Sp-qpsk: a New Modulation Technique for Satellite and Land-mobile Digital Broadcasting

A new modulation technique, "SP-QPSK" (sinusoidal shaped d4-QPSK) suitable for land-mobile and satellite digital broadcasting systems applications is introduced. In digital data and/or sound broadcasting systems, which may have a relatively low bit rate transmission requirement, the residual phase noise introduced by the Doppler shift of moving vehicles presents a high bit error floor in coherently demodulated systems. To avoid this problem, non-coherent detection methods may have to be employed. Even though these systems require a higher C/N than their theoretical coherent counterparts in stationary AWGN environments, the overall performance of non-coherent systems is frequently superior in a mobile radio environment. In addition, to satisfy the high power and spectral efficiency requirements of emerging digital broadcast systems, nonlinear, saturated amplifiers may become essential subsystems. We introduce a new modulation technique, SP-QPSK, which combines the advantages of the IJF-OQPSK narrowband satellite systems and of the d4-QPSK systems which have been adopted as the second generation landmobile cellular standards, i.e., the US digital cellular standard. Two-symbol-interval (TSI) QPSK modulation techniques [ l ] , such as IJF-OQPSK, SQAM, etc., have been developed and are in use in several satellite communication systems which require efficient nonlinear power amplification and reduced out-of-band radiation. However, these schemes need coherent detection due to the fact that they have "offset" I and Q baseband channels by half a symbol duration. This "offset" mode is not suitable for conventional differential noncoherent reception. On the other hand, for differential or discriminator detection, d4-QPSK [2; 3 and 61 is an improved QPSK-based modulation technique proposed for the US digital cellular standard. However, it has a major drawback in nonlinearly amplified systems, i.e., a significant out-of-band spectral radiation. We invented a new modulation technique, sinusoidal shaped d4-QPSK, or for short, "SP-QPSK," which has the combined advantages of the TSI-QPSK and also of the d4-QPSK systems. 2. TSI-xI4-QPSK Systems Even though the d4-QPSK modulator is basically a QPSK (four state) modulator, it has eight signaling phase 3ates as illustrated in Fig. 2.1. The principles of this modulation technique are described in [2; 3 and 61. The The performance of our new generation of SP-QPSK systems is investigated by computer simulations a r d experimentally. Digital signal processing implementati.xi techniques have been used in the experimental prototype design. We demonstrate that nonlinearly amplified SP-QPSK has a 1OdB lower out-of-band radiated power than conventional QPSK and it is suitable for differential and discriminator detection. Improved performance and simplified (noncoherent hardware) receivers could lead to novel digital broadcasting applications of this powerful modulation technique.