Interference of Wireless LAN and Mitigation Technique on TD-CDMA System for City Lifelines Monitoring
A dedicated wireless data collection system to monitor city lifelines, i.e., water, electricity and gas supply, duringand post seismic hazard has been investigated using an experimental system. The system employed a 2.4GHz TD-CDMA technique as a new application of CDMA. The TD-CDMA system collected data from 256 household terminals in a cell in 10.24sec with a frame error rate (FER) at 2•~10-1 When a wireless LAN (W-LAN) was brought into operation in the same frequency band as the experimental system, interference occurred. A method using an attenuator placed in the input port of the base station receiver in conjunction with CDMA power control has been developed to mitigate the interference in a CDMA fixed station. While W-LAN operating, the interference power increased from -106dBm to -87dBm, and the FER deteriorated to 3•~10-2 or more. When attenuation in the range of 3dB-11dB was placed in the input port of the receiver, CINR (Carrier-to-Interference-Noise Ratio) improved from -13dB to -10dB or more, provided that the power control function remained effective. As a result, the FER recovered to a level at 1•~10-3 The experiment has demonstrated the effectiveness of the interference mitigation technique.