GB2441805A

GB2441805A - Testing Television Signals using a Mobile Device

Info

Publication number: GB2441805A
Application number: GB0618228A
Authority: GB
Inventors: Russell Inman; Phillip Osborne; Steven Carr; Richard Ashley Mason
Original assignee: NAT GRID WIRELESS Ltd
Current assignee: NAT GRID WIRELESS Ltd
Priority date: 2006-09-15
Filing date: 2006-09-15
Publication date: 2008-03-19
Also published as: GB0618228D0; GB2441837A; GB0706804D0

Abstract

A mobile television signal testing apparatus comprising receiving means for receiving a television signal; a screen for displaying an image generated from the received television signal; a detector for detecting at least a part of the image; and output means for outputting a signal derived from the detector, for providing a measure of the reception quality of the received television signal. The detector may be a photodetector, and the mobile television receiver may also comprise a mask for shielding the photodetector from extraneous light. The mask may be removable from the mobile television receiver, and the photodetector may be attached to the mask. Alternatively, the detector may be an internal detector which directly detects an electronic signal from the video decoder output.

Description

2441805

1

Mobile Television Signal Testing Apparatus

The present invention relates to an apparatus for signal testing, and in particular, to a mobile apparatus for testing of television signals.

In recent years, there has been a convergence of television, multimedia services, and mobile applications. It has become common for mobile devices such as mobile telephones and PDAs (personal digital assistants) to be capable of browsing the internet, displaying movie clips, sending picture messages, and many other multimedia applications. One particular recent application is the ability to view television broadcasts on a mobile device such as a mobile telephone. The DVB-H standard defines features to make this practical. For example, it defines a time slicing process to maximise the battery life of a mobile device by receiving data in bursts, and switching off its receiver between the bursts. The DVB-H standard also defines forward error correction parameters to minimise problems with mobile environments.

One problem with mobile television reception, either using a dedicated mobile television set or using any other mobile device, is that the signal quality may vary considerably as the physical location of the mobile television receiver is changed. This is not such a problem for fixed-position television receivers, because a fixed television antenna may be adjusted to a position of maximum signal strength. However, in a mobile situation, the physical location of the antenna is constantly changing and hence the quality of the displayed video and audio can be subject to large variations which, at one extreme, may be a loss of service.

Service may be impaired or lost completely by a wide-range of radio propagation mechanisms. The most obvious is a prevailing signal level below the threshold of the receiver i.e. insufficient power flux density at the point of reception. However, many other mechanisms exist which can impair reception and these may occur, for example, due to interference caused by reflections off buildings or geographical features,

2

scattering, diffraction or other phenomena. Where multiple receive paths are present, the distance between a location with a minimum signal strength and a location with a maximum signal strength may be very small, e.g. on the order of a few centimetres or metres. Thus, a person using a mobile television receiver in a mobile environment may experience frequent disruption to the signal as they move from regions of maximum signal strength to regions of minimum signal strength.

To address these problem with signal reception, it is possible to add extra transmitters to cover regions in which low signal strength andAx nulls are a particular problem, or to improve coverage and signal quality by adjusting the transmission power, transmitting antenna orientation, or other parameters associated with one or more transmitters. To identify the locations of the nulls, a mobile test apparatus may be used.

A wide-range of equipment is available for measuring technical parameters pertaining to the received signal such as received signal strength and bit error rate. These can be logged and, when combined with positional information such as that from a GPS receiver, can be used to display the measured values on a map. However, as useful as these technical parameters are, they do not intrinsically indicate the subjective performance; that is, the service as viewed or heard by the user of the receiver. Extrapolations can be made between technical parameters (setting thresholds) and the anticipated subjective service but these are predictive and not absolute.

In modern mobile TV systems, the use of a high degree of Forward Error Correction (FEC) means that the failure profile is very steep (also known as the 'waterfall' curve). This means that the difference in Bit Error Rate (BER) between a fully working service (as defined by an unimpaired moving picture) and a failed service (as defined by a loss of picture or a frozen picture) can be very small. In most decoding systems, this means that the received video as displayed on the receiver is usually one of two states - either fully functional or not functional, e.g. frozen (static) or a black screen. There is a small intermediate state where the picture still has motion (but has impairments such as 'blocking') but, as stated, due to FEC in mobile systems, this is over a very small range of BER.

3

One aspect of the present invention provides a mobile television signal testing apparatus comprising receiving means for receiving a television signal; a screen for displaying an image generated from the received television signal; a photodetector for detecting at least a part of the image on said screen; and output means for outputting a signal obtained using the photodetector, for providing a measure of the reception quality of the received television signal. The mobile television signal testing apparatus may be used for testing a television signal in different locations.

Embodiments of the present invention allow a measure of the subjective performance to be ascertained and presented to the logging equipment alongside technical parameters such as received signal strength and bit error rate.

Embodiments of the present invention determine whether the displayed video is frozen or has a blank screen. This status is then relayed to logging equipment. As discussed above, it is then possible to ascertain with reasonable certainty how the actual mobile television service performs at given geographical locations in terms of the video output displayed rather than just from technical parameters.

In some embodiments, a mask may be provided for shielding the photodetector from light sources other than said screen. The photodetector may be attached to the mask. The mask may be a removable mask, for example, it may comprise a velcro™ strip.

Signal processing circuitry may be provided for comparing the detected signal with a predetermined test pattern. The signal processing circuitry may be adapted to allow a selection from a number of different test patterns, and it may be programmable to allow new test patterns to be added.

The output means may simply output the detected signal from the photodetector, or a processed version of this signal. For example, the processed signal may be processed to remove noise, to convert to a suitable digital format, and/or to compare the photodetector output with a predetermined test pattern. The output means may provide a digital output indicating a result of a comparison of the photodetector signal with a test

4

pattern. Any deviation from the known test pattern sequence may be indicated via such a digital output and may operate in real-time.

Storage means may be provided for storing an output from the output means or for storing a signal derived from this output. The storage means may be separate to the mobile television receiver, or may be attached to the mobile television receiver, or may be built into the mobile television receiver.

In some embodiments of the present invention, the photodetector and/or signal processing circuitry is attached to the mobile television receiver as an ancillary item. In other embodiments, the photodetector and/or signal processing circuitry is built in to the mobile television receiving apparatus.

However, in a further aspect of the invention, the detection of the video pattern as output by the video decoder in the receiver is carried out in software, or with in-build circuitry, and is integral to the receiving device. In this way, the need to display the video and then detect the pattern with a photodetector is circumvented. In such embodiments, it is not essential that the television receiver is provided with a screen, e.g. embodiments of the invention could be used with a digital television receiver which is configured to output a video signal to an external screen.

Thus, a further aspect of the invention comprises a mobile television signal testing apparatus comprising receiving means for receiving a television signal; generating means for generating a video signal comprising an image generated from the received television signal; detection means for detecting at least a part of the image; and output means for outputting a signal obtained using the detection means, said signal providing a measure of the reception quality of the received television signal.

Embodiments of the invention may be implemented wholly or partially as software running on a mobile television receiver apparatus.

The mobile television receiver and/or the logging equipment may be provided with a geographical positioning system for detecting a current physical location of the mobile

5

television receiver. This may be a GPS device, or some other type of positioning system.

The mobile television receiver may comprise a dedicated television receiver, or another type of mobile electronic device such as a mobile telephone or PDA.

Other aspects of the present invention do not themselves include a television receiving apparatus, but can be used with any existing television receiving apparatus. Benefits of the invention may be obtained due to the test waveform used and the associated ancillary equipment that detects and analyses the received waveform, rather than the particular television receiver used to detect the signal.

A further aspect of the invention comprises a mask for a mobile television receiver screen, the mask comprising a photodetector for detecting an image on at least a part of said screen; an opaque material for shielding the photodetector from light that is not generated at the screen; and an output for outputting a signal to indicate whether or not the displayed video correlates with the test waveform.

A yet further aspect of the invention comprises a method of testing a television signal reception quality in a chosen location, the method comprising receiving a television signal on said mobile television receiver, wherein said television signal may be displayed as an image on a screen of the mobile television receiver or on an external screen; using a photodetector or other detection means for detecting at least a part of the image; comparing a signal obtained using the photodetector or other detection means to an expected signal corresponding to a predetermined test pattern; and outputting a measure of the reception quality of the received television signal using said comparison.

The method may further include detecting a geographical position of the mobile television receiver and storing said geographical position together with said measure of the reception quality. A measure of the reception quality may be determined at a plurality of geographical positions, and a map of the signal reception quality over a selected area (e.g. a room, a building or an outdoor area) may be generated.

6

Embodiments of the present invention are intended for use with television receivers which receive a wireless television signal from a television transmitter. The wireless television signal may be a digital signal or an analogue signal, and may be transmitted using radio waves, or some other type of signal carrier.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic diagram of a mobile television network and a television receiver in an embodiment of the invention;

Figure 2 is a block diagram showing a more detailed view of the television receiver and signal conditioning unit of figure 1.

Figure 1 shows an example of a mobile television transmission network 100, which transmits digital television signals. A television receiver 150 is used to receive a signal transmitted from the mobile television transmission network 100, in an embodiment of the invention, and to measure a reception quality of the signal.

A test signal is generated for the mobile television transmission network 100 using a signal generator and encoder arrangement. Firstly, a video signal generator 104, which may be an analogue signal generator, is used to generate a video signal, for example, a test pattern. The test pattern may follow a pre-defined sequence (including the video content and the timing of the changes of that content). The video signal output of the video signal generator 104 is sent to a video input of an encoder 105. At the encoder, the video signal is converted into a suitable digital signal format. In some embodiments, the video signal generator 104 and the encoder 105 may be combined in a single device.

The encoder output is sent to an IP encapsulator and multiplexer unit 120, where the digital data is encapsulated into a digital video transport stream, e.g. an MPEG-4 transport stream. The IP encapsulator and multiplexer unit 120 also receives inputs from other encoders 110, which it encapsulates into digital video transport streams. These other encoders 110 may include test channels and/or normal television or multimedia

7

broadcast services. The multiplexer in the IP encapsulator and multiplexer unit 120 combines multiple transport streams from different encoders, to increase the bandwidth utilisation. The signal is then output to the mobile television transmission network 100, where it is broadcast from one or more transmitters.

The signal generated by the video signal generator 104 preferably corresponds to a type of test pattern, for example, switching between black and white at a fixed rate, e.g. 25 times per second. Other types of test pattern may alternatively be used, e.g. a uniform screen colour, a striped pattern, a rectangular pattern, a pattern of graduated brightness, etc. The test pattern may be colour, greyscale or black and white. The test pattern may be a stationary pattern, or it may change at predetermined time intervals, or the test pattern may be a pattern that moves across the screen of a television receiver.

The broadcast television signal is detected by a mobile television receiver 150, via an antenna 151. The structure of the mobile television receiver 150 is shown in more detail in figure 2.

Figure 2 shows a schematic diagram of the mobile television receiver 150, in an embodiment of the invention. The mobile television receiver 150 has an antenna 151 for detecting a television signal, a screen 152 for displaying a television picture, and a keypad 153 or other user input device. The keypad may be configured to allow a user to select the channel, and other parameters such as brightness, contrast, volume, etc. The screen 152 may be a colour screen, a greyscale screen or a monochrome screen. The screen 152 may be an LCD screen, or may use some other type of display technology.

The mobile television receiver 150 may be a dedicated television receiver, or it may be a multi-purpose mobile device such as a mobile telephone, PDA, or portable computer that is capable of receiving and displaying television signals. It may be an off-the-shelf consumer device that has been adapted for making test measurements, or it may be a dedicated test device.

The mobile television receiver has a photodetector 155 attached to the screen 152. The photodetector 155 may be a photodiode, a phototransistor, or some other type of light

8

detection element. The photodetector 155 may be monochromatic, or may be a colour detector. It may be a single pixel detector or a multi-pixel detector. The purpose of this photodetector 155 is to detect light emitted by the screen of the mobile television receiver 150, and to generate a signal using this detected light, where the signal can be used to determine the quality of the image on the television screen. The quality of the image displayed when the mobile television receiver is in a particular location provides an indication of the television reception quality at that particular location.

When a test pattern is transmitted from the mobile television transmission network, this test pattern is received by the mobile television receiver, and displayed on the screen 152, where the quality of the image on the screen indicates the quality of the signal reception at the mobile television receiver. The photodetector detects at least a part of this displayed test pattern and outputs a signal from which a measure of the reception quality of the television signal can be derived.

In the embodiment of figure 2, the mobile television receiver 150 is provided with a mask 154. The purpose of the mask is to shield the photodetector 155 from extraneous light, e.g. daylight, artificial room light, etc, so that the photodetector output provides a measure of light emitted from the screen 152 of the mobile television receiver 150. Optionally, the mask 154 may also provide a means of attaching the photodetector 155 to the screen 152. The photodetector may be physically attached to the mask, or in embodiments where it is not physically attached, the mask may be designed to hold it in place against the screen.

The mask 154 may be a fabric mask, a plastic mask, a paper mask, or some other type of mask. The mask comprises an opaque material, to absorb light from sources other than the screen area to be detected.

In some embodiments, the photodetector may be positioned at any part of the screen. For example, in an embodiment where the test pattern switches between a black screen and a white screen at a predetermined rate, any area of the screen can be used by the photodetector to detect this switching. However, it may be preferable to avoid edge areas of the screen, in order to maximise the signal detected by the photodetector.

9

In alternative embodiments, the photodetector may be positioned in a specified location on the screen. For example, it may be used to detect the presence or absence of a boundary within a non-uniform test pattern on the screen. For a high quality signal, this boundary may be sharp and crisp on the screen, but for a low quality signal, this boundary may be blurred by noise. In yet further embodiments, a plurality of photodetectors may be provided on the screen, and their signals may be compared or combined to detect the image quality on the screen.

The mask 154 may attach to the screen by straps, such as velcro™ straps, or the mask may be constructed as a velcro™ strip. Any alternative type of fastener strap or strip may be used instead of velcro™, e.g. any type of hook and loop fastener. Alternatively, the mask may be attached to the screen by a sleeve which sits over the body of the television receiver, by adhesive means, by mechanical attachment means e.g. using screws or other mechanical fasteners, or by any other means.

The mobile television receiver 150 may comprise a retail device for use by consumers to watch television or a multi-purpose consumer retail device such as a PDA, which is adapted for use in the invention by having the photodetector 155 attached to it, either directly or via the mask. Thus, the mask may be sized, shaped or otherwise adapted to fit a particular type or model of mobile television receiver, for example, it may be designed to fit onto a particular size of mobile telephone or to a particular type of PDA.

In the embodiment of figure 2, the output signal from the photodetector is sent to a signal conditioning unit 160. The signal conditioning unit 160 may include a filter to remove noise from the signal. The signal conditioning unit 160 includes an analogue to digital converter (ADC) for converting the analogue signal from the photodetector into a digital signal. The signal conditioning unit 160 may also have a phase locked loop (PLL) 162 and a comparator (163). The PLL and comparator allow a comparison of the signal detected by the photodetector with an expected signal for a particular test pattern. The output of the comparator 163 indicates whether the test pattern detected at the photodetector matches the test pattern that was transmitted by the mobile television transmission network. The required matching criteria may be different in different

10

embodiments- In some embodiments, a quantitative measure of the quality of the match may be output, and in other embodiments, a qualitative indication may be output. If the detected pattern does match the expected pattern, this indicates that a good quality signal has been received. If the detected pattern does not match, this indicates that the video output is not correlated with the test waveform and is therefore subject to an impairment. The output of the comparator may be sent to storage means, such as a hard disk drive, optical storage device, flash memory, etc.

In some embodiments, the signal conditioning unit 160 may also be attached to the mask 154. In other embodiments, the signal conditioning unit may be separate hardware which receives a signal from the photodetector, either via a wire or via a wireless link. In some embodiments, a storage device for storing the output signal from the comparator may be attached to the mask 154. For example, the signal conditioning unit and storage unit may be provided in a single packaging. In other embodiments, the storage device may be a separate unit, which receives a signal from the signal conditioning unit via a cable or via a wireless link. In further embodiments, the mobile television receiver itself may contain a data storage means which can be used to store the results of the signal test measurements. For example, where the television receiver is a PDA, the PDA is already provided with data storage memory. The signal conditioning unit may send the test data to the data storage means on the mobile television receiver using a wireless link, or using a cable, for example, a USB cable, which is plugged into the mobile television receiver. The above described wireless links may be Bluetooth links, infrared links, wireless LAN links, or some other kind of wireless link.

In other embodiments, the correlation of the signal at the output of the receiver's video decoder with that of the test waveform may be carried out digitally and therefore would obviate the need for the photodetector. For example, the receiver may contain processing circuitry that analyses the digital data between the decoder output and the screen and directly interprets the signal without the need for it to be displayed as a light source on the screen. Whilst this may offer advantages in terms of ease of use and operational convenience, one of the principal advantages of some embodiments of the current invention is that they can be applied to any receiver which has a video display.

11

With an integrated detection mechanism that analyses the electrical output from the video decoder rather than employing a photodetector, it may be possible for the test waveform to be part of a standard television signal but occupying a very small area of the active visible area. This would obviate the need for a specific channel carrying only the test waveform.

The photodetector, signal conditioning unit, and/or storage device may be powered from the power supply of the mobile television receiver, or may have their own separate power source.

The mobile television receiver may be provided with a device to indicate its physical location, such as a GPS (Global Positioning System) device or any other type of geographical positioning system. The position of the device may be stored in the storage means together with the corresponding signal quality data. This may subsequently be used to identify areas with particularly poor reception of the television broadcast.

While the invention has been described in terms of what are at present its preferred embodiments, it will be apparent to those skilled in the art that various changes can be made to the preferred embodiments without departing from the scope of the invention, which is defined by the claims.

Claims

CLAIMS: 12

1. A mobile television signal testing apparatus comprising:

receiving means for receiving a television signal;

generating means for generating a video signal comprising an image generated from the received television signal;

detection means for detecting at least a part of the image; and output means for outputting a signal obtained using the detection means, said signal providing a measure of the reception quality of the received television signal.

2. The apparatus of claim 1, further comprising a screen for displaying said image.

3. The apparatus of claim 1 or claim 2, wherein the detection means is a photodetector for detecting at least a part of the image displayed on said screen.

4. The apparatus of claim 3, further comprising a mask for shielding the photodetector from light sources other than said screen.

5. The apparatus of claim 4, wherein the photodetector is attached to the mask

6. The apparatus of claim 4 or claim 5, wherein the mask is a removable mask

7. The apparatus of any one of claims 4 to 6, wherein the mask comprises a hook and loop fastener strip.

8. The apparatus of any one of claims 1 to 7, further comprising signal processing circuitry for comparing the detected signal with a predetermined test pattern.

9. The apparatus of claim 8, wherein said output means comprises a logic output indicating a result of said comparison.

10. The apparatus of any previous claim, further comprising storage means for storing said output signal or a signal derived from said output signal.

13

11. The apparatus of claim 10, wherein the storage means is built into the mobile television receiver.

12. The apparatus of claim 1, wherein the detection means is built into the mobile television receiver, the mobile television receiver further comprises built in signal processing circuitry, and wherein said output is configured to output an indication of the received signal quality.

13. The apparatus of any previous claim, further comprising a geographical positioning system for detecting a current physical location of the mobile television receiver.

14. A mobile telephone or PDA configured as the mobile television receiver according to any previous claim.

15. A mask for a mobile television receiver screen, the mask comprising: a photodetector for detecting an image on at least a part of said screen;

an opaque material for shielding the photodetector from light that is not generated at the screen; and output means for outputting a signal obtained using the photodetector, for providing a measure of the reception quality of the received television signal.

16. The mask of claim 15, wherein the photodetector is attached to the mask

17. The mask of claim 15 or claim 16, wherein the mask comprises a hook and loop fastener strip.

18. The mask of any one of claims 15 to 17, further comprising signal processing circuitry for comparing the detected signal with a predetermined test pattern.

19. The mask of claim 18, wherein said output means comprises a logic output indicating a result of said comparison.

14

20. The mask of any one of claims 15 to 19, further comprising storage means for storing said output signal or a signal derived from said output signal.

21. The mask of any one of claims 15 to 20, further comprising a geographical positioning system for detecting a current physical location of the mobile television receiver.

22. A method of testing a television signal reception quality in a chosen location, the method comprising;

receiving a television signal on said mobile television receiver, wherein said television signal is displayable as an image on a screen of the mobile television receiver or on an external screen;

using a detector for detecting at least a part of said image ;

comparing a signal obtained using the detector to an expected signal corresponding to a predetermined test pattern; and outputting a measure of the reception quality of the received television signal using said comparison.

23. The method of claim 22, wherein the detector is a photodetector, and said using a detector comprises detecting at least a part of the image on the screen using the photodetector.

24. The method of claim 23, further comprising detecting a geographical position of the mobile television receiver and storing said geographical position together with said measure of the reception quality.

25. The method of claim 24, further comprising determining a measure of the reception quality at a plurality of geographical positions, and generating a map of the signal reception quality over a selected area.

15

26. A mobile television signal testing apparatus comprising:

receiving means for receiving a television signal;

a screen for displaying an image generated from the received television signal; a photodetector positioned for detecting at least a part of the image on said screen; and output means for outputting a signal obtained using the photodetector, for providing a measure of the reception quality of the received television signal.