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Day 2-t10-1630 martin-nuss-20120524


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LTE World Summit Barcelona May 2012 Day 2

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Day 2-t10-1630 martin-nuss-20120524

  1. 1. GPS-quality Network Timing forTD-LTE and LTE-AdvancedMartin Nuss – CTO, Vitesse SemiconductorLTE World Summit, BarcelonaMay 2012
  2. 2. 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
  3. 3. 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
  4. 4. Traditional Base Station Timing Architectures GPS Rx Primary Reference  Traditionally timing (frequency) E1/T1 Clock derived from E1/T1 operator connections to the base station Ethernet  For Time-of-Day (phase) GPS receiver at each base station most E1/T1 commonly deployed  With 4G/LTE, this timing model All Ethernet is challenged:  E1/T1 replaced by Ethernet, requiring new network timing solutions Ethernet Network Timing:  Many more (small) cell sites, most of 1) SyncE – Frequency only them with poor GPS visibility 2) IEEE 1588 – Frequency and  Other concerns about GPS (ease of Phase (Time-of-Day) jamming, US-controlled, etc..) 4
  5. 5. Outdoor Small Cells Will Require Network Timing  GPS satellite visibility is poor in urban corridors  Network timing required  Fiber-to-the-lamppost not common  Timing over Microwave essential 5
  6. 6. 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
  7. 7. Timing Gets Even Tougher for TD-LTE and LTE-A 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 AccuracyGSM ≤ ±50 ppb N/AUMTS FDD ≤ ±50 ppb N/AUMTS TDD ≤ ±50 ppb ≤ 2.5 µsec3GPP2 CDMA200 ≤ ±50 ppb ≤ 3 µsecTD-SCDMA ≤ ±50 ppb ≤ 3 µsecLTE Long-term cumulative error ≤ 1.5 µsecLTE-Advanced/MIMO ≤ 0.5 µsec between neighboring towers 7
  8. 8. Intro to Timing Through Packets – IEEE 1588 Traditional Frequency Synchronization Master Network Slave Clock Impairments are short-term jitter and long-term phase stability (wander)  IEEE 1588v2 Precision Timing Packets can be used for synchronization Protocol estimates the time if time stamped by a Master Clock at the slave by calculating the propagation delay between Impairments are packet delay variations through the network (jitter) and long-term master/slave via a series of time stability (wander) time-stamped messages Packet networks can have large packet delay variations, introducing timing inaccuracies 8
  9. 9. Solutions to Packet Delay Variations in IEEE1588 Packet Delay Variation (PDV) algorithm on subset of packetsPDV Filtering that have experienced the least delay in Software Usually requires reserving the highest priority queue for 1588 packets1588 Boundary Each network element engages in deriving Time-of-Day using Clocks in the 1588 protocol, and updates the time stamps before sendingEvery Network out to next network element Element Very similar to BITS/SyncE model Network elements perform time stamping at the port/PHY-level 1588 only and update time stamps on egress Transparent Clocks Boundary clocks can be sprinkled throughout network to create 1588 domains 9
  10. 10. Network Timing Cost Comparison Boundary Clocks Cost – Needs DPLL, OCXO, CPU in every node – Difficult to support multiple timing domains, MPLS-LSR PDV Filtering Transparent Clocks + Low implementation cost + Do not need DPLL, OCXO, (Software only) CPU in every node – Phase accuracy usually not + Supports multiple timing good enough for TD-LTE domains, MPLS-LSR Performance Transparent clocks are the most cost effective and least disruptive way to provide nanosecond-accurate timing 10
  11. 11. TCs Easily Support Multi-Operator Environments Transport Operator Frequency (TOD not required)Operator 1Controller / UNI Operator 1 UNI Base Station With transparent Gateway clocks, transport Operator 1 PRCOperator 2 UNI UNI-N Transport UNI-N Operator 2 UNI Base Station operators can offer OperatorController / Gateway a synchronization UNI-C Synchronous Ethernet Domain UNI-C service to multiple Synchronization Service: Transparent Clock service providers Grand Slave TC TC TC Master Grand Slave TC TC TC Master Transparent clocks No TC With TC improve 1588 packet 0.5 us time accuracy 1000x 0 from microseconds to nanoseconds!-0.5 us 11
  12. 12. Network Solutions to LTE/LTE-A Timing Problems 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 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
  13. 13. 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 Vitesse is leading the way with TD-LTE/LTE-A ready technologies. Learn more at 13
  14. 14. Thank YouMartin Nuss – CTO, Vitesse