Mahesh K. Marina

Performance comparison of two on-demand routing protocols for ad hoc networks

Ad hoc networks are characterized by multihop wireless connectivity, frequently changing network topology and the need for efficient dynamic routing protocols. We compare the performance of two prominent on-demand routing protocols for mobile ad hoc networks: dynamic source routing (DSR) and ad hoc on-demand distance vector routing (AODV). A detailed simulation model with MAC and physical layer models is used to study interlayer interactions and their performance implications. We demonstrate that even though DSR and AODV share similar on-demand behavior, the differences in the protocol mechanics can lead to significant performance differentials. The performance differentials are analyzed using varying network load, mobility, and network size. Based on the observations, we make recommendations about how the performance of either protocol can be improved.

Ad hoc on‐demand multipath distance vector routing

We develop an on-demand, multipath distance vector routing protocol for mobile ad hoc networks. Specifically, we propose multipath extensions to a well-studied single path routing protocol known as ad hoc on-demand distance vector (AODV). The resulting protocol is referred to as ad hoc on-demand multipath distance vector (AOMDV). The protocol guarantees loop freedom and disjointness of alternate paths. Performance comparison of AOMDV with AODV using ns-2 simulations shows that AOMDV is able to effectively cope with mobility-induced route failures. In particular, it reduces the packet loss by up to 40% and achieves a remarkable improvement in the end-to-end delay (often more than a factor of two). AOMDV also reduces routing overhead by about 30% by reducing the frequency of route discovery operations. Copyright

A topology control approach for utilizing multiple channels in multi-radio wireless mesh networks

We consider the channel assignment problem in a multi-radio wireless mesh network that involves assigning channels to radio interfaces for achieving efficient channel utilization. We propose the notion of a traffic-independent base channel assignment to ease coordination and enable dynamic, efficient and flexible channel assignment. We present a novel formulation of the base channel assignment as a topology control problem, and show that the resulting optimization problem is NP-complete. We then develop a new greedy heuristic channel assignment algorithm (termed CLICA) for finding connected, low interference topologies by utilizing multiple channels. Our extensive simulation studies show that the proposed CLICA algorithm can provide large reduction in interference (even with a small number of radios per node), which in turn leads to significant gains in both link layer and multihop performance in 802.11-based multi-radio mesh networks.

Performance of route caching strategies in Dynamic Source Routing

On-demand routing protocols for mobile ad hoc networks utilize route caching in different forms in order to reduce the routing overheads as well as to improve the route discovery latency. For route caches to be effective, they need to adapt to frequent topology changes. Using an on-demand protocol called Dynamic Source Routing (DSR), we study the problem of keeping the caches up-to-date in dynamic ad hoc networks. Previous studies have shown that cache staleness in DSR can significantly degrade performance. We present and evaluate three techniques to improve cache correctness in DSR namely wider error notification, route expiry mechanism with adaptive timeout selection and the use of negative caches. Simulation results show that the combination of the proposed techniques not only result in substantial improvement of both application and cache performance but also reduce the overheads.

Routing performance in the presence of unidirectional links in multihop wireless networks

We examine two aspects concerning the influence of unidirectional links on routing performance in multihop wireless networks. In the first part of the paper we evaluate the benefit from utilizing unidirectional links for routing as opposed to using only bidirectional links. Our evaluations are based on three transmit power assignment models that reflect some realistic network scenarios with unidirectional links. Our results indicate that the marginal benefit of using a high-overhead routing protocol to utilize unidirectional links is questionable.Most common routing protocols however simply assume that all network links are bidirectional and thus may need additional protocol actions to remove unidirectional links from route computations. In the second part of the paper we investigate this issue using a well known on-demand routing protocol Ad hoc On-demand Distance Vector (AODV) as a case study. We study the performance of three techniques for AODV for efficient operation in presence of unidirectional links viz. BlackListing Hello and ReversePathSearch. While BlackListing and Hello techniques explicitly eliminate unidirectional links the ReversePathSearch technique exploits the greater network connectivity offered by the existence of multiple paths between nodes. Performance results using ns-2 simulations under varying number of unidirectional links and node speeds show that all three techniques improve performance by avoiding unidirectional links the ReversePathSearch technique being the most effective.

Virtual dynamic backbone for mobile ad hoc networks

In this paper, we propose the virtual dynamic backbone protocol (VDBP) for ad hoc networks. VDBP constructs a backbone from a subset of the nodes in the network satisfying these two properties: (i) Any node in the network is either a backbone node or is a neighbor of a backbone node (dominating set property), (ii) any pair of backbone nodes is connected via other backbone nodes (connectivity property). VDBP provides explicit mechanisms to handle the mobility of the nodes and depends on local computations to a large extent. Thus it is highly self-organizing even under highly dynamic topologies. Such a backbone can be potentially used by a routing protocol to disseminate broadcast or multicast messages as well as to handle QoS traffic in mobile ad hoc networks. We present the performance of VDBP in terms of backbone size and connectivity using simulations.

OpenAirInterface: A Flexible Platform for 5G Research

Driven by the need to cope with exponentially growing mobile data traffic and to support new traffic types from massive numbers of machine-type devices, academia and industry are thinking beyond the current generation of mobile cellular networks to chalk a path towards fifth generation (5G) mobile networks. Several new approaches and technologies are being considered as potential elements making up such a future mobile network, including cloud RANs, application of SDN principles, exploiting new and unused portions of spectrum, use of massive MIMO and full-duplex communications. Research on these technologies requires realistic and flexible experimentation platforms that offer a wide range of experimentation modes from real-world experimentation to controlled and scalable evaluations while at the same time retaining backward compatibility with current generation systems. Towards this end, we present OpenAirInterface (OAI) as a suitably flexible platform. In addition, we discuss the use of OAI in the context of several widely mentioned 5G research directions.

SQualNet: a scalable simulation framework for sensor networks

We have developed a scalable sensor network simulation framework called sQualnet [1]. sQualnet is based on the well-known Qualnet simulator; it benefits from Qualnet’s greater scalability, realistic and detailed propagation models, and support for easing model development. sQualnet features a rich suite of detailed and accurate sensor network specific models, including: sensing and radio channels, sensor protocols (MAC, routing), battery and power consumption models, support for multi-tiered sensor network evaluations. The observed network performance is highly dependent on the model accuracy, as shown in [2]. Besides, sQualnet provides real code simulation capability for motes [3]. Specifically, it allows the use of unmodified TinyOS applications (written in NesC) and SOS applications (written in C), thereby enabling easy transition between simulation and real experimentation on a deployed sensor network. Through the aforementioned features, sQualnet overcomes limitations of existing sensor network evaluation tools. Compared to common wireless network simulators (e.g., ns-2, OPNET, Qualnet) and other sensor-specific simulators (e.g., SensorSim), sQualnet has the additional capability for real-code simulation. With its support for accurate radio propagation models, it also addresses a key limitation of existing real-code simulators (e.g., TOSSIM) and hardware emulators (e.g., ATEMU). In addition, sQualnet offers hybrid simulation capability to support varying degrees of integration of real and simulated network components, which can aid in system development and enable large-scale evaluations in a cost-effective manner. Using this capability, one can model a network where some nodes are simulated while the rest are real physical nodes, or where some layers of the network

Tegola tiered mesh network testbed in rural Scotland

Many rural and remote communities around the world see themselves on the wrong side of the digital divide. In particular, there is evidence to suggest that there is a growing digital divide between urban and rural areas in terms of broadband Internet access with people living in rural areas having fewer choices and pay higher prices for slower speeds. This is true even in developed countries. Motivated by the above observations, there has been an increasing interest in deploying and researching low cost rural wireless networks with active community participation. This paper presents an overview of our efforts in this direction in deploying a rural WiFibased long distance mesh network testbed in the Scottish Highlands and Islands. We highlight the unique aspects of our testbed that differentiate it from other existing rural wireless testbeds. We also outline some of the research issues that are currently being investigated in this project.

HiMLoc: Indoor smartphone localization via activity aware Pedestrian Dead Reckoning with selective crowdsourced WiFi fingerprinting

The large number of applications that rely on indoor positioning encourages more advancement in this field. Smartphones are becoming a common presence in our daily life, so taking advantage of their sensors can help to provide ubiquitous positioning solution. We propose HiMLoc, a novel solution that synergistically uses Pedestrian Dead Reckoning (PDR) and WiFi fingerprinting to exploit their positive aspects and limit the impact of their negative aspects. Specifically, HiMLoc combines location tracking and activity recognition using inertial sensors on mobile devices with location-specific weighted assistance from a crowd-sourced WiFi fingerprinting system via a particle filter. By using just the most common sensors available on the large majority of smartphones (accelerometer, compass, and WiFi card) and offering an easily deployable method (requiring just the locations of stairs, elevators, corners and entrances), HiMLoc is shown to achieve median accuracies lower than 3 meters in most cases.