User's Manual
Table Of Contents
- Volume III
- e. Technical Description Of Operation
- Fixed channel Mode
- Auto-select Channel Mode
- g. OEM radio card
- All three cards have a transmitting frequency range of 2.4 GHz to 2.4835 GHz with a transmitting power measured at the antenna of 100 milliwatts. The radio functions as a "frequency hopper" and by definition will "hop" between a preset range of frequenci
- h. Understanding Signal Interference
- Physical Obstructions and Communication Range
- RF Interference
- i. Coverage Area
- j. Possible Monitor & WNI Configurations
- k. Communication Limitations of the Wireless Network
- m. Installation Hardware
For example, the floor plan on page 9 illustrates one room where two WNI’s are clearly seen. Let’s say
that any wireless monitor placed in that room frequently has gaps in the waveform at the central station.
You can use the RangeLAN2 program to determine which WNI the wireless monitor in the problem room
is communicating with. You may find that the wireless monitor is subject to more dropouts when it is
synchronized with WNI A than WNI B. To determine this, use Site Survey tool as previously described, to
determine the actual throughput of the bedside to WNI A and WNI B.
Upon power up of a wireless monitor (or laptop), it will search for and synch to the first WNI (master) it
sees generating a signal known as a “beacon”. The beacon tells the wireless monitor the master’s next
frequency hop. There are other factors involved, but simply stated, the first valid WNI the wireless monitor
sees is the one that it will synch to. You can observe this by placing the laptop between two WNI’s.
Repeatedly open, and then exit the site survey mode. By observing the percentage of times the laptop
synchs to one WNI over another, you can approximate how a wireless monitor would act, if booted in the
same location. If you want to link to a WNI you can carry the laptop to that location and wait for it to
switch. Or you can disable Roaming and force the laptop to connect to a specific WNI.
Going back to our example, in the suspect room you find a tendency to synch to WNI A about 30% of the
time, and WNI B 70 %. Open a Directed Link to WNI A and WNI B and observe the throughput data. In
this example, the data throughput from the suspect location to WNI A is actually 10-15 kB/sec, and the
data throughput to WNI B is closer to 40-50 kB/sec.
The reason that data throughput falls is that the radio portion of the network guarantees delivery. If the
radio need to re-send packets, the throughput naturally falls. This can occur for many reasons:
interference from microwaves or other sources; radio malfunctions; metal carts rolling down a corridor; fire
doors closing; a large crowd of people gathered in a corridor. 10 Kb/sec throughput means that data is
still getting through, but some packets may be lost because at the monitor level, waveform packets are
sent as multicast messages. This means that there is no destination address associated with the
waveform; therefore, the sender (wireless monitor) does not know that packets are missed and will not re-
transmit. The result is gaps or holes in the waveform.
Part Number 062-0983-01 Rev C page 3 - 26