The chip set replaces the tuner and demodulator sections of satellite set-top boxes and adds support for the so-called Turbo coding scheme that U.S. satellite TV broadcasters plan to use. Turbo forward error correction coding should allow broadcasters to squeeze up to 50 percent more channels or data into their existing bandwidth allocations, STMicroelectronics said.

The company has licensed key patents from France Telecom to allow it to build Turbo-code processing into its chips. STMicroelectronics expects to find additional applications and is working on hard disk drive read-channel ICs that will use Turbo coding to increase storage capacity.

Turbo codes form a relatively new class of encoding schemes that are being adopted in such areas as the third-generation Universal Mobile Telephone System standard. The codes may also find their way into next-generation GSM and Digital Video Broadcast services.

Europe's DVB organization is drafting a standard for the use of Turbo codes in its systems. But the United States is expected to be the first to adopt a system based on the codes. STMicroelectronics claims that the France Telecom patents are fundamental to the use of Turbo codes and will ultimately have to be licensed by other technology suppliers.

Jacques Meyer, integrated system architecture group manager for STMicroelectronics, said that Turbo codes employ a convolutional encoding scheme similar to that used by Viterbi-based systems. They differ from Viterbi codes in that they use an iterative decoder, which uses less power on the comparatively long convolution sequences needed for high coding efficiency.

Compatibility missing

Offering channel gain of up to 3 dB, Turbo codes could let service providers increase the number of TV channels by up to 50 percent or offer data transmission services. But their implementation would entail eventually replacing the large installed base of set-top boxes in the United States. The codes and the 8-PSK (phase-shift keying) modulation scheme that is expected to be adopted is not backward-compatible with current schemes. Satellites will not necessarily have to be changed, although 8-PSK modulation has higher channel power than quadrature phase-shift keying.

"We know that the first operator will adopt this technology next year," said Philippe Geyres, corporate vice president of STMicroelectronics' consumer broadband group. "It will mean higher bandwidth demands in the transition period because operators will be operating two services. But the old boxes would be replaced anyway."

The two-piece chip set that ST has developed can switch from the current QPSK-based codes to Turbo code transmission. The front-end demodulator chip uses a zero IF architecture and includes the standard demodulation circuitry. The Turbo code chip is an add-on.

As Turbo code systems are more widely adopted, the company plans to integrate the technology into one device.

"Both chips are based on standard 0.18-micron CMOS technology, so that should not be a problem. With the current design, we can offer an immediate cost reduction to set-top box builders," said Geyres.

"We didn't push for exclusivity on the patent license, because we want the France Telecom Turbo code technology to be the standard," said Armando Caltabiano, business unit director for the satellite and terrestrial front-end group within ST's consumer broadband division. "However, if another system is chosen, we have the know-how to be able to work with that.

"We see a big push from the set-top box manufacturers to align the U.S. and European systems," he added. "Which one will have control is still to be determined."

Chris Edwards is a contributing editor with Electronics Times, EE Times' sister publication in the United Kingdom.