[Soekris] OT: Dual antenna (diversity) on 802.11 used as AP

[Martin Johnson]

On 11 Feb 2008, at 16:47, Andreas Schweigstill wrote:

> The design of the "pseudo-Ethernet" W-LAN also doesn't allow proper
> antenna diversity and transmit power setting because it is a broadcast
> media and not timeslot based like GSM or DECT.

That sounds very plausible.  So the diversity system only works if the  
low-level and high-level protocols combine to send enough retry  
attempts on failed packets, to compensate for when the wrong antenna  
is used for a given station. Not a very robust solution.

Recently I bought an Atheros AR5008-based Mini-PCI Express card.  It  
turns out that I can't use it yet because MadWiFi doesn't really  
support it: it works in Kismet, but it can't connect to my WPA  
network.  But being an 802.11n-capable card, it claims to implement  
MIMO mode.   Such cards have either two or three complete radio  
transceivers in them.  The advertised benefit is that 802.11n MIMO  
mode enables very high speeds - up to 300 megabits over short  
distances - by exploiting spatial diversity (provided that both ends  
have MIMO cards).  However, probably more useful than the speed  
increase, is the possibility that in the ordinary 802.11a/b/g modes  
such cards would be able to implement diversity properly, if the  
manufacturer has bothered to implement it properly in the firmware.

- Martin.