Design and analysis of wireless communication systems with limited CSIT feedback.

摘要

In the past decade, wireless communication industry grows tremendously and improve our life dramatically. Nowadays, as 3G systems such as WCDMA, CDMA2000 and TD-SCDMA become mature and goes into business, people start to concentrate on the reach of the next generation wireless communication systems. Next generation wireless communication systems are expected to provide high data rate and robust transmission so as to support new applications like high quality multimedia services and high speed data transfer. To meet the demands, we have to increase the operation band and/or increase the spectrum efficiency. Since spectrum is a precious resource in wireless communications, a number of new technologies are developed to enhance the spectrum efficiency such as multiple-input multiple-output (MIMO), cross layer scheduling, orthogonal frequency division multiplexing (OFDM), joint source channel coding (JSCC) etc. Most of these technologies require channel state information at the transmitter (CSIT) to enhance the performance. However, perfect CSIT is hard to obtain in practice. In FDD systems, only a limited number of bits (e.g. 6 bits for WiMAX [1]) can be allocated to carry the CSIT feedback, namely the limited feedback. Moreover, the feedback CSIT may not be error free due to the feedback channel noise. Hence the efficient utilization of the limited feedback bits and the robustness of the feedback design become important.;In this Thesis, we focus on the following problems related to the design and analysis of wireless communication systems with limited CSIT feedback:;Optimal feedback design for MIMO-OFDM systems: We first consider error free limited feedback and propose a systematic design framework for MIMO-OFDM systems on frequency selective channels. We formulate the design problem into the classical vector quantization problem with a modified distortion metric. We find that with a small number of bits for CSIT feedback, there is significant capacity gain in the MIMO-OFDM systems.;MIMO Joint Source Channel Coding (JSCC) with Limited Feedback: In nonergodic channels where ergodic capacity cannot be achieved or in the applications where large delay can not be tolerated, Shannon's source-channel separation theorem does not hold and the optimal performance (end to end distortion) requires a joint optimization of source and channel coding (JSCC). We shall study the system performance with error free limited feedback from this new angle of view. We focus on the design and asymptotic performance analysis of joint source channel coding for MIMO channels with limited CSIT feedback. We show that with a small number of feedback bits, the achieved distortion is already close to the optimal distortion with perfect CSIT.;Capacity of Fast Fading MIMO Channels with Noisy Limited Feedback: We consider noisy limited feedback on MIMO system over fast fading channels where ergodic capacity can be achieved. We propose two robust limited feedback designs for MIMO adaptation and find that for large number of feedback bits Cfb, the MIMO capacity loss (due to noisy feedback) of the proposed robust design scales like O&parl0;Pe2-C fbt+1&parr0; for some positive integer t. Hence, the penalty due to noisy limited feedback in the proposed robust design approaches zero as Cfb increases.;Adaptation for Slow Fading MIMO Channels with Noisy Limited Feedback: We consider noisy limited feedback on MIMO system over slow fading channels in chapter 6. To take into consideration of the potential packet errors, we optimize the system goodput (b/s/Hz successfully delivered to the receiver) with respect to a general model of limited feedback error. We show that the codebook design that maximizes the system goodput can be converted to an equivalent "maximin" problem. Simulation results demonstrated the importance of taking the potential CSIT errors into the limited feedback design for robust performance in both cases.;Multi-User SDMA Systems with Noisy Limited CSIT Feedback: We consider spatial-division multiple-access (SDMA) systems with one multiple antenna base station and a number of single antenna mobiles under noisy limited CSIT feedback. We proposed a robust noisy limited feedback design for SDMA systems. The solution consists of a real-time robust SDMA precoding, user selection and rate adaptation as well as an offline feedback index assignment algorithm. The index assignment problem is cast into a Traveling Sales Man problem (TSP). Based on the specific structure of the feedback constellation and the precoder, we derive a low complexity but asymptotically optimal solution. We show that the average system goodput scales as O&parl0;nT1 -3nT -1 (Cfb - log2(N n))) and O (nT · log2 P ) in the interference limited regime (Cfb (nT - 1) log2 P + log2 Nn) and noise-limited regime respectively. Hence, despite the noisy feedback channel, the average SDMA system goodput grows with the number of feedback bits in the interference limited regime while in noise limited regime increases linearly with the number of transmit antenna and the forward channel SNR (log2 P).