Finite-alphabet based channel estimation for OFDM and related multicarriersystems

Novel blind channel estimators based on the finite alphabet property of inf ormation symbols are derived in this paper for OFDM and related multicarrie r code-division multiple access (MC-CDMA) systems. The resulting algorithms are applicable not only to standard OFDM transmitters with cyclic prefix, but also to the recently proposed zero padded OFDM transmissions that impro ve symbol recovery at the expense of altering the transmitter and complicat ing the equalizer. Based on FFT-processed received data, channel identifiab ility is guaranteed regardless of channel zero locations and various channe l estimation algorithms become available by trading off complexity for perf ormance. Unlike existing blind channel estimators, the proposed alternative s require short data records especially for PSK transmissions. The inherent scalar ambiguity is easily resolved because it has unit amplitude and phas e values drawn from a finite set. Decoupling channel from symbol estimation enables a phase-directed operation that improves upon decision-directed sc hemes that are known to suffer from error propagation. Practical issues are also addressed including the presence of frequency guard intervals, conste llation and power loading, various frame designs, coded transmissions as we ll as semi-blind and online implementations for systems with training seque nces. The algorithms are tested with simulations and also compared with exi sting alternatives in a realistic HIPERLAN/2 setting.