Electronic Design

Newest Wireless Standard Gives Designers Choices, Not Compromises

IEEE wireless standard gives RFID implementers a new option

There always seems to be room for one more wireless standard. I have actually stopped being amazed at how many standards there are. For every new standard developed, a different segment of wireless applications is covered. But each new standard always tends to omit some needs—leaving the door open to a new standard later. And with so many standards to choose from, designers are not forced into compromises by existing standards when there always seems to be a new one that is a better fit. So I guess one more new standard is good news. This one offers another way to do RFID-like tracking and identification functions. Here is a quick introduction to this new wireless tool:

The latest wireless standard is referred to as RuBee. It is being developed by the IEEE Standards Association and has been designated IEEE P1902.1. RuBee is basically an alternative to other RFID. Actually, there are quite a few RFID options, which include the older original 125 kHz systems, the widely used 13.56 MHz systems, and the newer Gen2 UHF (915 MHz) systems. Something for everyone, more or less. Each of these existing standards has its own unique features, benefits, and downsides. The new RuBee P1902.1 standard overlaps those standards and provides new benefits and features of its own.

There are a number of key issues that plaque RFID systems: read range and an inability to work around metal or liquids. The range over which an RFID tag can be read is pretty short (like no more than a few feet and sometimes within inches). You can blame the passive nature of the tag for such a short read range, as the tag has to convert the RF energy from the reader into DC power to turn on the tag so it can transmit data back to the reader. Low power translates into short range. But in most cases, the tags have a useful range. Nevertheless, there are some applications where RFID would be useful if the range was longer.

This is where RuBee comes in. Its range is as high as 50 to 100 feet. Longer range means that the tag is not typically going to be passive, but an active tag with its own battery. This gives it considerably more power and range. The tag, therefore, is an actual wireless transceiver, rather than the weird backscatter modulated circuitry of common passive tags.

Another problem with some RFID tags is their inability to work in the presence of metal. Metal blocks and reflects signal. A product with a tag sitting on a metal shelf is hard to read—if it can be read at all. A toll tag attached to a license plate on a vehicle is less likely to work than if that tag were attached to a windshield. This is a result of both the metal and the distance between the license plate and the windshield. P1902.1 tags are expected to overcome this problem.

Another problem solved by P1902.1 tags is the liquid problem. Liquid absorbs and attenuates RF signals significantly, thereby shortening their range or killing all operations completely. A tag used on an animal for tracking or a human in a hospital usually doesn't work as well, as animals are mostly around water anyway. The RuBee tag is expected to work under water or near it.

How Does It Work?

The proposed new P1902.1 protocol will hopefully solve all of these RFID problems by operating at a very low frequency. The operating frequency will be less than 450 kHz, with a typical expected frequency of 132 kHz. Such low frequencies penetrate metal and liquid far better than RF tags at 13.56 MHz and above. They could even work underground to some extent. At such a low frequency, the wavelength is very long. Remember that wireless signals are made up of both near field and far field signals. The near field is within about one wavelength of the device, while the far field is beyond one wavelength. It is the far field that is the radio signal made up of both magnetic and electric fields. The near field is mostly the magnetic field. For that reason, RuBee, and any low frequency RFID tag for that matter, works more like a transformer using magnetic induction. That's why it can overcome the metal and liquid problem. And because the operating frequency is so low, one wavelength is about 852 feet long. No wonder the range is longer.

Anyway, remember that the attenuation of a radio signal (far field) is proportional to the square of the range. For a magnetic signal, the attenuation is proportional to the cube of the range. That is both good news and bad news. The bad news being the range is more limited, but still useful. The good news is there should be less interference from other nearby tags and readers.

One down side of a low frequency tag is that the data rate will naturally be limited because the available bandwidth at 132 kHz is very limited. However, those developing the standard believe the data rate can be as high as 9600 baud. Something in the 300 to 1200 bps range is more likely. Slow, but who cares. Most data transmitted with these tags are very short, so it is not an issue. Of course, you cannot read very many tags in a short time. With 13.56 and 916 MHz tags, read rates can be hundreds of tags per second. With RuBee, that may only be a few tags per second. If you need the higher tag read rate, RuBee is not for you.

An interesting feature of the P1902.1 protocol is that it is a peer-to-peer (P2P) protocol. That means each tag could potentially be a reader. And in any case, any tag can speak to another tag if you set it up that way. The protocol is expected to be real-time and searchable using IPv4 addresses and subnet addresses. Each P1902.1 tag, if correctly enabled, can be discovered and monitored over the Internet. You search for and find any tag using your Internet browser, then read it. Cool....

The RuBee tags will not be the 5 cents variety that big retailers have been looking for. They will cost much more because of the battery and a larger chip that will contain EEPROM and most likely a 4-bit embedded controller that can be programmed. But the cost will no doubt be justified where the object to be tracked or located is a major asset, either a piece of equipment or even a human or animal. Battery life is expected to be at least 10 years or more, depending upon usage.

RuBee tags and equipment are not yet available. The IEEE is just now beginning to work on the protocol. The initial expectation is that a draft of the standard will be available later in the year. The first formal meeting of the P1902.1 working group will be held February 20 at the Marriott Copley Hotel in Boston one day before the RFID Smart Labels Conference.

Those who have used RFID know that not all tags fit all apps. One size does not fit all. No surprise there if you have been following the whole wireless standard progression over the years. This one is sure to capture new users because of its unique qualities. And it certainly won't kill off any other forms of RFID. It is just one more option to consider.

For more on RFID, refer to RFID Forecasts, Players & Opportunities 2007-2017. My personal thanks to Sarah Lee at IDTechEx of Cambridge, UK for permission to reprint this report.

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