When unauthorized or disruptive signals are present in connected vehicle environments, interference source localization is critical for maintaining channel integrity. This paper addresses the complexities of accurately localizing interference sources when key parameters such as transmit power (TP) and path loss exponent (PLE) are unknown. Traditional methods often assume prior knowledge of these parameters, limiting their practicality in real-world scenarios. To overcome these limitations, this study introduces a novel approach integrating geometric methods, clustering techniques using Gaussian Mixture Models (GMM), and differential evolution algorithms to simultaneously estimate unknown TP, PLE, and the number and locations of interference sources. The proposed approach leverages clustering to reduce computational complexity, effectively identifying unique interference sources though analysis of received signal strength (RSS) measurements. Simulation results demonstrate the methodology’s capability to provide accurate localization even under uncertain conditions, significantly improving upon traditional techniques and highlighting areas for further enhancement through advanced unsupervised learning methods.

Various hardware and software defects may distort or impair the channel-measurement data produced by millimetre-wave channel sounders. The IEEE Standard Association’s P2982 standards development effort was begun with the understanding that the ad hoc and incomplete verification methods in common use today are inadequate for the task and a consensus-based approach is the best method to achieve methods that are complete, effective, and economical and which will be widely accepted and adopted. Past efforts have focused on identifying discrepancies between actual and expected channel responses, but have not incorporated these processes into a formal quality control system. Here, we show how formal quality control can be incorporated into the P2982 vison for millimetre-wave channel sounder verification and thereby: 1) allow more effective identification and correction of shortcomings in channel sounder performance and/or post-processing techniques, 2) give greater confidence that a given set of channel measurement data is suitable for inclusion in a pooled database, and 3) align more closely with metrology practices in other disciplines.

Stochastic dynamic models of rain attenuation play a critical role in the development of fade mitigation techniques for wireless systems operating at frequencies above 10 GHz. The widely used Maseng-Bakken model is based on the observation that rain attenuation is lognormally distributed and can be modelled as a one-dimensional stationary Gauss-Markov (also known as an Ornstein-Uhlenbeck process). A key aspect of the model is the use of a single dynamic parameter,$\beta$, to capture the time variation of rain fades. The model has been used to model rain fading on both terrestrial fixed links and Earth-space links to geostationary satellites, and a form of the model has been recommended by ITU-R. Previous attempts to extend the model to Earth-space links to LEO satellites have been reported, but, without explanation, have used the same value of the dynamic parameter as used in the geostationary case even though the cause of the time variation is quite different. Here, we show how the dynamic parameter can be determined for the case of links from ground stations to LEO satellites by simulating rain fading based on realistic two-dimensional maps of rain cells generated using synthetic storm techniques, estimating the fade slope distribution, and then adjusting$\beta$in the Maseng-Bakken model to generate fading with a matching distribution. This approach has allowed us to reveal the power law relationship between$\beta$and satellite altitude, and thereby correct a major limitation of previous efforts.

Connected Vehicle (CV) wireless networks based on DSRC, ITS-G5 and C-V2X technology are susceptible to interference from both unintentional emitters and non-CV devices that are authorized to share the same or adjacent bands. Such interference may lead to unreliable communication and disruption of CV services with particular impact on safety-related applications. In previous work, we proposed and demonstrated that interference and congestion (i.e., spectrum misbehavior) in DSRC and ITS-G5 networks can be detected simply and inexpensively using capabilities already incorporated into the IEEE 802.11p PHY/MAC standard. Furthermore, we suggested that the simplest way to report spectrum misbehavior to network operators or spectrum regulators would be through the IEEE 1609 Security Credential Management System (SCMS). The last step is to implement a central authority that collects the spectrum misbehavior reports, analyzes them, and takes action to ensure the reliability of the wireless medium. Because no such system currently exists, here we propose a reference design for a Spectrum Misbehavior Authority (SMA) that meets the requirements of connected vehicle networks. We have implemented and validated a proof-of-concept interference source localization scheme as one of the important elements and key features of the SMA.

Connected Vehicle (CV) wireless networks based on DSRC and C-V2X technology are susceptible to interference from both non-CV devices that may be authorized to share the same band and unintentional emitters. In previous work, we proposed and demonstrated that interference and congestion in DSRC networks can be detected simply and inexpensively using capabilities already incorporated into the IEEE 802.11p PHY/MAC standard. However, our detection scheme is still untenable if the expense associated with a dedicated backhaul must be incurred. Here, we suggest that the simplest method for reporting interference or congestion to operators or regulators would be to clone a second instance of the subsystem used to report untrustworthy digital certificates within the IEEE 1609 Security Credential Management System (SCMS) and deliver reports of possible interference to a Spectrum Misbehaviour Authority (SMA). This involves defining both new message types and interference reports for two implementation scenarios, one in which roadside units (RSUs) alone report and another in which onboard units (OBUs) report as well. After identifying and validating the interference, the SMA can both inform regulators about the problem and broadcast warning messages concerning possible reduction of the quality of service and reliability of safety-critical applications. The outcomes of this work will inform inclusion of spectrum misbehavior reporting into the next version of the IEEE 1609 standard.

Blockchain technology has been widely explored in the automotive sector for a variety of applications. In particular, Mobility Open Blockchain Initiative (MOBI)-a non-profit alliance with over 70% of the world's large automakers-is actively developing a vehicle identity standard, which will serve as the foundation for other blockchain use cases such as vehicle-tovehicle payments and automotive financing. Despite the great potential of the vehicle identity standard as outlined in MOBI's official documents, a cost-effective design and implementation is still missing in the literature. In response, we propose CVIN (Connected Vehicle Information Network) as our technical design and implementation of MOBI's vehicle identity standard. First, we explain why Hyperledger Indy and Aries can be used as a basic building block of CVIN and describe how other building blocks can be integrated with Indy and Aries in order to offer additional advantages. Second, we propose to use the AURORA Connected Vehicle Testbed to evaluate the performances of CVIN with a particular focus on its security, privacy, latency, and interoperability. Third, we identify two major technical challenges and propose several solutions by leveraging edge computing and sidechain technology. Finally, we plan to opensource parts or all of CVIN, and we believe that our contribution together with the AURORA testbed will support our research community for rapid innovation.

Development of a comprehensive channel propagation model for high-fidelity design and deployment of wireless communication networks necessitates an exhaustive measurement campaign in a variety of operating environments and with different configuration settings. As the campaign is time-consuming and expensive, the effort is typically shared by multiple organizations, inevitably with their own channel-sounder architectures and processing methods. Without proper benchmarking, it cannot be discerned whether observed differences in the measurements are actually due to the varying environments or to discrepancies between the channel sounders themselves. The simplest approach for benchmarking is to transport participant channel sounders to a common environment, collect data, and compare results. Because this is rarely feasible, this paper proposes an alternative methodology - which is both practical and reliable - based on a mathematical system model to represent the channel sounder. The model parameters correspond to the hardware features specific to each system, characterized through precision, in situ calibration to ensure accurate representation; to ensure fair comparison, the model is applied to a ground-truth channel response that is identical for all systems. Five worldwide organizations participated in the cross-validation of their systems through the proposed methodology. Channel sounder descriptions, calibration procedures, and processing methods are provided for each organization as well as results and comparisons for 20 ground-truth channel responses.

Recent proposals to permit Wi-Fi to share the 5.9 GHz spectrum currently reserved exclusively for Dedicated Short Range Communications (DSRC) have elicited strong reactions from both the wireless and connected vehicle communities. A variety of lab-based studies and simulation-based investigations have been conducted in an attempt to resolve the issue but the results have not resolved the issue. One possible solution is to provide DSRC networks with the capability to detect and report interference to a central authority so that appropriate action can be taken by Wi-Fi operators or spectrum regulators to resolve the issue. Here we propose and demonstrate that interference to DSRC networks can be detected simply and inexpensively using capabilities already incorporated into the IEEE 802.11p standard. We further propose that a simple and inexpensive method for reporting interference to DSRC networks would be to clone a second instance of the subsystem used to report untrustworthy digital certificates within the DSRC Security Credential Management System (SCMS) and deliver reports of possible interference events to a Spectrum Misbehavior Authority. Such a combined capability would resolve a longstanding but underappreciated concern that DSRC networks are vulnerable to a variety of short-range interferers but lack the capability to detect or report same. Although our focus is on DSRC, similar considerations apply to related schemes such as C-V2X.

Performance of MIMO technology is highly dependent on the surrounding propagation environment and antenna configuration. In order to benefit from MIMO technology inside underground mines with low angular spread, careful antenna design and deployment strategies are required. In this regard, we studied the effect of uniform-linear-array (ULA) configuration on the MIMO channel capacity inside a short underground service tunnel. With its extensive infrastructure, this tunnel represents a typical midsize underground-mine tunnel. We simulated and measured channel frequency response at 2.49 GHz for grids of transmitters and receivers in different parts of the tunnel while taking into account practical considerations for access point (AP) deployments. All the ULA configurations were deployed either close to the sidewalls or under the ceiling. Among them, two configurations, which show the best performance for AP communications, were identified. For these configurations, we found that interelement separation requires to be four times longer than in conventional indoor environment with rich multipath (i.e., 2λ) to provide decorrelation among MIMO subchannels. We also found that infrastructure which has been neglected in previous studies, significantly degrades MIMO performance. Insightful results and guidelines for employing MIMO technology in underground mines can significantly benefit mining industry.

In this paper, we propose a received signal strength indication-based distributed Bayesian localization algorithm based on message passing to solve the approximate inference problem. The algorithm is designed for precision agriculture applications, such as pest management and pH sensing in large farms, where greater power efficiency besides communication and computational scalability is needed but location accuracy requirements are less demanding. Communication overhead, which is a key limitation of popular non-Bayesian and Bayesian distributed techniques, is avoided by a message passing schedule, in which outgoing message by each node does not depend on the destination node, and therefore is a fixed size. Fast convergence is achieved by: 1) eliminating the setup phase linked with spanning tree construction, which is frequent in belief propagation schemes and 2) the parallel nature of the updates, since no message needs to be exchanged among nodes during each update, which is called the coupled variables phenomenon in non-Bayesian techniques and accounts for a significant amount of communication overhead. These features make the proposed algorithm highly compatible with realistic wireless sensor network (WSN) deployments, e.g., ZigBee, that are based upon the ad hoc on-demand distance vector, where route request and route reply packets are flooded in the network during route discovery phase.

The user behavior is one of the key factors to impact the communication performance of vehicular ad hoc networks. Generally, more active vehicles can enhance the connectivity performance. Nevertheless, an increasing number of active vehicles may bring about significant interference and thus negatively affect the connectivity. In this paper, a highway model is presented to study the effects of active vehicle ratio on connectivity performance in the presence of co-channel interference. A closed form expression of the inter-vehicle connectivity probability is also derived to evaluate the impacts of active ratio, traffic flow, and fading factors under Nakagami fading channel. Analytical results of inter-vehicle connectivity probability are shown to be consistent with the simulation results, and can be applied to estimate connectivity performance with interference in the network design for highway vehicular scenarios.

In this paper, we consider the problem of vehicular positioning enhancement with emerging connected vehicles (CV) technologies. In order to actually describe the scenario, the Interacting Multiple Model (IMM) filter is used for depicting varies of observation models. A CV-enhanced IMM filtering approach is proposed to locate a vehicle by data fusion from both coarse GPS data and the Doppler frequency shifts (DFS) measured from dedicated short-range communications (DSRC) radio signals. Simulation results state the effectiveness of the proposed approach.

Most of the existing channel models are based on the assumption of wide sense stationary uncorrelated scattering (WSSUS) properties, which are not suitable for time-varying vehicle-to-vehicle (V2V) channels. A method for generating correlated taps in stochastic V2V channel model is proposed in this paper, which represents the non-WSSUS properties adequately. With the method for generating correlated taps, the proposed tapped delay line channel model is correlated both in the amplitude part and the phase part. In the model, the amplitude statistics follows the Weibull distribution, and the phase statistics follows the linear function of uniform distribution, which are more accurate to represent the fading properties of V2V channel. Furthermore, simulation results show that the proposed model can generate correlated V2V channel with arbitrary amplitude and phase correlation coefficients accurately.

Relaying is an emerging technique for 3G/4G high bandwidth networks in order to improve the capacity of edge nodes. As the deployment cost is high, there might be a few number of relay nodes in the cell which can help the edge nodes to transmit their data. From this perspective, one of the key problems in a relay equipped node is to make decision which edge nodes to be helped and how much power need to be disseminated among them in order to maximize the system capacity. This problem is formulated as an optimization problem given individual node and total available power constraints. The objective function of the formulated problem is non-convex, and we solve this using geometric programming (GP)-based method. Since the solution of this problem is computationally expensive, we propose a low complexity suboptimal solution. Having noticed the selfless nature of the sources in the centralized solution, we also provide a game theoretical solution. Two separate Stackelberg games are required to solve this power allocation problem. Moreover, given the total power constraint, a centralized entity is necessary to connect these two games. For assigning power among the sources, the centralized entity plays the buyer level game, whereas the sources act as power sellers. On the other hand, to disseminate relay power among the sources, roles of the players are just interchanged. Besides, before staring the game, the centralized entity determines, of total power, how much is for the transmit operation of the sources and how much is for their relay operation. We show that there is a unique Stackelberg Equilibrium (SE) for both games under certain convergence condition. Finally, the proposed game theoretical solution can achieve comparable performance in terms of resource allocation with the centralized optimal one.

Vehicle-to-Vehicle (V2V) communication is widely used to improve traffic safety. However, the V2V link is easily blocked due to the low antenna height. The vehicular obstructions also lead to strong shadowing effect, which has been ignored in the V2V system performance evaluation. By incorporating channel state transition with a measurement-based dual-slope path loss model, a light-of-sight (LOS) blocked model is presented for the V2V highway scenarios. The joint effects of radio environment and traffic flow on link connectivity are investigated to represent the obstruction probability and inter-vehicle connectivity probability. All the analytical results are validated by extensive simulations under a measurement-based propagation model. The results can be used for the system design and development of a channel simulator for V2V communications.

One of the biggest challenges facing wireless designers is determining how to configure multiple-input-multipleoutput (MIMO) antennas in underground-environments, such as mines, so that they deliver best performance. Here, we showed that angular dispersion of the signal, a phenomenon that greatly impacts channel capacity, can be accurately predicted in both near-field and far-field of underground tunnels using a multimode waveguide. Not only this analytical model is much faster than other methods, but also it does not have other shortcomings of measurement-based modeling (e.g., poor resolution for far distances in the tunnel). Further, we characterized angular-spread for different tunnel sizes and showed that the power-azimuthspectrum can be modeled by a zero-mean Gaussian distribution whose standard-deviation (angular-spread) is dependent on the tunnel dimension and the transmitter-receiver distance. Angular-spread is found to be a decreasing function of axial distance. After a certain distance, it becomes very small (about 4°) and independent of tunnel transverse dimension. Our results are useful for design of MIMO systems in underground tunnels and sufficient to permit the correlation-matrix required to extend the IEEE 802.11n MIMO channel model to underground environments.

High-speed railway (HSR) brings convenience to peoples' lives and is generally considered as one of the most sustainable developments for ground transportation. One of the important parts of HSR construction is the signaling system, which is also called the “operation control system,” where wireless communications play a key role in the transmission of train control data. We discuss in detail the main differences in scientific research for wireless communications between the HSR operation scenarios and the conventional public land mobile scenarios. The latest research progress in wireless channel modeling in viaducts, cuttings, and tunnels scenarios are discussed. The characteristics of nonstationary channel and the line-of-sight (LOS) sparse and LOS multiple-input-multiple-output channels, which are the typical channels in HSR scenarios, are analyzed. Some novel concepts such as composite transportation and key challenging techniques such as train-to-train communication, vacuum maglev train techniques, the security for HSR, and the fifth-generation wireless communications related techniques for future HSR development for safer, more comfortable, and more secure HSR operation are also discussed.

Low angular spread of propagation environments and small interelement spacing within mobile terminals are two main factors degrading the capacity of multiple-input-multiple-output (MIMO) systems. This is particularly more evident in underground tunnels and mines that have lower angular spread compared to conventional environments. In such environments where colocated MIMO (C-MIMO) systems may not perform properly, we have shown that for access-point-to-mobile communications with limited and fixed antenna spacing at the mobile end, capacity close to that of an independent and identically distributed Rayleigh channel is achievable by employing distributed MIMO (D-MIMO) systems. To find and optimize C-MIMO and D-MIMO average capacities, we employed the waveguide-multimode model and particle-swarm-optimization method. We found that D-MIMO systems show desirable performance while significantly outperforming C-MIMO configurations. Nevertheless, D-MIMO desirable performance depends on the antennas' placement and is achievable for optimized locations. Based on the results, by uniformly distributing D-MIMO antennas along the tunnel axis and optimizing the transverse location of antennas afterward, suitable performance can be achieved. This paper is concluded by providing implications for D-MIMO antenna deployment in underground mines.

Relaying is a major technique to increase network lifetime in wireless sensor networks (WSNs) and body area networks (BANs). The results of relaying studies highly depend on power consumption model of relay's transmitter and receiver radio, channel and mobility models. In this work, we study the effect of relaying with 2.4GHz IEEE802.15.4 modules on network lifetime. We analytically derive the energy expenditure of relays in which we use the path loss probability distribution function (PDF) over links, which is derived from our link characterization using micaZ motes, and the existing power consumption models. It turns out that in order for relaying to be beneficial to network lifetime and for the same transmitter power amplifier efficiency, receive power consumption of IEEE802.15.4 widely used RF modules, e.g., micaZ motes are required to be decreased. For instance, receive power of 17mW helps us achieve 25% more lifetime with 3-relay scheme than single-hop transmission over ankle-waist link during walking, whereas with the current receiver, we achieve 12% less lifetime compared to single-hop scenario.

It has been shown that for multi-carrier signals with \n subcarriers, the peak-to-mean envelope power ratio (PMEPR) of a random codeword generated from a symmetric spherical, QAM or PSK constellation is \log(n) asymptotically. Motivated by this result, recently a coding scheme with a rate of 1-\log_q(2) over a symmetric q-ary constellation has been proposed that achieves a PMEPR less than c \log(n), where c is a constant. The idea of this coding scheme is to adjust the sign of subcarriers using so-called Chernoff bound-based derandomization algorithm. In this paper, using Chernoff bound and second order exponential Markov bound in conjunction with Gaussian approximation, two new variations of the derandomization algorithm are presented that yield roughly the same statistical PMEPR at the same rate. Moreover, it is rigorously established that the asymptotic PMEPR of both these algorithms is exactly the same as that of the original derandomization algorithm. Given a fixed amount of memory, our new algorithms can reduce the complexity up to one order, i.e. from \O(n^3) to \O(n^2). On the other hand, given a fixed computational complexity, our algorithms can reduce the required memory down to half.

Energy-efficient communication protocols in resource-constrained networks and specifically wireless body area networks (WBANs) has been of significant importance since they emerged nearly last decade. In this work, we use the periodic nature of body actions to propose an action-based scheduling technique in which time-slot allocations are adapted to the periodic connectedness of on-body links. In other words, the periodicity of on-body links is employed to predict the future behaviours of links to help develop energy-efficient communications between on-body nodes, thereby elongating the network lifetime. Analysis and measurement with 2.4GHz IEEE 802.15.4/ZigBee compliant micaZ motes in a fitness environment serve as our tool to do action recognition and subsequently scheduling. The proposed technique helps us reach within less than 7% of power consumption lower bound while it does not have complexity of most channel prediction algorithms that can result in excessive process power consumption.

Excess path loss due to obstruction by building corners at road intersections in urban and suburban areas (and the consequent loss of connectivity between vehicles or vehicles and infrastructure) limits the performance of vehicular ad hoc networks, especially those used to implement cooperative collision avoidance systems and emergency vehicle alert systems that warn drivers of oncoming traffic on cross streets. In recent years, researchers have developed simplified models of the excess path loss due to propagation around intersection corners that are useful in the simulation of vehicular ad hoc networks in suburban and urban environments. However, the geometry of actual intersections often exhibit a great deal more complexity than the simplified or idealized versions that form the basis for such existing excess path loss models. Here, we use ray-tracing simulations based upon accurate renderings of thirty-five intersections in and around urban and suburban areas of Vancouver, BC. to assess the accuracy of commonly used closed- form corner propagation models and compare the performance of assisted and unassisted cooperative collision avoidance systems.

Growing use of point-to-multipoint fixed wireless networks to support network access and SCADA applications in suburban macrocell environments has prompted regulators to re-allocate various bands between 200 MHz and 2 GHz to such applications. Links in such networks are usually obstructed by buildings and foliage and are classified as non-line-of-sight. Although it is well-known that such links are susceptible to fading caused by windblown trees and foliage, most past efforts to characterize fading on such links have focused on frequency bands at 1.9 GHz and above. Here, we show how signal fading in the 220, 850 and 1900 MHz bands vary with both distance and time-averaged wind speed in a representative macrocell environment. Based upon time-series of received signal strength collected in a typical macrocell environment with moderate foliage at locations between 1 and 4 km from a transmitting site located 80 m above ground level, we show that fading on such links is relatively severe at 1.9 GHz but decreases rapidly as the carrier frequency decreases. We have expressed our results in the form of a first-order simulation model. Additional data will be required to estimate standardized model parameters that can be applied to a broad range of environments.

We observed temporal fading on 1.9 GHz fixed wireless channels during short-term measurements at 107 different locations in a suburban macrocell environment characterized by flat terrain and heavy foliage in order to determine how the rate of fading varies with average wind speed and distance. For each location, we estimated: (1) the Ricean K-factor using a moment-based estimator and (2) an equivalent Doppler frequency which is related to the maximum Doppler frequency by a factor that depends upon the shape of the Doppler spectrum. We did so by fitting the measured level crossing rate (LCR) and average fade duration (AFD) distributions to expressions normally justified for mobile wireless links using a method recently proposed by Feick, Valenzuela and Ahumada (2007). As has been observed at other sites, the Ricean K-factor decreased with both average wind speed and distance. However, we found that the equivalent Doppler frequency was effectively uncorrelated with wind speed and noticeably increased with distance. Similar measurements at other sites will be required to determine the extent to which these trends are affected by foliage density and tower height.

Fixed wireless multipoint communication systems are increasingly being deployed in suburban macrocell environments, either to provide voice and data services to residences (wideband systems) or to supply automated meter reading and related supervisory control and data acquisition services (narrowband systems). Here, we show that a particularly simple yet complete first-order statistical characterization of two-branch diversity reception over fixed wireless channels can be given in terms of just five channel parameters: the average path gains and Ricean K-factors for each branch and the complex envelope correlation coefficient between the time-varying parts of the two path gains. We further show that all five parameters can be estimated from amplitude-only measurements of path gain vs. time, subject only to the assumption that the time-varying component of the path gain is complex Gaussian. We present representative sets of model parameters based upon data collected in typical suburban macrocell environments over time, location, and/or frequency using polarization diversity antennas. Because each of the model parameters, or its logarithm, is close to Gaussian, the set may be cast as a five-element vector of jointly random Gaussian processes. Despite obvious physical differences between the environments, the results show a remarkable consistency.

We show by simulation that when the fading signals observed on orthogonally polarized diversity branches follow Ricean statistics, the distribution of polarization states on the Poincare sphere is well-approximated by a Fisher distribution. Further, we show that the Fisher concentration parameter is: (1) completely determined by the corresponding Ricean Kfactors and the cross-correlation coefficient between the diversity branches, both of which can be estimated from simple measurements of received power vs. time, and (2) a good indicator of the level of cross-polar discrimination (XPD) on the channel. The insights gained are potentially useful to those engaged in the development and validation of schemes that use either polarization re-use or polarized MIMO.

Based upon coherent (amplitude and phase) received signal strength data collected over fixed wireless macrocell channels at almost 100 locations in residential, campus and open area environments near the University of British Columbia, we have shown that Thoen's model for fixed wireless Doppler spectra fits observed Doppler spectra remarkably well. This allows us to extract the equivalent maximum Doppler frequency for such channels and determine both: (1) its marginal distribution, which is surprisingly narrow, and (2) its joint distribution with Ricean K-factor and wind speed in typical suburban macrocell environments. Incorporating wind effects into the model helps us to improve the accuracy of the model by helping us account for the differences between the wind speed distributions observed during the measurement campaigns and those observed over the long term.

We have determined the form of the distributions that best describe the manner in which polarization states disperse across the Poincare sphere over time, i.e., the second- order statistics of dispersion, and how the parameters of these distributions are related to the Ricean K-factors and the cross- correlation coefficient that describe the diversity channel. When sampled over time, the trajectory taken by the polarization states resembles a random walk across the sphere. Of particular note is our observation that the form of the turning angle distribution provides a mechanism that constrains the size of the polarization cluster when the Ricean K-factors and cross-correlation between diversity branches are both high. The results will be of interest to those engaged in the design of polarization adaptive antennas and methods for simulating polarization dispersion.

In many cases of practical interest, the angle of arrival distribution at the receiver is sufficiently narrow that one can use knowledge of the mean received signal levels, Ricean K-factors and the cross-correlation coefficient that characterize fading signals observed on orthogonally polarized diversity branches to predict the of polarization state dispersion. This allows one to use simple power-only measurements of narrowband polarization diversity to predict the performance of alternative polarization diversity schemes or polarization adaptive antennas in realistic environments. Moreover, our results offer a useful geometric interpretation of how decorrelation between polarization diversity branches arises: As the angular spread of the polarization state distribution on the Poincare sphere broadens, the correlation between branches decreases. However, knowledge of the angular spread alone is not sufficient to predict the cross-correlation coefficient; the Ricean K-factors on the branches must be known as well. Otherwise, the analogy to a similar relationship between the angle of arrival distribution and correlation between branches in space diversity is striking.

Past efforts to develop measurement-based models of the UWB propagation channel have focused on residential, office, and industrial environments. However, with its confined volume and cylindrical structure, the geometry of the passenger cabin of a jet aircraft is fundamentally different from those environments considered previously. Here, we characterize large-scale aspects of UWB propagation within the passenger cabin of a typical mid-size airliner. Our measurement database consists of hundreds of frequency responses over the range 3.0 - 10.6 GHz that we collected aboard a Boeing 737-200 aircraft. The data were collected in a point-to-multipoint configuration in which a biconical UWB transmitting antenna was mounted at one of three locations near the cabin ceiling and an identical receiving antenna was mounted at headrest, armrest, and footrest level at over 50 locations throughout the cabin. We have accounted for the effects of human presence by collecting this data with the cabin empty, with passengers occupying half of the seats, and with passengers occupying virtually all of the seats. Our initial data reduction efforts have focused on the manner in which human presence and/or receiving antenna mounting location affects five large scale aspects of UWB propagation, i.e., those that affect coverage and reliability: (1) the distance dependence of path loss, (2) the frequency dependence of path loss, (3) the ratio of the energy in the line-of-sight component to the scattered components of the channel impulse response, (4) the RMS delay spread, and (5) the locations and distribution of the poles of the corresponding autoregressive frequency domain model.

Because the motion of a LEO satellite across the sky causes the earth-space path to pass through any rain cells in the vicinity very quickly, the degree of rain fading on such paths changes more rapidly and leads to steeper fade slopes than in the geostationary case. This has important implications for the performance of the power control algorithms and other techniques used to mitigate such fading. Because comprehensive measurement data have not yet been compiled for fading on LEO links at Ka-band, we must resort to simulation to predict the statistics of such fading. Here we use an approach based upon the well-known EXCELL model of horizontal rain structure and Goldhirsh's method for obtaining the parameters of the EXCELL model from ITU-R rain zone parameters. As the satellite sweeps across the sky, we determine the intersection of the earth-space path with rain cells in the vicinity. Given the corresponding rain rates, and accounting for attenuation by atmospheric gases, cloud and fog, we predict the total attenuation along the path at each instant during the pass. Our results suggest that: (1) fade slopes observed on earth-space links to LEO can be between two and ten times greater than those reported previously for the geostationary case, (2) fade slopes will become steeper as the altitude of the satellite decreases, (3) fade slopes will become steeper with increasing carrier frequency, (4) rising and falling fade slopes of a given value are equally likely and (5) the probability of exceeding a given fade slope value tends to increase rapidly in regions with higher average rain rates.

The CM 1-8 UWB statistical channel impulse response (OR) models adopted by the IEEE 802.15.4a task group are widely used to fairly compare the performance of alternative UWB signaling schemes under representative line-of-sight and non-line-of-sight conditions in four different environments: residential, office, industrial, and outdoor. However, with the advent of MB-OFDM and related schemes, channel frequency response (CFR) models are becoming more pertinent than CIR models. Here, we analyze the CM 1-8 models using autoregressive frequency domain (AR-FD) modeling techniques with four aims. First, we use the Akaike information criterion (AIC) to determine the order of the AR-FD model most appropriate to each case. Second, we use the distribution of the poles in the equivalent AR-FD model to interpret both the physical significance and diversity of each of the CM models. Third, we determine the probability distribution that best describes the pole locations and other parameters of the AR-FD model so that we may specify a set of frequency domain alternatives to the IEEE 802.15.4a models which we refer to as CFR 1-8. Finally, we assess the suitability of the AR-FD approach in each of the eight cases by comparing the envelope distribution and RMS delay spread predicted by the AR-FD models to those of the original CIR data.

The tendency for wind blowing through foliage and related environmental disturbances to cause fading events on nonline-of-sight fixed and stationary wireless channels has been well studied in recent years. However, the implications of such fading for the performance of point-to-multipoint wireless communications systems has apparently not been considered previously. Here, we present preliminary measurement data from a suburban macrocell environment which shows that: (1)fixed wireless links tend to exhibit highly variable behaviour over time with periods of calm interleaved with well-defined fading events lasting tens of minutes to hours; (2)some links are more fragile than others and exhibit a greater range of fading behaviour; and (3)fading events on different links within the same cell tend to be correlated with each other. While advanced signal schemes such as MIMO technology can often mitigate such fading, many practical systems continue to employ conventional technology and are susceptible. We show how such fading could degrade the capacity of such systems and the throughput and delay experienced by users.

Knowledge of the Ricean K-factor is important for accurate assessment and simulation of wireless channels, particularly those in which both terminals are stationary and a strong line-of-sight or fixed component exists. While previous work has focused on development of novel K-factor estimators, the practical matter of determining the minimum number of samples N (or minimum sample duration T) required to estimate K to within a specified confidence interval sigmaKhas not received much attention. Here, for the case of a simple moment-based K-factor estimator, we use Monte Carlo simulations to show how N and T depend upon the value of K, the confidence interval sigmaK, the correlation between successive samples, and the sampling interval DeltaT. The results will be useful to those who use such an estimator in practical systems for the purposes of channel state estimation and/or radio resource management.

Although interest in deploying short-range wireless communications technology in vehicular environments has increased markedly in recent years, there is a remarkable dearth of information that can assist antenna designers and wireless system developers who are working in such environments. Under the auspices of the IEEE VT-S Technical Committee on Radiowave Propagation and Channel Modelling, the University of British Columbia's Radio Science Laboratory and the BMW Group Technology Office have formed an informal study group in order to elucidate the requirements for standard radiowave propagation models for vehicular environments. The work of the study group is proceedng in three stages. First, a framework for developing appropriate use cases is being proposed. Second, criteria for assessing the suitability of the models for practical applications are being developed. Finally, possible forms of these models are being proposed. It is anticipated that the efforts of this informal study group will stimulate interest in this important, but so far underexplored, area.

The task of a packet scheduler for real-time traffic is to ensure that packet arrivals satisfy certain quality of service (QoS) requirements. At the same time, it is necessary to make efficient use of the limited capacity of the time-varying wireless fading channel. These two requirements are often in conflict to each other. Most existing schedulers either concentrate on the effective use of the radio resource, or only focus on QoS provisioning. By introducing the concept of flexible time and urgent time period, we propose an opportunistic QoS enhanced scheduler (OQES) which tries to maximize system throughput by exploiting the time-varying channel by applying multi-user diversity as well as a "meets delay" requirement. To avoid wasting bandwidth, a simple proactive packet discarding mechanism has also been introduced to discard packets that are to be dropped. Simulation results show that OQES outperforms existing schedulers for realtime traffic.

This paper deals with the measurement and modeling of multipath delay on fixed wireless paths at 1.9 GHz in suburban environments. The primary focus is on the delay profile, which is the normalized plot of received power versus delay in response to an RT "impulse." We describe measurement campaigns in the western suburbs of Chicago, IL, and in suburban north-central New Jersey. Our analysis of the data suggests to us that, for directive terminal antennas, the delay profile can be modeled as having a "spike-plus-exponential" shape, i.e., a strong return ("spike") at the lowest delay, plus a set of returns whose mean powers decay exponentially with delay. This delay profile can be characterized by just two parameters (both variable over the terrain), namely, the ratio (K/sub 0/) of the average powers in the "spike" and "exponential" components and the decay time constant (/spl tau//sub 0/) of the "exponential" component. No such simple structure appears to apply for delay profiles using omnidirectional antennas. For a directive antenna with a 32/spl deg/ beamwidth, we find that: (1) the statistical correlation between the profile parameters K/sub 0/ and /spl tau//sub 0/ is negligible; (2) these parameters are relatively insensitive to antenna height and path length; and (3) over each measured region (Illinois and New Jersey), K/sub 0/ and /spl tau//sub 0/ have median values close to 8 dB and just below 0.2 /spl mu/s, respectively. Moreover, we have found simple probability distributions that accurately portray the variability of K/sub 0/ and /spl tau//sub 0/ over the terrain.