Comparison of 3 DTTB systems

1. Foreword

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.

Table 1: Broadcasting service of 3 DTTB systems
Item ATSC DVB-T ISDB-T
HDTV / SDTV fixed reception Yes Yes Yes
Data Broadcasting Possible (Note 1) Possible (Note 1) In service
SFN (Single Frequency Network) No Yes Yes
HDTV mobile reception Impossible Impossible (Note 2) Good
Portable reception by Cellular phone Impossible Possible (Note 3) Good
Internet access No good Possible Good
Note1: For ATSC and DVB-T, actual commercial service is not popular
Note2: For DVB-T, SDTV mobile reception is possible.
Note3: In case of DVB-T, another frequency should be required for portable reception service.
As shown above table, the feature of ISDB-T, "Segmented OFDM transmission" enables both fixed and portable reception service in the same channel.

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 1: Receiving performance under impulse noise condition

Figure 2: Receiving performance under multipath interference

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

Figure 3: Coverage, outdoor reception


5. Summary

The summary is shown in Table 2

Table 2: Summary of 3 DTTB systems comparison
Requirements System conform to
requirements
Note
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
Hierarchical transmission
(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)