| Summary: | 碩士 === 國立清華大學 === 通訊工程研究所 === 94 === In recent years, ultra wide band (UWB) has become the key technology of wireless personal area network (WPAN). It is not only used for high speed data transmission but also has the characteristics of low power consumption and low interference. When sharing the same frequency band with protected communication systems, UWB might severely degrade the service quality of coexisting systems. Cognitive radio is an emerging approach which enables UWB aware of the existence of protected systems. When being notified of the existence of other systems, UWB can limit its transmitted power; thus, the resources of frequency and power can be utilized more efficiently.
In this thesis, we employ multi-band orthogonal frequency division multiplexing (MB-OFDM) as the physical layer transmission scheme, and we investigate the interference avoidance technologies about coexistence between UWB and protected radio services. We will introduce existing interference avoidance methods: window method and active interference canceling (AIC). The window method is to multiply original transmitted data symbol by a non-rectangular window, so that the spectrum shape will be more concentrated. The goal of alleviating interference to licensed band is achieved. The AIC is to calculate the interference resulting from all data sub-carriers toward the protected band, and we use several unused sub-carriers to carry information which can neutralize interference, both transmit these sub-carriers at the same time to achieve interference canceling.
Next we will put forward similar methods based on existing technologies, include revision of window method and another kind of AIC. And then combining methods to relax interference is observed. Finally, compare these methods and put forward the conclusion.
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