Ad Hoc多媒體網路中公平排程機制之探討
Fair Scheduling in Multimedia Mobile Ad Hoc Networks
Date Issued
2004
Date
2004
Author(s)
Chao, Hsi-Lu
DOI
en-US
Abstract
An ad hoc network is a self-organizing wireless network comprised only of mobile nodes. In such a network, there is no need for preexisting fixed infrastructure, and each node plays both roles of a terminal and a router. Therefore, an ad hoc network can be created and used by “anytime, anywhere.” This advantage elicits ad hoc networks been immediate interested among military, police, rescue agencies, especially under disorganized or hostile environments, and home area (e.g., a conference or classroom, single building, convention center). Resource management is essential to provide multimedia application service in ad hoc networks.
This dissertation studies resource management for multimedia mobile ad hoc networks. In particular, we focus on providing fair scheduling with Quality of Service (QoS) support for mobile ad hoc networks. We consider two types of flows to be transmitted by nodes: guaranteed and best effort flows. The goal is to satisfy the QoS requirements of guaranteed flows and to provide global fairness among all flows.
We propose a distributed flow weight calculation scheme which can be integrated with existing timestamp-based fair scheduling protocols for ad hoc networks to guarantee QoS demands and fairly allocate residual bandwidth to all flows. In addition, we propose a credit-based fair scheduling mechanism, called Credit-based Slot Allocation Protocol (CSAP). In CSAP, nodes are logically grouped into clusters, each with a scheduler. The scheduler assigns time slots to mobiles in its cluster based on the first tier algorithm. The mobile scheduled to send at the next time slot then in turn assigns the time slot to a relayed flow determined by the second tier algorithm. We elaborate CSAP detailed operations.
As we know that each node in an ad hoc network is capable of free movement. However, mobility will causes the constructed path to break due to some path nodes move away, and thus definitely has a great impact on the performance of fair scheduling protocol. We use CSAP as an example to illustrate how to deal with node mobility and still can achieve our design goals. Besides, we model each multihop flow as multiple single-hop flow segments. These segments are then correlated such that a downstream segment will not be allocated a slot unless the upstream segments have all been allocated.
It is obvious that the error rate of a wireless network is much higher than that of a wireline network. Imaging one situation that a node, say node N, is the channel possessor to transmit packets, however, it incurs channel error. That means it cannot transmit packets successfully, and the overall network throughput degrades. One possible solution is for node N to release the channel to other nodes capable of successful transmissions, and then be compensated later. For this channel error issue, we propose two mechanisms: Credit-Based Compensation Protocol (CBCP), and Timestamp-Based Compensation Protocol (TBCP). The major differences between CBCP and TBCP are twofold: one is the scheduling parameter, and the other is operation characteristic (CBCP is a centralized with distributed mechanism, and in contrast, TBCP is a distributed one).
We evaluate the performance of all proposed mechanisms by simulations. The results show that all mechanisms can guarantee QoS flows’ service demands, provides global fairness for best effort flows, and improves overall system throughput.
Subjects
公平性
公平排程
移動性
ad hoc無線網路
頻寬補償
fairness
mobility
fair scheduling
ad hoc wireless networks
channel compensation
multihop
Type
thesis
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