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    Exploiting Low Complexity Beam Allocation in Multi-User Switched Beam Millimeter Wave Systems

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    Switched-beam systems offer a promising solution for realizing multi-user communications at millimeter wave (mmWave) frequencies. A low-complexity beam allocation (LBA) algorithm has been proposed to solve the challenging problem of maximizing sum data-rates. However, there are practical limitations in mmWave systems, such as restrictions in the number of available radio frequency transceiver chains at the base station, sensitivity to sidelobe interference and the beam generation techniques. In this paper, using generalized beam-patterns, we present the maximum sum data-rates achievable in switched-beam mmWave systems compared with fixed-beam systems by applying LBA. Then, the impact on maximum sum data rates of actual beam-patterns, obtained from a practical mmWave lens antenna, which have higher and non-uniform sidelobes compared with the theoretical beams, is assessed. Finally, as a guide for practical wireless system design, benchmarks are established for relative sidelobe levels that provide acceptable sum data-rate performance when considering generalized beam patterns

    Achievable Rates of Multi-User Millimeter Wave Systems with Hybrid Precoding

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    Millimeter wave (mmWave) systems will likely employ large antenna arrays at both the transmitters and receivers. A natural application of antenna arrays is simultaneous transmission to multiple users, which requires multi-user precoding at the transmitter. Hardware constraints, however, make it difficult to apply conventional lower frequency MIMO precoding techniques at mmWave. This paper proposes and analyzes a low complexity hybrid analog/digital beamforming algorithm for downlink multi-user mmWave systems. Hybrid precoding involves a combination of analog and digital processing that is motivated by the requirement to reduce the power consumption of the complete radio frequency and mixed signal hardware. The proposed algorithm configures hybrid precoders at the transmitter and analog combiners at multiple receivers with a small training and feedback overhead. For this algorithm, we derive a lower bound on the achievable rate for the case of single-path channels, show its asymptotic optimality at large numbers of antennas, and make useful insights for more general cases. Simulation results show that the proposed algorithm offers higher sum rates compared with analog-only beamforming, and approaches the performance of the unconstrained digital precoding solutions.Comment: to be presented in IEEE ICC 2015 - Workshop on 5G & Beyond - Enabling Technologies and Application
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