26.1313GPPRelease 18RequirementsTerminal acoustic characteristics for telephonyTS
The interfaces required to define terminal electro-acoustic characteristics are shown in TS 26.132. These are the air interface and the point of interconnect (POI). The interfaces are shown for one-channel (mono) operation, interfaces for two-channel (stereo) operation are for further study.
Measurements can be made using the system simulator (SS) described in TS 26.132. MTSI speech aspects are specified by TS 26.114 .
4.2 Air interfaces
The Air Interfaces for GSM, 3G, LTE and NR are specified by GSM 05, 3GPP 45, 3GPP 25, 3GPP 36 and 3GPP 38 series specifications, and the Air Interface for WLAN access to EPC is specified by WLAN access to EPC as defined in TS 23.402  and TS 24.302 .
The POI with the public switched telephone network (PSTN) is considered to have a relative level of 0 dBr.
4.3 Acoustical interfaces
The following classes of acoustical interface are considered in this specification:
– Handset UE including softphone UE used as a handset;
– Headset UE including softphone UE used with headset;
– Desktop-mounted hands-free UE including softphone UE with external loudspeaker(s) used in hands-free mode;
– Hand-held hands-free UE including softphone UE with internal loudspeaker(s) used in hands-free mode.
(See definition of softphone in Clause 3.1)
Vehicle Mounted Hands-free UE is out of scope. In case performance evaluations are planned for Vehicle Mounted Hands-free UE, test setup, methods and requirements specified in Recommendation ITU-T P.1100  (for NB), P.1110  (for WB) or P.1120  (for SWB and FB) can be used.
The requirements and performance objectives for a softphone UE shall be derived according to the following rules:
– When using a softphone UE as a handset: requirements and performance objectives shall correspond to handset mode.
– When using a softphone UE with headset: requirements and performance objectives shall correspond to headset mode.
– When using a softphone UE in hands-free mode:
– When using internal loudspeaker(s), requirements and performance objectives shall correspond to hand-held hands-free.
– When using external loudspeaker(s), requirements and performance objectives shall correspond to desktop-mounted hands-free.
4.4 Electrical interfaces
An electrical interface is considered in this specification and details on standardized analogue (wired) and digital (wired and wireless) headset interfaces can be found in TS 26.132. For the electrical interface, the POI in sending / receiving direction is respectively defined as the input / output of the reference speech coder of the system simulator.
Any of the UE types mentioned in clause 4.3 providing an electrical interface can be considered as Electrical Interface UE.