An asynchronous digital demodulator for TDMA

BNR Europe Limited has developed a digitally realised demodulator for use in Time Division Multiple Access mobile communication systems. This is aimed particularly at low power, low cost in-building wireless, specifically the DECT system, and is compatible with other common angle modulation standards. The demodulator includes sampling at IF, digital down conversion and phase discrimination followed by digital timing recovery and burst correlation. The demodulator deals with the problem of variable burst to burst timing requiring fast capture of the optimum bit timing position with a minimum overhead. This is achieved by novel symbol timing estimation using an asynchronous system clock avoiding the need for storage of the entire burst. The paper describes the principles of the design together with aspects of its practical implementation as relevant. The paper concludes with a discussion of the measured performance.