Resource Allocation For Multi-user Systems Based On OFDMA

With the rapid development of life quality, people’s requirement for communication service becomes higher and higher, which the existing communication system has been unable to meet. Thus researchers are working on new communication technologies. Cooperative relay communication sufficiently utilizes broadcast characteristics of wireless medium and flexibly combines with other technologies, which increases the coverage and robustness while improving the reliability and transmission rate. Power line communication is based on the existing power line networks without laying extra wires, so that it can provide wide coverage, low cost, stability, etc. However, the existing power line networks are not originally designed for communication, where there is still multi-path, frequency selectivity, impedance mismatch problems. OFDMA can effectively resist multi-path and frequency selectivity, and also conveniently combine with dynamic resource allocation to utilize spectrum resources reasonably. That is why it is widely used in cooperative relay communication and power line communication systems. Therefore, this paper investigates resource allocation problems for multi-user cooperative relay communication and power line communication systems based on OFDMA. The innovations are outlined as follows:(1) For the joint optimization problem involving subcarrier assignment, relay selection and power allocation in multi-user cooperative relay communication systems, a resource allocation algorithm based on improved subcarrier assignment is proposed. Firstly, according to the equivalent channel gains, the cooperative transmissions are equal to virtual direct transmissions. Then with the principle of best channel conditions and target rates of users, the subcarrier assignment and relay selection are achieved by a method of subcarriers selecting users, which effectively avoids each subcarrier assigned to multiple users and reduces computational complexity.(2) For the power minimization problem in multi-user cooperative relay communication systems, a resource allocation algorithm based on subcarrier pairing is proposed. Firstly, according to the average channel gain and target rates of users, the assignment of subcarrier numbers is addressed. Then the optimal subcarrier allocation in each time slot is achieved by respectively subcarrier pairing in the cooperative transmissions and virtual pairing in the direct transmissions, which can minimize the total transmission power while jointly conducting subcarrier pairing and assignment at the same time.(3) For the resource allocation problem with proportional rate constraints in multi-user power line communication systems, a resource allocation algorithm based on bit exchange is proposed. First of all,equal bit allocation is conducted according to the target rates of users. Then the remaining bits are allocated to the subcarriers with minimum power consumption. Finally, optimal power allocation is achieved by adjusting bits among subcarriers under the condition that each user meets its target rate.