KR101631800B1 - Method and Apparatus for Multi-hop Clock Synchronization Based on Robust Reference Node Selection for SANET - Google Patents

Abstract

A robust base node selection based multi-hop clock synchronization method and apparatus for SANET is presented. The robust base node selection based multi-hop clock synchronization method according to the present invention comprises the steps of initializing a hop identifier and arbitrarily selecting one of the vessels located in the first hop, Determining whether GPS is available and synchronizing the ship with a ship having the earliest clock among the vessels located in the first hop, displaying the identifier by selecting HBSs to be synchronized to the second hop in the sequence following the first hop, Determining whether UTC or GPS is available for all vessels located in the second hop, detecting and decoding a beacon of the HBS having the smallest hop identifier, determining whether the first hop Determines if a plurality of HBSs are detected by the vessels located in the second hop, and if the plurality of HBSs are detected, And synchronizing the ships having detected the HBSs to the HBS having the closest communication distance.

Description

TECHNICAL FIELD [0001] The present invention relates to a multi-hop clock synchronization method and apparatus based on robust base node selection for SANET,

The present invention relates to a robust reference node selection based multi-hop clock synchronization method and apparatus for SANET (Ship Ad-hoc NETwork).

The prior art clock synchronization algorithms have been proposed only to reduce the probability of beacon collision between the terminals to reduce clock drift. However, SANET (Ship Ad-hoc NETwork) is a large-scale network, in other words, 100 km in terms of geographical coverage. A key factor affecting synchronization performance is signal propagation delay, which is not considered significant in prior art algorithms.

Therefore, this requires a robust multi-hop synchronization algorithm to support communication between hundreds of ships in the marine environment. The proposed technique faces several challenges and must be overcome. In other words, the physical clock (for example, UTC / GPS) can not be used in SANET due to severe weather, network link stability, and large propagation delays.

SANET can provide a ship with various multimedia services. Based on the surveys of terrestrial vehicle ad-hoc network and marine communication environment, realization of RTT of terrestrial vehicle ad-hoc network for maritime communication with many problems and problems is realized. For example, SANET often has huge communication coverage over 100 km, which requires multi-hop functionality to maintain link reliability.

In a marine environment, for realization of real-time services, a robust multi-hop synchronization algorithm is needed to support communication between hundreds of ships connected to SANET. Efficient clock synchronization is needed to help the ship accurately specify the boundaries of the frame, sub-frames, and timeslots during communication. In general, in a distributed system all terminals are required to operate at the same time, and this time need not be exactly the same in real time. For example, even though it operates at the actual time of 10:02, it is assumed that all terminals operate at 10:00 on the logical clock.

According to the survey, existing algorithms have been proposed only to reduce the probability of beacon collision to improve the performance of logical clock synchronization. However, propagation delay is an important factor affecting synchronization performance in a large-scale network in terms of geographical coverage, and this is not considered carefully in existing algorithms. Therefore, a logical clock synchronization algorithm with a multi-hop function for SANET is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a multi-hop logical clock synchronization (MCSS) for SANET (Ship Ad-hoc NETwork) capable of solving a propagation delay for improving synchronization performance, Method and apparatus. In the absence of UTC / GPS, the proposed MCSS ad-hoc method operates and, for example, a multi-hop capability for a large-scale SANET over a 100 Km range provides a method and apparatus for ensuring link reliability.

In one aspect, the robust base node selection based multi-hop clock synchronization method proposed by the present invention includes the steps of initializing a hop identifier and randomly selecting one ship located in a first hop, To the ship having the earliest clock among the vessels located in the first hop, selecting the HBSs to be synchronized to the second hop in the sequence next to the first hop Determining whether UTC or GPS is available for all vessels located in the second hop, and detecting and decoding a beacon of the HBS with the smallest hop identifier , Determining in the first hop that a plurality of HBSs are detected by the vessels located in the second hop, , Synchronizing the ships having detected the plurality of HBSs to the HBS having the closest communication distance.

Wherein the step of determining whether UTC or GPS is available for all the vessels located in the first hop and synchronizing to the vessel having the earliest clock among the vessels located in the first hop, And at least one of the vessels located in the first hop that is not available is synchronized to the ship having the earliest clock among the vessels located in the first hop when the UTC or GPS is not available.

Determining whether UTC or GPS is available for all vessels located in the second hop, and detecting and decoding a beacon of the HBS having the smallest hop identifier comprises detecting at least one of all vessels located in the second hop If the UTC or GPS is not available, the beacon of the HBS having the smallest hop identifier is detected and decoded.

If all the vessels located in the first hop are available for UTC or GPS, synchronize all the vessels to the UTC or GPS, and if all vessels located in the second hop are available for UTC or GPS, And synchronizes the vessels to the UTC or GPS.

Determining that a plurality of HBSs in the first hop are detected by vessels located in the second hop and, when detecting the plurality of HBSs, detecting the plurality of HBSs in an HBS having a closest communication distance Wherein synchronizing comprises: determining if a plurality of HBSs are detected by the vessels located in the second hop at the first hop, and if the plurality of HBSs are detected, detecting the detected plurality of HBSs and the plurality of HBSs Determining whether the detected vessel has a similar distance, and synchronizing the detected plurality of HBSs to the HBS having the closest communication distance if the vessel detecting the plurality of HBSs does not have a similar distance.

If the detected plurality of HBSs and the vessel detecting the plurality of HBSs do not have a similar distance, synchronizing to the HBS having the closest communication distance may be performed by using the decoded timestamp of the nearest distance HBS, Adjust the ship's timer to detect HBSs.

According to another aspect of the present invention, there is provided a robust base node selection based multi-hop clock synchronization apparatus, comprising: an initialization unit for initializing a hop identifier; a selection unit for arbitrarily selecting one ship located in a first hop; Determining whether UTC or GPS is available for all vessels located in the first hop, determining whether UTC or GPS is available for all vessels located in the second hop, determining whether UTC or GPS is available for all vessels located in the second hop, The HBSs are synchronized with the ship having the fastest clock among the vessels located in the first hop, and the HBSs to be synchronized with the second hop in the sequence following the first hop are selected, Updates the selected HBSs and identifiers, and if a plurality of HBSs at the first hop are detected by the vessels located at the second hop, A synchronization unit for synchronizing the ships having detected the plurality of HBSs to the HBS having the closest communication distance, and a UBS or GPS having the smallest hop identifier for all the vessels located in the second hop, And a controller for adjusting the timer of the ship which detects the plurality of HBSs with the decoded timestamp of the HBS of the closest distance.

Wherein the synchronization unit is configured to synchronize the vessels located in the first hop that are not available with at least one of the vessels located in the first hop to the vessels located in the first hop, Synchronize to the ship with the fastest clock.

The detecting and decoding unit detects and decodes the beacon of the HBS having the smallest hop identifier when at least one of all the vessels located in the second hop is not available to UTC or GPS.

The synchronization unit synchronizes all the vessels to the UTC or GPS when all the vessels located in the first hop are available for the UTC or GPS and if all the vessels located in the second hop are available for the UTC or GPS , And synchronizes all of the vessels to the UTC or GPS.

Wherein the determination unit determines whether a plurality of HBSs are detected by the vessels located in the second hop in the first hop and detects the detected plurality of HBSs and the plurality of HBSs when the plurality of HBSs are detected It is judged that the ship has a similar distance.

The synchronization unit synchronizes the detected plurality of HBSs with the HBS having the closest communication distance when the ship having detected the plurality of HBSs does not have a similar distance.

According to the embodiments of the present invention, for the two proposed criteria, propagation delay can be avoided by the first criterion 'selection of previous hop boundary vessels' and the second criterion 'transmission delay reduction'.

The first criterion can guarantee synchronization to a group of HBSs close to the network route ship, except where the vessels are located in the hop-1 region, and one of them with the fastest oscillator is located in the hop-1 region. Referring to Figure 1, in the hop-2 region, a ship can simultaneously detect beacons from HBS-3 and HBS-4, where HBS-3 is directly synchronized to the network route ship and HBS- It is indirectly synchronized via STRN. Therefore, compared to HBS-4, HBS-3 has a higher priority to be selected as STRN for second hop area vessels.

The second criterion ensures vessel synchronization for the HBS with the closest distance, which also helps to reduce the clock drift caused by the propagation delay. In addition, ATSP-based MCSS is superior to TSF-based MCSS because it can further reduce the possibility of beacon submissions crashing.

1 is a diagram illustrating a proposed beacon contention window (BCW) for SANET according to an embodiment of the present invention.
2 is a diagram illustrating a proposed SANET frame structure having an integrated beacon contention window (BCW) according to an embodiment of the present invention.
3 is a diagram illustrating a multi-hop SANET deployment model in accordance with an embodiment of the present invention.
FIG. 4 is a flowchart illustrating a robust reference node selection based multi-hop clock synchronization method for a SANET according to an embodiment of the present invention.
5 is a block diagram of a robust reference node selection based multi-hop clock synchronization apparatus for SANET according to an embodiment of the present invention.
6 is a graph showing changes in estimated ACD according to a network range according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram illustrating a proposed beacon contention window (BCW) for Ship Ad-hoc NETwork (SANET) according to an embodiment of the present invention.

Beacons and BCW start are very important for SANET, and important indexes must adapt to the maritime communication environment. Figure 1 shows a proposed BCW with the same length of data slots. Referring to FIG. 1, the BCW has 24 beacons, each of which consists of 16 symbols. The beacon restores the information including the ship identifier, the hop indicator (HI) reflects the hop index of the ship currently located, and the time-stamp value in US units representing the ship's clock value . The 69.4 us period assigned to the symbol is assigned as the guard time between neighboring beacons.

2 is a diagram illustrating a proposed SANET frame structure having an integrated beacon contention window (BCW) according to an embodiment of the present invention.

2 shows the proposed SANET frame structure by including BCWs. For example, the network setup duration is allocated to 64 BCWs. The frame length is set to one minute consisting of 2250 data slots of the same length.

There are four subframes assigned to one frame, the first subframe is provided to the ship located in the first hop, and the remaining three subframes are provided to the next hops. The length of the subframes is different due to various ship densities at each hop. The first sub-frame has 1125 data slots occupying half the total number of slots in the frame; The second subframe includes 625 slots having a length of 16.667 seconds; The third subframe has 375 data slots with a length of 10 seconds, and the fourth subframe is allocated with 125 data slots. To avoid inter-slot interference, a guard time assigned to each slot is required. The length of the guard time is calculated to guarantee a propagation delay of at least 30 km in the single hop and is thus set to 0.417 ms.

3 is a diagram illustrating a multi-hop SANET deployment model in accordance with an embodiment of the present invention.

The present invention proposes a logical clock synchronization algorithm having a multi-hop function for SANET, and is called MCSS. This operates in an add-on method where UTC / GPS is not available, and the multi-hop function ensures link stability of the network.

For the proposed MCSS, the synchronization time reference nodes (STRNs) are efficiently selected by considering propagation delay, and the beacon collision is selected by adaptive timing synchronization (ATSP) procedure. < / RTI >

Consider SANET in a coastal area with a large number of ships distributed as shown in FIG. The number of ships located near the beach is usually more than far from the beach. In Fig. 3, the white circles represent general vessels, the black circles represent hop boundary ships (HBSs), the triangle represents a new access ship (NAS) And operates as a connecting ship. At this time, the following points are assumed.

- The physical clock reference, or coordinated universal time (UTC), or GPS is not available due to severe weather conditions.

- A large number of ships can be deployed in the network.

- Each hop cover is approximately 30 km.

- All ships can communicate with equal transmission power.

FIG. 4 is a flowchart illustrating a robust reference node selection based multi-hop clock synchronization method for a SANET according to an embodiment of the present invention.

The proposed multi-hop clock synchronization scheme for SANET is based on the selection of synchronization time reference nodes (STRNs) by selecting the previous HBSs hop boundary ships' and 'propagation delay reduction' criteria.

The robust base node selection based multi-hop clock synchronization method includes the steps of initializing a hop identifier and randomly selecting one vessel located in a first hop (step 410), determining whether all vessels located in the first hop are UTC or GPS (420), synchronizing (421) with the ship having the earliest clock among the vessels located in the first hop, selecting (430) HBSs for synchronizing to the second hop of the next hop, (460) the selected HBSs and identifiers (450), determining (460) whether UTC or GPS is available for all vessels located in the second hop (460), displaying the smallest hop identifier (470) a step (461) of detecting and decoding a beacon of an HBS having a plurality of HBSs having a plurality of HBSs in the first hop, determining whether a plurality of HBSs are detected by the vessels located in the second hop in the first hop , And synchronizing (481) the vessels that have detected the plurality of HBSs to the HBS having the closest communication distance.

In step 410, the hop identifier is initialized, and one vessel at the first hop is arbitrarily selected. For example, the HI (h) (hop indicator) is initialized to 1 and the vessel located in the first hop is arbitrarily selected to send a beacon as a wake up signal.

In step 420, it is determined whether UTC or GPS is available for all vessels located in the first hop.

If all the vessels located in the first hop are available UTC or GPS, all the vessels are synchronized to UTC or GPS (step 422).

On the other hand, when at least one of all the vessels located in the first hop is not usable by the UTC or GPS, the vessels located in the first hop that are not available are selected among the vessels located in the first hop Synchronize to the ship with the fastest clock (421). Ships located in the first hop can perform TSF or ATSP to synchronize to the ship with the fastest clock. ATSP performs better than TSF by reducing the probability of collision of beacon submissions.

(430) the HBSs to synchronize to the second hop in the order of the first hop to display the identifier (440), and updates the selected HBSs and identifier (450). Under the assumption that all vessels communicate with the same transmit power, the HBS selection is based on the transmit power attenuation aspect and path-loss.

For example, the HBSs shown in Figure 1 as black circles usually receive the lowest power from the previous hop HBSs in the first hop or transmit the wake up signal. The selected HBSs are then indicated as h to specify the hop identifier. This information is then updated in the beacons of the HBSs for synchronization of the next hop. Then, h is updated to (h + 1) indicating the synchronization procedure for the next hop.

(460) whether UTC or GPS is available for all the vessels located in the second hop, and detects and decodes (461) the beacon of the HBS having the smallest hop identifier.

If all the vessels located in the second hop are available UTC or GPS, all the vessels are synchronized to the UTC or GPS (422).

On the other hand, if at least one of all the vessels located in the second hop is not UTC or GPS capable, it detects and decodes (461) the beacon of the HBS having the smallest hop identifier.

In other words, when UTC / GPS is available in the next hop, all vessels located in the (h + 1) th hop area are synchronized to UTC / GPS. Otherwise, the HBSs transmit beacons and assume at least one HBS with HI = h that can be detected by the vessels at the next hop. Then the next hop vessels (i.e., with HI = h + 1) will synchronize to the HBSs from the previous hop. This criterion ensures that the vessels synchronize to HBSs near the network route vessel to avoid an increase in propagation delay. The network root ship has the fastest oscillator located in the hop-1 region.

Next, it is determined whether a plurality of HBSs are detected by the vessels located in the second hop at the first hop, and when the plurality of HBSs are detected, (470) determining if a plurality of HBSs are detected by the vessels located in the second hop at the first hop, if the plurality of HBSs are detected, (480) if the detected HBSs and the vessel detecting the plurality of HBSs have similar distances (480); and if the vessel detecting the detected plurality of HBSs and the plurality of HBSs does not have a similar distance, (481) to the HBS having the HBS. At this time, the timer of the ship that detects the plurality of HBSs is adjusted with the decoded time stamp of the HBS of the closest distance. The jth ship timer is adjusted by detecting the timestamp of the STRN.

On the other hand, if the detected plurality of HBSs and the vessel detecting the plurality of HBSs have similar distances, they are decoded 481 into one of the timestamps received from the HBSs.

When a plurality of HBSs at the previous hop are detected by (h + 1) th regional hop ships, these vessels synchronize to the HBS with the closest communication distance. For example, when the j-th ship detects beacons from HBS-1 and HBS-2 as shown in FIG. 1, the j-th ship is shorter in transmission distance than the HBS- 1. The choice of HBS-1 is also based on a comparison of the transmission power attenuation aspect and path-loss. If the detected HBSs have a transmission distance similar to that of the j-th ship, then the ship may select one of them for synchronization. The last selected HBS was known as the STRN for the jth ship.

Finally, it is determined whether h> H (490). If h > H, the robust base node selection based multi-hop clock synchronization method ends; otherwise, it is repeated from step 430. Where H denotes the maximum number of hops.

5 is a block diagram of a robust reference node selection based multi-hop clock synchronization apparatus for SANET according to an embodiment of the present invention.

The robust reference node selection based multi-hop clock synchronization apparatus 500 for SANET includes an initialization unit 510, a selection unit 520, a determination unit 530, a synchronization unit 540, a detection and decoding unit 550, And an adjustment unit 560.

The initialization unit 510 initializes the hop identifier. The selection unit 520 arbitrarily selects one ship located in the first hop. For example, the HI (h) (hop indicator) is initialized to 1 and the vessel located in the first hop is arbitrarily selected to send a beacon as a wake up signal.

The determination unit 530 determines whether UTC or GPS is available for all the vessels located in the first hop. Then, it is determined whether UTC or GPS is available for all the vessels located in the second hop. In the first hop, it is determined whether a plurality of HBSs are detected by the vessels located in the second hop.

The synchronization unit 540 synchronizes with the ship having the earliest clock among the ships positioned in the first hop. Then, HBSs for synchronizing to the second hop of the first hop next order are selected to display an identifier, and the selected HBSs and identifiers are updated.

On the other hand, when at least one of all the vessels located in the first hop is not usable by the UTC or GPS, the vessels located in the first hop that are not available are selected among the vessels located in the first hop Synchronize to the ship with the fastest clock. Ships located in the first hop can perform TSF or ATSP to synchronize to the ship with the fastest clock. ATSP performs better than TSF by reducing the probability of collision of beacon submissions.

Selects the HBSs to be synchronized to the second hop of the first hop next order, displays the identifier, and updates the selected HBSs and identifier. Under the assumption that all vessels communicate with the same transmit power, the HBS selection is based on the transmit power attenuation aspect and path-loss.

For example, the HBSs shown in Figure 1 as black circles usually receive the lowest power from the previous hop HBSs in the first hop or transmit the wake up signal. The selected HBSs are then indicated as h to specify the hop identifier. This information is then updated in the beacons of the HBSs for synchronization of the next hop. Then, h is updated to (h + 1) indicating a synchronization procedure for the next hop

Further, when a plurality of HBSs are detected by the vessels located in the second hop at the first hop, the vessels that detect the plurality of HBSs are synchronized with the HBS having the closest communication distance.

If at least one of all the vessels located in the first hop is not available to UTC or GPS, the synchronization unit 540 may transmit the vessels located in the first hop that are not available to the first hop Synchronize to the ship with the fastest clock among the ships.

The synchronization unit 540 synchronizes all the vessels to the UTC or GPS when all the vessels located in the first hop are available for the UTC or GPS. If all the vessels located in the second hop are available UTC or GPS, all the vessels are synchronized with the UTC or GPS.

The detection and decoding unit 550 detects and decodes the beacon of the HBS having the smallest hop identifier when UTC or GPS is not available for all the vessels located in the second hop.

The detection and decoding unit 550 detects and decodes the beacon of the HBS having the smallest hop ID if at least one of all the vessels located in the second hop is not available to UTC or GPS. On the other hand, if the detected plurality of HBSs and the vessel detecting the plurality of HBSs have similar distances, they decode to one of the timestamps received from the HBSs.

In other words, when UTC / GPS is available in the next hop, all vessels located in the (h + 1) th hop area are synchronized to UTC / GPS. Otherwise, the HBSs transmit beacons and assume at least one HBS with HI = h that can be detected by the vessels at the next hop. Then the next hop vessels (i.e., with HI = h + 1) will synchronize to the HBSs from the previous hop. This criterion ensures that the vessels synchronize to HBSs near the network route vessel to avoid an increase in propagation delay. The network root ship has the fastest oscillator located in the hop-1 region.

The determination unit 530 determines whether a plurality of HBSs are detected by the vessels located in the second hop in the first hop and determines whether the detected plurality of HBSs and the plurality of HBSs To determine whether the ship having detected a similar distance.

The synchronization unit 540 synchronizes the detected plurality of HBSs with the HBS having the closest communication distance when the ship detecting the plurality of HBSs does not have a similar distance.

The adjustment unit 560 adjusts the timer of the ship that detected the plurality of HBSs with the decoded time stamp of the HBS of the closest distance.

When a plurality of HBSs at the previous hop are detected by (h + 1) th regional hop ships, these vessels synchronize to the HBS with the closest communication distance. For example, when the j-th ship detects beacons from HBS-1 and HBS-2 as shown in FIG. 1, the j-th ship is shorter in transmission distance than the HBS- 1. The choice of HBS-1 is also based on a comparison of the transmission power attenuation aspect and path-loss. If the detected HBSs have a transmission distance similar to that of the j-th ship, then the ship may select one of them for synchronization. The last selected HBS was known as the STRN for the jth ship.

Finally, the determination unit 530 determines whether h > H. If H> H, the robust base node selection based multi-hop clock synchronization method is terminated, and the process of selecting HBSs for synchronizing to the second hop of the next hop sequence is repeated. Where H denotes the maximum number of hops.

Table 1 details the parameters used for the accumulated clock drift (ACD) analysis.

<Table 1>

For FTSP, the estimated ACD for ship i, which is the furthest from the network route ship, can be given as Equation (1).

수학식1

Equation 1

Where E {.} Represents the expected value. Term-1 indicates ACD due to beacon collision, Term-2 indicates ACD generated by delay at the first hop, and Term-3 indicates ACD at the remaining hops.

In the proposed technique, the estimated ACD for vessel i can be given as: &lt; EMI ID = 2.0 &gt;

수학식2

Equation 2

Here, Term-1 indicates ACD due to beacon collision, Term-2 indicates ACD generated by delay from the first hop to (H-1) th hop, and Term-3 indicates ACD in the remaining hop.

6 is a graph showing changes in estimated ACD according to a network range according to an embodiment of the present invention.

Figure 6 shows the numerical results of ACD for FTSP and MCSS, where ACD linearly increases with increasing network coverage. The slope of the FTSP in the estimated ACD is larger than the proposed MCSS because the proposed MCSS can effectively avoid the propagation delay increase to maintain a small ACD.

For the two proposed criteria, propagation delay can be avoided by the first criterion 'selection of previous hop boundary vessels' and the second criterion 'transmission delay reduction'.

The first criterion can guarantee synchronization to a group of HBSs close to the network route ship, except where the vessels are located in the hop-1 region, and one of them with the fastest oscillator is located in the hop-1 region. Referring to Figure 1, in the hop-2 region, a ship can simultaneously detect beacons from HBS-3 and HBS-4, where HBS-3 is directly synchronized to the network route ship and HBS- It is indirectly synchronized via STRN. Therefore, compared to HBS-4, HBS-3 has a higher priority to be selected as STRN for second hop area vessels.

The second criterion ensures vessel synchronization for the HBS with the closest distance, which also helps to reduce the clock drift caused by the propagation delay. In addition, ATSP-based MCSS is superior to TSF-based MCSS because it can further reduce the possibility of beacon submissions crashing.

The apparatus described above may be implemented as a hardware component, a software component, and / or a combination of hardware components and software components. For example, the apparatus and components described in the embodiments may be implemented within a computer system, such as, for example, a processor, a controller, an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable array (FPA) A programmable logic unit (PLU), a microprocessor, or any other device capable of executing and responding to instructions. The processing device may execute an operating system (OS) and one or more software applications running on the operating system. The processing device may also access, store, manipulate, process, and generate data in response to execution of the software. For ease of understanding, the processing apparatus may be described as being used singly, but those skilled in the art will recognize that the processing apparatus may have a plurality of processing elements and / As shown in FIG. For example, the processing unit may comprise a plurality of processors or one processor and one controller. Other processing configurations are also possible, such as a parallel processor.

The software may include a computer program, code, instructions, or a combination of one or more of the foregoing, and may be configured to configure the processing device to operate as desired or to process it collectively or collectively Device can be commanded. The software and / or data may be in the form of any type of machine, component, physical device, virtual equipment, computer storage media, or device , Or may be permanently or temporarily embodied in a transmitted signal wave. The software may be distributed over a networked computer system and stored or executed in a distributed manner. The software and data may be stored on one or more computer readable recording media.

The method according to an embodiment may be implemented in the form of a program command that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions to be recorded on the medium may be those specially designed and configured for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. For example, it is to be understood that the techniques described may be performed in a different order than the described methods, and / or that components of the described systems, structures, devices, circuits, Lt; / RTI &gt; or equivalents, even if it is replaced or replaced.

Therefore, other implementations, other embodiments, and equivalents to the claims are also within the scope of the following claims.

Claims (12)

A robust base node selection based multi-hop clock synchronization method,
Initializing the hop identifier, and optionally selecting one ship located in the first hop;
Determining whether UTC or GPS is available for all the vessels located in the first hop and synchronizing to the ship having the earliest clock among the vessels located in the first hop;
Selecting the HBSs to synchronize to the second hop of the first hop next order, displaying the identifier, and updating the selected HBSs and identifier;
Determining whether UTC or GPS is available for all the vessels located in the second hop, detecting and decoding beacons of the HBS having the smallest hop identifier; And
Determining that a plurality of HBSs in the first hop are detected by vessels located in the second hop and, when detecting the plurality of HBSs, detecting the plurality of HBSs in an HBS having a closest communication distance Steps to synchronize
Based multi-hop clock synchronization method. The method according to claim 1,
Wherein the step of determining whether UTC or GPS is available for all the vessels located in the first hop and synchronizing to the ship having the earliest clock among the vessels located in the first hop,
When at least one of all the vessels located in the first hop is not available to use the UTC or GPS, the vessels located in the first hop that are not available are selected from among the vessels located in the first hop To a ship having
And a robust base node selection based multi-hop clock synchronization method. The method according to claim 1,
Determining whether UTC or GPS is available for all vessels located in the second hop, and detecting and decoding the beacon of the HBS having the smallest hop identifier,
If at least one of all vessels located in the second hop is not UTC or GPS available, detecting and decoding beacon of the HBS having the smallest hop identifier
And a robust base node selection based multi-hop clock synchronization method. The method according to claim 1,
Synchronizing all the vessels to the UTC or GPS when all the vessels located in the first hop are available with UTC or GPS,
Synchronizing all the vessels to the UTC or GPS when all vessels located in the second hop are available UTC or GPS;
And a robust base node selection based multi-hop clock synchronization method. The method according to claim 1,
Determining that a plurality of HBSs in the first hop are detected by vessels located in the second hop and, when detecting the plurality of HBSs, detecting the plurality of HBSs in an HBS having a closest communication distance The step of synchronizing comprises:
Determining at the first hop that a plurality of HBSs are detected by the vessels located in the second hop;
Determining, when the plurality of HBSs are detected, whether the detected plurality of HBSs and the ship having detected the plurality of HBSs have similar distances; And
If the detected plurality of HBSs and the vessel detecting the plurality of HBSs do not have a similar distance, synchronizing to the HBS having the closest communication distance
Based multi-hop clock synchronization method. 6. The method of claim 5,
The step of synchronizing to the HBS having the closest communication distance if the detected plurality of HBSs and the vessel detecting the plurality of HBSs do not have a similar distance,
Adjusting the timer of the ship which detected the plurality of HBSs with the decoded time stamp of the HBS of the closest communication distance
And a robust base node selection based multi-hop clock synchronization method. A robust base node selection based multi-hop clock synchronization apparatus,
An initialization unit for initializing a hop identifier;
A selection unit for arbitrarily selecting one ship positioned in the first hop;
Determining whether UTC or GPS is available for all vessels located in the first hop, determining whether UTC or GPS is available for all vessels located in the second hop, and determining whether a plurality of HBSs in the first hop A judging unit for judging whether or not it is detected by ships located in two hops;
Selects the HBSs to be synchronized to the second hop of the next hop in the order of the first hop to display the identifier, updates the selected HBSs and the identifier A synchronization unit for synchronizing the ships having detected the plurality of HBSs to the HBS having the closest communication distance when a plurality of HBSs at the first hop are detected by the vessels located at the second hop;
A detection and decoding unit for detecting and decoding a beacon of the HBS having the smallest hop identifier when UTC or GPS is not available for all the vessels located in the second hop; And
An adjustment unit for adjusting a timer of the ship which detected the plurality of HBSs with a decoded time stamp of the HBS of the closest communication distance,
Based multi-hop clock synchronization apparatus. 8. The method of claim 7,
Wherein the synchronization unit comprises:
When at least one of all the vessels located in the first hop is not available to use the UTC or GPS, the vessels located in the first hop that are not available are selected from among the vessels located in the first hop To a ship having
And a robust base node selection based multi-hop clock synchronization device. 8. The method of claim 7,
Wherein the detecting and decoding unit comprises:
If at least one of all vessels located in the second hop is not UTC or GPS available, detecting and decoding beacon of the HBS having the smallest hop identifier
And a robust base node selection based multi-hop clock synchronization device. 8. The method of claim 7,
Wherein the synchronization unit comprises:
Synchronizing all the vessels to the UTC or GPS when all the vessels located in the first hop are available with UTC or GPS,
Synchronizing all the vessels to the UTC or GPS when all vessels located in the second hop are available UTC or GPS;
And a robust base node selection based multi-hop clock synchronization device. 8. The method of claim 7,
Wherein,
The method comprising: determining whether a plurality of HBSs in the first hop are detected by vessels located in the second hop; and, when the plurality of HBSs are detected, detecting the detected plurality of HBSs and the plurality of HBSs are similar Determining if you have distance
And a robust base node selection based multi-hop clock synchronization device. 12. The method of claim 11,
Wherein the synchronization unit comprises:
If the detected plurality of HBSs and the vessel detecting the plurality of HBSs do not have a similar distance, then synchronizing to the HBS having the closest communication distance
And a robust base node selection based multi-hop clock synchronization device.

Images