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- Cognitive radio for medical body area networks using ultra widebandPublication . Chavez-Santiago, Raul; Nolan, Keith E.; Holland, Oliver; De Nardis, Luca; Ferro, João M.; Barroca, Norberto; Borges, Luís M.; Velez, Fernando J.; Goncalves, Vânia; Balasingham, IlangkoWearable wireless medical sensors beneficially impact the healthcare sector, and this market is experiencing rapid growth. In the United States alone, the telecommunications services market for the healthcare sector is forecast to increase from $7.5 billion in 2008 to $11.3 billion in 2013. Medical body area networks improve the mobility of patients and medical personnel during surgery, accelerate the patients’ recovery, and facilitate the remote monitoring of patients suffering from chronic diseases. Currently, MBANs are being introduced in unlicensed frequency bands, where the risk of mutual interference with other electronic devices can be high. Techniques developed during the evolution of cognitive radio can potentially alleviate these problems in medical communication environments. In addition, these techniques can help increase the efficiency of spectrum usage to accommodate the rapidly growing demand for wireless MBAN solutions and enhance coexistence with other collocated wireless systems. This article proposes a viable architecture of an MBAN with practical CR features based on ultra wideband radio technology. UWB signals offer many advantages to MBANs, and some features of this technology can be exploited for effective implementation of CR. We discuss the physical and MAC layer aspects of the proposal in addition to the implementation challenges.
- Impact of Switching Latency Times in Energy Consumption of IEEE 802.15.4 Radio TransceiversPublication . Barroca, Norberto; Gouveia, Paulo T.; Velez, FernandoThe energy efficiency of wireless sensor networks medium access control protocols depends on the adopted radio transceiver. This paper addresses the influence of the switching latency times in the energy consumption of IEEE 802.15.4 radio transceivers. Three different radio transceivers have been considered operating in the 2.4 GHz band. Simulation results performed in OMNET++ show that the radio transceiver with the shortest latency switching time has better performance in terms of energy consumption.
- Impact of using CSS PHY and RTS/CTS Combined with Frame Concatenation in the IEEE 802.15.4 Non-beacon Enabled Mode PerformancePublication . Barroca, Norberto; Borges, Luís M.; Chatzimisios, Periklis; Velez, Fernando J.This paper studies the performance improvement of the IEEE 802.15.4 non-beacon-enabled mode originated by the inclusion of the Request-To-Send/Clear-To-Send (RTS/CTS) handshake mechanism resulting in frame concatenation. Under IEEE 802.15.4 employing RTS/CTS, the backoff procedure is not repeated for each data frame sent but only for each RTS/CTS set. The maximum throughput and minimum delay performance are mathematically derived for both the Chirp Spread Spectrum and Direct Sequence Spread Spectrum Physical layers for the 2.4 GHz band. Results show that the utilization of RTS/CTS significantly enhances the performance of IEEE 802.15.4 applied to healthcare in terms of bandwidth efficiency.
- Wireless Flex Sensor Belt Networks for Foetal Movement Monitoring in Low Risk PregnanciesPublication . Borges, Luís M.; Barroca, Norberto; Zamith, Fernando; Lebres, António SérgioIn this work two flex sensor belts were produced to count the foetal movements in the last four weeks of pregnancy. While one is a standalone solution the other is a wireless flex sensor belt network one. A description of the type of sensors is followed by the discussion of the different types of acquisition and data treatment methodologies. The application to display the deformation angles is presented as well. The wireless sensor network solution is based on the IEEE 802.15.4 standard, and the hierarchical wireless network solutions include a Wi-Fi layer. Preliminary results highlight the need for accounting for mother respiration movements and actual experiences with pregnant woman will facilitate tuning the threshold-trigger, to improve the detection performance.
- Radio‐frequency energy harvesting for wearable sensorsPublication . Borges, Luís M.; Chávez‐Santiago, Raul; Barroca, Norberto; Velez, Fernando José; Balasingham, IlangkoThe use of wearable biomedical sensors for the continuous monitoring of physiological signals will facilitate the involvement of the patients in the prevention and management of chronic diseases. The fabrication of small biomedical sensors transmitting physiological data wirelessly is possible as a result of the tremendous advances in ultra-low power electronics and radio communications. However, the widespread adoption of these devices depends very much on their ability to operate for long periods of time without the need to frequently change, recharge or even use batteries. In this context, energy harvesting (EH) is the disruptive technology that can pave the road towards the massive utilisation of wireless wearable sensors for patient self-monitoring and daily healthcare. Radio-frequency (RF) transmissions from commercial telecommunication networks represent reliable ambient energy that can be harvested as they are ubiquitous in urban and suburban areas. The state-of-the-art in RF EH for wearable biomedical sensors specifically targeting the global system of mobile 900/1800 cellular and 700 MHz digital terrestrial television networks as ambient RF energy sources are showcased. Furthermore, guidelines for the choice of the number of stages for the RF energy harvester are presented, depending on the requirements from the embedded system to power supply, which is useful for other researchers that work in the same area. The present authors' recent advances towards the development of an efficient RF energy harvester and storing system are presented and thoroughly discussed too.
- Wearable Sensors for Foetal Movement Monitoring in Low Risk PregnanciesPublication . Borges, Luís M.; Araújo, Pedro; Lebres, António S.; Rente, Andreia; Salvado, Rita; Velez, Fernando J.; Martinez-de-Oliveira, J.; Barroca, Norberto; Ferro, João MiguelIn low risk pregnancies, the continuous monitoring of the foetal health is based on traditional protocols for counting the foetal movements felt by the mother. Although the maternal perception is a relevant characteristic for the evaluation of the foetal health, this kind of monitoring is hard to accomplish and being subjective can induce into errors due to mother’s anxiety and lack of concentration. Furthermore, the majority of foetal fatalities occur during the last weeks of low risk pregnancies. Therefore, it is important to obtain a universal electronic obstetric tracing, allowing for the identification of sudden changes in the foetus health, by continuously monitoring the foetus movements. The Smart-Clothing project aim has been the development of easy-to-wear belts with a telemedicine system for this purpose. One of the tried solutions is the Flex sensor belt system, which guarantees real-time and continuous foetal monitoring while creating effective interfaces for querying sensor data and store all the medical record (which can later be accessed by health professionals). Another developed belt has piezoelectric sensors incorporated onto it. The piezoelectric sensor belt has shown a high capacity to detect foetal movements, isolating them from external interferences.
- Energy-Aware Wireless Sensor Networks MAC Modelling and Simulation with Efficient TransceiversPublication . Barroca, Norberto; Velez, Fernando J.; Ferro, João Miguel; Mihovska, Albena Dimitrova; Lebres, António S.This paper addresses an analytical model that may be applied to different Wireless Sensor Networks (WSNs) Medium Access Control (MAC) protocols using different efficient transceivers. Our model accounts for the impact of several simultaneous factors, including periodic receive/transmit and sleep cycles, the length of the transmitted packet and data rate. The Sensor Block Acknowledgement MAC, a new innovative WSNs MAC protocol that uses a Block Acknowledgement scheme to achieve energy efficiency, is proposed as well. Our implementation takes into account the average delay, which can be clearly reduced when a Block Acknowledgement Scheme is used. In terms of energy consumption and average delay the efficient radio transceivers that operate in the 2.4GHz band have better results that the ones that use the 900MHz band. Adaptive listening (AL) enables radio transceivers to stay alert after the communication between two neighbour nodes before going to sleep, allowing for energy saving when synchronisation is involved.
- Frame Capture and Reliability Based Decider Implementation in the MiXiM IEEE 802.15.4 FrameworkPublication . Borges, Luís M.; Velez, Fernando J.; Barroca, Norberto; Lebres, AntónioThe task of properly modelling the physical (PHY) layer constitutes the most challenging endeavor in wireless networks simulation. Unfortunately, today, the majority of the wireless sensor network (WSN) simulators consider a simple model for the PHY frame reception, which does not account for emerging research on the frame capture (FC) effect. In this paper, we present enhancements for the PHY layer model for the IEEE 802.15.4 standard employed in the MiXiM framework, to account for the FC effect within WSN-based simulations. These improvements are as follows: i) proposal of a formulation for the PHY layer packet reception based on a reliability concept, identified as the Enhanced Reliability Decision Algorithm, which guarantees the delivery of a packet received by the PHY layer to the medium access control (MAC) layer, with a certain value for the reliability (0.9 and 0.99); ii) different frame overlapping scenarios, and iii) different values for the thresholds to decide frame recovery. The work includes the description, implementation and performance evaluation of the proposed decision algorithm, jointly with the FC effect, in the MiXiM framework simulator, for basic MAC and scheduled channel polling (SCP) MAC protocols. Based on the simulation results, the proposed approach can significantly improve simulation accuracy and provide a PHY decision algorithm that guarantees, with a certain reliability, the delivery of frames to the MAC layer.
- Smart-clothing wireless flex sensor belt network for foetal health monitoringPublication . Borges, Luís M.; Barroca, Norberto; Velez, Fernando J.; Lebres, AntónioIn the past years low power circuits design and networking techniques not only reduce the total power, requirements for Wireless Sensor Networks (WSNs) but also allow for supporting more complexity. In this paper we present solutions for WSN applications, and design aspects in the context of patient monitoring. The solution presented whose primary function is to collect the vital data remotely from the various sensors in low-rate wireless personal area network (LR-WPAN) is based on the IEEE 802.15.4 standard. It also will includes a Wi-Fi Layer in the context of hybrid networks. The application being dealt here consist of several flex sensors attached to a wearable monitoring belt, and allows for monitoring the foetal movements for a pregnant woman.
- Block acknowledgment mechanisms for the optimization of channel use in wireless sensor networksPublication . Barroca, Norberto; Velez, Fernando J.; Chatzimisios, PeriklisOne of the fundamental reasons for the IEEE 802.15.4 standard Medium Access Control (MAC) inefficiency is overhead. The current paper proposes and analyses the Sensor Block Acknowledgment MAC (SBACK-MAC) protocol, a new innovative protocol that allows the aggregation of several acknowledgment responses in one special BACK Response packet. Two different solutions are addressed. The first one considers the SBACK-MAC protocol in the presence of BACK Request (concatenation) while the second one considers the SBACK-MAC in the absence of BACK Request (piggyback). The proposed solutions address a distributed scenario with single-destination and single-rate frame aggregation. The throughput and delay performance is mathematically derived under ideal conditions (a channel environment with no transmission errors). The proposed schemes are compared against the basic access mode of IEEE 802.15.4 through extensive simulations by employing the OM-NET++ simulator. We demonstrate that the network performance is significantly improved in terms of throughput and end-to-end delay.
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