Improved symbol rate identification method for on–off keying and advanced modulation format signals based on asynchronous delayed sampling

• Published in: Optics communications 2015-11, Vol.354, p.218-224
• Main Authors: Cui, Sheng, Jin, Shang, Xia, Wenjuan, Ke, Changjian, Liu, Deming
• Format: Article
• Language: English
• Subjects: Asynchronous delayed sampling; Autocorrelation function; Modulation; Optical fiber communication; Symbol rate identification
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2015.05.056

Symbol rate identification (SRI) based on asynchronous delayed sampling is accurate, cost-effective and robust to impairments. For on–off keying (OOK) signals the symbol rate can be derived from the periodicity of the second-order autocorrelation function (ACF2) of the delay tap samples. But it is found that when applied this method to advanced modulation format signals with auxiliary amplitude modulation (AAM), incorrect results may be produced because AAM has significant impact on ACF2 periodicity, which makes the symbol period harder or even unable to be correctly identified. In this paper it is demonstrated that for these signals the first order autocorrelation function (ACF1) has stronger periodicity and can be used to replace ACF2 to produce more accurate and robust results. Utilizing the characteristics of the ACFs, an improved SRI method is proposed to accommodate both OOK and advanced modulation formant signals in a transparent manner. Furthermore it is proposed that by minimizing the peak to average ratio (PAPR) of the delay tap samples with an additional tunable dispersion compensator (TDC) the limited dispersion tolerance can be expanded to desired values. •For advanced modulation format signals, the previous second order autocorrelation function based method may fail.•An improved SRI method is proposed to accommodate different signals in a transparent manner.•The dispersion tolerance can be expanded by minimizing the PAPR with additional tunable dispersion compensators.