基于数字波形合成的PCM/FM调制技术

随着无线通信向数字化、软件化发展,采用软件无线电技术实现各种通信功能成为目前研究的热点。在广泛应用的PCM/FM遥测体制中,PCM/FM调制模块也可采用基于软件无线电的数字方法来实现。相比于模拟技术,数字技术可以改善模拟锁相调频电路的低频响应特性,有利于增强系统的稳定性和灵活性,并能有效地提高传输效率和保证传输性能。在PCM/FM调制的数字化实现方案中,结合了直接波形合成(DWS)及数字上变频(DUC)技术,以DSP为核心,通过软件算法将PCM信号分解为基带I、Q(同相、正交)信号,I、Q信号分别与各自的载波相乘后相加形成正交调制数据流,然后经过D/A转换得到正交调制模拟信号。其中的软件算法部分采用MATLAB语言进行全精度仿真及验证。

PCM/FM Modulation Based on DWS

Along with the development of telecommunication, software radio technique is widely used in various communication application. In PCM/FM telemetry system, modulation module can be implemented by digital method based on software radio. Compared with analog technology, digital technology can improve the low frequency response of PLL-FM circuit. The stability, flexibility and transmission efficiency of system can be improved by using digital technology too. The design of PCM/FM modulation module based on DSP, direct waveform synthesis (DWS) and digital up-conversion (DUC) are combined with the use of DSP. PCM signal is transformed into I and Q data by software algorithm. The I and Q data is respectively multiplied by the respective carrier and then summed together to produce a quadrature-modulated data stream. The digital data stream is applied to DAC to become the quadrature-modulated analog output signal. The software algorithm of the design is simulated and proved by MATLAB Simulation. The result of simulation is presented too.