KR20110109099A - Ad-hoc self organizing time division multiple access medium access control protocol for ship ad-hoc network - Google Patents

Abstract

A node and a communication method therefor according to at least one embodiment of the present invention determine a hop and subframe of the node, including whether there is a (neighbor) node around the node and the determined subframe. It is determined whether there is an idle time slot in the available subframes of the node, and if it is determined that the (neighbor) node exists and there is an idle time slot, the available subframe determined that there is an idle time slot. By selecting each time slot and transmitting data through the selected time slot, it is possible to smoothly provide a multimedia service and to ensure stable data transmission while reducing the possibility of reception collision.

Description

Node and communication method for marine mobile ad hoc network {Ad-hoc Self Organizing Time Division Multiple Access Medium Access Control protocol for Ship Ad-hoc NETwork}

The present invention relates to a maritime vehicle, such as a ship, and more particularly to a node and a communication method for a network between maritime vehicles.

VANET (Vehicular Ad-hoc NETwork) uses IEEE 802.11 Media Access Control (MAC) and has a communication distance of several meters under a topology where nodes (e.g. automobiles) are located in a regular direction and partially concentrated by traffic congestion. On the other hand, SANET (Ship Ad-hoc NETwork) has a communication distance of several tens of kilometers in a randomly scattered topology of nodes (eg ships) and uses SO-TDMA (Self-Organizing Time Division Multiple Access) as MAC. do.

Such SO-TDMA only provides the ship's location and identification information and has many limitations in providing multimedia services. It is also vulnerable to reception collisions and difficult to guarantee stable data transmission.

The technical problem to be achieved by at least one embodiment of the present invention is to provide a node capable of smoothly providing a multimedia service as well as ensuring a stable data transmission while reducing the possibility of reception collisions.

Another technical problem to be achieved by at least one embodiment of the present invention is to provide a communication method capable of smoothly providing a multimedia service as well as ensuring stable data transmission while reducing the possibility of reception collision.

Another technical problem to be achieved by at least one embodiment of the present invention is to provide a multimedia service as well as a computer-readable recording storing a computer program for ensuring stable data transmission while reducing the possibility of reception conflicts To provide the medium.

In order to achieve the above object, the node according to at least one embodiment of the present invention capable of ad hoc communication, Decision unit for determining the hop (hop) and sub-frame of the node; A control unit for determining whether the node exists around the node and whether there is an idle time slot in available subframes of the node including the determined subframe; And if it is determined that the node exists and the idle time slot exists, selecting the time slot for each of the available subframes determined that the idle time slot exists and transmitting data through the selected time slot. It may include a data transmission unit.

Here, the usable subframes may be subframes other than the determined subframe and a predetermined number of subframes before and after the determined subframe in the frame. In this case, the excluded subframes may be subframes except the two immediately preceding subframes and the immediately following two subframes in the frame.

In this case, if it is determined that the node does not exist or the idle time slot does not exist, the controller operates again for one frame.

Here, the determination unit and the control unit may operate again while the data transmission unit operates.

Here, after the operation of the data transmitter is started, the controller may determine whether to stop the data transmission and release the selected time slot when it is determined that the data transmission is stopped.

Herein, after the operation of the data transmission unit is started, the controller determines whether the hop is changed and whether the time slot determination update frame has elapsed, and when the hop is changed or when the time slot determination update frame has elapsed, You can release the selected time slot.

The data transmitter may retransmit the data when the one-hop ACK packet or the one-hop NACK packet of the data is not received for a predetermined number of frames after the data is transmitted.

Here, the node may be implemented in a marine mobile.

Ad hoc communication method according to at least one embodiment of the present invention carried out in a node capable of ad hoc communication to achieve the other object, (a) determining the hop (hop) and sub-frame of the node; (b) determining whether the node exists around the node and whether there is an idle time slot in the available subframes of the node including the determined subframe; And (c) if it is determined that the node exists and it is determined that the idle time slot exists, the time slot is selected for each of the available subframes determined that the idle time slot exists, and data is selected through the selected time slot. It may include the step of transmitting.

Here, the usable subframes may be subframes other than the determined subframe and a predetermined number of subframes before and after the determined subframe in the frame. In this case, the excluded subframes may be subframes excluding the two immediately preceding subframes and the immediately following two subframes in the frame.

Here, step (b) may be performed again for one frame when it is determined that the node does not exist or when the idle time slot does not exist.

Here, while step (c) is performed, step (a) and (b) may be performed again.

Here, after the step (c) is initiated, determining whether to stop the data transmission; And releasing the selected time slot if it is determined that the data transmission is stopped.

Determining whether the hop is changed and whether the time slot determination update frame has elapsed after the step (c) is started; And if it is determined that the hop has changed or the time slot determination update frame has elapsed, the method may further include releasing the selected time slot.

Here, in step (c), if the one-hop ACK packet or the one-hop NACK packet of the data is not received for a predetermined number of frames after the data is transmitted, the data may be retransmitted.

The computer-readable recording medium according to at least one embodiment of the present invention for an ad hoc communicable node to attain another object comprises determining a hop and subframe of the node; Determining whether the node exists around the node and whether there is an idle time slot in the available subframes of the node including the determined subframe; And if it is determined that the node exists and the idle time slot exists, selecting the time slot for each of the available subframes determined that the idle time slot exists and transmitting data through the selected time slot. You can store a computer program that runs the steps on your computer.

A node and a communication method therefor according to at least one embodiment of the present invention determine a hop and subframe of the node, including whether there is a (neighbor) node around the node and the determined subframe. It is determined whether there is an idle time slot in the available subframes of the node, and if it is determined that the (neighbor) node exists and there is an idle time slot, the available subframe determined that there is an idle time slot. By selecting each time slot and transmitting data through the selected time slot, it is possible to smoothly provide a multimedia service and to ensure stable data transmission while reducing the possibility of reception collision.

1 is a reference diagram for explaining a SANET.
2 is a reference diagram for explaining a frame structure according to at least one embodiment of the present invention.
3 is a block diagram illustrating a node according to at least one embodiment of the invention.
4 and 5 are flowcharts for explaining a communication method according to at least one embodiment of the present invention.

In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings that illustrate preferred embodiments of the present invention and the accompanying drawings.

Hereinafter, a node and a communication method for a marine mobile ad hoc network according to at least one embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a reference diagram for explaining a SANET.

As mentioned above, the SANET (Ship Ad-hoc NETwork) has a communication distance of several tens of kilometers under a randomly scattered topology of nodes (e.g., ships in flight) and SO-TDMA (Self- Refers to a network using Organizing Time Division Multiple Access.

As shown in FIG. 1, the SANET may be composed of a plurality of base stations (BSs) and marine vessels. The node according to at least one embodiment of the present invention may be implemented in a maritime vehicle, such as each of these maritime vessels. Hereinafter, for convenience of explanation, it is assumed that the marine moving body is a marine vessel.

The Land Base Station (BS) is connected to the grounded Internet Protocol (IP) backbone network to provide a variety of multimedia services to marine vessels.

Maritime vessels may be randomly scattered throughout the entire ocean, but generally are more distributed along the coast or coast than they do. A 'node' implemented on each of these maritime vessels can communicate with a nearby maritime vessel (strictly, a node implemented on its surrounding maritime vessel) or a land base station. To this end, each maritime vessel is equipped with a VHF (Very High Frequency) transceiver. On the other hand, each maritime vessel is equipped with a communication system of the HF (High Frequency) or satellite frequency band in preparation for the VHF band communication interruption.

The fact that a node communicates with a neighboring node assumes that the neighboring node is located within a communication distance of the node (about 30 km in the case of VHF). Here, the communication distance means a distance at which a node can exchange information with another node.

Meanwhile, nodes according to at least one embodiment of the present invention ad-hoc communicate with each other, and each of them transmits its own data or data received from neighboring nodes through a communication path determined by a given routing protocol. .

2 is a reference diagram for explaining a frame structure according to at least one embodiment of the present invention.

One frame according to at least one embodiment of the present invention consists of a plurality of sub-frames, each of which consists of one or more time slots. That is, a subframe is a higher concept of a time slot, and a frame is a higher concept of a subframe.

In this specification, the 'hop' of a node is determined according to the straight line distance (D) from the land base station closest to the node. For example, the hop number i is determined by the ceil function. Specifically, the hop number i is determined by ceil (D / 30km), so that when D is any value less than 30 km, i = 1 is determined, and when D is any value greater than 30 km or less than 60 km, i = 2 is determined. If D is any value greater than 60 km but less than 90 km, i = 3 is determined.

Subframes are determined for each node, and the determined subframe number of each node matches the hop number of each node. That is, the subframe number i and the hop number i are the same (where i and m are integers of 1 ≦ i ≦ m and m is the total number of hops).

In FIG. 2, Nf is the number of time slots allocated to one frame, and is the number of time slots belonging to the i-th subframe. Since many ships are distributed on the coast and coast, in general, when determining the number of time slots per subframe, Nm <Nm-1 <... <N2 <N1.

3 is a block diagram illustrating a node according to at least one embodiment of the present invention, wherein the node according to at least one embodiment of the present invention includes a determination unit 310, a control unit 320, and a data transmission unit 330. do.

The determination unit 310 determines the hop and subframe of the node.

The controller 320 determines whether another node is present in the vicinity of the node (ie, whether the neighboring node exists within the communication distance of the node to which the controller 320 belongs) and the node including the determined subframe. It is determined whether or not there is an idle time slot in available subframes. In the present specification, usable subframes mean 'the determined subframe (i-th subframe)' and 'subframes except for a predetermined number of subframes before and after the determined subframe within the frame'. Here, 'subframes excluding a predetermined number of subframes before and after the determined subframe in the frame' means two subframes (i-1, i) immediately before the determined subframe (i-th subframe) in one frame. Subframes other than the -2nd subframe) and immediately following two subframes (i + 1 and i + 2th subframes).

If it is determined by the controller 320 that there is no neighbor node or if there is no idle time slot, the controller 320 operates again for one frame.

On the other hand, if it is determined by the controller 320 that there is a neighboring node and there is an idle time slot, the data transmitter 330 determines one available subframe for each available subframe determined to have an idle time slot. Randomly selects a time slot and transmits data through the selected time slot.

In this way, the determination unit 310 and the control unit 320 operate again while the data transmission unit 330 transmits data. This is because the node's hops and subframes may change over time as the node is mobile. If the hops and subframes currently determined by the determiner 310 are different from the previously determined hops and subframes, the data transmitter 330 transmits data in a new time slot according to the changed subframes.

On the other hand, after the data transmission operation of the data transmission unit 330 is started, the controller 320 determines whether an interruption of data transmission occurs, and if it is determined that an interruption of data transmission occurs, the controller 320 releases the selected time slot. do.

In addition, after the data transmission operation of the data transmission unit 330 is started, the controller 320 determines whether the hop of the node has changed and whether the time slot determination update frame has elapsed, and if it is determined that the hop has changed, the time slot Even if it is determined that the decision update frame has elapsed, the selected time slot is released. Changes in the hop of a node can occur as the node itself moves. In this specification, the term 'time slot determination update frame' means that in the SO-TDMA even if the hop has not been changed since the data transmission is initiated by the data transmission unit 330 and a reception collision has not occurred in the currently used time slot. In order to reduce reception collisions such as the present invention, the present invention re-determines hops and subframes every predetermined time (e.g., n frames (where n is a natural number)) and selects a time slot again. , n).

In the previous two paragraphs, the case of releasing time slots has been described. In this case, when the time slots are released, the data transmission unit 330 suspends the data transmission work being performed and transmits the data after the time slot is determined later. To resume.

On the other hand, the data transmission unit 330 in order to ensure a reliable transmission in data transmission, one hop (ACK) acknowledgment (ACK) of the data for a certain number of frames (for example, two frames) after transmitting the data If a packet or one-hop NACK packet is not received, the data is retransmitted. When a node transmits data to another neighbor node, if the neighbor node has received the data correctly without error, the neighbor node transmits data to inform the other node of that data, which is one-hop of the data. hop) It is called an ACK packet. In contrast, if the neighbor node receives the data but there is an error in the received data, in this case, the neighbor node transmits a packet to the other node to inform it. Named hop NACK packet.

The previous paragraph is described in terms of a node transmitting 'data' to a neighbor node, but vice versa, if a 'data' is received from a neighbor node but there is an error in the data, the NACK packet for that 'data' is sent to the neighbor node. In view of the node transmitting the previous paragraph again, if the node transmits a NACK packet to the neighboring node and has not received the 'data' for a certain number of frames (for example, two frames) since then, the node Retransmits the NACK packet to its neighboring nodes.

The communication method according to at least one embodiment of the present invention (hereinafter, referred to as 'Ad hoc SO-TDMA Media Access Control (ASO-TDMA MAC) protocol') is largely composed of three steps. The initialization phase (IP) phase, the network entry phase (NEP) phase, and the data transmission phase (DTP) phase are the three phases.

First, the initialization phase phase is described, in which each node determines the hops and subframes according to its position, searches for neighboring node (s), and stores idle time slots in all subframes available to it. Scan and determine (select) a time slot among idle time slots. In this process, the 'time slot decision rule' proposed by the present invention is applied.

In other words, in the initialization phase, each node basically scans the neighboring nodes that can communicate with it and updates the list of neighboring nodes. As mentioned above, the subframes available to each node are the subframes to which they belong. This subframe) is not limited to other subframes that can be allocated, and other subframes are determined according to a time slot determination rule.

The time slot determination rule determines a node's 'subframes' and 'subframes except a predetermined number of subframes before and after the determined subframes' in the frame as 'usable subframes' of the node, Means scanning the idle time slot for each of these usable subframes and selecting one time slot of the found idle time slots for each of the available subframes. As mentioned earlier, if a node is assigned a hop number i and can use subframe i, then the subframes that the node can use without receiving dispatch are i-1, i-2, among all subframes in the frame. The remaining surf frames except for the i + 1 and i + 2 th subframes. For example, when m = 5, a node belonging to hop number 1 may use fourth and fifth subframes together with the first subframe. Each node randomly selects one of the idle time slots in its subframe, and determines the time slot in the same manner in other available subframes.

Meanwhile, a time slot that a node can actually use in one subframe is one time slot. Thus, if there are x subframes available to the node, then the number of time slots available to that node is x.

Next, referring to the second step, the network entry phase step, the network entry phase step is a step of transmitting the first data in the time slot determined in the initialization phase step, and a frame for transmitting the first data after the 'initialization phase step'. After this has elapsed, the data transfer phase step will be described later to transmit data. If there is a node with which the node can communicate around it and there are idle time slots within its available subframes, the network entry phase step as described above and the data transfer phase step described below will be performed. If there are no transmittable nodes (e.g., neighboring vessels) in the vicinity or there are no idle time slots in their available subframes, the node rescans if an idle time slot occurs during one frame and determines the time slots to retrieve the data. Should be sent.

Finally, a third step, the data transfer phase step, is used in order to ensure stable data transmission, after a node transmits data for a certain number of frames (for example, two frames). If one-hop ACK packet or one-hop NACK packet is not received, the data is transmitted by retransmitting the data. Similarly, in the data transmission phase, a node receiving data from a neighbor node but having an error in the data and transmitting a NACK packet for the data to the neighbor node transmits a NACK packet and then sends a certain number of frames (eg, If the data is not received during the two frames, the NACK packet is retransmitted to the neighbor node, thereby ensuring that the neighbor node can perform the data transmission stably.

While this data transfer phase phase is performed, the initialization phase and the network entry phase phase also continue.

On the other hand, the node periodically changes the occupied time slots to exclude reception collisions while the data transmission is smoothly performed. That is, in order to reduce reception collisions as in SO-TDMA, each node may determine n frames (where n is a random number and reflect the network environment in the MAC design) even when data transmission is started, even while performing data transmission. After the time elapses, the time slots used by the user are released and the time slot is determined again according to the time slot determination rule.

In addition, when the hop of the node that the node can move is changed, the node re-determines the subframe and changes the time slot according to the time slot determination rule.

In both cases immediately preceding this paragraph, data transmission is suspended until the time slot is determined after release, and data transmission is resumed only after the time slot is determined again.

In the phase of data transmission, the node transmits data to its neighboring nodes (e.g., neighboring vessels) determined through the routing table in the time slots that it assigns, in which each node acts as a source node due to the nature of the ad hoc network. It can either act as a relay node, or as a destination node. When acting as a relay node, the next node in the routing table can pass data to be delivered to its assigned time slot. To send.

4 and 5 are flowcharts for explaining a communication method according to at least one embodiment of the present invention. Specifically, FIG. 4 is a flowchart for explaining an initialization phase step and a network entry phase step, and FIG. 5 is a flowchart for explaining a data transmission phase step.

First, Fig. 4 will be described.

The node determines its hop and subframe (step 410).

After operation 410, the node determines whether there is a node located within a distance capable of communicating with itself (operation 412). In FIG. 4, NS refers to a neighboring ship and eventually a neighboring node.

If it is determined in step 412 that the node exists, the node checks idle time slots in its available subframes (step 414). Here, the 'usable subframes of the node' are subframes determined according to the time slot determination rule, that is, 'subframe determined by the node (i-th subframe)', and 'i-2, i-1' within the frame. The subframes other than the i + 1 and i + 2 th surf frames are already mentioned above.

After step 414, the node determines whether there are idle time slots in its available subframes (step 416).

If it is determined in step 416 that it does not exist or it is determined in step 412 that it does not exist, the node waits for one frame (step 418) and then proceeds to step 412.

On the contrary, if it is determined in step 416, the node randomly selects one of the available time slots if there is at least one idle time slot for each of its available subframes (step 420).

After step 420, the node transmits data in the time slot determined in step 420 (step 422).

The network entry phase step is terminated by transmitting the first data in step 422, after which the data transmission phase step is started and described below with reference to FIG. 5.

The node transmits one of data, (one hop) ACK packet, and (one hop) NACK packet (step 510).

After operation 510, the node determines whether the data transmission phase step is stopped (operation 512).

If it is determined in step 512 that it has been "suspended," the node releases a time slot in use (step 514).

On the other hand, if it is determined in step 512 that it has not been interrupted, the node waits for the next frame and scans the next frame (step 516).

After step 516, the node determines whether there is a node located within a distance capable of communicating with itself (step 518). NS described in FIG. 5 has the same meaning as NS described in FIG. 4.

If it is determined in step 518 that it does not exist, the flow proceeds to step 516.

On the other hand, if it is determined that the 'exists' in step 518, the node determines whether the hop has changed or n has passed (step 520).

If it is determined in step 520 that the hop has not been changed and n has not elapsed, the process proceeds to step 510.

On the other hand, if it is determined in step 520 that the hop has been changed or n has elapsed, the node notifies the neighboring node NS of the release of the time slot (step 522).

After operation 522, the node determines whether there are idle time slots in its available subframes (operation 524).

If it is determined in step 524 that there is no existence, the flow proceeds to step 516.

On the other hand, if it is determined in step 524 that the node exists, the node randomly selects one time slot among one or more idle time slots for each of its available subframes (step 526). The flow proceeds to step 510.

The program for executing the communication method according to the present invention mentioned above on a computer may be stored in a computer-readable recording medium.

Here, the computer-readable recording medium may be a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), and an optical reading medium (for example, a CD-ROM, a DVD). : Digital Versatile Disc).

So far, the present invention has been described with reference to the preferred embodiments. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

Claims (15)

In a node capable of ad hoc communication,
A decision unit to determine hops and subframes of the node;
A control unit for determining whether the node exists around the node and whether there is an idle time slot in available subframes of the node including the determined subframe; And
If it is determined that the node exists and the idle time slot exists, data for selecting the time slot for each of the available subframes determined that the idle time slot exists and transmitting data through the selected time slot Node containing a transmission unit. The method of claim 1, wherein the usable subframes are
And subframes excluding the determined subframe and a predetermined number of subframes before and after the determined subframe within the frame. The node of claim 2, wherein the excluded subframes are subframes except for two immediately preceding subframes and two immediately preceding subframes in the frame. The method of claim 1, wherein the control unit
And if it is determined that the node does not exist or the idle time slot does not exist, the node operates again for one frame. The node of claim 1, wherein the determination unit and the control unit operate again while the data transmission unit is in operation. The node of claim 1, wherein after the operation of the data transmitter is started, the controller determines whether to stop the data transmission and releases the selected time slot when it is determined that the data transmission is stopped. The method of claim 1, wherein after the operation of the data transmission unit is started,
The controller determines whether the hop has been changed and whether the time slot determination update frame has elapsed, and releases the selected time slot when it is determined that the hop has changed or the time slot determination update frame has elapsed. . In an ad hoc communication method performed in an ad hoc communication capable node,
(a) determining hops and subframes of the node;
(b) determining whether the node exists around the node and whether there is an idle time slot in the available subframes of the node including the determined subframe; And
(c) if it is determined that the node exists and the idle time slot is present, the time slot is selected for each of the available subframes determined that the idle time slot exists, and data is selected through the selected time slot. Communication method comprising the step of transmitting. The method of claim 8, wherein the usable subframes are
And the determined subframes and subframes excluding a predetermined number of subframes before and after the determined subframes in the frame. The communication method according to claim 9, wherein the excluded subframes are subframes except for two immediately preceding subframes and two immediately preceding subframes in the frame. The method of claim 8, wherein step (b)
And if it is determined that the node does not exist or the idle time slot does not exist, the communication method is performed again for one frame. The method of claim 8,
While step (c) is performed, step (a) and (b) are performed again. The method of claim 8,
Determining whether to stop the data transmission after the step (c) is started; And
Releasing the selected time slot if it is determined that the data transmission has been interrupted. The method of claim 8,
Determining whether the hop has been changed and whether the time slot determination update frame has elapsed since the step (c) is started; And
Releasing the selected time slot if it is determined that the hop has changed or the time slot determination update frame has elapsed. A computer-readable recording medium storing a computer program for executing the method of any one of claims 8 to 14.

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