Abstract
Next generation wireless networks are expected to provide much higher data throughput and reliable connections for a far larger number of wireless service subscribers and machine-type nodes, which results in increasingly stringent requirements of spectral efficiency (SE) and energy efficiency (EE). Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) stands out as a promising solution to satisfy the SE requirement with a reasonable increase in system complexity. However, the EE of OFDM-IM is still required to be enhanced. Moreover, diversity gain is difficult to harvest from the frequency domain without affecting the SE for OFDM-IM systems, which hinders further reliability enhancement. In this regard, relay-assisted OFDM-IM, as a promising joint paradigm to achieve both high SE and EE, was proposed and has been studied since last year. The objectives of this study are to summarize the recent achievements of this joint paradigm, articulate its pros and cons, and reveal the corresponding challenges and future work. More importantly, we provide a full picture and insights into the implementation of this new paradigm in next generation networks.
Highlights
Current studies have foreboded the tendency that data throughput and the number of connected nodes in generation wireless networks will tremendously increase, which results in increasingly stringent requirements of spectral efficiency (SE) and energy efficiency (EE) (Andrews et al, 2014; Dang et al, 2020)
Numerical results verify the analysis presented and confirm that the error performance of both primary and secondary user pairs is improved by adopting orthogonal frequency-division multiplexing with index modulation (OFDM-IM) over the cooperative dual-hop structure for overlay cognitive radio (CR)
Apart from the original OFDM-IM scheme relying on the lookup table method and the combinatorial method proposed by Basar et al (2013), there are a plenty of advanced and derivative OFDM-IM schemes, for example, OFDM with generalized IM (OFDM-GIM), OFDM with precoded IM (OFDM-PIM), enhanced OFDM-IM (E-OFDM-IM), vector OFDM-IM (V-OFDM-IM), differential OFDM-IM (D-OFDMIM), multiple-mode OFDM-IM (MM-OFDM-IM), and so on (Basar et al, 2017)
Summary
Current studies have foreboded the tendency that data throughput and the number of connected nodes in generation wireless networks will tremendously increase, which results in increasingly stringent requirements of spectral efficiency (SE) and energy efficiency (EE) (Andrews et al, 2014; Dang et al, 2020) To meet these two requirements, orthogonal frequency-division multiplexing with index modulation (OFDM-IM) was proposed to introduce another modulation domain and an extra degree of freedom (Basar et al, 2013). One can shrink the number of legitimate SAPs to a power of two and resort to the index of SAP to modulate extra bit stream in addition to the bit stream modulated by data constellation symbols carried on active subcarriers In this way, under appropriate system configurations, OFDM-IM is superior to plain OFDM in terms of SE and/or error performance.
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