Tolga Numanoglu

Analytical performance of soft clustering protocols

The success of a mobile ad hoc network (MANET) is strongly related to the protocol used at the medium access control (MAC) layer. Depending on the requirements and the specific network under concern, the protocol parameters at the MAC layer can be arbitrated to make best use of the channel resources. Typically, extensive simulation studies are used to find the best values for these variables. The problem with this approach is the need for excessive amounts of processing power and time. As the dimensions of the decision space increase, the need for processing power grows exponentially. This paper addresses this problem by developing an analytical model that reflects the relationships between protocol parameters and the overall performance of the protocol under various network conditions. Specifically, we model the MH-TRACE cluster-based protocol, which is capable of supporting real-time data transmission. The model is capable of estimating performance measures such as energy consumption and number of receptions while being simple enough to be run for a large set of parameters. The model can be used to optimize parameters of the protocol (such as the number of frames per superframe) as well as to predict the performance variations as the external conditions (such as data generation rate) vary.

Energy efficiency and error resilience in coordinated and non-coordinated medium access control protocols

Energy efficiency of a MAC protocol is one of the most important performance metrics, especially in mobile ad hoc networks, where the energy sources are limited. Two key factors in achieving energy efficiency for a MAC protocol are coordination among the nodes and schedule-based channel access. In order to achieve a sufficient level of coordination among the nodes, and hence to achieve energy efficiency, the exchange of control information via control packets is vital. As such, coordinated MAC protocols, which regulate channel access through scheduling, have been shown to achieve very high energy efficiencies when compared to non-coordinated MAC protocols, which do not employ scheduling. However, due to their increased vulnerability to channel errors, the performance of coordinated MAC protocols is affected more by the channel bit error rate (BER) than non-coordinated MAC protocols, which lack such control packets. In this paper, we investigate the energy efficiency and resilience against channel errors for coordinated and non-coordinated MAC protocols. Our results reveal that it is possible to achieve better system performance with coordinated MAC protocols even in lossy channels, provided that the BER level is not extremely high.

The effects of channel errors on coordinated and non-coordinated medium access control protocols

In this paper, we investigate the effects of channel noise on the performance of coordinated and non-coordinated MAC protocols. Comparative evaluations of these protocols under a perfect channel assumption have shown that coordinated MAC protocols, which regulate channel access locally, outperform non-coordinated channel access schemes in terms of energy efficiency and throughput. However, coordinated MAC protocols are more vulnerable than non-coordinated MAC protocols to channel noise due to their dependence on the robustness of the control traffic. In order to observe the degradation in performance of a coordinated MAC protocol (MH-TRACE), we investigate the impact of losing control packets. Furthermore, the performance in terms of throughput, delay, and energy efficiency of both coordinated (MH-TRACE) and non-coordinated (IEEE 802.11) MAC protocols is explored using a general error model that takes into account the length of the packets. Our results show that despite its higher level of vulnerability, the coordinated MAC protocols performance is superior to the performance of the non-coordinated MAC protocol even when error rates are high.

Adaptation of TDMA Parameters Based on Network Conditions

Soft clustering of the nodes combined with time division multiple access (TDMA) channel access within a cluster has been shown to provide an energy-efficient solution for Mobile Ad-Hoc Networks (MANET). Such channel access schemes use a parameter that is critical in determining network performance: the number of frames per superframe, which determines the amount of spatial reuse possible, similar to the frequency reuse factor in cellular networks. When a smaller number of frames per superframe is used, each frame will consist of a larger number of slots, enabling the frame (i.e., cluster) to support more nodes, but also limiting the choices of frames for clusterheads to select, causing higher co-channel interference and collisions. Conversely, when a larger number of frames per superframe is used, the clusterheads will only be able to grant channel access to a limited number of nodes, which in turn increases the number of dropped packets (i.e., blocked channel access). The optimum value of the number of frames is the one that minimizes the combined effect of both collisions and dropped packets. By analytically determining the effects of dropped packets and collisions, we can find the optimal value for any given scenario. This paper develops a model to determine the optimal TDMA structure under various settings, showing the advantages that can be obtained by adapting protocol parameters as network conditions change.

Multi-rate support for network-wide broadcasting in MANETs

Mobile ad-hoc networks (MANETs) utilize broadcast channels, where wireless transmissions occur from one user to many others. In a broadcast channel the same transmission can lead to different information rates to different users depending on the channel capacity between the transmitter and receiver pair. According to coding theory, there is a certain channel capacity that limits the rate of information that can be sent through the channel. Thus, different channel capacities result in different acceptable rates for the users. In this paper, we utilize a superposed coding scheme in a MANET scenario to provide different rates for users with different channel capacities using a single broadcast transmission. We have created techniques to extend this multi-rate concept to network-wide broadcasting scenarios, providing the ability for nodes to appropriately trade-off delay vs. quality. We describe our approach and provide simulation results showing the benefits and limitations of superposed coding in network-wide broadcasting.

Improving QoS in Multicasting Through Adaptive Redundancy

In mobile ad hoc networks (MANETs), Quality of Service (QoS) of a multicast protocol is one of the most important performance metrics. Channel conditions and network topology frequently change, and in order to achieve a certain QoS, complex algorithms and protocols are needed. Often channel conditions are neglected during the design of a multicast protocol. However, vulnerability against channel errors can severely cripple the performance of a multicast protocol. Mesh networking inspired multicasting approaches introduce increased redundancy in the routing process to overcome the performance loss due to channel errors. Although utilizing multiple paths from senders to receivers results in higher reliability, under better channel conditions the additional redundancy may not be needed in terms of reliability, and increased redundancy causes increased overhead. Therefore, we propose a mesh networking inspired approach that adapts the amount of redundancy according to the current link conditions. We show that this approach can achieve good QoS levels for real-time traffic scenarios while simultaneously reducing unnecessary energy dissipation.

Improving QoS under lossy channels through adaptive redundancy

Quality of service (QoS) of a network-wide broadcast (NWB) protocol is one of the most important performance metrics, especially in mobile ad hoc networks, where channel conditions and network topology change frequently. We propose a mesh networking inspired approach to overcome the performance degradation caused by lossy channels. We show that our adaptive approach, whereby the amount of redundancy is adjusted to the current link conditions, can achieve good performance while simultaneously reducing unnecessary energy dissipation.

Conjunction of heuristic algorithms with multidimensional scaling for localization at wireless ad-hoc networks

In wireless networks, the nodes are generally distributed in a field randomly. The topological information about the nodes is only supported from the distances between each node. This distance information may not be available due to the imperfect conditions among nodes. The positions of the distributed nodes on the field by using available distance data is called node localization problem. One of the methods which can be solved this problem is classical multidimensional algorithm (cMDS). In this study, cMDS is improved with the aid of heuristic algorithms. Three heuristic algorithms (simulated annealing, particle swarm optimization and genetic algorithm) are applied and results are compared with each other.

Maximum-weight scheduling with hierarchical modulation

In this paper, hierarchical modulation is used in conjunction with maximum-weight scheduling to achieve lower transmission delays. Via hierarchical modulation, the scheduled user has the option to transmit to two users simultaneously. The results are compared with classical single-layered transmission. Simulation results show that packet transmission delays are lowered without any loss in throughput. In addition to this, it is demonstrated that hierarchical modulation is robust in point-to-point settings, and prove to be as good as adaptive modulation techniques, without the need for transmitter side channel state information.

An embedded radio software emulation platform using OPNET and VxWorks to develop distributed algorithms for military ad-hoc networks

Military radios have been evolving from push to talk devices into multitasking, networking capable, handheld mobile ad-hoc computers. Software defined radio technology has been fueling this evolution and as result, responsibilities and utilization of military radios along with the military network sizes have been increasing. As the complexity of ad-hoc networking radios continue to increase, the distributed protocols designed to manage the networking requirements, such as medium access control and routing, are becoming more complex and harder to analyze than they have ever been. In this paper, we present an embedded radio software emulation platform that we have developed to facilitate distributed algorithm design for military ad-hoc networks This platform enables the development and testing of distributed network protocols through emulation of the embedded software implementing these protocols. Distributed networking protocols used by the radios are emulated using the radio softwares native operating system, Wind River VxWorks, which is virtualized by using Wind River Hypervisor to run on a personal computer. The remaining parts of the radio software, physical layer properties, air interface of the radio, and all networking scenario details (e.g., terrain, mobility, and user generated traffic) are implemented in OPNET, through co-simulation. Performing design, evaluation, and debugging of distributed network algorithms on this platform will significantly reduce the amount of time spent on field tests, which can require hundreds of radios and last for months for each enhanced or modified version of the algorithms.