Asymptotic energy-distortion performance of zero- and low-delay communication scenarios under additive white Gaussian noise is investigated, both in point-to-point and broadcast settings. Using high-resolution analysis for quantizer design coupled with orthogonal signaling, achievable values for the leading term in the negative logarithm of the distortion, the energy-distortion exponent, are derived. 

In the point-to-point scenario, the higher-order term, the energy-distortion dispersion, is also investigated and optimized while keeping the energy-distortion exponent, at its optimal (respectively, the best known) value, for the zero-delay (respectively, low-delay) regime. In contrast with the decaying dispersion previously reported in the literature, the proposed coding scheme achieves a constant dispersion. When the scheme is optimized, this constant can be increased considerably with respect to its naive value, i.e., that achieved by optimizing purely the source coding performance instead of the end-to-end distortion.