# Patent

## Title
System and method for large dimension equalization using small dimension equalizers and bypassed equalizers

## Abstract

An equalizer circuit of a particular equalization stage of a equalizer circuit is omitted, and input signals that would have otherwise been received at the omitted equalization circuit bypass the equalization stage and are instead processed at an equalizer circuit included at the next stage. Thus, a subset of the received frequency-domain signals can be processed by equalizer circuits at a first stage, while the remaining received frequency-domain signals bypass the first stage and are processed at an equalizer circuit included at a second stage.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
Related subject matter is contained in co-pending U.S. patent application Ser. No. 14/861,354, entitled “System and Method For Large Dimension Equalization Using Small Dimension Equalizers,” filed on Sep. 22, 2015, the disclosure of which is hereby incorporated by reference.
FIELD OF THE DISCLOSURE
This disclosure generally relates to wireless communication of high-speed data, and more particularly relates to a system and method for large dimension equalization using small dimension equalizers in a wireless communication network.
BACKGROUND
High-speed wireless data communication networks form the basis for cellular and mobile communications, and have become increasingly important in expanding access and availability to the rich functions, features, and capabilities that are associated with smart phones and connected tablet devices. High-speed data communication networks evolved through second generation (2G) wireless networks and third generation (3G) wireless networks into the current fourth generation (4G) wireless networks such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A) networks and Wireless Metropolitan Area Networks (MAN)-Advanced networks. In the future, fifth generation (5G) networks such as Cloud-Radio Access Network (C-RAN), Coordinated Multi Point (CoMP), and future 3rd Generation Partnership Project (3GPP) will add enhanced capabilities to support a broad range of communication, media, and computing capabilities as will be needed for the features of the future.
The later generation (4G and 5G) wireless network technologies have adopted Multiple-Input and Multiple-Output (MIMO) transmission technology that uses multiple transmit and receive antennas to exploit multipath signal propagation, in order to improve the transmission of the information. For example, the LTE (4G) network technology calls for up to eight antennas. The upcoming 4G releases and next generation 5G network technologies under development will utilize Massive-MIMO arrays of 16, 24, and more antennas. One challenge created by the use of Massive-MIMO is the need to equalize the signals received from the individual antennas to account for differences in the phase shift and loss associated with the different channels, especially as the number of antennas in the MIMO array increases.



BRIEF DESCRIPTION OF THE DRAWINGS
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the Figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements. Embodiments incorporating teachings of the present disclosure are shown and described with respect to the drawings presented herein, in which:
FIG. 1 is an illustration of a MIMO system according to an embodiment of the present disclosure;
FIG. 2 is an block diagram illustrating a MIMO receiver for a high-speed wireless data communication network according to an embodiment of the present disclosure;
FIG. 3 is a block diagram of a multi-stage equalizer that uses small dimension equalizer circuits according to various embodiments of the present disclosure;
FIG. 4 is a flowchart illustrating a method for large dimension equalization using small dimension equalizer circuits according to an embodiment of the present disclosure;
FIG. 5 is a block diagram of an equalizer that utilizes equalizer circuit reuse according an embodiment of the present disclosure;
FIG. 6 is block diagram of a multi-stage equalizer according an embodiment of the present disclosure;
FIG. 7 is block diagram of a multi-stage equalizer with stage bypassing according an embodiment of the present disclosure;
FIG. 8 illustrates a method for bypassing an equalizer circuit in a multi-stage equalizer according to an embodiment of the present disclosure; and
FIG. 9 illustrates a method for bypassing an equalizer circuit in a multi-stage equalizer according to another embodiment of the present disclosure.



The use of the same reference symbols in different drawings indicates similar or identical items.
DETAILED DESCRIPTION OF DRAWINGS
A high-speed wireless data communication network can include a MIMO receiver that receives radio signals transmitted from a MIMO transmitter. The MIMO transmitter encodes data into a radio signal that is transmitted to the MIMO receiver by a plurality of antennas. The MIMO receiver converts each of the radio signals received at each antenna from time domain signals to frequency-domain signals using a Fast Fourier Transform (FFT), and the frequency-domain signals are equalized in order to reverse the effects of distortion in the channels between the transmitter antennas and the receiver antennas. The equalized signals are then further processed to recover the data encoded therein.
An equalizer according to an embodiment of the present disclosure equalizes the signals received by a MIMO array by utilizing multiple equalizer circuits configured in two or more equalization stages. In an initial stage, a plurality of equalizer circuits are each configured to receive frequency-domain signals from a subset of the antennas of the MIMO array, along with channel characteristic information associated with each of the received frequency-domain signals. The initial stage equalizer circuits each equalize their set of received frequency-domain signals based upon the frequency-domain signals themselves and the channel characteristic information corresponding to the signals' channels, and generate an initial stage equalized signal and associated initial stage output statistics.
In a next stage, one or more equalizer circuits are connected to receive a number of the initial stage equalized signals and the initial stage output statistics associated with each received initial stage equalized signal. These next stage equalizer circuits then equalize the initial stage equalized signals based upon the initial stage equalized signals and the initial stage output statistics, and generates a next stage equalized signal and associated next stage output statistics. In each additional equalization stage, one or more equalization circuits are connected to receive a number of equalized signals and the associated output statistics from the preceding equalization stage. The equalization circuits each equalize the received signals based upon the received signals and associated output statistics to generate an equalized signal and associated output statistics for a subsequent equalization stage. Thus, additional equalization stages are utilized to further decrease the number of equalized signals until, in a final equalization stage, a single final stage equalized signal is generated. The final stage equalized signal is utilized in data recovery operations of the receiver. In this way, a number of simple equalizer circuits are utilized in stages to equalize the frequency-domain signals from a large number of antennas, instead of designing and implementing a single equalizer that is capable of equalizing all of the radio signals in a single operation.
In one embodiment of the present invention, an equalizer circuit of a particular equalization stage can be omitted, and input signals that would have been received at the omitted equalization circuit bypass the equalization stage and are instead processed at an equalizer circuit included at the next stage. For example, a subset of the received frequency-domain signals can be processed by equalizer circuits at a first stage, while the remaining received frequency-domain signals bypass the first stage and are processed at an equalizer circuit included at a second stage. This equalizer circuit can process signals provided by equalizer circuit of the first stage and the remaining received frequency-domain signals, thereby performing a combining function as well as an equalization function. Furthermore, this equalizer circuit can utilize original channel characteristic information corresponding to the signals that bypassed the first stage, while using output statistics corresponding to equalized signals that are generated at the first stage. The opportunity to omit bypass can be determined based on a number of antennas providing the multiple received frequency-domain signals, a number of signals that each equalizer circuit can process, and a number of data streams, herein referred to as a layer, that are included in the received transmission.
FIG. 1 illustrates a MIMO system 100 including four transmit antennas 102, 104, 106, and 108, and four receive antennas 112, 114, 116, and 118. In a particular embodiment, a transmitter of MIMO system 100 operates using Orthogonal Frequency-Division Multiplexing (OFDM) to transmit a time-domain radio signal that encodes a particular set of symbols representing digital data over a plurality of transmit antennas 102-108. A receiver of MIMO system 100 includes receive antennas 112-118, each of which provide a corresponding time-domain radio signal to the receiver for further processing to decode the particular set of symbols and retrieve the digital data. Each transmit antenna 102-108 is coupled to each of receive antennas 112-118 via a unique channel. Each channel, here represented by “hij,” represents a model of the transmission path that is unique to the antenna pair represented by the channel. Transmit antenna 102 is coupled to receive antenna 112 via channel h11, to receive antenna 114 via channel h12, to receive antenna 116 via channel h13, and to receive antenna 118 via channel h14. Receive antennas 104-108 are similarly coupled to each of receive antennas 112, 114, 116, and 118. Note that a particular radio signal is characterized by its carrier frequency and its bandwidth, and that a radio signal that uses OFDM will divide the bandwidth into multiple frequency sub-bands. The frequency-domain representation of the time-domain signal that is received by each of receive antennas 112-118 is given generally as:

y=Hx+n  Equation 1

where y is the frequency-domain representation of the received signal, represented by the frequency-domain vector [Rx×1], H is the channel matrix, represented by the frequency-domain vector [Rx×Tx], x is the frequency-domain representation of the transmitted signal, e.g., the idealized signal, represented by the frequency-domain vector [Tx×1], and n is the noise in the receiver.

The channel matrix H includes signal path characteristic information that distorts the idealized signal x, such that its inverse can be used to correct the received signals when the characteristics—are known. The signal path characteristics represent the combined effects of, for example, scattering, fading, and power decay with distance. The channel matrix H can be determined via various techniques as are known in the art, such as where channel characteristic information is derived from channel measurements taken at the receiver in response to a received channel training sequence, or pilot signal, that includes known signal characteristics. The channel characteristic information is derived by comparing the known signal characteristics of the training sequence with the signal characteristics of the received signal to determine the signal path characteristics. The channel matrix H can also be obtained based on various channel estimation techniques. The techniques and method for deriving channel characteristic information is known in the art. It will be understood that each channel is characterized by its own channel matrix H, and that the channel matrix will include channel characteristic information associated with each frequency sub-band. Channel characteristic information may also be referred to as channel estimation information.
It will be understood that, with the increased use of Massive-MIMO, the number of antenna signals that will need to be equalized will increase as compared to previous systems. As such, the design and development of massively parallel equalizer circuits will become an increasing challenge. In a particular embodiment of the present disclosure, a multi-stage equalizer meets this challenge by utilizing multiple stages of lower order equalizer circuits to perform analogous functions to a single, higher order, hardware equalizer. For example, where a typical equalizer circuit can equalize eight (8) antenna signals, eight (8) of such equalizer circuits can be used to perform a first stage of equalization on up to 64 antenna signals to generate eight first stage equalized signals. Then another equalizer circuit can receive the eight first stage equalized signals and perform a second stage of equalization to generate a final equalized signal for all 64 antenna signals.
FIG. 2 illustrates an embodiment of a MIMO receiver 200 for a high-speed wireless data communication network, such as may be found in a LTE uplink receiver base station. Receiver 200 includes a MIMO array 210, a Fast Fourier Transform (FFT) circuit 220, a multi-stage equalizer 230, a channel characteristic information module 240, and a data recovery module 250. Radio signals 205 encode symbols representative of high-speed digital data from a MIMO transmitter. MIMO array 210 represents a number of receive antennas that each receive radio signals 205 and provide time-domain signals 215 to FFT circuit 220. As such, MIMO array 210 will be understood to include various analog devices such as amplifiers, mixers, phase shifters, and the like, as needed or desired. Time-domain signals 215 are received by FFT circuit 220 and are transformed into associated frequency-domain signals 225. Here a first time-domain signal 215 received on a first antenna of MIMO array 210 is transformed via FFT circuit 220 into an associated first frequency-domain signal 225, and each other time-domain signal is transformed into an associated frequency-domain signal. Frequency-domain signals 225 are equalized in multi-stage equalizer 230 based upon channel characteristic information 245 from channel characteristic information module 240, and the multi-stage equalizer generates an equalized signal 235 based upon the frequency-domain signals and the channel characteristic information. Equalized signal 235 is provided to data recovery module 250 to decode symbols and extract the high-speed digital data encoded thereon. As such, data recovery module 250 operates to apply various signal processing techniques to equalized signal 235, including Inverse Digital Fourier Transform (IDFT), Log Likelihood Ratio (LLR) generation, Hybrid Automatic Repeat Request (HARQ) combining, turbo encoding, and the like.
Channel characteristic information module 240 includes information related to the signal path characteristics of radio signals 205 as they propagate from the MIMO transmitter to MIMO receiver 100. The signal path characteristics represent the combined effects of, for example, scattering, fading, and power decay with distance. Channel characteristic information module 240 provides channel characteristic information 245 to multi-stage equalizer 230. In a particular embodiment, channel characteristic information module 240 derives the channel characteristic information based upon channel training sequence. In another embodiment, channel characteristic information module 240 determines the channel characteristic information based upon an ongoing estimate of the signal path characteristics.
FIG. 3 illustrates an exemplary embodiment of a multi-stage equalizer 300 similar to multi-stage equalizer 230, and that provides two stages of equalization for 16 received radio signals from 16 antennas using equalizer circuits that equalize four (4) frequency-domain signals. Multi-stage Equalizer 300 includes first stage equalizer circuits 302, 304, 306, and 308, and a second stage equalizer circuit 310. Multi-stage equalizer 300 receives 16 frequency-domain signals (Rx1, Rx2, . . . , Rx16) from the 16 antennas, and the channel characteristic information associated with each antenna (H1, H2, . . . , H16).
In the first stage, equalizer circuit 302 is configured to receive four (4) frequency-domain signals (Rx1, Rx2, Rx3, and Rx4), and associated channel characteristic information (H1, H2, H3, and H4). Equalizer circuit 302 equalizes frequency-domain signals (Rx1, Rx2, Rx3, and Rx4) based upon the frequency-domain signals and channel characteristic information (H1, H2, H3, and H4), and generates a first stage equalized signal Eq1 and output statistics OS1, described below. Similarly, equalizer circuit 304 equalizes frequency-domain (Rx5, Rx6, Rx7, and Rx8) signals based on the frequency-domain signals and channel characteristic information (H5, H6, H7, and H8), and generates a first stage equalized signal Eq2 and output statistics OS2, equalizer circuit 306 equalizes frequency-domain signals (Rx9, Rx10, Rx11, and Rx12) based on the frequency-domain signals and channel characteristic information (H9, H10, H11, and H12), and generates a first stage equalized signal Eq3 and output statistics OS3, and equalizer circuit 308 equalizes frequency-domain signals (Rx13, Rx14, Rx15, and Rx16) based on the frequency-domain signals and channel characteristic information (H13, H14, H15, and H16), and generates a first stage equalized signal Eq4 and output statistics OS4. In the second stage, equalizer circuit 310 is configured to receive four (4) frequency-domain signals (Eq1, Eq2, Eq3, and Eq4), and associated output statistics (OS1, OS2, OS3, and OS4), and the equalizer circuit equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a second stage equalized signal EqOUT.
In a particular embodiment, equalizer circuits 302, 304, 306, and 308 operate to equalize the frequency-domain signals and determine an estimated signal as:

{circumflex over (x)}=[HHS−1H+1]−1HHS−1y  Equation 2

where {circumflex over (x)} is the estimated signal, H is the channel characteristic information, and S is a noise covariance that is calculated by a channel measurement or estimation. The output statistics are provided as:

β=diag{[HHS−1H+1]−1HHS−1H}  Equation 3

and:

NV=diag{[HHS−1H+1]−1}  Equation 4

where β is the estimated amplitude attenuation and NV is the estimated error variance. In a particular embodiment, the channel characteristic information is determined based upon a channel training sequence. In another embodiment, the channel characteristic information is provided as an ongoing estimate of the signal path characteristics.

The skilled artisan will recognize that the teachings shown in equalizer 300 can be generalized, and that an equalizer can provide for different numbers of radio signals received on a greater or a lesser number of antennas, that the number of frequency-domain signals that can be equalized by a particular equalizer circuit is not fixed, and that equalizer circuits that can perform 10, 16, 32, or another number of equalizations can be utilized, as needed or desired. Moreover, where the number of equalized signals from a particular configuration of first stage equalizer circuits exceeds the number of frequency-domain signals to a particular second stage equalizer circuit, the second stage of equalization can include multiple equalizer circuits, each providing its own equalized signal and output statistics that feed into one or more third stage equalizer to provide third stage equalized signals and associated output statistics. Further, equalization stages of the, fourth, or greater, order can also be provided, as needed or desired. Further, it is not necessary that the number of frequency-domain signals that the equalizer circuits can equalize is the same for all equalizer circuits within a particular equalization stage, or between equalization stages, but a mix of different equalizer circuits can be configured as needed or desired. It will be further understood that the equalization performed and the output statistics generated by an equalizer circuit of the present disclosure may be performed by different methods, as known to the skilled artisan. Further, it will be understood that an equalizer circuit may receive the channel characteristic associated with the respective signals on a single input to the equalizer circuit, or on separate inputs to the equalizer circuit, as needed or desired.
FIG. 4 illustrates a method for large dimension equalization using small dimension equalizer circuits in a wireless communication network, starting at block 402. A receiver receives N frequency-domain signals (R0, R1, RN−1) from N antennas, and channel characteristic associated with the N frequency-domain signals, in block 404. For example, receiver 200 can be part of a high-speed wireless data communication network, and can operate to receive 32 frequency-domain signals from 32 antennas in a Massive-MIMO configuration. Equalization circuits are provided in block 406, such that P frequency-domain signals are equalized by each equalizer circuit, where:

P<N  Equation 5.

For example, an equalizer circuit can be configured to provide equalization to up to eight (8) received frequency-domain signals. “C” of the particular equalizer circuits are provided in bloc 408, where each of the C equalizer circuits equalizes N frequency-domain signals, where:

C=ceiling(N/P)  Equation 6.

For example, to provide first stage equalization to 32 frequency-domain signals from 32 antennas using equalizer circuits that are configured to provide equalization to eight (8) frequency-domain signals, at least four (4) equalizer circuits are needed in the first stage.

The C equalizer circuits each generate a first stage equalized signal using the channel characteristic associated with each frequency-domain signal in block 410, where:

Y0=EQ(R0,R1, . . . ,RP−1)  Equation 7,

Y1=EQ(RP,RP+1, . . . ,R2P−1)  Equation 8,

YC−1=EQ(R(C−1)P,R(C−1)P+1, . . . ,RN−1)  Equation 9,

and where YX is a first stage equalized signal from one of the C equalizer circuits. For example, the four (4) equalization circuits can generate an equalized signal based upon the received frequency-domain signals and channel characteristic.

Each of the C equalizer circuits generates output statistics associated with the equalized signal in block 412. The output statistics provide a statistical evaluation of the channel characteristic, and can include an output constellation magnitude E[Ŷ] and a noise/estimation error variance and magnitude of output E[|Ŷ−Y|2].
Finally, a second stage equalized signal is generated based upon the C equalized signals and the associated output statistics through a second stage equalizer circuit in block 414, where:

Z=EQ(Y0,Y1, . . . ,YC−1)  Equation 10,

and the method ends in block 416.

The skilled artisan will recognize that the method of FIG. 4 can be generalized to provide for different numbers of frequency-domain signals received from a greater or a lesser number of antennas, that the number of frequency-domain signals that can be equalized by a particular equalizer circuit is not fixed, and further, equalization stages of the third, fourth, or greater, order can be provided, as needed or desired.
FIG. 5 illustrates an exemplary embodiment of an equalizer 500 that reuses a single equalizer circuit that provides channel equalization on P signals to equalize N received radio signal from N antennas. Equalizer 500 includes a receiver module 510, a channel switcher 520, an equalizer circuit 530, a memory 540, and an estimate and statistics switcher (estimate switcher) 550. Receiver module 510 operates to receive N radio signals (R0, R1, . . . , RN) from the N antennas and to provide N frequency-domain signals 515 to channel switcher 520. Channel switcher 520 operates in a first stage mode to select a first set of up to P of the frequency-domain signals, and to provide the first set of frequency-domain signals to equalizer circuit 530. At the same time, channel characteristic information 505 from the N antennas is provided to estimate switcher 550, and the estimate switcher operates in the first mode to select a first set of channel characteristic information associated with the first set of frequency-domain signals selected by channel switcher 520, and to provide the first set of channel characteristic information to equalizer circuit 530.
When equalizer circuit 530 receives both the first set of frequency-domain signals and the first set of channel characteristic information, the equalizer circuit generates a first stage equalized signal 535 and output statistics 537 associated with the first stage equalized signal, and stores both the first stage equalized signal and the associated output statistics in memory 540. The first stage mode continues with channel switcher 520 successively selecting additional sets of up to P of frequency-domain signals 515 that are provided to equalizer circuit 530, with estimate switcher 550 selecting the associated sets of channel characteristic information 505 that are provided to the equalizer circuit, and with the equalizer circuit generating successive first stage equalized signals 535 and associated output statistics 537 and storing the first stage equalized signals and associated output statistics to memory 540, until all of the N frequency-domain signals 515 have been equalized.
In subsequent stages, channel switcher 520 operates to select sets of the stored first stage equalized signals 545 from memory 540, and to sequentially provide the sets of stored first stage equalized signals to equalizer circuit 530. Similarly, estimate switcher 550 operates to select the associated sets of the stored output statistics 547, and to provide the sets of stored output statistics to equalizer circuit 530. Equalizer circuit 530 then equalizes the received first stage equalized signals based upon the received first stage equalized signals and the associated output statistics, and to store the next stage equalized signals 535 and next stage output statistics 537 to memory 640. Each subsequent stage continues in like manner until all of the previous stage equalized signals have been processed. Then, in a final stage, when all previous stage signals have been equalized, equalizer circuit 530 provides a final equalization signal 535.
FIG. 6 illustrates an exemplary embodiment of a multi-stage equalizer 600 similar to multi-stage equalizers 230 and 300, and that provides three stages of equalization for 14 received radio signals from 14 antennas using equalizer circuits that equalize four (4) frequency-domain signals. Equalizer 600 is configured to support two data streams. Multi-stage equalizer 600 includes first stage equalizer circuits 602, 604, 606, and 608, second stage equalizer circuits 610 and 612, and a third stage equalizer circuit 614. Multi-stage equalizer 600 receives 14 frequency-domain signals (Rx1, Rx2, . . . , Rx14) from the 14 antennas, and the channel characteristic information associated with each antenna (H1, H2, . . . , H14).
In the first stage, equalizer circuit 602 is configured to receive four (4) frequency-domain signals (Rx1, Rx2, Rx3, and Rx4), and associated channel characteristic information (H1, H2, H3, and H4). Equalizer circuit 602 equalizes frequency-domain signals (Rx1, Rx2, Rx3, and Rx4) based upon the frequency-domain signals and channel characteristic information (H1, H2, H3, and H4), and generates a first stage equalized signal Eq1 and output statistics OS1, described below. Similarly, equalizer circuit 604 equalizes frequency-domain (Rx5, Rx6, Rx7, and Rx8) signals based on the frequency-domain signals and channel characteristic information (H5, H6, H7, and H8), and generates a first stage equalized signal Eq2 and output statistics OS2, equalizer circuit 606 equalizes frequency-domain signals (Rx9, Rx10, Rx11, and Rx12) based on the frequency-domain signals and channel characteristic information (H9, H10, H11, and H12), and generates a first stage equalized signal Eq3 and output statistics OS3, and equalizer circuit 608 equalizes frequency-domain signals (Rx13, and Rx14) based on the frequency-domain signals and channel characteristic information (H13, and H14), and generates a first stage equalized signal Eq4 and output statistics OS4.
In the second stage, equalizer circuit 610 is configured to receive two (2) frequency-domain signals (Eq1, and Eq2), and associated output statistics (OS1, and OS2), and the equalizer circuit equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a second stage equalized signal Eq5. Similarly, equalizer circuit 612 is configured to receive two (2) frequency-domain signals (Eq3, and Eq4), and associated output statistics (OS3, and OS4), and the equalizer circuit equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a second stage equalized signal Eq6 and statistics OS6.
In the final stage, equalizer circuit 610 is configured to receive two (2) frequency-domain signals (Eq5, and Eq6), and associated output statistics (OS5, and OS6), and the equalizer circuit equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a third stage equalized signal EqOUT and corresponding output statistics OSOUT. Operation of multi-stage equalizer 600 is similar to the operation of equalizer 300 of FIG. 3 described above. One of skill will appreciate that the number of equalizer circuits included in each stage can vary based on the number of frequency-domain signals received at the first stage, and the number of signals that each equalizer circuit can process.
The number of stages that are required to process N signals from N antennas can be determined based on a number of signals that each equalizer circuit can process, P, and the number of layers, L, using the following pseudo-code:

1. Stage=1  (1)

2. N_EQ(stage)=ceiling(N_inputs(stage)/P)  (2)

3. For stage(i), distribute input signals to each equalizer:  (3)

    
    
        If N_EQ(stage)×P==N, each equalizer receives P signals
        Else:
        First [N_EQ(stage)−1] equalizers each receives P signals
        If (N_inputs(stage) % P)<L:
        
            Last EQ should borrow signals from equalizer N_EQ(stage)−1 in order to have at least L input antennas
        
        
        Else:
        
            Last antenna should receive the remaining (N_inputs(stage) % P antennas

4. N_inputs(stage+1)=ceiling(N_inputs(stage)/P)×L  (4)

5. If N_inputs(stage+1)==L  (5)

        
        
        N_EQ(stage+1)=1
        End
    
    


Else:

    
    
        stage=stage+1
        Go to step 2
    
    


At line (1), an initial stage receives all N signals from N antennas. At (2), a number of equalizers at stage(i), N_EQ(stage) is determined based on the number of frequency-domain signals received at stage(i) and the number of signals that each equalizer circuit can process, P. At (3), input signals provided to stage(i) are distributed amongst the equalizer circuits included in stage(i). For example, equalizer circuits 602, 604, and 606 each receive four frequency-domain signals, and the remaining two signals of the fourteen input signals are provided to equalizer circuit 608. In the example of FIG. 6, the number of remaining signals provided to equalizer circuit 602 is equal to the number of layers, L. If the number of signals remaining for the last equalizer circuit was less than L, signals are borrowed from the adjacent equalizer so that L signals are provided to the last equalizer in this stage. At (4), the number of equalizers included at the next stage is determined. For example, two equalizer circuits, 610 and 612 are required to process the four frequency-domain signals generated at the first stage. At (5), it is determined whether an additional stage is required. In the example of FIG. 6, one more stage is required.
FIG. 7 illustrates an exemplary embodiment of a multi-stage equalizer 700. In particular, equalizer 700 illustrates how one equalizer circuit of multi-stage equalizer 600 can be omitted. Equalizer 700 provides three stages of equalization for fourteen (14) received radio signals from fourteen antennas using equalizer circuits that equalize four (4) frequency-domain signals. Equalizer 700 is configured to support two (2) data streams. Multi-stage equalizer 700 includes first stage equalizer circuits 702, 704, and 706, second stage equalizer circuits 710 and 712, and a third stage equalizer circuit 714. Multi-stage equalizer 700 receives fourteen frequency-domain signals (Rx1, Rx2, . . . , Rx14) from the fourteen antennas, and the channel characteristic information associated with each antenna (H1, H2, . . . , H14).
In the first stage, equalizer circuit 702 is configured to receive four (4) frequency-domain signals (Rx1, Rx2, Rx3, and Rx4), and associated channel characteristic information (H1, H2, H3, and H4). Equalizer circuit 702 equalizes frequency-domain signals (Rx1, Rx2, Rx3, and Rx4) based upon the frequency-domain signals and channel characteristic information (H1, H2, H3, and H4), and generates a first stage equalized signal Eq1 and output statistics OS1, described below. Similarly, equalizer circuit 704 equalizes frequency-domain (Rx5, Rx6, Rx7, and Rx8) signals based on the frequency-domain signals and channel characteristic information (H5, H6, H7, and H8), and generates a first stage equalized signal Eq2 and output statistics OS2, and equalizer circuit 606 equalizes frequency-domain signals (Rx9, Rx10, Rx11, and Rx12) based on the frequency-domain signals and channel characteristic information (H9, H10, H11, and H12), and generates a first stage equalized signal Eq3 and output statistics OS3.
In the second stage, equalizer circuit 710 is configured to receive two (2) frequency-domain signals (Eq1, and Eq2), and associated output statistics (OS1, and OS2), and equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a second stage equalized signal Eq5. Equalizer circuit 712 is configured to receive frequency-domain signals Eq3 and associated output statistics OS3 from equalizer circuit 706 of the first stage. Equalizer circuit 712 also receives frequency-domain signals Rx13 and Rx14 and channel characteristic information H13 and H14 that bypassed the first stage. Equalizer circuit 712 equalizes the frequency-domain signals based upon the frequency-domain signals, the output statistics, and the channel characterization information to provide a second stage equalized signal Eq6 and statistics OS6.
In the final stage, equalizer circuit 610 is configured to receive two (2) frequency-domain signals (Eq5, and Eq6), and associated output statistics (OS5, and OS6), and the equalizer circuit equalizes the frequency-domain signals based upon the frequency-domain signals and the output statistics to provide a third stage equalized signal EqOUT and corresponding output statistics OSOUT. Operation of multi-stage equalizer 700 is similar to the operation of equalizer 600 of FIG. 6 described above. In addition to the cost benefit of requiring fewer equalizer circuits, there is also a performance benefit, because equalizer circuit 712 receives actual channel characteristic information, H13 and H14, instead of equalizer output statistics, such as OS4 of FIG. 6.
As described above with reference to equalizer 600, the number of equalizer circuits included in each stage can vary based on the number of frequency-domain signals received at the first stage, and the number of signals that each equalizer circuit can process. In one embodiment of the present disclosure, a multi-stage equalizer can include only one equalizer in each of the first stage and the second stage. For example, if twelve (12) frequency domain signals corresponding to twelve antennas are received, and each equalizer circuit can support eight (8) signals, a single equalizer in a first stage can process eight of the incoming signals, while a second equalizer circuit in a second stage can process the four (4) remaining incoming signals in addition to the combined frequency-domain signal generated by the equalizer in the first stage. Similar to the operation of equalizer circuit 712, the second equalizer can utilize output statistics generated by the first equalizer to complement the first eight frequency-domain signals, and utilize actual channel characteristic information associated with the remaining four incoming signals that bypassed the first stage.
The number of stages that are required to process N signals from N antennas can be determined based on a number of signals that each equalizer circuit can process, P, and the number of layers, L, using the following pseudo-code:

1. Stage=1  (1)

2. If [N_inputs(stage) % P+floor(N_inputs(stage)/P)×L]<=N_EQ(stage+1)×P  (2)

    
    
        a. Remove last EQ in this stage
        b. If not all EQs in this stage are not fully utilized, than load them
        c. Remaining inputs at this stage are input to next stage

3. stage=stage+1  (3)

4. Go to 2.

    
    


At line (1), an initial stage receives all N signals from N antennas. At (2), it is determined whether an equalizer at this stage can be removed. Each equalizer in this stage should include P inputs so that they are fully utilized. The remaining frequency-domain signals, which will be less than P signals, bypass this stage and are provided as inputs to the next stage.
FIG. 8 illustrates a method 800 for bypassing an equalizer circuit in a multi-stage equalizer according to a specific embodiment of the present disclosure. Method 800 begins at block 802 where a subset of a first plurality of antenna signals are received at one or more equalizers included at a first stage of a multi-stage antenna equalizer. For example, equalizer circuits 702-706 receive Rx1-Rx12 of the fourteen frequency-domain antenna signals. Method 800 continues at block 804 where equalization signals and statistical data generated by equalizers at the first stage are received at one or more equalizers at a second stage of the multi-stage antenna equalizer. For example, signals frequency-domain signals Eq1, and Eq2, and associated output statistics OS1, and OS2 are received at second stage equalizer circuit 710 of FIG. 7. Method 800 concludes at block 806 where a second subset of the first plurality of antenna signals and corresponding channel characteristic information are received at one of the one or more equalizers included at the second stage of the multi-stage antenna equalizer. For example, equalizer circuit 712 of FIG. 7 is configured to receive antenna signals Rx13 and Rx14 and corresponding channel characteristic information H13 and H14 in addition to signals Eq3 and OS3 from first stage equalizer circuit 706.
FIG. 9 illustrates a method 900 for bypassing an equalizer circuit in a multi-stage equalizer according to a specific embodiment of the present disclosure. Method 900 is similar to method 800, but illustrates bypassing an equalizer circuit at any at a later stage of a multi-stage equalizer. Method 900 begins at block 902 where a first set of equalization signals and statistical data is received from equalizers at stage(n−1) at one or more equalizers included at a stage(n) of a multi-stage antenna equalizer. The method continues at block 904 where a second set of equalization signals and statistical data from equalizers at stage(n−2) is received at one of the one or more equalizers included at stage(n) of the multi-stage antenna equalizer. In an embodiment, signals corresponding to stage(n−2) can include first frequency-domain signals 225 of FIG. 2, such as frequency-domain signals Rx13, and Rx14 of FIG. 7. For example, equalizer circuits 710 and 712 can correspond to stage(n−2), equalizer circuits, equalizer circuits 702-706 can correspond to stage(n) equalizer circuits. Accordingly, stage(n−2) corresponds to the individual antenna frequency-domain signals and channel characteristic information. Method 900 concludes at block 906 where if stage(n−2) corresponds to antenna signals, channel characteristic information corresponding to the second set of equalization signals is utilized instead of equalizer output statistics.
Embodiments incorporating teachings of the present disclosure are shown and described with respect to the drawings presented herein. In one aspect, a method includes receiving a first frequency-domain signal, a second frequency-domain signal, and a third frequency-domain signal; generating, at a first equalization circuit, a first equalized signal based upon the first frequency-domain signal and the second frequency-domain signal; and generating, at a second equalization circuit, a second equalized signal based upon the first equalized signal and the third frequency-domain signal. In an embodiment of the first aspect, the first equalized signal is further based upon first channel characteristic information associated with the first frequency-domain signal and second channel characteristic information associated with the second frequency-domain signal. In another embodiment of the first aspect, the method further includes generating, at the first equalization circuit, first output statistics based upon the first frequency-domain signal, the second frequency-domain signal, the first channel characteristic information and the second channel characteristic information.
In still another embodiment of the first aspect, the method further includes generating the second equalized signal based on the first output statistics and third channel characteristic information associated with the third frequency-domain signal. The first output statistics can include a first magnitude of an output constellation of the first equalized signal, and can include a first noise/estimation error variance of the first equalized signal. In an embodiment of the first aspect, the method includes receiving a training sequence, wherein the first channel characteristic information, the second channel characteristic information, and the third channel characteristic information are based upon the training sequence. In another embodiment of the first aspect, the method includes generating, at a third equalization circuit, a third equalized signal based on the second equalized signal and a fourth equalized signal; and generating, at the third equalization circuit, third output statistics based upon the second equalized signal, the fourth equalized signal, the second output statistics and fourth output statistics. In yet another embodiment of the first aspect, the method includes receiving the first frequency-domain signal, the second frequency-domain signal, and the third frequency-domain signal from a Multiple-Input Multiple-Output (MIMO) antenna array.
In a second aspect, an equalizer includes a first equalizer circuit and a second equalizer. The first equalizer circuit includes a first signal input configured to receive a first frequency-domain signal, a second signal input configured to receive a second frequency-domain signal, and an equalized signal output configured to provide a first equalized signal based upon the first and second frequency-domain signals. The second equalizer circuit includes a first signal input configured to receive a the first equalized signal, a second signal input configured to receive a third frequency-domain signal, and an equalized signal output configured to provide a second equalized signal based upon the first equalized signal and the third frequency-domain signals. In an embodiment of the second aspect the first equalizer circuit further includes a channel characteristic input configured to receive first and second channel characteristic information associated with the respective first and second frequency-domain signals, wherein the first equalized signal is further based upon the first and second channel characteristic information, and an output statistics output configured to provide first output statistics based upon the first and second frequency-domain signals and the first and second channel characteristic information.
In another embodiment of the second aspect, the second equalizer circuit further includes a channel characteristic input configured to receive the first output statistics, a second channel characteristic input configured to receive third channel characteristic information associated with the third frequency-domain signal, and an output statistics output configured to provide second output statistics based upon the first equalized signal, the first output statistics, the third frequency-domain signal, and the third channel characteristic information. In still another embodiment of the second aspect, the equalizer circuit includes a third equalizer circuit. The third equalizer circuit includes an output configured to provide a third equalized signal, a first signal input coupled to the equalized signal output of the second equalizer circuit configured to receive the second equalized signal, and a second signal input configured to receive a fourth equalized signal, the third equalized signal based upon the second and fourth equalized signals. The third equalizer circuit can include channel characteristic inputs configured to receive the second output statistics and fourth output statistics, and an output configured to provide third output statistics generated based upon the second equalized signal, the fourth equalized signal, the second output statistics and the fourth output statistics. In an embodiment of the second aspect, the equalizer circuit includes a Multiple-Input Multiple-Output (MIMO) antenna array configured to provide the first frequency-domain signal, the second frequency-domain signal, and the third frequency-domain signal.
In a third aspect, a receiver includes N antennas; and an equalizer coupled to the N antennas. The equalizer includes C first stage equalizer circuits including a first equalizer circuit, the first equalizer circuit includes P inputs configured to receive P frequency-domain signals from a subset of the N antennas, and an output configured to provide a first stage equalized signal based on the P frequency-domain signals, wherein P<N, and wherein C<NIP; and a second stage equalizer circuit includes a first signal input configured to receive the first stage equalized signal, a second signal input configured to receive one of the N antennas frequency-domain signal not provided to one of the C first stage equalizer circuits, and an equalized signal output configured to provide a second equalized signal based upon the signals received at the first and second signal inputs. In an embodiment of the third aspect, the first equalizer circuit further includes a channel characteristic input configured to receive channel characteristic information associated with the respective P frequency-domain signals, wherein the first stage equalized signal is further based upon the associated channel characteristic information, and an output statistics output configured to provide first output statistics based upon the P frequency-domain signals and the associated channel characteristic information. In another embodiment of the third aspect, the second equalizer circuit further includes a first channel characteristic input configured to receive the first output statistics, a second channel characteristic input configured to receive channel characteristic information associated with the one of the N antennas frequency-domain signal, and an output statistics output configured to provide second output statistics based upon the first stage equalized signal, the first output statistics, and the one of the N antenna frequency-domain signal and associated channel characteristic information.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the Figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements.
It will be appreciated that the devices disclosed herein can be implemented in various manners using various types of memory. In particular, the application of the equalization as described herein, is not limited to applications in the disclosed embodiments, but can be applied in other instances where signal equalization is needed or desired.
The preceding description in combination with the Figures was provided to assist in understanding the teachings disclosed herein. The discussion focused on specific implementations and embodiments of the teachings. This focus was provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings. However, other teachings can certainly be used in this application. The teachings can also be used in other applications, and with several different types of architectures.
In this document, relational terms such as “first” and “second”, and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.
The term “another”, as used herein, is defined as at least a second or more. The terms “including”, “having”, or any variation thereof, as used herein, are defined as comprising. The term “coupled”, as used herein with reference to electro-optical technology, is defined as connected, although not necessarily directly, and not necessarily mechanically.
The terms “assert” or “set” and “negate” (or “deassert” or “clear”) are used when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level zero. And if the logically true state is a logic level zero, the logically false state is a logic level one.
As used herein, the term “bus” is used to refer to a plurality of signals or conductors that may be used to transfer one or more various types of information, such as data, addresses, control, or status. The conductors as discussed herein may be illustrated or described in reference to being a single conductor, a plurality of conductors, unidirectional conductors, or bidirectional conductors. However, different embodiments may vary the implementation of the conductors. For example, separate unidirectional conductors may be used rather than bidirectional conductors and vice versa. Also, plurality of conductors may be replaced with a single conductor that transfers multiple signals serially or in a time multiplexed manner. Likewise, single conductors carrying multiple signals may be separated out into various different conductors carrying subsets of these signals. Therefore, many options exist for transferring signals.
As used herein, the term “machine-executable code” can refer to instructions that can be provided to a processing device and can be executed by an execution unit. The machine-executable code can be provided from a system memory, and can include a system BIOS, firmware, or other programs. In addition, machine-executable code can refer to microcode instructions that can be used by a processing device to execute instructions, and can be provided by a microcode memory of the processing device.
Other embodiments, uses, and advantages of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. The specification and drawings should be considered exemplary only, and the scope of the disclosure is accordingly intended to be limited only by the following claims and equivalents thereof.

## Claims

1. A method, comprising:
receiving a first frequency-domain signal, a second frequency-domain signal, and a third frequency-domain signal;
generating, at a first equalization circuit, a first equalized signal based upon the first frequency-domain signal and the second frequency-domain signal, first channel characteristic information associated with the first frequency-domain signal, and second channel characteristic information associated with the second frequency-domain signal;
generating, at the first equalization circuit, first output statistics based upon the first frequency-domain signal, the second frequency-domain signal, the first channel characteristic information, and the second channel characteristic information; and
generating, at a second equalization circuit, a second equalized signal based upon the first equalized signal and the third frequency-domain signal.

2. The method of claim 1, further comprising:
generating the second equalized signal based on the first output statistics and third channel characteristic information associated with the third frequency-domain signal.

3. The method of claim 1, wherein the first output statistics comprise a first magnitude of an output constellation of the first equalized signal.

4. The method of claim 1, wherein the first output statistics comprise a first noise/estimation error variance of the first equalized signal.

5. The method of claim 2, further comprising:
receiving a training sequence, wherein the first channel characteristic information, the second channel characteristic information, and the third channel characteristic information are based upon the training sequence.

6. The method of claim 1, further comprising:
generating, at a third equalization circuit, a third equalized signal based on the second equalized signal and a fourth equalized signal.

7. The method of claim 6, further comprising:
generating, at the third equalization circuit, third output statistics based upon the second equalized signal, the fourth equalized signal, the second output statistics and fourth output statistics.

8. The method of claim 1, further comprising:
receiving the first frequency-domain signal, the second frequency-domain signal, and the third frequency-domain signal from a Multiple-Input Multiple-Output (MIMO) antenna array.

9. An equalizer, comprising:
a first equalizer circuit comprises
a first signal input configured to receive a first frequency-domain signal,
a second signal input configured to receive a second frequency-domain signal,
an equalized signal output configured to provide a first equalized signal based upon the first and second frequency-domain signals,
a channel characteristic input configured to receive first and second channel characteristic information associated with the respective first and second frequency-domain signals, wherein the first equalized signal is based upon the first and second channel characteristic information, and
an output statistics output configured to provide first output statistics based upon the first and second frequency-domain signals and the first and second channel characteristic information; and

a second equalizer circuit comprises
a first signal input configured to receive the first equalized signal,
a second signal input configured to receive a third frequency-domain signal, and
an equalized signal output configured to provide a second equalized signal based upon the first equalized signal and the third frequency-domain signal.

10. The equalizer of claim 9, wherein:
the second equalizer circuit further comprises a channel characteristic input configured to receive the first output statistics, a second channel characteristic input configured to receive third channel characteristic information associated with the third frequency-domain signal, and an output statistics output configured to provide second output statistics based upon the first equalized signal, the first output statistics, the third frequency-domain signal, and the third channel characteristic information.

11. The equalizer of claim 9, further comprising:
a third equalizer circuit comprises an output configured to provide a third equalized signal, a first signal input coupled to the equalized signal output of the second equalizer circuit configured to receive the second equalized signal, and a second signal input configured to receive a fourth equalized signal, the third equalized signal based upon the second and fourth equalized signals.

12. The equalizer of claim 11, wherein the third equalizer circuit further comprises:
channel characteristic inputs configured to receive the second output statistics and fourth output statistics, and an output configured to provide third output statistics generated based upon the second equalized signal, the fourth equalized signal, the second output statistics and the fourth output statistics.

13. The equalizer of claim 9, further comprising:
a Multiple-Input Multiple-Output (MIMO) antenna array configured to provide the first frequency-domain signal, the second frequency-domain signal, and the third frequency-domain signal.

14. A receiver, comprising:
N antennas; and
an equalizer coupled to the N antennas, the equalizer comprising:
C first stage equalizer circuits including a first equalizer circuit, the first equalizer circuit comprises P inputs configured to receive P frequency-domain signals from a subset of the N antennas, and an output configured to provide a first stage equalized signal based on the P frequency-domain signals, wherein P<N, and wherein C<N/P; and
a second stage equalizer circuit comprises a first signal input configured to receive the first stage equalized signal, a second signal input configured to receive one of the N antennas frequency-domain signal not provided to one of the C first stage equalizer circuits, and an equalized signal output configured to provide a second equalized signal based upon the signals received at the first and second signal inputs.

15. The equalizer of claim 14, wherein:
the first equalizer circuit further comprises a channel characteristic input configured to receive channel characteristic information associated with the respective P frequency-domain signals, wherein the first stage equalized signal is further based upon the associated channel characteristic information, and an output statistics output configured to provide first output statistics based upon the P frequency-domain signals and the associated channel characteristic information.

16. The equalizer of claim 15, wherein:
the second equalizer circuit further comprises a first channel characteristic input configured to receive the first output statistics, a second channel characteristic input configured to receive channel characteristic information associated with the one of the N antennas frequency-domain signal, and an output statistics output configured to provide second output statistics based upon the first stage equalized signal, the first output statistics, and the one of the N antenna frequency-domain signal and associated channel characteristic information.