DVB-RCS2:第二代数字卫星视频广播的编码与调制技术

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"DVB-RCS2是一种先进的数字卫星通信标准，主要应用于双向卫星通信系统，如宽带互联网接入、远程教育、电视会议等。该标准由欧洲电信标准协会(ETSI)制定，详细规定了帧结构、信道编码和调制解调方式，以提高数据传输效率和系统的抗干扰能力。DVB-RCS2是DVB-RCS的升级版，旨在提供更高的带宽效率和更低的误码率，以适应不断增长的数据传输需求。" 在DVB-RCS2中，信道编码是确保数据在经过信道传输时能抵抗噪声和干扰的关键部分。通常，这涉及到使用先进的编码技术，如低密度奇偶校验(LDPC)码或涡轮码。这些纠错编码可以检测并纠正传输过程中可能出现的错误，从而提高数据的可靠性。LDPC码以其高效性能而闻名，能够在保持较低复杂度的同时实现接近香农限的编码效率。调制解调是将数字信号转换为适合无线信道传输的模拟信号，以及在接收端将模拟信号恢复为原始数字数据的过程。DVB-RCS2可能支持多种调制方式，例如QPSK（四相相移键控）、16QAM（16进制正交幅度调制）和32QAM、64QAM，甚至更高阶的QAM调制，以适应不同的信道条件和带宽需求。高阶调制虽然可以提供更高的频谱效率，但对信道质量的要求也更高。在接收端，解调器会根据接收到的信号质量选择最合适的解调方法。 DVB-RCS2标准还考虑了动态资源分配，这意味着系统可以根据实时的信道状态和用户需求动态调整编码率和调制方式，以优化整体系统性能。此外，前向纠错(FEC)和混合自动重传请求(HARQ)机制也是DVB-RCS2的重要组成部分，它们通过错误检测和纠正，以及请求重传的方式，进一步增强了数据传输的可靠性。在DVB-RCS2的框架下，MPEG（Moving Picture Experts Group）压缩标准可能会被用于音频和视频数据的编码，以降低带宽需求。此外，该标准可能还包括对服务质量(QoS)的管理和保证，确保关键应用如语音和实时视频流的顺畅进行。 DVB-RCS2是一个全面的数字卫星通信标准，它涵盖了从帧结构设计到信道编码和调制解调的多个层面，旨在提供高效、可靠和灵活的双向卫星通信服务。随着技术的不断发展，DVB-RCS2将持续演进以满足未来对高速、高质量卫星通信的需求。

ETSI

ETSI EN 302 769 V1.1.1 (2010

04)

4 DVB-C2 System architecture

4.1 System overview

The generic C2 System model is represented in figure 1. The system input(s) may be one or more MPEG-2 Transport

Stream(s) [i.1] and/or one or more Generic Stream(s) [i.2]. The Input pre-processor, which is not part of the C2 System,

may include a service splitter or a demultiplexer for Transport Streams (TS) used to separate the services into the C2

System inputs, which are one or more logical data streams. These are then carried in individual Physical Layer

Pipes (PLPs).

The system output is a single signal to be transmitted on a single RF channel.

Bit

Interleaved

Coding &

Modulation

Data Slice

+ Frame

Builder

OFDM

generation

TS or

GSE inputs

Input

processing

C2 system

DVB-C2

output

Figure 1: High level C2 block diagram

The input data streams shall be subject to the constraint that, over the duration of one physical-layer frame (C2 Frame),

the total input data capacity (in terms of cell throughput, following Null Packet Deletion, if applicable, and after coding

and modulation), shall not exceed the C2 available capacity (in terms of Data Cells, constant in time) of the C2 Frame

for the current frame parameters. One or more PLPs are arranged in a group of PLPs and one or more of such groups of

PLPs form a Data Slice. A C2 System may consist of one or more Data Slices. Each group of PLPs may contain one

Common PLP, but a group of PLPs need not contain a Common PLP. When the DVB-C2 signal carries a single PLP

there is no Common PLP. It is assumed that the receiver will always be able to receive one Data PLP and its associated

Common PLP, if any.

More generally, the group of statistically multiplexed services can use Variable Coding and Modulation (VCM) for

different services, provided they generate a constant total output capacity (i.e. in terms of cell rate including FEC and

modulation).

When multiple input MPEG-2 TSs are transmitted via a group of PLPs, splitting of input TSs into TSPS streams

(carried via the Data PLPs) and a TSPSC stream (carried via the associated Common PLP), as described in annex D,

shall be performed immediately before the Input processing block shown in figure 1. This processing shall be

considered an integral part of an extended DVB-C2 System.

4.2 System architecture

The C2 input processing block diagram is shown in figures 2, which is split into several parts. Figure 2(a) shows the

input processing in case of multiple PLPs. Figure 2(a) shows the BICM module and figure 2(c) shows the frame builder

module. Figure 2(d) shows the OFDM generation module.

ETSI

ETSI EN 302 769 V1.1.1 (2010

04)

FEC

+ BI

QAM

Mapper

Time +

Frequency

Interleaving

Input

Sync

IFFT

Guard

Interval

Pilot

Insertion

DAC

PLPs

Signal

Gen.

L1 Config.

Input

Sync

Input

Sync

Input

Sync

FEC

+ BI

FEC

+ BI

FEC

+ BI

QAM

Mapper

QAM

Mapper

QAM

Mapper

Time +

Frequency

Interleaving

FEC

+ BI

QAM

Mapper

Time

Inter-

leaving

Block

Builder

Freq.

Inter-

leaving

Figure 2(e): DVB-C2 modulator block diagram

4.3 Target performance

If the received signal is above the C/N+I threshold, the Forward Error Correction (FEC) technique adopted in the C2

System is designed to provide a "Quasi Error Free" (QEF) quality target. The definition of QEF adopted for DVB-C2 is

"less than one uncorrected error-event per transmission hour at the level of a 5 Mbit/s single TV service decoder",

corresponding to a Transport Stream Packet Error Rate of approximately PER < 10

-7

measured at the input of the

demultiplexer unit at the receiving end.

5 Input processing

5.1 Mode adaptation

The input to the C2 System shall consist of one or more logical data streams. One logical data stream is carried by one

Physical Layer Pipe (PLP). The mode adaptation modules, which operate separately on the contents of each PLP, slice

the input data stream into data fields which, after stream adaptation, will form baseband frames (BBFrame). The mode

adaptation module comprises the input interface, followed by three optional sub-systems (the input stream synchronizer,

the Null Packet deletion unit and the CRC-8 encoder) and then finishes by slicing the incoming data stream into data

fields and inserting the baseband header (BBHeader) at the start of each data field. Each of these sub-systems is

described in the following clauses.

Each input PLP may have one of the formats specified in clause 5.1.1. The mode adaptation module can process input

data in one of two modes, normal mode (NM) or high efficiency mode (HEM). These modes are described in

clauses 5.1.6 and 5.1.7 respectively. NM is in line with the Mode Adaptation in [i.3], whereas in HEM, further stream

specific optimizations may be performed to reduce signalling overhead. The BBHeader (see clause 5.1.6) signals the

input stream type and the processing mode.

ETSI

ETSI EN 302 769 V1.1.1 (2010

04)

5.1.1 Input Formats

The input signals in terms of either single or multiple streams (one connected to each Mode Adaptation Module)

(see figure 1) shall be supplied to the Mode Adaptation Module(s). In the case of a Transport Stream (TS), the packet

rate will be a constant value, although only a proportion of the packets may correspond to service data and the

remainder may be Null Packets.

Each input stream (PLP) of the C2 System shall be associated with a modulation and FEC protection mode which is

statically configurable.

Each input PLP may take one of the following formats:

• Transport Stream (TS).

• Generic Encapsulated Stream (GSE) [i.2].

• Generic Continuous Stream (GCS) (a variable length packet stream where the modulator is not aware of the

packet boundaries).

• Generic Fixed-length Packetized Stream (GFPS); this form is retained for compatibility with DVB-S2, but it is

expected that GSE would now be used instead.

A Transport Stream shall be characterized by User Packets (UP) of fixed length O-UPL = 188 × 8 bits (one MPEG TS

packet), the first byte being a SYNC byte (47

HEX

) and shall be signalled in the BBHeader TS/GS field, see clause 5.1.6.

A GSE stream shall be characterized by variable length packets or constant length packets, as signalled within GSE

packet headers, and shall be signalled in the BBHeader by TS/GS field, see clause 5.1.6.

A GCS shall be characterized by a continuous bit-stream and shall be signalled in the BBHeader by TS/GS field and

UPL = 0

, see clause 5.1.6. A variable length packet stream where the modulator is not aware of the packet boundaries,

or a constant length packet stream exceeding 64 kbit, shall be treated as a GCS, and shall be signalled in the BBHeader

by TS/GS field as a GCS and UPL = 0

, see clause 5.1.6.

A GFPS shall be a stream of constant-length User Packets (UP), with length O-UPL bits (maximum O-UPL value

64 K), and shall be signalled in the BBHeader TS/GS field, see clause 5.1.6. O-UPL is the Original User Packet Length.

UPL is the transmitted User Packet Length, as signalled in the BBHeader.

5.1.2 Input Interface

The input interface sub-system shall map the input into internal logical-bit format. The first received bit will be

indicated as the Most Significant Bit (MSB). Input interfacing is applied separately for each single Physical Layer Pipe

(PLP), see figure 2(a).

The Input Interface shall read a data field, composed of DFL bits (Data Field Length), where:

0 <

DFL < (K

bch

- 80)

where K

bch

is the number of bits protected by the BCH and LDPC codes (see clause 6.1).

The maximum value of DFL depends on the chosen LDPC code, carrying a protected payload of K

bch

bits. The 10-byte

(80 bits) BBHeader is appended to the front of the data field, and is also protected by the BCH and LDPC codes.

The input interface shall either allocate a number of input bits equally to the available data field capacity, thus breaking

UPs in subsequent data fields (this operation being called "fragmentation"), or shall allocate an integer number of UPs

within the data field (no fragmentation). The available data field capacity is equal to K

bch

- 80. When the value of

DFL < K

bch

- 80, a padding field shall be inserted by the stream adapter (see clause 5.2) to complete the LDPC/BCH

code block capacity.

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DVB-RCS2:第二代数字卫星视频广播的编码与调制技术

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