DVB-H: Technology

I read some papers that provide specific information about the technical characteristics of the DVB-H technology but I consider more appropriate to provide a general view of the technical aspects, although for those readers that want to know more about that approach I recommend them to read the following article (link1) or the chapter 7 of the book “Mobile TV: DVB-H, DMB, 3G Systems and Rich Media Applications” by Amitabh Kumar (2007). As I mentioned before

DVB-H is built upon the principles of the DVB-T standard, the DVB-H standard adds functional elements that are necessary to fulfill the requirements of the mobile handheld devices reception case. DVB-T and DVB-H use the same physical layer and what is interesting is that DVB-H can be backward compatible with DVB-T. DVB-H like DVB-T can carry the same MPEG-2 transport stream and use the same transmitter and OFDM modulators for its signal. Another positive fact is that DVB-H system is compatible with DVB-T networks, that allows to share the use of the DVB frequency bands without jamming the performance of the cellular bands. (DigiTag, 2008) DVB-H uses IP datacasting. So the system requires a process that involves packaging of digital data into IP packets and then delivering these packets in a reliable manner. The use of IP has the advantage that the data including content is compatible with Internet technology, in other words the content can be managed by the same protocols and devices that are used extensively on the Internet (Kumar, A., 2007). So the DVB-H payload are IP-datagrams.

DVB-H systems have been made the following enhancements that distinguish it from DVB-T:

- Time slicing: DVB-H uses time slicing to reduce the power consumption. Time slicing means that the data from a particular services is delivered to the handheld device in bursts at given intervals of time. When the receiver is not receiving the wanted burst (tv content), the tuner contained in the handheld devices remains “inactive” that contributes to use less power. Time-slicing contribures with a 95% reduction in power consumption compared to continuously operating DVB-T tuners. Because in DVB-T the cannels follow sequentially, so the receiver for each channel needs to be active all the time because the data is continuously arriving (DigiTag, 2008). In the case of DVB-H the IP encapsulator gives the full capacity of the multiplex for a limited time to only one channel, is necessary to mention that power is consumed continually by other parts of the receiver notably the video and audio decoders and the display. (Kumar, A., 2007). Time slicing also contributes enabling smooth and seamless frequency handover. (GERARD FARIA, 2006)

- OFDM: The use of multiple carriers, OFDM (Orthogonal Frequency Division Multiplex) systems excel at handling multi-path interference (EBU-EUR / DVB-H, 2004) In addition to the 2k and 8k modes available in DVB-T, a new 4k mode ortogongal frequency division multiplexing is adopterd giving increased flexibility for network design, is an option complementing the 8K and28K modes that also available. (GERARD FARIA, 2006). This 4K mode is also used for a trading off mobility and single-frequency network (SFN) cell size, allowing a single antenna reception in medium SFNs at high speeds. (EBU-EUR / DVB-H, 2004)

- MPE-FEC(Multi Protocol Encapsulation-Forward Error Correction): the reception in handheld devices have small antennas and have low gain and require reception from different location (mobile environment), so is necessary a strong transmission system able to cope with transmission errors, improve C/N performance and Doppler effects in mobile channels (Kumar, A., 2007) . So the MPE-FEC module offers in addition to the physical layer transmission a complementary forward error function that offers improved transmission robustness. The MPE-FEC processing is takes place on the link layer process the IP input streams before they are encapsulated by means of the MPE. MPE-FEC is not mandatory for DVB-H. (EBU-EUR / DVB-H, 2004)

The following diagram provides a general view of the DVB-H protocol stack:

Figure 1: DVB-H Protocol Stack (Kmar, 2007)

I have found interesting the following diagram that show the system architecture for collaboration between mobile and broadcast operators:

Figure 2 (DigiTag,2008)

With this entry I tried to explain the most important technic features of DVB-H standard by using the ETSI Digital Video Broadcasting standards, for more information consult the standard specification.

References:

DigiTag. (2008). Television on ahandheld receiver - broadcaster with DVB-H. Retrieved 07 20, 2009, from http://www.digitag.org/DTTResources/DVBHandbook.pdf

DVB. (2009). What is the DVB Project? Retrieved 7 2009, 15, from http://www.dvb.org/
EBU-EUR / DVB-H. (2004). DVB-H Standard Specification: ETSI EN 302 304 V1.1.1. Retrieved 07 2009, 19, from http://www.dvb-h.org/PDF/DVB-H%20Specification%20-%20En302304.V1.1.1.pdf

Faria, G., Henriksson, J., Stare, E., & Talmola, P. (2006). IEEE Xplore. Retrieved 06 2009, 13, from DVB-H: Digital Broadcast Services to Handheld Devices: http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F5%2F33232%2F01566629.pdf%3Farnumber%3D1566629&authDecision=-203

GERARD FARIA, J. A. (Genuary de 2006). DVB-H. Recuperado el 20 de 07 de 2009, de DVB-H: Digital Broadcast Services to Handheld Devices: http://www.dvb-h.org/PDF/01566629_DVB-H.pdf

Kumar, A. (2007). Mobile TV: DVB-H, DMB, 3G Systems and Rich Media Applications . Fucal Press Media Technoly Professional.

UE. (2008, 3 17). Mobile TV across Europe: Commission endorses addition of DVB-H to EU List of Official Standards. Retrieved 7 15, 2009, from http://europa.eu/rapid/pressReleasesAction.do?reference=IP/08/451