DVB-T2：欧洲第二代数字地面电视标准

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"DVB-T2标准是欧洲数字电视广播联盟（European Broadcasting Union, EBU）和欧洲电信标准协会（European Telecommunications Standards Institute, ETSI）共同制定的第二代地面数字电视广播系统标准。该标准详细规定了帧结构、信道编码和调制方式，以提高数字地面电视的传输效率和服务质量。DVB-T2标准的目标是在有限的频谱资源下提供更高的数据传输速率和更好的接收质量，支持高清和超高清电视服务。" DVB-T2标准的核心技术包括以下几个方面： 1. **多载波传输（Multi-Carrier Transmission）**：DVB-T2采用了更先进的多载波传输技术，即Fast-FEC框架下的OFDM（Orthogonal Frequency Division Multiplexing），相较于DVB-T的单载波和Coded OFDM，能更有效地抵抗多径衰落，提高系统稳健性。 2. **灵活的帧结构**：DVB-T2允许更灵活的帧结构设计，可以根据不同的信道条件和业务需求调整帧的长度和结构，以适应不同环境和提高效率。 3. **高级信道编码**：DVB-T2引入了低密度奇偶校验码（LDPC, Low-Density Parity Check）作为前向错误纠正（FEC）码，相比于DVB-T使用的卷积码，LDPC码能提供更高的纠错能力，从而在同样的误码率下提高比特率。 4. **分层传输（Layered Transmission）**：通过将信号分为多个层次，DVB-T2可以实现服务质量（QoS）的不同等级，例如，较低层服务于移动接收，较高层则为固定接收提供更高清晰度的视频。 5. **高效交织（Flexible Interleaving）**：DVB-T2的交织设计更加灵活，可以针对不同信道特性进行优化，有助于减少突发错误的影响。 6. **增强型服务导引（Service Guide Enhancement）**：DVB-T2提供了更强大的服务引导功能，使用户能够更容易地找到和选择感兴趣的内容。 7. **多码率支持（Adaptive Bit-Rate）**：通过动态调整编码率和星座图，DVB-T2能够在不同的接收条件下提供最佳的观看体验。 8. **时间分集（Time Diversity）**：通过在不同时间发送相同的传输块，DVB-T2增加了抵抗快衰落的能力，提高了接收可靠性。 DVB-T2标准通过一系列技术创新，极大地提升了数字地面电视广播的性能，不仅增强了广播覆盖，还为高清、超高清电视及交互式服务提供了可能，推动了数字电视产业的发展。其技术细节和实施规范在ETSI EN 302 755标准文档中进行了详尽的描述。

ETSI

Draft ETSI EN 302 755 V1.1

.1 (2008

10)

QPSK Quaternary Phase Shift Keying

RF Radio Frequency

SDT Service Description Table

SIS Single Input Stream

SISO Single Input Single Output (meaning one transmitting and one receiving antenna)

SoAC Sum of AutoCorrelation

TDM Time Division Multiplex

TF Time/Frequency

TFS Time-Frequency Slicing

TS Transport Stream

TSPS Transport Stream Partial Stream

TSPSC Transport Stream Partial Stream Common

TTO Time To Output

TV TeleVision

UP User Packet

UPL User Packet Length

VCM Variable Coding and Modulation

4 DVB-T2 System architecture

4.1 System overview

The generic T2 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 T2 system,

may include a Service splitter or de-multiplexer for Transport Streams (TS) for separating the services into the T2

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

(PLPs).

The system output is typically a single signal to be transmitted on a single RF channel. Optionally, the system can

generate a second set of output signals, to be conveyed to a second set of antennas in what is called MISO transmission

mode.

The present document defines a single profile which incorporates time-slicing but not time-frequency-slicing (TFS).

Features which would allow a possible future implementation of TFS (for receivers with two tuners/front-ends) can be

found in annex E. It is not intended that a receiver with a single tuner should support TFS.

Bit

Interleaved

Coding &

Modulation

Frame

Builder

OFDM

generation

TS or

inputs

Input

processing

Input

pre-

processor(s)

T2 system

Figure 1: High level T2 block diagram

The input data streams shall be subject to the constraint that, over the duration of one physical-layer frame (T2-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 T2 available capacity (in terms of data cells, constant in time) of the T2-frame for

the current frame parameters. Typically, this will be achieved by arranging that PLPs within a group of PLPs will

always use same modulation and coding (MODCOD), and interleaving depth, and that one or more groups of PLPs with

the same MODCOD and interleaving depth originate from a single, constant bit-rate, statistically-multiplexed source.

Each group of PLPs may contain one common PLP, but a group of PLPs need not contain a common PLP. When the

DVB-T2 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.

ETSI

Draft ETSI EN 302 755 V1.1.1 (2008

10)

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-T2 system.

The maximum input rate for any TS, including null packets, shall be 72 Mbit/s. The maximum achievable throughput

rate, after deletion of null packets when applicable, is more than 50 Mbit/s (in an 8 MHz channel).

4.2 System architecture

The T2 system block diagram is shown in Figure 2, which is split into several parts. Figure 2(a) shows the input

processing for input mode 'A' (single PLP), and Figure 2(b) and Figure 2(c) show the case of input mode 'B' (multiple

PLPs). Figure 2(d) shows the BICM module and Figure 2(e) shows the frame builder module. Figure 2(f) shows the

OFDM generation module.

Input

interface

CRC-8

encoder

Single

input

stream

BB Header

insertion

Padding

insertion

Mode adaptation

Stream adaptation

To BICM

module

Scrambler

Figure 2: System block diagram

(a) Input processing module for input mode 'A' (single PLP)

Multiple

input

streams

PLPn

Input

interface

Input

Stream

Synchroniser

Null-

packet

deletion

CRC-8

encoder

PLP0

Header

insertion

To stream

adaptation

Input

interface

Input

Stream

Synchroniser

Null-

packet

deletion

CRC-8

encoder

Header

insertion

PLP1

Input

interface

Input

Stream

Synchroniser

Null-

packet

deletion

CRC-8

encoder

Header

insertion

Comp-

ensating

delay

Comp-

ensating

delay

Comp-

ensating

delay

Figure 2(b): Mode adaptation for input mode 'B' (multiple PLP)

ETSI

Draft ETSI EN 302 755 V1.1.1 (2008

10)

5 Input processing

5.1 Mode adaptation

The input to the T2 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 (BBFRAMEs). The

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

synchronizer, null packet deletion 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), which are described in clauses 5.1.7 and

5.1.8 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 5.1.7) signals the input

stream type and the processing mode.

5.1.1 Input Formats

The Input Pre-processor/Service Splitter (see Figure 1) shall supply to the Mode Adaptation Module(s) a single or

multiple streams (one for each Mode Adaptation Module). In the case of a 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 T2 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) [i.1].

• 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 [i.3],

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

packet), the first byte being a Sync-byte (47

HEX

). It shall be signalled in the BBHEADER TS/GS field, see

clause 5.1.7.

NOTE: The maximum achievable throughput rate, after deletion of null packets when applicable, is

approximately 50.3 Mbit/s (in an 8 MHz channel).

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 5.1.7.

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 5.1.7. 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 5.1.7.

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 base-band header TS/GS field, see clause 5.1.7. O-UPL is the Original User Packet

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

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