Single carrier flexible bit rate transceiver for coherent optical network
An apparatus comprising a digital signal processor (DSP) configured to code a plurality of data sub-streams using a plurality of modulation formats to generate a plurality of coded data symbols, wherein each modulation format leads to a unique bit rate for coded data symbols associated with a modulation format, transform the coded data symbols into a frequency domain by applying Fourier transform on each coded data symbol, map the frequency-transformed data symbols onto a plurality of subcarrier signals associated with a plurality of frequency tones, wherein at least two of the subcarrier signals correspond to different modulation formats, and generate an electrical signal in a time domain based on the subcarrier signals.
1. An apparatus comprising:
a frontend configured to:
receive an optical signal modulated on a single optical carrier; and
generate a digital electrical signal based on the optical signal; and
one or more processors coupled to the frontend and configured to:
transform the digital electrical signal from a time domain to a frequency domain by applying a Fourier transform to generate a plurality of subcarrier signals, wherein a frequency spectrum associated with the subcarrier signals comprises a plurality of frequency bands separated by spectral gaps;
estimate a frequency offset for a local oscillator based on powers of frequency bins around a spectral gap position of one of the spectral gaps;
generate a plurality of coded data symbols in the time domain based on the subcarrier signals and the frequency offset, wherein generating the coded data symbols comprises applying an inverse Fourier transform on each subcarrier signal; and
decode the coded data symbols using a plurality of demodulation formats to generate a plurality of decoded data sub-streams, wherein different demodulation formats are applied on the coded data symbols with different symbol bit rates.
2. The apparatus of claim 1 , wherein the one or more processors are further configured to convert the decoded data sub-streams into one data stream via parallel-to-serial conversion, and wherein the apparatus further comprises a transmitter coupled to the one or more processors and configured to transmit the data stream.
3. The apparatus of claim 1 , wherein the one or more processors are further configured to estimate the frequency offset by accumulating the powers.
4. The apparatus of claim 1 , wherein the spectral gap position is associated with a pre-determined first frequency bin, wherein a second frequency bin has a minimum power among the powers, and wherein the one or more processors are further configured to further estimate the frequency offset as a frequency difference between the first frequency bin and the second frequency bin.
5. The apparatus of claim 1 , wherein the one or more processors are further configured to determine an optical signal-to-noise ratio (OSNR) based on the powers.
6. The apparatus of claim 5 , wherein the one or more processors are further configured to further determine the OSNR by accumulating the powers.
7. The apparatus of claim 1 , wherein the Fourier transform is a fast Fourier transform (FFT), wherein the inverse Fourier transform is an inverse FFT (IFFT), and wherein the plurality of demodulation formats comprises one or more of binary phase shift keying (BPSK) demodulation, quadrature phase shift keying (QPSK) demodulation, 8-level quadrature amplitude modulation (8QAM) demodulation, and 16QAM demodulation.