Specifications

Selection Phase
Summit WM20 Technical Reference Guide, Software Version 4.2 95
In addition to listening for existing devices operating on the channel, the DRM APs notify other DRM
APs that they are in the process of selecting a channel. This serves the following purpose:
● Synchronize all DRM APs during the channel selection process (only applies to situations where all
APs are booting at the same time such as after a power failure).
Once the data is collected about existing APs operating on all channels in the environment and other
DRM APs that are booting, DRM APs move onto the Selection phase.
Selection Phase
This phase determines the best channel to operate on. In DRM Version 1.0, the algorithm scans the
information obtained in the scanning phase looking for the loudest transmitting device on each channel.
The result is a list similar to the following:
Each channels loudest signal is captured. These signals are scanned and the channel with the quietest
signal is selected. In the example above, Channel 6 would be selected because -50dHWC is the weakest
signal.
The selection process for DRM Version 1.2 is quite a bit more sophisticated. The information obtained in
the scanning phase is fed into an algorithm to create a Channel Quality Index (CQI). The channel with
the lowest CQI is then selected as the best channel. The CQI is computed using the following
information:
● Loudest transmitting device operating on a channel
● Noise floor of the channel
● Other transmitting devices on the channel
● Transmitting devices on neighboring channels
● Transmitting devices on overlapping channels (Turbo-channels)
The CQI value is designed to take into account all forms of possible interference on a particular channel.
If the noise floor is high on a channel, that channel’s CQI is adjusted to look proportionally worse than
a channel with no noise. If there are transmitters operating on adjacent channels, the overlapping
channels CQI is adjusted to take this into account.
Each channels CQI is computed and the channel with the lowest CQI is chosen as the best channel.
Negotiation Phase
Once the channel has been selected (either using the V1.0 method or the V1.2 method), the negotiation
process begins. The purpose of this process is to give the requested channel to the AP that needs it
most. APs in dense areas get priority over other APs.
During the negotiation process, DRM APs communicate their selected channel and information about
their denseness situation over the selected channel. The negotiation period lasts long enough for all APs
Channel 1: -32dHWC
Channel 6: -50dHWC
Channel 11: -29dHWC