Mobile path loss estimation models for small cell area on a sloping terrain become important function in the radio link design of cellular systems. Okumura and Lee models are known for the sloping terrain path loss estimation, but the applicable cell size is lager than today's small cell area with less than 1.5km radius. Recently, a new estimation model called Fujitani model has been proposed for such a small cell including sloping terrain area. However, there were no comparison discussions about the estimation by the other models. In this paper, the path loss estimation comparisons by Okumura, Fujitani, and Lee models are discussed based on the same data measured in a typical short distance sloping terrain area. The result shows that Fujitani model is prospective for such sloping terrain path loss estimation in a small cell, but further measurement studies in various slope terrain areas and additional parameter considerations are needed to realize general applicability.

This paper proposes an adaptive non-linear distortion noise control method for low-priority systems under spectrum sharing environments. The proposed method adaptively controls distortion noise power of a transmitter to improve reception quality of shared bands with transmission power control. The distortion power is reduced to meet a required transmission quality. In this paper, the spectrum property and BER performance with the method are evaluated by computer simulations. The results confirm that the proposed method can effectively reduce the distortion power and adaptively control transmission SNRs according to the required transmission quality.

This paper proposes a non-linear distortion noise control method for secondary systems in spectrum sharing. The proposed method is based on conventional clipping and filtering methods, and adaptively shapes distortion noise power to improve reception quality of secondary users with transmission power control. In this paper, optimal clipping levels to control in-band distortion noise are investigated, and then the spectrum property and BER performance with the clipping levels are evaluated. The results confirm that the proposed method can control the distortion power effectively in shared bands and realize secondary systems with less degradation of reception quality when sharing spectrum with transmission power control.

Service area upgrading and expanding is expected in current and future cellular systems. Since residential areas on a hilly and/or slope terrain are spreading in the outskirts of cities in Japan, the correction for the urban mobile propagation loss formula becomes one of the important issues in radio link and cell layout designs in those areas, especially within 1km distance from a base station. This paper introduces an example of correction formula for the slope terrain area based on an experimental study of mobile path loss prediction. The result shows the path loss at the objective point can be estimated by the urban mobile path loss and the correction value according to the factor expressed by the elevation angle from the base station antenna top. Although the average slope angle is only used as a parameter in the conventional correction for the slope terrain area with at least 5 to 10km length, the result means it is not enough for the correction to the area within 1km distance from a base station.

This paper proposes an adaptive soft clipping method for spectrum sharing OFDMA systems. The proposed method controls in-band and out-of-band distortion power by changing the nonlinearity parameter of soft clipping. The simulation results show that the proposed method can control the distortion power by 10 dB for a practical power amplifier. The results also show that a low-peak OFDMA transmitter can be realize with reasonable computational complexity because iterative processing for peak power reduction is unnecessary.

In the radio link design of cellular CDMA system, system capacity has been estimated with the uniform traffic distribution condition so far. In many cases, however, actual traffic in a service area is not distributed uniformly. Therefore, this paper discusses the up link capacity of the cellular CDMA system applied in a service area with tapered traffic distribution condition. The analytical result shows that the system capacity is degraded according to the degree of traffic concentration to the service area center. It is also suggested that the cell size change in inverse to the degree of traffic concentration is effective to mitigate the system capacity degradation

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.