KR101009807B1 - Method and apparatus for detecting ook signal based on snr in wireless telecommunications system - Google Patents

Abstract

The present invention relates to a method and apparatus for detecting a signal modulated by an on / off keying (OOK) scheme in a wireless communication system. In the wireless communication system, an apparatus for detecting a signal of a channel that is modulated by on / off keying (OOK) is transmitted, and receives a signal of a OOK channel for each path and a pilot channel for an assigned path among multiple paths, and receives the pilot channel signal. A plurality of fingers for calculating a signal-to-noise ratio (SNR) for each signal with respect to a signal of a signal, a symbol combiner for outputting an OOK channel signal by combining a signal of the path-specific OOK channel for the multipath, and in the multipath An SNR combiner for combining the respective SNRs for each path and outputting a total SNR, a threshold calculator for multiplying a predetermined constant value according to an error rate required for the SNR, and a threshold calculator for calculating a threshold value; And a symbol detector for detecting the OOK symbol in comparison with the. The present invention improves the detection performance of the OOK channel by maintaining the error rate required even in a receiver that does not know the transmission power of the OOK channel.

OOK DETECTION, SNR, QPCH, Quick Paging, ACK / NACK control channel

Description

METHOD AND APPARATUS FOR DETECTING OOK SIGNAL BASED ON SNR IN WIRELESS TELECOMMUNICATIONS SYSTEM}

1 is a block diagram illustrating a receiver structure for detection of an OOK signal in a typical wireless communication system.

2 is a rake receiver structure for receiving a OOK channel in a wireless communication system according to a preferred embodiment of the present invention.

Figure 3 is a block diagram showing in more detail the structure for performing OOK detection in accordance with a preferred embodiment of the present invention.

4 is a flowchart illustrating an operation of performing OOK detection according to a preferred embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wireless communication systems, and more particularly, to a method and apparatus for detecting a modulated signal in an on-off keying (OOK) scheme.

On / off keying (OOK) is a commonly used modulation scheme for delivering only one or zero information in a wireless communication system. Typically, in the Quick Paging Channel (QPCH) of the Code Division Multiple Access (CDMA) 2000 1X system, a 1-bit paging indicator for informing the terminal whether or not there is paging information in a paging slot on a slot basis, OOK modulates and transmits. This QPCH is used to reduce power consumption of the terminal by preventing unnecessary paging channel demodulation.

In general, the OOK modulation method is worse in terms of power efficiency than the Binary Phase Shift Keying (BPSK) modulation method. Nevertheless, the use of OOK is advantageous in terms of system capacity because the probability of sending "ON" is relatively smaller than the probability of sending "OFF", which can reduce interference to other users.

On the other hand, even in a system (eg, High Rate Packet Data (HRPD) Rev. A) that performs a packet transmission of a hybrid automatic repeat request (HARQ) scheme of the physical layer, ACK (Acknowledgement) / NAK (Non) To transmit acknowledgment, OOK modulates the transmission symbol of the ACK / NAK channel.

However, in the CDMA2000 1X system, the transmit power for the "ON" signal of the QPCH is a value having a specific offset with respect to the transmit power of the pilot channel, and is indicated to the receiver by higher signaling. Therefore, the receiver performs OOK detection using the energy ratio of the pilot channel and the QPCH.

1 illustrates a receiver structure for detecting a OOK signal in a typical wireless communication system. Here, the receiver structure for the case of spreading the OOK channel through Walsh code W _ook and transmitting the pilot channel through Walsh code W _p will be described.

Referring to FIG. 1, the first despreader 102 despreads the received CDMA signal with the Walsh code _Wook of the OOK channel. Meanwhile, the second despreader 114 despreads the received CDMA signal with the Walsh code W _p of the pilot channel to output a pilot channel signal, and the channel estimator 116 uses the pilot channel signal to transmit a receiver to the receiver. Compute a channel estimate representing the channel characteristics of the furnace. Conjugate 122 obtains the conjugate complex value of the channel estimate.

The multiplier 106 multiplies the despread signal from the first despreader 102 by the conjugate complex value of the channel estimate, and the energy calculator 108 calculates the energy A for the output from the multiplier 106. Calculate Meanwhile, a squarer 118 squares the channel estimate, and the multiplier 120 sets a detection threshold B by multiplying the squared gain value G by the square of the channel estimate. The comparator 110 compares the energy A and the detection threshold B, and determines that the transmitted OOK symbol is ON when the energy A is large. Here, the appropriate gain value G means the offset of the OOK channel with respect to the transmission power of the pilot channel.

As described above, the OOK receiver sets the detection threshold value and performs OOK detection based on the offset of the pilot transmission power and the OOK transmission power.

However, the ACK / NAK control channel of HRPD Rev. A does not inform the receiver of the transmit power of the OOK symbol. Moreover, the transmit power of the OOK symbol may be power controlled for power efficiency of the wireless channel. In this case, the receiver cannot use the transmit power ratio with the pilot channel for OOK detection. Therefore, detection probability may be lowered or false alarm (FA) probability may increase according to the good or bad wireless channel environment.

Accordingly, the present invention devised to solve the problems of the prior art operating as described above, provides a method and apparatus for detecting a OOK signal when the transmission power of the OOK channel is unknown to the receiver.

The present invention provides a method and apparatus for improving detection performance while maintaining a constant false rate in detecting an OOK signal.

According to a preferred embodiment of the present invention, a method for detecting a signal of a channel that is transmitted by being on / off keyed (OOK) modulated in a wireless communication system includes receiving a signal of an OOK channel and a signal of a pilot channel, Calculating a signal-to-noise ratio (SNR) for the signal, multiplying a predetermined constant value according to an error rate required for the SNR, calculating a threshold value, and comparing a signal of the OOK channel with the threshold value to obtain a OOK symbol. It includes the process of detecting.

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According to another embodiment of the present invention, an apparatus for detecting a signal of a channel transmitted on / off keying (OOK) is transmitted in a wireless communication system, the signal of the OOK channel for each path for the assigned path of the multi-path and the pilot channel Receiving a signal, combining the plurality of fingers to calculate the signal-to-noise ratio (SNR) for each path of the pilot channel signal, and the signal of the OOK channel for each path for the multi-path to output a OOK channel signal A symbol combiner, an SNR combiner for combining the path-specific SNRs for the multiple paths, and outputting a total SNR; a threshold calculator for multiplying a predetermined constant value according to an error rate required for the SNR; And a symbol detector for detecting a OOK symbol by comparing the signal of the OOK channel with the threshold.

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The operation principle of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intention or custom of a user or an operator. Therefore, the definition should be based on the contents throughout this specification.

The main subject of the present invention to be described later is to detect an OOK signal in a wireless communication system using an on / off keying (OOK) modulation scheme, and in particular, the OOK detection scheme when the transmission power of the OOK channel is unknown to the receiver. to provide. Examples of the OOK channel include a quick paging channel (QPCH) and an ACK / NACK control channel.

2 illustrates a receiver structure for receiving a OOK channel in a wireless communication system according to an exemplary embodiment of the present invention. The receiver input stage processor 202 and the fingers 204, symbol combinations, and signal to noise ratios (Signal to Noise Ratio (SNR) combiner 206, symbol detector 208, multi-path searcher 210, microprocessor 212, and threshold calculator 214 are shown.

Referring to FIG. 2, the receiver input stage processor 202 includes a receiver antenna, a radio frequency (RF) receiver module, an analog to digital converter (ADC), and the like, which are generally used in a digital wireless communication terminal. Low Pass Filter (LPF), an interpolator may be further included. The receiver input stage processor 202 converts the received RF signal into a baseband digital received signal.

The multipath searcher 210 detects the energy of each multipath of the received signal output from the receiver input stage processor 202 and sends the multipath signals having the energy above a predetermined threshold value to the fingers 204 in order of energy magnitude. Assign as Fingers 204 despread and demodulate each of the assigned path signals, and the symbols demodulated by fingers 204 are combined by symbol combining and SNR combiner 206. Such a structure for demodulating and combining multipath signals for each path is widely known as a RAKE receiver.

At this time, each finger 204 performs symbol demodulation for each assigned path, and simultaneously calculates and transmits a signal-to-noise ratio (SNR) for each path to the symbol combiner and the SNR combiner 206, respectively. The symbol combining and SNR combiner 206 combines the path-specific symbols to output to the symbol detector 208, and also combines the path-specific SNRs to the threshold calculator 214. The threshold calculator 214 sets a threshold by multiplying the combined SNR by a constant gain value determined by the microprocessor 212 and provides the set threshold to the symbol detector 208. The symbol detector 208 then detects a OOK symbol using the threshold for the combined symbol.

As is known, the CDMA communication scheme spreads and transmits information symbols with an orthogonal spreading code such as a Walsh code. By doing so, the immunity to noise can be increased. Typically, in a wireless communication system such as CDMA 1X or HRPD or Wideband CDMA (WCDMA), a pilot channel is transmitted as a phase reference signal for coherent symbol demodulation. Here, the pilot channel signal is an unmodulated signal having a symbol value of 1 always. The pilot channel signal can be used to compensate for phase distortion due to fading, or can be used for noise measurement of the received signal and for synchronization of the receiver (e.g., symbol synchronization and frequency synchronization), in particular bursts such as HRPD. If a pilot is used, it can also be used to measure the SNR for rate selection.

)를 계산하고, 또한 파일럿 채널의 경로별 SNR을 계산하여 OOK 심볼의 검출을 위한 임계값을 계산한다.Therefore, in the preferred embodiment of the present invention, the weight of each path of the rake receiver performing the maximum ratio combining using the pilot channel in the HRPD system (

), And calculates a path-specific SNR of the pilot channel to calculate a threshold for detection of the OOK symbol.

는 하기 <수학식 1>과 같이 표현된다.Received signal that is output from receiver input stage processor 202 that has passed through a wireless channel

Is expressed by Equation 1 below.

는 HRPD 송신신호이고,

는 무선 채널의 페이딩 성분을 나타내는 채널 임펄스응답, 즉 채널 추정값이며,

는 무선 채널에서 가해지는 평균 0, 분산

의 가우시안 잡음이다.here,

Is an HRPD transmission signal,

Is a channel impulse response, i.e., channel estimate, representing the fading component of the wireless channel,

Is the mean zero, variance,

Gaussian noise of.

가 적용된 이후의 OOK 채널의 수신 신호는 다음 <수학식 2>와 같이 표현된다.Weighted after Walsh despread with Walsh code _Wook in OOK channel

The received signal of the OOK channel after is applied is expressed as Equation 2 below.

는 OOK 심볼 값이며,

는 OOK 채널의 전송전력이고,

는 파일럿 채널 전송전력이다. 상기 <수학식 2>에서 통상 파일럿 전송전력은 일정하므로 편의상

로 가정하여 생략 가능하다. 따라서 OOK 채널의 수신 신호는 간단히 하기 <수학식 3>와 같이 나타낼 수 있다.here,

Is the OOK symbol value,

Is the transmit power of the OOK channel,

Is the pilot channel transmit power. In Equation 2, the pilot transmission power is generally constant.

Can be omitted. Therefore, the received signal of the OOK channel can be simply expressed as Equation 3 below.

이면, 수신 신호는 평균 0, 분산

의 가우시안 잡음과 동일하게 된다. 따라서

일 때 수신 신호의 사후 확률 분포는 다음의 <수학식 4>가 된다.Where the OOK symbol

If, then the received signal is 0 average, variance

It is equal to the Gaussian noise of. therefore

When the posterior probability distribution of the received signal is given by Equation 4 below.

를 넘는 값을 ON으로 판정하는 오보율을

이라 설정하면, 임계값과 오보율 및 SNR과는 다음 <수학식 5>와 같은 관계가 성립한다.Threshold

The error rate that determines that a value exceeding

In this case, the relationship between the threshold value, the false error rate, and the SNR is shown in Equation 5 below.

Where erf is a well-known error function (ie Gaussian error function).

와 채널 추정치(

)의 곱으로부터

로서 계산된다. 또한 <수학식 5>의 임계값에서,

는 상수 값으로서 오보율(

)에 따라 미리 계산되어 룩-업 테이블에 저장될 수 있다. 결과적으로 임계값

은 SNR과 오보율의 함수가 된다. 상기와 같이 설정된 임계값에 따라, 수신 신호가 상기 임계값보다 작으면 OOK 심볼을 OFF로 판정하고, 그렇지 않으면 OOK 심볼을 ON으로 판정한다. In Equation 5, SNR is weighted according to the maximum ratio combining method.

And channel estimates (

From the product of

Is calculated as Also, at the threshold of Equation 5,

Is a constant value, where

May be calculated in advance and stored in the look-up table. As a result, the threshold

Is a function of SNR and false rate. According to the threshold set as described above, if the received signal is smaller than the threshold, the OOK symbol is determined to be OFF, otherwise the OOK symbol is determined to be ON.

는 제곱근 연산을 취해야 하므로, 계산이 용이하지 않다. 따라서 다른 실시예로, 임계값을

으로 설정하고, SNR은 앞서 언급된

로서 계산하며,

을 미리 계산하여 룩-업 테이블에 상수값으로서 저장함으로써, 요구되는 오보율에 따라 상기 룩-업 테이블의 해당하는 값을 선택함으로써 OOK 검출을 위한 임계값을 계산한다. However, in calculating the threshold,

Since we need to take the square root operation, it is not easy to calculate. Thus, in another embodiment, the threshold is

And the SNR is

As

Is calculated in advance and stored as a constant value in the look-up table, thereby calculating the threshold for OOK detection by selecting the corresponding value of the look-up table according to the required false rate.

3 is a block diagram illustrating a structure for performing OOK detection in detail according to a preferred embodiment of the present invention, in which a receiver input processor 302, a finger 304, a symbol combiner 306a, and an SNR combiner 306b are shown. The threshold calculator 314 and the symbol detector 308 are shown.

Referring to FIG. 3, the receiver input stage processor 302 converts a received RF signal into a baseband digital received signal. Finger 304 despreads and demodulates the signal of the path assigned by multipath searcher 210, demodulated symbols are passed to symbol combiner 306a, and the SNR calculated for the assigned path is an SNR combiner. Forward to 306b. The detailed structure of the finger 304 will be described below.

을 계산한다. 잡음 추정기(326)는 마찬가지로 상기 파일럿 채널 신호를 이용하여 잡음 성분의 분산

을 구한다.The received signal from the receive end processor 302 is provided to the Walsh discoveries 320 and 324 of the finger 304. The first Walsh decover 320 despreads (ie, Walsh decovers) the received signal with a Walsh code _Wook of the OOK channel. In addition, the second Walsh decover 324 outputs a pilot channel signal by despreading (ie, Walsh decovering) the received signal with the Walsh code W _p of the pilot channel, and the channel estimator 332 uses the pilot channel signal. Channel estimates representing channel characteristics from transmitter to receiver

. Noise estimator 326 likewise uses the pilot channel signal to distribute noise components

.

The weight calculator 328 calculates the weight as the ratio of the noise variance to the conjugate complex value of the channel estimate and then provides the weight to the multiplier 322. The multiplier 322 multiplies the despread signal from the first Walsh cover 324 by the weight to provide a symbol combiner 306a. The symbol combiner 306a provides the OOK channel signal obtained by combining the outputs from the plurality of fingers, including the finger 304, to the symbol detector 308.

에 따른 상수값을 룩-업 테이블로부터 검색하여, 앞서 언급한 <수학식 5>에 의해 임계값을 계산한 후, 상기 계산된 임계값을 심볼 검출기(308)로 제공한다.On the other hand, the multiplier 330 in the finger 304 calculates the SNR for each path of the pilot channel signal by multiplying the weight calculated by the weight calculator 328 by the channel estimate from the channel estimator 332 to obtain an SNR combiner ( 306b). SNR combiner 306b provides threshold calculator 314 with the total SNR obtained by combining path-specific SNRs from a plurality of fingers, including finger 304. Threshold calculator 314 then uses the SNR and sets a preset false rate.

The constant value is calculated from the look-up table, the threshold value is calculated by Equation 5, and the calculated threshold value is provided to the symbol detector 308.

The symbol detector 308 compares the energy of the OOK channel signal provided from the symbol combiner 306a with the threshold provided from the threshold calculator 314 to determine whether the detected OOK symbol is ON or OFF. As an example, when symbol mapping of {ON (+1), OFF (0)} is used in OOK modulation, the procedure for OOK detection may be expressed as the algorithm of Table 1 below. Performed by the symbol detector 308.

< 0
검출 심볼 = OFF
ELSE
IF

<

검출 심볼 = OFF
ELSE
검출 심볼 = ON
ENDIF

<0
Detection symbol = OFF
ELSE
IF

<

Detection symbol = OFF
ELSE
Detect symbol = ON
END

> 0을 판단하게 된다.As another example, when a symbol mapping of {ON (-1), OFF (0)} is used, the first If statement in Table 1 above is used.

> 0.

혹은

은 OOK 채널의 전송전력인

와 상관없이 설정되므로, OOK 채널의 전송전력을 알지 못하는 수신기에서도 OOK 심볼 검출을 수행할 수 있다. As shown in Equation 5, the threshold for OOK symbol detection

or

Is the transmit power of the OOK channel

Since it is set regardless of, the OOK symbol detection can be performed even in a receiver that does not know the transmission power of the OOK channel.

4 is a flowchart illustrating an operation of performing OOK detection according to an exemplary embodiment of the present invention.

)을 결정한다. Referring to FIG. 4, in step 402, a receiver obtains channel estimates and noise variances using a pilot channel signal, and calculates weighted paths and SNRs using paths using the pilot channel signals. In step 404, the receiver combines the SNR values for each path to calculate the total SNR value. In step 406, the receiver multiplies the SNR value by a constant value obtained from a look-up table according to a predetermined error rate.

Is determined.

In step 408, the receiver combines the weighted demodulation signals for each path to obtain an OOK channel signal. In step 410, the receiver compares the energy of the OOK channel signal with the threshold to determine whether the OOK channel signal is an OOK symbol indicating ON. Or OOK symbol indicating OFF.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

In the present invention that operates as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

According to the present invention, by setting a threshold value for OOK symbol detection irrespective of the transmit power of the OOK channel, it is possible to maintain the required error rate even in a receiver that does not know the transmit power of the OOK channel, and performs the OOK by performing the maximum ratio combining. There is an effect that can improve the detection performance of the channel.

Claims (10)

A method of detecting a signal of a channel transmitted on / off keying (OOK) in a wireless communication system, Receiving a signal of an OOK channel and a signal of a pilot channel, and calculating a signal-to-noise ratio (SNR) for the signal of the pilot channel; Calculating a threshold value by multiplying a predetermined constant value according to an error rate required for the SNR; And detecting a OOK symbol by comparing the signal of the OOK channel with the threshold value. The method of claim 1, wherein the constant value is calculated as in the following equation.

Where erf represents an error function,

Represents the required false rate. The method of claim 1, wherein the calculating of the SNR comprises: Despreading a signal of each path through a wireless channel with a spreading code of the pilot channel; Estimating noise variance of the wireless channel using the despread signal; Estimating a channel estimate of the wireless channel using the despread signal; Calculating a weight as the ratio of the noise variance to the conjugate complex value of the channel estimate; Calculating an SNR for each path by multiplying the weight by the channel estimate; And calculating a total SNR by combining the path-specific SNRs. The method of claim 1, wherein the predetermined constant value according to the required false rate is managed as a look-up table. The method of claim 1, wherein when the OOK symbol is mapped to +1 when ON and 0 when OFF, the detecting of the OOK symbol includes: If the energy of the signal of the OOK channel is less than 0, the OOK symbol is determined to be OFF. If the power of the signal of the OOK channel is smaller than the threshold, the OOK symbol is determined to be OFF and the power of the signal of the OOK channel is determined. And if it is not smaller than the threshold, determining the OOK symbol to be ON. An apparatus for detecting a signal of a channel transmitted by on / off keying (OOK) modulation in a wireless communication system, A plurality of fingers for receiving a signal of a OOK channel and a pilot channel for each of the allocated paths among the multipaths, and calculating signal-to-noise ratios (SNRs) for the paths of the signals of the pilot channel; A symbol combiner for outputting a OOK channel signal by combining the OOK channel signal for each path for the multipath; An SNR combiner for combining the path-specific SNRs for the multipaths and outputting a total SNR; A threshold calculator for calculating a threshold value by multiplying a predetermined constant value according to an error rate required for the SNR; And a symbol detector for detecting a OOK symbol by comparing the signal of the OOK channel with the threshold value. 7. The apparatus of claim 6, wherein the constant value is calculated as in the following equation.

Where erf represents an error function,

Represents the required false rate. The method of claim 6, wherein each of the fingers, A first Walsh decover for despreading the signal of the assigned path with a spreading code of the OOK channel; A second Walsh decover for despreading the signal of the assigned path with a spreading code of the pilot channel; A noise estimator for estimating noise variance of a wireless channel using the despread signal of the pilot channel; A channel estimator for estimating a channel estimate of the wireless channel using the despread signal of the pilot channel; A weight calculator for calculating a weight as a ratio of the noise variance to a conjugate complex value of the channel estimate; A first multiplier configured to multiply the despread signal of the OOK channel by the weight to output a signal of the OOK channel for each path; And a second multiplier for calculating path-specific SNRs by multiplying the weights by the channel estimates. 7. The apparatus of claim 6, wherein a predetermined constant value according to the required error rate is managed as a look-up table. The symbol detector of claim 6, wherein when the OOK symbol is mapped to +1 when ON and 0 when OFF, the symbol detector includes: If the energy of the signal of the OOK channel is less than 0, the OOK symbol is determined to be OFF. If the power of the signal of the OOK channel is smaller than the threshold, the OOK symbol is determined to be OFF and the received signal of the OOK channel is determined. And determining that the OOK symbol is ON when the power is not smaller than the threshold value.

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