Learn more about wireless TECHNOLOGY
There are in general two different ways to transmitt DMX Data wireless, to give a better overview and understanding of wireless control we have put together a Wireless ABC for you.
DSSS vs. FHSS (or AFHSS)
There are two basic ways to transmit data over a defined wide bandwidth. These involve spread-spectrum techniques. It is helpful to know the difference, as these methods are relevant when it comes to interference.
Spread-spectrum techniques are ways in which energy generated at one or more frequencies is spread in either frequency or time domains. This is done to establish secure communications, resist interference, and prevent detection, among other things.
Direct Sequence Spread Spectrum (DSSS) transmissions multiply the data being transmitted by a "noise" signal. This noise signal is a pseudorandom sequence of 1 and -1 values, at a frequency much higher than that of the original signal, thereby spreading the energy of the original signal into a much wider band.
The resulting signal resembles white noise, like an audio recording of "static", except that this noise can be filtered out at the receiving end to recover the original data, by again multiplying the same pseudorandom sequence to the received signal (because 1 × 1 = 1, and -1 × -1 = 1). This process, known as "de-spreading", mathematically constitutes a correlation of the transmitted PN sequence with the receiver's assumed sequence.
For de-spreading to work correctly, the transmitting and receiving sequences must be synchronized. This means that the receiver must synchronize its sequence with the transmitter's sequence via some sort of timing search process.
Frequency Hopping Spread Spectrum (FHSS) works by jumping from subchannel to subchannel at a rapid pace (normally over 1000 times per second), using a pseudo-random sequence known to both the transmitter and receiver. A variant on FHSS is Adaptive Frequency Hopping Spread Spectrum (AFHSS) which intelligently seeks busy channels and purposely avoids them, to further reduce interference. W-DMX by Wireless Solution is the only system that uses AFHSS, with a custom encryption sequence.
Frequency hopping techniques were first used by the U.S. military, since they are difficult to intentionally jam and, unless you know the frequency hopping sequence, practically impossible to listen in on.
TDMA
Time Division Multiple Access (TDMA) enables a part of the radio spectrum to be used "simultaneously" by having different devices use it at different time instants. This is typically done by allocating specific time slots to the various transmitters. Some wireless DMX systems have adapted the Time Division Multiplexing standards from ATM communication links, designed to transport many simultaneous sessions in links handling massive amounts of data every second. The usage of TDMA fits very well in the DMX situation, where the protocol is required to send several channels in a near-simultaneous way.
ETSI/FCC/ARIB
Because communication regulations vary worldwide, be sure to look for a system that is compliant. The European Telecommunications Standards Institute (ETSI), Federal Communications Commission (FCC) and Association of Radio Industries and Businesses (ARIB) have standards in place in Europe, United States, and Japan, respectively, that require any radio communications to fall within their guidelines. Be sure that the system you plan to use is compliant in the country in which you plan to use it.