Channel estimation and tracking algorithms for vehicle to vehicle communications

The vehicle-to-vehicle (V2V) communications channels are highly time-varying, making reliable communication difficult. This problem is particularly challenging because the standard of the V2V communications (IEEE 802.11p standard) is based on the WLAN IEEE 802.11a standard, which was designed for indoor, relatively stationary channels; so the IEEE 802.11p standard is not customized for outdo or, highly mobile non-stationary channels. In this thesis,We propose Channel estimation and tracking algorithms that are suitable for highly-time varying channels. The proposed algorithms utilize the finite alphabet property of the transmitted symbol, time domain truncation, decision-directed as well as pilot information. The proposed algorithm s improve the overall system performance in terms of bit error rates, enabling the system to achieve higher data rates and larger packet lengths at high relative velocities. Simulation results show that the proposed algorithms achieve improved performance for all the V2V channel models with different velocities, and for different modulation schemes and packet sizes as compared to the conventional least squares and other previously proposed channel estimation techniques for V2V channels

Enhanced Channel Estimation Algorithm for Dedicated Short-Range Communication Systems

The Dedicated Short-Range Communication (DSRC) has been widely accepted as a promising wireless technology for enhancing traffic safety. In such DSRC-based vehicle-to-vehicle (V2V) communication systems, because of the extremely time-varying characteristic of wireless propagation channels, accurate channel estimation is essential for reliable information exchange between vehicles. In this paper, the characteristics of the propagation channel and several traditional channel estimation schemes for V2V communications are reviewed. Then, a delay-based channel-frequency-response decomposition scheme is proposed to estimate and predict the double-selective V2V channel while adhering to the IEEE 802.11p standard. The proposed method achieves a more favorable performance than the traditional methods in V2V scenarios by combining the least square estimation in the frequency domain with the linear prediction in time domain. The performance advantages of the proposed scheme are verified by the simulation results from three typical scenarios. Furthermore, a reference design on a field-programmable gate array for the proposed channel estimation scheme is presented for the purpose of demonstrating its implementation feasibility and complexity

Channel Impulse Response Estimation in IEEE 802.11p via Data Fusion and MMSE Estimator

Tracking the channel impulse response in systems based on the IEEE 802.11p standard, the most widely accepted standard for the physical layer in vehicular area networks (VANETs), is still an open research topic. In this paper we aim to improve previously proposed channel estimators by utilizing data aided algorithm that includes the channel decoding to enhance the quality of the estimated data. Moreover we propose a novel technique that exploits information provided by external sensors like GPS or speedometer, usually present in vehicles. The algorithm proposed so far has been analyzed in non-line-of-sight link conditions; in this paper we present an analysis of performances in the line-of-sight condition as well. Simulations show that both proposals give considerable improvements in terms of packet error rate and channel estimation error in the highway scenario which is surely the most stressing environment for the channel response tracker

Data decoding aided channel estimation techniques for OFDM systems in vehicular environment

L'oggetto del presente lavoro di tesi è costituito dallo studio e sviluppo di algoritmi di inseguimento di canale per sistemi basati su una modulazione di tipo Orthogonal Frequency Division Multiplexing (OFDM), con riferimento allo standard IEEE802.11p per comunicazioni mobili di tipo Wireless Local Area Network (WLAN), tra veicolo e veicolo e tra veicolo e infrastruttura. La caratteristica principale dei sistemi wireless in ambiente veicolare µe la presenza dell'effetto Doppler dovuto alla velocità relativa tra trasmettitore e ricevitore che rende il canale wireless tempo variante

High mobility in OFDM based wireless communication systems

Orthogonal Frequency Division Multiplexing (OFDM) has been adopted as the transmission scheme in most of the wireless systems we use on a daily basis. It brings with it several inherent advantages that make it an ideal waveform candidate in the physical layer. However, OFDM based wireless systems are severely affected in High Mobility scenarios. In this thesis, we investigate the effects of mobility on OFDM based wireless systems and develop novel techniques to estimate the channel and compensate its effects at the receiver. Compressed Sensing (CS) based channel estimation techniques like the Rake Matching Pursuit (RMP) and the Gradient Rake Matching Pursuit (GRMP) are developed to estimate the channel in a precise, robust and computationally efficient manner. In addition to this, a Cognitive Framework that can detect the mobility in the channel and configure an optimal estimation scheme is also developed and tested. The Cognitive Framework ensures a computationally optimal channel estimation scheme in all channel conditions. We also demonstrate that the proposed schemes can be adapted to other wireless standards easily. Accordingly, evaluation is done for three current broadcast, broadband and cellular standards. The results show the clear benefit of the proposed schemes in enabling high mobility in OFDM based wireless communication systems.Orthogonal Frequency Division Multiplexing (OFDM) wurde als Übertragungsschema in die meisten drahtlosen Systemen, die wir täglich verwenden, übernommen. Es bringt mehrere inhärente Vorteile mit sich, die es zu einem idealen Waveform-Kandidaten in der Bitübertragungsschicht (Physical Layer) machen. Allerdings sind OFDM-basierte drahtlose Systeme in Szenarien mit hoher Mobilität stark beeinträchtigt. In dieser Arbeit untersuchen wir die Auswirkungen der Mobilität auf OFDM-basierte drahtlose Systeme und entwickeln neuartige Techniken, um das Verhalten des Kanals abzuschätzen und seine Auswirkungen am Empfänger zu kompensieren. Auf Compressed Sensing (CS) basierende Kanalschätzverfahren wie das Rake Matching Pursuit (RMP) und das Gradient Rake Matching Pursuit (GRMP) werden entwickelt, um den Kanal präzise, robust und rechnerisch effizient abzuschätzen. Darüber hinaus wird ein Cognitive Framework entwickelt und getestet, das die Mobilität im Kanal erkennt und ein optimales Schätzungsschema konfiguriert. Das Cognitive Framework gewährleistet ein rechnerisch optimales Kanalschätzungsschema für alle möglichen Kanalbedingungen. Wir zeigen außerdem, dass die vorgeschlagenen Schemata auch leicht an andere Funkstandards angepasst werden können. Dementsprechend wird eine Evaluierung für drei aktuelle Rundfunk-, Breitband- und Mobilfunkstandards durchgeführt. Die Ergebnisse zeigen den klaren Vorteil der vorgeschlagenen Schemata bei der Ermöglichung hoher Mobilität in OFDM-basierten drahtlosen Kommunikationssystemen

Robust Vehicular Communications for Traffic Safety---Channel Estimation and Multiantenna Schemes

Vehicular communications, where vehicles exchange information with other vehicles or entities in the road traffic environment, is expected to be a part of the future transportation system and promises to support a plethora of applications for traffic safety and efficiency. In particular, vehicle-to-vehicle (V2V) communication promises to support numerous traffic safety applications by enabling a vehicle to broadcast its current status to all the other vehicles in its surrounding.\ua0 \ua0 Vehicular wireless channels can be highly time- and/or frequency-selective due to high mobility of the vehicles and/or large delay spreads. IEEE 802.11p has been specified as the physical layer standard for vehicular communications, where the pilots are densely concentrated at the beginning of a frame. As a consequence, accurate channel estimation in later parts of the frame becomes a challenging task. In this thesis, a solution to overcome the ill-suited pilot pattern is studied; a cross-layered scheme to insert complementary pilots into an 802.11p frame is proposed. The scheme does not require modifications to the 802.11p standard and a modified receiver can utilize the complementary pilots for accurate channel estimation in vehicular channels.\ua0 \ua0 The metallic components of present-day vehicles pose a challenge in designing antenna systems that satisfy a minimum required directive gain in the entire horizontal plane. Multiple antennas with contrasting directive gain patterns can be used to alleviate the problems due to low directive gains. A scheme that combines the output of L antennas to the input of a single-port receiver is proposed in the thesis. The combining scheme is designed to minimize the probability of a burst error, i.e., an unsuccessful decoding of K consecutive packets from a transmitter arriving in the direction of low directive gains of the individual antennas. To minimize complexity, the scheme does not estimate or use any channel state information. It is shown using measured and simulated directive gain patterns that the probability of burst errors for packets arriving in the direction of low directive gains of the individual antenna elements can be minimized.\ua0 \ua0 The enhanced distributed channel access (EDCA) scheme is used in V2V communications to facilitate the sharing of allocated time-frequency resources. The packet success ratio (PSR) of the broadcast messages in the EDCA scheme depends on the number of vehicles and the packet transmission rate. The interference at a receiving vehicle increases due to multiple simultaneous transmissions when the number of vehicles grows beyond a limit, resulting in the decrease of the PSR. A receiver setup with sector antennas, where the output of each antenna can be processed separately to decode a packet, is described in the thesis with a detailed performance analysis. A significant increase in the PSR is shown in a dense vehicular scenario by using four partially overlapping sector antennas compared with a single omnidirectional antenna setup

Low Complexity Scalable Iterative Algorithms for IEEE 802.11p Receivers

In this paper, we investigate receivers for Vehicular to Vehicular (V2V) and Vehicular to Infrastructure (V2I) communications. Vehicular channels are characterized by multiple paths and time variations, which introduces challenges in the design of receivers. We propose an algorithm for IEEE 802.11p compliant receivers, based on Orthogonal Frequency Division Multiplexing (OFDM). We employ iterative structures in the receiver as a way to estimate the channel despite variations within a frame. The channel estimator is based on factor graphs, which allow the design of soft iterative receivers while keeping an acceptable computational complexity. Throughout this work, we focus on designing a receiver offering a good complexity performance trade-off. Moreover, we propose a scalable algorithm in order to be able to tune the trade-off depending on the channel conditions. Our algorithm allows reliable communications while offering a considerable decrease in computational complexity. In particular, numerical results show the trade-off between complexity and performance measured in computational time and BER as well as FER achieved by various interpolation lengths used by the estimator which both outperform by decades the standard least square solution. Furthermore our adaptive algorithm shows a considerable improvement in terms of computational time and complexity against state of the art and classical receptors whilst showing acceptable BER and FER performance

Rapid Prototyping for Evaluating Vehicular Communications

[Abstract] This Thesis details the different elements of a rapid prototyping system able to implement and evaluate vehicular communications fast, according to the continuously evolving requirements of the industry. The system is basically composed of a testbed and a channel emulator, which allow evaluating communication transceivers in realistic vehicular scenarios. Two different testbeds are introduced: a generic 2x2 system and a vehicular platform. The former is used to compare and study space-time block coding (STBC) transmissions at 2.4 GHz over different indoor channels. The latter makes use of software transceivers whose performance is evaluated when they work under artificial high-speed Rayleigh-fading scenarios. To show the capabilities of both platforms, three software transceivers have been developed following the specifications for the physical layers of the standards IEEE 802.11p, IEEE 802.11a and IEEE 802.16e (Mobile WiMAX). The present work details the different elements that make up each transceiver and indicates how to connect them to the rest of the system to perform evaluation measurements. Finally, single-antenna and multi-antenna performances are measured thanks to the design and implementation of three FPGA-based channel emulators that are able to recreate up to seven different vehicular scenarios that include urban canyons, suburban areas and highways[Resumo] A presente Tese detalla os elementos necesarios para constituir un sistema basado en prototipado rápido capaz de levar a cabo e avaliar comunicacións vehiculares. O hardware do sistema está composto básicamente por unha plataforma de probas (testbed) e un emulador de canal, os cales permiten avaliar o rendemento de transceptores inartiamicos recreando diferentes escenarios vehiculares. Inicialmente, este traballo céntrase na descripción do hardware do sistema, detallando a construcción e proba dunha plataforma multi-antena e un testebed vehicular. Estos sistemas permitiron, respectivamente, estudar o comportamento de códigos STBC (space-time block codes) en interiores e medir o rendemento de tranceptores software ao traballar a distintas velocidades vehiculares en canais con desvaecemento Rayleigh. Tres transceptores software foron creados seguindo as especificacións das capas físicas dos estándares IEEE 802.11p, IEEE 802.11a e IEEE 802.16e (Mobile WiMAX). Este traballo detalla os diferentes componentes de cada transceptor, indicando cómo conectalos ao resto do sistema para realizar a avaliacition do seu rendemento. Dita avaliación realizouse coa axuda de tres emuladores de canal basados en tecnoloxía FPGA (Field Programmable Gate Array), os cales son capaces de recrear ata sete escenarios vehiculares distintos, incluindo cañóns urbanos, zonas suburbanas e autopistas.[Resumen] La presente Tesis detalla los elementos necesarios para constituir un sistema basado en prototipado rtiapido capaz de llevar a cabo y evaluar comunicaciones vehiculares. El hardware del sistema está compuesto por una plataforma de pruebas (testbed) y un emulador de canal, los cuales permiten evaluar el rendimiento de transceptores inaltiambricos recreando diferentes escenarios vehiculares. Inicialmente, este trabajo se centra en la descripcition del hardware del sistema, detallando la construccition y prueba de una plataforma multi-antena y un testebed vehicular. Estos sistemas han permitido, respectivamente, estudiar el comportamiento de ctiodigos STBC (space-time block codes) en interiores y medir el rendimiento en canal con desvanecimiento Rayleigh de tranceptores software a distintas velocidades vehiculares. Tres transceptores software han sido creados siguiendo las especificaciones de las capas físicas de los estandares IEEE 802.11p, IEEE 802.11a e IEEE 802.16e (Mobile WiMAX). Este trabajo detalla los diferentes componentes de cada transceptor, indicando ctiomo conectarlos al resto del sistema para realizar la evaluacition de su rendimiento. Dicha evaluacition se realiztio con la ayuda de tres emuladores de canal basados en FPGAs (Field Programmable Gate Array), los cuales son capaces de recrear comunicaciones multi-antena en hasta siete escenarios vehiculares distintos, incluyendo cañones urbanos, zonas suburbanas y autopistas