126 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
Interference-Based Optimal Power-Efficient Access Scheme for Cognitive Radio Networks
In this paper, we propose a new optimization-based access strategy of
multipacket reception (MPR) channel for multiple secondary users (SUs)
accessing the primary user (PU) spectrum opportunistically. We devise an
analytical model that realizes the multipacket access strategy of SUs that
maximizes the throughput of individual backlogged SUs subject to queue
stability of the PU. All the network receiving nodes have MPR capability. We
aim at maximizing the throughput of the individual SUs such that the PU's queue
is maintained stable. Moreover, we are interested in providing an
energy-efficient cognitive scheme. Therefore, we include energy constraints on
the PU and SU average transmitted energy to the optimization problem. Each SU
accesses the medium with certain probability that depends on the PU's activity,
i.e., active or inactive. The numerical results show the advantage in terms of
SU throughput of the proposed scheme over the conventional access scheme, where
the SUs access the channel randomly with fixed power when the PU is sensed to
be idle
Modern Random Access for Satellite Communications
The present PhD dissertation focuses on modern random access (RA) techniques.
In the first part an slot- and frame-asynchronous RA scheme adopting replicas,
successive interference cancellation and combining techniques is presented and
its performance analysed. The comparison of both slot-synchronous and
asynchronous RA at higher layer, follows. Next, the optimization procedure, for
slot-synchronous RA with irregular repetitions, is extended to the Rayleigh
block fading channel. Finally, random access with multiple receivers is
considered.Comment: PhD Thesis, 196 page
Relay-assisted Multiple Access with Full-duplex Multi-Packet Reception
The effect of full-duplex cooperative relaying in a random access multiuser
network is investigated here. First, we model the self-interference incurred
due to full-duplex operation, assuming multi-packet reception capabilities for
both the relay and the destination node. Traffic at the source nodes is
considered saturated and the cooperative relay, which does not have packets of
its own, stores a source packet that it receives successfully in its queue when
the transmission to the destination has failed. We obtain analytical
expressions for key performance metrics at the relay, such as arrival and
service rates, stability conditions, and average queue length, as functions of
the transmission probabilities, the self interference coefficient, and the
links' outage probabilities. Furthermore, we study the impact of the relay node
and the self-interference coefficient on the per-user and aggregate throughput,
and the average delay per packet. We show that perfect self-interference
cancelation plays a crucial role when the SINR threshold is small, since it may
result to worse performance in throughput and delay comparing with the
half-duplex case. This is because perfect self-interference cancelation can
cause an unstable queue at the relay under some conditions.Comment: Accepted for publication in the IEEE Transactions on Wireless
Communication
Throughput, stability and fairness of carrier-sense multiple access with cooperative diversity
Cooperative diversity has been identified as a potential candidate for boosting the physical (PHY) layer performance of future wireless networks. However, several issues remain open today in the design of an appropriate medium access control (MAC) layer for this type of system. This paper attempts to partially fill this gap by addressing the MAC-PHY cross-layer design of a class of carrier-sense multiple access protocols where collision-free transmissions are assisted by the potential cooperative retransmission of the remaining silent terminals in the network. Unlike previous works, the analysis is focused on full asymmetrical settings, where terminals experience different channel and queuing statistics. To achieve this goal, a packet reception model is here proposed for cooperative schemes where the relaying phase is activated only when the reception of previous (re)transmissions has failed. Closed-form expressions of correct reception probability are derived for Rayleigh fading channels assuming that correct reception occurs only when the instantaneous signal-to-noise ratio (SNR) exceeds a reception threshold. This reception model allows for a MAC-layer design aware of PHY-layer information, and vice versa, PHY-layer enhancement and activation using MAC-layer information. The boundary of the throughput region (i.e., the set of all achievable throughput values) is derived in a parametric closed-form expression using a multi-objective optimization approach. A method for deriving a non-parametric form was further proposed, which allows for a geometric interpretation of the two-user case. Stability features such as backlog user distribution and backlog delay are evaluated by using a novel Markov model for asymmetrical systems. Fairness is evaluated by means of the Gini index, which is a metric commonly used in the field of economics to measure income inequality. The protocol is shown to outperform its non-cooperative counterparts under diverse network conditions that are here discussed
- …