Implementation And Structure For Short Wave Baseband Serial Modem Based On PC Platform

HF communication is use of the ionospheric transmitter to the receiver equipment. It becomes the main way in long distance communication and it’s the primary means of remote communication. It has an important position in military communication, this traditional means of communication are still subject to widespread attention around the world, and it is rapidly developing.HF data communications generally use 3kHz bandwidth in short-wave band transmission of data, the current fixed-frequency short-wave high-speed data transmission system is mainly into two categories:serial and parallel system of institutions. Since the high data rate and low peaks in serial data transmission system, more modem short-wave serial data communication systems are typically used. The short-wave communication transmission channel is a variable parameter channel, the Doppler frequency shift, time-varying fading and multipath effects serious impact on the validity and reliability of data transmission, so the key point of development of high performance serial modem is to study receiver signal processing and efficient implementation.The main purpose of this project is:study a set of receiver signal processing algorithms, the theoretical analysis, based on the combination of hardware platforms and software radio implementation of a PC, PC-based serial modem transceiver system, and introduces the DSP24 Digital Audio and dedicated audio interface AES3 in this project,Based on the different focus, this article is divided into three parts:The first part describes the characteristics of short-wave communication and the development of the current serial modem status and trends, also introduced the PC-based Serial Modem features.The second part describes the general overall structure of the serial modem transceiver, detailing the originator pulse shaping filter with over-sampling and down-sampling process. Frequently at the receiving end of the pilot carrier estimation studies, analysis of several common pilot estimation algorithms, such as the double amplitude (RIFE) algorithm, the improved FFT algorithm, and analyzes their performance of the algorithm and the required computation. On this basis, proposed a theory based on the feedback phase-locked loop approximation algorithm, this method can be calculated in a smaller amount in the case to get good results. And describes the system used in the frame synchronization algorithms and data guide adaptive equalization algorithms.The third part detailed description of the programming under Windows audio technology and audio preservation techniques, and introduced the software structure of PC-based serial modem. Finally, there is a summary of the issues and prospects. The current system has been passed the loop test between software radio hardware platform and the PC platform.