WO2008140268A2

WO2008140268A2 - Apparatus and method for processing collaborative mimo

Info

Publication number: WO2008140268A2
Application number: PCT/KR2008/002705
Authority: WO
Inventors: Zheng Zi Li; Sang-Kook Yeh; Jian Jun Li; Dong-Jun Lee
Original assignee: Posdata Co., Ltd.
Priority date: 2007-05-16
Filing date: 2008-05-15
Publication date: 2008-11-20
Also published as: WO2008140268A3

Abstract

An apparatus and method for processing collaborative Multiple Input Multiple Output (MIMO) is provided. A terminal searcher searches for terminals capable of Collaborative MIMO depending on a basic capacity exchanged with terminals. A terminal information collector collects at least one of position information, channel quality information, Carrier to Interference and Noise Ratio (CINR) information, power allocation ratio information, and Modulation and Coding Scheme (MCS) level information, for the terminals capable of Collaborative MIMO. A terminal grouper groups the terminals capable of Collaborative MIMO based on the collected at least one information, increasing QoS and ensuring efficient utilization of resources.

Description

Apparatus and method for processing collaborative MIMO Technical Field

[1] The present invention relates generally to an apparatus and method for processing

Collaborative Multiple Input Multiple Output (MIMO) in a wireless communication system, and in particular, to an apparatus and method for processing Collaborative MIMO by efficiently grouping terminals having a low channel correlation in a MIMO wireless communication system that follows the standards such as IEEE 802.16d/e, Wireless Broadband Internet (WiBro), and Worldwide Interoperability for Microwave Access (WiMAX), and supports Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA). Background Art

[2] To meet the recent increasing need to transmit a large amount of data at high speed using wireless channels, intensive research is being conducted on a high-speed wireless data transmission system for supporting portable Internet services in the mobile environments, and attention is paid to a MIMO system to support high-speed portable Internet services in the mobile environments.

[3] FIG. 1 is diagram illustrating the outlines of general Single Input Single Output

(SISO) system and MIMO system, respectively.

[4] As illustrated in FIG. 1, a SISO system (100), a technology in which a transmitter and a receiver use one antenna TxAnt and RxAnt, respectively, transmissions/receptions a signal through one channel H formed between a terminal with one antenna TxAnt and a base station with one antenna RxAnt.

[5] And, a MIMO system (150) is a technology for increasing the number of antennas for a terminal and a base station to transmit data through several paths. In this technology, a transmitter can increase transmission efficiency through space-time diversity and spatial multiplexing, and a receiver can reduce interference by detecting signals received through the paths. For example, shown in FIG. 1 is a 2x2 MIMO system including a terminal with two antennas TxAntO and TxAnt 1, and a base station with two antennas RxAntO and RxAnt 1. As illustrated, four channels of a first channel HOO, a second channel HOl, a third channel HlO and a fourth channel HI l are formed between first and second antennas TxAntO and TxAnt 1 of the terminal, and first and second antennas RxAntO and RxAntl of the base station.

[6] Since the MIMO system (150) has a higher data rate as it includes multiple transmission/reception antennas, the MIMO system (150) is superior to the SISO system (100) in terms of the capacity of a wireless link between a transmitter and a receiver. That is, in the multipath-rich environment, as multiple orthogonal channels can be formed between a transmitter and a receiver, the data for a single user can be simultaneously transmitted in parallel through the orthogonal channels using the same bandwidth, so that the MIMO system (150) can achieve higher spectral efficiency compared with the SISO system (100).

[7] As described above, however, in the general 2x2 MIMO system, each terminal should have two antennas, causing an increase in power loss and hardware complexity of the terminal. Therefore, a sturdy is being conducted on Collaborative MIMO for increasing its data rate to that of the conventional MIMO using a terminal with one antenna having a simpler hardware structure, and there is a demand for schemes which are more efficient in processing such Collaborative MIMO. Disclosure of Invention Technical Problem

[8] An aspect of the present invention is to address at least the problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and method for processing Collaborative MIMO by efficiently grouping terminals capable of Collaborative MIMO in an environment where SISO and MIMO coexist.

[9] Another aspect of the present invention is to provide a Collaborative MIMO processing apparatus and method capable of increasing Quality of Service (QoS) by grouping terminals having a low channel correlation using an orthogonal value and an eigen ratio of channels during Collaborative MIMO processing.

[10] Further another aspect of the present invention is to provide a Collaborative MIMO processing apparatus and method for grouping terminals by sorting terminals according to their power strength and calculating a channel correlation according to the sorted order during Collaborative MIMO processing.

[11] Yet another aspect of the present invention is to provide a Collaborative MIMO processing apparatus and method capable of improving the total throughput by allocating more resources for a terminal group having a lower channel correlation. Technical Solution

[12] According to one aspect of the present invention, there is provided an apparatus for processing collaborative Multiple Input Multiple Output (MIMO). The apparatus includes a terminal searcher for searching for terminals capable of collaborative MIMO depending on a basic capacity exchanged with terminals; a terminal information collector for collecting at least one of position information, channel quality information, Carrier to Interference and Noise Ratio (CINR) information, power allocation ratio information, and Modulation and Coding Scheme (MCS) level in- formation, for the terminals capable of collaborative MIMO; and a terminal grouper for grouping the terminals capable of collaborative MIMO based on the collected at least one information.

[13] According to another aspect of the present invention, there is provided a method for processing collaborative Multiple Input Multiple Output (MIMO). The method includes registering terminals to/from which a base station with multiple antennas will transmit/receive data; selecting terminals, to which collaborative MIMO is applicable, among the registered terminals, based on at least one of position information, channel quality information, Carrier to Interference and Noise Ratio (CINR) information, power allocation ratio information, and Modulation and Coding Scheme (MCS) level information of a terminal; and determining terminals to which collaborative MIMO is to be applied, among the selected terminals, and allocating resources to the determined terminals.

Advantageous Effects

[14] Accordingly, the present invention processes Collaborative MIMO by efficiently grouping terminals capable of Collaborative MIMO in an environment where SISO and MIMO coexist, thereby efficiently utilizing the limited resources and contributing to performance improvement of a wireless communication system.

[15] Further, the present invention groups terminals having a low channel correlation using an orthogonal value and an eigen ratio of channels during Collaborative MIMO processing, thus contributing to an increase in QoS.

[16] Moreover, the present invention efficiently allocates resources for the terminals grouped based on a channel correlation during Collaborative MIMO processing, thereby making the best use of the limited resources and contributing to an increase in the system performance. Brief Description of the Drawings

[17] The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

[18] FIG. 1 is diagram illustrating the outlines of general SISO system and MIMO system, respectively;

[19] FIG. 2 is a diagram illustrating a 2x2 Collaborative MIMO system performed between two terminals and one base station;

[20] FIG. 3 is a diagram illustrating pilot patterns applied to a UL PUSC mode in a 2x2

Collaborative MIMO system according to the present invention;

[21] FIG. 4 is a diagram illustrating exemplary resource allocation schemes for non-

MIMO and Collaborative MIMO, respectively; [22] FIG. 5 is a diagram illustrating a structure of a base station to which a Collaborative

MIMO processing apparatus according to the present invention;

[23] FIG. 6 is a diagram illustrating a structure of a Collaborative MIMO processing apparatus according to the present invention;

[24] FIG. 7 is a flowchart illustrating a Collaborative MIMO processing method according to the present invention;

[25] FIG. 8 is a flowchart illustrating a detailed example of the scheduling step of FIG. 7 according to the present invention; and

[26] FIG. 9 is a flowchart illustrating another example of the scheduling step of FIG. 7 according to the present invention. Mode for the Invention

[27] Preferred embodiments of the present invention will now be described in detail with reference to the annexed drawings. In the following description, a detailed description of known functions and configurations incorporated herein has been omitted for clarity and conciseness.

[28] FIG. 2 illustrates an Uplink (UL) Multiple Input Multiple Output (MIMO) system, and in particular, illustrates a 2x2 Collaborative MIMO system including two terminals, e.g. Mobile Station (MS)/Portable Subscriber Station (PSS) and one base station, e.g. Base Station (BS)/Radio Access Station (RAS).

[29] In brief, a first terminal and a second terminal perform transmission through a first transmission antenna TxAntO and a second transmission antenna TxAntl using different pilot patterns, respectively. For reference, FIG. 3 illustrates pilot patterns transmitted by a first transmission antenna TxAntO (300) and a second transmission antenna TxAntl (350), respectively, for a UL Partial Usage of Sub-Channel (PUSC) mode of a 2x2 Collaborative MIMO system. A signal of a first channel HOO and a third channel HlO transmitted by the first terminal and a signal of a second channel HOl and a fourth channel HI l transmitted by the second terminal are transmitted through the same subcarriers using different pilot patterns after undergoing spatial multiplexing. Then, a base station with first and second reception antennas RxAntO and RxAntl receives both signals transmitted from the first terminal and the second terminal.

[30] In this context, FIG. 4 illustrates exemplary resource allocation schemes for non-

MIMO (400) and Collaborative MIMO (450), respectively. It can be appreciated from Collaborative MIMO (450) transmits multiple bursts, e.g., UL Burst #1 and UL Burst #2, using the same subchannel, thereby making it possible to transmit more data with the limited resources.

[31] FIG. 5 illustrates a structure of a base station 500 to which a Collaborative MIMO processing apparatus according to the present invention. [32] As illustrated in FIG. 5, a base station 500 includes an interface 510, a band signal processor 520, a transmitter 530, a receiver 560, a scheduler 550, and antennas 540. The illustrated base station 500 supports Time Division Multiplexing (TDD), and also supports 2x2 MIMO by transmitting/receiving signals through transmission paths and reception paths of two antennas included therein.

[33] In the reception paths, the receiver 560 receives more than one radio signals transmitted by terminals, via the antennas 540, and converts the received radio signals into a baseband signal. For example, for data reception of the base station 500, the receiver 560 removes noises from the received signal, amplifies the noise-removed signal, down-converts the amplified signal into a baseband signal, and digitalizes the down-converted baseband signal. The band signal processor 520 extracts information or data bits from the digitalized signal, and performs demodulation, decoding and error correction thereon.

[34] In the transmission paths, the interface 510 receives voice, data and/or control information from a base station controller or a radio network, and the band signal processor 520 encodes the voice, data and/or control information and then transfers them to the transmitter 530. The transmitter 530 modulates the encoded voice, data and/or control information into a carrier signal having a desired transmission frequency or frequencies, amplifies the modulated carrier signal to a level suitable for transmission, and transmits the amplified carrier signal on the air via the antennas 540.

[35] Meanwhile, the scheduler 550 performs scheduling by allocating DL-MAP, UL-

MAP, Downlink (DL) bursts and UL bursts to a frame which is formed of symbols and subchannels for their transmission/reception with terminals. In this case, if Collaborative MIMO is applied, the scheduler 550 performs scheduling by means of grouping (or grouping) terminals capable of Collaborative MIMO. Therefore, the Collaborative MIMO processing apparatus according to the present invention can be realized as a scheduler itself or a part of it, and can also be realized as a separate apparatus.

[36] FIG. 6 is a diagram illustrating a structure of a Collaborative MIMO processing apparatus 600 according to the present invention. As illustrated, the Collaborative MIMO processing apparatus 600 according to the present invention includes a terminal searcher 610, a terminal information collector 620, a terminal sorter 630, a channel correlation calculator 640, a terminal grouper 650, and a resource allocator 660.

[37] The terminal searcher 610 searches for terminals capable of Collaborative MIMO in a system environment where SISO and MIMO coexist, depending on the basic capacity, such as physical parameter information, and bandwidth allocation information, provided from terminals.

[38] The terminal information collector 620 acquires information on the terminals capable of Collaborative MIMO, searched by the terminal searcher 610. Such information on the terminals can include position information of the terminals, and channel quality information of the terminals, and the channel quality information of the terminals can include parameters such as, for example, ranging channel information, UL sounding channel information, Carrier to Interference and Noise Ratio (CINR) information based on a Channel Quality Indicator (CQI) channel, power allocation ratio information, and Modulation and Coding Scheme (MCS) level information. For example, the position information of the terminals can be obtained through the Global Positioning System (GPS), or can be obtained through a path loss of transmission/ reception power during initial call setup between a base station and a terminal.

[39] The terminal sorter 630 sorts terminals using the parameters or a combination of the parameters. For example, the terminal sorter 630 sorts terminals in the order of the terminals closer to the base station, using the position information of the terminals, or sorts terminals in the order of the terminals having a better channel state, using the CINR information of the terminals. Here, in an embodiment of the present invention, the terminal sorter 630 sorts terminals in power strength order, or sorts terminals in channel gain order. In this case, the terminal sorter 630 can also sort terminals taking more than two parameters into account.

[40] The channel correlation calculator 640 calculates a channel correlation between terminals using a channel orthogonal value and a channel eigen ratio, for the terminals searched by the terminal searcher 610. Channels that need channel correlation calculation can include, for example, a ranging channel, a sounding channel, and a channel with a pilot. The channel correlation indicates a degree by which channels are affected due to interference between terminals, and it is preferable for the channel correlation to be zero (0) or low if possible, in order to guarantee performance of the Collaborative MIMO system.

[41] The terminal grouper 650 determines terminals to which it will apply Collaborative

MIMO, based on the information provided from the terminal searcher 610, the terminal information collector 620, the terminal sorter 630 and the channel correlation calculator 640, and groups the determined terminals.

[42] In this case, most simply, the terminal grouper 650 can consider grouping the terminals on a random basis, or grouping the terminals in their sorted order. And, it is preferable to group the terminals using the provided information, and an example thereof is as follows.

[43] It is preferable to group the terminals closest to the base station when grouping terminals using position information of the terminals; to group the terminals having a lower channel correlation when grouping terminals using channel correlation between the terminals; to group the terminals having a higher CINR when grouping terminals using CINR information of the terminals; to group the terminals having the same MCS level (e.g., 16-ary Quadrature Amplitude Modulation (16QAM) 1/2) or having a smaller MCS level difference when grouping terminals using MCS levels of the terminals; and to group the terminals whose power allocation ratio is included in a threshold range when grouping terminals using power allocation ratios of the terminals.

[44] In particular, according to the present invention, it is preferable to group terminals with the following schemes (algorithms), when grouping terminals using the channel correlation.

[45] A first scheme groups terminals in the order of the terminals having the lowest channel orthogonal value (hereinafter referred to as an 'orthogonal value' for short) between terminals.

[46] Specifically, the first scheme calculates an orthogonal value for each of all user terminals. The first scheme selects the terminals having the lowest orthogonal value, and groups the selected terminals. Similarly, for the remaining terminals, the first scheme selects the terminals having the lowest orthogonal value and groups the selected terminals. By repeating this, the first scheme groups all terminals.

[47] For reference, an orthogonal value can be calculated using Equation (1) and Equation

(2).

[48] [Equation 1]

[49]

[50] [Equation 2]

[51] ^N«

^ Orth _ valne(userl, userX, sc) Orth{user\,userX) = —

[52] where 'user#' denotes an index of a #-th user terminal, 'sc' denotes a subcarrier index,

¹H' denotes a channel response, and ¹H^*' denotes a conjugate of H. Further, 'channel_gain' denotes a channel gain, 'power' denotes power of a user terminal, and 'Orth_value' denotes an orthogonal value between user terminals at an sc-th subcarrier. In addition, 'Orth' denotes an orthogonal value between user terminals for all sub- carriers, and 'Nsc' denotes the number of subcarriers.

[53] A second scheme groups terminals in the order of the terminals having the lowest channel eigen ratio (hereinafter referred to as an 'eigen ratio' for short) between terminals.

[54] Specifically, the second scheme calculates an eigen ratio for each of all user terminal.

The second scheme selects the terminals having the lowest eigen ratio, and groups the selected terminals. Similarly, for the remaining terminals, the second scheme selects the terminals having the lowest eigen ratio and groups the selected terminals. By repeating this, the second scheme groups all terminals.

[55] For reference, an eigen ratio can be calculated using Equation (3).

[56] [Equation 3]

[57] Eigen Ratio = (eigen jyalue _μserX) j (eigen jyahie jiiserY)

[58] where 'X' and 'Y' denote user indexes, and 'eigen_value' denotes a channel- specific value.

[59] A third scheme groups terminals in the order of the terminals having the greatest signal strength difference (or power offset) between terminals.

[60] Specifically, the third scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The third scheme selects the terminals having the greatest offset between their products of power and channel gains, and groups the selected terminals. Similarly, for the remaining terminals, the third scheme selects the terminals having the greatest offset between their products of power and channel gains, and groups the selected terminals. By repeating this, the third scheme groups all terminals.

[61] Example 1 shows the result obtained by sorting 10 terminals in the order of the product (Power*Channel_Gain) of power and a channel gain, and then grouping the terminals in the order of the terminals having the greatest offset between their products of power and channel gains.

[62] Example 1

[63] User index: [1 2 3 4 5 6 7 8 9 10]

[64] Sorted index: [2 4 5 9 10 3 7 6 8 1]

[65] Grouped index: {[2 1] [4 8] [5 6] [9 7] [10 3] }

[66] A fourth scheme sorts terminals in the order of the signal strength, and then groups the sorted terminals.

[67] Specifically, the fourth scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The fourth scheme selects a group of the terminals having the greatest product of power and a channel gain and the terminals having the second greatest product of power and a channel gain, and groups the selected terminals. Similarly, for the remaining terminals, the fourth scheme selects a group of the terminals having the greatest product of power and a channel gain and the terminals having the second greatest product of power and a channel gain, and groups the selected terminals. By repeating this, the fourth scheme groups all terminals.

[68] Example 2 shows the result obtained by sorting 10 terminals in the order of the product (Power*Channel_Gain) of power and a channel gain, and then grouping the terminals in order.

[69] Example 2

[70] User index: [1 2 3 4 5 6 7 8 9 10]

[71] Sorted index: [2 4 5 9 10 3 7 6 8 1]

[72] Grouped index: {[2 4] [5 9] [10 3] [7 6] [8 1] }

[73] Meanwhile, combinations of the foregoing schemes can be considered. In this case, for example, it is possible to randomly select one terminal, or select the terminals having the highest or lowest signal strength, thereby reducing the calculation required for calculating an orthogonal value and an eigen ratio for all combinations of terminals. A description thereof will be given below.

[74] A fifth scheme gives a priority to the terminals having the highest signal strength, and calculates its orthogonal value with the remaining terminals to group the terminals having the highest signal strength and the terminals having the least orthogonal value.

[75] Specifically, the fifth scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The fifth scheme selects the terminals having the greatest product of power and a channel gain, and calculates an orthogonal value between the selected terminals and each of the remaining terminals. The fifth scheme groups the selected terminals and the terminals having the least orthogonal value. Similarly, for the remaining terminals, the fifth scheme selects the terminals having the greatest product of power and a channel gain, and groups the selected terminals and the terminals having the least orthogonal value.

[76] Example 3 shows the result obtained by sorting 10 terminals in the order of the product (Power*Channel_Gain) of power and a channel gain, calculating an orthogonal value between the terminal (with user index = 2) having the highest signal strength and each of the 9 remaining terminals (with user indexes = 1, 3, 4, 5, 6, 7, 8, 9 and 10), and then grouping the terminal (with user index = 2) having the highest signal strength and the terminal (with user index = 8) having the least orthogonal value. By repeating this process, the fifth scheme groups all terminals.

[77] Example 3

[78] User index: [1 2 3 4 5 6 7 8 9 10]

[79] Sorted index: [2 4 5 9 10 3 7 6 8 1]

[80] 2^nd Sorted index: [4 5 9 10 3 7 6 1] <- 1^st Grouped index: [2 8]

[81] A sixth scheme gives a priority to the terminals having the lowest signal strength, and calculates its orthogonal value with the remaining terminals to group the terminals having the lowest signal strength and the terminals having the least orthogonal value.

[82] Specifically, the sixth scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The sixth scheme selects the terminals having the least product of power and a channel gain, and calculates an orthogonal value between the selected terminals and each of the remaining terminals. The sixth scheme groups the selected terminals and the terminals having the least orthogonal value. Similarly, for the remaining terminals, the sixth scheme selects the terminals having the least product of power and a channel gain, and groups the selected terminals and the terminals having the least orthogonal value.

[83] A seventh scheme gives a priority to the terminals having the greatest signal strength, and calculates its eigen ratio with the remaining terminals to group the terminals having the greatest signal strength and the terminals having the lowest eigen ratio.

[84] Specifically, the seventh scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The seventh scheme selects the terminals having the greatest product of power and a channel gain, and calculates an eigen ratio between the selected terminals and each of the remaining terminals. The seventh scheme groups the selected terminals and the terminals having the lowest eigen ratio. Similarly, for the remaining terminals, the seventh scheme selects the terminals having the greatest product of power and a channel gain, and groups the selected terminals and the terminals having the lowest eigen ratio.

[85] An eighth scheme gives a priority to the terminals having the lowest signal strength, and calculates its eigen ratio with the remaining terminals to group the terminals having the lowest signal strength and the terminals having the lowest eigen ratio.

[86] Specifically, the eighth scheme calculates a product (Power*Channel_Gain) of power and a channel gain for all terminals, and sorts the terminals based thereon. The eighth scheme selects the terminals having the least product of power and a channel gain, and calculates an eigen ratio between the selected terminals and each of the remaining terminals. The eighth scheme groups the selected terminals and the terminals having the lowest eigen ratio. Similarly, for the remaining terminals, the eighth scheme selects the terminals having the least product of power and a channel gain, and groups the selected terminals and the terminals having the lowest eigen ratio.

[87] A ninth scheme randomly selects one terminal, and groups the selected terminal and the terminals having the least power offset with the selected terminal. Similarly, for the remaining terminals, the ninth scheme groups the terminals in the same manner.

[88] Meanwhile, even though terminals are grouped with the foregoing schemes, if a channel correlation between the grouped terminals is greater than or equal to a particular threshold, Collaborative MIMO may not be applied to the grouped terminals.

[89] Finally, the resource allocator 260 allocates radio resources to the terminals grouped according to the foregoing schemes. The resource allocator 260 can allocate radio resources based on positions and channel qualities of terminals. For example, the resource allocator 260 can allocate more radio resources to the terminals having the less orthogonal value and eigen ratio, thereby improving the system performance.

[90] With reference to FIGs. 7 to 9, a description will now be made of a Collaborative

MIMO processing method according to the present invention.

[91] FIG. 7 is a flowchart illustrating a Collaborative MIMO processing method according to the present invention.

[92] Referring to FIG. 7, each terminal notifies its own capability to a base station through a Subscriber Station Basic Capability Request (SBC-REQ) message, and the base station determines a basic capacity between the terminals and the base station taking the notified capability into account, and then responds to the notification through a Subscriber Station Basic Capability Response (SBC-RSP) message (Step S710). Subsequently, the terminal transmits a Registration Request (REG-REQ) message to the base station, and the base station responds thereto with a REG-RSP message, thereby performing registration (Step S720). The base station performs scheduling for data exchange with the terminals (Step S730). At this point, a scheduler selects terminals capable of Collaborative MIMO, groups the selected terminals, and designates a burst region for the grouped terminals in an UL frame, for resource allocation. When UL- MAP is generated by the resource allocation, the base station includes the UL-MAP in a DL frame, and transmits it to the terminal (Step S740). The terminal decodes the UL- MAP (Step S750), and then transmits data on a designated UL burst to the base station (Step S760). Here, the grouped terminals transmit data on the same burst using different pilot patterns.

[93] FIG. 8 is a flowchart illustrating a detailed example of the scheduling step (S730) of

FIG. 7 according to the present invention.

[94] Referring to FIG. 8, a scheduler searches for terminals capable of Collaborative

MIMO in a system environment where SISO and MIMO coexist, depending on a basic capacity exchanged between terminals and a base station (Step S810). Further, the scheduler determines whether it will apply Collaborative MIMO to the searched terminals in the current state. The criterion can be set depending on a channel correlation between ranging channels, a channel correlation based on a UL sounding channel, a channel correlation between pilots, etc., and when the channel correlation is less than or equal to a predetermined threshold, Collaborative MIMO is applied.

[95] Thereafter, the scheduler acquires information on the searched target terminals to which Collaborative MIMO is to be applied (Step S 820). The information on the terminals can include parameters such as, for example, positions of terminals, a channel correlation between terminals, CINRs of terminals, MCS levels of terminals, and power allocation ratios of terminals.

[96] The scheduler groups terminals using the information (Step S830). Preferably, in this case, for example, the scheduler groups the terminals closest to the base station when grouping terminals using position information of the terminals; groups the terminals having a lower channel correlation when grouping terminals using channel correlation between the terminals; groups the terminals having a higher CINR when grouping terminals using CINR information of the terminals; groups the terminals having the same MCS level (e.g., 16QAM 1/2) or having a smaller MCS level difference when grouping terminals using MCS levels of the terminals; and groups the terminals whose power allocation ratio is included in a threshold range when grouping terminals using power allocation ratios of the terminals. It is also preferable to group terminals using a combination of more than two kinds of the information.

[97] Next, the scheduler allocates resources for Collaborative MIMO based on the terminals grouped in step S830 (Step S840). In step S840, the scheduler can allocate the resources based on positions of terminals in the cell; can allocate the resources based on channel qualities of terminals; or can allocate the resources based on at least two kinds of information.

[98] For example, when allocating radio resources based on the terminal positions, the scheduler allocates the same data bursts through UL-MAP for the terminals having the similar distance from the base station. On the contrary, for the terminals having different distances from the base station, the scheduler allocates a greater amount of data bursts in UL-MAP for the terminals closer to the base station, and allocates a less amount of data bursts in UL-MAP for the terminals farther from the base station, making it possible to increase resource efficiency.

[99] Meanwhile, when allocating radio resources based on the channel qualities, the scheduler allocates a greater amount of data bursts in UL-MAP for the terminals having a high channel quality, and allocates a less amount of data bursts in UL-MAP for the terminals having a low channel quality. As a result, the need for allocating higher transmission power for the terminals having a low channel quality is reduced, contributing to a decrease in interference to adjacent cells compared with the case where the higher power should be allocated for such terminals.

[100] FIG. 9 is a flowchart illustrating another example of the scheduling step (S730) of FIG. 7 according to the present invention, and a description thereof will be given in brief, since reference can be made to the foregoing description.

[101] A scheduler searches for terminals capable of Collaborative MIMO in an environment where SISO and MIMO coexist, depending on a basic capacity exchanged between terminals and a base station (Step S910). Subsequently, the scheduler acquires parameters for the searched terminals (Step S920). Such parameters can include, for example, positions of terminals, CINRs of terminals, allocated power of terminals, etc.

[102] Next, the scheduler sorts terminals using the parameters or a combination of the parameters (Step S930). In this case, the terminal grouper according to the present invention sorts the terminals in the order of the signal strength.

[103] Thereafter, the scheduler groups the sorted terminals (Step S940). For this, reference can be made to the foregoing grouping schemes that use an orthogonal value and an eigen ratio. Finally, the scheduler allocates resources for the grouped terminals (step S950).

[104] Although the invention uses a product of power and a channel gain for all terminals when calculating signal strength of the terminals, by way of example, the scheme by the invention can also be applied to use reception power of the terminals.

[105] While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[1] An apparatus for processing collaborative Multiple Input Multiple Output

(MIMO), the apparatus comprising: a terminal searcher for searching for terminals capable of collaborative MIMO depending on a basic capacity exchanged with terminals; a terminal information collector for collecting at least one of position information, channel quality information, Carrier to Interference and Noise Ratio (CINR) information, power allocation ratio information, and Modulation and Coding Scheme (MCS) level information, for the terminals capable of collaborative MIMO; and a terminal grouper for grouping the terminals capable of collaborative MIMO based on the collected at least one information.

[2] The apparatus of claim 1, further comprising: a channel correlation calculator for calculating a channel correlation for a combination of the terminals capable of collaborative MIMO; wherein the terminal grouper groups the terminals capable of collaborative MIMO in the order of terminals having the lowest channel correlation.

[3] The apparatus of claim 2, wherein the channel correlation is at least one of a channel orthogonal value and a channel eigen ratio.

[4] The apparatus of claim 3, wherein the channel orthogonal value is calculated by the following equations;

H(mer\, sc) x H ^" (userX, sc) x -J power(userX) x channel _ gaιn(userX)

Orth _ value(userl, userX, sc) = yj ^' poweriuserl) x channel _ gam(iιser\)

2^ Orth _ valιte{ιιser\, user X ,sc) Orth(user\userX) = —

where 'user#' denotes an index of a #-th user terminal, 'sc' denotes a subcarrier index, ¹H' denotes a channel response, ¹H^*' denotes a conjugate of H, 'channel_gain' denotes a channel gain, 'power' denotes power of a user terminal, 'Orth_value' denotes an orthogonal value between user terminals at an sc-th subcarrier, 'Orth' denotes an orthogonal value between user terminals for all sub- carriers, and 'Nsc' denotes the number of subcarriers.

[5] The apparatus of claim 2, further comprising: a terminal sorter for sorting the terminals capable of collaborative MIMO based on a parameter; wherein the channel correlation calculator calculates a channel correlation between terminals based on the sorted order.

[6] The apparatus of claim 5, wherein the terminal sorter sorts the terminals according to signal strength of the terminals; wherein terminal grouper preferentially groups terminals having the highest signal strength or terminals having the lowest signal strength.

[7] The apparatus of claim 2, wherein the terminal grouper groups terminals whose channel correlation is lesser than a particular threshold.

[8] The apparatus of claim 1, further comprising: a terminal sorter for sorting the terminals capable of collaborative MIMO based on a parameter; wherein the terminal grouper groups the terminals based on the sorted order.

[9] The apparatus of claim 8, further comprising: a channel correlation calculator for calculating a channel correlation for a combination of the terminals capable of collaborative MIMO; wherein the terminal grouper preferentially groups terminals having the lowest channel correlation in combination of terminals sorted with the highest priority or the lowest priority and the remaining terminals among the sorted terminals.

[10] The apparatus of claim 9, wherein the channel correlation is at least one of a channel orthogonal value and a channel eigen ratio.

[11] The apparatus of claim 8, wherein the terminal grouper preferentially groups the highest-priority terminals and the lowest-priority terminals.

[12] The apparatus of claim 8, wherein the terminal grouper preferentially groups the highest-priority terminals and the second-highest-priority terminals.

[13] The apparatus of claim 8, wherein the parameter comprises signal strength of the terminals capable of collaborative MIMO.

[14] The apparatus of claim 1, further comprising: a resource allocator for differently allocating radio resources for collaborative MIMO to the grouped terminals, based on the collected at least one information.

[15] A method for processing collaborative Multiple Input Multiple Output (MIMO), the method comprising: registering terminals to/from which a base station with multiple antennas will transmit/receive data; selecting terminals, to which collaborative MIMO is applicable, among the registered terminals, based on at least one of position information, channel quality information, Carrier to Interference and Noise Ratio (CINR) information, power allocation ratio information, and Modulation and Coding Scheme (MCS) level information of a terminal; and determining terminals to which collaborative MIMO is to be applied, among the selected terminals, and allocating resources to the determined terminals.

[16] The method of claim 15, further comprising: transmitting an uplink MAP to the selected terminals during downlink transmission.

[17] The method of claim 15, wherein the step selecting terminals comprises: selecting terminals, to which collaborative MIMO is applicable, among the registered terminals, based on at least one of a channel correlation between ranging channels for the registered terminals, a channel correlation between uplink sounding channels, and a channel correlation between pilots.

[18] The method of claim 17, wherein the step selecting terminals comprises: selecting terminals to which collaborative MIMO is applicable, when a channel correlation between ranging channels for the corresponding terminals or a channel correlation between uplink sounding channels is less than or equal to a threshold.

[19] The method of claim 15, wherein the step allocating resources comprises: grouping the selected terminals based on at least one of positions of the selected terminals, a channel correlation between the terminals, CINRs of the terminals, MCS levels of the terminals, power allocation ratios of the terminals, and velocities of the terminals, and allocating resources to the grouped terminals.

[20] The method of claim 15, wherein the step allocating resources comprises: allocating the resources based on positions of the terminals or channel qualities of the terminals.

[21] The method of claim 20, wherein the step allocating resources comprises: allocating a greater amount data bursts to terminals located within a particular distance compared with terminals located far from the particular distance, when allocating the resources based on positions of the terminals.

[22] The method of claim 20, wherein the step allocating resources comprises: allocating a greater amount of data bursts to terminals whose channel quality is higher than or equal to a particular channel quality, compared with terminals whose channel quality is lower than the particular channel quality, when allocating the resources based on channel qualities of the terminals.

[23] The method of claim 15, wherein the step allocating resources comprises: calculating a channel correlation for a combination of the terminals capable of collaborative MIMO; and grouping the terminals capable of collaborative MIMO in the order of terminals having the lowest channel correlation.

[24] The method of claim 23, further comprising: before the step calculating a channel correlation, selecting terminals having the highest signal strength or terminals having the lowest signal strength among the terminals capable of collaborative MIMO; wherein the step calculating a channel correlation comprises calculating a channel correlation between the terminals having the highest strength or the terminals having the lowest signal strength and remaining terminals. [25] The method of claim 23, wherein the channel correlation is at least one of a channel orthogonal value and a channel eigen ratio. [26] The method of claim 15, wherein the step allocating resources comprises: sorting the terminals capable of collaborative MIMO based on a parameter; and grouping the terminals capable of collaborative MIMO based on the sorted order. [27] The method of claim 26, wherein the step grouping comprises preferentially grouping the highest-priority terminals and the second-highest-priority terminals. [28] The method of claim 15, wherein the step allocating resources comprises: sorting the terminals capable of collaborative MIMO based on a parameter; calculating a channel correlation between the highest-priority terminals among the sorted terminals and each of remaining terminals; and preferentially grouping terminals having the lowest channel correlation. [29] The method of claim 28, wherein the parameter comprises signal strength of terminals. [30] The method of claim 28, wherein the channel correlation is at least one of a channel orthogonal value and a channel eigen ratio. [31] The method of claim 15, wherein the step allocating resources comprises: randomly selecting one terminal among the terminals capable of collaborative

MIMO; grouping the selected terminal and a terminal having the least power offset with the selected terminal; and repeating the step selecting one terminal and the step grouping for remaining terminals of the terminals capable of collaborative MIMO.