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Data-intensive consumer and business applications are driving the need for speed and accuracy in data communication systems.
As bandwidth demands increase and the tolerance for errors and latency decreases, designers of data-communication systems are looking for new ways to expand available bandwidth and improve the quality of transmission. One solution isn't actually new, but has been around for a while. Nevertheless, it could prove quite useful. Called forward error correction (FEC), this design technology has been used for years to enable efficient, highquality data communication over noisy channels, such as those found in satellite and digital cellular-communications applications.
Recently, there have been significant advances in FEC technology that allow today's systems to approach the Shannon limit. Theoretically, this is the maximum level of information content for any given channel. These advances are being used successfully to reduce cost and increase performance in a variety of wireless communications systems including satellites, wireless LANs, and fiber communications. In addition, high-speed silicon ASICs for FEC applications have been developed, promising to further revolutionize communication systems design.
The big attraction of FEC technology is how it adds redundant information to a data stream. This enables a receiver to identify and correct errors without the need for retransmission.
As the capabilities of FEC increase, the number of errors that can be corrected also increases. The advantage is obvious. Noisy channels create a relatively large number of errors. The ability to correct these errors means that the noisy channel can be used reliably. This enhancement can be parlayed into several system improvements, including bandwidth efficiency, extended range, higher data rate, and greater power efficiency, as well as increased data reliability.
FEC requires that data first be encoded. The original user data to be transmitted over the channel is called information bits, while the data after the addition of error-correction information is called coded bits.
For k information bits, the encoding process results in n coded bits where n > k. All n bits are transmitted. At the receiver, channel measurements are made and estimates of the transmitted n bits are generated. An FEC decoder utilizes these n bit estimates, along with knowledge of how all n bits were created, to generate estimates of the k information bits. The decoding...