Feature Article (Part 1) - September 2024
brought to you by IEEE Open Journal of Vehicular Technology
IM-OFDM ISAC Outperforms OFDM ISAC by Combining Multiple Sensing Observations
Authors: Hugo Hawkins; Chao Xu; Lie-Liang Yang; Lajos Hanzo
Published in volume 5, IEEE Open Journal of Vehicular Technology
IEEExplore version: https://lnkd.in/eh5ucr89
OFDM has found its way into both the 4G and 5G systems, as well as Wi-Fi and other standards. It has also been investigated in the context of integrated sensing and communications known as ISAC. However, research is under way for enhancing its capabilities and index modulation (IM) is one of the promising exploratory avenues. Briefly, if for example only one out of four subcarriers of a subblock is activated, this allows the transmission of two extra bits and the power conserved by the deactivated subcarriers can be added to the activated one. The associated peak-to-average ratio is also investigated in the paper. However, no evidence is found in the open literature that IM-OFDM sensing is capable of outperforming OFDM sensing, because the blank subcarriers impair the system's sensing functionality. The existing solutions either insert a radar signal into the deactivated subcarriers, thereby using a radar signal for sensing, or employ compressed sensing, which leads to a lower sensing performance than that of OFDM ISAC. Hence, a novel low complexity algorithm is proposed by the authors for ensuring that IM-OFDM does succeed in outperforming its OFDM ISAC counterpart for both communication and sensing. The algorithm collects observations of the received signal to “fill in” the blank subcarriers in the sensing data created by im-ofdm, whilst taking advantage of the increased subcarrier power attained by activating fewer subcarriers. This occurs over multiple transmit frames, which inevitably delays the target estimation. However, since sensing assumes low target velocities, this delay is shown to have a modest impact on the sensing performance of IM-OFDM.
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