JPH02100521A - Carrier sensing system - Google Patents

Abstract

PURPOSE:To securely attain carrier-sensing with respect to a nonmodulation wave input by modulating a local oscillator in the receiver of a direct conversion system and obtaining a carrier sense output. CONSTITUTION:For sensing a carrier, the local signal of the local oscillator 15 is frequency-modulated by using the modulation signal of a low frequency from a modulation wave source 21. Thus, a low frequency signal corresponding to the modulation signal of the modulation wave source 21 is generated from a mixer 14 and it is outputted through a low pass filter 18 and an amplifier 20. When a reception input signal is the non-modulation wave, an AC signal corresponding to the modulation signal is outputted from an adder 28 by permitting the modulation wave source 21 to modulate the local signal, and therefore the presence or absence of a reception signal can be decided by using the signal as a carrier sense output.

Description

[Detailed Description of the Invention] [Summary] Regarding a carrier sense method for detecting a carrier in a receiver of a direct conversion communication system, carrier sense can be performed even if the transmitted signal is an unmodulated wave. In a direct conversion type receiver comprising an i-phone tuner and a local oscillator that generates a local signal for demodulating an input signal in the demodulator, the receiver aims to provide a carrier sense system. It is constructed by providing a modulated wave source that modulates a signal and performing carrier sensing using the output of the receiver obtained by modulating the local signal.

[Industrial application field]

The present invention relates to a carrier sense method for detecting a carrier, and more particularly to a carrier sense method for detecting a carrier in a receiver of a direct conversion communication system.

There are two methods for receiving wireless communication signals: the direct conversion method that converts the received signal to the baseband signal band with a single frequency conversion operation, and the superheterodyne method that converts the received signal to the baseband signal band using multiple frequency conversion operations. However, the present invention relates to a carrier sense method in the direct conversion method.

FIG. 4 shows a direct conversion type communication system, in which a number of stations A and B are equipped with transmitters and receivers.

A case is shown in which C2-...- communicate with each other using the same carrier f1.

FIG. 5 shows how carrier f is used over time in this case. For example, from time TO to T1, station A transmits and station B receives, thereby communicating between stations A and B. , Similarly, during time T2 to T3, when station B and station A are communicating with each other, and station C newly attempts to communicate with station A, station C is station A
, B can receive the transmitted signals of stations A, B, and
When station A detects that there is no communication between station A and
You will be able to communicate with.

Therefore, station C always detects carrier f, and when there is no signal in the frequency band of f, station A detects carrier f.

It is determined that the communication between B and B is completed, and transmission is performed from time T6 to T7 from the own station.

The same applies to other stations, and before each station transmits, it is necessary to perform carrier sense to detect the presence or absence of a carrier in the frequency band to which the station is attempting to transmit. Note that on the upper side, the times T1 to T2 . between the transmission times of each station are shown. T3
~T6. -.- is a guard time provided for switching between transmission and reception.

It is desired that carrier sensing in such a direct conversion method can be performed not only for modulated waves but also for non-modulated waves.

[Conventional technology]

In the case of the superhetero gain method, the frequency conversion operation is performed multiple times, so the presence or absence of a carrier can be detected in the intermediate frequency band.

However, in the direct conversion method, there has been no known method for carrying out carrier sensing, especially in the case of unmodulated waves.

[Problem to be solved by the invention]

FIG. 6 shows a schematic configuration of a communication device in the direct conversion method, in which (al indicates the transmitting side, and (b) indicates the receiving side.

On the transmitting side, a baseband signal (2) having a band of 0 to rb is input to a modulator 1, and by modulating a local signal of frequency f1 from a local oscillator 2, a carrier f, flfb-f, and f, ~[, +
A modulated wave having a band fb is generated, and this signal is sent out through the antenna 3.

On the receiving side, this signal is received via an antenna 4, and demodulated by a local signal of frequency f from a local oscillator 6 in a demodulator 5, thereby reproducing a baseband signal (2) having a band of 0 to fb.

To perform carrier sense in the direct conversion method, by inputting a DC level signal on the transmitting side,
By transmitting a signal with the same frequency as the local signal and demodulating it on the receiving side, a DC level demodulated signal can be obtained, and carrier sensing may be performed using this signal.

However, there are problems with local signal frequency drift and offset, and each stage of the transceiver is generally connected by AC coupling. Therefore, unmodulated waves cannot be transmitted. (Actually, the local frequencies on both the transmitting and receiving sides do not match completely, so the demodulated signal of the unmodulated wave does not become DC, but due to AC coupling, signals near zero frequency are blocked and difficult to detect. ) On the other hand, in the case of a modulated wave, carrier sensing can be performed by demodulating it on the receiving side, but the modulated wave is not always sent out on the transmitting side.

The present invention aims to solve the problems of the prior art, and in a direct conversion communication system,
It is an object of the present invention to provide a carrier sensing method that allows carrier sensing to be performed on the receiving side even if the transmitted signal is an unmodulated wave.

[Means to solve the problem]

As shown in FIG. 1, the present invention provides a direct conversion type receiver comprising a demodulator 5 and a local oscillator 6 that generates a local signal for demodulating an input signal in the demodulator 5. , a modulated wave source 9 is provided, and carrier sensing is performed using the output of the receiver obtained by modulating the local signal.

The modulated wave source 9 modulates the local signal of the local oscillator 6.

[For production]

In FIG. 1, the local oscillator 6 is, for example, a voltage controlled oscillator (
VCO). The selector switch 7 is normally switched to the DC power supply 8 side, and the local oscillator 6 generates an unmodulated local signal f1.

In the demodulator 5, the input signal having the carrier f1 is converted into iM K”A by the local signal f1 of the local oscillator 6.
Obtain the baseband signal output by

When carrying out carrier sensing, the selector switch 7 is switched to the modulated wave source 9 side. The modulated wave source 9 generates a low frequency signal with a frequency fm, and the local oscillator 6 receives this signal to generate a local signal f modulated with a frequency fm.
, occurs.

As a result, an output signal corresponding to the modulation frequency fm is obtained as a baseband signal in response to the input of the carrier f from the demodulator 5, and this is used as a carrier sense output.

Therefore, in the carrier sensing method of the present invention, carrier sensing can be performed even when the received signal is an unmodulated wave.

〔Example〕

FIG. 2 shows the configuration of an embodiment of the present invention, illustrating a case where a receiver performs orthogonal detection of a received signal to obtain two outputs, I and Q. However, the present invention is not limited to this, and it is also possible to receive only one signal.

In the embodiment shown in FIG. 2, carrier sensing is performed by detecting the demodulated output of one Q of the orthogonal signals.

The received signal of carrier frequency f from the antenna 11 is
After being amplified through the low noise amplifier 12, the mixer 13.1
4 and are quadrature detected by mixing the local signal of frequency f from the local oscillator 15 or a signal whose phase is shifted through the 90° phase shifter 16. The outputs of both mixers 13 and 14 are each passed through a low-pass filter (
Only the baseband signal is taken out through LPF) 17 and 18, and each amplifier 1 for baseband signal amplification
9.20 and is amplified to produce an output of 1. Get Q.

When performing carrier sensing, the local signal of the local oscillator 15 is frequency-modulated using a low-frequency modulation signal from the modulation wave source 21. As a result, a low frequency signal corresponding to the modulated signal of the modulated wave source 21 is generated from the mixer 14, and a low frequency signal corresponding to the modulated signal of the modulated wave source 21 is generated. The signal is output via an amplifier 20. Buffer amplifiers 22 and 23 amplify input and output signals of the amplifier 20,
The full-wave rectifiers 24.25 perform full-wave rectification on the outputs of the buffer amplifiers 22.23, and the integrators 26 and 27 perform full-wave rectification on the outputs of the buffer amplifiers 22.23.
25 rectified output is smoothed.

Adder 28 adds the outputs of both vertex separators 26 and 27 to generate an output. In this case, the detection circuit consisting of the buffer amplifier 22, the full-wave rectifier, and the integrator 27 operates effectively when the receiving input level is low.
4. When the receiving power level of the detection circuit consisting of the integrator 26 is high and the output level of the former detection circuit becomes saturated,
It works effectively.

Therefore, even when the received input signal is an unmodulated wave, by modulating the local signal by the modulated wave source 21, the adder 28 outputs an AC signal corresponding to the modulated signal, and this signal is output as a carrier sense output. The presence or absence of a received signal can be determined by using it as a signal.

FIG. 3 shows an example of actually measured carrier sense output in the embodiment shown in FIG. In the figure, / indicates the case where the receiving input is a modulated signal and the local signal is unmodulated, × indicates the case where the receiving input is an unmodulated signal and the local signal is modulated, and Δ indicates the case where the receiving input is a modulated signal and the local signal is modulated. Each figure shows the case where the local signal is converted. In this case, the frequency deviation Δ
f is 4°5 kHz, and the modulation frequency is 500 t(z). Also, the receiving characteristics of the receiver used in this experiment are that the error rate is 10-2 at a received signal level of 125 dBm.
It is.

From the actual measurement example in Figure 3, the received signal level is 1110 dBm.
If so, it is clear that career sense is possible.

〔Effect of the invention〕

As explained above, according to the present invention, the local oscillator is modulated in the direct conversion receiver to obtain the carrier sense output, so carrier sense can be reliably performed even for unmodulated wave input. can.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the principle configuration of the present invention, Fig. 2 is a diagram showing an embodiment of the present invention, Fig. 3 is a diagram showing an actual measurement example of carrier sense output, and Fig. 4 is a diagram showing a direct conversion method. FIG. 5 is a diagram showing a communication system using the direct conversion method, and FIG. 6 is a diagram showing a schematic configuration of a communication device using the direct conversion method. 1...-Modulator 2.6-Local oscillator 3.4--Antenna 5...-Demodulator 7--Switch 9--Modulating wave source

Claims (1)

[Scope of Claims] A direct conversion receiver comprising a demodulator (5) and a local oscillator (6) that generates a local signal for demodulating an input signal in the demodulator (5), comprising: A carrier sensing method characterized in that a modulated wave source (9) for modulating the local signal of (6) is provided, and carrier sensing is performed using the output of the receiver obtained by modulating the local signal.