Comparison of 3 DTTB systems
So-called 3 major DTTB( Digital Terrestrial TV Broadcasting) systems are:
|(1)||ATSC: Advanced Television System Committee, Developed in USA, and now used.|
|(2)||DVB-T: Digital Video Broadcasting – Terrestrial, developed in EU, and now used.|
|(3)||ISDB-T: Integrated Service Digital Broadcasting – Terrestrial, developed in Japan and now used in Japan and Latin America.|
Among them, ISDB-T is a superior broadcasting system which has many advantages such as, "segmented OFDM Transmission", "Time interleave", etc.
2. Comparison from service aspect
Table 1 shows the summary of the performances of 3 DTTB systems from service aspect.
3. Advantage of ISDB-T on "Time Interleave"
ISDB-T has "Time Interleave" function. This function enables the following features especially for mobile/portable reception.
|(1)||As the experimental result, Time Interleave improves required C/N ratio about 7 dB in mobile environment on 16QAM.|
|(2)||Diversity reception improves about 7 dB on 16QAM|
|(3)||Time Interleave (Time diversity) works independently from space diversity|
|(4)||That is the reason for advantage of ISDB-T in mobile environment.|
In addition, indoor reception is also improved because Time Interleave improves robustness against impulse noise interference that comes from power line and motor cycle engine.
4. Some comparison test results
Results of Brazilian Tests
Brazil had a comparison test of 3 DTTB systems from August 1999 to April 2000.
- (a) Laboratory tests
- Receiving performances under AWGN + Impulse noise (see Figure 1)
- Receiving performances under multipath interference (see Figure 2)
Figure 1: Receiving performance under impulse noise condition
Figure 2: Receiving performance under multipath interference
- (b) Field tests
- Figure 3 shows the relation between reception percentage and distance from transmitter site. As shown in figure, ISDB-T shows the best reception performance.
Figure 3: Coverage, outdoor reception
The summary is shown in Table 2
|Requirements||System conform to
|Maximum bit rate under Gaussian noise environment||ATSC|
|Robustness against multi-path interference||DVB-T, ISDB-T||Note 1|
|Robustness against impulse noise||ISDB-T||Thanks for time interleave|
|Wide area Single Frequency Network (SFN) operation||DVB-T, ISDB-T|
|Mobility and portability||ISDB-T >> DVB-T||Thanks for time interleave|
(Multiple modulation systems simultaneously in same channel is possible)
|ISDB-T >> DVB-T||Note 2|
|System commonality with digital terrestrial sound broadcasting||ISDB-T|
|Note1:||Under the static multipath condition, DVB-T and ISDB-T are almost same, but under the dynamic multipath condition, ISDB-T is superior than DVB-T thanks for "time interleave"|
|Note2:||DVB-T has a function of hierarchical transmission function( non-uniform transmission), but no practical service in the world (because of lower receiving performance)|