MeshLinx MWI-5000 User Guide
MESHLINX CONFIDENTIAL
8
7.1.10 Diversity
Diversity controls the use of antennas on the MWI-5000. Each wireless interface has a
primary antenna (Antenna 1, default) and a secondary antenna (Antenna 2). Either of
these antennas can be selected manually for an interface. The setting applies to both
receive and transmit operations.
Setting Diversity to Both causes the device driver to alternately try each antenna,
eventually settling on the antenna that yields the best performance.
For transmit (using Both), the preferred antenna setting is maintained on a per-station
basis and attempts to transmit to a station are tried first using the preferred antenna from
the last transmission.
For receive (using Both), the antenna setting is mostly driven by the transmit diversity
algorithm (transmit diversity trumps receive diversity). When there is little transmit
activity to drive diversity, the receive diversity algorithm selects an antenna that has the
highest RSSI for all stations combined. Typically, it is not the case that traffic will be
mostly receive traffic and most of the time, diversity will be driven by the transmit
algorithm.
The need to modify this parameter is site-dependent. Some users may find that setting
Diversity to Both yields better overall performance for all stations. Other users may find
that best performance is achieved by selecting a particular antenna. The best way to
establish this is to experiment with the three settings, measure the performance yield of
each setting and make a decision based on those results.
7.1.11 Header (preamble)
The Header parameter determines the default preamble type that the MWI-5000 MAC
will use to transmit in 11B mode. It has no meaning in OFDM modes (11G or 11A).
In 11B mode, a longer preamble allows the receiving side greater time to synch-up on the
incoming frame (144 microseconds for long, 72 microseconds for short). The MWI-5000
will receive 11B frames that are transmitted by a station with
either
long or short
preamble and will respond to (acknowledge) received frames using the same preamble
length as the received frame. To summarize:
•
The header parameter is specific to 11B mode
•
It determines only how the MWI-5000 will transmit 11B frames
•
It takes 72 microseconds longer to transmit a 11B frame with a long preamble
•
Using long preamble may achieve greater interoperability with legacy 11B
stations
