333 research outputs found
Performance issues in cellular wireless mesh networks
This thesis proposes a potential solution for future ubiquitous broadband wireless access networks, called a cellular wireless mesh network (CMESH), and investigates a number of its performance issues. A CMESH is organized in multi-radio, multi-channel, multi-rate and multi-hop radio cells. It can operate on abundant high radio frequencies, such as 5-50 GHz, and thus may satisfy the bandwidth requirements of future ubiquitous wireless applications.
Each CMESH cell has a single Internet-connected gateway and serves up to hundreds of mesh nodes within its coverage area. This thesis studies performance issues in a CMESH, focusing on cell capacity, expressed in terms of the max-min throughput. In addition to introducing the concept of a CMESH, this thesis makes the following contributions.
The first contribution is a new method for analyzing theoretical cell capacity. This new method is based on a new concept called Channel Transport Capacity (CTC), and derives new analytic expressions for capacity bounds for carrier-sense-based CMESH cells.
The second contribution is a new algorithm called the Maximum Channel Collision Time (MCCT) algorithm and an expression for the nominal capacity of CMESH cells. This thesis proves that the nominal cell capacity is achievable and is the exact cell capacity for small cells within the abstract models.
Finally, based on the MCCT algorithm, this thesis proposes a series of greedy algorithms for channel assignment and routing in CMESH cells. Simulation results show that these greedy algorithms can significantly improve the capacity of CMESH cells, compared with algorithms proposed by other researchers
DYNAMIC ROUTING WITH CROSS-LAYER ADAPTATIONS FOR MULTI-HOP WIRELESS NETWORKS
In recent years there has been a proliferation of research on a number of wireless multi-hop networks that include mobile ad-hoc networks, wireless mesh networks, and wireless sensor networks (WSNs). Routing protocols in such networks are of- ten required to meet design objectives that include a combination of factors such as throughput, delay, energy consumption, network lifetime etc. In addition, many mod- ern wireless networks are equipped with multi-channel radios, where channel selection plays an important role in achieving the same design objectives. Consequently, ad- dressing the routing problem together with cross-layer adaptations such as channel selection is an important issue in such networks. In this work, we study the joint routing and channel selection problem that spans two domains of wireless networks. The first is a cost-effective and scalable wireless-optical access networks which is a combination of high-capacity optical access and unethered wireless access. The joint routing and channel selection problem in this case is addressed under an anycasting paradigm. In addition, we address two other problems in the context of wireless- optical access networks. The first is on optimal gateway placement and network planning for serving a given set of users. And the second is the development of an analytical model to evaluate the performance of the IEEE 802.11 DCF in radio-over- fiber wireless LANs. The second domain involves resource constrained WSNs where we focus on route and channel selection for network lifetime maximization. Here, the problem is further exacerbated by distributed power control, that introduces addi- tional design considerations. Both problems involve cross-layer adaptations that must be solved together with routing. Finally, we present an analytical model for lifetime calculation in multi-channel, asynchronous WSNs under optimal power control
The min-max edge q-coloring problem
In this paper we introduce and study a new problem named \emph{min-max edge
-coloring} which is motivated by applications in wireless mesh networks. The
input of the problem consists of an undirected graph and an integer . The
goal is to color the edges of the graph with as many colors as possible such
that: (a) any vertex is incident to at most different colors, and (b) the
maximum size of a color group (i.e. set of edges identically colored) is
minimized. We show the following results: 1. Min-max edge -coloring is
NP-hard, for any . 2. A polynomial time exact algorithm for min-max
edge -coloring on trees. 3. Exact formulas of the optimal solution for
cliques and almost tight bounds for bicliques and hypergraphs. 4. A non-trivial
lower bound of the optimal solution with respect to the average degree of the
graph. 5. An approximation algorithm for planar graphs.Comment: 16 pages, 5 figure
Analysis and mitigation of interference in multi-radio multi-channel wireless mesh networks
Ankara : The Department of Computer Engineering and the Graduate School of Engineering and Science of Bilkent Univ., 2013.Thesis (Ph. D.) -- Bilkent University, 2013.Includes bibliographical references leaves 162-170.Wireless mesh networking, which is basically forming a backbone network
of mesh routers using wireless links, is becoming increasingly popular for a
broad range of applications from last-mile broadband access to disaster networking
or P2P communications, because of its easy deployment, self-forming,
self-configuration, and self-healing properties. The multi-hop nature of wireless
mesh networks (WMNs) aggravates inter-flow interference and causes intra-flow
interference and severely limits the network capacity. One technique to mitigate
interference and increase network capacity is to equip the mesh routers with multiple
radios and use multiple channels. The radios of a mesh router can then
simultaneously send or receive packets on different wireless channels. However,
careful and intelligent radio resource planning, including flow-radio and channel
assignment, is necessary to efficiently make use of multiple radios and channels.
This first requires analyzing and modeling the nature of co-channel and adjacent
channel interference in a WMN.
Through real-world experiments and observations made in an indoor multihop
multi-radio 802.11b/g mesh networking testbed we established, BilMesh, we
first analyze and model the nature of co-channel and adjacent channel interference.
We conduct extensive experiments on this testbed to understand the effects
of using multi-radio, multi-channel relay nodes in terms of network and application
layer performance metrics. We also report our results on using overlapping in
addition to orthogonal channels for the radios of the mesh routers. We then turn
our attention to modeling and quantifying adjacent channel interference. Extending
BilMesh with IEEE 802.15.4 nodes, we propose computational methods
to quantify interference between channels of a wireless communication standard
and between channels of two different standards (such as Wi-Fi and ZigBee).
Majority of the studies in the literature on channel assignment consider only
orthogonal channels for the radios of a multi-radio WMN. Having developed quantitative
models of interference, next we propose two optimization models, which
use overlapping channels, for the joint flow-radio and channel assignment problems
in WMNs. Then we propose efficient centralized and distributed heuristic
algorithms for coupling flows and assigning channels to the radios of a WMN. The
proposed centralized and distributed schemes make use of overlapping channels to
increase spectrum utilization. Using solid interference and capacity metrics, we
evaluate the performances of the proposed schemes via extensive simulation experiments,
and we observe that our schemes can achieve substantial improvement
over single-channel and random flow-radio and channel assignment schemes.Uluçınar, Alper RifatPh.D
Distributed joint flow-radio and channel assignment using partially overlapping channels in multi-radio wireless mesh networks
Equipping mesh nodes with multiple radios that support multiple wireless channels is considered a promising solution to overcome the capacity limitation of single-radio wireless mesh networks. However, careful and intelligent radio resource management is needed to take full advantage of the extra radios on the mesh nodes. Flow-radio assignment and channel assignment procedures should obey the physical constraints imposed by the radios as well as the topological constraints imposed by routing. Varying numbers of wireless channels are available for the channel assignment procedure for different wireless communication standards. To further complicate the problem, the wireless communication standard implemented by the radios of the wireless mesh network may define overlapping as well as orthogonal channels, as in the case of the IEEE 802.11b/g family of standards. This paper presents Distributed Flow-Radio Channel Assignment, a distributed joint flow-radio and channel assignment scheme and the accompanying distributed protocol in the context of multi-channel multi-radio wireless mesh networks. The scheme’s performance is evaluated on small networks for which the optimal flow-radio and channel configuration can be computed, as well as on large random topologies. © 2015, Springer Science+Business Media New York
Performance Optimization in Wireless Local Area Networks
Wireless Local Area Networks (WLAN) are becoming more and more important
for providing wireless broadband access. Applications and networking
scenarios evolve continuously and in an unpredictable way, attracting the
attention of academic institutions, research centers and industry. For designing
an e cient WLAN is necessary to carefully plan coverage and to
optimize the network design parameters, such as AP locations, channel assignment,
power allocation, MAC protocol, routing algorithm, etc... In this
thesis we approach performance optimization in WLAN at di erent layer
of the OSI model. Our rst approach is at Network layer. Starting from
a Hybrid System modeling the
ow of tra c in the network, we propose a
Hybrid Linear Varying Parameter algorithm for identifying the link quality
that could be used as metric in routing algorithms. Go down to Data Link,
it is well known that CSMA (Carrier Sense Multiple Access) protocols exhibit
very poor performance in case of multi-hop transmissions, because of
inter-link interference due to imperfect carrier sensing. We propose two novel
algorithms, that are combining Time Division Multiple Access for grouping
contending nodes in non-interfering sets with Carrier Sense Multiple Access
for managing the channel access behind a set. In the rst solution, a game
theoretical study of intra slot contention is introduced, in the second solution
we apply an optimization algorithm to nd the optimal degree between
contention and scheduling. Both the presented solutions improve the network
performance with respect to CSMA and TDMA algorithms. Finally we
analyze the network performance at Physical Layer. In case of WLAN, we
can only use three orthogonal channels in an unlicensed spectrum, so the frequency
assignments should be subject to frequent adjustments, according to
the time-varying amount of interference which is not under the control of the
provider. This problem make necessary the introduction of an automatic network
planning solution, since a network administrator cannot continuously
monitor and correct the interference conditions su ered in the network. We
propose a novel protocol based on a distributed machine learning mechanism
in which the nodes choose, automatically and autonomously in each time
slot, the optimal channel for transmitting through a weighted combination
of protocols
- …