A new protocol for concurrently allocating licensed spectrum to underlay cognitive users

Abstract

Cognitive radio technology makes efficient use of the valuable radio frequency spectrum in a non-interfering manner to solve the problem of spectrum scarcity. This paper aims to design a scheme for the concurrent use of licensed frequencies by Underlay Cognitive Users (UCUs). We develop a new receiver-initiated Medium Access Control (MAC) protocol to facilitate the selections of alternative reliable carrier frequencies. A circuit is designed to establish reliable carrier selections based on the Received Signal Strength Indicator (RSSI) at the receiving end. Based on both packet-level simulations and various performance parameters, a comparison is carried out among conventional techniques, including the Multiple Access with Collision Avoidance (MACA) and MACA by invitation(MACA-BI) techniques, and our scheme. The simulated results demonstrate that when conventional techniques are used, the system overhead time increases from 0.5s on the first attempt to 16.5s on the sixth attempt. In the proposed scheme under the same failure condition, overhead time varies from 0.5s to 2s. This improvement is due to the complete elimination of the exponential waiting time that occurs during failed transmissions. An average efficiency of 60% is achieved with our scheme while only 43% and 34% average efficiencies are achieved with the MACA and MACA-BI techniques, respectively. The throughput performance of our scheme on the fourth attempt is 7 Mbps, whereas for the MACA and MACA-BI protocols, it is 1.9 Mbps and 2.2 Mbps respectively.