1. 1 1 Title:Proposal for Addition of Fixed Rate 2 kbps Mode to EVRC-B Abstract:This contribution provides a proposal for adding a fixed rate 2 kbps vocoder to EVRC-B family of vocoders. The new low rate vocoder is intended to be used in xHRPD application. Source: Rhys W. Robinson (Rhys.Robinson@terrestar.com).Rhys.Robinson@terrestar.com TerreStar Networks Sourabh Gupta (Sourabh.gupta@ico.com)Sourabh.gupta@ico.com DBSD North America (ICO) Eric Jacks (Eric.Jacks@skyterra.com)Eric.Jacks@skyterra.com Skyterra Communications Alok Gupta (alokg@qualcomm.com)alokg@qualcomm.com Qualcomm Incorporated Date:March 01, 2010 Recommendation:Review and adopt Notice Skyterra Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated grant a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner’s name any Organizational Partner’s standards publication even though it may include all or portions of this contribution; and at the Organizational Partner’s sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner’s standards publication. Skyterra Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution. This document has been prepared by Skyterra Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on Skyterra Communications, DBSD North America (ICO), or QUALCOMM Incorporated. Skyterra Communications, DBSD North America (ICO), TerreStar Networks, and QUALCOMM Incorporated specifically reserve the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of Skyterra Communications, DBSD North America (ICO), TerreStar Networks, or QUALCOMM Incorporated other than provided in the copyright statement above.

2. Proposal for Adding Fixed Rate 2 kbps Vocoder to EVRC-B

3. 3 Outline EVRC-B Frame Type Classifications 2 kbps Vocoder Choices 2 kbps Vocoder Approach Encoder-Decoder Block Diagram Conclusions

4. 4 EVRC-B Frame Type Classifications In EVRC-B Vocoder, a 20 ms speech frame is classified into following frame types:  Silence Eighth-rate (16 bits) vocoder to transmit the background noise  Unvoiced Quarter rate NELP(Noise Excited Linear Prediction) (40 bits)  Voiced Quarter (40 bits) and Full rate (171 bits) PPP (Prototype Pitch Period) or half rate CELP (Codebook Excited Linear Prediction)  Up-transient Transition between voiced and unvoiced segments Full/half rate (171 bits) CELP  Transient Usually in the middle or towards the end of the voiced segment, where pitch is changing Full/half rate (171 bits) CELP  Down-transient Transition from voiced to unvoiced segment Half rate (80 bits) CELP

5. 5 2 kbps Vocoder Choices Not many choices! Quarter rate NELP for unvoiced and may be for down transient frames Only quarter rate PPP available for up-transient, voiced and transient frames Can work with some changes, like non-differential encoding of pitch and prototype waveform parameters

6. 6 2 kbps Vocoder Choices (cont.) QPPP is ideally suited for purely voiced frame  Zero bits on the phase of the prototype waveform QPPP can cope with gradual change of pitch over a voiced segment  Cannot handle large pitch change Use of QPPP for coding all the transient frames result in poor quality

7. 7 2 kbps Vocoder Approach Need a new coding scheme to encode the transient frames at 2 kbps The other areas that need to be worked or improved in order to have a good quality 2 kbps vocoder  Pitch estimation: Re-visit range and accuracy  Revisit QPPP to make it more robust in the absence of FPPP  Fine tuning of mode decision algorithm

8. 8 Top Level Changes FCELP, HCELP or FPPP not used New scheme for coding transient frames at 2 kbps Enhanced pitch estimation QPPP for voiced frame with modifications like non- differential quantization Mode-decision tuning

9. 9 Decoder Block Diagram

10. 10 Encoder Block Diagram Green: unchanged blocks Blue: modified blocks Yellow: new block

11. 11 Conclusions There is a need for a new scheme to encode transient frame at quarter rate There is a need to improve the range and accuracy of pitch estimation There is need to make some of the quantization in QPPP non-differential There is a need to enhance the mode decision