Single Radio Voice Call Continuity – SRVCC
The SRVCC is an LTE functionality that allows a VoIP/IMS call in the LTE packet domain to be moved to a legacy voice domain (GSM/UMTS or CDMA 1x).
As in the definition, SRVCC is a method for ensuring fast and reliable handover of an LTE user to a legacy network coverage area, while it is in an active IMS based voice session. One challenge with SRVCC is to handover while the UE is connected to only a single radio at a given time.
The UE, LTE Network, and Target Legacy Networks should all support SRVCC. In addition, a special interface known as Sv is formed between MME and MSC Server. The Sv interface is an interface between the Mobility Management Entity (MME), or Serving GPRS Support Node (SGSN), and 3GPP MSC server enhanced for SRVCC.
The Sv interface is used to support Inter-RAT handover from VoIP/IMS over EPS to CS domain over 3GPP UTRAN/GERAN access.
To support SRVCC the IMS network should also include Application Server called SCC-AS.
The SCC (Service Centralization and Continuity) AS is responsible for handling the signalling required for the process.
Select The Appropriate Test Configuration for Field Testing
Anechoic Chamber Tests
The SRVCC can be tested, as example, into a controlled environment as a TEST LAB. In this test configuration, the UE will be positioned into an Anechoic Chamber and will be irradiated by controlled signals in 2G/3G/4G. These signals, 2G/3G and 4G, can be controlled by a specific RF Matrix in order to simulate many tests.
As example, for an LTE UE there is a list of RF Conformance Tests that could be done:
- Ue Maximum Output Power
- Maximum Power Reduction (Mpr)
- Power Control
- Minimum Output Power
- Transmit Off Power
- Frequency Error
- Min. Transmit Error Vector Magnitude (Evm)
- Occupied Bandwidth
- Spectrum Emission Mask
- Aclr (Adjacent Channel Leakage Power Ratio)
- Transmitter Spurious Emissions
- Transmit Intermodulation
- Reference Sensitivity Level
- Maximum Input Level
- Adjacent Channel Selectivity
- In-Band Blocking
- Out-Of-Band Blocking
- Narrow Band Blocking
- Spurious Response
- Wide Band Intermodulation
- Narrow Band Intermodulation
- Spurious Emissions
- PDSCH Single Antenna Port Performance
- PDSCH Transmit Diversity Performance
- PDSCH Open Loop Spatial Multiplexing Performance
- PDSCH Closed Loop Spatial Multiplexing Performance
- Control Channel Performance D-BCH PCH
- Demodulation Of PDSCH (User-Specific Reference Symbols)
- PCFICH/PDCCH Single Antenna Port Performance
- PCFICH/PDCCH Transmit Diversity Performance
- Demodulation Of PHICH
- Demoduation Of PBCH
Of course, this type of test is oriented to check the UE functionalities and not to the network behaviour.Live Environment Tests
To test the SRVCC on Live Network we considered two different options:
- Perform the test in a Drive Test Mode and drive to a Non-LTE area during an active VoLTE call
- Build a Custom Solution System to test it
Most of the time, the first choice could become complicated,expensive and frustrated. In fact, as example, if the MNO set the SRVCC to 2G and in the test city there are no boundary areas between 4G and 2G, the tester will have to move far away to find it. Furthermore, from the moment that Network planning is not based on your on field tests, could happen that a good selected area could change the RF condition without notice…
At laroccasolutions, in partnership with FOCUS-INFOCOM, we found a couple of set up to use for sch tests.
Basically we have 2 different possibilities:
- Picture 1: modify the UE and connect the antenna to an external splitter and, subsequently, to different attenuators based on frequencies
- Picture 2: non modify the UE and put it into a controlled environment (Portable RF Shield-Box) with an internal antenna connected to different attenuators based on frequencies
Our best choice is this second one because any customer will be able to Test any type of UE without any modification. This will help also to feel the Customer Experience in different Real Scenarios.