Performance estimation of DSSS wireless systems in impulsive interference

Radiated interference environments can significantly degrade the performance of the digital communication systems that are widely used today. Problems from such intersystem interference might need to be analyzed beforehand or as problems occur. Another application where such analysis is of interest is in systems using dynamic allocation of spectrum, where it serves as basis for spectrum allocation. To be useful in on-line applications, the analysis method should be fast and of low complexity. A common method is therefore to approximate the interference as Additive White Gaussian Noise, AWGN. However, if the noise is impulsive, this approximation can cause large errors in Bit Error Probability (BEP) estimation. It is desirable to avoid both under- and overestimations. Underestimations can lead to interference problems in the application, while overestimating could cause expensive protection measures to be used unnecessarily. One type of systems that have not received much interest regarding error estimation are those using both error correcting codes and direct sequence spread sprectrum, DSSS. Two systems using this combination are the third generation mobile telephony standard 3G UMTS, and the global navigation systems GPS and Galileo. In this paper we derive necessary conditions for when the Gaussian approximation can be used accurately for impulsive interference, in a DSSS system using convolutional coding.