1. Efficient Beam Finding and Tracking in mmW Systems
Irmak Aykin and Marwan Krunz
Millimeter-Wave RCN
University of Arizona, Tucson, AZ
Introduction
Overview
Existing Scanning Techniques:
Motivation:
mmW communications are highly directional
Initial access & network discovery can be challenging, esp. under mobility
Frequent significant beam misalignments (even under pedestrian speeds)
Received energy is clustered into multiple distinct angular directions
Exhaustive search: Brute-force sequential beam scanning
Iterative search: Two-stage (wide and narrow) scanning of angular space
CI-based search: Relies on GPS to locate BS and MUs
Provide different tradeoffs between discovery time and misdetection prob.
Beam Finding:
Rx power varies with orientation of receive beam, displaying multiple peaks
[Source: NYU Poly]
28 GHz
73 GHz
Main Research Thrusts:
Design computationally efficient & secure beam finding and tracking methods
High alignment accuracy, low discovery time & confidentiality
Optimize tradeoff between discovery time & misdetection probability
Integrate algorithms into a novel link-establishment protocol
Verify results via simulations & hardware experiments
Single-peak Finding
Multi-peak Finding
Preliminary Design
Evaluation
Peak Finding Algorithm:
Effect of K:
Distance = 170m
Distance = 170m
Effect of Distance on Discovery Time:
K= 20
K= 20
Received energy for Tx angle θTx and Rx angle θRx is formulated as:
which can be rewritten as:
Future Tasks
Here, α is a random variable representing the overlap between receiver’s main lobe and one of the AoA clusters
Link establishment protocol for mobile mmW nets
Beam tracking algorithm:
Exploit machine learning to infer mobility patterns
Simultaneous multi-node device discovery:
BS discovers several UEs simultaneously
Multi-homed UEs (associate with several BSs)
D2D communications
Hardware experiments (NI FlexRIO & SiBeam phased array antennas with 23 dB gain)
Application to directional MANETs
High security (via directional communications)
Limited data interruptions (high reliability)
Main Idea: Divide the whole region into K sub-regions such that each is likely to contain a single peak & run the peak finding algorithm in each sub-region
Selection of K is critical: Discovery time vs. misdetection probability tradeoff
Larger K = Higher discovery time = lower misdetection probability
Beam Tracking:
Act proactively to reduce readjustment overhead
Find several Tx-Rx beam pairs that satisfy link budget during initial access
If quality of current pair is expected to worsen, run peak finding algorithm in reduced search space
Adapt beamwidth to overcome blockage and achieve high SNR