U-blox Ag

Heinz Mathis

Andreas Thiel

Daniel Kaegi

Michael Ammann

Etienne Favey

Pascal Flammant

In a GNSS receiver data sequences derived from a digital signal each with an internally generated correlation sequence derived from a basic sequence and mixed with frequency signals corresponding to various Doppler frequencies and in various phase positions with respect to the data sequence are correlated and the correlation values evaluated. In difficult conditions, e.g., RF levels of the signal of &#x2212;145 dBm and less, correlation values produced with the same correlation sequence and phase position but with a plurality of data sequences are evaluated together in that, in an evaluator (), every-correlation value is, in a comparator (), compared with at least a first value threshold and a second value threshold, with the latter having a value between 1.3 and 1.7 times the value of the first and values &#x2212;1, 0 or +1 assigned accordingly to a correlation term which is then added to an integer correlation counter which varies over a counter interval, e.g., [0, 15], in an adding unit (). The correlation counters corresponding to the various Doppler frequencies and phase positions are stored in a memory unit (). In an arbitration unit () a correlation indicator is derived from each correlation counter and the latest corresponding correlation value and the six largest correlation indicators selected and stored together with their Doppler frequencies and phase positions.

Method of processing a digital signal derived from a direct-sequence spread spectrum signal

A sychronization circuit comprising an analog feedback shift register for generating an internal sequence which is synchronized with an external sequence containing repetitions of a fundamental sequence has a feedback circuit which, for the formation of a new value of a fundamental sequence, combines at least two values (x,x) stored in the shift register according to a feedback function (f(x,x)), which is then scaled with a factor k, 0.9&#x3c;k&#x3c;0.99. The synchronization behaviour is improved, especially in the case of signals with strong background noise, by using a feedback function which is substantially linear in the sectors defined by the signs of the arguments and whose sign corresponds to that of the negative of the product of the negative arguments and whose magnitude is 1 if the magnitudes of the arguments are each 1. A function which meets these requirements and has proved useful is f(x, . . . , x)=&#x2212;sig((&#x2212;x)&#xb7; . . . &#xb7;(&#x2212;x))&#xb7;(|x|+ . . . +|x|)/m. For improving the signal/noise ratio, there is a buffer in front of the analog feedback shift register, where, for the generation of the external sequence, segments of an input sequence which contain several, e.g. twenty, successive instances of the fundamental sequence are added and then read out repeatedly.

Synchronization circuit

A method for generating an internal sequence of analog values having a specific period includes producing an intermediate value by a logical combination of an actual value of the external sequence with an actual value of a second generating sequence, producing an input value to an analog feedback shift register by superposition of the intermediate value with an analog feedback value derived according to a feedback function from analog values in the analog feedback shift register, and feeding the input value to an input of the analog feedback shift register. A position of an actual value of the second generating sequence corresponds to a position of a segment in the first generating sequence, the segment including a determinative set of n binary values derived from the analog values in the analog feedback shift register.

Method for producing a sequence synchronized with an external signal and synchronization circuit and receiver

For allowing positioning of a GPS receiver within a building, GPS primary positioning signals received by an outdoor receive antenna are up-converted to different carrier frequencies in the 2.4 GHz ISM band and the converted signals are transmitted each by a transmit antenna inside the building, the transmit antennas serving at the same time as access points of a WLAN which is used for transmitting additional positioning data like the positions of the transmit antennas and the signal delay times associated with them. By cycling through the secondary positioning signals received from the transmit antennas, i.e., down-converting each of them during an assigned time slot, and determining clock bias differences in the receiver, the position of the latter is determined using TDOA algorithms.

Growing community of inventors

Uerikon, Switzerland

Heinz Mathis