Power Allocation Strategies for Wireless Relay Networks with Analog Network Coding: Survey

Relay aided communication with network coding can bring spectacular performance enhancements for wireless networks. The proper design of power allocated to each of the nodes involved in the communication is essential as it has impact on the performance when Analog Network coding (ANC) is used. This paper presents a survey on recent power allocation strategies, intended objectives, practical constraints that have been considered, and corresponding performances for networks with ANC protocol

Energy efficient offloading techniques for heterogeneous networks

Mobile data offloading has been proposed as a solution for the network congestion problem that is continuously aggravating due to the increase in mobile data demand. The concept of offloading refers to the exploitation of network heterogeneity with the objective to mitigate the load of the cellular network infrastructure. In this thesis a multicast protocol for short range networks that exploits the characteristics of physical layer network coding is presented. In the proposed protocol, named CooPNC, a novel cooperative approach is provided that allows collision resolutions with the use of an indirect inter-network cooperation scheme. Through this scheme, a reliable multicast protocol for partially overlapping short range networks with low control overhead is provided. It is shown that with CooPNC, higher throughput and energy efficiency are achieved, while it presents lower delay compared to state-of-the-art multicast protocols. A detailed description of the proposed protocol is provided, with a simple scenario of overlapping networks and also for a generalised scalable scenario. Through mathematical analysis and simulations it is proved that CooPNC presents significant performance gains compared to other state-of-the-art multicast protocols for short range networks. In order to reveal the performance bounds of Physical Layer Network Coding, the so-called Cross Network is investigated under diverse Network Coding (NC) techniques. The impact of Medium Access Control (MAC) layer fairness on the throughput performance of the network is provided, for the cases of pure relaying, digital NC with and without overhearing and physical layer NC with and without overhearing. A comparison among these techniques is presented and the throughput bounds, caused by MAC layer limitations, are discussed. Furthermore, it is shown that significant coding gains are achieved with digital and physical layer NC and the energy efficiency performance of each NC case is presented, when applied on the Cross Network.In the second part of this thesis, the uplink offloading using IP Flow Mobility (IFOM) is also investigated. IFOM allows a LTE mobile User Equipment (UE) to maintain two concurrent data streams, one through LTE and the other through WiFi access technology, that presents uplink limitations due to the inherent fairness design of IEEE 802.11 DCF. To overcome these limitations, a weighted proportionally fair bandwidth allocation algorithm is proposed, regarding the data volume that is being offloaded through WiFi, in conjunction with a pricing-based rate allocation algorithm for the rest of the data volume needs of the UEs that are transmitted through the LTE uplink. With the proposed approach, the energy efficiency of the UEs is improved, and the offloaded data volume is increased under the concurrent use of access technologies that IFOM allows. In the weighted proportionally fair WiFi bandwidth allocation, both the different upload data needs of the UEs, along with their LTE spectrum efficiency are considered, and an access mechanism is proposed that improves the use of WiFi access in uplink offloading. In the LTE part, a two-stage pricing-based rate allocation is proposed, under both linear and exponential pricing approaches, with the objective to satisfy all offloading UEs regarding their LTE uplink access. The existence of a malicious UE is also considered that aims to exploit the WiFi bandwidth against its peers in order to upload less data through the energy demanding LTE uplink and a reputation based method is proposed to combat its selfish operation. This approach is theoretically analysed and its performance is evaluated, regarding the malicious and the truthful UEs in terms of energy efficiency. It is shown that while the malicious UE presents better energy efficiency before being detected, its performance is significantly degraded with the proposed reaction method.La derivación del tráfico de datos móviles (en inglés data offloading) ha sido propuesta como una solución al problema de la congestión de la red, un problema que empeora continuamente debido al incremento de la demanda de datos móviles. El concepto de offloading se entiende como la explotación de la heterogeneidad de la red con el objetivo de mitigar la carga de la infraestructura de las redes celulares. En esta tesis se presenta un protocolo multicast para redes de corto alcance (short range networks) que explota las características de la codificación de red en la capa física (physical layer network coding). En el protocolo propuesto, llamado CooPMC, se implementa una solución cooperativa que permite la resolución de colisiones mediante la utilización de un esquema indirecto de cooperación entre redes. Gracias a este esquema, se consigue un protocolo multicast fiable i con poco overhead de control para redes de corto alcance parcialmente solapadas. Se demuestra que el protocolo CooPNC consigue una mayor tasa de transmisión neta (throughput) y una mejor eficiencia energética, a la vez que el retardo se mantiene por debajo del obtenido con los protocolos multicast del estado del arte. La tesis ofrece una descripción detallada del protocolo propuesto, tanto para un escenario simple de redes solapadas como también para un escenario general escalable. Se demuestra mediante análisis matemático y simulaciones que CooPNC ofrece mejoras significativas en comparación con los protocolos multicast para redes de corto alcance del estado del arte. Con el objetivo de encontrar los límites de la codificación de red en la capa física (physical layer network coding), se estudia el llamado Cross Network bajo distintas técnicas de Network Coding (NC). Se proporciona el impacto de la equidad (fairness) de la capa de control de acceso al medio (Medium Access Control, MAC), para los casos de repetidor puro (pure relaying), NC digital con y sin escucha del medio, y NC en la capa física con y sin escucha del medio. En la segunda parte de la tesis se investiga el offloading en el enlace ascendente mediante IP Flow Mobility (IFOM). El IFOM permite a los usuarios móviles de LTE mantener dos flujos de datos concurrentes, uno a través de LTE y el otro a través de la tecnología de acceso WiFi, que presenta limitaciones en el enlace ascendente debido a la equidad (fairness) inherente del diseño de IEEE 802.11 DCF. Para superar estas limitaciones, se propone un algoritmo proporcional ponderado de asignación de banda para el volumen de datos derivado a través de WiFi, junto con un algoritmo de asignación de tasa de transmisión basado en pricing para el volumen de datos del enlace ascendente de LTE. Con la solución propuesta, se mejora la eficiencia energética de los usuarios móviles, y se incrementa el volumen de datos que se pueden derivar gracias a la utilización concurrente de tecnologías de acceso que permite IFOM. En el algoritmo proporcional ponderado de asignación de banda de WiFi, se toman en consideración tanto las distintas necesidades de los usuarios en el enlace ascendente como su eficiencia espectral en LTE, y se propone un mecanismo de acceso que mejora el uso de WiFi para el tráfico derivado en el enlace ascendente. En cuanto a la parte de LTE, se propone un algoritmo en dos etapas de asignación de tasa de transmisión basada en pricing (con propuestas de pricing exponencial y lineal) con el objetivo de satisfacer el enlace ascendente de los usuarios en LTE. También se contempla la existencia de usuarios maliciosos, que pretenden utilizar el ancho de banda WiFi contra sus iguales para transmitir menos datos a través del enlace ascendente de LTE (menos eficiente energéticamente). Para ello se propone un método basado en la reputación que combate el funcionamiento egoísta (selfish).Postprint (published version

Spectrum Allocation Algorithms for Cognitive Radio Mesh Networks

Empowered by the cognitive radio technology, and motivated by the sporadic channel utilization, both spatially and temporally, dynamic spectrum access networks (also referred to as cognitive radio networks and next generation wireless networks) have emerged as a solution to improve spectrum utilization and provide more flexibility to wireless communication. A cognitive radio network is composed of wireless users, referred to as secondary users, which are allowed to use licensed spectrum bands as long as their are no primary, licensed, users occupying the channel in their vicinity. This restricted spectrum access strategy leads to heterogeneity in channel availability among secondary users. This heterogeneity forms a significant source of performance degradation for cognitive radio networks, and poses a great challenge on protocol design. In this dissertation, we propose spectrum allocation algorithms that take into consideration the heterogeneity property and its effect on the network performance. The spectrum allocation solutions proposed in this dissertation address three major objectives in cognitive radio mesh networks. The first objective is maximizing the network coverage, in terms of the total number of served clients, and at the same time simplifying the communication coordination function. To address this objective, we proposed a received based channel allocation strategy that alleviates the need for a common control channel, thus simplifying the coordination function, and at the same time maximizes the number of clients served with link reliability guarantees. We show the superiority of the proposed allocation strategy over other existing strategies. The second objective is improving the multicast throughput to compensate for the performance degradation caused by channel heterogeneity. We proposed a scheduling algorithm that schedules multicast transmissions over both time and frequency and integrates that with the use of network coding. This algorithm achieves a significant gain, measured as the reduction in the total multicast time, as the simulation results prove. We also proposed a failure recovery algorithm that can adaptively adjust the schedule in response to temporary changes in channel availability. The last objective is minimizing the effect of channel switching on the end-to-end delay and network throughput. Channel switching can be a significant source of delay and bandwidth wastage, especially if the secondary users are utilizing a wide spectrum band. To address this issue, we proposed an on-demand multicast routing algorithm for cognitive radio mesh networks based on dynamic programming. The algorithm finds the best available route in terms of end-to-end delay, taking into consideration the switching latency at individual nodes and the transmission time on different channels. We also presented the extensibility of the proposed algorithm to different routing metric. Furthermore, a route recovery algorithm that takes into consideration the overhead of rerouting and the route cost was also proposed. The gain of these algorithms was proved by simulation

Enabling Hardware Green Internet of Things: A review of Substantial Issues

Between now and the near future, the Internet of Things (IoT) will redesign the socio-ecological morphology of the human terrain. The IoT ecosystem deploys diverse sensor platforms connecting millions of heterogeneous objects through the Internet. Irrespective of sensor functionality, most sensors are low energy consumption devices and are designed to transmit sporadically or continuously. However, when we consider the millions of connected sensors powering various user applications, their energy efficiency (EE) becomes a critical issue. Therefore, the importance of EE in IoT technology, as well as the development of EE solutions for sustainable IoT technology, cannot be overemphasised. Propelled by this need, EE proposals are expected to address the EE issues in the IoT context. Consequently, many developments continue to emerge, and the need to highlight them to provide clear insights to researchers on eco-sustainable and green IoT technologies becomes a crucial task. To pursue a clear vision of green IoT, this study aims to present the current state-of-the art insights into energy saving practices and strategies on green IoT. The major contribution of this study includes reviews and discussions of substantial issues in the enabling of hardware green IoT, such as green machine to machine, green wireless sensor networks, green radio frequency identification, green microcontroller units, integrated circuits and processors. This review will contribute significantly towards the future implementation of green and eco-sustainable IoT

Wireless sensor networks using network coding for structural health monitoring

Wireless Sensor Networks (WSNs) have been deployed for the purpose of structural health monitoring (SHM) of civil engineering structures, e.g. bridges. SHM applications can potentially produce a high volume of sensing data, which consumes much transmission power and thus decreases the lifetime of the battery-run networks. We employ the network coding technique to improve the network efficiency and prolong its lifetime. By increasing the transmission power, we change the node connectivity and control the number of nodes that can overhear transmitted messages so as to hopefully realize the capacity gain by use of network coding. In Chapter 1, we present the background, to enable the reader to understand the need for SHM, advantages and drawbacks of WSNs and potential the application of network coding techniques has. In Chapter 2 we provide a review of related research explaining how it relates to our work, and why it is not fully applicable in our case. In Chapter 3, we propose to control transmission power as a means to adjust the number of nodes that can overhear a message transmission by a neighbouring node. However, too much of the overhearing by high power transmission consumes aggressively limited battery energy. We investigate the interplay between transmission power and network coding operations in Chapter 4. We show that our solution reduces the overall volume of data transfer, thus leading to significant energy savings and prolonged network lifetime. We present the mathematical analysis of our proposed algorithm. By simulation, we also study the trade-offs between overhearing and power consumption for the network coding scheme. In Chapter 5, we propose a methodology for the optimal placement of sensor nodes in linear network topologies (e.g., along the length of a bridge), that aims to minimise the link connectivity problems and maximise the lifetime of the network. Both simple packet relay and network coding are considered for the routing of the collected data packets towards two sink nodes positioned at both ends of the bridge. Our mathematical analysis, verified by simulation results, shows that the proposed methodology can lead to significant energy saving and prolong the lifetime of the underlying wireless sensor network. Chapter 6 is dedicated to the delay analysis. We analytically calculate the gains in terms of packet delay obtained by the use of network coding in linear multi-hop wireless sensor network topologies. Moreover, we calculate the exact packet delay (from the packet generation time to the time it is delivered to the sink nodes) as a function of the location of the source sensor node within the linear network. The derived packet delay distribution formulas have been verified by simulations and can provide a benchmark for the delay performance of linear sensor networks. In the Chapter 7, we propose an adaptive version of network coding based algorithm. In the case of packet loss, nodes do not necessary retransmit messages as they are able to internally decide how to cope with the situation. The goal of this algorithm is to reduce the power consumption, and decrease delays whenever it can. This algorithm achieves the delay similar to that of three-hop direct-connectivity version of the deterministic algorithm, and consumes power almost like one-hop direct-connectivity version of deterministic algorithm. In very poor channel conditions, this protocol outperforms the deterministic algorithm both in terms of delay and power consumption. In Chapter 8, we explain the direction of our future work. Particularly, we are interested in the application of combined TDMA/FDMA technique to our algorithm.Open Acces

Energy-Efficient and Overhead-Aware Cooperative Communications

Due to the rapid growth of energy-hungry wireless multimedia services, telecom energy consumption is increasing at an extraordinary rate. Besides negative environmental impacts and higher energy bills for operators, it also affects user experience as improvements in battery technologies have not kept up with increasing mobile energy demands. Therefore, how to increase the energy efficiency (EE) of wireless communications has gained a lot of attention recently. Cooperative communication, where relays cooperatively retransmit the received data from the source to the destination, is seen as a promising technique to increases EE. Nevertheless, it requires more overhead than direct communication that needs to be taken into account for practical wireless cooperative networks. In order to achieve potential energy savings promised by cooperative communications in practical systems, overhead-aware cooperative relaying schemes with low overhead are imperative. For the case that not all relays can hear each other, i.e., hidden relays exist, an energy-efficient and a low-overhead cooperative relaying scheme is proposed. This scheme selects a subset of relays before data transmission, through the proactive participation of available relays using their local timers. Theoretical analysis of average EE under maximum transmission power constraint, using practical data packet length, and taking account of the overhead for obtaining channel state information (CSI), relay selection, and cooperative beamforming, is performed and a closed-form approximate expression for the optimal position of relays is derived. Furthermore, the overhead of the proposed scheme and the impact of data packet lengths on EE, are analysed. The analytical and simulation results reveal that the proposed scheme is significantly more energy-efficient than direct transmission, best relay selection, all relay selection, and a state-of-the-art existing cooperative relaying scheme. Moreover, the proposed scheme reduces the overhead and achieves higher energy savings for larger data packets. The conventional cooperative beamforming schemes rely on the feedback of CSIs of the best relays from the destination, which cause extra energy consumption and are prone to quantization errors in practical systems. In the case of clustered relays with location awareness and timer-based relay selection, where relays can overhear the transmission and know the location of each other, an energy-efficient overhead-aware cooperative relaying scheme is proposed, making CSI feedback from the destination dispensable. In order to avoid possible collisions between relay transmissions during best relays selection, a distributed mechanism for the selected relays to appropriately insert guard intervals before their transmissions is proposed. Average EE of the proposed scheme considering the related overhead is analysed. Moreover, the impact of the number of available relays, the number of selected relays and the location of relay cluster on EE is studied. The simulation results indicate that the proposed cooperative relaying scheme achieves higher EE than direct communication, best relay selection, and all relay selection for relay clusters located close to the source. Independent of the relay cluster location, the proposed scheme exhibits significantly higher EE than an existing cooperative relaying scheme. Device-to-device (D2D) communication in cellular networks that enable direct transmissions between user equipments (UEs) is seen as a promising way to improve both EE and spectral efficiency (SE). If the source UE (SUE) and the destination UE (DUE) are far away from each other or if the channel between them is too weak for direct transmission, then two-hop D2D communications, where relay UEs (RUEs) forward the SUE's data packets to the DUE, can be used. An energy- and spectral-efficient optimal adaptive forwarding strategy (OAFS) for two-hop D2D communications is proposed. In a distributed manner, the OAFS adaptively chooses between the best relay forwarding (BRF) and the cooperative relay beamforming (CRB) with the optimal number of selected RUEs, depending on which of them provides the higher instantaneous EE. In order to reduce the computational complexity of relay selection, a low-complexity sub-optimal adaptive forwarding strategy (SAFS) is proposed that selects between the BRF and the CRB with two RUEs by comparing their instantaneous EE. Theoretical analysis of the average EE and SE for the proposed adaptive forwarding strategies is performed considering maximum transmission power constraints, circuit power consumption and the overhead for the acquisition of CSI, forwarding mode selection and cooperative beamforming. The theoretical and simulation results show that the proposed OAFS and SAFS exhibit significantly higher EE and SE than the BRF, CRB, direct D2D communications and conventional cellular communications. For short to moderate SUE-to-DUE distances, SAFS is almost as energy- and spectral-efficient as OAFS

Optimising lower layers of the protocol stack to improve communication performance in a wireless temperature sensor network

The function of wireless sensor networks is to monitor events or gather information and report the information to a sink node, a central location or a base station. It is a requirement that the information is transmitted through the network efficiently. Wireless communication is the main activity that consumes energy in wireless sensor networks through idle listening, overhearing, interference and collision. It becomes essential to limit energy usage while maintaining communication between the sensor nodes and the sink node as the nodes die after the battery has been exhausted. Thus, conserving energy in a wireless sensor network is of utmost importance. Numerous methods to decrease energy expenditure and extend the lifetime of the network have been proposed. Researchers have devised methods to efficiently utilise the limited energy available for wireless sensor networks by optimising the design parameters and protocols. Cross-layer optimisation is an approach that has been employed to improve wireless communication. The essence of cross-layer scheme is to optimise the exchange and control of data between two or more layers to improve efficiency. The number of transmissions is therefore a vital element in evaluating overall energy usage. In this dissertation, a Markov Chain model was employed to analyse the tuning of two layers of the protocol stack, namely the Physical Layer (PHY) and Media Access Control layer (MAC), to find possible energy gains. The study was conducted utilising the IEEE 802.11 channel, SensorMAC (SMAC) and Slotted-Aloha (S-Aloha) medium access protocols in a star topology Wireless Temperature Sensor Network (WTSN). The research explored the prospective energy gains that could be realised through optimizing the Forward Error Correction (FEC) rate. Different Reed Solomon codes were analysed to explore the effect of protocol tuning on energy efficiency, namely transmission power, modulation method, and channel access. The case where no FEC code was used and analysed as the control condition. A MATLAB simulation model was used to identify the statistics of collisions, overall packets transmitted, as well as the total number of slots used during the transmission phase. The bit error probability results computed analytically were utilised in the simulation model to measure the probability of successful transmitting data in the physical layer. The analytical values and the simulation results were compared to corroborate the correctness of the models. The results indicate that energy gains can be accomplished by the suggested layer tuning approach.Electrical and Mining EngineeringM. Tech. (Electrical Engineering