■ Code name: GB 20600-2006
■ Standard name: Framing structure, channel coding and modulation for digital television terrestrial broadcasting system
■ Authorized date: August 18, 2006
■ Effective date: August 1, 2007
■ Standard type: Mandatory standard
GB20600-2006 is an innovative standard specification, developed independently for the terrestrial television broadcasting in China. It uses many advanced technologies to improve its system performance, such as: Pseudo-random Noise (PN) sequence as a guard interval that provides fast system synchronization and precise channel estimation and equalization; Low Density Parity Check (LDPC) coding; Time Domain Synchronization – Orthogonal Frequency Division Multiplexing (TDS-OFDM); multi-layer frame structure that is synchronized with absolute time; spread spectrum encoded Transmission Parameter Signaling (TPS), etc. The GB20600digital terrestrial television broadcasting standard supports transmission rates from 4.813Mbps to 32.486Mbps.
The GB20600 Standard is the most important component in the television broadcast system in China. In addition to the basic functions of the traditional television service, it provides the capabilities to accommodate new additional services utilizing the television broadcasting system. The GB20600system supports both the fixed (indoor & outdoor) and mobile reception of Digital Television Terrestrial Broadcasting (DTTB). The mobile reception supports standard definition digital television broadcasting, digital audio broadcasting, multimedia broadcasting, and data broadcasting service. In addition to the above services, the fixed reception also supports the high definition digital TV broadcasting.
The GB20600 system supports both MFN (multi-frequency network) and SFN (single-frequency network) broadcasting modes. Different modes and parameters can be chosen based on the service type and the network environment, thus giving more flexibility to the services. The system also supports mixed MFN and SFN mode operations.
■ GB20600-2006 Transmission System Structure
The transmission system of GB20600Standard performs the signal conversion from the input data stream to the terrestrial TV signal output. The input data stream goes through the scrambler, FEC (forward error correction) process, the constellation mapping process that converts the bit stream to symbol stream, and then the time interleaver process to produce the basic data block. The data block and the TPS information are multiplexed and then go through the data process to form the frame body. The frame body and frame header (constructed by PN sequence) combine together to form the signal frame, and then pass through the SRRC (square-root raised cosine) filter to become the output signal within an 8MHz bandwidth channel. Finally, a frequency converter will convert this output baseband signal to RF signal (within the UHF or VHF range).
■ Core Technologies:
● TDS-OFDM (Time Domain Synchronization-Orthogonal Frequency Division Multiplexing) -High spectrum efficiency, excellent multi-path performance, and suitable for the broadband transmission.
● LDPC (Low Density Parity Check) -Near Shannon Limit Forward Error Correction code.
● PN sequence channel estimation-use the pseudorandom binary sequence (PN sequence) as the reference signal.
■ Advanced Features of GB20600-2006:
● High capacity-High data transmission rate. An 8 MHz channel can carry 6 to 15 SD (standard-definition) television programs or 1 to 2 HD (high-definition) television programs.
● High reliability-High transmission quality, strong anti-interference ability, and outstanding high speed reception. Has the same reception quality as cable television.
● Strong compatibility-Adapts suitably to the Chinese national television network condition and is compat ible with the existing analog television systems. Enables new networks to be built up quickly with low cost. The existing microwave link, mountain transmission station, analog transmitters, and spare spectrum can be used for the new standard.
● One platform, three receptions-the standard will support fixed reception, portable reception, and mobile/ handheld reception.
● Large coverage-large service coverage area.
● Expandability-Converges wireless communication technologies by providing the ability to support two-way multi-media communication services.
● Mature system-The industry food chain includes the transmission equipment, receiver devices, test equipment, and semiconductor ASIC components that are all ready today.
■ GB20600-2006 System Components:
The system components include encoder (usually MPEG-2 encoder or H.264/MPEG-4 encoder), TS multiplexer, scrambler, GB20600-2006 exciter, SFN adapter, GPS receiver, digital television transmitter, antenna feeder system, and related control software. The system can be simplifed according to the different broadcasting operation modes. The digital television terrestrial broadcasting can also use the existing analog antenna feeder system, thus it can save significant resources and time.
In addition, some test equipment can be borrowed when needed, such as field intensity meter, power meter, spectrum analyzer，standard receive antenna, GPS，etc. from the existing analog television deployments.
■ GB20600-2006 Solution:
● The existing MMDS/MUDS system can be used for the new GB20600-2006 standard by replacing the modulator at the transmitter end and the STB at the receiver end. This will protect the investment benefits of the old system, and also help to prepare the customer resource for the future use of the high power GB20600 transmission equipment.
● Existing DMB-T/DVB-T system can be switched to the new GB20600-2006 standard by updating the exciter and STB.