| ABSTRACT
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. To improve the sensing performance, we first propose a
quiet-active sensing scheme in which inactive customer-provided
equipments (CPEs) will sense the channels in both the quiet and
active periods. To avoid quiet-period synchronization, we further
propose to utilize (optimized) active sensing, in which the quiet
periods are replaced by `quiet samples' in other domains, such as
quiet sub-carriers in OFDMA systems. By doing so, we not only save
the need for synchronization, but also achieve selection diversity
by choosing quiet sub-carriers based on channel conditions. The
proposed active sensing scheme is also promising for spectrum
sharing applications where both the cognitive and primary systems can be active
simultaneously.
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