KR101483732B1 - Media access control method in distributed cognitive radio networks - Google Patents

Abstract

The present invention relates to a method for controlling medium access in a distributed cognitive radio network, which can prevent the collision of control messages. According to the present invention, the method comprises: a step in which a mini-slot is assigned to each secondary user through a common control channel; a step in which each secondary user detects a data channel corresponding to the assigned mini-slot among a plurality of data channels, and reports a result of the data channel detection through the common control channel at the assigned mini-slot; and a step in which at least a part of the secondary users performs a negotiation on the usage of the data channel using the assigned mini-slot through the common control channel, if a predetermined event is generated.

Description

[0001] MEDIA ACCESS CONTROL METHOD IN DISTRIBUTED COGNITIVE RADIO NETWORKS [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a distributed cognitive radio network, and more particularly, to a medium access control method in a distributed cognitive radio network.

Currently, wireless networks are suffering from lack of spectrum resources due to the development of wireless communication technology and the increasing demand of new application services. To address this resource shortage, the Federal Communications Commission (FCC) has recently approved the use of unauthorized devices (SUs, secondary users) in the licensed band. As a result, a dynamic spectrum access (DSA) technique has been proposed to solve this spectral inefficiency problem. This new area of research has improved the efficiency of spectrum resources by developing cognitive radio (CR) networks.

In order to facilitate control and management of communication on a wireless channel in any CR network, it is necessary to develop an efficient and intelligent MAC (medium access control) protocol. Therefore, the MAC protocol should be capable of smartly adapting the characteristics of a CR network and maintaining performance in a very dynamic environment.

A CR network is generally divided into a centralized structure and a distributed structure. A centralized structure has a central unit, such as a base station (BS), which collects information about the wireless environment and manages communications between the sub-users in its coverage area.

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) AP, access point), and forms a peer-to-peer (P2P) network between the sub-users. Generally, in a distributed type wireless network, the sub users have a function of detecting a channel and performing a negotiation for using a data channel.

The present invention provides a medium access control method capable of simultaneously using a data channel and a control channel in a distributed cognitive radio network and solving a multi-channel hidden terminal problem (MHTP) There is.

The present invention also provides a medium access control method capable of preventing collision of control messages transmitted in a process of reporting a detection result of a data channel between sub-users in a distributed type or wireless network or performing negotiation for use of a data channel There is.

According to another aspect of the present invention, there is provided a method of controlling access to a medium in a distributed cognitive radio network, comprising: allocating a minislot to each of sub-users through a common control channel; Each of the secondary users senses a data channel corresponding to a minislot assigned to itself among a plurality of data channels and reports a detection result of the data channel in a minislot allocated to the secondary channel through the common control channel ; And performing negotiation for use of the data channel by using at least a part of the sub-users through the common control channel, when a predetermined event occurs, using the minislot assigned to the sub-user.

One time slot of the common control channel may include a reporting interval for the reporting step and a negotiation interval for performing the negotiation.

The reporting step may report the detection result of the data channel in a minislot included in the reporting period.

The negotiating step may perform the negotiation using a minislot included in the negotiation interval.

The step of allocating the minislot may include allocating a minislot to a sub-user requesting participation of the coordinator, which is one of the sub-users, in the network, transmitting a beacon message including mini- Can be transmitted.

The sub-user who wants to join the network can transmit a join request message including his or her ID in response to the beacon message.

Wherein the detection result is one of a busy state and an idle state and the medium access control method further includes the step of determining the state of each data channel using the detection results reported from the secondary users can do.

Determining the state of a data channel in the determining step may be determined according to the ratio of the busy state or the idle state among at least one detection result reported for the data channel.

The negotiating step may include transmitting a request to send (RTS) packet to a destination user in a minislot allocated to the source user, and transmitting the RTS to the destination user in response to the RTS packet. A clear to send (CTS) packet is transmitted from the slot to the source user.

In the negotiation, the source user transmits the RTS packet including the available channel list identified through the reporting step, and the destination user includes any one of the available channels in the available channel list And transmit the CTS packet.

If the same data channel is reserved for use by a plurality of sub-users as a result of the negotiation, the plurality of sub-users may transmit data through the reserved data channel in a round-robin manner.

The secondary users may have a secondary user table including an ID of the secondary users participating in the network and an index of a minislot allocated to each secondary user.

The secondary users may have an available channel list including status information of each of the plurality of data channels.

According to the medium access control method of the present invention, the data channel and the control channel can be simultaneously used and the multi-channel hidden terminal problem (MHTP) can be solved.

In addition, it is possible to prevent collision of the control messages transmitted during the process of reporting the detection result of the data channel between the secondary users or performing the negotiation for using the data channel.

1 shows a time structure for a medium access control method according to an embodiment of the present invention.
FIG. 2 shows an example of a data channel index and a channel status to be detected by a sub-user assigned a minislot according to an embodiment of the present invention.
FIG. 3 illustrates a process of exchanging an RTS packet and a CTS packet through a minislot allocated between sub-users according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description and the accompanying drawings, substantially the same components are denoted by the same reference numerals, and redundant description will be omitted. 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 embodiments of the present invention, each sub-user is equipped with two half-duplex transceivers. One transceiver is a control transceiver and operates on a dedicated common control channel (CCC). Each sub-user uses the control transceiver to perform the following setup, reporting, and negotiation steps on the common control channel. The other transceiver is a data transceiver and is channel adjustable to operate on any one of a plurality of (N) data channels. Each sub-user performs spectral sensing using a data transceiver and transmits data through the data channel.

<Time structure>

1 shows a time structure for a medium access control method according to an embodiment of the present invention.

Referring to FIG. 1, the time axis is divided into periodic time slots. The common control channel and data channel are all has time slots of equal length T _s, time slot of the common control channel and the data channel are tailored, the time synchronization.

One time slot on the common control channel is composed of a Configuration Period (CP), a Reporting Period (RP), and a Negotiation Period (NP) And an interval for performing the negotiation step. The lengths of the setting interval, the reporting interval, and the negotiation interval are T _cp , T _rp , and T _np, respectively.

One time slot is composed of several minislots. The setting interval is two minislots of a beaconing slot (B) and a signaling slot (S). The reporting interval and negotiation interval are M minislots (0, 1, ..., M-1). The length of the minislot is T _ms , which is sufficient to transmit the control message over one minislot in the common control channel, and is set to a time sufficient to sense one data channel. The length of one time slot can be expressed by the following equation.

In data channels, a sensing period (SP) for sensing a data channel is assigned a minislot of length T _ms and is located after a beaconing slot of a reporting interval on the common control channel. Therefore, the secondary user can transmit data for the time corresponding to 2M minislots through the data channel.

<Setting step>

In the embodiment of the present invention, the setting step is a step in which a minislot is allocated to each of the secondary users through the common control channel. As described above, the setting period for the setting step is composed of a beacon slot and a signal slot. The secondary users select the coordinator to allocate the minislot to the secondary users using the beacon slot, synchronize their time with each other, and perform the participation function to the network using the signal slot.

In the embodiment of the present invention, the coordinator, which is one of the minor users, allocates a minislot to the sub-user requesting participation in the network and transmits a beacon message including the minislot allocation information in the beacon slot on the common control channel .

The secondary user who wants to join the network first receives the beacon message in the beacon slot on the common control channel and synchronizes with the rest of the users in the network. If the beacon message is not received for T _s time, the negative user decides to be the coordinator and begins to periodically transmit the beacon message to T _s . If a beacon message is received within T _s time, the secondary user sends a join request message through the signaling slot on the common control channel in response to the beacon message. This join request message includes the ID of the corresponding sub-user. In transmitting the join request message, for example, a p-persistent CSMA technique may be used to minimize the collision probability with other sub-users.

Upon receiving the join request message, the coordinator adds the ID of the requested minor user to the list, and assigns a different minislot to each requested minor user. To this end, the coordinator allocates different minislot indices for each requested subuser. Then, the coordinator transmits the beacon message including the ID of the minor user and the minislot index through the next beacon slot. When the beacon message is received, the secondary users are synchronized in time. The secondary user IDs included in the beacon message and the assigned minislot indexes are used to identify the subscribers participating in the network, And stores a sub-user table (SU table, SUT). That is, the secondary user table includes a secondary user ID and a corresponding minislot index, and may be updated when a beacon message is received. Since the beacon message is transmitted to all of the subscribers participating in the network, all the subscribers in the network maintain the same sub-user table. Further, each sub-user determines a data channel to be sensed among a plurality of data channels using the minislot index allocated to the sub-user. If an m &lt; th &gt; minislot is assigned to a sub-user, the index A (m) of the data channel to be sensed can be determined according to the following equation.

Here, u denotes the number of sub-users in the network, M denotes the number of minislots, and N denotes the number of data channels.

If the beacon message does not include the sub-user ID and the minislot index, it is possible to consider that there is no sub-user desiring to join the network, or that a collision has occurred in the beacon message.

<Reporting step>

In the embodiment of the present invention, the reporting step is a step for allowing the secondary users to know the state of all the data channels, and each of the secondary users detects the data channel corresponding to the minislot allocated to the secondary users among the plurality of data channels And reports the detection result of the data channel in the minislot allocated to itself through the common control channel. In the embodiment of the present invention, it is assumed that each sub-user can detect one data channel during a given sensing period due to hardware restriction. Therefore, each sub-user detects the data channel corresponding to the corresponding minislot according to Equation (2) using the minislot index allocated to the sub-user, Overlapping.

Since the secondary user can sense one data channel during the sensing period, the secondary user alone has a limitation in knowing the state of all the data channels. In this case, cooperative sensing techniques are essential. As described above, the reporting interval for the reporting step is composed of M minislots, and each subscriber reports the detection result using the minislot allocated to him on the common control channel.

In an embodiment of the present invention, the detection result of the data channel by the secondary user may be either a busy state or an idle state. That is, if a sub-user assigned m (m = 0,1,2, ..., u-1) th mini-slot in t (t = 0,1,2, , 2, ..., n-1 ) ( when called _{t), X m, n (} t) is idle (X _{m, n} (t) for the channel state X _{m, n} when detecting a second data channel = 0 ) Or busy state (X _{m, n} (t) = 1). FIG. 2 shows an example of a data channel index n and a channel state X _{m, n} (t) to be detected by a sub-user assigned an m-th minislot according to Equation (2). Here, it is assumed that the number u of sub-users is greater than the number N of data channels. As described above, in the case of u> N, the number of sub users B (n) that sense n (n = 0, 1, 2, ..., N-1) th data channel is one or more and can be expressed by the following equation .

B (n)> 1 means that more than one secondary user can simultaneously detect for the nth data channel. In this case, the channel state detected by the secondary users may be changed due to a false-alarm probability and a miss-detection probability. Therefore, in the embodiment of the present invention, in determining the state of a certain data channel, the secondary user determines the busy state or the idle state based on the detected result (channel state) of the data channel. For example, if the rate detected in the busy state exceeds a certain threshold value, the state of the data channel is determined to be in a busy state, and otherwise, it is determined to be in an idle state. the ratio of the n (n = 0, 1, 2, ..., N-1) th data channels detected by the B (n) sub users in the busy state in the time slot t (t = 0,1,2, A comparison of R (X _n (t) = 1) and a threshold value can be expressed by the following equation.

Here,? Represents a threshold value used as a criterion for determining the state of the data channel, and the numerator of the right side means the number of sub users who sense the n-th data channel as busy. In Equation _{4, R (X n (t} ) = 1) when ≤ θ a, Part users of n determines the state of the second data channel is idle, and _{R (X n (t) =} 1)> θ , It is determined that the n-th data channel is busy. The secondary users determine the state of each of the data channels through this process and store an available channel list (ACL) including the state information of each data channel. That is, the available channel list includes indexes of respective data channels and corresponding status information (e.g., 0 or 1) and is updated by determining the status of each data channel each time a detection result is received.

<Negotiation phase>

The negotiation step is a step in which the sub-users perform channel negotiation and reservation, and at least a part of the sub-users negotiate and reserve for use of the data channel in the minislot allocated to the sub-users through the common control channel. In the embodiment of the present invention, the negotiation step is started when at least one of the following predetermined events (S _e = {e ₁ , e ₂ , e ₃ }) has occurred to a certain negative user.

e ₁ ) If there is no data channel allocated to the secondary user to transmit data

e ₂ ) When the state of the data channel allocated to the sub user to which data is to be transmitted is busy

e ₃ ) If one or more data channels are idle and no one else uses the channel

In an embodiment of the present invention, the secondary user table (SUT) further includes an index of the data channel being used by the secondary user in the network, in addition to the secondary user's ID and the allocated minislot index. That is, the secondary user table includes the index of the data channel in use corresponding to the ID of the secondary user. As will be described later, the negotiation and reservation of the data channel is performed through the exchange of a Request to Send (RTS) packet and a Clear To Send (CTS) packet. Since a CTS packet occurring in the network reaches all the sub users of the network, The sub-users can know the reservation status of the data channel based on the selected channel number (SCN) included in the data channel. Also, as will be described later, a secondary user transmits a FIN packet in a minislot allocated to itself on the common control channel to inform the user of the completion of the data transmission. When the secondary user in the network receives the termination packet, It can recognize that the channel has been used and update the secondary user table (SUT).

The secondary users can use the reserved data channel until the data transmission ends, by using the above-described sub-user table and the above-described available channel list (ACL), unless events included in the above-mentioned S _e occur .

In an embodiment of the present invention, the secondary users exchange RTS packets and CTS packets in a minislot assigned to them on the common control channel in order to negotiate and reserve the use of the data channel. The multi-channel hidden terminal problem (MHTP) is solved by allowing the secondary users to exchange RTS packets and CTS packets on the common control channel. Also, collision with other control messages is prevented by transmitting RTS packets and CTS packets through minislots independently allocated to each sub user.

FIG. 3 illustrates a procedure code for exchanging an RTS packet and a CTS packet through a minislot allocated between sub-users according to an embodiment of the present invention.

3, if at least one of the events included in the S _e occurs in the source user to transmit data, the RTS packet includes an available channel list, and uses the m _s minislot allocated to the user Transmits the RTS packet to the destination sub-user, and sets the expiration time T _exp . The expiration time T _exp is for recognizing the failure of the RTS / CTS exchange and can be set as the following equation.

_{Here, m s (m s = 0,1,2} , ..., M-1), m d (m d = 0,1,2, ..., M-1) is allocated to each user unit a source user and a destination part &Lt; / RTI > Referring to equation (5), in the case in the time slot in the case of m _s <m _d a mini-slot of the destination sub-user following more mini-slot of the source unit user, remaining from the expiration time T _exp is m _s th minislot Is the length of the negotiation section (NP). m _s> within the time slot if m _d as if a mini-slot of the destination unit user precedes a mini-slot of the source sub-users, the expiration time T _exp is m _s negotiating period (NP) remaining from the first mini-slot And the length Ts plus the length of the time slot.

The source subscriber who transmitted the RTS packet retries the channel negotiation and reservation if the CTS packet is not received from the destination subscriber until the expiration time T _exp elapses.

Referring to FIG. 3, when the destination user receives at least one RTS packet, the destination user selects an arbitrary source user among the source users S _u that have transmitted the RTS packet. Then, the selected channel number (SCN) is selected from the available channel list included in the RTS packet of the selected source subscriber. The destination side user includes the information of the SCN in the CTS packet and transmits the CTS packet to the selected source side user in the m _d minislot allocated to the destination side user. The source user receives the CTS packet and the channel negotiation and reservation are completed. Thus, the source user can transmit data to the destination user through the data channel specified in the CTS packet.

<Transmission step>

As described above, the secondary users transmit data on the data channel using the data transceiver. After subscribing and negotiating the channel, the secondary user transmits the data using the following time slot instead of immediately transmitting the data in the corresponding time slot.

In an embodiment of the present invention, one data channel may be reserved by two or more sub-users. For example, one data channel determined to be idle in a certain time slot may be reserved by a different source-destination pair. As described above, all the sub-users in the network can recognize that the data channel is redundantly reserved because the sub-user table (SUT) includes the ID of the sub-user and the index of the data channel in use corresponding thereto. When one data channel is reserved as redundant, in the embodiment of the present invention, the sub-users reserving the corresponding data channel transmit data in a reserved data channel in a round-robin manner in order to guarantee fairness. The secondary users can use the secondary user table (SUT) to grasp the number of secondary users using the reserved data channel, and transmit data in a round-robin manner by waiting for their order in the reserved data channel .

In case that the data to be transmitted is delay-sensitive voice traffic, the secondary user can guarantee QoS by transmitting several voice packets in one time slot.

The secondary users can also use the available channel list (ACL) to determine whether the reserved data channel is busy or idle due to activity of the primary user (PU).

When the secondary user changes the data channel that has been terminated or used to another data channel, it transmits a FIN packet in its assigned minislot on the common control channel. When the end user of the network receives the end packet, it confirms that the end user has completed the data transmission on the data channel and updates the end user table (SUT).

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium. The computer-readable recording medium includes a storage medium such as a magnetic storage medium (e.g., ROM, floppy disk, hard disk, etc.), optical reading medium (e.g., CD ROM,

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

Claims (13)

A medium access control method in a distributed cognitive radio network,
Allocating a minislot to each of the secondary users through a common control channel;
Each of the secondary users senses a data channel corresponding to a minislot assigned to itself among a plurality of data channels and reports a detection result of the data channel in a minislot allocated to the secondary channel through the common control channel ; And
And performing negotiation for use of a data channel using at least a part of the sub-users through the common control channel using a minislot allocated to the sub-users, when a predetermined event occurs, Way. The method according to claim 1,
Wherein one time slot of the common control channel includes a reporting interval for the reporting step and a negotiation interval for performing the negotiation. 3. The method of claim 2,
Wherein the reporting step reports the detection result of the data channel in a minislot included in the reporting period. 3. The method of claim 2,
Wherein the performing of the negotiation comprises performing the negotiation using a minislot included in the negotiation interval. The method according to claim 1,
Wherein the step of allocating the minislot comprises:
Wherein the coordinator, which is one of the sub-users, allocates a minislot to the sub-user requesting participation in the network, and transmits a beacon message including minislot allocation information in the beacon slot on the common control channel. Control method. 6. The method of claim 5,
Wherein the secondary user attempting to join the network transmits a join request message including its ID in response to the beacon message. The method according to claim 1,
Wherein the detection result is one of a busy state and an idle state and further includes determining a state of each data channel using detection results reported from the secondary users, Access control method. 8. The method of claim 7,
Wherein the determination of the state of a data channel in the determining step is performed according to a ratio of a busy state or an idle state among at least one of the detection results reported for the data channel. The method according to claim 1,
Wherein performing the negotiation comprises:
A source user transmits a request to send (RTS) packet to a destination user in a minislot allocated to the source user. The destination user transmits a RTS (Request to Send) packet to the source user in a minislot allocated to the source in response to the RTS packet. (Clear To Send) packet. 10. The method of claim 9,
In the negotiation, the source user transmits the RTS packet including the available channel list identified through the reporting step, and the destination user includes any one of the available channels in the available channel list And transmits the CTS packet. 10. The method of claim 9,
Wherein the plurality of sub-users transmit data through the reserved data channel in a round-robin manner when the same data channel is reserved for use by a plurality of sub-users as a result of the negotiation being performed. Control method. The method according to claim 1,
Wherein the secondary users have a secondary user table including an ID of the secondary users participating in the network and an index of a minislot allocated to each secondary user. The method according to claim 1,
Wherein the secondary users have an available channel list including status information of each of the plurality of data channels.

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