Abstract:
The present disclosure relates to a wireless communication apparatus capable of increasing throughput using MIMO in an LOS environment and a method for the same. A wireless communication apparatus based on the LOS-MIMO technique may comprise a multi-link configuration unit, a frequency response correction unit, a signal compensation unit, and a feedback unit. In the apparatus, an additional LOS-MIMO equalizer is used at the front of an LOS-MIMO estimator and a coding unit in order to compensate in-band frequency characteristics of frequency response characteristics estimated by the LOS-MIMO estimator and a signal channel estimator, whereby the LOS-MIMO estimation performance can be remarkably enhanced. Also, precise separation of multiplexed signals through the above-described LOS equalizer can make it possible to increase transmission capacity by using the LOS-MIMO which can be applied to high-order mode (e.g., over 16 quadrature amplitude modulation (QAM)) digital communications.

Description:
CLAIM FOR PRIORITY 
       [0001]    This application claims priority to Korean Patent Application No. 2016-0032282 filed on Mar. 17, 2016 in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to a wireless communication technology using line-of-sight (LOS) multi-input multi-output (MIMO), and more particularly, to a wireless communication apparatus capable of increasing throughput using the MIMO in the LOS environment and a method for the same. 
         [0004]    2. Related Art 
         [0005]    In the conventional MIMO system in the LOS channel environment, transmit/receive antennas are arranged so that an arrival path difference of a signal transmitted from each transmit antenna to each receive antenna is 90 degrees (λ/4), and a simple operation is performed on a signal received at the receive antenna in order to recover an original signal for the received signal. 
         [0006]    However, there is a problem that installation intervals among the antennas are determined fixedly according to signal frequencies and link distances between the transmit and receive antennas in order to make the arrival path difference of 90 degrees. 
       SUMMARY 
       [0007]    Accordingly, exemplary embodiments of the present disclosure are provided to substantially obviate one or more problems due to limitations and disadvantages of the related art. 
         [0008]    Exemplary embodiments of the present disclosure provide a wireless communication apparatus capable of increasing transmission capacity (throughput) using MIMO in an LOS environment (referred to as ‘LOS-MIMO’) and a method for the same. According to exemplary embodiments of the present disclosure, in the wireless communication system using the LOS-MIMO technique, an additional LOS-MIMO equalizer is used at the front of an LOS-MIMO estimator and a coding unit in order to compensate in-band frequency characteristics of frequency response characteristics estimated by the LOS-MIMO estimator and a signal channel estimator, whereby the LOS-MIMO estimation performance can be remarkably enhanced. Also, accurate separation of multiplexed signals through the above-described LOS equalizer can make it possible to increase the transmission capacity by using the LOS-MIMO which can be applied to high-order mode (e.g., over 16 quadrature amplitude modulation (QAM)) digital communications. 
         [0009]    Technical objects of the present disclosure are not limited to the aforementioned technical objects and other technical objects which are not mentioned will be apparently appreciated by those skilled in the art from the following description. 
         [0010]    In order to achieve the above-described objective, an aspect of the present disclosure provides a wireless communication apparatus based on a line-of-sight (LOS) multiple input and multiple output (MIMO) technique. The apparatus may comprise a multi-link configuration unit configured to configure multiple links by using at least one transmit antenna and at least one receive antenna; a frequency response correction unit for estimating and correcting frequency responses of signals received from the at least one transmit antenna; and a signal compensation unit for estimating and compensating phases and sizes of the signals received from the at least one transmit antenna so that a path difference between the signals received from the at least one transmit antenna becomes 90 degrees. 
         [0011]    The apparatus may further comprise a feedback unit for estimating and correcting the frequency responses of signals received from the at least one transmit antenna by using channel estimation information received from a channel estimator. 
         [0012]    Here, multipath frequency responses of the signals received from the at least one transmit antenna may be estimated and corrected through a multipath frequency response estimation and correction step, and frequency response characteristics of the corrected signals may be estimated and compensated through a channel estimation and compensation step. 
         [0013]    In order to achieve the above-described objective, another aspect of the present disclosure provides a wireless communication method based on a line-of-sight (LOS) multiple input and multiple output (MIMO) technique. The method may comprise configuring multiple links by using at least one transmit antenna and at least one receive antenna; estimating and correcting frequency responses of signals received from the at least one transmit antenna; and estimating and compensating phases and sizes of the signals received from the at least one transmit antenna so that a path difference between the signals received from the at least one transmit antenna becomes 90 degrees. 
         [0014]    The method may further comprise estimating and correcting the frequency responses of signals received from the at least one transmit antenna by using received channel estimation information. 
         [0015]    Here, multipath frequency responses of the signals received from the at least one transmit antenna may be estimated and corrected through a multipath frequency response estimation and correction step, and frequency response characteristics of the corrected signals may be estimated and compensated through a channel estimation and compensation step. 
         [0016]    According to the present disclosure, a structure that reflects a frequency response on a reception side, but frees antenna intervals without a feedback is provided. The provided apparatus and method can improve the LOS-MIMO estimation performance for broadband signals, improve LOS-MIMO estimation performance, and precisely separate multiplexed signals to prevent performance degradation due to interference signals. Thus, it can be applied to higher-order mode (e.g., over  16 QAM) digital communications. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]    Exemplary embodiments of the present disclosure will become more apparent by describing in detail exemplary embodiments of the present disclosure with reference to the accompanying drawings, in which: 
           [0018]      FIG. 1  is a diagram illustrating a structure of a conventional 2×2 LOS MIMO wireless communication apparatus; 
           [0019]      FIG. 2  is a diagram illustrating signal processing according to reception characteristics in a 2×2 LOS MIMO wireless communication apparatus according to the related art; 
           [0020]      FIG. 3  is a block diagram of a wireless communication apparatus capable of increasing transmission capacity by using LOS-MIMO according to an exemplary embodiment of the present disclosure; 
           [0021]      FIG. 4  is a diagram illustrating a structure of a wireless communication apparatus using a 2×2 LOS-MIMO according to an exemplary embodiment of the present disclosure; 
           [0022]      FIG. 5  is a diagram illustrating signal processing according to reception characteristics in a wireless communication apparatus using a 2×2 LOS MIM according to an exemplary embodiment of the present disclosure; 
           [0023]      FIG. 6  is a diagram illustrating signal processing according to reception characteristics in a wireless communication apparatus using a 2×2 LOS MIMO according to an exemplary embodiment of the present disclosure when frequency response characteristics differ only in one path; 
           [0024]      FIG. 7  is a diagram illustrating a preamble structure according to an exemplary embodiment of the present disclosure; 
           [0025]      FIG. 8  is a diagram illustrating a structure of a wireless communication apparatus according to an exemplary embodiment in which a feedback unit is further used; and 
           [0026]      FIG. 9  is a flowchart explaining a wireless communication method capable of increasing transmission capacity using LOS-MIMO according to an exemplary embodiment of the present disclosure. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0027]    The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be apparent to one of ordinary skill in the art. Also, descriptions of functions and constructions that are well known to one of ordinary skill in the art may be omitted for increased clarity and conciseness. 
         [0028]    Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative size, proportions, and depiction of elements in the drawings may be exaggerated for clarity, illustration, and convenience. 
         [0029]    The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided so that this disclosure will be thorough and complete, and will convey the full scope of the disclosure to one of ordinary skill in the art. 
         [0030]    Combinations of respective blocks in an accompanying block diagram and respective operations in a flowchart may be performed by computer program instructions. These computer program instructions can be mounted on a processor of a general purpose computer, a special purpose computer, or other programmable data processing equipment, and thus the instructions performed by the processor of the computer or other programmable data processing equipment generate a means for performing functions described in the respective blocks of the block diagram or the respective operations of the flowchart. To implement functions in a specific way, these computer program instructions can be stored in a computer-usable or computer-readable memory capable of aiming for a computer or other programmable data processing equipment, so that the instructions stored in the computer-usable or computer-readable memory can also produce a manufactured item including an instruction means for performing functions described in the respective blocks of the block diagram or the respective operations of the flowchart. 
         [0031]    In addition, each block or operation may indicate a part of a module, a segment or a code including one or more executable instructions for executing specific logical function(s). It should be noted that mentioned functions described in blocks or operations can be executed out of order in some alternative embodiments. For example, two consecutively shown blocks or operations can be performed substantially at the same time, or can be performed in a reverse order according to the corresponding functions. 
         [0032]    Hereinafter, exemplary embodiments according to the present disclosure will be described in detail by referring to accompanying drawings. However, the exemplary embodiments according to the present disclosure may be changed into various forms, and thus the scope of the present disclosure is not limited to the exemplary embodiments which will be described. The exemplary embodiments are provided to assist the one of ordinary skill in the art. in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. 
         [0033]      FIG. 1  is a diagram illustrating a structure of a conventional 2×2 LOS MIMO wireless communication apparatus. 
         [0034]    Referring to  FIG. 1 , illustrated is a structure of a 2×2 LOS MIMO wireless communication apparatus according to the related art having a channel coding unit for estimating a path difference of signals received from transmit antennas disposed with an arbitrary antenna interval, and finally obtaining a channel response forming 90 degrees at a received signal. 
         [0035]    The structure of the 2×2 LOS MIMO wireless communication apparatus according to the related art as illustrated in  FIG. 1  is a structure that can be used without feedback. However, since it uses a method that estimates only gain and phase information, in future wireless systems adopting millimeter wave bands in which the LOS-MIMO technique is usually used or broadband signals, there may be a problem that the performance is drastically degraded due to in-band frequency characteristics according to antennas, RF transceivers, and installation environments in the system configuration, even in the LOS environment. 
         [0036]      FIG. 2  is a diagram illustrating signal processing according to reception characteristics in a 2×2 LOS MIMO wireless communication apparatus according to the related art. 
         [0037]    As illustrated in  FIG. 2 , in case of non-flat frequency response characteristics, even if accurate frequency and phase information are estimated, both of a TxANT 1  signal component and a TxANT 2  signal component may exist in an RxANT 1  signal. Here, the TxANT 1  signal may refer to a signal transmitted from a transmit antenna TxANT 1 , and the TxANT 2  signal may refer to a signal transmitted from a transmit antenna TxANT 2 . Also, the RxANT 1  signal may refer to a signal received at a receive antenna RxANT 1 . 
         [0038]    Similarly, both of a TxANT 1  component and a TxANT 2  signal component may be present in a signal received at an RxANT 2  antenna. 
         [0039]    In this reason, a signal of a specific transmit antenna may act as an interference signal to signals of other transmit antennas, thereby deteriorating signal-to-interference-plus-noise ratio (SINR) characteristics. 
         [0040]      FIG. 3  is a block diagram of a wireless communication apparatus capable of increasing transmission capacity by using LOS-MIMO according to an exemplary embodiment of the present disclosure. 
         [0041]    Referring to  FIG. 3 , a wireless communication apparatus according to an exemplary embodiment of the present disclosure may comprise a multi-link configuration unit  100 , a frequency response correction unit  200 , and a signal compensation unit  300 . 
         [0042]    The multi-link configuration unit  100  may use at least one transmit antenna and at least one receive antenna in order to configure multiple links. 
         [0043]    The frequency response correction unit  200  may estimate and correct the frequency response of the signal received from each of the at least one transmit antenna. 
         [0044]    The signal compensation unit  300  may estimate and compensate phases and sizes of the signals received from the at least one transmit antenna so that a path difference of the signals received from the respective transmit antennas form 90 degrees with each other. 
         [0045]    According to an exemplary embodiment, the apparatus may further comprise a feedback unit for estimating and correcting the frequency response of the signal received from each of the transmit antennas using the channel estimation information received from the channel estimator. 
         [0046]    The structure of the wireless communication apparatus further including the feedback unit according to the above embodiment will be described in more detail with reference to  FIG. 8 . 
         [0047]    According to an exemplary embodiment of the present disclosure, a multipath frequency response estimation and correction step for estimating and correcting a multipath frequency response of the signal received from each transmit antenna and a channel estimation and compensation step for compensating frequency response characteristics of the corrected signal may be performed. 
         [0048]      FIG. 4  is a diagram illustrating a structure of a wireless communication apparatus using a 2×2 LOS-MIMO according to an exemplary embodiment of the present disclosure. 
         [0049]    Referring to  FIG. 4 , the interval between the transmit antennas TxANT 1  and TxANT 2  may be assumed to be D 1 , and the interval between the receive antennas RxANT 1  and RxANT 2  may be assumed to be D 2 . Also, a link distance between the TxANT 1  and the RxANT 1  is assumed to be R. In the conventional method, the per-path phases and sizes of signals received at RxANT 1  and RxANT 2  from TxANT 1  and the per-path phases and sizes of signals received at RxANT 1  and RxANT 2  from TxANT 2  may be estimated, and corrected so that the paths have a difference of 90 degrees. However, in the present method, the frequency characteristics of each path may be estimated and corrected first, and then the phase delay for each path may be corrected. 
         [0050]      FIG. 5  is a diagram illustrating signal processing according to reception characteristics in a wireless communication apparatus using a 2×2 LOS MIM according to an exemplary embodiment of the present disclosure. 
         [0051]    In the case of non-flat frequency response characteristics, even if the conventional 2×2 LOS MIMO wireless communication apparatus estimates accurate phase and size information, since both the TxANT 1  signal component and TxANT 2  signal component are present in the signal received at RxANT 1 , the SINR may deteriorate. On the contrary, referring to  FIG. 5 , a wireless communication apparatus according to an exemplary embodiment of the present disclosure can precisely separate two signal components in a receive antenna by first correcting the frequency response characteristics, so that signals may not act as interfering signals to each other. 
         [0052]      FIG. 6  is a diagram illustrating signal processing according to reception characteristics in a wireless communication apparatus using a 2×2 LOS MIMO according to an exemplary embodiment of the present disclosure when frequency response characteristics differ only in one path. 
         [0053]    Referring to  FIG. 6 , even in case that a frequency response characteristic is different for only one path, the wireless communication apparatus according to an exemplary embodiment may accurately separate the received signal into two signal components even when different frequency characteristic is generated in only the path from TxANT 2  to RxANT 1 . 
         [0054]    In the above case, although the frequency response characteristics of the separated signals are distorted, they may be compensated by channel estimation and compensation functions possessed by a general digital receiver, thereby preventing characteristic deterioration due to an interference signal. 
         [0055]      FIG. 7  is a diagram illustrating a preamble structure according to an exemplary embodiment of the present disclosure. 
         [0056]    As described above, in an exemplary embodiment of the present disclosure, a preamble section (e.g., preamble  2   a  or preamble  2   b ) according to the preamble structure of an exemplary embodiment, during which only one transmit antenna performs transmission, may be used in order to accurately estimate the phase, size, and frequency response characteristics of the LOS MIMO. 
         [0057]      FIG. 8  is a diagram illustrating a structure of a wireless communication apparatus according to an exemplary embodiment in which a feedback unit is further used. 
         [0058]    Referring to  FIG. 8 , illustrated is a structure of a wireless communication apparatus according to an exemplary embodiment in which a feedback unit implemented by applying a conventional digital signal processing block is used. 
         [0059]    According to an exemplary embodiment, a series of processes of signal detection, time synchronization, automatic gain control (AGC), automatic frequency control (AFC), phase correction, channel estimation and correction, and demodulation used in an usual digital radio receiver may be performed. Also, the LOS-MIMO estimator and coder for size and phase estimation may be added to perform a feedback function. 
         [0060]    According to an exemplary embodiment, a frequency response may be identified in a channel estimator using the preamble structure of  FIG. 7 , and information on the frequency response may be fed back to an equalizer so that correction may be performed based on the feedback information at the front of the LOS-MIMO estimator and the coder. 
         [0061]      FIG. 9  is a flowchart explaining a wireless communication method capable of increasing transmission capacity using LOS-MIMO according to an exemplary embodiment of the present disclosure. 
         [0062]    Multiple links may be configured (S 910 ). 
         [0063]    In the step  5910 , the multiple links may be configured by using at least one transmit antenna and at least one receive antenna. 
         [0064]    Frequency response characteristics of a received signal may be estimated and corrected (S 920 ). 
         [0065]    In the step  5920 , frequency response characteristics of the signal received at each receive antenna from the at least one transmit antenna may be estimated and corrected. 
         [0066]    Phases and sizes may be estimated and compensated (S 930 ). 
         [0067]    According to an exemplary embodiment, phase and size may be estimated and compensated so that a path difference between the signals received from the respective transmit antennas becomes 90 degrees. 
         [0068]    According to an exemplary embodiment, a frequency response of a signal received from each of the transmit antennas may be estimated and corrected using the channel estimation information received from the channel estimator. 
         [0069]    According to an exemplary embodiment, a channel estimation and correction step may be performed to estimate and correct the multipath frequency response of the signal received from each transmit antenna and to compensate the frequency response characteristic of the corrected signal. 
         [0070]    The methods according to exemplary embodiments of the present disclosure may be implemented as program instructions executable by a variety of computers and recorded on a computer readable medium. The computer readable medium may include a program instruction, a data file, a data structure, or a combination thereof. The program instructions recorded on the computer readable medium may be designed and configured specifically for the present disclosure or can be publicly known and available to those who are skilled in the field of computer software. Examples of the computer readable medium may include a hardware device such as ROM, RAM, and flash memory, which are specifically configured to store and execute the program instructions. Examples of the program instructions include machine codes made by, for example, a compiler, as well as high-level language codes executable by a computer, using an interpreter. The above exemplary hardware device can be configured to operate as at least one software module in order to perform the operation of the present disclosure, and vice versa. 
         [0071]    While the embodiments of the present disclosure and their advantages have been described in detail above, it should be understood that various changes, substitutions and alterations may be made herein without departing from the scope of the disclosure. 
         [0072]    A number of examples have been described above. Nevertheless, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.