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Objectives and Challenges

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This article discusses the objectives, challenges, and trends in 5G technology, including higher data rates, lower latency, V2X applications, smaller cells, more antennas, and spectrum sharing models.

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Objectives and Challenges

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  1. Michael Honig Department of EECS Northwestern University Objectives and Challenges March 2019 5GWorkshop, Ottawa

  2. Cellular Evolution Applications voice, moderate data rates voice, high-speed data, limited video IoT V2X AR,VR voice, low capacity voice,limited data 2020 1980 1990 2000 2010 2GDigital CDMA 1GAnalogFDMA 3G CDMAScheduling 4G/LTE OFDMAMIMO 5G ?? Technologies 5G Workshop, Ottawa, March 2019

  3. 5G Performance Objectives • Higher data rates • 3-4 times spectral efficiency of 4G • Data rates >100 Mbps up to several Gbps • Lower latency (~1 ms) • V2X, robotics • High connection density (IoT) 3GPP “New Radio (NR)” standard under development. 5G Workshop, Ottawa, March 2019

  4. 4G Foundations and Extensions • OFDMA • Dynamic uplink/downlink TDD • Mini-time slots for low latency • Multi-user MIMO • Channel estimation, pilot management • Improved coding schemes (LDPC, polar codes) • Significant but modest improvements 5G Workshop, Ottawa, March 2019

  5. 5G Trends • Smaller cells • More antennas • More spectrum 5G Workshop, Ottawa, March 2019

  6. 5G Trends • Smaller cells  Heterogeneous networks • More antennas  Massive MIMO • More spectrum • Millimeter wave • Sharing (CBRS) 5G Workshop, Ottawa, March 2019

  7. 5G Trends • Smaller cells  Heterogeneous networks • More antennas • More spectrum 5G Workshop, Ottawa, March 2019

  8. Spectrum Management: Propagation • Coverage is easy • Interference management is difficult Low Freqs. (< 2 GHz) High Freqs.(> 5 GHz) Frequency  • Coverage is difficult • Interference management is easy 5G Workshop, Ottawa, March 2019

  9. Shrinking Cells Low Freqs. (< 2 GHz) High Freqs.(> 5 GHz) Frequency  • Large-cells • Coordinated interference management • Expensive infrastructure • Small-cells/WiFi • Distributed interference management (random access) • Inexpensive 5G Workshop, Ottawa, March 2019

  10. Spectrum Sharing Models • Exclusive use (licensed) • Encourages investment in interference management Low Freqs. (< 2 GHz) High Freqs.(> 5 GHz) Frequency  • Open access • Public (unlicensed) • Private(licensed) 5G Workshop, Ottawa, March 2019

  11. Spectrum Sharing Models • Large-cells • Coordinated interference management • Expensive infrastructure Cellular (< 2 GHz) Dynamic Spectrum Markets? Open Access (> 5 GHz) Frequency  • Femto-cells/WiFi • Distributed interference management (random access) • Inexpensive • Small-cells • Light interference management • Spectrum servers • Rapid transactions 5G Workshop, Ottawa, March 2019

  12. Heterogeneous Network How to do interference management? Source: Qualcomm 5G Workshop, Ottawa, March 2019

  13. Offline Frequency Planning (1G-4G) 5G Workshop, Ottawa, March 2019

  14. Heterogeneous Spectrum Allocation Macro BTS Pico BTS 5G Workshop, Ottawa, March 2019

  15. 5G Trends: Spectrum • Smaller cells • More antennas  Massive MIMO • More spectrum 5G Workshop, Ottawa, March 2019

  16. Multiple Antennas (MIMO) Substream 1 Single-user (SU)-MIMO Multi-Channel Detector Estimated Data Substream M Multi-user (MU)-MIMO • Multiple antennas at transmitter and receiver(s). • Data rate (Shannon capacity) is proportional to M (rich scattering). M antennas • LTE, WiFi (802.11ac) • Assumes that the transmitter knows the channel. N antennas frequency reuse across beams 5G Workshop, Ottawa, March 2019

  17. Massive: ≥ 16 antennas,sub-6 GHz. Source: techblog.comsoc.org 5G Workshop, Ottawa, March 2019

  18. Massive MIMO: Challenges • Channel estimation: lots of channels to estimate! • 4G/FDD with codebook feedback not good enough 5G Workshop, Ottawa, March 2019

  19. Beam-scanning Protocols • BTS transmits on designated beams. • Mobile determines best beam, transmits in reverse direction. X X X X X X X X X X X X X X X X Base Station 5G Workshop, Ottawa, March 2019

  20. Beam-scanning Protocols • BTS transmits on designated beams. • Mobile determines best beam, transmits in reverse direction. • BTS selects best arrival beam. arrival path X X X X departure path X X X X X X X X X X X X Base Station 5G Workshop, Ottawa, March 2019

  21. Beam-scanning Protocols • BTS transmits on designated beams. • Mobile determines best beam, transmits in reverse direction. • BTS selects best arrival beam. BTS beam mobile beam X X X X X X X X X X X X X X X X Base Station 5G Workshop, Ottawa, March 2019

  22. Massive MIMO: Channel Estimation • Beam-scanning • Exploit TDD, channel reciprocity • Multi-cell scenario becomes challenging inter-cell interference 5G Workshop, Ottawa, March 2019

  23. 5G Trends • Smaller cells • More antennas • More spectrum • Millimeter wave • Sharing (CBRS) 5G Workshop, Ottawa, March 2019

  24. mmWave: motivation 13.85 GHz licensed bands • About 30 GHz of available bandwidth • Acceptable attenuation for cellular applications (~28 GHz) • Initial applications: fixed wireless (backhaul) 14 GHz (unlicensed) 40 57 38.6 71 76 81 86 27.5 28.35 37 6 GHz 5G Workshop, Ottawa, March 2019

  25. mmWave: challenges 13.85 GHz licensed bands 14 GHz (unlicensed) 40 57 38.6 71 76 81 86 27.5 28.35 37 6 GHz • Need focused beams to compensate for attenuation 5G Workshop, Ottawa, March 2019

  26. mmWave: Focused Beams 5G Workshop, Ottawa, March 2019

  27. mmWave: challenges 13.85 GHz licensed bands 14 GHz (unlicensed) 40 57 38.6 71 76 81 86 27.5 28.35 37 6 GHz • Need focused beams to compensate for attenuation • All-digital beamforming not practical 5G Workshop, Ottawa, March 2019

  28. Hybrid (Analog/Digital) Beamformer • “Phased-array” front-end controls beam directions • Reduces RF chains Analog phase shifters Baseband Precoding/ Combining RF Chain … x1 … … xK RF Chain … 5G Workshop, Ottawa, March 2019

  29. Hybrid (Analog/Digital) Beamformer • Requires beam-sweeping for acquisition • Assumes channel sparsity Analog phase shifters Baseband Precoding/ Combining RF Chain … x1 … … xK RF Chain … 5G Workshop, Ottawa, March 2019

  30. mmWave: challenges 13.85 GHz licensed bands 14 GHz (unlicensed) 40 57 38.6 71 76 81 86 27.5 28.35 37 6 GHz • Need focused beams to compensate for attenuation • All-digital beamforming not practical • Acquisition, outage due to blockage • Limited coverage (cellular) 5G Workshop, Ottawa, March 2019

  31. Acquisition, Blockage Blocking requires re-acquisition via beam-sweeping. 5G Workshop, Ottawa, March 2019

  32. 5G Trends • Smaller cells • More antennas • More spectrum • Millimeter wave • Sharing (CBRS) 5G Workshop, Ottawa, March 2019

  33. CBRS Band Citizen’s Broadband Radio Services (CBRS) 100 MHz shared with naval radar incumbent. Technical standards developed by: 5G Workshop, Ottawa, March 2019

  34. Three-Tier Sharing priority President’s Council of Advisors on Science and Technology (PCAST) report 2012 5G Workshop, Ottawa, March 2019

  35. Spectrum Access System (SAS) 5G Workshop, Ottawa, March 2019

  36. Challenges • Coordination, interference management • Protecting incumbent (navy) • Security, privacy • Dynamic assignments • PAL constraints may limit investment • Skews incentives towards open access 5G Workshop, Ottawa, March 2019

  37. Modeling Incentives • Incumbent service providers (SPs) have licensed bands. … SP 1 SP 2 SP 3 frequency 5G Workshop, Ottawa, March 2019

  38. Modeling Incentives: Open Access • Incumbent service providers (SPs) have licensed bands. • All incumbents and new entrants have access to open access (unlicensed) band. • How does this additional spectrum affect total welfare? … open access SP 1 SP 2 SP 3 frequency 5G Workshop, Ottawa, March 2019

  39. Model Assumptions • Each SP competes for pool of customers by announcing prices for licensed and open access bands. • Customers choose SP (band) based on Total price = Announced price + Congestion cost … open access SP 1 SP 2 SP 3 frequency 5G Workshop, Ottawa, March 2019

  40. Total Welfare Adding a small amount of unlicensed spectrum can decrease total welfare (consumer + SP revenue). … open access SP 1 SP 2 SP 3 frequency T. Nguyen, H. Zhou, R. Berry, MH, R. Vohra. "The Cost of Free Spectrum." Operations Research 64.6 (2016): 1217-1229. 5G Workshop, Ottawa, March 2019

  41. Conclusions • 5G objectives are ambitious • Involves significant changes to 4G/LTE standard • New Radio  New Services! 5G Workshop, Ottawa, March 2019

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