A Class of Two-Symbol-Interval Modems for Nonlinear Radio Systems

Based on Feher's nonlinear filter (NLF) invention, we developed a class of intersymbol-interference and jitter-free (IJF) baseband signals and JJF-OQPSK systems. In [14] and [18] we demonstrated the performance advantages of these systems over QPSK, OQPSK, and MSK systems. In this paper a new class of IJF two-symbol-interval (TSI) baseband pulse shapes is introduced. The spectral properties and the P
e
performance of these TSI-OQPSK modulated systems is investigated. We show that in a hard-limited radio system the main lobe of the
n \geq 2
, TSI-OQPSK is narrower and that the sidelobes, in the critical
|(f-f_{c})T_{s}| < 2
region, are lower than that of QPSK, OQPSK, MSK, and
N = 1
, IJF-OQPSK systems. A new filtering strategy, the sum of approximate eye (SAE), is also introduced. It is shown that SAE filters may reduce the
E_{b}/N_{0}
requirements of band-limited and hard-limited TSI-OQPSK modems.