RFID Regulations:
RFID Regulations
The higher frequency bands hold the most potential to realize the goals of retail. These
bands allow the use of small low cost tags due to the smaller wavelength. They also allow
fast data transfer due to the available bandwidth. However, there are some propagation
issues such as,
o Blockage Effects
o Attenuation by Moisture
o Mounting to Conductors
Of the available frequencies, the 900MHz band seems to provide the best set of tradeoffs
for most applications. World wide the frequency bands vary. A broadband antenna that
covers 865-954MHz frequency band would be usable over the vast majority of the world.
A narrower 865-928MHz band would not be usable in Japan but would work pretty much
everywhere else.
There are no worldwide standards for RFID. In the United States, the FCC allows
companies to deploy RFID readers that emit 4 watts effective isotropic radiated power in
the Industrial, Scientific, and Medical (ISM) band from 902 to 928 MHz. The modulation
is Frequency Hopping Spread Spectrum, (FHSS). This is a category of spread spectrum
modulation in which each bit of data is divided into chips and each chip is represented by
a different spectral component or tone in the spread spectrum band using a pseudorandom
sequence to assign tones. Modulated in this way, the transmissions hop from frequency to
frequency within the band, requiring a receiver synchronised to the pseudorandom
chipping sequence to recover the data. In Europe, ETSI allows only half a watt of
effective radiated power (ERP) in a narrow 250 kHz band from 869.4 MHz to 869.65
MHz. This allocation is for non-specific short-range devices, which can be on only 10
percent of the time (0.1 duty cycles). Due to a lack of read range the European
restrictions are likely to change. Most likely, readers will be allowed to emit 2 watts of
ERP between 865.6 MHz and 867.6 MHz. The band is divided into 10 channels of 200
kHz. Europe employs a system where readers listen for other transmitters using the same
channel before trying to communicate with tags. This is called listen before talk, or
(LBT). The regulations set the LBT sensitivity at -96 decibels. The reader employs
Adaptive Frequency Agility (AFA). If another transmitter is detected, the reader tries
another channel until it finds a free channel.
Other popular RFID frequency bands include the following;
Low 125kHz, 1.95MHz, 3.25MHz, 4.75MHz, 8.2MHz, 13.56MHz, 27MHz
Medium 430-460MHz, 865-928MHz
High 2350-2450MHz, 5400-6800MHz
The low bands tend to be very short range. This is largely because of the inefficiency of
the tag antennas that are just simply to small when measured in wavelengths. The high
frequencies allow for high performance tags but the propagation characteristics do not
allow the signals to easily penetrate crates or to travel around boxes.
All of the power output specifications have been written in terms of EIRP (or ERP). ERP
can be converted to EIRP by adding the gain of a theoretical dipole (2.15dB). Since the
specification is in EIRP rather than simply radiated power, systems using higher gain
antennas need to have the input power to the antenna reduced. Hence, antenna gain is not
useful parameter for increasing the tag illumination. Cushcraft has designed custom
antenna solutions that increase the near field illumination with out forming directional
beams. As such, the input power can remain high with an antenna that focuses the power
on the tags rather than into a far-field beam. One of these techniques is shown in figure 2.
This method is particularly useful for Conveyer applications.