DE102011007007A1 - System for generating and transmitting data flow in digital sound broadcasting system i.e. digital radio, has transmitter comprising computing unit for adjusting time base of transmitter to time base of server based on data flow - Google Patents

Abstract

The system has a content-server (1) for generating asynchronous data flow, and a transmitter (3) comprising a modulator (31) for modulating the data flow. Digital-to-analog converters (33, 34) convert the modulated data flow into an analog transmission signal. An amplifier (35) amplifies the transmission signal, where the server has a time base for generating the data flow and the transmitter has another time base. The transmitter has a computing unit for adjusting the time base of the transmitter to the time base of the server based on the data flow received from the server. An independent claim is also included for a method for generating and transmitting data flow in a digital sound broadcasting system.

Description

The invention relates to a system for generating and transmitting a data stream in a digital radio system according to the preamble of claim 1 and to a method for generating and transmitting a data stream in a digital radio system.

Such a system comprises a content server for generating an asynchronous data stream and a transmitter comprising a modulator for modulating a data stream obtained from the content server, a digital-to-analog converter for converting the modulated data stream into an analog transmission signal and an amplifier for amplifying the send signal.

In this context, a content server is understood to be a server that provides content for generating a data stream. The content server can be realized, for example, by a computer system with audio inputs and a number of data interfaces that encodes one or more audio signals and possibly additional data services (for example images, static websites or value-added services) and asynchronous from these different contents Data stream generated. This asynchronous data stream is then distributed, for example via a packet-oriented data connection such as the Internet, to one or more transmitters and broadcast via the transmitters to provide a digital radio program.

The transmitter has a modulator and a (power) amplifier. The modulator hereby receives the asynchronous data stream from the content server and uses this to form a transmission signal, which is converted by the digital-to-analog converter and output to the amplifier in order subsequently to be emitted via an antenna.

The radio system concerned here (also referred to as digital radio) can in particular work on the basis of the DRM standard (DRM: Digital Radio Mondiale). The DRM standard includes both long, medium and short wave transmission frequencies below 30 MHz (referred to as "DRM30") and transmission frequencies between 30 MHz and 174 MHz (called "DRM +"). Audio data is compressed using MPEG-4 and transmitted via OFDM / COFDM (OFDM: Orthogonal Frequency Division Multiplexing, in German: Orthogonal Frequency Division Multiplexing, COFDM: Coded Orthogonal Frequency Division Multiplexing).

In principle, however, the system affected here can also be used for other digital radio standards.

The content server and the transmitter can be arranged spatially both directly next to one another and very far apart (possibly over several thousand kilometers). If the content server and the sender have synchronous time bases - for example a common time base provided by the so-called Global Positioning System (GPS) - then it can be ensured that the transmission signal is emitted with a system-related, constant delay but continuously, without there being any time differences between the data stream generated by the content server and the signal sent by the sender. However, synchronous time bases, such as a GPS based common time base, may not be available to the content server and the transmitter, for example because a transmitter is to be inexpensively equipped without expensive GPS receivers.

In the system concerned, the content server has a first time base for generating the asynchronous data stream, and the transmitter has a second time base independent of the first time base for generating a clock rate of the digital-to-analog converter. Based on the first time base, which corresponds to a system clock of the content server, the content server generates the asynchronous data stream and data packets that are transmitted to the sender. Based on the second time base, which corresponds to a system clock of the transmitter, a clock rate for the digital-to-analog converter is generated, based on which the digital-to-analog converter converts the modulator modulated data stream and passes as an analog transmission signal to the amplifier ,

Because the first time base of the content server and the second time base of the sender are independent of each other and may therefore differ slightly, the differences in the time bases over days, weeks and months can accumulate during continuous operation of the system Absolute time difference between the first time base of the content server and the second time base of the sender can arise. Depending on whether the difference in speed between the time bases is positive or negative, the time difference of the transmitted transmission signal to the desired radiation time of the content stream generated by the content server is always greater (because the data provided by the content server faster) transmit the modulator as they are written out by the digital-to-analog converter) or too little data is available to the digital-to-analog converter (because the content server is generating the data stream too slowly or the digital-to-analog converter is too slow). Analog converter reads the data at too high a clock rate, so that an internal memory of the transmitter runs empty). Both can be of considerable disadvantage to the operation of the digital radios, because in the first case a radio program may be sent out too late (messages that should have been sent at 12 o'clock, will be sent at 12:05 o'clock) or in the second case on a high performance of For example, 1 MW designed amplifier must be turned off during operation, because the transmitter no data for transmission are available, which may be associated with significant technical problems.

Object of the present invention is to provide a system and a method of the type mentioned above, with which in a system with a content server and a transmitter with independent Zeitbase a coordination of the time bases to each other in a simple, cost-effective manner possible ,

This object is achieved by a system having the features of claim 1.

Accordingly, the transmitter has a control unit, which is designed to use the data stream received from the content server to tune the second time base of the transmitter to the first time base of the content server.

Advantageous embodiments of the system can be taken from the subclaims.

In particular, the content server can generate a data stream compliant with the so-called multiplex distribution interface (MDI) within the scope of the DRM standard and transmit the generated data stream to the transmitter in a packet-oriented manner via a transmission medium, for example the Internet.

The transmitter generally has a buffer for buffering the modulated data stream generated by the modulator.

In a first variant for tuning the time bases on each other, the control unit may be configured to compare a buffer level of the buffer with a predetermined setpoint and adjust the clock rate of the digital-to-analog converter to tune the second time base to the first time base so that the Buffer level is regulated to the predetermined setpoint. The tuning of the second time base (of the transmitter) to the first time base (of the content server) thus takes place in that the fill level of a buffer of the transmitter is continuously monitored and the clock rate of the digital-to-analog converter is regulated on the basis of the fill level.

By means of the clock rate in this case the frequency is determined with which the buffered data stream is read into the digital-to-analog converter and transferred from the digital-to-analog converter to the amplifier to the converted data stream as an analog transmission signal via a Broadcast antenna. If it is determined that the buffer level is above the predetermined setpoint, the clock rate is increased and thus the buffer is read out faster. If, however, it is determined that the buffer level is below the predetermined setpoint. Thus, the control unit down the clock rate, so that the buffer is read out more slowly. If the buffer level is controlled to be constant at the setpoint, it is ensured that the time bases of the content server and the sender are approximately in sync, because the data packets provided by the content server feed data into the buffer at the same speed as they do from the digital -to-analog converter for generating the transmission signal are read so that it is ensured that neither a continuous growth or emptying of the amount of data stored in the buffer can take place and thus neither the between the generated radio program and the emitted transmission signal existing time difference excessively increases an intermediate shutdown of the amplifier on the part of the transmitter is required. A long-term stability of the system during operation is guaranteed.

In a second variant, the content server can be configured to transmit to the transmitter, as part of the data stream, a time information indicating the first time base. The control unit is then designed to use this time information to set the clock rate of the digital-to-analog converter such that the second time base (of the transmitter) is matched to the first time base (of the content server). In other words, time information is taken from the data stream generated by the content server on the transmitter side, on the basis of which the control unit of the transmitter adjusts the clock rate for the digital-to-analog converter, so that the time bases of the content server and the sender are synchronized with each other.

The time information can be passed, for example, on the basis of the so-called Network Time Protocol (NTP) in the Internet from the content server to the modulator. This allows a sufficiently long-term stability of the clock rate of the digital-to-analog converter, in order to avoid accumulation of a time difference of the different time bases in this way.

In this variant, advantageously, a bidirectional connection between the content server and the modulator of the transmitter can be provided, so that via the bidirectional connection, a further synchronization of the time bases by communication between the content server and the sender is possible.

• – ein Content-Server einen asynchronen Datenstrom erzeugt und an einen Sender überträgt,
• – ein Modulator des Senders den vom Content-Server erhaltenen Datenstrom moduliert,
• – ein Digital-zu-Analog-Wandler des Senders den modulierten Datenstrom in ein analoges Sendesignal wandelt und
• – ein Verstärker das Sendesignal verstärkt.

The object is also achieved by a method for generating and transmitting a data stream in a digital radio system, in which

• A content server generates an asynchronous data stream and transmits it to a sender,
• A modulator of the transmitter modulates the data stream received from the content server,
• - A digital-to-analog converter of the transmitter converts the modulated data stream into an analog transmission signal and
• - An amplifier amplifies the transmission signal.

In this case, the content server has a first time base for generating the asynchronous data stream, and the transmitter has a second time base independent of the first time base for generating a clock rate of the digital-to-analog converter. In this case, it is provided that the transmitter has a control unit which tunes the second time base of the transmitter to the first time base of the content server on the basis of the data stream received from the content server.

The advantages and refinements described above for the system are also transferable to the method.

In particular, in a first variant, the transmitter may comprise a buffer for buffering the modulated data stream generated by the modulator, the control unit comparing the buffer level of the buffer with a predetermined setpoint and adjusting the clock rate of the digital-to-analog to tune the second time base to the first time base Converter so that the buffer level is regulated to the predetermined setpoint.

In a second, alternative variant, the content server can transmit a time base information indicating the first time base to the transmitter as part of the data stream, the control unit using the time information sets the clock rate of the digital-to-analog converter to the second time base on the first time base to vote.

The idea underlying the invention will be explained in more detail with reference to the embodiments illustrated in the figures. Show it:

1 a schematic view of a system with a content server and a transmitter for generating and transmitting a data stream in a digital radio system;

2 a schematic view of a system with a content server and a transmitter for generating and transmitting a data stream in a digital radio system, comprising a control unit for generating a clock rate of the transmitter in response to a buffer level and

3 a schematic view of a system with a content server and a transmitter for generating and transmitting a data stream in a digital radio system, comprising a control unit for regulating a clock rate of the transmitter in response to a time from the content server with the data stream emitted time information.

1 shows in a first schematic view of the basic structure of a system for generating and transmitting a data stream in the context of a digital radio system.

The system has a content server 1 which receives and stores content via external data interfaces and audio inputs, and from content, such as audio and other data services, such as images, static web pages, or digital value-added services, generates a digital asynchronous data stream over a transmission medium 2 trained by the Internet to a broadcaster 3 transfers.

The transmitter 3 has a modulator 31 the asynchronous stream from the content server 1 receives and generates from the data stream by means of Quadrature Amplitude Modulation (QAM) two digital baseband signals I and Q (also referred to as IQ modulation), for example, have a bit rate of 192 kbit / s. These baseband signals are provided by the modulator 31 a buffer in the form of a buffer 32 available, which caches the baseband signals.

For reading the baseband signals I and Q from the buffer 32 are two digital-to-analog converters 33 . 34 provided that the respectively associated baseband signal I or Q as a digital, modulated data stream from the buffer 32 read out and as an analog transmission signal to an analog amplifier 35 with a rated power of, for example, 1 MW output, which amplifies the thus obtained quadrature transmission signals and an output 36 to an antenna for emitting emits.

The content server 1 generates an asynchronous data stream compliant with the so-called Multiplex Distribution Interface (MDI) under the DRM standard. The content server 1 transmits the data stream thus generated in the form of individual data packets via the transmission medium 2 (ie the Internet) to the transmitter 3 that's about his modulator 31 receives the data in the form of data packets, modulated and in the buffer 32 feeds.

The content server 1 generates the data packets as part of the data stream on the basis of its own time base 10 , For example, the content server 1 every 100 ms generate a data packet with a length of 100 ms and this over the transmission medium 2 to the transmitter 3 send out.

The transmitter 3 For its part, it also has its own time base 30 regardless of the time base 10 of the content server 1 is and thus (slightly) different from the time base 10 of the content server. Depending on his time base 30 the transmitter generates 3 by means of a clock generator 301 a clock by which each digital-to-analog converter 33 . 34 the basic signal to be processed by him from the buffer 32 reads out, converts and to the amplifier 35 emits.

Because the time bases 10 . 30 of the content server 1 and the sender 3 may be different, there may be a time difference Δτ (t) between the time bases 10 . 30 vary with time, in particular accumulate cumulatively in one direction or the other in the other direction over time.

Run the time base 10 of the content server 1 (slightly) faster than the time base 30 the transmitter 3 so does the content server 1 the data packets of the data stream at a speed greater than the readout rate of the data from the buffer 32 is, leaving a buffer level of the buffer 32 on the side of the transmitter 3 continuously growing. This is - a sufficient buffer size of the buffer 32 provided - technically unproblematic in itself, however, can cause the time difference over a long period of operation reaches a significant size, so that one from the content server 1 generated radio program from the transmitter 3 will be aired at a much later date (which is unpleasant, for example, when news is scheduled to air at 12:00, but in fact it is not broadcast until 12:15, due to the accumulated time difference between the different time bases 10 . 30 ).

Does the time run according to the time base? 10 on the content server side 1 slower than time due to the time base 30 on the side of the transmitter 3 So this can cause the content server 1 the data to be broadcasted to the sender 3 with a too low speed provides or the buffer 32 on the side of the transmitter 3 is read out with a too high clock rate, so that on the part of the transmitter 3 not enough data is available to broadcast and the buffer 32 idle, so possibly the amplifier 35 must be temporarily switched off - which can be problematic for a power amplifier in the megawatt range.

At the in 2 and 3 schematically illustrated solutions to this problem are addressed by the time bases 10 . 30 of the content server 1 and the sender 3 coordinated and thus at least approximately synchronized.

In the system according to 2 is also a control unit 302 provided by a regulator 305 in the form of a comparator, a buffer level 303 of the buffer 32 with a setpoint 304 compares and, depending on this comparison, the clock rate of the digital-to-analog converter 33 . 34 over the clock generator 301 controls. About the control unit 302 Thus, the clock rate of the digital-to-analog converter 33 . 34 adjusted so that the buffer level 303 about the setpoint 304 is regulated, so that the amount of data in the buffer 32 neither excessively above the setpoint 304 increase still excessively below the target value 304 can fall. The clock rate is thus adjusted to the amount of data that is transmitted via the content server 1 the modulator 31 provided and about it in the buffer 32 is fed, so the clock rate on the time base 10 of the content server 1 is tuned.

If the buffer level is regulated to the setpoint, then the clock rate of the clock generator corresponds 301 just the clock rate, the synchronous Zeitbasen 10 . 30 would be obtained and a write out of the buffer 32 using the digital-to-analog converter 33 . 34 at the same speed with feeding the data into the buffer 32 causes.

In an alternative, in 3 variant shown is a control unit 302 provided that over the clock generator 301 generated clock rate of the digital-to-analog converter 33 . 34 depending on one of the content server 1 over the transmission medium 2 in the form of the Internet broadcast time information. In this variant, the content server adds 1 add to the generated data stream for the radio program time information containing information about the time base 10 of the content server 1 includes. This time information is used as a time base 10 ' in the form of a time module 304 ' a controller 305 supplied in the form of a comparator, which is the time module 304 ' with a time module 303 ' that is the current clock rate of the clock generator 301 is derived and indicative of the current time base 30 the transmitter 3 is, compares and, depending on this comparison, the clock rate of the clock generator 301 regulates. Depending on the time information of the time base 10 of the content server 1 Thus, the clock rate for the digital-to-analog converter 33 . 34 the transmitter 3 set this to the time base 10 of the content server 1 is tuned and thus a synchronization of the time bases 10 . 30 of the content server 1 and the sender 3 he follows.

The time information can, for example, based on the so-called Network Time Protocol (NTP) from the content server 1 to the transmitter 3 be transmitted. On the basis of the NTP, a sufficiently long-term stability of the system can be achieved in order to avoid accumulation of a time difference of the different time bases in this way.

In this variant can also be a bidirectional connection between the content server 1 and the modulator 31 the transmitter 3 be provided so that via the bidirectional connection of the content server 1 with the transmitter 3 can communicate to a further synchronization of the time bases.

The idea underlying the invention is not limited to the above-described embodiments, but can in principle be realized in other embodiments. By means of the solution according to the invention, a synchronization of the time bases from the content server and transmitter to one another is made possible here solely from the data stream provided by the content server, without a superordinate, common time base having to be installed by expensive additives.

LIST OF REFERENCE NUMBERS

1

Content Server

10, 10 '

time basis

2

transmission medium

3

transmitter

30

time basis

300

clock

301

Controlled clock generator

302

control unit

303

buffer level

303 '

time module

304

setpoint

304

time module

305

Controller (comparator)

31

modulator

32

Buffer (cache)

33, 34

Digital-to-analog converter

35

amplifier

36

Radio-frequency output

Claims (12)

A system for generating and transmitting a data stream in a digital radio system, comprising - a content server for generating an asynchronous data stream, and - a transmitter comprising a modulator for modulating a data stream received from the content server, a digital-to-analog converter for Converting the modulated data stream into an analog transmit signal and an amplifier for amplifying the transmit signal, the content server having a first time base for generating the asynchronous data stream and the transmitters having a second time base independent of the first time base for generating a clock rate of the digital to Analog converter, characterized in that the transmitter ( 3 ) a control unit ( 302 ), which is formed on the basis of the content server ( 1 ) received the second time base ( 30 ) of the transmitter ( 3 ) on the first time base ( 10 ) of the content server ( 1 ) to vote. System according to claim 1, characterized in that the content server ( 1 ) generates a data stream conforming to the multiplex distribution interface. System according to claim 1 or 2, characterized in that the content server ( 1 ) the generated data stream via a transmission medium ( 2 ) in individual data packets to the transmitter ( 3 ) transmits. System according to claim 3, characterized in that the transmission medium ( 2 ) the internet is. System according to one of the preceding claims, characterized in that the transmitter ( 3 ) a buffer ( 32 ) for buffering the from the modulator ( 31 ) has generated modulated data stream. System according to claim 5, characterized in that the control unit ( 302 ) is formed, a buffer level ( 303 ) of the buffer ( 32 ) with a predetermined setpoint ( 302 ) and to tune the second time base ( 30 ) on the first time base ( 10 ) the clock rate of the digital-to-analog converter ( 33 . 34 ) so that the buffer level ( 303 ) to the predetermined setpoint ( 302 ) is regulated. System according to claim 6, characterized in that the clock rate - is increased when the buffer level ( 303 ) above the predetermined setpoint ( 302 ), or - is reduced when the buffer level ( 303 ) below the predetermined setpoint ( 302 ) lies. System according to one of claims 1 to 5, characterized in that the content server ( 1 ) in the context of the data stream a the first time base ( 10 ) indicating time information to the transmitter ( 3 ), the control unit ( 302 ), based on the time information, the clock rate of the digital-to-analog converter ( 33 . 34 ) to the second time base ( 30 ) on the first time base ( 10 ) to vote. System according to claim 8, characterized in that the content server ( 1 ) and the modulator ( 31 ) are connected to each other via a bidirectional connection. Method for generating and transmitting a data stream in a digital radio system, in which - a content server generates an asynchronous data stream and transmits it to a transmitter, - a modulator of the transmitter modulates the data stream received from the content server, - a digital-to-analogue Transmitter converts the modulated data stream into an analog transmit signal, and an amplifier amplifies the transmit signal, the content server having a first time base for generating the asynchronous data stream and the transmitter having a second time base independent of the first time base for generating a clock rate of the Digital-to-analog converter, characterized in that the transmitter ( 3 ) a control unit ( 302 ) based on the content server ( 1 ) received the second time base ( 30 ) of the transmitter ( 3 ) on the first time base ( 10 ) of the content server ( 1 ) votes. Method according to claim 10, characterized in that the transmitter ( 3 ) a buffer ( 32 ) for buffering the from the modulator ( 31 ) has generated modulated data stream, wherein the control unit ( 302 ) a buffer level ( 303 ) of the buffer ( 32 ) with a predetermined setpoint ( 302 ) and to tune the second time base ( 30 ) on the first time base ( 10 ) the clock rate of the digital-to-analog converter ( 33 . 34 ) so that the buffer level ( 303 ) to the predetermined setpoint ( 302 ) is regulated. Method according to claim 10, characterized in that the content server ( 1 ) in the context of the data stream a the first time base ( 10 ) indicating time information to the transmitter ( 3 ), the control unit ( 302 ) based on the time information, the clock rate of the digital-to-analog converter ( 33 . 34 ) to the second time base ( 30 ) on the first time base ( 10 ) to vote.

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