Research On Power Allocation Algorithm Withimperfect CSI For V-BLAST Systems

On the basis of MIMO transmission technique, V-BLAST structure can exploit high MIMO channel capacity and high efficiency. By applying the OFDM technique to V-BLAST structure, the system could effectively combat multipath fading and alleviate the inter symbol interference. The power allocation scheme can realize adaptive transmit power adjustment according to the dynamic change of wireless channel environment. In this thesis, with the imperfect channel state information including the channel correlation, estimation error and channel feedback delay, the power allocation algorithm is well investigated for V-BLAST and V-BLAST OFDM system which can achieve better system performance and provide a basis for further practical application. The main contents in this thesis are summarized as follows:1. The approximate expression of the sub-stream’s BER for V-BLAST system is derived with interference cancellation of ZF and MMSE detection which ignoring the propagation error. Meanwhile the power allocation scheme which based on Lagrange multiplier method and equal SINR method is investigated with perfect CSI. Then simulation results prove the validity of the theoretical results and the power allocation schemes.2. A new effective transmit power allocation algorithm is proposed that aims at minimize BER performance for a correlated V-BLAST system considers the channel estimation error based on ZF and MMSE detection. However the BER performance of V-BLAST system degrades with the increase of channel correlation, then a decorrelation method is proposed according to the CSI to improve the system performance. The performance analysis of the proposed power allocation algorithm is also given. Compared with the traditional equal power allocation scheme, the presented algorithm in combination with decorrelation method can achieve better BER performance.3. The adaptive transmit power allocation algorithm is proposed for V-BLAST system with channel estimation error and channel feedback delay based on MMSE detection. The conditional probability density function(PDF) of the SINR and the instantaneous BER expression is deduced. At the transmitter, under the total transmit power constraint, the power allocation matrix can be computed to minimize BER performance. Compared with the equal power allocation scheme, using the proposed transmit power allocation algorithm can achieve better BER performance and more practical.4. The V-BLAST OFDM is introduced which considers the channel correlation and estimation error. A new effective transmit power allocation algorithm is proposed that aims at minimize BERperformance. Considering the impact of the channel correlation, then a decorrelation method is employed. Simulation results show that the V-BLAST OFDM system can combat ISI in broadband frequency selective fading channel and achieve a significance improvement in system performance by combined with the TPA scheme and the decorrelation method.