Parallel frequency searching in an acquisition correlator

A method for detecting correlation in a spread spectrum pseudorandom noise receiver, the method comprising:

• comparing a first detected code and a second detected code to a reference code and generating a first output and a second output in a digital matched filter, where the first and second outputs are respective summations of comparisons between the first detected code and the reference code and comparisons between the second detected code and the reference code;
• generating a product by multiplying a first number by a second number, where the first number is defined by the first output and the second output where the first output corresponds to a real part of the first number and the second output corresponds to an imaginary part of the first number, and where the second number corresponds to an ejωT term from a DFT computation;
• and
• maintaining the product of the multiplication such that products of multiplies pertaining to a tap in the digital matched filter are identifiably maintained separately from products of multiplies of other taps.

A correlation circuit for acquiring a pseudorandom noise (PN) code signal, the correlation circuit comprising:

• a comparison circuit;
• a digital matched filter adapted to receive a reference code, a first detected code, and a second detected code, the digital matched filter shifting the first and second detected codes through a first and a second shift register, the first and second shift registers containing taps such that the comparison circuit compares the reference code to the first and second code as accessed through the taps, the comparison circuit generating a first output and a second output where the first output peaks when the first detected code substantially matches the reference code and the second output peaks when the second detected code substantially matches the reference code;
• a multiplier circuit adapted to receive the first and second outputs of the digital matched filter, where the multiplier circuit computes a plurality of complex multiplication products of a complex number defined by the first and second output, the plurality of products spanning a first angular range relative to the complex number defined by the first and second output;
• an angle selector coupled to the multiplier circuit, where the angle selector receives the plurality of products and is adapted to select the product from the plurality of products with the rotation that corresponds to an angle indicated by a DFT computation;
• a first coherent integration memory adapted to receive and accumulate real parts of the complex multiplication result from the multiplier circuit, the first coherent integration memory relating the complex multiplication result to an address in the first coherent integration memory, where the address in memory corresponds to a position of a tap in the digital matched filter, where the tap position indicates a relative position of the first detected code within the digital matched filter, the first coherent integration memory further accumulating real parts of the complex multiplication products with a content of the first coherent integration memory at the memory address indicated by the tap position;
• and
• a second coherent integration memory adapted to receive and accumulate imaginary parts of the complex multiplication products from the multiplier circuit, the second coherent integration memory relating the complex multiplication products to an address in the second coherent integration memory, where the address corresponds to a position of a tap in the digital matched filter, where the tap position indicates a relative position of the first detected code within the digital matched filter, the second coherent integration memory further accumulating the imaginary parts of the complex multiplication products with a content of the second coherent integration memory at the memory address indicated by the tap position.

A method for detecting correlation in a spread spectrum pseudorandom noise receiver, the method comprising:

• comparing first and second detected codes to a reference code;
• generating a first output and a second output in a digital matched filter, where the first and second outputs are respective summations of comparisons between the first detected code and the reference code and comparisons between the second detected code and the reference code, and where the first output corresponds to a real part of a number and the second output corresponds to an imaginary part of a number;
• storing the first and second outputs;
• retrieving the first and second outputs in an order such that a series of first and second outputs corresponding to data from a common tap is retrieved;
• generating a plurality of products by multiplying the first and second outputs in the complex domain by a plurality of multipliers, where the plurality of multipliers rotate the first and second outputs in a first range in the complex plane;
• selecting a product from the plurality of products that corresponds to a phase of a DFT product;
• and
• accumulating the plurality of products of the multiplication such that an accumulation of products of multiplies pertaining to a first tap in the digital matched filter is identifiably maintained separately from an accumulation of products of a second tap.

A circuit useful for acquiring a pseudorandom noise (PN) code signal, the correlation circuit comprising:

• means for comparing a first detected code and second detected code to a reference code and for generating first and second outputs, where the first and second outputs are respective summations of a comparison between the first detected code and the reference code and a comparison between the second detected code and reference code;
• means for multiplying a first number defined by the first and second outputs in the complex domain by a second number, where the first output corresponds to a real part of the first number and the second output corresponds to an imaginary part of the first number, where the second number is a term from a DFT computation;
• means for converting the product of the multiplication of the first number and the second number into a scalar value representing a magnitude of the product;
• and
• means for searching a collection of products, comparing elements of the collection to a predetermined threshold, and providing an indication when an element of the collection is at least as high as the predetermined threshold.