773 research outputs found
Queue-Aware Distributive Resource Control for Delay-Sensitive Two-Hop MIMO Cooperative Systems
In this paper, we consider a queue-aware distributive resource control
algorithm for two-hop MIMO cooperative systems. We shall illustrate that relay
buffering is an effective way to reduce the intrinsic half-duplex penalty in
cooperative systems. The complex interactions of the queues at the source node
and the relays are modeled as an average-cost infinite horizon Markov Decision
Process (MDP). The traditional approach solving this MDP problem involves
centralized control with huge complexity. To obtain a distributive and low
complexity solution, we introduce a linear structure which approximates the
value function of the associated Bellman equation by the sum of per-node value
functions. We derive a distributive two-stage two-winner auction-based control
policy which is a function of the local CSI and local QSI only. Furthermore, to
estimate the best fit approximation parameter, we propose a distributive online
stochastic learning algorithm using stochastic approximation theory. Finally,
we establish technical conditions for almost-sure convergence and show that
under heavy traffic, the proposed low complexity distributive control is global
optimal.Comment: 30 pages, 7 figure
Buffer-Aided Relaying with Adaptive Link Selection - Fixed and Mixed Rate Transmission
We consider a simple network consisting of a source, a half-duplex DF relay
with a buffer, and a destination. We assume that the direct source-destination
link is not available and all links undergo fading. We propose two new
buffer-aided relaying schemes. In the first scheme, neither the source nor the
relay have CSIT, and consequently, both nodes are forced to transmit with fixed
rates. In contrast, in the second scheme, the source does not have CSIT and
transmits with fixed rate but the relay has CSIT and adapts its transmission
rate accordingly. In the absence of delay constraints, for both fixed rate and
mixed rate transmission, we derive the throughput-optimal buffer-aided relaying
protocols which select either the source or the relay for transmission based on
the instantaneous SNRs of the source-relay and the relay-destination links. In
addition, for the delay constrained case, we develop buffer-aided relaying
protocols that achieve a predefined average delay. Compared to conventional
relaying protocols, which select the transmitting node according to a
predefined schedule independent of the link instantaneous SNRs, the proposed
buffer-aided protocols with adaptive link selection achieve large performance
gains. In particular, for fixed rate transmission, we show that the proposed
protocol achieves a diversity gain of two as long as an average delay of more
than three time slots can be afforded. Furthermore, for mixed rate transmission
with an average delay of time slots, a multiplexing gain of
is achieved. Hence, for mixed rate transmission, for
sufficiently large average delays, buffer-aided half-duplex relaying with and
without adaptive link selection does not suffer from a multiplexing gain loss
compared to full-duplex relaying.Comment: IEEE Transactions on Information Theory. (Published
Buffer-Aided Relaying with Adaptive Link Selection
In this paper, we consider a simple network consisting of a source, a
half-duplex decode-and-forward relay, and a destination. We propose a new
relaying protocol employing adaptive link selection, i.e., in any given time
slot, based on the channel state information of the source-relay and the
relay-destination link a decision is made whether the source or the relay
transmits. In order to avoid data loss at the relay, adaptive link selection
requires the relay to be equipped with a buffer such that data can be queued
until the relay-destination link is selected for transmission. We study both
delay constrained and delay unconstrained transmission. For the delay
unconstrained case, we characterize the optimal link selection policy, derive
the corresponding throughput, and develop an optimal power allocation scheme.
For the delay constrained case, we propose to starve the buffer of the relay by
choosing the decision threshold of the link selection policy smaller than the
optimal one and derive a corresponding upper bound on the average delay.
Furthermore, we propose a modified link selection protocol which avoids buffer
overflow by limiting the queue size. Our analytical and numerical results show
that buffer-aided relaying with adaptive link selection achieves significant
throughput gains compared to conventional relaying protocols with and without
buffers where the relay employs a fixed schedule for reception and
transmission.Comment: IEEE Journal on Selected Areas in Communications; Special Issue on
Theories and Methods for Advanced Wireless Relay
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