JPH06125329A - Receiver and tuning method for multi-path signal - Google Patents

Abstract

PURPOSE:To eliminate useless power consumption by latching the tuning of a multi-path signal only for a prescribed time when a signal intensity of a path is rapidly deteriorated to avoid switching control operation of the useless tuning state of the signal when the signal is recovered. CONSTITUTION:A control circuit 16 controls each of demodulation sections 141-143 to demodulate, e.g. three multi-path signals in the order of the strength of signals in response to an output from a correlation detector 15. Whether or not the intensity of the selected three multi-path signals is deteriorated to a prescribed threshold level or below within a prescribed time is detected. When the strength reaches a prescribed threshold level or below, the selection state of the three multi-path signals for a prescribed time only is latched. That is, when the signal intensity reaches the threshold level or below within a prescribed time, it is discriminated that the signal is rapidly missing due to a cause such as interruption of a path with a sender side for a short period depending on the position of a mobile body during movement at communication. Thus, the tuning state so far is latched only for a prescribed time and the recovery of the signal due to a change in the moving position is awaited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus and a multipath signal selecting method for selecting and demodulating n multipath signals in order of increasing signal strength in a received signal including a plurality of multipath signals. Regarding

[0002]

2. Description of the Related Art In recent years, it has been studied to use a so-called spread spectrum communication system for terrestrial mobile communication. In the case of this terrestrial mobile communication, the signal transmitted from the base station is input to the mobile terminal as a so-called multipath signal which has been subjected to various reflections and interferences. As one of the methods for effectively demodulating this multipath, for example, CDMA (Code Division Mult) as disclosed in International Publication No. WO91 / 07036.
There is a so-called multi-rake (RAKE) method, which is a type of iple access method.

This system takes advantage of the fact that the pseudo noise sequence used in spread spectrum communication is sufficiently high in comparison with the data transmission rate, so that it is received with a slight time delay (delayed). It is intended to effectively perform demodulation by separating path signals, independently demodulating each signal by a plurality of demodulation units provided in advance, and appropriately processing the result. Lake (RAK
E) means “rake” and is named after collecting multipaths with a rake (a plurality of demodulation units). Each of the plurality of demodulation units is also called a finger.

In such a so-called rake type receiver, a spread spectrum signal including the multipath signal converted into an intermediate frequency (IF) signal is sent to a multiplier, and a signal of the frequency of the IF signal is sent. The output of the voltage controlled oscillator (VCO) is multiplied by the output to obtain a spread spectrum signal converted to almost 0 Hz, and the multiplied output is output to a plurality of demodulators (fingers) corresponding to the rake. It is sent and demodulated, and the final demodulated data is obtained based on each demodulation result from each of these fingers.

[0005]

If n (n is an integer of 2 or more) fingers (demodulation section) are provided in advance in such a conventional so-called rake type receiving device, these For n fingers (demodulation unit),
In general, n pieces of the received multipath signals are selected and transmitted in the descending order of signal strength. Therefore, at least one of the n signals currently selected (X
If the signal strength of (1) is lower than the (n + 1) th signal strength or lower than a predetermined threshold value, the signal X is not selected, and the (n + 1) th multipath signal up to that time is not selected. A signal with a signal strength of will be selected instead.

Here, in the case of an actual multipath signal of mobile communication, its distribution is almost fixed in a short time,
Even if the signal disappears due to a momentary interruption of one path due to the movement of the mobile object, the same distribution often appears at the next moment. However, in the conventional receiving apparatus, even when one signal disappears for a short period of time, the combination of the selected signals is switched, so that the correspondence relationship between the demodulation unit and the multipath signal is switched, and the smooth demodulation is performed. Cannot be performed, control operations are complicated, power consumption is increased, and other adverse effects occur.

The present invention has been made in view of the above circumstances, and in a receiving apparatus such as the so-called Rake spread spectrum receiver as described above, each demodulation unit for a received multipath signal is It is an object of the present invention to provide a receiving apparatus that prevents the adverse effect caused by the switching of the signal selection state due to a short-term change in the path state or the like and enables optimum control.

[0008]

A receiving apparatus according to the present invention selects a multipath signal having a strong signal strength from a plurality of multipath signals in a received signal to form a demodulated signal. In, correlation detection means for detecting the signal strength and delay time information of the plurality of multipath signals,
N demodulation means for respectively demodulating the input signals, and the n demodulation means for demodulating n multipath signals having a specific time distribution based on the signal strength information and the delay time information. And a first control unit for controlling the signal strength information of n multipath signals having the specific time distribution, the first control unit controlling the signal strength information for a predetermined time ΔT.
When the value becomes equal to or less than the predetermined value S _TH within the predetermined range, the above-mentioned problem is solved by controlling the demodulation of n multipath signals having the above-mentioned specific time distribution for a certain time T _W.

Here, it is preferable that the received signal is a spread spectrum signal which is spread by a predetermined pseudo noise code. The correlation detecting means includes a pseudo noise generating means for generating the predetermined pseudo noise code, a second control means for controlling a generation timing of the predetermined pseudo noise code, the predetermined pseudo noise code and the above. Despreading means for mixing the received signal, and based on the output of the despreading means, the correlation value between the received signal and the pseudo noise code is detected, and the correlation value is output as the signal strength information. It may be configured with a detection circuit. Further, the demodulating means is a despreading means for mixing the pseudo noise generating means whose generation timing of the predetermined pseudo noise code is controlled by the first controlling means and the predetermined pseudo noise code transistor multipath signal. And the data demodulating means for demodulating the data despread by the despreading means.

Next, according to the method of selecting a multipath signal according to the present invention, when n multipath signals are selected and demodulated in descending order of signal strength among a plurality of multipath signals in a received signal. In the method of selecting multipath signals of No. 1, when the signal strength of the n multipath signals currently selected drops below a predetermined value within a predetermined time, the n multipath signals selected for a fixed time are Retaining the selection of path signals solves the above problems.

Also in this case, it is preferable that the received signal is a spread spectrum signal which is spread by a predetermined pseudo noise code.

[0012]

In a temporary interruption state of a path caused by the movement of at least one of the transmitting side and the receiving side in mobile communication, the signal strength of the path is rapidly lowered and disappears. By holding the selection of multipath signals for a certain time (prohibiting new selection) when there is a significant signal strength drop, it is not necessary to switch the previous signal selection state when the signal is restored next time. In addition, unnecessary switching control operation of the signal selection state can be omitted, wasteful power consumption can be eliminated, and demodulation processing in each demodulation unit can be smoothly continued.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block circuit diagram showing a schematic structure of a main part of a so-called rake type receiving apparatus as an example of a receiving apparatus according to the present invention. In the illustrated example, the demodulators (fingers) 14 ₁ , 14 ₂ , 14 ₃ perform digital processing, and the number of fingers is, for example, 3
However, any number of 2 or more is acceptable.

In FIG. 1, a spread spectrum signal converted to an intermediate frequency (IF) is input to an input terminal 10 and includes a multipath signal as described above in terrestrial mobile communication. This input IF signal is sent to the multiplier 11, and the voltage controlled oscillator (VCO) 12
Is multiplied by the output from. Since the VCO 12 is preset to output the signal of the above intermediate frequency (IF), the frequency of the output from the multiplier 11 is approximately 0 Hz, and the so-called quasi-synchronous detection circuit is formed by these multiplier 11 and VCO 12. Will be configured.

The output from the multiplier 11 is converted into a digital signal by an A / D (analog / digital) converter 13. As a sampling frequency for this A / D conversion, a frequency f _over which is higher than the frequency f _{PN of the} pseudo noise (PN) series used for the spread spectrum is used to perform so-called oversampling. A / D converter 1
The output from 3 is sent to a plurality of, for example, three demodulation units (fingers) 14 ₁ , 14 ₂ and 14 ₃ and a correlation detector (searcher) 15. Demodulation unit 14 (14 ₁ , 14 ₂ ,
14 ₃ ) is a circuit for performing despreading, synchronization acquisition, data demodulation, and frequency error detection.
Is for detecting signal strength information and delay time information of the multipath signal, and further, for example, three are selected in descending order of signal strength by judging the distribution state of the signal strength and delay time of these multipath signals. You may have the function to do.

The output from the correlation detector 15 is a control circuit 16 as a control means using a so-called microprocessor.
Sent to. According to the output from the correlation detector 15, the control circuit 16 outputs, for example, three multipath signals in descending order of signal strength to the demodulation units (fingers) 14 ₁ , 14 ₂ ,
14 ₃ to are those controls to demodulate, the demodulator 14 _1, 14 _2, 14 ₃ for each pseudo noise (PN) generator has therein is the selected 3
Addresses for demodulating (especially despreading) each of the two signals are sent. The signals demodulated by the demodulators 14 ₁ , 14 ₂ and 14 ₃ are sent to the signal synthesizing circuit 17, are synthesized, and are taken out from the output terminal 18 as demodulated data. The frequency error Delta] f ₁ from the demodulator _{14 1, 14 2, 14 3} , Δf 2, Δf 3 be combined, but not sent to the control terminal of the VCO12 through the output terminal 19, the frequency As a method of combining, for example, not only the frequency error of each signal demodulated by each demodulation unit but also the signal strength is taken into consideration, that is, each frequency error is weighted by each signal strength and added and combined. ,
The VCO control signal is obtained.

Here, in the embodiment of the present invention, the control circuit 16 determines whether or not the signal intensities of the three selected multipath signals have fallen below a predetermined threshold value S _{TH within a} predetermined time ΔT. When it is detected and becomes less than or equal to the predetermined threshold value S _TH within the predetermined time ΔT, the operation of holding the selected state of the three selected multipath signals for the constant time T _W is performed. That is, when the signal strength becomes equal to or lower than the threshold value S _TH within the predetermined time ΔT, the signal is caused due to a short-term interruption of the path with the transmitting side due to the position in motion during mobile communication. Can be determined to have disappeared abruptly, so that the selection state until then is held (prohibition of the selection of a new signal next time) for a certain time T _W , and the signal recovery due to the change in the movement position is waited for. .

Next, the above correlation detector (searcher) 15
A specific example of the above will be described with reference to FIG. In FIG. 2, the input terminal 21 is connected to the multiplier 1 of FIG.
A digital signal which is quasi-coherently detected by 1 and the VCO 12, converted to approximately 0 Hz, and A / D converted by the A / D converter 13 is supplied. In the A / D converter 13, the P
Since the signal from the input terminal 21 is decimated by the decimating circuit 22, the signal from the input terminal 21 is rate-converted into the signal of the frequency f _{PN because} the signal from the input terminal 21 is so-called oversampled at the frequency f _over higher than the N-series generation frequency f _PN . It is sent to the despreading circuit 23. PN (pseudo noise) generator 24
Can generate the same PN sequence as that used for spreading on the transmitting side, send this to the despreading unit 23 by arbitrarily shifting (delaying) the PN generation at regular intervals and sending the decimated signal. And the correlation value (or signal strength information) is detected by the correlation value detection circuit 25. The PN generator 24 determines the PN at which timing the PN is generated.
The start address of occurrence (or delay time information) is sent to a microprocessor (CPU) 26 as a control means,
Further, the correlation value detection circuit 25 sends the correlation value at that time to the microprocessor 26. In this case, the microprocessor 2 uses the property that a large correlation value is obtained only when the PN used for spreading on the transmission side matches (timing).
6 detects the PN address at that time in order from the largest input correlation value. By this operation, it is possible to judge how the multipath signals are distributed. The correlation value (signal strength information) and the PN address (delay time information) from the microprocessor 26 as the control means are taken out via the terminal 27 and sent to the control circuit 16 in FIG.

FIG. 3 is a diagram for explaining this correlation detecting operation, and the correlation value (signal strength information) at each timing.
Is shown. Here, the input signal is a multipath signal and has a delicate time delay. First, the PN generator 24
Generates PN at the timing of point A in FIG.
An address (delay time information) corresponding to the point is sent to the microprocessor 26. Since there is no corresponding signal at this timing, the correlation value is almost 0, and the correlation value detection circuit 25 sends this correlation value to the microprocessor 26. The microprocessor 26 recognizes that the correlation value at the address corresponding to the point A is 0. Next, the PN generator 24
Generates PN at the timing of point B in FIG.
The address corresponding to the point is sent to the microprocessor 26, and at this timing, the correlation value detection circuit 25 detects the correlation value of the corresponding signal and sends it to the microprocessor 26. At this time, since the signal exists although the signal strength is slightly small, the correlation value has a certain value according to the signal strength. The microprocessor 26 recognizes the correlation value at the address corresponding to point B. Such operation is performed up to, for example, point F in FIG.
6 judges. In the example of FIG. 3, the point C is the largest,
B point and E point can be selected, and these C point, B point and E point can be selected.
The address corresponding to each point is detected.
The above is the operation of the correlation detection unit. However, the control circuit 16 of FIG. 1 may be caused to perform the process of selecting the three signals in descending order of the signal strength.

Next, each demodulation unit 14 serving as the above finger.
Any one of ₁ , 14 ₂ and 14 ₃ will be described with reference to FIG. The digital signal converted to approximately 0 Hz by the quasi-synchronous detection is input to the input terminal 31.
It is supplied from the converter 13. Since this signal is oversampled at the frequency f _over , it is decimated by the decimating circuit 32 and converted into a signal at the frequency f _PN . At this time, which signal is used as the decimating point is determined by a clock control signal CN _CK described later. The signal with the correct timing (On Time signal) S _OT in this decimating circuit 32 is sent to the despreading circuit 33, and the signal with a timing (Ea) that is deviated by ± 1 / (2f _PN ) in time from the correct timing.
The rly / Late signal) S _{E / L} is sent to the despreading circuit 34.

In the PN (pseudo noise) generator 36 provided in each demodulation section (finger), the address assigned to each demodulation section from the control circuit 16 in FIG. 1 is input via the input terminal 35. Is supplied as a signal, a PN (pseudo noise) series signal is generated at that timing.
One of the generated PN signals is sent to the despreading circuit 33 to be used for despreading the signal (On Time signal) S _{OT with} the correct timing, and the other is sent to the despreading circuit 34 for the above-mentioned time. It is used for despreading of signals (Early / Late signals) S _{E / L} with deviated timing.

The Ea despread by the despreading circuit 34.
The rly / Late signal S _{E / L} is input to a synchronization holding circuit 41 such as a so-called DLL (delay lock loop), and here a clock control signal CN _CK is sent to the decimating circuit 32 as a signal for holding synchronization. . This signal is for adjusting the decimating point performed in the decimating circuit 32.

As a concrete example, the A / D converter 13 shown in FIG.
For example, the input signal that is oversampled by 8 times is set to 1
The case of decimating to / 8 will be described. If the sync hold circuit 41 determines that the current timing is acceptable, the decimate circuit 32 outputs a signal every 8th bit to complete ⅛ decimate. However, for example, if it is determined that the current timing is too late, the timing of outputting every 8th time until now is set to 7
The timing is adjusted by outputting every other piece. Here, the timing means a deviation between the clock when spread using PN on the transmitting side and the clock on the receiving side. This is because correct despreading cannot be performed unless the clock of the transmitting side is set.

Due to the effect of this clock control,
The despreading of the On Time signal S _OT is always performed at the correct timing, and the signal is sent to the data demodulation circuit 37. In the data demodulation circuit 37, data demodulation is performed by a circuit such as a so-called Costas loop, and the demodulated data is taken out from the output terminal 39. Also,
A part of the signal from the data demodulation circuit 37 is sent to the frequency error detection circuit 38, the frequency error is detected, and the result is taken out from the output terminal 40. When the Costas loop circuit is used as the data demodulation circuit 37, the input signal to the VCO in the Costas loop is a signal representing the frequency error as it is, and therefore the frequency error can be detected by extracting this.

As described above, FIG.
The data and the frequency error signal demodulated by each of the demodulation units 14 ₁ , 14 ₂ , and 14 ₃ are sent to the signal synthesis circuit 17. In the signal synthesizing circuit 17, each demodulated data is synthesized in consideration of the time delay, and the final demodulated data is output terminal 18
Is output to. Further, the frequency error is also synthesized, and the quasi-synchronous detection circuit is configured to eliminate the frequency error by controlling the oscillation frequency of the VCO 12 as the control signal Δf _CNT .

Here, in the embodiment of the present invention, the control circuit 16 of FIG. 1 is caused to perform the processing as shown in FIG. Note that part of the processing shown in FIG. 5 may be performed by the microprocessor 27, which is the control means in FIG.

In FIG. 5, first, in step S1, among the correlation values (for example, see FIG. 3) of each multipath signal detected by the correlation detection circuit (searcher) 15, the signal strength is high (large or strong). ) Select 3 (best 3) in order. In the next step S2, these selected signals are sent to the respective demodulators (fingers) 1
4 _1, 14 _2, 14 in order to demodulate at _3, delay time information (timing, PN generation address) of each signal the demodulator 14 ₁ as a control signal, 14 _2, 14 ₃ of the PN generator 36 (FIG. Please refer to 4). The processing up to this point is the same as the conventional one.

In the next step S3, the selected 3
Detects whether two signals have disappeared. That is, when the signal strength of the above three signals currently demodulated by the demodulation units 14 ₁ , 14 ₂ , and 14 ₃ becomes less than or equal to a predetermined threshold value S _TH within a predetermined time ΔT set in advance, Judges that the signal has disappeared due to some change in the situation, and advances the process to the next step S4. Even if the signal strength becomes equal to or lower than the threshold value S _TH , if it takes more than the predetermined time ΔT, it is determined that the signal strength is not changing but the signal strength is gradually changed, and the same process as the conventional process is performed. The process returns to step S1 to perform the above. When it is determined that the data has disappeared and the process proceeds to step S4, the process returns to step S1 after waiting for a predetermined time T _W set in advance. By waiting for this time T _W , if the above-mentioned disappearance occurs due to a short-term path interruption or the like accompanying the movement of the moving body, the lost signal will be generated again at the same position, which is wasteful. Optimal reception becomes possible without performing control (selection of new best 3). When the signal does not re-occur even after waiting the time T _W , the new best 3 (three in descending order of signal strength) is selected as in the conventional case and the control is continued.

The present invention is not limited to the above-described embodiment. For example, the configuration of the correlation detector is not limited to the example of FIG. 2, and the specific configuration of the demodulation unit is also the example of FIG. Not limited. Further, the number of demodulation units is not limited to three as in the example of FIG. 1, and it goes without saying that various configurations can be adopted without departing from the scope of the present invention.

[0030]

As is clear from the above description, according to the receiving apparatus of the present invention, a specific time distribution is determined based on the signal strength and delay time information of a plurality of multipath signals in the received signal. As first control means for controlling the n demodulation means so as to demodulate the n multipath signals that it has,
When the signal strength information of the n multipath signals having the specific time distribution becomes less than or equal to the predetermined value S _TH within the predetermined time ΔT, the n having the specific time distribution for the constant time T _W
Since control is performed so as to demodulate each multipath signal, even if a certain effective signal is lost, by waiting for the re-generation of the signal for a fixed time T _W , complicated control is eliminated and wasteful. It is possible to eliminate unnecessary power consumption, and optimal demodulation is possible.

This is because the signal strength of the path is rapidly reduced to the disappearance state in the temporary cutoff state of the path caused by the movement of at least one of the transmitting side and the receiving side in the mobile communication. , When this rapid decrease in signal strength occurs, the selection of multipath signals is held for a certain period of time (new selection is prohibited), and the previous signal selection state is switched when the signal is restored next time. It becomes unnecessary, the unnecessary switching control operation of the signal selection state can be omitted, wasteful power consumption can be eliminated, and the demodulation processing in each demodulator can be smoothly continued.

Further, according to the multipath signal selection method of the present invention, when n multipath signals are selected and demodulated in descending order of signal strength among a plurality of multipath signals in the received signal. In the method for selecting multipath signals, when the signal strengths of the currently selected n multipath signals fall below a predetermined value within a predetermined time, the n multipaths selected for a certain period of time are selected. Since the signal selection is retained, complicated control can be eliminated and unnecessary power consumption can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall schematic configuration of an embodiment of a receiving apparatus according to the present invention.

FIG. 2 is a block circuit diagram showing a specific example of a correlation detector used in the receiving apparatus of the embodiment.

FIG. 3 is a diagram for explaining the operation of the correlation detector of FIG.

FIG. 4 is a block circuit diagram showing a specific example of a demodulation unit used in the receiving apparatus of the embodiment.

FIG. 5 is a flowchart for explaining the operation of the main part of the receiving apparatus according to the embodiment of the present invention.

[Explanation of symbols]

10 ... Input Terminal 12 ... Multiplier 13 ... A / D (Analog / Digital) Converter 14 ₁ , 14 ₂ , 14 ₃ ... Demodulator 15 ... ... Correlation detector 16 ... Control circuit 17 ... Signal synthesis circuit 18 ... Output terminal

Claims (6)

[Claims] 1. A receiving apparatus for forming a demodulated signal by selecting n multipath signals having a high signal strength from a plurality of multipath signals in a received signal, the signal strength of the plurality of multipath signals, and Correlation detection means for detecting delay time information, n demodulation means for respectively demodulating an input signal, and n multipaths having a specific time distribution based on the signal strength information and the delay time information. A first control means for controlling the n demodulation means to demodulate a signal, the first control means comprising n having the specific time distribution.
When the signal strength information of the plurality of multipath signals becomes less than or equal to a predetermined value within a predetermined time, control is performed so as to demodulate the n multipath signals having the specific time distribution for a predetermined time. Receiving device. 2. The receiving apparatus according to claim 1, wherein the received signal is a spread spectrum signal subjected to spread processing with a predetermined pseudo noise code. 3. The correlation detecting means, pseudo noise generating means for generating the predetermined pseudo noise code, second control means for controlling generation timing of the predetermined pseudo noise code, and the predetermined pseudo noise. Despreading means for mixing a code and the received signal, and a correlation value between the received signal and the pseudo noise code is detected based on the output of the despreading means, and the correlation value is output as the signal strength information. 3. The receiving apparatus according to claim 2, further comprising: 4. The demodulation means mixes pseudo noise generating means, in which the generation timing of the predetermined pseudo noise code is controlled by the first control means, with the predetermined pseudo noise code transistor, and the multipath signal. 3. The receiving apparatus according to claim 2, further comprising: despreading means for performing despreading, and data demodulating means for demodulating the data despread by the despreading means. 5. A multipath signal selection method for selecting and demodulating n multipath signals in descending order of signal strength among a plurality of multipath signals in a received signal, and selecting n at the present time. A multipath signal, characterized in that, when the signal strength of the multipath signals drops below a predetermined value within a predetermined time, the selection of the selected n multipath signals is held for a fixed time. Selection method. 6. The method for selecting a multipath signal according to claim 6, wherein the received signal is a spread spectrum signal subjected to spread processing with a predetermined pseudo noise code.