KR20140059929A

KR20140059929A - Method and apparatus for estimating channel based on compressive sensing in multicarrier system

Info

Publication number: KR20140059929A
Application number: KR1020120126312A
Authority: KR
Inventors: 김지형; 김정현; 김현재; 임광재; 권동승
Original assignee: 한국전자통신연구원
Priority date: 2012-11-08
Filing date: 2012-11-08
Publication date: 2014-05-19

Abstract

In a method of estimating a channel in a multicarrier system, a channel path is estimated if a signal is received through a multi-path channel. A channel is estimated based on the signal received from the estimated channel path. A compressive sensing-based channel estimate for repeatedly performing such path estimate and channel estimate is carried out.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for estimating a channel based on compression sensing in a multi-

The present invention relates to a method and apparatus for channel estimation, and more particularly, to a method and apparatus for estimating a channel based on compression sensing in a multi-carrier system.

In a multicarrier system for transmitting data using a multi-carrier such as Orthogonal Frequency Division Multiplexing (OFDM), a serial symbol sequence is parallel-converted, Carriers to a plurality of sub-carriers having orthogonality. In such a system, a frequency domain is divided into subchannels of a plurality of subcarriers, a time domain is divided into a plurality of time slots, and subchannels are allocated to each user to perform resource allocation considering both time and frequency domains. Data is transmitted in units of.

In such a multi-carrier system, a channel estimation method based on compressive sensing (CS) estimates a channel by restoring a signal based on compression sensing theory.

In order to estimate the channel, a precondition for knowing the number of multipaths of the channel is required. Therefore, when the CS channel estimation scheme is practically applied to the communication system, channel estimation is performed on the assumption that the number of multipaths of the channel is known.

However, since the channel estimation is performed assuming only the multipath number, accurate channel estimation is not performed according to the current channel environment.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for performing channel estimation based on compression sensing by estimating the number of multipaths of a channel in a multi-carrier system.

According to an aspect of the present invention, there is provided a channel estimation method for estimating a channel in a multi-carrier system, comprising: estimating a delay of a predetermined channel path when a signal is received through a multi-path channel; And performing channel estimation on a received signal corresponding to a position of the estimated channel path, wherein the step of estimating the delay and the step of performing channel estimation are repeatedly performed until a predetermined condition is satisfied. .

According to an embodiment of the present invention, when channel estimation is performed based on compression sensing in a multi-carrier system, the number of multi-paths of a channel can be estimated effectively. Therefore, channel estimation using compression sensing can be accurately performed based on the estimated number of multipaths of the channel.

1 is a flowchart of a channel estimation method according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating an example of estimating a channel using linear interpolation according to an embodiment of the present invention. Referring to FIG.
3 is a diagram illustrating a structure of a channel estimation 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, when an element is referred to as "comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

In this specification, a terminal includes a terrestrial station, a return channel satellite terminal (RCST), a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station Station, a PSS, a user equipment (UE), an access terminal (AT), and the like, and may include all or part of an earth station, RCST, mobile terminal, subscriber station, mobile subscriber station, May include the functions of

In this specification, a central station includes a base station (BS), an access point (AP), a radio access station (RAS), a node B, a base transceiver station (BTS) Mobile Multihop Relay (MMR) -BS, or the like, and may include all or some functions of an access point, a radio access station, a Node B, a base transceiver station, and an MMR-BS.

Hereinafter, a compression-sensing-based channel estimation method and apparatus in a multi-carrier system according to an embodiment of the present invention will be described with reference to the drawings.

1 is a flowchart of a channel estimation method according to an embodiment of the present invention.

In a multi-carrier system, the received signal can be expressed as:

Here, Y represents a vector for a received signal on the frequency domain, that is, a received vector, and in particular represents a vector for a received signal based on a k × 1 th subcarrier. k denotes a subcarrier.

X is a transmit signal, and is made up of a k x k diagonal matrix. h is a channel characteristic on the time axis, and can be represented by an L _h × 1 channel vector. N denotes a k x 1 AWGN vector, which is additive white Gaussian noise (AWGN) added to the k x 1-th received signal. F _h is k × L _h Matrix, the front of the k × k fast Fourier transform (FFT) matrix L _h Denotes a matrix having four columns.

The frequency-axis channel characteristics are as follows.

Here, H represents the characteristic of the frequency axis channel.

In signal transmission in a multi-carrier system, a pilot tone is inserted for channel estimation. The positions of the subcarriers on which the pilot tones are arranged are represented by indices Pi (i = 1, 2, ..., L _p ). At the subcarrier position of the pilot tone, the reception signal according to Equation (1) can be expressed as follows.

Here, Y _p denotes an L _p x 1 reception vector for a reception signal corresponding to a subcarrier on which a pilot tone is arranged, and X _p denotes a transmission signal L _p X L _p diagonal matrix. h denotes an L x 1 channel vector, and N _p denotes an L _p x 1 AWGN vector. F _p is L _p × L _h matrix, and D is a matrix composed of rows matched to Pi at F _h and X _p F _p where L _p × L _h matrix.

When a channel estimation is performed based on a LS (Least Square) channel estimation method for a reception signal corresponding to a subcarrier on which a pilot tone on the frequency axis is arranged, a channel frequency response, that is, a channel estimation value is as follows.

Here, various channel estimation methods such as a minimum mean square error (MMSE) may be applied instead of the LS channel estimation method.

A channel can be estimated using linear interpolation for a portion where a pilot tone on the frequency axis is not arranged, and the channel estimation value is as follows.

Where I _p represents the spacing between pilot tones.

FIG. 2 is a diagram illustrating an example of estimating a channel using linear interpolation according to an embodiment of the present invention. Referring to FIG. The channel estimation values for the subcarriers on which the pilot tones are not arranged on the frequency axis are shown in Fig.

Let Ω _p be a set of pilot tone positions, which are subcarriers corresponding to positions where pilot tones are arranged, and Ω _{c be a} set of C subcarriers located before and after the pilot tone, , The entire set of positions can be expressed as Ω _s = Ω _p + Ω _c . For example, when C is 1, Ω _c is (Pi + 1) (i = 1, 2, ..., L p -1) and, (Pi-1) (i = 1, 2, ..., L p -1).

In this manner, the channel estimation value (referred to as a first estimation value) estimated for the reception signal corresponding to the sub-

To obtain channel estimates (referred to as second estimates) for subcarriers on which no pilot tones are arranged on the frequency axis, where various interpolation methods other than linear interpolation may be applied .

In the embodiment of the present invention, channel estimation is performed using compression sense (CS) based on an estimated channel estimation value for a reception signal corresponding to a subcarrier on which pilot tones are arranged.

The channel estimation using CS is as follows.

In the CS channel estimation, each channel path is individually estimated based on the channel property, and channel estimation values estimated for a received signal corresponding to a subcarrier in which channel length and pilot tone are arranged are initialized. Then, the following process is repeatedly performed to estimate a channel path and estimate a channel.

The path delay for the ith received signal over the multipath channel can be expressed as:

Here, τ _i represents the delay of the i-th path. As an initial value, R = Y.

D matrix < RTI ID = 0.0 &

₍ L _p x L _h matrix), which represents the conjugate transpose of the jth row of the matrix. L _h represents the length of the cyclic prefix (CP).

here,

Represents the τ _i -th row of the D matrix

Wow

Is a matrix of i-th iterations, all initial values are null, and whenever channel estimation is repeated, τ _i is

Lt; / RTI >

end

Are added to the matrix. That is, the row of the matrix becomes larger.

In this communication environment, a channel value is estimated for a reception signal having an i-th predetermined subcarrier, as follows.

The channel estimation value is changed to the frequency axis as follows.

here

(J ∈ Ω _p or j ∈ Ω _s )

The frequency response obtained through equations (4) and (5)

. Change the vector

As follows.

As described above, path estimation and channel estimation are performed on the i-th received signal received through the multipath channel, and the channel estimation process is repeatedly performed. The conditions under which the iterative channel estimation is terminated are as follows.

Where α is a constant.

Thus, on the basis of? _S or? _P , the CS channel estimation is repeatedly performed until a condition that the relation of the channel estimation values satisfies the above-mentioned expression (12) is established.

3 is a diagram illustrating a structure of a channel estimation apparatus according to an embodiment of the present invention.

3, the channel estimation apparatus 1 according to the embodiment of the present invention includes a frequency domain channel response unit 11, a multipath number estimation unit 12, and a channel estimation unit 13 .

The frequency domain channel response unit 11 obtains a frequency domain channel response for a received signal received by the channel estimation device 1 through the multipath channel.

The multipath number estimating section 12 estimates a predetermined channel path in a multi-channel path environment. In particular, the delay of a predetermined channel path is estimated based on Equations (6) and (7).

The channel estimation unit 13 performs channel estimation on a received signal, and in particular, performs CS channel estimation. The channel estimation unit 13 obtains a channel estimation value based on a reception signal corresponding to a position corresponding to the channel path delay estimated by the multipath number estimation unit 12. [

The multipath number estimating unit 12 and the channel estimating unit 13 repeatedly perform path estimation and channel estimation until the set condition is satisfied.

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

In a method of estimating a channel in a multi-carrier system,
Estimating a delay of a predetermined channel path when a signal is received through the multipath channel;
Performing channel estimation on a received signal corresponding to a delay of the estimated channel path
Lt; / RTI >
Estimating the delay and performing the channel estimation are repeatedly performed until a set condition is satisfied.