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UBC Theses and Dissertations

A broadband self-interference cancellation circuit for simultaneous full-duplex radio applications El Sayed, Ahmed


All wireless communication systems so far have employed either time division duplexing (TDD), where the transmitter and receiver share the same frequency band but operate in orthogonal time slots, or frequency division duplexing (FDD), where the time slots are shared but orthogonal frequency bands are used. In order to meet the requirements for the upcoming 5G mobile standards, the concept of simultaneous full-duplex is being actively pursued, where both time slots and frequency bands can be shared between the transmitter and the receiver. The greatest hurdle in achieving full-duplex communication is the self-interference from the transmitter that is several orders of magnitude stronger than the desired signal at the receiver. Realizing such broadband cancellation has been hitherto very challenging, because not only does it demand broadband cancellation in amplitude, phase and group delay of the echo signals, but also require such a cancellation circuit to be linear, low-noise and ultra-compact for a mobile form factor. This work will demonstrate the first self-interference radio-frequency cancellation circuit that achieves an 80 MHz linear time evolution (LTE) cancellation bandwidth in a linear, tunable, compact, and fully monolithic integrated circuit (IC) implementation for such full-duplex radios. A proof-of-concept prototype is realized in 0.13 µm complementary metal oxide semiconductor (CMOS) process that utilizes techniques such as frequency translations and baseband Hilbert transforms to attain a measured 23 dB of self-interference cancellation over an 80MHz signal bandwidth. The entire circuit consumes 34 mW from a 1.2V supply in an active area of just 0.84 mm².

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