John H. Gibson

Tight Performance Bounds of Multihop Fair Access for MAC Protocols in Wireless Sensor Networks and Underwater Sensor Networks

This paper investigates the fundamental performance limits of medium access control (MAC) protocols for particular multihop, RF-based wireless sensor networks and underwater sensor networks. A key aspect of this study is the modeling of a fair-access criterion that requires sensors to have an equal rate of underwater frame delivery to the base station. Tight upper bounds on network utilization and tight lower bounds on the minimum time between samples are derived for fixed linear and grid topologies. The significance of these bounds is two-fold: First, they hold for any MAC protocol under both single-channel and half-duplex radios; second, they are provably tight. For underwater sensor networks, under certain conditions, we derive a tight upper bound on network utilization and demonstrate a significant fact that the utilization in networks with propagation delay is larger than that in networks with no propagation delay. The challenge of this work about underwater sensor networks lies in the fact that the propagation delay impact on underwater sensor networks is difficult to model. Finally, we explore bounds in networks with more complex topologies.

A network layer protocol for UANs to address propagation delay induced performance limitations

This paper provides a description of a novel network layer protocol for underwater acoustic networking (UAN) that provides a mechanism for network control and management enabling the implementation of responsive, self-configuring, adaptable, and scalable networks whose performance are predictable. The protocol draws from the demonstrated efficiencies of multi-protocol labeled switching, dynamic source routing, and multi-constraint based resource allocation schemes. The paper describes the expected benefits of establishing full duplex functionality between network nodes and presents some of the preliminary simulation findings regarding the viability of autonomously determining the network topology utilizing the full duplex node connections.

Incorporating Realistic Acoustic Propagation Models in Simulation of Underwater Acoustic Networks: A Statistical Approach

The development of protocols to advance the state of the art in underwater acoustic networks (UANs) relies on the use of computer simulations to analyze protocol performance. It is typical for designers to abstract away much of the detail of the physical environment in order to simplify the development of the simulation and ensure the simulation runtime performance is reasonable. The validity of the simulation results becomes questionable. There are, though, very high fidelity models developed by acoustic engineers and physicists for predicting acoustic propagation characteristics. In addition to these models, empirical data collections have been generated for many geographic regions of interest to UAN planners. However, incorporating these engineering and physics models or data collections into a network simulation is problematic, as the models are computationally complex and the data sets are not directly usable for acoustic signal propagation characterization. This paper presents a statistical method for developing a computationally efficient and simulation friendly approximation of a physics model of path loss. This method may also be used to adapt empirical data sets for use in network simulation in the same manner. The method was applied to the output of the Monterey-Miami Parabolic Equation model to assess its impact on the runtime performance of an OPNET-based simulation. Results of that simulation are compared to results from a previous OPNET simulation that simply used distance to determine reception. The simulation results confirm the incorporation of the MMPE approximation does not noticeably impact the runtime performance of the simulation. Anecdotally, the simulation confirms earlier results that suggest contention-based access controls without collision avoidance techniques may outperform the typical access technique adapted from wireless radio networks that employs collision avoidance, contrary to conventional wisdom

Analyzing the Performance of Multi-hop Underwater Acoustic Sensor Networks

Multi-hop underwater acoustic sensor networks constrain the performance of medium access control protocols. The efficiency of the well-known RTS-CTS scheme is degraded due to long propagation delays of such networks. Recently, interest in Aloha variants has surfaced; however, the performance of such protocols within the context of multi-hop networks is not well studied. In this paper, we identify the challenges of modeling contention-based medium access control protocols and present a model for analyzing Aloha variants for a simple string topology as a first step toward analyzing the performance of contention-based proposals in multi-hop underwater acoustic sensor networks. An application of the model suggests that Aloha variants are vary sensitive to traffic loads and network size.

Performance Limits of Fair-Access in Sensor Networks with Linear and Selected Grid Topologies

This paper investigates fundamental performance limits of medium access control (MAC) protocols for multi-hop sensor networks. A unique aspect of this study is the modeling of a fair-access criterion requiring that sensors have an equal rate of frame delivery to the base station. Tight upper bounds on network utilization and tight lower bounds on minimum time between samples are derived for fixed linear and grid topologies. The significance of these bounds is two-fold: First, they are universal, i.e., they hold for any MAC protocol. Second, they are provably tight, i.e., they can be achieved by a version of time division multiple access (TDMA) protocol that is self-clocking, and therefore does not require system-wide clock synchronization. The paper also examines the implication of the end-to-end performance bounds regarding the traffic rate and sensing time interval of individual sensors.

Performance analysis of ALOHA and p-persistent ALOHA for multi-hop underwater acoustic sensor networks

The extreme conditions under which multi-hop underwater acoustic sensor networks (UASNs) operate constrain the performance of medium access control (MAC) protocols. The MAC protocol employed significantly impacts the operation of the network supported, and such impacts must be carefully considered when developing protocols for networks constrained by both bandwidth and propagation delay.Time-based coordination, such as TDMA, have limited applicability due to the dynamic nature of the water channel used to propagate the sound signals, as well as the significant effect of relatively small changes in propagation distance on the propagation time. These effects cause inaccurate time synchronization and therefore make time-based access protocols less viable. The large propagation delays also diminish the effectiveness of carrier sense protocols as they do not predict with any certainty the status of the intended recipients at the point when the traffic would arrive. Thus, CSMA protocols do not perform well in UASNs, either.Reservation-based protocols have seldom been successful in commercial products over the past 50 years due to many drawbacks, such as limited scalability, relatively low robustness, etc. In particular, the impact of propagation delays in UASNs and other such constrained networks obfuscate the operation of the reservation protocols and diminish, if not completely negate, the benefit of reservations. The efficacy of the well-known RTS-CTS scheme, as a reservation-based enhancement to the CSMA protocol, is also adversely impacted by long propagation delays.An alternative to these MAC protocols is the much less complex ALOHA protocol, or one of its variants. However, the performance of such protocols within the context of multi-hop networks is not well studied. In this paper we identify the challenges of modeling contention-based MAC protocols and present models for analyzing ALOHA and p-persistent ALOHA variants for a simple string topology. As expected, an application of the model suggests that ALOHA variants are very sensitive to traffic loads. Indeed, when the traffic load is small, utilization becomes insensible to p values. A key finding, though, is the significance of the network size on the protocols’ performance, in terms of successful delivery of traffic from outlying nodes, indicating that such protocols are only appropriate for very small networks, as measured by hop count.

Extending UAV Video Dissemination via Seamless Handover: A Proof of Concept Evaluation of the IEEE 802.21 Standard

With an increase in the amount of daily UAV flights and the number of Digital Video Broadcast Return Channel Satellite (DVBRCS) suites in the Central Command (CENTCOM) Theater of Operations, the demand for a constant access to the operational picture has also increased. Until recently, there have been limited solutions for enlarging the access to DVBRCS video feeds. With the advent of wireless technologies, such as WiFi, WiMAX, 3G, and LTE, the opportunity to extend the access should be considered. In particular, the IEEE 802.21 standard, known as Media Independent Handover services, could be the solution to not only extending the network beyond the reaches of the forward operating bases, but allowing for no loss in connectivity, due to its ability to conduct seamless handovers, while on the move. In this thesis, a proof of concept evaluation of the compatibility of the IEEE 802.21 standard and the DVBRCS system, using an open source implementation, is presented. This work is to determine if the standard is to be a viable solution for extending the services of DVBRCS to forward deployed units via wireless networks.

Performance Limits of Fair-Access in Underwater Sensor Networks

This paper investigates fundamental performance limits of medium access control (MAC) protocols for particular underwater multi-hop sensor networks under a fair-access criterion requiring that sensors have an equal rate of underwater frame delivery to a base station. Tight upper bounds on network utilization and tight lower bounds on minimum time between samples are derived for fixed linear topology. The paper also examines the implication of the end-to-end performance bounds regarding the traffic rate and sensing time interval of individual sensors.