Forward Error Correction (FEC) Solutions

Error-correcting code (ECC) is an essential part of virtually any communication system. It works by introducing redundancy to a digital stream, using it to correct possible errors.

Low error probability can be achieved by increasing transmitter's power, but this solution is often undesirable (especially in wireless, satellite and mobile applications). Error-correcting codes decrease the error probability (BER) without increasing the transmitting power, providing a coding gain (which is defined as difference between signal to noise ratios in the systems with and without coding, needed to maintain the same error probability).

Forward error correction coder (decoder) design is a complex task requiring both knowledge and experience. Implementation of ECC coders and decoders in hardware places even more restrictions.

We are experts in the field of error correction and detection. We have experience designing forward error correction (FEC) coders and decoders since 2004, being able to implement both standard and custom error-correcting codes and to conduct the relevant research concerning selection of the codes or code combinations. We can implement a complete coding solution on the basis of FPGA, DSP, or as a part of the system-on-chip (SoC).

We have also developed a few novel forward error correction algorithms implementations.

Choosing an Error-Correcting Code

Thorough research, both theoretical and numerical, must precede the design of ECC coder and decoder. There are many error-correcting codes and their combinations, each fitting the particular task. The forward error correction coding scheme is chosen after thorough trade-off studies involving analysis of the correcting capability (for the particular channel) and estimated implementation complexity.

The basic issues one needs to take into account in order to choose an error-correcting code (ECC) are:

1. Physical channel characteristics (S/N ratio, presence of memory, e.g. fading)
2. Modulation type.
3. Desirable channel characteristics (information rate, BER - bit error probability).

The most commonly used error-correcting codes are:

• Hamming codes - having low correcting capability, they are also very easy to implement in hardware.
• Reed-Solomon codes and BCH codes provide good error-correcting capabilities, but require complex algorithms for decoding
• Convolutional codes, decoded either with a Viterbi decoder or a sequential decoder, perform well for Gaussian channels.
• Turbo codes perform exceptionally well on very bad channels, almost reaching the Shannon limit.
• Low-density parity check codes (LDPC codes) - probably the most effective class of error-correcting codes currently known.

Standard Forward Error Correction Coders and Decoders Design

We have ready-to-use solutions for decoding of the standard codes:

• DVB-S, DVB-S2
• Intelsat (IESS standard series)
• WiMAX

Novel Approaches to Forward Error Correction

Although very good error-correcting codes have been introduced that are able to approarch the Shannon limit, they have too complex decoding procedure. One of the current trends in forward error correction decoder design is to develop new implementations for particular classes of codes (primarily Turbo and LDPC codes).

Some of the new opportunities:

• increasing turbo-code implementation efficiency using special interleaver design suitable for parallel implementation;
• using very long generalized low-density parity check codes with simple components;
• using specially designed parity-check matrices for LDPC codes.

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