There are different standards that regulate the use of UHF RFID throughout the world. The three main regulations are: FCC, ETSI Lower band, and ETSI Upper band. Whilst the protocol remains the same, the frequency and technique to communicate with the tag are different. Here is a summary of three widely used regulations:
|Standard Name||Primary Regions of Operation||Frequency Range||R-->T Technique||Max Radiated Power|
|FCC||FCC part 15.247 & 15.249||North America||902-928 MHz||FHSS||4W EIRP|
|ETSI Lower||EN 302 208-2 v2.1.1||Europe||865-868 MHz||4 channel plan||2W ERP|
|ETSI Upper||EN 302 208 v3.2.0||Europe||915-921 MHz||3 channel plan||4W ERP|
The above powers are the maximum power radiated from the antenna. The reader maximum power is calculated taking into account antenna gain and cable loss.
The maximum allowable reader power for the FCC regulations is calculated by the following formula:
Maximum reader transmit power (in dBm) = 36 dBm (FCC limit) – Antenna Gain (in dBi) + Cable loss (in dB)
For the ETSI Lower band, the maximum allowable reader power is calculated by the following formula:
Maximum reader transmit power (in dBm) = 33 dBm (ETSI lower band limit) – Antenna Gain (in dBd) + Cable loss (in dB)
For the ETSI Upper band substitute 36 dBm for the 33 dBm in the above equation to account for the higher limit.
For regulations that are stated in ERP, the antenna gain must be in dBd (gain compared to a reference dipole) units and if the regulations are stated in EIRP, the antenna gain must be in dBi (gain compared to an isotropic radiator) units. Typically, antenna gain is given in dBi so this needs to be converted to dBd for standards that use ERP for their radiated power limits (e.g. ETSI).
The formula for conversion is dBi = dBd + 2.15
Please consult the Installation and Operations Guide of the specific reader model you are installing for more information.
For more information regarding the regulations worldwide, please refer to this EPC Global document.
For more information about the differences between the measure of power, please refer to EIRP and ERP article.
This article describes the best practices for selecting channels when operating in the ETSI Lower band (865 MHz - 868 MHz).
- For more information regarding the ETSI Upper band (915 MHz - 921 MHz), please refer to the following article:
Transitioning from Lower to Upper ETSI Band using Impinj Readers and Gateways
For ETSI Lower band, there are 4 transmit channels available (hence the name “four channel plan”) where the reader can transmit the maximum allowable power from the antenna (namely 2W ERP, 33dBm).
Due to having significantly less channels, less power and less bandwidth per channel than in FCC regions, applications designed for ETSI regions often have to consider channel selection.
Here are some basic best practice tips:
1. Ensure you’re using the correct channels; use all four channels whenever you can; but this is not always possible due to other readers transmitting in close proximity; (if using ItemTest to test your reader, select “Use Specified Frequencies” in "Frequency Settings (ETSI Only)" section and select all 4 channels, as shown below)
2. If you have more than one reader in close proximity that will be operating at the same time then use alternate output channels as follows;
Reader A: channel 4 (865.7 MHz) and channel 7 (866.3 MHz)
Reader B: channel 10 (866.9 MHz) and channel 13 (867.5 MHz)
Red bands: Reader A
Blue bands: Reader B
This can be important for times when two readers are used to create a portal or when two dock door portals are in close proximity. When readers are actively transmitting, if this separation of channels is not designed into the system there is a 25% chance that they will be transmitting at the same time; thereby increasing the chances of interference; and with it the chances of not reading tags.
3. Considerations if you have to use a single channel; ETSI regulations dictate that it is only permitted to transmit on a single channel for a certain period of time. 4 seconds if tags are being read and only one second if no tags are being read... if this happens then the reader must stop transmitting for a period of 100 ms. The reader ensures it complies with the regulations automatically, therefore, it’s important, where possible, to ensure more than one channel is selected.
If you have more than two active readers in close proximity; careful consideration must be given to the design of the system. Which channels to use, separation of antennas, angle of antennas and how operation of the reader is triggered are all variables that can affect the operation of the RFID solution. Please also see this post to learn how to select specific channels when using ETSI readers: Selecting Specific Channels Using ETSI Regulations