Research On The LDPC-OFDM High Speed Wireless Transmission System

This paper mainly conducts research on the application of LDPC-OFDM system in wireless data transmission. The main contents include:1. Research on Orthogonal Frequency Division Multiplexing technique. The implementation methods of channel estimation and synchronization for OFDM are analyzed and the concrete implementation method suitable for the high speed wireless transmission system is identified. The architecture of the OFDM system and the concrete parameter are identified and the pros and cons of OFDM system are analyzed.2. Research on the generation of check matrix and coding method for LDPC codes. Various generation algorithms for LDPC codes are implemented and the PEG generation algorithm for non-regular LDPC code is improved which can produce non-regular LDPC codes with any kinds of degree distribution order. Aimed at the complexity for the coding algorithm of traditional group codes, an effective coding algorithm for LDPC is realized and the coding complexity is reduced.3. Realize the hard decoding and soft decoding algorithm separately. The sum-product algorithm in the soft decoding algorithm for LDPC codes is discussed in detail and implemented in probability measurement,likelihood measurement and log likelihood measurement separately and the performance in different measurements is analyzed. The concrete implementation method of the sum-product algorithm in multi-band modulation is studied. The initialization method of LDPC decoding algorithm in some typical wireless channel model is given.4. Using MATLAB, the bit error performance of both non-regular and regular LDPC codes with the same rate and length are simulated in Gauss channel, Rayleigh channel and Rice channel. The result shows that non-regular LDPC codes with good degree distribution performs better than regular LDPC codes. The effect of channel state information, different code length and iterative number on LDPC codes are also simulated in Rayleigh channel and Rice channel. Based on this the length of the LDPC codes and also the iterative number are identified.5. The bit error rate and frame error rate for LDPC-OFDM system with multi-band modulation in Gauss channel, Rayleigh channel and Rice channel are studied and analyzed. The result shows that LDPC-OFDM system is quite suitable for the high speed wireless transmission system.