Degrees of Freedom in Scattered Fields for Trade-off in Joint Communications and Sensing

In joint communications and sensing (JCS), the same electromagnetic (EM) wave is used for both functions, in the forward (incident) and backward (scattered) channels, respectively. The communication channel is determined by scatterers (also as sensing targets), thus coupling the performances of communications and sensing. More scattering targets generate more degrees of freedom (DoFs) for communications, thus improving the channel capacity given sufficient antennas. Meanwhile, they also result in more sensing errors due to the increasing complexity of EM field. The complexity analysis of EM field, in terms of DoFs, is applied to analyze the trade-off between communications and sensing, as the complexity of scattering targets increases. Numerical results are calculated to demonstrate the performance trade-off between communications and sensing.