A class of Two-Symbol Interval modems for nonlinear radio channels

A new class to Two-Symbol Interval (TSI) pulse shapes is introduced. This class of signals, when applied to an Offset-Keyed-Quadrature-Phase-Shift-Keying (OQPSK) modulator and passed through a nonlinear system has significant spectral advantages over conventional raised cosine filtered MSK, QPSK and OQPSK modems. Power Spectral density, phase transition and envelope fluctuations of TSI-OQPSK signals are derived and found to be in close agreement with experimental results. The receive eye diagrams of hardlimited TSI-OQPSK are also obtained. From these receive eye diagrams a new filtering strategy called Sum of Approximate Eye (SAE) is proposed. Computer simulation shows that the SAE filter has significantly improved the probability of error (Pe) performance and the Carrier to Interference (C/I) power ratio compared with a Zero Forcing Filter.