WO2008082117A1

WO2008082117A1 - Method and apparatus for estimating carrier to interference and noise ratio

Info

Publication number: WO2008082117A1
Application number: PCT/KR2007/006762
Authority: WO
Inventors: Dong-Kwan Lee; Jung-Ju Kim
Original assignee: Posdata Co., Ltd.
Priority date: 2006-12-29
Filing date: 2007-12-21
Publication date: 2008-07-10
Also published as: KR20080062803A; KR100870671B1

Abstract

The present invention relates to the method and apparatus for estimating a carrier to interference and noise ratio (CINR) in a wireless communication system. The apparatus for estimating a CINR includes a channel power estimator for calculating a channel power for an estimated channel value; a channel power differential calculation unit for calculating a differential power for a difference between a received pilot and the estimated channel value; a first CINR calculation unit for estimating a CINR of a channel by utilizing a ratio of the channel power calculated in the channel power estimator to the differential power calculated in the channel power differential calculation unit, when a signal to noise ratio (SNR) of the channel is smaller than a threshold value; and a second CINR calculation unit for estimating a CINR of the channel by utilizing a ratio of the channel power calculated in the channel power estimator to a value amending the differential power calculated in the channel power differential calculation unit with a residual value using an autocorrelation function, when the SNR is larger than the threshold value.

Description

Description Method and Apparatus for Estimating Carrier to Interference and

Noise Ratio Technical Field

[1] The present invention relates to the wireless portable internet system, more particularly, to the method and apparatus for estimating an exact carrier to interference and noise ratio (CINR) in a wireless communication system by eliminating a noise component with using a channel correlation coefficient. Background Art

[2] The system using the orthogonal frequency division multiplexing (OFDM) or the orthogonal frequency division multiplexing access (OFDMA) scheme is a system which can transmit data at high speed by using a plurality of subcarriers having an orthogonality. In the system of the OFDM or the OFDMA scheme, the high speed data transmission is required. In this way, for the high speed data transmission, the modulation system of high order is required. The modulation system is classified into the low modulation order scheme of the BPSK (Binary Phase Shift Keying) or the QPSK (Quadrature Phase Shift Keying) scheme and the high modulation order scheme including the 16QAM (Quadrature Amplitude Modulation) or the 64QAM. The performance of the transmission method using such high modulation order scheme depends on the state of a channel.

[3] That is, in case the channel stateis excellent, it can have very high transmission rate, while many retransmission is required in case the channel state is bad. Thus, the use of high modulation order scheme can cause the degradation of a performance rather than using the low modulation order scheme. Therefore, in the wireless communication system, it is important to accurately detect the state of a channel and use a suitable modulation scheme.

[4] In this way, as to the method in which the transmitter of the wireless communication system grasps the state of a channel, a receiver estimates the CINR of aspecial signal which has transmitted from a transmitter, and the channel state can be known by transmitting the estimated CINR to the transmitter through a predetermined feedback channel. Here, the special signal means a signal transmitting to a corresponding user.

[5] Additionally, the transmitter determines the transmission rate of data by using the information received through the feedback channel. In this way, the information received through the feedback channel is use for various uses. Generally, in the wireless communication system of the OFDM or the OFDMA scheme, the method for estimating the CINR is as follows.

[6] Fig. 1 is a block diagram that shows the configuration of a receiver equipped with the CINR estimator in the OFDM or the OFDMA system of the related art.

[7] The signal received from the antenna (ANT) extracts the analog signal of the baseband from the signal which is band up converted for the transmission in a radio unit 110 to output. In this way, the analog signal transformed into the baseband in the radio unit 110 is inputted to a CP (Cyclic Prefix) deleting and serial/parallel converter 140 after transforming into the digital signal in an analog to digital converter (ADC) 120 and filtered in a filter 130. After deleting CP polluted by a multi-transmission path, the CP deleting and serial/parallel converter 140 converts a serial digital signal into a parallel analog signal to output. Since the parallely transformed signal is fast Fourier transformed in an N-pt (point) fast Fourier transformer (FFT) 150, the signal of time domain is transformed into the signal of frequency domain and inputted to a signal combiner 170.

[8] In the meantime, a PN (Pseudo Noise) user code generator 160 for generating an inherent PN code allocated to each user generates an inherent PN code allotted to itself and outputs to the signal combiner 170. In this way, the PN code allotted to the corresponding user and the signal transformed into the frequency domain are synthesized so that only the signal that is received to oneself can be extracted. The signal extracted from the signal combiner 170 is separated into two and one of the two is inputted to a CINR estimator 180. The other signal is inputted to a channel estimator 190.

[9] The CINR estimator 180 estimates the ratio of a desired signal and an inadvertent noise component included in the transmission in the received signal and outputs. Additionally, the channel estimator 190 estimates the transient state and channel condition of a channel and outputs. As described above, a receiver transmits the estimated CINR to a transmitter through a predetermined feedback channel. After determining the modulation order and modulating data by using the feed back information, the transmitter transmits to the receiver. At this time, it is necessary to estimate an exact CINR by quantifying the variation of the adjacent pilot in the fading channel. Disclosure of Invention Technical Problem

[10] Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art. It is an object of the present invention to provide the method and apparatus for estimating an exact carrier to interference and noise ratio (CINR) of a wireless communication system by eliminating a noise component with using a channel correlation coefficient. Technical Solution [11] In order to accomplish the object, according to an aspect of the present invention, provided is an apparatus for estimating a carrier to interference and noise ratio (CINR) in a wireless communication system, which comprises a channel power estimator for calculating a channel power for an estimated channel value; a channel power differential calculation unit for calculating a differential power for a difference between a received pilot and the estimated channel value; a first CINR calculation unit for estimating a CINR of a channel by utilizing a ratio of the channel power calculated in the channel power estimator to the differential power calculated in the channel power differential calculation unit, when a signal to noise ratio (SNR) of the channel is smaller than a threshold value; and a second CINR calculation unit for estimating a CINR of the channel by utilizing a ratio of the channel power calculated in the channel power estimator to a value amending the differential power calculated in the channel power differential calculation unit with a residual value using an autocorrelation function, when the SNR is larger than the threshold value.

[12] The pilot is at least one of a first pilot of a preamble and a second pilot excepting the first pilot. An aspect of the invention further comprises a residual calculation unit for calculating a residual value for a difference of the differential power by using the autocorrelation function. The residual calculation unit includes at least one of: a first pilot autocorrelation calculation unit for calculating the autocorrelation of the first pilot arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and a second pilot autocorrelation calculation unit for calculating the autocorrelation of the second pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O). The second CINR calculation unit estimates the CINR of the channel by using a residual value calculated by at least one of an autocorrelation function of the first pilot and an autocorrelation function of the second pilot. The residual value is a value which calculates an autocorrelation having a non-zero delay by using the correlation of the pilots which are symmetrical each other.

[13] According to another aspect of the present invention, provided is an apparatus for estimating a carrier to interference and noise ratio (CINR) for a channel in a receiver of a wireless communication system, the apparatus comprising: a channel power estimator for calculating a channel power for an estimated channel value; a channel power differential calculation unit for calculating a differential power for a difference of a received pilot and the estimated channel value; a first CINR calculation unit for estimating a CINR of a channel by utilizing a ratio of the channel power calculated in the channel power estimator to the differential power calculated in the channel power differential calculation unit; a second CINR calculation unit for estimating the CINR of the channel by utilizing a ratio of the channel power calculated in the channel power estimator to a value amending the differential power calculated in the channel power differential calculation unit with a residual value using an autocorrelation function; and a CINR selecting unit for selecting at least one of the first CINR calculation unit and the second CINR calculation unit based on a threshold value, and estimating the CINR of the channel to output.

[14] Another aspect of the present invention further comprises a residual calculation unit for calculating a residual value for a difference of the differential power by using an autocorrelation function. The residual calculation unit includes at least one of: a first pilot autocorrelation calculation unit for calculating the autocorrelation of the first pilot arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and a second pilot autocorrelation calculation unit for calculating the autocorrelation of the second pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O). The second CINR calculation unit estimates the CINR of the channel by using a residual value calculated by at least one of an autocorrelation function of the first pilot and an autocorrelation function of the second pilot. The residual value is a value which calculates an autocorrelation having a non-zero delay by using the correlation of the pilots which are symmetrical each other. The threshold value of the CINR selecting unit is a threshold value for a signal to noise ratio (SNR).

[15] According to still another aspect of the present invention, provided is a method for estimating a carrier to interference and noise ratio (CINR) for a channel in a receiverof a wireless communication system, the method comprising the steps of: (a) calculating a channel power for an estimated channel value; (b) calculating a differential power for a difference between a received pilot and the estimated channel value; and (c) estimating a second CINR of a channel by utilizing a ratio of the channel power calculated at the step (a) to a value amending the differential power calculated at the step (b) with a residual value using an autocorrelation function. The step (c) comprises: calculating a difference of the differential power by using the autocorrelation function and estimating a CINR of the channel by utilizing a ratio of the channel power calculated at the step (a) to a value amending the differential power calculated at the step (b) with the residual value. The residual calculation is performed by at least one of: calculating an autocorrelation of a preamble arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and calculating an autocorrelation of a pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O). The step (c) comprises: estimating a first CINR of the channel by utilizing a ratio of the channel power calculated at the step (a) to the differential power calculated at the step (b). The step (c), further comprises the step (d) of: selecting the first CINR when a signal to noise ratio (SNR) is smaller than a threshold value; and selecting the second CINR when the SNR is larger than the threshold value.

Advantageous Effects

[16] According to the present invention, the CINR can be more accurately estimated by eliminating a remained noise component with using a channel correlation coefficient in estimating the CINR. That is, the variation of the adjacent pilot can be quantified for an exact CINR estimation. Further, the present invention can be applied to the WiBro/ WiMAX system and the OFDM system.

Brief Description of the Drawings

[17] The above and other exemplary features, aspects, and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[18] Fig. 1 is a block diagram that shows the configuration of a receiver equipped with the CINR estimator in the OFDM or the OFDMA system of the related art;

[19] Fig. 2 is a block diagram that shows the configuration of an embodiment of a carrier to interference and noise ratio(CINR) estimator in a wireless communication system according to the present invention;

[20] Fig. 3 shows the method for minimizing the residual value (res) while maintaining t he symmetric having N=3 in the channel estimation;

[21] Fig. 4 is a block diagram that shows the configuration of another embodiment of a carrier to interference and noise ratio (CINR) estimator in a wireless communication system according to the present invention;

[22] Fig. 5 is a flowchart that shows the method of estimating the carrier to interference and noise ratio (CINR) of a wireless communication system according to the present invention. Mode for the Invention

[23] Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. The same elements will be designated by the same reference numerals all through the following description and drawings although they are shown in different drawings. Further, in the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

[24] The important concept of the invention is to calculate the residual component which is remained due to the channel fading by using the auto-correlation coefficient of a channel besides the interference of other user and the AWGN (additive white Gaussian noise), and correct by using the residual component in the carrier to interference and noise ratio (CINR) estimation for the exact CINR estimation.

[25] Fig. 2 is a block diagram that shows the configuration of an embodiment of a CINR estimator in a wireless communication system according to the present invention. The CINR estimator includes a channel power estimator 210, a channel power differential calculation unit 220, a first CINR calculation unit 260 and a second CINR calculation unit 270, preferably, further including a residual calculation unit 230. The channel power estimator 210 calculates the power for the estimated channel value. As a rule, the received preamble pilot can be expressed like the following Equation 1.

[26] [Equation 1]

[27]

P(k ) = sh(k) + sb, (k)h, (k) + n(k)

[28] Here, the description of each element in Equation 1 is as follows. Here, P(k) is the received preamble having the index k in one frame, s is a preamble gain ( 2y"2 = 9 dB), h(k) is a channel response of a target user, h i (k) is a channel response of an interferer, b (k) is a binary number (in case the mask of an interferer is the same as the mask of a target user, then it is 1, otherwise, -1) , and n(k) is a complex Gaussian noise having the variance σ . The estimated channel value which is averaged for a first pilot (tone) of N number which is neighbored and includes the preamble P(k) received in Equation 1 can be expressed like the following Equation 2.

[29] [Equation 2]

[30] sh(k) = ∑_^ P(I) I N where , 1 is around k including k

[31] The power of the estimated channel value can be expressed like the following

Equation 3.

[32] [Equation 3]

[33]

2i r I JL I JL i JL ² sh{k) = E 77∑ *A(0 + ^∑>, (l)h, (I) + ±∑ fl(0

[34] The channel power differential calculation unit 220 calculates the power for the difference between the received pilot and the estimated channel value. The pilot indicates a second pilot except for the first pilot (tone) of the preamble or the preamble pilot. The power for the difference between the received first pilot and the estimated channel value can be expressed like the following Equation 4. In the Equation 4, P(k), P (k), b (k) and n(k) have no mutual correlation, and in case it is l≠k, then, b (k) and b

(1) also have no correlation.

[35] [Equation 4] [36] p(k) - sh(k)

N - I N - I

= E — sh(k) -— y Sh(I) + E sb,(k)h,(k) - — ∑ sh, (l)h,(.I)

N N at_* N Nάt_*

£_A ²Δ[*(/)*»]

[37] When the signal to noise ratio (SNR) of a channel is smaller than a threshold value, the first CINR calculation unit 260 estimates the CINR of a channel by utilizing the ratio of channel power calculated in the channel power estimator 210 to channel power difference which is calculated in the channel power differential calculation unit 220. When it is h(k)=h(l) and h (k)=h (1), that is, it is the flat fading environment, Equation 3 and Equation 4 are can be rearranged to be the following Equation 5 and Equation 6.

[38] [Equation 5] [39]

[40] [Equation 6] [41]

[42] By using Equation 5 and Equation 6, the CINR estimation by using a preamble can be expressed like the following Equation 7.

[43] [Equation 7] [44] E\ sh(k)

N N

CINR

N - I

E p{k) - sh{k) /ψλ,(/t)| + σ ^~ N - I N - I N - I

sh(k)

N - I

CINR_pleambh =

N

E p(k) - sh{k) N

[45] Equation 7 can accurately estimate the CINR at the low SNR, however, the estimation becomes inaccurate at the high SNR since it highly depends on the residual term shown in the Equation 8.

[46] [Equation 8]

[47]

[48] Equation 7 shows the estimation of the CINR by using a preamble while assuming that the residual term (res) shown in Equation 8 is 0. When the res is not 0, the channel coefficient which is used for the channel estimation is not a constant. In a high SNR, the res cannot be overlooked when comparing to the noise interference power.

[49] When the SNR of a channel is larger than a threshold value, the second CINR calculation unit 270 estimates the CINR of the channel by utilizing the ratio of the channel power calculated in the channel power estimator 210 to the value which amended the channel power calculated in the channel power differential calculation unit 220 with the residual value (res) using the autocorrelation function. The CINR of the channel using a preamble, which is amended with the res, can be expressed like the Equation 9.

[50] [Equation 9] [51]

ClNR_n

[52] As to the power difference of the difference between the receive pilot and the estimation channel value, the residual calculation unit 230 calculates the residual value (res) by using the autocorrelation. The residual calculation unit 230 includes at least one pilot autocorrelation calculation unit among a first pilot autocorrelation calculation unit 240 and asecond pilot autocorrelation calculation unit 250. When the autocorrelation for the channel signal itself is AR (autocorrelation) (0), the one pilot autocorrelation calculation unit calculates the autocorrelation of the preamble arranged in the frequency domain by using the Taylor series for the AR(O). When the autocorrelation for the channel signal itself is AR(O), the one pilot autocorrelation calculation unit calculates the autocorrelation of the preamble arranged in the time domain or in the frequency domain by using the Taylor series for the AR(O). As described above, the residual value (res) can be expressed like Equation 8.

[53] Fig. 3 shows the method for minimizing the residual value (res) while maintaining the symmetric having N=3 in the channel estimation.

[54] Assuming that the average (primary average) and the autocorrelation function

(secondary average) are wide sense stationary with N=3, the res can be induced to be expressed like the following Equation 10.

[55] [Equation 10]

[56] h(k - 1) + h(k + 1) ^: res = s"Jϊ -A(Jt) -

= |.v² + \)}+ Rc{κ[h(k)h' (k - 1)]})+ |.r (Re {fφ(* - I)A^* (k + 1)]})

+ 1)]})+ →⁷ (R_e{E[h(k - l)h"{k + 1)]})

[57] Equation 11 defines the autocorrelation.

[58] [Equation 11]

[59]

AR (I) = s^: Re

[h(k)h"(k + /)]} (AR = Aut ocorrel al ion)

[60] (AR = Autocorrelation)

[61] Equation 10 can be rearranged to express Equation 12 by using Equation 11.

[62] [Equation 12]

[63] res = - AR(O) - -AR(I) + -AR(T)

[64] Equation 13 obtains the correlation between the adjacent first pilots, and the autocorrelation of the channel response having non-zero delay can be obtained. [65] [Equation 13]

[66]

= dfclik) + sb, (Ii)H₁ (k) + n(kγfcHk + l) + sb, (k + I)Ir₁ (k + l) + n(k + [)}" ] = s²E[h(k)h^*(k + /)] (where / ≠O)

[67] The AR(I) and the AR(2) shown in Equation 13 can be obtained by using Equation

11. However, the AR(O) can be deduced by using the autocorrelation which is adjacent 0. Equation 14 considers the frequency response of the fading channel having an arbitrary delay power profile in which the delay time is small in comparison with the section of a symbol, in order to obtain the autocorrelation function of the channel response which is adjacent 0. [68] [Equation 14]

[69] h(k) = ^ A,(n)e where, h_t(n) is the Jading channel coefficient with delay n

[70] Equation 15 indicates the correlation of a channel on the assumption that the fading coming from each path has the independency

{E[h, (n)h ' (m)] = 0 if , n Φ m) that has no correlation each other. [71] [Equation 15]

[72]

= ^Λ∑'iψ»|²] , lccos :iπln \

N J

[73] In the Equation 15, h (n) is not 0 only when n is very small in comparison with N .

By using the Taylor series x² x⁴ (cos(x) « 1 + — ) y ' 2 24"

, the AR(O) can be obtained by using the autocorrelation function to express Equation

16.

[74] [Equation 16]

[75]

AR(I) = K _c - K₂I² + KJ'

AR(I) = K₀ - K_{2 +} K ₁ AR(2) = K₀ - 4K₂ + lβK _l AR(J) = K₀ - 9K₂ + 81K ₁

Tlien, AR(H) = K₀ = -AR(I) - ^AR(2) + —AR(3)

[76] Equation 17 is obtained by rearranging Equation 13 using Equation 16, statistically finding the residual term. However, in order to obtain the exact res, many first pilot samples are required. In the Equation 14, when the residual term is obtained by inducing to the biquadratic Taylor series, more exact residual term can be obtained.

[77] [Equation 17]

[78] res

= -AR(l) -—AR(2) + — ARO) 9 45 15

[79] The above-described description illustrates the CINR estimation based on a first pilot of a preamble. The CINR estimation based on a second pilot except of the first pilot performed by the same method as the preamble based CINR estimation except that the pilot sub-carrier gain is 2.5 dB from Equation 1 to Equation 9, and the average value of the frequency domain or the time domain is used. The CINR estimation by using the pilot sub-carrier can be expressed like the Equation 18.

[80] [Equation 18] [81]

sh{k)

N - I

CINR_pύoι

N p(k) - s-h(k)

[82] The CINR estimation by using the pilot sub-carrier much more depends on the residual term shown in Equation 8 like the case in which the CINR estimation is performed by using the preamble subcarrier. Equation 19 expresses the estimation of the carrier to interference and noise ratio base on the pilot sub-carrier considering the residual term expressed in Equation 8.

[83] [Equation 19] [84]

[85] Equation 20 is rearranged to adjust to the estimation of the pilot sub-carrier based SNR by using the Equation 16 and Equation 17.

[86] [Equation 20] [87]

AR(I) = s² Re{φ(£)/z^" (£ + /)]} res = - AR(O) -- AR(I) + - AR(I)

[88] Equation 21 is expressed by using the relation that the autocorrelation function of the Rayleigh fading channel is the zero-th order Bessel function of the first kind.

[89] [Equation 21] [90]

AR(I) = s² Re{E[h(k)h^"(k + /)]}= s²J₀(x) = ₄-- J — i-li- rj ffjir(/w + i)

^■*'-'.fH f (where, 0 < x « 1) [91] Equation 22 obtains AR(O), and statistically obtains the residual term finally. [92] [Equation 22] [93]

ARO) = KJ₀ (A) = κ\ : - ^- + ^

4 64

AR(I) = XZ₀ (2Δ) = £ 1 - Δ" + — Δ⁴ 1

4

J 32 ARQ) - ?, AR(Z) ) ₂ ( 64ΛΛ0) - 64AR(Z)) _

\ 6ARQ) - AR(Z) ) \ \ GAR(\) - AR(2) J

(32ARQ) - XAR(Z) ) , „ ( 64ARQ) - 64AR(Z) )

Let, a - — — and β - — — L Then,

{ 16ΛΛ0) - AR(Z) ) ^ \ 6AR(\) - AR(Z) ) x² = a - ^a² - β ≡ γ

AR(Z) 4AR(Z)

AR(O) = K = -

: - x² + — *~ (2 - /)²

4

res + -, 1_ - Δ_- +. — , ^, = -

[94] A number of a second pilot samples are required for estimating the CINR by obtaining an accurate residual.

[95] Fig. 4 is a block diagram that shows the configuration of another embodiment of a

CINR estimator in a wireless communication system according to the present invention. The CINR estimator includes a channel power estimator 410, a channel power differential calculation unit 420, a first CINR calculation unit 460, a second CINR calculation unit 470 and a CINR selecting unit 480, and, preferably, further including a residual calculation unit 430. The channel power estimator 410, the channel power differential calculation unit 420 and the residual calculation unit 430 are identical with the channel power estimator 210, the channel power differential calculation unit 220 and the residual calculation unit 230of an embodiment of the present invention shown in Fig. 2.

[96] The first CINR calculation unit 460 estimates the CINR of a channel by utilizing the ratio of the channel power calculated in the channel power estimator 410 to the channel power difference calculated in the channel power differential calculation unit 420. The second CINR calculation unit 460 estimates the CINR of a channel by utilizing the ratio of the channel power calculated in the channel power estimator 41O t othe value amending the channel power calculated in the channel power differential calculation unit 420 with the residual value (res) using the autocorrelation function. The CINR selecting unit 480 selects the first CINR calculation unit 460 or the second CINR calculation unit 470 based on a threshold value, preferably, on an SNR of a channel, and estimates the CINR of a channel to output.

[97] Fig. 5 is a flowchart that shows the method of estimating the CINR in a wireless communication system according to the present invention.

[98] Firstly, in order to the estimation of the CINR for a channel in the receiver of a wireless communication system, the channel power estimator 210 calculates the power of the estimated channel value (S510 step). This can be indicated like the Equation 5. Further, the channel power differential calculation unit 220 calculates the power for the difference between the received pilot at the flat fading environment and the estimated channel value (S520 step). That is, when it is h(k)=h(l) and h (k)=h (1), the Equation 4 can be rearranged to be the Equation 6.

[99] When the SNR is smaller than a threshold value (S530 step), for example, when the

SNR is smaller than 30 dB or the channel quickly changes, the CINR of a channel can be estimated by utilizing the ratio of the channel power calculated in the S510 step by the first CINR calculation unit 260 to the channel power difference which is calculated at the S520 step (S540 step). As to the CINR estimated from the first CINR calculation unit 260, the CINR estimation based on the first pilot of a preamble can be expressed like the Equation 7, and the CINR based on the second pilot can be expressed like the Equation 18.

[100] When the SNR is larger than a threshold value (S530 step), by utilizing the ratio of the channel power calculated in the S510 step by the second CINR calculation unit 270 to the value amending the channel power calculated in the S520 step with the residual value (res) using the autocorrelation function (S550 step).

[101] As to the CINR estimated by the second CINR estimator 270, the CINR estimation based on the first pilot of a preamble can be expressed like the Equation 9, and the CINR based on the second pilot can be expressed like the Equation 19. The residual value (res) can be expressed like the Equation 8, and the power difference between the received pilot and the difference of the estimated channel value is calculated by using the autocorrelation. Particularly, when the autocorrelation for the channel signal itself is the AR(O), the residual value (res) is calculated by calculating the autocorrelation of a first pilot arranged in the frequency domain and the autocorrelation of a second pilot arranged in the time domain or the frequency domain, by using the Taylor series for the AR(O).

[102] Meanwhile, functions used in an apparatus and a method disclosed in the present specification can be embodied in storage media that a computer can read as codes that the computer can read. The storage media that the computer can read, include all sorts of record devices in which data that can be read by a computer system is stored. Examples of the storage media that the computer can read, include ROMs, RAMs, CD- ROMs, magnetic tape, floppy discs, optic data storage devices, etc., and also, include things embodied in the form of carrier wave (e.g., transmission through the internet). Furthermore, the storage media that the computer can read is distributed in a computer system connected with networks. Then, the codes that the computer can read, are stored in the distributed storage media in a distribution scheme, and the codes can be executed in the distribution scheme. 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 carrier to interference and noise ratio (CINR) for a channel in a receiver of a wireless communication system, the apparatus comprising: a channel power estimator for calculating a channel power for an estimated channel value; a channel power differential calculation unit for calculating a differential power for a difference between a received pilot and the estimated channel value; a first CINR calculation unit for estimating a CINR of a channel by utilizing aratio of the channel power calculated in the channel power estimator to the differential power calculated in the channel power differential calculation unit, when a signal to noise ratio (SNR) of the channel is smaller than a threshold value; and a second CINR calculation unit for estimating a CINR of the channel by utilizing a ratio of the channel power calculated in the channel power estimator to a value amending the differential power calculated in the channel power differential calculation unit with a residual value using an autocorrelation function, when the SNR is larger than the threshold value.

[2] The apparatus of claim 1, wherein the pilot is at least one of a first pilot of a preamble and a second pilot excepting the first pilot.

[3] The apparatus of claim 2, further comprising a residual calculation unit for calculating a residual value for a difference of the differential power by using the autocorrelation function.

[4] The apparatus of claim 3, wherein the residual calculation unit includes at least one of: a first pilot autocorrelation calculation unit for calculating the autocorrelation of the first pilot arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and a second pilot autocorrelation calculation unit for calculating the autocorrelation of the second pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O).

[5] The apparatus of claim 2, wherein the second CINR calculation unit estimates the CINR of the channel by using a residual value calculated by at least one of an autocorrelation function of the first pilot and an autocorrelation function of the second pilot.

[6] The apparatus of claim 1, wherein the residual value is a value which calculates an autocorrelation having a non-zero delay by using the correlation of the pilots which are symmetrical each other.

[7] An apparatus for estimating a carrier to interference and noise ratio (CINR) for a channel in a receiver of a wireless communication system, the apparatus comprising: a channel power estimator for calculating a channel power for an estimated channel value; a channel power differential calculation unit for calculating a differential power for a difference of areceived pilot and the estimated channel value; a first CINR calculation unit for estimating a CINR of a channel by utilizing a ratio of the channel power calculated in the channel power estimator to the differential power calculated in the channel power differential calculation unit; a second CINR calculation unit for estimating the CINR of the channel by utilizing a ratio of the channel power calculated in the channel power estimator to a value amending the differential power calculated in the channel power differential calculation unit with a residual value using an autocorrelation function; and a CINR selecting unit for selecting at least one of the first CINR calculation unit and the second CINR calculation unit based on a threshold value, and estimating the CINR of the channel to output.

[8] The apparatus of claim 7, wherein the pilot is at least one of a first pilot of a preamble and a second pilot excepting the first pilot.

[9] The apparatus of claim 8, further comprising a residual calculation unit for calculating a residual value for a difference of the differential power by using an autocorrelation function.

[10] The apparatus of claim 9, wherein the residual calculation unit includes at least one of: a first pilot autocorrelation calculation unit for calculating the autocorrelation of the first pilot arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and a second pilot autocorrelation calculation unit for calculating the autocorrelation of the second pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O).

[11] The apparatus of claim 8, wherein the second CINR calculation unit estimates the CINR of the channel by using a residual value calculated by at least one of an autocorrelation function of the first pilot and an autocorrelation function of the second pilot.

[12] The apparatus of claim 7, wherein the residual value is a value which calculates an autocorrelation having a non-zero delay by using the correlation of the pilots which are symmetrical each other.

[13] The apparatus of claim 7, wherein the threshold value of the CINR selecting unit is a threshold value for a signal to noise ratio (SNR).

[14] A method for estimating a carrier to interference and noise ratio (CINR) for a channel in a receiver of a wireless communication system, the method comprising the steps of:

(a) calculating a channel power for an estimated channel value;

(b) calculating a differential power for adifference between a received pilot and the estimated channel value; and

(c) estimating a second CINR of a channel by utilizing a ratio of the channel power calculated at the step (a) to a value amending the differential power calculated at the step (b) with a residual value using an autocorrelation function.

[15] The method of claim 14, wherein the step (c) comprises: calculating a difference of the differential power by using the autocorrelation function; and estimating a CINR of the channel by utilizing a ratio of the channel power calculated at the step (a) to a value amending the differential power calculated at the step (b) with the residual value. [16] The method of claim 14, wherein the residual calculation is performed by at least one of: calculating an autocorrelation of a preamble arranged in a frequency domain by using a Taylor series for AR(O), when the autocorrelation for a channel signal itself is the AR(O); and calculating an autocorrelation of a pilot arranged in a time domain or the frequency domain by using the Taylor series for AR(O), when the autocorrelation for the channel signal itself is the AR(O). [17] The method of claim 14, wherein the step (c) comprises: estimating a first CINR of the channel by utilizing a ratio of the channel power calculated at the step (a) to the differential power calculated at the step (b). [18] The method of claim 17, after the step (c), further comprising the step (d) of: selecting the first CINR when a signal to noise ratio (SNR) is smaller than a threshold value; and selecting the second CINR when the SNR is larger than the threshold value.