667 research outputs found
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
Outage rates and outage durations of opportunistic relaying systems
Opportunistic relaying is a simple yet efficient cooperation scheme that
achieves full diversity and preserves the spectral efficiency among the
spatially distributed stations. However, the stations' mobility causes temporal
correlation of the system's capacity outage events, which gives rise to its
important second-order outage statistical parameters, such as the average
outage rate (AOR) and the average outage duration (AOD). This letter presents
exact analytical expressions for the AOR and the AOD of an opportunistic
relaying system, which employs a mobile source and a mobile destination
(without a direct path), and an arbitrary number of (fixed-gain
amplify-and-forward or decode-and-forward) mobile relays in Rayleigh fading
environment
- β¦