A novel interference reduction method, transmit power and window control (TPWC), is proposed to enhance the system capacity in the downlink of code division multiple access (CDMA) cellular packet systems. TPWC measures the propagation conditions and calculates the required instantaneous transmit power between a base station (BS) and a mobile station (MS). Then, TPWC sends packets only during a transmit time-window, in which the packets can be sent with less power than a predetermined threshold. TPWC reduces the average transmit power at the cost of an extra transmission delay at the BS. Computer simulations show that TPWC enhances the system capacity by two-fold in a CDMA cellular packet system when each MS has a loading ratio of 0.5 and an average delay allowance of 5 ms for the unit packet length of 1 ms. Furthermore, this paper proposes a multi-link packet transmission (MLPT) scheme in order to reduce the delay caused by TPWC. When an MS is at the cell edge, packets are distributed by MLPT to multiple BSs, from which packets are sent to the MS; thus, the transmission delay can be reduced by utilizing the transmit windows of each BS.

This paper proposes a multi-hop wireless link system for radio access networks (RANs) of new generation mobile communication systems. The performance of the multi-hop wireless link system is evaluated from the viewpoints of total output power, co-frequency interference characteristics, and the system frequency bandwidth based on a comparison with that of the single-hop wireless link system, which is currently used as a RAN. The proposed system is effective in realizing an enormous approach link capacity from both the total output power and the co-frequency interference viewpoints. From the system frequency bandwidth viewpoint, the optimum number of relays in the multi-hop connection is determined to be three hops in a line-of-sight propagation environment in order to minimize the frequency bandwidth for transferring traffic. We conclude that the multi-hop wireless link system is suitable for new generation mobile communication systems.

Radio access networks (RANs) for new generation mobile communication systems are required to construct economical high capacity networks. An optical wireless link is expected as a solution to the linking method in the construction of these networks. The optical wireless link provides high bit-rate transmission and allows for easy installation. However, optical-waves are severely attenuated in free-space transmission due to weather conditions and cannot provide a high level of link availability in long-distance communications. This paper describes the applicability of an optical wireless link to the RAN based on obtained atmosphere propagation properties from experiments on an 800-nm band optical wireless link from the viewpoint of link availability. The experimental results show that the BER performance of the optical wireless link exhibits a sufficiently low power penalty of less than 1 dB compared to that of the optical fiber link. Moreover, the results confirm that atmosphere attenuation of an 800-nm band optical wave due to fog and rainfall can be estimated by using a simple estimation equation. The optical wireless link could be used for RAN approach links with the range of less than 350 m to achieve the link outage rate of 0.004% from the viewpoint of the link budget design.

Frequency channel allocation according to the interference among links is important in autonomous distributed control wireless base station networks from the viewpoint of efficient frequency utilization. It is generally difficult to estimate the interference imposed on other links in a distributed control scheme. This paper proposes a novel frequency channel allocation scheme employing distributed control utilizing broadcast signals to estimate the intensities and frequencies of the interference to other links. The frequency channel, which can be allocated to a link from the viewpoint of the degree of the interference imposed on other links, can be found by receiving broadcast signals. Simulation results show that the proposed scheme efficiently allocates frequency channels to each link to avoid the interference.