441 research outputs found
Optimal Power Control for Analog Bidirectional Relaying with Long-Term Relay Power Constraint
Wireless systems that carry delay-sensitive information (such as speech
and/or video signals) typically transmit with fixed data rates, but may
occasionally suffer from transmission outages caused by the random nature of
the fading channels. If the transmitter has instantaneous channel state
information (CSI) available, it can compensate for a significant portion of
these outages by utilizing power allocation. In a conventional dual-hop
bidirectional amplify-and-forward (AF) relaying system, the relay already has
instantaneous CSI of both links available, as this is required for relay gain
adjustment. We therefore develop an optimal power allocation strategy for the
relay, which adjusts its instantaneous output power to the minimum level
required to avoid outages, but only if the required output power is below some
cutoff level; otherwise, the relay is silent in order to conserve power and
prolong its lifetime. The proposed scheme is proven to minimize the system
outage probability, subject to an average power constraint at the relay and
fixed output powers at the end nodes.Comment: conference IEEE Globecom 2013, Atlanta, Georgia, U
Optimal Beamforming for Two-Way Multi-Antenna Relay Channel with Analogue Network Coding
This paper studies the wireless two-way relay channel (TWRC), where two
source nodes, S1 and S2, exchange information through an assisting relay node,
R. It is assumed that R receives the sum signal from S1 and S2 in one
time-slot, and then amplifies and forwards the received signal to both S1 and
S2 in the next time-slot. By applying the principle of analogue network (ANC),
each of S1 and S2 cancels the so-called "self-interference" in the received
signal from R and then decodes the desired message. Assuming that S1 and S2 are
each equipped with a single antenna and R with multi-antennas, this paper
analyzes the capacity region of an ANC-based TWRC with linear processing
(beamforming) at R. The capacity region contains all the achievable
bidirectional rate-pairs of S1 and S2 under the given transmit power
constraints at S1, S2, and R. We present the optimal relay beamforming
structure as well as an efficient algorithm to compute the optimal beamforming
matrix based on convex optimization techniques. Low-complexity suboptimal relay
beamforming schemes are also presented, and their achievable rates are compared
against the capacity with the optimal scheme.Comment: to appear in JSAC, 200
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