| With the increasing development of wireless communication technology and the wider use of smart mobile devices, the future mobile communication system requires the system transmission rate to improve thousands of times of the present system. With the potential large gains in spectral efficiency and energy efficiency, massive MIMO is one of the key technology of the next generation mobile communication system. In order to reduce the receive complexity, this dissertation investigates massive MIMO uplink reception theory and method.Firstly, focus on the significantly high complexity of MMSE(Minimum Mean Square Error) detection in massive MIMO systems, we propose the simplified MMSE iterative receiver of massive MIMO systems. Based on the traditional MMSE iterative receiver, using the approximate and with the property that the chan-nel matrix of massive MIMO systems is approximately orthogonal, we simplify the matrix to be inversed in MMSE detection with its diagonal matrix. Then we define the metric of computational complexity and compute the complexity of traditional MMSE iterative receiver and the proposed simplified iterative receiv-er. Simulation results show that, compared to the traditional SISO(Soft-Input Soft-Output) MMSE detection based iterative receiver, the proposed simplified MMSE iterative receiver can reduce the computational com-plexity significantly.Then, we propose the factor graph based receiver for massive MIMO systems in beam domain. With the understanding of the factor graph and sum-product algorithm, we discuss the theory of message passing on factor graph and the BP(belief propagation) algorithm and the AMP(approximate message passing algorithm). And then, we study the power distribute property of massive MIMO systems in beam domain from three aspects, such as system configuration and system model and numerical simulation results. System modeling, followed by beam selection scheme and detection algorithm description, we detailed the factor graph receiver based on the beam domain property for massive MIMO systems. Simulation results demonstrate that in massive MIMO systems the proposed beam domain factor graph based receiver has much lower complexity than traditional MMSE receiver, without much loss in performance.Finally, as the complexity of per-tone detection in OFDM(Orthogonal Frequency Division Multiplexing) transmission system is too high, with the frequency characteristics of MIMO-OFDM systems, we propose a fast method to calculate the MMSE detection matrix. First of all, we define the MMSE detection matrix and briefly introduce the theory of computing the MMSE detection with QR decomposition, which is referred to MMSE-QR decomposition. Then, we study the method of the interpolation in frequency domain for massive MIMO-OFDM systems and establish the channel model. And then, we detailed the BF(brute force) per-tone MMSE-QR decomposition algorithm and the MMSE-QR decomposition with single interpolation and multiple interpolations, respectively. Complexity analyse show that, the complexity of the MMSE-QR de-composition algorithms with interpolation is much lower than the complexity of the BF per-tone MMSE-QR decomposition algorithm. |
