Saturday, 22 March 2008

And the winner is . . . DVB-H

Brussels has now officially endorsed DVB-H as the mobile TV technology of choice in Europe. This means that member states are now required to "encourage" use of the technology, though the commission has no advice as to how to encourage punters to tune in.

In the UK both T-Mobile and Orange are about to launch trials using the competing MBMS (Multimedia Broadcast Multicast Service) technology, which utilises existing 3G networks and spectrum. The technology for that trial is being provided by NextWave Wireless, and CMO Jon Hambidge is dismissive of EU attempts to mandate a mobile TV technology "when [the network operators] spent billions of dollars on their licences MBMS [was] part of that business case".

Note that in an earlier blog I had mentioned that Mobile TV and MBMS will co-exist. See here.

Viviane Reding, EU telecoms commissioner, has made it clear that if companies don't migrate to DVB-H she'll use regulatory measures to create an EU-wide standard.

Background Material:

The DVB-H standard is a recent extension of the DVB-T standard. It is intended to allow reception of television programs with portable and mobile terminals of relatively small size (the H of DVB-H means “handheld,” which indicates the primary type of devices targeted).

In most cases, the terminal will be a mobile phone. In fact, one of the main goals of DVB-H is to avoid the limitation inherent to UMTS of the number of terminals which can receive the same broadcast television program at one time. The main extensions of DVB-H compared to DVB-T are as follows (their use is signaled by specific TPS bits):

• addition of a 4 k COFDM mode, better suited to the implementation of SFN networks of medium cell size and allowing a reduction of the power consumption of the terminal compared to the 8 k mode;
• addition of a longer time interleaving (double for the 4 k mode and quadruple for the 2 k mode), which improves the behavior in case of signal fading and resistance to impulsive noise;
transmission of a given service in periodic bursts by a process known as “time slicing” which permits a subscriber to activate the receiver only during a fraction of the time (5 to 10%) in order to reduce the power consumption, thus increasing the battery operating time;
• the ability to increase robustness by means of an optional additional link layer error correction (MPE-FEC) to improve the reception with an integrated antenna of necessarily very limited performances.

In order to allow the best use of these extensions, TV programs or other broadcast services are transmitted to mobile terminals as elementary streams (ES) formatted as IP (Internet Protocol) datagrams. The use of the IP protocol is, however, different from the one in TV by ADSL using DVB-IP: in DVB-H, the IP datagrams are encapsulated according to the so-called multiprotocol encapsulation (MPE) and then inserted in an MPEG-2 transport stream for transmission (in DVB-IP, it’s the transport stream which is IP encapsulated). This operation consists of encapsultaing the IP datagrams in DSM-CC sections by adding a header and a CRC termination. These sections are then segmented into MPEG-2 transport packets.

In order to realize the desired time-slicing, sections are not transmitted immediately, but are accumulated in order to form records of a maximum size of 191 kb, which will correspond to the duration of the time slice allocated to a service. These records can be represented as a table of 191 colums by a maximum of 1024 rows on which an optional additional error correction called “MPE-FEC” can be applied. This MPE-FEC consists of a Reed–Solomon coding RS (255,191) applied to words of 191 bytes made of the lines of this table. This will produce a second table made of an RS word of 64 bytes for each line of the original table. The result will be a new table of 255 colums by a maximum of 1024 lines which will be read column by column for transmission.

The DVB-H standard can be used in the UHF TV band with usual DVB-T channel widths (6, 7, or 8 MHz, depending on the region) or in other frequency bands (e.g., L-band in the United States around 1.67GHz with other channel widths, 5MHz in this case).

One of the problems with the use of the UHF band for TV reception in a GSM phone is the proximity of the high part of the UHF band (up to 862 MHz) to the GSM 900 transmit band of the terminal (880 to 915 MHz). Taking into account the current filtering capabilities, this prevents in practice the possibility of using the high UHF channels (>750 MHz) in a TV receiver integrated into an operating GSM phone.

The DVB-H standard can in principle use all the combinations of modulation parameters allowed by the standard (QPSK to 64-QAM, etc.) but, given the required robustness of this application, in practice only QPSK and 16-QAM with FEC of 1/2 or 2/3 are realistically usable, which permits bit-rates of 5 to 11 Mb/s in an 8MHz channel (without MPE-FEC correction). The video encoding used will be mainly H.264 with a CIF or QCIF resolution and bit-rates in the order of 256 to 384 kb/s.

Various experiments took place in Europe from 2004 onward to test the technical performances of the system in order to define the characteristics of the network, and to find out the user acceptance and expectations in order to establish a viable business model. The reactions of the test sample have been positive or enthusiastic everywhere. The first commercial DVB-H services started in Finland and Italy in mid-2006.
For more information see:

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