Frequency Hopping Radio Systems co-exist with DSSS Radio Systems

[ronaldlee]

Hi,

I am working on a requirement to phase in a migration from FHSS to DSSS based on the Aironet1240 for a outdoor deployment. However, the nature of the project requires co-existance of the two radio systems for a period of 6 months. Does anyone have had experiences in such a deployment scenarios and what is the field experienced impact of the DSSS system?

[scottmac]

The operation of both systems concurrently should not be an issue.

The FHSS system shouldn't dwell an a given freq long enough to cause any serious interference.

The DSSS system has enough redundant information for any given chunk o' data that even if the FHSS system did pass through or dwell ona freq in the middle of the DSSS channel, the data will be still be intact.

You may be able to set the FHSS system to "hop around" the chosen DSSS, or possibly restrict the hops / hopping sequence to avoid most or all of the DSSS channel, or limit the dwell time to minimize the interference.

Good Luck

Scott

[ronaldlee]

thanks scott.

[thisisshanky]

Recently I did a wireless install for a hospital where all their ECG equipments were usinga FHSS system while access points in the same floor were using 802.11g. A study was done during the survey to find out how much interference occurs between the two systems. I found reasonable interference between the two. Like Scott suggested, the time for which FHSS system will interfere is very minimal. Still there are reports of reduction in throughput of the 802.11b/g system by 40% when both systems coexist in the same area.

The interference can be minimized to a greater extent by spacing the antennas of the two systems wide apart in a given area. I barely found any drop in ECG readings, with a 2.4ghz access point and the FHSS ecg system placed in the same area.

[virgilpei]

I think it's like coexistance with Bluetooth. Bluetooth is frequency hopping in a group of 27 x 1MHz adjacent channels. There are 3 groups.

[vsnl_chennai]

Hi,

I am sharing this information for outdoor deployments of FHSSS and DSSS based systems.

You can always reduce the interference , if both FHSSS and DSSS systems coexist by -

1) Use smaller channel width in FHSSS systems

2) Use simple modulation like FSK if bandwidth is not a constraint .

3) Try to work on C/I ratio

4) Use antennas intellingenlty

We deployed 2.4 Ghz FHSSS and DSSS systems coexisting in the same location , and are working satisfactorly

I recommend take care of RF chemistry ....

wish you all Sucess