Backtracking Search Optimization for Collaborative Beamforming in Wireless Sensor Networks

Due to energy limitation and constraint in communication capabilities, the undesirable high battery power consumption has become one of the major issues in wireless sensor network (WSN). Therefore, a collaborative beamforming (CB) method was introduced with the aim to improve the radiation beampattern in order to compensate the power consumption. A CB is a technique which can increase the sensor node gain and performance by aiming at the desired objectives through intelligent capabilities. The sensor nodes were located randomly in WSN environment. The nodes were designed to cooperate among each other and act as a collaborative antenna array. The configuration of the collaborative nodes was modeled in circular array formation. The position of array nodes was determined by obtaining the optimum parameters pertaining to the antenna array which implemented by using Backtracking Search Optimization Algorithm (BSA). The parameter considered in the project was the side-lobe level minimization. It was observed that, the suppression of side-lobe level for BSA was better compared to the radiation beampattern obtained for conventional uniform circular array

Cooperative beamsteering in wireless sensor network based on backtracking search algorithm

The progressive development of Wireless Sensor Network (WSNs) contributes to many applications such as in the intelligent transport system (ITS), safety monitoring, military and in natural disasters prevention. In parallel to WSNs, the idea of internet of things (IoT) is developed where IoT can be defined as an interconnection between identifiable devices within the internet connection in sensing and monitoring processes. With recent growth in both size and power efficient computing, the concept of the ubiquitous WSN has aggressively emerged as an acknowledged research topic. As the capabilities of individual nodes in WSNs increase, so does the opportunity to perform more complicated tasks, such as cooperative beamsteering (CB). This CB manages to improve the range of communications and save precious battery power during the transmission. Therefore, this research proposes a meta-heuristic algorithm to organize node location in array arrangement. It is expected to effectively improve radiation beampattern fluctuations, exhibits lower complexity and less energy. From the simulation that has been done, it's observed that the proposed algorithm helps to reduce the side lobe level, thus better radiation beampattern is achieved

A review on frequency synchronization in collaborative beamforming: a practical approach

Coherent signal reception from distributed beamforming nodes of virtual antenna array formation requires frequency synchronization of the participating nodes. Signals at the target receiver are out of phase due to unsynchronized local oscillator’s (LO) reference signal of all the nodes in the systems. Practical cases of this problem are considered. In this article, a brief overview is presented of the need for the frequency synchronization and the resulting effect of mitigation avoidance. A variant of the closed-loop feedback algorithm is used to provide LO drifts information to the beamforming transmitters. These feedbacks are used to estimate, correct, and predict the nonlinear LO offsets that will result in near (0) phase offset of the received signal. The algorithms are implemented in software defined radio (SDR) and transmitted through the RF front end of devices like the NI 2920/N210 USRP

Robust beamforming for collaborative MIMO-OFDM wireless systems

Collaborative beamforming is a powerful technique to increase communication energy efficiency and range in an energy-constrained network. To achieve high performance, collaborative beamforming requires accurate knowledge of channel state information (CSI) at the transmitters (collaborative nodes). In practice, however, such exact knowledge of CSI is not available. A robust transmitter design based on partial CSI is required to mitigate the effects of CSI mismatches.This thesis focuses on the design and evaluation of a beamforming scheme that is robust to CSI mismatches for collaborative multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless systems. Using a max-min robust design approach, the robust beamformer is designed to maximize the minimum (worst-case) received signal-to-noise ratio (SNR) within a predefined uncertainty region at each OFDM subcarrier. In addition, several subcarrier power allocation strategies are investigated to further improve the robustness of collaborative systems. Numerical simulation results show that the robust beamformer offers improved performance over the nonrobust beamformers and the use of power allocation strategies among subcarriers further improves the system performance

A Study Of Aperiodic (Random) Arrays of Various Geometries

The use of wireless communication techniques and network centric topologies for portable communication networks and platforms makes it important to investigate new distributed beamforming techniques. Platforms such as micro air vehicles (MAVs), unattended ground sensors (UGSs), and unpiloted aerial vehicles (UAVs) can all benefit from advances in this area by enabling advantages in stealth, enhanced survivability, and maximum maneuverability. Collaborative beamforming is an example of a new technique to utilize these systems which uses a randomly distributed antenna array with a fitting phase coefficient for the elements. In this example, the radiated signal power of each element is coherently added in the far-field region of a specified target direction with net destructive interference occurring in all other regions to suppress sidelobe behavior. A wide variety of topologies can be used to confine geometrically these mobile random arrays for analysis. The distribution function for these topologies must be able to generalize the randomness within the geometry. Gaussian and Uniform distributions are investigated in this analysis, since they provide a way to calculate the statistically averaged beampattern for linear, planar (square and circular), and volumetric (cubical, cylindrical, and spherical) geometries. They are also of practical interest since the impact of array topology on the beampattern can typically be described in closed form. A rigorous analysis is presented first for disc-shaped topologies to motivate the discussion on random array properties and provide several new insights into their behavior. The analyses of volumetric geometries which are of interest to this work are drawn from this planar topology to provide a tractable and coherent discussion on the properties of more complex geometries. This analysis considers Normal and Gaussian distributed array element populations to derive the average beampattern, sidelobe behavior, beamwidth, and directivity. The beampattern is also examined in a similar manor for circular and spherical arrays with a truncated Gaussian distribution. A summary of the random array analysis and its results concludes this thesis

Theory and Applications of Aperiodic (Random) Phased Arrays

A need for network centric topologies using mobile wireless communications makes it important to investigate new distributed beamforming techniques. Platforms such as micro air vehicles (MAVs), unattended ground sensors (UGSs), and unpiloted aerial vehicles (UAVs) can all benefit from advances in this area utilizing advantages in stealth, enhanced survivability and maximum maneuverability. Moreover, in this dissertation, electromagnetic radiation is investigated such that the signal power of each element is coherently added in the far-field region of a specified target direction with net destructive interference occurring in all other regions to suppress sidelobe behavior. This provides superior range and resolution characteristics for a variety of applications including; early warning radar, ballistic missile defense and search and rescue efforts. A wide variety of topologies can be used to confine geometrically these mobile random arrays for analysis. The distribution function for these topologies must be able to generalize the randomness within the geometry. By this means it is feasible to assume the random element distribution of a very large volumetric space will yield either a normal or Gaussian distribution. Therefore the underlying assumption stands that the statistically averaged beam pattern develops from an arrangement of uniformly or Gaussian distrusted elements; both confined to a variety of geometry of radius A and is further generalized using a simple theory based upon the Fourier Transform. Hence, this theory will be derived and serve as the foundation for advanced performance characteristics of these arrays such as its ability for sidelobe tapering, adaptive nulling and multi beam control. In addition it will be shown that for the most ideal of conditions a steerable beam pattern free of sidelobe behavior (better known as a Gaussian distribution) is quite possible. As well these random array structures will be shown to provide superior bandwidth capability over tradiational array structures since they are frequency independent. Last of all a summary of the random array analysis and its results concludes this dissertation

Positioning of a wireless relay node for useful cooperative communication

Given the exorbitant amount of data transmitted and the increasing demand for data connectivity in the 21st century, it has become imperative to search for pro-active and sustainable solutions to the effectively alleviate the overwhelming burden imposed on wireless networks. In this study a Decode and Forward cooperative relay channel is analyzed, with the employment of Maximal Ratio Combining at the destination node as the method of offering diversity combining. The system framework used is based on a three-node relay channel with a source node, relay node and a destination node. A model for the wireless communications channel is formulated in order for simulation to be carried out to investigate the impact on performance of relaying on a node placed at the edge of cell. Firstly, an AWGN channel is used before the effect of Rayleigh fading is taken into consideration. Result shows that performance of cooperative relaying performance is always superior or similar to conventional relaying. Additionally, relaying is beneficial when the relay is placed closer to the receiver

Desenvolvimento de metodologias para localização indoor de smartphones com exatidão ao centímetro

Doutoramento em Engenharia ElectrotécnicaThis thesis describes the design and implementation of a reliable centimeter-level indoor positioning system fully compatible with a conventional smartphone. The proposed system takes advantage of the smartphone audio I/O and processing capabilities to perform acoustic ranging in the audio band using non-invasive audio signals and it has been developed having in mind applications that require high accuracy, such as augmented reality, virtual reality, gaming and audio guides. The system works in a distributed operation mode, i.e. each smartphone is able to obtain its own position using only acoustic signals. To support the positioning system, a Wireless Sensor Network (WSN) of synchronized acoustic beacons is used. To keep the infrastructure in sync we have developed an Automatic Time Synchronization and Syntonization (ATSS) protocol with a standard deviation of the sync offset error below 1.25 μs. Using an improved Time Difference of Arrival (TDoA) estimation approach (which takes advantage of the beacon signals’ periodicity) and by performing Non-Line-of-Sight (NLoS) mitigation, we were able to obtain very stable and accurate position estimates with an absolute mean error of less than 10 cm in 95% of the cases and a mean standard deviation of 2.2 cm for a position refresh period of 350 ms.Esta tese descreve o projeto e a implementação de um sistema de localização para ambientes interiores totalmente compatível com um smartphone convencional. O sistema proposto explora a capacidade de aquisição de sinais áudio e de processamento do smartphone para medir distâncias utilizando sinais acústicos na banda do audível; foram utilizados sinais áudio não-invasivos, i.e. com reduzido impacto perceptual em humanos. No desenvolvimento deste sistema foram consideradas aplicações que exigem elevada exatidão, na ordem dos centímetros, tais como realidade aumentada, realidade virtual, jogos ou guias virtuais. Utilizou-se uma infraestrutura de faróis de baixo custo suportada por uma rede de sensores sem fios (RSSF). Para manter a infraestrutura síncrona, foi desenvolvido um protocolo de sincronização e sintonização automática, (Automatic Time Synchronization and Syntonization - ATSS) que garante um desvio padrão do erro de offset abaixo de 1.25 μs. Cada smartphone efectua medidas MT-TDoA que posteriormente são utilizadas pelo algoritmo de localização hiperbólica. As estimativas de posição resultantes são estáveis e precisas, com um erro médio absoluto menor do que 10 cm em 95% dos casos e um desvio padrão médio de 2.2 cm, para um período de atualização de posição de 350 ms