Research On Device-to-Device Communication In Multiuser MIMO Wireless Networks

With the rapid popularization of intelligent terminals and the explosive growth of network communication capacity,the demand for the development of new technology of wireless communication is more and more clear and urgent.Device-to-Device(D2D)communication emerges as the times require.With D2D communication,proximity users in a cellular network can communicate directly to each other without going through the base station.D2D communication has advantages as follows: it can increase spectral efficiency and data transmission rate,reduce the transmission power of the mobile terminal,prolong the battery life,etc.However,the existence of D2D communication also makes the interference environment more complex.Therefore,it is important to manage the interference effectively and design the user’s communication mode reasonably.The situation that in a MIMO system with D2D communication has been studied in this thesis,where D2D users share the spectrum resources with the cellular users and have the same priority.First,the same problem as [1] has been studied in this thesis,to maximize system sum-rate when users use both base station forwarding mode and D2D communication mode.Since the sum-rate maximization problem in MIMO system has been proved to be NP-hard,some relaxation are needed.The original problem is divided into two separate sub-problems by some transformation.Based on the block coordinate descent method,an iterative algorithm is designed.At each iteration of this method,a single block of variables is optimized,while the remaining variables are held fixed.The complexity and convergence analysis of the algorithm are given next,also the simulation results.However,in the practical application scenario,there are some cases where the distance between user-pairs is relatively too far or the channel states of the direct link is poor.Therefore,a more flexible sum-rate maximization algorithm based on mode selection has been designed,which jointly optimizes user’s communication mode and transmitter.While excessive D2D users will increase the overhead of the system with a lot of feedback information,thus sparse optimization is added to the problem to limit the number of D2D user-pairs.Since the original problem can not be solved directly,some approximate processing has been done to design an iterative updating algorithm,in which the problem is divided into three sub-problems and is updated alternately.The simulation results show that the system sum-rate achieved by the algorithm is better than all by base station forwarding communication or D2D mode communication,and the validity of the algorithm is illustrated by comparing with the random mode-selection of D2D users.