JP2002135833A - Radio terminal position measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of requiring a large quantity of memories for performing long-term common-mode addition. SOLUTION: Cyclic signals are transmitted from a cellular base station. This instrument has a storage circuit 17 the cycle of which is as large as the cycle. By adding information stored in the storage circuit 17 and newly received information and storing the result in the storage means again, the storage circuit 17 for the cycle can store received information. Therefore, the capacity of the memory can be reduced and a number of operations required for preparing a profile can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal device for measuring a terminal position using cellular communication.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Hei 7-181242 discloses a system that measures the position of a terminal by observing the reception timing of a pilot signal arriving from each base station in a system using a CDMA system in which each base station is GPS-synchronized in a cellular system. It is disclosed to do.

FIG. 3 shows an example of a correlation operation result. The figure is called a delay profile, and shows what delay path is observed. The horizontal axis is the delay time, that is, the reception timing corrected by the transmission timing. The unit corresponds to the chip of the spreading code. The vertical axis indicates the correlation calculation output, and a portion having a large correlation value indicates that a signal has been received, that is, the presence of a path. Using this result, the relative delay time required for the radio wave to reach the terminal from the base station can be obtained. Here, the delay time is a relative value because the terminal does not know the absolute time. The relative propagation distance difference can be obtained by multiplying the obtained relative delay time by the speed of light. If the relative propagation distance difference is obtained for at least three or more base stations, the terminal position can be estimated by triangulation.

[0004]

A terminal estimates a path position using a correlation operation device (despreading circuit) for detecting a signal from a base station. Further, in order to estimate the detailed path position, a delay profile as shown in FIG. 3 is created, and several phases of the peak code are picked up and an interpolation operation is performed.
Estimate peaks present within the sample interval. As described above, in the position detection, the despreading operation is performed for many code phases. However, having a large number of despreading circuits in parallel in hardware causes an increase in circuit size.

On the other hand, the work of position detection does not require immediate response. Therefore, temporarily storing received data in a memory and repeatedly using a small number of despreading circuits suppresses an increase in circuit scale. However, among multiple base stations,
Since a signal from a distant base station is weaker than that of a near base station, a long-term correlation operation is required. To store that long-term data requires a large amount of memory.

Another problem in performing a long-term correlation operation will be described. In mobile communication terminals, local oscillators with low frequency accuracy are used to reduce costs, and carrier frequency deviation is reduced by synchronizing with the nearest base station (AutoFrequency Control function) .
However, due to the limitation of the AFC function, a frequency difference of several Hz remains between the terminal and the base station, and complete synchronization cannot be achieved even if there is no fading. For this reason, the phase of the received signal has a slow rotational motion of several Hz. For this reason, even when the terminal user is only standing still or moving slowly at about the walking speed, the received signal is rotating rapidly, and it is difficult to perform in-phase addition for a long time.

Here, the in-phase addition indicates a process of adding signals while correcting the phase of the signals. By the in-phase addition of the N code, the desired signal component becomes the power of the square of N,
The noise power or the interference power becomes N times. Therefore, an N-fold improvement in the signal-to-noise power ratio can be obtained. If the phase is rotated, the desired signal cannot be added in the same phase, so that the effect cannot be improved.

A signal from a distant base station is equivalent to S / I
Since the (signal-to-interference power ratio) is low, it is desirable to increase the number of times of in-phase addition to improve the signal quality. However, the number of additions cannot be made longer than a certain degree due to the phase rotation phenomenon. For example, carrier frequency 800 MHz, AFC
If there is a terminal whose later frequency stability is 0.01 ppm, the phase rotation frequency will be 8 Hz. If the allowable phase rotation required for in-phase addition is within 45 degrees, 1/8 x 45/360 = 0.01562
It can be seen that in-phase addition is possible within 5 [seconds]. If the number of in-phase additions is longer than this, the signal vector will rotate and the S / I will deteriorate.

[0009]

The object of the present invention is to provide a wireless terminal position measuring apparatus for estimating the position of a terminal by using signals coming from at least first and second base stations of a cellular communication system. This problem is solved by a wireless terminal position measuring device characterized by including a storage circuit for estimating a phase rotation amount of a received signal from a base station and storing a signal obtained by correcting the phase rotation of the received signal.

A periodic signal is transmitted from a cellular base station. The storage circuit has a capacity capable of storing signals for the period. By adding the information stored in the storage circuit and the newly received information and storing the added information again in the storage circuit, a storage capacity larger than that of the storage circuit for the above cycle becomes unnecessary. Since the pilot signal transmitted from the CDMA base station is an unmodulated signal, the same pattern is repeated at a PN cycle of 26.6 ms. Therefore, in this case, 2
It is sufficient that the storage circuit has a capacity capable of storing information for 6.6 ms.

[0011]

FIG. 1 shows an embodiment of the present invention.

The signal received by the antenna 1 is converted by the RF unit 2 into a baseband signal. The converted signal is converted into a digital signal by the A / D converter 3. The CDMA signal processing unit 4 measures the reception timing of the reference signal output from the base station. The reception timing is the correlation operation (respreading) between the received signal and the reference signal.
Is obtained. The CDMA signal processing unit 4
Also receives the information of the base station. For example, in a cdmaOne type cellular system, the timing at which each base station transmits a reference signal can be known from the offset value of the PN code transmission timing stored in the sync channel. From this, the transmission timing can be calculated.
The terminal calculates the propagation delay by subtracting the transmission timing from the reception timing. The CPU 6 is a unit that estimates the propagation distance from the obtained transmission / reception timing and estimates the position of the terminal from the information.

FIG. 2 shows details of the CDMA signal processing section 4.

The output of the A / D converter 3 is selected by a selector 18 and input to a peak detection circuit. The peak detection circuit has a despreading circuit 19 and a profile creation circuit 21. The despreading circuit 19 performs a sliding correlation operation and searches for a path reception timing while changing the spreading code. The profile creation 21 is a device for finding an effective path with large power.

[0015] If a path is found, the sink channel receiver shifts to the operation of receiving the sink channel simultaneously transmitted from the base station. Information on the transmission timing of the base station, ie, P
The N code timing offset value is stored. This information indicates the delay of the transmission timing with respect to the system time when the base station transmits the PN code, and it becomes clear at which timing the base station transmitted the signal. Further, since the ID for identifying the base station is also included, the base station can be specified. The base station ID information can be used to search for the position of the base station. The position information of the base station may be stored in a storage device of the terminal or may be obtained via a network.

The reception of the sync channel is performed in the following procedure. That is, the code generation circuit of the despreading circuit 7 performs despreading using the spread code of the sync channel at the path phase detected by the peak detection circuit. The despreading circuit 8 performs despreading with the path phase detected by the peak detection circuit and using the spreading code of the pilot channel. The propagation path estimation circuit 9 estimates the propagation path by averaging the results of the despreading circuit 8. By calculating the complex conjugate of the estimated propagation path, a vector for compensating the phase rotation received on the propagation path is obtained. The detection circuit 10 performs detection by multiplying the output of the despreading circuit 8 by a vector for phase rotation compensation. Subsequent deinterleave circuit 1
1, depletion circuit 12, Viterbi decoding circuit 13,
The deframing circuit 14 is a group of units that decodes a transmission line code applied for transmitting information and decomposes a frame, and through which the base station information (PN code timing offset) included in the sync channel is transmitted. , Base station ID, etc.).

A frequency difference between the terminal and the base station is detected from the result of the propagation path estimating circuit 9, and control information of the AFC 5 in FIG. 1 is created. Also, the phase rotation of the received signal can be estimated from the estimated propagation path. The integrator 15 compensates for the phase rotation of the obtained received signal. The received signal whose phase rotation has been suppressed is stored in the memory circuit 17. Here, the memory circuit 17 can store data corresponding to the PN code length of the pilot signal. PN received subsequently
The information for the code length is stored in a memory circuit in an adder 16.
17 is added to the information stored in the past, and the result is stored in the memory circuit 17 again. As a result, the memory circuit 1
7 is updated. The more this update is performed, the better the S / I (signal-to-interference power ratio).

The adding method will be described with reference to FIG. The pilot signal in the received information is an unmodulated signal, and each P
The same pattern is repeated in N cycles. GP between base stations
Since synchronization is ensured in S, the pilot signals do not slip with each other. The received pilot signal is rotation-compensated by the propagation path estimation circuit 9 and the integrator 15 in FIG. Therefore, the accumulation result of each cycle is
The in-phase addition of the pilot signal in the received signal is performed by adding the sample timing. FIG. 4 shows a state in which signals sampled at the same sample timing in each cycle from 1 to N are added in that order.

The rotation compensation will be described. The phase rotation is estimated using a signal from a base station having the best reception quality.
The cause of the rotation of the phase of the received signal is due to the shift of the carrier frequency between the base station and the terminal and to the effect of fading due to the fluctuation of the propagation path.

Since the frequency shift between base stations is small, the carrier frequency shift for all base stations can be compensated for by the rotation correction obtained from the signal of the specific base station.
Since the frequency shift is an offset value with a small time variation, a primary correction for estimating the offset value by statistical calculation is effective. With this method, the frequency offset can be estimated from a signal received in the past. Of course, a method of estimating the propagation path for each PN cycle or frame cycle and estimating the amount of phase rotation compensation in the next cycle is also effective.

On the other hand, since the influence of fading differs for each base station, it is not possible to compensate for signals of all base stations from information of one base station. Therefore, when the influence of fading is large, a method of terminating the operation at an appropriate number of in-phase additions is required.

A condition for terminating the in-phase addition will be described. A despreading circuit 8 and a propagation path estimation circuit 9 for estimating a propagation path perform propagation path estimation of pilot signals of a plurality of base stations, not one station. The correlation operation circuit 22 calculates a correlation value of the estimation results of the different base stations. If the absolute value of the correlation value is small, it indicates that the effect of fading is large. Therefore, when the correlation value becomes equal to or less than the threshold value, the information storage in the memory circuit 17 is stopped. For example, about 0.7 is appropriate as the threshold value. This value corresponds to the fact that the signal from the second base station is rotated by 45 degrees with respect to the signal from the first base station.
It means the degradation of dB.

Next, other termination conditions will be described. The problem with the in-phase addition is when the difference between the phase rotation amounts of the base stations becomes large. Therefore, a propagation path is estimated from pilot signals of a plurality of base stations, and a difference in phase rotation of the propagation path between the base stations is obtained. If this difference becomes larger than a certain value, it indicates that the effect of fading is increased, and the accumulation in the memory circuit 17 is stopped. For example, the case where the phase rotation difference becomes 45 degrees or more is set as the termination condition. This condition corresponds to 0.7 when the determination is made based on the correlation value.

After accumulating data for an appropriate PN cycle in the memory circuit 17 based on the above-mentioned termination condition, the selector 18 is switched to input the contents accumulated in the memory circuit 17 to the peak detection circuit. This makes it possible to despread the pilot signal stored in the memory circuit 17. Since the received data is stored in the memory circuit 17, the same information can be transmitted many times. If the code phase of the despreading circuit 19 is changed, despreading with a changed amount of delay becomes possible. Therefore, it is possible to create a delay profile without increasing the scale of the despreading circuit. Further, since the memory circuit 17 only needs to have a capacity corresponding to the PN cycle, the scale of the memory circuit can be reduced. The in-phase adder 20 is a unit that performs in-phase addition for the PN code length. Since the in-phase addition over a plurality of PN code lengths has been completed at the time when they are stored in the memory circuit 17, the calculation of the in-phase addition is sufficient for the PN code length. Therefore, it is possible to reduce the number of calculations required to create a delay profile.

To reduce the scale of the memory circuit 17,
It is desirable to reduce the number of oversamples. Since the interpolation calculation is performed when estimating the peak value from the profile creation, if the information stored in the memory circuit 17 is twice oversampled, the effect of reducing the memory amount is high.

[0026]

According to the present invention, when positioning a terminal using a cellular communication system, the circuit scale and the amount of memory can be reduced, and the number of operations required for long-term in-phase addition can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a terminal configuration according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a terminal configuration according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a result of performing a correlation operation on a signal received by a terminal.

FIG. 4 is a diagram showing a method for storing information in a memory circuit.

[Explanation of symbols]

1 ... antenna, 2 ... radio unit (RF unit), 3 ... AD converter, 4 ... CDMA signal processing circuit, 5 ... AFC circuit, 6 ...
CPU, 7, 8, 19 ... despreader, 9 ... propagation path estimation circuit, 10 ... detection circuit, 11 ... deinterleave circuit, 12 ...
Depletion circuit, 13 ... Viterbi decoding circuit, 14 ... Deframing circuit, 15 ... Integrator, 16 ... Adder, 17 ...
Memory circuit, 18 ... Selector circuit, 21 ... Delay profile creation circuit, 22 ... Correlation operation circuit, 40, 41, 42, 43 ...
Peak of correlation calculation result, 44 ... Difference of shortest propagation distance signal (relative delay difference).

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5J062 AA08 CC07 CC11 DD15 EE00 FF01 5K004 AA01 BA02 BD00 5K022 EE01 EE21 EE31 5K067 AA42 BB04 CC10 DD17 DD25 EE02 EE10 HH21 HH23 JJ52 JJ54 KK13

Claims (8)

[Claims] 1. A wireless terminal position measuring device for estimating a position of a terminal using signals arriving from at least first and second base stations of a cellular communication system, wherein a phase of a signal received from the first base station is determined. A wireless terminal position measuring device comprising a storage circuit for estimating a rotation amount and accumulating a signal obtained by correcting the phase rotation of the received signal. 2. The storage circuit according to claim 1, wherein said reception signal synchronized with the signal periodically transmitted from said first base station and having been subjected to said phase rotation correction is stored in said storage circuit. A wireless terminal position measuring device comprising an adder for adding to timing information. 3. A phase rotation estimating circuit for estimating a phase rotation amount for the second base station, and a phase difference for calculating a difference between the phase rotation amounts for the first and second base stations. A wireless terminal position measuring device comprising an arithmetic circuit, wherein the value of the storage circuit is repeatedly updated while the phase rotation amount difference is equal to or less than a threshold value. 4. A phase rotation estimating circuit for estimating a phase rotation amount for the second base station and a correlation between the phase rotation amounts for the first and second base stations according to claim 2. A wireless terminal position measuring device comprising a correlation operation circuit, wherein the value of the storage circuit is repeatedly updated while the correlation value is equal to or larger than a threshold value. 5. The wireless terminal position measuring apparatus according to claim 1, wherein said storage circuit stores information of twice or more oversampling. 6. A propagation path estimating circuit for estimating a phase rotation amount of a signal received from a base station, an integrating circuit for correcting the phase rotation of the received signal, and a storage circuit for storing the signal corrected by the integrating circuit. A wireless terminal position measuring device comprising: 7. The information according to claim 1, wherein said received signal, which is synchronized with a signal periodically transmitted from said base station and whose phase rotation is corrected, is stored in said storage circuit at the same timing of said cycle. A wireless terminal position measuring device, comprising: 8. A wireless terminal position measuring apparatus according to claim 6, wherein said storage circuit stores information of two times oversampling or more.