Hardware implementation of a differential QAM modem

A QAM modem based on certain modifications of the CCITT Recommendation V.29, is presented. A predominantly digital implementation without the use of DSP devices is given. Although the implementation is for telephone bandwidth the idea can be expanded to achieve higher rates. In this design approach the modulation is based on ROM-stored symbols while the demodulation is based on a symbol-by-symbol determination for the recovery of the original information bits. Specifically, the paper refers to a D16QAM design. Most of the stages are digital, a feature that simplifies the VLSI implementation. The synchronisation (timing recovery) is based on a modified phase locked loop.