The M/H system uses MPEG-4 HE AAC v2 audio coding as described in ISO/IEC 14496 Part 3, with certain constraints. HE AAC v2 is used to code mono or stereo audio. HE AAC v2 is the combination of three audio coding tools, MPEG-4 AAC, Spectral Band Replication (SBR) and Parametric Stereo (PS).
System Configuration Signaling Recognizing that the mobile sector of the economy is subject to rapid technology change, the needs for continued viability of the system in the face of change were formalized. As there are many technological elements of the system, they were grouped into functional units called elementary subsystems.
1.6.1 DVB-T variants
The DVB-T standard allows for different levels of modulation and different code rates to be used to trade bit rate versus ruggedness. As some variants can be selected as representative of the much larger set of all variants, it will be necessary to select such a sub-set for the planning Conference. This subset is useful to avoid too many options that would otherwise need to be displayed.
The non-hierarchical variants are chosen as being typical of some expressed requirements and are close to others; for the DVB-T example, it is to be expected that channel requirements for a variant with a code rate of 2/3 will be similar to those for a variant with a code rate of 3/4, for the same modulation.
A2: QPSK, 2/3: this variant provides a low data capacity of only 6 to 8 Mbit/s but it does provide a very rugged service.
B2: 16-QAM, 2/3: the data capacity is moderate at 13 Mbit/s to 16 Mbit/s and this variant may be of interest for providing reasonably rugged services especially for portable or mobile reception.
C2: 64-QAM, 2/3: this variant has a high data capacity, 20 Mbit/s to 24 Mbit/s but provides less rugged services and is particularly sensitive to self-interference effects in large area SFNs.
1.6.2 Hierarchical variant
Hierarchical DVB-T system variants mean that the MPEG-2 bit stream is divided into two parts: the high priority stream and the low priority stream. The high priority stream is the rugged part of the hierarchical system and uses QPSK modulation and an appropriate code rate to provide the necessary protection against noise and interference. Because of the type of modulation, the data capacity is low (about 5 to 6 Mbit/s). However, the C/I ratio is worse than that for a non-hierarchical QPSK system although the data capacity is the same as that of a QPSK system of the same code rate.
The low priority stream is the more fragile part of the hierarchical system and may be either 16QAM or
64-QAM. Not much consideration has been given to a low priority stream using 16QAM because the data capacity of the low priority stream is about the same as that of the high priority stream. A low priority stream using 64-QAM provides about twice the capacity of the high priority QPSK stream. Its exact capacity relative to that of the high priority stream depends on the relative code rate of the two streams.
The hierarchical system variants could be used in several ways. One example would be for a combination of fixed and mobile services in the same area, where the high priority stream gives robust mobile coverage and the low priority stream provides fixed antenna reception.
1.6.3 Guard interval
OFDM, as used in DVB-T, exhibits relatively long symbol periods due to its multi-carrier nature. This long symbol period provides a degree of protection against inter-symbol interference caused by multipath propagation. This protection can, however, be greatly enhanced by use of a guard interval. The guard interval is a cyclic extension of the symbol. In simplistic terms, a section of the start of the symbol is simply added to the end of the symbol.
For MFNs, small guard intervals are used while for SFNs, larger guard intervals are required. There is a trade-off between the length of the guard interval and the data capacity. For a given DVB-T variant, a larger guard interval length implies a lower data capacity.
1.6.4 DVB-T in Band III
There are indications that the use of Band III (174-230 MHz) is being considered for DVB-T in some countries. Band III propagation is particularly suitable for portable and mobile reception, because of the uniform field strength distribution that can be achieved in that band, together with the possibility of achieving large area coverage with lower power than would be needed using UHF frequencies. However, in some parts of the planning area (eastern Mediterranean area and Gulf area) the situation is different due to propagation anomalies such as ducting and super-refraction.
A challenge to be faced within Band III is the existence of several channelling arrangements, including the use of 7 MHz and 8 MHz bandwidth channels. Any possible move to a uniform channel raster presents a long-term challenge due to the existing complex non-uniform situation.
The following advantages have led to an increased interest in DVB-T in VHF Band III:
– coverage for large areas is achieved with fewer transmitters than are required at UHF;
– mobile reception (reduction of Doppler effect).
At VHF, propagation conditions are different from UHF; therefore suitable networks may also be different. Furthermore the Doppler shift for mobile reception is less at VHF than at UHF due to the lower frequencies. This is a clear advantage for VHF when administrations consider deploying mobile DVB-T.
1.7.1 Building and validating an open and scalable network architecture
The interworking points between the different domains and actors will also be identified with the objective of defining interworking units whenever required. System engineering rules will be articulated in order to cope with scalability issues. This in particular requires identifying the parameters that are key when scaling up the system. This is crucial to allow the successful progressive introduction of open systems with distributed management functions.
Field trials that include testing of an open operational architecture composed of several broadcast cells will give final input on the viability of the overall system. The novelty will consist in having an open demonstrator addressing the complete/commercial-like architecture. Roaming will be tested between different partners' sites, for instance. Feedback from a panel of users will determine whether the services have sufficiently user-friendly interfaces and will qualify the technical and commercial viability of the services.
Technology development in the project is articulated around three domains that intend to make particularly innovative contributions on:
− content, services and applications,
− user devices,
1.7.2 Content, services and applications
The business motivation in this area is to increase content/service creation productivity because of the increasingly diverse means of accessing services in terms of networks and terminals. This productivity is enhanced only at the expense of making common as many steps as possible in the content/service creation process.
In content generation and production, the migration from the more or less autonomous production workflows of separate departments to workflows where content is created in a multitude of formats to be transmitted via a number of platforms and channels to different terminals will be planned. Content will be produced, generated and edited from a number of sources. A central server architecture connected to a content management system will be implemented allowing for quick, cost-efficient and automated content editing. A mechanism will be established for ensuring that user privacy and security is kept in a common digital environment.
1.7.3 User devices
The main user-device-related objective is to pave the way for the commercial introduction of end-user devices able to provide intuitive access to mobile/portable broadcast and broadband services in collaborating networks. The eEurope 2005 action plan recognizes that the development of such terminals is crucial to social inclusion.
Assuming that national regulations will evolve according to EC recommendations, the opportunity exists to deploy new networks specifically targeting broadcast-based mobile and indoor reception, with better geographical granularity (i.e. smaller cells). This will lead to the definition and field validation of deployment rules for a cellularized DVB-T/H system. Because of the potential co-location of low power DVB-T/H transmitters with 2G/3G base stations, co-existence rules will be defined, depending on the identified interference scenarios.
Digital Video Broadcasting Handheld (DVBH) is a new standard for digital terrestrial TV broadcasting to handheld portable/mobile terminals.
It has been standardised in 2004 by ETSI EN 302 304: “Digital Video Broadcasting (DVB); Transmission System for Handheld Terminals” (DVB H).
The introduction of DVB-H implied to modify slightly few DVB standards. DVB-T has been improved with the introduction of a 4 K carriers mode, a depth interleaver, new time stamps (TPS) and a 5 MHz RF bandwidth. Some people are thinking to introduce 1,5, 3 and 4,5 MHz RF bandwidth in order to fit with the frequency grid in the L band in region 1 and 3 (RRC). 5 MHz RF channel is used in USA in the L band.
The main objective is to deliver various content (video and audio) compressed with MPEG4 encapsulated in IP bursts. One of the main challenges was to reduce the power consumption of the handheld devices (mobile phones, PDA or portable PC) and to allow the reception in various conditions.
In the future, it could be large power transmitter in order to cover a great number of users at once (one to many) with a dedicated format of content and even to be able to deliver interactive services in small cells with low power transmitters compatible with GSM or UMTS cells.
There are two options in term of frequency usage:
− UHF for large coverage areas, from one DVB-H service up to a full channel filled with DVB-H services (see figure hereafter which shows a DVB-T service + several DVB-H services in the same channel. The DVB-T transport stream (service 4 ) has a constant bitrate the other services (1, 2 and 3) are DVB-H IP bursts) .
− L bands for small coverage areas with full channel filled with DVB-H services.
In one 8 MHz channel, it is possible to broadcast up to 50 different programs with an average of 400 kbits/s MPEG4 streams.
The definition of the image is fitting with the size of the display of the handheld device which means (CIF or QVGA).
DVB-H benefits of the advantages of OFDM modulation scheme combined with IP slicing.
In term of usage, DVB-H is a relevant example of converging technology: Convergence between Broadcasting and Telecommunication. However, the introduction of that technology has to be managed carefully in term of frequency allocation and/or sharing.