The service limitations of conventional orthogonal frequency division multiplexing (OFDM)-based technologies have motivated academia and industry to seek for new solutions in order to support the emerging services and use cases of future wireless networks. In this chapter, promising frequency-domain index modulation (IM) options, i.e., OFDM with IM (OFDM-IM), generalized OFDM with index modulation (OFDM-GIM), dual-mode OFDM (DM-OFDM), OFDM with interleaved subcarrier IM (OFDM-ISIM), are considered as complementary waveforms of classical OFDM. In frequency-domain IM, data information is sent not only via modulated subcarriers but also via proper activation of the subcarriers resulting in higher spectral efficiency (SE) and better error performance compared with OFDM-based schemes. Furthermore, features of OFDM, including intelligent subcarrier selection and adaptive activation ratio, are assessed. Lastly, the flexible utilization of these features is discussed to control channel effects, hardware impairments, asynchronicity, and to serve wide range requirements of fifth generation (5G) and beyond networks.

Chapter Contents:

• 6.1 Introduction
• 6.2 Index modulation in frequency domain: OFDM with index modulation
• 6.2.1 Maximum likelihood detector
• 6.2.2 Log-likelihood ratio detector
• 6.3 State-of-the-art OFDM-IM solutions
• 6.3.1 Interleaved OFDM-IM
• 6.3.2 Generalized OFDM-IM
• 6.3.3 Dual-mode OFDM
• 6.3.4 Coordinate interleaved OFDM-IM
• 6.4 Flexible OFDM with IM
• 6.4.1 Subcarrier mapping scheme
• 6.4.1.1 Equal bit protection
• 6.4.1.2 Robustness against asynchronous transmission
• 6.4.1.3 Avoiding deep fading
• 6.4.2 Subcarrier activation ratio
• 6.4.2.1 Avoiding Doppler spread
• 6.4.2.2 Robustness against hardware imperfection
• 6.4.2.3 Securing communication link
• 6.5 Discussions and future directions
• 6.6 Conclusion
• Acknowledgment
• References

Inspec keywords: frequency-domain analysis; OFDM modulation; waveform analysis; wireless channels; 5G mobile communication

Other keywords: interleaved subcarrier IM; frequency-domain index modulation options; orthogonal frequency division multiplexing; modulated subcarriers; DM-OFDM; intelligent subcarrier selection; fifth generation networks; service limitations; OFDM-based schemes; future wireless networks; index modulation-based flexible waveform design; 5G neworks; classical OFDM; OFDM-ISIM; OFDM-IM; frequency-domain IM; adaptive activation rati; dual-mode OFDM; OFDM-GIM

Subjects: Mathematical analysis; Mobile radio systems; Modulation and coding methods