Design and experimental evaluation of C-MAC solutions for heterogeneous spectrum sharing

Cognitive medium access control (C-MAC) protocols employ several mechanisms that deal with the heterogeneity of a coexistence scenario with multiple wireless systems in the same band. The underutilized channels of some bands such as the TV white spaces (TVWS), are valuable and tangible resources within the congested spectrum for providing new wireless services on licensed and license-exempt basis. This paper presents a new C-MAC protocol based on a sequential frequency hopping scheme with a proactive spectrum sensing phase for opportunistic spectrum sharing. The proposal has been implemented over a software defined radio (SDR) testbed and experimentally assessed in indoor radio-propagation conditions. In addition, the performance of the proposed protocol has been compared with other C-MAC schemes, also implemented over the SDR-based framework. Performance results in terms of free-collision channel occupation rate and transmission throughput show that the proposed architecture outperforms other C-MAC protocols in scenarios with low and medium density of cognitive users per available channel. In contrast, experimental results have shown that partially observable Markov decision process (POMDP)-based solutions are more suitable when the available channels are fewer than the cognitive links.