Even if the signals from an AP reach the intended terminal, communication failure can occur if a signal received from another AP(s) is stronger. To insure the effectiveness of the Wi-Fi environment, it is imperative that signals reach the required area at an intensity greater than the threshold. Thus, we felt it important to investigate the possibility of signals from outside the hospital that might interfere with the efficient operation of our system.
To do this measurement, we walked around the areas in which the wireless LAN use was planed, checking the whole area, not specific intervals. When we found a signal coming from outside, the intensity was measured. Both IEEES02.11a
and 11g were measured using an Air Magnet Surveyor (AirMagnet Inc.). Whether the invasion was from outside or inside the hospital was confirmed by the received service set identifier (SSlD). Because the fourth floor was only for the staff and there was no plan for AP installation, it was not measured. Measurement was performed after the building was completed, but before it began to be used. No APs other than those we planned existed in this building at the time of measurement.