Showing posts with label QoE. Show all posts
Showing posts with label QoE. Show all posts

Wednesday, December 4, 2019

Challenges of 5G Inter-Node Handovers

In all mobile communication networks handovers are the most complex signaling procedures, because multiple network elements (or network functions) are involved. Thus, it is logical that dual connectivity with two different base stations contributing to the radio connection simultaneously are even more complicated. And in EN-DC these two base stations are often covering different footprints using different carrier frequencies.This leads to a situation where we have more options for performing a handover in detail compared with plain LTE handover scenarios before.

The two signaling scenarios presented below illustrate in which different ways a change of the LTE master eNodeB can be performed during an ongoing EN-DC radio connection by using the X2 interface. In a very similar way it is also possible to perform S1 handover from old to new MeNB.

The pros and cons of these options have been discussed already by Martin Sauter in his Wireless Moves blog.

Inter-MeNB Handover without 5G Inter-Site Anchor

Figure 1 shows the easiest way of handing over the signaling connection from one MeNB to another one. Here it is up to the new MeNB to decide if and how the 5G part of the radio connection is continued.

Figure 1: X2 Handoverof EN-DC connection without 5G inter-site anchor

The handover is triggered when the UE sends a RRC Measurement Report (step 1) indicating that a stronger 4G cell than the currently used primary cell was measured. From its neighbor list the current MeNB detects that this better cell belongs to a neighbor eNB.

To provide both, the the Master Cell Group (MCG) and Secondary Cell Group (SCG) parameters to this neighbor eNB the old MeNB queries the SCG configuration parameters from the old SgNB by performing the X2AP SgNB Modification procedure (step 2+3).

Then it sends the X2AP Handover Request message to the target MeNB (step 4) including all information necessary to continue the 5G radio link in case the target MeNB decides to go for this option.

However, what comes back from the target MeNB is a plain LTE handover command (LTE RRC Connection Reconfiguration message [step 6]) embedded in the X2AP Handover Request Acknowledge message (step 5).

Due to this the old MeNB releases all 5G resources and the UE context in the SgNB (steps 7 + 10).

After the UE  successfully connected via radio interface with the target cell in the new MeNB the S1AP Path Switch procedure is executed to re-route the GTP/IP-Tunnels on S1-U (step 8) and releases the X2 UE context in the old MeNB (step 9)

The new MeNB then waits for a new inter-RAT measurement event B1 (step 11) before starting a new SgNB addition procedure (step 12).  Once the SgNB addition is successfully completed including all necessary reconfigurations/modifications on RRC and S1 the payload transmission over 5G resources is continued.

Inter-MeNB Handover with 5G Inter-Site Anchor

Now figure 2 shows what happens when the new MeNB decides to keep the existing UE context in the SgNB while the RRC measurement results and parameters are identical with what was presented above. 
Figure 2: X2 Handoverof EN-DC connection with 5G inter-site anchor

The difference in the call flow starts at step 5 when the new MeNB after receiving the X2AP Handover Request (step 4) starts the X2AP SgNB Addition procedure towards the SgNB (old = new!). The SgNB-UE-X2AP-ID earlier requested in step 2+3 acts as the reference number for the existing context that is going to be continued.

After adding the SgNB UE context successfully the new MeNB sends the X2AP Handover Request Acknowledge message including an UE Context Kept = "true" flag and the Handover Command (step 8).

After the UE successfully connected to the target cell of the new MeNB the S1AP Path Switch procedure is performed and the temporary X2 UE context between old and new MeNB is released (step 10).

The big advantage of handling the handover in this way: The duration of the interruption of the payload transmission over 5G radio resources is minimalized and subscriber experience is significantly better compared to the scenario in figure 1.

Tuesday, January 16, 2018

3GPP-VRIF workshop on Virtual Reality Ecosystem & Standards in 5G

Its been a year since I last posted about Augmented / Virtual Reality Requirements for 5G. The topic of Virtual Reality has since made good progress for 5G. There are 2 technical reports that is looking at VR specifically. They are:

The second one is work in progress though. 

Anyway, back in Dec. 3GPP and Virtual Reality Industry Forum (VRIF) held a workshop on VR Ecosystem & Standards. All the materials, including agenda is available here. The final report is not there yet but I assume that there will be a press release when the report is published.

While there are some interesting presentations, here is what I found interesting:

From presentation by Gordon Castle, Head of Strategy Development, Ericsson





From presentation by Martin Renschler, Senior Director Technology, Qualcomm


For anyone wanting to learn more about 6 degrees of freedom (6- DoF), see this Wikipedia entry. According to the Nokia presentation, Facebook’s marketing people call this “6DOF;” the engineers at MPEG call it “3DOF+.”
XR is 'cross reality', which is any hardware that combines aspects of AR, MR and VR; such as Google Tango.

From presentation by Devon Copley, Former Head of Product, Nokia Ozo VR Platform
Some good stuff in the pres.

From presentation by Youngkwon Lim, Samsung Research America; the presentation provided a link to a recent YouTube video on this presentation. I really liked it so I am embedding that here:



Finally, from presentation by Gilles Teniou, SA4 Vice chairman - Video SWG chairman, 3GPP





You can check and download all the presentations here.

Further Reading:

Sunday, November 1, 2015

Quick Summary of LTE Voice Summit 2015 (#LTEVoice)

Last year's summary of the LTE voice summit was very much appreciated so I have created one this year too.

The status of VoLTE can be very well summarised as can be seen in the image above.
‘VoLTE network deployment is the one of the most difficult project ever, the implementation complexity and workload is unparalleled in history’ - China Mobile group vice-president Mr.Liu Aili
Surprisingly, not many presentations were shared so I have gone back to the tweets and the pictures I took to compile this report. You may want to download the PDF from slideshare to be able to see the links. Hope you find it useful.



Related links:

Saturday, August 25, 2012