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The digital television terrestrial mobile broadcasting coverage technology optimization scheme

Author: WangShuai WangYanTao From: www.yourpaper.net Posted: 2010-06-23 05:06:26 Read:
Keywords: mathematical terrestrial mobile technology optimization of
Abstract: in the research of digital TV broadcast of the scientific researchers in China made a big flea work, puts forward several sets of programs, digital terrestrial Duoxian body / advanced digital television broadcasting ADTB system the author take Shanghai Jiao Tong University proposed transfer Discovery Scheme and Electronic Engineering Department of Tsinghua University proposed television broadcast transmission system ((DMB-T.) is more mature, in the digital television terrestrial broadcasting system actual have trial, this article makes research.
1 Shanghai Jiao Tong University AD B in a terrestrial digital TV transmission scheme of
ADTB T is a "single carrier" scheme, which adopts offset quadrature amplitude modulation (OffsetQuadrate Am-plitude Modulation OQAM) using 4 or 16 bits and 32 bits OQAM modulation mode, and the averaging technique, unique in the use of 8M Hz bandwidth with lOMbitls,  , SMbit/s. 20Mbit/s; three transmission modes.The working process of ADTB scheme is roughly: various data stream into data buffer, after scrambling, external code (RS code), interleaving, coding, by the synchronous signal insertion, pilots, OQAM modulation after the formation of baseband signal, the frequency conversion for RF signal.Figure 1 is the ADT 'B-T program flow diagram.
including its main technical composition and characteristics: the effective data structure: meet the integrated service digital flexible and anti-interference requirements, double pilot aided synchronization technology: robust under the pilot aided synchronization, carrier recovery and timing recovery is more robust, reliable.Using the cascade interleaving and channel coding and decoding technology code.Due to the adoption of single carrier modulation, signal peak-to-average ratio is low, carrier to noise ratio threshold low, is conducive to spectrum planning, do a better signal coverage, the ability to fight the phase noise is strong, ability to track rapid changes in channel of strong.Equalization technology to combat channel fading: more powerful and before, to echo after.More efficient reception processing technology: digital signal processing common tuner complex.Large capacity mobile reception: mobile condition rate up to 12Mbps.
2 Tsinghua University.MB digital television terrestrial transmission scheme of
Tsinghua University DMB T digital television terrestrial transmission scheme, using time domain synchronous orthogonal frequency division multiplexing (PN sequence filling TDS OFDM) multi-carrier modulation technology, organically combine the transmission signal in time domain and frequency domain, a control signal for synchronization, education aim.In the frequency domain transfer of payload, in the time domain by using spread spectrum technology transfer channel estimation, synchronization tracking performance to realize fast code acquisition and robust.
in the technology, the traditional OFDM modulation for insertion of high power synchronous pilot, defects in validity, reliability of transmission system losses, the invention of the high protection of synchronous transmission technology of PN sequence spread spectrum technology and clever use of filling technology based on OFDM guard interval, at the same time the spectrum transmission system to improve the efficiency and noise performance.According to the estimation problem of iterative process longer channel of digital terrestrial television broadcasting of existing transmission standard, the invention of the TDS-OFDM channel estimation technique (channel estimation at the receiver using PN sequence), improves the performance of system for mobile reception.Application of a new error correction codec (FEC) (by trellis codes, convolutional interleaving concatenated codes and R a S block code.) technology, effectively improve the reality of multicarrier OFDM system error threshold difference, DMB-T also uses a hierarchical is different from the standard for digital TV technology and nature time synchronization of the complex frame structure, to support the single frequency network.Support for mobile digital TV service single frequency network can not only better, and can solve the problem of blind by a single transmitter cannot cover.

3 two kinds of program performance and characteristics analysis of
soil sea traffic university ADTB T terrestrial digital TV transmission scheme is a "single carrier" program, Tsinghua University's DMB T digital television terrestrial transmission scheme for multi-carrier mode.For the two scheme performance and characteristic are analyzed in this section the single-carrier and multi-carrier angle. single carrier frequency spectrum efficiency is high, the corresponding reduction in the adjacent frequency interference, is advantageous to the frequency planning.Single carrier signal peak-to-average ratio is relatively low, the nonlinear distortion is small, the coverage of the same circumstances, the realization of digital TV transmitter can use less power.The receiving sensitivity of single carrier receiver threshold low, high, easy to receive the signal is weak.Single carrier mode to realize single frequency network is relatively simple, requiring no external clock information.Single carrier in support of mobile technology developed late receiver, transmitter and receiver corresponding high cost.
multi-carrier mode by adding method of protecting interval, the multipath interference problem, and the interleaving technique and different number of carriers and the selection of modulation mode through coding and, effectively improve the mobile reception ability, in mobile reception, the measured data confirm the multi-carrier mode is superior to single carrier mode spectrum of rectangle coefficient. Form the multi-carrier mode, with steep edges, low requirement to the transmitter output filter technology.Multi-carrier way through "spectrum slotted" technology to solve the problem of same frequency interference, a single carrier mode is more suitable for multicast and analog tv.Multicarrier PAPR of PAPR than the single carrier mode high z .Sas, easy to produce nonlinear distortion in the zone, causing intermodulation distortion, with external cause adjacent frequency interference, so the power capacity of the transmitter with high requirements, and requires the use of nonlinear distortion correction technology.
characteristics of digital TV, the ratio of signal and noise over a threshold image quality is always very clear, if smaller than the threshold value, will appear black, this is called a "cliff" effect.In the area of coverage edge, the side of the road image is very good, the next road is nothing.This and the analog TV with the signal is weak, the image becomes difference is small.The bus on the road, even in the area of coverage at some point will appear black, these points are called "black spot".This is the mountain in ten rejection, echo, shadows."Shadow" is the same as the sun's shadow, is a small wave irradiation to place behind the building.In order to reduce the "black spots" problem, now transmitting system adopts distributed.The transmitter and antenna dielectric physical distribution in several locations, and transmit the same signal with the same frequency, which is called a single frequency network (SFN).Shanghai and Singapore are arranged in single frequency network such that minimize, black.So the digital TV and broadcasting system to be used for mobile TV must be able to form a single frequency network.

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