Nokia Corporation

Nokia Mobile Phones Limited

Nokia Siemens Networks Oy

David Akopian

Harri Valio

Jari Syrjarinne

Jari Syrj&auml;rinne

Seppo Turunen

Jari Tapani Syrjärinne

Ilkka Kontola

In order to prevent an incorrect synchronization between a received code-modulated signal and an available replica code, partial correlations are performed between a respective subset of samples of the replica code and samples of the received code-modulated signal associated to the respective subset of samples of the replica code at a specific alignment between the received code-modulated signal and the replica code. The results of the partial correlations are then compared to each other, and it may be decided based on this comparison whether the replica code corresponds to a code employed for code-modulating the received code-modulated signal.

Preventing an incorrect synchronization between a received code-modulated signal and a replica code

The invention relates to an apparatus supporting an acquisition of a received code modulated signal by determining the correlation between the received code modulated signal and an available replica code sequence at different code phases. It is proposed that the apparatus comprises a first acquisition engine for selecting code phases which are good candidates for being the code phase at which a received code modulated signal and an available replica code sequence have the highest correlation. The apparatus further comprises a second acquisition engine for performing a refined comparison between a received code modulated signal and an available replica code sequence for each code phase selected by the first acquisition engine. The invention relates equally to a corresponding method and to a system comprising such an apparatus and a network.

Acquisition of a code modulated signal

The invention relates to a method for determining the correlation phase between a signal received at a receiver and a replica sequence. A matched filter multiplies samples () of the received signal with samples () of the replica and sums the resulting products to obtain a correlation value for a specific correlation phase. The samples of the received signal and the replica are shifted relative to each other for each correlation phase that is to be checked. In order to reduce the computational load, it is proposed that results obtained in the correlation calculations for one correlation phase are used by the matched filter also for calculations for a subsequent correlation phase. The invention relates equally to a corresponding receiver, to an electronic device comprising such a receiver, to a device cooperating with such a receiver and to a corresponding system.

Determination of the correlation phase between a signal and a replica sequence

The invention relates to a method, a processing unit and a system for determining the correlation between samples of a received code modulated signal and samples of replica code sequences. In order to simplify and accelerate the process, it is proposed that the received samples and the replica samples are aligned to each other and that the positions of the samples in the received signal and in the replica code sequences are grouped, each group comprising all positions at which the composition of the values of the samples of all of the replica code sequences is similar. The values of the received samples which are associated to a respective group are combined separately for each group to obtain a respective preliminary result. Then, a correlation value is determined for each replica code sequence by combining the preliminary results obtained for all groups separately for each replica code sequence, taking into account the values of the samples of the replica sequences in the respective group.

Determining the correlation between received samples and available replica samples

The invention relates to a method, a processing unit and a system for determining the correlation between consecutive sets of samples of a received, code modulated signal and replica samples. In order to reduce the computational load, the positions of samples in said replica code sequence are grouped, each of these positions and a predetermined number of respective subsequent positions forming a subgroup and each group comprising the respective first position of all subgroups with positions associated with a similar composition of consecutive replica samples. The method combines those values of samples of the first set of samples, which are associated by their position to a respective group, separately for each group to obtain a respective preliminary result. Determining a correlation value for each of the sets of samples then comprises combining the obtained preliminary results for all groups separately for each of the sets of samples.

To reduce the complexity of the correlation in a correlation based tracking of a code modulated signal received at a receiver, received samples and available replica samples are aligned to each other and the positions of the samples in the received signal and in the replica code sequences are grouped, each group comprising all positions at which the composition of the values of the samples of all of the replica code sequences is similar. The values of the received samples which are associated to a respective group are combined separately for each group to obtain a respective intermediate result. Then, a correlation value is determined for each replica code sequence by combining the intermediate results obtained for all groups separately for each replica code sequence, taking into account the values of the samples of the replica sequences in the respective group.

Tracking a code modulated signal

A method and corresponding apparatus for accurately determining the offset of the carrier frequency of a received signal from a nominal frequency (the offset due to for example Doppler shifting), such as is done in a ranging receiver when acquiring or tracking a signal transmitted by a beacon (such as a satellite) of a positioning system. The method amplifies a conventional correlation by performing a special noncoherent integration of the real and imaginary components of the output of a conventional (coherent) correlation calculation, resulting in a complex phasor having a phase that bears information about the offset of the carrier frequency from the nominal carrier frequency.

Method and apparatus for acquiring a ranging signal of a positioning system

A method for validating detected code modulated signals transmitted by beacons of a positioning system and received by a receiver comprises as a first step performing measurements for the detected beacon signals. Then, at least one of the detected beacon signals is selected as a calibration signal. In a next step, at least one allowed range for results of measurements for detected beacon signals other than the calibration signal are determined based on measurements for the detected calibration signal and on an available reference position of the receiver. Finally, each detection of a beacon signal for which results of performed measurements are outside of an allowed range is rejected. The invention relates equally to a corresponding receiver, to an electronic device comprising such a receiver, to a device cooperating with such a receiver and to a corresponding positioning system.

Validation of beacon signals

The invention relates to a method for acquiring a receiver () into a code modulated spread spectrum signal received by the receiver (). In the method at least one replica code (r) is used which corresponds to a code used with the modulation having a pre-determined number of chips, and an examination phase is performed, in which a frequency shift of the signal within a selected frequency area is examined, and a code phase of the code used with the modulation is examined. In the method the frequency shift examination is divided into a first estimation phase and a second estimation phase, wherein in the first estimation phase the selected frequency area is divided into a first set of frequencies, and in the second estimation phase a second set of frequencies is examined nearby each frequency of the first set of frequencies. Further, a comparison for frequencies of the second set of frequencies is performed using the received signal and the replica code (r), and the results of the comparison are used to estimate the correct frequency shift.

Method in a receiver and a receiver

A method, corresponding apparatus, and corresponding system for acquiring a received spread spectrum signal, the received signal having a carrier component at a carrier frequency, a code component having a code period, and a data component, the acquiring including matching the phase of a replica of the code component to the phase of the received code component and also determining any shift in the carrier frequency away from a transmitted carrier frequency, the method including the steps of: performing a first acquisition of the received signal so as to provide an approximately estimated carrier frequency and a phase of the replica and also so as to provide a code-wiped and an approximately carrier-wiped signal; and performing a second acquisition of the approximately carrier-wiped signal, the second acquisition including a substep of data wipe-off involving a squaring or similar operation on a signal derived from the approximately carrier-wiped signal; thereby providing a correction to the approximately estimated carrier frequency, a correction that accounts for the carrier frequency shift remaining after the first acquisition. The invention also comprehends a method including only a single acquisition, an acquisition including a data wipe-off involving a squaring or similar operation on a signal having a data component and a frequency component, i.e. the invention is of use in acquiring any kind of signal having a carrier component and a data component, regardless of whether a first, typically relatively coarse acquisition is performed.

System for method for fine acquisition of a spread spectrum signal

The invention relates to a method for estimating the position of a receiver receiving code modulated signals from at least one beacon. The method comprises delimiting a region containing the receiver position based on a code modulated signal received at the receiver from at least one beacon and on available information including at least an initial information on the receiver position. The method further comprises estimating the receiver position as a position within the delimited region which minimizes an error criterion. The invention relates equally to such a receiver, to a system comprising such a receiver and to a corresponding software program product enabling an estimation of the position of a receiver.

Position estimation

The invention relates to a method and to devices for determining in a positioning system the time of reception of a beacon signal which was received and tracked by a receiver. In order to enable a re-acquisition of the system time based on a noisy received signal, it is proposed that the method comprises as a first step reconstructing a beacon signal for an interval based on available information. Then, a cross-correlation is performed between the reconstructed signal and the received signal at different relative positions to each other. Next, the time of transmission of the received signal is determined based on information for the reconstructed signal and on the relative position resulting in the maximum correlation value. Finally, a time of reception of said received signal is determined as the sum of the determined time of transmission of the received signal and of a calculated time of flight of the received signal.

Method, receiver and system for determining the time of reception of a beacon signal

An apparatus, system, and corresponding method for acquiring a spread spectrum signal, where the acquiring includes matching the phase of a replica of a code component to the phase of the received code component and also determining the carrier frequency including any Doppler or other shifting, the apparatus including: a multi-section matched filter for providing successive section outputs each including elements corresponding to a different replica code phase; and a compensated acquisition module, responsive to each section output of each of the sections, for providing a sequence of frequency indicators, each corresponding to a different frequency offset, with each section output having elements each of which corresponds to a particular value of replica code phase, wherein each frequency indicator is based on a combining, phase element-wise, of the section outputs using compensating factors that depend on the corresponding frequency offset.

System for acquiring spread spectrum signals

The invention relates to a method for determining the time of transmission of a signal part of a code modulated signal transmitted by a beacon of a positioning system and received by a receiver of the positioning system. In order to enable such a determination in weak signal conditions, it is proposed that measured subcomponents of the time of transmission of at least two signal parts are compared with corresponding predicted subcomponents in a way resulting in a combined difference for all signal parts. The comparison is performed for a plurality of assumed errors in the predicted subcomponent. The accurate time of transmission of a signal part is then determined based on the determined error value which results in the smallest combined difference. The invention relates equally to a corresponding receiver and to a corresponding positioning system.

Determination of the transmission time of a signal part in a positioning system

The invention relates to a method for determining the correlation between a signal transmitted by a beacon and tracked by a receiver and a reconstructed signal expected to be received at the receiver, wherein the received signal and the reconstructed signal are shifted against each other. In order to provide a possibility of compensating residual sinusoidal modulations in the tracked signal, it is proposed that at each shifting position, the samples of the received and the reconstructed signal are multiplied and integrated separately in a plurality of sections. The results are multiplied with a shifted and complex conjugated version of itself. The products resulting in this second multiplication are integrated to receive a single final value for each shifting position. Finally, the maximum final value resulting for the different shifting positions is determined, the shifting position with the maximum value being considered as the shifting position with the maximum correlation.

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Tampere, Finland

David Akopian