Radar, like a bat in a cave, sends out a pulse and listens for the echo. But a microscopic imbalance in the receiver is unavoidable: it scrambles frequencies and creates a phantom twin for each target, like a second, slightly distorted echo.
Usually, these phantoms just get in the way and are cleaned up beforehand. In this new work, ghost echoes become an ally. Each real target and its twin are tightly linked, like a figure and its shadow. Scientists built an algorithm that, for any point in space, cycles through all possible 'target-phantom' pairs, comparing them through a special mathematical pattern. This makes it easier to spot faint objects — even when receiver distortions are large.
The method was tested in simulations. Surprisingly, the more noticeable the hardware defect, the more reliably the algorithm works, because the phantoms become brighter. This approach is a step toward systems that simultaneously transmit data and scan the surroundings (ISAC). In spirit, it resembles the search for dark matter by its invisible influence or teasing out gravitational waves from noise. At its core lies signal spectroscopy — breaking down frequencies, without which radar would remain blind.
as written by the authors arXiv:2607.14775
Receiver in-phase/quadrature imbalance (IQI) couples each OFDM subcarrier with its mirror counterpart, creating ghost targets and degrading range-Doppler recovery in orthogonal frequency division multiplexing (OFDM) integrated sensing and communication (ISAC). Instead of first compensating for IQI and then applying conventional processing, this letter exploits the structure of the IQI-impaired observation directly. We show that each physical target induces coupled direct and mirror components linked through the target coefficient and its conjugate, which motivates an elliptic atom group representation for each candidate delay-Doppler cell. Based on this model, we propose an elliptic group orthogonal matching pursuit detector that performs sparse recovery directly on the received OFDM grid. The required correlations are computed efficiently through two weighted two-dimensional fast Fourier transforms (FFTs) followed by local group projections. Numerical results show that the proposed method improves exact support recovery and weak-target detection compared to corresponding benchmarks, especially under moderate and strong receiver IQI.
ISAC systems let a single device transmit data and scan the environment simultaneously, as if your Wi-Fi router could see through walls.
Such radars bring us closer to Star Trek technology, where ships instantly detect each other across vast distances despite any interference.