DE19857888A1 - Digital audio broadcasting receiver controls DAB and RDS for receiving units so that they receive programs with corresponding program identifier with switch which is changed over through control unit quality - Google Patents

Abstract

RDS and DAB decoders determine program identifier of discontinued FM program and DAB program radio broadcasting respectively. Evaluation unit interprets reception quality of DAB and RDS FM receiving units. The control unit controls receiving units so that they receive program with corresponding program identifier with a switch changed through control unit quality based on input between receiving units. The control unit is formed in such a way that before program conversion or before transmitter search run of DAB receiver, the switch is controlled in predefined manner so that the reception signal of RDS FM receiver is led across the switch. The control is also formed in such a way that after program conversion or after transmitter search run of DAB receiver, the switch is controlled in predefined manner so that the reception signal of the DAB receiver is led across the switch.

Description

1 INTRODUCTION

We are briefly about the introduction of a new digital radio, called DAB.

As the area coverage of DAB is currently very low compared to FM broadcasting, the DAB listener will expect losses in reception quality and program diversity have to.

The aim of this diploma thesis is to develop a strategy that switches to the same or an equivalent program on FM in the case of poor DAB reception conditions, in order to always offer the listener the selected program in the best possible reception quality and at the same time increase the ease of use and functionality of the system 211 .

USED ABBREVIATIONS:

AM: amplitude modulation
DAB: digital audio broadcasting
EId: ensemble identifier; identifies a specific DAB ensemble (length: 32 bits)
FIB: Fast information block
FIC: Fast Information Channel
FIG: Fast Information Group
FM: frequency modulation
OE: Other Ensembles; signals which other ensembles / services can be received
PI: program identifier; identifies a specific FM-RDS program (length: 16 bits)
RDS: radio data system
SId: service identifier; identifies a specific DAB service
TA: Traffic announcement
TII: Transmitter identification information
GPS: global positioning system

2. PROBLEM ANALYSIS

At the beginning as well as in the course of each project you face problems that are discussed and have to be solved. The special thing about this topic is that here the digital broadcasting world, in the form of DAB, with which the analog broadcasting world meets.

At this point, the characteristics, requirements, advantages and limitations of such Systems are explained.

2.1 PRINCIPLE CONSIDERATIONS 2.1.1 REQUIREMENT FOR A DIVERSITY SYSTEM

The aim of a diversity system is to provide the listener with the best possible reception enable without disturbing interruptions or switching noises.

High-quality FM double tuner solutions can nowadays accomplish this task unnoticed because the FM Master tuners very fast frequency changes, as well as a responsive quality assessment feature.

However, if a digital system such. B. DAB, with an FM receiver to a diversity System is combined, there are some problems and limitations that need to be considered Request analysis (see 2.1.2).

2.1.2 WEAKNESSES FROM DAB TO FM

• - DAB audio signal is about 0.5 compared to FM. . . 2 seconds delayed
• - The quality criterion of the DAB receiver used reacts very slowly (see 4.2.3)
• - The resulting noise in poor reception is unacceptable for the listener
• - The quality of the audio signal remains to a certain extent as the reception deteriorates Perfect point, but then decreases rapidly.
• - Long switching times (approx. 0.7 sec) between different frequencies (ensembles), due to synchronization processes, time deinterleaving and audio decoding of the signal (cf. duration of frequency change with FM <1.5 ms). This state of affairs is. Illustrated by Figure 2.1.

Fig. 2.1

Representation of the switching times

To Fig. 2.1

Fig. 2.1 shows the switching options that are possible in a DAB / FM divesity system. It is easy to see which switch paths can be carried out quickly and which are not. When switching between systems, you can always switch directly, provided that both receivers are tuned to the same program. The transmitter tracking within FM usually also goes unnoticed because, as the diagram shows, the switchover time is very short. If, however, service tracking is to take place within DAB, that is to say switching between ensembles (eg "SWR1"), there is a system-related pause of approx. 0.7 seconds that the DAB receiver needs to complete the ensemble change. This time is extended by the duration of the quality assessment (5... 7.5 sec), since it must first be checked whether the new ensemble can be received in sufficient quality before it is offered to the listener. At this break from 6. . . Bridging for 8 seconds can, if available, be switched to an FM-RDS program with the same content (eg "SWR1"). However, it is worrying that, in the relatively short period of 8 seconds, the system is switched twice, which means that the time delay of the DAB signal of approx. 1. . . 2 sec is very annoying. It is therefore advisable to simply switch to FM for a longer period of time (<20 sec), which somewhat reduces the disturbing influence of the signal delay of DAB and at the same time brings greater certainty with the quality statement of DAB.

2.1.3 CONSEQUENCES FOR A DAB / FM DIVERSITY SYSTEM

The problems described above have the following consequences for switching between DAB and FM:

• - If possible, it should not be switched between the systems too often, because of the signal delay of DAB the switching process is always audible.
• - The inertia of the quality assessment also speaks for longer time intervals between the Switching operations
• - Given the rapid drop in audio quality from DAB to bad ones Reception conditions, the limit value of the DAB bit error rate must be defined very precisely, so that a good compromise between acceptable hearing quality and long range can be achieved can.
• - Consideration should be given to the extent to which GP3 can be used in order to To compensate for the disadvantages of DAB.

2.1.4 SWITCHING MECHANISMS

A basic function of this diversity system is switching between the two Systems. For this it is necessary that DAB and FM-RDS programs have the same content can be assigned. The respective specifications see, among others, the following mechanisms described. There are basically two types of program references:

Hardlink

A hard link is a fixed reference to a program that is identical in terms of content, which in the additional data (e.g. RDS) of the referring service.

Soft latch

One speaks of a soft link if a service refers to a service associated with content. An example of this are the program types (PTy's), which are used to determine the program content of the classify the selected service according to type or style of music (e.g. news, pop, classical, Disaster alarm).  

2.4.1 Programs with the same content

Fig. 2.2

Different hard links between DAB and FM

2.1.5 SELECTED SOLUTION 2.1.5.1 Service detection

Switching between services with the same content was carried out as a soft link, with the Services are identified via the DAB-SId or the RDS-PI code. The use of a hard link, in this case the reference to the RDS-PI code in the DAB-FIC, was not implemented because this hardlink is not available in Baden-Württemberg. The switch to similar services, with the help of PTy's, was also not possible implemented because this mechanism is not yet sufficiently available (in Baden-Württemberg only in volume III).

No OUs because they do not exist.

The FM radio takes over the FM transmitter chain tracking, in the usual way, via the Alternative frequencies (AF tables) that are broadcast in the RDS data stream. That mechanism was already present in the FM device and did not require any special treatment. The opportunity to support the switchover strategy with GPS was discovered in the course of the diploma thesis only a detailed theoretical consideration (see 4.5), as here too the required data in the DAB Data stream was missing.

2.1.5.2 LF switchover

The switchover between the DAB and the FM-NF signal was carried out without delay and without cracking. Subjective tests showed that a delay-free switchover, despite the signal delay between DAB and FM, has a much less disruptive effect than a switchover in which the signal is muted for a period of time (1... 5 seconds) in order to conceal the signal delay. The switchover was implemented with the I ² C-bus controlled audio processor TDA7310 from SGS-Thomson, since this is already available on the FM radio and has been found to be suitable for this purpose.

2.1.5.3 Quality assessment of the DAB signal

For this purpose, an average filtering of the EFC was provided in the software, the characteristics of which are: can be changed online in the radio software. In addition to the mean value control, the instantaneous value of the EFC was also monitored implemented to take account of any short-term drops in reception. This Monitoring can also be parameterized online.  

This evaluation strategy was later optimized through tests. The results and the characteristics the switchover is described under point 4.1.  

3.1 How the system works

Fig. 3.1

Block diagram of the test system

The system is divided into four function blocks:

• - DAB receiver
• - FM receiver
• - GPS receiver
• - stationary PC or laptop

The three receivers are each equipped with a serial interface (RS-232), which are connected to a PC via external level converters. A software runs on the PC, which has the task of controlling the DAB receiver and the FM radio, as well as reading out and evaluating the data of the DAB and FM receiver relevant for the assessment of the reception quality and deriving a switchover strategy from this. Furthermore, the data read out are stored in a file together with the current GPS data, that is to say with the current geographical position, the current time, the date, and the speed and the course. This data is then available for later evaluation (visual representation, etc.). The switching of the LF source (DAB or FM), as well as the volume setting, is controlled via an I ² C bus in the TDA7310 sound controller of the Becker FM radio.

3.2 THE GRUNDIG DAB RECEIVER 3.2.1 HARDWARE

The "DAB receiver used is with a so-called DAPI interface (DAB application programmable interface). This interface enables easy access to the functions of the receiver. There is a selection of commands for the most important functions such as. B. changing channels, Frequency change and reading out data such. B. station name, frequency and bit error rate. Communication takes place via an RS-232 interface and a software specified by Grundig Protocol. For exact details of the commands and the protocol should here for reasons of Confidentiality can be waived. It should also be noted that there is still an EMC-compliant connection field for the receiver had to be produced because various EMC measurements indicated this.  

3.2.2 SOFTWARE

For test purposes, a Windows interface had to be created for the DAB receiver, which the DAPI communication mechanisms, as well as some of the DAPI commands First of all, make sure that this recipient has suitable mechanisms at all Enable diversity strategy. Since this program module should serve as the basis for the final software of the test system, later expanded to include additional functions. The detailed description of this software can be found in the appendix.

3.2.3 QUALITY ASSESSMENT OF THE DAB SIGNAL

The error flag counter provided by the DAB receiver indicates the number of occurrences Bit errors in the FIC again that occur over a period of 100 CIF's (Common Interleaved Frames) ≘ 2.4 sec occurred. This parameter allows a reliable quality assessment, but with the Disadvantage of the somewhat slow response time. Very short and strong reception disturbances can therefore not be adequately recorded.

Describe the function of the EFC in more detail (accuracy 10 exp-4)

After carrying out intensive tests, the following guideline values resulted for the evaluation:

Fig. 3.2

DAB Q rating

These benchmarks have a certain amount of room for maneuver in the somewhat slow response time of the EFC of 2.4 sec.  

Fig. 3.3

Test software for FM radio

3.3.3 QUALITY ASSESSMENT OF THE FM SIGNAL

The FM radio provides the following quality parameters:

• - field strength value (1 byte)
• - multipath value (1 byte)
• - RDS swing counter (1 byte)

After consultation with an employee of Becker's software development department, the result was The following guidelines for evaluating quality parameters:

Fig. 3.4

FM quality assessment

4. RESULTS

Below is a discussion of the results, as well as some theoretical considerations and Views.

4.1 QUALITY ASSESSMENT ALGORITHM

Fig. 4.1

Dynamic behavior of quality assessment

Fig. 4.1 shows the basic behavior of the DAB quality assessment. It is a laboratory simulation in which, with the help of an adjustable attenuator, a deterioration in reception was caused in the antenna feed of the DAB receiver. The functioning of the quality assessment will now be explained on the basis of this diagram.

Mean value monitoring

The left part of the diagram provides information about the behavior of the mean filter. The peculiarity here is that the mean value (green curve) in DAB mode is the instantaneous value (red curve) follows faster than in FM mode. The reason for this is that the EFC values in the DAB Operation with a higher weight (here: weight = 3) is included in the mean value, while in FM Operation the instantaneous values get weight 1.  

This ensures that the system reacts faster to fluctuations in DAB reception and is therefore able to switch to FM as early as possible, and still short-term, small To suppress exceedances of the switch-off threshold. The response to EFC changes in FM mode, which is slower by a factor of 3, was chosen to Make sure that you only switch back to DAB when the reception is sufficient has stabilized to avoid unnecessary switching operations. Furthermore, the mean value shutdown was equipped with a hysteresis behavior, which is also used for Stabilization of the switching behavior is used. In the example above, the shutdown threshold was 3800 Bit error, the switch-on threshold set to 4300 bit error, and thus the hysteresis to 500 bit error. These values were tested and confirmed during test drives. Another feature is that the mean value does not exceed an upper limit (here: 5500 bit errors) to prevent the system from taking too long after very large interference has subsided Time needed to turn on again.

Immediate shutdown

The behavior of the immediate shutdown can be seen in the right part of Fig. 4.1. This has the task of switching to FM immediately if the reception disturbances increase rapidly after the upper limit (here: 5500 bit errors) has been exceeded. This mechanism is necessary because the shutdown of the mean value would react too slowly. After the changeover, the mean value is then set to the value of the upper limit. The switch back to DAB takes place again via the mean value monitoring after the switch-on threshold is undershot.

To further clarify the above-mentioned facts, the flow chart of the switchover strategy is shown in Fig. 4.2.

Fig. 4.2

Simplified flowchart of the switch strategy

4.3 STRATEGY FOR TREATING TRAFFIC INFORMATION

In a double tuner receiver, the handling of traffic reports (so-called Traffic announcements (TA for short) are some special features that should be considered briefly here.

4.3.1 TYPES OF SIGNALING TA'S

There are two ways to signal TAs in the FIC of the DAB data stream:

• - A TA is signaled in the service currently in use
• - A TA is signaled which is broadcast in another ensemble (so-called other ensemble signaling, or OE signaling for short)

Then there are the TAs that are broadcast on FM-RDS

4.3.2 USEFUL USE OF TA'S

In the following, some recommendations are presented that should enable the TA's to be used as sensibly as possible.

• 1. A currently heard TA should not be interrupted by another TA.
• 2. If several TAs occur at the same time, the TA, its associated one, always has priority Program is currently being used.
• 3. You should refrain from using OE signaling because there is a change of the Ensemble, which carries the risk that the signaled ensemble is not at the moment is receivable. There is then a pause of several seconds due to the change, which is very annoying for the user.
• 4. If the DAB reception is good, the FM tuner can take over the task of Search the tape cyclically for RDS-TA's, which are then sent to the user (taking point 1 and 2) can be imported into its ongoing DAB service.

annotation

The treatment of TAs was limited to the theoretical part of the thesis Consideration, since in Baden-Württemberg the necessary data was not available in the FIC at this time Were available.  

4.5 MEANING OF GPS IN DAB / FM DIVERSITY SYSTEMS

The presence of a self-location possibility of a DAB receiver, e.g. B. with the help of GPS, opens up new perspectives in relation to diversity systems. Since navigation systems in vehicles are becoming more and more important, it is conceivable that GPS is used in such devices to support the diversity system could. In the FIC of the DAB signal, some data can be fed in by the broadcasters that are related to are quite suitable for this purpose. Some of the implementation options are described below.

4.5.1 REGION IDENTIFIER

With the help of the region identifier, a transmission area can be specified by specifying the latitude and Length of the corner points of a rectangle. If a receiver now has a positioning system (GPS), it can be done easily be determined whether the recipient is in the transmission area or is leaving it. This makes it possible to estimate whether high-quality reception is possible or not. Based on this estimate, the quality assessment criteria can then be made accordingly be adjusted. A self-learning function can also be implemented, in such a way that the receiver is all received region IDs and is thus able to recognize via the location system when entering a new transmission area. Such functionality has the advantage that a search can be started specifically if indicated by a saved region id, new services can be suspected. Such an adaptive system has the advantage that the user, in the frequently used by him Areas with the best possible range of programs with minimal operating effort can.  

4.5.2 TRANSMITTER IDENTIFICATION INFORMATION (TII)

The TII contains the geographical coordinates of the transmitters involved in the transmission of the corresponding ensembles are involved. It makes sense to use this information in a similar way as described under 4.5.1. The only difference is that, knowing your own position, the distances to the surrounding stations can be determined. A rough estimate of how the Reception quality will behave. The evaluation criteria can then be adjusted accordingly. An adaptive solution is also conceivable; it could look like this: A radius is assigned to each TII that has already been received Quality course is determined. A database is created in which all the transmitters already received with their estimated ones Range are included. The receiver is now able to recognize in advance when in a Transmission area is entered and can, according to the database, selectively a few frequencies scan cyclically.

Claims (5)

1. DAB receiver with an RDS-FM receiver
with an RDS decoder to determine the program name of the set FM radio program,
with a DAB decoder to determine the program name of the set DAB radio program,
with a quality evaluation unit for evaluating the reception quality of the DAB receiver and the RDS-FM receiver,
with a control unit that controls the DAB receiver and the RDS-FM receiver so that they receive programs with the corresponding program name,
with a switch which, controlled by the control unit, switches on the quality side on the input side between the DAB receiver and the RDS-FM receiver and feeds the received signal to an output of the DAB receiver with an RDS-FM receiver. 2. DAB receiver with an RDS-FM receiver according to claim 1, characterized characterized as a unit for education over a given period of time averaged quality values is provided and their averaged quality values the Control unit are fed. 3. DAB receiver with an RDS-FM receiver according to claim 2, characterized characterized in that the unit for the formation of averaged quality values is designed is that the specified period for averaging the quality values of the RDS-FM Recipient is selected longer than the specified period for the DAB Receiver. 4. DAB receiver with an RDS-FM receiver according to claim 1, 2 or 3, characterized characterized in that the control unit is designed such that before a Program change or before a channel search by the DAB receiver Switch is controlled so that the received signal of the RDS-FM receiver the switch is fed to the output.   5. DAB receiver with an RDS-FM receiver according to claim 2, characterized characterized in that the control unit is designed so that after a Program change or after a station search by the DAB receiver Switch is controlled so that the received signal of the DAB receiver via the Switch is fed to the output.