Research On Cooperation Relay And Power Allocation In Cognitive Radio Networks

To improve spectrum utilization, cognitive radios (CRs) have recently attracted considerable interest in the wireless communication. There are three well known approaches for the cognitive transmission, namely the overlay, the underlay and the interweave approach. In our study, the interweave approach is applied, that is, secondary users (SUs) transmit in the spectrum gaps that are not in use by primary users (PUs), while the spectrum portions where the primary system is active are prohibited for cognitive transmission. The available spectrum for SUs with different location is heterogeneous, dis-contiguous, changing due to the dynamic traffic demands and randomly accessing the system spectrum of PUs. To satisfy a certain traffic demand, some SUs are spectrum-abundant, whilst those with less available spectrum will be spectrum-short. The resource unbalance in CR networks is severer than in traditional wireless networks. However, the unbalanced spectrum usage in CR networks has not drawn much attention before. In this dissertation, the unbalanced spectrum usage and power allocation algorithms are analyzed by using a cooperation relay in the uncertain cognitive setting. The main issues of this paper are as follows:Chapter 1 introduces the background and significance of study about the cooperation relay and power allocation in cognitive radio networks and the structure of the dissertation.Chapter 2 introduces the definition, key technologies and Standardization of cognitive radio briefly.In chapter 3, an adaptive unbalanced spectrum usage (AUSU) scheme is firstly proposed according to the different relationships of the spectrum pools belonging to different SUs. To further enhance the spectrum efficiency, the subcarrier pairing of the spectrum pools is considered. Moreover, the optimal power allocation problem is formulated under the total power constraint based on the presented spectrum usage scheme and perfect channel state information (CSI). Simulation results show the proposed scheme is very effective.In chapter 4, the AUSU scheme based on the cooperation relay is further optimized. In the uncertain setting, where the available spectrum of different SUs is changing and dis-contiguous and, the CSI at the SUs' transmitter is imperfect, a minimum power consumption algorithm based on the AUSU scheme is proposed while the expected data rate and the bit-to-error ratio (BER) are maintained at a desired level. With some simplifications, the problem is cast into a convex optimization problem which is able to use the past CSI. Numerical results show that the proposed AUSU scheme and the minimum power consumption based on AUSU scheme are feasible and can obtain remarkable performance gains.Chapter 5 summarizes the dissertation and points out the directions for further study.