Physical Limits for In-Band Full Duplex in Frequency-Hopping Tactical Radio Systems

Theoretically, in-band full duplex can double the spectral efficiency of a radio link by using the channel resources in both directions simultaneously. To achieve this, however, the suppression of self-interference must be sufficiently large. In this contribution we investigate the gain in spectral efficiency for full duplex, compared to half duplex, that can be achieved at different levels of self-interference suppression for radio links with parameters typical for tactical radio systems and WiFi systems. Furthermore, we investigate the effects of frequency hopping on the spectral efficiency of full-duplex radio links, and compare this with the corresponding effects on spectral efficiency on half-duplex systems. Numerical examples show that the coupling factor required to achieve a similar relative spectral efficiency gain is in the order of 40 dB more demanding for tactical radio systems than for WiFi systems. It is also concluded that the coupling factor required to achieve a certain spectral efficiency gain decreases with decreasing propagation loss. That is, it is easier to make use of in-band full duplex at shorter communication distances.