Small Cell Timing and Sync Presentation SCA 2013
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Presentation given at Small Cells Americas December 2013 explaining and positioning timing and sychronisation requirements and solutions for small cells. This highlights the need for Phase sychronisation for more advanced LTE features, which is technically demanding. The alternative synchronisation schemes are discussed, concluding in a range of recommended solutions.
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Small Cell Timing and Sync Presentation SCA 2013
- 1. Timing is everything: Navigating Small Cell Timing & Sync David Chambers ThinkSmallCell.com © 2013 Small Cell Americas, Dallas, Dec 2013
- 2. About ThinkSmallCell • Founded Sept 2007 as ThinkFemtocell • Independent news, analysis, insight into Small Cells • Based on a belief that small cell architecture is the only credible solution for high data traffic © 2013 • David Chambers, B.Sc. (Hons), MIET, C.Eng, Dip. M., MCIM, Chartered Marketer • Career includes – Telecom software engineer – Telecom product manager – Standards (ETSI, 3GPP) – Chartered Engineer monthly – Chartered Marketer newsletter at Sign up for our free ThinkSmallCell.com Small Cell Americas, Dallas, Dec 2013 2
- 3. Question #1 How far does a radio wave travel in 1 nanosecond? A mile A yard A foot © 2013 Small Cell Americas, Dallas, Dec 2013
- 4. Answer #1 How far does a radio wave travel in 1 nanosecond? Given: Speed of light = 300,000,000 metres/second 1,000,000,000 nanoseconds in 1 second Answer: 0.3 metres (approx 1 foot) © 2013 Small Cell Americas, Dallas, Dec 2013
- 5. Why Timing and Sync? End User Experience - Seamless Handovers - Fewer Dropped calls - Avoid data stream glitches © 2013 Spectral Efficiency - Squeezing the most out of available spectrum - Avoiding the need for extra cellsites Cell Edge Performance - Improving service at borders between neighbouring cells Small Cell Americas, Dallas, Dec 2013
- 6. The Three levels of Sync None Frequency Frequency & Phase Wi-Fi 3G UMTS 3G CDMA Bluetooth 3G TD-SCDMA 4G FDD LTE TD-LTE LTE-Advanced At the same time, backhaul transmission is migrating from T1/E1 to Ethernet © 2013 Small Cell Americas, Dallas, Dec 2013
- 7. Three Competing Forces Maximise Spectral Efficiency Maximise Spatial Efficiency - LTE-Advanced - CoMP - eMBMS - eICIC - Add more small cells Derive sync via backhaul Derive sync independently - Sync Ethernet - PTP (IEEE 1588 v2) - NTP - GNSS - Neighbour Cellsite Sniffing FDD TDD - Doesn’t (always) require Phase Sync - Requires Phase Sync © 2013 Small Cell Americas, Dallas, Dec 2013
- 8. Wide Range of Timing Tolerances Residential Small Cell Enterprise Small Cell Urban Small Cell Cloud RAN LTE-A 50ppb 50ppb 50ppb/1.5 μs 50ppb/0.5 μs TD-LTE 250ppb 50ppb 50ppb/1.5 μs 50ppb/ 1.5 to 5μs LTE 50ppb 50ppb 50ppb 50ppb 3G 250ppb 100ppb 50ppb 50ppb © 2013 Small Cell Americas, Dallas, Dec 2013
- 9. Synchronisation Technology Options GNSS NTP 1588v2 (PTP) SyncE Sniffing Transport Physical Layer 3 Layer 2 & 3 Physical Physical Use cases North American femtocells; Any 3G/LTE small cell 3G UMTS Enterprise Femtocells & and Urban Enterprise small cells Urban small cells Residential and standalone Enterprise Limitations Possible poor indoor signal reception Packet delay variations in wireline broadband Must be end-to-end SyncE throughout Reception from nearby cell towers Frequency Phase © 2013 Packet delay variation in backhaul Small Cell Americas, Dallas, Dec 2013
- 10. GNSS Developments • It’s no longer just GPS – GLONASS (Russian) – Compass (Chinese) – Galileo (European) • Multi-standard receivers now more common – Soon up to 300 different satellites • Increased receiver performance – Demonstrated down to -175dBm – More likely to work indoors than before © 2013 Small Cell Americas, Dallas, Dec 2013
- 11. Some poor GPS installations © 2013 Small Cell Americas, Dallas, Dec 2013
- 12. Precise Time Protocol (PTP) 1588v2 • PTP (IEEE1588v) provides high clock accuracy in a packet network • The “grandmaster clock” generates timestamps and responds to requests • Only boundary clocks need to be aware of the nature of packets • Exchange of timestamp packets ensures all nodes retain frequency and phase accuracy • Only nodes that need time information need to be upgraded © 2013 Grandmaster Clock 1 12 1 2 3 4 6 5 Packet Packet Packet Packet 1 12 1 2 3 4 6 5 RAN Base station Small Cell Americas, Dallas, Dec 2013 12
- 13. Packet Delay Variation • Phase timing requires low PDV not latency – Variation in end-to-end delay – Asymmetry of delay variation uplink/downlink • Consequences – Sync acquisition time, recovery time • Specifications – Previously end-to-end – Recently changed to “per hop” © 2013 Small Cell Americas, Dallas, Dec 2013
- 14. Synchronous Ethernet (SyncE) • All ports in the link must be SyncE enabled RAN NC SyncE • SyncE is a good compromise between TDM and Ethernet SyncE • It provides frequency synchronisation at the physical layer SyncE SyncE • Managing SyncE can significantly increase network TCO © 2013 RAN Base station Small Cell Americas, Dallas, Dec 2013 14
- 15. Question #2 Do signals travel faster/slower/same down optical fibre than via microwave link? © 2013 Small Cell Americas, Dallas, Dec 2013
- 16. Answer #2 Do signals travel faster/slower/same down optical fibre than via microwave link? Given: Light waves are reflected off the sides of optical fibre, so travel further than direct radio transmissions Answer: Slower © 2013 Small Cell Americas, Dallas, Dec 2013
- 17. Wide Range of Timing Tolerances Residential Small Cell TD-LTE Urban Small Cell 50ppb 50ppb Frequency Sync LTE-A Enterprise Small Cell 50ppb/1.5 μs 50ppb GNSS and PTP (IEEE 1588v2) 50ppb/1.5 μs 50ppb 50ppb 50ppb 100ppb 50ppb 50ppb 250ppb Cloud RAN 50ppb/0.5 Frequency μs + Phase 50ppb/ Dark 1.5 to 5μs Fibre NTP LTE 3G 50ppb Optionally GNSS 250ppb © 2013 Small Cell Americas, Dallas, Dec 2013
- 18. Question #3 What is the PHASE holdover time of an oscillator with FREQUENCY holdover of 1 month? 1 Week © 2013 1 Day 12 Hours Small Cell Americas, Dallas, Dec 2013 1 Hour
- 19. Commercial Oscillator Specifications Time to Reach Phase Error Limit Freq. Oscillator Type vs Aging Temp. (±20°C. variation error limit at 10°C/hour) 24 Hours Holdover 1 µs 3 µs 7 µs (Calm Air) OCXO ±0.1 ppb ≤0.05 ppb/day 12 hours 48 hours 144 hours <1 µs OCXO ±0.5 ppb ≤0.1 ppb/day 3 hours 12 hours 36 hours 3 µs ±5 ppb ≤1 ppb/day 30 minutes 2 hours 4 hours 50 µs ±5 ppb ≤1 ppb/day 30 minutes 2 hours 4 hours 50 µs ±10 ppb ≤2 ppb/day 20 minutes 35 minutes 55 minutes 100 µs ±10 ppb ≤40 ppb/day 5 minutes 10 minutes 15 minutes 1000 µs (ROX-T1/T2) OCXO (ROX-T3) OCXO (ROX-T5/S4) OCXO (Mercury™) TCXO (RPT, RTX) © 2013 Small Cell Americas, Dallas, Dec 2013 Source: Rakon
- 20. Conclusion In-building: Residential 3G/SoHo NTPCloud RAN Urban Enterprise NTP or PTP/SyncE Small Cell Urban: Combination of GNSS/SyncE/1588 Backhaul SyncE/1588 capable Phase Sync: Demands better oscillator holdover Cloud RAN needs dark fibre to site © 2013 Small Cell Americas, Dallas, Dec 2013