Study On OQPSK Modulation And Demodulation Performance

Along with the extensive research of information technology, communication's upsurge caused the human society to enter a new era of information. Subsequent development of more comprehensive and more efficient communication systems has become more urgent. Offset Quadraphase Phase Shift Keying (OQPSK: Offset Quadraphase Phase Shift Keying) modulation technique is a permanent envelope modulation technique with high spectral efficiency and power efficiency, and good spectral properties. It is widely used in real application environment request data transfer systems, satellite communication and mobile communication. It is a more valuable research direction that OQPSK modulation and demodulation used in high-speed wireless data transmission system, especially in satellite communications systems and terrestrial mobile communication systems. Therefore, the study of OQPSK Modulation Technology has more profound application and theoretical value. With the development of the software radio theory and digital communication technologies, the implement of digital wireless communication systems become more and more popular. The task of this issue is to study and analyze the OQPSK modem technology and performance. The OQPSK system is achieved by FPGA hardware according to the need of project.First of all, the OQPSK modulation and demodulation technology development as well as the background and study of current conditions is introduced and followed by a simple expound of QPSK modulation and demodulation principle. Because OQPSK is an improved version of QPSK, they share the same phase relationship, except that OQPSK put the in-phase and quadrature two tributaries of the Bitstream in time staggered half the code element cycle, there will not be two branch code element polarity reversal of the situation at the same time. Then the OQPSK modulation and demodulation principles of the OQPSK modulation and demodulation process using key technologies which including digital down-conversion, shaping filter and other related technologies is analyzed. And simulation platform in MATLAB is created.Secondly, the cross product auto frequency tracking algorithm, digital COSTAS loop algorithm and its hard-decision algorithm COSTAS loop is studied in carrier synchronization, while these algorithms are achieved in MATLAB. The hard decision algorithm has simple structure and calculation, which is easy to realize in engineering; the demodulation of carrier synchronization symbol synchronization algorithm for interpolation in timing is studied by MATLAB simulation.Finally, VHDL hardware description language is adopted to design and implement follow algorithm modules in Quartus II: string and transform and constellation mapping module, carrier and timing synchronization module and so on. Combine the modulation and demodulation modules and make simulation, which verifies the correctness of OQPSK modulation and demodulation. Design with Protel 99 and the hardware circuit board, and write good programs to download to the hardware circuit board running the program successfully download and signal output. Measured waveforms show that the design of OQPSK modulation and demodulation system meets the design requirements to achieve the right side of the transceiver modem. On the practical, the task has a certain significance and research value.