Adaptive pilot design based on Doppler frequency shift estimation for OFDM system

In the Orthogonal Frequency Division Multiplexing (OFDM) system, pilot signals are transmitted for the receiving device to estimate the channel´s response. The interval of such pilot is often designed to accommodate the devices under most extreme channel conditions or the average conditions of the environment. This scenario design either results in unnecessary overhead that could have been used for data transmission otherwise, or causes the significant degradation of the system performance when the environment worsens. In this paper, we propose an adaptive pilot system with low complexity that sends pilot signals adaptively based on the Doppler frequency shift estimation. It reacts to the environment conditions and reduces the overall pilot overhead when the ideal performance is guaranteed. Furthermore, the placement of signals in channel and the flowcharts on both TDD and FDD systems to facilitate this adaptive operation have also been addressed. Simulation results show that the proposed scheme can remarkably improve the system performance with low pilot overhead compared to the conventional schemes.