Reception apparatus performing turbo equalizations
Disclosed is a reception apparatus that has solved a problem that fluctuations cannot be followed immediately after a commencement of turbo equalization in a high-speed fading environment. A reception apparatus includes a soft interference canceller, an MMSE equalizer, a likelihood calculator, a de-interleaver, an SISO decoder, an information bit hard decision unit, a subtracter, an interleaver, a soft estimation value calculator, a zero storage unit, a known signal memory unit, a transmission path estimator, and a plurality of switches. At the time of equalization, the transmission path estimator uses, as a reference signal, a known signal stored in the known signal memory unit or an output of the MMSE equalizer. Meanwhile, at the time of a first equalization, the soft interference canceller is given a ‘0’ value from the zero storage unit as a reference signal.
1. A reception apparatus which receives a digitally modulated single-carrier transmission signal from a transmitter and performs turbo equalization, the reception apparatus comprising:
a transmission path estimator configured to perform a transmission path estimation between transmission and reception by using a received signal and a first reference signal;
an interference canceller configured to remove an interference signal from the received signal by using a second reference signal and an output of the transmission path estimator;
an equalizer configured to correct a phase and an amplitude of an output signal of the interference canceller;
a bit log-likelihood calculator configured to calculate bit log-likelihoods of an output signal of the equalizer;
a de-interleaver configured to restore a sequence of the bit log-likelihoods outputted from the bit log-likelihood calculator, which is arranged in a predetermined order at a transmission side, into an ordinary sequence;
an SISO decoder configured to perform soft-input soft-output error correction decoding on the bit log-likelihoods of which the sequence is restored by the de-interleaver;
an interleaver configured to rearrange the sequence of the bit log-likelihoods, which has undergone error correction in the SISO decoder, in the predetermined order;
a soft estimation value calculator configured to calculate soft estimation values by converting the bit log-likelihoods outputted from the interleaver into bit probabilities;
a first reference signal switch configured to select zero in the first iteration of the turbo equalization where the soft estimation value is not obtained, and select the soft estimation value in the second and subsequent iterations of the turbo equalization where the soft estimation value is obtained, so that the selected value is assigned as the second reference signal to the interference canceller;
a second reference signal switch configured to assign a known signal being held, instead of the soft estimation value, in a known signal section; and
a third reference signal switch configured to select the known signal in the known signal section or select the output signal of the equalizer in signal sections other than the known signal section, so that the selected signal is assigned as the first reference signal to the transmission path estimator.
2. The reception apparatus of claim 1 , wherein an equalized signal hard decision unit is provided between an output of the equalizer and the third reference signal switch.
3. The reception apparatus of claim 1 , wherein the interference canceller generates a replica signal corresponding to an intersymbol interference signal and removes the replica signal from the received signal, and
wherein the bit log-likelihood calculator calculates a distance between an ideal point in mapping of the digital modulation and the output signal of the equalizer, and calculates the bit log-likelihoods based on a minimum distance to an ideal point which becomes 0 and a minimum distance to an ideal point which becomes 1 for each modulation bit.