Terrestrial Digital Tv Standard Dtmb National Technology (part Ii) - Digital Terrestrial Tv, Dvb-t,

Connected to the article: Terrestrial digital TV standard DTMB national technical interpretation (on)

DTMB Technical Features GB DTMB to time-domain orthogonal frequency division multiplexing (TDS-OFDM) modulation technology as the core, formed its own intellectual property system, the technology has its own distinct characteristics.

1. OFDM modulation synchronization time-domain Synchronization in OFDM systems is the most important part of setting one of OFDM systems is the focus of the most important innovation.

In the European DVB-T of C-OFDM, the system synchronization is in the frequency domain OFDM symbol by inserting pilot achieved, that is, frequency-domain synchronization. With the use of C-OFDM in DVB-T systems, the national standard DTMB PN sequence used as time-domain synchronous orthogonal frequency-filled division multiplexing (TDS-OFDM) technology, will fill the traditional PN sequence as guard interval OFDM-frame header , since the frame header signal is known, can be removed at the receiving end, so the same sense against the ISI to zero fill the guard interval. Meanwhile, PN sequence as synchronization sequence, and be used to achieve synchronization. Moreover, the receiver can calculate the PN sequence through the relevant wireless channel's time domain to estimate the impact of response time.

2. OFDM modulation to protect the new definition of interval

In OFDM systems, OFDM signal structure is the block structure, each signal block is called OFDM symbols, which in the time domain consists of two parts: a data portion, the other is the guard interval. OFDM signal block of data is partly defined in the frequency domain, resistance to multipath interference intervals must be protected, generally greater than the guard interval length of the transmission delay spread of multipath signals.

OFDM symbol guard interval according to the fill signal, the conventional OFDM symbol, there are two separate definitions: the first is zero filled (Zero-padding) of the guard interval (referred to as Z-OFDM), as receiver more complex processing algorithms, this model has not been widely used, as have a number of advantages, it has recently become the object of study. The second is to be widely used cyclic prefix fill (Cyclic-Prefix) guard interval (referred to as C-OFDM).

DTMB innovation define a PN sequence (PN-Padding) OFDM signal for the protection interval (referred to as TDS-OFDM). In the TDS-OFDM system, guard interval of the PN sequences have the following fill an important role in:

A. OFDM modulation as the guard interval. PN sequence at the receiving end is known, then can be removed, theoretically equal to zero fill (Zero-padding) of the guard interval.

B. for system synchronization. PN sequence as the synchronization sequence is used to implement the system frame synchronization, frequency synchronization, time synchronization.

C. used for channel estimation and tracking of phase noise. Available at the receiving end of the PN sequence obtained by calculating the relevant time domain for the wireless channel impulse response estimate, and the phase noise suppression.

3. With absolute time synchronization layer frame structure

GB DTMB has been using different standards for digital television technology, the unique complex hierarchical frame structure. This absolute time synchronization with the hierarchical frame structure, the physical layer can provide a single frequency network corresponding to the second TS stream synchronization clock, easy single-frequency network; by calendar days with the broadcast table for the period tie, easy to carry out regular receiver; also conducive to the future expansion of system functions, such as two-way interaction and positioning functions; its also beneficial to hand-held portable receiver power control, this is an important feature for applications to adapt to the future of digital television broadcasting system needs to make arrangements for the physical layer, will help make future systems more secure.

4. Transmission efficiency or spectrum efficiency

In the European DVB-T, for synchronization and channel estimation of the number of pilot carrier 10% of the total carrier.

GB DTMB the PN sequence on the guard interval in OFDM, both as a frame synchronization, and as the guard interval OFDM.

European DVB-TC-OFDM subcarriers with 10% transmission for synchronization and channel estimation pilot signal, simultaneously cyclic prefix guard interval, while the TDS-OFDM guard interval while the time for the transmission channel estimation signal, therefore the transmission of DVB-T system efficiency can only reach the national standard DTMB system of 90%.

Transmission efficiency in the multi-carrier technology and when comparing single-carrier technology, multi-carrier technology is considered the weakness of the national standard for DTMB's core technology is developed to solve this problem.

5. Anti-strong multi-path interference

Multi-carrier system and compared to single-carrier system, OFDM system has the capacity of anti-multipath interference, the size of resistance to multipath interference intervals equal to the length of protection. Given that the subject inserted guard interval of time is known (after synchronization) PN sequence, the channel characteristics in a given case, PN sequence in the receive signal can be directly calculated, and remove. Removed after the PN sequence and time intervals for OFDM signals fill the OFDM signal is zero value equivalent, and time intervals for zero values filling the OFDM guard interval and time extension for the period of the OFDM in the same channel performance is so price. Moreover, in multi-path delay over time intervals for the case, the national standard DTMB still work. TDS-OFDM OFDM frame can be several PN sequence and processing, the resistance to multipath interference from guard interval length of the delay length restrictions, but the traditional OFDM guard interval length of the design requirements must be greater than the delay of multipath interference length.

by: gaga

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