Tracking Area List concept in LTE

[faisaladeem]

Can someone shed some light on Tracking Area List (TAL) concept in LTE. Apparently a TAL contains 1 or more TACs and a UE need not perform TAU while moving across TAs belonging to its TAL. On the other hand, UE will be paged in all the TACs included in its TAL. This could have been achieved by simply defining a bigger TA (i.e. TA equivalent to all the TAs in a TAL) ? Is it due to maximum number of eNBs limitation in a TA (typically 100 or less) ? Or is it intended for having UEs in the same area with different TALs e.g. UEs having high mobility will be assigned a bigger TAL while static UEs will be assigned a smaller TAL containing a single TAC ?

[giegala]

Hi,

this a solution to paging problem in 2G and 3G, where pagings are lost at the border of 2 LAs. In 2G and 3G UE would not listen to correct LA for paging during LAU and/or core would not send paging to correct LA.

When UE is registered to several TA, it would be paged to all of them (old and new), and paging loss is expected to be smaller that for 2g/3g

[faisaladeem]

Hi, this problem can still happen if UE is at the border of two TALs! One advantage of TAL is that different TALs can overlap and if somehow TALs can be dynamically updated based on users mobility, it might be more efficient. Also it is easier to add/remove TAs from TALs if TAs need to be merged or divided for optimization purposes.

[jayk]

A UE does not initiate a TA Update if it enters in a TA which is in its TAL. It helps to reduce the Signalling peak when a bunch of UE's change TA simultaneously for example when a Train passes by a TA boundary the signalling peaks are avoided.