Design of Integrated Full-Duplex Wireless Transceivers
Demand for mobile data traffic is projected to exceed 30 exabytes per month in 2020, representing an over 100x increase since 2010. Prior generations of cellular deployments have serviced increased demand largely through use of more bandwidth - from 200KHz in GSM, to now 100MHz in CA-LTE. This method of scaling is closed, as low frequency spectrum has crowded and saturated. A proposed technique to enhance spectrum access in 5G deployments is agile full-duplex (FD) transceivers, which can transmit and receive at overlapped frequencies, or tune to arbitrarily spaced transmit/receive(TX/RX) frequency division duplexed (FDD) channels, to make use of available spectrum. The key problem in such a system is mitigating the interference the system's own transmitter creates for its receiver during simultaneous operation. Current implementations mitigate TX to RX interference at the antenna interface using off-chip, fixed-frequency duplexers, limiting a device's spectrum access to a handful of pre-defined, widely separated TX/RX band combinations. Accordingly, a universal mobile device tunable across global carrier band combinations does not exist.
This work develops a transceiver architecture enabling simultaneous transmission and reception on a single single shared antenna, over a wide frequency tuning range, for FD/FDD systems. The architecture is enabled by an active TX replica which cancels interference at the RX input, a highly linear passive-mixer first receiver design based on class-AB transconductors which operates linearly in the presence of residual TX interference, and digital adaptation techniques which match the interference over time-varying operating conditions. Analysis is presented for the system's fundamental performance bounds in power and sensitivity, leading to noise mitigation techniques which minimize receiver degradation in the presence of the cancellation circuits. The analysis is validated by two chip prototypes, which demonstrate over $>$50dB cancellation of a +16dBm peak 20MHz TX signal, from 1GHz to 2GHz, up to an antenna VSWR of 5:1. This work demonstrates the potential for a fully integrated, frequency-tunable FD/FDD transceiver system, which could ultimately double existing mobile network capacity, and enable a universal duplexer-less radio.