Alvin C. Valera

Cooperative packet caching and shortest multipath routing in mobile ad hoc networks

A mobile ad hoc network is an autonomous system of infrastructureless, multihop wireless mobile nodes. Reactive routing protocols perform well in such an environment due to their ability to cope quickly against topological changes. In this paper, we propose a new routing protocol called Caching and Multipath (CHAMP) Routing Protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route breakdowns. Simulation results reveal that by using a five-packet data cache, CHAMP exhibits excellent improvement in packet delivery, outperforming AODV and DSR by at most 30% in stressful scenarios. Furthermore, end-to-end delay is significantly reduced while routing overhead is lower at high mobility rates.

Performance evaluation of MQTT and CoAP via a common middleware

Wireless sensor networks (WSNs) typically consist of sensor nodes and gateways that operate on devices with limited resources. As a result, WSNs require bandwidth-efficient and energy-efficient application protocols for data transmission. Message Queue Telemetry Transport (MQTT) and Constrained Application Protocol (CoAP) are two such protocols proposed for resource-constrained devices. In this paper, we design and implement a common middleware that supports MQTT and CoAP and provides a common programming interface. We design the middleware to be extensible to support future protocols. Using the common middleware, we conducted experiments to study the performance of MQTT and CoAP in terms of end-to-end delay and bandwidth consumption. Experimental results reveal that MQTT messages have lower delay than CoAP messages at lower packet loss rates and higher delay than CoAP messages at higher loss rates. Moreover, when the message size is small and the loss rate is equal to or less than 25%, CoAP generates lower additional traffic than MQTT to ensure message reliability.

Improving protocol robustness in ad hoc networks through cooperative packet caching and shortest multipath routing

A mobile ad hoc network is an autonomous system of infrastructure-less, multihop, wireless mobile nodes. Reactive routing protocols perform well in this environment due to their ability to cope quickly against topological changes. This paper proposes a new routing protocol named CHAMP (caching and multiple path) routing protocol. CHAMP uses cooperative packet caching and shortest multipath routing to reduce packet loss due to frequent route failures. We show through extensive simulation results that these two techniques yield significant improvement in terms of packet delivery, end-to-end delay and routing overhead. We also show that existing protocol optimizations employed to reduce packet loss due to frequent route failures, namely local repair in AODV and packet salvaging in DSR, are not effective at high mobility rates and high network traffic.

Opportunistic ARQ with bidirectional overhearing for reliable multihop underwater networking

As reliable data delivery over a long-range single-hop underwater acoustic link is considerably challenging due to severe channel impairments, multihop data transmission schemes over one or more relay nodes have been proposed. In this paper, we propose a data delivery scheme using a fully-opportunistic ARQ that employs bidirectional overhearing, whereby nodes leverage on the broadcast nature of acoustic channels and their spatial and temporal variance to overhear (i) data packets from all upstream (nearer to source) nodes to speed up data delivery and (ii) data & acknowledgement packets from all downstream (nearer to sink) nodes as implicit acknowledgements. The cross-layer scheme uses implicit acknowledgements to purge duplicates at both data-link and network layer. We demonstrate using simulations that, when implemented on an Interweaved TDMA MAC scheme, the proposed delivery scheme achieves better reliability, energy-efficiency and latency as compared to non-opportunistic or semi-opportunistic schemes in multihop underwater acoustic networks with linear topology. Over a 10-hop network, the proposed scheme outperforms its non-opportunistic counterpart, delivers 88% more packets, consumes 43% less energy and achieves an 8% improvement in latency (per packet delivered).

Survey on wakeup scheduling for environmentally-powered wireless sensor networks

Abstract Advances in energy harvesting technologies and ultra low-power computing and communication devices are enabling the realization of environmentally-powered wireless sensor networks (EPWSNs). Because of limited and dynamic energy supply, EPWSNs are duty-cycled to achieve energy-neutrality, a condition where the energy demand does not exceed the energy supply. Duty cycling entails nodes to sleep and wakeup according to a wakeup scheduling scheme. In this paper, we survey the various wakeup scheduling schemes, with focus on their suitability for EPWSNs. A classification scheme is proposed to characterize existing wakeup scheduling schemes, with three main categories, namely, asynchronous, synchronous, and hybrid. Each wakeup scheduling scheme is presented and discussed under the appropriate category. The paper concludes with open research issues.

CHAMP: a highly-resilient and energy-efficient routing protocol for mobile ad hoc networks

We present the caching and multipath (CHAMP) routing protocol, a new protocol for mobile ad hoc networks that uses data caching and shortest multiple path routing to achieve both robustness against mobility and energy-efficiency. Simulation results show that a 5-packet FIFO data cache combined with 2 routes exhibits significantly better performance compared to DSR (dynamic source routing) and AODV (ad-hoc on demand distance vector) routing. At very high loads, CHAMP outperforms DSR and AODV, delivering 50% and 30% more packets, respectively, while consuming 1/3 and 1/2 less energy (per packet delivered), respectively.

Implementation and evaluation of multihop ARQ for reliable communications in underwater acoustic networks

Underwater acoustic networking is an emerging technology platform for oceanographic data collection, pollution monitoring, offshore exploration and tactical surveillance applications. Design of reliable and efficient communications protocols is challenging due to the unique characteristics of underwater acoustic channels. In this paper, we present a modular and lightweight implementation of an opportunistic multihop automatic repeat request (ARQ) scheme in a real system. We evaluate the performance of the opportunistic ARQ using inexpensive underwater acoustic modems in a shallow underwater environment.

Adaptive Duty Cycling in Sensor Networks With Energy Harvesting Using Continuous-Time Markov Chain and Fluid Models

The dynamic and unpredictable nature of energy harvesting sources available for wireless sensor networks, and the time variation in network statistics like packet transmission rates and link qualities, necessitate the use of adaptive duty cycling techniques. Such adaptive control allows sensor nodes to achieve long-run energy neutrality, where energy supply and demand are balanced in a dynamic environment such that the nodes function continuously. In this paper, we develop a new framework enabling an adaptive duty cycling scheme for sensor networks that takes into account the node battery level, ambient energy that can be harvested, and application-level QoS requirements. We model the system as a Markov decision process (MDP) that modifies its state transition policy using reinforcement learning. The MDP uses continuous time Markov chains (CTMCs) to model the network state of a node to obtain key QoS metrics like latency, loss probability, and power consumption, as well as to model the node battery level taking into account physically feasible rates of change. We show that with an appropriate choice of the reward function for the MDP, as well as a suitable learning rate, exploitation probability, and discount factor, the need to maintain minimum QoS levels for optimal network performance can be balanced with the need to promote the maintenance of a finite battery level to ensure node operability. Extensive simulation results show the benefit of our algorithm for different reward functions and parameters.

Energy-neutral scheduling and forwarding in environmentally-powered wireless sensor networks

In environmentally-powered wireless sensor networks (EPWSNs), low latency wakeup scheduling and packet forwarding is challenging due to dynamic duty cycling, posing time-varying sleep latencies and necessitating the use of dynamic wakeup schedules. We show that the variance of the intervals between receiving wakeup slots affects the expected sleep latency: when the variance of the intervals is low (high), the expected latency is low (high). We therefore propose a novel scheduling scheme that uses the bit-reversal permutation sequence (BRPS) - a finite integer sequence that positions receiving wakeup slots as evenly as possible to reduce the expected sleep latency. At the same time, the sequence serves as a compact representation of wakeup schedules thereby reducing storage and communication overhead. But while low latency wakeup schedule can reduce per-hop delay in ideal conditions, it does not necessarily lead to low latency end-to-end paths because wireless link quality also plays a significant role in the performance of packet forwarding. We therefore formulate expected transmission delay (ETD), a metric that simultaneously considers sleep latency and wireless link quality. We show that the metric is left-monotonic and left-isotonic, proving that its use in distributed algorithms such as the distributed Bellman-Ford yields consistent, loop-free and optimal paths. We perform extensive simulations using real-world energy harvesting traces to evaluate the performance of the scheduling and forwarding scheme.

Improving link failure detection and response in IEEE 802.11 wireless ad hoc networks

Wireless multihop ad hoc networks face a multitude of challenging problems including highly dynamic multihop topologies, lossy and noisy communication channels, and sporadic connectivity which contribute to frequent link failures. Rapid and accurate link failure detection is therefore important to maintain correct and optimum operation of network routing protocols. In this paper, we propose a unified link failure detection and recovery architecture (ulfra) which uses link layer feedback for rapid failure detection and packet salvaging for packet recovery. While link layer feedback and packet salvaging have been studied in simulations and simple experiments, no thorough experimental study have been undertaken to evaluate their real-world performance. This paper essentially fills this void as we implement and evaluate ulfra in an IEEE 802.11 multihop ad hoc network. Our experimental results show that link layer feedback, as modeled in current network simulators, actually performs worse than hello beaconing as it generates excessive false failure detections. To improve its performance, we implement a veto mechanism to reduce spurious detections. Experimental results show that the veto mechanism dramatically improves the performance of link layer feedback in terms of packet delivery, delay, and routing overhead as it considerably reduces the number of false detections. Compared with hello, it delivers 15–20% more packets at high node failure and 12–20% more at high network traffic.