Systems and methods for mapping and demapping digitized signals for optical transmission
An optical network includes a transmitter portion configured to transmit a digitized stream of symbols over a digital optical link, a mapping unit disposed within the transmitter portion and configured to code the transmitted digitized stream of symbols with a mapping code prior to transmission over the digital optical link, a receiver portion configured to recover the coded stream of symbols from the digital optical link, and a demapping unit disposed within the receiver portion and configured to map the recovered coded stream of symbols into an uncoded digitized signal corresponding to the digitized stream of symbols at the transmitter portion prior to coding by the mapping unit.
1. A method of transmitting information over an optical transmission link, the method comprising the steps of:
receiving an input analog signal having a first Gaussian distribution of symbol amplitude values;
digitizing the input analog signal into a digitized series of symbols having a second Gaussian distribution, the digitized series of symbols including at least one input occurrence of a first symbol having a first symbol amplitude value and at least one input occurrence of a second symbol having a second symbol amplitude value;
mapping the first symbol to the second symbol and the second symbol to the first symbol to generate a mapped signal; and
modulating the mapped signal for transmission over the optical transmission link,
wherein the second symbol amplitude value is greater than the first symbol amplitude value.
2. The method of claim 1 , wherein the sign of the first and second symbols remains unchanged after mapping to the other of the first and second symbols.
3. The method of claim 1 , further comprising the step of applying a scrambling code to each input occurrence of the first and second symbols.
4. The method of claim 3 , wherein the scrambling code comprises a periodic pseudo-random bit stream of 0 and 1 values having substantially equal probabilities of occurrence.
5. The method of claim 4 , wherein, for each occurrence of the first input symbol, the first symbol is mapped to the second symbol when the scrambling code has a 1 value, and the first symbol remains unchanged when the scrambling code has a 0 value.
6. The method of claim 3 , wherein the scrambling code comprises a periodic pseudo-random bit stream of −1, 0, and 1 values, wherein the −1 and 1 values each have a 25% probability of occurrence, and wherein the 0 value has a 50% probability of occurrence.
7. The method of claim 6 , wherein, for each occurrence of the first symbol, the first symbol is mapped to the second symbol when the scrambling code has a −1 or 1 value, and the first symbol remains unchanged when the scrambling code has a 0 value.
8. The method of claim 7 , wherein, for each mapping of the first symbol to the second symbol, the symbol amplitude value of the mapped first symbol will be equal to the symbol amplitude value of the second symbol, the sign of the mapped first symbol will remain unchanged when the scrambling code has a 1 value, and the sign of the mapped first symbol will be reversed when the scrambling code has a −1 value.
9. The method of claim 1 , wherein the first symbol has a ±1 value in the second symbol has a ±3 value.
10. The method of claim 1 , wherein the series of transmitted symbols represents a PAM4 signal.
11. The method of claim 1 , wherein the digitized signal is a DOCSIS 3.1 signal.