relative sensitivity on intermediate channels

In the CTIA_Test plan for Mobile performance,the document need to test the relative sensivity on intermediate channels.
Who know the useful of the test of relative sensitivity on intermediate channels?
What can we get from the test of relative sensitivity on intermediate channels?
The progress of measuring the test of relative sensitivity on intermediate channels is following:

1. Move the EUT and chamber positioner(s) to the location & polarization resulting in
the best-radiated sensitivity measured for the closest, in frequency, fully measured
channel, now used as a Reference Channel. A single orientation may be used for all
three Reference Channels, provided that the measured radiated sensitivity of that
orientation for each reference channel is within 3 dB of the best sensitivity measured
for that channel. It is important that the level to be measured is well away from any
nulls in the pattern to minimize the uncertainty introduced by any positioning
repeatability.
2. Increase the RF signal level of the base station simulator by 5 dB over that used at
the same spherical spatial location for the respective Reference Channel.
3. Using the base station simulator, measure the FER using the required number of
frames as described above. The measured FER must not exceed 0.5%.
4. Report the pass/fail status of each intermediate channel.

This is a standard procedure to get the all-channel radiated sensitivity, using as a reference a quiet channel (Reference Channel).
I don't know what wireless system is about, but I would prefer when doing radiated sensitivity to use BER (bit error rate) instead FER (frame error rate).
BER is direct related to SNR of the receiver, when FER is given by a particular threshold set by the system designer.

Thank you for your reply.When measureing the TIS ,The procedure is using BER.But when measuring relative sensitivity on intermediate channels,the procedure is using FER.