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Call Waiting Caller ID (Standard) Detector DSP C Code

Description: implements the landline telephony function of Call Waiting Caller IDentity (CWCID) generation. CWCID is sent off-hook in an established call to pass the identity of a third party trying to call one of the talking parties. The talking party can then accept the call by a hook-flash. CWCID is signalled from the exchange - the Generator end - by an alerting dual-tone signal CAS, and acknowledged by the subscriber - the Detector end - with another dual-tone signal ACK. The Caller ID message bytes are then sent by V.23 or Bell 202 modem modulation, formatted as in on-hook Caller ID. The CWCID Detector is for "standard" locales - eg ETSI, UK SIN 227, US Bellcore SDMF/MDMF, Bell Canada - but not for Japan. The software function summary is:

CWCID Detector: on detecting CAS it sends ACK, then demodulates the Caller ID data verified against the checksum, using the on-hook CID decoder routine. The Detector returns diagnostics, signalling CAS-detected for voice-blocking, then full message reception, or else failure due eg a CRC error.

The Detector forms a buffer of the complete message data for the user interface in parameterised byte form, excluding the checksum byte. Message de-parameterisation in the user code gives flexibility in dealing with Caller ID categories. The message buffer format is 2 per 16-bit word for efficiency in multi-channel use.
         The C code is suitable for any processor with an ANSI-compliant C compiler. It is designed especially for efficient operation on low-cost fixed-point DSP- and general-purpose micro-processors. All data memory is specified as 16-bit integer words. Multiplies are integer 16x16-bit with 32-bit products. Sample rates of 8.0kHz and 9.6kHz can be selected. The function has an initialisation call and a per-sample main routine call, and is re-entrant with memory offset-addressing for multi-channel operation. A comprehensive user's guide is provided with the code.

CAS detector performance:

False detections: 1 in ~4.5hours speech
Missed detections: 1 in ~40000 CAS signals + speech

Detector data receiver performance:

SNR for 10-6 BER on Flat Channel: 12.0dB - Bell 202 ; 12.5dB - V.23 (4kHz BW noise)
Local loop line length for no errors: >9km

Processor Load:

Function MIPS# Data memory (words) Prog memory (bytes)#
CWCID-S Detector (+ CID Decoder/Rx) 3.5 (28 + M) x N 2.3k

- #example figures from compiling for the TI TMS320C5000(C55x) DSP processor at 8.0kHz sampling
in data memory figures M is the user-set buffer size at 2 bytes per word and N is no. of channels

Availability: NOW - sale is under licence - integration support offered

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