Feedback Receivers: Specification and State-of-the-Art Review

In transmitters of cellular modems of many generations, feedback receivers (FBR) have been playing an important role in controlling the quality of the transmit signal. What set feedback receivers apart from other receivers (RX) are their requirements needed to provide measurements of the transmitter (TX) on-chip while not consuming significant extra power. Whereas many publications and proposed architectures for normal receivers exist, there is very little literature dedicated for feedback receivers. This paper explains the requirements of cellular modems' feedback receivers, describes some of its design challenges with examples based on the 5G NR standard, and outlines some of the state-of-the-arts descriptions. This paper should serve as a motivation and basis for other researchers to contribute to the field.