They therefore need other solutions to make them
out-of-band, if this is the design goal. Synchronous and asynchronous wakeup
protocols will be discussed in Sections 4 and 5 of this chapter, respectively.
3 On-demand Paging
3.1 Principle
In on-demand paging, the main radio is completely turned o?® when the node
is in the dormant state. The wakeup functionality is o??oaded to a separate
device, which typically has substantially lower power consumption. This separate
paging device can therefore always be kept active, and messages sent to
it can be used to instruct the node to turn on the main radio.
This basic idea was proposed for PicoRadio [15] [16]. Specialized hardware
is used to serve as a wakeup page receiver. Since this functionality is substantially
less complex than the full radio receiver design, this specialized piece
of hardware consumes only very limited idle power. In principle, the wakeup
page could use the same resources as the regular data channel, and therefore
be categorized as in-band. By using a di?®erent frequency, an out-of-band
scheme is created. Overall, using a dedicated device to handle the wakeup is
the most flexible and energy e?±cient solution, but might be di?±cult or costly
to produce.
A less sophisticated solution is utilizing another radio technology to serve
as the wakeup communication channel. This is the principle behind wake-onwireless
[17]. In this project, hand-held devices, in this case iPAQs, are proposed
as versatile platforms to support wireless interactive voice applications
such as IP telephony.
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