Spectral considerations for time division duplex CPM with application to future personal communications

There is now very considerable emphasis on mobility in telecommunications with interest ranging from mobile radio through cordless telephony and aimed ultimately at the realisation of a flexible personal communicator providing a range of voice and data services. The need is clearly for a digital system, with anticipated high take up and utilisation bringing spectral and power efficiency to the fore. Conventional modulation schemes such as QPSK or MSK may not adequately meet the demands of these applications as penetration and utilisation expand; accordingly the authors have been studying a promising alternative category of modulation schemes based on continuous phase modulation (CPM). For continuous digital transmission, CPM schemes are known to provide very good spectral efficiency especially when combined with partial response coding. For personal communicator applications though, there is the added dimension of time division duplex (TDD) operation to be considered and it is this observation which motivates and orientates the present study