MIDU: Enabling MIMO Full Duplex

Transcription

1 MIDU: Enabling MIMO Full Duplex Ehsan Aryafar Princeton NEC Labs Karthik Sundaresan NEC Labs Sampath Rangarajan NEC Labs Mung Chiang Princeton ACM MobiCom 2012

2 Background AP Current wireless radios are hlfd half duplex p1 p2

3 Background AP p1 p2 Current wireless radios are hlfd half duplex Same band Full duplex is hard Self interference is very high: 75 db for 15 dbm Tx power Transmitted signal is known self interference cancellation Self interference can be significantly reduced by adding a cancellation circuit: e.g., a cancelling antenna

4 Background AP p1 p2 Current wireless radios are hlfd half duplex Same band Full duplex is hard Self interference is very high: 75 db for 15 dbm Tx power Self interference can be significantly cancelled by adding a cancellation circuit: e.g., a cancelling antenna Can full duplex wireless double the capacity?

5 Full Duplex vs. MIMO Hardware complexity, performance, size, cost metrics

6 Full Duplex vs. MIMO Hardware complexity, performance, size, cost metrics Antenna Conserved (AC): Same # antennas

7 Full Duplex vs. MIMO Hardware complexity, performance, size, cost metrics Antenna Conserved (AC): Same # antennas RF Chain Conserved (RC): Same # chains

8 Full Duplex vs. MIMO Hardware complexity, SI loss: 6 db Ant Correlation: 0.1 performance, size, cost metrics Antenna Conserved (AC): Same # antennas RF Chain Conserved (RC): Same # chains ty (bit/ chann nel use) FD- RC HD FD- AC = 0.01 Significant FD gains in RC model Limited FD gains with small # 20 antennas in AC model higher gains with more antennas Capaci Number of Antennas

9 Full Duplex vs. MIMO Hardware complexity, SI loss: 6 db Ant Correlation: 0.1 performance, cost metrics Antenna Conserved (AC): Same # antennas = FD- RC HD Regions of pronounced 80 full FD- AC duplex gains in RF Chain Conserved (RC): Same # chains Significant FD gains in RC model ty (bit/ chann nel use) both RC and AC 60 models Limited FD gains with small # antennas in AC model high gains with more antennas Capaci Number of Antennas

10 Outline Background Design of MIDU Experimental Evaluation Conclusion

11 MIDU: MImo full DUplex Symmetric antenna T' R T placement d d π Input Signal

12 MIDU: MImo full DUplex Symmetric antenna placement RX Chain 2 level of antenna cancellation Tx cancellation followed by Rx cancellation Proved in theory to have additive gains under imbalancedgains/phase or imprecise placement π T' 1 π R' 1 R 1 T 1 TX Chain

13 MIDU: MImo full DUplex Symmetric antenna placement 2 level of antenna cancellation Tx cancellation followed by Rx cancellation Proved in theory to have additive gains under imbalancedgains/phase or imprecise placement Easy scalability lbl to MIMO R 3 R 2 R 1 T' 1 T' 2 T' 3 T 1 T 2 T 3 R' 1 R' 2 R' 3

14 Implementation WarpLab implementation Narrow band 625 KHz Open space environment MIDU + MU MIMO MIMO Virtex IV Pro FPGA

15 Implementation WarpLab implementation Narrow band 625 KHz Open space environment MIDU + MU MIMO MIMO Performance metric: SNR or the corresponding Shannon capacity Virtex IV Pro FPGA

16 Implementation WarpLab implementation Narrow band 625 KHz Open space environment MIDU + MU MIMO MIMO Performance metric: SNR or the corresponding Shannon capacity Virtex IV Pro FPGA Spectrum analyzerbased measurement or the SNR reported by WARP

17 Experimental Evaluation Feasibility Channel distance relationship Stability Impact on far field field users Cancellation R 1 R 2 R 3 Single level 2 level and MIMO T' 1 T' 2 T' 3 T 1 T 2 T 3 Comparison with MIMO Single link Single cell R' 1 R' 2 R' 3

18 Issue: How does symmetric antenna placement impact the far field users? Impact of MIDU on Far Field Users

19 Impact of MIDU on Far Field Users Issue: How does symmetric antenna placement impact the far field users? TX <3m> 19 18

20 Issue: How does symmetric antenna placement impact the far field users? Achieved SNR can be up to 4 db higher/lower Impact of MIDU on Far Field Users Inner Circle Outer Circle

21 Issue: How does symmetric antenna placement impact the far field users? Achieved SNR can be up to 4 db higher/lower In far field fi antenna cancellation has very limited effect due to signal scattering (fading) Similar results hold for RX cancellation Impact of MIDU on Far Field Users Inner Circle Outer Circle

22 Experimental Evaluation Feasibility Channel distance relationship Stability Impact on far field field users Cancellation R 1 R 2 R 3 Single level 2 level and MIMO T' 1 T' 2 T' 3 T 1 T 2 T 3 Comparison with MIMO Single link Single cell R' 1 R' 2 R' 3

23 Cancellation Issue: Is 2 level cancellation T' R T additive? Is MIDU scalable? Connect the receiver to a spectrum analyzer d π d Input Signal

24 Cancellation Issue: Is 2 level cancellation additive? Is MIDU scalable? db cancellation on each level separately Cancellation remains relatively unchanged with Tx power

25 Cancellation Issue: Is 2 level cancellation additive? Is MIDU scalable? RX Chain Θ R 1 Phase shifter on each path to handle insertion loss and delay T' 1 T 1 Θ+π R' 1 Θ+π Θ TX Chain

26 Cancellation Issue: Is 2 level cancellation additive? Is MIDU scalable? Phase shifter on each path to handle insertion loss and delay RX cancellation on top of TX cancellation is additive

27 Cancellation Issue: Is 2 level cancellation additive? Is MIDU scalable? Phase shifter on each path to handle insertion loss and delay RX cancellation on top of TX cancellation is additive 4 db decrease in cancellation for the first added pair, 5 db with 3 total pairs

28 Experimental Evaluation Feasibility Channel distance relationship Stability Impact on far field field users Cancellation R 1 R 2 R 3 Single level 2 level and MIMO T' 1 T' 2 T' 3 T 1 T 2 T 3 Comparison with MIMO Single link Single cell R' 1 R' 2 R' 3

29 Comparison with MIMO Compare MIDU to MU MIMO RF Chain conserved model Multi user beamfoming/filtering for MU MIMO in each direction UL DL interference in MIDU R 2 MIDU BS R 1 R 6 Metric: Shannon capacity of the measured SNR R 3 R 5 2m R 4

30 Comparison with MIMO Compare MIDU to MU MIMO M: #UL Streams N: #DL Streams RF Chain conserved model Multi user beamfoming/filtering for MU MIMO in each direction UL DL interference in MIDU Full duplex gains diminish as the number of streams is scaled

31 Comparison with MIMO Compare MIDU to MU MIMO 3 DL Streams Var UL Streams RF Chain conserved model Multi user beamfoming/filtering for MU MIMO in each direction UL DL interference in MIDU Full duplex gains diminish as the number of streams is scaled For maximum full duplex gains, the numberof streams between UL and DL should be dis proportionate

32 Comparison with MIMO Compare MIDU to MU MIMO 3 DL Streams Var UL Streams RF Chain conserved model Multi user beamfoming/filtering for MU MIMO in each direction UL DL interference in MIDU Full duplex has great potential in practical single sng cell MU-MIMO M MO schemes s in which the number of streams is small Full duplex gains diminish as the number of streams is scaled For maximum full duplex gains, the numberof streams between UL and DL should be dis proportionate

33 Related Work Single antenna full duplex M. Knox, Self jamming for full duplex Enhanced Circulator design for full duplex wireless Tx Signal Tx Output Interference Cancellation Circuit + Rx Input Rx Signal

34 Related Work Single antenna full duplex M. Knox, Self jamming for full duplex Asymmetric Antenna cancellation J. Choi, et. al., Achieving single channel full duplex

35 Related Work Single antenna full duplex M. Knox, Self jamming for full duplex Asymmetric Antenna cancellation J. Choi, et. al., Achieving single channel full duplex Analogue cancellation M. Jain, et. al., Practical full duplex M. Durate, et. al., Fullduplex withoff the shelf radios"

36 Related Work Single antenna full duplex M. Knox, Self jamming for full duplex Asymmetric Antenna cancellation J. Choi, et. al., Achieving single channel full duplex Analogue cancellation M. Jain, et. al., Practical full duplex M. Durate, et. al., Fullduplex withoff the shelf radios" Our work presents the design and implementation of the first MIMO full duplex system

37 In Summary Designed and implemented MIDU, the first MIMO full duplex wireless system Enabled two stages of antenna cancellation with additive gains that provided as high as 45 db self interference cancellation Built a prototype of MIDU with joint operation of 3x3 MIMO + Full Duplex in practice Provided guidelines for the design of an efficient MAC for single cells employing MIDU nodes NEC Labs: labs.com/ Princeton EdgeLab: