789 research outputs found
Relay Selection with Network Coding in Two-Way Relay Channels
In this paper, we consider the design of joint network coding (NC)and relay
selection (RS) in two-way relay channels. In the proposed schemes, two users
first sequentially broadcast their respective information to all the relays. We
propose two RS schemes, a single relay selection with NC and a dual relay
selection with NC. For both schemes, the selected relay(s) perform NC on the
received signals sent from the two users and forward them to both users. The
proposed schemes are analyzed and the exact bit error rate (BER) expressions
are derived and verified through Monte Carlo simulations. It is shown that the
dual relay selection with NC outperforms other considered relay selection
schemes in two-way relay channels. The results also reveal that the proposed NC
relay selection schemes provide a selection gain compared to a NC scheme with
no relay selection, and a network coding gain relative to a conventional relay
selection scheme with no NC.Comment: 11 pages, 5 figure
Distributed MAC Protocol Supporting Physical-Layer Network Coding
Physical-layer network coding (PNC) is a promising approach for wireless
networks. It allows nodes to transmit simultaneously. Due to the difficulties
of scheduling simultaneous transmissions, existing works on PNC are based on
simplified medium access control (MAC) protocols, which are not applicable to
general multi-hop wireless networks, to the best of our knowledge. In this
paper, we propose a distributed MAC protocol that supports PNC in multi-hop
wireless networks. The proposed MAC protocol is based on the carrier sense
multiple access (CSMA) strategy and can be regarded as an extension to the IEEE
802.11 MAC protocol. In the proposed protocol, each node collects information
on the queue status of its neighboring nodes. When a node finds that there is
an opportunity for some of its neighbors to perform PNC, it notifies its
corresponding neighboring nodes and initiates the process of packet exchange
using PNC, with the node itself as a relay. During the packet exchange process,
the relay also works as a coordinator which coordinates the transmission of
source nodes. Meanwhile, the proposed protocol is compatible with conventional
network coding and conventional transmission schemes. Simulation results show
that the proposed protocol is advantageous in various scenarios of wireless
applications.Comment: Final versio
Divide-and-conquer: Approaching the capacity of the two-pair bidirectional Gaussian relay network
The capacity region of multi-pair bidirectional relay networks, in which a
relay node facilitates the communication between multiple pairs of users, is
studied. This problem is first examined in the context of the linear shift
deterministic channel model. The capacity region of this network when the relay
is operating at either full-duplex mode or half-duplex mode for arbitrary
number of pairs is characterized. It is shown that the cut-set upper-bound is
tight and the capacity region is achieved by a so called divide-and-conquer
relaying strategy. The insights gained from the deterministic network are then
used for the Gaussian bidirectional relay network. The strategy in the
deterministic channel translates to a specific superposition of lattice codes
and random Gaussian codes at the source nodes and successive interference
cancelation at the receiving nodes for the Gaussian network. The achievable
rate of this scheme with two pairs is analyzed and it is shown that for all
channel gains it achieves to within 3 bits/sec/Hz per user of the cut-set
upper-bound. Hence, the capacity region of the two-pair bidirectional Gaussian
relay network to within 3 bits/sec/Hz per user is characterized.Comment: IEEE Trans. on Information Theory, accepte
Decoupled Uplink and Downlink in a Wireless System with Buffer-Aided Relaying
The paper treats a multiuser relay scenario where multiple user equipments
(UEs) have a two-way communication with a common Base Station (BS) in the
presence of a buffer-equipped Relay Station (RS). Each of the uplink (UL) and
downlink (DL) transmission can take place over a direct or over a relayed path.
Traditionally, the UL and the DL path of a given two-way link are coupled, that
is, either both are direct links or both are relayed links. By removing the
restriction for coupling, one opens the design space for a decoupled two-way
links. Following this, we devise two protocols: orthogonal decoupled UL/DL
buffer-aided (ODBA) relaying protocol and non-orthogonal decoupled UL/DL
buffer-aided (NODBA) relaying protocol. In NODBA, the receiver can use
successive interference cancellation (SIC) to extract the desired signal from a
collision between UL and DL signals. For both protocols, we characterize the
transmission decision policies in terms of maximization of the average two-way
sum rate of the system. The numerical results show that decoupling association
and non-orthogonal radio access lead to significant throughput gains for
two-way traffic.Comment: 27 pages, 10 figures, submitted to IEEE Transactions on
Communication
Reliable Physical Layer Network Coding
When two or more users in a wireless network transmit simultaneously, their
electromagnetic signals are linearly superimposed on the channel. As a result,
a receiver that is interested in one of these signals sees the others as
unwanted interference. This property of the wireless medium is typically viewed
as a hindrance to reliable communication over a network. However, using a
recently developed coding strategy, interference can in fact be harnessed for
network coding. In a wired network, (linear) network coding refers to each
intermediate node taking its received packets, computing a linear combination
over a finite field, and forwarding the outcome towards the destinations. Then,
given an appropriate set of linear combinations, a destination can solve for
its desired packets. For certain topologies, this strategy can attain
significantly higher throughputs over routing-based strategies. Reliable
physical layer network coding takes this idea one step further: using
judiciously chosen linear error-correcting codes, intermediate nodes in a
wireless network can directly recover linear combinations of the packets from
the observed noisy superpositions of transmitted signals. Starting with some
simple examples, this survey explores the core ideas behind this new technique
and the possibilities it offers for communication over interference-limited
wireless networks.Comment: 19 pages, 14 figures, survey paper to appear in Proceedings of the
IEE
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