  We consider the problem of transmitting a source over an infinite-bandwidth
additive white Gaussian noise channel with unknown noise level under an input
energy constraint. We construct a universal scheme that uses modulo-lattice
modulation with multiple layers; for each layer, we employ either analog linear
modulation or analog pulse position modulation (PPM). We show that the designed
scheme with linear layers requires less energy compared to existing solutions
to achieve the same quadratically increasing distortion profile with the noise
level; replacing the linear layers with PPM layers offers an additional
improvement.
