新型MC-2D-CDMA通信系统与检测方法研究

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本文主要探讨了一种新颖的多载波-二维编码分组多址（MC-2D-CDMA）通信系统及其检测方法。MC-2D-CDMA是基于多载波技术的一种创新传输方式，其特别之处在于充分利用了二维扩频特性，从而显著提高了抗衰落（fading）和多接入干扰（Multiple Access Interference, MAI）的能力。在无线通信系统中，如未来的4G网络，这种系统具有广阔的应用前景。论文首先介绍了MC-2D-CDMA系统的概念，强调了其在移动通信网络中的潜力，特别是在提高信号稳定性和多用户环境下的性能优化。作者 Lei Xiao 和 Qinglin Liang 分别来自中国的 Siemens Ltd. 信息与通信网络研究团队以及北京大学电子系，他们的研究关注于系统的设计、多样化的组合方法以及其实现策略。研究中，作者考察了多种检测方法，包括： 1. **加权最小二乘组合（Weighted Least Square Combination, WLSC）**：尽管WLSC表现出较好的性能，但其对于前向链路（forward link）的要求较高，可能需要对其他用户的信号和噪声有一定的先验知识，因此在实际应用中可能存在一定的局限性。 2. **辅助向量组合（Auxiliary Vector Combination, AVC）**：这种方法结合了最大比合并（Maximum Ratio Combination, MRC）和正交恢复相关性（Orthogonality Restoring Correlation, ORC）。AVC的优势在于其简单且鲁棒，不需要关于其他用户或噪声的先验信息，非常适合前向链路的环境，因为它能够有效地对抗衰落和MAI。通过模拟实验，论文验证了这些检测方法的有效性，证实了MC-2D-CDMA通信系统在实际无线通信环境中的抗干扰能力。这项研究为提高无线通信系统的可靠性和容量提供了新的解决方案，对于4G及后续无线技术的发展具有重要意义。未来的研究可以进一步优化这些算法，以适应不断变化的通信需求和技术进步。

Novel MC-2D-CDMA Communication

Systems

and Its Detection Methods

Lei

Xiao

New Generation of Mobile Networks

Information

Communication Networks Group

Siemens Ltd., China

Qinglin

Liang

Electronics Department

Peking University

China

:lh.strtrcr-This paper presents a novel multicarrier-2-

Dimension-code division multiple access (MC-2D-CDMA)

system for forward

link.

Because of the full utilization of

Dimension spreading characteristic, the ability to reject fading

ancl multiple access interference (MAI) is enhanced. For this

system, we examine some diversity combination methods.

Among them, Weighted Least Square Combination (WLSC) has

better performance but is not very suitable for forward link;

Auxiliary Vector Combination (AVC), the combination of

Maximum Ratio Combination (MRC) and Orthogonality

Restoring Correlation (ORC) is very simple and robust, and

very suitable for forward

link

because it does not require any

prior knowledge about other users and noise. The simulation

results show their validity to anti-fading and anti-MAL

INTRODUCTION

Recently, the multicarrier modulation scheme,

orthogonal frequency-division multiplexing (OFDM) has

drawn a lot of attention because of its anti-fading capability

and the need to transmit high data rate. By using the fast

Fourier transform (FFT) and inverse transform

(IFFT),

the

multicarrier scheme not increases the complexities but

achieve high spectral efficiency.

To provide higher capacity, the combination of

multicarrier and code division multiple access (CDMA)

also

developed[2]. According to their multiple access

characteristics, these systems can be categorized into two

types, spreading and multiple access in the frequency field,

called MC-CDMA[3]-[5],

spreading and multiple access

in the time field, called Multicarrier DS-CDMA[6][7]. In the

former system, a spreading sequence is serial-to-parallel

converted and modulates different carriers, and different

users utilize different spreading codes in the frequency field.

In the latter system, each carrier is used to transmit a

narrowband DS waveform, and different users utilize

different spreading codes in the time field.

This paper presents a novel MC-2D-CDMA system for

forward link. In this system, spreading and multiple access

are carried out both in the frequency field and in the time

field. Compared with MC-CDMA, MC-2D-CDMA has better

anti-MA1 capability due to spreading in the time field.

Compared with Multicarrier DS-CDMA, MC-2D-CDMA has

better anti-fading capability due to frequency diversity

resulting from spreading in the frequency field. Because of

the full utilization of 2-Dimension spreading characteristic,

the capability of multi-access is increased greatly and the

frequency diversity provides anti-fading ability.

In the MC-2D-CDMA system, two spreading sequences

are used, one in the frequency field and the other in the time

field. Some users are discriminated by different spreading

codes in the time field, and others are discriminated by

different spreading codes in the frequency field. For the

former, the simple matched filter can distinguish them very

well because the orthogonality between spreading codes are

maintained due to frequency-nonselective fading in each

carrier. For the latter, many detection schemes for MC-

CDMA, such as MRC, ORC, EGC, MLD, MMSEC, MUD

and

on[l], are also suitable to distinguish these users.

However, due to multiple access interference (MAI),

conventional detection schemes, such as MRC and EGC,

perform not well, while performancewise detection schemes,

such as MLD, MMSEC and MUD, require the prior

knowledge about other users and are usually very complex.

So,

for this system, we present and examine some new

diversity combination methods. Among them, WLSC and

MMSEC have better performance since they consider the

signal and interference comprehensively. However they

require the knowledge about other users’ signal, which is an

unrealistic requirement for forward link, and their complexity

increase greatly with the increase of the number of users and

the number of carriers. We also provide simpler

approximating algorithm for them. Moreover, for decreasing

the complexity further, we present Auxiliary Vector

Combination (AVC), the combination of Maximum Ratio

Combination (MRC) and Orthogonality Restoring

Correlation (ORC). Due to the good anti-fading capability

MRC and good anti-MA1 capability of ORC, the AVC

receiver has great capability

reject

both

fading and MAI,

but avoids their drawbacks. Moreover, AVC is very simple

and robust, and very suitable for forward link because it does

not require any prior knowledge about other users and noise.

This paper firstly presents system description in section

including channel model, transmitter model and receiver

model. Then we examine some diversity combination

methods in section

111

and verify their performances by

simulation in section IV. Finally conclusions are presented in

section V.

11.

SYSTEM DESCRlPTlON

Channel

Model

his

work

was finished when the author was studying for doctor degree in Peking University

1223

0-7803-6283-7/00/$10.00

2000

IEEE

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