As a result, these
tags not only receive information from a query, they also receive energy. This energy is
used to power the tag to determine and send a response to the query. Although passive
tags are generally cheaper than active tags, they have two major disadvantages: (1) range
of passive tags is signi?¬?cantly lower than active tags and (2) complexity of response is
signi?¬?cantly reduced over active tags because of the limited energy budget. However,
active tags, in addition to being more costly than passive tags, often require battery
replacement.
Power consumption affects both passive and active devices. For an active device, the
amount of power=energy consumption required by the tag dictates the lifetime that a tag
may operate. Ranges and complexity of computation of passive devices for features such as
added security capability or access to sensors are directly impacted by power usage. In this
chapter, we present techniques and architectures that are applicable to either passive or
active tags, or both. These techniques are designed to address the concerns of reducing
power in RFID systems without compromising their capability or to extend their capability
in a power-ef?¬?cient manner.
The remainder of this chapter is organized as follows: Section 11.2 presents a technique to
signi?¬?cantly increase the memory capacity of a passive tag while minimizing the amount of
additional energy required.
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