This is a significant improvement compared to hard-limited QPSK, OQPSK, and MSK systems.

TLDR: In this article, the performance of the IJF-OQPSK modulation schemes in the presence of adjacent-channel and cochannel interference (AC1,CCI) and additive white Gaussian noise (AWGN) is investigated and presented.

Abstract: achieve high power and spectral efficiency in digital communi- cation systems. The spectral properties and probability of error (P,) performance of IJF-OQPSK modems in linear and nonlinear channels were reported in our previous publications. It was shown that the IJF-OQPSK schemes have significant spectral advantages over QPSK, offset-QPSK, and MSK, and a better performance in saturated channels. As an extension of our previous work, the P, performance of the IJF-OQPSK modulation schemes in the presence of adjacent-channel and cochannel interference (AC1,CCI) and additive white Gaussian noise (AWGN) is investigated and presented in this paper. Section I1 presents a computer simulation technique used to evaluate the performance of IJF-OQPSK schemes in both linear and hard-limited multichannel systems. This technique makes use of a computation of all the conditional error pro- babilities followed by an average over the conditioning random variables. Illustrative Pe performance results of an IJF-OQPSK modem in the presence of ACI, CCI, and AWGN are reported in Section 111. The results indicate that the receive raised- cosine-type filter having a rolloff factor CY = 0.4 provides the best performance for narrow channel spacings. The effects of ACI on the performance of the IJF-OQPSK scheme are also experimentally investigated. The experimental IJF-OQPSK modem has a bit rate of 64 kbits/s, an intermed- iate carrier frequency of 512 kHz, and a sixth-order elliptic equalized receive bandpass filter. The experimental results, re- ported in Section IV, are in agreement with the simulation results.