DTMB(Digital Terrestrial Multimedia Broadcast) & DVB-C(Digital Video Broadcasting - Cable) Difference | Soukacatv.com


Posted March 14, 2019 by tracyhe

DTMB (Digital Terrestrial Multimedia Broadcast) is the TV standard for mobile and fixed terminals used in the People's Republic of China, Cuba, Hong Kong and Macau.

 
DTMB (Digital Terrestrial Multimedia Broadcast) is the TV standard for mobile and fixed terminals used in the People's Republic of China, Cuba, Hong Kong and Macau.

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Previously known as DMB-T/H (Digital Multimedia Broadcast-Terrestrial/Handheld), the DTMB is a merger of the standards ADTB-T (developed by the Shanghai Jiao Tong University), DMB-T (developed by Tsinghua University) and TiMi (Terrestrial Interactive Multiservice Infrastructure); this last one is the standard proposed by the Academy of Broadcasting Science in 2002.




DVB-T And ISDB-T Encoder Modulator
At first, neither Shanghai Jiao Tong University nor Tsinghua had enough political strength to make their own technology become the unique standard, so the final decision was to opt for a double standard, merged with the TIMI 3 standard, responding to a need for backward compatibility.

The DTMB was created in 2004 and finally became an official DTT standard in 2006.

DTMB in China
· 2005 trial

· 18/08/2006 formal adoption as a DTT standard

· 2008 analogue to digital switchover

· 2015-2018 analog switchoff

· In 2020, the terrestrial digital TV of the People's Republic of China will be fully turned to high definition.

DTMB channel available in China
· National:

· CCTV-1, 2, 4, 7, 9, 10, 11, 12, 13, 14, 15, CGTN English

· Provinces:

Main channel of province TV in each province

· High Definition Channel:

· Varies

· City or Local channel:

· Varies

DTMB in Hong Kong
Main article: Television in Hong Kong § Digital television

· 18/08/2006 formal adoption as a DTT standard

· 31/12/2007 analogue to digital switchover

· 2020 analogue switchoff

DTMB in Macau
· 18/08/2006 formal adoption as a DTT standard

Description
Besides the basic functions of traditional television service, the DTMB allows additional services using the new television broadcasting system. DTMB system is compatible with fixed reception (indoor and outdoor) and mobile digital terrestrial television.
· Mobile reception: is compatible with digital broadcasting TV in standard definition (SD), digital audio broadcasting, multimedia broadcasting and data broadcasting service.

· Fixed reception: in addition to the previous services, also supports high definition digital broadcasting (HDTV).

Modulation
The DTMB standard uses many advanced technologies to improve their performance, for example, a pseudo-random noise code (PN) as a guard interval that allows faster synchronization system and a more accurate channel estimation, Low-Density Parity Check (LDPC) for error correction, modulation Time Domain Synchronization - Orthogonal Frequency Division Multiplexing (TDS-OFDM) which allows the combination of broadcasting in SD, HD and multimedia services, etc.

This system gives flexibility to the services offered to support the combination of single-frequency networks (SFN) and multi-frequency networks (MFN). The different modes and parameters can be chosen depending on the type of service and network's environment.

The sequence of pseudo-random pattern is defined in time domain and the information of the Discrete Fourier transform (DFT) is defined in the frequency domain. The two frames are multiplexed in the time domain, resulting in Time domain synchronization (TDS).

Functional scheme
This transmission system makes the conversion of the input signal to the output data of terrestrial TV signal.

The data passes through the encoder, the error protection process FEC (Forward Error Correction), through the constellation mapping process and then the interleaving processes the information to create the data blocks. The data block and the TPS information are multiplexed, and pass through the data processor to form the body structure. It combines information from the body and the head to form the frame and this is passed through the SRRC (Square Root Raised Cosine) filter to become a signal within an 8 MHz channel bandwidth. Finally the signal is modulated to put it in the corresponding frequency band.

Features
· Bit-rate: from 4.813 Mbit/s to 32.486 Mbit/s

· Combination of SD, HD, and multimedia services

· Flexibility of services

· Time and frequency domain of data-processing

· Broadcasting of between 6 and 15 SD channels and 1 or 2 HD channels

· Same quality of reception as wire broadcast



DVB-C
DVB-C stands for "Digital Video Broadcasting - Cable" and it is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 or MPEG-4 family digital audio/digital video stream, using a QAM modulationwith channel coding. The standard was first published by the ETSI in 1994, and subsequently became the most widely used transmission system for digital cable television in Europe, Asia and South America.It is deployed worldwide in systems ranging from the larger cable television networks (CATV) down to smaller satellite master antenna TV (SMATV) systems.
DVB-C transmitter



Scheme of a DVB-C transmission system

With reference to the figure, a short description of the single processing blocks follows.




HD Encoder To DVB-C Modulator
· Source coding and MPEG-2 multiplexing (MUX): video, audio, and data streams are multiplexed into an MPEG program stream (MPEG-PS). One or more MPEG-PSs are joined together into an MPEG transport stream (MPEG-TS). This is the basic digital stream which is being transmitted and received by home set top boxes (STB) or relevant integrable decoder (e.g.Conax) module. Allowed bitrates for the transported MPEG-2 depend on a number of modulation parameters: it can range from about 6 to about 64 Mbit/s (see the bottom figure for a complete listing).

· MUX adaptation and energy dispersal: the MPEG-TS is identified as a sequence of data packets, of fixed length (188 bytes). With a technique called energy dispersal, the byte sequence is decorrelated.

· External encoder: a first level of protection is applied to the transmitted data, using a nonbinary block code, a Reed-Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet.

· External interleaver: convolutional interleaving is used to rearrange the transmitted data sequence, such way it becomes more rugged to long sequences of errors.

· Byte/m-tuple conversion: data bytes are encoded into bit m-tuples (m = 4, 5, 6, 7, or 8).

· Differential coding: In order to get a rotation-invariant constellation, this unit shall apply a differential encoding of the two Most Significant Bits (MSBs) of each symbol.

· QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM.

· Base-band shaping: the QAM signal is filtered with a raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.

· DAC and front-end: the digital signal is transformed into an analog signal, with a digital-to-analog converter (DAC), and then modulated to radio frequency by the RF front-end.

Available bitrates for a DVB-C system (Mbit/s)

Modulation

Bandwidth (MHz)

2

4

6

8

10

16-QAM

6.41

12.82

19.23

25.64

32.05

32-QAM

8.01

16.03

24.04

32.05

40.07

64-QAM

9.62

19.23

28.85

38.47

48.08

128-QAM

11.22

22.44

33.66

44.88

56.10

256-QAM

12.82

25.64

38.47

51.29

64.11

DVB-C receiver
The receiving STB adopts techniques which are dual to those ones used in the transmission.

· Front-end and ADC: the analog RF signal is converted to base-band and transformed into a digital signal, using an analog-to-digital converter (ADC).

· QAM Demodulation

· Equalization

· Differential decoding

· Outer interleaving

· Outer decoding

· MUX adaptation

· MPEG-2 demultiplexing and source decoding

· Programmable Transport Stream

DVB-C2
On February 18, 2008 it was announced that a new standard – DVB-C2 – would be developed during 2008, and a "Call for Technologies" was issued. Proposals including simulation programs and information on patent rights could be submitted until June 16, 2008.
"The results of the DVB-C2 Study Mission already provided clear indications that technologies are available allowing the performance of the second generation DVB cable transmission system to get so close to the theoretical Shannon Limit that any further improvements in the future would most likely not be able to justify the introduction of a disruptive third generation of cable transmission system." (DVB-C2 CfT)

By using state of the art coding and modulation techniques, DVB-C2 should offer greater than 30% higher spectrum efficiency under the same conditions, and the gains in downstream channel capacity will be greater than 60% for optimized HFC networks.

The final DVB-C2 specification was approved by the DVB Steering Board in April 2009.

DVB-C2 allows bitrates up to 83.1 Mbit/s on an 8 MHz channel bandwidth when using 4096-QAM modulation; future extensions will allow up to 97 Mbit/s and 110.8 Mbit/s per channel using 16384-QAM and 65536-AQAM modulation.

Modes and features of DVB-C2 in comparison to DVB-C:



DVB-C

DVB-C2

Input Interface

Single Transport Stream (TS)

Multiple Transport Stream and Generic Stream Encapsulation (GSE)

Modes

Constant Coding & Modulation

Variable Coding & Modulation and Adaptive Coding & Modulation

FEC

Reed Solomon (RS)

LDPC + BCH 1/2, 2/3, 3/4, 3/5, 4/5, 5/6, 6/7, 7/8, 8/9, 9/10

Modulation

Single Carrier QAM

absolute OFDM

Modulation Schemes

16- to 256-QAM

16- to 4096-QAM

Guard Interval

Not Applicable

1/64 or 1/128

Inverse Fast Fourier transform (IFFT) size

Not Applicable

4k

Interleaving

Bit-Interleaving

Bit- Time- and Frequency-Interleaving

Pilots

Not Applicable

Scattered and Continual Pilots

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Source: wikipedia
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