LPI/LPD communication systems
View Patent ↗In a wireless communication system, a secure communication link is provided by selecting a decoy data signal vector for transmission, generating a MIMO precoding matrix from a message to be sent; and multiplying the decoy data signal vector by the MIMO precoding matrix to construct a precoded signal vector. The MIMO precoding matrix produces information-bearing synthesized channel distortions in the transmitted signal. An undistorted version of the decoy data may be transmitted to an intended receiver. The receiver distinguishes between the synthesized information-bearing channel distortions and natural channel distortions to decrypt the information, while an eavesdropper would find it difficult to distinguish between natural and synthesized channel distortions in the signals it receives.
1. A communication method, comprising:
selecting a decoy data signal vector for transmission;
generating a MIMO precoding matrix from a message to be sent; and
multiplying the decoy data signal vector by the MIMO precoding matrix for constructing a precoded signal to be transmitted, the precoded signal comprising information-bearing synthesized channel distortions;
multiplexing a reference signal and the precoded signal for transmission to a receiver; wherein the receiver decrypts the message in the precoded signal based on channel estimation performed on the reference signal.
2. The method of claim 1 , wherein the MIMO precoding matrix is a function of channel measurements.
3. The method of claim 1 , wherein the MIMO precoding matrix comprises transmit power values for each of a plurality of spatial subchannels based on the message and calculated eigenvalues of matrix HH † , where H is an estimated MIMO channel matrix.
4. The method of claim 1 , wherein generating the MIMO precoding matrix comprises generating time-varying features of the MIMO precoding matrix based on the message.
5. The method of claim 1 , wherein generating a MIMO precoding matrix comprises employing Cooperative MIMO.
6. The method of claim 1 , further comprising receiving the precoded signal at an intended receiver, the intended receiver configured to remove the decoy data signal vector and decrypt the message by decoding the MIMO precoding matrix.
7. The method of claim 1 , wherein generating the MIMO precoding matrix comprises producing transmit power values for each spatial subchannel based on calculated eigenvalues and the message.
8. The method of claim 1 , wherein the precoded signal matrix is expressed by a linear transformation, s=VPx, where V is an N T ×N SS transmit beamforming/precoding matrix obtained from a singular value decomposition of H, P is an N SS ×N SS diagonal matrix where [P] i,i =P i for i=1, 2, . . . , N SS , where each P i represents transmit power allocated to a corresponding i th spatial subchannel, and xϵA N ss is a reference symbol vector drawn from a unit-energy constellation set A, and wherein N T is a number of uncorrelated transmitting antennas, and N SS is a number of spatial subchannels per subcarrier frequency.
9. The method of claim 1 , further comprising providing the decoy data signal vector to an intended receiver by at least one of transmitting a clean version of the decoy data signal vector; employing a predetermined third-party broadcast to produce the decoy data signal vector; providing the decoy data signal vector to the intended receiver prior to employing the decoy data signal vector as a carrier signal; providing for generating a copy of the decoy data signal vector at the intended receiver; and employing channel measurements for determining the decoy data signal vector.
10. A non-transitory computer readable storage medium having computer readable code thereon configured to perform the method of claim 1 .
11. A communication method, comprising:
determining a decoy data signal vector used in a precoded signal in a transmission received from a transmitter;
determining a secret key from an estimated channel matrix H; and
decrypting a message embedded in the precoded signal, wherein decrypting comprises removing the decoy data signal vector and channel distortions from the precoded signal.
12. The communication method of claim 11 , wherein determining the decoy data signal vector comprises at least one of receiving a clean version of the decoy data signal vector from a transmission by the intended transmitter, receiving the clean version of the decoy data signal vector from a third-party broadcast, receiving a predetermined decoy data signal vector prior to the received transmission from the intended transmitter, and locally generating a copy of the decoy data signal vector.
13. The communication method of claim 11 , wherein decrypting comprises performing a singular value decomposition of H, and calculating corresponding eigenvalues.
14. A non-transitory computer readable storage medium having computer readable code thereon configured to perform the method of claim 11 .
15. A transmitter, comprising:
a reference signal generator configured to produce a decoy data signal vector for transmission;
a distortion synthesizer configured to produce a MIMO precoding matrix from a data signal and channel state information; and
a precoder configured to employ the MIMO precoding matrix to precode the decoy data signal vector to produce a precoded signal to be transmitted;
a multiplexer configured to multiplex a reference signal and the precoded signal for transmission to a receiver; wherein the receiver decrypts the message in the precoded signal based on channel estimation performed on the reference signal.
16. The transmitter of claim 11 , wherein the reference signal generator comprises an OFDM transmitter, and the decoy data signal vector comprises at least one of data subchannels and pilot subchannels.
17. The transmitter of claim 11 , wherein the distortion synthesizer comprises a singular value decomposition beamformer.
18. The transmitter of claim 11 , further comprising an RF front end that comprises a distributed antenna system.