
Beamforming on Mobile Devices:A First Study Hang Yu, Lin Zhong, Ashutosh Sabharwal and David Kao
Directional antenna • Beamforming Solutions?
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.
Small size Is Beamforming Feasible At All?
Small size • High mobility Is Beamforming Feasible At All? 70 miles/h
Small size • High mobility • Limited power Is Beamforming Feasible At All? 70 miles/h
Single-chip beamforming transceiver Form Factor?
Single-chip beamforming transceiver • Antenna spacing Form Factor?
Single-chip beamforming transceiver • Antenna spacing • 0.3-0.4 λ(4.5-6 cm at 2 GHz) Form Factor?
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
Not only move but also rotate Mobility?
Not only move but also rotate • Channel amplitude and phase Mobility?
Not only move but also rotate • Channel amplitude and phase • Beamforming gain under device rotation? Mobility?
Not only move but also rotate • Channel amplitude and phase • Beamforming gain under device rotation? Mobility? Beamforming gain? Client Node Infrastructure Node
DROPPED Beamforming Gain • CSI estimation every 100 ms
MAXIMAL Beamforming Gain • CSI estimation every 10 ms
DAC Mixer Filter • PA1 Filter • Negligible baseband power overhead • RF components Baseband Signal Power? Frequency Synthesizer N DAC Filter Filter • PAN Baseband Signal Mixer
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
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
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
P = PTX/η + NPCircuit + PShared Power Tradeoff
P = PTX/η + NPCircuit + PShared Power Tradeoff Transmit Power Circuit Power
A single uplink channel Tradeoff Analysis Uplink
A single uplink channel Tradeoff Analysis Uplink
A single uplink channel • Beamforming can be more efficient than omni Power Tradeoff BF > Omni
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
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
The Optimal N? Uplink
The Optimal N? Uplink Uplink
Your # of antennas? The Optimal N? Your # of antennas? • Brute-force method needs client cooperation
Power of client i Formulation • SINR of client i • # of antennas of client i
Algorithm Uplink Uplink
Close-to-optimal Performance A few samples Statistical information
Prototype WARPLab
Infrastructure Node 1 Infrastructure Node 2 Experimental Setup Ethernet Router Uplink (Wireless) Uplink (Wireless) Client Node 1 Client Node 2 Laptop with MATLAB