SIST ETS 300 395-2 E1:2003

Terrestrial Trunked Radio (TETRA); Speech codec for full-rate traffic channel; Part 2: TETRA codec

Selection and specification of the speech codec for TETRA voice plus data standard

Radijska oprema in sistemi (RES) – Vseevropski snopovni radio – Govorni kodek za prometni kanal s polno hitrostjo – 2. del: Kodek TETRA

General Information

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.10 - Terrestrial Trunked Radio (TETRA)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Mandate: T-300/2
• Ref Project: ETSI ETS 300 395-2 ed.1 (1996-12) - Terrestrial Trunked Radio (TETRA); Speech codec for full-rate traffic channel; Part 2: TETRA codec

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ETS 300 395-2 E1:2003
01-december-2003
Radijska oprema in sistemi (RES) – Vseevropski snopovni radio – Govorni kodek
za prometni kanal s polno hitrostjo – 2. del: Kodek TETRA
Terrestrial Trunked Radio (TETRA); Speech codec for full-rate traffic channel; Part 2:
TETRA codec
Ta slovenski standard je istoveten z: ETS 300 395-2 Edition 1
ICS:
33.070.10 Prizemni snopovni radio Terrestrial Trunked Radio
(TETRA) (TETRA)
SIST ETS 300 395-2 E1:2003 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ETS 300 395-2 E1:2003

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SIST ETS 300 395-2 E1:2003
EUROPEAN ETS 300 395-2
TELECOMMUNICATION December 1996
STANDARD
Source: ETSI TC-RES Reference: DE/RES-06002-2
ICS: 33.060, 30.060.50
Key words: TETRA, codec
Radio Equipment and Systems (RES);
Trans-European Trunked Radio (TETRA);
Speech codec for full-rate traffic channel;
Part 2: TETRA codec
ETSI
European Telecommunications Standards Institute
ETSI Secretariat
Postal address: F-06921 Sophia Antipolis CEDEX - FRANCE
Office address: 650 Route des Lucioles - Sophia Antipolis - Valbonne - FRANCE
X.400: c=fr, a=atlas, p=etsi, s=secretariat - Internet: [e-mail]
Tel.: [phone] - Fax: [phone]
Copyright Notification: No part may be reproduced except as authorized by written permission. The copyright and the
foregoing restriction extend to reproduction in all media.
© European Telecommunications Standards Institute 1996. All rights reserved.

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ETS 300 395-2: December 1996
Whilst every care has been taken in the preparation and publication of this document, errors in content,
typographical or otherwise, may occur. If you have comments concerning its accuracy, please write to
"ETSI Editing and Committee Support Dept." at the address shown on the title page.

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Contents
Foreword .7
1 Scope .9
2 Normative references.9
3 Abbreviations.9
4 Full rate codec.9
4.1 Structure of the codec.9
4.2 Functional description of the codec .12
4.2.1 Pre-and post-processing .12
4.2.2 Encoder .12
4.2.2.1 Short-term prediction .13
4.2.2.2 LP to LSP and LSP to LP conversion.14
4.2.2.3 Quantization and interpolation of LP parameters .16
4.2.2.4 Long-term prediction analysis.17
4.2.2.5 Algebraic codebook: structure and search .18
4.2.2.6 Quantization of the gains.21
4.2.2.7 Detailed bit allocation.23
4.2.3 Decoder.23
4.2.3.1 Decoding process.24
4.2.3.1.1 Decoding of LP filter parameters .24
4.2.3.1.2 Decoding of the adaptive codebook
vector .24
4.2.3.1.3 Decoding of the innovation vector.25
4.2.3.1.4 Decoding of the adaptive and
innovative codebook gains.25
4.2.3.1.5 Computation of the reconstructed
speech .25
4.2.3.2 Error concealment .25
5 Channel coding for speech.26
5.1 General .26
5.2 Interfaces in the error control structure.26
5.3 Notations.28
5.4 Definition of sensitivity classes and error control codes .28
5.4.1 Sensitivity classes .28
5.4.2 CRC codes.28
5.4.3 16-state RCPC codes.30
5.4.3.1 Encoding by the 16-state mother code of rate 1/3.30
5.4.3.2 Puncturing of the mother code .30
5.5 Error control scheme for normal speech traffic channel.31
5.5.1 CRC code.31
5.5.2 RCPC codes.31
5.5.2.1 Puncturing scheme of the RCPC code of rate 8/12 (equal
to 2/3).31
5.5.2.2 Puncturing scheme of the RCPC code of rate 8/18 .31
5.5.3 Matrix Interleaving .32
5.6 Error control scheme for speech traffic channel with frame stealing activated .34
5.6.1 CRC code.34
5.6.2 RCPC codes.35
5.6.2.1 Puncturing scheme of the RCPC code of rate 8/17 .36
5.6.3 Interleaving.36
6 Channel decoding for speech.36
6.1 General .36

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ETS 300 395-2: December 1996
6.2 Error control structure . 36
7 Codec performance. 37
8 Bit exact description of the TETRA codec. 37
Annex A (informative): Implementation of speech channel decoding . 39
A.1 Algorithmic description of speech channel decoding. 39
A.1.1 Definition of error control codes . 39
A.1.1.1 16-state RCPC codes. 39
A.1.1.1.1 Obtaining the mother code from punctured code . 39
A.1.1.1.2 Viterbi decoding of the 16-state mother code of the rate
1/3 . 39
A.1.1.2 CRC codes . 40
A.1.1.3 Type-4 bits . 40
A.1.2 Error control scheme for normal speech traffic channel . 40
A.1.2.1 Matrix Interleaving . 40
A.1.2.2 RCPC codes. 40
A.1.2.2.1 Puncturing scheme of the RCPC code of rate 8/12 (equal
to 2/3). 41
A.1.2.2.2 Puncturing scheme of the RCPC code of rate 8/18. 41
A.1.2.3 CRC code . 41
A.1.2.4 Speech parameters . 41
A.1.3 Error control scheme for speech traffic channel with frame stealing activated. 41
A.1.3.1 Interleaving . 41
A.1.3.2 RCPC codes. 41
A.1.3.2.1 Puncturing scheme of the RCPC code of rate 8/17. 42
A.1.3.3 CRC code . 42
A.1.3.4 Speech parameters . 42
A.2 C Code for speech channel decoding . 42
Annex B (informative): Indexes . 43
B.1 Index of C code routines. 43
B.2 Index of files. 46
Annex C (informative): Bibliography . 47
Annex D (informative): Codec performance . 48
D.1 General. 48
D.2 Quality. 48
D.2.1 Subjective speech quality. 48
D.2.1.1 Description of characterization tests. 48
D.2.1.2 Absolute speech quality. 48
D.2.1.3 Effect of input level . 48
D.2.1.4 Effect of input frequency characteristic. 48
D.2.1.5 Effect of transmission errors. 48
D.2.1.6 Effect of tandeming. 49
D.2.1.7 Effect of acoustic background noise. 49
D.2.1.8 Effect of vocal effort. 49
D.2.1.9 Effect of frame stealing. 49
D.2.1.10 Speaker and language dependency . 49
D.2.2 Comparison with analogue FM. 49
D.2.2.1 Analogue and digital systems results . 49
D.2.2.2 All conditions. 50
D.2.2.3 Input level. 50
D.2.2.4 Error patterns. 51
D.2.2.5 Background noise. 51

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ETS 300 395-2: December 1996
D.2.3 Additional tests.51
D.2.3.1 Types of signals .51
D.2.3.2 Codec behaviour .51
D.3 Performance of the channel coding/decoding for speech.52
D.3.1 Classes of simulation environment conditions.52
D.3.2 Classes of equipment .52
D.3.3 Classes of bits .53
D.3.4 Channel conditions .53
D.3.5 Results for normal case.53
D.4 Complexity.54
D.4.1 Complexity analysis .54
D.4.1.1 Measurement methodology.54
D.4.1.2 TETRA basic operators.54
D.4.1.3 Worst case path for speech encoder .56
D.4.1.4 Worst case path for speech decoder .57
D.4.1.5 Condensed complexity values for encoder and decoder .58
D.4.2 DSP independence.59
D.4.2.1 Program control structure.59
D.4.2.2 Basic operator implementation.59
D.4.2.3 Additional operator implementation.59
D.5 Delay .59
Annex E (informative): Results of the TETRA codec characterization listening and complexity tests.60
E.1 Characterization listening test .60
E.1.1 Experimental conditions.60
E.1.2 Tables of results .61
E.2 TETRA codec complexity study .70
E.2.1 Computational analysis results .70
E.2.1.1 TETRA speech encoder.70
E.2.1.2 TETRA speech decoder.78
E.2.1.3 TETRA channel encoder and decoder.81
E.2.2 Memory requirements analysis results .83
E.2.2.1 TETRA speech encoder.83
E.2.2.2 TETRA speech decoder.84
E.2.2.3 TETRA speech channel encoder .84
E.2.2.4 TETRA speech channel decoder .85
Annex F (informative): Description of attached computer files .86
F.1 Directory C-WORD.86
F.2 Directory C-CODE.86
History.87

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ETS 300 395-2: December 1996
Foreword
This European Telecommunication Standard (ETS) has been produced by the Radio Equipment and
Systems (RES) Technical Committee of the European Telecommunications Standards Institute (ETSI).
This ETS consists of four parts as follows:
Part 1: "General description of speech functions".
Part 2: "TETRA codec".
Part 3: "Specific operating features".
Part 4: "Codec conformance testing".
Clause 4 provides a complete description of the full rate speech source encoder and decoder, whilst
clause 5 describes the speech channel encoder, and clause 6 the speech channel decoder.
Clause 7 describes the codec performance.
Finally, clause 8 introduces the bit exact description of the codec. This description is given as an
ANSI C code, fixed point, bit exact. The whole C code corresponding to the TETRA codec is given in
computer files attached to this ETS, and are an integral part of this ETS.
In addition to these clauses, five informative annexes are provided.
Annex A describes a possible implementation of the speech channel decoding function.
Annex B provides comprehensive indexes of all the routines and files included in the C code associated
with this ETS.
Annex C lists informative references relevant to the speech codec.
Annex D describes the actual quality, performance and complexity aspects of the codec.
Annex E reports detailed results from codec characterization listening and complexity tests.
Annex F contains instructions for the use of the attached electronic files.
Transposition dates
Date of adoption 22 November 1996
Date of latest announcement of this ETS (doa): 31 March 1997
Date of latest publication of new National Standard
or endorsement of this ETS (dop/e): 30 September 1997
Date of withdrawal of any conflicting National Standard (dow): 30 September 1997

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ETS 300 395-2: December 1996
1 Scope
This European Telecommunication Standard (ETS) contains the full specification of the speech codec for
use in the Trans-European Trunked Radio (TETRA) system.
2 Normative references
This ETS incorporates by dated and undated reference, provisions from other publications.
These normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this ETS only when incorporated in it by amendment or revision. For undated references the latest
edition of the publication referred to applies.
[1] ETS 300 392-2: "Radio Equipment and Systems (RES); Trans-European
Trunked Radio (TETRA) system; Voice plus Data; Part 2: Air Interface".
[2] CCITT Recommendation P.48 (1988): "Specifications for an Intermediate
Reference System".
3 Abbreviations
For the purposes of this ETS, the following abbreviations apply:
ACELP Algebraic CELP
ANSI American National Standards Institute
BER Bit Error Ratio
BFI Bad Frame Indicator
BS Base Station
CELP Code-Excited Linear Predictive
CRC Cyclic Redundancy Code
DSP Digital Signal Processor
DTMF Dual Tone Multiple Frequency
EP Error Pattern
FIR Finite Impulse Response
IRS Intermediate Reference System
LP Linear Prediction
LPC Linear Predictive Coding
LSF Line Spectral Frequency
LSP Line Spectral Pair
MER Message Error Rate
MNRU Multiplicative Noise Reference Unit
MOS Mean Opinion Score
MS Mobile Station
MSE Mean Square Error
PDF Probability Density Function
PUEM Probability of Undetected Erroneous Message
RCPC Rate-Compatible Punctured Convolutional
RF Radio Frequency
VQ Vector Quantization
4 Full rate codec
4.1 Structure of the codec
The TETRA speech codec is based on the Code-Excited Linear Predictive (CELP) coding model. In this
model, a block of N speech samples is synthesized by filtering an appropriate innovation sequence from a
codebook, scaled by a gain factor g , through two time varying filters. A simplified high level block
c
diagram of this synthesis process, as implemented in the TETRA codec, is shown in figure 1.

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ETS 300 395-2: December 1996
Digital
Input
Algebraic codebook index
D
E
Pitch delay
M
U
L
T
GAIN PREDICTION
Gains I
P
AND VQ
L
E
Past
X
Excitation
g
T
p
ADAPTIVE
LPC Info
CODEBOOK
SHORT-TERM
LONG-TERM SYNTHESIS FILTER Output
SYNTHESIS FILTER
Speech
g
k
c
ALGEBRAIC
CODEBOOK
Figure 1: High level block diagram of the TETRA speech synthesizer
The first filter is a long-term prediction filter (pitch filter) aiming at modelling the pseudo-periodicity in the
speech signal and the second is a short-term prediction filter modelling the speech spectral envelope.
The long-term or pitch, synthesis filter is given by:
11
= (1)
−
T
Bz
()
1−gz
p
where T is the pitch delay and g is the pitch gain. The pitch synthesis filter is implemented as an adaptive
p
codebook, where for delays less than the sub-frame length the past excitation is repeated.
The short-term synthesis filter is given by:
11
Hz==
() (2)
p
Az
()
−i
1+∑az
i
i=1
where ai,,=1.,p, are the Linear Prediction (LP) parameters and p is the predictor order. In the
i
TETRA codec p shall be 10.
The TETRA encoder uses an analysis-by-synthesis technique to determine the pitch and excitation
codebook parameters. The simplified block diagram of the TETRA encoder is shown in figure 2.

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ETS 300 395-2: December 1996
Input
Speech
LPC ANALYSIS
Unquantized
QUANTIZATION
LPC info
& INTERPOLATION
T
0
OPEN LOOP PERCEPTUAL
PITCH ANALYSIS WEIGHTING
Past
Excitation
g
T p
ADAPTIVE LPC Info
CODEBOOK
SHORT-TERM
SYNTHESIS FILTER
g
k c
ALGEBRAIC
CODEBOOK
PERCEPTUAL
MSE SEARCH
WEIGHTING
Gains M
GAIN VQ
U
L
Pitch delay (T)
T
I
Codebook index (k)
P
L
LPC info Digital
E
Output
X
Figure 2: High level block diagram of the TETRA speech encoder
In this analysis-by-synthesis technique, the synthetic speech is computed for all candidate innovation
sequences retaining the particular sequence that produces the output closer to the original signal
according to a perceptually weighted distortion measure. The perceptual weighting filter de-emphasizes
the error at the formant regions of the speech spectrum and is given by:
Az
()
Wz = (3)
()
Az γ
()
where A(z) is the LP inverse filter (as in Equation (2)) and 01<≤γ . The value γ =08, 5 shall be used.
1
Both the weighting filter, Wz , and formant synthesis filter, Hz , shall use the quantized LP
() ()
parameters.
In the Algebraic CELP (ACELP) technique, special innovation codebooks having an algebraic structure
are used. This algebraic structure has several advantages in terms of storage, search complexity, and
robustness. The TETRA codec shall use a specific dynamic algebraic excitation codebook whereby the
fixed excitation vectors are shaped by a dynamic shaping matrix (see annex C {1}). The shaping matrix is
a function of the LP model Az , and its main role is to shape the excitation vectors in the frequency
()
domain so that their energies are concentrated in the important frequency bands. The shaping matrix
used is a Toeplitz lower triangular matrix constructed from the impulse response of the filter:
Az/γ
()
1
Fz = (4)
()
Az/γ
()
2
where Az is the LP inverse filter. The values γ =07, 5 and γ =08, 5 shall be used.
()
1 2

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ETS 300 395-2: December 1996
In the TETRA codec, 30 ms speech frames shall be used. It is required that the short-term prediction
parameters (or LP parameters) are computed and transmitted every speech frame. The speech frame
shall be divided into 4 sub-frames of 7,5 ms (60 samples). The pitch and algebraic codebook parameters
have also to be transmitted every sub-frame.
Table 1 gives the bit allocation for the TETRA codec. 137 bits shall be produced for each frame of 30 ms
resulting in a bit rate of 4 567 bit/s.
Table 1: Bit allocation for the TETRA codec
Parameter 1st subframe 2nd subframe 3rd subframe 4th subframe Total per frame
LP filter 26
Pitch delay 8 5 5 5 23
Algebraic code 16 16 16 16 64
VQ of 2 gains 6 6 6 6 24
Total 137
More details about the sequence of bits within the speech frame of 137 bits per 30 ms, with reference to
the speech parameters, can be found in subclause 4.2.2.7, table 3.
4.2 Functional description of the codec
4.2.1 Pre-and post-processing
Before starting the encoding process, the speech signal shall be pre-processed using the offset
compensation filter:
−1
 
1 1−z
 
Hz= (5)
()
p
 
−1
2
1−αz
 
where α = 32 735/32 768. In the time domain, this filter corresponds to:
''
s()n=−sn()//21sn(− )2+αs(n−1) (6)
'
where sn() is the input signal and sn() is the pre-processed signal. The purpose of this pre-processing
is firstly to remove the dc from the signal (offset compensation), and secondly, to scale down the input
signal in order to avoid saturation of the synthesis filtering.
At the decoder, the post-processing consists of scaling up the reconstructed signal (multiplication by 2
with saturation control).
4.2.2 Encoder
Figure 3 presents a detailed block diagram of the TETRA encoder illustrating the major parts of the codec
as well as signal flow. On this figure, names appearing at the bottom of the various building blocks
correspond to the C code routines associated with this ETS.

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Input
OFFSET
Speech INTERPOLATION
COMPENSATION LSP
Pre-processing FOR THE 4
AND DIVISION QUANTIZATION
s(n) ^
SUBFRAMES
A(z)
BY 2
Int_Lpc4 Lsp_Az Clsp_334
Pre_Process
s'(n)
f
WINDOWING
r LEVINSON
AND
a LPC analysis DURBIN A(z)       LSP
AUTOCORRELATION
m R [ ]       A(z)
R [ ]
Lag_Window Az_Lsp
e Autocorr Levin_32
COMPUTE
INTERPOLATE
Open-loop WEIGHTED FIND
4 SUBFRAMES
pitch search SPEECH OPEN-LOOP PITCH
LSP       A(z)
(4 SUBFRAMES)
Int_Lpc4 Lsp_Az Pitch_Ol_Dec
Pond_Ai Residu Syn_Filt
T
0
^
A(z)
LSP index
COMPUTE
COMPUTE TARGET
Adaptive x(n)
FIND BEST DELAY ADAPTIVE
codebook FOR ADAPTIVE
AND GAIN CODEBOOK
search
CODEBOOK
CONTRIBUTION
Pitch_Fr
Syn_Filt Pred_Lt G_Pitch
pitch index
x(n)
s
u
b
COMPUTE TARGET FIND BEST
Innovative xn2(n)
f code index
codebook FOR INNOVATION
r
search INNOVATION AND GAIN
a
D4i60_16 G_Code
m
e
gains index
GAINS
UPDATE FILTER
Compute
COMPUTE QUANTIZATION
MEMORIES FOR
error EXCITATION IN ENERGY
NEXT SUBFRAME
DOMAIN
Syn_Filt
Ener_Qua
Figure 3: Signal flow at the encoder
4.2.2.1 Short-term prediction
Short-term prediction (LP or LPC analysis) shall be performed every 30 ms. The auto-correlation
approach shall be used with an asymmetric analysis window. The LP analysis window consists of two
halves of Hamming windows with different lengths. This window is given by:
 
πn
wn =−05,,4 0 46cos , nL=−01,.,
()  
1
L−1
 
1
(7)
 πnL− 
()
1
=+05, 4 0,46cos , nL=+,.,L L−1
 
11 2
L−1
 
...