications, Nanjing 210003, China.
Email: meizh@njupt.edu.cn.
suppress MAI. It is well known that these detectors
fall into linear multiuser detector and can not
perform soft-output detections.
The Probabilistic Data Association (PDA) de-
tector which is firstly proposed in Ref. [3] provides
near-optimal performance at a low overall com-
plexity of
3
()(KKO is the number of users). Fur-
thermore, it can give soft-output and may be
combined with the Soft-Input Soft-Output (SISO)
decoder to form the iterative receiver. Thus, re-
cently, the PDA detector has received much at-
tention and been widely applied to CDMA net-
works or MIMO systems
[4–6]
. In this paper, the PDA
detector is extensively considered for the coopera-
tive CDMA networks where MAI exists not only at
the base node, but also at the relay nodes. At the
relay node, we derive the average Symbol Error
Ratio (SER) expression for the PDA detector; at
the base node, by approximate the MAI plus noise
to be Gaussian distribution, we give the soft output
of the PDA detector. To evaluate its performance,
some comparisons are made between the PDA
detector and the MMSE detector under the same
cooperative system model.
II.
System Model
Consider a synchronous DS/CDMA network
which employs non-orthogonal spreading codes. At