Hiroaki Nakabayashi

Theoretical analysis of frequency-correlation coefficient for received signal level in mobile communications

Frequency-correlation coefficient characteristics that define frequency separation in frequency-diversity techniques were studied theoretically using a propagation model that makes allowances for received bandwidth. Equations of frequency-correlation coefficients in non- and line-of-sight propagation paths were derived. The equations showed that frequency-correlation coefficient depends on such factors as frequency separation, received bandwidth, differences in pathlengths, and the power ratios of the direct to indirect waves. The frequency-correlation coefficient increases as the received bandwidth increases and decreases as the difference in pathlength increases. However, when the difference in the pathlength was small (30 m), the effect of the received bandwidth was minimal. The frequency-correlation coefficient also depended somewhat on the power ratio. To confirm the accuracy of our theoretical derivations, computer simulations were performed. Frequency-correlation coefficients were calculated by simulating instantaneous received signal levels. The theoretical results matched those of the simulation.

MIMO Channel Model with Propagation Mechanism and the Properties of Correlation and Eigenvalue in Mobile Environments

This paper described a spatial correlation and eigenvalue in a multiple-input multiple-output (MIMO) channel. A MIMO channel model with a multipath propagation mechanism was proposed and showed the channel matrix. The spatial correlation coefficient formula 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) between MIMO channel matrix elements was derived for the model and was expressed as a directive wave term added to the product of mobile site correlation 𝜌𝑖−𝑖′(𝑚) and base site correlation 𝜌𝑗−𝑗′(𝑏) without LOS path, which are calculated independently of each other. By using 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚), it is possible to create the channel matrix element with a fixed correlation value estimated by 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) for a given multipath condition and a given antenna configuration. Furthermore, the correlation and the channel matrix eigenvalue were simulated, and the simulated and theoretical correlation values agreed well. The simulated eigenvalue showed that the average of the first eigenvalue λ1 hardly depends on the correlation 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚), but the others do depend on 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) and approach 𝜆1 as 𝜌𝑖−𝑗,𝑖′−𝑗′(𝑏𝑚) decreases. Moreover, as the path moves into LOS, the 𝜆1 state with mobile movement becomes more stable than the 𝜆1 of NLOS path.

A method for expressing mobile propagation loss characteristics in a street microcell system

Data from the received signal-level in the personal handy-phone system commercial communication service are used to evaluate a method for expressing mobile propagation loss characteristics. The standard deviation of the difference between the measured signal level and the signal level given by empirical equations is calculated on the basis of a macrocell mode (loss versus direct distance from base station) and a street microcell mode (classified as base-station road and crossed road). The results show that the expression of street microcell mode is better than that of the macrocell mode.