DVB-S2X标准详解：卫星通信的帧结构与编码调制

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"DVB-S2 Extensions (DVB-S2X)是数字视频广播（DVB）的第二代帧结构、信道编码和调制系统的扩展标准，由欧洲电信标准协会（ETSI）发布，具体标准文件为ETSI EN 302 307-2 V1.3.1 (2021-07)。这个标准主要涵盖了卫星广播、交互式服务、新闻采集和其他宽带卫星应用的技术规范。" DVB-S2X是DVB-S2标准的增强版，旨在提高卫星通信的效率和性能。以下是对该标准中涉及的关键知识点的详细说明： 1. **帧结构**：DVB-S2X引入了更灵活的帧结构，允许更高效的频谱利用。这包括不同长度的传输块（TBs）和物理层包头（PHs）的可变配置，以适应不同的信道条件和传输需求。 2. **信道编码**：在编码方面，DVB-S2X支持更高的编码率和更复杂的编码方案，如低密度奇偶校验（LDPC）码，以提高纠错能力。这些编码技术能有效地对抗信道中的噪声和干扰，确保数据传输的可靠性。 3. **调制方式**：DVB-S2X增加了新的调制模式，如256-QAM和更高阶的调制，以提高频谱效率。高阶调制允许在同一频率带宽内传输更多的数据，但对信道质量的要求也更高。 4. **多流传输**：DVB-S2X支持多个独立的数据流在同一卫星载波上传输，这称为多流技术。这种技术可以优化频谱分配，为不同的服务提供定制化的传输方案。 5. **高级前向错误校正（FEC）策略**：除了基本的LDPC编码，DVB-S2X还引入了增强的交织和混合FEC策略，以适应快速变化的信道条件，进一步提升系统性能。 6. **预编码和功率控制**：DVB-S2X标准考虑了预编码技术，通过预先调整信号来补偿预期的信道失真，以及更精细的功率控制，以优化整个卫星系统的整体性能。 7. **增强型滚降系数**：DVB-S2X提供了可变滚降系数，允许调整以减少信号边缘的衰减，从而改善邻近频道的共存问题。 8. **快速帧头定位**：DVB-S2X的帧头设计允许更快的同步和解码器锁定，降低了延迟并提高了系统响应速度。 DVB-S2X标准通过这些技术改进，不仅提升了卫星广播服务质量，也为高清和超高清电视、交互式服务以及数据传输等应用提供了更强的技术支撑。此外，由于这些技术的进步，DVB-S2X还能够更好地适应未来的宽带卫星通信需求，比如物联网（IoT）和移动通信等。

ETSI

ETSI EN 302 307

2 V1.3.1 (2021

07)

Within the present document, a number of configurations and mechanisms are defined as "Optional". Configurations

and mechanisms explicitly indicated as "optional" within the present document, for a given application area, need not be

implemented in the equipment to comply with the present document. Nevertheless, when an "optional" mode or

mechanism is implemented, it shall comply with the specification as given in the present document.

5 Subsystems specifications

5.1 Mode adaptation

5.1.0 General aspects

See ETSI EN 302 307-1 [3], clause 5.1.

According to Figure 3, the input sequence(s) is (are):

• Single or multiple Transport Streams (TS).

• Single or multiple Generic Streams (packetized, continuous or high-efficiency mode (HEM) packetized).

The output sequence is a BBHEADER (80 bits) followed by a DATA FIELD.

5.1.1 Input Interfaces

See ETSI EN 302 307-1 [3], clause 5.1.1.

An efficient input interface has been introduced as GSE-HEM. For details of GSE-HEM, see clause 5.1.7.

5.1.2 Input stream synchronizer (optional, not relevant for single TS - BS)

See ETSI EN 302 307-1 [3], clause 5.1.2.

5.1.3 Null-Packet Deletion (ACM and Transport Stream only)

See ETSI EN 302 307-1 [3], clause 5.1.3.

5.1.4 CRC-8 encoder (for packetized streams only)

See ETSI EN 302 307-1 [3], clause 5.1.4.

5.1.5 Merger/Slicer

See ETSI EN 302 307-1 [3], clause 5.1.5.

5.1.6 Base-Band Header insertion

See ETSI EN 302 307-1 [3], clause 5.1.6.

First byte (MATYPE-1):

• TS/GS field (2 bits): Transport Stream Input, Generic Stream Input (packetized or continuous) or GSE-HEM.

• SIS/MIS field (1 bit): Single Input Stream or Multiple Input Stream.

• CCM/ACM field (1 bit): Constant Coding and Modulation or Adaptive Coding and Modulation (VCM is

signalled as ACM).

ETSI

ETSI EN 302 307

2 V1.3.1 (2021

07)

• ISSYI (1 bit), (Input Stream Synchronization Indicator): If ISSYI = 1 = active, the ISSY field (see Annex D) is

inserted after UPs or in the baseband header in GSE-HEM.

• For TS input mode:

- NPD (1 bit): Null-packet deletion active/not active.

• For GSE/Generic Continuous/Generic Packetized modes:

- GSE-Lite (1 bit): GSE stream is GSE-Lite compliant/non-compliant.

• RO (2 bits): Transmission Roll-off factor (α). Three additional roll-off factors shall be available, 0,15; 0,10

and 0,05. Signalling shall be according to the following rule (Table 2):

- If RO bits are signalled consistently from BBHEADER to BBHEADER as either 00, 01, 10 the

backward compatible definition (High roll-off range) applies:



00 = 0,35.



01 = 0,25.



10 = 0,20.

- If RO bits are signalled from BBHEADER to BBHEADER in an alternating way with 11 then their

interpretation shall be Low roll-off range:



00 = 0,15.



01 = 0,10.



10 = 0,05.

It shall be ensured that in a Multiple Input Stream configuration (SIS/MIS field = 0) alternation is

unambiguously evident over all Input Streams (for every ISI) and MODCOD combinations, such that any

receiver will receive regular alternation. Any receiver, once locked will switch to low roll-off range on first

detection of '11'.

Table 2 (see ETSI EN 302 307-1 [3], Table 3): MATYPE-1 field mapping

TS/GS SIS/MIS CCM/ACM ISSYI NPD/GSE-Lite

Alternation

with 11 =

high roll-off

range

Alternation

with 11 =

low roll-off

range

11 = Transport

00 = Generic Packetized

01 = Generic continuous

10 = GSE-HEM

1 = single

0 = multiple

1 = CCM

0 = ACM

1 = active

0 = not-active

1 = active

0 = not-active

00 = 0,35

01 = 0,25

10 = 0,20

00 = 0,15

01 = 0,10

10 = 0,05

NOTE: GSE-Lite signals are defined in Annex D of ETSI TS 102 606-1 [2].

5.1.7 GSE High Efficiency Mode (GSE-HEM)

GSE variable-length or constant length UPs may be transmitted in GSE-HEM. In GSE-HEM, slicing of GSE packets is

performed and SYNCD shall always be computed. The receiver may derive the length of the UPs from the packet

header, therefore UPL transmission in BBHEADER is not performed. UPs shall not be sliced when there is a

BBFRAME from a different stream following, splitting is only possible with the immediately following BBFRAME.

The optional ISSY field is transmitted in the BBHEADER.

The Mode Adaptation unit shall perform the following sequence of operations (see Figure 1):

• Optional input stream synchronization (see ETSI EN 302 307-1 [3], clause D.2) relevant to the first

transmitted UP which starts in the data field; ISSY field inserted in the UPL and SYNC fields of the

BBHEADER.

ETSI

ETSI EN 302 307

2 V1.3.1 (2021

07)

• Null-packet Deletion and CRC-8 at UP level shall not be computed nor inserted.

• SYNCD computation (pointing at the first bit of the first transmitted UP which starts in the Data Field) and

storage in BBHEADER. The transmitted UP corresponds exactly to the original UP itself. Hence SYNCD

points to the first bit of the original UP.

• CRC8_MODE computation. This is the EXOR of the CRC-8 (1-byte) field with the MODE (1-byte) field.

CRC-8 is the error detection code applied to the first 9 bytes of the BBHEADER. MODE (8 bits) shall be 1_D

for GSE-HEM.

• UPL not computed nor transmitted.

• GSE-Lite compliance of the stream shall be signalled in the 6

bit of the MATYPE-1 field. GSE-Lite=1

means a GSE-Lite compliant signal is transmitted. GSE-Lite=0 means that the transmitted GSE stream may

not meet the definition of a GSE-Lite signal.

Figure 1: Stream format at the output of the MODE ADAPTER, High Efficiency Mode for GSE

(no CRC-8 computed for UPs, optional single ISSY inserted

in the BBHEADER, UPL not transmitted)

5.1.8 Channel bonding for multi-tuner (L) receivers

5.1.8.1 Introduction to channel bonding

The present document provides tools to implement "channel bonding", where a single input stream is carried in parallel

over L transponders. The maximum number of bonded transponders shall be 3 (L ≤ 3).

Channel bonding allows for example to avoid un-used capacity in a transponder in case of Constant Bit-Rate (CBR)

video programmes, and /or to maximize the statistical multiplexing gain in case of Variable Bit-Rate (VBR) video

programmes.

The bonded channels shall lie in the same frequency band. Further, channel bonding shall use CCM only, and shall not

be combined with wideband tuners (according to Annex M of ETSI EN 302 307-1 [3] and Annex M of the present

document).

In the following clauses, channel bonding for TS transmission (clause 5.1.8.2) and for GSE (clause 5.1.8.3) will be

described in more detail.

User Packet

DATA FIELD

BBHEADER

DFL

80 bits

SYNCD

ISSY

(1 LSB)

MATYPE

(2 bytes)

DFL

(2 bytes)

ISSY

(2 MSB)

SYNCD

(2 bytes)

Time

GSE

CRC-8

MODE

(1 byte)

Optional

UPL (in GSE Headers)

ETSI

ETSI EN 302 307

2 V1.3.1 (2021

07)

5.1.8.2 Channel bonding for TS transmission

Channel bonding for TS transmission allows a single "big-Transport-Stream" to be carried in parallel over L

transponders (L ≤ 3). This requires that the receivers are equipped with L tuners/S2X decoders, receiving in parallel the

L "partial" Transport Streams from the L transponders, and reconstructing the original "big-Transport-Stream". The L

S2X modulators are allowed to adopt the same symbol-rate and MODCOD or different ones.

The number of bonded transponders and their carrier frequencies are signalled in the SI tables according to ETSI

EN 300 468 [5]. These SI tables shall be transmitted in parallel over each of the bonded transponders. This allows an

initial signal scan with a single tuner to extract SI tables. The principle of the S2X transmitting side shall be according

to Figure 2, where the L S2X modulators use the same modulo 2

ISSY counter, clocked by the symbol-rate of a

master channel (in Figure 2, modulator number 1 as example), to implement Input-Stream Synchronization (ISSY, see

ETSI EN 302 307-1 [3], clause D.2). The correspondence between the RF channel and master channel shall be signalled

to the receivers via the SI. Null-Packet deletion is implemented in all modulators according to ETSI EN 302 307-1 [3],

clause D.3.

The input "big-TS" shall be split at TS-packet level over L branches, as follows:

• For PIDs ∉ {SI tables}, when a TS packet is routed into a branch, corresponding Null Packets shall be

generated on the other output branches.

• For PIDs ∈ {SI tables}, the packet shall be copied in all the output branches.

Each input packet with PID ∉ {SI tables} shall be routed into a branch such that the interval between two useful packets

with PIDs ∉ {SI tables} (in terms of TS packets) which are separated by Null Packets, not including packets with PIDs

∈ {SI tables}, generated in the SPLIT block, is kept to a minimum and as uniform as possible.

The useful packet intervals shall be according to the ratio of the total bitrate of the bonded channels to the TS rate of

each channel.

For example for L = 2 channels, this can be fulfilled if the useful packet interval of transponder k takes on only two

different values:

floor(total TS rate/TS rate of transponder k) and/or ceil(total TS rate/TS rate of transponder k),

in which floor(x) and ceil(x) denote the flooring and ceiling operation, respectively. The useful packet interval is

defined as the number of Null Packets, not including packets with PIDs ∈ {SI tables}, inserted into two useful packets

in the SPLIT block plus 1. For example, in Figure 2 the useful packets 1 and 3 are separated by one Null Packet in

transponder 1, resulting in a useful packet interval of 2.

The TS rate of each transponder k = 1, 2…, L is the rate used for transferring packets with PIDs ∉{SI tables} in

channel bonding on this transponder. This corresponds to the total TS rate of the transponder minus the data rate

occupied by PIDs ∈{SI tables}. The total TS rate in above equations is the sum of such TS rates of all transponders.

Each S2X modulator shall activate Input Stream Synchronization by setting the suitable ISSY field.

Transport Stream rate-adapters (i.e. adding or deleting Null-Packets and adjusting the MPEG time-stamps) shall not be

inserted after the SPLIT.

NOTE: Rate-adapters may be inserted before the SPLIT if required.

Clause D.1 shows rules for implementation of channel bonding for TS transmissions.

ETSI

ETSI EN 302 307

2 V1.3.1 (2021

07)

Figure 2: Principle of the transmitting modulators configurations for channel bonding

5.1.8.3 Channel bonding for GSE transmission

5.1.8.3.0 General aspects

Generic Stream Encapsulation (GSE) (ETSI TS 102 606-1 [2]) is an extremely flexible method to transmit any kind of

data, including popular formats such as IP packets or TS packets where the data can be of fixed or variable length. GSE

can be used for bonded channels to support a higher data rate than can be carried in a single RF channel. A maximum of

L channels (L ≤ 3) is supported. The number of bonded transponders and associated information is signalled in the

GSE-LLC tables according to ETSI TS 102 606-2 [6]. These GSE-LLC tables shall be transmitted in parallel over each

of the bonded transponders. To ensure maximum efficiency in S2X, it is recommended to use GSE-HEM (see

clause 5.1.7). The following describes the use of channel boding in GSE-HEM.

Channel bonding for GSE transmission is similar to the TS method of bonding described in clause 5.1.8.2, using the

ISCR timing data in the ISSY field to allow the receiver to align packets from different RF channels (see ETSI

EN 302 307-1 [3], Annex D for ISSY details). However ISSY is not added per UP, but per baseband frame

(BBFRAME). ISSY shall always be used for bonded GSE channels. In the ISSY field, ISCR shall be transmitted every

BBFRAME. BUFS and BUFSTAT shall not be transmitted.

At the modulator, input UPs (GSE packets) are continuously added to the Data Field of a single BBFRAME until it is

complete. Appropriate ISSY information is added to the baseband frame header (BBHEADER) of each BBFRAME.

ISSY information refers to the first transmitted UP which starts in the Data Field. UPs shall be transparently sliced

between BBFRAMEs on different RF channels as necessary - it is not required to slice UPs on BBFRAMEs using the

same RF channel. The order of input UPs shall be maintained in the bonding process. Each BBFRAME is constructed

with a length that is derived according to the modulation and coding parameters for that RF channel. Each RF channel

may have different modulation and coding parameters. In order to reduce buffering requirements, BBFRAMEs shall be

created for each RF channel according to the ratio of the bitrate of each RF channel. For example if the bitrates of two

bonded RF channels are equal, BBFRAMEs for each RF channel shall occur in alternating fashion.

An example of the transmission of bonded GSE channels is shown in Figure 3.

“big Input-TS”

TS packets

…

Ch#L

Null

Packet

Deletion

Input-

Stream

Synch

FEC/

MOD

Buffers

SPLIT

S2X modulator (1)

ISSY

Counter

Ch#1

Null

Packet

Deletion

Input-

Stream

Synch

FEC/

MOD

Symbol

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