Lte a icic_2_pres_1103_ericsson
- 1. Interference management Within 3GPP LTE advanced – Part ii Konstantinos Dimou, PhD Senior Research Engineer, Wireless Access Networks, Ericsson research [email protected]
- 2. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Outline I. Interference Management within LTE – LTE - Basic Principles › OFDM, SC-FDMA › Link adapation, scheduling, hybrid-ARQ – Interference Management within LTE › Goal › Interference from other systems › Intra-LTE Interference › Inter-Cell Interference Coordination - Data Channels II. LTE (Advanced) - Carrier Aggregation (CA) - Heterogeneous Networks (HetNet) - Interference Management for Heterogeneous Networks - Control Channels - Data Channels Series of two seminars
- 3. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Recap from Previous Sessions FDD and TDD support Bandwidth flexibility ICIC Multi-antenna support data1 data2 data3 data4 Channel-dependent scheduling Hybrid ARQ IFFT Transmission scheme DL OFDM, UL DFTS-OFDM LTE Rel-8
- 4. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Recap from Previous Session data1 data2 data3 data4 LTE Rel-8 Dual-stream Beamforming Positioning LTE Rel-9 MBSFN
- 5. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 MIMO extensions Up to 4x4 UL and 8x8 DL Carrier Aggregation Relaying Reduced latency Recap from Previous Session data1 data2 data3 data4 LTE Rel-8 LTE Rel-10 LTE Rel-9 Heterogeneous networks
- 6. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Lte – dl PHYSICAL CHANNEL STRUCTURE › Transmitted within first 1-3 OFDM symbols of each DL subframe – Transmission over all system bandwidth › Layer 1 control signaling – UL/DL channel allocations › Physical Dedicated Control Channel (PDCCH) – Format of the L1 control signaling channel › Physical Control Format Indicator Channel (PCFICH) One subframe Control signaling Cell-specific reference symbols (CRS) Physical Control Channel Transmission with QPSK modulation
- 7. Release 10 features Carrier aggregation
- 8. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 › Contiguous Carrier Aggregation of up to 5 component carriers in each direction › Non-contiguous intra-band Carrier Aggregation of up to 5 component carriers in each direction › Inter-band Carrier Aggregation (a.k.a. spectrum aggregation) of up to 5 component carriers in each direction Types of Carrier Aggregation Intra- and Inter-Band Carrier Aggregation One component carrier One component carrier One component carrier
- 9. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Terminology › DCI Downlink Control Information › CC Component Carrier › PCC Primary Component Carrier › SCC Secondary Component Carrier › PCell Primary Cell; cell configured on PCC › SCell Secondary Cell; cell configured on SCC
- 10. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Primary and Secondary Serving Cells Among the configured component carriers of a UE, we have: › One DL Primary Component Carrier (DL PCC) – UE specific – Cannot be de-activated – System information monitoring á la Rel-8 on the DL PCC – The cell configured on the DL PCC is the Primary Serving Cell PCell › One UL Primary Component Carrier (UL PCC) – UE specific – Carries UL L1 Control Signaling (Physical Uplink Control Channel (PUCCH)) – Random access limited to UL PCC › The "rest" are Secondary Component Carriers (UL/DL SCC) – Can be regarded as “additional resources” – Can be de-activated – The cell configured on a DL SCC is a Secondary Serving Cell SCell 4 UL & 4 DL CCs
- 11. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 PDCCH Carrier Indicator Field (CIF) › Reuse Rel-8 PDCCH structure (coding, mapping etc.) – Each DL or UL shared channel transmission has its own PDCCH containing DL assignment or UL grant › Rel-8 DCI formats can be augmented with Carrier Indication Field (CIF, 3 bit) – Enables cross-carrier scheduling (i.e. PDCCH for a shared channel data transmission can be transmitted on another cell than data) – Semi-static configuration indicates presence/absence of CIF per cell – Interpretation of CIF is UE specific CIF configured CIF not configured Parallel Rel-8 operation
- 12. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 PCFICH › Each cell has its own individual control region size indicated by PCFICH › PCFICH read by terminals operating – in Rel-8 mode or – Rel-10 terminals using Carrier Aggregation with in-carrier PDCCH – Non successful decoding of PCFICH results into loss of the current subframe PCFICH PCFICH Control region size is wrongly decoded and thus PDCCH (and PDSCH) cannot be decoded
- 13. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 PCFICH Cross-Carrier Scheduling › Cross-carrier scheduled assignment – Upon non successful PCFICH decoding, loss of data is observed › Very likely loss can be corrected only by higher layer retransmission – PCFICH on cross-carrier scheduled cell needs higher reliability than on PDCCH cell › In some CA deployment scenarios (e.g. HetNets) quality on cross-carrier scheduled cell can be low and PCFICH performance cannot be guaranteed - Solution: PDSCH starting position is semi-statically configured for cross-carrier scheduled cells, i.e. PCFICH is overruled by semi-static configuration cross-carrier scheduled PDSCH: terminal starts to decode PDSCH at wrong OFDM symbol in-carrier scheduled PDSCH: terminal fails to decode PDCCH and PDSCH PCFICH PCFICH (wrongly decoded)
- 14. Release 10 features Heterogeneous networks
- 15. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Heterogeneous Networks › Refer to deployments of a mixture of cells with different characteristics, mainly in terms of output power, operating (partially) on same set of frequencies – “Low power nodes are placed throughout a macro-cell layout” Cluster of femto cells Pico cell Relay (20 dBm) (24-37 dBm) (20 dBm)
- 16. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Why Heterogeneous Networks? › Higher data rates need denser infrastructure – …but user distribution and traffic density is often non-uniform › Alt 1 – Denser "macro cells" – Not cost efficient (in case of non-uniform traffic) – Issues with rapidly moving users – frequent handovers › Alt 2 – Heterogeneous Networks – Macro for coverage, pico for capacity – Semi-static, or dynamic, sharing of resources across macro - pico layers
- 17. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 How do they defer from Existing types of networks? › In its simplest form similar to Hierarchical Cell Structures (HCS)... › ...but – LTE offers/will offer tools for efficient macro-pico/femto resource sharing and interference coordination – Different types of small base stations – Possibly mixing open access and closed subscriber group small base stations in the same spectrum › Open Access (OA) – "Any user" can connect to the small (pico) cell › Closed Subscriber Group (CSG) – Only a subset of users can connect to the small (femto) cell (e.g. home eNodeB)
- 18. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Example HetNet Realizations • Conventional loosely coordinated pico or home eNB deployment – Individual pico / home eNBs, independent from overlaid macro layer – Operator or end-user driven – Rudimentary/basic coordination • Tightly coordinated pico deployment – Individual pico eNB – Operator driven – Allows for any type of coordination from semi-static allocation of resources till COMP, or "SHO-like" schemes • Radio Remote Unit (RRU) deployment (centralized processing) – Pico layer tied to overlaid macro layer – Allows for tight coordination • Relay deployment – Basic Coordination
- 19. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Interference description › Significant imbalance in the DL Tx powers of macro eNB & low power NBs › Scenario: Open Access Picos, No Extended Range, No Interference Management – Same interference situation as within homogeneous networks › Scenarios with pico cells using extended range or with CSG low power nodes – Interference problems on DL Control Channel Region – Interference management mechanisms need some new thinking › E.g, CA, Almost Blank Subframes (ABSF) Pico eNBMacro eNB UL pathloss based cell edge DL received signal strength cell edge
- 21. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Interference Management › Downlink carrier aggregation – Rel-10 carrier aggregation used for interference management › Macro and pico operate DL control signaling on different primary component carriers › Macro and pico operate data on same carrier frequencies – All building blocks are present in Rel-10 › "Same carrier" ("single carrier", "co-carrier") – Macro and pico operate on the same carrier frequency – Larger coordination effort
- 22. Interference Management for heterogeneous networks Carrier aggregation
- 23. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Downlink Carrier Aggregation › Data – Can use multiple component carriers as determined by ICIC › L1 Control signaling (including broadcast, synchronization channels & reference symbols) – Interference management in frequency domain – Macro › f1: normal operation (primary component carrier) › f2: low/zero-power for control (secondary component carrier) – Pico › f1: low or zero power for control › f2: normal operation – Macro CRS should preferably collide with pico CRS Macro Pico f1 f2 f1 f2
- 24. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 Downlink Carrier Aggregation › All major building blocks are present in Rel-10 CA-based heterogeneous network support › Need to split overall spectrum into multiple carriers – Rel-8/9 UEs can only access one component carrier can access pico cell but do not benefit from all available spectrum › Pico CRS can be severely interfered – Need for mechanisms removing interference originating from neighbor macro cells
- 25. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 CA FOR HETNETS – PRACTICAL ISSUES › Time alignment between cell layers assumed – Known which REs in pico that are heavily interfered from macro (control, RS, synchronization & broadcast channels) – Can be beneficial to ensure cell-specific RS ‘collide’ between layers One subframe Control signaling Cell-specific reference symbols Pico REs with strong interference Macro layer Pico layer f1 PCC SCC
- 27. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 "Same-Carrier" Approach › L1 Control signaling (PDCCH, PCFICH) – interference avoidance only in time domain › Almost blank subframes (ABSF) - One layer does not transmit L1 control signaling within given subframes Macro Pico f1 f1
- 28. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 ALMOST BLANK SUBFRAMES (absf) › During certain subframes – no L1 control signaling is transmitted – CRS are still present › Data not transmitted during ABSF (neither DL or UL) – Resources not fully utilized › Cross subframe scheduling might improve this non-efficient use of resources
- 29. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 INTERFERENCE MANAGEMENT FOR DATA › Mechanisms devised for homogeneous networks are applicable within heterogeneous networks as well – ICIC based on › Random Index Frequency Start › Fractional Frequency Reuse – Fractional Power Control – Joint scheduling – IRC – SIC › Adjustment of these schemes to the heterogeneous deployments is needed
- 30. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01 SUMMARY › Interference Management Mechanisms – Based on › RRM › Advanced Receivers › Coordination between neighbor base stations › Combination of the above – Deployments of heterogeneous networks sets new challenges & requires new thinking for interference management techniques
- 31. © Ericsson AB 2011 | Ericsson External | KTH | Wireless Seminar In Signals, Sensors, Systems | Intercell Interference Within 3GPP Rel. 10 | 2011-03-01