Application Of OFDM In HF Communication

Shortwave communication has been occupying an important position in the modern communication, is one of the important means of long distance wireless communication, the communication speed and efficiency has long been widely concerned question. However, due to its smaller bandwidth and channel complex constraints, despite the emergence of new modulation and transmission technology of all kinds, shortwave communication rate increased the problem has still not been fundamentally changed. OFDM is a new type of multi carrier modulation technology, which can effectively utilize the limited frequency band, while improving the spectrum utilization rate to increase the information transmission rate of the system; it also greatly reduces the system to equilibrium requirements.The emergence of OFDM has promoted the development of communications technologies, also make the short wave communication is facing new opportunities and challenges. The application of OFDM in HF communication, can reduce the bandwidth of shortwave communication rate constraints, reduce the effect of multipath channel characteristics, such as the system to improve the speed of information transmission. Therefore, has considerable appeal application of OFDM in HF communication.This paper mainly focuses on the theory and method of realizing short wave OFDM baseband part of the study of the use of large-scale digital signal processor.This paper first briefly introduces the theory and the practice, short wave OFDM communication system research background, the research of shortwave OFDM system, focus on the analysis of the technical details of the main short wave OFDM system, including the HF channel model construction, the transmitter / receiver / RF part of the realization of.Subsequently, engaged by theory and simulation, focusing on the two key technologies in the process of the realization of HF OFDM system: synchronization and PAPR reduction technique. The synchronization technology, according to the decision variable size packet detection uncertainty, we on the delay correlation algorithm part of improvement; at the same time, the time domain method fully completed the OFDM symbol detection and frequency error estimation, and reduces the complexity of implementation. In the PAPR reduction, we made a comparison of several kinds of commonly used methods, and use is convenient to realize the clipping filtering method for the effect illustrated by simulation examples.Finally, introduced with emphasis the HF OFDM baseband DSP details. From the parameters of HF channel set start, we gradually of the HF OFDM baseband part of the implementation process needs to consider the error correcting code, IFFT/FFT implementation, synchronization method and clipping and filtering method of concrete realization of the process, and their performances are simulated.