The Discrete Hilbert Transform for Non-Periodic Signals
  This note investigates the size of the guard band for non-periodic discrete Hilbert transform, which has recently been proposed for data hiding and security applications. It is shown that a guard band equal to the duration of the message is sufficient for a variety of analog signals and is, therefore, likely to be adequate for discrete or digital data. 
Sumanth Kumar Reddy Gangasani