Dynamic channel allocation for GPS receivers

• US 5,600,670 A
• Filed: 12/21/1994
• Issued: 02/04/1997
• Est. Priority Date: 12/21/1994
• Status: Expired due to Fees

• Current Assignee: Trimble Navigation Limited (Trimble Inc.)
• Original Assignee: Trimble Navigation Limited (Trimble Inc.)
• Inventors: Turney, Paul F.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Webster, Bryan E.
• Application Number:
  US08/363,385
• Time in Patent Office: 776 Days
• Field of Search: 375/200, 375/201, 375/206, 375/207, 375/208, 375/209, 375/210, 375/236, 375/343, 370/18, 370/107, 370/105, 370/108, 455/3.2, 455/11.1, 455/12.1, 455/13.2, 455/39, 455/54.1, 455/49.1
• US Class Current: 375/150
• CPC Class Codes: G01S 19/24 Acquisition or tracking or demodulation of signals transmitted by the system synchronisation aspects of direct sequence spread spectrum modulation H04B1/7073
• CPC Class Codes: G01S 19/37 Hardware or software details of the signal processing chain
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04B 1/711 the interference being multi-path interference
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 2201/70715 with application-specific features

Abstract

The channels of a GPS receiver system are dynamically allocated during acquisition mode to hierarchically chain a slave channel module to a master channel. Each channel circuit includes two correlators, where each correlator receives a digitized received GPS signal and a delayed local PRN reference code signal to provide an output signal to an accumulator. During acquisition, the system provides two correlator channels where each channel includes two correlators for a total of four correllators. A PRN reference code signal is progressively delayed to provide a sequence of progressively delayed PRN reference code signals, where one of the sequence of progressively delayed PRN reference code signals are applied to each of the correlators. Each correlator channel also includes a digital mixer which receives a digitized GPS IF signal and a digital carrier reference signal and which provides the digitized received GPS signal.

Claims

1. A GPS channel system for acquiring a GPS signal, comprising:

a first channel module including a first correlator which receives a first digitized received GPS signal and a local PRN reference code signal to provide an output signal to a first accumulator;

said first channel module also including a second correlator which receives the first digitized received GPS signal and a first delayed local PRN reference code signal to provide an output signal to a second accumulator;

means for additionally delaying the first delayed local PRN reference code signal to provide a second delayed PRN reference code signal;

a second channel module including a third correlator which receives the first digitized received GPS signal and the second delayed local PRN reference code signal to provide an output signal to a third accumulator;

means for additionally delaying the second delayed local PRN reference code signal to provide a third delayed PRN reference code signal;

said second channel module also including a fourth correlator which receives the first digitized received GPS signal and the third delayed local PRN reference code signal to provide an output signal to a fourth accumulator;

said first channel module also including the second correlator which receives the first digitized received GPS signal and a first delayed local PRN reference code signal to provide an output signal to the second accumulator;

switch means for applying the second delayed PRN reference code signal to the third correlator of the second channel module and for applying the third delayed PRN reference code signal to the fourth correlator of the second channel module when the GPS channel system is in an acquisition mode of operation to allow the third and fourth correlators of the second channel to be switchably connected in a cascaded, serial configuration for the acquisition mode of operation, and

wherein the switch means includes means for applying a sequence of other PRN reference code signals to the third and fourth correlator of the second channel module when the GPS channel system is in a tracking mode of operation to allow the third and fourth correlators to be applied to a separate GPS signal.

2. The system of claim 1 including:

a first digital mixer which receives a digitized IF signal and a digital carrier reference signal to provide the first digitized received GPS signal for the first channel module;

a second digital mixer which receives a second digitized IF signal and a second digital carrier reference signal to provide the second digitized received GPS signal for the second channel module; and

switch means for applying the first digital carrier reference signal to the second digital mixer when the GPS channel system is in an acquisition mode of operation, wherein the switch means includes means for applying the second digital carrier reference signal PRN to the second digital mixer when the GPS channel system is in a tracking mode of operation.

3. A method of improving acquisition of a GPS receiver system during an acquisition mode of operation, comprising the steps of:

hierarchically chaining a plurality of channel circuits in series during acquisition mode, where each channel circuit includes two correlators;

progressively delaying a PRN reference code signal to provide a sequence of progressively delayed PRN reference code signals;

applying one of the sequence of progressively delayed PRN reference code signals to each of said correlators wherein the PRN reference code signal applied to the second correlator of each channel module is delayed further than the PRN reference code signal applied to the first correlator of each channel module;

applying the third delayed PRN reference code signal through a switch to the third correlator when the GPS channel system is in an acquisition mode of operation and when the third correlator is determined to be unused and available for assisting the first and second correlators in acquiring a GPS signal; and

applying another PRN reference code signal through the switch to the third correlator when the GPS channel system is in a tracking mode of operation.

4. A method of dynamically allocating otherwise unused correlator channels of a GPS receiver for improving acquisition of a GPS signal, where a correlator channel includes two correlators, comprising the steps of:

providing a local PRN reference code signal;

correlating a digitized received GPS signal with the local PRN reference code signal in a first correlator of a first channel and providing an output signal to a first accumulator;

delaying the local PRN reference code signal to provide a first delayed PRN reference code signal;

correlating the digitized received GPS signal with the first delayed local PRN code signal in a second correlator of the first channel and providing an output signal to a second accumulator;

delaying the first delayed local PRN reference code signal to provide a second delayed PRN reference code signal;

determining that a second channel having a third and a fourth correlator are unused and available for assisting the first and second correlators of the first channel in acquiring a GPS signal;

correlating the digitized received GPS signal with the second delayed local PRN code signal in the third correlator and providing an output signal to a third accumulator;

delaying the second delayed local PRN reference code signal to provide a third delayed PRN reference code signal;

correlating the digitized received GPS signal with the third delayed local PRN code signal in the fourth correlator and providing an output signal to a fourth accumulator;

applying the third delayed PRN reference code signal through a switch to the third correlator when the GPS channel system is in an acquisition mode of operation and when the third correlator is determined to be unused and available for assisting the first and second correlators in acquiring a GPS signal; and

applying another PRN reference code signal through the switch to the third correlator when the GPS channel system is in a tracking mode of operation.

5. The method of claim 4 including the steps of:

mixing a digitized IF signal and a digital carrier reference signal to provide the digitized received GPS signal for the first and second correlators; and

mixing the digitized IF signal and the digital carrier reference signal to provide the digitized received GPS signal for the third and fourth correlators.