Time-division duplex (TDD) is the most efficient technique for acquiring channel state information in massivemultiple-inputmultiple-output (MIMO) systems where the reciprocity between the uplink and downlink channel...
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Time-division duplex (TDD) is the most efficient technique for acquiring channel state information in massivemultiple-inputmultiple-output (MIMO) systems where the reciprocity between the uplink and downlink channels is utilised by the pilot signals to extract the channel parameters. In this study, the authors consider the pilot contamination problem in TDD multicell multiuser massive MIMO systems and examine two different pilot signal allocation schemes for which they derive the lower bounds on the achievable rate on the uplink for the cases of maximum-ratio combining (MRC) and zero-forcing (ZF) detectors. To achieve further performance enhancements, they propose a new algorithm for pilot sequences allocation in which the multiplicity of the pilot sequences over the number of users in each cell is exploited. The authors' results show that when pilot contamination is severe, allocating more system resources for channel estimation results in a better system performance especially in limited mobility environments. Moreover, they show that when the signal-to-interference plus noise ratio is low, MRC is superior to ZF, and vice versa. Finally, they demonstrate that their proposed allocation algorithm can significantly improve the spectral efficiency of the network compared to the conventional pilot allocation method.
The addition of analogue processing to the digital precoding, known as hybrid beamforming (HB), is an efficient solution for massivemultiple-inputmultiple-output (MIMO) systems. The design of a phase shifter (PS) ne...
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The addition of analogue processing to the digital precoding, known as hybrid beamforming (HB), is an efficient solution for massivemultiple-inputmultiple-output (MIMO) systems. The design of a phase shifter (PS) network plays an important role in the complete precoder operation because it necessitates accurate components for realising precise phases, and that can be costly. Finite resolution PSs are good alternatives because they need simpler hardware implementation than those with infinite resolution. However, the degradation of performance of a MIMO system with very low-resolution PSs is significant. Although recent studies suggest adding extra radio frequency (RF) chains to substitute for the accuracy of the PSs, it is complex, expensive and not energy efficient. This study demonstrates that HB with low-resolution PSs can realise a high performance without increasing the number of RF chains. The authors proposed solution relies on a proper selection of the weights of the RF beamformer, hence exploiting the structure of the multipath propagation channel to maximise the system capacity. They also show that separating antennas from each other by sufficient distance, results in a less correlated channel, and thus, a minimal loss in the capacity and the antenna gains are assured.
In massivemultiple-inputmultiple-output (MIMO) systems with hundreds of antennas at the base station (BS) and few users with a single transmitter antenna, linear detectors, such as zero-forcing (ZF), achieve near-op...
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In massivemultiple-inputmultiple-output (MIMO) systems with hundreds of antennas at the base station (BS) and few users with a single transmitter antenna, linear detectors, such as zero-forcing (ZF), achieve near-optimum performance due to the property of asymptotically orthogonal channel matrix. However, how far away is ZF from the optimum performance. To answer this question, in this Letter, closed-form bit error rate (BER) expressions are derived. These BER expressions are subsequently used to evaluate the performance difference between ZF and the optimum detector, which is a function of the number of antennas at the BS and the number of users. Numerical results verify the tightness of the performance difference.
The traditional fully-digital beamforming is realised by the full radio-frequency (RF) chain configuration, which will be impracticable in massivemultiple-inputmultiple-output (MIMO) systems because of the overburde...
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The traditional fully-digital beamforming is realised by the full radio-frequency (RF) chain configuration, which will be impracticable in massivemultiple-inputmultiple-output (MIMO) systems because of the overburden energy consumption of RF chains at millimetre wave frequencies. To address this issue, a series of hybrid beamforming schemes have been proposed to reduce the number of RF chains. Although the hybrid beamforming schemes for single-user MIMO (SU-MIMO) have been studied extensively, the performance of hybrid beamforming for multi-user MIMO (MU-MIMO), especially for partially-connected hybrid architecture, still has room for improvement. In this study, the authors propose a hybrid beamforming scheme for MU-MIMO systems. Specifically, they focus on the design of analogue beamforming and optimise the analogue RF precoders and combiners jointly. The simulation results show that the proposed hybrid beamforming in fully-connected structure can achieve a better performance compared with the existing hybrid beamforming schemes in both SU-MIMO and MU-MIMO systems. It is also observed that the proposed hybrid beamforming can achieve significant performance advantages compared with the existing hybrid beamforming schemes in partially-connected structures.
Intelligent terminals often produce a large number of data packets of small lengths. For these packets, it is inefficient to follow the conventional medium access control (MAC) protocols because they lead to poor util...
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ISBN:
(纸本)9781479941452
Intelligent terminals often produce a large number of data packets of small lengths. For these packets, it is inefficient to follow the conventional medium access control (MAC) protocols because they lead to poor utilization of service resources. We propose a novel multiple access scheme that targets massivemultiple-inputmultiple-output (MIMO) systems based on compressive sensing (CS). We employ block precoding in the time domain to enable the simultaneous transmissions of many users, which could be even more than the number of receive antennas at the base station. We develop a block-sparse system model and adopt the block orthogonal matching pursuit (BOMP) algorithm to recover the transmitted signals. Conditions for data recovery guarantees are identified and numerical results demonstrate that our scheme is efficient for uplink small packet transmission.
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