A patented France Telecom broadband forward error-correction method known as Turbo Code has been licensed on a worldwide basis to STMicroelectronics. This advancement will significantly enhance the information-carrying capacity of a communications system. Moreover, it is likely to affect the digital satellite TV market by maximizing the amount of channels currently being broadcast. STMicroelectronics' first Turbo Code products are scheduled for release later this year.
Armando Caltabiano, director of STMicroelectronics' satellite and terrestrial broadcast unit, points out one of the advantages of this development. "Turbo Code is the first coding scheme that approaches the theoretical limit expressed by the Shannon-Hartley law. The code approaches up to 0.5 dB of the theoretical limit, while conventional code needs about 3 to 4 dB more than the theoretical limit."
Turbo 8-PSK-coded (phase-shift-keying) modulation achieves nearly 50% more spectral efficiency than quadrature phase-shift keying (QPSK) with Viterbi-RS (Reed-Solomon) coding. Consequently, it allows an increase in the data throughput with a practical gain of 2.0 dB. This means that when placed under the same conditions, Turbo coding allows for 50% more data transmission than QPSK with Viterbi-RS coding (about 40 to 50 Mbits b/s versus around 26 to 35 Mbits/s).
Two HDTV Channels On A Transponder
Unlike QPSK, Turbo Code allows for two HDTV stream channels to be broadcast on a 27-MHz transponder. Furthermore, it increases the maximum number of standard TV channels from five to eight. If the system is used with the same data rate as QPSK with Viterbi-RS coding, the area size of its antenna may be reduced by 30%.
For the first application of Turbo Code technology, STMicroelectronics is targeting the U.S. digital satellite market. Philippe Geyres, corporate vice president and general manager of STMicroelectronics' consumer and microcontroller groups, estimates an initial demand for more than ten million new set-top boxes. "That's because U.S. operators are keen to increase their channel offerings," he says.
"The more efficient use of available bandwidth means that existing satellites could not only broadcast more TV channels, but would also have sufficient bandwidth left over to handle both high-speed Internet downloads and a return channel for use in interactive satellite TV," he adds.
According to Geyres, Turbo Code technology is already a standard part of the universal mobile telephone system. France Telecom has been issued a major patent for using Turbo Code in this area. STMicroelectronics would like to participate in this market with a device that offers a bit-error rate of 10-6. For hard-disk drives, the company is planning to implement a Turbo Code-based solution with a data throughput of up to 700 Mbits/s and a bit error rate of 10-14.
A chip designed by France Telecom in cooperation with STMicroelectronics has already been produced at the STMicroelectronics plant in Crolles, France. Working demonstrations based on the first samples have been presented as well.
Customer samples of model STV0399-8P are available now. This IC contains an 8/QPSK demodulator with internal forward error-correction. Plus, the device includes an I/O to an external forward error-correction and a zero IF (ZIF) tuner. Another benefit is that it provides worldwide satellite coverage (Canal+, Dish, DirectTV, BSkyB, and FarEast). Also, its performance ranges from one to more than 45 Msymbols/s. Because the CMOS IC contains an entire conventional RF stage, there 's no need for a difficult RF layout.
STMicroelectronics intends to introduce the STV0399-TC before the end of this year. A single-chip IC, this device maintains turbo code forward-error correction capabilities. Slated for circulation in 2001 is the STV0499. This IC will be suited for both high- and low-end applications. It will integrate ZIF, 8/QPSK, and Turbo Code forward error-correction circuitry on one die.
For more information, contact STMicroelectronics at TO KUM, or visit www.st.com.