In warehousing applications, this allows a
WPAN to span an entire stack of shelves, using
only a single upload device, whereas multiple
RFID readers are required, each having an upload
capability. Upload devices and RFID readers cost
more than regular WPAN devices and RFID tags,
so that using less of them gives a potential cost
advantage to WPAN over RFID. Another advantage
of WPAN is that additional sensor devices
can be added to monitor temperature and humidity,
which is important in the case of perishable
products. This can be done in a standardized way
with WPAN sensors; however sensors interfaced
to RFID tags require a proprietary interface (Philipose
et al., 2005). The final advantage of WPAN
is improved reliability, due to the use of an error
control protocol. Any low power wireless communication
can be unreliable in the presence of
metal, for example, in warehouse shelving and in
the products themselves, and read ratios on RFID
readers are often