KR100976856B1 - Apparatus and method for estimating fine timing offset of downlink based on ofdm systems - Google Patents

Apparatus and method for estimating fine timing offset of downlink based on ofdm systems Download PDF

Info

Publication number
KR100976856B1
KR100976856B1 KR1020100040993A KR20100040993A KR100976856B1 KR 100976856 B1 KR100976856 B1 KR 100976856B1 KR 1020100040993 A KR1020100040993 A KR 1020100040993A KR 20100040993 A KR20100040993 A KR 20100040993A KR 100976856 B1 KR100976856 B1 KR 100976856B1
Authority
KR
South Korea
Prior art keywords
value
fine
ratio
peak
maximum value
Prior art date
Application number
KR1020100040993A
Other languages
Korean (ko)
Inventor
한철희
Original Assignee
삼성탈레스 주식회사
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 삼성탈레스 주식회사 filed Critical 삼성탈레스 주식회사
Priority to KR1020100040993A priority Critical patent/KR100976856B1/en
Application granted granted Critical
Publication of KR100976856B1 publication Critical patent/KR100976856B1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only
    • H04L27/2655—Synchronisation arrangements
    • H04L27/2662—Symbol synchronisation
    • H04L27/2665—Fine synchronisation, e.g. by positioning the FFT window

Landscapes

  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Synchronisation In Digital Transmission Systems (AREA)

Abstract

The present invention relates to an apparatus and method for downlink fine time synchronization in an OFDM system, and more particularly, to an apparatus and method for downlink fine time synchronization in an OFDM system capable of tracking fine synchronization with stable and small error. To this end, the present invention provides a method for estimating downlink fine time synchronization of a mobile station in an orthogonal frequency division multiplexing system, the method comprising: obtaining an absolute value of a correlation value within a window period of a signal received from a base station by a predetermined search period, and the obtained absolute value Calculating a maximum value and a time index of the maximum value, calculating a peak-to-average ratio (PAR), and determining whether the calculated ratio value obtains fine synchronization. When the value is greater than the first reference value to be determined, comparing the ratio value with a second reference value indicating a criterion of reception quality, and setting a preceding peak threshold value differently according to the ratio of the ratio value and the second reference value; The correlation between the preceding peak threshold value and the correlation value within a preceding peak search window defined such that the calculated ratio value is temporally ahead of the maximum value point. And determining a fine synchronization point as a point that is greater than or equal to the product of the absolute values.

Description

Apparatus and method for downlink fine-time synchronization estimation of OPDM system {APPARATUS AND METHOD FOR ESTIMATING FINE TIMING OFFSET OF DOWNLINK BASED ON OFDM SYSTEMS}

The present invention relates to an apparatus and method for downlink fine time synchronization in an OFDM system, and more particularly, to an apparatus and method for downlink fine time synchronization in an OFDM system capable of tracking fine synchronization with stable and small error.

In general, next-generation communication systems have evolved to provide a service for transmitting and receiving large-capacity data at high speed to mobile stations (MSs). A representative example of the next generation communication system is the Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system. The IEEE 802.16e communication system is called Orthogonal Frequency Division Multiplexing (OFDM) and Orthogonal Frequency Division Multiple Access (OFDMA). Representative communication system using the method.

Such a frequency division multiplexing system allocates different frequencies to a plurality of mobile terminals that want to access each other, and a plurality of mobile terminals frequently request a base station, whereby a plurality of mobile terminals are allocated channels from the base station and communicate with each other. Multiple access schemes include frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), and the like. In this multiple access scheme, each base station transmits a signal at a frequency assigned to the base station itself, and the mobile terminal identifies the base station at the frequency of the received signal and detects the base station incoming signal from the address number in the signal to communicate.

And, the mobile terminal using the OFDMA method mainly uses the cross-correlation method to estimate the downlink fine time synchronization. The method of using cross-correlation estimates time synchronization by taking a cross-correlation in a time domain from a signal preamble signal known from a cell search result and a signal received from a base station from a time synchronization or a synchronization position of a previous frame. do. However, in the Rayleigh fading channel, the cross-correlation size of a subsequent peak may be larger than that of the first peak. If the point having the maximum value is determined as a time synchronization, the orthogonality is broken by synchronizing to the next peak point.

If the microcorrelation is taken from the position where the cross-correlation is maximum, before a particular sample, to maintain the orthogonality even in the case where the subsequent peak is larger in the Rayleigh fading channel, the synchronization is advanced by a value larger than the maximum delay spread of the channel. You have to catch it. In this case, the compensation is possible in the channel equalizer in general, but the average synchronization error may be increased, thereby degrading the performance of blocks sensitive to time synchronization error.

In the case of finding the position of the earliest point beyond the threshold within a specific window area from the position having the maximum value, when the signal-to-noise ratio decreases, the peak of the cross-correlation value is clearly detected, but the values other than the peak increase due to the degradation of the correlation characteristic due to noise. In the non-peak position, the threshold will occur. This can result in worse results than synchronous with the maximum value.

Therefore, a newer method is needed to track fine synchronization with stable and small error regardless of signal to noise ratio.

SUMMARY OF THE INVENTION The present invention has been conceived to solve the above-mentioned conventional problems, and an apparatus for estimating downlink fine time synchronization of an OFDM system capable of tracking fine synchronization with stable and small errors regardless of a signal-to-noise ratio of a received signal even in a Rayleigh fading channel; Provide a method. The present invention also provides an apparatus and method for downlink fine time synchronization of an OFDM system capable of maintaining orthogonality with low synchronization error by synchronizing to a leading peak point of a cross-correlation value when the signal-to-noise ratio is good.

The present invention for achieving the above-described cross-correlation in the downlink fine time synchronization estimation apparatus of the mobile terminal in the orthogonal frequency division multiplexing system to obtain the absolute value of the correlation value within a window interval of the signal received from the base station by a predetermined search interval A maximum value detection unit for obtaining a maximum value of the obtained absolute value and a time index of the maximum value, an operation unit for calculating a peak-to-average ratio (PAR) of the maximum value and the average value, and the calculated ratio If the value is larger than a first reference value for determining whether to obtain fine synchronous, and compared with the second reference value representing the ratio value and the reference of the reception quality, the peak according to the magnitude of the ratio value and the second reference value A threshold adjustment unit for setting a threshold differently, and a preceding peak search window in which the calculated ratio value is temporally ahead of the maximum value point; And a preceding peak search unit for determining a point at which the preceding peak threshold value is greater than or equal to the product of the absolute value of the correlation value as a fine synchronization point.

In addition, the present invention for achieving the above-described method in the downlink fine time synchronization estimation method of the mobile terminal in the orthogonal frequency division multiplexing system, the absolute value of the correlation value within the window period of the signal received from the base station to obtain a predetermined search interval And calculating a maximum value of the obtained absolute value and a time index of the maximum value, calculating a peak-to-average ratio (PAR) of the maximum value and the average value, and calculating the If it is greater than a first reference value for determining whether to obtain the fine synchronization, and compared with the second reference value indicating the ratio of the ratio and the reception quality criteria, and the preceding peak threshold value according to the magnitude of the ratio value and the second reference value Setting differently, and the preceding peak in the preceding peak search window defined such that the calculated ratio value is temporally ahead of the maximum value point. Threshold and includes a process of determining the point at which greater than or equal to the product of the absolute value of the correlation value to the fine synchronization point.

As described above, the present invention provides a downlink fine time synchronization estimation apparatus and method of an OFDM system, so that fine synchronization can be maintained by stable and small error tracking for a case having a wide range of signal-to-noise ratio. have. In addition, the present invention has the effect of increasing the stability by minimizing the frame in which a gap occurs in the downlink communication by reducing the phenomenon of starting again from the initial synchronization to miss the fine synchronization.

1 is a block diagram illustrating an apparatus for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an exemplary embodiment of the present invention.
2 is a flowchart illustrating a method for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an exemplary embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the preferred embodiment of the present invention. 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 a user, a user's intention or custom. Therefore, the definition should be made based on the contents throughout the specification.

The present invention provides an apparatus and method for estimating downlink fine time synchronization of an orthogonal frequency division multiplexing system capable of tracking stable and low error roll fine synchronization when having a wide range of signal-to-noise ratios. Therefore, an embodiment of the present invention to be described later will be described in detail with reference to the drawings and apparatus for estimating the downlink fine time synchronization.

1 is a block diagram illustrating an apparatus for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an embodiment of the present invention.

As illustrated, the apparatus for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an embodiment of the present invention includes a cross-correlator 101 that stores an absolute value of a cross-correlation value by a predetermined search interval, and the mutual correlation. The maximum value detection unit 102 for obtaining the maximum value of the absolute value of the correlation value stored in the correlation unit 101 and the time index of the maximum value, the average value of the absolute value of the correlation value stored in the cross correlation unit 101 and the Compares the calculation unit 103 for calculating the ratio of the maximum value obtained by the maximum value detection unit 102 with a reference value for determining whether the ratio of the maximum value to the average value calculated in the operation unit 103 and the fine synchronization have been obtained or not; The threshold value adjusting unit 104 and the maximum value detecting unit 102 detect the threshold value of the preceding peak search unit by comparing whether the signal-to-noise ratio (SNR) is good or not according to the result. Search for the earliest point at which the ratio of the maximum value to the average value becomes a leading peak threshold value (Th_pre_peak) x the maximum value of the absolute value of the correlation value (XCR_max) within a predetermined window interval before the maximum value point. A leading peak search unit 105 for determining the sync point is included.

Hereinafter, an apparatus for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an embodiment of the present invention will be described in detail with reference to FIG. 1.

The cross correlation unit 101 cross-correlates in a time domain a signal of a specific region located before and after a time synchronization or a synchronization position of a previous frame among preambles of a signal transmitted from a base station and a noisy signal received from the base station, The absolute value of the correlation value is stored for a predetermined search period and transferred to the maximum value detector 102. The time domain signal of the preamble can be known through a search result of a cell served by the base station, and the base station transmits this signal to the mobile terminal. Then, the mobile terminal estimates the downlink time synchronization through this signal received from the base station. As such, in order to estimate downlink time synchronization, the maximum value detector 102 of the mobile terminal obtains the maximum value XCR_max of the absolute values of the correlation values stored in the cross-correlator 101, and calculates the maximum value. Get the time index of a value. In addition, the maximum value detector 102 stores the obtained maximum value and time index and transmits the calculated maximum value to the operation unit 103. The calculation unit 103 calculates the ratio of the average value of the absolute values of the correlation values obtained by the cross correlation unit 101 and the maximum value obtained by the maximum value detection unit 102, and transfers the calculated values to the threshold adjustment unit 104. do.

The threshold controller 104 acquires a peak-to-average ratio (PAR) and fine synchronization of the average value of the absolute values of the correlation values calculated by the calculator 103 and the maximum value obtained by the maximum detector 102. The size of the first reference value Th_fine for determining whether or not to compare is compared. The first reference value Th_fine selects an appropriate value capable of achieving synchronization even in a very bad signal-to-noise ratio and reducing false alarm rates. If the ratio PAR is not greater than the first reference value, it is determined that fine synchronization acquisition has failed. If the ratio PAR is greater than the first reference value, the ratio PAR and the signal-to-noise ratio Signal-to Compared to the second reference value Th1 indicating whether the noise ratio (SNR) is good or bad. That is, the ratio PAR is greater than the second reference value Th1 means that the peak value of the absolute value of the cross-correlation value is much larger than the surrounding values, so that the noise components of the surrounding values are less, so that the threshold value is smaller than the previous peak search. Searching by value means that you can have high reliability. In addition, since the ratio PAR has a property that is proportional to the signal-to-noise ratio of the received signal, the greater the ratio PAR than the second reference value Th1 indicates that the signal-to-noise ratio of the received signal is good.

If the ratio PAR is greater than the reference value Th1, the leading peak threshold Th_pre_peak is set to Th_L, and if the ratio PAR is larger than Th_L, it is set to Th_H.

The ratio PAR is greater than the second reference value Th1 means that the signal-to-noise ratio of the received signal is good and the marginal value of the cross-correlation value due to the noise component is very small. This means that reliability is guaranteed even if Therefore, Th_L is set to a small value in consideration of this.

On the contrary, the fact that the ratio PAR is not larger than the second reference value Th1 means that the signal-to-noise ratio of the received signal is poor and the peripheral value of the cross-correlation value is increased due to the noise component. Applying a time threshold implies low reliability. Therefore, Th_H is set to a value larger than Th_L in consideration of this.

The first and second reference values and Th_H and Th_L are preset or changeable according to system conditions.

In addition, the preceding peak search unit 105 has a ratio PAR of the absolute value of the preceding peak threshold value Th_pre_peak × correlation value within a window section previously determined before the maximum value point detected by the maximum value detector 102. The earliest point that is the maximum value XCR_max is searched, and the point is determined as a fine synchronization point.

2 is a flowchart illustrating a method for estimating downlink fine time synchronization in an orthogonal frequency division multiplexing system according to an embodiment of the present invention.

As shown, in the orthogonal frequency division multiplexing system according to the present invention, the method for estimating downlink fine time synchronization is based on a time-domain signal of a preamble transmitted from a base station and a signal received from the base station. Cross-correlation of a signal of a specific area is taken, and an absolute value of the correlation value is calculated and stored for a predetermined search period (S201). The time index having the maximum value of the absolute value and the maximum value is calculated, and the ratio PAR of the average value to the maximum value of the absolute value is calculated (S203). When the ratio PAR is calculated, the calculated ratio PAR is compared with the magnitude of the fine synchronization reference value (S205). The fine synchronization reference value is a reference value Th_fine that determines whether fine synchronization is obtained. As a result of the comparison, if the ratio PAR is not greater than the reference value Th_fine, it is determined that fine synchronization acquisition has failed and ends (S205-S207). If the ratio PAR is greater than the reference value Th_fine in the step S205, the ratio PAR is compared with the SNR reference value (S209). The SNR reference value is a reference value that can determine whether the SNR is good or bad. If the ratio PAR is not greater than the SNR reference value in step S209, the preceding peak threshold value is set to Th_H (S211). If the ratio PAR is greater than the SNR reference value in step S209, the leading peak threshold is set to Th_L (S213). If the ratio PAR is set to Th_H or Th_L, the ratio PAR calculated in the step S203 is the maximum value of the absolute value of the preceding peak threshold value and the correlation value set in the step S211 or S213. The point equal to the multiplied value is searched for, and the point is determined as a fine synchronization point (S215).

Claims (8)

An apparatus for estimating downlink fine time synchronization of a mobile terminal in an orthogonal frequency division multiplexing system,
A cross-correlator for obtaining an absolute value of a correlation value within a window section of a signal received from the base station by a predetermined search section;
A maximum value detector for obtaining a maximum value of the obtained absolute value and a time index of the maximum value;
An operation unit for calculating a peak-to-average ratio (PAR) of the maximum value of the absolute value and the average value of the absolute value;
If the calculated ratio value is greater than a first reference value for determining whether to obtain fine synchronization, the ratio is compared with a second reference value indicating a criterion of the reception quality and the magnitude of the ratio value and the second reference value. A threshold adjuster for differently setting the leading peak threshold according to;
Predetermining a fine sync point, a point at which the calculated ratio value is greater than or equal to a value obtained by multiplying the absolute value of the preceding peak threshold value and the correlation value in the preceding peak search window determined to be temporally ahead of the maximum value point. Fine time synchronization estimation device including a peak search unit.
The method of claim 1, wherein the maximum value detector
And calculating the maximum value of the absolute value of the correlation value within the window period of the received signal, and detecting a time index of the calculated maximum value.
The method of claim 1, wherein the threshold adjustment unit
If the calculated ratio value is greater than the second reference value, the preceding peak threshold is set to a smaller value to estimate the preceding peak, and if the calculated ratio value is not greater than the second reference value, the preceding peak threshold A fine time synchronization estimation device for estimating time synchronization by setting a large value to exclude noise components.
The method of claim 1, wherein the determined fine sync point is
A fine time synchronization estimation device, characterized in that the point having the fastest time.
A downlink fine time synchronization estimation method of a mobile terminal in an orthogonal frequency division multiplexing system,
Obtaining an absolute value of a correlation value within a window section of a signal received from the base station by a predetermined search section;
Obtaining a maximum value of the obtained absolute value and a time index of the maximum value,
Calculating a peak-to-average ratio (PAR) of the maximum value of the absolute value and the average value of the absolute value;
If the calculated ratio value is greater than a first reference value for determining whether to obtain fine synchronization, the ratio is compared with a second reference value indicating a criterion of the reception quality and the magnitude of the ratio value and the second reference value. Setting different peak peak thresholds according to
Determining as a fine synchronization point a point at which the calculated ratio value is greater than or equal to a value obtained by multiplying an absolute value of the preceding peak threshold value and the correlation value within a predetermined peak search window to be temporally preceded the maximum value point. Fine time synchronization estimation method comprising a.
The method of claim 5,
Calculating a maximum value of an absolute value of the correlation value within a window period of the received signal, and detecting a time index of the calculated maximum value.
The method of claim 5, wherein the setting of the preceding peak threshold value is different.
If the calculated ratio value is greater than the second reference value, the preceding peak threshold is set to a smaller value to estimate the preceding peak, and if the calculated ratio value is not greater than the second reference value, the preceding peak threshold A fine time synchronization estimation method characterized by reducing a preceding peak search error due to a noise component by setting a value to a large value.
The method of claim 5, wherein the determined fine sync point is
A fine time synchronization estimation method, characterized in that the point having the fastest time.


KR1020100040993A 2010-04-30 2010-04-30 Apparatus and method for estimating fine timing offset of downlink based on ofdm systems KR100976856B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
KR1020100040993A KR100976856B1 (en) 2010-04-30 2010-04-30 Apparatus and method for estimating fine timing offset of downlink based on ofdm systems

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
KR1020100040993A KR100976856B1 (en) 2010-04-30 2010-04-30 Apparatus and method for estimating fine timing offset of downlink based on ofdm systems

Publications (1)

Publication Number Publication Date
KR100976856B1 true KR100976856B1 (en) 2010-08-20

Family

ID=42759805

Family Applications (1)

Application Number Title Priority Date Filing Date
KR1020100040993A KR100976856B1 (en) 2010-04-30 2010-04-30 Apparatus and method for estimating fine timing offset of downlink based on ofdm systems

Country Status (1)

Country Link
KR (1) KR100976856B1 (en)

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20040105512A1 (en) 2002-12-02 2004-06-03 Nokia Corporation Two step synchronization procedure for orthogonal frequency division multiplexing (OFDM) receivers
KR20040045996A (en) * 2002-11-26 2004-06-05 한국전자통신연구원 Method and apparatus embodying and synchronizing downlink signal in mobile communication system and method for searching cell using the same
KR20050039263A (en) * 2003-10-24 2005-04-29 한국전자통신연구원 Method and apparatus for embodying downlink signal in mobile communication system, and method and apparatus for synchronizing and searching cell using the same
US20070053473A1 (en) 2003-06-30 2007-03-08 Arto Palin Faster fine timing operation in multi-carrier system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20040045996A (en) * 2002-11-26 2004-06-05 한국전자통신연구원 Method and apparatus embodying and synchronizing downlink signal in mobile communication system and method for searching cell using the same
US20040105512A1 (en) 2002-12-02 2004-06-03 Nokia Corporation Two step synchronization procedure for orthogonal frequency division multiplexing (OFDM) receivers
US20070053473A1 (en) 2003-06-30 2007-03-08 Arto Palin Faster fine timing operation in multi-carrier system
KR20050039263A (en) * 2003-10-24 2005-04-29 한국전자통신연구원 Method and apparatus for embodying downlink signal in mobile communication system, and method and apparatus for synchronizing and searching cell using the same

Similar Documents

Publication Publication Date Title
JP4763692B2 (en) Signal acquisition in wireless communication systems
JP5280486B2 (en) Timing acquisition and mode and guard detection for OFDM transmission
KR101314314B1 (en) Method and Apparatus for Uplink Timing Synchronization with Ranging Signal in TDD Mobile Communication System
KR100799539B1 (en) Time and frequency synchronization method on based ofdm
KR101656083B1 (en) Apparatus and method for obtaining reception synchronization in wireless communication system
US8451957B2 (en) System and method for time synchronization of OFDM-based communications
KR20070056881A (en) Apparatus and method for recovering frequency in orthogonal frequency division multiple system
KR101505091B1 (en) Apparatus and method for initial synchronization wireless communication system based on ofdm
KR20090063340A (en) Apparatus and method for detecting a ranging signal in wireless communiation system
WO2009097295A1 (en) Downlink acquisition
EP2617172A1 (en) A receiver node and a method therein for compensating frequency offset
US9451569B1 (en) Systems and methods for detecting a primary synchronization signal in a wireless communication system
WO2015013310A1 (en) Method and apparatus for estimating signal to interference plus noise ratio for a random access channel of a wireless network
WO2006105177A2 (en) Optimal timing and frequency acquisition for ofdm systems
KR20200092096A (en) Wireless communication apparatus including synchronization signal detector and cell searching method thereof
TW200840284A (en) Method of and apparatus for adaptive frequency error estimation
CN112449403A (en) Random access channel transmission method and device in low-earth-orbit satellite communication
KR100976856B1 (en) Apparatus and method for estimating fine timing offset of downlink based on ofdm systems
EP3804248B1 (en) Radio signal detection
CN104684071B (en) The up Timing Synchronization trackings of LTE
KR20070081867A (en) Apparatus and method for frequency offset assumption in ofdm system
KR20150076367A (en) Method for performing initial ranging in cognitive radio network and system thereof
CN112399552B (en) Synchronization method, user equipment and computer-readable storage medium
JP5595952B2 (en) Cell search apparatus and method, and mobile station
JP2000299676A (en) Reception equipment

Legal Events

Date Code Title Description
A201 Request for examination
A302 Request for accelerated examination
E902 Notification of reason for refusal
E701 Decision to grant or registration of patent right
GRNT Written decision to grant
FPAY Annual fee payment

Payment date: 20130730

Year of fee payment: 4

FPAY Annual fee payment

Payment date: 20140729

Year of fee payment: 5

FPAY Annual fee payment

Payment date: 20150729

Year of fee payment: 6

FPAY Annual fee payment

Payment date: 20160729

Year of fee payment: 7