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To achieve universal connectivity, the telecommunications community has developed complex rules for network providers and equipment manufacturers. The G.726 standard, an adaptive differential-pulse-code modulation (ADPCM)-based speech compression algorithm, enables network-capacity (calls/lines) enhancements. The standard offers a variety of bit rates: 40 kbits/second, 32 kbits/s for toll-quality applications, 24 kbits/s (communication quality) and 16 kbits/s. The G.726 ADPCM 32 kbits/s is widely used in digital cordless-telephone standards around the world.
The transition of the telecommunications market from analog to digital systems in compliance with those standards requires equipment with significant DSP capabilities. These are needed to perform operations associated with the digital transmission, such as speech coding and echo control. Various nodes on the network may need different processing capability. While the central-office equipment and the basestation need to handle multiple channels, the handset handles a single channel. Power-consumption restrictions exist in all cases for varying reasons-packaging and system operation considerations, as in the former cases, or battery-operated equipment, as in the latter. Price and size are also key factors in implementation decisions.
Most of the available low-end general-purpose DSP processors have problems coping with a single, full-duplex channel processing, let alone additional processing. Using them in the basestation, where multichannel capability is required, results in a large, power-hungry and expensive solution. Their power consumption also makes them unfavorable even for the battery-operated, single-channel handset. The hard-wired solutions, on the other hand, provide the required performance at an acceptable power consumption but without the flexibility to use the same hardware for additional processing.
Telecore is a middle-of-the-road solution, offering an architecture optimized for the speech-compression needs, yet with enough general DSP capability and microcoded high-level control (instruction set) to perform additional processing, such as echo cancellation and similar filtering operations. A very small, extremely low-power ASIC cell, the Telecore was designed for minimized power and scalable performance. A unique and innovative approach to the ITU G.726 ADPCM speech-coding standard implementation allows for full processing of a single-input sample (in either encode or decode) in less than half the clock cycles in any other implementation. The resulting cell requires a 512-kHz clock for a single, full-duplex channel and can support up to eight full-duplex channels with scalable clock rates of up 8.192 MHz. The required RAM...