KR20100030084A - Method for allocating a frequency channel to a cluster head - Google Patents

Abstract

PURPOSE: A method for allocating a frequency channel to a cluster head is provided to exempt a channel with interference by checking whether interference exists, thereby generating a list by only a channel which can avoid interference. CONSTITUTION: A logical channel list about a logical channel is generated(S302). The first search channel is selected from the logical channel list(S303). It is checked whether interference due to the second wireless network exists(S304). It is determined whether to exempt the first search channel. The logical channel list is updated. A frequency channel for a cluster head is allocated(S310).

Description

Frequency channel allocation method for cluster heads {METHOD FOR ALLOCATING A FREQUENCY CHANNEL TO A CLUSTER HEAD}

The present invention relates to a frequency channel allocation method for a cluster head, and more particularly, to a heterogeneous network (i.e., an access point of a wireless local area network) and a homogeneous network (i.e., a wireless personal) in a cluster head such as a wireless personal network (WPAN). For cluster heads to check whether there is interference by adjacent cluster heads in the network and to create a list of channels that can avoid interference by excluding channels with interference, The present invention relates to a frequency channel allocation method.

The IEEE 802 standard can use 800 MHz band, 900 MHz band, 2.4 GHz band (ISM band), but research has been conducted to use the 2.4 GHz band. Here, the standards of the IEEE 802 series include the IEEE 802.11b standard, the IEEE 802.15.1 standard, the IEEE 802.15.4 standard, and the like.

In particular, the IEEE 802.15.4 standard deals with wireless channels for designing low-speed wireless personal area networks (WPANs) and corresponding communication access control layers, and studies are mainly conducted for wireless sensor networks. It became.

On the other hand, the research on the interference avoidance of the frequency band common environment in the IEEE 802 series standard has been mainly focused on the IEEE 802.15.1 standard called Bluetooth (bluetooth), the situation is rare in the IEEE 802.15.4 standard.

However, in the conventional IEEE 802.15.4 standard, the following scheme has been proposed mainly for avoiding interference with adjacent clusters.

First, the 'interference cancellation method through beacon scheduling' uses the characteristics of active / inactive intervals of the IEEE 802.15.4 standard to apply the beacon's temporal scheduling used in the beginning of the superframe structure between neighboring clusters. Is the way to avoid. Here, since the interference cancellation method through beacon scheduling is limited in density of nodes that can be handled through scheduling, there is a limit that is difficult to apply in an environment where IEEE 802.15.4 devices are densely distributed.

In addition, the 'distributed channel allocation method' determines the channel from the cluster head having the highest importance among neighboring clusters according to the importance calculated from the connectivity, and then informs the neighboring node or cluster, the neighboring cluster. Among them, a cluster head having a low importance may select another channel that can avoid interference with each other by referring to channel information transmitted from a larger cluster head. In this case, the distributed channel allocation method has a large number of messages for channel allocation. Therefore, the ratio of communication used for channel allocation is high at higher density than the actual communication of data. have.

The 'beacon based interference detection method' is a method of avoiding interference after detecting the interference according to whether the beacon transmitted from the cluster head succeeds or fails. Here, the beacon-based interference detection method is used only when transmitting a beacon signal from the interference source, and thus cannot be considered at all in the case of interference of heterogeneous networks.

In addition, the 'ACK / NACK-based interference detection method' is a method of avoiding interference after detecting the interference according to whether the transmission data has received (ACK) or failed (NACK) through the transmission packet of the transmission data. In the test packet-based interference detection method, when a test packet is periodically transmitted, when the test packet is not properly transmitted, the test packet is detected and the interference is avoided. When in the range of nodes, only nodes in the range use a different channel from the previously used channel to avoid interference.

Here, 'ACK / NACK-based interference detection method', 'test packet-based interference detection method', and 'group forming method' are characteristics of an interference source using a wireless communication network (that is, a short time for wireless communication). Although it is very flexible in the interval, but it is difficult to reflect all of them in reality, rather than responding to the change of all the sources of interference, it is necessary to set a predetermined time interval and establish a channel allocation policy according to the statistical characteristics of the interference occurring in the interval. However, there is a limit to the efficiency that does not accurately reflect this.

On the other hand, in the channel allocation scheme currently in use, a given channel list is fixed. It performs channel search according to the evaluation for every channel every time, which is very inefficient in the time of searching in the environment where there are many sources of interference.

Next, there is a method of using only guard-band channels in which frequency bands do not overlap in the IEEE 802.11b standard and frequency common environment, which is the theoretical number of channels given in the IEEE 802.15.4 standard and 16 guard-band channels. In consideration of the number of four, it can be seen that radio resource management is very inefficient.

Therefore, in the conventional method, in consideration of the characteristics of a device using a wireless communication network, a method of avoiding interference of heterogeneous networks (especially IEEE 802.11b) in an environment where clusters of the IEEE 802.15.4 standard are densely distributed. This needs to be proposed. That is, in the conventional scheme, the cluster head of the IEEE 802.15.4 standard avoids interference in a heterogeneous network (especially, the IEEE 802.11b standard) and a frequency common environment to guarantee a quality of service for a user. An allocation scheme needs to be proposed.

Therefore, the present invention checks whether there is interference by heterogeneous and homogeneous networks in a cluster head such as a wireless personal network (WPAN), and generates a list by using only channels that can avoid interference by excluding channels with interference. It is an object of the present invention to provide a frequency channel allocation method for a cluster head, so that a channel can be allocated to a channel.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned above can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. Also, it will be readily appreciated that the objects and advantages of the present invention may be realized by the means and combinations thereof indicated in the claims.

In order to achieve the above object, the present invention provides a method for allocating a frequency channel for a cluster head, the method comprising: generating a logical channel list for a logical channel in a frequency common environment of a first wireless network and a second wireless network, Selecting a first search channel from the channel; A first checking step of confirming whether there is interference by the second wireless network by performing energy detection and carrier detection on the first search channel; A first update step of updating the logical channel list by determining whether to exclude the first search channel from the logical channel list according to a result of the confirmation of the first verification step; And assigning a frequency channel for the cluster head of the first wireless network by using the updated logical channel list.

In addition, the present invention includes a second selection step of selecting, after the first channel assignment step, a second search channel to check whether there is interference for an adjacent cluster head from the updated logical channel list; A second checking step of performing energy detection on the second search channel to check whether there is interference by an adjacent first wireless network; A second update step of re-renewing the updated logical channel list by determining whether to exclude the second search channel from the updated logical channel list according to the confirmation result of the second confirmation step; And a second channel assignment step of allocating a frequency channel belonging to the re-updated logical channel list for the cluster head of the first radio network.

In addition, the present invention provides a method for allocating a frequency channel for a cluster head, the method comprising: generating a logical channel list for a logical channel in a frequency common environment of a first wireless network and an adjacent first wireless network, and generating a search channel from the logical channel list. A selection step of selecting; Confirming whether there is interference by the adjacent first wireless network by performing energy detection on the search channel; An update step of updating the logical channel list by determining whether to exclude the search channel from the logical channel list according to the verification result; And assigning a frequency channel belonging to the updated logical channel list for the cluster head of the first wireless network.

The present invention has the effect of allocating channels by avoiding interference by heterogeneous and homogeneous networks in a cluster head such as a wireless personal network. In addition, the present invention has the effect of effectively controlling interference and optimizing the performance of the system by avoiding interference in a frequency common environment. In addition, the present invention has the effect of optimizing the utilization of radio resources by maximizing the number of channels that can be used in a frequency common environment.

The above objects, features, and advantages will become more apparent from the detailed description given hereinafter with reference to the accompanying drawings, and accordingly, those skilled in the art to which the present invention pertains may share the technical idea of the present invention. It will be easy to implement. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted. Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The present invention can be applied to a case where one network allocates a channel avoiding an interference signal from another network in an environment in which frequency bands are shared between heterogeneous networks.

However, in the present invention, a wireless personal network user is guaranteed a quality of service (QoS), mainly in an environment in which frequency bands are shared between 'WLAN' and 'WPAN' as heterogeneous networks for convenience. A case where a channel can be allocated is described, but it will be easily understood by those skilled in the art.

At this time, in the present invention, in order to measure the performance of the service quality of the user in the wireless personal network, packet error probability (PEP) according to the channel environment is used (see FIG. 4 to be described later).

Hereinafter, the consideration of the packet error probability according to the channel environment will be briefly described.

First, in the wireless personal network of the present invention, assume a channel environment in which fading exists. At this time, in the present invention, a formula for a signal-to-noise ratio for the channel environment is constructed.

Noise includes interference signals of interfering sources corresponding to 'signals of adjacent cluster heads using the same channel in the homogeneous network' and 'signals of access pointers using overlapping frequency bands in the heterogeneous network'.

In particular, the formula for the signal-to-noise ratio is based on the difference between the signals of devices that use overlapping frequency bands in the heterogeneous network (in this case, the access point of the wireless local area network) and the frequencies used by the wireless private network. Since the influence of the interference signal is different, the difference between the center frequency axis of the interference source signal and the center frequency axis currently used in the wireless personal network, that is, the strength of the interference source signal according to the frequency shift is reflected.

On the other hand, based on the equation for the signal-to-noise ratio, the present invention builds the packet error probability for measuring the performance of the wireless personal network according to the channel environment, through which the wireless personal network that is homogeneous in the receiving environment of the wireless personal network In addition to avoiding interference from other devices in use, it is also possible to avoid interference from devices using heterogeneous wireless local area networks.

1 is an explanatory diagram of a frequency common environment to which the present invention is applied.

As shown in FIG. 1, in a frequency common environment to which the present invention is applied, a cell of a wireless local area network (WLAN) and a cluster of a wireless personal network (WPAN) are densely arranged to overlap each other. It is assumed that the frequency band is shared in the environment.

This assumes the frequency common environment, and is intended to examine the effects of coexistence between wireless devices using the same frequency band (that is, access points of wireless local area networks and cluster heads of wireless private networks).

In this case, since the cluster of the wireless personal network generally has a lower signal strength than the cells of the wireless local area network, interference by signals from cells of the wireless local area network may easily occur.

This common frequency environment is an example where a user in the home uses a home automation system (eg, lighting control, temperature control, unmanned security, etc.) via a wireless personal network while surfing the web or checking e-mail through the wireless local area network. As shown in FIG. 2, the present invention shows an environment capable of providing a service according to each network characteristic through frequency channel allocation according to the present invention even if the same frequency band is shared in a wireless local area network and a wireless private network.

In the wireless local area network and the wireless private network of the present invention, one of the 800 MHz band, 900 MHz band, and 2.4 GHz band (that is, the ISM band) may be selectively applied, but preferably the 2.4 GHz band is shared. The case will be described on the assumption. In this case, the present invention assumes only 16 channels used in the 2.4 GHz band.

That is, the cluster head (CH) 110 of the wireless private network manages the cluster using the 2.4 GHz band, and the access point (AP) 120 of the wireless local area network also has 2.4 GHz. The band is used to govern the cell.

Hereinafter, the wireless personal network and the wireless local area network will be described.

First, it is assumed that a wireless personal network is formed in a cluster tree structure according to a corresponding wireless communication standard (for example, IEEE 802.15.4 standard), and operates in a wide spatial range that can cover an indoor environment. In this case, one cluster is formed as one node of the nodes is determined as the cluster head 110, and peripheral nodes that are in communication with the cluster head 110 are determined as cluster members. This is a distributed cluster formation method by connectivity between nodes.

At this time, the 'node to be the cluster head' informs the 'near nodes' in the communication distance of their existence, and then determines that they are the top-level nodes compared to the 'near nodes' (for example, each node Comparing the ID value of), and defines itself as the cluster head 110 and informs it to the 'near nodes'. The 'neighboring nodes' define themselves as cluster members for the cluster head 110. Accordingly, nodes are defined as cluster heads 110 and cluster members, respectively, to form a cluster.

One cluster is composed of nodes (i.e., cluster members) one hop away from the cluster head 110, and data communication is performed between the cluster head 110 and the cluster members through one channel. . Here, the cluster head 110 performs a coordinator function in the cluster. In this case, the cluster head 110 has an equivalent relationship or a vertical relationship with the adjacent cluster head, and is responsible for the coordinator (ie, PAN coordinator) function of the entire wireless personal network in the case of the highest layer.

Meanwhile, the cluster head 110 should select which channel to use when forming the cluster. That is, the cluster head 110 performs a channel assignment process at the time of forming the network for the first time and when it is necessary to change the channel to avoid the interference occurring at any time in the active network. That is, in the present invention, after the cluster head 110 avoids the interference by the access point 120 of the wireless local area network, the cluster head 110 avoids the interference by the adjacent cluster head and performs frequency channel allocation (described later with reference to FIGS. 2A and FIG. 3a).

In particular, the cluster head 110, when performing a clear channel assessment (CCA) of a carrier sense multiple access / collision avoidance (CSMA / CA) for data transmission, the process of determining whether the frequency channel is used [CCA mode 1 : Not only energy detection, but also a process of determining whether a network using a frequency channel is homogeneous or heterogeneous [CCA mode 2: carrier sense].

Meanwhile, after allocating a channel for its cluster, the cluster head 110 communicates only with cluster members of the cluster to which it belongs. At this time, the cluster head 110 collects data from each cluster member through one-hop communication, and then transmits the data to a destination through multi-hop communication to an adjacent cluster head. This corresponds to data transmission in the case of uplink, and in contrast to uplink in the case of downlink.

In detail, the cluster head 110 may communicate with the cluster member and the adjacent cluster head by applying the following scheme.

First, the cluster head 110 transmits the data collected from the cluster member to the neighboring cluster head to transmit the data to the channel currently used by the neighboring cluster head (ie, the cluster relaying method).

In contrast, the cluster head 110 communicates by setting a channel (intra cluster channel) for communicating with a cluster member and a channel (inter cluster channel) for communicating with an adjacent cluster head differently (that is, a dedicated channel setting method). . To this end, the cluster head 110 should be able to communicate over different channels in a simultaneous or time-division region, and should have at least two RF receivers or a frequency switching function that randomly changes the operating frequency.

Next, in the wireless local area network, a wireless Internet is formed according to a corresponding wireless communication standard (for example, IEEE 802.11b). Such a wireless local area network provides a high speed internet service to a user by establishing a communication environment that does not require complicated wiring, and a network interface card (NIC) should be provided for each terminal. Here, the wireless local area network assumes an infrastructure structure, which is an infrastructure in which the access point 120 is connected to the wired network, which will be omitted by a person skilled in the art.

Hereinafter, a process of creating a channel list that the cluster head 110 can select to obtain a desired performance in a frequency coexistence environment or to avoid interference will be described in detail with reference to FIGS. 2A to 3B.

FIG. 2A is an exemplary diagram illustrating frequency channel allocation between a cluster head and an adjacent cluster head according to the present invention, and FIG.

As shown in FIGS. 2A and 2B, when forming a cluster-based network, the cluster head 110 allocates a frequency channel by avoiding interference on the frequency channel being used by adjacent cluster heads (ie, homogeneous networks). Assigning a channel by avoiding interference between channels).

To this end, in the present invention, the cluster head 110 sets an initial value for allocating a channel by avoiding a channel being used by an adjacent cluster head as follows (S201).

First, in the present invention, when the clusters adjacent to each other select a channel, it is assumed that the minimum distance that can avoid interference even if the same channel is used, that is, the minimum channel reuse distance is 'd (min) = 8m'. This is generally because the cluster head 110 can communicate with a cluster member within a radius of 8 m at line of sight (LOS).

In addition, in the present invention, it is assumed that the transmission power of the cluster head 110 is '0dBm'. At this time, the cluster member does not exceed the transmit power of the cluster head 110. Here, the transmission power of the cluster head 110 may apply the power size actually implemented by the user.

Next, in the present invention, a threshold value for determining whether a predetermined frequency channel is interfered by an adjacent cluster head of a wireless personal network that is homogeneous with itself in the cluster head 110 (hereinafter referred to as a "homogeneous network threshold"). ).

Here, the homogeneous network threshold is set by applying a normal distance loss model to the transmission power of the cluster head 110. In general, all transmission signals attenuate according to the distance loss model suitable for the channel environment as the distance increases. In the present invention, the distance loss model is applied to accurately predict the reception power at a predetermined distance according to a predetermined transmission power of the cluster head 110.

Therefore, the homogeneous network threshold is set to determine whether there is interference by an adjacent cluster head as the transmission power, the minimum channel reuse distance, and the distance loss model of the cluster head 110 are simultaneously applied. Specifically, the homogeneous network threshold value is equal to the homogeneous network threshold value ＝ = transmission power 거리 distance loss 클 of the cluster head 110, and the distance applied to the distance loss model is a channel reuse minimum distance. is equal to 'd (min) = 8m'.

Hereinafter, after setting the initial value as described above (S201), the process of allocating the frequency channel by avoiding the interference to the adjacent cluster head will be described in detail.

First, the cluster head 110 checks all logical channels that may exist for each cluster member, and generates a channel list to be determined whether there is interference by an adjacent cluster head (S202). .

Thereafter, the cluster head 110 performs an energy detection process on the corresponding channel belonging to the channel list generated as described above (S203). At this time, when the cluster head 110 selects the corresponding channel belonging to the channel list, the cluster head 110 sequentially selects the first channel to the last channel for the corresponding channel included in the channel list, or in any order for the corresponding channel belonging to the channel list. You can choose.

Next, the cluster head 110 compares the 'energy detection result value' and the 'homogeneous network threshold value' with each other to determine whether the corresponding channel has interference by an adjacent cluster head (S204). That is, when the energy detection result is greater than the homogeneous network threshold (S204), the cluster head 110 determines that the corresponding channel has interference by the adjacent cluster head and excludes the corresponding channel from the channel list (S205). On the other hand, if the cluster head 110 determines that the energy detection result value is smaller than the homogeneous network threshold (S204), the cluster head 110 determines that the channel does not have interference by the adjacent cluster head and maintains the channel in the channel list (S206). ).

Then, when the corresponding channel in the channel list is the last channel to perform energy detection, the cluster head 110 selects an optimal channel and ends by allocating the channel (S209) (see Equations 1 and 2 to be described later). Otherwise, the same process is repeated by selecting another channel belonging to the channel list (S207 and S208).

As such, the cluster head 110 performs energy detection on each channel in the channel list, excluding a channel that may cause interference with an adjacent cluster head, and leaving a channel that may avoid interference with an adjacent cluster head. By retaining, it is possible to obtain a channel list consisting of only channels that can ultimately avoid interference with adjacent cluster heads.

In other words, the cluster head 110 finally obtains through an update process of determining whether to exclude or maintain each channel belonging to the channel list through energy detection of whether there is interference by an adjacent cluster head. Regardless of which channel is selected in the channel list, it is possible to avoid a channel that may cause interference by an adjacent cluster head.

FIG. 3A is an exemplary diagram of frequency channel allocation between a cluster head and an access point according to the present invention, and FIG. 3B is a flowchart illustrating an example of a frequency channel allocation method between the cluster head and an access point according to the present invention.

As shown in FIGS. 3A and 3B, in the cluster head 110, when the frequency bands used by the access points 120 of the heterogeneous networks overlap with the frequency bands that the 120 is using, the access point The signal coming from 120 is the biggest kind of interference.

In this case, the cluster head 110 allocates a channel by avoiding interference on the channel being used by the access point 120. First, after avoiding interference on the channel with the access point 120, FIGS. 2A and FIG. The channel is allocated by avoiding interference with a channel with an adjacent cluster head mentioned in 2b (that is, a process of allocating a channel by avoiding interference with a channel between heterogeneous networks).

2A and 2B, in the present invention, the cluster head 110 sets an initial value for allocating a channel by avoiding the channel being used by the access point 120 as follows (S301).

First, in FIG. 3A and FIG. 3B, the minimum channel reuse distance is assumed to be 'd (min) = 8m'.

In addition, since channel allocation is described by avoiding interference between heterogeneous networks, that is, interference with signals of the access point 120 in the cluster head 110, the access point 120 as well as the transmission power of the cluster head 110 are described. Information about the transmit power of is needed. That is, it is assumed that the transmission power of the cluster head 110 is '0dBm' and the transmission power of the access point 120 is '14dBm'. Here, the transmission power of the cluster head 110 and the access point 120 may be reset by the user.

In particular, in addition to the above-mentioned 'homogeneous network threshold', another threshold is further set. That is, the cluster head 110 further sets a threshold value (hereinafter, referred to as a “heterogeneous network threshold”) for determining whether a predetermined channel has interference by the access point 120 that is a heterogeneous network with the self 110. do.

At this time, the heterogeneous network threshold is set in consideration of the power spectrum density function of the wireless local area network, and reflects '30 dBr 'corresponding to the transmission mask of the first side lobe. To determine whether the signal coming from the access point 120 comes from the main lobe.

Here, the power spectral density function is adjusted to the transmission mask of the access point 120 because the power emission of the access point 120 of the wireless local area network is not uniform in the frequency domain.

The power spectral density function is used to accurately calculate the degree of interference due to the frequency shift of the signal transmitted from the access point 120 at the cluster head 110 (i.e., the degree to which the channels between each other overlap the frequency axis). . At this time, the power spectral density function decreases as it moves away from the center frequency.

This means that when the signal transmitted from the access point 120 acts as an interference signal to the cluster head 110, the performance of the cluster head 110 can be evaluated as the frequency shift.

In other words, since the signal of the access point 120 is considerably larger than the signal of the cluster head 110, the cluster head 110 exhibits satisfactory performance when the frequency shift with respect to the access point 120 and the center frequency is small. That means it's hard to expect.

Therefore, when the cluster head 110 determines that the interference source, i.e., the interference signal of the access point 120 for each channel is greater than the heterogeneous network threshold, it is difficult to show satisfactory performance, the cluster head 110 does not allocate the corresponding channel. The evaluation will be repeated.

Accordingly, the cluster head 110 achieves efficient interference avoidance by selecting one of the channels that can completely avoid the remaining interference after completing channel evaluation for all available channels.

Also, the heterogeneous network threshold is set by applying a normal distance loss model (ie, a distance loss model according to the IEEE 802.11b standard) to the transmission power of the access point 120. Specifically, the heterogeneous network threshold value is equal to the " heterogeneous network threshold value (dB) = transmission power of the access point 120-30 dBr-distance loss (k) '.

On the other hand, since the homogeneous network threshold is set in the same manner as described above, a detailed description thereof will be omitted, but specifically, the homogeneous network threshold value is' the homogeneous network threshold value (dB) = transmission power of the cluster head 110 − Distance loss'.

In addition, when considering interference between two or more heterogeneous networks, information on transmission power for each device, heterogeneous network threshold values according to a distance loss model for each device, and the like may be different from those of the access point 120 described above. It must be reflected together.

Hereinafter, after setting an initial value as described above (S301), the cluster head 110 avoids interference with the access point 120 and then avoids interference with adjacent cluster heads to allocate a frequency channel. This will be described in detail.

First, the cluster head 110 checks all logical channels that may exist for each cluster member, and sets a channel group according to the frequency channel distribution of the access point 120 (S302).

In general, since the 'frequency range for one channel used by the access point 120' corresponds to the frequency range for four channels used by the cluster head 110, it will be described accordingly.

Additionally, if the 'frequency range for one channel used by cluster head 100' is greater than 'frequency range for one channel used by access point 120', cluster head 100 One channel used by) is set to one group. On the other hand, if the frequency range for one channel used by cluster head 100 is less than the frequency range for one channel used by access point 120, One group is set according to the frequency range for one channel used by (i.e., if applicable to the present invention).

Specifically, in the present invention, the channel group is set in the cluster head 110 as follows.

In FIG. 3A, when there are 16 logical channels from logical channel numbers '11' to '26', the logical channels are grouped into four channels and set as one group.

First, the 'channel used by the cluster head 110' and the 'channel used by the access point 120' overlap each other, and thus the 'group of logical channels 11 to 14' 1 channel group ")," group of logical channels 16 to 19 "(hereinafter referred to as" second group ") and" group of logical channels from 21 to 24 "(hereinafter referred to as" third group " Group ".

Next, 'channels used by the cluster head 110' and 'channels used by the access point 120' do not overlap with each other, and are referred to as '15, 20, 25 and 26 '. Group of logical channels' (hereinafter referred to as "guardband channel group").

Here, a list of all channels belonging to the first channel group through the third channel group and the guard band channel group, that is, a total of 16 logical channels is referred to as a "logical channel list".

Thereafter, the cluster head 110 selects a 'representative channel' from channels belonging to each channel group except the guardband channel group, and determines a list of channels (hereinafter, referred to as “representative channels”) to determine whether there is interference by the access point 120. Create a " search channel list " (S303).

Here, the 'representative channel' is a channel having the smallest frequency shift in the center frequency axis of the corresponding channel group (ie, the channel group except the guardband channel group), and one channel (ie, used for the access point 120). , Which corresponds to the frequency range of one channel group).

Accordingly, the cluster head 110 selects the second channel or the third channel from the channel group as the representative channel of the corresponding channel group. For example, the cluster head 110 may use the second channel, '12 channel 'or the third channel, '13 channel', as the representative channel in the first channel group (channel groups 11 to 14). Choose.

On the other hand, the cluster head 110 performs 'energy detection' and 'carrier detection' for the corresponding representative channel belonging to the search channel list (S304). The cluster head 110 determines whether there is interference by the access point 120 only with respect to the representative channel of the channel group, but determines whether all channels belonging to the channel group have interference by the access point 120. It's a process.

Specifically, when the 'energy detection result value' is larger than the heterogeneous network threshold value and the 'carrier detection' fails for the representative channel belonging to the corresponding search channel list (S305), the cluster head 110 accesses the access point 120. By determining that the group to which the corresponding channel belongs is being interfered with, the group is excluded from the logical channel list (S306).

On the other hand, if the cluster head 110 does not satisfy the condition that the 'energy detection result value' is larger than the heterogeneous network threshold for the representative channel belonging to the corresponding search channel list and fails to 'carrier detection' (S305), access It is determined by the point 120 that the group to which the channel belongs does not interfere, and maintains the group in the logical channel list (S307).

Thereafter, when the representative channel belonging to the search channel list is not the last representative channel, the cluster head 110 selects another representative channel belonging to the search channel list and repeats the above process (S308 and S309).

Otherwise, the cluster head 110 checks whether there is interference by the neighboring cluster head described above with reference to FIGS. 2A and 2B and performs channel allocation (S310). Detailed description thereof will apply mutatis mutandis to the above-described description of FIGS. 2A and 2B.

However, the cluster head 110 checks whether there is interference by a neighboring cluster head for a channel belonging to the logical channel list except for the interference channel by determining whether there is interference on the representative channel of the search channel list. do.

For example, if it is determined that the interference is caused by the representative channel '12' channel of the first channel group, the cluster head 110 includes a channel belonging to the first channel group, that is, 'channels 11 through 14'. Verify that there is interference by neighboring cluster heads against the logical channel list excluding the target.

Accordingly, the cluster head 110 avoids the interference by the access point 120 and then avoids the interference by the adjacent cluster head, and finally allocates a channel to the cluster.

In addition, although the cluster head 110 may arbitrarily select one of the channels in the channel list in the present invention, it is preferable to perform one optimal channel in the channel list to optimize the overall network performance. Equation 1] and the following [Equation 2] is selected.

Here, 'j' in Equation 1 represents each cluster, and the objective function indicates that the performance of the entire network is optimized based on a value for the signal-to-noise ratio (SNR). For specific implementation, Equation 1 may be expressed as Equation 2 below.

Here, 'ED ()' of Equation 2 represents energy detection for the corresponding channel.

Therefore, in the present invention, through [Equation 1] and [Equation 2], it is possible to allocate a channel that can optimize the performance of the entire network.

Through this, those skilled in the art will be able to easily understand the frequency channel allocation method of the wireless personal network of the present invention through FIGS. 3A and 3B.

4 is a diagram showing an experimental result of the average packet error probability according to the cluster density according to the present invention.

The cluster head 110 receives two interference signals by the wireless local area network and the wireless private network in a multi-cell environment where the wireless local area network and the wireless private network overlap each other. To this end, in the present invention, the cluster head 110 applies an average packet error probability (P _PEP ) to verify the degree of interference received by the wireless local area network and the wireless private network.

Here, 'average packet error probability (P _PEP )' may be calculated through 'symbol error rate (P _s )' and 'bit error rate (P _b )'.

Since the present invention assumes that the frequency common environment is implemented in a low mobility indoor environment, it can be assumed that the signal fading is kept constant for one packet duration as the fading indicates low fading.

In addition, the cluster head 110 of the wireless personal network modulates the offset Qaudrature Phase Shift Keying (O-QPSK) of the half-sine shape in the 2.4 GHz band. Accordingly, the symbol error rate in the fading channel is expressed by Equation 3 below.

Here, 'E _s / N ₀ ' denotes a symbol noise density, and M is a codebook of 16 symbols. K represents a Rice factor, which is the ratio of direct wave component magnitude (power) to indirect wave component magnitude (power) in a multipath channel. In this case, using the ratio of the chip ratio and the bit ratio, the bit error ratio to the symbol error ratio, the 'bit error ratio' can be obtained as shown in Equation 4 below.

On the other hand, assuming a noise fading independent of the slow fading channel, the average packet error probability of length L bits can be obtained as shown in Equation 5 below.

In FIG. 4, the average packet error probability for the cluster head 110 is calculated while varying the cluster radius of the wireless private network to reflect the density of the node, and the channel of each cluster of the wireless private network and each cell of the wireless local area network. The probability distribution for the selection assumes a uniform distribution.

In the experiment of FIG. 4, since the access point 120 of the wireless local area network, which is a transmitter, and the cluster head 110 of the wireless personal network, which is a receiver, are set close to about 2 m, the frequency deviation is small (ie, 0 MHz to 12 MHz). ), It can be seen that the interference of the access point 120 of the wireless local area network is prominent, and in the period where the frequency shift is large (that is, 12 MHz or more), the density of the nodes, that is, the radius of the clusters, decreases. It can be seen that interference from the system affects system performance.

However, since the transmission power of the cluster head 10 is assumed to be 0 dBm, it can be seen that the influence of interference due to the increase of the density of the node is limited to when the radius of the cluster is within about 8 m.

On the other hand, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily inferred by a computer programmer in the art. In addition, the written program is stored in a computer-readable recording medium (information storage medium), and read and executed by a computer to implement the method of the present invention. The recording medium may include any type of computer readable recording medium.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

1 is an explanatory diagram of a frequency common environment to which the present invention is applied;

2A is an exemplary diagram of frequency channel allocation between a cluster head and an adjacent cluster head in accordance with the present invention;

2b is a flow diagram of an embodiment of a method for allocating a frequency channel between a cluster head and an adjacent cluster head according to the present invention;

3A is an exemplary diagram of frequency channel allocation between a cluster head and an access point according to the present invention;

3b is a flow diagram of an embodiment of a method for allocating a frequency channel between a cluster head and an access point according to the present invention;

4 is a diagram showing an experimental result of the average packet error probability according to the cluster density according to the present invention.

* Explanation of symbols for the main parts of the drawings

110: cluster head

120: access point

Claims (17)

In the frequency channel allocation method for the cluster head, A first selecting step of generating a logical channel list for a logical channel in a frequency common environment of the first wireless network and the second wireless network, and selecting a first search channel from the logical channel list; A first checking step of confirming whether there is interference by the second wireless network by performing energy detection and carrier detection on the first search channel; A first update step of updating the logical channel list by determining whether to exclude the first search channel from the logical channel list according to a result of the confirmation of the first verification step; And A first channel allocation step of allocating a frequency channel for the cluster head of the first wireless network by using the updated logical channel list Frequency channel assignment method comprising a. The method of claim 1, The first selection step, In the logical channel list, a channel corresponding to 'the frequency range for one channel used by the second wireless network' is set as one channel group, and the lowest frequency in the center frequency axis for each channel group is set. And selecting one of two channels having a shift as the first search channel. The method of claim 1, The first checking step, When the energy detection result of the first search channel is larger than a predetermined heterogeneous network threshold and fails to detect a carrier, the first search channel is identified as having interference by the second wireless network. Channel assignment method. The method of claim 3, wherein The heterogeneous network threshold value, And a preset frequency channel allocation function in consideration of the transmission power, the power spectral density function, and the distance loss model of the second wireless network. The method according to any one of claims 1 to 4, After the first channel assignment step, A second selecting step of selecting a second search channel to check whether there is interference for an adjacent cluster head from the updated logical channel list; A second checking step of performing energy detection on the second search channel to check whether there is interference by an adjacent first wireless network; A second update step of re-renewing the updated logical channel list by determining whether to exclude the second search channel from the updated logical channel list according to the confirmation result of the second confirmation step; And A second channel allocation step of allocating a frequency channel belonging to the re-updated logical channel list for the cluster head of the first wireless network Frequency channel assignment method further comprising. The method of claim 5, wherein The second selection step, And selecting all channels belonging to the updated logical channel list as the second search channel. The method of claim 5, wherein The second confirmation step, And when the energy detection result of the second search channel is greater than a preset homogeneous network threshold, confirming that the second search channel has interference by the adjacent first wireless network. The method of claim 7, wherein The homogeneous network threshold is, And a preset frequency channel allocation method in consideration of a transmission power and a distance loss model of the adjacent first wireless network. The method of claim 5, wherein The frequency common environment, Frequency channel allocation method characterized in that the signal environment considering the fading channel. The method of claim 5, wherein The second channel assignment step, And assigning a frequency channel to the cluster head to optimize the performance of the entire network based on a value for a signal-to-noise ratio (SNR) among the channels of the re-update logical channel list. In the frequency channel allocation method for the cluster head, A selection step of generating a logical channel list for a logical channel in a frequency common environment of a first wireless network and an adjacent first wireless network, and selecting a search channel from the logical channel list; Confirming whether there is interference by the adjacent first wireless network by performing energy detection on the search channel; An update step of updating the logical channel list by determining whether to exclude the search channel from the logical channel list according to the verification result; And Allocating a frequency channel belonging to the updated logical channel list for the cluster head of the first wireless network Frequency channel assignment method comprising a. The method of claim 11, The selection step, And selecting all channels belonging to the logical channel list as the search channel. The method of claim 11, The checking step, And when the energy detection result value of the search channel is larger than a preset homogeneous network threshold, confirming that the search channel has interference by the adjacent first wireless network. The method of claim 13, The homogeneous network threshold is, And a preset frequency channel allocation method in consideration of a transmission power and a distance loss model of the adjacent first wireless network. The method of claim 11, The channel assignment step, And assigning a frequency channel to the cluster head to optimize the performance of the entire network based on a value of a signal-to-noise ratio (SNR) among the channels of the updated logical channel list. In the cluster head with the processor, A first selection function of generating a logical channel list for a logical channel in a frequency common environment of the first wireless network and the second wireless network, and selecting a first search channel from the logical channel list; A first checking function of checking an interference by the second wireless network by performing energy detection and carrier detection on the first search channel; A first update function for updating the logical channel list by determining whether to exclude the first search channel from the logical channel list according to a result of the check in the first confirmation function; And A first channel assignment function for allocating a frequency channel for the cluster head of the first wireless network by using the updated logical channel list A computer-readable recording medium having recorded thereon a program for realizing this. In the cluster head with the processor, A selection function of generating a logical channel list for a logical channel in a frequency common environment of a first wireless network and an adjacent first wireless network, and selecting a search channel from the logical channel list; A confirmation function of performing energy detection on the search channel to check whether there is interference by the adjacent first wireless network; An update function of determining whether to exclude the search channel from the logical channel list according to a result of the checking and updating the logical channel list; And A channel allocation function for allocating a frequency channel belonging to the updated logical channel list for the cluster head of the first wireless network A computer-readable recording medium having recorded thereon a program for realizing this.

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