A patient bed includes a patient support, with a headboard, a footboard, and a plurality of side rails. A message with a smallest backoff time is selected and placed into the hardware backoff counter. The method includes identifying one or more unmodulated subcarriers in a received waveform, processing the one or more unmodulated subcarriers to produce a demodulated output, and determining a noise variance based on the demodulated output. Accordingly, while sitting on the chair, the present invention allows no deformation on the rigid hemispherical seat, and keeps the spine of the user in a desirable alignment, further improving the internal function of the user’s organs. The method includes converting an input image of a first non-linear color space into a second linear color space; determining a brightness control ratio; adjusting channels of the second linear color space according to the brightness control ratio; converting the second linear color space into the first non-linear color space to form an output image.