The Algorithm Of Serial Modem For Shortwave Communication And Its DSP Platform Realization

Shortwave communication is wireless communication which uses ionosphere to transmit data. And its equipment is easy and flexible. It becomes the main way in long distance communication, and plays an important part in the military domain. With the increasing data communication services needs of people and the needs about telecommunication quality, the innovation of shortwave communication is extremely urgent.There are multipath time-delay and Doppler frequency shift in shortwave channel. These will impact the quality of communication. A better modulation technology can weaken to a great extent this impact. There are some modulation schemes:the multitone parallel modem, the single-tone serial modem, high speed frequency-hop modem and so on. As the BER of single tone serial modem is low and the data transmittal rate is high, the serial modem is becoming a kind of trend. The purpose of the thesis is to study the algorithm of baseband serial modem, realize it on DSP hardware platform, and optimize it.In this thesis, research areas and the characteristic of shortwave communication are summarized. Then the scheme of modulation and its logical architecture of the receiver and transceiver are given. The contents of this thesis are as follows:In the research of synchronization algorithm, the characteristic of synchronization header is summarized and discussed. According to Its good correlation properties, some synchronization algorithms are compared on their performance and complexity. Simulations are performed to confirm the wiener filter algorithm is better than others. And it is realized on fixed point DSP chip. In the research of channel estimation and equalization, least mean square (LMS) algorithm is discussed. And its convergence rate is simulated. Based on data's frame structure, LMS algorithm is used in channel estimation after finding the synchronization header. Then nonlinear data directed estimation (NDDE) are implemented to recover original signal.In the research of decoding, the system's coding scheme is introduced firstly. A soft decision method applied to 8PSK is proposed. Demodulation and decoding modules are concerned with soft decision. Soft demodulation can provide more information to decoding module. In this thesis, an abstraction of soft information algorithm is given. And this soft information is used to decode.Finally, the DSP hardware platform is set up. TMS320VC5510 DSP chip of TI Company is used to study and realize receiver algorithms. And under the chip's characteristic, some codes are optimized. Besides, the method of constructing data Rx and Tx platform with DSP and EMIF is proposed. And with DSP/BIOS real-time operating system, modules are well scheduled. At last, the serial modem algorithms work well on this platform.