3G-2G Handover Scenarios

is this Nitin Garg?

In more detail, an IRAT handover works as follows:

On Call initiation, the RNC sends predefined thresholds to the UE for Event 2d RSCP and Ec/No. Event 2d tells the UE when to request entry into compressed mode so that it can simultaneously measure GSM neighbour signals.

When the UE received signals fall below the Event 2d thresholds, the UE sends an Event 2d to the RNC which responds with a compressed mode entry sequence, followed by sending the UE a GSM composite neighbour list – which contains the thresholds for another event – event 3a – which is the trigger level at which the UE will request an IRAT handover.

The UE then starts scanning for the GSM BCCH-BSIC combinations contained in the neighbour list and GSM neighbours which fall above the broadcasted GSM signal minimum level will be reported to the RNC as soon as the UMTS signal falls below the Event 3a threshold conditions.

Once the RNC receives an Event 3a, it sets up the handover call via the MSCs to the associated GSM BSC, requests resources on the GSM base, and when all of that is confirmed, the RNC issues a handover command to the UE, instructing it which GSM base station to hand over to.

The UE then relocates and sets up it’s call on GSM and the connection then continues on the new RAN. If the handover fails, the UE relocates back to UMTS and the RNC will prepare to try again – either to the same GSM signal or to another one of the UE sent multiple candidates in the Event 3a.

Thats a broad outline of the steps involved in an IRAT handover – hope that helps. For more info refer to the RRC management 3GPP standard (sorry cant remember which one it is).

WirelessNetNut
last time looked at IRAT and the Event2d and 3a it was in 3GPP TS 25331 ver 4.17.0, 7.3.0….

I strongly belive HOs between 2G and 3G are needed. Why? Well, there any many reasons. Currently the coverage of the most 3G networks is not as good as with 2G, so if there were not HO from 3G to 2G, then user in the edge of 3G would experience drop if not handed over to 2G. This is just one example. Then, some vendors may have different type of algorithms to free 3G capacity for high bitrate users. This requires also HO from 3G to 2G in case where e.g. AMR call has been started in 3G, but it is wanted to be handed over to 2G. One more thing; building capacity even for AMR is much cheaper with 3G. One WCDMA cell can easily handle tens of calls, and for same amount of calls GSM cell would need quite big amount of TRXs. This will be trend we are seeing, and deployment UMTS900 will make 3G even favourable over the 2G.

2G and 2.5 can survive perfectly well on it own. It really doesn’t need 3G.

3G is there because people have ideas and convince other to have those ideas. It is not logical to assume that what 3G offers is what the customer actual wants, it provides what the customer has been told they will have.

3G does need GSM/GPRS for at least teh following reasons:

– fallback when 3G doesn’t work or poor, ailing or no coverage spots (thus needs 2G spectrum)
– needs 2G Mast installation for co-location
– needs 2G Customers for traffic and revenue
– needs 2G and 2.5G networks for least cost routing
– etc

Getting away from the politics and studying the technical aspects, it is quite clever the way they have got the technologies to work together if I can set out this crude outline:

UTRAN
GERAN
GSM GPRS
GSM

using Inter Radio Access Technology (IRAT) because it requires (obviously) the symbiotic relationship to work between radio network, handset and USIM.

For Chris.

“It’s clearly a lot of cheaper to build voice capacity with WCDMA than with GSM.”

WCDMA is not a addon or a patch! I think so. You have to format the whole system. Look….

1.You have to change the BTS with Node-B.

2. You have to change the BSC with RNC.

3. You have to change the MSC with MGW/Server.

4. You have to change the handset of customer.

Then what is left??? Everything has been changed.

So, don’t you think they have brought a NEW NETWORK altogether. And justification for introducing this NEW NETWORK is not the speech
but data. High Data rates???
And if they finally start using this NEW NETWORK for speech then what is the fun? More over by doing this they have reached the heights of complex networks. I don’t like the idea or may be i am still not aware of the real picture.

Tell me one thing …An operator presently running a 2G/2.5G network applies for a CDMA2000 license and get it. He starts a NEW NETWORK on CDMA2000 technology
and he shares the same mast, media, power , space resources of the 2G/2.5G network. And he introduces a convergent billing system. I mean a single bill for all services.

Then what is the difference in former and latter NEW NETWORK.

regards

Hi,
Is handover from 3G to 2G generally seamless?