2. Selection of the Short-Range Wireless Communication Method
Applications like the one illustrated in Fig. 1 require wireless communication with a relatively short range (20-30m). Currently available methods for such short-range communication include wireless LAN, Bluetooth®, Bluetooth® low energy, and ZigBee. In developing a network-linked healthcare device, the ideal method is selected in consideration of a number of factors, including frequency band used, data rate, communication range, power consumption (peak/mean), communication partner, cost and size. In the case of the ring pulse meter, the selection focused on data rate and mean power consumption.
Figure 3 shows a rough comparison between data rate and mean power consumption. Once every 200ms, the prototype ring pulse meter transmits a few bytes of measured data on heart rate and blood oxygen levels. The effective data rate is, therefore, in hundreds of bps. For such data rate levels, Bluetooth® low energy technology has the lowest power requirement. This and other important advantages, such as the possibility of accommodating uses linked with mobile phones, made this technology an ideal choice.
Fig. 1 Use of network-linked healthcare equipment
Fig. 3 Data rates and mean current consumption for different short-range
wireless communication methods