Licensed vs. Unlicensed Bands
What is the difference between the licensed and unlicensed bands and why should I care?
Signed, Bandied About
Wise Guy: In addition to fining Howard Stern, the Federal Communications Commission (FCC) regulates radio usage in the U.S., allocating the RF spectrum usage to various applications. Portions of the band are allocated to military usage, portions are set aside for radio and television broadcasting, portions are alotted to cellular communications, and some segments are the "unlicensed" (also called industrial, scientific, and medical—or ISM) bands.
Within the ISM bands, the FCC allows us to use garage door openers, cordless phones, or WiFi systems without applying to government agencies for permission. Availability of the unlicensed bands has led to widespread use of radio devices in many consumer applications. Most wireless sensors operate in the unlicensed bands, meaning you don't have to fill out government forms to use them.
For mission- or safety-critical applications people will want sensors to communicate in reserved and regulated bands to ensure there will be no interference. Going this route requires submitting to a licensing process.
Wireless sensor networking vendors are working to advance reliability so that systems become increasingly trustworthy even using the unlicensed bands. Progress toward this goal will reduce the regulatory burden and increase the adoption of wireless sensors.
Security in Self-Organizing Meshes
What is really meant by the term "self-organizing mesh"? Is there no configuration involved at all? And if not, how are you protected from unwanted nodes jumping onto the mesh?
Signed, A. Fine Mesh
Wise Guy: A self-organizing mesh is a network of devices that automatically builds a web of connections. A system constructed in this way provides reliability by building-in redundancy. The mesh allows data to be passed from one node to the next through the network, and, if one path in the network is blocked, the network automatically reroutes the data through an unblocked path. When you install a self-organizing network you do not have to tell the network which device should talk to which; the devices configure themselves.
As with WiFi, there are a couple approaches to security that prevent unwanted nodes from joining the network. The first is MAC address blocking, whereby only nodes listed in the master table are allowed to join the network; no unauthorized node can join. The other approach is to have a secret network ID and password that a node must know in order to join the network. This information has to be programmed into the node before it can join the network.
Can Wireless Signals Harm Me?
With all of these wireless signals floating around in the ether, should I be concerned for my personal safety?
Signed, M. I. Safe
Wise Guy: I think you're asking whether the wireless signal will cause cellular damage to your body. To answer this, you need to know whether the wireless signal's frequency has enough energy to ionize the location of absorption. If the photon (packet of energy) associated with the wireless signal has enough energy, it will blow electrons right off the absorbing molecules in your cells – thus ionizing them and triggering problems such as genetic alteration. It's important to know which wireless signals are at an ionizing frequency/wavelength.
In Figure 1 you'll see that at higher frequencies, each photon has more energy (the guiding equation is E = hf, where E is the energy of the photon, h is Planck's constant, and f is the signal frequency) and therefore has the ability to cause trouble. That's why ultraviolet radiation (one variety of wireless signal) damages the skin, but a nice green photon doesn't. Referring to the chart, a wireless signal at one of the ISM bands (433, 915, 2400 MHz) just doesn't have enough pop to cause any sort of cellular damage.
Figure 1. The electromagnetic spectrum and wireless signals
Relax. You can change your initials to I. M.