RU2554507C2 - Method and system for transmitting digital information via broadcast channel - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: present invention relates to transmission of digital messages embedded in the audio program of analogue radio broadcast stations. The method of transmitting digital information over a broadcast channel includes decoding a resultant audio signal with simultaneous transmission and repeating the embedding of an encoded information message until successful restoration of said message during said decoding.

EFFECT: enabling transmission of a large amount of information without loss of subjective sound quality over a minimal time.

9 cl, 6 dwg

Description

The proposed technical solutions relate to methods and devices for broadcasting, in particular to the technique of transmitting digital messages embedded in the audio program of analogue broadcasting stations.

Despite the fact that digital broadcasting has been developing recently (the corresponding standards, methods and devices for digital data transmission have appeared), analogue broadcasting systems based on amplitude (AM) and frequency modulation (FM) are still very popular due to a number of advantages, such as:

(1) simplicity, and consequently, the cheapness of the implementation of both transmitting and receiving equipment;

(2) the presence of a huge number of devices for receiving analog broadcasting signals (especially for FM standards);

(3) high quality sound programs (for FM stereo broadcasting).

It is worth noting that so far (2010) not a single country, even among the most advanced and technologically advanced, has completely abandoned analogue broadcasting. Given these circumstances, we can expect that analog broadcasting will continue to be one of the basic methods of sound broadcasting for decades.

However, analogue broadcasting systems still have drawbacks and limitations - this is, first of all, the lack of integrated digital services, such as multimedia content transfer (photos, formatted text, web services), already familiar and expected by the user of modern digital equipment.

Currently, there are options for expanding the functionality of analog broadcasting.

Known is the method proposed by Nokia for transmitting digital information together with the transmission of the main audio program in an analogue broadcasting system (Nokia Visual Radio - “Visual Radio”, [1]), which provides the transmission of multimedia content (web pages, graphics, etc.) simultaneously with audio transmission. In accordance with the concept of “Visual Radio”, additional multimedia information associated with the main audio program is pre-loaded onto the central server of the “visual radio” system, then this information is transmitted at certain points in time (synchronously with the sound program) via the mobile Internet via a mobile operator to a mobile phone to a user (FIG. 1). Thus, the user, together with the audio program transmitted over one communication channel, receives digital information associated with it through another communication channel.

This method has several disadvantages:

(1) an active connection to the mobile Internet is mandatory, which is technically not always justified, therefore the scope of this technology is limited to mobile phones;

(2) consumption of mobile Internet traffic, which requires payment by the user (radio listener);

(3) the simultaneous download of the same data on the channels of the mobile Internet by each of the users, which leads to inefficient consumption of the mobile operator’s resource and even to network congestion with a large number of users (for example, during mass events, such as popular sports, etc.) .

Another option for transmitting digital information in a broadcasting channel is a digital broadcasting system (Radio Data System - RDS) [2] for FM radio stations operating in the range 87.5-108 MHz, including an audio program source connected to one input of an insert module connected to a radio transmitter for broadcasting, and a source of information messages connected to another input of the insert module through the shaper (encoder) of information messages (figure 2).

Such systems are used to transmit basic information about the radio station (for example, the name of the station), as well as other short current textual information (for example, the name of the song being played) due to the fact that, as in traditional methods of digital broadcasting, they use a constant transmission speed, which ineffective in this case, since this speed should be minimal, calculated for the worst case in order to avoid loss of information messages. In this regard, the use of this system for the transmission of multimedia data, such as, for example, web pages, is limited by the low speed of the digital stream, the high redundancy of the protocol, as well as the absence of a mechanism for error correction during transmission.

Besides:

- for RDS, a separate frequency resource is used, which could be more efficiently used to transfer other programs or data;

- data transmitted via RDS is not synchronized with the main program, which creates difficulties in relaying and organizing a channel for delivering a signal from a radio studio to a transmitter;

- To transmit RDS signals, radio equipment is required, which requires economic costs for calibration, certification and maintenance. In addition, the radio must support RDS decoding at the hardware level, and if this is not provided by the manufacturer (for example, to minimize the cost of the receiver), then there is no way to decode RDS data programmatically;

- the impossibility of using AM broadcasting where additional subcarriers cannot be used.

The closest analogue of the proposed method for transmitting digital information in a broadcasting channel is a method for transmitting digital information in a broadcasting channel (EP 9700338 Al, H04H 1/00, publ. 09/12/1997), including encoding an information message, then convert it into an audio signal using a psychoacoustic model, and the original audio signal is converted by inserting into it an audio signal with an informational message. To implement the method, a system is used, which is the closest analogue of the claimed system for transmitting digital information in a broadcasting channel, including an insertion module, to the first input of which an audio program source is connected, to the second input is an information message shaper, to the input of which an information message source is connected. Through the output of the insertion module, the total audio signal is transmitted to the radio transmitter.

Despite the fact that using the method disclosed in EP 9700338, it is possible to insert digital information directly into the audio track of a broadcast signal, the amount of such information is very limited and is intended to “insert” some digital code into the audio signal to identify the broadcast channel. This code, as a rule, does not change over a sufficiently long period of time, so the equivalent throughput of such a “data transmission channel” is very limited (a few bits per second or even less). Of course, it would be possible to change the transmitted data (code) at some predetermined time intervals and, thus, ensure the transfer of large amounts of information, but such a method and system are unsuitable for practical applications because the reliability of decoding the transmitted signal is highly dependent on the current spectral-temporal characteristics of the original audio signal. For example, the presence of small pauses in the fragment of the audio signal or the localization of the spectrum of the signal in a narrow frequency band leads to the fact that decoding the information inserted into such a fragment may not be possible or will be performed with a high probability of error. To insert one single channel identifier code, this situation is not a serious problem, since the same code can be decoded using the next fragment of the audio signal or after some time. However, for the transmission of large data packets, this situation is critical, since a lost data block cannot be recovered. There is no opportunity to request the retransmission of lost data from the receiving devices, since in the system under consideration, information is transmitted in only one direction.

The purpose of this application is to create a method and system for transmitting digital information in a broadcasting channel that allows you to simulate (simulate) on the transmitting side the reception of the total audio signal (from the original audio signal and the encoded information message) and extract the original information message from it, which will determine the time of delivery of the transmitted information message with the initially selected coding redundancy, reducing the transmission time of the information message, increase Audio channel bandwidth for transmitting large volumes of information messages.

The goal is achieved in a method for transmitting digital information in a broadcasting channel, including the simultaneous transmission of an informational message and an audio signal, while encoding an informational message, inserting a coded informational message converted into an audio signal using a psychoacoustic model, and transmitting the resulting total audio signal over the broadcasting channel. At the same time, the decoding of the total audio signal is carried out simultaneously with the transmission in order to restore the transmitted information message, and the insert of the encoded information message is repeated until this message is successfully restored with the decoding mentioned.

It is advisable that in the method for reinserting into the original audio signal, the encoding redundancy of the information message is increased.

It is advisable that in the method before decoding the total audio signal was previously distorted to simulate its passage over the radio channel.

It is advisable to carry out the insertion by replacing part of the original audio signal with an audio signal with an encoded information message.

It is also advisable to carry out the insertion by supplementing the original audio signal with an audio signal with an encoded information message.

The goal is also achieved in a digital information transmission system in a broadcasting channel (hereinafter referred to as a transmission system), comprising an audio program source, an information message source, an information message shaper, a device (module) for inserting an information message into an audio program and a radio transmitter, by performing an information message shaper with the possibility of retransmission encoded information message to the insertion device and the introduction of the decoder of the information signal, configured to signal generation to change the information message. In this case, the source of the audio program is connected to the first input of the insertion device, the source of information messages is connected to the first input of the shaper of information messages, the output of which is connected to the second input of the insertion device, the output of which is connected to a radio transmitter, as well as a decoder connected to the second input of the shaper of information messages. In the case when the transmitted informational message is not restored in the decoder, the former sends it again to the insertion device for retransmission.

Thus, the idea of this approach is that the shaper transmits an information message to the insertion device to continue embedding digital information in the audio signal of the radio program that is somehow related to the same information message (in the simplest case, it simply repeats the same message ) until it is highly likely to be delivered to potential recipients. The system allows you to apply minimal redundancy in message encoding and achieve the highest possible digital information transfer rate. In this case, the heterogeneity of the sound program of almost any radio station is used. As a rule, a sound program includes music of various styles, speech of DJs, advertising, etc., therefore, for objective reasons, the bandwidth of the data channel when embedding a digital transmission signal in an audio program cannot be constant. At some points in time, the transmission speed can be very low, and at others it can significantly exceed the average throughput of the system.

It is possible to gradually increase coding redundancy in the information message generator with a low program throughput.

Additionally, between the output of the insertion device and the decoder, a radio channel simulator can be included to simulate interference and distortion of the output radio signal.

It is advisable that the insertion device in the system is configured to replace a portion of the original audio signal with an audio signal with an encoded information message.

It is advisable that the insertion device in the system is configured to supplement the original audio signal with an audio signal with an encoded information message.

It is advisable that in the system in the insertion device, the encoded information message converted to the audio signal is inserted into the original audio signal using a psychoacoustic model.

In practice, the proposed technical solutions, when a digital information signal is embedded in the audio program of analogue broadcasting radio stations, can be implemented both software and hardware. In the case of a hardware implementation, an insertion device, a digital information message generator, an information message decoder, a signal distortion simulator in a radio channel can be implemented as a separate hardware-software complex included in the gap of an audio signal coming from an audio program source to a radio transmitter. In the case of software implementation, the above modules can be implemented in the form of software (software) that is installed on the same computer as the software for broadcast automation. In this embodiment, the software for inserting an information signal can programmatically break the audio signal transmission circuit from the software source of the audio program to the software of the radio transmitter. For example, on a Windows system, this is possible using plug-ins for processing a DirectX signal or by implementing a driver for a virtual audio I / O device.

The implementation of the receiving device is possible by software on mobile phones and smartphones or on audio players and wearable computers, which include integrated devices for receiving sound broadcasting signals; or software on any mobile device that includes a microphone.

Next, the transmission method in the preferred embodiment will be described by the example of the operation of the device for inserting digital information into an audio signal and a digital information transmission system in a broadcasting channel in preferred embodiments.

Figure 1 - structural diagram of Nokia Visual Radio.

Figure 2 is a structural diagram of a Radio Data System.

Figure 3 is a structural diagram of a device for inserting digital information into an audio signal in a preferred embodiment (with an additional insertion device).

Figure 4 - options (a, b) selection band-pass filter of the main signal.

5 is a structural diagram of a system for transmitting digital information in a broadcasting channel in a preferred embodiment.

6 - options for user reception of transmitted digital information (a - a mobile device with a built-in radio, 6 - a mobile device through a stand-alone radio).

The bandpass filter 2 and the first input of the subtracter 3 are connected to the first input (Bx1) of the device for inserting digital information into the audio signal 1 (insertion device) shown in Fig. 3, and the second input of the subtractor 3 and the first input of the adder 4 are connected to the output of the filter ("+ "). The output of the subtractor through a series-connected residual signal analyzer 5 and the replacement signal generator (generator) 6 is connected to the second input of the adder 4. The additional input of the replacement signal generator is connected to the second input (Bx2) of the insertion device. The described part of the insertion device constitutes the main insertion device according to the first embodiment of the invention or the first insertion circuit of a digital information signal into an audio signal.

The output of the adder 4 is connected to the first input of the additional adder 7 ("+"), as well as to its second input through a series-connected signal splitter 8, an amplitude spectrum calculator 9, a global masking threshold calculator 10, and a complementary signal shaper 11. The output of the adder 7 is an output (Exit) insertion device. In this case, the additional input of the additional signal driver is connected to the second input (Bx2) of the insertion device. The described part of the insertion device constitutes an additional insertion device or a second (optional) insertion circuit.

The insertion device that implements the integrated embedding of information messages in the original audio signal operates as follows. Bx1 serves the original audio signal of the radio program. At the first stage, using a filter and a subtractor, the signal is divided into two components: the "main" component with the most audible signal content and the "residual" component with less noticeable content. In this case, both components can intersect in frequency, that is, for example, the filter can have a smooth decline at the border of the passband (Fig. 4a). In a preferred embodiment, the band-pass (dividing) filter forms one or more dips in the frequency domain, the least audible to the human ear [3] (Fig.4b). From the output of the subtractor, the “residual” signal enters the analyzer of the residual signal 5, where its spectral composition is analyzed (for example, using the Fourier transform or another method).

The found spectral characteristics of the “residual” signal are transmitted to the shaper (generator) of the replacement signal 6, to the additional input (Bx2 of the insertion device) which also receives a coded digital message (including modulated, containing sync packets). In the shaper 6 form a "replacement" signal containing data of a digital message and having spectral characteristics similar to the "residual" signal. The “replacement” signal formed in this way takes into account the psychoacoustic features of the perception of sound by the human ear (insensitivity to phase distortion), and therefore is almost indistinguishable from the original “residual” signal. Next, in the adder 4, the "main" signal from the output of the filter is summed with a "replacement" signal that carries digital information.

To facilitate the process of generating a "replacement" signal, it is possible to split the "residual" component of the signal into segments of a duration not exceeding the interval of quasistationarity of the original sound signal (approximately 10-40 ms). The “total" signal at the output of the adder 4 (the output of the device in the first embodiment) has the same spectral composition as the original signal, but a slightly changed structure of the phase spectrum (it contains the digital information component). With a careful choice of the shape of the band-pass filter, it is possible to achieve almost complete subjective acoustic invisibility of phase modifications introduced by the "residual" signal, converted into a "substitute".

At the second stage, a “complementary” signal is generated, which is additively added to the audio signal obtained at the first stage and which is the source for the additional insertion device. The formation of "complementary" acoustic signal is as follows. First, the audio signal (“total” - from the output of the first adder or “source” - from the Bx1 device in the second embodiment, when only the second circuit is used in the insertion unit) is split in the signal splitter 8 into short segments that do not exceed the interval of quasi-stationarity of the original audio signal. Then, in block 9, the amplitude spectrum of the audio segment is calculated using, for example, a fast Fourier transform (FFT), and then in block 10, based on the psychoacoustic model, the global masking threshold is calculated. The global masking threshold determines the level and shape of the amplitude spectrum of the signal, which can be added to the total (original - in the second embodiment) audio segment, without compromising the subjective quality of the sound program. The procedure for calculating the global masking threshold based on the psychoacoustic model is known and used in almost all modern audio file compression schemes, such as, for example, MPEG Layer II / III [4], and therefore this procedure is not described in detail in this application.

Further, the global masking threshold is used in the shaper of the complementary signal 11 to form the amplitude spectrum of a modulated digital signal carrying an information message received from the device Bx2. The “complementary” signal thus formed in the additional adder is added to the audio signal generated at the first stage, with the resultant (“total” for the additional insertion device) being obtained. Since the “complementary” signal is always below the threshold of audibility (since it is the maximum possible signal not exceeding the masking threshold), its presence in the “total” signal at the output of the insertion device does not affect the subjective quality of this final sound signal.

Thus, one informational message is used to generate two types of signals (“replacing” and “complementing”) and their “coherent” summation. It turns out that as a result, one signal is added, consisting of two components. Due to this, a more confident reception (faster in the described insertion device) of the embedded message is achieved.

The described procedure for adding "substitute" and "complementary" signals allows you to achieve maximum data transfer speed through the information channel with minimal acoustic noticeability of changes made to the original audio signal. Built-in digital information does not impair subjective sound quality and is completely invisible to the listener, as It is well masked by the main sound signal. In this case, the communication signal is transmitted exclusively in the audible frequency range of 30 Hz to 15-16 kHz for FM radio stations and up to 5-10 kHz for AM radio stations, i.e. does not contain frequencies that could be inaudible to the human ear.

In the case of stereo broadcasting, to obtain better results, the specified insertion procedure is implemented separately for each audio channel.

The digital information transmission system in the broadcasting channel shown in FIG. 5 contains an audio program source 21 (IP) connected to the first input Bx1 of the device 1 for inserting an information message into the audio program, to the output (s) of which a radio transmitter 22 is connected. Information source Messages 23 (IP) is connected to the first input Bx1 of the information message generator 24 (FIS), the output of which is connected to the second input Bx2 of HC 1. The output (Output) of HC 1 is also connected to the second input (Bx2) of FIS 24 through series-connected simulations a radio channel 25 torus (RBI) and an information signal decoder 26.

IP can be an internal archive on an electronic medium into which information messages are pre-recorded, or a local / global computer network from which information messages are dynamically loaded.

The system operates as follows. IP 21 transmits the radio program to the first input (Vx1) of HC 1. At the required time from the IS 23, a digital information message is transmitted to the FIS 24. In this case, the messages can be either associated with the current sound stream or completely independent. A combination of these options is also possible. FIS at each time interval generates an information packet for transmission, which, one way or another, is associated with the current information message. In the simplest version, this can be a cyclic repetition of the same information, in a more complex version, they can use a gradual increase in coding redundancy and the transfer of additional redundant information bits associated with the original message. Such encoding methods are widely known (see, for example, [5]) and are not discussed in this application.

Then, in the FIS, modulation and insertion of clock packages into an encoded information message is carried out.

The received encoded message is transmitted to Vx2 HC 1, where it is inserted into the audio program, as described above, and the total audio signal is transmitted from the output of HC 1 to the air through radio transmitter 22. From the output of HC 1, the total audio signal is also sent to decoder 26 (via RBI 25) . In case of successful decoding of the message, the decoder gives a signal to FIS 24 to change the information message, by which the FIS stops transmitting to HC 1. That is, simultaneously with the transmission, the decoding of the total audio signal is carried out. Thus, it is assumed that the decoder on the user side must also have time to decode this message. RBI 25 is used to simulate typical or worst-case conditions for distortion of an audio signal when passing through a radio link. Typically, such an imitation consists in adding noise to the signal from HC 1 to reduce the signal-to-noise ratio, although other distortions can be simulated. Thus, more accurately predict the time interval necessary for reliable reception of the message at the receiving side. Only after decoding the total audio signal, the transition to the transmission of the next message is made (the FIS starts receiving and processing the message from the IC). Thus carry out the transmission of independent information messages.

The correct decoding in the decoder is determined in the usual way, using additional redundant information embedded in the transmitted FIS signal, for example, CRC (cyclic check), message hash, checksum, etc.

If necessary, synchronize the transmission of digital messages with the radio program also use known methods. For example, at the beginning of a new audio program (its fragment), an additional signal is sent to the input of the IC (not shown in FIG. 5) through an additional output of the IP; The command submission time is determined by the playlist in the IP, which indicates when a new program starts, and it controls the transfer in this situation.

If there is a temporary absence of information messages (for example, when the message associated with this program has already been transmitted, and the next one has not yet arrived), the original audio signal (radio transmission from source 21) is received into the radio transmitter, i.e. the total audio signal is equal to the original.

Thus, the insertion of the encoded informational message is repeated until the successful restoration of this message with said decoding.

The described system allows you to use the heterogeneity of the sound program (fluctuating theoretical bandwidth of the radio channel) to match the duration of the transmission of a single embedded information message with the nature and properties of the outgoing material of the audio program.

Figure 6 (a, b) shows the options for the user to receive the radio program and the information messages transmitted therein. In the first embodiment (Fig. 6 (a)), on the receiving side, an information signal decoder can be integrated into a portable or mobile device with an integrated analogue broadcast radio. The radio receiver receives the total signal and transmits to the audio output, from which the user perceives it through the loudspeaker as a normal radio transmission, due to the above-described properties of this signal. From the audio output, the total signal is also input to the decoder, i.e. can be connected in parallel to a speaker or headphones. After receiving and decoding the received digital message, it is transmitted through the decoder output to the information message display device for the user.

In an alternative embodiment (Fig. 6 (b)), digital messages embedded in the sound program can be received using two devices: a standard sound broadcasting radio receiver (with speaker) and a portable device with a built-in microphone and an information message decoder, through the output of which information messages are transmitted to the display device (Fig.6b). The latter option is possible, since all digital information is embedded directly in the audio signal, and accordingly it is transmitted (albeit with some losses) even when the sound is relayed through a loudspeaker-microphone chain.

Although the invention has been shown and described with reference to its specific embodiments, those skilled in the art should understand that various changes in form and content can be made without departing from the spirit and scope of the invention as defined by the appended claims.

In particular, as an insertion device, in addition to the one described above, any of the known devices can be used.

For example, as described in the closest analogue (EP 9700338), in the insertion device, the information message (from Input 2) is modulated into a spreading carrier signal, while the current audibility threshold of the original audio signal (from Input 1) is determined. Reduce the signal level with spreading the spectrum below the current threshold of audibility and then summarize the received signal with the original audio signal for transmission over the air (through the output of the insertion device).

Another example of an insertion device is the device described in the source [6], where a delayed copy of the same signal is added to the original audio signal, where the delay is determined by the bits of the information message. Next, the total signal with a modulated echo is transmitted through the output of the device for transmission over the air.

Other methods for inserting digital information into an acoustic signal may also be used.

Thus, the claimed method and system make it possible to achieve the claimed technical result in any radio transmission systems - including analog ones, both with AM and FM, as well as in systems with the transmission of information messages at parallel frequencies.

The proposed technical solutions are universal, because do not require an additional frequency resource. When used in FM broadcasting, the free subcarrier (as opposed to the method in RDS systems) can be used to transmit additional data (for example, traffic information). In addition, the receiver does not require a mobile Internet channel, i.e. there is no need to pay for the service on the part of the user and the range of devices suitable for receiving multimedia content is significantly expanding.

Literature

1.http: //en.wikipedia.org/wiki/Visual_Radio (last checked on 2010.03.01).

2. D. Kopitz, RDS: The Radio Data System, Artech House Publishers, 1998, 376 pp.

3. I. Aldoshina, Fundamentals of psychoacoustics, part 12: Volume of complex sounds, // Sound Engineer, No. 9, 2000 (http://rus.625-net.ru/audioproducer/2000/09/aldoshina.htm).

4. Standard ISO-IEC 11172, part 3, Annex D.

5. A. Shokrollahi, Raptor Codes, IEEE Trans. Information theory, vol. 52, no. 6, p. 2551-2567, 2006.

6. D. Gruhl, A. Lu, W. Bender, "Echo Hiding," Information Hiding, Lecture Notes in Computer Science, Volume 1174, 1996, p. 295-315.

Claims (9)

1. A method of transmitting digital information in a broadcasting channel, including encoding an informational message, inserting a coded informational message converted to an audio signal into the original audio signal using a psychoacoustic model, transmitting the received total audio signal over the broadcasting channel, characterized in that the total audio signal is decoded simultaneously with the transmission, and the insertion of the encoded informational message is repeated until the successful restoration of this message, etc. and said decoding. 2. The method according to claim 1, characterized in that the encoding redundancy of the information message for re-insertion into the original audio signal is increased. 3. The method according to claim 1, characterized in that they decode the previously distorted total audio signal. 4. The method according to claim 1, characterized in that the insertion is carried out by replacing part of the original audio signal with an audio signal with an encoded information message. 5. The method according to claim 1, characterized in that the insertion is carried out by supplementing the original audio signal with an audio signal with an encoded information message. 6. A digital information transmission system in a broadcasting channel, comprising an audio program source, an information message source, an information message generator for encoding an information message, an insertion device and a radio transmitter, characterized in that the audio program source is connected to the first input of the insertion device, the information message source is connected to the first the input of the shaper information messages, configured to retransmit the encoded information message Whose output is connected to the second input inserter, which is connected to the output of a radio transmitter, and a decoder coupled to the second input of the information messages and adapted to generate a signal change information message. 7. The system according to claim 6, characterized in that the information message shaper is configured to increase the encoding redundancy of the information message. 8. The system according to claim 6, characterized in that the decoder is connected to the output of the insertion device through a radio channel simulator. 9. The system according to claim 6, characterized in that in the insertion device, an encoded informational message converted to an audio signal is inserted into the original audio signal using a psychoacoustic model.

Images