801 research outputs found
Network-Level Performance Evaluation of a Two-Relay Cooperative Random Access Wireless System
In wireless networks relay nodes can be used to assist the users'
transmissions to reach their destination. Work on relay cooperation, from a
physical layer perspective, has up to now yielded well-known results. This
paper takes a different stance focusing on network-level cooperation. Extending
previous results for a single relay, we investigate here the benefits from the
deployment of a second one. We assume that the two relays do not generate
packets of their own and the system employs random access to the medium; we
further consider slotted time and that the users have saturated queues. We
obtain analytical expressions for the arrival and service rates of the queues
of the two relays and the stability conditions. We investigate a model of the
system, in which the users are divided into clusters, each being served by one
relay, and show its advantages in terms of aggregate and throughput per user.
We quantify the above, analytically for the case of the collision channel and
through simulations for the case of Multi-Packet Reception (MPR), and we
provide insight on when the deployment of a second relay in the system can
yield significant advantages.Comment: Submitted for journal publicatio
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
Max-gain relay selection scheme for wireless networks
© 2020 Karabuk University Next generation wireless systems are supposed to handle high amount of data with broader coverage and high quality of service (QoS). When a signal travels from a source to destination, the signal quality may suffer from the fading, which makes it difficult to receive correct messages. To handle the impact of fading, various diversity techniques are performed with Multiple Input Multiple Output (MIMO). Considering cooperative wireless networks, virtual MIMOs are being used, which also called cooperative diversity. In this paper, we propose a max-gain relay selection scheme (MGRS) for buffer-aided wireless cooperative networks. This scheme determines the best link using the maximum gain based on quality of link and available buffer size. The time slot is divided into two parts, one is used to choose the best link from the source to relay transmission (odd slot) and another time slot (even) is used based on the selection of the best link from the relay to destination. Markov chain model is use to measure buffer status and QoS parameters to evaluate the performance. The proposed scheme provides better QoS (12%) compared to the existing relay selection schemes with respect to throughput, end-to-end delay and outage probability
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