Correlation estimation for digital communications using transmitted reference technique with wideband random noise waveforms
Ultra wideband (UWB) noise communication system using spread spectrum technique is proposed for a covert data transmission through additive white Gaussian noise (AGWN) channel. Wireless communication systems apply the transmitted reference (TR) techniques for a covert data transmission on the base of UWB noise waveforms. Coherent noise reference, required for optimal signal processing in correlation receiver, is transmitted through wireless channel simultaneously with informative noise waveforms modulated by data symbols. Proposed communication system, using the time diversity of the noise reference, accomplishes the relative time delay of informative noise carriers at different time intervals Т <sub>1</sub> or Т <sub>0</sub>. Noise signals with the time delay Т <sub>1</sub> are modulated by antipodal informative symbols according to data stream. Noise signals delayed at the time Т <sub>0</sub> are modulated by conjugate binary symbols . The spectral interference in result of the linear superposition is occurred between the noise reference and delayed informative noise signals in TR transmitter. Spectral power density of result noise signals is modulated by three harmonic functions with the periods in inverse proportion to relative time delays: Т <sub>1</sub>; Т <sub>0</sub>; ( Т <sub>1</sub> - Т <sub>0</sub>). The time convolution of received continuous noise waveforms during every informative symbol is produced using the two-channel correlation receiver. The time delay in each receiver correlation channel corresponds to the diversity time delay Т <sub>1</sub> or Т <sub>0</sub> of informative noise signals. The correlation estimation problem arises when data transmitting is produced utilizing continuous noise waveforms. The potentially performances of communication systems normally degrade, if the energy of informative noise carriers randomly varies in the digital data stream. Correlation estimations are statistical evaluated for data transmission throw AGWN channel. Intersystem jamming is excited at the output of two channel correlation receiver even if message data are transmitted over a wireless channel without thermal noise. This paper proposes the method of intersystem jamming reduction when the necessary requirements are satisfied, namely informative time delays ( Т <sub>1</sub>, Т <sub>0</sub>), its difference ( Т <sub>1</sub> - Т <sub>0</sub>) and next expressions ( Т <sub>1</sub> - 2 Т <sub>0</sub>); ( Т <sub>0</sub> - 2 Т <sub>1</sub>) significantly exceed the coherent interval of UWB noise carriers. Exclusion principles to utilize closely spaced and two multiple informative time delays in the process of the spectrum modulation are considered.