Christian Chatellier

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.

Embedded zerotree runlength wavelet image coding

This paper presents a simple and effective image coding technique: the embedded zerotree runlength wavelet (EZRW) image coding algorithm. The main idea behind EZRW is making use of the correlation among the data output by dominant pass and subordinate pass in the embedded zerotree wavelet (EZW) image encoding process. With this algorithm, the compression ratio is better than the EZW algorithm and comparable with that of the SPIHT algorithm for most test images.

Next WSN applications using ZigBee

Among the latest events of the wireless revolution, the fast-growing of ZigBee as a standard for WSN (Wireless Sensors Networks) is certainly one of these. ZigBee and 802.15.4 had been proving in the last years that they can achieve the results that Wi-Fi had achieved for high bit-rate wireless LANs and some large reliable deployments are now in place implementing ad-hoc WSN in critical applications. Therefore this paper will emphasize on the past, present and future features for ZigBee, taking a look on the feedback from previous implementations to finally design the next generations of WSN based on ZigBee.

Deterministic propagation model influence on a wireless digital transmission simulation in real environment

The purpose of This work is to describe the results of a CDMA digital transmission simulation in terms of quality, based on deterministic modeling of the propagation channel. This modeling allows a fast computation of the channel power delay profile (PDP), which is the common input of a digital transmission system. Thus, the harmful impact of the channel is shown under the original form of bit error rate (BER) maps. Such a representation becomes possible because of our propagation model efficiency, particularly compared to a ray tracing one. These maps represent a part of the Poitiers University in France.

A PDE-based method for ringing artifact removal on grayscale and color JPEG2000 images

As successor to JPEG, JPEG2000 aims to realize a very low bitrate. Although JPEG2000s rate distortion has been improved by approximately 30% against JPEG, as on most images compressed using overlapping transforms-based algorithms, one can notice visible spurious oscillations, or ringing artifacts, around the edges of a JPEG2000-compressed image. In this paper, we propose a partial differential equations, or PDE-based image enhancement technique, in order to remove these ringing artifacts, while keeping the images edges. Results are provided on grayscale and color images, showing a visible enhancement, confirmed by the PSNR increase.

A multi-resolution, geometry-driven error concealment method for corrupted JPEG color images

Resume In this article, we propose a new multi-resolution, geometry-driven error concealment method for missing data recovery on gray-level and color JPEG images. Beside JPEG applications, our algorithm can also be used for any block-based compression scheme, including MPEG. It requires no extra redundancy bits nor source–destination interactions, as opposed to classical FEC/ARQ schemes. The reconstruction process consists in interpolating error-free decoded spatial information into corrupted areas, using the actual geometry of local structures. In addition, a multi-resolution scheme is used to organize the recovery process, from coarse to fine structures, and achieve better performances in terms of approximation and computation time. We will demonstrate that our model can also be used to conceal quantization errors (compression artifacts).

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

Robust image transmission strategies for fading channels

The aim of this paper is to present a robust still-image transmission scheme and show its performance when used on a frequency flat fading channel. By following a Joint Source- Channel Coding approach, it is shown that image transmission with good visual quality is possible even with BER as high as 4%. Furthermore, this scheme only requires 26% redundancy for Error Control Coding (ECC). The ECC part can be completed by an original PDE-based restoration algorithm to further improve the visual quality of the image.

Transmission and quantization error concealment for JPEG color images using geometry-driven diffusion

In this article, we propose a new multi-resolution, geometry-driven error concealment method for missing data recovery on grey-level and color for any block-based compression schemes, such as JPEG or MPEG. It requires no extra redundancy bits nor source-destination interactions, as opposed to classical FEC/ARQ schemes. The reconstruction process consists in interpolating error-free decoded spatial information into corrupted areas, using the actual geometry of local structures. In addition, a multi-resolution scheme is used to organize the recovery process, from coarse to fine structures, and achieve better performances in terms of approximation and computation time. We demonstrate that beside transmission errors, our model can also be used to conceal quantization errors (compression artifacts).

Improved compression by coupling of coding techniques and redundant transform

The techniques commonly used in image coding (JPEG, MPEG, ...) have as the main objective to compress as much as possible while retaining most of the information. These methods are often based on the use of the discrete cosine transform (DCT) and the wavelet transform (WT). Our purpose is to consider the necessary redundancy to achieve a good reception in the case of heavy interruptions of bits transmission. There is however a contradiction between an optimal compression and the redundancy required. It is thus necessary to master and compress the information to be transmitted as much as possible and to withstand the noise on the transmission channel. This article makes a contribution to this difficult problem: its originality resides in the coupling of orthogonal transforms and a redundant transform. Simulation results are provided using our method and the results are compared with that of DCT and WT based methods for Lena and Mountain images.