This technology enables synthetic or inverse synthetic aperture radar (I/SAR) techniques to be performed on independent transmitters and receivers, which do not necessarily share a common frequency or clock reference. It has commercial applications in processes that involve synthetic aperture radar imaging, localization, and gesture sensing between distributed wireless nodes, and can be used for example, to develop a wireless device that can identify the locations of cellular phones in the environment or a Wi-Fi access point that can localize surrounding client nodes.
A receiving wireless node may perform SAR and ISAR techniques on signals from independent transmitter devices to measure the relative power of the signals it receives from this transmitter. The key challenge to enable this technology is that radar techniques require both the transmitter and receiver to share a common frequency or clock reference. This is because independent transmitters and receivers suffer from a frequency offset between their clocks, as well as phase noise. The Inventors have developed a technology which leverages the multiple-input, multiple output (MIMO) capability of a multi-antenna receiver to perform radar techniques despite these frequency offsets.
This method considers a multi-antenna MIMO receiver that receives signals from a single or multi-antenna transmitter node. At least one of the antennas of the receiver can either translate or rotate, while at least one other antenna remains static. The receiver measures the wireless channels from the transmitter node to these antennas over time. The inventors show that the ratio of the channels from any single transmit antenna to the receiver’s moving antenna and static antennas is independent of frequency offset. This ratio can therefore be used instead of the wireless channels themselves to perform SAR. As a consequence, this system allows a wireless receiver to calculate the relative power of the signals it receives from any particular wireless transmitter along any given direction. Further, it does not require any additional modification to or feedback from the transmitter nodes.
To perform SAR, a wireless receiver must periodically estimate the wireless channel from a transmitter node. As a result, the receiver needs to be aware of the actual signal transmitted by the wireless transmitter. However, if the transmitter is a single-antenna device, this system offers the additional advantage of not requiring prior knowledge of the actual signal transmitted by the transmitter node. In other words, the receiver can perform SAR from a single-antenna transmitter, purely from the received signals, without actually estimating the wireless channels from this transmitter to its receiver antennas.
- System can perform SAR from a single-antenna transmitting node without being aware of the precise signal transmitted by that node in the specified frequency
- Technology can extend to the case of a multi-antenna transmitter or generalize to single antenna OFDM transmitters