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The Role of Small Cells in an LTE Environment

The Role of Small Cells in an LTE Environment






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  • Thanks for uploading this slide deck. It appropriately explains the role small cells are going to play in enhancing the capacity and coverage of LTE networks and also explains well how to manage them efficiently in order to derive maximum ROI from it.
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    The Role of Small Cells in an LTE Environment The Role of Small Cells in an LTE Environment Presentation Transcript

    • Small Cells Americas 2012 December 3, 2012 DallasThe Role of Small Cells in an LTE Environment Ahmad Armand, Ph.D. Staff Vice President CTO Office 1
    • Agenda LTE Capacity Limits LTE Advanced Why Small Cells Small Cell Architecture Options Small cell Deployment Options Interference Scenarios Interference Mitigation Conclusions 2
    • Enhancing Data Capacity LTE Capacity Limits: I I  Spectrum  Modulation order (QAM level) Q Q  MIMO order  Baseband Processing capability 16-QAM, 4 bits/symbol 64-QAM, 6 bits/symbol  Backhaul Capacity  UE capability  Traffic Mix MIMO order LTE Advanced Capacity Enhancements  Carrier Aggregation  Extension of MIMO techniques - Up to 8 layer transmission in downlink - Up to 4 layer transmission in uplink  Coordinated Multi-Point Transmission / Reception (CoMP)  HetNets  Relaying  SON techniques 3
    • LTE Advanced Carrier AggregationMulti-Antenna Enhancements Relaying 4
    • Homogenous Networks Base stations are in a planned layout Base stations have similar transmit and receive characteristics (same transmit power levels, antenna patterns, receivers , etc.) Locations of macro base stations are primarily chosen to maximize the coverage As the traffic demand grows and the RF environment changes, the network relies on cell splitting or additional carriers to overcome capacity and link budget limitations Site acquisition for macro base stations with towers becomes more difficult in dense urban areas. 5
    • Why Small Cells (1/3) 6
    • Why Small Cells (2/3) 7
    • Why Small Cells (3/3) 8
    • Heterogeneous Networks Macro Cell 60 W +Micro Cell Pico Cell 5-10 W 1-2 W Heterogeneous Networks DAS Femto Cell WiFI 9
    • Small Cell Architecture Options S1/X2 X2 RRH RRH X2 X2 CPRI CPRI Tight Coupling Loose Coupling Same vendor Same or different vendor?? Fiber interconnection Fiber/Microwave/Ethernet backhaul S1No Coupling S1 S1Same or different vendorFiber/Microwave/Ethernet backhaul 10
    • HetNet Deployment Options Microwave: LOS or NLOS 11
    • Same Frequency Operation Focus of LTE Release 10 & 11 InterferenceSelect node with highest DL power Expanded pico capture area“Conventional” node selection Extended off-loadingNot necessarily the cell with least path loss Enhanced uplink performanceReduced uplink performance Potentially severe DL interference fromSmall pico uptake area macro site to pico UEsSelect based on path lossNot necessarily the cell with strongest downlinkHigher downlink interference 12
    • Separate -Band Operation Focus of LTE Release 12Low band, e.g. AWS/PCS: macroHigh band, e.g. 3.5 GHz: small cell Macro Small cell 13
    • Small Cell Throughput Gains RP = Resource Partitioning“A Survey on 3GPP Heterogeneous Networks,” Aleksandar Damnjanovic, et al, IEEE wireless Communications, June 2011 14
    • Small Cell Interference Examples (c) (a) (b)(a) A macro user interfered by the small cell (b) A macro user causes severe interference towards the small cell (c) A small cell user is interfered by another small cell 15
    • Cell Selection and Range ExtensionSelect node with highest DL power“Conventional” node selectionNot necessarily the cell with least path lossReduced uplink performanceSmall pico uptake areaSelect based on path lossNot necessarily the cell with strongest downlinkHigher downlink interferenceExpanded pico capture areaExtended off-loading InterferenceEnhanced uplink performancePotentially severe DL interference frommacro site to pico UEs 16
    • Cell Range Extension Cell range extension enables small cell to capture more traffic Range extension is achieved by applying a bias to the RSRP of the small cell during cell selection The amount of bias is limited by the performance of control channels Improved uplink speed, leveraging small cell link budget Improved downlink speed, thanks to macro offload 17
    • Inter Cell Interference Coordination Load balancing between macro cell and small cell eICIC – Almost Blank Subframes (ABS) Improves control channel Micro performance Requires perfect synchronization Pico between macro and small cell X2 signaling used to exchange Regular Protected ABS information about protected subframe subframe subframe subframes Inter cell interference of control ePDCCH – Enhanced DL Control Channel channels avoided by coordinated placement of ePDCCH between Macrocell PDCCH Macrocell PDCCH Picocell PDCCH Picocell PDCCH macro and small cell layers UE will get control information localized PDCCH PDCCH PDCCH PDCCH within particular resource blocks The existing PDCCH may remain unchanged for the Release 10 and earlier UEs Placement of ePDCCH must be coordinated between cells, not specified in 3GPP 18
    • Reducing Interference via Cross Carrier Scheduling Carrier aggregation with cross carrier scheduling Avoids interference of PDCCH between macro and pico cells Partition component carriers in each cell layer into two sets, one set used for data and control and one set used mainly for data and possibly control signalling with reduced transmission power Macro UE Macro UE Pico UE • Control signaling on f1 and/or f2 • Control signaling on f1 • Control signaling on f2 • Data on f1 and/or f2 • Data on f1 and/or f2 • Data on f1 and/or f2 Pico Macro f1 f1 f2 f2 19
    • Conclusions Satisfying the ever-increasing demand for data requires continuous growth in the overall LTE system throughput LTE-Advanced multi-antenna and carrier aggregation techniques certainly enhance the LTE throughput, but, may not always be feasible or cost effective Small cells offer an alternative to pure macro cell splitting and play an important role in addressing capacity limitations A key challenge in small cell deployment is the management of interference among different cell types LTE Release 8/9 techniques along with small cell power management techniques could provide adequate interference management LTE-Advanced (Release 10 and beyond) provide further improvements in small cell interference management and the overall system throughput 20