KR101568235B1 - Apparatus for deciding synchronization and spectrum sensing duration in distrubuted cognitive radio neworks and method thereof - Google Patents

Abstract

The present invention relates to a device and a method for determining a synchronization and spectrum sensing period in a distributed cognition radio network. According to the present invention, the device includes: a channel status determining unit which senses the status of a corresponding channel for a preset period to determine the channel status based on the sensing execution result; a parameter updating unit which updates a preset parameter according to the determination result; and a sensing period determining unit which determines the sensing period for a corresponding cycle based on a preset parameter being updated.

Description

[0001] APPARATUS FOR DECIDING SYNCHRONIZATION AND SPECTRUM SENSING DURATION IN DISTRUBULED COGNITIVE RADIO NEWORKS AND METHOD THEREOF [0002]

The present invention relates to a cognitive radio field, and more particularly, to an apparatus and method for determining a synchronization and spectrum sensing period in a distributed cognitive radio network.

Due to the rise of ubiquitous environment and the increase of the frequency resources due to the surge of smartphone supply, frequency shortage problem has been caused. The Federal Communications Commission (FCC) has authorized unauthorized users to use the frequency band of authorized users as a solution to this frequency shortage problem. In the future, cognitive radio (CR) has been continuously studied for improving spectral efficiency.

Spectrum detection is the most basic of the four spectrum management functions, sensing non-occupied bandwidth and ensuring transmission opportunities for secondary users (SUs).

In the case of the MAC access protocol proposed in the CR environment, spectrum detection is performed at regular intervals. This period is referred to as a sensing period. The time taken to determine the channel state within this sensing period is called sensing time. Thus, the sensing overhead represents the percentage of sensing time over the sensing period.

If we focus on detecting the primary user (PU) rather than the data transmission by reducing the detection period, the detection load may increase and the spectral efficiency may be degraded.

On the other hand, the use of a larger sensing period reduces the sensing load, but has a complementary feature that can cause interference with the PU due to the slow response time to the re-appearance of the PU and loss of transmission opportunities.

Therefore, it is necessary to study various techniques for determining the appropriate sensing period according to the channel environment in order to secure the transmission opportunity and reduce the sensing load.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide a method and apparatus for determining a channel state for a predetermined time, exchanging control packets according to the determined result, And an apparatus and method for determining a synchronization and a spectrum sensing period in a distributed cognitive radio network in which synchronization and a spectrum sensing period are variably determined based on updated parameters.

However, the objects of the present invention are not limited to those mentioned above, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to achieve the above objects, an apparatus for determining a synchronization and a spectrum sensing period in a distributed cognitive radio network according to an aspect of the present invention performs a state detection of a corresponding channel for a preset time, A channel state determination unit for determining the channel state; A parameter updating unit for updating a predetermined parameter according to the determined result; And a sensing period determiner for determining a sensing period of the corresponding period based on the updated predetermined parameter.

Preferably, the predetermined parameter includes a size of the sensing window.

Preferably, the parameter updating unit updates the kth detection window by increasing a size of the kth detection window by a predetermined value when the channel state is unoccupied as a kth determination result.

Preferably, the parameter updating unit updates a predetermined parameter based on the exchanged control packet after exchanging a predetermined control packet when the channel status is unoccupied with a k-th determination result.

Preferably, the control packet includes an RTS packet and a CTS packet.

Preferably, the parameter updating unit reduces the size of the k-th detection window to a predetermined value and updates the k-th detection window when the channel state is occupied as the k-th determination result.

Preferably, the detection period determiner determines a k-th detection period based on the updated predetermined parameter, and other users excluding the transmission / reception pair using the determined k-th detection period also calculate an end time of the k-th detection period .

According to another aspect of the present invention, there is provided a method for determining a synchronization and a spectrum sensing period in a distributed cognitive radio network, comprising: determining a channel state as a result of performing a state detection of a corresponding channel during a sensing time; A parameter updating step of updating a predetermined parameter according to the determined result; And a sensing period determining step of determining a sensing period of the corresponding period based on the updated predetermined parameter.

Preferably, the predetermined parameter includes a size of the sensing window.

Preferably, the parameter updating step updates the size of the k-th sensing window by a predetermined value when the channel state is not occupied as a result of the k-th determination.

Preferably, the parameter updating step updates a predetermined parameter based on the exchanged control packet after exchanging a predetermined control packet when the channel status is unoccupied with a k-th determination result.

Preferably, the control packet includes an RTS packet and a CTS packet.

Preferably, the parameter updating step reduces the size of the k-th sensing window to a predetermined value and updates the k-th sensing window when the channel state is occupied by the k-th determination result.

The sensing period determination step determines a k-th sensing period based on the updated preset parameter, and other users except for the transmission / reception pair use the determined k-th sensing period to determine an end time of the k-th sensing period .

Accordingly, the present invention determines a channel state for a predetermined time, exchanges control packets according to the determination result, updates a predetermined detection window based on the exchanged control packets, and generates synchronization and spectrum based on the updated detection window. By determining the detection period variably, there is an effect that the synchronization setting and spectrum use efficiency of the secondary user can be improved.

In addition, since the present invention considers the case where the secondary user network can use the licensed primary user network resource, interference with the primary user can be prevented.

In addition, since the present invention synchronizes the networks, all the nodes on the network simultaneously perform detection, so that sensing opportunities can be equally given.

1 is a diagram illustrating a structure of an entire sensing period according to an embodiment of the present invention.
2 is a block diagram of an apparatus for determining a sensing period according to an embodiment of the present invention.
3 is a diagram illustrating a parameter update algorithm in accordance with an embodiment of the present invention.
4 is a diagram showing a system utilization rate of a secondary user according to a channel utilization rate of a primary user.
FIG. 5 is a diagram illustrating a method for determining a sensing period according to an embodiment of the present invention. Referring to FIG.

Hereinafter, an apparatus and method for determining a synchronization and spectrum sensing period in a distributed cognitive radio network according to an embodiment of the present invention will be described with reference to the accompanying drawings. The present invention will be described in detail with reference to the portions necessary for understanding the operation and operation according to the present invention.

In describing the constituent elements of the present invention, the same reference numerals may be given to constituent elements having the same name, and the same reference numerals may be given thereto even though they are different from each other. However, even in such a case, it does not mean that the corresponding component has different functions according to the embodiment, or does not mean that the different components have the same function. It should be judged based on the description of each component in the example.

In particular, in the present invention, a channel state is determined during a detection time, control packets are exchanged according to the determination result, a predetermined detection window is updated based on the exchanged control packets, To be determined variably.

At this time, in the present invention, the sub-users can use a Distributed Cognitive Radio Network (DCRN) to form a network without the help of a central device such as a base station (BS) of a cellular network or an access point (AP) of a wireless local area network .

In the present invention, the case where the secondary user can use the network resource of the licensed primary user is considered. For this purpose, the opportunistic frequency sharing technique is a technique in which a sub-user uses a comparatively large transmission output of about the signal level of the main user, while using an overlay ) Based Dynamic Spectrum Access (DSA), and the secondary user can use the spectrum only at the moment when the primary user does not use the spectrum applied to the primary user.

The channel in the time slot is indexed by x (x = 0, 1, 2, ..., T, T + 1, T + 2, ...), the state of the channel is represented by S (x) Are represented by binary random variables of 0 and 1. The duration of each state follows the geometric distribution within the time interval τ.

At this time, the average channel use rate ρ of the main user can be expressed by the following equation (1).

[Equation 1]

Here, T _on and T _off represent the average ON and OFF periods, respectively.

1 is a diagram illustrating a structure of an entire sensing period according to an embodiment of the present invention.

1, the whole detection period T _sp is the detection time T _sens, back-off time _{T bo, RTS / CTS (Request} -to-Send / Clear-to-Send) exchange time T _ctrl, data transfer time T _data .

은 다음의 [수학식 2]와 같이 나타낼 수 있다.You should consider the detection time and the detection period to see if the spectrum is in use before the start of data transmission. Average backoff time for competition

Can be expressed by the following equation (2).

&Quot; (2) "

Here, T _slot represents a slot time for a contention window, m represents a number of retransmissions, p represents a collision probability, and W represents a contention window.

And the secondary user who has won the competition enters the RTS / CTS exchange phase. The RTS / CTS exchange time T _ctrl can be expressed as the following equation (3).

&Quot; (3) "

Here, SIFS denotes a short interframe space, and? Denotes a transmission delay time.

Accordingly, the data transmission time T _data can be expressed by the following equation (4).

&Quot; (4) "

2 is a block diagram of an apparatus for determining a sensing period according to an embodiment of the present invention.

2, the apparatus for determining a synchronization and spectrum sensing period according to the present invention includes a channel state determiner 110, a parameter updater 110, a sensing period determiner 130, (140).

The channel state determination unit 110 may detect the state of the corresponding channel during a predetermined time T _sens based on whether or not the data packet is received, and may determine the channel state as a result of performing the state detection.

At this time, if the channel state R (k) is obtained using the kth sensing time, the following Equation (5) is obtained.

&Quot; (5) "

Here, _tk represents the start time of the kth sensing period, and tau represents the time interval.

The channel state determination unit 110 determines that the channel is in a non-occupied state when the channel state R (k) is 0, and determines that the channel is occupied by the main user when the channel state R (k) is 1. That is, when receiving the data packet, the channel state determination unit 110 determines that the channel is occupied and determines that the channel is not occupied if the data packet is not received.

In this case, it is important to synchronize the transmission and reception data at the same time by sharing the time information among the network elements in order to transmit accurate information in the wireless network having the characteristics of the fluctuation of the nodes constituting the network. In particular, in the process of transmitting the spectrum detection cycle to neighboring users in the vicinity, there is a possibility that the detection result may be different and the detection period may be calculated differently due to the synchronization failure or the detection error, The probability of causing interference increases and this is a factor of degradation of the performance of the entire network. Therefore, in the present invention, the determination of the sensing period is the same as the synchronization process.

The parameter updating unit 120 may update the predetermined parameter according to the determined channel state. That is, when the determined channel state is the unoccupied state, the parameter updating unit 120 updates preset parameters based on the exchanged control packet after exchanging predetermined control packets, for example, RTS packets and CTS packets.

At least one parameter may be set in this control packet, where a value N _sw (k) representing the size of the sensing window may be used as a parameter.

For example, when the sub user joins the network, the parameter N _sw (k) = 1 is set to the initial value, and the predetermined parameter N _sw (k) is updated according to the channel state.

3 is a diagram illustrating a parameter update algorithm in accordance with an embodiment of the present invention.

Referring to FIG. 3, the size N _sw (k) of the k-th detection window is updated to N _sw (k-1) + i when the channel state R (k) Update, i.e., increases by a predetermined value.

On the other hand, since the kth channel can be used with a very high probability when the channel state R (k) is occupied by the kth detection result, the size _Nsw (k) of the kth detection window is reduced to a predetermined value .

At this time, the system utilization rate of the secondary user on the saturated network is expressed by the following Equation (6).

&Quot; (6) "

4 is a diagram showing a system utilization rate of a secondary user according to a channel utilization rate of a primary user.

Referring to FIG. 4, the simulation results of the system utilization rate of the secondary user according to the channel utilization rate of the primary user when the sensing time T _sens is 1, 5, and 9 ms are shown.

Through these simulation results, the transmission opportunity can be affected not only by the channel utilization rate of the main user but also by the sensing overhead.

Compared with a method using a fixed sensing period, it can be seen that as the sensing time increases, the present invention has a smaller decrease width than a method using a fixed sensing period.

The sensing period determiner 130 may determine the sensing period of the next period based on the updated N _sw (k). That is, the sensing period determiner 140 determines the sensing period of the corresponding period based on the updated parameter N _sw (k). The sensing period thus determined can be expressed by the following Equation (7).

&Quot; (7) "

Here, N _sw (k) represents the k-th detection window length and T _msw represents the minimum detection window length.

The sensing period determiner 130 can predict the start time of the next T _sp (k + 1), i.e., the sensing period of the next period, using the T _sp (k) value corresponding to the sensing period thus determined, .

At this time, other users other than the transmission / reception pair can know the end time of the k-th sensing period using the k-th sensing period thus determined, so that the synchronization can be achieved.

When the sensing period of the next period is determined through the above process, the data transmitting unit 140 may transmit the data packet based on the sensing period of the determined next period.

The present invention is based on IEEE 802.11 Distributed Coordination Function (DCF), and a sub-user can use one half-duplex transceiver. Therefore, the secondary user performs both control and data transfer using one transceiver.

The sub-user can receive the data packet transmitted on the channel preferentially when first subscribing to the CR network. If no packets are received in consecutive K detection windows, it is judged to be the first subscribed user on the network.

As a result of this determination, the secondary user determined to be the first user to participate in the process sets the value of N _sw (k) representing the size of the detection window, which is a parameter for determining the detection period, to a predetermined initial value.

On the other hand, if the secondary user already exists in the CR network, the secondary user who subscribes subsequently waits to receive the RTS / CTS packet of the secondary user already subscribed to the network.

At this time, the secondary user transmits its own N _sw (k) value when transmitting the RTS of T _ctrl time.

Therefore, the nodes joined to the network receive the RTS / CTS exchange packet, predict the next sensing period, participate in the network, and synchronize the entire network through the piggyback process. After synchronization is established, the nodes on the network perform detection simultaneously and use the channel in a contention-based access manner, thereby giving equal opportunities to detect.

1, when a RTS including a synchronization field is transmitted from a source node that has received a transmission opportunity after a backoff step to a destination node, a destination node transmits a CTS and a node other than the destination transmits an RTS field By calculating the next sensing period using the excluded parameter fields, the nodes on the network are synchronized.

FIG. 5 is a diagram illustrating a method for determining a sensing period according to an embodiment of the present invention. Referring to FIG.

As shown in FIG. 5, an apparatus for determining a sensing period according to the present invention (hereinafter, referred to as a sensing period determining apparatus) performs a state sensing of a corresponding channel for a preset time, (S720). That is, when the packet is received, the detection period determiner determines that the channel is in a busy state, and determines that the channel is idle if the packet is not received.

Next, in step S730, the detection period determining apparatus may exchange predetermined data packets according to the determined channel state, and update predetermined parameters based on the exchanged data packets. That is, if the channel status is unoccupied, the detection period determining apparatus updates the predetermined parameters managed by the base station based on parameters in the exchanged data packet after exchanging the data packet.

Here, the control packet may include an RTS packet and a CTS packet.

Specifically, when the channel state is unoccupied with the k-th detection result, the detection period determiner determines N _sw (k) based on the exchanged control packet as a value set in N _sw (k-1) 1 "

On the other hand, when the channel state is occupied by the k-th detection result, the detection period determining apparatus updates the predetermined parameter N _sw (k) to a predetermined value, for example,

Next, the detection period determining apparatus can determine the detection period based on the updated parameters, and users other than the transmission / reception pair can also determine the k-th detection period (S740).

Thereafter, the detection period determining device may transmit the data packet based on the determined sensing period.

It is to be understood that the present invention is not limited to these embodiments, and all of the elements constituting the embodiments of the present invention described above are described as being combined or operated together. That is, within the scope of the present invention, all of the components may be selectively coupled to one or more of them. In addition, although all of the components may be implemented as one independent hardware, some or all of the components may be selectively combined to perform a part or all of the functions in one or a plurality of hardware. As shown in FIG. In addition, such a computer program may be stored in a computer-readable medium such as a USB memory, a CD disk, a flash memory, etc., and read and executed by a computer to implement embodiments of the present invention. The storage medium of the computer program may include a magnetic recording medium, an optical recording medium, a carrier wave medium, and the like.

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 or essential characteristics thereof. Therefore, the embodiments disclosed in the present invention are intended to illustrate rather than limit the scope of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas within the scope of equivalents should be construed as falling within the scope of the present invention.

110: channel state determination unit
120: Parameter update unit
130:
140: Data transfer unit

Claims (14)

A channel state determiner for detecting a state of the corresponding channel for a predetermined time and determining a channel state as a result of the detection;
A parameter updating unit for updating a predetermined parameter according to the determined result; And
A sensing period determiner for determining a sensing period of the period based on the updated preset parameter;
And for determining a synchronization and spectral detection period in the distributed cognitive radio network. The method according to claim 1,
Wherein the predetermined parameter comprises a size of a detection window. ≪ Desc / Clms Page number 19 > 3. The method of claim 2,
Wherein the parameter updating unit comprises:
and when the channel state is in a non-occupied state as a result of the k-th determination, the size of the k-th detection window is increased by a predetermined value and updated. The method according to claim 1,
Wherein the parameter updating unit comprises:
and when the channel state is in the non-occupied state as a result of the k-th determination, the predetermined parameter is updated based on the exchanged control packet after exchanging the preset control packet. Apparatus for determining duration. 5. The method of claim 4,
Wherein the control packet includes an RTS packet and a CTS packet. 8. The apparatus of claim 7, wherein the control packet includes an RTS packet and a CTS packet. 3. The method of claim 2,
Wherein the parameter updating unit comprises:
and when the channel state is the occupied state as a result of the k-th determination, the size of the k-th sensing window is reduced to a preset value and updated. The method according to claim 1,
Wherein the sensing period determiner determines,
Determining a k-th sensing period based on the updated predetermined parameter, and determining, by using the determined k-th sensing period, the end time of the k-th sensing period other than the transmission / reception pair. An apparatus for determining synchronization and spectral detection periods in a wireless network. A channel state determination step of detecting a state of the corresponding channel during the sensing time and determining a channel state as a result of the detection;
A parameter updating step of updating a predetermined parameter according to the determined result; And
Determining a sensing period of the cycle based on the updated parameter;
The method comprising the steps of: determining a duration of a synchronization and a spectral sense in a distributed cognitive radio network. 9. The method of claim 8,
Wherein the predetermined parameter comprises a size of a detection window. ≪ Desc / Clms Page number 21 > 10. The method of claim 9,
Wherein the parameter updating step comprises:
and when the channel state is in a non-occupied state as a result of the k-th determination, the size of the k-th detection window is increased by a predetermined value, and the updated window is updated to update the synchronization and spectral detection period in the distributed cognitive radio network. 9. The method of claim 8,
Wherein the parameter updating step comprises:
and when the channel state is in the non-occupied state as a result of the k-th determination, the predetermined parameter is updated based on the exchanged control packet after exchanging the preset control packet. A method for determining a duration. 12. The method of claim 11,
Wherein the control packet comprises an RTS packet and a CTS packet. ≪ Desc / Clms Page number 19 > 9. The method of claim 8,
Wherein the parameter updating step comprises:
and when the channel state is the occupied state as a result of the k-th determination, the size of the k-th sensing window is reduced to a preset value and the updated window is updated to update the synchronization and spectral sensing period in the distributed cognitive radio network. 9. The method of claim 8,
The sensing period determination step may include:
Determining a k-th sensing period based on the updated predetermined parameter, and determining, by using the determined k-th sensing period, the end time of the k-th sensing period other than the transmission / reception pair. A method for determining synchronization and spectrum sensing periods in a wireless network.

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