JPH09298487A - Receiver for spread spectrum signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver with excellent interference resistance and high sensitivity for a spread spectrum signal. SOLUTION: The receiver 20 receives a spread spectrum signal by a receiving antenna 11 and conducts inverse spread demodulation and demodulates information. In this case, a low-pass filter(LPF) 18 is interposed between an inverse spread demodulation circuit 14 applying inverse spread demodulation to the received spread spectrum signal and a spread code generating circuit 13 applying a spread code to the inverse spread demodulation circuit 14 so as to eliminate the need for a band-pass filter(BPF) between the receiving antenna 11 and a high frequency amplifier circuit amplifying the output signal of the receiving antenna 11.

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, and more particularly to a receiving apparatus having excellent interference resistance and high receiving sensitivity.

[0002]

2. Description of the Related Art In recent years, communication using a spread spectrum (hereinafter abbreviated as SS) method has been increasingly applied to the consumer field. Above all, application to mobile phones and wireless LAN systems is known.

References of the SS system are, for example, Japanese Patent Laid-Open No. 3-159333 and Japanese Patent Laid-Open No. 4-334222.
JP-A-5-114895, JP-B-6-5
2891, Japanese Patent Publication No. 6-52892, Japanese Patent Publication No. 6-52893, and the like.

A basic configuration diagram of a wireless communication device using the SS system is shown in FIGS. 5 and 6. FIG. 5 is a basic configuration diagram of an SS signal transmitting device, and FIG. 6 is a basic configuration diagram of an SS signal receiving device.

When an information signal such as data is supplied to the information modulating circuit 2 from the input terminal 1 of FIG. 5, the information modulating circuit 2 modulates the information signal. An FSK modulation circuit, a PSK modulation circuit, or the like is used for the information modulation circuit 2.

The information modulated wave output from the information modulating circuit 2 is supplied to the spread modulating circuit 4. The spread code is supplied from the spread code generation circuit 3 to the spread modulation circuit 4.

The spread modulation circuit 4 spread-modulates the information modulated wave and outputs an SS signal (SS modulated wave), and the SS signal is a BPF.
It is transmitted from the transmitting antenna 6 via 5.

SS received by the receiving antenna 11 of FIG.
The unnecessary frequency band component of the signal is suppressed via the BPF 12, amplified by a high frequency amplifier circuit (not shown), and supplied to the despread demodulation circuit 14. Here, the unnecessary frequency band component is a signal component smaller than the frequency f1 and (2 × f2−
The signal component is larger than f1).

FIG. 7 shows a frequency spectrum diagram of a signal in each stage of the receiver 120. The vertical axis represents signal magnitude (level), and the horizontal axis represents frequency f. A frequency spectrum diagram of the SS signal received by the receiving antenna 11 is shown in FIG. In FIG. 7A, there is the frequency component SSD of the SS signal centered on the carrier frequency f2, and the frequency f
This is an example in which the frequency component U of the interfering signal exists in the vicinity of 1.

A frequency spectrum diagram of the signal output from the BPF 12 is shown in FIG. 7B. S due to the filter effect
The frequency component SSD of the S signal is slightly attenuated, and the frequency component U of the interference signal is considerably attenuated.

The despreading demodulation circuit 14 is supplied with a spreading code having the same pattern and time as the spreading code used in the transmitting apparatus 110 of FIG.
The signal output from 12 is subjected to despread demodulation (correlation demodulation).

A frequency spectrum diagram of the output signal of the despreading demodulation circuit 14 is shown in FIG. 7C. The frequency component SSD of the SS signal is despread and demodulated to become the frequency component D of the information modulated wave. On the other hand, the frequency component U of the interfering signal becomes the spread-modulated frequency component SSU.

The frequency component D near the frequency f2 is extracted from the output signal of the despread demodulation circuit 14 via the BPF 15 and supplied to the information demodulation circuit 16. A frequency spectrum diagram of the signal output from the BPF 15 is shown in FIG. A part of the frequency component SSU near the frequency f2 is mixed with the frequency component D of the information modulated wave as noise (diffusion noise) n.

The level of the diffusion noise n depends on the amplitude-frequency characteristic of the BPF 12. Therefore, in order to improve the S / N ratio, the BPF 12 is required to have a sharp cutoff characteristic near the frequency f1.

FIG. 8 is a characteristic example of a SAW filter having a relatively steep filter characteristic. It has cutoff frequencies fca and fcb centered on the frequency f2, and has an amplitude L at a frequency fcc (= fcb-Δf) lower than the cutoff frequency fcb by Δf.
Shown as cc (<Lcb). The cutoff frequency fcb is set to the frequency f1 shown in FIG.

The cutoff characteristic of the frequencies fcc to fcb in FIG. 8 is steep, but has a certain degree of inclination, and the frequency component U of the interference signal and the diffusion noise n shown in FIG. 7 remain corresponding to the inclination. Will be done.

[0017]

The BPF 12 is required to have a steep cutoff characteristic in the vicinity of the cutoff frequency fcb. However, the steeper cutoff characteristic increases the insertion loss of the filter.
There is a problem that the reception sensitivity is significantly reduced.

Therefore, the conventional SS signal receiving apparatus 120 is used.
The BPF 12 used for is used so as not to increase the insertion loss without providing a sharp cutoff characteristic.

In such a method of using the BPF 12, when an interfering signal such as a communication radio wave or an interfering radio wave due to unnecessary radiation from an electric appliance occurs near the cutoff frequencies fca and fcb of the BPF 12, the interfering signal is sufficiently provided. Attenuating is difficult.

In particular, in the application of SS technology in the 2.4 GHz band, unnecessary radiation from a microwave oven is a big problem, and when there is such a strong interfering signal, a special process indicated by the spreading factor of the SS system. There is a problem that it may not be possible to utilize the gain.

[0021]

As a means for solving the above-mentioned conventional problems, in claim 1, a spread spectrum signal transmitted from a transmitter is received, and is received by a receiver for performing despread demodulation and information demodulation. By interposing a low-pass filter (LPF) between a despread demodulation circuit for despread demodulating a spread spectrum signal and a spread code generation circuit for supplying a spread code to this despread demodulation circuit, a receiving antenna and this receiving signal are received. It is characterized in that a bandpass filter is not necessary between the antenna and a high-frequency amplifier circuit that amplifies the output signal of the antenna.

The product of the frequency component U of the interference signal and the spread code output from the LPF is the spread-modulated frequency component SSU of the interference signal. Therefore, by attenuating the high frequency component of the spread code with the LPF, the frequency component SS
The spread of U can be suppressed, and this spread can be adjusted.

According to a second aspect of the present invention, in the receiving apparatus according to the first aspect, the cutoff frequency of the low pass filter (LPF) is set to be less than or equal to the reciprocal of the clock rate of the spread code.

Of the frequency components of the spread code, the component (absolute value of frequency) which is less than or equal to the reciprocal of the clock rate is directly related to the spread of the frequency component SSU. Therefore, by setting the cutoff frequency of the LPF to be less than or equal to the reciprocal of the clock rate, the spread of the frequency component SSU can be suppressed more effectively, and this spread can be directly adjusted.

According to a third aspect of the present invention, in the receiving apparatus according to the second aspect, the cutoff frequency of the low pass filter (LPF) is set to the same value as the reciprocal or a value in the vicinity thereof.

Among the frequency components of the spread code, the components in the vicinity of the reciprocal are attenuated, and the components less than that are left,
It is possible to improve the S / N ratio of the information modulated wave obtained by despread demodulation.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on embodiments shown in the drawings. FIG. 1 is a basic configuration diagram of an SS signal receiving apparatus 20 according to the present invention. The same components as those of the receiving device 120 in FIG. 6 are designated by the same reference numerals.

SS transmitted from the transmitter 110 of FIG.
The signal is received by the receiving antenna 11 of FIG. 1 and supplied to the despread demodulation circuit 14. FIG. 4A shows a frequency spectrum diagram of this SS signal. It has the same characteristics as FIG. 7 [A].

The spreading code generation circuit 13 generates a spreading code having the same time and pattern as the spreading code used by the transmitter 110 of FIG. FIG. 2A is a frequency spectrum diagram of this spread code and shows a main lobe from -1 / T to 1 / T. T is a spread code clock rate (clock signal rate), for example, 0.05 μs.
ec.

This spread code is supplied to a correlator (not shown) of the despread demodulation circuit 14 via the LPF 18. FIG.
(B) is a frequency spectrum diagram of the spread code that has passed through the LPF 18.

FIG. 3 shows the amplitude-frequency characteristics of the LPF 18. Frequency fb is a cutoff frequency, for example, several MHz
Up to several tens of MHz At a frequency fc (= fb + Δf) that is higher than the frequency fb by Δf, the amplitude level is Lc (<
Lb).

The LPF 18 is a conventional BPF 12 for filtering the output signal of the receiving antenna 11 (see FIG. 6).
Can be replaced equivalently.

That is, the frequency spectrum of the spread code that has passed through the LPF 18 is shown in FIG. 2B, and (sinX) in the frequency spectrum of such a spread code.
The frequency 1 / T (or -1 /) along the envelope characteristic of / X
When the cutoff frequency fb of the LPF 18 is set in the main lobe near (T), the output signal of the despread demodulation circuit 14 is the spread-modulated frequency component SSU of the interference signal and the information as shown in FIG. The frequency component D of the modulated wave does not mix with each other.

The product of the frequency component U of the interfering signal and the spread code (the frequency component thereof) output from the LPF 18 becomes the spread-modulated frequency component SSU of the interfering signal. The effect of not mixing depends on the cutoff frequency fb and the cutoff characteristic of the LPF 18.

When the cutoff frequency fb of the LPF 18 is set to a value equal to or less than the reciprocal (1 / T) of the clock rate T of the spread code, for example, 20 MHz and the carrier frequency f2 of the SS signal is 2 GHz, the frequency ratio is 100 ( =
2 GHz / 20 MHz).

Then, the cutoff characteristic of the LPF 18 is BPF1.
This is 1/100 of the breaking characteristic of 2. That is, if the LPF 18 is provided with a cutoff characteristic equal to that of the conventional BPF 12, the LPF 18 is equivalent to the BPF.
The cutoff characteristic replaced by is made 100 times steeper than the cutoff characteristic of the conventional BPF 12.

From the output signal of the despread demodulation circuit 14, B
As shown in FIG. 4C, the frequency component D of the information modulated wave is extracted via the PF 15 and supplied to the information demodulation circuit 16 for information demodulation. An information signal is output to the output terminal 17.

As described above, B, which has been conventionally required to filter the output signal of the receiving antenna 11, is required.
The PF 12 can be omitted. That is, the input BPF
LPF 18 can be substituted for 12. This is an effect peculiar to the SS method.

Even if the BPF 12 is omitted, since the receiving sensitivity of the receiving antenna 11 is tuned to the frequency band to be received, interference due to communication radio waves or interfering radio waves having a frequency away from the frequency band of the SS signal may occur. There is almost no influence of interference or the like.

The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment.

[0041]

By using the LPF 18 of the present invention, the BPF 12 used between the receiving antenna and the high frequency amplifier circuit, which is required in the receiving device of the conventional wireless communication device, can be eliminated. Therefore, since the insertion loss due to the BPF 12 does not occur, the SS signal reception sensitivity can be improved.

By using the LPF 18, this L
The cutoff characteristic of the equivalent BPF corresponding to the cutoff characteristic of the PF 18 can be set. According to this, the cutoff characteristic of the equivalent BPF in the frequency band of the carrier can be made much steeper than that of the conventional BPF 12. Therefore, BPF1
In principle, an increase in insertion loss, which is a problem when the cutoff characteristic of 2 is made steep, does not occur.

As described above, according to the SS signal receiving apparatus of the present invention, it is possible to provide a receiving apparatus having excellent interference resistance and improved receiving sensitivity.

[Brief description of drawings]

FIG. 1 is a spread spectrum signal receiving apparatus 2 according to the present invention.
Basic configuration diagram of 0

FIG. 2 is a frequency spectrum diagram of spread codes before and after the LPF 18.

FIG. 3 is an amplitude vs. frequency characteristic diagram of the LPF 18.

FIG. 4 is a frequency spectrum diagram of a signal in each stage of the receiver 20.

FIG. 5 is a basic configuration diagram showing a conventional spread spectrum signal transmission device 110.

FIG. 6 is a basic configuration diagram showing a conventional spread spectrum signal receiving apparatus 120.

FIG. 7 is a frequency spectrum diagram of a signal in each stage of the receiver 120.

FIG. 8 is an amplitude vs. frequency characteristic diagram of the BPF 12.

[Explanation of symbols]

1 ... Input terminal, 2 ... Information modulation circuit (primary modulation circuit),
3, 13 ... Spread code generation circuit (PNG), 4 ... Spread modulation circuit (secondary modulation circuit), 5, 12, 15 ... BPF (band pass filter), 6 ... Transmit antenna, 11 ... Receive antenna, 14 ... Inverse Spreading demodulation circuit (secondary demodulation circuit), 16 ...
Information demodulation circuit (primary demodulation circuit), 17 ... Output terminal, 18
... LPF (low pass filter), 20, 120 ... Receiving device, 110 ... Transmitting device, D ... Frequency component of information modulated wave,
La, Lb, Lc, Lca, Lcb, Lcc ... Amplitude, T ... Clock rate, U ... Interfering signal frequency component, SSD ... SS
Frequency component of signal, SSU ... Spread-modulated frequency component of interference signal, f, fa, fcc ... Frequency, fb, fca, f
cb ... cutoff frequency, f2 ... carrier frequency, n ... spread noise.

Claims (3)

[Claims] 1. A despread demodulation circuit for despreading a received spread spectrum signal in a receiving device for receiving a spread spectrum signal transmitted from a transmitting device by a receiving antenna and performing despread demodulation and information demodulation, and a despread demodulation circuit thereof. By placing a low-pass filter between the spread code generator that supplies the spread code to the spread demodulation circuit, a band pass filter is not required between the receiving antenna and the high-frequency amplifier circuit that amplifies the output signal of this receiving antenna. The receiving device characterized in that 2. The cutoff frequency of the low-pass filter,
The receiving apparatus according to claim 1, wherein the receiving rate is set to be less than or equal to the reciprocal of the clock rate of the spread code. 3. The cutoff frequency of the low-pass filter,
The receiving apparatus according to claim 2, wherein the value is set to the same value as the reciprocal or a value in the vicinity thereof.