DS-CDMA合作系统中的PDA检测器

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"PDA DETECTOR FOR DS-CDMA COOPERATIVE SYSTEM.pdf" 本文主要探讨了在直扩码分多址(DS-CDMA)合作系统中的上行链路设计，其中部分移动节点作为源节点，而其他节点则作为中继节点。在非正交扩频码的情况下，中继节点和基站在接收信号时会遭遇多址干扰(MAI)，这会导致分集增益降低。为了减轻MAI的影响并充分利用合作通信的优势，文章提出了概率数据关联(PDA)检测器。概率数据关联(PDA)检测器是一种创新的解决方案，它在中继节点和基站端被应用。PDA方法的核心在于通过概率统计的方法来处理多址干扰，以提高信号的检测性能。与传统的最小均方误差(MMSE)检测器相比，PDA检测器在高信噪比(SNR)环境下能获得更好的性能增益。在高SNR条件下，PDA检测器能更有效地识别和分离多个用户信号，从而降低误码率并提高系统的整体效率。然而，当SNR较低时，情况反转，MMSE检测器的表现可能优于PDA检测器。这是因为在低SNR环境下，MMSE检测器更注重减小均方误差，从而可能在一定程度上弥补了噪声带来的影响。文章通过仿真结果验证了PDA检测器的效果。这些结果展示了在不同SNR条件下，PDA检测器相对于MMSE检测器的性能优势。这些发现对于优化DS-CDMA合作系统的性能，尤其是在网络覆盖边缘和高用户密度区域，具有重要的实际意义。总结关键词：合作通信、概率数据关联、多址干扰、直扩码分多址、中继节点、基站、信噪比、最小均方误差检测器。通过PDA技术的应用，可以在不显著增加系统复杂性的同时，提高DS-CDMA合作系统的抗干扰能力和通信质量，这对于未来无线通信网络的设计和优化提供了有价值的参考。

Vol.26 No.6 JOURNAL OF ELECTRONICS (CHINA) November 2009

PDA DETECTOR FOR DS-CDMA COOPERATIVE SYSTEM

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

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

()(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

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