JP2009177532A - Base station device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a base station device autonomously select whether to be synchronized by the use of a receiving wave from which base station device, no matter how it has previously been decided that the synchronization between base stations is taken by the use of the receiving wave from which base station device. <P>SOLUTION: This base station device can be synchronized between the base stations by the use of the receiving wave of a radio from the other base station device. The base station device includes a scanning part 12 for scanning the receiving wave from the other base station device, and a selection part 14 for selecting a source receiving wave which is used for the synchronization between the base stations from among a plurality of receiving waves obtained by scanning. The selection part 14 selects the receiving wave from the base station device near its own device as a source receiving wave, and is synchronized between the base stations by the use of the source receiving wave. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base station apparatus capable of performing inter-base station synchronization using a radio reception wave from another base station apparatus.

  In a wireless communication system in which mobile terminals can communicate, such as WiMAX, a large number of base stations are installed in various places. A mobile terminal in an area (cell) covered by each base station can communicate with a base station covering the area.

When the mobile terminal moves, the base station with which the mobile terminal communicates is changed. However, when the base station is changed, the mobile terminal simultaneously changes from two base stations (serving base station and target base station). Will be received.
For this reason, in order to smoothly move the mobile terminal between base stations, it is necessary to ensure synchronization between base stations in which the transmission timing and the carrier frequency are uniform between adjacent base stations.

When synchronization between base stations is established, when a mobile terminal moves between base stations, the mobile terminal can simultaneously receive signals from two base stations, and can smoothly move between base stations.
Here, as a technique for synchronization between base stations, for example, there is one described in Patent Document 1.
JP 59-6642 A

In order to achieve synchronization between base stations, it is conceivable that each base station apparatus receives a GPS signal from a GPS satellite and each base station operates with a common synchronization signal as in Patent Document 1.
However, when synchronizing using a GPS signal, each base station device needs to be equipped with a GPS receiver, resulting in an increase in size and cost. In addition, in the case of a base station apparatus installed in an environment that cannot receive GPS signals such as indoors, it becomes impossible to establish synchronization between base stations.

Thus, it is conceivable to detect the transmission timing of the adjacent base station using a received wave of a signal (preamble or the like) transmitted by another adjacent base station, and to synchronize at the transmission timing.
In this case, since synchronization can be achieved by wireless communication using the same frequency as that used for communication with the mobile terminal, a special receiving system for synchronization is not required unlike a GPS receiver for receiving GPS signals.
For this reason, it is possible to reduce the size and cost of the base station, and it is suitable as a small base station installed indoors.

  Here, as seen from a certain base station, the number of other base stations that are adjacent to each other so that a received wave is obtained is not limited to one, and there may be a plurality of base stations. Even if there are a plurality of adjacent base stations, there is no problem as long as it is determined in advance from which base station the received wave is used to synchronize between base stations.

However, when trying to determine in advance which base station to use for the synchronization between base stations, the base station installer is considered in consideration of various factors such as the location and environment where the base station is installed. Has to be decided, and enormous labor and cost are generated.
In addition, in the above case, it is necessary to re-determine which base station uses the received wave from other base stations to synchronize between base stations even if only one additional base station is installed. , Making system operation very complicated.

  Therefore, the present invention provides that the base station apparatus uses the received wave from which base station apparatus to synchronize, even if it has not previously determined which base station apparatus uses the received wave to synchronize between base stations. The purpose is to be able to select autonomously.

  The present invention is a base station apparatus capable of performing synchronization between base stations using a wireless received wave from another base station apparatus, and a scanning unit that scans a received wave from another base station apparatus; A selection unit that selects a source reception wave used for synchronization between base stations from a plurality of reception waves obtained by scanning, and synchronization between base stations is performed using the source reception wave selected by the selection unit. It is a base station apparatus characterized by performing.

  According to the present invention, since the base station apparatus includes a selection unit that selects a source received wave from a plurality of received waves, the base station apparatus can autonomously select the received wave and set the source received wave in advance. There is no need to do.

  The selection unit receives the source received wave based on a received wave characteristic of each of a plurality of received waves obtained by scanning and indicating that the received wave characteristic is transmitted from a base station apparatus close to the own apparatus. It is preferable to select. In this case, since the received wave from the base station apparatus close to the own apparatus is selected as the source received wave, the timing error due to the propagation delay is small and appropriate selection is performed.

  The selection unit preferably selects the source received wave based on the received wave intensity of each of the plurality of received waves obtained by scanning. This is because it is considered that the distance is relatively close if the received wave intensity is high.

  It is preferable that the selection unit selects the source received wave based on timings of a plurality of received waves obtained by scanning. This is because if the timing is early, the distance is considered to be relatively close.

  The selection unit, when a received wave intensity difference between the first received wave having the highest received wave intensity and the other received waves among a plurality of received waves obtained by scanning is smaller than a threshold, Of the received wave and the received wave whose received wave intensity difference is smaller than the threshold value, the received wave having the earliest received wave timing is preferably selected as the source received wave. When the received wave intensity difference is small, more appropriate selection can be performed by selecting the timing with priority.

  When the selection unit includes a reception wave from a master base station device that does not require a reception wave from another base station for synchronization between base stations in the plurality of reception waves obtained by scanning In this case, it is preferable to select the received wave from the master base station apparatus as the source received wave. In this case, a master base station device without delay is preferentially selected.

  In addition to the received wave characteristic indicating that the selection unit has transmitted from a base station apparatus close to its own apparatus, the received wave requires a received wave from another base station for inter-base station synchronization. It is preferable to select the source received wave in consideration of whether or not the received wave is from a master base station apparatus that does not. In this case, the received wave from the master base station apparatus can be prioritized while being based on the received wave characteristic, so that a more appropriate selection can be made.

  The own device is a slave base station device that requires a received wave from another base station for synchronization between base stations, or does not require a received wave from another base station for synchronization between base stations A determination unit configured to determine whether the base station device is a master base station device; when the determination unit determines that the device is a slave base station device, the base station uses a received wave from another base station device It is preferable to perform inter-synchronization. In this case, when it is determined that the base station device is a slave base station device, synchronization between base stations can be performed using received waves from other base station devices.

  The determination unit refers to setting information stored in a storage unit included in the own device, and when the setting information indicating that the own device is a master base station device exists in the storage unit, It is preferable to determine that it is a master base station. In this case, it is easy to set the master.

  The determination unit preferably determines that the own device is a master base station when there is no received wave that can be scanned as a result of scanning the received wave from another base station device. In this case, setting as a master is unnecessary.

A GPS detector for detecting the presence or absence of a GPS signal output from the GPS receiver;
When the determination unit detects that there is a GPS signal, the determination unit preferably determines that the own device is a master base station. In this case, if there is a GPS signal, it can be used as a master.

  According to the present invention, it is possible for the base station apparatus to autonomously select which base station apparatus is to be used for synchronization.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a wireless communication system having a plurality of base station devices (BS) 1, 1a, 1b, 1c. In this wireless communication system, for example, in order to realize broadband wireless communication, a method based on “WiMAX” defined in IEEE 802.16 that supports an orthogonal frequency division multiple access (OFDMA) method is adopted.

  As shown in FIG. 2, one frame in WiMAX is configured by arranging a preamble (Preamble), a downlink subframe (DL), and an uplink subframe (UL), which are known signals, in the time axis direction. Note that the length of one frame is 5 msec. Also, a plurality of patterns are prepared for the preamble by changing the frequency and code used.

  FIG. 3 shows the state of areas (cells) E1, E2 covered by adjacent base station apparatuses (BS1, BS2). FIG. 3 also shows how a mobile terminal (MS) 2 that communicates with a base station apparatus moves from one base station apparatus BS2 to another adjacent base station apparatus B1. .

  When the mobile terminal MS moves between base stations, the mobile terminal MS communicates with both the serving base station device BS2 that is currently communicating and the target base station device BS1 that is next to communicate, but is adjacent to each other. When the base station apparatuses BS1 and BS2 are synchronized, as shown in FIG. 4, the transmission timing (downlink subframe timing) from each base station BS1 and BS2 and each base station, as viewed from the mobile terminal MS, The reception timing timings (uplink subframe timings) of BS1 and BS2 coincide with each other. As a result, the mobile terminal MS can receive signals from the two base station apparatuses, and can smoothly move between base stations.

  Returning to FIG. 1, the radio communication system according to the present embodiment includes, as base station apparatuses 1, 1 a, 1 b, and 1 c, a master base station apparatus (hereinafter, referred to as “master BS”) 1 and a slave base station apparatus (hereinafter, “ 1a, 1b, 1c). Since the base station apparatuses 1, 1a, 1b, and 1c of the present embodiment do not have a GPS receiver, it is possible to reduce the size and cost. It can also be installed in places where GPS signals are difficult to receive, such as inside buildings.

  The master BS 1 is a base station device that does not need to detect and acquire the timing for synchronization between base stations from the received waves of the signals transmitted by the other base station devices 1a, 1b, 1c. It is configured as a self-running master base station device that determines signal transmission timing based on a synchronization signal (clock) generated by the own device. Note that the master BS 1 may include a GPS receiver and determine a signal transmission timing using a GPS signal.

Slave BS1a, 1b, 1c is a base station apparatus which detects and acquires the timing for the synchronization between base stations from the received wave of the signal which other base station apparatuses 1a, 1b, 1c transmitted.
Each of the slave BSs 1a, 1, 1c is a source base station device (hereinafter referred to as a “source BS”), out of a plurality of other base station devices (master base station device or other slave base station devices). ) And a received wave (source received wave) of a signal (preamble; known signal) transmitted by the source BS is detected, and a timing (signal transmission timing) for synchronization between base stations is acquired.

  The slave BSs 1a, 1b, and 1c are configured as autonomously synchronized base station apparatuses that can autonomously select which base station apparatus is used to synchronize. That is, the base station installer does not need to determine in advance which base station apparatus uses the received wave for synchronization.

The master BS 1 and the slave BSs 1a, 1b, and 1c each include a processing unit (processor) that processes a received signal, and a memory that stores a computer program executed by the processing unit and necessary information (setting information and the like). Have.
5 and 6 show functions realized by the processors of the base stations 1, 1a, 1b, and 1c executing the computer program. The functions shown in FIGS. 5 and 6 are exclusively used by the slave BS, but also include a master BS1.

As shown in FIG. 5, the base stations 1, 1a, 1b, and 1c are slave base station devices 1a, 1b, and 1c whose own devices require received waves from other base stations for synchronization between base stations. Or a determination unit 11 that determines whether the master base station device 1 does not require a received wave from another base station for synchronization between base stations. When the determination unit 11 determines that the own apparatus is the master base station apparatus 1, the transmission timing is determined using a clock generated by a clock generator (not shown) included in the own apparatus as a synchronization signal.
Therefore, the other base station apparatuses 1a, 1b, and 1c can receive the signal transmitted at the transmission timing determined by the master BS and synchronize with the timing of the received wave.

When the determination unit 11 determines that the own device is the slave base station device 1a, 1b, or 1c, the base station receives a preamble (synchronization signal) transmitted from another base station (source BS). The timing of the preamble is detected by the wave, and processing for obtaining the synchronization timing is performed.
Since the source BS may be a base station device that is transmitting a signal, it may be a master BS or a slave BS. Since the wireless communication system of the present embodiment includes at least one master BS, synchronization between base stations can be established directly or indirectly with the master BS.

As shown in FIG. 5, each of the base stations 1, 1a, 1b, and 1c includes a scanning unit 12 that scans a received wave from a base station adjacent to the base station.
The scanning unit 12 receives receivable signals and calculates the RSSI and preamble timing (timing offset).

  The scanning unit 12 has, in a memory, a plurality of preamble patterns (with different use frequencies and codes) that may be used by other base station apparatuses as known patterns. The scanning unit 12 uses a known preamble pattern to specify the type of preamble included in the received wave, and detects the RSSI (received wave intensity) and timing of the preamble.

FIG. 7 shows a method of detecting the preamble timing. Since the preamble is a known signal, the signal waveform of the preamble is also known. Assuming that the signal in the time domain of the preamble is P (n), a sliding correlation of P (n) is obtained in the time direction with respect to the received wave shown in FIG.
The scanning unit 12 performs the sliding correlation on a plurality of types of preamble patterns, so that the pattern that matches the received wave (the pattern having the highest correlation) can be specified as the preamble pattern of the received wave. Further, the correlation value is the received wave intensity (RSSI).
Further, as shown in FIG. 7B, the scanning unit 12 can detect the position where the received wave and the P (n) correlation value have taken a peak as the preamble timing.

  Of the detected received waves, those whose RSSI does not exceed the RSSI threshold value TR are not used for source BS selection because the received wave intensity is too weak.

  A combination (measurement result) of information, timing, and RSSI indicating the preamble pattern specified by the scanning unit 12 is stored in the memory by the collection unit 13 and can be referred to by the selection unit 14 described later.

  Since a plurality of types of preamble patterns are prepared as described above, even if a plurality of base stations receive a plurality of received waves almost simultaneously by using different patterns of preambles, Characteristics such as RSSI and timing can be distinguished and detected for each received wave.

  Now, the number of received waves (exceeding the RSSI threshold value) scanned (detected) by the scanning unit 12 may be 0, 1, and a plurality.

  When the number of received waves that can be received from other base stations is 0, it is considered that the master BS1 is not activated, and thus the scanning unit 12 continues scanning until at least one received wave can be detected.

  When the number of received waves that can be received from another base station is 1, since the timing can only be determined based on the received waves, the preamble timing from the received waves is set as the synchronization timing.

  When there are a plurality of reception waves that can be received from other base stations, one source reception wave used for determining the synchronization timing is selected from the plurality of reception waves. This selection is performed by the selection unit 14.

The selection of the source received wave is not particularly limited as long as one received wave can be selected from a plurality of received waves, but in this embodiment, the source received wave is selected. As a main criterion, the received wave from the base station apparatus closest to the own apparatus is selected as the source received wave.
This is because synchronization with a nearby base station is considered to have better synchronization accuracy. For this reason, the base station apparatus should just measure the received wave characteristic which is influenced by the distance between base stations from a received wave. In the present embodiment, the selection is performed based on the RSSI (received signal strength) of each received wave. If the RSSI is large, it can be determined that the distance to the own device is close, and if the RSSI is small, the distance to the own device is large.
The received wave characteristic affected by the distance between base stations may be a characteristic indicating received signal quality such as CINR.

  Hereinafter, the flow of processing for the base station apparatus to determine the synchronization timing will be described with reference to FIG. Note that the process for determining the synchronization timing is performed immediately after the base station apparatus is powered on. Moreover, you may perform periodically after power-on.

  When the base station apparatus is powered on, first, the determination unit 11 determines whether or not the own apparatus is the master BS1 (step S1). Since the source BS (source received wave) is not necessary when the own device is the master BS1, the synchronization timing is determined based on the clock signal of the clock generator and the GPS signal of the own device (step S2).

  In the present embodiment, the determination unit 11 refers to the setting information (config) recorded in the memory (setting information storage unit 15) in order to determine whether or not the own device is the master BS1. In the case of a base station apparatus used as a master BS, information indicating that the own apparatus is the master BS is set as setting information in advance, and therefore, the determination part 11 refers to the setting information, and the own apparatus is included in the setting information. If the information indicating that it is the master BS is included, it can be determined that the own device is the master BS.

  In addition, since the base station apparatus itself can determine the master BS and the slave BS by referring to the setting information, except for the setting information, the base station apparatus configuration (particularly the computer program) is changed to the master BS. Can be shared by the slave BS and a highly versatile device can be obtained. Further, if the setting information is changed, the master BS and the slave BS can be easily changed from each other.

  In addition, in order to determine whether or not the own device is the master BS1, the determination unit 11 causes the scanning unit 12 to perform scanning of received waves from other base station devices, and the received waves (RSSI) that can be scanned. If there is no received wave equal to or greater than the threshold value TR, the device itself may be determined to be the master BS. In this case, it is not necessary to set information indicating that the own apparatus is the master BS for the master BS.

  As will be described later, when the synchronization timing is generated from the GPS signal, it may be determined whether or not the own apparatus is the master BS 1 based on the presence or absence of the GPS signal.

  If it is not determined in step S1 that the own device is the master BS1, that is, if it is determined that the own device is a slave BS, the scanning unit 12 scans the received waves, and each of the plurality of received waves is scanned. A measurement result (RSSI, timing) is obtained (step S3).

  Then, the selection unit 14 selects a source received wave used for synchronization between base stations from a plurality of received waves (step S4). Hereinafter, this selection logic will be described in detail. Note that here, as a result of the scanning performed by the slave BS-C in FIG. 1, the received waves from the two base stations of the slave BS-A and the slave BS-B can be received, and the measurement results are obtained. Suppose you are.

Here, the signal strength (RSSI) of the received wave from the slave BS-A is “A”, and the signal strength (RSSI) of the received wave from the slave BS-B is “B”. Further, the timing of the preamble in the received wave from the slave BS-A is “t _A ”, and the timing of the preamble in the received wave from the slave BS-B is “t _B ”.

In the selection logic of step S4, first, the RSSI of the received wave (preamble) is compared (S4-1). Here, it is determined whether or not the absolute value of AB (received wave intensity difference) is larger than the threshold value Th, that is, whether or not there is a sufficient difference between the intensity of the two received waves.
If the absolute value of the received wave intensity difference is larger than the threshold Th, it is assumed that the larger received wave of A and B is transmitted from the base station located closer to the source received wave. Select (steps S4-2 to S4-4). That is, if A is larger, the received wave from slave BS-A is selected as the source received wave (step S4-3), and if B is larger, the received wave from slave BS-B is the source received wave. (Step S4-4).

If the absolute value of the received wave intensity difference is smaller than the threshold Th in step S4-1, that is, if there is not much difference between the intensity of the two received waves, the preamble timings t _A and t _B are used instead of RSSI. Use to select the source received wave.
Specifically, t _A and t _B are compared, and the received wave with the earlier timing is selected as the source received wave (steps S4-5 to S4-7). That is, if t _A is earlier, the received wave from slave BS-A is selected as the source received wave (step S4-6), and if t _B is earlier, the received wave from slave BS-B is the source received wave. (Step S4-7).
Then, the timing t _A or t _{B of} the selected source reception wave is used as the synchronization timing. This achieves synchronization between base stations with the source BS.

  In the selection logic of FIG. 6, the case where there are two received waves has been described. However, even when there are three or more received waves, the source BS can be selected by the same process. That is, basically, the RSSI having the largest RSSI among the RSSIs of three or more received waves may be selected as the source received wave. Also, when the received wave intensity difference between the received wave (first received wave) having the strongest RSSI (received intensity) and the received wave having the RSSI from the second to the second and subsequent is smaller than the threshold Th, the RSSI Regardless, the received wave having the earliest timing among the received waves may be selected as the source received wave.

  Here, from the viewpoint of setting the base station close to the own device as the source base station, the selection logic of step S4 is configured from step S4-2, step S4-3, and step S4-4, Steps may be omitted. That is, the source BS (source received wave) may be selected using only RSSI (first modification).

Differences between the selection logic (step S4) in FIG. 6 and the selection logic according to the first modification will be described. As shown in FIG. 8A, when the received wave from the slave BS-A has a larger RSSI (A> B) and the timing t _A is earlier than the received wave from the slave BS-B. In both the selection logic of FIG. 6 and the selection logic according to the first modification, the received wave from the slave BS-A is selected as the source received wave.

On the other hand, as shown in FIGS. 8B and 8C, the received wave from the slave BS-A is larger in RSSI than the received wave from the slave BS-B, but the timing is t _B. In the early case, the selection logic of FIG. 6 and the selection logic according to the first modification may have different received waves selected as source received waves.

  That is, in the selection logic according to the first modification, only the RSSI is considered, and therefore, the received wave from the slave BS-A is selected as the source received wave in both cases of FIGS.

On the other hand, in the selection logic of FIG. 6, as shown in FIG. 8B, when the difference Diff between the received wave strengths (RSSI) A and B is smaller than the threshold value Th, even if the RSSI is small, The reception wave from the slave BS-B with the earlier timing is selected as the source reception wave.
As shown in FIG. 8C, when the difference Diff between the received wave strengths (RSSI) A and B is larger than the threshold Th, the received wave from the slave BS-A having a large RSSI is the source received wave. Selected as.

  When the slave BS-A is closer and the slave BS-B is farther as viewed from the own apparatus, generally, the relationship between RSSI and timing is as shown in FIG. This is because if the distance is short, the received power is large and the propagation delay is small, so that the timing is advanced.

  However, as shown in FIGS. 8B and 8C, there is a case where the timing is delayed when the distance is close and the RSSI is large (slave BS-A). As shown in FIG. 9, this is a source BS whose root is the master BS, and in a tree structure in which base stations that are the source BSs of the slave BSs are connected, the own device (slave BS) T1 is shown in FIG. Occurs when in position.

  That is, the slave BS-A is connected in a daisy chain such that the slave BS-B is the source BS, the slave BS-B is the slave BS-D is the source BS, and the slave BS-D is the master BS. In this case, synchronization timing shifts (delays) D1, D2, and D3 due to propagation delays occur in each node of the tree structure.

  In FIG. 9, the base station closest to the own device T1 is the slave BS-A. In this case, if the slave BS-A is the source BS, the delay D3 is added, so the timing error due to the delay increases. . In this case, if the reception strength from the slave BS-B is sufficient, it is advantageous to reduce the timing error by using the slave BS-B as the source BS.

  The case as shown in FIG. 9 corresponds to FIG. 8B, and in the case of FIG. 8B, the slave BS-B is used as the source BS to reduce the timing error due to the propagation delay. Can do. Thus, by considering not only RSSI but also timing, a more appropriate base station can be selected as the source BS.

  As a second modification of the selection logic (step S4) shown in FIG. 6, the selection logic of step S4 is composed of step S4-5, step S4-6, and step S4-7, and the other steps are performed. It may be omitted. That is, the source BS (source received wave) may be selected using only the timing. In this case, since a base station apparatus with a short distance and a small propagation delay is easily selected as the source BS, the timing error can be reduced. However, since the accuracy of the detected timing may be low when the received wave intensity is low, it is more preferable to use RSSI and timing together.

  Furthermore, as a third modification of the selection logic, when a received wave from the master BS is included in a plurality of received waves obtained by scanning, characteristics such as RSSI and timing are not considered. The master BS may always be the source BS. For example, when the own device (slave BS) T2 is in the position of FIG. 9, the closest base station device is the slave BS-D. However, if the own device (slave BS) T2 can detect the received wave from the master BS, the master BS preferentially becomes the source BS. As a result, the timing error due to propagation delay is reduced.

  Here, in order to distinguish whether the received wave is from the master BS or the slave BS, the preamble pattern transmitted from the master BS is different from the preamble pattern transmitted from the slave BS. Just keep it.

  That is, when the base station apparatus determines that the own apparatus is a master BS by the determination unit 11, the base station apparatus uses a preamble pattern for the master BS. If it is determined that the own device is a slave BS, a preamble pattern for the slave BS is used. As a result, the slave BS that has received the preamble can detect whether or not the received wave includes the signal from the master BS.

FIG. 10 shows a fourth modification of the selection logic.
The selection logic of FIG. 10 is different from the selection logic of FIG. 6 in that weighting processing (step S3-1) is provided after RSSI collection (step S3).

The weighting process in step S3-1 is for weighting the RSSI and / or timing of the master BS so that the master BS is preferentially selected as the source BS.
For example, the RSSI of the received wave from the master BS is multiplied by a weight of α (α> 1) to increase the RSSI, and the master BS is easily selected as the source BS in step S4-2.
Also, the timing of the received wave from the master BS is multiplied by the weight of β (β <1), so that the timing is advanced, and the master BS is easily selected as the source BS in step S4-5.

  Note that the process for giving priority to the master BS is not limited to that in step S3-1. For example, a plurality of higher-order candidates are selected from a plurality of received waves by a selection logic as in step S4. If the master BS is included in the top candidates, the master BS is selected as the source BS, and if the master BS is not included, the first candidate is selected as the source BS. There may be.

  In addition, in order to distinguish whether the received wave is from the master BS or the slave BS, as described above, the preamble pattern transmitted from the master BS and the preamble transmitted from the slave BS are You only need to use different patterns.

Here, the weighting may be performed not only on the received wave from the master BS but also on the slave BS.
For example, as shown in FIG. 9, in a tree structure having a master BS as a root, a first-tier base station apparatus group having a master BS as a source BS is L1, and a base station apparatus belonging to the first hierarchy L1 is a source BS. Let L2 be a base station group in the second hierarchy, and let L3 be a base station group in the third hierarchy with a base station apparatus belonging to the second hierarchy L2 as a source BS.
At this time, by setting the priority of weighting as “master BS”> first hierarchy L1> second hierarchy L2> third hierarchy,..., Priority is given among slave BSs, and the hierarchy closer to the master BS is set. The base station apparatus to which it belongs is easily selected as the source BS.

  In order to distinguish which base station apparatus the received wave is transmitted from, the preamble pattern may be different for each layer. That is, a predetermined preamble pattern is assigned to the master BS and each layer, and the base station device itself recognizes the layer to which it belongs, selects a preamble pattern according to the layer, and transmits with the preamble pattern. Do. Here, the base station apparatus recognizes the hierarchy of the preamble pattern of the source received wave, and recognizes the next hierarchy as the hierarchy to which the base station belongs.

  FIG. 11 shows a modification of the base station apparatus. This base station device includes a GPS detection unit 16 and can detect the presence or absence of a GPS signal output from a GPS receiver. The GPS receiver 20 may be externally attached via a connector provided in the base station device, or may be built in the base station device. The points that are not described with respect to FIG. 11 are the same as those in FIG.

  FIG. 12 is a flowchart showing processing in the base station apparatus of FIG. In FIG. 12, when the GPS signal can be detected by the GPS detector 16 (step S11-1), the determination unit 11 determines that the own device is the master BS and generates synchronization timing from the GPS signal. (Step S11-2). When the GPS signal cannot be detected, the processing from step S1 is performed as in FIG.

As described above, when a GPS signal is obtained, a highly accurate timing can be obtained by using the GPS signal as a synchronization timing.
In addition, when the process of step S11-1, S11-2 is provided, you may abbreviate | omit providing the process of step S1, S2.

  13 to 16 show another example of the flow of processing for the base station apparatus to determine the synchronization timing (there may be the same as the previous example). Although FIG. 6 etc. mainly demonstrated the case where the two received waves which could be scanned were demonstrated, in FIGS. 13-16, it demonstrates with the flowchart when the number of received waves is not specifically limited. The points that are not particularly described with respect to FIGS. 13 to 16 are the same as in the previous example.

FIG. 13 shows a case where the source BS is selected based on the collected RSSI values alone.
First, when the power is turned on to the base station apparatus, first, the determination unit 11 determines whether or not the own apparatus is the master BS1 (step S101). When the own device is the master BS1, the source BS (source received wave) is not necessary, and therefore the synchronization timing is determined based on the clock signal (self-running mode) of the clock generator and the GPS signal of the own device (step S102) ).

  In step S101, when it is not determined that the own apparatus is the master BS1, that is, when it is determined that the own apparatus is the slave BS, the scanning unit 12 scans the received wave from the adjacent BS. And among the received waves (BS) detected by scanning, a list A (first BS list) of received waves whose RSSI value exceeds the RSSI threshold value TR is generated (step S103). The list includes information that identifies the preamble pattern of the detected received wave, an RSSI value, and timing as data. The generated list of received waves (BS) is stored in the memory (step S104).

Then, it is determined whether or not a received wave (BS) exists in the list A (step S105). The RSSI threshold value TR is provided for performing scanning again if the received wave intensity is not sufficient. If there is no received wave (BS) in the list A (exceeding the RSSI threshold value TR), the process returns to step S103 again to perform scanning.
Note that the RSSI threshold value TR may be zero.

  Subsequently, it is determined whether there are a plurality of received waves (BS) in the list A (step S106). If there is only one received wave (BS) in the list A (exceeding the RSSI threshold value TR), the detected received wave (BS) is set as the source received wave (source BS) (step S107).

If it is determined in step S106 that there are a plurality of received waves (BS) in the list A, it is subsequently determined whether the list A includes received waves from the free-running BS (master BS). (Step S108).
When the received wave from the free-running BS (master BS) is included in the list A, a weight is added to the RSSI and / or timing of the received wave from the free-running BS (master BS) (step S109). The weight increases RSSI and accelerates timing. The weight value may be zero. That is, step S109 may be omitted.

Then, the received wave (BS) having the largest RSSI value is selected from the received waves in the list A as the source received wave (source BS) (step S110).
Through the above processing, the detected received wave having the largest RSSI value can be selected. In addition, since the free-running BS (source BS) is weighted and preferentially selected, there is a high possibility that even if the actual RSSI value is somewhat small, it is selected as the source BS.

  FIG. 14 shows a case where the source BS is selected by the collected timing (timing offset) alone. In FIG. 14, steps S101 to S109 are the same as those in FIG. The same applies to FIGS.

In FIG. 14, after step S109, the received wave (BS) having the smallest timing offset is selected from the received waves in the list A as the source received wave (source BS) (step S111).
Through the above processing, the detected reception wave having the smallest timing offset can be selected. In addition, since the free-running BS (source BS) is weighted and preferentially selected, there is a high possibility that it is selected as the source BS even if the actual timing offset is somewhat large.

FIG. 15 shows a case where the source BS is selected based on the timing (timing offset) while using both the RSSI value and the timing (timing offset).
In FIG. 15, after step S109, the BS (received wave) with the smallest timing offset is determined from the received waves in list A (step S112).

  Then, the timing offset difference (absolute value) is obtained for the received wave (BS) having the smallest timing offset and each received wave (BS) in the list A. Then, among the received waves (BS) in the list A, a list B (second list) of received waves (BS) whose timing offset difference (absolute value) is less than the threshold Tht is created (step S113). . This list B is stored in the memory. The threshold Tht may be zero.

Further, the determination unit 11 acquires the RSSI (and timing) of the received wave in the list B from the list B of the memory (step S114). Then, the received wave (BS) having the largest RSSI value is determined from the list B, and the received wave is selected as the source received wave (source BS) (step S115).
Through the above processing, the received wave having the maximum RSSI is selected from the received waves having a relatively small timing offset.

FIG. 16 shows a case where the source BS is selected based on the RSSI value while using both the RSSI value and the timing (timing offset).
In FIG. 16, after step S109, the BS (received wave) having the largest RSSI value is determined from the received waves in list A (step S116).

  Then, the difference (absolute value) between the RSSI values is obtained for the received wave (BS) having the largest RSSI value and each received wave (BS) in the list A. Then, among the received waves (BS) in the list A, a list B (second list) of received waves (BS) whose RSSI difference (absolute value) is less than the threshold Thr is created (step S117). This list B is stored in the memory. Note that the threshold Thr may be zero.

Further, the determination unit 11 acquires the timing offset (and RSSI) of the received wave in the list B from the list B of the memory (step S118). Then, the received wave (BS) having the smallest timing offset is determined from the list B, and the received wave is selected as the source received wave (source BS) (step S119).
Through the above processing, a received wave having the smallest timing offset is selected from received waves having a relatively large RSSI value.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is an overall view of a wireless communication system. It is a frame block diagram in WiMAX. It is a figure which shows the area for every base station apparatus, and the mobile terminal contained in the area. It is a timing chart which shows a mode that the synchronization is taken between two base station apparatuses. It is a functional block diagram of a base station apparatus. It is a flowchart for selecting a source BS. It is explanatory drawing for detecting the timing of a preamble. It is explanatory drawing of the received waves A and B. FIG. It is a hierarchical diagram of a base station apparatus. It is a modification of the process of FIG. It is a functional block diagram of the base station apparatus which concerns on a modification. 12 is a process flowchart in the base station apparatus shown in FIG. 11. It is a flowchart which shows the other example of a process. It is a flowchart which shows the other example of a process. It is a flowchart which shows the other example of a process. It is a flowchart which shows the other example of a process.

Explanation of symbols

  1: Master base station device, 1a, 1b, 1c: Slave base station device, 11: Determination unit, 12: Scanning unit, 13: Collection unit, 14: Selection unit, 15: Setting information storage unit, 16: GPS detection unit , 20: GPS receiver

Claims (11)

A base station device capable of performing synchronization between base stations using radio reception waves from other base station devices,
A scanning unit that scans received waves from other base station devices;
A selection unit that selects a source received wave used for synchronization between base stations from a plurality of received waves obtained by scanning;
With
A base station apparatus that performs inter-base station synchronization using a source received wave selected by the selection unit.   The selection unit receives the source received wave based on a received wave characteristic of each of a plurality of received waves obtained by scanning and indicating that the received wave characteristic is transmitted from a base station apparatus close to the own apparatus. The base station apparatus according to claim 1 to be selected.   The base station apparatus according to claim 2, wherein the selection unit selects the source received wave based on a received wave intensity of each of a plurality of received waves obtained by scanning.   The base station apparatus according to any one of claims 1 to 3, wherein the selection unit selects the source received wave based on timings of a plurality of received waves obtained by scanning. The selection unit includes:
Among the plurality of received waves obtained by scanning, when the received wave intensity difference between the first received wave having the highest received wave intensity and the other received waves is smaller than the threshold,
5. The received wave having the earliest received wave timing is selected as the source received wave from the first received wave and the received wave having a received wave intensity difference smaller than the threshold value. The base station apparatus as described in.   When the selection unit includes a reception wave from a master base station device that does not require a reception wave from another base station for synchronization between base stations in the plurality of reception waves obtained by scanning The base station apparatus according to claim 1, wherein a received wave from the master base station apparatus is selected as the source received wave. The selection unit includes:
In addition to the received wave characteristic indicating that the signal is transmitted from a base station device close to its own device,
The source received wave is selected in consideration of whether or not the received wave is a received wave from a master base station apparatus that does not require a received wave from another base station for synchronization between base stations. Item 5. The base station apparatus according to any one of Items 2 to 4. The own device is a slave base station device that requires a received wave from another base station for synchronization between base stations, or does not require a received wave from another base station for synchronization between base stations A determination unit that determines whether the master base station device is provided,
The base station synchronization according to any one of claims 1 to 7, wherein, when the determination unit determines that the own device is a slave base station device, synchronization between base stations is performed using a received wave from another base station device. Base station device.   The determination unit refers to setting information stored in a storage unit included in the own device, and when the setting information indicating that the own device is a master base station device exists in the storage unit, The base station apparatus according to claim 8, wherein the base station apparatus is determined to be a master base station.   The base station according to claim 8 or 9, wherein the determination unit determines that the own device is a master base station when there is no received wave that can be scanned as a result of scanning a received wave from another base station device. apparatus. A GPS detector for detecting the presence or absence of a GPS signal output from the GPS receiver;
The said determination part is a base station apparatus of any one of Claims 8-10 which determines that an own apparatus is a master base station, if it detects that there exists a GPS signal.

Images