JP2003324412A - Radio access system, and radio equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio access system and a radio equipment in which transmission timings are easily synchronized between radio nodes. <P>SOLUTION: In the TDD radio access system wherein a network is composed of the plurality of radio nodes, two of the plurality of radio nodes are respectively connected by a wireless link. Between the two radio nodes, a radio node for producing a transmission timing to be a reference is defined as a high-order radio nodes, and a radio node to reproduce its own transmission timing based upon the transmission timing of the high-order radio node is defined as a low- order radio node. A propagation delay quantity on the wireless link is measured, and the transmission timing of the low-order radio node is corrected based upon the measured result and synchronized with the transmission timing of the high-order radio node. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio access system for providing a user with a high-speed and large-capacity line by utilizing radio, and in particular to a TDD (establishing synchronization of transmission timing between radio nodes). Time Divisio
n Duplex) and other wireless access systems and wireless devices.

[0002]

2. Description of the Related Art As the next-generation ultra-high-speed information communication infrastructure is being developed, high-speed lines using microwave radio are provided to subscribers for the purpose of complementary use of optical fiber networks and inter-island communication. Subscriber wireless access system (FWA: Fixed)
Wireless Access: The demand for wireless access systems) is growing. Conventionally, as this wireless access system, PP (Po
int-Point) method and general housing and small office (SOH
O: P for small office home office)
MP (Point-Multi Point) method is considered,
It is considered that a mesh-type TDD wireless access system that is high-speed, large-capacity and highly efficient will be put to practical use in the future by arranging wireless nodes in a mesh shape and autonomously setting the line capacity and the route.

Here, an outline of the configuration of the mesh type TDD radio access system will be described with reference to FIG.
FIG. 10 is a diagram showing an example of a schematic configuration of a mesh type TDD wireless access system. As shown in FIG.
A plurality of wireless nodes 1 arranged in a mesh are connected by a wireless link 2. The wireless node transmits and receives information to and from other wireless nodes, and also operates according to the network information of the mesh type TDD wireless access system. If the wireless node is a terminal station, information is exchanged with the user via the user terminal provided in the wireless node. Further, the wireless node has a relay function, and relays between wireless nodes to which a wireless link is not directly connected, if necessary. The wireless node performs wireless transmission with one or a plurality of other wireless nodes connected by a wireless link. Also, the wireless node forms a mesh type network by relaying. FIG. 10 shows an example in which one wireless node performs wireless transmission with one to four wireless nodes.

Between wireless nodes connected by a wireless link, it is necessary to adjust transmission timing for realizing wireless transmission by TDD and establish synchronization. Since one wireless node is linked to each of a plurality of wireless nodes, when a mesh type TDD wireless access system is constructed, it is also configured to avoid unnecessary interference and improve frequency utilization efficiency. It may be desirable to establish synchronization of transmission timings for all wireless nodes.

Here, a technique for establishing synchronization of transmission timings between wireless nodes will be described using the P-MP method as an example. FIG. 11 is a diagram showing an example of a schematic configuration of the P-MP method. As shown in FIG. 11, this PM
The P system is composed of a base station 11 which is an upper station and a plurality of subscriber stations 13 which are lower stations, and the base station 11 and the plurality of subscriber stations 13 are connected by a wireless link 12.

As a first example of a technique for establishing synchronization of transmission timings between wireless nodes, Japanese Patent Laid-Open No. 11-1643
There is a "transmission timing adjustment method in a wireless communication system" disclosed in Japanese Patent No. 53. This is a technique in which when a new subscriber station is installed in the P-MP system shown in FIG. 11, the transmission timing to the base station is set in advance to the subscriber station. In this technology, if there is no response from the base station that tried to communicate, the subscriber station determines that the transmission timing setting value needs to be changed, and the base station performs an operation to change the setting value stored in the transmission timing setting memory. Is repeated until a response from is obtained.

As a second example of a technique for establishing synchronization of transmission timings between wireless nodes, Japanese Patent Laid-Open No. 2001-2001
There is a "radio access system" disclosed in Japanese Patent No. 169345. This is a technique in which when a new subscriber station is installed in the P-MP system shown in FIG. 11, the transmission timing with respect to the propagation delay amount due to the distance from the base station is set on the subscriber station side. This technique measures the timing deviation by transmitting and receiving a specific signal between the base station and the subscriber station, and corrects the timing deviation on the subscriber station side.

Further, in the mesh type TDD radio access system shown in FIG. 10, even if the transmission timings in the respective directions within the radio node are not synchronized, if the transmission timings are matched for the respective radio links, communication is not possible. Since this is possible, it is possible to construct a wireless access system in which the transmission timing between wireless nodes is asynchronous.

[0009]

However, in the first example, even if the setting value calculated on the desk is applied to the subscriber station,
It is unlikely that synchronization with the base station can be established.
Therefore, it is necessary to make fine adjustments while actually monitoring the communication state in the field, and it is difficult to set the transmission timing in the subscriber station.

On the other hand, in the mesh type TDD radio access system, the transmission timing received from the upper radio node is reproduced as the transmission timing of its own node and passed to the lower radio node, and some radio nodes are damaged due to a disaster or the like. It is assumed that the transmission timing is exchanged between the wireless nodes different from the former one when the wireless communication is disabled or returned. In this case, it is difficult to apply the second example to the mesh type TDD radio access system because each radio node is required to have a configuration for managing and controlling the transmission timing.

Further, in the mesh type TDD radio access system in which the transmission timings between radio nodes are asynchronous, when one radio node uses the same frequency for links in a plurality of directions, or one radio node has adjacent frequencies. When using, there is a possibility that interference or the like may occur unless the transmission timing is correct. Therefore, there is a problem that the frequency utilization efficiency of the mesh type network becomes low.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a radio access system and a radio which can easily establish synchronization of transmission timing between radio nodes.

[0013]

In order to achieve the above-mentioned object, the present invention is a radio access system for constructing a network with a plurality of radios, wherein each of the plurality of radios has two radios. Of the two radios, which is connected by a radio link, the radio that generates the reference transmission timing is the upper radio, and the transmission timing of its own is determined based on the transmission timing of the upper radio. The reproduction wireless device is a lower wireless device, the propagation delay amount in the wireless link is measured, the transmission timing of the lower wireless device is corrected based on the result of the measurement, and the transmission timing of the upper wireless device. It is characterized by establishing synchronization with.

According to this structure, the lower radios correct their own transmission timings according to the value notified from the upper radios, so that the synchronization with the upper radios can be easily established. You can

Further, in the radio access system according to the present invention, the upper radio transmits the first radio signal including a synchronization pattern to the lower radio and receives the first radio signal. The lower wireless device transmits a second wireless signal including a synchronization pattern to the upper wireless device, and the upper wireless device that has received the second wireless signal is based on the second wireless signal. The propagation delay amount in the wireless link is measured, a correction signal based on the result of the measurement is transmitted to the lower wireless device, and the lower wireless device that receives the correction signal transmits based on the correction signal. It is characterized in that the timing is corrected and synchronization with the transmission timing of the upper radio is established.

With such a configuration, the lower radios correct their own transmission timings according to the value notified from the upper radios, so that the synchronization with the upper radios can be easily established. You can

Further, in the radio access system according to the present invention, the subordinate radio shifts its own transmission timing by a half symbol before a symbol clock for sampling the received transmission timing. It is a thing.

With such a configuration, the jitter can be evenly distributed to the timings before and after the transmission timing of the highest-level radio, and the influence of the jitter generated by the reproduction of the transmission timing can be reduced. be able to.

Further, in the radio access system according to the present invention, a guard time for absorbing a propagation delay amount is provided after the radio signal, and the lower radio sets, when the propagation delay amount exceeds the guard time, The second wireless signal is shortened by a predetermined length.

According to such a configuration, even when the propagation delay amount in the wireless link is larger than the guard time, it is possible to avoid the overlap of the transmission section and the reception section in the upper radio.

In the radio access system according to the present invention, when the subordinate radio is connected to another radio by another radio link, the subordinate radio is used to establish synchronization in the another radio link. The wireless device operates as the upper wireless device, and the other wireless device operates as the lower wireless device.

According to this structure, the mesh type network is realized by repeatedly establishing the synchronization between the wireless device having the transmission timing synchronization established and the wireless device having the transmission timing synchronization not established. It is possible to establish synchronization of transmission timings of all wireless nodes configured in the above.

Further, according to the present invention, in a radio connected to a network composed of radio links of two radios, among the two radios connected by the radio link in the previous term,
A high-order radio that generates a reference transmission timing, or a radio that operates as a low-order radio that reproduces its own transmission timing according to the transmission timing of the high-order radio, In some cases, in establishing transmission timing synchronization with the lower radio,
A first radio signal including a synchronization pattern is transmitted to the lower radio, the propagation delay amount by the radio link is measured based on the radio signal received from the lower radio, and the propagation delay is measured. When the correction signal is transmitted to the lower radio and the lower radio is established, the first signal is transmitted when the transmission timing is synchronized with the upper radio.
Is received, a second wireless signal including a synchronization pattern is transmitted to the upper radio, and the transmission timing of its own is corrected according to the correction signal received from the upper radio. It is what

With such a configuration, the lower radios correct their own transmission timings according to the value notified from the upper radios, so that it is easy to establish synchronization with the upper radios. You can

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment,
As an example of the wireless access system, the mesh type TDD wireless access system shown in FIG. 10 will be described. FIG. 1 is a block diagram showing an example of the configuration of a TDD radio access system according to an embodiment of the present invention. As shown in FIG. 1, wireless nodes 1 arranged in a mesh shape
00 to 400 are connected by a wireless link 500 and form a mesh type network.

Each of the wireless nodes 100 to 400 is provided with a directional antenna facing each other connected wireless node in each direction. When establishing transmission timing synchronization between wireless nodes in the TDD wireless access system shown in FIG. 1, since transmission timings are exchanged between the wireless nodes, a relationship between an upper wireless node and a lower wireless node occurs. Here, the upper wireless node is
There is a relationship that the transmission timing generated or reproduced by the own node is used, and the lower wireless node uses the transmission timing matched with the transmission timing of the upper wireless node. In FIG. 1, “upper” in the wireless nodes represents a higher wireless node, and “lower” in the wireless nodes represents a lower wireless node. The lower wireless node synchronizes the transmission timing, reproduces the transmission timing in its own node, and then establishes the synchronization of the transmission timing with the lower wireless node as the upper wireless node in another link. By performing such synchronization establishment processing for each wireless node, it is possible to establish synchronization of transmission timings over all the wireless nodes of the mesh type TDD wireless access system.

Next, the configuration of the wireless node in the TDD wireless access system according to the embodiment of the present invention will be described with reference to FIG. The wireless device in this embodiment is a wireless node. Here, for the sake of explanation, the wireless node 100 and the wireless node 200 shown in FIG.
Will be described as an example. FIG. 2 is a block diagram showing an example of the configuration of the wireless node according to the embodiment of the present invention.
As shown in FIG. 2, the wireless node 100 includes a directional antenna 101, a transmission / reception switching unit 102, and a reception RF (Radio Fr).
equency) unit 103 and a reception IF (Intermediate Frequent)
ncy) section 104, reception BB (Base Band) section 105,
Clock unit 106, control unit 107, and user terminal 1
08, a transmission BB unit 109, a transmission IF unit 110, and a transmission RF unit 111. The wireless node 100 and the wireless node 200 have equivalent functions and facilities, and perform wireless transmission using the directional antennas 101 and 201, respectively.

Next, the operation of the wireless node in the mesh type TDD wireless access system according to the embodiment of the present invention will be described with reference to FIG. First, the wireless node 2
The radio signal transmitted from the directional antenna 201 in the wireless communication node 00 in
1 is received, and the transmission / reception switching unit 102 receives the reception RF unit 1
It is output to 03. The wireless signal is received by the receiving RF unit 103.
The signal is converted into an F signal, converted into a baseband signal in the reception IF unit 104, data demodulated in the reception BB unit 105, and output to the control unit 107 as reception data.

The clock section 106 supplies a clock to each section and reproduces the transmission timing. Specifically, the clock unit 106 always reproduces the transmission timing based on the received signal, and the reproduced transmission timing can be used in the wireless node 100.

The control unit 107 controls processing of transmitted / received data and operation adapted to the network information of the mesh type TDD radio access system. Specifically, the control unit 107 reads the destination information included in the received data and outputs a signal to the user terminal 108 when the destination information is the information addressed to the own node,
If the information is addressed to another wireless node, control is performed to output a signal to the transmission BB unit 109 as a relay station. Further, the control unit 107 receives the transmission data from the user terminal 108 and outputs it to the transmission BB unit 109.

When the own node is an upper wireless node, the control unit 107 generates a synchronization signal as a wireless signal for synchronizing with the lower wireless node in the process of establishing the synchronization of the transmission timing between the wireless nodes. Then, an instruction to transmit the generated synchronization signal to the lower wireless node is issued. After that, the propagation delay amount by the wireless link is measured from the response signal received from the lower wireless node, and an instruction to send the correction signal based on the measured propagation delay amount to the lower wireless node is issued. On the other hand, when the own node is a lower wireless node, the control unit 107 receives the synchronization signal from the upper wireless node and measures the propagation delay amount in the process of establishing synchronization of the transmission timing between the wireless nodes. A response signal is generated as a wireless signal, and an instruction to transmit the generated response signal to the upper wireless node is issued. After that, the transmission timing of the own node is corrected according to the correction signal received from the upper wireless node. Note that the first wireless signal in this embodiment is a synchronization signal and the second wireless signal is a response signal.

The transmission data is modulated in the transmission BB unit 109 and converted into a baseband signal, and the transmission IF unit 1
10, an RF signal is converted into an IF signal, a transmission RF unit 111 converts it into an RF signal, and the transmission / reception switching unit 102 outputs it to the directional antenna 101, and the directional antenna 1 as a radio signal.
Sent from 01. The above is the operation of the wireless node.

Next, a frame format of a radio signal transmitted / received in the TDD radio access system according to the embodiment of the present invention will be described with reference to FIG. The upper part of FIG. 3 shows the frame format, and the lower part of FIG. 3 shows the transmission / reception timing. One frame is composed of a radio signal and a guard time (GT). The radio signal is composed of a control signal and data. The control signal includes a synchronization pattern necessary for establishing frame synchronization, and is located before the data. In order to absorb the delay due to the propagation distance,
A guard time is set after the radio signal. If the signal indicating the transmission / reception timing is Hi, it indicates the transmission section, and the rising edge indicates the transmission timing. If the signal indicating the transmission / reception timing is Low, it indicates the reception section, and the falling edge indicates the reception timing.

Next, a process of establishing synchronization of transmission timing between wireless nodes will be described with reference to FIGS. 4 and 5. FIG. 4 is a sequence showing an example of a process of establishing synchronization of transmission timing between wireless nodes. FIG. 5 is a time chart showing an example of transmission timing synchronization establishment processing between wireless nodes. In each step of FIG. 5, the upper part represents the wireless signal transmitted / received by the wireless node, and the lower part represents the transmission / reception timing of the wireless node. Further, of the wireless signals, Tx represents a transmission signal and Rx represents a reception signal.

When the transmission timing synchronization is established between the wireless nodes for which the transmission timing synchronization has not been established, the azimuth adjustment of the directional antenna is performed between the two wireless nodes, and then the upper radio node is set to the lower radio node. The transmission timing synchronization establishment process is executed for the node. Here, regarding the relationship between the upper and lower layers, for example, the one installed first is the upper wireless node. First, the upper wireless node transmits a synchronization signal to the lower wireless node (S1). Here, assuming that there is no propagation delay between both stations, the upper radio node transmits the synchronization signal to the lower radio node and then the lower radio node, as shown in step 1 of FIG. The timing of the synchronization pattern included in the response signal can be estimated. The timing estimated here is defined as a synchronization pattern detection estimation timing a.

On the other hand, the lower wireless node reproduces the transmission timing from the received synchronization signal, but since it does not correct the propagation delay amount, it deviates from the upper wireless node transmission timing. As for the transmission timing here, as shown in step 1 of FIG. 5, the beginning of Tx is treated as the transmission timing. The lower wireless nodes are
The response signal including the synchronization pattern is transmitted to the upper wireless node at the reproduced transmission timing (S2).

Next, as shown in step 2 of FIG. 5, the upper wireless node obtains the synchronization pattern detection timing b from the synchronization pattern included in the received response signal, and based on the difference from the synchronization pattern detection estimated timing a. Propagation delay amount Δ = (b−a) / 2 of the one-way propagation path in the wireless link is calculated. Here, first, the upper wireless node measures (b
-A) is the propagation delay amount of the round-trip propagation path, and the propagation delay amount of the one-way propagation path is calculated as Δ = (ba) / 2, which is half the value. If the propagation delay amount (ba) of the round-trip propagation path becomes a value that cannot be divided, it may be rounded up or rounded down. The upper wireless node transmits the propagation delay amount Δ as a correction signal to the lower wireless node so as to correct the transmission timing of the lower wireless node (S3).

On the other hand, the lower radio node corrects the transmission timing by the propagation delay amount Δ in advance according to the received correction signal, as shown in step 3 of FIG. As a result, the lower wireless node can establish synchronization with the upper wireless node. As shown in FIG. 4, after the propagation delay amount is corrected, a process of shifting the transmission timing by half a symbol is performed. This process will be described in a countermeasure against jitter described later. The lower wireless node, which has established the synchronization of the transmission timing with the upper wireless node, communicates with other wireless nodes using this transmission timing. The lower-level wireless node is connected to the upper-level wireless node by a wireless link, but the transmission timing synchronization is established as the upper-level wireless node with respect to other wireless nodes for which transmission timing synchronization has not been established at this point. Perform processing. By repeatedly performing such processing between a wireless node for which transmission timing synchronization has been established and a wireless node for which transmission timing synchronization has not been established, transmission of all wireless nodes configured in the mesh network is performed. It becomes possible to establish timing synchronization.

Since the guard time shown in the frame format of FIG. 3 corresponds to the maximum delay amount that can be tolerated in the round-trip propagation path, if the propagation delay amount (ba) of the round-trip propagation path is not less than the guard time, the transmission timing is changed. No synchronization is established. If the propagation delay amount (ba) of the round trip propagation path is smaller than the guard time, the transmission timing synchronization can be established using the frame format of FIG. If a) is longer than the guard time, the transmission section and the reception section of the upper wireless node will overlap and communication failure will occur.

Here, the propagation delay amount (b-
A process for establishing synchronization of transmission timing when a) is longer than the guard time will be described with reference to FIG. Step 1 in FIG. 6 is the same as step 1 in FIG. 5, except that in step 2 in FIG. 6, the propagation delay amount (ba) of the round-trip propagation path is larger than the guard time. When the propagation delay amount (ba) of the round-trip propagation path is equal to or longer than the guard time, it is assumed that the reception section in the upper wireless node overlaps with the transmission section as shown in step 2 of FIG. Occurs.

In order to avoid this obstacle, the propagation delay amount (ba) of the round-trip propagation path in the measurement of the propagation delay amount before that.
If is longer than the guard time, it is effective to shorten the data portion of the response signal transmitted by the lower wireless node by the guard time or more to establish the synchronization of the transmission timing. As shown in step 2 ′ of FIG. 6, by shortening the response signal in the lower wireless node, it is possible to avoid the overlapping of the reception section and the transmission section in the upper wireless node.

Further, in order to avoid this obstacle, in the measurement of the propagation delay amount before that, the propagation delay amount (b
If -a) exceeds the guard time, it is effective to use only the control signal as the response signal transmitted by the lower radio node to establish the synchronization of the transmission timing. The transmission timing synchronization establishment processing in this case will be described with reference to FIG. Step 1 in FIG. 7 is the same as step 1 in FIG. In FIG. 7, as shown in step 2 of FIG. 7, the response signal transmitted by the lower wireless node is only the control signal including the synchronization pattern. As a result, as in the case described with reference to FIG. 6, it is possible to avoid duplication of the reception section and the transmission section in the upper radio node, and the lower radio node, as shown in step 3 of FIG. Accordingly, the transmission timing is corrected in advance by the propagation delay amount Δ. As described above, according to the procedure shown in FIGS. 6 and 7, it is possible to perform the transmission timing synchronization establishment process even when the propagation delay amount (ba) of the round-trip propagation path is larger than the guard time.

Next, countermeasures against jitter occurring in the mesh type TDD radio access system will be described. When establishing synchronization of transmission timing, the subordinate wireless node uses the symbol clock of its own node as the source oscillation in order to generate a stable signal with low noise. Therefore, even if transmission timing is adjusted, Jitter within 1 symbol occurs.

FIG. 8 is a diagram showing an example of jitter generated by reproduction of transmission timing in the mesh type TDD radio access system. Hereinafter, for the sake of explanation, the wireless nodes A, B,
Radio node C and radio node D. First, the upper wireless node A passes the transmission timing of its own node to the lower wireless node B. The wireless node B uses the symbol clock of its own node as a source oscillation and reproduces the transmission timing of its own node according to the transmission timing received from the wireless node A.

Here, since the transmission timing in the wireless node B is sampled at the rising edge of the symbol clock, a shift as shown in FIG. 8 occurs with respect to the received transmission timing. This deviation is not fixed, and jitter that is delayed by a maximum of one symbol from the correct transmission timing is generated every time the transmission timing is reproduced by each wireless node. When the transmission timing of the wireless node B is passed to a lower wireless node C and the wireless node C uses the symbol clock of its own node as the source oscillation and reproduces the transmission timing according to the transmission timing received from the wireless node B, a maximum delay of 1 symbol is further delayed. Jitter will occur. As a result, the transmission timing received by the wireless node D has a maximum delay of 2 symbols from the correct transmission timing. Due to the method of reproducing the transmission timing, this jitter increases from the transmission timing of the highest wireless node in the delay direction.

In the mesh type TDD radio access system, establishing the synchronization of the transmission timing means that the reproduced transmission timing is used as the transmission timing of the upper radio node to establish the synchronization with the next lower radio node. Therefore, it is unavoidable that the jitter increases as the number of hops increases.

Therefore, in order to minimize this jitter, in the synchronization establishment process, the transmission timing of the lower radio node is shifted by a half symbol before the symbol clock, so that the transmission timing of the highest radio node is shifted. It becomes possible to evenly distribute the jitter to the front and rear timings with respect to. Hereinafter, a detailed description will be given with reference to FIG. FIG. 9 is a diagram showing an example of jitter generated by reproduction of transmission timing when a countermeasure against jitter is taken in the mesh type TDD radio access system. First, the upper wireless node A passes the transmission timing of its own node to the lower wireless node B. The wireless node B reproduces the transmission timing according to the transmission timing received from the wireless node A.

Here, the radio node B uses the symbol clock of its own node as the source oscillation and reproduces the transmission timing in accordance with the transmission timing received from the radio node A. At this time, the transmission timing is further shifted by half a symbol. . The transmission timing is a case where the rising edge of the symbol clock in the wireless node B coincides with the received transmission timing, and is shifted by half a symbol before the reproduced transmission timing. Actually, since the rising edge of the symbol clock in the wireless node B does not coincide with the received transmission timing, as shown in the transmission timing, the transmission timing reproduced by the wireless node B has a maximum of 1 before and after the received transmission timing. Jitter with the width of the symbol occurs.

The wireless node B passes the transmission timing to the lower wireless node C. The wireless node C uses the symbol clocks of the wireless node B and its own node as the source oscillation, reproduces the transmission timing according to the transmission timing received from the wireless node B, and similarly shifts the transmission timing by half a symbol. The same operation is performed in the lower wireless node D. When this method is used to increase the number of hops, as shown in FIG. 9, the jitter is distributed to the front and back around the transmission timing of the highest-level wireless node, compared to the case where this method is not used. As a result, the magnitude of jitter is reduced to about 1/2, so that the number of hops can be increased and a larger mesh network can be constructed.

In FIG. 4, the process of shifting the transmission timing by a half symbol is performed after the correction of the propagation delay amount as an example, but the position of this process is not limited to after the correction of the propagation delay amount. . Further, the clock unit 106 in the wireless node constantly performs a process of shifting the transmission timing by half a symbol before in the operation of reproducing the transmission timing of the own node from the received transmission timing.

As described above, according to the mesh type TDD radio access system according to the embodiment of the present invention, when the transmission timing synchronization is established from the upper radio node to the lower radio node, the notification is given from the upper radio node. Since the lower wireless node corrects the transmission timing of its own node according to the value thus set, it is possible to easily establish synchronization with the upper wireless node. Further, when the lower wireless node regenerates the transmission timing, the transmission timing is further shifted by a half symbol before, so that it is possible to reduce the influence of the jitter generated by the reproduction of the transmission timing.

[0052]

As described in detail above, according to the present invention,
For example, it is possible to easily establish transmission timing synchronization between wireless nodes installed in a mesh shape, and to construct a high-speed, large-capacity, highly efficient mesh-type wireless access system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a configuration of a TDD wireless access system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a configuration of a wireless node according to an embodiment of the present invention.

FIG. 3 is a diagram showing an example of a configuration of a frame format of a radio signal transmitted and received in the TDD radio access system according to the embodiment of the present invention.

FIG. 4 is a sequence showing an example of synchronization establishment processing of transmission timing between wireless nodes.

FIG. 5 is a time chart showing an example of transmission timing synchronization establishment processing between wireless nodes.

FIG. 6 is a time chart showing an example of transmission timing synchronization establishment processing between wireless nodes when the propagation delay amount is larger than the guard time amount.

FIG. 7 is a time chart showing another example of transmission timing synchronization establishment processing between wireless nodes when the propagation delay amount is larger than the guard time amount.

FIG. 8 is a diagram showing an example of jitter generated by reproduction of transmission timing in a mesh type TDD wireless access system.

FIG. 9 is a diagram showing an example of jitter generated by reproduction of transmission timing when a countermeasure against jitter is taken in the mesh type TDD radio access system.

FIG. 10 is a diagram showing an example of a schematic configuration of a mesh type TDD wireless access system.

FIG. 11 is a diagram showing an example of a schematic configuration of a P-MP system.

[Explanation of symbols]

100, 200, 300, 400 wireless node, 500
Wireless link, 101, 201 directional antenna, 10
2 transmission / reception switching unit, 103 reception RF unit, 104 reception IF
Section, 105 reception BB section, 106 clock section, 107
Control unit, 108 user terminal, 109 transmission BB
Section, 110 transmission IF section, 111 transmission RF section.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor ▲ Taka ▼ Tsutomu Hashi             3-14-20 Higashi-Nakano, Nakano-ku, Tokyo Stocks             Hitachi Kokusai Electric Co., Ltd. (72) Inventor Satoshi Konishi             2-15-1 Ohara, Kamifukuoka City, Saitama Stock             Company CAD Research Institute (72) Inventor Shinobu Namba             2-15-1 Ohara, Kamifukuoka City, Saitama Stock             Company CAD Research Institute (72) Inventor Shinichi Nomoto             2-15-1 Ohara, Kamifukuoka City, Saitama Stock             Company CAD Research Institute F term (reference) 5K047 AA03 BB01 HH42 JJ08 MM38

Claims (6)

[Claims] 1. In a wireless access system for constructing a network with a plurality of wireless devices, two wireless devices of each of the plurality of wireless devices are connected by a wireless link, and a standard of the two wireless devices is used. A radio device that generates a transmission timing to be the upper radio device, a radio device that reproduces the transmission timing of the own device based on the transmission timing of the higher radio device is a lower radio device, and a propagation delay in the radio link A radio access system which measures an amount, corrects a transmission timing of the lower radio device based on a result of the measurement, and establishes synchronization with a transmission timing of the upper radio device. 2. The radio access system according to claim 1, wherein the upper radio transmits a first radio signal including a synchronization pattern to the lower radio and receives the first radio signal. The lower wireless device that has transmitted the second wireless signal including a synchronization pattern to the upper wireless device, and the upper wireless device that has received the second wireless signal changes the second wireless signal to the second wireless signal. Based on the correction signal, the propagation delay amount in the wireless link is measured based on the measurement result, the correction signal based on the measurement result is transmitted to the lower-order radio device, and the lower-order radio device that receives the correction signal is based on the correction signal. A radio access system for correcting the transmission timing to establish synchronization with the transmission timing of the upper radio. 3. The radio access system according to claim 1, wherein the lower radio shifts its own transmission timing by a half symbol before a symbol clock for sampling the received transmission timing. A wireless access system characterized by: 4. The radio access system according to claim 2, further comprising a guard time that absorbs a propagation delay amount after the radio signal, wherein the lower-level radio sets the propagation delay amount to the guard time. A radio access system, wherein when the time is exceeded, the second radio signal is shortened by a predetermined length. 5. The radio access system according to claim 1, wherein when the lower radio connects to another radio by another radio link, synchronization in the another radio link The wireless access system is characterized in that, in establishing the above, the lower radio operates as the higher radio and the other radio operates as the lower radio. 6. A radio that connects to a network configured by radio links of two radios, and a higher radio that generates a reference transmission timing among the two radios connected by the radio link in the previous period. Or a radio that operates as a subordinate radio that reproduces its own transmission timing according to the transmission timing of the subordinate radio, and when the subordinate radio is the top radio, the transmission with the subordinate radio In establishing timing synchronization, a first radio signal including a synchronization pattern is transmitted to the lower radio, and the propagation delay amount by the radio link is measured based on the radio signal received from the lower radio, and the measurement is performed. The correction signal based on the propagation delay amount is transmitted to the lower radio, and if the lower radio is the lower radio, the synchronization of transmission timing with the upper radio is confirmed. In, the first wireless signal is received, a second wireless signal including a synchronization pattern is transmitted to the upper wireless device, and the transmission timing of the own device is corrected according to the correction signal received from the upper wireless device. A radio that is characterized by performing.