oefficient value fc = 13 results in long bias since the initial value happened to be higher than the average over the observation interval. This could result in false triggering of a measurement event if the time to trigger is shorter than the filtering delay. In general, controlling measurement event triggering delay is easier and more intuitive with time to trigger than with filter coefficient. Therefore, a simple approach is to set the filter coefficient to a fixed value and simply tune the time to trigger to control ping-pong. Time to trigger can also be defined per measurement event whereas filter coefficient is defined per measurement quantity (RSRP, RSRQ). Table 15.8 summarizes the basic measurement events. In the table 'Ms' and 'Mn' indicate serving and neighbour cell measurements, respectively. The LTE measurement quantity can be Inter-layer Mobility Optimization Impact of filtering coefficient fc on L3 averaging delay fading signal L3 signal fc = 4 L3 signal fc = 13 sampling point Time (ms) Figure 15.5 Example of L3 filtering; Doppler frequency is 3 Hz RSRP or RSRQ while inter-RAT measurement quantity may be RSCP, Ec/NO or GSM RSSI. All measurements and thresholds are in decibel-milliwatts or decibels. In the table, the hysteresis parameter and other constants are subsumed in the threshold on the right-hand side of the inequality. Often there is no use case for adding superfluous additional constants (like hysteresis or frequency offset), as it typically only complicates the simple event triggering rule without adding benefit; indeed, all such extra modifiers can be lumped into one constant in order to keep the number of tunable network parameters as small as possible. Measurement gaps can be activated with A1 and A2 events or by a service or load-based trigger such as CSFB call setup or cell congestion. Having measurement gaps active constantly is not in general recommended, since for 40-ms gaps, this results in a theoretical 6/40 = 15% loss of scheduled UE throughput. In practice the throughput loss i