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MOBILE TV -Narendranath Kanukolanu
Topics w Introduction w DVB-T w DVB-H w Issues and Solutions w Conclusion w References
Introduction w Convergence of digital media and communication give users possibility to consume most digital content also in mobile environment w The emerging DVB-H standard aims to provide digital TV reception in mobile devices n Earlier known as DVB-X w DVB-H is being standardized by and ad hoc group of the DVB organization n Expected to be standardized in the first quarter of 2004 w DVB-H combines traditional television broadcast standards with elements specific to handheld devices; mobility, smaller screens and antennas, indoor coverage and reliance on battery power
DVB-T n n DVB-T stands for Digital Video Broadcasting Terrestrial and it is the DVB European consortium standard for the broadcast transmission of digital terrestrial television. This system transmits an MPEG-2 family digital audio/video stream, using OFDM modulation with concatenated channel coding
DVB-T w One-to-many broadband wireless data transport n n n Video, audio, data and – importantly – IP packets Scalable: cell size up to 100 km (DVB-H cell size is smaller) Huge capacity: 54 channels each 5 -32 Mbit/s w Shut down of analog TV will free up huge frequency capacity for DVB-T usage DVB-T = Digital Video Broadcasting - Terrestrial
DVB-T w Developed for MPEG-2 stream distribution, but can basically carry any data n Flexible, has many modes, 4. 98 -31. 67 Mbit/s @ C/N=25 d. B w COFDM multi-carrier modulation with 2 k and 8 k modes n One DVB channel is ~8 MHz 1705 sub carriers (spacing: 4464 Hz) - 2 k mode l 6817 sub carriers (spacing: 1116 Hz) - 8 k mode Carrier modulation: QPSK, 16 QAM or 64 QAM Error correction: convolution code and Salomon-Reed l n n w Basic mode in Finland: n n 64 QAM, code rate = 2/3, guard interval 1/8 Gives 22. 12 Mbits/s capacity when C/N=19. 2 d. B and 8 MHz channel COFDM = Coded Orthogonal Frequency Division Multiplexing C/N = Carrier to Noise ratio
Mobile reception of DVB-T w DVB-T includes hierarchical modes where two transport streams can be sent simultaneously n Low capacity, high capacity w DVB-T can also be used for broadcast to mobile devices, but a suitable mode have to be selected n 8 k 64 QAM: < 50 km/h n 2 k QPSK: > 400 km/h tolerable w A separate network for DVB-H is desired n Optimization of speed, coverage and capacity
World Standards w DAB and E-DMB-in Europe and China w DVB-H- USA/Europe and any where there is digital TV spectrum w HD Radio-USA w Media FLO (Qualcomm)-USA w T-DMB-Korea and Possibly Europe and China w ISDB-T- Japan
Motivation for creating DVB-H w Why not use UMTS? n n Not scalable for mass content delivery For delivery of mass media content, broadcast networks should be preferred over point-to-point cellular networks w Why not use DVB-T? n n n Was designed for rooftop reception Need for an efficient power saving mechanism Inadequate impulse noise protection w Why not use DAB? n Designed for devices with similar power constraints but too narrow spectrum is assigned for data transmission DAB = Digital Audio Broadcasting
Mobile. TV What Is Mobile TV = DVB-H n On-line video services n n Mobile Broadcast A Small digital TV, set top box receiver Watch and record TV programs, interact with programs and other viewers Other Rich Media experiences On-line video services n Access on-line services to rent or buy TV shows, videos, and movies; download them to mobile device Video to-go n n Store videos to mobile format and manage them with Nokia PC Suite Transfer and syncronize recorded, downloaded or ripped videos from PC/Mac or home media devices
DVB-H Introduction w Convergence of digital media and communication give users possibility to consume most digital content also in mobile environment w The emerging DVB-H standard aims to provide digital TV reception in mobile devices n Earlier known as DVB-X w DVB-H is being standardized by and ad hoc group of the DVB organization n Standardized in the first quarter of 2004
DVB-H w The DVB-H system is largely compatible to the DVB-T standard, which means that the modulator and RF circuits can be reused with only slight additions. It is possible to have both DVB-T services and DVB-H services broadcast by a single transmitter
Contd. . w DVB-H combines traditional television broadcast standards with elements specific to handheld devices; mobility, smaller screens and antennas, indoor coverage and reliance on battery power are the challenges w Re-uses basically the well-known DVB-T transmission parameters w Inheriting the DVB-T flexibility & performance, w Offering additional delivery methods to extend the traditional tradeoff bit rate capacity & ruggedness & cell size to a new dimension: the “nomad city”.
DVB-H system elements w Time slicing for power saving n Time between the bursts gives the power saving (off time) Timesliced: 1 2 3 1 2 4 Not timesliced: • Service 1 • Service 4 • Service 2 • Service 3 w MPE-FEC for performance w 4 k mode was chosen to provide mobility in medium SFNs MPE = Multiprotocoll encapsulation FEC= Forward Error Correction w Extended TPS bits for efficient signaling SFN= Single Frequency Network
Drivers for Mobile TV w w TV application missing from Mobile Phone TV is bigger application than telephone globally Daily amount of time spent on multimedia is more Digital convergence happening in Mobile Handsets
Mobile reception of DVB-T w DVB-T includes hierarchical modes where two transport streams can be sent simultaneously n Low capacity, high capacity w A separate network for DVB-H is desired n Optimization of speed, coverage and capacity
What the Consumer expect? . Good picture and sound quality Service availability Value for money Single Device to carry (phone) Simplicity of use Right selection of channels Multimedia Device
DVB-H System overview. OPTIONAL: DVB-T SERVICES DVB-H SERVICES ERROR PROTECTION (MPE-FEC) IP ENCAPSULATION TIME SLICING TRANSPORT STREAM MULTIPLEXER DVB-T CODER/MODULATOR 4 k-MODE SIGNALLING
When will it be used?
System Architecture For Collaboration Between Mobile and Broadcast Operators
Network Design Flexibility & Signaling w Different datacast network operator and cellular network operator w Digital broadcast infrastructure w More transmission sites than normal broadcast networks required, but less than normal cellular phone networks – existing masts can be reused w Cellular networks used for payment and administrative data w Cellular network and broadcast network can share same core network ISP IP Backbone Mobile Operator UTMS Core Base station DVB-T Broadcasters DVB-H Broadcasters Mux DVB-H transmitter Broadcast operator
DVB-H features/pros w Cost efficient delivery of broadcast content to a large audience w Low time to market and complexity w Flexible transport stream sharing between DVB-T and DVB -H possible w Based on DVB-T with minimal changes w Only IP based services possible w Reduced power saving when total bit rate for DVB-H services is very low (no big “bursts” possible)
DVB-T and DVB-H coexistence DVB-T RF in DVB-T ETS 300 744 , 8 k, 2 k 4 k, TPS Time Slicing MPE FEC DVB-H CODEC IP-out
IP Datacast (IPDC) w “IP data casting is a service where digital content formats, software applications, programming interfaces and multimedia services are combined through IP (Internet Protocol) with digital broadcasting. ” All content delivered as IP packets n Connectivity layer convergence w DVB-H combined with IP data casting enables distribution of many kinds of digital content n TV broadcast, music, games etc.
Power consumption and handover w IP encapsulation allows sending the data in bursts to the mobile station and this saves energy (battery power) w Power consumption and handover n n 2 Mbit buffer Handover possible during off time (services can be used even if the terminal has moved during off time)
Mobile Terminal w FE = Front End, contains radio receiver and demultiplexer FE WLAN Cellular Link CPU Media decoder Display
ISSUES w Battery Power w Loss Free Handover for IP Data Cast w Continuous Transmission
ISSUE 1: Battery Power w TIME SLICING is the mechanism DVB-H uses to transmit data in periodic bursts with significant and higher instantaneous bit rates w Using TDM significant power savings can be achieved w TDM (Time Division Multiplexing) is the technology used in Time Slicing. w TDM combines data streams by assigning each stream a different time slice in a set. w TDM repeatedly transmits a fixed sequence of time slices over a single transmission channel.
TIME SLICING TECHNIQUE S E R VI C E SERVICE 1 SERVICE 2 SERVICE 3 DVB-H SERVICE 4 DVB-T REGULAR DVB-T MULTIPLEX S E R VI C E 1 1 SERVICE 4 TV DVB-H Time Slices “always on-not used data is skipped” SLEEP MODE
Contd… w Time slicing enables a receiver to stay active only a fraction of time while receiving bursts of a requested service saving battery power. w When the receiver is tuned to receive one of the programs it has to receive the other unwanted programs at the same time consuming a lot of battery. w The High bit rate signals are buffered in the time slicing memory of the DVB-H capable receiver.
Contd… w The DVB-H receiver will receive its intended high bit rate service in one time slice and make the front end sleep during the other slices, w The High end Bit rate service received will be buffered in the receiver memory and played out continuously to provide the desired Qo. S.
Time Slicing Contd… 1536 kbps_DVBH 153 6 k bps 1536 kbps Content Provider 1536 kbps_DVBH ps kb 536 1 s p kb 1536 kbps_DVBH 6 53 1 1536 kbps_DVBH DVB-H TOWER Ethernet Switch
ISSUE 2: Continuous Transmission w A DVB-H receiver is expected to usually be a single antenna terminal. w As the DVB-H cell becomes smaller up to several kilometers radius, handover between different cells will happen. w When the receiver works in time slicing mode, it can measure the signal SNR value In the off burst time and eventually perform soft handover. w Thus the time slicing mode makes seamless soft handover possible for single antenna DVB-H reception.
Calculation w If a service has an average bite rate of ravg is transmitted in bursts with the bit rate rburst and the time between two bursts of the same service (cycle time) is called t, the burst duration tburst that may be calculated from the other values using… tburst = ravg/ rburst * t
Contd. . w As the off time toff is the difference between the cycle time and the burst time, w toff = 1 - ravg/ rburst * t
TIME SLICING TECHNIQUE w Continuous Transmission C a p a c it y SERVICE 1 SERVICE 2 SERVICE 3 SERVICE 4 Time
Continuous Transmission. 384 kbps_DVBH kb ps 384 kbps Content Provider 384 kbps_DVBH kb 84 ps 3 DVB-H TOWER 384 kbps_DVBH s p kb 4 38 384 kbps_DVBH Ethernet Switch
Contd… w Each receiver will receive an effective bit rate of 384 Kbps and the other 1152 Kbps of unwanted traffic. Thus each receiver will receive 1536 Kbps in total of which three quarters is unwanted traffic.
ISSUE 3: Loss Free Handover for IP Data Cast w Mobility is the most important feature of handheld devices and uninterrupted service has to be provided when there is movement. w A technology called “Phase shifting” is proposed for Loss free handover.
Contd… w The main challenge in today's field of communication is to offer high data rates while having a error-prone communication channel and only a small battery power budget Additionally, seamless mobility is a strong demand. w An Algorithm for synchronizing adjacent cells in order to ensure seamless handovers is proposed. w Time slicing is also important for handover.
Handover in Broadcast Systems w The Technique used is PHASE SHIFTING. w Different from cellular Telecommunication systems as no return channel exists. w Emphasis on how the signals of neighboring DVB-H cells may be synchronized and under which conditions seamless handover themselves may actually be one.
Contd. . w The network's infrastructure has no feedback about who is using the services and possibly moving from one cell to another. All the information for performing handovers has to be deployed to the terminals which will perform the handovers on their own. w The term cell in this context is used for a subsystem that may consist of one or more several transmitters sending entirely identical content on the same frequency. w A Cell Handover in this context is the change of frequency and data stream in order to receive the same service continued within another cell.
Phase Shifting Algorithm w When a terminal changes from one DVB-H cell to another, ideally it should be able to seamlessly continue receiving the current service in the new cell without any packet loss, assuming that the service is available in both cells. w The Phase shifting should be big enough so that there is no overlapping between the time slices of the adjacent cell and the necessary synchronization time for the terminal to change from one signal to another.
Algorithm. IP FEEDING STREAM TO CELL 1 IP PACKET 4 5 6 SIGNAL OF CELL 1 IP FEEDING STREAM TO CELL 2 SIGNAL OF CELL 2 7 8 6 7 8 1 1 1 2 9 123 1 0 1 1 1 2 456789 PHASE SHIFT 1 1 1 3 4 5 1 6 111 789 012 DVB-H TIME SLICE 123456 4 5 1 0 9 1 1 1 3 4 5 1 6
Contd. . w There is an overlapping of IP packets between two consecutive time slices of two different cells. This ensures, even with significant tolerance towards IP feeding stream delays, seamless loss-free handovers. w More than two cells have common borders, so more than two different phase shifts are needed.
4 -Coloring Graph Problem w The various phase shifts that are necessary for n adjacent cells can be interpreted mathematically as colors in a graph coloring problem, never allowing twice the same color in adjacent nodes. w With four different phase shifts loss-free handover between any two cells will be possible, no matter how the shape of the cells might be. (Ideally Hexagonal)
Quantitative Analysis wtburst = ravg/ rburst * wtoff 1 - ravg/ rburst * = w From Equation 1 and 2 t (1) t (2)
Contd. . w To simplify the equation the sum of tsync and tsafety is defined as being tsetup
Contd. . w From Eq 1, 2, 4
Contd. . w The result is that the ratio between the average data rate of a service and the whole data rate that can be used for a service supporting soft handover must be smaller than 25%reduced by the ratio of the setup time and t. w At is also dependent of ravg as the memory of the terminal mbuf is limited. w For the consumption of a service, only half of the terminal buffer size mbuf can be used, as the other half is needed to monitor the same service of an adjacent cell, at least in handover status.
Conclusion w Traditional broadcasting is undergoing a process of change as a consequence of the move towards an all-digital broadcasting environment. New technology, such as DVBH, streaming technology and personal video recorders (PVRs) can complement traditional broadcasting.
References w w w Loss-free handover for IP datacast over DVB-H networks May, G. ; Consumer Electronics, 2005. (ISCE 2005). Proceedings of the Ninth International Symposium on 14 -16 June 2005 Performance analysis of time slicing in DVB-H Yang, X. D. ; Song, Y. H. ; Owens, T. J. ; Cosmas, J. ; Itagaki, T. ; Mobile Future, 2004 and the Symposium on Trends in Communications. Sympo TIC '04. Joint IST Workshop on 24 -26 Oct. 2004 Digital Video Broadcast - Handheld (DVB-H)-A Mobile Last-Mile Tactical Broadcast Solution Bennett, B. ; Hemmings, P. ; Holt, C. ; Military Communications Conference, 2005. MILCOM 2005. IEEE 17 -20 Oct. 2005
w DVB-H – digital TV for handhelds? Jukka Henriksson, Nokia w Content Distribution Using Wireless Broadcast and Multicast Communication Networks. Janne Aaltonen, Thesis for Degree of Doctor, Tampere University of Technology w DVB