WO2011085513A1

WO2011085513A1 - Soft frequency reuse method and base station using the method

Info

Publication number: WO2011085513A1
Application number: PCT/CN2010/000054
Authority: WO
Inventors: 王栋耀; 庞继勇; 蒋琦; 刘建国
Original assignee: 上海贝尔股份有限公司; 阿尔卡特朗讯
Priority date: 2010-01-13
Filing date: 2010-01-13
Publication date: 2011-07-21
Also published as: CN102577469B; CN102577469A

Abstract

Provided in the invention is a soft frequency reuse method for downlink transmission, which includes the following steps: for N cells, the system bandwidth is divided into multiple frequency bands, wherein N≥1; for each cell, the frequency band used for serving cell edge user devices in the cell is selected; and relay nodes in each cell are notified in order that the frequency band which is different from the frequency band used for serving cell edge user devices in the cell is used to serve relay user devices. The soft frequency reuse method according to the invention can be used in Long Term Evolution-Advanced (LTE-A) system, and better cell average spectrum effectiveness and cell edge spectrum effectiveness can be achieved.

Description

Soft frequency multiplexing method and base station using the same

The present invention relates to an LTE-A (Long Term Evolution Advance) system, and more particularly to a soft frequency multiplexing method for downlink transmission in an LTE-A system and a base station using the same. Background technique .

Inter-Cell Interference Coordination (ICIC) is an important issue in the field of wireless communication systems. It is used to deal with inter-cell interference and improve the bit rate of cell edges. Some ICIC solutions have been proposed and discussed in LTE. The most common method of ICIC is the semi-static scheme of Soft Frequency Reuse (SFR). In essence, the soft frequency reuse scheme works in a power coordinated manner. In the soft frequency reuse scheme, for each cell in the network, a part of the frequency band is reserved for the cell edge user, and the transmission power is amplified in the reserved frequency band. In a three-cell cellular network, the reserved portion is typically 1/3 of the total frequency band and is orthogonal between adjacent cells. Since the cell edge user is limited to using only the reserved frequency band, the reserved 1/3 band having the amplified power is referred to as the cell edge band. On the other hand, since the other 2/3 bands for other users are used only by users of the cell center, this 2/3 band is referred to as a cell center band. However, when the cell edge user does not occupy the cell edge band, the cell internal user can use the cell edge band. Fig. 8 shows the spectrum setting of a three-cell cellular layout according to the existing soft frequency reuse method.

However, the LTE specification does not allow for downlink power control. This is because the downlink power control interferes with the CQI (Channel Quality Indicator) measurement, thus affecting the accuracy of downlink scheduling. Therefore, the above soft frequency reuse scheme requiring downlink power control cannot be applied to downlink transmission of LTE.

The present invention proposes a soft frequency multiplexing method for downlink transmission of an LTE system. Summary of the invention

It is an object of the present invention to provide a soft frequency reuse method that does not require power control and thus can be applied to downlink transmission of an LTE system.

According to a first aspect of the present invention, a soft frequency multiplexing method for downlink transmission is proposed. The method includes the following steps: dividing, for N cells, a system bandwidth into multiple frequency bands, where N^l; for each cell, selecting a frequency band for serving a cell edge user equipment of the cell; and notifying a relay node in each cell The serving user equipment is served by using a frequency band different from the frequency band of the cell edge user equipment serving the cell.

Preferably, the method further comprises the steps of: selecting, for all N cells, a frequency band for serving internal user equipment in each cell; wherein, the frequency band used for serving the internal user equipment is used for serving the cell edge user equipment The frequency band is different from the frequency band used to serve the relay user equipment.

Preferably, the frequency band of the selected serving cell edge user equipment is different between adjacent cells. Preferably, the frequency band of the selected serving cell edge user equipment is different between the cells. Preferably, the relay node serves to relay the user equipment using all frequency bands except the frequency band of the serving cell edge user equipment and the frequency band serving the internal user equipment.

Preferably, the soft frequency reuse method further includes the step of: determining, according to the user equipment association scheme, the relay user equipment to be served by the relay node.

Preferably, the soft frequency multiplexing method further includes the steps of: determining, by the user equipment other than the relay user equipment, that the user equipment is an internal user equipment when the receiving quality of the user equipment is greater than a predetermined threshold, otherwise determining the user The device is a cell edge user equipment.

Preferably, for each cell, the relay node is located at the center of the cell.

Preferably, each cell ή is arranged with one or more relay nodes.

Preferably, backhaul transmission from the base station to the relay node is performed in some subframes for downlink transmission.

Preferably, the method is applied to an LTE-A system.

According to a second aspect of the present invention, a base station is provided, comprising: a frequency band dividing unit, configured to divide a system bandwidth into a plurality of frequency bands for each cell, where Ν ≥ 1 ; a frequency band scheduling unit, configured for each cell And selecting a frequency band for serving the cell edge user equipment of the cell; and a relay node notification unit, configured to notify the relay node in each cell to use a frequency band different from a frequency band of the cell edge user equipment serving the cell The service relays the user equipment.

Preferably, the frequency band scheduling unit further selects a frequency band for serving all internal user equipments in each cell for all the cells, wherein the frequency band used for serving the internal user equipment and the user equipment for serving the cell edge are used. The frequency band and the frequency band used to serve the relay user equipment are different.

Preferably, the frequency band scheduling unit selects a frequency band of the serving cell edge user equipment selected by the neighboring cell Different.

Preferably, the frequency band scheduling unit has different frequency bands for the serving cell edge user equipment selected for each cell.

Preferably, the relay node uses all frequency bands except the frequency band of the serving cell ii user equipment and the frequency band serving the internal user equipment to serve the relay user equipment.

Preferably, the base station further includes a user equipment determining unit, configured to determine, according to the user equipment association scheme, a relay user equipment to be served by the relay node. '

Preferably, the user equipment determining unit determines, for the user equipment other than the relay user equipment, that the user equipment is an internal user equipment when the receiving quality of the user equipment is greater than a predetermined threshold, and otherwise determines that the user equipment is a cell edge user equipment.

Preferably, for each cell, the relay node is located at the center of the cell.

Preferably, one or more relay nodes are arranged within each cell.

Preferably, the base station is applied to an LTE-A system. DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from

1 is a flowchart showing a soft frequency multiplexing method according to a first embodiment of the present invention; FIG. 2 is a diagram showing a spectrum setting of a three-cell cellular network layout of a soft frequency multiplexing method according to a first embodiment of the present invention;

3 is a block diagram showing a system for implementing a soft frequency multiplexing method according to a second embodiment of the present invention; FIG. 4 is a diagram showing a spectrum of a three-cell cellular network layout of a soft frequency multiplexing method according to a second embodiment of the present invention; Setting

FIG. 5 shows an LTE frame structure that can be used with the soft frequency reuse method according to the second embodiment of the present invention;

6 is a diagram showing a relationship between a subframe and a spectrum setting of a soft frequency multiplexing method according to a second embodiment of the present invention;

Figure 7 is a diagram showing simulation results of a soft frequency reuse method according to the present invention; FIG. 8 shows a specific embodiment of a spectrum design of a three-cell cellular network layout according to an existing soft frequency reuse method

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, some specific embodiments are for illustrative purposes only and are not to be construed as limiting the invention in any way. It is to be noted that the illustrations are only illustrative of the differences from the prior art, and the conventional structures or structures are omitted so as not to obscure the understanding of the present invention.

In LTE-A, the relay is used as an enhancement technique for implementing traffic/signaling forwarding between the base station and the user equipment to achieve better coverage and throughput. Compared to a base station, a relay node has a lower transmit power and therefore less interference to neighboring cells.

The inventors of the present application have recognized that this feature of the relay node can be used such that soft frequency reuse techniques can be used in downlink transmissions. .

1 is a flow chart showing a soft frequency multiplexing method according to a first embodiment of the present invention; and FIG. 2 is a diagram showing a spectrum setting of a three-cell cellular network layout of a soft frequency multiplexing method according to a first embodiment of the present invention.

In the soft frequency reuse method according to the first embodiment of the present invention, a relay node is deployed at the center of each cell.

In addition, user equipment in each cell is classified into three categories;

中继 Relay user equipment: served by the base station through the relay node;

小区 Cell edge user equipment: Directly served by the base station, usually located at the edge of the cell, subject to strong interference from neighboring cells;

0 Internal user equipment: Other user equipment directly served by the base station, usually located at the center of the cell, has good reception quality.

As shown in FIG. 1, the soft frequency multiplexing method according to the first embodiment of the present invention includes the following steps: Step S101, dividing a frequency band.

The entire system bandwidth is divided into four sub-bands, namely F], F2, F3 and F4, as shown on the right side of Figure 2. Here, the number of divided sub-bands is not necessarily limited to four. For example, when there is no internal user equipment, that is, only the relay user equipment and the cell edge user equipment, three sub-bands can be divided, one of which is used by the base station and serves the cell edge user equipment, and the other two are used by the relay node. And serve to relay user equipment.

Step S103, selecting a frequency band for serving internal user equipment in each cell. In the absence of This step can be omitted when the internal user equipment is used.

Step S105: For each cell, select a frequency band different from a frequency band used for serving the internal user equipment to serve the cell edge user equipment of the cell.

Step S107, notifying the relay node in each cell to serve the relay user equipment by using one or more frequency bands different from the frequency band of the serving internal user equipment and the service edge user equipment.

The frequency band of the selected serving cell edge user equipment may be different between adjacent cells or different between all cells.

As shown on the left side of FIG. 2, in the three-cell network according to the first embodiment of the present invention, the frequency band F4 will be used by the base station to provide services to its internal user equipment in each cell, and the frequency bands F1, F2 and F3 are allocated to Three cells are provided to provide services to corresponding cell edge user equipment. Bands F1, F2 and F3 are orthogonal. Furthermore, for a particular cell, when the base station uses the frequency band Fi (i = 1, 2 or 3) to serve its edge user equipment, the relay node can use any one or both of the other two frequency bands to service its associated Relay user equipment.

Obviously, for cell edge user equipment, strong interference from neighboring cells is reduced due to orthogonality between frequency bands, so better system performance can be achieved for these cell edge user equipments.

In addition, a plurality of relay nodes are configured at the center of the cell, and since the relay nodes have lower transmission power, interference between them is small, so that spectrum multiplexing between the relay nodes in the cell can be realized. Better cell average performance.

For backhaul transmission from the base station to the relay node, some specific time slots may be reserved for the entire cellular network for backhaul transmission. Generally, the relay node is located at the center of the cell and is fixed, so that link performance between the base station and the relay node can be ensured by a multi-antenna technique or the like. 3 is a block diagram showing a system for implementing a soft frequency multiplexing method according to a second embodiment of the present invention; FIG. 4 is a diagram showing spectrum setting of a three-cell cellular layout of a soft frequency multiplexing method according to a second embodiment of the present invention; FIG. 5 shows an LTE frame structure usable with the soft frequency multiplexing method according to the second embodiment of the present invention; FIG. 6 shows a subframe and a soft frequency multiplexing method according to a second embodiment of the present invention; A diagram of the spectrum settings.

As shown in FIG. 3, in a system for implementing a soft frequency multiplexing method according to a second embodiment of the present invention, a base station 10 includes a frequency band dividing unit 102, configured to divide a system bandwidth into a plurality of frequency bands for N cells, where N3⁄4 l; a frequency band scheduling unit 103, configured to select, for each cell, a cell for serving the cell a frequency band of the cell edge user equipment; and a relay node notification unit 104, configured to notify the relay node in each cell to serve the relay using one or more frequency bands different from the frequency band of the cell edge user equipment serving the cell User equipment.

The base station 10 may further include a user equipment determining unit 101 for determining that the user equipment in each cell is one of an internal user equipment, a cell edge user equipment, and a relay user equipment. In the case where it is determined that there is an internal user equipment, the band scheduling unit 103 also selects one frequency band for all N cells for serving the internal user equipment in each cell. In the soft frequency multiplexing method according to the second embodiment of the present invention, a three-cell (N=3) network is taken as an example for description.

As shown in Fig. 4, in the soft frequency multiplexing method according to the second embodiment of the present invention, four relay nodes are arranged at the center of each cell. Of course, the number of relay nodes and the way they are deployed can be changed according to actual conditions.

Assume that an average of 25 user equipments are served in each cell.

The user equipment determining unit 101 determines that four relay nodes can serve 10 user equipments according to an appropriate user equipment association scheme, such as maximum received power, etc., that is, 10 user equipments are determined as relay user equipments. For other user equipments, the user equipment determining unit 101 uses the appropriate metric as a threshold, for example, a 5 dB reception quality threshold, and determines the user equipment as an internal user equipment when the receiving quality of the user equipment is greater than 5 dB, otherwise, the user equipment determines It is a cell edge user equipment. In the soft frequency multiplexing method according to the second embodiment of the present invention, five user equipments are determined as cell edge user equipments, and the other ten user equipments are determined as internal user equipments.

For a typical LTE system, each radio frame is 10ms, including 20 time slots with a length of 0.5ms. These time slots are numbered 0~19, as shown in Figure 5. Two consecutive time slots are defined as subframes, where subframe i consists of time slot 2i and time slot 2i+1. Therefore, there are 10 subframes available for downlink transmission.

In the case where the system band is 10 MHz, there are a total of 50 physical resource blocks PRB (Physical Resource Block;) per subframe.

The frequency band dividing unit 102 can divide the entire system bandwidth into the following four frequency bands according to factors such as the number of relay nodes, the deployment mode, and the multiplexing mode:

Fl: 1~8 PRB;

F2: 9-16 PRB;

F3: 17~24 PRB; and F4: 25~50 PRB.

A relationship diagram between a subframe and a spectrum setting of the soft frequency multiplexing method according to the second embodiment of the present invention is as shown in FIG. 6. .

In the soft frequency multiplexing method according to the second embodiment of the present invention, subframe 2 and subframe 3 are reserved for backhaul transmission. Of course, it is also feasible to select other subframes for backhaul transmission. Therefore, on these two subframes, the data transmission of the relay backhaul link from the base station to the relay node will be scheduled with the highest priority. If the backhaul transmission does not exhaust all of the resources in the two subframes, the remaining resources can also be scheduled for data transmission from the base station to the internal user equipment.

For other subframes, band F4 is scheduled for data transmission from the base station to internal user equipment in all cells. However, in cell I, band F1 is only scheduled for data transmission from the base station to the cell edge user equipment. Bands F2 and F3 are scheduled for data transfer from the relay node to its relay user equipment. In cell Π, band F2 is only scheduled for data transmission from the base station to the cell edge user equipment. Bands F1 and F3 are scheduled for data transmission from the relay node to its relay user equipment. Finally, in cell III, band F3 is only scheduled for data transmission from the base station to the cell edge user equipment. Bands F1 and F2 are scheduled for data transmission from the relay node to its relay user equipment.

Under the above resource allocation, when the base station serves its cell edge user equipment in one frequency band, only the relay node transmits data on the frequency band in its neighboring cell. Since the transmission power of the relay node is much lower than the transmission power of the base station, the interference received by these cell edge user equipments is small, and the reception quality can be greatly improved. On the other hand, since the relay node is placed at the center of the cell, the relayed user equipment it serves is also located at the center of the cell, so the interference received by the relay user equipment from the neighboring cell is also low. In addition, since the distance of the relay user equipment received from the relay node is very large due to the short distance, the reception quality of the relay user equipment is also improved. For internal user equipment, the reception quality is not affected.

The soft frequency multiplexing method according to the second embodiment of the present invention does not require power control at the base station, and therefore, can be applied to a relay enhanced network.

The soft frequency reuse method according to an embodiment of the present invention can provide better system performance, including cell average spectral efficiency and cell edge spectrum efficiency, compared to the performance of a non-relayed cellular network.

Fig. 7 is a diagram showing simulation results of a soft frequency multiplexing method according to the present invention.

Use the simulation parameters shown in Table 1 below.

Parameter value

The peak nest layout is hexagonal, 7 base stations, each base station has three cells

II Prob(R)=0.5-min(0^5 3exp(-0.3!R))+m1n(0.5,3exp(-R/0.095))

Table 1: Simulation parameters

In the simulation, some specific subframes are reserved for backhaul transmission from the base station to the relay node, and the relay user equipment served by the relay node omits these subframes. If the backhaul transmission does not exhaust all reserved resources, the internal user equipment in the cell can also use the remaining reserved resources. In addition, when deploying the relay node, the base station transmit power is adjusted to 38 dBm.

Table 2 below shows the simulation results of the soft frequency reuse method of the non-relayed cellular network and the cell average spectral efficiency and cell edge spectral efficiency of the method of the present invention.

Table 2: Performance Comparison The simulation results show that the soft frequency reuse method according to the present invention can provide better cell average spectral efficiency and cell edge spectral efficiency. '

The soft frequency reuse method according to the present invention can reduce the base station transmission power and improve the cell capacity, and the experience of the cell edge user is also improved.

Furthermore, the soft frequency reuse method according to the present invention can be applied to class I relays and class II relays.

Although the above description relates to a plurality of units, the present invention can also be implemented by dividing one unit into a plurality of units or combining a plurality of units into one unit as long as it can still perform the corresponding functions.

Those skilled in the art will readily recognize that the different steps of the above methods can be implemented by a programmed computer. Herein, some embodiments also include a machine readable or computer readable program storage device (eg, a digital data storage medium) and encoding machine executable or computer executable program instructions, wherein the instructions perform some of the above methods or All steps. For example, the program storage device can be a digital memory, a magnetic storage medium (such as a disk and tape), a hardware or an optically readable digital data storage medium. The implementation also includes a programming computer that performs the steps of the above method.

The description and drawings merely illustrate the principles of the invention. It will be appreciated that those skilled in the art are able to devise various structures, and the various structures are not described or illustrated herein. In addition, all the examples mentioned herein are expressly used primarily for teaching purposes to assist the reader in understanding the principles of the invention and the contribution of the inventors to the field. 0054

Conception, and should be construed as not limiting the specific examples and conditions mentioned. In addition, all statements herein reciting principles, aspects, and embodiments of the invention, as well as the specific examples thereof,

The above description is only for implementing the embodiments of the present invention, and those skilled in the art should understand that any modifications or partial substitutions of the scope of the present invention should fall within the scope defined by the claims of the present invention. The scope of protection of the invention should be determined by the scope of the claims.

Claims

Rights request

A soft frequency reuse method for downlink transmission, comprising the steps of:

For N cells, the system bandwidth is divided into multiple frequency bands, where N≥l;

For each cell, selecting a frequency band for serving the cell edge user equipment of the cell; and notifying the relay node in each cell to serve the relay user using a frequency band different from the frequency band of the cell edge user equipment serving the cell device.

2. The method of claim 1 further comprising the step of:

For all N cells, a frequency band is selected for serving internal user equipment in each cell; wherein, a frequency band for serving the internal user equipment and a frequency band for serving the cell edge user equipment and for serving the relay user equipment The frequency bands are different.

The soft frequency multiplexing method according to claim 1 or 2, wherein the frequency band of the selected serving cell edge user equipment is different between adjacent cells.

The soft frequency multiplexing method according to claim 1 or 2, wherein the frequency band of the selected serving cell edge user equipment is different between the cells.

The soft frequency multiplexing method according to claim 2, wherein the relay node serves the relay user equipment using all frequency bands except the frequency band of the serving cell edge user equipment and the frequency band of the serving internal user equipment.

6. The soft frequency reuse method according to claim 1, further comprising the step of: determining a relay user equipment to be served by the relay node according to the user equipment association scheme.

The soft frequency multiplexing method according to claim 6, further comprising the steps of: determining, by the user equipment other than the relay user equipment, that the user equipment is an internal user equipment when the receiving quality of the user equipment is greater than a predetermined threshold, Otherwise, the user equipment is determined to be a cell edge user equipment.

The soft frequency multiplexing method according to claim 1, wherein, for each cell, a relay node is located at a cell center.

The soft frequency multiplexing method according to claim 8, wherein one or more relay nodes are arranged in each cell.

The soft frequency multiplexing method according to claim 1, wherein the backhaul transmission from the base station to the relay node is performed in some subframes for downlink transmission.

The soft frequency multiplexing method according to claim 1, wherein the method is applied to LTE-A In the system.

12. A base station comprising:

a frequency band dividing unit, configured to divide a system bandwidth into a plurality of frequency bands for the N cells, where the N-band scheduling unit is configured to select, for each cell, a frequency band of a cell edge user equipment serving the cell;

The relay node notifying unit is configured to notify the relay node in each cell to serve the relay user equipment by using a frequency band different from the frequency band of the cell edge user equipment serving the cell.

The base station according to claim 12, wherein the frequency band scheduling unit further selects one frequency band for serving all internal user equipments in each cell for all N cells; wherein, for serving internal user equipments The frequency band is different from the frequency band used to serve the cell edge user equipment and the frequency band used to serve the relay user equipment.

The base station according to claim 12 or 13, wherein the frequency band scheduling unit has different frequency bands for the serving cell edge user equipments selected by the neighboring cells.

The base station according to claim 12 or 13, wherein the band scheduling unit has different frequency bands for the serving cell edge user equipment selected for each cell.

16. The base station according to claim 13, wherein the relay node serves to relay the user equipment using all frequency bands except the frequency band of the serving cell edge user equipment and the frequency band serving the internal user equipment.

The base station according to claim 12, further comprising a user equipment determining unit, configured to determine, according to the user equipment association scheme, a relay user equipment to be served by the relay node.

The base station according to claim 17, wherein the user equipment determining unit determines, for the user equipment other than the relay user equipment, that the user equipment is an internal user equipment when the receiving quality of the user equipment is greater than a predetermined threshold, otherwise, The user equipment is determined to be a cell edge user equipment.

19. The base station according to claim 12, wherein, for each cell, the relay node is located at a center of the cell.

20. The base station according to claim 19, wherein one or more relay nodes are arranged within each cell.

The base station according to claim 12, wherein the backhaul transmission from the base station to the relay node is performed in some subframes for downlink transmission.

22. The base station according to claim 12, wherein the base station is applied to an LTE-A system.