Adaptive Power Allocation And Subcarrier Paring In Df Mimo-ofdm Relay System

The appearance of relay based wireless communication systems have solved a lot of problems that existed in the traditional wireless communication systems, such as a lack of expansibility and robustness. In this communication system, the source terminal transmits the information to the destination terminal with the help of relay, which can enlarge the communication area. That is a good way to realize the reliable transmission and extend the coverage area. So relay communication technology, widely regard as the most promising solution, has attracted much attention for its advantage.In order to optimize the system performance, the limited communication resource should be limited efficiently. So the adaptive resource allocation is a practical technology to optimize the system performance. Different from the traditional single-hop communication, the resource allocation in relay communication system should take the speciality of each hop into account.In broadband wireless communication system, Orthogonal Frequency Division Multiplexing (OFDM) which transforms the wide band frequency selective fading into a set of independent parallel flat fading channel, will be widely adopted in the future communication system. The combination of OFDM and relay system can solve problem which is caused by frequency selective fading, but the resource optimization becomes more complicated in OFDM based relay wireless communication system where the subcarrier and power allocation are required be jointly allocated to each hop, so that the system performance can be optimized.In this paper, the power allocation schemes in relay system and the system combine with relay is concluded firstly, then a two hop MIMO-OFDM relay system is considered with a source, a decoded-and-forwarded (DF) relay and a destination, where each terminal is equipped with multiple antennas. Firstly, with the goal of maximizing the system capacity, a suboptimal subcarrier power allocation algorithm under the total transmits power constraint is proposed. Further, the power allocation of each antenna and subcarrier paring strategy are studied in DF MIMO-OFDM relay system. The power allocated to each subcarrier is derived first based on uniform power allocation to each antenna. In order to further enhance the system capacity, the power allocated to each antenna can be obtained by applying the waterfilling algorithm. The simulation results show that the proposed subcarrier paring algorithm and power allocation strategy for each antenna are effective ways to enhance the relay wireless communication system capacity.