Self-Alignment of Interference Arising From Hallway Guidance of Diffuse Fields

Propagation theory is developed to get analytic expressions for both guided and diffusely scattered 3-D fields in common indoor environments, with access points (APs) placed along a hallway and mobile nodes in the rooms. Resulting predictions agree with measurements of both path loss and single-user multiple-input-multiple-output link capacity. In particular, the model reproduces the observed reduction in normalized channel capacity with increasing range. This effect, occurring in a common indoor environment, can be beneficial. Interfering APs, which tend to be further away, occupy channel dimensions corresponding to low-order hallway modes, causing total interference to concentrate in a small subset of the channel dimensions, in a manner reminiscent of interference alignment. The channel for the desired signal has a greater number of effective degrees of freedom (EDOFs) due to a shorter distance from its serving AP. The disparity in the number of EDOFs between the signal and the interference leads to higher rates, which can be further increased through water filling applied individually to each link, with no interlink coordination. The resulting rates are on the order of 30% greater than would be anticipated in range-independent scattering models.