Base station for cdma system and initial synchronization acquisition method for the base station

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to the position estimation of a mobile station in a base station of a CDMA system, and more particularly to a control method for initial synchronous acquisition of a position estimation signal transmitted from the mobile station when the position of the mobile station is estimated in the base station. ..

【0002】

[Conventional technology]

Conventionally, in CDMA systems, the position of mobile stations has been estimated.

【0003】

Hereinafter, a method of estimating the position of a mobile station in a CDMA system will be described with reference to the drawings.

【0004】

FIG. 6 is a diagram showing the relationship between each station in the position estimation of the CDMA system.

【0005】

The central base station 50 and the first base station 1 to the third base station 3 are each connected by a dedicated line. Mobile station 60 is moving in the area surrounded by each base station 1 to 3, but currently, since the second base station 2 is the closest, it is communicating via the second base station. And.

【0006】

The position estimation method of the mobile station 60 in the case of FIG. 6 is carried out as follows.

【0007】

First, the central base station 50 is composed of two base stations (first base station 1 and first base station 1) involved in the position estimation of the mobile station 60 from all the base stations around the second base station 2 communicating with the mobile station 60. By selecting 3 base stations 3), 3 base stations 1 to 3 are selected together with the 2nd base station 2 in communication, and the upper ranks that generate the reference time for each base station 1 to 3 Synchronize using one of the systems, the Global Positioning System (GPS). Further, since the mobile station 60 is in communication with the second base station 2 and is synchronized with the second base station 2, it is not necessary to newly perform the synchronization. After that, the central base station 50 sends the position estimation signals 31 to 33 from the mobile station 60 at the reference time via the second base station 2. In FIG. 6, the position estimation signals 31 to 33 are drawn separately in three directions, but this is when one position estimation signal transmitted from the mobile station 60 reaches each base station. Since they are received through different reception delay times D1 to D3, they are described separately for convenience, and there are not three types of position estimation signals transmitted from the mobile station 60.

【0008】

FIG. 7 is a diagram showing the relationship between the base stations 1 to 3 and the position estimation signals 31 to 33.

【0009】

When the position estimation signal is transmitted from the mobile station 60 at the reference time t0, the first base station 1 starts receiving the position estimation signal 31 at the earliest leading wave reception time t1 delayed by the delay time D1. Similarly, the second base station 2 starts receiving the position estimation signal 32 at the reception time t2 of the earliest wave delayed by the delay time D2, and the third base station 3 starts receiving the position estimation signal 32, and the third base station 3 is the earliest wave delayed by the delay time D3. The position estimation signal 31 starts to be received at the reception time t3.

【0010】

In this way, each of the three base stations 1 to 3 around the mobile station 60 receives the position estimation signal transmitted from the mobile station 60 at the reference time t0, and each base station 1 to 3 receives the reference time. By obtaining each delay time D1 to D3 from t0 to receiving the position estimation signal and calculating the product of each delay time D1 to D3 and the propagation speed of the radio wave, each base station 1 to 3 and the mobile station Find the distance between 60. At this point, the distance between each base station 1 to 3 and the mobile station 60 can be obtained, but it is unclear in which direction the mobile station 60 is located in each base station 1 to 3. Therefore, each of the base stations 1 to 3 transmits the obtained data of the distance to the mobile station 60 to the central base station 50.

【0011】

In the central base station 50, based on the distance data from each base station 1 to 3 to the mobile station 60 received, three positions centered on each base station 1 to 3 are displayed on the map data as shown in FIG. Draw estimated circles 41 to 43, and estimate the intersection of the three circles 41 to 43 as the position of mobile station 60. In this way, the position of the mobile station 60 can be estimated on the map data.

【0012】

In the position estimation of the mobile station 60 described above, the delay times D1 to D3 from the reference time t0 to the reception of the position estimation signals 31 to 33 are simply obtained, but each base station 1 of the actual CDMA system is obtained. In ~ 3, since it is necessary to decode the signal received from the mobile station 60, the phase of the signal received from the mobile station 60 by the base station at the start of communication and the phase of the signal generated inside the base stations 1 to 3 By detecting the signal for synchronizing, each delay time D1 to D3 from the above reference time t0 to the reception of the position estimation signals 31 to 33 is obtained. ..

【0013】

For example, from the mobile station 60, a narrow band signal (for example, position estimation signals 31 to 33) obtained by spreading (secondary modulation) the mobile station 60 using a spreading code that can distinguish the mobile station 60 from other mobile stations is transmitted from base stations 1 to. When transmitting to 3, the base stations 1 to 3 that received the signal obtain the original signal by despreading using the same spreading code (spreading code replica) as the spreading code used in the mobile station 60. There is.

【0014】

In the despreading process in the base stations 1 to 3, an operation for obtaining the correlation between the received signal and the spreading code replica is performed, but in order to perform the correlation calculation, the spreading code in the received signal is used at the start of communication. It is necessary to synchronize the phase with the internally generated diffusion code replica. The process of synchronizing the phase of the received diffusion code and the diffusion code replica at the start of communication in this way is called initial synchronous acquisition, and each delay in the position estimation of the mobile station 60 due to this initial synchronous acquisition. We are looking for times D1 ~ D3.

【0015】

Further, in the initial synchronous acquisition, for example, a phase range is set corresponding to the time when the signal for position estimation is transmitted from the mobile station 60, and all the receptions received by the base stations 1 to 3 in the phase range are received. Correlation calculation is performed on the signals to obtain the correlated power value for each received signal. Then, the correlated power value for each received signal is compared with a preset threshold value (correlation power determination threshold value), and the correlated power value is calculated for each signal having the correlated power value exceeding the threshold value. Arrange in descending order.

【0016】

Next, signals having a higher correlation power value are selected, and the phase positions of those signals are set as candidates for the phase position for synchronization. That is, any one of the signals having a higher correlation power value is regarded as the earliest wave of the position estimation signal, and the source is compensated by the amount of the phase of the signal deviating from the reference time. It will be possible to obtain synchronization with the mobile station of.

【0017】

By the way, in base stations 1 to 3 of a conventional CDMA system, the threshold value used when selecting a signal having a higher correlated power value is the size of the service area covered by the base stations 1 to 3, etc. It is a fixed value set according to the conditions of. Therefore, the base stations 1 to 3 of the conventional CDMA system determine the correlated power value of the received signal using a fixed threshold value, and perform initial synchronous acquisition based on the correlated power value.

【0018】

[Problems to be Solved by the Invention]

However, among the base stations 1 to 3 of the conventional CDMA system, the adjacent base station 1 or 2 selected by the centralized base station 50 to perform the position estimation of the mobile station 60, although not communicating with the mobile station 60. Then, if the threshold value is a fixed value as described above, the initial synchronous acquisition may fail.

【0019】

FIG. 8 is a diagram showing an example in which the adjacent base station 1 or 2 fails in the initial synchronous acquisition of the signal from the mobile station 60 due to false detection of noise. When the horizontal axis of FIG. 8 indicates the phase, the vertical axis indicates the correlated power value, and the signal of the correlated power value (position estimation signal PS) is the threshold value FS1 or higher, it is a candidate for the most preceding wave W1. Detected.

【0020】

In Fig. 8, the correlation power value level of the noise floor NF rises above the threshold value FS1 set to a fixed value due to the size of the service area, etc., and is faster than the earliest wave W1 of the position estimation signal PS. An example is shown in which the generated noise N1 is erroneously detected as a candidate for the synchronization phase.

【0021】

FIG. 9 is a diagram showing a case where the threshold value set to a fixed value is set high in order to avoid the situation of the example of FIG. Similar to FIG. 8, when the horizontal axis indicates the phase, the vertical axis indicates the correlated power value, and the signal of the correlated power value (position estimation signal PS) is the threshold value FS2 or more, the most preceding wave W1 Is detected as a candidate for.

【0022】

In the case of the example of FIG. 9, since the threshold value FS2 is set high, the earliest leading wave W1 of the position estimation signal PS to be detected as a candidate for the synchronous phase cannot be detected.

【0023】

As shown in FIGS. 8 and 9, there is a problem that the initial synchronous acquisition may fail in the base station of the conventional CDMA system that uses the threshold value of the fixed value for determining the correlation power value.

【0024】

The present invention has been made to solve the conventional problems as described above, and provides a base station of a CDMA system and a method for initial synchronous acquisition of base stations that can reduce the failure of initial synchronous acquisition and stably estimate the position. The purpose is to provide.

【0025】

[Means for solving problems]

In order to achieve the above object, the base station of the CDMA system of the present invention described in claim 1 converts an analog received signal received delayed from the reference time by the distance from the mobile station into a digital signal. A position estimation signal output from the mobile station as a result of back-spreading the analog / digital (A / D) conversion unit that detects the electric field strength value of the received signal and the digital signal output from the A / D conversion unit. It is set to detect the reverse diffusion circuit that detects the earliest wave, delay time information indicating the time that the earliest wave is delayed from the reference time, power value information of the earliest wave, and the earliest wave. A search unit having an earliest wave information collecting circuit that collects the threshold information of the correlated power, and at least one correlated power threshold set for detecting the earliest wave in the search unit and a threshold value of at least one correlated power. A storage circuit that stores the distance to the mobile station calculated from the delay time information, and a control unit having a mobile station distance estimation circuit that estimates the distance to the mobile station based on the delay time information of the most preceding wave. The search unit is a base station of the CDMA system provided, and the search unit uses the threshold value currently set in the reverse spread circuit from the reference start time of the initial synchronous acquisition set by using the reference time of the host system. A timer circuit that measures up to a set time for determining that synchronous acquisition is not possible is further provided, and the control unit is based on the electric field strength value of the received signal detected by the A / D conversion unit. It further includes a conversion table used when setting the first threshold value, and a threshold value change circuit that outputs an instruction to lower the threshold value by one step when the time measurement of the timer circuit is completed. , The storage circuit stores a plurality of steps of threshold values corresponding to changes in the electric field strength value of the received signal, and when the instruction from the threshold change circuit is input, it is selected by the instruction. It is characterized in that the threshold value and the initial synchronous acquisition instruction again are output to the reverse diffusion circuit.

【0026】

The initial synchronous acquisition method of the base station of the CDMA system of the present invention according to claim 2 is set at a time when the earliest leading wave of the position estimation signal output from the mobile station of the CDMA system is received with a delay from the reference time. Based on this, it is an initial synchronous acquisition method of the base station of the CDMA system when estimating the distance to the mobile station, and is a position estimation signal that becomes a back-spread correlated power value based on the electric field strength of the received signal. It was set to set the initial value of the threshold value to detect the earliest wave of the system, and to start the initial synchronous acquisition by the set threshold value and to determine that the initial synchronous acquisition cannot be performed. It is characterized by having a step of measuring the time and a step of lowering the threshold value by one step and restarting the initial synchronous acquisition when the initial synchronous acquisition is not completed by the time the timer ends. ..

【0027】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described based on the illustrated embodiment.

【0028】

FIG. 1 is a block diagram showing a configuration of a reception-related block of a base station according to an embodiment of the present invention.

【0029】

The base station 1 of the present embodiment of FIG. 1 has a radio unit 11 that demolishes a radio signal received with a delay from the reference time by the distance from the mobile station 60 and converts it into an analog electric signal, and a digital analog signal. Communication control between an analog / digital (A / D) converter 12 that converts a signal and detects the electric field strength value of the received signal, mobile station 60 and base station 1, or base station 1 and central base station 50, and , The control unit 13 that outputs various instructions for controlling each part in the base station 1, and the search unit 14 that back-spreads the received signal according to the instruction from the control unit 13 and calculates the correlated power value. It is composed of an output unit 15 that outputs the received signal that has become the correlated power value to the control base station 50 after performing decoding processing or the like as necessary.

【0030】

The search unit 14 has a despread circuit 20 that despreads the received signal to calculate the correlated power value, and delay time information, received power information, and maximum that indicate the reception timing of the earliest preceding wave from the received signal that has become the correlated power value. Initial synchronous acquisition set using the most preceding wave information collection circuit 21 that collects threshold information at the time of preceding wave detection and the global positioning system (GPS) as one of the higher-level systems that generate the reference time. It is composed of a timer circuit 22 that measures from the reference start time of the above to the set time in order to determine that the initial synchronous acquisition using the threshold value currently set in the despreading circuit cannot be performed. In addition, as a higher-level system that generates the above-mentioned reference time, for example, a master clock is installed in a control station or one of the base stations, and the time of this master clock is used as a reference time in another base station. You may use what was made to supply.

【0031】

Despreading circuit 20 further includes a code replica generating circuit 23 for generating a spreading code replica set, spread code replica and the correlation Starring a correlation computing circuit 24 for performing the correlation calculation of the received signal by receiving the calculation start instruction The searcher circuit 25 determines whether or not the correlated power value of the received signal is equal to or higher than the threshold value based on the calculation result of the correlation calculation circuit 24.

【0032】

FIG. 2 is a block diagram showing a configuration of a control unit 13 of the base station 1 of FIG.

【0033】

The control unit 13 detects the leading wave in the conversion table 26 used when setting the first threshold value based on the electric field strength value of the received signal detected by the A / D conversion unit 12 and the search unit 14. A storage circuit 27 that stores the distance to the mobile station 60 calculated from the threshold value and delay time information of at least one correlated power set to perform, and the mobile station based on the delay time information of the most preceding wave. It is provided with a mobile station distance estimation circuit 29 that estimates the distance to the threshold value, and a threshold value change circuit 28 that outputs an instruction to lower the threshold value by one step in response to the end of the timer circuit 22. A multi-step threshold value is stored in the storage circuit 27. When an instruction to lower the threshold value by one step is input from the threshold value change circuit 28, the storage circuit 27 outputs the threshold value selected by the instruction to the reverse diffusion circuit 20.

【0034】

Next, the operation of the base station 1 of the present embodiment will be described.

【0035】

FIG. 3 is a flowchart showing the operation of the base station 1 shown in FIGS. 1 and 2.

【0036】

The received signal demodulated by the radio unit 11 is converted into a digital signal by the A / D converter 12 and the electric field strength is detected (step S1). In the control unit 13, the initial value of the threshold value for detecting the correlated power value is determined by the conversion table 26 based on the electric field strength value obtained from the A / D conversion unit 12 (step S2), and the threshold value is determined. And the initial synchronous acquisition start instruction is notified to the searcher circuit 25 of the reverse diffusion circuit 20 (step S3).

【0037】

Here, as shown in step S2, when the initial value of the threshold value for detecting the correlated power value is determined by the conversion table 26 based on the electric field strength value obtained from the A / D conversion unit 12. The effect will be explained.

【0038】

FIG. 4 is a diagram showing a case where the threshold value is set based on the electric field strength value. When the horizontal axis of FIG. 4 indicates the phase, the vertical axis indicates the correlated power value, and the signal of the correlated power value (position estimation signal PS) is the threshold value VS0 or more, it is a candidate for the most preceding wave W1. Detected.

【0039】

In FIG. 4, the threshold value VS0 is determined by the conversion table 26 based on the electric power strength value obtained from the A / D conversion unit 12, so that when the noise floor NF rises, the threshold value VS0 also rises. Since it is set higher than the correlation power value level of the noise floor NF, the noise N1 generated earlier than the earliest wave W1 of the position estimation signal PS is not mistakenly detected as a candidate for the synchronization phase. .. Therefore, it is possible to reduce the situation where the initial synchronous acquisition fails.

【0040】

In the searcher circuit 25 that received the initial synchronous acquisition start instruction from the control unit 13 shown in step S3, the initial setting using the global positioning system (GPS), which is one of the higher-level systems that generate the reference time. The timer 22 is set so that the time from the reference start time of synchronous acquisition to the time set to determine that the initial synchronous acquisition using the threshold value currently set in the reverse diffusion circuit 20 cannot be performed can be measured. And start the initial synchronous acquisition (step S4). As a higher-level system that generates the above-mentioned reference time, for example, a master clock is installed in the control station or one of the base stations, and the time of this master clock is used as the reference time in another base. You may use the one that is supplied to the station.

【0041】

The control unit 13 determines whether or not the time timing set for the timer 22 has ended (step S5), and if the time measurement time has not ended (step S5: NO), the initial synchronous acquisition is performed. When it is determined whether or not the above is completed (step S6) and the time timing is completed (step S5: YES), the current threshold value information is obtained from the earliest leading wave information collection circuit 21 and the threshold value is obtained. The threshold value that outputs the instruction from the change circuit 28 and outputs from the storage circuit 27 to the searcher circuit 25 is lowered by one step (step S8).

【0042】

Next, the control unit 13 determines whether or not the threshold value lowered by one step is equal to or higher than the lower limit value of the correlated power (step S9), and if it is equal to or higher than the lower limit value (step S9: YES). , The process of notifying the searcher circuit 25 of the reverse diffusion circuit 20 of the threshold value of step S3 and the initial synchronous acquisition start instruction is performed again. If it is less than the lower limit (step S9: NO), the initial synchronous acquisition has failed, and the process ends. The lower limit of the correlated power is set in advance according to the range of the service area of each base station and the like.

【0043】

On the other hand, when the initial synchronous acquisition is completed (step S6: YES), the control unit 13 estimates the distance to the mobile station by the mobile station distance estimation circuit 29, and does not complete the initial synchronous acquisition (step). For S6: NO), the judgment of step S5 is performed again.

【0044】

Here, as shown in step S8, regarding the threshold value for detecting the correlated power value, if the initial synchronous acquisition cannot be performed until the timer times out, the current threshold value VS0 is lowered by one step. The effect of the initial synchronous acquisition will be described.

【0045】

FIG. 5 is a diagram showing an example in which the threshold value VS0 is lowered step by step and the initial synchronous acquisition is performed again. When the horizontal axis of FIG. 5 indicates the phase, the vertical axis indicates the correlated power value, and the signal of the correlated power value (position estimation signal PS) is the threshold value VS0, VS1, or VS2 or higher, the first precedent. Detected as a candidate for wave W1.

【0046】

In FIG. 5, the first threshold value VS0 is the same as in FIG. 4. In this state, the most preceding wave W1 cannot be detected. However, by the process shown in step S8 in Fig. 3, the threshold value is lowered by one step, the second threshold value is set to VS1, and then the initial synchronous acquisition is performed again, and the earliest leading wave W1 can still be detected. Therefore, the earliest leading wave W1 can be detected by further lowering the threshold value by one step, setting the third threshold value to VS2, and then performing the initial synchronous acquisition again.

【0047】

In this way, for example, since the transmission power from the mobile station 60 is not sufficiently larger than the noise floor NF, the conventional fixed value threshold values FS1 and FS2 and the A / D converter as shown in step S2 In this embodiment, as shown in step S8, the earliest leading wave W1 cannot be detected only by the threshold value VS0 determined by the conversion table 26 based on the electric field strength value obtained from 12. Since the thresholds VS1 and VS2 are gradually lowered, not only the earliest wave W1 can be detected, but also the earliest wave W1 can be set to the highest threshold value that can be detected. .. Therefore, the detection accuracy of the most preceding wave W1 in the initial synchronous acquisition can be improved.

【0048】

Therefore, since the distance estimation accuracy between the base station 1 and the mobile station 60 can be improved, the movement is performed by the intersection of the position estimation circles 41 to 43 centered on the base stations 1 to 3 in the central base station 50. The position estimation accuracy when performing the position estimation of the station 60 can also be improved.

【0049】

As described above, in the present embodiment, when the noise floor NF rises, the initial threshold value VS0 is also raised so that the noise floor NF is set higher than the correlated power value level of the noise floor NF. Noise N1 generated earlier than the earliest leading wave W1 of the signal PS is no longer mistakenly detected as a candidate for the synchronization phase, and the initial synchronization acquisition can be performed correctly, and the initial synchronization acquisition fails. Can be reduced.

【0050】

Further, in the present embodiment, if the first initial synchronous acquisition fails, the threshold value is lowered by one step and the synchronous acquisition is performed again. Therefore, not only the earliest leading wave W1 can be detected, but also the leadingmost wave W1 can be detected. Since the wave W1 can be set to the highest threshold value that can be detected, the detection accuracy of the earliest leading wave W1 in the initial synchronous acquisition can be improved. Therefore, since the distance estimation accuracy between the base station 1 and the mobile station 60 can be improved, the position estimation accuracy of the mobile station 60 in the central base station 50 can also be improved.

【0051】

In the first base station 1 of the present embodiment shown in FIG. 1, the most preceding wave information collecting circuit 21 and the timer circuit 22 are described by being built in the search unit 14, but these circuits are described, for example, in the control unit. It may be built into 13 or other circuits. Further, the threshold value changing circuit 28 and the mobile station distance estimation circuit 29 in the control unit 13 may also be built in, for example, in the search unit 14 or another circuit. Further, in the present embodiment, the threshold value of a plurality of stages is described in three stages, but the present invention is not limited to this. You may lower the threshold value with.

【0052】

[Effect of the invention]

As described above, when the noise floor rises, the present invention also raises the initial threshold value so that it is set higher than the correlated power value level of the noise floor. Noise generated earlier than the preceding wave is not mistakenly detected as a candidate for the synchronization phase, the initial synchronization acquisition can be performed correctly, and the situation where the initial synchronization acquisition fails can be reduced.

【0053】

Further, in the present invention, if the first initial synchronous acquisition fails, the threshold value is lowered step by step and synchronous acquisition is performed again. Therefore, not only the earliest wave can be detected but also the earliest wave can be detected. Since the highest threshold value can be set among the detectable threshold values, the detection accuracy of the most preceding wave in the initial synchronous acquisition can be improved. Therefore, since the accuracy of distance estimation between the base station and the mobile station can be improved, the accuracy of position estimation of the mobile station in the centralized base station can also be improved.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram which shows the structure of the reception relation block of the base station of one Embodiment of this invention.

[Figure 2]

It is a block diagram which shows the structure of the control part 13 of the base station 1 of FIG.

[Fig. 3]

It is a flowchart which shows the operation of the base station 1 shown in FIG. 1 and FIG.

[Fig. 4]

It is a figure which showed the case where the threshold value is set based on the electric field strength value.

[Fig. 5]

It is the figure which showed the example of the case where the threshold value is lowered step by step and the initial synchronous acquisition is performed again.

[Fig. 6]

It is a figure which shows the relationship of each station in the position estimation of a CDMA system.

[Fig. 7]

It is a figure which shows the relationship between each base station and a signal for position estimation.

[Fig. 8]

It is a figure which showed the example of the case where an adjacent base station fails in the initial synchronous acquisition of a signal from a mobile station by erroneously detecting noise.

[Fig. 9]

It is a figure which showed the case where the threshold value set to a fixed value is set high in order to avoid the situation of the example of FIG.

[Explanation of symbols]

1 1st base station, 11 radio section, 12 analog / digital (A / D) converter section, 13 control section, 14 search section, 15 output section, 20 reverse diffusion circuit, 21 most leading wave information collection circuit, 22 timer circuit , 23 Code replica generation circuit, 24 Correlation calculation circuit, 25 Searcher circuit, 26 Conversion table, 27 Storage circuit, 28 Threshold change circuit, 29 Mobile station distance estimation circuit, 31 Position estimation signal.