  We consider the problem of Spectrum Sensing in Cognitive Radio Systems. We
have developed a distributed algorithm that the Secondary users can run to
sense the channel cooperatively. It is based on sequential detection algorithms
which optimally use the past observations. We use the algorithm on secondary
users with energy detectors although it can be used with matched filter and
other spectrum sensing algorithms also. The algorithm provides very low
detection delays and also consumes little energy. Furthermore it causes low
interference to the primary users. We compare this algorithm to several
recently proposed algorithms and show that it detects changes in spectrum
faster than these algorithms and uses significantly less energy.
