JPS5974742A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To decrease the time of fix synchronism from an asynchronous state and to improve the communication efficiency, by separating a fixing loop of frequency synchronization and phase locking of carrier wave from synchronous detection of a PN code. CONSTITUTION:A received spread spectrum signal is multiplied by a locally oscillated carrier wave 43 of the output of a voltage control oscillator VCO37 through a multiplier 33 and converted into a data PN code modulated signal 44 through BPF34. The level of the DC component of the signal 44 is discriminated by a maximum value discriminator 36, and a control signal which always reaches its maximum value is sent to the VCO37. This loop secures the frequency synchronism and phase locking between the wave 43 and a received carrier wave. While a PN code of a PN code generator is supplied to an exclusive logical adder 41 together with the signal 44 to undergo the reverse diffusion and then fed to an LPF42. Then the received data 45 is reproduced. In such a way, there is no relationship between the frequency synchronism and phase locking of a carrier wave and the correlation of the PN code. This decreases the time to fix synchronism and locking and improves the communication efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a spread spectrum method that can shorten synchronization establishment time and improve synchronization detection accuracy.

[Prior art]

A communication system using a spread spectrum (hereinafter abbreviated as DS-8S) method using direct spreading consists of the side 1a shown in Figure 1, and
and a receiving side shown in FIG.

On the transmitting side, transmission information 11 enters a spreading modulator 12 and is converted into P from a pseudo-noise (hereinafter abbreviated as PN) code generator 14.
It is spread modulated by the NI signal and then input to the high frequency modulator 13.
, the carrier wave from the oscillator 15 is modulated and transmitted. On the receiving side, the received signal is amplified by a high frequency amplifier circuit 21 and supplied to a synchronization circuit 24 and a despreader 22. On the other hand, P.N.
The code generator 25 generates a PN code that is the same as that on the transmitting side. This PN code is supplied to the synchronization circuit 24,
Synchronized to the received signal. This synchronized PN
The code is supplied to a despreading demodulator 22, which despreads the received signal into received information 23.

The conventional synchronization method in the above-mentioned DS-88 system is as follows:
This takes advantage of the high autocorrelation of the PN code.

This is because the local oscillation carrier wave on the receiving side modulated by the same PN code as that on the transmitting side is correlated with the received signal while changing at a free-running frequency, and synchronization is established when the correlation value reaches the maximum. In this correlation loop, the frequency, phase, and PN code of the local oscillation carrier and the received signal are
Establishing synchronization takes time because two synchronizations must match.

Now, it takes 1NIIYNC to go from asynchronous state to synchronous state.
j frequency/phase transitions are required, the PN code generation rate is IVpn bits/sec, and the IPN code bit length is 1 kLp.
Assuming N bits, the maximum synchronization establishment time P N Tl1YNc≦ (1+N5ysc) ・
□・・・・”(1) P
N Here, the frequency/phase transition number N8YNC is as follows.

Fc −LpN NSYN(!≦N, rp +
□HI+-” (2) NTR-VP
N NFP is the number of transitions necessary for synchronizing the frequency and phase of the carrier wave, and the second term on the right side is the number of transitions necessary for synchronizing the PN code. It is assumed that one frequency/phase transition is made in NOR carrier wave cycles.

Fc is the carrier frequency.

According to this, for example, Nyp=16 times, Fc=10M
Hz, NTR = 16 times + Vps = l M bi
ts/sec, LpN=1 kbits,
T8YNC≦6421nS. When time-division communication is performed between multiple stations, synchronization takes nearly one second, reducing transmission efficiency.

[Purpose of the invention]

An object of the present invention is to provide a spectrum wave number communication system that can quickly and accurately shorten synchronization establishment time.

[Summary of the invention]

In order to satisfy the above object, the present invention reduces the correlation with the received signal to 1
The two loops are divided into two loops: a loop for establishing frequency and phase synchronization between the received signal and the local oscillation carrier on the receiving side, and a correlation synchronization loop for the PN code, and are operated independently. This shortens the synchronization establishment time on both sides.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In this figure, a spread spectrum signal sent by a transmitter is received by an antenna 31 and a high frequency amplifier 32
and enters the multiplier 33. In the multiplier 33, the multiplier is multiplied by a local oscillation carrier wave 43 which is the output of the voltage controlled oscillator (hereinafter abbreviated as CO) 37,
The data and PN code modulated signal 44 from which the carrier component has been removed is obtained. This signal 44 passes through the smoothing circuit 35 and enters the maximum value discriminator 36, where the magnitude of the DC component is determined.
The control signal is output to VCO3 so that it always takes the maximum value.
Sent to 7. This loop synchronizes the frequency and phase of the locally oscillated carrier wave and the received carrier wave. Meanwhile, signal 44 is also directed to PN code synchronization detector 38. Here, for example, by detecting a predetermined bit code at the end of the PN code, it is possible to know the start point of despreading of the PN code. This synchronization detection signal is transmitted to the PN code generator 40
control the generation of the PN code.

These synchronization detectors 38. The clock signal used by the PN code generator 40 is generated by dividing the output 43 of the vC037 by the frequency divider 39. The PN code generated by the PN code generator 40 is despread together with a signal 44 into a two-phase transducer, here an exclusive logic adder 41, and its output signal is input into a low-pass filter 42 and received. Data 45 is reproduced. The receiver is constructed as described above.

In this embodiment, since the frequency phase synchronization of the carrier wave is performed regardless of the correlation of the PN code, +g in the conventional method,
For equation (2), the synchronization establishment time worst* value T8YNO is given by the following equation.

According to this, under the same conditions as the conventional method, Tsysc≦2
, 03 ms, the time for establishing synchronization can be significantly shortened. Furthermore, since the start point of the PN code is detected in the second loop, accurate despreading can be performed.

In addition, in this embodiment, in order to synchronize the frequency and phase, the speed P L L (Phas, e Locke
The synchronization establishment time can be similarly shortened by using a phase-locked loop (dLOVIg).

〔Effect of the invention〕

According to the present invention, since the carrier wave frequency and phase synchronization establishment loop and the PN code synchronization detection are separated, the PN code is synchronized after the carrier wave synchronization is established, and the asynchronous state is changed to the synchronous state. The time required to establish synchronization is reduced. This is effective in improving communication efficiency when performing random access communication using the DS-8S method between multiple stations.

[Brief explanation of drawings]

FIG. 1 shows the configuration of the transmitting side of a spread spectrum communication system, FIG. 2 shows the configuration of the receiving side, and FIG. 13 shows an example of the spread spectrum communication system using the method of the present invention. FIG. 2 is a block diagram of a receiver.

Claims (1)

[Claims] 1. In a spread spectrum communication system,
A spread spectrum communication system characterized in that a first loop for establishing synchronization of the frequency and phase of carrier waves and a second loop for detecting synchronization of pseudo noise codes are provided on the receiving side. 2. In the spread spectrum communication system according to claim 1, the first loop is multiplied by the local oscillation carrier wave so that the output of the received signal and the local oscillation carrier wave is maximized. A spread spectrum communication method that uses a frequency/phase locked loop that changes the frequency. 3. The spread spectrum communication system according to claim 1, wherein a high-speed phase-locked loop is used for the first loop. 4. The spread spectrum communication system according to claim 1, characterized in that the second loop uses a loop adapted to detect a code string of a predetermined number of bits of a pseudo-noise code string. Spread spectrum communication method.