"Recent increases in demand for cognitive radio technology have driven researchers and technologists to rethink the implications of the traditional engineering designs and approaches to communications and networking. One issue is that the traditional thinking is that one should try to have more bandwidth, more resources, and more of everything, while we have come to the realization that the problem is not that we don't have enough bandwidth or resources. It is rather that the bandwidth/resource utilization rates in many cases are too low. For examples, the TV bandwidth utilization nowadays in the USA is less than 6%, which is quite similar to that in most developed countries"--