RU2395163C2 - Calibration of antenna matrix for multi-input-multi-output systems of wireless communication - Google Patents

Abstract

FIELD: information technologies. ^ SUBSTANCE: substance of invention consists in calibration of antenna matrix of access point in wireless network, including stages of receiving the first channel estimates that correspond to transfers from access point to each of at least two antennas, at least two access terminals, detection of the second channel estimates that correspond to transfers from each of at least two antennas of at least two of specified access terminals to point of access, identification of calibration ratio on the basis of mentioned estimates and calibration of antenna matrix of access point by application of calibration ratio to transfer scale of access point. ^ EFFECT: expansion and improvement of wireless communication devices. ^ 28 cl, 9 dwg

Description

Priority Statement

This application claims priority to 35 US Convention §119 (e) of Provisional Patent Application No. 60 / 733,021, entitled “Calibration of an Antenna Array for Multiple Output Multiple Output Wireless Systems,” filed November 2, 2005, and also claims priority to 35 US Convention § 120 according to the application No. 11 / 398,077, entitled "Calibration of the antenna matrix for wireless communication systems", filed April 4, 2006, both owned by the patent holder of this application and, thus, is specifically incorporated here by reference.

FIELD OF THE INVENTION

The following description relates generally to wireless transmissions and, inter alia, to calibration of an antenna array for multi-input multi-output wireless communication systems.

State of the art

Wireless communication systems have become widespread means by which most people around the world began to communicate. Wireless devices have become smaller and more powerful to meet consumer needs and to improve mobility and convenience. The increase in processing power in mobile devices, such as cell phones, has increased the demands on wireless transmission systems. Such systems are usually not easy to upgrade, like cellular devices that communicate through them. As mobile device capabilities expand, it can be difficult to maintain older wireless systems in such a way as to facilitate the full operation of new and improved wireless device capabilities.

More specifically, in frequency division, the spectrum is usually divided into different channels by dividing it into equal parts of the frequency band, for example, dividing the frequency band allocated for communication of cordless cell phones can be dividing into channels, each of which can carry a voice dialogue or digital service to carry digital data. Each channel can be assigned to only one user at a time. One commonly used option is the orthogonal frequency division technique, which effectively partitions the entire system bandwidth into multiple orthogonal subbands. These subbands are also referred to as tones, carriers, subcarriers, sections and / or frequency channels. Each subband is associated with a subcarrier that can be modulated with data. With time division methods, a strip is divided in time into successive time strips or time intervals. Each channel user is provided with a time strip for transmitting and receiving information according to the round-robin algorithm. For example, at any specific time t, the user is provided with access to the channel for transmitting short packets. Then, access is switched to other users, which are provided with short time intervals for transmitting and receiving information. The cycle of "rotation" continues and, ultimately, each user is provided with many transmission and reception intervals.

Code division techniques typically transmit data by the number of frequencies available at any time in a range. In general, data is digitized and distributed over an accessible frequency band, where many users can be combined on a channel and unique sequences codes can be assigned to corresponding users. Users can transmit in the same broadband portion of the spectrum, where each user signal is distributed across the entire frequency band through a corresponding unique spreading code. This method provides sharing where one or more users can simultaneously transmit and receive. Such sharing can be achieved through digital modulation of the spectral range, where the user bitstream is encoded and distributed over the broadband channel in a pseudo-random manner. The receiver recognizes the associated unique sequence code and eliminates randomization to collect bits for a particular user in a coherent manner.

A known type of communication system is a multi-input multi-output (MIMO) communication system, where the transmitter and receiver have multiple receiving and transmitting antennas for communication. A mobile terminal with multiple receiving and transmitting antennas in the coverage area of a base station with multiple receiving and transmitting antennas may be busy receiving one, more than one, or all data streams from the base station. Similarly, a mobile terminal may 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 deteriorate, respectively, with channel changes and / or changes in interference power. For example, the above changes may affect base station scheduling, power control, and / or speed prediction for one or more mobile terminals.

When the antenna array and / or base stations are used in conjunction with a time domain duplex (TDD) transmission method, very large gains can be achieved. A key condition for achieving these amplifications is that, in accordance with the nature of TDD transmission and reception, the forward channel (FL) and reverse channel (RL) comply with similar physical transmission channels corresponding to the total carrier frequency. However, in practice, all transmit and receive circuits, which may include analog input blocks and digital reference transmitters and receivers, as well as physical cables and antenna architecture, contribute to the overall channel response observed by the receiver. In other words, the receiver will see the full or equivalent channel between the input of the digital-to-analog converter (DAC) of the transmitter and the output of the analog to digital converter (ADC) of the receiver, which may contain an analog transmitter circuit, a physical propagation channel, a physical antenna array structure (including cables), and an analog receive chain.

In connection with the foregoing, there is a need for a prior art in a system and / or methodology for calibrating an antenna array in wireless communication devices.

SUMMARY OF THE INVENTION

The following is a simplified summary of one or more embodiments to provide a basic understanding of such embodiments. This summary is not a broad overview of all considered embodiments, and is intended to provide clarifying or admitting elements of all embodiments not limited to the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

In accordance with an aspect, a method for calibrating an antenna array in a wireless network comprises determining channel estimates for at least two antennas of at least two access terminals and determining a calibration relationship based on each of the channel estimates for at least two antennas.

To the accomplishment of the foregoing and related ends, one or more embodiments comprises features that are fully described below and specifically indicated in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of one or more embodiments. These aspects are indicative, however, only a few different ways in which the principles of various embodiments can be used and the described embodiments are intended to include all such aspects and their equivalents.

Brief Description of the Drawings

FIG. 1 shows aspects of a multiple access wireless communication system.

FIG. 2 is an antenna structure comprising a receive chain and a transmit chain, in accordance with various aspects described herein.

FIG. 3 illustrates aspects of a timing diagram for calibration operations.

FIG. 4 are aspects of a logic that facilitates calibration of an antenna array to compensate for gain mismatch.

FIG. 5 are aspects of a system that facilitate calibration of an antenna array to compensate for gain mismatch.

FIG. 6 illustrates aspects of a methodology for calibrating an antenna array.

FIG. 7 illustrates aspects of a methodology for calibrating an antenna array.

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

FIG. 9 are aspects of an access point.

Detailed description

Various embodiments are now described with reference to the drawings, in which like reference numerals are used to refer to like elements. In the following description, for purposes of explanation, various specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be obvious, however, that such embodiment (s) may be applied without these specific details. In other examples, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments.

Used in this application, the terms "component", "system" and the like are intended to mean a computer-implemented object or equipment, a combination of hardware and software, software or software in execution. For example, a component may be, but is not limited to, a process running on a processor, a processor, an object, a program being executed, a thread of execution, a program, and / or a computer. One or more components may belong to a process and / or thread of execution, and the component may be located on one computer and / or distributed between two or more computers. Also, these components can be executed from various computer-readable media having various data structures stored on them. Components can communicate through local and / or remote processes, such as in accordance with signals having one or more data packets (for example, data from one component interacting with another component in a local system, distributed system, and / or over a network, such as Internet with other systems via signal).

In addition, various embodiments are described herein in conjunction with a subscriber station. A subscriber station may also be called a system, subscriber unit, mobile station, mobile, remote station, access point, base station, remote terminal, access terminal, user terminal, user agent, user equipment, etc. The user station may be a cell phone, a cordless telephone, a Session Initiation Protocol (SIP) telephone, a local radio communication station (WLL), a personal digital assistant (PDA), a handheld device with wireless capability, or another processing device connected to a wireless modem.

In addition, various aspects or features described herein may be implemented as a method, device, or product of a manufacturer using standard programming and / or engineering methods. The term “manufacturer's product”, as used herein, is intended to encompass a computer program accessible from any computer-readable device, carrier, or medium. For example, computer-readable media may include, but are not limited to, magnetic storage devices (e.g., hard disk, floppy disk, magnetic tapes ...), optical disks (e.g., compact disc (CD), digital versatile disk (DVD) ...) , smart cards, flash memory (eg cards, stack, key drive ...) and integrated circuits such as read-only memory devices, programmable read-only memory devices and electrically erasable programmable read-only memory devices.

In FIG. 1 shows a multiple access wireless communication system in accordance with one embodiment. A multiple access wireless communication system 1 includes a plurality of cells, for example, cells 2, 104 and 106. In FIG. 1, each cell 2, 4, and 6 may include an access point that includes multiple sectors. Many sectors are formed by groups of antennas, each responsible for communication with access terminals in parts of the cell. In cell 2, groups of 12, 14, and 16 antennas each correspond to a different sector. In cell 4, groups of 18, 20, and 22 antennas each correspond to a different sector. In cell 6, groups 24, 26, and 28 each correspond to a different sector.

Each cell includes several access terminals that communicate with one or more sectors of each access point. For example, access terminals 20 and 22 communicate with the base of access point 42, terminals 24 and 26 communicate with access point 44, and terminals 28 and 40 communicate with access point 46.

A controller 50 is connected to each cell 2, 4, and 6. The controller 50 may comprise one or more connections to multiple networks, such as the Internet, or other packet-based networks, or voice-activated circuits that provide information to and from terminals access in connection with cells of a multiple access wireless communication system 1. The controller 50 includes or is connected to a scheduler that schedules transmission from and to access terminals. In other embodiments, a scheduler may be located in each individual cell, each sector of a cell, or a combination thereof.

To facilitate the calibration of transmissions to access terminals, it is advisable to calibrate the calibration cycle of amplification of the access point to deal with mismatches corresponding to the transmitting and receiving chains of the access point. However, as a result of noise in the channel, any calibration estimates based on the signals received at the access terminals, the forward channel and transmitted from the access terminals, the reverse channel, may contain noise and other channel changes that may cast doubt on the estimates provided. To overcome the effects of channel noise, multiple calibrations of the forward channel and reverse channel are used for multiple access terminals. In certain aspects, multiple transmissions to and from each antenna of each access terminal are taken into account in order to calibrate a given sector. In certain aspects, multiple antennas may be used to calibrate transmission for a single access terminal. In other aspects, one or less than all antennas for a group of access terminals may be used to communicate with all antennas for a group of access terminals.

In certain aspects, a transmit chain or a receive chain of an access point may be calibrated. This can be done, for example, by using a calibration ratio to calibrate the receiver chain of the access point to its transmitter chain or to calibrate its transmitter chain to its receiver chain.

In the case of a MIMO system, each antenna of each access terminal can be interpreted as a separate access terminal for the purpose of determining the calibration ratio. Then, when the calibration relationships are combined, each individual calibration relationship or calibration information for each antenna of each access terminal can be used as a separate component.

As used here, the access point may be a fixed station used to communicate with the terminals, and may also be called and include some or all of the functions of the base station, Node B, or some other terminology. An access terminal may also be called and include some or all of the functions of a user equipment (UE), wireless communication device, terminal, mobile station, or some other terminology.

It should be noted that although FIG. 1 shows physical sectors, i.e. having different antenna groups for different sectors, other approaches may be used. For example, the use of a plurality of fixed “beams”, each of which covers different areas of a cell in the frequency domain, can be used instead of or in combination with physical sectors. This approach is shown and described in pending patent application No. 11 / 260,895, entitled “Adaptive sectorization in a cellular system”, which is incorporated herein by reference.

In FIG. 2, the antenna structure 100 comprises a receiving circuit 102 and a transmitting circuit 104 in accordance with various aspects described herein. The receiving circuit 102 comprises a down-converter component 106 that down-converts the signal to the baseband at reception. The down converter component 106 is operatively coupled to a block of the automatic gain control (AGC) function 108, which determines the intensity of the received signal and automatically adjusts the gain applied to the received signal to maintain the receiving circuit 102 in the associated linear operation range and to maintain a constant signal intensity for output via transmit chain 104. It will be understood that AGC 108 may be optional for some of the embodiments described herein (eg, automatic p gain adjustment is not required in each embodiment). The AGC 108 is operatively coupled to an analog-to-digital (A / D) converter 110, which converts the received signal to digital format before the signal is smoothed by a digital low-pass filter (LPF) 112, which can attenuate small fluctuations in the received signal. As a result, the receiver chain 102 may include a receiver processor 114 that processes the received signal and can transmit the signal to one or more components of the transmitter chain 104.

The transmitter chain 104 may include a transmitter processor 116 that receives a signal from the receiver chain 102 (for example, the transmitter receives a signal that was originally received by the receiver chain 102 and subjected to various processes associated with their components ...). The processor 116 of the transmitter is operatively connected to the pulse shaper 118, which can facilitate the manipulation of the signal to be transmitted, so that the signal can be formed in a limited frequency band when it is attenuated and / or intersymbol interference is eliminated. Once a signal is generated, it can undergo digital-to-analog (D / A) conversion through a D / A converter 120 before it is smoothed in an operatively coupled low-pass filter (LPF) 122 in the transmit chain 104. The pulse amplifier (PA) component 124 can amplify the pulse / the signal before the conversion with increasing unmodulated transmission through the Converter 126 with increasing.

Antenna array 100 may exist for each antenna at the access point and access terminal. The differences observed between the transfer characteristics of the transmit chain 102 and the receive chain 102 and / or samples of these targets may also be noticeable, the relationship of the equivalent channel and / or changes in the transmitter / receiver may not be taken into account. When calibrating the array of antennas 100, an understanding of the magnitude of the changes in the effect on the phase and / or amplitude of the signals transmitted through the transmitting and receiving chains, and their influence on the accuracy of the intended relationship can be used to facilitate the calibration process. In addition, in the case of an antenna array, typically each antenna 100 has a different transmit chain 104 and a receive chain 102 than each other antenna. Therefore, each other transmit chain 104 may have different results in phase and / or amplitude, like any other transmit chain 104, respectively. Similar may be true for receive circuits 102 of each antenna 100.

The discrepancies in the results may correspond to the physical structure of the antenna 100, component differences, or a number of other factors. Such mismatches may include, for example, the effects of interconnection, the effects of towers, knowledge of defects in the location of elements, amplitude or phase mismatches corresponding to an antenna cable, etc. Additionally, the mismatches may correspond to hardware elements in the transmitting circuit 104 and / or the receiving circuit 102 of each antenna 100. For example, such mismatches may be associated with analog filters, I and Q imbalance, phase mismatch and / or gain mismatch of a low noise amplifier or pulse amplifier in the circuits , various nonlinear influences, etc.

For an access point to calibrate each transmitter chain to its corresponding receiver chain (i.e., the receiver chain corresponding to the same antenna), an integrated and potentially cumbersome process will be required independently. In addition, any particular feedback for forward channel transmission or pilot signals used for reverse channel transmission for any particular access terminal is subject to noise for this user. Therefore, for any specific calibration ratio estimated based on the forward and reverse channels, there is some error represented by channel variation and noise. Therefore, in some aspects, one or more calibration ratios evaluated for a number of different antennas of different access terminals are combined to provide a single calibration ratio used by the access point to transmit to one or all access terminals. In certain aspects, the combination may comprise an average of all calibration ratios for each antenna of each access terminal communicating with the access point, or some predetermined subset. In another aspect, the combination can be made in the form of a connection optimization, where channel measurements from and for each antenna of each access terminal are combined to estimate a single calibration ratio, which is a combination of gain mismatches for each antenna of each access terminal, without calculating a separate calibration ratio for each antenna each access terminal.

For any specific antenna of each access terminal, the access point uses its channel estimates of the reverse channel for this antenna, as well as channel estimates of the forward channel, which are performed at the access terminal and returned to the access point to estimate or calculate the calibration ratio based on this antenna of this access terminal.

, прямого канала может оцениваться в терминале доступа для передач от i-й передающей антенны точки доступа к антенне терминала доступа. Однако любая канальная оценка будет иметь компоненты, относящиеся к шуму канала, наряду с любым усилением или искажением, вызванным передающей цепью точек доступа и передающей цепью терминалов доступа. Канальная оценка прямого канала может затем записываться как:Channel estimation

, the forward channel can be estimated at the access terminal for transmissions from the ith transmitting antenna of the access point to the antenna of the access terminal. However, any channel estimate will have channel noise related components, along with any gain or distortion caused by the transmit chain of the access points and the transmit chain of the access terminals. The forward channel estimate may then be written as:

передающей цепи точки доступа, h_i, которая является физическим каналом между двумя измеряемыми антеннами, и шума n_i канала, который является частью канальной оценки.In formula 1, the channel estimate is a mismatch function β _{AT of the} gain of the receiving circuit of the access terminal for a specific antenna, the mismatch

the transmitting chain of the access point, h _i , which is the physical channel between the two measured antennas, and the channel noise n _i , which is part of the channel estimate.

доступа, по существу равна инверсии формулы 1. Это можно видеть в формуле 2 ниже:In the case of transmissions on the reverse channel, the channel estimate in the ith receiving antenna of the access point corresponding to the transmission from the terminal antenna

access is essentially equal to the inverse of formula 1. This can be seen in formula 2 below:

усиления принимающей цепи точки доступа, h_i, которая является физическим каналом между двумя измеряемыми антеннами, и шума

канала, который является частью канальной оценки.In formula 2, this channel estimate is a function of the mismatch α _AT gain of the transmit chain of the access terminal for this antenna, the mismatch

gain of the receiving circuit of the access point, h _i , which is the physical channel between the two measured antennas, and noise

a channel that is part of a channel estimate.

To calibrate the antenna matrix, mismatches between the receiving circuits 102 and the transmit circuits 104 of the antenna 100 are shown below in formula 3. It should be noted that other methods and mathematical relations can be used to achieve matrix calibration in conjunction with, instead, the methods and mathematical relations described here.

In formula 3, c _i is the total mismatch ratio between the reverse channel transmissions and the forward channel transmission, γ is the gain mismatch ratio between the transmitting and receiving circuits of the access terminal for a specific antenna, and η _i is the mismatch ratio of the receiving and transmitting circuits for the ith antenna at the access point. It should be noted that γ is essentially constant for each pair of antennas at the access point. Also, in some respects, Formula 3 is idealized since the noise estimate is not included here.

, для каждой антенны в терминале доступа, который может быть назван - «вектор калибровки».The calibration relations c _i , i = 1, ..., M, where M is the antenna number in the antenna matrix of the access point, can be grouped into one vector

, for each antenna in the access terminal, which may be called a “calibration vector”.

соответствуют оценками для каждой антенны точки доступа по отношению к единственной антенне терминала доступа. Следует отметить, что элементы вектора

могут быть комплексными числами, включающими в себя амплитудное и фазовое рассогласование для каждой передающей и принимающей цепей антенной матрицы точки доступа, а также общее рассогласование, соответствующее рассогласованию передачи и приему передающей и принимающей цепей точки доступа для конкретной антенны. Следует отметить, что, хотя формула 4 описывает вектор, который имеет объекты для антенн одного терминала доступа, он может включать в себя объекты для множества терминалов доступа или множества антенн терминалов доступа.In the formula 4, vector objects

correspond to the estimates for each antenna of the access point with respect to a single antenna of the access terminal. It should be noted that the elements of the vector

can be complex numbers, including the amplitude and phase mismatch for each transmit and receive chains of the antenna matrix of the access point, as well as the total mismatch corresponding to the mismatch of the transmission and reception of the transmit and receive chains of the access point for a specific antenna. It should be noted that although Formula 4 describes a vector that has objects for the antennas of one access terminal, it may include objects for multiple access terminals or multiple antennas of access terminals.

The noise vector η includes the error results (MSE) of the channel measurements and also the decorrelation results of the channel measurements, since the gain measurements are performed at different points in time, thus allowing a channel change in the dynamics over time, as well as temperature and other changes for the measurement.

калибровки, соответствующий терминалу u доступа, может определяться, как показано ниже в формуле 5.Rated vector

the calibration corresponding to the access terminal u may be determined as shown below in formula 5.

определяется для всех антенн антенной матрицы точки доступа по отношению к каждой антенне каждого терминала доступа.where γ _u is the gain mismatch corresponding to the transmitting and receiving chains of the access terminal antenna, and η is the mismatch vector corresponding to the transmitting and receiving chains of the access point antenna matrix. Vector

is determined for all antennas of the antenna matrix of the access point with respect to each antenna of each access terminal.

In the above, it should be noted that there are several methods for combining various estimates of calibration vectors (corresponding to measurements from different antennas of different access terminals) to form a common or combined calibration vector. One way to perform this combination is to average all the estimates of the calibration vector to obtain a single estimate.

In this approach, each calibration vector estimate includes a multiplier, γ _u , which is different for different access terminals. In the case where one or more access terminals have a very large gain mismatch γ _u , simple averaging can lead to results s of the average offset to the antennas having the largest gain mismatch γ _u .

In another aspect, each calibration vector estimate corresponding to a particular access terminal is normalized to a corresponding vector element. This can provide minimization in cases where one or more access terminals have a large gain mismatch γ _u . This process is shown below in formula 6.

.It should be noted that in certain aspects, the normalization element can be any element of the calibration vector, since it is the same element for each estimate of the calibration vector, for example, the first element. The sum of the normalized elements is then divided by the total number of elements U of the vector

.

Another approach that can be used to combine the various estimates of the calibration vectors may be based on the combination of the estimated vectors in the matrix. For example, in certain aspects, each calibration vector estimate may be a cyclically shifted and scaled version of the same vector η, and the cyclic bias and scaling corresponds to different mismatches γ _u for different access terminals. One way to get rid of this scaling and cyclic shift is to first normalize each calibration vector to a unit norm. Then the Q matrix, whose columns are normalized calibration estimates, can be formed from calibration vectors. The only estimate for the calibration vector is obtained by decomposing the matrix, for example, the only decomposition of the value on the matrix Q. The eigenvector corresponding to the maximum single value can be used as a complete estimate of the calibration vector, for example, as shown in formula (7) below.

As explained in the above three approaches, the calibration ratio is usually evaluated in two steps. First, the values corresponding to the elements of the calibration vectors are calculated for the antenna array or those antennas that are involved. Calibration vectors are then combined in accordance with one or more different mathematical methods.

Alternatively, to optimize a plurality of calibration vectors, a connection optimization procedure using a plurality of access points and access measurements is used, as described below. In some cases, the antennas of the access terminal and the access point can form their channel estimates for different frequency tones and at different time intervals. In addition, there may be a temporary error τ _{k, u} between the access point and the u-th access terminal at time k. In this case, the vector channel estimate g _{i, k, u of the} forward channel measured at the antenna of the access terminal may relate to the vector channel estimate h _{i, k, u of the} reverse channel measured at the access point. One approach using the calibration vector η and the mismatch γ _{u of the} antenna of the access terminal is shown in formula 8 below.

. Индексы i, k, u являются тоном, временем и пользовательскими индексами соответственно. В указанной выше формуле неизвестным является вектор η калибровки и рассогласование γ_i,k,u конкретного терминала доступа. Особенность формулы 8 заключается в том, что рассогласование терминала доступа включает в себя результат временного рассогласования между точкой доступа и антенной терминала доступа в дополнение к рассогласованию усиления, соответствующему передающей и принимающей цепям терминала доступа для этой антенны. Другим способом получения решения для η и γ_j,k,u является использование подхода квадратичной ошибки с минимальным значением (MMSE), как показано в формуле 9.In formula 8, Z _{i, k, u} is the diagonal matrix whose diagonal elements are elements of the vector channel estimate h _{i, k, u of the} return channel and

. The indices i, k, u are tone, time and user indices respectively. In the above formula, the calibration vector η and the mismatch γ _{i, k, u of a} particular access terminal are unknown. A feature of Formula 8 is that the mismatch of the access terminal includes the result of a temporary mismatch between the access point and the antenna of the access terminal in addition to the gain mismatch corresponding to the transmit and receive circuits of the access terminal for this antenna. Another way to obtain a solution for η and γ _{j, k, u} is to use the quadratic error with minimum value (MMSE) approach, as shown in formula 9.

Solutions for η and γ _{i, k, u} can be obtained from formula 10 below.

η □ minimum eigenvector

ортогональной проекции может определяться какwhere for the vector x the operator

orthogonal projection can be defined as

To compensate for the mismatch, the calibration relationships can be used to change the gain, with respect to both or any, of the phase and amplitude of the transmitting chain of the access point to match it with the receiving chain, or equivalently, to change the gain of the receiving chain of the access point to match it with the transmitting chain.

More specifically, an access point may use beamforming with a maximum ratio combining (MRC), equalization beamforming (EGC), or any other spatial preprocessing techniques for transmission to any access terminal. Namely, if the channel vector of the return channel is h , the access point uses the following preprocessing weights for transmission:

With an estimate of η of the calibration vector, the access point can use the following preprocessing weights to compensate for the mismatches of its transmitting and receiving chains:

Although FIG. 2 shows and describes one embodiment of a receive chain 102 and a transmit chain 104, other schemes and structures may be used. For example, a different number of components may be used in the receiving circuit 102 and the transmitting circuit 104. Additionally, various devices and structures may also be used.

It should be noted that the combined or connected calibration vectors can be generated by processing each antenna or group of antennas of a particular access terminal as a separate access terminal. In this case, the calibration process can be simplified and each access terminal does not require independent calibration.

FIG. 3 shows a time cycle for calibration from a single access terminal using a TDD system having a single forward channel frame or interval adjacent to a single reverse channel frame or interval. As you can see, one or more pilot signals transmitted from each antenna on the reverse channel is measured (s) at the access point. The measurement time period is a function of the decoding time at the access point. During this decoding period, one or more pilot signals are transmitted on the forward channel to the access terminal. The access terminal then measures the pilot signals to estimate the forward channel for each receiving antenna. As with reverse channel estimates, there are some decoding delays. The decoded forward channel estimates must be sent back to the access point to form a calibration relationship. Therefore, it can be seen that there is a certain minimum amount of time, and therefore the maximum speed of the access terminal, for which calibration can be maintained without slowing down, is a significant or essentially interfering factor.

As can be seen from FIG. 3, if multiple channel estimates from multiple access terminals are used, noise and associated deceleration can be reduced, or at least sampled, in the time slot and receiving chains. In addition, if multiple antennas are used for each access terminal, and independently processed deviation and noise can be better estimated, since noise and deviation can be more uniform for these antennas of a single access terminal, then any anomalies for this antenna are reduced.

FIG. 4 shows aspects of a logic that facilitates calibration of an antenna array to compensate for gain mismatch. The system 300 includes a calibration component 302 that includes a mismatch estimation component 304 that analyzes the output signals of the receiving circuits and / or compares the output signals of the receiving circuit and a relationship sum calculator 306 that calculates the ratios that are used to generate the vector η, and summarizes them for use in one of the methods described above, for combining different measurements from different antennas of different access terminals.

FIG. 5 shows aspects of a system that facilitates calibrating an antenna array to compensate for gain mismatch. System 400 includes a processor 402 that is operatively coupled to an antenna array 404. Processor 402 can determine gain mismatches for individual antenna combinations at the access terminal and access point using calibration component 406. The processor 402 further comprises a calibration component 406 that determines the calibration relationships and then generates and uses the vector η .

The system 400 may further comprise a memory 408 that is operatively coupled to the processor 402 and which stores information related to matrix calibration, generation and utilization of the relation, and generates calibration generation data, etc., and any other relevant information related to antenna calibration matrices 404. It will be appreciated that processor 402 may be a processor for analyzing and / or generating information received by processor 402, a processor that controls one or more system components threads 400, and / or a processor that analyzes and generates information received by the processor 402, and controls one or more components of the system 400.

Memory 408 may further store protocols associated with generating copies of signals and models / representations, mismatch estimates, etc., so that system 400 can use stored protocols and / or algorithms to achieve antenna calibration and / or mismatch compensation, as described herein . It will be apparent that the storage components (eg, memory) described herein may be volatile memory or non-volatile memory, or may include volatile and non-volatile memory. By way of illustration, but not limitation, non-volatile memory may include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM), which acts as an external cache. By way of illustration and not limitation, RAM is available in many forms, such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDR SDRAM), extended SDRAM (ESDRAM), DRAM with a synchronization channel (SLDRAM) and RAM from Rambus (DRRAM). A memory 408 of object systems and methods is contemplated for containing, without limitation, these and any other suitable types of memory.

калибровки для каждого состояния, т.е. уровень усиления, AGC. В таких аспектах для каждой передачи процессор 402 может иметь доступ к вектору

калибровки для состояния AGC без выполнения калибровки. Решение относительно выполнения дополнительной калибровки или доступа к предыдущему вектору

калибровки для данной передачи может быть с учетом временного периода или числа передач, если был получен вектор

калибровки для состояния AGC. Оно может быть системным параметром или может изменяться с учетом канальных условий, например загрузки канала.In certain aspects, memory 408 may store vectors

calibrations for each state, i.e. gain level, AGC. In such aspects, for each transmission, processor 402 may have access to a vector

calibrations for AGC state without performing calibration. The decision to perform additional calibration or access to the previous vector

calibration for a given transmission can be based on the time period or the number of transfers, if a vector was received

calibration for the state of AGC. It can be a system parameter or can be changed taking into account channel conditions, for example, channel loading.

In FIG. Figure 6 shows the methodology related to the formation of additional system resource assignments. For example, techniques may relate to calibrating an antenna array in a TDMA environment, an OFDM environment, an OFDMA environment, a CDMA environment, or any other suitable wireless environment. Although for the purpose of simplifying the explanation, the technique is shown and described as a sequence of operations, it is clear and appreciated that the techniques are not limited to the order of operations, since some operations may appear in different orders and / or simultaneously with other operations in accordance with one or more embodiments, which are shown and described here. For example, one skilled in the art will understand and appreciate that a technique can alternatively be represented as sequences of interrelated states or cases, such as in a state diagram. In addition, not all operations shown may be required to implement a methodology in accordance with one or more embodiments.

FIG. 6 shows a technique for calibrating an array of antennas for transmission. Channel estimates for the forward channel are received from the access terminals for each receive antenna of the access terminal, block 500. As discussed above, these channel estimates can be generated from forward channel pilots transmitted by the access point. Additionally, channel estimates for reverse channel information, such as channel reverse channel pilot, are generated by an access point for each transmit antenna of the access terminal, block 502.

After collecting channel estimates of the forward channel and the return channel, block 504 can determine the calibration ratios for each antenna of the access terminal and the antenna of the access point. In certain aspects, the most recent channel estimate of the forward channel and the return channel with respect to each other over time is used to formulate a calibration relation. In this case, a plurality of estimates for a given access terminal may be performed taking into account successive pairs of channel estimates from the estimates of the forward channel and the reverse channel.

As discussed with respect to FIG. 3, there may be some time lag between different calculations and transfers. In addition, the function of blocks 500 and 502 can occur essentially simultaneously or at different times for the same or different access terminals, although they are probably the same for different antennas of a single access terminal. Therefore, the calibration ratio can be determined for a given antenna of a given access terminal, taking into account channel estimates of transmissions on the forward channel and on the reverse channel, which may or may not be sequential in time.

The calibration relationships are then combined to form a calibration estimate for multiple access terminals, block 506. This combined calibration relationship may include calibration relationships for some or all antennas of different access terminals in a given sector or cell and have a different or the same number of calibration relationships for each antenna an access terminal for which one or more calibration relationships have been received.

The combined calibration ratio can be obtained by simply averaging the calibration ratios or using other approaches discussed with respect to FIG. 2, for example, the approaches discussed in relation to formulas 5 or 7.

Each transmission from each transmitter chain of the access point is then weighed by the balance taking into account the combined calibration ratio for that transmitter chain. An integrated or connected set of calibration weights can also be used for one or more transmitter circuits of the access point. Alternatively, it is possible to transmit this combined calibration ratio or calibration command, taking into account the combined calibration ratio, to one or more antennas of the access terminal. The access terminals will then apply weights based on the integrated calibration ratio to decode the transmissions received at the antenna of the access terminal.

Also in some aspects, calibration weights are used for a particular AGC state, and not for other AGC states. Essentially, block 508 will then only apply to the AGC state during block 500.

FIG. 7 shows another technique for calibrating an antenna array for transmission. Channel estimates for the forward channel are received from the access terminals for each receiving antenna of the access terminal, block 600. As discussed above, these channel estimates can be generated from forward channel pilots transmitted by the access point. Additionally, channel estimates for reverse channel information, such as channel reverse channel pilot, are generated by an access point for each transmit antenna of the access terminal, block 602.

After that, the channel estimates of the forward channel and the return channel are collected, a calibration ratio that uses the multiple channel estimates for the multiple antennas of the multiple access terminals, block 604. In certain aspects, the most recent channel estimate of the forward channel and the return channel with respect to each other in time is used. In such cases, a plurality of estimates for a given access terminal may be performed taking into account pairs of consecutive channel estimates from channel estimates of the forward channel and the reverse channel.

As discussed with respect to FIG. 3, there may be some time lag between different calculations and transfers. In addition, the function of blocks 600 and 602 can occur essentially simultaneously or at different times for the same or different access terminals, although they are probably the same for different antennas of the same access terminal. Therefore, channel estimates can be determined for a given antenna of a given access terminal, taking into account channel estimates of transmissions on the forward channel and the reverse channel, which may or may not be sequential in time.

The connected calibration ratio can be obtained by using the compound optimization process, as discussed in relation to FIG. 2, for example, formula 8.

Each transmission from each transmitter chain of the access point is then weighted taking into account the connected calibration ratio for that transmitter chain. An integrated or connected set of calibration weights can also be used for one or more transmitter circuits of the access point. Alternatively, it is possible to transmit this connected calibration ratio or calibration command, taking into account the connected calibration ratio, to one or more antennas of one or more access terminals. The access terminals will then apply weights based on the connected calibration relation to decode the transmissions received at the antenna of the access terminal.

Also in some aspects, calibration weights are used for a particular AGC state, and not for other AGC states. Essentially, block 608 will then only be applied to the AGC state during block 600.

FIG. 8 shows an example wireless communication system 1300. Wireless communication system 1300 shows one base station and one terminal for short. However, it is understood that the system may include more than one base station and / or more than one terminal, where the additional base stations and / or terminals may be substantially the same or different from the exemplary base station and terminal described below. In addition, it is understood that the base station and / or terminal may use the systems (FIGS. 1-5) and / or methods (FIGS. 6-7) described herein to facilitate wireless communication between them.

In FIG. 8 shows a transmitter and a receiver in a multiple access wireless communication system. At transmitter system 1310, traffic data for a number of data streams is provided from a data source 1312 to a transmit (TX) data processor 1344. In an embodiment, each data stream is transmitted through a respective transmit antenna. TX data processor 1344 formats, codes, and interleaves the traffic data based on the particular coding scheme selected for this data stream to provide coded data. In some embodiments, TX data processor 1344 applies beamforming weights to the symbols of the data streams given the user to whom the symbols are transmitted and the antenna from which the symbols are transmitted. In some embodiments, beamforming weights may be formed taking into account channel response information that indicates transmission path conditions between the access point and the access terminal. Channel response information may be generated using CQI information or channel estimates provided by the user. In addition, in such cases of scheduled transmissions, the TX data processor 1344 may select a packet format based on the rank information that is transmitted from the user.

The encoded data for each data stream may be multiplexed with pilot data using OFDM techniques. The pilot data is usually known data samples that are processed in a known manner and can be used in the receiving system to estimate the channel response. The multiplexed pilots and encoded data for each data stream are then modulated (i.e., symbol-mapped) based on the particular modulation scheme (e.g., BPSK, QSPK, M-PSK or M-QAM) selected for that data stream to provide symbols modulation. The data rate, coding, and modulation for each data stream may be determined by instructions executed by processor 1330. In some embodiments, a number of parallel spatial streams may vary in accordance with the rank information that is transmitted from the user.

Modulation symbols for all data streams are then provided to a TX MIMO processor 1346, which may further process modulation symbols (eg, for OFDM). TX MIMO processor 1346 then provides N _T symbol streams for N _T transmitters (TMTR) 1322a-1322t. In certain embodiments, TX MIMO processor 1320 applies beamforming weights to the symbols of the data streams based on the user to whom the symbols are transmitted and the antenna from which the symbols are transmitted from user channel response information.

Each transmitter 1322 receives and processes a respective symbol stream to provide one or more analog signals and further processes (e.g., amplifies, filters, and upconverts) the analog signals to provide modulated signals suitable for transmission over the MIMO channel. N _T modulated signals from transmitters 1322a through 1322t are then transmitted from N _T antennas 1324a through 1324t, respectively.

In the receiver system 1320, the transmitted modulated signals are received by N _R antennas 1352a-1352r, and the received signal from each antenna 1352 is transmitted to a respective receiver (RCVR) 1354a-1354r. Each receiver 1354 processes (eg, filters, amplifies, and downconverts) the corresponding received signal, digitizes the processed signal to provide samples, and further processes the samples to provide a stream corresponding to the “received” symbols.

An RX data processor 1360 then receives and processes N _R received symbol streams from N _R receivers 1354a through 1354r based on a particular receiver processing method to provide a ranked number of “defined” symbol streams. The processing by RX data processor 1360 is described in further detail below. Each specific symbol stream includes symbols, which are estimates of the modulation symbols transmitted for the corresponding data stream. RX data processor 1360 then demodulates, deinterleaves, and decodes each specific symbol stream to recover traffic data for a data stream that is provided to data receiver 1364 for storage and / or additional processing. The processing by RX data processor 1360 is in addition to that performed by TX MIMO processor 1346 and TX data processor 1344 in transmitter system 1310.

The channel response estimate generated by the 1360 RX processor can be used to perform spatial, spatial / temporal processing at the receiver, equalize power levels, change relationships or modulation schemes, or other actions. The RX processor 1360 may also evaluate the signal-to-noise-noise-ratio (SNR) of a particular symbol stream and other possible channel characteristics and provide these values to a processor 1370. An RX data processor 1360 or a processor 1370 may further obtain “effective” SNR estimates for the system . The processor 1370 then provides information (CSI) of the estimated channel, which may contain various types of information related to the communication channel and / or stream of received data. For example, a CSI may contain only the current SNR. In some embodiments, the channel information may comprise a signal-to-noise-to-noise ratio (SINR). The CSI is then processed by a TX data processor 1378, which also receives traffic data for a number of data streams from a data source 1376 modulated by a modulator 1380, processed by a transmitter 1354a-1354r, and transmitted back to a transmitter system 1310.

At transmitter system 1310, modulated signals from receiver system 1350 are received by antennas 1324, processed by receiver 1322, demodulated by demodulator 1390, and processed by RX data processor 1392 to recover the CSI reported by the receiver system and to provide data to data receiver 1394 for storage and / or additional processing . The reported CSI is then provided to the processor 1330 and used to (1) determine the data rate and coding and modulation schemes used for the data streams, and (2) generate various control signals for the TX data processor 1344 and TX MIMO processor 1346.

The processor 1390 may also perform the formation of calibration relationships and a combined calibration relationship or a connected calibration relationship, as discussed in relation to FIG. 2, 6 and 7, respectively. In addition, each antenna 1352a-1352r may be considered as a separate terminal for the purpose of a combined or connected calibration estimate.

In FIG. 9, the access point may comprise a main unit (MU) 1450 and a radio unit (RU) 1475. The MU 1450 includes digital unmodulated transmission components of the access point. For example, the MU 1450 may include an unmodulated transmission component 1405 and a digital intermediate frequency (IF) processing unit 1410. IF digital processing unit 1410 processes the data of the radio channel at an intermediate frequency by performing functions such as filtering, drainage, modulation, and so on. RU 1475 includes analog radio parts of an access point. As used herein, a radio unit is an analog radio part of an access point or other type of transmitter station with direct or indirect connection to a mobile switching center or associated device. A radio unit typically serves a particular sector in a communication system. For example, RU 1475 may include one or more receivers 1430 associated with one or more antennas 1435a-t for receiving radio transmissions from mobile subscriber units. In an aspect, one or more power amplifiers 1482a-t are coupled to one or more antennas 1435a-t. An analog-to-digital (A / D) converter 1425 is connected to the receiver 1430. The A / D converter 1425 converts the analog radio transmissions received by the receiver 1430 into a digital input signal for transmission to the unmodulated transmission component 1405 via the IF digital processing unit 1410. RU 1475 may also include one or more transmitters 120 connected to the same or different antennas 1435 for transmitting radio transmissions to access terminals. The digital-to-analog (D / A) converter 1415 is connected to the transmitter 1420. The D / A converter 1415 converts the digital transmissions received from the unmodulated transmission component 1405 through the IF digital processing unit 1410 into an analog output signal for transmission to mobile subscriber units. In some aspects, a multiplexer 1484 for multiplexing multi-channel signals and multiplexing different signals includes a voice signal and a data signal. The central processor 1480 is connected to the main unit 1450 and the radio unit to control various processes, which include the processing of a voice signal or a data signal.

For a multiple access system (e.g., a frequency division multiple access system (FDMA), an orthogonal frequency division multiple access system (OFDMA), a code division multiple access system (CDMA), a time division multiple access system (TDMA), etc. e.) many terminals can transmit simultaneously on the reverse channel. For such a system, pilot subcarriers may be distributed among various terminals. Channel estimation methods can be used in the case where the pilot subcarriers for each terminal cover the entire working frequency band (it is possible to exclude the ends of the frequency band). Such a pilot subcarrier structure would be desirable to obtain frequency diversity for each terminal. The methods described here can be implemented by various means. For example, these methods may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for channel estimation can be implemented in one or more specialized integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), user programmable gate arrays (FPGA), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described here, or combinations thereof. In a software implementation, there may be modules (e.g., procedures, functions, etc.) that perform the functions described herein. Software codes may be stored in a memory unit and executed by processors 1390 and 1350.

What has been described above includes examples of one or more embodiments. Of course, it is not possible to describe every possible combination of components or methods for the purposes of the above-mentioned embodiments, but each of those skilled in the art may recognize that many other combinations and variations of various embodiments are possible. Accordingly, the described embodiments are intended to include all such changes, modifications and variations that fall within the spirit and scope of the appended claims. In addition, the scope of this term “includes” is used in the detailed description or in the formula, such a term is intended to be included in a manner similar to the term “comprising”, as “comprising” is interpreted when used as a regular word in the formula.

Claims (28)

1. A method for calibrating an antenna matrix of an access point in a wireless network, comprising the steps of: receiving first channel estimates corresponding to transmissions from the access point to each of at least two antennas, at least two access terminals, and at least at least two antennas include different antennas of one of the at least two access terminals; determining second channel estimates corresponding to transmissions from each of at least two antennas of said at least two access terminals to an access point; determining a calibration ratio based on the first channel estimates and second channel estimates, and calibrating the antenna matrix of the access point by applying the calibration ratio to the transmission weights of the access point. 2. The method according to claim 1, wherein the step of determining the calibration ratio comprises the step of determining the calibration ratio of the antennas of the access terminals independently. 3. The method according to claim 2, in which the step of determining the calibration relationship comprises the step of combining each of said calibration relationships. 4. The method according to claim 3, in which the combining step comprises the step of averaging each of said calibration ratios. 5. The method according to claim 3, in which each of the said calibration relations contains a plurality of elements, and in which the combining step comprises the steps of normalizing each calibration ratio and determining the calibration ratio based on a matrix including normalized calibration relations. 6. The method according to claim 5, in which the step of determining the calibration relationship based on the matrix comprises the step of expanding the matrix using a singular decomposition. 7. The method according to claim 1, wherein the step of determining the calibration ratio comprises the step of determining the connected calibration ratio based on the first and second channel estimates. 8. The method according to claim 1, in which the step of determining the calibration ratio comprises the step of solving the equation

where Z _{i, k, u} is the diagonal matrix, whose diagonal elements are elements of the second channel estimates h _{i, k, u} , γ _{i, u} = γ _u

and indices i, k, u represent tone, time, and user indices, respectively. 9. The method according to claim 8, in which the solution step includes the use of the method of minimum mean square error (MMSE) to solve the equation. 10. The method according to claim 1, wherein the step of determining the calibration ratio comprises the step of using a combined optimization scheme with first and second channel estimates. 11. A wireless communication device comprising at least two antennas and a processor coupled to said at least two antennas, the processor being configured to receive first channel estimates corresponding to transmissions from the device to each of the at least two antennas at least two access terminals, wherein at least two antennas include different antennas of one of the at least two access terminals, determine second channel estimates corresponding to transmissions from each from at least two antennas of said at least two access terminals to the device, and determine the calibration ratio based on the first channel estimates and second channel estimates. 12. The wireless communications apparatus of claim 11, wherein the processor is configured to determine a calibration relationship for each antenna of the access terminals and determine a calibration relationship based on the combination of each of the calibration relationships for each of said antennas of the access terminals. 13. The wireless communications apparatus of claim 12, wherein the processor is configured to combine said relationships by averaging each of said calibration relationships. 14. The wireless communications apparatus of claim 12, wherein the processor is configured to combine said relationships by normalizing each calibration relationship and to determine a calibration relationship based on a matrix including each of said calibration relationships. 15. The wireless communications apparatus of claim 14, wherein the processor is configured to use singular decomposition to decompose said matrix to obtain a calibration ratio. 16. The wireless communications apparatus of claim 11, wherein the processor is configured to determine a calibration ratio using a connected calibration ratio based on the first and second channel estimates. 17. The wireless communications apparatus of claim 11, wherein the processor is configured to determine a calibration ratio by solving the equation

where Z _{i, k, u} is the diagonal matrix, whose diagonal elements are elements of the second channel estimates h _{i, k, u} , γ _{i, u} = γ _u

and indices i, k, u represent tone, time, and user indices, respectively. 18. The wireless communications apparatus of claim 17, wherein the processor is configured to solve said equation by using a minimum mean square error (MMSE) method. 19. The wireless communications apparatus of claim 17, wherein the processor is configured to determine a calibration relationship using an integrated optimization scheme with a plurality of first and second channel estimates. 20. An apparatus for calibrating an antenna matrix of an access point, comprising means for receiving first channel estimates corresponding to transmissions from an access point to each of at least two antennas, at least two access terminals, and received from said at least two access terminals, wherein at least two antennas include different antennas of one of the at least two access terminals; means for determining second channel estimates corresponding to transmissions from each of at least two antennas of said at least two access terminals to an access point; means for determining a calibration ratio based on the first channel estimates and second channel estimates; and means for calibrating the antenna matrix of the access point by applying the calibration ratio to the transmission weights of the access point. 21. The device according to claim 20, in which the means for determining the calibration ratio includes means for determining the calibration ratio for each of the antenna access points independently. 22. The device according to item 21, in which the means for determining the calibration ratio for each antenna independently comprises means for combining each of the aforementioned calibration relations. 23. The device according to item 22, in which the means for combining includes means for averaging each of the aforementioned calibration relations. 24. The device according to item 22, in which each of these calibration relationships contains many elements and in which the means for combining includes means for normalizing each calibration relationship and means for determining the calibration relationship based on a matrix including normalized calibration relations. 25. The device according to claim 20, in which the means for determining the calibration relationship comprises means for determining the connected calibration relationship based on the first and second channel estimates. 26. The device according to claim 20, in which the means for determining the calibration ratio contains means for solving the equation

where Z _{i, k, u} is the diagonal matrix, whose diagonal elements are elements of the second channel estimates h _{i, k, u} , γ _{i, u} = γ _u

and indices i, k, u represent indices of tone, time, and user, respectively. 27. The device according to claim 20, in which the means for determining the calibration ratio comprises means for using the combined optimization scheme with the first and second channel estimates. 28. A computer-readable medium having instructions stored on it for use by a processor, the instructions comprising instructions for
receiving first channel estimates corresponding to transmissions from an access point to each of at least two antennas of at least two access terminals, wherein at least two antennas include different antennas of one of at least two access terminals; determining second channel estimates corresponding to transmissions from each of said at least two antennas of said at least two access terminals to an access point; and determining a calibration ratio based on the first channel estimates and second channel estimates.

Images