EP1730843A2 - Method and apparatus for classifying importance of encoded frames in a digital communications system - Google Patents

Method and apparatus for classifying importance of encoded frames in a digital communications system

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Publication number
EP1730843A2
EP1730843A2 EP05727757A EP05727757A EP1730843A2 EP 1730843 A2 EP1730843 A2 EP 1730843A2 EP 05727757 A EP05727757 A EP 05727757A EP 05727757 A EP05727757 A EP 05727757A EP 1730843 A2 EP1730843 A2 EP 1730843A2
Authority
EP
European Patent Office
Prior art keywords
decoding
frame
error detection
energy difference
detection means
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP05727757A
Other languages
German (de)
French (fr)
Other versions
EP1730843A4 (en
Inventor
Hans Christian Blomberg
Peter William Hilding Svendsen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Motorola Solutions Inc
Original Assignee
Motorola Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Motorola Inc filed Critical Motorola Inc
Publication of EP1730843A2 publication Critical patent/EP1730843A2/en
Publication of EP1730843A4 publication Critical patent/EP1730843A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/0078—Avoidance of errors by organising the transmitted data in a format specifically designed to deal with errors, e.g. location
    • H04L1/0086—Unequal error protection
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056—Systems characterized by the type of code used
    • H04L1/0061—Error detection codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/20—Arrangements for detecting or preventing errors in the information received using signal quality detector
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/12—Transmitting and receiving encryption devices synchronised or initially set up in a particular manner
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/005—Correction of errors induced by the transmission channel, if related to the coding algorithm
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/012—Comfort noise or silence coding
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L2019/0001—Codebooks
    • G10L2019/0007—Codebook element generation
    • G10L2019/0008—Algebraic codebooks
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L2209/00—Additional information or applications relating to cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00
    • H04L2209/80—Wireless
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
    • H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
    • H04M11/064—Data transmission during pauses in telephone conversation

Definitions

  • the present invention relates to communications systems, in general, and in particular, to a method and an apparatus for classifying importance of encoded frames in communications systems with end-to-end encryption.
  • TETRA TErrestrial Trunked RAdio
  • the synchronization information which synchronizes the decryption module in the receiving terminal with the encryption module in the transmitting terminal is embedded in the audio data stream. Especially in the very beginning of encrypted audio data stream repeated synchronization information replaces voice information so as to ensure that the decryption module is synchronized when encrypted voice data starts coming through.
  • the synchronization information is placed repeatedly as to allow so called late entry and the time period between placing synchronization information is randomized. The late entry occurs when two secure systems are communicating and the two parties need to be in exactly the same vector state in the crypto algorithm. Most secure systems therefore send this vector as the first data.
  • the receiving party misses this vector (the receiving Mobile Station could be switched off) then it would never be able to decrypt the remaining part of the message. And to overcome this problem additional synchronization is required. Therefore the crypto vector is sent in small parts interleaved into the data. This enables the Mobile Station to regain the crypto synchronization even if it had lost the first part.
  • This additional synchronization is implemented as so called frame stealing.
  • the frame stealing is implemented in such a way that the synchronization information replaces some of the audio frames. The audio data replaced by the synchronization information is discarded.
  • a method of classifying importance of encoded frames in a digital communications system by calculating an energy difference between outputs of a frame first decoding with an error detection and said frame second decoding without said error detection.
  • said frames are encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP) and said method comprises the following steps : a) first decoding a frame in an ACELP decoder with a Bad Frame Indication (BFI) function enabled; b) second decoding said frame in said ACELP decoder with said BFI function disabled; c) calculating an energy difference between said first and said second decoding output.
  • Said calculated energy difference is a measure of said importance.
  • Said outputs of said first and said second decoding are Pulse Code Modulation Signals .
  • a state of the ACELP decoder is stored before said first decoding step and reset to the saved state before the second decoding step.
  • outputs of said first decoding and said second decoding are saved for said calculation of said energy difference.
  • steps a) through c) are performed on each ACELP encoded frame in a data stream.
  • VAD Voice Activity Detect
  • an apparatus for classifying importance of encoded frames in a digital communications system comprises a decoding means and an error detection means, wherein said decoding means is adapted to decode a frame with said error detection means activated and to decode said frame with said error detection means deactivated.
  • the apparatus further comprises a processor adapted to calculate an energy difference between outputs of said frame decoding with said error detection means activated and said frame decoding with said error detection means deactivated.
  • said decoding means is an Algebraic Code Excited Linear Predictive (ACELP) decoder and said error detection means is a Bad Frame Indication (BFI) function.
  • the apparatus further comprises a memory for storing state of the ACELP decoder before sai first decoding with said error detection activated and for resetting said ACELP decoder to the saved state before said second decoding with said error detection deactivated.
  • Said memory is also adapted to store outputs of said decoding with said error detection activated and said decoding with said error detection deactivated. The outputs are necessary for said calculation of said energy difference.
  • Said processor is adapted to calculate the energy difference using a basic energy estimate or alternatively a Voice Activity Detect (VAD) method.
  • VAD Voice Activity Detect
  • the present invention beneficially allows for: • quick synchronization without severe audio degradation, • improving quality of audio in the speaker of the Mobile Station.
  • FIG. 1 is a flow chart illustrating a method of classifying importance of encoded frames in a digital communications system in one embodiment of the present invention
  • FIG. 2 is a diagram illustrating apparatus adapted to implement the method of classifying importance of encoded frames in a digital communications system in one embodiment of the present invention.
  • FIG. 1 and FIG. 2 one embodiment of a method of classifying importance of encoded frames in a digital communications system according to the present invention is shown.
  • radio signal in a form of frames encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP) are received 102 by an ACELP decoder 202.
  • ACELP decoder 202 receives 102 by an ACELP decoder 202.
  • a first frame is first decoded 106 in said ACELP decoder 202 with an error detection means 204 activated.
  • a state of the ACELP decoder 202 is stored 104 in a memory 208 of an apparatus 200.
  • the term "state of the ACELP decoder” refers to a set of parameters of an ACELP decoder in a particular time.
  • said error detection means 204 is a Bad Frame Indication (BFI) function.
  • BFI Bad Frame Indication
  • the ACELP decoder's state is restored 110 to the state stored in said memory 208.
  • a second decoding 112 of said frame in said ACELP decoder 202 is carried out with said error detection means 204 deactivated. Outputs of said first decoding 106 and said second decoding 112 are saved 108, 114 in said memory 208.
  • the output of the ACELP decoder 202 is a Pulse Code Modulation signal. Said outputs saved in the memory 208 are used for calculating 116 an energy difference between said first 106 and said second 112 decoding output. The energy difference is a measure of said importance.
  • a basic energy estimate is used.
  • the basic energy estimate is hardware or software implemented calculation function that estimates Root Mean Square (RMS) power of the incoming signal.
  • RMS Root Mean Square
  • VAD Voice Activity Detect
  • the VAD method is well known in communications systems, e.g. in
  • GSM Global System for Mobile communications
  • TETRA Global System for Mobile communications
  • the method of classifying importance of the frames based on energy difference calculated as described above is carried out on each ACELP encoded frame in a data stream.
  • the method of classifying importance of encoded frames is used in a digital communications system where a frame synchronization process with frame stealing is implemented. When the frame to be stolen is selected based on its importance (i.e the frame to be stolen has low importance relative to importance of other frames) the negative impact on audio quality of the frame stealing is minimized.
  • FIG. 2 an apparatus 200 for classifying importance of encoded frames in a digital communications system is shown.
  • the apparatus 200 comprises a decoding means 202 and an error detection means 204.
  • said decoding means 202 is an Algebraic Code Excited Linear Predictive (ACELP) decoder and said error detection means 204 is a Bad Frame Indication (BFI) function.
  • ACELP Algebraic Code Excited Linear Predictive
  • BFI Bad Frame Indication
  • Said decoding means 202 is adapted to decode a frame with said error detection means 204 activated and to decode said frame with said error detection means 204 deactivated.
  • the apparatus 200 further comprises a processor 206 adapted to calculate an energy difference between outputs of said frame first decoding 106 with said error detection means 204 activated and said frame second decoding 112 with said error detection means 204 deactivated. Said energy difference is a measure of said importance.
  • the apparatus 200 further comprises a memory 208 for storing state of the decoding means 202 before said step of first decoding 106 with said error detection means 204 activated. Said stored state is used for resetting said decoding means 202 to the stored state before said step of second decoding 112 with said error detection means 204 deactivated.
  • the memory when a capacity of the memory 208 is big enough the memory can be used for storing both the state of the ACELP decoder 202 and the outputs of the ACELP decoder 202.
  • two memory modules can be used, wherein a first memory module is used for storing said state and a second memory module is used for storing said ACELP decoder's outputs.
  • the memory 208 is a Random Access Memory (RAM) .
  • said processor 206 is adapted to calculate the energy difference using a basic energy estimate. In alternative embodiment said processor 206 is adapted to calculate the energy difference using a Voice Activity Detect (VAD) method.
  • VAD Voice Activity Detect
  • the basic energy estimate or the VAD method may be hardware implemented in a form of specialized integrated circuit.
  • Said memory 208 is adapted to store outputs of said first decoding 106 carried out with said error detection activated and said second decoding 112 carried out with said error detection deactivated. The stored outputs are then used in said process of calculation 116 of said energy difference. After calculating said energy difference said processor 206 indicates the importance of particular frames by flagging them 118.
  • the ACELP decoder is used for the purpose of classification of importance of the encoded frames. The ACELP decoder is used to exactly simulate what will take place in the remote decoder. As it is not an estimation what will happen on the remote decoder but an exact simulation of the remote decoder the obtained results of classification are better than in other methods.
  • the ACELP decoder is also used to classify the importance of the frames but the flags are added by the processor 206 to respective frames of the encoded data stream. Further in the transmission path a frame with a flag indicating low importance is stolen from the stream of encoded frames and replaced with synchronization information.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Probability & Statistics with Applications (AREA)
  • Theoretical Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Quality & Reliability (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

A method of classifying importance of encoded frames in a digital communications system by calculating an energy difference between outputs of a frame decoding with an error detection and said frame decoding without said error detection. Said frames are encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP). Said method comprises the following steps: first decoding (106) a frame in an ACELP decoder with a Bad Frame Indication (BFI) function enabled; second decoding (112) said frame in said ACELP decoder with said BFI function disabled; calculating (116) an energy difference between said first and said second decoding output. Said calculated energy difference is a measure of said importance.

Description

METHOD AND APPARATUS FOR CLASSIFYING IMPORTANCE OF ENCODED FRAMES IN A DIGITAL COMMUNICATIONS SYSTEM
Field of the Invention The present invention relates to communications systems, in general, and in particular, to a method and an apparatus for classifying importance of encoded frames in communications systems with end-to-end encryption.
Background of the Invention For radio communication systems with end-to-end encryption, like for instance TErrestrial Trunked RAdio (TETRA) system, as defined by the European
Telecommunications Standards Institute (ETSI) , the synchronization information which synchronizes the decryption module in the receiving terminal with the encryption module in the transmitting terminal is embedded in the audio data stream. Especially in the very beginning of encrypted audio data stream repeated synchronization information replaces voice information so as to ensure that the decryption module is synchronized when encrypted voice data starts coming through. The synchronization information is placed repeatedly as to allow so called late entry and the time period between placing synchronization information is randomized. The late entry occurs when two secure systems are communicating and the two parties need to be in exactly the same vector state in the crypto algorithm. Most secure systems therefore send this vector as the first data. However if the receiving party misses this vector (the receiving Mobile Station could be switched off) then it would never be able to decrypt the remaining part of the message. And to overcome this problem additional synchronization is required. Therefore the crypto vector is sent in small parts interleaved into the data. This enables the Mobile Station to regain the crypto synchronization even if it had lost the first part. This additional synchronization is implemented as so called frame stealing. The frame stealing is implemented in such a way that the synchronization information replaces some of the audio frames. The audio data replaced by the synchronization information is discarded.
Although the frame stealing technique allows for synchronization of the decryption module in the receiving terminal with the encryption module in the transmitting terminal this process has some significant drawbacks.
In the TETRA communications system if a frame has been stolen and used for synchronization an ACELP (Algebraic Code Excited Linear Predictive) decoder tries to reconstruct the missing frame using a Bad Frame Indication (BFI) algorithm. BFI algorithm is a part of the ACELP standard. However results of the reconstruction quite often are far from ideal and quality of the audio signal in the speaker of the Mobile Station is poor.
Summary of the Invention According to a first aspect of the present invention there is provided a method of classifying importance of encoded frames in a digital communications system by calculating an energy difference between outputs of a frame first decoding with an error detection and said frame second decoding without said error detection. Preferably, said frames are encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP) and said method comprises the following steps : a) first decoding a frame in an ACELP decoder with a Bad Frame Indication (BFI) function enabled; b) second decoding said frame in said ACELP decoder with said BFI function disabled; c) calculating an energy difference between said first and said second decoding output. Said calculated energy difference is a measure of said importance. Said outputs of said first and said second decoding are Pulse Code Modulation Signals .
To allow for performing the two steps of decoding in the same conditions a state of the ACELP decoder is stored before said first decoding step and reset to the saved state before the second decoding step. In addition outputs of said first decoding and said second decoding are saved for said calculation of said energy difference.
In one embodiment the steps a) through c) are performed on each ACELP encoded frame in a data stream.
Preferably in said step of calculating a basic energy estimate is used. Alternatively a Voice Activity Detect (VAD) method can be implemented.
According to a second aspect of the present invention there is provided an apparatus for classifying importance of encoded frames in a digital communications system. The apparatus comprises a decoding means and an error detection means, wherein said decoding means is adapted to decode a frame with said error detection means activated and to decode said frame with said error detection means deactivated. The apparatus further comprises a processor adapted to calculate an energy difference between outputs of said frame decoding with said error detection means activated and said frame decoding with said error detection means deactivated.
Preferably said decoding means is an Algebraic Code Excited Linear Predictive (ACELP) decoder and said error detection means is a Bad Frame Indication (BFI) function. The apparatus further comprises a memory for storing state of the ACELP decoder before sai first decoding with said error detection activated and for resetting said ACELP decoder to the saved state before said second decoding with said error detection deactivated. Said memory is also adapted to store outputs of said decoding with said error detection activated and said decoding with said error detection deactivated. The outputs are necessary for said calculation of said energy difference. Said processor is adapted to calculate the energy difference using a basic energy estimate or alternatively a Voice Activity Detect (VAD) method.
The present invention beneficially allows for: • quick synchronization without severe audio degradation, • improving quality of audio in the speaker of the Mobile Station.
Brief description of the drawings The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which:
FIG. 1 is a flow chart illustrating a method of classifying importance of encoded frames in a digital communications system in one embodiment of the present invention,
FIG. 2 is a diagram illustrating apparatus adapted to implement the method of classifying importance of encoded frames in a digital communications system in one embodiment of the present invention.
Description of an embodiment of the invention Referring to FIG. 1 and FIG. 2 one embodiment of a method of classifying importance of encoded frames in a digital communications system according to the present invention is shown. In this embodiment radio signal in a form of frames encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP) are received 102 by an ACELP decoder 202. Then a first frame is first decoded 106 in said ACELP decoder 202 with an error detection means 204 activated. Before said step of first decoding 106 a state of the ACELP decoder 202 is stored 104 in a memory 208 of an apparatus 200. The term "state of the ACELP decoder" refers to a set of parameters of an ACELP decoder in a particular time. In one embodiment said error detection means 204 is a Bad Frame Indication (BFI) function. In the next step the ACELP decoder's state is restored 110 to the state stored in said memory 208. Next, a second decoding 112 of said frame in said ACELP decoder 202 is carried out with said error detection means 204 deactivated. Outputs of said first decoding 106 and said second decoding 112 are saved 108, 114 in said memory 208. The output of the ACELP decoder 202 is a Pulse Code Modulation signal. Said outputs saved in the memory 208 are used for calculating 116 an energy difference between said first 106 and said second 112 decoding output. The energy difference is a measure of said importance.
In said step of calculating 116 a basic energy estimate is used. The basic energy estimate is hardware or software implemented calculation function that estimates Root Mean Square (RMS) power of the incoming signal. Alternatively, in the step of calculating 116 Voice Activity Detect (VAD) method is used. The VAD method is well known in communications systems, e.g. in
Global System for Mobile communications (GSM) or in TETRA it is a process used to identify presence or absence of speech data bits. In operation the method of classifying importance of the frames based on energy difference calculated as described above is carried out on each ACELP encoded frame in a data stream. In practical implementation the method of classifying importance of encoded frames is used in a digital communications system where a frame synchronization process with frame stealing is implemented. When the frame to be stolen is selected based on its importance (i.e the frame to be stolen has low importance relative to importance of other frames) the negative impact on audio quality of the frame stealing is minimized. With reference to FIG. 2 an apparatus 200 for classifying importance of encoded frames in a digital communications system is shown. The apparatus 200 comprises a decoding means 202 and an error detection means 204.
In one embodiment, particularly applicable in TETRA system, said decoding means 202 is an Algebraic Code Excited Linear Predictive (ACELP) decoder and said error detection means 204 is a Bad Frame Indication (BFI) function.
Said decoding means 202 is adapted to decode a frame with said error detection means 204 activated and to decode said frame with said error detection means 204 deactivated. The apparatus 200 further comprises a processor 206 adapted to calculate an energy difference between outputs of said frame first decoding 106 with said error detection means 204 activated and said frame second decoding 112 with said error detection means 204 deactivated. Said energy difference is a measure of said importance.
The apparatus 200 further comprises a memory 208 for storing state of the decoding means 202 before said step of first decoding 106 with said error detection means 204 activated. Said stored state is used for resetting said decoding means 202 to the stored state before said step of second decoding 112 with said error detection means 204 deactivated.
In one embodiment, when a capacity of the memory 208 is big enough the memory can be used for storing both the state of the ACELP decoder 202 and the outputs of the ACELP decoder 202. Alternatively two memory modules can be used, wherein a first memory module is used for storing said state and a second memory module is used for storing said ACELP decoder's outputs.
The memory 208 is a Random Access Memory (RAM) .
In one embodiment said processor 206 is adapted to calculate the energy difference using a basic energy estimate. In alternative embodiment said processor 206 is adapted to calculate the energy difference using a Voice Activity Detect (VAD) method.
In yet another embodiment the basic energy estimate or the VAD method may be hardware implemented in a form of specialized integrated circuit.
Said memory 208 is adapted to store outputs of said first decoding 106 carried out with said error detection activated and said second decoding 112 carried out with said error detection deactivated. The stored outputs are then used in said process of calculation 116 of said energy difference. After calculating said energy difference said processor 206 indicates the importance of particular frames by flagging them 118. For the purpose of classification of importance of the encoded frames the ACELP decoder is used. The ACELP decoder is used to exactly simulate what will take place in the remote decoder. As it is not an estimation what will happen on the remote decoder but an exact simulation of the remote decoder the obtained results of classification are better than in other methods. The ACELP decoder is also used to classify the importance of the frames but the flags are added by the processor 206 to respective frames of the encoded data stream. Further in the transmission path a frame with a flag indicating low importance is stolen from the stream of encoded frames and replaced with synchronization information.
As the invention is applicable to transmission path of the elements of communication system it can be implemented both in the Mobile Station and in the infrastructure of the communications system.

Claims

Claims
1. A method of classifying importance of encoded frames in a digital communications system by calculating (116) an energy difference between outputs of a first decoding (106) a frame carried out with an error detection activated and a second decoding (112) said frame carried out with said error detection deactivated.
2. A method according to claim 1, wherein said frames are encoded in accordance with an Algebraic Code Excited Linear Predictive (ACELP) , said method comprising the steps : a) first decoding (106) a frame in an ACELP decoder with a Bad Frame Indication (BFI) function enabled; b) second decoding (112) said frame in said ACELP decoder with said BFI function disabled; c) calculating (116) an energy difference between said first (106) and said second (112) decoding output, wherein said energy difference is a measure of said importance.
3. The method according to claim 2, wherein a state of the ACELP decoder is stored before (104) said first decoding (106) and reset (110) to the saved state before the second decoding (112) .
4. The method according to claim 2 or claim 3, wherein in said step of calculating (116) Voice Activity Detect (VAD) method is used.
5. The method according to claim 2 or claim 3, wherein in said step of calculating (116) a basic energy estimate is used.
6. An apparatus (200) for classifying importance of encoded frames in a digital communications system comprising a decoding means (202) and an error detection means (204), wherein said decoding means (202) is adapted to decode a frame with said error detection means (204) activated and to decode said frame with said error detection means (204) deactivated and further comprising a processor (206) adapted to calculate an energy difference between outputs of said frame decoding with said error detection means (204) activated and said frame decoding with said error detection means (204) deactivated wherein said energy difference is a measure of said importance.
7. The apparatus (200) according to claim 6, wherein said decoding means (202) is an Algebraic Code Excited Linear Predictive (ACELP) decoder and said error detection means (204) is a Bad Frame Indication (BFI) function.
8. The apparatus (200) according to claim 6 or claim 7, further comprising a memory (208) for storing a state of the decoding means (202) before said first decoding (106) with said error detection means (204) activated and for resetting said decoding means (202) to the stored state before said second decoding (112) with said error detection means (204) deactivated.
9. The apparatus (200) according to any one of claims 6 to 8, wherein said processor (206) is adapted to calculate the energy difference using a Voice Activity Detect (VAD) method.
10. The apparatus (200) according to any one of claims 6 to 8, wherein said processor (206) is adapted to calculate the energy difference using a basic energy estimate.
EP05727757A 2004-03-16 2005-03-10 Method and apparatus for classifying importance of encoded frames in a digital communications system Withdrawn EP1730843A4 (en)

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PCT/US2005/007844 WO2005089178A2 (en) 2004-03-16 2005-03-10 Method and apparatus for classifying importance of encoded frames in a digital communications system

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EP1730843A4 (en) 2008-03-12
KR20060125902A (en) 2006-12-06
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WO2005089178A2 (en) 2005-09-29

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