1. Field of the Invention
The present general inventive concept relates to a carrier recovery apparatus usable with a vestigial side band (VSB) receiver and a method thereof. More specifically, the present general inventive concept relates to a carrier recovery apparatus using not only a pilot signal, but also upper and lower sidebands of a received VSB signal, and a method thereof.
2. Description of the Related Art
In order for a data receiver to accurately demodulate VSB-modulated data, it is necessary to minimize frequency offset and high levels of phase noise (jitter) generated from a tuner or an RF (radio frequency) oscillator used for data receiving. This procedure is called ‘carrier recovery’.
A digital broadcast system based on a VSB modulation method in conformity with the standards of the Advanced Television Systems Committee (ATSC) uses a pilot signal in a transmitting signal for carrier synchronization. Here, the pilot signal is a signal loaded on a carrier during the transmission for accurate carrier recovery.
FIG. 1 is a block diagram illustrating a conventional carrier recovery circuit 100 for phase detection. Referring to FIG. 1, the conventional carrier recovery circuit 100 comprises a multiplier 101, a pilot detector 103, a phase detector 105, a loop filter 107, and a numerically controlled oscillator (NCO) 109.
A received VSB signal is digitalized by an analog-to-digital converter (ADC) (not shown), and output as a baseband signal by the multiplier 101.
The pilot detector 103 detects a pilot signal from the baseband signal, and the phase detector 105 reads phase information of the pilot signal. There are many methods for reading phase information of the pilot signal, and a suitable method is selected depending on the application. The phase information read by the phase detector 105 goes through the loop filter 107, is converted to a frequency component through the NCO 109, and is multiplied with the received VSB signal by the multiplier 101 to output the baseband signal.
The above-described procedure is repeatedly performed according to a feedback operation until a phase error of the pilot signal becomes zero.
However, if the pilot signal in the wireless environment is corrupted, a received signal cannot be recovered properly. The unwanted pilot signal corruption occurs often in a multi-path environment, and eventually causes performance degradation of the VSB receiver. This problem can occur in any American digital broadcasting system using the VSB method.