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ABSTRACT: We address channel code rate optimization for transmission of non-scalable coded video sequences over orthogonal frequency division multiplexing networks. A slice loss visibility (SLV) model is used to evaluate the visual importance of each H.264 slice. Based on both the SLV model and the frequency diversity order available from the channel, we propose a cross-layer technique to allocate video slices within a 2-D time-frequency resource block, and optimize the unequal channel code rate profile, in order to better protect more visually important slices. The proposed algorithm outperforms baseline ones which do not take into account the SLV.
Multimedia and Expo (ICME), 2011 IEEE International Conference on; 08/2011
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ABSTRACT: In this work we propose an adaptive source coding addressing the need of scalability for video streaming over wireless networks. Due to the coexistence of multiple access technologies, the future fourth-generation wireless networks will be characterized by an increasing heterogeneity. In this scenario, the “always best connected” (ABC) service is a challenging research topic, where the access network selection is a key issue. When a multimedia transmission is considered, the ABC can be improved by the optimization of the source coding. In this paper we propose a multiple description based source coding method, able to meet the need of a heterogenous network and to be robust to packet loss at the same time. From a single coding process, obeying on the user requirements and constraints, the algorithm is able to optimize the quality vs. compression efficiency tradeoff, thanks to its scalability and flexibility.
Network Operations and Management Symposium Workshops (NOMS Wksps), 2010 IEEE/IFIP; 05/2010
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ABSTRACT: Coding and diversity are very effective techniques for improving transmission reliability in a mobile wireless environment. The use of diversity is particularly important for multimedia communications over fading channels. In this work, we study the transmission of progressive image bitstreams using channel coding in a 2D time-frequency resource block in an OFDM network, employing time and frequency diversities simultaneously. In particular, in the frequency domain, based on the order of diversity and the correlation of individual subcarriers, we construct symmetric n -channel FEC-based multiple descriptions using channel erasure codes combined with embedded image coding. In the time domain, a concatenation of RCPC codes and CRC codes is employed to protect individual descriptions. We consider the physical channel conditions arising from various coherence bandwidths and coherence times, leading to a range of orders of diversities available in the time and frequency domains. We investigate the effects of different error patterns on the delivered image quality due to various fade rates. We also study the tradeoffs and compare the relative effectiveness associated with the use of erasure codes in the frequency domain and convolutional codes in the time domain under different physical environments. Both the effects of intercarrier interference and channel estimation errors are included in our study. Specifically, the effects of channel estimation errors, frequency selectivity and the rate of the channel variations are taken into consideration for the construction of the 2D time-frequency block. We provide results showing the gain that the proposed model achieves compared to a system without temporal coding. In one example, for a system experiencing flat fading, low Doppler, and imperfect CSI, we find that the increase in PSNR compared to a system without time diversity is as much as 9.4 dB.
IEEE Transactions on Image Processing 12/2009; · 3.04 Impact Factor
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ABSTRACT: This paper investigates the effects of non-ideal channel state information in adaptive M-ary quadrature amplitude modulation systems with subset diversity. The slow adaptive modulation (SAM) technique, which adapts the modulation parameters to slow channel variations, is considered. With respects to fixed scheme modulation systems, SAM achieves a good gain in terms of spectral efficiency (SE) and outage probability and, compared to fast adaptive modulation, reduces the system complexity by lowering the feedback rate. Resources dedicated to channel estimation affect both the system performance, in terms of error and outage probability, and the effective SE for which a proper definition is needed. Here, we evaluate the performance of SAM technique when pilot-assisted channel estimation errors are considered. Taking into account the number of pilot symbols transmitted, an effective SE is obtained to address the tradeoff between channel estimation quality and SE.
Wireless Communication Systems, 2009. ISWCS 2009. 6th International Symposium on; 10/2009
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ABSTRACT: Coding and diversity are very effective techniques for improving transmission reliability in a mobile wireless environment. The use of diversity is particularly important for multimedia communications over fading channels. In this work, we study the transmission of progressive image bitstreams using channel coding in a 2-D time-frequency resource block in an OFDM network, employing time and frequency diversities simultaneously. In particular, in the frequency domain, based on the order of diversity and the correlation of individual subcarriers, we construct symmetric ra-channel FEC-based multiple descriptions using channel erasure codes combined with embedded image coding. In the time domain, a concatenation of RCPC codes and CRC codes is employed to protect individual descriptions. We consider the physical channel conditions arising from various different coherence bandwidths and coherence times, leading to various orders of diversities available in the time and frequency domains. We also study the tradeoffs and the relative effectiveness associated with the use of erasure codes in the frequency domain and convolutional codes in the time domain under different physical environments.
Signals, Systems and Computers, 2007. ACSSC 2007. Conference Record of the Forty-First Asilomar Conference on; 12/2007
