JPS63256021A - Mobile radio equipment having frequency stabilizing function - Google Patents

Abstract

PURPOSE:To attain the extreme high stability for frequencies by providing plural series of receivers and a comparator comparing reception electric field levels of receivers and a changeover switch selecting a receiver giving a maximum reception electric field level according to the result of comparison to give an IF output. CONSTITUTION:The noise of IF output of receivers 1, 2 generated when a reception electric field level is lowered goes to almost timewise independent. In taking notice thereof, the reception level of 2 series of receivers is always compared by a comparator 3.5 and the IF output of a receiver having always a larger level is selected by a switch 3.6, then the IF output with less noise is obtained. Thus, even if the mean value of the reception electric field level of one series is lowered, the noise generated in the IF band caused by momentary decrease in the reception electric field due to Rayleigh fluctuation is increased and the measurement error of the frequency is caused, the frequency mis-measurement due to the noise is suppressed and the accuracy of frequency stabilization is improved.

Description

Detailed Description of the Invention (Industrial Applications) The present invention is applicable to communications that use angular modulation and require extremely small carrier wave drift, such as narrowband mobile communications in the UHF band. The present invention relates to a mobile radio device having a function of automatically controlling a carrier frequency to a predetermined value.

(Prior Art) In communication systems, carrier wave drift significantly degrades transmission quality. Conventional techniques for stabilizing the carrier frequency in a mobile radio device having a multi-channel switching function include: (1) AFC that uses the DC component of a frequency discriminator as frequency control information; (2) AFC that uses the DC component of a frequency discriminator as frequency control information; There are techniques such as applying a PLL to a local oscillator based on this signal. However, these techniques cannot be used in mobile radio propagation paths that are unique to mobile communications and require extremely high carrier frequency stability. As stated in Japanese Patent Application No. Sho 61-168004, it is extremely difficult to apply this method to a communication system that uses the same technology.

Therefore, in Japanese Patent Application No. 61-168004, as a means to solve this problem, we received highly stable base station transmission waves,
A method for accurately measuring the frequency is shown, and patent application 1986-
In No. 168005, we proposed a means to dramatically improve the frequency stability of mobile radio equipment. Figure 1 shows its configuration. The stable base station transmission wave received from the antenna 1.1 is frequency-converted by the receiver 1-2, passed through the IF ratio output noise removal means 1.3, and measured by the frequency counter 1.4. A temperature compensated crystal oscillator (TCXO) 1.5 is controlled by the TCXO control section, and S controls the temperature compensated crystal oscillator (TCXO) 1.5 so that As a result, the frequency synthesizer 1.7 based on the TCXO has frequency stability equivalent to that of the base station.

In addition, in mobile radio equipment that uses 1.7 in common with a transmitting section consisting of modulation @ 1.8, mixer 1.9, and power amplification type 1.10, the base station has a stable transmission frequency stability. Can it be made equivalent to the transmission wave frequency accuracy?

(Problem to be Solved by the Invention) However, in this frequency stabilization circuit configuration, in order to measure one series of reception IF frequencies, Rayleigh fading, which is unique to mobile communications as shown in Fig. 2, occurs. If an attempt is made to measure the frequency of a received wave that has undergone fluctuations in the received electric field, and the median value of the received electric field decreases, the frequency of the noise will be measured instead of the original received wave frequency.

The received electric field fluctuation under Rayleigh fading is several tens of d
For example, if the transmission frequency is 900 MH
If the moving speed of the moving object is 50 km/h in z, the drop in the received electric field due to fading is approximately 40 km/h per second.
Occurs several times. Conventional frequency measurement systems with only one receiver have the disadvantage that when the median value of the received electric field decreases, the frequency of the noise is measured, so the measured frequency does not match the true received frequency. Was. This reduces the frequency stabilization accuracy when performing the frequency stabilization shown in FIG.

The purpose of the invention is to improve the accuracy of frequency stabilization by 7! when the receiving electric field level is low in a mobile radio device used in a communication system using angle modulation, which requires carrier wave drift to be suppressed to an extremely small level. , (The purpose is to solve the drawback of frequency degradation and provide a frequency stabilization circuit with high precision even in a low electric field.

(Means for Solving the Problems) The present invention provides a mobile radio with a plurality of receiving sections (here, for the sake of explanation, two systems), and compares the instantaneous levels of received electric fields under Rayleigh fading. The most important feature is that the IF ratio output of the receiving section with the highest level is always selected, the frequency is measured, and the frequency stabilization operation is performed based on this. The difference from the conventional technology is that the number of receiving units is increased from one system to multiple systems, the frequency of a received wave with a high received electric field level is measured, and frequency stabilization is performed based on this.

(Example) FIG. 3 is a diagram explaining the present invention in detail, &1 is the antenna of the receiver 1, 3.2 is the antenna of the receiver 2, 3.
3 and 3.4 are receivers with outputs of received electric field level 1 and received electric field level 2, respectively, &5 is a received electric field level comparator, and 3.6 is controlled by 3.5 and always has a received electric field level of This is a switch that changes the IF ratio output of a high receiver. The other parts have the same configuration as in FIG. 1.

FIG. 4 will also be used to explain the present invention in detail. 4
．． 1 and 4.2 are the electric field levels of receiver 1 and receiver 2 under Rayleigh fading, respectively. Under Rayleigh fading, if the two antennas are installed with a distance of 174 wavelengths or more of the received waves, there will be almost no correlation in received wave level fluctuations, as shown in Figure 4. The probability that the level has not decreased becomes very large.

Therefore, the received electric field levels 4.1 and 4.2 decrease and ts
At times, the noise generated in the IF ratio outputs of receiver 1 and receiver 2 becomes almost independent in time. Focusing on this,
Comparison 93.5 in Figure 3 always compares the reception level of the receiver in two series, and this is always the highest of the receiver! F ratio output 3.
If you select at 6, it will be shown at 45 in Figure 4! Like the F ratio output, it is possible to obtain an IF ratio output with less noise. Therefore, in the conventional method, the average value of the received electric field level of one series decreases, the noise generated in the IF band due to the instantaneous drop in the received electric field due to Rayleigh fluctuation increases, and frequency measurement errors occur. Even in this case, by adopting the configuration shown in FIG. 3, erroneous frequency measurement due to noise can be suppressed, and the accuracy of frequency stabilization can be improved.

This effect is shown in FIG. The horizontal axis represents the average received electric field level to noise power ratio (CNR), and the vertical axis represents the measurement frequency. (a) is the average value of the measured frequency with the configuration shown in Figure 1, (
b) is the average value of the measured frequencies according to the configuration shown in FIG.

When the CNR (vR transmission to noise power ratio) is high, the IF frequency of the desired wave is accurately measured in any configuration, but as the CNR decreases, the frequency of the noise is measured. The average value of the noise frequency is equal to the center frequency of the IF filter, but the dispersion of the measured frequency in this case is very large, and for example, even if the received CNR can be known, the desired wave frequency cannot be estimated. Therefore, it is necessary to actually measure the IF frequency.

The effects of the present invention can be easily understood by comparing the measurement frequency errors of the conventional method and the present invention. For example, when comparing the reception CNR of the conventional method and the present invention to obtain the point (cl) that causes an error of 100 Hz from the measured frequency of the desired wave, it becomes (di, tel), and the CNR of the present invention is lower than that of the conventional method. It may be lower by 5 dB. Therefore, the measurement accuracy of the reception frequency is improved, and there is an advantage that frequency stabilization can be performed with high precision even in a low electric field.

Furthermore, it goes without saying that methods for further improving frequency measurement accuracy, such as the method for correcting the frequency error from the second IF station, disclosed in Japanese Patent Application No. 18004/1982, can be applied to the present invention. An example of this is shown in FIG. In FIG. 6, the input of the frequency counter 1.4 is intermittently switched to the second local oscillation frequency by the switch SW. The switching is performed under the control of the TCXO control section 1.5.

(Effects of the Invention) As described above, the present invention can be expected to perform highly accurate frequency stabilization even when the received electric field level decreases. In mobile communications, there are two lines of receivers,
A method of performing diversity reception to improve signal transmission quality is becoming popular. If the present invention is applied to such mobile radio equipment, it is possible to achieve ultra-high frequency stabilization, which was previously impossible. This is extremely effective in communication systems that require frequency stabilization, such as mobile communication systems.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a conventional mobile radio having a frequency stabilization function. FIG. 2 is a diagram showing fluctuations in the received electric field in mobile communication. FIG. 3 is a diagram showing an embodiment of the present invention. FIG. 4 is a diagram showing the effects of the embodiment of the present invention in the time domain. FIG. 5 is a diagram quantitatively showing the effects of the embodiment of the present invention. FIG. 6 (Another embodiment of the civil engineering invention. 1.1...Antenna, 1.2...Receiver, 1.3.
...Noise removal means, 1.4...Frequency counter, 1
, 5-TCXOl 1.6-TCXOCX-ray, 1.7... Frequency synthesizer, 1.8... Modulator, 1.9... Mixer, 1.10... Power amplifier, 3.1. ...Antenna 1, 3.2...Antenna 2.3.3...Receiver 1, 3.4...Receiver 2.3.569. Comparator, 3.5...
Switch, 4.1...Electric field level of received wave 1, 4.2...Electric field level of received wave 2, 4.3...Receiver 1! F ratio output 4.4...IF ratio output 4.5 of receiver 2...Selected IF ratio output Patent Applicant: Nippon Telegraph and Telephone Corporation Patent Application Agent

Claims (1)

[Scope of Claims] A receiver capable of measuring a received electric field level, a noise removing means for removing noise in its IF output, a frequency measuring means connected to the output, a reference oscillator, and a A mobile radio device comprising a control section that controls according to the output of the measuring means, and a frequency synthesizer that uses the output frequency of the reference oscillator as a reference and provides a local oscillation frequency to the receiver, wherein a plurality of series of the receivers are provided, The frequency stabilization function is characterized by having a comparator that compares the received electric field level of each receiver, and a changeover switch that selects the receiver that gives the maximum received electric field level according to the comparison result and gives an IF output. Mobile radio with.