1,622 research outputs found
The Gaussian Interference Relay Channel: Improved Achievable Rates and Sum Rate Upperbounds Using a Potent Relay
We consider the Gaussian interference channel with an intermediate relay as a
main building block for cooperative interference networks. On the achievability
side, we consider compress-and-forward based strategies. Specifically, a
generalized compress-and-forward strategy, where the destinations jointly
decode the compression indices and the source messages, is shown to improve
upon the compress-and-forward strategy which sequentially decodes the
compression indices and source messages, and the recently proposed generalized
hash-and-forward strategy. We also construct a nested lattice code based
compute-and-forward relaying scheme, which outperforms other relaying schemes
when the direct link is weak. In this case, it is shown that, with a relay, the
interference link can be useful for decoding the source messages. Noting the
need for upperbounding the capacity for this channel, we propose a new
technique with which the sum rate can be bounded. In particular, the sum
capacity is upperbounded by considering the channel when the relay node has
abundant power and is named potent for that reason. For the Gaussian
interference relay channel with potent relay, we study the strong and the weak
interference regimes and establish the sum capacity, which, in turn, serve as
upperbounds for the sum capacity of the GIFRC with finite relay power.
Numerical results demonstrate that upperbounds are tighter than the cut-set
bound, and coincide with known achievable sum rates for many scenarios of
interest. Additionally, the degrees of freedom of the GIFRC are shown to be 2
when the relay has large power, achievable using compress-and-forward.Comment: 35 pages, 9 figures, to appear in IEEE Transactions on Information
Theory, Special Issue on Interference Networks, 201
The Impact of CSI and Power Allocation on Relay Channel Capacity and Cooperation Strategies
Capacity gains from transmitter and receiver cooperation are compared in a
relay network where the cooperating nodes are close together. Under
quasi-static phase fading, when all nodes have equal average transmit power
along with full channel state information (CSI), it is shown that transmitter
cooperation outperforms receiver cooperation, whereas the opposite is true when
power is optimally allocated among the cooperating nodes but only CSI at the
receiver (CSIR) is available. When the nodes have equal power with CSIR only,
cooperative schemes are shown to offer no capacity improvement over
non-cooperation under the same network power constraint. When the system is
under optimal power allocation with full CSI, the decode-and-forward
transmitter cooperation rate is close to its cut-set capacity upper bound, and
outperforms compress-and-forward receiver cooperation. Under fast Rayleigh
fading in the high SNR regime, similar conclusions follow. Cooperative systems
provide resilience to fading in channel magnitudes; however, capacity becomes
more sensitive to power allocation, and the cooperating nodes need to be closer
together for the decode-and-forward scheme to be capacity-achieving. Moreover,
to realize capacity improvement, full CSI is necessary in transmitter
cooperation, while in receiver cooperation optimal power allocation is
essential.Comment: Accepted for publication in IEEE Transactions on Wireless
Communication
Approximate Capacity of Gaussian Relay Networks
We present an achievable rate for general Gaussian relay networks. We show
that the achievable rate is within a constant number of bits from the
information-theoretic cut-set upper bound on the capacity of these networks.
This constant depends on the topology of the network, but not the values of the
channel gains. Therefore, we uniformly characterize the capacity of Gaussian
relay networks within a constant number of bits, for all channel parameters.Comment: This paper is submited to 2008 IEEE International Symposium on
Information Theory (ISIT 2008) -In the revised format the approximation gap
(\kappa) is sharpene
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
The Three Node Wireless Network: Achievable Rates and Cooperation Strategies
We consider a wireless network composed of three nodes and limited by the
half-duplex and total power constraints. This formulation encompasses many of
the special cases studied in the literature and allows for capturing the common
features shared by them. Here, we focus on three special cases, namely 1) Relay
Channel, 2) Multicast Channel, and 3) Conference Channel. These special cases
are judicially chosen to reflect varying degrees of complexity while
highlighting the common ground shared by the different variants of the three
node wireless network. For the relay channel, we propose a new cooperation
scheme that exploits the wireless feedback gain. This scheme combines the
benefits of decode-and-forward and compress-and-forward strategies and avoids
the idealistic feedback assumption adopted in earlier works. Our analysis of
the achievable rate of this scheme reveals the diminishing feedback gain at
both the low and high signal-to-noise ratio regimes. Inspired by the proposed
feedback strategy, we identify a greedy cooperation framework applicable to
both the multicast and conference channels. Our performance analysis reveals
several nice properties of the proposed greedy approach and the central role of
cooperative source-channel coding in exploiting the receiver side information
in the wireless network setting. Our proofs for the cooperative multicast with
side-information rely on novel nested and independent binning encoders along
with a list decoder.Comment: 52 page
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