WO2010007581A1

WO2010007581A1 - Method and apparatus for detecting analogue and digital signals

Info

Publication number: WO2010007581A1
Application number: PCT/IB2009/053042
Authority: WO
Inventors: Frederic Pirot
Original assignee: Nxp B.V.
Priority date: 2008-07-14
Filing date: 2009-07-14
Publication date: 2010-01-21

Abstract

The present invention relates to an electronic apparatus for detecting analogue and digital signals comprising scanning means and a memory unit, wherein the scanning means are configured to perform at least one pre-scanning step of the available bandwidth so as to identify potential analogue and digital signals and store the result in a pre-scanning table comprised in the memory unit, wherein the scanning means are further configured to perform at least one digital scanning step by tuning on each signal listed as digital signal in the pre- scanning table, wherein the scanning means are further configured to perform at least one analogue scanning step by tuning on each signal listed as analogue signal in the pre-scanning table. Moreover, the invention relates to method for detecting analogue and digital signals.

Description

Method and apparatus for detecting analogue and digital signals

FIELD OF THE INVENTION

In the past most radio and television signals as well as amateur, police, military and other radio signals were analogue in nature and thus required analogue transmitter and receiver units. In the last decade digital transmission of television and radio signals of various kinds became more and more common which required the provision of digital devices, e.g. digital television and radio receivers. In order to update their equipment so as to allow for the reception of digital television signals the end users placed a set top box comprising a digital receiver on top of their analogue TV.

BACKGROUND OF THE INVENTION

In order to receive both analogue and digital signals the user has to use a hybrid device which allows for receiving and displaying both analogue and digital signals. Hybrid television sets which are becoming more and more popular, however, require a cumbersome and time consuming installation procedure in the course of which scanning for analogue and digital signals is carried out. Usually this scanning is split into two steps, namely a first step which comprises analogue scanning and a second step which comprises digital scanning. Naturally, the two steps may be swapped. The two successive scanning steps take a long time and thus TV makers are looking for solutions to speed up the scanning of the available analogue and digital television channels. In order to avoid detecting previously analyzed channels the hybrid device may, during the analogue scanning, leave out channels where the level was identified to be too low to allow reception of a valid analogue signal. However, even with these measures, the overall scanning still is very long. For a scanning of the VHF TV band (84 MHz), and the UHF TV Band (392 MHz), it will last typically, with a well-implemented system, between 4 and 9 minutes until an overall scanning is completed.

In US2005/0073614 Al a broadcasting receiver capable of performing a typical two-step scanning procedure is disclosed. In the first step an analogue tuner comprising an automatic gain control amplifier (AGC) scans the frequency bands for signals. When the AGC circuit detects a video signal an AV detection circuit checks whether there is a synchronizing signal. If a synchronizing signal is found the system controller of the broadcasting receiver stores the channel as an analogue channel in a memory. If a synchronizing signal is not found the system controller stores the channel as a digital channel in the memory. In a second step, which may be carried out independently from the first step, the digital tuner post-scans the digital channels so as to acquire digital transmission information.

The present invention is based on the object to provide an electronic apparatus capable of performing scanning of both analogue and digital signals within a much shorter time when compared to devices, especially TV sets, known from the prior art, and thus improving usability and convenience.

SUMMARY OF THE INVENTION

According to the present invention there is provided an electronic apparatus for detecting analogue and digital signals comprising scanning means and a memory unit. The scanning means are configured to perform at least one pre-scanning step of the available bandwidth so as to identify potential analogue and digital signals and store the result in a pre- scanning table comprised in the memory unit. The analogue and digital signals may be analogue or digital signals of any kind, e.g. TV or radio signals. According to the invention the scanning means are further configured to perform at least one digital scanning step by tuning on each signal listed as digital signal in the pre-scanning table. The scanning means are further configured to perform at least one analogue scanning step by tuning on each signal listed as analogue signal in the pre-scanning table.

The electronic apparatus according to the invention may be part of any hybrid receiver, e.g. a hybrid TV receiver or a hybrid radio receiver. The TV receiver may be adapted for any analogue or digital television system, such as NTSC, PAL or SECAM as analogue television system or DVB-T, DVB-S, DVB-C, DMB-T/H, ISDB, ATSC, SBTVD as digital television systems. The hybrid radio receiver may be adapted for any analogue or digital radio signals, e.g. AM, FM or DAB, DRM, FM IBOC, Satellite Radio (WorldSpace, Sirius, XM radio,...). The electronic apparatus according to the invention is configured to perform a three-step hybrid scanning procedure. Though this procedure comprises an additional scanning step when compared to conventional solutions it allows for a overall faster scanning procedure. In the first step a pre-scanning is performed by detecting and identifying all signals over the available bandwidth. The result of this pre-scanning step is then stored in a pre-scanning table comprised in the memory unit. In case of an analogue signal which has been detected during pre-scanning the pre-scanning table may contain the position of the carrier frequency and the analogue transmission standard (e.g. PAL-I in case of TV signals) received. In case of digital signal, e.g. an OFDM modulated digital signal (e.g. DAM, DRM, DVB-T), the table may contain, by way of example, the position of the center carrier and the width of the OFDM spectrum. This operation each lasts only a few milliseconds.

After completing the pre-scanning step the apparatus performs two scanning steps, namely a digital scanning step and an analogue scanning step. The digital scanning step may be carried out first. As an alternative, the analogue scanning step may be carried out first. In the digital scanning step the scanning means check the pre-scanning table with respect to the digital signals detected and tunes on the digital signals listed in the pre- scanning table. After successfully tuning on a digital signal, e.g. a digital TV signal, the scanning means may extract information from the signal and store in the memory unit. In the analogue scanning step the scanning means check the pre-scanning table with respect to the analogue signals detected and tunes on the analogue signals listed in the pre-scanning table. The scanning means may also extract information, e.g. program information, from the analogue signal and store it in the memory unit.

According to an exemplary embodiment of the invention the scanning means comprise a digital demodulator and an analogue demodulator, wherein the digital demodulator may be configured to perform the pre-scanning step. This has the advantage that the apparatus according to the invention may be designed using electronic components available on the market.

In another exemplary embodiment of the invention the digital demodulator may be an OFDM demodulator. This has the advantage that the FFT capability of the OFDM demodulator may be used in order to perform the pre-scanning step by spectrum analyzing the available bandwidth.

According to the present invention there is further provided a method for detecting analogue and digital signals, comprising the following method steps: pre-scanning the available bandwidth so as to identify potential analogue and digital signals and storing the result in a pre-scanning table; performing digital scanning by tuning on each signal listed as digital signal in the pre-scanning table, performing analogue scanning by tuning on each signal listed as analogue signal in the pre-scanning table. BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 is a flow chart showing a hybrid scanning procedure according to the prior art;

Fig. 2 is a flow chart illustrating digital scanning as part of the hybrid scanning procedure of Fig. 1 according to the prior art;

Fig. 3 is a flow chart illustrating analogue scanning as part of the hybrid scanning procedure of Fig. 1 according to the prior art;

Fig. 4 is a block diagram illustrating an electronic apparatus for detecting analogue and digital signals according to the invention; Fig. 5 is a flow chart showing a method for detecting analogue and digital signals according to the invention;

Fig. 6 is a flow chart illustrating pre-scanning as part of the method according to the invention shown in Fig. 5;

Fig. 7 is a flow chart illustrating digital scanning as part of the method according to the invention shown in Fig. 5;

Fig. 8 is a flow chart illustrating analogue scanning as part of the method according to the invention shown in Fig. 5;

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows a flow chart showing a hybrid scanning procedure according to the prior art. By way of example, the hybrid scanning procedure may be implemented on a conventional hybrid television set adapted for receiving and displaying analogue and digital TV.

In a start step 10 hybrid scanning is started. This start step 10 may be executed during first-time installation. As today's hybrid TV sets are replacement products for conventional analogue TV sets including a set-top box for receiving digital TV digital scanning and analogue scanning are performed consecutively in any sequence. In the present example analogue scanning 20 is performed first and digital scanning 30 is performed once analogue scanning 20 is completed. After completion of digital scanning 30 the hybrid scanning is terminated as symbolized by the step "scanning done" 40. In order to speed up the scanning procedure special techniques may be implemented, such as, when digital scanning is performed first, to avoid channels where digital signal has been identified during the previously done digital scanning or, during analogue scanning, to avoid channels where the signal level was identified to be too low to allow reception of a valid analogue signal. However, the overall scanning procedure still turns out to be very long, namely between 4 and 9 minutes for scanning the VHF TV band (84 MHz) and the UHF TV Band (392 MHz).

The digital scanning 30 in the scanning procedure as shown in Fig. 1 is illustrated in detail in Fig. 2 and comprises the following steps: In a first step 301 digital scanning is started. In 302 the digital tuner comprised in the conventional hybrid TV set checks whether the current frequency is the stop frequency, which may stand for the highest channel in the TV band to be scanned. If so, digital scanning is terminated in step 308. If the current channel is not the stop frequency the tuner is programmed on the center carrier «current_freq» of the channel (303). Then the tuner tries to lock the channel decoder on the channel (304). If the channel decoder is successfully locked on a channel then in step 305 it extracts available information from the transport stream (TS) signal and stores the center frequency «current_freq» of the current channel with associated information in a table (step 306). Then in step 307 the system will increment to the next channel and, after having checked whether or not the next channel comprises the stop frequency, the scanning is either terminated (308) or continued (303).

If the channel decoder cannot be locked on the channel it may report in 309 that no digital signal is available. In this case the tuner will increment to the next channel (step 307) immediately. In case no such report is issued and no lock occurs after time-out 310 (typically a few seconds) then step 307 is carried out. In digital scanning as described above the frequency step (increment) is equal to the pre-defined channel width (typically, 7MHz in VHF and 8MHz in UHF). For a scanning of the VHF TV band (12 channels 7MHz), and the UHF TV Band (49 channels 8MHz), it will last typically, with a well-implemented system, between 2 and 4 minutes. Fig. 3 illustrates analogue scanning 20 as part of the hybrid scanning procedure as shown in Fig. 1. Analogue scanning 20 comprises the following steps:

In a first step 201 analogue scanning 20 is started. In 202 the analogue tuner comprised in the conventional hybrid TV set checks whether the current frequency is the stop frequency. If so, analogue scanning is terminated in step 208. If the current frequency is not the stop frequency the PLL demodulator is programmed on current frequency (step 203). If the PLL demodulator is successfully locked on the current frequency in 204 then in step 205 the received analogue standard is determined and available information from the demodulated signal is extracted and the current frequency along with associated information is stored in a table (step 206). Then, in step 207 the PLL demodulator increments by a step of typically 1 or 2 MHz to the next frequency and, after having checked whether or not the next frequency is the stop frequency, the scanning is either terminated (208) or continued (203). If the PLL demodulator cannot be locked on the frequency after time-out 209 (typically a few seconds) then step 207 is carried out.

In analogue scanning as described above, the frequency step is equal to the PLL Frequency recovery range (typically, 1 to 2 MHz). For a scanning of the VHF TV band (84 MHz), and the UHF TV Band (392 MHz), it will last typically, with a well-implemented system, between 2 and 5 minutes. Therefore, conventional hybrid scanning of the available bandwidth will last 4 to 9 min.

In Fig. 4 a block diagram illustrating an electronic apparatus for detecting analogue and digital signals according to the invention is shown. The electronic apparatus 1 may be, by way of example, part of a hybrid TV set. Alternatively it may be part of any other device which requires detecting digital and analogue signals. The apparatus 12 shown in Fig. 4 comprises scanning means 2 and a memory unit 3, wherein the memory unit 3 is connected to the scanning means 2 for read and write access. Presently, the scanning means comprise a digital demodulator 2a and an analogue demodulator 2b. Both demodulators 2a, 2b are each connected to the memory unit 3 for read and write access. Further, the digital demodulator 2a and the analogue demodulator 2b are each connected to an antenna 4 which is optimized for receiving digital and analogue television signals. By way of example, the digital demodulator 2a is an OFDM demodulator for demodulating digital signals according to OFDM standards, e.g. DVB-T, ISDB-T, DMB-T or else. The analogue demodulator may be a known demodulator adapted for demodulating analogue television signals of any known standard, such as PAL, SECAM or NTSC.

According to the invention the scanning means 2 are configured to perform a pre-scanning step of the available bandwidth so as to identify potential analogue and/or digital signals and store the result in a pre-scanning table comprised in the memory unit 3. Presently, pre-scanning is performed by the OFDM demodulator 2a by analyzing the power density spectrum generated via the FFT module comprised in the OFDM demodulator 2a. Furthermore, the OFDM demodulator 2a is configured to perform digital scanning by tuning on each signal listed as digital signal in the pre-scanning table. The analogue demodulator 2b for its part is configured to perform analogue scanning by tuning on each signal listed as analogue signal in the pre-scanning table. During digital scanning ("digital post-scanning") and analogue scanning ("analogue port-scanning") the digital OFDM demodulator 2a and the analogue demodulator 2b each may extract information from the respective signals and store it in a post-scanning table comprised in the memory unit 3. Fig. 5 shows a flow chart illustrating a method for detecting analogue and digital signals according to the invention. The method may be carried out by an electronic apparatus as shown in Fig. 4. By way of example, the method may be implemented as a hybrid scanning procedure on a hybrid television set adapted for receiving and displaying analogue and digital TV.

In a start step 50 hybrid scanning is started. This start step 50 may be executed during first-time installation of the TV set. According to the invention, a pre-scanning step 60 is carried out as a first scanning step. Pre-scanning comprises scanning the full bandwidth to identify potential analogue and digital signals. The result of the pre-scanning is stored in a pre-scanning table. As already mentioned, this may be carried out by a digital OFDM demodulator as shown in Fig. 4.

In a second scanning step analogue scanning 70 ("post-scanning analogue") is carried out. This step 70 comprises checking the pre-scanning table with respect to the analogue signals detected during pre-scanning and tuning on the analogue signals listed in the pre-scanning table. The result of analogue scanning 70 may then be stored in an analogue scanning table. Moreover, information, e.g. program information, may be extracted from the analogue signal and stored. By way of example, the analogue scanning step 70 is carried out by the analogue demodulator 2b of apparatus 1 and the analogue scanning table as well as the information extracted from the analogue signals may be stored in the memory unit 3. It is to be understood that more than one analogue scanning step may be carried out. However, it is preferred to carry out only one analogue scanning step to save time.

In a third scanning step digital scanning 80 ("post-scanning digital") is carried out. This may be performed by the OFDM demodulator 2a which has already performed the pre-scanning step 60. Consequently, no additional hardware is needed. The digital scanning step 80 comprises checking the pre-scanning table with respect to the digital signals detected and tuning on the digital signals listed in the pre-scanning table. The result of the digital scanning may be stored in a digital scanning table. Furthermore, information may be extracted from the signals and stored in the memory unit 3. Both the digital scanning table and the information extracted from the signals may be stored in the memory unit 3 of apparatus 1. Again, more than one digital scanning step may be carried out. In case several analogue and digital scanning steps are carried out the order of the steps is arbitrary.

After completion of the scanning steps 70, 80 the scanning procedure is terminated (step 90). In Fig. 6 the pre-scanning step 60 of the method shown in Fig. 5 is illustrated in detail. The digital OFDM demodulator 2b of the apparatus 1 according to the invention utilizes its embedded FFT module in order to generate a power density spectrum of the television band to be scanned. This kind of analysis allows the channel decoder to estimate input characteristics. First, the type of signal can be determined, i.e. whether the signal is an analogue or digital signal (e.g. an analogue or digital TV signal). If an analogue television signal is detected pre-scanning provides at least the position of the video carrier and the analogue standard received. If a digital television signal is detected pre-scanning provides at least the position of the center carrier and the width of the spectrum. As shown in Fig. 6 the pre-scanning step 60 starts with step 601. In 602 the digital demodulator checks whether the current frequency is the stop frequency. If so, pre- scanning is terminated in step 608. If the current channel is not the stop frequency the demodulator tuner is programmed on the center carrier «current_freq» of the channel (603). After a timeout (a few milliseconds - step 604) information on the current channel is extracted (step 605). If the information extracted allows for a determination as to whether the signal is analogue or digital (606) the extracted information is stored in the pre-scanning table (step 607). The determination may be based on a likelihood. If the signal is too weak or too noisy for determining its characteristics, especially whether it is analogue or digital, then the tuner increments to the next channel (step 609). Analyzing an individual channel as described above lasts only a few milliseconds. During pre-scanning the frequency step is equal to the pre-defined channel width (typically, 7MHz in VHF and 8MHz in UHF). Pre-scanning of the VHF TV band (84 MHz) and the UHF TV Band (392 MHz) lasts typically between 1 and 5 seconds.

Fig. 7 illustrates the digital scanning step 80 ("digital post-scanning") of the flow chart shown in Fig. 5 in detail.

During digital scanning 80, only the channels identified as carrying potentially digital signals are further analyzed. For this, digital scanning is started in step 801. First, it is checked whether all channels which have been identified as carrying potentially digital channels ("digital flagged") have been tested. If so, digital scanning is terminated (step 808). Else, the demodulator tuner is programmed on the center carrier of the, by way of example, lowest potential digital channel (step 803). If the channel decoder locks on the channel (804) available information, e.g. program information, is extracted from the transport stream (TS) signal in step 805 and the digital channel is stored with the associated information in a digital channel table. Subsequently, the demodulator tuner is programmed on the next channel which has been "digital flagged" in the pre-scanning table (step 807).

If the channel decoder cannot be locked on the channel it may report in 809 that no digital signal is available. In this case the tuner will increment to the next channel (step 807) immediately. In case no such report is issued and no lock occurs after time-out 810

(typically a few seconds) then step 807 is carried out.

During digital (post-)scanning of a TV band only identified potential digital channels are tried. For a scanning of 10 potential digital channels with 6 real digital signals over 10, scanning will last between 1 and 3 minutes. Fig. 8 illustrates the analogue scanning step 70 ("analogue post-scanning") of the flow chart shown in Fig. 5 in detail.

During analogue scanning 70, only the channels identified as carrying potentially an analogue signal are further analyzed. In short: this is achieved by analyzing the table of potential analogue channels and trying to lock the channel decoder on the signal. In detail, analogue scanning is started in step 701. First, it is checked whether all channels which have been identified as carrying potentially an analogue signal ("analogue flagged") have been tested. If so, analogue scanning is terminated (step 708). Else, the demodulator

PLL is programmed on the "flagged channel" frequency (step 703) which may be, by way of example, the video carrier frequency of the lowest "analogue flagged" channel. If the PLL is locked on the video carrier position of the "analogue flagged" channel (704) then the analogue standard is determined (in case of TV signals). This may be dispensable in case the analogue standard has already been determined during pre-scanning

60. Moreover, available information, e.g. program information, is extracted from the demodulated signal in step 705 and the analogue channel is stored with the associated information in an analogue channel table. Subsequently, the demodulator PLL tuner increments to the next potential analogue channel according to the pre-scanning table (step

707).

If the PLL cannot be locked on the video carrier position after timeout 709

(typically a few seconds) then step 707 is carried out. During analogue (post-) scanning of a TV band only identified potential analogue channels are tried. For a scanning of 10 potential analogue channels with 6 real analogue signals over 10, it will last less than 1 minute.

Claims

CLAIMS:

1. Electronic apparatus for detecting analogue and digital signals comprising scanning means and a memory unit, wherein the scanning means are configured to perform at least one pre- scanning step of the available bandwidth so as to identify potential analogue and digital signals and store the result in a pre-scanning table comprised in the memory unit, wherein the scanning means are further configured to perform at least one digital scanning step by tuning on each signal listed as digital signal in the pre-scanning table, wherein the scanning means are further configured to perform at least one analogue scanning step by tuning on each signal listed as analogue signal in the pre-scanning table.

2. Electronic apparatus according to claim 1, wherein the scanning means comprise a digital demodulator and an analogue demodulator.

3. Electronic apparatus according to claim 2, wherein the digital demodulator is configured to perform the pre-scanning step.

4. Electronic apparatus according to one of claims 2 or 3, wherein the digital demodulator is an OFDM demodulator.

5. Electronic apparatus according to one of the preceding claims, wherein the scanning means are configured to generate a power density spectrum of the available bandwidth in the course of the pre-scanning.

6. Electronic apparatus according to claim 5, wherein the power density spectrum of the available bandwidth is generated via Fast Fourier Transform (FFT).

7. Hybrid television receiver comprising an electronic apparatus according to one of the preceding claims.

8. Method for detecting analogue and digital signals, comprising the following steps: pre-scanning the available bandwidth so as to identify potential analogue and digital signals and storing the result in a pre-scanning table; performing digital scanning by tuning on each signal listed as digital signal in the pre-scanning table, performing analogue scanning by tuning on each signal listed as analogue signal in the pre-scanning table.

9. Method according to claim 8, wherein the steps of performing digital scanning and analogue scanning each comprise extracting information from the respective signals and storing it in a post-scanning table.