Background Art Recently, there have been various attempts to meet a high demand on providing multimedia broadcasting services including moving pictures even in mobile environments. A digital audio broadcasting (DAB) system having an enhanced reception in the mobile state is one contrived approach.

For example, a DAB transmission system based on Eureka 147 of a European style has been used mainly for the purpose of digitalizing analogue audio broadcasting so that the DAB transmission system has been originally developed to process audio data or only a small amount of data information.

Currently, the moving pictures are serviced by using a moving picture experts group-2 (MPEG-2) in digital television (TV) broadcasting. In case of transmitting multimedia data in a MPEG-2 system standard used for the digital TV broadcasting, there are a lot of advantages in

multiplexing and synchronizing. Accordingly, if the multimedia data including moving picture data are processed in the MPEG-2 system standard and then, are transmitted by using the DAB transmission system strong in the reception in the mobile state, it is expected to provide much stable multimedia broadcasting services even during the mobile reception state.

However, to service the data processed in the MPEG-2 system standard by using, for example, the DAB transmission system based on the Eureka 147, it is necessary to have an interface having compatibility between two systems.

Despite the aforementioned fact, the two systems actually <BR> <BR> have different interfaces, i. e. , the two systems do not have the compatibility; and thus, it is not possible to process the MPEG-2 data in the present DAB transmission system. Accordingly, it is required to develop a method for transmitting a MPEG-2 transmission stream in the DAB transmission system.

Even though there is a suggested technology for applying a packet inputted from a digital packet network to a radio broadcasting system operating based on DAB technology in U. S. patent No. 6,075, 789, issued to Mika Kasslin, Mika Rinne and Ari Salomaki on June 13,2000, entitled"System for connecting a packet data network to a digital radio network" (hereinafter referred to as a first conventional art), the first conventional art transmits the DAB data by converting the packet inputted from the digital packet network such as an asynchronous transfer mode (ATM) into the DAB data. However, the present invention receives a MPEG-2 transport stream (TS) and converts the MPEG-2 TS into the DAB data.

Meanwhile, as another example of the related conventional arts, there is another suggested technology allowing a user to view multimedia data such as moving pictures compressed by a moving picture experts group

(MPEG) and still pictures compressed by a joint photographic experts group (JPEG) through a small terminal in an article by K. Fazel, S. Align, A. Romanowski and M.

J. Ruf, entitled"Mobile Multimedia Services via DAB : DMB", Global telecommunications conference, volume 3/3-8, pp. 1312-1317, 1997. Hereinafter, this suggested technology is referred to as a second conventional art.

However, compared with the present invention, the second conventional art compresses the multimedia data through the MPEG or the JPEG, makes the multimedia data coded and converts the multimedia data into the DAB data, thereby providing the intended broadcasting services. In this point, the second conventional art is similar with the present invention. That is, both of the second conventional art and the present invention transmits the multimedia data by using the DAB transmission system.

However, the present invention is contrasted to the second conventional art more particularly in the point that the present invention can efficiently uses a data bit amount for every interval of the transmission frames.

Furthermore, as still another example of the related conventional arts, there is another contrived technology capable of providing moving picture services with a high quality even in the mobile state by transmitting the moving picture data compressed by a MPEG-4 in the DAB system in an article by M. Grube, P. Siepen, C. Mittendorf, M. Boltz and M. Srinivasan, entitled to"Application of MPEG-4: Digital Multimedia Broadcasting", IEEE Transactions on Consumer Electronics, volume 47, issue 3, pp. 474-484,2001.

Hereinafter, this contrived technology is referred to as a third conventional art. However, compared with the present invention, the third conventional art also compresses the multimedia data through the MPEG-4 and then, processes the multimedia data into the MPEG-2 system standard, thereby providing the broadcasting through the DAB system. In this

point, the third conventional art is similar with the present invention. That is, the multimedia data are transmitted by using the DAB transmission system according to both of the conventional third art and the present invention. However, the present invention is different from the third conventional art more particularly in this point that the present invention efficiently uses the data bit amount for every interval of the transmission frames.

In sum, the second and the third conventional arts include a technological idea transmitting the MPEG-2 transmission stream by using the DAB transmission system.

However, in order to transmit the MPEG-2 transmission stream through the DAB transmission system, it is necessary to perform an outer coding to the MPEG-2 transmission stream in a packet unit to make the MPEG-2 transmission stream tolerate to errors during the transmission.

Particularly, for every interval of the DAB transmission frames, the outer coded MPEG-2 data are transmitted by loading a data amount as much as a stream length (STL) value into a stream data field of the DAB transmission frames.

However, the data amount according to the STL value in an ensemble transport interface (ETI), which is one of the DAB transmission interface standards, is an 8 byte unit.

However, in case of performing the outer coding to a data stream in a packet unit of 204 bytes that is not a multiple of the 8 bytes, the data amount becomes the multiple of the 204 bytes. In this case, if a quantity of the packets with an even number is subjected to the outer coding every interval of the ETI frames, i. e. , the DAB transmission frames, the outer coded data packets are transmitted by being loaded as much as the STL value into the ETI frames for every interval of the ETI frames. However, a waste of the data bit amount is generated.

Accordingly, when the multimedia data, i. e. , the MPEG-

2 data, is transmitted to the DAB transmission system, it is essentially required to develop a method for performing the outer coding to the multimedia data in a packet unit without wasting the data bit amount; and more particularly, a method for efficiently using the data bit amount by transmitting the outer coded multimedia data with an amount loaded as much as the STL value into the ETI frames for every interval of the ETI frames.

Disclosure of the Invention It is, therefore, an object of the present invention to provide a method for controlling a bit rate in a digital audio broadcasting (DAB) system by performing an outer coding to an output value of MPEG-2 data in a packet unit without wasting a bit amount and particularly by transmitting the outer coded MPEG-2 transmission stream with a data amount loaded as much as a stream length (STL) value into a DAB transmission frame for every interval of the DAB transmission frames.

It is another object of the present invention to provide an apparatus and a method for converting a media stream by using the bit rate controlling method.

In accordance with the present invention, there is provided a media stream conversion apparatus for providing a multimedia service in a digital audio broadcasting (DAB) transmission system, including: a data analyzing means for determining a data amount of an input moving picture transmission stream and calculating a stream length (STL) value indicating a data amount to be loaded into individual DAB transmission frames by using the data amount of the input moving picture transmission stream; a first storing means for storing a data of an effective packet in the moving picture transmission stream; a null packet forming means for forming a null packet to adjust the data amount;

a multiplexing means for calculating a data amount to be subjected to an outer coding for every interval of the DAB transmission frames based on the STL value and multiplexing the effective packet and the null packet to output the data as much as the corresponding size ; an outer coding means for making an output value of the multiplexing means outer coded in a packet unit to make the output value tolerate to errors during transmission ; a second storing means for storing the outer coded moving picture transmission stream; and a transmission frame configuration means for reading the moving picture transmission stream stored in the second storing means as much as the data amount according to the STL value for every interval of the DAB transmission frames, thereby configuring the DAB transmission frames and outputting the data amount according to the STL value.

In accordance with the present invention, there is provided a method for controlling a bit rate in a digital audio broadcasting (DAB) transmission system, including the steps of: (a) receiving a stream length (STL) value indicating a data amount to be loaded into individual DAB transmission frames; (b) calculating a data amount to be subjected to an outer coding for every interval of the DAB transmission frames based on the STL value ; and (c) performing an outer coding to a data with a multiple size of a packet unit for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average.

In accordance with the present invention, there is provided a method for converting a media stream for providing a multimedia service in a digital audio broadcasting (DAB) transmission system, including the steps of: (a) determining a data amount of an inputted moving picture transmission stream and calculating a stream length (STL) value indicating a data amount to be loaded into individual DAB transmission frames ; (b) calculating a data

amount to be subjected to an outer coding for every interval of the DAB transmission frames based on the STL value ; (c) performing an outer coding to a data with a multiple size of a packet unit for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average; and (d) reading the outer coded moving picture transmission stream as much as the predetermined data amount according to the STL value for every interval of the DAB transmission frames to configure the DAB transmission frames and outputting the moving picture transmission stream.

Brief Description of the Drawings Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, in which: Fig. 1 is a diagram showing an embodied configuration of a media stream conversion apparatus in accordance with the present invention ; Fig. 2 is a detailed diagram showing an embodied method for controlling a bit rate in accordance with the present invention; and Fig. 3 is a flowchart showing a method for converting a media stream in accordance with the present invention.

Best Mode for Carrying, out the Invention Hereinafter, a method for controlling a bit rate in a digital audio broadcasting (DAB) system and an apparatus and a method for converting a media stream by using the same in accordance with a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 1 is a diagram showing an embodied configuration

of a media stream conversion apparatus in accordance with the present invention.

As shown, the media stream conversion apparatus for the purpose of providing multimedia services in a DAB transmission system in accordance with the present invention includes a moving picture experts group-2 (MPEG- 2) data analyzing unit 11 for figuring out a data amount of an inputted MPEG-2 transmission stream and calculating a stream length (STL) value indicating a data amount to be loaded into a DAB transmission frame by using the data amount of the inputted MPEG-2 transmission stream, a buffer for MPEG-2 data 12 storing a data of an effective packet in MPEG-2 transmission frames ; a null packet forming unit 13 for forming a null packet to adjust the data amount; an MPEG-2 data multiplexing unit 14 for outputting calculating a data amount to be subjected to an outer coding activity for every interval of the DAB transmission frames, i. e. , an ensemble transport interface (ETI) frames, based on the STL value and multiplexing the effective packet and the null packet to output a data with the corresponding amount; an outer coding unit 15 for making an output value of the MPEG-2 data multiplexing unit 14 outer coded in a packet unit to let the output value of the MPEG-2 data multiplexing unit 14 tolerate to errors during transmission; a buffer for stream data 16 for storing the outer coded MPEG-2 transmission stream ; and a transmission frame configuration unit 17 for outputting the MPEG-2 transmission stream stored in the buffer for stream data 16 by configuring the DAB transmission frames through reading the data amount as much as the STL value for every interval of the DAB transmission frames.

A physical interface such as a society of motion picture and television engineers (SMPTE) 310M or a digital video broadcasting-asynchronous serial interface (DVB-ASI) mainly used for the digital television (TV) broadcasting

can be used to input the MPEG-2 transmission stream to the media stream conversion apparatus.

The MPEG-2 data analyzing unit 11 receives the MPEG-2 transmission stream and then, calculates the data amount of the effective packet except the null packet in the data inputted to the MPEG-2 data analyzing unit 11. Afterwards, the STL value obtained in an 8 bytes unit of the data amount to be loaded into the DAB transmission frame is figured out by using the data amount of the effective packet, thereby outputting the STL value to the MPEG-2 data multiplexing unit 14 and the transmission frame configuration unit 17. Furthermore, a data of the effective packet is outputted and stored in the buffer for MPEG-2 data 12.

Herein, in case of calculating the STL value, it is preferable to calculate the STL value with marginal values by rounding up the obtained STL value or adding a small number to the obtained STL value to prevent an excessiveness of the buffer for MPEG-2 data 12.

Especially, in the MPEG-2 data multiplexing unit 14, the STL value indicating the data amount to be loaded into the DAB transmission frame is inputted to the MPEG-2 data multiplexing unit 14 from the MPEG-2 data analyzing unit 11 or the outside. Afterwards, the data amount with a multiple size of a packet unit is calculated for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average.

Thereafter, the data corresponding to the size of the data amount is read from the buffer for MPEG-2 data 12, or the null packet data is read from the null packet forming unit 13. Then, this read data is multiplexed in a packet unit and is transmitted to the outer coding unit 15. That is, if the data is stored in the buffer for MPEG-2 data 12, the MPEG-2 data multiplexing unit 14 reads the data of the effective packet in the buffer for MPEG-2 data 12. If

otherwise, the MPEG-2 data multiplexing unit 14 reads the data of the null packet from the null packet forming unit 13. The MPEG-2 data multiplexing unit 14 then multiplexes the effective packet and the null packet and outputs the multiplexed effective packet and the multiplexed null packet to the outer coding unit 15. Herein, the data with the multiple size of the packet unit is transmitted to the outer coding unit 15 for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average.

Then, in the outer coding unit 15, to make the MPEG-2 transmission stream inputted from the MPEG-2'multiplexing unit 14 tolerate to the errors during the transmission, the data with the multiple size of the packet unit is subjected to the outer coding and then, transmitted to the buffer for stream data 16 for interval of the DAB transmission frames as maintaining the data amount according to the STL value on average. That is, the MPEG-2 multiplexing unit 14 multiplexes the null packet formed to adjust the data amount with respect to the effective packet of the inputted MPEG-2 transmission stream, i. e. , during multiplexing the null packet, the data with the multiple size of the packet unit is outputted for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average, and in the outer coding unit 15, only the data amount according to the STL value is subjected to the outer coding. That is, in the outer coding unit 15, the data with the multiple size of the packet unit is subjected to the outer coding for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average.

In the transmission frame configuration unit 17, each field value of the DAB transmission frames is generated and then, outputted. At this time, when configuring the DAB transmission frame, the buffer for stream data 16 reads the

outer coded MPEG-2 data as much as the data amount corresponding to the STL value and then, the read portion of the MPEG-2 data is transmitted by being loaded into the stream data field of the DAB transmission frame.

Fig. 2 is a detailed diagram showing an embodied method for controlling a bit rate in accordance with the present invention. Especially, Fig. 2 illustrates steps of obtaining a data amount to be subjected to an outer coding for every interval of ETI frames in the DAB transmission system performing the outer coding in 204 bytes and using ETI that is one of the DAB transmission standards. In the outer coding unit 15, this data amount determined through these steps is subjected to the outer coding.

Herein, assuming that the STL value in the ETI frames is continuously processed in 192, the steps of determining the above data amount in the course of transmitting the data with the multiple size of the packet unit to the outer coding unit 15 for every interval of the ETI frames as maintaining the data amount according to the STL value on average are described.

In order to load the data amount according to the STL value into the stream data field for every interval of the ETI frames, 1,536 bytes, i. e. , the data amount corresponding to'the STL value obtained by multiplying 192 with 8, are transmitted to the outer coding unit 15 on average for every interval of the ETI frames.

Therefore, it is possible to assume that 1,536 bytes are stored in the buffer for MPEG-2 data 12 for every interval of the ETI frames. If the data amount of the buffer for MPEG-2 data 12 is read more than 1,536 bytes, i. e. , the data amount corresponding to the STL value in the previous interval of the ETI frames, the data amount of the buffer for MPEG-2 data 12 is reduced by a difference between 1,536 bytes and the value more than 1,536 bytes.

If the data amount of the buffer for MPEG-2 data 12 is read

less than 1,536 bytes, the data amount of the buffer for MPEG-2 data 12 is increased by a difference between 1,536 bytes and the value less than 1,536 bytes. To prevent the buffer for MPEG-2 data 12 from exceeding, it is necessary to process the predetermined data amount, in this case, 1,536 bytes within the interval of the corresponding ETI frames. Specifically, the data to be processed within the interval of the corresponding ETI frames to prevent the buffer for MPEG-2 data 12 from exceeding is called a virtual data amount 201.

For instance, if the STL value is 192, a first virtual data amount (201-1) stored in the buffer 12 within a first interval of the ETI frames is 1,536 bytes obtained by multiplying 192 with 8. To convert the first data amount (201-1) having the size of 1,536 bytes into the data with the multiple size of the packet unit and transmit the converted data, at least 1,632 bytes obtained by multiplying 204 with 8 are required. Accordingly, within the first interval of the ETI frames, a first MPEG-2 data (202-1) having the size of 1,632 bytes is transmitted to the outer coding unit 15.

Afterwards, since 96 bytes, which is a first difference in a data amount in the first interval (203-1), are more transmitted than the expected data amount of 1,536 bytes in the first interval of the ETI frames, if this first difference in the data amount (203-1), i. e. , 96 bytes, are reflected to a second virtual data amount (201- 2) in a second interval of the ETI frames, the second virtual data amount (201-2) is 1,440 bytes obtained by subtracting 96 from 1,536. To transmit 1,440 bytes in the multiple size of the packet unit, 1,632 bytes are necessary; and thus, a second MPEG-2 data (202-2) in the second interval of the ETI frames is transmitted with the size of 1,632 bytes to the outer coding unit 15.

Next, since 96 bytes, which is a second difference in

a data amount in the second interval (203-2), are more transmitted than the expected data amount of 1,536 bytes in the second interval of the ETI frames, if the second <BR> <BR> difference in the data amount (203-2), i. e. , 96 bytes, are reflected to a third virtual data amount in a third interval of the ETI frames, the third virtual data amount (201-3) is 1,344 bytes obtained by subtracting 96 from 1,440. To transmit 1,344 bytes in the multiple size of the packet unit, 1,428 bytes obtained by multiplying 204 with 7 are necessary; and thus, a third MPEG-2 data in the third interval of the ETI frames (202-3) is transmitted with the size of 1,428 bytes to the outer coding unit 15.

If the MPEG-2 transmission stream is transmitted to the outer coding unit 15 by using the above described method, the MPEG-2 transmission stream can be transmitted to the outer coding unit 15 in the multiple size of the packet unit for every ETI frame as simultaneously maintaining the data amount according to the STL value on average.

The MPEG-2 transmission stream with the amount determined by the above described method is transmitted to the outer coding unit 15 for every interval of the DAB transmission frames. At this time, if the data is stored in the buffer for MPEG-2 data 12, the MPEG-2 stream is read in the buffer for MPEG-2 data 12 and transmitted thereafter. If the data is not stored in the buffer for MPEG-2 buffer 12, the null packet is read in the null packet forming unit 13, thereby multiplexing the effective packet and the null packet. Thus, the MPEG-2 data with the multiple size of the MPEG-2 packet unit is transmitted to the outer coding unit 15 for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average.

Fig. 3 is a flowchart showing a method for converting a media stream in accordance with the present invention.

As shown, for the method for converting the media stream for providing multimedia services in a DAB transmission system in accordance with the present invention, a MPEG-2 transmission stream is first inputted through a physical interface such as a SMPTE 310M or a DVB- ASI mainly used for digital TV broadcasting at step S301.

Then, at step S302, a data amount of the MPEG-2 transmission stream is determined in the MPEG-2 data analyzing unit 11. Afterwards, at step S303, based on the above determined data amount of the MPEG-2 transmission stream a STL value is obtained in the unit of 8 bytes of a data amount to be loaded into individual DAB transmission frames. Then, a data of an effective packet in the MPEG-2 transmission stream is stored into the buffer for MPEG-2 data 12 at step S304. At this time, during calculating the data amount, to prevent an excessiveness of the buffer for MPEG-2 data 12, the data amount is a value calculated by rounding up the actually obtained data amount or adding a smaller number to the actually obtained data amount.

Thereafter, in the MPEG-2 data multiplexing unit 14, the STL value indicating the data amount to be loaded into the individual DAB transmission frames is inputted from the MPEG-2 data analyzing unit 11 or the outside. Then, a data amount that is to be transmitted for every interval of the DAB transmission frames as simultaneously maintaining the data amount according to the STL value on average is calculated in a multiple size of a packet unit. Therefore, at step S305, the MPEG-2 data multiplexing unit 14 reads the data as much as the calculated data amount with the multiple size of the packet unit from the buffer for MPEG-2 data 12 or, a null packet from the null packet forming unit 13. Then, the MPEG-2 data multiplexing unit 14 multiplexes the data with the multiple size of the packet unit.

Next, at step S306, in the outer coding unit 15, to make the MPEG-2 transmission stream inputted from the MPEG-

2 data multiplexing unit 14 tolerate to errors during the transmission, for every interval of the DAB transmission frames, the data with the multiple size of the packet unit is subjected to the outer coding carried out in the packet unit as maintaining the data amount according to the STL value every interval of the DAB transmission frames, on average.

In conclusion, in the MPEG-2 multiplexing unit 14, the null packet formed to adjust the data amount with respect to the effective packet of the inputted MPEG-2 transmission stream is multiplexed at step S305. During multiplexing the null packet, the data with the multiple size of the packet unit is outputted for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average. In the outer coding unit 15, the data with the multiple size of the packet unit is subjected to the outer coding carried out for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average at step S306.

The outer coded MPEG-2 transmission stream is temporarily stored in the buffer for stream data 16 at step S307. In the transmission frame configuration unit 17, each stream data field value of the DAB transmission frames is determined and then, outputted. At this time, when configuring the DAB transmission frames, the outer coded MPEG-2 data is read as much as the data amount corresponding to the STL value from the buffer for stream and as a result, the MPEG-2 data is loaded into a stream data field of the DAB transmission frame at step S308.

The present invention as described above makes it possible to transmit the multimedia data processed in the form of the MPEG-2 system standard by using a conventional DAB transmission system, thereby showing an effect of proving multimedia services by using the DAB transmission

system.

Furthermore, compared with transmitting the multimedia data by using the digital TV broadcasting system, a method for transmitting the multimedia data by using the DAB transmission system based on Eureka 147 is much tolerated to errors during the transmission. Accordingly, there is an effect of providing stable multimedia services through a small terminal even in a mobile state.

Furthermore, by using the present invention, it is possible to subject the MEPG-2 transmission stream to the outer coding in the multiple size of the packet unit for every interval of the DAB transmission frames as maintaining the data amount according to the STL value on average, and as a result, there is provided an effect of efficiently using the data bit amount.

Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.