KR102127119B1 - Massive antenna hybrid half/full-duplex device and method - Google Patents

Abstract

According to the present invention, a large-scale antenna hybrid full-duplex/half-duplex apparatus and a method thereof are disclosed. According to the present invention, a macro-cell of a heterogeneous cellular network system having at least one small cell and a wireless backhaul link comprises a macro-cell MIMO antenna and a macro-cell circulator. The macro-cell circulator uses an antenna corresponding to the number of small cells (S) among macro-cell MIMO antennas in a first time period for transmission, sets the remaining M_rx antennas to be used for reception, uses an antenna corresponding to the number of small cells (S) among the macro-cell MIMO antennas for reception in a second time period, and sets the remaining M_tx antennas to be used for transmission. According to the present invention, wireless backhaul communication with excellent channel capacity performance is possible in a heterogeneous network system.

Description

Massive antenna hybrid full-duplex/half-duplex device and method {MASSIVE ANTENNA HYBRID HALF/FULL-DUPLEX DEVICE AND METHOD}

The present invention relates to a large-scale antenna hybrid full-duplex/half-duplex apparatus and method, and more specifically, to communicate in full-duplex mode when the antenna has more than the critical antenna number, and to communicate in a half-duplex mode when the antenna has less than the critical antenna number A large-scale antenna hybrid full-duplex/half-duplex apparatus and method.

To meet the ever-increasing demand for wireless data, several advanced communication technologies are being developed. Among these technologies, massive multiple-input multiple-output (MIMO), full-duplex (FD) communication, and heterogeneous networks (HetNet) are emerging.

Massive MIMO (MIMO) includes base stations (BSs) with hundreds of antenna rows, far greater than the number of user terminals (UTs). Many of the antenna rows can emit energy with a precise focus on the desired customer terminal, resulting in a significant improvement in energy efficiency (EE). In addition, the use of large-scale MIMO can significantly reduce noise effects, eliminate fast fading and interference, and increase spectral efficiency (SE).

In-band full-duplex (FD) communication is another technology that brings a lot of attention in the field of communication research. In an FD system, a base station (BS) transceiver simultaneously transmits and receives using the same frequency band. As a result, the channel capacity is theoretically doubled as half-duplex (HD) communication. However, instead of potentially doubling the channel capacity, magnetic interference (SI) occurs where leakage of the transmitted signal affects the received signal. Therefore, additional spatial and temporal techniques are needed to offset SI.

On the other hand, in the case of large-scale MIMO using FD, the SI gradually decreases as the number of antennas increases infinitely without using a complicated SI removal method.

In order to efficiently provide coverage, which is a range in which information can be transmitted and received, cellular networks have traditionally been used efficiently. However, as the number of customer terminals (UTs) increases, energy efficiency (EE) and frequency efficiency (SE) decrease rapidly. In order to solve this problem, a heterogeneous network (HetNet) is being researched.

Heterogeneous networks (HetNet) have a multi-cell structure in which a large number of low-power small cells (SCs) are superimposed in a high-power macro cell (MC). Heterogeneous networks take advantage of the fact that most communications occur locally, and service requests are made by stationary customer terminals with little mobility. If a heterogeneous network is implemented, the distance between the customer terminals (USs) and the base stations (BSs) is reduced, thus reducing path loss, reducing battery consumption, and eventually increasing energy efficiency (EE) and frequency efficiency (SE). .

Heterogeneous networks use high-speed backhaul links for data transmission of small cells (SCs), as well as control and coordination between small cells (SCs) and macro cells (MC). Optical communication provides the reliable and high data rates required for backhaul links. However, it is very difficult to install an optical cable in every small cell (SC), it is expensive, and it is difficult to respond flexibly. Thus, a large-scale MIMO macrocell (MC) is wireless in a two-tier heterogeneous network that provides services to mobile customer terminals (UTs) with a single antenna and small cells (SCs) with multiple single antennas. Backhaul is being studied.

In Patent Registration No. 10-1802078, “A wireless communication system using a variable full-duplex method and a method for improving communication performance using the same”, the relay node detects and compares the channel status, and compares the full-duplex (FD) method and the half-duplex (HD) according to the threshold A method for reducing power consumption and improving communication performance by selecting a communication method is disclosed. However, it is related to cooperative communication using a relay node, not a backhaul link of a heterogeneous network.

In Patent Publication No. 10-2017-0113225, “Full-duplex wireless backhaul system using Massive MIMO,” the communication state is monitored in a backhaul signal transmission method between base stations having a large-scale MIMO antenna, and a part of the antenna is transmitted or received in a reception mode. A method for converting to a mode is disclosed. However, the communication method is made in full-duplex (FD) and half-duplex (HD) is not considered.

Patent Registration No. 10-1802078 “Wireless communication system using variable full-duplex method and communication performance improvement method using the same” Patent Publication No. 10-2017-0113225 “Full Duplex Wireless Backhaul System Using Massive MIMO”

An object of the present invention is to provide an apparatus and method for selecting a full duplex/half duplex mode so that the total channel capacity of a backhaul base station in a heterogeneous network is excellent.

It is an object of the present invention to provide a large-scale antenna hybrid full-duplex/half-duplex apparatus and method with excellent total channel capacity of a backhaul base station in a heterogeneous network and low transmission power.

An object of the present invention is to provide an apparatus and method for selecting a full-duplex/half-duplex mode according to the number of antennas used for reception among large-scale MIMO antennas so that the total channel capacity of a backhaul base station in a heterogeneous network is excellent.

Another object of the present invention is to provide an apparatus and method for selecting an optimal pilot length capable of maximizing frequency efficiency.

The objects of the present invention are not limited to the objects mentioned above, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

According to one aspect for achieving the above object, the present invention includes a macrocell MIMO antenna, a macrocell circulator and a macrocell control unit in a macrocell of a heterogeneous cellular network system having one or more small cells and a wireless backhaul link. .

The macrocell circulator uses an antenna corresponding to the small cell number S among the macrocell MIMO antennas in a first time period for transmission, and sets the remaining M _rx antennas for reception, and a second time period. In the macro cell MIMO antenna, an antenna corresponding to the number of small cells S is used for reception, and the remaining M _tx antennas are set to be used for transmission.

In the first time period, if the number of receive antennas M _rx of the macro cell MIMO antenna is smaller than the receive antenna threshold M _rx0 , the macro cell circulator uses all of the macro cell MIMO antennas for transmission in the first time period. It can be set to be used to receive all of the macro cell MIMO antenna in the second time interval.

The reception antenna threshold value M _rx0 of the macro cell can be obtained by Equation (25).

[Equation 25]

이고, p₁ 은 스몰셀 송신 전력이고, p₂ 는 매크로셀 송신 전력이고, σ_m ² 은 매크로셀 내의 자기간섭 채널의 세기이고,

(A=1) 이고, τ_p 는 파일럿 시퀀스의 길이이고, p_τ 는 파일럿 전력이고, β_1k 는 대규모 페이딩 효과이다.)(From here,

, P ₁ is the small cell transmission power, p ₂ is the macro cell transmission power, σ _m ² is the strength of the self-interference channel in the macro cell,

(A=1), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _1k is a large-scale fading effect.)

In the first time period, when the intensity of the self-interference (SI) of the macro cell MIMO antenna is greater than the self-interference threshold value σ _m,0 ² , the macro cell circulator, the macro cell MIMO antenna in the first time period It is possible to set all to be used for transmission, and to use all of the macro cell MIMO antenna for reception in the second time period.

According to another aspect for achieving the above object, the present invention includes a small cell MIMO antenna, a small cell circulator, and a small cell control unit in one or more small cells of a heterogeneous cellular network system having a macro cell and a wireless backhaul link.

The small cell circulator is configured to use one antenna among the small cell MIMO antennas for transmission in a first time period, and use the remaining N _rx antennas for reception, and among the small cell MIMO antennas for a second time period. One antenna is used for reception and the remaining N _tx antennas are configured for transmission.

In the first time period, if the number of receive antennas N _rx of the small cell MIMO antenna is smaller than the receive antenna threshold N _rx0 , the small cell circulator uses all of the small cell MIMO antennas for reception in the first time period. In the second time period, the small cell MIMO antenna may be set to be used for transmission.

The reception antenna threshold value N _rx0 of the small cell may be obtained by Equation (27).

[Equation 27]

이고,

이고, p₁ 은 스몰셀 송신 전력이고, p₂ 는 매크로셀 송신 전력이고, σ_s,k ² 는 스몰셀 내의 자기간섭 채널의 세기이고, σ_c,kj ² 는 스몰셀간 간섭 채널의 세기이고,

(A=2) 이고, τ_p 는 파일럿 시퀀스의 길이이고, p_τ 는 파일럿 전력이고, β_2k 는 대규모 페이딩 효과이다.)(From here,

ego,

, P ₁ is the small cell transmit power, p ₂ is the macro cell transmit power, σ _s,k ² is the strength of the self-interference channel in the small cell, and σ _c,kj ² is the strength of the inter-small cell interference channel,

(A=2), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _2k is a large-scale fading effect.)

In the case of the macro cell or the small cell, when the number S of the small cells is 4 or more, the pilot length τ _p may be double the number of the small cells.

The macro cell or the small cell, the pilot length τ _p may be selected as a value that maximizes the R _SE value of Equation 32 from among values that are two times or more of the small cell number S and less than or equal to the coherence length T.

[Equation 32]

(Here, R _k is the channel capacity of the full duplex wireless backhaul link of the macrocell in the first time period and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the first time period and the second time period. This is the sum of the channel capacity of the full duplex wireless backhaul link of the macro cell and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the second time period, where τ _p is the length of the pilot sequence.)

According to another aspect for achieving the above object, the present invention is a method for communicating a macro cell of a heterogeneous cellular network system having one or more small cells and a wireless backhaul link, wherein the macro cell circulator is the small cell among the macro cell MIMO antennas. Setting an antenna corresponding to the number to be used for transmission and setting the remaining M _rx antennas to be used for reception; Receiving data transmitted from a small cell through the M _rx antennas among the macro cell MIMO antennas in a first time period; Setting the macrocell circulator to use the antenna corresponding to the number of small cells among the macrocell MIMO antennas for reception and setting the remaining M _tx antennas to be used for transmission; And transmitting data to the small cell using the M _tx antennas among the macro cell MIMO antennas in a second time period.

The communication method of the macro cell may include comparing, in the first time period, the number of receive antennas M _rx of the macro cell MIMO antenna and the receive antenna threshold M _rx0 ; In the first time period, if the number of receive antennas M _rx of the macro cell MIMO antenna is smaller than the receive antenna threshold M _rx0 , setting the macro cell circulator to use all macro cell MIMO antennas for transmission; Transmitting data to the small cell in the first time period using the macro cell MIMO antenna; Setting the macrocell circulator to use all macrocell MIMO antennas for reception; And receiving data transmitted from a small cell using the macro cell MIMO antenna in a second time period.

The communication method of the macro cell may further include the step of obtaining a reception antenna threshold value M _rx0 of the macro cell by Equation (25).

The communication method of the macro cell may include comparing _, in the first time period, the intensity of self-interference and the threshold of self-interference σ _m,0 ² of the macro cell MIMO antenna; In the first time period, if the intensity of the self-interference of the macrocell MIMO antenna is greater than the self-interference threshold σ _m,0 ² , setting the macrocell circulator to use all the macrocell MIMO antennas for transmission. ; Transmitting data to the small cell in the first time period using the macro cell MIMO antenna; Setting the macrocell circulator to use all macrocell MIMO antennas for reception; And receiving data transmitted from a small cell using the macro cell MIMO antenna in a second time period.

According to another aspect for achieving the above object, the present invention is a method for communicating one or more small cells of a heterogeneous cellular network system having a macro cell and a wireless backhaul link, wherein the small cell circulator is one antenna among the small cell MIMO antennas. Is set to be used for transmission and the remaining N _rx antennas are used for reception; Receiving data transmitted from the macro cell with the N _rx antennas among the small cell MIMO antennas in a first time period; Setting the small cell circulator to use one antenna among the small cell MIMO antennas for reception and setting the remaining N _tx antennas to be used for transmission; And transmitting data to the macrocell using the N _tx antennas among the small cell MIMO antennas in a second time period.

The communication method of the small cell may include comparing the number of receiving antennas N _rx of the small cell MIMO antenna and the receiving antenna threshold value N _rx0 in the first time period; In the first time period, when the number of receive antennas N _rx of the small cell MIMO antenna is smaller than the receive antenna threshold N _rx0 , setting the small cell circulator to use all the small cell MIMO antennas for reception; Receiving data transmitted from the macro cell in the first time period using the small cell MIMO antenna; Setting the small cell circulator to use all small cell MIMO antennas for transmission; And transmitting data to the macrocell using the small cell MIMO antenna in a second time period.

The communication method of the small cell may further include the step of obtaining the reception antenna threshold value N _rx0 of the small cell by Equation (27).

The method for communicating the macro cell or the small cell may further include setting a pilot length τ _p to be twice the number of the small cells when the number S of the small cells is 4 or more.

In the communication method of the macro cell or small cell, a pilot length τ _p is selected as a value that maximizes the R _SE value of Equation 32 from among values that are two times or more of the number of small cells S and coherence length T or less. Step; may further include.

The large-scale antenna hybrid full-duplex/half-duplex apparatus and method according to the present invention has excellent total channel capacity and can maintain good communication quality.

The large-scale antenna hybrid full-duplex/half-duplex apparatus and method according to the present invention can maintain good communication quality with low transmission power by using multiple receive antennas in the first time period and using multiple transmit antennas in the second time period.

The large-scale antenna hybrid full-duplex/half-duplex apparatus and method according to the present invention can select a full-duplex/half-duplex mode according to the number of antennas used for reception among the large-scale MIMO antennas so that the total channel capacity is maximized.

The large-scale antenna hybrid full-duplex/half-duplex apparatus and method according to the present invention can maximize frequency efficiency by selecting an optimal pilot length.

1 is a conceptual diagram illustrating a method of implementing backhaul link wireless communication in a heterogeneous network system according to an embodiment of the present invention.
2 is a conceptual diagram showing a detailed configuration of the coherence length used in backhaul link wireless communication of a heterogeneous network system according to an embodiment of the present invention.
3 is a graph comparing the results obtained by simulation with the results obtained by mathematically calculating the achievable total transmission rate according to SNR in the first step of backhaul wireless communication in a heterogeneous network system according to an embodiment of the present invention.
4 is a graph showing a sum-rate of an uplink (UL) according to the number of macro cell (MC) receiving antennas M _rx in a heterogeneous network system according to an embodiment of the present invention.
5 is a graph showing a small cell (SC) the downlink (DL) rate total (sum-rate) according to the number of reception antennas N _rx in a heterogeneous network system according to an embodiment of the present invention.
6 is a graph showing a sum-rate of an uplink (UL) according to the size of self-interference (SI) in a heterogeneous network system according to an embodiment of the present invention.
FIG. 7 is a graph showing a sum-rate of downlink (DL) according to the magnitude of self-interference (SI) and small-cell (SC-to-SC) interference in a heterogeneous network system according to an embodiment of the present invention. to be.
8 is a graph showing a total transmission rate of uplink (UL) and downlink (DL) according to the number of receive antennas in a heterogeneous network system according to an embodiment of the present invention.
9 is a graph showing power for obtaining a constant uplink (UL) and downlink (DL) transmission rate in a heterogeneous network system according to a change in the number of receiving antennas according to an embodiment of the present invention.
FIG. 10 is a graph comparing the results obtained through the simulation with the results obtained through the equation for the achievable total transmission rate according to the SNR in the second step of the backhaul link wireless communication of the heterogeneous network system according to an embodiment of the present invention.
11 is a graph showing the overall spectral efficiency (SE) for a pilot length for several small cell numbers S in a heterogeneous network system according to an embodiment of the present invention.
12 is a graph showing the comparison of the overall spectrum efficiency (SE) for SNR in the case of a fixed pilot length and the case of an optimized pilot length in a heterogeneous network system according to an embodiment of the present invention.
13 is a flowchart illustrating a method for communicating a macro cell in a heterogeneous network system according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings and the contents described below. However, the present invention is not limited to the embodiments described herein, but may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed contents are thorough and complete and that the spirit of the present invention is sufficiently conveyed to those skilled in the art. Throughout the specification, the same reference numbers refer to the same components. Meanwhile, the terminology used herein is for describing the embodiments and is not intended to limit the present invention. In the present specification, the singular form also includes the plural form unless otherwise specified in the phrase. As used herein, "comprises" and/or "comprising" refers to the presence of one or more other components, steps, operations and/or elements in which the mentioned component, step, operation and/or element is present. Or do not exclude additions.

A channel is a physical channel used to send information from one place to another.

The channel capacity (achievable rate) refers to the maximum achievable capacity that information can be transmitted in a channel without generating an error, and is simply expressed by reducing it to a rate. In this specification, the transmission rate and the channel capacity are used interchangeably.

The macro cell (MC) base station and the small cell (SC) base station in which wireless backhaul communication is performed are simply expressed as a macro cell (MC) and a small cell (SC), respectively, and a full-duplex (FD) mode system and a half-duplex (HD) mode system are also provided. It can be briefly expressed in full-duplex (FD) mode and half-duplex (HD) mode.

σ _m ² , σ _s,k ² , σ _c,kj ² are self-interference (SI) channels in the macrocell MC, self-interference (SI) channels in the k-th small cell SC, and k-th small cell, respectively. It is the dispersion of elements representing the interference channel from the j th small cell (SC) in (SC), and represents the respective intensity.

The coherence interval refers to a time when the channel shows uniform characteristics, and can be expressed as a coherence interval and a coherence time.

Hereinafter, a large-scale antenna hybrid full-duplex/half-duplex apparatus and method according to an embodiment of the present invention will be described in detail with reference to the drawings.

1 is a conceptual diagram illustrating a method of simultaneously implementing wireless power and information transmission in a cooperative relay network according to an embodiment of the present invention.

In the present invention, a heterogeneous network (HetNet) considering a wireless backhaul link using a massive multiple-input multiple-output (MIMO) and full-duplex (FD) mode ) Is initiated.

In Figure 1a, the heterogeneous network system 100 is composed of a macro cell (MC) 110 and small cells (SCs) 130 and 150. The area of the macro cell overlaps the area of the small cells. The macro cell 110 has a dedicated optical cable backbone link, but the small cells 130 and 150 are connected through a wireless backhaul link with the macro cell. The macro cell 110 has a macro cell base station (BS) 111, and the small cells 130 and 150 also have base stations 131 and 151, respectively. Hereinafter, the macro cell base station (MC BS) is simply indicated as a macro cell (MC), and the small cell base station is also simply indicated as a small cell.

The macro cell MC includes a macro cell MIMO antenna, a macro cell circulator, and a macro cell control unit. The small cell SC also includes a small cell MIMO antenna, a small cell circulator, and a small cell control unit.

Data communication according to an embodiment of the present invention consists of two phases.

In the first step shown in FIG. 1A, the base stations of the macro cell (MC) and the small cell (SC) are composed of many receive antennas and fewer transmit antennas. In the first step, the base stations of the macro cell (MC) and the small cell (SC) provide uplink (UL) access to user terminals (UTs) by a plurality of receiving antennas.

The macro cell 111 is provided with transmission antennas 112 and 113 according to the number S of small cells. The remaining M _rx antennas 114, ..., 116, 117 operate as receive antennas. The receiving antennas receive data from the customer terminal 119 and the small cell's transmit antennas 132,152.

The small cell 130 on the right operates with one transmit antenna 132 and N _rx receive antennas 134, ..., 137. The receiving antennas receive data from the customer terminal 139 and the macro cell's transmit antenna 112. The same can be applied to the small cell 150 on the left.

When the first step is over, the receive antenna operates as a transmit antenna and the transmit antenna operates as a receive antenna by a circulator that is a transmit/receive switch.

In the second stage heterogeneous network 200 shown in FIG. 1B, many transmit antennas and fewer receive antennas are implemented in the base stations of the macro cell 210 and the small cells 230 and 250. The configuration of the second step may provide downlink (DL) access to customer terminals (UTs) by multiple transmit antennas of the base stations of the macro cell (MC) and the small cell (SC).

The macro cell base station 211 includes reception antennas 212 and 213 in accordance with the number of small cells S. The remaining antennas 214, ..., 216, 217 act as transmit antennas. The transmitting antennas transmit data to the customer terminal 219 and the receiving antennas 232 and 252 of the small cell.

The small cell base station 231 on the right operates with one receiving antenna 232 and multiple transmitting antennas 234, ..., 237. The transmitting antennas transmit data to the customer terminal 239 and the receiving antenna 212 of the macro cell. The same can be applied to the small cell base station 251 on the left.

2 is a conceptual diagram showing a detailed configuration of the coherence length used in backhaul link wireless communication of a heterogeneous network system according to an embodiment of the present invention.

Referring to FIG. 2, in a coherence interval T, a τ _p symbol is used for channel training through pilot sounding, and the remaining time slots are obtained from a first time interval (first step) for data communication. It is divided equally into 2 time periods (second stage).

By assuming a time division duplex (TDD) protocol and using the channel reciprocal principle, the same channel estimate used for data decoding during the first phase (first time interval) is transmitted in the second phase (second time interval). For precoding (precoding) data can be applied.

During the first step, the macro cell MC has many receive antennas M _rx and fewer transmit antennas M _tx . The number of active transmit antennas is selected to be equal to the number S of small cells. That is, M _rx >> M _tx = S.

In the first step, the small cell SC has many receive antennas N _rx and a single transmit antenna. That is, N _rx >> N _tx = 1.

When the second step starts, the circulator switches the roles of the transmitting antenna and the receiving antenna in both the macro cell (MC) and the small cell (SC). That is, the macro cell MC has many transmit antennas M _tx and fewer receive antennas M _rx . That is, M _tx >> M _rx = S.

In the second step, each small cell SC has a number of transmit antennas Ntx and a single receive antenna. That is, N _tx >> N _rx = 1.

First step

Referring to FIG. 1A, each small cell (SC) base station transmits its data to a macro cell (MC) base station. At the same time, the k th transmit antenna of the macro cell (MC) base station is used to transmit independent data to the k th small cell (SC) base station.

Since the communication is in full-duplex (FD) mode, the macro cell MC receives not only the desired signal from the small cell SC (black solid arrow) but also the macro cell MC's own transmission signal (red dotted arrow) to self-interference. (SI).

Similarly, each small cell SC is transmitted from a signal (red dotted arrow) and other small cells SCs transmitted from the small cell itself in addition to a transmission signal (black dotted arrow) from the macro cell MC that is desired to receive. The unintended transmission signal (blue dotted arrow) of the receiver is received together, causing interference between self-interference (SI) and small cells (SC-to-SC).

If the signal transmitted from the k th small cell (SC) to the macro cell (MC) is x _1k , and the signal transmitted from the macro cell (MC) to the k th small cell (SC) is x _2k , x _1k and x _2k is an independent and identically distributed (iid) complex Gaussian random variable with mean 0 and variance 1.

Considering the interference, the signal y _1k received from the signal transmitted from the k th small cell SC to the macro cell MC can be expressed by Equation 1, and the k th small from the signal transmitted from the macro cell MC The signal y _2k received from the cell SC can be expressed by Equation (2).

[Equation 1]

[Equation 2]

Here, p ₁ represents the small cell (SC) transmission power, and p ₂ represents the macro cell (MC) transmission power. Channel vector h _lk , h _2k Denotes a channel between a macrocell (MC) in a k-th small cell (SC) and a channel between a k-th small cell (SC) in a macrocell (MC), considering the fading effect of a small scale and a large scale, on average 0 And distributions with independent Gaussian (iid) complex Gaussian random variables with variances of β _1k I _Mrx and β _2k I _Nrx respectively. At this time, β _1k and β _2k show a large-scale fading effect, and can be assumed to be constants in several coherence intervals.

G _m , g _s,k , g _c,kj The interference from the self-interference (SI) channel in the macrocell MC, the self-interference (SI) channel in the k-th small cell SC, and the j-th small cell SC in the k-th small cell SC, respectively. Represents a channel, and the elements are independent Gaussian (iid) complex Gaussian random variables with mean 0 and variance σ _m ² , σ _s,k ² , and σ _c,kj ² respectively.

Rayleigh fading assumptions can be applied in the self-interference (SI) channel. When the transmitting antenna and the receiving antenna are installed at appropriate intervals, a shielding plate is installed between the antennas, or the hardware self-interference (SI) extinction technology is applied, residual interference is distributed by Rayleigh. Similarly, the same assumption can be applied to a small-cell (SC-to-SC) interference channel. That is, σ _m ² is the intensity of self-interference (SI) in the macro cell MC, and σ _s,k ² and σ _c,kj ² are the self-interference (SI) and the k-th small cell SC, respectively. It can be interpreted as the intensity of small-cell (SC-to-SC) interference.

On the other hand, n _lk and n _2k represent the reception noise vectors of the macro cell (MC) and the k th small cell (SC), respectively, and each element has an average of 0 and the variance of 1 is independent independent distribution (iid) complex Gaussian random variable. to be. r _lk ^H And r _2k ^H denote a macro cell (MC) and a k th small cell (SC) receiving filter, respectively. x ₂ is [x ₂₁ , x ₂₂ , ..., x _2S ] ^T.

Second stage

Referring to FIG. 1B, in the second step, the macro cell MC precodes data and transmits each data to all small cells SC. At the same time, each small cell (SC) precodes its data and transmits it to a corresponding receiving antenna of the macro cell (MC).

The k-th reception antenna of the macro cell MC receives a desired signal from the corresponding k-th small cell SC, but also receives a macro cell MC transmission signal causing self-interference (SI). Likewise, each small cell (SC) receives a desired signal from the macro cell (MC), but its own transmission signal causing self-interference (SI) and other small cells causing interference between small cells (SC-to-SC). Unintended signals from cells SC are also received.

Since the time division duplex (TDD) protocol is used, the downlink (DL) channel of the second stage is the same as the conjugate transpose of the uplink (UL) channel of the first stage, and vice versa.

If the signal transmitted from the k th small cell SC to the k th antenna of the macro cell MC is b _1k , and the signal transmitted from the macro cell MC to the k th small cell SC is b _2k , b _1k and b _2k are independent Gaussian (iid) complex Gaussian random variables with mean 0 and variance 1.

In consideration of interference, the signal w _1k received at the k-th receiving antenna of the macro cell MC may be expressed by Equation 3, and the signal w _2k received at the k-th small cell SC may be expressed by Equation 4. have.

[Equation 3]

[Equation 4]

Here, q _m,k , q _s,k , q _c,kj vectors are self-interference (SI) channel of the k-th receiving antenna of the macrocell MC, and self-interference in the k-th small cell (SC), respectively. SI) channel, represents a small-cell (SC-to-SC) interference channel from the j-th small cell (SC) in the k-th small cell (SC), the elements have an average of 0 and a variance of η _m,k, respectively Independent identity distribution (iid) complex Gaussian random variables with ² , η _s,k ² , and η _c,kj ² .

On the other hand, ν _1k is the noise of the macrocell (MC) receiving antenna, ν _1k is the noise of the k th small cell (SC) receiving antenna, and the mean is 0 and the variance is 1, the independent identifiable distribution (iid) complex Gaussian random variables. . F ₂ is a macro cell (MC) precoding matrix [ f ₂₁ , f ₂₂ , ..., f _2S ], and f _1k is a k th small cell (SC) precoding vector. b ₂ is [b ₂₁ , b ₂₂ , ..., b _2S ] ^T.

Channel estimation

Obtaining complete channel state information (CSI) is critical to fully unlocking the potential of large-scale MIMO and full-duplex (FD) communication technologies. However, both the macro cell (MC) and the small cell (SC) can only obtain an estimate of the actual channel vector. Therefore, it is more realistic to assume that the channel state information (CSI) is incomplete.

Referring to FIG. 2, a pilot sequence is used for channel estimation in large-scale MIMO. For a coherence interval of length T consisting of symbols, with pilot power p _τ , each small cell SC has a pilot sequence of length τ _p for uplink (UL) channel estimation. Transmitting to the macro cell (MC), the macro cell (MC) transmit antenna transmits a pilot sequence of the same length to the small cells (SCs) for downlink (DL) channel estimation.

To avoid pilot contamination in a time division duplex (TDD) system, mutually orthogonal pilot sequences are used for channel estimation. For this, for each coherence time T, the length τ _p of the pilot sequence should be greater than twice the number S of the small cells SC. That is, τ _p ≥ 2S.

는 수학식 5와 같이 나누어 표현할 수 있다.A true channel vector is obtained by correlating the obtained training signals with corresponding pilot sequences and using a minimum mean square error (MMSE) channel estimate.

Can be expressed by dividing as in Equation 5.

[Equation 5]

및 추정치 에러 벡터

는 상호 독립적인 벡터이다. 첨자 A는 통신 방향에 따라, k 번째 스몰셀(SC)에서 매크로셀(MC)로의 방향은 1이고, 매크로셀(MC)에서 k 번째 스몰셀(SC)로의 방향은 2이다.

와

벡터의 원소들은 평균이 0이고 분산은 각각 수학식 6과 수학식 7로 정의되는 독립항등분포(i.i.d.) 복소 가우시안 랜덤 변수이다. Estimate vector here

And estimate error vector

Is a mutually independent vector. In the subscript A, the direction from the k th small cell SC to the macro cell MC is 1, and the direction from the macro cell MC to the k th small cell SC is 2.

Wow

The elements of the vector are independent independent distribution (iid) complex Gaussian random variables defined by the equations (6) and (7), with an average of 0 and variance.

[Equation 6]

[Equation 7]

Signal detection and precoding

In the first step, a maximum ratio combining (MRC) receive filter is used, and in the second step, a maximum ratio transmission (MRT) precoding is applied. Linear processing techniques such as MRC/MRT can achieve high frequency spectrum efficiency (SE) when using many antennas.

Further, the maximum ratio processing can be implemented by a dispersion method. That is, each antenna can amplify the received signal using a conjugate of the channel without sending the entire baseband signal to the base station for signal processing.

The MRC reception filter can be expressed as Equation (8).

[Equation 8]

The precoding matrix used by the macro cell MC can be obtained by Equation (9).

[Equation 9]

는 전력 정규화 인자(power normalization factor)이고,

는 추정된 채널 행렬이다.From here,

Is the power normalization factor,

Is an estimated channel matrix.

Since there is no cooperation between the small cells SC, each small cell SC independently precodes data, so channel state information CSI of the other small cells SC is not required.

The precoder used by the k-th small cell SC is expressed by Equation (10).

[Equation 10]

는 k 번째 스몰셀(SC)에서의 전력 정규화 인자(power normalization factor)이다. From here,

Is a power normalization factor in the k th small cell SC.

Because the self-interference (SI) and the small-cell (SC-to-SC) interference nulling strategy are not used, the channel state information of the self-interference (SI) channel and the small-cell (SC-to-SC) channel ( CSI) is not required.

Channel capacity

To obtain the uplink/downlink channel rate (achievable rate) of a large-scale MIMO, the received signal is expressed by a mean gain, and the desired transmission signal is added with effective noise, which is not correlated. Is amplified.

Since the effective noise entropy has an upper limit by Gaussian noise entropy, the lower limit of the channel capacity can be obtained using this.

In the first step, in order to calculate the uplink (UL) channel capacity (achievable rate) in the macro cell MC, Equation 11 may be obtained by referring to Equation 1.

[Equation 11]

Here, the first term is the desired signal, and the second term is the effective noise defined by the following equation.

이다.In Equation 11, the effective noise and the desired signal are not correlated with each other. That is, the expected value

to be.

Since independent Gaussian noise with the same variance is the worst case of uncorrelated addition noise, the achievable rate of the macrocell (MC) uplink (UL) for the k th small cell (SC) is mathematical Equation 12 is given.

[Equation 12]

Here, the desired signal power in the macro cell (MC) base station (desired signal power), effective channel variance (variance), multi-cell interference, magnetic interference (SI), and noise amplification factors are defined as follows.

In the first step, the downlink (DL) channel capacity (achievable rate) from the macro cell (MC) to the k th small cell (SC) can also be expressed as shown in Equation (13) by using a similar approach to Equation (2) above. have.

[Equation 13]

Here, each parameter is defined as in the following equation, as in equation (12).

The last parameter added is a small-cell (SC-to-SC) interference term.

In the second step, Equation 3 is used for the uplink (UL), and Equation 4 is used for the downlink (DL), and the method used in the first step is applied to obtain an achievable rate. Can.

In the second step, the channel capacity (achievable rate) of the k-th receiving antenna of the macro cell MC can be expressed by Equation (14).

[Equation 14]

Here, each parameter is defined as follows.

In the second step, the channel capacity (achievable rate) in the k-th small cell SC is obtained by Equation 15.

[Equation 15]

Here, each parameter is defined as follows.

Large system analysis

In order to obtain an analytically closed equation for the channel capacity (achievable rate), Equations 12 to 15 can be approximated in a large antenna area.

In the first step, M _tx in the macro cell MC is kept constant as the number of small cells S while M _rx → ∞ may be approximated. Each small cell (SC) has a single transmit antenna and can be approximated by N _rx → ∞.

In the second step, M _tx → ∞ and N _tx → ∞ may be approximated with a fixed receiving antenna.

Using the results of the law of large number and random matrix theory, the closed-form solution to the uplink (UL)/downlink (DL) channel capacity (achievable rate) is It can be obtained as theorem 1 and theorem 2.

[Clearance 1]

In the first step, when the MRC reception filter is adopted for both the macro cell (MC) and the small cell (SC), even if it has incomplete channel state information (CSI), the macro cell (MC) and the k th small cell (SC) ), the channel capacity of the full-duplex (FD) wireless backhaul link can be expressed by Equation 16 and Equation 17, respectively.

[Equation 16]

[Equation 17]

[Theorem 2]

In the second step, in case of performing MRT processing with incomplete channel state information (CST) in the macro cell (MC) and the small cell (SC), the full-duplex (FD) radio in the macro cell (MC) and each small cell (SC) The channel capacity (achievable rate) of the backhaul link can be expressed by Equation 18 and Equation 19, respectively.

[Equation 18]

[Equation 19]

In Theorem 1, as can be seen from Equation 16 and Equation 17, the channel capacity (achievable rate) includes channel estimation accuracy, large-scale fading coefficients, total small cell (SC) number, receiving antenna number, and self-interference (SI). It is a function of several factors, including intensity, small-cell (SC-to-SC) interference intensity, and transmit power.

In Equation 16, the uplink (UL) channel capacity (achievable rate) can be increased by increasing the number of receive antennas M _rx of the macro cell MC, and in Equation 17, the downlink (DL) channel capacity (achievable) It can be seen that the rate) can be increased by increasing the number N _rx of the reception antennas of the k-th small cell SC. That is, by increasing the number of receiving antennas in the macro cell (MC) and the small cell (SC), it is possible to overcome the effects of self-interference (SI) and small-cell (SC-to-SC) interference. On the other hand, the achievable rate improves with increasing channel estimation accuracy.

In Equation 18 of Theorem 2, it can be seen that the uplink (UL) channel capacity (achievable rate) in the macrocell (MC) is improved by increasing the number N _tx of the small cell (SC) transmit antennas. In addition, since the increase in the number of small cells (SC) increases the strength of the self-interference (SI) term, the uplink (UL) channel capacity (achievable rate) is greatly affected by the number of small cells S.

In Equation 19, a similar analysis is possible for the downlink (DL) channel capacity (achievable rate) in the k th small cell SC.

Increasing the number of small cells (SC) increases the intensity of small-cell (SC-to-SC) interference, and consequently affects the achievable rate of the k th small cell (SC). However, since increasing the number of small cells (SC) generally improves the overall sum-rate of the network, a compromise must be determined for the sum-rate.

Comparison of full-duplex (FD) mode and half-duplex (HD) mode

Using the closed-form equations previously obtained, the performance of achievable rates in full-duplex (FD) mode and half-duplex (HD) mode of a wireless communication system according to an embodiment of the present invention is compared.

According to an embodiment of the present invention, it is possible to provide a hybrid full-duplex (FD)/half-duplex (HD) system capable of changing modes according to interference strength and number of antennas.

When operating in the half-duplex (HD) mode, the transceiver of the base station (BS) transmits or receives in each time slot, so only half of the total time is used for transmission. Therefore, a half-duplex (HD) mode base station uses only half the transmit power of a full-duplex (FD) mode base station.

For a fair comparison, the half-duplex (HD) mode is set to use twice the transmit power used in the full-duplex (FD) mode. Unlike full-duplex (FD) mode, since half-duplex (HD) mode does not simultaneously transmit and receive, self-interference (SI) and small-cell (SC-to-SC) interference are not generated. However, the half-duplex (HD) mode needs to be multiplied by 1/2 before the log value in the rate expression compared to the full-duplex (FD) mode.

The channel capacity (achievable rate) of a half-duplex (HD) system ignores self-interference (SI) and small-cell (SC-to-SC) interference terms in Equations 16 to 19 regarding full-duplex (FD) channel capacity, and transmit power. Can be obtained by doubling and adding 1/2 to the front of the log.

That is, in the first step, the uplink (UL)/downlink (DL) rate in half-duplex (HD) mode may be expressed by Equation 20 and Equation 21, respectively.

[Equation 20]

[Equation 21]

In the second step, the uplink (UL)/downlink (DL) rate of the half-duplex (HD) mode may be expressed by Equation 22 and Equation 23, respectively.

[Equation 22]

[Equation 23]

Full-duplex (FD) systems are limited to self-interference (SI) and small-cell (SC-to-SC) interference, while half-duplex (HD) systems are limited by factor 1/2 before the logarithm.

In order to determine the standard for selecting the mode of the hybrid system in terms of self-interference (SI) and small-cell (SC-to-SC) interference, the achievable rate of the half-duplex (HD) mode and full-duplex (FD) mode is determined. The interference parameters to be equal must be determined.

In the case of the uplink (UL) rate in the macro cell MC, only self-interference (SI) is considered.

Then, the self-interference (SI) intensity parameter σ _m,0 ² in which the uplink (UL) rate is the same in the macro cell MC between the half-duplex (HD) mode and the full-duplex (FD) mode is Equation 16 And is obtained from Equation 20 as in Equation 24.

[Equation 24]

이다.From here,

to be.

Since the cross value in Equation 24 depends only on long-term channel statistics, it can be calculated in the macro cell MC. That is, if σ _m ² <σ _m,0 ² , it may be implemented to operate in full-duplex (FD) mode, or otherwise operate in half-duplex (HD) mode.

In addition, when long-term channel statistics are known, the number of macrocell (MC) receive antennas M _rx0 required for the full-duplex (FD) mode to be higher than the half-duplex (HD) mode may be determined by Equation (25).

[Equation 25]

이다. From here,

to be.

For the link to the macro-cell (MC) in each small cell (SC), for the construction of full-duplex (FD) mode overcome the effects of self-interference (SI) and to surpass the half-duplex (HD) mode, a receive antenna M _rx > Must be an integer with M _rx0 .

For the downlink (DL) rate in the k-th small cell (SC), the thresholds of self-interference (SI) and small-cell (SC-to-SC) interference for the hybrid method can be obtained using Equation (26). have.

[Equation 26]

로 정의된다.Here, σ _t0,k ² represents the combined effect of self-interference (SI) and small-cell (SC-to-SC) interference in the k th small cell (SC),

Is defined as

Full-duplex (FD) mode downlink (DL) when the combined effect of self-interference (SI) and small-cell (SC-to-SC) interference in the k th small cell (SC) is greater than σ _t0,k ² The rate is lower than the half-duplex (HD) mode rate.

In order for the full-duplex (FD) mode to exhibit better performance than the half-duplex (HD) mode, the number of antennas required for the k-th small cell SC may be calculated by Equation (27).

[Equation 27]

이고,

이다.From here,

ego,

to be.

In Equation 27, a mode with a better sum-rate can be selected from a full-duplex (FD) mode and a half-duplex (HD) mode according to long-term channel statistics and the number of small cells (SC).

In addition, a hybrid full-duplex/half-duplex (FD/HD) system based on long-term channel information can be designed for a small cell (SC) base station in the same manner as a macro cell (MC) base station.

Since the second step can be analyzed similarly to the first step, specific details are omitted.

According to an embodiment of the present invention, in the full duplex (FD) mode of the macro cell, the macro cell circulator transmits an antenna corresponding to the number S of small cells among the macro cell MIMO antennas in the first step (first time interval). The remaining M _rx antennas are set to be used for reception, and transmission and reception are simultaneously performed. In the second step (second time period), among the macro cell MIMO antennas, an antenna corresponding to the number S of small cells is used for reception, and the remaining M _tx antennas are set to be used for transmission.

In the full-duplex (FD) mode of the small cell, the small cell circulator uses one antenna among the small cell MIMO antennas for transmission in the first time period, and the remaining N _rx antennas are used for reception, thereby simultaneously transmitting and receiving. Conduct. In the second time period, one antenna of the small cell MIMO antenna is used for reception, and the remaining N _tx antennas are set to be used for transmission.

According to another embodiment of the present invention, in the half-duplex (HD) mode of the macrocell, the macrocell circulator uses all the macrocell MIMO antennas for transmission in the first step (first time period), and the second step In the 2nd time period), all macro cell MIMO antennas are set to be used for reception, so that reception and transmission occur at separate times.

In the half-duplex (HD) mode of the small cell, the small cell circulator uses all the small cell MIMO antennas for reception in the first time interval, and the small cell MIMO antennas are used for transmission in the second time interval, and then receives And transmit at separate times.

Power scaling law

When the accuracy of channel estimation is fixed, the transmission power can be reduced by a large number of receive antennas in the first stage and a large number of transmit antennas in the second stage.

[Bojungjori 1]

In the first step, the transmission power of the k th small cell SC and the transmission power of the macro cell MC are scaled according to p ₁ = E ₁ /M _rx and p ₂ = E ₂ /N _rx , respectively (E ₁ and E ₂ are fixed values irrespective of M _rx and N _rx ), and when M _rx and N _rx increase infinitely at the same rate, Equations 16 and 17 respectively represent Equations 28 and Equations It can be represented as 29.

[Equation 28]

[Equation 29]

[Bojungjori 2]

In the second step, when p ₁ = E ₁ /N _tx and p ₂ = E ₂ /M _tx are scaled (E ₁ and E ₂ are fixed values independent of N _tx and M _tx ), M _tx and When N _tx increases to infinity at the same speed, Equation 18 and Equation 19 may be expressed by Equation 30 and Equation 31, respectively.

[Equation 30]

[Equation 31]

In auxiliary theorem 1, for the fixed channel accuracy in the kth small cell (SC) and the macro cell (MC) and a large reception antenna, the transmission power of the kth small cell (SC) and the macro cell (MC) in the first step Even if is decreased in proportion to 1/M _rx and 1/N _rx , respectively, it is possible to maintain a constant uplink/downlink (UL/DL) rate. That is, the transmission power can be reduced to 1/M _rx and 1/N _rx while maintaining the same transmission rate.

In addition, in the auxiliary theorem 2, in the large-scale transmission antenna region in each small cell (SC) and macro cell (MC), the transmission power of the macro cell (MC) and the k th small cell (SC) is 1/M _tx , respectively. And 1/N _tx , the same channel capacity can be maintained. That is, transmission power can be reduced to 1/M _tx and 1/N _tx while maintaining the same channel capacity.

Frequency efficiency (SE) analysis

The total frequency efficiency or spectral efficiency (SE) can be defined as the sum-rate for channel use.

Referring to FIG. 2, when the coherence length of the T time slot and the pilot training slot of τ _p are obtained, the sum spectral efficiency (sum SE) may be expressed by Equation (32).

[Equation 32]

이며, 수학식 16 내지 19를 이용하여 구할 수 있다.Here, R _k is the total uplink/downlink (UL/DL) channel capacity (achievable rate) of the k th small cell (SC) in the first and second stage data transmission,

It can be obtained by using the equations 16 to 19.

In Equation 32, it can be seen that the increase in pilot length τ _p improves the channel capacity (achievable rate) while reducing the total SE.

Therefore, in order to maximize the sum SE, the pilot length τ _p can be optimized as shown in Equations 33 to 34.

[Equation 33]

[Equation 34]

The constraint of Equation (34) is to ensure that the pilot sequences used for channel estimation are orthogonal to each other.

Since the optimization problem of Equation 33 has convexity, it is possible to efficiently obtain an optimal value using a one-dimensional line search method like a bisection method.

<Example> Simulation Result-First Step

로 정의한다. Monte Carlo simulation was performed on the system disclosed in the present invention to evaluate the performance of the system. All simulations were performed for 10 ⁵ channels, and the signal-to-noise ratio (SNR) was

Is defined as

In the case of uplink (UL), unless specifically stated for the first phase (first phase), β _1k = β ₁ = 0.1, which shows a large-scale fading effect for all k, and a macro cell (MC). The magnitude of self interference (SI) at σ _m ² = 0.3.

In the case of a downlink (DL), β _2k = β ₂ = 0.1 for all k, and self interference (SI) in the k th small cell (SC) is σ _s,k ² = σ _s ² = 0.3, and inter-small (SC-to-SC) interference in the k th small cell (SC) is σ _c,k ² = σ _c ² = 0.3.

The pilot power is p _τ = 10 dB, and the pilot length is τ _p = 2S. Here, S is the number of small cells (SCs). Also, unless otherwise specified, p ₁ =p ₂ =10 dB.

3 is a graph comparing results obtained through simulation with results obtained by mathematically calculating the achievable total transmission rate according to SNR in the first step of backhaul wireless communication in a heterogeneous network system according to an embodiment of the present invention.

In order to obtain an achievable sum-rate in the first step, for all small cells (SCs), the uplink achievable rate R _m,k ⁽ Eq. 16) to each macro cell (MC) ¹⁾ was obtained, and the downlink achievable transmission rate R _s,k ⁽¹⁾ to each small cell (SC ⁾ was obtained from Equation (17). And to obtain the total sum rate (total sum-rate), uplink rate (UL rate) and downlink rate (DL rate) were added to all small cells (SCs).

The asterisk is the result of the simulation, and the solid line is the result obtained from the equation. Even in the case of a relatively small number of antennas in which the number of receive antennas of the macro cell MC is _rx = 200 and the number of receive antennas of each of the two small cells (S = 2) N _rx = 100, It can be seen that the obtained achievable sum-rate results agree well with the simulation results. That is, it can be seen that the results obtained by Equation 16 and Equation 17 of Theorem 1 can predict system performance well.

The sum-rate increases as the SNR increases, but when the SNR exceeds 14 dB, the rate begins to saturate. In addition, it can be seen that the sum-rate is improved as the number S of small cells SCs and the number of receive antennas M _rx and N _rx increase.

4 is a graph showing a sum-rate of an uplink (UL) according to the number of macro cell (MC) receiving antennas M _rx in a heterogeneous network system according to an embodiment of the present invention.

The asterisk is the result of the simulation, the solid line is the result of the full-duplex (FD) mode obtained by Equation 16, and the single-dashed line is the result of the half-duplex (HD) mode obtained by the Equation 20. In the FD mode as well as the HD mode, the sum-rate is improved as the number of macro cell (MC) receiving antennas M _rx increases.

In the FD mode, the total transmission rate decreases as the strengths of the interferences σ _m ² , σ _s ² , and σ _c ² increase. When the number S of small cells increases, it shows a high transmission rate, but because the interference between small cells increases, in order to overcome the adverse effects of self-interference (SI) and small-cell interference (SC-to-SC interference), in the FD mode, more An antenna is required.

That is, in the FD mode of FIG. 4, when the number of small cells S increases from 5 to 10, a high sum-rate is exhibited, but when the magnitude of self-interference (SI) σ _m ² increases from 0.4 to 0.5, It can be seen that a much larger number of receiving antennas is needed to overcome the interference and obtain a higher total transmission rate than the HD mode.

When the number of receive antennas M _rx is small, the total transmission rate of the FD mode is lower than the total transmission rate of the HD mode due to the effect of self-interference (SI). If the number of macro cell (MC) receiving antennas corresponding to the transmission point intersection of the FD mode and the HD mode is M _rx0 , the upload link (UL) overcomes the influence of self-interference (SI), and the FD mode has a higher transmission rate than the HD mode. The number of receiving antennas of the macro cell should be M _rx > M _rx0 . In FIG. 4, the intersection corresponding to M _rx0 is indicated by ○ .

5 is a graph showing a small cell (SC) the downlink (DL) rate total (sum-rate) according to the number of reception antennas N _rx in a heterogeneous network system according to an embodiment of the present invention.

The asterisk is the result of the simulation, the solid line is the result of the full-duplex (FD) mode obtained by Equation 17, and the single-dashed line is the result of the half-duplex (HD) mode obtained by the Equation 21. In FIG. 5, as in FIG. 4, in FD mode as well as in HD mode, the sum-rate is improved as the number of small cell (SC) receiving antennas N _rx increases.

In the FD mode, the total transmission rate decreases as the strengths of the interferences σ _m ² , σ _s ² , and σ _c ² increase. When the number S of small cells increases, it shows a high transmission rate, but because the interference between small cells increases, in order to overcome the adverse effects of self-interference (SI) and small-cell interference (SC-to-SC interference), in the FD mode, more An antenna is required.

That is, in the FD mode of FIG. 5, when the number S of small cells increases from 5 to 10, a high sum-rate is exhibited, but the magnitude of self-interference (SI) σ _s ² increases from 0.4 to 0.5, It can be seen that when the size of the small-cell interference σ _c ² increases from 0.3 to 0.4, a much larger number of receiving antennas is required to overcome the self-interference and obtain a higher total transmission rate than the HD mode.

When the number of receive antennas N _rx is small, the total transmission rate in the FD mode is lower than the total transmission rate in the HD mode due to the effects of self-interference (SI) and small-cell interference (SC-to-SC interference). If the number of small cell (MC) receive antennas corresponding to the transmission point intersection of the FD mode and the HD mode is N _rx0 , the download link (DL) overcomes the effects of self-interference and interference between the small cells, and the FD mode has a higher transmission rate than the HD mode. The number of small cell receiving antennas must be N _rx > N _rx0 . In FIG. 5, the intersection corresponding to N _rx0 is indicated by ○ .

6 is a graph showing a sum-rate of an uplink (UL) according to the size of self-interference (SI) in a heterogeneous network system according to an embodiment of the present invention.

In the case of S = 5, the asterisk is the result of the simulation, the solid line is the result of the full duplex (FD) mode, and the dashed line is the result of the half duplex (HD) mode. Since the HD system is not affected by self-interference (SI), the HD total transmission rate shows a fixed value. On the other hand, in the FD system, as the magnitude of the magnetic interference (SI) from the transmit antenna to the receive antenna of the macrocell σ _m ² increases, the total transmission rate decreases rapidly. The intersection of the HD mode and the FD mode can be accurately calculated by Equation (24).

Since the FD system shows better performance than the HD system in a low self-interference region, it is preferable to apply a hybrid FD/HD system capable of changing the operation mode according to the size of the self-interference (SI).

FIG. 7 is a graph showing a sum-rate of downlink (DL) according to the magnitude of self-interference (SI) and small-cell (SC-to-SC) interference in a heterogeneous network system according to an embodiment of the present invention. to be.

In the case of S = 5, the asterisk is the result of the simulation, the solid line is the result of the full duplex (FD) mode, and the dashed line is the result of the half duplex (HD) mode. Since the HD system is not affected by self-interference (SI), the HD total transmission rate shows a fixed value. On the other hand, in the FD system, the magnitude of self-interference (SI) _{s s} ² from the transmitting antenna of the small cell to the receiving antenna and the magnitude of inter-small (SC-to-SC) interference from the transmitting antenna of the other small cell σ _c ² As this increase, the total transmission rate decreases rapidly. The intersection of the HD mode and the FD mode can be accurately calculated by Equation (26).

Since the FD system shows better performance than the HD system in the low self-interference area, a hybrid FD/HD system that can change the operation mode according to the size of self-interference (SI) and small-cell (SC-to-SC) interference is applied. It is desirable to do.

8 is a graph showing a total transmission rate of uplink (UL) and downlink (DL) according to the number of receive antennas in a heterogeneous network system according to an embodiment of the present invention.

The size of the self-interference (SI) in the macro cell (MC) is set to σ _m ² = 0.4, and the self-interference (SI) in the small cell (SC) is σ _s,k ² = σ _s ² = 0.4, small Inter-cell (SC-to-SC) interference was also set to σ _c,k ² =σ _c ² =0.4. In addition, p ₁ = E ₁ / M _rx , P ₂ = E ₂ / N _rx , where E ₁ and E ₂ are always set to E ₁ = E ₂ = 15 dB so that the number of antennas is always constant even when the number of antennas increases. Did. The number of receiving antennas of the small cell was set to half of the number of receiving antennas of the macro cell. That is, N _rx = M _rx / 2.

The asterisk is the result of the simulation, and the solid line is the result of the full duplex (FD) mode. In each graph, the upper case is S = 5, and the lower case is S = 3. The total transmission rate increases as the number of receiving antennas increases, but it gradually becomes saturated. This is due to the balance between the effect of increasing the transmission rate with the increase in the number of receiving antennas and the effect of reducing the transmission powers p1 and p2. These results are consistent with the results of Equation 28 and Equation 29.

9 is a graph showing power for obtaining a constant uplink (UL) and downlink (DL) transmission rate in a heterogeneous network system according to a change in the number of receiving antennas according to an embodiment of the present invention.

The size of the self-interference (SI) in the macro cell (MC) and the small cell (SC) was set to σ _m ² = σ _s ² = 0.4, but the interference between the small cells (SC-to-SC) was σ _c ² = 0.2. Was set to.

In Case 1, the transmission power of the macro cell (MC) is fixed to p ₂ = 5 dB, and for the number of receive antennas M _rx of each macro cell (MC), the k th small so that the upload (UL) transmission rate becomes 1 bps/Hz. The cell SC transmission power p ₁ was determined.

When the number of macro cell reception antennas M _rx = 20, the small cell (SC) transmission power was 4.01 dB, but when the number of macro cell reception antennas was increased to M _rx = 400, the small cell transmission power was significantly reduced to -9.5467 dB. do.

When the number of small cells S is increased from 2 to 5, the self-interference of the small cells and the interference between the small cells increase, thereby increasing the small cell transmission power.

In Case 2, the kth small cell (SC) transmission power was fixed to p ₁ = 5 dB, and for each small cell (SC) receiving antenna number N _rx , the macro so that the download (DL) transmission rate was 1 bps/Hz. The cell (MC) transmission power p ₂ was determined.

As in Case 1, in Case 2, when the number of small cell reception antennas N _rx increases, the transmission power of the macro cell decreases. When the number of small cells S is increased from 2 to 5, the transmission power of the macro cell is slightly increased.

<Example> Simulation result-second step

In the case of uplink (UL), unless specifically stated for the second phase, β _2k = β ₂ = 0.1, which shows a large-scale fading effect for all k, and dispersion η _m,k ² = η _m ² =0.3.

For the downlink (DL), for all k, β _1k = β ₁ = 0.1, variance η _s,k ² = η _s ² = 0.3, variance η _c,k ² = η _c ² = 0.3 to be.

The pilot power is p _τ = 10 dB, and the pilot length is τ _p = 2S. Here, S is the number of small cells (SCs). And σ _m ² = σ _s ² = σ _c ² = 0.3.

10 is a graph comparing a result obtained by a simulation with a result obtained by mathematically calculating the achievable total transmission rate according to SNR in the second step of backhaul wireless communication of a heterogeneous network system according to an embodiment of the present invention.

In order to obtain an achievable sum-rate in the second step, for all small cells (SCs), the uplink achievable rate R _m,k ⁽ Eq. 18) to each macro cell (MC) ²⁾ was obtained, and the downlink achievable transmission rate R _s,k ⁽²⁾ to each small cell (SC ⁾ was obtained from Equation (19). And to obtain the total sum rate (total sum-rate), uplink rate (UL rate) and downlink rate (DL rate) were added to all small cells (SCs).

The asterisk is the result of the simulation, and the solid line is the result obtained from the equation. Even in the case of a relatively small number of antennas, where the number of transmit antennas of the macro cell MC is M _tx = 200 and the number of transmit antennas of each of the two small cells (S = 2) N _tx = 100, It can be seen that the obtained achievable sum-rate results agree well with the simulation results. That is, the result of the second step obtained by Equation 18 and Equation 19 of Theorem 2 is the same as the first result using the same parameters. Therefore, in the second stage, the system obtained in the first stage can be used identically.

<Example> Simulation result-Pilot length effect

The effect of pilot length τ _p on the total sum spectral efficiency (SE) of the proposed system was examined. Unless otherwise specified, the pilot power is p _τ = 0 dB, and the coherence interval is T = 50. Standard deviation β ₁ = β ₂ = 0.1, variance η _m ² = η _s ² = η _c ² = 0.3, and interference was set to σ _m ² = σ _s ² = σ _c ² = 0.3.

11 is a graph showing the overall spectral efficiency (SE) for a pilot length for several small cell numbers S in a heterogeneous network system according to an embodiment of the present invention.

For each small cell number S, the pilot length τ _p was changed to a value from 2S to T to obtain the total spectral efficiency (SE).

The overall spectral efficiency SE initially increases with the pilot length, but begins to decrease after the optimal pilot length τ _p ^* . Therefore, there is a trade-off between the overall spectrum efficiency (SE) and the pilot length that can be used for channel estimation. Therefore, it is desirable to use the optimal pilot length τ _p ^* that can maximize the overall spectral efficiency (SE). The optimum pilot length τ _p ^* can be obtained using a gradient descent method. In FIG. 11, the position corresponding to the optimal pilot length τ _p ^* is indicated by ○.

FIG. 12 is a graph comparing total spectrum efficiency (SE) for SNR in a heterogeneous network system according to an embodiment of the present invention with respect to a fixed pilot length and an optimized pilot length.

The overall spectral efficiency (SE) of the optimized pilot length τ _p ^* is higher in all SNR regions than when the pilot length is fixed at τ _p = 2S. However, as the number S of small cells increases, it can be seen that the spectral efficiency (SE) when the pilot length is fixed at τ _p = 2S approaches the case of the optimized pilot length.

13 is a flowchart illustrating a method for communicating a macro cell in a heterogeneous network system according to an embodiment of the present invention.

In the control unit of the macro cell, in the first time period, the number of receive antennas M _rx of the macro cell MIMO antenna is compared with the receive antenna threshold M _rx0 (S700).

When the number of receive antennas M _rx of the macro cell MIMO antenna of the first time period is greater than the receive antenna threshold M _rx0 , the mode operates in full-duplex (FD) mode.

In the first time interval (first step) (S710), the macrocell circulator is set to use an antenna corresponding to the number of small cells among the macrocell MIMO antennas for transmission, and the remaining M _rx antennas are set to use for reception. (S731). Among the macro cell MIMO antennas, S transmission cells are respectively transmitted to S small cells, and data transmitted from the small cells are simultaneously received at M _rx reception antennas (S733).

In the second time period (second step) (S720), the macrocell circulator is set to use an antenna corresponding to the number of small cells among the macrocell MIMO antennas, and the remaining M _tx antennas are set to be used for transmission. (S735). Among the macro cell MIMO antennas, data transmitted from S small cells are respectively received by S receiving antennas, and data are simultaneously transmitted to the small cells using M _tx antennas (S737).

If the number of receive antennas M _rx of the macro cell MIMO antenna of the first time period is smaller than the receive antenna threshold M _rx0 , the UE operates in a half-duplex (HD) mode.

In the first time period S710, the macro cell circulator is set to use all the macro cell MIMO antennas for transmission (S741). The macro cell MIMO antenna is used to transmit data to the small cell (S743).

In the second time period S720, the macro cell circulator is set to use all the macro cell MIMO antennas for reception (S745). Data transmitted from the small cell is received using the macro cell MIMO antenna (S747).

The communication method of the small cell (SC) can also be performed in a similar way to the macro cell (MC), and is apparent to those skilled in the art.

The present invention has been described in detail through representative embodiments, but those skilled in the art to which the present invention pertains can make various modifications within the limits without departing from the scope of the present invention for the above-described embodiments. Will understand. Therefore, the scope of rights of the present invention should not be limited to the described embodiments, and should be determined not only by the claims to be described later, but also by all modified or modified forms derived from the claims and equivalent concepts.

110: macro cell (MC)
111: macro cell base station
112, 113: macro cell transmit antenna
114, 116, 117: macro cell receiving antenna
119: customer terminal
130, 150: Small cell (SC)
131, 151: Small cell base station
131, 152: Small cell transmit antenna
134, 137, 154, 157: Small cell receiving antenna
139, 159: customer terminal

Claims (18)

delete In a macro cell of a heterogeneous cellular network system having one or more small cells and a wireless backhaul link,
Macro cell MIMO antenna;
Macrocell circulator; And
Includes a macro cell control unit;
The macro cell circulator,
In the first time period, an antenna corresponding to the number S of the small cells among the macro cell MIMO antennas is used for transmission, and the remaining M _rx antennas are set to be used for reception,
In the second time period, among the macro cell MIMO antennas, an antenna corresponding to the number of small cells S is used for reception, and the remaining M _tx antennas are set to be used for transmission,
In the first time period, if the number of receive antennas M _rx of the macro cell MIMO antenna is less than the receive antenna threshold M _rx0 ,
The macro cell circulator,
In the first time period, all the macro cell MIMO antennas are set to be used for transmission,
Heterogeneous cellular network system, characterized in that the second cell is set to use all of the macro cell MIMO antenna for reception. According to claim 2,
The heterogeneous cellular network system, characterized in that the reception antenna threshold value M _rx0 of the macro cell is obtained by Equation 25 below.
[Equation 25]

(From here,

, P ₁ is the small cell transmission power, p ₂ is the macro cell transmission power, σ _m ² is the strength of the self-interference channel in the macro cell,

(A=1), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _1k is a large-scale fading effect.) According to claim 2,
In the first time period, when the intensity of the self-interference (SI) of the macro cell MIMO antenna is greater than the self-interference threshold σ _m,0 ² ,
The macro cell circulator,
In the first time period, all the macro cell MIMO antennas are set to be used for transmission,
Heterogeneous cellular network system, characterized in that the second cell is set to use all of the macro cell MIMO antenna for reception. delete In one or more small cells of a heterogeneous cellular network system having a macro cell and a wireless backhaul link,
Small cell MIMO antenna;
Small cell circulator; And
Small cell control unit; includes,
The small cell circulator,
In the first time period, one of the small cell MIMO antennas is used for transmission, and the remaining N _rx antennas are set to be used for reception,
In the second time period, one of the small cell MIMO antennas is used for reception, and the remaining N _tx antennas are set to be used for transmission,
In the first time period, if the number of receive antennas N _rx of the small cell MIMO antenna is less than the receive antenna threshold N _rx0 ,
The small cell circulator,
Set to use all of the small cell MIMO antenna for reception in the first time period,
Heterogeneous cellular network system, characterized in that the small cell MIMO antenna is set to be used for transmission in a second time period. The method of claim 6,
A heterogeneous cellular network system, characterized in that the reception antenna threshold value N _rx0 of the small cell is obtained by Equation (27) below.
[Equation 27]

(From here,

ego,

, P ₁ is the small cell transmit power, p ₂ is the macro cell transmit power, σ _s,k ² is the strength of the self-interference channel in the small cell, and σ _c,kj ² is the strength of the inter-small cell interference channel,

(A=2), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _2k is a large-scale fading effect.) The method of claim 2 or 6,
When the number S of the small cells is 4 or more, the pilot length τ _p is a heterogeneous cellular network system, characterized in that it is twice the number of the small cells. The method of claim 2 or 6,
The pilot length τ _p is a heterogeneous cellular network system characterized in that R _SE value of Equation 32 below is selected as a maximum value among values smaller than or equal to twice the number of small cells S and coherence length T or less. .
[Equation 32]

(Here, R _k is the channel capacity of the full duplex wireless backhaul link of the macrocell in the first time period and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the first time period and the second time period. This is the sum of the channel capacity of the full duplex wireless backhaul link of the macro cell and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the second time period, where τ _p is the length of the pilot sequence.) delete In the communication method of a macro cell of a heterogeneous cellular network system having one or more small cells and a wireless backhaul link,
Setting a macrocell circulator to use an antenna corresponding to the number S of the small cells among the macrocell MIMO antennas for transmission, and setting the remaining M _rx antennas for reception;
Receiving data transmitted from a small cell through the M _rx antennas among the macro cell MIMO antennas in a first time period;
Setting the macrocell circulator to use the antenna corresponding to the number of small cells among the macrocell MIMO antennas for reception and setting the remaining M _tx antennas to be used for transmission; And
And transmitting data to the small cell using the M _tx antennas among the macro cell MIMO antennas in a second time period.
Comparing, in the first time period, the number of receive antennas M _rx of the macro cell MIMO antenna and the receive antenna threshold M _rx0 ;
In the first time period, if the number of receive antennas M _rx of the macro cell MIMO antenna is less than the receive antenna threshold M _rx0 ,
Setting the macrocell circulator to use all macrocell MIMO antennas for transmission;
Transmitting data to the small cell in the first time period using the macro cell MIMO antenna;
Setting the macrocell circulator to use all macrocell MIMO antennas for reception; And
And receiving data transmitted from a small cell using the macro cell MIMO antenna in a second time period. The communication method of the macro cell of the heterogeneous cellular network system further comprises. The method of claim 11,
And obtaining the reception antenna threshold value M _rx0 of the macro cell by the following equation (25): A method of communicating a macro cell in a heterogeneous cellular network system.
[Equation 25]

(From here,

, P ₁ is the small cell transmission power, p ₂ is the macro cell transmission power, σ _m ² is the strength of the self-interference channel in the macro cell,

(A=1), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _1k is a large-scale fading effect.) The method of claim 11,
Comparing the intensity of self-interference and the threshold value of self-interference σ _m,0 ² of the macrocell MIMO antenna in the first time period;
In the first time period, when the intensity of self-interference of the macro cell MIMO antenna is greater than the threshold of self-interference σ _m,0 ² ,
Setting the macrocell circulator to use all macrocell MIMO antennas for transmission;
Transmitting data to the small cell in the first time period using the macro cell MIMO antenna;
Setting the macrocell circulator to use all macrocell MIMO antennas for reception; And
And receiving data transmitted from the small cell using the macro cell MIMO antenna in a second time period. The communication method of the macro cell of the heterogeneous cellular network system further comprises. delete In the communication method of one or more small cells of a heterogeneous cellular network system having a macro cell and a wireless backhaul link,
Setting a small cell circulator to use one antenna among the small cell MIMO antennas for transmission and setting the remaining N _rx antennas to use for reception;
Receiving data transmitted from the macro cell with the N _rx antennas among the small cell MIMO antennas in a first time period;
Setting the small cell circulator to use one antenna among the small cell MIMO antennas for reception and setting the remaining N _tx antennas to be used for transmission; And
And transmitting data to the macrocell using the N _tx antennas among the small cell MIMO antennas in a second time period.
Comparing, in the first time period, the number of receive antennas N _rx of the small cell MIMO antenna and the receive antenna threshold N _rx0 ;
In the first time period, if the number of receive antennas N _rx of the small cell MIMO antenna is less than the receive antenna threshold N _rx0 ,
Setting the small cell circulator to use all small cell MIMO antennas for reception;
Receiving data transmitted from the macro cell in the first time period using the small cell MIMO antenna;
Setting the small cell circulator to use all small cell MIMO antennas for transmission; And
And transmitting data to the macrocell using the small cell MIMO antenna in a second time period. The communication method of the macrocell of the heterogeneous cellular network system further comprises. The method of claim 15,
And obtaining the reception antenna threshold value N _rx0 of the small cell by Equation (27) below: A method of communicating macrocells in a heterogeneous cellular network system.
[Equation 27]

(From here,

ego,

, P ₁ is the small cell transmit power, p ₂ is the macro cell transmit power, σ _s,k ² is the strength of the self-interference channel in the small cell, and σ _c,kj ² is the strength of the inter-small cell interference channel,

(A=2), τ _p is the length of the pilot sequence, p _τ is the pilot power, and β _2k is a large-scale fading effect.) The method of claim 11 or 15,
And when the number S of the small cells is 4 or more, setting a pilot length τ _p to be twice the number of the small cells; further comprising a method for communicating a macro cell in a heterogeneous cellular network system. The method of claim 11 or 15,
And selecting a pilot length τ _p as a value that maximizes an R _SE value of Equation 32 below from a value that is two times or more of the number of small cells S and a coherence length T or less. Macro cell communication method of a heterogeneous cellular network system.
[Equation 32]

(Here, R _k is the channel capacity of the full duplex wireless backhaul link of the macrocell in the first time period and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the first time period and the second time period. This is the sum of the channel capacity of the full duplex wireless backhaul link of the macro cell and the channel capacity of the full duplex wireless backhaul link in the k th small cell in the second time period, where τ _p is the length of the pilot sequence.)

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