Hervé Boeglen

A survey of V2V channel modeling for VANET simulations

Most Vehicle to Vehicle (V2V) network protocols are evaluated by simulation. However in most network simulators, the physical layer suffers from a lack of realism. Therefore, realistic V2V channel modeling has become a crucial issue in Intelligent Transportation Systems (ITS) networks. V2V channels are known to exhibit specific features which imply the design of new simulation models. In this survey paper, we first recall the main physical features of such wireless time and frequency dispersive channels. Next, three “simulation-ready” V2V channel models found in the literature are reviewed. Finally, two complete VANET simulation frameworks are presented. They illustrate the importance of a realistic channel and physical layer modeling in vehicular networking.

An enhanced AODV protocol for VANETs with realistic radio propagation model validation

In this paper we evaluate V-AODV a version of AODV (Ad-hoc On-demand Distance Vector) especially created for Vehicular Ad-hoc NETworks (VANETs). V-AODV is designed to run with a complex cross layered metric based on both delay from node to node and Bit Error Rate (BER) coming from the physical layer. We conducted simulations with the NS2 simulator taking in account a realistic environment tool called Communication Ray Tracer (CRT). Our results show that the basic propagation models usually in use with NS2 are not suitable for VANETs simulations. We also show that when using a routing metric based on delay and BER, the first parameter is more relevant in terms of QoS than the second one.

A robust joint source channel coding scheme for image transmission over the ionospheric channel

In this paper, we propose a joint source channel coding (JSCC) scheme to the transmission of fixed images for wireless communication applications. The ionospheric channel which presents some characteristics identical to those found on mobile radio channels, like fading, multipath and Doppler effect is our test channel. As this method based on a wavelet transform, a self-organising map (SOM) vector quantization (VQ) optimally mapped on a QAM digital modulation and an unequal error protection (UEP) strategy, this method is particularly well adapted to low bit-rate applications. The compression process consists in applying a SOM VQ on the discrete wavelet transform coefficients and computing several codebooks depending on the sub-images preserved. An UEP is achieved with a correcting code applied on the most significant data. The JSCC consists of an optimal mapping of the VQ codebook vectors on a high spectral efficiency digital modulation. This feature allows preserving the topological organization of the codebook along the transmission chain while keeping a reduced complexity system. This method applied on grey level images can be used for colour images as well. Several tests of transmission for different images have shown the robustness of this method even for high bit error rate (BER>10^-^2). In order to qualify the quality of the image after transmission, we use a PSNR% (peak signal-to-noise ratio) parameter which is the value of the difference of the PSNR after compression at the transmitter and after reception at the receiver. This parameter clearly shows that 95% of the PSNR is preserved when the BER is less than 10^-^2.

A Semi-Deterministic Channel Model for VANETs Simulations

Todays advanced simulators facilitate thorough studies on Vehicular Ad hoc NETworks (VANETs). However the choice of the physical layer model in such simulators is a crucial issue that impacts the results. A solution to this challenge might be found with a hybrid model. In this paper, we propose a semi-deterministic channel propagation model for VANETs called UM-CRT. It is based on CRT (Communication Ray Tracer) and SCME—UM (Spatial Channel Model Extended—Urban Micro) which are, respectively, a deterministic channel simulator and a statistical channel model. It uses a process which adjusts the statistical model using relevant parameters obtained from the deterministic simulator. To evaluate realistic VANET transmissions, we have integrated our hybrid model in fully compliant 802.11 p and 802.11 n physical layers. This framework is then used with the NS-2 network simulator. Our simulation results show that UM-CRT is adapted for VANETs simulations in urban areas as it gives a good approximation of realistic channel propagation mechanisms while improving significantly simulation time.

AODV enhancements in a realistic VANET context

Ad hoc On demand Distance Vector (AODV) is a commonly used routing protocol for Vehicular Ad hoc NETworks (VANET). This paper presents and analyzes several AODV enhancements propositions dedicated to the VANET context. Communication protocol tuning can yield significant gains in energy efficiency, resource requirement, and overall network performance, all of which is of particular importance in VANETs. Alternatively, multipath routing allows the establishment of multiple paths between a pair of source and destination nodes in mobile ad hoc networks. It has recently received more and more attention and is typically proposed to increase the reliability of data transmission. This paper shows how AODV tuning and multipath routing behave under realistic VANET simulations.

Performance Analysis of Closed-Loop MIMO Precoder Based on the Probability of Minimum Distance

Linear closed-loop MIMO precoders are attractive owing to their scalability. They can significantly improve the received signal via optimization of pertinent criterion. The solution of max-dmin precoding is optimal for 4-QAM as it utilizes the channel state information at the transmitter (CSIT) to minimize the system error probability making it very attractive. However, as M increases the solution which is dependent on channel angle gets complex, due to its multi-form precoder search. Motivated by a requirement to provide MIMO system evaluation parameters to upper layer protocol(s) as a function of precoder optimization criterion, we propose deriving a general expression for the probability density function (pdf) of max-dmin. Our approach applies numerical approximations to derive the system bit error rate (BER) and ergodic capacity for any values of M, nr, and nt, and with b = 2 data streams. Results show that the performance of our numerical approximation approach is close to the analytical simulation method.

Impact of Realistic Simulation on the Evaluation of Mobile Ad Hoc Routing Protocols

Todays advanced simulators facilitate thorough studies on vehicular ad hoc networks (VANETs). However, the choice of the physical layer and the mobility models in such simulators is a crucial issue that greatly impacts the results. Realistic simulation of routing protocols in VANETs is still an open question. Indeed, only a few works address routing protocols comparison performed under realistic conditions. This paper compares common reactive, proactive, hybrid, and geographic routing protocols using a simulation platform integrating a realistic physical layer and mobility models. It also presents and analyzes several reactive protocol enhancement propositions dedicated to the VANETs context, such as multipath routing, but also protocols tuning, which allows it to adapt faster. They all have lot of attention and are typically proposed to increase the reliability of data transmission. This paper studies the behavior of each protocol in different situations and analyzed their advantages and drawbacks. Results presented in this paper give an important explanation on the contradictory results found in similar works. Finally, our realistic simulations show that reactive protocols are the best suited for VANETs, and more especially the dynamic Mobile Adhoc NETwork on-demand protocol.

LAR Image Transmission over Fading Channels: A Hierarchical Protection Solution

The aim of this paper is to present an efficient scheme to transmit a compressed digital image over a non frequency selective Rayleigh fading channel. The proposed scheme is based on the Locally Adaptive Resolution (LAR) algorithm, and the Reed-Solomon error correcting code is used to protect the data against the channel errors. In order to optimize the protection rate and ensure better protection we introduce an Unequal Error Protection (UEP) strategy, where we take the hierarchy of the information into account. The digital communication system also includes appropriate interleaving and differential modulation. Simulation results clearly show that our scheme presents an efficient solution for image transmission over wireless channels, and provides a high quality of service, outperforming the JPWL scheme in high bit error rate conditions.

On the robustness of a joint source-channel coding scheme for image transmission over non frequency selective Rayleigh fading channels

The aim of this paper is to present a joint source channel coding scheme for image transmission over a non frequency selective Rayleigh fading channel. Because of the very high BER, a JPEG or JPEG2000 compressed image cannot be transmitted without major visual degradation quality. On the one hand we use a compression algorithm based on wavelet transform and vector quantization called WTSOM (wavelet transform self organized map), and on the other hand we combine differential modulation, symbol interleaving, unequal error protection and antenna diversity to improve the performance of the transmission. The results show a relation between the received images PSNR and the normalized Doppler frequency of the Rayleigh channel. The performance of this joint source channel scheme allows us to obtain a good visual quality of the images even with very bad transmissions conditions

Partial discharge impulsive noise in 735 kV electricity substations and its impacts on 2.4 GHz ZigBee communications

Installation of wireless sensor networks in power substations is becoming unavoidable for developing smart electrical network. High-voltage equipment in a power substation may produce impulsive noise that happens to be much more troublesome for wireless communications than conventional white noise. Indeed, the choice of physical layer for communication network is not easy. It fits to evaluate attentively the advantages and downsides bound to the different technologies of communication. Before deploying the network, electromagnetic environment has to be characterized and tests have to be performed in order to estimate communication performances. This paper presents an investigation of ZigBee (IEEE 802.15.4/2.4 GHz) narrowband system performance in high voltage substations. We use recorded data from the measurement campaign to identify the models. Substation noise obtained is modeled as a Middleton Class A process and a recent model (Au). By using several statistical tests, we evaluated the two models. First, the results show that Middleton Class A is not accurate for modeling partial discharges at 735 kV electricity substations. Au model is more accurate to model impulsive noise in high voltage substation compare to Middleton Class A and Gaussian models. In addition, the BER performances of the ZigBee 2.4 GHz PHY layer are studied in a substation environment. The results show that the impulsive noise influence is close to a Gaussian noise or a Rayleigh noise according to the SNR.