Mikio Kuwahara

Code reassignment scheme on CDMA smart antenna systems

This paper proposed code reassignment scheme on CDMA smart antenna systems. The proposed scheme suppresses multi-channel access interference (MAI) caused by the shortage of an orthogonal spreading code in a sector. Computer simulation shows an 18% capacity gain and 3 dB reduction of Tx power on the down link.

Field tests of space-time packet scheduler with exchanging beam schedule information

To evaluate the feasibility of the proposed space-time packet scheduler (STPS), the test bed including two experimental access points (AP) was constructed in a suburban area. Two effects of proposed STPS were confirmed through the field tests. One of them is that inter-AP interference decreases by the proposed scheduler, and a high-quality communication is possible even if access terminal is present in the environment of strong inter-AP interference. The other one is that the packet collision ratio in downlink reduces from about 23% to less than 1%.

A study of space-time packet scheduler with exchanging beam schedule information

A novel technique to reduce inner and inter cell interference for the cellular packet data transmission on the downlink is proposed. In this method, the base transmission station (BTS) has a space-time scheduling which uses beam schedule information of adjacent cell BTS. This method drastically improves frequency efficiency by suppression of inter-cell interference. According to the simulation results, the frequency efficiency of a twelve-beam array antenna system can be improved on by eighty percent compared to the scheduling without using beam schedule information.

A study on the accuracy of a CDMA-based location system

Recently, positioning of the handset from which the calls occur has been required for public safety. For emergency services, USA wireless carriers have been obligated to provide a position location at the handset and the services are called Enhanced 911 (E911). We have developed a IS-95-based location system which uses forward link trilation (FLT) techniques. Performance evaluations in various environments through simulations are often required and the evaluation technique is the key issue for efficient development of such location systems. In this paper, the simulation model proposed here is verified with a field trial. The simulation results and the trial results show good agreement. The results show that the proposed scheme could give the ability to evaluate the performance of the location system. Then, this paper shows simulation results of the location accuracy in typical environments with actual geometric configuration of the handset and the base stations. The results show that the location system achieves positioning accuracy which satisfies the E911 requirements.