Cognitive radio (CR) is introduced to improve spectrum efficiency by unlicensed usage when a licensed band is idle. These devices monitor licensed users to find spectral opportunities for transmission. A cognitive radio network (CRN) is defined as a structure, which is constructed by both licensed users and unlicensed CR users. In an effort to improve spectrum efficiency, CR users' spectrum issues have been widely studied over the last few years. However, the existing solutions are not capable of dealing with the following scenario: multiple CRNs operating simultaneously without a centralized coordinator. This issue is often referred to as a coexistence problem of heterogeneous CRNs. This problem is caused in a distributed framework of CRNs without a centralized component to negotiate spectrum usages with one another. The system characteristics of these heterogeneous networks are different; thus, the fairness issue between CR users must be considered. In this paper, a decentralized solution that does not limit the hardware capacity of a CR device is proposed as an added fairness feature. Several Markov chain models are proposed to study these unfairness conditions, and a medium access control layer approach is introduced. Numerical and simulation results are presented to verify the proposed solution.
['Yu-Chun Cheng', 'Eric Hsiao-Kuang Wu', 'Gen-Huey Chen']
A Decentralized MAC Protocol for Unfairness Problems in Coexistent Heterogeneous Cognitive Radio Networks Scenarios With Collision-Based Primary Users