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Gen 2 RFID not too far away

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SUNSHINE Technologies and Alien Technologies are successfully deploying Gen 1 RFID tags and readers within a broad range of industries including pathology and forensics, defence, health, manufacturing as well as numerous supply chain and logistics applications.<[etk]>

According to Scott Austin, MD of Sunshine Technologies, the Class 1 Gen 2 air interface protocol – which has been approved by EPCglobal - provides a number of enhancements that will help solidify the adoption of RFID in the UHF bandwidth.

Established to have one standard single UHF specification worldwide, Gen 2 addresses emerging UHF regulations in many different regions. Gen 2 improves on the best features of preceding specifications and anticipates a range of future applications and product extensions including higher-function sensor tags.

Class 1 Gen 2 RFID is faster, with a more flexible read and write speed. It also offers higher reliability in tag counting, more robust performance of readers in close proximity and enhanced security.

Faster, more flexible read speeds

Like people talking in a noisy room, RFID tags and readers can talk fast and will understand each other in close proximity or in a quiet spot, or they can talk slower and be understood with more background noise and at a greater distance.

The difference with Gen 2 RFID is that it provides four different communication speeds, providing more flexibility for different operating environments. Running at top speed, Gen 2 systems have the theoretical potential to read over 1,000 tags a second in applications which are well insulated from RF noise. They can also slow down in noisy conditions and still read 100 or more tags a second with high reliability.

In applications where the faster Gen 2 communication modes can be used, users should expect to see enhanced system performance and read robustness. This flexibility is expected to have the biggest impact in regions operating under stringent regulatory limits, particularly Europe and Asian countries.

Gen 2 sets aggressive targets for the speed at which tags can be programmed and dictates that tags can be writeable at a minimum rate of about five a second and sets a target of 30 a second. Hitting this target would allow RFID tag integration and programming on most high-speed assembly and packaging lines.

The Q protocol and symmetry

RFID tags at the outer edge of a reader’s range experience only brief and intermittent moments of power from the reader, and are therefore difficult to read reliably. In its ’Q’ protocol and the use of symmetric persistent states, Gen 2 builds on several principles proven effective in Gen 1 systems to address this challenge.

The Q protocol uses short, simple query/acknowledgement interchanges between readers and tags so that a tag experiencing only brief moments of power can be read.

Implementing Q, a reader issues a query and each tag responds with a randomly generated number. The reader then issues an acknowledgement that includes a single tag’s random number, which prompts that tag to send its ID.

This process continues until all tags in the reader’s field have been counted. By using random numbers generated by individual tags as the basis for sorting rather than EPC numbers, all tags can be identified uniquely even if the same EPC number is shared among many tags.

To further enhance efficiency and speed, the ability to quiet tags after they have been read helps focus a reader’s efforts on getting the most difficult-to-read tags at the edge of the field or on an RF-absorptive material.

Users familiar with Gen 1 protocol understand how it puts tags to “sleep” after they have been read. With the easy-to-read tags quieted, the reader can focus on only the more challenging tags in the field that haven’t yet been counted.

To begin a new count or sort, the reader issues a wake-up or activation command to ensure that all tags will be awake and ready to read.

Gen 2 refines the process by introducing a dual-state, symmetric inventory scheme which enables a new count to start without tags needing to hear and react to a wake-up command.

Under this approach, a tag changes its state each time it is read. As the reader counts each tag in the ‘A’ state, those tags move automatically to the ‘B’ state. And as each B tag is counted, its state changes back to A.

Much like repeated wake-sleep cycles deployed under Gen 1, a Gen 2 reader repeats counts of A and B tags until all tags in the field have been identified.

Mitigating reader interference

In terms of RF power transmitted, RFID readers “shout” their commands to tags, providing enough energy to the tags that they can “whisper” their response. Too many readers operating in close proximity and shouting at the same time can drown out the whispered responses of the tags.

Gen 2’s following features will allow users to develop tailored solutions for their applications, even ones requiring many readers operating in close proximity:

• Gen 2 seeks to improve ‘dense-reader’ operation in several ways. First it is designed to use available RF bandwidth as efficiently as possible. The baseline RF signalling approach is relatively quiet, particularly compared to some preceding protocols such as EPC Class O. The Q protocol also sorts tags with minimal data exchange required between the reader and tag.

• Gen 2 also introduces a radio signalling mode that can isolate tag response into a side channel where it can be better heard. Miller sub-carrier rates allow the reader to specify side channels of varying widths according to the overall environmental noise conditions. The narrower the side channels, the easier it is for the reader to focus in on what the tags are saying. Gen 2 provides for an “FMO” signalling mode that can enable faster reads through the Miller sub-carriers. This mode is relatively susceptible to RF noises. Users should expect that noisy conveyors, electric equipment or even fluorescent lights may create enough interferences to challenge this mode.

• Gen 2 calls for three modes of reader operation: single reader, multi-reader and dense-reader. Under the dense reader mode, reader transmissions are segregated into distinct RF channels offset from the response channels of tags to keep tag transmissions from colliding with reader transmissions.

• Gen 2 ensures accurate reads in noisy conditions by implementing a similar data verification approach as Gen 1, thereby avoiding the “ghost read” problems experiences with Gen 1 systems. In addition to verifying read data, Gen 2 adds a feature that confirms when tags have been written correctly.

Parallel counting

Gen 2 also anticipates situations where there are several readers simultaneously communicate with the same tag. Under the dual-state symmetric tag sort approach there is a risk that one reader will change a tag’s state in the middle of another nearby reader’s inventory cycle, causing the second reader to miss the tag. In many situations this is not a problem. Software often needs to know only that an item has been read by one of several readers. For applications that depend on knowing which specific reader has read the tag, Gen 2 provides the solution.

Using Gen 2 “sessions” allows a single tag to communicate with two or more readers in parallel. Readers can be assigned to use any one of four logical sessions for reads. In a warehouse as an example, readers at alternating dock doors could use different sessions to avoid interfering with each other’s transaction. Mobile readers, such as hand-helds and forklifts, could be assigned to a third session. As outside vendors’ hardware might be assigned the fourth session. Up to four separate identifications of the same tag can be undertaken simultaneously without interference and without having to wait for any one reader to complete its sort. The monitoring and allocation of sessions can be managed via readers or a central control point.

Enhanced security

With some incremental expense for additional memory to the tag, Gen 2 takes a more traditional approach to security than Gen 1 by using 32-bit passwords. These passwords can be used for activating kill commands to permanently shut down tags as well as for accessing and re-locking a tag’s memory.

For protection against eavesdropping on tag reading by unauthorised devices, the Q protocol never requires the communication of an entire tag ID over the airwaves. Even if a receiver is positioned to listen to a reader’s communication with a tag population, the signals are so scrambled it is virtually impossible to determine the EPCV numbers.

The Gen 2 transition

The largest global drivers for RFID, mandates from Wal-Mart and the US Department of Defense, are well underway with integration of RFID into supply chains and daily operations of suppliers. These deployments are based on RFID technology and products that are well established and broadly available today. As such, Gen 1 will continue to be an allowable technology for these mandates for some time to come and will be accepted in their systems for at least a year after Gen 2 is first permitted.

Users who are just getting started with RFID in Australia face a different choice. One option is to get started with Gen 2 products as they become available over the next year or so, which obviates the need for a future transition from Gen 1. Alternatively, new users can initiate an implementation with Gen 1 hardware and tags for which the performance, cost and availability is well known. Given the complexity of some RFID deployments, this can be a more predictable approach.

The next several years will be exciting as the promise of Gen 2 is realised. Every iteration of hardware will move closer to achieving the great potential inherent in Gen 2. With UHF RFID already well established and ramping, the Gen 2 standard will ultimately be instrumental in extending its global coverage.

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