2 research outputs found
Fading Two-Way Relay Channels: Physical-Layer Versus Digital Network Coding
In this paper, we consider three transmit strategies for the fading
three-node, two-way relay network (TWRN) -- physical-layer network coding
(PNC), digital network coding (DNC) and codeword superposition (CW-Sup). The
aim is to minimize the total average energy needed to deliver a given pair of
required average rates. Full channel state information is assumed to be
available at all transmitters and receivers. The optimization problems
corresponding to the various strategies in fading channels are formulated,
solved and compared. For the DNC-based strategies, a simple time sharing of
transmission of the network-coded message and the remaining bits of the larger
message (DNC-TS) is considered first. We extend this approach to include a
superposition strategy (DNC-Sup), in which the network-coded message and the
remainder of the longer source message are superimposed before transmission. It
is demonstrated theoretically that DNC-Sup outperforms DNC-TS and CW-Sup in
terms of total average energy usage. More importantly, it is shown in
simulation that DNC-Sup performs better than PNC if the required rate is low
and worse otherwise. Finally, an algorithm to select the optimal strategy in
terms of energy usage subject to different rate pair requirements is presented.Comment: 25 pages, 5 figure
Digital Network Coding Aided Two-way Relaying: Energy Minimization and Queue Analysis
In this paper, we consider a three node, two-way relay system with digital
network coding over static channels where all link gains are assumed to be
constant during transmission. The aim is to minimize total energy consumption
while ensuring queue stability at all nodes, for a given pair of random packet
arrival rates. Specifically, we allow for a set of transmission modes and solve
for the optimal fraction of resources allocated to each mode, including
multiaccess uplink transmission mode and network coding broadcasting mode. In
addition, for the downlink, we find the condition to determine whether
superposition coding with excess data over the better link and network coded
data for both users is energy efficient and the corresponding optimization is
formulated and solved. To tackle the queue evolution in this network, we
present a detailed analysis of the queues at each node using a random
scheduling method that closely approximates the theoretical design, through a
two-dimensional Markov chain model