We provide a broad look at the field of limited feedback in wireless communication.We review works of limited feedback with various combinations of single antenna,multiple antenna,single-user and multiuser technology and provide a synopsis of the role of limited feedback in wireless communication systems.We also study how the feedback rate can be minimized without losing the gains due to adaptive transmission and multiuser diversity.It seems that the best possible feedback scheme is not invented yet.As another conclusion is that there are still many issues to study before the scheme can be used in practice.
In order to better assess the performance of wireless communication systems,it is desirable to produce multiple Rayleigh fading envelopes with specified correlations.In this paper,we analyze theoretically a procedure which generates correlated Gaussian random variables from independent Gaussian random variables and give a physical explanation for the limitation of this procedure.Then,based on some uncorrelated Rayleigh fading envelopes,a simple but efficient procedure for generating an arbitrary number of cross-correlated Rayleigh fading envelopes is proposed.Simulation results and computational complexity analysis are presented,which show that the proposed method has some advantages,such as high accuracy,low computational complexity and easy implementation,over the conventional simulation method.
In wireless communications systems with time-division duplex (TDD) deployment, channel reciprocity and symmetric interference between transmitter and receiver sides are two widely-adopted assumptions for the design of optimal adaptation transmission mode. However, in practice, there is an undesirable but non-negligible effect, namely the asymmetric interference, that makes the assumptions no longer valid. In this paper, a simple closed-loop feedback method of compensating interference asymmetry in TDD multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) system is proposed. The system makes the estimated interference at transmit-side be able to track the instantaneous receive-side interference dynamically. The proposed method maintains constant frame error rate (FER) by adopting adaptive modulation coding (AMC) and power loading. The final simulations have verified the effectiveness of the new method.
An optimal linear precoding scheme based on Particle Swarm Optimization(PSO),which aims to maximize the system capacity of the cooperative transmission in the downlink channel,is proposed for a multicell multiuser single input single output system.With such a scheme,the optimal precoding vector could be easily searched for each user according to a simplified objective function.Simulation results show that the proposed scheme can obtain larger average spectrum efficiency and a better Bit Error Rate(BER) performance than Zero Forcing(ZF) and Minimum Mean Square Error(MMSE) algorithm.
