KR101222667B1 - Signal receiving method and apparatus for interference cancellation against the interferences due to large channel delay in wireless communication systems - Google Patents

Abstract

Disclosed are a method and apparatus for canceling interference according to channel delay in a wireless communication environment. In an interference cancellation method according to an embodiment of the present invention, a threshold value reflecting channel characteristics and noise characteristics in a frequency domain is selected, a data symbol having a channel equal to or greater than a set threshold value is selected and fed back through a feedback circuit to superimpose it. Generating a symbol having a double-windowed structure and synthesizing the generated double-window to obtain a gain of a signal-to-interference ratio.

Description

Signal receiving method and apparatus for canceling interference due to channel delay in wireless communication environment {Signal receiving method and apparatus for interference cancellation against the interferences due to large channel delay in wireless communication systems}

One aspect of the present invention relates to a communication technique using a multicarrier transmission scheme, and more particularly, to a technique for removing interference even when a delay wave longer than a guard interval occurs.

The present invention is derived from the research conducted as part of the IT growth engine technology development project of the Ministry of Knowledge Economy. [Task Management Number: 2008-S-002-02, Title: Development of 3GPP LTE Terminal Modem Chipset]

In a wireless communication system environment employing Orthogonal frequency-division multiple (OFDM) scheme, Guard Interval (GI) insertion is used to reduce the complexity of the receiver and the preparation for interference caused by multipath waves. Is possible.

However, insertion of guard intervals is associated with inefficient use of transmit power and limited radio resources. In particular, inter-symbol interference and intra-symbol interference in an OFDM system when channel delays exceed the guard interval in MBMSN over a Single Frequency Network (MBSFN) and terrestrial broadcast receivers that require long intervals of guard intervals. The orthogonal collapse between subcarriers in can result in system performance degradation.

According to an aspect, a technique for canceling interference in a wireless communication environment in which interference exists according to channel delay is proposed.

According to an aspect of the present invention, a method for removing interference in a wireless communication environment in which interference occurs according to a channel delay includes: setting a threshold value reflecting channel characteristics and noise characteristics in a frequency domain, and a data symbol having a channel greater than or equal to a set threshold value Selecting and feeding the feedback through a feedback circuit to generate a symbol having a superimposed double window structure, and synthesizing the generated double window to obtain a gain of a signal-to-interference ratio.

According to an embodiment, an OFDM symbol having a superimposed double window structure and a method of synthesizing the superimposed double window structure obtain a gain of signal-to-interference ratio during signal processing and efficiently reduce interference due to channel delay. Can be removed.

In addition, when generating the overlapped double window structure, the threshold value is set by reflecting the channel characteristics in the frequency domain and the noise power at the receiving end, and the feedback of the data symbol having a channel below the threshold value is repeated during repetitive signal processing. By limiting, performance degradation of the system can be prevented.

1 is a reference diagram for explaining intersymbol interference for a delay wave over a guard interval according to an embodiment of the present invention;
2 is a block diagram of a receiver for estimating channel characteristics in a time and frequency domain using downlink pilot symbols according to an embodiment of the present invention;
3 is a reception apparatus according to an embodiment of the present invention i ^th Reference diagram showing an extended window through a process of removing ISI and performing cyclic reconstruction using symbol replicas fed back through control using a threshold value for an OFDM symbol,
4 is a block diagram of a receiver for synthesizing an extended window according to an embodiment of the present invention;
FIG. 5 is a reference diagram for describing a process of selectively detecting a symbol by using a frequency domain characteristic of a radio channel response received in a multipath wave-rich channel environment according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described embodiments of the present invention; In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. In addition, terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to intention or custom of a user or an operator. Therefore, the definition should be based on the contents throughout this specification.

The present invention proposes an efficient interference cancellation technique in a wireless communication environment in which interference exists according to channel delay. In order to perform efficient interference cancellation, the receiver of the present invention generates an OFDM symbol having an overlapping double window structure by looking at the entire interval of the OFDM symbol having interference as a signal processing interval. In addition, a gain of a signal-to-interference ratio in signal processing is obtained by synthesizing the overlapped double windows.

In addition, when generating the overlapped double window structure, the threshold value is set by reflecting the channel characteristics in the frequency domain and the noise power at the receiving end, and the feedback of the data symbol having a channel below the threshold value is repeated during repetitive signal processing. Limiting prevents performance degradation of the system.

The present invention can be applied to downlink transmission with high propagation delay as in MBMS service and broadcast communication of 3GPP LTE, which is one of the next generation cellular mobile communication methods.

1 is a reference diagram for explaining intersymbol interference for a delay wave over a guard interval according to an embodiment of the present invention.

Referring to FIG. 1, received OFDM symbols in an OFDM communication environment include interference components from adjacent symbols. Assume that the three symbols shown in FIG. 1 are the previous symbol: ( i- 1) ^th , the current symbol: i ^th, and the subsequent symbol: (i + 1) ^th , and detect data for the i ^th symbol. Inside the i ^th symbol of the N-point IFFT length there is a signal component from ( i -1) ^th . This is the inter-symbol interference (ISI) component. In FIG. 1, G denotes a guard interval length, MCD denotes a maximum channel delay, and N denotes an FFT length.

2 is a block diagram of a receiver for estimating channel characteristics in a time and frequency domain using downlink pilot symbols according to an embodiment of the present invention.

Referring to FIG. 2, in downlink reference (DL-RS) symbols for downlink channel estimation as in 3GE LTE, the receiver 1 may obtain channel characteristics in a time and frequency domain. have.

The first FFT unit 200 converts the received signal from the time domain to the frequency domain by performing fast Fourier transform. The pilot symbol extractor 210 extracts a pilot symbol inserted at the transmitting end. The IFFT unit 220 converts the input signal into a fast inverse Fourier transform from the frequency domain to the time domain. In this case, the time domain channel response characteristic may be estimated.

The noise estimator 230 estimates noise power. On the other hand, noise estimation may use a guard band in OFDM. The second FFT unit 240 performs fast Fourier transform on the input signal and converts the input signal from the time domain to the frequency domain. The subcarrier selection unit 250 selects a subcarrier having a value equal to or greater than a preset threshold value. The function of the subcarrier selection unit 250 will be described in detail later with reference to FIG. 5.

Meanwhile, the receiver of the present invention acquires the maximum delay information of the channel through the channel response characteristic on the time axis, and determines whether or not the interference cancellation operation of the receiver, which will be described later in FIG. 4, is performed. Referring to the entire i ^th symbol of FIG. 1, when the channel delay exceeds the guard interval, all the symbols in the OFDM packet are interfered with from the adjacent symbols (( i -1) ^th , (i + 1) ^th ). In an environment where interference exists, certain symbols in a packet are associated with neighboring symbols. In this case, a method of configuring a double overlapped window is as follows. An i ^th symbol having interference due to adjacent symbols may be represented by Equation 1.

The first right term of Equation 1 refers to a region where no interference exists in the i ^th symbol of FIG. 1, and the second right term is (i-1) ^th A region in which interference by a symbol exists is represented as in Equation 2.

On the other hand, the third term on the right is an area where interference by the (i + 1) ^th symbol is present as shown in Equation 3.

Finally, ω means the receiver noise signal component.

I ^th in Equation 2 and Equation 3 Equations 2 and 3 can be converted into a signal with reduced interference if the replica information of the symbol and adjacent OFDM symbols can be known. This conversion process is performed through a signal processing such as an ISI removal process for removing adjacent interference signals through the adjacent symbol interference cancellation unit 400 shown in FIG. 4 and cyclic reconstruction through the cyclic construction unit 410. Is performed. The i ^th OFDM symbol obtained through the above-described signal processing is reconstructed as shown in FIG. 3.

3 is a reception apparatus according to an embodiment of the present invention;i ^th Reference diagram showing an extended window through a process of removing ISI and performing cyclic reconstruction using symbol replicas fed back through control using a threshold value for an OFDM symbol.

Referring to FIG. 3, the receiving apparatus expands a window by using a window technique of overlapping a signal of a benefit symbol and a next symbol.

4 is a block diagram of a receiver for synthesizing an extended window according to an embodiment of the present invention.

Referring to FIG. 4, the receiver of the present invention removes interference of neighboring symbols with respect to the current symbol through the neighbor symbol interference canceller 400 and cyclically expands the symbol through the cyclic constructor 410.

Meanwhile, the window separator 420 configures an i ^th OFDM symbol with two overlapped windows, a pre-window and a post-window. An example of the overlapped windows is as described above in FIG. 3. The FFT unit 430 performs fast Fourier transform of the separated windows, the frequency domain equalizer (FDE) 440 performs a channel equalization process, and the window synthesis unit 450 synthesizes the separated OFDM symbols. The LLR calculator 460 calculates a log likelihood ratio constituting the symbol, and the symbol is decoded by the decoder 470.

FIG. 5 is a reference diagram for describing a process of selectively detecting a symbol by using a frequency domain characteristic of a radio channel response received in a multipath wave-rich channel environment according to an embodiment of the present invention.

Referring to FIG. 5, data within the current OFDM symbol and data of an adjacent OFDM symbol are used as data information used when generating the overlapped double window. I ^th If signal processing is performed on an OFDM symbol, the adjacent symbols (i-1) ^th and (i + 1) ^th Requires symbols In other words, it uses a signal processing scheme that generates replicas for each symbol and feeds them back repeatedly.

The reliability of the symbol replica is the key to the overall interference cancellation performance. Therefore, in the present invention, when generating a symbol replica, a threshold using frequency channel response characteristics and noise variance is applied. At this time, the data contained in the subcarrier having a channel characteristic of less than or equal to the threshold value is used to exclude the feedback. For example, as shown in FIG. 5, in a frequency selective fading channel of an environment having a frequency response characteristic, a power smaller than the sum (N + I) of the noise signal (noise) N and the interference signal I is obtained. Detection is not performed on the data component of the subcarrier. As a result, it is possible to prevent an interference noise increase phenomenon generated from a data symbol replica that is incorrectly detected.

The embodiments of the present invention have been described above. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

200: first FFT unit 210: pilot symbol extraction unit
220: IFFT unit 230: noise estimation unit
240: second FFT section 250: subcarrier selection section
400: adjacent symbol interference cancellation unit 410: circular construction unit
420: window separation unit 430: FFT unit
440: FDE unit 450: window synthesis unit
460: LLR calculator 470: decoder

Claims (8)

In the method for receiving a signal in a wireless communication environment,
Setting the sum of the received noise and the interference signal size as a threshold by reflecting the channel response characteristic and the received noise in the frequency domain;
Selecting a data symbol having a channel characteristic greater than or equal to the set threshold value among the received data symbols and feeding it back through a feedback circuit to generate a symbol having an overlapped double window structure; And
Synthesizing the generated double window to obtain a gain of a signal-to-interference ratio. delete The method of claim 1, wherein generating a symbol having the overlapped double window structure comprises:
The method of claim 1, wherein the feedback of data symbols having channel characteristics below the set threshold is limited among the received data symbols to prevent performance degradation. The method of claim 1, wherein generating a symbol having the overlapped double window structure comprises:
Area where interference does not exist in the current reception symbol (i ^th ), where interference exists by the previous reception symbol (i-1 ^th ), and where there is interference by the subsequent reception symbol (i + 1 ^th ) And calculating a region having interference by the adjacent symbols of the current reception symbol (i ^th ) through a sum operation of noise to generate a symbol having the overlapping double window. delete An apparatus for receiving a signal in a wireless communication environment,
A subcarrier selector configured to set a threshold value reflecting channel response characteristics and reception noise in a frequency domain, and to select a data symbol having a channel characteristic equal to or greater than the set threshold value among the received current symbols;
An adjacent symbol interference canceller which removes interference of adjacent symbols with respect to the selected data symbol;
A cyclic constructing unit cyclically expanding the current symbol from which the interference is removed to generate an expanded window;
A window separator for dividing the expanded window into an overlapping double window including a previous window and a subsequent window; And
A window synthesizer for synthesizing the separated double windows;
Signal receiving apparatus comprising a. The method of claim 6, wherein the subcarrier selection unit,
Signal receiving apparatus, characterized in that for preventing the performance degradation by limiting the feedback of the symbol having a channel characteristic of less than the set threshold value among the received current symbols. The method of claim 6, wherein the adjacent symbol interference cancellation unit,
And a symbol replica fed back with a channel characteristic greater than or equal to the threshold for the current symbol to remove interference of adjacent symbols with respect to the current symbol.

Images