Massive MIMO Wireless Transmission With Pilot Reuse

In order to meet the exponentially growing demand in wireless services, future wireless communication systems require breakthroughs in several aspects includ-ing, e.g., wireless physical layer transmission. Massive multiple-input multiple-output (MIMO) transmission, which employs a large number of antennas at the base station (BS), can significantly improve the spectral efficiency and energy efficiency, and is believed to be a promising technology for future wireless commu-nication systems. Acquisition of channel state information (CSI) is the foundation for wireless transmission. Up to now, most of the works on massive MIMO trans-mission assumes periodically inserted orthogonal pilot signals for CSI acquisition, and the corresponding pilot overhead scales linearly with the number of anten-nas. In medium to high mobility scenarios, the heavy pilot overhead decreases the system efficiency greatly and can become the system bottleneck. For realistic outdoor wireless propagation environments, most of the channel power is usually concentrated in a finite region of delays and/or angles due to limited scattering. With this channel property, pilot reuse is feasible and beneficial for reducing the pilot overhead. Motivated by these reasons, we investigate massive MIMO wireless transmission with pilot reuse in this dissertation. The major results and contri-butions of this dissertation are listed as follows:Firstly, we propose pilot reuse (PR) in the angle domain for massive MIMO wireless transmission over flat fading channels. Based on a physically motivated channel model, we investigate spatially correlated Rayleigh fading channels. We show that when the number of BS antennas tends to infinity, eigenvectors of the channel covariance matrix are determined by the BS array response vectors, while eigenvalues depend on the channel power angle spectra (PAS), which reveals a relationship between channel spatial correlations and channel power distribution in the angular domain. With this channel model, we show that sum mean square error (MSE) of channel estimation can be minimized provided that channel an-gle of arrival (AoA) intervals of the user terminals (UTs) reusing the pilots are non-overlapping, which shows feasibility of PR over spatially correlated massive MIMO channels with constrained angular spreads. Regarding that channel estima-tion performance might degrade due to PR, we further investigate robust wireless transmission. We develop the closed-form robust multiuser uplink receiver and downlink precoder that minimize sum MSE of signal detection, and reveal a dual-ity between them. Subsequently, we investigate pilot scheduling under minimum MSE of channel estimation and signal detection criteria, and show that both cri-teria can be optimized provided that channel AoA intervals of the UTs reusing the pilots are non-overlapping. Motivated by this optimal condition, we propose a low complexity pilot scheduling algorithm which relies on the channel statistics only. Simulation results show that the proposed PR approach provides significant performance gains over the conventional orthogonal pilot approach in terms of net spectral efficiency.Secondly, we propose PR in the angle-delay domain for wideband massive MIMO transmission employing orthogonal frequency division multiplexing (OFD-M) modulation. Based on a physically motivated channel model, we establish a relationship between the space-frequency domain channel covariance matrix (SFC-CM) and the channel power angle-delay spectrum for massive MIMO-OFDM. We show that when the number of BS antennas is sufficiently large, the eigenvectors of the SFCCMs for different UTs tend to be equal, while the eigenvalues depend on the respective channel power angle-delay spectra, which reveals the channel sparsity in the angle-delay domain. With this channel model, we then investigate CSI acquisition, including channel estimation and channel prediction, for massive MIMO-OFDM with adjustable phase shift pilots (APSPs). We show that CSI ac-quisition performance in terms of sum MSE can be minimized if the UTs’channel power distributions in the angle-delay domain can be made non-overlapping with proper phase shift scheduling. A simplified pilot phase shift scheduling algorithm is developed based on this optimal channel acquisition condition. The performance of APSPs is investigated for both one symbol and multiple symbol data models. Simulation results demonstrate that the proposed APSP approach can provide substantial performance gains in terms of achievable spectral efficiency over the conventional phase shift orthogonal pilot approach in typical mobility scenarios.Finally, we propose beam division multiple access (BDMA) transmission with per-beam synchronization for millimeter-wave (mmW)/Terahertz (THz) massive MIMO. We introduce a physically motivated beam domain channel model for mas-sive MIMO. We show that when both the numbers of antennas at the BS and UTs are sufficiently large, the beam domain channel elements tend to be statistically uncorrelated and the respective variances depend on the channel PAS, meanwhile envelopes of the beam domain channel elements tend to be independent of time and frequency. Motivated by the beam domain channel properties, we then propose per-beam time and frequency synchronization for mmW/THz massive MIMO. We show that both the effective delay and Doppler frequency spreads of wideband massive MIMO channels with per-beam synchronization applied are reduced by a factor of the number of UT antennas compared with conventional antenna domain synchronization approaches. Subsequently, we apply per-beam synchronization to BDMA. We investigate beam scheduling to maximize the achievable ergodic rates for both the uplink and the downlink BDMA with limited numbers of radio fre-quency chains, and we develop a greedy beam scheduling algorithm based on the beam domain channel statistics. Simulation results show that for BDMA trans-mission in typical mobility scenarios, compared with conventional antenna domain synchronization, the proposed per-beam synchronization can significantly reduce the multipath effect and Doppler effect, improve the performance of CSI acquisi-tion with PR and wireless transmission, and provide support for UTs with mobility over mmW/THz channels.