Future wireless communication systems require more and more antennas at the transceiver to improve the achievable rates. Multi-user multiple-input multiple-output (MU-MIMO) technique is regarded as a potential techniq...
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Future wireless communication systems require more and more antennas at the transceiver to improve the achievable rates. Multi-user multiple-input multiple-output (MU-MIMO) technique is regarded as a potential technique to serve large number of users simultaneously to further increase the achievable rates in MIMO systems. If the number of antennas at the transceiver is large, the computational complexity of precoding becomes the bottleneck and a big challenge in MU-MIMO system. In this paper, a simplified QR decomposition with lattice reduction assisted MU-MIMO precodingscheme named S-QR-LR is proposed as a low-complexity MU-MIMO transmission scheme. The simplified QR decomposition method is delicately designed and operated twice for the proposed precodingscheme not only to achieve good performance but also reduce the computational complexity significantly. The proposed S-QR-LR scheme first uses the simplified QR decomposition operation to balance the multi-user interference and the noise. Then, the proposed S-QR-LR precodingscheme utilizes the simplified QR decomposition method again with the assist of lattice reduction to obtain the precoding gain to further improve the performance with low computational complexity. Analytical and simulation results show that the proposed S-QR-LR precodingscheme achieves best performance among the existing precodingschemes, but requires the lowest computational complexity.
We analyze the downlink multiuser precoding of massive multiple input multiple output (MIMO) system, where the base station (BS) has ideal channel state information (CSI) and adopts three types of different linear pre...
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We analyze the downlink multiuser precoding of massive multiple input multiple output (MIMO) system, where the base station (BS) has ideal channel state information (CSI) and adopts three types of different linear precoding schemes, i.e., maximum ratio transmission (MRT), zero-forcing (ZF), and minimum mean squared error (MMSE). Under a Rayleigh fading channel, we attain the exact expressions on the achievable rate for these three precodingschemes. Moreover, we provide several insights on the achievable rates and reveal the relation of the number of BS antennas, the number of users, and the input signal-to-noise ratio (SNR) with the achievable rates respectively. It is found in general that the achievable rate increases with the number of BS antennas and the input SNR. To be more specific, the MRT precodingscheme is much inferior to the ZF and MMSE precodingschemes and tends to be at a fixed rate at the high SNR case. On the contrary, the MRT precodingscheme outperforms ZF precodingschemes at the low SNR case. Moreover, the total achievable rate always does not increase with the number of users and the optimal number of users always exists for the ZF and MMSE precodingschemes.
A precodingscheme for physical layer security of multiple-input single-output (MISO) wiretap channel with spatial correlation is designed. Quality-of-service (QoS) of the link is defined in terms of upper bounds on a...
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A precodingscheme for physical layer security of multiple-input single-output (MISO) wiretap channel with spatial correlation is designed. Quality-of-service (QoS) of the link is defined in terms of upper bounds on average symbol error rate function at Bob (legitimate user) and Eve (illegitimate user). Specifically, two problems are considered. First, a precoder matrix is designed to minimise the average transmitted power subject to QoS requirements at Bob and Eve. Next, we propose two algorithms to minimize QoS of illegitimate party for a given reliability level, depending on whether main user link has no correlation or is fully correlated. Our result for uncorrelated case demonstrate that by increasing the allocated power, main user can increase secrecy level up to an optimum point above which both legitimate and illegitimate receivers experience adequate QoS in their links. In fully correlated case, the problem is identified as an instance of concave minimisation over a polytope, and optimum power allocation is obtained via the widely known vertex enumeration algorithm. In both cases, our simulations validate the analysis significantly. The results confirm that linearprecoding is able to trade average power against minimum achievable Eve performance.
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