OFDM Communication Systems Based LDPC Coded And Performance Simulation

As B3G and 4G high-speed wireless mobile communications research and application, signal modulation techniques are optimized constantly and are developed from traditional single-carrier modulation to multi-carrier modulation. Today, orthogonal frequency division multiplexing(OFDM) which belongs to multi-carrier modulation techniques attract people's attention more and more. Multi-level modulation used in the Physical layer can improve the spectrum efficiency and be against multipath fading. To further improve the error performance,the channel coding is used in communications systems. The following aspects were studied in this paper:1.The basic principle of OFDM are introduced:such as serial and parallel conversion,sub-carrier modulation protection,circular prefix, modulation and demodulation system with IFFT/FFT,etc. The key technologies of OFDM are studied: such as reducing the peak power technology,synchronization technology,channel estimation, etc. Through constructing OFDM system model and selection the basic parameters, the OFDM systems's temporal profile and the power spectrum are simulated by Matlab;2.The basic principles,the code algorithm and decoding algorithm of LDPC were introduced. Because LDPC code is a channel coding,channel characteristics,the white gaussian noise channel and the Rayleigh channel are introduced firstly. The coding principle of Shannon channel and different channel coding performance.are analyzed. Because LDPC code belongs to linear space-time block codes, this article introduces linear space-time block codes firstly. Then representation methods and classification of LDPC code are introduced.The constructing methods of LDPC check-up matrix and the modulation method based binary coding and decoding are analyzed in detail. This paper focuses on the improvement of logarithmic likelihood BP algorithm based binary logarithm. This new logarithmic can reduce the complexity of decoding. The paper studies the LDPC coding and decoding method based multi-band also;3.The multi-band LDPC code can apply to the OFDM systems based on multi-band multi-band modulation. Using Matlab to build LDPC-OFDM model and simulate the system Performance. The simulation results show the improved LDPC channel coding used in OFDM systems can effectively improve the transmission performance.