JPH09130436A - Demodulator in digital modulating system and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a demodulator which is capable of exactly performing the decision of a code word. SOLUTION: This device is provided with a frequency detector 2 detecting the frequency of a modulation signal, phase detectors 3 and 4 detecting the phases of modulation signals, and a decoder 5 converting the signal into a preliminarily set cord word based on the frequency and phase detection results, performing the maximum likelifood decision of the converted cord word and decoding digital data based on the decision result. When the valid phase detection results can not be obtained by the phase detector 3 and 4, the decoder 5 sets phase candidates and converts them into the cord words and the decoder refers to the cord word having the possibility of being converted by the combinations of the frequency and plural phase candidates based on the detection result of the frequency detector 2 when the maximum likelihood decision is performed by using the converted cord words.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulation apparatus and a demodulation method in a digital modulation system by a hybrid of M-ary multi-valued frequency shift keying (M-ary FSK) and phase shift keying (PSK), and more specifically, Is M-ary for primary modulation
The present invention relates to a demodulation device and a demodulation method in a spread spectrum (hereinafter referred to as SS) modulation method that employs a frequency hopping (hereinafter referred to as FH) method for secondary modulation in the FSK / PSK method.

[0002]

2. Description of the Related Art This type of SS communication system is strong against interference and
It has signal concealment and excellent characteristics such as high resolution lateral distance, and is used in the fields of satellite communication and land communication. In recent years, application to mobile communication, premises communication and the like has been further advanced by utilizing expected utilization efficiency of frequencies and coexistence with existing systems.

Typical systems for realizing SS communication include a direct spread (hereinafter referred to as DS) system and an FH system. The DS method is a method of spreading an occupied frequency band to a high band by directly performing a balanced modulation on a spread code signal with respect to a data signal modulated by a carrier. The FH method is a method that uses a wide occupied frequency band by switching the carrier of a data signal according to a spreading code.

For the primary modulation in the FH system, a multi-level FS for generating a frequency corresponding to each code after encoding
K, PS that performs phase modulation corresponding to each code after encoding
K, M-aryFSK that changes the frequency periodically with a pattern corresponding to each code after encoding, and further M-aryFSK
/ PSK etc.

A typical example of the FH-multilevel FSK system is "Frequency-Hopp" by DJ Goodman et al.
ed Multilevel FSK for Mobile Radio ”, The Bell Sys
temTechnical Journal, Vol. 59, No. 7, p1257 ~ p127
5, 1980. The M-ary FSK method is an improvement of the multi-level FSK, and as a representative one, Eimori Moriyama et al., "Outline and Basic Characteristics of Frequency Hopping Communication Experimental Equipment for Land Mobile", Radio Research Institute Quarterly Report,
Vol. 32, No. 164, p165 to p177, 1986.

The M-aryFSK / PSK system is based on the M-aryFS
This is to obtain a further improvement in frequency utilization efficiency by combining the PSK system with the K system as a base. less than,
M-ary FSK using 2 types of frequency and 2 types of phase
The / PSK method will be described as an example.

As shown in FIG. 13, the transmitter includes an encoder 4
1, code word frequency generator 42, code word phase modulator 4
And a secondary modulator 50 having an address generator 45, a hopping frequency generator 46, a 2.4 GHz band frequency generator 47, and two frequency mixers 48, 49. There is.

The encoder 41 converts the binary data signal shown in FIG. 16 (a) into a code in k (k = 2 in this case) bit unit as shown in FIG. 16 (b). Then, each code is converted into a code word as shown in FIG. 16C using the code word conversion table T1 shown in FIG.
The code word conversion table T1 is 2 ^K (in this case, 2 ² =
4) It has a code word corresponding to each type of code, and each code word is
It is composed of multiple numbers called codeword chips. For example, 2-bit data "1,0" is converted into a code "2" by primary encoding, and the code "2" is converted into a code word "2,3,0" by the code word conversion table T1. To be done.

Next, the encoder 41 uses the frequency / phase conversion table T2 shown in FIG. 15 to determine the frequency / phase corresponding to each codeword chip forming the codeword, and to output the determined frequency data. The included frequency control signal is output to the code word frequency generator 42, and the phase control signal including the determined phase data is output to the code word phase generator 43. The frequency generator 42 generates a tone signal based on the frequency control signal and outputs the tone signal to the phase modulator 43. The phase modulator 43 modulates the phase of the tone signal from the frequency generator 42 based on the phase control signal. In this way, as shown in FIG. 16D, the tone signal, which is a matrix of frequency phase slots and time slots in codeword units, is used as the primary modulation signal in the first frequency mixer of the secondary modulator 50. It is output to 48. FIG.
(E) is a waveform diagram showing a primary modulation signal.

The hopping frequency generator 46 outputs a hopping frequency signal corresponding to the address signal output from the address generator 45 (this signal is fixed for each communication channel) to the first frequency mixer 48. Output. The first frequency mixer 48 mixes the primary modulation signal and the hopping frequency signal to generate an intermediate frequency spread spectrum signal. The second frequency mixer 49 mixes the intermediate frequency spread spectrum signal and the 2.4 GHz band local oscillation signal output from the 2.4 GHz band frequency generator 47 to generate a transmission spread spectrum signal,
It is transmitted via the antenna 51.

As shown in FIG. 17, the receiver includes a primary demodulator 64 having a frequency detector 61, a phase detector 62, and a decoder 63, an address generator 65, hopping frequency generators 66, 2. A 4 GHz band frequency generator 67 and a secondary demodulator 70 having two frequency mixers 68 and 69 are provided.

The transmission spread spectrum signal received via the antenna 71 is mixed with the local oscillation signal by the first frequency mixer 69 and then filtered by the first filter (not shown) to form the intermediate frequency spread spectrum signal. Become. The intermediate frequency spread spectrum signal is
After being mixed with the hopping frequency signal by the second frequency mixer 68, the signal is filtered by a second filter (not shown) to obtain a signal as shown in FIG.
It becomes a reception tone signal as the next demodulation signal.

The frequency detector 61 is shown in FIGS.
As shown in FIG. 8 (c), the frequency f0 or the frequency f1 of the reception tone signal is detected for each time slot, and the detection result is output to the decoder 63. The phase detector 62 detects the phase of the reception tone signal that has passed through the frequency detector 61 for each time slot, and outputs the detection result to the decoder 63.
The decoder 63 uses the frequency / phase conversion table T2 (FIG. 15) to convert the received tone signal into a codeword chip for each time slot based on the detection result of the frequency and the phase.

Further, the decoder 63 sequentially compares, for each time slot, the converted codeword chip and the codeword chips of all the codeword candidates in the codeword conversion table T1. Mark (○), and if they do not match, a space (×) is added.

For example, when the received tone signal is only the desired tone signal, as shown in FIGS. 18D and 19A, the code word chip converted based on the detection of the frequency / phase "f0p0". “0” and codeword candidate “0, 1, 2”
Since it matches the code word chip “0” of, it becomes a mark.
In this way, the time slots are marked in the order of f0p0-f0p1-f1p0.

The decoder 63 then outputs 1 for the mark.
0 points are given to points and spaces, the total point for each code word is calculated, and the code word with the highest total point is determined as the most probable code word. This determination method is called maximum likelihood determination. This maximum likelihood determination is performed because if the desired tone signal and the undesired tone signal are mixed in the received tone signal, inconvenience occurs in the selection of the code word. Undesired tones are various disturbing tones such as noise, other communication signals, and fading.

In the above example, as shown in FIG. 19 (b), the code word candidate "0, 1, 2" has the highest total score of 3 points, so that the code word candidate is the most probable code word. Is determined (FIG. 18 (e)). The decoder 63
The selected codeword is converted into a code by using the codeword conversion table T1, and the code is converted into binary data (see FIG. 1).
8 (f), FIG. 18 (g)).

[0018]

However, in the above-described method of the decoder 63, when the desired tone signal and the undesired tone signal are mixed, it may not be possible to accurately determine the code word. There is a problem. In particular, 1
In the time slot, when the frequency of the desired tone signal and the frequency of the undesired tone signal are detected at the same time and no phase is detected, the decoder 63 selects an arbitrary codeword chip.

For example, as shown in FIG. 20 (a), f1p1
It is assumed that marks are made for each time slot in the order of −f1p1−f1p0 (desired tone is indicated by ◯, undesired tone is indicated by Δ). When the total points for each code word are calculated by giving points according to this mark, as shown in FIG.
Code word candidates “3,2,1”, “2,3,0”,
The total points of "0, 1, 2" are lined up with one point each. Therefore, the decoder 63 arbitrarily selects one of the three codeword candidates and determines the selected codeword candidate as the most probable codeword. Therefore, the code word candidate “0, 1, 2” corresponding to the desired tone
The probability of selecting is 1/3, and there is a possibility of selecting the wrong codeword. In cases other than the above example, the total score of erroneous codeword candidates may exceed the total score of correct codeword candidates, and the incorrect codeword candidate may be selected.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a demodulation apparatus and a demodulation method in a digital modulation system capable of accurately determining a codeword. is there.

[0021]

In order to solve the above-mentioned problems, the invention according to claim 1 is to detect a frequency of a modulated signal, to detect a frequency of the modulated signal, and to detect a phase of the modulated signal, The code word is converted to a preset code word based on the detection result of the frequency and the phase, maximum likelihood judgment of the converted code word is performed, and decoding means for decoding digital data based on the judgment result is provided, When the decoding means cannot obtain an effective phase detection result by the phase detection means, sets a phase candidate and converts the phase candidate into a code word, and performs the maximum likelihood determination using the converted code word. To
The gist of the present invention is to refer to a code word that may be converted by a combination of at least one frequency and a plurality of phase candidates based on the detection result of the frequency detection means.

According to a second aspect of the present invention, the digital data is converted into a preset code word for each predetermined bit unit, and the frequency and the phase are shifted according to the converted code word to generate a modulated signal. A demodulator in a digital modulation system for detecting a frequency of the modulated signal, a phase detecting means for detecting a phase of the modulated signal, a frequency detection result by the frequency detecting means and a phase detecting means. And a decoding means for converting the modulated signal into a code word based on the detection result of the phase by the method, performing maximum likelihood determination of the converted code word, and decoding the digital data based on the determination result, The decryption means
When an effective phase detection result is not obtained by the phase detection means, a phase candidate is set and converted into a code word, and when performing maximum likelihood determination using the converted code word, the frequency detection is performed. The gist is to refer to a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates based on the detection result of the means.

The invention described in claim 3 is the first or second invention.
In the demodulation device according to the item (1), the phase detecting means includes means for detecting a plurality of phases effective for decoding the digital data and a plurality of phases invalid for decoding the digital data, and the decoding means. When the invalid phase is detected by the phase detection means, a plurality of effective phases having an angle close to the angle of the invalid phase is determined as the plurality of phase candidates.

According to a fourth aspect of the present invention, in the demodulation device according to the third aspect, the phase detecting means detects a plurality of first phases effective for decoding the digital data. The gist is that the detection means and a plurality of second detection means for detecting a plurality of phases invalid for decoding the digital data are provided.

According to a fifth aspect of the present invention, in the demodulating apparatus according to any one of the first to fourth aspects, the decoding means, in the maximum likelihood determination, the converted codeword,
Sequentially comparing a plurality of preset codeword candidates, numerically representing whether or not they match each other in units of a plurality of codeword chips each of the codeword and the codeword candidate, When referring to a codeword in the maximum likelihood determination, a numerical value indicating that the codeword chip of the reference codeword matches the codeword chip of the codeword candidate is divided by the number of the plurality of phase candidates. The point is to express it with a value.

According to a sixth aspect of the present invention, in the demodulating apparatus according to the fourth aspect, the decoding means determines the converted codeword and a plurality of preset codeword candidates in the maximum likelihood determination. Are sequentially compared with each other to numerically indicate whether or not they match with each other by a unit of a plurality of code word chips included in each of the code word and the code word candidate, and the second detection means invalidates A different phase is detected and the invalid phase has an angle closer to that of the valid phase,
The effective phase is determined as a first phase candidate, and at least one effective phase having an angle close to that of the first phase candidate is determined as a second phase candidate, and the code word is used in the maximum likelihood determination. , The numerical value indicating that the codeword chip of the reference codeword based on the first phase candidate and the codeword chip of the codeword candidate match, based on the second phase candidate. The gist is to represent the code word chip of the reference code word and the code word chip of the code word candidate with a value higher than a numerical value indicating that they match.

According to a seventh aspect of the present invention, the frequency of the modulation signal is detected and the phase of the modulation signal is detected.
Based on the detection result of the frequency and phase, it is converted into a preset codeword, the maximum likelihood judgment of the converted codeword is performed, and the demodulation method of decoding digital data based on the judgment result When no effective detection result is obtained in the detection, the phase candidate is set and converted into a code word, and when the maximum likelihood determination is performed using the converted code word, based on the frequency detection result. Then, the gist is to refer to a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates.

According to the invention described in claim 1, even when an effective phase detection result is not obtained, the decoding means sets the phase candidate and converts it into a code word, and the converted code word is converted into a code word. The maximum likelihood determination is performed using this. At this time, based on the detection result of the frequency detection means, a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates is referred to. Therefore, even if an undesired tone such as an interfering tone is mixed in the modulated signal, the codeword can be accurately determined.

According to the invention described in claim 2, according to claim 1
When the maximum likelihood determination is performed in the same manner as in the invention described in (1), reference is made to a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates based on the detection result of the frequency detection means. Therefore, the codeword can be accurately determined.

According to the third aspect of the invention, when the invalid phase is detected by the phase detecting means, a plurality of effective phases having an angle close to the angle of the invalid phase are detected by the decoding means. It is determined as a plurality of phase candidates. Therefore, by referring to the code word based on the determined phase candidate, the code word can be accurately determined.

According to the invention described in claim 4, when the invalid phase is detected by the second detecting means, a plurality of effective angles having an angle close to the angle of the invalid phase are detected by the decoding means. The phase is determined as a plurality of phase candidates.

According to the invention described in claim 5, when the codeword is referred to in the maximum likelihood determination, the numerical value indicating that the codeword chip of the reference codeword matches the codeword chip of the codeword candidate is: It is represented by a value divided by the number of a plurality of phase candidates. Therefore, the degree of coincidence between each codeword candidate and the reference codeword is represented as a reference value, so that the codeword can be accurately determined based on the reference value.

According to the invention described in claim 6, when the codeword is referred to in the maximum likelihood determination, the codeword chip of the reference codeword based on the first phase candidate and the codeword chip of the codeword candidate are The numerical value indicating the match is represented by a value higher than the code word chip of the reference code word based on the second phase candidate and the numerical value indicating the match with the code word chip of the code word candidate. Therefore, a reference codeword based on the first phase candidate,
Since there is a difference in the determination result from the reference codeword based on the second phase candidate, the determination of the codeword can be performed more accurately.

According to the invention described in claim 7, when no effective detection result is obtained in the phase detection, a phase candidate is set and converted into a code word, and the converted code word is used. When performing the maximum likelihood determination, a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates is referred to based on the frequency detection result.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

The receiver comprises a frequency detector 2, first and second
Primary demodulator 1 having phase detectors 3, 4 and decoder 5 of
Address generator 65, hopping frequency generator 6
6, a 2.4 GHz band frequency generator 67, and a secondary demodulator 70 having two frequency mixers 68, 69. The primary demodulator 1 corresponds to the primary modulator on the transmitter side that employs the M-ary FSK / PSK method using two types of frequencies and two types of phases. In the present embodiment, the secondary demodulator 70 has the same configuration as that of the conventional example, and therefore the same reference numerals are given and detailed description thereof is omitted.

The frequency detector 2 detects the frequency of the reception tone signal output from the frequency mixer 68 for each time slot. Based on the detection result, the decoder 5 gives a mark (hereinafter, referred to as frequency mark) when either the frequency f0 or the frequency f1 is detected, and gives a space (hereinafter, referred to as frequency space) when not detected. . Two frequency f0, f in one time slot
When 1's are detected at the same time, marks are added for both frequencies f0, f1.

When the received tone signal that has passed through the frequency detector 2 has a level above a predetermined value within a predetermined detection range 0 ± θ, as shown in FIG. The φ1 phase of the received tone signal is detected for each time slot. The second phase detector 4 detects the phase p0 of the received tone signal for each time slot when the received tone signal exhibits a level of a predetermined value or more within a predetermined detection range π ± θ. The decoder 5 gives a mark (hereinafter referred to as a phase mark) when the phase p0 or the phase p1 is detected, and when the phase is not detected (when the phase is outside the detection range 0 ± θ or π ± θ), the space (Hereinafter, referred to as a phase space).

The decoder 5 is shown in FIG. 15 based on the frequency mark and the phase mark as the detection result of the frequency and the phase.
The received tone signal is converted into codeword chips for each time slot using the frequency / phase conversion table T2 shown in FIG. Prior to converting the received tone signal into the code word chip, the decoder 5 determines that one of the two frequencies f0 and f1 is detected at the same time when two frequency marks are detected in one time slot. Is selected, and conversion is performed based on the selected frequency and phase detection result. This is done because it is not known which of the two types of frequencies f0 and f1 is the frequency of the desired tone.

The decoder 5 includes the converted codeword chip,
Each of the codeword chips included in the four types of codeword candidates in the codeword conversion table T1 is sequentially compared for each time slot,
A mark (hereinafter, referred to as a chip mark) is provided when they match and a space (hereinafter, referred to as a chip space) is provided when they do not match.

The decoder 5 gives one point as a judgment numerical value to the chip mark for each time slot. 0.5 points and 0 points are selectively given to the chip space. The 0.5 point is a chip that may be chip-marked with a combination of a frequency and two types of phases not selected when the codeword chip is converted when there are two frequency marks in one time slot. Given for space. This score is a value obtained by dividing the numerical value “1” by the number of phase types (= 2). In this way, numerical weighting is also performed on the two codeword chips corresponding to the combination of the unselected frequency and the two types of phases.
The 0 point is given to each chip space when there is only one frequency mark in one time slot (when the rest is frequency space).

The decoder 5 calculates total points for the four types of codeword candidates, and determines the codeword with the highest total score as the most probable codeword. Then, the decoder 5 converts the selected codeword into a code using the codeword conversion table T1 shown in FIG. 14, and converts the code into binary data.

Next, the operation of the receiver configured as described above will be described. For example, when the desired tone signal and the undesired tone signal are mixed in the received tone signal, FIG.
As shown in (a), the frequency detector 2 causes f1 · f0−f1
・ It is assumed that frequency marks (desired tones are indicated by ○ and undesired tones are indicated by Δ) are assigned to each time slot in the order of f0-f1. At this point, it is not known in practice which frequency is the desired tone or the undesired tone, but it is made clear for convenience of explanation. Further, as shown in FIG. 3B, based on the detection result of the frequency and the phase, f1
It is assumed that chip marks are added to each time slot in the order of p1-f1p1-f1p0.

By the decoder 5, for each time slot,
One point is given as a judgment numerical value for the chip mark (△ or ○). When there are two frequency marks in one time slot, the frequency chip "0" corresponding to the frequency fo and the phase p0 that were not selected when the codeword chip was converted
For the chip space of, 0.5 points are given.
Further, the chip space of the frequency chip "1" corresponding to the frequency fo and the phase p1 is also given 0.5 points. 0 points are given to each of the remaining chip spaces.
In this way, as shown in FIG. 3C, the determination value is obtained for each codeword chip of the four types of codeword candidates, and the total score for each codeword candidate is calculated. In this case, three codeword candidates “3,2,1”, “2,3,0”, “1,”
The total score of "0, 3" is 1 point, but the total score of the remaining codeword candidates "0, 1, 2" is 2, so that the codeword candidate "0, 1, 2" is the most. It is judged as a certain code word.

On the other hand, when the received tone signal is only the desired tone signal, frequency marks are added in the order of f0-f0-f1 as shown in FIG. 4 (a), and as shown in FIG. 4 (b). , F0p0−f0p1−f1p0 in this order, the chip mark is assigned to each time slot. Then, 1 point is given to the chip mark and 0 point is given to the chip space, the total score of each code word candidate is calculated, and the code word candidate “0, 1, 2” having the highest total score is the most. It is judged as a certain code word.

As described above in detail, according to the present embodiment, the following effects can be obtained. (1) When a desired tone signal and an undesired tone signal are mixed in the received tone signal, the undesired tone signal is converted into a codeword chip, and a point (1 point) is given to the codeword chip. Even so, the code word chip corresponding to the desired tone signal is given a score (0.5 point) as a weight based on the frequency detection result of the desired tone signal. Therefore, unlike the conventional method, a difference occurs in the total points of the codeword candidates, and the codeword can be accurately determined.

(2) In the above embodiment, the code word length (the number of code word chips) is set to 3 chips, but the code word length is usually several to ten or more. In this case, as the number of chips increases, the difference between the total points of the codeword candidates also increases, and the codeword can be determined more accurately.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS. The primary demodulator 1 in the present embodiment corresponds to the primary modulator on the transmitter side that employs the M-ary FSK / PSK system using two types of frequencies f0 and f1 and four types of phases p0 to p3. ing. The primary demodulator 1 includes the same frequency detector 2 as in the first embodiment and eight phase detectors (four phase detectors 10 and 1 in the drawing).
(Only shown in figures 1, 12, 17) and a decoder 20.

The first phase detector 10 is the frequency detector 2
As shown in FIG. 6, when the reception tone signal that has passed through the above shows a level equal to or higher than a predetermined value within a predetermined detection range 0 ± θ, the phase p0 of the reception tone signal is detected for each time slot. The second phase detector 11 has a detection range π / 2.
The phase p1 within ± θ is detected, the third phase detector 12 detects the phase p2 within the detection range π ± θ, and the fourth phase detector is the phase within the detection range 3π / 2 ± θ. Detect p3.

The fifth phase detector has detection ranges 0 ± θ and π.
The second phase detector detects the phase φ1 located between the first and second phases, and the sixth phase detector detects the phase φ2 between the detection range π / 2 ± θ and π ± θ and detects the seventh phase. The detector detects the phase φ3 between the detection ranges π ± θ and 3π / 2 ± θ, and the eighth phase detector 17 detects the phase φ4 between the detection ranges 3π / 2 ± θ and 0 ± θ. To detect. The decoder 20 gives a phase mark when any of the phases p0 to p3 and the phases φ1 to φ4 is detected.

The decoder 20 uses the frequency mark and the phase mark to generate the frequency / phase conversion table T shown in FIG.
3 is used to convert the received tone signal into codeword chips for each time slot. In this embodiment, eight codeword chips (0 to 7) are set based on a combination of two types of frequencies (f0, f1) and four types of phases (p0, p1, p2, p3). There is. Then, as shown in FIG. 9, each of the eight types of codeword candidates has seven codeword chips configured so as not to overlap each other on a time slot basis.

The decoder 20 gives one point as a judgment numerical value to the chip mark for each time slot. 0.5 points and 0 points are selectively given to the chip space. 0.5 point is given to a chip space corresponding to the following when there are two frequency marks in one time slot and any one of the phases φ1 to φ4 is detected. That is, a chip mark is made by a combination of a frequency that is not selected when converting the codeword chip and two types of phase candidates (for example, p0 and p1) located on both sides of the detected phase (for example, φ1). Given for possible chip space. 0 point has only one frequency mark in one time slot,
And, when any one of the phases p0 to p3 is detected, it is given to each chip space.

Next, the operation of the receiver configured as described above will be described. Note that the desired tone signal and the undesired tone signal are mixed in the received tone signal, and up to 3 time slots, as shown in FIG. -Frequency marks are assigned to each time slot in the order of f0-f1 and f0-f1. Although not shown, it is assumed that chip marks are added to each time slot in the order of f1p0-f1p0-f0p2 up to 3 time slots. It should be noted that illustration of points after the 3 time slots is omitted.

In the first time slot, when there are two frequency marks and the phase φ1 is detected, as indicated by the asterisk in FIG. 8, the decoder 20 causes the code word chip conversion 0.5 points are given to the chip mark of the frequency chip "0" based on the frequency fo which was not selected at this time and the phase p0 adjacent to the detected phase φ1.
Further, based on the frequency fo and the phase p1 adjacent to the phase φ1, the chip mark of the frequency chip “1” is also
0.5 points will be given. 0 points are given to each of the remaining chip spaces. In this way, the determination value is obtained for each codeword chip of the eight types of codeword candidates, the total score for each codeword candidate is calculated, and the codeword is determined.

As described above, according to the second embodiment, even if none of the four phases p0 to p3 is detected, the phases φ1 to φ1 outside the detection range of the phases p0 to p3 are detected.
Two phase candidates are selected based on the detection of φ4, and a score as a weight is given to the chip space based on the phase candidates. Therefore, similarly to the first embodiment, the codeword can be accurately determined.

(Third Embodiment) Next, a third embodiment will be described with reference to FIGS. The present embodiment is different from the second embodiment in the numerical value of the points given to the chip space.

The decoder 20 selectively gives 0.7 point, 0.3 point and 0 point to the chip space. 0.
7 points are given for the following chip spaces. That is, which of the detected phases (eg, φ1) of the phases φ1 to φ4 is closer to the detection range angle of the two types of phase candidates (eg, p0 and p1) located on both sides of the phase? To be judged. Then, based on the determination, 0.7 points are added to the chip space that may be chip-marked by the combination of the closer phase candidate and the frequency not selected at the time of codeword chip conversion. Is given. Based on the determination result based on the phase angle, 0.3 point is given to the chip space that may be chip-marked by the combination of the phase candidate on the side not close to the phase angle and the frequency.

For example, as shown in FIG. 10, two types of phase candidates p whose angles of the phase φ1 are located on both sides of the phase φ1.
When it is determined that the detection range angle of 0, p1 is closer to the phase p0 side, 0.7 points are given to the chip mark of the frequency chip “0” based on the frequency fo and the phase p0, as shown in FIG. To be Further, 0.3 points are given to the chip mark of the frequency chip "1" based on the phase p1 and the frequency fo on the side not close to the phase angle.

As described above, according to the second embodiment, even if none of the four phases p0 to p3 is detected, the phase φ detected outside the detection range of the phases p0 to p3.
It is determined which one of the detected angles of 1 to φ4 is closer to the angle of the phase detection range of the two phase candidates, and based on the determination result, the chip space corresponding to the phase candidate on the near side is determined. I tried to give a high score. Therefore, similarly to the first and second embodiments, the codeword can be accurately determined.

The present invention is not limited to the above embodiment, but may be carried out as follows. (1) In the third embodiment, a chip that may be chip-marked by a combination of two types of phase candidates and frequencies located on both sides of the phase detected outside the detection range of the phases p0 to p3 Based on the detected phase angle, 0.7 points and 0.3 points are given to the space in order of decreasing angle. The points of this score may be changed to 0.6 and 0.4, or 0.8 and 0.2.

Further, as shown in FIG. 12, all four types are set as phase candidates, and the chip space corresponding to the combination of each phase candidate and frequency is, for example, calculated based on the detected phase angle. 0.5 point, 0.3 point,
You may give 0.2 points and 0 points. Furthermore, 4
For all types of phase candidates, points may be given in proportion to the difference between the detected phase angle and the phase angle of each phase candidate.

(2) In the first embodiment, the M-ary FSK / PS using two kinds of frequencies and two kinds of phases is used.
In the K method, the second and third embodiments, the M-ary FSK / PSK method using two kinds of frequencies and four kinds of phases is embodied, but a plurality of other frequencies and a plurality of phases are used. The present invention may be embodied in the existing M-ary FSK / PSK system.

Inventions other than the claims that can be understood from the above-described embodiment will be described below along with their effects. The demodulation device according to claim 6, wherein the decoding means (20)
Is a numerical value indicating that the codeword chip of the reference codeword based on the first phase candidate and the codeword chip of the codeword candidate match when referring to the codeword in the maximum likelihood determination. , A value higher than a numerical value indicating that the codeword chip of the reference codeword based on the second phase candidate and the codeword chip of the codeword candidate are higher, and the detected invalid A demodulator, which is represented in proportion to a phase angle between a phase and the first and second phase candidates. Even in this case, the maximum likelihood determination can be accurately performed.

[0064]

As described above in detail, according to the present invention, it is possible to accurately determine a code word even when an undesired tone such as an interfering tone is mixed in a modulated signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a receiver according to a first embodiment.

FIG. 2 is an explanatory diagram showing a phase detection range of a phase detector.

FIG. 3 is an explanatory diagram of maximum likelihood determination when a desired tone and an undesired tone coexist.

FIG. 4 is an explanatory diagram of maximum likelihood determination in the case of only a desired tone.

FIG. 5 is a block diagram showing a receiver of the second embodiment.

FIG. 6 is an explanatory diagram showing a phase detection range of a phase detector.

FIG. 7 is an explanatory diagram showing a frequency / phase conversion table.

FIG. 8 is an explanatory diagram showing positions of detected phases.

FIG. 9 is an explanatory diagram of maximum likelihood determination when desired tones and undesired tones coexist.

FIG. 10 is an explanatory diagram showing the positions of detected phases in the third embodiment.

FIG. 11 is an explanatory diagram of maximum likelihood determination when desired tones and undesired tones are mixed.

FIG. 12 is an explanatory diagram of maximum likelihood determination when a desired tone and an undesired tone coexist.

FIG. 13 is a block diagram showing a transmitter.

FIG. 14 is an explanatory diagram showing a codeword conversion table.

FIG. 15 is an explanatory diagram showing a frequency / phase conversion table.

FIG. 16 is an explanatory diagram showing a transmission procedure.

FIG. 17 is an explanatory diagram showing a conventional receiver.

FIG. 18 is an explanatory diagram showing a reception procedure.

FIG. 19 is an explanatory diagram of maximum likelihood determination in the case of only a desired tone.

FIG. 20 is an explanatory diagram of maximum likelihood determination when a desired tone and an undesired tone coexist.

[Explanation of symbols]

2 ... Frequency detector as frequency detecting means 3 ... Phase detector as phase detecting means 5, 20 ... Decoder as decoding means 10, 11, 12 ... Phase detector as first phase detecting means 17 ... Phase detector as phase detector 2

Claims (7)

[Claims] 1. A frequency detection means (2) for detecting the frequency of a modulation signal, a phase detection means (3, 4) for detecting the phase of the modulation signal, and preset based on the frequency and phase detection results. A decoding means (5, 20) for converting the converted code word into a code word, performing maximum likelihood judgment of the converted code word, and decoding digital data based on the judgment result. Is the phase detection means (3,
When the effective phase detection result is not obtained in 4), the phase detection unit sets the phase candidate, converts it into a code word, and performs the maximum likelihood determination using the converted code word, the frequency detecting means. A demodulator which refers to a codeword that may be converted in a combination of at least one frequency and a plurality of phase candidates based on the detection result of (2). 2. A demodulator in a digital modulation system for converting digital data into a preset code word for each predetermined bit unit, and shifting a frequency and a phase according to the converted code word to generate a modulation signal. And frequency detecting means for detecting the frequency of the modulated signal (2)
And phase detection means (3, 4) for detecting the phase of the modulated signal
And converting the modulated signal into a code word based on the frequency detection result of the frequency detection means (2) and the phase detection result of the phase detection means (3, 4), and the maximum likelihood of the converted code word. A decoding means (5, 20) for making a judgment and decoding the digital data based on the judgment result, wherein the decoding means (5, 20) comprises the phase detecting means (3, 20).
When the effective phase detection result is not obtained in 4), the phase detection unit sets the phase candidate, converts it into a code word, and performs the maximum likelihood determination using the converted code word, the frequency detecting means. A demodulator which refers to a codeword that may be converted in a combination of at least one frequency and a plurality of phase candidates based on the detection result of (2). 3. The demodulator according to claim 1 or 2, wherein the phase detecting means (3, 4) has a plurality of phases effective for decoding the digital data and invalid for decoding the digital data. The decoding means (20) comprises means for detecting a plurality of phases, and when the invalid phase is detected by the phase detection means, the decoding means (20) has a plurality of valid angles having angles close to the angles of the invalid phases. Demodulation device, characterized in that a typical phase is determined as the plurality of phase candidates. 4. The demodulating device according to claim 3, wherein the phase detecting means (3, 4) detects a plurality of first phases effective for decoding the digital data.
And a plurality of second detecting means for detecting a plurality of phases invalid for decoding the digital data. 5. The demodulation device according to claim 1, wherein the decoding means (5, 20) is preset with the converted codeword in the maximum likelihood determination. A plurality of codeword candidates are sequentially compared, and whether or not they match each other is numerically expressed in units of a plurality of codeword chips that each of the codeword and the codeword candidate has, and the maximum likelihood determination is performed. When referring to a codeword in, a numerical value indicating that the codeword chip of the reference codeword matches the codeword chip of the codeword candidate is represented by a value divided by the number of the plurality of phase candidates. A demodulator characterized by. 6. The demodulation device according to claim 4, wherein the decoding means (20) sequentially compares the converted codeword with a plurality of preset codeword candidates in the maximum likelihood determination. Then, it is numerically expressed in units of a plurality of codeword chips included in each of the codeword and the codeword candidate whether or not they match, and an invalid phase is detected by the second detection means. And the invalid phase has an angle closer to the angle of the valid phase, the valid phase is defined as a first phase candidate, and at least one of the first phase candidate and the next closest angle is included. If one effective phase is determined as a second phase candidate and a codeword is referred to in the maximum likelihood determination, the first
The codeword chip of the reference codeword based on the phase candidate of,
A numerical value indicating that the codeword chip of the codeword candidate matches the codeword chip of the reference codeword based on the second phase candidate and the codeword chip of the codeword candidate match. A demodulator which is represented by a value higher than a numerical value indicating that. 7. The frequency of the modulated signal is detected, and
The phase of the modulated signal is detected, based on the frequency and phase detection results, converted to a preset code word, the maximum likelihood judgment of the converted code word is performed, and the digital is based on the judgment result. In a demodulation method for decoding data, if an effective detection result is not obtained in phase detection, a phase candidate is set and converted into a code word, and the maximum likelihood judgment is performed using the converted code word. Sometimes, based on the frequency detection result, a demodulation method characterized by referring to a codeword that may be converted by a combination of at least one frequency and a plurality of phase candidates.