盲解扩频WCDMA信号的忙序列识别方法

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本文主要探讨了WCDMA（宽带码分多址）信号的盲解扩技术。WCDMA是第三代移动通信系统中的关键技术，广泛应用于全球许多运营商的网络中。文章关注的核心问题是如何在无需预先知道扩频码或载波相位的情况下，有效地从无线信道中恢复数据。首先，作者提出了一种方法，通过利用WCDMA信号与不同延迟的最优m-序列的四阶累积量片的最大值，来估计黄金序列的相位。黄金序列是一种特殊的伪随机序列，具有良好的自相关性，这对于盲解扩过程至关重要。这种方法允许系统在不知道精确序列的情况下，对信号进行初步的解扩。接着，利用OFDM（正交频分复用）码的特殊结构，信号的同步是通过计算信号片段之间的互相关函数的最大值实现的。OFDM编码的特点在于其频域上的正交性，这使得在时间域内可以有效地检测到信号的时移并进行同步。在信号被解扩和同步后，文章进一步利用汉明矩阵的特性。通过对每一行的信号与已处理信号进行交叉相关计算，寻找出与特定列对应的OVSF（正交 walsh Hadamard 码）码，从而完全确定了信号的码字，完成了整个解扩和同步的过程。这项工作对于WCDMA系统的实时性和鲁棒性有着显著的提升，尤其是在没有预先配置或者信道条件恶劣的情况下，盲解扩技术能够确保通信的稳定性和数据的正确接收。同时，这种算法也为未来的无线通信系统提供了有价值的研究方向，特别是在物联网、5G等高速移动通信场景中，对信号处理的高效性和灵活性有很高的需求。

BLIND DESPREADING OF WCDMA SIGNALS

ZHAO Zhi-jin

a,b

, GU Xiao-wei

, SHEN Lei

, ZHAN Yi

Zhejiang Provincial Key Lab of Data Storage and Transmission Technology, Hangzhou Dianzi

University, Hangzhou Zhejiang 310018 a

State Key Lab of Information Control Technology in Communication System of No.36 Research

Institute，China Electronic Technology Corporation, Jiaxing Zhejiang 314001 b

zhaozj03@hdu.edu.cn, johnsongutc@126.com, shenlei@ hdu.edu.cn

ABSTRACT

Aiming at despreading Wideband Code Division Multiple

Access (WCDMA) signal blindly, the phase of Gold

sequence is estimated firstly by utilizing the maximum value

of the fourth-order cumulant slice of the product of

WCDMA signal with the optimum m-sequences of different

delays, and then the signal is descrambled. With the

utilization of particular structure of OVSF codes, the signal

is synchronized through the maximum value of cross-

correlation function of signal’s segments. By calculating the

cross-correlation of each row of Hadamard matrix with the

signal that has been descrambled and synchronized before,

the OVSF code is obtained from the column of the matrix

corresponding to the largest value of the cross-correlation

function, and the signal is despread finally. Simulation

results show the better performance of the proposed method

in despreading WCDMA signals under the background of

additive white Gaussian noise.

Index Terms—Wideband Code Division Multiple Access

(WCDMA) signals, Fourth-order cumulant slice, Blind

despreading, Orthogonal Variable Spreading Factor (OVSF)

code estimation

1. INTRODUCTION

Due to its exceptional resistance to inference and strong

confidentiality, Wideband Code Division Multiple Access

(WCDMA) communication systems are widely used in civil

and military applications. The need for blind despreading

the WCDMA signals in non-cooperative communications

becomes increasingly urgent.

References [1,2] investigate the blind despreading

methods of periodic long code direct sequence spread

spectrum (DS-SS) signals. Through segmentation

processing and average cross-correlation calculation, the

starting symbol of PN sequence is determined, and PN

sequence is estimated by utilizing the eigen-analysis

technique in reference [1]. In reference [2], the synchronous

multi-user long-code DS-SS signals are converted as the

short-code ones with missing data, and then the users’

spreading waveform subspace is estimated by utilizing the

Singular Value Thresholding (SVT) algorithm, and finally

the Expectation Maximization (EM) algorithm is used to

blindly despreading the signals.

Despite of the strong need, few methods of detection

and blind despreading of WCDMA signals are published at

present, and most of which use higher order statistics to

detect signal because of its inhibition effect on additive

white Gaussian noise (AWGN)

[3],[4]

. WCDMA signals use

Orthogonal Variable Spreading Factor (OVSF) codes as

spreading codes, which have ideal orthogonal property only

when signals are synchronous

[5]

. Reference [6] mainly uses

eigenvalue decomposition (EVD) to estimate OVSF codes

of WCDMA signals. As WCDMA signals are scrambled by

Gold sequences, EVD method can not be applied to signals

that contain two pseudo-random (PN) codes, a method about

blind despreading WCDMA signal has not been seen yet.

In this paper, an investigation of blind descrambling

and despreading method for WCDMA signals is conducted

when primitive polynomials of optimum m-sequences pair

of Gold sequence and period of OVSF code are known. The

rest of the paper is organized as follows. In section 2, the

signal model of WCDMA signal is given. The blind

despreading algorithm of WCDMA signal is proposed in

section3. Simulations and analyses are presented in section

4 and finally, the concluding remarks are given in section 5.

2. SIGNAL MODEL

The WCDMA signal is supposed to use the values +1, -1

instead of 0 and 1. After sampling the signal with chip rate

of OVSF code, the received base-band WCDMA signal can

be expressed as

()rn , 0,1, 2, 1nN=−" :

() ()()() ()rn Adnongn wn

=+ (1)

where,

A is the amplitude of the signal, n denotes the

sampling time. ( )

dn is the data sequence in signal, each

symbol is sampled by

times. Walsh code generated by

Hadamard matrix with dimension of

is used as the

ICSP2014 Proceedings

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