Quadrature-Quadrature Phase Shift Keying.

Abstract

Quadrature - Quadrature Phase Shift Keying (Q('2)PSK) is a new spectrally efficient digital modulation scheme. It utilizes available signal space dimensions in a more efficient way than the known schemes such as Quadrature Phase Shift Keying (QPSK) and Minimum Shift Keying (MSK). It is observed that QPSK and MSK do not take advantage of all available signal space dimensions; only as much as half of them are utilized. The new scheme, on the other h and , makes full utilization of all available dimensions and increases the data transmission rate by a factor of two over QPSK and MSK. Just at QPSK brought improvement over Binary Phase Shift Keying (BPSK), Q('2)PSK does it again over QPSK. However, in a b and limited situation, Q('2)PSK and QPSK both require a small increase in bit energy as compared to MSK. For certain nonlinear channels a constant envelope in the modulated signal may be a desirable feature. Without additional constraints, Q('2)PSK signal does not have a constant envelope. However, a simple block code provides a constant envelope signal. This coded signal substantially outperforms, in b and width efficiency, the constant envelope signals of Minimum Shift Keying and Tamed Frequency Modulation. Like MSK, Q('2)PSK also has self clocking and self synchronizing ability. A synchronization scheme is presented for coherent demodulation of Q('2)PSK signal. The concept of Q('2)PSK has been generalized to bring additional features. One generalization, which maintains binary nature communication, achieves the Nyquist rate of two bits per second per Hertz; the same rate is also achieved in the Duobinary scheme but at the cost of three level detection and hence more bit energy expenditure.