12 research outputs found
Impact of Relay Cooperation on the Performance of Large-scale Multipair Two-way Relay Networks
We consider a multipair two-way relay communication network, where pairs of
user devices exchange information via a relay system. The communication between
users employs time division duplex, with all users transmitting simultaneously
to relays in one time slot and relays sending the processed information to all
users in the next time slot. The relay system consists of a large number of
single antenna units that can form groups. Within each group, relays exchange
channel state information (CSI), signals received in the uplink and signals
intended for downlink transmission. On the other hand, per-group CSI and
uplink/downlink signals (data) are not exchanged between groups, which perform
the data processing completely independently. Assuming that the groups perform
zero-forcing in both uplink and downlink, we derive a lower bound for the
ergodic sumrate of the described system as a function of the relay group size.
By close observation of this lower bound, it is concluded that the sumrate is
essentially independent of group size when the group size is much larger than
the number of user pairs. This indicates that a very large group of cooperating
relays can be substituted by a number of smaller groups, without incurring any
significant performance reduction. Moreover, this result implies that relay
cooperation is more efficient (in terms of resources spent on cooperation) when
several smaller relay groups are used in contrast to a single, large group.Comment: Accepted to Globecom 2018. Copyright 2018 IEE
Multipair Massive MIMO Relaying Systems with One-Bit ADCs and DACs
This paper considers a multipair amplify-and-forward massive MIMO relaying
system with one-bit ADCs and one-bit DACs at the relay. The channel state
information is estimated via pilot training, and then utilized by the relay to
perform simple maximum-ratio combining/maximum-ratio transmission processing.
Leveraging on the Bussgang decomposition, an exact achievable rate is derived
for the system with correlated quantization noise. Based on this, a closed-form
asymptotic approximation for the achievable rate is presented, thereby enabling
efficient evaluation of the impact of key parameters on the system performance.
Furthermore, power scaling laws are characterized to study the potential energy
efficiency associated with deploying massive one-bit antenna arrays at the
relay. In addition, a power allocation strategy is designed to compensate for
the rate degradation caused by the coarse quantization. Our results suggest
that the quality of the channel estimates depends on the specific orthogonal
pilot sequences that are used, contrary to unquantized systems where any set of
orthogonal pilot sequences gives the same result. Moreover, the sum rate gap
between the double-quantized relay system and an ideal non-quantized system is
a moderate factor of in the low power regime.Comment: 14 pages, 10 figures, submitted to IEEE Trans. Signal Processin
Secure Multiple Amplify-and-Forward Relaying Over Correlated Fading Channels
This paper quantifies the impact of correlated fading
on secure communication of multiple amplify-and-forward (AF)
relaying networks. In such a network, the base station (BS) is
equipped with multiple antennas and communicates with the
destination through multiple AF relays, while the message from
the relays can be overheard by an eavesdropper. We focus
on the practical communication scenario, where the main and
eavesdropper’s channels are correlated. In order to enhance
the transmission security, transmit antenna selection (TAS) is
performed at the BS, and the best relay is chosen according to the
full or partial relay selection criterion, which relies on the dualhop
relay channels or the second-hop relay channels, respectively.
For these criteria, we study the impact of correlated fading
on the network secrecy performance, by deriving an analytical
approximation for the secrecy outage probability (SOP) and an
asymptotic expression for the high main-to-eavesdropper ratio
(MER). From these results, it is concluded that the channel
correlation is always beneficial to the secrecy performance of full
relay selection. However, it deteriorates the secrecy performance
if partial relay selection is used, when the number of antennas
at the BS is less than the number of relays.ARC Discovery Projects Grant DP150103905
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