Radio communications considerations
 
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Last time, I discussed the basics of direct sequence spread spectrum and frequency hopping spread spectrum. These two radio transmission mechanisms take different approaches to avoiding interference from other devices running in the same frequency band, including the receivers of would-be intruders.
Each spread spectrum technology has its merits and its drawbacks in terms of data rates and amount of power emitted. Their differing approaches might be worth considering when deciding whether to install HomeRF or IEEE 802.11 LANs, for example.
In addition to the respective pros and cons of the two interference techniques, there are a couple of other considerations about radio communications you might want to keep in mind:
* There is no mandate by the FCC for consistency of media access control protocols used by the various networks running in a given unlicensed frequency band. For example, network devices in the 2.4 GHz band occupied by HomeRF, 802.11b, Bluetooth, some proprietary wireless LANs and cordless phones, follow different rules for when they are allowed to transmit. Because each type of device uses a different protocol that the others don't understand, collisions among these different devices are likely.
* Interference issues are particularly thorny in multiple-tenant office buildings. The farther users wander from their access point, the more likely they are to be closer to a source of interference, say, from a next-door neighbor's microwave oven. Similarly, if one suite is running an 802.11b LAN and the neighbor is running a HomeRF LAN, transmissions can degrade. For example, a DSSS-based 802.11b LAN is always transmitting on every frequency in the band, so a nearby FHSS system could have trouble finding clear channels on which to hop.
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Joanie Wexler is an independent networking technology writer/editor in Campbell, Calif., who has spent most of her career analyzing trends and news in the computer networking industry. She welcomes your comments on the articles published in this newsletter, as well as your ideas for future article topics. Reach her at joanie@jwexler.com.
Network World Wireless archive
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