I am trying to implement angle of arrival (AoA) estimator with Wi-Fi APs and a device. To this end, I am employing ULA-MUSIC algorithm.
Since I am not familiar with antenna theory, I have three questions about antenna configuration. The configuration and symbol is drawn in the attached figure.
1. Spacing between adjacent antennas (symbol: ;capital delta)
With some literature search, I learned and am pretty sure that spacing should be a half of wavelength. Larger spacing would introduce grating lobes.
2. Length of each antenna (symbol: lower case a)
Many literature say that a length of dipole antennas also should be a half of wavelength. In case of Wi-Fi @ 2.4 GHz, the value would be 6.25 cm (2.46 inches). However, I have only VERT2450 antennas (https://www.ettus.com/product/details/VERT2450). I didn't look into a plastic cover, but its length seems around 12 cm (4.7 inches) or longer.
Can I use this antenna to get correct signal, channel matrix, or channel state information for ULA-MUSIC?
3. Length of cables connecting antennas and Wi-Fi card (symbol: l1, l2, l3)
I've asked an impact of a length of cable connecting an antenna and Wi-Fi card in other forum run with mailing list. And a response says, a length of cable affects to channel measurement. On the other hand, I am curious that, if ULA-MUSIC algorithm is interested in phase difference (If it is wrong, please let me know it), is it okay to use cables with the same length?
Regards.
References for applying ULA-MUSIC algorithm to Wi-Fi
[1]R. Schmidt, “Multiple emitter location and signal parameter estimation,” IEEE Transactions on Antennas and Propagation, vol. 34, no. 3, pp. 276–280, Mar. 1986.
[2] J. Xiong and K. Jamieson, “ArrayTrack: A Fine-Grained Indoor Location System,” in Presented as part of the 10th USENIX Symposium on Networked Systems Design and Implementation (NSDI 13), Lombard, IL, 2013, pp. 71–84.
[3] M. Kotaru, K. Joshi, D. Bharadia, and S. Katti, “SpotFi: Decimeter Level Localization Using WiFi,” SIGCOMM Comput. Commun. Rev., vol. 45, no. 4, pp. 269–282, Aug. 2015.
For better performance Use Dipole along with reflector and Director , which will improve the Gain
You can try simply using beamforming (capon or basic) instead of MUSIC. As long as the spacing distance is half-lamda, it will produce acceptable accuracy angle estimation.
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