RuBee

RuBee (IEEE P1902.1) is a two way, active wireless protocol that uses Long Wave (LW) magnetic signals to send and receive short (128 byte) data packets in a local regional network. The protocol is similar to the IEEE 802 protocols which are also known as WiFi (IEEE 802.11), WPAN (IEEE 802.15.4) and Bluetooth (IEEE 802.15.1), in that RuBee is networked by using on-demand, peer-to-peer, active radiating transceivers. RuBee is different in that it uses a low frequency (131 kHz) carrier. One result is that RuBee is very slow (1,200 baud) compared to other packet based network data standards. 131 kHz as an operating frequency provides RuBee with the advantages of ultra low power consumption (battery life measured in years), and normal operation near steel and/or water. These features make it easy to deploy sensors, controls, or even actuators and indicators.

RuBee is often confused with RF ID Radio-frequency identification, but it does not work like RF ID. All RF ID protocols use what is known as backscattered transmission mode. RF ID tags act like a mirror, and work as reflective transponders, as opposed to RuBee that is a networked transceiver that actually transmits a data signal. The P1902.1 standard is in its final stages of approval by the IEEE. [cite web
url = http://www.engadget.com/2006/06/13/rubee-protocol-overcomes-rfid-shortcomings/
title = RuBee protocol overcomes RFID shortcomings
accessdate = 2007-09-02] . RuBee received the Technology of the year award from Frost & Sullivan in 2007. [cite web
url = http://www.pictpix.com/PPM/Frost%20%26%20Sullivan.pdf
title = 2007 North American Supply Chain Visibility Solutions Technology Innovation of the Year Award
publisher = Frost & Sullivan
accessdate = 2007-09-02] .

The IEEE P1902.1 protocol details

P1902.1 is the "physical layer" workgroup with 17 corporate members. The Workgroup was formed in late 2006. The final specification and issued standard are expected early in 2008. The standard includes such things as packet encoding and addressing specifications. The protocol has already been in commercial use by several companies, in asset visibility systems and networks. However, IEEE P1902.1 will be used in many sensor network applications, requiring this physical layer standard in order to establish interoperability between manufacturers. A second standard has been drafted 1902.2 for higher level data functions required in Visibility networks. Visibility networks provide the real-time status, pedigree and location of people, livestock, medical supplies or other high-value assets within a local network. The second standard will address the data-link layers based on existing uses of the RuBee protocol. This standard, which will be essential for the widespread use of RuBee in visibility application's, will support interoperability of RuBee tags, RuBee chips, RuBee network routers and other RuBee equipment at the data-link layer.

RuBee tag details

A typical RuBee Radio Tag has: a 4 bit CPU, 1 kB sRam, crystal, and lithium battery with expected life of five years. ) depending on the antenna configuration. By 'harsh environment' we mean situations in which one or both ends of the communication is near steel or water. RuBee radio tags function in environments where other radio tags and RFID may have problems. RuBee networks are in use in many visibility applications, including: smart shelves for high-value medical devices in hospitals and operating rooms; smart entry/exit portals; and a variety of agricultural visibility networks for livestock, elk and other exotic animals.

How RuBee works

IEEE P1902.1 RuBee uses magnetic waves also often called inductive communication. James Clerk Maxwell presented his now famous set of equations (Maxwell's Equations) to the Royal Society in 1864. These equations describe what happens when an electron travels along a conductive wire. Two fields are created, the Electric Field, labeled E, and the Magnetic Field, labeled H. These electric and magnetic fields travel through the aether, (i.e. outer space or the far field), at the speed of light with an assumed impedance of 377 Ω. E, the electric field, may be given in watts or volts per meter, and H, the magnetic field, may be given in gauss or amperes per meter. The two fields are tied together with the aether to form simple electric circuit capable of transferring power. However, when these two fields are measured in what is called the near field (much less than the wavelength of the signal) very strange things happen. ( [http://www.edn.com/contents/images/150828.pdf Also see Capps “Near Field or Far Field"] ). E and H are no longer connected in a simple predictable manner. The value of "c" (speed of light) and the resistance of the aether are altered and it is possible to produce large H values with low E values. It is as if the aether impedance has been reduced to only a few ohms.

Virtually all of the energy radiated by a RuBee base station or a RuBee radio tag is contained in the magnetic field (H), not the electric (E) field. This stems from the fact that the RuBee antennas are short relative to the wavelength (about a mile and half or 2½ km at 131 kHz), and RuBee operates in the near field. A typical emitted E from a RuBee base station is about 40-50 nanowatts (10^-9, and H is about 900 milligauss (90 µT). Finally, RuBee is a packet based protocol in which only one end of the communication at a time generates fields, that is, a RuBee tag is a radiating transceiver.

RuBee is not RFID. In contrast, radio-frequency identification (RFID) works in backscatter transponder mode, and simply reflects the radio signal. RFID tags do not transmit E or H signal, they just reflect the base-station carrier like a mirror. The RFID base-station must provide three things to a tag - a communication carrier so the tag has something to reflect, enough power to make the tag operate, and timing clock. As result the RFID base-station must produce a lot of power. Some RFID base-stations produce as much as 12 watts, but more typically around 4 watts. Various RFID designs work at: Low frequency (LF - usually around 125 kHz) high frequency (HF - 13.56 MHz), or ultra high frequency (UHF - 915 MHz). Some RFID tags have batteries (so called "active" tags), but in some cases the battery only powers internal functions; these tags still communicate using backscattered mode. A RuBee tag operates as a radiating transceiver, powering its emissions using its battery and timing them using its internal (crystal) clock.

RuBee feng shui

RF is based on physics, and can be reliably modeled with prediction tools and tuned models (See [http://www.commsdesign.com/main/2000/06/0006build.htm RF Microwaves, and Migraines] , [http://www.amazon.com/dp/product-description/0750674032 Electro Magnetics Explained] .) RF is not always predictable because the active environment (people, steel shelves, floors, cabinets, doors) are all part of the same tuned circuit, and change with time. For example, a cell phone call to a phone in a building is modified by steel in the building. Maybe reception can improved by moving the phone near a window, or pointing the antenna in some hard to predict direction -- That's RF Feng Shui. Radio waves are effected by just about everything around us. Many environmental factors influence performance. The obvious ones are steel and water, but people and electrical noise sources are also on top of list.

Magnetic waves can pass through almost anything, even rock. That same rock blocks RF after only a few feet. An RF signal falls off as 1/"r", whereas the strength of a magnetic wave falls off far faster at the rate of 1/"r"³. This means that the magnetic signal will not travel nearly as far as the RF signal. At first glance this difference in fall-off rate may appear as a negative for the range of a tag using magnetic signaling, but, as explained below, it turns out to be quite a plus in a local visibility network. Secondly, an unexpected advantage is that the noise RuBee sees is also magnetic, so it too falls off 1/"r"³. Noise and interference sources must be much more local to have significant strength, and tend to be easy to locate and minimize in an IEEE 1902.1 network.

RuBee is 99.99% magnetic waves it therefore is not affected at all by people or animals, mud or water. Steel can alter performance, but steel can actually enhance a magnetic signal. A high frequency (over 1 MHz) RF antenna on or near a steel shelf has three problems: 1. The steel detunes the antenna; 2. RF nulls will appear on the shelf with no signal at all (Swiss cheese field) this is because steel blocks radio waves; and 3. Steel also reflects the radio waves (E in Maxwell's equations) contributing to communication errors and shelf nulls.

In contrast Long Wavelength magnetic transmissions (below 1 MHz) is not blocked or reflected by steel so nulls do not occur. The loop antennas may be detuned by the steel, just like higher frequencies. But, unlike higher frequencies, magnetic loop antennas may be re-tuned with external capacitors, and, in many cases, circuits can be created that dynamically pick the optimal external capacitor for the antenna. Thus the de-tuning issue can vanish in a RuBee network. But the tuning has to be set to the right frequency by adjusting the capacitor to match the tuning curve with steel in place.

Parasitic inductance and capacitance (see Self-resonant frequency) of the antenna wire and the shelf steel limit the range of tuned frequency of any antenna circuit. A simple loop of speaker wire about 100 ft (30 m) in diameter maybe tuned to resonate at 131 kHz with a simple external capacitor. A loop of only a 1 inch (25 mm) may be also tuned to resonate at 131 kHz. At 30 MHz, however, you might be able to tune the 1 inch (25 mm) antenna, but not the 100 ft (30 m) antenna, and not the shelf. At 30 MHz the largest tunable loop is about convert|1|ft|m|0|sing=on. RuBee's frequency is low on purpose so that it can nearly always re-tune to compensate for the parasitic inductance and capacitance despite use in harsh environments like steel shelves (see Roche et al. 2007). Back to the shelf example -- the RuBee installation actually tunes the steel in the shelf, and the shelf itself becomes the antenna - the shelf becomes part of the resonate circuit and the H signal gets stronger near the shelf. For frequencies over 1 MHz it's not possible to incorporate most things you find in a warehouse, office building or factory as part of the antenna.

RuBee has good Feng Shui in harsh environments because most steel items resonate well at the RuBee frequency of 131 kHz. As the frequency goes up over 1 MHz fewer steel items resonate. At a frequency of 10 MHz for example, nothing large made of steel can be tuned to resonance.

How big can a RuBee loop antenna be? As the antennas get larger and larger noise becomes the gate keeper. A 100 ft (30 m) diameter loop can detect lighting storms 100's of miles away. The biggest source of noise is deep space kilometric noise. While it is possible build a second antenna and do differential subtraction, a convert|10000|sqft|m2|-3|abbr=on limit of a RuBee network is adequate for most practical visibility applications.

RuBee disadvantages and advantages

The major disadvantage RuBee has over other protocols is speed and packet size. The RuBee protocol is limited to 1,200 baud in existing applications. It is expected that IEEE P1902.1 will also specify 1,200 baud. The protocol could go to 9,600 baud with some loss of range and reduced Feng Shui. However, most visibility applications work well at 1,200 baud. Packet size is limited tens to hundreds of bytes. RuBee's design forgos high bandwidth, high speed communication because most visibility applications do not require them.

The use of LW magnetic energy brings about a number of advantages:

* Long battery life – Because of the use of low frequencies and data rates the chips and detectors can run at low speed. Using (lowest cost) 4 micrometre CMOS chip technology, this leads to extremely low power consumption. LW magnetic wave tag systems can and have achieved 15 year lives using low-cost lithium batteries. This is also the expected battery shelf life.

* Tag data travels with the asset – Because data is stored in the tag, IT (Information Technology) costs are reduced. This means that with a low-cost handheld reader one can simply read a RuBee tag and learn about the asset — manufacturing data, expiry date, lot number, etc. — without having to go to an IT system to look it up. In addition, the distance between the reader and the asset is not critical. RuBee can also write to a tag at the same range as it can read it. RFID, on the other hand, uses EEPROM memory, and writing to the tag is awkward. (In the case of RFID, range is limited, more power is required and write times are long.)

* Safe – A RuBee base station produces only nanowatts of radio energy. RuBee's LW magnetic waves are not absorbed by biological tissues and are not even regulated by OSHA. In fact, RuBee produces less power and lower field strengths than the metal detectors in airports and the anti-theft detectors in retail stores operating at similar frequencies — by a factor of about 10 to 100. Recently published studies show that RuBee has no effect on pacemakers or other implantable devices (Hayes et. al, 2007).

* High security and privacy RuBee tags have many unique advantages in high security applications. The Eavesdropping range (the range at which a person with unlimited funds can listen to tag conversations) is the same as tag range. That means if someone is listening, they must be close enough for you to be able to see them. This is not true for RFID or 802 protocols (see Wall Street Journal May 4 [http://online.wsj.com/article_email/article_print/SB117824446226991797-lMyQjAxMDE3NzA4NDIwNDQ0Wj.html |Credit Card Data] ). That means no one can secretly listen to tag/base station conversations. In addition, since RuBee tags have a battery, a crystal and sRAM memory, they can use strong encryption with nearly uncrackable one time keys, or totally uncrackable one time pads. RuBee is in use today in many high security applications for these reasons.

* Controlled volumetric range – RuBee has a maximum volumetric range of approximately 10,000 square feet (900 m²), using volumetric loop antennas — From even a small volumetric antenna of 1 sq ft (900 cm²), RuBee can read a tag within an egg-shaped (ellipsoid) volume of about 10 x 10 x 15 ft (3 x 3 x 5 m). A special feature of IEEE P1902.1 known as Clip makes it possible to place many adjacent loop antennas in an antenna farm, and read from tenss to hundreds of base-stations simultaneously.

* Cost effective - With RuBee, relatively simple base stations and routers can be employed, which means receivers and card readers can be reasonably priced as compared to higher frequency transceivers. In addition, the tags often include a single chip, a battery, a crystal and an antenna, and can be priced competitively with respect to active RFID tags (those including a battery).

* Less noise – Because ambient noise in a region falls off as 1/"r"³, RuBee exhibits reduced susceptibility to extraneous noise. The major limit to antenna size is deep space noise.

Notes

References

* Prithvi Raj, 2007 North American Supply Chain Visibility Solutions Technology Innovation of the Year Award, Frost&Sullivan [http://www.pictpix.com/PPM/Frost%20%26%20Sullivan.pdf Frost & Sullivan]
* "IEEE Begins Wireless, Long-Wave Standard for Healthcare, Retail and Livestock Visibility Networks; IEEE P1902.1 Standard to Offer Local Network Protocol for Thousands of Low-Cost Radio Tags Having a Long Battery Life," "Business Wire", June 8, 2006
* "Visible Assets Promotes RuBee Tags for Tough-to-Track Goods," by Mary Catherine O'Connor, "RF Journal", June 19, *2006, http://www.rfidjournal.com/article/articleprint/2436/-1/1/
* Charles Capps, “Near Field or Far Field,” EDN, August 16, 2001, pp. 95-102. This excellent article is available online at: [http://www.edn.com/contents/images/150828.pdf Near Far Field RF]
* Hayes DL, Eisinger G, Hyberger L, Stevens JK. Electromagnetic interference (EMI) and electromagnetic compatibility (EMC) of an active kHz radio tag (Rubee [TM] , IEEE P1901.1) with pacemakers (PM) and ICDs. Heart Rhythm 2007;4:S398 (Supplement - Abs). [http://picasaweb.google.com/visibleassets/MayoClinic?authkey=4ORtVU2brxQ Mayo Clinic Study]
* Martin Roche MD, Cindy Waters RN, Eileen Walsh RN, Visibility Systems in Delivery of Orthopedic Care Enable Unprecedented Savings and Efficiencies. U.S. Orthopedic Product News, May/June 2007 [http://picasaweb.google.com/visibleassets/Ortho?authkey=_5FDQiJLTBk Orthopedic Visibility]