One-Way Ramp to a Two-Way Highway

Since the invention of the radio, transmission and reception have been separated to protect the receiver (Rx) from being jammed by self-interference (SI), i.e., the interference that comes from the colocated radio transmitter (Tx). This separation is called duplexing. Today's wireless systems still rely on duplexing to avoid SI-many short-range or local area radios, such as Bluetooth and WiFi transceivers, transmit and receive in nonoverlapping time slots, called time-division duplexing (TDD), while other modern wireless systems, such as the majority of today's cellular systems, use frequencydivision duplexing (FDD) to separate the transmission and reception in the frequency domain. Both TDD and FDD are half duplex, where the separation of the transmitted and received signals of a single user in either frequency or time causes © 2000-2012 IEEE.