# US 2019/0173518 A1 · Method and system for spread spectrum code acquisition > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0173518 A1 - Document ID: US20190173518A1 - Status: Published application - Kind: A1 - Application number: 16/205,097 - Filed: 2018-11-29 - Published: 2019-06-06 - Earliest claimed: 2017-12-01 - Assignees: RAM Photonics, LLC - Applicants: RAM Photonics, LLC - Inventors: Vahid Ataie - Web page: https://patentgrep.com/patent/US20190173518A1 ## CPC - H04B 1/70754: {Setting of search window, i.e. range of code offsets to be searched (H04B1/70758 takes precedence)} - H04B 1/7085: using a code tracking loop, e.g. a delay-locked loop - H04B 10/2575: Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier - H04B 10/506: {Multiwavelength transmitters} - H04B 10/616: {Details of the electronic signal processing in coherent optical receivers} - H04B 10/6164: {Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator} - H04J 14/0205: {Select and combine arrangements, e.g. with an optical combiner at the output after adding or dropping} - H04L 7/0041: {Delay of data signal} - H04L 7/0075: {with photonic or optical means} - H04B 2001/6908: {using time hopping} - H04B 2201/7073: Direct sequence modulation synchronisation - H04B 2210/006: Devices for generating or processing an RF signal by optical means - H04B: TRANSMISSION - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A code acquisition module for a direct sequence spread spectrum (DSSS) receiver includes: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame. ## Claims ### Claim 1 A method for synchronizing a direct sequence spread spectrum (DSSS) frame, the method comprising: generating a preamble-codeword in a frequency domain for the DSSS frame by selecting a finite number of non-uniformly distributed frequencies corresponding to frequencies detectable by a Sparse Discrete Fourier Transform (SDFT) at which spectral peaks will occur; generating a preamble in a time domain based on the preamble-codeword; prepending the preamble to a coded data stream to form the DSSS frame; and transmitting the DSSS frame. ### Claim 2 (depends on 1) The method of claim 1, wherein each of the finite number of non-uniformly distributed frequencies have higher spectral power than a background power spectral density of the preamble-codeword. ### Claim 3 (depends on 1) The method of claim 1, wherein the finite number of non-uniformly distributed frequencies comprise randomly selected frequencies. ### Claim 4 (depends on 1) The method of claim 1, wherein the finite number of non-uniformly distributed frequencies comprise specifically selected frequencies. ### Claim 5 (depends on 1) The method of claim 1, further comprising generating a different preamble-codeword after the preamble-codeword has been used for a predetermined period of time. ### Claim 6 (depends on 1) The method of claim 1, further comprising: receiving the DSSS frame; generating sparse Fourier coefficients of the preamble-codeword by performing the SDFT on the preamble; generating complex conjugates of the sparse Fourier coefficients based on a reference codeword; and multiplying the sparse Fourier coefficients by the complex conjugates of the sparse Fourier coefficients. ### Claim 7 (depends on 6) The method of claim 6, wherein the reference codeword comprises the preamble-codeword agreed upon in advance between a transmitter and a receiver. ### Claim 8 (depends on 6) The method of claim 6, further comprising generating a delay estimation signal by applying an iterative filtering algorithm to results of the multiplication. ### Claim 9 (depends on 6) The method of claim 6, further comprising generating a delay estimation signal by applying a Sparse inverse Discrete Fourier Transform (SiDFT) algorithm to results of the multiplication. ### Claim 10 A code acquisition module for a direct sequence spread spectrum (DSSS) receiver, the code acquisition module comprising: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame. ### Claim 11 (depends on 10) The code acquisition module of claim 10, wherein the finite number of non-uniformly distributed frequencies comprise sparsely allocated spectral peaks determined by a preamble-codeword. ### Claim 12 (depends on 10) The code acquisition module of claim 10, wherein the complex conjugate Fourier coefficients are calculated based on a reference codeword, wherein the reference codeword comprises a preamble-codeword agreed upon in advance by the DSSS receiver and a transmitter. ### Claim 13 (depends on 10) The code acquisition module of claim 10, wherein the filter module is configured to accept an input signal from the multiplier, apply an iterative filtering algorithm to the input signal, and output a delay estimation signal. ### Claim 14 (depends on 10) The code acquisition module of claim 10, wherein the filter module is configured to accept an input signal from the multiplier, apply a Sparse inverse Discrete Fourier Transform (SiDFT) algorithm to the input signal, and output a delay estimation signal. ### Claim 15 (depends on 10) The code acquisition module of claim 10, wherein the SDFT module, the multiplier, and the filter module comprise a digital signal processor. ### Claim at position 16 -20. (canceled) ### Claim 21 (depends on 1) The method of claim 1, wherein a ratio of preamble duration to coded data stream in each DSSS frame is assigned to hide the spectral peaks of a preamble portion of the DSSS frame in a white noise spectrum of the coded data stream. ### Claim 22 (depends on 1) The method of claim 1, further comprising generating a different preamble-codeword after the preamble-codeword has been used for a predetermined number of transmitted frames. ### Claim 23 (depends on 3) The method of claim 3, wherein the randomly selected frequencies are randomly distributed within negative and positive frequencies. ### Claim 24 (depends on 4) The method of claim 4, wherein the specifically selected frequencies are selected symmetrically around a center frequency. ### Claim 25 (depends on 10) The code acquisition module of claim 10, wherein the SDFT module comprises an application specific integrated circuit (ASIC).