1,912 research outputs found
Performance of distributed mechanisms for flow admission in wireless adhoc networks
Given a wireless network where some pairs of communication links interfere
with each other, we study sufficient conditions for determining whether a given
set of minimum bandwidth quality-of-service (QoS) requirements can be
satisfied. We are especially interested in algorithms which have low
communication overhead and low processing complexity. The interference in the
network is modeled using a conflict graph whose vertices correspond to the
communication links in the network. Two links are adjacent in this graph if and
only if they interfere with each other due to being in the same vicinity and
hence cannot be simultaneously active. The problem of scheduling the
transmission of the various links is then essentially a fractional, weighted
vertex coloring problem, for which upper bounds on the fractional chromatic
number are sought using only localized information. We recall some distributed
algorithms for this problem, and then assess their worst-case performance. Our
results on this fundamental problem imply that for some well known classes of
networks and interference models, the performance of these distributed
algorithms is within a bounded factor away from that of an optimal, centralized
algorithm. The performance bounds are simple expressions in terms of graph
invariants. It is seen that the induced star number of a network plays an
important role in the design and performance of such networks.Comment: 21 pages, submitted. Journal version of arXiv:0906.378
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Performance enhancements for single hop and multi-hop meshed high data rate wireless personal area networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The High Data Rate (HDR) Wireless Personal Area Networks (WPANs) typically have a limited operating range and are intended to support demanding multi-media applications at high data rates. In order to extend the communication range, HDR WPANs can operate in a wireless mesh configuration (i.e. enable multiple WPAN clusters) to communicate in a multi-hop fashion. HDR WPANs face several research challenges and some of the open key issues are limited capacity, optimum resource allocation to requesting devices and maintaining Quality of Service (QoS) for real time multimedia flows. Although, there have been some scheduling algorithms proposed for HDR WPANs, the main objective is to maintain the QoS in most cases whereas efficient and fair utilization of network capacity is still largely open for research. This thesis mainly intends to resolve the issues related to capacity of HDR WPANs such as admission control, fair allocation of Channel Time Allocations (CTAs), improvement in capacity through transmission power control, and efficient utilization of time by each flow. A technique which re-orders the time slots to reduce queuing delay for meshed WPANs is also proposed and evaluated.
The first contribution aims to improve peer-to-peer connectivity in case of two or more independent piconet devices by proposing an inter-PAN communication framework that is augmented by an admission control strategy to handle the cases when the superframe capacity is congested. The queued devices are prioritized by proposing a parameter called the Rejection Ratio. The second contribution consists of a resource allocation framework for meshed WPANs. The main objectives are to reduce the control traffic due to high volume of channel time reservation requests and introduce an element of fairness in the channel time allocated to requesting devices. The objectives are achieved by using traffic prediction techniques and an estimated backoff procedure to reduce control traffic, and define different policies based on offered traffic for fair allocation of channel time. The centralized scheme uses traffic prediction techniques to use the proposed concept of bulk reservations. Based on the bulk reservations and resource allocation policies, the overall overhead is reduced while an element of fairness is shown to be maintained for certain scenarios. In the third contribution, the concepts of Time Efficiency and CTA switching are introduced to improve communication efficiency and utilization of superframe capacity in meshed WPANs. Two metrics known as Switched Time Slot (STS) and Switched Time Slot with Re-ordering (STS-R) are proposed which aim to achieve the purpose. The final contribution proposes and evaluates a technique called CTA overlappnig to improve capacity in single hop and meshed WPANs using tramission power control. Extensive simulation studies are performed to analyze and to evaluate the proposed techniques. Simulation results demonstrate significant improvements in meshed WPANs performance in terms of capacity utilization, improvement in fairness index for CTA allocation by upto 62% in some cases, reduction in control traffic overhead by upto 70% and reduction in delay for real time flows by more than 10% in some cases
SIMULATIVE ANALYSIS OF ROUTING AND LINK ALLOCATION STRATEGIES IN ATM NETWORKS
For Broadband Integrated Services Digital (B-ISDN) networks ATM is a promising technology,
because it supports a wide range of services with different bandwidth demands,
traffic characteristics and QoS requirements. This diversity of services makes traffic control
in these networks much more complicated than in existing circuit or packet switched
networks. Traffic control procedures include both actions necessary for setting up virtual
connections (VC), such as bandwidth assignment, call admission, routing and resource
allocation and congestion control measures necessary to maintain throughput in overload
situations.
This paper deals with routing and link allocation, and analyses the performance of
such algorithms in terms of call blocking probability, link capacity utilization and QoS
parameters. In our model the network carries out the following steps when a call is offered
to the network:
(1) Assign an appropriate bandwidth to an offered call (Bandwidth assignment)
(2) Find a transmission path between the source and destination with enough available
transmission capacity (Routing)
(3) Allocate resource along that path (Link allocation)
We consider an example 5-node network [7], conduct an extensive survey of routing,
and link allocation algorithms. Regarding step (1) we employ the equivalent link capacity
assignment presented by various interesting papers [1]-[5]. We find that the choice of routing
and link allocation algorithms has a great impact on network performance, and that
different routing algorithms perform best under different network load values. Shortest
path routing (SPR) is a good candidate for low, alternate routing (AR) for medium and
non-alternate routing (NAR) for high traffic load values.
Concerning link allocation strategies, we find that partial overlap (POL) strategies
that seem to be able to present near optimal performance are superior to complete sharing
(CS) and complete partitioning (CP) strategies. As a further improvement of the POL
scheme, we propose a 2-level link allocation algorithm, which yields highest link utilization.
In this scheme, not only the accesses of different service classes to different virtual
paths (VPs) are controlled, but also an individual VP's transmission capacity is optimally
allocated to the service classes according to their bandwidth requirements in order to
assure high link utilization. This method seems to be adjustable to the fine degree of
granularity of bandwidth demands in B-ISDN networks.
It is shown that in order to minimize cell loss the call level resource allocation
plays a significant role: networks with the same buffer size switches display different cell
loss probabilities in the nodes and impose different end-to-end delay on cells if the link
allocation and routing differ. Again, we find that when traffic is tolerable by the network,
SPR causes the least cell loss. This can be explained by the fact that SPR spreads the
incoming calls in the network. It eagerly seeks new routes instead of utilizing the already
used but still not congested routes. SPR obviously wastes more rapidly link and buffer
capacity as traffic load becomes higher than the AR, which chooses a new route only
when it has to, i.e. when the route of higher priority becomes congested. That is why
we experience that as soon as the SPR starts loosing cells, it indicates that available
resources have been consumed and it rapidly goes up to very high blocking probabilities
after a small further increase of load
Energy-efficient wireless communication
In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters
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