A blind algorithm is proposed in order to compensate for the phase noise resulting from imperfect oscillators in orthogonal frequency-division multiplexing (OFDM) systems over constant modulus modulation. In the proposed algorithm, one received OFDM symbol is partitioned into subblocks in the time domain and the phase noise over each subblock is approximated as its time-average. Under the approximation, the squared magnitude of the channel gain multiplied by the data symbol at each subcarrier is shown to be expressed in terms of these time-averages and the discrete Fourier transform (DFT) coefficients of the received samples at each subblock with zero padding. Based on the relation, the proposed algorithm compensates for the phase noise without pilot symbols. Numerical results show that the proposed algorithm outperforms conventional algorithms as well as it requires lower computational complexity.

An iterative algorithm employing decision feedback provided by either an equalizer or a channel decoder is proposed in order to compensate for the phase noise resulting from imperfect oscillators in orthogonal frequency-division multiplexing (OFDM) systems. In the proposed algorithm, the received OFDM symbol is partitioned into subblocks in the time domain and the estimate of the time-average of the phase noise at each subblock is used to compensate for the phase noise. A formula for the signal-to-interference-plus-noise ratio (SINR) after phase noise compensation is derived and its values are evaluated under a variety of conditions in order to demonstrate the efficiency of the proposed algorithm. Numerical results show that the proposed algorithm achieves performance close to that of an OFDM system without phase noise over a wide range of conditions, while requiring only one-half the complexity of the partial intercarrier interference reduction algorithm.

A new scheduling to reduce the complexity of a turbo equalizer (TE) combined with a low-density parity-check (LDPC) decoder is proposed. Simple metrics and criteria for the proposed scheduling are derived from its convergence behavior. The TE with the proposed scheduling monitors the status of its iterative process and determines whether additional equalization is needed or not. Based on the decision, it adjusts performing equalization and reduces the execution number of equalization. Consequently, this leads to lowering the overall complexity of the TE. Numerical results show that the proposed scheduling has lower complexity than conventional schedulings, while they have almost the same performance.

In this paper we propose a stopping rule for adaptive turbo equalizers based on low-density parity-check (LDPC) codes. Using an extrinsic information transfer (EXIT) chart, we analyze the convergence behavior of a turbo equalizer and devise an adaptive turbo equalizer with stopping rule. It monitors the status of iterative decoding and stops performing equalization when the decoding messages are reliable enough to converge successfully only by LDPC decoding. Simulation results show that the proposed scheme has lower complexity than the conventional schemes, while it has a similar performance.