Showing papers on "Multipath propagation published in 2009"

Underwater acoustic communication channels: Propagation models and statistical characterization

Abstract: Acoustic propagation is characterized by three major factors: attenuation that increases with signal frequency, time-varying multipath propagation, and low speed of sound (1500 m/s). The background noise, although often characterized as Gaussian, is not white, but has a decaying power spectral density. The channel capacity depends on the distance, and may be extremely limited. Because acoustic propagation is best supported at low frequencies, although the total available bandwidth may be low, an acoustic communication system is inherently wideband in the sense that the bandwidth is not negligible with respect to its center frequency. The channel can have a sparse impulse response, where each physical path acts as a time-varying low-pass filter, and motion introduces additional Doppler spreading and shifting. Surface waves, internal turbulence, fluctuations in the sound speed, and other small-scale phenomena contribute to random signal variations. At this time, there are no standardized models for the acoustic channel fading, and experimental measurements are often made to assess the statistical properties of the channel in particular deployment sites.

Ranging With Ultrawide Bandwidth Signals in Multipath Environments

Abstract: Over the coming decades, high-definition situationally-aware networks have the potential to create revolutionary applications in the social, scientific, commercial, and military sectors Ultrawide bandwidth (UWB) technology is a viable candidate for enabling accurate localization capabilities through time-of-arrival (TOA)-based ranging techniques These techniques exploit the fine delay resolution property of UWB signals by estimating the TOA of the first signal path Exploiting the full capabilities of UWB TOA estimation can be challenging, especially when operating in harsh propagation environments, since the direct path may not exist or it may not be the strongest In this paper, we first give an overview of ranging techniques together with the primary sources of TOA error (including propagation effects, clock drift, and interference) We then describe fundamental TOA bounds (such as the Cramer-Rao bound and the tighter Ziv-Zakai bound) in both ideal and multipath environments These bounds serve as useful benchmarks in assessing the performance of TOA estimation techniques We also explore practical low-complexity TOA estimation techniques and analyze their performance in the presence of multipath and interference using IEEE 802154a channel models as well as experimental data measured in indoor residential environments

A Mathematical Theory of Network Interference and Its Applications

Abstract: In this paper, we introduce a mathematical framework for the characterization of network interference in wireless systems. We consider a network in which the interferers are scattered according to a spatial Poisson process and are operating asynchronously in a wireless environment subject to path loss, shadowing, and multipath fading. We start by determining the statistical distribution of the aggregate network interference. We then investigate four applications of the proposed model: 1) interference in cognitive radio networks; 2) interference in wireless packet networks; 3) spectrum of the aggregate radio-frequency emission of wireless networks; and 4) coexistence between ultrawideband and narrowband systems. Our framework accounts for all the essential physical parameters that affect network interference, such as the wireless propagation effects, the transmission technology, the spatial density of interferers, and the transmitted power of the interferers.

Orthogonal Frequency Division Multiplexing for Wireless Communications

Abstract: Orthogonal Frequency Division Multiplexing for Wireless Communications is an edited volume with contributions by leading authorities in the subject of OFDM. Its coverage consists of principles, important wireless topics (e.g. Synchronization, channel estimation, etc.) and techniques. Included is information for advancing wireless communication in a multipath environment with an emphasis on implementation of OFDM in base stations. Orthogonal Frequency Division Multiplexing for Wireless Communications provides a comprehensive introduction of the theory and practice of OFDM. Chapter 1, by G. Stber, briefly introduces the history of OFDM or multicarrier modulation and basic concepts of OFDM, Chapter 2, by Y. (G.) Li, presents design of OFDM systems for wireless communications, various impairments caused by wireless channels, and some other types of OFDM related modulation. Chapter 3 to Chapter 6 address different techniques to mitigate the impairments and to improve the performance of OFDM systems. Chapter 3, by J. Cioffi and L. Hoo, focuses on system optimization techniques, including channel partitioning, loading of parallel channels, and optimization through coding. Chapter 4, by S. Wilson and P. dling, addresses timing- and frequency-offset estimation in OFDM systems. It also briefly discusses sampling clock offset estimation and correction. Chapter 5, by Y. (G.) Li, deals with pilot aided and decision-directed channel estimation for OFDM systems. Chapter 6, by C. Tellambura and M. Friese, discusses various techniques to reduce the peak-to-average power ratio of OFDM signals. To facilitate the readers, extensive subject indices and references are given at the end of the book. Even though each chapter is written by different experts, symbols and notations in all chapters of the book are consistent.

Characterization of On-Body Communication Channel and Energy Efficient Topology Design for Wireless Body Area Networks

Abstract: Wireless body area networks (WBANs) offer many promising new applications in the area of remote health monitoring. An important element in the development of a WBAN is the characterization of the physical layer of the network, including an estimation of the delay spread and the path loss between two nodes on the body. This paper discusses the propagation channel between two half-wavelength dipoles at 2.45 GHz, placed near a human body and presents an application for cross-layer design in order to optimize the energy consumption of different topologies. Propagation measurements are performed on real humans in a multipath environment, considering different parts of the body separately. In addition, path loss has been numerically investigated with an anatomically correct model of the human body in free space using a 3-D electromagnetic solver. Path loss parameters and time-domain channel characteristics are extracted from the measurement and simulation data. A semi-empirical path loss model is presented for an antenna height above the body of 5 mm and antenna separations from 5 cm up to 40 cm. A time-domain analysis is performed and models are presented for the mean excess delay and the delay spread. As a cross-layer application, the proposed path loss models are used to evaluate the energy efficiency of single-hop and multihop network topologies.

A CDMA-based Medium Access Control for UnderWater Acoustic Sensor Networks

Abstract: UnderWater Acoustic Sensor Networks (UW-ASNs) consist of sensors and Autonomous Underwater Vehicles (AUVs) performing collaborative monitoring tasks. In this article, UWMAC, a distributed Medium Access Control (MAC) protocol designed for UW-ASNs, is introduced. The proposed MAC protocol is a transmitter-based Code Division Multiple Access (CDMA) scheme that incorporates a novel closed-loop distributed algorithm to jointly set the optimal transmit power and code length. CDMA is the most promising physical layer and multiple access technique for UW-ASNs because it is robust to frequency-selective fading, it compensates for the effect of multipath at the receiver, and it allows receivers to distinguish among signals simultaneously transmitted by multiple devices. UW-MAC aims at achieving three objectives, i.e., guarantee i) high network throughput, ii) low channel access delay, and iii) low energy consumption. It is demonstrated that UW-MAC simultaneously achieves these three objectives in deep water communications (where the ocean depth is more than 100 m), which are usually not severely affected by multipath. In shallow water communications, which may be heavily affected by multipath, it dynamically finds the optimal trade-off among these objectives according to the application requirements. UW-MAC is the first protocol that leverages CDMA properties to achieve multiple access to the scarce underwater bandwidth, while other protocols tailored for this environment have considered CDMA merely from a physical layer perspective. Experiments show that UW-MAC outperforms many existing MAC protocols tuned for the underwater environment under different architecture scenarios and simulation settings.

Reliability through frequency diversity: why channel hopping makes sense

Abstract: Wireless sensor networks (WSNs) face the challenge of ensuring end-to-end communication while operating over individually unreliable wireless links. This paper addresses channel hopping, a class of frequency diverse communication protocols in which subsequent packets are sent over different frequency channels. Channel hopping combats external interference and persistent multipath fading, two of the main causes of failure along a communication link.This paper is, to our knowledge, the first to address the impact of channel hopping on routing. We simulate the performance of channel hopping and single channel solutions on connectivity traces gathered from a real-world office WSN deployment.Results indicate that the most basic channel hopping protocol increases connectivity along communication links, improving network efficiency (measured by the expected transmission count ETX) by 56% and network stability (measured by the average churn) by 38%. Further improvement can be achieved through the use of whitelisting - selective channel hopping over a subset of the available frequencies.

Receiver-Autonomous Spoofing Detection: Experimental Results of a Multi-Antenna Receiver Defense against a Portable Civil GPS Spoofer

Abstract: In this work we demonstrate the use of a dual antenna receiver that employs a receiver-autonomous angle-ofarrival spoofing countermeasure. This defense is conjectured to be effective against all but the most sophisticated spoofing attempts. The technique is based on observation of L1 carrier differences between multiple antennas referenced to a common oscillator. We first employ a moderately sophisticated spoofer to "fool" a single-antenna civil receiver. We then deploy the same attack after augmenting the receiver with an additional antenna and with receiver-autonomous spoofdetection software. The work discusses the experimental results together with various issues related to sensitivity, probability of false alarm, impact of carrier multipath, line-bias-calibration, and physical setup and security. We suggest that this work is important to the community as it provides experimental validation of a low-cost technique for receiver-autonomous spoofing detection. Furthermore, the technique, when combined with physical security of the antenna installation, provides a strong defense against even a sophisticated attack. The receiver employed is an L1-only civil GPS receiver with multiple antenna capability. The GPS chipset employed is the venerable GP2015/GP2021 that has been freely available for over a decade. As such, this receiver is representative of many civil receivers in use today for a variety of applications. Multiple antennas are enabled either through multiple independent RF front ends and correlators or via antenna multiplexing into a single RF front end and correlator bank.

Wireless tracking system and method utilizing multiple location algorithms

Abstract: The present invention provides a solution to mistaken location calculations based on multipath effects. The present invention utilizes tags attached to objects that transmit signals at various power levels for reception by sensors stationed throughout a facility. Sensor readings at the various power levels are utilized to determine the location of the tagged object.

GPS Multipath Mitigation for Urban Area Using Omnidirectional Infrared Camera

Abstract: This paper describes a precision positioning technique that can be applied to vehicles in urban areas. The proposed technique mitigates Global Positioning System (GPS) multipath by means of an omnidirectional infrared (IR) camera that can eliminate the need for invisible satellites [a satellite detected by the receiver but without line of sight (LOS)] by using IR images. Some simple GPS multipath mitigation techniques, such as the installation of antennas away from buildings and using choke ring antennas, are well known. Further, various correlator techniques can also be employed. However, when a direct signal cannot be received by the antenna, these techniques do not provide satisfactory results because they presume that the antenna chiefly receives direct signals. On the other hand, the proposed technique can mitigate GPS multipath, even if a direct signal cannot be received because it can recognize the surrounding environment by means of an omnidirectional IR camera. With the IR camera, the sky appears distinctively dark; this facilitates the detection of the borderline between the sky and the surrounding buildings, which are captured in white, due to the difference in the atmospheric transmittance rate between visible light and IR rays. Positioning is performed only with visible satellites having fewer multipath errors and without using invisible satellites. With the proposed system, static and kinematic evaluations in which invisible satellites are discriminated through observation using an omnidirectional IR camera are conducted. Hence, signals are received even if satellites are hidden behind buildings; furthermore, the exclusion of satellites having large errors from the positioning computation becomes possible. The evaluation results confirm the effectiveness of the proposed technique and the feasibility of highly accurate positioning.

Ground-Based Wireless Positioning

Abstract: Ground Based Wireless Positioning provides an in-depth treatment of non-GPS based wireless positioning techniques, with a balance between theory and engineering practice. The book presents the architecture, design and testing of a variety of wireless positioning systems based on the time-of-arrival, signal strength, and angle-of-arrival measurements. These techniques are essential for developing accurate wireless positioning systems which can operate reliably in both indoor and outdoor environments where the Global Positioning System (GPS) proves to be inadequate. The book covers a wide range of issues including radio propagation, parameter identification, statistical signal processing, optimization, and localization in large and multi-hop networks. A comprehensive study on the state-of-the-art techniques and methodologies in wireless positioning and tracking is provided, including anchor-based and anchor-free localisation in wireless sensor networks (WSN). The authors address real world issues such as multipath, non-line-of-sight (NLOS) propagation, accuracy limitations and measurement errors. Presenting the latest advances in the field, Ground Based Wireless Positioning is one of the first books to cover non-GPS based technologies for wireless positioning. It serves as an indispensable reference for researchers and engineers specialising in the fields of localization and tracking, and wireless sensor networks. Provides a comprehensive treatment of methodologies and algorithms for positioning and tracking Includes practical issues and case studies in designing real wireless positioning systems Explains non-line-of-sight (NLOS) radio propagation and NLOS mitigation techniques Balances solid theory with engineering practice of non-GPS wireless systems

Coexistence Between UWB and Narrow-Band Wireless Communication Systems

Abstract: Ultra-wide-band (UWB) signals are suitable for underlay communications, over a frequency band where, possibly, other systems are active. Such coexistence of UWB and other systems is possible if the mutual interference has a small impact on their respective performance. This paper aims to present recent results on the interference and coexistence among UWB systems and other conventional narrow-band (NB) systems. Specifically, we consider a point-to-point UWB (NB) under the interference generated by a finite number of NB (UWB) radio transmitters. We consider channels including additive white Gaussian noise and multipath fading both for the victim and the interfering links, and different receiver architectures. While our main focus is on UWB systems based on impulse radio, wide-band systems employing carrier-based direct-sequence spread-spectrum and orthogonal frequency-division multiplexing are also considered.

Polynomial Estimation of Time-Varying Multipath Gains With Intercarrier Interference Mitigation in OFDM Systems

Abstract: In this paper, we consider the case of a high-speed mobile receiver operating in an orthogonal frequency-division multiplexing (OFDM) communication system. We present an iterative algorithm for estimating multipath complex gains with intersubcarrier interference (ICI) mitigation (using comb-type pilots). Each complex gain variation is approximated by a polynomial representation within several OFDM symbols. Assuming knowledge of delay-related information, polynomial coefficients are obtained from time-averaged gain values, which are estimated using the least-square (LS) criterion. The channel matrix is easily computed, and the ICI is reduced by using successive interference suppression (SIS) during data symbol detection. The algorithm's performance is further enhanced by an iterative procedure, performing channel estimation and ICI mitigation at each iteration. Theoretical analysis and simulation results for a Rayleigh fading channel show that the proposed algorithm has low computational complexity and good performance in the presence of high normalized Doppler spread.

Radio Link Budgets for UHF RFID on Multipath Environments

Abstract: Radio frequency identification (RFID) applications are growing rapidly, especially in the UHF frequency band, which is being used in inventory management. Passive UHF tags are preferred for this application. However, the read range is often overestimated using free space calculations. This paper presents a method to estimate the read range in multipath environments. Other effects with a direct impact on read range as the effect of materials on tag performance are also addressed. Using the proposed model and the ray trace method a RFID system simulator is presented.

On the Distribution of the Sum of Gamma-Gamma Variates and Applications in RF and Optical Wireless Communications

Abstract: The Gamma-Gamma (GG) distribution has recently attracted the interest within the research community due to its involvement in various communication systems. In the context of RF wireless communications, GG distribution accurately models the power statistics in composite shadowing/fading channels as well as in cascade multipath fading channels, while in optical wireless (OW) systems, it describes the fluctuations of the irradiance of optical signals distorted by atmospheric turbulence. Although GG channel model offers analytical tractability in the analysis of single input single output (SISO) wireless systems, difficulties arise when studying multiple input multiple output (MIMO) systems, where the distribution of the sum of independent GG variates is required. In this paper, we present a novel simple closed-form approximation for the distribution of the sum of independent, but not necessarily identically distributed GG variates. It is shown that the probability density function (PDF) of the GG sum can be efficiently approximated either by the PDF of a single GG distribution, or by a finite weighted sum of PDFs of GG distributions. To reveal the importance of the proposed approximation, the performance of RF wireless systems in the presence of composite fading, as well as MIMO OW systems impaired by atmospheric turbulence, are investigated. Numerical results and simulations illustrate the accuracy of the proposed approach.

Three-dimensional modeling and simulation of wideband MIMO mobile-to-mobile channels

Abstract: A three-dimensional (3-D) geometrical propagation model for wideband multiple-input multiple-output (MIMO) mobile-to-mobile (M-to-M) communications is proposed. Based on the geometrical model, a 3-D parametric reference model for wideband MIMO M-to-M multipath fading channels is developed. From the reference model, the corresponding space-time-frequency correlation function is derived for a 3-D non-isotropic scattering environment. It is shown that the time and frequency dispersion of a wide sense stationary uncorrelated scattering channel cannot be treated independently, contrary to common practice. From the space-time-frequency correlation function, the space-Doppler power spectral density and the power space-delay spectrum are derived and compared with measured data. Finally, a new sum-of-sinusoids based simulation model for wideband MIMO M-to-M Ricean fading channels is proposed. The statistics of the simulation model are verified by simulation. The results show that the simulation model is a good approximation of the reference model.

On the performance analysis of composite multipath/shadowing channels using the G-distribution

Abstract: Composite multipath fading/shadowing environments are frequently encountered in different realistic scenarios. These channels are generally modeled as a mixture of Nakagami-m multipath fading and log-normal shadowing. The resulting composite probability density function (pdf) is not available in closed form, thereby making the performance evaluation of communication links in these channels cumbersome. In this paper, we propose to model composite channels by the G-distribution. This pdf arises when the log-normal shadowing is substituted by the inverse-Gaussian one. This substitution will prove to be very accurate for several shadowing conditions. In this paper we conduct a performance evaluation of single-user communication systems operating in a composite channel. Our study starts by deriving an analytical expression for the outage probability. Then, we derive the moment generating function of the G-distribution, hence facilitating the calculation of average bit error probabilities. We also derive analytical expressions for the channel capacity for three adaptive transmission techniques, namely, i) optimal rate adaptation with constant power, ii) optimal power and rate adaptation, and iii) channel inversion with fixed rate.

A Low-Multipath Wideband GPS Antenna With Cutoff or Non-Cutoff Corrugated Ground Plane

Abstract: We compare the performance of the classic global positioning system (GPS) choke ring ground plane with a new shallower design. Both the choke ring and the new ground plane are here designed to operate uniformly between 1.15 GHz and 1.60 GHz while maintaining the required low-multipath performance in the whole bandwidth. To achieve reception in this wide range of frequencies, the radiating element chosen is a droopy bowtie turnstile. A classic choke ring is composed of deep concentric rings on a flat circular metal ground plane. We have modeled the choke ring as a metal corrugated surface of depth d such that lambda/4lesdleslambda/2 , operating at cutoff: the multipath suppression (i.e., the proper RHCP/LHCP pattern shaping) is obtained by eliminating the surface wave on the ground plane in a certain frequency band. When shallower concentric rings of depth dleslambda/4 are used, the corrugated surface operates at non-cutoff: the required multipath rejection can be achieved by cancellation (destructive interference) rather than suppression of surface waves. The comparisons performed in this study include theory, numerical simulations, and hardware tests. Our results show that both configurations, when properly optimized, are good candidates for reception of modernized GPS, GLONASS, and GALILEO satellite signals from GPS permanent stations.

Designing Time-Hopping Ultrawide Bandwidth Receivers for Multiuser Interference Environments

Abstract: The multiple-user interference (MUI) in time-hopped impulse-radio ultrawide bandwidth (UWB) systems is impulse-like and poorly approximated by a Gaussian distribution. Therefore, conventional matched filter receiver designs, which are optimal for Gaussian noise, are not fully efficient for UWB applications. Several alternative distributions for approximating the MUI process and the MUI-plus-noise process in UWB systems are motivated and compared. These distributions have in common that they are more impulsive than the Gaussian approximation, with a greater area in the tails of the probability density function (pdf) compared to a Gaussian pdf. The improved MUI and MUI-plus-noise models are utilized to derive new receiver designs for UWB applications, which are shown to be superior to the conventional matched filter receiver. Multipath propagation is abundant in UWB channels and is exploited by a Rake receiver. A Rake receiver uses multiple fingers to comb the multipath rays with a conventional matched filter implemented in each finger. Rake structures utilizing the new receiver designs that are suitable for reception of UWB signals in multipath fading channels are provided. An optimal performance benchmark, based on an accurate theoretical model for the interference that fully explains the features of the MUI pdf, is also presented. Analysis and simulation results are shown for the novel receivers, which demonstrate that the new designs have superior performance compared to the conventional linear receiver when MUI is significant. Several adaptive receivers are shown to always match or exceed the performance of the conventional linear receiver in all MUI-plus-noise environments. Parameter estimation for the new receivers also is discussed.

Automatic modulation classification algorithm using higher-order cumulants under real-world channel conditions

Abstract: An automatic modulation classification algorithm for application in communications via multipath fading channels, without a priori information on channel characteristics, based on normalized sixth-order cumulants is described. In comparison with existing approaches, proposed algorithm can achieve much better classification accuracy in distinguishing BPSK from complex-valued modulation techniques. Theoretical analysis is verified via extensive simulations, under real-world channel propagation conditions.

A Bayesian Approach to Multipath Mitigation in GNSS Receivers

Abstract: Multipath is known to be one of the most dominant sources of accuracy degradation in satellite-based navigation systems. Multipath may cause biased position estimates that could jeopardize high-precision applications. This paper considers the problem of tracking the time-variant synchronization parameters of both the line-of-sight signal (LOSS) and its multipath replicas. In particular, the proposed algorithm tracks time-delays, amplitudes, phases and proposes a procedure to extract Doppler shifts from complex amplitudes. However, the interest is focused on LOSS time-delay estimates, since those provide the means to compute user's position. The undertaken Bayesian approach is implemented by a particle filter. The selection of the importance density function, from which particles are generated, is performed using a Gaussian approximation of the posterior function. This selection provides a particle generating function close to the optimal, which yields to an efficient usage of particles. The complex-linear part of the model, i.e., complex amplitudes, is tackled by a Rao-Blackwellization procedure that implements a complex Kalman filter for each generated particle, thus reducing the computational load. Computer simulation results are compared to other Bayesian filtering alternatives (namely, the extended Kalman filter, the unscented Kalman filter and the sequential importance resampling algorithms) and the posterior Cramer-Rao bound.

Weibull-gamma composite distribution: alternative multipath/shadowing fading model

Abstract: The Weibull-gamma (WG) distribution, which is appropriate for modelling fading environments when multipath is superimposed on shadowing, is introduced and studied. For this composite distribution the probability density, cumulative distribution, characteristic functions and the moments are derived in closed form. Furthermore, the average bit error and outage probabilities of a receiver operating over WG fading channels are assessed and compared with the corresponding performances obtained using other composite distributions.

Long GPS coordinate time series: multipath and geometry effects

Abstract: Within analyses of Global Positioning System (GPS) observations, unmodelled sub-daily signals are known to propagate into long-period signals via a number of different mechanisms. We report on the effects of time-variable satellite geometry and the propagation of an unmodelled multipath signal. Multipath reflectors at H=3D 0.1 m, 0.2 m and 1.5 m below the antenna are modelled and their effects on GPS coordinate time series are examined. Simulated time series at 20 global IGS sites for 2000-2008 were derived using the satellite geometry as defined by daily broadcast orbits, in addition to that defined using a perfectly repeating synthetic orbit. For the simulations generated using the broadcast orbits with a perfectly clear horizon, we observe the introduction of a time variable bias in the time series of up to several centimetres. Considerable site to site variability of the frequency and magnitude of the signal is observed, in addition to variation as a function of multipath source. When adopting realistic GPS observation geometries obtained from real data (e.g., those that include the effects of tracking outages, local obstructions, etc.), we observe concerning levels of temporal coordinate variation in the presence of the multipath signals. In these cases, we observe spurious signals across the frequency domain, in addition to what appears as offsets and secular trends. Velocity biases of more than 1mm/yr are evident at some few sites. The propagated signal in the vertical component is consistent with a noise model with a spectral index marginally above flicker noise (mean index -1.4), with some sites exhibiting power law magnitudes at comparable levels to actual height time series generated in GIPSY. The propagated signal also shows clear spectral peaks across all coordinate components at harmonics of the draconitic year for a GPS satellite (351.2 days). When a perfectly repeating synthetic GPS constellation is used, the simulations show near-negligible power law variability highlighting that subtle variations in the GPS constellation can propagate multipath signals differently over time, producing significant temporal variations in time series. We conclude that the time variable nature of GPS observation geometry and satellite orbits combined with a multipath signal that is manifested as an elevation dependent bias can introduce a spurious signal that is a potential significant contributor to time-correlated noise present in GPS time series. Further, the spurious signal also makes a potential significant contribution to the energy present at frequencies related to the draconitic year and harmonic thereof observed in GPS analyses.

The Application of Ray-Tracing to Mobile Localization Using the Direction of Arrival and Received Signal Strength in Multipath Indoor Environments

Abstract: This work presents a new indoor localization method based on the fingerprinting technique. The proposed method uses a ray-tracing model that provides information about multipath effects. This information is stored in a dataset during the first stage of the fingerprinting method. The direction of arrival (DOA) and received signal strength (RSS) are used in the fingerprinting technique as a hybrid system. The localization estimation is calculated while taking into account the Euclidian distance between the DOA and the RSS from each unknown position and the information of the fingerprints. Numerical calculations were performed to show the mean and the standard deviation of the estimated error.

A simplified model for the indoor power line channel

Abstract: We report for the first time some statistical properties of the indoor power line (PL) channel that exhibit some interesting similarities to the wireless channel, although some fundamental differences are also pointed out. In particular, we argue here that, while multipath propagation in wireless channels gives rise to Rayleigh distributed fading, multipath in PL channels gives rise to lognormally distributed fading similarly to shadow fading. We also report for the first time that both channel gain and Root-Mean-Square Delay Spread (RMS-DS) of indoor channels are lognormally distributed, leptokurtic and negatively correlated, thus suggesting that channels that introduce severe multipath are also characterized by large attenuation. These results are used to define a simplified PL channel model useful for comparative analysis of communication schemes and, at the same time, to draw some general conclusions on the design of multicarrier schemes.

Empirical Evaluation of the Limits on Localization Using Signal Strength

Abstract: This work investigates the lower bounds of wireless localization accuracy using signal strength on commodity hardware. Our work relies on trace-driven analysis using an extensive indoor experimental infrastructure. First, we report the best experimental accuracy, twice the best prior reported accuracy for any localization system. We experimentally show that adding more and more resources (e.g., training points or landmarks) beyond a certain limit, can degrade the localization performance for lateration-based algorithms, and that it could only be improved further by "cleaning" the data. However, matching algorithms are more robust to poor quality RSS measurements. We next compare with a theoretical lower bound using standard Cramer Rao Bound (CRB) analysis for unbiased estimators, which is frequently used to provide bounds on localization precision. Because many localization algorithms are based on different mathematical foundations, we apply a diverse set of existing algorithms to our packet traces and found that the variance of the localization errors from these algorithms are smaller than the variance bound established by the CRB. Finally, we found that there exists a wide discrepancy from what freespace models predict in the signal to distance function even in an environment with limited shadowing and multipath, thereby imposing a fundamental limit on the achievable localization accuracy indoors.

Space-time constant modulus algorithm for multipath removal on the reference signal exploited by passive bistatic radar

Abstract: The authors address the problem of multipath cancellation in the reference signal used in passive bistatic radar (PBR), which exploits an existing transmitter as emitter of opportunity. The presence of multipath echoes in the reference signal is demonstrated to strongly affect the detection performance of passive radar. Based on the well-known constant modulus algorithm (CMA) approach in the time-domain, new multi-dimensional techniques are considered for the adaptive equalisation of the reference signal based on an array of antennas and multiple receiving channels. The effectiveness of these techniques for PBR purposes is demonstrated with reference to typical simulated scenarios. The considered strategies, addressed as space-CMA and space-time-CMA, are shown to be able to recover the performance loss because of the multipath contribution in the reference signal so that they appear as very appealing solutions for PBR equipped with an array of antennas and multiple receiving channels.

Virtual time-slot allocation scheme for throughput enhancement in a millimeter-wave multi-Gbps WPAN system

Abstract: This paper proposes a virtual time-slot allocation (VTSA) scheme for throughput enhancement to realize a multi-Gbps time division multiple access (TDMA) wireless personal area network (WPAN) system in a realistic millimeter-wave residential multipath environment TDMA system without time-slot-reuse mechanism conventionally allocates one TDMA time-slot to only one communication link at a time In the proposed VTSA scheme, taking advantage on the large path loss in the millimeterwave band, a single TDMA time-slot can be reallocated and reused by multiple communication links simultaneously (hence the name virtual), thus significantly increasing system throughput On the other hand, allowing multiple communication links to occupy the same time-slot causes the generation of co-channel interference (CCI) The cross layer VTSA scheme is therefore designed to be able to maximize the throughput improvement by adaptively scheduling the sharing of time-slots, and at the same time monitor the potential performance degradation due to CCI As a result, it is found that the VTSA scheme is capable of improving system throughput as much as 30% in both AWGN and multipath channels (line-of-sight (LOS) and non-line-of-sight (NLOS) environment) Additionally, by coupling with higher-order modulation schemes, the system is able to achieve up to a maximum throughput of 38 Gbps It is also observed that higher-order modulations although have higher maximum achievable throughput in low CCI environment, the tolerance against increasing CCI is considerably lower than that of the lower-order modulations