RF signals (waves) travel almost forever and pass through many solid materials (though their strength does get reduced due to path loss and absorption). Therefore, they cannot be easily contained within a desired space, nor can we ignore the effects of radio signals transmitted by devices located in a long distance, even thousands of feet, away. These devices can interfere with your RF system, and your system can interfere with them. These types of interferences affect the performance of an RF system. They may, depending on their relative strength, reduce the read range of your system or render the system inoperable.
RF regulations typically vary from one country to another or from one region to another, due to the legacy usage of various portions of RF spectrum. In the technology’s early years, various countries or regions assigned different chunks of the RF spectrum for different uses. No worldwide standard was available, and even now none exist for many parts of the spectrum. Finding a worldwide RF range for new RF applications is a problem. For example, in the US, the UHF RFID systems are allocated a frequency range of from 902 to 928 MHz, but in European countries, that range was already assigned to other uses and is therefore not available. In Europe, UHF RFID systems are assigned frequency range of 865 to 868 MHz. As a result, a tag designed for the US will have problems being read in Europe and vice versa. To overcome these problems, RFID systems must be designed to incorporate all the frequency ranges (within the UHF band) used all over the world. This has been accomplished by EPCglobal Gen-2 and ISO 18000-6C standards. Readers and tags designed according to these standards will interoperate anywhere in the world.
• RF field power Effective Isotropic Radiated Power (EIRP) in watts.
• Bandwidth usage The frequency range allocated.
• Channels and channel spacing How the allocated frequency range is divided into channels to incorporate reader to reader interference.
• Duty cycle The percentage of time a reader can actively transmit.
RFID devices operating at UHF frequencies are allowed for operation in the Industrial, Scientific, and Medical (ISM) bands under conditions defined in FCC part 15 rules, section 15.247. Section 15.247 defines operation within the bands 902–928 MHz, 2400.0–2483.5 MHz, and 5725–5850 MHz. The 902–928 MHz band offers optimum range of operation and is usually preferred for supply chain applications. Part 15–compliant RFID systems typically use a frequency-hopping spread spectrum modulation technique to benefit from maximum reader transmitted power allowances. Part 15–compliant UHF readers can operate at a maximum transmitted power of 1 watt, or up to 4 watts with a directional antenna, if they hop across a minimum of 50 channels. For more details, you can download Part 15 rules from the FCC website.
• If the 20 dB bandwidth of the hopping channel is less than 250 kHz, the system shall use at least 50 hopping frequencies and the average time of occupancy on any frequency shall not be greater than 0.4 seconds within a 20-second period.
• If the 20 dB bandwidth of the hopping channel is 250 kHz or greater, the system shall use at least 25 hopping frequencies and the average time of occupancy on any frequency shall not be greater than 0.4 seconds within a 10-second period.
• The maximum allowed 20 dB bandwidth of the hopping channel is 500 kHz.
• FCC Section 15.247(b) deals with maximum peak conducted output power of intentional radiators:
• For systems using digital modulation in the 902–928 MHz, 2400.0–2483.5 MHz, and 5725–5850 MHz bands, the maximum peak conducted output power of intentional radiators is 1 watt.
• The conducted output power limit for various frequency bands is based on the use of antennas with directional gains that do not exceed 6 dBi.
• If transmitting antennas of directional gain greater than 6 dBi are used (see Section 15.247(c)), the conducted output power from the intentional radiator shall be reduced below the stated values, as appropriate, by the amount in dB that the directional gain of the antenna exceeds 6 dBi.
• As an alternative to a peak power measurement, compliance with the 1-watt limit can be based on a measurement of the maximum conducted output power.
Some of the parameters defined are frequency range 869.4 to 869.65 MHz, bandwidth 0.25 MHz, maximum allowable power 0.5 watts ERP, one channel, and 10 percent duty cycle. National restrictions may apply to the regulation. This very restrictive regulation severely limited the operations of RFID systems in Europe, until the new regulation was ratified the ETSI EN 302-308.
The key features of ETSI regulation EN 302-208 are as follows:
• Shared operation in band 865–868 MHz at transmit powers up to 2 watts effective radiated power (ERP)
• Operation in sub-bands of 200 kHz
• Mandatory “listen before talk” function
• Power levels of 100 mW, 500 mW, and 2 W ERP
• Mandatory listen time of more than 5 ms before each transmission
• Maximum period of continuous transmission of 4 seconds
• Pause of 100 ms between repeated transmissions on the same sub-band, or the interrogator will move immediately to another vacant sub-band
This regulation allows European RFID interrogators operating in the UHF band to perform nearly as well as UHF interrogators operating under FCC rules in the United States. It provides an additional frequency range, compared to EN 302-200, from 865 to 868 MHz for RFID interrogator operation. This increases the spectrum band from 250 kHz to 3 MHz. The number of channels on which readers can broadcast has been increased from 1 to 15. The new band is divided into three sub-bands. Under the old regulations EN 300-220, UHF readers were restricted to half a watt of ERP. The new regulations allow them to emit up to 0.1 watt ERP between 865 and 865.5 MHz, 2 watts ERP between 865.6 and 867.6 MHz, and 0.5 watt ERP between 867.6 and 868 MHz.
The Ministry of Public Management, Home Affairs, Post and Telecommunications (MPHPT), whose English name has been recently changed to Ministry of Internal Affairs and Communications (MIC), is responsible for formulating policies related to communications, which includes setting up of RFID standards within Japan. MIC has agreed to open up the UHF spectrum range of 952–954 MHz for RFID use. High-powered passive tag systems can use an antenna power between 10 mW to 1 W and an antenna gain of 6 dBi, which gives maximum power equivalent to 4 W EIRP. Users must obtain a license to use this RFID system. For low-powered systems of up to 10 mW, no user license is required.
In the last few years, China has been in the process of developing its own RFID standards to be in line with global standards. Standardization in China starts with the Standardization Administration of China (SAC), a ministry-level organization in the Chinese government. Under this organization are many Technical Committees focused on specific technology and business areas. The RFID National Standards Working Group, under China National Registry of Product and Service Codes (NPC), is responsible for standardizing hardware-related issues including frequency allocation, bandwidth, and tag-to-reader communication. The Article Numbering Center of China (ANCC) is focused on the tag encoding format making sure that goods tagged in China are compliant with the Electronic Product Code (EPC) coding scheme.
The Indian government arm that regulates applications of radio waves, the Department of Telecommunication (under the Ministry of Communications and Information Technology), has recently delicensed the spectrum in the 865–867 MHz band for use by RFID devices. The regulation on the use of wireless equipment in the band 865–867 MHz specifies that no license is required by any person to establish, maintain, work, possess, or deal in RFID on noninterference, nonprotection, and nonexclusive bases, in the frequency band 865–867 MHz with maximum 1 W transmitter power, 4 W ERP, and 200 kHz carrier bandwidth.
The UHF band for RFID operations in Australia is 918–926 MHz with a power of 1 W EIRP. The cattle, food, and beverages industry is supporting Australia’s drive to integrate internationally with the RFID technology. The Australian Communication Authority, responsible for setting RFID standards within Australia, has been considering the globally accepted industry-driven standards for the EPC.
The Infocomm Development Authority (IDA) of Singapore regulates radio frequencies allocated for various applications within Singapore. The IDA has recently announced the new spectrum allocation and power limits for RFID usage in Singapore in the UHF band.
Singapore allows use of the 866–869 MHz and 923–925 MHz bands within the UHF spectrum for RFID activities. The power limit for both bands is 0.5 W. It is expected that the power limit for the 923–925 MHz band will be increased to 2 W for RFID devices.