KR100344693B1 - AFC for the muti-carrier CDMA system and method for the compensating of frequency error - Google Patents

Abstract

The present invention detects a finger in a locked state among a plurality of fingers and calculates an average frequency error so that the corrected frequency error correction can be made by reflecting the error that is actually generated. And a frequency correction method.

To this end, the present invention provides a lock state finger count detection step of detecting whether the demodulated predetermined energy level for each of the fingers or more, summing the number of fingers above a certain energy; A division step of calculating a frequency error for each finger and dividing by the number of fingers detected in the lock state finger detection step; An average frequency error calculating step of calculating an average frequency error by summing each finger signal divided in the dividing step; And a control voltage generation step of generating a control voltage for correcting the frequency by the average value calculated in the average frequency error calculating step.

Description

AFC for the muti-carrier CDMA system and method for the compensating of frequency error}

The present invention detects a finger in a locked state among a plurality of fingers and calculates an average frequency error so that an accurate frequency error correction is performed to reflect an error actually occurring. And a frequency correction method.

The spread spectrum communication method has been increased in use because of its excellent interference resistance and interference resistance, and the reception characteristics are gradually improved even in a multi-path environment. In addition, in the spread spectrum communication method, it is common to select a high spreading frequency and to apply a lake reception method by distinguishing a difference between multipath propagation paths. The lake reception communication separates the multipath propagation paths for each pass, estimates propagation path characteristics for each path, compensates for each propagation path characteristic for the received signal of each path, and then synthesizes in phase to obtain the pass diversity effect. It is a technology to realize diversity effect. In the rake reception method, a portion for estimating characteristics for each pass of the propagation path of the multipath and performing compensation thereof is called a finger. For this purpose, the finger includes a correlator which despreads the spectral spreading code.

Conventionally, AFC calculates by dividing the error of each finger signal by the number of physical fingers to extract the average error from the plurality of finger signals.

1 shows a block diagram of a conventional AFC.

The base band analog (BBA) chip 10 receives a finger signal and detects two received reference signals that are orthogonal to each other. A modem chip that outputs as a baseband signal. The phase I and Q components of BBA 10 are despread in a PN despreading11, through a pilot filter 12 and a Cross Product Frequency Difference Detector (CPFDD) 13. Detect errors In the CPFDD13, an error of each phase of the finger input signal is multiplied by a phase component delayed by a predetermined interval of other phases detected at a predetermined period, and the multiplied signals are summed to output a frequency error Freq_Err. When four finger signals are input, the output signal Freq_Err of the CPFDD13 is divided into 1/4 and input to the adder 14 as the first finger signal frequency error Freq_Err1. In this manner, the respective finger signals Freq_Err2, Freq_Err3 and Freq_Err4 are summed in the adder 14 to output an average frequency error SUM_FE. The SUM_FE is input to the loop filter 15 through adjustment of amplification or the like. The loop filter 15 is a circuit that receives the average frequency error and suppresses the effect of the error and outputs the result. The output of the loop filter 15 is input to a voltage controlled oscillator (VCO) 16, and in the voltage controlled oscillator 16, the frequency error is changed to change the reference frequency in an error-free direction by setting the output voltage level as the control voltage (TRK_LO_ADJ). The voltage is output in the decreasing direction to generate a corrected frequency ideally set to zero frequency error and used for demodulation.

In the conventional AFC, the frequency error of signals received through each finger is added together, divided by the number of physical fingers (for example, 4), and summed to obtain an average frequency error. However, in the real environment, the finger signals for calculating the average frequency error are not maintained at four physical numbers. When the received signal of the finger is below a certain energy level (hereinafter referred to as an "un-look" state), the finger is not operated. In this case, the finger signal generating an average frequency error has a constant energy level. Only the error values due to the abnormal finger signals (hereinafter referred to as a "look" state) are summed and divided by the number of physical finger signals with respect to them, so that the average frequency error is substantially smaller than the normal value. Therefore, if all the fingers are locked, the average frequency error is calculated with the correct arithmetic mean so that the correct average frequency error is calculated. However, if some fingers are not in the locked state, a smaller value than the actual average frequency error is calculated. As such, when the average frequency error is small, the voltage controller is generated based on this.

As a result, the control voltage input to 16 becomes smaller, resulting in a smaller frequency correction range that the AFC can correct.

In particular, when the number of fingers constituting the rake receiver is increased because the frequency bandwidth is large or the number of fingers constituting the rake receiver is increased in order to increase the diversity effect, this phenomenon occurs even more and cannot achieve proper frequency correction.

The present invention is to solve this problem, to detect the number of fingers in the unlocked state and to obtain an accurate correction by obtaining the average frequency error in the excluded state.

Another object of the present invention is to provide an AFC applied to a multi-carrier code division multiple access system (Muti-carrier CDMA system).

Still another object of the present invention is to provide a circuit configuration capable of maximizing the effect of frequency correction without greatly converting the conventional AFC.

1 shows a block diagram of a conventional AFC.

2 is a block diagram illustrating an embodiment of the present invention.

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

10: BBA 11: PN despreader

12: pilot filter 13: cross multiplication error detector

14: adder 15: loop filter

16: voltage controller

The present invention to achieve the above object

In the AFC (Automatic Frequency Controller) of a multicarrier code division multiple system,

A base band analog chip for receiving respective finger signals and outputting in-phase components and quadrature components that are orthogonal to each other as a baseband signal;

Despreading (PN despreading) for despreading the in-phase and quadrature components output from the baseband analog chip;

A cross product frequency difference detector (CPFDD) for detecting a frequency error of each finger signal from an in-phase component and an orthogonal component filtered by a pilot filter;

Locked state detecting means for extracting finger signals of a predetermined energy level or higher from respective finger signals;

A divider for dividing the frequency error detected by the cross multiplication error detector by the number of fingers in the locked state detected by the locked state detecting means;

An adder for summing each frequency error output from the divider and outputting an average frequency error;

A loop filter receiving a mean frequency error from the adder and outputting a voltage level suppressing the influence of the error;

Voltage controlled oscillator for supplying the frequency according to the voltage level to the outside as a reception reference signal using the voltage of the loop filter as a control voltage (Voltage Controlled)

Ocillator: VCO) is characterized in that it comprises.

Although the present invention can be effectively applied to a CDMA system, it is more effective to have a large number of input finger signals in order to be utilized more appropriately. That is, the present invention is based on the third generation multicarrier system (3G-3 × MC) having three carrier frequencies, rather than the voice-oriented IS-95A or IS-95B or the single carrier carrier multicarrier system (3G-1 × MC). The effect of becomes more pronounced.

In the 3G-3 × multicarrier method, a frequency correction may be performed based on a carrier frequency located in the middle of three carrier frequencies received from a terminal, and a frequency error correction may be performed based on the carrier frequency. However, when the interval between the frequencies of each carrier is wide, there is a drawback that the phase error can be large for each carrier frequency.

In addition, there may be a method of performing frequency error correction independently for three carrier frequencies. This method may be the most accurate method, but H / W is required because an independent voltage controller must be installed and managed for each carrier frequency. And the complexity of S / W.

In addition, there may be a method of reflecting the frequency error of each carrier on average. That is, all the fingers corresponding to each carrier frequency are used simultaneously by calculating the frequency error average value. In case of the 3 × MC method, there are 12 fingers in total, 4 for each carrier frequency. The average frequency error is calculated by summing the frequencies calculated from each finger, and based on this, a control voltage input to the voltage controller is generated. In calculating the average frequency error, instead of dividing the number of physical fingers into 12, the number of fingers in the locked state is obtained to obtain a substantial average frequency error so as to correct the frequency.

Hereinafter, the third method presented above will be described in detail with reference to the accompanying drawings as an embodiment of the present invention.

2 is a block diagram illustrating an embodiment of the present invention.

In the present embodiment, a third generation 3x multicarrier method (3G-3x) has three carrier frequencies, and four finger signals are input to each BBA10 for each carrier frequency. The signal is divided into an in-phase component (I component) and a vertical component (Q component) with respect to the reference frequency and despread by the PN despreader 11. After the inverted finger signal is filtered by the pilot filter, a frequency error is detected by the cross multiplication error detector 13 at a predetermined period.

Further, the number of locked fingers is detected by the finger count detecting means 21 in the locked state, which can be demodulated for each of the 12 finger signals. The number of finger detection means 21 in the locked state detects whether the energy level of the finger signal is above a certain level by the energy level detector. If it is above a certain level, the finger number detecting means 21 displays this in a register, and adds up the values of the registers corresponding to each finger. The number of fingers in the locked state is calculated. The number of fingers m in the locked state is transmitted to the divider 20, and divided by m for each frequency error signal and transmitted to the adder 14. In the adder 14, the frequency error value of each finger signal output from the divider 20 is added to find an average frequency error. Average frequency error output from adder 14 is loop filter

It is input to (loop filter) 15 and outputs the voltage level suppressing the influence of error. Using a voltage output from the loop filter 15 as a control voltage, a voltage controlled oscillator (VCO) 16 generates a reference signal based on the frequency according to the voltage level.

According to the present invention having such a configuration, since the frequency error average value is obtained by considering only the number of fingers in the locked state, an accurate frequency error average value can be obtained to achieve accurate frequency correction. In particular, since the third generation 3 carrier frequency multicarrier method (3G-3 x MC) has three times the number of fingers in the 1 carrier (3G-1 x MC), the possibility of a large number of unlocked fingers may exist. This is high. Therefore, the present invention brings a high frequency compensation effect to the communication method using a plurality of carrier frequencies.

Claims (3)

In a multicarrier reception frequency compensation method using multiple carrier frequencies: A lock state finger number detection step of detecting whether the respective fingers have a demodulated constant energy level or more, and summing the number of fingers that are above a certain energy; A division step of calculating a frequency error for each finger and dividing by the number of fingers detected in the lock state finger detection step; An average frequency error calculating step of calculating an average value of frequency errors by adding up the respective finger signals divided in the dividing step; And a control voltage generation step of generating a control voltage for correcting the frequency based on the average value calculated in the average frequency error calculating step. In the AFC (Automatic Frequency Controller) of a multicarrier code division multiple system, A base band analog chip for receiving respective finger signals and outputting in-phase components and quadrature components that are orthogonal to each other as a baseband signal; Despreading (PN despreading) for despreading the in-phase and quadrature components output from the baseband analog chip; A cross product frequency difference detector (CPFDD) for detecting a frequency error of each finger signal from an in-phase component and an orthogonal component filtered by a pilot filter; Locked state detecting means for extracting finger signals of a predetermined energy level or higher from respective finger signals; A divider for dividing the frequency error detected by the cross multiplication error detector by the number of fingers in the locked state detected by the locked state detecting means; An adder for summing each frequency error output from the divider and outputting an average frequency error; A loop filter receiving a mean frequency error from the adder and outputting a voltage level suppressing the influence of the error; AFC of a multi-carrier code division multiple system comprising a voltage controlled oscillator (VCO) for supplying a frequency according to a voltage level to the outside as a reception reference signal using the voltage of the loop filter as a control voltage. Automatic Frequency Controller). 3. The lock state detection means according to claim 2, An energy level detector for detecting whether each of the finger signals is above a demodable energy level; Registers provided corresponding to each finger to indicate when the energy level detector is above the level; AFC (Automatic Frequency Controller) of a multi-carrier code division multiple system, characterized in that the adder for summing the number of fingers having a certain level of energy indicated in the register.