Interference Cancellation in Impulse Radio

Ultra wideband (UWB) technology has recently received much attention as a potential candidate for low-cost short-range ultra high-speed wireless communications. One of the enabling techniques for ultra wideband (UWB) communications is impulse radio. Impulse radio employs short-duration pulses, producing a signal with an ultra wide (several GHz) bandwidth. This radio system has to co-exist with many existing communication systems transmitting on the same frequency band, for example, IEEE 802.11a WLANs operating around 5GHz, so interference poses problems for its use. In this thesis, two schemes are proposed for interference cancellation in impulse radio. In the first scheme, a preprocessor for ultra wideband (UWB) communications using impulse radio is proposed. The received UWB signal is divided into subband signals, which can be individually processed and recombined before demodulation of the signal. Perfect reconstruction of the pulses via analog subband processing is
achieved. The division of subbands is flexible and the number depends on the number of frequency bands that require processing. Only the subbands that require processing need to be digitized, so the sampling rate requirement is greatly reduced. The proposed preprocessor can be applied to signal processing in impulse radio. The application of the preprocessor to narrowband or wideband interference cancellation is demonstrated, and found to be effective and robust. In the second scheme, the effect of interference on the performance of the UWB system is analyzed and interference cancellation by template design is proposed. Simulation results show that the scheme can effectively suppress interference and improve system performance. The scheme is applicable to both wideband and narrowband interference cancellation. For high speed ultra wideband communications using impulse radio, intersymbol interference (ISI) is unavoidable. The traditional method of combating ISI is to employ an equalizer. Due to the low duty cycle of UWB pulses and extremely short UWB pulse width, however, the number of the equalizer taps has to be impractically large and equalization is only achievable at an exceptionally high pulse rate. A novel ISI cancellation scheme based on wavelet transformation is also proposed. Knowledge of the channel is not required. The desired signal pulse can be distinguished from the interference pulse and precisely located. Instead of using the traditional received pulse, wavelet transformation is applied to generate a new spike signal for demodulation. A detailed theoretical analysis is presented and close-form expressions are derived. Finally, the ISI cancellation algorithm is modified to handle false alarms in noisy environments. 2
DOI: 10.5353/th_b3145936
Subjects:
Radio - Interference
Radio frequency
Ultra-wideband devices