Section 3.1. Limitations of RFID


3.1. Limitations of RFID

The current limitations of RFID include the following:

  • Poor performance with RF-opaque and RF-absorbent objects. This is a frequency-dependent behavior. The current technology does not work well with these materials and, in some cases, fail completely.

  • Impacted by environmental factors. Surrounding conditions can greatly impact RFID solutions.

  • Limitation on actual tag reads. A practical limit applies as to how many tags can be read within a particular time.

  • Impacted by hardware interference. An RFID solution can be negatively impacted if the hardware setup (for example, antenna placement and orientation) is not done properly.

  • Limited penetrating power of the RF energy. Although RFID does not need line of sight, there is a limit as to how deep the RF energy can reach, even through RF-lucent objects.

  • Immature technology. Although it is good news that the RFID technology is undergoing rapid changes, those changes can spell inconvenience for the unwary.

The remainder of this chapter discusses these limitations in detail.

3.1.1. Poor Performance with RF-Opaque and RF-Absorbent Objects

If high UHF and microwave frequencies are used, and if the tagged object is made of RF-opaque material such as metal, some type of RF-absorbent material such as water, or if the object is packaged inside such RF-opaque material, an RFID reader might partially or completely fail to read the tag data. Custom tags are available that alleviate some of the read problems for particular types of RF-opaque and RF-absorbent materials. In addition, packaging can present problems if made of RF-opaque materials such as metal foils.

It is expected that improvement in the tag technology will overcome several of the current problems associated with RF-opaque/RF-absorbent objects.

3.1.2. Impacted by Environmental Factors

If the operations environment has large amounts of metal, liquids, and so on, those might affect the read accuracy of the tags, depending on the frequency. The reflection of reader antenna signals on RF-opaque objects causes what is known as multipath (see Chapter 1, "Technology Overview"). It is a safe bet in these types of environments to provide a direct line of sight to the tags from a reader. Although the tag reading distance, reader energy, and reader antenna configuration are the major parameters that need to be configured in these cases to counter the environmental impact, a line of sight helps to achieve this configuration. In some cases, however, this might not be possible (for example, in an operating environment where there is high human traffic). A human body contains a large amount of water, which is RF-absorbent at high UHF and microwave frequencies. Therefore, when a person is in between a tag and a reader, there is a good possibility that this reader cannot read the tag before this person moves away. So, serious degradation of system performance might result. In addition, the existence of almost any type of wireless network within the operating environment can interfere with the reader operation. Electric motors and motor controllers can also act as a source of noise that can impact a reader's performance. Some older wireless LANs (WLANs) in the 900 MHz range can interfere with the readers. This problem mostly exists in older facilities that have not upgraded their WLAN equipment.

This issue most probably will remain for some time. Some of the present interference issues might remain unresolved.

3.1.3. Limitations on Actual Tag Reads

The number of tags that a reader can identify uniquely per unit time (for example, per second) is limited. For example, today, a reader on average can uniquely identify a few to several tags per second. To achieve this number, this reader has to read tags' responses several hundred times a second. Why? Because the reader has to employ some kind of anti-collision algorithm to identify these tags; to identify a single tag, a reader has to walk down the range of possible values (see Chapter 5, "Privacy Concerns"). Therefore, several readings of tag responses are required before a reader can uniquely determine tag data. A limit applies as to how many such reads a reader can perform within a unit time, which, in turn, dictates a limit on the number of unique tags that can be identified within this same time period.

Improvement in the reader technology will undoubtedly increase the number of tags that can be uniquely identified per unit time, but there will always be an ultimate limit on this number that no reader will be able to exceed.

3.1.4. Impacted by Hardware Interference

RFID readers can exhibit reader collision (see Chapter 1) if improperly installed. A reader collision happens when the coverage areas of two readers overlap and the signal of one reader interferes with the other in this common coverage area. This issue must be taken into account when an RFID installation plan is worked out. Otherwise, degradation of system performance might take place.

This issue can be somewhat solved today by using what is known as time division multiple access (TDMA). This technique instructs each reader to read at different times rather than both reading at the same time. As a result, two readers interfere with one another no longer. However, a tag in the overlapping area of these two readers might be read twice. Therefore, the RFID application must have an intelligent filtering mechanism to eliminate duplicate tag reads. As RFID technology improves, new solutions to this issue might become available.

3.1.5. Limited Penetrating Power of the RF Energy

The penetrating power of RF energy finally depends on the transmitter power of the reader and duty cycle, which are regulated in several countries around the world (see Chapter 1). For example, a reader might fail to read some cases on a pallet if they are stacked too deep, even if these cases are all made of RF-lucent material for the frequency used. How many such cases can be put on a pallet for proper reading? You can only determine the answer to this question by experimenting with actual boxes stacked on an actual pallet in the actual operating environment using actual RFID hardware. This number will also vary from country to country, depending on the restriction of reader power and duty cycle. Therefore, the answer needs to be determined experimentally; it is very difficult, if not impossible, to determine it theoretically.

Unfortunately, this limitation will remain as long as international restrictions on reader power and duty cycle remain. Therefore, if you need to deploy a solution in multiple countries, you must seriously consider this issue.

3.1.6. Immature Technology

Immature technology is a practical issue facing RFID technology today. An RFID solution can only be as good as the hardware currently available from the vendors. The vendors are doing their best to develop improved products, but maturity might not be available for some time to come. For example, it is not uncommon for passive UHF tags currently used in supply-chain operations to get damaged when subjected to existing handling techniques, with the defective tag rates shooting up as high as 20 percent or more.

The same tag types (for example, passive 915 MHz for metal) from different vendors might perform differently. It is possible that a tag needed for satisfactory read accuracy for a specific application is not currently available, despite intensive research being conducted both at the theoretical (for example, antenna design) and manufacturing (for example, material used, processing techniques) levels to build tags of different kinds. Building a custom tag for an application can be very expensive (typically in the range of $100,000).

Readers have come a long way in the past two years, gradually transitioning from a simple interrogator to a well-defined network device with built-in intelligence to support several functions needed by an RFID application. Some of these functions are filtering, caching recent tag reads, input from external sensors, output for activating sensors and actuators, and so on. Similarly, antenna technology is making antennas smaller and cheaper. However, a side effect of these improvements is that new RFID hardware is coming out at a very fast rate, which might urge businesses to upgrade their equipment at the same rate! Such rapid upgrades are generally not necessary because the products are backward compatible in most cases. Business has to implement realistic strategies so that its current investment in RFID hardware is not wasted as new products come out.

The issue of immaturity/maturity will continue to be part of RFID technology in the near future. Stabilization of the technology in terms of products and globally acceptable standards will eradicate this issue, but a prediction of the timeline for such stabilization is difficult to make.



    RFID Sourcebook
    RFID Sourcebook (paperback)
    ISBN: 0132762021
    EAN: 2147483647
    Year: 2006
    Pages: 100
    Authors: Sandip Lahiri

    flylib.com © 2008-2017.
    If you may any questions please contact us: flylib@qtcs.net