Advanced VSB (A-VSB) demonstrated for ATSC transmitting stations
We had mentioned in the book (Chapter 5, Overview of Mobile TV Technologies) that the ATSC systems which use single carrier for modulation ( i.e. 8VSB) have severe limitations for carrying the Mobile TV channels as compared to OFDM based systems such as DVB-H or FLO. The ATSC systems also have limitations in forming Single frequency networks (SFNs) owing to the absence of synchronization timing information which could be used by adjacent transmitters.
OFDM based systems are highly resistant to multipath fading as experienced in Non-line of Sight (NLOS) and mobile handheld environments. The DVB-H technologies in fact take advantage of the structure of DVB-T to add on additional features for error correction and power saving in handsets. Using 4096 carriers (4K mode), for example, reduces the possibility of any significant Inter-symbol Interference. Also as detailed in Chapter 8 (DVB-H Technologies), the DVB-H standards have been designed for additional Forward Error Correction (FEC) and Multi-protocol Encapsulation (MPE) to provide error free transmissions in the mobile environment.
As the DTV transition is moving ahead strongly the ATSC is also adding on features to support mobile TV by some enhancements to the ATSC standard.
There were two approaches which were demonstrated at the NAB 2007 for supporting mobile TV and future incorporation in ATSC standards.
