KR101447220B1 - Apparatus and method for measurementing carrier to interference noise ratio in orthogonal frequency division multiplexing access system - Google Patents

Abstract

The present invention relates to a method and apparatus for estimating Carrier to Interference and Noise Ratio (CINR) in an orthogonal frequency division multiplexing (OFDM) system, and more particularly, to a method and apparatus for estimating a CINR And a second CINR estimator for estimating a CINR for adaptive modulation and coding according to a channel state, and estimates a CINR suitable for a channel condition or robust against a time error according to a use purpose of the CINR The throughput of the system can be increased, and continuous handover can be guaranteed.

CINR, differential correlation, FIR filter

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an orthogonal frequency division multiple access (OFDM)

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for estimating a Carrier to Interference and Noise Ratio (CINR) in a system using an Orthogonal Frequency Division Multiplexing (OFDM) And a method and an apparatus for estimating the CINR by selecting an estimation algorithm suitable for the use of the CINR in an OFDMA (Frequency Division Multiplexing) system and an OFDMA (Orthogonal Frequency Division Multiplexing Access) system.

2. Description of the Related Art In an OFDM communication system, a UE increases the throughput of a system and performs adaptive modulation and coding (AMC) on a downlink for seamless handover. And a CINR for the handover.

FIG. 1 shows a block configuration for estimating a CINR in a terminal of a communication system of a general OFDM scheme.

1, a terminal converts a signal received through an antenna 101 into a baseband signal through a RF (Radio Frequency) unit 103 and transmits the baseband signal through an ADC (Analog Digital Converter) 105 And the received signal is filtered by the reception filter 107. Then, the terminal removes the CP from the filtered signal through a CP (Cyclic Prefix) eliminator and a deserializer (109), converts the CP into an analog signal in parallel, and then, in a fast Fourier transform (FFT) Area signal. Thereafter, the terminal combines the PN code allocated to each user and the converted signal in the PN code generator 115 in the signal synthesizer 113 to extract only the received signal from the PN synthesizer 113, and outputs the combined signal to the CINR estimator 117 And separates the interference and noise components from the extracted signal to estimate the ratio of the received signal to the interference and noise components. At this time, as shown in FIG. 2, the CINR estimator 117 separates interference and noise components from the extracted signal using an FIR filter having band pass or high pass characteristics do.

In the conventional OFDM system as described above, since the CINR is used to determine the modulation and coding scheme of data to be allocated to the UE by the BS, the range of the CINR to be estimated by the UE is very large. It is affected by channel conditions. For example, in the case of mWiMAX, the range of CINR estimation for adaptive modulation and coding ranges from -3dB to 28dB, and the higher the CINR, the more sensitive the CINR estimation performance depends on the channel condition. Therefore, the CINR estimator optimized to have high accuracy in a specific channel condition has a problem that the accuracy is relatively low in other channel conditions.

Meanwhile, in order to estimate the CINR for handover, the UE must estimate the CINR for the signal of the base station to which the handover is to be performed in a situation where the CINR of the base station signal to which the UE belongs is low. However, even in the synchronous OFDM system in which the synchronization between the base stations is ensured, there is a problem that it is difficult to secure synchronization with the base station signal to be handed over due to the propagation delay. As shown in FIG. 3, when a time error occurs due to insufficient synchronization, the high-pass FIR filter separates noise and interference signals. As shown in FIG. 4, A problem may arise in which the CINR is estimated lower than the situation.

That is, the CINR estimation for the AMC must have an accurate estimation performance even in the case of a high signal-to-noise interference ratio, and the CINR estimation for the handover must be robust against the time error. Accordingly, there is a need to provide a method of estimating the CINR suitable for the use of the CINR.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide an apparatus and method for improving a carrier-to-interference and noise ratio (CINR) in an Orthogonal Frequency Division Multiplexing (Hereinafter referred to as " a ").

It is another object of the present invention to provide a method and apparatus for estimating the CINR by selecting an estimation algorithm suitable for the use of CINR in an OFDM system.

It is still another object of the present invention to provide a method and apparatus for estimating CINR using a filter suitable for a channel condition in an OFDM system.

It is still another object of the present invention to provide a method and apparatus for estimating robust CINR for time errors in an OFDM system.

According to a first aspect of the present invention, there is provided an apparatus for estimating a Carrier to Interference and Noise Ratio (CINR) in an orthogonal frequency division multiplexing (OFDM) And a second CINR estimator for estimating a CINR for adaptive modulation and coding according to one of a channel time delay and a Doppler frequency of a channel, and a second CINR estimator for estimating CINR for adaptive modulation and coding .

According to a second aspect of the present invention, there is provided a method of estimating Carrier to Interference and Noise Ratio (CINR) in an orthogonal frequency division multiplexing (OFDM) system, Determining whether the use is for adaptive modulation and coding or handover, and estimating the CINR by selecting a CINR estimation algorithm according to the use of the CINR.

In the orthogonal frequency division multiplexing (OFDM) system, a CINR estimator is divided into a CINR estimator for adaptive modulation and coding and a CINR estimator for handover, and CINRs are estimated using different channel estimation methods. Accordingly, it is possible to estimate the CINR suitable for the channel condition or robust against the time error, thereby increasing the throughput of the system and ensuring seamless handover.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, 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.

Hereinafter, the present invention selects an estimation algorithm suitable for the use of a Carrier to Interference and Noise Ratio (CINR) in a system using an Orthogonal Frequency Division Multiplexing (OFDM) scheme, I will explain the estimation technique.

FIG. 5 is a block diagram illustrating a CINR estimation method in a terminal of an OFDM system according to the present invention.

5, the terminal includes an antenna 501, an RF unit 503, an analog / digital converter (ADC) 505, a reception filter 507, a Cyclic Prefix (CP) A first CINR estimator 517, a second CINR estimator 519, a CINR estimation method 516, a CINR estimation method 516, A selector 521, and a channel information estimator 523.

The RF unit 503 converts the signal received through the antenna 501 to a baseband signal, and the ADC 505 converts the baseband analog signal into a digital signal. The reception filter 507 converts And the digital signal is filtered and output. The CP (Cyclic Prefix) eliminator / deserializer 509 removes the CP from the filtered signal, converts the CP into a parallel analog signal, and outputs the parallel analog signal to the FFT unit 511. The FFT unit 511 Converts the time domain signal into a frequency domain signal, and outputs the signal.

The PN code generator 515 descrambles a scrambled preamble or a pilot signal to generate a unique PN code allocated to each user.

The signal synthesizer 513 synthesizes the user-specific PN code generated by the PN code generator 515 and the frequency-domain signal.

The first CINR estimator 517 estimates CINR for handover from the combined signal using differential correlation using delay. The first CINR estimator 517 will be described with reference to FIG.

The second CINR estimator 519 estimates a CINR for Adaptive Modulation and Coding (AMC) from the combined signal using a method selected by the CINR estimation method selector 521 do.

The channel information estimator 523 estimates channel information between the BS and the UE using the descrambled and synthesized signal. For example, the channel information estimator 523 may use a channel delay estimator for estimating a time delay of a channel and a Doppler frequency estimator for estimating a Doppler frequency of a channel related to a moving speed of the terminal .

The CINR estimation method selector 521 receives the channel estimation information from the channel information estimator 523 and selects a CINR estimation method suitable for the channel condition. 6, the CINR estimation method selector 603 receives a channel delay value estimated by the channel delay estimator 601 and adjusts or selects a coefficient of an FIR filter according to a channel delay situation, for example, And may be applied to the FIR filter of the second CINR estimator 605. Here, the CINR estimation method selector 521 adjusts or selects the filter coefficient so that the path range of the FIR filter is widened when the channel delay value is large, and when the channel delay value is small, The filter coefficient is adjusted or selected to narrow the filter coefficient.

7 is a block diagram illustrating a CINR estimator using a differential correlator in an OFDM system according to the present invention.

Referring to FIG. 7, the first CINR estimator for handover includes a differential correlator 701, a size estimator 703, a size accumulator 705, a squarer 707, a CINR calculator 709 ).

The differential correlator 701 calculates a differential correlation value with a predetermined delay d from the descrambled frequency domain signal.

The size estimator 703 calculates the magnitude of the differential correlation value output from the differential correlator 701 and outputs the magnitude of the differential correlation value to the magnitude accumulator 705. The magnitude accumulator 705 multiplies the magnitude of the differential correlation value Accumulate the size.

 The squared accumulator 707 calculates the squared value of the descrambled frequency domain signal, and then calculates the sum of the power of the received signal by accumulating the calculated squared value.

The CINR calculator 709 calculates the CINR using the magnitude of the accumulated differential correlation value and the power sum of the received signal. That is, the CINR is calculated by subtracting the accumulated differential correlation value from the accumulated square value representing the power sum of the received signal, and then calculating the ratio of the subtracted value to the accumulated correlation value.

The CINR estimation method using the differential correlation as described above will be described using mathematical expressions.

First, the signal x (n) of the time domain transmitted from the transmitter is expressed by Equation (1) and the frequency domain signal Y (k) received by the receiver is expressed by Equation (2).

Here, X (k) represents a frequency-domain signal transmitted from the transmitter, and y (n) represents a signal of a time domain received by the receiver. N represents the size of the FFT, and τ represents the time error generated when the FFT is performed at the receiving end.

The frequency domain signal Y (k) as shown in Equation (2) can be expressed by Equation (3) below.

Here, H (k) denotes a channel frequency response, I (k) denotes an interference signal component in the frequency domain, and W (k) denotes a noise component.

At this time, the signal Y _d (k) that is des-crimped to the transmitted signal in the frequency domain can be expressed as Equation (4).

Assuming that the absolute value of X (k) is 1 in Equation (4), the power of the signal component can be expressed by Equation (5) below as the magnitude of the differential correlation value.

Here, Wd (k) is the interference and the handoff component, and the expected value of the sum of Wd (k) converges to zero. Assuming that the channels between the subcarrier spacing d are the same, the magnitude component of the sum of the differential correlation values becomes the power value of the signal component as the sum of the channel sizes between the transmitting end and the receiving end. The delay value d of the differential correlation according to the present invention should be determined to be smaller than the coherence bandwidth of the channel.

Then, the sum of the powers of the received signals is calculated as shown in Equation (6) below, and CINR as shown in Equation (7) is estimated.

As described above, the CINR for handover calculates the magnitude of the differential correlation value using the accumulated value Ps and the power sum Pr of the received signal.

8 is a diagram illustrating a procedure for estimating a CINR according to an application in a terminal of an OFDM system according to an embodiment of the present invention.

Referring to FIG. 8, when a signal is received through an antenna in step 801, the terminal converts the received analog signal into a digital signal in step 803, filters the converted digital signal in step 805, .

Then, in step 807, the terminal performs an FFT to convert a time domain signal into a frequency domain signal. In step 809, the terminal generates a unique PN code allocated to each user and combines the signal with the frequency domain signal.

Then, the UE determines whether to use the CINR to be estimated in step 911, i.e., whether the CINR is for AMC or for handover.

If the CINR is for AMC, the UE proceeds to step 813 and estimates a channel delay using the combined signal. In step 815, the UE calculates a coefficient of an FIR filter for estimating a CINR according to the estimated channel delay result And then in step 817, the CINR is estimated using the FIR filter whose filter coefficient is adjusted. Here, the UE may adjust the filter coefficient so that the path area of the FIR filter is widened when the channel delay value is large, and the filter coefficient may be adjusted so that the path area of the FIR filter is narrowed when the channel delay value is small .

Thereafter, the terminal terminates the algorithm according to the present invention.

If the CINR is for handover, the UE computes a differential correlation value using the delay value from the combined signal as shown in Equation (5) in step 819, accumulates the correlation value, and then, in step 821 The square of the synthesized signal is calculated and accumulated as shown in Equation (6).

In step 823, the terminal estimates the CINR using the accumulated two values as shown in Equation (7), and then ends the algorithm according to the present invention.

FIG. 9 is a graph illustrating a CINR estimation performance according to a conventional technique and a CINR estimation performance using a difference correlator according to an embodiment of the present invention. Here, the horizontal axis of the graph represents a time error, and the vertical axis represents an estimated CINR.

FIG. 9 shows a comparison between the result of CINR estimation using a high pass filter (HPF) and the performance of a CINR estimation result using a difference correlator when a time error exists. Herein, HPF1 and HPF2 are CINR estimation methods using an FIR filter having a conventional high pass characteristic. The HPF1 has a normalize frequency of 0.2 at a pass frequency, and HPF2 uses an FIR filter having a pass frequency of 0.75 at a normalize frequency.

Referring to FIG. 9, the CINR estimation method using the difference correlator according to the present invention has a superior CINR estimation performance even when the time error is larger than that of the conventional HP1 and HP2 methods.

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. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

Brief Description of the Drawings Fig. 1 is a diagram showing a block configuration for estimating a CINR in a terminal of a general OFDM system;

2 is a block diagram of a CINR estimator using an FIR filter in a terminal of a general OFDM system,

3 is a diagram showing a concept of estimating a signal-to-noise ratio using an FIR filter,

4 is a diagram showing a concept of estimating a signal-to-noise ratio using an FIR filter in the presence of a time error;

5 is a block diagram illustrating a CINR estimation method in a terminal of an OFDM system according to the present invention.

6 is a block diagram of a CINR estimator for adjusting FIR filter coefficients in a terminal of an OFDM system according to the present invention;

FIG. 7 is a block diagram illustrating a CINR estimator using a differential correlator in an OFDM system according to the present invention. FIG.

FIG. 8 is a diagram illustrating a procedure for estimating a CINR according to an application in a terminal of an OFDM system according to an embodiment of the present invention; and

9 is a graph showing a CINR estimation performance according to a conventional technique and a CINR estimation performance using a difference correlator according to an embodiment of the present invention.

Claims (13)

In an apparatus for estimating Carrier to Interference and Noise Ratio (CINR) in an orthogonal frequency division multiplexing (OFDM) system, A first CINR estimator for estimating a CINR for handover using differential correlation; A second CINR estimator for estimating a CINR for adaptive modulation and coding according to one of a time delay of the channel and a Doppler frequency of the channel. The method according to claim 1, Wherein the first CINR estimator comprises: A differential correlator for calculating a differential correlation value from the descrambled signal with a predetermined delay, A magnitude estimating and accumulating unit for accumulating and accumulating the magnitude of the calculated differential correlation value, A squared accumulator for calculating and accumulating the squared value of the descrambled signal, And a CINR calculator for calculating a CINR using the magnitude of the accumulated correlation correlation value and the accumulated squared value. 3. The method of claim 2, Wherein the CINR calculator calculates the CINR using a ratio of a value obtained by subtracting the accumulated difference correlation value from the cumulative sum value to the cumulative difference correlation value. The method according to claim 1, A channel estimator for estimating a time delay of a channel connecting a base station and a terminal from the descrambled signal or estimating a Doppler frequency of a channel related to a moving speed of the terminal, And an estimation method selector for selecting a CINR estimation algorithm used in the second CINR estimator according to the estimated channel information. delete 5. The method of claim 4, The estimation method selector comprises: And adjusts the FIR filter coefficient of the second CINR estimator according to the channel delay value estimated by the channel estimator. A method for estimating Carrier to Interference and Noise Ratio (CINR) in an orthogonal frequency division multiple access (OFDM) system, Determining whether the intended use of the CINR to be estimated is for adaptive modulation and coding or handover; And estimating a CINR by selecting a CINR estimation algorithm according to a use purpose of the CINR. 8. The method of claim 7, The step of estimating the CINR includes: And estimating the CINR using differential correlation when the use of the CINR is for handover. 9. The method of claim 8, The process of estimating the CINR using the differential correlation may include: Calculating a differential correlation value from a descrambled signal with a predetermined delay; Calculating and accumulating the magnitude of the calculated differential correlation value; Calculating and accumulating the squared value of the descrambled signal; And calculating a CINR using the magnitude of the accumulated correlation correlation value and the accumulated squared value. 10. The method of claim 9, Wherein the calculation of the CINR is performed using a ratio of a value obtained by subtracting the accumulated difference correlation value from the accumulated sum value to the cumulative difference correlation value. 8. The method of claim 7, The step of estimating the CINR includes: Estimating a time delay of a channel connecting a base station and a terminal from a descrambled signal or estimating a Doppler frequency of a channel related to a moving speed of the terminal when the use of the CINR is for adaptive modulation and coding; And estimating the CINR by changing a CINR estimation algorithm according to the estimated channel information. delete 12. The method of claim 11, Wherein the step of estimating the CINR by changing the CINR estimation algorithm comprises: Adjusting an FIR filter coefficient according to a channel delay value estimated by the channel estimator, And estimating the CINR of the FIR filter with the filter coefficient adjusted.

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