Mobile telephony devices and voice services continue to develop and evolve and their associated minimum performance requirements and test methodologies also need to stay relevant and representative of quality demands. While many advances were made in Release 11 to the acoustic requirements and test specifications in TS 26.131 and TS 26.132 many items therein were left marked "for further study" and require a final decision by SA4. Additionally, there are new acoustic requirements and emerging tests worth considering in a future release, but that require further study before incorporation into specifications. This technical report will, first and foremost, address the remaining items presently designated as "for further study" in TS 26.131 and TS 26.132. The present document will also examine opportunities for new acoustic tests and requirements that help us to better characterize the UE acoustic experience, opportunities to replace existing test methods with others that are more accurate or more efficient and make specific recommendations for their inclusion in existing or new specifications.

The scope of the present document is to investigate, first and foremost, the existing items presently designated as "for further study" in TS 26.131 and TS 26.132. The investigation will additionally identify, examine and evaluate opportunities for new acoustic tests and requirements that better help characterize the UE acoustic experience, opportunities to replace existing test methods with others that are more accurate or more efficient and to make specific recommendations for their inclusion in existing or new specifications. While many advances were made in Release 11 to the acoustic requirements and test specifications in TS 26.131 and TS 26.132 many items therein were left marked "for further study" and require a final disposition by SA4 including:

• NB & WB Stability loss, Headset UE (TS 26.131, subclause 5.6 & TS 26.131, subclause 6.6).
• NB & WB Delay, Wireless Headset (TS 26.131, subclause 5.12.2.2 & TS 26.131, subclause 6.11.2.2).
• NB & WB Echo control ("double-talk") characteristics (TS 26.131, subclause 5.13 & TS 26.131, subclause 6.12, TS 26.132, subclause 8.11).
• Handset, Headset, Handheld hands-free, Desktop and vehicle mounted hands-free are all marked FFS.
• NB & WB Free-field measurements for vehicle-mounted hands-free (TS 26.132, subclause 7.2.3 & TS 26.132, subclause 8.2.3).
• NB & WB Idle Channel Noise, Sending/Receiving of test signal (TS 26.132, subclause 7.3.1, TS 26.132, subclause 7.3.2, TS 26.132, subclause 8.3.1 & TS 26.132, subclause 8.3.2).

Additionally, there are new acoustic requirements and emerging tests that may be considered in a future release, but require further study before incorporation to our specifications. It has been anticipated that topics in this area would include, but would not be limited to, an evaluation of:

• Time-variant user behaviour.
• Additional UE usage environments.
• New or refined test methods for existing requirements.
• Acceptance of updates (if any) to existing ETSI and ITU-T dependencies.