James Aweya

An Empirical Evaluation of a Probabilistic RF Signature for WLAN Location Fingerprinting

Localization for indoor environments has gained considerable attention over the last decade. The most popular technique is based on location fingerprinting using received signal strength (RSS) mainly due to the fact that it exploits the available wireless infrastructure and that RSS fingerprints are readily available using different wireless standards (IEEE 802.11, etc.). This simplicity however incurs a cost in accuracy and researchers focus on improving the performance from a pattern recognition perspective. Recently improvement in performance has been demonstrated using physical layer channel-based fingerprints such as the Channel Transfer Function (CTF) and Channel Impulse Response (CIR) at a cost of increased storage and computation requirements. In this paper we experimentally evaluate the performance of a probabilistic physical layer fingerprint that is based on entropy of the magnitude and phase of the CTF. We will show through extensive frequency domain channel measurements in an indoor office environment that entropy can be a practical alternative to RSS fingerprinting; where it shares the latters simplicity of structure (scalar) but outperforms RSS and complex CIR fingerprints. We further investigate the impact of realistic channel and system impairments such as small-scale fading (Doppler), Signal-to-noise ratio (SNR) and interference on the performance of the proposed fingerprint signature.

Technique for Differential Timing Transfer Over Packet Networks

Accurate timing transfer and recovery over packet networks (IP, Ethernet, MPLS, etc.) has become an important requirement for delivering many telecommunication services. This requirement stems from the fact that current networks are migrating from time-division multiplexing (TDM) technologies to packet based ones, and also the need to synchronize the many timing-dependent devices like TDM access devices and wireless base stations. Unlike TDM, packet networks are asynchronous by design and do not have embedded timing transfer capabilities. Differential clocking is used when there is a network interface with its own reference source clock (the service clock) and there is the need to transfer this clock over a core packet network (with its own independent reference network clock) to another interface. The network clock serves as a sampling clock for the service clock. Timing transfer and recovery over a packet network is a networked control problem given the difficulty in making the recovered clock at the remote location compliant with strict telecom standards. In this paper, we describe the architecture, servo algorithm, and phase-locked loop (PLL) of a method for implementing differential clock recovery over packet networks. The technique involves a clock source or transmitter sending counter values to a receiver from a counter that is clocked and reset, respectively, by the service clock and network clock. It is general enough to be applied in a wide variety of packet networks such IP, MPLS, Ethernet, etc.

Performance evaluation of CIR based location fingerprinting

Location fingerprinting has received considerable attention as a practical solution to the indoor localization problem. Specifically Received Signal Strength (RSS) based fingerprinting has been studied extensively and some improvements in performance have been reported for certain pattern recognition algorithms. Recently channel impulse response (CIR) based fingerprinting received attention due to its potential for significant improvements in accuracy. The performance evaluation of CIR fingerprinting, however, has not been addressed adequately in literature. This paper presents the performance evaluation of CIR location fingerprinting in an indoor environment. A simulation framework has been developed using the Ray-Tracing software to emulate the indoor wireless channel. The CIR-based simulation results showed noticeable improvements in the location estimation compared to the RSS-based approach. The paper highlights new findings for some parameters that affect the performance of the CIR-based fingerprinting with respect to the system bandwidth and training point spacing.

Adaptive zero-crossing digital phase-locked loop for packet synchronization

This paper describes the design and performance analysis of a new approach for frequencysynchronization and transfer over packet networks. The proposed system utilizestimestamps-based with raised cosine pulse shaping first order adaptive zero-crossing digital phase-locked loop (AZC-DPLL). The system is designedto recover frequency as well as packets, independently of the input signal level in the presence of noise. This technique provides reliable locking by adjusting the loop gain, with the aid of finite state machine (FSM), and hence both system locking range and acquisition are improved.

Real time evaluation of RF fingerprints in wireless LAN localization systems

RF location fingerprinting has received significant attention as a practical solution to the indoor localization problem due to its use of the available wireless infrastructure (WLANs) and the simplicity of measuring the Received Signal Strength (RSS) fingerprint. The improvement of RSS-based fingerprinting has been limited due to RSS being a weak fingerprint structure; where it has been reported in literature that using more complex pattern recognition algorithms provides diminishing gains. Recently channel-based RF fingerprints such as the channel impulse response (CIR), channel transfer function (CTF) and frequency coherence function (FCF) have been proposed to improve the accuracy at the physical layer. An empirical evaluation of the physical layer fingerprints does not exist in literature and there is a need to understand the advantages/limitations of these fingerprint structures/signatures. As a result in this paper we provide a comprehensive empirical performance evaluation of location fingerprinting with a focus on analytical comparison of the RSS, CIR, CTF and FCF -based fingerprints using the weighted k-nearest neighbor (kNN) pattern recognition technique. By conducting frequency domain channel measurements in the IEEE 802.11 band at the university campus we evaluate the accuracy of the fingerprints and their robustness to human induced motion perturbations to the channel. We also provide analysis on the impact of system parameters such as the number of access points and the number of nearest neighbors.

Role of Time Synchronization in Power System Automation and Smart Grids

Utilities and operators are looking for new packet-based time synchronization solutions with Global Positioning System (GPS) level accuracies beyond those attainable using the traditional packet method like Network Time Protocol (NTP). Advances in high speed packet switching and communications over wide areas has made time synchronization over packet networks an attractive solution for many industries. This paper provides a tutorial discussion on the role of time synchronization in a power system environment. It provides an overview of current methods for time synchronization and also emerging packet-based alternatives that provide comparable performance over high speed communication links. These newer solutions have a number of potential applications in power system automation and also for wide area measurement systems (WAMS).

Implementing Synchronous Ethernet in Telecommunication Systems

Network infrastructures are gradually migrating from time-division multiplexing (TDM) based onto packet-based architectures. In spite of this convergence, there are a significant number of synchronous applications that require accurate timing to be distributed over the packet networks. Examples of precision timing sensitive applications that need the transport of synchronization over packet networks include interconnection and transport of TDM services over packet networks (TDM switches, TDM PBXs, voice, video-conferencing and broadband video), and connections to 2G, 3G, and 4G wireless base stations. TDM networks, unlike packet networks (e.g., Ethernet, IP, MPLS), have timing transfer inherently built into them. Native Ethernet (IEEE 802.3) is inherently asynchronous and was not designed with timing transfer in mind. Synchronous Ethernet (Sync-E), defined by the ITU-T, has emerged as a powerful, yet simple technology, for accurate timing transfer over Ethernet networks using quotedblleft TDM-likequotedblright (precisely, SDH/SONET) timing techniques. This discussion explains what Sync-E is, followed by a detailed discussion on which flavors of Ethernet can support Sync-E and which cannot. The discussion includes how Sync-E can be implemented in the popular Ethernet versions. We then describe example Sync-E node timing architectures, and some network timing applications and related issues.

Entropy-based location fingerprinting for WLAN systems

Localization for indoor environments has gained considerable attention over the last decade due to the enormous potential in the technology and the significant challenges facing this area of research. One practical localization technique that relies on the available fixed wireless infrastructure is RF location fingerprinting. Received Signal Strength (RSS)-based location fingerprinting has been the dominant fingerprinting approach in the literature due to the simplicity and practicality of measuring the RSS in a variety of wireless technologies (such as IEEE 802.11 and UMTS). Recognizing the diminishing gains using the RSS-based techniques, researchers have recently shifted focus to proposing improvements at the physical layer by adopting the channel impulse response (CIR) as an alternate fingerprint. In this paper we propose a novel fingerprint structure that is based on the entropy estimation of the channel; which provides a more unique/robust fingerprint that is capable of distinguishing between locations more effectively. Through extensive frequency domain channel measurements and analysis in a typical indoor environment we further validate the proposed technique and compare it against RSS and CIR-based fingerprinting. We will show that the technique combines the advantage of RSS-based fingerprinting simplicity of structure (storage and pattern recognition requirements) and improves on the robustness of the CIR-based fingerprinting techniques. Finally we will illustrate that our entropy-based location fingerprinting can be practically integrated into the architecture of popular OFDM-based WLAN systems.

Clock Synchronization Over Communication Paths With Queue-Induced Delay Asymmetries

Timing protocols such as the IEEE 1588 Precision Time Protocol and the Network Time Protocol require an accurate measurement of the communication path delay between the time server (master) and the client (slave) in order to provide a precise timing synchronization. The precise time at the clients site is then estimated using an assumption that forward and backward delays due to physical propagation time through network are equal, or any difference between them is calibrated beforehand. Apart from physical link delays, a timing packet experiences queue-induced delay due to switching/routing devices on the path. This queuing delay is usually different in forward and backward directions, thus introducing the queue-induced asymmetry (QIA), which is a major contributor to the time error between master and slave clocks if physical asymmetries are calibrated. This letter proposes a new technique for QIA compensation that does not require any on-path timing support, thus is easily deployed with current network devices.

Efficient and precise simulation model of synchronization clocks in packet networks

As packet technologies like Ethernet and IP are becoming the dominant in modern telecommunication networks, clock frequency and time synchronization over packet networks is an active area of research. Packet networks are asynchronous by design so frequency and time synchronization with sub-microsecond precision is a demanding task due to packet delay variations. A design of proper algorithms, that meet the telecommunication requirements, usually involves simulations over long period of time with nanoseconds resolution. Such precise and long-term simulation of synchronization performance is challenging, because of the vast amount of computer resources involved. This paper describes a simulation model that is both, efficient and highly precise. The model is able to simulate algorithms behavior over long period of time (tens of hours) while the computation time remains within interval of few minutes.