Guangtongxin yanjiu (Aug 2024)
A Step-by-step Optimal Signal Mapping Method for O-OFDM Index Modulation
Abstract
【Objective】The use of random mapping and traditional constellations in Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) - Index Modulation (IM) system cannot reach the optimal Bit Error Rate (BER) performance. Therefore, a step-by-step optimal signal mapping method is proposed based on the optimal selection of active sub-carriers and the optimal rotation of constellation to improve the BER performance of O-OFDM-IM system.【Methods】At the transmitter side, the method firstly selects the optimal combination of active subcarriers based on the channel state information and the channel norm maximization criterion. Then considering ∂=0.5° as the step size, an exhaustive search algorithm is used to obtain the optimal constellation by using the channel state information. Next, the optimal constellation graph obtained by rotation is loaded on the active sub-carrier for signal transmission. At last, the Maximum Likelihood (ML) detection algorithm is used to recover the original signal at the receiver to minimize the system error probability.【Results】The results show that at the condition of BER=10-4 and strong turbulence, the Signal to Noise Ratio (SNR) is improved by about 1.45 dB when the modulation order is 16 in (4, 2) system. In addition, with the increase of turbulence intensity, the improvement of BER performance is more obvious. For example, when the BER=10-4 the SNR of the (4, 2) system at 8 Quadrature Amplitude Modulation (QAM) is improved by about 1.35 dB in strong turbulence and 1.2 dB in weak turbulence.【Conclusion】Based on the known channel state information, a step-by-step optimal signal mapping method for O-OFDM-IM is proposed in this paper, which can effectively improve the BER performance of the system in strong turbulence channels.
