Third-generation Wireless Systems Research Articles

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.

Software-defined radio architectures for interference cancellation in DS-CDMA systems

Third-generation wireless systems call for strategies that can improve achievable performance and data rates while providing flexibility and affordability. Software-defined radio technology is promising to provide the required flexibility in radio frequency, intermediate frequency, and baseband signal processing stages. Baseband signal processing techniques such as interference cancellation for direct-sequence code-division multiple access systems have the potential to provide the higher performance requirements of 3G systems. With advances in digital signal processor technology, the gap between the complexity of interference cancellation algorithms and available processing speeds is narrowing. However, 3G system requirements are ever pushing the envelope of signal processing algorithms required, including multi-user detection schemes, that are considered to be attractive and viable candidates. WINLAB has been working on an attractive SDR solution, to provide flexibility and handle the processing speeds required of 3G radio receivers. The approach is based on SDR architectures that partition radio receiver processing into two core technologies (field programmable gate arrays and DSP devices). We present a summary of the SDR work at WINLAB that is based on using this mixed signal processing approach for implementation of nonlinear interference cancellation and linear multi-user detection algorithms.