Design and Realization of OQPSK Modulation Circuit Based on FPGA
Technology of digital modulation plays an important role in digital communication system, the combination of digital communication technology and FPGA is an inevitable trend. This paper designs and realizes a new OQPSK modulator based on FPGA. The simulat
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Design and Realization of OQPSK Modulation Circuit Based on FPGA HongLi Zhu and Xia Sun
Abstract Technology of digital modulation plays an important role in digital communication system, the combination of digital communication technology and FPGA is an inevitable trend. This paper designs and realizes a new OQPSK modulator based on FPGA. The simulation result provides the correction of the modulator. With simple solution, high integration and high reliability, this OQPSK modulator can be widely used in digital communication field. Keywords OQPSK • FPGA • DDS
184.1
Foreword
Digital modulation means that the baseband signals are used to modulate, by means of keying, the amplitude, frequency and phase of carried signals, whose courses can be named respectively, amplitude shift keying, frequency shift keying and phase shift keying. According to the difference of number system of employed baseband signals, they can be categorized into binary modulation and multi-system modulation (M-system). Among various realizations of multi-system phase shift modulation, the offset quadrature phase shift keying (OQPSK) is a constant envelope digital modulation technology developed based on a quadrature phase shift keying (QPSK), with good spectral efficiency and constant envelope characteristics, and has been widely used in the narrowband CDMA, satellite communications and other communication systems [1, 2].
H. Zhu (*) • X. Sun Henan University of Technology, Zhenzhou 450001, China e-mail: [email protected] S. Zhong (ed.), Proceedings of the 2012 International Conference on Cybernetics 1445 and Informatics, Lecture Notes in Electrical Engineering 163, DOI 10.1007/978-1-4614-3872-4_184, # Springer Science+Business Media New York 2014
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H. Zhu and X. Sun
This paper presents a novel OQPSK modulator, which, added to the solution based on the programmable logic array (FPGA) technology, not only is highly integrated, stable and reliable, inexpensive, but also makes full use of FPGA features, making internal modules in the FPGA easily realized.
184.2
Principle of OQPSK
As data streams a, b, in the in-phase branch and orthogonal branch, may change at the same time, QPSK modulation could have a 180 phase mutation, which will cause large fluctuations of the signal envelope in the band-limited system, interfering adjacent channels. OQPSK modulation has been improved in this aspect, as its functional block diagram is shown in Fig. 184.1 [3]. First, baseband signals A (t), through Series to Parallel Converter, output two signals a and b; then the signals a are required to delay by Tb/2 (half a code period) and become signals a*, by this way adjacent codes in two branches cannot change simultaneously, making the maximum phase difference of adjacent codes narrowing to 90 , thus reducing the fluctuations of the signal envelope. NCO (numerically controlled oscillator) produces two orthogonal carriers: the in-phase carrier cos (ωct) and quadrature carrier sin (ωct). Multiply both of them respectively by a* and b, and add the two resu
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