ATSC 3.0 Mobile Support. Luke Fay

Transcription

1 ATSC 3.0 Mobile Support Luke Fay

2 Outline Mobile Service definition LTE currently is used by mobile [cellular] operators to deliver mobile service. But let s look at what that means for broadcasters. Network support that works with LTE (use in broadcaster context) Dense cell [yes] Sparse cell [no] Single large cell (big stick) [no] Broadcaster mobile desires Definition of mobile service for broadcasters How proposed ATSC 3.0 PHY supports these needs Support for other standards by FEF (LTE, WiFi, others) Summary

3 LTE Mobile Service Wireless communication of high-speed data for mobile phones and data terminals. Network Downlink Uplink LTE access likelihood * AT&T 18.6Mbps avg. 9.0Mbps avg. 81.7% Sprint 10.3Mbps avg. 4.4Mbps avg. 50.2% T-Mobile (non-lte) 7.3Mbps avg. 1.5Mbps avg. N/A Verizon 14.3Mbps avg. 8.5Mbps avg. 93.2% Source: LTE s Lightning-Fast speeds are slower on average than broadcast speeds of ATSC 1.0 today. LTE is made for unicast and updated for multicast while keeping infrastructure for unicast. *likelihood of accessing 4G speeds, connection speed drops to 3G rates if access is not acquired.

4 4 New EBU Technical Report 27 The EBU has released a report on DELIVERY OF BROADCAST CONTENT OVER LTE NETWORKS Available at Summary The participant included broadcasters and mobile equipment manufacturers but not mobile operators. Technically free-to-air delivery could in principle be enabled by LTE embms Mobile industry: Delivery costs for broadcast over LTE may be reduced by an efficient combination of unicast and embms capabilities LTE delivery costs still seen as significantly higher than the current costs of TV distribution LTE for large-scale distribution of TV services and as possible replacement for current DTV delivery are not clear and require further study LTE networks for a large scale TV distribution is not envisaged in the short term

5 Network Support: Dense cell 3GPP TS V8.0.0 ( ), TS & TS physical layer description 512 point FFT for 5MHz bandwidth (15kHz subcarrier spacing) over compensates for Doppler spread Reference [1] shows that error-free mobile reception can be done with speeds up to 130km/hr with 500Hz (MUCH LESS) carrier spacing at 600MHz RF center frequency Cyclic Prefix = usec or usec for embms, no wide range of choices Optimized for small cell network with unicast data Receiver device battery power savings in mind (lower transmit power needed as towers are close together) Covers multipath propagation within 5km, broadcast SFNs cover much larger areas resulting in longer delay spreads. Fixed values limits PHY flexibility, precludes sparse SFN FEC: 1/3 turbo code selected some time ago and likely stayed for legacy reasons Unicast has TCP/IP communication where return link delay is of concern in QoS provisions for a transfer latency of < 5msec in the Radio Access Network. Broadcast is multicast data where TCP/IP links do not exist; UDP links exist and higher block lengths can be used. embms has to suffer all the choices of unicast LTE Received signal strength is driving factor for mobile support Indoor reception on smartphones with antenna LOSS is compensated with many low power low tower cells LTE is optimized for unicast communications with dense cell networks. [1] Projektrat DVB-T2 Modellversuch Norddeutschland: Terrestrik der Zukunft Zukunft der Terrestrik. Shaker Verlag. Aachen, 2012

6 Network Support: Sparse cell 3GPP TS V8.0.0 ( ), TS & TS physical layer description 512 point FFT is still over-robust Cyclic Prefix = usec or usec is not large enough to support large distance communication with long echo patterns FEC: 1/3 turbo code may have to correct for longer echoes outside the guard interval (cyclic prefix) Perhaps even at high received signal strength Received signal strength is the key driver for mobile support Medium power medium tower SFN can support mobile devices with less capital However, UNICAST mobile devices need to transmit more power to reach the towers further away LTE cannot support sparse cell networks.

7 Network Support: Single large cell 3GPP TS V8.0.0 ( ), TS & TS physical layer description 512 point FFT is still over-robust Cyclic Prefix = usec or usec is not large enough to support VERY large distance communication with long echo patterns FEC: 1/3 turbo code WILL have to correct for longer echoes outside the guard interval (cyclic prefix) Received signal strength is the key driver for mobile support Single high power high tower may NOT support mobile devices Environmental factors of terrain will create holes in coverage Higher transmit power will not fill-in coverage holes inside buildings and outside severe multipath channels It is a physics and geometry of the market issue LTE cannot support single large cell networks.

8 Broadcaster Mobile Service What Mobile Means to Us The term mobile as applied to ATSC 3.0 has become somewhat fuzzy and possibly overloaded. To provide greater clarity, we present the following understanding of what mobile service means to us: 1) Mobile Service expectations: We expect ATSC 3.0 transmissions to address all of the following use cases and device types: Pedestrian handheld (outdoor) Vehicular built-in receiver (stationary or in motion) Fixed or portable device using external indoor antenna Handheld or other portable (e.g., tablet) used in-vehicle Handheld, other portable (e.g., tablet), or fixed device with embedded antenna used indoors We recognize that the range of signal levels required for successful over-the-air reception on all of the above may be wide, but our definition of mobile service would ideally include all of these use cases. Most important among these, however, is the Handheld/Portable Indoor case. 2) Maximum speed of motion: We expect that successful reception in a moving vehicle (whether using handheld/portable or built-in vehicular receivers) will be possible at ground speeds of up to 150 km/h (90 mph). 3) Mobile emergency alerting: We expect that a mobile-optimized emergency alerting modality will be included in ATSC 3.0 service. 4) Handoff: We expect that mobile service will provide a means for broadcasters to enable handoff of a receiver between affiliated stations or services across neighboring markets. Definition of mobile is different between broadcaster and wireless carriers

9 ATSC 3.0 Network Support: All ATSC 3.0 physical layer description FFT baseline starts with 8K,16K and 32K FFT sizes and can signal other options and not overcompensate for Doppler (optimize spectral use) Guard Interval table starts with 12 separate entries giving a range of options to broadcasters from 28usec to over 700usec (Supporting cell radii range of Km). Scattered Pilot patterns setup for robust modes and high capacity modes for each guard interval. FEC starts with the most powerful known today (LDPC) to have stronger protection in difficult channels Higher spectral efficient capacity ATSC 3.0 is built from the beginning to enable all devices and architecture types (no limiting backward compatibility constraint) Received signal strength is the driving factor for mobile support Indoor reception on smartphones with antenna LOSS is compensated with a range of options: low power, medium power and high powers on different tower heights ATSC 3.0 can support all network types and is flexible for future adaptations

10 ATSC 3.0 Network Optimizations ATSC 3.0 PHY 3 Tower SFN ATSC 3.0 PHY 6 Tower SFN 10~300kWatt 10~300kWatt large distance, far out echoes {range of cyclic prefix options} ~2kWatt Small distance, close in echoes {33usec cyclic prefix optimized} large distance, far out echoes {range of cyclic prefix options} ~2kWatt Small distance, close in echoes {33usec cyclic prefix optimized} ATSC 3.0 allows flexibility for broadcasters to tune their own SFNs for best received signal strength

11 ATSC 3.0 Functional Architecture uplink Data Return Channel Link Layer downlink Control Info Signaling Data Input Formatting Coded Modulation Structure Waveform Generation Performance of some downlink functional blocks already shows improvement over LTE

12 Input and Coded Modulation Blocks Signaling Input Streams Framer Scheduler / Scrambler Forward Error Correction Bit Interleaver Mapper Time Interleaver Combines multiple input streams into frame(s) with many physical layer pipes Places frames in a selected order and scrambles data per pipe Adds information data protection per pipe Randomizes data bit placement within a pipe to reduce channel s effects Assigns a group of data bits to a symbol per pipe Randomizes symbols per pipe to reduce channel s effect (e.g. deep fades) Input Formatting Coded Modulation

13 Coded Modulation Key Considerations Forward Error Correction Codes Function gives receiver ability to correct errors in the transmitted signal LDPC (Low Density Parity Check) state-of-the-art codes increase robustness (closer to Shannon) Enables higher protection with less overhead Constellation Mapping Range of QPSK to high order QAM enables robust and high capacity modes Non-uniform mapping enables more robust operation in difficult channels (1 to 2dB gain depending on the QAM size) Time Interleaver Function distributes burst noise more evenly to improve performance of FEC

14 LDPC FEC Performance (AWGN) LDPC Capacity Curve in AWGN at BER=1E Capacity (bits/sec/hz) dB gain QPSK 16QAM 64QAM 256QAM 1024QAM 3 A/53 LTE 2 Shannon Limit Es/No (db) MANY operating points that are always more efficient than LTE

15 Turbo Codes Vs LDPC Turbo code was adopted as a FEC for 3GPP technologies (3G, HSDPA, LTE) LTE was designed to work with HARQ, a very low FER is not critical (10% BLER is a typical operating point in point to point (unicast) LTE with retransmission) When used for Multicast/Broadcast, the absence of HARQ reduces the performance of Turbo codes. In ATSC3.0, there was a consensus to adopt LDPC as a FEC LDPC codes have a very good performance without a return channel (Quasi Error Free, suitable for broadcasting)

16 Structure and Waveform Blocks Signaling OFDM Framer Frequency Interleaver Pilots Insertion IFFT Guard Int. Insertion Preamble Insertion Combines multiple inputs into single stream and format it in frames Randomizes data cells to reduce channel s effect (e.g. deep fades) Inserts pilots and reserved tones for channel estimation, synchronization, PAPR reduction Generates OFDM waveform Inserts GI Inserts a preamble for detection, synchronization, signaling Structure Waveform Generator

17 Waveform Key Considerations Flexibility: network types, network sizes, service types Different combinations of FFT sizes, GI, scattered pilots patterns, different frame types Robustness Increased signaling data robustness Reduced overhead to increase payload Optimized pilots patterns for channel BW and propagation conditions Power savings Time Division Multiplexing (TDM) of data frames Reduced complexity for easy implementation H/W implementation and Testing Future extensibility Futures extension frame parts

18 Physical Layer Frame Structure Preamble Core Preamble Enhanced Preamble Core Preamble Future Extendibility OR: Preamble Enhanced & Core Preamble Enhanced & Core Preamble Enhanced & Core Preamble Future Extendibility Frame Length Frame Length Frame Length Future Extension Frame (FEF) Time division multiplexing (TDM) Each physical frame should start with a preamble FEF allows for future technology or current other technology to be incorporated

19 FEF: doorway to the future Start with known preamble, clean slate to put any modulation inside that frame Expandability for future growth Ability to try new technology without breaking existing service and receivers. FEF s enable integration of different wireless standards as various signal formats are not restricted by PHY parameters in ATSC 3.0. Example integration of LTE into a FEF can be seen in Point-To- MultiPoint-Overlay (P2MP) for LTE-Advanced using DVB-T paper by Reimers and Juretzek from IEEE-BTS conference on Oct 14, Worldwide Interoperability for Microwave Access (WiMAX) example Can transmit FEF s with your own technology while not breaking ATSC 3.0 service

20 Future Extension Frame (FEF) Broadcast Overlays Preamble Future Extendibility LTE subframe OR: e subframe 10~300kWatt OR: Proprietary subframe ~40Watt WiMAX e: <4km, close in echoes {<22usec cyclic prefix} ATSC 3.0: >25km, far out echoes {28 709usec of cyclic prefix options} ~2kWatt LTE embms: <10km, close in echoes {33usec cyclic prefix optimized}

21 Receiver Complexity Desired handset feature (by broadcasters) is TV broadcast reception MYTH: Do LTE and it will automatically be in handset False: Broadcaster s frequency is different from wireless carriers, antenna loss is worse at lower UHF / VHF; control of tuner and other phone operation is from wireless carriers, not the user. MYTH: adding broadcast capability to handset is trivial False: embms from a broadcaster has above issues and additional complexity. Note: embms from wireless carriers is being tested now and search is on for content. Totally separate video function that will NOT impact other operations of the phone Separate RF paths of LTE vs. ATSC 3.0 Space is increasing on phones as displays are getting larger PHY Demodulator chip can still be relatively small and port IP packets to an existing video decoder already on handset Broadcast is reception only, no transmission energy that interferes with other radios Return link possible through IP connection via WiFi or LTE uplinks (data plans) for interactivity Dual Operation (receive phone calls while watching a video on the handset) is possible Use SEPARATE RESOURCES; either one instance of the LTE embms which is hamstrung from a design for unicast data OR an instance of ATSC 3.0 PHY optimally designed (very spectrally efficient) to deliver video content. We can make a standard to support a technical solution/option, but deployment/use in devices is based on business considerations.

22 Summary ATSC 3.0 offers more flexibility and robustness than LTE. No network architecture is precluded, dense, sparse and single cells are enabled! Wide range of guard intervals and pilot patterns to choose from Powerful FEC to protect data with different rate/robustness tradeoffs Fully configurable to target all devices, mobile and fixed in the same emission ATSC 3.0 will be a flexible standard with a starting point that is more efficient than LTE Future Extension Frames Other standards can be incorporated Broadcast overlay concepts are enabled Experimental proprietary modulations can be tested without breaking ATSC 3.0 service