KR20180126132A - Method and apparatus for transmitting wireless signal in multi-user interference channel environment - Google Patents

Abstract

Provided are a method and an apparatus for transmitting a wireless signal in a multi-user interference channel environment. The method comprises: obtaining a channel matrix; performing singular value decomposition on the channel matrix; setting a beam forming vector based on a left singular matrix and a right singular matrix acquired according to the singular value decomposition; and applying the set beam forming vector to a signal to be transmitted to transmit the signal.

Description

[0001] The present invention relates to a method and apparatus for transmitting a wireless signal in a multi-user interference channel environment,

The present invention relates to wireless signal transmission, and more particularly, to a method and apparatus for transmitting wireless signals in a multi-user interference channel environment.

The theoretical limitations that can be transmitted in point - to - point MIMO channels with multiple antennas have been identified. In a point-to-point MIMO channel, a theoretical limit is reached by using a matrix or vector derived from a singular value decomposition (SVD) of a point-to-point MIMO channel (H) for transmission / reception beamforming and power allocation.

The MIMO interference channel is an environment in which each of a plurality of transceiver pairs transmit and receive signals through multiple antennas, and interference occurs from other antennas and users when a signal is received. In this MIMO interference environment, the channel capacity has not been theoretically clarified yet, and only Degrees of Freedom corresponding to the number of signals that can be sent independently in an environment where the signal-to-noise ratio is infinite is known. K user M x N The degree of freedom in the MIMO interference channel environment is known when R is an integer when max (M, N) / min (M, N) is defined as R.

It is proved that the maximum multiplexing gain or degree of freedom in the interfering channel can be reached through Interference Alignment (IA) technique. Based on this, it is shown that interference- Research on IA has been actively conducted as an efficient interference control method in the environment. IA is a transmission and reception technique that maximizes the degree of freedom by aligning all interfering signals within an acceptable dimension by extending the signal space to the time, frequency, and space dimensions in a multi-user interfering channel. However, recent IA studies have shown that in a multi-antenna environment, which can be reached through limited spatial resources in a constant single-channel environment, because the infinite signal spacing in time-varying / frequency selective channels is required to reach the maximum degree of freedom. Analysis of the degree of freedom and the design of the transceiver have been performed mainly.

In the MIMO interference environment, the theoretical maximum degree of freedom can be reached by the above interference sorting technique, but the performance is degraded in a low signal-to-noise ratio environment. Specifically, the interference alignment exhibits performance close to the theoretical limit when the signal-to-noise ratio is high, but when the actual signal-to-noise ratio of the actual communication system is low, performance degradation occurs. In other words, interference sorting is a way to transmit signals so that there is no influence of interference, not to increase their signal strength. In an environment with a low signal-to-noise ratio, do.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and an apparatus for transmitting a radio signal through signal maximization in order to receive one signal at a high power in a multi-user interference channel environment.

A method for transmitting a wireless signal according to an exemplary embodiment of the present invention includes: acquiring a channel matrix; Performing singular value decomposition on the channel matrix; Setting a beamforming vector based on a left singular matrix and a right singular matrix obtained according to the singular value decomposition; And applying the set beamforming vector to a signal to be transmitted to transmit the signal.

The setting may comprise setting a vector of a first column of the right singular matrix to a transmit beamforming vector, wherein the transmitting step applies the transmit beamforming vector to the signal to be transmitted, Can be transmitted.

The setting may comprise setting a vector of a first column of the left singular matrix to a receive beamforming vector.

On the other hand, the transmitting step may allocate all available transmit power to the signal to be transmitted, and transmit the signal.

In the multi-user interfering channel environment, it may be an interference channel environment in which K transceivers simultaneously transmit data, where M antennas of each transmitter and N antennas of each receiver are N antennas.

A wireless signal transmission apparatus according to another embodiment of the present invention is a wireless signal transmission apparatus in a multi-user interference channel environment, comprising: a transmission / reception unit for transmitting / receiving signals through an antenna; Wherein the processor performs singular value decomposition on a channel matrix and sets a beamforming vector based on a left singular matrix and a right singular matrix obtained according to the singular value decomposition, To the signal to be transmitted.

The processor may be configured to set the vector of the first column of the right singular matrix to a transmit beamforming vector and to apply the transmit beamforming vector to the signal to transmit. In this case, the transceiver may be configured to transmit the signal to which the transmission beamforming vector is applied.

The processor may be configured to set the vector of the first column of the left singular matrix to a receive beamforming vector and to apply the receive beamforming vector to a signal received by the transceiver.

In addition, the processor may be configured to allocate all available transmit power to the signal to be transmitted, and in this case, the transceiver may be configured to transmit the signal with the available transmit power.

According to the embodiment of the present invention, in a multiple input multiple output (MIMO) interfering channel environment, each transceiver transmits a plurality of signals to increase the degree of freedom thereof, thereby maximizing and transmitting signal strength without transmitting signals. As a result, good performance can be obtained even at a low signal-to-noise ratio.

1 is a diagram illustrating an interference alignment method.
2 is a diagram illustrating a channel environment according to an embodiment of the present invention.
FIG. 3 is a graph illustrating a transmission rate according to another simulation of a wireless signal transmission method and an existing method according to an embodiment of the present invention.
4 is a flowchart of a wireless signal transmission method according to an embodiment of the present invention.
5 is a structural diagram of a radio signal transmission apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification and claims, when a section is referred to as including an element, it is understood that it may include other elements as well, without departing from the other elements unless specifically stated otherwise.

Throughout the specification, a terminal may be referred to as a user equipment (UE), a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS) a high reliability mobile station (HR-MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT) , AMS, HR-MS, SS, PSS, AT, and the like.

Also, a base station (BS) is an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B, eNodeB or eNB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR) a relay station (RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, a high reliability relay station A femto BS, a home Node B, a home eNodeB, a pico BS, a metro BS, a micro base station (BS) and a small base station (eNodeB), eNodeB, eNodeB, eNB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR- And the like.

Hereinafter, a method and apparatus for transmitting a radio signal in a multi-user interference channel environment according to an embodiment of the present invention will be described.

In the interference channel where a large number of transceivers are present, the theoretical limit of transmission is not clarified, and only the maximum degree of freedom (Degrees of Freedom) corresponding to the number of signals that can be independently transmitted in an environment where the SNR is infinite is known . There is an interference alignment that separates the own signal and the interference signal in the signal space in such a way as to reach the theoretical maximum degree of freedom.

1 is a diagram illustrating an interference alignment method.

The interference alignment is a method of separating the signal subspace and the interference subspace from the signal vector space of the receiving end and transmitting the interference signals in the interfering space. For example, in the case of a three-user interfering channel, such as in FIG. 1, the transmitter constructs a beamforming vector as the eigenvectors of the channel so that the interference is aligned in the same direction at the receiver, Lt; RTI ID = 0.0 > beamforming < / RTI >

This interference alignment shows performance close to the theoretical limit when the signal-to-noise ratio is high, but performance degradation occurs when the actual signal-to-noise ratio of the actual communication system is low. In other words, interference sorting is a way to transmit signals so that there is no influence of interference, not to increase their signal strength. In an environment with a low signal-to-noise ratio, do.

In the embodiment of the present invention, in a multiple input multiple output (MIMO) interfering channel environment, each terminal performs beamforming and power allocation so as to maximize its signal while transmitting the signal with a degree of freedom of 1.

2 is a diagram illustrating a channel environment according to an embodiment of the present invention.

In the embodiment of the present invention, as shown in FIG. 2, the K transceivers transmit data at the same time, Mk antennas of each transmitter, and Nk personal communication systems (hereinafter, K user MIMO interference channel), K transceivers transmit data at the same time, and each transmitter maximizes its signal and transmits.

K user In a MIMO interfering channel, if the k k user (or terminal) transmits the d _k signals s _{k, m} to be transmitted on the transmit beamforming matrix (or transmit beamforming vector) P _k of the transmitter, The signal x _k transmitted through the antenna can be expressed as follows.

Here, s _k denotes a data vector (Dx 1 matrix), and D denotes the number of data transmitted from each transmitting end.

The received signal y _k of the _kth receiver received via channel H can be expressed as:

Where H _kk is the channel matrix at the j-th transmitter to the k-th receiver (NxM matrix) to indicate, P _k denotes a transmit beam forming matrix of a k th transmitter (MxD matrix), s _k is the data vector (Dx1 matrix) , Z _k represents a thermal noise (Nx 1 matrix), and D represents the number of data sent from each transmitting end.

received signal y _k to the reception beam forming matrix of a k-th receiver (or receive beamforming vectors) to obtain signals s _k with F _k can be expressed as follows:

In the interference alignment scheme, each transceiver transmits a plurality of signals, thereby increasing the number of signals that each transceiver independently sends to improve performance. However, in the embodiment of the present invention, each transceiver transmits only one signal, but the intensity of one transmitted signal can be maximized.

The kth transmission and reception period channel is denoted by _Hkk , and the channel can be expressed by SVD as follows.

U represents a left singular matrix of N x N dimensions, V represents a right singular matrix of M x M dimensions, and Σ represents a diagonal matrix of N xM dimensions representing singular values of rank of the matrix.

Generally, when SVD is applied to a channel, the vector corresponding to the largest singular vector is given by the first column of the left singular matrix U _kk and the right singular matrix V _kk corresponding to the kth transmitting and receiving period channel. Therefore, in the embodiment of the present invention, in order to transmit a signal through the largest channel among the signals of the channel modified through the SVD, the beamforming vector P _k of the k-th transmitter is set to be the first column of the _right- .

Also, the beamforming vector f _k of the kth receiver is set to be the first column of the left-handed U _kk matrix as follows.

In order to maximize the signal transmitted by the arbitrary transmitter, the beamforming vector P _k of the transmitter is converted into a vector located in the first column of the right-handed matrix obtained by singular value decomposition (SVD) of the channel matrix And sets the beamforming vector f _k of the receiver to the vector located in the first column of the left singular matrix obtained by singular value decomposition (SVD) of the channel matrix.

In addition to performing transmit / receive beamforming to transmit and receive signals maximally as described above, power allocation control is performed.

Specifically, when the available transmission power of the k-th transmitter is Po _k , the transmitter allocates available transmission power Po _k to one signal transmission transmitted by itself. Therefore, the k-th transmitter transmits one signal with the available transmission power Po _k .

As described above, in the K-user MIMO interfering channel, each transceiver transmits a plurality of signals to increase its signal strength, rather than increasing the degree of freedom, thereby achieving good performance at a low signal-to-noise ratio.

The transmission rate of the kth transceiver can be expressed as follows.

이다. here,

to be.

The total transmission rate obtained from the whole system is as follows.

For example, the transmission rate that a first user can obtain in a 3-user interference channel is as follows.

은 H₁₁의 가장 큰 특이 벡터를 나타낸다. here,

Represents the largest singular vector of H ₁₁ .

As a result of applying the radio signal transmission method according to the embodiment of the present invention to, for example, a 3-user 4x4 MIMO interference channel, results as shown in FIG. 3 were obtained.

FIG. 3 is a graph illustrating a transmission rate according to another simulation of a wireless signal transmission method and an existing method according to an embodiment of the present invention.

As shown in FIG. 3, according to the radio signal transmission method according to the embodiment of the present invention, when each transmitter maximizes the strength of its own signal and transmits it (bold dotted line or bold dotted chain line) It can be seen that it has a better performance (transmission rate) at a low signal-to-noise ratio, compared with the point-limit reaching method (bold solid line) and the existing interference alignment method (fine dashed line or thin solid line).

Specifically, in a point-to-point environment, when the method of reaching the theoretical limit, that is, the point-to-point theoretical limit approach (thick solid line) is applied to a communication environment having four transceiver antennas for three pairs of users, Even if the noise ratio is increased, the interference also increases, so there is no performance improvement. However, according to the wireless signal transmission method according to the embodiment of the present invention, it can be seen that the wireless signal transmission method has superior performance to interference alignment at a low signal-to-noise ratio.

4 is a flowchart of a wireless signal transmission method according to an embodiment of the present invention.

As shown in the attached FIG. 4, in a K-user MxN interference channel environment, each transmitter performs beamforming.

First, the channel matrix of the transmitter is acquired (S100), and the singular value decomposition (SVD) of the channel matrix is performed (S110).

Then, the transmission beamforming vector is set using the right-specific matrix obtained according to the singular value decomposition of the channel matrix. That is, the vector of the first column of the right specific matrix is set as a transmission beamforming vector (S120). Also, the reception beamforming vector is set using the left singular matrix obtained according to the singular value decomposition of the channel matrix. That is, the vector of the first column of the left singular matrix is set as the reception beamforming vector (S130).

After setting the beamforming vector as described above, the transmitter applies the beamforming vector to the transmitted signal and transmits the signal (S140). At this time, the transmitter allocates available transmit power to a signal to be transmitted, and transmits the signal with usable transmit power (S150).

5 is a structural diagram of a radio signal transmission apparatus according to an embodiment of the present invention.

5, the wireless signal transmission apparatus 1 according to the embodiment of the present invention includes a processor 110, a memory 120, and a transceiver 130. [ The processor 110 may be configured to implement the methods described above based on Figs. 2-4.

The memory 120 is coupled to the processor 110 and stores various information related to the operation of the processor 110. [ The memory 120 stores instructions to be executed by the processor 110, or may temporarily store an instruction loaded from a storage device (not shown). The processor 110 may execute instructions that are stored or loaded into the memory 120. The processor 110 and the memory 120 are connected to each other via a bus (not shown), and an input / output interface (not shown) may be connected to the bus.

The transceiver 130 is connected to the processor 110 and transmits or receives a radio signal.

The embodiments of the present invention are not limited to the above-described apparatuses and / or methods, but may be implemented through a program for realizing functions corresponding to the configuration of the embodiment of the present invention, a recording medium on which the program is recorded And such an embodiment can be easily implemented by those skilled in the art from the description of the embodiments described above.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It belongs to the scope of right.

Claims (9)

In a multi-user interfering channel environment, in a method of transmitting a wireless signal,
Obtaining a channel matrix;
Performing singular value decomposition on the channel matrix;
Setting a beamforming vector based on a left singular matrix and a right singular matrix obtained according to the singular value decomposition; And
Applying the set beamforming vector to a signal to be transmitted and transmitting the signal
/ RTI > The method of claim 1, wherein
Wherein the setting step comprises:
Setting a vector of a first column of the right specific matrix to a transmit beamforming vector
Lt; / RTI >
The transmitting step
And applying the transmission beamforming vector to the signal to be transmitted to transmit the signal. The method of claim 1, wherein
Wherein the setting step comprises:
Setting a vector of a first column of the left singular matrix to a receive beamforming vector
/ RTI > The method of claim 1, wherein
Wherein the transmitting step allocates all available transmit power to the signal to be transmitted, and transmits the signal. The method of claim 1, wherein
Wherein in the multi-user interfering channel environment, the M antennas of each transmitter and N antennas of each receiver are interference channel environments in which K transceivers simultaneously transmit data. In a wireless signal transmission apparatus in a multi-user interference channel environment,
A transmitting and receiving unit for transmitting and receiving signals through an antenna, and
And a processor coupled to the transceiver and performing wireless signal transmission,
The processor comprising:
A singular value decomposition is performed on the channel matrix, a beamforming vector is set based on a left singular matrix and a right singular matrix obtained according to the singular value decomposition, and the set beamforming vector is applied to a signal to be transmitted , A wireless signal transmission device. The method of claim 6, wherein
Wherein the processor is configured to set the vector of the first column of the right singular matrix to a transmit beamforming vector and apply the transmit beamforming vector to the signal to transmit,
Wherein the transceiver is configured to transmit the signal to which the transmit beamforming vector is applied. The method of claim 6, wherein
The processor comprising:
Set the vector of the first column of the left singular matrix to a receive beamforming vector and apply the receive beamforming vector to a signal received by the transceiver. The method of claim 6, wherein
Wherein the processor is configured to allocate all available transmit power to the signal to be transmitted,
And the transmitter / receiver is configured to transmit the signal with the available transmit power.

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