  Energy efficient watermarking preserves the watermark energy after linear
attack as much as possible. We consider in this letter non-stationary signal
models and derive conditions for energy efficient watermarking under random
vector model without WSS assumption. We find that the covariance matrix of the
energy efficient watermark should be proportional to host covariance matrix to
best resist the optimal linear removal attacks. In WSS process our result
reduces to the well known power spectrum condition. Intuitive geometric
interpretation of the results are also discussed which in turn also provide
more simpler proof of the main results.
