A Study of the Bit Error Performance of Convolutional Coded Spread Spectrum Communication Systems

Abstract

In this paper a study of the effect of convolutional coding in Direct Sequence Spread Spectrum (DSSS) and Frequency-Hopping Spread Spectrum (FHSS) in the presence of the Gaussian, Pulse and Partial band jamming has been made and compared with the bit error performance of the uncoded scheme under the same total bandwidth constraint. This study has been made with respect to the variation in thermal noise density and jamming-to-signal power ratio. Different values of the constraint length and the processing gain are considered. The Viterbi decoding scheme with soft decision has been used for the convolutional decoding. A table look-up method has been employed to determine the signal-to-noise power ratio. The possible burst errors present here are randomised through an interleaving-deinterleaving operation.

The coding of the DSSS is found to improve the bit error performance in-spite-of the reduced processing gain over a range of signal-to-thermal noise density ratio and jamming-to-signal power ratio. Thus this is a study of the trade-off between the advantage due to processing gain and coding with correspondingly reduced processing gain. The comparison of the bit error performance of the different spread spectrum systems under different types of jamming conditions show that the coding is more effective in improving the performance of the DSSS scheme than FHSS in Gaussian jamming environment. This improvement due to coding is more pronounced at higher values of processing gains and code rates. The performance improvement in DSSS under pulse jamming conditions and in FHSS in partial band jamming also depend upon the processing gain and the code rate used.

Indexing terms:

• Direct sequence spread spectrum (DSSS)
• Frequency-hopping spread spectrum (FHSS)
• Convolutional coding in DSSS and FHSS
• Viterbi decoding
• Gaussian jammer
• Pulse jammer