Advantages of shannon code modulation
Answers
Explanation:
Novel coding techniques
According to the information theory, optimum coding is needed to approach the Shannon limit [2]. Forward error correction (FEC) is one type of coding schemes capable of providing substantial coding gain with small overhead [55]. FEC decoding can be performed after the received “analog” samples are quantized to recover the transmitted data, often referred to as hard-decision decoding, or before the quantization, often referred to as soft-decision decoding, which outperforms the earlier [55,105]. With digital coherent detection, multi-bit representation of each received sample is available, so soft-decision decoding can be straightforwardly implemented. With the use of 3-bit soft decision, a net coding gain of 10.2 dB was demonstrated at 10 Gb/s with a FEC overhead of 25% using a block turbo code (BTC) [106]. The performance of the demonstrated BTC is about 2.2 dB from the Shannon limit [106]. Better performance may be achieved by low-density parity check codes [106–108].
In high spectral efficiency transmission, multi-level modulation formats are used, and a special coding technique called trellis-coded modulation (TCM) [109,110] is well suited. In TCM, modulation is considered an integral part of the coding process, and high coding gain can be obtained by using redundant signal sets rather than expanding the signal bandwidth [109,110].
A technical difficulty in implementing the advanced coding schemes at high data rates is associated with the high DSP complexity and computational load usually required by these schemes. It is expected that future advances in silicon technology will help push the system performance toward the Shannon limit.