研究目的
To investigate the impacts of chromatic dispersion on Kramers-Kronig (KK) and signal-signal beat interference iterative cancellation (IC) receivers in direct-detection systems for short-reach communications.
研究成果
The study demonstrates that chromatic dispersion increases the optimal CSPR for KK receivers due to PAPR increase violating the minimum phase condition, making KK performance CD-dependent. In contrast, IC receivers are robust against CD regardless of CSPR, with lower required OSNR after long-distance transmission. IC receiver outperforms KK receiver by 1.9 dB in OSNR after 160 km, indicating better suitability for CD-affected short-reach systems.
研究不足
The KK receiver requires high sample rates or upsampling due to its algorithm complexity, increasing hardware demands. The IC receiver has high DSP complexity from iterations, though reduced to 2 iterations in this study. The study is limited to 160 km transmission and specific modulation formats (QPSK), and may not generalize to other distances or modulations.
1：Experimental Design and Method Selection:
An 80-Gb/s transmission experiment over up to 160 km of standard single-mode fiber (SSMF) was conducted to compare KK and IC receivers. Single-carrier and OFDM modulation formats were used with QPSK signals. The experiment involved varying carrier-to-signal power ratio (CSPR) from 4 to 14 dB and transmission distance from 0 to 160 km in 40 km steps.
2：Sample Selection and Data Sources:
Digital signals were generated for 40-Gbaud QPSK with a roll-off factor of 0 for single-carrier and OFDM with FFT size of 4096 and 2176 data subcarriers. A digital RF tone was inserted with a 0.625 GHz frequency gap. Training sequences were used for channel estimation in OFDM.
3：625 GHz frequency gap. Training sequences were used for channel estimation in OFDM.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: External cavity laser (ECL) at 1550 nm, digital-to-analog converter (DAC) with 80 GSa/s arbitrary waveform generator (AWG), 35-GHz IQ modulator, electrical amplifiers, Erbium-doped fiber amplifier (EDFA), SSMF, 43-GHz photodetector (PD), oscilloscope with 160 GSa/s sample rate, polarization controller (PC).
4：Experimental Procedures and Operational Workflow:
Signals were modulated, amplified, transmitted over fiber, detected by PD, and digitized. DSP included KK algorithm for field reconstruction and SSBI iterative cancellation. For KK receiver, DSP involved logarithm and exponential functions; for IC receiver, iterative subtraction of SSBI was performed with 2 iterations chosen for complexity reduction.
5：Data Analysis Methods:
Q-factor and bit error rate (BER) were measured as functions of CSPR, OSNR, and transmission distance. PAPR was measured to assess CD impacts. Least-mean square algorithm was used for equalization in single-carrier signals, and interpolation for channel response in OFDM.
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