KR200427973Y1 - Frequency offset estimation apparatus in wireless telecommunication system - Google Patents

Abstract

The present invention relates to an apparatus for estimating a frequency offset of a wireless communication system.

According to the present invention, a cyclic prefix (CP) present in each symbol is not used to estimate an initial frequency offset by using a preamble signal, which is the first symbol of a frame, when estimating a frequency offset of a wireless communication system. By estimating the frequency offset using the correlation of), it is possible to easily estimate the frequency offset using only the input signal without having to regenerate the information on the separate preamble signal and the preamble signal.

Description

Frequency offset estimation apparatus and wireless estimator in wireless communication system

1 is a schematic diagram of an apparatus for estimating frequency offset in a wireless communication system.

2 is a diagram illustrating a frame structure used in a wireless communication system.

FIG. 3 is a diagram illustrating a structure of a symbol constituting the frame shown in FIG. 2.

4 is a detailed configuration diagram of a frequency offset estimating apparatus of a wireless communication system according to a first embodiment of the present invention.

5 is a detailed configuration diagram of a frequency offset estimation apparatus of a wireless communication system according to a second embodiment of the present invention.

6 is a flowchart illustrating a process of obtaining an average value of correlation values of symbols in a frequency offset estimation apparatus of a wireless communication system according to the present invention.

Explanation of symbols on the main parts of the drawings

110: antenna 120: RF / IF module

130: analog-to-digital converter 140: baseband filter

150: decimator 160: frequency offset estimator

170: baseband demodulator 400, 500: frequency offset estimator

420 and 520: correlation measurer 440 and 540: frequency offset calculator

450, 550: scaling unit 510: cyclic prefix buffer

530: average value calculation unit

The present invention relates to an apparatus for estimating a frequency offset of a wireless communication system, and more particularly, to a cyclic prefix existing in every symbol of a frame used in a portable internet system. The present invention relates to an apparatus for estimating a frequency offset occurring during initial synchronization in a terminal using a CP. Therefore, the frequency offset estimation apparatus according to the present invention may be implemented in the form of a receiver or a transceiver of a portable Internet system.

Since the cellular cellular mobile telecommunication system was developed in the United States in the late 1970s, AMPS (Advanced Mobile Phone Service), which can be called the analog 1st generation (1G) mobile communication system in Korea, Began to provide voice communication services. After that, the 2G (2G) mobile communication system began to be commercialized in the mid-1990s, and IMT, a 3G (3G) mobile communication system, started in the late 1990s with the aim of wireless multimedia and high-speed data services. -2000 (International Mobile Telecommunication-2000) has been commercialized and operated in part.

On the other hand, with the development of 3G mobile communication system to 4G (4th Generation) mobile communication system, the mobile Internet technology that can provide faster data transmission service than 3G mobile communication system Research is actively underway.

The mobile internet is not only able to satisfy the user's desire to provide high-speed internet service anytime and anywhere with a portable device, but it is also expected to be a new promising industry in the future because it has little impact on the overall information and communication industry in Korea. Accordingly, international standardization of the mobile Internet is currently progressing mainly on IEEE 802.16e.

The above-described portable Internet system is implemented to use a portable Internet service even during a high-speed movement by using an orthogonal frequency division multiple access (OFDMA) scheme and a time division duplex (TDD) scheme.

The OFDMA method used in the portable Internet system uses a plurality of subcarriers within a channel bandwidth to transmit data, and the subcarriers are arranged to optimize the bandwidth to avoid intercarrier interference and mitigate losses due to frequency-selective paging. Frequency diversity advantage. Accordingly, in the portable Internet system, symbol / frequency and offset estimation, symbol / frequency compensation, and symbol / frequency synchronization of OFDMA signals transmitted and received are more important problems.

The present invention is intended to more accurately estimate and compensate for an initial frequency offset that may occur during reception of a wireless communication system.

Specifically, it is an object of the present invention to provide an apparatus capable of accurately estimating a frequency offset using a cyclic prefix (CP) present in every symbol.

Another object of the present invention is to offset the frequency offset by buffering the portion corresponding to the cyclic prefix of the symbol and correlating it with the portion corresponding to the last N _CP samples of the symbol transmitted in the same way as the cyclic prefix. It is to provide a device that can easily estimate the.

Another object of the present invention is to provide an apparatus capable of estimating a frequency offset more accurately by calculating the sum of each correlation for a plurality of symbols and using the average value.

To this end, the frequency offset estimation apparatus of the wireless communication system according to the present invention, Analog to digital converter for converting the analog signal received from the antenna to a digital signal; A decimator for re-sampling the over-sampled digital signal output from the analog / digital converter; And a frequency offset estimator for measuring correlation values of N _CP samples before and after each symbol in units of symbols with respect to the samples output from the data, and estimating a frequency offset value based on the measured correlation values. It is characterized by.

The frequency offset estimator of the wireless communication system according to the present invention includes: a correlation measurer for measuring correlation values of N _CP samples before and after samples in units of symbols; And a frequency offset calculator for estimating a frequency offset value based on the measured correlation value.

Preferably, the frequency offset estimator further includes an average calculator for summing correlation values measured in units of symbols by the correlation measurer for a plurality of symbols and calculating an average value of the summed correlation values.

The frequency offset estimator may further include a cyclic prefix buffer for buffering the cyclic prefix of each symbol on a symbol basis with respect to samples. Accordingly, the correlation measurer may determine a correlation value between the cyclic prefix stored in the cyclic prefix buffer and the last N _CP samples of the symbol transmitted in the same manner as the cyclic prefix when the cyclic prefix of each symbol is input. It can be measured easily.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments. For reference, in the following description, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention are omitted.

Referring to FIG. 2, a structure of a frame used in a portable Internet system of time division duplexing (TDD) is as follows.

The time division duplexing scheme divides one frame inside for transmission and reception in time in a time division transmission scheme. As shown in FIG. 2, one frame is uplinked with a downlink frame 210. It is divided into an uplink frame 220 to perform bidirectional communication at the same frequency. In FIG. 2, one frame is composed of N _frm samples, where the downlink frame 210 is composed of N _DL samples, and the uplink frame 220 is composed of N _UL samples. Meanwhile, the downlink frame and the uplink frame are each divided into a unit called a symbol, and the symbol is similarly formed of a plurality of samples.

The downlink frame 210 starts with a preamble symbol and then a data symbol, and the preamble symbol may be used for initial synchronization, cell search, frequency offset, and channel estimation. In addition, a TTG (Transmit / receive Transition Gap) section 230 exists between the downlink frame 210 and the uplink frame 220. During this TTG period, the base station is in a transmission mode and a reception mode, and the terminals are in a reception mode. The transmission mode is switched. At the end of the frame, there is a Receive / Transmit Transition Gap (RTG) section 240 that distinguishes the current uplink frame 220 and the downlink frame 210 that is subsequently transmitted. In the mode to the transmission mode, the terminals are switched from the transmission mode to the reception mode.

Hereinafter, a structure of a symbol constituting the frame will be described with reference to FIG. 3.

One symbol has a valid symbol interval consisting of N _FFT samples for T _b time, and a cyclic prefix for copying and pasting N _CP samples for the last T _g time of the valid symbol interval and preceding the valid symbol interval. exist. The cyclic prefix is used to collect multipath signals and maintain orthogonality between subcarriers. Therefore, one symbol is N _FFT + N _CP is composed of the sample, the N _CP samples earlier in each symbol and N _CP samples of the back are transmitted with the same signal.

Therefore, a method of estimating a frequency offset using a preamble in a downlink frame, which is one of the characteristics of the frame structure used in the above-described portable Internet system, may be used. In this case, the preamble index used in a specific cell is used. A problem arises in that a preamble index must be known and a preamble signal for the preamble index must be regenerated. In particular, in a multi-cell in which several cells coexist, a serious problem of inaccurate frequency offset estimation occurs in estimating an initial frequency offset using a preamble signal.

In order to solve the above problems, the present invention utilizes the feature that the front and rear N _CP samples are the same signal in each symbol of the frame structure used in the portable Internet system, and between the front and rear N _CP samples. The main technical feature is to obtain the channel characteristics between the transceivers by obtaining the correlation and to estimate the frequency offset.

4 is a detailed configuration diagram of a frequency offset estimating apparatus of a wireless communication system according to a first embodiment of the present invention.

Since the signal received from the antenna is input to the frequency offset estimator through the RF / IF module, analog / digital converter, baseband filter, and decimator is similar to the reception process of the above-described wireless communication system, a repetitive description is omitted. Hereinafter, a frequency offset estimator according to the present invention will be described in detail.

The frequency offset estimator 400 according to the first embodiment of the present invention is largely composed of a correlation measurer 420, a frequency offset calculator 440, and a scaler 450.

The correlation measurer 420 detects N _CP samples before and after each symbol in units of symbols for samples input in real time from the decimator 150 and measures correlation values therebetween. For example, assuming that r (n) is an input signal, N _CP is the size of the cyclic prefix, and N _FFT is the FFT size, the value R output from the correlation measurer 420 is expressed by Equation 1 below.

In the above Equation 1, the period in which the accumulation is actually performed is during the cyclic prefix period of the symbol.

The result R of Equation 1 becomes a complex signal, and the frequency offset calculator 440 performs an operation to obtain a phase of the result value, that is, a phase difference between N _CP samples before and after. do. In this case, an arctangent operation is generally performed.

The frequency offset value of the current symbol, which is a result of the frequency offset calculator 440, is input to the scaling unit 450 and scaled to a desired dimension. The output of the scaling unit 450 is input to the RF / IF module 120 again and used to compensate for the initial frequency offset of the terminal.

5 is a detailed configuration diagram of a frequency offset estimation apparatus of a wireless communication system according to a second embodiment of the present invention.

The frequency offset estimator 500 according to the second embodiment of the present invention has a large cyclic prefix buffer 510, a correlation measurer 520, an average value calculator 530, a frequency offset calculator 540, and a scaler. 550.

First, the cyclic prefix buffer 510 buffers the first N _CP samples corresponding to the cyclic prefix on a symbol basis with respect to samples input in real time from the decimator 150. In addition, the correlation measurer 520 determines that the first N _CP samples of the symbols stored in the cyclic prefix buffer 510 in the sample portion where the output signal of the decimator 150 corresponds to the last N _CP samples of the symbol. Measure the correlation between them. The average value calculator 530 calculates an average value by summing the measured correlation result values for a predetermined section. The sum of correlation results obtained through this process represents a complex value, and the phase becomes the phase difference between the N _CP samples at the front of the symbol and the N _CP samples at the rear of the symbol. This value is the frequency error of the current symbol. A process of obtaining an average value of correlation values of a plurality of samples will be described in detail below.

The frequency offset calculator 540 performs an arctangent operation to obtain a phase of an average value. When the phase value obtained by performing the arc tangent operation shows a result between [−π, π], the actual frequency offset value may be obtained through Equation 2 below.

f _offset = d _iff × 10 ⁷ / (2π × 1024) [Hz]

In Equation 2, f _offset represents a frequency offset value, and φ _diff represents a phase difference.

Finally, the frequency offset value of the current symbol, which is a result of the frequency offset calculator 540, is input to the scaling unit 550 and scaled to a desired dimension, and the output of the scaling unit 550 is again RF / IF. The module 120 is used to compensate for the initial frequency offset of the terminal.

6 is a flowchart illustrating a process of obtaining an average value of correlation values of symbols in a frequency offset estimation apparatus of a wireless communication system according to the present invention. For reference, processes before the specific steps illustrated in FIG. 6 may be referred to the related art described with reference to FIG. 1.

First, in step S610, the variable iSymbol is set to '0'. The variable iSymbol is used for the purpose of counting the number of symbols. In operation S620, the _{cyclic prefix} buffer 510 buffers the first N _CP samples in symbol units for the samples input from the decimator 150. By buffering the first N _CP samples of a symbol, samples corresponding to the cyclic prefix are temporarily stored in the cyclic prefix buffer 510. In operation S630, the correlation estimator 520 measures a correlation between the buffered N _CP samples and the last N _CP samples of a symbol. As a result, a correlation value between N _CP samples before and after is measured. In step S640, the average value calculator 530 first accumulates the correlation result. In step S650, the value of the variable iSymbol is compared with the desired cumulative number of symbols N _SYM, and if the value of iSymbol is smaller than the value of N _SYM , the process proceeds to step S660 to increase the value of iSymbol by one. Thereafter, steps S620 to S660 are repeated, and if the iSymbol value is greater than or equal to the N _SYM value, the process proceeds to step S670. The average value calculator 530 calculates an average value for the N _SYM result values in step S670. In operation S680, the frequency offset calculator 540 calculates a phase difference between N _CP samples before and after the arc tangent operation. Finally, in step S690, the scaling unit 550 scales the phase difference calculated in step S680 to a desired size, thereby performing frequency offset estimation.

Of course, after the frequency offset estimation is performed, it can be used to compensate for the initial frequency offset value of the terminal.

Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art to which the present invention pertains can be implemented in other specific forms without changing the technical spirit or essential features, The examples are to be understood in all respects as illustrative and not restrictive.

And, the scope of the present invention is specified by the utility model registration claims to be described later than the above detailed description, and all changes or modifications derived from the meaning and scope of the utility model registration claims and the equivalent concept of the present invention It should be construed as being included in the scope.

According to the present invention, when estimating the initial frequency offset of a terminal in a wireless communication system, there is an effect of estimating the frequency offset using only an input signal, that is, a symbol, without having to reconstruct information on a preamble signal and regeneration of a preamble signal. Have

In addition, according to the present invention, unlike the preamble existing only in the first symbol of the frame, the cyclic prefix existing in each symbol is used. Therefore, the sum of correlations performed on a plurality of symbols and the average value are used to obtain a more accurate frequency. This has the effect of obtaining an offset.

In addition, according to the present invention, by buffering a portion corresponding to the cyclic prefix of the symbol (symbol) has an effect that can easily calculate the correlation of the symbol.

Claims (12)

An apparatus for estimating frequency offset in a wireless communication system, An analog / digital converter for converting an analog signal received from an antenna into a digital signal; A decimator for re-sampling the over-sampled digital signal output from the analog / digital converter; And And a frequency offset estimator for measuring correlation values between N _CP samples before and after each of the samples output from the decimator in symbol units, and estimating a frequency offset value based on the measured correlation values. Frequency offset estimation apparatus for a wireless communication system. The method of claim 1, Further comprising an RF / IF module performing at least one of demodulation, amplification, and filtering in the RF / IF band, The frequency offset estimator transmits the estimated frequency offset value to the RF / IF module, and the RF / IF module corrects the frequency offset of the terminal based on the frequency offset value. Offset estimation device. The method of claim 2, And the frequency offset estimator performs scaling on the estimated frequency offset value and transmits the frequency offset estimator to the RF / IF module. The method according to any one of claims 1 to 3, The frequency offset estimator adds a correlation value measured in units of symbols with respect to a plurality of symbols, and estimates a frequency offset value based on the average value of the summed correlation values. Device. The method according to any one of claims 1 to 3, The frequency offset estimator buffers the cyclic prefix of each symbol on a symbol-by-symbol basis for the samples, and between the buffered cyclic prefix and the last N _CP samples upon inputting the last N _CP samples of each symbol. Frequency offset estimation apparatus of a wireless communication system, characterized in that for measuring the correlation value. The method according to any one of claims 1 to 3, The apparatus for estimating frequency offset is an apparatus for estimating a frequency offset in a wireless communication system, characterized in that the receiver or transceiver of a portable internet system. A frequency offset estimator in a wireless communication system, A correlation measuring unit for measuring correlation values between N _CP samples before and after samples in units of symbols; And And a frequency offset calculator for estimating a frequency offset value based on the measured correlation value. The method of claim 7, wherein The apparatus may further include an average calculator configured to add correlation values measured in symbol units by the correlation measuring unit to a plurality of symbols and calculate an average value of the summed correlation values. And the frequency offset calculator estimates a frequency offset value based on the average value. The method according to claim 7 or 8, A cyclic prefix buffer for buffering the cyclic prefix of each symbol on a symbol basis for the samples; The correlation measuring unit measures a correlation value between the cyclic prefix stored in the cyclic prefix buffer and the last N _CP samples when inputting the last N _CP samples of each symbol. Frequency offset estimator. The method according to claim 7 or 8, The frequency offset calculator estimates a frequency offset by performing an arctangent operation on the correlation value. The method according to claim 7 or 8, And a scaling unit configured to perform scaling by adjusting a dimension of the frequency offset value output from the frequency offset calculating unit. A frequency offset estimator in a wireless communication system, A cyclic prefix buffer for temporarily storing the first N _CP samples of each symbol in symbol units and transmitting the temporary N _CP samples to a correlation measurer; A correlation measuring unit measuring a correlation value with the first N _CP samples of the symbol stored in the cyclic prefix when the last N _CP samples of the symbol are input; And An average value calculator for accumulating and adding the correlation values transmitted from the correlation measurer to a predetermined number of symbols, and calculating an average value thereof; And And a frequency offset calculator configured to calculate a frequency offset value by performing an arc tangent operation on the average value calculated by the average value calculator.

Images