JP2001094506A - Fsk receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reception by a system in which plural stations performs simultaneous transmission over the same channel even in a reception area wherein transmitted waves from plural transmitting stations are superposed and interfere with each other. SOLUTION: When an equi-field interference state detecting means 105 detects FSK signals sent from multiple transmitting stations being superposed with nearly equal levels and different delay time differences and receive signals being in an interference state, an interference-caused position specifying means 105 specifies the position of an interference-caused symbol by using an AM detection signal, an interference-caused symbol specifying means 107 specifies which of '0' and '1' the symbol being interferred with is, and a symbol data replacing means 108 replaces the symbol at the specified position with a specified symbol to reduce the error of the specific symbol affected by the interference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention mainly relates to FSK (F
The present invention relates to an FSK receiver in a system where modulated signals are transmitted simultaneously from a plurality of transmitting stations at substantially the same frequency.

[0002]

2. Description of the Related Art In recent years, various mobile communication systems have become widespread with advances in wireless communication technology, miniaturization and low power consumption of communication terminals, and reduction in communication charges. Among them,
Paging systems are widely used, taking advantage of their features such as simple message communication using ultra-small terminals with long battery life and high transparency that can be received even inside buildings.

[0003] Paging system standards include:
The POCSAG method and the FLEX-TD method are known, and are each ARIB standard (RCR STD-4).
2, 43) are disclosed. In a paging system, generally, the same transmission data is FSK-modulated and transmitted simultaneously from a plurality of transmitting stations in the same frequency channel.
A method of simultaneous transmission of a plurality of stations on the same channel is adopted.

With reference to FIG. 4, a paging system based on the FSK modulation method and a configuration and operation of a receiver thereof will be briefly described as an example of a conventional simultaneous transmission method for a plurality of stations on the same channel.

[0005] The transmission data to the pager terminal 410 generated by the control station 401 is supplied to a plurality of transmission stations 403 a and 403 b via the network 402.
Here, the number of transmitting stations is two. In each transmitting station, the supplied transmission data is FSK-modulated and transmitted with the same transmission channel and the same timing.

In the pager terminal 410, the channel transmitted from the transmitting stations 403a and 403b is selectively received by the receiving frequency converting means 411 and frequency-converted.
The frequency-converted signal is subjected to FSK detection in FSK detection means 412, and the detected signal is subjected to symbol determination in symbol determination means 413, and is output as a received symbol data sequence. According to the contents of the received symbol data string, processing such as sounding and message display is performed.

Here, a plurality of transmitting stations 403a, 403b
When the pager terminal 410 is located in an area where the transmission waves from the transmission waves are superimposed and received, if the difference between the reception levels of the respective transmission waves is large, the influence of the mutual interference is hardly affected as a feature of the FSK modulation method. However, when the difference between the two reception levels is small, a mutual interference caused by the reception phase difference between the transmission waves causes a dead area where reception is impossible. In order to prevent this, a known transmission frequency offset technique may be adopted.

That is, each of the transmitting stations 403a, 403a,
By slightly offsetting the transmission frequency in 03b, a beat is generated in the received wave to be superimposed, and the reception level in a specific area is prevented from constantly falling.

As described above, in a system such as a paging system that employs a simultaneous transmission system of a plurality of stations, a device is devised so that reception is possible even in an area where transmission waves from a plurality of transmission stations are superimposed. ing.

[0010]

However, in the conventional paging system as shown in FIG. 4, when the following conditions are overlapped, reception sometimes becomes difficult. This is a case where the difference between the reception levels of the transmission waves from both transmitting stations is small, and the optical path difference is large, causing a time delay that cannot be ignored in the transmission symbol timing. FIG. 5 shows an example of changes in instantaneous frequencies f1, f2, instantaneous phases θ1, θ2, and phase difference Δθ of transmission waves from both transmitting stations under such a situation. Thus, if a time delay occurs in the symbol switching timing, a phenomenon occurs in which the phase difference Δθ between both transmission waves changes according to the symbol data to be transmitted.

Depending on the relationship between the phase of each transmission wave and the amount of time delay, the phase difference Δθ may be in the opposite phase at the time of one symbol data (here, when the data is “1”). Then, a phenomenon occurs in which the transmission waves cancel each other, and the reception level drops. Under such circumstances, the reception error rate of one of the symbol data is extremely deteriorated, and the reception becomes impossible.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problem in a system using the FSK modulation method and the simultaneous transmission method for a plurality of stations on the same channel, and transmission waves from a plurality of transmission stations are superimposed. It is an object of the present invention to enable reception at a receiving terminal even in a reception area where mutual interference occurs.

[0013]

In order to achieve this object, an FSK receiver according to the present invention comprises a receiving frequency converting means for selectively receiving an FSK modulated signal and outputting a frequency-converted signal; FSK detection means for performing FSK detection and outputting an FSK detection signal, symbol determination means for performing symbol determination on the FSK detection signal, and outputting a determined symbol data sequence, and AM detection for a signal output from the reception frequency conversion means. , An AM detection means for outputting an AM detection signal, and a signal output from the reception frequency conversion means as inputs, and signals transmitted from a plurality of transmitting stations are superimposed at substantially the same level and with different delay time differences. Using the equal electric field interference state detecting means for detecting whether or not an interference state exists and the AM detection signal output from the AM detection means, the influence of interference To identify the position of the received symbol,
Interfered position specifying means for outputting interfered position information, and an interfering symbol for specifying a correct symbol at the position of interference based on the symbol data sequence and the interfered position information when an equal electric field interference state is detected. A symbol data replacement unit that replaces the symbol data at the interfered position identified by the interfered position identification unit with the symbol identified by the interfered symbol identification unit and outputs the symbol data to the symbol data sequence. Is provided.

According to the present invention, when the received FSK signal is in an interference state, the symbol affected by the interference and its position are specified by using the detection output of the AM detection means, and if it is correct. By replacing the estimated symbol data, errors in the received symbol data can be reduced, and FSK modulated signals can be received even in an environment of mutual interference due to superposition of transmission waves from multiple stations. Becomes

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention relates to a system in which FSK (Frequency Shift Keying) modulated signals are simultaneously transmitted from a plurality of transmitting stations on the same frequency channel. Receiving frequency conversion means for selectively receiving the modulated signal and outputting a frequency-converted signal, FSK detection means for detecting a signal output from the reception frequency conversion means, and outputting an FSK detection signal; Symbol determination, symbol determination means for outputting the determined symbol data sequence, AM detection of the signal output from the reception frequency conversion means, AM detection means for outputting an AM detection signal, and the reception frequency conversion means The output signal is input, and the signals transmitted from the plurality of transmitting stations are superimposed at substantially the same level and with different delay time differences, and the received signal is There an equal electric field interference state detecting means for detecting whether a interference condition, with AM detection signal output from said AM detection means,
The position of the symbol affected by the interference is specified, and the interference position specifying means for outputting the interference position information, and when the equal electric field interference state is detected by the equal electric field interference state detecting means, the symbol data sequence Based on the interfered position information, an interfered symbol identifying unit that identifies a correct symbol at the position where interference has occurred, and a symbol at the interfered position identified by the interfered position identifying unit for the symbol data sequence. Symbol data replacing means for replacing the data with the symbol specified by the interfered symbol specifying means and outputting the data. When it is detected that an equi-field interference state is detected, the AM of the received signal is Using the detection output signal, the position of the symbol affected by the equal electric field interference and its symbol data are specified, and it is estimated that the symbol is correct. Replacing the symbol data, an effect that.

According to a second aspect of the present invention, there is provided the FSK receiver according to the first aspect, wherein:
Is provided with the threshold value determination means of
The M detection signal has an effect that a position of a symbol lower than a predetermined threshold value is output as interfered position information.

According to a third aspect of the present invention, there is provided an FSK receiver according to the first aspect, wherein:
Symbol appearance frequency counting means for counting the appearance frequency of each symbol except for the symbol data at the interfered position determined by the interfered position specifying means in the symbol data sequence output from the symbol determining means; The frequency counting means is provided with a minimum frequency symbol judging means for outputting the smallest symbol among the count results for each symbol by the frequency counting means, and has an effect of specifying a symbol affected by the equal electric field interference.

According to a fourth aspect of the present invention, there is provided an FSK receiver according to the first aspect, wherein:
Using a signal output from the reception frequency conversion unit, a reception level measurement unit that measures and outputs a reception level for each symbol, and a fluctuation range of the reception level measured by the reception level measurement unit is predetermined. A first level fluctuation detecting means for outputting fluctuation range increase information when the threshold value is exceeded, and has an operation of outputting the fluctuation range increase information as isoelectric field interference state detection information. .

According to a fifth aspect of the present invention, an input signal to the reception frequency conversion means is used as an input to the reception level measurement means in the FSK receiver according to the fourth aspect, instead of an output signal of the reception frequency conversion means. This has the effect that the reception level is measured using the signal at the input stage of the reception frequency conversion means.

According to a sixth aspect of the present invention, there is provided an FSK receiver according to the first aspect, wherein:
An AM detection signal output from the AM detection means is input instead of the output signal of the reception frequency conversion means, and an equal electric field is generated when a fluctuation width of each symbol of the AM detection signal exceeds a predetermined threshold. A second level fluctuation detecting means for outputting interference state detection information is provided.
It has the effect of detecting the presence of interference by an equal electric field using the output signal of the detection means.

According to a seventh aspect of the present invention, in the FSK receiver according to the first aspect, the FSK-modulated signal is a signal obtained by performing FSK modulation on data which has been error-correction-coded or error-detection-coded in advance. Instead of the interfering symbol identification means and the symbol data replacement means,
A symbol generation unit that sequentially outputs all symbols mapped by modulation, and a symbol data sequence output from the symbol determination unit when an equal electric field interference state is detected by the equal electric field interference state detection unit. The operation of replacing the data of the single or multiple interfered positions specified by the position specifying means with the symbols output from the symbol generation means and performing error correction is performed on all the symbols output from the symbol generation means. And an error correction trial means for sequentially outputting an error-corrected data sequence, and when the error correction trial means attempts error correction, no error occurs or the likelihood is highest in the error correction. Selection means for selecting and outputting a high data string, which is affected by isoelectric interference. The symbol data at the position estimated to be replaced with each symbol mapped by FSK modulation in order, and an error correction is attempted, and a data string in which no error occurs or the likelihood is high is demodulated and decoded. As an output.

According to an eighth aspect of the present invention, there is provided an FSK receiver according to the first aspect, wherein:
In addition to the reception level measurement means and the level fluctuation detection means, an average reception level measurement means for outputting a value obtained by averaging the reception level of the reception signal over a section sufficiently longer than the symbol length as an average reception level; A second threshold value judging means for outputting high reception level judgment information when a predetermined threshold value is exceeded, and an increase in the fluctuation width is outputted by the level fluctuation detecting means, and the second threshold value is outputted. The value judging means is provided with a judging means for outputting the equi-electric field interference state detection information only when the high reception level judgment information is outputted, and the equi-electric field is obtained only when the level of the received signal is sufficiently high. This has the effect of performing interference state detection and symbol data replacement processing.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG.

(Embodiment 1) FIG. 1 shows a configuration of an FSK receiver according to a first embodiment.
The SK receiver 100 is a receiver of a system in which FSK-modulated signals are simultaneously transmitted from a plurality of transmitting stations on the same frequency channel. Here, FSK modulation is binary FSK.
This is modulation.

The receiving frequency conversion means 101 is a binary FSK
The modulation signal is selectively received, frequency-converted and output, and is composed of, for example, an antenna, a low-noise amplifier, a filter, a mixer, a local oscillator, etc., and has an intermediate frequency (IF).
It is assumed that a signal converted to a signal is output. FSK detection means 102 detects the binary FSK modulated signal,
It outputs a detection signal. For example, it is assumed that quadrature detection is performed on a binary FSK modulation signal converted into an IF signal. The symbol determination means 103 performs symbol determination on the binary FSK detection signal and outputs the determined symbol data sequence. For example, the symbol determination is performed on the detection signal by positive / negative determination, and the symbol data sequence represented by 1, 0 Output.

The AM detection means 104 detects an input signal by AM and outputs an AM detection signal, and is constituted by, for example, a means for detecting an input signal by envelope detection. The equal electric field interference state detecting means 105 determines whether the received FSK modulated signal is in the equal electric field interference state, that is, whether the transmission signals from the plurality of transmitting stations are superimposed at substantially the same level and with a delay time difference. It is to detect and output detection information, and is configured by, for example, a reception level measuring means 105a and a level fluctuation detecting means 105b.

The receiving level measuring means 105a measures and outputs the level of each IF symbol signal section. The level fluctuation detecting means 105b outputs fluctuation range increase information as detection information of the equal electric field interference state when the level fluctuation width of the reception level in each symbol data section exceeds a predetermined threshold value. .

The interfered position specifying means 106 specifies the position of a symbol affected by interference between signals transmitted from a plurality of transmitting stations (hereinafter referred to as isoelectric interference). 106a. The threshold value judging means 106a outputs information when the input AM detection signal is lower than a predetermined threshold value as interference position information.

The symbol-to-be-interfered specifying means 107 specifies symbols affected by the isoelectric field interference. In the present embodiment, of the symbols “1” and “0” of the binary FSK modulation signal, whether the symbol affected by the equal electric field interference is “1” or “0” is specified. , Symbol appearance frequency counting means 107a and minimum frequency symbol determination means 107b. The symbol appearance frequency counting means 107 a outputs the symbol “1” except for the data at the position determined to be interfered by the interfered position specifying means 106 in the symbol data sequence output from the symbol determining means 103.
The appearance frequency of each “0” is counted.
The minimum frequency symbol determination means 107b specifies the interference symbol using the count result of the symbol appearance frequency counting means 107a, and the detailed operation will be described below.

The symbol data replacing means 108 replaces the symbol data string determined by the symbol determining means 103 with the symbol data at the position identified as the interfered position by the interfered position identifying means 106, Is output after replacing the symbol data specified in.

The receiving operation in the normal state in the FSK receiver configured as described above is the same as the operation in FIG. Here, an operation in a state where transmission waves from a plurality of transmitting stations are superimposed at substantially the same level and with a delay time difference (equivalent electric field interference state) will be described below.

The AM detector 104 performs AM detection of the binary FSK signal converted into the IF signal, and outputs a detected signal. Normally, in a state where there is no interference, the FSK modulation signal has a constant envelope, but when transmission waves from a plurality of transmitting stations are superimposed at substantially the same level and with a delay time difference, depending on the phase difference between the transmission waves. , The phases of the two arriving waves are canceled with opposite phases only for a specific symbol,
A fall in the envelope occurs. Therefore, a drop occurs in the AM detection signal in this portion.

This drop is determined by the interference position specifying means 10.
6 is specified by the threshold value judging means 106a.
If the equal electric field interference state detecting means 105 estimates that the electric field is in the equal electric field interference state, the symbol appearance frequency counting means 107a causes the symbol position Except for the data at the position specified to have been received, the appearance frequency (N1,
N0) is counted.

Here, assuming that a portion corresponding to the symbol "1" is affected by the isoelectric interference, the appearance frequency N of the symbol of the portion which is not specified as the position to be interfered is assumed.
For 0 and N1, N0≫N1.

In the minimum frequency symbol determination means 107b,
The magnitude of the two values N0 and N1 counted earlier is determined, and the one with the smaller value is identified as a symbol affected by isoelectric interference. In this case, N1 is smaller, and symbol "1" is specified as a symbol affected by interference. Symbol data replacement means 1
In step 08, the symbol data at the interfered position specified by the interfered position specifying means 106 in the symbol data sequence output from the symbol determining means 103 is replaced with the symbol “1” and output.

As described above, according to the embodiment of the present invention, when a state in which a specific symbol is affected by isoelectric field interference is detected, the position of the affected symbol and the symbol are specified. By performing the replacement, it is possible to reduce errors and receive the received signal.

In this embodiment, the reception level measurement means 105a for measuring the level of the IF signal output from the reception frequency conversion means 101 is provided as the equal electric field interference state detection means 105. The present invention is not limited to this. For example, a configuration may be adopted in which the detection signal in the AM detection unit 104 is supplied to the level fluctuation detection unit 105b.
Further, the configuration is such that an IF signal is used as an input to the reception level measuring means 105a.
Instead of the F signal, a configuration may be adopted in which the reception level of the received FSK modulation signal is directly measured.

(Embodiment 2) FIG. 2 shows a configuration of an FSK receiver according to a second embodiment.
The input FSK modulated signal 200 is subjected to error correction coding or error detection coding in advance,
This is a modulated signal. In this embodiment, it is assumed that a parity code is added after BCH encoding.
The FSK modulation is binary FSK modulation.

The symbol generation means 201 sequentially outputs all the symbols mapped by the FSK modulation. In the present embodiment, the symbols "0" and "1" are output.
Are sequentially output. Error correction trial means 2
02 repeats several times the operation of trying the error correction after replacing the symbol at the interfered position with the symbol data sequence output from the symbol determination means 103. The detailed operation is described below. State.

The selection means 203 is provided for the error correction trial means 20.
2, the most reliable result is selected from among the several error correction results tried and output as a received data string. The detailed operation will be described below.
The other configurations and operations in FIG.
It is the same as FIG. 1 except that is removed.

The operation of the FSK receiver configured as described above, which is different from that of the first embodiment, will be described below. In the error correction trial unit 202, in the symbol data sequence output from the symbol determination unit 103, all symbols at positions identified as being affected by the equal electric field interference by the interfered position identification unit 106 are first set to “0”. "
And performs BCH error correction processing, and outputs an error correction result.

Next, BCH error correction processing is performed by replacing all the symbols replaced with "0" earlier with "1".

Here, assuming that the symbol affected by the isoelectric field interference is "1", if the symbol is replaced with "0", the bit error becomes very large, so that the error correction is performed. It is not performed normally and an error is detected at the time of parity check.

On the other hand, when it is replaced with "1",
Since the error correction processing is performed after the bit error caused by the equal electric field interference is almost corrected, the error correction decoding is normally performed, and there is a high possibility that there is no error even during the parity check. The selecting unit 203 selects and outputs the data sequence having the normal parity check result as the received data sequence.

As described above, according to the embodiment of the present invention, the process of replacing the symbol at the position specified as being affected by the equal electric field interference with the assumed symbol and performing the error correction decoding process Is repeated, and the data sequence in which the error correction is normally performed is selected, so that reception can be performed with reduced errors even under the influence of the equal electric field interference.

In this embodiment, the BCH code is used as the error correction code and the parity code is used as the error check code. However, the present invention is not limited to this. May be configured to use a metric value at the time of Viterbi decoding as a criterion for selection in. Further, a configuration using only the error check code without using the error correction code or a configuration using only the error correction code may be used.

(Embodiment 3) FIG. 3 shows a configuration of an FSK receiver according to a third embodiment.
The equal electric field interference state detecting means 301 detects whether or not there is an equal electric field interference state, and includes a receiving level measuring means 302, a level fluctuation detecting means 303, an average receiving level measuring means 304, a threshold value judging means 305, Judgment means 30
6. The reception level measuring means 302 is the same as the reception level measuring means 105a in FIG.

The level fluctuation detecting means 303 is the same as the level fluctuation detecting means 105b in FIG. The average reception level measuring means 304 outputs a value obtained by averaging the reception level of the reception signal over a section sufficiently longer than the symbol length as an average reception level. The threshold value determination means 305 outputs high reception level determination information when an input signal exceeds a predetermined threshold value. The determining means 306 determines whether or not the apparatus is in the isoelectric interference state, and details of the operation will be described below. Other configurations and operations in FIG. 3 are the same as those in FIG.

In the FSK receiver configured as described above, the operation other than the detection of the isoelectric field interference state is the same as that of the first embodiment. Hereinafter, the operation of detecting the equi-electric field interference state will be described.

As in the first embodiment, the reception level measuring means 302 and the level fluctuation detecting means 303 measure the reception level for each symbol of the received signal, and the fluctuation width is set to a predetermined threshold value. If it exceeds, output fluctuation range increase information. Here, when the average reception level of the FSK modulated signal to be received is weak, when measuring the reception level for each symbol, the level fluctuation for each reception symbol becomes large due to the influence of noise. In some cases, the level fluctuation detecting means 303 outputs fluctuation range increase information.

The average reception level measuring means 304 averages the reception level for each symbol measured by the reception level measurement means 302 over a sufficiently long section, and outputs an average reception level which does not depend on the fluctuation for each symbol.

When the average reception level exceeds a predetermined threshold, the threshold determination means 305 outputs high reception level determination information. Judgment means 30
In step S6, the equal field interference state detection information is output only when the fluctuation level increase information is output from the level fluctuation detection means 303 and the high reception level determination information is output from the threshold value determination means 305.

As described above, according to the embodiment of the present invention, the detection of the equal electric field interference state is performed only when the average reception level is high. The fluctuation range of the level increases, and it becomes possible to prevent the erroneous detection of the equal electric field interference state,
It is possible to receive with reduced errors.

In the present embodiment, the average reception level measuring means 304 averages the measurement results of the reception level measuring means 302. However, the present invention is not limited to this. Alternatively, the average level of the input signal may be directly measured over a long section.

[0055]

As described above, according to the present invention, FSK-modulated signals are transmitted from a plurality of transmitting stations at substantially the same frequency and interfere with each other at substantially the same level and with a delay time. In the case of reception, the reception sensitivity of the FSK detection output is replaced by using the AM detection output by utilizing the characteristic that the reception level of the specific symbol drops and the error is likely to occur, thereby improving the reception sensitivity. .

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an FSK receiver according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an FSK receiver according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of an FSK receiver according to a third embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing an example of a conventional paging system and an FSK receiver.

FIG. 5 is a waveform diagram showing an example of a superimposed wave of a plurality of transmission waves in an equal electric field interference state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Receiving frequency conversion means 102 FSK detection means 103 Symbol determination means 104 AM detection means 105 Isoelectric field interference state detection means 106 Interfered position specifying means 107 Interfered symbol specifying means 108 Symbol data replacing means

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04Q 7/12 H04L 27/14 Z H04L 27/14 27/26 (72) Inventor Makoto Hasegawa Kawasaki-shi, Kanagawa Matsushita Giken Co., Ltd., 3-10-1 Higashi-Mita, Tama-ku (72) Inventor Hiroshi Katayama 4-3-1 Tsunashimahigashi, Kohoku-ku, Yokohama, Kanagawa Prefecture F-term in Matsushita Communication Industrial Co., Ltd. 5K004 AA04 ED05 EH03 5K059 BB01 CC02 CC04 EE02 5K067 AA03 BB22 CC12 EE02 HH22 HH25

Claims (8)

[Claims] In a system in which FSK-modulated signals are simultaneously transmitted from a plurality of transmitting stations on the same frequency channel, reception frequency conversion means for selectively receiving and frequency-converting the FSK-modulated signals, and The signal output from the reception frequency conversion means is subjected to FSK detection and FS
FSK detection means for outputting a K detection signal, symbol determination means for symbol-determining the FSK detection signal and outputting a symbol data sequence determined, and AM detection for a signal output from the reception frequency conversion means. AM detection means for outputting a detection signal, and a signal output from the reception frequency conversion means as inputs, and signals transmitted from the plurality of transmission stations are superimposed at substantially equal levels and with different delay time differences. Using an equal electric field interference state detecting means for detecting whether or not an interference state is present, and an AM detection signal output from the AM detection means, specifying a position of a symbol affected by the interference, The interference position specifying means for outputting information, and when the equal electric field interference state is detected by the equal electric field interference state detecting means, the symbol data sequence is An interfering symbol identification unit that identifies a correct symbol at the position of interference based on the interfered position information, and symbol data at the interfered position identified by the interfered position identification unit with respect to the symbol data sequence. And a symbol data replacing means for replacing the symbol with the symbol specified by the interfered symbol specifying means and outputting the symbol. 2. The method according to claim 1, wherein the interference detection position identification means includes a first threshold value determination means for outputting, as interference position information, a position of a symbol whose input AM detection signal is lower than a predetermined threshold value. The FSK receiver according to claim 1, wherein the FSK receiver is provided. 3. An interfering symbol specifying unit that determines the appearance frequency of each symbol except for the symbol data at the interfering position specified by the interfering position specifying unit in the symbol data sequence output from the symbol determining unit. A symbol appearance frequency counting means for counting, and a minimum frequency symbol judging means for outputting a smallest symbol as an interfered symbol among counting results for each symbol in the symbol appearance frequency counting means, are provided. 2. The FSK receiver according to 1. 4. A receiving level measuring means for measuring and outputting a receiving level for each symbol by using a signal output from a receiving frequency converting means as an isoelectric field interference state detecting means, and measuring by the receiving level measuring means. Level variation detection means for outputting variation range increase information when the variation range of the received level exceeds a predetermined threshold value, and detecting the variation range increase information as an equal electric field interference state. 2. The FSK receiver according to claim 1, wherein the FSK receiver outputs the information. 5. An input signal to said reception frequency conversion means, not an output signal of said reception frequency conversion means, as an input to said reception level measurement means.
FSK receiver described 6. An equal-electric-field interference state detection means, which receives an AM detection signal output from an AM detection means instead of an output signal of a reception frequency conversion means, and sets a fluctuation width of the AM detection signal for each symbol in advance. Second output of equal electric field interference state detection information when exceeding a predetermined threshold value
2. The FSK receiver according to claim 1, further comprising a level fluctuation detecting means. 7. An FSK modulation signal is obtained by converting data that has been previously subjected to error correction coding or error detection coding into FSK.
It is assumed that the signal is a modulated signal. Instead of the interfering symbol specifying means and the symbol data replacing means, a symbol generating means for sequentially outputting all symbols mapped by FSK modulation, and an equal electric field detecting means for equal electric field interference state detecting means. When the interference state is detected, in the symbol data string output from the symbol determination means, the data of the single or plural interfered positions identified by the interfered position identification means is output from the symbol generation means. Error correction trial means for repeating the operation of replacing the symbols and performing error correction for all the symbols generated by the symbol generation means, and sequentially outputting the error-corrected data sequence; and No error occurred when error correction was attempted in FS according to claim 1, wherein Tsu data string selected by the characterized in that a selection means for outputting
K receiver. 8. As the equal electric field interference state detecting means, in addition to the receiving level measuring means and the level fluctuation detecting means, a value obtained by averaging the receiving level of the received signal over a section sufficiently longer than the symbol length is output as an average receiving level. Average receiving level measuring means, a second threshold value determining means for outputting high receiving level determination information when the average receiving level exceeds a predetermined threshold value, and the level fluctuation detecting means. A step of outputting the isoelectric field interference state detection information only when the fluctuation range increase information is output and the second threshold value determination means outputs the high reception level determination information. The FSK receiver according to claim 1, wherein: