RALCWI Family Grows With Duplex Vocoder IC

15th April 2008

ES Admin

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CML Microcircuits announces a new RALCWI integrated circuit to its Vocoder family. The new CMX638, is a flexible, highly integrated, high performance duplex vocoder, utilising RALCWI (Robust Advanced Low Complexity Waveform Interpolation) technology. CML now offers the CMX608, CMX618 and CMX638 high performance vocoders, which all offer near toll-quality voice performance at very low bit-rates.

A Forward Error Correction (FEC) engine provides optimum performance in real-life applications, with the RALCWI vocoder being comprised of four independent functions, which are selectable by the host: Voice Encoder, FEC Encoder, Voice Decoder, FEC Decoder.

The CMX608 and CMX618 are half-duplex ICs, with the new CMX638 offering full-duplex capability. The CMX618 and CMX638 include an integrated voice CODEC, for complete analogue voice to low bit-rate vocoded data function (with integrated channel filters, removing the need for external components). The CMX608 is offered without the CODEC, for customers wishing to use a different CODEC solution.

Encoding: The voice encoder uses a 20ms voice frame size, with 3 programmable bit-rates (2050bps, 2400bps or 2750bps), The optional FEC encoder performs channel coding of the encoded voice (at the rate selected) and forms an encoded, interleaved bit-stream of 3600bps (216 bits per 60ms packet or 288 bits per 80ms packet). The FEC operation utilises a packet of either 3 or 4 x 20ms vocoder frames for optimum error correction performance.

Decoding: The optional FEC decoder performs de-interleaving and channel decoding of the coded bit-stream (216 bits per 60ms packet or 288 bits per 80ms packet) and forms an error-corrected bit-stream of encoded voice at 2050bps, 2400bps or 2750bps, depending on the mode selected. The FEC decoder can optionally use 'soft-decision' metrics to enhance its decoding ability. The voice decoder then converts the error-corrected bit-stream back to a digitised voice signal.

For optimum voice performance the following functions are included:

- Soft Decision Decoding (SDD)
- Discontinuous Transmission Detection (DTX)
- Voice Activity Detection (VAD)
- Comfort Noise Generation (CNG)
- Single (STD) and Dual (DTMF) Tones (can be detected, sent separately in the coded bit-stream, then regenerated at the far-end)

Vocoder applications include: Voices storage and playback devices, VoIP, Voice pagers, Digital WLL, Digital PMR/LMR, Voice Radio, Digital Trunking, Regenerative digital voice repeaters, digital voice scrambling and encryption and much more.