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<p>In communication systems, inadequate receiver bandwidth can disrupt the perpendicular alignment of Nyquist-shaped formats, causing cross-over symbol interference (ISI) and suboptimal system functionality. Nyquist pulses, like increased cosine pulses, are supposed to be orthogonal. This orthogonality is achieved by carefully structuring the pulse's frequency spectrum to meet the Nyquist requirement for zero ISI, which states that the pulse spectrum must have zero energy at integer multiples of the symbol rate except at the sampling sites' centers. If the receiver's bandwidth is insufficient, it functions as a low-pass filter, truncating the signal spectrum, particularly at the borders of the Nyquist pulse spectrum. Insufficient bandwidth truncates the high-frequency components of the Nyquist-shaped pulse, changing its shape in both the time and frequency domains. The missing spectral components alter the time-domain pulse structure, causing it to lose orthogonality. This means that energy from one pulse might cross over to neighbouring pulses, resulting in ISI. The proposed method employs an optical pre-sampler to minimize receiver bandwidth through pulse reshaping. theoretical mathematical Simulations and hardware governed tests conducted with an optically formed 48-Gbaud Nyquist-shaped 4-QAM demonstrate receiver sensitivity boosts of 10.1 and 5.2&#xa0;dB at 15- and 10-GHz receiver electrical bandwidths, respectively.</p>

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Theoretical and Experimental Analysis of 4-QAM System Utilizing Nyquist- Modeled Optical Sampling Technique in Restricted Receiver Capacity Signal Detection

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • Deepak Sahu,
  • Chakresh Kumar,
  • Ghanendra Kumar

摘要

In communication systems, inadequate receiver bandwidth can disrupt the perpendicular alignment of Nyquist-shaped formats, causing cross-over symbol interference (ISI) and suboptimal system functionality. Nyquist pulses, like increased cosine pulses, are supposed to be orthogonal. This orthogonality is achieved by carefully structuring the pulse's frequency spectrum to meet the Nyquist requirement for zero ISI, which states that the pulse spectrum must have zero energy at integer multiples of the symbol rate except at the sampling sites' centers. If the receiver's bandwidth is insufficient, it functions as a low-pass filter, truncating the signal spectrum, particularly at the borders of the Nyquist pulse spectrum. Insufficient bandwidth truncates the high-frequency components of the Nyquist-shaped pulse, changing its shape in both the time and frequency domains. The missing spectral components alter the time-domain pulse structure, causing it to lose orthogonality. This means that energy from one pulse might cross over to neighbouring pulses, resulting in ISI. The proposed method employs an optical pre-sampler to minimize receiver bandwidth through pulse reshaping. theoretical mathematical Simulations and hardware governed tests conducted with an optically formed 48-Gbaud Nyquist-shaped 4-QAM demonstrate receiver sensitivity boosts of 10.1 and 5.2 dB at 15- and 10-GHz receiver electrical bandwidths, respectively.