KR20110008704A - Space division multi access service method for future wireless communication system based virtual sector - Google Patents

Abstract

PURPOSE: A space division multi access service method for a virtual sector based adaptive antenna system is provided to allocate transmission power through one or more time scheduling operations of terminals selected in a virtual sector. CONSTITUTION: A base station receives a report about a beam index and SINR information for each beam index with each user terminal, wherein the beam index is selected in advance from minimum width beams transmitted from the base station based on a higher SINR(Signal to Interference Noise Ratio)(S503). The base station selects a user terminal for each virtual sector(S507) and determines the kind of beams allocated to the user terminal(S509). The base station allocates transmission power to the user terminal(S511).

Description

{Space division multi access service method for future wireless communication system based virtual sector}

The present invention relates to a virtual sector-based adaptive antenna system, and more particularly, in a next generation mobile communication system using an array antenna, a network is configured to facilitate space reuse for a plurality of users simultaneously considering a user's location. The present invention relates to a spatial segmentation multiple access service method in a virtual sector based adaptive antenna system for identifying a user's location based on a virtual sector and allocating an optimal transmission power for each beam in consideration of a channel state of each user.

The mobile communication system started with providing a voice-oriented low-speed service, but recently, a system for providing a high quality multimedia service based on a wireless data packet has been developed. Currently, 3GPP Long Term Evolution (LTE) centering on 3rd Generation Partnership Project (3GPP) and Ultra Mobile Broadband (UMB) centering on 3rd Generation Partnership Project 2 (3GPP2) have been developed and standardized. It is a representative example of efforts to develop high speed, high quality wireless data packet transmission system of several tens of Mbps or more in 4th generation mobile communication system.

Since the fourth generation mobile communication system is based on the provision of high-speed, high-quality virtual multimedia services beyond the existing communication system, techniques for providing high-speed data services using limited frequency resources have been proposed. These technologies include SDMA for maximizing space resource reuse with beamforming technology using multiple antennas, and multiple input / output antenna technology using multiple antennas of a transmitter and a receiver.

In terms of standardization, SDMA is currently standardized under the name of an adaptive antenna system (AAS) in IEEE 802.16e (Mobile WiMAX). This spatial division multiple access technology is a technology that simultaneously serves a terminal with low spatial correlation at the same frequency and time using an array antenna capable of forming a beam. It is a system in a wireless cellular network in which a plurality of terminals exist in a wide area. It is a wireless communication technology that can dramatically improve the capacity of. The beamforming technique used in IEEE 802.16e is classified into a beamforming technique using symmetry of up / down channels based on a time division duplex (TDD) and a codebook based beamforming technique.

A beamforming technique using symmetry of uplink / downlink channels of TDD is a method in which a base station estimates a downlink channel state of a corresponding UE based on a signal received from a UE to obtain a transmission weight factor of an array antenna. This technique has the advantage that the uplink channel state of the UE can be directly used for the downlink beam configuration, so that it can cope with the channel change faster than the codebook-based beamforming technique. However, a separate reverse preamble is used for uplink channel estimation. The same additional signal transmission overhead occurs.

In the codebook-based beamforming technology, the UE estimates a downlink channel state using a preamble signal received from a base station, selects an optimal code from a beamforming codebook, and feeds back the information to the base station. Technology to form. This method has the advantage that the overhead is low because no additional signal is required other than the existing preamble to identify the downlink channel state of the UE, but the point of obtaining the antenna weight for beamforming and the point of forming and transmitting the actual beam Due to the large delay time, performance deterioration has a significant disadvantage in a large channel change.

When the beamforming technique is applied to the spatial division multiple access scheme, the base station can allocate radio resources to multiple terminals at the same time. At this time, if a beam is formed to transmit data to service a terminal allocated to a radio resource, interference may occur between beams, and the interference may make it difficult to extract a magnetic signal by lowering a signal-to-noise and interference ratio of the terminal. .

Therefore, in order to improve system capacity by using a space division multiple access technique, an efficient scheduling algorithm for selecting a user group that uses the same frequency at the same time in one cell is required.

Looking at the prior art in this field, most of the technologies first select a user to be serviced first in the current timeslot, and then gradually add users, the interference degree is compared by comparing the threshold between the beam interference by the added user If it is not larger than the threshold, repeat the process of adding the user.

However, in case of using such a conventional user scheduling algorithm, the performance variation of SDMA varies greatly depending on how the first user is selected, and it is necessary to calculate all the degree of interference for all users. There is a problem that there is a lot of channel information and the complexity of the algorithm is too high to operate in a real system.

Accordingly, an object of the present invention for solving the above problems of the prior art is to provide a low complexity space division multiple access service method for minimizing overhead in a next generation mobile communication system implemented with a virtual sector based adaptive antenna system. will be.

In order to achieve the above object, the spatial segment multiple access service method of the virtual sector based adaptive antenna system according to the present invention includes a virtual sector in which each of the sectors divided by the linear array antenna is divided into a plurality of virtual sectors. In the adaptive antenna system, a first step of the base station selects one user terminal for each virtual sector, a second step for the base station determines the type of beam to be assigned to the user terminal selected for each virtual sector, and the base station And a third step of allocating transmission power to the user terminal selected for each of the virtual sectors.

In addition, the spatial division multiple access service method of the virtual sector based adaptive antenna system according to the present invention, the first step in which the base station rotates and transmits the smallest beam including the beam index information, the base station is each user in the cell A second step in which each user terminal reports a predetermined number of beam indexes and received signal strength information for each beam index in order of receiving signal strength being highest among minimum width beams transmitted from the base station; A third step of selecting a user terminal for each user; and a fourth step of determining, by the base station, a beam width to be allocated to the user terminal using received signal strength information for each beam index received from the user terminal selected for each virtual sector; And a fifth step of the base station forming a beam according to the direction of the user terminal.

As described above, the present invention, in the virtual sector-based adaptive antenna system using the virtual sector to select the low spatial correlation terminals with low complexity, using the rotating minimum width beam to determine the position of the terminal and narrow the terminal By deciding whether to allocate a beam or an optical beam and proposing a method of allocating transmission power by scheduling the terminals selected once in the virtual sector, there is an advantage of maximizing the performance of the system with low complexity.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, only parts necessary for understanding the operation of the present invention will be described.

1 is a diagram illustrating a general three sector antenna system using a fixed beam. In a typical three sector antenna system, a base station has a separate antenna for each sector, and one sector antenna forms a beam of 120 degrees to serve one sector. Since a typical three sector antenna system serves all users equally with a wide beam of 120 degrees, the terminal MS1 located at the edge far from the base station BS does not receive smooth service with low antenna gain. In addition, the conventional three-sector antenna system does not form an optimized beam according to the position, movement speed and channel state of each terminal (MS2, MS3, MS4), there is a problem that can not guarantee a high quality of service compared to available space resources have. In addition, since the power transmitted by the base station (BS) is transmitted in all directions irrespective of the position of the terminal receiving the service, there is a problem that deepens the interference between adjacent cells to lower the overall capacity of the system.

In order to solve the problem of the general three-sector antenna system, the space division multiple access technology has been actively studied and standardized.

2 shows an example of applying a space division multiple access technique to a three sector antenna system. In the case of using the spatial division multiple access technique in the three-sector antenna system, since the narrow beam is allocated to each terminal, the antenna gain is improved even in the case of the terminal MS1 having a poor channel condition away from the base station BS. You can get services. In addition, in the case of the terminal MS2 located in the base station BS and the invisible channel (NLOS) region or the terminal MS4 having a high moving speed, a relatively wide beam is allocated or a service using beam tracking technology is used. Can provide. In addition, the terminal MS3 located in an area close to the base station BS can be serviced with low transmission power.

However, in order to adaptively form a beam according to the state of the terminal as described above, a technique for selecting a plurality of users having low spatial correlation and forming an optimal beam for each selected user is required. Since the spatial correlation is related to the user's channel status, moving speed, and position, in order to select a terminal with low spatial correlation, the channel status and moving speed between all antennas in the service area of the cellular base station and all antennas of the base station are selected. And location information is needed.

In order for the base station to know all of this information, the amount of information that the terminal must report to the base station is too large, and the overhead is very large.Also, even if the base station knows all of the above information, the algorithm and algorithm for searching for the terminal having low spatial correlation The amount of computation required to form the beam by calculating the weight value in real time is too large.

3 is a diagram illustrating a virtual sector based adaptive antenna system according to an embodiment of the present invention.

In the present invention, the physical sector is divided into a plurality of virtual sectors. In order to select a terminal having low spatial correlation, only one terminal is serviced within one virtual sector, and a narrow beam is rotated to determine a channel state and position of the terminal.

3 is a diagram illustrating an overall operation scenario of an adaptive antenna system composed of six virtual sectors. Base station (BS) is composed of three sectors (Sector1, Sector2, Sector3), each sector includes a linear array antenna 308 beam direction and beam adaptively according to the position of the terminal and the channel conditions in each sector You can control the width of. In the case of FIG. 3, since the actual number of sectors of the base station BS is three, the base station has three linear array antennas, and each linear array antenna can generate a beam having a width of 0 to 120 degrees, and the direction of the beam is also zero. Adjustable up to ~ 120 degrees. As shown in FIG. 3, the base station has three physical sectors, and each sector is divided into two sub-sectors and divided into six virtual sectors. In this case, the number of virtual sectors is adjustable according to the minimum / maximum beam width that the base station can make.

Since the base station selects one user from one virtual sector and forms a beam toward the corresponding user, the virtual sector is equal to the number of terminals that can be simultaneously serviced by the base station through space division multiple access. In order to select a user to be serviced in the virtual sector and to find the direction of the beam and the width of the beam, it is necessary to know the current position and channel state of the terminal.

As shown in FIG. 4, the base station rotates a beam having the minimum width that the base station can make, thereby determining the position and channel state of the terminal. That is, assuming that the width of the minimum width beam is a, the minimum width beam is transmitted in the direction of 2π / a, and the direction index value of each beam is transmitted to each minimum width beam. The base station can rotate the beam of this minimum width periodically. The terminal measures the signal to interference noise ratio (SINR) of each minimum width beam transmitted by the base station, selects N in order of the highest SINR, and reports the index of the minimum width beam and the SINR value to the base station. . The base station performs a user scheduling and beam allocation process using the index of the minimum width beam and SINR values reported from each terminal.

FIG. 5 is a flowchart illustrating a method for selecting a terminal location and a beam type for a spatial division multiple access service of the aforementioned virtual sector based adaptive antenna system.

First, the base station transmits the rotating minimum width beams toward the terminals with the index (S501). After receiving the minimum width beams, all terminals select N pieces in the order of the highest SINR values among the narrow width beams, and report the indexes and SINR values of the N minimum width beams to the base station (S503).

Next, the base station selects a user for all virtual sectors and adjusts a beam for allocating a corresponding terminal based on the beam index reported by the selected user and its SINR value. First, the virtual sector number i is initialized to 0 (S505). The user terminal is selected according to the scheduling policy in the i-th virtual sector (S507). That is, step S507 is a process of selecting which terminal to serve in the current timeslot since a plurality of terminals exist in the virtual sector, and the scheduling policy of step S507 follows a general scheduling algorithm.

N minimum width beams reported by the user terminal of the i-th virtual sector have a specific condition (the maximum SINR value of the N minimum width beams is larger than the threshold SINR value, or the variance of the SINR values of the N minimum width beams is critically distributed). Is less than the value) (S509). As a result of the determination in step S509, when the maximum SINR value is larger than the threshold SINR value or the dispersion value of the SINR values is smaller than the threshold dispersion value, it may be determined that the channel state of the base station and the terminal is in a very good state for a specific minimum width beam. Therefore, in this case, among the N minimum width beams reported by the user terminal of the i-th virtual sector, a narrow beam having a maximum SINR value is allocated to the corresponding user terminal (S511).

On the contrary, if the maximum SINR value is not greater than the threshold SINR value and the variance value of the SINR values is not smaller than the threshold dispersion value, the channel state is not good as the invisible channel (NLOS) or the mobile station is moved. In this case, since the gain of the beam is reduced due to the high speed, in this case, a wide area covering all the virtual sectors including the index of the N minimum width beams reported by the user terminal of the i-th virtual sector is wide. The beam is allocated to the corresponding user terminal (S513).

Exceptionally, if the SINR values of the N minimum-width beams reported by the terminal are all higher than the threshold value (max (SINRK = SINR_THR), this is the case where the terminal is located very close to the base station, so that even in this case, the narrow beam is allocated to the terminal. The threshold SINR and the threshold variance can be adjusted to maximize the capacity of the system.

Next, the base station calculates an antenna weight value to be used when transmitting data to the actual terminal to form a beam optimized for the terminal direction (S515). In this process, the base station forms a beam by considering only the direction of the terminal without considering channel information or location mobility of each terminal, and thus can be implemented with very low complexity.

Next, the virtual sector number i is incremented by one (S517). If i is smaller than the number of virtual sectors, the process returns to step S507 and repeats if i is greater than or equal to the number of virtual sectors.

6 is an operation flowchart illustrating a resource allocation method for a spatial division multiple access service of a virtual sector based adaptive antenna system according to an embodiment of the present invention. Since the required capacity and delay value are determined according to the service QoS of the selected terminal for each virtual sector, there is a need for a resource allocation method for satisfying the QoS for the terminals selected for each physical sector.

First, the variable N is the number of virtual sectors, the virtual sector number (i) is initialized to 0, the total remaining power (Ptotal) is set to the maximum transmission power (Pmax) and the temporary variable (Ptx) is initialized to 0 (S601). . A resource allocation priority is determined among the user terminals selected for each virtual sector (S603). The determination of resource allocation priority in step S603 is based on existing scheduling techniques (max-min, proportional fair, max throughput).

Next, resources are allocated to the selected user terminal by using the user terminal selected by the virtual sector, the beam allocated to the user terminal and the SINR value of the beam, and the base station is configured to satisfy the QoS of the user terminal selected in the i-th virtual sector. The minimum transmission power satisfying the minimum SINR value is calculated and set as a temporary variable Ptx (S605).

Next, if the required minimum transmit power of the user terminal selected in the i-th virtual sector set in the temporary variable Ptx is smaller than the total remaining power (S607), the Ptx value is set in P (i) and the total remaining power (Ptotal) is set. The value obtained by subtracting P (i) is reset to the total residual power Ptotal and the virtual sector number i is increased by 1 (S609).

Next, if i is less than N and the total remaining power Ptotal is greater than 0 (S611), the process returns to step S605 to repeat the process of allocating the transmission power to the selected user terminal of the next virtual sector, and i is not less than N If the total remaining power Ptotal is not greater than zero (S611), the flow advances to step S613.

If the total remaining power (Ptotal) is greater than zero in step S613, the total remaining power is additionally divided and allocated to the user terminals allocated the transmission power through the above process using a water-filing algorithm. (S615). This water-filling algorithm uses the remaining power to allocate resources to maximize capacity.

The technical spirit of the present invention has been described above with reference to the accompanying drawings, but this is by way of example only for describing the best embodiment of the present invention and not for limiting the present invention. In addition, it is a matter of course that various modifications and variations are possible without departing from the scope of the technical idea of the present invention by anyone having ordinary skill in the art.

1 illustrates a typical three sector antenna system using a fixed beam;

2 is a diagram illustrating an example of applying a space division multiple access technology to a three sector antenna system;

3 is a view illustrating a virtual sector based adaptive antenna system according to an embodiment of the present invention;

4 is a diagram illustrating a process of determining a location and a channel state of a terminal by rotating a minimum width beam by a base station;

5 is a flowchart illustrating a method of selecting a terminal location and a beam type for a spatial division multiple access service of a virtual sector based adaptive antenna system according to an embodiment of the present invention;

6 is an operation flowchart illustrating a resource allocation method for a spatial division multiple access service of a virtual sector based adaptive antenna system according to an embodiment of the present invention.

Claims (14)

A spatial segmentation multiple access service method of a virtual sector based adaptive antenna system in which a plurality of sectors divided by a linear array antenna are subdivided into a plurality of virtual sectors, A first step of the base station selecting one user terminal for each virtual sector; A second step of determining, by the base station, a type of beam to be allocated to a user terminal selected for each virtual sector; And a third step of the base station allocating transmission power to user terminals selected for each of the virtual sectors. The method of claim 1, wherein the first step, A first sub-step of the base station rotating and transmitting the minimum width beam including beam index information; A second sub where the base station reports a predetermined number of beam indices and received signal strength information for each beam index in order of increasing received signal strength among the minimum width beams transmitted from the base station from each user terminal in a cell; Steps, And a third sub-step of selecting a user terminal for each virtual sector. The method of claim 2, wherein the second step, A first sub step of determining, by the base station, a beam width to be allocated to the user terminal by using received signal strength information for each beam index received from the user terminal selected for each virtual sector; And a second sub step of forming, by the base station, a beam according to the direction of the user terminal. The method of claim 3, wherein the first sub-step of the second step, The base station determines the narrow beam when the received signal strength for each beam index received from the user terminal selected for each virtual sector satisfies a specific condition, and determines the narrow beam if the specified condition does not satisfy the specific condition. In the virtual sector based adaptive antenna system, the maximum value of the received signal strength for each beam index is greater than the threshold received signal strength or the dispersion value of the received signal strength for each beam index is less than the threshold dispersion value. Space division multiple access service method. 5. The method of claim 4, wherein the optical beam covers a virtual sector including the largest beam index received from the user terminal. 6. 5. The method of claim 4, wherein the threshold received signal strength and the threshold dispersion value are values that maximize the capacity of the antenna system. The method of claim 1, wherein the third step, A first sub-step of the base station scheduling a transmission power allocation order for the user terminals selected for each virtual sector; A second sub step of calculating a transmission power for satisfying the minimum received signal strength of the user terminal in the scheduling order of the first sub step; A third sub-step of allocating the transmission power to the user terminal of the second sub-step and repeating from the second sub-step if the transmission power calculated in the second sub-step is not greater than the total remaining power; And a fourth sub step of not allocating the transmission power to the user terminal of the second sub step if the transmission power calculated in the second sub step is larger than the total remaining power. Split Multiple Access Service Method. The method of claim 7, wherein the third step, After the fourth sub-step, if the total remaining power is greater than zero, the total remaining power is further divided by dividing the total remaining power to the user terminals allocated the transmission power through the second sub-step and the third sub-step by using a water filling algorithm. Spatial division multiple access service method of a virtual sector based adaptive antenna system, further comprising a fifth sub-step. A spatial segmentation multiple access service method of a virtual sector based adaptive antenna system in which a plurality of sectors divided by a linear array antenna are subdivided into a plurality of virtual sectors, A first step of the base station rotating and transmitting the minimum width beam including the beam index information; A second step in which the base station reports, from each user terminal in a cell, a predetermined number of beam indexes and received signal strength information for each beam index in order of increasing received signal strength among the minimum width beams transmitted from the base station; Wow, A third step of the base station selecting a user terminal for each virtual sector; Determining, by the base station, a beam width to be allocated to the user terminal using received signal strength information for each beam index received from the user terminal selected for each virtual sector; And a fifth step of forming, by the base station, a beam according to the direction of the user terminal. The method of claim 9, wherein the fourth step, The base station determines the narrow beam when the received signal strength for each beam index received from the user terminal selected for each virtual sector satisfies a specific condition, and determines the narrow beam if the specified condition does not satisfy the specific condition. In the virtual sector based adaptive antenna system, the maximum value of the received signal strength for each beam index is greater than the threshold received signal strength or the dispersion value of the received signal strength for each beam index is less than the threshold dispersion value. Space division multiple access service method. 12. The method of claim 10, wherein the optical beam covers a virtual sector including the largest beam index received from the user terminal. 12. The method of claim 10, wherein the threshold received signal strength and the threshold variance are maximum values of the capacity of the antenna system. The method of claim 9, A sixth step of the base station scheduling the transmission power allocation order for the user terminals selected for each of the virtual sectors; A seventh step of calculating transmission power for satisfying the minimum received signal strength of the user terminal in the scheduling order of the sixth step; An eighth step of allocating the transmission power to the user terminal of the seventh step and repeating the operation from the seventh step if the transmission power calculated in the seventh step is not greater than the total remaining power; If the transmission power calculated in the seventh step is greater than the total remaining power, the spatial division multiple access of the virtual sector based adaptive antenna system comprising a ninth step of not allocating the transmission power to the user terminal of the seventh step How to service. The method of claim 13, After the ninth step, if the total remaining power is greater than zero, a tenth step of dividing and further allocating the total remaining power to user terminals to which transmission power is allocated in the seventh and eighth steps using a waterfilling algorithm. Spatial segmentation multiple access service method of a virtual sector based adaptive antenna system, further comprising the step.

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