In a wired/wireless communication system, an original signal is restored from a received signal by modulating the received signal through a radio frequency (RF) module and an intermediate frequency (IF) module. Due to the incompleteness of an analog local oscillator in the RF/IF module, a signal having a carrier frequency error is inputted into a demodulator during baseband down-conversion. Also, a signal having a Doppler frequency error is inputted into a demodulator. The frequency errors disable the received signal from being recovered. Therefore, the received signal is generally restored after the frequency errors are removed from the received signal through a frequency restoring circuit in a baseband.
Although the frequency errors are removed from the received signal, a phase error is remained in the received signal. The remained phase error is shown as a predetermined phase pattern with irregular noise. Although the phase error is very small, the phase error significantly degrades the performance when a receiver employs an error correction code such as a turbo code that provides superior performance in a low signal-to-noise ratio. In order to overcome such a drawback, a conventional method for estimating a phase error was introduced in an article by Vincenzo Lottici and Marco Luise, entitled “embedding Carrier Phase Recovery Into Interactive Decoding of Turbo-Coded Linear Modulation”, IEEE transactions On Communications, Vol. 52, no. 4, April, 2004. In the conventional method for estimating a phase error, a maximum likelihood (ML) mode is applied into the phase error estimation.
The conventional method estimates the phase error under an assumption that a phase error model is uniform in one data block. That is, the conventional method considers a comparatively simple phase error model for estimating phase error. Also, the conventional method uses the average of all symbols to obtain the probability value of transmission symbols obtained from a turbo decoder.
In order to restore a received signal in a TDMA satellite communication system, the carrier phase error must be corrected. Especially, a system using an error correction code such as a turbo code requires a noise-resistant phase correction method because a small phase error significantly degrades performance in the system using an error correction code such as a turbo code operated in a low signal to noise ratio.
USPTO Backgrounds
USPTO Backgrounds