A Cooperative Multiple Access Scheme Based On Lattice Reduction

Cooperative multiple access is a hot researching point and arouses people’s much interest in recent years.Cooperative communication is in the style of the cooperation by the nodes and form a virtual MIMO system.It can take fully use of the MIMO spatial diversity gain against the multipath fading and improve system performance.Multiple access is one of the key technology in mobile communication to solve the problem of the connection in multi-channel in cellular networks.Introducing the advantages of the cooperative communication into the multiple access system can improve the diversity gain and multiplexing gain of the system.Lattice Reduction is based on the lattice theory,and has been widely used in the field of information area.The goal of the theory is to find a short routhly orthogonal vector when input an integer lattice basis.There are many algorithms can realize the theory and the common one is the LLL algorithm.Running time of the algorithm is at least around the exponential lattice.This algorithm was originally applied in the detection of the MIMO system.The receiver is equivalent to turn the channel matrix to roughly orthogonal and obtains good results.In this article,lattice reduction is applied to cooperative multiple access (CMA) system and propose a new cooperative multiple access scheme. This scheme turn the transmission process into a virtual MIMO system.We code in the source and deal the signals with the LLL algorithm first and then decode using the MMSE-SIC algorithm. We analysis the feasibility of this program from the bit error rate of the system and the complexity of the algorithm and verify the conclusion by the computer simulation. Finally, demonstrate the scheme can get the optimal DMT (diversity- multiplexing tradeoff).