Passive RFID Using UHF Delivers Long-Range Benefits In The IoT

For consumers, the impact of the IoT may be summarised as greater convenience. We have grown to expect certain things to happen ‘automatically’, without knowing how, and the IoT will accelerate and expand that.

For example, many people now use contactless payment, something that is enabled by short-range RF communications between a payment terminal and a bank card, mobile phone or smart watch equipped with the same technology. This avoids the need to physically insert a card into the payment terminal and enter a PIN; on the face of it, it may seem like a small thing, but as anyone who uses it regularly will appreciate, it can significantly speed up the purchasing process.

RF technology has the potential to change many more aspects of modern life. One of the most established forms of RF communication used in the IoT is RFID technology, and research shows that its adoption amongst retailers to tag clothing is set to increase massively before the end of the century. Tagging items allows them to be identified by a payment terminal as soon as they are presented, making the customer’s purchasing experience even more convenient.

RFID technology has been around for many years and its use in the IoT is entirely synergistic. Because each RFID device has a unique identity, it can be used to identify practically anything. When the reader is part of a connected system, it enables almost unlimited potential for new applications. Recently, the introduction of Ultra-High Frequency (UHF) RFID technology has further extended that potential.

UHF RFID
RFID is a contactless technology that can operate over a range from a few centimetres to several metres, using frequencies of 120 to 150 kHz (Low Frequency, or LF), 13.56 MHz (High Frequency, or HF) and 860 to 960 MHz (Ultra-High Frequency, or UHF). Most of the existing applications (such as identification, access control and payment) use passive devices; that is, the RFID device does not have its own power source, such as a primary cell. This is the primary feature of RFID devices and, in general, devices in the LF and HF frequency ranges receive their power through inductive coupling (or near-field), while UHF devices use Electro-Magnetic Wave (or far-field) Propagation.

Standards organisations are actively developing the standards necessary to make RFID more widely deployable, which includes ISO and IEC as well as EPC Global; in 2009, ISO/IEC integrated UHF EPC Gen 2 into ISO 18000-6 as Mode C.
RFID UHF bands vary in different countries and include frequencies between 860 MHz and 960 MHz (EPC global standard).

The most important characteristic in RFID system performance is range, or the maximum distance over which an RFID reader can either read information from, or write information to, the tag. Tag range is defined in terms of a successful read/write rate, expressed as a percentage. The rate will vary with distance, but it also depends on the RFID reader’s characteristics and how the operating environment effects the propagation of the signal.

In general, read and write ranges are different due to the different amounts of power required by the transponder chip for each of these operations.

The main challenges involved with developing and operating a UHF RFID system reside in the reader and the passive tag, as outlined below.

Tag Limitations:

• The most important tag limitation is the chip sensitivity threshold. This is the minimum amount of received RF energy that is needed in order to power the RFID chip.
• Antenna gain
• Antenna polarization. For maximum range this must be matched between the tag and the reader antenna.
• Impedance match between the antenna and the RFID chip

Reader Limitations:

• EIRP (equivalent isotropic radiated power). This determines the power of the signal transmitted by the reader in the direction of the tag.
• Reader sensitivity. This is usually defined with respect to a certain signal-to-noise ratio or error probability at the receiver.

In general, the range of passive UHF RFID systems is limited by factors such as the tag characteristics, the propagation environment and the RFID reader parameters. Typically, if reader sensitivity is high then the tag limitations prevail. However, tag range can be maximized by designing a high-gain antenna that is well matched to the chip impedance.

UHF RFID in the IoT
In order to support the use of UHF RFID as an IoT solution, a global alliance was formed in 2014 by Google, Intel, Impinj, Smartrac and AIM (the industry association representing the automatic identification industry). It now has over 160 members, including NXP Semiconductors. Marketed as RAIN RFID, it has adopted the EPC Gen 2 specification, as incorporated into the ISO/IEC 18000-63 standard. If a solution is referred to as RAIN RFID, it will be using UHF RFID technology that complies with this standard and the alliance’s goals.

UCODE DNA makes toll roads simpler
Toll roads are becoming more common across Europe, providing a solution to congestion through charges that help expand and maintain the transport infrastructure. Collecting tolls can often require the driver to slow down, but using UHF RFID it is possible to make the process transparent.

By working together, Avnet Silica, systems integrator Kathrein Solutions GmbH and vehicle identification specialist Tönnjes successfully developed a system that can identify individual vehicles travelling on a motorway at a range of 20 metres and speeds of up to 250km/h. As such, the technology can be mounted in gantries over the motorway and collect data completely unobtrusively. This can be more reliable and carry a lower TCO than an image-based approach using cameras and vehicle registration recognition algorithms.

The system brings together the RRU 4500 UHF RAIN RFID Reader Unit developed by Kathrein, with the IDePLATE and IDeSTIX from Tönnjes, which is also RAIN RFID compliant and enabled by the ‘UCODE DNA’ UHF RFID integrated solution developed by NXP. The IDePLATE is a number plate which replaces the vehicle’s existing plate, and contains the passive UHF RFID chip, while the IDeSTIX contains the same technology housed in a simple label that is attached to the inside of the vehicle’s windscreen.

RFID revolutionises car rental
Using RFID technology to locate assets can streamline processes, including car rental. By implementing RFID in its rental vehicles, Sixt has reduced the amount of time it takes to locate keys for rental customers, but in addition it can now offer more precise time stamps on vehicle returns, more easily track a returned vehicle through its booking system and more quickly unite a customer with their rental.

With 2,200 branches worldwide and over 144,000 vehicles in its fleet, adding RFID has changed the way Sixt operates, reducing the average wait for customers picking up the keys to their rental vehicle from 3 minutes to just 20 seconds. As many branches are located in airports, servicing upwards of 600 rentals per day, this represents a significant improvement to the customer experience.

RFID and security
Every conversation about the IoT must also acknowledge the need for security in a more connected world. RFID is no exception and as the technology has evolved it has introduced greater levels of security in terms of authentication and cryptography. The latest iteration of NXP’s UHF RFID technology, available through Avnet Silica, is UCODE DNA.

It adds high levels of security to its existing long-range UCODE UHF RFID portfolio, combining all the functionality and security into a single IC. It adds two 128bit AES keys securely stored on the chip, that are used by the on-chip AES accelerator for cryptographic authentication. The keys are stored in an area of memory that is locked at production; the keys can be generated by NXP or by the customer, and are typically used for tag authentication and tag group authentication.