938 research outputs found
On Optimizing the Backoff Interval for Random Access Schemes
To improve the channel throughput and the fairness
of random access channels, we propose a new backoff algorithm,
namely, the sensing backoff algorithm (SBA). A novel feature of
the SBA scheme is the sensing mechanism, in which every node
modifies its backoff interval according to the results of the sensed
channel activities. In particular, every active node sensing the successful
transmission decreases its backoff interval by an additive
factor of the transmission time of a packet. In order to find the
optimum parameters for the SBA scheme, we have studied the optimum
backoff intervals as a function of different number of active
nodes (N) in a single transmission area with pure ALOHA-type
channels.We have found that the optimum backoff interval should
be 4N times the transmission time of a packet when the random
access channel operates under a pure ALOHA scheme. Based on
this result, we have numerically calculated the optimum values of
the parameters for SBA, which are independent of N. The SBA
scheme operates close to the optimum backoff interval. Furthermore,
its operation does not depend on the knowledge of N. The
optimum backoff interval and the SBA scheme are also studied by
simulative means. It is shown that the SBA scheme out-performs
other backoff schemes, such as binary exponential backoff (BEB)
and multiplicative increase linear decrease (MILD). As a point of
reference, the SBA scheme offers a channel capacity of 0.19 when N
is 10, while the MILD scheme can only offer 0.125. The performance
gain is about 50%
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
Survey of Spectrum Sharing for Inter-Technology Coexistence
Increasing capacity demands in emerging wireless technologies are expected to
be met by network densification and spectrum bands open to multiple
technologies. These will, in turn, increase the level of interference and also
result in more complex inter-technology interactions, which will need to be
managed through spectrum sharing mechanisms. Consequently, novel spectrum
sharing mechanisms should be designed to allow spectrum access for multiple
technologies, while efficiently utilizing the spectrum resources overall.
Importantly, it is not trivial to design such efficient mechanisms, not only
due to technical aspects, but also due to regulatory and business model
constraints. In this survey we address spectrum sharing mechanisms for wireless
inter-technology coexistence by means of a technology circle that incorporates
in a unified, system-level view the technical and non-technical aspects. We
thus systematically explore the spectrum sharing design space consisting of
parameters at different layers. Using this framework, we present a literature
review on inter-technology coexistence with a focus on wireless technologies
with equal spectrum access rights, i.e. (i) primary/primary, (ii)
secondary/secondary, and (iii) technologies operating in a spectrum commons.
Moreover, we reflect on our literature review to identify possible spectrum
sharing design solutions and performance evaluation approaches useful for
future coexistence cases. Finally, we discuss spectrum sharing design
challenges and suggest future research directions
Low-complexity medium access control protocols for QoS support in third-generation radio access networks
One approach to maximizing the efficiency of
medium access control (MAC) on the uplink in a future wideband
code-division multiple-access (WCDMA)-based third-generation
radio access network, and hence maximize spectral efficiency,
is to employ a low-complexity distributed scheduling control
approach. The maximization of spectral efficiency in third-generation
radio access networks is complicated by the need to
provide bandwidth-on-demand to diverse services characterized
by diverse quality of service (QoS) requirements in an interference
limited environment. However, the ability to exploit the full
potential of resource allocation algorithms in third-generation
radio access networks has been limited by the absence of a metric
that captures the two-dimensional radio resource requirement,
in terms of power and bandwidth, in the third-generation radio
access network environment, where different users may have
different signal-to-interference ratio requirements. This paper
presents a novel resource metric as a solution to this fundamental
problem. Also, a novel deadline-driven backoff procedure has
been presented as the backoff scheme of the proposed distributed
scheduling MAC protocols to enable the efficient support of
services with QoS imposed delay constraints without the need
for centralized scheduling. The main conclusion is that low-complexity
distributed scheduling control strategies using overload
avoidance/overload detection can be designed using the proposed
resource metric to give near optimal performance and thus maintain
a high spectral efficiency in third-generation radio access
networks and that importantly overload detection is superior to
overload avoidance
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