JPH08172385A - Diversity receiver - Google Patents

Abstract

PURPOSE: To reduce the degradation of the transmission quality due to drop-out of a prescribed frequency component in the case of high-speed radio transmission of FSK in transmission line circumstances where multipath delay exists. CONSTITUTION: Diversity switching or synthesis is independently performed for each frequency component in the succeeding stage of band filters 11 to 14 which extract frequency components corresponding to an information signal in an FSK receiver. If multipath delay exists and a frequency component f1 is dropped out in a diversity antenna #1 and a frequency component f2 is dropped out in an antenna #2, the diversity effect appears by this diversity reception though the diversity effect doesn't appear regardless of non- correlations between two antennas in a conventional FSK receiver, and the satisfactory transmission quality is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver, and particularly to frequency modulation (FSK) in wireless transmission.
The present invention relates to a diversity receiver in a wireless transmission system that performs the ncy shift keying) method.

[0002]

2. Description of the Related Art A conventional diversity receiver applied to the FSK system is shown in FIG. This conventional example shows antenna selection diversity.

A received signal input from the two antennas 1 and 2 is selected by a switch 5, and a radio frequency (R) for converting the radio frequency of the received signal into an intermediate frequency is used.
After passing through the F) / intermediate frequency (IF) circuit 3, the band is limited by two band pass filters. FIG. 16 shows how the received signal subjected to FSK modulation is observed on the frequency axis.
Shown in Here, binary FSK will be described as an example. F
In SK, a binary information signal (0, 1) is transmitted at each frequency f1, f
Transmission is performed in correspondence with 2. When the information signal is 0, the frequency f1 is transmitted, and when the information signal is 1, the frequency f2 is transmitted. On the receiving side, the bandpass filters 11 and 12 tuned to the respective frequencies f1 and f2 are used, and the power of the output is calculated by the envelope detection circuits 15 and 16, and the subtractor 23 determines which bandpass filter has a larger output. And the decision circuit 25 decides which is larger at an appropriate time to decide which of the information signals has been sent.

Antenna selection is performed as shown in FIG. The signal level is measured in the subsequent stage of the RF / IF circuit 3, and when the measured signal level becomes equal to or lower than the switching level, switching to the other antenna is performed. FIG.
In FIG. 5, the solid line shows the reception level of the antenna 1, the dotted line shows the reception level of the antenna 2, and the thick line shows the selected reception level. Looking at the reception level of the antenna 1 indicated by the solid line, it can be seen that the reception level varies with time. The reception level of a wireless station in wireless communication is affected by reflection, diffraction, scattering, etc. due to the topography and features around the wireless station, and there are a high reception level and a low reception level. As the wireless station moves to a high level or a low level, its reception level fluctuates with time. This fluctuation of the reception level is called fading. By performing diversity as shown in FIG. 12, it is possible to prevent deterioration of transmission quality due to fading.

FIG. 13 shows an example of diversity after detection. In the diversity after detection, the received signals input from the two antennas 1 and 2 are each detected by a circuit similar to the receiver shown in FIG. The detected determination signals S1 and S2 corresponding to the respective antennas are input to the selection circuit 5A, and the selected determination value S3 is output. The state of selection is shown in FIG. The level of the output of each RF / IF circuit 3 is detected and compared, and the one with the larger level is selected. Compared with the antenna selection diversity, both levels can be detected, so that there is an advantage that an antenna with a large level can always be selected. Further, switching of the antenna is switching by an analog switch, and switching noise is generated, so a countermeasure for it is necessary, but it is not necessary in post-detection selection diversity.
However, the post-detection selection diversity requires two systems for each circuit (especially the RF / IF circuit) as compared with the antenna selection, and therefore has a drawback that measures must be taken to reduce the size and power consumption. .

FIG. 13 shows a conventional example of combined diversity. The received signals input from the two antennas 1 and 2 pass through the RF / IF circuits 3 and 4 and then are combined in the adder 10A. When the signals are combined, the phases of the signals before the combination must be matched. Therefore, the phase difference is detected by the phase detection circuit 9 from the output signals of the RF / IF circuits 3 and 4, and the phase shifter 10 is used to bring them into phase Convert the phase with. After performing the in-phase synthesis, the two band-pass filters 11
And 12 and envelope detectors 15 and 16 for demodulation.

[0007]

In any of the antenna selection diversity and post-detection selection diversity, the conventional diversity receiver has the following drawbacks.

[0008] When wireless transmission is attempted at high speed, a problem that multipath delay occurs occurs conspicuously. In wireless transmission, a radio wave directly coming from a transmitting station to a receiving station and a radio wave reflected from a surrounding reflector are simultaneously received. The reflected wave has a time delay because it has a different propagation distance than the direct wave. FIG. 17 shows frequency characteristics when a direct wave and a delayed wave with a time delay are simultaneously received.
Shown in The direct wave and the delayed wave strengthen each other at a certain frequency because their phases match each other, and weaken each other because they have opposite phases at a certain frequency. FIG. 18 shows frequency characteristics in which received power drops at frequencies fa and fb. This falling frequency is determined by the phases of the direct wave and the delayed wave. The interval of the frequency (fa and fb) that falls is determined by the delay amount of the delayed wave.

It is assumed that FSK transmission shown in FIG. 17 is performed through a transmission line having a frequency characteristic as shown in FIG. Depending on the phases of the direct wave and the delayed wave, the received power may drop at the frequency f1. In this case, the frequency component corresponding to the information signal 0 is missing,
This causes a serious deterioration in communication quality (FIG. 19 (a)). The conventional selection diversity is applied in such a transmission path condition. 19A shows an input signal of the antenna 1, and FIG.
Let (b) be the input signal of the antenna 2. Each input signal is affected by each transmission line, and the frequency of f1 is lowered in the antenna 1 and f2 is lowered in the antenna 2. In diversity, the effect does not appear when the inputs of multiple antennas are correlated. However, the two inputs shown in FIG. 18 are uncorrelated. In this case, the effect of diversity should appear. However, no matter which of these two received signals is selected, the frequency region on one side is lost, so that the diversity effect does not appear at all.

The above example has a fatal disadvantage that the diversity effect does not appear at all even though there is no correlation between a plurality of antennas.

In addition, the phase detection circuit is required in the synthesis diversity. When the terminal moves at high speed, the fading becomes faster. In fading, there is a sudden change in the phase at the valley. A large-scale calculation is required to construct a phase detection circuit that follows this phase fluctuation. Although various arithmetic algorithms have been proposed, generally, when trying to obtain a high-speed tracking characteristic, the arithmetic scale increases in proportion to it. In addition, the following characteristics are improved, but deterioration factors such as lack of stability also occur.

[0012] In wireless communication, the mobility of the terminal is drawing attention. Further, from the perspective of pursuing mobility, downsizing, low power consumption, and portability of terminals are desired. The in-phase combining diversity system provided with the phase detection circuit has a drawback that it cannot satisfy these requirements in terms of a large amount of calculation and feasibility of the variable phase shifter 10.

[0013]

In order to solve the above problems, a diversity receiver according to the present invention is an antenna which receives a signal frequency-modulated by a specific frequency modulation system, and an antenna which is unique to the frequency modulation system. A plurality of receiving sections each including a plurality of bandpass means having characteristics tuned to a frequency and a detection means for detecting the output of the band notification means corresponding to each of these bandpass means, And a processing unit that performs diversity processing based on output signals from a plurality of receiving units corresponding to the respective frequencies.

The processing section may include a selection circuit for selectively outputting output signals from a plurality of receiving sections corresponding to respective natural frequencies, independently for each frequency unique to the frequency modulation method. .

Further, the processing section includes a synthesizing circuit which outputs a synthetic signal of output signals from a plurality of receiving sections corresponding to respective natural frequencies, independently for each frequency unique to the frequency modulation method. You may stay.

[0016]

The present invention is one method of diversity after detection.

The received signal input from each antenna is R
Although passed through the F / IF circuit, it passes through a bandpass filter tuned to the frequency assigned to each information signal. The output of the bandpass filter can be switched independently of the output of the bandpass filter of the same frequency on the different antenna side.

The input of each antenna is affected by the frequency characteristics of the transmission line due to the phase relationship between the direct wave and the delayed wave at each antenna end. Here, consider a case where the frequencies at which the received power drops at the respective antennas are different. That is, consider a case where there is no correlation between the antennas in terms of their frequency characteristics. In the present invention, the bandpass filter output tuned to each frequency is independently selected. Therefore, even if there is a drop in a certain frequency region in a certain antenna and the frequency region corresponding to a certain information signal is missing, in order to select the signal in the same frequency region with another antenna, diversity processing is performed. After this, it is possible to compensate for the missing part in each frequency region, and it is possible to reduce transmission errors.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the diversity receiver according to the present invention will be described in detail with reference to the drawings.

A first embodiment of the present invention is shown in FIG. FIG.
In FIG. 12, the parts designated by the same reference numerals as those in FIGS. 12 to 14 show the same or corresponding components as those of the conventional diversity receiver.

This embodiment will be described using binary FSK. The binary FSK modulated wave signal transmits information at two frequencies corresponding to the two information signals shown in FIG.

In this embodiment, the diversity method of the present invention is applied to the asynchronous detection of FSK.

In FIG. 1, the diversity receiver according to the first embodiment has first and second antennas 1 and 2, and
R to convert radio frequency of received signal to intermediate frequency
The RF / IF circuits 3 and 4 and two RF / IF circuits 3 and 4 are provided for each of the RF / IF circuits 3 and 4, and the RF / IF circuit 3 has two frequencies f1 and f2 corresponding to binary information signals (0, 1).
Bandpass filters 11 and 12 and bandpass filters 13 and 14 that tune the outputs of the filters 4 and 4, and envelope detection circuits 15 to 18 that are respectively connected to the bandpass filters 11 to 14 and perform envelope detection of the outputs of the filters.
And a processing unit 21 for performing diversity processing to obtain a desired gain by selecting or combining the outputs of the envelope detection circuits 15 and 16 and the envelope detection circuits 17 and 1.
Diversity processing means 20 including a processing unit 22 for performing diversity processing on the output of 8 and two processing units 21 and 22.
And a decision circuit 24 for deciding which input of the antenna 1 or 2 is preferable based on the output of the subtracter 23.

Next, a diversity receiver according to the second embodiment of the present invention will be described with reference to FIGS.

The received signal input from the first antenna 1 passes through a radio frequency / intermediate frequency conversion (RF / IF) circuit 3 and is converted into an IF signal. The converted signals are separated by bandpass filters 11 and 12 which are tuned to the frequencies corresponding to the respective information signals contained in the received signal. The received signal input from the second antenna 2 is also divided by the third and fourth bandpass filters 13 and 14. Here, the RF / IF circuits 3 and 4 convert the radio frequency (RF) signal input from the antenna into an intermediate frequency (I
F) or a circuit for converting into a baseband signal, and includes all the circuits in the preceding stage of the bandpass filter for extracting the information signal normally used in the FSK receiver. In FSK, an amplitude limiter is often inserted in the preceding stage of the bandpass filter, and it is also included in the RF / IF circuit.

Now, it is assumed that the received signal input from the antenna 1 is affected by the transmission path and is as shown in FIG. 3 (a). This means that the transmission line has frequency characteristics and the frequency f1 for the information signal 0 has just been dropped. Similarly, in the antenna 2, the frequency f2 is missing as shown in FIG.

Here, the output of each band filter is shown in FIG.
As shown in (c) to FIG. 3 (f). antenna#
At the output A point of the BPF 11 on the 1st side, a signal lacking the frequency f1 is obtained. Output B of BPF 13 on the side of antenna # 2
At this point, a signal without frequency f1 is obtained. At the output C point of the BPF 12 on the antenna # 1 side, a signal without the loss of the frequency f2 is obtained. At the output point D of the BPF 14 on the antenna # 2 side, a signal lacking the frequency f2 is obtained. The output of the BPF 12 and the output of the BPF 13 are independently selected from the antenna # 1 side and the antenna # 2 side. The output of each bandpass filter is subjected to envelope detection by the detection circuits 15 to 18, and electric power is output. In the comparator 26, the output power of the BPF 11 on the antenna # 1 side and the B on the antenna # 2 side
The output power of the PF 13 is compared, and the selection circuit 27 selects the larger one. In FIG. 3, since the antenna # 2 side is larger, the output on the antenna # 2 side is selected. Similarly, the comparator 28
Then, as the output of the BPF for f2, the BP on the antenna # 1 side
Select the output of F12. As a result of the selection, FIG.
As shown in (g), it is possible to obtain the same quality as a received signal with no frequency loss.

A third embodiment is shown in FIG. The difference from the second embodiment is that averaging circuits 30 to 33 are provided for performing envelope detection on the outputs of the band-pass filters 11 to 14 and averaging the envelope detection outputs before comparison. By averaging, noise components can be suppressed and higher diversity gain can be obtained. In conventional switching diversity, the effect of diversity tends to be lost when averaging is performed even when switching antennas or after detection diversity, but the output after envelope detection is averaged. Good diversity effect can be obtained by comparing and selecting.

A fourth embodiment is shown in FIG. In the circuit diagrams of the receiver after FIG. 5, the RF / IF circuit and the subsequent parts of FIG. 1 and FIG. 2 are shown. Further, FIG. 6 shows the state of diversity performed in the circuit of FIG. 5 on the frequency axis.

The received signal input from the antenna 1 side is a bandpass filter 11 of frequency f1 and a bandpass filter 12 of f2.
Divided by Similarly, the received signal input from the antenna # 2 side is also divided by the band filters 13 and 14 (FIGS. 6A to 6G). The output of each bandpass filter is subjected to envelope detection, and the power is calculated. Antenna 1
The envelope detection outputs corresponding to the band-pass filter output on the side of the antenna 2 and the envelope detection output corresponding to the side of the antenna 2 are added and synthesized with the same frequency. The frequency f1 is combined by the adder 34, and the frequency f2 is combined by the adder 35 (FIGS. 6C to 6G). The outputs synthesized in the respective frequency regions are compared by the comparator 23, and are discriminated at an appropriate time. 2
By doing so, demodulation into an information signal is performed. High pass filter (high pass filter) 2 between the comparator 23 and the determiner 25
4 is inserted for the purpose of removing the DC component from the input of the determiner 25.

By combining with the electric power after passing through such a bandpass filter, it is possible to obtain the diversity effect without performing the adjustment to the same phase, which is necessary for the conventional combining diversity. . Further, it is possible to save the drop in the frequency domain due to the presence of the delayed wave, and it is possible to obtain the characteristic without loss on the frequency axis as shown in FIG. 6 (g).

The fifth embodiment is shown in FIG.

FIG. 7 shows a circuit equivalent to the combined diversity of FIG. The result of envelope detection of the output of the band-pass filter 11 is a1, the following 12 is a2, 13 is b1, and 14 is b2.
And

In the fourth embodiment of FIG. 5, the input to the discriminator is (a1 + b1)-(a2 + b2) (1), and in the fifth embodiment of FIG. 7, it is (a1-a2) + (b1-b2). … (2). As is clear from the equations (1) and (2), the two embodiments change the order of addition and subtraction.

In the fifth embodiment as well, by performing the synthesis in the latter stage of the band-pass filter, the phase detection circuit and the phase shifter for the in-phase synthesis are unnecessary, and it is possible to reduce the size and power consumption of the radio device. Become.

The sixth embodiment is shown in FIG. In the sixth embodiment, the diversity method of the present invention is applied to the FSK synchronous detection method.

The received signal on the antenna # 1 side is converted into an IF signal and then divided into respective frequency regions by band filters 11 and 12 of f1 and f2, respectively. After that, the frequencies 41 and f2 are respectively multiplied by the multipliers 41 to 44.
Carrier waves COS (2πf1t), COS (2π
Only the signal multiplied by f2t) and converted to the base band by the low pass filters 45 to 48 is extracted. The same procedure is performed on the antenna 2 side.

The outputs corresponding to the band-pass filters of f1 on the antenna 1 side and the antenna 2 side are compared in magnitude by level comparison circuits 51 and 52, and one having a larger power is selected by selection circuits 53 and 54. The output corresponding to the f2 bandpass filter is similarly selected.

After that, as in the conventional synchronous detection circuit, the outputs corresponding to f1 and f2 are compared by the comparator 55,
The decision unit makes a decision at an appropriate time point and demodulates into an information signal.

As described above, even in the FSK synchronous detection system, the diversity receiver can be constructed similarly to the asynchronous detection system, and the same effect can be obtained. That is, it is possible to provide a diversity receiver capable of improving the deterioration caused by the drop of the specific frequency on the frequency axis due to the presence of the delayed wave.

In the sixth embodiment, the selective diversity is taken as an example in the case of the synchronous detection system, but the composition diversity is introduced by incorporating the configuration similar to those of the fourth and fifth embodiments into the synchronous detection system. Can also be realized.

FIG. 9 shows the seventh embodiment.

The seventh embodiment is the same as the fourth embodiment shown in FIG. 5, except that a weighting calculation circuit 65 and a weighting circuit 6 for each output are provided.
1 to 64 are added. It is possible to combine the signals combined by the weighting calculation circuit 65 with such weights as to obtain optimum reception characteristics. In the seventh embodiment, the weighting is calculated using the output of each envelope detection circuit, but the combined output 66 and the demodulated result 67 are used.
Can be used for weighting calculation, and the same effect can be obtained by weighting the bandpass filter outputs 11 to 14. In this case, not only the weight of the amplitude but also the phase of the bandpass filter output can be controlled, and a better reception characteristic can be obtained.

The diversity technique can be used in combination with the interleave method. This will be described with reference to FIG. FIG. 10 shows the configuration of a communication system 70 according to the eighth embodiment in which this diversity method and interleaving are combined.

In the system 71 on the transmitting side, the information sequences 71A to 71K are error correction encoders 72A to 72K, respectively.
Error correction coding is performed using K. The error correction coded K information sequences are input to the interleaver 73 and exchanged with the M sequences 73A to 73M. These series 73A to 73M are respectively transmitted by the transmitter 74 of the transmitter 74.
The signals are modulated by M different frequencies by A to 74M and transmitted.

The receiving system 75 has N antennas 76.
Each antenna which has A to 76N and constitutes the receiving unit 77 receives the sequence modulated into M frequencies.

The N-branch diversity receivers 77A to 77M receive the corresponding frequencies from the respective antennas 76A to 76N, select the branch having the maximum likelihood, demodulate the modulated sequence of the selected branch,
The demodulation sequences 78A to 78M are passed to the deinterleaver 78. The deinterleaver 78 performs the reverse operation of the interleaver 73 to convert the demodulation sequences 78A to 78M into K sequences. Each of the K sequences is an error correction decoder 79A.
To 79K, error-correction decoding is performed, and the original information sequence is obtained. According to the system configured as described above, it is possible to further reduce the code error rate reduced by diversity by combining interleaving and error correction code 1 decoding.

FIG. 11 shows a diversity receiver according to the ninth embodiment of the present invention. In the ninth embodiment, the processing performed in the second embodiment is performed by digital signal processing, and the band filter and the envelope detector, which required four systems, are performed in a single circuit in a time division manner.

The outputs of the RF / IF circuits 3 and 4 are A / D converted by A / D converters 81 and 82, respectively, and input to the digital signal processing circuit 90 as digital signals. The input signal is stored in the memories 83 and 84. The values read into the memories 83 and 84 are sequentially input to the digital filter 85 in a time-divisional manner, and the envelope detection circuit 86 performs band-pass filter processing of the frequencies f1 and f2, respectively, and stores them in the memories 91 to 94. To be done. The outputs of the antenna 1 and the antenna 2 are compared by the comparator 87 and the larger output is selected by the switch 95 for the band-filtered signal of the frequency f1. A similar selection is performed by the comparator 88 and the switch 95 for the band-pass filter processing of the frequency of f2, and the determination circuit 98 demodulates by using the selection result via the subtractor 97.

In the ninth embodiment, the diversity processing is performed by digital signal processing to reduce the circuit scale. Although the circuit configuration is physically different, it is logically equivalent to the second embodiment, and in the present invention, what is logically equivalent to the second embodiment is the gist of the invention.

[0051]

As described above, in the FSK modulation method, the multipath delay is generated by selecting or combining the bandpass filters that are tuned in correspondence with the respective information signals of the demodulators and performing diversity. It is possible to improve the deterioration of quality due to the drop of the specific frequency on the frequency axis.

Further, since the synthesis can be performed in the form in which the phase of the carrier wave is removed or the form in which the phase of the received signal is removed, the phase detection circuit and the shift for the in-phase synthesis which are conventionally required for the synthesis diversity. The phaser can be omitted, and the size and power consumption of the wireless device can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a diversity receiver according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a diversity receiver according to a second embodiment of the present invention.

FIG. 3 is a waveform diagram showing frequency characteristics of the diversity receiver according to the second embodiment of the present invention.

FIG. 4 is a block diagram showing a diversity receiver according to a third exemplary embodiment of the present invention.

FIG. 5 is a block diagram showing a diversity receiver according to a fourth exemplary embodiment of the present invention.

FIG. 6 is a waveform diagram showing the frequency characteristics of the diversity receiver according to the fourth embodiment of the present invention.

FIG. 7 is a block diagram showing a diversity receiver according to a fifth exemplary embodiment of the present invention.

FIG. 8 is a block diagram showing a diversity receiver according to a sixth exemplary embodiment of the present invention.

FIG. 9 is a block diagram showing a diversity receiver according to a seventh embodiment of the present invention.

FIG. 10 is a block diagram showing a communication system according to an eighth embodiment in which the diversity receiver according to the present invention is incorporated in the receiving system side.

FIG. 11 is a block diagram showing a diversity receiver according to a ninth exemplary embodiment of the present invention.

FIG. 12 is a circuit block diagram showing a first conventional example of a diversity receiver.

FIG. 13 is a circuit block diagram showing a second conventional example of the diversity receiver.

FIG. 14 is a circuit block diagram showing a third conventional example of a diversity receiver.

FIG. 15 is an explanatory diagram for explaining a conventional diversity method.

FIG. 16 is an explanatory diagram for explaining a conventional diversity method.

FIG. 17 is an explanatory diagram for explaining a frequency modulation method.

FIG. 18 is a frequency characteristic diagram for explaining problems of the conventional example.

FIG. 19 is a frequency characteristic diagram for explaining the problems of the conventional example.

[Explanation of symbols]

 1, 2 antenna 11 band filter (tuned to f1 frequency) 12 band filter (tuned to f2 frequency) 15, 16 envelope detection circuit 20 diversity processing means 21, 22 processing unit 24 determination circuit

Claims (3)

[Claims] 1. An antenna for receiving a signal frequency-modulated by a specific frequency modulation method, a plurality of band-passing means each having a characteristic tuned to a frequency peculiar to the frequency modulation method, and these band-passing means. A plurality of receiving units each including a detecting unit that detects the output of the band notifying unit corresponding to the respective units are provided, and diversity processing is performed based on output signals from the plurality of receiving units corresponding to each of the unique frequencies. A diversity receiver including a processing unit. 2. The processing unit includes a selection circuit that selectively outputs output signals from a plurality of receiving units corresponding to respective natural frequencies, independently for each frequency unique to the frequency modulation method. The diversity receiver according to claim 1, wherein: 3. The processing unit includes a synthesizing circuit that outputs a synthesized signal of output signals from a plurality of receiving units corresponding to respective natural frequencies, independently for each frequency unique to the frequency modulation method. The diversity receiver according to claim 1, wherein: