57 research outputs found
Multipair Relaying With Space-Constrained Large-Scale MIMO Arrays: Spectral and Energy Efficiency Analysis With Incomplete CSI
In this paper, we study a multi-pair two-way large-scale multiple-input multiple-output (MIMO) decode-and-forward relay system. Multiple single-antenna user pairs exchange information via a shared relay working at half-duplex. The proposed scenario considers a practical case where an increasing number of antennas is deployed in a fixed physical space, giving rise to a trade-off between antenna gain and spatial correlation. The channel is assumed imperfectly known, and the relay employs linear processing methods. We study the large-scale approximations of the sum spectral efficiency (SE) and investigate the energy efficiency (EE) with a practical power consumption model when the number of relay antennas becomes large. We demonstrate the impact of the relay antenna number and spatial correlation with reducing inter-antenna distance on the EE performance. We exploit the increasing spatial correlation to allow an incomplete channel state information (CSI) acquisition where explicit CSI is acquired only for a subset of antennas. Our analytical derivations and numerical results show that applying the incomplete CSI strategy in the proposed system can improve the EE against complete CSI systems while maintaining the average SE performance
Multipair Two-Way DF Relaying with Cell-Free Massive MIMO
We consider a two-way half-duplex decode-and-forward (DF) relaying system
with multiple pairs of single-antenna users assisted by a cell-free (CF)
massive multiple-input multiple-output (mMIMO) architecture with
multiple-antenna access points (APs). Under the practical constraint of
imperfect channel state information (CSI), we derive the achievable sum
spectral efficiency (SE) for a finite number of APs with maximum ratio (MR)
linear processing for both reception and transmission in closed-form. Notably,
the proposed CF mMIMO relaying architecture, exploiting the spatial diversity,
and providing better coverage, outperforms the conventional collocated mMIMO
deployment. Moreover, we shed light on the power-scaling laws maintaining a
specific SE as the number of APs grows. A thorough examination of the interplay
between the transmit powers per pilot symbol and user/APs takes place, and
useful conclusions are extracted. Finally, differently to the common approach
for power control in CF mMIMO systems, we design a power allocation scheme
maximizing the sum SE.Comment: 15 pages, 8 figures, This work was accepted in IEEE Trans. Green
Commun. Net. Copyright may be transferred without notice, after which this
version may no longer be accessibl
Rate-Splitting Robustness in Multi-Pair Massive MIMO Relay Systems
Relay systems improve both coverage and system capacity. Toward this direction, a full-duplex (FD) technology, being able to boost the spectral efficiency by transmitting and receiving simultaneously on the same frequency and time resources, is envisaged to play a key role in future networks. However, its benefits come at the expense of self-interference (SI) from their own transmit signal. At the same time, massive multiple-input massive multiple-output systems, bringing unconventionally many antennas, emerge as a promising technology with huge degrees-of-freedom. To this end, this paper considers a multi-pair decode-and-forward FD relay channel, where the relay station is deployed with a large number of antennas. Moreover, the rate-splitting (RS) transmission has recently been shown to provide significant performance benefits in various multi-user scenarios with imperfect channel state information at the transmitter (CSIT). Engaging the RS approach, we employ the deterministic equivalent analysis to derive the corresponding sum-rates in the presence of interferences. Initially, numerical results demonstrate the robustness of RS in half-duplex (HD) systems, since the achievable sum-rate increases without bound, i.e., it does not saturate at high signal-to-noise ratio. Next, we tackle the detrimental effect of SI in FD. In particular, and most importantly, not only FD outperforms HD, but also RS enables increasing the range of SI over which FD outperforms HD. Furthermore, increasing the number of relay station antennas, RS appears to be more efficacious due to imperfect CSIT, since SI decreases. Interestingly, increasing the number of users, the efficiency of RS worsens and its implementation becomes less favorable under these conditions. Finally, we verify that the proposed DEs, being accurate for a large number of relay station antennas, are tight approximations even for realistic system dimensions.Peer reviewedFinal Accepted Versio
Multipair Full-Duplex Relaying with Massive Arrays and Linear Processing
We consider a multipair decode-and-forward relay channel, where multiple
sources transmit simultaneously their signals to multiple destinations with the
help of a full-duplex relay station. We assume that the relay station is
equipped with massive arrays, while all sources and destinations have a single
antenna. The relay station uses channel estimates obtained from received pilots
and zero-forcing (ZF) or maximum-ratio combining/maximum-ratio transmission
(MRC/MRT) to process the signals. To reduce significantly the loop interference
effect, we propose two techniques: i) using a massive receive antenna array; or
ii) using a massive transmit antenna array together with very low transmit
power at the relay station. We derive an exact achievable rate in closed-form
for MRC/MRT processing and an analytical approximation of the achievable rate
for ZF processing. This approximation is very tight, especially for large
number of relay station antennas. These closed-form expressions enable us to
determine the regions where the full-duplex mode outperforms the half-duplex
mode, as well as, to design an optimal power allocation scheme. This optimal
power allocation scheme aims to maximize the energy efficiency for a given sum
spectral efficiency and under peak power constraints at the relay station and
sources. Numerical results verify the effectiveness of the optimal power
allocation scheme. Furthermore, we show that, by doubling the number of
transmit/receive antennas at the relay station, the transmit power of each
source and of the relay station can be reduced by 1.5dB if the pilot power is
equal to the signal power, and by 3dB if the pilot power is kept fixed, while
maintaining a given quality-of-service
On the Effects of Channel Aging in D2D Two-Way Relaying with Space-Constrained Massive MIMO
This paper studies the spectral efficiency (SE) of a space-constrained multi-pair two-way massive multiple-input multiple-output (MIMO) decode-and-forward (DF) relay system with channel aging for device-to-device (D2D) communications in the Internet of Things (IoT) environments. Maximum ratio combininy-Maximum ratio transmission (MRC/MRT) processing is employed at the relay and imperfect channel estimation is assumed. With the consideration of the spatial correlation due to insufficiently spaced antennas, and the time correlation due to channel aging, we study the closed-form large-scale approximations of the SE performance. Our analytical studies and performance results demonstrate that a degree of both spatial correlation due to antenna proximity, and time correlation due to channel aging can be tolerated in the massive MIMO regime without significant performance degradation
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
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