A GPS receiver in one embodiment includes an antenna which receives GPS signals at an RF frequency from in view satellites; a downconverter coupled to the antenna for reducing the RF frequency of the received GPS signals to an intermediate frequency (IF); a digitizer coupled to the downconverter and sampling the IF GPS signals at a predetermined rate to produce sampled IF GPS signals; a memory coupled to the digitizer storing the sampled IF GPS signals (a snapshot of GPS signals); and a digital signal processor (DSP) coupled to the memory and operating under stored instructions thereby performing Fast Fourier Transform (FFT) operations on the sampled IF GPS signals to provide pseudorange information. These operations typically also include preprocessing and post processing of the GPS signals. After a snapshot of data is taken, the receiver front end is powered down. The GPS receiver in one embodiment also includes other power management features and includes, in another embodiment the capability to correct for errors in its local oscillator which is used to sample the GPS signals. The calculation speed of pseudoranges, and sensitivity of operation, is enhanced by the transmission of the Doppler frequency shifts of in view satellites to the receiver from an external source, such as a basestation in one embodiment of the invention.

GPS receiver and method for processing GPS signals

The present invention discloses a GPS system (100) that can operate in different modes depending on the network facilities and bandwidth available, the GPS information (114) that can be acquired, or user or system requirements. The modes comprise standalone mode, where a mobile communications device (104) computes the position of the device, an autonomous mode, where the mobile communications device (104) transmits the computed position to a server (108), application (110), or PSAP (112) in a communications network, a network aided mode, where the network aides the mobile communications device (104) in determining the position of the device, a network based mode, and other modes.

Multi-mode global positioning system for use with wireless networks

The present invention discloses a GPS system that can operate in different modes depending on the network facilities and bandwidth available, the GPS information that can be acquired, or user or system requirements. The modes comprise standalone mode, where a mobile communications device computes the position of the device, an autonomous mode, where the mobile communications device transmits the computed position to a server, application, or PSAP in a communications network, a network aided mode, where the network aides the mobile communications device in determining the position of the device, a network based mode, and other modes.

Information transfer in a multi-mode global positioning system used with wireless networks

A Global Positioning System (GPS) receiver uses satellite signals to determine position, velocity, and timing information. Measurements are obtained by synchronising the locally generated signal in the receiver with the signals received. A synchronisation procedure called acquisition adjusts the code phases of the incoming signal and the locally generated pseudo-random replica sequence of the corresponding satellite to a small timing offset and finds the residual frequency modulation after carrier wipe-off. New fast techniques for acquiring signals indoors in conditions that require a significant number of computations are presented. In this work many arithmetic operations are shared when exploring different search options by using fast Fourier transform (FFT) and a technique based on the frequency domain replica shifting. It is shown that FFT can be used for the joint processing of multiple (code-phase/frequency) search options in both dimensions at once. With a slight degradation in performance, the algorithm has a modified version that implements the technique using two-dimensional FFT. Several possible processing schemes are presented. Moreover, the presented shifting replica approach in the frequency domain can significantly reduce computational complexity by jointly acquiring different satellites.

Fast FFT based GPS satellite acquisition methods

Method and apparatus providing enhanced sensitivity for GPS receivers (400, 500, 600, 700) by allowing coherent integration of a correlation over several code periods of a GPS signal in one embodiment, and by performing a time to frequency domain conversion to the output from a correlation processor (507) in a second embodiment. In the case in which coherent integration is performed over several code periods, advantage is taken of the fact that CDMA cellular telephone base stations transmit information that allows the receiver to determine GPS time before beginning a GPS signal acquisition process. The integration can be expanded to include code periods from more than one bit period, if the GPS receiver (400, 500, 600, 700) takes advantage of the fact that known bit patterns are transmitted at particular times within the transmission from a GPS satellite. If no base station is within range, then the output from a correlator (507) that integrates a correlation over one code period is used to generate values that are input to a discrete time domain to frequency domain transform processor (511). The output from the transform processor (511) will indicate the presence of a signal from a particular satellite and the offset between locally generated signal and the received GPS signal.

Method and apparatus for increasing the sensitivity of a global positioning satellite receiver

A new spread-spectrum code-acquisition technique for the navigation systems Navstar/GPS and Glonass is introduced. This technique uses the FFT to compute the correlation function, thereby eliminating the time-consuming code phase shift process. Comparisons with existing systems show a theoretical reduction in acquisition time of about 2000 times.

New Fast GPS code-acquisition technique using FFT

A novel ‘differential’ decoding technique is proposed which enables pre-averaging instead of postintegration for a substantially low update rate ‘FFT-IFT’ correlation in sprcadspectrum (navigational) receivers. N-channel code acquisition can be performed to monitor the time dispersion with FFT time left to analyse frequency dispersion in highly reflective areas (e.g. an urban environment).

Novel fast GPS/GLONASS code-acquisition technique using low update rate FFT

Analysis of coherent and noncoherent delay lock loops shows that a smaller early-late spacing than the commonly used one chip time reduces multipath tracking error considerably. The results are especially interesting for spread-spectrum ranging systems such as GPS.

Reducing multipath tracking errors in spread-spectrum ranging systems

The effects of multipath when rotating the antenna of a GPS receiver are investigated. It is demonstrated that range errors decrease considerably (a factor 7 is possible). Measurements confirm the given analysis.

D.J.R. van Nee

Papers

New Fast GPS code-acquisition technique using FFT

Novel fast GPS/GLONASS code-acquisition technique using low update rate FFT

Reducing multipath tracking errors in spread-spectrum ranging systems

GPS multipath mitigation by antenna movements