1,689 research outputs found
Opportunistic Relaying in Wireless Networks
Relay networks having source-to-destination pairs and half-duplex
relays, all operating in the same frequency band in the presence of block
fading, are analyzed. This setup has attracted significant attention and
several relaying protocols have been reported in the literature. However, most
of the proposed solutions require either centrally coordinated scheduling or
detailed channel state information (CSI) at the transmitter side. Here, an
opportunistic relaying scheme is proposed, which alleviates these limitations.
The scheme entails a two-hop communication protocol, in which sources
communicate with destinations only through half-duplex relays. The key idea is
to schedule at each hop only a subset of nodes that can benefit from
\emph{multiuser diversity}. To select the source and destination nodes for each
hop, it requires only CSI at receivers (relays for the first hop, and
destination nodes for the second hop) and an integer-value CSI feedback to the
transmitters. For the case when is large and is fixed, it is shown that
the proposed scheme achieves a system throughput of bits/s/Hz. In
contrast, the information-theoretic upper bound of bits/s/Hz
is achievable only with more demanding CSI assumptions and cooperation between
the relays. Furthermore, it is shown that, under the condition that the product
of block duration and system bandwidth scales faster than , the
achievable throughput of the proposed scheme scales as .
Notably, this is proven to be the optimal throughput scaling even if
centralized scheduling is allowed, thus proving the optimality of the proposed
scheme in the scaling law sense.Comment: 17 pages, 8 figures, To appear in IEEE Transactions on Information
Theor
Recovering Multiplexing Loss Through Successive Relaying Using Repetition Coding
In this paper, a transmission protocol is studied for a two relay wireless
network in which simple repetition coding is applied at the relays.
Information-theoretic achievable rates for this transmission scheme are given,
and a space-time V-BLAST signalling and detection method that can approach them
is developed. It is shown through the diversity multiplexing tradeoff analysis
that this transmission scheme can recover the multiplexing loss of the
half-duplex relay network, while retaining some diversity gain. This scheme is
also compared with conventional transmission protocols that exploit only the
diversity of the network at the cost of a multiplexing loss. It is shown that
the new transmission protocol offers significant performance advantages over
conventional protocols, especially when the interference between the two relays
is sufficiently strong.Comment: To appear in the IEEE Transactions on Wireless Communication
On the Achievable Rates of Multihop Virtual Full-Duplex Relay Channels
We study a multihop "virtual" full-duplex relay channel as a special case of
a general multiple multicast relay network. For such channel,
quantize-map-and-forward (QMF) (or noisy network coding (NNC)) achieves the
cut-set upper bound within a constant gap where the gap grows {\em linearly}
with the number of relay stages . However, this gap may not be negligible
for the systems with multihop transmissions (i.e., a wireless backhaul
operating at higher frequencies). We have recently attained an improved result
to the capacity scaling where the gap grows {\em logarithmically} as ,
by using an optimal quantization at relays and by exploiting relays' messages
(decoded in the previous time slot) as side-information. In this paper, we
further improve the performance of this network by presenting a mixed scheme
where each relay can perform either decode-and-forward (DF) or QMF with
possibly rate-splitting. We derive the achievable rate and show that the
proposed scheme outperforms the QMF-optimized scheme. Furthermore, we
demonstrate that this performance improvement increases with .Comment: To be presented at ISIT 201
Compute-and-Forward: Harnessing Interference through Structured Codes
Interference is usually viewed as an obstacle to communication in wireless
networks. This paper proposes a new strategy, compute-and-forward, that
exploits interference to obtain significantly higher rates between users in a
network. The key idea is that relays should decode linear functions of
transmitted messages according to their observed channel coefficients rather
than ignoring the interference as noise. After decoding these linear equations,
the relays simply send them towards the destinations, which given enough
equations, can recover their desired messages. The underlying codes are based
on nested lattices whose algebraic structure ensures that integer combinations
of codewords can be decoded reliably. Encoders map messages from a finite field
to a lattice and decoders recover equations of lattice points which are then
mapped back to equations over the finite field. This scheme is applicable even
if the transmitters lack channel state information.Comment: IEEE Trans. Info Theory, to appear. 23 pages, 13 figure
Cooperative Radar and Communications Signaling: The Estimation and Information Theory Odd Couple
We investigate cooperative radar and communications signaling. While each
system typically considers the other system a source of interference, by
considering the radar and communications operations to be a single joint
system, the performance of both systems can, under certain conditions, be
improved by the existence of the other. As an initial demonstration, we focus
on the radar as relay scenario and present an approach denoted multiuser
detection radar (MUDR). A novel joint estimation and information theoretic
bound formulation is constructed for a receiver that observes communications
and radar return in the same frequency allocation. The joint performance bound
is presented in terms of the communication rate and the estimation rate of the
system.Comment: 6 pages, 2 figures, to be presented at 2014 IEEE Radar Conferenc
- …