Four-dimensional optical multiband-OFDM for beyond 1.4Tb/s serial optical transmission
View Patent ↗Systems and methods are disclosed to perform four-dimensional optical multiband OFDM communication by organizing an N-dimensional (ND) signal constellation points as a signal matrix; performing 2D-inverse FFT and 2D-FFT to perform modulation and demodulation, respectively; and applying both orthogonal polarizations in the OFDM communication to deal with chromatic dispersion, PMD and PDL effects, and multidimensional signal constellation to improve optical signal-to-noise ratio (OSNR) sensitivity.
1. A method to perform four-dimensional optical multiband OFDM communication, comprising:
organizing an N-dimensional (ND) signal constellation points as a signal matrix;
performing 2D-inverse FFT and 2D-FFT to perform modulation and demodulation, respectively;
applying both orthogonal polarizations in the OFDM communication to deal with chromatic dispersion, PMD and PDL effects, and multidimensional signal constellation to improve optical signal-to-noise ratio (OSNR) sensitivity; and
comprising performing a 4D mapping and writing outputs of 4D mapping column-wise into a 4×M symbol-like interleaver and providing to a two-dimensional inverse discrete Fourier transform (2D-IDFT) with
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to generate
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where s ij =(s ijJ s ijO ), with subscripts I and Q corresponding to in-phase and quadrature channels, respectively.
2. The method of claim 1 , wherein signal constellation points are represented in matrix form by placing coordinates of signal constellation points along columns of signal matrix.
3. The method of claim 1 , comprising applying 2D inverse FFT to obtain 2D array of complex numbers, where coordinates of complex numbers correspond to I and Q channels, while even and odd rows of 2D array correspond to x- and y-polarizations, respectively.
4. The method of claim 1 , comprising encoding m independent data streams using different LDPC (n,k l ) codes (l=1, . . . ,m), where n denotes a codeword length and k l is an information word length of lth component code and wherein the codewords are written row-wise into an m×n bit interleaver.
5. The method of claim 1 , comprising selecting m bits from a bit interleaver column-wise at every symbol slot i and performing 4D mapping to select one constellation point out of 2 m , depending on information content.
6. The method of claim 5 , wherein the 4D mapping comprises a look-up table (LUT) with m input bits serving as a memory address that selects four coordinates of 4D signal constellation point.
7. The method of claim 1 , comprising representing symbol interleaving content as a two-dimensional array (matrix) as:
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where the jth column S j =[S j,0 , S j,1 S j,2 S j,3 ] T represents the coordinates of jth 4D signal constellation point (S j (0) ,S j (1) ,S j (2) ,S j (3) )(j=0, 1, . . . , M−1) and rows correspond to the dimensions and columns correspond to subcarriers.
8. The method of claim 1 , comprising serializing the matrix into two vector-streams {right arrow over (x)}=[s 00 s 10 . . . s M−1,0 s 02 s 12 . . . s M−1,2 . . . ] and {right arrow over (y)}=[s 01 s 11 . . . s −1,1 s 03 s 13 . . . s M−1,3 . . . ].
9. The method of claim 1 , comprising receiving data with a polarization-diversity receiver, followed by a 2D-FFT demapping of the data.
10. The method of claim 9 , comprising using a polarization beam splitter (PBS), the optical signal is split into two orthogonal polarizations that are used as input into two balanced coherent detectors.
11. The method of claim 10 , wherein the balanced coherent detectors provide estimated in-phase and quadrature information for both polarizations.
12. The method of claim 9 , comprising deinterleaving and determining a symbol log-likelihood ratios (LLRs) with a posteriori probability (APP) demapping.
13. The method of claim 12 , comprising determining
λ( S i )=log [ P ( S i S 0 |R i )/ P =( S i ≠S 0 |R i )],
where P(S i |R i ) is determined by Bayes' rule as:
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14. The method of claim 12 , comprising determining bit LLRs in LDPC decoding from the symbol LLRs as follows
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.
15. The method of claim 1 , comprising
multiplexing/demultiplexing data based on multiband 4D-OFDM.
16. The method of claim 15 , comprising using frames corresponding organized in a plurality of OFDM bands with guard spacing between two neighboring OFDM bands as Δf G =mΔf sc (m is a positive integer), where Δf sc is a subcarrier spacing.
17. The method of claim 1 , comprising forming a two-layer integrated circuit hierarchy.
18. The method of claim 17 , comprising forming a baseband level and a second layer as a photonics layer.
19. The method of claim 17 , comprising integrating five-frequency locked lasers combined optically into 1.4 Tb/s optical transport signal.