JPS58197935A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE:To perform stabilized communication by keeping synchronization even in low receiving conditions, by controlling the threshold level of a synchronizing detector according to the condition of receiving. CONSTITUTION:When shifted to tracking mode, an input signal Vd for a synchronizing detection circuit 10 is inputted to a memory 14 and a terminal 19 of a differential amplifier 5'. The memory 14 picks up the max. value of the signal Vd to input to the other terminal 20 of the amplifier. Since voltages inputted to the terminals 19 and 20 of the amplifier 5' are equal to each other in the effective area of an AGC, the output of the amplifier is zero. Therefore, a controlling part 16 does not operate, and the threshold level voltage Vs of a circuit 13 for setting threshold level continues to be the previous value. However, if enters the ineffective area of the AGC, the signal Vd lowers to induce voltage in the output of the amplifier 5' that lowers the voltage Vs through the control part 16. As a result, a code error rate is not deteriorated, and better communication is realized even in the ineffective area of the AGC.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spread spectrum receiving apparatus, and more specifically, to a configuration of a synchronization control section of a receiving apparatus used in a spectrum number communication system.

Synchronous recognition reception signal vI of conventional spectrum value receiver
In addition to desired waves modulated by the same code sequence as the local reference code on the receiving side, undesired waves that are spread modulated by a code sequence different from the local reference code, undesired waves such as existing AM or FM signals, Furthermore, various 11! Contains sounds etc.

The procedure for obtaining synchronization in this situation can be divided into two modes: search mode and tracking mode. First, in the search mode, the local reference code V whose phase is slipping with respect to the received signal and the received signal V+ are detected by the correlator 3.
The signals are combined, the correlator output signal passes through an intermediate frequency stage 4, enters a demodulator 5, is demodulated, and a quantity indicating the presence of the signal is input to a synchronization determination block 6. In the synchronization determination block, when the signal exceeds the threshold level, a search stop signal is generated and a transition is made to the tracking mode.

In the tracking mode, the clock generator 7 of the phase-locked loop is controlled so that the timing difference becomes zero, synchronization is completed, and communication with the partner station is started. An automatic gain control (AGC) circuit 9 is provided which detects the output of the amplifier l with a detector 2 and controls the gain of the amplifier in order to stabilize the receiver against variations in the Kabel signal. FIG. 2 shows the relationship between received power PL and detected output. As shown by the dotted line in the figure, the detection output is held constant to the extent that the received power is 130 dB. The detection output level at which this AGC is applied affects signal detection and synchronization error probability. Normally, the detection output that applies AGC with
, is set to a value that is larger than the noise voltage V, in anticipation of a somewhat hidden interference signal. However, as can be seen from Figure 2, if we take the above into account and determine the V at which AGC is applied, AGC does not work within a range of approximately 15 dB from -63 dB to -63 dB of received power P+. For example, when the received power P1 is -57 dB or less, the voltage V corresponding to the threshold voltage V of the synchronization judgment block 6 is generated.
A phenomenon occurs in which the b and shi are also rotated downwards and the synchronization is lost. In addition, in the area where AGC does not work, the probability of g4 error is high, and the information signal V! A problem arises in that the code error rate also increases.

Therefore, it has become clear that a technique for automatically controlling the threshold level voltage V1 in accordance with the received power when entering a region where AGC does not work is important.

Therefore, the object of the present invention is to provide A
It is an object of the present invention to realize a spread spectrum receiver that operates stably even when the input level fluctuates, in which a GC moves effectively and synchronization with interference waves is reliably maintained.

In order to achieve the above object, the present invention controls the threshold level of a synchronous detector according to the reception state, and maintains synchronization in a low reception level state to perform stable communication.

The present invention will be explained in detail below with reference to Examples.

FIG. 3 shows a schematic diagram of an embodiment of a spread spectrum receiver according to the present invention. The figure shows a phase-locked loop (for example, a delay lock or a tau dither), a 0-reference circuit for regenerating the carrier wave, and a carrier wave regeneration unit, which are not directly related to the description of the invention, so they are omitted. , is naturally included in an actual receiving device. First, in the code synchronization search mode, the synchronization detection circuit 10, control unit 12, and threshold level setter 13 detect the human input signal level Va. The optimum threshold level voltage V is automatically set.This voltage
, is set to a value sufficiently larger than the V-value in the state where code synchronization is initially achieved, and the search mode is entered. At that time, the control section 12 operates by taking advantage of the fact that no signal is output from the synchronization detection circuit 10.

Then, the output signal of the control section 12 controls the V, 1SII adjustment section of the threshold level setter 13 to lower the V value, and the value (V- with the sign synchronization established) is reduced.
(lower than the value of the noise voltage and larger than the noise voltage). As a result, the TTL generated in the output of the synchronization detection circuit 10
The synchronization determination circuit 11 is activated by the level signal, a code search stop signal is generated, and a transition is made to the tracking mode. At that time, a signal is generated at the output of the synchronization determination circuit 11 to turn off the switch 17 and turn on the switch 18.

As a result, the mode shifts to tracking mode and code synchronization is completed. As mentioned above, the received power range (in Figure 2, from -30 dB to -6
The threshold level voltage V in the region of 5d B,
The control method is as follows. First, the synchronization detection circuit 10
The input signal - is also input to the memory 14 and the input signal 19 of the differential amplifier. 5 may be a device that outputs a voltage proportional to the difference between the signals input to the input quadruplets 19 and 20, so it may be a simple subtracter instead of a differential amplifier.

The memory 14 outputs the maximum value of -) and inputs it to the other input terminal 20 of the differential amplifier 5 (the maximum output of this memory is A
This voltage corresponds to the detection output (■) in the region where the GC is active). In the region where AGC is active (when the detection output is V), the voltages input to 19.20 of differential amplifier a5 are equal, so the output of differential amplifier 5' is zero, and the control section 16 is in operation. Therefore, the threshold level voltage continues to maintain its previous value. However, when the AGC does not work (when the detection output becomes a value lower than V), the voltage applied to the differential amplifier 5' input voltage decreases, so the voltage at the output of the differential amplifier decreases. occurs, and the control unit 1 lowers the threshold level voltage ■ through the control unit 16.
6 is activated. The more the detection output decreases than V,
The control unit 16 operates to significantly lower the threshold level voltage V. Therefore, even if the AGC does not work in the region, the threshold level voltage can be controlled according to the value of the detection output, so good communication is possible without deteriorating the bit error rate. Note that the memory 14 is reset by the output signal of the synchronization determination circuit 11 when the synchronization is lost.

As described above, the spread spectrum receiving device of the present invention sets the threshold according to the human input signal when A()C does not work and the human input signal of the synchronization detection circuit enters a region where it changes. The repellent pressure can be controlled. As a result, it is possible to solve conventional problems such as loss of code synchronization and increase in code error rate.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining synchronization recognition in a conventional spread spectrum receiver, FIG. 2 is a diagram showing the relationship between reception power and detection output, and FIG. 3 is a diagram showing the spectrum according to the present invention. This is a configuration of an embodiment of a spread reception device. 1... Amplifier 111i, 2... Detector, 3... Correlator, 4... Intermediate frequency stage, 5... Demodulator, 5'...
・Differential amplifier, 7... Cronk generator, 8... PN
Code generator, 9...AGCl path, 10... Synchronization detector, 11... Synchronization determination circuit, 12.16... Control i
, 13...Sun 7 hold repetition x l times (A α'F γ digit

Claims (1)

[Claims] 1. From the carrier wave modulated by the pseudo-noise code and the information 1d code, use the same code as the above-mentioned pseudo-noise code to generate the above variation aI1.
In a spread spectrum receiver that receives the above information signal by demodulating a single signal, the signal input to the synchronization detection circuit is acquired after synchronization is acquired while automatic gain control is applied to the reception input level. What is claimed is: 1. A spread spectrum receiver comprising: comparing the signal with the maximum weight of the signal; and controlling a threshold level of a synchronization detection circuit according to the difference.