Carlos A. Pomalaza-Raez

Energy optimization in multihop wireless embedded and sensor networks

This paper provides an analytical model for the study of energy consumption in multihop wireless embedded and sensor networks where nodes are extremely power constrained. Low-power optimization techniques developed for conventional ad hoc networks are not sufficient as they do not properly address particular features of embedded and sensor networks. It is not enough to reduce overall energy consumption, it is also important to maximize the lifetime of the entire network, that is, maintain full network connectivity for as long as possible. This paper considers different multihop scenarios to compute the energy per bit, efficiency and energy consumed by individual nodes and the network as a whole. The analysis uses a detailed model for the energy consumed by the radio at each node. Multihop topologies with equidistant and optimal node spacing are studied. Numerical computations illustrate the effects of packet routing, and explore the effects of coding and medium access control. These results show that always using a simple multihop message relay strategy is not always the best procedure.

Modeling primary user emulation attacks and defenses in cognitive radio networks

Primary user emulation attacks are a potential security threat to cognitive radio networks. In this work, we attempt to characterize an advanced primary user emulation attack and an advanced countermeasure against such an attack. Specifically, we show that both the attacker and the defender can apply estimation techniques and learning methods to obtain the key information of the environment and thus design better strategies. We further demonstrate that the advanced attack strategy can defeat the naive defense technique that focuses only on the received signal power, whereas the advanced defense strategy that exploits the invariant of communication channels can counteract the advanced attack effectively.

Cross-layer Energy Analysis of Multi-hop Wireless Sensor Networks

In this paper, we propose a detailed energy survey of the physical, data link, and network layer by analytical techniques. We also show the impact of regular sleep periods on node energy consumption and present a comparison analysis of single-hop vs. multi-hop communications in the energy realm. A detailed energy expenditure analysis of not only the physical layer but also the link and network layer provides a basis for developing new energy efficient wireless sensor networks. Regular, coordinated sleeping extends the lifetime of sensor nodes, but systems can only benefit from sleeping in terms of transmitted packets if the data arrival rate to the system is low. Energy efficiency is the driving motivation for it can be considered the most important factor for wireless sensor networks because of the power constraints set by battery operation. Radio solutions in the lower ISM bands are attractive because of their relatively easy implementation and low power consumption. However, the data rates of these commercial radios are also relatively low, limiting transmittable frame sizes to a few tens of octets along with strict duty cycle requirements. From the analysis we extract key parameters of selected MAC protocols and show that some traditional mechanisms, such as binary exponential backoff, have some inherent problems. We also argue that single-hop communications has up to 40% lower energy consumption than multihop forwarding within the feasible transmission distances of an ISM radio.

Coding for energy efficient wireless embedded networks

This paper studies the effect of coding on the energy consumption in wireless embedded networks. An analytical model of the radio energy consumption is developed to study how different DC balanced codes affect the energy consumption for the one-hop case. A Rayleigh fading channel is assumed. The analysis is extended to include multihop scenarios in order to study the tradeoff between coding overhead and energy consumption. The numerical results obtained show that energy efficiencies of the codes used in a multihop routing scenario are strongly dependent on the channel conditions and on the number of hops used.

UWB channel modelling for wireless body area networks in a hospital

This paper describes an experimental study of the ultra wideband (UWB) wireless body area network (WBAN) channel in a hospital environment. The measured data are used to develop statistical models for the channel, which can then be used to design efficient and safe communication networks. WBANs are expected to be used in the healthcare field to enable concepts such as telemedicine. The human body has a complex shape and consists of different tissues. It is then expected that the propagation of the electromagnetic waves near a patients body will have unique characteristics. In a hospital environment, there are also a variety of electronic devices and specialised medical equipment, which have impact on the electromagnetic propagation. To properly design WBANs is then necessary to have a good understanding of the characteristics of the radio channel in the proximity of the human body within a hospital.

Multihop medium access control for WSNs: an energy analysis model

We present an energy analysis technique applicable to medium access control (MAC) and multihop communications. Furthermore, the techniques application gives insight on using multihop forwarding instead of single-hop communications. Using the technique, we perform an energy analysis of carrier-sense-multiple-access (CSMA-) based MAC protocols with sleeping schemes. Power constraints set by battery operation raise energy efficiency as the prime factor for wireless sensor networks. A detailed energy expenditure analysis of the physical, the link, and the network layers together can provide a basis for developing new energy-efficient wireless sensor networks. The presented technique provides a set of analytical tools for accomplishing this. With those tools, the energy impact of radio, MAC, and topology parameters on the network can be investigated. From the analysis, we extract key parameters of selected MAC protocols and show that some traditional mechanisms, such as binary exponential backoff, have inherent problems.

Models for the modern power grid

This article reviews different kinds of models for the electric power grid that can be used to understand the modern power system, the smart grid. From the physical network to abstract energy markets, we identify in the literature different aspects that co-determine the spatio-temporal multilayer dynamics of power system. We start our review by showing how the generation, transmission and distribution characteristics of the traditional power grids are already subject to complex behaviour appearing as a result of the the interplay between dynamics of the nodes and topology, namely synchronisation and cascade effects. When dealing with smart grids, the system complexity increases even more: on top of the physical network of power lines and controllable sources of electricity, the modernisation brings information networks, renewable intermittent generation, market liberalisation, prosumers, among other aspects. In this case, we forecast a dynamical co-evolution of the smart grid and other kind of networked systems that cannot be understood isolated. This review compiles recent results that model electric power grids as complex systems, going beyond pure technological aspects. From this perspective, we then indicate possible ways to incorporate the diverse co-evolving systems into the smart grid model using, for example, network theory and multi-agent simulation.

Design and Evaluation of a Wireless Body Sensor System for Smart Home Health Monitoring

Advances in wireless sensor networks and embedded devices make it possible to develop new solutions for smart home health care at a low cost. This paper describes a wireless body sensor system that monitors physiological vital signs of a person while staying at home. Specifically, a waist-mounted triaxial accelerometer unit is used to record human movements. Sampled data are transmitted using an IEEE 802.15.4 wireless transceiver to a data logger unit. The acceleration measurement tests show that it is possible to classify different human motion through the acceleration reading. When IEEE 802.15.4 devices are used at home, there is interference from nearby IEEE 802.11 signals and microwave ovens. The data delivery performance, however, is found to be satisfactory and can be improved by selecting an appropriate channel. On the other hand, the wireless signal can be attenuated by housing materials, home appliances, and even plants. Therefore, the deployment of wireless body sensor systems at home needs to take these factors into consideration.

Effect of body motion and the type of antenna on the measured UWB channel characteristics in medical applications of wireless body area networks

Wireless body area networks (WBAN) are being considered as one of the most suitable technologies for remote health monitoring. This technology has the potential to increase the quality of medical care as well as keeping under control the associated costs. Due to the complexity of the human organisms and the nature of its different tissues it is expected that the propagation characteristics of the radio channel, when measured in close proximity of a human body, to be different than those found in other scenarios. The work described in this papers aims to expand the knowledge of the ultra-wideband (UWB) channel in the frequency range of 3.1–10 GHz, for the case of WBANs, under static and dynamic scenarios. Two different type of antennas are used, the SkyCross SMT-3TO10M-A and the P200 BroadSpec™. To minimize the effects of the environment the measurements were conducted in an anechoic chamber.

Effect of Impulse Radio–Ultrawideband Based on Energy Collection on MAC Protocol Performance

In this paper, we analyze the effects of the probabilities of detection, false alarm, and frame collision survival (in the presence of simultaneous transmissions) on medium access control (MAC) protocols using impulse-radio-ultrawideband (IR-UWB) energy-collection noncoherent receivers. The MAC protocols that were considered are all IEEE 802.15.4 compatible, i.e., the IEEE 802.15.4a optional UWB clear-channel-assessment mode, the IEEE 802.15.4a ALOHA mode, and a protocol termed preamble sense multiple access (PSMA). The impact on the network throughput, energy consumption, and delay are analytically derived and verified by simulation. The results show that these effects have a considerable impact on the performance of IR-UWB MAC protocols, and a classical analysis does not properly evaluate the protocolspsila performances. The results compare the performances of the MAC protocols and highlight a number of issues with regard to adapting narrowband protocols to UWB systems. The probability of frame collision survival on simultaneous transmissions is shown to have a significant impact on the performance of a MAC protocol. The comparison shows superior performance of the PSMA protocol under typical wireless-sensor-network operation ranges.