FAQ about ISDB-T

FAQ Category

This category is consisted of the questions which refer to the general explanation for the digital broadcasting.
This category is consisted of the questions which refer to the digital broadcasting service such as the number of the program, HDTV service, SDTV service etc.
This category is consisted of the questions which refer to the receivers and STB (Set Top Box)

FAQ Category 1   "General"

001 Q What are the differences between the Japanese and Brazilian standards?
A Brazil adopted ISDB-T transmission system. Brazil transmission system is same as Japanese system except transmission spectrum mask and receiver IF frequency.
For other area, Brazil adopts MPEG-4 as video coding system, and also adopts GINGA, Brazilian data casting system, which had been developed by Brazil.
For handheld service named "One-seg", field frequency is different. In addition, the SBR (Spectral Band Replication) is available for audio coding in Brazil.

FAQ Category 2   "ISDB-T transmission system"

001 Q What is the bit rate of ISDB-T for fixed and mobile/ handheld reception?
A In case of ISDB-T system, it is slightly complicate to calculate bit rate because hierarchical transmission is possible.
An example of bit rate for fixed reception and mobile/ handheld reception
HD fixed reception + One-seg service in one 6MHz bandwidth
(a) HD service for fixe reception: 12segment, 64QAM, r=3/4, bit rate=16.85 Mbps
(b) One-seg service for portable reception: 1 segment, QPSK, r=2/3, bit rate=416 kbps
002 Q What is the time interleaving and how does it work for portability and mobile?
A In generally, digital communication system adopts error correction system with interleave technology. The error correction system shows best performance in case of random error pattern.
Time interleave technology is adopted to randomize many degradation factors, such as man-made noise, multi-path fading, interference to get best error correction process.
In this respect, time interleave technology is very effective to improve receiving performance and it much contribute to the realization for mobile/ portable reception and indoor fixed reception.
003 Q Is SFN possible for ATSC and DVB-T?
A Because ATSC adopts single carrier system, it is quite difficult for ATSC to work in SFN.
On the other hand, ISDB-T and DVB-T adopt multi-carrier system, named OFDM, therefore, basically both systems can work in SFN.
DVB-T does not adopt a time interleave technology, therefore, mobile/ indoor reception performance of DVB-T is inferior to that of ISDB-T in SFN.
004 Q Do all the segments have the same number of carriers? Including the One-seg segment?
A Yes, each segment composing ISDB-T signal has same band-width/number of carrier/carrier spacing. (note)
(note) the number of carrier/channel spacing is different depends on "mode", but these parameters of each segment are same.

FAQ Category 3   "Digital broadcasting service"

001 Q How is it possible to broadcast digital TV in many languages?
A Japan adopts MPEG2-AAC and Brazil adopts MPEG4-AAC for audio coding system respectively. These coding systems support monaural, stereo, multi-channel stereo, dual and multi-audio service.
This is the reason for supporting multi-lingual service in ISDB-T system.
002 Q What kinds of video/audio format are used? HD? or multi-SD?
A Both Japan and Brazil digital broadcasting system support both HD and Multi-SD service.
If your country adopt ISDB-T based on Japan/Brazil system, you can enjoy select any of HD, Multi-SD or compound service of HD/SD. In case of DVB-T system, many countries adopt Multi-SD service only.
003 Q How many programs can be broadcast at the same time?
A ISDB-T adopts MPEG-2 systems for service multiplexing system. The number of service in a channel should be decided as a operational guideline considering a trade off of service request and service quality.
In Japan, broadcasting companies usually provide One HD program and sometimes up to 3 SD programs.

FAQ Category 4   "Receiver & STB (Set Top Box)"

001 Q What are primary factors which influence STB prices?
A The most important factor for STB price is its performance, especially video coding system and input/output video format.
The following table shows a segmentation of STB performance.
Table: classification of STB performance
Coding system Input →output (video format)
MPEG-2 (a)SD in →SD out (c)SD /HD in →SD out (e)HD/SD in →HD/SD out
MPEG-4 (b)SD in →SD out (d)SD /HD in →SD out (f)HD/SD in →HD/SD out
The Cheapest type in above table is case (a), the most expensive type is case (f). In Japan, digital terrestrial service is provided in the format of both HD and Multi-SD, therefore, current STB in market is case (e).
It is said that STB price depends on transmission system, such as DVB-T, ISDB-T, ATSC. However, this is not correct but just misunderstanding. Because the difference of STB hardware based on transmission system is very small part, this factor does not influences to STB price.
The market size is also an considerable factor on STB price. However, It is expected that when the size of the market is over 1 million, the STB price is not much affected by that of the market. Nowadays, any of transmission system (ISDB-T,DVB-T, ATSC) has larger market than 1 million, therefore, market size is not so important factor on STB price.
002 Q Can a STB receive HD as well as SD?
A The STB, for ISDB-T system, both Japan and Brazil, has a function to receive/decode any both HDTV and SDTV.