Network Time Synchronization: A Full Hardware Approach

Complex digital systems are typically built on top of several abstraction levels: digital, RTL, computer, operating system and software application. Each abstraction level greatly facilitates the design task at the cost of paying in performance and hardware resources usage. Network time synchronization is a good example of a complex system using several abstraction levels since the traditional solutions are a software application running on top of several software and hardware layers. In this contribution we study the case where a standards-compliant network time synchronization solution is fully implemented in hardware on a FPGA chip doing without any software layer. This solution makes it possible to implement very compact, inexpensive and accurate synchronization systems to be used either stand-alone or as embedded cores. Some general aspects of the design experience are commented together with some figures of merit. As a conclusion, full hardware implementations of complex digital systems should be seen as a feasible design option, from which great performance advantages can be expected, provided that we can find a suitable set of tools and control the design development costs

A clustering approach in sensor network time synchronization

In recent years tremendous technological advances have led to the development of low-cost sensors capable of data processing activities. These sensor nodes are organized in to a network typically called wireless Sensor Network. WSN\u27s are based on the principle of Data Fusion where the data collected from each sensor node is condensed into one meaningful result: Data Fusion is achieved by exchanging messages between the sensors. These messages are time stamped by each sensor node\u27s local clock fuse reading. As noted in various references, Time Synchronization is a common feature used in networking in order to give the nodes a common time reference. Time Synchronization is an important middleware service in Wireless Sensor Networks, as physical time is needed to relate events to the physical world. WSN\u27s require a great deal of synchronization accuracy so that information from many nodes can be cohesively integrated without creating time skews in the data. State-of-the-art research has been investigating the sources of error in attempting to synchronize the nodes in a network. The objective of this thesis is to define a Time Synchronization protocol for a Hierarchical Cluster Head based Wireless Sensor Network. Thus, the goals of this thesis are three fold: We first analyze the shortcomings of existing time synchronization protocols and propose a novel time synchronization protocol based on cluster tree based routing. We perform hardware-based simulation using Mica motes, TinyOS operating system and NesC programming language. Finally, we estimate the various sources of time error in package transmission in a WSN through basic simulation using OMNET++

Signal Detection and Estimation for MIMO radar and Network Time Synchronization

The theory of signal detection and estimation concerns the recovery of useful information from signals corrupted by random perturbations. This dissertation discusses the application of signal detection and estimation principles to two problems of significant practical interest: MIMO (multiple-input multiple output) radar, and time synchronization over packet switched networks. Under the first topic, we study the extension of several conventional radar analysis techniques to recently developed MIMO radars. Under the second topic, we develop new estimation techniques to improve the performance of widely used packet-based time synchronization algorithms. The ambiguity function is a popular mathematical tool for designing and optimizing the performance of radar detectors. Motivated by Neyman-Pearson testing principles, an alternative definition of the ambiguity function is proposed under the first topic. This definition directly associates with each pair of true and assumed target parameters the probability that the radar will declare a target present. We demonstrate that the new definition is better suited for the analysis of MIMO radars that perform non-coherent processing, while being equivalent to the original ambiguity function when applied to conventional radars. Based on the nature of antenna placements, transmit waveforms and the observed clutter and noise, several types of MIMO radar detectors have been individually studied in literature. A second investigation into MIMO radar presents a general method to model and analyze the detection performance of such systems. We develop closed-form expressions for a Neyman-Pearson optimum detector that is valid for a wide class of radars. Further, general closed-form expressions for the detector SNR, another tool used to quantify radar performance, are derived. Theoretical and numerical results demonstrating the value of the proposed techniques to optimize and predict the performance of arbitrary radar configurations are presented.There has been renewed recent interest in the application of packet-based time synchronization algorithms such as the IEEE 1588 Precision Time Protocol (PTP), to meet challenges posed by next-generation mobile telecommunication networks. In packet based time synchronization protocols, clock phase offsets are determined via two-way message exchanges between a master and a slave. Since the end-to-end delays in packet networks are inherently stochastic in nature, the recovery of phase offsets from message exchanges must be treated as a statistical estimation problem. While many simple intuitively motivated estimators for this problem exist in the literature, in the second part of this dissertation we use estimation theoretic principles to develop new estimators that offer significant performance benefits. To this end, we first describe new lower bounds on the error variance of phase offset estimation schemes. These bounds are obtained by re-deriving two Bayesian estimation bounds, namely the Ziv-Zakai and Weiss-Weinstien bounds, for use under a non-Bayesian formulation. Next, we describe new minimax estimators for the problem of phase offset estimation, that are optimum in terms of minimizing the maximum mean squared error over all possible values of the unknown parameters.Minimax estimators that utilize information from past timestamps to improve accuracy are also introduced. These minimax estimators provide fundamental limits on the performance of phase offset estimation schemes.Finally, a restricted class of estimators referred to as L-estimators are considered, that are linear functions of order statistics. The problem of designing optimum L-estimators is studied under several hitherto unconsidered criteria of optimality. We address the case where the queuing delay distributions are fully known, as well as the case where network model uncertainty exists.Optimum L-estimators that utilize information from past observation windows to improve performance are also described.Simulation results indicate that significant performance gains over conventional estimators can be obtained via the proposed optimum processing techniques

Network Time Synchronization in Time Division - LTE systems

Network time synchronization is a requirement for TD-LTE systems to prevent multi-access and cross-slot interference. Network listening is a technique used for network time synchronization in femto cellular networks. However, femto BSs which use network listening technique for synchronization suffer from interference coming from neighboring femto BSs. In this thesis the possibility to coordinate the reception times of the non-synchronized femto BSs is investigated so as to combat the interference issues in network listening based synchronization for TD-LTE femto BSs. This coordination effectively reduces the interference among the non-synchronized femto BSs and thereby enables the network to converge to a common frame timing. Further coordinated reception is combined with and compared to coordinated transmission methods. Also a proof of concept implementation of a simple network time synchronization scheme based on network listening is done on a test bed with the help of Software Defined Radios (SDRs)

Seamless roaming and guaranteed communication using a synchronized single-hop multi-gateway 802.15.4e TSCH network

Industrial wireless sensor networks (WSNs) are being used to improve the efficiency, productivity and safety of industrial processes. An open standard that is commonly used in such cases is IEEE 802.15.4e. Its TSCH mode employs a time synchronized based MAC scheme together with channel hopping to alleviate the impact of channel fading. Until now, most of the industrial WSNs have been designed to only support static nodes and are not able to deal with mobility. In this paper, we show how a single-hop, multi-gateway IEEE 802.15.4e TSCH network architecture can tackle the mobility problem. We introduce the Virtual Grand Master (VGM) concept that moves the synchronization point from separated Backbone Border Routers (BBRs) towards the backbone network. With time synchronization of all BBRs, mobile nodes can roam from one BBR to another without time desynchronization. In addition to time synchronization, we introduce a mechanism to synchronize the schedules between BBRs to support fast handover of mobile nodes.Comment: Short paper version of a paper submitted to Ad-Hoc Networks Journal by Elsevie