Software based spread spectrum signal processing

摘要

The present invention relates to production of a decoded signal (A_tau) based on in an incoming stream of data samples (d(k)) representing at least one downconverted digitized spread spectrum source signal. A number (NM) of the received data samples (d(k)) are divided into a first number (N) of data blocks, where each data block contains a second number (M) of samples. The second number (M) is an integer larger than or equal to two. Each of the data blocks is then correlated with a respective local code replica segment (p(k)) to produce a first number (N) of intermediate accumulation results (Sigma_I; Sigma_Q). To enable production of a decoded signal (A_tau) being compensated for a Doppler shift relative to a downconverting frequency for the least one spread spectrum source signal, the intermediate accumulation results (Sigma_I; Sigma_Q) are correlated with a carrier vector (s[z]_I; s[z_Q) expressing such a Doppler shift. However, according to the invention, the carrier vector (s[z]_I; s[z]_Q) only contains a target number (Z) of carrier values (s_1I:s_ZI; s_1Q:s_ZQ) (i.e. different carrier amplitude levels), where the target number (Z) is smaller than or equal to the first number (N). Normally, the target number (Z) is substantially smaller than the first number (N). Thus, depending on the first number (N) and the target number (Z) for the relevant carrier vector (s[Z]_I; s[Z]_Q), a number of consecutive results of the intermediate accumulation results (Sigma_I; Sigma_Q) are combined into a number of aggregated accumulation results (c_1I:c_ZI; c_1Q:c_ZQ), which is equal to the target number (Z). Thereafter, the aggregated accumulation results (c_1I:c_ZI; c_1Q:c_ZQ) are correlated with the carrier vector (s[Z]_I; s[z]_Q) to produce the decoded signal (A_tau). The invention is well adapted for implementation of software GNSS receivers.