Contents I. Introduction
There are multitudes of modulation techniques available for a designer of communication system. The use of particular modulation technique depends on the channel requirement, available bandwidth and power. Satellite communication system in particular require a modulation techniques which is bandwidth and power efficient and has constant envelop to deal with the no. linearties of channel. Apart from these basic requirements, complexity of demodulator and hardware utilization are also some of the important parameters. In general M-PSK modulation techniques like BPSK, OPSK, O-QPSK, 8-PSK and 16-PSK satisfied all the above criteria and therefore best suited for satellite communication. At present BPSK modulation is used for telecommand and telemetry system while O-QPSK and QPSK is for payload data transfer. The paper mainly concentrate on the hardware realization of modulators for aforesaid techniques The digital implementation with the use of DSP techniques, in realizing complex communication system has greatly enhanced the performance and offers various methods for realization to designer. The paper presents three method for realizing QPSK modulator and two for 8-PSK. The use of CORDIC and look-up table based DDFS has been explained and compared. DDFS technique offer precise control over amplitude, phase and frequency of the system along with robustness from aging and temperature variation of components [1]. The paper is organized as follows. Section II deals with the brief description of M-PSK modulation technique followed by DDFS. Design of QPSK with various techniques is presented in section IV. Section V deals with the design of 8-PSK modulator. System level simulation and FPGA realization is describe in section VI. Analysis and implementation results are presented in section VII. Finally conclusion is presented at the end.
