The Key Technology Research On Channel Estimation And Channel Coding For OFDM/OQAM Systems

The rapid development of society requires higher-rate communication systemswith more reliability. So, the cutting-edge technology in communication systems getsrapid development. Orthogonal frequency division multiplexing (OFDM) is the keytechnology in recent communication systems. The traditional OFDM with cylic prefix(CP-OFDM) utilizes CP to against multipath interference. But, several inherentproblems exist in CP-OFDM system, including peak-to-average, the characteristics ofsensitive to frequency offset, the spectrum resources waste result from CP. In order tosolve those problems, this paper studies the novel multicarrier modulation which isnamed orthogonal frequency division multiplexing with offset quadrature amplitudemodulation (OFDM/OQAM). OFDM/OQAM utilizes well designed pulse-shaping filterto implement the multi-carrier communication. Because of the advantage oftime-frequency zoom and absence of CP, it can solve some puzzle about CP-OFDM.Firstly, this article introduces the principle of CP-OFDM systems andOFDM/OQAM systems. Then, it compares the bit error rate of both systems. Some keytechnology about both systems is studied. Simulation results prove that OFDM/OQAMsystems have a very big advantage to CP-OFDM systems in some fields. But, somediffcult of channel estimation exists in OFDM/OQAM systems.Some researchers proposed the channel estimation method based on interferenceapproximation method (IAM) and the channel estimation method based on pair of realpilots (POP) for OFDM/OQAM systems. Inspired by the theory of compressive sensing(CS), the novel interference approximation method which reconstructs channel impulseresponse by utilizing orthogonal matching pursuit based on interference approximationchannel estimation method is proposed. The simulation results prove that theperformance of estimator utilizing the CS theory gets remarkable improvementcompared with that of the original channel estimation method. The bit error ratioperformance of OFDM/OQAM systems depending on the novel channel estimationmethod is close to that of the system based on the perfect channel estimator. This paperalso studies the cyclostationarity of OFDM/OQAM and the blind channel estimationmethod, which is named two cycle subspace approach (TSCA). By optimizing choice ofthe cycle about TCSA, this paper designs modified two cycle subspace approach(MTCSA) for blind channel estimation. Moreover, this paper proposes another new blind channel estimation method, which uses only one cycle and is called one cyclesubspace approach (OCSA). The simulation results show that three methods canestimate the channel well. The method named MTSCA improves the estimatedperformance enormously compared with original TSCA, and OCSA can obtain3dBSNR gain compared with MTSCA.The hardware implemention of channel encoder and decoder for OFDM/OQAMsystems are completed in this paper. LDPC whose capability is get close toshannon-limited is the ideal choice of channel encoding in OFDM/OQAM systems.Recently, many articles are focused on the design of encoding algorithm and decodingalgorithm. The main work of this paper is the implemention of LDPC encoder andLDPC decoder based on FPGA. The H matrixs of LDPC is from IEEE802.16e standard.The functions of LDPC encoder and LDPC decoder are validated by the simulation toolnamed modelsim. With the quartus ii software, it proves the encoder and the decoderwork well in real communication systems. The implemention of LDPC encoder andLDPC decoder based on FPGA lays a good foundation for the hardware implementionof OFDM/OQAM systems.