The Algorithm Research Of Dynamic Resource Allocation In Cooperative OFDM Communication System

Cooperative communication technology, which could set up virtual antenna array (VAA) between multi-nodes in wireless network, so that some small mobile terminals can get diversity effect without deploying multi-antennas, has been rapidly developed. Orthogonal Frequency Division Multiplexing (OFDM) technology is well known for high spectral efficiency and greatly reducing Inter Symbol Interference. Therefore, the application of OFDM technology and cooperative communication technology in wireless network, which is called cooperative OFDM (C-OFDM) technology, takes the both advantages.However, due to the frequency selectivity of channels which means that each sub-carrier undergoes different channel fading, effective resource allocation schemes in cooperative OFDM system could get additional Quantity of Service (QoS) except above advantages. In this paper, the resource allocation algorithm for single relay cooperative OFDM system is investigated, which was based on the radio channel characteristics, diversity technology and the basic principles of cooperative communication.In the system with a relay which decodes and forwards (DF) the received data and with Binary Differential Phase Shift Keying (BDPSK) modulation, the optimal power allocation algorithm to minimize Average Bit Error Rate (ABER) is researched according to the convex optimization theory and its KKT (Karush-Kuhn-Tucker) conditions and the dichotomy searching process of power is proposed. In this algorithm, the system firstly allocates power to each sub-carrier pair, and then allocates power in every sub-carrier pair. In addition, the sub-carrier pairing algorithm based on sorting method is proposed. Simulation results show that the cooperative communication system can significantly reduce the Average Bit Error Rate of receiver, and the proposed power allocation algorithm has a better transmission performance.In the system with a relay which amplifies and forwards (AF) the received signal and multiple users which share sub-channels by employing Orthogonal Frequency Division Multiple Access (OFDMA) technology, the step-by-step resource allocation algorithm based on proportional fairness requirements among users is proposed according to treating the sum of logarithm of each user’s transmission rate as the optimization objective function. Firstly, the system allocates sub-carriers to every user in the condition of equal power allocation according to the proportional fairness of users. Then according to proportional fairness and the number of sub-carrier pairs of all users, the system allocates power to every user, and each user allocates power to each sub-carrier pair by making use of water-filling algorithm. Finally, the system completes the final power allocation according to the power allocation algorithm of sub-carrier pair. Simulation results show that the algorithm improves system’s spectral efficiency while ensuring the fairness of users.