RuBee
RuBee (IEEE P1902.1) is a two way radio tag protocol that uses Long Wave (LW) magnetic signals to send and receive data packets in a local regional network. The standard is in its final stages of approval by the IEEE.[1]. However the protocol has been in commercial use in asset visibility systems and networks for several years. The protocol is similar to IEEE 802 known as WiFi IEEE 802.11, Zigbee IEEE 802.15.4 and Bluetooth IEEE 802.15.1 in that RuBee radio tags are networked radiating transceivers, but different in that it uses 131 kHz as a frequency. IEEE P1902.1 is the physical layer workgroup and was formed in late 2006 with the final specification expected early 2008. 1902 will be used in visibility network applications providing asset visibility. Visibility networks are employed to provide the status, pedigree and location of people, livestock, medical supplies or other high-value assets within a local network. RuBee received the Technology of the year award from Frost & Sullivan in 2007.
A typical RuBee Radio Tag - Has a 4 bit CPU,1 Kbytes sRam, crystal, and Li battery with expected life of five years.
RuBee is bidirectional, on-demand, peer-to-peer and can operate at other frequencies (e.g 450 kHz) but optimally at 131 kHz. RuBee tags can have sensors (temperature, humidity, jog), optional displays and may have a full 4 bit microprocessor with static memory. The RuBee protocol uses Internet Protocol (IP) or IP Address and may hold data in its own memory. Some tags have as much as 5 kilobytes of memory. This protocol functions successfully in harsh environments with networks of many thousands of tags and has a range of 3 to 100 feet depending on the antenna configuration. By 'harsh environments' is meant the ability to read and write data near steel or water. RuBee radio tags function in environments where other radio tags and RFID may have problems.
RuBee networks are in commercial use in applications including smart shelves for high-value medical devices in hospitals and operating rooms; smart, in-store and warehouse shelves for inventory tracking and a variety of agricultural visibility networks for livestock, elk and other exotic animals. The new IEEE P1902.1 standard will address physical and data-link layers based on existing RuBee protocol now in use. This standard, which will be essential for the widespread international use of RuBee, will support interoperation of RuBee tags, RuBee chips, RuBee network routers and other RuBee equipment now slated to be rolled out by several manufacturers.
How RuBee Works
James Clerk Maxwell | |
|---|---|
 James Clerk Maxwell | |
| Born | 13 June, 1831 |
| Died | 5 November, 1879 |
| Known for | Maxwell's Equations, The Maxwell Distribution |
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 or E and the Magnetic Field 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's or amps 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. (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 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. Finally, RuBee is a packet based protocol, that means 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 extra power. Some RFID base-stations produce as much as 12 watts, and typically most are around 4 watts. RFID may also work at a Low frequency (LF - usually around 125 kHz) high frequency (HF - 13.56 MHz), or ultra high frequency (UHF - 915 MHz). Some "active" RFID tags have batteries, but these tags still operate in backscattered mode. Again, RuBee operates as a radiating transceiver, has a battery and a crystal (internal clock).
RuBee Feng Shui
Often a cell phone call to a phone in a building is blocked by steel. Reception can improve by moving the phone near a window or pointing the antenna in one 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 noise 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/r3. 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 a magnetic signal's tag range, 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 and so it too falls off 1/r3. Local noise and interference tends to be easy to locate and is minimized in a IEEE 1902.1 network.
RuBee is 99.99% magnetic waves it therefore is not effected 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 to not occur. The loop antennas maybe detuned by the steel just like higher frequencies. But, unlike higher frequncies 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-tunning issue can vanish in a RuBee network. But the tuning has to be the right frequency by adjusting the capacitor to match the tunning curve with steel in place.
Parasitic inductance and capacitance (see Self-resonant frequency) of the antenna wire and the shelf, steel limit the tuned frequency of any antenna circuit. A simple loop of speaker wire about 100 ft (30 m) in diameter maybe tunned to resonate at 131Kz with a simple external capacitor. A loop of only a 1 inch (25 mm) may be also tunned to resonate at 131 kHz. However, at 30 MHz might be able to tune the 1 inch antenna, but not the 100' antenna and not the shelf.
If you operate at 30 MHz the largest tunable loop is about 1 foot. RuBee's frequency is low on purpose so that it can near always re-tune to compensate for the parasitic inductance and capacitance in most harsh environments and objects like steel shelves (see Roche et al. 2007). Back to the shelf example -- RuBee 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. That is not possible with frequencies over 1 MHz with most things you find in a warehouse, office building or factory --
RuBee has good Feng Shui in harsh environments. The reason -- is most steel items resonant 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 resonate.
How big can a RuBee loop antenna be ? As the antennas get larger and larger noise becomes the gate keeper. A 100' foot diameter loop can detect lighting storms 100's of miles away. The biggest source of noise is deep space kilometric noise. It is possible build a second antenna and do differential subtraction, however, again in practice 10,000 sq foot limit (100' x 100') of a RuBee network is adequate for most visibility applications.
RuBee disadvantages and advantages
The only major disadvantage RuBee has over other protocols is speed and packet size. The RuBee is currently limited to 1,200 baud. It is expected that the IEEE P1902.1 will also be 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 10's to 100's of bytes. RuBee was not designed for high bandwidth high speed communication. In most visibility applications these are not serious issues.
The use of LW magnetic energy brings about a number of advantages:
- Long battery life – Because lower frequencies are always used for magnetic waves, the chips and detectors can run at low speed, consuming almost no power and using lowest-cost chip technology (4 micrometre CMOS). LW magnetic wave tag systems can and have run on low-cost lithium batteries for 15 years – at 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. Whereas RFID 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. Recent published studies have been done that show 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 a person with unlimited funds can listen to tag conversations) is the same as tag range. That means if someone is listing you can see them. The is not true for RFID or 802 protocols (see Wall Street Journal May 4th [|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 near uncrackable one time keys, or totally uncrackable one time pads. RuBee is in use today in many high security applications for that reason.
- 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 square ft (900 cm²), RuBee can read a tag within an egg-shaped sphere of about 10 x 15 ft . 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 10's to 100's 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 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 with battery.
- Less noise – Because ambient noise in a region falls off as 1/r3, RuBee exhibits reduced susceptibility to any extraneous noise. The major limit to antenna size is deep space noise.
References
- Prithvi Raj, 2007 North American Supply Chain Visibility Solutions Technology Innovation of the Year Award, Frost&Sullivan [2007 Tech Award]
- "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: [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). [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 [Orthopedic Visibility]