4,745 research outputs found
Transmit Signal and Bandwidth Optimization in Multiple-Antenna Relay Channels
Transmit signal and bandwidth optimization is considered in multiple-antenna
relay channels. Assuming all terminals have channel state information, the
cut-set capacity upper bound and decode-and-forward rate under full-duplex
relaying are evaluated by formulating them as convex optimization problems. For
half-duplex relays, bandwidth allocation and transmit signals are optimized
jointly. Moreover, achievable rates based on the compress-and-forward
transmission strategy are presented using rate-distortion and Wyner-Ziv
compression schemes. It is observed that when the relay is close to the source,
decode-and-forward is almost optimal, whereas compress-and-forward achieves
good performance when the relay is close to the destination.Comment: 16 pages, 10 figure
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
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