Providing secondary access to licensed spectrum through coordination

Most wireless systems receive a license ~hat gives them exclusive access to a block of spectrum. Exclusivity guarantees adequate quality of service, but it also leads to inefficient use of spectrum. Even when the license holder is idle, no other device can use the spectrum. This paper explores an alternative paradigm for secondary access to spectrum, where a secondary device can transmit when and only when the primary license holder grants permission. In this .,spectrum usage paradigm, each secondary device makes a request for temporary access to spectrum by providing a primary license holder with information such as its required bandwidth, its required signal to interference ratio, its transmit power, and its location, which is essential for a primary license holder in making an admission decision. This explicit coordination makes it possible to protect the quality of service of both primary and secondary, while gaining the etficiency of spectrum sharing. In this paper, we consider the case where the primary license holder is a GSM-based cellular carrier. We show that our proposed sharing scheme works well even with simple admission control and pri~nitiw~ frequency assignment algorithms. Moreover, imprecise location information does not significantly undermine the performance of our scheme. W.e also demonstrate that our scheme is attractive to a license holder by showing that a cellular carrier can profit from offering a secondary device access to spectrum at a price lower than it would nor~nally charge a cellular call.