Energy-efficient wireless communication

In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters

Energy Harvesting Wireless Communications: A Review of Recent Advances

This article summarizes recent contributions in the broad area of energy harvesting wireless communications. In particular, we provide the current state of the art for wireless networks composed of energy harvesting nodes, starting from the information-theoretic performance limits to transmission scheduling policies and resource allocation, medium access and networking issues. The emerging related area of energy transfer for self-sustaining energy harvesting wireless networks is considered in detail covering both energy cooperation aspects and simultaneous energy and information transfer. Various potential models with energy harvesting nodes at different network scales are reviewed as well as models for energy consumption at the nodes.Comment: To appear in the IEEE Journal of Selected Areas in Communications (Special Issue: Wireless Communications Powered by Energy Harvesting and Wireless Energy Transfer

Time diversity solutions to cope with lost packets

A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation. An alternative to simple retransmission that can improve both power and spectral efficiency is to combine the signals associated to different transmission attempts. This thesis analyses two time diversity approaches to cope with lost packets that are relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems. It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs) than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration. Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/ 67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR project PTDC/EEA-TEL/115981/200

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

Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Centralized random backoff for collision free wireless local area networks

Over the past few decades, wireless local area networks (WLANs) have been widely deployed for data communication in indoor environments such as offices, houses, and airports. In order to fairly and efficiently use the unlicensed frequency band that Wi-Fi devices share, the devices follow a set of channel access rules, which is called a wireless medium access control (MAC) protocol. It is known that wireless devices following the 802.11 standard MAC protocol, i.e. the distributed coordination function (DCF), suffer from packet collisions when multiple nodes simultaneously transmit. This significantly degrades the throughput performance. Recently, several studies have reported access techniques to reduce the number of packet collisions and to achieve a collision free WLAN. Although these studies have shown that the number of collisions can be reduced to zero in a simple way, there have been a couple of remaining issues to solve, such as dynamic parameter adjustment and fairness to legacy DCF nodes in terms of channel access opportunity. Recently, In-Band Full Duplex (IBFD) communication has received much attention, because it has significant potential to improve the communication capacity of a radio band. IBFD means that a node can simultaneously transmit one signal and receive another signal in the same band at the same time. In order to maximize the performance of IBFD communication capability and to fairly share access to the wireless medium among distributed devices in WLANs, a number of IBFD MAC protocols have been proposed. However, little attention has been paid to fairness issues between half duplex nodes (i.e. nodes that can either transmit or receive but not both simultaneously in one time-frequency resource block) and IBFD capable nodes in the presence of the hidden node problem

Virtual sensing directional hub MAC (VSDH-MAC) protocol with power control

Medium access control (MAC) protocols play a vital role in making effective use of a multiple access channel as it governs the achievable performance such as channel utilization and corresponding quality of service of wireless sensor networks (WSNs). In this paper, a virtual carrier sensing directional hub (VSDH) MAC protocol incorporating realistic directional antenna patterns is proposed for directional single hub centralized WSNs. While in most instances, MAC protocols assume idealized directional antenna patterns, the proposed VSDH-MAC protocol incorporates realistic directional antenna patterns to deliver enhanced link performance. We demonstrate that the use of directional antennas with a suitable MAC protocol can provide enhanced communication range and increased throughput with reduced energy consumption at each node, compared to the case when only omnidirectional antennas are used. For the scenarios considered in this study, results show that the average transmit power of the sensor nodes can be reduced by a factor of two, and at the same time offer significantly extended lifetime

Energy-efficient diversity combining for different access schemes in a multi-path dispersive channel

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e ComputadoresThe forthcoming generation of mobile communications, 5G, will settle a new standard for a larger bandwidth and better Quality of Service (QoS). With the exploding growth rate of user generated data, wireless standards must cope with this growth and at the same time be energy efficient to avoid depleting the batteries of wireless devices. Besides these issues, in a broadband wireless setting QoS can be severely affected from a multipath dispersive channel and therefore be energy demanding. Cross-layered architectures are a good choice to enhance the overall performance of a wireless system. Examples of cross-layered Physical (PHY) - Medium Access Control (MAC) architectures are type-II Diversity Combining (DC) Hybrid-ARQ (H-ARQ) and Multi-user Detection (MUD) schemes. Cross-layered type-II DC H-ARQ schemes reuse failed packet transmissions to enhance data reception on posterior retransmissions; MUD schemes reuse data information from previously collided packets on posterior retransmissions to enhance data reception. For a multipath dispersive channel, a PHY layer analytical model is proposed for Single-Carrier with Frequency Domain Equalization (SC-FDE) that supports DC H-ARQ and MUD. Based on this analytical model, three PHY-MAC protocols are proposed. A crosslayered Time Division Multiple Access (TDMA) scheme that uses DC H-ARQ is modeled and its performance is studied in this document; the performance analysis shows that the scheme performs better with DC and achieves a better energy efficiency at the cost of a higher delay. A novel cross-layered prefix-assisted Direct-Sequence Code Division Multiple Access (DS-CDMA) scheme is proposed and modeled in this document, it uses principles of DC and MUD. This protocol performs better by means of additional retransmissions, achieving better energy efficiency, at the cost of higher redundancy from a code spreading gain. Finally, a novel cross-layered protocol H-ARQ Network Division Multiple Access (H-NDMA) is proposed and modeled, where the combination of DC H-ARQ and MUD is used with the intent of maximizing the system capacity with a lower delay; system results show that the proposed scheme achieves better energy efficiency and a better performance at the cost of a higher number of retransmissions. A comparison of the three cross-layered protocols is made, using the PHY analytical model, under normalized conditions using the same amount of maximum redundancy. Results show that the H-NDMA protocol, in general, obtains the best results, achieving a good performance and a good energy efficiency for a high channel load and low Signal-to-Noise Ratio (SNR). TDMA with DC H-ARQ achieves the best energy efficiency, although presenting the worst delay. Prefix-assisted DS-CDMA in the other hand shows good delay results but presents the worst throughput and energy efficiency

Оценка эффективности случайного множественного доступа к среде типа ALOHA при голосовых соединениях, передаче служебных команд, текстовых сообщений и мультимедийных файлов в условиях деструктивных воздействий

Оценка защищенности сетей цифровой радиосвязи при деструктивных воздействиях злоумышленника является важной задачей. Однако для случайного множественного доступа к среде типа ALOHA в сетях цифровой радиосвязи такая оценка не проводилась. В работе представлена аналитическая модель случайного множественного доступа к среде типа ALOHA в условиях деструктивных воздействий. В этой модели в качестве результирующего показателя оценки эффективности случайного доступа выступает обобщенный показатель, включающий вероятность успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла, степень наполнения и степень переполнения пакетами данных сети цифровой радиосвязи. Новый комплексный показатель — вероятность успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла — учитывает известные вероятности успешной доставки пакета данных, создания коллизии и свободного канала, а также новые средние времена передачи последовательности пакетов данных и коллизии, образованной при такой передаче. Новые показатели – степень наполнения и степень переполнения пакетами данных в сети цифровой радиосвязи определяют, насколько близко (далеко) от максимума находится значение комплексного показателя. Модель учитывает потенциально возможные деструктивные воздействия со стороны злоумышленника путем уточнения аналитических выражений для известных вероятностных и новых временных характеристик. Установлено, во-первых, количественная взаимосвязь между вероятностью успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла и средней длительностью коллизии в канале передачи данных, а, во-вторых, для гарантированного вывода из строя сети цифровой радиосвязи со случайным множественным доступом к среде типа ALOHA злоумышленник должен постоянно осуществлять деструктивное воздействие. Результаты работы применимы в области проектирования сетей цифровой радиосвязи, функционирующих в условиях деструктивных воздействий, а также при разработке автоматических систем оптимизации работы сетей цифровой радиосвязи и их защиты от таких воздействий

Оценка эффективности случайного множественного доступа к среде типа ALOHA при голосовых соединениях, передаче служебных команд, текстовых сообщений и мультимедийных файлов в условиях деструктивных воздействий

Assessing the security of digital radio networks in destructive impact conditions is an important task. However, such an assessment for random multiple access to the ALOHA-type environment in digital radio networks was not carried out. The paper presents an analytical model of random multiple access for the environment of digital radio networks of the ALOHA type in destructive impact conditions. In this model, acomplex measure, including the probability of a successful voice connection, the transfer of a service command, a text message or a multimedia file, the degree of filling and the degree of overflow of digital radio network data packets, serves as the resultant indicator for evaluating the effectiveness of random multiple media access. The new complex indicator of the probability of a successful voice connection, the transfer of a service command, a text message or a multimedia file takes into account the known probabilities of successful delivery of data packets, creation of a collision and a free channel, as well as new average transmission times for a sequence of data packets and a collision formed during such transmission. New indicators are the degree of filling and the degree of overflow of digital radio communications network data packets. They determine in saturated and supersaturated data networks of such a network how close (far) to maximum is the probability value of a successful voice connection, transmission of a service command, test message or multimedia file. The model takes into account the potential destructive effects of the attacker by refining the analytical expressions for the known probabilistic and new temporal characteristics. First, a quantitative relationship between the probability of a successful voice connection, the transfer of a service command, a text message or a multimedia file and the average duration of a data channel collisions is established./ Secondly, for guaranteed disabling a digital radio network with random multiple access to the medium ALOHA type attacker must constantly carry out a destructive impact. The results are applied in design of digital radio communications networks operating under destructive impacts, as well as in development of automatic systems for optimizing the operation of digital radio communications networks and protecting them from such impacts.Оценка защищенности сетей цифровой радиосвязи при деструктивных воздействиях злоумышленника является важной задачей. Однако для случайного множественного доступа к среде типа ALOHA в сетях цифровой радиосвязи такая оценка не проводилась. В работе представлена аналитическая модель случайного множественного доступа к среде типа ALOHA в условиях деструктивных воздействий. В этой модели в качестве результирующего показателя оценки эффективности случайного доступа выступает обобщенный показатель, включающий вероятность успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла, степень наполнения и степень переполнения пакетами данных сети цифровой радиосвязи. Новый комплексный показатель — вероятность успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла — учитывает известные вероятности успешной доставки пакета данных, создания коллизии и свободного канала, а также новые средние времена передачи последовательности пакетов данных и коллизии, образованной при такой передаче. Новые показатели – степень наполнения и степень переполнения пакетами данных в сети цифровой радиосвязи определяют, насколько близко (далеко) от максимума находится значение комплексного показателя. Модель учитывает потенциально возможные деструктивные воздействия со стороны злоумышленника путем уточнения аналитических выражений для известных вероятностных и новых временных характеристик. Установлено, во-первых, количественная взаимосвязь между вероятностью успешного голосового соединения, передачи служебной команды, тестового сообщения или мультимедийного файла и средней длительностью коллизии в канале передачи данных, а, во-вторых, для гарантированного вывода из строя сети цифровой радиосвязи со случайным множественным доступом к среде типа ALOHA злоумышленник должен постоянно осуществлять деструктивное воздействие. Результаты работы применимы в области проектирования сетей цифровой радиосвязи, функционирующих в условиях деструктивных воздействий, а также при разработке автоматических систем оптимизации работы сетей цифровой радиосвязи и их защиты от таких воздействий