1,145 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
Feedback-Aware Precoding for Millimeter Wave Massive MIMO Systems
Millimeter wave (mmWave) communication is a promising solution for coping
with the ever-increasing mobile data traffic because of its large bandwidth. To
enable a sufficient link margin, a large antenna array employing directional
beamforming, which is enabled by the availability of channel state information
at the transmitter (CSIT), is required. However, CSIT acquisition for mmWave
channels introduces a huge feedback overhead due to the typically large number
of transmit and receive antennas. Leveraging properties of mmWave channels,
this paper proposes a precoding strategy which enables a flexible adjustment of
the feedback overhead. In particular, the optimal unconstrained precoder is
approximated by selecting a variable number of elements from a basis that is
constructed as a function of the transmitter array response, where the number
of selected basis elements can be chosen according to the feedback constraint.
Simulation results show that the proposed precoding scheme can provide a
near-optimal solution if a higher feedback overhead can be afforded. For a low
overhead, it can still provide a good approximation of the optimal precoder.Comment: 7 pages, 5 figures, to appear at the IEEE International Symposium on
Personal, Indoor and Mobile Radio Communications (PIMRC) 201
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