Apparatus and method for communicating data over a communication channel
For some applications such as high-speed communication over short-reach links, the complexity and associated high latency provided by existing modulators may be unsuitable. According to an aspect, the present disclosure provides a modulator that can reduce latency for applications such as 40 G/100 G communication over copper cables or SMF. The modulator has a symbol mapper for mapping a bit stream into symbols, and a multi-level encoder including an inner encoder and an outer encoder for encoding only a portion of the bit stream. In some implementations, the multi-level encoder is configured such that an information block size of the inner encoder is small and matches a field size of the outer encoder. Therefore, components that would be used to accommodate larger block sizes can be omitted. The effect is that complexity and latency can be reduced. According to another aspect, the present disclosure provides a demodulator that is complementary to the modulator.
1. A modulator comprising:
a symbol mapper for mapping a bit stream into symbols; and
a multi-level encoder comprising an inner encoder and an outer encoder for encoding only a portion of the bit stream such that an information block size of the inner encoder is a multiple of a field size of the outer encoder;
wherein a portion of the bit stream comprises a least significant bit (LSB) sequence and a non-LSB sequence having p-times as many bits, p being an average number of bits per LSB; and
the symbol mapper being configured for mapping the bit stream into the symbols from a constellation of 2 N symbols, where N is an integer and is variable from symbol to symbol.
2. The modulator of claim 1 , wherein the multiple is a small multiple.
3. The modulator of claim 2 , wherein the small multiple is exactly two.
4. The modulator of claim 1 , wherein the portion of the bit stream comprises an LSB (Least Significant Bit) sequence.
5. The modulator of claim 4 , wherein the symbol mapper performs the mapping without a non-LSB sequence of the bit stream being encoded.
6. The modulator of claim 4 , wherein:
the bit stream further comprises a non-LSB sequence having (N−1)-times as many bits as the LSB sequence; and
the symbol mapper is configured for mapping the bit stream into symbols from a constellation of 2 N -PAM symbols, where N is an integer and is constant from symbol to symbol.
7. The modulator of claim 6 wherein a bit from each of the symbols is gray coded.
8. The modulator of claim 6 wherein the constellation has mixed gray/set-partitioned labelling.
9. The modulator of claim 4 , wherein:
the bit stream further comprises a non-LSB sequence having p-times as many bits as the LSB sequence, where p is an average number of bits per LSB; and
the symbol mapper is configured for mapping the bit stream into symbols from a constellation of 2 N symbols, where N is an integer and is variable from symbol to symbol.
10. The modulator of claim 4 , further comprising:
a second encoder for encoding a non-LSB sequence of the bit stream.
11. The modulator of claim 10 , wherein the second encoder is an RS (Reed-Solomon) encoder.
12. The modulator of claim 1 , wherein the field size of the outer encoder is at least 9.
13. The modulator of claim 1 , wherein:
the inner encoder is a block encoder; and
the outer encoder is an RS (Reed-Solomon) encoder.
14. The modulator of claim 1 , wherein:
the inner encoder is a Hamming or Extended Hamming encoder; and
the outer encoder is an RS (Reed-Solomon) encoder.
15. The modulator of claim 1 , wherein:
the inner encoder is a single-parity-check encoder; and
the outer encoder is an RS (Reed-Solomon) encoder.
16. The modulator of claim 1 , wherein:
the outer encoder is a Bose Ray-Chaudhuri Hocquenghem (BCH) encoder.
17. A method for modulating a bit stream into symbols, comprising:
encoding only a portion of a bit stream comprising an LSB (Least Significant Bit) sequence and a non-LSB sequence by a multi-level encoder comprising an inner encoder and an outer encoder, such that an information block size of the inner encoder is a multiple of a field size of the outer encoder, the non-LSB sequence having p-times as many bits as the LSB sequence, where p being an average number of bits per LSB; and
mapping the bit stream into the symbols from a constellation of 2 N symbols, where N is an integer and is variable from symbol to symbol.
18. The method of claim 17 , further comprising:
encoding, by a second encoder, a non-LSB sequence of the bit stream.
19. The method of claim 17 , wherein:
the bit stream further comprises a non-LSB sequence having (N−1)-times as many bits as the LSB sequence; and
the mapping comprises mapping the bit stream into the symbols from a constellation of 2 N -PAM symbols, where N is an integer and is constant from symbol to symbol.