Abstract
We investigate the constellation design and symbol error rate (SER) of set-partitioned (SP) quadrature amplitude modulation (QAM) formats. Based on the SER analysis, we derive the adaptive bit and power loading algorithm for SP QAM based intensity-modulation direct-detection (IM/DD) orthogonal frequency division multiplexing (OFDM). We experimentally show that the proposed system significantly outperforms the conventional adaptively-loaded IM/DD OFDM and can increase the data rate from 36 Gbit/s to 42 Gbit/s in the presence of severe dispersion-induced spectral nulls after 40-km single-mode fiber. It is also shown that the adaptive algorithm greatly enhances the tolerance to fiber nonlinearity and allows for more power budget.
Highlights
Optical orthogonal frequency division multiplexing (OFDM) [1,2] has attracted great interest for optical networks due to high spectral efficiency and efficient channel estimation and equalization
In order to derive the adaptive bit and power loading algorithm for the SP quadrature amplitude modulation (QAM) formats, we firstly study their symbol error rate (SER), aiming to obtain a general SER bound for all these formats
It is seen that at the same data rate, conventional loading algorithm can get slight performance improvement compared to systems with a single format for all subcarriers
Summary
Optical orthogonal frequency division multiplexing (OFDM) [1,2] has attracted great interest for optical networks due to high spectral efficiency and efficient channel estimation and equalization. By properly selecting the constellation points, this technology can achieve better power efficiency than the conventional QAM formats at the same data rate. This technology can generate different SEs with fine granularity without change of hardware, and can balance the performance and SE to meet the requirements of different optical systems. This type of formats has been studied in coherent systems, very few works have been done in IM/DD systems. Conventional adaptive loading algorithm cannot be applied to the SP QAM formats and should be re-designed according to the bound of their symbol error rate (SER)
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