WO2008082118A1

WO2008082118A1 - Apparatus and method for combining received signal considering interference for each antenna, apparatus and method for computing symbol metric using it

Info

Publication number: WO2008082118A1
Application number: PCT/KR2007/006763
Authority: WO
Inventors: Dong-Kwan Lee; Jung-Ju Kim; Jae-Hyeong Kim
Original assignee: Posdata Co Ltd
Current assignee: Posdata Co Ltd
Priority date: 2006-12-29
Filing date: 2007-12-21
Publication date: 2008-07-10
Anticipated expiration: 2009-06-29
Also published as: KR100841936B1

Abstract

Disclosed is an apparatus and method for combining a received signal considering interference for each antenna, and an apparatus and method for computing symbol metric using the same in a wireless communication system equipped with a plurality of transceiver antennas. The symbol metric calculation apparatus considering interference for each antenna comprises a channel estimator for receiving signals from the receive antenna, and estimating a channel by using a pilot signal of each signal received from the receive antenna; a noise and interference power estimator for receiving an output of the channel estimator, and estimating a noise and interference power of each channel; a combining unit for channel-compensating the channels estimated in the channel estimator and the noise and interference power estimated in the noise and interference power estimator, and combining the channel-compensated signals; a variance calculation unit for calculating a variance of data tone by using the ratio of the channel estimated in the channel estimator to a noise and interference estimated in the noise and interference power estimator; and a symbol metric calculation unit for calculates a symbol metric by using the variance calculated in the variance calculation unit and the signals combined in the combining unit.

Description

Apparatus and Method for Combining Received Signal Considering Interference for Each Antenna, Apparatus and Method for

Computing Symbol Metric using it Technical Field

[1] The present invention relates to a receiving apparatus and method of a wireless communication system equipped with a plurality of transceiver antennas, particularly, to an apparatus and method for combining a received signal considering interference for each antenna, and an apparatus and method for computing symbol metric using the same. Background Art

[2] Fig. 1 is a block diagram showing the configuration of a general OFDM (orthogonal frequency division multiplexing) receiver, schematically showing just only a part that restores data from a baseband signal obtained from a received signal.

[3] A burst symbol extracting unit 100 extracts the OFDM symbol from the baseband signal obtained from the received signal by a RF(Radio Frequency) processing unit (not shown). The OFDM symbol is extracted by the burst symbol extracting unit 100, and the CP (Cyclic Prefix) of the OFDM symbol which is inserted from a transmitter is eliminated by a CP deleting unit 102, and FFT (Fast Fourier Transform) is performed by a FFT unit 104 to apply to an equalizer 108.

[4] The equalizer 108 compensates for the channel distortion according to the channel characteristic value which is estimated by a channel estimator 106 for the FFT data signal. After the signal which is compensated for the channel distortion is demodulated in a demodulator 110, it is decoded by a decoder 112 and the data are restored by the determination of a decision unit 114. Here, it is assumed that the OFDM receiver is a multi-antenna receiver, and 16QAM (Quadrature Amplitude Modulation) modulation and demodulation are performed for an input signal.

[5] Further, in the transmitter, the n-th information bit u n is coded and interleaved to generate the bit string {b (k); 1=0, ..., 3} for mapping to the k-th symbol and modulated. In the modulation process, the mapping is performed from an interleaver with one 16QAM symbol s(k) per four bits. The transmitted symbol s(k) passes through the multiplicative flat fading channel of the response for the m-th antenna h . The k-th receiving symbol r (k) can be expressed like Equation 1.

[6] [Equation 1]

[7] r_m (k) = h_m {k)s{k) + v_m (k) [8] The received signal r (k) includes not only the faded symbol h (k)s(k) but also the noise v(k). The noise v(k) is the zero mean complex AWGN (Additive White Gaussian Noise) having the variance σ . In the MRC (Maximal Ratio Combining), the conjugate complex number of a corresponding weight a (k) (m=l~M) is multiplied to each signal from other antenna in order to compensate for the channel effect such as the signal-noise ratio or the carrier to noise plus interference ratio and to improve the quality of the combined signal. [9] Then, the antenna coupled and channel-compensated signal is demodulated

(demapping), and generates a set of LLR (Log Likelihood Ratio) {λ (k); i=0,..., 3} cor- responding to the code bit {b (k)} which is interleaved in a transmitter. The LLR is inputted to a de-interleaver and decoded to restore the transmitted information bit. On the other hand, the exact combining and symbol metric calculation is required in order to improve the portable Internet (WiBro/WiMax) system performance when the interference power of each antenna is different. That is, it is necessary to differentiate the weight for each channel when the interference power is different for each channel. Disclosure of Invention Technical Problem

[10] It is an object of the present invention to provide an apparatus and method for combining a received signal considering interference for each antenna when each antenna interference power is different, which is capable of improving the portable Internet (WiBro/WiMax) system performance by combining exact received signals when each antenna interference power is different. It is another object of the present invention to provide the symbol metric computing system and method considering interference for each antenna, using the apparatus and method for combining a received signal. Technical Solution

[11] In order to accomplish the object, according an aspect of the present invention, provided is a receive signal combining apparatus considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, which comprises a channel estimator for receiving signals from the receive antenna, and estimating a channel by using a pilot signal of each signal received from the receive antenna; a noise and interference power estimator for receiving an output of the channel estimator, and estimating a noise and interference power of each channel; and a combining unit for channel-compensating the channels estimated in the channel estimator and the noise and interference power estimated by channel in the noise and interference power estimator, and combining the channel-compensated signals.

[12] The signal C combined in the combining unit is expressed like the following Equation, [13] h\k)

C_mm = ∑r(k)

P_NI ⁽,k) [14] when,

Hk) is a channel estimated in the channel estimator, P NI (k) is a noise and interference power of the channel corresponding to k-th antenna estimated in the noise and interference power estimator, and r(k) is a signal received from the k-th antenna. [15] The combining unit performs channel-compensating by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combines the channel-compensated receive signals [16] The noise and interference power P is expressed like the following Equation,

NI

[17]

[18] when, h(k) is a channel estimated in the channel estimator, s is a pilot gain, P(k) is a received pilot within a frame, N is the number of neighboring pilot for channel estimation, and h i (k) is a channel response of an interferer.

[19] According another aspect of the present invention, provided is a method of receive signal combining considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, which comprises receiving signals corresponding to each of the receive antenna, and estimating a channel by using a pilot signal of each of the receive signal; receiving an estimation value corresponding to the estimated channel, and estimating a noise and interference power of each channel; and channel-compensating by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combining the channel-compensated signals.

[20] According to still another aspect of the present invention, provided is a symbol metric calculation apparatus considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, which comprises a channel estimator for receiving signals from the receive antenna, and estimating a channel by using a pilot signal of each signal received from the receive antenna; a noise and interference power estimator for receiving an output of the channel estimator, and estimating a noise and interference power of each channel; a combining unit for channel-compensating the channels estimated in the channel estimator and the noise and interference power estimated in the noise and interference power estimator, and combining the channel-compensated signals; a variance calculation unit for calculating a variance of data tone by using the ratio of the channel estimated in the channel estimator to a noise and interference estimated in the noise and interference power estimator; and a symbol metric calculation unit for calculating a symbol metric by using the variance calculated in the variance calculation unit and the signals combined in the combining unit. [21] The signal C combined in the combining unit is expressed like the following norm

Equation, [22]

<^■ norm ^~ U^' p / n

[23] when, h{k) is a channel estimated in the channel estimator, P (k) is a noise and interference power

NI of the channel corresponding to k-th antenna estimated in the noise and interference power estimator, and r(k) is a signal received from the k-th antenna. [24] The combining unit channel-compensates by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combines the channel-compensated signals. [25] The noise and interference power P is expressed like the following Equation,

NI

[26]

[27] when,

Hk) is a channel estimated in the channel estimator, s is a pilot gain, P(k) is a received pilot within a frame, N is the number of neighboring pilot for channel estimation, and h (k) is a channel response of an interferer. [28] The variance

Var calculated in the variance calculation unit is expressed like the following Equation, [29]

[30] when, the channel estimated in the channel estimator is h{k)

, the noise and interference power estimated in the noise and interference power estimator is P (k), the sum of the interference from an antenna k is

NI i(k)

, and the estimated variance of a complex gaussian noise from an antenna k is σ

[31] The variance calculation unit calculates a variance of signal constellation of data tone by utilizing the ratio of the estimated channel to the estimated noise and interference. The symbol metric calculation unit can express an LLR (Log Likelihood Ratio) like the following Equation, in case of QPSK (Quadrature Phase Shift Keying),

[32]

[33] The symbol metric calculation unit can express an LLR like the following Equation, in case of 16QAM Quadrature Amplitude Modulation), [34]

LLR₁

Var

[35] mm Im{C_naJ- S, - mm _^ Im{C_ }-S,

LLR, * ^'V7πr77?

Var

J_ILR_A „

Var

[36] According to still another aspect of the present invention, provided is a method of calculating a symbol metric considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, which comprises receiving signals corresponding to each of the receive antenna, and estimating a channel by using a pilot signal of each of the receive signal; receiving an estimation value corresponding to the estimated channel, and estimating a noise and interference power of each channel; channel-compensating by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combining the channel-compensated signals; calculating a variance of signal constellation of data tone by utilizing the ratio of the estimated channel to a estimated noise and interference; and calculating a symbol metric by using the calculated variance and the combined signals.

Advantageous Effects

[37] According to the present invention, it is capable of improving the portable Internet

(WiBro/WiMax) system performance by calculating the exact combining and symbol metric when each antenna interference power is different. Further, the present invention can be applied to the Wibro/WiMAX and the OFDM system. Brief Description of the Drawings

[38] 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:

[39] Fig. 1 is a block diagram that shows the configuration of a general OFDM receiver;

[40] Fig. 2 is a block diagram that shows the configuration of the received signal combining apparatus considering the interference for each antenna in a wireless communication system equipped with a plurality of receive antennas according to the present invention;

[41] Fig. 3 is a block diagram that shows the configuration of the received signal combining apparatus considering the interference for each antenna, using the received signal combining apparatus considering the interference for each antenna according to the present invention;

[42] Fig. 4 is a flowchart that shows the received signal combining method considering the interference for each antenna in a wireless communication system equipped with a plurality of receive antennas according to the present invention;

[43] Fig. 5 is a flowchart that shows the symbol metric calculating method considering the interference for each antenna, using the received signal combining method of Fig. 4 according to the present invention. Mode for the Invention

[44] Hereinafter, exemplary embodiments of thepresent 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.

[45] The main concept of the invention is to calculate the interference power for the exact signal combining and the symbol metric calculation when the interference power of each antenna is different, and to use it in the signal combining and symbol metric calculation. That is, the invention performs the exact MRC(Maximal Ratio Combining) and the symbol metric calculation by using the noise and interference power received from each antenna.

[46] Fig. 2 is a block diagram that shows the configuration of the received signal combining apparatus considering the interference for each antenna in a wireless communication system equipped with a plurality of receive antennas according to the present invention. The received signal combining apparatus includes a channel estimator 210, a noise and interference power estimator 220 and a combining unit 230.

[47] After each of a plurality of received signals corresponding to the receive antenna is inputted, the channel estimator 210 estimates a channel by using the pilot signal neighboring of data tone of the each received signal. The noise and interference power estimator 220 receives a plurality of outputs which are channel estimated in the channel estimator 210, and estimates the noise and interference power of each channel. The noise and interference power P estimated in the noise and interference power estimator 220 can be expressed like Equation 2.

[48] [Equation 2]

[49]

[50] Here,

is a channel which is estimated in the channel estimator 210, s is a pilot gain, P(k) is a received pilot within a frame, N is the number of neighboring pilot for the channel estimation, and h i (k) is a channel response of an interferer (not shown). The combining unit 230 performs channel-compensating by corresponding data tone for the channels which are estimated in the channel estimator 210 and the noise and interference powers which are estimated in the noise and interference power estimator 220, thereby, combing the received signals which are channel-compensated. The received signal including the interference received from the antenna can be expressed show like Equation 3.

[51] [Equation 3] [52] r(k) = s h(k) + i(k) + n(k)

[53] Here, r(k)(k is 1, 2, ..., L) is a signal received from the antenna k, s' is a modulated symbol, h (k) (k is 1, 2, ..., L) is a channel response of a target user for the antenna k, i(k) (k is 1, 2, ..., L) is a sum of the interference from the antenna k, and n (k) (k is 1, 2, ..., L) is a complex Gaussian noise (variance σ ) from the antenna k. The general MRC based on Equation 3 can be expressed show like Equation 4.

[54] [Equation 4] [55]

[56] The normalized combined signal by using Equation 3 and Equation 4 can be expressed show like Equation 5.

[57] [Equation 5] [58]

[59] In case the signal combined in the combining unit 230, the C can be expressed normal like Equation 6.

[60] [Equation 6] [61]

[62] Here, h(k) is a channel estimated in the channel estimator 210, P (k) is a noise and interference

NI power of the channel corresponding to k-th antenna estimated in the noise and interference power estimator 220, and r(k) is a signal received from the k-th antenna. [63] Fig. 3 is a block diagram that shows the configuration of the received signal combining apparatus considering the interference for each antenna, using the received signal combining apparatus considering the interference for each antenna according to the present invention. The received signal combining apparatus includes achannel estimator 310, a noise and interference power estimator 320, a variance calculation unit 330, a combining unit 340 and a symbol metric calculation unit 350.

[64] The channel estimator 310 receives a plurality of signals corresponding to each receive antenna, and estimates a channel by using the pilot signal of the neighbor of data tone of each received signal, being identical with the channel estimator 210 of Fig. 2. The noise and interference power estimator 320 receives a plurality of outputs which are channel estimated in the channel estimator 310, and estimates the noise and interference power of each channel. And it is identical with the noise and interference power estimator 220 of Fig. 2.

[65] The combining unit 340 performs channel-compensating by corresponding data tone for the channels which are estimated in the channel estimator 310 and the noise and interference powers which are estimated in the noise and interference power estimator 320, thereby, combing the received signals which are channel-compensated. And it is identical with the combining unit 230 of Fig. 2. The variance calculation unit 330 calculates the variance of the signal constellation of data tone by utilizing the ratio of the channel estimated in the channel estimator 310 to the interference and noise estimated in the noise and interference power estimator 320. The symbol metric calculation unit 350 calculates a symbol metric, by using the variance calculated in the variance calculation unit 330 and the received signals combined in the combining unit 340.

[66] Equation 7 is the variance of N' which is obtained when it is

in Equation 5.

[67] Here, N' is a complex Gaussian random variable having zero mean.

[68] [Equation 7]

[70] Equation 8 is a SINR obtained by using Equation 7. [71] [Equation 8] [72]

Els

SINR = ^■ = Σ = ∑SlNR(k)

^VarQf) f-r 4w|²]^{+ σ2}

[73] Here, SINR (k) is the SINR (Signal Interference to Noise Ratio) in the k-th antenna. [74] Since the decoder 360 requires the LLR (Log-Likelihood Ratio) for each information bit, the LLR is calculated based on the combined signal in the symbol metric calculation after combining. The C obtained in Equation 5 is a circular-symmetric normal complex Gaussian distribution, having the mean s and the variance Var(N'). In case the Var(N') of the m-th data tone within the FEC (Forward Error Correction) block is denoted as Var(m), the modulate symbol and the combined symbol are expressed as s(m) and C (m) respectively. In case of BPSK (Binary Phase Shift Keying) having normal the equi-probable source, Equation 9 obtains the LLR of the m-th data tone. Here, since the variance of the real and imaginary part of the C (m ) are the same, the normal variance becomes Var(m)

[75] [Equation 9] [76]

P(s(m) = -1 /A transmitted | C₀₀₁₁₁₁ (m) is received)

LLR (OT) = log P(s(tn) = 1 is transmitted | C_πarm (m) is received)

[77] Like the Equation 9, Equations 10 and 11 obtains the LLR of the b-th bit of the m- th data tone in QPSK (Quadrature Phase Shift Keying) and 16QAM (Quadrature Amplitude Modulation). In case 64QAM is also obtained like this. [78] [Equation 10]

[79]

QSPK

, , _» ,^ - 2Re{C_ (/«)} _, , , „ ,„, _ 2lm{C_πorm (m)}

Var{m) Var(m)

[80] [Equation H]

[81]

[6QAM

LLRAm) *

^ VTo v /TToo VTo V TToo

Var(m) min Re{C_BO, „^(«)}- s, ^" - min Re{C_∞)m (W)J-S₁ ²

LLRΛm) ViO yϊϋ Vio _/To

Var (ni )

min

„ -1 Λ^m)\-^S,\² - ^J™¹¹ Im{C,«™ (,«)}-£, I²

LLRAm) ' Vi O Vi o Vio

Var(m)

[82] In the symbol matrix computation 350, in case of QPSK, the LLR can be expressed like Equation 10, and, in case of 16QAM, it can be expressed like Equation 11. The LLR which it is obtained in the Equation 10 and Equation 11 is used in the symbol metric calculation. If the Var(m) is not changed in this one frame, it gives a identical contribution in the branch metric calculations within the trellis in decoding, therefore, the Var(m) can be ignored. In other words, If the Var(m) is changed tone-by-tone or slot-by-slot, the Var(m) should be considered in the symbol metric calculation as far as possible. The estimation Equation of the Var(m) is shown in Equation 12.

[83] [Equation 12]

[84]

[85] The variance

Var calculated in the variance calculation unit 330 can be expressed like Equation 13, when the channel estimated in the channel estimator 310 is h(k)

, the noise and interference power estimated in the noise and interference power estimator 320 is P (k), the sum of the interference from the antenna k is

NI Ϊ(k)

, and the estimated variance of the complex gaussian noise from the antenna k is σ²

[86] [Equation 13]

[87]

Var =

[88] The channel estimation for each data tone in Equation 12 is not different from the existing mode, and the estimation of the Noise + Interference Power (Var(m)) is as follows. Equation 14 expresses the received pilot signal.

[89] [Equation 14]

[90]

P(k ) = sh(k) + sb, (Ar)A, (A:) + n{k)

[91] Here, P(k) is a received pilot having the index k in one frame, s is a pilot gain, h(k) is a channel response of a target user, h i (k) is a channel response of an interferer, b i (k) is a binary number (in case the mask of an interferer is identical with the mask of a target user, it is 1, otherwise, it is -1) , and n(k) is a complex gaussian noise having the variance σ . Equation 15 expresses the estimated channel response which is made by averaging the pilot signal shown in Equation 14 for the neighboring N pilot including its own signal.

[92] [Equation 15]

[93] sh(k) — ~y\ P(J) I N where , / is around k including k

[94] Assuming that h(k) = h(l) and hi(k) = hi(l), Equation 16 expresses the calculation of noise + interference power. [95] [Equation 16]

[96] -.5[.A, (ZT)I²JH -σ^~

[97] Equation 17 is expresses the power of noise and interference P by using the

NI estimated channel , the pilot gain s, the received pilot within a frame P(k), and the number N of a neighboring pilot for the channel estimation. [98] [Equation 17]

[99]

Noise plus Interference power ≡ P_M E\ p(k) — sh(k)

[100] Fig. 4 is a flowchart that shows the received signal combining method considering the interference for each antenna in a wireless communication system equipped with a plurality of receive antennas according to the present invention.

[101] Firstly, when a channel is allocated by data tone corresponding to each receive antenna, channels are estimated by using the pilot signals neighboring of the data tone (S410 step). Equation 15 expresses the estimated channel response which is made by averaging the pilot signal for the neighboring N pilot including its own signal. Then, the noise and interference powers of a channel are estimated by the plurality of channels (S420 step).

[102] The estimated noise and interference power P can be expressed like Equation 2.

After the channels are estimated and the noiseand interference powers estimated by channel are obtained, the channel-compensated received signals are combined by channel-compensating for data tone corresponding to each channel, the noise and the interference power (S430 step). When the combined signal is C norm , the C norm can ex- pressedlike Equation 6.

[103] Fig. 5 is a flowchart that shows the symbol metric calculating method considering the interference for each antenna, using the received signal combining considering the interference for each antenna according to the present invention.

[104] When a channel is allocated by data tone corresponding to each receive antenna, channels are estimated by using the pilot signals neighboring of the data tone (S510 step). It is identical with the step S410 of Fig. 4. Then, the noise and interference powers of a channel are estimated by the plurality of channels (S520 step). It is identical with the step S410 of Fig. 4. Thereafter, in order to combine the channel, it is channel compensated by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and then, the channel-compensated received signals are combined (S530 step). It is identical with the step S430 of Fig. 4.

[105] In the meantime, the variance ofthe signal constellation of data tone is calculated by utilizing the ratio of the estimated channel to the estimated noise and interference (S540 step). The calculated variance

can be expressed like Equation 13, when the estimated channel is

Hk) , the estimated noise and interference power is P (k), the sum of the interference from

NI the antenna k is ϊ(k)

, and the estimated variance of the complex gaussian noise from the antenna k is σ

. Finally, the symbol metric is calculated by using the calculated variance and the combined receive signals (S550 step). In case of QPSK, the LLR used in the symbol metric calculation can be expressed like Equation 10, while, in case of 16QAM, it can be expressed like Equation 11.

[106] 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.

[107] 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] A receive signal combining apparatus considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, the receive signal combining apparatus comprising: a channel estimator for receiving signals from the receive antenna, and estimating a channel by using a pilot signal of each signal received from the receive antenna; a noise and interference power estimator for receiving an output of the channel estimator, and estimating a noise and interference power of each channel; and a combining unit for channel-compensating the channels estimated in the channel estimator and the noise and interference power estimated by channel in the noise and interference power estimator, and combining the channel-compensated signals.

[2] The receive signal combining apparatus of claim 1, wherein the signal C norm combined in the combining unit is expressed like the following Equation,

k =] ^rNl \^K l when, h{k) is a channel estimated in the channel estimator, P NI (k) is a noise and interference power of the channel corresponding to k-th antenna estimated in the noise and interference power estimator, and r(k) is a signal received from the k-th antenna.

[3] The receive signal combining apparatus of claim 1, wherein the combining unit channel-compensates by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combines the channel-compensated signals.

[4] The receive signal combining apparatus of claim 1, wherein the noise and interference power P is expressed like the following Equation,

when, h(k) is a channel estimated in the channel estimator, s is a pilot gain, P(k) is a received pilot within a frame, N is the number of neighboring pilot for channel estimation, and h (k) is a channel response of an interferer.

[5] A method of receive signal combining considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, the method comprising: receiving signals corresponding to each of the receive antenna, and estimating a channel by using a pilot signal of each of the receive signal; receiving an estimation value corresponding to the estimated channel, and estimating a noise and interference power of each channel; and channel-compensating by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combining the channel-compensated signals.

[6] A symbol metric calculation apparatus considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, the symbol metric calculation apparatus comprising: a channel estimator for receiving signals from the receive antenna, and estimating a channel by using a pilot signal of each signal received from the receive antenna; a noise and interference power estimator for receiving an output of the channel estimator, and estimating a noise and interference power of each channel; a combining unit for channel-compensating the channel estimated in the channel estimator and the noise and interference power estimated in the noise and interference power estimator, and combining the channel-compensated signals; a variance calculation unit for calculating avariance of data tone by using the ratio of the channel estimated in the channel estimator to a noise and interference estimated in the noise and interference power estimator; and a symbol metric calculation unit for calculating a symbol metric by using the variance calculated in the variance calculation unit and the signals combined in the combining unit.

[7] The symbol metric calculation apparatus of claim 6, wherein the signal C norm combined in the combining unit is expressed like the following Equation,

when, h(k) is a channel estimated in the channel estimator, P NI (k) is a noise and interference power of the channel corresponding to k-th antenna estimated in the noise and interference power estimator, and r(k) is a signal received from the k-th antenna.

[8] The symbol metric calculation apparatus of claim 6, wherein the combining unit channel-compensates by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combines the channel-compensated signals.

[9] The symbol metric calculation apparatus of claim 6, wherein the noise and interference power P is expressed like the following Equation,

NI sh(k)

when, h{k) is a channel estimated in the channel estimator, s is a pilot gain, P(k) is a received pilot within a frame, N is the number of neighboring pilot for channel estimation, and h (k) is a channel response of an interferer.

[10] The symbol metric calculation apparatus of claim 6, wherein the variance recalculated in the variance calculation unit is expressed like the following Equation,

when, the channel estimated in the channel estimator is h{k)

NI

, and the estimated variance of a complex gaussian noise from an antenna k is σ ^ 2

[11] The symbol metric calculation apparatus of claim 6, wherein the variance calculation unit calculates a variance of signal constellation of data tone by utilizing the ratio of the estimated channel to the estimated noise and interference.

[12] The symbol metric calculation apparatus of claim 6, wherein the symbol metric calculation unit can express an LLR (Log Likelihood Ratio) like the following Equation, in case of QPSK (Quadrature Phase Shift Keying),

_{LLRι =}≡^J Var

_ 2Im{r_norJ

LLR, =

Var

[13] The symbol metric calculation apparatus of claim 6, wherein the symbol metric calculation unit can express an LLR (Log Likelihood Ratio) like the following Equation, in case of 16QAM (Quadrature Amplitude Modulation),

Re{C_}-S,|² - m -1m - ReJC₁₁₀J-S₁

S,=

LLR, ,'10 'vlO v 10 VlO

Var

2 min Re{C_BOTB }- S, ^■ rmn _^ Re(C₁₁₀J- S,

_{LLR β} *⁼7Io-7i7 ^"'^{^}vIo VΪO

Var min ^ |lm{C,,₀J-S, - m im Im(C₁₁₀J-S,

LLR,

Var mm ImJT₁₁₀J- S, - mm im{r,,_orJ-s,|^:

LLR_Λ * ^V1" ^

Far

[14] A method of calculating a symbol metric considering interference for each antenna in a wireless communication system equipped with at least one receive antenna, the method comprising: receiving signals corresponding to each of the receive antenna, and estimating a channel by using a pilot signal of each of the receive signal; receiving an estimation value corresponding to the estimated channel, and estimating a noise and interference power of each channel; channel-compensating by data tone corresponding to the estimated channel and the noise and interference power estimated by channel, and combining the channel-compensated signals; calculating a variance of signal constellation of data tone by utilizing the ratio of the estimated channel to a estimated noise and interference; and calculating a symbol metric by using the calculated variance and the combined signals.