Spectrum sensing in cognitive radio networks: the cooperation-processing tradeoff

Opportunistic unlicensed access to the (temporarily) unused frequency bands across the licensed radio spectrum is currently being investigated as a means to mitigate the spectrum scarcity. Such opportunistic access calls for the implementation of safeguards so that the ongoing licensed operations are not interfered with. Among different candidates, sensing-based access, where the secondary (unlicensed) users transmit if they sense the primary (licensed) band to be free, is particularly appealing due to its low deployment cost and its compatibility with legacy primary systems. Incorporating such spectral awareness functionality into the radio transceivers is a major step towards the realization of the cognitive radios. In this paper performance of spectrum-sensing cognitive radios is studied under channel fading. In particular, it is shown that due to the uncertainty resulting from fading, local signal processing alone may be inadequate to meet the performance requirements. To remedy this issue, cooperation among secondary users is proposed and studied in this paper. Moreover, we characterize and study a tradeoff between local processing and cooperation, which should be balanced in order to maximize the spectrum utilization. Copyright (c) 2007 John Wiley & Sons, Ltd.