# A Novel Space–Time Coding Echo Separation Scheme with Orthogonal Frequency Division Multiplexing Chirp Waveforms for Multi-Input Multi-Output Synthetic Aperture Radar

## TL;DR

This paper introduces a new method to separate overlapping radar signals in MIMO-SAR systems using space-time coding and OFDM chirp waveforms to reduce interference and improve signal quality.

## Contribution

A novel STC scheme using complex orthogonal matrices and OFDM waveforms is proposed for effective echo separation in MIMO-SAR systems.

## Key findings

- The proposed STC scheme forms a multidimensional orthogonal matrix to recover superposed signals and improve SNR.
- OFDM waveforms reduce cross-correlation interference, enabling effective echo separation.
- Numerical experiments confirm the effectiveness of the new waveform scheme.

## Abstract

Multi-input Multi-output Synthetic Aperture Radar (MIMO-SAR) systems significantly improve the performance of traditional SAR systems by providing more system freedom. However, in the working mode of the simultaneous transceiver, each receiving antenna will receive the scattered echoes of all transmitting antennas, resulting in the overlapping of echo data and serious related interference, which becomes the main obstacle to the further development and application of MIMO-SAR system. Therefore, achieving effective echo separation is the key technical challenge faced by the MIMO-SAR system. Space–time coding (STC) uses multiple dimensions, such as space, time, and frequency. Through the process of encoding and decoding in these dimensions, channel information can be obtained, and echo separation can be realized. STC is suitable for MIMO-SAR system on different platforms, such as airborne, and has wide applicability. When the traditional scheme uses STC as a coding scheme, it is generally limited by the two-dimensional sending and receiving matrix of Alamouti code. To solve this problem, a new STC scheme based on complex orthogonal matrix design is proposed in this paper. The scheme can form a multidimensional orthogonal STC matrix, recover the superposed signal by echo decoding, and improve the echo signal-to-noise ratio (SNR) of MIMO-SAR. In addition, the use of orthogonal frequency division multiplexing (OFDM) waveform can further reduce cross-correlation interference to achieve effective separation of MIMO-SAR echoes. The effectiveness of the waveform scheme is verified by numerical experiments.