QDMA radio technology uses Direct Sequence Spread Spectrum (DSSS) and operates in the ISM II 2.4 GHz bands. This radio is specifically designed and optimized for wide area, mobile mesh networking systems. It incorporates a multi-channel MAC (3 data channels and one control channel) that enables support for a higher density of meshed users than single channel MAC radios. Position/location technology is built-in to the QDMA radio and does not rely on GPS.

QDMA™ and the 802.11 Radio Protocol Compared

The question is often asked, “ What is the difference between 802.11 and QDMA radio platforms? ” The simple answer is that the radios are designed for different applications. The QDMA radio exists to address markets that 802.11 cannot - specifically wide area & mobile data applications.

802.11 Background
The 802.11 radio protocol was designed to provide a cost effective alternative to the piece of LAN cable between the wall and the user’s computer. When 802.11 was being designed, it was expected that the radio would be deployed indoors and the computer would remain relatively immobile. Subsequently, 802.11 was designed to provide very high data rates over short distances to stationary computers using a very low cost, low powered radio.

However, 802.11 has very little immunity from either self-induced or externally generated interference. These and other trade-offs were made to reduce the cost of 802.11. Unfortunately, it also worked to limit radio performance in such a way as to render 802.11unusable in wide area mobile applications. Current 802.11 technology provides an excellent short range, fixed wireless solution as long as the required level of performance can be supported within the restrictions of these inherent limitations.

QDMA Background
On the other hand, QDMA broadband radios are optimized specifically for wide area, mobile ad hoc networking applications. With origins based on military specifications and requirements, it was designed to provide reliable communications under the most demanding battlefield conditions.
QDMA radios benefit from having a high performance RF front end that includes capabilities such as multi-tap rake receivers (commonly found in cell phones) and real-time equalization algorithms to compensate for the rapidly varying RF environments typically encountered in real-world mobile environments.

QDMA mobile broadband radios also incorporate increased error correction capability- again necessary for wide area and mobile communications. While this does limit the overall maximum burst data rate to 6 Mbps, it also improves the effective range for mobile users. Rather than the typical maximum of 300 feet for line of sight (LOS) transmissions for 802.11, QDMA radios have a range of 1 mile LOS. Both of these ranges are typical when using omni-direction antennas.

Enhanced interference rejection and signal sensitivity allow QDMA-based networks to provide multi-megabit data rates at speeds up to 250 mph, whereas 802.11 drops the radio link at about 20 mph under real world Multipath conditions.

QDMA also offers additional capabilities not found in the 802.11 standard. One very significant feature is a position location capability that provides better than 10 meter accuracy in a high speed mobile environment which is not reliant on GPS.

Conclusion
Both 802.11 and QDMA radio protocols provide excellent performance for their intended applications. For local area, fixed wireless connectivity - 802.11 is an excellent choice. But if your application calls for wide area, high-speed mobile connectivity, or precision position location – then QDMA (used in our MEA/QDMA mobile ad hoc networking product line) is the right choice to fit your needs.