116 research outputs found
On the performance of STDMA Link Scheduling and Switched Beamforming Antennas in Wireless Mesh Networks
Projecte final de carrera realitzat en col.laboració amb King's College LondonWireless Mesh Networks (WMNs) aim to revolutionize Internet connectivity due to
its high throughput, cost-e ectiveness and ease deployment by providing last mile
connectivity and/or backhaul support to di erent cellular networks. In order not to
jeopardize their successful deployment, several key issues must be investigated and
overcome to fully realize its potential. For WMNs that utilize Spatial Reuse TDMA
as the medium access control, link scheduling still requires further enhancements.
The rst main contribution of this thesis is a fast randomized parallel link swap
based packing (RSP) algorithm for timeslot allocation in a spatial time division multiple
access (STDMA) wireless mesh network. The proposed randomized algorithm
extends several greedy scheduling algorithms that utilize the physical interference
model by applying a local search that leads to a substantial improvement in the
spatial timeslot reuse. Numerical simulations reveal that compared to previously
scheduling schemes the proposed randomized algorithm can achieve a performance
gain of up to 11%. A signi cant bene t of the proposed scheme is that the computations
can be parallelized and therefore can e ciently utilize commoditized and
emerging multi-core and/or multi-CPU processors.
Furthermore, the use of selectable multi-beam directional antennas in WMNs,
such as beam switched phase array antennas, can assist to signi cantly enhance
the overall reuse of timeslots by reducing interference levels across the network and
thereby increasing the spectral e ciency of the system. To perform though a switch
on the antenna beam it may require up to 0.25 ms in practical deployed networks,
while at the same time very frequent beam switchings can a ect frame acquisition
and overall reliability of the deployed mesh network.
The second key contribution of this thesis is a set of algorithms that minimize the
overall number of required beam switchings in the mesh network without penalizing
the spatial reuse of timeslots, i.e., keeping the same overall frame length in the
network. Numerical investigations reveal that the proposed set of algorithms can
reduce the number of beam switchings by almost 90% without a ecting the frame
length of the network
Joint Routing and STDMA-based Scheduling to Minimize Delays in Grid Wireless Sensor Networks
In this report, we study the issue of delay optimization and energy
efficiency in grid wireless sensor networks (WSNs). We focus on STDMA (Spatial
Reuse TDMA)) scheduling, where a predefined cycle is repeated, and where each
node has fixed transmission opportunities during specific slots (defined by
colors). We assume a STDMA algorithm that takes advantage of the regularity of
grid topology to also provide a spatially periodic coloring ("tiling" of the
same color pattern). In this setting, the key challenges are: 1) minimizing the
average routing delay by ordering the slots in the cycle 2) being energy
efficient. Our work follows two directions: first, the baseline performance is
evaluated when nothing specific is done and the colors are randomly ordered in
the STDMA cycle. Then, we propose a solution, ORCHID that deliberately
constructs an efficient STDMA schedule. It proceeds in two steps. In the first
step, ORCHID starts form a colored grid and builds a hierarchical routing based
on these colors. In the second step, ORCHID builds a color ordering, by
considering jointly both routing and scheduling so as to ensure that any node
will reach a sink in a single STDMA cycle. We study the performance of these
solutions by means of simulations and modeling. Results show the excellent
performance of ORCHID in terms of delays and energy compared to a shortest path
routing that uses the delay as a heuristic. We also present the adaptation of
ORCHID to general networks under the SINR interference model
Modified Greedy Physical Link Scheduling Algorithm for Improving Wireless Mesh Network Performance
The algorithm to allocate mesh active link to radio resource timeslot in wireless mesh network (WMN) is investigated. This paper proposes the novel method to allocate multiple links in one timeslot for improving the wireless mesh network throughput via spatial time division multiple access (STDMA) protocol. The throughput improvement is obtained by modifying greedy based algorithm that is widely known as a low complexity algorithm. We propose and investigate new parameters in the greedy based algorithm that can be used as scheduling control parameters, i.e. interference weight, scheduling weight, and the sum of link’s degree. Simulation results indicate that this approximation increases network performance in throughput and length of scheduling performance closed to the upper bound performance that is achieved by the algorithm that uses the physical interference model.
Joint Link Scheduling and Routing for Load Balancing in STDMA Wireless Mesh Networks
In wireless mesh networks, it is known to be effective to use a TDMA based MAC than a contention-based CSMA. In addition, if spatial TDMA is used, network performance can be improved further because of its spatial reuse effect. However this scheme still has a disadvantage in the system performance aspect without a load-balanced routing because the resource of links that are not used is wasted and frequently used links are out of resources. That is, the number of available flows in network is limited because load balancing is not performed. In this paper, we propose joint link scheduling and routing through a cross-layer scheme. For this, we propose a load balancing routing method to maximize available resources under the given traffic pattern and scheduling method for maximizing link utilization on the given route. These two methods are iterated until an optimized solution can be obtained. The proposed algorithm can be formulated using a mathematical LP problem and we show that it is very effective for load balancing compared to simple adoption of IEEE 802.11s which is a standard TDMA protocol in wireless mesh network. If the proposed algorithm is applied to initial design solution such as Smart Grid, the number of available flows can be increased and the load on each link can be balanced
Topology design and scheduling in STDMA based wireless ad hoc networks
Cataloged from PDF version of article.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.Ergin, Sadettin AlpM.S
On the performance of STDMA Link Scheduling and Switched Beamforming Antennas in Wireless Mesh Networks
Projecte final de carrera realitzat en col.laboració amb King's College LondonWireless Mesh Networks (WMNs) aim to revolutionize Internet connectivity due to
its high throughput, cost-e ectiveness and ease deployment by providing last mile
connectivity and/or backhaul support to di erent cellular networks. In order not to
jeopardize their successful deployment, several key issues must be investigated and
overcome to fully realize its potential. For WMNs that utilize Spatial Reuse TDMA
as the medium access control, link scheduling still requires further enhancements.
The rst main contribution of this thesis is a fast randomized parallel link swap
based packing (RSP) algorithm for timeslot allocation in a spatial time division multiple
access (STDMA) wireless mesh network. The proposed randomized algorithm
extends several greedy scheduling algorithms that utilize the physical interference
model by applying a local search that leads to a substantial improvement in the
spatial timeslot reuse. Numerical simulations reveal that compared to previously
scheduling schemes the proposed randomized algorithm can achieve a performance
gain of up to 11%. A signi cant bene t of the proposed scheme is that the computations
can be parallelized and therefore can e ciently utilize commoditized and
emerging multi-core and/or multi-CPU processors.
Furthermore, the use of selectable multi-beam directional antennas in WMNs,
such as beam switched phase array antennas, can assist to signi cantly enhance
the overall reuse of timeslots by reducing interference levels across the network and
thereby increasing the spectral e ciency of the system. To perform though a switch
on the antenna beam it may require up to 0.25 ms in practical deployed networks,
while at the same time very frequent beam switchings can a ect frame acquisition
and overall reliability of the deployed mesh network.
The second key contribution of this thesis is a set of algorithms that minimize the
overall number of required beam switchings in the mesh network without penalizing
the spatial reuse of timeslots, i.e., keeping the same overall frame length in the
network. Numerical investigations reveal that the proposed set of algorithms can
reduce the number of beam switchings by almost 90% without a ecting the frame
length of the network
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