O-OFDM索引调制的分步优化信号映射方法

A Step-by-step Optimal Signal Mapping Method for O-OFDM Index Modulation

【目的】采用随机映射以及传统星座图会导致已有光正交频分复用(O-OFDM)-索引调制(IM)系统的误码率(BER)性能无法达到最优,因此,文章基于激活子载波的最优选择以及星座图的最优旋转提出了一种分步优化信号映射方法,旨在通过分步优化信号映射方法实现O-OFDM-IM系统BER性能的改善。【方法】在发射端,首先依据信道状态信息,采用信道范数最大化准则选择最优激活子载波组合;其次,利用信道状态信息,以∂=0.5°为步长,采用穷举搜索算法得到最优星座图;之后,将通过旋转获得的最优星座图加载到激活的子载波上进行信号传输;最后在接收端利用最大似然(ML)检测算法对原始信号进行恢复来实现最小的系统错误概率。【结果】仿真表明,在强湍流、BER=10-4和调制阶数为16的条件下,采用文章所提方法后,(4,2)O-OFDM-IM系统的信噪比(SNR)降低了约1.45 dB。此外,随着湍流强度的增大,BER性能的改善更明显。如,8正交幅度(QAM)、BER=10-4时,(4,2)O-OFDM-IM系统的SNR在强湍流下降低了约1.35 dB,在弱湍流下则降低了1.2 dB。【结论】由仿真结果可知,在已知信道状态信息的前提下,文章所提方法可有效改善湍流信道下系统的BER性能。

【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.