HK1051574B - Radiofrequency signal receiver with means for improving the reception dynamic of said signals - Google Patents

Description

Radio frequency signal receiver with means for improving the reception dynamics of the signal

Technical Field

The present invention relates to a receiver for radio frequency signals transmitted by a transmitter source, in particular to a receiver of the GPS type. The receiver has means for improving the reception dynamics of the signal, for example when the signal is shielded by obstacles.

Background

In current GPS navigation systems, 24 satellites are placed in orbits at a distance of 20,200 kilometers near the surface of the earth, in 6 orbital planes each 55 degrees offset from the equator. The time taken for a complete rotation in orbit by one satellite before returning to the same point on earth is approximately 12 hours. The distribution of satellites in orbit allows a terrestrial GPS receiver to receive GPS signals from at least four visible satellites to determine, for example, its position, velocity and local time.

In civilian use, each satellite in orbit transmits a radio frequency signal consisting of carrier frequency L1 at 1.57542GHz, on which a 1.023MHz pseudo-random PRN code unique to each satellite and a 50Hz GPS message are modulated. The GPS messages contain almanac date and almanac data from the transmitting satellites that are particularly useful for calculating X, Y, Z position, velocity, and time.

In particular the golden code type PRN code (pseudo random noise) is different for each satellite. The gold code is a digital signal consisting of 1023 chips that repeat every millisecond. The repetition period is also defined by the term gold code "period (epoch)". It should be noted that one chip takes a value of 1 or 0 with respect to one bit. However, the chips in GPS technology are different from the bits used to define a data unit.

The gold codes defined for 32 satellite identification numbers have an orthogonal nature. By correlating them with each other, the correlation result gives a value close to 0. This feature thus allows several radio frequency signals originating from several satellites and transmitted at the same time on the same frequency to be processed independently in several channels of the same GPS receiver.

Currently, GPS receivers, portable or particularly included in vehicles, are used to allow navigation data to be provided to users during several daily activities. This data encourages orientation towards the desired target and allows the user to know their orientation. In addition, portable GPS receivers are of a small size in order to enable them to be included in objects that can be easily transported by a person, such as a cellular phone or a watch. However, in these small-sized objects, it is generally desirable to minimize the energy consumed by the receiver, since these objects are powered by batteries or small-sized batteries.

In order to determine, in particular, the position and time-related data of a GPS receiver, the GPS receiver needs to receive radio frequency signals transmitted by at least four visible satellites. However, the receiver is able to receive almanac data specific to each satellite by individually locking onto one of the visible satellites.

As symbolically represented in fig. 1, the GPS receiver 1 comprises an antenna 2 for receiving radio frequency signals SV1 to SV4 transmitted by at least four visible satellites S1 to S4. However, certain radio frequency signals can encounter various obstacles in their path, such as for example trees a that can be corrupted by the signal reception of the receiver. As shown in fig. 1, this masking of signals SV1 to SV3 results in the fact that the relevant channels set in the receiver to operate for searching and tracking satellites S1 and S3 may momentarily lose the signals SV1 and SV 3. Thus, the receiver in the satellite search and tracking phase cannot extract the information needed to calculate its position, which is a disadvantage.

This phenomenon may also occur when the portable GPS receiver is moving in, for example, a road vehicle. In this case, it is common for the radio frequency signals received by the mobile receiver from certain visible satellites to be masked for a number of treelises arranged alongside the road. With the loss of the masked signal, the receiver must perform a new search and tracking in order to lock onto at least four visible satellites. In this way, all operations for determining position, velocity and time are slowed down.

With regard to the rapid recovery of lost signals due to obstacles such as trees or tunnels, european patent document No. 0429783 discloses a method for a GPS receiver placed in particular in a vehicle to track GPS-type satellite signals. As soon as an obstacle leaves, the receiver searches for satellites at the highest elevation angle that prevents the signal from being shielded by the trees as much as possible. The frequency of the satellite signal is divided into frequency bands, where each frequency band is assigned to one of the associated channels to speed up the reception of the satellite. In this way, several associated channels are used for the same satellite.

However, in order to quickly search for the same satellite at the highest elevation angle, the channels that must be locked to the same satellite are configured differently, which is a disadvantage even if the satellite is found quickly. When the signal originates from a visible satellite without the highest elevation angle, no method is provided for preventing the momentary loss of signal that is attenuated by passing an obstruction such as a tree.

Disclosure of Invention

It is an object of the present invention to provide a receiver of radio frequency signals, in particular of the GPS type, which prevents the momentary loss of signals received by at least one channel of the receiver, said signals being shielded by an obstacle in their path, said receiver overcoming the drawbacks of the prior art receivers.

The receiver comprises receiving and shaping means having frequency translation for the radio frequency signal to produce an intermediate frequency signal; a correlation stage consisting of several correlation channels for receiving the intermediate frequency signals in order to correlate them in an operating channel control loop with the carrier frequency and a specific code copy (replica) of the visible transmission sources to be searched and tracked, each channel being provided with a correlator, wherein at least one integrator counter is capable of providing at the end of each determined integration period of the correlated signals a binary output word whose value, compared with a determined detection threshold, allows detecting the presence or absence of a visible transmission source to be searched and tracked; and microprocessor means connected to the correlation stage for processing data extracted from the radio frequency signal after correlation. In the case of a GPS receiver, the data extracted from the signal is in particular a GPS message and a pseudorange.

This and other objects are achieved by a receiver as described above, characterized in that: the microprocessor means is arranged to configure at least one unused channel arranged to operate in parallel with one of the working channels for searching and/or tracking the same visible transmission source, the unused channel being configured such that the integration period of its integrator counter is different from the integration period of the integrator counter of the working channel.

One advantage of the receiver is that it is able to adjust the detection sensitivity of the receiver by changing the time or integration period of the integrator counter defined as the unused channel. Thus, the unused channels are configured to search and track the same transmission source, such as a satellite, as one of the operating channels.

If the integration period of the integrator counter of an unused channel is greater than the conventional integration period, the integrator counter of the unused channel will become saturated during normal, obstacle-free operation. In this case only data from the normally configured channel is taken into account by the microprocessor means. Conversely, when the signal is attenuated by passing through an obstacle or momentary interruption, the unused channel with its larger integration period can try to detect the presence of a satellite. The microprocessor detects loss of signal for the operating channel configured in a standard manner to extract data from the unused channel.

Another advantage of the inventive receiver is that it allows fast position calculation even if the radio frequency signal from a visible satellite is shielded in its path by an obstacle, since the unused channels are connected in parallel with a normally configured channel. The unused channels can be connected in parallel with one of the selected operating channels once it is no longer detected that a particular satellite is being tracked or from the beginning of the search for the selected channel.

In principle, from the beginning of the acquisition phase, the microprocessor means are able to automatically select a first channel configured in a standard manner in parallel with another unused channel configured with a larger integration period. More than one unused channel may be connected in parallel with a selected channel in order to lock to the same visible satellite.

The integration period for the unused channels is preferably twice the integration period for the channels configured in the conventional manner. The one or more unused channels connected to the selected operating channel preferably remain open for all of the time expected to be lost by the signal of the selected channel. However, to conserve energy, it is desirable to only periodically turn on one or more unused channels, or only on certain satellites.

The repetition length of the particular pseudo-random code of the transmitting satellite is used as a basis for defining the integration period of the channel in the normal, obstacle-free mode of operation. The size of the integrator counter depends on the length of the pseudo random code defining the receiver dynamics.

The receiver must include a greater number of channels than the number of visible satellites. This allows channels unused in normal operation to be configured differently in any masking of signals expected to be received by one of the channels.

Another advantage of connecting an unused channel to one of the working channels to prevent momentary loss of signal is to ensure continuity in the extraction of data from the working channel by the microprocessor means.

Another advantage of the receiver of the present invention is that it is also possible to provide a controller for each channel to relieve the microprocessor means of all synchronization tasks for searching and tracking satellites. This enables a reduction in the multiple data transfers from the operating channel to the microprocessor during all of these satellite search and operating phases.

The radio frequency signal receiver of the invention can of course also be used in a satellite navigation system of the GLONASS or GALILEO type. Also, the receiver can be used in a mobile telephone network, for example of the CDMA (code division multiple access) type. In this case, the transmission source is no longer a satellite, but a basic cell of the telephone network, and the data processed relates to audible or legible messages.

Drawings

Objects, advantages and features of a radio frequency signal receiver having means for improving signal reception dynamics will become apparent from the following description of embodiments taken in conjunction with the accompanying drawings, in which:

figure 1, already cited, represents a radio-frequency signal receiver of the GPS type receiving signals from at least four satellites, two of which are shielded by obstacles;

FIG. 2 schematically illustrates portions of a radio frequency signal receiver according to the present invention;

figure 3 shows schematically the elements of a correlator of one channel of the correlation stage of a receiver according to the invention; and

fig. 4 shows a diagram of the binary word value at the output of the integrator counter as a function of the integration time.

Detailed Description

In the following description, only a few elements of a radio-frequency signal receiver, in particular of the GPS type, well known to a person skilled in the art are mentioned in a simplified manner. The receiver described below is preferably a GPS receiver. However, it can be used in the GLONASS or GALILEO navigation system or any other navigation system or in a mobile phone network.

As shown in FIG. 1, four visible satellites S1-S4 transmit radio frequency signals SV 1-SV 4. The signals SV1 to SV4 of these four satellites are necessary for the GPS receiver 1 to be able to extract all the information used for calculating its position, velocity and/or time. However, in the path of the radio frequency signal, various obstacles such as tree a may disrupt the detection of the signal by the relevant channel of the receiver 1. The radio frequency signals SV1 and SV3 shown have to pass through an obstacle in order to be received by the antenna 2 of the receiver 1. The relevant channels in the search and tracking phases of satellites S1 and S3 may therefore momentarily lose signals SV1 and SV 3. In order to prevent the loss of signals shielded by the obstacles, the means for improving the reception dynamics described below are provided in the GPS receiver.

In order to provide location, speed and local time according to the needs of the person wearing the watch, the GPS receiver can preferably be mounted in a portable object such as the watch. Since the watch has a small size battery or cells, the power consumption during operation of the GPS receiver must be as small as possible.

Of course, the GPS receiver may be mounted in other portable objects of small size and low power consumption, such as a portable telephone also mounted with a secondary battery or a battery.

The GPS receiver 1 is schematically shown in fig. 2. It comprises receiving and shaping means 3 for frequency-converting the radio-frequency signal supplied by the antenna 2 to generate an intermediate frequency signal IF; a correlation stage 7, constituted by 12 channels 7', for receiving the intermediate frequency signal IF; a data transfer bus 10 connecting each channel to a respective buffer register 11; and finally each buffer register is connected to the data bus 13 of the microprocessor means 12.

The intermediate frequency signal IF is preferably formed in complex form by an in-phase signal component I and a quadrature signal component Q at a frequency of approximately 400kHz provided by the shaping means 3. The complex intermediate frequency signal IF is represented in fig. 2 by a solid line intersecting with an oblique line defining 2 bits.

The number of channels 7' available in the receiver 1 must be higher than the maximum number of visible satellites at any point on the earth in order to maintain a certain number of unused channels. These unused channels are used in parallel connection with the working channels to prevent momentary loss of signal by these channels as described below with particular reference to fig. 3 and 4.

Conventionally, in the receiving means 3, the first electronic circuit 4' transforms the first of all the radio-frequency signals with a frequency of 1.57542GHz into a frequency of 179MHz, for example. The second electronic circuit IF 4 "then performs a double conversion to firstly convert the GPS signals to a frequency of 4.76MHz and finally to a frequency of, for example, 400kHz by sampling at 4.36 MHz. Thus, the intermediate complex signal IF sampled and quantized at a frequency of about 400kHz is supplied to the channel 7' of the correlation stage 7.

For the frequency conversion operation a clock signal generator 5 forms part of the receiving and shaping means for the radio frequency signal 3. The generator is for example equipped with a quartz oscillator, which is not shown calibrated at a frequency of about 17.6 MHz. Two clock signals CLK and CLK16 are provided to the correlation stage 7 and the microprocessor means 12 in particular to clock all the operations of these elements. The first clock frequency CLK may have a value of 4.36MHz, while the second clock frequency may be fixed at 1/16 of 4.36MHz, i.e. 272.5kHz, for most of the relevant stages in order to save energy consumption.

It should be noted that instead of being integrated with the clock signal generator 5 in the receiving means 3 to obtain the clock signal CLK16, a divider placed in the relevant stage may be used.

The signal provided by the second circuit 4 "gives signals of different parity (+1 and-1) in half the cases. Therefore, for the demodulation operation of the GPS signal in the receiver, the parity has to be considered. In an alternative embodiment the second circuit 4 "is able to give the signal (+ 3; + 1; -1; -3) distributed over 2 output bits for the in-phase component as well as the quadrature-phase component.

In the case of the GPS receiver of the invention, the intermediate frequency signal IF is provided to the correlation stage with a 1-bit quantization of the carrier frequency, even IF this quantization produces an additional loss of about 3dB in the carrier signal-to-noise ratio (SNR).

The register 11 of each channel is able to receive configuration data or parameters originating from the microprocessor means. Each channel is capable of transmitting data about the GPS message, the state of the PRN code, frequency increments related to doppler, pseudoranges and other data after correlation and locking onto a particular satellite through registers.

The buffer register 11 is made up of several types of registers, such as command and status registers, registers for NCO (numerically controlled oscillator) oscillators for channels, pseudorange registers, energy registers, offset and delta registers for carriers and codes, and test registers. It should be noted that these registers are capable of accumulating data in the relevant stages for use in the acquisition and tracking process of the satellite, without the need for automatic transfer to the microprocessor.

In an alternative embodiment, a single block of registers 11 may be designed for all channels 7', provided that certain data placed in the register unit is common for each channel.

Each channel 7' of the correlation stage 7 comprises a correlator 8 and a controller 9 intended to be set in operation by a dedicated method, in particular a signal processing algorithm for obtaining satellite signals and tracking the satellites detected by the channel.

The controller 9 for each channel comprises, among other things, a memory unit, an arithmetic unit, a data bit synchronization unit, a correlator control unit and an interrupt unit, which are not visible in fig. 1. The memory unit is in particular constituted by a RAM memory for storing transient data. The RAM memory is allocated in an irregular or regular structure. The arithmetic unit performs in particular addition, subtraction, multiplication, accumulation and shift operations.

Thus, all acquisition and tracking operations for the detected satellite are obtained independently in each respective channel of the correlation stage, which is in a bit parallel structure, in which several bits of calculation are obtained in one clock pulse. The digital signal is at 1kHz, which allows independent processing of the carrier frequency and the processing of the signal of the PRN code control loop at a frequency rate that is not too high. When a channel is locked to a satellite, the circuit synchronizes to the GPS data stream intended for subsequent calculations.

In this way, data transfer by means of the microprocessor means 12 no longer occurs in all relevant steps. The unique result of the correlation of each channel 7' transmitted to the correlation stage 7 of the microprocessor is in particular a GPS message at a frequency of 50 Hz. This results in a substantial reduction in current consumption.

Accordingly, microprocessor 12 is preferably an 8-bit CoolRISC-816 microprocessor including EM Microelectronic-Marin, Switzerland. The processor is clocked by a clock signal of 4.36 MHz. The microprocessor means 12 also comprise memory means, not shown, in which all the information relating to the positions of said satellites, their gold codes and the information that can be received by the terrestrial GPS receiver are stored.

During all satellite search and tracking, the operating channel 7' sends interrupt signals INT1 to INT12 to the microprocessor to alert the microprocessor that it can extract. Upon receiving the interrupt signal, the microprocessor typically looks for the channel from which the data to be extracted originated among all channels. The data may relate to, for example, configuration parameters, GPS messages, the status of the PRN code, frequency increments due to doppler effects, pseudoranges, modes for interrupting the receiving device, the status of the integrator counter, and other information.

Since several interrupt signals INT1 to INT12 can occur simultaneously, the microprocessor means 12 can also comprise a priority decoder for operating the channel 7'. Thus, the microprocessor may directly access a priority channel that transmits interrupt signals according to a determined priority order.

In another embodiment, not shown, the priority decoder may also be integrated in the correlation stage.

A single semiconductor substrate may contain all of the relevant stages including registers, priority decoders, microprocessors, and possibly a portion of the clock signal generator.

When the receiver 1 is set to operate, several channels 7' of the correlation stage 7 are configured by the microprocessor means 12. Each channel is configured to have introduced therein different parameters with respect to the carrier frequency and PRN code of a particular satellite to be searched and tracked. In one normal mode of operation, each channel is configured differently for searching and tracking its own satellites. Since the working channel is only locked to the visual satellite, several unused channels remain.

It is known that certain visible satellites are located lower in the horizontal plane than other satellites. Thus, the likelihood of obstructions momentarily attenuating the radio frequency signals from these satellites is greater than for those satellites located toward the zenith (zenith). In this case, it is sensitive to place unused channels configured to overcome the momentary loss of signal by the selected channel in parallel with the selected channel locked onto such a satellite.

As shown in fig. 3 and 4, one or more unused channels placed in parallel with the selected channel allows a larger satellite detection window to be obtained, and thus a larger reception dynamics for the satellite signal. If the signals from the satellites are no longer shielded by obstacles, these unused channels tend to saturate and cannot be used. Conversely, as soon as the signal is attenuated, the microprocessor means can use the data provided by the unused channel operating in place of the selected channel from which the tracked satellite was lost.

Fig. 3 shows a correlator 8, one part for the PRN code control loop and the other part for the carrier frequency control loop. The correlator 8 is the same in each channel 7' of the correlation stage 7, but is configured differently in each channel. For more details on the individual elements of the correlator, the reader is referred to the teachings of chapter five (in particular fig. 5.8 and 5.13) of the book "Understanding GPS Principles and applications" by Phillip Ward (edited by Elliott d. kaplan, Artech House Publishers, usa, 1996, version number ISBN 0-89006-.

Referring to fig. 3, an intermediate frequency signal IF represented in the figure by a solid line crossing an oblique line defining two bits is a complex signal (I + iQ) composed of a 1-bit in-phase signal component and a 1-bit quadrature signal component Q. The intermediate frequency signal IF has been sampled and quantized and first passes through a first mixer 20 of the carrier wave. A mixer or multiplier 21 multiplies the signal IF by the cosine of the internally generated copy of the carrier frequency (replica) minus I times the sine of the internally generated copy of the carrier frequency to extract the in-phase signal I from the complex signal, and a mixer or multiplier 22 multiplies the signal IF by the minus sine of the internally generated copy of the carrier frequency minus I times the cosine of the internally generated copy of the carrier frequency to extract the quadrature signal Q from the complex signal.

The sine and cosine signals are derived from block 45 of the COS/SIN table of the copy signal. The purpose of said first step in the first mixer 20 is to extract the carrier frequency from the signal carrying the GPS message.

After said operation, the equivalent of the PRN code of the signal from one channel to be acquired and the PRN code generated in said channel corresponding to the desired satellite must be found in the active or open channel. To this end, the in-phase and quadrature signals are passed through a second mixer 23 to correlate the signals I and Q with an early copy and a late copy of the PRN code to obtain four correlated signals. In each channel of the correlation stage, only the early and late copies are retained, regardless of the on-time copy. This minimizes the number of related components. However, by removing the on-time component from the code control loop, a loss in signal-to-noise ratio of approximately 2.5dB is observed.

Mixer or multiplier 24 receives signal I and early copy signal E from a 2-bit register 36 and provides a related early in-phase signal. Mixer or multiplier 25 receives signal I and the subsequent copy signal L from register 36 and provides a related subsequent in-phase signal. A mixer or multiplier 26 receives the quadrature signal Q and the early signal E and provides an associated early quadrature signal. Finally, a mixer or multiplier 27 receives the signal Q and the subsequent copy signal L and provides a subsequent quadrature signal. In the embodiment of the present invention, the drift or offset between the early copy E and the late copy L is half a chip, which means that the drift of a central on-time component P is 1/4 chips. For simplicity, the multiplier may be implemented, for example, using XOR logic gates.

Each of the four correlation signals enters one of the integrator counters 28, 29, 30, 31 as a pre-detection element, whose binary output word I_ES、I_LS、Q_ESAnd Q_LSIs represented over 10 bits. Of binary words at the output of an integrator counterThe number of bits defines the reception dynamics of the receiver. It is defined as the number of chips that can sum to 1023, which is equal to the PRN code. Each of the integrator counters 28, 29, 30, 31 of a channel selected by the microprocessor means at the start of a search is configured to provide a complete set of binary words I every millisecond_ES、I_LS、Q_ESAnd Q_LS。

Conversely, when an unused channel is selectively connected in parallel with a selected channel, the unused channel is configured so that the integration period of its integrator counter is greater than the standard integration period. Thus, the microprocessor means will signal S_TCTo each integrator counter to request it to count over a period greater than 1 millisecond. Preferably, the integration period of the unused channels is fixed at twice the standard integration period, but of course it may be fixed at time T_DAn integer multiple of (fig. 4).

Thus, the variation in the integration period of the integrator counter allows the sensitivity of the receiver to be adjusted, i.e. the signal reception dynamics to be increased. Therefore, the weak radio frequency signal received by the receiver has more chance to be above the detection threshold of each integrator counter at the end of the integration period. Thus, the configured unused channels have more opportunities than the conventionally configured selected channels to track a satellite whose signal is shielded by an obstruction.

The detection threshold is selected to detect the presence or absence of a searched or tracked satellite, taking into account that the radio frequency signal is "noisy".

All operations in the loop after these integrators occur in a bit-parallel configuration with the signal at a frequency of 1 kHz. To remove a portion of the noise of the useful signal to be demodulated, only the 8 most significant bits are used for the remainder of the digital signal processing chain.

The binary output word I represented in the figure by a solid line crossed by a diagonal line defining 8 bits_ES、I_LS、Q_ESAnd Q_LSEnters a code loop discriminator 32 and enters a code loop filter 33. The code loop discriminator performs the calculation of the signal I_ES、I_LS、Q_ESAnd Q_LSOperation of the energy of (1). The accumulation of values over a determined number of N (e.g., 16 cycles) integration periods is obtained in the code discriminator. Thus, the microprocessor means will also signal S_TCApplied to a discriminator 32 for unused channels placed in parallel with the selected channel.

The discriminator is irrelevant and of the Delay Locked Loop (DLL) type. It is composed in particular of an 8-bit multiplier and a 20-bit accumulator. At this discriminator, a correlation is generated from the carrier loop, since the doppler effect is felt not only at the carrier frequency but also at the PRN code modulated at the carrier frequency during the transmission of the signal by the satellite. Bringing the carrier to the code loop discriminator corresponds to dividing the carrier frequency drift increment by 1540.

Based on the filtered result of the discriminator, a phase increment is applied by the 28-bit NCO oscillator to the PRN code generator 35 so that it sends the PRN code bit sequence to the register 36 for a new correlation. The frequency resolution of this 28-bit NCO is about 16mHz (for a clock frequency of 4.36 mHz).

The controller processes the various results of the loop so that it can coordinate the acquisition and tracking operations. Once synchronized and locked to the desired satellite, the value I_ESAnd I_LSIs introduced into a demodulation element 50 which is capable of supplying 50Hz data messages to the microprocessor means over the data input and output registers at 1 bit. In addition to the messages, the microprocessor means also uses information, in particular relating to the incoming pseudoranges in buffer registers, in order to calculate X, Y and Z position, velocity and precise local time.

Any of the elements described above will not be described in detail since it is assumed that these are common knowledge to those skilled in the art.

Signal I_ESAnd I_LSThe sum in adder 37 is used to create signal I_PSAnd a signal Q_ESAnd Q_LSThe sum in the adder being used to create the signal Q_PSBoth represented by 8 bits. These binary words are introduced into the carrier loop discriminator 42 (envelope detection) at a frequency of 1kHz to calculate the energy of the signal before a carrier loop filter 43. The discriminator is formed in particular by an 8-bit multiplier and a 20-bit accumulator. It is of the frequency and phase locked loop type.

An averaging operation is performed on the frequency discriminator to improve the robustness and accuracy of the carrier tracking loop. The accumulation provided in the discriminator lasts for N cycles, for example 16 cycles, which corresponds to 16 milliseconds. The microprocessor device also outputs a signal S_TCApplied to a discriminator 42 for unused channels placed in parallel with the selected channel.

Based on the result of the discriminator, and after passing through the filter, the carrier 24-bit NCO oscillator 44 receives a frequency tool (instance) (bin) for correcting the carrier frequency copy. This 24-bit NCO has a frequency resolution of about 260 mHz.

Although the carrier tracking loop is updated only after confirmation of the presence of the satellite signal, the two controls or constraints of the code and carrier are synchronized during the tracking process.

It will be appreciated that in the course of a radio frequency signal transmitted by a satellite, the doppler effect has an effect on the signal on both the carrier frequency and the PRN code, which means that the code and carrier control loops are interconnected to achieve better accuracy of adjustment of the PRN code level and the carrier frequency received at the receiver.

The PRN code phase is delayed by a step size of 1 chip per correlation period. This allows the code to be shifted in time to find the satellite phase drift. Once the satellite has been found, the carrier frequency, including the doppler effect present in one of the control loops of the carrier, must be corrected. In addition to the doppler effect, the lack of accuracy of the internal oscillator and the ionospheric effect must also be considered. These errors, which are corrected in the code and carrier loops, correspond to a frequency drift of 7.5 kHz.

Since the rf signal may be interrupted after passing an obstacle, an interruption check must be performed on the selected operating channel. Data from unused channels placed in parallel are taken into account by the microprocessor means as soon as said channels no longer provide binary words from their adder counters above a certain satellite detection threshold. Since the integration period is no longer in the unused channel, it must have more opportunities to detect the obstacle-attenuated signal from the visible satellite.

Fig. 4 shows, by way of example, a diagram of the binary word value as a function of the integration time during integration of an adder counter. In the ideal case, for a perfect correlation, in particular of the code copy, with the intermediate frequency signal, the output binary word of an adder counter is maximized, i.e. 2ⁿOr 1023, during an integration period T_DAt the end there is a copy of the PRN code. At the end of the integration period, the counter is reset to zero to perform a new integration count step.

For the present invention, the channel selected for searching and tracking the visible satellites has an integration period fixed at 1 millisecond. In contrast, unused channels connected in parallel with the selected channel are configured with a larger integration period, preferably about 2 milliseconds. However, most of the time, during the tracking of a visible satellite, during period T_DThe last binary value is between the maximum capacity value and a certain threshold level. At each clock pulse T₁Or CLK, the integrator counter increments or decrements the binary word as a function of the correlation signal it receives.

If an obstacle appears in the path of a signal received by a selected channel of the receiver for a visible satellite, the summer counter for that channel will be in each integration period T_DProvides a binary word whose value is below the threshold level. By increasing the integration period of the adder counter, the channelThere is more opportunity to avoid losing the signal shielded by the obstacle.

As mentioned above, all information about the position of the satellites, their gold codes and what can be observed by a terrestrial GPS receiver is stored in the memory of the microprocessor means. Typically, at the start, all channels of the receiver are configured in a conventional manner so that each searches for and tracks a particular satellite. However, after the first phase, only a certain number of channels set to work are locked to one visible satellite. Thus, after this step, several deactivated or unused channels remain.

Subsequently, the microprocessor means can reactivate the unused channels in order to prevent signal loss of the selected channel during the visual satellite tracking phase. To this end, the non-periodic channels as defined above are each placed in parallel with a respective working channel. The unused channels are configured with a larger integration period than the active channels to improve signal reception dynamics. In theory, the unused channels are only connected in parallel with channels locked to a visible satellite that may shield the signal from obstructions.

In another approach, it is also possible to design the connection unused channels so that once the receiver is turned on, it configures only channels that can lock to a particular visible satellite in the conventional manner. Thereafter, at least one unused channel is connected in parallel with one of the operating channels to prevent momentary loss of signal due to obstruction masking.

If the GPS receiver is installed in a low power portable object equipped with a battery or accumulator, it is generally not necessary to open all channels. At least four channels, each locked to a particular visible satellite, are sufficient to provide data to the microprocessor for calculating position, velocity, and/or time. These four channels are configured in a conventional manner. Thus, in accordance with the present invention, it is desirable to configure additional unused channels, each placed in parallel with a respective selected channel having a larger integration period.

Several channels may also be configured differently in parallel in order to search for and/or track the same satellites whose radio frequency signals may be shielded by obstacles in the path of these signals. Each channel may be configured by the microprocessor device to have a different integration time than their integrator counters. Likewise, if the microprocessor means observes that the channel no longer detects the radio frequency signal from the tracked visible satellite, it is possible to increase the integration period of the integrator counter of one operating channel.

From the above description it is clear that many different embodiments of the receiver, in particular of the GPS type, are possible without departing from the scope of the invention as defined in the appended claims.

Claims (10)

1. Receiver for a radio frequency signal transmitted by a transmission source, said receiver comprising:

-receiving and shaping means (3) for frequency translating the radio frequency signal to generate an intermediate frequency signal (IF),

-a correlation stage (7) consisting of several correlation channels (7') for receiving the intermediate frequency signals in order to correlate them in a working channel control loop with the frequency carrier and a specific code copy of the visual transmission source to be searched and tracked, each channel being equipped with a correlator (8), wherein at least one integrator counter (28, 29, 30, 31) can be providedCapable of providing a binary output word (I) at the end of each determined integration period (TD) of the correlated signal_ES，I_LS，Q_ES，Q_LS) A value that, compared to a determined detection threshold, allows the detection of the presence or absence of the transmission source being searched and tracked,

-microprocessor means (12) connected to the correlation stage for processing data extracted from the radio frequency signal after correlation, said receiver being characterized in that: the microprocessor means is arranged to configure at least one unused channel arranged to operate in parallel with one of the operating channels for searching and/or tracking the same visible transmission source, the unused channel being configured such that the integration period of its integrator counter is different from the integration period of the integrator counter of the operating channel.

2. A receiver according to claim 1 for receiving radio frequency signals transmitted by satellites, characterized in that: the correlation stage (7) comprises a greater number of correlated channels than visible satellites so that at least one unused channel can be connected to operate in parallel with one operating channel for searching and/or tracking the same particular visible satellite.

3. A receiver as claimed in claim 2, characterized in that the number of channels is greater than or equal to 12.

4. A receiver as claimed in claim 1, characterised in that several unused channels are arranged so as to be connected to operate each channel in parallel with one of the operating channels, the integration period of the integrator counter of each unused channel being greater than the integration period of the integrator counter of the respective operating channel.

5. A receiver according to claim 1, for receiving radio frequency signals transmitted by a satellite, characterized in that the integration period of the integrator counter of a channel operating in the visible satellite search and/or tracking phase is equal to the repetition period of the specific code of the transmitting satellite, and in that an integrator counter of an unused channel connected to operate in parallel with the operating channel has an integration period greater than the repetition period of the specific code and equal to twice said repetition period.

6. A receiver as claimed in claim 1, characterized in that a set of data input and output registers (11) is arranged as an interface between the correlation stage (7) and the microprocessor means (12) for receiving data transmitted by the microprocessor to the correlation stage and data supplied by the correlation stage to the microprocessor.

7. A receiver as claimed in claim 6, characterized in that a set of registers (11) is provided for each channel (7') of the correlation stage (7).

8. A receiver as claimed in claim 1, for receiving radio frequency signals transmitted by satellites, characterized in that in each channel a controller (9) comprising a digital signal processing algorithm is associated with the correlator (8) so as to allow all synchronization tasks of searching and tracking satellites to be performed independently of the microprocessor means (12) when the channel (7') is set in operation.

9. A receiver as claimed in claim 1, for receiving radio frequency signals transmitted by satellites, characterized in that each channel receives a complex intermediate frequency signal consisting of an in-phase signal component (I) and a quadrature signal component (Q), and in that each correlator of a channel comprises:

-a first mixer (20) for correlating the in-phase signal component with a first copy of the carrier frequency and for correlating the quadrature signal component with a second copy of the carrier frequency offset by 90 ° with respect to the first copy of the carrier frequency;

-a second mixer (23) for correlating the output in-phase signal of the first mixer with a first earlier specific code copy and with a second later specific code copy and for correlating the quadrature output signal of the first mixer with the first earlier specific code copy and with the second later specific code copy, and in that four integrator counters (28, 29, 30, 31) per channel receive the correlated output signals from the second mixer so as to each provide a binary output word whose value, compared to a determined detection threshold level, allows the detection of the presence or absence of a searched and tracked satellite.

10. A receiver as claimed in claim 1, characterised in that after the integrator counters, each channel correlator comprises a carrier discriminator (42) in the carrier correction control loop and a code discriminator (32) in the code correction control loop, each discriminator being arranged by the microprocessor means (12) to consider the output value of the integrator counters over a discriminator period which is N times greater than the integration period, where N is an integer, the discriminator period of an unused channel connected to operate in parallel with an operating channel being greater than the discriminator period of the operating channel and equal to twice said discriminator period.