1,016 research outputs found
Multiuser Millimeter Wave Beamforming Strategies with Quantized and Statistical CSIT
To alleviate the high cost of hardware in mmWave systems, hybrid
analog/digital precoding is typically employed. In the conventional two-stage
feedback scheme, the analog beamformer is determined by beam search and
feedback to maximize the desired signal power of each user. The digital
precoder is designed based on quantization and feedback of effective channel to
mitigate multiuser interference. Alternatively, we propose a one-stage feedback
scheme which effectively reduces the complexity of the signalling and feedback
procedure. Specifically, the second-order channel statistics are leveraged to
design digital precoder for interference mitigation while all feedback overhead
is reserved for precise analog beamforming. Under a fixed total feedback
constraint, we investigate the conditions under which the one-stage feedback
scheme outperforms the conventional two-stage counterpart. Moreover, a rate
splitting (RS) transmission strategy is introduced to further tackle the
multiuser interference and enhance the rate performance. Consider (1) RS
precoded by the one-stage feedback scheme and (2) conventional transmission
strategy precoded by the two-stage scheme with the same first-stage feedback as
(1) and also certain amount of extra second-stage feedback. We show that (1)
can achieve a sum rate comparable to that of (2). Hence, RS enables remarkable
saving in the second-stage training and feedback overhead.Comment: submitted to TW
Adaptive hybrid precoding for multiuser massive MIMO
Hybrid precoding (HP) is widely utilized in millimeter wave-based massive MIMO systems with significantly reduced radio frequency (RF) chains, but it requires a large number of analog phase shifters (APSs) and RF adders to realize the connection between RF chains and antenna elements. In this letter, an adaptive hybrid precoding (AHP) is proposed to approach the performance of the conventional HP with reduced complexity. Different from the conventional HP where each antenna is connected to all RF chains through APSs and RF adders, the proposed AHP connects each antenna with only one RF chain through an adaptive connection network. This adaptive connection network and the phases of APSs are jointly designed, which is formulated as an optimization problem to maximize the users' average downlink achievable rate. Moreover, a multiuser adaptive analog precoding (MU-AAP) algorithm is proposed to provide a near-optimal solution to this joint-design problem. Simulation results verify the performance gain of the proposed AHP in typical multiuser massive MIMO scenario
On the Number of RF Chains and Phase Shifters, and Scheduling Design with Hybrid Analog-Digital Beamforming
This paper considers hybrid beamforming (HB) for downlink multiuser massive
multiple input multiple output (MIMO) systems with frequency selective
channels. For this system, first we determine the required number of radio
frequency (RF) chains and phase shifters (PSs) such that the proposed HB
achieves the same performance as that of the digital beamforming (DB) which
utilizes (number of transmitter antennas) RF chains. We show that the
performance of the DB can be achieved with our HB just by utilizing RF
chains and PSs, where is the rank of the
combined digital precoder matrices of all sub-carriers. Second, we provide a
simple and novel approach to reduce the number of PSs with only a negligible
performance degradation. Numerical results reveal that only PSs per RF
chain are sufficient for practically relevant parameter settings. Finally, for
the scenario where the deployed number of RF chains is less than ,
we propose a simple user scheduling algorithm to select the best set of users
in each sub-carrier. Simulation results validate theoretical expressions, and
demonstrate the superiority of the proposed HB design over the existing HB
designs in both flat fading and frequency selective channels.Comment: IEEE Transactions on Wireless Communications (Minor Revision
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