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Tripling the capacity of wireless communications using electromagnetic polarization


Wireless communications are a fundamental part of modern information infrastructure. But wireless bandwidth is costly1, prompting a close examination of the data channels available using electromagnetic waves. Classically, radio communications have relied on one channel per frequency, although it is well understood that the two polarization states of planar waves2 allow two distinct information channels; techniques such as ‘polarization diversity’ already take advantage of this3. Recent work4,5,6,7 has shown that environments with scattering, such as urban areas or indoors, also possess independent spatial channels that can be used to enhance capacity greatly. In either case, the relevant signal processing techniques come under the heading of ‘multiple-input/multiple-output’ communications, because multiple antennae are required to access the polarization or spatial channels. Here we show that, in a scattering environment, an extra factor of three in channel capacity can be obtained, relative to the conventional limit using dual-polarized radio signals. The extra capacity arises because there are six distinguishable electric and magnetic states of polarization at a given point, rather than two as is usually assumed.

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Figure 1: Communicating with electric fields in the presence of a mirror.
Figure 2: Eigenvalues of HH in a two-mirror idealized scattering environment.
Figure 3: Tri-polarized antenna (tripole).
Figure 4: Capacity of the tripole antenna.

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This work is supported by internal funding at Bell Labs, Lucent Technologies. We are grateful to W. M. MacDonald for his assistance in characterizing our antenna's radiation patterns, and to M. J. Gans for his insights and discussions concerning magnetic polarization.

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Correspondence to Michael R. Andrews.

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Andrews, M., Mitra, P. & deCarvalho, R. Tripling the capacity of wireless communications using electromagnetic polarization. Nature 409, 316–318 (2001).

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