User manual

WI-MOD-9-E Wireless Ethernet User Manual
WI-MOD-9-E Manual V1.9 Page 34
Fade Margin
This is the difference (in
dB) between the received
radio signal and the
receiver sensitivity
(minimum radio signal).
When automatic rate is selected, the WI-MOD-9-E initially chooses
a rate based on the received signal strength of transmissions.
Firmware version 1.32 and later will then adjust rate on each channel
to according to packet errors. Earlier versions will adjust rate based
upon the received signal strength. The Fade Margin value is used by
the WI-MOD-9-E to determine what initial data rate should be
selected. In firmware versions before v1.32, it is also used to select
the current radio rate. A larger Fade Margin means that the WI-
MOD-9-E will select a lower initial rate.
The default value is 10 dB.
Dwell Time
The amount of time, in
milliseconds, the WI-
MOD-9-E remains on a
particular frequency
whilst frequency hopping
Reducing this value will improve performance if there is a high level
of radio interference. This also has an impact on the maximum size
of packet that may be transmitted. Refer to “Fragmentation
Threshold” for more information.
The default value is 400 milliseconds.
Beacon Period
This interval is the period
between beacon
transmissions sent by an
Access Point.
The Beacon Interval is also related to the scan period on a Client.
Reassociation interval is (6) times the Beacon Interval when the link
has been inactive.
Access Points will timeout after 12 times the Beacon Interval if no
response is heard.
Refer to Section 3.1 for more information.
The default value is 10 seconds. This should be adjusted to larger
values as the system is increased in size. This will reduce the
overhead of checking each link, at the expense of response time
when a link is dropped.
Frequency Hopset
There are eight hopsets
available (0-7)
Selected automatically via the System Generator String
Fragmentation Threshold
The maximum
transmission unit (MTU)
of data over the radio.
This selects the maximum number of bytes that will be transmitted
in one message. If more than this number of bytes is input into the
WI-MOD-9-E, the module will transmit more than one message.
The default value is 500 bytes.
If fixed radio rates are configured, this value can be increased and
will reduce radio transmission overhead. For 200Kbps and
100Kbps, the fragmentation threshold can be increased to 2000, and
at 38.4Kbps, to 1000. However if the radio path is poor, or there is
high radio interference, increasing this value will decrease system
performance as the number of re-try messages will increase.
If Ethernet traffic is only small packets sizes (ie <300 bytes), an