Figure 1

Example: relative positions of a sensor (${\mathbf{x}}_{{\mathit{S}}_{\mathit{j}}}$)and of a primary user(${\mathbf{x}}_{{\mathit{P}}_{\mathit{i}}}$). The angle θ_i,j is defined with respect to a common reference system (horizontal axis in the figure), while ${\tilde{\theta }}_{i,j}$ is defined with respect to the orthogonal to the positive direction of the sensor array axis.