JP3029219B2 - Spread spectrum signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum signal receiving apparatus which shortens the time required for synchronously acquiring a spread code.

[0002]

2. Description of the Related Art A spread spectrum communication system transmits a signal by spreading the signal over a wide frequency band. The power per unit hertz is small, and there is little interference with other communication. In recent years, it is often used for data transmission and the like using a noisy communication line .

FIGS. 2 and 3 show a conventional example of the configuration of each device for transmission and reception using this communication system. Spread signal generator PNG In Figure 2 follows the clock signal f _T supplied from the clock generator OSC, it generates a spreading code p (t),
The transmission data d (t) is spread in the spreading modulator M1 by the spreading code p (t).

[0004] The carrier fc supplied from the oscillator CG is
The modulated signal is modulated by the spread signal in the modulator M2 and transmitted. The transmitted signal x (t) is represented by x (t) = d (t) p (t) cos (2πfct).

In FIG. 3, a received signal y (t) is expressed as follows: y (t) = x (t) + n (t) (where n (t)
Is noise).

[0006] The received signal y (t) is applied to a despread modulator M
3, the signal is despread by the spread signal p ′ (t) generated on the receiving side, and the despread interference signal and the like are removed by the bandpass filter BPF1. (T) is restored.

The spread signal p '(t) on the receiving side must be synchronized with the spreading code p (t) on the transmitting side. There are various methods for acquiring the synchronization, but the circuit configuration is relatively simple. Therefore, a sliding correlator is often used.

The receiving apparatus shown in FIG. 3 also uses this method, and the output of the despread modulator M3 is a band-pass filter BPF
The signal is supplied to the square wave detector 12 through 2 to remove the carrier component. The signal RS is integrated by the integrator 13 during a period T of one cycle of the spread code p ′ (t), and this integrated value is transmitted as the spread code p (t) on the transmission side and the spread code p ′ on the reception side.
This represents the correlation value r (τ) of (t), which becomes maximum when the phases match, that is, when synchronization is acquired.

At the time of synchronization acquisition, the receiving side spreading code p '(t)
△ f and the frequency f _T of the transmission-side spreading code p (t). Thereby, both phases change at the speed of Δf . This finds a sync point. The time when r (τ) becomes equal to or more than a predetermined value is the time of synchronization acquisition (synchronization establishment).

The binarizing circuit 14 outputs the output r of the integrator 13
When (τ) exceeds a predetermined value, a SYNC signal indicating that synchronization has been acquired is generated, and the switch circuit 15 is switched by this signal, and the voltage controlled oscillator VCO thereafter outputs the output voltage V _{DLL of the} delay locked loop _DLL. Is controlled by

That is, the oscillation frequency (spread signal clock frequency) fr of the voltage controlled oscillator VCO and the input control voltage Vc
Is expressed as follows. During synchronization acquisition operation fr = f _T + Δf, Vc = Vo + ΔV After synchronization is established frΔf _T , Vc = V _DLL where Vo is Vc when fr = f _T and V _DLL ≒
Vo However, in the above-described conventional synchronization acquisition method, the synchronization acquisition time is long because a method of searching for a synchronization point while shifting the phase of the receiving side little by little at a rate of 2π △ f radians per second,
If △ f is increased, the synchronization acquisition time can be shortened. However, if this is the case, the time during which synchronization is acquired is shortened, so that the correlation value r (τ) is reduced, and it is easily affected by transmission line noise and interference signals. This introduces a new problem that the synchronization acquisition becomes congested.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the conventional spread spectrum signal receiving apparatus and to provide an apparatus which can speed up initial synchronization acquisition.

[0013]

SUMMARY OF THE INVENTION Accordingly, the present invention provides an integrator for integrating a despread and detected received signal for a predetermined interval , a spreading code generator for generating the despreading spread code, and a spread code generator. A clock signal generator for supplying a clock signal for use in the system is provided, and the frequency at the time of initial synchronization pull-in of the clock signal generator is changed in accordance with the output of the integrator to solve the above-mentioned problem.

At the time of synchronization acquisition, the despread signal is
By performing long-range integration from the signal cycle , the output r of the integrator
_N (τ) is substantially equivalent to power such as noise in the transmission path .
During synchronization acquisition , the value of Δf is changed in inverse proportion to the magnitude of the output r _N (τ), that is, the noise level. In this way, when the line noise is small, Δf is increased to improve the synchronization acquisition speed. Conversely, when the noise level is large, Δf is decreased to maintain the synchronization although the time required for synchronization acquisition becomes longer. It is possible to prevent the synchronization acquisition function from deteriorating due to noise or noise.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a block diagram showing one embodiment of a spread spectrum signal receiving apparatus according to the present invention. In the figure, 21
Is an integrator that integrates a square detector output RS for a predetermined interval ,
Output the integral value r _N (τ). 22 is a △ V control circuit,
The voltage deviation value ΔV (r) corresponding to this integral value r _N (τ)
_N ) is selected, added to the reference voltage Vo, and supplied to the switch circuit 15.

The oscillation frequency (spread signal clock frequency) fr of the voltage controlled oscillator VCO and the input control voltage Vc are expressed as follows. During synchronization acquisition operation fr = f _T + △ f (r _N ), Vc = V
o + △ V (r _N ) After synchronization is established fr ≒ f _T , Vc = V
_DLL where Vo is Vc when fr = f _T and V _DLL ≒
Vo By changing the synchronization acquisition voltage Vc in accordance with the state of noise or the like in the transmission path, the synchronization acquisition time can be made the shortest according to the level of noise or the like at that time.

When the synchronization is acquired in the shortest time and the output r (τ) of the integrator 13 exceeds a predetermined value, that is, when the synchronization is acquired, the binarization circuit 14 generates a SYNC signal.
The switch circuit 15 is switched by this signal. Thereafter, the voltage controlled oscillator VCO is controlled by the output voltage V _DLL of the delay locked loop DLL as shown in the above equation.

The SYNC signal is used as a reset signal.
In response to this, the circuit 22 returns to the initial state, and at the start of the next synchronization acquisition operation, a new voltage corresponding to the output r _N (τ) of the integrator 21 at that time. The shift value ΔV (r _N ) is selected.

The integration period of the integrator 21 (the predetermined period
The section is determined according to the characteristics of the transmission path, but in this embodiment, it is set to a code length (N) times the period (T) of the spread code p (t). For example, if T = 2047 bits long and N = 10 , the integration period is 20.470 bits long.

As described above, the output r _N (τ) becomes equivalent to the power such as noise in the transmission line by performing the integration with a long period to some extent.

There are several ways to determine the beginning and end of the integration period of the integrator 21. For example, the synchronization acquisition operation may be performed prior to the start of the synchronization acquisition operation, and the result (integral value r _N (τ)) may be reflected in the voltage deviation value ΔV (r _N ) to start the synchronization acquisition operation. The integration operation may be started before the operation is started, and then the synchronization acquisition operation may be started, and the result (integral value r _N (τ)) may be reflected on the voltage deviation value ΔV (r _N ) from the middle.

Furthermore, the start of the synchronization acquisition operation and the integration operation may be started simultaneously, and the result (integral value r _N (τ)) may be reflected on the voltage deviation value ΔV (r _N ) from the time when the result is obtained. Still further, the moving average integration may be constantly performed irrespective of the timing of the synchronization acquisition operation. For example, as in the above example, when the integration period T · N = 2047 bit length × 10, the square wave detector 12 outputs RS every period T (2047 bit length).
Take the integral value r _NT (τ) of These are sequentially stored, and N (10) data are held, and the held data is N (10).
), The oldest data is discarded and new data is added last, and the integrated value r _N (τ) is obtained by summing the N (10) data.

The integral value r _N (τ) and the voltage deviation value ΔV (r
_N ) has an inversely proportional relationship, and the proportional function is determined according to the characteristics of the transmission path. For example, the standard integral value is r _NO (τ), and the standard voltage deviation value corresponding thereto is ΔV _O
(R _N ), an integrated value r _N1 (τ) at a certain time, and a standard voltage deviation value corresponding thereto is ΔV ₁ (r _N ), and an increase rate r
When _N1 a _{(τ) / r NO (τ} ) and p, such examples of example below as a function of the proportional are contemplated. ΔV ₁ (r _N ) = − p △ V _O (r _N ) ΔV ₁ (r _N ) = − p ² ΔV _O (r _N ) The other parts are the same as the conventional example. The same reference numerals are given and the description is omitted.

As described above, in the present invention, the reception signal despread and detected is integrated for a predetermined period, and the following speed of the reception side spreading code at the time of initial synchronization pull-in is adjusted in accordance with the magnitude of the integration. did. Therefore, the synchronization acquisition time can be shortened and the data communication can be performed efficiently and reliably while maintaining the same performance as the conventional one against noise and interference.

[Brief description of the drawings]

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

FIG. 2 is a block diagram showing a circuit configuration on a transmission side.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

RS Despread and detected reception signal NT predetermined section p '(t) Despread code PNG Spread code generator f _R Clock signal VCO Clock signal generator

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04J 13/00

Claims (2)

(57) [Claims] 1. A despreading modulator, a spreading code generator for generating the same spreading code as the transmitting side, a variable frequency generator for generating a clock signal to be supplied to the spreading code generator, In a spread signal receiving apparatus provided with a sliding correlation means for shifting a signal frequency from that of a transmission side spread code by a required amount Δf, at the time of the initial synchronization acquisition, the despread signal is integrated over a longer period than the spread code period. an integrating means for spread signal receiving apparatus characterized by comprising a control means in response to the noise level in the output of the integrating means to vary the in frequency deviation Δf in the sliding correlation means. 2. A despreading modulator, a spreading code generator for generating the same spreading signal as the transmitting side, a variable frequency generator for generating a clock signal to be supplied to the spreading code generator, and a despread signal. a section variable integrator for a predetermined interval integral, with the initial synchronization acquisition sender spreading code said clock signal frequency when it and the sliding correlator means as shifting requirements Delta] f, during the initial synchronization acquisition, the slide
The frequency shift amount Δf of the
Large when the noise level included in the output of the type integrator is low
So that if it is large, it will be changed to be small
Spread signal receiving apparatus characterized by constituting the.