A General Receiver and Constant Envelope Direct Sequence Signals

Future military communication systems should support different modulations since requirements of communications vary remarkably and one modulation cannot satisfy all the requirements. In one end one may require a high speed data link without significant protection against interference whereas at the another end quite low data rates are sufficient but extreme interference tolerance is demanded. Therefore, the used modulations will vary from OFDM for high data rates to MC-CDMA with or without frequency hopping even to hybrid direct sequence frequency hopping signalling. In addition, the transceivers may have a limited energy source such that power efficient modulations are needed. At the same time, the architecture of the receivers should be as similar as possible in each case to ease the design process and for efficient platforms. Therefore, this paper investigates reception of constant envelope MSK and MIL-STD signals using a receiver structure which is readily used with the OFDM, MC-CDMA, (O)QPSK and BPSK. The receiver has the frequency domain correlator for demodulation and the frequency domain matched filter for fast acquisition and, thus, it inherently involves the OFDM option. The paper introduces the receiver structure and discusses how interference cancellation units may be incorporated to it. The performance is studied in synchronization of a DS signal. The DS-MSK and DS-MIL-STD signals are compared to a band limited DS-QPSK signal, which serves as a benchmark since it is known to have an optimum performance with this receiver structure.