Research On Power Allocation Algorithm With Imperfect Feedback Information For MIMO Systems

Multiple-Input Multiple-Output (MIMO) system is capable of improving the performance ofwireless communication systems. Vertical-Bell Laboratories Layered Space Time (V-BLAST) is akind of space-time transmission technique based on MIMO. The ideas of Turbo codes combined withV-BLAST are Turbo-BLAST system, and the iterative detection at the receiver can improve the biterror rate (BER) effectively. In addition, the adaptive transmit power allocation algorithm can also beapplied to multi-antenna system to enhance the BER performance. In this paper, V-BLAST detectionscheme, Turbo-BLAST iterative detection scheme and Turbo-BLAST double iterative detectionscheme are researched. And for a V-BLAST system with imperfect information caused by channelfeedback delay, the adaptive transmit power allocation algorithms are proposed when zero forcing (ZF)detection and minimum mean square error (MMSE) detection schemes are adopted, respectively. Themain work of this paper is listed as follows:1. Inspired by the ideas of bit interleaved coded modulation with iterative decoding (BICM-ID), amodified Turbo-BLAST double iterative detection algorithm is proposed which is based on theouter iterative detection between the detector and the decoder, and the inner iterative decodingbetween the demodulator and the decoder. Compared with the traditional Turbo-BLAST iterativedetection scheme, the proposed algorithm can improve the BER performance further.2. The suboptimal and optimal adaptive transmit power allocation algorithms based on ZF detectionare proposed to minimize the BER performance for V-BLAST system with channel feedbackdelay. The distribution of the instantaneous signal to interference plus noise power ratio (SINR)is deduced by system modeling and performance analysis. The system BER can be computedusing mathematical transformation. At the transmitter, with the total transmit power constraint,the suboptimal and optimal transmit power schemes can be presented by using the Lagrangemultiplier method and Newton iteration technique, respectively. The computational complexityand performance analysis between the proposed power allocation algorithms is also given.Compared with the equal power allocation algorithm, the presented schemes can achieve thebetter BER performance.3. The adaptive transmit power allocation algorithm based on MMSE detection is proposed forV-BLAST system with channel feedback delay. Different from the ZF detection, it is verydifficult to deduce the distribution of the SINR directly. The solution to the presented scheme is to decompose the SINR into two independent parts, and then deduce the conditional probabilitydensity function (PDF) of the SINR. The system BER can be computed using mathematicaltransformation. At the transmitter, with the total transmit power constraint, the transmit powerallocation matrix can be computed by using the Lagrange multiplier method. Compared with theequal power allocation algorithm and the transmit power allocation algorithm based on ZFdetection, using the proposed transmit power allocation algorithm can achieve the better BERperformance and the iterative detection at the receiver can improve the BER performance further.