DE4417993A1 - Method for transmitting digital audio signals and device for transmitting digital audio signals - Google Patents

Abstract

The proposal is for a process for the transmission of audio signals. Two combined signals are formed from the right and left-hand stereo signals of an audio stereo signal. The combined signal is provided with error protection in varying degrees during its transmission. In the receiver, either the right and left-hand stereo channels are found from the combined signal and reproduced or, if a combined signal is too distorted, the other combined signal is reproduced. The varying error protection makes it possible to increase the range of a combined signal as against prior art proceses.

Description

State of the art

The invention is based on a method for transmission of digital audio signals according to the genus of the main saying. It is already a process for transferring digital audio signals from the patent DE 36 38 922 known, being a stereo audio signal that arises from a and a left stereo channel is transmitted. The right and left stereo channels become independent coded from each other and ver with the same error protection see broadcast, with the right and left stereo channels be transmitted at a certain time. The right and left stereo channels are on the receiver accordingly delayed so that the original Stereo audio signal is recovered.

Advantages of the invention

The method according to the invention with the features of the independent dependent claims 1, 3 and 4 and the invention direction with the features of independent claim 6 ha ben compared the advantage that with the same utility carrying capacity has a greater range for at least one Audio signal is reached. This makes it possible for the  Probability of total failure of the whole Audio signals is minimized. In an advantageous manner achieves that a receiver has at least one audio signal can receive a greater distance, though for this Procedure for the audio signals to be transmitted in Ver equally weighted data frames for all audio signals overall no additional transmission capacity is necessary for further error protection.

The device according to the invention with the features of the Proverb 6 has the advantage that the reception quality of a receiver for longer distances despite Failure of an audio signal or combination signal for the received audio signal or combination signal ver is better.

By the measures listed in the subclaims advantageous developments and improvements in the independent claims 1, 3 and 4 specified methods and the device described in independent claim 6 possible. An advantageous extension consists of the audio signals before transmission, combination signals to form and transmit the combination signals. At the Receivers become the audio sig from the combination signals nale determined again, using only the combination signals can be used, the a predetermined error frequency un step over. This way it is possible to get over to better protect carrying audio signals against errors.

It is particularly advantageous to have a soft output viterbide to use decoder for channel decoding, as this results in a additional reliability information about the detected Combination signals or audio signals is obtained. The Reliability information is used to decode decide which combination signals to determine a  Audio signals are used or which audio signals be issued.

drawing

An embodiment of the invention is in the drawing shown and in the description below he purifies. Show it

Fig. 1 is a schematic representation of the transmission of stereo audio signals and Fig. 2 shows the bit significance of the data frame of two combination signals.

Description of the embodiment

Fig. 1 shows a first input 1, is present on the audio signal as a right stereo signal in digitized form. The right stereo signal is passed from the first input 1 via a first digital line 31 to an adder 4 . A second input 2 is arranged, at which an audio signal is a left stereo signal in digitized form. The left stereo signal is passed on from the second input 2 via a second digital line 32 to a first phase shifter 3 .

The first phase shifter 3 carries out a phase shift of the left stereo signal by 90 °. The phase-shifted left stereo signal is fed to the adder 4 via a third signal line 33 . The adder 4 forms a first combination signal from the stereo signals supplied, which consists of the sum of the right stereo signal and the phase-shifted left stereo signal. Furthermore, the adder 4 forms a second combination signal, which consists of the difference between the right stereo signal and the left phase-shifted stereo signal. The first combination signal is fed to a first encoder 5 via a first signal line 34 . In parallel, the second combination signal is fed via a second signal line 35 to a second encoder 6 .

In particularly simple versions, both the phase shifter 3 and / or the adder 4 can be omitted, so that the audio signals or an audio signal and a phase-shifted audio signal are transmitted. The function of the adder 4 can also be taken over by a combiner who forms the corresponding combination signals from audio signals.

The first encoder 5 performs a data reduction of the first combination signal, information redundancy and information irrelevance being reduced in the first combination signal. The first encoder 5 works according to the ISO-MPEG 11 17 2/3 standard. The reduced first combination signal is fed via a first coding line 36 to a convolutional encoder 7 . The second encoder 6 processes the second combination signal in accordance with the norm of the first encoder 5 .

Corresponding coding methods are e.g. B. at Stoll, "Source coding for DAB and the evaluation of its performance: A major application for the new ISQ audio coding standard ", Proc. 1st Int. Symposium on DAB, pp. 83-97, 1982 ben.

The second reduced signal is conducted via a second coding line 37 to a second convolution encoder 8 . The first convolutional encoder 7 carries out channel coding of the first reduced combination signal. Channel coding methods are e.g. B. at Hagenauer, "Joint Source and Channel Coding for Broadcast Applications", Proc. of the 6th Tirrenia In ternational Workshop on Digital Communications, Elsevier, Amsterdam. The channel-coded reduced first signal is fed via a first channel coding line 38 to a multiplexer 9 .

The second convolutional encoder 8 performs channel coding of the second reduced combination signal in accordance with the first convolutional encoder 7 . The channel-coded reduced second signal is supplied to the multiplexer 9 via a second channel coding line 39 . The multiplexer 9 forms a multiplex signal from the supplied signals, which is fed via a multiplex line 40 to an OFDM modulator with high frequency stage 10 . The OFDM modulator carries out an orthogonal frequency division multiplex modulation and transforms the received signal in the high-frequency stage into a high-frequency signal and emits it via a transmitting antenna 11 . OFDM modulation methods are known and z. B. at basalle, "Principles of Modulation and Channel Coding for Digital Broadcasting for Mobile Receivers", EBU Review-Technical, No. 224 - August 1987, page 168 ff. The previously described method is carried out by a transmitter, which is shown schematically in FIG. 1.

The reception of the transmitted audio signals or combi nation signals is carried out by a receiver, which is shown in Fig. 1, and will be described below.

The emitted high-frequency signal is received via a receiving antenna 12 and fed to a high-frequency stage with OFDM demodulator 13 . The received high-frequency signal is frequency shifted and demodulated using the OFDM demodulator. The demodulated signal is supplied via a demodulator line 41 to a demultiplexer 14 . The demultiplexer 14 forms a reduced and coded first and second signal from the demodulated signal. The first reduced and coded signal is fed via a first demultiplexer line 43 to a first Viterbide encoder 15 . The second reduced and channel-coded signal is fed to a second Viterbi decoder 16 via a second demultiplexer line 42 . Corresponding Viterbi decoding methods are available from Hagenauer, "Joint Source and Channel Coding for Broadcast Applications", Proc. of the 6th Tirrenia International Workshop on Digital Communications, Elsevier, Amsterdam.

The first Viterbi decoder 15 performs channel decoding and determines reliability information which is a measure of the probability that the channel decoding has been carried out correctly. The channel-decoded first signal is fed to a first decoder 17 via a first Viterbi decoder line 44 . The second Viterbi decoder 16 determines a second channel-decoded signal from the second reduced channel-coded signal by performing channel decoding. The second Viterbi decoder 16 additionally determines reliability information which indicates a probability that the channel decoding has been carried out correctly.

The second reduced signal is supplied from the second Viterbide encoder 16 to a second decoder 18 via a second Viterbide decoder line 45 . The first decoder 17 determines from the supplied first channel-decoded signal in accordance with the ISQ-MPEG 11 17 2/3 standard, the first signal consisting of the addition of the right and left phase-shifted stereo signals. The first signal is fed to a switched adder 19 via a first decoder line 46 . The first decoder 17 also determines an error detection and leads this via a first error line 53 to the switched adder 19 . Likewise, the first Viterbi decoder 15 feeds the determined reliability information to the switched adder 19 via a first reliability line 51 .

The second decoder 18 uses the channel-coded second signal in accordance with the ISO-MPEG 11 172/3 standard to determine the second signal, which consists of the right stereo signal minus the phase-shifted left stereo signal. The second signal is fed to the switched adder 19 via a second decoder line 47 . In addition, the second decoder 18 performs an error detection which, for. B. is determined using test bits. This error detection is fed to the switched adder 19 via a second error line 54 . Likewise, the second Viterbi decoder 16 feeds the determined reliability information to the switched adder 19 via a second reliability line 52 .

The reliability information about correct detection of the transmitted audio signals or combination signals in the Viterbi decoder 15 , 16 is used e.g. B. according to the Viterbi algorithm with soft decision output as described by Hagenauer, "A Viterbi algorithm with soft decision outputs and its applications", Global Telecommunications Conference, Dallas 1989, calculated. The switched adder 19 determines from the supplied first signal and the supplied second signal output signals as a function of the supplied reliability information of the first and second Viterbi decoders 15 , 16 and the error detections of the first and second decoders 17 , 18 . If neither the reliability information nor the error identifiers indicate that an incorrect signal has been decoded, the switched adder 19 outputs the right stereo signal via a first output 48 and the left phase-shifted stereo signal via a second output 49 .

The right stereo signal is output after a Digi tal-analog conversion via a first speaker 21 . The left stereo signal is first fed to a second phase shifter 20 and then subjected to a digital-to-analog conversion. The second phase shifter 20 carries out a phase shift of the left stereo signal so that the right and left stereo signals are again in phase. The left stereo signal is then likewise output via a second loudspeaker 22 .

If the error detection of the first decoder 17 and the reliability information of the first Viterbi decoder 15 indicate that a transmission error has occurred, the switched adder 19 outputs the second signal via the first and second outputs 48, 49 , which results from the right stereo Signal minus the left, phase-shifted stereo signal consists of, if it was received without errors.

If the reliability information of the second Viterbide encoder 16 and the error detection of the second decoder 18 result in an incorrectly received signal, the switched adder 19 outputs the first signal via the first and second outputs 48 , 49 , which is the sum of the right and the phase shifted, Left stereo signal consists of, if it was received without errors.

If both the reliability information of the first Viterbi decoder 15 , the second Viterbi decoder 16 and the error detection of the first decoder 17 and the second decoder 18 indicate that the signals have been decoded incorrectly, no signal is output by the switched adder 19 .

The arrangement according to FIG. 1 functions as follows: The right or left stereo signal is prepared as described, the first convolutional encoder 7 using more error protection per data frame when coding the first combination signal than the second convolutional encoder 8 for the second combination signal. Instead of the first convolutional encoder 7 , however, the second folding encoder 8 can also apply a higher level of error protection during coding. The reduced and encoded signal is transmitted and recovered accordingly.

In this way it is ensured that either the second or the first reduced and channel-coded signal has a higher error protection and thus has a larger, error-free range than the other signal. It is thus possible, in the switched adder 19 , to ascertain the signal, which has a higher error protection, without errors at a greater distance than in previous systems.

Fig. 2 shows a first data frame 76 of a first combination signal. The first data frame 76 consists of five subareas, the first subarea 62 representing a header, the second subarea 63 having a bit allocation table, the third subarea containing 64 scale factors, the fourth subarea 65 samples and the fifth subarea 66 containing program-related data.

Data frames for DAB are available from Stoll, "Source coding for DAB and the evaluation of its performance: A major application for the new ISO audio coding standard ", Proc. Is Int. Sym posium on DAB, pp. 83-97, 1982.

A bit significance division 60 is shown above the first data frame 76 of the first combination signal. The bit significance, ie the importance of the individual bits, is plotted upwards. The first data frame 76 is plotted to the right, as shown. The header 62 and the bit allocation table 63 have a high bit signifi cance, ie these two areas are provided with high error protection. The third section 64 , which contains the scale factors, has a medium bit significance, so that the third section 64 receives less error protection than the first two sections. The fourth sub-area 65 , which contains the samples, has a low bit significance. Therefore, the fourth sub-area 65 receives little error protection. The fifth partial area 66 has a higher bit significance than the fourth partial area 65 . For this reason, greater error protection is added to the fifth partial area 66 than the fourth partial area 65 .

Correspondingly, a second data frame 77 of a second combination signal is shown schematically in FIG. 2. The second data frame 77 also has a header 71 , a bit allocation table 72 , scale factors 73 , samples 74 and data 75 accompanying the program. A bit significance distribution 61 of the second combination signal is shown above the second data frame 77 . It can be seen that the individual subareas 71 to 75 of the second data frame 77 of the second combination signal have a correspondingly graded bit significance as the subareas 62 to 66 of the first data frame 76 of the first combination signal. However, it can be clearly seen that the individual subareas 71 to 75 of the second data frame 77 of the second combination signal have a higher bit significance than the subareas 62 to 66 of the first data frame 76 of the first combination signal. From Fig. 2 it can thus be seen that the second combination signal is provided with a higher error protection than the first combination signal.

Instead of the components described, the digital Stereo signals also with the help of an arithmetic unit with memory  cher and the corresponding control programs processed become.

The transmission of audio signals was based on two Audio signals described, the Ver drive, the transmitter according to the invention and the inventive Receiver can transmit any number of audio signals.

Claims (7)

1. A method for the transmission of digital audio signals, in which at least two audio signals are coded separately from one another in a transmitter and are provided with error protection and transmitted to a receiver, the coded and error-protected audio signals being decoded by the receiver and the decoded Audio signals are checked for errors and, depending on the errors that occur, one or more audio signals are selected and reproduced, the error rates of which do not exceed a predetermined frequency, characterized in that the audio signals in the form of data frames ( 76 , 77 ) are transmitted such that the bits of a data frame ( 76 , 77 ) of each audio signal are provided with different error protection according to their importance, and that the data frames ( 76 , 77 ) of at least two different audio signals have differently sized error protection point. 2. The method according to claim 1, characterized in that before transmission from the digital audio signals min least two combination signals are formed that the Combination signals coded separately from each other and with be provided with an error protection that after the transmission the coded and error-protected combination signals de  encoded and checked for errors that from the deco dated combination signals audio signals formed and from be given, the combination signal, the one before exceeds the given error limit to determine the Audio signals is not used. 3. A method for sending digital signals containing audio signals or combination signals from audio signals, wherein at least two audio signals or two combination signals are separately coded and provided with error protection, characterized in that the digital signals in the form of data frames ( 76 , 77 ) are sent that the bits of a data frame ( 76 , 77 ) of each audio signal or each combination signal are provided with different error protection according to their importance, and that the data frames ( 76 , 77 ) of at least two audio Signals or at least two combination signals have differently sized error protection. 4. A method for receiving digital audio signals or digital combination signals, which are formed from audio signals, wherein coded and error-protected audio signals or coded and error-protected combination signals are decoded and the decoded audio signals or the decoded combination signals are checked for errors and, depending on the errors occurring, one or more audio signals or one or more combination signals are selected and output, in which the error rate is below a predetermined threshold, characterized in that the audio signals or the combination signals are received using data frames, that at least two audio signals or at least two combination signals are decoded and checked for errors whose data frames ( 76 , 77 ) have differently sized error protection. 5. The method according to claim 1, 2 and 4, characterized in that a channel decoder is provided for decoding the digital signals, which is designed as a soft output Viterbi decoder ( 15 , 16 ). 6. Device for receiving audio signals or combi nation signals, which are formed from audio signals, with a demodulator ( 13 ) which is connected to a demultiplexer ( 14 ), with at least two data outputs of the de multiplexer ( 14 ) A channel decoder ( 15 , 16 ) is connected and the data output of each channel decoder ( 15 , 16 ) is connected to a data input of a decoder ( 17 , 18 ) and the data output of each decoder ( 17 , 18 ) is connected to a data input of an evaluation circuit ( 19 ) is performed, each decoder ( 17 , 18 ) is connected via an error line to an error input of the evaluation circuit ( 19 ) and, when an error rate occurs in the audio signal or in the combination signal, which is above a predetermined threshold, a signal to the Evaluation circuit ( 19 ), characterized in that at least two decoders ( 17 , 18 ) and at least two channel decoders ( 15 , 16 ) are arranged, the at least two audio Decode signals or two combination signals whose data frames ( 76 , 77 ) have differently sized error protection. 7. The device according to claim 6, characterized in that a Viterbi decoder is arranged as a channel decoder ( 15 , 16 ), and that from the Viterbi decoder ( 15 , 16 ) a decoder line ( 51 , 52 ) is guided to the evaluation circuit ( 19 ) and the Viterbi decoder ( 15 , 16 ) gives reliability information about the channel-decoded audio signal or the channel-decoded combination signal to the evaluation circuit ( 19 ) and the evaluation circuit ( 19 ) selects the audio signals or the combination signals, the reliability information of which lies above a predetermined threshold and which outputs the audio signal or which determines the audio signal from the combination signals and then outputs.