telecom • networking • design

an EventHelix.com blog


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S1AP View of Inter-MME S1 Handover

Here we look at the S1 handover that involves an MME change. The S1 handover is analyzed at the S1AP interface. S1AP messages involved in S1 handover are shown just before the message. The messages show a high level structure of the complex messages involved in the interaction.

Inter-MME-S1-handover

Additionally, you can click on any S1AP message to see the complete field level details like the one shown below.

PDCP-transfer


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LTE Network Design and Planning Videos

Learn about LTE network design and planning from this video series. Issues involved in RF planning and resource allocation are covered in detail.

The video tutorial series is divided into the following videos:

  1. dimensioning user traffic in 4G networks
  2. overhead in LTE dimensioning
  3. customer experience in wireless network design
  4. measurements in LTE
  5. downlink parameter dimensioning in LTE
  6. uplink parameter dimensioning in LTE
  7. LTE spectrum analysis

Frequency reuse in LTE

 

 


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Tracking Area Updates in an LTE Network

LTE Tracking Area Update signaling flow describes how mobiles keep the network updated about their location.

A Tracking Area Update takes place if:

  • UE detects it has entered a new Tracking Area that is not in the list of TAIs that the UE registered with the network;
  • the periodic Tracking Area 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”;
  • a change of the UE Core Network Capability and/or UE Specific DRX Parameters information of the UE.

Tracking area update in LTE


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LTE Physical Layer Introductory Videos

Learn about the LTE physical layer from the video series from IEEE and Ericsson. Th video series covers:

  1. LTE protocol structure and architecture
  2. Downlink frame structure, reference signal and MIMO
  3. Downlink control signaling
  4. Uplink SC-FDMA, reference signals and control signaling
  5. TDD and half duplex FDD
  6. Transmission procedures
  7. Cell search, SI and random access procedures

LTE multi antenna transmission


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LTE Random Access Procedure and Contention Resolution

LTE random access procedure is used by the UEs to initiate a data transfer. The UEs also obtain uplink timing information from the initial handshake.

This sequence diagram describes the tale of three UEs (UE-A, UE-B and UE-C) that are powered on at the same time:

  1. UEs synchronize with the downlink channel by decoding the PSS and SSS signal. The UEs are synchronized to the downlink frames after completing this procedure.
  2. The three UEs initiate the random access procedure at exactly the same time. Two of them (UE-A and UE-B) happen to pick the same preamble. This results in a resulting in a collision. UE-C picks a distinct preamble so it succeeds in the random access procedure.
  3. Contention between UE-A and UE-B is resolved in UE-A’S favor. UE-A proceeds with the RRC connection.
  4. UE-C times out and retries the random access procedure.

LTE random access procedure


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S1AP View of LTE Attach and EPS Bearer Setup

This sequence diagram looks at LTE Attach and EPS Bearer Setup from the S1AP vantage point. The following signaling is covered:

  1. UE Attach, authentication and security signaling
  2. Setup of two EPS Bearers (RAB id 5 and 6)
  3. Release of UE context due to inactivity
  4. Reestablishment of the UE context with a Service Request.

You can click on individual messages in the sequence diagram to see field level details.

Click to see the "S1AP View of LTE Attach & EPS Bearer Setup"  sequence diagram


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Voice Over LTE (VoLTE) Originating Call

Voice over LTE (VoLTE) is the standard for voice call setup in LTE networks. When VoLTE is deployed, phones will not need to fallback to 3G for voice calls.

VoLTE uses IMS SIP signaling to set up voice calls. The following VoLTE call flow describes the IMS call setup and release. An example of sending an SMS over IMS is also included. Sample RTP and RTCP messages are also shown in the flow.
Voice over LTE Call Flow