Image transmission quality analysis over adaptive BCH coding LAMIA CHAARI, MOHAMED FOURATI, NOURI MASMOUDI, LOTFI KAMOUN Laboratoire d’Electronique et des Technologies de L’Information (L.E.T.I) Ecole National d’Ingénieur de Sfax, 3038 SFAX TUNISIE Lamia.chaari@tunet.tn Mohamed.Fourati@isecs.rnu.tn Abstract :. Image communication over telephone wireline and wireless networks is becoming a standard way of communication due to very efficient compression algorithms for reducing the required channel capacity. However, all standard compression techniques are strongly sensitive to channel noise. For noisy channels it is necessary to investigate in order to select the appropriate channel coding method as a tradeoff between the image quality and the ability to control errors caused by noise. BCH (Bose, Chaudhuri, Hocquenghem) codes are becoming more frequently used due to the availability of VLSI components. BCH codes have a powerful random and burst correcting ability. BCH codes also leave the data in its original form which allows image and video decoders to be specified with "optional" error correction. In order to overcome the outlined drawbacks of fixed channel protection, Adaptive Protection is needed. AP adds redundancy as a function of the current channel characteristics. The BCH code can be adapted towards the burst error correcting capabilities and this will be shown in the contribution. This paper investigates the effects of noise- induced transmission errors on the performance of BCH coding methods for different errors correction capability. First, the relations among the bit error rate, signal-to-noise ratio (SNR), and code lengths are analyzed. Further, the transmission performance of BCH codes association with different modem schemes are analyzed. QCIF image transmission quality over BCH codes for different errors capability are simulated, discussed and compared. The results listed in this article denote the effects of the using BCH codes in a selected method. Based on this analysis an adaptive BCH scheme is proposed to pick the correcting capabilities that offers the best reconstructed image quality for each average SNR. Keywords: BCH , QCIF image, transmission, AWGN, PSNR performance, adaptive. 1. Introduction Videoconferencing has been conjured to be a key mode of communication between people in the future. Multimedia allows people to share media rich information in a format that is comprised of text, audio, images, and video. The advances in low bit-rate for images and video coding technologies have led to the possibility of delivering services to users through band-limited wireless networks but transmission quality guarantee is still one of the major challenges that need solution to overcome signal interference, route disruption, congestion and fluctuations which cause several consecutive bits arriving at the receiver in error. Error control such as FEC and retransmission protocols are the primary tools for providing QoS. Among the techniques to limit the effect of error propagation in low bit rate image and video coding, the use of forward error correction (FEC) [1] and automatic repeat request strategies each has its own benefits with regard to error robustness and network trafic load. The error handling method in tradition communication protocols (HDLC, ISO/OSI-TP4, TCP/IP) is error detection and retransmission which is very used because of the following reasons:  Error detecting codes require less redundancy than error correcting codes thus save bandwidth.  Error detecting codes require less computational effort.  Retransmission is implemented in order to recover from loss of complete packets. However this method is inappropriate for distributed multimedia systems for two reasons: It introduces variable delay unacceptable for isochronous streams, and it is very inefficient and difficult to use in the multicast environment typical for many multimedia applications. Retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission bit rate. Also, ARQ may not be appropriate for multicast scenarios due to their inherent scalability problems. This is because retransmission typically benefits only a small portion of receivers while all others waiting unproductively, resulting in poor throughput. For these reasons, FEC-based techniques are currently under consideration by the Internet Engineering Task Force (IETF) as a proposed standard in supporting error resilience. WSEAS TRANSACTIONS on COMMUNICATIONS Lamia Chaari, Mohamed Fourati, Nouri Masmoudi, Lotfi Kamoun ISSN: 1109-2742 584 Issue 6, Volume 7, June 2008