Stylianos Papanastasiou

Performance Analysis of Adjusted Probabilistic Broadcasting in Mobile Ad Hoc Networks

Broadcasting in Mobile Ad Hoc Networks (MANETs) is a fundamental data dissemination mechanism with a number of important applications in, e.g., route discovery, address resolution. However, broadcasting induces what is known as the “broadcast storm problem” which causes severe degradation in network performance due to excessive redundant retransmission, collision, and contention. Broadcasting in MANETs has traditionally been based on flooding, which simply swamps the network with large number of rebroadcast messages in order to reach all network nodes. Although probabilistic flooding has been one of the earliest suggested schemes to broadcasting, there has not been so far any attempt to analyse its performance behaviour in a MANET environment. In an effort to fill this gap, this paper investigates using extensive ns-2 simulations the effects of a number of important system parameters in a typical MANET, including node speed, pause time, traffic load, and node density on the performance of probabilistic flooding. The results reveal that most of these parameters have a critical impact on the reachability and the number of saved rebroadcast messages achieved by probabilistic flooding.

Improving route discovery in on-demand routing protocols using local topology information in MANETs

Most existing routing protocols proposed for MANETs use flooding as a broadcast technique for the propagation of network control packets; a particular example of this is the dissemination of route requests (RREQs), which facilitate route discovery. In flooding, each mobile node rebroadcasts received packets, which, in this manner, are propagated network-wide with considerable overhead. This paper improves on the performance of existing routing protocols by reducing the communication overhead incurred during the route discovery process by implementing a new broadcast algorithm called the adjusted probabilistic flooding on the Ad-Hoc on Demand Distance Vector (AODV) protocol. AODV [3] is a well-known and widely studied algorithm which has been shown over the past few years to maintain an overall lower routing overhead compared to traditional proactive schemes, even though it uses flooding to propagate RREQs. Our results, as presented in this paper, reveal that equipping AODV with fixed and adjusted probabilistic flooding, instead, helps reduce the overhead of the route discovery process whilst maintaining comparable performance levels in terms of saved rebroadcasts and reachability as achieved by conventional AODV\@. Moreover, the results indicate that the adjusted probabilistic technique results in better performance compared to the fixed one for both of these metrics

Human–machine collaboration through vehicle head up display interface

This work introduces a novel design for an automotive full-windshield head-up display (HUD) interface which aims to improve the driver’s spatial awareness and response times under low visibility conditions. To fulfil these requirements, we have designed and implemented a working prototype of a human–machine interface (HMI). Particular emphasis was placed on the prioritisation and effective presentation of information available through vehicular sensors, which would assist, without distracting, the driver in successfully navigating the vehicle under low visibility conditions. The proposed interface is based on minimalist visual representations of real objects to offer a new form of interactive guidance for motorway environments. Overall, this work discusses the design challenges of such a human–machine system, elaborates on the interface design philosophy and presents the outcome of user trials that contrasted the effectiveness of our proposed HUD against a typical head-down display (HDD).

On the Performance of Probabilistic Flooding in Mobile Ad Hoc Networks

This paper investigates using extensive simulations the effects of a number of important system parameters in a typical MANETs, including node speed, pause time, traffic load, and node density on the performance of probabilistic flooding. The results reveal that most of these parameters have a critical impact on the reachability and the number of saved rebroadcast messages achieved by probabilistic flooding, prompting the need for dynamically adjusting nodal retransmission probabilities depending on the current state of the network

Exploring the performance of TCP vegas in mobile ad hoc networks

Recent research efforts in mobile ad hoc networks have concentrated on examining the behaviour of TCP Reno over various ad hoc routing protocols and have suggested a number of extensions to improve its performance. TCP Vegas, which takes a proactive approach to congestion avoidance, has not so far been examined as a viable alternative to TCP Reno in wireless environments and no effort has been made to analyse its performance over routing protocols for MANETs. This paper evaluates using extensive simulation experiments the performance behaviour of TCP Vegas over a proactive (destination sequenced distance vector) and two reactive (dynamic source routing and ad hoc on demand distance vector) routing protocols and compares it against that of TCP Reno. Copyright

On the interaction of TCP and Routing Protocols in MANETs

Recent research in mobile ad hoc networks (MANETs) has highlighted the detrimental effect of multiple retransmission timeouts (RTOs) on TCP throughput. However, the effect of the routing protocol’s buffering strategy on this phenomenon has not been explicitly demonstrated or studied. In this paper, we present and analyse through simulations using functional testbed routing agents, TCP throughput performance during a route break event. The results of our analysis on three popular routing protocols, namely AODV, DSR and OLSR, produces insight into the different behavioural patterns of TCP during this event, and highlights the mechanisms of each routing protocol that affect it. Further, trade-offs in the choice of the routing parameters with respect to TCP performance are discussed.

TCP congestion window evolution and spatial reuse in MANETs

A number of recent research studies have explored ways to improve TCP throughput in mobile ad hoc networks by improving its interaction with the IEEE 802.11 medium access control (MAC) layer. In particular, the hidden terminal effects caused by interference can impact TCP performance dramatically and have been dealt with in the past by restricting the maximum sending window size. We have developed a TCP variant, which instead, adjusts the sending rate increase to achieve competitive goodput for TCP connections. Extensive simulation experiments indicate that a slower sending rate increase during the congestion avoidance phase of TCP leads to improved performance for TCP Reno while eliminating the negative effects inherent in restricting the maximum sending window size. This work discusses the applicability of our TCP oriented solution to the hidden terminal effect, includes a performance comparison against existing solutions and discusses its performance merits under various mobility conditions. Copyright

Designing a direct manipulation HUD interface for in-vehicle infotainment

This paper introduces a novel design approach for an automotive direct manipulation interface. The proposed design, as applied in a full-windshield Head-Up Display system, aims to improve the drivers situational awareness by considering information as it becomes available from various sources such as incoming mobile phone calls, text and email messages. The vehicles windshield effectively becomes an interactive display area which allows the system to increase the quality as well as throttle the quantity of information distilled to the driver in typical driving situations by utilising the existing mobile phone network. Opting for a simplistic approach of interaction, the interface elements are based on minimalist visual representation of real objects. This paper discusses the challenges involved in the HUD design, introduces the visual components of the interface and presents the outcome of a preliminary evaluation of the system on a group of ten users, as performed using a driving simulator.

The Effect of the RTS/CTS Handshake on TCP

Previous research enquiries into TCP performance in MANETs have largely assumed that the 802.11 RTS/CTS mechanism remains in full effect throughout the connection time. In this work we evaluate the effects on TCP goodput of utilising other modes of operation for the 802.11 handshake whilst remaining compliant with the original specification. To identify the source of the goodput discrepancies amongst the different modes of operation we introduce two new metrics to characterise spatial connection along a TCP connection and then use them to account for TCP goodput in string and mesh topologies when using different RTS/CTS strategies.

Reducing the degrading effect of hidden terminal interference in MANETs

A number of recent research studies have explored ways to improve TCP throughput in IEEE 802.11 mobile ad hoc networks. In particular, hidden terminal effects caused by interference have been shown to degrade TCP performance and have been dealt with, in previous work, by restricting the maximum congestion window size. We have pursued an alternative approach and have developed a TCP variant which adjusts the sending rate increase to achieve competitive goodput for TCP connections. In this paper, we demonstrate that a slower sending rate increase during the congestion avoidance phase of TCP leads to improved performance for TCP Reno while eliminating the negative effects inherent in restricting the maximum congestion window size. A performance comparison against existing solutions under various mobility conditions is also included.