COMPARING THE CAPABILITIESOF BLUETOOTH AND WI-FI:

POWER CONSUMPTION
Power consumption is a critical consideration as it directly affects device battery life. This consideration is obviously most crucial for devices that spend most or all their operating hours on battery power – devices such as PDAs and mobile phones. From its inception, Bluetooth was designed to be a small-form factor, low-cost, low-power technology. The Bluetooth specification incorporates a number of power saving features in order to keep power use to a minimum. These features include a standby mode as well as four connected modes – parked, hold, sniff and active. An adaptive transmission power feature further minimizes power use.

In order to achieve Ethernet-level data rates, Wi- Fi operates with higher radio power on fixed channels of greater bandwidth. Wi-Fi offers a power save mode in which STAs “sleep,” then reawaken periodically to check for messages. Bluetooth and Wi-Fi modules are available in many different form factors including PC cards 9PCMCIA), Compact Flash (CF) cards, Secure Digital (SD) cards, Springboard modules, PCI cards and mini-PCI cards. Table 1 below summarizes the power requirements of various Bluetooth and Wi-Fi devices classes under various operating modes.

As shown in the table above, current Bluetooth devices have a minimum current that is approximately one-tenth the amount of minimum Wi-Fi current requirements, and a transmit current as little as a tenth of Wi-Fi’s transmit current, depending upon the output power of the devices in question. The implication is that Bluetooth will drain the battery less quickly than will Wi-Fi, making Bluetooth a more attractive option for users with smaller devices. In fact, a typical PDA with a 500 mA-hr battery life could support Bluetooth running in idle mode for more than 250 hours, whereas Wi-Fi could only be supported for 20 – 50 hours in sleep mode. If both technologies were in full transmit or receive mode, a PDA using Wi-Fi could expect little more than an hour of operation while a PDA using Bluetooth could operate for five to ten hours.