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TCCE

TCCE WG 5 ToR

TETRA WG5 Terms of Reference

1 Introduction

This document contains the Terms of Reference for the work on the Speech Coding of TETRA Release 2. The information is based on the TC TETRA approved work programme for TETRA 2 EPT13(00)17r1 which builds upon the ETSI Board input paper for TETRA 2 ETSI/B28(00)12.

2 WG5 Organisation

The WG5 Speech coding consists of chair Michael Street.

3 Primary objective

Selection and standardisation of additional speech codec(s) for TETRA, to enable intercommunication between TETRA and other 3G networks without transcoding, and to provide enhanced voice quality for TETRA by using the latest low bit rate voice codec technology.

4 Timings

The timescale for this work is to complete the codec(s) study around the end of 2000 followed by codec(s) selection in early 2001. The complete standardisation will be done by the end of Q3 2001. However due to the availability of commercial codec(s) the work may be extended in 2002.

Voice Coding

Voluntary work

Project work including use of STF support (and STF mm required)

5 Planned deliverables

One or more TS deliverable expected. Areas involved expected to include:
-    speech coding;
-    codec characterisation
-    FEC, CRC, interleaving;
-    protocol amendment;
-    inter-system interface.
-    channel adaptation (if required)
-    gateway function
-    DMO services
-    DTX, SID, SCR

Additional amendments will be required by other WGs for some of the above deliverables.

Milestones Define selection critera 15 Dec 2000

Selection of codec(s) 15 Feb 2001

STF Work Program Defined 15 Feb 2001

Draft Standards Produced 31 Aug 2001

ETSI EPT Approval of Technical Specification 19 Oct 2001

6 Manpower

Work will proceed on voluntary bases pending the appointment of an STF. Both voluntary and STF contributions will be necessary for the completion of the work.

7 Background

The TETRA standard currently defines a standard codec which employs Arithmetic Codebook Excited Linear Prediction (ACELP) technology. This codec was selected in 1994 as a result of a competition between codecs submitted by several manufacturers. This codec provides robust operation in typical TETRA operational scenarios for public safety and shared system use.

However, it is clear that codec technology is advancing rapidly and it is appropriate for standards to accommodate such advances. This trend is evident in the GSM standard where the original RPE-LTP full rate codec running at a bit rate of 13 kbps has been supplemented by enhanced codecs:
- the half rate VSELP codec (5.6 kbps),
- the enhanced full rate ACELP codec (12.2 kbps) and an advanced multi-rate ACELP codec (4.75 to 12.2 kbps).

In addition, 3GPP™ is currently standardising a wideband codec operating at bit rates of approximately 12 kbps and above. Such evolving codec technology is also being incorporated into other wireless communications standards around the world.

8 Selection Criteria Guide

Given that TETRA is being deployed in many markets around the world, it is appropriate that work begins to select an enhanced codec for incorporation into the next phase of TETRA standardisation. Within the context of the primary objective several criteria should be considered in the selection of a codec(s):

·    Enhanced Quality – speech quality is an important factor in the usability of a communications technology and a prime factor in choosing a codec should be to maximise the quality and intelligibility in typical user environments across a defined coverage area which can be either a noise limited or an interference limited system;
·    Backward Compatibility – the selected codec(s) needs to co-exist with the existing TETRA codec to ensure that it can be easily deployed into systems with an existing infrastructure subscriber and base (note that this requirement does not imply that an existing codec should be able to receive speech transmitted by the new codec or vice-versa);
·    Re-use of Existing Codec Technology – TETRA does not necessarily need to invent a new codec, but should first seek to re-use one of the many existing codecs already developed while taking account of the unique operational environments of TETRA user communities;
·    Inter-working with Other Systems – the rapid take-up of wireless communications equipment increases the likelihood of communications between users of different systems; hence a next-generation TETRA codec should provide superior inter-working performance with other standards such as GSM and UMTS™.

The tasks for this work item would include a study of existing codec technology and an assessment of candidates for TETRA according to the above selection criteria. This study would be followed by an evaluation by the working group.

9 Working Relationships

Continuous co-operation will be maintained with the TC TETRA Management Committee and Working Groups.

10 Dependencies

The work will require a great deal of co-operation with WG2/3 and WG8. Co-operation with 3GPP™ and other bodies (possibly outside ETSI) may be required. The exact nature of the co-operation cannot be identified before of the technological solution.