Resource Allocation Research In Multiuser OFDM Cognitive Radio Systems

With the rapid development of wireless communication technology, spectrum resources have become increasingly scared. Traditional static spectrum management has caused some of the wireless spectrum is usually under unutilized, which limits the spectrum efficiency. In the recent years, Cognitive Radio was proposed to increase the utilization of the spectrum, to meet the growing demand for wireless communications services. Cognitive radio is an intelligent wireless communication system, able to perceive the external environment; it can learn from the environment and dynamically adjust its internal working condition in accordance with changes in the environment, such as operating frequency, transmit power, modulation methods for effective use of idle spectrum, while avoiding the interference to the licensed users.At present, there are two cases of the use of Cognitive Radio for dynamic spectrum access. One is sharing the unlicensed and opening spectrum bands, such as the WLAN (Wireless Local Area Network) in 2.4 GHz and IEEE 802.16h/g WMAN (Wireless Metropolitan Area Network); the other is accessing the licensed spectrum bands opportunistically. Such as the IEEE 802.22 WRAN (Wireless Regional Area Network), the secondary users dynamically access the licensed digital broadcast spectrum bands. The latter approach involves the spectrum sensing for utilization of licensed bands as well as avoiding creating interference to the licensed users, which are the key technologies and difficulties in Cognitive Radio.In this paper, one of the key technologies——dynamic resource allocation algorithm for dynamic spectrum access in Cognitive Radio system, was deeply researched. First, analysis of resource allocation model and associated algorithms in the traditional multi-user OFDM system was presented and then we smoothly transited to the resource allocation model and associated algorithms in multi-user cognitive radio system, the details are as follows:The QoS-based dynamic resource allocation algorithm in multi-user OFDM cognitive radio system was proposed:we analyzed the allocation model and minimizing transmission power algorithm, minimizing the secondary users＇interference to the primary users and the reduced complexity and tradeoff algorithm between the two which are based on the greedy algorithm. On this basis, we improved the system allocation model, taking into account different QoS requirements:real-time and non real-time services, and studied the maximizing system throughput algorithm based on greedy algorithm. The simulation results showed the relationships among the interference threshold, transmission power and system throughput.Analysis of the differences between proportional allocation and the strange allocation in Jewish Bible "Talmud" on the problem "fortune allocation among the three wives" was presented. Combining the deduction of the allocation approach from three users to the several users, with the features of multiuser OFDM Cognitive Radio systems, the Talmud fair allocation algorithm based on users＇bidding in multiuser OFDM Cognitive Radio systems was proposed in this paper.We also studied the interference reduction issue to the primary user, considering using subcarrier nulling to the subcarriers on both sides of the primary user's band. The simulation results were given on the analysis of zero-bit-loading for zero, one or both two subcarriers on the two sides of the primary user's sub-channel.