JPH08172423A - Antenna diversity reception system - Google Patents

Abstract

(57) [Summary] [Structure] In an antenna diversity receiving system in digital mobile radio, a plurality of antenna diversity receivers having a correlation detector store a known pattern of a frame synchronization signal, and the correlation detector inputs the input signal. The antenna diversity reception system is configured to detect the correlation output of the stored signal and select and switch the diversity branch according to the detected correlation output result. [Effect] Overcoming frequency-selective fading, which is difficult to deal with simply by adding simple hardware. It is possible to prevent a decrease in throughput.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna diversity receiving system which is one of space diversity applied to digital mobile communication.

[0002]

2. Description of the Related Art Antenna switching space diversity is widely known as one of methods for overcoming a poor propagation environment due to fading which is a characteristic of mobile communication.

This antenna switching space diversity is
Multiple antennas are installed at positions far enough apart that the correlation coefficient of each received signal is sufficiently small, and the best receiving system is selected from each received signal whose signal quality fluctuates due to fading. This is a method of avoiding a steep drop in signal level due to movement by switching.

The evaluation of each receiving system is usually performed by RSSI (Receiv
This is performed by the input signal level to the IF band amplifier called ed Signal Strength Indicator), and the receiving system with the largest RSSI is selected from among the receiving systems.

On the other hand, fading is classified into Nakagami-Rice fading, Rayleigh fading, etc. according to the amplitude and phase variation distribution. Another factor that characterizes fading is frequency selectivity (selective). There is a distinction between fading and non-selective (flat) fading. This is to distinguish whether the arrival time difference of multiple waves that cause fading can be ignored with respect to the reciprocal of the modulation signal band.

[0006]

In the case of non-selective (flat) fading in which the time difference of arrival of multiple waves can be ignored, the main factor that determines the quality of the input signal is the C / N ratio. There is no problem in selecting the input system by RSSI. However, if there is an incoming wave with a long delay time due to mountains around it, or if the transmission rate becomes high such as high-speed digital mobile communication that is expected to be realized in the future, frequency selective (selective) fading will occur. appear. That is, an interference wave having a delay time is generated in addition to the main wave, and such an incoming wave is a good signal no matter how large the C / N ratio is because the frequency characteristics are deteriorated. It cannot be.

Therefore, in the conventional selection of the input system by the RSSI, even if the apparent signal level is large, an unfavorable input system in which a large amount of the power thereof is composed of delayed wave components is selected, and the frequency selectivity is increased. (Selective) There was a problem that improvement effect could not be expected for fading. A technique such as an adaptive equalizer is known as a method for preventing frequency selective fading. However, in order to configure an adaptive equalizer, not only large-scale hardware is required, but also steep It is very difficult to realize an algorithm that reliably follows the fading and converges.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome these problems of the prior art and to overcome frequency selective fading very easily and efficiently.

In order to solve the above-mentioned problems, the present invention stores a known pattern of a frame synchronization signal in a plurality of antenna diversity receivers having a correlation detector in an antenna diversity receiving system in digital mobile radio. The antenna diversity receiving system is configured to detect the correlation output of the input signal and the stored signal by the correlation detector and select and switch the diversity branch according to the detected correlation output result.

[0010]

According to the above construction, the input system having the largest output can be selected according to the correlation output results of the plurality of antenna diversity receivers.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

The present invention shows an antenna diversity system which operates well even in a propagation environment in which selective fading occurs such as high-speed digital mobile communication.

As described above, in a situation where selective fading occurs, an input signal having a large C / N ratio is not always the optimum signal. The RSSI level also includes the power of the delayed wave, and does not indicate the level of only the desired wave component that is truly desired. Therefore, consider antenna diversity in which a signal representing only the level of the main wave is detected and the antenna is switched or selected accordingly. Here, digital phase modulation is assumed as the modulation method.

In digital phase modulation, in addition to data for transmission such as voice data, various data for realizing communication are transmitted. Among them, there is information that the pattern of data transition needs to be known, including the synchronization word. By using these pieces of information, a sequence having a sharp peak in the autocorrelation function on the time axis is constructed and phase modulation is performed. The above correlation calculation is performed in each input system, and the input system with the largest output is selected. The principle of the above method will be described.

FIG. 1 shows the autocorrelation function of an M-sequence code, which is one of the sequences having sharp autocorrelation characteristics. As shown in the figure, a sharp peak occurs only when the patterns match with each other, and when the patterns deviate by 1 bit or more, only a certain small correlation value is shown. A transmission signal is modulated by forming a series A having such a sharp autocorrelation characteristic using a frame synchronization signal and other data.

FIG. 2 shows the format of the transmission signal. The transmission signal of FIG. 2 arrives at the receiver as a multiple wave having a delay time as shown in the timing chart of the correlation calculation of FIG. Each of the sequences arrives at the receiver with a difference of arrival time difference. The receiver remembers the pattern of the sequence, and since the synchronization is captured to read the data, the time of arrival of the sequence is also known. Therefore, if the correlation calculation between the input signal and the stored sequence pattern is performed at the time when the sequence is input, the pattern does not match the sequence of the delayed wave, so the correlation output is not affected and the calculation result is desired. It only represents the magnitude of the wave component. Therefore,
By performing the correlation calculation in each input system and selecting the input system having the largest calculation result, it is possible to configure the antenna diversity which is effective against the selective fading.

FIG. 4 shows an embodiment embodying the principle of the present invention as described above.

In FIG. 4, the incoming waves received from the antennas 1 and 2 are converted into IF signals by the mixer 3 and the frequency synthesizer 4 and input to the mixers 5 and 6. On the other hand, the detection output I and Q signals are used to generate a coherent carrier that is not modulated and has no phase error. The coherent carrier is input to the mixer 5 to detect the I component signal, and the coherent carrier whose phase is shifted by 90 degrees by the phase shifter 7 is input to the mixer 6 to detect the Q component signal.

The above is the same as the configuration and operation of normal synchronous detection.

In the present invention, in addition to the above configuration and operation,
The coherent carrier is input to the modulator 8. The modulator 8 modulates the coherent carrier with the same sequence as the transmitted sequence, and outputs it to the mixer 9. Mixer 9 and LPF
10, the correlation calculation between the input signal and the signal modulated by the receiver is performed. I, Q signals and correlation coefficient are A
It is input to the signal processing circuit 14 via the / D converters 11, 12, and 13.

A plurality of the above receiving systems are prepared, and a plurality of I, Q signals and correlation coefficients are input to the signal processing circuit 14. 15 is a bandpass filter, 16 and 17 are lowpass filters LPF, 18 is a carrier generator, 19
Is a sequence generator.

The signal processing circuit 14 selects the receiving system having the largest correlation coefficient output at the time of series reception from the received signals, and reads the I and Q signals of the receiving system.

[0023]

As described above, according to the configuration and method of the present invention, frequency selective fading, which is difficult to be dealt with by simply adding simple hardware generally used in the conventional antenna diversity, is eliminated. It is to overcome. In addition, although a known data pattern with sharp autocorrelation characteristics is required for the transmission signal, in the case of digital communication, the known pattern is indispensable for establishing synchronization, etc. It is possible to prevent a decrease in throughput due to the application of the invention. Overcoming frequency selective fading is one of the most important techniques for high-speed digital mobile communication expected to be realized in the future, and the present invention very easily and efficiently overcomes frequency selective fading.

[Brief description of drawings]

FIG. 1 is a diagram showing an autocorrelation function of an M-sequence code.

FIG. 2 is a diagram showing a format of a transmission signal.

FIG. 3 is a timing diagram of correlation calculation of the transmission signal of FIG.

FIG. 4 is a circuit diagram showing an embodiment embodying the principle of the present invention.

[Explanation of symbols]

 1 Antenna 2 Antenna 3 Mixer 4 Frequency Synthesizer 5 Mixer 6 Mixer 7 Phase Shifter 8 Modulator 9 Mixer 10 LPF 11 A / D Converter 12 A / D Converter 13 A / D Converter 14 Signal Processing Circuit 15 Bandpass Filter 16 Band pass filter 17 LPF 18 Carrier generator 19 Series generator

Claims (1)

[Claims] 1. In an antenna diversity receiving system for digital mobile radio, a plurality of antenna diversity receivers having a correlation detector store a known pattern of a frame synchronization signal, and the correlation detector detects an input signal and a stored signal. An antenna diversity receiving system, characterized in that a correlation output is detected and a diversity branch is selected and switched according to the detected correlation output result.