5G PS Icon Indicator on Mobile Phones

If you are working in Wireless communications for modem/device or RAN industry

Have you ever wondered when the 5G ICON is displayed on the mobile?

A UE will display 5G PS ICON when it is in the SA Coverage area and when it is in the EN-DC Coverage area.

Since EN-DC is initially being deployed widely, I will give more details about EN-DC and since Stand Alone 5G-NR is similar to LTE in terms of 5G PS icon display.

Ideally, a UE should display a 5G icon when it is connected to the 5G Cell either in EN-DC mode or SA Mode, but Since the coverage of a 5G Cell and LTE cell might be different. So the GSM Association (GSMA) Conducted surveys and discussions among operator members and came up with four configurations that should be supported for deciding when to present a 5G status icon.  

The configurations consist of the following states and are

  1. EPS NR NSA (EN-DC) capable UE attached to EPC and currently in IDLE state under or in RRC_connected state connected to E-UTRAN cell not supporting LTE-NR dual connectivity
  2. EPS NR NSA (EN-DC) capable UE attached to EPC and currently in IDLE state under or in RRC_Connected state connected to AND active on LTE for uplink and downlink on only E-UTRAN cell supporting LTE-NR dual connectivity and has not detected NR coverage (i.e. UE is not under NR coverage and/or not configured to make NR measurements)
  3. EPS NR NSA (EN-DC) capable UE attached to EPC and currently in RRC_Connected state connected to E-UTRAN cell (supporting dual connectivity) and active on LTE for uplink and downlink only and has detected NR coverage (i.e. UE is under NR coverage and has been configured to make NR measurements)
  4. EPS NR NSA (EN-DC) capable UE attached to EPC and currently in IDLE state under E-UTRAN cell supporting LTE-NR dual connectivity and has detected NR coverage (i.e. UE is under NR coverage and has been configured to make NR measurements)
  5. EPS NR NSA (EN-DC) capable UE attached to EPC and currently in RRC_Connected state connected to E-UTRAN cell (supporting dual connectivity) and active on LTE and NR for uplink and/or downlink
  6. 5GS capable UE attached to 5GC and currently in IDLE state under or in RRC_Connected state connected to NG-RAN (eLTE (option 5 or 7) or NR (option 2 or 4) cell)
5g PS ICON Configurations

As there was no consensus on a single preferred configuration, it is desirable to make the display of 5G status icon in the UE configurable such that the display of the 5G status icon can be made depending on operator preference.

As per the 3GPP Specifications, The 5G Status Indicator broadcast by SIB2 and Use of the 5G Status Indicator is dependent upon the UE implementation. A UE is expected to evaluate certain conditions before displaying the 5G status indicator or the 5G PS Icon.

  • LTE SIB-2 Indicates support for NR and the PLMN- Info-r15 contains parameter upperLayerIndication-r15 set to true.
  • During Attach Request If the UE supports dual connectivity with New Radio (NR), then the UE indicate to NW about its 5G Capability by setting the DCNR bit to 1 i.e.  in the UE network capability IE of the ATTACH REQUEST message.
    • If DCNR = 0 Dual connectivity with NR is supported
    • If DCNR =1 Dual connectivity with NR is not supported
  • The MME decides and signals  to the UE and the eNB during attach accept if the subscriber can use the NR cell through RestrictDCNR parameter.
    • If the UE receives RestrictDCNR = 0 or RestrictDCNR is not present , then the UE can display the 5G icon.
    • If the MME sets RestrictDCNR =1  then dual connectivity with NR is restricted and the UE cannot display 5G icon and displays LTE icon.

If the RestrictDCNR bit is set to “Use of dual connectivity with NR is restricted” in the EPS network feature support IE of the ATTACH ACCEPT message, the UE shall provide the indication that dual connectivity with NR is restricted to the upper layers.

If the UE indicates support for dual connectivity with NR in the TRACKING AREA UPDATE REQUEST message, and the MME decides to restrict the use of dual connectivity with NR for the UE, then the MME shall set the RestrictDCNR bit to “Use of dual connectivity with NR is restricted” in the EPS network feature support IE of the TRACKING AREA UPDATE ACCEPT message.

If the RestrictDCNR bit is set to “Use of dual connectivity with NR is restricted” in the EPS network feature support IE of the TRACKING AREA UPDATE ACCEPT message, the UE shall provide the indication that dual connectivity with NR is restricted to the upper layers.

A will not display 5G ICON if it’s a 5G Capable phone but it is not subscribed to 5G services from the network service provider. An operator might provide 5G services to premium plans initially.

Now It’s again up to on Operators implementation which defines rules custom rules when which PS ICON should be displayed in certain conditions and how long it should be displayed. Let me explain by giving an example.

Suppose we have an Operator named “BREW” and we have 5G EN-DC Coverage for both NSA-FR1 and NSA-FR2(mmw) and the operator wants to display different 5G PS Icons when in FR1 and FR2.

  • When in camped on LTE- network with underlying 5G Coverage either FR1 or FR2 display “5G” PS ICON.
  • When in UE is in EN-DC FR1 connected mode , then display “5G” PS ICON.
  • When UE is in EN-DC FR2 connected mode , then display “5G++” PS ICON.

These are certain examples where an operator might define certain rules but it defers from operator to operator.

References :

  • R2-1713952 LS Reply to SA WG2 on Status Icon related to 5G
  • S2-178933 LS Reply to SA WG2 on Status Icon related to 5G
  • 3GPP TS 24.301 UMTS/LTE/5G Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS)