Pilot schemes for time-varying channel estimation in OFDM systems

We compare diverse frequency-domain multiplexed pilot arrangement schemes for time-varying channel estimation in an orthogonal frequency-division multiplexing (OFDM) system. In the first scheme, the comb-type, only a fraction of the subcarriers is dedicated to the pilots, but the pilots are carried by each OFDM symbol. In the second scheme, the block-type, the pilots occupy all subcarriers, but such pilot OFDM symbols are interleaved with data OFDM symbols. The third scheme, the mixed-type, is a combination of the two previous schemes. Pilot-aided channel estimators are applied, which take into account the channel variation within one OFDM symbol. The performance of the three pilot schemes is compared for different channel situations. We will show that the comb-type scheme can be opted for estimating short but fast channels, while the block-type scheme is promising for long but slow channels. The mixed-type scheme yields a good tradeoff between these two channel situations.