Section 6.2. Advantages of RFID Over Bar Codes

6.2. Advantages of RFID Over Bar Codes

The advantages of RFID over bar codes are as follows:

• Support for nonstatic data. An RFID tag data can be rewritten many times (assuming, of course, that the RFID tag is an RW tag). The data on a bar code is static and cannot be changed.

• No need for line of sight. Generally, an RFID reader does not need a line of sight to read an RFID tag's data. A bar code reader always needs a line of sight to read a bar code.

• Longer read range. An RFID tag can have a much longer read range than a bar code. Depending on several factors, this can range from several feet to a few hundred feet

• Larger data capacity. An RFID tag can store more data than a bar code.

• Multiple reads. A suitable reader can read several RFID tags within a very short period of time, automatically, using a feature called anti-collision. A bar code reader, however, can only scan one bar code at a time.

• Sustainability. An RFID tag is generally rugged and resistant to harsh environmental operating conditions (to a fair extent). A bar code is easily damaged (for example, by moisture or dirt).

• Intelligent behavior. An RFID tag can be used to do other tasks besides simply being a data carrier and transporter. A bar code, however, does not have any intelligence and is a vehicle for only storing data.

The following, although often mentioned in the media, are dubious and therefore are not considered clear advantages of RFID over bar codes:

• Read accuracy. RFID is far more accurate than bar codes.

• Item-level tagging. A bar code does not support item-level tagging.

The following sections discuss these points in more detail.

6.2.1. Support for Nonstatic Data

You can rewrite the data on a read-write RFID tag many times. How many times? In general, you can rewrite an RW RFID tag on the market today at least 10,000 times, with vendors claiming 100,000 times or more! Rewriting proves useful if you use the tag to record data that was not available when it was created. A tag is created when some data is initially put on the tag to make the tag usable. This data might be an identifier that identifies this tag uniquely from the set of all possible tags. Other types of additional information (generally about the object on which this tag is attached) are also possible. Why would you want to rewrite the data on a tag? It depends on the application for which this tag is used. For example, suppose that an RW tag is attached to an item that is being built as it moves through a production line. As the item moves through the different stages of the production line, the time taken to complete each stage can be recorded on the tag. Finally, when the item rolls off the production line, the data recorded on the tag can be used to analyze, for example, the production-line bottlenecks (that is, places where this item is spending most of its time). Also, if an RFID tag needs to be recycled in an application, it may need to rewrite its old data with new data.

A bar code, in contrast, can only store static data (that is, data that cannot be rewritten with new data). A new bar code has to be created every time to store this new data.

6.2.2. No Need for Line of Sight

One of the distinct advantages of RFID is that it does not require line of sight. Suppose, for instance, that an RFID tag is attached to an object and that object is placed inside a container made of some RF-lucent material (for the frequency used) such as paper. An RFID reader can read this tag right through the container without any need to open it! Therefore, the reader does not need to "see" the tag to read its data. In some situations, however, this is not true. In these situations, a line of sight must be established between the reader and the tag for the tag data to be read reliably. (Although establishing a line of sight does not guarantee improved readability, it helps to configure the critical factors such as tag read distance, reader energy, and reader antenna positioning to counter the environmental impact.) In these situations, UHF tags are used, and there is a significant amount of RF-reflecting material, such as metal, present in the operating environment. A classic example is an automobile production line, where essentially everything is made of metal and there is a high degree of RF wave reflections in the surroundings. If a UHF RFID tag is placed on a vehicle to track it in the production line, the tag and the readers must be placed in such a manner that a line of sight can be clearly established at the points where readings will take place (to avoid multipath signals and antenna nulls). In these situations, an RFID tag offers no advantage over bar codes.

A bar code reader always needs a clear line of sight to a bar code to scan it. Therefore, it might perform poorly in some typical applications, such as airline baggage handling (where the tagged objects [baggage] are oriented randomly on the luggage belt). In this scenario, a good chance exists that overlapping bags will obstruct the line of sight to a bar code on other bags. In addition, a bar code on a bag might be oriented in such a manner that the bar code reader cannot read it. These factors will lead to poor read performance. If suitable RFID tags and readers are used, however, orientation of the tag to the reader might not have a significant impact as compared to bar codes. In addition, because line of sight is not needed, most of these tags can be read through overlapping suitcases (assuming made of RF-luent material for the frequency used). Therefore, read accuracy of RFID luggage tags can be substantial higher (more than 15 percent higher has been reported) than with bar coded tags.

6.2.3. Longer Read Range

A passive RFID tag operating in the UHF range has a read range of about 30 feet (about 9 meters) under ideal conditions. An active tag in the low UHF range (433 MHz) has a read range of about 300 feet (about 91 meters). An active tag operating in the 2.45 GHz range has a read range of more than 100 feet (about 30.5 meters).

The principle of bar code reading is tied to optics, and the read range of a bar code reader depends on the focal range of the reader. The read range of commercially available readers is 30 feet (about 9 meters) or less.

6.2.4. Larger Data Capacity

A two-dimensional bar code, such as Aztec, can encode up to 3,750 characters of data from the entire 256 ASCII characters, which is substantial. There is not a huge difference today in data capacity as far as passive tags are concerned, but this might change in the future. Custom active tags, theoretically, have unlimited data capacity.

What does a tag with large memory buy for its user? This is a loaded question for which there is no easy answer. Clearly, for an active tag that needs a large amount of memory to perform specialized tasks, a large tag memory is an advantage. With regard to the amount of data transferred, the transmission time and the error rate of reading increases with an increase in data transfer size. Therefore, a tag with a large memory capacity for (storing and) transferring a large amount of data to a reader can prove to be a disadvantage!

6.2.5. Support for Multiple Reads

An RFID reader can automatically identify a few to several tags in its read zone in a short period of time. This capability to automatically identify multiple tags can make tag-reading operations fast.

A bar code reader can only read one bar code at a time, which means a longer read time of bar codes compared to the same number of RFID tags by an RFID reader. Therefore, if the cost of an RFID system is acceptable, existing operations that use bar codes might be made more efficient.

6.2.6. Sustainability

An RFID tag can (to a fair degree) withstand harsh environmental conditions such as heat, humidity, corrosive chemicals, mechanical vibration, and shock. Note that currently no single tag can withstand all these environmental conditions. Generally, a particular tag from a specific vendor is resistant to one or a few of these conditions.

A bar code is only as good as the material on which it is printed. Therefore, a bar code printed on paper is easily damaged in the presence of moisture or heat. A bar code can be easily smudged in presence of dirt and paint. A bumpy bar code can withstand high temperatures.

6.2.7. Support Intelligent Behavior

An RFID active tag can carry on-board electronics and a power supply (battery) to perform functions such as monitoring its surrounding temperature, humidity, and so forth. The tag can then use this data to dynamically calculate other parameters and transmit it (with its unique ID) to a suitable reader.

In contrast, a bar code is just a repository of static data and nothing else.

6.2.8. Read Accuracy

Now back to the original issue of read accuracy. A common statement today is "RFID is far more accurate than bar codes." However, this statement has two problems. First is the availability of official, objective data on the accuracy of bar codes. Second is the complete lack of availability of official, objective data on the accuracy of RFID tag reads over bar codes. With an absence of hard data on RFID accuracy, but the presence of hard data about bar code accuracy, it is unfair to say RFID is "far more accurate" than bar code.

In the classic bar code accuracy study conducted by Ohio University, using DataMatrix symbology, the worst rate of error was 1 per 10.5 million; the best rate of error was 1 per 612.9 million reads! These are accurate numbers indeed! Table 6-1 lists a summary of findings.

From my experience with clients who have existing automated bar code systems in production, the accuracy of bar code reads (after system tuning) is typically in the 90 percent range or higher. Therefore, the accuracy advantage of RFID over existing bar code systems seems equal or less than 10 percent (in general, and at the best) for these types of bar code solutions. In some situations, this can hardly be called "substantial," assuming, of course, that RFID will actually increase the accuracy rate at this level. If the environment is not well suited for RFID, the accuracy improvement rate using RFID over bar code might be zero (or even negative)! Then again, depending on the application, RFID might offer accuracy benefits of more than 10 percent (the airline baggage-handling example, for instance). In addition, for a particular application, an increase of even a few percentage points might bring substantial value to a business.

6.2.9. Support Item-Level Tagging

There seems to be a growing belief that only RFID can support item-level tagging, whereas bar code cannot. This is untrue. Different types of bar codes have varying capacity for storing data. The linear bar code types that are used most widely for item level tagging (for example, UPC) do not have sufficient storage to identify an item uniquely. However, other bar code types, if used, have more than enough characters to identify any item uniquely. For example, assuming alphanumeric data storage, DataMatrix can store up to 3,116 bytes; Aztec 3,750 bytes; and PDF417 1,850 bytes. These capacities are more than enough to contain a unique number of 1,024 bits, which itself is more than enough to uniquely identify any particular item.

At this point, you might thinking that, with so many advantages, RFID is a clear winner over bar codes. Hold this thought. Although RFID has several advantages over bar code, the next section covers the advantages bar code has over RFID.