Angularly phase shifted propagation channels for MIMO N × N

Abstract

The aim of this paper is to define new uncorrelated propagation channels for Multiple-Input-Multiple-Output (MIMO) purposes by producing angular phase differences in the transmission. The phase difference can be created such that the radiation power of the signal does not change when selecting correct values for real and imaginary parts of the complex value $$a+jb$$. This results in the same signal amplitudes, i.e., coverage area or antenna power radiation pattern, but multi path signal components are received with phase differences. These phase differences then allow uncorrelated propagation channels to be used in MIMO N $$ imes $$ N. In 5G/6G mobile networks, mostly only line-of-sight (LOS) connections between base stations and mobiles are available at very high frequencies, and small cell implementations with MIMO are needed to maximize the system capacity. However, MIMO has performance limitations in LOS environments due to lacking the required phase difference between MIMO channels when traditional antenna space separation is used. Thus, these new uncorrelated channels are especially needed in high-capacity small cell implementations but also in nearly LOS-type environments, as on highways. Ray-tracing simulations were done at 28 GHz frequency in a small cell LOS environment to show the impact of angular phase differences. Fast fading statistics and signal cross-correlations were analyzed to see the potential of utilizing MIMO N $$ imes $$ N in LOS propagation paths. MIMO system capacities were calculated for different MIMO configurations, and these results were compared with the results of traditional spatially separated configurations. The simulated results showed that sufficient angular phase difference offers independent propagation channels in a small cell LOS environment with cross-correlation factors of 0.01–0.44. These low correlated propagation channels yielded a capacity increase of 3.44–3.88 times from SISO to MIMO 4 $$ imes $$ 4 with one polarization and with different directional antennas. This capacity was even 95 % higher than the capacity with only spatially separated directional antennas.