Terrestrial digital TV standard DTMB National Technical Interpretation (I)
GB DTMB technical solutions and performance index
GB DTMB provide terrestrial digital multimedia services, including HDTV, audio, video, data broadcasting and interactive multimedia, key features include:
High information capacity: for the HDTV program provides more than 24Mb / s single-channel bit rate.
highly flexible mode of operation: By selecting a different modulation mode and address information, the system can support fixed, portable, walk or high-speed mobile reception.
highly flexible frequency planning and coverage areas: use of single frequency networks and coverage with Channel Expander / gap filling device concept, by choosing different modes of protection intervals can be constructed 16 km and 36 km single-frequency coverage net.
support different applications: HDTV, SDTV, data broadcasting, the Internet, messaging, etc..
support multiple transmission / network protocols, such as MPEG2 and IP protocol set. Easily with other broadcast and communications systems to connect.
in OFDM modulation system (TDS-OFDM) to achieve an advanced channel coding and time domain channel estimation / synchronization and reduce the system C / N threshold in order to reduce transmission power, thereby reducing the existing analogue television interference.
support low-power mode portable terminal. Support multiple working modes (already implemented part of the operating mode, see Table 1).
Transmission speed selectable range of 5.414 ~ 32.486Mbps; modulation selectable QPSK, 16QAM, 64QAM; guard interval optional 55.6ms, 125ms; inner code rate options 0.4,0.6,0.8.
Figure 1 GB DTMB transmission data rate (Mbps)
GB DTMB program elements shown in Figure 1. TV programs or data, text, images, voice and other multimedia information after source coding, channel coding, the adoption of one or more of the transmitter launched, covering a certain area. According to terrestrial digital multimedia broadcasting
demand for services, transport conditions and channel characteristics, the national standard DTMB transmission system uses an innovative time-domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) multicarrier modulation alone. This modulation is mainly for terrestrial digital multimedia broadcasting transmission channel linear time-varying characteristics of the broadband transmission channel (frequency selective and time-domain selectivity of concurrent transmission channel) designed. As the TDS-OFDM for the multi-path interference and Doppler frequency shift of the transmission channel, so the same applies to terrestrial digital multimedia broadcasting transmission system other than broadband.
1. Innovative TDS-OFDM modulation
GB DTMB system uses the TDS-OFDM, which is characterized by simultaneous first pseudo-random sequence used in each OFDM guard interval inserted periodically time-domain synchronous orthogonal coding of the frame sequence, TDS-OFDM modulation in accordance with the following steps to: a. input MPEG-TS stream after channel coding processed through the constellation form a 3780 point constellation mapping; b. 3780 point constellation using IDFT transform the growing degree of 3780 discrete sample value (single-carrier model does not need this step) body frame (500 s); c. the guard interval in OFDM insert length of 420 (or 595,945) the PN sequence as a frame header; d. the frame header and frame length of time for the body to form 555.56 s (or 578.7 s, 625 s) the signal frame; e. using a linear phase delay characteristics of FIR low-pass filter to the frequency domain signal shaping; f. the baseband signal Upconversion to RF carrier.
About the Author
I am a professional writer from China Crafts Suppliers, which contains a great deal of information about $keyword_li, welcome to visit!
Poker After Dark Season 7 Episode 36 – PLO 100k, Part 2 [HD]