Pilot-assisted 16-level QAM for wireless video

Abstract

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.