A Semi-blind Frequency-Domain Concurrent Equalizer for OFDM Systems

This paper proposes a semi-blind algorithm for frequency-domain (post-FFT) soft-decision concurrent equalization in OFDM systems. The objective is to improve system performance by increasing data throughput or decreasing power requirements, when compared with pilot based conventional channel estimation techniques. The constant modulus algorithm and the soft decision-directed technique were concurrently employed to adjust the coefficients of a post-FFT equalizer bank. The algorithm works in a semi-blind mode because it uses channel information, obtained from pilot subcarriers, to initialize and to supervise the equalizer bank when pilots are present, otherwise remaining blind in the equalization process. To support such a concurrent equalization, the system should provide pilot subcarriers only in the first symbol of each OFDM super-frame, allowing algorithm initialization when the receiver is turned on. In the remaining super-frame symbols, pilot subcarriers can be suppressed to increase the overall system throughput.