131 research outputs found
Connectivity, Coverage and Placement in Wireless Sensor Networks
Wireless communication between sensors allows the formation of flexible sensor networks, which can be deployed rapidly over wide or inaccessible areas. However, the need to gather data from all sensors in the network imposes constraints on the distances between sensors. This survey describes the state of the art in techniques for determining the minimum density and optimal locations of relay nodes and ordinary sensors to ensure connectivity, subject to various degrees of uncertainty in the locations of the nodes
Resource Allocation in Relay Enhanced Broadband Wireless Access Networks
The use of relay nodes to improve the performance of broadband wireless access (BWA) networks has been the subject of intense research activities in recent years. Relay enhanced BWA networks are anticipated to support multimedia traffic (i.e., voice,
video, and data traffic). In order to guarantee service to network users, efficient resource distribution is imperative. Wireless multihop networks are characterized by two inherent dynamic characteristics: 1) the existence of wireless interference and 2) mobility of user nodes. Both mobility and interference greatly influence the ability of users to obtain the necessary resources for service. In this dissertation we conduct a comprehensive research study on the topic of resource allocation in the presence of interference and mobility. Specifically, this dissertation investigates the impact interference and mobility have on various aspects of resource allocation, ranging from fairness to spectrum utilization. We study four important resource allocation algorithms for relay enhanced BWA networks. The problems and our research achievements are briefly outlined as follows.
First, we propose an interference aware rate adaptive subcarrier and power allocation
algorithm using maximum multicommodity
flow optimization. We consider the impact of
the wireless interference constraints using Signal to Interference Noise Ratio (SINR). We
exploit spatial reuse to allocate subcarriers in the network and show that an intelligent
reuse of resources can improve throughput while mitigating the impact of interference.
We provide a sub-optimal heuristic to solve the rate adaptive resource allocation problem. We demonstrate that aggressive spatial reuse and fine tuned-interference modeling garner advantages in terms of throughput, end-to-end delay and power distribution.
Second, we investigate the benefits of decoupled optimization of interference aware
routing and scheduling using SINR and spatial reuse to improve the overall achievable
throughput. We model the routing optimization problem as a linear program using maximum concurrent flows. We develop an optimization formulation to schedule the link traffic such that interference is mitigated and time slots are reused appropriately based on spatial TDMA (STDMA). The scheduling problem is shown to be NP-hard and is solved using the column generation technique. We compare our formulations to conventional counterparts in the literature and show that our approach guarantees higher throughput by mitigating the effect of interference effectively.
Third, we investigate the problem of multipath flow routing and fair bandwidth allocation under interference constraints for multihop wireless networks. We first develop a novel isotonic routing metric, RI3M, considering the influence of interflow and intraflow interference. Second, in order to ensure QoS, an interference-aware max-min fair bandwidth allocation algorithm, LMX:M3F, is proposed where the lexicographically largest bandwidth allocation vector is found among all optimal allocation vectors while considering constraints of interference on the flows. We compare with various interference based routing metrics and interference aware bandwidth allocation algorithms established in the literature to show that RI3M and LMX:M3F succeed in improving network performance in terms of delay, packet loss ratio and bandwidth usage.
Lastly, we develop a user mobility prediction model using the Hidden Markov Model(HMM) in which prediction control is transferred to the various fixed relay nodes in the
network. Given the HMM prediction model, we develop a routing protocol which uses
the location information of the mobile user to determine the interference level on links
in its surrounding neighborhood. We use SINR as the routing metric to calculate the
interference on a specific link (link cost). We minimize the total cost of routing as a
cost function of SINR while guaranteeing that the load on each link does not exceed
its capacity. The routing protocol is formulated and solved as a minimum cost
flow optimization problem. We compare our SINR based routing algorithm with conventional counterparts in the literature and show that our algorithm reinforces routing paths with high link quality and low latency, therefore improving overall system throughput.
The research solutions obtained in this dissertation improve the service reliability and QoS assurance of emerging BWA networks
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
A survey of network lifetime maximization techniques in wireless sensor networks
Emerging technologies, such as the Internet of things, smart applications, smart grids and machine-to-machine networks stimulate the deployment of autonomous, selfconfiguring, large-scale wireless sensor networks (WSNs). Efficient energy utilization is crucially important in order to maintain a fully operational network for the longest period of time possible. Therefore, network lifetime (NL) maximization techniques have attracted a lot of research attention owing to their importance in terms of extending the flawless operation of battery-constrained WSNs. In this paper, we review the recent developments in WSNs, including their applications, design constraints and lifetime estimation models. Commencing with the portrayal of rich variety definitions of NL design objective used for WSNs, the family of NL maximization techniques is introduced and some design guidelines with examples are provided to show the potential improvements of the different design criteri
Algorithm for Optimizing Packet Size in Mobile Ad Hoc Networks
This thesis proposes an algorithm to optimize packet size in mobile ad hoc networks (MANET). In this thesis, the packet size is adapted to maximize the communication performance through the automatic repeat request (ARQ) protocol. The optimal packet size is chosen by an algorithm based on the estimation of the channel from the number of retransmission requests and the link statistics obtained from the mobility pattern. By adapting the non-uniform distribution of the bit error rate (BER) obtained from the mobility pattern analysis, it is possible to estimate channel conditions more accurately from the number of retransmission requests and to improve the system performance. It was found that the distribution of the link distance among mobile nodes following the Gauss-Markov mobility pattern in a circularly shaped area well fits the Beta distribution function. From the simulation results it is observed that when the interference increases, or the path loss exponent increases, or when the size of history decreases, the throughput and efficiency performance will decrease. Based on an analysis in various wireless environments, the algorithm proposed in this thesis shows almost an optimal throughput efficiency performance, and it gives better performance than the algorithm in [6], which uses an uniform distribution function for the estimation of the channel condition. By adapting the Beta distribution of the BER obtained from the mobility pattern, it is possible to estimate the channel conditions more accurately from the number of retransmission requests and to improve the throughput and utilization performance of MANET communication systems.School of Electrical & Computer Engineerin
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