Happy New Year!

To you all - Happy New 2013!
All the best in New Year, for you, your families and close ones.


Have a good time. Regards,
Bart Barton

P.S. Come back for more of LTE/EPC shortly ;-)

Resource: filtering, principles, measurements durring HO, and more on Radio part

Yesterday I found good resource on multiple LTE Radio topics covered by one site.
To Whom it may concern.

Enjoy!

Multiple LTE Radio topics

• How Handover Filtering by UE in LT?
• Handover principles and Handover measurements in LTE
• Handover Algorithm and Procedure in LTE
• What is AMC & its Algorithm in LTE  
• How UE Switch to Service types in LTE?
• PLMN selection in “IDEL Mode” for LTE-UE
•   
• and much more from radio side
http://www.teletopix.org/category/4g-lte

EPS Mobility Management (EMM) and Connection Management (ECM) states

The EPS Mobility Management (EMM) states describe the Mobility Management states that result from the mobility management procedures e.g. Attach and Tracking Area Update procedures.
There are two EMM states described in Specs:

• EMM-DEREGISTERED
• EMM-REGISTERED

The EPS Connection Management (ECM) states describe the signalling connectivity between the UE and the EPC.
There are two ECM states described in Specs:

• ECM-IDLE
• ECM-CONNECTED

In general, the ECM and EMM states are independent of each other. Transition from EMM-REGISTERED to EMM-DEREGISTERED can occur regardless of the ECM state, e.g. by explicit detach signalling in ECM-CONNECTED or by implicit detach locally in the MME during ECM-IDLE. However there are some relations, e.g. to transition from EMM-DEREGISTERED to EMM-REGISTERED the UE has to be in the ECM-CONNECTED state.

The Sy interface - between PCRF and OCS

Now I have more work to do then I had and it's all focused on GGSN node part and additional equipment not covered by 3GPP specs.Few months ago, in comments some of you asked me to look deeper into the Sy interface. Have to admit that hadn't have much time lately and.. let's be honest, some kind of a mood to research, put together and publish new articles.

Back to the point where we should start.
     

The Sy interface overview

The Sy reference point is defined between the PCRF and the OCS. Big picture of the relationships between functional entities are shown in Fig 1. below.

Fig. 1. Sy overview

As you may (even should) notice on Fig 1. above are simoultaneously SPR and UDR. Those entities work separetly, that means if there is SPR with Sp interface, there is no UDR with Ud interface in the network. Those were put one one figure to save space. Cojunction or means there is the one OR the other. When UDC architecture is used, the SPR with Sp interface, whenever mentioned in this document, is replaced by UDR and Ud.

Resource: RF and Microwave Engineering Tutorial Site

Lately I don't have spare time to read and prepare something for all of you.

Today I hit really good resource covering RF and Microwave and radio signal modulation in one place.
I wish I found that when I was at the University. For all of you who can find it useful.

Enjoy!

RF and Microwave Engineering Tutorial Site

• Comprehensive – Everything about Wireless, RF and Microwave
• Media rich - Graphics, Images, Videos, Animations, Flashes, Calculators, Java Applets
• Unique - No such tutorial exists today anywhere on the Web!
• Practical
• Free
http://rf-mw.org/table_of_contents_toc.html

Tracking Area Update (TAU) procedure

In this article major topic will be Tracking Area Update (TAU) procedure. What cause it, how the procedure made and what it causes for UE.

Because there are couple of reasons why TAU can take place we won't start from picture as always.

Almost all what you will see below you can read in details in 3GPP TS 23.401.
Also, maybe you are looking for Periodic Tracking Area Update, don't you huh?

Triggers for TAU procedure

When TAU procedure is taking place SGW can be changed or not, but what really bring Tracking Area Update procedure to live is what we should ask about.
According to the spec I've mentioned above a standalone tracking area update occurs when a GPRS-attached or E UTRAN-attached UE experiences any of the following conditions:

• UE detects it has entered a new TA (Tracking Area) that is not in the list of TAIs (Tracking Area Indicators) that the UE registered with the network;
• the periodic TA update timer has expired;
• UE was in UTRAN PMM_Connected state (e.g. URA_PCH) when it reselects to E-UTRAN;
• UE was in GPRS READY state when it reselects to E-UTRAN;
• the TIN indicates "P-TMSI" when the UE reselects to E-UTRAN (e.g. due to bearer configuration modifications performed on GERAN/UTRAN);
• the RRC connection was released with release cause "load re-balancing TAU required";
• the RRC layer in the UE informs the UE's NAS layer that an RRC connection failure (in either E-UTRAN or UTRAN) has occurred;
• when the UE changes the radio capability of at least one of the following radio access technologies: GERAN, UTRAN or CDMA 2000;  *
• for a UE supporting CS fallback, or configured to support IMS voice, or both, a change of the UE's usage setting or voice domain preference for E-UTRAN.
• for a SR-VCC capable UE, a change of MS Classmark 2 and/or MS Classmark 3 and/or Supported Codecs.
• UE manually selects a CSG cell whose CSG ID is absent from both the UE's Allowed CSG list and the UE's Operator CSG list.

For all cases except case "periodic TA update timer" UE shall set the EPS update type IE to "TA updating", but for "TA update timer" case the UE shall set the EPS update type IE to "periodic updating".
For trigger marked with "*" the UE shall include a UE radio capability information update needed IE in the TRACKING AREA UPDATE REQUEST message.
The TAU procedure is initiated by an UE in either ECM-IDLE state or ECM-CONNECTED state. The decision to perform SGW change during the tracking area update procedure is made by the MME independently from the triggers above.

The eNodeB shall include TAI+ECGI of the current cell in every S1AP Uplink NAS Transport message it sends. There are situations where eNodeB can contain cells from more than one TA and cell changes that happen on same sNodeB are not notified to the MME. However to finish TAU procedure with accept message MME needs to know UE's current TAI.

eUTRAN to UTRAN (4G to 3G) Iu mode handover

Few last articles were about Handover in LTE network. From old eNB to new eNB, with or without using new MME/SGW, with or without using X2 interface, and so on.
Today we will be talking about handovers from eUTRAN to UTRAN, from 4G to 3G.

Sorry guys, today I don't have time to create abstract picture which we could use to start from.
But it should be easy for you to imagine.
UE is moving from area where is 4g coverage to area where is only 3g coverage.
eNBs change to RNCs, MME to SGSN, only the mobility anchor (PGW) stays the same.

More about this you can find in 3GPP TS 23.401.

Inter RAT handover - general information

During Inter RAT handover indirect forwarding may apply for the dowlink data forwarding performed as part of the handover. From its configuration data the MME knows whether indirect forwarding applies and it allocates a dowlink data forwarding path on a Serving GWs for indirect forwarding. From its configuration data the S4 SGSN knows whether indirect forwarding applies and it allocates dowlink data forwarding paths on Serving GWs for indirect forwarding. It is configured on MME and S4 SGSN whether indirect dowlink data forwarding does not apply, applies always or applies only for inter PLMN inter RAT handovers.

eUTRAN to UTRAN Iu mode Inter RAT handover

General information

Pre-conditions:

• The UE is in ECM-CONNECTED state (E-UTRAN mode).

If emergency bearer services are ongoing for an UE, handover to the target RNC is performed independent of the Handover Restriction List. The SGSN checks, as part of the Routing Area Update in the execution phase, if the handover is to a restricted area and if so SGSN deactivate the non-emergency PDP context.

S1 interface based handover

 Last two articles (you can find them here1 and here2) were about handover in scenario where there is direct connectivity between eNB. But what happen when there is no X2 connection old and new eNodeB?
Answer to that is S1 based handover procedure which you can find described below.

All of this information you can find by reading specific section of 3GPP TS 23.401 document.

As it is now like a little tradition, we will start with high level of abstract image.

Fig. 1. UE is moving from old to new RAN coverage provided by eNodeB.

This image should look familiar for those who was reading about X2-based handover. The thing what has change in this scenario is that there is lack of connectivity between two eNBs between which UE moves.
That's why, to do the handover the MMEl has to be involved directly. If you compare previous cases with this one, the first thing that each one of you should notice is that here eNodeB is contacting with MME, and the target eNodeB address is found because of SGW.
Before we will see detailed call flow please keep in mind few general S1 handover information.

X2-based handover with SGW relocation

Last time article was about handover based on X2 interface but without SGW change, that is why it's time to deal with X2 based handover with SGW relocation.

All of this information you can find by reading 3GPP TS 23.401.
Today as usually we will start with a high level of abstract picture. Please see below.

As you can see Fig. 1. is almost the same as it was in X2 based handover, where the green arrow was demonstrating the case we talked about last time (if interested you can read about it here) where was no need to change SGW. Today we are interested in case illustrated by blue (azure? blueish?) arrow. Where handover is done bye X2 interface with SGW relocation.
Lines that are green, between UE and eNB, showing changed path on the end of handover operation without SGW change. Blue lines between UE, eNB, MME and new SGW are showing new path after changing old SGW to new.

Fig. 1. UE is moving from old to new RAN coverage provided by eNodeB.

Before we will jump into detailed description of handover few general information about X2 interface based handover.

X2-based handover without SGW relocation

Last article was about IMSI, TMSI and GUTI, and how they are created, it was also mentioned there that GUTI is used in handover (HO) procedure. I thought that today is a good time to say few words about handover.
There are two general types of handovers in LTE.

• X2 based, and
• S1 based

In this article I'm going to describe only X2 based HO and to be perfectly honest with you I have to admit, that I will publish information about X2 based handover with case where no SGW is changed.

For others types please look for different article (After publishing articles describing other HOs I will update this line with direct links. [Update-16-03-2012] First one is X2-based handover with SGW relocation).

All of this information you can find by yourself just by reading 3GPP TS 23.401.

As always it's good to start with general picture, so here it is.

Fig. 1. UE is moving from old to new RAN coverage provided by eNodeB,

As you can see, green arrow is demonstrating UE movement between two eNodeBs controlled by the same MME. Such procedure as you should know is called a handover. In this procedure every bearer set between UE and PGW will be moved to new eNodeB(if target eNodeB is able to handle them).
Please see below general description of X2-based handover according to specyfication.