Friday, December 16, 2011

Work or Study Item List for LTE Release 11: LTE 2 Advanced ?

Evolving Random Access Channel
What Is The Next for Mobile System Design?
How Much Feedback Is Enough for MIMO?
How to Broadcast Multimedia Contents?
Interference Cancellation: A Short Overview
Location Based Services for Mobiles

From Chair's notes, there are more than 40 work or study items proposed for enhancing LTE Advanced or  both LTE-Advanced and HSPA. They will be completed by September 2012.
  1. Further Enhanced Non CA-based ICIC for LTE
  2. LTE Carrier Aggregation Enhancements
  3. Study on Coordinated Multi-Point Operation for LTE
  4. Study on Enhanced Uplink Transmission for LTE
  5. Study on further Downlink MIMO enhancements for LTE-Advanced
  6. Study on Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation
  7. Coordinated Multi-Point Operation for LTE
  8. Provision of low-cost MTC UEs based on LTE
  9. Proposed SI on LTE Coverage Enhancements
  10. Improvements to LTE Relay Backhaul
  11. Study on LTE Device to Device Discovery and Communication - Radio Aspects
  12. Network-Based Positioning Support for LTE
  13. Service continuity and location information for MBMS for LTE
  14. LTE RAN Enhancements for Diverse Data Applications
  15. Study on signaling and procedure for interference avoidance for in-device coexistence
  16. Study on HetNet mobility enhancements for LTE
  17. Study on RAN improvements for Machine-Type Communications
  18. RAN overload control for Machine-Type Communications
  19. Study Item on Further RAN Improvements for Machine-type Communications
  20. study item proposal for LTE and HSDPA Carrier Aggregation
  21. Enhancement of Minimization of Drive Tests for E-UTRAN and UTRAN
  22. Signalling and procedure for interference avoidance for in-device coexistence
  23. Study Item Proposal for Opportunistic Carrier Aggregation across 3GPP-LTE and WLAN
  24. Carrier based HetNet ICIC for LTE
  25. Study on further enhancements for HNB and HeNB
  26. LIPA Mobility and SIPTO at the Local Network RAN Completion
  27. Further Self Optimizing Networks (SON) Enhancements
  28. SI: Mobile Relay for E-UTRA
  29. Network Energy Saving for E-UTRAN
  30. UE Over the Air (Antenna) conformance testing methodology- Laptop Mounted Equipment Free Space test
  31. UE demodulation performance requirements under multiple-cell scenario for 1.28Mcps TDD
  32. Uplink Transmit Diversity for HSPA – Open Loop
  33. Non-contiguous 4C-HSDPA operation
  34. Study on Measurement of Radiated Performance for MIMO and multi-antenna reception for HSPA and LTE terminals
  35. Study on Inclusion of RF Pattern Matching Technologies as a positioning method in the E-UTRAN
  36. Relays for LTE (part 2)
  37. Enhanced performance requirement for LTE UE
  38. Electromagnetic Compatibility (EMC) Requirements for Multi-Standard Mobile Terminals and Ancillary Equipment
  39. SI: Passive InterModulation (PIM) handling for Base Stations
  40. E-UTRA medium range and MSR medium range/local area BS class requirements
  41. SI: Study of RF and EMC Requirements for Active Antenna Array System (AAS) Base Station
  42. RF Requirements for Multi-band and Multi-standard Radio (MB-MSR) Base Station
There are additional 11 work or study items for further enhancing HSPA itself.
  1. Eight carrier HSDPA
  2. Uplink Transmit Diversity for HSPA – Closed Loop
  3. Study on Uplink MIMO
  4. Study on HSDPA multipoint transmission
  5. Study item on HSPA enhancement for LCR TDD
  6. Four Branch MIMO transmission for HSDPA
  7. Uplink MIMO with 64QAM for HSUPA
  8. Further Enhancements to CELL_FACH
  9. HSDPA Multiflow Data Transmission
  10. Single Radio Voice Call Continuity from UTRAN/GERAN to E-UTRAN/HSPA
  11. SID: Introduction of Hand phantoms for UE OTA antenna testing

Saturday, December 10, 2011

Evolved Handovers: EV-DO and LTE

One key feature of any mobile communication system is to provide a mobility mechanism for mobiles to do fast and seamless switching between serving cells. There are many different handover mechanisms for achieving this goal. They include soft handover, which is mostly used for voice services, and hard handover, which is designed for data services. Hard handovers can be further classified as network-controlled handovers and mobile-based handovers. The interesting thing is if you look at the basic handover or handoff procedures I will explain in the next, you may feel a long-time debate on which entity , base stations or mobiles, should control handover or handoff.

Traditionally there is no standardized direct connection between two BTS's, even they both belong to the same BSC. Therefore, there usually are a long outage for a mobile do hard handover. For example, the default forward traffic channel MAC handover scheme of CDMA2000 EV-DO Rev. 0 usually results in 100~200ms outage. In order to minimize this outage for some delay-sensitive services, EV-DO Rev. A specially provides a new uplink channel,  DSC (Data Source Control) channel, for mobile to indicate early knowledge of its upcoming handover. When a mobile starts a handover in EV-DO Rev. A network, it sends a forward cell switch indication, a new DSC, to a target BTS for a duration of DSCLength. Meanwhile, it is still receiving data from its current serving BTS until this mobile performs a DRCCover change to the target BTS.  DRCCover is used by the mobile to specify its best serving BTS. During this moment, the queue transfer will be completed from the source BTS to the target BTS.

In LTE Release 8, things changed a little bit. A X2 connection between base stations, eNodeBs, is standardized and it is assumed to always exist as long as they belong to the same pooling area defined by a MME. The basic procedure for a LTE mobile to do handover becomes that the mobile sends Measurement Reports back to its current serving eNodeB and its serving eNodeB decides if to perform a handover and selects a target eNodeB. Source eNodeB then issues a Handover Request message to target eNodeB and passes necessary information. After target eNodeB accepts the request, it will prepare for it and acknowledge it after the preparation is done. As soon as source eNodeB receives Handover Request Acknowledge message, both a handover command and data forwarding are transmitted.

However, story doesn't stop here. Since a LTE mobile starts its handover when the radio link it sees from its serving eNodeB isn't very good, there is a possibility that it detects a radio link failure and can't successfully decode the handover command. In this case, it starts a RLF (Radio Link Failure) timer. Upon the expiration of RLF timer, the mobile searches for a good target eNodeB and tries to re-establish its connection with the target eNodeB while remain in connected state. During the period before a successful connection to eNobeB, source eNodeB will notice the changes and communicate with target eNodeBs through X2 interface to ensure the L1/L2 handover. If the re-connection failed, the mobile will switch from connected state to idle state and do a NAS recovery after that.

Wait a minute ... there is more.  Usually RLF timer is optimized to be several hundred ms. This means the delay of RLF timer based handover can be relatively long. If the mobile can send re-connection request to target eNodeB before RLF timer expires and target eNodeB can request handover from source eNodeB instead of waiting, the handover delay can be reduced accordingly. In this case, the handover sounds more like to be mobile-initiated or mobile-based.