Method and system for spread spectrum code acquisition
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.
1. A method for operating a direct sequence spread spectrum (DSSS) receiver, the method comprising:
receiving a synthesized preamble codeword (c[n]);
receiving a coded DSSS frame including the synthesized preamble codeword and a coded data stream;
performing sparse discrete Fourier transform (SDFT) on the coded DSSS frame to produce sparse Fourier coefficients of the coded DSSS frame;
generating complex conjugate SDFT coefficients (C*[K]) of the synthesized preamble codeword;
multiplying the sparse Fourier coefficients of the coded DSSS frame by the complex conjugate SDFT coefficients of the synthesized preamble codeword to generate a Fourier transform of a cross-correlation between the coded DSSS frame and the synthesized preamble codeword;
generating a delay estimation signal, wherein generating the delay estimation signal comprises applying an iterative filtering algorithm to the Fourier transform that is generated by multiplying the sparse Fourier coefficients of the coded DSSS frame by the complex conjugate SDFT coefficients of the synthesized preamble codeword; and
despreading the coded DSSS frame.
2. The method of claim 1 , wherein the complex conjugate SDFT coefficients of the synthesized preamble codeword are generated by performing SDFT on the synthesized preamble codeword.
3. The method of claim 1 , further comprising using a different preamble codeword after the synthesized preamble codeword has been used for a predetermined period of time.
4. The method of claim 1 , further comprising using the delay estimation signal as an input to a despreading module to synchronize decoding of the coded DSSS frame.
5. The method of claim 4 , wherein the despreading module is operable to produce early and late coded signals to be used as an input for a fine tracking module.
6. The method of claim 5 , further comprising using an output of the fine tracking module as an input for the despreading module to synchronize decoding of the coded DSSS frame.