A common challenge in designing a wireless system is to overcome the effects of the wireless channel, such as multi-path propagation, and Inter-symbol Interference. and the ability of OFDM to combat the effects of multi-path propagation made it the modulation of choice for third and fourth generation networks. In OFDM system we transmit data symbols on a large number of subcarriers, and these data symbols exposed to changes in amplitude and phase, caused of noise and frequency selective fading and Doppler shift . To get the transmitted data at the receiver we must cope with these changes, so we need to know the channel response at every subcarrier and every symbol, and for that reason we use PILOTS and we use many methods to estimate the channel response depend on pilots, and the most important channel is LMMSE Method. We will discuss in these issue the wiener filtering method (LMMSE) which give best performance but it is very complicated, so we will use Discrete Fourier Transform (DFT) to reduce the complexity of these method and we will study the BER and MSE in both case when we use QPSK or 16QAM Modulation .