JP2786391B2 - Multi-level phase modulation / demodulation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-level phase modulation / demodulation system used in a direct spread modulation type spread spectrum communication system.

[0002]

2. Description of the Related Art In recent years, spread spectrum communication has been applied to not only military and satellite communications but also industrial and consumer equipment due to the development of LSIs and the like. Particularly in the United States and the like, the use of cellular type mobile communication is being considered, and attention is being paid to it. Application to wireless LANs and the like is also expected in Japan. Among them, a direct spreading modulation method for spreading data by a spreading code called a spreading signal is an LSI.
Each research institute is developing it because it is possible to measure distance by checking the ease of configuration and correlation time.

[0003] Hereinafter, a communication method of the conventional direct spread modulation type spread spectrum communication will be briefly described.

FIGS. 6 (a) and 6 (b) are block diagrams of transmission and reception circuits of a direct spread type spread spectrum communication system using a conventional four-phase modulation system (hereinafter referred to as QPSK).

[0005] On the transmitting side in FIG. 1A, an input signal is first converted to a QPSK symbol signal to be mapped to a QPSK symbol signal.
The data is input to the K encoder 101 and is converted into a data sequence for each of two symbols, I and Q. Those data strings are mod
Multipliers 103i and q of ulo2 multiply the signals from the corresponding spreading code generators 104i and 104q and send the result to the next orthogonal modulator 109. Here, a pseudo noise sequence (PN code) is often used as the spread signal, and the spectrum of the transmission data is spread by the spread signal. The quadrature modulator 109 is a portion surrounded by a dotted line in FIG.
The phase of the signal from the local oscillator 107 and π / 2
The signals are mixed with each other and added by the adder 108. Thereafter, the signal of the second local oscillator 111
At 0, it is converted to a carrier band and transmitted from antenna 112.

On the receiving side shown in FIG. 1B, a signal from an antenna 113 is converted into a first local oscillator 115 by a mixer 114.
And converts it to an intermediate frequency band. The converted signal is the signal of the second local oscillator and the same
At 17, the signals subjected to the π / 2 phase shift are converted into I and Q baseband signals by mixers 116 i and q. The frequency conversion of the orthogonal signal into a baseband signal is referred to as orthogonal detection, and is referred to as an orthogonal detection unit 118.
Thereafter, the correlation value of the data signal is obtained by the spread code generators 121i and q that generate the same spread code as that of the transmission side.
9 is the carrier frequency of the transmitting side (in this example, the first frequency of the transmitting side).
(A value obtained by adding the second local oscillation frequency) rarely coincides with each other, so that a rotation phenomenon on a data phase plane occurs. Therefore, in order to decode the data, the correlation is obtained using the four correlators 120a to 120d, the phase rotation angle and the like are obtained in the phase detection circuit 701, and the data is decoded while the frequency offset is compensated in the QPSK data decoder 702. I do.

[0007]

However, in the above-mentioned conventional configuration, the phase detection circuit and the QPSK data decoder based thereon are complicated, and
When the transmission rate is increased, there is a problem that the processing speed of the circuit is easily limited.

The present invention solves the above-mentioned problems of the prior art. In the case of the same transmission speed as that of the prior art, the decoding unit can be configured with a simple circuit configuration without expanding a required band, and a frequency offset compensation circuit is provided. Good characteristics can be obtained even without it. Therefore, the characteristics of the multiplexing which is a characteristic of the spread spectrum communication system can be improved. Further, the signal processing circuit can perform processing at about half the speed of the QPSK modulation method.

[0009]

In order to achieve the above object, the present invention provides a data sequence encoded for each symbol of a multi-level phase modulation system, the data sequence having a phase corresponding to the phase difference of the multi-level phase modulation system. Differential BPSK (hereinafter D) at different carrier frequencies
BPSK) or BPSK modulation, synthesis and transmission. On the receiving side, the signal after the quadrature detection is converted into a BPSK signal by a correlator output signal.
It is characterized by delay detection or BPSK detection.
Means for calculating and compensating for the phase rotation angle due to the frequency offset from the corresponding correlator output from the correlator output, and further combining using the corresponding correlation values in i and q to cope with the rotation on the phase plane. Can be combined.

[0010]

According to the present invention, since the baseband decoding at the receiving unit in the direct spread spectrum communication can be signal-processed by the BPSK decoding even in the case of the multi-level modulation method, the present invention makes it possible to perform signal processing. Can be simplified and the processing speed can be reduced. Then, to reproduce the original data sequence, B
The PSK-based decoded data sequence may be decoded again by the used coding method. Therefore, the effect of simplification increases as the number of values increases. In the BPSK differential detection, highly reliable data decoding close to that of a synchronous detection system of a multilevel phase modulation system can be performed under the conditions described later. Further, the phase rotation angle based on the frequency offset is obtained from the corresponding correlator output to correct the frequency of the receiving local oscillator, or to return the phase rotation of the data at the time of decoding to determine the data, thereby obtaining the frequency offset. Compensation can be made. Here, because of the rotation on the phase plane, for example, the correlator output on the reception I side corresponding to the spreading code i becomes 0 when the phase angle is π / 2 or π, and the correlation of the corresponding IQ When the frequency offset is compensated by adding the outputs of the devices, a circuit (separation by conditions) when no addition is performed can be omitted, so that the circuit can be further simplified, and the effect is further enhanced.

[0011]

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.

FIGS. 1A and 1B are block diagrams of a transmission (spreading unit) and a receiving circuit (despreading unit) of a direct spread spectrum spread communication system corresponding to a QPSK modulation system in an embodiment of the present invention. FIG.

In FIG. 1A, reference numeral 101 denotes an encoder for converting an input signal into a data sequence for each of two symbols I and Q, and reference numerals 102i and q denote a data sequence which is an output of the encoder 101. The differential encoders 103i, q are multipliers for mixing the respective input signals with the spread signals from the spread code generators 104i, q. 109 is a quadrature modulator, through the multiplier 103i and the output of the mixer 105i mixing the signal of the first local oscillator 107, a multiplier 103 q of the output signal a [pi / 2 phase shifter 106 of the first local oscillator 107 Mixer 105 q , mixers 105 i , 105 for mixing the extracted signals
It comprises an adder 108 for adding both outputs of q . 110 is a mixer for mixing the output of the quadrature modulator 109 and the signal of the second local oscillator 111, and 112 is an antenna.

In the above configuration, an input signal shown in FIG. 1A is first input to an encoder 101 for mapping to a QPSK symbol signal, and is converted into a data sequence for each of two symbols, I and Q. . After these data strings are differentiated in the differential encoder 102, they are multiplied by spreading signals from the corresponding spreading code generators 104i, q in the modulo 2 multipliers 103i, q, and the next quadrature modulator It is sent to 109. In the quadrature modulator 109, the signals from the first local oscillator 107 are mixed by the mixers 105i and q with the signal obtained by π / 2 the phase of the same signal. This is DBPSK modulation on the phase plane, and is added by the adder 108. The spectrum of this signal is similar to that of QPSK modulation. After that, the signal is converted into a carrier band by the mixer 110 by the signal of the second local oscillator 111 and transmitted from the antenna 112.

On the other hand, in FIG. 1B, reference numeral 113 denotes an antenna for inputting a signal transmitted from the antenna 112;
14 is the input signal to be demodulated from the antenna 113 and the first
The mixer mixes the signal of the local oscillator 115. 1
18 is a quadrature detection unit, and the mixer 116i, signal a signal output and the second local oscillator 119 of the mixer 114 via the [pi / 2 phase shifter 117 for mixing the signal of the output and the second local oscillator 119 of the mixer 114 It is constituted by a mixer 116 q mixing. 120a to 120d are mixers 1
16i, 116 outputs a spread code 121i of q, 121 q
, A reference numeral 122i, q denotes a BPSK differential detection unit, and a reference numeral 123 denotes a QPSK decoder.

In the above configuration, the signal converted into the intermediate frequency band by the mixer 114 is converted into a baseband signal by the quadrature detector 118 on the receiving side in FIG. Thereafter, the data signal is obtained by using four correlators 120a to 120d as in the conventional example. Here, BPSK delay detection is performed using the correlator outputs V1 and V3, and V2 and V4, respectively (BPSK delay detection). Circuit 122),
The signals corresponding to the I data stream and the Q data stream are detected. At this time, the output of each correlator changes as the phase rotates due to the frequency offset, so that the output of the correlator is detected while processing such as switching (for example, V1 and V3). After that, the transmission data is decoded using the QPSK decoder 123.

As described above, in this embodiment, transmission data is QPSK
Although transmission and reception are performed like modulation, the actual detection method is orthogonally multiplexed DBPSK modulation, which has advantages such as being more resistant to frequency offset than the QPSK system.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows a QP similar to that of the first embodiment shown in FIG.
The receiving unit of the direct spread type spread spectrum communication system corresponding to the SK modulation system is different in that a frequency offset compensation circuit is added.

In the figure, a phase detection circuit 124 for detecting the phase rotation angle is provided for the output of the correlator, and the phase rotation angle is calculated.
FIG. 7A shows a method of detecting the phase after compensating the phase at the time of the BPSK delay detection, and FIG. 7B shows a method of controlling the oscillation frequency of the first local oscillator 115 and compensating for the frequency offset. In both cases, wider offset compensation can be performed.

Although the first local oscillator 115 is controlled in the embodiment shown in FIG. 2B, it goes without saying that the second local oscillator 119 has the same effect.

Embodiment 3 Hereinafter, a third embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram of a transmitting unit of the direct spread spectrum spread communication system of the QPSK modulation system and a receiving unit using the method of the present invention.

FIG. 6A is the same as the transmission system in the conventional QPSK modulation system (FIG. 6A), and the description is omitted.

FIG. 2B shows a configuration equivalent to that of FIG. 2B. In the configuration of FIG. 2B, BPSK detection is performed once with each spread code to the I / Q signal in transmission at the time of decoding. , Are QPSK decoded. Then, the phase detection circuit 123 detects the phase rotation angle from the output from the correlator 120,
The BPSK detection circuit 125 performs phase compensation as frequency offset compensation.

Although not shown here, the oscillation frequency of the first or second local oscillator 115 or 119 is controlled by the output signal of the phase detection circuit 124 as in the second embodiment.
It goes without saying that the same effect is obtained even when the frequency offset is compensated.

(Embodiment 4) Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a view for explaining a method of compensating for frequency offset compensation. FIG.
7A and 7B are diagrams for explaining the phase rotation of the correlator output on the side, and FIG. 7B is a block diagram of a decoding unit when performing phase compensation.

FIG. 3A shows the correlator 120 according to the first embodiment.
The outputs for outputs V1 and V3 of a and c are indicated by points Ri. The angle θ of this point with respect to the V1 axis is the absolute phase angle when there is a frequency offset. The phase detector 123 detects this angle and calculates the amount of rotation. When the angle becomes π / 2, the output V1
Becomes "0", and the other output signals must be decoded in different cases depending on conditions. Thus, in this example, the output signals of the correlators forming a pair are added to form a decoding signal.

FIG. 2B is a block diagram of a receiving system below the correlator 120. The BPSK differential detector 1 according to the first embodiment is shown in FIG.
22 that are provided adder 126i, 126 q are different before. With this configuration, a special case is not required, and the receiving unit can be further simplified.

FIG. 5 shows an example of characteristics when the configuration of the third embodiment is used. FIG. 1A shows a conventional DQPSK.
In the state where there is no frequency offset in the system, FIG. 12B shows an example in which frequency correction is performed.
It can be seen that the BER characteristic is higher than that of the related art, and the frequency deviation of about ± 15% (with respect to the symbol rate) is improved by almost one digit even without frequency offset compensation. Also, when frequency offset compensation is performed, the BER characteristic becomes almost flat up to about ± 15% of the symbol rate, which indicates the effectiveness of the present method. The above characteristic examples clearly show the effectiveness of the present embodiment, and the receiving circuit can be simplified.

In the above embodiment, the local oscillators are replaced by the first and second local oscillators.
However, it goes without saying that the same effect can be obtained even if the number is increased to one or increased depending on the situation of the communication system.

[0033]

As described above, according to the present invention, a data sequence encoded for each symbol of a multi-level phase modulation system is modulated by a DBPSK modulation method using carrier frequencies having different phases according to the phase difference of the multi-level phase modulation system. Then, they are combined and transmitted. On the other hand, on the receiving side, the signal after quadrature detection is subjected to BPSK delay detection or BPSK detection by the corresponding correlator output signal, and the phase rotation angle due to the frequency offset is obtained from the corresponding correlator output to obtain the reception local oscillator. The frequency offset can be compensated by correcting the frequency of the data or by returning the phase rotation of the data at the time of decoding to determine the data. Further, in order to cope with the rotation on the phase plane, a combination with a decoding means using a signal obtained by adding the corresponding correlation values at i and q is also possible.

According to the present invention, the baseband decoding in the direct spread spectrum communication using the multi-level modulation method can be signal-processed by the BPSK decoding method by the above configuration, so that the circuit of the receiving section is simplified. In addition to performing frequency offset compensation, more reliable data communication can be performed. Therefore, multiplexing, which is a feature of spread spectrum communication,
This results in improved characteristics.

[Brief description of the drawings]

FIG. 1A is a block connection diagram of a transmission circuit of a direct spread spectrum spread communication system corresponding to a multi-level phase modulation system according to a first embodiment of the present invention. FIG. 1B is a block connection diagram of the reception circuit.

FIG. 2A is a block diagram of a receiving circuit of a direct spread spectrum spread communication system corresponding to a multilevel phase modulation system according to a second embodiment of the present invention; FIG. 2B is a block diagram of the receiving circuit;

FIG. 3A is a block diagram of a transmission circuit of a direct spread spectrum spread communication system corresponding to a multi-level phase modulation system according to a third embodiment of the present invention. FIG. 3B is a block diagram of the reception circuit.

FIG. 4A is a conceptual diagram illustrating a method of compensating for frequency offset compensation in a multi-level phase modulation system of the present invention. FIG. 4B is a direct spread type corresponding to the multi-level phase modulation system in a fourth embodiment of the present invention. Block connection diagram of receiver circuit for spread spectrum communication

5A is a diagram showing a C / N-BER characteristic in the embodiment; FIG. 5B is a diagram showing a frequency offset characteristic in the embodiment;

6A is a block connection diagram of a transmission circuit of a direct spread spectrum spread communication system using a conventional QPSK modulation system, and FIG. 6B is a block connection diagram of the same reception circuit.

[Explanation of symbols]

 Reference Signs List 101 QPSK encoder 103 Multiplier of modulo 2 104, 121 Spreading code generator 105, 110, 114, 116 Mixer 106, 117 π / 2 phase shifter 107 Transmitter first local oscillator 108 Adder 109 Quadrature modulator 111 Transmitter 111 2 local oscillators 112, 113 Antenna 115 Receiving first local oscillator 119 Receiving second local oscillator 118 Quadrature detector 120 Correlator 122 BPSK delay detector 123 QPSK decoder 124 Phase detector 125 BPSK detector 126 Adder 701 Phase Detection circuit 702 QPSK data decoder

────────────────────────────────────────────────── (5) References JP-A-5-114894 (JP, A) US Patent 5,103,459 (US, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 13 / 00

Claims (4)

(57) [Claims] At the transmitting side, an input signal is in quadrature with an in-phase component.
And convert it to a data string for each two symbols
And a first encoder that differentiates the data stream of the in-phase component.
And a differential encoder for differentiating the data stream of the orthogonal component
The second differential encoder and the output of the first differential encoder are expanded.
A first spreading code generator for outputting a first spreading signal to be scattered
And a second spreading means for spreading the output of the second differential encoder
A second spreading code generator for outputting a signal;
The output of the dynamic encoder and the output of the first spreading code generator
A first multiplier for mixing and an output of the second differential encoder
And a second signal for mixing the output of the second spreading code generator
A multiplier, an output of the first multiplier, and the second multiplier
The quadrature modulation section that performs quadrature modulation by inputting the output of
The output of the quadrature modulator and the first local transmission signal are input and transmitted.
A first mixer for generating a transmission signal and outputting a transmission signal
The receiving side receives the transmission signal using a transmitting antenna.
A receiving antenna for receiving and generating a received signal;
Signal and the second local transmission signal to input the intermediate frequency signal.
And a second mixer for outputting the intermediate frequency signal.
Two baseband signals of in-phase component and quadrature component
And a quadrature detector for outputting the same spread signal as the first spread signal.
A third spreading code for outputting a third spreading signal having a spreading code
A generator and a second signal having the same spreading code as the second spreading signal.
A fourth spreading code generator that outputs a fourth spreading signal;
Input of baseband signal of in-phase component and third spread signal
A first correlator for outputting a first correlation value,
Input the baseband signal of the component and the fourth spread signal
A second correlator for outputting a second correlation value;
Input of the baseband signal and the third spread signal
A third correlator that outputs a correlation value of
Input the baseband signal and the fourth spread signal to form a fourth phase signal.
A fourth correlator that outputs a correlation value;
The third correlation value is input and the first BPSK differential detection is performed.
BPSK differential detection unit, the second correlation value and the fourth
BPSK delay detection by inputting the correlation value of
An SK delay detector and an output of the first BPSK delay detector;
And input the output of the second BPSK differential detection unit
By using a decoder that decodes data,
A multi-level phase modulation / demodulation method characterized by performing scatter-type spread spectrum communication . 2. The receiving section further comprising a first correlation value and a second correlation value.
Phase detection that detects the amount of phase rotation by inputting the correlation value of 3
A second local oscillation signal using the phase rotation amount.
Or the phase rotation amount is changed between the first and second
2 to the BPSK differential detection unit
And perform compensation at the time of BPSK differential detection,
Features spread-spectrum spread-spectrum communication
The multi-level phase modulation / demodulation method according to claim 1 . 3. The transmitting side converts an input signal into an in-phase component and a quadrature signal.
And convert it to a data string for each two symbols
A first encoder for spreading the data stream of the in-phase component
A first spreading code generator for outputting a spreading signal;
A second signal for outputting a second spread signal for spreading the component data sequence
2, a spreading code generator, a data string of the in-phase component,
A first multiplier for mixing with an output of a first spreading code generator
And the orthogonal component data sequence and the second spreading code generation.
A second multiplier for mixing the output of the multiplier and the first multiplier
The output of the multiplier and the output of the second multiplier
A quadrature modulation section for performing modulation, and an output of the quadrature modulation section and a first
A first transmitter for receiving a local transmission signal and generating a transmission signal;
And a transmitting antenna for outputting a transmitting signal.
The receiving side receives the transmission signal and generates a reception signal
Receiving antenna, said received signal and a second local transmitted signal
Second mixer for inputting a signal and outputting an intermediate frequency signal
And the in-phase component and the quadrature component
A quadrature detection unit that outputs two baseband signals:
A third spreading signal having the same spreading code as the first spreading signal;
A third spreading code generator for outputting a second spreading code;
Output a fourth spread signal having the same spreading code as the signal
4 and a baseband signal of the in-phase component.
Signal and the third spread signal are input and a first correlation value is output.
A first correlator, and a baseband signal of the in-phase component.
A fourth spreading signal is input and a second correlation value is output;
2 correlator, the baseband signal of the quadrature component and a third
And outputs the third correlation value
A correlator, a baseband signal of the quadrature component and a fourth extension
A fourth correlation for inputting a scattered signal and outputting a fourth correlation value
Inputting the first correlation value and the third correlation value
A first BPSK detector for detecting BPSK by
BPSK detection by inputting the correlation value of
A fourth BPSK detector for performing the first BPSK detection
And the output of the second BPSK detector
A decoder for performing data decoding by using a first correlation value and a third phase
And a phase detector that detects the amount of phase rotation by inputting
And the receiving unit uses the phase rotation amount to perform a second
Compensating for the local signal or the phase rotation
To the first and second BPSK detectors,
By compensating the components at the time of BPSK detection,
It features direct spread spectrum spread communication.
Multi-level phase modulation and demodulation system to be. 4. A receiving unit, further comprising: a first correlation value;
The third sum for obtaining the sum with the third correlation value and outputting the first sum signal
1 and the sum of the second correlation value and the fourth correlation value is calculated.
And a second adder for outputting a second sum signal.
Instead of inputting the first and third correlation values, the first
Is input to a first BPSK differential detection unit and
Instead of entering the second and fourth correlation values, the second
Whether the sum signal is input to the second BPSK delay detector,
Instead of entering the first and third correlation values,
The first sum signal is input to a first BPSK detector and
Instead of inputting the second and fourth correlation values, the second
Is input to the second BPSK detector.
To perform direct spread-spectrum spread spectrum communication.
4. The multi-level phase modulation / demodulation method according to claim 1, wherein: