JPH0746281A - Differential phase shift keying modulation and demodulation device - Google Patents

Abstract

PURPOSE:To accurately demodulate data by eliminating a phase error due to an intermediate frequency component in the differential phase shift keying modulation and demodulation device. CONSTITUTION:A transmitter S uses a differential coder 2a to apply differential coding to a 1st data series 1 to be sent to generate a 2nd data series, a differential coder 2b applies differential coding to the 2nd data series, applies BPSK modulation to a 3rd data series, executes frequency conversion and power amplification and the result is sent from a transmission antenna 7. A receiver S applies power amplification and frequency conversion to the signal received by a reception antenna 8 and a differential decoding section 11a applies differential decoding to the signal to generate a 4th data series and a differential decoding section 11b applies differential decoding again to the 4th data series. Thus, a phase error due to intermediate frequency component included in the 4th data series is cancelled to obtain the 1st data series.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a differential phase shift keying modulation / demodulation device, and more particularly to improvement of differential encoding and differential decoding systems.

[0002]

2. Description of the Related Art Generally, BPS is used in digital wireless communication.
K (Binary PSK: two-phase PSK), QPSK
(Quadrature PSK: Orthogonal PSK), AS
K (Amplitude Shift Keying:
Amplitude shift keying) FSK (Frequency)
Shift Keying: Frequency Shift Keying, MSK (Minimum Shift Keyi)
ng: minimum shift keying) or the like is used. Among them, BPSK and QPSK have the best error rate characteristics and are considered to be ideal modulation methods. However, in these modulation methods, the phase of the carrier wave is changed to BPSK depending on the data.
0 degree, 180 degree 2 phase, QPSK 0 degree, 90 degree, 1
Since modulation is performed by changing the four phases of 80 degrees and 270 degrees, it is necessary for the receiving side to perform frequency tuning and phase synchronization with the carrier. This requires a feedback loop structure, which increases the circuit size of the receiving device and also requires synchronization time, which makes it unsuitable for bursty communication.

As a method for solving these problems, there is a differential coding modulation method. In principle, this system can be a differential detection system in which a reference carrier wave is not generated in the receiving device, but a carrier wave one symbol before data is used as a reference carrier wave for demodulation.

FIG. 7 is a block diagram showing an outline of the differential phase shift keying modulation / demodulation device as described above. Referring to FIG. 7, this device includes a transmitting device S and a receiving device R. The receiving device S may be the first data series.
Information source 1 generating ₁ (K) and first data sequence d ₁
A differential decoder 27 that differentially encodes (k) and the data one symbol before to generate a _second data sequence d ₂ (k);
A reference carrier generator 29 for generating a reference carrier having an angular frequency ω _C, and a BPS for BPSK-modulating the second data sequence.
K modulator 28, frequency converter 30, RF amplifier 31
And a transmitting antenna 32. The receiving device R includes a receiving antenna 33, a power amplifier 34, and a frequency converter 35.
And a differential decoding unit 36 and an information output unit 37. Since the differential decoding unit 36 multiplies not only the carrier wave but also the data one symbol before, the differential decoding unit 27 in the transmission device preliminarily performs a differential code between one data and the data one symbol before. Send and convert.

FIG. 8 is a block diagram showing an example of the differential encoder 27 shown in FIG. This differential encoder 27
Is a data input terminal Din, a data output terminal Dout,
It includes an EX-OR circuit 38 and a delay circuit 39 composed of a shift register or a flip-flop.

In operation, the output data output from the EX-OR circuit 38 is applied to the data output terminal Dout and the delay circuit 39. Delay circuit 3
9 delays the output data by one data symbol,
-It is given to the input of the OR circuit 38. EX-OR circuit 38
Takes the EX-OR logic of the input data and the data delayed by one symbol. In this way, the input data is differentially encoded.

FIG. 9 is a block diagram showing an example of the differential decoding section 36 shown in FIG. The differential decoding unit 36 includes a data input terminal Din, a data output terminal Dout, a delay circuit 40 including a shift register or a flip-flop, and a multiplier 41.

In operation, the input data is the delay circuit 4
0 and the multiplier 41. The data supplied to the delay circuit 40 is delayed by one symbol of data and then supplied to the multiplier 41. The multiplier 41 multiplies the current input data by the data delayed by one data symbol. In this way, the phase difference between the current data and the data one symbol before is detected.

Next, the operation of the differential phase shift keying modulator / demodulator shown in FIGS. 7 to 9 will be described.

First, the information source 1 generates a data sequence d ₁ (k) to be transmitted. Here, d ₁ (k) is binary data as represented by +1 or −1. This d ₁
After that, (k) is differentially encoded by the differential encoder 27 and becomes d ₂ (k).

The second data sequence d ₂ (k) thus obtained is given to the BPSK modulator 28, and the BPS
The K modulator 28 performs BPSK modulation using the carrier having the angular frequency ω _C from the reference carrier generator 20. The modulated wave thus modulated is designated as c ₁ (t). Where c ₁ (t) is

[0012]

[Equation 1]

It is decided as follows. The c ₁ (t) thus obtained is R by the frequency conversion unit 30.
After being frequency-converted to the F band, power-amplified by the RF amplification unit 31, and transmitted by the transmission antenna 32.

Next, the operation of the receiver R will be described.
The signal received by the receiving antenna 33 is first power-amplified by the power amplifier 34 and frequency-converted to the IF band by the frequency converter 35. The signal here is r ₁
(T)

[0015]

[Equation 2]

It can be expressed as However, here B
(T) represents amplitude, ω _R represents receiver intermediate frequency, and Δθ represents phase. The differential decoding unit 36 differentially decodes this signal. The differential decoding is, as is clear from FIG.
Since this is to multiply by the signal delayed by the time T [sec] for the data symbol, if the output of this differential decoding unit 36 is r ₂ (t),

[0017]

[Equation 3]

It can be expressed as Here, if the high frequency component is removed by a low pass filter and the amplitude component is ignored,

[0019]

[Equation 4]

[0020] If ω _R has a very low frequency and the 2ω _R component shown in equation (3) cannot be removed by a filter or the like, a differential decoding unit as shown in FIG. 10 is used.

Referring to FIG. 10, this differential decoding unit has a terminal Iin to which the in-phase component Iin is input and a quadrature component Qin.
Input terminal Qin, delay circuits 42 and 43, multipliers 44, 45, 46 and 47, adders 48 and 4
Including 9.

In operation, the in-phase component Iin is differentially decoded by the delay circuit 42 and the multipliers 44 and 45.
The quadrature component Qin is differentially decoded by the delay circuit 43 and the multipliers 46 and 47. Multipliers 44 and 47
The outputs of the above are added in the adder 48. The outputs of the multipliers 45 and 46 are subtracted by the adder 49. By performing such processing, the sum component can be corrected.

In the above equation (4), {θ (k) -θ
(K-1)} represents the phase difference between the front and rear data, and if (-
When ω _R T) = 0, information demodulation can be performed using r ₂ (t).

These encoding and decoding processes will be described with reference to FIG. First data sequence d ₁ (t) to be transmitted
Is data as shown in (1) of FIG.
The second data series d ₂ (t) is as shown in (2) of FIG. 11. This second data sequence is subjected to BPSK modulation, so that the phase information θ as shown in (3) of FIG.
(K) is converted and transmitted. The received signal is first subjected to differential detection (differential decoding), the phase difference between the preceding and following data is confirmed, and information such as (4) in FIG. 11 is obtained. This represents the previously described equation (4) {θ (k) -θ (k -1) -ω R T}. Here the phase difference components described above (-ω _R T) = 0
Is calculated as By discriminating this data, the first data series t as shown in (5) of FIG. 12 is obtained.
₁ (t) is obtained.

When the differential coding modulation / demodulation method is used in this way, since the reference carrier is not generated in the receiving device, the reference carrier also contains the same amount of noise and the error rate characteristic is slightly deteriorated. The carrier recovery loop is not required, high-speed synchronization is possible, and the component corresponding to the difference between the preceding and following data is transmitted, which has the advantage of canceling the phase indeterminacy. Therefore, it is a very effective communication method for packet communication.

This system uses a differential BPSK (Differ
initial BPSK: hereinafter referred to as DPSK), differential QPSK (differential QPSK: hereinafter referred to as DQPSK), and other differential coded modulation (D
It is applicable to MSK, DFSK, etc.). These are described in detail in "Digital Communication System" of HBJ Publishing (written by Peyton Z. Peebles, Jr.).

[0027]

In the demodulation process as described above, if the intermediate frequency ω _R is not an integral multiple of the data (ω _R T ≠ 0), the demodulated data {θ (k) -θ
(K-1)} error is added by the carrier wave, if the (omega _R T) is ± 90 degrees or more in the case of BPSK, QPSK
In case of ± 45 degrees or more, an error occurs. In the case of demodulation using quadrature signal, and calculates the phase error component (-ω _R T) from the output of both the I and Q, there is also a method of correcting it, in the case of BPSK In this case |
ω _R T | ≧ 90 degrees, | ω _R T | ≧ 45 in the case of QPSK
When it comes to degrees, it becomes very difficult to correct.

Therefore, an object of the present invention is to demodulate data having no phase error in a differential phase shift keying modulator / demodulator even if the intermediate frequency is not an integral multiple of the data rate.

[0029]

According to a first aspect of the present invention, there is provided a differential phase shift keying modulation / demodulation device comprising a first differential encoding means, a second differential encoding means, and a PSK modulation means. And a receiver including a first differential decoding unit and a second differential decoding unit. The first differential encoding means differentially encodes the first data sequence to be transmitted to generate a second data sequence. The second differential encoding means is the second differential encoding means generated by the first differential encoding means.
Differentially encode the data sequence of 1 to generate a third data sequence. The PSK modulation means performs phase shift keying modulation on the third data sequence generated by the second differential encoding means. The first differential decoding means receives a transmission signal from the transmitting device, differentially decodes the received signal, and
Generate a data series of. The second differential decoding means is the first
Differentially decodes the fourth data series generated by the differential decoding means of (1) to combine the first data series.

[0030]

According to the present invention described above, the transmitter differentially encodes the first data sequence by the first and second differential encoding means to generate the third data sequence. The third data sequence thus generated is PSK modulated. The receiving device receives the PSK modulated signal transmitted by the transmitting device, and differentially decodes the received signal twice. Since the fourth data series is differentially decoded by the second differential decoding means, the difference between the current fourth data series and the fourth data series one symbol before the data is output. Therefore, it is possible to cancel out the intermediate frequency components included in the current fourth data series and the fourth data series one symbol before the data.

[0031]

1 is a block diagram showing a first embodiment of the present invention. With reference to FIG. 1, the modulation / demodulation device includes a transmission device S and a reception device R. Transmitter S
Is an information source 0, a differential encoder 2a, a differential encoder 2b,
A BPSK modulator 3, a reference carrier generator 4, a frequency converter 5, an RF amplifier 6, and a transmission antenna 7 are provided. The reception device S includes a reception antenna 8, an RF amplification unit 9, a frequency conversion unit 13, a differential decoding unit 11a, a differential decoding unit 11b, and an information output unit 12. Comparing the modulation / demodulation apparatus shown in FIG. 1 with the modulation / demodulation apparatus shown in FIG. 5, a differential encoder is added to the transmission apparatus S shown in FIG.
Is added with a differential decoding unit 11b.

Next, the operation of the differential phase shift keying modulator / demodulator shown in FIG. 1 will be described. Data generator 1
Produces a _first data sequence d ₁ (k). This first
Data sequence d ₁ (k) is differentially encoded by the differential encoder 2a to become the second data sequence d ₂ (k). Where d ₂ (k) is

[0033]

[Equation 5]

Is determined as follows. Where k is k
It means that it is the th symbol.

The second data series d ₂ (k) thus obtained is further differentially encoded by the differential encoder 2b to become the third data series d ₃ (k).
This series is

[0036]

[Equation 6]

Is determined to be The third data sequence d ₃ (k) thus obtained is BPSK-modulated by the reference carrier of each frequency ω _c generated by the reference carrier generator 4 in the BPSK modulator 3 to be c (t). Becomes Where c (t) is

[0038]

[Equation 7]

[0039] After this, the BPSK modulated wave c (t)
Is frequency-converted into the RF band by the frequency converter 5 and R
The power is amplified by the F amplification unit 6 and then transmitted from the transmission antenna 7.

Next, the operation of the receiver R will be described.
The received signal received by the receiving antenna 8 is first power-amplified by the power amplifier 9 and then further converted into the frequency converter 10.
Then, the frequency is converted into r ₁ (t). This r
₁ (t) is differentially decoded by the differential decoding unit 11a and becomes r ₂ (t) as shown in the above equation (3).

Then, if the high frequency component of r ₂ (t) is removed by a low-pass filter or the like and the amplitude term is ignored, the phase component represented by the above-mentioned equation (4) is extracted. In this equation (4), which clearly Δθ is erased, uncertainty phase has been removed, (- omega _R T) and remains section entitled, conventional differential phase shift keying modulation scheme Then this section becomes a problem. In other words, this term becomes a phase error, and in the BPS modulation method, this term is ± 90 °.
If it exceeds (± π / 2 rad ·), an error will occur.

In the present invention, after this, the second differential decoding section 11b is passed through again to perform differential decoding, and r ₃
Generate (t). The differential decoding process here is realized by the circuit as shown in FIG. r ₃ (t) is

[0043]

[Equation 8]

Is calculated. These encoding and decoding processes will be described with reference to FIG. First to send
If the data series d ₁ (t) of FIG. 2 is the data shown in (1) of FIG. 2, the second data series d ₂ (t) of FIG.
It becomes like (2). The third data series d ₃ (t) obtained by further differentially decoding this is expressed as (3) in FIG. In order to BPSK-modulate this, the phase information θ (k) as shown in (4) of FIG. 2 is modulated and transmitted. This transmitted signal is the receiving device S
The received signal is received first by differential detection (differential decoding).
Then, the phase between the before and after data is confirmed, and the information as shown in (5) of FIG. 2 is obtained. This is the above-mentioned {θ (k) −θ (k−
Represent 1) -ω _R T}. Here, it is calculated as above-described phase difference component (-ω _R T) = 0.

Thereafter, the differential decoding is performed once more to obtain the information [{θ (k) -θ (k) of (6) in FIG.
-1)}-{θ (k-1) -θ (k-2)}] is obtained.
By discriminating this data, the first data series d ₁ (t) shown in (7) of FIG. 2 is obtained.

[0046] If, - coding in the case of a (ω _R T) ≠ 0, the demodulation process example shown in FIG. In FIG. 3, the coding on the transmitting side is the same as in FIG. 2, but when the phase difference between the preceding and following data is confirmed by differential detection (differential demodulation) on the receiving side (−ω
_R T) = π / 2, which means the case of (5) in FIG. As a result, the stage (5) of FIG. 3 is different from the stage (5) of FIG.
Since (6) and (7) are the same and the transmission data is correctly demodulated, the effectiveness of the present invention can be confirmed.

FIG. 4 is a block diagram showing a second embodiment of the present invention. Referring to FIG. 4, this modulation / demodulation apparatus differs from the modulation / demodulation apparatus shown in FIG. 1 in that BPSK modulation is performed in the embodiment of FIG. 1, whereas QPSK modulation is performed in this embodiment. It is that. Referring to FIG. 4, the transmission device S includes an information source 1 and a P / S converter 1.
3, differential encoder 14a, differential encoder 14b, QPS
K modulator 15, reference carrier generator 16, frequency converter 1
7, an RF amplification unit 18 and a transmission antenna 19 are included. The reception device includes a reception antenna 20, a power amplification unit 21, a frequency conversion unit 22, an orthogonal signal generation unit 23, a differential decoding unit 24a,
The differential decoding unit 24b, the P / S conversion unit 25, and the information output unit 26 are included.

Next, the operation of the differential phase shift keying modulator / demodulator shown in FIG. 4 will be described. First to send
Data series d ₁ (k) of the two data series d ₂ I (k) so that the P / S converter 13 uses them for orthogonal signals.
And d ₂ Q (k) are parallel / serial converted into a second data series. The second data sequence thus obtained is differential QPSK encoded by the first differential QPSK encoder 14a according to the rule as shown in FIG. 12, and the third data sequence d ₃ I (k ) And d ₃ Q (k). The differential encoder 14a is realized by a circuit as shown in FIG. The third data sequence thus obtained is further differentially QPSK encoded by the second differential QPSK encoder 14b, and the fourth data sequence d ₄ I (k) and d ₄ Q (k) is obtained. become. Such a second differential QPSK encoder 14b is also realized by the circuit configuration shown in FIG. 13 as described above. Although the circuit shown in FIG. 13 is conventional, the present invention can be realized by connecting two stages.

Using the fourth data sequence thus obtained, QPSK modulation is performed in the QPSK modulator 15 by the reference carrier of each frequency ω _C generated by the reference carrier generator 16. If the signal here is c (t),

[0050]

[Equation 9]

Represents After that, c (t) is frequency-converted into the RF band by the frequency converter 17 as in the embodiment of FIG. 11, and then power-amplified by the RF amplifier 18 and transmitted by the transmitting antenna 19.

Next, the operation of the receiver S will be described. Also here, the signal received by the receiving antenna 20 is power-amplified by the power amplifier 21 and frequency-converted to the IF band by the frequency converter 22 as in the first embodiment. If the signal thus obtained is r (t),

[0053]

[Equation 10]

It is represented by Where B (t) is the amplitude,
ω _R represents each intermediate frequency, and Δθ represents a phase difference between the transmitting and receiving devices. This signal is divided into I and Q quadrature signals in the quadrature signal generation unit 23, and Iin (k) and Qin
Get (k). this is

[0055]

[Equation 11]

An output that can be expressed as follows is obtained. Conventional DQ
If PSK demodulation, (-ω _RT) is a problem
Therefore, it becomes an error if this term exceeds ± 45 °.

In the present invention, the DOT1 obtained here is obtained.
(K) and CROSS ₁ (k) are differentially QPSK decoded again by the differential decoder 24b. As a result,

[0058]

[Equation 12]

Therefore, the (−ω _R T) term, which has been a problem, disappears, and reliable demodulation is possible.

The encoding and decoding processes up to this point will be described with reference to FIG. First, the first data sequence d to be transmitted
The second data series obtained by serial / parallel conversion of ₁ (t) is as shown in (1) of FIG. Here, the upper row represents the I data series d ₂ I (t), and the lower row represents the Q data series d ₂ Q (t). The third data sequence obtained by differentially QPSK encoding the second data sequence is as shown in (2) of FIG. Here, the upper row is the I data series d ₃ I (t), and the lower row is the Q data series d ₃ Q.
Represents (t). A fourth data sequence obtained by performing differential QPSK coding on this data sequence again is as shown in (3) of FIG. Here, the upper part is the data series d _{4 of} I.
I (t), the lower part represents the Q data series d ₄ Q (t). In order to QPSK-modulate the signal thus obtained, it is converted into phase information θ (k) as shown in (4) of FIG. 5 and transmitted. The received signal is first subjected to differential detection (differential decoding), the phase difference between the preceding and following data is confirmed, and information as shown in (5) of FIG. 5 is obtained. This is the above {θ
Represents a (k) -θ (k-1 ) -ω R T}. here,
Previously mentioned phase difference component is calculated as (-ω _R T) = 0. After this, by performing differential decoding again,
Phase information [{θ (k) -θ (k-
1)}-{θ (k-1) -θ (k-2)}] is obtained. By discriminating this data, the second data series d ₂ I (t) and d ₂ Q (t) shown in (7) of FIG. 5 are obtained.

[0061] If, (- ω _R T) coding in the case of a ≠ 0, is shown in FIG. 6 the demodulation process example. In FIG. 6, the coding on the transmitting side is the same as in FIG. 5, but when the phase between the preceding and following data is confirmed by differential detection (differential demodulation) on the receiving side (−ω
_R T) = _π / 2, and the means when it becomes as shown in FIG. 6 (5). As a result, at the stage of (5) in FIG.
(6) and (7) of FIG. 6 though different from (5) of FIG.
, And the transmission data is correctly demodulated, the effectiveness of the present invention can be confirmed.

[0062]

As described above, according to the present invention, by performing the differential encoding and the differential decoding twice, it is possible to cancel the intermediate frequency component generated during the differential decoding.
Data can be accurately demodulated without reproducing the carrier wave.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a process of encoding and decoding in the differential phase shift keying modulation / demodulation system when ω _R T = 0 in the first embodiment.

FIG. 3 is a diagram showing a process of encoding and decoding in the differential phase shift keying modulation / demodulation system when ω _R T ≠ 0 according to the first embodiment.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a process of encoding and decoding in the differential quadrature phase shift keying modulation / demodulation system when ω _R T = 0 in the second embodiment.

FIG. 6 is a diagram showing a process of encoding and decoding in the differential quadrature phase shift keying modulation / demodulation system when ω _R T ≠ 0 in the second embodiment.

FIG. 7 is a schematic block diagram of a conventional differential phase shift keying modulation / demodulation device.

8 is a block diagram showing an example of the differential encoder shown in FIG. 7. FIG.

9 is a block diagram of the differential decoding unit shown in FIG. 7.

10 is a block diagram showing another example of the differential decoding unit shown in FIG. 7.

11 is a diagram showing a process of encoding and decoding in the differential phase shift keying modulation / demodulation device shown in FIG.

FIG. 12 is a diagram showing differential QPSK encoding conventionally used.

FIG. 13 is a block diagram showing a conventionally used differential QPSK encoder.

[Explanation of symbols]

 1 Information Sources 2a, 2b, 14a, 14b Differential Encoder 3 BPSK Modulator 4, 16 Reference Carrier Generator 5, 10, 17, 22 Frequency Conversion Circuit 6, 18 RF Amplifier 7, 19 Transmission Antenna 8, 20 Receiving antennas 9 and 21 Power amplification units 11a, 11b, 24a and 24b Differential decoding units 12 and 26 Information output units 13 Serial / parallel conversion circuits 25 Parallel / serial conversion circuits

Claims (3)

[Claims] 1. A first differential encoding unit for differentially encoding a first data sequence to be transmitted and generating a second data sequence, the first differential encoding unit generating the second data sequence. And a second differential encoding means for differentially encoding the second data sequence to generate a third data sequence, and third data produced by the second differential encoding means. A transmitter including PSK modulation means for performing phase shift keying modulation on a sequence, a first signal for receiving a transmission signal from the transmitter, differentially decoding the received signal, and generating a fourth data sequence. A differential decoding means, a receiving device including a second differential decoding means that differentially decodes the fourth data sequence generated by the first differential decoding means and combines the first data sequence. Differential phase shift keying modulator / demodulator with 2. The differential phase shift keying modulator / demodulator according to claim 1, wherein the PSK modulator is a BPSK modulator. 3. The differential phase shift keying modulation / demodulation apparatus according to claim 1, wherein the PSK modulation means is a QPSK modulator.