KR101521049B1 - Base station and Relay station included in multi-hop cellular network, and Method for controlling the base station - Google Patents

Abstract

Disclosed are a base station and a relay station included in a multi-hop cellular network and a method for controlling the base station. A base station disclosed herein comprises: a reception unit which receives interference lists including information on a plurality of neighboring relay stations interfering with a given relay station, respectively, from N relay stations included in the base station; a channel assignment unit which uses the interference lists to generate a frequency reuse table and uses the frequency reuse table to perform channel assignment; and a channel switching unit which determines the interference between each of the N relay stations and the relay stations of a neighboring base station and, if an ith relay station among the N relay stations is interfered from the relay station of the neighboring base station, switches the channel assigned to the Ith relay station to another channel.

Description

A base station and a repeater included in the multi-hop cellular network, a control method of the base station, and a method for controlling the base station,

Embodiments of the present invention relate to a base station and a repeater included in a multi-hop cellular network, and a control method of the base station.

Next-generation cellular networks, such as LTE-advanced and IEEE 802.16m, provide high-quality multimedia services at low cost using repeaters such as femtocells and microcells. In particular, a network combined with Orthogonal Frequency Division Multiple Access (OFDMA) has attracted a great deal of attention due to the possibility of flexible radio resource management, and much research is underway.

As the demand for various types of wireless communication has increased, the issue of license frequency allocation among heterogeneous networks providing current services has become an important issue. Therefore, it is important to improve the spectrum efficiency by using the narrow frequency band as efficiently as possible It is being studied as one of the fields.

Frequency reuse is an essential technique for improving spectral efficiency in cellular networks with limited resources. This frequency reuse has been proposed as a research for a conventional single hop cellular network, but in recent years, studies are being conducted to apply a frequency reuse technique to a multi-hop cellular network.

1 is a diagram showing a concept of conventional frequency reuse.

In FIG. 1, one cell is shown, and six repeaters symmetrically distributed around a central base station (BS) are located. A region with the same pattern pattern means using the same frequency.

Referring to FIG. 1, in terms of spectrum efficiency, it is preferable that all base stations and repeaters simultaneously use all frequency bands as shown in FIG. 1 (c), but performance deterioration occurs at the boundaries of relay periods due to intensified interference. If each repeater uses different frequencies, the effect of interference can be minimized, but the spectral efficiency sharply decreases.

In general, a repeater can be installed at an arbitrary position according to the user's intention. However, existing researches can not be practically applied because a small number of repeaters propose a frequency reuse pattern considering only an evenly distributed topology. Therefore, a frequency reuse scheme of repeaters having arbitrary topology needs to be newly investigated.

Further, in a multi-hop cellular network having an arbitrary topology, each base station and a repeater can use all of a plurality of OFDMA channels having a narrow bandwidth. At this time, performance deterioration due to interference is serious particularly in the OFDMA downlink access link in which a base station or a repeater directly transmits a signal to a user terminal. This is because a large amount of data is simultaneously transmitted from the base station or the repeater to the user terminal using all the channels during the ODFMA downlink frame period.

A resource allocation method for controlling interference between repeaters, which has been studied in the prior art, basically assumes that all repeaters are allocated the entire frequency band of the system. Therefore, in order to solve the system optimization problem, all repeaters have to exchange information on the channel state among each other, which means that the number of repeaters increases exponentially as the number of repeaters increases.

In order to solve the above-described problems of the prior art, the present invention provides a method and apparatus for reducing traffic load from a repeater, controlling interference to satisfy a minimum requirement of traffic quality, And a repeater included in the base station and its cell area.

Other objects of the invention will be apparent to those skilled in the art from the following examples.

To achieve the above object, according to a preferred embodiment of the present invention, there is provided a base station, comprising: an interference list including information of a plurality of adjacent repeaters which interfere with a corresponding relay from N repeaters included in the base station, A receiving unit for receiving; A channel allocation unit for generating a frequency reuse table of the N repeaters using the interference list and performing channel allocation using the frequency reuse table; And determining whether interference between repeaters of each of the N repeaters and adjacent base stations is interfered by using the interference list, and when the i < th > repeater of the N repeaters is interfered by the repeater of the adjacent base station, And a channel switching unit for switching the selected channel to another channel.

Each of the N repeaters may measure a reception intensity of a radio signal transmitted from each of the plurality of neighboring repeaters, generate the interference list using information of the reception strength, and transmit the interference list to the base station.

Each of the N repeaters generates a set Qi including the plurality of adjacent repeaters, and when the total sum of the reception intensities of adjacent repeaters included in the set Qi is equal to or greater than a predetermined interference limit point, And the neighboring repeaters having the largest reception strength are removed from the set Qi, the process is repeated, and the reception strength of the neighboring repeaters included in the set Qi The process is terminated, and the generated interference list can be transmitted to the base station when the sum is less than or equal to the predetermined interference threshold.

The information of the plurality of neighboring repeaters included in the interference list may include information of a first neighboring repeater included in the base station and information of a second neighboring repeater included in the neighboring base station.

Wherein the channel allocation unit generates the frequency reuse table using the information of the first neighboring repeater, the frequency reuse table including information of a repeater that interferes with each of the N repeaters, the channel allocation causing interference The same channel can be allocated to the plurality of repeaters.

Wherein the receiver receives channel allocation information from the neighbor base station and the channel switching unit uses the channel allocation information and the information of the second neighboring repeater to determine interference between repeaters included in each of the N repeaters and adjacent repeaters, .

According to another embodiment of the present invention, there is provided a repeater comprising: a reception strength measurement unit measuring a reception strength of a radio signal transmitted from each of a plurality of adjacent repeaters; An interference list generation unit for generating an interference list including information on neighboring repeaters that interfere with the repeater among the plurality of adjacent repeaters using the information of the reception strength; And a transmission unit for transmitting the interference list to a base station having a cell including the repeater, wherein the interference list is used for channel allocation of N repeaters included in the base station, do.

According to another embodiment of the present invention, there is provided a method of controlling a base station, the method comprising: receiving an interference list including information on a plurality of neighboring repeaters which interfere with the repeater from N repeaters included in the base station; Generating a frequency reuse table of the N repeaters using the interference list; Performing channel allocation using the frequency reuse table; Checking whether there is interference between each of the N repeaters and a repeater included in the adjacent base station using the interference list; And switching the channel allocated to the i-th relay to another channel when the i-th relay station of the N repeaters is interfered with by the relay station of the neighboring base station. do.

According to the present invention, there is an advantage of increasing the data transmission rate with relatively high spectral efficiency while controlling interference to reduce the traffic load from the repeater and to satisfy the minimum requirement of traffic quality.

1 is a diagram showing a concept of conventional frequency reuse.
FIG. 2 is a diagram illustrating a schematic configuration of a multi-hop cellular network system according to an embodiment of the present invention.
3 is a diagram illustrating a schematic configuration of a repeater according to an embodiment of the present invention.
4 is a diagram for explaining a process in which the interference list generator generates an interference list according to an embodiment of the present invention.
5 is a diagram illustrating the meaning of an interference limit point according to an embodiment of the present invention.
6 is a diagram illustrating a schematic configuration of a base station according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating an overall flow of a base station control method (i.e., a channel allocation method of a base station) according to an embodiment of the present invention.
8 is a diagram for explaining the concept of the operation of the channel allocation unit according to an embodiment of the present invention.
9 is a view for explaining the concept of the operation of the channel switching unit according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a diagram illustrating a schematic configuration of a multi-hop cellular network system according to an embodiment of the present invention.

A multi-hop cellular network system 210 according to an exemplary embodiment of the present invention includes a plurality of base stations 210 and a plurality of relays 220 (for example, microcells, Etc.). A plurality of repeaters 220 are located in the cell 230 area of each base station 210.

As described above, in the multi-hop cellular network system, the base station 210 communicates with a terminal (not shown) through a repeater 220, and the repeater 220 uses a frequency reuse concept to transmit the base station 230, A plurality of channels are allocated from the plurality of channels.

2, it is assumed that the multi-hop cellular network system 200 is composed of seven cells 230, and the base station 210 located at the center of the cell 230 transmits the cell 230, and each of the repeaters 220 can be installed at any position. In addition, it is assumed that the repeater 220 allocated with a specific channel uses all the symbols of the corresponding channel and is equipped with a non-directional antenna. In general, since the distance between the repeater 220 and the repeater 220 is far greater than the distance between the terminal (not shown) and the repeater 220, It is assumed that the strength of the interference measured by the repeater 220 managing the strength and the corresponding terminal (not shown) is the same.

Hereinafter, the configuration of the base station 210 and the repeater 220 according to an embodiment of the present invention will be described in detail with reference to FIG. 3 and FIG.

3 is a diagram illustrating a schematic configuration of a repeater according to an embodiment of the present invention.

3 represents a repeater 220 shown in FIG. 2. The repeater 300 includes a receiving unit 310, a receiving strength measuring unit 320, an interference list generating unit 330, and a transmitting unit 340, .

The receiving unit 310 receives radio signals transmitted from a plurality of adjacent repeaters adjacent to the repeater 300, respectively. At this time, a plurality of neighboring relays include a neighboring repeater (hereinafter referred to as a "first neighboring repeater") included in a base station (hereinafter referred to as "the corresponding base station") in charge of a cell to which the relay device 300 belongs (Hereinafter referred to as a "second adjacent repeater") included in a cell managed by a neighboring base station adjacent to the base station.

 According to an embodiment of the present invention, a radio signal transmitted from each of a plurality of neighboring relays may be a pilot signal transmitted in a ranging interval of a contention-based channel access method. In this case, the ranging period includes a periodic ranging period.

The reception strength measuring unit 320 measures received signal strength indication (RSSI) of the received radio signal.

The interference list generator 330 generates an interference list using the information of the reception strength of the radio signal. Herein, the interference list includes information of adjacent repeaters that interfere with the repeater 300 among a plurality of adjacent repeaters. In addition, as described below, the interference list is used for channel allocation of N repeaters included in the base station of the cell in which the repeater 300 is located.

Hereinafter, a process of generating the interference list by the interference list generator 330 will be described in detail with reference to FIG.

Step 410 generates a set Qi comprising a plurality of adjacent repeaters.

In step 420, the sum of the radio signal reception strengths of adjacent repeaters included in the set Qi is calculated.

In step 430, it is determined whether the sum of radio signal reception strengths of adjacent repeaters included in the set Qi is equal to or greater than a predetermined interference threshold.

According to an embodiment of the present invention, the interference threshold may mean the maximum amount of interference that the repeater 300 can tolerate, as shown in FIG. As an example, the interference threshold can be expressed as: < EMI ID = 1.0 >

는 해당 중계기(300) 및 해당 중계기(300)와 통신을 수행하는 단말기들간의 채널 평균 이득,

는 해당 중계기(300)의 최대전송전력,

는 잡음 인자,

는 해당 중계기(300)의 최소 요구 신호 대 간섭 잡음비를 의미한다. here,

The channel average gain between the repeater 300 and the terminals performing communication with the repeater 300,

The maximum transmission power of the repeater 300,

Is a noise factor,

Denotes a minimum required signal-to-interference noise ratio of the repeater 300.

If the sum of the radio signal reception strengths of the neighboring repeaters included in the set Qi is equal to or greater than the preset interference limit, the adjacent repeater having the largest radio signal reception strength among the sets Qi is added to the interference list in step 440, (450) removes adjacent repeaters having the largest radio signal reception strength from the set Qi.

On the other hand, if the sum of the reception intensities of the adjacent repeaters included in the set Qi is equal to or less than the predetermined interference limit point, the interference list generation process is terminated.

In addition, the steps 420 to 450 are repeatedly performed, and the interference list generated after the termination is the final interference list.

Meanwhile, the transmitting unit 340 transmits the final interference list to the corresponding base station.

6 is a diagram illustrating a schematic configuration of a base station according to an embodiment of the present invention.

6 represents a base station 210 shown in FIG. 2 and includes a receiving unit 610, a channel assigning unit 620, a channel switching unit 630, and a transmitting unit 640 do.

7 is a diagram illustrating an overall flow of a control method of a base station (i.e., a channel allocation method of a base station) according to an embodiment of the present invention.

Hereinafter, the function of each component and the process performed for each step will be described in detail with reference to FIGS. 6 and 7. FIG.

First, in step 710, the receiving unit 610 receives the interference list from each of the N (two or more integers) repeaters included in the corresponding base station 600.

Next, in step 720, the channel allocator 620 generates a frequency reuse table of N relays using the interference list received from the N relays. Here, the frequency reuse table refers to a table containing information that summarizes which repeaters cause interference with which repeaters.

According to an embodiment of the present invention, the channel allocation unit may generate the frequency reuse table using the information of the adjacent repeater included in the base station 600, that is, information of the first adjacent repeater.

Thereafter, in step 730, the channel allocation unit 620 performs channel allocation using the frequency reuse table. At this time, one channel can be allocated to a plurality of repeaters, and channel allocation can allocate the same channel to a plurality of repeaters without interference.

That is, in steps 720 and 730, the base station 600 collects the interference information of its own intra-cell repeater and transmits the interference information to the base station 600 so that the interference can be duplicated within a range not exceeding a predetermined level And performs "interference mitigation operation inside sal" which allocates channels to the respective repeaters.

FIG. 8 shows the concept of the operation of the channel allocation unit 620. FIG.

Assuming that five repeaters are located in the cell area of the base station 600 in FIG. 8A, the base station 600 receives the interference list from the five repeaters.

Then, the base station 600 generates the frequency reuse table as shown in FIG. 8B by using the information of the first neighbor list in the interference list.

As an example, the repeater 1 exchanges serious interference with the adjacent repeaters 2 and 5, and the information of the repeaters 2 and 5 is included in the interference list of the repeater 1 at this time. Likewise, the interference list of the repeater 4 includes the information of the repeater 3. Because the frequency reuse table always needs to maintain diagonalization, the diagonalization is maintained by multiplying the lower triangle and upper triangle of the table by their elements.

Thereafter, the final channel allocation is performed as shown in FIG. 6 (c) by allocating the same channel to the repeaters having the identifiers of the rows and columns having the element 1 among the upper triangle of the frequency reuse table.

Since the allocated channel communicates only the repeaters that do not satisfy the interference list, the minimum signal-to-interference noise ratio requirement can always be satisfied unlike the method in which the repeater is allocated all the channels. In addition, since the frequency recycling ratio is higher than that of the orthogonal allocation method in which one channel is allocated to one repeater, the spectral efficiency also increases.

Next, in step 740, the channel switching unit 630 uses the interference list received from the N repeaters to check whether there is interference between each of the N repeaters and the repeaters included in the adjacent base station.

If the i < th > repeater of the N repeaters is interfered by the repeater of the adjacent base station, the channel switching unit 630 switches the channel assigned to the i < th > On the other hand, when the i-th relay station is not interfered with the relay station of the adjacent base station, no operation is performed. Also, step 750 is performed for all N repeaters.

In short, even after resolving the inter-cell interference through steps 720 and 730, there may still be interference between adjacent cells, or "out-of-cell interference. &Quot; In order to solve this problem, the base station 600 uses the interference list received from the N repeaters and the information exchange (sharing the channel allocation information through the backbone network) with the neighbor base stations, Channel switching is performed for a channel with less interference.

FIG. 9 shows the concept of the operation of the channel switching unit 630. FIG.

As described above, in order to mitigate inter-cell interference, each base station shares channel allocation information with neighboring base stations. In general, base stations are connected to each other by a wired backbone network, so they do not use additional radio resources when sharing channel allocation information.

9A, the Node B 1 can confirm the identifiers of the RSs allocated to the respective channels of the neighbor BS 2 and compare the identifiers of the RSs of the BS 1 with the interference lists of the BSs 1 , And it is confirmed whether deep interference occurs. At this time, the base station 1 confirms the interference outside the cell using a neighboring relay located outside the cell, i.e., the second neighboring relay.

All the base stations that are experiencing interference outside the deepened cell perform channel switching as shown in FIG. 9 (b) independently of each other to mitigate interference, and this is done by a distributed processing method.

That is, in FIG. 9A, it can be seen that the repeater 14 of the base station 2 is included in the interference list of the repeater 3 of the base station 1, and the two repeaters are equally allocated to the third channel. To mitigate severe interference in the third channel, the base station 1 switches the channel assigned to the repeater 3 and the repeater 4 to another channel that does not violate the interference list as shown in FIG. 9 (b).

According to an embodiment of the present invention, the channel switching unit 630 implements a channel switching scheme using the k-coloring problem of the graph theory.

The K-coloring problem is a method of assigning k colors to vertices of a graph G = (E, V) so that two vertexes connected to each other by an edge (E) . The base station performing the channel switching defines a vertex of the graph G = (E, V) as a relay pair assigned to each channel, and connects corners when significant interference is detected between the vertices. At each corner, a unique color is assigned to the assigned channel. The base station uses the channel allocation information of the adjacent cell to draw such a graph for all vertices connected to it. Then, we examine the edge connected to the adjacent cell, and when two vertexes connected by each edge are given the same color, we set the color of their vertex through the k-coloring problem.

The solution of K-coloring problem is various, but the following method is proposed in this paper. A color is assigned in order of the vertexes having the highest edges, and a color different from the color of the vertexes belonging to the adjacent vertexes is arbitrarily assigned. This process is performed until all the corners are assigned colors.

In summary, a base station and its control method according to an embodiment of the present invention can be classified into a method of mitigating interference in a cell, a method of mitigating interference within a cell, a method of allocating a channel considering interference between repeaters in a multihop cellular network in which a repeater having a certain topology is introduced, (Inter-cell) interference mitigation method.

In the existing frequency reuse scheme, only a small number of symmetrically distributed repeaters have been considered, and therefore, it has been difficult to apply the present invention to a real environment having high randomness of the repeater location. However, according to the present invention, it is advantageous to increase the signal-to-interference noise ratio by controlling the interference below the interference threshold, and reduce the amount of messages required for power control by reducing the category of the repeater where frequency reuse occurs. In addition, through improved frequency reuse and improved signal-to-interference noise ratio, it guarantees improved data rate while maintaining a small frame share.

In addition, the above-described technical features may be implemented in the form of program instructions that can be executed through various computer means and recorded in a computer-readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the embodiments or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules to perform the operations of the embodiments, and vice versa.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and limited embodiments and drawings. However, it should be understood that the present invention is not limited to the above- Various modifications and variations may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

Claims (11)

In the base station,
A receiver for receiving, from each of the N repeaters included in the base station, an interference list including information on a plurality of adjacent repeaters that interfere with the repeaters;
A channel allocation unit for generating a frequency reuse table of the N repeaters using the interference list and performing channel allocation using the frequency reuse table; And
The interference list is used to check whether there is interference between the N repeaters and the repeaters of the neighbor base stations. If the i < th > repeater of the N repeaters receives interference from the repeaters of the neighbor base stations, And a channel switching unit for switching the channel to another channel,
Wherein each of the N repeaters comprises:
Generates a set Qi including the plurality of adjacent relays,
When the sum of the reception intensities of the adjacent relays included in the set Qi is equal to or greater than a predetermined interference limit point, the adjacent repeater having the largest reception strength among the sets Qi is added to the interference list, Performs an interference list generation process to remove from the set Qi,
Wherein the interference limit point is expressed by the following equation as an amount of maximum interference that the repeater can tolerate.

here,

A channel average gain between the terminals performing communication with the repeater and the repeater,

The maximum transmission power of the repeater,

Is a noise factor,

Means the minimum required signal to interference noise ratio of the repeater. delete The method according to claim 1,
Wherein each of the N repeaters comprises:
Wherein the interference list generation process is terminated when the total sum of reception intensities of neighboring repeaters included in the set Qi is equal to or less than the interference limit point, and the generated interference list is transmitted to the base station. The method according to claim 1,
Wherein the information of the plurality of neighboring repeaters included in the interference list includes information of a first neighboring repeater included in the base station and information of a second neighboring repeater included in the neighboring base station. 5. The method of claim 4,
Wherein the channel allocation unit generates the frequency reuse table by using the information of the first adjacent repeater,
Wherein the frequency reuse table includes information on a repeater that interferes with each of the N repeaters, and the channel allocation allocates the same channel to a plurality of repeaters without interference. 5. The method of claim 4,
The receiver receives channel allocation information from the neighbor base station,
Wherein the channel switching unit checks interference between each of the N repeaters and a repeater included in a neighboring base station using the channel allocation information and the information of the second neighboring repeater. In the repeater,
A reception strength measuring unit measuring a reception strength of a radio signal transmitted from each of a plurality of adjacent repeaters;
An interference list generation unit for generating an interference list including information on neighboring repeaters that interfere with the repeater among the plurality of adjacent repeaters using the information of the reception strength; And
And a transmitting unit for transmitting the interference list to a base station that manages a cell including the repeater,
The interference list is used for channel allocation of N repeaters included in the base station,
The interference list generator
Generates a set Qi including the plurality of adjacent relays,
When the sum of the reception intensities of the adjacent relays included in the set Qi is equal to or greater than a predetermined interference limit point, the adjacent repeater having the largest reception strength among the sets Qi is added to the interference list, Performs an interference list generation process to remove from the set Qi,
Wherein the interference limit point is expressed by the following equation as an amount of maximum interference that the repeater can tolerate.

here,

A channel average gain between the terminals performing communication with the repeater and the repeater,

The maximum transmission power of the repeater,

Is a noise factor,

Denotes a minimum required signal to interference noise ratio of the repeater. 8. The method of claim 7,
The interference list generation unit generates,
And terminates the interference list generation process when the total sum of reception intensities of neighboring repeaters included in the set Qi is equal to or less than the interference limit point, and transmits the generated interference list to the base station after finishing the interference list generation process. delete 8. The method of claim 7,
Wherein the plurality of neighboring relays include a neighboring repeater included in the base station and a neighboring repeater included in the neighboring base station. delete

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