37 research outputs found
Interference Channel with a Half-Duplex Out-of-Band Relay
A Gaussian interference channel (IC) aided by a half-duplex relay is
considered, in which the relay receives and transmits in an orthogonal band
with respect to the IC. The system thus consists of two parallel channels, the
IC and the channel over which the relay is active, which is referred to as
Out-of-Band Relay Channel (OBRC). The OBRC is operated by separating a multiple
access phase from the sources to the relay and a broadcast phase from the relay
to the destinations. Conditions under which the optimal operation, in terms of
the sum-capacity, entails either signal relaying and/or interference forwarding
by the relay are identified. These conditions also assess the optimality of
either separable or non-separable transmission over the IC and OBRC.
Specifically, the optimality of signal relaying and separable coding is
established for scenarios where the relay-to-destination channels set the
performance bottleneck with respect to the source-to-relay channels on the
OBRC. Optimality of interference forwarding and non-separable operation is also
established in special cases.Comment: 5 pages, 5 figures, to appear in Proceedings of IEEE ISIT 201
When Can a Relay Reduce End-to-End Communication Delay?
The impact of relaying on the latency of communication in a relay channel is
studied. Both decode-forward (DF) and amplify-forward (AF) are considered, and
are compared with the point-to-point (P2P) scheme which does not use the relay.
The question as to whether DF and AF can decrease the latency of communicating
a number of bits with a given reliability requirement is addressed. Latency
expressions for the three schemes are derived. Although both DF and AF use a
block-transmission structure which sends the information over multiple
transmission blocks, they can both achieve latencies lower that P2P. Conditions
under which this occurs are obtained. Interestingly, these conditions are more
strict when compared to the conditions under which DF and AF achieve higher
information-theoretic rates than P2P.Comment: 6 pages, 4 figure
Incremental Relaying for the Gaussian Interference Channel with a Degraded Broadcasting Relay
This paper studies incremental relay strategies for a two-user Gaussian
relay-interference channel with an in-band-reception and
out-of-band-transmission relay, where the link between the relay and the two
receivers is modelled as a degraded broadcast channel. It is shown that
generalized hash-and-forward (GHF) can achieve the capacity region of this
channel to within a constant number of bits in a certain weak relay regime,
where the transmitter-to-relay link gains are not unboundedly stronger than the
interference links between the transmitters and the receivers. The GHF relaying
strategy is ideally suited for the broadcasting relay because it can be
implemented in an incremental fashion, i.e., the relay message to one receiver
is a degraded version of the message to the other receiver. A
generalized-degree-of-freedom (GDoF) analysis in the high signal-to-noise ratio
(SNR) regime reveals that in the symmetric channel setting, each common relay
bit can improve the sum rate roughly by either one bit or two bits
asymptotically depending on the operating regime, and the rate gain can be
interpreted as coming solely from the improvement of the common message rates,
or alternatively in the very weak interference regime as solely coming from the
rate improvement of the private messages. Further, this paper studies an
asymmetric case in which the relay has only a single single link to one of the
destinations. It is shown that with only one relay-destination link, the
approximate capacity region can be established for a larger regime of channel
parameters. Further, from a GDoF point of view, the sum-capacity gain due to
the relay can now be thought as coming from either signal relaying only, or
interference forwarding only.Comment: To appear in IEEE Trans. on Inf. Theor
Relaying for Multiuser Networks in the Absence of Codebook Information
This work considers relay assisted transmission for multiuser networks when
the relay has no access to the codebooks used by the transmitters. The relay is
called oblivious for this reason. Of particular interest is the generalized
compress-and-forward (GCF) strategy, where the destinations jointly decode the
compression indices and the transmitted messages, and their optimality in this
setting. The relay-to-destination links are assumed to be out-of-band with
finite capacity. Two models are investigated: the multiple access relay channel
(MARC) and the interference relay channel (IFRC). For the MARC with an
oblivious relay, a new outerbound is derived and it is shown to be tight by
means of achievability of the capacity region using GCF scheme. For the IFRC
with an oblivious relay, a new strong interference condition is established,
under which the capacity region is found by deriving a new outerbound and
showing that it is achievable using GCF scheme. The result is further extended
to establish the capacity region of M-user MARC with an oblivious relay, and
multicast networks containing M sources and K destinations with an oblivious
relay.Comment: submitted to IEEE Transactions on Information Theor
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