Weidmuller WI-MOD-945-E: 900Mhz Wireless Ethernet & Device Server v2.16 - Manual (Page 80)

Weidmuller Wireless Ethernet Modem & Device Server WI-MOD-945-E User Manual
Page 80 www.weidmuller.com Rev 2.136
4.2 - Channel Survey (Utilisation)
Channel Utilisation gives a visual display of how busy the current channel is over a given time period. Channel Utilisation
is made up of 3 components: transmissions made by this radio; data received by this radio; and noise or interference that
this radio can hear. These 3 components may also be viewed individually on the Custom Survey page. Channel Utilisation
is logged by the radio for 3 separate time intervals: every second for the last 60 seconds; every minute for the last 60
minutes; and every hour for the last 60 hours.
The Weidmuller 802.11 Ethernet modem utilizes a half-duplex radio channel for communications. At any given time, an
Access Point and its associated clients occupy a radio channel. These radio channels, or frequencies, are license free
and may contain interference from any number of other radio transmitters. When installing or diagnosing a 245 modem,
the potential capacity of a given radio channel will be reduced by the existence of these other RF signals on the same
channel.
Channel Utilisation allows us to see how much RF activity is on a given channel as a percentage of the total utilisation. A
channel that is very busy will have high channel utilisation (usually 50% or greater). Conversely a channel that is quiet will
have low channel utilisation.
Channel Survey and Custom Survey can therefore be valuable tools to use when performing site surveys in order to
determine the best RF channel to use. It is also a valuable diagnostics tool for identifying the spare capacity on a given
channel, as well as possible sources of interference.
Channel Utilisation on a Live System:
Channel Utilisation can be used on a live system to get an indication of how much spare capacity the channel has for
additional data transfer. To identify possible interference on the current channel, observe the Percent Busy and Percent
Rx on the Custom Survey page. If possible, also temporarily disable all data transfer on the system, and if the Channel
Utilisation remains high this will confirm the presence of interference.
Using Channel Utilisation for Channel Selection or RF Path Testing:
When used on an inactive system, the Channel Utilisation will indicate how quiet the current channel is, and therefore
indicate how much interference is present. To select the quietest channel, configure the radio as an Access Point with no
data transfer and on each channel of interest record the Channel Utilisation over a period of time. The channel with the
lowest Channel Utilisation will be the quietest channel, and therefore is likely to provide the best performance. This
procedure, in addition to the
“Throughput Test”, is recommended for complete radio path testing.
Diagnosing Low Throughput:
When iperf throughput testing has given poor results, Channel Utilisation can be used to confirm whether or not the poor
results were due to interference. If the Channel Utilisation (excluding the time period while iperf was running) is seen to be
high, then this will confirm that the poor throughput was due to other RF interference. Alternatively if the Channel
Utilisation is seen to be low (indicating little interference), then the poor throughput would more likely be attributed to poor
RSSI - which could be confirmed on the
“Connectivity” page.
Solutions for High Channel Utilisation:
When substantial interference has been identified using Channel Survey or Custom Survey, the simplest solution is to
change to another channel that is seen to have lower Channel Utilisation. If a better channel is not available, configuring a
fixed noise floor can often greatly improve performance. Configuring a fixed noise floor can be performed on the
“Advance
Radio Configuration” page. The fixed noise floor should be at least 8dB greater than the weakest RSSI of any connected
modem, otherwise communications could be lost. After configuring the fixed noise floor, confirm that the Channel
Utilisation has dropped to a desirable level, and where possible perform a
“Throughput Test” to confirm acceptable performance.
Channel Survey screen displays a graph showing the percentage of time that a channel is being utilised by any of the
following causes:
1. The connected modem is transmitting.
2. The connected modem is receiving valid data from another modem.