Updates on Mobile TV
edited: Wednesday, June 13, 2007
By Amitabh Kumar
Rated "G" by the Author.
Posted: Wednesday, June 13, 2007
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Mobile TV world is a very dynamic industry.No week goes by when new handsets or features are not introduced.
Advanced VSB (A-VSB)
The Advanced-VSB approach was demonstrated by Samsung in cooperation with Rhode and Schwarz and ATSC. The A-VSB attempts to address both the issues of Synchronization in Single frequency Networks (SFNs) and the high error rate in a typical handheld mobile environment due to sharp variations in signal strength from point to point as well as multipath propagation in NLOS environments. The issue of timing is addressed by adding a Supplementary Reference Sequence(SRS) in the transmitted signal.
This helps the receiver to stay locked in an NLOS environment characterized by severe frequency selective fading as well as mobile handheld environment where the variations in signal strength can cause occasional loss of received signal. The second mechanism to permit mobility is the feature of turbo coding which is in essence incorporation of high FEC so that the received signal can be reconstructed after removing errors in the received signal during the short periods of sever fading. The turbo coding ( for example half rate) is used to add additional error correcting bits which are used for error correction in the receiver. The A-VSB is designed to add Turbo coded streams within the main transmitted stream carrying DTV.
It was claimed that by using the SRS and Turbo coding the Synchronization problems between adjacent transmitters can be resolved while making the signal more robust for handheld reception. If ATSC transmitters are able to operate in SFNs as in the case of DVB-H or DVB-T, this will help improve the quality of reception as the signals of adjacent transmitters add to the received signal ( owing to being in phase) and make the reception by handhelds more robust.
Mobile Pedestrian Handheld (MPH)
An alternative technology for enhancing the capabilities of ATSC transmitters for delivering TV to the mobiles was demonstrated by LG Electronics in cooperation with Harris Corporation and was termed as Mobile Pedestrian Handheld (MPH).
The MPH is based on the use of Enhanced VSB (E-VSB) modulation already approved by the ATSC. E-VSB primarily improves signal reception in far flung areas rather than in the urban areas as it still does not fully address the problem of multi-path propagation.
An advantage of E-VSB standard is the support for MPEG4 and Windows Media 9 (VC1) standards for advanced compression. These are better suited for Mobile TV than MPEG2 as detailed in Chapter 1 of the book. (Introduction to Digital Multimedia). There will need to be a wider availability of receivers for E-VSB for success of this technology.