Full-duplex Wireless: From Experiments to Theory

Transcription

1 Full-duplex Wireless: From Experiments to Theory Achaleshwar Sahai, Melissa Duarte #, Evan Everett, Jingwen Bai, Gaurav Patel, Chris Dick* and Ashu Sabharwal Department of ECE Rice University # Now at EPFL/UCLA *Xilinx, Inc.

2 Half-duplex for Bi-directional Cellular FDD, TDD WiFi TDD Uplink and downlink on different bands or time-slots Difficult to transmit & receive in the same band at the same time.

3 Recent Full-duplex News Node 1 x 1 DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn Rice (Duarte et. al, 2010) Rice, AT&T (Duarte et. al, 2012) Stanford 1 (Choi et. al, 2010) l l phase shifter splitter Stanford II (Jain et. al, 2011) Princeton, NEC (Aryafar et. al, 2012)

4 Today s Story Line

5 Today s Story Line Experimental Full-duplex Explain the performance (Characterize bottlenecks) Distributed Full-duplex 2012-

6 Five 5MD* Sessions 2013 Distributed Full-duplex Passive Cancellation Bottleneck 2012 Q&A History Analog Canceller Bottleneck Main Challenge Main Techniques *5MD = 5 Minutes & Done

7 Main Challenge of Full-duplex Node 1 Node 2 DAC RF UP RF UP DAC ADC RF Down RF Down ADC Self-interference is huge since h I >> h S dB larger than signal of interest, depending on inter-node distance

8 Bottleneck in Implementation Node 1 Node 2 DAC RF UP RF UP DAC ADC RF Down RF Down ADC Analog-to-Digital Conversion is the bottleneck

9 Analog to Digital Conversion RF Down ADC

10 Analog to Digital Conversion Quantization of sum signal

11 Digital Cancellation Alone Insufficient: Signal of Interest Swamped Quantized sum signal Signal of interest Only a few bits for the signal of interest Most baseband receivers need at least 6 bits For 12 bit ADC, INR(dB) > SNR(dB) + 35 db implies selfinterference is too strong

12 Digital Cancellation Alone Insufficient: Signal of Interest Swamped Quantized sum signal Signal of interest Need to reduce strength of self-interference before ADC

13 Use Better ADCs Make ADC more capable? No Moore s law for ADC Limited by thermal noise No consensus on limits of current technology But consensus that progress is very slow Fundamentally limited by Heisenberg s uncertainty Walden 1999 Krone and Fettweis, 2009

14 Five 5MD Sessions 2013 Distributed Full-duplex Passive Cancellation Bottleneck 2012 Q&A History Analog Canceller Bottleneck Main Challenge Main Techniques

15 Recent Full-duplex Designs Node 1 x 1 DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn Rice (Duarte et. al, 2010) Rice, AT&T (Duarte et. al, 2012) Stanford 1 (Choi et. al, 2010) l l phase shifter splitter Stanford II (Jain et. al, 2011) Princeton, NEC (Aryafar et. al, 2012)

16 Main Principle of All Techniques Engineer Self-interference Channel

17 Self-Interference Channel Tx h I x[n] h S Rx baseband x[n] RF Up Tx Antenna h I Rx Antenna

18 Engineering h I : Passive Suppression x[n] RF Up Tx Antenna h I Rx Antenna Design antennas to increase propagation loss of h I

19 Engineering h I : Active Cancellation Self-interference signal is known Exploit it to cancel interference Many methods since 1998

20 Engineering h I : Active Analog Cancellation x[n] RF Up h I Cancellation Path + 0 Objective is to achieve exact 0 at the Rx antenna Cancellation path = negative of interfering path These techniques need analog parts

21 Engineering h I : Active Digital Cancellation x[n] RF Up h I + RF Down Baseband Cancellation Path Cancel interference at baseband Conceptually simpler requires no new parts Useless if interference is too strong (ADC bottleneck)

22 Rice WARP (warp.rice.edu) V1 V2 Up to 4-antenna MIMO per node Open-source design flows Operational networks out-of-the-box 125+ worldwide users, 140+ papers V3 (Mango)

23 Rice MIMO Full-duplex Median 85dB of total self-interference suppression [Duarte et. al, Dissertation and Journal 2012, arxiv ] 20 MHz OFDM implementation Antennas on a laptop Analog cancellation Digital cancellation R1/ T3 T2 T1/ R2

24 Rice MIMO Full-duplex Median 85dB of total self-interference suppression [Duarte et. al, Dissertation and Journal 2012, arxiv ] 20 MHz OFDM implementation Antennas on a laptop Analog cancellation Digital cancellation R1/ T3 T2 T1/ R2 5-node testbed with line-of-sight, 1, 2 and 3 walls links 5 PHY: 1x1, 2x1 Full-duplex, 2x1, 3x1 and 2x2 Half-duplex Month-long trials in regular office environments

25 Rate Performance 2x1 Full-duplex Rate > 2x2 Half-duplex for [15-30] db WiFi designed for [0,30] db 5 4 Ergodic Rate (bps/hz) FD1X1 Experiments FD2X1 Experiments HD2X1 Experiments HD3X1 Experiments HD2X2 Experiments FD1X1 Linear Fit FD2X1 Linear Fit HD2X1 Linear Fit HD3X1 Linear Fit HD2X2 Linear Fit SNR (db)

26 I am Convinced Full-duplex not just a headline Additional reduction in self-interference means higher rates How do we reduce self-interference?

27 Five 5MD Sessions 2013 Distributed Full-duplex Passive Cancellation Bottleneck 2012 Q&A History Analog Canceller Bottleneck Main Challenge Main Techniques

28 Node 1 x 1 All Analog Cancellers Are Imperfect. Question 1: Why? Why these numbers? DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn 34dB 30dB l l phase shifter splitter 45 db 45 db

29 Total Cancellation < Sum of Max Question 2: Why? x[n] h I Analog Canceller ADC Digital Canceller Digital cancellation by itself achieves ~30dB Analog is 30-45dB But total is closer to 35-50dB, not 60-75dB More analog cancels digital cancels less See Sahai, Patel, Dick and Sabharwal, 2012 (arxiv )

30 Analog Cancellers Bottleneck Phase Noise

31 Engineering h I : Analog Cancellation x[n] RF Up h I Cancellation Path + 0 Objective is to achieve exact 0 at the Rx antenna Cancellation path = negative of interfering path These techniques need analog parts

32 At-antenna Analog Cancellation RF Up h I x[n] + f( ) RF Up Pre-mixer x[n] RF Up h I + Post-mixer RF Up g( )

33 Classifying Recent Designs Node 1 x 1 DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn Pre-mixer Post-mixer l l phase shifter splitter Post-mixer Post-mixer

34 Question 1: Why Rice Analog Cancels 34dB? Errors in up-conversion RF Up h I x[n] + f( ) RF Up Residual Errors in implementing ideal f( )

35 Single-tap Delay Channel RF Up x[n] + f( ) RF Up h (t )

36 Errors in Up-conversion: Phase Noise x[n] + j(!t+ (t)) e x h (t ) f( ) x All oscillators are imperfect, Random phase variations

37 Perfect Channel Estimate x[n] j(!t+ (t)) + e x f( ) x h (t ) residual f( ) = h (t )e j! Same phase noise goes through different channels residual = hx(t )e j!(t ) e j (t ) e j (t) jhx(t )e j!(t ) ( (t ) (t)) time-varying

38 Perfect Channel Estimate x[n] j(!t+ (t)) + e x f( ) x h (t ) residual f( ) = h (t )e j! Same phase noise goes through different channels residual = hx(t )e j!(t ) e j (t ) e j (t) jhx(t )e j!(t ) ( (t ) (t)) E residual 2 2 h 2 2 (1 R ( )) + 2 noise

39 No Channel Estimation Error Cancelation (in db) SigGen! 1 10 log WARP (in degrees)

40 Measured Versus Predicted 70 Cancelation (in db) X SigGen Pre-mixer: 56dB ( perfect )! 1 10 log WARP (in degrees) X Pre-mixer: 36dB ( perfect ) Experiments over wire ( near-perfect channel estimates)

41 Impact of Channel Estimation Error 70 Cancelation (in db) X X SigGen Pre-radio: 56dB ( perfect ) Duarte 10 : 50dB (imperfect)! 1 10 log WARP (in degrees) X X Pre-radio: 36dB ( perfect ) Duarte 10: 34dB (imperfect)

42 Possible to Circumvent Phase Noise? x h (t ) x[n] + j(!t+ (t)) e x g( ) g( ) = h (t ) In theory, possible to achieve zero residual.

43 Most post-radio report 30-45dB cancellation (not infinite db) Node 1 x 1 DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn Pre-mixer 34dB Post-mixer 30dB l l phase shifter splitter Post-mixer 45 db Post-mixer 45 db

44 Recall the Numbers Node 1 x 1 DAC BB Tx RF Radio c 1 DAC BB Tx Radio RF h z h ab y 1 ADC BB Rx Radio RF + Antenn 34dB Pre-mixer Post-mixer l l phase shifter splitter 45 db Post-mixer WARP Post-mixer 45 db

45 Pre Versus Post 70 Cancelation (in db) X X SigGen Pre-radio: 56dB ( perfect ) Duarte 10 : 50dB (imperfect)! 1 10 log WARP (in degrees) X X X Post-radio: 50dB (narrowband) Stanford 11: 45dB (wideband with flat fading) Not measured by us Pre-radio: 36dB ( perfect ) Duarte 10: 34dB (imperfect) Sahai, Patel, Dick, Sabharwal, 2012 (arxiv )

46 Five 5MD Sessions 2013 Distributed Full-duplex Passive Cancellation Bottleneck 2012 Q&A History Analog Canceller Bottleneck Main Challenge Main Techniques

47 Rice MIMO Full-duplex Median 85dB of total self-interference suppression [Duarte et. al, Dissertation and Journal 2012, arxiv ] 20 MHz OFDM implementation Antennas on a laptop Analog cancellation Digital cancellation R1/ T3 T2 T1/ R2 5-node testbed with line-of-sight, 1, 2 and 3 walls links 5 PHY: 1x1, 2x1 Full-duplex, 2x1, 3x1 and 2x2 Half-duplex Month-long trials in regular office environments

48 Rice MIMO Full-duplex Median 85dB of total self-interference suppression T2 65 db Passive 20 db Active R1/ T3 T1/ R2 Passive dominates the total cancellation!

49 Self-Interference Channel Local scattering Tx Direct path Rx Full-duplex Node

50 Self-Interference Channel Local scattering Tx Direct path Rx Full-duplex Node Can actively address this

51 Option 1: Antenna Placement Tx Rx Tx d Rx Possibility for mobile nodes (Duarte, et. al. 2012)

52 Option 1I: RF Absorbers Tx Rx Full-duplex Node Possibility for infrastructure nodes

53 Option 1II: Cross Polarization H V Tx Rx Full-duplex Node Possibility for mobile & infrastructure nodes

54 Option 1V: Directional Communication Tx Rx Full-duplex Node Possibility for infrastructure nodes

55 Infrastructure Nodes B AP RF Absorber Dual-polarized directional antennas

56 Tests 50 cm 50 cm 35 cm 50 cm 50 cm 50 cm 50 cm 35 cm 35 ion I: 90 beamwidth (b) Configuration II: 90 beamwidth (c) Configuration III: 90 beamwidth Configuration I: 90 beamwidth (b) Configuration II: 90 beamwidth (c)separation, Configuration 90(a)beam separation, antennas, 60 beam separation, antennas,(c) 60 Configuration beam figuration I: 90 beamwidth (b) Configuration II: 90 beamwidth III: 90 III be antennas, beam separation, antennas, beam separation, antennas, 60sepa bea enna 50 cm antenna separation. 35 cm antenna separation. nas, separation. 90 beam90 separation, antennas, 60 beam60separation, antennas, 60 beam 50 cmseparation. antenna separation. 50 cmseparation. antenna separation. 35 cm antenna se m antenna 50 cm antenna 35 cm antenna separation D : Directional DA : Directional + Absorber DC : Directional + Cross-pol DCA : Directional + Cross-pol + Absorber 50 cm (d) Configuration IV: 50 cm 50 cm Omnidirectional antennas, Configuration IV: 50 (d) cm Configuration antenna(d)separation. IV: 35 cm (e) Configuration V: 35 cm Omnidirectional antennas,35 cm (e) Configuration V: 35 cm antenna separation. (e) Configuration V: Omnidirectional antennas, Omnidirectional antennas, Omnidirectional antennas, Omnidirectional antennas, 50 cm antenna separation. 35 cm antenna separation. cmthe antenna separation. 35 cmwe antenna separation. ures evaluated50 in passive suppression characterization. do not designate one antennas

57 Reflections are the Bottleneck 80 NASA Anechoic Chamber 74 db 70 A Very Reflective Room Room Passive Suppression (db) Passive Suppression (db) db 20 Config I Config II Config III Reflections harder to control for mobile Easier for infrastructure nodes Stationary Carefully placed 20 Config I Config II Config III

58 We Tried This Up to 120 meters

59 Self-Interference Close to Noise Floor w/o Cross pol: passive w/o Cross pol: passive + active w/ Cross pol: passive w/ Cross pol: passive + active DCA + Active Mean 95dB+ CDF Self Interference Supression (db) Everett, Sahai, Sabharwal, 2013 (arxiv )

60 Five 5MD Sessions 2013 Distributed Full-duplex Passive Cancellation Bottleneck 2012 Q&A History Analog Canceller Bottleneck Main Challenge Main Techniques

61 First Potential Use Case Full-duplex Infrastructure I Half-duplex M 1 M 2 Inter-node Interference Half-duplex

62 New Bad News Inter-node Interference Very weak Very strong Multiplexing gain New bad news! Dead Zone Strength of Inter-node Interference

63 New Question How do we achieve multiplexing gain of 2? (Get the full-duplex benefit)

64 Compare These Two Scenarios I I M M 1 M 2 Tx and Rx are co-located Can we mimic it here?

65 Mobile Devices Today Cellular Band: 800, 850, 900, 1800, 1900, 2100 MHz WiFi : 2.4GHz and 5GHz iphone 5

66 Add Side Channel: ISM-in-Cellular I Cellular M 1 M 2 ISM

67 Near-optimal Scheme: Bin-and-cancel I Cellular M 1 M 2 ISM Use ISM side-channel to cancel the main channel interference Finite bit optimal for all SNR regimes Bai and Sabharwal, arxiv , December 2012

68 Parameter of Interest I Cellular M 1 M 2 ISM Bandwidth Ratio B = BW side BW main

69 B = 0.5 Red: Bin-and-cancel Multiplexing gain Blue: Decodeand-cancel 50% Cyan: Best achievable scheme without side channel log INR SNR

70 B ~ 5 Red: Bin-and-cancel Multiplexing gain Blue: Decodeand-cancel Cyan: Best achievable scheme without side channel log INR SNR Bai, Sabharwal, 2012 (arxiv )

71 So What Next? (argos.rice.edu) Lots of interesting ideas Both on infrastructure and mobile side -+./01*% -'./0'**+0!"#$""%&!"#$% &'()*+, 5+6#)& 7.*1+$#..1$*) 24.$ '()*+(,-*(#.!"#$%& '() 64-element Argos!"#$%& '()*+(,-*(#. /*01+.1*& 23(*$0

72 Questions & Comments? JSAC Special Issue on Full-duplex Wireless, Oct WARP Project - ARGOS Project