small cell timing and sync presentation sca 2013
DESCRIPTION
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.TRANSCRIPT
© 2013 Small Cell Americas, Dallas, Dec 2013
Timing is everything:Navigating Small Cell Timing & Sync
David ChambersThinkSmallCell.com
© 2013 Small Cell Americas, Dallas, Dec 2013
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
• 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– Chartered Marketer
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© 2013 Small Cell Americas, Dallas, Dec 2013
Question #1
How far does a radio wave travel in 1 nanosecond?
A foot
A yard
A mile
© 2013 Small Cell Americas, Dallas, Dec 2013
Answer #1
How far does a radio wave travel in 1 nanosecond?
Given:
Speed of light = 300,000,000 metres/second1,000,000,000 nanoseconds in 1 second
Answer: 0.3 metres
(approx 1 foot)
© 2013 Small Cell Americas, Dallas, Dec 2013
Why Timing and Sync?
End User Experience- Seamless
Handovers- Fewer Dropped
calls- Avoid data stream
glitches
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
© 2013 Small Cell Americas, Dallas, Dec 2013
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
Three Competing Forces
Maximise Spectral Efficiency- LTE-Advanced
- CoMP- eMBMS- eICIC
Maximise Spatial Efficiency- Add more small cells
Derive sync via backhaul- Sync Ethernet- PTP (IEEE 1588 v2)- NTP
Derive sync independently- GNSS- Neighbour Cellsite Sniffing
FDD- Doesn’t (always) require
Phase Sync
TDD- Requires Phase Sync
© 2013 Small Cell Americas, Dallas, Dec 2013
Wide Range of Timing Tolerances
ResidentialSmall Cell
EnterpriseSmall Cell
UrbanSmall Cell
Cloud RAN
3G 250ppb 100ppb 50ppb 50ppb
LTE-A 50ppb 50ppb 50ppb/1.5μs
50ppb/0.5μs
LTE 50ppb 50ppb 50ppb 50ppb
TD-LTE 50ppb 50ppb/1.5μs
50ppb/1.5 to 5μs
250ppb
© 2013 Small Cell Americas, Dallas, Dec 2013
Synchronisation Technology Options
GNSS NTP 1588v2 (PTP)
SyncE Sniffing
Frequency
Phase
Transport Physical Layer 3 Layer 2 & 3 Physical Physical
Use cases North American femtocells; Any 3G/LTE small cell
3G UMTS Femtocells & Enterprise
Enterprise and Urban small cells
Urban small cells
Residential and standalone Enterprise
Limitations Possible poor indoor signal reception
Packet delay variations in wireline broadband
Packet delay variation in backhaul
Must be end-to-end SyncE throughout
Reception from nearby cell towers
© 2013 Small Cell Americas, Dallas, Dec 2013
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
Some poor GPS installations
© 2013 Small Cell Americas, Dallas, Dec 2013
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
RAN Base station
Grandmaster Clock12 1
3
1
4
2
56
12 1
3
1
4
2
56
Packet
Packet
Packet
Packet
12
© 2013 Small Cell Americas, Dallas, Dec 2013
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
Synchronous Ethernet (SyncE)
• All ports in the link must be SyncE enabled
• SyncE is a good compromise between TDM and Ethernet
• It provides frequency synchronisation at the physical layer
• Managing SyncE can significantly increase network TCO
SyncE
SyncE
SyncE
SyncE
RAN Base station
RAN NC
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© 2013 Small Cell Americas, Dallas, Dec 2013
Question #2
Do signals travel faster/slower/same down optical fibre than via microwave link?
© 2013 Small Cell Americas, Dallas, Dec 2013
Answer #2
Do signals travel faster/slower/same down optical fibre than via microwave link?
Given:
Light waves are reflected offthe sides of optical fibre, so travel
further than direct radio transmissions
Answer: Slower
© 2013 Small Cell Americas, Dallas, Dec 2013
Wide Range of Timing Tolerances
ResidentialSmall Cell
EnterpriseSmall Cell
UrbanSmall Cell
Cloud RAN
3G 250ppb 100ppb 50ppb 50ppb
LTE-A 50ppb 50ppb 50ppb/1.5μs
50ppb/0.5μs
LTE 50ppb 50ppb 50ppb 50ppb
TD-LTE 50ppb 50ppb/1.5μs
50ppb/1.5 to 5μs
250ppb
NTP
Optionally GNSS
GNSS andPTP (IEEE 1588v2)
Frequency Sync Frequency +Phase
Dark Fibre
© 2013 Small Cell Americas, Dallas, Dec 2013
Question #3
What is the PHASE holdover time of an oscillator with FREQUENCY holdover of 1 month?
1 Week 12 Hours 1 Hour1 Day
© 2013 Small Cell Americas, Dallas, Dec 2013
Commercial Oscillator Specifications
Oscillator TypeFreq.
vs Temp.
Aging
Time to Reach Phase Error Limit(±20°C. variation error limit at 10°C/hour) 24 Hours
Holdover(Calm Air)1 µs 3 µs 7 µs
OCXO ±0.1 ppb
≤0.05 ppb/day
12 hours
48 hours
144 hours
<1 µs
OCXO(ROX-T1/T2)
±0.5 ppb
≤0.1 ppb/day
3 hours
12 hours
36 hours
3 µs
OCXO(ROX-T3)
±5 ppb
≤1 ppb/day
30 minutes
2 hours
4 hours
50 µs
OCXO(ROX-T5/S4)
±5 ppb
≤1 ppb/day
30 minutes
2 hours
4 hours
50 µs
OCXO (Mercury™)
±10 ppb
≤2 ppb/day
20 minutes
35 minutes
55 minutes
100 µs
TCXO(RPT, RTX)
±10 ppb
≤40 ppb/day
5 minutes
10 minutes
15 minutes
1000 µs
Source: Rakon
© 2013 Small Cell Americas, Dallas, Dec 2013
Conclusion
UrbanSmall Cell
Cloud RAN
In-building:Residential 3G/SoHo NTPEnterprise NTP or PTP/SyncE
Urban: Combination of GNSS/SyncE/1588
Backhaul SyncE/1588 capable
Phase Sync: Demands better oscillator
holdoverCloud RAN needs dark fibre to site