In this paper, a novel opportunistic spectrum sharing scheme, based on orthogonal frequency division multiplexing with index modulation (OFDM-IM), is proposed for cognitive radio (CR) networks. In the considered OFDM-IM based CR (OFDM-IM-CR) model, the primary transmitter (PT) communicates with the primary receiver with the aid of an amplify-and-forward (AF) relay by transmitting OFDM-IM signals. Meanwhile, the secondary transmitter (ST) passively senses the spectrum and transmits its own information over those inactive subcarriers of the primary network to the secondary receiver if the signal-to-noise ratio of the PT $\to $ ST link is above a predefined threshold; otherwise, the ST stays in silent mode. Two different types of maximum-likelihood (ML) detectors are designed for the primary network, based on the knowledge of either the estimated channel state information or the statistical channel information of the secondary network. A complexity-reducing method, which is applicable to both types and achieves near optimal performance, is further proposed. To evaluate the performance, a tight upper bound on the bit error rate (BER) is derived, assuming the first type of ML detection. Simulation results corroborate the analysis and show that OFDM-IM-CR has the potential of outperforming OFDM-CR and OFDM-IM-AF in terms of BER with higher spectral efficiency.

中文翻译：

---

基于OFDM和索引调制的机会频谱共享

在本文中，针对认知无线电 (CR) 网络提出了一种基于正交频分复用和索引调制 (OFDM-IM) 的新型机会频谱共享方案。在所考虑的基于 OFDM-IM 的 CR (OFDM-IM-CR) 模型中，主发射机 (PT) 借助放大转发 (AF) 中继通过传输 OFDM-IM 信号与主接收机进行通信。同时，如果 PT $\to $ ST 链路的信噪比高于预定值，辅助发射机 (ST) 会被动地感知频谱，并通过主网络的那些非活动子载波将自己的信息传输到辅助接收机临界点; 否则，ST 保持静默模式。为主要网络设计了两种不同类型的最大似然 (ML) 检测器，基于对次要网络的估计信道状态信息或统计信道信息的了解。进一步提出了一种适用于两种类型并实现接近最佳性能的降低复杂性的方法。为了评估性能，假设第一种类型的 ML 检测，推导出了比特误码率 (BER) 的严格上限。仿真结果证实了分析，并表明 OFDM-IM-CR 在 BER 方面具有优于 OFDM-CR 和 OFDM-IM-AF 的潜力，具有更高的频谱效率。假设第一种类型的 ML 检测，推导出了比特误码率 (BER) 的严格上限。仿真结果证实了该分析，并表明 OFDM-IM-CR 在 BER 方面具有优于 OFDM-CR 和 OFDM-IM-AF 的潜力，具有更高的频谱效率。假设第一种类型的 ML 检测，推导出了比特误码率 (BER) 的严格上限。仿真结果证实了分析，并表明 OFDM-IM-CR 在 BER 方面具有优于 OFDM-CR 和 OFDM-IM-AF 的潜力，具有更高的频谱效率。