8 research outputs found
Hybrid Processing Design for Multipair Massive MIMO Relaying with Channel Spatial Correlation
Massive multiple-input multiple-output (MIMO) avails of simple transceiver
design which can tackle many drawbacks of relay systems in terms of complicated
signal processing, latency, and noise amplification. However, the cost and
circuit complexity of having one radio frequency (RF) chain dedicated to each
antenna element are prohibitive in practice. In this paper, we address this
critical issue in amplify-and-forward (AF) relay systems using a hybrid analog
and digital (A/D) transceiver structure. More specifically, leveraging the
channel long-term properties, we design the analog beamformer which aims to
minimize the channel estimation error and remain invariant over a long
timescale. Then, the beamforming is completed by simple digital signal
processing, i.e., maximum ratio combining/maximum ratio transmission (MRC/MRT)
or zero-forcing (ZF) in the baseband domain. We present analytical bounds on
the achievable spectral efficiency taking into account the spatial correlation
and imperfect channel state information at the relay station. Our analytical
results reveal that the hybrid A/D structure with ZF digital processor exploits
spatial correlation and offers a higher spectral efficiency compared to the
hybrid A/D structure with MRC/MRT scheme. Our numerical results showcase that
the hybrid A/D beamforming design captures nearly 95% of the spectral
efficiency of a fully digital AF relaying topology even by removing half of the
RF chains. It is also shown that the hybrid A/D structure is robust to coarse
quantization, and even with 2-bit resolution, the system can achieve more than
93% of the spectral efficiency offered by the same hybrid A/D topology with
infinite resolution phase shifters.Comment: 17 pages, 13 figures, to appear in IEEE Transactions on
Communication
Massive MIMO relaying with hybrid processing
Massive multiple-input multiple-output (MIMO) relaying is a promising
technological paradigm which can offer high spectral efficiency and
substantially improved coverage. Yet, these configurations face some formidable
challenges in terms of digital signal processing (DSP) power consumption and
circuitry complexity, since the number of radio frequency (RF) chains may scale
with the number of antennas at the relay station. In this paper, we advocate
that performing a portion of the power-intensive DSP in the analog domain,
using simple phase shifters and with a reduced number of RF paths, can address
these challenges. In particular, we consider a multipair amplify-and-forward
(AF) relay system with maximum ratio combining/transmission (MRC/MRT) and we
determine the asymptotic spectral efficiency for this hybrid analog/digital
architecture. After that, we extend our analytical results to account for
heavily quantized analog phase shifters and show that the performance loss with
2 quantization bits is only 10%
MIMO performance evaluation of isotropic, directional and highly-directional antenna systems for mm-wave communications
In this paper, we investigate how directional and highly-directional antenna systems using fixed beams can be beneficial in terms of aggregated channel and antenna gains, channel correlation and the massive multiple-input multiple-output (MIMO) capacity in both line-of-sight (LOS) and non-LOS (NLOS) scenarios for single user MIMO (SU-MIMO). It is shown that narrower beams have stronger aggregated channel and antenna gain. However, narrow beamwidth triggers a higher channel correlation as fewer scatterers are seen. A possible solution to reduce the correlation among the beams is to properly decorrelate the beams in advance. To this end, we partition the area of interest and devote one specific partition to each beam to minimize the possible overlaps among the beams. Simulation results show that fixed beam SU-MIMO systems using such highly-directional beams can provide higher MIMO capacity in comparison to isotropic and directional antenna systems
MIMO performance evaluation of isotropic, directional and highly-directional antenna systems for mm-wave communications
\u3cp\u3eIn this paper, we investigate how directional and highly-directional antenna systems using fixed beams can be beneficial in terms of aggregated channel and antenna gains, channel correlation and the massive multiple-input multiple-output (MIMO) capacity in both line-of-sight (LOS) and non-LOS (NLOS) scenarios for single user MIMO (SU-MIMO). It is shown that narrower beams have stronger aggregated channel and antenna gain. However, narrow beamwidth triggers a higher channel correlation as fewer scatterers are seen. A possible solution to reduce the correlation among the beams is to properly decorrelate the beams in advance. To this end, we partition the area of interest and devote one specific partition to each beam to minimize the possible overlaps among the beams. Simulation results show that fixed beam SU-MIMO systems using such highly-directional beams can provide higher MIMO capacity in comparison to isotropic and directional antenna systems.\u3c/p\u3