Yüksek Mobilite Ortamında Kanal Kestirimi ve Eşzamanlama Algoritmalarının FPGA Üzerinde Tasarımı

Abstract

The aim of the thesis is to design channel synchronization and estimation method on FPGA for wireless communication between high speed air vehicles. In air-to-air wireless communication, the channel is exposed to high doppler and delay propagation. These values are increasing in high altitude aircraft. High latency propagation increases the number of multi-path components in the channel and as a result the complexity of the channel synchronization and estimation method increases. As a result of high doppler, the channel changes rapidly and the pilot symbols that can be used for estimation in the fast changing channel are reduced. For these problems, f-OFDM offers a good solution. With this method the band is divided into subbands and the symbol duration increases. Increasing the symbol duration reduces the destructive effect of the multi-path components. In-band noise is reduced in subbands and channel estimation, synchronization, and symbol detection processes become more robust.

f-OFDM modulation is recommended for high-speed aircrafts and the band is subdivided into same subband. Although each subband is unrelated, the physical environment for the subband channels is common. Therefore, it can be said that it has similar channel characteristics between subbands. Symbol timing should be done very well in the OFDM system. Failure to perform symbol timing causes problems such as the loss of orthogonality, carriers and inter-symbol interference between the sub-channels. The same problems apply in the f-OFDM system. In the thesis, symbol time estimation periodic pilot symbols for f-OFDM are proposed. A common pilot sequence is used for each subband and the timing error from the channel in each subband is equal. Accordingly, a single estimator can be used for time estimation of subbands. %Sum of the signals from each subband is used for time estimation. At the same time, the noise is reduced and the estimation error is reduced due to the sum of %the independent noises in the subband. The correlation between the signal obtained from the sum of the subband signals and the pilot symbols is used for time %estimation.

The air-to-air wireless communication have sparse channel property like rural channel. Sparse channel vector estimation method has been proposed suitable for f-OFDM system. This method uses the common features of the subband channels to find the position of the coefficients of the channel vector. The new method is proposed using the correlation method with the estimation of the sparse channel vector. Sufficient BER values were obtained as a result of simul