174 research outputs found
Millimeter Wave Beam Alignment: Large Deviations Analysis and Design Insights
In millimeter wave cellular communication, fast and reliable beam alignment
via beam training is crucial to harvest sufficient beamforming gain for the
subsequent data transmission. In this paper, we establish fundamental limits in
beam-alignment performance under both the exhaustive search and the
hierarchical search that adopts multi-resolution beamforming codebooks,
accounting for time-domain training overhead. Specifically, we derive lower and
upper bounds on the probability of misalignment for an arbitrary level in the
hierarchical search, based on a single-path channel model. Using the method of
large deviations, we characterize the decay rate functions of both bounds and
show that the bounds coincide as the training sequence length goes large. We go
on to characterize the asymptotic misalignment probability of both the
hierarchical and exhaustive search, and show that the latter asymptotically
outperforms the former, subject to the same training overhead and codebook
resolution. We show via numerical results that this relative performance
behavior holds in the non-asymptotic regime. Moreover, the exhaustive search is
shown to achieve significantly higher worst-case spectrum efficiency than the
hierarchical search, when the pre-beamforming signal-to-noise ratio (SNR) is
relatively low. This study hence implies that the exhaustive search is more
effective for users situated further from base stations, as they tend to have
low SNR.Comment: Author final manuscript, to appear in IEEE Journal on Selected Areas
in Communications (JSAC), Special Issue on Millimeter Wave Communications for
Future Mobile Networks, 2017 (corresponding author: Min Li
Uplink Beam Management for Millimeter Wave Cellular MIMO Systems with Hybrid Beamforming
Hybrid analog and digital BeamForming (HBF) is one of the enabling
transceiver technologies for millimeter Wave (mmWave) Multiple Input Multiple
Output (MIMO) systems. This technology offers highly directional communication,
which is able to confront the intrinsic characteristics of mmWave signal
propagation. However, the small coherence time in mmWave systems, especially
under mobility conditions, renders efficient Beam Management (BM) in standalone
mmWave communication a very difficult task. In this paper, we consider HBF
transceivers with planar antenna panels and design a multi-level beam codebook
for the analog beamformer comprising flat top beams with variable widths. These
beams exhibit an almost constant array gain for the whole desired angle width,
thereby facilitating efficient hierarchical BM. Focusing on the uplink
communication, we present a novel beam training algorithm with dynamic beam
ordering, which is suitable for the stringent latency requirements of the
latest mmWave standard discussions. Our simulation results showcase the latency
performance improvement and received signal-to-noise ratio with different
variations of the proposed scheme over the optimum beam training scheme based
on exhaustive narrow beam search.Comment: 7 pages; 6 figures; accepted to an IEEE conferenc
Hierarchical Beamforming: Resource Allocation, Fairness and Flow Level Performance
We consider hierarchical beamforming in wireless networks. For a given
population of flows, we propose computationally efficient algorithms for fair
rate allocation including proportional fairness and max-min fairness. We next
propose closed-form formulas for flow level performance, for both elastic (with
either proportional fairness and max-min fairness) and streaming traffic. We
further assess the performance of hierarchical beamforming using numerical
experiments. Since the proposed solutions have low complexity compared to
conventional beamforming, our work suggests that hierarchical beamforming is a
promising candidate for the implementation of beamforming in future cellular
networks.Comment: 34 page
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