Vhf Band Aeronautical Radio Channel Estimation And Equalization,

The main object in the design of digital communication system is to achieve the highest possible transmission rate with acceptable level of reliability. In wireless communications the basic problem is the time dispersion introduced by the Rayleigh or Ricean fading Multipath channel. Thus, the signal dispersion caused by frequency selective Multipath fading and the time-varying signal propagation resulting from vehicular motions introduce intersymbol interference (181) and random Doppler fading. In order to combat intersymbol interference (181) and rapid time dispersion variation in wireless communications occurring over frequency selective fading Multipath channels, we investigated a efficient channel estimation and equalization receiver structure to combat the wireless fading.In this paper, we propose a VHF aeronautical channel model and suggest typical and worst-case parameter sets and present a channel emulator, which is easy to implement on digital computers or in hardware. Then we address the issue of the rapidly time-varying DCR channel by employing block adaptation based on a signaling format consisting of contiguous frames of transmitted data within a long TDMA time slot. Specifically, the start of each data frame contains a known training sequence, which is used to estimate the impulse response. In the period of the training data, we used an optimal windowed recursive least squares (OW-RLS) algorithm to estimate the CIR. This is the first stage of the channel estimation. And in the second stage, we utilize linear interpolator to yield channel estimates in the data segment of the packet. The interpolator weights are adjusted optimally, depending on the SNR in each acquired channel tap.After we obtained the channel estimation, the next work we should do is to present an algorithm for mapping the channel parameters to the equalizer efficient. Here we utilize the simple T-spaced equalization structure. And in the algorithm we further revise the equalizer efficient by minimizing the noise effects.The algorithm performance is shown by analysis and simulation using MAILAB in the condition of different SNR, different maximum Doppler frequency shift and different normalized sampling rate.