As more than one wireless technology is often used in parallel, there could potentially be disturbances resulting in higher latency or even data losses. These potential side effects cannot be accepted in mission-critical industrial and medical applications. Therefore, it is important to optimize coexistence of various wireless technologies in order to get a disturbance-free operation.
All of today’s most used wireless technologies operate in the 2.4 GHz band and they address potential disturbances in the following manner:
- Wireless LAN / WLAN, also commonly referred to as Wi-Fi, has three non-overlapping channels with a bandwidth of 22 MHz and is using Direct-Sequence Spread Spectrum (DSSS). DSSS makes sure that the transmitted signal takes up more bandwidth than the information signal that is being modulated and thereby the wireless communication link becomes less vulnerable to disturbances.
- Classic Bluetooth technology has 79 channels with a bandwidth of 1 MHz and combines this with Adaptive Frequency Hopping (AFH) in order to avoid interferences. AFH monitors the bit-rate and when disturbances (such as when another wireless technology occupies the link) are found, Bluetooth technology stops to use the channels that are occupied. The channel is monitored in the background and as soon as the occupied channel is free, it can be used again.
- Bluetooth low energy technology also uses AFH; but Bluetooth low energy technology only uses 40 2 MHz wide channels.
- IEEE 802.15.4 has 11 channels with a bandwidth of 5 MHz and is using Direct-Sequence Spread Spectrum (DSSS).
Caption: WLAN, Bluetooth and IEEE 802.15.4 work in the same 2.4 GHz frequency band.
Enhanced WLAN Coexistence Possibilities
As you see above the 2.4 GHz frequency band is very crowded. Besides WLAN, Bluetooth, IEEE 802.15.4/ ZigBee/Wireless HART, several proprietary technologies operate in the 2.4GHz band. WLAN is well-established throughout offices on to the production planning; and therefore, in order to get disturbance-free communication, one first has to secure that WLAN is not disturbed.
Implement 5GHz WLAN
The WLAN IEEE 802.11 b, g radios utilize the 2.4GHz frequency band and the IEEE 802.11a radio utilizes the 5GHz frequency band. IEEE 802.11n radios can operate in either frequency band. In order to get disturbance-free WLAN communication links, it is thus possible to use the 5 GHz band instead of the 2.4 GHz band. However, even though the 5 GHz band is increasing in popularity in industrial and medical applications, there is a large installed base of IEEE 802.11 b, g networks that requires a good coexistence solution.
In order to secure disturbance-free communication for WLAN in the 2.4GHs band, it is possible to use special antenna solutions (like leakage cables); however, these solutions are typical expensive installations.
It is also possible to beforehand choose channels that are not to be used (frequency planning) in order to avoid interference with other wireless systems used in the same environment.
For instance, in cases where WLAN and IEEE 802.15.4 are used in parallel, coexistence can be implemented by making room for some IEEE 802.15.4 channels in-between the three WLAN channels. By doing so, it is possible for WLAN and IEEE 802.15.4 to work reliably in parallel.
Adaptive Frequency Hopping (AFH)
Both Classic Bluetooth and Bluetooth low energy apply the Adaptive Frequency Hopping (AFH) feature which detects potential channel interference; for instance, a WLAN 802.11 b, g, n device transmitting in close proximity. If such interference is found the channel is automatically blacklisted. In order to handle temporary interference, an implemented scheme re-tries the blacklisted channels and if the interference has ceased the channel can be used. AFH prevents Bluetooth from interfering with other nearby wireless technologies.
Low Emission Mode®
Classic Bluetooth is built to be robust mainly thanks to AFH. But when performing device discovery or establishing a device connection, the Bluetooth activities can disturb a WLAN network.
In order to make sure that Classic Bluetooth operates smoothly in parallel with other wireless technologies, connectBlue has developed an extended Bluetooth coexistence feature which is named connectBlue Low Emission Mode®. With the connectBlue Low Emission Mode, coexistence is solved during device discovery and connection set-up without jeopardizing the Bluetooth Specification or interoperability between various Bluetooth enabled products.