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This paper proposes an uneven pilot-assisted channel estimation (CE) technique for OFDM systems in mobile environments. We find that the prerequisites of most previous studies are using an equal spaced pilots pattern and sample-spaced channels. This is not the case in practical systems. According to conventional pilot-assisted estimators, we develop an improved channel estimation method based on the criteria of least square (LS) for IEEE 802.16e OFDM systems. In this practical system, pilots are not evenly inserted in the frequency band and the non-sample-spaced multipath delay leads to channel impulse response (CIR) leakage in the time domain. The proposed uneven pilot-assisted CE method is conducted in the frequency domain and it uses a linear model to approximate the time-varying characteristic of CIR in the frequency domain during each OFDM symbol. Analysis and simulations demonstrate its low computational complexity, good performance and practicability in actual OFDM systems.