EFFICIENCY OF SPREADING SPECTRUM IN DSSS SYSTEMS WITH GOLD SEQUENCES

Headnote

Abstract: Using spread spectrum technique provides, in addition to efficient use of frequency bands, protection against eavesdropping, interferences and high noise immunity, remarkable qualities for military applications. The purpose of this paper is to present experimental results for the study of spectral spreading efficiency when using Gold sequences as pseudo-noise generators. Experiments are intended to highlight the spread spectrum and noise immunity (minimum SNR for extracting data correctly) for three code lenghts.

Keywords: communications, spread spectrum, Gold sequences.

1. INTRODUCTION

The spread spectrum (SS) communication is a transmission technique in which a pseudonoise (PN) code (independently from the data) is used as a waveform to spread the signal energy over a bandwidth much wider than the initial bandwidth occupied by data. In receiver, the signal is despread using a local replica synchronized PN code used in transmitter.

There are several methods for spreading the spectrum, which are distinguished by the place where, in transmission chain, the PN code is inserted. The basics are:

* Direct Sequence Spread Spectrum DSSS: PN code is inserted at the level of input data;

* Frequency Hopping Spred Spectrum FHSS: PN code acts on the carrier frequency.

Especially for military applications, the advantages of using the SS communications are particularly attractive:

* Protection against eavesdropping

* High immunity to fading appeared on communication channel;

* Protection against interference with other communications;

* Anti-jamming.

Order to ensure efficient SS communications, PN code has a few rules on length, autocorrelation, crosscorrelation, orthogonality and bits balance. Commonly used PN codes are: Barker, Gold, Walsh- Hadamard. Note that a complex code sequence provides a more robust link, but the price paid is in complex electronics, especially in receiver blocks, to synchronize the local PN code with the received signal, for despread the spectrum.

Gold sequences are a class of codes which provide larger sets of sequences with good crosscorelation properties.

The purpose of this paper is to present experimental results for the study of spectral spreading efficiency when using Gold sequences as PN generators.

2. COMMUNICATION SYSTEM STRUCTURE PROPOSED

2.1 The work environment. To meet the requirements...