Towards More Reliable MAC and PHY Layer Designs for High QoS Achievements for Safety Messaging in DSRC Systems

Broadcast communications are widely proposed for safety messaging. In the case of highway vehicular networks and constantly communicating safety messages inevitably cause the well-known hidden terminal problem. Three existing leading repetition-based broadcasting protocols have shown to meet the reliability and delay requirements for Dedicated Short Range Communications (DSRC) safety systems. We propose a quantitative model to evaluate the quality of service (QoS) of DSRC systems using these three leading repetition-based protocols under hidden terminals and highway scenarios. The performance of our model is analyzed by means of probability of success and delay performances. We also present three new Medium Access Control (MAC) layer design protocols for safety messaging applications. The main protocol we introduce is known as Passive Cooperative Collision Warning (PCCW) protocol for repetition based vehicular safety message reception reliability improvement in DSRC. The PCCW protocol and jointly proposed Enhanced-PCCW (EPCCW) and emergency-PCCW (ePCCW) protocols variants can work on top of existing repetition protocols for serving as a passive collision warning mechanism in the MAC Layer. A full analytical derivation of the relative reliability and delay performances for all three PCCW, EPCCW and ePCCW protocols are provided, serving as intuitive performance evaluators. EPCCW employs the physical (PHY) layer to create sub-slots for the purpose of further increasing reliability by both avoiding and minimizing probability of collision at slots that would nominally fail. Analytical and simulation results of PCCW and EPCCW agree, and show a significant reduction in message failure rate versus the leading repetition protocols, especially under high collision scenarios up to 40% at optimal, and 80% at higher repetitions. Additionally, an improvement in average timeslots delay is observed, which facilitates improved vehicular safety messaging. ePCCW is particularly useful for emergency vehicle (EV) communications. This enhancement makes meeting stringent quality of service (QoS) requirements particularly prevalent in safety applications of DSRC systems. ePCCW show up to 77% reliability improvement relative to a leading alternative is realized. Additionally, the proposed system is shown to have a decreased average timeslots delay that is well within acceptable delay threshold, and provides the best reliability in its class, which is key to safety messaging. In all our simulation results, we use our accurate Orthogonal Frequency Division (OFDM) MAC and physical (PHY) layer designs. The PHY layer simulator is a new object-oriented simulation environment, and is achieved using high-level design, parallelism and usability for the simulation environment. A high-level design and GUI layouts of the proposed simulator is shown in details. This can serve as a learning/research tool for students or practiced professionals to investigate particular designs. In addition, we provide a simple technique to implement simulation partitioning for increased parallel performance of reconfigurable object-oriented OFDM simulators. This simple technique applies to scenarios where there is disproportionate simulation duration between different OFDM configurations. It is shown to decrease total simulation time considerably. Additionally, we present a study on different demapping schemes at the PHY level. We propose the use of a linear demapper over a recently proposed non-linear demapper. The study is also presented under different decoding schemes of DSRC receivers. We also propose the use of equalization concepts in frequency domain that exploit the frequency domain channel matrix to combat inter-carrier interference (ICI) instead of inter-symbol interference (ISI) in DSRC systems. It is shown that the DSRC system with the frequency-domain equalization scheme achieves a considerable performance enhancement compared to both the conventional and the Viterbi-aided channel estimation schemes that try to combat ISI in terms of both Packet Error Rate (PER) and Bit Error Rate (BER) at relatively high and low velocities

Performance Enhancement of the OFDM-Based DSRC System Using Frequency-Domain MAP Equalization and Soft-Output Demappers

5.9 GHz Dedicated Short-Range Communication (DSRC) systems are based on the orthogonal frequency division multiplexing (OFDM) systems. OFDM systems are well known for their abilities to combat inter-symbol interference (ISI) in time-invariant, frequency-selective channels. We propose a receiver design to enhance the overall performance of the DSRC system to combat ICI instead of ISI caused by the time-varying channel. Most researchers focus on the time-domain channel model and MAP equalization to combat ISI. It is shown that the proposed receiver design outperforms the conventional DSRC system by up to 15 dB for the same bit error rate (BER) level. This improvement was achieved through a worst-case scenario study, i.e. time-varying Rayleigh faded channel. Furthermore, soft demapping schemes were compared with one another at varying SNRs and velocities. When they were tested at worst-case scenario environments, very little improvements in the DSRC performance were achieved

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

Channel Fading in Mobile Broadband Systems: Challenges and Opportunities

High-speed data signals transmitted over mobile broadband channels are seriously distorted by both time-varying effect and frequency-selective fading (FSF). These distortions introduce challenges since channel variances in both time-domain and frequency-domain form a two-dimensional channel matrix which is hard to estimate, but meanwhile provide opportunities for information security since all signals are directly encrypted by the channels which are adequately random over time, frequency and space. These challenges and opportunities are studied in this thesis as two parts. In the first part, we propose a novel time-varying channel estimation (TVCE) algorithm named piece-wise time-invariant approximation (PITIA) to estimate a typical type of mobile broadband channels - the high-speed train (HST) channels. PITIA customizes general time-varying channel models according to HST channels' specific features, and outperforms conventional TVCE algorithms by about 3-dB in terms of estimation error. In the second part, we propose the first physical-layer challenge-response authentication mechanism (PHY-CRAM) which uses the mobile broadband channels to prevent eavesdropping during authentication. Since pilots and reference signals are eliminated, eavesdroppers cannot demodulate credential information, while legitimate receivers use the channels' reciprocal property to cancel FSF. PITIA is evaluated by computer based simulations, and the effectiveness of PHY-CRAM is validated by prototyping and real-world experiments. Both pieces of works are built upon a unified system model and orthogonal frequency-division multiplexing (OFDM) modulation.Ph.D.College of Engineering and Computer ScienceUniversity of Michigan-Dearbornhttp://deepblue.lib.umich.edu/bitstream/2027.42/106584/1/Dissertation_Dan_Shan.pd

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

Waveform Advancements and Synchronization Techniques for Generalized Frequency Division Multiplexing

To enable a new level of connectivity among machines as well as between people and machines, future wireless applications will demand higher requirements on data rates, response time, and reliability from the communication system. This will lead to a different system design, comprising a wide range of deployment scenarios. One important aspect is the evolution of physical layer (PHY), specifically the waveform modulation. The novel generalized frequency division multiplexing (GFDM) technique is a prominent proposal for a flexible block filtered multicarrier modulation. This thesis introduces an advanced GFDM concept that enables the emulation of other prominent waveform candidates in scenarios where they perform best. Hence, a unique modulation framework is presented that is capable of addressing a wide range of scenarios and to upgrade the PHY for 5G networks. In particular, for a subset of system parameters of the modulation framework, the problem of symbol time offset (STO) and carrier frequency offset (CFO) estimation is investigated and synchronization approaches, which can operate in burst and continuous transmissions, are designed. The first part of this work presents the modulation principles of prominent 5G candidate waveforms and then focuses on the GFDM basic and advanced attributes. The GFDM concept is extended towards the use of OQAM, introducing the novel frequency-shift OQAM-GFDM, and a new low complexity model based on signal processing carried out in the time domain. A new prototype filter proposal highlights the benefits obtained in terms of a reduced out-of-band (OOB) radiation and more attractive hardware implementation cost. With proper parameterization of the advanced GFDM, the achieved gains are applicable to other filtered OFDM waveforms. In the second part, a search approach for estimating STO and CFO in GFDM is evaluated. A self-interference metric is proposed to quantify the effective SNR penalty caused by the residual time and frequency misalignment or intrinsic inter-symbol interference (ISI) and inter-carrier interference (ICI) for arbitrary pulse shape design in GFDM. In particular, the ICI can be used as a non-data aided approach for frequency estimation. Then, GFDM training sequences, defined either as an isolated preamble or embedded as a midamble or pseudo-circular pre/post-amble, are designed. Simulations show better OOB emission and good estimation results, either comparable or superior, to state-of-the-art OFDM system in wireless channels

Advanced Applications of Rapid Prototyping Technology in Modern Engineering

Rapid prototyping (RP) technology has been widely known and appreciated due to its flexible and customized manufacturing capabilities. The widely studied RP techniques include stereolithography apparatus (SLA), selective laser sintering (SLS), three-dimensional printing (3DP), fused deposition modeling (FDM), 3D plotting, solid ground curing (SGC), multiphase jet solidification (MJS), laminated object manufacturing (LOM). Different techniques are associated with different materials and/or processing principles and thus are devoted to specific applications. RP technology has no longer been only for prototype building rather has been extended for real industrial manufacturing solutions. Today, the RP technology has contributed to almost all engineering areas that include mechanical, materials, industrial, aerospace, electrical and most recently biomedical engineering. This book aims to present the advanced development of RP technologies in various engineering areas as the solutions to the real world engineering problems

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin