Quadrature phase shift keying modulation (Quaternary Phase Shift Keying, QPSK) is a linear narrowband digital modulation techniques, it has played an important role in the digital modulation technique is widely used in satellite communications, mobile communications, video conferencing systems , cellular phones and other areas of digital communications. It has the advantages of high frequency band utilization, good spectral characteristics, strong anti-fading performance, and low bit error rate.
DSP technology mainly refers to the ways and methods of implementing the basic theory and algorithm of DSP. Traditional DSP technology is a widely used DSP processor solution, and this solution is increasingly facing increasing challenges. Its own technical bottleneck leads to the road of this solution in many new applications of DSP. The narrower the walk. Modern DSP techniques are concerned with respect to traditional DSP technology is based on a programmable system SOPC (System on a Programmable Chip) DSP technology technology, EDA and FPGA implementation of the technology, is the product of the modern electronic technology, it effectively Overcoming many bottlenecks in traditional DSP technology, showing outstanding advantages in many aspects, such as high speed and real-time, high reliability, independent intellectual property, system reconfiguration and hardware reconfigurability, single-chip DSP system The achievability and standardization and high efficiency of development technology. The QPSK design uses MATLAB/Simulink DSP Builder to develop a quadrature signal generation unit for QPSK modulation. In the formation of the circuit module, the DSP Builder module is used instead of the cumbersome VHDL program, so that the desired result is conveniently obtained. The implementation of the system uses FPGA as the physical carrier, which is faster, more convenient and more flexible than the traditional hardware description language based design.
1 QPSK modulation principle
The so-called QPSK modulation uses four different phases of the carrier to characterize the digital information, each carrier phase representing two binary code meta-information. Since each carrier phase represents two binary symbol information, each of the four binary symbols is also referred to as a two-bit symbol.
The expression of the QPSK signal is
Write formula (1) as
The modulation of QPSK signal can be divided into phase selection method and phase modulation method. This paper adopts phase modulation method to design, and its modulation block diagram is shown in Figure 1.
In Figure 1, the serial/parallel converter divides the input binary sequence into two parallel bipolar code sequences. Let the binary numbers be a and b, respectively. The bipolar a and b pulses respectively perform two-phase modulation on the in-phase carrier and the quadrature carrier through two balanced modulators, and the two outputs are superimposed to obtain the QPSK signal.
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