JP2008017516A - Adaptive array base station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive array base station showing an optimum adaptive array effect continuously by checking an antenna configuration automatically. <P>SOLUTION: Through the antenna configuration check, it is determined whether calibration of a radio frequency has succeeded at the transmission and reception section. Through the check, it is also determined whether the radio frequency reception section of the adaptive array base station, a radio frequency transmission section, an antenna, and the connection cable between the antenna and a base station body and the connected state thereof are normal. The check is performed when the base station is installed or there is a small amount of traffic in the night. The check is determined comprehensively by RSSI check statuses, a Tx Weights status, Cal magnitude status, Cal consistency status, and Cal accuracy status. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio base station of a mobile communication terminal, and more specifically to an adaptive array base station having a function of automatically performing an antenna configuration check.

  Since the PHS terminal, which is a mobile communication terminal, has a low call charge, and is small and light, it has been able to acquire many users from the beginning. However, the reduction in call charges for mobile phones and the reduction in size and weight have reduced the merits of PHS terminals, and conversely, the disadvantages have been highlighted and some users have switched from PHS terminals to mobile phones.

  In other words, the PHS terminal has advantages such as a clear voice call and high-speed data communication and low power consumption compared to a mobile phone, but the call area is narrower than a mobile phone and the call is disconnected. However, there are demerits such as being easily generated while moving and making it difficult to make a call. Therefore, as a next-generation PHS base station that solves such a problem of the PHS terminal, an adaptive array base station that can improve the call quality while expanding the serviceable area by suppressing interference has been developed.

  The adaptive array base station means a base station equipped with adaptive array technology such as adaptive beam forming and adaptive null steering. Here, adaptive beamforming is a function that enables transmission with the maximum transmission power to a desired PHS terminal that performs communication. Adaptive null steering is a function of performing null transmission so as not to affect an interfering PHS terminal that does not perform communication.

  FIG. 3 is an explanatory diagram showing an outline of these functions in the adaptive array base station. In FIG. 3, the base station 40 is an adaptive array base station, and the base station 50 is a normal PHS base station. The PHS terminal PS1 communicates with the adaptive array base station 40, and the PHS terminal PS2 communicates with the base station 50 by the radio wave 500. Further, it is assumed that the PHS terminal PS1 and the PHS terminal PS2 communicate with the base station using the same time slot at the same frequency.

  When the adaptive array base station 40 communicates with the PHS terminal PS1, the adaptive beamforming function allows the radio wave blowing function (amplitude and phase) to be transmitted to the PHS terminal PS1, which is the desired PHS terminal, so that the maximum transmission power is obtained. Control.

The adaptive array base station 40 also uses the adaptive null steering function to control the amplitude and phase of the radio wave so as to suppress uplink interference (dotted line 520) from the PHS terminal PS2 that is the interfering PHS terminal.

As a result, the adaptive array base station 40 blows radio waves with the maximum transmission power as indicated by the radio wave 400 with respect to the PHS terminal PS1 and with the amplitude and phase controlled so as not to affect the PHS terminal PS2. By communicating with a PHS terminal using such a radio wave 400, C / I (ratio between desired level and interference level) is improved by suppressing uplink and downlink interference, and call quality with the desired PHS terminal is significantly improved. Can do. In addition, since the adaptive array base station has the interference suppression capability as described above, the effective frequency utilization rate can be remarkably improved as compared with the conventional PHS base station. As a result, the traffic capacity can be improved. it can.
As described above, the adaptive array base station does not radiate radio waves evenly, but controls and outputs the radio wave amplitude and phase by the adaptive beam forming function and the adaptive null steering function. As a result, it is possible to transmit radio waves to the desired PHS terminal with the maximum transmission power, and to give directivity to the radio wave so that null transmission is performed for the interfering PHS terminal.

  Conventionally, in such an adaptive array base station, whether or not the hardware configuration including the antenna of the base station is normal is checked by logging in to the base station locally or remotely when the base station is installed. It was judged by calibrating the frequency transmitting / receiving unit and checking the result. Further, the detection of the antenna abnormality is individually performed by statistically processing the received electric field strength upstream from the PHS terminal.

  As described above, in the conventional adaptive array base station, since the calibration could not be automatically performed and the result could not be checked, there was a problem that a lot of time and labor were required for operation. . In addition, when an abnormality occurs in the hardware, it is impossible to immediately detect and deal with the location. In addition, the calibration check was not performed with clear specifications. In addition, when detecting an abnormality in an antenna or an antenna cable, the conventional technique generally collects the received field strength of the uplink during a call with a PHS terminal and statistically processes it. However, in this method, depending on the position of the PHS terminal, the received electric field intensity at each antenna may vary greatly, which causes a problem of erroneous detection. An object of the present invention is to solve such problems of the prior art and to provide an adaptive array base station that can always exhibit an optimal adaptive array effect.

  In order to solve the above-described problems, the adaptive array base station includes an first beam to an nth antenna, and an adaptive beam that communicates with a maximum transmission power to a mobile communication terminal that performs communication. The adaptive null steering is performed so as not to affect the interfering mobile communication terminal that is not performing communication. The adaptive array base station transmits a weak radio wave with a known amplitude and phase one by one from the first antenna to the nth antenna in order, and the transmitted radio wave is transmitted from an antenna other than the antenna that transmitted the radio wave. By receiving, calibration of the characteristics of the radio frequency transmitting / receiving unit in each of the first to n-th antennas is performed. The result of this calibration is checked, and an antenna configuration check is performed to automatically determine whether the hardware configuration of the base station is normal. To be able to demonstrate.

  As described above, according to the adaptive array base station of the present invention, whether or not the calibration is accurately performed by automatically performing the hardware configuration check including the antenna periodically including the installation time. It is possible to check. In addition, when an abnormality such as a failure or failure occurs in the adaptive array base station, the location is notified so that it can be dealt with promptly. Therefore, it is possible to provide an adaptive array base station that can always exhibit the optimum adaptive array effect.

  Next, an embodiment of an adaptive array base station according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown a functional block diagram showing an embodiment when an adaptive array base station according to the present invention is applied to a PHS base station which is an adaptive array base station for digital radio communication. The adaptive array base station according to the present embodiment has a function of periodically checking the hardware configuration including the antenna even during installation, so that an optimal adaptive array effect is always expected. it can. In this specification, a hardware configuration check using a function for calibrating the characteristics of a radio frequency transmission / reception unit is referred to as an antenna configuration check.

  In FIG. 1, the adaptive array base station 10 according to the present embodiment includes four antennas ANT1 to ANT4, and these antennas ANT are connected to a transmission / reception changeover switch 12. The transmission / reception selector switch 12 controls these antennas ANT1 to ANT4 in a time-sharing manner to perform switching control between transmission and reception. A reception system module 14 and a transmission system module 22 are connected to the transmission / reception selector switch 12.

  The reception module 14 includes four low noise amplifiers (LNA) 16, a down converter (D / C) 18, and an A / D converter (A / S) 20 provided for each antenna ANT. The reception system module 14 is also connected to the modem unit 30, and the low noise amplifier 16, the down converter 18 and the A / D converter (A / S) 20 are sent from the transmission / reception changeover switch 12, which is a signal path, toward the modem unit 30. Connected in order.

  Similarly, the transmission system module 22 includes four D / A converters (D / A) 24, an upper converter (U / C) 26, and a power amplifier (P / A) 28 provided for each antenna ANT. ing. The transmission system module 22 is also connected to the modem unit 30, and the D / A converter 24, the upper converter 26 and the power amplifier 28 are connected in this order from the modem unit 30 which is a signal path to the transmission / reception system changeover switch 12. ing.

  The modem unit 30 includes a plurality of CPUs, and performs phase control by modulation / demodulation of transmission / reception data and digital signal processing. Specifically, the following five controls are performed.

  1. For example, D / U (Desire / Undesire) of the digital signal converted at the final stage of the reception system module 14 is synthesized and demodulated so as to be maximized.

  2. The phase of reception at the antenna ANT is calculated, and control is performed so that the phase is equivalent at the antenna end during transmission. Thereby, directivity can be imparted to the transmission / reception in the direction of the PHS terminal that performs communication.

  3. Suppression is achieved by creating a null point in the direction of arrival of interference and delayed waves.

  4). By controlling the phase of the signals supplied to the n antennas, it is possible to transmit with the beam narrowed with directivity in an arbitrary direction.

  5. Interference in the downlink direction is reduced with respect to PHS terminals other than the PHS terminal that is exchanging data (communications) during a call with surrounding base stations.

  The modem unit 30 is connected to the control unit 32.

  The control unit 30 includes a plurality of CPUs and controls the entire adaptive array base station 10. Specifically, the following two controls are performed.

  1. Necessary parameters and timings are instructed to the modem unit 30, and the data received by the modem unit 30 is processed. Further, data to be radiated in the air is created and passed to the modem unit 30. Further, the control of the transmission output by weighting calculated by the calibration is instructed.

  2. It is connected to the ISDN line and executes processing of an interface with the ISDN line.

  The power supply unit 34 is a power supply unit that receives a power supply of 100 V and supplies power to the adaptive array base station 10. The modem unit 30 and the control unit 32 form a digital signal processing unit.

  The adaptive array base station transmits each antenna with a predetermined weight based on reception information (amplitude and phase) received from N (N is a natural number of 2 or more) antennas. Thereby, adaptive beam forming and adaptive null steering are possible. However, since each antenna and cable have different characteristics such as isolation and loss, even if transmission is performed with a predetermined weight from a digital signal processing unit to a radio frequency (RF) transmission unit such as a transmission system module, At the end, it is not always transmitted with the expected weight.

  In general, adaptive null steering requires more precise amplitude and phase control at each antenna than adaptive beamforming. Therefore, it is necessary to recognize the characteristics of each antenna and each cable by calibration and reflect them in actual weighted transmission.

  The contents of the antenna configuration check in the adaptive array base station shown in FIG. 1 are shown below.

  1. It is determined whether or not the radio frequency transmission / reception unit has been successfully calibrated.

  2. It is determined whether the radio frequency receiver, radio frequency transmitter, antenna, connection cable between the antenna and the base station body, and the connection state of the base station are normal.

  When calibrating radio frequency transmission / reception units, if the base station is composed of n (n is a natural number of 2 or more) antennas, the slot timing is sequentially consecutive from antenna 0 to antenna n-1. Then, a weak radio wave with a known amplitude and phase is transmitted in the reception slot. At that time, the reception information of the remaining n-1 antennas is used to calibrate the characteristics of the radio frequency transmission / reception unit.

  The transmission weight at the time of calibration is performed considering the following points. That is, when a radio wave transmitted from one antenna is received by another antenna, it is important that C / I (ratio of desired level and interference level) is as high as possible and not saturated. Otherwise, the accuracy of calibration is not guaranteed. For this reason, in this calibration, the best transmission weight is determined by several calibrations, and thereafter, calibration is performed with the transmission weight.

  Software that performs an antenna configuration check that automatically determines whether the hardware configuration of an adaptive array base station is normal performs the antenna configuration check at the following two occasions.

  1. The software is downloaded to each processor of the base station and implemented after synchronization with other base stations is established.

  2. This is done after stopping the transmission of the control channel in a time zone with little traffic at night and confirming air synchronization with other base stations.

  As a result of the automatically performed antenna configuration check, if any abnormality is found, the network center is promptly notified with a result report. FIG. 2 is a conceptual diagram of a PHS system including a network center. In FIG. 2, CS-1 to CS-3 are adaptive array base stations, and these base stations are connected to the local exchange LS-1 by an ISDN interface. The local exchange LS-1 is also connected to a local exchange LS-2 connected to the network center. For example, when something abnormal occurs in the adaptive array base station CS-3, a report indicating the content of the failure is sent to the network center via the ISDN interface.

  The antenna configuration check is comprehensively judged based on the following five statuses.

1. Received field strength check status (RSSI Check Status)
2. Transmission weight status (Tx Weights Status)
3. Cal Magnitude Status
4). Cal Consistency Status
5. Cal Accuracy Status
If any one of the above five statuses is NG, the antenna configuration check is NG.

Hereinafter, the five statuses will be described.
“1. Received electric field strength check status” will be described below.
When the calibration is performed, transmission is sequentially performed with n antennas at the same transmission weight W01, and the received electric field intensity at each antenna is recorded. Actually, the received electric field strength is recorded in a matrix display. Note that the received electric field strength transmitted by antenna i and received by antenna i has no meaning, and the diagonal elements of the matrix are ignored.

  The received field strength check status is determined by the following method.

Create reception field strength matrix during calibration (when there are four antennas)
(1) The calibration is executed m times (this is the number of times that the calibration is performed to check the relative difference in received field strength).
(2) A reception electric field strength matrix as shown below is created for each calibration.

As a result of m times of calibration, m received field intensity matrices are generated, so an average of m times is obtained for each element. If the received electric field strength matrix for m times is Rij,

It becomes.

The calculation of the received field strength check status is shown below.
First, in the above formulas 1 and 2, “*” is ignored because it is the received electric field intensity received by the transmitting antenna. The maximum value in Rij is CalRssiMax. Rij consists of Tx rows and Rx columns. That is, each i row indicates the received electric field strength at the other three antennas when transmitted by the antenna i. Each j column indicates the received electric field strength when the antenna j receives transmissions from the other three antennas. Therefore, the abnormality of the transmission system / reception system of each antenna in the reception field strength check status is determined under the following conditions.

Antenna 0 transmission system
CalRssiMax-Max (R0j (J ≠ 0))> CalRssiMargin
Antenna 1 transmission system
CalRssiMax-Max (R1j (J ≠ 1))> CalRssiMargin
Antenna 2 transmission system
CalRssiMax-Max (R2j (J ≠ 2))> CalRssiMargin
Antenna 3 transmission system
CalRssiMax-Max (R3j (J ≠ 3))> CalRssiMargin
Antenna 0 reception system
CalRssiMax-Max (Ri0 (i ≠ 0))> CalRssiMargin
Antenna 1 receiving system
CalRssiMax-Max (Ri1 (i ≠ 1))> CalRssiMargin
Antenna 2 receiving system
CalRssiMax-Max (Ri2 (i ≠ 2))> CalRssiMargin
Antenna 3 reception system
Cal RssiMax-Max (Ri3 (i ≠ 3))> CalRssiMargin
Here, Cal Rssi Margin is a threshold value for determining RSSI Check Status. It is determined that the transmission system or reception system of the antenna i that satisfies the above equation is abnormal.

  If the transmission weight used when judging the received field strength check status is high, the received field strength of the good antenna is saturated, and the received field strength of the abnormal antenna and other antennas when transmitting with the abnormal antenna The reception electric field strength at the point becomes sufficiently high. Therefore, there are cases where an abnormality cannot be detected even though an appropriate CalRssiMargin is set.

  Therefore, an appropriate value must be used for the transmission weight. In this calibration, the target value of the received electric field strength is set to CalTargetRSSI, and a transmission weight is recorded so that the received electric field strength at other antennas becomes CalTargetRSSI when transmitting by each antenna. The smallest transmission weight among them is used for calibration when calculating the actual reception field strength check status.

“2. Transmission weight status” will be described below.
In this calibration, as described above, the transmission weight of each antenna is varied so that the received electric field strength at the other antenna becomes CalTargetRSSI when transmitted by each antenna. The CalTarget RSSI is a target value of the received electric field strength at another antenna in calibration. Transmission weights corresponding to other antennas in each antenna are as follows in matrix display.

The row of this matrix indicates the transmission weight of antenna i such that the received electric field strength at other antennas is CalTargetRSSI. Therefore, if all transmission weights (Wi0, Wi1, Wi2) corresponding to each antenna are smaller than MinTxWeights or larger than MaxTxWeights, it is determined that TxWeightsStatus of the corresponding antenna is NG. Here, MinTxWeights is defined as the minimum value of the transmission weight, and is determined in consideration of transmission noise. MaxTxWeights is defined as the maximum value of the transmission weight.

  “3. Cal magnitude status” will be described below. This is the status of the amplitude of the calibration vector for each antenna. In this calibration, the calibration vectors of antennas 1, 2, and 3 are expressed as relative vectors of the calibration vector of antenna 0 with antenna 0 as a reference.

  As the amplitude of the relative calibration vector, the status is determined by defining ColNormalRatio which is a ratio (variation width) to the amplitude of the calibration vector of the antenna 0. That is, assuming that the calibration vectors for each antenna are H0, H2, H3, and H4, if each amplitude is smaller than 1 / ColNormalRatio or greater than ColNoMialRatio, the amplitude status of the calibration vector for that antenna is determined to be NG.

  In general, when the receiving unit of antenna n is defective, the amplitude of the corresponding calibration vector is smaller than 1 / ColnomialRatio, and when the transmitting unit of antenna n is defective, the amplitude of the corresponding calibration vector is larger than ColNormalRatio. . The status is described as “Under Range” when the amplitude is smaller than 1 / ColnomialRatio, and as “Over Range” when the amplitude is larger than ColNoMialRatio. Therefore, the failure of the radio frequency transmission unit and the reception unit can be specified to some extent depending on whether this status is Under Range or Over Range. In general, when the antenna and the antenna cable are defective, this status is not NG.

  ColNominalRatio controls the transmission gain for each antenna in order to keep the transmission output of the base station constant by ALC (Auto Level Control), but there is a limit to the dynamic range that can be controlled. Therefore, since the radio frequency transmitter cannot be corrected beyond this limit, the Colnomial Ratio must be determined in consideration of the limit of the dynamic range.

  “4. Cal Consistency Status” will be described below. This is a status indicating the reliability (consistency) of calibration. In this status, calibration is performed k times to check each correlation. Specifically, when the standard deviation of the amplitudes of the calibration vectors H0, H1, H2, and H3 is greater than CalMagStdSpec, which is the standard deviation of the amplitudes of the calibration vectors of the respective antennas, or the calibration of the phase of each antenna is calibrated. If it is greater than CalPhaseStdSpec, which is the standard deviation of the phase of the motion vector, it is determined that the amplitude and phase are out of specification, and the status is NG.

  The values of CalMagStdSpec and CalPhaseStdSpec are determined in consideration of the downlink interference suppression capability by adaptive null steering. A smaller value of CalMagStdSpec and CalPhaseStdSpec indicates that there is room for improving the downlink interference suppression capability by software algorithm. On the other hand, if these specifications cannot be satisfied due to defective hardware, it means that there is no sufficient adaptive null steering effect.

  “5. Cal Accuracy Status” will be described below. This is a status indicating the accuracy of calibration. In this status, test calibration is performed t times to check the calibration accuracy. Test calibration is the transmission of two different transmission methods, adaptive beamforming and adaptive null steering, to any other target antenna using any two antennas. The difference between the received electric field strengths is defined and recorded as FOM (Figure of Merit).

  When there are four antennas, there are 12 FOMs in one test calibration. After calculating the average of twelve FOMs in t test calibrations, sort the items in descending order and check whether the average of the top four FOMs is greater than the CalFomSpec, which is the FOM spec of the test calibration result To do. If it is smaller than CalFomSpec, the cal accuracy status is NG. This CalFomSpec is determined in consideration of the fact that the accuracy of calibration does not become a factor limiting the downlink interference suppression capability even in a mobility environment.

  Next, a method for displaying (notifying) each status of the antenna configuration will be described. In the reception field strength check status, the diagnosis result is displayed for each of the transmission system and the reception system for each antenna using the reception field strength information of each antenna at the time of calibration. As shown in FIG. 4, the result is expressed by 8 bits, 2 bits for each antenna.

  In the transmission weight status, it is diagnosed whether the weight transmitted by each antenna during calibration is within a predetermined range. As shown in FIG. 5, the result is represented by 8 bits, 2 bits for each antenna. In the cal magnitude status, the normality of the amplitude of the calibration vectors of the antennas 0, 1, 2, and 3 is diagnosed. Therefore, when the relative calibration vector amplitudes of the antennas 1, 2 and 3 are (1) 1 / CalNominalRatio to ColnomialRatio normal, (2) Under 1 / CalnomialRatio is Under Range, and NG, (3) Over OverCalnomialRatio Becomes RANGE and becomes NG. As shown in FIG. 6, the result is represented by 8 bits, 2 bits for each antenna.

The cal consistency status indicates the diagnostic result of the calibration consistency. As shown in FIG. 7, the result is displayed for each bit with respect to the amplitude and phase of the relative calibration of each antenna, and is represented by a total of 8 bits. In the calibration accuracy status, the accuracy of calibration is diagnosed. A case where the average FOM of t test calibrations is CalFomSpcc or more is normal. The result is 8 bits and is expressed as follows: Oh (00000000) ... OK, 1h (00000001) ... NG
As described above, according to the adaptive array base station according to the present embodiment, the antenna configuration check is automatically performed by software, so it is necessary to confirm whether the calibration functions correctly. Can save time and labor in operation. As a result of the antenna configuration check, if there is an abnormality such as a failure or failure, the information can be uploaded to the network center immediately. As a result, appropriate processing can be performed promptly.

  Furthermore, it is possible to quickly detect construction mistakes and component defects during initial installation. It can also detect failures due to aging after installation. Specifically, it can be detected earlier by selecting a time zone with less nighttime traffic and performing an antenna configuration check once a day. Further, when an abnormality occurs in the antenna configuration check, it is possible to identify to some extent where the abnormality is in the base station.

  In this embodiment, the adaptive array base station according to the present invention is applied to a PHS base station. However, the present invention is not particularly limited to a PHS base station. For example, PDC (Personal Digital Cellular) or CDMA (Code Division The same applies to base stations such as (Multiple Access).

The functional block diagram which shows embodiment when the adaptive array base station by this invention is applied to a PHS base station. The network block diagram of a PHS system. Explanatory drawing of the adaptive beam forming and adaptive null steering in an adaptive array base station. Diagnosis result of transmission system and reception system for each antenna in electric field reception strength check status. The diagnosis result of the transmission wait status. Diagnostic result of cal magnitude status. Diagnostic result of cal consistency status.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Adaptive array base station 12 Transmission / reception changeover switch 14 Reception system module 22 Transmission system module 30 Modem part 32 Control part 34 Power supply part

Claims (4)

Adaptive null steering that performs adaptive beamforming that communicates with the maximum transmission power for mobile communication terminals that perform communication and does not affect interfering mobile communication terminals that do not perform communication In an adaptive array base station with first to nth antennas,
Transmitting means for transmitting weak radio waves with known amplitudes and phases one by one from the first antenna to the n-th antenna;
Receiving means for receiving the transmitted radio wave with an antenna other than the antenna that transmitted the radio wave with the transmitting means;
Calibration execution means for calibrating characteristics of radio frequency transmission / reception units in the first to n-th antennas;
Antenna configuration check means that checks the result of calibration performed by the calibration execution means and automatically determines whether or not the hardware configuration of the base station is normal,
An adaptive array base station characterized in that an optimum adaptive array effect can always be exhibited. The adaptive array base station according to claim 1, wherein the antenna configuration check includes:
After the antenna configuration check program that automatically determines whether the hardware configuration is normal is downloaded to the base station and synchronization with other base stations is established,
And after stopping the control channel transmission and checking for air synchronization with other base stations during low traffic hours at night,
An adaptive array base station that is automatically implemented. In the adaptive array base station according to claim 2, when an abnormality is detected as a result of the automatically performed antenna configuration check, a report describing the content of the abnormality is attached and notified to the network center. An adaptive array base station. 2. The adaptive array base station according to claim 1, wherein the antenna configuration check is comprehensively determined based on five statuses: a reception field strength check status, a transmission weight status, a cal magnitude status, a cal consistency status, and a cal accuracy status. An adaptive array base station.

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