Ogawa Masakatsu

People often have to stand waiting in a queue, which they may find disagreeable. Facilities where people must wait, for example, food courts, banks and amusement parks, need to recognize and provide an estimated wait time to increase customer satisfaction. Hence, there is demand for wait time estimation methods. Also, the requirement for estimation accuracy changes with the length of the queue. In this paper, we propose a cooperative line wait time estimation method using Bluetooth low energy (BLE, marketed as Bluetooth Smart) on a smartphone. To estimate the wait time, we utilize the stay-times of users approaching and moving past two preinstalled receivers. The wait time is estimated by the difference between the two stay-times. Our stay-time estimation includes two methods: a direct-wave blocking method and a stay-time estimation method. We experimentally evaluated with our method in a passageway of our university campus for different values of the range value which is a parameter used in the stay-time estimation. It was found that when the range value was set to 4-8 dB, almost all of the devices estimated the wait time to be within 20 s of from the expected wait time. This result satisfied the requirement of all users according to our questionnaire about discontent with erroneously estimated wait times.

The requirements for wireless sensor networks are low power consumption and long lifetime because sensor nodes are not always supplied by mains electric power. To reduce power consumption, sensor nodes have to reduce the idle listening duration. In this paper, we propose a MAC protocol without using carrier sensing. Packets of all sensor nodes are randomly transmitted within a frame which length is as long as data collecting interval. We perform the theoretical analysis of our protocol and derive the successful transmission rate in case that packets are transmitted in different duration. We simulate our protocol to verify the theoretical analysis.

The ZigBee has attracted attention as the smart home network. Already the wireless LAN (WLAN) has been introduced in the home network. Both the ZigBee and WLAN use 2.4 GHz frequency band, and the carrier sensing mechanism is used for contentions, but the collisions are occurred because the access control procedure is different. Therefore, it is necessary to improve the transmission success ratio for the sensing data periodically sent by the ZigBee. This paper proposes a media access control for improving the transmission success ratio in coexistence environment between the ZigBee and WLAN. The point of proposal is the collaboration between the ZigBee coordinator and WLAN access point. When the ZigBee coordinator detects the signal for ZigBee, the access parameter, DIFS, for the WLAN is changed. Simulation results show the transmission success ratio is improved by reducing the collisions between the ZigBee and WLAN.