Patent ID: 8542788
Filing Date: 2013-09-24
Classification: H04L

Abstract:
1. A blind scan system in a DVB-S system, comprising: an analog tuner for receiving a radio frequency (RF) signal of an antenna and tuning the RF signal down to a baseband according to a designated analog carrier frequency offset so as to produce an analog baseband signal; an analog to digital converter (ADC) connected to the analog tuner for converting the analog baseband signal into a digital baseband signal; a digital mixer for receiving the digital baseband signal and performing a frequency shifting on the digital baseband signal based on a digital carrier frequency offset, so as to produce an offset baseband signal; a digital auto-gain controller (DAGC) connected to the digital mixer for performing an auto-gain adjustment on the offset baseband signal to produce a gain adjusted baseband signal; a digital matched filer (DMF) connected to the digital AGC for filtering the gain adjusted baseband signal to produce a filtered baseband signal; a spectrum computation device connected to the digital matched filter for calculating and producing a spectrum of the filtered baseband signal; a spectrum parameter extractor connected to the spectrum computation device for calculating first and second cross points of the spectrum of the filtered baseband signal with a threshold based on a control signal configured by a controller, so as to calculate a coarse carrier frequency offset and a fine carrier frequency offset of the spectrum, and a fine symbol rate and a coarse symbol rate of the digital baseband signal, and generating the first cross point, the second cross point, the coarse carrier frequency offset, the fine carrier frequency offset, the coarse symbol rate, and the fine symbol rate to the controller; and the controller connected to the analog tuner, the digital mixer, the spectrum computation device and the spectrum parameter extractor for deciding the analog carrier frequency offset according to a search range of spectrum, and determining whether a signal is detected in the spectrum of the filtered baseband signal generated by the DMF, wherein, when there is no signal detected, the controller controls the analog tuner to shift main component of a spectrum of a signal under test to a working bandwidth of the DMF thereby acquiring parameters of the signal under test, calculates a digital carrier frequency offset of the spectrum of the signal under test based on a coarse carrier frequency offset of the spectrum of the signal under test, and controls the digital mixer to perform a frequency shifting on the digital baseband signal; wherein the analog tuner fetches a section of spectrum from the search range of spectrum and produces the analog baseband signal based on an analog carrier frequency offset designated by the controller, where the analog carrier frequency offset is a start of the search range of spectrum, and the controller arranges a first boundary and a second boundary based on the working bandwidth of the DMF, arranges a first mask index based on the working bandwidth and direct current (DC) part of the DMF, determines whether a signal is detected in the spectrum generated by the DMF based on whether the first cross point generated by the spectrum parameter extractor is greater than or equal to the first mask index, and determines whether a spectrum of the signal detected is included in the DMF based on whether the first cross point touches the second boundary or whether the second cross point touches the first boundary.