Fast Millimeter Wave Beam Alignment Omid Abari Haitham Hassanieh, Michael Rodriguez, Mohammed Abdelghany, Dina Katabi, and Piotr Indyk
Emerging Applications VR stream 7 Gbps of data from PC to headset One autonomous car will generate 4TB of data per day 5G promises 1000 times faster than 4G Today s wireless networks can not support future applications
mmwave Technology
mmwave Technology Currently we operate here Millimeter Wave Bands 0 10GHz 20GHz 30GHz 40GHz 50GHz 60GHz 70GHz 80GHZ 90GHz 100GHz Frequency Spectrum Enable high-throughput wireless links
mmwave changes how wireless systems operate Today: Broadcast
mmwave changes how wireless systems operate mmwave: Pencil-beam Antennas Problem Statement: how can we align the beams to establish a link?
mmwave radios use phased arrays to create a beam
Naïve Approach: Exhaustive Scan N : number of possible directions AP N directions N directions Client O N - measurements à Too slow
802.11ad Scan Stage 1: Client uses omni-directional; AP scans directions AP Client
802.11ad Scan Stage 2: AP uses omni-directional; client scans directions AP Client O N measurements àstill Too Slow [MOBICOM 14, SIGMETRICS 15, NSDI 16]
Can we find the best beam alignment without scanning the space?
Agile-Link A millimeter wave system that can quickly establish a link without scanning the space Works within the existing 802.11ad standard, and can support both clients and access points Implemented and evaluated in practical settings
AP 60 o Agile-Link Idea Potential Direction of the Client: 0 o, 60 o, 90 o or 120 o 40 o, 60 o, 100 o or 150 o Client 60 o is direction of client Construct a Multi-Armed Beam: Simultaneously collects signals from multiple directions. 120 90 60 120 90 60 150 30 150 30 180 0 180 0
1. How do we create multi-armed beams? 2. What is the best choice of multi-armed beams to minimize the number of measurements?
Creating Multi-Armed Beams Phase Shifters a / h / h - For an Antenna Array: h = F 7 x, F is Inverse Fourier Matrix y i = a i h = a i F 7 x y i a i 90 a 0 F h 0 0 180 Divide a i into segments 90 a i = F 0 180
1. How do we create multi-armed beams? 2. What is the best choice of multi-armed beams to minimize the number of measurements?
Why do we need to choose the beams carefully? AP 180 0 150 30 120 60 90 Client Signals traveling along different paths can cancel each other
Best Choice of Multi-Armed Beams AP 180 0 60 o 150 30 120 60 90 Spatial Directions 0 o 30 o 60 o 90 o 120 o 150 o 180 o Hashing Client Bins: 1 2 3 4 Pick multi-armed beams to create random hash functions Voting Estimate the true direction using voting
Theorem (Informal) - Assuming: - N possible directions - K signal paths - Our algorithm finds the optimal beam alignment in O K log N measurements.
Experimental Results
Implementation and Evaluation Built a Millimeter Wave Radio with a Phased Array.
Number of Measurements Reduction in the Number Reduction of Measurements in Search Time 10000 1000 100 10 1 Our system vs. Exhaustive Our system vs. 802.11ad Agile-Link vs Exhaustive Search Agile-Link vs 802.11ad 0 50 100 150 200 250 Number of Potential Directions (N) Our system requires orders of magnitude fewer measurements
Beam Alignment Latency Number of Directions 802.11ad 802.11ad with our algorithm 16 1ms 0.5ms 64 4ms 0.8ms 128 106ms 0.9ms 256 310ms 1.0ms Achieved fast beam alignment (less than 1ms)
Beam Alignment Accuracy 1 0.8 CDF 0.6 0.4 0.2 Agile-Link 802.11ad Exhaustive Search 0 0 1 2 3 4 5 6 7 8 SNR Loss (db) Agile-Link performs much better than Exhaustive search and 802.11ad
Related Work Past Work on Beam Alignment: [D. Araujo EUSIPCO 14, J. Kim Jour. Communications 14, B. Li Trans. Wireless 13, Y. M. Tsang Globecom 11, J. Wang Communications 09, W. Yuan PIMR 15, L. Zhou PIMRC 12, D. Ramasamy Allerton 12, A. Alkhateeb IEEESP 14, B. Gao. IET 14, B.Li Trans. Wireless 13, T. Nitsche ENET 15, T. Nitsche Infocom 15,etc] Past Work on mmwave Channel Studies: [C. R. Anderson Trans. Wireless 04, S. Collonge Trans. Wireless 04, S. Rangan IEEE 14, M. Smulders Trans on Ant. 09, J. Violette NASA report, J. Comm. 02, S. Sur SIGMETRIC 15, A. Saeed VTC 16, X. Tie PAM 11, etc] Past Work on using Sparsity: [E. Eltayeb GLOBESIP 15, A. Alkhateeb J. IEEE 14, B. Gao IET14, D. Ramasamy, IEEE 14, etc]
Conclusion Establishing communication links in millimeter wave networks is challenging due to directionality. Agile-Link: millimeter wave system that can quickly establish a link without having to scan the space. Exciting time for millimeter wave networks!
Fast Millimeter Wave Beam Alignment Omid Abari Haitham Hassanieh, Michael Rodriguez, Mohammed Abdelghany, Dina Katabi, and Piotr Indyk