Successive pairs of OFDM symbols are transmitted by an OFDM transmitter and received by an OFDM receiver. The successive pairs include a first pair of OFDM symbols. First and second OFDM symbols of the first pair both include pilot symbols on two subcarriers that are symmetric about a center carrier frequency. The two subcarriers are the same for the first and second OFDM symbols. The pilot symbols on the two subcarriers for the first and second OFDM symbols compose an orthogonal matrix. The OFDM receiver estimates frequency responses at frequencies including the frequencies of the two subcarriers and compensates for signal impairment based at least in part on the estimated frequency responses.