978 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
Channel-Aware Random Access in the Presence of Channel Estimation Errors
In this work, we consider the random access of nodes adapting their
transmission probability based on the local channel state information (CSI) in
a decentralized manner, which is called CARA. The CSI is not directly available
to each node but estimated with some errors in our scenario. Thus, the impact
of imperfect CSI on the performance of CARA is our main concern. Specifically,
an exact stability analysis is carried out when a pair of bursty sources are
competing for a common receiver and, thereby, have interdependent services. The
analysis also takes into account the compound effects of the multipacket
reception (MPR) capability at the receiver. The contributions in this paper are
twofold: first, we obtain the exact stability region of CARA in the presence of
channel estimation errors; such an assessment is necessary as the errors in
channel estimation are inevitable in the practical situation. Secondly, we
compare the performance of CARA to that achieved by the class of stationary
scheduling policies that make decisions in a centralized manner based on the
CSI feedback. It is shown that the stability region of CARA is not necessarily
a subset of that of centralized schedulers as the MPR capability improves.Comment: The material in this paper was presented in part at the IEEE
International Symposium on Information Theory, Cambridge, MA, USA, July 201
Measurement-Adaptive Cellular Random Access Protocols
This work considers a single-cell random access channel (RACH) in cellular
wireless networks. Communications over RACH take place when users try to
connect to a base station during a handover or when establishing a new
connection. Within the framework of Self-Organizing Networks (SONs), the system
should self- adapt to dynamically changing environments (channel fading,
mobility, etc.) without human intervention. For the performance improvement of
the RACH procedure, we aim here at maximizing throughput or alternatively
minimizing the user dropping rate. In the context of SON, we propose protocols
which exploit information from measurements and user reports in order to
estimate current values of the system unknowns and broadcast global
action-related values to all users. The protocols suggest an optimal pair of
user actions (transmission power and back-off probability) found by minimizing
the drift of a certain function. Numerical results illustrate considerable
benefits of the dropping rate, at a very low or even zero cost in power
expenditure and delay, as well as the fast adaptability of the protocols to
environment changes. Although the proposed protocol is designed to minimize
primarily the amount of discarded users per cell, our framework allows for
other variations (power or delay minimization) as well.Comment: 31 pages, 13 figures, 3 tables. Springer Wireless Networks 201
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