A system can comprise a memory that is configured to store and retrieve a first signal. The system can comprise a generator that is configured to generate first in-phase, quadrature sub-carrier values. The system can comprise a look up table that stores predetermined second in-phase, quadrature sub-carrier values. The system can comprise a pseudo-random look up table generator that is configured to operate on the predetermined second in-phase, quadrature sub-carrier values to produce pseudo-random data values. The system can comprise a component that is configured to inject a second signal into a radio unit, wherein the second signal is selected from the memory, the generator, the look up table, and the pseudo-random look up table generator, and wherein the second signal is configurably switched between a time domain path of a digital front end of the system, and a frequency domain path of the digital front end.