# US 10,122,694 B2 · LPI/LPD communication systems > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,122,694 B2 - Document ID: US10122694B2 - Status: Granted - Kind: B2 - Application number: 15/943,683 - Filed: 2018-04-02 - Published: 2018-08-16 - Granted: 2018-11-06 - Earliest claimed: 2012-02-02 - Assignees: Department 13, LLC - Applicants: Department 13, Inc. - Inventors: Steve J Shattil; Robi Sen - Web page: https://patentgrep.com/patent/US10122694B2 ## CPC - H04W 16/14: Spectrum sharing arrangements {between different networks} - H04B 7/0456: Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting - H04L 5/0007: {the frequencies being orthogonal, e.g. OFDM(A) or DMT} - H04L 5/0055: {Physical resource allocation for ACK/NACK (for physical mapping arrangements in ARQ protocols H04L1/1861)} - H04L 9/0875: {based on channel impulse response [CIR]} - H04L 63/061: {for key exchange, e.g. in peer-to-peer networks (cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838)} - H04W 12/041: Key generation or derivation - H04W 12/08: Access security - H04W 72/541: using the level of interference - H04L 63/0435: {wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption (cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06)} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract 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. ## Claims ### Claim 1 An apparatus, comprising: at least one processor; and a non-transitory computer-readable memory communicatively coupled to the at least one processor, the memory including a set of instructions stored thereon and executable by the processor for: selecting a decoy data signal vector for transmission; generating a MIMO precoding matrix from a message to be sent; multiplying the decoy data signal vector by the MIMO precoding matrix to construct a precoded signal to be transmitted, the precoded signal comprising information-bearing synthesized channel distortions; and multiplexing a reference signal with the precoded signal to produce a multiplexed signal to be transmitted to a receiver, wherein the receiver employs channel estimates and the reference signal to decrypt the precoded signal. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the MIMO precoding matrix is a function of channel measurements. ### Claim 3 (depends on 1) The apparatus 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. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein generating the MIMO precoding matrix comprises generating time-varying features of the MIMO precoding matrix based on the message. ### Claim 5 (depends on 1) The apparatus of claim 1, wherein generating a MIMO precoding matrix comprises employing Cooperative MIMO. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the non-transitory computer-readable memory further comprises instructions for transmitting the precoded signal to an intended receiver, the intended receiver configured to remove the decoy data signal vector and decrypt the message by decoding the MIMO precoding matrix. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein generating the MIMO precoding matrix comprises producing transmit power values for each of a plurality of spatial subchannels based on calculated eigenvalues and the message. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the precoded signal matrix is expressed by a linear transformation, s=VPx, where V is an NT×Nss transmit beamforming/precoding matrix obtained from a singular value decomposition of H, P is an Nss×Nss diagonal matrix where [P]i,i=Pi for i=1, 2, . . . , Nss, where each Pi represents transmit power allocated to a corresponding ith spatial subchannel, and x∈ANss is a reference symbol vector drawn from a unit-energy constellation set A, and wherein NT is a number of uncorrelated transmitting antennas, and Nss is a number of spatial subchannels per subcarrier frequency. ### Claim 9 (depends on 1) The apparatus of claim 1, wherein the non-transitory computer-readable memory further comprises instructions for 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. ### Claim 10 An apparatus, comprising: a processor; and a non-transitory computer-readable memory communicatively coupled to the processor, the memory including a set of instructions stored thereon and executable by the processor for: 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. ### Claim 11 (depends on 10) The apparatus of claim 10, 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. ### Claim 12 (depends on 10) The apparatus of claim 10, wherein decrypting comprises performing a singular value decomposition of H, and calculating corresponding eigenvalues. ### Claim 13 (depends on 10) The apparatus of claim 10, wherein the estimated channel matrix H is calculated following a discrete Fourier transform of the transmission received from the transmitter. ### Claim 14 (depends on 10) The apparatus of claim 10, wherein the estimated channel matrix H is a multiple-input, multiple-output (MIMO) channel matrix. ### Claim 15 (depends on 10) The apparatus of claim 10, wherein decrypting comprises performing multiple-input, multiple-output (MIMO) processing. ### Claim 16 (depends on 10) The apparatus of claim 10, wherein determining the secret key comprises calculating eigenvalues of matrix HH†. ### Claim 17 An apparatus, comprising: a processor; and a non-transitory computer-readable memory communicatively coupled to the processor, the memory including a set of instructions stored thereon and executable by the processor for: producing a decoy data signal vector for transmission; generating a MIMO precoding matrix from a data signal and channel state information; employing the MIMO precoding matrix to precode the decoy data signal vector to produce a precoded signal to be transmitted; and multiplexing a reference signal with the precoded signal to produce a multiplexed signal to be transmitted to a receiver, wherein the receiver employs channel estimates and the reference signal to decrypt the precoded signal. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the decoy data signal vector comprises at least one of data subchannels and pilot subchannels. ### Claim 19 (depends on 17) The apparatus of claim 17, wherein generating the MIMO precoding matrix comprises singular value decomposition. ### Claim 20 (depends on 17) The apparatus of claim 17, further comprising instructions stored on the non-transitory computer-readable memory configured for transmitting the precoded signal and the decoy data signal from a distributed antenna system.