Research Of Channel Estimation Technologies In Short-Wave Ofdm System

Shortwave communication is widely used in military, marine communication, emergency response, etc as it has some irreplaceable advantages such as simple equipment, high flexibility, and the communication system is difficult to be destroyed. Orthogonal Frequency Division Multiplexing technology (OFDM) has resistance to multipath fading and high spectrum utilization, which is very suitable for short wave communication. So when OFDM technique is applied to shortwave communication, it can effectively solve the problems of the resource scarcity and multipath fading. Because the condition of shortwave channel is serious, channel estimation is an indispensable part of the shortwave communication system.This paper mainly studies the DFT channel estimation algorithm based on the LS criterion. LS algorithm is often used to estimate pilot subcarriesrs in practical application because of its low complexity and the simple realization, and the interpolation algorithm based on DFT can achieve a good channel estimation.performance while its complexity is very low.When a part of the subcarriers are set to be virtual subcarriers in shortwave communicaiton, it would lead to energy leakage. And when the signal noise ratio (SNR) is high, it will cause "floor effect". This paper proposed a new pilot patten, which can effectively estimate the virtual subcarries.After the compensation of the virtual pilot, channel estimation based on DFT can effectively eliminate "floor effect". Compared with the existing virtual pilot compensation algorithm based on comb pilot patten, the proposed method havs a3-5db SNR ascension without any increase in complexity. In practical application the channel estimation of pilot is mostly based on LS criterion, but it doesn’t take the noise into consideration. The effect of noise have a great influence on the accuracy, therefore, a further management to the noise is very important. This paper purposed a new effective algorithm which combined the adaptive effective path selection which decision feedback algorithm. The advantage of the presented algorithm is that it can adaptively select the channel effective CIR path, and then reduce the noise influence with a combining with further process with decision feedback method. Simulation results show that the new algorithm can effectively restrain the noise with respect to the threshold algorithmand decision feedback algorithm.After the estimation of the virtual carrieries, the DFT channel estimation algorithm can work well in short wave OFDM system. And the noise suppression of LS algorithm, can further improve the accuracy of the channel estimation. The thoretical research and simulation results of these two aspects can provide a theoretical basis for the practical application.