Channel Estimation Technique Based On TD-LTE Standard In High-Speed Mobile Scenario

With the continuous development of mobile communication technology, the LTE system begins to be applied commercially all over the world. It uses Orthogonal Frequency Division Multiplexing (OFDM) technology, which can modulate serial high speed data stream onto N parallel orthogonal sub-carriers by Fast Fourier Transform (FFT). In this way, OFDM technology converts a frequency selective channel into a non-frequency selective channel so that the Inter-Symbol Interface (ISI) caused by multiple paths and the multipath fading can be avoided. Receivers usually use coherent detection to acquire the data in the frequency domain. In order to recover the transmitted information, the effect of channel on the transmitted signal must be correctly estimated, which needs to estimate the channel coefficients effectively. Therefore, Channel estimation is an important part for the design of receivers in mobile communication systems.First of all, we analyze the current channel estimation methods, which usually assume that the channel coefficients within an OFDM symbol period are constant. The channel estimation methods based on LTE are pilot-assisted estimation, which consists of two steps. Firstly, statistical estimation of the channel at OFDM tones consisting of reference symbols is determined mainly using Least Squares (LS) algorithm and Minimum Mean Squared Error (MMSE) algorithm. Other methods including low rank LMMSE, SVD and transform-domain lower noise algorithm are improved algorithms based on the two basic methods. Subsequently, the response of the channel at data subcarriers is determined by interpolation techniques. The main interpolators used for the purpose of estimation are constant value, linear, second order, spline and so on. Simulation results of these channel estimation methods based on TD-LTE standard are given.Afterwards, we research the channel estimation methods in high-speed mobile scenario. When a mobile terminal moves very fast, it would cause Doppler effects and make the channel time-selective. Therefore, the channels within an OFDM symbol vary obviously and the Inter-Carrier Interference (ICI) will affect the performance of conventional channel estimation methods, which degrades the performance greatly. In this paper, a method in which the variations of wireless channels are modeled in the form of power series is proposed. The number of channel coefficients is reduced greatly by converting the time-varying channels to the projections of finite parameter variables on the basis of power series. Theoretical analysis and simulation results based on TD-LTE release8both show that this method can achieve a good performance by tracing and estimating the time-varying channel coefficients efficiently.