JPH06232841A - Synchronism holding device for spread spectrum communication system - Google Patents

Abstract

PURPOSE:To provide a synchronism holding device whose operation is sure and stable at low cost. CONSTITUTION:The device is provided with a spread code generating circuit 28 for demodulation to respectively output a spread code advanced for prescribed chip time and a spread code delayed for prescribed chip time, first and second correlating means MX2 and MX3 for correlating these respective spread codes with an input spread spectrum signal, first and second angle demodulating means 17 and 18 for providing angle demodulated outputs by demodulating the angles of respective correlated outputs, first and second filter means BF5, BF6, 19 and 20 for removing carrier components or the like from the respective angle demodulated outputs, subtracting means 23, D1, D2 and 40 for subtracting the outputs of both filter means, and clock signal generating means 26 and 27 for providing clock signals by converting the provided subtracted outputs to error signals and supplying them to a voltage controlled oscillator. Then, a synchronism holding loop is constituted by generating these two kinds of spread codes by supplying these clock signals to the spread code generating circuit and supplying them to the respective correlating means.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronization holding device in a spread spectrum (hereinafter referred to as "SS") communication system, and in particular, eliminates the need for an AGC (automatic gain control) circuit, which is essential for holding synchronization. Moreover, the present invention relates to a synchronization holding device that enables highly stable synchronization holding operation.

[0002]

TECHNICAL BACKGROUND In recent SS communication (wireless transmission) technology, mobile communication using a multiple access method based on the SS technology has reached a practical range. As is well known, since radio resources are limited, it is necessary to effectively use frequencies. That point, SS
The signal is spread over a wide frequency band and its power spectral density becomes extremely small, which has a small effect on other communications and allows it to be mixed in existing communication frequency bands. In principle, it can contribute to the improvement of frequency utilization efficiency. Recently, the Ministry of Posts and Telecommunications in Japan is also approving a frequency band dedicated to SS communication, and its application is expanding to wireless transmission of audio equipment for business use or household use in the future. Is greatly desired.

[0003]

2. Description of the Related Art In a receiver (demodulation device) for SS communication, synchronization acquisition and synchronization holding during demodulation operation are basically important, and various synchronization acquisition methods and holding methods have been proposed so far. Has been put to practical use. In particular, if the level fluctuation of the SS modulation signal supplied to the demodulation device is too large, it is easy to lose synchronization and it is difficult to hold it. Therefore, connect an AGC (automatic gain control) circuit in the preceding stage of the demodulation circuit, Input SS
It was an essential requirement that the level of the modulation signal be attenuated when it is too high, and that it be amplified when it is low to maintain the level within a predetermined range.

Before describing such a conventional demodulation device and synchronization holding device with reference to the drawings, FIG. Will be explained together. In the figure, 2 is an angle modulation circuit (MOD), 5 is a spread code generator (PN).
G) and BF1 are bandpass filters (BPF), and Mx1 is a multiplier. The angle modulation circuit 2 performs angle modulation, which is a primary modulation, on a modulated signal such as voice or information. The angle modulation includes FM (frequency modulation) and PM (phase modulation).
Especially when the modulated signal is a digital signal, Shift Keyi
It is called ng (shift keying; SK). F for this
(Frequency) SK, P (Phase) SK, M (Minimum) SK
And modulation methods such as GM (Gausian Minimum) SK,
Conventionally, PSK modulation was performed.

The modulated signal S (t) such as voice and information supplied from the input terminal In1 is PSK-modulated by the angle modulation circuit 2 and becomes a primary modulation signal f (t). On the other hand, the clock signal C (t) is supplied from the input terminal In2 to the spread code generating circuit 5,
Here, the spread code Pn (t-τ ₀ ) having the phase τ ₀ is generated and output to the multiplier Mx1 for spread modulation. Therefore,
The multiplier Mx1 multiplies the spread code and the angle modulation output signal f (t) to generate a spread spectrum modulated wave SS (t), and after removing unnecessary frequency components by BPFBF1,
It is output from an antenna (not shown) via the output terminal Out1.

The SS modulated wave is caught by an antenna (not shown) on the receiver side through a transmission medium such as the atmosphere, demodulated by an SS demodulator, and returned to the original voice, information or the like. Hereinafter, regarding the conventional example of the SS demodulator,
As will be described with reference to the block diagram of FIG. 2, most S
The S communication device includes both the configurations of the SS modulator and the SS demodulator of FIG. 1 as a modulator and a demodulator, and in that case, some components such as an antenna and PNG are shared. .

As shown in FIG. 2, the conventional SS demodulation device is as follows.
Three BPFs BF2 to BF4, automatic gain control (AGC) circuit 3
3, spreading code generation circuit (PNG) 28, two multipliers M
x2, Mx3 and envelope detector (Env.DET) 38, 3
9; has a subtraction circuit 40, a loop filter (LF) 26, a voltage controlled oscillator (VCO) 27, etc., and these are connected as shown in the drawing. Of these, BPFBF2
The portion excluding the AGC circuit 33 and the AGC circuit 33 is the configuration of the synchronization holding device, and the spreading code generator 28 uses two kinds of spreading codes, that is, a predetermined chip time T (1/2
Chip) advanced spread code R _E (t) and spread code R _L (t) delayed by 1/2 chip.

Next, the SS demodulation operation and the synchronization holding operation (apparatus) will be described with reference to the correlation characteristic diagram for explaining the synchronization holding operation in FIG. If white Gaussian noise n (t) is the noise mixed in while passing through the transmission medium, the SS modulation signal Cs (t) coming into the input terminal In3 is Cs (t) = AP (t−τ ₀ ) sinωt + n (t) ……………………
………… It is expressed as (1). The SS signal Cs (t) is supplied to the bandpass filter BF.
Unnecessary frequency components are removed by 2 and AGC circuit 3
Amplified or attenuated to an appropriate level at 3 and multiplier Mx2
And Mx3.

The multiplier Mx2 has a spreading code R that is 1/2 chip ahead of the correct synchronization position from the spreading code generator 28.
_E (t) is supplied, and the spread code _RL (t) delayed by 1/2 chip is supplied to the multiplier Mx3. Representing these spreading codes R _E (t) and R _L (t) by the following equations, respectively, R _E (t) = P {t−τ + (Δ / 2)} ……………………
…………… (2) _RL (t) = P {t−τ− (Δ / 2)} ……………………
(3) Output C _SL (t) of multiplier Mx2 and output C of multiplier Mx3
_SE (t) is C _SL (t) = AP (t−τ ₀ ) * P {t−τ + (Δ / 2)} sinωt + n (t)
P {t−τ + (Δ / 2)} …… (4) C _SE (t) = AP (t−τ ₀ ) * P {t
−τ− (Δ / 2)} sinωt + n (t) P {t−τ− (Δ / 2)} (5) Note that τ is the time estimation error amount and Δ is the spreading code 1
Indicates tip time.

Usually, the multipliers Mx2 and Mx3 perform demodulation by despreading, but only the operation for holding synchronization will be described below. In these equations (6) and (7),
The term of the white Gaussian noise n (t) can be ignored in the calculation of the loop response in the synchronization holding device, so that the respective outputs are as follows.

C _SL (t) = ARP {−τ ₀ + τ− (Δ / 2)} sinωt ...
…………… (6) C _SE (t) = ARP {-τ ₀ + τ + (Δ / 2)} sinωt ………
…………… (7) Each of these multiplication outputs is extracted by the band-pass filters BF3 and BF4, only the necessary frequency components, and envelope-detected by the envelope detectors 38 and 39. 3 (A) and
The waveform is as shown in (B). Both outputs are subtraction circuit 4
0 and are subtracted from each other, and the loop filter 26
Therefore, the error voltage Es (τ ₀ −τ) is obtained.

When τ ₀ −τ = ε is set here, Es (ε) = RP {-ε- (Δ / 2)}-RP {-ε + (Δ / 2)} .....
…………… (8). The error voltage Es (ε) is supplied to the voltage controlled oscillator 27 to control the oscillation frequency of the voltage controlled oscillator 27, thereby obtaining the clock signal for generating the spread code. This clock signal is supplied to the spread code generator 28,
By appropriately selecting each bit clock, two kinds of spreading codes R _E (t) and R _L (t) are generated. The error voltage Es for VCO expressed by the equation (10) is shown in FIG. 3 (C).
The correlation characteristic of (ε) is shown. In the same figure (C), the position of 0 point is an ideal synchronization holding point.

[0013]

In the synchronization holding device in the conventional spread spectrum communication system, it is necessary to keep the input level supplied to the multipliers Mx2 and Mx3 constant, and the AGC circuit 33 is used for that purpose. . However, the actual AGC circuit does not become an ideal output whose output is constant, and some level fluctuation occurs. When such a level change occurs, the output levels of the multipliers Mx2 and Mx3 naturally change, the loop gain changes, and it is difficult to keep the synchronization stable. Further, as is well known, the AGC circuit has a large circuit scale, and there is a problem that the system cost becomes high.

[0014]

A synchronization holding device in a spread spectrum communication system according to the present invention is a spread code generating circuit for demodulation which outputs a spread code advanced by a predetermined chip time and a spread code delayed by a predetermined chip time. And first and second correlating means for correlating each spread code from the spread code generating circuit with the input spread spectrum signal, and first and second correlating outputs of these correlation outputs to obtain an angle demodulated output. Two angle demodulation means, first and second filter means for removing carrier components from the obtained respective angle demodulation outputs, and subtraction means for subtracting the outputs of both filter means to obtain a subtractive force. Clock signal generating means for converting the obtained subtraction calculation force into an error signal and supplying it to a voltage controlled oscillator to obtain a clock signal, and supplying the obtained clock signal to the spread code generating circuit for a predetermined chip. Generates a spreading code delayed spread code and the predetermined chip time advanced between, by configuring the synchronization hold loop to supply to the correlation means of the respective, the above-mentioned problems are eliminated.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a synchronization holding device in a spread spectrum communication system of the present invention will be described with reference to FIG. FIG. 4 is a block system diagram of the synchronization holding device 1 in the spread spectrum system of the present invention. In this figure, 17 and 18 are an angle demodulation circuit (DEM), 19, 20.
Is a low pass filter (LPF), 23 is an inverting amplifier, D _{1 and} D ₂
Is a diode, and other components that are the same as those of the conventional device shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

It is to be noted that a transmitter (S) which is a side for transmitting a signal is sent to a demodulating device (receiver) including the synchronization holding device.
Although the configuration of the S modulator) is not so different from that shown in FIG. 1, the angle modulation circuit (MOD) 2 performs FM modulation on a modulated signal such as voice or information as follows.

The modulated signal s (t) such as voice and information supplied from the input terminal In1 is transmitted by the carrier wave Esin in the angle modulation circuit 2.
The signal is FM-modulated by ωt and the primary modulation signal f (t): f (t) = E sin {ωt + s (t)} ……………………………
… (9). On the other hand, the spread code generating circuit 5 generates a spread code P (t) based on the clock signal C (t) from the input terminal In2 and outputs the spread code P (t) to the multiplier Mx1 for spread modulation. Therefore,
Here, the spread code and the angle modulation output signal f (t) are multiplied to generate a spread spectrum modulated wave SS (t) as shown in the following equation, and after unnecessary frequency components are removed by BPFBF1 , Is output from an antenna (not shown) via the output terminal Out1.

SS (t) = EP (t) sin {ωt + s (t)} ...
(10) Next, referring to the waveform diagrams of FIGS. 4 and 5, the synchronization holding device of the present invention will be described. The spread spectrum modulated wave coming from the input terminal In3 contains white Gaussian noise n (t) as in the above-mentioned conventional example, and a bandpass filter (BPF).
It is supplied to the correlation demodulating multipliers Mx2 and Mx3 via BF2. Normally, in the multipliers Mx2 and Mx3, multiplication with the spread code from the spread code generator 28, that is, despread demodulation, is performed, but since it is not directly related to the gist of the present invention, the synchronization is maintained here as in the conventional example. Only the operation regarding will be described.

The spread code generator 28 supplies the spread code Pn (t-τ + Δ / 2) = R _E (t) to the multiplier Mx2 by advancing the predetermined chip time T of the spread code, that is, 0.5 chip time. , The spreading code Pn (t-τ- is delayed by 0.5 chip time in the multiplier Mx3.
Δ / 2) = _RL (t) is supplied. Therefore, the multiplier M
The outputs e _L (t) and e _E (t) of x2 and Mx3 are respectively e _L (t) = ERP {-τ ₀ + τ- (Δ / 2)} sin {ωt + s (t)} + n (t) Pn {t-τ + (Δ / 2)} …… (11) e _E (t) = ERP {-τ ₀ + τ + (Δ / 2)} sin {ωt + s (t)} + n (t) Pn {t-τ- (Δ / 2)} (12) Note that RP {-τ ₀ + τ- (Δ / 2)} and RP {-τ ₀ +
τ + (Δ / 2)} is the correlation gain.

Here, if τ−τ ₀ is τ _E and the term n (t) is ignored in the loop analysis, (11), (12)
The formulas are e _L (t) = ERP {τ _E- (Δ / 2)} sin {ωt + s (t)} …………
……… (13) e _E (t) = ERP {τ _E + (Δ / 2)} sin {ωt + s (t)} …………
……… (14) Obviously from the characteristic diagram of FIG. 3, RP {τ _E- (Δ
/ 2)} is

[0021]

[Equation 1] …………………… It can be approximated with (15). Similarly, RP {τ _E + (Δ / 2)} is

[Equation 2] …………………… (16). Therefore, equations (13) and (14) are

E _L (t) = E {(1/2) + (τ _E / Δ)} sin {ωt + s (t)} ………
………… (17) e _E (t) = E {(1/2)-(τ _E / Δ)} sin {ωt + s (t)} ………
………… It becomes (18). E in equations (17) and (18) is the overall amplitude value,
1/2 indicates the amplitude of the angle modulated wave. Further, τ _E / Δ is also a function of time, and can actually be expressed as a diffusion component Pn (t).

The respective correlation outputs are supplied to the angle demodulation circuits 17 and 18 via BPFBF3 and BF4, respectively, and the angle demodulation is performed. The angle demodulation is generally performed by limiting the amplitude of the input signal, differentiating it, and further performing envelope detection (envelope detection). Therefore, the angle demodulation circuits 17, 1
A demodulation output D _L (t) of the angle demodulation circuit 17 is composed of an amplitude limiter (limiter), an envelope detector and the like.
Is E = 1 and the amplitude of the angle modulated wave is 1,

D _L (t) = s ′ (t) + Pn (t) s ′ (t) + Pn ′ (t) …………
………… (19), and similarly the demodulation output D _E (t) of the angle demodulation circuit 18
Is D _E (t) = s' (t) -Pn (t) s' (t) -Pn '(t) …………
………… It becomes (20). Each component s '(t), Pn (t) s' included in both equations
Waveforms of (t) and Pn '(t) are shown in (A), (B), and (C) of FIG. 5, respectively. It should be noted that the addition of "" as in s' (t) means that the signal waveform is differentiated from the original signal s (t). The FM signal is expressed in this way because information is demodulated by differentiating it and performing envelope detection (envelope detection).

By the way, in equations (19) and (20), Pn (t) s'
Since (t) is small in level, demodulation output D _L (t) and D _E
(t) can be approximated as follows.

[Equation 3] …………………………(twenty one)

[Equation 4] …………………………(twenty two)

Pn '(t) on the right side of the equations (21) and (22) is a demodulated spread component, and the reciprocal of the period of the spread code is the fundamental frequency,
It can be understood that it can be used as an error signal if it is composed of components including the higher-order harmonic components and the levels of the components are compared. Therefore, after removing the information signal frequency band by BPFBF5 and BF6, only the output of BPFBF5 is inverted (and level adjusted) by the inverting amplifier 23, and the diode 2
Subtracting both BPF outputs using 4, 25 yields the following error signal ε (t).

Ε (t) = (τ _E / Δ) d / dt where | τ _E | ≦ (Δ / 2)
(23) This τ _E exists as an error component, is converted into an error voltage by the loop filter 26 in the next stage, and is supplied to the voltage controlled oscillator 27. Due to this error voltage, the voltage controlled oscillator 27
The output frequency is controlled to settle at the 0 point in FIG. 3 (C), and the synchronization of the loop is maintained. Note that the error signal ε (t) is actually detected as an instantaneous frequency component of τ _E / Δ by the amplitude limiting operation in the angle demodulation circuit, and the demodulation error signal level is the time difference τ _E.
Proportional only to. Therefore, τ _E / Δ does not change even if the amplitude of the input spread spectrum modulated wave SS ′ (t) of the synchronization holding device changes, so that the loop operates normally.

Next, a second embodiment of the device of the present invention will be described. From the configuration of the first embodiment device shown in FIG. 4,
BPF BF5, BF6, inverting amplifier 23, and diode D _1,
D ₂ is removed and only the subtraction circuit 40 is added, and the configuration is simpler than that of the first embodiment device. Since the other configurations are the same, the same reference numerals are given and detailed description of the operation is omitted. That is, the LPFs 19 and 20 have the same configuration, and the outputs of the LPFs 19 and 20 are respectively set to D _L (t), D
_{If E} (t), the output of the subtraction circuit 40 is

[0029]

[Equation 5] ………………………… (24). In this case, the information s (t) must be canceled by subtraction. Actually, the demodulation information s'in Eqs. (21) and (22)
Since the demodulation levels of (t) are the same, the information is canceled and the normal operation is achieved. Therefore, the level adjusting means such as the inverting amplifier 23 is unnecessary, and the transmission line after the angle demodulation circuit may be based on direct current transmission.

[0030]

Since the synchronization holding device in the spread spectrum communication system of the present invention is configured as described above, the use of the angle demodulation circuit eliminates the need for the AGC circuit which is essential to the conventional synchronization holding device. Is simplified, and yet
The problem of loop gain variation caused by the non-ideal characteristics of the AGC circuit in the conventional device is eliminated. As a result, the synchronization holding device of the present invention operates stably even if the input level changes, and the basic characteristics and operation of the loop are the same as those of the conventional synchronization holding device, so that a normal synchronization holding operation can be realized. Further, the structure as in the second embodiment has a feature that the structure is further simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing a general SS modulator in a spread spectrum system.

FIG. 2 is a block configuration diagram of a conventional synchronization holding device in an SS reception unit (demodulation unit).

FIG. 3 is a correlation characteristic diagram for explaining the synchronization holding operation in the conventional device and the device of the present invention.

FIG. 4 is a block configuration diagram of a first embodiment of a synchronization holding device of the present invention.

FIG. 5 is a waveform diagram of each signal component included in the demodulation output of the angle demodulation circuit.

FIG. 6 is a block configuration diagram of a second embodiment of the synchronization holding device of the present invention.

[Explanation of symbols]

2 angle modulation circuit 5,28 spreading code generator (PNG) 17,18 angle demodulation circuit (DEM) 19,20 low pass filter (LPF) 23 inverting amplifier 26 loop filter (LF) 27 voltage controlled oscillator (VCO) 40 subtraction circuit BF1 ～BF6 bandpass filter (BPF) D _1, D ₂ diodes Mx1~Mx6 multiplier

Claims (2)

[Claims] 1. A synchronization holding device used in a demodulating device for further spread-spectrum modulating an angle-modulated wave in which information is angle-modulated and receiving and demodulating a spread-spectrum signal transmitted, wherein the spread is advanced by a predetermined chip time. Code and a spreading code generating circuit for demodulation that outputs a spreading code delayed by a predetermined chip time, and first and second correlations for correlating each spreading code from the spreading code generating circuit with the input spread spectrum signal Means and
First and second angle demodulation means for angle demodulating these correlation outputs to obtain an angle demodulation output, and first and second filter means for removing a carrier component from each of the obtained angle demodulation outputs. And a subtraction unit for subtracting the output of the filter unit to obtain a subtraction calculation force, and a clock signal generation unit for converting the obtained subtraction calculation force into an error signal and supplying the error signal to a voltage controlled oscillator to obtain a clock signal. A synchronization holding loop for supplying the obtained clock signal to the spreading code generation circuit to generate the spreading code advanced by the predetermined chip time and the spreading code delayed by the predetermined chip time, and supplying the generated diffusion code to each of the correlating means. A synchronization holding device in a spread spectrum communication system, characterized in that 2. A synchronization holding device used in a demodulation device for receiving and demodulating a spread spectrum signal transmitted by spread spectrum modulating an angle modulated wave whose information is angle modulated, and a predetermined chip for despread demodulation. A first correlating means for correlating the spread code and the input spread spectrum signal which are advanced in time, and a second correlating means for correlating the spread code and the input spread spectrum signal which are delayed by a predetermined chip for despread demodulation. , First and second angle demodulating means for angle demodulating the correlation outputs of the first and second correlating means to obtain angle demodulating outputs, and demodulation information and carrier components from the obtained angle demodulating outputs. First and second filter means to be removed, and subtraction to obtain an error signal by detecting and subtracting each residual demodulation diffusion component from which the demodulation information from the first and second filter means is removed Means and got A clock signal generating means for converting the generated error signal into a control voltage and supplying it to a voltage controlled oscillator to obtain a clock signal; and a spreading code advanced by the predetermined chip time and a diffusion code delayed by the predetermined chip time based on the clock signal. And a spreading code generating circuit for demodulation, and a synchronization holding loop is configured by supplying the obtained two kinds of spreading codes to the first and second correlation means, respectively. , Synchronization holding device in spread spectrum communication system.