This communication method creates a type of interference called inter-symbol interference, or ISI, for any intended receivers of the carrier transmission. ISI is basically what happens when echoes cause a signal to interfere with itself. Since this communication method modulates the amount of echo in the carrier transmission, I can only assume that any typical anti-ISI techniques used by most receiver designs (e.g. rake receiver) would be confused by the rapidly-changing ISI caused by these devices, increasing the total noise present in the received signal.