KR20190022092A - Method of Phase Synchronization for Distributed Beamforming System - Google Patents

Abstract

The present invention provides a phase synchronization method in a distributed beamforming system that is capable of sequentially adjusting phases of nodes to allow strength of a received signal of an access point to be maximized, thereby making a beam having large gain and reducing the time required for phase synchronization. According to the present invention, the phase synchronization method in a distributed beamforming system having an access point (AP) and a plurality of nodes, the AP being adapted to determine the adjustment node one by one from the plurality of nodes to synchronize the phase of the adjustment node, includes the steps of: receiving a signal (hereinafter, referred to as ′first test signal′) moving a phase of a transmission signal in a positive direction by an adjustment value from the adjustment node and a signal (hereinafter, referred to as ′second test signal′) moving a phase of the transmission signal in a negative direction by the adjustment value from the adjustment node, through the AP; comparing received signal strength (RSS) of the first test signal with the RSS of the second test signal; and transmitting a feedback signal to the adjustment node according to the compared result.

Description

[0001] The present invention relates to a phase synchronization method for a distributed beamforming system,

The present invention relates to a phase synchronization method in a distributed beamforming system, and more particularly, to a phase synchronization method for performing optimal distributed beamforming in a limited feedback environment.

The contents described in this section merely provide background information on the present invention and do not constitute the prior art.

Wireless signals transmitted over a wireless link are not ideal, resulting in weak signals or distorted signals. This is called a fading phenomenon. Various diversity techniques such as space diversity, time diversity, and frequency diversity have been studied to reduce the fading phenomenon.

Space diversity is a method of obtaining a diversity effect by using a plurality of spaced apart antennas. Specifically, a transmitting base station having multiple antennas transmits a signal through an antenna on another radio channel, and a fading problem is solved by selecting a signal having a small influence of fading in the receiving base station or synthesizing the received signal. However, since space diversity requires a plurality of antennas to be installed in one base station, there is a problem in terms of complexity and transmission power.

The diversity technique designed to solve the above problem is the cooperation diversity technique. Among the cooperative diversity techniques, distributed beamforming capable of increasing the system capacity and transmission distance is attracting attention. Distributed beamforming is a technique in which a plurality of transmission units (hereinafter referred to as 'nodes') transmit the same signal and a plurality of identical signals are received in one reception unit (hereinafter, 'AP') to obtain a beam forming gain.

When a plurality of nodes transmit the same radio signal toward one AP, the signal strength enhancement occurs due to the constructive interference of the signals in the AP, so that the signal weakness and distortion can be prevented. The node is physically dispersed and the beamforming phenomenon occurs in the AP due to signal concentration, and this is called distributed beamforming.

Distributed beamforming is a technology that can be used in wireless power transmission systems as well as to reduce fading in wireless communication systems. In a wireless power transmission system, when a wireless power transmission signal is transmitted using distributed beamforming, an AP may receive a wireless power transmission signal transmitted from a plurality of nodes to increase a wireless power transmission capacity.

However, in the distributed beamforming, a plurality of nodes that are separated by geographical distances transmit the same radio signal. Because a plurality of nodes are separated from each other, the same radio signal propagates through multiple paths, , Which may result in weakening or distortion of the signal.

In the case of the conventional beamforming, since the spacing between the antennas is not wide and the antennas are uniformly arranged, the phases of the signals received by the receiving unit are the same even if the same signal is transmitted through the plurality of antennas. However, in the case of distributed beamforming, a plurality of nodes located at different positions transmit signals using respective oscillators, so that the phase of a signal received by the AP can be changed even if the same signal is transmitted. Therefore, it is necessary to synchronize the phases of the respective nodes in order to obtain the optimum beamforming gain in the distributed beamforming.

A method of synchronizing the phase of a signal transmitted by each node in distributed beamforming is disclosed in U.S. Patent No. 6,952,455 (Registered on April 10, 2005) and US 8,666,309 (Registered on Apr. 4, 2014). U.S. Patent Nos. 6,952,455 and 8,666,309 disclose a method for synchronizing the phase of a signal transmitted by each node in a distributed beamforming system using a random gradient search method.

FIG. 1 is a view for explaining a random coefficient search method according to the related art, and is a diagram illustrating a distributed beamforming system composed of one AP and six nodes.

In the random coefficient search method, a plurality of nodes simultaneously transmit a signal in which a transmission object signal is shifted by a random value. The AP measures RSS (Received Signal Strength) of signals received from a plurality of nodes and updates the maximum RSS if the RSS of the newly received signal is larger than the existing maximum RSS. The plurality of nodes again transmit a signal in which the transmission object signal is shifted by a new random value.

In this manner, the AP continuously updates the maximum RSS, and if a certain condition is satisfied, the AP determines the final maximum RSS (hereinafter referred to as 'final RSS') and feeds back to each node. For example, when a predetermined time or a certain number of test iterations have elapsed since the start of synchronization, the test is stopped and the maximum RSS until that time is determined as the final RSS. The signal transmitted by each node at the time when the final RSS value is updated becomes the phase synchronization signal of each node.

As described above, the random coefficient search method synchronizes the phases of each node by using random parameters. Therefore, the time required for phase synchronization increases as the number of nodes increases. In addition, since the maximum RSS until a predetermined time or a certain number of iterations of test is determined by the final RSS, even if the RSS is locally maximum RSS but not the maximum RSS when viewed from the whole viewpoint, There is a possibility to misjudge. That is, the local maxima may be misinterpreted as the maximum RSS, so that accurate phase synchronization may not be performed.

In summary, the random coefficient search method, which is a conventional phase synchronization method in a distributed beamforming system, synchronizes the phases of the respective nodes using random parameters, so that not only the time required for synchronization increases significantly according to the number of nodes, There is a problem that the phase may not converge correctly due to the problem of the maximum value.

The phase synchronization method for distributed beamforming proposed in the present invention adapts the phases of the respective nodes sequentially in the direction in which the strength of the received signal of the AP is maximized to thereby create a beam having a large gain and further reduce the time required for phase synchronization .

According to an aspect of the present invention, in an AP (Access Point) and a distributed beamforming system including a plurality of nodes, the AP determines an adjustment target node sequentially one by one among the plurality of nodes and synchronizes the phase of the adjustment target node (Hereinafter referred to as "first test signal") in which the phase of the transmission subject signal is shifted in the positive direction by the adjustment value from the adjustment object node and the phase of the transmission subject signal is adjusted (Hereinafter referred to as " second test signal ") that is shifted in the negative direction by a predetermined value; Comparing RSS (Received Signal Strength) of the first test signal with RSS of the second test signal; And transmitting a feedback signal to the node to be adjusted according to the comparison result.

According to another aspect of the present invention, there is provided a method of synchronizing the phase of a transmission subject signal sequentially with each of a plurality of nodes in a distributed beamforming system including an Access Point (AP) and a plurality of nodes, (Hereinafter referred to as a "first test signal") in which the phase of the transmission subject signal is shifted in a positive direction by an adjustment value and a signal (hereinafter referred to as a "first test signal") in which the phase of the transmission subject signal is shifted in the negative direction A second test signal '); Receiving a feedback signal indicating a result of comparing RSS (Received Signal Strength) of the first test signal and RSS of the second test signal from the AP; And adjusting the phase of the transmission subject signal according to the feedback signal.

According to another aspect of the present invention, there is provided a method for the AP to synchronize the phases of a plurality of nodes in a distributed beamforming system including an access point (AP) and a plurality of nodes, To a plurality of clusters; Designating a cluster (hereinafter referred to as a 'local synchronization cluster') to perform local synchronization among the plurality of clusters; And controlling the nodes grouped in the local synchronization cluster to perform local synchronization.

According to another aspect of the present invention, there is provided a method of synchronizing the phases of a plurality of nodes in an AP (Access Point) and a distributed beamforming system including a plurality of nodes, the method comprising: Hereinafter, a process of stopping signal transmission by nodes grouped in a cluster other than the 'local synchronization cluster'); And synchronizing the nodes grouped in the local synchronization cluster by the AP.

According to the present invention, it is possible to perform fast and accurate phase synchronization between nodes when performing distributed beamforming in an environment in which an AP having multiple antennas and a plurality of nodes having a single antenna communicate with each other.

FIG. 1 is a view for explaining a random coefficient search method according to the related art, and is a diagram illustrating a distributed beamforming system composed of one AP and six nodes.
2 is a diagram illustrating a bisection based method as a phase synchronization method in a distributed beamforming system according to an embodiment of the present invention.
FIG. 3 shows experimental results comparing a conventional random-number search method and a bisection-based method according to an embodiment of the present invention.
4 and 5 are diagrams illustrating a cluster based method as a phase synchronization method in a distributed beamforming system according to an embodiment of the present invention.
6 is an experimental result of a cluster based method according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described in detail with reference to exemplary drawings. It should be noted that, in the drawings, like reference numerals are used to denote like elements in the drawings, even though they are shown in different drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

In describing the constituent elements of an embodiment of the present invention, the first, second, i), ii), a), b) and the like can be used. Such a code is intended to distinguish the constituent element from another constituent element, but the nature of the constituent element, the order, the order, and the like are not limited by the code. It is to be understood that when a component is referred to as being "comprising" or "comprising," it should be understood that this section does not exclude the presence of other components, And the like. The term 'module' refers to a unit that processes at least one function or operation, and may be implemented as 'hardware', 'software', or 'combination of hardware and software'.

Hereinafter, in the distributed beamforming system, the same signal transmitted from each node to the AP is referred to as a 'transmission object signal', and a signal synchronized in phase between the nodes is referred to as a 'phase synchronization signal' .

Meanwhile, in the phase synchronization method in the distributed beamforming system according to an embodiment of the present invention, the wireless signal to be adjusted may be a wireless communication signal or a wireless power transmission signal. If the bisection based method according to an embodiment of the present invention is used for the distributed beamforming of a wireless communication signal, the fading phenomenon can be reduced by fast and accurate phase synchronization. Meanwhile, if the bisection based method according to an embodiment of the present invention is used for the distributed beamforming of the wireless power transmission signal, the wireless power transmission capacity can be increased by fast and accurate phase synchronization.

1. Bisection based method

2 is a diagram illustrating a bisection based method as a phase synchronization method in a distributed beamforming system according to an embodiment of the present invention. Although FIG. 2 illustrates a distributed beamforming system composed of one AP 100 and six nodes 111 through 116, the number of nodes may be more or less than six.

In the distributed beamforming system, when the AP 100 receives the same signal from N nodes, the signal received by the AP 100 in the nth time slot is expressed by Equation (1).

In Equation (1), A includes transmit power, channel gain, and path-loss.

When one AP 100 receives the same radio signal from a plurality of nodes, signal reinforcement occurs in the AP 100 due to constructive interference of signals.

However, since each node is geographically separated, the phase of the wireless signal may be changed during the propagation through the multipath, so that the phase of each signal received by the AP 100 may be changed. In this case, the signal is not sufficiently reinforced and the beam forming gain is reduced.

In order to maximize the beamforming gain in the distributed beamforming, the phases of the signals transmitted by the respective nodes must be synchronized. That is, the signals received from each node of the AP 100 must have the same phase. This can be expressed by the following equation (2).

In Equation (2), &thetas; is a phase rotated by each node, and is a value that can be controlled by each node. γ denotes a phase change according to the distance between the AP 100 and each node, and Φ denotes a phase change according to hardware characteristics of each node. The phase change due to γ and Φ is difficult to control at each node.

The phase shift of each node is expressed as θ + γ + Φ. In order to increase the beamforming gain by making AP (100) receive signals from each node the same, the values of θ + γ + Φ of each node are the same The phase must be synchronized to Among the factors affecting the phase, only θ that rotates at each node can be controlled, so the θ value is adjusted at each node to synchronize the phase of each node. In this case, there is a problem in determining how much the phase should be rotated at each node.

In the bisection based method according to an exemplary embodiment of the present invention, each node continuously transmits two test signals, and the AP 100 compares the RSS of the received two test signals and adaptively adjusts the phase that maximizes the RSS The rotation value? Is determined.

Hereinafter, a bisection based method according to an embodiment of the present invention will be described in detail.

In the random coefficient search method, a plurality of nodes simultaneously transmit signals to synchronize the phases, but in the bisection based method according to an embodiment of the present invention, each node sequentially synchronizes the phases. In the bisection based method, a node that is the current synchronization sequence is referred to as a 'target node' hereinafter.

Assuming that the i-th node is the adjustment-target node 111, the phase of the signal transmitted first by the i-th node is expressed by Equation (3).

The adjustment target node 111 adjusts the phase of the signal to be transmitted (hereinafter, referred to as 'first test signal') shifted in the positive direction by an adjustment value (Hereinafter referred to as " second test signal ") in the negative direction.

The first test signal is shown in Equation (4).

The second test signal is shown in Equation (5).

으로 설정할 수 있다. 본 발명의 일 실시예에 따른 bisection based method에서는 조정값을 점차 감소시켜 적응적으로 정밀한 위상 동기화를 수행하게 된다.The first adjustment value in the first and second test signals is

. In the bisection based method according to an embodiment of the present invention, the adjustment value is gradually decreased to perform adaptively precise phase synchronization.

When each node transmits the first test signal and the second test signal in order, the AP 100 measures RSS of the first test signal and the second test signal. When the RSS of the first test signal is Y _i1 [n] and the RSS of the second test signal is Y _i2 [n], the AP 100 compares Y _i1 [n] with Y _i2 [n] _{Y i1 [n] ≥ Y i2} [n] if and sends a feedback signal "1" to adjust the target node _{(111), Y i1 [n} ] <Y i2 [n] If the feedback signal to adjust the target node 111 " 0 " In order to reduce the load of the distributed beamforming system, the size of the feedback signal is preferably 1 bit.

The adjustment target node 111 moves the phase of the transmission object signal in the positive direction by the adjustment value? When receiving the feedback signal " 1 ", and when receiving the feedback signal " 0 & (?).

The AP 100 updates the adjustment value for adaptive adjustment and transmits the updated adjustment value to the adjustment target node 111. [

The adjustment value update is performed as follows.

For example, the adjustment value can be updated according to the number of update of the adjustment value by using the lookup table in which the adjustment value according to the update count is stored.

For example, the adjustment value can be updated by subtracting a predetermined subtraction value from the adjustment value.

For example, the adjustment value can be updated by dividing the adjustment value by a predetermined divisor at every update. For example, the adjustment value can be updated by dividing the adjustment value by 2 every time it is updated. In this case, the relationship between the adjustment value of the n-th order and the adjustment value of the (n + 1)

 On the other hand, the update may be made in the adjustment target node 111 rather than in the AP 100. [ In this case, instead of the AP 100 updating the adjustment value and transmitting the updated adjustment value to the adjustment target node 111, the adjustment target node 111 itself updates the adjustment value. Since the concrete adjustment value updating method differs from the adjustment value updating method of the AP 100, detailed description is omitted.

FIG. 3 shows experimental results comparing a conventional random-number search method and a bisection-based method according to an embodiment of the present invention.

As shown in FIG. 3, according to the conventional random coefficient search method, when the total sum of the signal strengths received from the plurality of nodes is about 180, about 220, about 250, about 320, A problem of local maxima occurs.

According to the related art, since the maximum RSS until a predetermined time or a predetermined number of iterations is determined as the final RSS after the start of the synchronization, if the RSS is locally the maximum RSS but not the maximum RSS The RSS can be misinterpreted as the final RSS.

For example, in FIG. 3, if the number of test iterations is set to 500 and the final RSS is determined, there is a risk that the RSS is determined to be 250 as the final RSS.

On the other hand, when the bisection based method according to an embodiment of the present invention is used, the RSS rises continuously as the test is repeated, and the RSS rise is stopped only when the RSS is maximized. Therefore, unlike the random coefficient search method, (Local Maxima).

2. Cluster based method

The cluster based method according to an embodiment of the present invention is a method of performing phase synchronization in each cluster unit after grouping a plurality of nodes into a plurality of clusters, and then performing phase synchronization among a plurality of clusters.

Phase synchronization performed between nodes included in each cluster in each cluster is hereinafter referred to as 'local synchronization', and phase synchronization performed between a plurality of clusters after completion of local synchronization is hereinafter referred to as 'global synchronization'.

2-1. Cluster based method - Phase 1 (local synchronization)

4 and 5 are diagrams illustrating a cluster based method as a phase synchronization method in a distributed beamforming system according to an embodiment of the present invention.

4 is a diagram illustrating a local synchronization method as a first step of a cluster based method.

FIG. 4 illustrates a case where three clusters 210, 220 and 230 are designated in a distributed beamforming system composed of one AP 200 and fifteen nodes, but the number of nodes may be more or less than 15 , Clusters may be more or less than three.

The AP 200 groups the plurality of nodes into a smaller number of clusters than the number of nodes.

The AP 200 designates a cluster (hereinafter referred to as a 'local synchronization cluster') to perform local synchronization among a plurality of clusters and controls the nodes 211 to 216 grouped in the local synchronization cluster to perform local synchronization.

Since a plurality of nodes are classified into a plurality of clusters, the number of nodes included in one cluster is relatively small. Therefore, even if synchronization is performed using a conventional random gradient search method without using the bisection based method described above, a satisfactory synchronization speed can be obtained.

Hereinafter, local synchronization is performed by a random gradient search method. However, it goes without saying that the local synchronization may be performed using the above-described bisection based method or a random gradient search method to be described in addition to the random gradient search method.

When the AP 200 instructs the local synchronization, the nodes other than the nodes grouped in the local synchronization cluster (nodes other than 211 to 216) stop transmitting signals, and the nodes 211 to 216 grouped in the local synchronization cluster, (Hereinafter referred to as &quot; local test signal &quot;) in which the transmission target signal is moved by a random value. In this case, the random value is preferably a random value independently generated at each node.

The AP 200 receives a signal transmitted simultaneously by the nodes 211 to 216 grouped in the local synchronization cluster and measures RSS (hereinafter referred to as 'local RSS').

The AP 200 measures the local RSS and updates the maximum local RSS if the measured local RSS is greater than the existing maximum local RSS.

The nodes 211 to 216 grouped in the local synchronization cluster adjust the phase adaptively according to the update of the maximum local RSS of the AP 200. [ At this time, the nodes 211 to 216 grouped in the local synchronization cluster may reflect the maximum local RSS update of the AP 200 every update or the last one.

2-1-1. Reflected on every update

The AP 200 measures the local RSS and updates the maximum local RSS if the measured local RSS is greater than the existing maximum local RSS.

The AP 200 transmits the maximum local RSS update fact to the nodes 211 to 216 grouped in the local synchronization cluster.

The nodes 211 to 216 grouped in the local synchronization cluster store the signal transmitted immediately before the maximum local RSS update in the existing address of the memory when receiving the maximum local RSS update fact. The information stored in the memory is overwritten and deleted.

The nodes 211 to 216 grouped in the local synchronization cluster again generate a new random value and then transmit a signal in which the transmission target signal is moved by a random value again.

The AP 200 instructs the nodes 211 to 216 grouped in the local synchronization cluster to terminate the local synchronization after a predetermined time or a certain number of test iterations after the start of the local synchronization.

Upon receiving the end of the local synchronization, the nodes 211 to 216 grouped in the local synchronization cluster read signals stored in the memory in the memory and determine them as phase synchronization signals.

2-1-2. Reflection of the last one

Nodes 211 to 216 grouped in the local synchronization cluster simultaneously transmit a signal for moving the transmission subject signal by a random value and store the transmitted signal in a new address in the memory. The information that was previously stored in the memory is retained.

The AP 200 measures the local RSS and updates the maximum local RSS if the measured local RSS is greater than the existing maximum local RSS.

The nodes 211 to 216 grouped in the local synchronization cluster again generate a new random value and then transmit a signal in which the transmission target signal is moved by a random value again.

The AP 200 determines the last updated maximum local RSS as a final local RSS after a certain period of time or after a certain number of iterations after the start of the local synchronization and then transmits the final local RSS to the nodes 211 to 216 grouped in the local synchronization cluster And feed back the time when the local RSS is updated.

The nodes 211 to 216 grouped in the local synchronization cluster receive the updated time of the last local RSS from the AP 200 and read the signal transmitted from each node at the time when the last local RSS is updated, Signal.

2-2. Cluster based method - Phase 2 (global synchronization)

When the local synchronization is completed, the phases are synchronized among the nodes in each cluster. However, since the phase is not synchronized with other clusters, it is necessary to synchronize the phases of the distributed beamforming system by performing synchronization between the clusters. The inter-cluster synchronization performed after completion of local synchronization is referred to as 'global synchronization' below.

5 is a diagram illustrating a global synchronization method as a second step of the cluster based method.

The AP 200 designates a cluster (hereinafter referred to as a 'global synchronization cluster') to perform global synchronization among a plurality of clusters and controls the nodes 311 to 316 grouped in the global synchronization cluster to perform global synchronization.

In the global synchronization process, the phase of all the nodes included in one cluster must be changed in common, so it is preferable to use the grid gradient search method described below.

Hereinafter, global synchronization is performed using a random gradient search method. However, it goes without saying that the global synchronization may be performed using the random gradient search method or the bisection based method described above in addition to the random gradient search method.

When the AP 200 commands global synchronization, the nodes (excluding the nodes 311 to 316) grouped in the cluster other than the global synchronization cluster transmit the determined phase synchronization signal in the local synchronization process. The nodes 311 to 316 grouped in the global synchronization cluster transmit a signal (hereinafter referred to as 'global test signal') shifting the phase of the phase synchronization signal determined in the local synchronization process by a grid value.

When G is a natural number, the grid value may be n times 2π / G (n is an integer between 0 and G). The value of n can be incremented by 1 for each transmission of the global test signal, starting at 1. That is, the phase shifts by 2? / G every time a constant global test signal is transmitted.

The AP 200 measures the RSS (hereinafter referred to as 'global RSS') by receiving signals transmitted from all the nodes at the same time.

The AP 200 measures the global RSS and updates the maximum global RSS if the measured global RSS is larger than the existing maximum global RSS.

The nodes 311 to 316 grouped in the global synchronization cluster adaptively adjust the phase according to the update of the maximum global RSS of the AP 200. [ In this case, the nodes 311 to 316 grouped in the global synchronization cluster may reflect the maximum global RSS update of the AP 200 at every update or at the last time.

2-2-1. Reflected on every update

The AP 200 measures the global RSS and updates the maximum global RSS if the measured global RSS is larger than the existing maximum global RSS.

The AP 200 transmits the maximum global RSS update fact to the nodes 311 to 316 grouped in the global synchronization cluster.

The nodes 311 to 316 grouped in the global synchronization cluster store the signal transmitted immediately before the maximum global RSS update in the existing address of the memory when receiving the maximum global RSS update fact. The information stored in the memory is overwritten and deleted.

Nodes 311 to 316 grouped in the global synchronization cluster again transmit a signal in which the transmission object signal is shifted by 2? / G.

The AP 200 instructs the nodes 311 to 316 grouped in the global synchronization cluster to terminate the global synchronization after a predetermined time or a certain number of test iterations after the start of the global synchronization.

Upon receiving the termination of the global synchronization, the nodes 311 to 316 grouped in the global synchronization cluster read the signal stored in the memory and determine the final phase synchronization signal.

2-2-2. Reflection of the last one

The nodes 311 to 316 grouped in the global synchronization cluster simultaneously transmit a signal shifting the transmission subject signal by a random value and store the transmitted signal in a new address in the memory. The information that was previously stored in the memory is retained.

The AP 200 measures the global RSS and updates the maximum global RSS if the measured global RSS is larger than the existing maximum global RSS.

Nodes 311 to 316 grouped in the global synchronization cluster again transmit a signal in which the transmission object signal is shifted by 2? / G.

The AP 200 determines the last updated maximum global RSS as a final global RSS after a certain period of time or after a certain number of iterations after the start of global synchronization, and then transmits the final global RSS to the nodes 311 to 316 And feed back the time when the global RSS is updated.

The nodes 311 to 316 grouped in the global synchronization cluster receive signals from the APs 200 when the last global RSS is updated, It is determined as a synchronization signal

6 is an experimental result of a cluster based method according to an embodiment of the present invention.

FIG. 6A shows cluster-based RSS in a cluster-based method, and FIG. 6B shows received RSS in a cluster-based method.

3. Comparative experiment results

Table 1 compares the performance of each method.

Number of nodes (N) Item Conventional method bisection method cluster method N = 20 iteration 288 320 288 N = 20 Converged RSS value 365 376 378 N = 40 iteration 783 640 644 N = 40 Converged RSS value 1433 1459 1494 N = 60 iteration 1361 960 1048 N = 60 Converged RSS value 3175 3196 3314 N = 100 iteration 4521 1600 2060 N = 100 Converged RSS value 8766 8610 9094

Table 1 shows that the final RSS value is 365 when the conventional method is used for synchronization of the distributed beamforming system having 20 nodes, the final RSS value is 376 when the bisection based method is used, The value is 376. Since the difference in the final RSS value is not large, the degree of beamforming performance improvement is similar. However, there is a difference in synchronization speed up to maximum performance improvement.

When the number of nodes is 20, the number of tests until the maximum RSS performance is obtained is 288 times for the conventional method, 320 times for the bisection based method, and 288 times for the cluster based method. When the number of nodes is small, it can be seen that the synchronization speed is sufficiently fast even if the conventional method is used.

When the number of nodes is 40, the number of tests until the maximum RSS performance is obtained is 783 times for the conventional method, 640 times for the bisection based method, and 644 times for the cluster based method.

When the number of nodes is 60, the number of tests until the maximum RSS performance is obtained is 1361 in the conventional method, 960 in the bisection based method, and 1048 in the cluster based method.

When the number of nodes is 100, the number of tests until the maximum RSS performance is obtained is 4521 in the conventional method, 1600 in the bisection based method, and 2060 in the cluster based method.

That is, as the number of nodes increases, the synchronization speed of the bisection based method or the cluster based method according to an embodiment of the present invention is relatively faster than that of the conventional method.

Meanwhile, the phase synchronization method of the distributed beamforming system described in the above embodiments can be implemented as a computer or smart phone readable code on a recording medium readable by a computer or smart phone. A recording medium readable by a computer or a smart phone includes all kinds of recording devices in which data that can be read by a computer system is stored. That is, the recording medium that can be read by a computer or a smart phone includes a magnetic storage medium (e.g., a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (e.g., CD- (E.g., USB, SSD) and carrier waves (e.g., transmission over the Internet). In addition, code that is distributed to networked computer systems and readable by a computer or smartphone in a distributed manner can be stored and executed.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

The present invention is not intended to limit the scope of the present invention but to limit the scope of the present invention. The scope of protection of the present invention should be construed according to the claims, and all technical ideas considered to be equivalent or equivalent thereto should be construed as being included in the scope of the present invention.

100: AP 111 to 116: Node
200: AP 211 to 216: Node
311 to 316:

Claims (39)

A method for synchronizing a phase of an adjustment target node with an AP in an AP (Access Point) and a distributed beamforming system including a plurality of nodes, the AP determining a target node sequentially one by one from the plurality of nodes,
(Hereinafter referred to as &quot; first test signal &quot;) in which the phase of the transmission object signal is shifted in the positive direction by the adjustment value from the adjustment object node and the phase of the transmission object signal in the negative direction (Hereinafter referred to as a &quot; second test signal &quot;);
Comparing RSS (Received Signal Strength) of the first test signal with RSS of the second test signal; And
And transmitting a feedback signal to the node to be adjusted according to the comparison result. The method according to claim 1,
Wherein the size of the feedback signal is one bit. The method according to claim 1,
Wherein the distributed beamforming system performs distributed beamforming of a wireless communication signal. The method according to claim 1,
Wherein the distributed beamforming system is a distributed beamforming of a wireless power transmission signal. The method according to claim 1,
After the step of transmitting the feedback signal,
And transmitting the updated adjustment value to the adjustment target node after updating the adjustment value. 6. The method of claim 5,
Wherein the adjustment value updating unit updates the adjustment value according to the number of times the adjustment value is updated by using a lookup table storing an adjustment value according to the number of update times. 6. The method of claim 5,
Wherein the adjustment value update subtracts a predetermined subtraction value from the adjustment value. 6. The method of claim 5,
Wherein the adjustment value update divides the adjustment value by a predetermined divisor. 9. The method of claim 8,
Wherein the divisor is two. In a distributed beamforming system including an Access Point (AP) and a plurality of nodes, a method of sequentially synchronizing the phases of signals to be broadcasted by the plurality of nodes,
(Hereinafter referred to as a "first test signal") in which the phase of the transmission subject signal is shifted in a positive direction by an adjustment value and a signal (hereinafter referred to as a "first test signal") in which the phase of the transmission subject signal is shifted in the negative direction A second test signal ');
Receiving a feedback signal indicating a result of comparing RSS (Received Signal Strength) of the first test signal and RSS of the second test signal from the AP; And
And adjusting a phase of the transmission subject signal according to the feedback signal. 11. The method of claim 10,
Wherein the step of adjusting the phase of the transmission subject signal comprises:
When each of the plurality of nodes receives a feedback signal indicating that the RSS of the first test signal is greater than or equal to RSS of the second test signal, the phase of the transmission target signal is shifted in the positive direction by the adjustment value And,
When each of the plurality of nodes receives a feedback signal indicating that the RSS of the first test signal is smaller than the RSS of the second test signal, the phase of the transmission target signal is shifted in the negative direction by the adjustment value / RTI &gt; 11. The method of claim 10,
Wherein the size of the feedback signal is one bit. 11. The method of claim 10,
Wherein the distributed beamforming system performs distributed beamforming of a wireless communication signal. 11. The method of claim 10,
Wherein the distributed beamforming system is a distributed beamforming of a wireless power transmission signal. 11. The method of claim 10,
After the step of adjusting the phase,
And updating the adjustment value. &Lt; Desc / Clms Page number 19 &gt; 16. The method of claim 15,
Wherein the step of updating the adjustment value updates the adjustment value according to the number of update of the adjustment value using a lookup table storing an adjustment value according to the number of updates. 16. The method of claim 15,
Wherein the step of updating the adjustment value subtracts a predetermined subtraction value from the adjustment value. 16. The method of claim 15,
Wherein the step of updating the adjustment value divides the adjustment value by a predetermined divisor. 19. The method of claim 18,
Wherein the divisor is two. A method for the AP to synchronize the phases of a plurality of nodes in an AP (Access Point) and a distributed beamforming system including a plurality of nodes,
Grouping the plurality of nodes into a plurality of clusters;
Designating a cluster (hereinafter referred to as a 'local synchronization cluster') to perform local synchronization among the plurality of clusters; And
And controlling the nodes grouped in the local synchronization cluster to perform local synchronization. 21. The method of claim 20,
Wherein the step of controlling the nodes grouped in the local synchronization cluster to perform local synchronization comprises:
Receiving signals simultaneously transmitted from nodes grouped in the local synchronization cluster;
Measuring a local RSS (Received Signal Strength) of the received signal; And
And updating the maximum local RSS if the measured local RSS is greater than the maximum local RSS measured. 22. The method of claim 21,
After the updating process,
Further comprising the step of transmitting, to the nodes grouped in the local synchronization cluster, the fact that the maximum local RSS has been updated. 22. The method of claim 21,
After the updating process,
And transmitting the latest update time of the maximum local RSS to the nodes grouped in the local synchronization cluster when a predetermined time elapses from the start time of the local synchronization. 22. The method of claim 21,
After the updating process,
And transmitting the latest update time of the maximum local RSS to nodes grouped in the local synchronization cluster if the number of times of measuring the local RSS exceeds a predetermined number. 21. The method of claim 20,
When the local synchronization of the plurality of clusters is completed,
(Hereinafter referred to as &quot; global synchronization &quot;) between the plurality of clusters. 26. The method of claim 25,
Wherein the controlling to perform the global synchronization comprises:
A process of designating a cluster (hereinafter referred to as a 'global synchronization cluster') to perform inter-cluster synchronization;
Receiving RSS (hereinafter referred to as 'global RSS') of signals transmitted by the plurality of nodes; And
And updating the maximum global RSS if the measured global RSS is greater than the measured maximum global RSS. 27. The method of claim 26,
After the updating process,
And transmitting the updated global RSS to the nodes grouped in the global synchronization cluster. 27. The method of claim 26,
After the updating process,
And transmitting the latest update time of the maximum global RSS to nodes grouped in the global synchronization cluster when a predetermined time elapses from the start time of the global synchronization. 27. The method of claim 26,
After the updating process,
And transmitting the latest update time of the maximum global RSS to nodes grouped in the global synchronization cluster if the number of times of measuring the global RSS exceeds a predetermined number. A method for synchronizing a phase of a plurality of nodes in an AP (Access Point) and a distributed beamforming system including a plurality of nodes,
Stopping signal transmission by nodes grouped in a cluster other than a cluster to be locally synchronized by the AP (hereinafter referred to as 'local synchronization cluster'); And
And synchronizing nodes grouped in the local synchronization cluster by the AP. 31. The method of claim 30,
Wherein the step of performing the local synchronization comprises:
And simultaneously transmitting a signal (hereinafter referred to as 'local test signal') in which each of the nodes grouped in the local synchronization cluster shifts the phase of the transmission subject signal by a random value independently generated at each node / RTI &gt; 32. The method of claim 31,
After the process of simultaneously transmitting the local test signal,
Receiving, by each of the nodes grouped in the local synchronization cluster, the fact that the maximum local RSS has been updated from the AP; And
Further comprising the step of storing, when each of the nodes grouped in the local synchronization cluster receives the fact that the maximum local RSS has been updated, the local test signal transmitted immediately before updating the maximum local RSS. 32. The method of claim 31,
After the process of simultaneously transmitting the local test signal,
Each of the nodes grouped in the local synchronization cluster receiving a latest update time point of the maximum local RSS from the AP; And
Wherein each of the nodes grouped in the local synchronization cluster transmits a local test signal sent by each of the nodes grouped in the local synchronization cluster at the last update time of the maximum local RSS to the transmission of each of the nodes grouped in the local synchronization cluster Determining a phase synchronization signal for a target signal;
Wherein the phase synchronization method further comprises: 31. The method of claim 30,
When the local synchronization of the plurality of clusters is completed,
Wherein the nodes included in each cluster perform the synchronization between the plurality of clusters (hereinafter, referred to as 'global synchronization'). 35. The method of claim 34,
Wherein the step of performing the global synchronization comprises:
Simultaneously transmitting a phase synchronization signal determined through a local synchronization process to nodes grouped in a cluster not designated as a cluster (hereinafter, referred to as 'global synchronization cluster') for performing inter-cluster synchronization by the AP;
Transmitting a signal (hereinafter referred to as 'global test signal') in which each of the nodes grouped in the global synchronization cluster by the AP shifts the phase of the phase synchronization signal determined in each local synchronization process by a grid value; And
And updating the grid value each time the global test signal is transmitted. 36. The method of claim 35,
Wherein the grid value is n? / G, G is a natural number, n is an integer between 0 and G, and the value of n is incremented by 1 each time the global test signal is transmitted starting from 1 Phase synchronization. 36. The method of claim 35,
After the simultaneous transmission of the global test signals,
Receiving, by each of the nodes grouped in the global synchronization cluster, a fact that the maximum global RSS has been updated from the AP; And
Further comprising the step of storing a global test signal transmitted immediately before the maximum global RSS update if each of the nodes grouped in the global synchronization cluster receives the fact that the maximum global RSS has been updated. 36. The method of claim 35,
After the simultaneous transmission of the global test signals,
Receiving, by each of the nodes grouped in the global synchronization cluster, a latest update time point of the maximum global RSS from the AP; And
Wherein each of the nodes grouped in the global synchronization cluster sends a global test signal sent by each of the nodes grouped in the global synchronization cluster at the last update time of the maximum global RSS, And determining a final phase synchronization signal for the target signal. A computer-readable recording medium on which a program for executing the method of any one of claims 1 to 38 is recorded.

Images