MXPA04010332A

MXPA04010332A - Synchronization loss resilient digital communication system using forward erasure correction.

Info

Publication number: MXPA04010332A
Application number: MXPA04010332A
Authority: MX
Inventors: Macdonald Boyce Jill
Original assignee: Thomson Licensing Sa
Priority date: 2002-04-19
Filing date: 2003-04-17
Publication date: 2005-02-03
Also published as: EP1497925A1; CN1656691A; KR100996619B1; EP1497925A4; CN1656691B; KR20050005449A; AU2003222632A1; JP2005523637A; JP4226481B2; WO2003090360A1

Abstract

There is provided an apparatus for enabling recovery of missing information (Fig. 3) in a digital communication system (100). The apparatus includes a Forward Erasure Correction (FXC) encoder (110) for computing FXC parity superpackets across information superpackets for subsequent recovery of any entire ones of the information superpackets that have been at least partially compromised due to synchronization loss.

Description

FLEXIBLE DIGITAL COMMUNICATION SYSTEM TO LOSS OF SICRONIZATION USING ADVANCED REMOVAL CORRECTION BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention in general relates to communication systems and, more particularly, to a flexible digital communication system at loss of synchronization using Advanced Elimination Correction (FXC).

BACKGROUND OF THE INVENTION Wireless digital communication systems are subjected to muti-path and gradual fades, which can lead to the loss of synchronization. Data transmitted during periods of lost synchronization are normally lost by the receiver. Therefore, the problem to solve is how to design a wireless digital communication system that is flexible to loss of synchronization due to multi-path and fading, with a general as low as possible. The result of fading and multi-path effects in wireless digital communication links are well understood and their likely characteristics have been documented. For example, in the Committee on Advanced Television Systems (ATSC) Rudimentary Lateral Band 8 (8VSB), transmission systems for High Definition Television (HDTV) broadcast in the United States, the probability of distribution of duration of fading has been studied . The reception of the 8VSB system in a mobile device also increases the probability of loss of synchronization. Even after the synchronization is acquired again, utility data can not be recovered in an ATSC 8VSB system until the latched decoding is repaired, and an interlibrator starts a new block. The ATSC 8VSB system includes several types of channel coding to protect against noisy transmission, including lattice encoding, inter-release, and Advanced Error Correction (FEC) from Reed Solomon (RS). But when loss of synchronization occurs, channel coding methods often do not help in data recovery. The transmission of data repeatedly can improve the loss of resilience synchronization of the system, but at the cost of high generality. Assigning more of the available broadband for repeated data transmission reduces the amount of original data that can be transmitted, which means few programs or poor quality of the transmitted programs. It has also been proposed that instead of repeatedly transmitting the original data, the overall ratio can be reduced by redundantly transmitting a low bit rate version of the original data. When the original data is lost due to loss of synchronization, the reduced resolution version is used by the receiver. This allows for delicate degradation, that is, you can get a low quality version of the original data instead of the original data. However, if the original high resolution data is required, the reduced resolution version may be unsatisfactory.

Accordingly, it would be desirable and highly advantageous to have a flexible digital communications system at loss of synchronization that overcomes the problems set forth in the prior art mentioned above.

BRIEF DESCRIPTION OF THE INVENTION The above-mentioned problems, as well as other related problems of the prior art, are solved with the present invention, a digital communication system resistant to loss of synchronization using Advanced Elimination Correction (FXC). According to an aspect of the present invention, an apparatus is provided to allow the retrieval of lost information in a digital communication system. The device includes an Advanced Elimination Correction (FXC) encoder to compute FXC parity superpackets through superpacks of information for subsequent recovery in its entirety from any of the information superpacks that have been at least partially compromised due to loss of data. synchronization. According to another aspect of the present invention, an apparatus for the retrieval of lost information in a digital communication system is provided. The apparatus includes an Advanced Elimination Correction (FXC) decoder to decode previously computed FXC parity superpacks through information superpacks to fully recover any of the information superpacks that have been at least partially compromised due to loss of synchronization.

However, according to another aspect of the present invention, a method is provided to allow the retrieval of lost information in a digital communication system. The method includes the step of computerizing FXC parity superpacks, through superpacks of information for subsequent recovery in its entirety from any of the information superpacks that have been at least partially compromised due to loss of synchronization. However, according to yet another aspect of the present invention, a method for recovering lost information in a digital communication system is provided. The method includes the step of decoding FXC parity superpacks previously computerized through superpacks of information to fully recover any of the superpacks that have been at least partially compromised due to loss of synchronization. These and other aspects, features and advantages of the present invention will become apparent in the following detailed description of the preferred embodiments, which is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram illustrating a Rudimentary Lateral Band Transmitter (VSB), according to an illustrative embodiment of the present invention. Figure 2 is a schematic diagram illustrating a Rudimentary Lateral Band (VSB) receiver, according to an illustrative embodiment of the present invention. Figure 3 is a diagram illustrating a drawing of an example of superpacket loss, according to an illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention addresses a flexible digital communication system at loss of synchronization using Advanced Elimination Correction (FXC). The present invention employs Advanced Elimination Correction (FXC) codes to recover the loss of synchronization, treating periods of loss of synchronization as packet eliminations. Additional parity data to recover those packet deletions are transmitted in a backward compatible manner. -This allows a reduction in the general proportion, compared to the transmission of data repeatedly. It is understood that the present invention can be implemented in various forms of hardware, software, firmware, processors with special purposes, or a combination thereof. Preferably, the present invention is implemented as a combination of hardware and software. In addition, the software is preferably implemented as an application program tangibly embodied in a program storage device. The application program can be transferred to, and executed by a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random access memory (RAM), and input / output interface (s) (I / O) ). The computer platform also includes an operating system and a code of micro-instruction. The variety of processes and functions described herein may be either part of the microinstruction code or part of the application program (or a combination thereof) that is executed via the operating system. In addition, various other peripheral devices can be connected to the computer platform such as an additional data storage apparatus and a printing apparatus. It is further understood that, because some of the constituent system components and method steps are represented in the accompanying figures, these are preferably implemented in software, the current connections between the system components or processing steps) can be different, depending on the way in which the present invention is programmed. Given the teachings here, someone of ordinary skill in the referred art will be able to contemplate these and similar implementations or configurations of the present invention. Advanced Elimination Correction Codes (FXC) apply to the transmission of packet data to protect against packet loss in data transmissions over packet networks, such as those that use Internet Protocol (Pl). Any type of FXC codes can be used including, but not limited to, for example, Reed Solomon (RS) codes. Reed Solomon codes are systematic codes, that is, the original information bits are transmitted as well as the additional parity bits. In the absence of channel loss, the receiver can use only the original information bits received, and does not need to do any FXC decoding. Packet networks tend to lose entire packets of data, instead of individual packets. When FXC is used to protect against packet loss, typically (but not necessarily) a bit of each packet is used to form an FXC keyword. For example, if 10 packets of 1024-bit length were encoded using FXC, using RS codes (15.10), 10 packets and length information of 1024 and 5 parity packets of 1024 capacity will be transmitted. Therefore, 1024 different RS keywords will be formed by taking one bit of each packet. Therefore, protection against loss of data due to loss of synchronization in a digital communications system is achieved by including an Advanced Elimination Correction (FXC) layer, with computerized parity data for periods of time corresponding to the expected duration of the synchronization loss periods. The periods of data loss due to a synchronization failure are considered packet eliminations in the FXC decoder. Because the term package is generally used to refer to a smaller time scale in this system (such as, for example, a 188-bit PEG-2 transport package), as the term "super package" is used here. it will be used to refer to a package unit used in, or capable of being used in the FXC decoder. It is understood that the present invention is independent of the type of data that is transmitted and, therefore, can be used for the transmission of any type of data. It is further understood that the present invention is not limited to audio / video programs and, therefore, can be used for any type of program. In accordance with the present invention, FXC is further used for other channel coding methods in the digital communications system that protects against impulse noise. For example, in the ATSC 8VSB system, the FXC coding is included in the system's lattice encoding, interleaving and Advanced Error Correction (FXC) coding by Reed Solomon (RS). The FXC used may be any systematic advanced elimination correction code that includes, but is not limited to, for example, Reed Solomon (RS) codes. When a systematic code is used, the present invention may be backwards compatible. That is, an existing decoder can ignore the additional parity superpackets transmitted and normally decode the information superpacks without changing. The FXC encoder and decoder are different from any FEC RS code already used in an existing digital communications system. For example, FXC keywords are computerized through superpacks (for example, one bit per superpack) and protected against loss (Elimination) of entire superpacks. In contrast, the existing RS FEC protects against random bits or bit errors, not deletions, within a given packet, with samples taken from nearby points in time. In a preferred embodiment of the present invention, the FXC n and k faces and the length of the super package, are selected based on the desired loss protection level and the allowable delay.

The n parameter indicates the block duration of an FXC keyword. The parameter k indicates the number of information symbols in an FXC keyword. It is understood that the phrases "FXC keywords" and "FXC parity superpackets" are used interchangeably here, and are not contrasted with "information superpacks" which are the data elements from which the FXC parity superpackets are computerized. . The expected duration of missed synchronization should be equal to or less than: s * (n / k) * h, (where h = n-k). The general ratio for FXC coding is h / k. So, for example, in a system that transmits 19.2 Mbps (that is, 2 4 Mbíies / sec), to protect against a fading of 500 msec, s * (n / k) * h < = 1 .2M Bites. If, for example, n = 6 and k = 4 (and, therefore, h = 2), then the general proportion is 50% and s = 400 Kbites. Additional storage may be required for the present invention, more than a standard ATSC 8VSB system would require, of s * nites, which for this example is 2.4 bits. If multiple programs share the broadband channel 19.2 Mbps, the storage requirements could be reduced by executing the FXC decoding only for the program being decoded. Figure 1 is a schematic diagram illustrating a Rudimentary Lateral Band (VSB) transmitter 100, according to an illustrative embodiment of the present invention. It is understood that, while a typical transmitter configuration has been described and shown here for illustrative purposes with respect to Figure 1, the present invention can easily be applied to other transmitter configurations with VSB signal transmission capability while maintaining the spirit and scope of the present invention. The transmitter 100 includes 1 source encoder 105, an FXC 110 encoder, a MUX transport 115, a structure synchronizer 120, a data scrambler 125, a Reed Solomon (RS) 130 encoder, a data interleaver 135, a data module SYNC insert 140, a pilot insertion module 145, a modulator 8-VSB 150, and an analogous updater 155. The compressed bit stream of source encoder 105 is handled by the FXC 110 encoder, which includes redundancy when creating superpacks of parity. The inputs of several sources are combined by the MUX transport 115 within a composite flow that is fed to the frame synchronizer 120. The data structures are created and delimited by a frame synchronizer 120. Each data structure includes two fields. Each data field has 313 data segments in the standard ATSC that includes a synchronized segment of structure. Each data segment carries a 188-bit transport packet and associated Advanced Error Correction (FEC). The data scrambler 125 is used in all input data to randomize only the data payload (it does not include synchronization and general elements). The Reed Solomon (RS) 130 encoder is a block encoder that hosts 187 bits and includes 20 parity bits for advanced error correction external to the receiver. The bit data is interleaved by the data interleaver 135, which uses a coiled interleaver that operates on 52 data segments (about one sixth depth of field). Two thirds of the state-4 lattice encoding scheme with a coded bit that is pre-coded is implemented by the lattice encoder 136. A data segment sync is inserted within each data segment and a field sync Data is inserted into each data segment and a data field sync is inserted within each data field, by the sync 140 insert module. These elements are not Reed Solomon or Lattice Encoded. A pilot signal is introduced including a Direct Current (DC) component in each symbol, by the pilot insertion module 145. Following this, the modulator 8-VSB 150 traces the symbols (generated at 10.76 Msymbols / seG) in a constellation 8-VSB and generates a Nyquist pulse of origin corresponding to each symbol. The analogue top updater 155 then converts the frequency signal of the desired conveyor for its transmission. The FXC 1 10 encoder is located after the source encoder 105, but before the MUX 1 15 transport and the channel coding blocks (for example, RS 130 encoder). Superpackets k, each with length s, are inserted into an FXC 1 10 encoder. The FXC 1 0 encoder generates parity superpackets h = n-k with length s. The original information superpacks and the parity superpackets are then multiplexed, using the MUX 1 15 transport. The ATSC 8VSB system uses PEG-2 Flows in the MUX 1 15 transport, which allows multiple programs to be multiplexed and sent on the same. channel, with each program assigned a different Procedure Identifier (PID). According to the present invention, the information superpacks are the same as those of a system that does not use FXC. According to the present invention, additional parity superpackets are transmitted and different PIDs are assigned by the MUX transport 115, than the information superpacks. If multiple programs are transmitted, each with a different PiD, then parity packages can be either computerized based on all the programs together, or based on one or more individual programs. All data is then sent to the remaining ATSC 8VSB channel decoding parts, which do not need to be changed from a standard system. To assist in synchronization at the receiver, special Sync FXC Transport Packs can be sent under a different PID, once for each of the n superpacks. These Sync FXC Transport Packages could indicate the correspondence between the start positions of the superpacket sequence number with MPEG-2 Transport Package PID and the_repair-time-program (PCR) and continuity_count, lobidity, superpacket, s, and Reed parameters fields Solomon (n, k). Figure 2, in a schematic diagram illustrating a Rudimentary Lateral Band (VSB) receiver 200, according to an illustrative embodiment of the present invention. It is understood that while a typical receiver configuration has been described and shown here for illustrative purposes with respect to Figure 2, the present invention can easily be applied to other receiver configurations with VSB signal reception capability while maintaining the spirit and scope of the present invention. The receiver 200 includes a tuner 205, an Intermediate Frequency Filter (IF) and SYNC Detector 210, a SYNC and regulation module 215, an equalizer 220, a phase tracker 225, a lattice decoder 230, a data interleaver 235 , a Reed Solomon (RS) decoder, a data descrambler 245, a DEMUX 250 transport, an FXC 260 decoder, and a source decoder 265. In a transmitted 8-VSB signal, digital information is transmitted exclusively in the amplitude of a cover RF and not in the phase. The eight levels of the transmitted signal are recovered by taking a sample only from the I-channel or in-phase information. Since any dependency on the Q-channel is eliminated, the receiver 200 has only to deal with the I-channel, therefore, halves the number of digital signal processing circuits required in the different phases in the receiver 200. It is clear that this results in greater simplicity and saves costs in the design of the receiver. The signals are demodulated in the receiver 200 by applying the opposite principles that were applied in the transmitter 100 of Figure 1. This is input VSB signals, they are received, subtransform, filtered and then they are detected. Segment synchronization and synchronization of structure are then recovered. An input signal is converted into an intermediate frequency by the tuner 205. The selectivity of the channel is executed by the IF filter and the SYNC 210 detector. Recovery of the regulation and recovery of the coarse conveyor are then executed by the SYNC and the regulation 215. The signal is then equalized in the equalizer 220 to remove all multi-path components. One of the advantages of the VSB system is that complex equalization is not necessary as long as the equalizer operates only on the I-channel or real information. The output of equalizer 220 is applied to a phase 225 tracer to remove the residual phase. The output of the phase tracer 225 is applied to a lattice decoder 230 corresponding to the internal code of the linked Advanced Error Correction (FXC) system. The output of the lattice decoder 230 is applied to a data deinterleaver 235 that propagates an error explosion caused by the lattice decoder. The uninterleaved data is then applied to a Reed Solomon (RS) decode based on block 240 that corresponds to the external code in the linked decoding system. The output of the RS 240 decoder, that is, the decoded channel is then treated by the data descrambler 245, which corresponds to the reverse process in the transmitter. The descrambled data is then fed by the transport demultiplexer 250, which separates the composite stream into component streams for processing respectively by an audio source decoder, a video source decoder, and a data source decoder (collectively represented by source decoder 260). The FXC decoder 260 is located after other channel decoding blocks (eg, RS 260 decoder) and transport DEMUX 250, and before the source decoder 265. The sequence numbers of the super packages and positions can be determined using the FXC Sync Transport Packages. The Elimination positions can be made accessible to the FXC 260 decoder using an error indication signal from one of the above channel coding blocks, such as the RS 240 decoder. For use in an MPEG-2 Transport Stream system, the transport field_ error_indicator, in the transport package can be used to indicate the location of the errors. If synchronization loss does not occur, the FXC decoding is not necessary, and the FXC 260 decoder only passes through the data in the information superpacks to the source decoder 265. If the synchronization loss occurs, and is detected, those superpacks with lost or altered data are marked as eliminations. If more superpacks are received correctly, whether the information or parity superpackets, the FXC 260 decoder perfectly reconstructs the lost information packets, executing the decoding of the keywords s RS (n, k), taking a bit of each superpacket for form the keywords. Of course, more than one bit can be taken from each superpacket to form the keywords. That is, given the teachings of the present invention provided herein, one of ordinary skill in the art referred to will contemplate these and several other data units for use in superpacket keyword formation. For example, a system with FXC RS (6.4) 6 super packages of 400 Kbit capacity is transmitted. 0-3 superpacks are information superpacks, and superpacks 4 and 5 are parity superpacks. Superpacks 3 and 4 are altered in the receiver due to loss of synchronization. The FXC decoding is executed in 400 thousand key words, each formed, taking the ith bit of superpacks 0, 1, 2, and 5 with the 3rd and 4th positions marked as eliminations. Superpack 3 is preferably rebuilt by the FXC 260 decoder, and superpacks 0-3 are sent to the source decoder 265. An illustration of this example is provided in FIG. 3 which is a diagram illustrating an example drawing 300 of a loss of superpacks, according to an illustrative embodiment of the present invention. It is understood that while the present invention has been described with respect to the Advanced Television Systems Committee (ATSC) digital communication system 8VSB, the present invention can be employed with any package based on a digital communication system. Although the illustrative embodiments have been described herein with reference to the accompanying drawings, it is understood that the present invention is not limited to these precise modalities, and that various changes and modifications may be affected herein by one of the ordinary techniques in the art. referred without departing from the scope or spirit of the invention, All these changes and modifications are intended to be included within the scope of the invention.

Claims

CLAIMS 1. An apparatus for enabling the retrieval of lost information in a digital communication system, comprising: an Advanced Elimination Correction (FXC) encoder 5 for computing FXC parity superpacks through superpacks of information for subsequent retrieval in its totality of any of the information superpacks that have been at least partially compromised due to loss of synchronization. 2. The apparatus of claim 1, characterized in that the 0 FXC encoder computes the FXC parity superpackets through the information superpacks in one bit for each of the information superpacks. 3. The apparatus of claim 1, characterized for information super-packages k, each of length s, said S FXC encoder computerized parity packages FXC h of length s, where h = n - k, n = a block duration of each of the FXC parity superpackets, and k = a number of information symbols in each of the parity superpackets. 4. The apparatus of claim 1, further comprising a multiplexer for multiplexing the information superpacks and the FXC parity superpacks before any transmission thereof. The apparatus of claim 1, characterized in that the multiplier allocates different Processing Identifiers (PIDs) to the FXC parity superpackets than to the information superpacks. 6. The apparatus of claim 1, characterized in that the FXC encoder computes the FXC parity superpackets using Reed Solomon (RS) codes. 7. The apparatus of claim 1 further comprises a multiplexer for generating sync FXC transport packets indicating a correspondence between the start positions of the superpacket sequence number. The apparatus of claim 1, characterized in that the FXC parity superpacks are computerized for periods of time corresponding to an expected duration of at least one loss of synchronization period. 9. An apparatus for recovering information lost in a digital communication system, comprising: an Advanced Elimination Correction (FXC) decoder for decoding previously computerized FXC parity superpacks through information superpacks to fully recover any of the superpacks of information that have been at least partially compromised due to loss of synchronization. 10. The apparatus of claim 9, characterized in that said FXC decoder further decodes sync FXC transport packets to determine superpacket positions and super packet sequence numbers for both FXC parity superpackets and information superpacks. The apparatus of claim 9, characterized in that said FXC decoder is adapted to receive an error signal indicating a deletion position corresponding to the super packages of information that has been at least partially compromised due to loss of synchronization . 12. A method to allow the retrieval of lost information in a digital communication system, comprises: computerizing FXC parity superpackets through superpacks of information for the subsequent recovery in its entirety from any of the superpacks of information that has been so least partially compromised due to the loss of synchronization. The method of claim 12, characterized in that a computerized stage comprises the computerization step of the FXC parity superpackets through the one-bit information superpacks for each of the information superpacks. The method of claim 12, characterized in that for information super-packages k, each of length s, said computerization stage comprises the computerization stage of parity superpackets FXC h of length s, where h = n - k, n = a block duration of each of the parity superpackets FXC, and k = a number of information symbols in each of the FXC parity superpackets. 15. The method of claim 12, further comprising the step of muitiplexing the information superpacks and FXC parity superpacks before any transmission thereof. The method of claim 12, characterized in that said step of multiplexing comprises the step of assigning different Processing Identifiers (IDPs) to the FXC parity superpackets than to the information superpacks. The method of claim 12, characterized in that said computerization stage computerizes the FXC parity superpackets using Reed Solomon (RS) codes. 18. The method of claim 12, further comprising the step of generating sync FXC transport packets indicating a correspondence between the start positions of the superpacket sequence number. The method of claim 12, characterized in that said computerization step computes the FXC parity superpacks for periods of time corresponding to the expected duration of at least one period of loss of synchronization. 20. A method for recovering information lost in a digital communication system, comprises: decoding of FXC parity superpacks previously computerized through superpacks of information to recover in full any of the information superpacks that have been at least partially compromised due to loss of synchronization. The method of claim 20, further comprising the step of decoding sync FXC transport packets to determine super packet sequence numbers and super packet positions for both FXC parity superpackets and information superpacks.