day 2-t10-1630 martin-nuss-20120524
DESCRIPTION
LTE World Summit Barcelona May 2012 Day 2TRANSCRIPT
GPS-quality Network Timing for
TD-LTE and LTE-Advanced
Martin Nuss – CTO, Vitesse Semiconductor
LTE World Summit, Barcelona
May 2012
Agenda
Synchronization requirements for TD-LTE and
LTE-Advanced (LTE-A)
GPS challenges for LTE small-cell deployments
Network solutions for GPS-quality network timing for LTE
and LTE-Advanced
2
Small (Pico/Femto) Cells Integral to LTE
Small cells are the
most obvious solution
to the spectrum/
bandwidth problem
Small cells allow
spatial re-use of the
same spectrum
But small cell backhaul
and timing delivery are
main challenges
3
Traditional Base Station Timing Architectures
Traditionally timing (frequency)
derived from E1/T1 operator
connections to the base station
For Time-of-Day (phase) GPS
receiver at each base station most
commonly deployed
With 4G/LTE, this timing model
is challenged:
E1/T1 replaced by Ethernet, requiring
new network timing solutions
Many more (small) cell sites, most of
them with poor GPS visibility
Other concerns about GPS (ease of
jamming, US-controlled, etc..)
4
E1/T1
GPS Rx
Ethernet
E1/T1
All Ethernet
Primary
Reference
Clock
Ethernet Network Timing:
1) SyncE – Frequency only
2) IEEE 1588 – Frequency and
Phase (Time-of-Day)
Outdoor Small Cells Will Require Network Timing
5
GPS satellite visibility is poor in urban corridors Network timing required
Fiber-to-the-lamppost not common Timing over Microwave essential
LTE Indoor Coverage and Timing Challenges
Common problem for LTE
will be indoor coverage, in
particular in the higher
frequency bands
Predominant access
technologies to buildings
(VDSL, FTTx) have problems
delivering good timing
Challenge: How to provide
accurate timing to LTE
femtocells inside building?
6
Timing Gets Even Tougher for TD-LTE and LTE-A
7
TDD Standards generally require tight
Phase/Time-of-Day synchronization
LTE-Advanced puts additional burden
on synchronization
For network timing distribution,
synchronization errors accumulate in
every network element
Timing Accuracy Requirements for 3G/4G
Technology Frequency Accuracy Phase Accuracy
GSM ≤ ±50 ppb N/A
UMTS FDD ≤ ±50 ppb N/A
UMTS TDD ≤ ±50 ppb ≤ 2.5 µsec
3GPP2 CDMA200 ≤ ±50 ppb ≤ 3 µsec
TD-SCDMA ≤ ±50 ppb ≤ 3 µsec
LTE Long-term cumulative error ≤ 1.5 µsec
LTE-Advanced/MIMO ≤ 0.5 µsec between neighboring towers
Intro to Timing Through Packets – IEEE 1588
8
IEEE 1588v2 Precision Timing
Protocol estimates the time
at the slave by calculating the
propagation delay between
master/slave via a series of
time-stamped messages
Traditional Frequency Synchronization
Packets can be used for synchronization
if time stamped by a Master Clock
Impairments are short-term jitter and
long-term phase stability (wander)
Impairments are packet delay variations
through the network (jitter) and long-term
time stability (wander)
Packet networks can have large packet delay variations,
introducing timing inaccuracies
Master
Clock Slave
Network
Solutions to Packet Delay Variations in IEEE1588
9
PDV Filtering
in Software
Packet Delay Variation (PDV) algorithm on subset of packets
that have experienced the least delay
Usually requires reserving the highest priority queue for
1588 packets
1588
Transparent
Clocks
Network elements perform time stamping at the port/PHY-level
only and update time stamps on egress
Boundary clocks can be sprinkled throughout network to create
1588 domains
Each network element engages in deriving Time-of-Day using
the 1588 protocol, and updates the time stamps before sending
out to next network element
Very similar to BITS/SyncE model
1588 Boundary
Clocks in
Every Network
Element
Network Timing Cost Comparison
10
Performance
Co
st
PDV Filtering
– Needs DPLL, OCXO, CPU
in every node
– Difficult to support multiple
timing domains, MPLS-LSR
Boundary Clocks
+ Do not need DPLL, OCXO,
CPU in every node
+ Supports multiple timing
domains, MPLS-LSR
Transparent Clocks
Transparent clocks are the most cost effective and least
disruptive way to provide nanosecond-accurate timing
+ Low implementation cost
(Software only)
– Phase accuracy usually not
good enough for TD-LTE
TCs Easily Support Multi-Operator Environments
11
With transparent
clocks, transport
operators can offer
a synchronization
service to multiple
service providers
Transparent clocks
improve 1588 packet
time accuracy 1000x
from microseconds
to nanoseconds!
0.5 us
-0.5 us
0
No TC With TC
TC TC TC Grand
Master Slave
TC TC TC Grand
Master Slave
Synchronization Service: Transparent Clock
Operator 1 PRC
Operator 1
Base Station
Transport
Operator UNI
UNI Operator 1
Controller /
Gateway
Operator 2
Controller /
Gateway
Operator 2
Base Station UNI
UNI
UNI-C UNI-C
UNI-N UNI-N
Synchronous Ethernet Domain
Transport Operator Frequency
(TOD not required)
Network Solutions to LTE/LTE-A Timing Problems
Femtocell Indoor Synchronization
Provide 1588 network timing through
the access network, or
GPS antenna on top of building generates 1588
packets for time distribution inside the building
12
Urban Picocell Synchronization
Provide 1588 Network Timing to the picocell
Transparent Clocks over Microwave
and Millimeter-wave links can easily
meet TD-LTE and LTE-A requirements
Summary
TD-LTE and LTE-Advanced require GPS-grade
timing/synchronization
Use of GPS is often not possible – both indoor and outdoor
IEEE1588 network timing is maturing and being implemented by all
major equipment manufacturers
Transparent clocks are the most cost effective and least disruptive
way to provide nanosecond-accurate timing
13
Vitesse is leading the way with TD-LTE/LTE-A ready technologies.
Learn more at www.vitesse.com/ce/ce_timing.php