KR20080046886A - Spatial-temporal adaptive equalizing method for interference canceling in wireless communication system - Google Patents

Abstract

A space-time adaptive equalizing method for interference canceling in a wireless communication system is provided to cancel a unknown interference such as multiple cell interference or interference between different users in the same cell in the downlink of a WCDMA(Wideband Code Division Multiple Access) system or an HSDPA(High Speed Downlink Packet Access) system, thereby lowering a BER(Bit Error Rate). Noise and interference have influence on a signal when the signal passes through a wireless channel via a node B. The signal passes through the RF(Radio Frequency)/IF(Intermediate Frequency) block of a receiver, an ADC(Analog to Digital Converter), an RRC(Root-Raised Cosine) filter, and an IC(Integrated Circuit)(10) maximizing an SINR(Signal to Noise Ratio). A unknown noise is cancelled through a channel compensation equalizer(30) and an adaptive interference canceling equalizer. Receiving data is generated by passing through a despreader, a demodulator, a TrCH(Transmission Channel) processor, and a channel decoder. The output signal of the adaptive interference canceling equalizer is transmitted to the despreader and the demodulator.

Description

SPACE-TEMPORAL ADAPTIVE EQUALIZING METHOD FOR INTERFERENCE CANCELING IN WIRELESS COMMUNICATION SYSTEM}

1 is a block diagram of a wireless communication system to which a space-time adaptive equalization method according to the present invention is applied.

2 shows the structure of a filter-based adaptive interference cancellation equalizer (TAICE) according to the present invention.

3 is a graph comparing bit error rates when a conventional receiver is used for a speech signal in a fixed channel, when only interference of CPICH is removed, and when the space-time adaptive equalization method of the present invention is applied after removing the CPICH. Shows.

4 is a graph comparing bit error rates for a data signal in a fixed channel when a conventional receiver is used, when only interference of a CPICH is removed, and when the space-time adaptive equalization method of the present invention is applied after the CPICH is removed. Shows.

5 is a graph comparing bit error rates when a conventional receiver is used for a voice signal in a fading channel, when only interference of CPICH is removed, and when the space-time adaptive equalization method of the present invention is applied after removing the CPICH. Shows.

<Explanation of symbols for the main parts of the drawings>

10: Interference Canceller

20: Adaptive Interference Cancellation Equalizer (TAICE)

21: Equalizer Filter

30: channel compensation equalizer

The present invention relates to a method for removing noise in signal reception in a wireless communication system, in particular, Wideband Code Division Multiple Access (WCDMA) and High Speed Downlink Packet Access (HSDPA) systems. The present invention relates to a reception method capable of effectively removing unknown interference.

In order to solve the problem of capacity shortage in the analog wireless communication system, CDMA (Code Division Multiple Access) system has been commercialized, and WCDMA and HSDPA systems have been used.

However, in the downlink of WCDMA and HSDPA systems, as the number of active users increases, the noise acting on each terminal increases, thereby increasing the bit error rate (BER) of the received signal, and eventually the performance of the system is increased. Degrades. These noises include not only interference using known codes, but also components that enable users to act as signals known to all users, such as CPICH, and interference that is not known to different users by using different codes.

The conventional method for removing signal noise in wireless communication is simply in the form of a matched filter that maximizes the received signal-to-noise ratio (SNR) using a code assigned to the user. It was a way of receiving. However, since the interference of other users is not considered at this time, the BER of the received signal is high.

In order to solve such a problem, in order to eliminate interference of other users, Patent Application No. 10-2006-0086280 discloses interference that maximizes the Signal to Interference plus Noise Ratio (SINR) that removes known signals such as CPICH using a code. The removal method is presented.

However, all of them have a problem that they cannot remove unknown signals such as signals from neighboring base stations and signals of other users in the same cell.

The present invention, in addition to removing the interference signal known in the downlink (Downlink) of the wireless communication system, especially WCDMA or HSDPA system using a code to remove the unknown interference.

Furthermore, the present invention is to make it easy to extend the equalization method for indirect removal in a wireless communication system even in an environment using multiple antennas.

In addition, the present invention is to provide an interference cancellation method using an interference canceller having a compatibility that can be easily added and applied to the interference canceller maximizing SNR and / or the interference canceller maximizing SINR.

The present invention is to achieve the above object, the space-time interference cancellation adaptive equalization method according to an aspect of the present invention, in the receiving method for removing noise in a wireless communication system, the received signal is input to the channel compensation equalizer Obtaining a channel compensated signal; Obtaining an error signal using the channel compensated signal as a reference signal and a difference between the reference signal and an output signal passed through an equalizer filter; Updating an equalizer filter tap by applying the reference signal, error signal, and received signal to an LMS algorithm; And multiplying the updated equalizer filter tap by the next received signal to obtain an output signal corresponding to the next received signal.

으로 나타낼 수 있다. 여기서

은

번째 사용자의 p번째 안테나의 적응 간섭제거 등화기의 n번째 출력신호이고,

은

번째 사용자의 p번째 안테나의 n번째 수신신호이고,

은 적응 간섭제거 등화기의 등화기 탭이고,

은 등화기 필터 탭의 수이다. Preferably, in the step of obtaining the output signal, the output signal is a plurality of equalizer filter taps.

It can be represented as here

silver

Output signal of the adaptive interference cancellation equalizer of the p-th antenna of the first user,

silver

N-th received signal of the p-th antenna of the first user,

Is the equalizer tab of the adaptive interference cancellation equalizer,

Is the number of equalizer filter taps.

으로 나타낼 수 있다. 여기서

은

번째 사용자의 적응 간섭제거 등화기의 n번째 출력신호이고,

은

번째 사용자의 상기 오차신호의 제곱을 평균 낸 기대값이다. More preferably, in the step of obtaining the output signal, the output signal, when using a multiple antenna

It can be represented as here

silver

Output signal of the user's adaptive interference cancellation equalizer,

silver

It is an expected value obtained by averaging the square of the error signal of the first user.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to preferred embodiments of the present invention.

1 is a block diagram of a wireless communication system to which a space-time adaptive equalization method according to the present invention is applied. In the mobile communication system using the WCDMA / HSDPA method, a process from a transmitter to a receiver is briefly described based on reception.

In FIG. 1, a signal passes through a Node-B over a Wireless Channel, where noise and interference affect the signal. In addition, the signal passes through the RF / IF block of the receiver and passes through an analog to digital converter (ADC), a root-raised cosine filter (RRC), and an IC 10 that maximizes SINR. The unknown compensation is removed through the channel compensation equalizer 30 and the adaptive interference cancellation equalizer (TAICE) 20, and a despreader, a demodulator, a TrCH processor, and a channel decoder. It passes through and generates received data.

In FIG. 1, interference cancellation may be performed by inserting a baseband signal having chip rate processing through an RRC filter of a WCDMA / HSDPA system receiver as an input of an IC 10 that maximizes SINR. The presence of the IC 10 that maximizes this SINR is optional and is compatible with the adaptive interference cancellation equalizer that is proposed. In addition, a Matched Filter (Maximum Signal-to-Noise Ratio) may be installed before or after the IC 10 that maximizes the SINR, or one of the two may be selectively installed.

The output of the IC 10 that maximizes the SINR having the chip speed processing is compensated by being put into the channel compensation equalizer 30 and the reliability of the received signal is increased. The output signal of the channel compensation equalizer 30 is used as a reference signal of the adaptive interference cancellation equalizer 20 to remove unknown interference. The output signal of the adaptive interference cancellation equalizer 20 is sent to a despreader and a demodulator.

The proposed space-time adaptive equalization method can reduce unknown interference signals because it adapts based on reference signals without using codes. On the other hand, since the reliability of the reference signal is important, performance can be improved by increasing the reliability of the reference signal through the existing channel compensation equalizer.

2 is a structural diagram of a filter-based adaptive interference cancellation equalizer (TAICE) according to the present invention, in which one antenna is used. Of course, the present invention can also be applied to a general plurality of antennas.

은

번째 사용자의 RRC 필터를 거치거나, RRC 필터 및 SINR을 최대로 하는 IC(10)를 차례로 거친 수신신호를 표시한다.

은 기준신호로써

을 채널보상 등화기(30)에 넣어 채널이 보상된 수신신호이다.

은 [수학식 1]과 같이

번째 사용자의 등화기 필터(21)를 거친 출력신호

과 기준신호

와의 차를 나타내는 오차신호가 된다. 등화기 필터는 FIR (Finite Impulse Response) 필터 등이 이용될 수 있다.In Figure 2

silver

The received signal passes through the RRC filter of the second user or through the IC 10 that maximizes the RRC filter and the SINR.

Is the reference signal

Is a channel-compensated equalizer 30 to compensate for the channel.

Is as shown in [Equation 1]

Output signal through the equalizer filter 21 of the first user

And reference signal

It is an error signal indicating a difference between and. The equalizer filter may be a finite impulse response (FIR) filter or the like.

Equation 1

개의 필터 탭을 가지고 있고 이는 칩 레벨로 동작하게 된다. 그리고 필터 탭을 적응시키기 위하여 최소 평균 제곱(LMS; Least Mean Square) 알고리즘이 사용된다. LMS 알고리즘은 정규 최소 평균 제곱(NLMS; Normalized Least Mean Square) 알고리즘, 싸인 LMS(Signed LMS) 알고리즘, 싸인-데이터 LMS(Sign-data LMS) 알고리즘 등을 포함한다. 이 중 NLMS은 간단하고 잡음에 강인한 특성을 지니고 있어 가장 효과적이며, 그 원리는 [수학식 2]에 나타내었다. The equalizer filter 21 of the adaptive interference cancellation equalizer in the present invention is

It has four filter taps, which operate at the chip level. The least mean square (LMS) algorithm is used to adapt the filter tap. LMS algorithms include a Normalized Least Mean Square (NLMS) algorithm, a Signed LMS (Signed LMS) algorithm, a Sign-data LMS (Signal-Data LMS) algorithm, and the like. Among them, NLMS is most effective because it is simple and robust against noise, and its principle is shown in [Equation 2].

Equation 2

는 기준신호이고,

은 등화기의 필터 탭으로

벡터이고,

는 입력신호를

개만큼 쌓은

벡터 이고,

는 적응상수이고, ( )^H는 허미션 연산이다. here

Is the reference signal,

To the filter tab of the equalizer

Vector,

Input signal

Stacked

Vector

Is an adaptive constant, and () ^H is a mission operation.

로 한다. In using the NLMS algorithm in the present invention, the reference signal is passed through the channel compensation equalizer 30.

Shall be.

At this time, the output of the adaptive interference cancellation equalizer 20 is shown in [Equation 3].

Equation 3

은

번째 사용자의 p번째 안테나의 적응 간섭제거 등화기의 n번째 출력신호이고,

은

번째 사용자의 p번째 안테나의 n번째 수신신호이고,

은 적응 간섭제거 등화기의 등화기 탭이고,

은 등화기 필터 탭의 수이다. here

silver

Output signal of the adaptive interference cancellation equalizer of the p-th antenna of the first user,

silver

N-th received signal of the p-th antenna of the first user,

Is the equalizer tab of the adaptive interference cancellation equalizer,

Is the number of equalizer filter taps.

의 역수이고, 각 안테나에서 나오는 신호를 가중치로 곱하여, 그 곱한 값을 모두 더한 총합이 출력신호가 된다. 복수 P개의 수신안테나를 사용하는 경우 출력신호는 [수학식 4]와 같이 나타낼 수 있다.If we use a total of P receive antennas, the weight needed to use multiple antennas is

It is the inverse of, and multiplies the signal from each antenna by the weight, and the sum of all the multiplied values is the output signal. When using a plurality of P receiving antennas, the output signal can be expressed as shown in [Equation 4].

Equation 4

은

번째 사용자의 적응 간섭제거 등화기의 n번째 출력신호이고,

은

번째 사용자의 상기 오차신호의 제곱을 평균 낸 기대값이 된다. here,

silver

Output signal of the user's adaptive interference cancellation equalizer,

silver

It is an expected value obtained by averaging the square of the error signal of the first user.

Since the output signal obtained by Equation 3 or Equation 4 is calculated without using a code, unknown interference can be eliminated in an adaptive manner. The output signal is sent to the despreader and demodulator so that the signal can be detected.

On the other hand, in the IC 10 that maximizes the SINR, the input signal, that is, the received signal, can be represented as shown in [Equation 5].

Equation 5

는

번째 사용자에게 할당된 고유 코드(code signature)로써 WCDMA/HSDPA 시스템에서는 이를 통해 각 사용자 또는 기지국을 구별한다.

는

번째 사용자 신호가 겪고 들어온 채널의 크기를 가리킨다. 그리고

는 칩 단위 수신신호를 확산코드 길이만큼의 쌓아놓은 수신 벡터이다.

는

번째 사용자가 보내는 n 번째 심볼(symbol)을 가리키며

의 통계적 특성을 가진다고 가정한다. 여기서

는

의 평균값을 가리키며,

는 크로네커 델타(Kronecker delta) 함수이다.Here

Is

As a unique code (code signature) assigned to the first user, the WCDMA / HSDPA system distinguishes each user or base station through this.

Is

Indicates the size of the channel received by the first user signal. And

Is a stacked reception vector stacking up to the spreading code length of the received signal per chip.

Is

Points to the nth symbol sent by the first user

Assume that it has a statistical characteristic of. here

Is

Mean value of,

Is the Kronecker delta function.

은

을 분산(또는 전력)으로 가지는 수신벡터에 더해진 백색 가우시안 잡음(AWGN)을 가리키며 크기는 수신신호

의 크기와 동일하다. Also

silver

Denotes a white Gaussian noise (AWGN) added to a received vector with variance (or power)

Is the same as.

명의 사용자는 간섭으로 가정하면, SINR을 최대로 하는 검파기의 형태는 [수학식 6]과 같이 나타낼 수 있다.Find the signal to detect the first user when there are multiple K users

Assume that the number of users assumes interference, the type of detector maximizing SINR can be expressed as shown in [Equation 6].

Equation 6

의 허미션(Hermitian)를 곱하는 연산은, 우선 간섭신호원과 백색잡음의 공분산(Covariance)의 역행렬의 허미션을 곱함으로써 이들의 효과를 없애주고, 다음으로 공간적 고유특성인

의 허미션을 곱함으로써 정합필터링(Matched filtering)의 효과를 내고 있다.

The operation of multiplying the Hermitian of the first method eliminates their effects by first multiplying the interference signal source by the inverse of the covariance of the white noise, then eliminating their effects.

By multiplying the hermit, the effect of matched filtering is achieved.

을 각 사용자의 고유 코드 벡터로 다시 표현하기 위한 구체적인 예로써, 하나의 간섭이 존재할 때, 즉 총 2명의 사용자가 존재하며 두 번째 사용자의 신호가 간섭 신호일 때, SINR을 최대로 하는 IC(10)에서 은 [수학식 7]과 같이 나타낼 수 있다.

As a specific example for re-expressing the X in a unique code vector of each user, the IC 10 maximizes the SINR when one interference exists, that is, when there are two users in total and the signal of the second user is an interference signal. in Can be expressed as shown in [Equation 7].

Equation 7

는 허미션 연산이고,

는 2번째 사용자의 수신 전력을 가리킨다. 또한

는 고유 행렬(Identity matrix)로 확산계수(Spreading Factor)만큼의 행과 열 크기를 가지는 정방행렬(square matrix)이다.here

Is a mission operation,

Indicates the received power of the second user. Also

Is an identity matrix and is a square matrix having a row and column size corresponding to a spreading factor.

명이고, 첫 번째 사용자 신호를 검파하는데 있어 나머지 사용자를 간섭으로 생각하면

은 [수학식 8]과 같다. On the other hand, a plurality of users in [Equation 7]

If you think of the rest of the users as interference in detecting the first user signal,

Is the same as [Equation 8].

Equation 8

을 적용하면, SINR을 최대로 하는 IC(10)에서의 선형 변환은 [수학식 9]과 같이 나타낼 수 있다.Also, Equation 8 shows the Sherman-Morrison-Woodbury formula, namely

Applying, the linear transformation in the IC 10 to maximize the SINR can be expressed as Equation (9).

Equation 9

는 해당 사용자를 제외한 간섭 사용자들의 고유 코드 열로 이루어진 행렬이며 제거하고자 하는 간섭 신호들의 개수를 (

)이라 하였을 때

이 된다. 이때

은 한번에 제거하고자 하는 칩 레벨의 신호를 쌓은 벡터의 길이이다.

는 각 간섭 사용자들의 신호의 크기를 원소로 가지는

의 대각행렬이다. here

Is a matrix of unique code sequences of interfering users other than the corresponding user.

When you say

Becomes At this time

Is the length of the vector of stacked chip level signals to be removed at once.

Is an element whose magnitude is the signal of each interfering user.

Diagonal matrix of.

는 코드 정보를 이용하기 때문에, 본 발명에 의한 잡음 제거방법은 모든 사용자가 알고 있는 채널 및 사용자 자신에게 할당된 데이터채널들 간의 간섭을 제거하는데 쓰인다. 이때 모든 사용자가 알고 있는 채널은 주로 파일럿 채널(Pilot Channel), 특히 공통 파일럿 채널(CPICH; Common Pilot Channel)이 될 수 있다. here

Since the code information is used, the noise canceling method according to the present invention is used to remove interference between channels known to all users and data channels assigned to the user himself. In this case, a channel known to all users may be a pilot channel, in particular, a common pilot channel (CPICH).

The detector maximizing SINR removes known signals such as CPICH first, and then removes unknown interference by space-time adaptive equalization.

On the other hand, to compare the performance of the method proposed in the present invention compared the performance with the conventional receiver through a simulation in various channel environments. The characteristics of the channels to be compared and the simulation environment are shown in [Table 1].

TABLE 1

DPCH Rate (SF) Channel (cell0) Ior / Ioc (dB) 10ms boundary delay of Cell1 compared to Cell0 finger count TV1 12.2 kbps (128) Static -One 300chip One TV2 64 kbps (32) Static -One 300chip One TV3 64 kbps (32) Case1 9 300chip 2 TV4 12.2 kbps (128) Static -5 300chip One TV5 12.2 kbps (128) Static 3 300chip One TV6 64 kbps (32) Static -5 300chip One TV7 64 kbps (32) Static 3 300chip One TV8 64 kbps (32) Case1 5 300chip 2 TV9 64 kbps (32) Case1 13 300chip 2

Assume two cells in each of three scenarios, and assume that only one base station belongs to an active set. For the voice service (12.2 kbps) fixed channel, the data service (64 kbps) fixed channel and the data service fading channel (Fading Channel; corresponding to Case1) were compared. Here, Case1 is a channel with two multipaths, and the delay time and relative signal power profiles are given by [0, 60] (chip / 16) and [1, 0.316228].

3 is a graph comparing bit error rates when a conventional receiver is used for a speech signal in a fixed channel, when only interference of CPICH is removed, and when the space-time adaptive equalization method of the present invention is applied after removing the CPICH. Fig. 4 compares the bit error rate for a data signal in a fixed channel when using a conventional receiver, removing only interference of the CPICH, and applying the space-time adaptive equalization method of the present invention after removing the CPICH. One graph.

5 is a graph comparing bit error rates when a conventional receiver is used for a voice signal in a fading channel, when only interference of CPICH is removed, and when the space-time adaptive equalization method of the present invention is applied after removing the CPICH. to be.

3 to 5, when only the interference of the CPICH is removed shows a lower BER than when using a conventional receiver, when applying the space-time interference cancellation adaptive equalization method according to the present invention than when only removing the interference of the CPICH It can be seen that having a lower BER significantly improved system performance. For reference, the values in FIGS. 3 to 5 do not apply the process of increasing the reliability of the reference signal used in the adaptive interference cancellation equalizer by applying the conventional channel compensation equalizer, but if applied, the performance improvement is greater than the result shown in the graph. There is this.

The spatiotemporal interference cancellation adaptive equalization method in the wireless communication system according to the present invention can be applied to various physical channels, can be used to remove an unknown code, and is also within the scope of the technical idea of the present invention. It can be modified and applied in various forms. That is, the embodiments and the drawings are only for the purpose of describing the contents of the invention in detail, and are not intended to limit the scope of the technical idea of the invention, the scope of the present invention is not limited to the claims to be described later, but the equivalent scope thereof. Should be judged.

According to the present invention, a bit error rate is lowered by removing unknown interference such as multi-cell interference or interference of different users in the same cell in downlink of a wireless communication system, particularly a WCDMA or HSDPA system.

In addition, the present invention can be easily extended to the space-time interference cancellation adaptive equalization method in a wireless communication system using multiple antennas, and its utility range is wide. It is possible to operate a performance interference canceller.

Claims (4)

In a reception method for removing noise in a wireless communication system, Inputting a received signal to a channel compensation equalizer to obtain a channel compensated signal; Obtaining an error signal using the channel compensated signal as a reference signal and using the difference between the reference signal and an output signal passed through an equalizer filter as a value; And Updating an equalizer filter tap by applying the reference signal, error signal, and received signal to an LMS algorithm; And And multiplying the updated equalizer filter tap by the next received signal to obtain an output signal corresponding to the next received signal. The method of claim 1, wherein the output signal in the step of obtaining the output signal can be represented by the following Equation (3) when there are a plurality of filter taps. Equation 3

here

silver

N th output signal of the adaptive interference cancellation equalizer of the p th antenna of the first user,

silver

N-th received signal of the p-th antenna of the first user,

Is the equalizer tab of the adaptive interference cancellation equalizer,

Is the number in the Equalizer Filters tab. The method according to claim 1 or 2, In the obtaining of the output signal, the output signal may be represented by Equation 4 below when using multiple antennas. Equation 4

here,

silver

Output signal of the user's adaptive interference cancellation equalizer,

silver

Expected average value of the square of the error signal of the second user. 3. The method of claim 1 or 2, wherein the received signal input to the channel compensation equalizer is a signal that passes through an IC that maximizes SINR.

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