Small Cell Timing and Sync Presentation SCA 2013

© 2013 Small Cell Americas, Dallas, Dec 2013

Timing is everything:Navigating Small Cell Timing & Sync

David ChambersThinkSmallCell.com


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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Question #1

How far does a radio wave travel in 1 nanosecond?

A foot

A yard

A mile


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)


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


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


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


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


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


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


Some poor GPS installations


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


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”


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

14


Question #2

Do signals travel faster/slower/same down optical fibre than via microwave link?


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


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


Question #3

What is the PHASE holdover time of an oscillator with FREQUENCY holdover of 1 month?

1 Week 12 Hours 1 Hour1 Day


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


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