1. Beamforming on Mobile Devices:A First Study Hang Yu, Lin Zhong, Ashutosh Sabharwal and David Kao

2. Wireless Networks are Congested

3. Spectrum Resource Will NEVER Grow

4. Mobile Devices are Power Constrained

5. Wireless Interfaces are Power Hungry

6. Mobile Devices are Omni-directional

7. Interference

8. Transmit Power Waste

9. Directional antenna • Beamforming Solutions?

10. Directional Antenna vs. Beamforming • Reference: Ardalan Amiri Sani, Lin Zhong, and Ashutosh Sabharwal, "Directional antenna diversity for mobile devices: characterizations and solutions," in Proc. ACM MobiCom, September 2010.

11. Is Beamforming Feasible At All?

12. Small size Is Beamforming Feasible At All?

13. Small size • High mobility Is Beamforming Feasible At All? 70 miles/h

14. Small size • High mobility • Limited power Is Beamforming Feasible At All? 70 miles/h

15. YesIt’s Feasible!

16. Form Factor?

17. Single-chip beamforming transceiver Form Factor?

18. Single-chip beamforming transceiver • Antenna spacing Form Factor?

19. Single-chip beamforming transceiver • Antenna spacing • 0.3-0.4 λ(4.5-6 cm at 2 GHz) Form Factor?

20. Single-chip beamforming transceiver • Antenna spacing • 0.3-0.4 λ(4.5-6 cm at 2 GHz) • Smartphone: circular array • Tablet: linear array Form Factor? 18 cm 6 cm 24 cm 12 cm

21. Not only move but also rotate Mobility?

22. Not only move but also rotate • Channel amplitude and phase Mobility?

23. Not only move but also rotate • Channel amplitude and phase • Beamforming gain under device rotation? Mobility?

24. Not only move but also rotate • Channel amplitude and phase • Beamforming gain under device rotation? Mobility? Beamforming gain? Client Node Infrastructure Node

25. DROPPED Beamforming Gain • CSI estimation every 100 ms

26. MAXIMAL Beamforming Gain • CSI estimation every 10 ms

27. Negligible baseband power overhead Power?

28. DAC Mixer Filter • PA1 Filter • Negligible baseband power overhead • RF components Baseband Signal Power? Frequency Synthesizer N DAC Filter Filter • PAN Baseband Signal Mixer

29. PPA =PTX/η DAC Mixer Filter • PA1 Filter • Negligible baseband power overhead • RF components Baseband Signal Power? Frequency Synthesizer N DAC Filter Filter • PAN Baseband Signal Mixer

30. PCircuit DAC Mixer Filter • PA1 Filter • Negligible baseband power overhead • RF components Baseband Signal Power? Frequency Synthesizer N • PPA =PTX/η DAC Filter Filter • PAN Baseband Signal Mixer

31. PCircuit DAC Mixer Filter • PA1 Filter • Negligible baseband power overhead • RF components Baseband Signal Power? Frequency Synthesizer N • PPA =PTX/η • PShared DAC Filter Filter • PAN Baseband Signal Mixer

32. P = PTX/η + NPCircuit + PShared Power Tradeoff

33. P = PTX/η + NPCircuit + PShared Power Tradeoff Transmit Power Circuit Power

34. A single uplink channel Tradeoff Analysis Uplink

35. A single uplink channel Tradeoff Analysis Uplink

36. A single uplink channel • Beamforming can be more efficient than omni Power Tradeoff BF > Omni

37. A single uplink channel • Beamforming can be more efficient than omni • Higher capacity leads to larger beamforming size Power Tradeoff Nopt=4 Nopt=3 Nopt=2 Nopt=1

38. A single uplink channel • Beamforming can be more efficient than omni • Higher capacity leads to larger beamforming size • Beamforming should be used adaptively Power Tradeoff Nopt=4 Nopt=3 Nopt=2 Nopt=1

39. The Optimal N?

40. The Optimal N? Uplink

41. The Optimal N? Uplink Uplink

42. The Optimal N?

43. Your # of antennas? The Optimal N? Your # of antennas? • Brute-force method needs client cooperation

44. Power of client i Formulation • SINR of client i • # of antennas of client i

45. Algorithm

46. Algorithm Uplink Uplink

47. Fast Convergence

48. Close-to-optimal Performance A few samples Statistical information

49. Prototype WARPLab

50. Infrastructure Node 1 Infrastructure Node 2 Experimental Setup Ethernet Router Uplink (Wireless) Uplink (Wireless) Client Node 1 Client Node 2 Laptop with MATLAB