Mahmoud Ali 

LTE Team Leader/SME at AdvaComm

All Articles by Mahmoud Ali

How to Optimize your TAL Size to avoid paging discards. (number of TAs (eNodeBs)) 

Intended Audience: RF Consultants working on Live networks.

Tracking Area List (TAL) : it is a group of Tracking Area Codes (TACs) which is used to page UE within the network TAL geographical area.

Tracking Area Codes (TACs) or TAs: it is group of eNodeBs in one small area with maximum number of 100 eNodeBs.

TAC and TAL planning is to determine the size of a TAC and TAL border. The TAC and TAL size is simply defined as the number of eNodeBs in the TAC or TACs in a TAL.

If only a few eNodeBs are in a TAL, Tracking Area Updates (TAUs) may occur frequently, and MME load and UE power consumption increase. If TAUs occur frequently, a UE cannot respond to a paging message during TAU, reducing the paging success rate.

If number of users increases in a TAL, paging load increases in this TAL and further split planning needed to solve paging overload.

Q: how can we decide what is the appropriate TAL Size?

During the LTE network deployment, the location area plan of the GSM and UMTS networks can be used as a reference for TA and TAL border. That is, the LTE TAL size and border are consistent with that of the LAs in the GSM and UMTS networks.

Q: why Good design of TAL means TAL=LAC in 3G? 

A TAL includes the optimum number of eNodeBs, balancing the TAU frequency and paging load.

The TAL size is estimated based on the following parameters:

• MME paging volume: includes the number of boards in an MME and board paging volume.

• eNodeB paging volume: includes the paging load processed by the CPU, paging overhead allowed by the PDCCH and PDSCH, and paging blocking rate.

• Maximum number of UEs concurrently attached to the network in the served area of an MME.

• Paging arrival rate during busy hours, which depends on the MME paging traffic model.

• Busy-hour paging traffic model of UEs.

Looking in into MME and eNodeB Paging Volume, normally MME supports paging volume 16 times more than eNodeB which lead us to a conclusion:

MME normally doesn't limit TAL size --> TAL size is limited by eNodeB capabilities for paging volume (pages/second).

Paging Capacity Analysis on the eNodeB:

1. PDSCH paging capacity is: (assuming 20MHz).

you can refer to 3GPP TS 36.304.

2. PDCCH paging capacity on the eNodeB (the nB parameter is set to 1.)

3. eNodeB paging Processing CPU capacity: i.e Huawei eNodeBs CPU max capability is 750 pages/s, we should assume 70% utilization as max to allow safe buffer zone.

=750*0.7=525 pages/s.

4. The paging blocking defined by C_Blocking.

Paging Traffic Model:

Paging traffic mode=Whole Network Paging volume (success reply)/ No of LTE subscribers.

assuming 1,000,000 subscriber with 16173740 page per busy hour.

=1617374/100,000 = 16.17 pages per subscriber/hour. --> 0.004492 page/s per subscriber.

now you can correlate directly Paging reply Volume(success reply from UE) with number of eNodeBs in one TAL.

example: if you have one TAL in your network with 300 eNodeBs in one TAL and Total paging reply volume as 2,000,000. and your limitation on eNodeB is 525 as Huawei eNodeB.

Maximum number of allowed eNBs in one TAL is = 525*3600*300/2,000,000=283 eNBs --> this means you need to split your TAL into 2 TALs in order to avoid any future paging discards.

note: you need to scale these numbers to your network BW, here it is for 20MHz.