Distributed Algorithm for Robust and Interference Free Topology in Cognitive Radio Networks
Ram Narayan Yadav, Rajiv Misra, Ayush Jain · 2017
The connection between two secondary users (SUs) in cognitive radio networks (CRNs) is not only determined by their transmission power and distance, it also depends on the availability of a common channel for both SUs to open it for communication. Due to dependency on channel availability, communication in CRNs is more challenging than traditional wireless networks. A CRN is said to be connectable if there exists a channel assignment under which all the SUs are connected by either bidirectional link or bidirectional path. In CRN, each SU is equipped with a number of antennas which is the maximum number of channels that it can open simultaneously, known as antenna constraint. As each SU has a limit on the maximum number of channels it can open simultaneously, the network may not be connectable. But, it is desirable to connect the largest subset of SUs when all the SUs of a given CRN can not be connected satisfying antenna constraint while minimizing severe interference introduced due to the nearby transmissions among SUs on the same channel. In this paper, we propose a distributed topology control algorithm with message complexity O(n2), which aims to connect the largest subset of SUs with robustness constraint (the network will not be partitioned when any primary user reclaims channel) and ensures conflict free transmissions among SUs, where n is the number of SUs. To address this NP-hard problem, we combine both topology control and channel assignment phase. In topology control phase, a network subgraph with bounded degree is derived with satisfying antenna resource constraint. In channel assignment phase, we utilize graph coloring algorithm to ensure conflict-free property. To the best of our knowledge, this is the first attempt to develop a distributed topology control algorithm when a given CRN is not connectable.