Centroid tracking for spread-spectrum communications

An improvement for tracking a spreading code in a multipath environment generating a plurality of multipath signals, used in a code division multiple access (CDMA) tracking circuit, the improvement comprising the steps of:

• sampling an input signal having spread spectrum modulation, with the first spreading code embedded in the spread-spectrum modulation having a plurality of chips;
• forming half-chip offset samples from the sampled input signal;
• grouping an even set of the half-chip offset samples into an early set of samples;
• grouping, alternatively, an odd set of the half-chip offset samples into a late set of samples;
• multiplying each early set of samples by the spreading code c(n+1), c(n+2), . . . , c(n+L), where L is small compared to the length of the spreading code and approximately equal to the number of chips of delay between the earliest and latest multipath signals, thereby generating a first plurality of products;
• computing a first plurality of sums from the first plurality of products, respectively;
• calculating a first plurality of magnitudes from the first plurality of sums, respectively;
• multiplying the first plurality of magnitudes by a first plurality of weights, to generate a first plurality of weighted-signal values, respectively;
• summing the first plurality of weighted-signal values to generate an early signal-energy value;
• multiplying each late set of samples by the spreading code c(n−1), c(n−2), . . . , c(n−L), thereby generating a second plurality of products;
• computing a second plurality of sums from the second plurality of products, respectively;
• calculating a second plurality of magnitudes from the second plurality of sums, respectively;
• multiplying the second plurality of magnitudes by a second plurality of weights, to generate a second plurality of weighted-signal values, respectively;
• summing the second plurality of weighted-signal values to generate a late signal-energy value;
• and
• calculating a difference between the early signal-energy value and the late signal-energy value, thereby producing an error signal.

An improvement for tracking a spreading code in a multipath environment generating a plurality of multipath signals, used in a code division multiple access (CDMA) tracking circuit, the improvement comprising:

• sampling means for sampling an input signal having spread-spectrum modulation, with the spreading code embedded in the spread-spectrum modulation having a plurality of chips, with said sampling means forming half-chip offset samples and grouping an even set of the half-chip offset samples into an early set of samples, and alternatively grouping an odd set of the half-chip offset samples into a late set of samples;
• first correlation means for multiplying each early set of samples by the spreading code c(n+1), c(n+2), . . . , c(n+L), where L is small compared to the spreading code length and approximately equal to a number of chips of delay between the earliest and latest multipath signals, thereby generating a first plurality of products;
• first sum-and-dump means for computing a first plurality of sums from the first plurality of products, respectively;
• first calculator means for calculating a first plurality of magnitudes from the first plurality of sums, respectively;
• a first multiplying means for multiplying the first plurality of magnitudes by a first plurality of weights, to generate a first plurality of weighted-signal values, respectively;
• first summer means for summing the first plurality of weighted-signal values to generate an early signal-energy value;
• second correlation means for multiplying each late set of samples by the spreading code c(n−1), c(n−2), . . . , c(n−L), thereby generating a second plurality of products;
• second sum-and-dump means for computing a second plurality of sums from the second plurality of products, respectively;
• second calculator means for calculating a second plurality of magnitudes from the second plurality of sums, respectively;
• second multiplying means for multiplying the second plurality of magnitudes by a second plurality of weights, to generate a second plurality of weighted-signal values, respectively;
• second summer means for summing the second plurality of weighted-signal values to generate a late signal-energy value;
• and
• subtractor means for calculating a difference between the early signal-energy value and the late signal-energy value, thereby producing an error signal.