研究目的
To compare the performance of M-ary pulse amplitude modulation (M-PAM) and three well-known optical orthogonal frequency division multiplexing (OFDM) schemes for LED-based communication systems, considering the bandwidth limit and constrained peak transmitted power characteristics of LEDs.
研究成果
M-PAM can provide a substantially higher data rate than OFDM for bandlimited channels. When the channel bandwidth is ample compared with the symbol rate, optical OFDM outperforms M-PAM. The choice between M-PAM and optical OFDM depends on the channel bandwidth and the system's power constraints.
研究不足
The study focuses on LED-based communication systems with specific constraints like bandwidth limit and peak transmitted power. The comparison is based on numerical results, and practical implementation challenges are not discussed.
1：Experimental Design and Method Selection:
The study compares M-PAM with DCO-, ACO-, and U-OFDM schemes. A bit loading algorithm and single-tap equalizer with an optimized modulation index are used for the optical OFDM schemes. For M-PAM, an optimized pulse shape and a minimum mean squared error (MMSE) equalizer are applied to reduce inter-symbol interference (ISI).
2：Sample Selection and Data Sources:
The channel is modeled as a first-order lowpass filter, with parameters such as 3 dB bandwidth of LEDs, noise spectral density, and peak received power specified.
3：List of Experimental Equipment and Materials:
The study assumes the use of LEDs as transmitters, with specific parameters like 3 dB bandwidth and peak power constraints.
4：Experimental Procedures and Operational Workflow:
The performance of each modulation scheme is evaluated through numerical results, considering the bandlimited characteristic and constrained transmitted power of LEDs.
5：Data Analysis Methods:
Analytical expressions are used for all results except for M-PAM with no equalization, which is found through Monte Carlo simulation.
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