Massive MIMO Full-duplex: Theory and Experiments

Transcription

1 Massive MIMO Full-duplex: Theory and Experiments Ashu Sabharwal Joint work with Evan Everett, Clay Shepard and Prof. Lin Zhong

2 Data Rate Through Generations Gains from Spectrum, Densification & Spectral Efficiency

3 In-band Full-duplex Wireless Base Station 2x Efficiency Mobile

4 In-band Full-duplex Wireless Base Station 2x Efficiency Downlink Uplink

5 Full-duplex Wireless: Two Main Interferences Self-interference Base Station Uplink Inter-node interference Downlink

6 Full-duplex Wireless: Focus on Self-Interference Self-interference Base Station 10 6 to10 9 x stronger Downlink Uplink

7 Self-interference bottleneck Rx Baseband Tx Baseband Rx RF Tx RF Self-interference Desired Signal

8 Self-interference bottleneck Rx Baseband Tx Baseband Overwhelms dynamic range Rx RF Tx RF Self-interference Desired Signal

9 Self-interference bottleneck Signal Distorted: Quantization noise Other effects Overwhelms dynamic range Rx Baseband Rx RF Tx Baseband Tx RF Self-interference Desired Signal

10 Self-interference suppression Rx Baseband Tx Baseband Rx RF Tx RF Analog Cx

11 Self-interference suppression Rx Baseband Tx Baseband Digital Cx Rx RF Tx RF Analog Cx

12 Two Experimental Demonstrations in 2010 Lots of well-deserved skepticism

13 Identifying The Bottlenecks 4302 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 11, NO. 12, DECEMBER αdc,i PT=0dBm α DC,i 8 90 P =5dBm T [f] (db) > 0) (%) αdc,i PT=10dBm αdc,i PT=15dBm αcon DC,i αlin DC,i Probability (α DC,i 4 α DC,i (db) cm m Node 2 Node RF combiner αac,i (db) αac,i [f] (db) Experimentally Fig. 5. Probability that digital cancellation after analog cancellation increases observed digital analog cancellation isthenot the total& amount of cancellation during a frame as a function cancellation achieved by analog cancellation. additive, and in fact, inversely related Fig. 4. Measurements of the average amount of cancellation achieved by digital cancellation and cancellation values computed based on the constant (db) = αcon αcon = and linear fit. The constant fit is equal to αcon DC,i ACDC,i AC,i lin lin 1.1 (db). We compute the linear fit using the equations for αac,i and αacdc,i. (db) = αlin (db) αlin (db) = The linear fit is equal to αlin DC,i ACDC,i AC,i lin lin λacdc (αac,i (db) βac )/λac + βacdc αac,i (db). analog cancellation. Results in Fig. 4 show that, in agreement achieves more than 32 db of cancellation, applying digital cancellation after analog cancellation is not effective since the probability that digital cancellation results in an increase of the total amount of cancellation is less than 50 % hence it

14 Identifying The Bottlenecks Phase noise x h (t ) x[n] j(!t+ (t)) + e f( ) x Experimentally observed digital & analog cancellation is not additive, and in fact, inversely related Culprit was transmitter phase noise, explained all our results

15 Practical Protocols with Experimental Demonstrations Multiple-antenna Full-duplex BS 2015 K u Inter-mobile Interference K d

16 Impact on Network Capacity Multiple-antenna Full-duplex BS K u Inter-mobile Interference K d

17 Multi-cell Analysis Promises Spectral Efficiency Gains Fig. 1: The full-duplex BS in each cell has antennas, and 2017 Network throughput gains, even with errors, half-duplex nodes and increased interference Asymptotically spectral efficiency approaches 2X With antenna gains approaches 1.8X (5G array sizes)

18 Full-duplex in Wireless and Wireline 3GPP full-duplex backhaul Cable Labs: next-gen cable modems FierceWireless, Sept 15 CableLabs, Feb 16

19 New Headache Too Much Analog! Complex analog circuity Scales with square of array size Ill-suited for large arrays Rx Baseband Digital Cx Rx RF Analog Cx Tx Baseband Tx RF

20 All-digital" Full-duplex (no new analog)? Must prevent RF saturation Rx Baseband Digital Cx Rx RF Tx Baseband Tx RF

21 Goal: All-digital Full-duplex Architecture via Beamforming Rx Baseband Digital Cx Rx RF Tx Baseband Tx Beamforming Tx RF

22 Questions to Answer Rx Baseband Digital Cx Rx RF Tx Baseband Tx Beamforming Tx RF 1. In what conditions is all-digital FD feasible? 2. What are practical algorithms for all-digital FD?

23 Questions to Answer Rx Baseband Tx Baseband Digital Cx Rx RF Tx Beamforming Tx RF 1. In what conditions is all-digital FD feasible? Answer with infotheoretic analysis 2. What are practical algorithms for all-digital FD? Answer with design and experiment

24 Components of Self-Interference Direct-path Rx Base station Tx Backscattered Everett, Sahai and Sabharwal Passive Self-interference Suppression For Full-duplex Infrastructure Nodes in IEEE Trans. Wireless Comm, 2014.

25 Experimental Evidence for Backscattering Room Anechoic Everett, Sahai and Sabharwal Passive Self-interference Suppression For Full-duplex Infrastructure Nodes in IEEE Trans. Wireless Comm, 2014.

26 The Challenge of Backscattering Direct-path Rx Base station Tx Backscattered Direct-path can be passively suppressed Backscattering becomes bottleneck Everett, Sahai and Sabharwal Passive Self-interference Suppression For Full-duplex Infrastructure Nodes in IEEE Trans. Wireless Comm, 2014.

27 Can we do a better job of spatial isolation in a backscattering environment? Yes, but there is a catch!

28 Half-duplex Spatial Multiplexing Base station Time slot 1 Rx Tx Downlink Uplink

29 Half-duplex Spatial Multiplexing Base station Time slot 2 Rx Tx Uplink Uplink DoF Downlink DoF = 2 data streams 2 time slots = 1 = 2 data streams 2 time slots = 1 Downlink

30 Full-duplex Spatial Multiplexing Base station Rx Tx Downlink Uplink The catch: beamformed suppression can cost spatial multiplexing

31 Full-duplex Spatial Multiplexing Base station Rx Tx Downlink Uplink How do we balance beamformed suppression and spatial multiplexing? Signal-scale Analysis of DoF

32 Rate Region for Wireless Full-duplex Up Base station Rx Tx Down Downlink degrees-of-freedom Ideal full-duplex Uplink degrees-of-freedom

33 Choosing the Model Need tractable model, captures the physics Two key aspects to model Antenna design Scattering

34 Modeling Antennas Rx Base station Tx Poon, Broderson, and Tse. Degrees of freedom in multiple-antenna channels: a signal space approach IEEE Trans Info Thry. Uplink Downlink

35 Modeling Antennas Rx Base station Tx Poon, Broderson, and Tse. Degrees of freedom in multiple-antenna channels: a signal space approach IEEE Trans Info Thry. Uplink Downlink

36 Modeling Scattering Rx Base station Tx Poon, Broderson, and Tse. Degrees of freedom in multiple-antenna channels: a signal space approach IEEE Trans Info Thry. Uplink Downlink

37 Modeling Scattering Rx Base station Tx Poon, Broderson, and Tse. Degrees of freedom in multiple-antenna channels: a signal space approach IEEE Trans Info Thry. Backscattering intervals Uplink Forward-scattering intervals Downlink

38 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

39 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

40 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

41 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

42 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

43 Solving the Degrees-of-freedom Tradeoff Everett and Sabharwal, Spatial Self-interference Isolation for In-band Fullduplex Wireless, Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

44 When, and By How Much, Is Full-duplex Better? Up Base station Rx Tx Down Downlink degrees-of-freedom? Uplink degrees-of-freedom

45 If scattering overlapped, and base station arrays no larger than mobile arrays, no gain Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

46 Gain proportional to non-overlap between backscattering forward scattering Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

47 Gain proportional to non-overlap between backscattering forward scattering Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom

48 Further improve full-duplex with larger arrays at base station Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom Leverage extra DoFs for nulling

49 Further improve full-duplex with larger arrays at base station Up Base station Rx Tx Down Downlink degrees-of-freedom Uplink degrees-of-freedom Leverage extra DoFs for nulling

50 Further improve full-duplex with larger arrays at base station ( Massive MIMO Regime ) Up Base station Rx Tx Down Downlink degrees-of-freedom Full duplex Uplink degrees-of-freedom

51 Questions to Answer Rx Baseband Tx Baseband Digital Cx Rx RF Tx Beamforming Tx RF 1. In what conditions is all-digital FD feasible? Answer with infotheoretic analysis 2. What are practical algorithms for all-digital FD? Answer with design and experiment

52 Suppression via Transmit Beamforming NASA array Lund array Rice Argos array Self-interference For 2D arrays, many direct self-interference path Transmit beamforming must suppress both direct and reflected paths

53 Nulling is Not Possible (# of Tx antennas) (# of Nulls) = # of Effective antennas More nulls means less power to each user

54 But we don t need to null self-interference? Rx Baseband Digital Cx Rx RF Tx Baseband SoftNull Tx RF

55 SoftNull Given a required # of effective Tx antennas, DTX Select beam-weight matrix, self-interference Effective self-interference channel:, which maximally suppresses Uplink Processing DTX Downlink Processing Digital Cx Rx RF Tx RF DTX DTX Simple closed form solution

56 SoftNull example: Self-interference power vs. # of effective Tx antennas, DTX DTX = 1 DTX = 2 DTX = 3 DTX = 4 DTX = 5 DTX = 6 DTX = 7 DTX = 8 DTX = 9 DTX = 10 DTX = 11 DTX = 12 DTX = 13 DTX = 14 DTX = 15 DTX = 16

57 SoftNull example: Self-interference power vs. # of effective Tx antennas, DTX DTX = 2 DTX = 3 DTX = 4 SoftNull tradeoff DTX = 6 DTX = 5 DTX = 7 DTX = 8 DTX = 1 As # of effective antennas decreases: Uplink benefits from better self-interference Dsuppression TX = 9 DTX = 10 DTX = 12 DTX = 11 Downlink DTX = 13 suffers due to lower SNR DTX = 14 DTX = 15 DTX = 16

58 SoftNull Feasibility Study Is a good SoftNull tradeoff feasible for real channels? Impact of array partitioning Impact of backscattering Is benefit to uplink SoftNull worth the cost to the downlink?

59 Argos-based Measurement Platform NASA Array+Argos Base Station 72 patch antennas, 8x9 grid 18 WARP nodes 4 Users via WARP Measure 72 X 72 self-coupling channel OFDM pilots from each antenna while all others listen Enables comparison of arbitrary Tx/Rx partitions Measure 72x4 uplink and 4x72 downlink channel

60 Measurement Campaign: 3 Environments Anechoic Chamber Outdoor Indoor

61 SoftNull Feasibility Study Is a good SoftNull tradeoff feasible for real channels? Impact of array partitioning Impact of backscattering Is benefit to uplink worth the cost to the downlink?

62 Tx/Rx Partitioning East-West North-South Northwest-Southeast (NW-SE) Interleaved

63 Tx/Rx Partitioning Results (Anechoic Chamber) East-West North-South Northwest-Southeast (NW-SE) Interleaved

64 Tx/Rx Partitioning Results (Anechoic Chamber) East-West North-South Northwest-Southeast (NW-SE) Interleaved Contiguous splits are best Minimizes angular spread of the self-interference

65 SoftNull Feasibility Study Is a good tradeoff feasible for real channels? Impact of array partitioning Impact of backscattering Is benefit to uplink worth the cost to the downlink?

66 Impact of Back-scattering East-West Outdoor Indoor More backscattering leads to less suppression (as theory predicts) Reason: backscatter breaks antenna correlation

67 SoftNull Feasibility Study Is a good tradeoff feasible for real channels? Impact of array partitioning Impact of backscattering Is benefit to uplink worth the cost to the downlink?

68 Is Benefit to Uplink Worth the Cost to the Downlink? East-West Outdoor Indoor Scenario: East-West split, indoor and outdoor Methodology: simulation using real measured channels Compare uplink and downlink rates of SoftNull versus half duplex and ideal full-duplex Simulation Parameters Base station power Mobile user power Noise power Dynamic range limit Number of users 4 Path Loss 0 dbm -10d Bm -95 dbm 25 db 85 db (300m)

69 Is benefit worth the loss in downlink SNR? East-West Outdoor Indoor Uplink: Downlink: Uplink+Downlink:

70 Is benefit worth the loss in downlink SNR? East-West Outdoor Indoor Uplink: Downlink: Uplink+Downlink:

71 Is benefit worth the loss in downlink SNR? East-West Outdoor Indoor Uplink: Downlink: Uplink+Downlink:

72 Is benefit worth the loss in downlink SNR? East-West Outdoor Indoor Uplink: Downlink: Uplink+Downlink:

73 Is benefit worth the loss in downlink SNR? East-West Outdoor Indoor Uplink: Downlink: Uplink+Downlink:

74 Impact of distance (i.e. path loss) East-West Outdoor 70 db path loss (50m LoS) 85 db path loss (300m LoS) 100 db path loss (1km LoS) Indoor

75 Impact of distance (i.e. path loss) East-West Outdoor 70 db path loss (50m LoS) 85 db path loss (300m LoS) 100 db path loss (1km LoS) Indoor

76 Impact of distance (i.e. path loss) East-West Outdoor 70 db path loss (50m LoS) 85 db path loss (300m LoS) 100 db path loss (1km LoS) Indoor

77 SoftNull Feasibility Study Is a good tradeoff feasible for real channels? Yes, when array partitioned contiguously Especially in low-backscattering deployments (like on basestations) Is benefit to uplink worth the cost to the downlink? Yes, for low to medium path losses Especially when # of antennas >> # number of users

78 JointNull: A Small # of Analog Cancellers Add a small number of analog cancellers, that can make any antenna full-duplex So there are three parts to overall cancellation Transmit pre-coding Analog cancellation Digital cancellation Sum-rate maximizing antenna configuration & precoding

79 JointNull: A Small # of Analog Cancellers Maximum sum-rate in bps/hz db analog cancelation 40 db analog cancelation 20 db analog cancelation 80 Half-duplex sum rate = 57.5 bps/hz Number of antennas = Number of analog cancelers If analog cancellers are low-quality, ~M/10 achieve 90% of max sum-rate If higher quality, need ~M/2 cancellers to achieve 90%

80 Conclusions Massive MIMO means many more transmit dimensions SoftNull uses it for all-digital full-duplex No new analog components build on today s radios JointNull generalizes it partial-analog full-duplex Platform crucial Have real-time implementation & evaluation of SoftNull Real-time results closely match today s results

81 Rice Argos V2: 96 Antennas (Scalable to 144 Antennas)

82 ArgosMobile

83 ArgosNet: Total of 400 Radios ArgosBS 1 (Outdoor) ArgosMobile 10 GbE ArgosMobile ArgosMobile 10 Server GbE NetFPGA 10 GbE ArgosBS 4 (Indoor) ArgosMobile NetFPGA Server 10 GbE NetFPGA Server 10 GbE ArgosCloud 10 GbE 10 GbE ArgosMobile ArgosBS 2 (Outdoor) ArgosBS 3 (Outdoor) NSF CRI : ArgosNet by Zhong, Knightly and Sabharwal

84 Questions or Comments? Full-duplex: WARP: Argos: Scalable Health: