KR20110076316A - Ofdm transmitter and receiver for spectrum efficiency - Google Patents

Abstract

PURPOSE: An OFDM(Orthogonal Frequency Division Multiplexing) transmitter and a receiver and a method thereof are provided to increase the efficiency of a frequency spectrum by reducing the number of a pilot. CONSTITUTION: A virtual data modulator(130) modulates virtual data. A modulation order increasing unit(140) increases the modulation order of the virtual data modulated by a virtual data modulator. A first channel estimator supposes the CFR(Channel Frequency Response) of the receiving symbol allocated to a pilot sub carrier. A second channel estimator calculates the CFR of the receiving symbol allocated to a virtual data sub carrier. A symbol repeater(160) outputs virtual data to the assignment unit of the sub carrier at least over twice.

Description

OPDM transmitter and receiver for spectrum efficiency

The present invention relates to an OFDM transceiver and method, and in particular, to increase the efficiency of the frequency spectrum by reducing the number of pilots as much as possible, and similar to before reducing the bit error rate (BER) or frame error rate (FER) performance The present invention relates to an OFDM transceiver and method for maintaining the same.

Recently, standards for OFDM-based broadcasting systems that provide services such as DTV (Digital Television), Internet, and data are being developed (Ref. [1] ETSI EN 302 755 V1.2.0c (2008.7), Digital Video Broadcasting ( DVB); Frame structure channel coding and modulation for a second generation digital broadcasting system (DVB-T2). [2] ESTI TR 102 831 V0.9.2 (2008.9), Digital Video Broadcasting (DVB); Implementation guidelines for a second generation digital broadcasting system (DVB-T2) [3] Seo Jung-wook, Kim Hyun-sik, Jeon Ki-ki, Baek Jong-ho, Kim Dong-gu, “Introduction of Next-Generation Terrestrial TV Standard DVB-T2 Technology for the ASO Era,” Journal of the Korean Institute of Communication Sciences, Vol. 25, No. 8, pp. 55 ~ 61, July 2008.).

Since such a broadcasting system must transmit a lot of data, it is advantageous in terms of frequency spectrum efficiency to reduce unnecessary overhead as much as possible. Pilot is an important overhead used for time and frequency synchronization or radio channel estimation in receivers, and an adequate number of pilots is required to ensure sufficient performance (Ref. [4] IEEE Std. 802.16-2004, ` `` IEEE standard for local and metropolitan area networks-Part 16: Air interface for fixed broadband wireless access systems, '' Oct. 2004. [5] BW Song, YF Guan, WJ Zhang, `` An efficient training sequences strategy for channel estimation in OFDM systems with transmit diversity, '' Journal of Zhejiang Univ. SCI, pp. 613-618, 2005. [6] D. Shen, Z. Diao, KK Wong, VOK Li, `` Analysis of pilot-assisted channel estimators for OFDM systems with transmit diversity, '' IEEE Trans.Broadcasting, vol. 52, no.2, June 2006.).

This pilot is assigned to a pilot subcarrier. In addition, nulls or zeros are assigned to the virtual carriers to reduce interference to systems using adjacent frequency bands and to mitigate the requirements of pulse shaping filters. Finally, actual data is allocated to the data subcarriers. The virtual carrier is also referred to as a virtual subcarrier.

1 shows a general subcarrier allocation technique for an OFDM-based system for portable mobile broadcasting.

As shown in FIG. 1, data subcarriers, pilot subcarriers, and virtual carriers are allocated around a direct current (DC) in a baseband. In particular, the pilot subcarriers are arranged at D _f intervals. The data subcarrier and the pilot subcarrier are called effective subcarriers.

As described above, according to the conventional OFDM-based broadcasting system, there is a problem that the frequency spectrum efficiency is lowered due to the pilot.

The present invention has been made to solve the above-described problem, and an object of the present invention is to provide an OFDM transmission apparatus and method capable of increasing the efficiency of the frequency spectrum by reducing the number of pilots as much as possible.

Another object of the present invention is to provide an OFDM receiver and a method for achieving excellent bit error rate (BER) or frame error rate (FER) performance even when a pilot subcarrier is reduced.

In order to achieve the above object, the OFDM transmission apparatus of the present invention comprises a virtual data modulator for modulating virtual data; A modulation order increaser for increasing a modulation order of virtual data modulated by the virtual data modulator; A symbol repeater for repeatedly outputting virtual data whose modulation order is increased by the modulation order increaser to a subcarrier allocator at least two times; And the subcarrier allocator for allocating virtual data input from the symbol repeater to the effective subcarriers among all subcarriers including a virtual carrier and an effective subcarrier.

The OFDM transmission apparatus of the present invention may further include a constellation rotator configured to constellation rotate virtual data whose modulation order is increased by the modulation order increaser. In this case, the symbol repeater is characterized in that for outputting at least two or more times the virtual data rotated in the constellation by the constellation rotation to the subcarrier allocator.

The OFDM transmission method of the present invention comprises the steps of: modulating virtual data; Increasing a modulation order of the modulated virtual data; Constellation rotation of the virtual data having increased modulation order; And allocating at least two times the constellation rotated virtual data to the effective subcarrier among all subcarriers including the virtual carrier and the effective subcarrier.

An OFDM receiver according to an embodiment of the present invention includes a first channel estimator for estimating a channel frequency response (CFR) of a received symbol allocated to a pilot subcarrier; A second channel estimator for estimating a CFR of a received symbol allocated to a virtual data subcarrier using the CFR estimated by the first channel estimator; A virtual data demodulator for demodulating virtual data using the CFR estimated by the second channel estimator or the CFR estimated by the fifth channel estimator; A third channel estimator for estimating a CFR of a received symbol assigned to a virtual data subcarrier using the demodulated virtual data; A fourth channel estimator for estimating the CFR of the received symbol allocated to the virtual pilot subcarrier using the CFR estimated by the first and third channel estimators; A fifth channel estimator for estimating a CFR of a received symbol allocated to a data subcarrier and a virtual data subcarrier, respectively, using the CFR estimated by the first, third and fourth channel estimators; And a data demodulator for demodulating data using the CFR estimated by the fifth channel estimator.

An OFDM receiver according to another embodiment of the present invention includes a first channel estimator for estimating a channel frequency response (CFR) of a received symbol assigned to a pilot subcarrier; A second channel estimator for estimating a CFR of a received symbol allocated to a virtual data subcarrier using the CFR estimated by the first channel estimator; A virtual data demodulator for demodulating virtual data using the CFR estimated by the second channel estimator or the CFR estimated by the third channel estimator; The third channel estimator for estimating a CFR of a received symbol assigned to a virtual data subcarrier using the demodulated virtual data; A fourth channel estimator for estimating the CFR of the received symbol allocated to the virtual pilot subcarrier using the CFR estimated by the first and third channel estimators; A fifth channel estimator for estimating a CFR of a received symbol allocated to a data subcarrier and a virtual data subcarrier, respectively, using the CFR estimated by the first, third and fourth channel estimators; And a data demodulator for demodulating data using the CFR estimated by the fifth channel estimator.

The OFDM reception method of the present invention comprises the steps of: (a) estimating a channel frequency response (CFR) of a received symbol assigned to a pilot subcarrier; (B) estimating the CFR of the received symbol assigned to the virtual data subcarrier using the CFR estimated in the step (a); (C) demodulating virtual data using the CFR estimated in step (b); (D) estimating the CFR of the received symbol allocated to the virtual data subcarrier using the virtual data demodulated in step (c); (E) estimating the CFR of the received symbol assigned to the virtual pilot subcarrier using the CFR estimated in steps (a) and (d); Estimating the CFR of the received symbol allocated to the data subcarrier and the virtual data subcarrier, respectively, using the CFR estimated in steps (a), (d) and (e); And (g) demodulating data and virtual data using the CFR estimated in step (f).

According to the OFDM transmission and reception apparatus and method of the present invention, as the number of pilots can be reduced, the efficiency of the frequency spectrum can be increased, and the degradation of BER or FER performance in a receiver due to a reduced pilot subcarrier can be prevented. .

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the OFDM transceiver and method according to a preferred embodiment of the present invention.

2 and 3 illustrate a structure and a subcarrier allocation scheme of an OFDM based transmitting apparatus for portable mobile broadcasting according to an embodiment of the present invention, respectively.

As shown in FIG. 2, the OFDM transmission apparatus according to the present invention includes a data modulator 110, a pilot modulator 120, a virtual data modulator 130, a modulation order increaser 140, a constellation diagram rotater 150, and a symbol. The repeater 160, the subcarrier allocator 170, the OFDM modulator 180, and the front end 190 may be formed.

The data modulator 110 converts the data into modulated symbols such as QPSK, M-ary, QAM, and the like.

The pilot modulator 120 converts the pilot into a modulated symbol, for example, QPSK, M-ary, QAM, or the like.

The virtual data modulator 130 also converts the virtual data into modulated symbols such as, for example, QPSK, M-ary, and QAM. Here, the virtual data refers to data allocated to the virtual data subcarriers arranged at D _f intervals between the pilot subcarriers as shown in FIG. 3.

The modulation order increaser 140 increases the modulation order of the virtual data modulated by the virtual data modulator 130. For example, if the modulation symbol is QPSK, the modulation order increaser 140 collects two QPSK modulation symbols to generate one 16QAM symbol having an increased modulation order. This conversion process is shown in Fig. 3- (1).

The constellation rotator 150 rotates the constellation rotation of the virtual data whose modulation order is increased by the modulation order increaser 140. An example of such a constellation rotation process is shown in Figure 3- (2). These constellation rotation symbols show good performance in fading channels with high frequency selectivity (Ref. [1] ETSI EN 302 755 V1.2.0c (2008.7), Digital Video Broadcasting (DVB); Frame structure channel coding and modulation). for a second generation digital broadcasting system (DVB-T2). [2] ESTI TR 102 831 V0.9.2 (2008.9), Digital Video Broadcasting (DVB); Implementation guidelines for a second generation digital broadcasting system (DVB-T2) [3 ] Jung-Wook Suh, Kim Hyun-sik, Jeon Ki-ki, Baek Jong-ho, Kim Dong-gu, “Introduction of DVB-T2 Technology for Next Generation Terrestrial TV Standards for the ASO Era”, Journal of the Korean Institute of Communication Sciences, Vol. 25, No. 8, pp. 55 ~ 61, July 2008.].

The symbol repeater 160 repeatedly outputs virtual data rotated by the constellation rotation machine 150 to the subcarrier allocator 170 two or more times.

The subcarrier allocator 170 allocates input data, pilot and virtual data to the corresponding subcarrier. In particular, the subcarrier allocator 170 repeatedly assigns constellation rotation symbols (virtual data) input from the symbol repeater 160 to the virtual data subcarriers. An example of such a virtual data subcarrier allocation process is illustrated in FIG. 3- (3). In addition, such symbol repetition provides excellent reception performance (Refer to [7] IEEE Std. 802.16-2004, `` IEEE standard for local and metropolitan area networks-Part 16: Air interface for fixed broadband wireless access systems, '' Oct. 2004.).

The OFDM modulator 180 converts an OFDM symbol input from the subcarrier allocator 170 into a time domain and outputs the converted OFDM symbol. The OFDM modulator 180 includes an IFFT for converting an input OFDM symbol into a fast fast Fourier transform and outputs a guard interval insertion unit for inserting and outputting a guard interval to the input OFDM symbol.

The front end 190 converts an input OFDM symbol into an analog signal and wirelessly transmits the converted signal.

As described above, according to the OFDM transmission apparatus of the present invention, as the number of pilots can be reduced, efficiency for the frequency spectrum can be increased. Note, however, that the spacing of pilot subcarriers has been separated by the virtual data subcarriers. That is, instead of reducing the number of pilot subcarriers by increasing the distance between pilot subcarriers, the virtual data subcarriers can be further used, thereby increasing the overall frequency efficiency. However, the reduced pilot subcarrier causes the channel estimation performance of the receiver to be degraded, resulting in a decrease in BER or FER performance. Therefore, there is a need for a reception technique to solve this problem.

4 and 5 illustrate a structure and an operation process of an OFDM based receiving apparatus for portable mobile broadcasting according to an embodiment of the present invention, respectively.

As shown in FIG. 4, the OFDM receiver according to the present invention includes a front end 210, an OFDM demodulator 220, a subcarrier divider 230, a LS (Least Squares) channel estimator 240, and a LMMSE (Linear Minimum Mean). Square Error interpolator 250, combined demodulator 260, decision-directed channel estimator 270, LMMSE predictor 280, discrete fourier transform based channel estimator 290 and demodulator 295.

The front end 210 amplifies and converts an electromagnetic wave signal received through the antenna into digital data.

The OFDM demodulator 220 converts an OFDM symbol input from the front end 210 into a frequency domain and outputs the converted frequency symbol. The OFDM demodulator 220 includes a guard interval removal unit for removing a guard interval from an input OFDM symbol, and an FFT for fast Fourier transforming and outputting the input OFDM symbol.

The subcarrier divider 230 divides the OFDM symbols input from the OFDM demodulator 220 into data, pilot, and virtual data and outputs them.

The LS channel estimator 240 is a first channel estimator and estimates a channel frequency response (CFR) of a received symbol allocated to a pilot subcarrier. The estimation method is shown in Equation 1.

은 파일럿 부반송파 인덱스,

는 파일럿 개수,

는 주파수 영역에서의 k번째 수신심볼,

는 k번째 파일럿,

는 k번째 추정된 CFR을 나타낸다. 이러한 과정의 일 예를 도 5-(1)에 나타내었다.here,

Is the pilot subcarrier index,

Is the number of pilots,

Is the kth received symbol in the frequency domain,

Kth pilot,

Denotes the k th estimated CFR. An example of such a process is shown in Figure 5- (1).

The LMMSE interpolator 250 is a second channel estimator. The LMMSE interpolator 250 estimates the CFR of the received symbol allocated to the virtual data subcarrier using the CFR estimated by the first channel estimator, that is, the LS channel estimator 240, and the LMMSE filter coefficients. . The estimation method is shown in Equation 2.

은 가상 데이터 부반송파 인덱스,

는 가상 데이터 개수를 나타낸다. 또한 LMMSE 필터계수

은 수학식 3과 같이 나타낼 수 있다.here,

Is the virtual data subcarrier index,

Represents the number of virtual data. LMMSE filter coefficients

Can be expressed as in Equation 3.

here,

는 이상적인 CFR과 추정된 CFR의 상호 상관행렬,

는 추정된 CFR의 자기 상관행렬,

는 역행렬 연산,

은 행렬의 m번째 행, n번째 열에 해당하는 원소를 나타낸다.

Is the cross-correlation matrix of the ideal and estimated CFRs,

Is the autocorrelation matrix of the estimated CFR,

Is an inverse matrix operation,

Denotes an element corresponding to the m th row and the n th column of the matrix.

The combined demodulator 260 is a virtual data demodulator that combines and demodulates two or more pieces of the same virtual data using the CFR estimated by the second channel estimator, that is, the LMMSE interpolator 250. The process of combining and demodulating the virtual data is as shown in Equations 4 and 5.

은

와 관련된 동일한 가상 데이터를 갖는 부반송파 인덱스,

은 동일한 가상 데이터 개수,

은 결합계수로써 수학식 6과 같이 표현될 수 있다.here,

silver

Subcarrier index with the same virtual data associated with,

Is the same number of virtual data,

May be expressed as Equation 6 as a coupling coefficient.

here,

는 복소공액(complex conjugation)을 나타낸다. 또한

는 복조기를 나타내는데, 성좌도 회전기, 변조차수 증가기, 가상 데이터 변조기에 대한 복조기 또는 데이터 변조기에 대한 복조기로 사용될 수 있다.

Denotes complex conjugation. Also

Denotes a demodulator, which may be used as a demodulator for a constellation rotator, a modulation order increaser, a virtual data modulator, or a demodulator for a data modulator.

The DD channel estimator 270 is a third channel estimator. The DD channel estimator 270 estimates the CFR of the received symbol assigned to the virtual data subcarrier using the virtual data demodulated by the combined demodulator 260. The estimation method is shown in equation (7).

The LMMSE predictor 280 is a fourth channel estimator and uses a CFR estimated by the first and third channel estimators, that is, the LS channel estimator 240 and the DD channel estimator 270 (FIG. 5- (5). Estimate the CFR of the received symbol assigned to The estimation method is shown in Equation 8.

은 가상 파일럿 부반송파 인덱스,

는 가상 파일럿 개수를 나타낸다.here,

Is the virtual pilot subcarrier index,

Represents the virtual pilot number.

The DFT-based channel estimator 290 is a fifth channel estimator, which uses the CFR estimated by the first, third and fourth channel estimators, that is, the LS channel estimator 240, the DD channel estimator 270, and the LMMSE predictor 280. The CFR of the received symbol allocated to the data subcarrier and the virtual data subcarrier, respectively, is estimated. The estimation method is shown in Equation (9).

은 데이터 부반송파와 가상 데이터 부반송파 위치에서의 CFR로 이루어진 추정된 채널벡터이고,

은

이다.here,

Is an estimated channel vector consisting of the CFR at the data subcarrier and the virtual data subcarrier location,

silver

to be.

는

DFT(Discrete Fourier Transform) 행렬(

는 데이터 개수,

는 CIR(Channel Impulse Response)의 샘플링 단위 길이)이고,

는

DFT 행렬이다.Also,

Is

Discrete Fourier Transform (DFT) matrix (

Is the data count,

Is the sampling unit length of the channel impulse response (CIR),

Is

DFT matrix.

은 복소공액 전치(Hermitian transpose)이고,

은 수학식 1로부터 얻은 추정된 CFR, 수학식 7로부터 얻은 추정된 CFR, 수학식 8로부터 얻은 추정된 CFR로 구성된 채널벡터를 나타낸다.Also,

Is a Hermitian transpose,

Denotes a channel vector composed of an estimated CFR obtained from Equation 1, an estimated CFR obtained from Equation 7, and an estimated CFR obtained from Equation 8.

Meanwhile, the combined demodulator 260 demodulates the virtual data using the CFR of the received symbol allocated to the virtual data subcarrier estimated by the fifth channel estimator, that is, the DFT-based channel estimator 290. The demodulation process is shown in equations (4) and (5).

The demodulator 295 is a data demodulator. The demodulator 295 demodulates data using the CFR of the received symbol allocated to the data subcarrier estimated by the DFT-based channel estimator 290. The demodulation process is shown in equation (5).

As described above, according to the OFDM receiver of the present invention, it is possible to prevent the BER or FER performance degradation in the receiver due to the reduced pilot subcarrier.

FIG. 6 shows a structure of an OFDM-based transmitting device for portable mobile broadcasting according to another embodiment of the present invention, and FIG. 7 shows an architecture of an OFDM-based receiving apparatus for portable mobile broadcasting according to another embodiment of the present invention.

As shown in FIG. 6, the constellation rotating machine may not be included in the OFDM transmission apparatus of the present invention.

In addition, as shown in FIG. 7, the combined demodulator may demodulate the virtual data using the CFR estimated by the third channel estimator, that is, the DD channel estimator.

As described above, the OFDM transmission and reception apparatus and method of the present invention are not limited to the above-described embodiments, and various modifications and implementations can be made within the range permitted by the technical idea of the present invention.

In addition, the present invention can be applied to multiple input multiple output (MIMO) and relay (Relay) technology.

1 shows a general subcarrier allocation technique for an OFDM-based system for portable mobile broadcasting.

2 and 3 illustrate a structure and a subcarrier allocation scheme of an OFDM based transmitting apparatus for portable mobile broadcasting according to an embodiment of the present invention, respectively.

4 and 5 illustrate a structure and an operation process of an OFDM based receiving apparatus for portable mobile broadcasting according to an embodiment of the present invention, respectively.

6 shows a structure of an OFDM based transmitting apparatus for portable mobile broadcasting according to another embodiment of the present invention.

7 shows a structure of an OFDM-based receiving device for portable mobile broadcasting according to another embodiment of the present invention.

*** Explanation of symbols for the main parts of the drawing ***

110: data modulator 120: pilot modulator

130: virtual data modulator 140: modulation order increaser

150: constellation rotation machine 160: symbol repeater

170: subcarrier allocator 180: OFDM modulator

190: front end

210: front end 220: OFDM demodulator

230: subcarrier divider 240: LS channel estimator

250: LMMSE interpolator 260: coupled demodulator

270: DD channel estimator 280: LMMSE predictor

290: DFT based channel estimator 295: demodulator

Claims (6)

A virtual data modulator for modulating the virtual data; A modulation order increaser for increasing a modulation order of virtual data modulated by the virtual data modulator; A symbol repeater for repeatedly outputting virtual data whose modulation order is increased by the modulation order increaser to a subcarrier allocator at least two times; And And a subcarrier allocator for allocating virtual data input from the symbol repeater to the effective subcarriers among all subcarriers including a virtual carrier and an effective subcarrier. The method of claim 1, And a constellation rotator configured to constellation rotate virtual data of which the modulation order is increased by the modulation order increaser. And the symbol repeater outputs virtual data rotated by the constellation rotation machine to the subcarrier allocator at least twice. Modulating the virtual data; Increasing a modulation order of the modulated virtual data; Constellation rotation of the virtual data having increased modulation order; And And allocating at least two times the constellation rotated virtual data to the effective subcarrier among all subcarriers including the virtual carrier and the effective subcarrier. A first channel estimator for estimating a channel frequency response (CFR) of a received symbol assigned to a pilot subcarrier; A second channel estimator for estimating a CFR of a received symbol allocated to a virtual data subcarrier using the CFR estimated by the first channel estimator; A virtual data demodulator for demodulating virtual data using the CFR estimated by the second channel estimator or the CFR estimated by the fifth channel estimator; A third channel estimator for estimating a CFR of a received symbol assigned to a virtual data subcarrier using the demodulated virtual data; A fourth channel estimator for estimating the CFR of the received symbol allocated to the virtual pilot subcarrier using the CFR estimated by the first and third channel estimators; A fifth channel estimator for estimating a CFR of a received symbol allocated to a data subcarrier and a virtual data subcarrier, respectively, using the CFR estimated by the first, third and fourth channel estimators; And And a data demodulator for demodulating data using the CFR estimated by the fifth channel estimator. A first channel estimator for estimating a channel frequency response (CFR) of a received symbol assigned to a pilot subcarrier; A second channel estimator for estimating a CFR of a received symbol allocated to a virtual data subcarrier using the CFR estimated by the first channel estimator; A virtual data demodulator for demodulating virtual data using the CFR estimated by the second channel estimator or the CFR estimated by the third channel estimator; The third channel estimator for estimating a CFR of a received symbol assigned to a virtual data subcarrier using the demodulated virtual data; A fourth channel estimator for estimating the CFR of the received symbol allocated to the virtual pilot subcarrier using the CFR estimated by the first and third channel estimators; A fifth channel estimator for estimating a CFR of a received symbol allocated to a data subcarrier and a virtual data subcarrier, respectively, using the CFR estimated by the first, third and fourth channel estimators; And And a data demodulator for demodulating data using the CFR estimated by the fifth channel estimator. Estimating a channel frequency response (CFR) of a received symbol assigned to a pilot subcarrier; (B) estimating the CFR of the received symbol assigned to the virtual data subcarrier using the CFR estimated in the step (a); (C) demodulating virtual data using the CFR estimated in step (b); (D) estimating the CFR of the received symbol allocated to the virtual data subcarrier using the virtual data demodulated in step (c); (E) estimating the CFR of the received symbol assigned to the virtual pilot subcarrier using the CFR estimated in steps (a) and (d); Estimating the CFR of the received symbol allocated to the data subcarrier and the virtual data subcarrier, respectively, using the CFR estimated in steps (a), (d) and (e); And And (g) demodulating data and virtual data using the CFR estimated in step (f).

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