JPH0137016B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to mobile and fixed receiving apparatuses that use spread spectrum modulation methods such as direct sequence modulation, frequency hopping modulation, pulsed frequency modulation, time hopping, and time frequency hopping.

In general, in a receiving device using a spread spectrum communication method, when performing mobile-to-mobile or mobile-to-fixed communication, the received power received from the transmitter always fluctuates, and the range of fluctuation is from the receiver minimum sensitivity power level to Receiver maximum input power level, ie, over the entire receiver input dynamics range.

A conventional spread spectrum communication receiver is configured as shown in Figure 1, in which the signal received by an antenna 1 is amplified by an RF amplifier 2 and sent to a wideband AGC detector 4.
Broadband AGC (AGC covering the entire spread band) is performed using the AGC signal from the 1st stage, and is input to the next stage heterodyne correlator 3. The correlator 3 performs initial synchronization acquisition necessary for the initial operation of this type of receiver by sliding correlation. A heterodyne correlation between the signal) and the output of the RF amplifier 2 is taken. In this way, the desired signal correlated with the local signal of the receiver by the heterodyne correlator 5 is subjected to synchronization determination in the basic circuit 6, and initial synchronization acquisition is completed. The synchronization circuit 6 also has a function of performing a tracking operation after synchronization. The IF amplifier 7 uses the output of the correlator 3 and the output of the decoder 17,
It is controlled by the AGC signal from the AGC amplifier 9.

When performing such an initial synchronization acquisition operation, the received power level changes significantly as described above.
It compensates for these changes and has a dynamic range equivalent to the receiver input dynamic range.
AGC circuits 2 and 4 are required before the sliding correlator. A receiver with such an AGC function is particularly useful when multiple lines use the same wave number band simultaneously, such as in spread spectrum modulation.
If the received power of the undesired wave is equal to or higher than that of the desired wave, the gain of the receiver is determined by the undesired wave due to the AGC function. That is, the received power of the desired wave is subjected to amplitude modulation due to the power level of the undesired wave, and initial synchronization acquisition in the spread spectrum modulation method may not be possible.

Furthermore, as mentioned above, since the AGC dynamic range is required to be equal to the receiver input dynamic range, there is a drawback that the AGC circuit is complicated and expensive.

The present invention uses a logarithmic amplifier to compensate for variations in the input received power level at the time of initial synchronization acquisition.
This solves the problem that the desired wave signal is amplitude modulated by the undesired wave signal, making initial synchronization acquisition impossible, and is simple.
An object of the present invention is to provide a device which, with an inexpensive equipment configuration, prevents desired wave signals from being interfered with by undesired wave signals, compensates for fluctuations in desired wave reception power, and enables initial synchronization acquisition.

Next, an embodiment of the present invention will be described with reference to FIG.

The receiving device according to the present invention includes a receiving antenna 1, an RF amplifier 2, a correlator 3, a local reference signal generator 5, the same basic circuit 6, and an IF similar to the conventional device shown in FIG.
Along with amplifier 7, decoder 8 and AGC amplifier 9,
A new logarithmic amplifier 10 is provided.

An incoming signal from a transmitter subjected to spread spectrum modulation is induced by a receiving antenna 1 and enters an RF amplifier 2. The RF amplifier 2 consists of a bandpass waveform generator for image reconstruction and a pre-amplifier that compensates for the deterioration of the receiver input equivalent noise figure. is added to the correlator 3. This correlator 3 uses a heterodyne correlator, which is a well-known method, and includes a local signal generated from a local reference signal generator 5 and spread spectrum modulated in the same format as the received signal using a pseudorandom code, and an input received signal. A heterodyne correlation is taken. (Such an operation will be referred to as a despreading operation hereinafter.) By this despreading operation, the desired wave is returned to the bandwidth before spreading, and the undesired signal is spread to a band greater than the input bandwidth. In other words, the desired wave signal to undesired wave signal ratio (hereinafter D/U
(referred to as the ratio) will increase. In other words, if the D/U ratio before the correlator (receiver input end) is lower than the broadband gain, reception is impossible.

To explain this point in more detail, in general, in mobile-to-mobile or mobile-to-fixed communication, the received power at the receiver usually varies by more than six orders of magnitude. The compensation method for these fluctuations in received power is based on the AGC function as in the conventional device shown in FIG. This AGC method satisfies its role in the case of only desired waves, but when desired waves and undesired waves coexist, especially when the undesired waves have the same or higher power than the desired waves, that is, D When the /U ratio is small, the AGC before the correlator as shown in Figure 1 is determined by the average power of the desired signal power and the undesired signal power.
Since it is an AGC function, the AGC function is determined mostly by the undesired wave power. In other words, the gain of the front end section from the receiver input to the correlator is determined by the undesired wave power, and the AGC function does not work for the desired wave.

Initial synchronization acquisition is performed by sliding correlation, which is a well-known method, by sliding the code position of a pseudorandom code possessed by the receiver to obtain correlation with the received signal.

The correlator output signal obtained by such sliding correlation is compared with a certain threshold value to determine whether it is a desired wave or an undesired wave. Therefore, this correlator output signal must have a level within the resolution of the threshold determination circuit included in the synchronization circuit 6, that is, within the input dynamic range of the initial synchronization acquisition circuit. In a situation where the D/U ratio is small using the conventional device shown in Figure 1, it is difficult to respond to the desired wave as described above.
Since the AGC function no longer works, the correlator output signal after correlation may be below the resolution of the threshold judgment circuit included in the synchronization circuit 6, that is, below the input dynamics range of the initial synchronization acquisition circuit, and the initial synchronization acquisition may be I won't be able to do it.

As shown in FIG. 2, the receiving device according to the present invention has the following features:
RF amplifier 2, correlator 3, local reference signal generator 5,
The above-mentioned initial synchronization acquisition operation is performed by the logarithmic amplifier 10 and the synchronization circuit 6.

First, the case of only desired waves will be explained. An incoming signal from a transmitter that has undergone spread spectrum modulation as described above is preamplified by an RF amplifier 2, subjected to sliding correlation by a correlator 3, and input to a logarithmic amplifier 10. In this case, the received signal normally has a power level fluctuation of six orders of magnitude or more as described above, and the input signal of the logarithmic amplifier 10, ie, the correlator output signal, also has a level fluctuation of nine orders of magnitude or more. but,
The output of the logarithmic amplifier logarithmically compresses the input fluctuation and has a level greater than the resolution of the threshold determination circuit. In other words, the received power that fluctuates by more than 6 orders of magnitude is 2
The fluctuation range is suppressed to ~3 digits, and is input to the threshold value determination circuit to enable initial synchronization acquisition.

Next, a case where desired waves and undesired waves coexist and the D/U ratio is small will be described. Since the RF amplifier 2 is a preamplifier and does not perform level compensation such as AGC, the D/U ratio at the receiver input becomes the D/U ratio at the correlator input. Here, as mentioned above, the correlator 3 performs a despreading operation in which the desired signal is returned to the narrow bandwidth before spreading, and the undesired signal is spread to a wider band than the input bandwidth. D/U
ratio is improved. The improved D/U ratio is input to the logarithmic amplifier 10, where the desired wave and the undesired wave are each independently logarithmically compressed, and then input to the threshold determination circuit where initial synchronization is determined. Unlike the conventional device shown in FIG. 1, even under such a situation where desired waves and undesired waves coexist, the initial synchronization acquisition operation is performed without the desired waves being interfered with by the undesired waves.

Next, the operation after initial synchronization acquisition will be explained.
When initial synchronization acquisition is completed by sliding the code phase of the pseudo-random code possessed by the receiver to obtain a correlation with the desired wave, the code is amplified to a predetermined level by the IF amplifier 7 and demodulated into data or voice by the decoder 8. In addition, the AGC amplifier 9 generates an AGC voltage from the desired signal component from the decoder 8, and the IF amplifier 7 generates an AGC voltage.
has an AGC function.

As another embodiment of the present invention, an example in which a logarithmic amplifier is inserted between the RF amplifier 2 and the correlator 5 can be considered. In this case, it is necessary to use this logarithmic amplifier only at the time of initial synchronization acquisition, and to provide a switch to directly connect the IF amplifier and the correlator after synchronization acquisition. That is, the logarithmic amplifier used in the present invention may be provided on the input side of the synchronous circuit.

As explained above, by using a logarithmic amplifier before and after the correlator in place of the AGC function in the front end of the receiver, compensation for input received power fluctuations can be achieved without using the AGC function. Initial synchronization acquisition can be performed without the wave signal being affected by unwanted wave signals, and the complex AGC circuit in the front end can be removed, simplifying the circuit configuration and reducing costs. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a conventional spread spectrum receiver, and FIG. 2 is a block diagram showing the configuration of an embodiment of the present invention. 1... Receiving antenna, 2... RF amplifier, 3...
... Correlator, 4 ... Wideband AGC detector, 5 ... Local reference signal generator, 6 ... Synchronization circuit, 7 ... IF
Amplifier, 8...Decoder, 9...IFAGC amplifier,
10... Logarithmic amplifier.

Claims (1)

[Claims] 1. In a reception device using a spread spectrum communication method, a synchronization circuit captures synchronization based on the correlation output between a received signal and a local reference signal of a predetermined sequence, and a logarithmic amplifier is provided on the input side of the synchronization circuit. A receiving device using a spread spectrum communication method, characterized by the following.