JPH0365827A - Diversity reception circuit - Google Patents

Abstract

PURPOSE:To improve the transmission characteristic of a radio line by comparing a detected data with an absolute phase with a data of a reference phase or an absolute phase detected in the past and controlling an antenna changeover means depending on the result of comparison. CONSTITUTION:The circuit is provided with a phase detection section 5 detecting a relative phase between a reference signal with an instantaneous phase of an angular modulation wave received by antennas 1, 2 selected by an antenna changeover means 3 and a phase data comparator circuit 8 comparing the detected data of the relative phase and a data of a reference phase or a relative phase detected in the past and controlling the antenna changeover means 3 depending on the result of comparison. Then phase information is detected from a reception signal and the phase information is compared with a phase of a reference signal or the phase detected in the past and the antenna 1(2) in use at present is switched into other antenna 2(1) when it is discriminated that the line condition is deteriorated and the selected antenna connects to a receiver 4. Thus, the detection of the reception level is not required and the characteristic approaches the ideal diversity and the effect of the diversity is obtained even to a deficient factor such as independent deterioration in the transmission characteristic such as thermal noise not only fading.

Description

[Detailed description of the invention] [Industrial application field] The present invention is used for wireless transmission of digital signals.

In particular, the present invention relates to a circuit that receives angle modulated waves in a diversity manner. The present invention improves the transmission characteristics of a wireless line by switching the receiving antenna based on the phase data of the received signal.

[Conventional technology]

Since wireless communication lines use radio waves as a transmission medium, fading, interference, and the like can cause level fluctuations and phase fluctuations in received signals, which can degrade transmission characteristics. It is known that a diversity reception method is effective against such deterioration of transmission characteristics.

The most typical diversity reception method is a selective diversity reception method in which one of the received waves having the highest reception level is selected and received from among received waves received by a plurality of antennas and which vary independently of each other. This method is based on the assumption that the higher the reception level, the higher the signal-to-noise ratio, the less phase fluctuation, and the higher the transmission quality.

However, this method requires multiple receivers, resulting in a large scale. Therefore, as a simple configuration method,
An antenna switching diversity reception method is used in which a single receiver receives signals by switching between multiple antennas.

FIG. 13 shows a typical conventional two-branch antenna switching diversity receiving circuit. two antennas 1 and 2
are installed at an appropriate distance so that mutually independent (uncorrelated) fading waves can be obtained. These antennas 1.2 are connected one of them to a receiver 4 by an antenna switching circuit 3. This switching is performed using comparison data from the level comparison circuit 22. That is, the reception level of the receiver 4 is detected by the reception level detection circuit 2.
1, and the level comparison circuit 22 compares this with a reference value. For example, when the envelope level of the received wave becomes below a certain threshold value, the antenna 1.2 is switched.

[Problem to be solved by the invention]

However, when the reception level is used as information for branch determination, the following drawbacks occur.

First, a high reception level state does not necessarily have better transmission quality than a low reception level state. Errors may occur even when the reception level is high, and no errors may occur even when the reception level is low. At this time, if a judgment is made only based on the reception level, a received wave containing an error will be selected.

Next, a log amplifier is used to detect the reception level, and the log amplifier is required to have level detection performance over a wide range of reception levels. However, in actual log amplifiers, the level detection characteristics often become saturated in regions where the reception level is particularly high or particularly low, and deviations from the straight line occur even in intermediate regions. In such a region, there is a drawback that the difference in output voltage becomes small even though the reception levels between the two antennas are different, making it impossible to accurately compare the reception levels and reducing the diversity effect.

Furthermore, if it is desired to obtain the average reception level as the output of the reception level detection circuit, a filter is generally inserted into the output. At this time, a delay occurs in the level comparison output, and when switching antennas at high speed, a sufficient diversity effect may not be obtained due to this delay.

Furthermore, if the reception input signal levels of the two branches are both low, the operation of the level comparison circuit may be affected by thermal noise, and an accurate comparison output of the average reception level may not be obtained. For example, as shown in FIGS. 10(a) to 10(c), when the desired wave level is almost the same but there is a lot of thermal noise, the level varies depending on the noise vector. Then, when diversity is performed using this comparison output,
On the contrary, there is a drawback that the transmission characteristics may be deteriorated.

The present invention solves the above problems, can obtain a diversity effect without detecting the reception level, and furthermore,
It is an object of the present invention to provide a diversity receiving circuit that is effective not only against fading but also against all factors that affect transmission lines.

[Means to solve the problem]

The diversity receiving circuit of the present invention includes a plurality of antennas for receiving angle modulated waves, and an antenna switching means for selecting one of the plurality of antennas and connecting it to a receiver. a phase detection unit that detects the relative phase between the instantaneous phase of the angle modulated wave received by the antenna selected by the reference signal and the reference signal;
A phase data comparison circuit that compares the relative phase data detected by the phase detection section with the reference phase or the previously detected relative phase data and controls the antenna switching means based on the comparison result. Features.

[For production]

Detects phase information from the received signal, compares the phase information with the reference signal phase or past detected phases, and if it is determined that the line condition is poor, switches the antenna currently in use to another antenna and receives the signal. Connect to the machine. This is based on the knowledge that phase information has a close relationship with transmission characteristics.

In this way, since the phase information from the angle modulated wave is used as the diversity switching information, there is no need to detect the reception level. In addition, since phase information is closely related to transmission characteristics, it is possible to approach ideal diversity and obtain diversity effects not only against fading but also against things that independently degrade transmission characteristics such as thermal noise. becomes possible.

〔Example〕

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

FIG. 1 is a block diagram showing a diversity receiving circuit according to an embodiment of the present invention. This example shows a case where the number of diversity branches is n=2.

This embodiment includes a plurality of antennas 1 that receive angle modulated waves.
．． 2, and an antenna switching circuit 3 that selects one of the antennas 1.2 and connects it to the receiver 4.

Here, the features of this embodiment include a phase detection section 5 that detects the relative phase between the instantaneous phase of the angle modulated wave received by the antenna 1 or 2 selected by the antenna switching circuit 3 and the reference signal; The phase data comparison circuit 8 compares the relative phase data detected by the phase detection unit 5 with the reference phase or the previously detected relative phase data, and controls the antenna switching circuit 3 based on the comparison result. There is a particular thing. The phase detection section 5 includes a detection circuit 6 and a relative phase detection circuit 7.

Next, the specific configuration and operation of each circuit will be explained.

FIG. 2 is a block diagram showing an example of the phase detection section 5. As shown in FIG.

The detection circuit 6 is a synchronous detection circuit when using a QPSK signal as an angle modulated wave, and includes multipliers 6-1, 6-2 and 6-3, and low-pass filters 6-4, 6-5 and 6-.
6, a π/2 phase shift circuit 6-7, a voltage controlled oscillator 6-8, and an identification circuit 6-9, and detects the angle modulated wave using the reproduced carrier wave.

The relative phase detection circuit 7 includes a phase shift circuit 9 including n delay lines 9-1 to 9-n, and a sample circuit 10 including (n+1) flip-flops 10-1 to 10-(n+1). Be prepared.

In the phase shift circuit 9, the reproduced carrier wave is used as a reference phase signal, and delay lines 9-1 to 9-n are used to divide the half cycle into n.
are sequentially shifted using , and output signals C6 to Co.

The delay amount of each of the delay lines 9-1 to 9-n is a value obtained by dividing the period of the reproduced carrier wave by 2n. Next, in the sample circuit 10, the angle modulated wave is sent to the flip-flops 10-1 to 10-(n+1) using the phase-shifted signal C3-co.
and output the relative phase data CQO”
"'Q, . . .". The relative phase data allows determining where the phase of the angle modulated wave is located with respect to the phase of the reference phase signal.

The operating principle of the relative phase detection circuit 7 is shown in FIGS. 3(a) and 3(a). For example, if the frequency of the carrier wave is 455kHz (1
period = 2197.8 nsec), each delay line 9-1
If you set the delay amount of ~9-n to 109.9nsec,
Regenerated carrier waves are obtained by shifting the carrier waves by 18 degrees. By means of these phase-shifted signals C3-C, .
As shown in FIG. 3(a), one period of the carrier wave is divided into 20 phase regions. Here, as shown in FIG. 3 (6), when the rising edge of the angle modulated wave signal is located in the phase region shown in the figure, the flip-flops 10-1 to 10- (n+1) are used as the sample circuit l510. , the relative phase data [Qo ""' Q-] becomes]000111111. This relative phase data (q
.

Q, ] differs depending on the phase position of the angle modulated wave, so conversely, this relative phase data [Q.

The phase relationship between the angle modulated wave and the recovered carrier wave can be determined from Q, ).

FIG. 4 is a block diagram showing another example of the phase detection section 5. In FIG.

As the phase shift circuit 9, in addition to being configured by connecting a plurality of delay lines, a shift register can also be used.

FIG. 4 shows a specific circuit example in that case.

When using a shift register, first the detection circuit 6
m of the carrier frequency fc as the voltage controlled oscillator 6-8 in
Use a device that can output twice the frequency, and divide it into the frequency divider 6
(2) The frequency is divided by m by 0 to obtain the reproduced carrier wave.

If the output signal of the voltage controlled oscillator 6-8 is used as a clock for the shift register of the phase shift circuit 9, the recovered carrier wave can be shifted every cycle of the output signal of the voltage controlled oscillator 6-8. Furthermore, the sample circuit 10 can be configured using an exclusive OR circuit and a low-pass filter in addition to flip-flops.

The phase data comparison circuit 8 compares the relative phase data from the phase detection section 5 with reference phase data or a plurality of past relative phase data. Furthermore, the phase data comparison circuit 8
If it is determined that the line quality has deteriorated based on the comparison data, the antenna switching circuit 3 is controlled to switch the antenna connected to the receiver 4.

As a comparison method, if the range of possible phases at that time is known in advance, a certain reference phase region that includes that region is determined, and when the phase at that time is located outside the reference phase region, other Use the method of switching to the antenna.

For example, in the case of a QPS signal, the signal phase on the signal space is represented by only four phase points as shown in FIG. Even when the QPS signal is band-limited with a roll-off filter, if only the optimal identification timing is focused, only four phase points will still be shown. If the carrier wave corresponding to the I-axis or Q-axis can be reproduced on the demodulation side, these four phase regions will be known. This holds true not only for synchronous detection but also for delayed detection.

When a QPSK signal passes through a transmission line where fading or the like exists, the phase varies randomly from four phase points as shown in FIG. At this time, the larger the deviation of the phase fluctuation, the higher the probability that an error will occur. Therefore, if the phase deviation is large at the identification timing, for example, if the antenna is located in the shaded area in FIG. 6 (outside the reference phase area), the antenna is switched to another antenna.

At this time, when the modulated signal phase of the angle modulated wave received from the switching destination antenna is again outside the reference phase region, there are the following two operating algorithms. One of them is
This is a method in which the antenna continues to be switched until an angle modulated wave whose modulated signal is located within the reference phase region is received. The other method is to continue reception with the new antenna for a certain period of time even if it is outside the reference phase region once the antenna is switched, and then switch can be made. Generally, in antenna switching diversity, the phase of the received wave jumps at the switching time, so line quality often deteriorates immediately after switching. Therefore, the latter switching method is often effective.

The above example shows the case where the phase fluctuates due to fading, but this method can be used not only when the phase fluctuates due to fading, but also when the phase fluctuates due to other factors such as thermal noise and interference.
If the fluctuations are independent in the two branches, a diversity effect can be expected.

FIG. 7 is a diagram showing the above-mentioned phase comparison method, and FIG.
The figure is a block diagram showing an example of a phase data comparison circuit that implements this method.

As shown in FIG. 7, weighting numbers are assigned to phase regions on the signal space, and weighting numbers for relative phase data from the phase detection section 5 are determined. This is as shown in Figure 8.
It can be easily constructed using the combinational logic circuit 8-1. Next, the subtraction circuit 8-2 subtracts the weight number for the relative phase data from the maximum weight number (2 in this case) of the reference phase region, and compares the magnitude of the weight number based on the sign bit.

When the weight number of the relative phase data is larger than the weight number of the reference phase region, the antenna is switched (in the example of FIG. 7, switching is performed when the weight number is 4).

As shown above, since this embodiment does not require a reception level, a log amplifier is not required, and the circuit can be simplified and no adjustment is required. There is no longer any restriction, and diversity effects can be obtained over a wide range of reception levels.

Further, when the correlation between the plurality of branches is small, a diversity effect can be obtained not only against fading but also against thermal noise and other factors that degrade transmission characteristics.

FIG. 9 shows a circuit configuration for reducing the correlation of thermal noise between branches. By connecting high gain receiving amplifiers 11.12 between each antenna 1.2 and antenna switching circuit 3, the correlation of thermal noise between each branch can be reduced.

FIG. 10 shows a signal vector diagram when the reception level is low. When the two reception levels are both small, errors may occur due to thermal noise even when the reception levels are compared. However, in this embodiment, even when there is a lot of thermal noise, a branch that is less affected by the vector of thermal noise is always selected, so that a diversity effect can be obtained even in a low-level region where conventionally there was no diversity effect.

FIG. 11 shows another example of the relative phase detection circuit 7.

In this example, the voltages of the ■ signal and the Q signal obtained by the detection circuit 6 are transferred to a comparator or an A/D converter 7-21.
~7-2n, ? -31 to 7-30 to convert into digital data. From this data, relative phase data is determined by calculation circuit 7-1.

FIG. 12 shows another example of the detection circuit 6. As the detection circuit 6, not only a synchronous detection circuit but also a delay detection circuit can be used. That is, it includes a π/2 phase shift circuit 6-11, multipliers 6-12 and 6-13, an identification circuit 6-14, and a delay circuit 6-15. The detection circuit 6 obtains a detection output regarding the phase difference component of the data signal by multiplying the input angle modulated wave by a signal delayed by the delay circuit 6-15.

In this case, as the reference phase signal inputted to the phase shift circuit 9, a signal obtained by delaying the angle modulated wave by the delay circuit 6-15 is used.

In the above description, the case where the number of diversity branches n=2 was explained, but the present invention can be implemented in the same way even when the number of diversity branches is n=3 or more.

〔Effect of the invention〕

As explained above, the present invention uses the phase information of the angle modulated wave as a method for selecting a branch, so that a reception level detection and comparison circuit is not required.

As a result, there is no need to adjust the reception level detection circuit or a log amplifier with a wide dynamic range, which simplifies the reception circuit, and also reduces the diversity effect due to incomplete adjustment of the reception level detection circuit. There is no risk of this occurring. Furthermore, since phase detection can be realized entirely by digital circuits, it is possible to eliminate the need for adjustment and has the advantage of extremely high reliability.

Furthermore, since diversity has an effect not only on fading but also on interference, thermal noise, etc., it is possible to improve the quality of transmission characteristics. From the above, the present invention is applicable to general wireless communication, and its practical effects are extremely large. Obtaining a diversity effect even with respect to thermal noise means that the receiving sensitivity of the radio equipment increases, and this effect is particularly large in satellite communications where even a slight increase in sensitivity is important.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an antenna switching diversity receiving circuit according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a phase detection section. FIG. 3 is an explanatory diagram of the operating principle of the relative phase detection circuit. FIG. 4 is a block diagram showing another example of the phase detection section. FIG. 5 is an explanatory diagram showing the signal phase of the QPSK signal on the signal space. FIG. 6 is an explanatory diagram showing the phase of a QPSK signal when it passes through a transmission line where fading occurs. FIG. 7 is an explanatory diagram of a branch determination method. FIG. 8 is a block diagram of a phase data comparison circuit that implements this method. FIG. 9 is a diagram showing a circuit configuration for reducing the correlation of thermal noise between branches. FIG. 10 is a signal vector diagram when the reception level is low. FIG. 11 is a block diagram showing another example of the relative phase detection circuit. FIG. 12 is a block diagram showing another example of the detection circuit. FIG. 13 is a block diagram of a conventional antenna switching diversity receiving circuit. 1.2... Antenna, 3... Antenna switching circuit, 4
... Receiver, 5... Phase detection section, 6... Detection circuit, 6-1 to 6-3.6-8.6-12.6-13...
Multiplier, 6-4 to 6-6...Low pass filter, 6-
7.6-11...π/2 phase shift circuit, 6-8...
・Voltage controlled oscillator, 6-9.6-14...Identification circuit,
6-lO... Frequency divider, 6-15... Delay circuit, 7.
...Relative phase detection circuit, 7-1...Calculation circuit, 7-2
1-7-2n. 7-31 to 7-3m... Comparator or A/D converter, 8... Phase data comparison circuit, 8-1... Combinational logic circuit, 8-2... Subtraction circuit, 9... Phase shift circuit, 9-1 to 9-n...delay line, 10...sample circuit, lo-1 to 1O-(n+1>...flip-flop, 11.12...high gain receiving amplifier, 21
. . . Reception level detection circuit, 22 . . . Level comparison circuit.

Claims (1)

[Claims] 1. A diversity receiving circuit comprising a plurality of antennas for receiving angle modulated waves and an antenna switching means for selecting one of the plurality of antennas and connecting it to a receiver, a phase detection section that detects the relative phase between the instantaneous phase of the angle modulated wave received by the antenna selected by the means and the reference signal; 1. A diversity receiving circuit comprising: a phase data comparison circuit that compares relative phase data of the antenna and controls the antenna switching means based on the comparison result.