DVB-H is extension of DVB-T with some backward compatibility i.e. it can share the same multiplex with DVB-T. IT DVB-H uses a mechanism called multi-protocol encapsulation (MPE) making it possible to transport data network protocols on top of MPEG-2 transport streams. A forward error correction scheme is used in conjunction with MPE to improve the robustness and thus mobility of the signal. Time slicing technology is employed to reduce power consumption for small handheld terminals.
IP datagrams are transmitted as data bursts in small time slots. The front end of the receiver switches on only for the time interval when the data burst of a selected service is on air. Within this short period of time a high data rate is received which can be stored in a buffer. This buffer can either store the downloaded applications or play out live streams. The achievable power saving depends on the relation of the on/off-time. If there are approximately ten or more bursted services in a DVB-H stream, the rate of the power saving for the front end could be up to 90%. With the addition of a 4K mode with 3409 active carriers, DVB-H benefits from compromise between the high speed & small area SFN capability of 2K DVB-T. In addition with the help of enhanced in-depth interleavers in the 2K & 4K modes, DVB-H has even better immunity to ignition interference.
DVB-H trials are either completed or underway in Helsinki, Oxford, Pittsburgh, Paris, Madrid, Sydney, South Africa, The Hague, Bern, Erlangen & SriLanka. Commercial launches of DVB-H services have been so far made in 2006 in Italy, Finland, Albania, Vietnam & Indonesia. More than 30 DVB-H technical and commercial trials have taken place all over the world and further commercial launches are expected in 2007 in Germany, Spain Russia, the USA and elsewhere.
DVB-H : TRIALS & DEPLOYMENT IN INDIA
Doordarshan India has installed DVB-H System at Delhi in May 2007. The existing DTT transmitter at Delhi was converted to carry DVB-H signal as follows:
The existing DTT transmitter at Pitampura was shifted to Akashwani Bhawan as the transmitter was away from central Delhi.
The shifting and re-installation of transmitter and antenna was done within a very short period.
Old DTT modulator model MT 5600 of Tandberg was not capable of carrying DVB-H service hence this modulator was replaced by NEC modulator/ exciter DM 3000A and integrated with 5 KW NEC transmitter. DVB-T and DVB-H coexistence from the same multiplex has been successfully tested on hierarchical modulation.
DD’s Pilot Project For DVB-H
During the trials the Transmitter was tested on various modes of modulation, code rates, guard interval, FEC etc. DVB-H (HP) with QPSK and DVB-T (LP) with 16- QAM results in 64 QAM overall modulation scheme. It was found that the range of DVB-H is drastically reduced (up to 2-3 Kms only) in hierarchical mode. 16 QAM provides more bit rate in the 8 MHz channel (double to that of QPSK). But range of reception was reduced to 4-5 Kms. QPSK was found to provide a reception range upto 10-12 Kms with the existing setup.
Delhi being a large city the decision to transmit only DVB-H Service was taken on most robust parameters to obtain maximum range compromising on the number of channels. Eight TV Channels with Video @ 384 kbps for each channel are being transmitted. The total bit rate including audio, video, MPE FEC, ESG and other overheads comes out to approximately 670 kbps for each TV channel.
The system was originally planned to carry 4 DVB-H channels and 4 DVB-T channels. Later keeping in view the low range of hierarchical modulation, it was decided to transmit only 8 DVB-H channels. The system consist of 8 MPEG-4 AVC encoders of M/s Envivio with 1 cold standby encoder. The system is proposed to be upgraded to 16 channels by using statistical multiplexing & additional hardware.
The DVB-H headend compuses of:-
2 Nos. 8x8 Leitch SDI routers.
2 Nos. 24x24 Cisco IP routers.
2 Nos. (1+1 Mode) IP Encapsulators from UD cast with HP Servers.
1 No. Broadcast Service Manager of M/s Nokia with HP Server.
A 5 KW DTT Transmitter of M/s NEC within antenna mounted on 100M High Tower at Akashwani Bhawan. Doordarshan’s DVB-H
The pilot DVB-H Service of Doordarshan has been inaugurated and commissioned on 23/06/07 by Hon’ble Minister of I & B, Sh Priya Ranjan Dasmunshi
The service is available in free to air mode at present. Business model with Public–Private participation is being studied. The present coverage of the service is around 10-12 Kms from the transmitter site. More areas around Delhi (adjoining townships) are proposed to be covered shortly. DD’s DVB-H Service is proposed to be extended to other metro cities in near future.
Next Steps For DVB-H
The DVB Group will shortly publish a draft specifications for DVB-SH i.e. satellite DVB-H Service for handheld in the S-Band below 3GHz as part of the mobile chain. These specifications are likely to be framed by Dec. 07. Some work for final elements of the DVB-IPDC Systems layer specifications is ongoing.
Mobile TV is a new technology to deliver the good old TV content. Hence there are regulatory issues both from technology point of view as well as content point of view. More prominent amonth them are. There is a need of separate spectrum for DVB-H as any spectrum assigned to DVB-H network will reduce the spectrum available for DVB-T.
Using an entire channel for DVB-H Services provides the added benefit to offer more DVB-H channels, with more viewers interest.
UHF Band IV (470 MHz to 650 MHz) is the preferred spectrum since it is low enough in frequency to offer long distance propagation and high enough to avoid the worst effects of man made noise interference.
Content protection, advertising and copyrights are other regulator issues to be resolved.
Traditional Broadcasting is undergoing a process of change as a consequence of move towards an all digital environment. More programmes, competition and new distribution platforms mean that TV viewing all change. New Technology such as UMTS are enabling mobile telecom operators to provide TV like services and enter broadcast arena. But they can’t provide these services at a reasonable cost. DVB-H services can be provided to masses at a reasonably affordable cost, because the ideal spectrum for DVB-H services is assigned to broadcasters, they will have a leading role to play in DVB-H Service. The mobile penetration in India is increasing at a very fast pace. The Indian public is crazy about cricket matches. This will drive the expansion of Mobile TV especially the DVB-H Service. The DVB-H Network can be used for entertainment, business, education, information social development, disaster management etc. Personal viewing experience shall provide a new dimension to the viewer.
By L.V. Sharma, CE