Handover Parameters (Part 3 of 3)

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Handover Parameters (Part 3 of 3)

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Filter Coefficient for Event a3

Once the UE is configured to do measurements, the UE starts measuring reference signals from the serving cell and any neighbors it detects. The next question is whether the UE should look at just the current measurement value, or if the recent history of measurements should be considered. LTE, like other wireless technologies, takes the approach of filtering the currently measured value with recent history. Since the UE is doing the measurement, the network conveys the filtering requirements to the UE in an RRC Connection reconfiguration message.

The UE filters the measured result, before using for evaluation of reporting criteria or for measurement reporting, by the following formula:

 

where

  • Mn is the latest received measurement result from the physical layer;
  • Fn is the updated filtered measurement result, that is used for evaluation of reporting criteria or for measurement reporting;
  • Fn-1 is the old filtered measurement result, where F0 is set to M1 when the first measurement result from the physical layer is received; and
  • a = 1 / 2(k/4), where k is the filterCoefficent for the corresponding measurement quantity received by the quantityConfig.

Then, the UE adapts the filter such that the time characteristics of the filter are preserved at different input rates, observing that the filterCoefficent k assumes a sample rate equal to 200 ms.

The parameter “a” defines the weight given to current value and (1-a) (i.e., the remaining weight is given to the last filtered value). For example, if filter coefficient k = 4, then a = ½^(4/4) =1/2. This means that new measurement has half the weight and the last filtered measurement gets the other half of the weight.

Example of Filter coefficient values are:

  • Case 1: value k = 8 , a = ¼, Fn = ¾ Old + ¼ New
  • Case 2: value k = 4, a = ½, Fn = ½ Old + ½ New

Optimization Rules:

a)     A high value of the parameter filtercoefficient will provide higher weight to old measurements (more stringent filter)(the opposite is true)

b)    The higher the values of filtercoefficient the higher the chances of eliminating fast fading effects on the measurement reports

  1. This eliminates reporting a cell which RSRP was suddenly changed due to multipath or fast fading
  2. Which in turns eliminates the chances to handover to a cell which RSRP was strong for some milliseconds
  3. Therefore reducing the chances for Ping-Pong effects

c)     A value of 8 is typically used in the network although a value of 16 might also be used in dense urban areas.

  • Thanks a lot for all these (3 of 3) HO new information. I would like to cite from them, what should I refer to.

    Regards,

    Yaseein

  • It is really perfect work.

    I have posted a question about mathematical analysis of handover in LTE ( the response did not answer my question). And it is very obvious that you have a thorough knowledge of mathematical analysis.

    Could you guide me to find a reference (i.e book, paper dco...) including all these analysis.

    Regards,

    Yaseein