Abstract
AbstractIn recent years, ultra wideband (UWB) has been widely implemented in high data rate indoor wireless communications. Due to a number of advantages such as robustness to interference and low power consumption, UWB is suitable for the connection of wireless local area network (WLAN) and wireless personal area network (WPAN).The ability to coexist with other systems is an important issue for UWB. The detect and avoid (DAA) technique is an approach which enables UWB to be aware of the existence of other systems and to take some actions for protecting systems in coexistence. In this thesis, the orthogonal frequency division multiplexing (OFDM) is employed as the physical layer transmission scheme, and we investigate the interference avoidance method. An interference avoidance method is an approach that shapes the transmit spectrum such that the interference to coexistent systems can be reduced to the least.We introduce briefly two existing interference avoidance methods: active interference canceling (AIC) and window method. The AIC is the method which uses several auxiliary sub-carriers near the protected band to neutralize interference. The window method is to multiply original transmitted data symbol by a non-rectangular window, so that the spectrum shape is more concentrated and a better decaying rate of side-lobe is achieved.Several issues regarding the AIC method and window method are investigated in this thesis. Without a constraint on the emitting power, UWB systems result in severe interfere to other coexistent systems. To conquer, we add a constraint on the least square (LS) criterion employed by AIC, which results in LS with quadrature inequality (LSQI). Secondly, AIC is combined with the window method to boost the performance of interference avoidance. Thirdly, conjugate gradient least square (CGLS) is used to reduce the computational complexity involved with the matrix inversion in AIC.