JP4543289B2 - Noise level measuring method and apparatus - Google Patents

Description

  The present invention relates to a radio communication apparatus, and more particularly to a method and apparatus for measuring a level (noise level) of an interference wave component from a received symbol.

  Generally, in a code division multiple access (CDMA) wireless communication apparatus, an RSCP (Received Signal Code Power) value that is a desired wave component measured from a received symbol and an ISCP (Interference Signal Code Power) value that is an interference wave component are obtained. The reception quality SIR (Signal to Interference Ratio) is detected using the received quality SIR, and transmission power control, synchronization determination, and the like are executed.

  FIG. 4A is a schematic block diagram of a general SIR measurement circuit. The receiving unit 301 outputs a received symbol by performing demodulation and despreading processing on the received RF signal, and the RSCP calculating unit 302 and the ISCP calculating unit 303 input the received symbol to obtain the RSCP value and the ISCP value, respectively. calculate. Further, SIR calculation section 304 calculates reception quality SIR from the RSCP value and the ISCP value, and outputs the reception quality SIR to the synchronization determination section or the like.

  Various techniques for accurately measuring such reception quality SIR have been proposed. For example, when a frequency error occurs in an oscillator provided in a transmission / reception unit of a wireless communication device, phase rotation due to the frequency error occurs. Patent Document 1 discloses a reception level measurement circuit that corrects this and improves the measurement accuracy. Specifically, the desired wave component (RSCP), the interference wave component (ISCP), and the frequency error vector are detected from the received symbol, and the desired wave component (RSCP) is corrected using a correction value for correcting the frequency error. Improve reception level measurement accuracy.

JP 2003-264514 A

  However, the ISCP value, which is a noise component, is also affected by frequency fluctuations. In the case of ISCP, if there is a frequency difference even in an environment where there is almost no background noise, the component of the frequency difference may appear as noise, and the ISCP value may be larger than the original value.

  FIG. 4B is a symbol layout diagram on the IQ plane showing the variation of the symbol position due to the frequency error. When a frequency error occurs, the received symbol position is displaced from the original symbol position 401 to the symbol position 402 as shown in FIG. 4B, and the difference 403 is also detected as noise. For this reason, the ISCP value increases, and the SIR value decreases accordingly. When the SIR value becomes small, the transmission side transmits with large transmission power by transmission power control, and as a result, useless power is consumed. Further, when the SIR value becomes smaller, it may be judged that the reception environment has deteriorated so much that the communication is disconnected.

  Accordingly, an object of the present invention is to provide a method and apparatus for measuring an accurate noise level while suppressing the influence of a frequency error, and a radio communication apparatus using the same.

The noise level measurement apparatus according to the present invention includes a detection unit that detects an interference wave component, a frequency difference, and a desired wave component from the received symbol , and a predetermined function that uses the frequency difference and the desired wave component as arguments . Correction amount calculating means for calculating a correction amount , and correction for generating a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component And means.

  According to the present invention, it is possible to measure an accurate noise level while suppressing the influence of a frequency error.

  FIG. 1 is a block diagram of a noise level measuring apparatus according to an embodiment of the present invention. Symbols that can be expressed as signal points on the IQ plane are input to the ISCP calculator 101, the frequency difference calculator 102, and the RSCP calculator 103, respectively.

  The ISCP calculation unit 101 calculates an ISCP value i, which is the power of the noise component, by a known calculation using symbol variance or the like, and outputs it to the forgetting processing unit 104. The forgetting processing unit 104 forgets the ISCP value i and outputs the ISCP value i ′ to the ISCP correction unit 105. However, it is possible not to perform the forgetting process. The ISCP correction unit 105 receives the ISCP value i ′ and the correction amount z, and outputs the corrected ISCP value iscp = f2 (i ′, z) as a noise level.

  The frequency difference calculation unit 102 calculates a shift (frequency difference x) between symbols from the received symbol by a known calculation and outputs the calculated difference to the forgetting processing unit 106. The forgetting processing unit 106 forgets the frequency difference x and outputs the frequency difference x ′ to the correction amount calculating unit 107. However, it is possible not to perform the forgetting process.

  The RSCP calculator 103 calculates an RSCP value y, which is signal component power, from the received symbol by a well-known calculation and outputs it to the correction amount calculator 107.

  The correction amount calculation unit 107 receives the frequency difference x ′ and the RSCP value y, calculates a correction amount z = f 1 (x ′, y), and outputs it to the ISCP correction unit 105. For example, the correction amount z can be obtained by the following equation.

  The function for obtaining the correction amount z is an arbitrary order n, and includes a multiplier of a coefficient α and a frequency error x (here, x ′ after forgetting processing) and an RSCP value y.

  The ISCP correction unit 105 inputs the ISCP value i ′ and the correction amount z, and calculates the corrected ISCP value iscp = f2 (i ′, z). For example, the ISCP value can be corrected by the following equation.

iscp = max {f2 (i ′, z, β), 0}
Where f2 (i ′, z, β) = i′−β × z
That is, the correction of the ISCP value i ′ is performed by a value obtained by multiplying the correction amount z by the effect coefficient β. However, max {} is used for conversion to z = 0 when the correction amount z is negative.

  The output i ′ of the forgetting processing unit 104 can be calculated by the following equation, for example.

i ' _m = γ × i' _m-1 + (1-γ) × i _m
The output x ′ of the forgetting processing unit 106 can be calculated by the following equation, for example.

x ' _m = γ × x' _m-1 + (1-γ) × x _m
In any forgetting process, the forgetting process can be omitted by setting the forgetting coefficient γ to 0. Also, it is possible to perform the same forgetting process using a filter instead of such an operation.

  Each function block of the noise level measuring apparatus shown in FIG. 1 can also realize the same function by executing a program on a program control processor such as a CPU.

  FIG. 2 is a block diagram schematically showing a receiving system of a wireless communication apparatus according to an embodiment of the present invention. The same blocks as those in the noise level measuring apparatus shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The receiving system of the wireless communication apparatus according to the present embodiment includes a receiving unit 201 that performs quadrature detection and the like, a despreading unit 202 for CPICH (Common Pilot Channel), a noise level measuring unit 203 that measures an ISCP value corrected from CPICH, and A signal processing unit 204 that performs signal processing such as calculation of reception quality SIR is included.

  Specifically, CPICH received symbols are input to the ISCP calculator 101, the frequency difference calculator 102, and the RSCP calculator 103, respectively, and the ISCP value i, the frequency difference x, and the RSCP value y are calculated simultaneously as described above. The correction amount calculation unit 107 calculates the correction amount z using a function f1 (x ′, y) having the frequency difference x ′ subjected to forgetting processing and the RSCp value y as arguments. However, the function z can be appropriately changed according to the effect amount to be corrected.

  The ISCP correction unit 105 obtains the final corrected ISCP value iscp by the function f2 (i ′, z, β) using the forgotten ISCP value i ′, the correction amount z, and the effect count β. By this correction, the phenomenon that the ISCP value appears larger than the original due to the influence of the frequency error is alleviated, and the problem that the SIR described above is unduly deteriorated can be solved.

  FIG. 3 is a graph showing quantitatively the effect of correction according to this embodiment. The horizontal axis represents the frequency difference x, and the vertical axis represents the magnitude of the ISCP value and the correction amount z. From this graph, it can be seen that the corrected ISCP value iscp is suppressed from increasing even if the frequency difference x increases. As described above, since the increase in the ISCP value due to the change in the frequency difference x is mitigated, it is possible to suppress the deterioration of the reception quality SIR, and to suppress the unnecessary increase in the transmission power from the transmission-side base station in the transmission power control loop. I can do it. In addition, since undue deterioration of the reception quality SIR can be prevented, the occurrence of unnecessary communication disconnection can be suppressed.

  The present invention is applicable to communication devices, mobile phones, and the like that use the CDMA system.

It is a block diagram of the noise level measurement apparatus by one Embodiment of this invention. It is a block diagram which shows roughly the receiving system of the radio | wireless communication apparatus by one Example of this invention. It is a graph which shows quantitatively the effect of amendment by this example. (A) is a schematic block diagram of a general SIR measurement circuit, and (B) is a symbol arrangement diagram on an IQ plane showing a change in symbol position due to a frequency error.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ISCP calculating part 102 Frequency difference calculating part 103 RSCP calculating part 104 Forgetting process part 105 Forgetting process part 106 ISCP correction part 107 Correction amount calculating part 201 Receiving part 202 Despreading part 203 Noise level measuring part 204 Signal processing part

Claims (13)

In a noise level measurement device that measures the noise level of a received symbol,
Detecting means for detecting an interference wave component, a frequency difference and a desired wave component from the received symbol;
A correction amount calculation means for calculating a correction amount of an interference wave component by a predetermined function using the frequency difference and the desired wave component as arguments ;
Correction means for generating a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component;
A noise level measuring apparatus comprising: 2. The correction amount z according to claim 1, wherein the correction amount calculation means calculates the correction amount z by the following formula when the frequency difference x, the desired wave component y, and the coefficient α corresponding to the desired correction effect amount are used. Noise level measuring device.
In the case where the correction means has an interference wave component i, a correction amount z, and an effect coefficient β,
iscp = max {f2 (i ′, z, β), 0}
Where f2 (i ′, z, β) = i′−β × z
The noise level measuring apparatus according to claim 1, wherein the interference wave component is corrected by the method. First forgetting processing means for outputting to the correcting means after performing forgetting processing with a forgetting coefficient on the interference wave component;
Second forgetting processing means for outputting to the correction amount calculating means after performing forgetting processing with a forgetting coefficient on the frequency difference;
Further comprising
If the interference wave component after the previous forgetting process is i ′ _m−1 , the interference wave component after the current forgetting process is i ′ _m , and the forgetting coefficient is γ,
i ' _m = γ x i' _m-1 + (1-γ) x i _m
Calculate the interference wave component by
The second forgetting processing means is assumed that the frequency difference after the previous forgetting process is x ′ _m−1 , the frequency difference after the current forgetting process is x ′ _m , and the forgetting factor is γ,
x ' _m = γ × x' _m-1 + (1-γ) × x _m
To calculate the frequency difference,
The noise level measuring apparatus according to any one of claims 1 to 3, wherein In a noise level measurement method for measuring the noise level of a received symbol,
Detecting means detects an interference wave component, a frequency difference and a desired wave component from the received symbol,
The correction amount calculation means calculates the correction amount of the interference wave component by a predetermined function using the frequency difference and the desired wave component as arguments ,
A correction means generates a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component.
A noise level measuring method characterized by that. 6. The noise level measuring method according to claim 5 , wherein the correction amount z is calculated by the following equation when the frequency difference x, the desired wave component y, and the coefficient α corresponding to the desired correction effect amount are used.
If the interference wave component i, the correction amount z, and the effect coefficient β,
iscp = max {f2 (i ′, z, β), 0}
Where f2 (i ′, z, β) = i′−β × z
The noise level measuring method according to claim 6 or 7 , wherein the interference wave component is corrected by the method. In a program that causes a computer to function as a noise level measuring device that measures the noise level of a received symbol,
A function of detecting an interference wave component, a frequency difference and a desired wave component from the received symbol;
A function of calculating a correction amount of the interference wave component by a predetermined function correction amount calculating means is an argument of the frequency difference and the desired signal component,
A function of generating a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component;
A program for causing the computer to realize the above. 9. The program according to claim 8 , wherein the correction amount z is calculated by the following equation when the frequency difference x, the desired wave component y, and the coefficient α corresponding to the desired correction effect amount are used .
If the interference wave component i, the correction amount z, and the effect coefficient β,
iscp = max {f2 (i ′, z, β), 0}
Where f2 (i ′, z, β) = i′−β × z
The program according to claim 7 or 8 , wherein the interference wave component is corrected by the method. In a wireless communication device having a function of measuring a noise level of a received symbol,
Detecting means for detecting an interference wave component, a frequency difference and a desired wave component from the received symbol;
A correction amount calculation means for calculating a correction amount of an interference wave component by a predetermined function using the frequency difference and the desired wave component as arguments ;
Correction means for generating a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component;
A wireless communication apparatus comprising: It further has a CDMA (Code Division Multiple Access) receiving means and a despreading means, and uses an ISCP (Interference Signal Code Power) value as the interference wave component and an RSCP (Received Signal Code Power) value as the desired wave component. The wireless communication apparatus according to claim 11 . In a wireless communication device having a program control processor,
On the program control processor,
A function of detecting an interference wave component, a frequency difference and a desired wave component from the received symbol;
A function of calculating a correction amount of the interference wave component by a predetermined function correction amount calculating means is an argument of the frequency difference and the desired signal component,
A function of generating a corrected interference wave component as a noise level by subtracting the correction amount multiplied by a coefficient for obtaining a desired correction effect from the interference wave component;
A wireless communication device that executes a program for realizing the above.