JP3095305B2 - Receive level measurement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applied to a mobile radio communication system. The present invention is used in a system in which a mobile station or a base station measures a received signal level of a radio wave from a partner station and uses the measurement result as data for connection control. INDUSTRIAL APPLICABILITY The present invention is suitable for use in a system in which the time for measuring the reception signal level when switching the use frequency may be extremely short.

[0002]

2. Description of the Related Art In mobile communications such as car phones,
As the mobile device moves, its reception level may fluctuate greatly with time. This fluctuation speed is proportional to both the radio frequency used and the moving speed. For example, in an 800 MHz band automobile / mobile phone, the fluctuation speed varies from several Hz or less to several tens Hz at the maximum. The distribution of fluctuation generally follows the Rayleigh distribution in many cases.

For this reason, in mobile communication, it is often necessary to measure the reception level and estimate the average reception level. For example, in a car / mobile phone, a radio channel is divided into a control channel and a communication channel, and all mobile devices need to select and receive a control channel correctly. The control channel is transmitted from each base station at a different frequency, and when the power is turned on, the mobile station receives a control channel radio wave from each base station and captures the control channel of the maximum reception level. . Also,
Even during communication, it is necessary to estimate the reception level of the currently communicating channel due to so-called handoff.

However, since the reception level fluctuates greatly, an error is inevitable in the estimation. If this error is large, for example, in the case of selecting a control channel, a control channel of a base station that is not at the maximum reception level may be erroneously selected, and stable and reliable connection control may not be performed.
Also, if there is an error in the reception level estimation during handoff, it is erroneously determined that the level is low enough to be handed off, and communication is performed with low communication quality.

Therefore, it is necessary to reduce the estimation error as much as possible. As a method for this, conventionally, the measurement time is made sufficiently long to find the average value or median value (level value at which the value of the cumulative distribution becomes 50%). There is known a method of absorbing a fluctuation in reception level by using this value as an estimated value. The time required for the averaging or the median processing is at least several to ten times as long as the fluctuation period determined by the speed of the fluctuation. Therefore, when the fluctuation speed is several tens Hz, it is 100 ms to several hundred ms, and the fluctuation speed is large. When the frequency is several Hz, a time of one second to several seconds is required. If the speed of fluctuation is not constant, as in the case of automobiles and mobile phones, it takes several seconds for the averaging or median processing time for safety.

[0006]

However, the measurement of the reception level is required not only in a case where the processing can be performed with sufficient time but also in a case where the measurement is required in a very short time. For example, during the time from when the power of the mobile device is turned on to when the control channel is correctly acquired, no control between the mobile device and the base station is possible at all, and thus the mobile device cannot be used. Most of the time until the control channel is captured is the time for measuring the reception level of radio waves from each base station. For example, if the number of base station control channels to be measured is 10 and the measurement time per channel is 5 seconds, the mobile station cannot be used for 10 × 5 = 50 seconds. Obviously this is not an acceptable range. For this reason, conventionally, the average reception level has been estimated based on a value measured in a short time while sacrificing accuracy.

In the method in which the 50% value of the cumulative distribution is used as the reception level estimation value, when the measurement time is short, the number of pieces of measured data is small. Is less accurate than the method

On the contrary, there is a case where a relatively long measurement time can be taken. For example, in the handoff control, if the reception level of the channel being communicated falls below a specified value and it is determined whether or not to perform handoff, it may take several seconds to measure the reception level. This is because communication is already in progress, and judging from the cell radius (usually 1.5 km or more) and the moving speed (vehicle speed 60 km / h = 16.6 m / s), even if the handoff is delayed by about 5 seconds, Is smaller than the cell radius and is sufficiently small to be negligible.

As described above, according to the conventional technique, although high accuracy can be obtained in the estimation of the reception level, which takes a long time for the measurement, when it is necessary to estimate the reception level in a short time by shortening the measurement time, The error was large.

[0010] The present invention provides a reception level that can maintain the conventional accuracy in estimating the reception level, which can take a long time for measurement, and reduce the estimation error when measuring in a short time. It is an object to provide a measurement circuit.

[0011]

A receiving level measuring circuit according to the present invention includes a receiving level measuring means for detecting a signal receiving level measurement value of a radio receiver as an electric signal, and taking in the electric signal over time t, and receiving the electric signal. In a reception level measuring circuit comprising: an arithmetic unit for performing an arithmetic processing on a signal and outputting the result as a reception level measurement result, the arithmetic unit holds a predetermined time t ₀ , and when the time t is t <t ₀ , the measurement is performed. The measurement result is calculated by omitting data whose value is equal to or less than a predetermined value. When the time t is t ≧ t _0, the measurement result is calculated without omitting a part of the measurement value. The predetermined value may be a predetermined value or a value adaptively determined based on the maximum value or the average value of the measured values.

[0012]

The reception level in mobile communication varies greatly depending on the distance between the mobile station and the base station, propagation path conditions around the mobile station, and the like. In order to detect a reception level which fluctuates greatly in this way, it is common to use a dB value expressed as a logarithm of the reception level.

By the way, when the fluctuation of the Rayleigh distribution is expressed in dB, considering the median as a center, the probability of falling to a level lower than the median is conversely higher than the probability of the level being higher than the median. There is great nature. That is, the Rayleigh fluctuation is a fluctuation generated as a result of combining a plurality of radio waves propagated through a plurality of paths, and the median or average value represents the average energy of the received radio wave. Therefore, the level rises above the median value when a plurality of radio waves are combined in phase, and the level falls below the median value when a plurality of radio waves are combined in opposite phases. The level can be reduced as much as the combined radio waves are exactly in opposite phases, but when combined in the same phase, the level cannot be so high from the viewpoint of the total energy.

As described above, although the measured level hardly increases extremely than the average level, it is relatively easy to measure a value extremely lower than the average level. For this reason, if a large level drop happens to be encountered in a short time measurement, the average value of the measured values within a short time will be lowered due to the low level value. Error increases.

Therefore, according to the present invention, when the measurement is performed in a short time, the calculation is performed while omitting data whose measured value is equal to or less than a predetermined value.
On the other hand, for measurements that can take some time,
The average value or the median value is used as the reception level estimation value as in the past. In the case of long-term measurement, even if a large level decrease is included in the measured value, it is considered that the level decrease is equivalent to the probability that the level decrease appears theoretically, and the true average value Or, the median is a value that includes these level reductions. Therefore, highly accurate measurement can be performed according to the length of the measurement time.

[0016]

FIG. 1 is a block diagram showing an embodiment of the present invention, and shows an example of a configuration having a reception level measuring circuit in a mobile station.

This mobile station comprises an antenna 1, a duplexer 2, a receiver 3, a transmitter 4, a synthesizer 5, a reception level measuring circuit 6, a control circuit 7, and a handset 8.

The reception level measurement circuit 6 includes a sampling circuit 10 and a level detection circuit 11 as reception level measurement means for detecting a signal reception level measurement value of the receiver 3 as an electric signal, and takes in the electric signal over time t. An arithmetic circuit 12 and a random access memory 13 are provided as arithmetic means for performing arithmetic processing on the electric signal and outputting the result as a reception level measurement result. Further, a clock generation circuit 14 for supplying these operation clocks is provided.

The feature of the present embodiment is that the arithmetic circuit 12 holds a predetermined time t ₀ , and the time t is t
When <t ₀ , there is provided a program means for calculating the measurement result while omitting data whose measured value is equal to or less than the predetermined value. This program means also calculates the measurement result without omitting a part of the measurement value when the time t is t ≧ t ₀ .

When the mobile station is waiting for reception or searching for a control channel, the radio wave from the base station is received and demodulated by the receiver 3 via the antenna 1 and the duplexer 2. The synthesizer 5 supplies a local frequency for a control channel to the receiver 3, and the reception channel of the receiver 3 is a control channel. The demodulated control signal is supplied to the control circuit 7 as a reception signal. The control circuit 7 includes a microprocessor, a ROM and a RAM,
It controls each section of the mobile device and processes control signals for the base station. The control procedure is stored in the ROM. If there is a control signal to be transmitted, the control signal generated by the control circuit 7 is modulated by the transmitter 4 and transmitted to the base station via the duplexer 2 and the antenna 1. The synthesizer 5 supplies a local frequency for a control channel to the transmitter 4. During communication, the synthesizer 5 supplies the local frequency for the communication channel to the receiver 3 and the transmitter 4, and transmits and receives voice signals from or to the handset 8.

In the reception level measuring circuit 6, the sampling level of the receiver 3 is sampled for each clock by the sampling circuit 10 and is measured by the level detection circuit 11.
The measured value is processed by the arithmetic circuit 12. The arithmetic circuit 12 temporarily accumulates the measured value of the dB display by the level detecting circuit 11 in the RAM 13, and after ending the measurement for the time t designated by the control circuit 7, averages the accumulated measured value, that is, the measurement result. I do. The processing result is output to the control circuit 7 as an estimated value of the reception level. Control circuit 7
Performs channel switching or handoff control based on the estimated value.

FIG. 2 shows the flow of control by the arithmetic circuit 12.

The time t for measuring the reception level is determined by the control circuit 7.
The arithmetic circuit 12 repeats the measurement for the time t and stores the measured value of the reception level in the RAM 13. If the measurement time t is shorter than the predetermined time t ₀ held by the user, only the data that is larger than the predetermined value is taken out of the accumulated measurement value data and the average value is obtained.
Output it as an estimate. The measurement time t is a predetermined time t
If it is ₀ or more, an average value is obtained using all of the accumulated measurement value data, and the average value is output as an estimated value.

The predetermined value that is used as a criterion for determining the magnitude is
A predetermined value may be used, a value smaller than the maximum measured value by a predetermined value may be used as the predetermined value, and further, a fixed number of measured values in order from the largest one May be used as the predetermined value.
Only the largest ones can be used.

In the above embodiment, the reception level measuring circuit 6 is shown as an individual circuit. However, the sampling circuit 10 and the level detecting circuit 11 can be provided as circuits in the receiver 3, and the arithmetic circuit 12 and the RAM 13 are controlled. It is practically desirable that the circuit is common to the circuit 7. The clock generation circuit 14 can also be used in the mobile device.

FIG. 3 shows a cumulative probability distribution of the Rayleigh distribution. The horizontal axis is the reception level of the dB display based on the median value. The probability of a 10 dB decrease from the median is less than 10%, while the probability of a 10 dB increase from the median is 10%.
0-99.99 = 0.01% only. Furthermore, the probability of a 20 dB decrease from the median is less than 1%, and the probability of a level higher than the median by 20 dB or more is 10 ^-28 % (outside the range in the figure). That is, the probability of being measured at least 20 dB lower than the median value in one measurement is relatively likely to be about once in 100 times, whereas the probability of being measured once every 100 times is relatively easy.
It can be said that B high levels are practically never measured.

FIG. 4 shows the standard deviation (variation) of the estimated value when the maximum measured level among the measured levels within a fixed time is used as the estimated value and when the average value is used as the estimated value. This value is obtained by computer simulation. The vertical axis indicates the level measurement time, and the vertical axis indicates the standard deviation of the estimated value when the level measurement and the estimation are performed many times. 5Hz fading speed expressed by the maximum Doppler frequency
The standard deviation when the value obtained by performing the conventional averaging process is used as the estimated value is shown by a solid line, and the standard deviation when the maximum measurement level is used as the estimated value is shown by a broken line. It can be seen that the processing with the maximum value has less variation until the measurement time is at least 100 ms. Considering the case where the standard deviation is suppressed within 4 dB, the conventional averaging process requires 50 to 100 ms.
In contrast, the processing with the maximum value needs only a little over 20 ms, and the measurement time is set to 1
It can be seen that it can be reduced to about / 3.

Such measurement is effective, for example, when the channels F1, F2, F3... To be measured are sequentially switched and the reception level of each channel is measured for a short fixed time dT. FIG. 5 shows an example of such channel switching.

FIG. 6 shows the standard deviation of the estimated values of the levels obtained by a plurality of measurements when the average value is the estimated value and when the maximum value is the estimated value. This value is obtained by computer simulation. The vertical axis indicates the level measurement time, and the vertical axis indicates the standard deviation of the estimated value when the level estimation is performed many times. The standard deviation when the fading speed expressed by the maximum Doppler frequency is 5 Hz and the estimated value is obtained by performing the conventional averaging process is represented by a solid line, and the standard deviation when the maximum measurement level is the estimated value is represented by the following equation. Shown by broken lines. The measurement interval in the multiple measurements was 0.35 seconds.

FIG. 7 shows an example in which such a measurement of the reception level is necessary. In this example, the reception level of each channel is instantaneously measured by sequentially switching channels, and once the channel has completed one cycle, the measurement of the instantaneous reception level is repeated from the first channel again. This is repeated N times to obtain N
Take measurements. The average value processing or the maximum value processing is performed on these N pieces. The number of measurements N corresponds to the horizontal axis in FIG.

In the example shown in FIG. 5, when the fading speed is low, the level fluctuation due to fading hardly appears in the dT measurement time, and the measurement in dT may be practically the same as the instantaneous measurement. Therefore, the total measurement time [(dT + synthesizer switching time) × the number of channels]
The accuracy cannot be obtained in exchange for it. On the other hand, in the example shown in FIG. 7, since the fading fluctuation over the entire measurement time can be measured, relatively high-accuracy measurement is possible. However, in the case of the example shown in FIG. 7, the switching time of the synthesizer needs to be fast. When the number of times of measurement is 1, the maximum value and the average value are the same, and the variation does not change. It can be seen that when the number of times of measurement is 2 or more and 8 times, the standard deviation is smaller in the maximum value processing and the measurement accuracy is improved. When the number of measurements is eight or more, the average value processing is more accurate. For example, when the standard deviation of the designated error is set to 3 dB or less, the conventional method requires four measurements, while the maximum value processing requires three measurements, and the measurement time can be reduced by 25%. Therefore, in this case, the maximum value processing is performed when the number of measurements is eight or less, and the average value processing is performed when the number of measurements exceeds eight.

When estimating the reception level from the maximum value, the expected value of the maximum value is larger than the true expected value (average value). When performing a relative comparison of the reception levels, any estimated value is increased by the same value as the average value, so there is no need to make any particular correction. The correction value is determined by the number of measurements and other factors, and FIG. 8 shows values obtained by computer simulation under the measurement conditions used in the simulation of FIG.

FIG. 9 shows the standard deviation of the estimated values when a plurality of measurements are performed in a short time and only a certain number of large measured values are taken out and the average value is used as the estimated value. This value was obtained by computer simulation under the same conditions as in FIG. 6, and the total number of measurements was five times, and the average value of the maximum N of them was the estimated value. Assuming that the average value of the maximum of two or three of the five detected values is the estimated value, the standard deviation of the error, that is, the variation is the smallest.

FIG. 10 shows the estimation error of the estimation error in the case where the measurement value measured lower than the maximum value or the average value by a certain value or more is rejected and the average value of the remaining measurement values is used as the estimation value. Shows the standard deviation. This means that, of the five measurements, the measured values that are lower than the maximum value (solid line in the figure) or the average value (dashed line in the figure) by the cutoff level on the horizontal axis are rejected and the average of the remaining measured values is rejected. The standard deviation of the estimation error when the value is used as the estimated value is obtained by simulation. The truncation level “infinity (∞)” is an average of all measured values, that is, an estimated value by a conventional method. The effect of truncation is recognized, albeit slightly.

[0035]

As described above, when the reception level measuring circuit of the present invention estimates the average reception level based on the level measurement in a short time, the remaining measurement values excluding the low reception level measurement values are estimated. Is estimated by As a result, the variation is smaller than in the case where all the measured values are averaged. If the measurement time is long, the average or the median of all the measured values is used as the estimated value. For this reason, a highly accurate estimated value can be obtained both when the measurement time is short and when the measurement time is long.

Therefore, according to the present invention, the time from when the power of the mobile device is turned on until communication becomes possible can be reduced, and the serviceability can be improved. Further, in the channel switching during communication, it is possible to maintain the same accuracy as before.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention;
FIG. 2 is a diagram showing a configuration example in which a reception level measurement circuit is provided in a mobile device.

FIG. 2 is a diagram showing a flow of control by an arithmetic circuit.

FIG. 3 is a diagram showing a cumulative probability distribution of a Rayleigh distribution.

FIG. 4 is a diagram showing a standard deviation of an estimated value when a maximum measured level among measured levels within a certain time is used as an estimated value and when an average value is used as an estimated value.

FIG. 5 is a diagram showing an example of channel switching that is effective using a maximum measurement level as an estimated value.

FIG. 6 is a diagram showing standard deviations of estimated values when a mean value is used as an estimated value and when a maximum value is used as an estimated value for levels obtained by a plurality of measurements.

FIG. 7 is a diagram showing an example of channel switching in which measurement of an instantaneous reception level is repeated.

FIG. 8 is a diagram showing correction values for the simulation shown in FIG. 6;

FIG. 9 is a diagram showing the standard deviation of estimated values when a plurality of measurements are performed in a short time, only a certain number of large measured values are taken out, and the average value is used as the estimated value.

FIG. 10 shows the standard deviation of the estimation error when a measured value measured lower than a maximum value or an average value by a certain value or more from a plurality of detection values is rejected, and the average value of the remaining measured values is used as an estimated value. FIG.

[Explanation of symbols]

 Reference Signs List 1 antenna 2 duplexer 3 receiver 4 transmitter 5 synthesizer 6 reception level measurement circuit 7 control circuit 8 handset 10 sampling circuit 11 level detection circuit 12 arithmetic circuit 13 random access memory 14 clock generation circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-313770 (JP, A) JP-A-3-226126 (JP, A) JP-A-4-213238 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H04B ^7/ 24-7/26 102 H04Q ^7/ 00-7/38

Claims (3)

(57) [Claims] 1. A reception level measuring means for detecting a signal reception level measurement value of a wireless receiver as an electric signal, capturing the electric signal over time t, performing an arithmetic processing on the electric signal, and outputting the result as a reception level measurement result. in the reception level measurement circuit and a calculating means for, in said calculating means is held for a predetermined time t _0, the measured value when the time t is t <t ₀ is omitted following data predetermined value the A reception level measurement circuit comprising means for calculating a measurement result. 2. The arithmetic means according to claim 1, wherein said time t is t ≧ t.
_2. The reception level measurement circuit according to claim 1, further comprising means for calculating the measurement result without omitting a part of the measurement value when the value is ₀ . 3. The reception level measuring circuit according to claim 1, wherein said predetermined value is adaptively determined by an electric signal taken over said time t.