Feasibility of full duplex communications for LEO satellite

Simultaneously transmitting and receiving on the same frequency has long been considered a fundamental impossibility in wireless communication. Recent research activity has sought to challenge this limit. The main challenge is dealing with very high self-interference due to the high power transmit (TX) signal leaking into the receive (RX) path. The larger the difference between the TX and RX power, the more challenging the problem. A link to a low Earth orbit (LEO) satellite requires at least 130 dB of cancellation for full duplex communication to be achievable. This paper presents initial results for a ground-LEO full-duplex link. Starting with a link budget, we derive the expected power levels, and therefore the required cancellation. We then formulate features of the satellite channel that make it feasible to even consider achieving 130 dB of cancellation. Unlike previous efforts that focused on relatively low-cost implementations suitable for commercial market, this effort relies on expensive and hand-tuned components. The initial goal is to develop a link suitable for a small LEO satellite (e.g. cubesat) with limited (1 MHz) bandwidth. The paper then provides initial experimental results using high-end RF and mixed-signal components. Cancellation is achieved using a combination of RF and baseband techniques. This paper presents the best known amount of self-interference cancellation with RF and baseband techniques. This goal is clearly ambitious and the work is not yet complete. However, the results are promising enough to warrant additional research.