802.11/802.11b/802.11g compatibility

[Mozz]

As far as I know 802.11 specifies the PHY flavours, DSSS, FHSS and IR.

I want to deploy an 802.11b/g solution but there is a 802.11 FHSS cells for inventory applications.

I think that 802.11b is not compatible with 802.11 FHSS, only DSSS. My question is, can I overlap 2 APs in order to work with 2 PHYs? One AP with 802.11 with FHSS and another one with 802.11b (DSSS) or 802.11g (OFDM). Do they interfer? It is possible or must I to replace the 802.11 with 802.11b/g? This last option implies to replace barcode scanners because there are no LMC cards.

Thanks in advance.

[dixho]

As long as they are not different clear channel (i.e. 1, 6, and 11), 802.11 FHSS should not interfer with 802.11g.

[crhyde]

Hi:

Clause 14 (FHSS), 15 (DSSS), 18 (HR/DSSS), and 19 (ERP) PHYs all use the 2.4 GHz ISM band. FHSS divides the band into 79 channels and uses all of them in quick succession. The other PHYs divide the band into 11 channels and normally use one channel persistently. A pair of collocated FHSS and DSSS/ERP PHYs will interfere with each other but probably not enough to ruin either's communication.

I hope this helps.

Thanks. /criss

[crhyde]

Hi:

The standards allow you to deploy both in the same space, and each will use its own methods to communicate in spite of the noise offered by the other. Only your experience will tell whether your throughput is acceptable.

One alternative is to use 802.11a devices for your new wireless LAN. Your two LANs, FHSS and OFDM, will operate in the same volume at the same time but at different frequencies and be entirely invisible to each other.

Another alternative might be to configure a custom hopping pattern for your old FHSS network that avoids one of the DSSS channels, and configure your new DSSS network to use only that channel.

I hope this helps.

Thanks. /criss