btb43503 lecture ivb-dvb broadcast systems

Mobile Communications II BTB43503 1

Lecture IV: Broadcast Systems

• Lecture I:- Mobile Radio Communications

• Lecture II:- Multiple Access Technique for Mobile Communications

• Lecture III:- Mobile Communications Systems and Standards

• Lecture IV: Broadcast Systems

http://en.wikipedia.org/wiki/File:Dvb_logo.png






– Digital Video Broadcast (DVB)

– Digital Audio Broadcast (DAB)– Orthogonal Frequency Division Multiplexing

(OFDM)



Digital Video Broadcast (DVB)







Introduction - History– The origins of DVB started the early years of 1990’s.

– The European television broadcasting formed an organization known as the European Launching Group - renamed to DVB Project and endorsed by European Telecommunications Standards Institute (ETSI).

– Major advantage of DVB is the protocol represents an open system as opposed to a closed broadcasting system.

– However, DVB can provide all the functionality of a closed system.



Introduction-History– A closed system is usually content provider specific and is

usually fixed rather than expandable.

– More than 500 million DVB receivers deployed



Introduction-History– DVB is the protocol that define how digital broadcasting

such as:

• DVB - Terrestrial2 (DVB-T2),

• DVB - Satellite2 (DVB-S2),

• DVB - Handheld (DVB-H)

• DVB - Satellite-Handheld (DVB-SH) and

• DVB - Cable2 (DVB-C2),



Digital Video Broadcast – Terrestrial2







DVB-T2• DVB-T2 is an abbreviation for Digital Video Broadcasting

– Terrestrial 2nd Generation.

• It is an extension television standard of DVB-T.

• DVB-T2 offers an increased efficiency of 30-50% in its use of spectrum compared to DVB-T.

• This system transmits compressed digital audio, video, and other data in "physical layer pipes“ using OFDM modulation scheme.



DVB-T2



Digital Video Broadcasting – Satellite2

(DVB-S2)







DVB-S2• DVB-S2 is known as Digital Video Broadcasting –

Satellite 2nd Generation is an enhanced specification to replace the DVB-S standard,

• DVB-S2 standard which is used for satellite broadcasting, and the standard, which is used by mobile units for sending external footage back to television stations.

• The development of DVB-S2 coincided with the introduction of HDTV and H.264 (MPEG-4 AVC) video codecs.



DVB-S2• DVB-S2 performance gain over DVB-S is around 30%

• Two new key features which were added to DVB-S2 are:

– VCM (Variable Coding and Modulation) which optimizes the transmission parameters for various users

– Changing encoding parameters in real time (ACM, Adaptive Coding and Modulation)



DVB-S2• Four modulation modes:

– QPSK and 8PSK are proposed for broadcast applications, and can be used in non-linear transponders.

– 16APSK and 32APSK are used mainly for professional broadcasted though they require a higher C/N and advanced pre-distortion technique for uplink to minimize the effect of transponder linearity.



DVB-S2• Depending on modulation and code rate, the system can

operate at a C/N between:

2.4 dB (QPSK, 1/4) and

16 dB (32APSK, 9/10)

• with a quasi-error free goal of a 10−7 packet error rate.



DVB-S2: Functional block diagram of the DVB-S2 System



DVB-S2

Mode adaptation

– that provide

• input stream interfacing,

• Input Stream Synchronization (optional),

• null-packet deletion

• CRC-8 coding for error detection

• merging of input streams and

• slicing into DATA FIELDs.



DVB-S2

Mode adaptation

– A Base-Band Header shall be appended in front of the Data Field, to notify the receiver of the input stream format and Mode Adaptation type.

– The MPEG multiplex transport packets may be asynchronously mapped to the Base-Band Frames.



DVB-S2: Stream format at the output of the MODE ADAPTER



DVB-S2• A fixed length base-band Header (BBHEADER) of 10 bytes

shall be inserted in front of the DATA FIELD, describing its format (the maximum efficiency loss introduced by the BBHEADER is 1 %)

– MATYPE (Mode Adaptation Type) (2 bytes): describes the input stream(s) format, the type of Mode Adaptation and the transmission Roll-off factor,

– UPL (2 bytes): User Packet Length in bits, in the range 0 to 65 535.



DVB-S2– DFL (2 bytes): Data Field Length in bits, in the range 0 to

58 112.

– SYNC (1 byte): User Packet Sync-byte.

– SYNCD (2 bytes): for packetized Transport or Generic Streams.

– CRC-8 (1 byte): error detection code applied to the first 9 bytes of the BBHEADER



DVB-S2• For ACM modes and Transport Stream input data format,

MPEG null-packets shall be identified (PID = 8191D) and

removed.

• A Transport Stream shall be characterized by User Packets (UP) of constant length UPL = 188 x 8 bits (one MPEG packet), the first byte being a Sync-byte (47HEX).

• The useful part of the UP (excluding the sync-byte) shall be processed by a systematic 8-bit CRC encoder.



DVB-S2

The 8-bit CRC generator polynomial shall be:

g(X) = X8+X7+X6+X4+X2+1



DVB-S2: Stream Adaptation

• Stream adaptation provides padding to complete a constant

length (Kbch bits) the output is known as BBFRAME

• Padding may be applied in circumstances when the user data

available for transmission are not sufficient to completely fill

a BBFRAME, or when an integer number of UPs has to be

allocated in a BBFRAME.



DVB-S2: Stream Adaptation

BBFRAME format at the output of the STREAM ADAPTER



DVB-S2: BB Scrambling• The complete BBFRAME shall be randomized and scrambled

• The randomization sequence shall be synchronous with the BBFRAME, starting from the MSB and ending after Kbch bits.

• The scrambling sequence shall be generated by the feed-back shift register.

• The polynomial for the Pseudo Random Binary Sequence (PRBS) generator shall be: 1 + X14 + X15



DVB-S2: BB Scrambling



DVB-S2: FEC Encoding• This sub-system shall perform outer coding (BCH),

Inner Coding (LDPC) and Bit interleaving.

• The input stream shall be composed of BBFRAMEs and the output stream of FECFRAMEs.

FECFRAME Format of data before bit interleaving



Digital Video Broadcasting – Handheld







DVB-H• Digital Video Broadcasting – Handheld (DVB-H) is one

of three mobile TV formats.

• It is a technical specification for bringing broadcast services to mobile handsets.

• DVB-H technology is a superset of the very successful DVB-T system for digital terrestrial television, with additional features to meet the specific requirements of handheld, battery-powered receivers.



DVB-H• DVB-H is designed to work in the following bands:

– VHF-III (170-230 MHz,)

– UHF-IV/V (470-862 MHz )

– L (1.452-1.492 GHz)

• DVB-H can coexist with DVB-T in the same multiplex.

• DVB-SH recently improved radio performances and can be seen as an evolution of DVB-H



DVB-H

http://hu.wikipedia.org/w/index.php?title=F%C3%A1jl:DVB-H_system.JPG&filetimestamp=20070603160040



DVB-H• IP datagrams are transmitted as data bursts in small time

slots.

• Each burst may contain up to two megabits of data.

• There are 64 parity bits for each 191 data bits, protected by Reed-Solomon codes.

• The front end of the receiver switches on only for the time interval when the data burst of a selected service is on air.



DVB-H• 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 playout live streams.



DVB-H

http://upload.wikimedia.org/wikipedia/en/a/ae/DVB-H-framestructure.svg



Digital Video Broadcasting – Satellite Handhelds

(DVB-SH)





DVB-SH• DVB-SH (Digital Video Broadcasting – Satellite services to

Handhelds) is an evolution of DVB-H.

• DVB-SH broadcast to a mobile/ small handheld devices such as mobile telephones, and to vehicle-mounted devices.

• DVB-SH is a hybrid satellite/terrestrial system

• The frequency spectrum below 3GHz, including UHF, L band and S band.



DVB-SH

A typical DVB-SH system is based on a hybrid architecture



DVB-SH• Like its sister specification (DVB-H), it is based on

DVB IP Datacast (IPDC) .

• DVB-SH specifies two operational modes:

– SH-A: specifies the use of COFDM modulation on both satellite and terrestrial links with the possibility of running both links in SFN mode.

– SH-B: uses Time-Division Multiplexing (TDM) on the satellite link and COFDM on the terrestrial link.



DVB-SH• The DVB-SH incorporates a number of enhancements

when compared to DVB-H:

– More alternative coding rates are available– The omission of the 64QAM modulation scheme – The inclusion of support for 1.7 MHz bandwidth and

1k FFT– FEC using Turbo coding – Improved time interleaving – Support for antenna diversity in terminals



DVB-SH: Architectures• OFDM is the natural choice for terrestrial modulation and is

the basis of both the DVB-H and DVB-T systems.

• When assessing whether SH-A or SH-B should be selected, two main classes of satellite payloads may be considered:

– Single DVB-SH

– Multiple DVB-SH.



DVB-SH: Architectures• A single-carrier (DVB-SH) - the payload configuration, exploitation

of the SH-B (TDM) configuration reduces the signal envelope peak-to-average factor, thus allowing HPA optimum operation close to its saturated power.

• A multi-carrier (DVB-SH) - there is little or no difference between the performances obtainable with the SH-A or SH-B configurations.

• SH-A requires satellite transponders operated in a quasi-linear mode, whereas SH-B targets satellite transponders operated at full saturation.



SH-B system architecture



Digital Video Broadcast – Cable2



DVB-C2 • Digital Video Broadcasting (Cable DVB-C2), it is the

protocol standard for the broadcast of digital television over cable.

• It uses the latest modulation (MPEG-2 or MPEG-4) and used QAM modulation with channel coding to enable highly efficient.

• DVB-C2 offer 30% higher spectrum efficiency under the same conditions.



DVB-C2 • The downstream capacity more than 60% for optimized

HFC networks

• DVB-C2 can be used for services, such as video-on-demand (VOD) as well for high definition television (HDTV).

• DVB-C2 will be the last cable standard ever, there will never be a -C3 standard.



DVB-C2 • The DVB-C2 transmission system get so close to the

theoretical Shannon Limit.



Scheme of a DVB-C/DVB-C2 Transmission System



DVB-C2 • Source coding and MPEG-2 multiplexing (MUX): video,

audio, and data streams are multiplexed into an MPEG program stream (MPEG-PS).

• One or more MPEG-PSs are joined together into an MPEG transport stream (MPEG-TS).

• This is the basic digital stream which is being transmitted and received by home set top boxes (STB).



DVB-C2 • Allowed bit rates for the transported MPEG-2 depend on a

number of modulation parameters: it can range from about 6 to 64 Mbit/s

• MUX adaptation and energy dispersal: the MPEG-TS is identified as a sequence of data packets, of fixed length (188 bytes).



DVB-C2 • External encoder: a first level of protection is applied to

the transmitted data, using a non binary block code, a Reed-Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet.

• External interleaver: convolutional interleaving is used to rearrange the transmitted data sequence, so it becomes more rugged to long sequences of errors.

• Byte/m-tuple conversion: data bytes are encoded into bit m-tuples (m = 4, 5, 6, 7, or 8).



DVB-C2 • Differential coding: In order to get a rotation-invariant

constellation, this unit shall apply a differential encoding of the two Most Significant Bits (MSBs) of each symbol.

• QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols, where 5 modulation modes are allows: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM

All (decimal) values in Mbit/s.



DVB-C2

All (decimal) values in Mbit/s.



DVB-C2 • Base-band shaping: the QAM signal is filtered with a

raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.

• DAC and front-end: the digital signal is transformed into an analog signal, with a digital-to-analog converter (DAC), and then modulated to radio frequency by the RF front-end.



DVB-C Vs DVB-C2

btb43503 lecture ivb-dvb broadcast systems

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