Performance of DS/GMSK/PSK modem using four-phase correlator

Direct-sequence spread-spectrum (DS/SS) system has been extensively studied for land mobile communications because of the notable and attractive features such as its robustness and applicability to code division multiple access (CDMA). We propose a DS/SS modulation method which employs Gaussian-filtered minimum-shift-keying (GMSK) and permits simple code acquisition. The modulated signal can be demodulated by a four-phase correlator which can obtain the correlation value of the received signal even if a phase difference between the transmitter and the receiver exists. The bit error performance obtained by the hardware experiments ensures the validity of this modulation method