A new algorithm is proposed for the segmentation of the lumen and bifurcation boundaries of the carotid artery in B-mode ultrasound images. It uses the hipoechogenic characteristics of the lumen for the identification of the carotid boundaries and the echogenic characteristics for the identification of the bifurcation boundaries. The image to be segmented is processed with the application of an anisotropic diffusion filter for speckle removal and morphologic operators are employed in the detection of the artery. The obtained information is then used in the definition of two initial contours, one corresponding to the lumen and the other to the bifurcation boundaries, for the posterior application of the Chan-vese level set segmentation model. A set of longitudinal B-mode images of the common carotid artery (CCA) was acquired with a GE Healthcare Vivid-e ultrasound system (GE Healthcare, United Kingdom). All the acquired images include a part of the CCA and of the bifurcation that separates the CCA into the internal and external carotid arteries. In order to achieve the uppermost robustness in the imaging acquisition process, i.e., images with high contrast and low speckle noise, the scanner was adjusted differently for each acquisition and according to the medical exam. The obtained results prove that we were able to successfully apply a carotid segmentation technique based on cervical ultrasonography. The main advantage of the new segmentation method relies on the automatic identification of the carotid lumen, overcoming the limitations of the traditional methods.
This paper evaluates the performance of a high frequency (HF) wireless network for transporting packet multimedia services. Beyond of allowing civil/amateur communications, HF bands are also used for long distance wireless military communications. Therefore, our work is based on NATO Link and Physical layer standards, STANAG 5066 and STANAG 4539 respectively. At each HF channel, a typical transmission bandwidth is about 3 kHz with the resulting throughput bit rate up to 12800 bps. This very low bit rate by itself imposes serious challenges for reliable and low delay real time multimedia communications. Thus, this paper discusses the performance of a real time communication system designed to allow an end-to-end communication through “best effort” networks. With HF channel diversity, the packet loss percentage, on average considering three channel conditions, is decreased by 16% in the channel SNR range from 0 to 45 dB.
Proc. SPIE. 5100, Digital Wireless Communications V
KEYWORDS: Signal to noise ratio, Quadrature amplitude modulation, Modulation, Modulators, Telecommunications, High dynamic range imaging, Multimedia, Forward error correction, Data communications, Error control coding
The recent rapid growth of multimedia communications has efficiently allowed delivering different services, formats and contents over an enormous variety of digital networks with IP acting as an integration protocol. The main objective of this research work is to evaluate the performance of an high frequency (HF) wireless network for transporting multimedia services according to UDP/IP protocol stack. Besides, allowing civil/amateur communications, HF bands are also used for long distance wireless military communications. Therefore, our work is based on NATO Link and Physical layer standards, STANAG 5066 and STANAG 4539, respectively. A typical transmission bandwidth is about 3 kHz resulting in a varying bit rate in the range between 75 and 12800 bps. This very low bit rate by itself imposes
serious challenges for reliable real time multimedia communications. This paper discusses optimal combinations of channel coders, modulators and packet sizes in order to achieve the greatest throughput in function of the signal-to-noise ratio and HF channel conditions.
Wireless access to encoded video requires sophisticated error resilient mechanisms. Although some video coding standards describe error resilience algorithms, they are inefficient at deep fading wireless and mobile channels. In this paper, we present a novel scheme of error protection for narrowband wireless channels which is independent of any video coding standard. Being, however, this scheme common to all standards, it provides some acceptable video quality degradation. We have evaluated the quality degradation of the Common solution in comparison to the optimal scheme of protection corresponding to the existence of a finite number of channel codes. Besides, we also present the quality degradation for both video coding standards, H.263 and MPEG-4, obtained from a finite number of codes in comparison with the ideal scheme corresponding to the existence of an infinite number of channel codes. Additionally, we proposed a protection solution tailored to H.263/MPEG-4 source coding with an average PSNR improvement of about 0.2 dB relatively to the above mentioned Common solution. Thus, in the framework of joint source-channel coding, we present an adaptive scheme of protection according to the channel bit error rate (BER) and with an overall transmission rate of 64 kbps. In our investigation, we used four QCIF video test sequences and rate compatible punctured convolutional (RCPC) codes. For instance, a PSNR gain of about 16.7 dB is obtained at BER=10-2 for 'Foreman' video sequence, encoded either by H.263 or by MPEG-4 and protected using the Common scheme in comparison to the unprotected case.
This paper considers the transmission of QCIF resolution MPEG-4 video signals over hostile channels like wireless and mobile at transmission rate of 64 kbps. Although MPEG-4 incorporates some error resilience tools, this standard is still fragile for video transmission over time-variant deep fading channels. We investigated the significance of MPEG-4 video syntactical elements considering MPEG-4 encoded streams, QPSK modulated and delivered through Binary, AWGN and Rayleigh (50 Km/h) channels with SNR range between 0 and 40 dB. We have used four QCIF video test sequences, Foreman, News, Container and Coastguard, and enabled slice resynchronization and data partitioning modes in MPEG-4 video coding. The simulation results show that despite significance of particular elements varies with the channel SNR and with the particular test sequence, we could graphically identify two classes of significance at low channel SNRs. The most significant class includes elements such as VOP header, Video Packet header, DC Marker and DC Coefficients of INTRA-VOP & MB header. At high Rayleigh channel SNR, above 15 dB, AC coefficients of INTRA-VOPs and Motion Vectors were found to be the most significant elements. Any unequal error protection, data partitioning and grouping strategies covering a wide range of SNRs can then be designed based on the significance results presented in this paper.
The purpose of our work is to report a solution for the problem of the Joint Source-Channel Coding (JSCC) of the H.263 bit stream to be transmitted through error prone channels. Our investigations led us to classify the H.263 syntactical elements into several classes of different significance. By identifying the most sensitive elements we developed a data partitioning (DP) technique which exhibits improved error resilience. A good reconstructed video quality is obtained for a constant 64 kbit/s transmission rate using Rate Compatible Punctured Convolutional (RCPC) codes of different rates for forward error protection. By exploiting the different syntactical element sensitivities we presented an Unequal Error Protection (UEP) scheme that surpasses the optimal Equal Error Protection (EEP). The forward error correction adopted has resulted in PSNR improvements over 20 dB for bit error rates higher than of 4 X 10-3.