Browsing by Author "Lakshmi, L.R."

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Achieving Fairness in IEEE 802.11ah Networks for IoT Applications with Different Requirements
(IEEE, 2019) Lakshmi, L.R.
The IEEE 802.11ah standard can provide cost-effective Internet access to a large number of devices in newly evolving Internet-of-Things (IoT) and machine-to-machine (M2M) networks. To handle high collision probability caused by a large number of devices, it adopts a group-based protocol at the MAC layer and divides nodes (or sensors) into a number of groups. The formed groups may not be uniform in terms of data rate requirements, since each group is a combination of sensors with different traffic characteristics. To achieve fair resource utilization across the groups which in turn maximizes the channel utilization, this paper formulates fair grouping in IEEE 802.11ah networks as an optimization problem, and we develop a heuristic method to solve the problem in real-time. In addition, to ensure fair channel utilization by the nodes in each group, a contention window selection and adjustment method is proposed. Results from extensive simulations conducted in a dense IoT network show that the proposed fairness model achieves a superior performance than the existing methods in terms of throughput, packet delay, energy efficiency, and fairness.
Adaptive Zone Size Selection Method for IEEE 802.16j Mobile Multihop Relay Networks
(Springer, 2017-08) Lakshmi, L.R.
IEEE 802.16j relay networks are capable of extending the coverage areas of IEEE 802.16 networks and can support the data rate requirements of users at cell edges. In these networks, each frame is divided into various zones to facilitate data transmission between various types of nodes. As the link qualities in the network change, accordingly the zone sizes should also change to support the Quality of Service (QoS) requirements of flows and to avoid bandwidth wastage. To address this issue, in this paper, we propose an adaptive zone size selection method for IEEE 802.16j networks. With this method, zone sizes of scheduling nodes are adaptively changed in accordance with their changing link qualities. As the link qualities degrade, the scheduling nodes may not be able to support the QoS requirements of flows due to the lack of free bandwidth availability in the corresponding zones. To handle this issue with less control overhead, we propose a cross-zone bandwidth allocation method. A zone size reselection method is also proposed to handle the situations where the cross-zone bandwidth allocation is not possible. Performance of the proposed method is compared with the performance of a fixed zone size selection method and a zone size selection method proposed in the literature. The proposed method shows significantly better performance than the other two methods in terms of traffic admittance, bandwidth utilization, and satisfaction ratios of flows.
Blockage Aware Fair Scheduling with Differentiated Service Support in mmWave WPANs/WLANs
(IEEE, 2020) Lakshmi, L.R.
Millimeter Wave (mmWave) communications are evolving as a potential and promising technology to address the ever increasing mobile data rate requirements. This paper addresses fair scheduling in directional antenna based mmWave wireless personal and local area networks with non-uniform traffic demand. Due to their small wavelength, mmWave signals are susceptible to blockage. The proposed fair schedulers handle the link blockage problem through relaying, and are capable of providing end-to-end fair bandwidth allocation to relay flows. To achieve differentiated and fair service allocation to various regions of the network while using only limited flow related information, a service tag based scheduler is proposed in this paper. Then, the performance bounds on the minimum throughput and unfairness of this scheduler are obtained. To approximate the performance of the service tag based scheduler while minimizing the control overhead, a heuristic fair scheduler is also proposed. Results from extensive simulations conducted in a mmWave WPAN deployed to support high data rate applications show the performance advantages of the proposed schedulers, compared to existing fair schedulers, in terms of throughput and fairness.
Cooperative data transmission framework for IEEE 802.16j mobile multihop relay networks
(ACM Digital Library, 2014-10) Lakshmi, L.R.
IEEE 802.16j Mobile Multihop Relay specification is an amendment of the IEEE 802.16 standard and it is developed to extend IEEE 802.16e. Quality of Service (QoS) constrained service flow management is an important issue related to these networks. In the situation where the link quality between a superordinate station and one of its subordinate Non-Transparent Relay Stations (NTRSs) is poor then it is difficult to fulfill the QoS requirements of the flows that are passing through that NTRS. To handle such situations, in this paper, a novel Cooperative Data Transmission (CDT) framework is proposed. It uses the Transparent Relay Stations (TRSs) which are the common neighbors of the NTRSs and their superordinate stations to fulfill the QoS requirements of the flows that are passing through the NTRSs. The changes required to the network entry, path establishment, bandwidth allocation and data transmission processes of the IEEE 802.16j standard for the CDT framework are proposed in this paper. Also, the performance gains achievable with the proposed CDT framework in terms of the throughput are analyzed numerically. The upper and lower bounds on the throughput gain are obtained. Through simulations, the performance of the proposed CDT framework is studied and compared with the performance of the normal data transmission where no cooperation from TRSs is involved in the data transmission. The CDT framework showed significant performance advantages when compared with the normal data transmission method.
Differentiated Service Support in Wireless Networks with Multibeam Antennas
(IEEE, 2020) Lakshmi, L.R.
Multibeam antenna arrays (MBAAs) have the capability to improve the capacity of a wireless network by facilitating simultaneous transmissions to multiple users. However, in practical deployments of wireless personal or local area networks (WPANs/WLANs) where piconet coordinators or access points (PNCs/APs) are deployed with MBAAs, it is quite likely to observe non-uniform node densities in various regions. To optimally utilize MBAAs in such scenarios, concurrent transmission scheduling in WPANs/WLANs is formulated as a multi-objective optimization problem. Then, a practical heuristic transmission scheduler that aims to maximize the number of concurrent communications by dynamically configuring the directions of beams is proposed. In addition, a service tag based fair scheduler is also proposed to achieve weighted fairness in WPANs/WLANs with MBAAs. Our results show that the performance improvements provided by the proposed heuristic scheduler are higher for antennas with lower beamwidths, and as the non-uniformity in the network increases, the traffic supported in the network increases in the range 24-41%, compared to the existing methods. The proposed service tag based scheduler can further improve the network throughput and achieve better fairness at the cost of a few beam direction reconfigurations, as compared to the existing methods and our heuristic scheduler.
A Dynamic Backup Path Management Method for TDMA Based WiMAX Client WMNs
(Springer, 2016-02) Lakshmi, L.R.
This paper proposes a backup path management method for time division multiple access (TDMA) based client wireless mesh networks (WMNs). In a TDMA based client WMN, as links/nodes fail or as nodes perform handover and as flows enter and leave the network, the paths between various nodes change as well as the bandwidth available along these paths. In these networks, to support the quality of service requirements of flows, backup paths with the required bandwidth need to be established dynamically. Some methods are proposed in the literature to establish backup paths which handle link/node failures and node handover in ad hoc networks, but none of these methods can provide backup paths with the required bandwidth dynamically. To address that issue, the present paper proposes a backup path management method which is adaptive to both topological changes and traffic changes in a network. Each node along the current path between a source and a destination finds backup paths with the required bandwidth in order to handle failure of the link to its downstream node and its own failure or handover. Nodes use twohop neighborhood information and slots status information of two-hop neighbors to establish backup paths. We prove that the number of backup paths available when a node N searches for backup paths to handle its own failure are more than the number of backup paths available when some other node searches for the backup paths for the failure of node N. Performance of the proposed method is compared with the performance of a naive path management (NPM) method in which always the source establishes backup paths whenever a link/node fails or a node performs handover, and also with the performance of a backup path management method proposed in the literature. The proposed method significantly outperforms the NPM method and the method selected from the literature. For example, when the speed of the mobile nodes is 50 m/s, the packet delivery ratio with the proposed method is 63 % more than the NPM method and 35 % more than the method selected from the literature.
Fair Scheduling in IEEE 802.11ah Networks for Internet of Things Applications
(IEEE, 2019) Lakshmi, L.R.
The IEEE 802.11ah standard has been developed to provide Internet access to a large number of devices in the Internet of Things (IoT) and machine-to-machine (M2M) networks. To handle contention from a large number of devices and reduce the collision probability, IEEE 802.11ah partitions nodes into groups by adopting a group-based MAC protocol. The formed groups may consist of nodes with different traffic patterns and hence, the data rate requirements of nodes in a group (and consequently the groups themselves) may not be uniform. To maximize the throughput while minimizing unfairness across groups, this paper formulates fair scheduling in IEEE 802.11ah networks as a multi-objective optimization problem. To maintain fairness among the nodes in a group, contention window size selection of nodes is formulated as an integer programming problem. Since it is difficult to solve these problems in real time, heuristic methods are also proposed. Performance of the proposed methods is evaluated in a dense IoT network and compared with the existing methods. As the number of nodes and groups increase, the proposed method consistently shows a superior performance in terms of fairness, throughput, delay, and power consumption, compared to the existing methods.
Fair Scheduling of Concurrent Transmissions in Directional Antenna Based WPANs/WLANs
(IEEE, 2018) Lakshmi, L.R.
With their capability to support high data rates, millimeter-Wave (mmWave) communications are evolving as a promising and potential technology to support high data rate applications in short range networks. This paper addresses the problem of fair scheduling in mmWave wireless personal and local area networks (WPANs/WLANs) to support applications with varying quality of service (QoS) requirements. To ensure fairness while exploiting the spatial reuse facilitated by directional antennas, concurrent transmission scheduling in mmWave WPANs/WLANs is formulated as a multi-objective optimization problem. Two heuristic schedulers are developed to obtain a schedule in real-time. These schedulers first satisfy the minimum QoS requirements of as many flows as possible, and then, allocate the remaining bandwidth to various flows while ensuring long-term and short-term fairness among the flows. Results from extensive simulations conducted in a dense mmWave WPAN show that the proposed fair schedulers provide better fairness and throughput, compared to existing methods
Handover management framework for WiMAX Point-to-Multi-Point networks
(Elsevier, 2016-11) Lakshmi, L.R.
In this paper, a distributed base station cooperation-based handover management method is proposed for WiMAX Point-to-Multi-Point networks to provide quality of service to handover nodes. Moreover, a delay reduction method is proposed to reduce the packet delivery delays during handover. A Call Admission Control (CAC) algorithm is proposed to handle handover calls of various service classes fairly, according to their priorities. A bandwidth borrowing scheme is proposed to reduce the handover call dropping probabilities of various service classes while not starving the ongoing calls of lower priority service classes. A Markov model is developed to analyze the proposed CAC method and to obtain the approximate handover call dropping probabilities of various service classes. Simulation experiments are conducted to establish the performance advantages of the proposed handover management and CAC methods.
Handover rate based dynamic guard bandwidth allocation method for call admission control in IEEE 802.16j Mobile Multihop Relay networks
(Elsevier, 2014-07) Lakshmi, L.R.
IEEE 802.16j MMR (Mobile Multihop Relay) networks are developed to extend the coverage area and enhance the throughput of IEEE 802.16 networks. Call Admission Control (CAC) is an important research issue related to these networks. In this paper, a novel dynamic guard bandwidth allocation method is proposed for CAC in IEEE 802.16j networks; the guard bandwidth allocated at a station depends upon the handover rates from its neighbors and at its descendent stations. A bandwidth wastage prevention policy is proposed to utilize the unused guard bandwidth to fulfill the requests of lower priority calls and eventually to improve the bandwidth utilization of the network. Based on the total amounts of the guard bandwidth received by the lower priority calls, a novel bandwidth borrowing scheme is proposed. A Markov model is developed to analyze the performance of the proposed CAC method; analytical handover call dropping probabilities and new call blocking probabilities of various service classes are obtained using the proposed Markov model. Simulation experiments are conducted to compare the performance of the proposed CAC method with a fixed guard bandwidth based CAC method. The proposed method showed superior performance than the fixed guard bandwidth based method. Also, the simulation results are compared with the analytical results.
Link Quality Based Path Selection Methods for IEEE 802.16j Mobile Multihop Relay Networks
(Springer, 2013-08) Lakshmi, L.R.
IEEE 802.16j mobile multihop relay (MMR) networks are developed to enhance the coverage area and the throughput of IEEE 802.16 networks. Path selection is an important research problem related to these networks. In the networks where the link qualities are highly varying, to provide consistent quality of service to the users, it is very important to select paths consisting of links with consistent link qualities. To address this issue, in this paper, two path consistency based path selection methods are proposed for IEEE 802.16j MMR networks. Through simulations, the performance of the method proposed for the mobile nodes is compared with the performance of two path selection methods proposed in the literature. It is observed that the proposed method provides better performance than the methods selected from the literature.
PRIME: A partial path establishment based handover management technique for QoS support in WiMAX based wireless mesh networks
(Elsevier, 2015-06) Lakshmi, L.R.
In this paper, we propose a novel handover management technique called PaRtIal path establishment based handover Management tEchnique (PRIME) for WiMAX based wireless mesh networks (WMNs). Different from the currently existing methods for WiMAX networks, PRIME addresses handover management in WiMAX WMNs deployed with distributed scheduling. In these networks, to continue the quality of service (QoS) constrained flows to a mobile node (MN) after its handover, a new path with the required bandwidth and which passes through its new base station (BS) needs to be established as quickly as possible. To address that issue, PRIME handles re-routing and scheduling issues of a handing over MN together. To provide lossless and seamless service, PRIME tries to establish new path(s) in the wireless mesh with the required bandwidth to the MN before it enters into the coverage area of the new BS. The present paper proposes a novel crossover node based partial path establishment algorithm to establish new path(s) which support QoS requirements of handoff calls. To analyze the performance of PRIME, the present paper proposes a multi-dimensional Markov model. Unlike previous models which analyze the performance of wireless networks, our proposed model represents nodes in terms of the number of transmission and reception available slots. The theoretical upper and lower bounds on the call dropping probabilities of handoff calls are obtained. To study the performance advantages of PRIME, we devise another handover management method called RFPHMT which does not use the concept of crossover base station in the new path establishment of a handing over node. The performance of PRIME and RFPHMT are compared in terms of call dropping probabilities and call setup delays. PRIME shows superior performance than RFPHMT. For a random topology, at a high call arrival rate of 1/2000 (calls/milliseconds), the handover call dropping probability of PRIME is 40% less than that of RFPHMT. The call dropping probabilities of PRIME with the simulations are always within the theoretical bounds which proves that the obtained bounds are close to the real call dropping probabilities.
STDMA scheduling for WLANs and WPANs with non-uniform traffic demand
(IEEE, 2017) Lakshmi, L.R.
Directional antennas provide many advantages such as higher gain, increased capacity, longer range, and reduced interference by concentrating radio signal energy in one direction. This paper addresses concurrent transmission scheduling in wireless personal or local area networks deployed with directional antennas. In typical network deployment scenarios, it is quite likely to have non-uniform node densities and traffic demands in various parts of the network. In such situations, to provide load-based service to various parts of the network while aiming to maximize the spatial reuse, this paper proposes a zone-based concurrent data transmission scheduling method. Simulation results show that the proposed method can support a larger number of flows while satisfying a greater fraction of the traffic demands from highly loaded regions, compared to existing methods.