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TitleGSM Optimization
TagsElectronic Engineering Computing Technology Telecommunications Engineering
File Size362.5 KB
Total Pages7
Document Text Contents
Page 4

 When will Cell Reselection occur ?!!!

1) Serving Cell became barred ( CB = YES )

2) C1 serving cell falls below zero for more than 5 seconds.

3) MS tried to access the network through this cell unsuccessfully for the

allowed no. of times defined by the parameter MAXRET

4) C2 neighbor cell ( one of the six strongest neighbors) became greater than C2 serving

cell for more than 5 seconds.

5) MS detects Downlink Signaling Failure.



 C2 is called “Cell Reselection Quantity”

C2 = C1 + CRO – TO * H( PT – T ) where PT ≠ 31

C2 = C1 – CRO where PT = 31

0 , X < 0

Where H(x)

1 , X ≥ 0

 CRO  Cell Reselection Offset, unit = 2 dB, value range = 0 to 63

 TO  Temporary Offset, unit = 10 dB, value range = 0 to 7

 PT  Penalty Time during which TO is valid

 T  Initiated from zero when the MS places the neighbor in the list of the

Six Strongest

 CRO : defines a signal strength offset to encourage or discourage MSs to reselect

that cell.

 TO : defines a negative temporary offset for certain time according to settings of

PT (Practically this is useful to prevent fast moving MS from camping on

microcells)

PT: If PT is set to 31, this means that a (–ve) SS offset “CRO” will be applied to this cell and it

appears less favorite for cell reselection

Page 5

 CRH ( Cell Reselection Hysteresis )

 Cell Reselection between two cells lie in two different Location Areas, will be

accompanied by Location Update.

 At the border between cells the Signal level may be comparable, cell reselection

may occur many times accompanied by many location updating leading to huge

signaling load.

 To avoid this, a parameter CRH is introduced such that a cell in another location

area LA2 should have C2LA2 should greater than C2LA1 of serving cell lie in LA1 by

at least CRH in order to be selected.

If C2LA1 = 5 dB, CRH = 4 dB, then C2LA2 ≥ 9 dB in order to be selected





4) Location Update

 In the Idle Mode, the Network knows the location of the MS on a Location area

resolution not on a cell resolution.

 There are three different types of location updating defined:

1) Normal Location Updating.

2) Periodic registration.

3) IMSI attach & IMSI detach (when the MS informs the network when it enters

an inactive state)

1. Normal Location Updating

2. Initiated by the MS when it enters a cell belongs to a new Location Area (LA).

3. The MS will compare the LAIold stored on the SIM with the LAInew broadcasted

from the new cell and it will found them different so it’ll perform Location Update

type normal.



1. Periodic Registration

2. Regularly the MS should update the Network with its current location Area.

3. The Network will inform the MS how often it should report the location Area he is

registering himself in.

4. Based on the value of the Parameter T3212 the MS will know how frequent it

should make periodic registration.

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