GB2477916A

GB2477916A - Multimedia redistribution device transmitting digital television signal through available white space.

Info

Publication number: GB2477916A
Application number: GB201002420A
Authority: GB
Inventors: Finbarr O'regan; Gerard Baldwin; David Naughton; Cormac De Frein
Original assignee: XERENET
Current assignee: XERENET
Priority date: 2010-02-12
Filing date: 2010-02-12
Publication date: 2011-08-24
Also published as: GB201002420D0

Abstract

Local distribution of multimedia content is performed by identifying available channels in the VHF/UHF spectrum in a local area, and transmitting the multimedia content using standard digital television signal as the modulation scheme. No adjustment to the digital television 20 receiver is necessary. The white space is analysed by means of a spectrum sensor 151 or a location unit 17. The spectrum sensor 151 can make use of time or frequency domain energy detection, wavelet spectrum estimation, covariance methods, matched filtering, spectral correlation, and higher order statistics. The location unit 17 determines the position of the device (for example through satellite or global positioning systems, GPS) and subsequently access geolocation databases 50 storing available stations. The conversion to a digital television format is operated via a transcoder 12 and a baseband processor 131. Examples of supported formats are: DVB-T, DVB-T2, DVB-H, DVB-SH, ATSC, ATSC-M/H, ISDB-T, 1seg, SBTVD, DMB-T, DMB-T/H, T-DMB.

Description

INTELLECTUAL

. .... PROPERTY OFFICE Application No. GB 1002420.6 RTM Date:22 March 2010 The following terms are registered trademarks and should be read as such wherever they occur in this document: Wi-Fl, MPEG, MP3, GIF, AVI, Ofcom, Windows, Blu-Ray, SONOS, Slingbox, Apple, BlackBeny, iPhone Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk

SYSTEM AND APPARATUS FOR DISTRIBUTING MULTIMEDIA CONTENT USING DIGITAL

TELEVISION SIGNALS

BACKGROUND

There are a wide variety of digital multimedia storage and playback devices available today which may be used with the present teaching including for example, digital versatile disk (DVD) players, compact disk (CD) players, laptops, personal computers (PC), set top boxes (STB), digital video recorders (DVR), digital video players, standalone hard drives, personal media players, universal serial bus (USB) drives, smart phones, the BlackBerryTM, the iPodTM and the iPhoneTM.

Whilst some of these devices comprise an integrated screen and\or audio output device (e.g. speakers or headphones) for viewing\listening to multimedia content, others require a connection to an output device for viewing and listening. Even where an integrated screen or audio output device is present, it may be desirable to connect the multimedia device to another for better performance. For example, a person with a laptop may wish to connect their laptop to a larger screen such as on a television for watching a movie or sharing a presentation with others.

A number of hardwired solutions exist for distributing digital multimedia content to digital televisions or displays. For example, a gateway or storage device may be connected to a digital television using an RF coaxial cable, a SCART cable, a HDMI cable, a S-video cable, a VGA cable, a DVI cable, an ethernet cable, a USB cable, a composite video cable or any other of a plurality of different types of cables which may carry digital multimedia content. A problem with these cables is that both the sending device and the television require a corresponding connector although converters exist to switch formats e.g. between DVI and HDMI.

In addition to hardwired solutions, a number of wireless solutions also exist for distributing digital multimedia content. In these wireless solutions, the cable employed in the hardwired arena is replaced with a wireless transmitter-receiver arrangement in much the same way as network communications over an Ethernet cable may be transmitted wirelessly using Wi-Fi or similar wireless technologies.

In fact, one possibility for distributing multimedia content is to use Wi-Fi technology and this is commonly employed for the distribution of low bandwidth multimedia content, for example audio, around buildings. Examples of such an audio system include the SONOSTM system from Sonos, Inc. of Santa Barbara, CA. For higher bandwidth content, the Wi-Fi link may not have the bandwidth required particularly in environments where there are a plurality of users and access points.

In addition, a number of proprietary methods exist capable of higher bandwidth transmission. These methods employ dedicated transmitters and receivers. Examples include US2004/0139477 which describes a wireless method of distributing multimedia content using proprietary modulation in the 60 GHz unlicensed frequency band and US2009/0235316 which describes a method in which multimedia content is parsed and transmitted over detected spectrum available in TV bands using a proprietary wavelet transform based transmission scheme.

Thus whilst wireless solutions may offer some advantages over wired solutions, a problem remains that a corresponding connector type or receiver is required at the end device to allow multimedia content to be received.

Summary

The present application addresses the problems of the prior art by providing a device that accepts multimedia content and transmits this content in a digital television broadcast signal within a determined channel which may be readily received by any digital television within range. Optionally, the digital television signal may be encrypted before transmission.

Suitably, the transmitted power of the television signal is limited to limit reception to within a small area of the transmitting device. The channel is one which is predetermined to be considered white space. A channel may be identified as a white space channel using geolocation database information or spectrum sensing or a combination thereof. The multimedia content may be received from a gateway or storage device which is connected to a transcoder followed by a baseband processor, and a combination of a transmitter and a cognitive radio engine, all of which are either located in, or connected to the gateway or storage device. The possible uses of the invention include but are not limited to video surveillance, television viewing, media streaming, internet browsing, IPTV streaming, and business presentation.

Suitably the transcoder of the device may convert multimedia content from its native signal format to a format suitable for digital television encoding. For example, whilst the primary format of digital television is typically an MPEG transport stream, the transcoder may accept multimedia content formats including video, audio, text, graphics and data formats, for example MP3, JPEG, GIF, AVI, MPEG-4.

The baseband processor is used to convert the transcoder output to an appropriate digital television signal format. The baseband processor may be adapted to provide more than one format of signal with the selected format being dependent on the region of operation of the device. The digital television signal formats which may be outputted may include one or more of the following: DVB-T, DVB-T2, DVB-H, DVB-SH, ATSC, ATSC-M/H, ISDB-T, iseg, SBTVD, DMB-T, DMB-T/H, T-DMB.

The device may comprise a cognitive radio engine. This engine is configured to perform spectrum sensing to detect at least one television channel that is fully unoccupied by a primary user. The term primary user1' refers to a licensed television broadcast, a wireless microphone system, or any other incumbent licensed wireless system. Optionally, the engine may, also detect and avoid television channels in which other cognitive radio systems are operating. Accordingly, a television channel would be determined to be available if its full width (for example, 6 MHz in the USA and 8 MHz in Europe) was not being used by a primary user, or, optionally another cognitive radio system. Spectrum sensing by the cognitive radio engine may be performed in a variety of ways, including but not limited to: time and/or frequency domain energy detection, wavelet spectrum estimation, covariance methods, matched filtering, spectral correlation, and higher order statistics.

As will be appreciated by those skilled in the art, the present application provides a low cost, spectrally efficient method of distributing multimedia content over unoccupied television channels. An advantage of the method is that no adjustment to the digital television receiver other than tuning may be required. The use of the television bands means that all the advantages associated with transmitting in the UHF/VHF bands apply. The application is spectrally efficient as available television channels in the licensed television bands are used to redistribute the multimedia.

The foregoing advantages are illustrative of those that can be achieved by the exemplary embodiments and are not intended to be exhaustive or limiting of the possible advantages that may be realised.

BRIEF DESCRIPTION OF THE DRAWINGS

The application will be more readily understood with reference to the following drawings wherein: Fig. 1 is a block diagram illustrating an embodiment of the invention wherein the output of a multimedia gateway or storage device is connected to the input of the device and transmitted on an available television white space channel in the form of a digital television signal. The multimedia gateway/storage device and the digital television do not form part of the invention but they are included in this figure to aid the description of the invention.

FIG2 is a flowchart of a method of transmitting multimedia content between a gateway or storage device and a digital TV over the television whitespace in the form of a digital television signal.

DETAILED DESCRIPTION

Much of the current wireless spectrum is licensed, leading to monopolisitic and therefore inefficient under-use of the resource. Spectrum regulators around the world are considering a less intrusive regulatory regime -one which allows multiple uses of spectrum, encourages innovation and maximizes the benefit to society of the finite usable spectrum. To do this, they have allowed unlicensed use of spectrum, for example the 2.4 GHz and 5.8 GHz unlicensed bands. In addition, spectrum regulators have recently allowed unlicensed low-power devices to operate in the television channels.

Spectrum allocated for television is divided into channels which are of fixed width. The exact licensed frequencies used for television broadcasting and the bandwidth of each television channel varies in different jurisdictions. For example, in the UK, the television band consists of the non-contiguous channels 21 up to 69, spanning 470 MHz -862 MHz, where each channel is 8 MHz wide. In the US, the television band consists of the non-contiguous channels 2 to 83, spanning 54MHz -890 MHz, and each of the channels is 6 MHz wide.

Historically, the licensed television bands were occupied by analog television broadcasters in formats such as PAL and NTSC. To mitigate against interference, television broadcasters on the same channel operate with a geographic separation. The use of low-power wireless microphones was also traditionally allowed in the television bands.

In recent years, advances in technology have allowed a switch from analog to digital television. Digital television offers improvements to viewers in terms of increased spectral efficiency, capacity, signal quality and user interactivity. (Examples of digital broadcast television standards include DVB-T, DVB-T2, DVB-H, DVB-SH, ATSC, ATSC-M/H, ISDB-T, lseg, SBTVD, DMB-T, DMB-T/H, T-DMB). The International Telecommunications Union (a UN agency) has agreed that the transition from analog to digital television should be completed by 17 June 2015. Some countries have already completed the transition to digital television (the US on 12 June 2009) while other countries anticipate to have made the transition by 2012 (many EU states). Some other states (for example the UK) are phasing digital television in on a rolling basis.

Coinciding with the transition from analog to digital television, a number of regulators have indicated that they may allow unlicensed devices to operate in the television white space provided no interference is caused to existing primary users -licensed television or wireless microphone services. Television white space consists of the unused spectrum in the television bands. This unused spectrum, also called interleaved spectrum in the UK, can vary from location to location. It can also vary temporally in any one location depending on primary user activity. The main unlicensed application identified for this white space is wireless broadband.

Unlicensed devices that operate in the television white space are called white space devices.

Some regulators (the FCC in the US and Ofcom in the UK) have already published rules which regulate the operation of white space devices in the unlicensed television white space spectrum. These rules are designed to facilitate the operation of white space devices in the television white space without causing interference to existing primary users. However, it will be appreciated that in some regions there may be no rules or the rules may differ from the ones which follow.

Typically the rules specify a number of performance requirements for white space devices, including transmit power levels, spectrum sensing capability, geolocation capability, and a requirement to regularly consult a database of primary users.

For example Ofcom is currently proposing to limit the transmit power as follows: 4 dBm (adjacent channels) to 17 dBm EIRP (assuming a 0dB antenna gain) into an 8 MHz channel with a specified out of band performance.

White space devices must also be able to perform spectrum sensing, that is to observe the RF spectrum environment in order to detect primary users already operating in the television band. For example, Ofcom require white space devices to be able to sense digital and analog television signals down to -120 dBm, wireless microphone signals down to -126 dBm, and to perform this sensing once every second.

The regulations also require the device to be location aware to an accuracy of lOOm and to access information from a geolocation database containing details of licensed primary users.

The primary proponents and supporters of white space advocate its use for wireless broadband applications using contention transmission processes similar to those employed for Wi-Fi.

In contrast, the present application counter intuitively seeks to use the white space to broadcast a low power digital television signal to a local area. More particularly, the present application provides methods and systems for redistribution of multimedia content (video, audio, data, or graphics) within a small area from a gateway or storage device to a digital television using existing digital television formats over the television white space.

The application will now be described in greater detail by way of example with reference to an exemplary transceiver 10, as shown in Fig. 1, which is in communication with one or more digital television devices 20 in a uni-directional broadcast relationship. The term "digital television device1' refers to a device consisting of a television band receiving antenna, a digital television capable receiver and a display. The antenna 21 may be external and removeably connected to the television.

Transceiver 10 suitably comprises a transcoder 12, a transmitter 13, a transmit antenna 14, a cognitive radio engine 15, a sensing antenna 16, and a location unit 17. The transceiver can be implemented on an ASIC, a PCMCIA card, an external device with a USB connection, or any other suitable form factor and technology.

For illustrative purposes the output of a gateway or storage device 11 is connected to the input of the transcoder 12. A plurality of possible multimedia formats exist, including but not limited to: audio video interleave format, motion picture experts group format, Windows media video format, waveform audio file format, Windows media audio format, Ogg Vorbis audio format, text format, joint photographic experts group format, graphics interchange format, and bitmap format.

It will be appreciated that other sources\formats of multimedia are possible as well. For example, the device may be adapted to receive a VGA signal from a computer and provide this as an input to the transcoder. Similarly, an audio signal may be received as an input to the transcoder. It will be appreciated that where the input to the transcoder is not in digital form that conversion by an appropriate converter may be required.

Examples of gateway devices include, but are not limited to, a WiMAX router, a DSL router, a digital radio, a digital camera, or a set top box (receiving satellite or cable television).

Examples of storage devices include, but are not limited to, digital media disks (eg. CD, DVD, Blu-Ray), external hard-drives, digital video players (e.g. SlingboxTM, Apple television), personal media players, or smart phones (BlackBerryTM, iPhoneTM). It will be appreciated that the interfaces 111 -117 illustrated in Fig. 1 are not exhaustive and that a device may be provided with any combination of these and others or indeed be configured to provide just one interface.

The transcoder 12 converts the format provided by the gateway or storage device to a format suitable for digital television encoding. For example, in the embodiment of the invention shown in Fig. 1, this is an MPEG transport stream.

The transmitter 13 consists of a baseband processor 131 and a tunable radio frequency front end 132.

The baseband processor 131 is designed such that it can convert the output of the transcoder 12 to any one of a plurality of digital broadcast television formats including but not limited to DVB-T, DVB-T2, DVB-H, DVB-SH, ATSC, ATSC-M/H, ISDB-T, lseg, SBTVD, DMB-T, DMB-T/H, T-DMB, and any future digital television standard. This conversion may be performed in software or in hardware such as an ASIC.

The tunable radio frequency front end 132 modulates the digital television signal output by the baseband processor 131 to the frequency of a selected television channel. Techniques for the implementation of the tunable radio frequency front ends 132 would be familiar to those skilled in the art. For further information, the reader is referred to "RF Microelectronics", by B. Razavi, ISBN 0138875715, the contents of which are herein incorporated by reference.

In a simple arrangement the device may select the television channel based on a user input.

In such an arrangement, the user could use their television to check for an available channel. However, it will be appreciated that whilst this may work for digital television signals, it may miss other cognitive radio users in the channel.

Thus in the embodiment shown the television channel used for transmission is determined by a cognitive radio engine 15 which consists suitably of a spectrum sensor 151 and a channel controller 152. The function of the cognitive radio engine is to identify an available television channel in the television white space.

The channel controller 152 obtains information about the licensed primary user devices operating in its geographic location from a geolocation database 50. In the embodiment shown, the device is equipped with a location unit 17 and can therefore determine its own geographic location using technologies such as GPS, Wi-Fi or any other appropriate technique. The geographic coordinates may also be coded into the device upon installation for example by an installer, if its location is fixed or manually changed by a user as the location changes. Alternatively, if the multimedia content is obtained via a subscriber service, the geolocation coordinates can be obtained from the subscriber ID on the subscriber card. The location or the geolocation database may be pre-installed or retrieved from elsewhere, for example by means of a download from the Internet. It will be appreciated that the database need not be stored locally and the device may be adapted to interrogate a remote database with its location to obtain a list of candidate channels.

Similarly, where a user's position is fixed and predetermined, the geolocation database may be unnecessary and replaced with a database of candidate channels for the location. Such a database for example may be uploaded to the device using a suitable network connection or manually entered by a user through an input device such as a keyboard.

The channel controller uses the information provided by the geolocation database 50 and its own location to select a candidate transmit channel. A candidate channel is a channel that does not have a registered primary user at the location of the device. Before transmission, the device 10 suitably performs spectrum sensing using the spectrum sensor 151 to confirm that no primary user is operating in this candidate channel. If the spectrum sensor determines the television channel to be unoccupied the channel controller sets the carrier frequency of the device to the carrier frequency of that television channel.

The channel controller instructs the spectrum sensor 151 to check the availability of the candidate channel using spectrum sensing. Many different spectrum sensing techniques are described in literature, including but not limited to: time and/or frequency domain energy detection, wavelet spectrum estimation, covariance methods, matched filtering, spectral correlation, and higher order statistics. The implementation of spectrum sensors would be familiar to those skilled in the art and is accordingly not described in further detail. The spectrum sensor confirms the availability of the candidate channel to the channel controller.

A particular example of the operation and use of the device is now described with reference to Fig. 1 and Fig. 2.

This exemplary embodiment describes a user streaming a music video from the internet via a laptop (a gateway) and displaying this music video on a digital television using the method described in this invention. The example assumes operation in a European country, i.e. the television channels are 8 MHz wide and the digital television used is capable of receiving DVB-T.

As shown in block 200 of Fig. 2, the user boots the device and initiates video streaming from the internet.

The channel controller 152 first obtains its geolocation co-ordinates as shown in block 201.

In this specific example, the device obtains its location using a satellite positioning unit (the location unit 17). The satellite positioning unit may for example be a GPS, Galileo, GLONASS, or any other satellite positioning system.

With knowledge of the geographic location of the device (from the GPS unit 17), the channel controller 152 requests the candidate channels for the location of the device 10 from the geolocation database 50. A candidate channel is one that does not have a registered primary user at the location of the device. Before transmission, the device 10 may perform spectrum sensing to confirm that no primary user is operating in this candidate channel.

In this example, the white space database 50 communicates that channels 22 (478 MHz to 486 MHz in the UK), 24 (494 MHz to 502 MHz in the UK), 25 (502 MHz to 510 MHz in the UK), 30 (542 MHz to 550 MHz in the UK), and 34 (574 MHz to 582 MHz in the UK) are candidate channels (block 202), i.e. there are no primary users operating on these television channels.

The channel controller 152 chooses one of these candidate channels, e.g. channel 24, as a candidate channel as shown in block 203. The frequency range of the selected candidate channel (channel 24 in this example) is relayed by the channel controller 152 to the spectrum sensor 151.

The spectrum sensor 151 analyzes the frequency band 494 MHz to 502 MHz, corresponding to digital television channel 24, to determine if a primary user device is operating in this spectrum as per block 204.

As shown in block 205, the result of the spectrum sensing 151 determines whether the channel controller 152 proceeds to block 206 or returns to block 203. The channel controller 152 can proceed to block 206 if the spectrum sensor 151 does not detect a primary user on channel 24. If the spectrum sensor 151 detects a primary user device operating on channel 24, the channel controller 152 selects another channel from one of the remaining candidate channels (22, 25, 30 and 34, in this example).

This process is repeated until an available channel is identified.

As shown in block 200 upon booting the device, multimedia is streamed (in flash format) to the transcoder 12 from a cable modem 115.

The flash format stream is converted by the transcoder 12 to an MPEG transport stream as shown in block 207. The baseband processor 131 converts the MPEG transport stream to a DVB-T signal as shown in block 208. The radio frequency front end 132 modulates the DVB-T signal from baseband to the frequency of the available channel provided by the channel controller 152 and transmits the signal wirelessly to digital television 20 via transmit antenna 14 as shown in block 209.

Claims

CLAIMS1. A device for local distribution of multimedia content, comprising: a baseband processor for receiving the multimedia content in a format suitable for digital TV encoding and for converting said multimedia content into at least one digital television signal format; a channel selector for identifying an available television channel to transmit in; a transmitter for transmitting the digital television signal in the identified available television channel.
2. A device according to claim 1, wherein the output power of the transmitter is less than 2W EIRP.
3. A device according to claim 1 or claim 2, further comprising a transcoder for receiving multimedia content in a first signal format, wherein the transcoder is configured to convert the multimedia content from the first format to the format suitable for digital TV encoding and to provide this converted multimedia content to the baseband processor.
4. A device according to claim 3, wherein the transcoder is configured to convert a plurality of different multimedia signal formats to the suitable for digital TV encoding.
5. A device according to any preceding claim, wherein the channel selector comprises a spectrum sensor capable of detecting unoccupied channels in the television band spectrum and the channel selector uses the spectrum sensor when making a determination of an available channel.
6. A device as claimed in claim 5, wherein the spectrum sensor employs one or more of the following spectrum sensing techniques; a) time and/or frequency domain energy detection, b) wave let spectrum estimation, c) covariance methods, d) matched filtering, e) spectral correlation, and f) higher order statistics to analyze the television band spectrum for available television channels.
7. A device according to any preceding claim, wherein the channel selector determines one or more available channels using the location of the device.
8. A device according to claim 7, further comprising a location sensor for determining the position for the device.
9. A device according to claim 8, wherein the location sensor determines the position from a satellite positioning system.
10. A device according to any one of claims 7 to 9, wherein the device is configured to access a geolocation database, the geolocation database storing available stations in a plurality of locations.
11. A device according to any preceding claim wherein the digital television signal format is one of the following: DVB-T, DVB-T2, DVB-H, DVB-SH, ATSC, ATSC-M/H, ISDB-T, iseg, SBTVD, DMB-T, DMB-T/H, T-DMB.
12. A multimedia gateway comprising the device of any preceding claim.
13. A multimedia storage device comprising the device of any preceding claim.
14. A device for transmitting multimedia content in a digital TV signal format, wherein the device is configured to use one or both of the following methods to determine an available channel: a) spectrum sensing, and b) using the device position to determine an available channel from a geolocation database.
15. A method for local distribution of multimedia content, comprising: a) receiving the multimedia content in a format suitable for digital TV encoding, b) converting said multimedia content into at least one digital television signal format; c) identifying an available television channel to transmit in; d) transmitting the digital television signal in the identified available television channel.