Compact Antenna Spacing in mmWave MIMO Systems Using Random Phase Precoding

Surabhi, G D and Chockalingam, A (2017) Compact Antenna Spacing in mmWave MIMO Systems Using Random Phase Precoding. In: 86th IEEE Vehicular Technology Conference (VTC-Fall, SEP 24-27, 2017, Toronto, CANADA.

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Abstract

Presence of strong line of sight (LOS) components in multiple-input multiple-output (MIMO) systems operating at mmWave frequencies result in ill-conditioned channel matrices. However, optimum inter-antenna spacing can result in orthogonal channel matrices under LOS conditions. This optimal spacing is typically large (of the order of tens of wavelengths). Antennas separated by less than optimal spacing result in degraded performance due to high spatial correlation. This motivates the need to investigate techniques that can reduce the spacing without compromising much in performance. In this work, we propose random phase precoding (RPP) as an attractive method to achieve this objective. Our contributions in this paper are two-fold. First, RPP for reducing inter-antenna spacing in mmWave communications is novel and has not been reported before. Our results show that, using RPP, the inter-antenna spacing can be reduced to the order of wavelength (5mm at 60 GHz frequency) compared to optimal spacing which is of the order of tens of wavelengths. This is achieved without the need for channel state information at the transmitter. We also present an analysis that shows that RPP reduces the effective correlation which, in turn, aids compact spacing. Second, we study an index modulation scheme where the random phase precoder matrices are indexed to convey additional information bits. The indexed RPP scheme is found to perform better than the non-indexed RPP scheme.

Item Type:	Conference Proceedings
Series.:	IEEE Vehicular Technology Conference VTC
Publisher:	IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA
Additional Information:	Copy right for this article belong to IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	07 May 2018 19:00
Last Modified:	07 May 2018 19:00
URI:	http://eprints.iisc.ac.in/id/eprint/59800

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