BIKRAMADITYA DAS et. al.: NARROWBAND INTERFERENCE REDUCTION TECHNIQUE IN IMPULSE RADIO (IR) UWB COMMUNICATION SYSTEM COEXISTING IN WPAN AND UNDERWATER ENVIRONMENT

The Impulse Radio based Ultra Wideband (IR-UWB) system transmits data by sending pulses, each with very small time duration followed by pauses that are approximately two hundred times that length. Rake receiver improves system performance by equalizing signals from different paths. This enables the use of Rake receiver techniques in UWB systems. For high data rate ultra-wideband communication system, performance comparison of ARake, PRake and SRake receivers are attempted. Although UWB communication offers a promising solution in an increasingly overcrowded frequency spectrum, mutual interference due to coexistence with other spectrally overlapping wireless system degrades the performance of both systems. The narrow band systems may cause interference with UWB devices as it is having very low transmission power and the large bandwidth. So it may jam the UWB receiver completely degrading their performance. Rake receiver alone fails to perform in such condition. A hybrid SRAKE-MMSE time domain equalizer is proposed to overcome this by taking into account both the effect of the number of rake fingers and equalizer taps. This scheme selects the first strongest multipath components and combines them using a SRake receiver based on the minimum mean square error (MMSE) criterion. It also combats inter-symbol interference by considering the same advantages. Study on non-line of sight indoor channel models illustrates that bit error rate performance of UWB SRAKE-MMSE (both LE and DFE types) improves for CM3 model with smaller spread compared to CM4 channel model cancelling out the narrowband interference. A modified UWB channel model is proposed using the Rician distribution for underwater communication. Again BER performance of the proposed receiver is compared with traditional receiver technique for the underwater UWB LOS channel model.