127 research outputs found
Stability Region of a Slotted Aloha Network with K-Exponential Backoff
Stability region of random access wireless networks is known for only simple
network scenarios. The main problem in this respect is due to interaction among
queues. When transmission probabilities during successive transmissions change,
e.g., when exponential backoff mechanism is exploited, the interactions in the
network are stimulated. In this paper, we derive the stability region of a
buffered slotted Aloha network with K-exponential backoff mechanism,
approximately, when a finite number of nodes exist. To this end, we propose a
new approach in modeling the interaction among wireless nodes. In this
approach, we model the network with inter-related quasi-birth-death (QBD)
processes such that at each QBD corresponding to each node, a finite number of
phases consider the status of the other nodes. Then, by exploiting the
available theorems on stability of QBDs, we find the stability region. We show
that exponential backoff mechanism is able to increase the area of the
stability region of a simple slotted Aloha network with two nodes, more than
40\%. We also show that a slotted Aloha network with exponential backoff may
perform very near to ideal scheduling. The accuracy of our modeling approach is
verified by simulation in different conditions.Comment: 30 pages, 6 figure
Modeling, Analysis and Impact of a Long Transitory Phase in Random Access Protocols
In random access protocols, the service rate depends on the number of
stations with a packet buffered for transmission. We demonstrate via numerical
analysis that this state-dependent rate along with the consideration of Poisson
traffic and infinite (or large enough to be considered infinite) buffer size
may cause a high-throughput and extremely long (in the order of hours)
transitory phase when traffic arrivals are right above the stability limit. We
also perform an experimental evaluation to provide further insight into the
characterisation of this transitory phase of the network by analysing
statistical properties of its duration. The identification of the presence as
well as the characterisation of this behaviour is crucial to avoid
misprediction, which has a significant potential impact on network performance
and optimisation. Furthermore, we discuss practical implications of this
finding and propose a distributed and low-complexity mechanism to keep the
network operating in the high-throughput phase.Comment: 13 pages, 10 figures, Submitted to IEEE/ACM Transactions on
Networkin
Analysis of Half-Duplex Two-Node Slotted ALOHA Network With Asynchronous Traffic
Despite the long history of research on slotted ALOHA, the exact analysis of
the average delay is still in question as the performance of each node is
coupled with the activity of other nodes. In this paper, we consider a network
comprised of two half-duplex transmitter nodes with asynchronous arrival
traffic that follow the slotted ALOHA protocol. We propose a new queueing
theoretic model based on the state-dependent queues to analyze the network. In
addition, we derive the exact values of delay and stability region for each
node. The numerical results demonstrate the accuracy of our proposed model.Comment: 5 pages, 5 figure
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