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qpsk satellite modulator implementation in fpga


Modulation is a key feature commonly used in wireless communication for data transmission and to minimize antenna design. QPSK (Quadrature Phase Shift Keying) is one type of digital modulation technique used to transfer the baseband data wirelessly in much efficient way compare to other modulation techniques. Conventional QPSK modulator operates by separation of baseband data into i and q phases and then add them to produce QPSK signal. The process of generating sine and cosine carrier wave to produce the i and q phases consume high power. For better efficiency in power consumption and area utilization, 2 new types of QPSK modulator proposed. The proposed method will eliminate the generation of 2 phases and will produce the QPSK output based on stored data in RAM. Verilog HDL used to implement the proposed QPSK modulators and it has been successfully simulated on Xilinx ISE 12.4 software platform. a comparision has been made with existing modulator and significant improvement can be seen in term of area and power consumption. Continuous growing demands from end user for more data have encouraged the engineers to develop many new types of modulation scheme in satellite communication system. New types of modulation technique introduced to increase the efficiency in data transmitting and receiving rate within the same bandwidth. One of the common modulation method used in satellite communication system is QPSK which is one form of PSK (Phase Shift Keying) modulation scheme. In PSK modulation, the phase changed according to the baseband data while the frequency and amplitude remain unchanged. In QPSK quadrature means 4 different states that is used to represent a group of 2 bits input data. The four different inputs are 00, 01, 10 and 11 and each group takes one form of QPSK states as shown in table 1. Table 1: QPSK phase with different input. The other most related to QPSK modulation scheme is BPSK (Binary Phase Sift Keying) modulation. In more practical understanding, QPSK is formed from 2 separate BPSK which combined together. However, the data transmission in QPSK is twice when compared to BPSK and the Bit Error Rate (BER) over signal to noise ratio (SNR) for both modulation schemes are same [8]. The symbol period for QPSK is 2 times the bit period, Ts=2Tb while for BPSK the symbol period is same as bit beriod Ts=Tb . Data transmission rate is very crucial for Low Earth Orbital (LEO) satellite system where the interaction time with earth ground station is very short. Implementing QPSK in full digital domain not only can save cost for long term but at the same time, it increases the wireless data immunity over surrounding noise . The high configurability and MIPS (million instructions per second) in FPGA (Field Programmable Gate Array) have made the implementation of digital signal processing possible.

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