Measurement gaps

What does measurement gap means? and how to calculate measurement gaps?

Before the handover, UE normally measure the cell power (signal quality) of the target cell and report it to the network, so that network can make a decision whether to allow UE to handover to the target cell or not.Issue does not come when UE  measure the signal quality of the target cell if the target cell is at the same frequency as the current cell (Intrafrequency measurement) but an issue when the target cell is at a different frequency from the current cell (Interfrequency measurement).

The simplest solution for Inter frequency measurement, the simplest solution for this would be to implement two RF tranciever on UE.

However, there are some problems with this kind of two transceiver solution. One of the problems is cost issue. It would require additional cost to implement the additional transceiver. The other problem would be the possible interference between the current frequency and target frequency especially when the current frequency and target frequency are close to each other

In short, measurement gaps are typically needed by the UE (having a single RF) to monitor cells on other frequencies than the serving cell, i.e. LTE inter-frequency as well as inter-RAT (e.g. GSM and 3G) cells

Same concept is implemented in UMTS as “compress mode” but now in LTE – the Measurement GAP((e.g, Starting Position of the Gap, Gap length, number of Gaps etc)  is to create a small gap during which no transmission and reception happens. since there is no signal transmission and reception during the gap, UE can switch to the target cell and perform the signal quality measurement and come back to the current cell.

Setup the measurement gap configuration indicated by the measGapConfig in accordance with the received gapOffset, i.e., the first subframe of each gap occurs at an SFN and subframe meeting the following condition:

SFN mod T = FLOOR(gapOffset/10);

with T = MGRP/10 as defined in TS 36.133 (T =40/10 =4)

subframe = gapOffset mod 10; 

(Example: if gapOffset is {gp0, 0 mod 10= 0} or {gp1 ,1 mod 10=1} )