A Novel Approach To Energy Efficient Mimo Cognitive Radio Networks

Cognitive radio, with the capability to flexibly adapt its transmission or reception parameters, has been proposed as the means for unlicensed secondary users (SUs) to dynamically access the licensed spectrum held by primary users (PUs) in order to increase the efficiency of spectrum utilization[1]. Recently, a new paradigm termed Cooperative Cognitive Radio Networks (CCRNs) has been advocated in CCRN, PUs may select some SUs to relay the primary traffic cooperatively, and in return grant portion of the channel access time to the SUs. By exploiting cooperative diversity, the transmission rates of PUs can be significantly improved. SUs, being the cooperative relays, as a consequence obtain opportunities to access the channel for their own data transmissions[1]. MIMO-CCRN framework for cooperation among SUs and PUs by exploiting MIMO antennas on SUs’ transceivers. MIMO is a physical layer technology that can provide many types of benefits through multiple antennas and advanced signal processing. Multiple independent data streams can be transmitted or received over the MIMO antenna elements. Furthermore MIMO can also realize interference suppression. Through beam-forming, a MIMO receiver can suppress interference from neighboring transmitters and a MIMO transmitter can null out its interference to other receivers. Given its potential, MIMO has been adopted in next-generation WiFi, WiMax, and cellular network standards. However researchers have not explored how to take advantage of the MIMO techniques in the context of CCRN. There is an ever-increasing demand for spectrum for emerging wireless applications and there is a spectrum shortage for the wireless applications. In view of this, the Federal Communications Commission (FCC) has considered making the licensed spectrum available to unlicensed users. This will allow unlicensed users to use the empty spectrum, provided they cause no interference to licensed users. Most radio systems today are aware of the radio spectrum. Cognitive radio is a new research area for wireless communication in which either a network or a wireless node is able to change its transmission or reception parameters to communicate efficiently by avoiding interference with Abstract: the energy-efficient transmissions for multiple-input multiple-output (MIMO) cognitive radio (CR) networks in which the secondary unlicensed users coexist with the primary licensed users. To optimize the time allocations and beam forming vectors for the secondary users (SUs), in order to minimize the energy consumption of the SUs while satisfying the SUs rate requirements and the primary receivers interference constraints. Compared with the traditional MIMO networks, the challenge is that the SUs may not be able to obtain the channel state information (CSI) of the primary receivers. Fortunately, when the SUs are not able to obtain the CSI, the optimal time allocation and the optimal beam forming vectors can be found very efficiently in polynomial-time through a proper Singular Value Decomposition (SVD). When the SUs have perfect CSI, the decomposition based algorithm is guaranteed to find the optimal solution when the secondary system is under-utilized. Simulation results show that the energy-optimal transmission scheme adapts to the traffic load of the secondary system where the SUs are able to decrease the energy consumption and the PUs experience less interference from the secondary system.