engleski

Self-recovering equalization in an OFDM system with cyclic prefix

Orthogonal frequency division multiplexing (OFDM) is recently being used for high rate data transmission, both in wireless and in wired environment. Equalizer is very important part of any multicarrier system, especially when higher order constellations on individual subcarriers are used. Channel estimation is usually performed with the training sequence aided algorithms, and the equalizer is realized as an one-tap equalizer in a frequency domain. Changes of the channel transfer function may cause significant performance degradation if retraining is not applied. This paper proposes the use of the redundancy of the cyclic prefix to adapt coefficients of the equalizer. The cyclic prefix, originally used as a guard interval between succeeding symbols, is simply the insertion of last L symbol samples in front of the symbol, and it can be used as a redundant information from which equalizer coefficients can be estimated, without the need for the training sequence. For equalizer coefficient calculation, gradient algorithm is used.

DSP applications in communications; OFDM; cyclic prefix; blind equalization

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