Research On The Key Techniques Of High-rate Short-wave Ofdm System And Its Implementation

Short-wave communication systems have strong resistance to destruction thanks to taking theionosphere as a transmission medium. They have incomparable superiority to other communicationsystems. However, the bad channel conditions seriously restricted their development. In traditionalsingle carrier systems, complicated channel estimation and equalization techniques are used to solvethis problem. But the complexity increases rapidly with the increment of transmission rate. So a newtransmission system is needed.Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier technique, developed inthe90s. It’s an effective way to solve the problem of frequency fading and its equalization is simplerthan the single-carrier. The system with OFDM and channel coding technology has a good time andfrequency diversity.This thesis is focused on the research of OFDM system scheme and key techniques, according tothe channel conditions and application requirements. The main works are as follows:1. A joint synchronization scheme is proposed to solve the problem of synchronization under lowSNR, which includes the coarse synchronization and fine synchronization.2. A joint channel estimation scheme is proposed, which includes the subspace track, iterativeDFT (Discrete Fourier Transformation) and time-domain interpolation low-pass filter. It has a betterperformance than the traditional algorithms and solves the problem of channel estimation under lowSNR.3. This thesis programmes the Low Density Parity Check codes (LDPC) on DSP by assemblylanguage, based on the oscillation Min-Sum algorithm. Under the short-wave fading channelcondition, it is better than (2,1,8) convolutional code by2~3dB.4. A lot of tests are taken by channel simulator and short-wave transmitter-receiver. The resultsshow that transmission rate can be up to9600bps under3KHz. The performances are better thanMDM-Q9604of ROCKWELL by2~4dB.Contribution of this thesis is to improve the unstablility and performance of OFDM system. Andthe works above have an important reference value for other communication systems.