55 research outputs found
Broadcast Capacity Region of Two-Phase Bidirectional Relaying
In a three-node network a half-duplex relay node enables bidirectional
communication between two nodes with a spectral efficient two phase protocol.
In the first phase, two nodes transmit their message to the relay node, which
decodes the messages and broadcast a re-encoded composition in the second
phase. In this work we determine the capacity region of the broadcast phase. In
this scenario each receiving node has perfect information about the message
that is intended for the other node. The resulting set of achievable rates of
the two-phase bidirectional relaying includes the region which can be achieved
by applying XOR on the decoded messages at the relay node. We also prove the
strong converse for the maximum error probability and show that this implies
that the [\eps_1,\eps_2]-capacity region defined with respect to the average
error probability is constant for small values of error parameters \eps_1,
\eps_2.Comment: 25 pages, 2 figures, submitted to IEEE Transactions on Information
Theor
The Degrees of Freedom of the MIMO Y-channel
The degrees of freedom (DoF) of the MIMO Y-channel, a multi-way communication
network consisting of 3 users and a relay, are characterized for arbitrary
number of antennas. The converse is provided by cut-set bounds and novel
genie-aided bounds. The achievability is shown by a scheme that uses
beamforming to establish network coding on-the-fly at the relay in the uplink,
and zero-forcing pre-coding in the downlink. It is shown that the network has
min{2M_2+2M_3,M_1+M_2+M_3,2N} DoF, where M_j and N represent the number of
antennas at user j and the relay, respectively. Thus, in the extreme case where
M_1+M_2+M_3 dominates the DoF expression and is smaller than N, the network has
the same DoF as the MAC between the 3 users and the relay. In this case, a
decode and forward strategy is optimal. In the other extreme where 2N
dominates, the DoF of the network is twice that of the aforementioned MAC, and
hence network coding is necessary. As a byproduct of this work, it is shown
that channel output feedback from the relay to the users has no impact on the
DoF of this channel.Comment: 5 pages, 4 figures, ISIT 201
A Unified Scheme for Two-Receiver Broadcast Channels with Receiver Message Side Information
This paper investigates the capacity regions of two-receiver broadcast
channels where each receiver (i) has both common and private-message requests,
and (ii) knows part of the private message requested by the other receiver as
side information. We first propose a transmission scheme and derive an inner
bound for the two-receiver memoryless broadcast channel. We next prove that
this inner bound is tight for the deterministic channel and the more capable
channel, thereby establishing their capacity regions. We show that this inner
bound is also tight for all classes of two-receiver broadcast channels whose
capacity regions were known prior to this work. Our proposed scheme is
consequently a unified capacity-achieving scheme for these classes of broadcast
channels.Comment: accepted and to be presented at the 2015 IEEE International Symposium
on Information Theory (ISIT 2015
The Capacity Region of Restricted Multi-Way Relay Channels with Deterministic Uplinks
This paper considers the multi-way relay channel (MWRC) where multiple users
exchange messages via a single relay. The capacity region is derived for a
special class of MWRCs where (i) the uplink and the downlink are separated in
the sense that there is no direct user-to-user links, (ii) the channel is
restricted in the sense that each user's transmitted channel symbols can depend
on only its own message, but not on its received channel symbols, and (iii) the
uplink is any deterministic function.Comment: Author's final version (to be presented at ISIT 2012
Coding Schemes for a Class of Receiver Message Side Information in AWGN Broadcast Channels
This paper considers the three-receiver AWGN broadcast channel where the
receivers (i) have private-message requests and (ii) know some of the messages
requested by other receivers as side information. For this setup, all possible
side information configurations have been recently classified into eight groups
and the capacity of the channel has been established for six groups (Asadi et
al., ISIT 2014). We propose inner and outer bounds for the two remaining
groups, groups 4 and 7. A distinguishing feature of these two groups is that
the weakest receiver knows the requested message of the strongest receiver as
side information while the in-between receiver does not. For group 4, the inner
and outer bounds coincide at certain regions. For group 7, the inner and outer
bounds coincide, thereby establishing the capacity, for four members out of all
eight members of the group; for the remaining four members, the proposed bounds
reduce the gap between the best known inner and outer bounds.Comment: accepted and to be presented at the 2014 IEEE Information Theory
Workshop (ITW
Functional-Decode-Forward for the General Discrete Memoryless Two-Way Relay Channel
We consider the general discrete memoryless two-way relay channel, where two
users exchange messages via a relay, and propose two functional-decode-forward
coding strategies for this channel. Functional-decode-forward involves the
relay decoding a function of the users' messages rather than the individual
messages themselves. This function is then broadcast back to the users, which
can be used in conjunction with the user's own message to decode the other
user's message. Via a numerical example, we show that functional-decode-forward
with linear codes is capable of achieving strictly larger sum rates than those
achievable by other strategies
On Achievable Rate Regions of the Asymmetric AWGN Two-Way Relay Channel
This paper investigates the additive white Gaussian noise two-way relay
channel, where two users exchange messages through a relay. Asymmetrical
channels are considered where the users can transmit data at different rates
and at different power levels. We modify and improve existing coding schemes to
obtain three new achievable rate regions. Comparing four downlink-optimal
coding schemes, we show that the scheme that gives the best sum-rate
performance is (i) complete-decode-forward, when both users transmit at low
signal-to-noise ratio (SNR); (ii) functional-decode-forward with nested lattice
codes, when both users transmit at high SNR; (iii) functional-decode-forward
with rate splitting and time-division multiplexing, when one user transmits at
low SNR and another user at medium--high SNR.Comment: to be presented at ISIT 201
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