Time- and Frequency-Varying KK-Factor of Non-Stationary Vehicular Channels for Safety Relevant Scenarios

Vehicular communication channels are characterized by a non-stationary time- and frequency-selective fading process due to fast changes in the environment. We characterize the distribution of the envelope of the first delay bin in vehicle-to-vehicle channels by means of its Rician $K$-factor. We analyze the time-frequency variability of this channel parameter using vehicular channel measurements at 5.6 GHz with a bandwidth of 240 MHz for safety-relevant scenarios in intelligent transportation systems (ITS). This data enables a frequency-variability analysis from an IEEE 802.11p system point of view, which uses 10 MHz channels. We show that the small-scale fading of the envelope of the first delay bin is Ricean distributed with a varying $K$-factor. The later delay bins are Rayleigh distributed. We demonstrate that the $K$-factor cannot be assumed to be constant in time and frequency. The causes of these variations are the frequency-varying antenna radiation patterns as well as the time-varying number of active scatterers, and the effects of vegetation. We also present a simple but accurate bi-modal Gaussian mixture model, that allows to capture the $K$-factor variability in time for safety-relevant ITS scenarios.Comment: 26 pages, 12 figures, submitted to IEEE Transactions on Intelligent Transportation Systems for possible publicatio

Including general environmental effects in K-factor approximation for rice-distributed VANET channels

© 2014. This paper presents a method of approximating the Rician K-factor based on the instantaneous static environment. The strongest signal propagation paths are resolved in order to determine specular and diffuse powers for approximation. The model is experimentally validated in two different urban areas in New South Wales, Australia. Good agreement between the model and experimental data was obtained over short-range communication links, demonstrating the suitability of the model in urban VANETs. The paper concludes with recommendations for methods to account for vehicles in the simulation and incorporating additional phenomena (such as scattering) in the approximation

Application of nonlinear regression in recognizing distribution of signals in wireless channels

In many applications, it is important to recognise the distribution of empirical data in almost real time. One of the specific applications is the identification of statistical models for fading in wireless systems of the base station receivers. This is one of the most important problems in spatial diversity. In this paper, we describe the methodology and the results of a nonlinear regression approach for recognising the distribution of the input signal with the values of its parameters. Furthermore, the proposed approach could be used for the real-time recognition of the probability distributions without any prior knowledge about the input signal. To prove its performance, the LevenbergâMarquardt nonlinear least-squares algorithm is tested on a large set of randomly generated signals with the Gamma, Rayleigh, Rician, Nakagami-m, and Weibull distributions. The experimental results demonstrate that this approach is accurate in recognizing statistical distributions from the signal

Multi-dimensional K-factor analysis for V2V radio channels in open sub-urban street crossings

In this paper we analyze the small-scale fading statistics for vehicle-to-vehicle (V2V) communications in a typical open sub-urban street crossing. The two cars approach the crossing from two different streets and the channel conditions vary from non line-of sight (NLOS) to line-of-sight (LOS). The small-scale fading of the first delay bin is Ricean distributed with a time-varying K-factor. The later delay bins are mostly Rayleigh distributed. The antenna arrays used for recording the multiple-input multiple-output channels are linear and consist of 4 elements with directional radiation patterns. We investigate the K-factor variation of the first delay bin in time, frequency, and space dimensions, where the measurement has a duration of 20 s, a bandwidth of 240 MHz, and 16 individual single-input single- output channels. We observe that the large/small K-factor values are not necessarily correlated with the received power. We show that the K-factor can not be assumed to be constant in any of the considered domains, not even in the frequency domain, as it has been always done for relative bandwidths up to 10%. The narrow- band K-factor for each frequency bin corroborates the need to consider its frequency variation. The antenna radiation patterns, and the illuminated objects by them at different time instances are the cause of these variations. We conclude that a multi- dimensional varying K-factor models the large-scale statistical behaviour more accurately than a constant K-factor

Measurement Based Vehicle-to-Vehicle Multi-link Channel Modeling and Relaying Performance

There has been intense research in vehicular communication in order to provide reliable low-latency vehicular communication links for developing intelligent transportation system (ITS). As one of the important properties, vehicle-to-vehicle (V2V) communication is learned to be inherently non-stationary due to the high mobility of both transmitter (TX) and receiver (RX). Therefore, the V2V system behavior is essentially different from previous mobile communication studies and needs to be understood. For V2V wireless communication systems, it is crucial to model the vehicular channel accurately to evaluate the quality of the system level applications. Among all channel properties in a V2V system, the shadow fading (i.e. large scale fading, LSF) from other vehicles has a significant adverse impact on the system performance. One promising approach to overcome this issue is by implementing multi-hop technology on the vehicular ad hoc network (VANETs). One goal of this thesis report is to implement relaying schemes on simulated Rician channel based on measurements to evaluate the performance of multi-hop technology in V2V systems. Two relaying schemes, Amplify-and-Forward (AF) and Decode-and-Forward (DF), are employed in the bit level simulation. The results of packet error rate (PER) are evaluated together with non-relaying situation for convoy and overtaking scenarios, respectively. Furthermore, a statistic model is created to model the measured highway environment. Pathloss parameters and shadowing loss together with correlation coefficients are derived. Line-of-sight (LOS) and obstructed line-of-sight (OLOS) conditions are manually separated through on-board video. Each scenario has its own parameter set. Maximum likelihood estimation (MLE) is utilized on the pathloss model to compensate the biasing from the measurement hardware. Also the shadowing is modeled as correlated Gaussian and we derived the decorrelation distance from the auto-correlation function (ACF). The model is also validated against the measurements. For an ad hoc network, the diversity schemes would be strongly affected by the multilink correlation. Only a few joint correlation studies for mobile ad hoc network have been made, but rarely for VANETs. The last goal of this report is to study the joint correlation on VANETs based on measurements for four-dimensional position joint correlation model where shadowing is affected by the vehicle distance. To be precise, we focus on the joint correlation of large scale fading affected by the distances between the two receiver vehicles under the same car obstruction. Finally, a stochastic model based on the sum of sinusoids approach is implemented.The fifth generation wireless systems denotes the next major phase of mobile telecommunications standards and is expected to meet consumer demands by 2020. One of the major approach is the vehicular ad hoc networks, which is a spontaneous creation of a wireless network for data exchange to the domain of vehicles. As a key component of the intelligent transportation systems, it is extremely importance to model the vehicular propagation channel in order to meet the requirement of low latency and high reliability. There are many parameters that could describe the channel characteristics. Among them all, the vehicular shadowing has a significant advise impact on the system performance which describes the signal fluctuation affected by an obstruction vehicle. In order to study it, a measurement was designed and took place in Sweden, road Rv 40. Four Volvo cars were forming convoy and overtaking scenarios with equipped signal-transmit-receive devices. Three major works are done in this thesis project based on this measured highway scenario: Firstly, a simulation is designed based on the multi-hop technology. A scenario is simulated where a source car sends packets to a destination car with the help of a relay car. All the packets are randomly generated with each containing proper coding and modulation to enhance the transmission quality as well as to check the success or failure of the transmission. The power properties of the wireless channels between each car-link are captured from the the measurements. They are simulated with a vehicular-based distribution while each byte of the signal would experiences a vehicular channel more close to practice. Two relaying schemes are implemented in the simulation with a different reaction at the relay car after receiving the signal from the source. The destination then combines the two signals from the source and relay. It decodes the signal and records the decoding results. For each observation, the ratio of successfully transmission number and total transmission number is recorded as packet error rate. Eventually, the packet error rate performances of different schemes are compared and evaluated. Secondly, based on whether the link between antennas are obstructed, two scenarios are separated manually by watching the on-board videos. After that, the signal penetration based on transmission distance and the signal fluctuation affected by large obstructions are modeled based on the individual scenario. An advanced estimation method is employed during the modeling of the signal penetration to efficiently include the lost packet information. As for the modeling of the signal fluctuation, an extended distribution is used to describe the facts that, when a transmission link is obstructed by another vehicle, it normally remains obstructed for a certain amount of time. Eventually, channel power can be regenerated based on the model containing the measured channel properties. At last, a model is created to describe the joint effects on the signal fluctuation based on the vehicles' movement and the distances between two receive cars whose signals are obstructed by the same vehicle. The vehicular shadowing following a certain distribution is approximately represented by the sum of many sinusoid waves with random phases and chosen frequencies. The frequencies are generated based on the power and joint correlation properties of the measured channel based on the two effects

Razvoj metoda i algoritama za procenu performansi komunikacionih sistema primenom aproksimacija specijalnih funkcija

The intensive development of wireless communication systems has been accompanied by the need to develop methods and algorithms for implementing appropriate approximations of special functions in order to efficiently estimate the corresponding performance of these services through their application. In order to evaluate the behavior of digital communications systems, it is necessary to estimate standard performance measures for the observed wireless communications systems, various modulation types application, detection types, as well as channel models, and observe relations between performance and key values of system parameters. The analysis of the average bit error rate at reception for the applied modulation format is one of the tools for assessing service performance, that describes the nature of the wireless communication system in the best manner. In order to analytically evaluate the average bit error rate for the applied modulation format, it is necessary to perform the most accurate implementation of the approximation of special functions erfc(x), erf (x), Marcum Q, in the widest input range values. The dissertation will present composite methods of the special functions’ approximations. In addition to the simplicity of realization in approximating the observed functions, the aspect of robustness of approximations absolute and relative error values in a wide range of input parameters values will be considered. The advantages of the proposed solutions will be highlighted by direct comparison with the absolute and relative errors obtained by using the known special functions’ approximations from the literature. Furthermore, when transferring information through fading communication channels, for cases of application of proposed special functions’ approximations, it will be proved that system performance can be determined more easily by applying solutions proposed in the dissertation. In this way, it would be easier to determine the probability of the error of communication systems due to different types of fading existance in the channel. By comparing predicted values of the average bit error rate at reception, when transmitting signals through various communication channels medias, for cases of application of existing, previously proposed special functions’ approximations, with the average bit error rate at reception obtained by calculation based on the proposed approximation solutions, it will be shown that communication performances can be calculated more precisely. Proposed approximations could also be used in the source coding of the signal and could simplify design and realization of the quantizers

A channel model and coding for vehicle to vehicle communication based on a developed V-SCME

Over the recent years, VANET communication has attracted a lot of attention due to its potential in facilitating the implementation of 'Intelligent Transport System'. Vehicular applications need to be completely tested before deploying them in the real world. In this context, VANET simulations would be preferred in order to evaluate and validate the proposed model, these simulations are considered inexpensive compared to the real world (hardware) tests. The development of a more realistic simulation environment for VANET is critical in ensuring high performance. Any environment required for simulating VANET, needs to be more realistic and include a precise representation of vehicle movements, as well as passing signals among different vehicles. In order to achieve efficient results that reflect the reality, a high computational power during the simulation is needed which consumes a lot of time. The existing simulation tools could not simulate the exact physical conditions of the real world, so results can be viewed as unsatisfactory when compared with real world experiments. This thesis describes two approaches to improve such vehicle to vehicle communication. The first one is based on the development of an already existing approach, the Spatial Channel Model Extended (SCME) for cellular communication which is a verified, validated and well-established communication channel model. The new developed model, is called Vehicular - Spatial Channel Model Extended (V-SCME) and can be utilised for Vehicle to Vehicle communication. V-SCME is a statistical channel model which was specifically developed and configured to satisfy the requirements of the highly dynamic network topology such as vehicle to vehicle communication. V-SCME provides a precise channel coefficients library for vehicle to vehicle communication for use by the research community, so as to reduce the overall simulation time. The second approach is to apply V-BLAST (MIMO) coding which can be implemented with vehicle to vehicle communication and improve its performance over the V-SCME. The V- SCME channel model with V-BLAST coding system was used to improve vehicle to vehicle physical layer performance, which is a novel contribution. Based on analysis and simulations, it was found that the developed channel model V-SCME is a good solution to satisfy the requirements of vehicle to vehicle communication, where it has considered a lot of parameters in order to obtain more realistic results compared with the real world tests. In addition, V-BLAST (MIMO) coding with the V-SCME has shown an improvement in the bit error rate. The obtained results were intensively compared with other types of MIMO coding