JPS6357972B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a time division diversity receiving apparatus that can cope with fluctuations in electric field strength (fading) of signals sent from a communication partner.

In general, a diversity method is adopted as a countermeasure against facing in shortwave communication over medium distances, non-line-of-sight communication, etc. This is to obtain two or more signals whose phasing conditions have as little correlation as possible, and to perform high-quality communication by selecting or combining these signals.

Conventional diversity methods include a running difference method, a selection method, an optimal ratio combination ratio, an equal gain combination method, etc., and signal transmission suitable for each method is possible. However, each of these systems requires the provision of two or more receivers of the same type, a level adjustment circuit for received signals, a phase synthesis circuit, etc., and the configuration thereof is often complicated. Particularly in mobile communications, there is a problem that the increasing complexity of communication equipment deteriorates the reliability and maintainability of the equipment, and increases cost, volume, etc.

In order to improve these drawbacks, the present invention switches multiple antennas at the Nyquist sampling rate or faster, without significantly changing the configuration of the receiver. The present invention is a time division diversity receiving device designed to ensure the signal-to-noise ratio of the obtained signal.

The invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the invention applicable to single sideband (SSB) communications. In the figure, 1 ₁
~1 _o is the receiving antenna group, 2 is each antenna group 1 ₁ ~
1 _o is a cyclic antenna switching device that selects one antenna according to a switching signal from an antenna switching controller 4, and 3 is a single sideband reception that inputs the output of the switched antenna switching device 2 and demodulates the received signal. It is a machine. This receiver 3 applies a local oscillator 17 to the received signal.
a mixer 5 that supplies a signal from the mixer and converts the frequency; band wave generators 6, 7, and 8 that extract signals in a predetermined band from the output of this mixer; each output of these band wave generators 6 to 8 is a carrier wave. Oscillators 12, 13,
The demodulator 14 includes demodulators 9, 10, and 11 which are each supplied with SSB signals and demodulates the SSB signals, a signal synthesizer 15 which synthesizes these demodulated signals, and a low frequency converter 16.

This antenna switching controller 4 controls the switching speed, connection time, and switching voltage waveform of the antenna switching device 2, and the waveform of the output signal of this controller 4 is as shown in FIG. _o receiver 3
It satisfies the following conditions so that it can be connected to:

T≦1/2m τ=T/n where T: Repetition period of control voltage m: Maximum frequency of baseband signal τ: Application time (width) of control voltage (pulse) n: Number of antennas In this case, the first The signal waveform V(t) (left side) and frequency spectrum (ω) (right side) at main points a to e in the figure are shown in FIGS. 3 a to e. FIG. 3a shows an example of the waveform of a signal sent from the communication partner on the time axis and the SSB signal expressed in the frequency domain. Here, ωs is the center angular frequency of the spectrum, and ωm is the maximum angular frequency of the baseband signal. Figure 3b shows two antennas (n=
2) shows the mixer output waveform and frequency spectrum when the output signal from the antenna switching device 2 received in step 2 is frequency-converted by the mixer 5. Here, ω's is the angular frequency after frequency conversion of ωs. Figure 3c shows the signal waveform and frequency spectrum after passing through bandpass filters (BPF) 6 to 8 with center frequencies of ωs, ωs′+2ωn, and ωs′−2ωn, respectively, which are greater than ωs′+4ωn and less than ωs′−4ωn. The unnecessary spectrum having the center frequency is removed by this BPF6 to 8. For example, taking a normal SSB receiver as an example, and assuming that ωs'=2π×3.18×10 ⁶ γad/sec ωm=2π×2.4×10 ³ γad/sec, the passband width of BPF6 to 8 is as follows.
If you choose between 2.4KHz and 7.2KHz, you will get a distortion-free signal. Therefore, even if the received signal is an intermittent signal whose sampling frequency is higher than the Nyquist sampling rate, normal demodulation of the received signal is possible.

In addition, as a modification of the configuration shown in Figure 1, the demodulation loss can be reduced to approximately
If the system can tolerate up to about 7dB, ωs′+
It is also possible to omit the band wave generators (for example, 6 and 8) having center frequencies at 2ωn and ωs'-2ωn, respectively, and the demodulators connected to each of them.

FIG. 3d shows the frequency spectrum of the input carrier wave for SSB wave demodulation, and FIG. 3e shows the signal waveform and frequency spectrum at the output of the low frequency converter 16 connected to the output terminal of the power combining circuit 15.

According to the present invention, even if the received signals incident on the antennas 1 ₁ to 1 _o are not at the same level and the received electric fields of all but one of the n antennas are extremely weak, T≦1/2m, If the condition τ=T/n is satisfied, deterioration in line quality due to facing can be prevented. In this case, the loss of signal power increases as n increases, but this loss can be reduced by using a triangular wave instead of a rectangular wave for the control waveform shown in Figure 2, and by making the received waveform also a triangular wave. can. In this case, a triangular received wave can be obtained by using a PIN diode whose resistance changes depending on the control signal level for antenna switching.

As explained above, when using SSB for mobile communications with large fading, it is necessary to
By installing two or more antennas at intervals of about 1/4 wavelength (in/4) to 1 wavelength (in) and connecting them to the receiver by switching at an appropriate speed, a demodulated signal with stable amplitude can be obtained. It will be done. In this case, the receiver may be an SSB receiver with a normal circuit configuration.

[Brief explanation of drawings]

Figure 1 is a block diagram of an embodiment of the present invention, Figure 2 is a waveform diagram of the antenna switching control signal in Figure 1, and Figure 3 is a waveform diagram of the antenna switching control signal in Figure 1.
Figures a to e are signal waveform diagrams and frequency spectra at main points a to e in Figure 1. In the figure, 1 ₁ ... _o ...receiving antenna, 2...
Antenna switching device, 3...Receiver, 4...Antenna switching control circuit, 5...Frequency conversion mixer, 6-
8... Bandwidth wave generator, 9-11... Signal demodulator, 1
2 to 14...Input carrier wave oscillator, 15...Signal synthesis circuit, 16...Low band generator, 17...Local oscillator.

Claims (1)

[Claims] 1. n antennas arranged at predetermined intervals, an antenna switching device that is connected to the feeder of these antennas and that sequentially switches these n antennas at a predetermined period to select one antenna; A frequency converter that is connected to a selected terminal to convert the frequency, an intermediate frequency converter that converts the output of this frequency converter, and a demodulator that demodulates the output of this intermediate frequency converter to a baseband signal of the highest frequency m. and a switching controller for controlling the switching period of the antenna switching device and the application time of the switching voltage, wherein the antenna switching period T is 1/2 m or less and the application time is T/n. A time division diversity receiving device characterized by: