Plasma turbulence can result in significant distortion of probing and receiving microwave beams, and this effect can modify the registered spectrum in a collective Thomson scattering (CTS) experiment. An analytical description of the CTS experiment is provided in this paper for the probing beam distortion due to the plasma edge turbulence. The effect of the registered frequency spectrum distortion by the turbulence is evaluated for different turbulence levels for plasma parameters similar to those excepted in ITER.