A method for determining a boundary of an information element, in which a repetition coded signal transmitted by satellites is received, which signal is modulated with information elements. A group of symbols forms one information element. A group of reference values are formed on the basis of the received signal. Of these reference values at least one vector is formed wherein the number of the elements corresponds to the number of symbols use in the transmission of the information element. A determination vector is formed on the basis of the at least one vector, whereafter the greatest of the elements of the determination vector is searched. The index of said elements indicates the boundary of the information element.
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0. 29. A method in an electronic device for detecting a boundary of an information element, in a received repetition-coded signal, wherein a group of symbols forms one information element, the method comprising:
forming reference values on the basis of the received signal with a filtering means of the electronic device, wherein a different group of symbols is used for each of said reference values;
searching a largest reference value from the reference values with the determination means of the electronic device, and
using said largest reference value for indicating the boundary of the information element.
0. 39. An electronic device comprising a receiver for receiving a repetition-coded signal, in which signal a group of symbols has been used for transferring one information element, wherein the receiver is configured to determine the boundary of the information element from the received signal, wherein the electronic device comprises at least:
a calculation block for forming reference values on the basis of the received signal, and
a determinator for searching a largest reference value from the reference values, wherein the electronic device is configured to use the largest reference value for indicating the boundary of the information element.
0. 34. A system comprising a receiver for receiving a repetition-coded signal, in which signal a group of symbols has been used for transferring one information element, wherein the receiver comprises a device for determining a boundary of the information element from the received signal, wherein the system further comprises at least:
a calculation block for forming reference values according to the received signal, wherein a different group of symbols is used for each of said reference values; and
a determinator for searching a largest reference value from the reference values, wherein the system is configured to use the largest reference value for indicating the boundary of the information element.
12. A system comprising a receiver for receiving a repetition-coded signal that is modulated with information elements, in which signal a group of symbols has been used for transferring one information element, wherein the receiver comprises means for determining a boundary of the information element from the received signal, wherein the system further comprises at least:
filtering means for forming reference values according to the received signal,
vector-forming means for forming elements of at least one vector on the basis of said reference values, in which the number of elements in said at least one vector equalling the number of symbols in said group of symbols forming the information element,
vector-processing means for forming elements of a determination vector on the basis of said at least one vector, and
determination means for searching the greatest element of said determination vector, wherein an index of the element is arranged to be used for indicating the boundary of the information element.
0. 48. An electronic device comprising a receiver for receiving a repetition-coded signal that is modulated with information elements, in which signal a group of symbols has been used for transferring one information element, wherein the receiver is configured to determine the boundary of the information element from the received signal, wherein the electronic device comprises at least:
a calculation block for forming reference values on the basis of the received signal,
a vector-forming block for forming elements of at least one vector on the basis of said reference values, in which the number of elements of said at least one vector equalling the number of symbols in said groups of symbols forming the information element,
a vector-processing block for forming elements of a determination vector on the basis of said at least one vector, and
a determinator for searching the greatest element of said determination vector, wherein an index of the element is arranged to be used for indicating the boundary of the information element.
20. An electronic device comprising a receiver for receiving a repetition-coded signal that is modulated with information elements, in which signal a group of symbols has been used for transferring one information element, wherein the receiver comprises means for determining the boundary of the information element from the received signal, wherein the electronic device further comprises at least:
filtering means for forming reference values on the basis of the received signal,
vector-forming means for forming elements of at least one vector on the basis of said reference values, in which the number of elements of said at least one vector equalling the number of symbols in said groups of symbols forming the information element,
vector-processing means for forming elements of a determination vector on the basis of said at least one vector, and
determination means for searching the greatest element of said determination vector, wherein an index of the element is arranged to be used for indicating the boundary of the information element.
1. A method in an electronic device having a receiver for detecting a boundary of an information element, the method comprising:
receiving a repetition-coded signal with the receiver, which is modulated with information elements, wherein a group of symbols forms one information element;
forming reference values on the basis of the received signal with a filtering means of the electronic device;
forming elements of at least one vector on the basis of the reference values with a vector-forming means of the electronic device, in which the number of elements of at least one vector equalling the number of symbols in said group of symbols forming the information element;
forming elements of a determination vector on the basis of said elements of said at least one vector with a vector-processing means of the electronic device;
searching the largest value of the elements of said determination vector with a determination means of the electronic device, and
using an index of the largest value of the element of said determination vector for indicating the boundary of the information element.
2. The method according to
3. The method according to
4. The method according to
5. The method according to
6. The method according to
7. The method according to
8. The method according to
9. The method according to
performing substantially simulataneously simultaneously for each signal an integration of the received signals in one-symbol-length integration intervals in order to form signal specific integration values,
defining a calculation window having a start and an end, forming signal specific reference values by taking samples of each signal specific integration value,
using, in each of said low-pass filtering steps as many signal specific integration values as there are symbols used in the transmission of one information element,
wherein the method comprises selecting for each of said low-pass filtering steps such signal specific integration values in which at least a half of the integrating interval is between the start and the end of the calculation window.
10. The method according to
11. The method according to
13. The system according to
14. The system according to
15. The system according to
16. The system according to
17. The system according to
18. The system according to
19. The system according to
21. The electronic device according to
22. The electronic device according to
23. The electronic device according to
24. The electronic device according to
25. The electronic device according to
26. The electronic device according to
27. The electronic device according to
28. The electronic device according to
0. 30. The method according to claim 29, wherein said searching comprises examining whether a value of at least one element adjacent to an element corresponding to the largest reference value is of the same order of magnitude, wherein deducing the boundary of the information element by interpolating, otherwise deducing the boundary of the information element according to said largest reference value.
0. 31. The method according to claim 30, wherein the interpolating comprises using said largest reference value as well as at least one value of an element adjacent to said largest reference value.
0. 32. The method according to claim 29, wherein said received repetition-coded signal comprises signals transmitted by satellites of a satellite positioning system.
0. 33. The method according to claim 29, wherein the information used is binary information, and one bit of said binary information comprises one of said information elements.
0. 35. The system according to claim 34, further comprising a device for integrating the received signal in integration intervals of one symbol in order to form integration values, and a device for low-pass filtering of the integration values formed in the integration intervals.
0. 36. The system according to claim 34, wherein the determinator comprises a device for comparing the largest reference value and values adjacent to said largest reference value, wherein if the value of at least one element adjacent to said largest reference value is of the same order of magnitude, the boundary of the information element is arranged to be deduced by interpolating, otherwise the boundary of the information element is arranged to be deduced on the basis of said largest reference value.
0. 37. The system according to claim 36, wherein in the interpolating said largest reference value, and at least the value of one adjacent element of the same order of magnitude is arranged to be used.
0. 38. The system according to claim 34, wherein said system is a satellite positioning system comprising satellites sending the repetition-coded signal.
0. 40. The electronic device according to claim 39, wherein at least two vectors are formed in the a calculation block, wherein the electronic device is configured to form a terminating vector by connecting said at least two vectors, counterpart element to counterpart element.
0. 41. The electronic device according to claim 39, wherein the electronic device comprises an integrator for integrating the received signal in one-symbol size integration intervals in order to form integration values, and a filter for low-pass filtering of the integration values formed in the integration intervals.
0. 42. The electronic device according to claim 39, wherein the low-pass filter is configured to form reference values without sign by using the absolute value of the reference values.
0. 43. The electronic device according to claim 39, wherein the determinator is configured to compare the largest reference value and values adjacent to said largest reference value, wherein if the value of at least one element adjacent to the largest reference value is of the same order of magnitude, the electronic device is configured to deduce the boundary of the information element by interpolating, in other case the electronic device is configured to deduce the boundary of the information element on the basis of said largest reference value.
0. 44. The electronic device according to claim 43, wherein the electronic device is configured to use in the interpolating, said largest reference value and at least the value of one adjacent element of the same order of magnitude.
0. 45. The electronic device according to claim 39, wherein the calculation block comprises a moving average block for performing a moving summing for reference values, wherein said moving average block is configured to form each reference value without sign by summing a defined number of integration values, and said moving average block is further configured to used partly different integration values in the forming of each reference value without sign.
0. 46. The electronic device according to claim 39, wherein the receiver is a satellite positioning receiver.
0. 47. The electronic device according to claim 39, further comprising a mobile station.
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In Formula 1, the average time of flight (ToF) of the signal from the satellite to the receiver is 78 ms. As a reference it is possible to use any such receiving channel in which the signal-to-noise ratio (SNR) is sufficient.
The time data (ToW) is transmitted in the navigation message at intervals of six seconds and it indicates the time passed from the latest change of the GPS week. Thus, the value range of the time data is the remainder of one week. In a corresponding manner Tmsj(k) equals the remainder of six seconds and Tchipj(k) equals the remainder of 1 ms. The first three terms of the Formula (1) can also be used in the measurement of the time of arrival (ToA) of the signal.
In poor receiving conditions, in which the navigation data cannot be detected e.g. due to a high bit error rate (BER), it is not possible to determine the GPS time directly by means of the Formula 1. However, the code phase can normally still be measured.
In poor signal conditions, it is possible to try to detect the moment of change for the bit (boundary). The detection of bit boundary is necessary in order to detect the navigation data, to use coherent integration in the tracking loop, and/or to calculate pseudo ranges in such a receiver in which the control is performed only according to the C/A code.
In some prior art receivers, so-called hard decisions are used for detecting the bit boundary. In the receivers, the received signal is integrated during an epoch. Subsequently (1 ms), the output signal of the correlator of the receiver is examined. In the histogram method the output value of the correlator is compared to the previous output value. In case the output values are of opposite sign, a decision is made that the sign of the data bit has changed. The reliability of each such decision made after a change in epoch is highly deteriorating as the signal/noise ratio (C/NO) deteriorates, wherein also the probability of erroneous positioning increases. Using this method presupposes that the synchronizing part of the receiver is phase-locked into the epoch. Additionally, it is troublesome to adapt this method in such receivers in which common dump is used.
In another receiver, correlation of a received signal is performed to a pre-synchronising part (preamble of Telemetry Word), whose contents are known. A drawback with this arrangement is that the synchronizing time is relatively long, on average at least 3 seconds. Additionally, the final error ratio is rather poor, because the length of the initial synchronizing part is only 8 bits.
The purpose of the present invention is to obtain an improved method for detecting the bit boundary from the received signal, and a receiver in which the aim is to detect the bit boundary. More precisely, the method according to the present invention is primarily characterized in what will be presented in the characterizing part of the appended claim 1. The system according to the present invention is primarily characterized in what will be presented in the characterizing part of the appended claim 12. The electronic device according to the present invention is primarily characterized in what will be presented in the characterizing part of the appended claim 20.
Considerable advantages are achieved by the present invention when compared with positioning systems and receivers of prior art. Because in the method of the invention the bit boundary can be detected also from a weak and noisy signal more reliably than when applying prior art methods, the positioning reliability can be improved. Moreover, when applying the method of the invention it is possible to detect the contents of the data transferred in the signal faster than in the prior art, because the bit boundary can be detected more precisely. The use of the method according to the invention allows positioning also indoors, which is not necessarily possible with prior art solutions.
In the following, the present invention will be described in more detail with reference to the appended drawings, in which
In the following, the operation of the method according to a preferred embodiment of the invention will be described with reference to the system shown in
Next, the operation of an advantageous receiver PR will be briefly described with reference to the reduced block charts of
An advantageous structure for the digital monitoring blocks 8a, 8b, 8n is shown in the block chart of
The receiver PR preferably also comprises means for performing the functions of the wireless communication device, such as a second antenna 20, a radio part 21, audio means, such as a codec 22a, a speaker 22b and a microphone 22c, a display 23, a keypad 24, and a memory 25. The control block 9 can be at least partly common for performing the functions of the receiver PR and performing functions of the wireless communication device, or separate processors, or the like, can be used for these functions. In the following, the invention will be described in more detail with reference to the receiver shown in
However, navigation data cannot be detected in poor signal conditions, but the synchronizing of the signal can, nevertheless, be possible. After the receiver PR has been locked to the signal to be received (frequency and/or code phase), the bit boundary detection is started by using the method of the invention in the following manner.
Transmission of different binary values is performed in code modulation for example in a manner that with the first value (e.g. +1) a modulating code is used as such and, in a corresponding manner, with a second binary value (e.g. −1), inverse values of the chips of the modulating mode are used.
In the analog/digital convener 6 an analog/digital conversion is performed to the satellite signals to be received, wherein the further processing of the signals can be carried out on the basis of digital signals. In a receiver comprising a plurality of receiving channels a separate analog/digital converter for each channel can be used, or a common converter is used for the channels, wherein the sorting of the channel signals is performed after the analog/digital conversion, as in the receiver according to
In practice, the moment the samples are taken is not always at the same point of the epoch, because in particular the Doppler shift and multipath propagation can cause time variable delay in the signal transmission time from satellite to receiver. In addition, the sample interval is not necessarily always exactly 1 ms inter alia due to inaccuracy of the clock of the receiver. In
In case the moving calculation block MA uses calculation that preserves the sign, such as average or summing, the absolute values of these reference values are computed in an absolute value block ABS in order to eliminate bit data dependency from the reference values. In this case, a group of numerical values as illustrated in
These determination values are processed in a determination block DET where preferably a maximum point, that is the greatest determination value, is searched. If only one such maximum point is found, its index indicates the location of the bit boundary. In the situation in
In the determination block DET it is possible, instead of searching for the maximum, to perform a comparison to a predetermined threshold value, wherein, when such a threshold value that is larger than (or as large as) the threshold value is found, the location point of the bit boundary is concluded from the determination value index exceeding this threshold value.
Even though it has been described above that for determining the determination values, certain measures are taken in separate blocks, and values are transferred between the blocks, it is obvious that these measures can be performed advantageously in the control block 9 as program codes of a signal processing unit (not shown), or the like. In this case it is not necessary to transfer the numerical values to different blocks, but for example in the memory means one or a plurality of areas of the memory means are allocated for storing these values. In this case, the function according to each block stores the values it has determined to a certain memory area, from which the function according to the following block retrieves these numerical values as the operation is proceeding.
The above mentioned operations are performed for a given period of time, for example until a wished number of vectors K have been formed, or until the maximum value exceeds a given threshold value. After this, a decision of the bit boundary is made in the determination block in a manner described above. The operation can also be repeated in case it is wished to redefine the location of the bit boundary, for example if the signal conditions change to a significant degree, or if the satellite, which the receiver has been following, changes.
In the embodiment described above, the integration of the signal was performed separately on each channel, wherein the moment when the integration is started or stopped is determined separately for each channel. Subsequently, a situation is described in which a so-called common dump is used, in which an integration is performed for every channel simultaneously, for example on the basis of the epoch of the signal of one channel. In this case, the timing of the epoch is not necessarily the same as that of the other channels, because the signals of different satellites have a different propagation time from the satellite to the receiver. However, the moving average is calculated in epochs. This requires some changes to the above-described method according to a preferred embodiment of the invention. For each channel, the phase of the epoch at the dump time has to be detected, so that the moment when the epoch is changing can be calculated relative to the integration time (that is, the moment in the integration interval at which the epoch changes). As the integration interval can, to a significant degree, differ from the timing of the epoch, the bit boundary can be situated relatively far from the moment when the integration interval is started or terminated. Thus, to form signal-specific reference values of each channel, a number of such signal-specific integration values are selected that are used in the transmission of one bit, in which values at least a half of the epochs belong to said integration interval. For example in the case of
Correspondingly, in a situation in which the epoch is shorter than the integration time it is possible to apply the above-described deduction analogically in order to determine which samples are selected to the selection window at a time. However, the selection criteria are different than those described in the above situation.
Also, it may be necessary to make changes in the decision block if it is possible that the epoch differs significantly from the integration time phase. If the integration time ends for example near the midpoint of the epoch, such (successive) calculation windows starting either just before the bit boundary or right after it, are substantially equally good in terms of bit energy. In this case, either of the calculation windows can be used in the coherent one-bit size integration. This means that there can be a difference of approximately 1 ms in the bit boundary detection depending on which of the calculation windows is used. This may cause significant errors in calculation of pseudo ranges and in positioning. The effect of this error can be advantageously reduced as follows. Comparison if performed for the components adjacent to the maximum component of the vector from which the bit boundary is determined. If either of these components is significantly greater than the other component and is approximately of the same order as the maximum value then this sample indicates the direction where the real bit boundary is different from the bit boundary indicated by the maximum value. In this examination the last (20th) and the first component of the vector are interpreted as adjacent values. The bit boundary can now be approximated for example by interpolating as follows:
in which chip_at_dump is the order number of the chip of the epoch at the end of the integration time, max_val is the maximum value, val_right is the value on the right of the maximum value, and val_left is the value on the left of the maximum value. If the maximum value is the first value of the calculation window, the last value of the calculation window is interpreted as the value on the left of the maximum value, and correspondingly, if the maximum value is the last value of the calculation window, the first value of the calculation window is interpreted as the value on the right of the maximum value.
In a situation when the receiver is (in the code phase and carrier wave block) only frequency locked, the signal to be integrated is in the complex form. Thus, complex calculation is used in the calculation of the moving average, wherein in the absolute value block ABS a complex absolute value is formed, or some other real number without sign, such as the sum of the absolute value of the real part and the absolute value of the imaginary part (abs(Re)+abs(Im)).
Instead of calculating the average value or summing the vectors performed in a determination-value-forming block AVG it is possible to use also some other low-pass filtering function. Additionally, in the determination-value-forming block AVG it is possible to use adaptive determination function; for example the threshold value can be changed on the basis of the noise contents of the received signal.
By using the above-described method, the positioning can be performed also in poor signalling conditions, also indoors. In the method no information on the data used in the modulation of the signal is necessary, such as navigation data, for bit boundary determination according to the above-described method. After the bit boundary has been determined, it is possible, if necessary for example by using correlators to attempt to determine the starting points of the frames used in the transmission of the navigation data.
In particular when using the common integration principle it is possible in some applications to decrease the noise effect in a manner that the first and last values of the window are weighed less than other values. In the calculation of the weigh coefficient it is possible to use for example the maximal ratio combining (MRC) formula known as such.
After detecting the bit boundary it is possible to perform the positioning, even if the receiver did not have navigation data and the exact time data. In this context it is possible to utilize for example auxiliary data obtained from the mobile communication network, but also other methods are possible to apply in connection with the method of the present invention.
Even if the invention has been exemplified above by using a spread-spectrum signal that is modulated from a repetition-coded signal modulated with an individual code, the invention can be applied also in other systems using repetition coding and in which different phases of binary and other information are modulated by using symbols.
It is obvious that the present invention is not limited solely to the above-presented embodiments, but it can be modified within the scope of the appended claims.
Kokkonen, Mikko, Pietila, Samuli
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