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Summary form only given, as follows. Laboratory experiments, carried out at MIT Plasma Science and Fusion Center with the Versatile Toroidal Facility, have been conducted to simulate ionospheric plasma heating caused by high frequency (HF) radio waves. Recent VTF laboratory experiments have successfully reproduced "cascading" and "Frequency-upshifted" spectra of HF wave-enhanced Langmuir waves resembling the spectra observed in Arecibo experiments. The VTF experimental results are well-explained using the source mechanism proposed by Kuo and Lee [Geophys. Res. Lett, 19, 249, 1992] to interpret observed Langmuir wave spectra at Arecibo, Puerto Rico. This mechanism is referred to as a nonlinear scattering of parametric decay instability (PDI)-excited Langmuir waves by pre-existing lower hybrid waves to preferentially produce anti-Stokes (i.e., frequency-upshifted) Langmuir waves. Recent radar spectral observations of anti-Stokes Langmuir waves at Arecibo with improved range and time resolution [Sulzer and Fejer, J. Geophys. Res., 99, 15,035, 1994] can be reasonably understood in terms of this nonlinear scattering process.