DRS compression applied to MPEG-2 video data transmitted over a satellite channel

Abstract

This paper shows how the adoption of a Dynamic Rate Shaping (DRS) to variable bit rate (VBR) MPEG-2 (Motion Pictures Expert Group-2) coded video data, in addition to different levels of data protection, adds more flexibility in the way 1: BackgroundIn [1] we analysed the relationships between bandwidth occupancy, satellite link degradation, and the quality of a video stream coded as the Motion Pictures Expert Group-2 (MPEG-2) standard [9], and sent over a satellite channel affected by unfavourable propagation conditions (fades). In satellite transmissions the signal attenuation due to rain imposes that fade countermeasures have to be adopted to ensure an acceptable level of link availability with a reasonable channel quality. The fade countermeasure used in our past experiment was based on * Work carried out in the framework of the Italian Coordinated Project: "Advanced applications for next generation packet-switching networks" funded by the Italian National Research Council (C.N.R.) the dynamic combination of the channel coding and bit rates variation applied to the data sent via satellite. This technique was made possible by the hardware equipment at our disposal (TDMA controller, burst mode modem, and codec, which together constitute an earth station), which had already been used in past experiments [5]. For the present experiment we used an emulated geostationary satellite channel affected by white Gaussian noise. The satellite emulator introduced the correct round trip time and the amount of noise needed to emulate fading situations. The experiment used the traces of the movie "The sheltering sky" 1 , coded according to the MPEG-2 standard. The samples obtained were transmitted between two real earth stations connected together via a satellite emulator. The received sequences, relative to the various transmission parameters needed to cope with the channel degradation level, were then analysed to evaluate the resulting video quality. The scenario produced showed the actual possibility of MPEG-2 video transmission over a degraded satellite link with limited resource requirements, by adopting a fade countermeasure technique based on both channel coding and bit rate variations. The logical continuation of the work in [1] was to study how to trim the data flow more gradually so that a wider variety of channel conditions could be addressed. The goal was to improve the results obtained in [1] by trimming the bitstream so that it could be better protected, while still occupying the same bandwidth, and to find out how to put a variable bit rate (VBR) transmission over a channel with limited bandwidth. Trimming can generally be performed by any intermediate node that knows the real channel conditions. Moreover, for practical reasons, 1 The authors would like to thank Videotime s.p.a. for providing the movie used in the simulations.

A practical foveation-based rate-shaping mechanism for MPEG videos

“…This work was later extended by considering perceptual-oriented image features, specifically, removing the blocking effect by preserving coefficients of edge blocks [25]. Recently, discarding slices (group of blocks) of bidirectional predicted pictures was proposed, together with the constrained DRS, for transmission MPEG-2 videos over satellite channels [26]. The concept of joint source-channel coding was brought up for rate shaping in [27], in which channel error conditions were taken into consideration.…”