October 07, 2005
The EPC Gen 2 system – part 1
The EPCGlobal Gen 2 standard promises to deliver increased functionality in RFID usage. However, it is important to realize that there will be differences in the functioning and the potential of the various products that comply with the Gen 2 specifications. Even though, Gen 2-compliant products can lead to improvements in inventory management and retail operations, a standard performance need not be a logical fallout of a standards-based approach. One of the main reasons for the difference in performance is that user environments differ even within an industry.
As Gen 2 is a standard, it only specifies the minimum performance criteria; for companies to implement Gen 2-compliant tagging, they need to be aware of the deliverables that they expect from the process. A company needs to assess itself in terms of the six important criteria that determine the deployment of a Gen 2-compliant system. These include speed, range, efficiency, reliability, security, and cost.
The Gen 2 specifications for speed were based on user experiences while using Gen 1 tags. The fundamental speed criterion is that the tag reading should not slow down the material handling process. Gen 2 standards do not have a minimum speed requirement as the identification speed depends on several factors such as the environment, the number of tags, power, etc.
The technical specs laid down for Gen 2 tags should allow 1500 readings/second in the US and 600 readings/second in Europe. Objects being transported on conveyor belts moving at speeds of 650 feet per second can be read by following the specs. The specs can help to achieve a write rate of around 10 tags per second.
Gen 2 provides specs that if followed will allow readers to select a group of tags for reading based on the structure of the data, for example, the readers can be programmed to read the tags on cases and ignore those on pallets. This allows the systems to process only the data that is necessary and increases operation speed. Persistence is an important functionality that is not mentioned in the Gen 2 specs but is critical for RFID performance. It implies the constant monitoring of the read fields to ensure that the tags that enter the read zone a little late do not miss out on getting read.
Gen 2 also has a feature referred to as the “Q algorithm”, which helps in tag identification and collision prevention. The algorithm is used to initiate a “sleep” mode in the tags such that they respond only when it is their turn to do so. It eliminates the problem of reidentifying tags. However, in case the tags present on the edge of the reading zone do not receive sufficient power, they may fail to remember if they have been identified previously.
Since the bandwidth on wireless networks is limited, it has to be managed carefully. This involves selecting the right frequency, creating the right environment, managing the power output, etc. Gen 1 regulations were based on the U.S Federal Communications Commission (FCC) radio regulations and were not compatible with the regulations in other countries. Often, users had to acquire site licenses. This is not the case with products based on Gen 2 standards; they do not require a site license and can be used globally in conformance with the user requirements. The Gen 2 products can operate in three modes such that bandwidth utilization is maximized. The three modes are single reader, multi reader, and dense reader.
Products operating in the single reader mode can meet the FCC requirements regarding management of bandwidth but cannot exist in compatibility with RF devices that are active in the vicinity. Devices that operate in the UHF mode and wireless phones that operate in the single reader mode can also cause interference. Products operating the multi reader mode make more efficient use of bandwidth. Up to ten readers can coexist in an environment without any major interference problems.
A majority of the distribution centers have more than ten readers operating in the given environment. They can make the best use of the allotted bandwidth by functioning in precise channels. This is facilitated by working in the dense reader mode. EPC equipment is best installed and managed in the dense reader mode. Single-reader mode devices are used in isolation, they have the advantage of being easy to produce and legacy RFID equipment can be upgraded to single reader mode. However, there are not many opportunities to employ a single-reader mode in today’s working environment.
Gen 2 specifications ensure faster and more accurate reading as compared to the Gen 1 specifications because the data checking is performed by the air interface instead of the reader. Moreover, the standard protects the system from receiving incorrect positive readings that are referred to as ghost tags. The phenomenon of ghost tag readings occurs when readers receive incomplete readings from more than one tag and interpret it as a reading from a single tag.
Reliability of the tags under different temperature conditions is also improved with the Gen 2 standards. Earlier, the tag and reader synchronization was achieved at the tag manufacturing stage, which was an expensive step and placed limitations on the range of temperature in which the tags could operate. The Gen 2 standard also supports data verification so that there will be fewer instances of lost and corrupted data. Write verification helps to maintain the integrity of the data written to the tags. This is important with respect to RFID operations as implementing RFID leads to an increase in automated and unattended operations. Therefore, remote monitoring and notification capabilities should be built into the system so that the performance and availability parameters of the system are met.
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