Trends in Small Cell Enhancements in LTE Advanced

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Trends in Small Cell Enhancements in LTE Advanced

  1. 1. Takehiro Nakamura, Satoshi Nagata, Anass Benjebbour, and Yoshihisa KishiyamaNTT DOCOMO, INCTang Hai, Shen Xiaodong, Yang Ning, and Li NanChina Mobile Research Institute7. Mar. 2012Bo-Min SeoTrends in Small Cell Enhancementsin LTE Advanced
  2. 2. Contents• Introduction• Deployment Scenarios• Technical Requirements• Operator Views on Small Cell Enhancements– NTT DOCOMO– CMCC• Conclusion2
  3. 3. Introduction• Currently, 4th generation wireless access systems usingLong Term Evolution (LTE) are being deployed by manyoperators worldwide in order to offer faster access withlower latency and more efficiency than 3G/3.5G• The anticipated future traffic growth is so tremendousthat there is a vastly increased need for further networkdensification using small cells to handle the capacityrequirements3
  4. 4. Introduction• Recent trends in mobile data usage– In 2011 alone, the volume of mobile data traffic grew 2.3 timeswith a nearly threefold– Many recent forecasts project mobile data traffic to grow morethan 24-fold between 2010 and 2015, and thus beyond 500-foldin 10 years (2010-2020)• Further reduction in the deployment cost of small cellswill be a necessity in the future• The key areas of enhancement– Capacity increase– Energy saving and cost efficiency– Support for diverse application and traffic types– Higher user experience/data rate– Backhaul enhancement4
  5. 5. Deployment Scenarios5standalone densesparse outdoor indoorwith macro cell
  6. 6. Deployment Scenarios• With & Without macro coverage– Cooperative mechanisms between macro cell and small cell, aswell as among small cells, may be beneficial• Outdoor & Indoor– The main difference between outdoor and indoor scenarios ismobility support– 3GPP has decided to focus on low speeds (0~3km/h) for indoor,medium speeds (up to 30km/h) for outdoor scenarios• Distribution of small cells– A single or few small cell node(s) is/are sparsely deployed– A large number of small cell nodes are densely deployed• Synchronization– Synchronized and unsynchronized scenarios between smallcells as well as between small cells and macrocell(s)6
  7. 7. Deployment Scenarios• Backhaul– The link connecting the radio access network and core network– Ideal backhaul• Very high throughput and very low latency• Dedicated point-to-point connection using optical fiber• Line of sight (LOS) microwave– Non-ideal backhaul• Typical backhaul widely deployed today• xDSL, non-LOS microwave• Backward compatibility– The possibility for legacy (pre-Rel 12) user equipment (UE) toaccess a small cell node/carrier should be guaranteed– The ability for legacy UE to benefit from small cell enhancementscan be considered7
  8. 8. Deployment Scenarios• Spectrum– Different frequency bands are separately assigned to the macrolayer and small cell layers– The macro and small cell layers share the same carrier shouldbe considered (co-channel deployment)– Small cell enhancements should be applicable to all existing aswell as future cellular bands• Traffic patterns– In small cell deployment, the traffic will fluctuate greatly since thenumber of users per small cell node is typically not large due tothe small coverage area– The user distribution is very non-uniform and fluctuates betweenthe small cell nodes– The traffic could be highly asymmetrical, either downlink- oruplink-centric8
  9. 9. Technical Requirements• Deployment-related requirements– Enhanced small cells can be deployed by either operators orindependent users– Small cell enhancement should minimize signaling load toincrease numbers of small-cell nodes• Operational requirements– Solutions for different backhauls– Allowing for low-cost deployment, and low operation andmaintenance tasks (e.g. self-organizing network)– Allowing for reduced base station implementation cost9
  10. 10. Technical Requirements• Capability and performance requirements– Support increased user throughput for both downlink and uplinkgiven a reasonable system complexity– Keep a fair distribution of user throughput for both DL and UL ina scenario where the user distribution changes dynamically– Capacity per unit area to be as high as possible for given userand small cell distribution– Provide improved system performance with realistic backhauldelays– The benefits of allowing high-speed UE should be evaluated– Real-time services should be supported by small cellenhancement10
  11. 11. Operator Views on Small Cell Enhancements• NTT DOCOMO11Phantom CellEnhanced Discoveryand MobilityDynamic TDD andInterference CoordinationMassive MIMO
  12. 12. Operator Views on Small Cell Enhancements• Phantom Cell (Macro-assisted small cells)– Control plane (C-plane) and use data plane (U-plane) are split– C-plane of small cell, C-plane and U-plane of macro cell uselower frequency band– U-plane of small cell uses higher frequency band12
  13. 13. Operator Views on Small Cell Enhancements– Benefits of Phantom Cell• Phantom cell can significantly reduce the control signaling due to frequenthandover between small cells and macro cells and among small cells• Phantom cell can be maintained connectivity even when using small cellsand higher frequency bands• Phantom cell is able to provide further benefits such as efficient energysavings, lower interference and hence higher spectral efficiency• Enhanced discovery and mobility– Newly defined discovery signals which are transmitted by smallcells in a time-synchronized manner with macro DL signals– Small cells can transmit the discovery signals simultaneouslywith a relatively long transmission interval– UE attempts the detection of discovery signals from small cellsonly in a short time interval– Discovery signals robust against inter-cell interference and canreduce cell planning effort13
  14. 14. Operator Views on Small Cell Enhancements• Dynamic TDD and Interference coordination– Dynamic spectrum sharing between the UL and DL wouldprovide gains in terms of spectral efficiency compared to semi-static partitioning of the UL and DL• Massive MIMO (Further topic)– Massive MIMO with an active antenna system (AAS)– Antenna elements can be miniaturized, and more elements canbe placed in the same place → very narrow beams can beformed– Very narrow beamforming will be essential in higher frequencybands in order to support practical coverage areas for small cellsby compensating for the increased path loss14
  15. 15. Operator Views on Small Cell Enhancements15LTE-HiLink-Level ImprovementPerformance Gain Providedby Cell DensificationSupport of LargeBandwidth
  16. 16. Operator Views on Small Cell Enhancements• LTE-Hi (LTE enhancements for hotspot and indoor)– LTE-Hi ensure the future competitiveness of 3GPP tech. wheredenser networks, easy-to-deploy low-power nodes, newtechniques to improve the spectrum efficiency and throughput,and large bandwidth support– Autonomous configuration acquisition/coordination is essentialfor the operators to reduce the complexity of network planning– Coordination with overlaid macrocells could help to ease thedifficulties of mobility and connectivity when UE device aremoving– For high-speed UE device, they may be more appropriate toreside in macrocells to avoid unnecessary handover– Support of “any backhaul”• Optical fiber & Ethernet• Microwave systems for indoor and outdoor hotspots• xDSL & Fiber to the home (FTTH)• Cable TV16
  17. 17. Operator Views on Small Cell Enhancements• Link-Level Improvement– 256-QAM– Flexible UL and DL timeslot allocation• Performance gain provided by cell densification– Fast cell discovery– Handling of macro-layer/small cell information exchange• Support of large bandwidth– The total spectrum requirement is about 1700-2100 MHz of thespectrum for International Mobile Telecommunications in 2020– CMCC’s target bands are 1.5GHz, 3.3-3.4GHz, 3.4-3.6GHz, andabove 5GHz17
  18. 18. Conclusion• Detailed technical studies of requirement and scenariosfor small cell enhancement are proceeding from the startof 2013• Two LTE operators, NTT DOCOMO and CMCC, havedescribed the current status of the small cellenhancement as well as their views on future tech.evolution for small cells– NTT DOCOMO• Phantom Cell & Enhanced Discovery and Mobility• Dynamic TDD and Interference Coordination & Massive MIMO– CMCC• LTE-Hi & Link-Level Improvement• Performance Gain Provided by Cell Densification• Support of Large Bandwidth18
  19. 19. Thank you for attention!

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