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Cooper Bussmann 945U-E Wireless Ethernet Modem & Device Server User Manual
Rev Version 2.14
the last 60 seconds, every minute for the last 60 minutes, and every hour for the last 60 hours.
The ELPRO 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
945U-E 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 utilization allows us to see how much RF activity is on a given channel as a percentage of the total
utilization. A channel that is very busy will have high channel utilization (usually 50% or greater). Conversely, a
channel that is quiet will have low channel utilization.
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 Utilization on a Live System
Channel utilization 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. If the
channel utilization remains high this will confirm the presence of interference.
Channel Utilization for Channel Selection
or RF Path Testing
When used on an inactive system, channel utilization 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 utilization over a period of time. The
channel with the lowest channel utilization will be the quietest channel and therefore 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 utilization can be used to confirm whether or not the
poor results were due to interference. If the channel utilization (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 utilization is seen to be low (indicating little interference), the poor throughput is more likely be attributed to
poor RSSI, which could be confirmed on the Connectivity page.
Solutions for High Channel Utilization
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 utilization. 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 8 dB greater than the
weakest RSSI of any connected modem, otherwise communications could be lost. After configuring the fixed noise
floor, confirm that the channel utilization has dropped to a desirable level, and where possible perform a throughput
test to confirm acceptable performance.
The Channel Survey screen displays a graph showing the percentage of time that a channel is being utilized by any
of the following causes:
• The connected modem is transmitting.
• The connected modem is receiving valid data from another modem.
• The connected modem has detected RF noise or interference.
Channel Survey shows the channel utilization and noise floor graph with 1-second, 1-minute and 1-hour periods.
Figure 74 shows a percent of the overall radio traffic on the channel that is currently being used.
