KR101662687B1 - Apparatus and Method of Energy-efficient Hybrid MAC Protocol in Cognitive Radio enabled Sensor Networks - Google Patents

Abstract

The present invention relates to an apparatus and a method for improving energy efficiency during spectrum access in a cognitive radio enabled sensor network (CRSN). A method for transmitting data in a CRSN according to the present invention comprises: a sensing step of checking the state of a channel for report (CRF) and a channel for use (CFU) by each secondary user who transceives a control message by using a control channel and transceives data by using a data channel; a reporting step of transceiving the state of the channels, which is checked by the secondary users, between the secondary users by using the control channel; a contention step of reserving the CRF according to the state of the channels by the secondary users; and a data transmission step of transmitting the data through the channel reserved by the secondary users. The method of the present invention can improve energy efficiency during MAC protocol operation in the CRSN of a multi-channel environment with limited power supply.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy-efficient hybrid medium access control

The present invention relates to an apparatus and method for improving energy efficiency in a spectral approach in a cognitive radio enabled sensor network (CRSN).

The Internet of Things (IoT) environment in which various objects or objects are connected by a network can be realized by utilizing a communication network for transferring information between objects. Among these communication networks, Wireless Sensor Network (WSN) has been used in various specific domain industrial applications such as smart power grid, intelligent traffic system, structural health status monitoring, environmental protection, smart agriculture and disaster management . Various multi-channel MAC (Medium Access Control) protocols have been proposed to efficiently utilize spectrum resources in such a wireless sensor network.

However, as the number of various services and systems using the Internet of objects increases, the number of sensor nodes constituting it will also increase rapidly. For example, according to Cisco, by 2020, the number of sensor nodes is expected to reach 50 billion, which is seven times the world's population. Therefore, a network technology that uses a limited spectrum resource while using several networks coexist on the same spectrum resource, for example, the same License Free Spectrum, is required. That is, there is a need to solve the interference problem and the shortage of spectrum resources that can be caused by a plurality of sensor nodes operating in the same spectrum band.

Cognitive Radio Technology (Cognitive Radio Technology) is one of the next generation wireless network technologies to solve the problem of lack of spectrum resources on wireless sensor networks. The Cognitive Radio-Enabled Sensor Network (CRSN) is a distributed wireless sensor network in which unauthorized Secondary Users (SUs) communicate with each other in an ad hoc manner without a central network unit And may have a structure of Distributed Cognitive Radio Networks (DCRN).

In the DCRN, which does not control the communication between sub-users (SUs) at the center, setting up a MAC protocol for sharing spectrum resources among sub-users (SUs) is an important issue. The MAC protocol in the distributed decryption radio network (DCRN) can be roughly divided into three types: a random access method, a time slotted method, and a hybrid method. Here, the hybrid method is made by taking advantage of random access method and time slot method, and is generally regarded as a more efficient MAC protocol.

However, most of the proposed hybrid MAC protocols have been designed to efficiently share spectrum resources, but they have not been designed to operate with less power in terms of energy efficiency have.

(Academic Publication 001) H. Su and X. Zhang, "Cross-Layer Based Opportunistic MAC Protocols for QoS Provisioning Over Cognitive Radio Wireless Networks," IEEE J. Sel. Areas Commun., Vol. 26, no. 1, pp. 118-129, Jan. 2008.

(Proceedings of the International Conference on Wireless Communications), IEEE Trans., Vol. 2, pp. Wireless Commun., Vol. 10, no. 10, pp. 3414-3425, Oct. 2011.

(Paper No. 003) M. Timmers, S. Pollin, A. Dejonghe, L. Van der Perre, and F. Atthoor, "A Distributed Multichannel MAC Protocol for Multihop Cognitive Radio Network," IEEE Trans. Veh. Tech., Vol. 59, no. 1, pp. 446-459, Jan. 2010.

S. M. Kamaruzzaman and M. A. Hamid, and M. Abdullah-Al-Wadud, "An Energy-efficient MAC Protocol for QoS provisioning in cognitive radio ad hoc networks," Radioengineering, vol. 19, no. 4, pp. 567-578, Dec. 2010.

In order to solve the above problems, the present invention provides a method and apparatus for minimizing a sensing time when using a data channel in a hybrid MAC protocol in a cognitive radio enabled sensor network (CRSN) To maximize the data transmission time, thereby providing a spectral approach to improve energy efficiency and an apparatus therefor.

The present invention also provides an apparatus and method for minimizing the average energy consumption of all users existing in the CRSN.

Further, in the present invention, in a cognitive radio-based sensor network in a multi-channel environment, each subuser (SU) that transmits and receives a control message using a control channel and transmits and receives data using a data channel, And the channel status can be confirmed by using the channel status information.

According to one aspect of the present invention, there is provided a medium access control method in a distributed-type wireless network in a multi-channel environment, wherein a secondary user included in the network, Detecting a state of the selected reporting target channel; detecting a status of the reporting target channel detected by each of the at least one or more sub users by using a control channel included in the network among the sub users; Receiving and reporting information on available channels among the data channels based on the status of the reporting target channel in the reporting step, And a competition step in which

Here, the secondary user has at least two transceivers, and transmits / receives a control signal through the control channel using the control transceiver among the transceivers, and transmits / receives data through the data channel using the data transceiver among the transceivers. And transmits and receives the data.

Here, the detecting step may include detecting a state of the use target channel reserved in the competing step of the previous time slot.

Here, the medium access control method according to the present invention may further include a data transmission step of transmitting data through the use target channel reserved by the sub user.

The data transmission step may include transmitting the data through the use target channel when the use target channel is detected as being usable as a result of detecting the status of the use target channel in the sensing step .

Wherein the detecting step detects the report target channel and the use target channel that are part of the data channels included in the network.

Wherein the detecting step detects the reporting target channel and the use target channel using two minislots included in the time slot, respectively.

Here, the detecting step may be such that the secondary user selects the reporting target channel according to a predetermined rule that each of the secondary users selects a different channel among the data channels as the reporting target channel.

Here, in order to improve the reliability of the detection result, the sensing step may be performed in accordance with a predetermined rule that each data channel is selected as the reporting target channel by the different sub-users for each time slot, And a target channel is selected.

Here, the sensing step may include selecting the reporting target channel using at least one of the number of the data channels existing on the network and the number of the secondary users and the index information of the secondary user .

Here, the detecting step may be characterized in that the secondary user selects the reporting target channel according to the rule of Equation (1).

[Formula 1]

(Where N _pu is the number of the data channel, N _su (t) is the number of the sub-user present in the t-th time slots, mod (a, b) is a module operation for obtaining a remainder obtained by dividing the a to b And I ( t , i ) is an index of the sub-user for selecting the i- th data channel as the reporting target channel in the t- th time slot.

Here, in the detecting step, the sub-user detects whether the main user included in the network is using the reporting target channel, and detects the status of the selected reporting target channel.

In the reporting step, the secondary user transmits a report message including information on the status of the reporting target channel sensed in the sensing step to at least one of the other secondary users through the control channel, And the user can identify the available channel among the data channels based on the received report message.

Wherein, in the reporting step, the sub-user manages and updates an available channel list containing information on the available channels on the network in accordance with the reporting message transmitted from the at least one other sub-user via the control channel .

Wherein in the competing step, the secondary user competes to reserve the channel to be used for transmitting data among the available channels identified in the reporting step, and the secondary user who has obtained priority in the competition And the channel to be used is reserved.

Here, in the competing step, the sub-user who has obtained the priority in the competition reserves the use-target channel, and then performs the competition again among the remaining sub-users, so that each of the sub- .

Herein, the medium access control method according to the present invention is a method of synchronizing time between sub-users included in the network using a beacon message, synchronizing information of the sub-users participating in the network, Step < / RTI >

In the network initialization step, a master user selected by the selected sub-users transmits the beacon message including time information to the other sub-users, and the sub-users receiving the beacon message include the beacon message A time synchronization step of synchronizing the time with the master part user using the time information, and the sub-user participating in the network transmits the participation message to the other sub-users via the control channel, User information synchronization step of transmitting the beacon message including information on the sub-users existing on the network to each of the sub-users in each time slot.

In order to solve the above problems, another type of embodiment of the present invention is a method for performing a medium access control method in combination with sub-user devices included in the network in a distributed-type wireless network in a multi-channel environment, And may be a computer program recorded on a medium.

According to another aspect of the present invention, a secondary user equipment included in a distributed cognitive radio network of a multi-channel environment according to another aspect of the present invention selects a reporting target channel among data channels included in the network, A sensing unit for sensing a state of the reporting target channel; A reporting unit for transmitting the state of the reporting object channel detected by the sensing unit using a control channel included in the network; And a channel reservation unit for reserving a use target channel, which is a channel to be used for data transmission, by using the information about the available channels among the data channels, which is grasped based on the status of the reporting target channel received from another auxiliary user apparatus .

According to the data transmission method in the cognitive radio-based sensor network according to the present invention, the energy efficiency can be improved during the MAC protocol operation in the cognitive radio-based sensor network (CRSN) in a multi-channel environment with limited power supply .

More specifically, according to the present invention, unlike the conventional method in which the time required to detect the state of all the data channels (the number of data channels) X (the detection time per channel (T)) is consumed in the sensing step, There is an advantage in that it requires only a time of 2 X (detection time per channel (T)) in order to check the state.

As described above, according to the present invention, it is possible to reduce power consumption by operating the IDLE mode for a shorter period of time by decreasing the sensing time, and to transmit data in more time slots remaining at the same time.

FIG. 1 is a reference diagram showing the above-described four steps performed in the hybrid MAC protocol.
FIG. 2 is a reference diagram showing the length of relative time required in the sensing, competition, and data transmission steps performed in the data channel.
3 is a flowchart of a medium access control method according to the present invention.
4 is a reference diagram for explaining the operation of the medium access control method according to the present invention with the passage of time.
5 is a reference diagram illustrating an example in which the detection step determines an index of a secondary user to detect each data channel.
6 is a reference diagram showing a power consumption mode or a state in four stages in the data channel.
FIG. 7 is a block diagram of a secondary user equipment included in a distributed cognitive radio network in a multi-channel environment performing a media access control method according to the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same reference numerals are used to designate the same or similar components throughout the drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, the preferred embodiments of the present invention will be described below, but it is needless to say that the technical idea of the present invention is not limited thereto and can be variously modified by those skilled in the art.

The Internet of Things (IoT) environment, in which various objects or objects are connected by a network, can be implemented through a wireless sensor network (WSN). In recent years, it has been used in a variety of specific domain industrial applications such as smart power grids, intelligent transportation systems, structural health monitoring, environmental protection, smart agriculture, and disaster management. Various multi-channel MAC (Medium Access Control) protocols have been proposed to efficiently utilize spectrum resources in such a wireless sensor network. However, as the number of various services and systems using the Internet of objects increases, the number of sensor nodes constituting it will also increase rapidly. Therefore, a network technology that uses a limited spectrum resource while using several networks coexist on the same spectrum resource, for example, the same License Free Spectrum, is required. That is, there is a need to solve the interference problem and the shortage of spectrum resources that can be caused by a plurality of sensor nodes operating in the same spectrum band.

Cognitive Radio Technology (Cognitive Radio Technology) is one of the next generation wireless network technologies to solve the problem of lack of spectrum resources on wireless sensor networks. Dynamic spectrum access (DSA) techniques have been proposed for use of spectrum resources by unauthorized devices, i.e., secondary users, in the applied band to solve the above-mentioned spectrum resource shortage, It is used in cognitive wireless networks to improve the efficiency of spectrum resources. In cognitive wireless networks, it is necessary to develop an efficient and intelligent MAC (medium access control) protocol to control and manage communication on a wireless channel. And the MAC protocol should be able to smartly adapt the characteristics of the cognitive radio network and maintain its performance even in a dynamic environment.

Such a cognitive radio network can be divided into a centralized structure and a distributed structure. The centralized architecture has a central unit, such as a base station (BS), in which the central unit collects information about the wireless environment and manages communication between the sub-users (SUs) within its coverage area do. On the other hand, a distributed structure, that is, distributed cognitive radio networks (DCRNs), can be used for a base station in a cellular network collecting radio environment information or a connection point in a wireless local area network (WLAN) (Peer-to-peer) network between sub-users (SUs) as a cognitive wireless network in which there is no access point (AP). Generally, in a distributed type wireless network, SUs have a function of detecting a channel and performing negotiation for use of the channel.

In the distributed cognitive radio network, the SUs themselves detect the channel and find out whether the main user is using the channels that the primary user (PU) originally uses, and the idle (SU) through an idle channel in an Ad-hoc manner. However, it is difficult to acquire accurate information because it is possible to acquire only a part of information of the entire spectrum due to the range and duration of the channel sensing by the secondary user (SU), hardware constraints, and the like. In order to overcome this problem, sub-users (SUs) in a distributed wireless perceived network exchange information of a partial spectrum sensed by themselves with other sub-users (SUs) (Cooperative Spectrum Sensing) function. At this time, in the distributed wireless perceived network environment, the SUs should organically perform the exchange of the detection result of the main user channel (PU channel), the negotiation and selection of the PU channel to be used, and the time synchronization operation without the central unit . These operations can be performed more efficiently through the Common Control Channel (CCC), which is granted to the SUs or is commonly known by the SUs.

As described above, the cognitive radio enabled sensor network (CRSN) is a system in which unauthorized secondary users (SUs) communicate with each other in an ad hoc manner without a central network unit And may have a structure of Distributed Cognitive Radio Networks (DCRN).

In the DCRN, which does not control the communication between sub-users (SUs) at the center, setting up a MAC protocol for sharing spectrum resources among sub-users (SUs) is an important issue. The MAC protocol in the distributed decryption radio network (DCRN) can be roughly divided into three types: a random access method, a time slotted method, and a hybrid method. Here, the hybrid method is made by taking advantage of random access method and time slot method, and is generally regarded as a more efficient MAC protocol.

However, most of the proposed hybrid MAC protocols have been designed to efficiently share spectrum resources, but they have not been designed to operate with less power in terms of energy efficiency have. In other words, existing hybrid medium access control (MAC) protocol schemes have limitations in terms of energy efficiency.

For example, O-MAC, OMC-MAC, MMAC-CR, and ECRQ-MAC are typical hybrid MAC protocols. The O-MAC protocol scheme is described in "H. Su and X. Zhang," Cross-Layer Based Opportunistic MAC Protocols for QoS Provisioning Over Cognitive Radio Wireless Networks, IEEE J. Sel. Areas Commun., Vol. , pp. 118-129, Jan. 2008. "The OMC-MAC protocol scheme is described in" SC Jha, U. Phuyal, MM Rashid, and VK Bhargava, "Design of OMC- MMAC-CR protocol scheme is described in "M. Timmers, S. Pollin ", " Provisioning for Distributed Cognitive Radio Networks," IEEE Trans. Wireless Commun., Vol. 10, no. 10, pp. 3414-3425, Oct. 2011. & , A. Dejonghe, L. Van der Perre, and F. Atthoor, "A distributed multichannel MAC protocol for multihop cognitive radio network," IEEE Trans. Veh. Tech., Vol. 59, no. 1, pp. 446-459 , Jan. 2010. ", the ECRQ-MAC protocol scheme is described in "SM Kamaruzzaman, and MA Hamid, and M. Abdullah-Al-Wadud," An energy-efficient MAC protocol for QoS provisioning in cognitive radio ad hoc networks, , vol. 19, no. 4, pp. 567-578, Dec. 2010. "

In such hybrid MAC protocol schemes, a main factor for determining the energy consumption is how the SU forms the channel access method including the sensing step, the reporting step, the competing step, and the data transmitting step.

FIG. 1 is a reference diagram showing the above-described four steps performed in the hybrid MAC protocol. Generally, the hybrid MAC protocol divides time into time slots as shown in FIG. 1 after time synchronization to perform the four steps necessary for channel access. First, in the detection phase, the channel state is checked using the spectrum detection function. Next, in the reporting step, one SU (SU) can provide the result detected by the SU to the SUs in its own network. At this time, if the sub-user (SU) uses the regional spectrum sensing method of accessing the channel using only the detection result of the user, the reporting step may be omitted. Next, in the competition step, each sub-user (SU) competes to acquire the usage right of the corresponding time slot based on the available channel information obtained through the sensing step and the reporting step. Finally, in the data transmission step, the data packet is transmitted in the time slot of the reserved channel through the sensing step, the reporting step, and the competition step.

In this case, the smaller the time (resource) allocated to the sensing step, the reporting step, and the competition step in the time slot of a certain length, the more time (resources) that can be allocated to the data transmission step increases and the larger amount of data is transmitted .

FIG. 2 is a reference diagram showing the length (amount) of relative time (resource) required in the sensing, competition, and data transmission steps performed in the data channel. The O-MAC uses an access method using a common control channel, thereby detecting all the data channel states in the detection step for channel reservation, and then reporting the detection result in the control channel. Therefore, additional transceivers are needed to use the control channel. Here, when the number of data channels is N _pu, and the time required for confirming one channel state is T _sens , a total N _pu X T _sens time is required in the sensing step. Based on the detection result, the contention stage is performed in the control channel, and the channels to be used are reserved. On the other hand, MMAC-CR, ECRQ-MAC, and OMC-MAC sequentially perform each step for channel access using only one transceiver. Therefore, N _pu X T _sens takes time as in O-MAC. In the case of the OMC-MAC, the MMAC-CR and the ECRQ-MAC are fixedly allocated for the contention stage, but considering the number of data channels and the number of competing sub-users (SU) It is variable. Therefore, assuming a time slot having a fixed length, the length of the data transmission step is fixed for MMAC-CR and ECRQ-MAC, and OMC-MAC is variable.

Since the O-MAC, MMAC-CR, and ECRQ-MAC schemes are used to allocate resources (time) in the contention stage in consideration of availability of all data channels existing in the network, There is a problem that the remainder excluding the amount of resources (time) used in the competition can be wasted. Therefore, there is a problem in that power is wasted due to the need to operate in the idle mode as much as the remaining resources (time) in the competition stage. In the OMC-MAC scheme, when there is a large number of available data channels, the remaining resources (time) after the competition are used for data transmission. Therefore, it is required to perform data transmission within a channel with a relatively small amount of resources Therefore, data transmission is performed relatively later than when the number of usable data channels is small, so that the system goes into the doze state late and power dissipation may occur.

Conventional hybrid MAC protocol schemes such as O-MAC, MMAC-CR, ECRQ-MAC, and OMC-MAC described above take time of N _pu X T _sens as shown in the sensing step of FIG. There is a limitation that it performs.

The present invention proposes an energy efficient hybrid medium access control method and apparatus for solving the problems of the conventional hybrid medium access control methods described above. To this end, the MAC protocol of the present invention includes a sensing step, a reporting step, a competition step, a data transmission step, and more particularly, to design a sensing step more energy-efficient, We propose an improved method of efficiency.

First, the structure of an apparatus and a system in which the medium access control method according to the present invention operates will be described.

The medium access control method according to the present invention operates on a cognitive radio sensor network (CRSN) in a multi-channel environment. In this case, there are N _pu data channels according to the number of primary users (PUs), and each data channel is allocated and used to the originally authorized main user (PU).

In the medium access control apparatus and method according to the present invention, a common control channel may be used to simultaneously process control signals and data transmission. The common control channel is a channel commonly used for transmitting / receiving a control signal between sub-users (SUs) distinguished from data channels, and can transmit / receive a control signal separately from data transmission / reception by using such a common control channel . In the medium access control apparatus and method according to the present invention, a common control channel access method is applied to more efficiently utilize spectrum resources, so that transmission and reception of control signals and data transmission can be performed simultaneously. At this time, it is preferable that the common control channel is a channel dedicated for use by SUs.

To this end, each subscriber (SU) has at least two transceivers, and can simultaneously process control signals and data transmissions using each transceiver. Where the secondary user (SU) can use each transceiver for one transceiver purpose for the control channel and another one transceiver for the data channels. For example, the secondary user (SU) may have two half-duplex transceivers. With such a configuration, each sub user SU can perform data transmission / reception using a data transceiver and transmit / receive control signals using a control transceiver. In addition, since the SUs can continuously grasp the control signals exchanged between neighboring SUs on the common control channel using the control transceiver, Hidden Terminal Problem) can be more easily solved.

Next, the operation of each step of the medium access control method according to the present invention will be described.

3 is a flowchart of a medium access control method according to the present invention.

As shown in FIG. 3, the method of controlling access to media according to the present invention includes a sensing step (SP) (S100), a reporting step (RP) (S200), and a contention phase (CP) can do. In addition, it may further include a data transfer phase (DTP) (S400) as required, and may further include a network initialization phase (NIP) (S50) as needed.

In the sensing step S100, a sub-user (SU) included in the network selects a reporting target channel among the data channels included in the network in a distributed-type wireless network in a multi-channel environment, Lt; / RTI >

The reporting step S200 transmits and receives the states of the reporting target channels detected by at least one or more of the sub users SU using the control channel included in the network between the sub users SU. Here, in step S200, the secondary user SU transmits a report message including information on the status of the reporting target channel sensed in the sensing step S100 to at least one of the other secondary users SU), and each of the secondary users (SU) can grasp a usable channel among the data channels based on the received report message.

In the competing step S300, the information about the usable channel among the data channels, which is grasped based on the status of the reporting target channel in the reporting step S200, To-be-used channel. In the competing step S300, the secondary user (SU) competes to reserve the channel to be used for transmitting data among the available channels identified in the reporting step S200, And the acquired sub-user (SU) reserves the use target channel.

Here, the detecting step S100 may include detecting the state of the use target channel reserved in the competing step S300 of the previous time slot. Here, the sensing step S100 may detect the reporting target channel and the target channel, which are a part of the data channels included in the network, and use the two minislots included in the time slot to detect the reporting target channel And the use target channel, respectively.

The data transfer step (S400) transmits data through the use target channel reserved by the secondary user (SU). If it is detected that the use target channel is available as a result of detecting the status of the use target channel in the sensing step S100, data can be transmitted through the used target channel.

The network initialization step (S50) synchronizes time between the sub-users (SU) included in the network using a beacon message, and performs initialization by sharing information of the sub-users (SU) participating in the network.

Hereinafter, a medium access control method according to the present invention will be described in detail.

4 is a reference diagram for explaining the operation of the medium access control method according to the present invention with the passage of time.

Hereinafter, each step of the medium access control method according to the present invention will be described in more detail with reference to FIG. 3 and FIG.

Referring to FIG. 4, the time axis on which the media access control method according to the present invention operates is divided into a plurality of periodic time slots having a predetermined length. Where each time slot may all have the same predetermined length. As shown in FIG. 4, the data channel and the control channel can be periodically divided into time slots having the same time length of Ts.

Here, the time slot may be further divided into a plurality of mini-slots having a predetermined length. Referring to FIG. 4, partial slots that distinguish one time slot, such as CFR and CFU shown in the data channel and B, J, 1, 2, ..., M shown in the control channel, )to be. Here, the number of minislots in one time slot can be set according to the number of data channels and the number of sub users (SU) existing in the network. For example, as shown in FIG. 4, the number of minislots included in the reporting step (S200) and the contention step (S300) may be a predetermined number (M). And where M can be greater than or equal to N _pu . Here, the length of one minislot is set so that the length of time for allowing the secondary user (SU) to check the status of the data channel within the time allocated to the minislot, or to exchange control messages for network participation or channel contention Can be set. Wherein the length of each mini-slot is referred to as T _ms.

In the network initialization step (S50), synchronization between the channels can be performed through the control channel when the time slot starts. For this purpose, the time slot of the control channel and the time slot of the data channel may be synchronized via a beacon message. Where the beacon message may be broadcast at the start of each time slot through the control channel.

The network initialization phase (NIP) (S50) synchronizes the time of sub-users (SUs) participating in the network. For this purpose, a Master Secondary Unit (MSU) and a Normal Secondary Unit (NSU) may be selected from SUs.

Here, the master sub user (MSU) can be selected as follows. First, the first SU participating in the network attempts to receive a beacon message. If the beacon message is not received for a predetermined time, the SU can determine that the SU is the first SU participating in the network and set the MS as the MSU. A secondary user set as the master subscriber (MSU) may periodically transmit a beacon message including time information such as a time stamp on the network. On the other hand, if the first SU participating in the network receives a beacon message for a predetermined time, it can set the NSU as a general user. And synchronize the time with the MSU using the time information included in the beacon message.

Here, if the master subscriber unit (MSU) disappears on the network, the subscriber unit can be selected and set as the master subscriber unit (MSU) according to predetermined rules among the NSUs. For this, if a beacon message is not received for a predetermined time, each sub-user (SU) recognizes that the master sub-user (MSU) is absent and, according to a predetermined rule, (MSU) can be selected. For example, a sub-user (SU) having the largest or smallest index of the sub-user (SU) is selected, or a sub-user (SU) is selected according to a predetermined rule regarding the index, can do.

Here, the master subscriber unit (MSU) transmits a beacon message at the beginning of each time slot. At this time, the beacon message can be transmitted through the control channel. This operation can be performed in the 'B' minislot as shown in FIG.

After the synchronization process described above, a sub-user (SU) participating in the network can transmit a join message through a control channel. This operation can be performed in the 'J' minislot as shown in FIG. In response to the participation message transmitted by the participating secondary user (SU), the master subscriber unit (MSU) can transmit the beacon message through the control channel. Here, the beacon message transmitted by the master subscriber unit (MSU) may include the number of sub users (SU) present on the network and the index and MAC address of the subscriber (SU) in each time slot. Therefore, when a new sub-user (SU) participates in a network, a beacon message to which an index of a sub-user (SU) is newly added is transmitted, so that each sub-user (SU) can grasp the participation of a new sub- It is possible to update the secondary user identifier list (SIT). Here, the index of the secondary user (SU) is an identifier for identifying a plurality of secondary users (SU) existing on the network, and can be allocated for each secondary user (SU) according to a predetermined rule. For example, the indexes of the secondary users (SU) may be assigned in the order in which they participate in the network, or they may be assigned according to various rules such as being given randomly within a certain range, Here, we do not limit the method of assigning indices to specific rules.

For example, the fields included in the beacon message may be (<MAC addr>, <SU index>), (<Nsu (t)>). Here, < MAC addr > is a field indicating a MAC address of a sub user (SU), < SU index > is a field indicating an index of a sub user Is a field indicating the number Nsu (t) of sub-users (SUs) present.

On the other hand, the secondary user can compete to participate in the network before joining the network after the synchronization process described above, and the secondary user who has won the competition can participate in the network. Here, the competition may use a backoff mechanism such as IEEE 802.11 DCF.

In the network initialization step S50, a master subscriber MSU selected among the SUs transmits the beacon message including time information to the other SUs, and transmits the beacon message A time synchronization step of synchronizing the time with the MSU using the time information included in the beacon message; and a time synchronization step of synchronizing the sub- (SUs) through a control channel, and wherein the master subscriber unit (MSU) includes information about the SUs existing on the network in each time slot And a secondary user information synchronization step of transmitting the beacon message to the other SUs.

Next, in the sensing step S100, each sub user SU senses a channel determined according to a predetermined rule for a predetermined time. Here, the channel to be detected is a channel belonging to a data channel existing on the network. Here, the secondary user (SU) detects whether the determined channel is in use or not, and can use the data transceiver to check whether another user is using the corresponding data channel. Wherein the amount of time that the duration detection step (S100) on the time slots are referred to as T _sp.

At this time, the sub-user (SU) can sense the CFR (Channel For Report) in the sensing step S100. Here, the report target channel is a channel to which a secondary user (SU) detects a state and reports the state detected in the next reporting step (S200). Also, in the sensing step S100, the secondary user (SU) can detect the CFU (Channel For Use). Here, the target channel is a channel to be reserved and used by the secondary user (SU).

In order to detect the reporting target channel and the target channel, the sensing step S100 may use two minislots allocated for sensing each channel. The number of minislots used in the sensing step S100 is preferably as small as possible. This is because the smaller the number of minislots allocated to the sensing step S100 is, the shorter the duration of the sensing step S100 is, and thus the length of time that can be allocated for data transmission within the same length of time slot increases It is because.

As described above, the sensing step S100 according to the present invention can detect only the two channels, unlike the conventional methods in which all the N _pu data channels existing in the network are detected. For example, in the sensing step S100, each sub-user (SU) determines whether the state of the reporting target channel CFR and the use target channel CFU is, for example, idle state (IDLE) or in use state (BUSY) Can be detected. Through the above configuration, the medium access control method according to the present invention can allocate more time resources to the data transmission step (S400).

Next, the operation of determining the report target channel (CFR) to be sensed by each sub-user (SU) in the sensing step (S100) will be described. As will be described below, each sub-user (SU) selects a report target channel (CFR) among the data channels on the network according to a predetermined rule and detects it.

Here, each sub-user (SU) can select one of the data channels on the network according to a predetermined rule and detect it as a report target channel (CFR). Here, the predetermined rule may be a rule determined between the sub-users (SU) to select one of the data channels on the network as a target channel. In this case, since the SUs existing in the network have different conditions locally, in order to improve the reliability of the detection result, the sensing step S100 is performed for each data channel in each time slot, It is preferable that the data channel to be sensed by each secondary user (SU) is selected so that the secondary user (SU) performs detection.

For this, the detection step S100 may select a specific data channel using at least one of the number of data channels existing on the network and the number of sub users (SU) and the index information of the sub user (SU) .

At this time, the rules for determining the CFR can be expressed by the following equations (1) and (2).

Where mod (a, b) is a module operation that obtains the remainder of dividing a by b.

Here, I ( t , i ) represents an index of a sub-user (SU) that selects the i- th channel as a reporting target channel (CFR) in the t- th time slot and detects the status of the corresponding channel. In other words, the secondary user (SU) having the I ( t , i ) index selects and detects the i-th channel of the data channel as the target channel in the t-th time slot.

Equation (1) can be used for a case where the number of sub users (SU) is larger than the number of data channels ( N _su ( t ) ≥ N _pu ) Can be used for a small number ( N _su ( t ) < N _pu ).

FIG. 5 is a flow chart illustrating an operation of detecting an index I ( t , I ) of a secondary user (SU) to detect an i-th data channel in two cases in which the number of sub- Fig.

5 (a), when the number N (su) of sub users ( N _su ( t )) is larger than the number of data channels ( N _pu ) as shown in FIG. 5 It is desirable that each time a different secondary user (SU) performs the detection.

In Figure 5 (b), if the number of users (SU) unit than the number of data channel is small as _{(N su (t) <N} pu), (N pu - N su (t)) the remaining data other than the data channel Sub-users (SUs) can perform detection on the channel. This is because the number of data channels that can be sensed by the secondary user (SU) is one, and one secondary user (SU) is allocated such that data can be transmitted using one available data channel.

In the sensing step S100, each sub user SU selects a report target channel and then performs detection on the selected report target channel.

In the sensing step S100, each sub-user (SU) may use an energy sensing mechanism, for example, used in a conventional cognitive radio network, to sense the data channel. For example, the operation of the energy sensing mechanism is introduced in "Optimal spectrum sensing framework for cognitive radio networks, Won-Yeol Lee and Akyildiz, IF, Wireless Communications, IEEE Transactions on Vol. 7, . Herein, each sub-user (SU) can detect whether or not each data channel is used by the corresponding main user.

According to the detection result, whether or not the i-th data channel (1? I? N _pu ) in the t-th time slot is occupied or used by the main user can be expressed by Equation (3).

As described above, in the sensing step S100, the SUs select different data channels and select the target data channel (CFR) for sensing. Thus, the medium access control method according to the present invention includes a plurality of sub users SU Can solve the collision problem occurring in the process of sensing and reporting the same channel, for example, the collision problem occurring in the conventional hybrid MAC protocol method such as O-MAC.

Also, in the sensing step S100, the SUs perform detection on only the selected channel according to a predetermined rule, rather than performing detection on all data channels, so that the medium access control method according to the present invention It has the advantage of shortening and saving the time and power consumed in detecting and reporting a plurality of channels.

Next, an operation of sensing the CFU in the sensing step S100 will be described.

Here, the use target channel CFU detected by the sensing step S100 is a channel reserved for use by the secondary user SU in the competition step S300 of the previous time slot. For example, detection is performed in the sensing step S100 of the (t + 1) th time slot for the use target channel CFU reserved in the competing step S300 of the t time slot.

In this manner, a channel reserved in the use target channel CFU in the previous t time slot is detected in the sensing step S100 of the (t + 1) time slot. If the channel is detected as usable at this time, (SU) that is reserved with the CFU transmits the data through the use target channel CFU in the data transmission step S400 of the (t + 1) th time slot.

However, if it is detected that the reserved channel is not available as a result of detecting the reserved channel in the previous t time slot in the use target channel CFU in the sensing step S100 of the (t + 1) It does not transmit data in the data transmission step (S400). In this case, the secondary user SU may compete for channel reservation again in the competing step S300 of the (t + 1) time slot.

In the reporting step S200, each sub-user SU reports the report target channel CFR detected in the sensing step S100 to the other sub-users SU. To this end, each sub-user (SU) can report information about the detected target channel by transmitting to the other sub-users (SU) using the common control channel.

To this end, the secondary user (SU) can transmit the report message through the control channel in the reporting step (S200). Herein, the report message may include information on an index of a secondary user (SU), a report target channel, and a status of a report target channel. For example, the reporting message may include fields such as (<SU index>, <CFR>, <Result>). Here, < SU index >, < CFR >, and < Result > are fields indicating the index of the secondary user (SU), the report target channel, and the report target channel. Here, the < Result > field may have 0 (idle) or 1 (busy) as in Equation (1).

In the reporting step S200, the detection result of the secondary user (SU) for the reporting target channel allocated to the corresponding minislot in each minislot may be transmitted in the form of the reporting message in the control channel. For example, in the i-th minislot, a secondary user (SU) detecting the i-th reporting target channel may transmit the detection result in the form of the reporting message in the control channel.

In step S200, each sub-user (SU) can generate an available channel list (ACL). Here, each sub-user (SU) can generate and manage an available channel list containing available information of data channels on the network using information received from other sub-users (SU) through the control channel. In the competition step S300 described below, a competition for reserving a channel between sub-users (SUs) using the available channel list can be performed.

In this manner, in the sensing step S100, each sub-user SU senses the CFR of the user's own report channel, reports the sensing result, and uses the cooperative spectrum sensing in a manner of sharing in step S200 Accordingly, in the sensing step S100, it is possible to reduce the sensing time by sensing only two channels, and at the same time, a plurality of sub users (SUs) (CFR) can be grasped.

In the competing step S300, each sub-user (SU) competes to reserve a CFU to be used for transmitting data among the usable channels identified in the reporting step S200. As described above, each sub-user (SU) updates and manages the available channel list using the information transmitted in the reporting step (S200). And the secondary users (SU) are reported in an idle state in the available channel list and compete to reserve available channels.

In the competing step (S300), a sub-user (SU) that has obtained a priority in the competition among the sub-users (SU), that has won the competition, can select the use target channel (CFU) among the available channel lists. The sub-user (SU) that has won the competition can transmit the selected target channel (CFU) information to another sub-user (SU) to receive or receive data from each other. Here, the secondary user (SU) having received the use target channel information can transmit a response thereto to the secondary user (SU) who has won the competition. Here, the SU (Subscriber) having received the use target channel information checks whether or not the use target channel received from the available channel list managed by the user is available, and if the available channel is available, SU). Here, it is possible to transmit a signal indicating the same use target channel as the received signal, for example, as the acceptance signal. Preferably, the sub-user (SU) that has won the competition can transmit the above-mentioned target channel (CFU) information in the RTS message and transmit the response to the sub-user (SU) Message and transmit it.

Here, in the competing step S300, the signals transmitted and received by the SUs may be transmitted through the control channel.

When the acceptance signal is transmitted and received between the sub user (SU) that has won the competition and the sub user (SU) that receives the use target channel information, the corresponding target channel is a sub user (SU) May be reserved for use between sub-users (SU) that receive the channel information to be used. The remaining sub-users (SU) can grasp the reservation result of the use target channel through the control channel. Then, the target channel can be deleted from the available channel list accordingly.

The secondary users SU can perform the above-described competition process based on the newly updated available channel list, and can reserve the used channel CFU for each of the available users SU for the remaining available channels.

At this time, a variety of existing competitive schemes can be used for a scheme in which an idle channel is competing for reservation by one of a plurality of sub users (SU). For example, the contention scheme can use a scheme in which a secondary user (SU) occupies a specific channel by exchanging a backoff time, a request to send (RTS), and a clear to send (CTS) . Herein, the competition step (S300) A distributed coordination function (DCF) method of 802.11 can be used.

In the case where the channel reserved in the use target channel CFU through the above process is detected in the detection step S100 of the next time slot and is detected as the usable state, in the data transmission step S400, And a sub user (SU) reserved on the channel (CFU) transmits the data using it.

However, if it is detected that the channel is not available as a result of sensing a channel reserved for the use target channel (CFU) in the next time slot sensing step S100, the sub-user (SU) S400). In this case, the secondary user (SU) can compete for channel reservation again in the contention stage (S300).

In the data transmission step (S400), the secondary user (SU) can transmit data using the use target channel (CFU) according to the detection result of the sensing step (S100) for the use target channel (CFU). That is, if it is detected that the channel reserved by the use target channel is usable as a result of sensing in the sensing step S100, data can be transmitted using the channel. The usable state here can be an idle state.

As described above, in the medium access control method according to the present invention, when the state of the report target channel (CFR) sensed by the respective sub users (SU) in the sensing step S100 is confirmed, in the reporting step S200, (SU) cooperatively share the information of the CRF. Therefore, unlike the conventional hybrid MAC schemes, when it is required to check the status of all the data channels, it takes a time of (data channel number ( N _pu )) X (detection time per channel) in the sensing step S100 The medium access control method according to the present invention is only 2 X (detection time per channel) Lt; RTI ID = 0.0 &gt; S100. &Lt; / RTI &gt; Here, the detection time per channel may be the minislot length ( T _ms ) described above. Therefore, power consumption can be reduced by shortening the time for performing the sensing step S100. As described below, the sensing step S100 operates in the idle mode during the power consumption mode, and the power consumption can be reduced by shortening the time for operating in the idle mode.

Also, according to the medium access control method of the present invention, since the detection time can be minimized and the remaining time of the time slot can be allocated to the time ( T _DTP ) of the data transmission step S400, ) Can enter the doze state to minimize power consumption.

Also, according to the medium access control method of the present invention, since the reporting step (S200) and the competing step (S300) are performed using the control channel, a waste of power used for sharing the channel state information and reserving the channel in each data channel There is an effect that can be minimized.

Therefore, according to the data transmission method in the cognitive radio-based sensor network according to the present invention, the energy efficiency can be improved in the MAC protocol operation in the cognitive radio-based sensor network (CRSN) have.

Another embodiment of the present invention relates to a method for controlling a medium access control method in a distributed cognitive radio network in a multi-channel environment, It can be a program.

Yet another embodiment of the present invention can be a secondary user equipment included in a distributed cognitive radio network operating in a multi-channel environment operating according to the medium access control method according to the present invention described above.

FIG. 7 is a block diagram of a secondary user equipment included in a distributed cognitive radio network in a multi-channel environment performing a media access control method according to the present invention.

Referring to FIG. 7, a secondary user device 10 according to the present invention includes a sensing unit 100 for selecting a reporting target channel among data channels included in the network and sensing a state of the selected reporting target channel; A reporting unit (200) for transmitting the state of the reporting object channel sensed by the sensing unit using a control channel included in the network; And a channel reservation unit 300 for reserving a channel to be used, which is a channel to be used for data transmission, using the information on the available channels among the data channels that are grasped based on the status of the reporting target channel received from the other auxiliary user equipment ).

Here, the sensing unit 100 may perform the same operation as the operation of the sensing step S100 described in the medium access control method according to the present invention, .

In addition, the reporting unit 200 may include an operation of the reporting step S200 described in the medium access control method according to the present invention, and the operation of transmitting the state of the reporting target channel using the control channel The same operation can be performed.

In addition, the channel reservation unit 300 may perform operations corresponding to the reservation of the channel to be used, including the operation of the contention step S300 described in the medium access control method according to the present invention.

Herein, the secondary user can operate according to the medium access control method according to the present invention. Therefore, redundant description will be omitted.

Hereinafter, the medium access control method according to the present invention and the energy efficiency of the apparatus are mathematically verified.

6 is a reference diagram showing a power consumption mode or a state in each of the four stages in the data channel.

Here, since the spectrum sensing function is performed in the sensing step S100, the idle mode is operated during the power consumption mode. Next, the reporting step S200 operates in a transmit mode when transmitting channel state information and in a receive mode when receiving the channel state information. Next, the contention step S300 is a transmission mode when transmitting a control message and a receive mode when a control message is received, because the channel is reserved using RTS / CTS exchange in all hybrid MAC protocols . Finally, in the data transmission step S400, the device transmitting the data packet operates in the transmit mode, the device receiving the data packet operates in the receive mode, and the neighboring devices ), It enters the doze state because it knows that it does not need to transmit and receive data packets in the competing step (S300).

First, in order to evaluate the energy efficiency of the medium access control method according to the present invention, it is possible to measure the network lifetime, which is the time required for the initial allocated energy to decrease. In the case of the cognitive radio based MAC protocol, a resource (time) for performing detection of data channels must be allocated, and the overall performance of the network can be determined according to the detection result.

Power consumption is divided into transmit, receive, idle mode and doze state as mentioned above.

Since the power consumption in the sensing step S100 operates in the idle mode, the average joule power consumption is expressed by Equation (4).

Where e _idle represents the power consumption in watts per idle mode. Therefore, in the spectrum sensing technology, the length of T _SP is the key to power consumption. Therefore, according to the medium access control method of the present invention, as compared with the conventional hybrid MAC protocol methods, it is possible to reduce the length of time T _SP required in the sensing step S100, thereby reducing the power consumption and improving the energy efficiency It is effective.

In the contention phase (S300), all of the mobile stations operate in a receive mode except for transmitting control messages. Sub users (SUs) are classified into senders, receivers, and neighbors according to their roles, and the average power consumption per row is expressed by Equation (5).

Where e _tx and e _rx represent the power consumption in watts of the transmit and receive modes, respectively. T _RTS and T _CTS represent the time required to transmit RTS and CTS messages in the network. And T _RTS represents the time length of the contention step S300. Competing neighbors operate in receive mode to overhear the exchange of control messages between senders and receivers.

Accordingly, the line unit average power consumption in the competition step S300 is expressed by Equation (6).

Where 2 · N _avg is the number of N _avg senders and corresponding receivers in the data channel competition.

In the data transmission step S400, it is assumed that there is no acknowledgment message at the time of data transmission for convenience of calculation. In the data transmission step S400 according to the role assigned to the sub users SU Is expressed by Equation (7). &Quot; (7) &quot;

Where e _doze represents the doze state power consumption in watts. Here, T _DTP represents the time length of the data transmission step (S400). Here, the neighbors that do not receive the data packet enter the doze state. This can solve the power dissipation problem due to unnecessary idle listening.

Therefore, the average power consumption per line in the data transmission step S400 is expressed by Equation (8).

Finally, the same as when the initial amount of power in watts (E _init) is given, the following equation 9, network lifetime (T _life).

It is to be understood that the present invention is not limited to these embodiments, and all elements constituting the embodiment of the present invention described above are described as being combined or operated in one operation. 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 an embodiment of the present invention. As the recording medium of the computer program, a magnetic recording medium, an optical recording medium, a carrier wave medium, and the like can be included.

Furthermore, all terms including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined in the Detailed Description. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

It will be apparent to those skilled in the art that various modifications, substitutions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. will be. Therefore, the embodiments disclosed in the present invention and the accompanying drawings are intended to illustrate and not to limit the technical spirit of the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments and the accompanying drawings . 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.

S50: Network initialization phase
S100: Detection step
S200: Reporting step
S300: Competitive stage
S400: Data transfer step

Claims (20)

A medium access control method comprising:
In a distributed cognitive radio network in a multi-channel environment, at least one or more sub-users included in the network may transmit different channels among data channels included in the network, at least one of the number of data channels and the number of sub- Wherein the reporting target channel is selected for each time slot having a predetermined length and each reporting target channel is different from the reporting target channel using index information of the secondary user, A sensing step of sensing a use target channel as a target channel and a data transmission channel, respectively;
A reporting step of transmitting and receiving the state of the reporting object channel detected by at least one or more of the secondary users using the control channel included in the network among the secondary users; And
And a competition step of reserving the use target channel, which is a channel to be used by the secondary user for data transmission, using the information about the available channel among the data channels, which is grasped based on the status of the reporting target channel in the reporting step / RTI &gt; The method according to claim 1,
Wherein the secondary user has at least two transceivers and transmits and receives control signals through the control channel using the control transceiver among the transceivers and transmits and receives data through the data channel using the data transceiver among the transceivers To the medium access control method. The method according to claim 1,
Wherein the sensing step comprises sensing a state of the use target channel reserved in the contention step of the previous time slot. The method of claim 3,
Further comprising a data transmission step of transmitting data through the use target channel reserved by the secondary user. 5. The method of claim 4,
Wherein the data transmission step transmits data through the use target channel when the use target channel is detected as a usable channel as a result of detecting the status of the use target channel in the sensing step. Access control method. delete The method according to claim 1,
Wherein the sensing step detects each of the reporting target channel and the use target channel using two minislots included in the time slot. delete delete The method according to claim 1,
When the number of the sub-users existing in the t-th time slot is equal to or greater than the number of the data channels, the number of the data channels, the number of the sub- Selects the reporting target channel using a value obtained by calculating the index information of the user,
If the number of sub-users existing in the t-th time slot is smaller than the number of data channels, the report target channel is selected using a value obtained by calculating the number of data channels and index information of the sub-user Lt; / RTI &gt; 11. The method of claim 10,
Wherein the index of the secondary user is determined according to the following equation (1).
[Formula 1]

Mod (a, b) is a module operation for obtaining a remainder obtained by dividing a by b, where _Npu is the number of data channels, _Nsu ( t ) is the number of sub- And I ( t , i ) is an index of the sub-user for selecting the i- th data channel as the reporting target channel in the t- th time slot. 12. A method according to any one of claims 7, 10 and 11,
Wherein the secondary user senses whether the main user included in the network is using the reporting target channel and detects the status of the selected reporting target channel in the sensing step. The method according to claim 1, wherein, in the reporting step,
Wherein the secondary user transmits a report message including information on the status of the reporting target channel sensed in the sensing step to at least one of the other secondary users via the control channel,
Wherein each of the sub-users grasps the available channel among the data channels based on the received report message. 14. The method of claim 13,
In the reporting step, the sub-user manages and updates an available channel list containing information on the available channels on the network according to the reporting message transmitted from the at least one other sub-user via the control channel Lt; / RTI &gt; 14. The method of claim 13,
Wherein the secondary user competes to reserve the channel to be used for transmitting data among the available channels identified in the reporting step,
And the sub-user obtaining the priority in the competition reserves the use target channel. 16. The method of claim 15,
After the sub-user having obtained the priority in the competition reserves the use target channel,
And the contention is re-performed between the remaining sub-users, and each of the sub-users reserves the use target channel. The method according to claim 1,
Further comprising a network initialization step of synchronizing time between the sub-users included in the network using a beacon message and performing initialization by synchronizing information of the sub-users participating in the network, Way. 18. The method of claim 17,
Wherein the master user selected by the master user transmits the beacon message including time information to the other sub users and the sub users receiving the beacon message use the time information included in the beacon message A time synchronization step of synchronizing time with the master part user; And
Wherein the sub-user participating in the network transmits the participation message to the other sub-users via the control channel, and the master sub-user includes information about the sub-users existing on the network in each time slot And transmitting the beacon message to the other sub-users. delete delete

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