Mário Macedo

Distributed Latency-Energy Minimization and interference avoidance in TDMA Wireless Sensor Networks

This paper presents Latency-Energy Minimization Medium Access (LEMMA), a new TDMA-based MAC protocol for Wireless Sensor Networks (WSNs), specially suited to extend the lifetime of networks supporting alarm-driven, delay-sensitive applications characterized by convergecast traffic patterns and sporadic traffic generation. Its cascading time-slot assignment scheme conciliates low end-to-end latency with a low duty-cycle, while supporting multi-sink WSN topologies. Unlike most of the current solutions, LEMMAs time-slot allocation protocol makes decisions based on the interference actually experienced by the nodes, instead of following the simple but potentially ineffective n-hop approach. Simulation results are presented to demonstrate the ineffectiveness of the n-hop time-slot allocation in comparison with LEMMA, as well as to evaluate the performance of LEMMA against L-MAC, T-MAC and Low Power Listening. The results show that under the target scenario conditions, LEMMA presents lower interference between assigned time-slots and lower end-to-end latency, while matching its best contender in terms of energy-efficiency.

A Service Discipline for Support of IP QoS in IEEE 802.11 Networks

This paper presents a QoS aware service discipline based on estimated transmission times for use in IEEE 802.11 networks. This algorithm works based on the flow specifications defined by the IETF for the IP QoS reference models, coupling layer 2 and layer 3 QoS. Simulation results show that the proposed service discipline performs better than Weighted Round Robin in IEEE 802.11b networks, providing a better optimisation of network resources while fulfilling the QoS requirements of real-time services such as packet telephony and videoconference.

Are there so many sons per node in a wireless sensor network data aggregation tree

Some authors seem to believe that the average number of sons in a Wireless Sensor Network (WSN) data aggregation tree can be kept constant, even when the distances from the sink increase. But this assumption is impossible to stand in a dense and uniformly deployed network, as the number of nodes in a given level would grow exponentially, while the perimeter just grows linearly. In this letter, it is shown that the average number of sons of a given tree node is in average a quite low number, slightly higher than one, and that it tends to 1, as the distance to sink, or node depth, increases, both for 2-D, and for 3-D WSNs.

Minimizing Interference in TDMA MAC Protocols for WSN Operating in Shadow-Fading Channels

This paper presents an analysis of the impact of shadow fading on the performance of TDMA slot allocation, with latter being measured in terms of the resultant in-network interference versus spatial reutilization. Simulations are presented which demonstrate that for Wireless Sensor Networks operating in shadow fading channels, protocols that feature TDMA slot allocation based on channel probing, e.g. LEMMA, lead to a significantly lower interferences when compared with protocols based on the n-hop neighborhood criterion. An extension of the basic LEMMA protocol is also presented, which leads to almost zero interferences.

An energy-efficient low-latency multi-sink MAC protocol for alarm-driven wireless sensor networks

This paper presents a novel MAC protocol for Wireless Sensor Networks (WSN)s designated Tone-Propagated MAC (TP-MAC). This protocol is specially suited for early warning and tracking applications, where sensor nodes generate sporadic asynchronous traffic (mainly consisting of uplink alert messages and downlink control messages) with stringent latency requirements. This protocol aims to maximize energy-efficiency while minimizing latency in source-to-sink and sink-to-source communication. This difficult objective is achieved integrating scheduled channel polling (i.e. synchronized low power listening) with rapid fast path establishment based on the propagation of short wake-up tones. An analytical model was used to compare TP-MAC with SCP-MAC. The results show that TP-MAC is able to achieve better target latencies even when its duty-cycle is lower during periods of inactivity. The results also show that the advantage of using TP-MAC increases with the hop-distance between source and sink.

Stealth constrained routing optimization using directional antennas in mobile ad-hoc networks

Low probability of detection (LPD) is an important requirement of mobile ad-hoc networks in battlefield applications. Although directional antennas are a suitable means to achieve LPD, related work on the use of directional antennas at the MAC and network layer has been mostly centered on improving network utilization and QoS, while LPD has been mostly addressed at the physical layer. The paper presents a novel scheme to optimize proactive link-state ad-hoc routing algorithms using directional antennas, taking into account LPD requirements. A power control algorithm is used to guarantee that the radiation footprint of a group of mobile nodes is never greater than a predefined maximum, even when directional transmission is allowed. This power control algorithm takes into account the radiation pattern of the antenna, network topology, mobile node positioning and a worst-case propagation model. Preliminary simulation results for the proposed scheme are presented and discussed.

IP QoS support in IEEE 802.11b WLANs

This paper addresses the support of IP with Quality of Service (QoS) in IEEE 802.11b WLANs. Both the Distributed Coordination Function (DCF) and Point Coordination Function (PCF) modes of operation are analysed and compared. For DCF, both the original standard and some of the enhancements proposed for IEEE 802.11e are considered. For PCF, two alternative scheduling disciplines are considered: Scheduling based on Estimated Transmission Times (SETT) proposed by the authors and Weighted Deficit Round Robin (WDRR). It is shown that while WDRR is suitable to perform fair bandwidth distribution, SETT also takes into account maximum transmission delay and service priority. Simulation results show that DCF cannot be used to support IP QoS even if 802.11e enhancements are used. On the other hand, PCF performs better with SETT than with WDRR. SETT is able to keep a similar level for network utilisation, while fulfilling the QoS requirements of real-time services such as packet telephony and videoconference, even in the presence of lower priority bursty data. The impact of the high overhead introduced by the IEEE 802.11 PHY and MAC layers was also evaluated, showing that for small packet traffic such as Voice over IP traffic, advanced voice compression is of limited usefulness.

Stealth optimized fisheye state routing in mobile ad-hoc networks using directional antennas

Research on the use of directional antennas in mobile ad-hoc networks has been mostly centered on improving spatial reuse, extending the transmission range and minimizing flooding overhead. However, directional antennas are also a suitable means to achieve low probability of detection in battlefield applications. This paper proposes mechanisms to minimize the number of hops and end-to-end delay when routing packets in a multi-hop ad-hoc network, while taking into account stealth requirements. This novel scheme is based on fisheye state routing, which is modified in order to take advantage of the extended range provided by directional antennas. The routing algorithm is coupled with a power control algorithm to guarantee a low probability of detection beyond the zone covered by the omni-directional radiation footprint of the network. The performance of the proposed scheme is evaluated through computer simulation and compared with the unmodified fisheye state routing algorithm.

Electronic protection and routing optimization of MANETs operating in an electronic warfare environment

Domination of the electromagnetic spectrum is a crucial component of the 21st century warfare. In the harsh electromagnetic environment of the modern battlefield, it is of the utmost importance to deny the opposing force the opportunity to attack or exploit the detection/interception of friendly communications assets through the deployment of electronic protection (EP) measures in order to attain low probability of detection (LPD), low probability of interception (LPI) and anti-jam (A/J). Given that directional antennas are a suitable means to achieve both extended range and LPD/LPI, this paper proposes mechanisms to optimize the trade-off between these capabilities, minimizing the number of hops and end-to-end delay when routing packets in a multi-hop ad-hoc network, while taking into account stealth requirements. The novel scheme is based on a variant of Fisheye State Routing, coupled with a power control algorithm to guarantee a LPD/LPI beyond the zone covered by the omni-directional radiation footprint of the network. The performance of the proposed scheme is evaluated through computer simulation.

Energy Efficient NDMA Multi-packet Detection with Multiple Power Levels

Multi-packet detection approaches handle packet collisions and errors by forcing packet retransmission and by processing the resulting signals. NDMA (Network Diversity Multiple Access) detection approach forces Q retransmissions by all stations when Q stations transmit in one collision slot. Previous work assumed that perfect power control is used, where the average reception power is equal for all stations. In this paper we handle the scenario where no power control is used, and multiple power levels are received. We propose a modification to the basic NDMA (Network Diversity Multiple Access) reception mechanism, where some of the stations may not retransmit its packets all the times.