Limited Battery Longevity

If you are using a portable computer in an automobile, performing an inventory in a warehouse, or caring for patients in a hospital, it's probably too cumbersome or impossible to plug your computer into an electrical outlet. Thus, you will depend on the computer's battery. The extra load of the wireless NIC in this situation can significantly decrease the amount of time you have available to operate the computer before needing to recharge the batteries. Your operating time, therefore, might decrease to less than an hour if you access the network often or perform other functions, such as printing.

To counter this problem, most vendors implement power management techniques in their radio cards and access points. Without power management, radio-based wireless components normally remain in a receptive state waiting for any information. For example, some vendors incorporate two modes to help conserve power: the Doze Mode and the Sleep Mode. The Doze Mode, which is the default state of the product, keeps the radio off most of the time and wakes it up periodically to determine if any messages await in a special mailbox. This mode alone uses approximately 50% less battery power. The Sleep Mode causes the radio to remain in a transmit-only standby mode. In other words, the radio wakes up and sends information if necessary, but it is not capable of receiving any information. Other products offer similar power management features.

NOTE The typical current draw of an IEEE 802.11b product is as follows:

Transmit: 350mA Receive: 250mA Sleep: less than 10mA

The aggregate power consumption of the wireless LAN device is dependent on utilization and configuration parameter settings. Higher utilization and settings resulting in higher rates of transmission will increase power consumption.