Code-time diversity for direct sequence spread spectrum systems.

A Y Hassan

doi:10.1155/2014/146186

Abstract

Time diversity is achieved in direct sequence spread spectrum by receiving different faded delayed copies of the transmitted symbols from different uncorrelated channel paths when the transmission signal bandwidth is greater than the coherence bandwidth of the channel. In this paper, a new time diversity scheme is proposed for spread spectrum systems. It is called code-time diversity. In this new scheme, N spreading codes are used to transmit one data symbol over N successive symbols interval. The diversity order in the proposed scheme equals to the number of the used spreading codes N multiplied by the number of the uncorrelated paths of the channel L. The paper represents the transmitted signal model. Two demodulators structures will be proposed based on the received signal models from Rayleigh flat and frequency selective fading channels. Probability of error in the proposed diversity scheme is also calculated for the same two fading channels. Finally, simulation results are represented and compared with that of maximal ration combiner (MRC) and multiple-input and multiple-output (MIMO) systems.

Highlights

Diversity techniques are used when the channel is in a deep fade
We propose a new diversity technique for single-input and single-output (SISO) spread spectrum systems that can achieve a diversity gain like that of the multiple-input and multiple-output (MIMO) system but with a single transmitting antenna and a single receiving antenna
The proposed system achieves the benefits of diversity systems as well as the benefits of spread spectrum systems

Summary

Introduction

Diversity techniques are used when the channel is in a deep fade. If several replicas of the same information signal are transmitted over independent fading channels, the probability that all signal components will fade simultaneously is reduced considerably. Multiple-input and multiple-output (MIMO) system is a well-known system that exploits the antenna diversity to enhance the bit error rate and the channel capacity in fading environments [10, 11] Time diversity is another diversity method where L independent fading version of the same information signal is achieved by transmitting the signal in L different time slots. The uncorrelated fading gains that come from the uncorrelated spatial paths, the different transmitting time slots, and the different transmitting carrier achieve the diversity gain at the receiver This system has large diversity gain and better performance than space-time coded MIMO systems. We propose a new diversity technique for SISO spread spectrum systems that can achieve a diversity gain like that of the MIMO system but with a single transmitting antenna and a single receiving antenna.

Code-Time Diversity

Transmitted Signal Model of Code-Time Diversity DSSS

Simulations

Conclusions

Definition of the Generalized Hypergeometric Function