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Changes between Version 2 and Version 3 of UserDocs/AntennaDiversity

Author:
matt (IP: 0.0.0.0)
Timestamp:
01/07/06 22:45:42 (13 years ago)
Comment:

fixed a couple of little typos.

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  • UserDocs/AntennaDiversity

    v2 v3  
    11= Antenna Diversity = 
    22 
    3 Antenna diversity is the terms used when the receiver and transmitter use multiple antennas in order to improve reception/transmission. Most Atheros radios have two antenna connectors which allows you to connect two antennas. Two antennas can be beneficial in a number of screnarios. One typical scenario is called polarization diversity. For example, most laptops have two small dipole antennas oriented differently because as you move around with the laptop one or the other antenna may "line up" better with the access point antenna polarization. There is also spatial diversity which exploits the fact that sometimes two antennas spaced more than a few (~10) wavelengths apart have different reception conditions due to reflections or fading, or other effects. 
     3Antenna diversity is the term used when the receiver and transmitter use multiple antennas in order to improve the quality of reception/transmission. Most Atheros radios have two antenna connectors which allows you to connect two antennas. Two antennas can be beneficial in a number of screnarios. One typical scenario is called polarization diversity. For example, most laptops have two small dipole antennas oriented differently because as you move around with the laptop one or the other antenna may "line up" better with the access point antenna polarization. There is also spatial diversity which exploits the fact that sometimes two antennas spaced more than a few (~10) wavelengths apart have different reception conditions due to reflections or fading, or other effects. 
    44 
    55== Receiver diversity == 
    4040== What doesn't work == 
    4141 
    42 Note that connecting antennas with different coverage areas doesn't really work. When reading about multiple antennas some people think they can connect one high-gain long range antenna for a long diatnce link and one omnidirectional antenna to serve for local connectivity to a single accesspoint radio. Or one high gain pointing in one direction and a second pointing in a different direction. While this can be made to work in principle, there are a number of problems. The first is that on an accesspoint beacons are only sent out one antenna, so stations on the other antenna are out of luck. The second problem is that when the AP transmits the stations on the other antenna don't hear the transmission and therefore don't do the collision avoidance properly. If you use RTS/CTS then also some stations don't get them at all. The bottom line is that diversity works well when one antenna is a few dB better than the other, which allows higher data rates and fewer packet losses. It does not work well if half the stations only hear one antenna and not at all the other. 
     42Note that connecting antennas with different coverage areas doesn't really work. When reading about multiple antennas some people think they can connect one high-gain long range antenna for a long distance link and one omnidirectional antenna to serve for local connectivity to a single accesspoint radio. Or one high gain pointing in one direction and a second pointing in a different direction. While this can be made to work in principle, there are a number of problems. The first is that on an accesspoint beacons are only sent out one antenna, so stations on the other antenna are out of luck. The second problem is that when the AP transmits the stations on the other antenna don't hear the transmission and therefore don't do the collision avoidance properly. If you use RTS/CTS then also some stations don't get them at all. The bottom line is that diversity works well when one antenna is a few dB better than the other, which allows higher data rates and fewer packet losses. It does not work well if half the stations only hear one antenna and not at all the other.