Browsing by Subject "STDMA"

Now showing 1 - 3 of 3

Open Access
Joint link
(2009) Kaybal, Fazlı
In this thesis, we study the joint scheduling and routing problem in spatial reuse Time Division Multiple Access (STDMA) based multi-channel/multiradio/multi-rate wireless mesh networks (WMNs). The main objective of the joint scheduling and routing problem addressed in thesis is to reduce the number of required TDMA time slots to deliver all packets to their destinations. Since the optimum solution to the problem is NP-hard, we propose a greedy iterative solution methodology. The problem is formulated as an integer linear program (ILP) under the physical interference model. We consider two versions of the problem in order to investigate the factors affecting the capacity of WMNs. In the first one, we perform scheduling and routing when the number of channels and number of radios are varied for multi-rate WMNs where nodes are equipped with omni-directional antennas. This analysis is done for both single-class (best-effort traffic) and two-class (best-effort and delay sensitive classes) traffic models. We then extend this analysis by adding the power control scheme which allows transmitters to change the transmitting powers slot-by-slot. Finally, joint scheduling and routing problem is extended for WMNs where nodes are equipped with multiple sectored antennas. We show that the network performance is improved with more radio resources, e.g., using multiple orthogonal channels, multiple radios per node, transmit power control scheme, and directional antennas in terms of delay and total dissipated energy. The network throughput when using 3 channels and 3 radios is increased by up to 67.2% compared to single channel WMNs and the total dissipated energy is reduced by up to 45.5% with transmit power control scheme. Finally, when directional antennas with 6 sectors are used at both transmitters and receivers, the network throughput increases by up to 72.6% compared to omni-directional antenna case.
Open Access
OLSR-Aware cross-layer channel access scheduling in wireless mesh networks
(2009) Kaş, Miray
A wireless mesh network (WMN) is a communications network in which the nodes are organized to form a mesh topology. WMNs are expected to resolve the limitations and significantly improve the performance of wireless ad-hoc, local area, personal area, and metropolitan area networks, which is the reason that they are experiencing fast-breaking progress and deployments. WMNs typically employ spatial TDMA (STDMA) based channel access schemes which are suitable for the high traffic demands of WMNs. Current research trends focus on using loosening the strict layered network implementation in order to look for possible ways of performance improvements. In this thesis, we propose two STDMA-based cross-layer OLSR-Aware channel access scheduling schemes (one distributed, one centralized) that aim better utilizing the network capacity and increasing the overall application throughput by using OLSR-specific routing layer information in link layer scheduling. The proposed centralized algorithm provides a modification of the traditional vertex coloring algorithm while the distributed algorithm is a fully distributed pseudo-random algorithm in which each node makes decisions using local information. Proposed schemes are compared against one another and against their Non-OLSR-Aware versions via extensive ns-2 simulations. Our simulation results indicate that MAC layer can obtain OLSR-specific information with no extra control overhead and utilizing OLSR-specific information significantly improves the overall network performance both in distributed and centralized schemes. We further show that link layer algorithms that target the maximization of concurrent slot allocations do not necessarily increase the application throughput.
Open Access
Topology design and scheduling in STDMA based wireless ad hoc networks
(2003) Ergin, Sadettin Alp
With current advances in technology, wireless networks are increasing in popularity. Wireless networks allow users the freedom to travel from one location to another without interruption of their communication activities. Ad hoc networks, a subset of wireless networks, allow the formation of a wireless network without the need for a base station. Since no fixed infrastructure is involved in the communication, the nodes of ad hoc networks can communicate with each other or can relay data to other nodes. With this flexibility, wireless ad hoc networks have the ability to form a network anywhere, at any time, as long as two or more wireless users are willing to communicate. Managing ad hoc networks is a significantly more difficult task than managing wireline networks. The network requirements should be met by combined efforts of all the mobile nodes themselves. The nodes of ad hoc networks often operate under severe constraints, such as limited battery power, variable link quality and limited shared bandwidth. In this study, the topology design issue in ad hoc wireless networks is investigated. We employ hierarchical routing where the network topology is composed of clusters interconnected via a root node. Cluster-based topologies are suitable for military services, an important application area for ad hoc networks. The common power control technique (COMPOW) is used in this thesis where all nodes transmit at the same power level. Nodes employ the spatial TDMA (STDMA) scheme in order to access the channel. An important task is how to produce a minimum STDMA frame length, and this problem is known to be NP complete. We develop a heuristic algorithm for generating the minimum STDMA frame length. A new interference model for ad hoc networks is proposed which utilizes a hypergraph model. The relationship between the frame length, number of clusters and the transmit power level are investigated through numerical examples using a 15- node network.