KR101523098B1 - Method of allocating resources for cooperative diversity - Google Patents

Abstract

A method for allocating resources for cooperation diversity in a wireless communication system, comprising: acquiring channel states for a plurality of source stations and a plurality of relay stations; allocating at least one subcarrier exclusively to each source station based on the channel state And selecting a relay station for each source station. The relay station performs cooperative diversity using the same subcarrier as the corresponding source station.

Description

[0001] METHOD OF ALLOCATING RESOURCES FOR COOPERATIVE DIVERSITY [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication, and more particularly, to a method for performing cooperative diversity in a wireless communication system.

Background of the Invention [0002] Wireless communication systems are widely deployed to provide various types of communication services such as voice and data. Generally, a wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access) systems.

Orthogonal frequency division multiple access (OFDMA) is a multiple access scheme that allocates subcarriers having orthogonality to each user. OFDMA can provide high data rate by mitigating intersymbol interference (ISI) and providing robust characteristics to frequency selective fading of a channel. In OFDMA, independent subcarriers are allocated among users so that the probability that a particular subcarrier falls into a deep fading state for all users is very low. Accordingly, the subcarriers have characteristics independent of each other, thereby enabling subcarriers to be adaptively allocated to users having good channel states, thereby reducing transmission power and improving throughput.

In order to overcome performance deterioration due to channel fading in wireless communication, spatial diversity using a multiple input multiple output (MIMO) system has been studied extensively. The MIMO system implements two or more antennas at the transmitter and receiver to provide high data rate, increased reliability, and increased channel capacity. However, despite the advantages of the MIMO system, the MIMO system is rarely implemented in uplink transmission due to constraints such as size, weight, and hardware complexity.

In the cooperative diversity, a source station and relay stations around the source station form a virtual MIMO system by sharing resources such as an antenna and a frequency band, To obtain a MIMO system. This means that, through cooperation diversity, even if only one transmission antenna is used for each terminal, advantages such as spatial diversity gain and channel capacity increase of the MIMO system can be obtained.

The relaying methods used in the relay station include amplify and forward (AF) and decode and forward (DF). According to the AF, the relay station amplifies the transmission signal received by the source station to a predetermined size and retransmits the signal. According to DF, a relay station decodes a transmission signal received from a source station and re-encodes the signal, and retransmits the generated signal to a destination station. According to AF, there is no signal processing process due to decoding, so that simple hardware implementation is possible. However, since noise added at the relay station is transmitted to the receiver, performance degradation may occur in a low signal-to-noise ratio (SNR) environment. According to DF, since a transmission signal received from a source station is decoded and re-coded by a relay station and transmitted, it is less affected by noise, but hardware complexity increases due to decoding.

Single relay based cooperation diversity uses the entire usable time slot divided into two orthogonal time slots. In the first time slot, the source station sends a transmission signal to at least one relay station and the destination station. In the second time slot, the relay station processes the transmission signal received from the source station according to the relaying method, and forwards the processed relaying signal to the destination station.

The multiple relay based cooperation diversity has a time slot structure of a repetition code type. The total available time slots are divided by the total number of source and relay stations. In the first time slot, the source station sends the transmission signal to the relay stations and the destination station. Then, in the time slot, the relay station processes the transmission signal received from the source station according to the predetermined relaying method and sequentially retransmits the relaying signal. However, there is a problem in that the bandwidth efficiency is reduced due to a decrease in the length of time slots allocated for transmission signals.

To solve the problem of bandwidth efficiency reduction, space-time coding based cooperative diversity has been proposed. The space - time coded cooperative diversity uses multiple relay stations, but has the same time slot structure as single relay based cooperation diversity. In the first time slot, the transmitting terminal sends the transmission signal to the relay station and the receiver. In a second time slot, a plurality of RSs space-time-encodes the received transmission signals and retransmits them to the receiver. Space - time coded cooperative diversity can solve the problem of bandwidth efficiency reduction, but optimal space - time coding has not been known yet and it is difficult to implement it due to synchronization problem between relay stations.

In order to improve the performance of the cooperative diversity, the power allocation between the source station and the relay station, the power allocation among the multiple relay stations, and the control of the time slot length between the source station and the relay station have been studied. In addition, studies have been made on subcarrier allocation and power allocation between subcarriers to improve the performance of cooperative diversity combined with orthogonal frequency division multiplexing (OFDM). However, collaborative diversity combined with OFDM is mostly studied only when there is a single source station.

In practical wireless communication systems, it is common for multiple source stations (e.g., multiple terminals) to exist at the same time. The prior art is difficult to apply to a wireless communication system in which a multi-source station exists at the same time when a single source station exists. Therefore, in a situation where multiple source stations and multiple relay stations exist at the same time, an efficient resource allocation method for cooperation diversity is needed.

According to an aspect of the present invention, there is provided a resource allocation method for cooperative diversity using a multi-source station and a multi-relay station.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for performing cooperative diversity in an OFDMA-based wireless communication system.

In an aspect, a method for allocating resources for cooperative diversity in a wireless communication system includes obtaining channel states for a plurality of source stations and a plurality of relay stations, and for each source station, Assigning one subcarrier, and selecting a relay station for each source station. The relay station performs cooperative diversity using the same subcarrier as the corresponding source station.

In another aspect, an apparatus for wireless communication includes an RF unit that transmits and receives a radio signal, and an RF unit that is connected to the RF unit and receives a transmission signal from a source station on a plurality of subcarriers, And a processor for retransmitting the processed signal on the plurality of sub-carriers to the destination station.

The data transmission rate of the entire system can be improved, and a certain level of QoS (Quality of Service) can be guaranteed for each user, thereby providing a high quality of service.

The following description is to be understood as illustrative and non-limiting, such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access And can be used in various wireless communication systems. CDMA may be implemented in radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA2000. The TDMA may be implemented in a wireless technology such as Global System for Mobile communications (GSM) / General Packet Radio Service (GPRS) / Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented in wireless technologies such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and Evolved UTRA (E-UTRA). UTRA is part of the Universal Mobile Telecommunications System (UMTS). 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) is a part of E-UMTS (Evolved UMTS) using E-UTRA, adopting OFDMA in downlink and SC-FDMA in uplink.

1 shows a wireless communication system.

Referring to FIG. 1, a wireless communication system 10 includes at least one base station 11 (BS). Each base station 11 provides a communication service to a specific geographical area (generally called a cell) 15a, 15b, 15c. The cell may again be divided into multiple regions (referred to as sectors).

A UE 12 may be fixed or mobile and may be a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, a personal digital assistant (PDA) A wireless modem, a handheld device, and the like. The base station 11 generally refers to a fixed station that communicates with the terminal 12 and may be referred to by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point have.

Hereinafter, downlink refers to communication from a base station to a terminal, and uplink refers to communication from a terminal to a base station. In the downlink, the transmitter may be part of the base station, and the receiver may be part of the terminal. In the uplink, the transmitter may be part of the terminal, and the receiver may be part of the base station.

2 shows a wireless communication system using a repeater. 2 shows one destination station 110, three relay stations 120, 122 and 124 and two source stations 130 and 132, the wireless communication system can be any number of destination stations, And a source station. In the uplink transmission, the source station may be a terminal and the destination station may be a base station. In the downlink transmission, the source station may be a base station and the destination station may be a terminal. The relay station may be a terminal or a separate repeater may be arranged. The base station can perform functions such as connectivity, management, control and resource allocation between the relay station and the terminal.

Referring to FIG. 2, the destination station 110 communicates with the source station 130 via the relay station 120. In the uplink transmission, the source station 130 sends the uplink data to the destination station 110 and the relay station 120, and the relay station 120 retransmits the received data.

The destination station 110 also communicates with the source station 132 via relay stations 122 and 124. In the uplink transmission, the source station 132 sends the uplink data to the destination station 110 and the relay stations 122 and 124, and the relay stations 122 and 124 retransmit the received data simultaneously or sequentially.

Any method such as amplify and forward (AF) and decode and forward (DF) may be used as a relaying method used in a relay station, and the technical idea of the present invention is not limited thereto.

3 is a flowchart illustrating a cooperative diversity performing method according to an embodiment of the present invention. This method can be performed at the base station.

Referring to FIG. 3, in step S110, a base station obtains an uplink channel state between a base station (destination station) and a terminal (source station), between a base station and a relay station, and between a source station and a relay station. The uplink channel state can be obtained by estimating a channel from a sounding signal or pilot transmitted from a mobile station.

In the terminal S120, the base station allocates resources for the source station and the relay station according to the resource allocation method. If the source station and the relay station are both terminals, resources are allocated to the terminal operating as the source station and the terminal operating as the relay station. The resource allocation method used will be described later.

In step S130, the base station sends allocation resource information to the source station and / or the relay station. The resource allocation information may be broadcast as part of the system information, or may be transmitted on a dedicated control channel to each terminal.

In step S140, the base station receives the uplink data using the cooperation diversity. The source station and the relay station perform cooperative diversity using the resource allocation information.

Hereinafter, a resource allocation method for the source station and the relay station will be described. Assuming cooperative diversity based on OFDMA with N subcarriers, all terminals (i.e., source stations) have one transmission antenna and all K source stations, M relay stations and one destination station (i.e., base station) Assume an existing cellular system. It is assumed that the source stations are evenly distributed in the cell.

The transmission signal of the source station can be transmitted to the destination station over two time slots. In the first time slot, each source station transmits data to the relay station and the destination station using subcarriers assigned to itself among N subcarriers. In the second time slot, each relay station retransmits the data processed by the relay method to the destination station by using the subcarrier allocated to the relay station.

Hereinafter, a time slot refers to a unit time required to transmit the scheduled data at one time, and is also referred to as a transmission time interval (TTI).

It is assumed that each subcarrier is exclusively allocated to one source station and one relay station due to interference, complexity and synchronization problems between source stations. It is assumed that the channel state between the terminals changes slowly so that a centralized resource allocation algorithm can be performed and the result of the resource allocation algorithm can be used during various OFDM frames.

The instantaneous data rate of the kth source station transmitted to the destination station over the two time slots can be expressed by the following equation.

Here, R _k denotes the instantaneous data rate of the source station k case where all the sub-carrier and the relay station is assigned to the source station k, ρ ⁽ⁿ⁾ _{k, m} is the information on the sub-carriers allocated with a value of 0 or 1, And R ⁽ⁿ⁾ _{k, m} represents the instantaneous data rate value when the source station k uses the relay station m and the subcarrier n. ρ ⁽ⁿ⁾ _{k, m} is 1 if sub-carrier n is assigned to source station k and relay station m, and 0 otherwise.

The user's instantaneous data rate R ⁽ⁿ⁾ _{k, m} according to the relaying method of the relay station is given by the following equation when AF is used.

Here, H ⁽ⁿ⁾ _k denotes a channel coefficient of a subcarrier n from a source station k to a destination station, F ⁽ⁿ⁾ _{k, m} denotes a channel coefficient of a subcarrier n from a source station k to a relay station m, G ⁽ⁿ⁾ _m denotes a channel coefficient of a sub-carrier n in the relay station m to the destination station, p ⁽ⁿ⁾ _{s, k} denotes a transmission power of the source station k is assigned to a sub-carrier n, p ⁽ⁿ⁾ _{r, m} is RS m represents the transmission power to be assigned to the subcarrier r, N _o denotes a power spectral density of the noise added at the relay station and the object (power spectral density).

Alternatively, the user's instantaneous data rate R ⁽ⁿ⁾ _{k, m} is given by the following equation when using DF.

A problem formulation of a resource allocation method for an OFDMA-based cooperative diversity network in which a multi-source station and a plurality of relay stations exist at the same time can be expressed by the following equation.

The constraint condition of the optimization problem can be expressed by the following five equations (5) to (9).

In Equations (5) to (11), R _min denotes a minimum data rate required for satisfying quality of service of each source station, P _{s, k} denotes a maximum transmit power available to the source station k _, Represents the maximum transmit power that can be used by relay station m.

The constraints of Equations (5) and (6) indicate that each subcarrier should be exclusively allocated to only one source station and one relay station due to interference, complexity and synchronization problems between source stations. The constraint of Equation (7) indicates that the minimum data rate must be satisfied for service quality satisfaction of all users on the wireless communication network. The minimum data rate for satisfying the user service quality can be arbitrarily set according to the wireless communication network. The constraints of Equations (8) and (9) represent the limit due to the maximum transmission power of each source station and the maximum transmission power of the relay station. The constraints of Equations (10) and (11) indicate that the transmission power of each source station and the transmission power of the relay station are positive.

The optimization problem shown in Equation (4) is classified into a mixed binary integer programming due to the binary variable p ⁽ⁿ⁾ _{k, m} in Equation (5). This problem is very complicated to obtain the solution and is classified as NP-hard. We use the convex optimization technique to relax the constraint that the binary variable ρ ⁽ⁿ⁾ _{k, m} can have a real value between 0 and 1 for the design of an efficient resource allocation algorithm with low complexity.

The lagrangian of the optimization problem where the constraint is relaxed is given by the following equation.

Here, λ _n , η _k , ν _m , μ _k , α _{k, n} , β _{m, n} and γ _{k, m and n} represent Lagrange coefficients having zero or positive values.

In order to find the optimal solution related to the subcarrier allocation, the above equation (12 ⁾ is differentiated by the variable ρ ⁽ⁿ⁾ _{k, m} related to the subcarrier allocation.

In the above equation, when the hardness value is 0 at the optimal position,? _{K, m, n} are given by the following equations.

In the above equation, since? _{K, m and n} are Lagrange coefficients having 0 or a positive value,? _N is given by the following equation.

The subcarrier allocation criterion can be obtained in a complementary slackness condition for ρ ⁽ⁿ⁾ _{k, m} . The condition for the redundancy for ρ ⁽ⁿ⁾ _{k, m} is given by

ρ ⁽ⁿ⁾ _k, the following equation from replacement property terms for _m ρ ⁽ⁿ⁾ _{k, m} is the case of γ _{k, m, n} are 0 has a positive _value, ρ ⁽ⁿ⁾ _{k, m} is γ _{k , and it} becomes 0 when _{m and n} are positive.

ρ ^{(n) If} _{k and m} are both positive, it indicates that sub-carrier n is allocated to source station k and relay station m. Therefore, this condition can be used for subcarrier allocation algorithm design.

According to Equation (17 ⁾ _, it can be seen that the necessary condition for ρ ⁽ⁿ⁾ _{k, m} to be positive is that the equations of γ _{k, m and n} must be equal to 0, It means to have it. In Equation (14), Equation (15) should be equal to Equation (15). Since? _n is the maximum upper limit of Equation (15), it can be seen that when the sub-carrier n is allocated to the source station k and the relay station m, which maximize the term of the right side of Equation 15,

The subcarrier allocation condition using the redundancy condition for ρ ⁽ⁿ⁾ _{k, m} is as follows.

Where k ^* denotes a source station selected for subcarrier n to be assigned, and m ^* denotes a relay station selected for subcarrier n to be assigned.

Although the subcarriers can be allocated using Equation (18) above, in order to select the optimal source station k ^* for allocating the subcarrier n, it is necessary to know the Lagrangian coefficient mu _k for all the source stations. Calculation of the exact Lagrangian coefficient μ _k is very complex, making it difficult to implement in real systems.

μ _k, substituting the right Lagrange coefficients μ _k from the replacement property conditions for the resource allocation algorithm, it is possible to obtain a variable that can be used in the design. The μ _{k k} is given by the following equations.

from extra St. condition of μ _k the Lagrange coefficients μ _k can be seen that acts as a control variable for adjusting the amount of information flow on the network.

According to Equation (20), it can be seen that when the source station k satisfies a data rate greater than the minimum data rate condition _Rmin for satisfaction of the service quality, the Lagrangian coefficient mu _k becomes zero. Also, it can be seen that the Lagrange coefficient μ _k has a positive value until the source station k satisfies the minimum data rate condition R _min for satisfaction of the service quality. That is, the Lagrangian coefficient μ _k must always be a positive number greater than or equal to zero, and if the source station k does not satisfy the minimum data rate condition, the Lagrangian coefficient μ _k for the source station k is large, Good subcarriers are given priority to be assigned. When the source station k satisfies the minimum data rate for satisfying the quality of service, the Lagrangian coefficient _k becomes 0 and no longer gives priority to the subcarrier allocation for satisfying the constraint of Equation (7).

In order to propose an efficient resource allocation algorithm with low complexity by using the Lagrangian coefficient μ _k as a control variable for the flow of network information, the following equation can be obtained.

Here, ζ _k is assumed to have a value proportional to μ _k , and is used for a heuristic algorithm.

Unlike the downlink system that allocates the sub-carriers according to the channel gain, in the uplink system, the sub-carriers are allocated based on the product of the channel gain of the sub-carriers and the transmission power due to the transmission power limitation condition of each terminal. The transmit power of each terminal for subcarrier allocation can be based on an equal power allocation method, such as assigning the same transmit power to the allocated subcarriers.

The equal power allocation method for the source station is as follows.

N _{s, k} denotes the number of sub-carriers allocated to the source station k, and N _{r, m} denotes the number of sub-carriers allocated to the relay station m.

The equal power allocation method for the relay station is as follows.

4 is a flowchart illustrating a resource allocation method according to an embodiment of the present invention. This is a resource allocation method that satisfies a minimum data rate required for satisfaction of a user's service quality while seeking to improve the total sum of data rates in an OFDMA-based cooperative diversity system in which multiple source stations and multiple relay stations exist at the same time. According to this method, the upper limit of the maximum transmission power that can be used by the subcarriers of each terminal during subcarrier allocation is set. If there is no upper limit of the transmit power available for one subcarrier during the subcarrier allocation procedure, the terminal that has been allocated a small amount of subcarriers at the beginning of the subcarrier allocation is allocated an excessively large transmit power, and an unreasonably large subcarrier transmit power This can result in a pair of relay stations. Therefore, after the sub-carrier allocation is completed, the source station and the relay station allocate power to the allocated sub-carriers using Equations (20) and (21), but it is assumed that the sub-carrier power exceeding the arbitrary transmission power upper limit can not be used during the sub-carrier allocation process.

Referring to Fig. 4, in step S410, a source station set K, a relay station set M, an available subcarrier set N, and a subcarrier allocation variable p ⁽ⁿ⁾ _{k, m} are initialized.

In step S420, a relay station and one subcarrier satisfying the following equation are assigned to each source station.

Then, the instantaneous data rate of each source station is calculated, and the subcarrier set is updated as N = N- {n ^* }.

In step S430, the source station k ^* having the largest ζ _k among the source station set K is selected. In step S440, it is determined whether the value of? _{K *} is greater than zero.

If? _{K *} is a positive number, then in step S450, the transmit power of the source station k ^* is calculated using Equation 22 and the transmit power upper limit, and the transmit power for each relay station Calculate the power. In step S452, the relay station and one subcarrier satisfying the above expression (24) are allocated to the source station. In step S454, the subcarrier set N is updated.

If? _{K *} is negative, in step S460, one subcarrier is arbitrarily selected from the subcarrier set N, and the transmit power of each source station is calculated using the above equation (22) and the transmit power upper limit, And calculates the transmission power for each relay station using the upper transmission power limit. In step S462, the selected sub-carrier is allocated to the source station and the relay station satisfying the following equation.

In step S464, the subcarrier set N is updated.

In step S470, the data rate of the user is updated. Then, in step S480, the steps from step S430 are repeated until all the sub-carriers are allocated.

5 shows an example of resource allocation to a source station and a relay station. According to this, subcarriers are exclusively allocated between the source stations based on the channel state. In addition, a relay station corresponding to the source station is assigned the same subcarrier as the source station. The relay station transmits the processed relay signal according to the relay method using the same subcarrier used for the transmission signal of the received source station.

The sub-carrier and the relay station are allocated to each source station so as to satisfy the minimum data rate required for satisfaction of the user's service quality while seeking to improve the total sum of the data rates for the wireless communication system. Thus, each relay station retransmits the relay signal on the subcarriers used by the signal received by the source station, so it is unnecessary to separately inform the relay station of the resource allocation information. Therefore, it is possible to reduce the radio resources according to the transmission of the resource allocation information.

We now verify the performance of the proposed method through simulation. The simulation environment assumes 128 subcarriers, 8 source stations and 4 relay stations. It is assumed that the relay station is fixed at a distance of 500 m in a cell with a radius of 1 Km. The minimum data rate for satisfying service quality is set to 1.25Mbps and is the result of simulation through 105 independent channel formation.

6 is a graph showing the data rate according to the average SNR when the AF relay station is used. 7 is a graph showing an outage probability according to an average SNR when the AF relay station is used. 8 is a graph showing the data rate according to the average SNR when the DF relay station is used. 9 is a graph showing the probability of failure according to the average SNR when the DF relay station is used. In the graphs of FIGS. 6 to 9, 'Sum rate maximization' is a result of the optimization problem except for the constraint of Equation (7), 'Proposed algorithm' is a result of the embodiment of the present invention, 'OFDM- Is the result for a conventional OFDM system. The graphs of FIGS. 6 and 8 show that although the data rate is reduced by about 0.3 bps / Hz in the higher SNR region than the 'Sum rate maximization' method, the performance of the OFDM-TDMA method is improved by about 2 bps / Hz . According to the graphs of FIGS. 7 and 9, the 'Sum rate maximization' method has a high probability that a user does not satisfy the quality of service, whereas the proposed method greatly improves the probability of satisfying the quality of service to the source station Lt; / RTI >

10 is a block diagram illustrating an apparatus for wireless communication according to an embodiment of the present invention. The device may be a terminal when operating as a source station or a relay station. Or the device may be a base station when operating as a destination station.

10, an apparatus 50 for wireless communication includes a processor 51, a memory 52, an RF unit 53, a display unit 54, (user interface unit) 55. The memory 52 is coupled to the processor 51 to store the drive system, applications and general files. The display unit 54 displays various information of the apparatus 50 and can use well known elements such as a liquid crystal display (LCD) and an organic light emitting diode (OLED). The user interface unit 55 may be a combination of a well-known user interface such as a keypad or a touch screen. The RF unit 53 is connected to the processor to transmit and / or receive a radio signal.

The processor 51 is connected to the RF unit 53 so that the above resource allocation method can be implemented when the apparatus 50 operates as a source station. Or the processor 51 may perform processing and retransmission according to the relay scheme when the apparatus 50 operates as a relay station.

11 is a flowchart illustrating a resource allocation method for cooperation diversity according to an embodiment of the present invention. This method can be performed at the base station or the target station. In step S610, the channel status for each source station is obtained. In step S620, at least one subcarrier is exclusively allocated to each source station based on the channel status, and a relay station for each source station is selected. The relay station performs cooperative diversity using the same subcarrier as the corresponding source station. The subcarriers are allocated so as to satisfy a minimum data rate required for each source station in order to satisfy a service quality of a user. In addition, the subcarriers and the relay stations allocated to each source station are selected to maximize the total sum of the data rates of the entire system.

12 is a flowchart illustrating a cooperative diversity performing method according to an embodiment of the present invention. This method can be performed at the relay station. In step S710, a transmission signal is received from the source station on a plurality of subcarriers. In step S720, the transmission signal is processed according to the relay scheme. In step S730, the processed signal is retransmitted to the destination station on the plurality of subcarriers. Subcarriers are exclusively allocated to each source station and the same subcarrier is allocated to the corresponding destination station, so that there is no need to send additional resource allocation information to the relay station.

The present invention may be implemented in hardware, software, or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In software implementation, it may be implemented as a module that performs the above-described functions. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand. Therefore, it is intended that the present invention covers all embodiments falling within the scope of the following claims, rather than being limited to the above-described embodiments.

1 shows a wireless communication system.

2 shows a wireless communication system using a repeater.

3 is a flowchart illustrating a cooperative diversity performing method according to an embodiment of the present invention.

4 is a flowchart illustrating a resource allocation method according to an embodiment of the present invention.

5 shows an example of resource allocation to a source station and a relay station.

6 is a graph showing the data rate according to the average SNR when the AF relay station is used.

7 is a graph showing an outage probability according to an average SNR when the AF relay station is used.

8 is a graph showing the data rate according to the average SNR when the DF relay station is used.

9 is a graph showing the probability of failure according to the average SNR when the DF relay station is used.

10 is a block diagram illustrating an apparatus for wireless communication according to an embodiment of the present invention.

11 is a flowchart illustrating a resource allocation method for cooperation diversity according to an embodiment of the present invention.

12 is a flowchart illustrating a cooperative diversity performing method according to an embodiment of the present invention.

Claims (12)

A method for resource allocation for cooperation diversity in a wireless communication system, Obtaining a channel state for a plurality of source stations and a plurality of relay stations; And Allocating at least one subcarrier exclusively to each source station based on the channel state and selecting a relay station for each source station, The relay station performs cooperative diversity using the same subcarrier as the corresponding source station, The subcarriers are allocated to satisfy a minimum data rate required for each source station in order to satisfy a service quality of a user, The instantaneous data rate of the source station k is given by the following equation,

Wherein R ⁽ⁿ⁾ _{k, m} is given by the following equation:

Here, K denotes the total number of the source station, M represents the total number of relay stations, N is the number of subcarriers, R _k is the source station k case where all the sub-carrier and the relay station is assigned to the source station k indicates the instantaneous data rate, ρ ⁽ⁿ⁾ _{k, m} denotes a variable indicating the information on the sub-carrier allocation, R ⁽ⁿ⁾ _{k, m} is an instantaneous data when the source station k use the relay station m and the sub-carrier n Represents a rate value, ^(N) _k denotes a channel coefficient of a subcarrier n from a source station k to a destination station, F ⁽ⁿ⁾ _{k, m} denotes a channel coefficient of a subcarrier n from a source station k to a relay station m ^, _m is the channel coefficient of the sub-carrier n in the relay station m to the destination station, p ⁽ⁿ⁾ _{s, k} denotes a transmission power of the source station k is assigned to a sub-carrier n, p ⁽ⁿ⁾ _{r, m} is the relay station m the represents the transmission power to be assigned to the subcarrier r, N _o denotes a power spectral density (power spectral density) of the noise added at junggyegukwa destination. delete delete delete A radio frequency (RF) unit for transmitting and receiving a radio signal; And And a processor coupled to the RF unit, The processor obtaining channel conditions for a plurality of source stations and a plurality of relay stations; And Allocating at least one subcarrier exclusively to each source station based on the channel state, selecting a relay station for each source station, The relay station performs cooperative diversity using the same subcarrier as the corresponding source station, The subcarriers are allocated to satisfy a minimum data rate required for each source station in order to satisfy a service quality of a user, The instantaneous data rate of the source station k is given by the following equation,

Wherein R ⁽ⁿ⁾ _{k, m} is given by the following equation:

Here, K denotes the total number of the source station, M represents the total number of relay stations, N is the number of subcarriers, R _k is the source station k case where all the sub-carrier and the relay station is assigned to the source station k indicates the instantaneous data rate, ρ ⁽ⁿ⁾ _{k, m} denotes a variable indicating the information on the sub-carrier allocation, R ⁽ⁿ⁾ _{k, m} is an instantaneous data when the source station k use the relay station m and the sub-carrier n Represents a rate value, ^(N) _k denotes a channel coefficient of a subcarrier n from a source station k to a destination station, F ⁽ⁿ⁾ _{k, m} denotes a channel coefficient of a subcarrier n from a source station k to a relay station m ^, _m is the channel coefficient of the sub-carrier n in the relay station m to the destination station, p ⁽ⁿ⁾ _{s, k} denotes a transmission power of the source station k is assigned to a sub-carrier n, p ⁽ⁿ⁾ _{r, m} is the relay station m the represents the transmission power to be assigned to the subcarrier r, N _o denotes a power spectral density (power spectral density) of the noise added at junggyegukwa destination. delete delete delete delete delete delete delete

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