Goodbye, ALOHA!

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The vision of the Internet of Things (IoT) to interconnect and Internet-connect everyday people, objects, and machines poses new challenges in the design of wireless communication networks. The design of medium access control (MAC) protocols has been traditionally an intense area of research due to their high impact on the overall performance of wireless communications. The majority of research activities in this field deal with different variations of protocols somehow based on ALOHA, either with or without listen before talk, i.e., carrier sensing multiple access. These protocols operate well under low traffic loads and low number of simultaneous devices. However, they suffer from congestion as the traffic load and the number of devices increase. For this reason, unless revisited, the MAC layer can become a bottleneck for the success of the IoT. In this paper, we provide an overview of the existing MAC solutions for the IoT, describing current limitations and envisioned challenges for the near future. Motivated by those, we identify a family of simple algorithms based on distributed queueing (DQ), which can operate for an infinite number of devices generating any traffic load and pattern. A description of the DQ mechanism is provided and most relevant existing studies of DQ applied in different scenarios are described in this paper. In addition, we provide a novel performance evaluation of DQ when applied for the IoT. Finally, a description of the very first demo of DQ for its use in the IoT is also included in this paper.Peer ReviewedPostprint (author's final draft

Medium access control in wireless network-on-chip: a context analysis

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Wireless on-chip communication is a promising candidate to address the performance and efficiency issues that arise when scaling current NoC techniques to manycore processors. A WNoC can serve global and broadcast traffic with ultra-low latency even in thousand-core chips, thus acting as a natural complement to conventional and throughput-oriented wireline NoCs. However, the development of MAC strategies needed to efficiently share the wireless medium among the increasing number of cores remains a considerable challenge given the singularities of the environment and the novelty of the research area. In this position article, we present a context analysis describing the physical constraints, performance objectives, and traffic characteristics of the on-chip communication paradigm. We summarize the main differences with respect to traditional wireless scenarios, and then discuss their implications on the design of MAC protocols for manycore WNoC, with the ultimate goal of kickstarting this arguably unexplored research area.Peer ReviewedPostprint (author's final draft

Machine Learning in Wireless Sensor Networks: Algorithms, Strategies, and Applications

Wireless sensor networks monitor dynamic environments that change rapidly over time. This dynamic behavior is either caused by external factors or initiated by the system designers themselves. To adapt to such conditions, sensor networks often adopt machine learning techniques to eliminate the need for unnecessary redesign. Machine learning also inspires many practical solutions that maximize resource utilization and prolong the lifespan of the network. In this paper, we present an extensive literature review over the period 2002-2013 of machine learning methods that were used to address common issues in wireless sensor networks (WSNs). The advantages and disadvantages of each proposed algorithm are evaluated against the corresponding problem. We also provide a comparative guide to aid WSN designers in developing suitable machine learning solutions for their specific application challenges.Comment: Accepted for publication in IEEE Communications Surveys and Tutorial

ZigBee-assisted ad-hoc networking of multi-interface mobile devices

Wireless ad hoc network is decentralized wireless network, which does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Instead, each node participates in routing by forwarding data for other nodes. The determination of which nodes forward data is made dynamically based on the network connectivity. Node density has a great impact on the performance and efficiency of wireless ad hoc networks by influencing some factors such as capacity, network contention, routing efficiency, delay, and connectivity. On one hand, maintaining stable connectivity is a big challenge for sparsely deployed and highly dynamic ad hoc wireless network. Vehicle ad hoc network (VANET) which consists of highly mobile vehicles with wireless interfaces is one type of such network, especially in rural areas where vehicles traffic are very sparse. One of the most important applications built on top of VANET is the safety application. In VANET safety applications, source vehicles that observe accidents or some other unsafe conditions of the roads generate warning messages about the conditions, and propagate the warning messages to the following vehicles. In this way, the following drivers have the opportunity to do some necessary action before they reach the potential danger zone to avoid accident. The safety application requires timely and accurate warning message detection and delivery. However, recent researches have shown that sparse and highly dynamic vehicle traffic leads network fragmentation, which poses a crucial research challenge for VANET safety application. On the other hand, reducing contention and thus maximizing the network throughput is also a big challenge for densely deployed ad hoc wireless network, especially when many devices are located in a small area and each device has heavy duty message to transmit. The WiFi interface perhaps is the most common interface found in mobile devices for data transfer as it provides good combination of throughout, range and power efficiency. However, the WiFi interface may have to consume a large amount of bandwidth and energy for contention and combating collision, especially when mobile devices located in a small area all have heavy traffic to transmit. Meanwhile, ZigBee is an emerging wireless communication technology which supports low-cost, low-power and short-range wireless communication. Nowadays, it has been common for a mobile device, such as smart phone, PDA and laptop, to have both WiFi and Bluetooth interfaces. As the ZigBee technology becomes more and more mature, it will not be surprising to see the ZigBee interface commonly embedded in mobile devices together with WiFi and Bluetooth interfaces in the near future. The co-existence of the ZigBee and the WiFi interfaces in the same mobile device inspires us to develop new techniques to address the above two issues. Specifically, this thesis presents two systems built based on ZigBee-assisted ad-hoc networking of multi-interface mobile devices. In order to achieve stable connectivity in a sparse and dynamic VANET, the first system integrates a network of static roadside sensors and highly mobile vehicles to improve driving safety. In order to reduce contention in a densely deployed ad hoc wireless network, the second system assists WiFi transmission with ZigBee interface for multi-interface mobile devices. Extensive implementations and experiments have been conducted to demonstrate the effectiveness of our proposed systems

Receiver-Initiated Handshaking MAC Based On Traffic Estimation for Underwater Sensor Networks

In underwater sensor networks (UWSNs), the unique characteristics of acoustic channels have posed great challenges for the design of medium access control (MAC) protocols. The long propagation delay problem has been widely explored in recent literature. However, the long preamble problem with acoustic modems revealed in real experiments brings new challenges to underwater MAC design. The overhead of control messages in handshaking-based protocols becomes significant due to the long preamble in underwater acoustic modems. To address this problem, we advocate the receiver-initiated handshaking method with parallel reservation to improve the handshaking efficiency. Despite some existing works along this direction, the data polling problem is still an open issue. Without knowing the status of senders, the receiver faces two challenges for efficient data polling: when to poll data from the sender and how much data to request. In this paper, we propose a traffic estimation-based receiver-initiated MAC (TERI-MAC) to solve this problem with an adaptive approach. Data polling in TERI-MAC depends on an online approximation of traffic distribution. It estimates the energy efficiency and network latency and starts the data request only when the preferred performance can be achieved. TERI-MAC can achieve a stable energy efficiency with arbitrary network traffic patterns. For traffic estimation, we employ a resampling technique to keep a small computation and memory overhead. The performance of TERI-MAC in terms of energy efficiency, channel utilization, and communication latency is verified in simulations. Our results show that, compared with existing receiver-initiated-based underwater MAC protocols, TERI-MAC can achieve higher energy efficiency at the price of a delay penalty. This confirms the strength of TERI-MAC for delay-tolerant applications

Receiver-Initiated Handshaking MAC Based on Traffic Estimation for Underwater Sensor Networks

In underwater sensor networks (UWSNs), the unique characteristics of acoustic channels have posed great challenges for the design of medium access control (MAC) protocols. The long propagation delay problem has been widely explored in recent literature. However,the long preamble problem with acoustic modems revealed in real experiments brings new challenges to underwater MAC design. The overhead of control messages in handshaking-based protocols becomes significant due to the long preamble in underwater acoustic modems. To address this problem, we advocate the receiver-initiated handshaking method with parallel reservation to improve the handshaking efficiency. Despite some existing works along this direction, the data polling problem is still an open issue. Without knowing the status of senders, the receiver faces two challenges for efficient data polling: when to poll data from the sender and how much data to request. In this paper, we propose a traffic estimation-basedreceiver-initiated MAC(TERI-MAC)to solve this problem with an adaptive approach. Data polling in TERI-MAC depends on an online approximation of traffic distribution. It estimates the energy efficiency and network latency and starts the data request only when the preferred performance can be achieved. TERI-MAC can achieve a stable energy efficiency with arbitrary network traffic patterns. For traffic estimation, we employ a resampling technique to keep a small computation and memory overhead. The performance of TERI-MAC in terms of energy efficiency, channel utilization, and communication latency is verified in simulations. Our results show that, compared with existing receiver-initiated-based underwater MAC protocols, TERI-MAC can achieve higher energy efficiency at the price of a delay penalty. This confirms the strength of TERI-MAC for delay-tolerant applications

IEEE 802.15.4 MAC Protocol Study and Improvement

IEEE 802.15.4 is a standard used for low rate personal area networks (PANs). It offers device level connectivity in applications with limited ower and relaxed throughput requirements. Devices with IEEE 802.15.4 technology can be used in many potential applications, such as home networking, industry/environments monitoring, healthcare equipments, etc, due to its extremely low power features. Although the superframe beacons play the key role in synchronizing channel access in IEEE 802.15.4, they are sources for energy inefficiency. This research focuses on exploring how to optimize the beacons, and designing novel schemes to distribute the information that are supposed to be delivered to a subset of PAN devices. In this work, an acknowledgement based scheme is proposed to reduce the energy consumption in the distribution of guaranteed time slot (GTS) descriptors. Based on the observation that the superframe beacon frame has global impact on all PAN devices, an energy-efficient channel reservation scheme is presented to deliver the information (GTS descriptors and pending addresses). In addition, the problem of channel underutilization is studied in the contention free period. To address the problem, a new GTS allocation scheme is proposed to improve the bandwidth utilization

A MAC protocol for quality of service provisioning in adaptive biomedical wireless sensor networks

Doctorate program on Electronics and Computer EngineeringNew healthcare solutions are being explored to improve the quality of care and the quality of life of patients, as well as the sustainability and efficiency of the healthcare services. In this context, wireless sensor networks (WSNs) constitute a key technology for closing the loop between patients and healthcare providers, as WSNs provide sensing ability, as well as mobility and portability, essential characteristics for wide acceptance of wireless healthcare technology. Despite the recent advances in the field, the wide adoption of healthcare WSNs is still conditioned by quality of service (QoS) issues, namely at the medium access control (MAC) level. MAC protocols currently available for WSNs are not able to provide the required QoS to healthcare applications in scenarios of medical emergency or intensive medical care. To cover this shortage, the present work introduces a MAC protocol with novel concepts to assure the required QoS regarding the data transmission robustness, packet delivery deadline, bandwidth efficiency, and energy preservation. The proposed MAC protocol provides a new and efficient dynamic reconfiguration mechanism, so that relevant operational parameters may be redefined dynamically in accordance with the patients’ clinical state. The protocol also provides a channel switching mechanism and the capacity of forwarding frames in two-tier network structures. To test the performance of the proposed MAC protocol and compare it with other MAC protocols, a simulation platform was implemented. In order to validate the simulation results, a physical testbed was implemented to replicate the tests and verify the results. Sensor nodes were specifically designed and assembled to implement this physical testbed. New healthcare solutions are being explored to improve the quality of care and the quality of life of patients, as well as the sustainability and efficiency of the healthcare services. In this context, wireless sensor networks (WSNs) constitute a key technology for closing the loop between patients and healthcare providers, as WSNs provide sensing ability, as well as mobility and portability, essential characteristics for wide acceptance of wireless healthcare technology. Despite the recent advances in the field, the wide adoption of healthcare WSNs is still conditioned by quality of service (QoS) issues, namely at the medium access control (MAC) level. MAC protocols currently available for WSNs are not able to provide the required QoS to healthcare applications in scenarios of medical emergency or intensive medical care. To cover this shortage, the present work introduces a MAC protocol with novel concepts to assure the required QoS regarding the data transmission robustness, packet delivery deadline, bandwidth efficiency, and energy preservation. The proposed MAC protocol provides a new and efficient dynamic reconfiguration mechanism, so that relevant operational parameters may be redefined dynamically in accordance with the patients’ clinical state. The protocol also provides a channel switching mechanism and the capacity of forwarding frames in two-tier network structures. To test the performance of the proposed MAC protocol and compare it with other MAC protocols, a simulation platform was implemented. In order to validate the simulation results, a physical testbed was implemented to replicate the tests and verify the results. Sensor nodes were specifically designed and assembled to implement this physical testbed. Preliminary tests using the simulation and physical platforms showed that simulation results diverge significantly from reality, if the performance of the WSN software components is not considered. Therefore, a parametric model was developed to reflect the impact of this aspect on a physical WSN. Simulation tests using the parametric model revealed that the results match satisfactorily those obtained in reality. After validating the simulation platform, comparative tests against IEEE 802.15.4, a prominent standard used in many wireless healthcare systems, showed that the proposed MAC protocol leads to a performance increase regarding diverse QoS metrics, such as packet loss and bandwidth efficiency, as well as scalability, adaptability, and power consumption. In this way, AR-MAC is a valuable contribution to the deployment of wireless e-health technology and related applications.Novas soluções de cuidados de saúde estão a ser exploradas para melhorar a qualidade de tratamento e a qualidade de vida dos pacientes, assim como a sustentabilidade e eficiência dos serviços de cuidado de saúde. Neste contexto, as redes de sensores sem fios (wireless sensor networks - WSN) são uma tecnologia chave para fecharem o ciclo entre os pacientes e os prestadores de cuidados de saúde, uma vez que as WSNs proporcionam não só capacidade sensorial mas também mobilidade e portabilidade, caracteristicas essenciais para a aceitação à larga escala da tecnologia dos cuidados de saúde sem fios. Apesar dos avanços recentes na área, a aceitação genérica das WSNs de cuidados de saúde ainda está condicionada por aspectos relacionados com a qualidade de serviço (quality of service - QoS), nomeadamente ao nível do controlo de acesso ao meio (medium access control - MAC). Os protocolos MAC actualmente disponíveis para WSNs são incapazes de fornecer a QoS desejada pelas aplicações médicas em cenários de emergência ou cuidados médicos intensivos. Para suprimir esta carência, o presente trabalho apresenta um protocolo MAC com novos conceitos a fim de assegurar a QoS respeitante à robustez de transmissão de dados, ao limite temporal da entrega de pacotes, à utilização da largura de banda e à preservação da energia eléctrica. O protocolo MAC proposto dispõe de um novo e eficiente mecanismo de reconfiguração para que os parâmetros operacionais relevantes possam ser redefinidos dinamicamente de acordo com o estado de saúde do paciente. O protocolo também oferece um mecanismo autónomo de comutação de canal, bem como a capacidade de encaminhar pacotes em redes de duas camadas. Para testar o desempenho do protocolo MAC proposto e compará-lo com outros protocolos MAC foi implementada uma plataforma de simulação. A fim de validar os resultados da simulação foi também implementada uma plataforma física para permitir replicar os testes e verificar os resultados. Esta plataforma física inclui nós sensoriais concebidos e construídos de raiz para o efeito. Testes preliminares usando as plataformas de simulação e física mostraram que os resultados de simulação divergem significativamente da realidade, caso o desempenho dos componentes do software presentes nos componentes da WSN não seja considerado. Por conseguinte, desenvolveu-se um modelo paramétrico para reflectir o impacto deste aspecto numa WSN real. Testes de simulação efectuados com o modelo paramétrico apresentaram resultados muito satisfatórios quando comparados com os obtidos na realidade. Uma vez validada a plataforma de simulação, efectuaram-se testes comparativos com a norma IEEE 802.15.4, proeminentemente usada em projectos académicos de cuidados de saúde sem fios. Os resultados mostraram que o protocolo MAC conduz a um desempenho superior no tocante a diversas métricas QoS, tais como perdas de pacotes e utilização de largura de banda, bem como no respeitante à escalabilidade, adaptabilidade e consumo de energia eléctrica. Assim sendo, o protocolo MAC proposto representa um valioso contributo para a concretização efectiva dos cuidados de saúde sem fios e suas aplicações