This would appear to come from a larger document referring to the process of ‘call handover’ between GSM base stations?
Train travel presents an unique challenge for cellular operators because of the need to maintain ‘signal strength’ within acceptable maxima/minima to enable continuous calls and avoid call ‘dropping’.
This document refers to the average and deviation in ‘Anbindungspegel’; literal translation of this would be ‘connection level’ but the relevant term used within Telecommunications would be: signal strength.
Donorpegel would be the signal strength from ‘node A’ that is handing the call to ‘node B’ in this example. The cellular handset measures the differential in ‘Anbindungspegel’ between the two nodes, and when node B presents a much stronger signal, initiates a call handover.