In this paper, we first present the results of an empirical study of the comparative statistics of fourteen interference features in licensed and unlicensed bands in a selected route in downtown Worcester, MA. Then, we benefit from these features to train a machine learning algorithm to predict the availability of the channels for intelligent spectrum access for a vehicle. The main component of the vehicular interference monitoring system is an ultra wideband programmable 26GHz Agilent E4407 spectrum analyzer, interfaced with a GPS device to record the location of measurements, and a laptop to store the results in a centralized database. With this measurement system loaded in a car we drive in a selected path to monitor the interference in 1.9-2.5 GHz frequency band, which includes high traffic density neighboring licensed and unlicensed bands. With the empirical monitored interference, we study the statistical behavior of fourteen interference features logically categorized into four classes: interference intensity, correlation properties, spectrum occupancy, and Doppler spectrum in licensed and unlicensed bands. Finally, We benefit from these features to train a machine learning algorithm to predict the availability of the licensed and unlicensed bands for vehicular network access to the fixed backbone network infrastructure.

Nearly 1 million people in the USA and 10 million people worldwide are living with Parkinson’s disease (PD) [1]. The progression of the disease can be inferred from the changes in the patients’ gait to inform early intervention. Due to their near-ubiquitous ownership, smartphone sensing is a very effective, highly available way of assessing gait. Objectives: In this work, we explore the inference of PD gait, by analyzing the patient’s walk data collected from a smartphone in the patients’ homes, using Deep Learning (DL) methods. Specifically, we investigate DL models to classify the severity of the motor part of the UPDRS (MDS-UPDRS 2.10-2.13). Methodology: Using data from the mPower study [2], we selected 152 PD patients who recorded at least 3 walks before taking their medication. We extracted gait cycles from the accelerometer and gyroscope sensor records and fed them to DeePaGait; our DL multi-layer Conventional Neural Network (CNN). DeePaGait operates on 1Dimensional convolution filters to classify 30 seconds of walking data into one of five severity levels (Normal, Slight, Mild, Moderate, Severe). Results: Our DeePaGait DL network was able to Classify the PD Walking-Balance, Shaking/Tremor, and Freeze of Gait (FoG) symptoms, with an accuracy of: 99.1%,98.4%, and 98.2% respectively. Conclusion: Despite the challenges of working with a patient-labeled, crowdsourced dataset, we were able to demonstrate that gait classification based on smartphone sensor data is a viable approach to infer the severity of PD gait anomalies.

This paper introduces an effective ranging technique for sensor nodes implanted within human body leveraging a novel merger of high-resolution time-of-arrival (ToA) and direction-of-arrival (DoA) estimations. Human body is an in-homogeneous media (IHM) consisting of frequency dispersive sub-media (body organs) with unknown thicknesses that entail addressing two open problems: 1) high-resolution ToA estimation of a wideband ranging waveform propagated within IHM consisting of multipath and dispersive channels and 2) calculation of straight line range between implanted sensor node and receiver sensor array on human body. In the proposed technique, pre-allocated orthogonal frequency division multiplexing is utilized to construct a ranging waveform leveraging equally spaced and orthogonality properties of its sub-carriers which enable high-performance ToA estimation in frequency domain. The estimated ToA, however, cannot be utilized to calculate the straight line range due to refraction of propagated waveform at sub-media boundaries. Therefore, a merger of ToA and DoA is proposed that exploits multiple measurements at different carrier frequencies to develop a system of linear equations. The straight line range, then, is estimated by solving this system of equations with respect to thicknesses of available sub-media. The exploited approximations are discussed and verified via theoretical evaluations and simulations for human body to prove the feasibility of the proposed technique.

With the emergence of the Internet-of-Things (IoT), a number of low-power RF devices with diversified power levels will be deployed in the smart buildings. The radiated Received-Signal-Strength (RSS) from these devices can be used to improve the precision of the commonly used RSS-based Wi-Fi localization. In this paper, we introduce an analytical framework for calculation of the Cramer-Rao Lower Bound (CRLB) in an environment with variable radiated powers from sensors to complement the Wi-Fi localization. Since the existing CRLB calculation for the RSS-Based localization uses the differential value of the RSS which eliminates the effect of the transmitted power from the sources, we also introduce the concept of Probability-of-Coverage (PoC), by using which, the transmitted power can be combined with the CRLB and provides more accurate performance evaluation. Experiments and simulations are conducted on the third floor of the Atwater Kent Laboratory at Worcester Polytechnic Institue, where scenarios are designed with deployment of both Wi-Fi and variety of low-power devices. Experimental results show that how different number, power level, and deployment of the low-power devices affect the localization performance and confirm that reasonable precision can be achieved in the dense IoT environment.

The real-time health monitoring system is a promising body area network application to enhance the safety of firefighters when they are working in harsh and dangerous environments. Other than monitoring the physiological status of the firefighters, on-body monitoring networks can be also regarded as a candidate solution of motion detection and classification. In this paper, we consider motion classification with features obtained from the on-body radio frequency (RF) channel. Various relevant RF features have been identified and a support vector machine (SVM) has been implemented to facilitate human motion classification. In particular, we distinguish the most frequently appearing human motions of firefighters including standing, walking, running, lying, crawling, climbing, and running upstairs with an average true classification rate of 88.69 percent. Classification performance has been analyzed from three different perspectives including typical classification results, effects of candidate human motions, and effects of on-body sensor locations. We prove that even a subset of available RF features provides an acceptable classification rate, which may result in less computational cost and easier implementation by using our proposed scheme.

Precise localization of Wireless Capsule Endoscopy (WCE) inside the curly, long, and compact small intestine remains a challenging problem facing researchers for more than a decade. Conventional Radio Frequency (RF) localization techniques, commonly used in outdoor and indoor area, have demonstrated a few centimeters accuracy when applying to the inside of human body. In this paper, using 3D Posterior Cramer-Rao Lower Bound (PCRLB) as a framework for performance evaluation, we demonstrated that millimetric accuracy can be achieved using hybrid RF and image processing localization technique. This level of accuracy enables precise simultaneous localization and mapping of the WCE movement path inside the small intestine. Using the PCRLB framework, we provided in-depth analysis on hybrid localization performance regarding the effects of WCE movement estimation, the effects of system bandwidth as well as the effects of on-body sensor numbers and placements.

Vehicular Swarm Network (VSN) technology enables real time inter-vehicular communications for broadcasting all kinds of data collection, including emergency video with high data rate. A challenge in VSN broadcasting is to achieve a high throughput rate while at the same time assure the delivery of video packet flows to all the vehicles traveling over a highway segment from the accident vehicle. This paper analyzed the throughput- distance relationship model of 802.11p standard in multi-relay VSN with Vehicle Backbone Sub-Network (VBSN). Also, this paper proposed Enhanced Throughput Capacity (ETC) scheme; using GPS, vehicles that positioned close to those throughput-optimal positions are elected as VSBN relays. The aim of this paper is two-fold: a. We analyze the property of optimal position for enhancing the broadcast throughput. b. We demonstrate the performance offered by this ETC scheme; it excludes additional VBSN rebuilt process, and has robustness of high throughput in different traffic density and vehicle speed.

Wireless Body Area Networks (WBANs) are specific purpose sensor networks designed to operate autonomously to connect various medical sensors, located inside and outside of a human body. WCE quickly becomes one of the most popular WBANs applications. Due to finite energy budget of sensor nodes, transmission power should be as low as possible in order to increase the life time of WBANs. To this end, we addressed a relay network model from in body Wireless Capsule Endoscopy (WCE), to on-body relay nodes, and finally to external Access Point (AP) for the energy-efficient of WBANs in heterogeneous environment for realistic medical applications. Also, we proposed WBANs-Shortest Path Algorithm (WBANs-Spa) of relay network to reduce total network power consumption using empirical pathloss model, which could find the optimal multi-hop path based on the network model. Simulation results showed our design was effective for minimizing total network energy consumption in relay network for WBANs, and the effect of on-body relay nodes and external AP deployment was provided.

RF based and image processing based hybrid localization for wireless capsule endoscopy (WCE) has been adopted as one of the leading in-body localization approach for its overwhelming advantage on the accuracy of location estimation. In this paper, in order to investigate the fundamental limits, we derived the 3-dimensional (3D) Posterior Cramer-Rao Lower Bound (PCRLB) for hybrid WCE localization with the knowledge of RF based range estimation and image processing based step length and heading measurements. In addition to the PCRLB derivation, numerical results of this work shows that when the accuracy of image processing based measurement is high enough or the number of on-body RF receiver is large enough, the root-mean-square error (RMSE) of hybrid WCE localization can be limited within 3cm.

In a multi-rate wireless data network, the data rate is a function of the distance from the Access Point (AP). To extend the coverage range of the data network and to increase the throughput to a target terminal outside the AP coverage range, relay nodes are inserted between the AP and the target terminal. Therefore, for a given throughput-distance relationship and a given distance between the access point and the target receiver, there must be a minimum number of nodes that provides the maximum throughput to the target receiver. In this paper we present an analytical approach to determine the optimal performance bounds and the number of relays for the optimal deployment of a multi-hop multi-rate wireless data network. The optimal number of relays is chosen to optimize the throughput for two scenarios. The first is to maximize the spatial throughput up to a desired coverage distance. The seconds is to maximize the throughput for a target receiver located at a specific distance from the access point.

RFID can play great roles in future context-aware applications such as ambient intelligence and internet of things. Ranging technology will be one of interesting topics for RFID application. In the paper we compare the phase of arrival (POA) and time of arrival (TOA) based ranging behavior for RFID application. We characterize the ranging behaviors from the view of Cramer-Rao lower bounds (CRLB), ray tracing and empirical measurements. First, we analyze and compare the CRLB for POA and TOA based ranging in AWGN environment theoretically. Second, we use ray tracing method to model the distance and bandwidth influence on POA and TOA based RFID ranging in multipath environment. Third, we perform measurement to validate the noise and multipath influence on POA and TOA based RFID ranging. The parameters in ray tracing and measurements are also provided to further support the behavior comparison between TOA and POA ranging. The results show that in short range application such as RFID, POA based ranging has a comparatively better performance than TOA. It will benefit the future selection of POA or TOA technique, narrowband or wideband ranging method regarding specific scenarios for RFID application.

In a multi-rate wireless data network, the data rate is a function of the distance from the Access Point (AP). To extend the coverage range of the data network and to increase the throughput to a target terminal outside the AP coverage range, relay nodes are inserted between the AP and the target terminal. Therefore, for a given throughput-distance relationship, and a given distance between the access point and the target receiver, there must be a minimum number of nodes that provides the maximum throughput to the target receiver. In this paper we present an analytical method to determine the optimal performance bounds, the minimum number of relays and the optimal deployment for a multi-hop multi-rate wireless data network, given that a target receiver located at a specific distance from the access point. The analytical solution is presented in the form of two theorems and their proofs. We apply the theorems to a general analytical model for the throughput distance relationship and compare the analytical model results with those of a network simulator.

The real-time health monitoring system is a promising body area network application to enhance the safety of fire fighters when they are working in harsh and dangerous environment. Except for monitoring the physiological status of the fire fighters, on-body monitoring network can be also regarded as a candidate solution of motion detection and classification. In this paper, a novel Support Vector Machine (SVM) classifier has been implemented using RF signals as classification features. The classifier is capable of detecting and classifying seven frequently appeared motions of fire fighters including standing, walking, running, lying, crawling, climbing and running up stairs. The average true classification rate of our classifier reaches 87.9175% and the effects of different human motions and sensor locations have been analyzed by plotting Receiver Operating Characteristics (ROC) curves.

This paper presents a empirical model for near human body UWB propagation channel that is valid for the frequency range from 3GHz to 8GHz. It is based on measurements conducted in a anechoic chamber which can be regarded as free space. The empirical model shows the joint propagation characteristics of the on body channel and the channel between body surface and external access point. It includes the loss of the first path, arrival time of the first path and the total pathloss. Models for all three aspects have been partitioned into two sections by a break point due to the geometrical property of human body and the creeping wave phenomenon. The investigation on first path behavior can be regarded as a theoretical basis of ray-tracing technique that takes the effects of human body into consideration.

Localization of Wireless Capsule Endoscope (WCE) inside the small intestine is a very challenging problem, which is very important for the diagnosis of certain diseases. Previous studies have shown that Time-of-Arrival (TOA) localization can be more effective than Received Signal Strength (RSS) based localization. Performance evaluation of TOA-based localization techniques for WCE requires understanding of wideband RF propagation characteristics from the internals of small intestines. Since these measurements are difficult, we need to resort to simulation techniques and validating the results of simulations with empirical measurements. In this paper, we first validate the measurements of wideband characteristics of RF signals pertinent to TOA in homogeneous tissues using a SEMCAD X simulation software platform. Then we use the software for simulation of TOA from inside the human body and the small intestine. Finally, we analyze and assess TOA techniques regarding the nonhomogeneous environment inside the human body.

Performance evaluation is an essential step in the development and deployment of an indoor TOA location system, in order to see the influence of multipath condition on ranging and localization accuracy. For field testing approach, multipath condition is invisible, uncontrollable and unrepeatable. Also it is usually not convenient due to system deployment. This paper presents a multipath visible, controllable and repeatable realtime testbed for indoor TOA location performance evaluation, based on RF channel emulator and Ray-tracing software. The testbed can provide accurate performance evaluation in specific indoor environments or specific multipath conditions without deployment. We evaluate the performance of an IEEE 802.15.4a Standard location system in typical office building with this testbed. The result was compared with the performance obtained in field testing to validate the feasibility of the testbed approach.

There is much current interest in wireless networking of sensors deployed on and around the human body, in view of many potential applications for health monitoring. In this paper, we conducted ultra-wide-band (UWB) measurements around human body and a phantom in order to develop angle based channel models for body area network (BAN) and to compare the measurement results in these two environments. By analyzing certain channel parameters such as, time-of-arrival (TOA), distance-measurement-error (DME), received signal strength (RSS) and total path-loss, we discuss the influencing factors when the signal traveling around the human body. We also analyze the influence of the human body on TOA ranging accuracy.

Location-aware techniques, which combine multiple sensors in the smart-phone, have been researched and developed to estimate accurate locations of the mobile users in the social networks. In cooperative localization, each mobile user with the WiFi and GPS sensors works in a peer-to-peer, independent and assistant mode. This paper provides a comparison of four probabilistic cooperative localization algorithms for smart-phone applications: Centroid method, Nearest Neighbor method, Kernel method and AP density method. The location of the unknown mobile user is estimated based on Receive Signal Strength (RSS) from the shared APs and GPS locations from reference nodes. An empirical evaluation of the system is given to demonstrate the feasibility of these algorithms by reporting the results in a real-world environment. And a Monte Carlo simulation is also carried out to evaluate the performance of the cooperative algorithms for social networks.

In Time of arrival (TOA) based indoor human tracking system, the human body mounted with the target sensor can cause non-line of sight (NLOS) scenario and result in significant ranging error. However, the previous studies on the behavior of indoor TOA ranging did not take the effects of human body into account. In this paper, we introduce a statistical TOA ranging error model for body mounted sensors based on the measurements in a typical office building. This model separates the ranging error into multipath error cased multipath combination and undetectable direct path (UDP) error derives from the body-caused NLOS. Both multipath error and UDP error are modeled as a Gaussian variable. The distribution of multipath error is relative to the bandwidth of the system and the distribution of UDP error is relative to the angle between the face direction and the direction of TX-RX, SNR and bandwidth of the system, clearly shows the effects of human body on TOA ranging.

Wi-Fi localization is currently the most promising approach to build indoor localization systems. Especially after the recent release of Google Indoor Map for the Android system smart phones, many companies such like Skyhook and TCS etc. have flourished into the business of developing accurate Wi-Fi based indoor localization techniques due to their numerous applications. In this paper, we proposed an accurate Wi-Fi based indoor localization algorithm with the help of Google Indoor Map. The initial position of the mobile station (MS) is estimated according to the received signal strength (RSS) from the calibrated Wi-Fi access points (APs). Then, the position of the MS is allocated by using the simulated annealing (SA) algorithm to search for a better solution. During the searching process, the SA takes the indoor map structure into consideration and updates the cost function weights accordingly. This procedure makes sure the final estimation reaches to a better convergence. Extensive experimental results confirm that our solution is able to provide a much better result compared with other existing indoor localization techniques.

This paper presents an analysis on localization accuracy of a capsule used for wireless endoscopy application when there are random variations in transmit power of sensor nodes. We use a three-dimensional human body model and the log normal model for Received Signal Strength (RSS) radio propagation from the implant to the sensor nodes on the body surface to find accuracy bounds in three digestive organs, namely stomach, small intestine, and large intestine, which form the human Gastro-Intestinal (GI) track. The analysis is done using Bayesian Crameŕ-Rao bound assuming that the transmit power is random process with known prior distribution. We provide analysis of the factors affecting localization accuracy including various organ environment, external sensor array topology. The simulation results show that the capsule localization inside large intestine is affected the most with the transmit power randomness, while wireless capsule can be localized with best accuracy inside the small intestine. Finally, we propose an approach to improve the attainable accuracy bounds.

The indoor localization has received considerable attention in the field of positioning. It has been reported that time-of-arrival (ToA) based localization performs superior in comparison to the received-signal-strength (RSS) and the angle-of-arrival (AoA) based techniques in line-of-sight (LOS) condition. However, the accuracy of such systems is limited mainly due to unexpected large ranging errors observed in indoor environment, which are primarily caused by obstruction of the direct path and the effect of diffraction of the radio waves around the edges of micro-metallic objects. It is known that the analysis of effects of the micro-metallic objects on the accuracy of the range estimates could be indeed a challenging problem. In this paper, we investigate both simulation and analytical approaches based on applicability of electromagnetic (EM) methods to analyze the effects of micro-metallic objects on the accuracy of the range estimates. According to the first approach, the results of MATLAB based 2D finite-difference-time-domain (FDTD) simulation are compared to the 500 MHz bandwidth channel profiles obtained from a real-time frequency-domain measurement to analyze the accuracy of 2D simulation. Subsequently, we compare the achieved results of our analytical calculations to that of 3GHz channel profile measurements. Our studies reveal the fact that the presented simulation and analytical results are in close agreement with the results attained from the measurement campaign.

Many current and future medical devices are wearable and the human body is used as a carrier for wireless communication, which implies that the human body is a crucial part of the transmission medium in Body Area Networks (BANs). In order to understand the propagation characteristics of the human body, it is imperative to analyze the Doppler spread spectrum, which is caused by human body motions. Using a network analyzer, Doppler spreads and coherence time of temporal variations caused by human body motions can be measured and analyzed using a single tone waveform for different scenarios in a shielded room. From the narrowband measurement results, the Doppler spread varies approximately from 0.6Hz to 12Hz for different scenarios, the RMS Doppler bandwidth is in the range from 0.6Hz to 4Hz, and the coherence time differs from 20ms to 1s, all of which are measured at the Medical Implant Communication Service (MICS) band, the Industrial Scientific Medical (ISM) band and the Ultra-Wideband (UWB) band. Root mean square fittings of three different functions to received signal strength measurements were performed for different scenarios. Results show that the Gaussian function generally provides a good fitting model, which is independent of center frequencies.

In this paper, we consider cooperative multi-hop wireless Body Area Networks (BANs), connecting sensor nodes to multiple data sinks, referred to as hubs. Each network comprises a set of sensory devices, as well as a data sink, and the coexisting BANs cooperate in order to enable the sensor nodes to have their data traffic delivered to one of the data sinks. To reach a hub, either located in the local- or a nearby network, each sensor should choose a route and communicate with the relay at the tail of the chosen route. We propose a stochastic route selection mechanism, which takes into account the maximum perceived outage probability, maximum queue utilization factor, and the minimum remaining battery power of the relays of each route to determine how probable the route is to be selected to deliver a requesting sensor node's traffic to a particular hub. The performance of the proposed scheme is assessed through system-level simulations, revealing that the introduced mechanism scales well with the increase of the number of sensor nodes.

In this paper, we derive and analyze cooperative localization bounds for endoscopic wireless capsule as it passes through the human gastrointestin (GI) tract. We derive the Cramer-Rao lower bound (CRLB) variance limits on location estimators which use measured received signal strength(RSS). Using a three-dimension human body model from a full wave simulation software and log-normal models for RSS propagation from implant organs to body surface, we calculate bounds on location estimators in three digestive organs: stomach, small intestine and large intestine. We provide analysis of the factors affecting localization accuracy including various organ environments, external sensor array topology and number of pills in cooperation. The simulation results show that the number of receiver sensors on body surface has more influence on the accuracy of localization than the number of pills in cooperation inside the GI tract.

A number of techniques for indoor and outdoor WiFi localization using received signal strength (RSS) signatures have been published. Little work has been performed to characterize the RSS signatures used by these WiFi localization techniques or to assess the accuracy of current channel models to represent the signatures. Without accurate characterization and models of the signatures, a large amount of empirical data is needed to evaluate the performance of the WiFi localization techniques. The goal of this paper is to characterize the RSS signatures and present a novel wall breakpoint model for use in WiFi localization simulations to eliminate the need for large empirical databases. In this paper, we present our empirical database of RSS signatures measured in the campus of the Worcester Polytechnic Institute, characterize the RSS signatures used in WiFi localization, evaluate the performance of the current WiFi channel model, and propose a novel wall breakpoint model, which exploits site-specific information to provide a tighter fit to the empirical RSS signatures. From the RSS signature characterization, it was observed that the behavior of the RSS signatures is dependant on the location of the Access Point (AP) with a building due to shadow fading. Our proposed model improves upon the simpler WiFi channel model by adding a dynamic site-specific wall breakpoint to account for the location of the AP within a building and allowing for proper simulation of the outdoor path-loss environment.

A ray optics based statistical multipath channel model has been developed to describe the indoor multipath propagation including the important parameters such as path gain, time-of-arrival, angle-of-arrival and number of multipath components. Development of such a model is crucial for performance evaluation of indoor positioning systems. Based on a comprehensive ray-tracing database obtained on the 3rd floor of Atwater Kent Laboratories at Worcester Polytechnic Institute, multipath time-of-arrival relative to first arrival has been modeled using a lognormal distribution, angle-of-arrival has been modeled as a 3 peak doppler-like probability density function relative to the transmitter-receiver interconnection line. Path gains have been modeled using the information obtained from path arrival along with statistical object interactions such as reflection and transmission, and the number of multipath components has been modeled by a distance dependent exponential function.

Time-of-Arrival (ToA) based localization has attracted considerable attention for solving the very complex and challenging problem of indoor localization, mainly due to its fine range estimation process. However, ToA-based localization systems are very vulnerable to the blockage of the direct path (DP) and occurrence of undetected direct path (UDP) conditions. Erroneous detection of other multipath components as DP, which corresponds to the true distance between transmitter and receiver, introduces substantial ranging and localization error into ToA-based systems. Therefore, in order to enable robust and accurate ToA-based indoor localization, it is important to identify and mitigate occurrence of DP blockage. In this paper we present two methodologies to identify and mitigate the UDP conditions in indoor environments. We first introduce our identification technique which utilizes the statistics of radio propagation channel metrics along with binary hypothesis testing and then we introduce our novel identification technique which integrates the same statistics into a neural network architecture. We analyze each approach and the effects of neural network parameters on the accuracy of the localization system. We also compare the results of the two approaches in a sample indoor environment using both real-time measurement and ray tracing simulation. The identification metrics are extracted from wideband frequency-domain measurements conducted in a typical office building with a system bandwidth of 500 MHz, centered around 1 GHz. Then we show that with the knowledge of the channel condition, it is possible to improve the localization performance by mitigating those UDP-induced ranging errors. Finally, we compare the standard deviation of localization error of traditional localization system and UDP identification-enhanced localization system with their respective lower bound.

The major challenge to accurate Time of Arrival (TOA) based indoor localization systems is ranging in non-line of sight (NLOS) environments. The high probability of Direct Path (DP) blockage causes large errors that cannot be mitigated by increasing system bandwidth alone. In this paper we propose a novel ultra wideband (UWB) multi-band (MB)-orthogonal frequency division multiplexing (OFDM) ranging technique that identifies and mitigates blockage in indoor environments through frequency diversity. Based on empirical UWB measurement data collected in a typical office environment we first analyze the correlation between the occurrences of DP blockage to the TOA estimation variations across different system sub-bands. Then we propose a hypothesis test to identify the occurrence of blockage. Frequency diversity is then used to minimize the estimation error in the absence and presence of DP blockage. Results show that employing MB-OFDM diversity outperforms single sub-band and large bandwidth estimations.

A realistic comparative performance evaluation of indoor geolocation systems is a complex and challenging problem facing the research community. This is due to the fact that performance of these systems depends on the statistical variations of the fading multipath characteristics of the wireless channel, the density and distribution of the access points in the area, and the number of the training points used by the positioning algorithm. This problem, in particular, becomes more challenging when we address RFID devices, because the RFID tags and the positioning algorithm are implemented in two separate devices. In this paper, we have designed and implemented a testbed for comparative performance evaluation of RFID localization systems in a controlled and repeatable laboratory environment. The testbed consists of a real-time RF channel simulator, several WiFi 802.11 access points, commercial RFID tags, and a laptop loaded with the positioning algorithm and its associated user interface. In the real-time channel simulator, the fading multipath characteristics of the wireless channel between the access points and the RFID tags is modeled by a modified site-specific IEEE 802.11 channel model which combines this model with the correlation model of shadow fading existing in the literature. The testbed is first used to compare the performance of the modified IEEE 802.11 channel model and the Ray Tracing channel model previously reported in the literature. Then, the testbed with the new channel model is used for comparative performance evaluation of two different WiFi RFID devices.

Time of Arrival (TOA) based indoor positioning systems are considered to be the high precision alternatives to other positioning systems employing received signal strength (RSS) or Angle of Arrival (AOA). However, such systems suffer from the blockage of the direct path (DP) and occurrence of undetected direct path (UDP) condition and their performance degrades drastically in such conditions. Erroneous detection of the other multipath components (MPCs) as DP, which is the indicator of the true distance between the transmitter and the receiver, will introduce substantial ranging and localization errors into the system. Therefore, identification of the occurrence of large ranging errors and absence of DP from the received radio signal is our subsequent concern. After identification, the second step is to remedy the ranging errors in such UDP conditions. In this paper we present a methodology, based on an application of artificial neural network (ANN) design, to identify the UDP conditions and mitigate the ranging error using statistics extracted from wideband frequency domain indoor measurements conducted in a typical office building. The system bandwidth used for the frequency domain measurement was 500 MHz centered around 1 GHz.

Indoor positioning systems employing high bandwidth (up to ultra-wideband) time-of-arrival methods have attracted a lot of attention recently owing to their potential for precise localization and tracking of personnel or assets inside buildings where the GPS systems fail to operate. However, these systems suffer heavily due to severe multipath in indoor areas, leading to large positioning errors since direct path cannot be detected due to obstructions. This in turn leads to a condition that we call undetected-direct-path condition. An effective solution would be to exploit other multipath components to aid in the localization by analyzing their persistency in indoor areas. Tracking the mobile station in the absence of direct path is dependent on the internal structure of the building. We present how this method can be applied in different buildings to aid in the time- of-arrival based ultra-wideband localization and we propose a methodology to analyze the effect of different parameters of a building on the statistical behavior of persistency.

This paper provides the results of comprehensive measurement and modelling of time of arrival (TOA) based UWB ranging in different indoor environments and ranging scenarios. We show that ranging accuracy of UWB systems is directly related to the physical constraints of the environment and system bandwidth. In addition we show through empirical measurement and modelling that the spatial characteristics of the ranging error depend on the presence and absence of the Direct Path (DP). In the former, the spatial error follow a normal distribution, while in the latter, the error behaviour is best modelled as lognormal.

Ultra-wideband (UWB) indoor positioning systems based on time of arrival (TOA) techniques are considered to be the high precision alternatives to those employing received signal strength (RSS) or angle of arrival (AOA) due to their superior time-domain resolution. However, the performance of such systems may easily be degraded by the blockage of the direct path (DP) and occurrence undetected direct path (UDP) condition. By erroneous detection of the other multipath components (MPCs) as DP, which is the indicator of the true distance between the transmitter and the receiver, substantial errors will be introduced into the system. The real challenge is to be able to identify the class of the receiver location, therefore, to remedy the ranging measurement in UDP condition. In this paper we propose a methodology to identify and mitigate the UDP conditions, which can substantially improve the overall indoor positioning accuracy.

In time of arrival (TOA)-based indoor geolocation systems ranging error is a function of the bandwidth of the system and the availability of the direct path between the transmitter and the receiver. With a detected direct path (DDP) conditions and ultra wideband (UWB) transmission, precise range estimates are feasible while in undetected direct path (UDP) conditions large ranging errors occur which can not be cured with the increase of the transmission power or bandwidth. UDP conditions are caused by large metallic objects between the transmitter and the receiver or increase in the distance of the transmitter and the receiver so that the direct path fades away but the receiver still receives signal from other paths. For a given location of the transmitter, with respect to the huge metallic objects, the probability of occurrence of the UDP conditions changes. This paper provides an analytical method for calculation of the overall statistics of the ranging error for different location of the transmitter in a typical indoor environment. Results can be used for the analysis of the performance of precise RF localization techniques for sensor networks. Based on this model we show that the IEEE P802.15.3 recommended model is not adequate to represent the behavior of the ranging errors in typical indoor environments.

Indoor geolocation using maximum likelihood algorithms applied to the measured reference radio map of the received signal strength (RSS) in indoor areas has attracted tremendous attention in the recent published literature. In this paper we examine generation of reference radio maps using two different radio propagation models to replace on site measurements for calibration of these indoor geolocation systems. The first model used for radio propagation is a statistical model recommended by the IEEE 802.11 standardization committee and the second model is a simple building-specific two dimensional ray tracing algorithm. The empirical reference radio map of the RSS from seven access points in 257 locations is collected in the first floor of the Atwater Kent Laboratory, Worcester Polytechnic Institute which represents a typical indoor office area. Using the empirical radio map and the radio map generated from the results of radio propagation modeling, the performance of the nearest neighbor and maximum likelihood location estimation techniques are compared.

Recently considerable attention has been given to indoor geolocation using WLAN and WPAN technologies. With respect to positioning, the difference between the two technologies is the system bandwidth, which is around 25 MHz for IEEE 802.11 WLAN devices and at least 500 MHz for IEEE 802.15.3a WPAN devices employing UWB technology. Various algorithms using Received Signal Strength (RSS) or Time of Arrival (TOA) have been implemented for indoor positioning using these technologies. The performance of the TOA based system is sensitive to bandwidth and occurrence of undetected direct path (UDP) conditions, which degrade performance significantly. The performance of the RSS systems is less sensitive to the bandwidth and occurrence of UDP conditions. This paper presents a new hybrid RSS-TOA based localization algorithm using neural networks. The performance of this algorithm is compared with traditional TOA and RSS based algorithms in a common repeatable framework, representing a typical office environment.

Recently, node localization for multi-hop sensor networks has attracted considerable attention. In these networks, error propagation provides a serious challenge to algorithm development and accuracy of final location estimates. In this paper we introduce a novel computationally efficient distributed algorithm, cooperative localization with optimum quality of estimate (CEOQ) which takes advantage of the behavior of the channel to provide accurate indoor positioning. This algorithm uses the quality of ranging and positioning estimates to provide practical and accurate results and more importantly reduce error propagation substantially. Using UWB measurements and modeling of the ranging error in a typical office building we compare the performance of this cooperative localization algorithm with a non-channel based algorithm for indoor ad-hoc sensor environments

WLAN-based music shower is music delivery system. In WLAN-based music shower high speed WLAN technologies will be used as underlying technologies to deliver music to the mobile user quickly and cheaply. The size of music file downloaded from the WLAN-based music shower depends on many factors such as distance between user and WLAN-based music shower, channel characteristics, as well as the underlying technologies used in the WLAN-based music shower. The impact of these factors can be characterized with throughput-distance relationship model. This paper provides a mathematical framework for calculating the received average throughput and total file size while randomly crossing the coverage area of an WLAN-based music shower. Two throughput-distance relationship models are presented to analyze the music file transfer during random crossing of the coverage area of an WLAN-based music shower. Utilizing the results of this analysis, the performance of WLAN-based music shower using IEEE 802.11b and IEEE 802.11g WLAN technologies are also compared

Recently, variety of algorithms using received signal strength (RSS) or time of arrival (TOA) has been examined for precise indoor localization. The performance of the TOA based systems is sensitive to bandwidth and occurrence of undetected direct path (UDP) conditions, which degrade the localization performance significantly. The performance of the RSS based systems is less sensitive to the bandwidth and occurrence of UDP conditions. This paper uses UWB measurements in a repeatable framework representing a typical office building to compare the performance of four different algorithms and analyze the effect of the system bandwidth. Two of the algorithms are assisted with the ray tracing (RT) simulated channel behaviour. These algorithms are the newly introduced RT assisted TOA closest neighbor (RT-TOA-CN) and RT assisted RSS closest neighbor (RT-RSS-CN). The other two algorithms are traditional least square TOA (LS-TOA) and closest neighbor with TOA grid (CN-TOAG), previously introduced in the literature. We show that under certain radio propagation conditions and bandwidth requirements the localization performance of a simple to implement RSS based algorithm can be close to the more sophisticated TOA based technique

The performance of ultra-wideband (UWB) indoor positioning systems based on time of arrival (TOA) techniques is generally affected by the density of reference points (RPs), as well as undetected direct path (UDP) conditions. For a fixed number of reference points (RPs), the performance of some indoor positioning algorithms tends to degrade as the size of the area is increased, i.e. the RP density is decreased. In this paper, we evaluate the effects of RP density on the performance of different positioning algorithms in the presence of empirical distance measurement error (DME) models derived from UWB measurements in typical indoor environments. We then present functional relationships between RP density and positioning mean-square error (MSE) for these algorithms. These relationships can be used for more effective indoor positioning system design and deployment. Finally, we investigate the effects of bandwidth with respect to improving the performance of these algorithms

Infostations system provides low-cost, delay insensitive high data rate services intermittently with its discontinuous coverage. Key factors that affects to maximize the amount of information downloaded from the infostation include channel characteristics, velocity of the user, distance between user and the infostation as well as the underlying technologies used in the infostation. In general, throughput increases as the distance between infostation and the user decreases. This phenomenon can be characterized with throughput-distance relationship model. This paper provides a mathematical framework for calculating the received average throughput and total file size while randomly crossing the coverage area of an infostation. Two throughput-distance relationship models are presented to analyze the information transfer during random crossing of the coverage area of an infostation. Utilizing the results of this analysis, the performance of infostation using IEEE802.11b and g WLAN technologies is also compared.

In TOA based indoor geolocation systems ranging error is a function of the bandwidth of the system and the availability of the direct path between the transmitter and the receiver. With a detected direct path (DDP) condition and UWB transmission, precise range estimates are feasible while in undetected direct path (UDP) conditions large ranging errors occur which can not be cured with the increase of the transmission power or bandwidth. This paper uses Markov chain and the results of measurement calibrated ray tracing with 500 MHz bandwidth in a typical office environment to introduce a novel model for the behavior of the ranging errors observed by a randomly moving mobile terminal in an indoor area. The model divides the behavior of the ranging error into three categories. The first is DDP where the errors are usually small and mainly caused by multipath. The second category, natural UDP (NUDP), is caused by path-loss and exhibits medium ranging errors. The third category, shadowed UDP (SUDP), is caused by objects blocking the direct path and demonstrates very large ranging errors. Parameters of the Markov model are calculated from the results of wideband channel characteristics for different locations of a mobile. Results of the simulated errors from the modeling and the actual errors from the channel profile show close agreement.

The presence of undetected direct path (UDP) conditions presents significant challenges for TOA-based indoor geolocation, since it introduces major errors into distance measurements. Therefore, it is critical to characterize the performance of indoor geolocation systems in the presence of UDP conditions. Until now, however, there has been no standard method of performance benchmarking for such cases. Towards that end, we present an analysis tool, known as the MSE profile, that can aid in this task. We use the MSE profile to analyze the performance of two TOA-based geolocation algorithms and show how the MSE profile can be used to gain insight into their performance, in the presence of distance measurement error (DME) models derived from Ultra-Wideband (UWB) measurements.

In this paper we study the effect of bandwidth on performance of positioning systems. We introduce a benchmark for performance evaluation, distance measurement error (DME). We analyze DME and introduce a model for it. We show that there are two causes for DME, multipath dispersion and undetected direct path (UDP), and we study the effect of bandwidth on each of these components in DME. We show that increasing the bandwidth can decrease the multipath DME, but for the UDP effect, beyond a certain point it increases the DME. Thus there is an optimum bandwidth for minimizing overall error. The results were obtained using a database of UWB measurements conducted in an indoor propagation environment

Recently wireless positioning using existing network infrastructure has become an attractive value added application in campus and local area networks. However, many complexities, intrinsic to indoor radio propagation create technical challenges for the localization algorithms to meet indoor positioning requirements. Variety of algorithms using received signal strength (RSS) or time of arrival (TOA) has been used for this purpose. There is a literature gap in performance and system bandwidth requirement comparison between RSS and TOA based techniques used for indoor geolocation. In this paper we present experimental results that demonstrate a systematic comparison between these two techniques. Using a 2D ray tracing (RT) software to create a common repeatable framework for performance evaluation, we present a comparison among two RSS based and two TOA based indoor positioning algorithms in a typical office environment

In this paper we introduce a model for the distance error measured from the estimated time of arrival (TOA) of the direct path (DP) in a typical multipath indoor environment. We use the results of our ultra-wideband (UWB) measurement database in a sample office environment. To begin modeling, first we separate the causes of the error into multipath and undetected direct path (UDP), and then we model them separately considering the variation of bandwidth of the system. We show that the behavior of the distance error consists of two parts; one that is from multipath, and the other one from UDP. Both errors can be modeled as Gaussian, so the final distance error is a mixture of two Gaussian distributions. We also related the statistics of the distributions to the bandwidth of the system.

The wireless local area network (WLAN) has been an emerging technology in the residential and enterprise market by providing high data rates at low cost. Future trends in the WLAN industry are targeted towards new applications with higher data rates, wider coverage, and increased QoS requirements. A user tracking system based on the WLAN infrastructure is a new service that helps network operators to monitor different aspects of their networks in addition to providing location aware services to their customers. We provide an overview of traditional location sensing algorithms and compare their performance with the new distance variance (DV) algorithm. These algorithms use the existing IEEE 802.11 infrastructure to locate a terminal. The newly introduced DV algorithm uses indoor radio propagation models to reduce the complexity of the calibration process used in conventional algorithms. The performances of the existing and new algorithm are compared using Monte Carlo simulations based on IEEE 802.11 channel models.

This work presents the CN-TOAG (closest-neighbor with TOA grid) algorithm, a new geolocation algorithm, which presents certain performance improvements in the indoor environment. We describe this algorithm, and quantitatively compare its performance to the standard least-squares (LS), as well as weighted least-squares (RWGH) algorithms in the presence of obstructed LOS (OLOS) channel conditions. The results indicate that the CN-TOAG algorithm can outperform the other two algorithms in the indoor environment.

Using TOA to determine the distance between the transmitter and the receiver is the most popular technique for accurate indoor positioning. Accuracy of measuring the distance using TOA is sensitive to the bandwidth of the system and the multipath condition between the wireless terminal and the access point. The behavior of the distance measurement error using TOA techniques in LOS and OLOS indoor environments are substantially different. In general, as the bandwidth increases the distance measurement error decreases. However, for the so called undetected direct path (UDP) conditions the system exhibits substantially high distance measurement errors that can not be eliminated with the increase in the bandwidth of the system. In this paper we provide an analysis of the behavior of super-resolution and traditional TOA estimation algorithms in LOS, OLOS and UDP conditions in indoor areas. The analysis is based on the frequency domain measurements of the indoor radio channel propagations in several indoor areas with special attention to the UDP conditions.

This paper presents a quantitative comparison of various geolocation algorithms for the indoor wireless environment. Using models recently developed for time-of-arrival (TOA) distance measurement errors in the indoor environment, we characterize the performance of standard least-square (LS), closest-neighbor (CN), and the residual weighting (RWGH) algorithms in line-of-sight (LOS), obstructed LOS (OLOS), and mixed LOS/OLOS channel conditions. We also evaluate the performance of these algorithms in relation to the size of the indoor area over which a user is to be located.

This paper presents an in-depth investigation of frequency-domain super-resolution time-of-arrival (TOA) estimation with diversity techniques for indoor geolocation applications. A methodology for performance evaluation of super-resolution techniques based on the measurements of indoor radio propagation channels is presented. The performance of super-resolution techniques is compared with the performance of conventional TOA estimation techniques. The effects of diversity techniques on the performance of super-resolution techniques are evaluated. The measurement and simulation methods presented in this paper can be used to establish empirical performance bounds for real implementation of super-resolution indoor geolocation systems.

In this paper we introduce a model for the distance error measured from the estimated time of arrival (TOA) of the direct path (DP) between the transmitter and the receiver in a typical multipath indoor environment. We use the results of a calibrated Ray tracing software in a sample office environment. First we divide the whole floor plan into LOS and Obstructed LOS (OLOS), and then we model the distance error in each environment considering the variation of bandwidth of the system. We show that the behavior of the distance error in LOS environment can be modeled as Gaussian, while behavior of the OLOS is a mixture of Gaussian and exponential distribution. We also related the statistics of the distributions to the bandwidth of the system.

Frequency domain techniques have been widely used for indoor radio propagation measurements and modeling for telecommunication applications. This paper addresses measurement of the time of arrival (TOA) of the first path for geolocation application using results of frequency domain channel measurements. First, we analyze the effect upon TOA measurement accuracy due to: sampling period of the radio channel in the frequency domain, sampling period in the time domain used for detection of the TOA and the windowing filter used before transformation to time domain. Then we provide some results of measurement in line of sight (LOS) and obstructed LOS (OLOS) indoor environments to compare the characteristics of the measured TOA in these two important scenarios for indoor geolocation applications.

This paper uses the results of a calibrated ray tracing software in a sample office environment to analyze and model the distance error measured from the estimated time of arrival (TOA) of the direct line-of-sight (LOS) path in a typical indoor environment. First, we analyze the effect of bandwidth on the measured distance error using TOA and then, we propose a model for simulation of the distance error in LOS and OLOS indoor areas.

Both 802.11b and Bluetooth operate in the 2.4 GHz ISM band and both these standards are expected to become prevalent in the near future. Thus, interference poses a major problem. The IEEE 802.15 wireless personal area networks (WPAN) group has done extensive mathematical modeling and simulation on this subject, but very little work has been done with actual Bluetooth and 802.11b radios with respect to actual office usage. This paper deals with actual radio interference experiments conducted in a typical office environment.

The problem of TOA (time of arrival) estimation in multipath channels is discussed. Brief introductions of TOA estimation techniques that can be used to improve the performance in multipath channels are presented. Some simulation results based on channel measurement data in the indoor environment is presented to demonstrate and compare the performance of different TOA estimation techniques.

The ray-tracing (RT) algorithm has been used for accurately predicting the site-specific radio propagation characteristics, in spite of its computational intensity. Statistical models, on the other hand, offers computational simplicity but low accuracy. In this paper, a new model is proposed for predicting the indoor radio propagation to achieve computational simplicity over the RT method and better accuracy than the statistical models. The new model is based on the statistical derivation of the ray-tracing operation, whose results are a number of paths between the transmitter and receiver, each path comprises a number of rays. The pattern and length of the rays in these paths are related to statistical parameters of the site-specific features of indoor environment, such as the floor plan geometry. A key equation is derived to relate the average path power to the site-specific parameters, which are: 1) mean free distance; 2) transmission coefficient; and 3) reflection coefficient. The equation of the average path power is then used to predict the received power in a typical indoor environment. To evaluate the accuracy of the new model in predicting the received power in a typical indoor environment, a comparison with RT results and with measurement data shows an error bound of less than 5 dB.

Mobility between dissimilar networks is one of the future trends in network design towards fourth generation of telecommunication systems. A cellular network can be overlaid with a spottish high data-rate WLAN network in areas such as business centers, hotels and airports. To avoid unnecessary search of WLAN beacon the terminal must be aware of the whereabouts of the overlay system to be visited. We suggest the usage of geolocation information in mobility management via distributed location databases to enable a moving host to prepare for handoff. Three scenarios and the related problems are presented, and the requirements for the system architecture and terminal are outlined. Considerations on the algorithm are given and preliminary simulation results of a fuzzy logic handoff algorithm are presented.

With the finalization of new series of IEEE 802.11 and ETSI HIPERLAN standards, it becomes very important and interesting to study the methods to integrate geolocation functionalities into the next generation wireless LANs. We investigate geolocation methods and system architectures using OFDM signals in HIPERLAN/2 wireless LANs. We propose a novel method to measure geolocation metrics by exploiting the HIPERLAN/2 MAC frame structure. Computer simulation results are presented to show the performance of the geolocation systems using OFDM signals.

The fourth generation of telecommunication networks will be a mix of existing and emerging wireless and wired networks. They will provide a framework for multi-service usage cases, such as Internet access, geolocation and real-time applications (such as voice and video). In this paper we refer this collection of interoperating networks as multi-service networks and elaborate the aspects of system architecture and mobility management in this heterogeneous environment. First, requirements for system architecture are outlined. A novel multi-service architecture is defined based on fully integration of location based services and IP mobility approach. Handoff decision policies for multi-service network scenarios are then considered and simulation results for the handoff algorithm are presented. The suitability of the fuzzy logic algorithm is discussed in this context.

Wideband and narrowband statistical modeling of radio power in an indoor environment is presented using ray-tracing (RT) software. The power delay profile, which represents the wideband characteristics, is estimated from the irregularly discrete channel profiles generated by the RT using three different techniques. The shape of the profile is found to be dependent on the location of the receiver. The amplitude of the individual path is shown to be a log-normal random variable. A new method is proposed to predict the received power, which represents the narrowband characteristics, based on the statistical description of the RT simulation. A comparison between the RT prediction and the new method shows a great deal of agreement.

A mathematical framework is introduced for statistical modelling of the wideband characteristics of the frequency selective multipath indoor radio channel for geolocation applications. The multipath characteristics of the channel are divided into three classes according to the availability and strength of the direct line-of-sight (DLOS) path with respect to the other paths. The distributions of the occurance of these classes as a function of distance are presented. The effects of the presence of an external wall between the transmitter and receiver are investigated.

In the relatively new field of wireless local area networks there exist three methods for performance evaluation: (1) mathematical analysis; (2) computer simulation; and (3) performance monitoring of a testbed. The data obtained from mathematical analysis and computer simulation are purely speculative, there is simply no way these methods can address all of the complexities associated with network protocols and indoor radio propagation. For this reason, the most useful performance data on wireless LAN hardware is that which is obtained directly from a fully functional working testbed. The National Science Foundation has provided funding for such a testbed that has been installed at the Center for Wireless Information Network Studies (CWINS) at Worcester Polytechnic Institute, Worcester, MA. The authors present the data obtained from this testbed. Their findings show the feasibility and practicality of installing an indoor wireless local area network.

This paper uses the results of ray tracing in a typical indoor test area to compare the performance of major radio transmission techniques that are used as the air interface in evolving standards and major wireless local area network (WLAN) products. The performance of direct sequence (DS) and frequency hopping spread spectrum (FHSS) in the test area are compared with the performance of multicarrier modems, as well as modems using decision feedback equalization (DFE) and sectored antenna systems (SAS). The validity of using ray tracing for performance evaluation is examined by comparing the results with the results of performance evaluation obtained from the empirical measurement of the channel characteristics. Based on the maximum achievable data rate and minimum power requirement determined in the test area, operation of all modems in bandlimited and power limited applications are discussed.

This paper presents a comparison among the performances of various transmission technologies in a typical indoor radio environment. The performance of fresuency hopping and direct sequence spread spectrum are compared with the performance of multicarrier, decision feedback equalizer, and sectored antenna systems. Given a maximum tolerable outage probability, the m a x i ” achievable data rates are obtained for the different modulation techniques. Outage probabilities are estimated through simulation, using channel impulse responses obtained from ray uacing. The bandwidth efficiency of spread spectrum modulation is shown be very low. For a fixed bandwidth, the minimum power requirement of each modulation technique is also presented, showing significantly lower power xqukments for spread spectrum. Overall, multicarrier modulation is found to present the best tradeoff between bandwidth efficiency and power consumption.

Recently JTC has proposed a new standard based on a time domain model to represent the statistical wideband characteristics of the indoor and outdoor radio channels. This paper presents a frequency domain autoregressive (AR) model for the simulation of the Joint Technical Committee (JTC) channel characteristics. The AR model requires less number of parameters for the realization of the channel. To compare the results of simulation from the JTC and the new AR model the cummulative probability distribution function of the RMS delay power spectrum is used. The delay power profiles defined by the JTC in the time domain are mapped to the poles of the AR model defined in the frequency domain. Several methods are proposed to match the CDF of /spl tau//sub RMS/ obtained from the time domain JTC model into the CDF obtained from the equivalent frequency domain AR model.

A three dimensional ray tracing model for microcellular radio wave propagation scenarios is presented based on ray optics and the uniform geometrical theory of diffraction. Propagation mechanisms for specular reflection, specular transmission, diffraction and diffuse scattering are included in the model. A semideterministic model is also used to provide complementary predictions in specific situations expanding the model's capabilities to include interference analysis in multiple base station environments. The accuracy of predictions is examined with measurement results in an urban local loop environment in a residential area in New York City. These results include propagation loss and polarization effects for different transmit/receive configurations in the immediate surroundings of a trial site for wireless loop applications.

Wireless data services and systems represent a rapidly growing and increasingly important segment of the communications industry. In the paper the authors present an overview of this field, emphasizing three major elements: (1) technologies utilized in existing and currently planned wireless data services, (2) issues related to the performance of these systems, and (3) discernible trends in the continuing development of wireless data systems. While the wireless data industry is becoming increasingly diverse and fragmented, one can identify a few mainstreams which relate directly to users requirement for data services. On one hand, there are requirements for relatively low-speed data services supporting mobile users over wide geographical areas, as provided by mobile data networks. On the other hand, there are requirements for high-speed data services in local areas, as provided by wireless LANs. The system-level issues are somewhat different for these two categories of services, and this has led to different technology choices in the two domains, which the authors discuss in the paper.>

The results of a performance evaluation of a wireless LAN (WLLAN) in an indoor environment are presented. The LAN operates in the ISM bands using spread spectrum technology. Hardware specific parameters such as bit error rate vs. signal to noise ratio (BER vs. SNR), maximum transmission rate, and platform software overhead are measured experimentally for a single node. These empirical data, in combination with manufacturer specifications, are then used as a basis for deriving a network simulation model. A ray trace algorithm is used to obtain the indoor channel characteristics for point to point transmissions within a test room. The network simulation uses the measured BER vs. SNR, node and hardware specifications, and the ray trace channel characteristics to model the behavior of a multiple node network in a wireless environment.

The measured multipath profiles from five different indoor areas are used for the performance analysis of a binary phase shift keying (BPSK) modem with a decision feedback equalizer (DFE). The performance from the measured multipath profiles is compared with the performance predictions based on a computer simulated channel model. Both average probability of error and probability of outage are calculated for a DFE with three fractionally spaced forward and three feedback taps. An equivalent delay power spectrum function, determined from the ensemble of the measured channel impulse responses, is defined. Using this function, analytical lower bounds on the average probability of error and the probability of outage of the BPSK/DFE modem with an infinite number of feedback taps and three forward taps are determined and compared with the results based on measured data and the computer generated channel impulse responses.>

A graphical user interface program that uses a ray tracing algorithm to predict the radio propagation in the indoor radio channel from the layout of the floor plan is presented. The program allows the user to interactively specify the location of the walls in the floor plan, the type of material in the construction, and the location of the radio transmitter and receiver. The ray tracing algorithm determines the magnitude, phase, time of arrival, and direction of every signal path between the specified radio transmitter and receiver when an RF pulse is transmitted. The accuracy of the model is examined by comparing the simulation results with results of empirical measurements made in a complex laboratory environment.>

Direct sequence code division multiple access (CDMA) with orthogonal codes is under consideration for use in indoor radio communications. Spread spectrum with its inherent resistance to multipath and orthogonal codes for increased bandwidth efficiency make this implementation attractive. This paper analyzes the performance of such a system using actual channel measurements rather than the usual assumption of a statistically modeled channel to determine performance. Measurements from five different locations are used with different coherent RAKE receiver structures. Performance is presented as average probability of error as a function of signal-to-noise ratio.>

This paper presents a graphical user interface program that uses a ray tracing algorithm to predict the radio propagation in the indoor radio channel from the layout of the floor plan. The program allows the user to interactively specify the location of the walls in the floor plan, the type of material in the construction, and the location of the radio transmitter and receiver. The ray tracing algorithm determines the magnitude, phase, time of arrival, and direction of every signal path between the specified radio transmitter and receiver when an RF pulse is transmitted. The accuracy of the model for a shielded cage is examined by comparing the results with those obtained from empirical measurements. Comparisons are also made between the simulation and the results of measurements in a complex laboratory environment at Worcester Polytechnic Institute.>

A deterministic model based on ray tracing algorithms for indoor radio propagation which is suitable for analyzing performance of sector antenna systems in indoor radio channels is presented. Using this model the outage probabilities of BPSK and BPSK/DFE radio modems with omnidirectional and six-sector antennas operating in a typical laboratory environment, which is a section of the Atwater Kent Laboratories at the Worcester Polytechnic Institute that includes seven different rooms, is compared. The effects of room size, data rate, and sector antenna patterns on the performance of the systems are analyzed.>

Based on frequency domain measurements in the 0.9-1.1-GHz band, an autoregressive model for the frequency response of the indoor radio channel is introduced. It is shown that a second-order process is sufficient to represent the important statistical characteristics of the channel both in the frequency domain and the time domain where each pole identifies the arrival of a cluster of paths. A comparison is made between the statistical characteristics of the empirical data and of the channel responses regenerated from the second-order AR processes. Four methods to regenerate the indoor radio channel responses from a second-order AR model are proposed. The accuracy of the methods is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3-dB width of the frequency correlation function with that of the measurements performed in global, local, and mixed indoor radio propagation experiments.>

A new method for the exact calculation of the throughput of a centralized slotted ALOHA packet radio network over slow Rayleigh-fading channels is presented and the results are compared with the computer simulations. Also, upper and lower bounds on the performance are provided. The effects of capture on the throughput of the system are related to the modulation and coding technique, signal to noise ratio of the received signal, general terminal distribution in the area, and the length of the transmitted packets. The binary phase shift keying (BPSK), coherent and noncoherent binary frequency shift keying (FSK) modulations and BCH coding are considered for the exact calculations. The results of the analysis show that the maximum average throughput of the slotted Aloha packet radio network is around 60% rather than 36% predicted from the simplified analysis. In contrast with some previous reports, it is shown that the throughput of the system is not affected significantly by the use of coding or the change of packet lengths.>

The author analyzes the effects of nonlinear quantizers, used in T1 carrier systems, on the performance of QAM (quadrature amplitude modulation) and TCM (trellis coded modulation) voiceband data communication modems, and introduces a method to counteract the effects of these nonlinearities. The effect of nonlinear quantizers is modeled as a source of multiplicative noise whose variance is proportional to the amplitude of the quantized signal. The relation between variance of the multiplicative noise, characteristics of the nonlinear quantizer, and impulse response of the pulse shaping filters used in the modems is derived. Effects of multiplicative noise on the performance of QAM and TCM modems are analyzed. A method for the design of QAM and TCM signal constellations is introduced which counteracts the harmful effects of nonlinear quantizers. The new constellations provide 2-3 dB performance improvements in multiplicative noise channels while losing less than 0.5 dB in additive noise channels.>

Direct-sequence spread spectrum, with its inherent resistance to multipath, is a promising technique for indoor wireless communication. To allow multiple users within a limited bandwidth, code division multiple access (CDMA) is needed. The bandwidth efficiency of M-ary CDMA systems in fading multipath indoor radio channels is analyzed. It is shown that M-ary signaling improves the bandwidth efficiency significantly when compared to binary signaling.>

A unified discrete channel model from the information source up to the sampler was developed for fading multipath channels. Different methods for adaptive channel measurement was studied. The performance of a discrete matched filter using different adaptation techniques and working over a troposcatter channel is predicted. It is shown that the effects of channel measurement noise are less damaging for the decision-directed adaptation technique as compared to any kind of reference-directed adaptation.>

The authors analyze the benefits of using a decision feedback equalizer (DFE) in the indoor radio environment and examine the results of performance predictions for different channel modelings. It is found that a QPSK/DFE modem with second-order diversity can operate at a data rate that is an order of magnitude higher than a QPSK (quadratic-phase-shift-keying) modem without equalization. A given set of measured profiles of the channel impulse response is interpreted using continuous and discrete channel models. The continuous channel model is represented by the delay power spectrum and the discrete channel model by the envelope delay power spectrum and the arrival rate of the paths. The sensitivity of the performance to the shape of the delay power spectrum, and the arrival rate of the paths is analyzed.>

An overview of the existing and growing demands for wireless office information networks is provided, and the existing research activities are assessed in some detail. The radio frequency (RF) and infrared (IR) communication technologies are examined as candidates for wireless intraoffice communications. The available bandwidths, according to federal regulations and characteristics of the channel for RF communications, are given. Digital narrow-band and wideband spread-spectrum RF communications are assessed in terms of supportable data rate or number of simultaneous users in one cell of a cellular architecture in an office environment. Various limitations of IR communications are discussed and existing systems and architectures are reviewed.

Performance degradation of data communication systems due to PCM facilities in telephone networks is a well known problem. This degradation is more noticeable for ultra high speed modems recently under development. The earlier analytical works is inadequate for analyzing these degradations. In this paper we suggest a new discrete analytical technique to analyze the effects of PCM systems on performance of data communication modems. Our model relates degradation in performance to nonlinear characteristics of quantizers used in PCM systems. Using this model we were able to analyze the performance degradation in this new generation of ultra high speed data communication systems.

This paper studies the effectiveness of adaptive equalizers used with QPSK, SQPSK, QPR, and SQPR modems over frequency selective microwave LOS channels. A power series model is employed to represent the channel model, giving special attention to the channels with a null in the passband. The effect of staggering the symbols on the performance of modems with and without an adaptive equalizer is provided. With a deep null in the passband of the channel, the performance of QPR modems is slightly worse than SQPR modems, while QPSK systems significantly outperform SQPSK systems. The general conclusion that a decision feedback equalizer is required for a robust performance by each modem is reached.