全数字变速率MSK调制信号的研究与实现

Study and Achievement of All Digital Variable Rate MSK Modulating Signals

最小频移键控（MSK—Minimum Frequency Shift Keying）是二进制频移键控（BINFSK—Binary Frequency Shift Kev—ing）的一种特殊形式，由于这种调制方式具有频带利用率高、带外辐射较小的优点，因此它在数字通信系统中已得到了广泛的应用。本文简要介绍了MSK信号的产生原理，并在DSP＋FPGA全数字架构的平台上，采用对加权函数采样点数的控制、DSP对AD9952的控制以及FPGA对DDR的读取控制来共同实现变速率MSK调制信号。在具体实现的过程中，把复杂的计算过程交给计算功能强大的DSP，而FPGA则主要用于实现时序控制。其中DSP在对加权函数的处理中，采用了查表的方法，从而使程序能够运行得更快。最后在DSP集成开发环境CCS中分别观察到了串并转换之后以及与加权函数相乘后的I、Q两路波形．满足了设计需求。

MSK （Minimum Frequency Shift Keying） is a special form of binary frequency shift keying （BIN FSK）. Due to this modulation mode with the advantages of higher bandwidth ratio and lesser out-of-band radiation, therefore it has been widely used in digital communication systems. This paper briefly introduces that the principle of MSK signals generation, and the variable rate MSK modulating signals are realized by jointly adopting the controlling for number of sampling points of the weighting function, the control- ling for AD9952 by using DSP and the controlling for time sequence of reading data from DDR by using FPGA on the DSP＋FPGA platform of all-digital architecture. In the realized process, the powerful DSP is responsible for the complex calculations and the FP- GA mainly is used to implement the sequential control, among the processing of the weighting function, the method of table look-up is adopted in the DSP, thus it can make the program runs faster. Finally, in the DSP integrated development environment CCS the two-channel waveforms of I ＆ Q have been observed respectively, which are generated by means of serial to parallel conversion and multiplying with the weighting function, so the design requirements have been fulfilled.