MmWave Beam Alignment for Vehicular Communications
The use of very large antenna arrays composed of tens to hundreds of elements at mmWave frequencies is necessary to maintain sufficient link quality. Such antenna arrays are feasible due to the small antennas at these high frequencies. Beam alignment of arrays at this scale is challenging due to the overhead in determining the optimal transmit and receive beams. Existing beam alignment schemes proposed for mmWave applications are largely based on beam sweeping and make use of hierarchical beam codebook for efficient algorithm design, which requires the use of wide beams at the start. Such wide beams suffer low antenna gains. They are also more susceptible to Doppler spread, which is another challenge for beam sweeping based method. It should be noted that these solutions do not make use of any side information. In vehicular environments, a large amount of side information can be available from various sources, e.g., automotive radars, visual cameras, LIDARs, or even DSRC devices. Motivated by this fact, we are developing a low overhead beam alignment algorithm leveraging the side information obtained from various sources using a learning based approach. The side information from sensors also can be used to predict possible millimeter wave signal blockages in advance and allow to have continuous, reliable data transmissions.
We recently have studied the potential of leveraging position information to switch the beams and eliminate the need for beam sweeping. In vehicular environments, the position information of vehicles can be available through DSRC or automotive sensors. Our result shows that mmWave with beam switching has the potential to provide multi-Gbps communications in vehicular environments. Position prediction accuracy is crucial for the success of this beam switching approach. Our analysis shows that there exists a fundamental tradeoff in the design of beamwidth: wider beams suffer from insufficient power but narrower beams are more sensitive to position estimation error. We also studied the impact of overlap between beams to mitigate the beam misalignment resulting from the position estimation error. We studied the impact to both the outage and the average rate. Using our analytical expression for the average, it is also possible to optimize the beamwidth of each beam in the coverage, i.e., beam design, to maximize the data rate. Our result shows that the equal coverage beam design, where the beams are designed such that they all have the same coverage length, is near-optimal with negligible loss to the optimal solution.
We are also investigating the possibility of connecting low-frequency channel information to millimeter wave spectrum. Due to hardware constraints mmWave channel is not directly accessible and hence estimating mmWave channel for beamforming is difficult. Further, sub-6 GHz and mmWave systems are envisioned to work together, so assuming the knowledge of sub-6 GHz channel is reasonable. With this in mind, we investigate how the correlation information obtained at sub-6 GHz can help in reducing the mmWave channel estimation or beamtraining overhead. We quantify the excess error incurred in mmWave channel estimation by using the correlation information that is translated from sub-6 GHz.
This research is partially supported by the U.S. Department of Transportation through the Data-Supported Transportation Operations and Planning (D-STOP) Tier 1 University Transportation Center, by the Texas Department of Transportation under Project 0-6877 entitled “Communications and Radar-Supported Transportation Operations and Planning (CAR-STOP),” by the National Science Foundation under Grant No. NSF-CCF-1319556, and by a gift from TOYOTA InfoTechnology Center, U.S.A., Inc.
V. Va, X. Zhang, and R. W. Heath, Jr., “Beam Switching for Millimeter Wave Communication to Support High Speed Trains,” in Proc. of the IEEE 82nd Vehicular Technology Conference (VTC2015-Fall), Boston, USA, pp. 1-5, Sep. 2015. Video of presentation.
V. Va, T. Shimizu, G. Bansal, and R. W. Heath, Jr., “ Beam Design for Beam Switching Based Millimeter Wave Vehicle-to-Infrastructure Communications,” Proc. of the IEEE International Conference on Communications, Kuala Lumpur, Malaysia, May 23-27, 2016, pp. 1-6. Video of presentation
J. Choi, N. González-Prelcic, R. Daniels, C. R. Bhat, and R. W. Heath, Jr., “Millimeter Wave Vehicular Communication to Support Massive Automotive Sensing,” IEEE Communications Magazine, vol. 54, no. 12, pp. 160-167, Dec. 2016.
A. Ali, N. González-Prelcic, and R. W. Heath, Jr., “Estimating Millimeter Wave Channels using Out-of-Band Measurements,” Proceedings of Information Theory and Applications (ITA) Workshop, 2016. Video of presentation
V. Va, T. Shimizu, G. Bansal and R. W. Heath, Jr., “Millimeter Wave Vehicular Communications: A Survey,” Foundations and Trends in Networking, vol. 10, no. 1, pp. 1-113, Jun. 2016.
M. E. Eltayeb, J. Choi, T. Y. Al-Naffouri, and R. W. Heath, Jr., “On the Security of Millimeter Wave Vehicular Communication Systems using Random Antenna Subsets,” Proc. of the IEEE 84th Vehicular Technology Conference, Montreal, Canada, Sep 18-21, 2016. Video of presentation
V. Va and R. W. Heath, Jr., “Performance Analysis of Beam Sweeping in Millimeter Wave Assuming Noise and Imperfect Antenna Patterns,” Proc. of the IEEE 84th Vehicular Technology Conference, Montreal, Canada, Sep 18-21, 2016. Video of presentation
Data-Supported Transportation Operations & Planning Center A Tier 1 USDOT University Transportation Center at The University of Texas at Austin