基于 ZCZ 序列的 MC-DS-CDMA 上行链路系统设计

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Uplink MC-DS-CDMA 使用 ZCZ 序列本文主要介绍了一种新的 Uplink MC-DS-CDMA 方案，该方案使用 ZCZ 序列来提高频率选择性阻塞衰落信道中的频率和时间多样性。该方案通过在时间和频率域上进行扩展来实现多用户接入，使用Almost optimal quadriphase ZCZ 序列来最小化多用户干扰。在频率选择性阻塞衰落信道中，MC-DS-CDMA 方案可以提供更好的频率多样性和时间多样性，从而提高系统的可靠性和容量。该方案使用 almost optimal quadriphase ZCZ 序列来生成扩展码，使得多用户之间的干扰最小化。同时，该方案还使用联合检测来提高接收端的检测性能。在该方案中，MC-DS-CDMA 系统可以在频率选择性阻塞衰落信道中提供更好的性能。该系统可以应用于各种无线通信系统，例如 5G、LTE、WiMAX 等。知识点： 1. MC-DS-CDMA 是一种多用户接入技术，使用扩展码来实现多用户之间的区分。 2. ZCZ 序列是一种特殊的扩展码，具有良好的自相关和互相关特性，从而可以最小化多用户干扰。 3. 频率选择性阻塞衰落信道是一种复杂的信道模型，会对信号传输产生严重的影响。 4. 联合检测是一种检测技术，使用多个检测器来提高检测性能。 5.Quadriphase ZCZ 序列是一种特殊的 ZCZ 序列，具有四个相位，能够提供更好的频率多样性和时间多样性。在该论文中，作者提出了一个新的 Uplink MC-DS-CDMA 方案，该方案使用 ZCZ 序列来提高频率选择性阻塞衰落信道中的频率和时间多样性。该方案可以应用于各种无线通信系统，提高系统的可靠性和容量。技术领域： 1. 通信技术 2. 网络技术 3. 广播技术 4. 计算机硬件/软件 5. 电romagnetics 6. 地球科学 7. 光子学和电光学 8. 能源和工业应用 9. 信号处理和分析标签：Fields, Waves 该论文的主要贡献是提出了一个新的 Uplink MC-DS-CDMA 方案，该方案使用 ZCZ 序列来提高频率选择性阻塞衰落信道中的频率和时间多样性。该方案可以应用于各种无线通信系统，提高系统的可靠性和容量。

Uplink MC-DS-CDMA using ZCZ sequences for

frequency-selective block-fading channels

D.J. Basilio, Member, IEEE, L.P. Linde, Senior Member, IEEE, and B.T. Maharaj, Member, IEEE

Department of Electrical, Electronic and Computer Engineering, University of Pretoria, Pretoria, South Africa

Email: s23361850@tuks.co.za, llinde@postino.up.ac.za, sunil.maharaj@up.ac.za

Abstract—In this paper, a time and frequency (TF) domain

spreading multicarrier direct sequence code division multiple

access (MC-DS-CDMA) scheme employing zero correlation zone

(ZCZ) sequences, designed speciﬁcally for quasi-synchronous

uplink transmissions, is proposed to exploit frequency and

temporal diversity in frequency-selective block-fading channels.

This is in contrast to previously proposed schemes designed

only to exploit frequency diversity in frequency-selective slow

fading channels. Almost optimal quadriphase ZCZ sequences

are employed to minimize multi-user interference (MUI) in the

uplink channel. Joint detection is employed at the receiver using

the optimal maximum likelihood (ML) detector and sub-optimal

minimum mean square error (MMSE) detector. When using

the ML detector, the proposed system showed a performance

improvement of 2.7 dB at a BER of 10

−4

over a previously

proposed scheme designed only to exploit frequency diversity.

I. Introduction

Among the multicarrier code division multiple access

(CDMA) schemes proposed in the literature, we can

distinguish between two diﬀerent approaches: frequency-

domain spreading, as in multicarrier CDMA (MC-CDMA)

systems [1], and time-domain spreading, as in MC

direct-sequence CDMA (MC-DS-CDMA) systems [2, 3].

Conventional MC-DS-CDMA does not achieve frequency

diversity without introducing redundancy [2, 3], and thus

there is a trade-oﬀ between data throughput and performance.

In [4], an amalgam of MC-CDMA and MC-DS-CDMA

known as time and frequency (TF) domain spreading MC-

DS-CDMA was proposed to achieve frequency diversity,

without introducing redundancy. TF-domain spreading MC-

DS-CDMA relies on joint detection at the receiver, and

generally has higher receiver decoding complexity compared

to conventional uncoded MC-DS-CDMA. Recently, a TF-

domain spreading MC-DS-CDMA scheme employing zero

correlation zone (ZCZ) time domain spreading sequences

was proposed for the quasi-synchronous uplink channel

[5]. The beneﬁt of employing ZCZ time domain spreading

sequences in the uplink is that they are capable of reducing

multi-user interference. Over the duration of the ZCZ, both

the cross-correlation and the auto-correlation properties of the

spreading sequences are zero, and thus there is no interference

between users separated by propagation delay diﬀerences that

are within the ZCZ (interference-free window). However, the

system in [5] is only designed to obtain frequency diversity

in frequency selective slow fading channel conditions and

does not consider the time selectivity of the wireless channel.

In this paper the authors present a system model for

TF-domain spreading MC-DS-CDMA that exploits frequency

and temporal diversity in frequency selective block-fading

channel conditions, where the fading coeﬃcients are constant

over one fading block but are independent from block to

block [6, 7]. It has been shown that the diversity gain in

block-fading channels can be improved by coding across

multiple fading blocks [6, 7]. Thus, the proposed system is

able to achieve frequency and temporal diversity instead of

just the frequency diversity achieved in [5]. Quadriphase ZCZ

sequences are employed as time-domain spreading sequences

to reduce multi-user interference (MUI) in the uplink. Joint

detection is done at the receiver using the optimal maximum

likelihood (ML) detector and the minimum mean square

error (MMSE) detector [8]. Simulation results reveal that the

proposed system performs better than the system proposed

in [5], due to the additional temporal diversity exploited in

block-fading channel conditions.

Notation: Column vectors (matrices) are denoted by

boldface lower (upper) case letters. Superscripts

and

∗

denote the transpose and complex conjugate operations,

respectively; diag(d

, . . . , d

) denotes a P ×P diagonal matrix

with diagonal entries d

. . . d

. I

is the N ×N identity matrix

and 0

N×M

is the N × M all zero matrix. F

is the P × P

discrete Fourier transform (DFT) matrix. The cardinality of a

set or the magnitude of an element is denoted by |.| and dxe is

the smallest integer larger than x. The remainder of division

of x by y is denoted by (x)mod(y).

II. Construction of ZCZ sequences

Traditional orthogonal spreading sequences, such as or-

thogonal Gold sequences and Walsh-Hadamard sequences [9],

exhibit non-zero oﬀ-peak cross-correlations, which limits the

achievable performance in asynchronous or quasi-synchronous

scenarios. However, ZCZ sequences exhibit an interference

free window over which both the cross-correlation and auto-

correlation function are zero. Consequently, ZCZ sequences

are able to suppress MUI in the quasi-synchronous uplink

channel. We denote a set of ZCZ sequences as (L

seq

, M

seq

, Z

ZCZ, where L

seq

is the sequence length, M

seq

is the sequence

family size and Z

is the one-sided ZCZ length in chips. For

a sequence set {s

}

seq

q=0

with family size M

seq

, and sequence

length L

seq

, the periodic correlation characteristics of ZCZ

IEEE AFRICON 2009

23 - 25 September 2009, Nairobi, Kenya

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