The Effect of Narrowband Interference on Wideband Wireless Communication Systems

Abstract

In this paper, we introduce the concept of nonsystematic turbo codes and compare them with classical systematic turbo codes. Nonsys- tematic turbo codes can achieve lower error floors than systematic turbo codes because of their superior effective free-distance properties. More- over, they can achieve comparable performance in the waterfall region if the nonsystematic constituent encoder has a lower weight feedforward in- verse. A uniform inteleaver analysis is used to show that rate turbo codes using nonsystematic constituent encoders have larger effective free distance than when systematic constituent encoders are used. Also, mutual information-based transfer characteristics and EXIT charts are used to show that rate turbo codes with nonsystematic con- stituent encoders having low-weight feedforward inverses achieve conver- gence thresholds comparable to those achieved with systematic constituent encoders. Catastrophic encoders, which do not possess a feedforward in- verse, are shown to be capable of achieving low convergence thresholds by doping the code with a small fraction of systematic bits. Finally, we give tables of good nonsystematic turbo codes and present simulation results comparing the performance of systematic and nonsystematic turbo codes. Abstract—This paper evaluates the performance of wideband commu- nication systems in the presence of narrowband interference. In partic- ular, we derive closed bit-error probability expressions for spread-spec- trum systems by approximating narrowband interferers as independent asynchronous tone interferers. The scenarios considered include additive white Gaussian noise channels, flat-fading channels, and frequency-selec- tive multipath fading channels. For multipath fading channels, we develop a new analytical framework based on perturbation theory to analyze the per- formance of a Rake receiver in Nakagami- channels. Simulation results for narrowband interference such as GSM and Bluetooth are in good agree- ment with our analytical results, showing the approach developed is useful for investigating the coexistence of ultrawide bandwidth systems with ex- isting wireless systems.