Constant Bit Rate Transmission Research Articles

Comparative analysis of a twin-class M-QAM transmission system for wireless video applications

This paper presents a unique set of techniques to support reliable and efficient video transmission over mobile channels. The transmission system is comprised of an M level Quadrature Amplitude Modulation (QAM) technique. A twin class uniform and non-uniform partitioned M-QAM system is used to transport a compressed video bitstream which is partitioned to match the bit-error sensitivity of the transmitted symbol in terms of mapping in the constellation diagram and picture quality. Video partitioning based on a separation of the Variable Length Coded (VLC) Discrete Cosine Transforms (DCT) coefficients within each block is considered for constant bitrate transmission (CBR). Various scenarios for splitting the bitstream are investigated and their results are compared and analysed thoroughly. The performance of the transmission system is evaluated under Additive White Gaussian Noise (AWGN) conditions. The simulation results showed that the video partition strategy results in a significantly higher quality of the reconstructed video data.

Pilot-assisted 16-level QAM for wireless video

This paper presents a twin-class transmission system for narrowband radio access channels suitable for handheld video phone and multimedia portable PC applications. The transmission system is comprised of a hierarchical 16-QAM modulation technique and a channel-coding scheme. The formation of dual-priority transmission is due to differing error resiliencies of the bits that make up a given symbol in a Gray-coded 16-QAM. On this basis, a twin-class pilot-assisted fade-estimation technique that can gracefully reduce the power loss caused by the transmission of pilot overhead is developed. The twin-class 16-QAM system is then used to transport a compressed video bitstream, which is partitioned to match the bit-error sensitivity of the transmitted symbol. The partitioning scheme is based on a separation of the variable-length (VL) coded discrete cosine transform (DCT) coefficients within each DCT block. This partitioning scheme is then applied to split the ITU-T H.263-coded bitstream. The scheme is suitable for constant bit-rate transmission (CBR), where the fraction of bits assigned to each of the two partitions can be adjusted according to the requirements of the unequal error protection scheme employed. The distribution of the VL-coded (VLC) information amongst the two partitions is performed adaptively. Finally, the performance of the partitioning scheme for transmission of video signals using our twin-class 16-QAM transmission system is evaluated under multipath fading conditions.

Video Transmission for Third Generation Wireless Communication Systems.

This paper presents a twin-class unequal protected video transmission system over wireless channels. Video partitioning based on a separation of the Variable Length Coded (VLC) Discrete Cosine Transform (DCT) coefficients within each block is considered for constant bitrate transmission (CBR). In the splitting process the fraction of bits assigned to each of the two partitions is adjusted according to the requirements of the unequal error protection scheme employed. Subsequently, partitioning is applied to the ITU-T H.263 coding standard. As a transport vehicle, we have considered one of the leading third generation cellular radio standards known as WCDMA. A dual-priority transmission system is then invoked on the WCDMA system where the video data, after being broken into two streams, is unequally protected. We use a very simple error correction coding scheme for illustration and then propose more sophisticated forms of unequal protection of the digitized video signals. We show that this strategy results in a significantly higher quality of the reconstructed video data when it is transmitted over time-varying multipath fading channels.

Multipriority video transmission for third-generation wireless communication systems

This paper presents a robust dual-priority video partitioning method suitable for twin-class unequal protected video transmission over wireless channels. The partitioning is based on a separation of the variable-length (VL) coded discrete cosine transform (DCT) coefficients within each block. The scheme is suitable for constant bit-rate transmission (CBR), where the fraction of bits assigned to each of the two partitions can be adjusted according to the requirements of the unequal error-protection scheme employed. The distribution of the VL-coded (VLC) information between the two partitions is performed adaptively. Subsequently, the partitioning method was applied to the ITU-T H.263 coding standard. It was shown that, for the input video with quarter common intermediate format (QCIF) spatial resolution (or less), the partitioning overhead can be embedded in the B-bit code word representing the group number (GN), thus avoiding transmission of additional bits. As a transport vehicle, we have considered one of the leading third generation cellular radio standards known as wide-band code division multiple access (W-CDMA). A dual-priority transmission system is then invoked on the W-CDMA system where the video data, after being broken into two streams, are unequally protected. We use a very simple error-correction coding scheme for illustration and then propose more sophisticated forms of unequal protection of the digitized video signals. We show that this strategy results in a significantly higher quality of the reconstructed video data when they are transmitted over time-varying multipath fading channels.

Quality-optimised MPEG2 video data rate control using fuzzy logic techniques

Fuzzy logic control has been employed to improve the rate control mechanism for a MPEG2 video encoder. The data rate of compressed video is controlled by video encoders for either variable bit rate (VBR) or constant bit rate (CBR) applications. In VBR video transmission, it is considered to be more efficient to regulate the video rate by the video coder than by network management in order to avoid network congestion and maintain stable video quality. This rationale can also be applied to CBR transmission. Two fuzzy-logic-based rate control techniques are proposed which maintain the buffer occupancy within a specified range. In the proposed technique for VBR applications, a video quality measure is taken as the crucial control parameter. In CBR rate control, the video data rate or the buffer occupancy is also considered as a fuzzy logic variable. The proposed techniques are designed to control either data rate or video quality, depending on the mode of transmission, i.e. CBR or VBR for the MPEG2 encoder. The performance is compared to a typical VBR MPEG video coder with fixed quantiser step sizes for VBR and also to the CBR video coder with MPEG2 TM5 at typical channel rates. Simulation results are presented with peak signal-to-noise ratio, data rate variation and buffer occupancy as the performance measures.

Optimal bit allocation for coding of video signals over ATM networks

We consider optimal encoding of video sequences for ATM networks. Two cases are investigated. In one, the video units are coded independently (e.g., motion JPEG), while in the other, the coding quality of a later picture may depend on that of an earlier picture (e.g., H.26x and MPEGx). The aggregate distortion-rate relationship for the latter case exhibits a tree structure, and its solution commands a higher degree of complexity than the former. For independent coding, we develop an algorithm which employs multiple Lagrange multipliers to find the constrained bit allocation. This algorithm is optimal up to a convex-hull approximation of the distortion-rate relations in the case of CBR (constant bit-rate) transmission. It is suboptimal in the case of VBR (variable bit-rate) transmission by the use of a suboptimal transmission rate control mechanism for simplicity. For dependent coding, the Lagrange-multiplier approach becomes rather unwieldy, and a constrained tree search method is used. The solution is optimal for both CBR and VBR transmission if the full constrained tree is searched. Simulation results are presented which confirm the superiority in coding quality of the encoding algorithms. We also compare the coded video quality and other characteristics of VBR and CBR transmission.