JPH11150749A - Radio base station synchronizing method and equipment in digital mobile communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To transmit and receive a signal without interfering with each other by the same frequency band by detecting the time of the transmitting slot from a radio base station and matching the leading position of the slot of its own station at the time of detection. SOLUTION: The synchronization control part 2 of its own radio base station 1 drives a slot synchronization control part 3 to generate plural judging points to a level measuring instrument 5 which synchronizing with the slot of its own station from a plural judging points generating means 3a in order to detect the slot timing of a signal transmitted from another station and the measured level signal of each judging point is inputted to a level changing point detecting means 3b to detect the changing point of a level. In this case, a method to additionally divide time taken-from before the change of the level until the judging point of level change detection, to measure through the use of a level measuring instrument 5 and the means 3a and to detect the correct time of the changing point by the means 3b is used. When the temporal position of the changing point is detected, a timing correcting means 3c corrects the slot time of its own station by the time difference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a radio base station synchronization method and apparatus for avoiding interference between a plurality of radio base stations in digital mobile communication.

Digital mobile communication, especially TDMA (Time
Division Maltiple Access) / TDD (Time Division
Duplex) In digital mobile communication employing a wireless communication system, the same frequency or different frequencies are used for TDM.
A performs communication between a wireless base station and a plurality of mobile devices, and a frequency (channel) is allocated between the plurality of wireless base stations so that interference does not occur.
Interference may occur depending on conditions, and in order to cope with the situation, when interference occurs, a method of switching a channel to a different time slot or a method of switching a channel to a slot on another frequency is adopted. However, since the wireless base stations operate independently of each other, they cannot be completely synchronized with each other, which may cause cases where they interfere with each other.

[0003]

2. Description of the Related Art FIG. 9 shows a conventional system configuration.
0 is a time chart showing transmission / reception timing, and FIG. 11 is a schematic configuration of a system of the radio base station.

In the conventional system configuration shown in FIG.
One of the line control stations 80 is connected to a public line or a PBX (private exchange), and the other is connected to a plurality of wireless base stations 81-1 to 81-1.
It is connected to 81-n by a line and has a function of an exchange or a maintenance center. In addition, each radio base station 81-1,
81-2,..., 81-n (hereinafter, B1, B2,.
) Wirelessly communicates with a plurality of mobile stations in each area. In the example of FIG. 9, the radio base station B1 communicates with the mobile stations 82-1 to 82-m, the radio base station B2 communicates with the mobile stations 83-1 to 83-m, and the radio base station Bn communicates with the mobile stations 83-1 to 83-m. It communicates with the mobile stations 84-1 to 84-m.

Each of the radio base stations B1 to Bn in FIG. 9 has the block configuration shown in the radio base station B2 in FIG. 11, and includes a hardware unit 810 including a level measuring device and a software unit 811.
(A) and (b) of FIG. 10 show a base station (same as a radio base station) B
The time charts of 1 and B2 are shown. In this example, TDMA / TDD of 4-channel multiplexing is adopted as an access method, and operation is performed at independent transmission / reception timings.

Here, the TDMA / TDD system will be described. In this system, transmission information and reception information are alternately communicated and multiplexed using each channel of a plurality of radio carriers usable in digital mobile communication. This is a transmission method. Specifically, one frequency is time-divided,
The wireless base station B1 shown in (a) has one frame of 5 ms,
It is divided into eight time slots, and the first four time slots (reception 1 to reception 4) are used to receive signals transmitted from different mobile stations, respectively, and the remaining four time slots (transmission 1 to 4) is the first 4
Used for transmission to four mobile stations using one time slot. Also, the radio base station B2 shown in FIG. 10B has the same frame configuration, in which the first four time slots are allocated for transmission and the remaining four time slots are allocated for reception. It may be the same as the station B1. Although an example in which one frequency is time-divided has been described, the frequency may change depending on the time slot in order to avoid interference described later.

One of the features of this method is that the reception level of the surrounding zone radio wave can be monitored by the level measuring device 812 using an empty slot. This is because it is difficult to assign a fixed radio frequency to each radio base station in advance in a radio system based on the small zone system of digital mobile communication. It employs a dynamic channel allocation method of performing communication by using a function of detecting interference between base stations. This avoids interference,
Here, a method of measuring the level of an empty channel and a method of avoiding interference will be described.

The method of measuring the level of an empty channel is shown in FIG.
(A) in the receiving slot 1 of the radio base station B1
The reception level is measured at the corresponding slot timing of the scheduled transmission frequency. The measurement of the reception level is as shown in FIG.
Level measuring device 81 from software unit 811 to hardware unit 810
Set the reception level measurement for 2. Next, the hardware unit 810 detects burst waves from a plurality of base stations on the same frequency, measures the level, and converts the result of the level measurement by the software unit 811 into an electric field intensity. The electric field strength is
The strength of a radio wave emitted from a certain point at the receiving point. If the electric field strength (reception level) is large, it is determined that the measurement frequency is being used at the specified slot timing, and this is called "interference". That.

Transmission slot 4 of radio base station B1 in FIG.
When the transmission is performed using the scheduled transmission frequency of the radio base station B2, since the electric field strength is increased in the portion indicated by NG, the free channel level was measured in the reception slots 1 and 2 of the radio base station B2. In this case, interference occurs.
In the case of "interference", if another wireless base station is using the same frequency and the same slot timing, the channel becomes naturally unusable, so that another channel must be searched. In conventional interference circuits, avoidance is performed by the following methods (1) and (2).

(1) The channel is switched to another slot on the same frequency. (2) Switch the channel to a slot on another frequency. At present, as shown in FIG. 10, the radio base stations B1 and B2 have a difference in slot timing (time position of each slot) and transmission / reception timing (time position of transmission and reception). In the middle case, the radio base station B2 determines that interference occurs in two slots. In order to avoid this, when the channel is switched to another slot on the same frequency in (1), an operation is to be performed on the same frequency band as the transmission slot 4 of B1. B
Since interference occurs in the reception slots 1 and 2 of the second slot, the slots for which the channel can be switched are limited to the slots 3 and 4. Therefore, the probability of switching to a slot on another frequency in (2) increases. In this case, there is a problem in that if the limited frequency is to be used effectively, the slot timing on the same frequency band is wasted. Also,
Even if the slot timing is synchronized, if the transmission / reception timing does not match, the radio base stations will interfere with each other, and the transmission timing of another radio base station will be detected at the reception timing and the number of slots that cannot be used will increase. I do.

[0011]

As described above, in the conventional system, since each radio base station operates independently, a slot timing shift occurs, the use of slots is restricted, and the same Time division multiplexing access cannot be performed in the frequency band, and another frequency is used.
This is a major problem in effective use of frequency, and asynchronous wireless base stations hinder the TDMA system.

An object of the present invention is to provide a method and apparatus for synchronizing a radio base station in digital mobile communication so as to enable transmission and reception in the same frequency band without interfering with each other.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. In FIG. 1, reference numeral 1 denotes a radio base station (sometimes referred to as a local radio base station), 2 denotes a synchronization control unit, 3 denotes a slot synchronization control unit, 3a denotes a plurality of decision point generating means, 3b denotes a level change point detecting means, and 3c. Is a timing correction means, 4 is a transmission / reception timing synchronization control section, 4a is a level detection means for the own-station reception timing, 4b is a slot correction means, and 5 is a level measuring device for a received signal.

In the present invention, in order to avoid interference between a plurality of adjacent radio base stations, a level measuring device 5 which has conventionally been used only to determine the presence / absence of interference of its own radio base station is used. One slot of the own wireless base station 1 is used for time-division and used for measurement at a plurality of (n) time points (points), and the presence or absence of interference is determined for each of a plurality of level measurement points in the designated slot Then, based on the level measurement result, the asynchronous detection at the slot timing with another radio base station on the time axis is performed. If an asynchronous time difference can be established, the slot timing of the own radio base station can be changed so as to synchronize with another radio base station. Also, as a result of measuring the reception level, if the slot timing is correct, but a shift in transmission / reception timing is detected, or if the level cannot be measured at multiple locations within one slot, the reception level of the specified slot The transmission / reception timing can be changed by identifying the interference by identifying the slot and searching for a slot with less interference.

In FIG. 1, the synchronization control unit 2 of the own radio base station 1
Drives the slot synchronization control unit 3 to detect the slot timing of the signal transmitted from the other station, so that the plurality of decision points (decision time) are synchronized with the slot of the own station by the plurality of decision point generating means 3a. The level signal generated at the measuring device 5 and measured at each determination point is input to the level change point detecting means 3b, where the level change point (the point at which the level of an interference wave from another base station is detected) is determined. To detect. In order to perform the change point detection operation with high accuracy, the time before the level change and the time to the judgment point of the level change detection are further divided and measured by the level measuring device 5 by the plural judgment point generating means 3a to check the level change. A method of detecting the time of an accurate change point by the output means 3b is used. When the time position of the change point (deviation from the slot time of the own radio base station) is detected, the slot time of the own station is corrected by the time by the timing correction means 3c. This allows synchronization with the slot time of another station.

After the slot time is adjusted and the slot timing is matched, the transmission / reception timing synchronization control unit 4
Is driven, the level detection means 4 of the own-station reception timing is used.
a operates to measure the level of the reception timing (a plurality of slots) in one frame of the own station by the level measuring station 5 and detect the level. The period in which the level is equal to or higher than the certain level is a timing period during which a radio signal is transmitted from another station, and the slot correction means 4b corrects the transmission timing of the own radio base station 1 based on the detection signal. As a result, the transmission timing of the radio base station 1 can be synchronized with the transmission timing of the transmission / reception signal of another station, and interference can be avoided.

[0017]

FIG. 2 shows the configuration of a radio base station in which the present invention is implemented. In the drawing, reference numeral 1 denotes a radio base station, and 10 denotes a CP.
U, a software control unit including a memory, etc., 11 is a radio control unit for controlling TDMA / TDD of transmitted / received radio signals, switching of channels, etc., and 12 is for controlling connection of outgoing and incoming calls. The call control unit 13 is a wired control unit that is connected to a higher-level device (such as an exchange) and controls the wired side. 14 is a hardware unit, 15 is a wireless device having a transmitting unit and a receiving unit, 16 is a level measuring device for measuring the level of a received signal at a plurality of decision points (measuring electric field strength) according to the present invention, and 17 is a wireless device A wired / wireless connection unit 15 having an interface function for interconnecting signals between the signal 15 and the wired side, and a wired unit 18 connected to a higher-level device (exchanger or the like) by wire. Reference numeral 6 denotes a higher-level device (exchanger or the like). The synchronization control of the radio base station of the present invention is executed by the joint operation of the software control unit 10 and the hardware unit 14 of FIG.

FIG. 3 is an explanatory diagram of the state of the shift between the slots of the two base stations and the correction. In FIG. 3, (1) shows the frame configuration of the base station B1, and (2) shows the frame configuration of the base station B2 provided near the area of the base station B1. In the case of FIG. 3, in order to correct the shift of the slot according to the present invention, the wireless control unit 11 of the software control unit 10 performs the synchronization control using the level measuring device 16 of the hardware unit 14.

The software controller 10 of the base station B2 instructs the level measuring device 16 to measure the reception electric field strength at n points (arbitrary points, for example, three points) within the slot timing of B2 of its own radio base station at each time point. Set. Level measuring device 16
Performs the reception level measurement at the set n points and notifies the software control unit 10 of the result. The wireless controller 11 of the software controller 10 determines the measured level at each time point. At this time, if no reception level can be detected in the measurement values between the n points from the reception level measurement result, or if no difference can be detected in the reception level, the other radio base station (FIG.
In the example of (1), it cannot be determined whether or not the slot is synchronized with the base station B1), so that the reception level measurement at the n points is performed again in the next slot. In this case, if the reception level is not detected in all the slots of one frame or if no difference is detected in the reception level, it is determined that the slot timing is synchronized.

If it is detected from the reception level measurement results that there are differences in the n reception levels at a certain measurement point, as shown in the level measurement result of slot R1 at the reception timing in FIG. It is determined that slot synchronization with the base station has not been achieved, and level measurement is again performed at n points between two measurement points at which a difference in reception level is detected. By repeating the level measurement as much as possible by the level measuring device 16 between the measurement points where the difference in the reception level is detected, the difference between the slot timing of the other radio base station and the slot timing of the own radio base station can be detected.
Finally, the head of the slot timing of the own radio base station is adjusted to the head of the slot timing of the other radio base station. As a result, in the wireless base station B2 in FIG. 3, the slot timing of (2) can be corrected to match the beginning of the slot timing of another wireless base station as shown in (3).

FIG. 4 shows a processing flow for synchronizing the slot timing, which is executed in the radio control unit of the software control unit in FIG. FIG. 5 is an explanatory diagram of the timing for detecting the difference between the slot timings of the two base stations.
(1) corresponds to the transmission slot timing S4 of the base station B1 in FIG. 3, and (2) corresponds to the reception slot timing R1 of the base station B2 in FIG.

The processing flow of FIG. 4 will be described with reference to the timing example shown in FIG. First, the software control unit of the base station B2 measures the level at the point n at the designated slot timing (S1 in FIG. 4). FIG.
In the example of (1), a1, a2, a3
At these three points, the signal of the transmission slot timing S4 of the base station B1 is received and the level is measured.

Next, it is determined whether a difference has been detected between the measurement points of the reception level (S2 in FIG. 4). If no frame has been detected, it is determined whether one frame has been measured (S6 in FIG. 4), and if not, the process proceeds to the next slot determination (S7). In the example of FIG. 5, as shown in (3), the measurement points a2 and a3
A difference is detected between.

When a difference is detected between the measurement points, the level measurement station determines whether the next measurement is possible (S in FIG. 4).
3) If a measurement is possible, a difference is detected in the reception level, and n-point level measurement is performed between the measurement points (S4), and S3
Return to If it is determined that measurement is not possible, the head of the slot timing of the own radio base station is adjusted to the head of the slot timing of the other radio base station (S5).

In the example of FIG. 5, three points b1, b2, b are set between the measurement points a2 and a3 detected in (3).
The level is measured at each of the three points, and between the measurement points at which the difference in the reception level is detected. As shown in (4), a difference is detected between the measurement points b1 and b2.
The reception level is measured by dividing the interval between 2 into three measurement points c1, c2, and c3. As a result, the measurement points c1 and c
2, a difference is detected in the reception level between three measurement points d1, d2 and d between c1 and c2 as shown in (6).
Measure at 3. As a result, a difference occurs in the reception level between d1 and d2. In the example of FIG. 5, the interval between the measurement points is the limit of the measurable level, and cannot be measured by the judgment in S3 in FIG. 4, and the slot timing of the radio base station B2 is adjusted to the timing d1. As shown in (7) of FIG. 5, the slot is the same as the slot of the radio base station B1 shown in (1).

FIG. 6 shows another processing flow for synchronizing the slot timing. In this processing flow, FIG.
The same processing as in steps S1 and S2 of FIG. 4 is performed, and even when the reception level does not detect any difference between the measurement points, the processing in steps S6 and S7
The same S7 and S8 as described above are performed, but if a difference is detected between the reception levels between the measurement points, the head of the slot timing of the own radio base station is detected and adjusted to the point (S3 in FIG. 6). This is (3)
This corresponds to aligning the head of the slot of the own radio base station with the position of a3 shown in FIG.

Thereafter, it is determined whether or not a difference between the reception level measurement points (measurement points at n points) between the reception level measurement points has been detected (4 in FIG. 6). It ends when they match,
When the difference is detected, it is determined whether the next level can be measured by the level measuring device (S5). Here, if possible, n is set between the measurement points at which the difference in the reception level is detected.
The point level is measured (S6 in FIG. 6). Thereafter, the process returns to S3, and ends if the beginning of the slot matches or if the next level cannot be measured by the level measuring device. In the case of the example of FIG. 5, after the top of the slot is adjusted to the position of a3 according to the above (3), the top of the slot is adjusted to the position of b2 shown in (4), and thereafter, c2 and (6) in (5) The head of the slot is adjusted to d2 of the above, and the position of the slot matches another base station.

FIG. 7 shows a processing flow for adjusting transmission / reception level timing, and FIG. 8 shows a transmission / reception timing and a burst waveform measured by a level measuring device. When the transmission / reception timing is adjusted in the radio base station, the level measurement is performed in slot units at the reception timing for one frame of the radio base station (S1 in FIG. 7). Next, it is compared with the threshold L from the measurement result to determine whether it is equal to or greater than the threshold L (S
2). If it is equal to or greater than the threshold value L, the start timing of the own frame is changed to a position where the reception level of the own reception slot is minimized (S3). After that, the process returns to S1 to measure the level of the reception timing for one frame in slot units.
In S2, the measurement result is compared with the threshold value L, and if it is found that the measured result is lower than the threshold value L, the process is terminated.

The above processing will be described with reference to FIG. 8. (1) to (4) of FIG. 8 show the frame configuration of the other radio base stations T 1 to T 4, and the transmission and reception timings (transmission timing and reception timing) are different. Synchronized. On the other hand, (5) shows a state before the transmission / reception synchronization processing of the own radio base station U1. When the level measurement for one frame is performed in the own radio base station U1 in S1 of FIG. 7 described above, from the transmission slot S2 to the reception slot R1 of the own radio base station U1 as indicated by the electric field strength shown in (6) of FIG. A reception level that can be recognized as being used by another wireless base station can be detected (S2 in FIG. 7). In this case, the reception slot R1 which is the reception timing of the own radio base station U1
Since the transmission slot S4 of the other radio base station T4 interferes with the other radio base station, it is determined that the transmission and reception timing of the other radio base station is not synchronized.

In order to minimize interference from the other radio base station in the reception timing of the own radio base station U1, the transmission and reception timing can be synchronized by shifting the synchronization of the own radio base station frame in slot units ( S3 in FIG. 7). FIG.
In the example of (6), from the result of the electric field strength in (6), it can be seen that the frame timing of the own radio base station U1 should be delayed by one slot in order to synchronize the transmission and reception timing with another radio base station. ), Delay by one slot,
The subsequent reception level measurement results in the electric field strength shown in (8) of FIG. In the electric field strength, the reception level at the reception timing is minimum, which means that the transmission and reception timing is synchronized with the other radio base stations.

[0031]

According to the present invention, in an environment where a plurality of base stations are present, when the base station is in an asynchronous state with another base station, the slot level of the own base station depends on the reception level at the slot timing of the other base station. It is possible to solve the problem that interference occurs in the timing, and the slots in which the channel can be switched to another slot on the same frequency are limited. Also, even if the slot timing is synchronized, if the transmission and reception timings do not match, the radio base stations will interfere with each other, and the reception timing will detect the interference of the transmission timing of other radio base stations and make the slot unusable. The problem of increase can be solved. As described above, according to the present invention, effective use of frequency can be realized in the time division multiple access TDMA system.

[Brief description of the drawings]

FIG. 1 is a diagram showing a principle configuration of the present invention.

FIG. 2 is a diagram illustrating a configuration of a wireless base station in which the present invention is implemented.

FIG. 3 is an explanatory diagram of a state of a slot shift between two base stations and a correction.

FIG. 4 is a diagram showing a processing flow for synchronizing slot timing.

FIG. 5 is an explanatory diagram of timing for detecting a shift in slot timing between two base stations.

FIG. 6 is a diagram showing another processing flow for synchronizing slot timing.

FIG. 7 is a diagram showing a processing flow for adjusting transmission / reception level timing.

FIG. 8 is a diagram showing transmission / reception timing and burst waveforms measured by a level measuring device.

FIG. 9 is a diagram showing a conventional system configuration.

FIG. 10 is a diagram showing a time chart showing transmission / reception timing.

FIG. 11 is a diagram showing a schematic configuration of a system of a wireless base station.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radio base station 2 Synchronization control part 3 Slot synchronization control part 3a Multiple measuring point generation means 3b Level change point detection means 3c Timing correction means 4 Transmission / reception timing synchronization control part 4a Local station reception timing level detection means 4b Slot correction means 5 Reception Signal level measuring instrument

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Fujii 14-15 Higashishiroshima-cho, Naka-ku, Hiroshima City, Hiroshima Prefecture Inside Fujitsu China Communication Systems Co., Ltd. No. 15 Fujitsu China Communication Systems Co., Ltd. (72) Inventor Yoshiko Tatsumi 14-15 Higashishirashimacho, Naka-ku, Hiroshima City, Hiroshima Prefecture Fujitsu China Communication Systems Co., Ltd. (72) Inventor Toshihiro Fujimoto Kawasaki, Kanagawa Prefecture Fujitsu Limited (72) 4-1-1, Ueodanaka, Nakahara-ku Minoru Kuroda 4-1-1, Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu Limited (72) Inventor Yasuhiro Suzuki Kawasaki, Kanagawa Prefecture Fujitsu Limited, 4-1-1 Kamiodanaka, Nakahara-ku, Yokohama

Claims (5)

[Claims] In a method of synchronizing a radio base station in digital mobile communication of a TDMA / TDD radio communication system, a radio base station uses a plurality of judgment points obtained by dividing one slot time of a frame of the self station into a plurality of time intervals. The reception level of a signal transmitted from another adjacent radio base station is measured, a change point is detected for the reception level of each judgment point, and the interval between the change point of the reception level and the judgment point before change is further increased by a plurality of times. By generating a plurality of determination points divided into intervals and measuring the reception level, the transmission slot time of the other radio base station is detected, and the start position of the slot of the own station is adjusted to the detection time. Radio base station synchronization method in digital mobile communications. 2. A radio base station synchronization method in digital mobile communication of a TDMA radio communication system, wherein a radio base station is adjacent at a plurality of decision points obtained by dividing one slot time of a frame of its own station into a plurality of time intervals. The reception level of a signal transmitted from another radio base station is measured, and when a change point is detected for the reception level at each determination point, the start position of the slot of the own station is adjusted to the time position of the conversion point, and the corrected Repeating the process of measuring the reception level of a signal transmitted from another adjacent radio base station and adjusting the head position of the own station slot at a plurality of decision points obtained by dividing one slot time of a frame into a plurality of time intervals. A radio base station synchronization method in digital mobile communication. 3. The radio base station according to claim 1, wherein when the slot of the frame of the radio base station is synchronized with another radio base station adjacent to the radio base station, the radio base station transmits one frame of the radio base station. The level of the received signal is measured, the reception level being used by another radio base station for transmission is detected, and when it is detected that the reception slot of the own station overlaps the detection section of the reception level, the frame of the own station is detected. A radio base station synchronization method in digital mobile communication, wherein transmission and reception timings are synchronized by shifting the transmission timing in slot units. 4. A radio base station synchronizer in a digital mobile communication system of a TDMA / TDD radio communication system, wherein a plurality of judgment points are generated in synchronism with a slot of the own station to divide a slot into a plurality of time intervals. A slot synchronization control unit comprising: a level measuring device for measuring a level of a signal transmitted from another station at the plurality of decision points; and a change point detecting means for detecting a change point of the measurement level at each of the decision points. The slot synchronization control unit, when the change point is detected by the change point detection means, the plurality of determination point generation means further divides the time interval between the determination points before the level change and the change point into a plurality of time intervals. The operation of generating the judgment points and detecting the change point of the measurement level at each judgment point is repeated, and when the time interval becomes impossible for the measuring instrument to measure, the detected level conversion point is automatically set. A radio base station synchronizer in digital mobile communication, comprising: timing correction means for adjusting a head position of a slot of a station. 5. The transmission / reception timing synchronization control unit according to claim 4, wherein the radio base station includes a transmission / reception timing synchronization control unit which is activated after matching a position of a slot of its own station with a slot of the adjacent other station,
The transmission / reception timing control unit measures the level of a reception signal in one frame of the own station by the level measuring device, and determines the timing of the transmission slot of the own station in slot units during a timing period when the reception level is equal to or higher than a certain level. A radio base station synchronizer in digital mobile communication, characterized in that it is modified.