Tuesday, December 14, 2010

Verizon 3G to LTE Handover Delay

This is purely my thought and may not be entirely true.

I read news that users of Verizon network are experiencing a delay of 2 minutes when moving from 3G to LTE network. Users are experiencing this when they are continuously transmitting the data. I also read that in few instances subscribers are forced to unplug their dongles and plug them back to get LTE access. I was wondering what could be the reasons and below is what I think!

Frist Reason:-

Verizon network is CDMA based. LTE is GSM based. Since both technologies are entirely different it gives an impression that handovers are not going to be smooth. However 3GPP specs does provide solutions for smooth handovers. So why the delay? The places where LTE is deployed would have had 3G coverage. When a 3G network detects that UE is receiving stronger 4G signal it has to handover the UE to 4G network. But not complete 3G network would have been converged to 4G, so in few cases the 3G network would simply ignore 4G networks presence and make the UE to hook on to it. In this case users should stop transmitting data for a while so the UE may go into idle mode. Once UE is in idle mode and if it wants to send some data, it will perform cell re-selection and choose LTE network instead of 3G thus bringing subscribers back to LTE. This could be one reason why few subscribers had to plug out their dongles and place them back to get 4G access.

Second Reason:-

Next, assume that 3G network is converged to 4G. In this case moving from 3G to 4G should be smooth. But if the network elements are far away then the delay in the core network might result in higher handover time.  However movement from 4G to 3G should be smooth, because where there is 4G network, 3G network would have been present and 4G network would have had complete information about it.

The fixes could go in several places. But I am assuming that first reason is what bothering the most and network should be fixed soon. Those who are interested to know more can refer to 3GPP Spec 23.402 for detailed call flows.


madona said...

This is a very helpful post, I hope this really helps me to complete my project.

Santosh said...

Nice to hear!

vishwa said...

Isn't it the UE which decides which network to choose when it is receiving signal from both the networks[3G and 4G] ??

Santosh said...

Yes, but cell reselection is possible when UE goes to idle mode, AFAIK.

Anonymous said...