A Perspective on Degrees of Freedom for Radar in Radar-Communication Interference Channel

Interference management is a key issue for radar-communication spectrum sharing. Degrees of Freedom (DoF) is a powerful tool to analyze and evaluate the performance of techniques in multi-user interference management scenarios. However, DoF have been studied in detail in communications systems but rarely considered in radar literature. In this paper, we propose a definition of DoF for radar using Rényi information dimension. The definition and properties of Rényi entropy and information dimension are considered. The relationships among radar DoF, diversity order, and diversity gain are studied as well. It is shown that radar diversity gain is controlled by radar DoF such that maximizing DoF leads to maximizing available diversity gain under Neyman-Pearson detection strategy. When exponential distribution assumption is applied, radar DoF equals to diversity gain. The single-user DoF upper bound is established as well. We also proposed a DoF formula for K
_c
+ K
_r
-users radar-communication interference channel. It is shown that interference alignment strategy [1] still works well in K
_c
+ K
_r
-users radar-communication interference channel.