WO2008082242A1

WO2008082242A1 - Apparatus and method for estimating channel of amc mode in mimo system based ofdm/ofdma

Info

Publication number: WO2008082242A1
Application number: PCT/KR2007/007043
Authority: WO
Inventors: Zheng Zi Li; Byung-Chul Kim
Original assignee: Posdata Co., Ltd.
Priority date: 2006-12-31
Filing date: 2007-12-31
Publication date: 2008-07-10

Abstract

The present invention relates to an apparatus and method for estimating a channel in a MIMO wireless telecommunication system supporting the 0FDM/0FDMA. The present invention, in the AMC mode in the MIMO wireless telecommunication system, comprises estimating at least one of a time offset and a carrier frequency offset by using two or more pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and a received signal of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; compensating at least one of the estimated time offset and the carrier frequency offset; and estimating a channel of each of the received signal by using pilots included in each of the received signal in which at least one of the time offset and the carrier frequency offset is compensated.

Description

Description Apparatus and Method for Estimating Channel of AMC Mode in

MIMO system based OFDM/OFDMA Technical Field

[1] The present invention relates to an apparatus and method for estimating a channel in a MIMO wireless telecommunication system supporting the OFDM/OFDMA, more particularly, to an apparatus and method for estimating and compensating a time offset and a carrier frequency offset for the downlink band AMC(Adaptive Modulation & Coding) mode and estimating a channel based on it in a MIMO wireless telecommunication system which supports the OFDM/OFDMA while employing a standard such as the IEEE 802.16d/e, Wibro, WiMAX. Background Art

[2] In the WiBro (Wireless Broadband Internet) which is a Korean wireless portable internet standard, the OFDM (Orthogonal Frequency Division Multiplexing) is used as a signal transmission scheme so as to provide the high speed data service in the radio environment when a user moves. In addition, the OFDMA (Orthogonal Frequency Division Multiple Access) which is based on the OFDM is used as a multiple access scheme so that multi users might simultaneously receive an internet service. The TDD (Time Division Duplexing) which classifies the downlink and the uplink according to a time is used as a duplexing scheme.

[3] In such a wireless telecommunication system supporting the OFDM and/or

OFDMA, in order to perform a smooth communication between a base station and a terminal, the characteristic of a channel which is mutually formed should be known. For this, firstly, the synchronization has to be mutually made. Further, the operation of an oscillator of a terminal has to be exact.

[4] However, in case of the terminal, the time offset and the carrier frequency offset can be generated due to various factors such as a multi path characteristic between the receiving side and the transmission side, the time- varying characteristic which is generated as the terminal or the electric wave obstacle moves. Therefore, the terminal should continuously estimate and compensate the time offset and the carrier frequency offset. Ultimately, the terminal should estimate and compensate the channel which is mutually formed based on this.

[5] In the meantime, in a MIMO (Multiple Input Multiple Output) system which performs the multiple input and multiple output transmission by using a plurality of transmitting antennas and a plurality of receiving antennas, a plurality of channels exist between the transmission side and the receiving side. In particular, it is necessary to estimate a time offset and a carrier frequency offset to be suitable for the downlink band AMC mode in the MIMO system, and based on them, to estimate and compensate a plurality of channels. Disclosure of Invention

Technical Problem

[6] The invention has been designed to solve the above-mentioned problems, and it is an object of the invention to provide an apparatus and method for estimating a channel in a MIMO wireless telecommunication system which supporting the OFDM/OFDMA.

[7] It is another object of the present invention to provide an apparatus and method for estimating and compensating a time offset by using a pilot pattern of the AMC mode, and estimating a channel based on it in a MIMO wireless telecommunication system supporting the OFDM/OFDMA.

[8] It are still another object of the present invention to provide an apparatus and method for efficiently estimating and compensating a carrier frequency offset by using a pilot pattern of the AMC mode, and estimating a channel based on it in a MIMO wireless telecommunication system supporting the OFDM/OFDMA. Technical Solution

[9] According to an aspect of the present invention, provided is an apparatus for estimating a channel, which comprises offset estimating means for estimating at least one of a time offset and a carrier frequency offset by using two or more pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; offset compensating means for compensating at least one of the estimated time offset and the carrier frequency offset; and channel estimating means for estimating a channel of each of the received signal by using pilots included in each of the received signal in which at least one of the time offset and the carrier frequency offset is compensated, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

[10] Preferably, the offset estimating means includes a time offset estimating means for estimating a time offset by using two or more pilots in which the carrier frequency offset is compensated or which have the same symbol index, and/or a carrier frequency offset estimating means for estimating a carrier frequency offset by using two or more pilots in which the time offset is compensated or which have the same subcarrier index. In addition, the channel estimating means estimates each channel by performing an averaging or an interpolation of the pilots included in each of the received signal. [11] According to an aspect of the present invention, provided is a method for estimating a channel comprising the steps of: a) estimating at least one of a time offset and a carrier frequency offset by using two or more pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; b) compensating at least one of the estimated time offset and the carrier frequency offset; and c) estimating a channel of each of the received signal by using pilots included in each of the received signal in which at least one of the time offset and the carrier frequency offset is compensated, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

Advantageous Effects

[12] According to the present invention, in a MIMO wireless telecommunication system supporting the OFDM/OFDM A, it has an effect that the time offset and/or the carrier frequency offset can be estimated and compensated by efficiently using a pilot pattern of the AMC mode. Further, according to the present invention, the channel can be accurately estimated, thereby, the receiving performance of a terminal can be enhanced. Brief Description of the Drawings

[13] Figure 1 is a drawing showing an example of a frame structure which is used in a portable Internet system supporting the IEEE 802.16d/e.

[14] Figure 2 is a detailed structure diagram for a downlink band AMC region of frame illustrated in Fig. 1.

[15] Figure 3 is a schematic diagram illustrating a SISO system and a MIMO system.

[16] Figure 4 is a drawing illustrating a signal transmission method between transmitting antennas and receiving antennas in a 2x2 MIMO system.

[17] Figure 5 is a drawing exemplifies pilot patterns of the AMC mode with which a first transmitting antenna and a second transmitting antenna transmit respectively in a 2x2 MIMO system.

[18] Figure 6 is a configuration diagram showing a channel estimating apparatus according the present invention.

[19] Figure 7 is a detailed configuration diagram for a time offset estimating means of Fig. 6. [20] Figure 8 is a drawing illustrating the preamble transmitting structure divided into three segments (Segment 0, Segment 1, Segment 2), in relating to a first time offset estimating method according the present invention. [21] Figure 9 is a drawing illustrating a second time offset estimating method according the present invention. [22] Figure 10 is a drawing illustrating a third time offset estimating method according the present invention. [23] Figure 11 is a detailed configuration diagram for a carrier frequency offset estimating means of Fig. 6. [24] Figure 12 is a drawing illustrating a first carrier frequency offset estimating method according the present invention. [25] Figure 13 is a drawing illustrating a second carrier frequency offset estimating method according the present invention. [26] Figure 14 is a drawing illustrating a first channel estimating method according the present invention. [27] Figures 15 and 16 are drawings illustrating a second channel estimating method according the present invention. [28] Figure 17 is a flowchart of a channel estimating method according to the present invention. [29] Figure 18 is a flowchart of a time offset estimating method according to the present invention. [30] Figure 19 is a flowchart of a carrier frequency offset estimating method according to the present invention.

Mode for the Invention [31] Hereinafter, an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. Well known functions and constructions are not described in detail since they would obscure the invention in unnecessary detail. [32] Figure 1 is a drawing showing an example of a frame structure which is used in a portable Internet system supporting the IEEE 802.16d/e. [33] In the portable Internet system employing a TDD, one frame is time-divided to be used for transmission and receiving. [34] Referring to Fig. 1, one frame is divided into a downlink frame where data is transmitted from a base station to a terminal and an uplink frame where data is transmitted from the terminal to the base station. A TTG (Transmit/receive Transition

Gap) and a RTG (Receive/transmit Transition Gap) are inserted respectively between the downlink frame and the uplink frame. In the illustrated example, the downlink frame includes at least one of a preamble region, a PUSC (Partial Usage of Subchannels) region, a FUSC (Full Usage of Subchannels) region, and an AMC (Adaptive Modulation & Coding) region, while the uplink frame includes at least one of an uplink control symbol region, a PUSC region, and an AMC region.

[35] The present invention is related with the downlink AMC region transmitting a pilot subcarrier and a data subcarrier in the AMC mode. In the meantime, in case the 1024 FFT (Fast Fourier Transform) is used among subcarrier allocation schemes for the downlink AMC mode, the allocation can be performed as shown in the following table 1. FIG. 2 illustrates part of a subcarrier allocation structure according to Table 1.

[36] Table 1

[37] Referring to Table 1 and Fig. 2, in the AMC mode using 1024 FFT, 80 and 79 subcarriers on the right and left side among the total 1024 subcarriers are used respectively as a safeguard region for alleviating the interference between neighboring channels, while one of them is used as a DC subcarrier. Further, 864 subcarriers excepting the above subcarriers are used as a valid subcarrier. In this case, among the valid subcarriers, 96 subcarriers are used as pilot subcarriers, while the remaining 768 subcarriers are used as data subcarriers.

[38] In case of the AMC mode, the basic unit of the AMC subchannel is a bin. The bin is comprised of nine subcarriers adjacent in the same symbol, while one of them is a pilot subcarrier, and the remaining eight subcarriers are data subcarrier. In addition, the AMC subchannel region is comprised of slots, while one slot is comprised of two bins and three OFDMA symbols in the subcarrier-symbol axis, thus, comprised of the total six adjacent bins. In addition, the dedicated pilot can be included in the burst.

[39] In the meantime, the present invention is applied to the MIMO system which performs the multiple input and multiple output transmission by using a plurality of transmitting antennas and a plurality of receiving antennas. Hereinafter, referring to Fig. 3 to Fig. 5, the MIMO system will be illustrated.

[40] Firstly, Figure 3 is a drawing illustrating the outline of the SISO system and the

MIMO system.

[41] As shown in Figure 3a, the SISO system performs the single input and single output transmission through one channel (H) which is formed between a transmitting antenna TxAnt and a receiving antenna RxAnt.

[42] Unlike the above configuration, the MIMO system performs the multiple input and multiple output transmission through a plurality of channels which are formed between a plurality of transmitting antennas and a plurality of receiving antennas. Figure 3b illustrates a 2x2 MIMO system using two transmitting antennas and two receiving antennas. As shown in the drawing, four channels, that is, a first channel HOO, a second channel HOl, a third channel HlO, and a fourth channel HI l) are formed between a first, a second transmitting antennas TxAntO, TxAnt 1, and a first, a second receiving antennas RxAntO, RxAnt 1. For reference, in marking the channel, the first index is related to the index of a receiving antenna, and the second index is related to the index of a transmitting antenna.

[43] Hereinafter, the signal transmission method of a 2x2 MIMO system will be illustrated with reference to Fig. 4.

[44] In the downlink region, the base station (Radio Access Station) transmits signals through two transmitting antennas (TxAntO, TxAnt 1), while the terminal (Mobile Station/Portable Subscriber Station) receives signals through two receiving antennas (RxAntO, RxAntl). In this case, a preamble is transmitted from one antenna of two transmitting antennas, while a first receiving antenna (RxAntO) and a second receiving antenna (RxAntl) receive the preamble through a first channel (HOO) and a third channel (HlO) respectively (refer to Fig. 4a).

[45] In the mean time, the pilots are transmitted from a first and a second transmitting antenna (TxAntO, TxAntl) with different patterns. A first receiving antenna (RxAntO) receives the pilots transmitted from the first and the second transmitting antenna through a first channel (HOO) and a second channel (HOl), while a second receiving antenna (RxAntl) receives the pilots transmitted from the first and the second transmitting antenna through a third channel (HlO) and a fourth channel (Hl 1) respectively (refer to Fig. 4b). [46] In the mean time, in case the AMC mode is used in the 2x2 MIMO system performing the space time code (STC) transmission, the locations of the pilots in the signal transmitted from the first and the second transmitting antenna can be calculated by the following Equation 1. For reference, in the following Equation 1, the locations of the pilots transmitted from the first transmitting antenna are related with the even symbol, while the locations of the pilots transmitted from the second transmitting antenna are related with the odd symbol.

[47] [Equation 1]

[48]

PilotsLocation = 9x + 3 (2 x LAMC_SymbolNumber/2j % 3) + 1 [49] Here, 'PilotsLocation' is a variable that indicates the location of the pilot, that is, indicates the subcarrier index in which the pilot is loaded. 'x(=0,l,2,...,95)' is a variable that indicates the location of the pilot according to the increase of subcarrier index for 96 pilots included in the same symbol. 'AMC_SymbolNumber' is a variable that indicates the symbol number or the symbol index in the AMC mode. In addition, '%' is a modular operator, '

L J

' is the gaussian function or the floor function.

[50] In the meantime, Figure 5 is a drawing showing pilot patterns of AMC mode in which the first transmitting antenna (TxAntO) and the second transmitting antenna (TxAntl) according to the above method (refer to Equation 1).

[51] Referring to Figure 5, the first transmitting antenna (TxAntO) transmits the pilot and data with the pattern illustrated in Fig. 5a, while the second transmitting antenna (TxAntl) transmits the pilot and data with the pattern illustrated in Fig. 5b. Then, the first receiving antenna (RxAntO) receives a first and a second received signal (that is, received signal of a first channel and a second channel) through the first and the second channel (HOO, HOl), while the second receiving antenna (RxAntl) receives a third and a fourth received signal (that is, received signal of a third channel and a fourth channel) through the third and the fourth channel (HlO, Hl 1). Thereby, all signals (downlink frame) transmitted from two transmitting antennas are received.

[52] Hereinafter, the apparatus and method for estimating a channel according to the present invention will be described with reference to Figure 6 to Figure 19. For reference, the present embodiment relates to the apparatus and method for estimating a channel applied to the 2x2 MIMO system. The AMC mode used in the present embodiment adapts the above described pilot patterns.

[53] As shown in Figure 6, the channel estimating apparatus according to the present invention includes a FFT (Fast Fourier Transform) means 100, an offset estimating means 200, an offset compensating means 300, and a channel estimating means 400.

[54] The FFT means 100 transforms the signal of the time domain which is received through a first and a second receiving antenna of a terminal respectively and converted into a signal of baseband, into a signal of the frequency domain. Here, the FFT means 100 can be comprised of a first FFT means 110 and a second FFT means 120. In this case, the first FFT means 110 converts the received signal of the first channel and the second channel of the time domain, which is received through the first receiving antenna, into the signal of the frequency domain. The second FFT means 120 converts the received signal of the third channel and the fourth channel of the time domain, which is received through the second receiving antenna, into the signal of the frequency domain. Of course, the FFT means 100 can be divided into four parts so as to convert the signal of the time domain received in each channel H00, HOl, HlO, Hl 1 into the signal of the frequency domain, whereas the signal of all time domains can be converted into the signal of the frequency domain in one FFT means.

[55] The offset estimating means 200 estimates a time offset (TO) and/or a carrier frequency offset (CFO) by using the transformed signal of frequency domain. The signal of frequency domain transformed in the FFT means 100 includes the preamble, the pilot, and data. The preamble is extracted in a preamble extracting means (not shown) and the pilot is extracted in a pilot extracting means (not shown), so that they are inputted into the offset estimating means 200. Then, the offset estimating means 200 estimates the time offset and the carrier frequency offset by using the preamble and the pilot which are extracted like this. The offset estimating means, as shown in Figure 6, is divided into a time offset estimating means 210 that estimates a time offset and a carrier frequency offset estimating means 220 that estimates a carrier frequency offset.

[56] Hereinafter, the time offset estimating means will be described in detail with reference to Figure 7 to Figure 10.

[57] As shown in Figure 7, the time offset estimating means 210 includes a first phase difference operator 211, a first phase difference accumulator 212, a first linear phase operator 213, and a time offset (TO) operator 214.

[58] The first phase difference operator 211 calculates the phase difference according to the time offset by using two or more preambles or pilots obtained from at least two or more bins for at least one received signal among the received signal of the first and the second channel which is received through the first receiving antenna, and the received signal of the third and the fourth channel which is received through the second receiving antenna.

[59] In order to accurately calculate the phase difference according to the time offset, the carrier frequency should not be reflected. For this, two or more pilots having the same symbol index can be selected to calculate the phase difference according to the time offset. Alternatively, the phase difference according to the time offset can be calculated by using two or more pilots in which the carrier frequency offset is compensated. The phase difference operator, for example, can be implemented as a multiplier performing the conjugate multiplication for two complex numbers.

[60] The first phase difference accumulator 212 generates a phase difference accumulation value by accumulating the phase differences according to the respective time offset which is calculated in the first phase difference operator 211. The first phase difference accumulator 212 can estimate more accurate time offset by accumulating the phase differences calculated for much more preambles and/or pilots. For reference, the first phase difference accumulator 212 can be implemented as an adder.

[61] The first linear phase operator 213 transforms the phase difference accumulation value accumulated in the first phase difference accumulator 212 into the linear phase (θ ) according to the time offset. The phase difference accumulation value can be expressed as complex number. Accordingly, the first linear phase operator 213 obtains the linear phase according to the time offset, as to the phase difference accumulation value with the form in which a real number part is the denominator while an imaginary number part is the numerator, by performing the arctan operation and dividing the result by the difference of the subcarrier index (that is, the difference of subcarrier location of the preamble or the pilot used in the phase difference operation). Here, the arctan operation can be performed by using a look-up table in which the input is the ratio of a real number part and an imaginary number part while the output is the calculated value by the arctan operation. Of course, the linear phase can also be obtained by using another well known method.

[62] The linear phase (θ ) for the time offset obtained like this indicates an average phase difference according to the time offset which occurs between adjacent subcarriers (that is, the subcarriers in which the difference of subcarrier index is 1).

[63] The time offset operator 214 transforms the linear phase (θ ) according to the time offset, which is calculated in the first linear phase operator 213, into the time offset TO. For example, in case 1024 FFT is used like the present embodiment, the time offset TO can be calculated like the following Equation 2.

[64] [Equation 2]

[65]

[66] Hereinafter, several methods of estimating a time offset described above will be illustrated in detail with reference to Figure 8 to Figure 10. [67] First, it is a method of estimating a phase difference according to a time offset by using a preamble (hereinafter, 'a first time offset estimating method'). [68] As shown in Figure 1, the first symbol of downlink frame is used as a preamble. Now that such preamble has a high signal level and the same symbol index, it is easy for estimating a phase difference according to the time offset.

[69] In Figure 8, the preamble transmission structure divided into three segments (Segment 0, Segment 1, Segment 2) is illustrated. The base station transmits the preamble subcarrier with a pattern corresponding to one of the three segments. [70] Referring to Figure 8, the guard bands (Left Guard, Right Guard) for reducing the interference of the neighboring frequency band are formed in the left and right of the preamble subcarrier, and the first segment (Segment 0) includes the DC subcarrier (the preamble subcarrier index = 142). In addition, it can be recognized that the phase difference corresponding to the treble of the linear phase according to the time offset is generated between the adjacent preamble subcarriers (when the difference of the preamble index is 1) in one segment, while the phase difference corresponding to the six-fold of the linear phase according to the time offset is generated in case the difference of the preamble index is 2.

[71] For reference, the following Equation 3 indicates an example of the operation result of the linear phase according to the time offset which is calculated in the first linear phase operator 213 after passing through the first phase difference operator 211 and the first phase difference accumulator 212. In the Equation 3, 'P' indicates a preamble subcarrier. 'k' indicates a preamble subcarrier index, 'm' indicates a receiving antenna index, and 'w' indicates a weight. Here, the weight can be calculated based on the subcarrier signal magnitude, and the CINR (Carrier to Interference and Noise Ratio) etc.

[72] [Equation 3] [73]

for Segment 0

for otherwise

[74] Second, it is method in which the phase difference is calculated according to the time offset by using a pilot pair having the same symbol index (hereinafter, 'a second time offset estimating method'). In this case, it is preferable that the pilot pair has the subcarrier index difference which is a multiple of 9. Referring to Figure 9, in the AMC mode, in connection with the first received signal and/or the third received signal, in case of the symbol index 0, the pilot 'Pl' is positioned in the subcarrier index 1 and the pilot 'P2' is positioned in the subcarrier index 9.

[75] Accordingly, since the pilot Pl and P2 have the same symbol index, and the difference of the subcarrier indexes is 9, it can be known that the phase difference corresponding to 9 times of the linear phase according to the time offset is generated. The following Equation 4 generalizes this, and obtains the linear phase according to the time offset calculated in the first linear phase operator 213 by using pilot P(I, s,c) and P(2,s,c) having the same symbol among pilots included in the first to the fourth received signal.

[76] Here, in the P(a,s,c), 'a' indicates a pilot index, V indicates a symbol index, and 'c' indicates a slot index, 'in' indicates a receiving antenna index, 'Num' indicates the number of symbol which is used, 'Cnum' indicates the index of a slot which is used, and 'w' indicates a weight value. For reference, the first received signal corresponds to the case in which s=0, m=0. The second received signal corresponds to the case in which s=l, m=0. The third received signal corresponds to the case in which s=0, m=l. The fourth received signal corresponds to the case in which s=l, m=l.

[77] [Equation 4]

[78]

[79] Third, it is a method in which the phase difference according to the time offset is calculated by using two pairs of pilots having the same symbol index difference (hereinafter, 'a third time offset estimating method').

[80] Here, two pairs of pilots do not certainly mean four pilots. As described later, it includes the case in which one pilot is in common.

[81] Referring to Figure 10, the linear phase according to the carrier frequency offset can be offset in case of using the relation (all the symbol index difference is 2) of a pilot pair of the pilot Pl having the subcarrier index 1 and the symbol index 0 and the pilot Pl having the subcarrier index 7 and the symbol index 2, and a pilot pair of the pilot Pl (it is a common pilot) having the subcarrier index 7 and the symbol index 2 and the pilot P2 having the subcarrier index 10 and the symbol index 0. Accordingly, the linear phase according to the time offset can be obtained.

[82] The following Equation 5 to Equation 9 are an example of generalizing it, indicating the result of the linear phase according to the time offset calculated in the first linear phase operator 213 with a various mode by using the location relation of three pilots.

[83] Here, in the P(a,s), 'a' indicates the pilot index, V indicates the symbol index, 'm' indicates the receiving antenna index, 'Num' indicates the number of symbol index which is used, and 'w' indicates a weight value. In addition, the first received signal corresponds to the case in which s=0, and m=0. The second received signal corresponds to the case in which s=l, and m=0. The third received signal corresponds to the case in which s=0, and m=l. The fourth received signal corresponds to the case in which s=l, and m=l. For reference, in the following Equation, 's=0:6:Num' means s=0, 0+6, 0+6+6, ..., Num.

[84] [Equation 5] [85] (5-1) [86]

[87] (5-2)

[88]

[89] (5-3)

[90]

[91] (5-4) [92]

[93] [Equation 6] [94] (6-1) [95]

[96] (6-2) [97]

[98] (6-3) [99] lm{ ∑ ∑∑ (P_m(ls + \,c) ■ P_m(\,s + 3,c)^" ■ w_m(s ,c))} tan

2 9 Re{ ∑ ∑∑(/⁾ _mα5+l,c)-P_m(l,s+3.c)^*-H'_m(s,c))}

hum Cnum 1

Im f ∑ ∑∑(/⁾ _m(l,s+3,6)-P_m(2.s₊l,6)^*-w_m(s,f))}

+ tan

Re{ ∑ ∑ ∑(P_ra (l,s + 3. c)- P_m (2,s + l. c)^" -w_m(s.c))}

[100] (6-4) [101]

Tm{ ∑ ∑ ∑(f_ra(l. s + I, c)-P_ra(l, ? + 3,c)^*-M-'_m(s,c))}

1 i tan^"

2 9

Re{ ∑ ∑ ∑(^p _m0-⁵ + l-c)- P_m(l. f + 3,c)^{* •} w_ra(.9,c))} j = loΛ»ra c=0 m=0

Im{ ∑ ∑ ∑(P_m(l,i' + 3,c)-P_m(2.5' + l,c)ⁱ-w_m(5,c))!

+ tan

^Re< Σ ∑∑(P_m(l-S + 3,c)-PJ2.s + l.cy-wJs.c))}

[102] [Equation 7] [103] (7-1) [104]

[105] (7-2) [106] 0_m

[107] (7-3) [108]

Im{ ^ ^ ∑(^(l-s +4.6)-P_Λ(l,_ +2,cγ- w_m(s, c))\ tan

2 9 Re{ £ ^ ^(i³ _m(l^ + 4.c)-P_m(l,i- + 2,c)^*-w_m(j-,c))}

[109] (7-4) [HO]

Im { £ ∑∑(P_m(l,s + 4,c) -P_1n(Ls + 2,c)^* -njs.t))}

1 i tan

2 9

Re{ ∑ ^C∑ ∑ (C 0Λ + 4, c) • /; (1..s + 2, c)^" • M „, ( Ϊ. c))} s=i r ιv™ _L=υ m=π

Im{ £ ∑ ∑(PJ},s + 2,c) ■ PJ2,s + 4.C)" -w_m(s,c))} tan s~\ 6 fywm c-O m-0

^Re< Σ ∑∑(PJls + 2,c)-P_m(2,s + 4.c)'-w_m(s,cm

[111] [Equation 8] [112] (8-1) [113]

[114] (8-2)

[115]

[116] (8-3)

[117]

Im { £ ∑∑(/^J _ra(l,9 + 4,c)-/^> _m(2.ϊ.c)^*-τ*_m(9.c))}

+ tan

Re{ ∑ ∑∑(P,.(l,5+4,c)-_JP₁.(2,ϊ.c)^*-iv_m(₅,c))}

[118] (8-4) [119]

+ tan

[120] [Equation 9] [121] (9-1) [122]

[123] (9-2)

[124]

[125] (9-3)

[126]

^Imϊ Σ ∑∑(^,(l^ + 2.c)-P_m(2^ + 4,c)^*-_Wm(^c))}

1 1 tan s-06 V;vm e-0 m-0 ~2V Re ! ∑ ∑ ∑ (P_n, (1. s + 2. c) • P_n, (2, s + 4. c)^" ■ w_m ( s , c))}

Im { ∑ ∑ ∑(P_m(2.i + 4.c)-P_m(2,5 + 2.c)^*-w_m(5',c))} tan S-U 6 m-0

^Re^ Σ Σ∑(^(²-^s+⁴^¹)-^,(2.s+2.6')^*->i'_B,(s,6))} s=ϋ o m = 0 [127] (9-4) [128] hum Cnum 1

Im { ∑ ∑ ∑(P_m(\.s + 2,c) - P_m{2.s + 4,c)^" - w_m(s,c))) tan

2 9 hum Cmim 1

^Reϊ Σ ∑ ∑(P_m(^ + 2.c) -P_m(2,s + 4.c)' - w_m(s,c))}

^Im! Σ ∑ ∑(PJ2._i + 4.c) -P_m(2._i + 2.c)" - wJs,c))\

+ tan hum Cnum

Re{ ∑ ∑ ∑ (P_m (2, s + 4. c) ■ P_m (2, s + 2, c)' ■ w_m (s. c))}

[129] In the meantime, besides the exemplified mode as described above, the linear phase according to the time offset can be obtained by using another combination of the preamble, the variable pilot, and the fixed pilot. [130] Finally, the linear phase (θ ) according to the time offset obtained like this is transformed into the time offset (TO) in the time offset operator 214, while it is used for compensating the time offset in the time offset compensating means 310.

[131] Hereinafter, referring to Figs. 11 to 13, a carrier frequency offset estimating means will be explained in detail. [132] As shown in Figure 11, a carrier frequency offset estimating means 220 includes a second phase difference operator 221, a second phase difference accumulator 222, a second linear phase operator 223, a carrier frequency offset (CFO) operator 224, and a parameter converter 225.

[133] The second phase difference operator 221 calculates the phase difference according to the carrier frequency offset by using two or more preambles and/or pilots obtained from at least two or more bins, for at least one received signal among the received signal of a first channel and a second channel (a first and a second received signal) received through a first receiving antenna and the received signal of a third channel and a fourth channel (a third and a fourth received signal) received through a second receiving antenna.

[134] In order to accurately calculate the phase difference according to the carrier frequency offset, the time offset should not be reflected. For this, the phase difference according to the carrier frequency offset can be calculated by selecting two or more preambles and/or pilots having the same subcarrier index. Alternately, the phase difference according to the carrier frequency offset can be calculated by using two or more pilots in which the time offset is compensated.

[135] The second phase difference accumulator 222 accumulates the phase difference according to each carrier frequency offset calculated in the second phase difference operator 221 to generate the accumulation value of phase difference. The second phase difference accumulator 222 accumulates the phase differences which are calculated for the more numbers of preambles and/or pilots, so that the more exact carrier frequency offset can be estimated.

[136] The second linear phase operator 223 converts the phase difference accumulative value accumulated in the second phase difference accumulator 222 into the linear r phase (θ CFO ) according ^& to the carrier freq ⁿuency ^J offset. The linear f phase ( ^\θ _CFQ )^/ according to the carrier frequency offset converted like this indicates the average phase difference for the carrier frequency offset which is generated between adjacent symbols (that is, subcarriers in which the difference of symbol index is 1).

[137] The carrier frequency offset operator 224 converts the linear phase (θ ) according to the carrier frequency offset, which is calculated in the second linear phase operator 223, into the carrier frequency offset CFO. For example, the carrier frequency offset CFO can be calculated by following Equation 10 in case the OFDM symbol region of a frame is 115.2D.

[138] [Equation 10]

[139]

CFϋ = θ_c,_o x —

[140] The parameter converter 225 converts the carrier frequency offset measured with the radian unit into the Hz (Hertz) value.

[141] Hereinafter, referring to Figs. 11 and 12, several examples of methods estimating the above-described carrier frequency offset will be explained.

[142] First, it relates to the above-described second time offset estimating method. It is method which calculate the phase difference according to the carrier frequency offset by using a pilot pair in which the time offset is compensated while having the different symbol index (hereinafter, 'a first carrier frequency offset estimating method'). The following Equation 11 generalizes it, indicating the result of the linear phase according to the carrier frequency offset calculated in the second linear phase operator 223 with a various method by using the location relation (refer to Figure 12) of two pilots in which the time offset is compensated.

[143] Here, '

P

' indicates the pilot in which the time offset is compensated. In the P(a,s), P(b,s), 'a(=0,l)'and 'b(=0,l)' indicates the pilot index. V indicates a symbol index, 'in' indicates the receiving antenna index. 'Num' indicates the number of symbol which is used, 'w' indicates a weight value. For reference, in following Equation (11-5), n=2, 4, 6, ..., 22.

[144] [Equation 11]

[145] (11-1) [146]

[147] (11-2) [148]

NumCmim 1

M∑ ΣΣ^PΛ^ s,c) -P_m(l,s + 2,c)' -w_m(s,c)}

, = — • tan NumCmim 1

Re J∑ ∑ ∑P_ra (2, s, c) ■ PJl, s + 2, c)" ■ wjs, c)}

[149] (11-3) [150]

[151] (11-4) [152]

^^{∑ ∑ ∑^c²'^^- ^^ ^²^⁾⁴ -^-^^

^_CJ-_O = - ' tan

^Ref∑ Σ ∑Λ(2,*,c)- Λ,(2,* + 2,f)^* -1",,(4-,C))

[153] (11-5) [154]

Num Cnum 1

Im{∑ ∑ ∑ 7^J _m(α, Λ-, c) • PJb, s + «, c)^" • Ή ',,,(Λ-, C)} r=n m=(ι

'^{CFO "} « ^{' tan} ' NumCmim 1

^Re(∑ Σ Σ ^P» (^- ^s' ^c) ^{■ P}» (*. ^s + "- ^c)^{" ■ lr}», (^ c)}

5=0 C=O m=O

[155] Second, it is the method that calculate the phase difference according to the carrier frequency offset by using two pairs of pilots having the same subcarrier index difference (hereinafter, 'a second carrier frequency offset estimating method'). Here, it dose not mean that two pairs of pilots are inevitably four pilots, and as described later, it includes the case in which one pilot is in common.

[156] Referring to Figure 13, the linear phase according to the time offset can be offset in case the relation (all subcarrier index difference is 3) of a pilot pair of pilot Pl having the subcarrier index 1 and the symbol index 0 and the pilot Pl having the subcarrier index 4 and the symbol index 4, and a pilot pair of pilot Pl (it is a common pilot) having the subcarrier index 4 and the symbol index 4 and the pilot Pl having the subcarrier index 7 and the symbol index 2 is used, thereby, the linear phase according to the carrier frequency offset can be obtained. [157] The Following Equations 12 to 14 is an example of generalizing this, indicating the result of the linear phase according to the carrier frequency offset calculated in the second linear phase operator 223 by using the location relation of three pilots. Here, in the P(a,s), 'a' indicates a pilot index, 's' indicates a symbol index, 'm' indicates a receiving antenna index. 'Num' indicates the number of symbol which is used, 'w' indicates a weight.

[158] [Equation 12] [159] (12-1) [160]

[161] (12-2) [162]

—

[163] (12-3) [164]

[165] (12-4) [166]

^Im* Σ ∑∑(^(l-* + 2,c) - /^> _M(l, ϊ + 4,c)^τ --*__I(.ϊ,c))}

+ tan

Re{ ∑ ∑ ∑(P_m(l.s + 2.c) -i^> _m(1.5 + 4,c)^* -w_m(s.c))}

[167] [Equation 13] [168] (13-1) [169]

[170] (13-2)

[171]

[172] (13-3)

[173]

Im{ ∑ ∑∑(Λ, (2- *, c)- ^(2,s + 2. C-)^" ._w,.(.-, c))} tan Λara Cmtm_\_

2 6 ^Rei Σ ∑∑(f.αw)-P,(2,j + 2,c)^*.».(_s,c))} s-06fywm C-I)

+ tan

[174] (13-4) [175]

hum Cnum 1

Im{ ∑ ∑∑CP_ra(2,,j.c)-.P_m(U + 4.c)^*- ,,(-?-c))}

+ tan

Re{ ∑ JX(P.(2,!_>c)'P.(l,! + 4.c)'.*.(j,c))}

[176] [Equation 14] [177] (14-1) [178]

[179] (14-2) [180] ^■ψ ^cψ^J ' P_m(2,s\c)-P_lι(2,Λ + 4,c)" -wjs;c) PJ2,* -2,c)- PJ2,s + 4,t)' -wjs,t)

7^ϊ,,(2,»,c)-^(2,» + 4,O P,, (2, i + 2, c ) ■ P_n, (2, i + 4, C-)

0_cro=^-tan-< wj c™, ⁱ Pj_2^ ^_c).p ₍2^ + 4,c)' w_^{s,c) ₊ P_m(2,s-2,c)-PJ2,s+4,c) -w_m(s,c) ,-ιft,,,, _< ,£~! P_m{2,s,c)-P,,(2,s I 4,cV k,(2,Λ I 2,c) P_m(2,ό I 4,c)^" '

[181] (14-3) [182]

Vum Om 1

Im{ ∑ ∑∑(P_M (2. s + 2, c) -P., (2. j + 4, c)^" -W₁. (j, c))}

+ tan

Re{ ∑ ∑∑(i³ _m(2,* + 2.c)-i³ _m(2.i + 4,c)"-M-_m(^c))} Vum c-0 m-0

[183] (14-4) [184]

[185] Third, it is method which calculate the phase difference according to the carrier frequency offset by using the preamble and the pilot transmitted from the same transmission antenna (hereinafter, 'a third time offset estimating method'). In this method, the linear phase according to the carrier frequency offset can be obtained by calculating the phase difference for the preamble and the pilot having the same subcarrier index and dividing this by the symbol index difference between the pilot and the preamble.

[186] In the meantime, besides the exemplified method as described above, the linear phase according to the carrier frequency offset can be obtained by using another combination of the pilot and the preamble.

[187] The linear phase (θ ) according to the carrier frequency offset obtained like this is transformed into the carrier frequency offset CFO of the radian unit in the carrier frequency offset operator 224. The carrier frequency offset CFO is transformed again into the Hz (Hertz) value in the parameter converter 225. Thereafter, it is used for compensating the carrier frequency offset in the carrier frequency offset compensating means 320. [188] Again, referring to Figure 6, the offset compensating means 300 compensates the carrier frequency offset and/or the time offset which is calculated as described above. For this, the offset compensating means 300 can be implemented to be divided into a time offset compensating means 310 compensating the time offset and a carrier frequency offset compensating means 320 compensating the carrier frequency offset.

[189] The time offset compensating means 310 compensates the error according to the time offset by amending the phase of the received signal by using the time offset estimated in the time offset estimating means 210. In addition, the carrier frequency offset compensating means 320 compensates the carrier frequency offset by amending the error of the oscillator through the AFC (Automatic Frequency Controller) based on the carrier frequency offset estimated in the carrier frequency offset estimating means 220.

[190] The channel estimating means 400 estimates each channel by using pilots included in each received signal in which the time offset and/or the carrier frequency offset is compensated. Referring to Figure 6, in the illustrated embodiment, the channel estimating means 400 can be implemented to be divided into a first channel estimating means 410 estimating a first channel (HOO) and a second channel (HOl) relating to the first receiving antenna and a second channel estimating means 420 estimating a third channel (HlO) and a fourth channel (Hl 1) relating to the second receiving antenna.

[191] Of course, the channel estimating means 400 can be implemented to be divided into four parts so as to estimate each channel (HOO, HOl, HlO, Hl 1). On the other hand, it can be implemented to estimate all channels in one channel estimating means.

[192] Hereinafter, referring to Figs. 14 to 16, the channel estimating method according to the present invention will be illustrated.

[193] First, it is the method in which the averaging of pilots included in each received signal which is received in the same receiving antenna after being transmitted from the same transmitting antenna is performed (hereinafter, 'a first channel estimating method'). That is, the channel estimating means 400 estimates the whole channel by averaging pilots included in a corresponding received signal by each channel for four channels (HOO, HOl, HlO, HI l).

[194] In this case, as shown in Fig. 14, the whole channel can be estimated by classifying a frame into a block consisting of the subcarrier and the symbol, averaging pilots included in each block, and estimating the channel for a corresponding block. In addition, the channel can be estimated after multiplying each pilot by weight before averaging the pilot. The described averaging method has the advantage in that it can be simply implemented and the computational complexity for the channel estimation is reduced.

[195] Second, it is the method in which the interpolation of pilots included in each received signal which is received in the same receiving antenna after being transmitted from the same transmitting antenna is performed (hereinafter, 'a second channel estimating method'). For example, in case of the first channel (HOO), as shown in Fig. 15, the channel of the symbol index axis is estimated by performing the interpolation, the copy, or the extrapolation in the direction of the symbol index axis, by using the pilots having the same subcarrier index.

[196] In this case, for the data which is positioned between two pilots on the symbol index axis, the interpolation is performed (refer to Fig. 15 ®). Additionally, for the data which is not positioned between two pilots on the symbol index axis, the copy of the estimation value of the adjacent pilot is performed or the extrapolation using two adjacent pilots is performed, so that the channel of the symbol index axis is estimated (refer to Fig. 15 ®' ).

[197] Further, now that the preamble is transmitted in the first channel (also, in the third channel), by interpolating by using the preamble, the estimation value of data which is not positioned between the two pilots can be obtained. In this way, after estimating the channel in the direction of the symbol index axis, by using this, the channel of the subcarrier index axis is estimated by performing the interpolation, the copy, and the extrapolation in the direction of the subcarrier index axis with the same method (refer to Fig. 16 ® (interpolation) and ©' (copy or extrapolation)). In case of the second to the fourth channel (HOl, HlO, Hl 1), the channel can be estimated with a similar method, thus the whole channel can be estimated.

[198] In the meantime, in the above-described example, by estimating channel in the direction of the subcarrier index axis after estimating channel in the direction of the symbol index axis, the whole channel was estimated. On the contrary, the method which estimates the whole channel by estimating channel in the direction of the symbol index axis after estimating channel in the direction of the subcarrier index axis can be used.

[199] It is a third method of combining (hereinafter, 'a third channel estimating method') the first channel estimating method (the average method) and the second channel estimating method (the interpolation method). That is, it is the method which performs the interpolation by using pilots included in an individual received signal which is transmitted from the same transmission antenna and received in the same receiving antenna, thereafter, the averaging it by block consisting of a predetermined subcarrier and symbol, and the estimation of the channel for a corresponding block.

[200] In this case, the computational complexity which obtains the channel gain in decoding can be reduced by forming the block consisting of a predetermined subcarrier and symbol to be identical with the block in which the decoding is performed.

[201] Hereinafter, referring to Figs. 17 to 19, channel estimating method according to the present invention will be illustrated. For reference, now that the detailed process or the principles of operation for channel estimating method can refer to the description of the above-described channel estimating apparatus, the overlapped detailed description will be omitted, and in the below, the time-serially generating step will be explained.

[202] Firstly, Figure 17 is a flowchart of the channel estimating method according to the present invention. As described above in the channel estimating apparatus, the signal of the time domain which is received respectively through the first and the second receiving antenna of the terminal and transformed into the base band is transformed into the signal of the frequency domain through the Fast Fourier Transform. In the transformed signal, the preamble, the pilot, and data are included. In the present embodiment, at least one is estimated among the time offset and the carrier frequency offset by using, mainly, the pilot.

[203] In detail, at step SI lO, among a plurality of receiving antennas, as to at least one received signal among the received signal of the first channel and the second channel received through the first receiving antenna and the received signal of the third channel and the fourth channel received through the second receiving antenna, at least one of the time offset and the carrier frequency offset is estimated by using two or more pilots obtained from at least two or more bins.

[204] The time offset can be estimated by using two or more pilots in which the carrier frequency offset is compensated or which have the same symbol index, while the carrier frequency offset be estimated by using two or more pilots in which the time offset is compensated or which have the same symbol index.

[205] Hereinafter, referring to Figure 18, the time offset estimating method will be simply illustrated. Firstly, at step S210, among a plurality of receiving antennas, as to at least one received signal among the received signal of the first channel and the second channel received through the first receiving antenna and the received signal of the third channel and the fourth channel received through the second receiving antenna, the phase difference according to the time offset is estimated for two or more pilots in which the carrier frequency offset is compensated or which have the same symbol index among the pilots obtained from at least two or more bins.

[206] At step S220, the phase difference according to the calculated time offset is accumulated. At step S230, the linear phase according to the time offset is calculated by using the phase difference according to the accumulated time offset. Finally, at step S240, the time offset is calculated based on the linear phase according to the time offset. The detailed description of the time offset estimating method can refer to the description of the time offset estimating means which is illustrated with reference to Figs. 7 to 10. In this case, the first to the third time offset estimating method can be applied. [207] Hereinafter, referring to Figure 19, the carrier frequency offset estimating method will be simply illustrated.

[208] Firstly, at step S310, among a plurality of receiving antennas, as to at least one received signal among the received signal of the first channel and the second channel received through the first receiving antenna and the received signal of the third channel and the fourth channel received through the second receiving antenna, the phase difference according to the carrier frequency offset is estimated for two or more pilots in which the time offset is compensated or which have the same subcarrier index among the pilots obtained from at least two or more bins.

[209] At step S320, the phase difference according to the calculated carrier frequency offset is accumulated. At step S330, the linear phase according to the carrier frequency offset is calculated by using the phase difference according to the accumulated carrier frequency offset. At step S340, the carrier frequency offset is calculated based on the linear phase according to the carrier frequency offset. Finally, at step S350, the carrier frequency offset is converted into the Hz (Hertz) value. Similarly, the detailed description of the carrier frequency offset estimating method can refer to the description of the carrier frequency offset estimating means which is illustrated with reference to Figs. 11 to 13. In this case, the first to the third carrier frequency offset estimating method can be applied.

[210] Again, referring to Figure 17, at step S 120, at least one of the estimated time offset and the carrier frequency offset is compensated. The time offset can be compensated, for example, by amending the phase of the received signal. The frequency offset can be compensated by amending the error of the oscillator through the AFC (Automatic Frequency Controller).

[211] Finally, at step S 130, each channel is estimated by using the pilot in which at least one among the time offset and the carrier frequency offset is compensated.

[212] As described in the first to the third channel estimating method, the channel can be estimated by averaging the pilots included in an individual received signal which is transmitted from the same transmission antenna and received in the same receiving antenna, or by performing the interpolation by using pilots transmitted from the same transmission antenna. Further, the channel can be estimated by the combination of the interpolation method and average method.

[213] In the meantime, the channel estimating apparatus can be applied to even in case of using a dedicated pilot. In this case, the channel can be estimated by extracting the dedicated pilots included in the same burst, and the process of offseting the weight vector multiplied in the transmission side is included.

[214] While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Therefore, the spirit and scope of the present invention must be defined not by described embodiments thereof but by the appended claims and equivalents of the appended claims.

Claims

[1] An apparatus for estimating a channel for AMC mode in a wireless telecommunication system supporting an OFDM or OFDMA, the apparatus comprising: offset estimating means for estimating at least one of a time offset and a carrier frequency offset by using two or more pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; offset compensating means for compensating at least one of the estimated time offset and the carrier frequency offset; and channel estimating means for estimating a channel of each of the received signal by using pilots included in each of the received signal in which at least one of the time offset and the carrier frequency offset is compensated, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

[2] The apparatus of claim 1, wherein the offset estimating means includes a time offset estimating means comprising: a first phase difference operator for calculating a phase difference according to the time offset for two or more pilots in which the carrier frequency offset is compensated or which have the same symbol index; a first phase difference accumulator for accumulating the calculated phase difference according to the time offset; a first linear phase operator for calculating a linear phase according to the time offset by using the accumulated phase difference according to the time offset; and a time offset operator for calculating the time offset based on the linear phase according to the time offset.

[3] The apparatus of claim 1, wherein the two or more pilots include a pilot pair which has a same symbol index while the difference of subcarrier index is a multiple of 9 in estimating the time offset.

[4] The apparatus of claim 1, wherein the two or more pilots include two pairs of pilots having the same symbol index difference in estimating the time offset.

[5] The apparatus of claim 1, wherein the offset estimating means includes a carrier frequency offset estimating means comprising: a second phase difference operator for calculating a phase difference according t o the carrier frequency offset for two or more pilots in which the time offset is compensated or which have the same subcarrier index; a second phase difference accumulator for accumulating the calculated phase difference according to the carrier frequency offset; a second linear phase operator for calculating a linear phase according to the carrier frequency offset by using the accumulated phase difference according to the carrier frequency offset; and a carrier frequency offset operator for calculating the carrier frequency offset based on the linear phase according to the carrier frequency offset.

[6] The apparatus of claim 1, wherein the two or more pilots include a pilot pair in which the time offset is compensated while having a different symbol index in estimating the carrier frequency offset.

[7] The apparatus of claim 1, wherein the two or more pilots include two pairs of pilots having the same subcarrier index difference in estimating the carrier frequency offset.

[8] The apparatus of claim 1, wherein the received signals of the first channel and the third channel include a preamble, and the offset estimating means estimates at least one of the time offset and the carrier frequency offset by additionally using the preamble included in at least one received signal among the received signals of the first channel and the third channel.

[9] The apparatus of claim 1, wherein the channel estimating means estimates each channel by performing an averaging or an interpolation of the pilots included in each of the received signal which is transmitted from a same transmitting antenna and received in a same receiving antenna.

[10] The apparatus of claim 9, wherein the channel estimating means performs an averaging or an interpolation of the pilots included in each block after classifying a frame into a block consisting of a predetermined subcarrier and symbol.

[11] The apparatus of claim 10, wherein the block consisting of the predetermined subcarrier and symbol is a slot.

[12] The apparatus of claim 9, in case the channel estimating means estimates the channel by performing the interpolation of the pilots, wherein the channel estimating means i) estimates the channel of subcarrier index axis after estimating the channel of symbol index axis by performing an interpolation, a copy, or an extrapolation in the direction of the symbol index axis by using the pilots having the same subcarrier index, or ii) estimates the channel of symbol index axis after estimating the channel of subcarrier index axis by performing the interpolation, the copy, or the extrapolation in the direction of the subcarrier index axis by using the pilots having the same symbol index.

[13] The apparatus of claim 1, wherein the channel estimating means supports at least one among IEEE 802.16d/e, Wibro, and WiMAX standard.

[14] A method for estimating a channel for AMC mode in a wireless telecommunication system supporting an OFDM or OFDMA, the method comprising the steps of: a) estimating at least one of a time offset and a carrier frequency offset by using two or more pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; b) compensating at least one of the estimated time offset and the carrier frequency offset; and c) estimating a channel of each of the received signal by using pilots included in each of the received signal in which at least one of the time offset and the carrier frequency offset is compensated, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

[15] The method of claim 14, wherein the step a) includes at least one of the steps of: a-1) estimating the time offset by using two or more pilots in which the carrier frequency offset is compensated or which have the same symbol index; and a-2) estimating the carrier frequency offset by using two or more pilots in which the time offset is compensated or which have the same subcarrier index.

[16] The method of claim 14, wherein, in the step c), each channel is estimated by performing an averaging or an interpolation of the pilots included in each of the received signal which is transmitted from a same transmitting antenna and received in a same receiving antenna.

[17] The method of claim 14, wherein the step c) includes the steps of: c-1) estimating the channel of symbol index axis by performing an interpolation, a copy, or an extrapolation in the direction of the symbol index axis by using the pilots having the same subcarrier index; and c-2) estimating the channel of subcarrier index axis by performing the interpolation, the copy, or the extrapolation in the direction of the subcarrier index axis by using the estimation value of the symbol index axis.

[18] The method of claim 14, wherein the step c) includes the steps of: c-1) estimating the channel of subcarrier index axis by performing an interpolation, a copy, or an extrapolation in the direction of the subcarrier index axis by using the pilots having the same symbol index; and c-2) estimating the channel of symbol index axis by performing the interpolation, the copy, or the extrapolation in the direction of the symbol index axis by using the estimation value of the subcarrier index axis.

[19] A method for estimating a channel for AMC mode in a wireless telecommunication system supporting an OFDM or OFDMA, the method comprising the steps of: a) estimating a phase difference according to a time offset for two or more pilots in which a carrier frequency offset is compensated or which have the same symbol index among pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; b) accumulating the calculated phase difference according to the time offset; c) calculating a linear phase according to the time offset by using the accumulated phase difference according to the time offset; and d) calculating the time offset based on the linear phase according to the time offset, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

[20] The method of claim 19, wherein the received signals of the first channel and the third channel include a preamble, and in the step a), time offset is estimated by using the preamble included in at least one received signal among the received signals of the first channel and the third channel.

[21] The method of claim 19, wherein, in the step a), the phase difference according to the time offset is calculated by using a pilot pair which has a same symbol index while the difference of subcarrier index is a multiple of 9.

[22] The method of claim 19, wherein, in the step a), the phase difference according to the time offset is calculated by using two pilot pairs which have a same symbol index difference.

[23] A method for estimating a channel for AMC mode in a wireless telecom- munication system supporting an OFDM or OFDMA, the method comprising the steps of: a) estimating a phase difference according to a carrier frequency offset for two or more pilots in which a time offset is compensated or which have the same subcarrier index among pilots obtained from at least two or more bins with respect to at least one received signal among received signals of a first channel and a second channel received through a first receiving antenna and received signals of a third channel and a fourth channel received through a second receiving antenna, among a plurality of receiving antennas; b) accumulating the calculated phase difference according to the carrier frequency offset; c) calculating a linear phase according to the carrier frequency offset by using the accumulated phase difference according to the carrier frequency offset; and d) calculating the carrier frequency offset based on the linear phase according to the carrier frequency offset, wherein the received signals of the first channel and the third channel are signals transmitted from a first transmitting antenna among a plurality of transmitting antennas, while the received signals of the second channel and the fourth channel are signals transmitted from a second transmitting antenna.

[24] The method of claim 23, wherein, in the step a), the phase difference according to the carrier frequency offset is calculated by using a pilot pair which has a different symbol index while the time offset is compensated.

[25] The method of claim 23, wherein, in the step a), the phase difference according to the carrier frequency offset is calculated by using two pilot pairs which have a same subcarrier index difference.