ETSI Multi-Channel GSM Speech Coders

MOTOROLA DSP56300GSMP/D Semiconductor Software Product Brief (Motorola Order Number) Rev. 0, 09/99 ETSI Multi-Channel GSM Speech Coders

Introduction Motorola and Signals + Software have jointly developed DSP software for GSM (Global Systems for Mobile Communications) applications for Motorola’s DSP56300 family. The suite includes the three speech coding functions of the ETSI GSM digital mobile telephone system: Half Rate, Full Rate, and Enhanced Full Rate vocoders. Background The ETSI GSM suite codes narrowband speech (300-3400Hz, sampled at 8kHz) to 13 kb/s, 12.2kb/s, and 5.6 kb/s, respectively. The suite includes the relevant voice activity detection, error concealment, and discontinuous transmission facilities for each coder. Table 1 lists the ETSI specifications that are implemented.

Table 1. ETSI GSM Specification Numbers

Full-Rate GSM Enhanced Full-Rate GSM Half-Rate GSM

Speech transcoding 06.10 06.60 06.20

Substitution/muting of lost 06.11 06.61 06.21 frames

Comfort noise generation 06.12 06.62 06.22

Discontinuous transmission 06.31 06.81 06.41

Voice activity detection 06.32 06.82 06.42

Features and Performance The full-rate speech coder uses a regular Pulse Excitation with Long-Term Prediction (RPE-LTP) algorithm. The audio performance for a single encode/decode is judged to be that some degradation is present compared to standard 64b/s PCM (G.711); the degradation is noticeable only over good loudspeaker systems. The enhanced full-rate speech coder uses a coding scheme known as Algebraic Code Excited Linear Prediction Coder (ACELP). The ACELP gives superior audio performance to full-rate GSM, especially for background noise and/or bit errors. The GSM half-rate algorithm is a variation of CELP known as VSELP (Vector-Sum Excited Linear Predictive Coding). The codebook used in VSELP has a predefined structure that significantly reduces the computational complexity of the codebook search. This codebook gives similar audio performance to full-rate GSM but at less than half the bit rate. The software passes all the ETSI GSM test vectors and is designed for multi-channel use.

CDMA Application Software

Interface Details For each speech coder there are a set of seven subroutines: a boot routine for common tables, and for both the encoder and decoder a boot routine, an initialization routine and a processing routine. The boot and initialization routines are normally called only DSP on reset. The audio input and output format is 8kHz linear samples, and the processing routines operate on 160 samples (20ms) frames. Each input frame of speech is converted by the encoder into a set of parameters depending on the coder. The decoder uses this data to reconstruct the speech frame. The code is available either as the individual speech coders or as a package consisting of all 3 coders DSP Requirements

Full-Rate GSM Program Memory X Data Memory Y Data Memory Processing Load (MIPS)*

Code Tables Variables Tables Variables Tables

Encoder and Decoder 2525 191+ 454n+440 33+ 117n+74 158+ 2.97n

Encoder only 1991 166+ 341n+440 8+ 103n+74 158+ 2.34n

Decoder only 786 101+ 113n+440 29+ 14n+74 172+ 0.63n

Enhanced Full-Rate Program Memory X Data Memory Y Data Memory Processing GSM Load (MIPS)*

Code Tables Variables Tables Variables Tables

Encoder and Decoder 9450 5192+ 2946n+500 618+ 913n+314 4574+ 18.05n

Encoder only 6563 5192+ 2351n+57 618+ 506n+314 4574+ 16.33n

Decoder only 2887 5192+ 595n+500 618+ 407n+314 4574+ 1.72n

Half-Rate GSM Program memory X Data Memory Y Data Memory Processing Load (MIPS)*

Code Tables Variables Tables Variables Tables

Encoder and Decoder 10457 7971+ 1520N+794 2550+ 562n+794 5421+ 17.8n

Encoder only 7843 7712+ 1029N+794 2513+ 314n+794 5199+ 2.93n

Decoder only 3857 7070+ 494N+394 1861+ 248n+349 5209+ 14.87n

NOTES: * All MIPS ﬁgures are worst case, assuming internal program and data memory. n = number of channels U These are tables that are copied from program memory during the initialization routines. Depending on your conﬁguration, it may not be necessary to do the copy, reducing the memory requirement.

1-2 CDMA Application Software Motorola Applications and Availability

Applications and Availability The code is available now, under license, for a one-time payment and/or royalties, depending on the commercial application. Also available are: • Demonstration systems • Application notes • Support consultancy for code porting and integration

Motorola 1-3 For further information, visit our Web site at http://www.sasl.com, send us email at [email protected], or contact your nearest Signals + Software Office at: Signals + Software, Ltd. Signals + Software , Inc. The Heights Sugarloaf Corporate Center, Lowlands Road, Harrow Suite 360, 2180 Satellite Blvd HA1 3AW Duluth, Georgia, United Kingdom

Tel: +44 (0) 208 872 9000 Tel: +1 (678) 584 8680 FAX: +44 (0) 208 872 9001 FAX: +1 (678) 584 8681

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