JP2002185424A - Diversity receiver and orthogonal frequency division multiplex signal receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive an orthogonal frequency division multiplex signal stably. SOLUTION: A demodulator 15 comprises an antenna control pointer 16 for pointing one of variable attenuators 9-12 subjected to attenuation switching control, and an antenna fixing pointer 17 for pointing a variable attenuator attenuation of which is fixed at zero. At the time of attenuation switching control of the variable attenuators 9-12, the demodulator 15 makes a decision whether a variable attenuator specified by the antenna control pointer 16 is identical to a variable attenuator specified by the antenna fixing pointer 17. When a decision is made that both variable attenuators are identical, the demodulator 15 alters the variable attenuator specified by the antenna control pointer 16 and performs attenuation switching control.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diversity receiver for receiving a radio signal using a plurality of antennas, and more particularly, to a diversity receiver for receiving a signal subjected to orthogonal frequency division multiplexing on a transmission side. Regarding the receiver.

[0002]

2. Description of the Related Art Orthogonal frequency division multiplexing (OFDM) is a system for transmitting digital signals wirelessly.
A requency division multiplex method is known.
In this orthogonal frequency division multiplexing method, digital signals can be transmitted efficiently by multiplexing and transmitting digital signals using a number of subcarriers having different frequencies. Further, in the orthogonal frequency division multiplexing method, by providing a guard interval section in front of an effective symbol section, it is possible to prevent deterioration of reception characteristics due to inter-symbol interference even when multipath occurs.

Conventionally, an antenna switching type diversity receiver as shown in FIG. 3 has been known to reduce the effects of fading due to mobile reception of radio signals subjected to such orthogonal frequency division multiplexing. ing.

The conventional diversity receiver shown in FIG. 3 converts a received signal received by each of the antennas 18 to 21 into
After being amplified by the LNAs 22 to 25, respectively, they are input to the selector 26. The selector 26 selects one received signal based on the select signal from the demodulator 28 and inputs it to the tuner 27. The tuner 27 converts an RF (Radio Frequency) signal of a desired band into an IF (Intermediate
Frequency) and converts the signal to a demodulator 28.

[0005] The tuner 27 detects the signal level of the received signal, and outputs a signal RSSI (Receiviv) indicating the received signal strength.
demodulator 28 using ed Signal Strength Indication).
Notify. The demodulator 28 monitors the signal RSSI, and controls the selector 26 to switch the selection of the received signal when the signal level falls below a predetermined threshold. If the signal level after switching the selection is also equal to or lower than the threshold, the operation for further switching the selection is repeated.

[0006]

In the above-mentioned conventional diversity receiver, it is not possible to detect in advance whether the signal level of the received signal is increased by switching the selection of the received signal. For this reason, the reception state after the switching may be worse than before the switching, and it may not be possible to stably receive the signal subjected to the orthogonal frequency division multiplexing.

When the demodulator 28 shown in FIG. 3 demodulates a digital signal transmitted by a configuration using a signal equalizing circuit, the frequency characteristic changes abruptly by switching the selection of a received signal. In some cases, an error in equalizing the received signal increases, and the possibility of occurrence of a demodulation error increases.

The present invention has been made in view of the above situation, and has as its object to provide a diversity receiver capable of stably receiving a signal subjected to orthogonal frequency division multiplexing.

[0009]

In order to achieve the above object, a diversity receiver according to a first aspect of the present invention receives an orthogonal frequency division multiplexed signal using a plurality of antennas. A plurality of amplifying means for amplifying a received signal received by each of the antennas; a plurality of attenuating means for attenuating the received signal amplified by each of the amplifying means with a variable amount of attenuation; and the plurality of attenuating means. Signal combining means for combining the received signal attenuated by the means,
Demodulating means for demodulating a digital signal from the signal synthesized by the signal synthesizing means and controlling switching of the attenuation in the plurality of attenuating means, wherein the demodulating means switches the amount of attenuation in the plurality of attenuating means. When controlling, an attenuation target designating unit that designates a switching unit of the attenuation amount among the plurality of attenuation units, and when switching control of the attenuation amount in the plurality of attenuation units, among the plurality of attenuation units, And a fixing target designating means for designating a fixed attenuation amount.

According to the present invention, the demodulating means demodulates the digital signal from the signal synthesized by the signal synthesizing means and controls switching of the attenuation in the plurality of attenuating means. Further, the demodulation means, when switching control of the attenuation amount in the plurality of attenuation means, the attenuation means for fixing the attenuation amount,
It can be specified by specifying the fixed target specifying means.
By doing so, the demodulation means can fix one of the attenuation amounts of the plurality of attenuation means and set an appropriate attenuation amount by a simple process when switching control of the attenuation amount. Can be. That is, it is possible to demodulate a transmitted digital signal without switching received signals received by a plurality of antennas, and to prevent a decrease in reception level and control an appropriate amount of attenuation when controlling the amount of attenuation. Can be set. As a result, it is possible to stably receive signals subjected to orthogonal frequency division multiplexing.

More specifically, the demodulating means, when switching control of the attenuation in the plurality of attenuating means, is controlled by the attenuating means specified by the attenuating target specifying means and the fixed target specifying means. It is desirable to determine whether or not the attenuation means is the same, and if it is determined that they are the same, it is desirable to change the attenuation means designated by the attenuation target designating means and switch the attenuation amount.

It is preferable that the fixed object designating means designates one of the plurality of attenuating means having an attenuation amount of zero.

An orthogonal frequency division multiplexed signal receiving method according to a second aspect of the present invention is a method for receiving an orthogonal frequency division multiplexed signal using a plurality of antennas. An amplification step of amplifying a reception signal received by an antenna, and a reception signal amplified in the amplification step, using a plurality of attenuators, an attenuation step of attenuating the variable amount of attenuation corresponding to each antenna,
A signal combining step of combining the received signals attenuated in the attenuating step, and demodulating a digital signal from the signal combined in the signal combining step, and attenuating the received signal corresponding to each of the antennas in the attenuating step Demodulation step of switching control of the amount of attenuation when performing the demodulation step, wherein the demodulation step includes the steps of: The one that switches the amount is designated by the first pointer, the one that fixes the attenuation amount among the plurality of attenuators is designated by the second pointer, and the attenuator designated by the first pointer and the second attenuator are used. It is determined whether or not the attenuator specified by the pointer is the same. Change the attenuator designated by 1 pointer, controls switching of the attenuation, characterized in that.

It is preferable that the attenuation in the attenuator designated by the second pointer is zero.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a diversity receiver 100 according to an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a diversity receiver 100 according to an embodiment of the present invention. As shown, the diversity receiver 100 includes a plurality of antennas 1 to 4 and a plurality of LNAs (Low Noise Amplifiers).
r) 5 to 8, a plurality of variable attenuators 9 to 12, a mixer 13, a tuner 14, and a demodulator 15.

A plurality of antennas 1 to 4 are provided on the transmitting side with orthogonal frequency division multiplexing (OFDM).
ivision Multiplex), and R transmitted by radio
This is for receiving an F (Radio Frequency) signal. Antenna 1 is coupled to variable attenuator 9 via LNA 5. Antenna 2 is coupled to variable attenuator 10 via LNA 6. Antenna 3
Are connected to the variable attenuator 11 via the LNA 7. Antenna 4 is coupled to variable attenuator 12 via LNA 8.

The orthogonal frequency division multiplexed RF signal received by the plurality of antennas 1 to 4 is a signal for transmitting digital data using a number of subcarriers orthogonal to each other in a symbol period. In addition, a symbol section of one cycle is divided into an effective symbol section and a guard interval section. The guard interval section is a redundant signal section that precedes the effective symbol section in the symbol period and copies the rear part of the effective symbol section.

The plurality of LNAs 5 to 8 are connected to a plurality of antennas 1.
, And amplifying circuits for amplifying the received signal. The LNAs 5 to 8 send the amplified reception signals to the variable attenuators 9 to 12, which are respectively coupled.

The plurality of variable attenuators 9 to 12 are attenuation circuits for defining attenuation according to the control signal sent from the demodulator 15 and attenuating the signals received from the LNAs 5 to 8 with variable attenuation. . That is, the variable attenuator 9 attenuates the signal received from the LNA 5 with an attenuation corresponding to the level of the signal C_ANT1 sent from the demodulator 15. The variable attenuator 10 has an attenuation amount corresponding to the level of the signal C_ANT2 sent from the demodulator 15 and LN
Attenuate the signal received from A6. Variable attenuator 1
Reference numeral 1 denotes an attenuation corresponding to the level of the signal C_ANT3 sent from the demodulator 15, and attenuates the signal received from the LNA. The variable attenuator 12 attenuates the signal received from the LNA 8 with an attenuation corresponding to the level of the signal C_ANT4 sent from the demodulator 15. For example, the signals C_ANT1 to C_ANT4
Is high, the attenuation in each of the variable attenuators 9 to 12 is large, and if the level is low, the attenuation is small. When the levels of the signals C_ANT1 to C_ANT4 are the lowest, the attenuation in each of the variable attenuators 9 to 12 is zero.

The mixer 13 includes a plurality of variable attenuators 9
This is for adding and combining the received signals sent from. The mixer 13 sends a signal obtained by combining the received signals to the tuner 14.

The tuner 14 is composed of a down converter, a band-pass filter, and the like.
iateFrequency (intermediate frequency) signal. Further, the tuner 14 measures the received signal strength based on the magnitude of the received signal sent from the mixer 13 and outputs a signal RSSI having a signal level corresponding to the received level.
Is generated and supplied to the demodulator 15.

The demodulator 15 has an A / D (Analog / Digital)
It is composed of a converter, an FFT (Fast Fourier Transform) circuit, a signal equalization circuit, a demapping circuit, etc., and demodulates and demodulates a digital signal transmitted by the orthogonal frequency division multiplexing method from the IF signal extracted by the tuner 14. It is for outputting as data.

Here, the demodulator 15 outputs the signals C_ANT1 to C_AN.
By generating T4 and sending the generated T4 to the variable attenuators 9 to 12, the attenuation of the received signals received by the antennas 1 to 4 is controlled. Further, the demodulator 15 includes an antenna control pointer 16 and an antenna fixed pointer 17.

The antenna control pointer 16 is for designating one of the variable attenuators 9 to 12 for which the switching control of the attenuation is to be performed. For example, the antenna control pointer 16 specifies the variable attenuator to be subjected to the attenuation amount switching control by storing data indicating any one of the variable attenuators 9 to 12 in the semiconductor memory.

The antenna fixing pointer 17 is used to designate one of the variable attenuators 9 to 12 that fixes the attenuation to zero when performing the switching control of the attenuation. For example, the antenna fixed pointer 17 stores the data indicating any one of the variable attenuators 9 to 12 in the semiconductor memory, so that when the attenuation level is switched and the reception level is measured, etc. Specify a variable attenuator whose amount is fixed to zero.

The operation of the diversity receiver 100 according to the embodiment of the present invention will be described below. R that is subjected to orthogonal frequency division multiplexing on the transmitting side and transmitted wirelessly
The F signal is received by a plurality of antennas 1-4.

Signals received by the plurality of antennas 1 to 4 are sent to LNAs 5 to 8 and amplified, respectively.
It is sent to variable attenuators 9-12.

Each of the variable attenuators 9 to 12 is a demodulator 1
The signal received by the plurality of antennas 1 to 4 is attenuated by the amount of attenuation corresponding to the level of the signals C_ANT1 to C_ANT4 received from 5, and sent to the mixer 13.

The mixer 13 is provided with each of the variable attenuators 9-1.
2 are combined and sent to the tuner 14.

The tuner 14 selects and extracts a reception signal in a band for transmitting a desired digital signal from the signal synthesized by the mixer 13, converts the reception signal into an IF signal, and sends the IF signal to the demodulator 15. At this time, the tuner 14 measures the received signal strength from the magnitude of the received signal, generates a signal RSSI indicating the received level, and sends it to the demodulator 15.

The demodulator 15 detects, for example, an effective symbol section of the received signal and executes a process for demodulating a digital signal, such as a fast Fourier transform or a signal equalization process.

Here, the demodulator 15 outputs the signals C_ANT1 to C_AN.
By generating T4 and sending it to the variable attenuators 9 to 12, the amount of attenuation in each of the variable attenuators 9 to 12 is controlled. For example, in order to improve the reception state, the demodulator 15 sequentially changes one of the variable attenuators 9 to 12 for which the amount of attenuation is to be switched and controls the change in the reception level caused by switching the amount of attenuation. Set appropriate attenuation by measuring.

At this time, the demodulator 15 controls the attenuation in each of the variable attenuators 9 to 12 so that at least one of the attenuations in the variable attenuators 9 to 12 becomes zero in order to prevent the reception level from lowering. The amount is controlled by switching.

That is, the demodulator 15 is a variable attenuator of the variable attenuators 9 to 12 that has a current attenuation of zero and maintains the attenuation at zero even when the attenuation is switched. Designated by the antenna fixed pointer 17.

Hereinafter, the demodulator 15 is connected to the variable attenuator 9
The operation at the time of switching control of the amount of attenuation in to 12 will be described with reference to the flowchart shown in FIG.

The demodulator 15 has variable attenuators 9 to 12
When the one that switches the attenuation is specified, the variable attenuator designated by the antenna control pointer 16 is changed to the one whose attenuation is to be switched (step S).
1).

At this time, the demodulator 15 determines whether the variable attenuator specified by the antenna control pointer 16 is the same as the variable attenuator specified by the antenna fixed pointer 17 (step S2).

When the demodulator 15 determines that the variable attenuators specified by the two pointers are the same (YES in step S2), the process returns to step S1 to change the variable attenuator specified by the antenna control pointer 16. Change the attenuator further. That is, the demodulator 1
5 changes the variable attenuator whose attenuation is to be switched to another variable attenuator when the variable attenuator set in the antenna control pointer 16 matches the variable attenuator designated by the antenna fixed pointer 17. Thus, the demodulator 15 can control the variable attenuators 9 to
The operation can be specified so that the attenuation amount of the pointer 12 designated by the antenna fixed pointer 17 is not switched.

On the other hand, when the demodulator 15 determines that the variable attenuators specified by the antenna control pointer 16 and the antenna fixed pointer 17 are not the same (NO in step S2), the demodulator 15 executes the operation of switching the attenuation (step S2). S3). That is, the demodulator 15 calculates the attenuation amount of the variable attenuators 9 to 12 designated by the antenna control pointer 16, for example, the signals C_ANT1 to C_AN.
Switch by changing the level of T4. On this occasion,
The demodulator 15 sets a more appropriate attenuation by measuring a reception level from the signal RSSI sent from the tuner 14, for example. As a result, while controlling at least one of the attenuation amounts of the variable attenuators 9 to 12 to zero, the attenuation amount can be switched and controlled to set a more appropriate attenuation amount. That is, stable reception of the signal subjected to orthogonal frequency division multiplexing becomes possible.

Thereafter, the demodulator 15 determines whether or not the attenuation in the variable attenuator whose attenuation has been switched, that is, the attenuation in the variable attenuator designated by the antenna control pointer 16 is zero (see FIG. 4). Step S4).

The demodulator 15 has an antenna control pointer 16
When it is determined that the attenuation amount in the variable attenuator specified by the above is zero (YES in step S4), the variable attenuator specified by the antenna control pointer 16 is set to the antenna fixed pointer 17 (step S5). Thereby, when the demodulator 15 controls switching of the attenuation in the variable attenuators 9 to 12 next time,
The variable attenuator that fixes the attenuation amount to zero can be changed, and a more appropriate attenuation amount can be specified.

On the other hand, when the demodulator 15 determines that the attenuation in the variable attenuator designated by the antenna control pointer 16 is not zero (N in step S4).
O), the step S5 is skipped, and the operation of switching control of the attenuation is ended.

As described above, when controlling the amount of attenuation in the variable attenuators 9 to 12, the variable attenuators 9 to 12 are controlled.
The attenuation amount of the antenna designated by the antenna fixing pointer 17 is fixed. This makes it possible to set a more appropriate amount of attenuation by controlling the amount of attenuation while fixing at least one of the amounts of attenuation in the variable attenuators 9 to 12 with a simple process. That is, it is possible to prevent a decrease in reception level when switching control of the amount of attenuation, and to stably receive a signal subjected to orthogonal frequency division multiplexing.

As described above, according to the present invention,
The demodulator 15 that controls the switching of the attenuation in the variable attenuators 9 to 12 executes the switching control of the attenuation while fixing the attenuation of the variable attenuator designated by the antenna fixing pointer 17. Thus, by a simple process, while at least one of the attenuation amounts of the variable attenuators 9 to 12 is fixed to zero, the attenuation amounts of the other variable attenuators are switched and controlled to perform orthogonal frequency division multiplexing. The received signal can be stably received.

Further, according to the present invention, selection of a received signal is not switched as in the prior art. Therefore, it is possible to prevent a sudden change in the frequency characteristics of the received signal, and it is possible to stably receive a signal subjected to orthogonal frequency division multiplexing.

The present invention is not limited to the above embodiment, and various modifications and applications are possible. For example, in the above embodiment, the description has been given assuming that signals transmitted wirelessly are received by the four antennas 1 to 4. However, the present invention is not limited to this. Considering the above, signals subjected to orthogonal frequency division multiplexing may be received by any number of antennas.

[0048]

As described above, according to the present invention, at the time of controlling the switching of the attenuation in a plurality of variable attenuators, at least one of the attenuations is fixed to zero and the simple processing is performed. Can set an appropriate amount of attenuation. As a result, it is possible to stably receive signals subjected to orthogonal frequency division multiplexing.

[Brief description of the drawings]

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

FIG. 2 is a flowchart for explaining an operation when a demodulator switches and controls the amount of attenuation in a variable attenuator.

FIG. 3 is a diagram illustrating a configuration of a conventional diversity receiver.

[Explanation of symbols]

 1-4, 18-21 Antennas 5-8, 22-25 LNA 9-12 Variable Attenuator 13 Mixer 14, 27 Tuner 15, 28 Demodulator 16 Antenna Control Pointer 17 Antenna Fixed Pointer 26 Selector 100 Diversity Receiver

Claims (5)

[Claims] 1. A signal subjected to orthogonal frequency division multiplexing,
A diversity receiver for receiving using a plurality of antennas, wherein a plurality of amplifying means for amplifying a received signal received by each of the antennas, and an attenuating variable amount of the received signal amplified by each of the amplifying means A plurality of attenuating means; a signal combining means for combining the received signals attenuated by the plurality of attenuating means; a digital signal demodulated from the signal combined by the signal combining means; and an amount of attenuation in the plurality of attenuating means. Demodulation means for switching control of the attenuation means, wherein the demodulation means, when switching control of the attenuation amount in the plurality of attenuation means, designates an attenuation target designation means for designating one of the plurality of attenuation means for switching the attenuation amount. When switching control of the amount of attenuation in the plurality of attenuating means, the one that fixes the amount of attenuation among the plurality of attenuating means is designated. And a fixed object specifying means. 2. The attenuating means specified by the attenuating target specifying means and the attenuating means specified by the fixed target specifying means, when the demodulating means controls the switching of the amount of attenuation in the plurality of attenuating means. Determine whether they are the same,
The diversity receiver according to claim 1, wherein, when it is determined that they are the same, the attenuation means designated by the attenuation target designation means is changed to switch and control the amount of attenuation. 3. The diversity receiver according to claim 1, wherein said fixed target designation means designates one of said plurality of attenuation means whose attenuation is zero. 4. A signal which has been subjected to orthogonal frequency division multiplexing,
An orthogonal frequency division multiplexing signal receiving method for receiving using a plurality of antennas, comprising: an amplification step of amplifying a reception signal received by each of the antennas; Attenuating step of attenuating the variable amount of attenuation corresponding to each of the antennas; a signal combining step of combining the received signals attenuated in the attenuating step; a digital signal from the signal combined in the signal combining step And demodulating the received signal corresponding to each of the antennas in the attenuating step. The demodulating step comprises: When switching control of the attenuation in the attenuation step, the attenuation is switched among the plurality of attenuators. The attenuator specified by the first pointer is designated by a first pointer, and the one that attenuates the fixed amount among the plurality of attenuators is designated by a second pointer. The attenuator designated by the first pointer and the second pointer It is determined whether or not the specified attenuator is the same, and if it is determined that the attenuator is the same, the attenuator specified by the first pointer is changed to control switching of the attenuation. An orthogonal frequency division multiplex signal receiving method. 5. The orthogonal frequency division multiplexed signal receiving method according to claim 4, wherein the attenuation in the attenuator specified by the second pointer is zero.