KR20080069227A - Antenna array calibration for multi-input multi-output wireless communication systems - Google Patents

Abstract

Calibration for a transmit chain of a device transmitting information to multiple devices over wireless links and receive chains of the multiple devices receiving information over one of the wireless links utilizing each of the estimates for different antennas of an access terminal as a separate estimate.

Description

ANTENNA ARRAY CALIBRATION FOR MULTI-INPUT MULTI-OUTPUT WIRELESS COMMUNICATION SYSTEMS

Claims of priority under sections 119 and 120 of the United States Patent Law

This application is filed on November 2, 2005, filed under US Provisional Patent Application No. 60 / 733,021, April 4, 2006, entitled "ANNTENNA ARRAY CALIBRATION FOR MULTI-INPUT MULTI-OUTPUT WIRELESS COMMUNICATION SYSTEMS." U.S. Patent Application No. 11 / 398,077 to this "ANNTENNA ARRAY CALIBRATION FOR WIRELESS COMMUNICATION SYSTEMS" claims the benefit of priority under section 119 (e) of the U.S. Patent Act, and two applications have been assigned to the assignee and are referred to herein. Included explicitly in the literature.

Background

1. Field

The following description relates generally to wireless communication, and more particularly, to calibrating an antenna array for a multiple input multiple output wireless communication system.

2. Background

Wireless networking systems have become a widespread means of communicating with the majority of people around the world. Wireless communication devices are becoming smaller and more powerful in order to satisfy consumer needs and to improve portability and convenience. Increasing processing power in mobile devices such as cellular telephones increases the demand for wireless network transmission systems. As cellular devices communicate through them, in general, such systems are not easily updated. As mobile device capacity expands, it may be more difficult to maintain existing wireless network systems in a manner that facilitates fully utilizing new and improved wireless device capabilities.

More specifically, frequency division based techniques generally divide the spectrum into individual channels by dividing the spectrum into uniform bandwidth chunks, e.g., of a frequency band allocated for wireless cellular telephony. The part may be divided into channels capable of conveying digital data, respectively, for conveying a voice conversation or using a digital service. Each channel can be assigned to only one user at a time. One variation commonly used is orthogonal frequency division, which effectively partitions the overall system bandwidth into multiple orthogonal subcarriers. Such subcarriers are also referred to as tones, carriers, bins, and / or frequency channels. Each subband is associated with a subcarrier that can be modulated with data. Using a time division based technique, the band is divided in time into sequential time slices or time slots. Each user of the channel may be provided with a time slice for transmitting and receiving information in a round-robin fashion. For example, at any given time t, access to the channel is provided to the user for a short burst. The switch is then accessed to another user who is given a short burst of time to send and receive information. The "taking turns" cycle continues, resulting in a number of transmit and receive bursts for each user.

Code division based techniques generally transmit data over a number of frequencies available at any time in range. In general, data is digitized and spread through the available bandwidth, where multiple users can be duplicated on a channel, and each user can be assigned a unique sequence code. Users can transmit on the same wideband chunk of the spectrum, with each user's signal spread over its entire bandwidth by its respective unique spreading code. The present technology can provide sharing, where more than one user can send and receive simultaneously. This sharing can be achieved through spread spectrum digital modulation in which a user stream of bits is encoded and spread over a very wide channel in a pseudo-random manner. The receiver is designed to recognize the associated unique sequence code and undo its randomization in order to collect bits for a particular user in a consistent manner.

A MIMO communication system is a known type of communication system in which both the transmitter and the receiver have a plurality of receive antennas and transmit antennas for communication. A mobile terminal having multiple receive antennas and transmit antennas within the coverage area of a base station may be interested in receiving one, two or more or all data streams delivered in a composite stream. Likewise, a mobile terminal can transmit data to a base station or other mobile terminal. Such communication between the base station and the mobile terminal or between the mobile terminals may be degraded due to channel variation and / or interference power variation. For example, the above mentioned changes may affect base station scheduling, power control, and / or rate prediction for one or more mobile terminals.

When antenna arrays and / or base stations are used in conjunction with a Time Domain Duplexed (TDD) channel transmission technique, very large gains can be realized. A key assumption for realizing this gain is due to the TDD nature of transmission and reception, where both the forward link (FL) and the reverse link (RL) observe similar physical propagation channels corresponding to a common carrier frequency. In practice, however, the physical cabling and antenna architecture as well as the overall transmit and receive chain, which may include analog front ends and digital sampling transmitters and receivers, contribute to the overall channel response experienced by the receiver. In other words, the receiver understands the aggregate channel or equivalent channel between the input of the transmitter digital-to-analog converter (DAC) and the output of the receiver analog-to-digital converter (ADC). Physical antenna array structures, and analog receiver chains.

Given at least the foregoing, there is a need for a calibrating system and / or methodology of an antenna array used in a wireless communication device.

summary

In the following, a simplified overview of these aspects is provided to provide a basic understanding of one or more aspects. This Summary is not an extensive overview of all contemplated aspects, nor is it intended to identify critical or critical elements of any aspect, nor to limit the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

According to an aspect, an antenna array in a wireless network comprising determining a channel estimate for at least two antennas of at least two access terminals and determining a calibration ratio based on each channel estimate for at least two antennas. A method of calibrating is disclosed.

To attain the foregoing related objects, one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the one or more aspects. These aspects are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed and the described aspects are intended to include all such aspects and their equivalents.

Brief description of the drawings

1 illustrates aspects of a multiple access wireless communication system.

2 illustrates an antenna arrangement that includes a receiver chain and a transmitter chain in accordance with various aspects described herein.

3 shows an aspect of timing for a calibration operation.

4 illustrates aspects of logic that facilitates calibrating an antenna array to compensate for gain mismatch.

5 illustrates an aspect of a system that facilitates calibrating an antenna array to compensate for gain mismatch.

6 shows an aspect of a methodology for calibrating an array of antennas.

7 illustrates an aspect of a methodology for calibrating an array of antennas.

8 illustrates aspects of a receiver and a transmitter in a wireless communication system.

9 illustrates aspects of an access point.

details

Hereinafter, various aspects are described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout the specification. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect (s) may be practiced without these specific details. In other embodiments, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more aspects.

As used herein, terms such as "component", "system" and the like refer to computer-related such as any of hardware, software, running software, firmware, middleware, microcode, and / or any combination thereof. It is intended to refer to an entity. For example, a component may be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and / or a computer. One or more components may reside within a process and / or thread of execution and a component may be centralized on one computer and / or distributed between two or more computers. In addition, these components can execute from various computer readable media having various data structures stored thereon. A component may, for example, contain one or more data packets (eg, data from a local system as a signal, another component in a distributed system and / or from one component interacting with another system over a network such as the Internet). Depending on the signal it has, it may communicate as a local process and / or a remote process.

In addition, various aspects are described herein in connection with a subscriber station. A subscriber station may also be referred to as a system, subscriber unit, mobile station, mobile, remote station, access point, remote terminal, access terminal, user terminal, user agent, user device, or user equipment. The subscriber station connects to a cellular telephone, a cordless telephone, a session initiation protocol (SIP) telephone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a portable device with wireless connectivity, or a wireless modem. May be another processing device.

In addition, various aspects or features described herein may be implemented as a method, apparatus, or article of manufacture using standard programming and / or engineering techniques. The term "article of manufacture" as used herein is intended to include a computer program accessible from any computer-readable device, carrier, or media. For example, a computer readable medium may include a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip, ...), an optical disk (e.g., Compact Disk (CD), Digital Versatile Disk (DVD), …), Smart cards, and flash memory devices (eg, cards, sticks, key drives,…), but are not limited thereto.

Referring to FIG. 1, a multiple access wireless communication system according to one embodiment is shown. The multiple access wireless communication system 1 includes a number of cells, for example cells 2, 4, and 6. In FIG. 1, each cell 2, 4, and 6 may include an access point that includes a number of sectors. Multiple sectors are formed of groups of antennas each responsible for communicating with an access terminal in a portion of a cell. In cell 2, antenna groups 12, 14, and 16 each correspond to a different sector. In cell 4, antenna groups 18, 20, and 22 each correspond to a different sector. In cell 6, antenna groups 24, 26, and 28 each correspond to a different sector.

Each cell includes several access terminals in communication with one or more sectors of each access point. For example, access terminals 20 and 22 are in communication with access point 42, access terminals 24 and 26 are in communication with access point 44, and access terminals 28 and 40 are in access point. In communication with (46).

The controller 50 is coupled to the respective cells 2, 4, and 6. The controller 50 provides information from / terminals to an access terminal in communication with a cell of a number of networks, eg, the Internet, other packet-based networks, or a number of access wireless communication systems 1. It may include one or more connections to a circuit switched voice network. The controller 50 includes or is coupled to a scheduler that schedules transmissions to and from the access terminal. In another embodiment, this scheduler may be in each individual cell, each sector of the cell, or a combination thereof.

To facilitate calibration of transmissions for the access terminal, it is helpful to calibrate the access point gain calibration loop to handle mismatches caused by the access and transmit chains of the access point. However, due to noise in the channel, any calibration estimates based on the signal of the forward link received at the access terminal and the signal of the reverse link transmitted from the access terminal may include other channel changes and noise that will question the provided estimate. It may be. To overcome the channel noise effect, multiple calibrations for both the forward and reverse links are used for multiple access terminals. In some aspects, multiple transmissions to / from each antenna of each access terminal are contemplated for performing calibration of a given sector. In some aspects, multiple antennas may be used to calibrate communication for a single access terminal. In another aspect, fewer than one or all of the antennas for the access terminal group may be used to communicate with all of the antennas for the access terminal group.

In some aspects, either the transmit chain of the access point or the receive chain of the access point may be calibrated. This may be accomplished, for example, by calibrating the receiving chain of the access point to the transmitting chain of the access point or the transmitting chain of the access point to the receiving chain of the access point using a calibration ratio.

In the case of a MIMO system, each antenna of each access terminal may be treated as a separate access terminal to determine calibration quantification. When the calibration ratios are combined, each individual calibration ratio or calibration information for each antenna of each access terminal may be used as a separate component.

As used herein, an access point may be a fixed station used to communicate with a terminal, may be referred to as a base station, Node B, or some other terminology, and includes some or all of the functionality of the base station, Node B. You may. An access terminal may be referred to as a user equipment (UE), a wireless communication device, a terminal, a mobile station, or some other terminology, and may include some or all of its functionality.

1 shows a physical sector with different antennas for different sectors, it is noted that other approaches may be used. For example, the use of multiple fixed "beams" each covering a different area of a cell in the frequency space may be used instead or in combination with a physical sector. This approach is disclosed in US patent application Ser. No. 11 / 260,890, which is incorporated herein by reference and is entitled "Adaptive Sectorization In Cellular System" and co-pending with the present application.

Referring to FIG. 2, an antenna arrangement 100 is shown that includes a receiver chain 102 and a transmitter chain 104 in accordance with various aspects. Receiver chain 102 includes a down converter component 106 that downconverts the signal to baseband upon signal reception. The down converter component 106 is operatively connected to an AGC (Automatic Gain Control) function 108, which accesses the received signal strength and automatically adjusts the gain applied to the received signal to the receiver. It keeps the chain 102 within the linear operating range associated with it and provides a constant signal strength output through the transmitter chain 104. It is understood that AGC 108 may be optional for some embodiments described herein (eg, automatic gain control need not be performed in combination with all embodiments). The AGC 108 is operably connected to an analog-to-digital (A / D) converter 110, which is received by the digital low pass filter (LPF) 112 before the signal is smoothed. Converting the signal to digital format, the digital low pass filter can mitigate short-term oscillations in the received signal. Finally, receiver chain 102 can include a receiver processor 114 that can process the received signal and communicate that signal to one or more components of transmitter chain 104.

Transmitter chain 104 may include transmitter processor 116 to receive signals from receiver chain 102 (eg, the transmitter was originally received by receiver chain 102 and associated with its components). Receive signals to be processed variously). Transmitter processor 116 is operably coupled to pulse shaper 118, which facilitates manipulation of the signal to be transmitted so that the signal can be shaped within bandwidth constraints, while Can be alleviated and / or eliminated. Once shaped, the signal is digital-to-analog (D / A) converted by the D / A converter 120 before being operatively connected to a low pass filter (LPF) 122 in the transmitter chain 104 to smooth out. May suffer. Pulse amplifier (PA) component 124 may amplify the pulse / signal prior to upconversion to baseband by upconverter 126.

Antenna array 100 may exist for each antenna of both the access point and the access terminal. As such, significant differences are observed between the transport characteristics of transmitter chain 104 and receiver chain 102 and the samples of transmitter chain 104 and receiver chain 102, such as transmitter / receiver changes and / or equivalents. The interrelationship of the channels may not be assumed. Understanding the magnitude of changes in the signals propagated along the transmitter and receiver chains and their effects on the accuracy of the interrelationship in terms of their effect on phase and / or amplitude when calibrating the antenna array 100. It is also possible to facilitate the calibration process using. Also, in the case of an antenna array, each antenna 100 generally has a transmitter chain 104 and a receiver chain 102 that are different from each other antenna. Thus, each different transmitter chain 104 may each have a different effect in terms of phase and / or amplitude than any other transmitter chain 104. The same is true for the receiver chain 102 of each antenna 100.

The effect of the mismatch can be due to the physical structure of the antenna 100, component differences, or a plurality of other factors. Such discrepancies may include, for example, amplitude and / or phase mismatches due to mutual coupling effects, tower effects, incomplete knowledge of element positions, antenna cabling, and the like. In addition, the discrepancies may be due to the hardware elements of the transmitter chain 104 and / or the receiver chain 102 of each antenna 100. For example, such discrepancies may be associated with analog filters, I and Q imbalances, phase and / or gain mismatches of pulse amplifiers or low-noise amplifiers in the chains, various nonlinear effects, and the like.

At the access point, it requires its own complex and potentially unwieldy process to calibrate each transmit chain for the corresponding receive chain (ie, receive chain corresponding to the same antenna). In addition, any particular feedback on the forward link transmission, or pilot for any given access terminal used for the forward link transmission, suffers from noise for that user. Thus, for any given calibration ratio estimated based on both the forward and reverse links, there are some errors introduced by channel variation and noise. Thus, of various aspects, one or more calibration rates estimated for different antennas of a plurality of different access terminals are combined to obtain a single calibration rate to be used by the access point for transmission to one or all of the access terminals. In certain aspects, the combination may constitute an average, or some predetermined subset, of all calibration rates for each antenna of each access terminal in communication with this access point. In another aspect, this combination combines the channel measurements from / to each antenna of each access terminal without calculating an individual calibration rate for each antenna of each access terminal to each of each access terminal. It may be completed with a joint optimization scheme that estimates a single calibration ratio that is a combination of gain mismatches for the antennas of < RTI ID = 0.0 >

At the antenna of any given access terminal, the access point is performed at the access terminal and fed back to the access point to estimate or calculate a calibration ratio based on the antenna of the access terminal. Forward link channel estimation.

는 액세스 포인트의 i번째 전송 안테나로부터 액세스 단말기의 안테나로의 전송을 위한 액세스 단말기에서 추정될 수도 있다. 그러나, 임의의 채널 추정치는, 액세스 포인트 전송 체인 및 액세스 단말기 수신 체인에 의해 발생된 임의의 이득 또는 왜곡과 함께, 그 채널의 노이즈와 관련된 컴포넌트를 가질 것이다. 순방향 링크 채널 추정치는 다음 식 1과 같이 쓸 수도 있다:Forward link channel estimate,

May be estimated at the access terminal for transmission from the i th transmit antenna of the access point to the antenna of the access terminal. However, any channel estimate will have a component associated with the noise of that channel, along with any gain or distortion generated by the access point transmission chain and the access terminal receive chain. The forward link channel estimate can also be written as

, 액세스 포인트의 전송기 체인의 이득 불일치

, 측정될 두 개의 안테나 사이에의 물리적 채널인

, 및 채널 추정치의 일부인 채널의 노이즈

의 함수이다. In equation 1, the channel estimate is a gain mismatch in the access terminal receiver chain for a particular antenna.

Gain mismatch in the transmitter chain of the access point

The physical channel between the two antennas to be measured

, And channel noise that is part of the channel estimate

Is a function of.

로부터의 전송으로 인한 액세스 포인트의 i번째 전송 안테나에서의 채널 추정치는 본질적으로 식 1의 역이다. 이것은 아래의 식 2로 나타낼 수 있다 : For reverse link transmission, the antenna of the access terminal

The channel estimate at the i < th > transmit antenna of the access point due to the transmission from < RTI ID = 0.0 > is < / RTI > This can be represented by Equation 2 below:

, 액세스 포인트 수신기 체인의 이득 불일치

, 측정될 두 개의 안테나들 사이의 물리적 채널인

, 및 채널 추정치의 일부인 채널의 노이즈

의 함수이다.In equation 2, this channel estimate is a gain mismatch in the access terminal transmission chain for the antenna.

Gain mismatch of the access point receiver chain

The physical channel between the two antennas to be measured

, And channel noise that is part of the channel estimate

Is a function of.

In order to calibrate the antenna array, the mismatch error between the receiver chain 102 and the transmitter chain 104 of the antenna 100 can be represented by Equation 3 below. Note that instead of the methodologies and mathematical relationships described herein, other methodologies and mathematical relationships may be used to achieve the associated array calibration.

는 역방향 링크 전송 및 순방향 링크 전송 사이의 전체적인 불일치 관계이고,

는 특정 안테나에 대한 액세스 단말기의 전송 체인과 수신 체인 사이의 이득 불일치율이고,

는 액세스 포인트에서 i번째 안테나에 대한 수신 체인 및 전송 체인 불일치율이다.

는 액세스 포인트에서 각각의 안테나 쌍에 대해 실질적으로 상수임을 주목한다. 또한, 식 3이 이상적인 점을 고려하면, 노이즈 추정치는 포함되지 않는다.In equation 3,

Is the overall mismatch between reverse link transmission and forward link transmission,

Is the gain mismatch rate between the transmit and receive chains of the access terminal for a particular antenna,

Is the receive chain and transmit chain mismatch rate for the ith antenna at the access point.

Note that is substantially constant for each antenna pair at the access point. Also, considering that Equation 3 is ideal, the noise estimate is not included.

는, 액세스 단말기에서 각각의 안테나에 대해, "캘리브레이션 벡터"라고 지칭될 수도 있는 하나의 벡터

로 그룹화될 수 있는데, 여기서, i=1,...,M 이고, M은 안테나의 수이다.Calibration Rate in Access Point Antenna Array

One vector, which may be referred to as a “calibration vector,” for each antenna in the access terminal

, Where i = 1, ..., M, where M is the number of antennas.

의 엔트리는, 액세스 단말기의 단일 안테나에 관하여 액세스 포인트의 각각의 안테나에 대한 추정치들과 대응한다. 벡터

의 엘리먼트는 액세스 포인트 안테나 어레이 각각의 전송 및 수신 체인에 대한 크기와 위상 불일치와, 특정 안테나에 대한 액세스 단말기 전송 및 수신 체인의 전송 및 수신 불일치에 대응하는 공통 불일치 모두를 포함하는 복소수일 수도 있음을 주목한다. 식 4가 하나의 액세스 단말기 안테나에 대한 엔트리를 갖는 벡터를 나타내지만, 이것은 다수의 액세스 단말기 또는 액세스 단말기의 다수의 안테나에 대한 엔트리를 포함할 수도 있다는 것을 주목한다.In expression 4, vector

The entry of s corresponds to the estimates for each antenna of the access point with respect to the single antenna of the access terminal. vector

The element of may be a complex number including both magnitude and phase mismatch for the transmit and receive chains of each of the access point antenna arrays and common mismatches corresponding to transmit and receive mismatches of the access terminal transmit and receive chains for a particular antenna. Pay attention. Note that although Equation 4 represents a vector with entries for one access terminal antenna, this may include entries for multiple access terminals or multiple antennas of the access terminal.

은 채널 측정 에러 (MSE) 의 효과를 포함하고, 또한, 채널 측정 역상관 (de-correlation) 의 효과를 포함하는데, 이득의 측정은 상이한 시간에 수행되므로, 시간과 온도에 따른 채널의 변화와, 측정에 영향을 미칠 다른 변화를 허용하기 때문이다.Noise vector

Includes the effect of channel measurement error (MSE), and also includes the effect of channel measurement de-correlation, since the measurement of gain is performed at different times, thus changing the channel with time and temperature, This is because it allows other changes to affect the measurement.

에 대응하는 추정된 캘리브레이션 벡터

는 식 5에 나타낸 것과 같이 결정될 수도 있다. Access terminal

Estimated calibration vector corresponding to

May be determined as shown in equation (5).

는 액세스 단말기 안테나의 전송 및 수신 체인에 대응하는 이득 불일치이고,

는 액세스 포인트 안테나 어레이 전송 및 수신 체인에 대응하는 불일치 벡터이다. 벡터

는 액세스 포인트 안테나 어레이의 모든 안테나에 대해 결정된다.here,

Is a gain mismatch corresponding to the transmit and receive chain of the access terminal antenna,

Is a mismatch vector corresponding to the access point antenna array transmit and receive chain. vector

Is determined for all antennas of the access point antenna array.

Note that there are various ways to combine different calibration vector estimates (corresponding to measurements from antennas of different access terminals) to generate a total calibration vector or a combined calibration vector. One method for this combining is to average all calibration vector estimates to obtain a single estimate.

를 포함한다. 하나 이상의 액세스 단말기가 매우 큰 이득 불일치

를 갖는 경우, 단일의 평균은, 가장 큰 이득 불일치

를 갖는 안테나를 향하여 평균이 치우칠 수도 있다.In this approach, each calibration vector estimate is a different multiplication factor for different access terminals.

It includes. One or more access terminals have very large gain mismatch

If we have a single mean, the largest gain mismatch

The average may be biased towards the antenna with.

를 갖는 경우에 최소화를 제공할 수도 있다. 이 프로세스를 식 6에 나타낸다.In another aspect, each calibration vector estimate corresponding to a particular access terminal is normalized according to the elements of the vector. This means that more than one access terminal has a high gain mismatch

Minimization may be provided when This process is shown in equation (6).

의 엘리먼트 U의 총 수로 나누어진다.Note that in some aspects, the normalized element may be any element of the calibration vector, provided that it is the same element for each calibration vector estimate, eg, the first element. Then, the sum of the normalized elements is a vector

Is divided by the total number of elements U.

의 순환되고 스케일링된 버전이고, 이 순환 및 스케일링은 상이한 액세스 단말기 불일치

로 인한 것일 수도 있다. 이 스케일링 및 순환을 제거하는 한 가지 방법은 하나의 기준을 갖도록 각각의 캘리브레이션 벡터를 먼저 정규화하는 것이다. 이후, 칼럼이 정규화된 캘리브레이션 벡터 추정치인 매트릭스

는 캘리브레이션 벡터들로부터 형성된 것일 수도 있다. 캘리브레이션 벡터에 대한 단일 추정치는 매트릭스의 분해, 예를 들어, 매트릭스

에 대한 특이값 분해를 수행함으로써 얻어진다. 최대 특이값에 대응하는 고유벡터는, 예를 들어, 식 7에 나타난 바와 같이, 총체적인 캘리브레이션 벡터 추정치로서 사용될 수도 있다.Another approach that may be used to combine different calibration vector estimates may be based on combining the estimated vectors in the matrix. For example, in some aspects, each calibration vector estimate is the same vector

Is a recursive and scaled version of, and this recursion and scaling is a different access terminal mismatch

It may be due to One way to eliminate this scaling and cycling is to first normalize each calibration vector to have one criterion. The matrix is then a matrix whose normalized calibration vector estimate

May be formed from calibration vectors. The single estimate for the calibration vector is a decomposition of the matrix, e.g.

It is obtained by performing singular value decomposition for. The eigenvector corresponding to the maximum singular value may be used as an overall calibration vector estimate, for example, as shown in equation (7).

As illustrated by the above three approaches, the calibration ratio is generally estimated within two steps. First, the value corresponding to the element of the calibration vector is calculated for the individual access terminal, for the antenna array, or for the antennas of interest. The calibration vectors are then combined according to one or more different mathematical processes.

가 존재할 수도 있다. 이러한 경우, 액세스 단말기의 안테나에서 측정된 순방향 링크 채널 벡터 추정치

은 액세스 포인트에서 측정된 역방향 링크 채널 벡터 추정치

와 관련될 수도 있다. 한가지 접근으로, 캘리브레이션 벡터

를 이용하여, 액세스 단말기 불일치

는 아래의 식 8로 나타난다.An alternative to calculating multiple calibration vectors is to use a joint optimization procedure using multiple access points and access measurements as follows. In some cases, the access terminal and the access point may generate their channel estimates for different frequency tones and at different time instants. Also, timing error between the access point and the u th access terminal at time k.

May be present. In this case, the forward link channel vector estimate measured at the antenna of the access terminal

Is the reverse link channel vector estimate measured at the access point.

May be associated with One approach, calibration vector

Access terminal mismatch

Is expressed by Equation 8 below.

는 대각 매트릭스로, 그 대각 요소는 역방향 링크 채널 벡터 추정치

의 엘리먼트이고,

이다. 아래 첨자 i,k,u는 각각 톤, 시간, 및 사용자 인덱스이다. 상기 식에서, 캘리브레이션 벡터

와 액세스 단말기 특정 불일치

는 알려지지 않았다. 식 8의 특징은, 액세스 단말기 불일치는, 안테나에 대한 액세스 단말기 전송 및 수신 체인으로 인한 이득 불일치 이 외에도 액세스 포인트 및 액세스 단말기의 안테나 사이의 타이밍 불일치의 영향을 포함한다는 것이다.

와

에 대한 솔루션을 얻는 한 가지 방법은 식 9로 나타낸 MMSE (Minimum Mean Squared Error) 접근을 이용하는 것이다.In Equation 8

Is a diagonal matrix whose diagonal element is the reverse link channel vector estimate

Is an element of

to be. The subscripts i, k, u are the tone, time, and user index, respectively. Where the calibration vector

Terminal specific inconsistency with

Is unknown. A feature of equation 8 is that the access terminal mismatch includes the effect of timing mismatch between the access point and the antenna of the access terminal in addition to the gain mismatch due to the access terminal transmit and receive chain for the antenna.

Wow

One way to get a solution to this is to use the Minimum Mean Squared Error (MMSE) approach shown in Equation 9.

와

에 대한 솔루션들이 아래의 식 10으로 주어질 수도 있다.

Wow

Solutions to may be given by Equation 10 below.

의 최소 고유벡터

Least eigenvectors of

에 대해, 직교 사영 연산자

는 다음과 같이 정의될 수도 있다.Where vector

For orthogonal projective operators

May be defined as follows.

To compensate for discrepancies, the calibration ratio may change the gain of the access point's transmitter chain such that the transmitter chain of the access point matches the receiver chain, in terms of both phase and amplitude, or equivalently receive the access point. The chain may be used to change the gain of the access chain's receive chain to match the transmit chain.

인 경우, 액세스 포인트는 다음의 전송을 위한 전처리 가중치 (pre-processing weights) 를 이용한다 :More specifically, the access point may use Maximum Ratio Combining (MRC) beamforming, Equal Gain Combining (EGC) beamforming, or any other spatial processing technique for transmission to any access terminal. That is, the reverse link channel vector

If, the access point uses pre-processing weights for the following transmissions:

에 따라서, 액세스 포인트는 다음의 전처리 가중치를 이용하여 그 전송 및 수신 체인 불일치들을 보상한다:Calibration Vector Estimates

Accordingly, the access point compensates for its transmit and receive chain mismatches using the following preprocessing weights:

이다.here,

to be.

2 illustrates one embodiment of receiver chain 102 and transmitter chain 104 in which other layouts and structures may be used. For example, different numbers of components may be used for both receiver chain 102 and transmitter chain 104. In addition, different devices and structures may also be substituted.

Combined or joint calibration vectors may be formed by processing each antenna, or group of antennas, of a given access terminal like a separate access terminal. In that way, this calibration process may be simplified so that each access terminal may not be independently calibrated.

3 shows a timing cycle for calibration from a single access terminal, and a TDD system with a single forward link frame or burst adjacent to a single reverse link frame or burst is used. As can be seen, from each antenna, one or more pilots transmitted on the reverse link are measured at the access point. The time period of the measurement is a function of the decoding time of the access point. During this decoding period, one or more pilots are sent on the forward link to the access terminal. The access terminal then measures the pilot to estimate the forward link channel for each receive antenna. In reverse link estimation, there is the same decoding lag. The decoded forward link estimate needs to be sent back to the access point to produce a calibration rate. Thus, it can be seen that since there is some minimum amount of time, there is a maximum access terminal speed at which calibration can be maintained without strong or substantially interference factors.

As can be seen in FIG. 3, if multiple channel estimates from multiple access terminals are used, the associated noise and drift may be reduced or sampled over at least the receive chain and the range of time. Also, if multiple antennas for each access terminal are used and handled independently, the drift and noise may be better estimated, where the noise and drift are more uniform for the antennas for a single access terminal so that any It can also weaken the abnormalities.

를 생성하는데 사용되는 비율을 계산하고 상이한 액세스 단말기의 상이한 안테나로부터의 상이한 측정들을 결합하기 위해 상술된 방법들 중 하나를 이용하여 이들을 모으는 비율 결합 계산기 (306; ratio aggregation calculator) 를 포함한다.4 illustrates aspects of logic that facilitates calibrating an antenna array to compensate for gain mismatch. System 300 includes calibration component 302, which includes a mismatch estimation component 304 that analyzes comparisons between receiver chain output signal and / or receiver chain output signals, and a vector;

A ratio aggregation calculator (306) is used to calculate the ratios used to generate and combine them using one of the methods described above to combine different measurements from different antennas of different access terminals.

를 생성하고 이용하는 캘리브레이션 컴포넌트 (406) 를 더 포함한다.5 illustrates an aspect of a system that facilitates calibrating an antenna array to compensate for gain mismatch. System 400 includes a processor 402 operatively coupled to antenna array 404. The processor 402 can use the calibration component 406 to determine gain mismatch for individual antenna coupling at the access terminal and the access point. After the processor 402 determines the calibration ratio, the vector

And a calibration component 406 for generating and using the.

The system 400 can additionally include a memory 408 operatively coupled to the processor 402, the memory 408 comprising information relating to array calibration, ratio generation and utilization, and generation of calibration data, and the like; And any other suitable information related to calibrating antenna array 404. Processor 402 is a processor dedicated to analyzing and / or generating information received by processor 402, a processor controlling one or more components of system 400, and / or received by processor 402. It may be a processor that both analyzes and generates information and controls one or more components of system 400.

The memory 408 may also store a protocol associated with generating signal copies and models / representations, mismatch estimates, and the like, such that the system 400 may perform antenna calibration and / or as described herein. Stored protocols and / or algorithms can be used to achieve mismatch compensation. It is understood that the data store (eg, memory) described herein can be either volatile memory or nonvolatile memory, and can include both volatile and nonvolatile memory. For illustrative purposes, nonvolatile memory may include, but is not limited to, Read Only Memory (ROM), Programmable ROM (PROM), Electrically Programmable ROM (EPROM), Electrically Erasable PROM (EEPROM), or Flash memory. Volatile memory can include random access memory (RAM), which acts as external cache memory. For illustration purposes, the RAM includes SRAM (Synchronous RAM), DRAM (Dynamic RAM), SDRAM (Synchronous DRAM), DDR SDRAM (Double Data Rate SDRAM), ESDRAM (Enhanced SDRAM), SLDRAM (SynchLink DRAM), and DRRAM (Direct Rambus). Available in many forms, such as but not limited to RAM. The memory 408 of this subject system and method is intended to include, but is not limited to, such memory and any other suitable type of memory.

를 저장할 수 있다. 이러한 양태에서, 각각의 전송을 위해, 프로세서 (402) 는 캘리브레이션을 수행하지 않고 AGC 상태에 대한 캘리브레이션 벡터

를 액세스할 수도 있다. 부가적인 캘리브레이션을 수행할지 또는 주어진 전송을 위해 이전 캘리브레이션 벡터

를 액세스할지 여부에 관한 결정은 시간 주기 또는 전송 횟수에 기초할 수도 있는데, AGC 상태에 대한 캘리브레이션 벡터

가 얻어지기 때문이다. 이것은 시스템 파라미터일 수도 있고, 채널 상태, 예를 들어 채널의 로딩에 기초하여 변할 수도 있다.In some aspects, the memory 408 is a calibration vector for each state of the AGC, i.e. the level of amplification.

Can be stored. In this aspect, for each transmission, the processor 402 does not perform a calibration and the calibration vector for the AGC state.

You can also access. Perform additional calibration or previous calibration vector for a given transmission

The decision as to whether to access the may be based on a time period or number of transmissions, the calibration vector for AGC status

Is obtained. This may be a system parameter and may change based on the channel condition, eg loading of the channel.

With reference to FIG. 6, a methodology related to creating supplemental system resources is described. For example, the methodology may relate to antenna array calibration in a TDMA environment, an OFDM environment, an OFDMA environment, a CDMA environment, or any other suitable wireless environment. For simplicity of description, the methodology is shown and described as a series of acts, while the methodology is not limited to the order of the acts, and some acts may differ in order from the acts shown and described in the specification and in accordance with one or more embodiments. Understand that it may occur concurrently with other actions. For example, those skilled in the art will understand that a methodology may alternatively be represented by a series of interrelated states or events, such as a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more embodiments.

6 shows a methodology for calibrating an array of antennas for transmission. Channel estimates for the forward link are received from the access terminal for each receive antenna of the access terminal (block 500). As mentioned above, this channel estimate may be generated from the forward link pilot sent by the access point. In addition, channel estimates for the reverse link information, eg, reverse link channel pilot, are generated by the access point for each receive antenna of the access terminal (block 502).

After both the forward link and reverse link channel estimates have been collected, a calibration ratio for each access terminal antenna and access point antenna may be determined (block 504). In some aspects, the most recent forward link and reverse link channel estimates are used in time with respect to each other to form a calibration ratio. In such a case, the plurality of estimates for a given access terminal may be performed based on successive channel estimate pairs of forward link and reverse link estimates.

As mentioned in FIG. 3, there may be some time delay between different calculations and transmissions. In addition, the correlation for blocks 500 and 502 may occur at substantially the same time or at different times for the same or different access terminals, even if the same for different antennas of a single access terminal. Thus, the calibration ratio may be determined for a given antenna of a given access terminal based on channel estimates of forward link and reverse link transmissions, which may or may not be continuous in time.

The calibration ratio is combined to form a calibration estimate across the plurality of access terminals (block 506). This combined calibration rate may include calibration rates for some or all antennas of different access terminals in a given sector or cell, and may be unequal or equivalent numbers for each access terminal antenna from which one or more calibration rates are obtained. It has a calibration ratio.

The combined calibration ratio may be obtained by simply averaging the calibration ratio or using other approaches discussed with respect to FIG. 2, for example, the approaches discussed with respect to Equation 5 or 7.

Each transmission from each transmission chain of the access point is then weighted with weights based on the combined calibration rate for that transmission chain. In addition, a combined set of joint weights or joint sets may be used for one or more transmission chains of an access point. Alternatively, it is possible to send this combined calibration rate or calibration command based on the combined calibration rate for one or more access terminal antennas. The access terminal then applies a weight based on the joint calibration ratio to the decoding of the transmission received at the antenna of the access terminal.

Also, in some aspects, calibration weights may be used for certain AGC states and not used for other AGC states. As such, block 508 only applies to the AGC state during block 500.

7 shows another methodology for calibrating an array of antennas for transmission. Channel estimates for the forward link are received from the access terminal for each receive antenna of the access terminal (block 600). As mentioned above, this channel estimate may be generated from the forward link pilot sent by the access point. Further, reverse link information, for example, channel estimates for the reverse link channel pilot, is generated by the access point for each transmit antenna of the access terminal (block 602).

After both the forward link and reverse link channel estimates have been collected, a calibration ratio that uses multiple channel estimates for multiple antennas of multiple access terminals may be determined (block 604). In some aspects, the most recent forward link and reverse link channel estimates are used in time with respect to each other. In such a case, the plurality of estimates for a given access terminal may be performed based on successive channel estimate pairs of forward link and reverse link estimates.

As mentioned in FIG. 3, there may be some time delay between different calculations and transmissions. In addition, the correlation for blocks 600, 602 may occur at substantially the same time or at different times for the same or different access terminals, even if the same for different antennas of a single access terminal. Thus, the calibration ratio may be determined for a given antenna of a given access terminal based on channel estimates of forward link and reverse link transmissions, which may or may not be continuous in time.

For example, the joint calibration ratio may be obtained by using the joint optimization processor mentioned with respect to FIG. 8.

Each transmission from each transmission chain of the access point is then weighted with a weight based on the joint calibration rate for that transmission chain. In addition, a combined set of joint weights or joint sets may be used for one or more transmission chains of an access point. Alternatively, it is possible to send this joint calibration rate or calibration command based on a joint calibration rate for one or more antennas of one or more access terminals. The access terminal then applies a weight based on the joint calibration ratio to the decoding of the transmission received at the antenna of the access terminal.

Also, in some aspects, calibration weights may be used for certain AGC states and not used for other AGC states. As such, block 608 only applies to the AGC state during block 600.

8 illustrates an example wireless communication system 1300. The wireless communication system 1300 shows one base station and one terminal for simplicity. However, it is understood that the system may include one or more base stations and / or one or more terminals, and additional base stations and / or terminals may be substantially similar or different from the exemplary base stations and terminals described below. Further, it is understood that the base station and the terminal may use the system (FIGS. 1-5) and / or facilitate wireless communication therebetween using the methods described herein (FIGS. 6, 7). do.

Referring to FIG. 8, transmitters and receivers in multiple access wireless communication systems are shown. In the transmitter system 1310, traffic data of the plurality of data streams is provided from the data source 1312 to the transmit (TX) data processor 1344. In one embodiment, each data stream is transmitted via a respective transmit antenna. TX data processor 1344 formats, codes, and interleaves the traffic data for each data stream based on a particular coding scheme selected for that data stream to provide coded data. In some embodiments, TX data processor 1344 applies beamforming weights to symbols in the data stream based on the user receiving the symbol and the antenna from which the symbol is transmitted. In some embodiments, beamforming weights may be generated based on channel response information that is an indication of the state of the transmission path between the access point and the access terminal. The channel response information may be generated using the channel estimate provided by the user and the CQ1 information. Also, in the case of a scheduled transmission, the TX data processor 1344 may select a packet format based on rank information sent from the user.

Coded data for each data stream may be multiplexed with an Orthogonal Frequency Division Multiplexing (OFDM) technique. Pilot data is generally a known data pattern that may be processed in a known manner and used in a receiver system to estimate channel response. The multiplexed pilot and coded data for each data stream is modulated (eg, symbol mapping) based on the particular modulation scheme selected for the data stream (e.g., BPSK, QPSK, M-PSK, M-QAM). May be Data rate, coding, and modulation for each data stream may be determined by instructions performed or provided by the processor 1030. In some embodiments, the number of parallel spatial streams may vary depending on rank information transmitted from the user.

The modulation symbol for the data stream may additionally be provided to the TX MIMO processor 1346, which may process the modulation symbol (eg, for OFDM). TX MIMO processor 1346 then provides N _T modulation symbol streams to N _T transmitters (TMTR) 1322a through 1322t. In various embodiments, TX MIMO processor 1320 applies beamforming weights to symbols in the data stream based on the user receiving the symbol and the antenna from which the symbol is transmitted from the user channel response information.

Each transmitter 1322 receives and processes each symbol stream to provide one or more analog signals, and also condition (eg, amplify, filter, and upconvert) the analog signals for transmission over a MIMO channel. Provide a suitable modulated signal. Also, N _T modulated signals from transmitters 1322a through 1322t are transmitted from N _T antennas 1324a through 1324t, respectively.

In the receiver system 1320, the transmitted and modulated signal is received by N _R antennas 1352a-1352r, and the received signal from each antenna 1352 is directed to each receiver (RCVR) 1354a-1354r. Is provided. Each receiver 1354 conditions (eg, filters, amplifies, and downconverts) each received signal to digitize the conditioned signal to provide a sample, and further process the sample to correspond to the corresponding " Received "symbol stream.

RX data processor 1360 provides a number of rank N _R N _R receivers of receiving the received symbol streams, and processing "detected" symbol streams from (1354a through 1354r) based on a particular receiver processing technique. Processing by the RX data processor 1360 is described in more detail below. Each detected symbol stream includes a symbol that is an estimate of the modulation symbol transmitted for the corresponding data stream. The RX data processor 1360 then demodulates, deinterleaves, and decodes each detected symbol stream to recover traffic data for the data stream provided to the data sink 1364 for storage and / or further processing. You may. The processing by the RX data processor 1360 is complementary to the processing performed by the TX MIMO processor 1346 and the TX data processor 1344 in the transmitter system 1310.

The channel estimate generated by the RX processor 1360 may be used for performing spatial, space / time processing, adjusting the power level, changing the modulation rate or scheme, or other behavior at the receiver. The RX processor 1360 also estimates the Signal-to-Noise-and-Interference ratio (SNR) of the detected symbol stream, and possibly other channel features, and provides this amount to the processor 1370. The RX data processor 1360 or processor 1370 may also derive an estimate of the “effective” SNR for the system. Processor 1370 then provides estimated channel information (CSI), which may include various types of information about the communication link and / or the received data stream. For example, the CSI may include only operating SNR. In some embodiments, the channel information may include signal interference noise rate (SINR). The CSI is then processed by the TX data processor 1375, receiving the traffic data for the multiple data streams from the data source 1336, modulated by the modulator 1380, and transmitted by the transmitters 1354a-1354r. It is conditioned and sent back to the transmitter system 1310.

In the transmitter system 1310, the modulated signal from the receiver system 1350 is received by the antenna 1324, conditioned by the receiver 1322, demodulated by the demodulator 1390, and an RX data processor 1372. ) Recovers the CSI reported by the receiver system and provides the data to the data sink 1394 for storage and / or further processing. The reported CSI is then provided to the processor 1330 to determine (1) the coding and modulation scheme and data rate used for the data streams, and (2) the TX data processor 1344 and the TX MIMO processor 1346. Used to create various controls for.

The processor 1390 may also be configured to perform generation of a calibration ratio and a combined calibration ratio, or a joint calibration ratio, as discussed with respect to FIGS. 2, 6, and 7, respectively. In addition, each antenna 1352a-1352r may be treated like a separate terminal for combined or joint calibration estimates.

Referring to FIG. 9, the access point may include a main unit (MU) 1450 and a radio unit (RU) 1475. MU 1450 includes a digital baseband component of an access point. For example, the MU 1450 can include a baseband component 1405 and a digital intermediate frequency (IF) processing unit 1410. The digital IF processing unit 1410 digitally processes radio channel data at intermediate frequencies by performing functions such as filtering, channelization, modulation, and the like. RU 1475 includes the analog radio portion of an access point. As used herein, a wireless unit is an analog radio portion of an access point or other type of transceiver having a direct or indirect connection to a mobile switching center or corresponding device. The wireless unit generally provides a particular sector in the communication system. For example, the RU 1475 may include one or more receivers 1430 connected to one or more antennas 1435a-t that receive wireless communication from a mobile subscriber unit. In one aspect, one or more power amplifiers 1462a-t are coupled to one or more antennas 1435a-t. An analog-to-digital (A / D) converter 1425 is connected to the receiver 1430. A / D Converter 1425 converts the analog wireless communication received by receiver 1430 into a digital input for transmission to baseband component 1405 via digital IF processing unit 1410. RU 1475 also includes: One or more transmitters 1420 connected to either the same or different antennas 1435 for transmitting wireless communications to the access terminal 1. Digital-to-analog (D / A) converter 1415 to transmitter 1420 D / A converter 1415 converts the digital communication received from baseband component 1405 via digital IF processing unit 1410 into an analog output for transmission to a mobile subscriber unit. In some aspects, the multiplexer 1484 is for multiplexing multiple channel signals and multiplexing various signals including voice signals and data signals. The central processing unit 1480 performs various processing including processing of voice or data signals. It is coupled to the main unit 1450 and the RU (Radio Unit) for control.

In a multiple access system (eg, FDMA system, OFDMA system, CDMA system, TDMA system, etc.), multiple terminals can transmit simultaneously on the reverse link. In such a system, the pilot subbands may be shared between different terminals. If the pilot subbands for each terminal span the entire operating band (possibly except for the band edges), channel estimation techniques may be used. In order to obtain frequency diversity for each terminal, such a pilot subcarrier structure would be desirable. These techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. In a hardware implementation, the processing unit used for channel estimation includes one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays. (FPGA), a processor, a controller, a microcontroller, a microprocessor, another electronic unit designed to perform the functions described herein, or a combination thereof. Using software, this implementation can be accomplished through a module (eg, procedure, function, etc.) that performs the functions described herein. The software code may be stored in a memory unit and executed by the processors 1390 and 1350.

The foregoing description includes embodiments of one or more aspects. Of course, it is not possible to describe every conceivable combination of components or methodology for the purpose of describing the foregoing aspects, but one of ordinary skill in the art will appreciate that many additional combinations and substitutions of various aspects are possible. It may be appreciated that this is possible. Accordingly, the foregoing embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. In addition, the term "include" is used in either the description or the claims, where "comprising" is to be interpreted when used as a transitional word in the claims. Likewise, these terms are intended to be inclusive in a manner similar to the term "equipment".

Claims (28)

A method of calibrating an antenna array in a wireless network, the method comprising: Receiving first channel estimate information corresponding to transmissions of at least two access terminals to at least two antennas, respectively; Determining second channel estimate information corresponding to transmissions from the at least two antennas of the at least two access terminals, respectively; And And determining a calibration ratio based on each of the first channel estimate information and each of the second channel estimate information. The method of claim 1, Determining the calibration rate comprises independently determining a calibration rate for each antenna. The method of claim 2, Determining the calibration ratio comprises combining each of the calibration ratios. The method of claim 3, wherein Combining each of the calibration ratios comprises averaging each of the calibration ratios. The method of claim 3, wherein Each of the calibration ratios comprises a plurality of elements, Combining each of the calibration ratios, Normalizing each calibration ratio; And Determining the calibration rate based on a matrix comprising the normalized calibration rate. The method of claim 5, wherein Determining the calibration ratio based on the matrix comprises decomposing the matrix using singular value decomposition. The method of claim 1, Determining the calibration ratio comprises determining a joint calibration ratio based on first calibration information and second calibration information. The method of claim 1, Determining the calibration ratio is, equation

And solving the problem, here,

Is a diagonal matrix, wherein the diagonal elements of the diagonal matrix are the channel estimation information.

Elements of,

And subscripts i, k, u are tone, time, and user indices, respectively. The method of claim 8, Solving the equation comprises using a Minimum Mean Squared Error (MMSE) technique to solve the equation. The method of claim 1, Determining the calibration ratio comprises using a joint optimization scheme with the first channel estimate information and the second channel estimate information. A wireless communication device, At least two antennas; And A processor coupled to the at least two antennas, The processor, First channel estimation information corresponding to transmissions to at least two antennas of at least two access terminals, respectively, and a second channel corresponding to transmissions from the at least two antennas of the at least two access terminals, respectively. And determine a calibration ratio based on the estimated information. The method of claim 11, The processor is configured to determine a calibration rate for each of the plurality of access terminals and to determine the calibration rate based on a combination of each of the calibration rates for each of the antennas. The method of claim 12, And the processor is configured to combine the calibration rates by averaging each of the calibration rates. The method of claim 12, And the processor is configured to combine the calibration rates by normalizing each calibration rate and to determine the calibration rate based on a matrix including each of the calibration rates. The method of claim 14, And the processor is configured to obtain the calibration ratio by decomposing the matrix using singular value decomposition. The method of claim 11, The processor is configured to determine the calibration rate using a joint calibration rate. The method of claim 11, The processor is an expression

Determine the calibration ratio by solving here,

Is a diagonal matrix, wherein elements of the diagonal matrix are reverse link channel vector estimation

Elements of,

And subscripts i, k, u are tone, time, and user indices, respectively. The method of claim 17, And the processor is configured to solve the equation by using MMSE technology. The method of claim 17, And the processor is configured to determine the calibration ratio using a joint optimization scheme along with the plurality of first channel estimate information and the second channel estimate information. Means for processing first channel estimation information received from the at least two access terminals, respectively, corresponding to transmissions to at least two antennas of at least two access terminals; Means for determining second channel estimate information corresponding to transmissions from the at least two antennas of the at least two access terminals, respectively; And Means for determining a calibration ratio based on each of the first channel estimate information and each of the second channel estimate information. The method of claim 20, And means for determining the calibration rate comprises means for independently determining the calibration rate for each antenna. The method of claim 21, Means for independently determining a calibration rate for each antenna comprises means for combining each of the calibration rates. The method of claim 22, Means for combining each of the calibration rates comprises means for averaging each of the calibration rates. The method of claim 22, Each of the calibration ratios includes a plurality of elements, Means for combining each of the calibration ratios, Means for normalizing each calibration ratio; And Means for determining the calibration rate based on a matrix comprising the normalized calibration rate. The method of claim 20, And means for determining the calibration ratio comprises means for determining a joint calibration ratio based on first calibration information and second calibration information. The method of claim 20, The means for determining the calibration ratio is

Means for solving the problem, here, Is a diagonal matrix, wherein diagonal elements of the diagonal matrix are the channel estimation information.

Elements of,

And the subscripts i, k, u are tones, respectively, and the user indices. The method of claim 20, Means for determining the calibration ratio comprises means using a joint optimization scheme with the first channel estimate information and the second channel estimate information. A processor readable medium having stored thereon instructions used by a processor, The commands are Instructions corresponding to transmissions to at least two antennas of at least two access terminals, respectively, for processing first channel estimation information received from the at least two access terminals; Instructions for determining second channel estimate information corresponding to transmissions from the at least two antennas of the at least two access terminals, respectively; And Instructions for determining a calibration ratio based on each of the first channel estimate information and each of the second channel estimate information.

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