RuBee

The IEEE 1902.1 protocol details

1902.1 is the "physical layer" workgroup with 17 corporate members. The Workgroup was formed in late 2006. The final specification was issued as an IEEE standard in March 2009. 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 (see www.rubee.com). However, IEEE 1902.1 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

RuBee is bidirectional, on-demand, and peer-to-peer. It can operate at other frequencies (e.g. 450 kHz) but 131 kHz is optimal. 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 an IP Address (Internet Protocol Address). A tag may hold data in its own memory (instead or in addition to having data stored on a server). Some tags have as much as 5 kB of memory. RuBee functions successfully in harsh environments, with networks of many thousands of tags, and has a range of 1 to 30 m (3 to 100 ft) 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: exit entry detection in high security government facilities, weapons and small arms in high security armories, mission critical specialized tools, smart shelves and racks for high-value assets; smart entry/exit portals.

How RuBee works

IEEE 1902.1 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 newtons per coulomb 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. (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, 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.

Environmental factors

RF is based on physics, and can be reliably modeled with prediction tools and tuned models (see RF Microwaves, and Migraines, 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. Reception may be improved by moving the phone near a window, or pointing the antenna in a particular direction. Radio waves are affected by just about everything around us. Many environmental factors influence performance. The more significant ones include steel and water, but people and electrical noise sources are also high on the 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 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/r³. 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 1-foot (30 cm). 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 works well 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 hundreds 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 10,000 sq ft (1,000 m²) limit of a RuBee network is adequate for most practical visibility applications. RuBee antennas may also use ferrite rods with wire coils and get same range but without large loops.

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. The IEEE 1902.1 specifies 1,200 baud. The protocol could go to 9,600 baud with some loss of range. However, most visibility applications work well at 1,200 baud. Packet size is limited tens to hundreds of bytes. RuBee's design forgoes 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:

Unique RuBee application example: mission critical asset availability and security

Because RuBee is secure and magnetic it can provide real-time automated visibility, and the highest possible security of Mission Critical Assets—Mission Critical Assets (MCA) are assets that simply can not be lost or stolen, worth far more on the street or in hands of terrorists than the cost to replace. Visible Assets, Inc., Dasco Date, Inc., SMi Ltd, and Laser Device Inc. provide RuBee based automated MCA visibility and security using three important security layers:

Security becomes far more reliant on human trust with loss of any layer. RuBee reduces that human trust reliance with full “process free” automation in all three layers. For example, if something is removed from inventory off the racks, but does not get checked out an alarm is issued. If an asset exits facility but is not checked out, an alarm is issued etc. RFID and barcode systems are blocked by steel and the human body. As a result, security is based on new human processes focused only on Layer 2. Both become human assisted asset tracking systems, not real-time automated security systems. Visible has repeatedly proven that RuBee is the wireless technology that can provide fully integrated, visibility with three security layer automation.

RFID and barcode systems are blocked by steel and the human body. As a result, security is based on new human processes focused only on Security Layer 2. Both become human assisted asset tracking systems, not real-time automated security systems. Many in-use secure sites provide, process-free, fully automated, RuBee visibility with three-layer security.

Compare to NFC and Qi Inductive Power Transfer

This protocol is similar at the physical level to NFC (13.56  MHz carrier, basically an air-core transformer pair) and also Qi's inductive energy transfer (100 kHz-300 kHz carrier). Both modulate the receiver's coil load to communicate to the sender. Some NFC tags can support simple processors and a handful of storage like this protocol. NFC also shares the physical security properties of "magnetic" communications like RuBee, however NFC signals can be detected miles from the source. RuBee signals are detectable maximum 20 meters from the source.