CMX608, CMX618 and CMX638 RALCWI Vocoder

Applications
Digital PMR, LMR, voice radio
Digital trunking
DMR TDMA
DMR FDMA, dPMR
Digital voice scrambling and encryption
Digital WLL
Voice storage and playback systems
Regenerative digital voice repeaters
Messaging systems
VoIP systems
Voice pagers
Half-Duplex vocoding (CMX608/CMX618)
Full-Duplex vocoding (CMX638 only)

Brief Description
The CMX608, CMX618, and CMX638 are flexible, high integration, high performance, RALCWI (Robust Advanced Low Complexity Waveform Interpolation) vocoders, offering near toll-quality voice at very low bit rates. A Forward Error Correction (FEC) engine provides optimum performance in real life applications.

The RALCWI vocoder comprises four independent functions, selectable by the host: Voice Encoder, FEC Encoder, Voice Decoder and FEC Decoder. The CMX608 and CMX618 are half-duplex vocoders and the CMX638 is a full-duplex vocoder with integrated voice CODEC. The CMX618 includes an integrated voice CODEC, offering a complete analogue voice to low bit rate vocoded data function with integrated channel filters removing the need for external components, whereas the CMX608 requires an external voice CODEC.

CMX608, 618 and 638 operate from a dual power supply (1.8V & 3.3V) and are available in both 48-pin LQFP (L4) and 48-pin VQFN (Q3) packages.

In encode mode, the voice encoder uses a 20ms voice frame size with 3 programmable bit rates: 2.05kbps, 2.4kbps or 2.75kbps. The optional FEC encoder performs channel coding of the encoded voice (2.05kbps, 2.4kbps or 2.75kbps, depending on selected mode) and forms an encoded, interleaved bitstream of 3.6kbps (216 bits per 60ms packet or 288 bits per 80ms packet). The FEC operation uses a packet of either 3 or 4 20ms vocoder frames to give optimum error correction performance. In decode mode, the 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 bitstream of encoded voice at 2.05kbps, 2.4kbps or 2.75kbps rate, depending on selected mode. The FEC decoder can optionally use "soft decision" metrics to improve its decoding ability. The voice decoder then converts the error-corrected bit-stream back into a digitised voice signal.

Soft Decision Decoding (SDD), Discontinuous Transmission Detection (DTX), Voice Activity Detection (VAD) and Comfort Noise Generation (CNG) functions are also included, to further enhance performance. Single (STD) and dual (DTMF) tones can be detected and sent separately in the coded bitstream, then regenerated at the far end.