Method for automatically searching a frequency range for signal channels in a receiver for digitally modulated signals, and receiver for applying such a method

• US 6,038,433 A
• Filed: 10/01/1997
• Issued: 03/14/2000
• Est. Priority Date: 10/02/1996
• Status: Expired due to Fees

• Current Assignee: Irdeto B.V. (MultiChoice Group Ltd.)
• Original Assignee: Irdeto B.V. (MultiChoice Group Ltd.)
• Inventors: Vegt, Arjen Van Der
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Woldetatios, Yemane
• Application Number:
  US08/942,158
• Time in Patent Office: 895 Days
• Field of Search: 455/161.1, 455/161.2, 455/161.3, 455/164.1, 455/164.2, 455/165.1, 455/169.1, 455/226.1, 455/226.2, 375/261, 375/279, 375/280, 375/281, 375/329, 375/332, 375/340, 375/345, 370/252
• US Class Current: 455/161.1
• CPC Class Codes: H03J 1/0091 provided with means for scanning over a band of frequencies H03J1/0058 takes precedence

Abstract

A method for automatically searching a frequency range for signal channels in a receiver for digitally modulated signals is described, each channel having a center frequency, a symbol rate, and a modulation type. The method comprises the steps of scanning the frequency range in first frequency steps corresponding with just less than half the minimum expected symbol rate of the channels, measuring the RF level at each frequency step and comparing the measured RF value with a threshold value, and, if the measured RF value is below the threshold value, continuing said scanning and measuring steps until the frequency range is fully scanned, and, if the measured RF value is above the threshold value, assuming the corresponding frequency as an indication of a digitally modulated signal channel and scanning a frequency area in second frequency steps to determine the edge frequencies of the channel, said second frequency steps being much smaller than said first frequency steps, determining the center frequency of the channel from said edge frequencies, and continuing said scanning and measuring steps for further signal channels until the frequency range is fully scanned.

Claims

1. Method for automatically searching a frequency range for signal channels in a receiver for digitally modulated signals, each channel having a center frequency, a symbol rate, and a modulation type, the method comprising the steps of

scanning the frequency range in first frequency steps corresponding with just less than half the minimum symbol rate of the channels that can be expected,

measuring the RF level at each frequency step and comparing the measured RF value with a threshold value, and,

if the measured RF value is below the threshold value, continuing said scanning and measuring steps until the frequency range is fully scanned, and,

if the measured RF value is above the threshold value, assuming the corresponding frequency as an indication of a digitally modulated signal channel and scanning a frequency area in second frequency steps to determine the edge frequencies of the channel, said second frequency steps being much smaller than said first frequency steps,

determining the center frequency of the channel from said edge frequencies, and

continuing said scanning and measuring steps for further signal channels until the frequency range is fully scanned.

2. Method according to claim 1, wherein, if the measured RF value is above the threshold value, the RF value is compared with the previous RF value, wherein the corresponding frequency is only assumed to be an indication of a digitally modulated channel if the RF value is within a predetermined range from the previous value.

3. Method according to claim 1, wherein the symbol rate is determined from the edge freqencies of the channel and wherein the modulation type is determined by trial and error.

4. Receiver for signals digitally modulated on a center frequency of a channel according to a modulation type and symbol rate, the receiver comprising a tuner, a demodulator for demodulating digitally modulated signals, and a control unit for controlling the tuner and the demodulator, wherein a narrowband RF level detector is provided receiving an output signal from the tuner and providing a RF level indication to the control unit, wherein said control unit is adapted to control the tuner for scanning a frequency range in first and second frequency steps, said first frequency steps corresponding with just less than half the minimum symbol rate of the channels that can be expected and said second frequency steps being much smaller than said first frequency steps, said control unit being adapted to control the tuner first to scan a frequency range at said first frequency steps until the output of the RF level detector provides an indication of a digitally modulated channel at a frequency and then to scan a frequency area around this frequency at said second frequency steps to determine the edge frequencies of the channel, wherein the control unit determines the center frequency from the edge frequencies found.

5. Receiver according to claim 4, wherein the control unit is adapted to compare the output value of the RF level detector with a predetermined threshold value, wherein this output value is further compared with the previous output value and the corresponding frequency is taken as indication of a digitally modulated channel if the output value is within a predetermined range from the previous output value.

6. Receiver according to claim 4, wherein the control unit determines the symbol rate of a channel from the edge frequencies.