In this paper, we present a mathematical and simulational model of an ultrasound backscattering communication link for a 1mm3 mm-sized brain implants. The mathematical model and different simulations are validated by measurement. Furthermore, using a piezoelectric crystal and an ultrasound transducer in a water tank setup, two different ultrasound reflection-based modulation methods are presented and measurement results are discussed. We compare the model, simulation, and measurement to gain a better understanding of the channel response. The results shows the poosibility of achieving a bandwidth of up to 140 kb/s using binary modulation and 280kb/s with 4-level ASK.