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Relaying of the primary signals by cognitive base- stations (CBSs) can help the primary system and thus win CBSs a higher chance to transmit their own signals. For this purpose, conventional zero- forcing (CZF) beamforming is a straightforward solution where the primary and cognitive signals are transmitted from a multi-antenna CBS without causing interference to each other. However, with CZF, no...
Spectrum sensing is critical for cognitive systems to locate spectrum holes. In the IEEE 802.22 proposal, short quiet periods are arranged inside frames to perform a coarse intra-frame sensing as a pre-alarm for fine inter-frame sensing. However, the limited sample size of the quiet periods may not guarantee a satisfying performance and an additional burden of quiet-period synchronization is required...
In this paper, we propose a new architecture for a closed-loop controlled antenna tuning unit (ATU) system (only transmitting path is shown). In contrast to previous work, no analog-to-digital converters (ADCs) are used. Using the ATU, the narrow instantaneous bandwidth of an electrically small antenna (ESA) is automatically tuned over a much wider frequency range by the ATU. This matching scheme...
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