Performance Analysis And Precoding Research For Future MIMO Technology

Multiple-input multiple-output (MIMO) has become one of the key tech-nologies for the fourth generation (4G) mobile communications systems and large-scale deployment of MIMO antennas is also one candidate of enabling technologies for future fifth generation (5G). Through the use of a large ex-cess of base station (BS) antennas over the number of user terminals (UTs), large-scale multiuser MIMO (MU-MIMO) systems can effectively reduce ad-verse effects due to channel variations and inter-user interference, thus bring huge improvements in throughput, spectrum efficiency and energy efficiency. In combination with relay technology, it can be envisioned that both benefits from relay and very large antenna arrays could be obtained. It is fundamental to analyze and evaluate the theoretical performance of relay systems with massive antennas in order to conduct other related researches. Based on the above, this thesis will concentrate on the performance analysis of future MIMO technology as well as relay systems. The main contribution of the thesis is summarized as follows:1. The joint estimation of synchronization impairments, that is, multiple tim-ing offsets (MTOs) and multiple carrier frequency offsets (MCFOs) in a multi-relay network is addressed. Due to the signal superposition, syn-chronization is a complex and challenging task. For achieving timing and frequency synchronization, a simple yet effective estimation method based on the devised training signals is presented by using a constant am-plitude zero autocorrelation (CAZAC) sequence and the maximum like-lihood (ML) criteria. Then, an iterative algorithm is further derived in order to improve the performance associated with the estimation of syn-chronization impairments. The proposed algorithm converts the difficult multiple parameter estimation problem into more tractable sub-problems of estimating many individual impairments pairs for the independent re-lays. Simulations indicate that, the proposed estimator not only reduces computation complexity, but also can asymptotically achieve the mean square error (MSE) for the ideal timing or frequency synchronized case.2. Considering a two-way relay system with massive antennas, two kinds of relay receive detection and transmit precoding matrices are proposed and the asymptotic end-to-end (e2e) signal-to-interference-noise ratio (SINR) of each UT is derived. The results show that the transmit power at each terminal or/and the relay can be scaled down inversely proportional to the number of relay antennas with no performance degradation, that is, relay systems can benefit significantly from the use of very large antenna arrays. Furthermore, the two-way relaying scheme outperforms the one-way relaying scheme. The numerical results corroborate the validity of the derived asymptotic approximation.3. The outage performance of a dual-hop multiple antennas relaying system is investigated by taking into account the co-channel interference (CCI) and additive white Gaussian noise (AWGN) at both the relay and desti-nation. New exact closed-form expressions for the outage probability of the system employing amplify-and-forward (AF) and decode-and-forward (DF) protocols are derived. Numerical results are presented to verify the theoretical analysis.4. The performance of a large-scale MU-MIMO system with AF relaying in the presence of CCI is analyzed. A sufficient tight analytical bound ex-pression on the achievable rate is derived. Also, a large system analysis is performed when the number of relay antennas goes to infinity. It is shown that the achievable rate will saturate to a floor by simply increasing the transmitted power. Notwithstanding, both analytical and simulation results reveal that the system can still be significantly improved by imple-menting more antennas at the relay.5. A single-cell uplink large-scale MU-MIMO system with linear receivers, that is, maximum ratio combining (MRC), zero-forcing (ZF) and mini-mum mean square error (MMSE), is studied. Exact analytical expressions that are valid for any number of BS antennas for the outage probability of all three schemes are derived. The asymptotic outage behavior of the considered system is also examined in the very large antennas regime. Ex-tensive numerical results are presented to verify the theoretical analysis.6. Several linear precoding methods for a single-cell downlink MU-MIMO system are discussed. The average rate per UT and outage probability of four precoding schemes are compared in terms of signal-to-noise ratio (SNR), the number of BS antennas and temporal fading coefficient, re-spectively. Specifically, the effect of regularization factor on regularized zero-forcing (RZF) precoding scheme is analyzed through simulations.