WO2008034290A1 - Mécanismes de verrouillage de trame efficaces pour prise en charge des systèmes de transmission numérique vcm/acm par satellite - Google Patents

Mécanismes de verrouillage de trame efficaces pour prise en charge des systèmes de transmission numérique vcm/acm par satellite Download PDF

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Publication number
WO2008034290A1
WO2008034290A1 PCT/CN2006/002425 CN2006002425W WO2008034290A1 WO 2008034290 A1 WO2008034290 A1 WO 2008034290A1 CN 2006002425 W CN2006002425 W CN 2006002425W WO 2008034290 A1 WO2008034290 A1 WO 2008034290A1
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WO
WIPO (PCT)
Prior art keywords
frame
communication system
digital communication
codewords
frames
Prior art date
Application number
PCT/CN2006/002425
Other languages
English (en)
Inventor
Fengwen Sun
Ming Yang
Yimin Jiang
Guofang Sheng
Zhenliang Shi
Yingjiu Xu
Original Assignee
Fengwen Sun
Ming Yang
Yimin Jiang
Guofang Sheng
Zhenliang Shi
Yingjiu Xu
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 Fengwen Sun, Ming Yang, Yimin Jiang, Guofang Sheng, Zhenliang Shi, Yingjiu Xu filed Critical Fengwen Sun
Priority to PCT/CN2006/002425 priority Critical patent/WO2008034290A1/fr
Priority to TW096107926A priority patent/TWI319686B/zh
Priority to EP07016671A priority patent/EP1901456A3/fr
Publication of WO2008034290A1 publication Critical patent/WO2008034290A1/fr
Priority to US12/771,723 priority patent/US20100316144A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/65—Arrangements characterised by transmission systems for broadcast
    • H04H20/71—Wireless systems
    • H04H20/74—Wireless systems of satellite networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H60/00—Arrangements for broadcast applications with a direct linking to broadcast information or broadcast space-time; Broadcast-related systems
    • H04H60/68—Systems specially adapted for using specific information, e.g. geographical or meteorological information
    • H04H60/73—Systems specially adapted for using specific information, e.g. geographical or meteorological information using meta-information

Definitions

  • the present invention relates to digital satellite communication and in particular a frame design for transmitted signals to provide better support for variable/adaptive coding and modulation schemes.
  • Symbol timing synchronization includes processes and methods for synchronizing received data streams with transmitted data streams at the symbol level.
  • Frame synchronization is critical for digital communications where digital data is sent frame by frame, and each frame contains a number of data bits. Depending on the system, frame sizes can vary. Each frame usually contains two parts: a header and a payload. Headers typically include important information for frame synchronization as well as a modulation type and a coding rate for the payload.
  • Payloads typically contain the actual data protected by the channel coding.
  • Frame formatting design is very critical for overall system performance and can directly impact product and operating costs.
  • a preferred frame format may result in high performance receivers that achieve fast frame acquisition and reliable tracking (time and frequency lock) to improve system performance in terms of either bit error rate and/or packet error rate with minimal overhead and a low cost implementation.
  • each frame has a fixed number of codewords. Because both VCM and ACM support different modulation schemes and forward error correction codes (FECs), the number of coded symbols and/or the length of payloads vary from frame to frame.
  • FECs forward error correction codes
  • each frame will have a different length/number of symbols depending on which modulation schemes and FEC codes are used. This difference in frame size complicates receiver design, which is usually further complicated by various channel distortions such as group delays, background noise, adjacent channels and/or other interferences.
  • each frame begins with a header that contains a synchronization waveform called a unique word (UW), followed by an auxiliary control code (ACC), which specifies the modulation scheme and the coding rate of the first codeword in the current frame.
  • UW unique word
  • ACC auxiliary control code
  • the first codeword may also contain a "next frame composition table" (NFCT) to specify modulation schemes and coding rates for some or all of the codewords in the next frame and/or the following frames.
  • NFCT next frame composition table
  • the total number of symbols in a frame or the frame size is fixed.
  • the receiver knows that the UW position is fixed in the ACM/VCM mode. Hence, synchronization control can be simplified.
  • Another benefit is that data streams of different modulation and/or code rates can be handled simultaneously in the ACM mode.
  • data of different modulation types are kept in different queues. For any particular queue, each queue must accumulate enough data to fill up one frame before it starts to transmit. Hence, this queuing delay is of a random nature and fluctuates depending on the instantaneous arrival rate of the data.
  • data of different modulation types and code rates can be sent in a single frame. Although sufficient data is generally accumulated to fill up one codeword, since the length of the codeword is much shorter than that of the DVB-S2 long codes, the average queuing delay and the extent of its variation will be much smaller.
  • VCM mode and the ACM mode are the same as those of the CCM mode, thus the VCM mode and the ACM mode are compatible with the CCM mode. Because the CCM mode are widely used in broadcasting services, this compatibility allows the VCM and the ACM modes to be easily integrated into existing systems without incurring huge equipment cost.
  • the VCM mode allows for flexibility in satisfying various link budget requirements without incurring additional cost in receiver design.
  • the VCM mode is designed to allow different users to use different modulation types and code rates depending on their individual link budget requirement.
  • the VCM mode provides more flexibility than the CCM mode, which by contrast can not change either the modulation or the code rate from one user to another.
  • the link budget requirements change with users, the link budget requirement for each user is usually fixed, hence the modulation and the code rate is usually fixed. Consequently the receiver design for the VCM mode is no more complicated than that for the CCM mode.
  • the number of pilot symbols can change the frame size.
  • pilot symbols may be inserted uniformly during a frame.
  • the frame size will vary accordingly.
  • the methods of using pilot symbols are usually fixed in real transmissions and will not change from one frame to another.
  • each frame has multiple LDPC codewords. The ACC only specifies the modulation and the code rate of the first codeword in the ACM mode, the remainder of the codewords are specified by the NFCT in the first codeword of the previous frame.
  • the use of NFCTs may result in smaller transmission overhead in ACM transmissions.
  • the modulation and/or the code rate are specified in a special part of the header called MODCOD, which encodes modulation and coding rate information using Reed-Muller code.
  • Each MODCOD has 64 QPSK symbols that jointly specify modulation and code rate for one LDPC codeword.
  • the transmission overhead due to MODCOD can be very high, especially for high-order modulation schemes like 16 APSK and 32APSK and DVB-S2 short codes.
  • the NFCT is encoded using LDPC codes whose rates are much higher than the Reed-Muller code used by the DVB-S2 standard.
  • various embodiments of the invention may use an LDPC encoder of rate of 1 A, the minimum code rate supported in the DVB-S2 standard, while the rate for the Reed-Muller code in DVB-S2 is 1/16.
  • the first codeword can be of any modulation schemes, such as, but not limited to, QPSK to 32APSK, which can further reduce the transmission overhead.
  • the NFCT has a delay of one frame is because the receiver does not typically know the content of the NFCT until the first codeword has been decoded by an LDPC decoder.
  • this one-frame delay is acceptable for most of applications. For example, in reality channel conditions due to rain and/or other environmental conditions usually change slowly, hence the ACM only needs to change the modulation and coding rate occasionally.
  • this one-frame delay is negligible compared to the satellite transmission delay, which is usually as high as a few hundred mille- seconds due to the height of the geostationary orbit. For instance, at a symbol rate of 30 Msps and a frame size of 30,000 symbols, a one-frame delay is only about 1 ms.
  • the modulation and/or coding rate of the first codeword in a frame may be overwritten by the ACC of the same frame in the ACM mode such that the one-frame delay may be eliminated for the first codeword. Accordingly, the first codeword can be used to carry delay- sensitive data while the other codewords can be used for non-delay-sensitive data.
  • an efficient framing scheme is used to support variable/adaptive coding and modulation (VCM/ACM) schemes in a digital satellite transmission system.
  • VCM variable/adaptive coding and modulation
  • ACM adaptive coding and modulation
  • modulation and coding rates change from frame to frame.
  • the ACM mode uses a return channel to adjust the modulation and/or coding rate based on feedback information.
  • improved support is provided for the VCM mode because the modulation/coding format does not change within a frame.
  • a NFCT is used in the first codeword of a frame, which specifies the modulation and coding of all the codewords in the next frame. Accordingly, different codewords can use different modulation types and coding rates while the total number of the symbols from all the codewords is fixed.
  • Various embodiments of the invention may include, a digital communication system using digital transmissions, the digital transmissions comprising: a plurality of frames to transmit data, wherein each of the plurality of frames has a frame structure; wherein each frame comprises, a frame header, and a plurality of codewords, one of which contains a Next Frame Composition Table to set the structure for the next frame.
  • the plurality of codewords in each frame comprises a first codeword, and the Next Frame Composition Table is in the first codeword.
  • the digital communication system uses the ACM mode.
  • the digital communication system uses the VCM mode.
  • the Next Frame Composition Table is to set the structure for the next frame.
  • the Next Frame Composition Table defines the number of codewords per frame.
  • each of the plurality of frames comprises at least one codeword.
  • a receiver can make use of the Next Frame Composition Table to determine where the codewords start and stop.
  • the Next Frame Composition Table defines a structure of the codewords for the next frame.
  • the Next Frame Composition Table defines a padding structure for the next frame.
  • the plurality of codewords in each frame comprises a first codeword
  • the Next Frame Composition Table is in a codeword other than the first codeword
  • the system uses at least one of the following modulation schemes: QPSK, 8PSK, 16APSK or 32APSK.
  • the structure for the second frame comprises a modulation and/or a coding format.
  • the modulation and/or coding format of the first codeword in a frame can be overwritten by the auxiliary control code in the frame header.
  • codewords in at least one of the plurality of frames use different modulation.
  • codewords in at least one of the plurality of frames use different FEC code rates.
  • the Next Frame Composition Table reduces transmission overhead when the system uses the ACM mode
  • delay-sensitive data is located in a first codeword of one frame and non-delay-sensitive data is located in other codewords in the frame.
  • VCM mode and the ACM mode are compatible with the CCM mode that is used in broadcasting services.
  • VCM mode can accommodate different users with different link budget requirements.
  • Various embodiments of the invention include, a digital communication system, comprising: a transmitter to transmit a digital signal; and a receiver to receive a digital signal; wherein the digital signal comprises, a plurality of frames to transmit data, wherein each of the plurality of frames has a frame structure; and wherein each frame comprises, a frame header, and a plurality of codewords, one of which contains a Next Frame Composition Table to set the structure for the next frame.
  • Figure 1 depicts an exemplary detailed frame format of a transmitted frame, according to an embodiment of the invention.
  • Figure 2 depicts an exemplary frame having a payload data structure using multiple LDPC codewords, according to an embodiment of the invention.
  • Figure 3 depicts an exemplary format of a first LPDC codeword of a frame, according to an embodiment of the invention.
  • Figure 4 depicts an exemplary format for additional LDPC codewords, according to an embodiment of the invention.
  • Figure 5 depicts an exemplary NFCT bit and byte structure, according to an embodiment of the invention.
  • Figure 1 depicts an exemplary detailed frame format of a transmitted frame.
  • the frame format starts with an X-symbol UW pattern, followed by a Y-symbol ACC, and m+1 segments of encoded data (or payload data) separated by m evenly distributed pilot sections.
  • the UW is designed to yield an improved correlation property for faster acquisition.
  • An exemplary UW may contain detailed information on frame structures.
  • the number of payload segments (m+1) in each frame is determined by the frame length in symbols and the distance between two consecutive segments, which may be designed to provide reliable synchronization with minimum overhead. For systems having severe channel conditions and using high dimensional modulations, more pilots are used. Furthermore, the size of each pilot segment may also be adjustable. According to an embodiment of the invention, in some cases frames having no pilot symbols may be used to achieve minimal overhead. In this case, modulation dimensions are usually low and the channel is usually in fair conditions. According to various embodiments of the invention, the number of pilot symbols used may be determined by the worst channel conditions and/or the most demanding modulation and/or coding rate; they may also be designed so as to not change from one frame to another.
  • an integer number of LDPC codewords is assigned in each frame as the payload data. This design leads to simple decoder control logic where the decoder does not need to decode payloads across a frame boundary.
  • the codeword itself may have a constant length in bits to simplify the decoding implementation. Additionally, each codeword may have a different modulation type and/or code rate to support the ACM mode. The number of codewords in a frame may depend on the modulation dimensions. Higher modulation dimensions may lead to more codewords in a frame.
  • Table 1 provides exemplary distributions of frame resources.
  • user data may not be continuous; accordingly, a format other than the format defined in the table may be used. Consequently, there may be some unused symbols towards the end of a frame which may be defined as dummy symbols and may be modulated by an all-zero or an all-one bit pattern.
  • codewords may be made up of information bits and FEC parity bytes having a CRC error checking field and/or an LDPC error correction field. But not all the codewords need to be designed to be the same.
  • the first codeword (as shown in Figure 3) is different from other codewords (shown in Figure 4) in that it contains header information for another frame.
  • the first three fields, NBYTES, FBYTE, and PSTART, may be used by all modes of operation.
  • the other fields depicted, LBYTE, PBYTES, and NFCT are typically not used in transport streams.
  • the NFCT may be used in only the ACM mode.
  • the NFCT is designed for ACM applications where each codeword maybe independent of others in a frame in terms of modulation type and/or code rate.
  • the NFCT defines the composition of the frame following the current frame.
  • An exemplary NFCT may follow the PBYTES and may have the syntax shown in Table 2. Corresponding exemplary bit and byte positions are also illustrated in Table 2.
  • Codeword_count_in_next_frame this is a 4-bit field indicating one less than the number of LDPC codewords in next frame.
  • the codeword index i starts from 0 to Codeword_count_in_next_frame > 0. Accordingly, in this embodiment, at least one codeword in a frame is always transmitted, i.e., the first codeword of each frame is guaranteed for transmission.
  • Modulation 2 bits to indicate the modulation scheme.
  • Codejrate 4 bits to indicate the code rate.
  • Padding_in_bytes zero padding in that particular codeword in bytes. The number of bytes to be padded with zeros is given by:

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Astronomy & Astrophysics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
  • Data Exchanges In Wide-Area Networks (AREA)
  • Radio Relay Systems (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Error Detection And Correction (AREA)

Abstract

L'invention concerne un système et un procédé de communication numérique faisant appel à un signal numérique possédant une pluralité de trames pour transmettre des données, notamment une première et une seconde trame, chacune de la pluralité de trames présentant une structure de trame, et la première trame contenant une pluralité de mots de code comprenant les données utilisateur, et une table de composition de la trame suivante, servant à définir la structure de la seconde trame, la seconde trame contenant au moins un mot de code.
PCT/CN2006/002425 2006-09-18 2006-09-18 Mécanismes de verrouillage de trame efficaces pour prise en charge des systèmes de transmission numérique vcm/acm par satellite WO2008034290A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
PCT/CN2006/002425 WO2008034290A1 (fr) 2006-09-18 2006-09-18 Mécanismes de verrouillage de trame efficaces pour prise en charge des systèmes de transmission numérique vcm/acm par satellite
TW096107926A TWI319686B (en) 2006-09-18 2007-03-07 Efficient framing schemes for supporting vcm/acm in digital satellite transmission systems
EP07016671A EP1901456A3 (fr) 2006-09-18 2007-08-24 Schéma de trame efficace pour la prise en charge de VCM/ACM dans des systèmes de transmission numérique par satellite
US12/771,723 US20100316144A1 (en) 2006-09-18 2010-04-30 Efficient framing schemes for supporting vcm/acm in digital satellite transmission systems

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/CN2006/002425 WO2008034290A1 (fr) 2006-09-18 2006-09-18 Mécanismes de verrouillage de trame efficaces pour prise en charge des systèmes de transmission numérique vcm/acm par satellite

Related Child Applications (2)

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US11813204 A-371-Of-International 2006-09-18
US12/771,723 Continuation US20100316144A1 (en) 2006-09-18 2010-04-30 Efficient framing schemes for supporting vcm/acm in digital satellite transmission systems

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Cited By (1)

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CN112511216A (zh) * 2020-11-27 2021-03-16 西安空间无线电技术研究所 一种低轨卫星的自适应编码调制方法及系统

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FR2951597B1 (fr) * 2009-10-16 2011-11-04 Thales Sa Dispositif et procede de controle des ressources radio pour systemes de communications par satellites
KR101309615B1 (ko) 2009-12-01 2013-09-23 한국전자통신연구원 소스-채널 결합 부호화 방법 및 이를 적용한 위성 방송 시스템
CN114978281B (zh) * 2022-05-11 2023-08-01 中国电子科技集团公司第十研究所 可变编码调制体制物理帧数据同步方法、接收方法及设备

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CN1295763A (zh) * 1999-01-28 2001-05-16 皇家菲利浦电子有限公司 传输系统
CN1799211A (zh) * 2003-05-30 2006-07-05 诺基亚有限公司 突发传输

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US7042949B1 (en) * 2001-04-03 2006-05-09 Rosum Corporation Robust data transmission using broadcast digital television signals
CA2470546C (fr) * 2003-06-13 2010-08-17 The Directv Group, Inc. Methode et appareils de synchronisation de porteuse dans des systemes interactifs et des systemes de diffusion numerique

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Publication number Priority date Publication date Assignee Title
CN1295763A (zh) * 1999-01-28 2001-05-16 皇家菲利浦电子有限公司 传输系统
CN1799211A (zh) * 2003-05-30 2006-07-05 诺基亚有限公司 突发传输

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112511216A (zh) * 2020-11-27 2021-03-16 西安空间无线电技术研究所 一种低轨卫星的自适应编码调制方法及系统

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TWI319686B (en) 2010-01-11
EP1901456A2 (fr) 2008-03-19
TW200816818A (en) 2008-04-01
EP1901456A3 (fr) 2008-10-29

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