1. What is Trusted Wireless™?

Trusted Wireless™ is OMNEX's proprietary, robust industrial wireless FHSS technology utilizing OMNEX custom designed RF hardware and OMNEX communication software to achieve superior data integrity over longer radio ranges in heavy interference environments. Learn more.

.

2. Why choose a license-free radio over a licensed radio?

License-free radios operating under FCC spread spectrum ISM band regulations tolerate interference from neighboring radios and interference from sources other than radios, making them less prone to signal loss.

Here’s why: The radio spectrum is divided into frequency bands, with each band divided into frequency channels.  The bands and channels are regulated around the world as licensed or license-free.

The term ‘licensed radio’ refers to a radio that is licensed by a government agency to operate on one channel in one geographic area at one time.  The intent is to protect the licensed radios from other radio interference by limiting the radios on a channel.  Unfortunately, while government agencies can control radio users, they cannot control interference that is generated on licensed frequencies by non-radio emission sources such as motors, drives, arc welders, power lines, etc.

The term ‘license-free radio’ refers to a radio operating with government permission on a specified frequency band which is open to multiple radios at one time. These license-free bands are known as the ISM (Industrial, Scientific and Medical) bands.  License-free radios use techniques such as frequency hopping and interference suppression to tolerate interference from neighboring radios on the same band, and more importantly, interference from sources other than radios.  These techniques are unavailable to fixed frequency licensed radios.

3. How does direct sequence spread spectrum (DSSS) differ from frequency hopping spread spectrum (FHSS)?

Direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) are the two most popular types of radios that the FCC permits to operate in the ISM (Industrial, Scientific and Medical) bands. 

A DSSS radio spreads its power across a very wide portion of the ISM band.  As a result, it has the capability of sending high-speed data across this extended bandwidth.  Wireless LAN (WLAN) radios utilizing IEEE Ethernet 802.11a/b/g standards use DSSS because of this capability.  The drawback is that a DSSS radio has very short range and low interference immunity.  DSSS radios attempt to surmount this by using a feature called processing gain to overcome a limited amount of interference.  Processing gain is the equivalent to a software filter – however, even the best processing gain will net only 10 to 20dB of interference suppression. 

FHSS radios constantly change frequency – 50 times or more per second.  They concentrate all their energy on a very narrow bandwidth as their transmitters and receivers hop in sync from one frequency to the next in a pseudo-random pattern.  The advantages of using an FHSS radio are range and interference tolerance, with a FHSS radio’s hardware filter yielding as much as 80 to 90dB of interference suppression in a well-engineered receiver.  By concentrating all its energy on a very narrow bandwidth, a FHSS radio can transmit its signal much further than a DSSS radio.  Also, because a FHSS radio constantly changes frequency, many systems can operate simultaneously in the same region without risk of interference.  If in the unlikely event that interference is encountered on a specific frequency, the radio simply hops to the next frequency and re-transmits the signal.  A FHSS radio has a relatively low data rate capability compared to a DSSS radio making it ideal for high-interference industrial applications where a continuous link is often more important than data rate.

4. What are the ISM frequency bands and which should be used?

The most commonly used ISM bands are referred to as the 900MHz, 2.4GHz and 5.8GHz bands.  All permit the use of license-free spread spectrum radios within them.  Generally, the 900MHz band is used in the Americas.  The 2.4GHz band is used (with differing power constraints) throughout most of the world.  While there are some differences between the characteristics of the two bands, the 900MHz band typically allows for higher power and longer distance transmissions while the 2.4GHz band, with its wider bandwidth, allows for higher data rates.  In Europe, the 869 MHz and 433 MHz bands are also classified as ISM bands and China has opened the 220MHz band to license-free radios.  The key consideration in terms of usage is most often determined by geographic location. 

5. What’s more important, transmit power or receiver sensitivity?

While both specifications influence how far, how fast and how accurately data can be sent, receiver sensitivity -- not transmit power -- is the critical measurement in determining the reliability of wireless communications.  Users of radio technology should not always assume that distance or obstruction challenges can be overcome by simply boosting power. The reason for this lies in the fact that more can be accomplished in terms of boosting a receiver’s sensitivity through the correct application of technology than can be accomplished by pushing raw power through a transmitter.  Why?  The amount of power available through a transmitter is regulated by government agencies, whereas the performance and sensitivity of a receiver are open to the dedication and quality individual radio manufacturers strive for.  When dealing with typical industrial signal strengths measured in the region of 1/1000000000000000000th of a Watt, OMNEX prides itself on manufacturing the highest quality receivers to maximize the performance and sensitivity of our industry proven radio links.

The spin-off benefit of having a very sensitive receiver is that transmitter power can be lowered thereby reducing power consumption and making it easier to operate transmitters for long periods of time using alternative power sources like solar panels and batteries.

6. Will OMNEX products be affected by other electronic/electrical equipment or severe weather?

Electronic equipment, such as the motors and drives typically found in-plant or on machines, create harmonics, RF spikes and background noise that may cause interference on particular radio frequencies.  In the case of fixed frequency radios, interference like this is often catastrophic if the interfering signal remains constant.  On the other hand, frequency-hopping radios tolerate multiple forms of electronic and RF interference very well because they hop away from interference and continually update the data they are sending elsewhere in a frequency band.  Depending on the product, OMNEX radio receivers will either hold the value of their last error-checked packet or, in the case of serial data products, request that lost packets be re-sent on interference-free frequencies (if programmed to do so). 

Questions also arise in terms of potential interference from cellular telephones and two-way radios, and the answer here is that because these products reside in non-ISM frequency bands, OMNEX products are not affected by their signals.

7. Can OMNEX products be ‘hacked’, ‘jammed’ or deliberately interfered with?

In short, no. For more information, read our white paper: Frequency Hopping and Unwanted Intruders.