Cognitive Radio Combined with Ultra Wideband Technology for Spectrum-Agile Wireless Communications

The emerging cognitive radio system can sense and adapt to the wireless environment in which it operates. Cognitive radio with intelligent capabilities of both radio link and network layers is capable of transmitting in an optimized way across the available signal dimensions allowing a potential huge increase in the prospects for spectrum efficiency, co-existence, compatibility and interoperability among the ever-proliferating wireless communication systems and devices. It’s a rather new concept, and currently, there is no consensus on the practical implementation issues. Ultra Wideband (UWB) represents an outstanding example of enabling technology for the implementation of the cognitive radio concept. As we know, UWB systems are appealing for their broadband features, their low-power noise-like signalling, which basically can be exploited in the transmission over (licensed) bands producing a controlled level of interference on existing communication systems. On the other hand, UWB will face and cause severe interference from and to nearby communication systems. In this respect, coexistence and compatibility are important open issues, demanding for innovative solutions. Cognitive radio will provide the required innovative solutions, and enable coexistence, compatibility, interference avoidance, and compliance with regulation through the attribution of UWB devices with cognitive radio capabilities. Started from this point of view, this research investigates the advantages and features of integrating the cognitive radio with the UWB technology. Research contributions include: Firstly, introducing the fundamental researches on the M-ary pulse shape modulation for PSWF (Prolate Spherodial Wave Functions) based UWB systems; Secondly, developing transmit power allocation schemes for throughput and BER performance improvement, respectively, among the orthogonal pulse waveforms in cognitive UWB radio; Thirdly, proposing spectrum adaptation techniques to get the spectrum-agile waveforms in cognitive UWB radio, namely, designing a number of adaptive pulse waveforms, corresponding to the expected UWB spectrum features and achieving the required spectral notches for mitigating interference to other radio systems (e.g., primary users) for effective coexistence;Fourthly, developing distributed nodes cooperation scheme in cognitive UWB radio using Space-Frequency block coding, and proposing an innovative Frequency Exchange (FE) decoupling algorithm in the UWB receiver side for the signal detection. Future research could be pursed for effective transmit power control in a decentralized network consisting of multiple cognitive UWB nodes. Future research also could include the detect techniques in cognitive UWB radio capable of sensing and monitoring the spectrum usage in frequency, time and space.