LTE tool box noise calibration

I am using the LTE Toolbox and exploring the example code: "PDSCH 2x2 Spatial Multiplexing Throughput Conformance Test". Thermal noise is added to the baseband LTE complex envelope starting at line 262 of the example code where calibration begins. Gaussian noise is added to the LTE waveform at line 276 of the example code. The calibration code is very simple Matlab code, however, the basis for the calibration in lines 262 through 276 seems, to me, to not be consistent with previous sources of noise calibration theory with which I am familiar. Specifically, "Simulation of Communication Systems" by Jeruhim, Balaban, and Shanmugan, Klewer, 2000, page 538. I will be grateful if someone could guide me to the theoretical foundation supporting lines 262 - 278 of the example code. S