The digital audio frequency broadcast (DAB) is after the amplitude modulation, frequency modulation’s new generation broadcast, has the emissive power to be small, the cover area is big, frequency spectrum use factor merits and so on high and transportable receive, simultaneously it is one kind of multimedia broadcast, may simultaneously transmit services and so on sound, image, writing, data and active phantom.
At present already had the DAB broadcast in many countries and the area, specially is very high in European and Asia’s some countries and the local DAB coverage fraction, and already succeeded realizes the commercialization. Follows the DAB technology in China’s promoted application, the market is also getting more and more urgent to the DAB receiver’s demand.
From the technical principle and the standard, the DAB receiver usually include three modules: RF demodulation module, baseband decoding (channel decoding and audio frequency decoding) module and control module. And the control module mainly uses in the fast message channel (FIC) decoding realization with the man-machine contact surface demonstration and the control. Electronic program guide (EPG)[1] provides the audio frequency and each kind of data traffic program to the user explains the information, it stated in FIC, through the main traffic channels traffic channel (MSC) transmission, usually an achievement man-machine contact surface’s part, provides to the user may choose program’s information, is the DAB receiver’s important component. This article mainly aims at British BBC and Digital One broadcast EPG data, west uses core micro electron company’s ID200 the DAB baseband decoding chip and components and so on TI Corporation’s MSP430, proposed that and realizes to the EPG information’s software decoding plan. West this project’s result will use in the core micro electron company’s DAB/DMB receiver appraisal board.
EPG introduced
1. EPG transmission content
In the DAB system, EPG uses for to transmit the audio frequency and each kind of data traffic program explains the information, after receiving the terminal decoding these explanation information demonstrates gives the user, by facilitates the user choice program. These showing information mainly includes the signal group (in a fixed frequency all broadcasting station to be called a signal group) to show that the information, the service (each kind of program’s general designation) showed the information as well as the program timetable, the program show the information and so on and the service and the service content related showing information.
2. EPG code structure
In the DAB broadcasting station transmitting end, the audio frequency and each kind of data traffic’s program showed that the information is processed first may expand sets the sign language (XML)[2] form document, in this process, to describe the program related explanation information to use the level nesting structure which as shown in Figure 1 to describe in the EPG information audio frequency and each kind of data traffic program explains between the information the level relations.
In EPG with element [3] expressed that the related information’s general designation, the element interior may contain many other elements and the attribute; Attribute [3] expresses the concrete meaning, for instance program’s starting time, closure time and so on. This structure has manifested between the different level element membership, as well as attribute and element respective relations. The most outer layer is the father element, the father element attribute and its daughter element belongs to the identical level, similar, the daughter element attribute and the second-level daughter element belong to the identical level. All levels of elements have the attribute which it is in sole possession, the attribute value has represented the concrete meaning.
Chart 1:EPG code structure
In the DAB receiving end, the EPG decoding’s goal is take suits all levels of elements and the corresponding attribute value the liquid crystal screen to demonstrate the way which and the people understand as to express. The father element is relative, any first-level element’s code structure is the same, is label (tag), length (len) and the value (value) combination, tag marks the different element and the attribute, len indicated that value the length, value is the attribute value, or is the subordinate element and the attribute. Like this may realize conveniently in the decoding end has the choice decoding, to is not interested the element to be possible to jump over the Len length directly the data, has provided the possible way for the highly effective decoding.
3. EPG transmission
EPG code flow as shown in Figure 2. Waits the transmission document the application layer to cross the EPG code immediately the document, passes through the multimedia objects to transmit the (MOT) encoder to produce completely including the extra message MOT object. Cuts the suitable size these objects the block, then transforms these blocks suits the DAB transmission the data packet, transmits through package of pattern [4] or in the X-PAD[4] data area.
Chart 2:EPG arranges the decoding flow schematic drawing
a. Transmission level data processing
Uses the MOT data transmission protocol transmission after the EPG code’s symbol stream. Above for ease of the nimble processing massive data (for example File), the MOT encoder (adds the object in front of main text namely becomes object) to divide Cheng Duoge the block, as shown in Figure 3.
Chart 3:MOT object block treating processes
May see the source document from Figure 3 first by Canada above, then information and the main text are divided independently separately many blocks, then also separately assigns a head for each block, uses for to mark the block the size as well as in the transmission multiplicity and so on important information. Most behind the block of information and the main text block of information composition different type’s MSC data set, the data set type and other related information define in MSC data set.
b. Network level data processing
In the DAB system, contains the MOT data the data set to be possible transmits through a package of pattern and the X-PAD data channel two ways. Here only as regularly explains the data processing take a package of pattern. Will contain MOT the data set pack, adds on Baotou and the package of tail information separately for each package, transmits (as shown in Figure by data packet’s form in the DAB channel 4).
Chart 4:MSC data set pack process
The EPG decoding’s software realizes
When has the massive EPG information needs to transmit, Chang Yi package of pattern transmission, therefore here discusses by a package of pattern.
The EPG decode procedure needs first from the network level start, namely the bale breaking, then the processing transmission level, namely the MOT decoding, processes the application layer finally first, namely EPG decoding. But because the entire process must realize finally on the mobile equipment, a impossible decoding, therefore we adopt the method is receives a package to process every time to the EPG decoding completes, then reprocessing next package.
The bale breaking process removes a Baotou package of tail, thus restores the MSC data set. In Baotou provides a package of length as well as wraps in the MSC data set the position and so on important information. Wraps the tail to serve as the CRC[3] verification, to simplify the software design to be possible to omit the CRC verification process, when processing direct jump package of tail then. Moreover, processes the CRC verification to be strict to the processor request, also, because DAB takes the broadcast system, its EPG information itself by repeatedly re-transmit, therefore is not the unnecessary waste resources, may omit the CRC verification process. In the following decode procedure many times will also meet the different level the CRC verification, may jump over does not process.
Solves the MSC data set process similarly is also removes the data set the head and tail, restores the main text the block, the block according to the data set type classification and according to the smooth combination, then restores the main text content. Carries on the EPG decoding again to the main text, then realizes the EPG decoding finally.
Moreover it is noteworthy that according to the DAB EPG agreement, the EPG decoding has two Profile to be possible to supply the choice, respectively is Basic Profile and Advance Profile[3], must carry on the choice according to the hardware source. Because this design in view of the mobile equipment, the choice processor is the lower end product, therefore chooses Basic Profile, like this is low to the hardware request and the processing speed request. Concrete EPG decoding flow as shown in Figure 5.
Figure 5: Concrete EPG decoding flow chart
EPG decoding hardware circuit
In this design proposal uses the DAB decoding chip is west core micro electron company’s ID200 DAB. ID200 can transmission frame carry on the full speed decoding to Eureka-147 the standard DAB, including the digital mixing, the synchronized/track and the demodulation, may simultaneously to transmit in the frame two groups audio frequencies, the data or the video frequency program carries on the decoding, after the decoding audio frequency program may through internal MPEG the L2 audio frequency decoder broadcast, but the data/video frequency program may send out through the SPI connection, further processes with other components until the demonstration.
Uses MCU is TI Corporation’s MSP430F147 processor, it is ultra low power loss Flash 16 RISC set of instructions monolithic integrated circuit, has formidable handling ability, on the rich piece the periphery module and the convenience development way. It provides 32kb FLASH ROM, 1kb RAM. Simultaneously to adapt the low end portable DAB receiver’s request, therefore uses Basic Profile to realize the EPG decoding.
This design’s hardware functional block diagram as shown in Figure 6, after the first DAB broadcast enters the RF module, is transformed into the intermediate frequency signal, transforms after A/D sends in the baseband decoding module, carries on the channel and the audio frequency decoding, simultaneously the baseband decoding module sends in the FIC information MCU to carry on the software decoding. Regarding the EPG decoding, MCU first carries on the analysis to FIC, the judgment choice and EPG related MSC, then from the baseband decoding module reads the correlation data, carries on the EPG decoding again to it, after finally will decode the EPG data to deliver to the graphic display device.
This article subtotal
This design realizes using the monolithic integrated circuit to DAB the EPG data message software decoding, and takes it as in the DAB receiver man-machine contact surface a module. This design method not only may reduce the baseband decoding module the hardware order of complexity, moreover is advantageous to the basis actual situation carries on the software to the product to promote nimbly, simultaneously keeps the next software decoding connection, facilitates uses Advanced Profile in view of higher paraffin MCU the EPG agreement the promotion application.
Reference:
[1] Digital Audio Broadcasting (DAB); Multimedia Object Transfer (MOT) Protocol. ETSI EN 301 234. 2006.1.
[2] Digital Audio Broadcasting (DAB); XML Specification for DAB Electronic Programme Guide (EPG). ETSI TS 102 818 .2006.2.
[3] Digital Audio Broadcasting (DAB); Digital Radio Mondiale (DRM); Transportation and Binary Encoding Specification for Electronic Programme Guide (EPG). ETSI TS 102 371 .2005.1.
[4] Mingying Lu, Guoyu Wang, Hongsheng Zhang, Embedded DAB Decoder IP for 3G/4G Mobile Application, 2005 Global Mobile Congress, 2005.10:236 - 240
[5] Radio broadcasting systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers.ETSI EN 300 401.2006.1
