A Joint Relay Selection, Spectrum Allocation and Rate Control Scheme in Relay-Assisted Cognitive Radio System

Cognitive Radio (CR) is proposed as a promising means to utilize the spectrum more efficiently. However, in cognitive radio system, how to achieve the users´ QoS requirements is a challenge. To solve this problem, cooperative relay transmission has been proposed as a powerful approach. In the relay-assisted CR system, users can not only obtain required service directly from the Cognitive Base Station (CBS), but also select other nodes as its relay and receive data with the relay cooperative transmission. This paper mainly focuses on how to allocate resource appropriately to fulfill users´ call-drop and datarate demands, and meanwhile increase the meaningful system throughput in the CR relay system. At first, a system model with Joint Relay selection, Spectrum allocation and Rate control (JRSR) is built and the problem is formulated. Then, a three-stage heuristic algorithm is proposed to address the JRSR problem and a suboptimal solution is found. In the three-stage JRSR scheme, the throughput directly from the CBS is maximized first, then some adjustments and supplements are made to achieve the media stream users´ service demands with priority as much as possible. Simulation results illustrate that our proposed JRSR scheme is effective on fulfilling the users´ call-drop and datarate demands, and it also performs well on increasing the meaningful system throughput.