Title: Interference in RFID Systems
1Interference inRFID Systems
- Rene MartinezIntermec TechnologiesUnited States
Delegation
2RFID Interference Paths
3Interference Terminology and Approach
- Terminology
- Source-on-victim nomenclature A sources
transmission can interfere with a victims
reception and corrupt the victims capability to
decode information - Rejection is a quantitative measure of rejecting
an interfering signal while receiving the desired
signal - Approach
- RFID tags have stringent demands on cost, size,
and power consumption, so tags should ultimately
limit interference performance of RFID system - Analyze reader-on-tag interference, and use this
to set expectations on reader-on-reader
interference.
4Tag and Reader Interference Rejection
- Tags principally reject interference using
amplitude selectivity - Tags receive and select the stronger signal as
the desired reader signal, and tags successfully
decode if the desired signal is large enough
relative to the interfering signal. - Tags reject a weaker signals from an interfering
reader, and the rejection secondarily depends on
frequency difference between the desired and
interfering readers. - Readers principally reject interference using
frequency to select and receive tag signals from
a desired frequency. - If the interference is outside of the desired
frequency channel, the reader can decode the
desired signal even if the interfering signal is
larger. - If the interference is inside of the desired
frequency and larger than the desired signal, the
reader can not receive.
Ears
Eyes
5Interference Rejection Ratio
- The interference rejection ratio (IRR) measures a
receivers capability to reject interference, and
it often depends on the offset frequency between
the interfering and desired signals - The Interference Rejection Ratio is the maximum
acceptable ratio of interference-to-desired power
for a tag or reader to operate - Better rejection, e.g. reader
- Appears as higher values on the IRR dB scale
- IRR gt 0dB means successful reception even if the
interferer is stronger than the desired signal - Worse rejection, e.g. tag
- Appears as lower values on the IRR dB scale
- IRR lt 0dB means successful reception only if the
desired signal is stronger than the interfering
signal
6IRR Measurement Data for Passive Tags
Based on measurements on passive tags, active
tagscould have IRR from -10dB to -6dB
7Interference distances
8Range for Interfering Reader
- Graph assumes free space and passive tag is 3
meters from desired reader. Also assumes antenna
boresights for interfering and desired readers
are aligned
9Interfering Distances
10Reader Rejection Dependence on Tag
- where the terms and estimates for the terms are
- Pxmt is the readers conducted transmit powers
(30dBm) - Mloss is the backscatter modulation loss of the
tag (6dB) - Pdt is the desired reader signal into the tag
-10dBm for passive tags -30dBm for battery
tags - Grdr is the readers antenna gains (6dBi)
- Gtag is the tags antenna gain (2dBi)
- IRRtag is the tag interference rejection ratio
0.02 to 0.25 for passive tags (-17dB to -6dB)
0.10 to 0.25 for battery tags (-10dB to -6dB)
11Reader Interference Rejection
- Reader IRR based on reader-to-tag interference
- Using measured and estimated IRR for
tags Reader IRR is 32 to 40dB for passive tag
readers Reader IRR is 58 to 60dB for battery tag
readers - Reader IRR based only on rdr-to-rdr interference
- Reader IRR equals the ratio of the maximum
interference (0dBm) to the minimum signal from a
tag Reader IRR is 56dB for passive tag
readers Reader IRR is 96dB for battery tag
readers -
12Conclusion
- Analysis exclusively based on reader-on-reader
interference for battery tags RFID systems leads
to a stringent reader rejection ratio of 90dB or
higher however, an analysis that includes
reader-on-tag interference leads to a much more
lenient ratio of 60dB or better - Mitigation of reader-on-tag interference, such as
temporal synchronization, may be needed, and
mitigation will similarly alleviate
reader-on-reader interference.
13BACKUP SLIDES FORREADER-ON-TAG INTERFERENCE
- Adrian WitherspoonRene MartinezIntermec
Technologies
14Received Signal into Tag No Interference
15Signal into Tag 4th Channel Interference
16Signal into Tag 2nd Channel Interference
17Signal into Tag Co-channel Interference
18 Simplified View of Tag Demodulation
- Regardless of complexity, all UHF RFID tags have
amplitude demodulation and detect an average of
the RF envelope - The demodulator rejects interference if the beat
frequency is significantly faster than the
demodulator (fbeat gtgt 1/RC) - As beat frequency decreases (fbeat 1/RC or
fbeat lt 1/RC), the demodulators filter does not
assist in rejecting interference
19Reader-to-tag Interference Test Setup
- Data sets collected with using same Gen2 tag chip
mfg, different chips, 50-100 max range, and
modulating/CW interference
20Co-channel Reader-on-tag Interference
- Readers with accurate or phase-locked references
can effectively eliminate beat frequency in
co-channel operation, but other problems remain. - With little or no beat frequency, co-channel
interfering signal appears identical to desired
signal - Modulating interference appears as a desired
modulating signal, and without a beat frequency,
tags cant discriminate between commands from the
desired and interfering readers. - Unmodulated (CW) interference limits the
modulation depth and corrupts tags ability to
decode commands. For example, a CIRR higher than
-13dB is difficult if the minimum voltage
modulation depth is 80
21Conclusions (for Backup Slides)
- To prevent reader-on-tag interference for Gen2
tags, the difference of readers carrier
frequencies should be more than 800kHz - Tags need significantly (13-20dB) more desired
signal power if the difference in readers
carrier frequencies is less than 800kHzHz. - Tags need nominally (6dB) more desired signal
power if the difference in readers carrier
frequencies is more than 800kHz