KR20130051350A - Synchronizing method for mesh node in wireless mesh system - Google Patents

Abstract

PURPOSE: A mesh node synchronization method in a wireless mesh system is provided to modulate a preamble of a neighbor node and broadcasting information. CONSTITUTION: An automatic gain controller transmits a network setup signal received from a neighbor node to a PHY(PHYsical Layer)(S531b). The PHY synchronizes time or frequency by using a preamble of the network setting signal(S532b). The PHY transmits the location information of a starting point of a super frame of the network setting signal to a DSP(Digital Signal Processor). The DSP synchronizes the clock of a mesh node through the location information. [Reference numerals] (AA) Automatic gain control unit; (BB) Power on; (DD) Network setting signal searching time; (EE) Location information transfer of network setting signal/super frame starting point; (S520,CC) Initial network setting mode request; (S531b) Network setting signal/PPA_en signal transfer; (S532b) Time/frequency synchronization network setting signal decoding; (S533b) Super frame starting point correction; (S540,FF) Normal network setting mode request; (S550b) Network entrance

Description

SYNCHRONIZING METHOD FOR MESH NODE IN WIRELESS MESH SYSTEM}

The present invention relates to a wireless mesh system, and more particularly to a method of synchronizing mesh nodes.

In a cellular system, a mobile station uses an automatic preamble transmitted from a base station to automatically gain control (AGC) and a base station for downlink data. And synchronization between the terminal and the terminal.

On the other hand, in a wireless mesh system, there is no preamble transmitted periodically. Therefore, each mesh node uses AGC and mesh nodes using a PPA-preamble (Punctured Primary Advanced preamble) of a network configuration (NCFG) signal that is aperiodically received through a mesh election process. Synchronize between them and receive broadcast information, for example, a network configuration message (NCFG message) and / or a distributed scheduling message (DSCH message).

An interface design between modules for each region (NCFG, DSCH, DATA) of the frame is required to meet the characteristics of the frame structure.

The present invention provides a network synchronization method in a wireless mesh system.

The present invention provides an interface method between modules for each region of a frame.

According to an embodiment of the present invention, a mesh node synchronization method in a wireless mesh system is provided. The mesh node synchronizing method may include transmitting, by an automatic gain controller, a network configuration (NCFG) signal received from an adjacent node to a physical layer (PHY), wherein the physical layer configures the network. Performing time or frequency synchronization using the preamble of the signal, and transmitting position information of the start point of the super frame of the network configuration signal to a digital signal processor (DSP), and the DSP using the position information, a mesh node Performing clock synchronization.

Preamble and broadcast information of a neighbor node transmitted aperiodically in a wireless mesh system may be demodulated.

1 shows an example of a wireless mesh communication system.
2 is a block diagram illustrating a mesh node according to an embodiment of the present invention.
3A and 3B are flowcharts illustrating a synchronization procedure of a mesh node according to an embodiment of the present invention.
4 is a schematic diagram illustrating a structure of a superframe of a network configuration signal and signal transmission between modules in an initial network configuration mode according to an embodiment of the present invention.
5A and 5B are flowcharts illustrating a synchronization procedure of a mesh node according to an embodiment of the present invention.
6 is a conceptual diagram illustrating an example in which a DSP of a mesh node synchronizes internal clock timings.
7 is a schematic diagram illustrating a normal network setup step according to an embodiment of the present invention.
8 is a schematic diagram illustrating a structure of a superframe of a network configuration signal and signal transmission between modules in a normal network configuration mode according to an embodiment of the present invention.
9 is a schematic diagram illustrating the structure of a superframe of a network configuration signal and signal transmission between modules in a normal distribution scheduling mode according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

1 shows an example of a wireless mesh communication system.

The wireless mesh system is a system that supports direct communication between a plurality of mesh nodes having a relay function. Mesh nodes in a wireless mesh system may have a separate communication path from each of the surrounding mesh nodes.

In a cellular system, a base station transmits a preamble continuously every frame. Accordingly, the cellular communication system performs automatic gain control (AGC) and / or auto frequency control (AFC) using a continuous preamble.

On the other hand, in the case of a wireless mesh system, it is not possible to continuously transmit a preamble per frame. Therefore, automatic gain control, synchronization of time and / or frequency for synchronization within one frame should be performed, and for this purpose, a PPA-preamble (Punctured Primary Advanced preamble), which is a preamble for automatic gain control, has been introduced. In addition, the mesh node performs time and / or frequency synchronization using a PA-primary advanced preamble and / or a SA-preamble, and then receives broadcast information data following the preamble.

The present specification proposes a procedure for performing network synchronization and / or system clock synchronization of a mesh node, and describes a mesh node synchronization method in two cases according to availability of a GPS signal according to a condition of a wireless mesh system.

* All mesh nodes are mesh nodes that can use GPS (Global Positioning System) signals

2 is a block diagram illustrating a mesh node according to an embodiment of the present invention.

Referring to FIG. 2, the mesh node 200 in the wireless mesh system includes a digital signal processor (DSP) 210, a physical layer (PHYs 220), an automatic gain controller (230), and an RF unit. 240.

The DSP 210 of the mesh node refers to an integrated circuit that allows a machine to process digital signals quickly. The DSP 210 mainly performs a low medium access control (LMAC) function and / or an upper MAC function.

The PHY 220 performs channel encoding / decoding, Fast Fourier Transform (FFT) / Inverse Fast Fourier Transform (IFFT), and the automatic gain control unit 230 A signal such as a preamble is changed into a signal having a size appropriate for a field-programmable gate array (FPGA). That is, the automatic gain control unit 230 controls the input signal so that the analog to digital converter (ADC) has a desired size so that the digital signal is less affected by quantization noise. The PHY 220 and the automatic gain control unit 230 may be implemented in one FPGA.

The RF unit 240 is connected to the automatic gain control unit 230 to transmit and / or receive a radio signal. The RF unit 240 may include a base band circuit for processing a radio signal.

3A and 3B are flowcharts illustrating a synchronization procedure of a mesh node according to an embodiment of the present invention.

If all mesh nodes of the wireless mesh system can use the GPS signal, the mesh node performs a synchronization procedure based on the GPS signal. In this case, every mesh node can know the superframe starting point of the GPS signal and the position of the network configuration frame (NCF) in the superframe.

3A and 3B, when the power of the wireless mesh system is turned on, the GPS signal is locked (S310). All mesh nodes perform superframe synchronization based on GPS signals. That is, the starting point of the superframe is adjusted to the GPS signal. All mesh nodes have a rising edge or falling edge of one Pulse Per Second (PPS) Synchronization Pulse generated from a GPS signal as a starting point of a superframe.

On the other hand, the DSP requests the operation of the initial NCFG mode to the PHY and the auto gain control unit to find the PPA-preamble of the network configuration (NCFG) signal received from the neighbor node. (S320). At this time, since the mesh node knows the position of the network configuration frame in the superframe, the PPA preamble is searched by scanning only the network configuration frame region in the superframe during the network configuration signal discovery time.

3A illustrates a case where an existing mesh node does not exist in a wireless mesh system.

If there is no existing mesh node in the wireless mesh system, the new node cannot receive the network configuration signal from the neighbor node. Therefore, the PHY and DSP of the new node cannot receive the PPA_en signal, which is a signal indicating that the automatic gain control unit has searched for the PPA preamble and converted to a signal having a proper size, from the automatic gain control unit. The new node's DSP, which has not received the PPA_en signal, does not perform a network entry procedure, but uses a rising edge or falling edge of a 1 PPS synchronization pulse of the GPS signal as a starting point of a superframe. Creates and broadcasts its information (S330a). The network configuration message includes a 12-bit superframe index and a 14-bit frame index. The superframe index increases from 0 to 4095 in units of superframes every 20 ms, and the frame index increases from 0 to 16380 in multiples of 4 from the superframe index.

Thereafter, the DSP requests a normal network configuration mode (normal NCFG mode) to the PHY and the automatic gain control unit (S340).

3B illustrates a case where an existing mesh node exists in a wireless mesh system.

If an existing mesh node exists in the wireless mesh system, the new node may receive a network configuration signal from an adjacent node. Accordingly, the automatic gain control unit automatically receives the network setting signal and transmits the gain to the PHY together with the PPA_en signal (S331b). The network configuration signal includes a PPA preamble, a PA preamble, and a SA preamble. The PHY receiving the PPA_en signal performs time and / or frequency synchronization using the PA-preamble, decodes the network configuration signal received from the neighbor node, and delivers the signal to the DSP (S332b). The DSP receives the decoded network configuration signal and synchronizes the superframe index and / or frame index (S333b).

Thereafter, the DSP requests the normal network setting mode to the PHY and the automatic gain control unit (S340).

In addition, the new node selects a sponsor node from the adjacent nodes and performs a network netry procedure (S350b). The existing node plays a role in helping the new node perform the network entry procedure when there is a new node entering the network. Therefore, when a new node is powered on, it finds adjacent nodes and designates the node having the best signal as the sponsor node.

4 is a schematic diagram illustrating a structure of a superframe of a network configuration signal and signal transmission between modules in an initial network configuration mode according to an embodiment of the present invention.

The superframe of the network configuration signal includes one network configuration frame (NCF) and three service delivery frames (SDF). Since each frame is 5 ms in length, one superframe is 20 ms in total. The network configuration frame includes a NENT (network entry) area and a NCFG (nerwork configuration) area. A mesh node in a wireless mesh system may receive a PPA preamble, a PA preamble, and an SA preamble in a reception interval of an NCFG region. The NCFG region is an area for broadcasting information of the mesh node itself.

The PHY of the mesh node receiving the network configuration signal requests the automatic gain control unit to operate the initial network configuration mode at the start of all NCFG regions of the network configuration frame. That is, the PHY transmits an automatic gain control signal (AGC signal) to the automatic gain control unit, and the automatic gain control unit performs an automatic gain control procedure in the PPA-preamble section of each NCFG region.

If the PPA preamble exists in the NCFG region of the network configuration signal received from the neighbor node, and the auto gain control unit completes the automatic gain control procedure using the PPA preamble, the auto gain control unit transmits the PPA_en signal to the PHY.

On the other hand, the PHY delivers a network configuration message, that is, a network configuration burst (NCFG burst) and / or node information collected from the network configuration frame to the DSP. Multiple delivery of network configuration messages to the DSP can cause delays due to frequent interrupts and context switching, so it is desirable to collect network configuration messages and send them once per frame.

* When mesh nodes that can use GPS signals and mesh nodes that cannot use GPS signals are mixed

5A and 5B are flowcharts illustrating a synchronization procedure of a mesh node according to an embodiment of the present invention.

When mesh nodes that can use GPS signals and mesh nodes that cannot use GPS signals are mixed, the new mesh node cannot know the starting point of the reference superframe of the wireless mesh system.

5A and 5B, when the wireless mesh system is powered on, the DSP of the new mesh node operates the initial network configuration mode to the PHY and auto gain control unit to find the PPA preamble of the network configuration signal received from the neighbor node. Request (S520). Since the starting point of the reference superframe is unknown, the new node must scan all regions within the superframe during the network configuration signal search time to search for the PPA-preamble of the network configuration signal.

5A illustrates a case where an existing mesh node does not exist in a wireless mesh system.

If there is no existing mesh node in the wireless mesh system, the new node cannot receive the network configuration signal from the neighbor node. Therefore, the PHY and DSP of the new node cannot receive the PPA_en signal from the automatic gain control.

The DSP of the new node that does not receive the PPA_en signal does not perform the network entry procedure. Instead, it generates a network configuration message that sets the rising edge or falling edge of the 1 PPS synchronization pulse generated from the internal clock as the starting point of the superframe. Broadcast (S530a).

The network configuration message includes a 12-bit superframe index and a 14-bit frame index. The superframe index increases from 0 to 4095 in units of superframes every 20 ms, and the frame index increases from 0 to 16380 in multiples of 4 from the superframe index.

Thereafter, the DSP requests the normal network setting mode to the PHY and the automatic gain control unit (S340).

5B illustrates a case where an existing mesh node exists in a wireless mesh system.

If an existing node exists in the wireless mesh system, the new node may receive a network configuration signal from an adjacent node. Therefore, the automatic gain control unit automatically receives the network setting signal and transmits the gain to the PHY together with the PPA_en signal (S531b). The PHY receiving the PPA_en signal performs time and / or frequency synchronization using the PA-preamble, decodes the network configuration signal received from the neighbor node, and delivers the signal to the DSP (S532b). On the other hand, since the starting point of the superframe generated by using the initial internal clock of the mesh node is different from the starting point of the superframe of the network configuration signal received from the neighboring node, the newly created node is different from the starting point of the superframe received from the neighboring node. You need to modify the internal clock to match. Therefore, the PHY delivers the position information of the start point of the existing superframe and the position information of the start point of the superframe of the network configuration signal received from the adjacent node to the DSP. The DSP modifies the starting point of the superframe by using the network setting transmission subframe position information parameter included in the network setting signal and corrects the starting point of the existing superframe (S533b). On the other hand, the starting point of the superframe is a reference of the clock of 5 ms unit and the clock of 20 ms unit shared by the DSP, PHY and automatic gain control unit. Details of the 5 ms clock and the 20 ms clock will be described with reference to FIG. 6.

Thereafter, the DSP requests a normal network configuration mode to the PHY and the automatic gain control unit (S540), selects a sponsor node from an adjacent node, and performs a network entry procedure (S550b).

6 is a conceptual diagram illustrating an example in which a DSP of a mesh node synchronizes internal clock timings.

When mesh nodes that cannot use GPS signals are mixed in the wireless mesh system, each mesh node has a different starting point of the superframe, and thus, the starting point of the superframe should be adjusted based on the first generated node. Accordingly, the DPS of each mesh node calculates a timing difference between a start point of a superframe and a clock of a network configuration signal received from an adjacent node and synchronizes the clocks of the corresponding mesh node. That is, the newly created node calculates the starting point of the superframe of the network configuration signal received from the neighboring node, and the reference interrupt (20ms INT), which is the clock of 20 ms indicating the superframe, and the clock of 5 ms, which indicates the frame, is calculated. Adjust the position of the frame interrupt (5ms INT). The starting point of the superframe can be known from a field specifying the position of the NCFG region of the network configuration signal. The 20 ms reference interrupt and the 5 ms frame interrupt are generated by an internal clock oscillator, e.g., temperature-compensated crystal oscillator (TCXO), DSP, PHY and automatic gain control unit, e.g. For example, it is an important signal because it is used as a reference time for interfacing between DSP, FPGA, and automatic gain control unit.

7 is a schematic diagram illustrating a normal network setup step according to an embodiment of the present invention.

The PHY requests the automatic gain control unit to operate in the normal network configuration mode. When the mesh node receives the network configuration signal by the mesh election, the automatic gain control unit is enabled (AGC enable). The automatic gain control unit first transmits the information on the TX subframe before transmitting the network configuration frame region to the DSP.

The auto gain control unit calculates an autocorr peak value from the ADC output signal of the PPA preamble for the network setup frame region, where the autocorrelation peak value exceeds the threshold value. Determine the starting point of the preamble. In the present specification, the window size for determining the starting point of the PPA-preamble is set to 512 window.

The automatic gain control unit calculates a Received Signal Strength Indicator (RSSI) value of the [512 X 2] section from the determined starting point of the PPA preamble. The automatic gain control unit transmits an automatic gain control value based on the calculated RSSI value to the RF unit.

The automatic gain control unit repeatedly performs RSSI measurement and gain control according to the gain control response speed of the RF unit. When gain control of the RF unit is completed, the automatic gain control unit transmits a PPA_en signal to the PHY.

The automatic gain control unit transfers the rear part of the gain-controlled PPA preamble, the PA preamble, and the SA preamble transmitted from the RF unit to the PHY. In addition, the automatic gain control unit transfers the gain control value and the RSSI measurement value of the automatic gain control unit and the RSSI measurement value of the RF unit to the PHY.

The AGC module receives the normal NCFG mode request signal from the PHY before starting the next NCFG interval, and repeats the above-described procedures.

Meanwhile, the auto gain control unit may determine the start point of the PA-preamble from the auto correlation peak value. In this specification, the window size for determining the start point of the PA-preamble is set to 512 × 3 windows. The mesh node may perform timing and fractional frequency offset compensation using the PA-preamble. In addition, the SA-preamble may be used to perform integer part frequency offset compensation and partial frequency / fine timing synchronization.

The automatic gain control unit may reset the RF unit to an automatic gain control reference value.

8 is a schematic diagram illustrating a structure of a superframe of a network configuration signal and signal transmission between modules in a normal network configuration mode according to an embodiment of the present invention.

The PHY of the mesh node requests the automatic gain control unit to operate in the normal network configuration mode. The PHY transfers the automatic gain control signal (AGC signal) to the automatic gain control unit only in the reception period of the NCFG region, and the automatic gain control unit transmits the PPA_en signal to the PHY when the PPA preamble exists in the NCFG region. The PHY delivers a network configuration message, that is, a network configuration burst (NCFG burst), collected from the network configuration frame to the DSP.

9 is a schematic diagram showing the structure of a superframe of a network configuration signal and signal transmission between modules in a normal distributed scheduling mode according to an embodiment of the present invention.

The DSCH region is a region for performing a 3-way handshaking procedure of Request / Grant / Confirm using a distribution scheduling message. The mesh node sends a distribution scheduling message to allocate resources with neighboring nodes.

The PHY of the mesh node requests the automatic gain control unit to operate the normal distributed scheduling mode. The PHY transmits an automatic gain control signal (AGC signal) to the AGC module only in a reception section of a distributed SCHeduling (DSCH) region, and the automatic gain control unit transmits a PPA_en signal to the PHY when a PA-preamble exists in the DSCH region. The PHY delivers a distribution scheduling message collected from the DSCH region, that is, a distribution scheduling burst (DSCH burst) to the DSP.

Claims (1)

In the mesh node synchronization method in a wireless mesh system,
Transmitting, by an automatic gain controller, a network configuration (NCFG) signal received from an adjacent node to a physical layer (PHY);
The physical layer performing time or frequency synchronization using the preamble of the network configuration signal, and transmitting position information of a start point of a super frame of the network configuration signal to a digital signal processor (DSP); And
And the DSP performing clock synchronization of a mesh node using the position information.

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