Comparison between Service Steering and Random Combing between different carriers

1. Overivew: Multi carrier solotion is one of the most common solotions that all network might be using now in order to enhance their capacity, RF conditions, and user perception after all

In order to use multi carrier solution we have to choose one of two access techniques either Random combing or service steering both are commonly used in many networks that already have multi carrier condition, but which one is better? And how to choose between them in the next points we will go deeply in order to understand which one we can use

2. What is service steering and how it work? Service steering is the technique in which we define special service to different carriers for example we define F1 (first carrier) for voice and R99 services and define F2 (second carrier) for the HSPA services, the benefit of this one is to force all the data traffic on F2 that will make the fist carrier more free with much better radio conditions so it will enhance the accessibility of voice services as there will be much improvement in f1 radio conditions

Also for the data services, all users can use all the power allowed on F2 which will enhance the throughput ( to certain point)

3. What is the bad effect of service steering? Service steering will work perfectly fine as long as the Data traffic is not high on the network, when the data traffic increase on the network you can easily see that there will be congestions on the data layer even that you will have many free resources that can be used, which is not our target for sure to ensure the maximum usage of the current available resources. Other problems will be demonstrated later

Also the service steering situation will lead to lower RAB Assignment Success rate, mainly due to the DRD usage also the time of call establishment will be much higher compared with random combing

4. Now what is the Random combing? Random combing is the opposite of service steering in this part we will not force the traffic on a certain carrier even more we will make it like free competition between different carriers, so all services will be available on all carriers in this case we will have the maximum utilization of the nodeB resources making sure that the users can get the maximum benefit available under condition that we can balance the traffic between these different carriers

5. Does Random combing have any problems? Sure it have, random combing to give the required effect the network should have continuous coverage in both carriers, since we are going to enable free combination between different carriers we also should have enough license to make both carriers have the same services

exactly no advantages can be giving to any one of them, any advantage will lead directly to non balanced situation of traffic

6. So which one we should use? If the network doesn’t have high data traffic and doesn’t have enough second carrier coverage so we don’t prefer the usage of the random camping service steering will be much better

But if we have high data traffic and continuous second carrier coverage, and want to enhance the RAB Setup success rate, enhance the access delay time, enhance the HSPA throughputs we have to use Random camping,

In the coming parts we will show with technical proof why we may have:

Long delay for RAB access Bad utilization of the resources Many RAB failures leading to low RAB Success

rate

7. Service steering bad effects technical analysis:

Long connection setup time: By comparing the RAB setup time of DRD with None-DRD from the test data, we found the average setup time with DRD is 200ms longer than none-DRD.

Below figures from the layer three messages and signalling trace to show the time delay exactly

RAB setup with DRD

Rab setup without DRD

This can confirm with no doubt that the time required to initiate a call using DRD is 200 ms longer than the time required for non DRD case under the same conditions

lower RAB setup success rateAccording to the process of DRD, every time when the DRD happens, the NODEB and UE will start the radio link synchronization again. The one more time RL synchronization will increase the chance of RAB setup failures. Basing on service steering strategy, (F2 carry HSPA traffic), the load of F1 and F2 is different, it will increase the chance of DRD failures

Unbalanced resource utilizationAs we mentioned before, in case of high traffic the usage of the resources will be much different between both carriers, clearly we will have more utilization on the second carrier than the first carrier specially in case of power below trends to show the different in TCP usage between service steering two carrier network

Also RTWP is showing big difference in the point of UL interference, since F2 s having more traffic so more UL interference will be found on F2

8. Now how we can implement the Random camping in order to avoid the above drawbacks?

In order to enable Random camping below parameters should be tuned as mentioned

Camping Policy F1,F2:Random Camping; Command reference as the following：ADD UINTERFREQNCELL:CELLID=F1, NCELLID=F2, IDLEQOFFSET2SN=0, BLINDHOFLAG=TRUE, SIB11IND=TRUE; ADD UINTERFREQNCELL:CELLID=F2, NCELLID=F1, IDLEQOFFSET2SN=0, BLINDHOFLAG=TRUE, SIB11IND=TRUE;

//BLINDHOFLAG: is on in order to allow LDR to be uses on the same sector cells only // IDLEQOFFSET2SN is set to zero in order to allow the free idle mood camping which is valid only when SIB11 Indicator is set as TRUE.

Access Policy • R99，HSPA service random camping on F1 or F2, and

launch access in the camping carrier. There is no DRD in HSPA service between two carriers. Detailed parameters is as following:

Disable ServiceDiffDrdSwitch of F1/F2 by the command MOD UCELLDRD;

Disable LdbDRDSwitchDCH of F1/F2 by the command MOD UCELLDRD;

Disable LdbDRDSwitchHSDPA of F1/F2 by the command MOD UCELLDRD

Connection Policy

• Adopt LDR: Detailed parameters is as following:

9. What is the improvement we can see after implementation?

In our case since we had big improvement in case of real field we had significant enhancement which can be proved by the below KPI trends

Below to show that we managed to balance the same HSDPA user number on both carriers

Average throughput on F1 increased with almost same throughput on F2 so this mean that overall throughput on the Area totally increased as well

Total HSDPA data volume also didn’t change much, but the traffic is passed from F2 to F1 leading to more data balance and resource utilization

PS RAB Setup success rate improved on F2 and on the area overall as in below trend

The RRC Call drop rate improved a lot as we decreased the DRD attempts

PS Call drop rate also improved a lot

10. Conclusion and summary: In the parts we covered we can get better understanding in the below main points:

What is service steering and what is random camping?

When we may prefer one of them on the other? What is the main drawbacks of service steering and

how we proved them? How to implement the random camping? What enhancement you may expect when you use

random camping