University of Canberra Advanced Communications TopicsTelevision Broadcasting into the Digital Eraby: Neil PickfordLecture 4DTTB TypesDigital Modulation Systems

Digital Terrestrial TV - Layers

Digital Television Encode Layers

Digital Television Decode Layers

Set top Box (STB) - InterfacingDomestic and Professional interfaces still to be definedMost probably Transport Stream via IEEE 1394 (Firewire)Baseband Audio & RGB/YUV Video signals.STB can convert between line standards so you do not have to have a HD display.Display and transmitted information must be at same Frame/Field rate. (25/50)

DTTB - Content & ServicesDTTB was designed to carry video, audio and program data for televisionDTTB can carry much more than just TVElectronic program guide, teletextBroadband multimedia data, news, weather Best of internet serviceInteractive servicesSoftware updates, gamesServices can be dynamically reconfigured

DVB Data ContainersMPEG Transport Stream is used to provide DVB data containers which may contain a flexible mixture of:VideoAudioData servicesStreams with variable data rate requirements can be Statistically Multiplexed together.Allows Six 2 Mb/s programs to be placed in a 8 Mb/s channel

Examples of DVB Data ContainersChannel bandwidth can be used in different ways:

Video Program Capacity1 HDTV service - sport & high action2 HDTV services - both film material1 HDTV + 1 or 2 SDTV non action/sport3 SDTV for high action & sport video6 SDTV for film, news & soap operasHowever you do not get more for nothing.More services means less qualityFor a payload of around 19 Mb/s

Spare Data CapacitySpare data capacity is available even on a fully loaded channel.Opportunistic use of spare data capacity when available can provide other non real time data services.Example: 51 second BMW commercialThe Commercial was shown using 1080 LinesInterlaced. 60 Mb of data was transferred during it. In the Final 3 seconds theBMW Logo was displayed allowing 3 Phone Booksof data to be transmitted.

Enabling TechnologiesSource digitisation (Rec 601 digital studio)Compression technology (MPEG, AC-3)Data multiplexing (MPEG)Transmission technology (modulation) Display technology (large wide screens)Production

Digital Television - TypesTerrestrial (DTTB)DVB-T / 8-VSBFree to air TV (broadcasting)Narrowcasting/value added servicesUntethered - portable reception

Digital Terrestrial Television Broadcasting - DTTBRegional free to air televisionReplacement of current analog PAL broadcast television servicesOperating in adjacent unused taboo channels to analog PAL serviceCarries a range of services HDTV, SDTV, audio, teletext, dataProviding an un-tethered portable service

Transmission TechnologyThe transmission system is used to transport the information to the consumer.The system protects the information being carried from the transmission environmentCurrent Australian analog television uses the PAL-B AM modulation system

Digital TV Transmission TechnologyThe transmission system is a data pipeTransports data rates of around 20 Mb/sTransports data in individual containers called packets4

Digital TV Transmission SystemsAustralia has been following Digital TV & HDTVEuropeans - Digital SDTV - 8 MHz on UHF - DVB-T (COFDM)Americans- Digital HDTV - 6 MHz VHF/UHF - ATSC (8-VSB)Japanese - Integrated Broadcasting - ISDB (BST-OFDM)

8-VSB - USA

Developed by the advance television systems committee - ATSCDeveloped for use in a 6 MHz channelA 7 MHz variant is possible but has not been produced.Uses a single carrier with pilot tone8 level amplitude modulation systemSingle Payload data rate of 19.39 Mb/sRelies on adaptive equalisationExisting AM technology highly developed

COFDM - EuropeDeveloped by the digital video broadcasting project group - DVBUses similar technology to DRBUses 1705 or 6817 carriersVariable carrier modulation types are defined allowing Payload data rates of 5-27 Mb/s in 7 MHzDeveloped for 8 MHz channelsA 7 & 6 MHz variants have been produced and tested.Can use single frequency networks - SFNsNew technology with scope for continued improvement & development

ISDB - JapanJapanese are developing integrated services digital broadcasting (ISDB)System integrates all forms of broadcasting services into one common data channel which can be passed by satellite, cable or terrestrial delivery systemsVideo servicesSound servicesBulk data servicesInteractive data services

ISDB - ConceptProposed to use band segmented transmission - orthogonal frequency division multiplex (BST-OFDM)

Terrestrial Transmission ProblemsMultipath interference - ghostsNoise interference - snowVariable path attenuation - fadingInterference to existing servicesInterference from other servicesChannel frequency assignment - where to place the signal

Digital Modulation - FunctionsSpreads the data evenly across the channelDistributes the data in timeMaintains synchronisation well below data thresholdEmploys sophisticated error correction.Equalises the channel for best performance

Digital ModulationTwo techniques:Conventional Single Carrier 8VSBMulticarrier/Spread Spectrum OFDM

8-VSB & COFDM - Spectrum8-VSBCOFDM

Sin(x)/x

Digital ModulationFcFc - FsFc + FsSin X/X shapingSpectrum of Conventional Multi-Phase Keyed Carrier Fc at Symbol Rate FsFrequencyAmplitude, dB

Digital ModulationFrequencyAmplitude, dBLow Symbol RateMedium Symbol RateHigh Symbol Rate

PSK

BPSK ModulationI AXIS0 1180 DegPhaseChange

QPSK ModulationI AXISQ AXISQPSKDistance0 01 10 11 0

16QAM ModulationI AXISQ AXIS16-QAMDistance1 1 0 01 1 0 11 1 1 00 01 10 11 01 1 1 10 0 0 00 0 1 00 0 1 10 0 0 1

8VSB ModulationI AXISQ AXIS16-QAMDistance1 1 0 01 1 0 11 1 1 00 01 10 11 01 1 1 10 0 0 00 0 1 00 0 1 10 0 0 1

Hierarchical Modulation1 1I AXISQ AXIS QPSKDistanceHierarchicalDistance1 1 0 01 1 0 11 1 1 01 1 1 10 0 0 00 0 1 10 0 0 10 11 00 0 1 0

Digital ModulationFrequencyAmplitudeFcFc - FsFc + FsOccupied Channel BandwidthTypical Filtered Spectrum to give about half original bandwidth

8-VSB Digital ModulationFrequencyAmplitudeFcFc - FsFc + FsOccupied Channel Bandwidth eg 6 MHz in USApplication of Vestigial Sideband Filter to give reduced spectral occupancy BUT with destruction of pure Amplitude modulation causing incidental Phase modulation but some power in a small carrier8VSB uses symbol Rate with period 93 nanoseconds

Normal FDMAmplitude, dBFrequencyCarrier 1Carrier 2Guard Band

Traditional SCPC ModulationFrequencyMinimum Carrier Spacing

Orthogonal ModulationFrequencyAmplitude, dB

Orthogonal ModulationFrequencyAmplitude, dB

COFDM - Orthogonal CarriersFrequency

Spectrum of COFDM DTTB6.67 MHz in 7 MHz ChannelAlmost Rectangular Shape1705 or 6817 CarriersCarrier Spacing2k Mode 3.91 kHz8k Mode 0.98 kHz

OFDMAmplitude, dBFrequencyFrequencyFcentreOccupied bandwidth is: No. of Carriers x Spectral Width. Create with FFTSpectral Width2k is 4x wider than 8k

DIGITAL TERRESTRIAL BROADCASTINGThe Terrestrial Broadcasting has to cope with multipath propagation and Doppler effects: COFDM is the response for these impairments !Among the four Digital Broadcasting standards available, three are based on the Coded Orthogonal Frequency Division Multiplex modulation.... Why ?

COFDM : HOW ?1 - Organize time & frequency partitions in the RF channel

COFDM : HOW ?2 - Spread sub-carriers over time vs frequency cells

COFDM : HOW ?3 - Insert Guard Interval to avoid inter-symbol interferenceGuard interval introduces a first loss in transport capacity

COFDM : HOW ?4 - Insert Synchronization Pilots Helps Receivers to lock onto the signalSynchronization markers introduce the second loss in transport capacity

COFDM : HOW ?5 - Prepare data to be carried on OFDM symbolsDATA to broadcastProtection codes introduce the third loss in transport capacity

COFDM : HOW ?6 - Map bits onto OFDM: Spread contiguous data bits over distant sub-carriersCreate frequency diversity to improve robustness against fading

DTTB - Channel EstimationThe Terrestrial transmission channel is continuously varying (position & time)Variations occur in Amplitude, Phase & FrequencyTo correct for this variation Information needs to be added to the transmission to quantify the channels response at any instantEqualisers in the Digital receiver use this information to remove these transmission impairments

Data Multiplex - 8-VSB

8-VSB Segment Sync & DataSymbol Duration 93 ns

Digital Modulation - 8-AM3 Bits/Symbol712345608-VSB - Coaxial Direct Feed through Tuner on Channel 8 VHFBefore EqualiserAfter Equaliser

8-VSB - Field SyncField Sync is Repeated Every 24 ms

8-VSB - Field Sync71234560Before EqualiserAfter Equaliser

8-VSB Frame832Symbols per Data Segment of 77.3 sDataDataTraining SequenceTraining SequenceSyncThe Training Sequence is only 0.3% of signal timeTotal Sync is only 0.8% of time313 DataSegmentsof 24.2 ms

DVB-T - Carriers + PilotsKminSYMBOLS IN SEQUENCE - 68 PER BLOCK.Kmax0.977/3.906 kHz

DVB-T Super FrameSuperFrame4 x 68Symbols=N MPEGPackets

DVB-T Transmission FrameDataScattered PilotTPS - PilotContinuous PilotKmin=0KmaxCarrier Spacing & Position2k mode - 3906 Hz - Kmax=17048k mode - 977 Hz - Kmax=6816Symbol Duration 256 us (2k) or 1024 us (8k)

DVB-T - Estimating the ChannelABCDEAB=3/4A+1/4EC=1/2(A+E)ED=1/4A+3/4EA to E - 1.024 ms (2k) - 4.096 ms (8k)For a varying transmission channel DVB-T estimation is 23.5 times faster than ATSC

DVB-T - Estimating the ChannelA B C D E F GA to D - 11.724 kHz (2k) - 2.931 kHz (8k)For a varying transmission channel DVB-T estimation is 23.5 times faster than ATSCA B C D E F GB=2/3A+1/3DC=1/3A+2/3DE=2/3D+1/3GF=1/3D+2/3G

Channel Estimation & EqualisationTimeTimeATSCDVB-T

Estimation Rate ComparisonATSC Equaliser is updated every 24 ms (~260 000 symbols)DVB-T Equaliser is updated every symbol period (256 us). 1/12 of data carriers are pilotsDVB-T Full Channel estimate is available every 4 symbols (1.024 ms)For a varying transmission channel DVB-T estimation is at least 23.5 times faster than ATSC

OFDM - Features Multicarrier - many carriers sharing Reduced C/N compared to Analogue Resistant to echoes, Interference etc Low symbol rate per carrier ~ 1 kBaud: Long Symbol Period, can Extend with Guard Interval With FEC becomes COFDM Uses Fast Fourier Transform [FFT] 2k and 8k versions Single Frequency Networks [SFN]

1DTTB is about layers.PictureCompressionTransport/MultiplexingTransmission

What are the inputs to these layers?At the receiver we simply select the portions of the existing data stream we wish to decode and throw away the rest.DTTB can carry many other things than just television.Interactive services need a back channel such as the telephone line or a cable/wireless modem.The analog television we are used to uses a very dumb device to display the pictures. Digital TV uses a smart box which can be dynamically re-configured. You can choose the change the channel/data structure mid program, upload new operating software with different funtions. No longer will the transmission be totally constrained by the dumb receiver at the other end.Focusing on the TV aspects.There are different ways the channel bandwidth can be used.As has been done in the UK, you can have a multiplex which has multiple standard definition programs within it.You can also have a multiplex which contains a single High Definition program which is the plan for many situations in Australia.There is also the facility to have simulcast, where you cut down a bit on the High Definition to allow the older receivers that are there to decode the Standard Definition variant. This may well be used in the future in the UK when the analog transmissions are turned off. The plan in most of Europe is for High definition to be introduced as a second phase as part of the analog turn off.

Digital TV will have a data capacity around 20 Mb/s.For Sport or high action we can have relatively few services.Films have high levels of temporal redundancy because both fields are scanned from the same frame. This allows the compression systems to perform higher levels of compression allowing spare data capacity and the ability to have more services.Generally News & Soapies have lower data requirements so more channels are possible.You do not ge more channels for nothing. More Services Means Less Quality.An example from tests in America.Other non-real time services can use opportunistic use of the DTV data pipe to transmit data when the full bandwidth of the channel is not required for the main services. These services would be data specifically intended for broadcast application with no need for acknowledgement or a back channel. Teletext or Newspaper type information are good examples.Digital TV has Key Technologies that make it possible. Most production within the current TV stations already happens in the digital domain using standards such as Rec 601 digital video. It only becomes analog when it is transmitted over the air to the viewer.Display technology has not reached the level needed for HDTV to be fully implementable at present.DTTB allows both fixed or portable operation.What is DTTB?The transmission technology protects the data from the communications environment.In something like the satellite environment it is very easy since there are not many variable sources of transmission impairment, A terrestrial system has to cope with obstructions, reflections, multipath, and various types of man made interferenceBeing Digital, it is just like any computer data. You put a byte of data into the pipe, you must receive the same byte out the end of the pipe. If it is different at the other end it simply does not work. The testing of these systems had primarily been done (95%) looking at Bit Error Rates (BER), not the displayed pictures. The data is transported in 188 byte groups called packets.ATSC developed out of the Grand Alliance which resulted at the end of the initial digital television race in America.Multicarrier SystemMany different combinations of system parametersTo change the bandwidth of the system you change the master system clock. As the clock rate increases the system carrier spacing & thus bandwidth decreases as an inverse proportion.Main TV menuNewspaper - Categories - Headlines Downloaded overnightTelevision ScheduleWeatherPreview of other stationsTime,Email,Interactive services16:9 Display.The current Analog TV system has lots of problems which can arise in the transmission path and are reflected in a poor quality picture.We also have problems with planning where to place these services, because we have to avoid known interference mechanisms.Digital modulation distributes the information across the channel bandwidth so the rectangular spectrum shown earlier is produced. This makes more efficient use of the spectrum.Highly rugged transmission techniques are used for the system synchronisation data such as QPSK and 2 level data. This is because if the system clock is lost, the whole system immediately stops working and may take some time to reaquire lock.Error correction techniques such as Reed Solomon and Viterbi Coding are used to correct errors in the data.38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace This is a spectrum analyser plot of the two digital systems being considered in Australia. The little hump on the left side of the 8-VSB spectrum (yellow) is the pilot carrier.These are averaged spectrums and have shoulder levels of around 35-40 dBThe spectrums are basically rectangular in shape. The COFDM signal is wider since it is a 7 MHz system in a 7 MHz channel while 8-VSB is 6 MHz wide.38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace What is this COFDM modulation?A Traditional Single Carrier Per Channel (SCPC) digital system there is a minimum spacing that you can put two individual carriers apart. It tends to be around 3 times the bessle frequency, where the modulation sidebands dimminish sufficiently to cause minimal interference to the adjacent carrier. SCPC is a type of Frequency Division Multiplex (FDM)38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace COFDM is Coded Orthogonal FDMIf you observe the carrier spacing they are much closer together. This thing called Orthogonality is the key. It means that the peak of the yellow carrier (and all others) coincides with a null on every other carrier. Each peak sits directly above a null. You cannot generate these carriers by having individual oscillators mixed together. They are all generated at the same time using an Inverse Fast Fourier Transform (IFFT) using the same clock.These 1000s of carriers form the observed rectangular spectrum.There are two modes for the system 2K & 8K. This referes to the size of the FFT used to generate and demodulate them. The 2k system has 1705 carriers and the 8k system uses 6817 carriers. The extra locations in the FFT are used to ensure that the signals have a sharp roll-off and good out of channel performance. 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technologyNDS receives upfront integration fees and ongoing royalties under these license arrangements Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace