Over the past sixteen years we have worked with and understood virtually every type of technology used for real time location systems. This is included but not limited to Wi-Fi, UWB (Ultrawide Band), Zigbee, Ultrasound, proprietary RF, and BTLE. All with the exception of Ultrasound have relied upon RF. Of all mentioned, we feel that BTLE offers the most potential for RTLS. In everyday use wireless communication does have it’s limitations. It is because wireless consists of propagating radio waves. We all know about using our smart phone….”can you hear me now”? The coating on commercial windows tends to keep the cellular signal from penetrating inside the building. Wi-Fi has issues around glass, metal, and water. There are a number of different factors which can affect a wireless signal however the most important is reflectivity.
Reflectivity – This is when a signal hits an object and is reflected off at an angle (which depends on the angle it hits the object at). When a radio frequency (RF) signal is transmitted towards the receiver, the general behavior of the RF signal is to grow wider as it is transmitted further. On its way, the RF signal encounters objects that reflect, refract, diffract or interfere with the signal. An amount of the energy is absorbed in the process. A possible outcome of reflection is multipath where several different signals reach the receiver each taking a different path, often arriving later, out of phase of the main stream.
Multipath delay causes the information symbols represented in 802.11 signals to overlap, which confuses the receiver. If the delays are great enough, bit errors in the packet occur. Diversity is the use of two antennas for each radio, to increase the odds that you receive a better signal on either of the antennas in the case of experiencing a null. The antennas used to provide a diversity solution can be in the same physical housing or must be two separate but equal antennas in the same location. (That is why you have two antennas on a WLAN Access Point!)
We feel that NFMI (Near Field Magnetics) offers the potential of providing precise location based knowledge in very harsh RF environments.
The basic premise behind the technology is that there is no propagating wave, just a magnetic field. (Think of mutual coupling in a transformer). The basic technology is running a modulated current through a coil to generate a time varying magnetic field (Ampere’s Law). https://en.wikipedia.org/wiki/Ampère’s_circuital_law
This time varying magnetic field will produce a voltage in a coil, (Faraday’s Law). https://en.wikipedia.org/wiki/Faraday’s_law_of_induction
Modulation can be ASK, PSK, FSK, QAM or any other scheme.
Integra Systems, Inc., is working with http://nearfieldmagnetics.com to explore the commercial use of this technology and applications specific to the healthcare industry as well as other vertical markets.
