JP2877243B2 - Spread spectrum communication 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 communication receiver for providing a time window for a despread signal, and detecting and demodulating only the signal passing through the time window. The present invention relates to a configuration of a receiver for spread spectrum communication that receives a signal accompanied by path fading.

[0002]

2. Description of the Related Art FIG. 2 is a diagram for explaining spread spectrum communication. In FIG. 1A, 21 is the frequency spectrum of the transmission signal, 22 is the frequency spectrum after spreading, 23 is the spreader, 24 is the transmitter, 25 is the transmission antenna, 26 is the reception antenna, 26 is the reception antenna, 27 is the receiver, and 28 is A despreader, 29 indicates the frequency spectrum of the received signal, and 30 indicates the frequency spectrum of the received signal after despreading.

[0003] In spread spectrum communication, as shown in the figure, a signal to be transmitted is transmitted by spreading a frequency band with a spreading code on a transmitting side, and the receiving side uses the same spreading code as that on the transmitting side to transmit the signal. This is a communication method for spreading data and demodulating data.

Since the spread spectrum communication system has such a configuration, it has a feature of being resistant to noise and having confidentiality. However, it is difficult to establish synchronization on the receiving side. There are also disadvantages.

On the other hand, in the mobile communication system, the propagation path is generally a multipath propagation path, so that the time required for a signal to reach a receiver differs depending on the delay time of each propagation path.

When a matched filter is used for despreading in a propagation path in which such a delayed wave exists, the output of the matched filter is as shown in FIG. FIG. 3 is a diagram showing an example of the configuration of a conventional spread spectrum communication receiver, wherein 15 is a matched filter, 2 is a time window controller, 3 is a delay detector, 4 is a diversity combiner, and 5 is a decoder. , 6 is an envelope detector, 7 is a peak position counter, 8
Is a changeover switch, 9 is an averager, 10 is a time window center position memory, 11 is a peak position comparator, 12 is an up / down (UP / DOWN) counter, 13 is an n divider, 1
Reference numeral 4 denotes an oscillator.

The operation will be described below with reference to FIG.
The orthogonal I and Q signals are input to the matched filter 15, and the correlation value with the spreading code is output from the matched filter 15.

The output signal of the matched filter 15 is output only while the time window is open in the time window controller 2. The output signal of the time window controller 2 is subjected to delay detection in the delay detector 3 for each spreading period, and the output signal of the delay detector 3 is subjected to diversity combining in the diversity combiner 4. The output signal of the diversity combiner 4 is input to the decoder 5 and decoded.

On the other hand, the output of the matched filter 15 is also input to an envelope detector 6, and after the envelope detection is performed, the output signal of the envelope detector 6 is input to a peak position counter 7, The position of the maximum peak in the code cycle is detected. The output signal of the peak position counter 7 is connected to a switch 8 for switching between an initial mode and a steady mode. First, when communication is started, the changeover switch 8 is set to the initial mode. In the initial mode, the averaging unit 9 averages the output signal of the peak position counter 7.

The output signal of the averager 9 is input to the time window center position memory 10 as the first position of the time window center position. Next, the changeover switch 8 is switched to the steady mode. In the steady mode, the peak position comparator 11
In the above, the output signal of the peak position counter 7 is compared with the center position of the time window, and when the output signal of the peak position counter 7 is larger than the center position of the time window, +1
Is small, -1 is output.

The output signal of the peak position comparator 11 is input to an up / down counter 12 and added. When the counter value of the up / down counter 12 exceeds the threshold value, a shift signal for instructing the shift of the position of the time window is sent to the time window center position memory 10 and the up / down counter is sent. The counter value of 12 is reset. From the time window center position memory 10, a signal indicating the center position of the time window is sent to the time window controller 2.

An oscillator 14 having a frequency n times the frequency of the spread code is supplied as a sampling clock to the time window center position memory 10 and the time window controller 2, and an n frequency divider for dividing the output of the oscillator by n. The output of 13 controls the timing of the matched filter 15, the delay detector 3, the diversity combiner 4, the envelope detector 6, and the peak position counter 7.

Regarding the above-mentioned conventional receiver for spread spectrum communication, see Suzuki and Kudo, "Sequence synchronization method suitable for RAKE combining after detection of DS / CDMA mobile radio", IEICE Spring Conference, B-361, ( 1992) ".

[0014]

In the prior art as described above, the phase of the sampling clock of the matched filter does not change when the time window is shifted. There is a drawback that the synchronization tracking becomes inaccurate because the sampling clock of the time window controller differs from that of the time window controller.

An object of the present invention is to provide a receiver for spread spectrum communication which can solve such a conventional problem.

[0016]

According to the present invention, the above problems are achieved by the means described in the appended claims. That is, the present invention is a spread spectrum communication receiver that provides a time window for a despread signal, detects a signal passing through the time window, and then demodulates the signal. A peak position counter to which a signal subjected to envelope detection is input, a switch for switching whether the output of the peak position counter is connected to an averager or a peak position comparator, and a switch connected to the averager. A time window center position memory connected to a time window controller that outputs a signal only while the time window is open;
An output signal of the peak position counter is input, and a peak position comparator connected to the time window center position memory;
An up / down counter to which an output signal of the peak position comparator is inputted, wherein the up / down counter is connected to a means for generating a sampling clock.

[0017]

In the receiver for spread spectrum communication of the present invention, the output signal of the up / down counter is connected to the n frequency divider, and the output signal of the n frequency divider is sampled to the passive correlator and the time window controller. It is supplied as a clock.
Then, the time window is controlled so as to include the delayed wave shown in FIG. 2 (b), and the diversity transmission (path diversity) is performed on the signal passing through the time window after the delay detection.

When shifting the center position of the time window,
The phase of the output signal of the n frequency divider is shifted. Further, by supplying the output signal of the n frequency divider to the passive correlator and the time window controller as a sampling clock, the sampling timings of the passive correlator and the time window controller are matched. This eliminates the need for high-accuracy tracking, and provides the effect of path diversity (diversity synthesis of delayed waves).

[0019]

FIG. 1 is a diagram showing an embodiment of the present invention. 3, the same components as those in FIG. 3 are denoted by the same reference numerals. Numeral 1 represents a passive correlator.

The operation of the embodiment will be described below with reference to FIG. The orthogonal I and Q signals are input to the passive correlator 1, and the correlation value with the spreading code is output from the passive correlator 1. The output signal of the passive correlator 1 is output only while the time window is open in the time window controller 2.

The output signal of the time window controller 2 is a delay detector 3
, The delay detection is performed for each spreading period, and the output signal of the delay detector 3 is subjected to diversity combining in the diversity combiner 4. The output signal of the diversity combiner 4 is input to the decoder 5 and decoded.

The output of the passive correlator 1 is an envelope detector 6
After the envelope detection is performed, the output signal of the envelope detector 6 is input to the peak position counter 7,
The position of the peak which is the maximum in the period of the spreading code is detected. The output signal of the peak position counter 7 is connected to a switch 8 that switches between an initial mode and a steady mode.
First, when communication is started, the changeover switch 8
Is set to the initial mode.

In the initial mode, the averager 9 performs averaging on the output signal of the peak position counter. The output signal of the averager 9 is input to the time window center position memory 10 as the first position of the time window center position. The output signal of the time window center position memory 10 is input to the time window controller 2, and an initial value of the center position of the time window is set. Next, the changeover switch 8 is switched to the steady mode.

In the steady mode, the output signal of the peak position counter 7 is compared with the center position of the time window in the peak position comparator 11, and the output signal of the peak position counter 7 is larger than the center position of the time window. If +1
Is small, -1 is output. The output signal of the peak position comparator 11 is input to an up / down counter 12 and added.

When the counter value of the up / down counter 12 exceeds the threshold value, a signal instructing to advance the phase when the phase of the time window is advanced is used. Is sent to the n frequency divider 13 and the counter value of the up / down counter 12 is reset.

The output of the oscillator 14 having a frequency which is n times the frequency of the spread signal is input to the n frequency divider 13 and its n
The output of the frequency divider 13 is connected as a sampling clock of the passive correlator 1, the time window controller 2, the delay detector 3, the diversity combiner 4, the envelope detector 6, and the peak position counter 7. Is done. The passive correlator 1 may be a matched filter or a convolver.

[0027]

As described above, in the receiver for spread spectrum communication of the present invention, since the sampling clock of the time window controller and the sampling clock of the passive correlator are the same, effective synchronous tracking can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating spread spectrum communication.

FIG. 3 is a diagram showing an example of a configuration of a conventional receiver for spread spectrum communication.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Passive correlator 2 Time window controller 3 Delay detector 4 Diversity combiner 5 Decoder 6 Envelope detector 7 Peak position counter 8 Changeover switch 9 Averager 10 Time window center position memory 11 Peak position comparator 12 Up / down Counter 13 n frequency divider 14 oscillator 15 matched filter

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04J 13/00

Claims (1)

(57) [Claims] 1. A spread spectrum communication receiver for providing a time window for a despread signal, detecting a signal passing through the time window, and then demodulating the signal. A peak position counter to which the signal subjected to the envelope detection is input, a switch for switching whether the output of the peak position counter is connected to an averager or a peak position comparator, and a switch connected to the averager And a time window center position memory connected to a time window controller that outputs a signal only while the time window is open; and an output signal of the peak position counter is input and connected to the time window center position memory. And an up / down counter to which an output signal of the peak position comparator is inputted, and wherein the up / down counter has a sampling clock. A receiver for spread spectrum communication, wherein the receiver is configured to be connected to a means for generating a signal.