Patent Application
20160219331
The present principles relate to communication systems and in particular to wakeup messages in digital television systems.
On Mar. 26, 2013, the Advanced Television Systems Committee (ATSC), which proposes terrestrial broadcasting digital television standards in the U.S., announced a call for proposals for the next generation (named ATSC 3.0) physical layer. ATSC 3.0 will provide even more services to the viewer and increased bandwidth efficiency and compression performance. This will require breaking backwards compatibility with the currently deployed version, ATSC A/53, which comprises an 8-VSB (8 level, Vestigial Sideband) modulation system. ATSC 3.0 is expected to emerge within the next decade and it intends to support delivery to fixed devices of content with video resolutions up to Ultra High Definition 3840×2160 at 60 frames per second (fps). The intention of the system is to support delivery to portable, handheld and vehicular devices of content with video resolution up to High Definition 1920×1080 at 60 fps. The system is also expected to support lower video resolutions and frame rates.
One of the main issues associated with the current ATSC standard is the vulnerability of the 8-VSB modulation system to multipath propagation and Doppler Effect. These impairments are present in the broadcast transmission environment, particularly in large metropolitan cities, and in the delivery to portable/handheld/vehicular devices (which ATSC intends to support). It is a consensus that multi-carrier modulation systems like, for example, the OFDM (orthogonal frequency division multiplex) modulation, are better choices of modulation to combat these impairments.
OFDM is a method of encoding digital data on multiple carrier frequencies. In OFDM, the sub-carrier frequencies are chosen so that the sub-carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver; unlike conventional FDM, a separate filter for each sub-channel is not required. The orthogonality allows for efficient modulator and demodulator implementation using the FFT (Fast Fourier Transform) algorithm on the receiver side, and inverse FFT on the transmitter side. In particular, the size of the FFT identifies the number of carriers in the OFDM modulation system. Frequency selective channels are characterized either by their delay spread or coherence bandwidth. In a single carrier system like 8-VSB, a single fade or interference can cause the whole link to fail, but in multi-carrier systems, like OFDM, only a few of the total sub carriers will be affected. This way, multipath fading can be easily eliminated in OFDM, with simpler equalization techniques than in single carrier systems.
When a new broadcast system is deployed in the US, as will eventually be the case for ATSC 3.0, one issue to consider is the requirement for broadcast systems to carry information related to the Emergency Alert System (EAS). The EAS is an American national public warning system that requires broadcasters, cable television systems, wireless cable systems, satellite digital audio radio service (SDARS) providers, and direct broadcast satellite (DBS) providers to provide the communications capability to the President to address the American public during a national emergency. The system may also be used by state and local authorities to deliver important emergency information, such as AMBER alerts (child abduction emergency) and weather information targeted to specific areas (e.g., tornadoes, blizzards, floods, etc.). Other countries may adopt similar systems.
For some receivers, in particular mobile and handheld devices, it is expensive in terms of energy consumption to keep the receiver powered up at all times to watch for this information. In many digital systems (e.g., DVB-T2 in Europe), a preamble is sent before the actual data, for each frame of data. The reason for the preamble signal is to allow for the receiver to quickly obtain timing and frequency lock as well as to describe the format of the data that follows (modulation parameters, FEC parameters, frame size, etc.). Typically, the preamble is constructed in such a way that it can be easily detected even when the receiver does not have timing and frequency lock.
The present principles propose to utilize the preamble of a multi-carrier (e.g., OFDM) based digital transmission system to indicate whether or not a special message (like the EAS messages) is available in the transmitted signal. As a result, the receiver periodically checks the preamble, which requires limited functionality and power and only completely wakes up if such a special message is detected. This results in power savings, particularly for portable and handheld devices.
The present principles provide methods and apparatuses which utilize the preamble of a multi-carrier modulation digital transmission system to indicate whether or not a special message (e.g., Emergency Alert System messages) is available for reception. When in power saving mode, the receiver periodically detects the preamble, which requires limited functionality and power, to check for the presence of such special messages. The receiver only completely wakes up additional functionalities if a special message is detected in the preamble. This results in advantageous savings in power consumption, particularly for portable and handheld devices, while having the capability of receiving special messages anytime.
According to one aspect of the present principles, an apparatus for transmitting a multi-carrier modulated signal is provided including: a source (111, 300) for providing data, the data divided into frames and including a wakeup message parameter which identifies whether or not a special message is included in the data; and a multi-carrier modulator (114) for modulating the data by allocating the data to a plurality of carriers in a plurality of modulation symbols, wherein the wakeup message parameter is included in a preamble symbol of a frame of data. The apparatus can further include a channel encoder (113) for channel encoding the data prior to the multi-carrier modulator.
According to one aspect of the present principles, an apparatus for receiving a multi-carrier modulated signal in power saving mode is provided, the apparatus including: a multi-carrier demodulator (124, 410) for periodically demodulating at least one preamble symbol of the modulated signal to create at least one demodulated preamble symbol, the at least one preamble symbol being at least one of a plurality of modulated symbols in a signal frame; and a signaling data detector (422) for detecting preamble data from the at least one demodulated preamble symbol and for recovering a wakeup message parameter from the preamble data, wherein the wakeup message parameter identifies whether or not a special message is included in the modulated signal. The signaling data detector may further wake up additional functional blocks if the special message is included, including: the multi-carrier demodulator (124, 410) for further demodulating additional modulated symbols of the modulated signal to recover the special message; and a display device to display the special message. The apparatus may further include a channel decoder (123, 420) for channel decoding the output of the multi-carrier demodulator prior to recovering the wakeup message parameter. The apparatus may further include a channel decoder (123, 420) for channel decoding the output of the multi-carrier demodulator prior to recovering the special message.
According to an aspect of the present principles, a method for transmitting a multi-carrier modulated signal is provided including: providing data (510), the data divided into frames and including a wakeup message parameter (520) which identifies whether or not a special message is included in the data; and modulating (540) the data by allocating the data to a plurality of carriers in a plurality of modulation symbols, wherein the wakeup message parameter is included in a preamble symbol of a frame of data. The method may further include channel encoding (540) the data prior to the step of modulating.
According to an aspect of the present principles, a method for receiving a multi-carrier modulated signal in power saving mode, the method including: periodically demodulating (610, 620) at least one preamble symbol of the modulated signal to create at least one demodulated preamble symbol, the at least one preamble symbol being at least one of a plurality of modulated symbols in a signal frame; and detecting preamble data (620) from the at least one demodulated preamble symbol; and recovering a wakeup message parameter (620) from the preamble data, wherein the wakeup message parameter identifies whether or not a special message (630) is included in the modulated signal. The method may further include: waking up additional functionalities (640) if the special message is included, including: demodulating additional modulated symbols of the modulated signal to recover the special message (650); and displaying the special message. The method may further include: channel decoding (620) after the step of demodulating and prior to recovering the wakeup message parameter. The method may further include channel decoding (620) after the step of demodulating and prior to recovering the special message.
In addition, according to one aspect of the present principles, the wakeup message parameter may include at least 1 bit. The wakeup message parameter may include unused bit combinations in the preamble data. The wakeup message parameter may further identify the type of message. The multi-carrier modulation may be OFDM.
Additional features and advantages of the present principles will be made apparent from the following detailed description of illustrative embodiments which proceeds with reference to the accompanying figures.
The present principles may be better understood in accordance with the following exemplary figures briefly described below:
The present principles relate to communication systems and in particular, to wakeup messages in digital television systems. Other than the inventive concept, several elements hereby discussed are well known and will not be described in detail. For example, other than the inventive concept, familiarity with the second generation digital terrestrial television broadcasting system for Digital Video Broadcasting (DVB-T2) is assumed and not described herein. In this regard, the standards and recommended practices of ETSI EN 302 755 and ETSI TS 102 832 are not described herein. Also, familiarity with the digital terrestrial television broadcasting system for the US (ATSC) is assumed and not described herein. In this regard, the standards and recommended practices of ATSC A/53, A/153 and A/54 are not described herein. Furthermore, familiarity with the US Emergency Alert System is assumed and not described herein. In this regard, the EAS Rules (47 C.F.R. Part 11) are not described herein. It should also be noted that the inventive concept may be implemented using conventional programming techniques, which, as such, will not be described herein.
a modulator 114 to convert the processed digital data into modulation symbols, which can be, for example, VSB (ATSC) or OFDM (DVB-T2). In addition, it includes the functionality of filtering and digital-to-analog (D/A) conversion; and
At the receiver device 120 of
A skilled artisan will appreciate that a source encoder 112 and a channel encoder 113, although common in general communications systems, are not essential for a system according to the present principles. Similarly, depending on the transmitter, a source decoder 122 and a channel decoder 123, although common in general communications systems, are not essential for a system according to the present principles. In addition, the transmitter and receiver may not require an antenna, if the transmission system is other than over-the-air (e.g., over cable). Furthermore, a receiving device includes, but is not limited to: a television, a set-top box, a computer, a mobile phone, an automobile receiver and a tablet.
One of the main issues associated with the current ATSC standard for digital terrestrial broadcasting of television in the US is the vulnerability of the 8-VSB modulation system to multipath propagation and Doppler Effect. These impairments are common in the broadcast transmission environment, particularly in large metropolitan cities, and in the delivery to portable/handheld/vehicular devices (which ATSC intends to support). It is a consensus that multi-carrier modulation systems like, for example, the OFDM (orthogonal frequency division multiplex) modulation are better choices of modulation to combat these impairments.
The OFDM modulation is adopted in other digital terrestrial television standards, e.g., the DVB-T/DVB-T2 standards in Europe, and the ISDB-T standard in Japan. DVB-T, the 1st generation of European DTT (Digital Terrestrial Television), is the most widely adopted and deployed standard. Since its publication in 1997, over 70 countries have deployed DVB-T services and 45 more have adopted (but not yet deployed) DVB-T. This well-established standard benefits from massive economies of scale and very low receiver prices. Like its predecessor, DVB-T2 uses OFDM (orthogonal frequency division multiplex) modulation with a large number of sub-carriers delivering a robust signal, and offers a range of different modes, making it a very flexible standard. DVB-T2 uses the same error correction coding as used in DVB-S2 and DVB-C2: LDPC (Low Density Parity Check) coding combined with BCH (Bose-Chaudhuri-Hocquengham) coding, offering a very robust signal. The number of carriers, guard interval sizes and pilot signals can be adjusted, so that the overheads can be optimized for any target transmission channel. DVB-T2 offers more robustness, flexibility and at least 50% more efficiency than any other DTT system. It supports SD, HD, UHD, mobile TV, or any combination thereof.
Tables 1, 2 and 3 characterize the S1 and S2 parameters, respectively in the DVB-T2 most basic functionality. The tables show that bits S1(2) and S2(0) are not utilized. Extensions of the DVB-T2 standard have added additional functionalities and mapping of the bits, e.g., T2_LITE, and will not be discussed in this application. Table 3 is for the S2 parameter when S1 is X10 (non-T2) and Table 2 is for the other cases of the S1 parameter. A skilled artisan will appreciate that there are unused bits in S1 and S2, as well as reserved combinations, which result in a plurality of unused combinations in the 7 bits of the P1 symbol of the preamble.
When a new broadcast system is deployed in the US, as it will eventually be the case for ATSC 3.0, one issue to consider is the requirement for broadcast systems to carry information related to the Emergency Alert System (EAS). The EAS requires two primary components. The first is a simple and efficient method to signal that there is a pending EAS message and the second is the message itself. For some receivers, in particular portable, mobile and handheld devices, it is expensive in terms of energy consumption to keep the receiver powered up at all times to watch for this information. Since the system intends to support handheld and portable devices, it is of interest to insure that such devices save as much power as possible while still being capable of receiving EAS messages anytime.
The present principles propose a way to utilize the preamble of a multi-carrier modulation digital system to indicate that there is an EAS message available in the transmitted signal. According to the present principles, apparatuses and methods are provided for a transmitter/transmitting and a receiver/receiving of a multi-carrier modulated signal which will transmit and receive special messages like the EAS messages. The transmitter transmits a signal comprising a preamble to permit fast and reliable initial acquisition, which includes a wakeup message to signal to the receiver that a special data message is being transmitted. At the receiver, a coarse demodulation and decoding is first performed to acquire the preamble and set other receiver parameters accordingly. This is efficient because it does not require the receiver to obtain full time/frequency synchronization to receive the data. A receiver can periodically wake-up, decode the preamble and go back to sleep if there is no “wake” signal in the wakeup message. In addition to EAS messages, this mechanism can be used for other services that require a device to wake up from a low-power mode. After acquisition of the preamble, the receiver identifies if there is a wakeup message in the transmission signal, which may prompt the receiver to power up additional functionalities in order to retrieve the special data message.
According to the present principles, the wakeup message may comprise one or a plurality of bits. If the wakeup message comprises a plurality of bits, the wakeup message identifies whether or not a special message is present in the transmitted stream or signal, and the type of special message in the transmission stream, e.g., AMBER alert, weather related message, presidential message, acts of terrorism, accidents, etc.
In an exemplary embodiment of the present principles, the preamble may comprise a P1 symbol similar to the one in the DVB-t2 system. In one embodiment, the wakeup message may utilize an unused combination of the preamble bits. For example, by assigning S1(2) & S2(0) to a certain value, like “11”, this can indicate the presence of a special message in the stream (e.g., Amber alert). In another example, S1=“X10” and S2=“001X” to “111X” may signal a special frame just for special messages. A plurality of other unused combinations of the preamble bits may be chosen to identify the presence of special messages in the stream. Or additional bits may be added to the preamble for the sole purpose of wakeup messages. It will be appreciated that other frame structures, hence other preamble structures are implementable in accordance with the present principles.
In an exemplary embodiment of the present principles, if the wakeup message consists of one bit, the corresponding wakeup bit is assigned to the unused bit in the S2 field of the P1 symbol (S2(0)). In another embodiment, for a system without T2-LITE, the wakeup bit is assigned to the unused bit of the S1 field of the P1 symbol (S1(2)). For example, S1 bit 2 in Table 1 would have the following values: “0”=no emergency/special message available and “1”=emergency/special message available. In yet another embodiment, the wakeup bit is assigned to a new (8th) bit in the P1 symbol. In another embodiment, the wakeup bit is assigned to an unused bit in a P2 symbol.
The modulator 114 according to the present principles creates a multi-carrier modulated signal, consisting of a sequence of modulation symbols, by allocating data to a plurality of carriers per modulation symbol, for signaling data and non-signaling data (video, audio, other ancillary data). In one embodiment of the present principles, the wakeup message parameter is sent in a preamble or header symbol for each frame of data, and is used to indicate the presence and/or type of the special message contained in the transmission signal.
At the receiver, the preamble symbol(s) is (are) first demodulated and the wakeup message parameter is recovered or extracted. If the presence of a special message is indicated, the receiver wakes up additional functionalities to receive the special message, which may include blocks associated with the reception of the data in the frame. Demodulation 124 is first performed to acquire the signaling data at a signaling data detector and set the receiver parameters accordingly. If the signaling data was channel encoded at the transmitter (at channel encoder 113), the signaling data detector must reside inside or after the channel decoder 123; otherwise, it can reside inside or after the demodulator 124. After the signaling data is recovered, the receiver extracts the various parameters contained in the signaling data to set its various modes of operation associated with its various data related blocks (including but not limited to modulation, e.g., constellation size, FFT size; FEC; interleaving; data distribution within the frame; etc.). The parameters are then sent to the various blocks in order for demodulation and decoding to be performed on the video, audio and other ancillary data.
In one embodiment of the present principles the transmitter establishes a minimum active time for the wakeup message to be set (that is, to identify that there is a special message) so that a receiver that is turned off or in a low or saving power mode can wake up only once during the active time and check the preamble wakeup message.
In one embodiment of the present principles, the transmitter sets the wakeup message for a prolonged period of time to insure that all receivers are able to receive it, regardless of battery or reception problems.
In one embodiment of the present principles, the transmitter sends the same special message more than once, at different times of the day. This implies alternate periods of turning the wakeup message on and off.
In one embodiment of the present principles, the transmitter changes the wakeup message (represented by an unused combination of the preamble bits) in a carrousel fashion when the special data message changes. This permits the receiver to skip a message that it has already received and remain in shut down or in low power mode for additional functionalities besides the preamble reception.
In one embodiment of the present principles, an interval of time is established for the receivers to repeatedly check the preamble for wakeup messages via a check timer.
In one embodiment of the present principles, the receiver identifies whether or not the special message has already been received. Once the special message associated with a wakeup message has been received, the receiver disregards the wakeup message, until the wakeup message changes. In another embodiment of the present principles, the receiver disregards a wakeup message if it has already received a wakeup message within a predetermined period of time.
In one embodiment, the multi-carrier modulated signal is a DVB-T2 type of signal, that is, a signal that has a frame, super-frame and physical layer pipe (PLP) architecture, modulation, FEC and signaling etc. defined similarly to DVB-T2, but with the addition of some important changes to accommodate new conditions and transmission systems not envisioned by the DVB-T2 standard body.
In one embodiment of the present principles, for a DVB-T2 or similar system, in order to make the processing of the emergency messages more efficient, two pieces of additional information are sent as part of the signaling data. These are a message version number and the Physical Layer Pipe (PLP) or virtual channel number where the emergency message can be found. This requires two new fields to be added to signaling data, for example, in the L1 pre signaling data of a DVB-T2 signal:
In view of the above, the foregoing merely illustrates the present principles, and it will thus be appreciated that those skilled in the art will be able to devise numerous alternative arrangements which, although not explicitly described herein, embody the present principles and are within its spirit and scope. For example, although illustrated in the context of separate functional elements, the various functional elements of a transmitter and/or receiver may be embodied in one, or more, integrated circuits (ICs). Similarly, although shown as separate elements, any or all of the elements may be implemented in a stored-program-controlled processor, e.g., a digital signal processor, which executes associated software, e.g., corresponding to one, or more, of steps. In addition, the present principles may apply to other multi-carrier modulation systems besides OFDM, e.g., discrete multi-tone (DMT) and to other types of single-carrier or multi-carrier pre-existing or legacy systems besides 8-VSB, e.g., single carrier QAM modulation. Further, the present principles are applicable to other types of communications systems, e.g., Wireless-Fidelity (Wi-Fi), cellular, cable, satellite, etc. Indeed, the inventive concept is also applicable to stationary or mobile receivers. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present principles.
This application claims the benefit of and priority to the U.S. Provisional Patent Applications: Ser. No. 61/868,847 and titled “WAKEUP MESSAGE FOR A DIGITAL TELEVISION SYSTEM”, filed on Aug. 22, 2013; Ser. No. 61/869,143 and titled “DIGITAL TELEVISION SIGNAL APPARATUS AND METHOD”, filed on Aug. 23, 2013; Ser. No. 61/882,827 and titled “DIGITAL TELEVISION SIGNAL APPARATUS AND METHOD”, filed on Sep. 26, 2013; and Ser. No. 61/891,563 and titled “METHOD AND APPARATUS FOR DELIVERING A BROADCAST DIGITAL TELEVISION SIGNAL”, filed on Oct. 16, 2013. The provisional applications are expressly incorporated by reference herein in their entirety for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/051658 | 8/19/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61868847 | Aug 2013 | US | |
| 61869143 | Aug 2013 | US | |
| 61882827 | Sep 2013 | US | |
| 61891563 | Oct 2013 | US |
