Title: Efficient Design of Waveforms for Robust Pulse Amplitude Modulation

In digital communication schemes based on pulse amplitude modulation, the transmitted signal is a linear combination of translated versions of a given waveform, the weights of which represent the message data. The choice of waveform critically impacts several performance criteria, including spectral efficiency, performance in an ideal channel, robustness to expected channel imperfections, and receiver complexity. In this talk we will develop design criteria for the waveform for applications in which the standard 'matched filter' receiver is employed. It is intended that the waveform be implemented in a digital signal processor, and hence the design variables are the coefficients of the finite impulse response filter which performs the modulation. Unfortunately, many common design criteria involve non-convex functions of the filter coefficients, and some result in an infinite number of constraints. Hence, any direct design algorithm must deal with the intricacies of local minima and the approximation of the infinite constraint sets. The key observation in obtaining our efficient algorithms is that the design criteria can be (precisely) expressed as convex and finite functions of the 'autocorrelation' of the filter coefficients. By reformulating the design in terms of the autocorrelation sequence we obtain convex symmetric cone programmes which can be efficiently solved. The convex formulation not only allows efficient evaluation of the inherent design tradeoffs between spectral efficiency, performance in the ideal channel, and robustness, but also provides filters which achieve these performance limits. In the design examples, we will use the convex formulation to design 'chip' waveforms with substantially improved performance over those specified in recent standards for digital mobile telephony.

Bio of Tim Davidson:
Tim Davidson received the B.Eng. (Hons. I) degree in Electronic Engineering from The University of Western Australia (UWA), Perth, in 1991 and the D.Phil. degree in Engineering Science from the The University of Oxford, Oxford, U.K., in 1995. He is currently an assistant professor in the Department of Electrical and Computer Engineering at McMaster University, Hamilton, Ont., Canada. His research interests are in signal processing and control, with current activity focused on signal processing for digital communication systems. He has held research positions at the Communications Research Laboratory at McMaster University, the Adaptive Signal Processing Laboratory at UWA and the Australian Telecommunications Research Institute at Curtin University of Technology, Perth, Western Australia, and brief visiting appointments at QPSX Communications and the Digital Signal Processing Laboratory at The Chinese University of Hong Kong. Dr. Davidson was awarded the 1991 J. A. Wood Memorial Prize (for ''the most outstanding [UWA] graduand'' in the pure and appliedsciences), and the 1991 Rhodes Scholarship for Western Australia.