JP2002152171A - Diversity receiver and orthogonal frequency-division multiplex signal receiving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably receive an orthogonal frequency-division multiplex signal with simple constitution. SOLUTION: A mixer 15 mixes and sends a receive signal amplified by an LNA 5 and receive signals having their phases shifted by phase shifters 9 to 11 to a tuner 16. According to the amplitudes of signals having triangular waveforms generated by triangular wave generators 12 to 14, the phase shifters 9 to 11 prescribe the phase shift quantities of the receive signals received by antennas 2 to 4 respectively. The phase shift quantities of the phase shifters 9 to 11 vary periodically, so the signal level after the synthesis by the mixer 15 varies periodically. Cycles of variation in the phase shift quantities of the phase shifters 9 to 11, i.e. Cycles of the signals generated by the triangular wave generators 12 to 14 are made shorter than the depth of time interleaving to disperse modulation errors, thereby enabling stable reception.

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 signals subjected to orthogonal frequency division multiplexing using a plurality of receiving antennas, and more particularly to a diversity receiver capable of stably receiving signals with a simple configuration. A possible diversity 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. 2 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. 2 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 receives RSSI (Received Signal Strength).
Notification to the demodulator 28 using an Indication signal. The demodulator 28 monitors the RSSI signal, and controls the selector 26 when the signal level falls below a predetermined threshold,
Switch the selection of the received signal. 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. 2 demodulates a digital signal transmitted by a configuration using an equalizer, the frequency characteristic changes abruptly by switching the selection of the received signal. In some cases, an error in equalizing a signal becomes large, and a possibility of occurrence of a demodulation error increases.

Furthermore, the above-mentioned conventional diversity receiver requires a circuit for controlling the operation of the selector 26 shown in FIG. 2 to switch the selection of the received signal, and has a problem that the circuit configuration becomes complicated.

The present invention has been made in view of the above situation, and provides a diversity receiver capable of stably receiving an orthogonal frequency division multiplexed signal with a simple configuration. With the goal.

[0010]

In order to achieve the above object, a diversity receiver according to a first aspect of the present invention comprises a plurality of antennas for receiving a radio signal subjected to orthogonal frequency division multiplexing; A phase shifter for shifting a phase of a reception signal received by a plurality of antennas; a reception signal received by one of the plurality of antennas not coupled to the phase shifter; and a reception shifted in phase by the phase shifter. A mixer for synthesizing a signal, a tuner for converting a signal of a predetermined band synthesized by the mixer to an intermediate frequency signal, and a demodulator for demodulating a digital signal from the intermediate frequency signal obtained by the tuner And characterized in that:

According to the present invention, the phase shifter shifts the phase of a signal received by a plurality of antennas. The mixer combines a reception signal received by one of the plurality of antennas that is not coupled to the phase shifter and a reception signal whose phase has been shifted by the phase shifter, and provides the digital signal for demodulation. As a result, the signal level can be increased in accordance with the phase relationship between the received signals received by the plurality of antennas, and the reception characteristics can be improved to enable stable reception. Also, there is no need to switch the selection of the received signals received by multiple antennas,
With a simple configuration, signals subjected to orthogonal frequency division multiplexing can be received stably.

Further, the apparatus further comprises a periodic signal generator for generating a signal having a predetermined period, wherein the phase shifter defines a phase shift amount in accordance with an amplitude of the signal generated by the periodic signal generator, thereby providing a reception signal. It is desirable to periodically fluctuate the phase shift amount. As a result, it is possible to prevent the reception level of the reception signal from remaining lowered for a long time,
Stable reception becomes possible.

More specifically, it is desirable that the period of the signal generated by the periodic signal generator is shorter than the depth of time interleaving performed for transmitting a digital signal on the transmission side. As a result, it is possible to easily correct the error by dispersing the demodulation error, and to suppress the deterioration of the reception characteristic.

For example, it is preferable that the periodic signal generator generates a signal whose voltage waveform has a substantially triangular shape.

In the orthogonal frequency division multiplexed signal receiving method according to a second aspect of the present invention, the signals received by a plurality of antennas are shifted in phase and then combined, and the combined signal of a predetermined band is subjected to frequency conversion. As an intermediate frequency,
The digital signal transmitted by the orthogonal frequency division multiplexing method is demodulated.

Here, it is desirable that the amount of phase shift when shifting the phase of the received signal is changed in a cycle shorter than the depth of time interleaving performed for transmitting the digital signal on the transmitting side.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a diversity receiver 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 phase shifters 9 to 11, a plurality of triangular wave generators 12 to 14, a mixer 15, a tuner 1
6 and a demodulator 17.

The 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 mixer 15 via LNA 5. Antenna 2 is coupled to phase shifter 9 via LNA 6. Antenna 3 is coupled to phase shifter 10 via LNA 7. The antenna 4 is L
It is coupled to the phase shifter 11 via NA8.

Here, 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, one symbol section 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 section and copies the rear part of the effective symbol section.

The plurality of LNAs 5 to 8 are low noise amplifier circuits for amplifying signals received by the antennas 1 to 4, respectively. The LNA 5 sends the amplified received signal to the mixer 15. The LNAs 6 to 8 send the amplified received signals to the phase shifters 9 to 11, respectively.

Each of the plurality of phase shifters 9 to 11 has L
This is for shifting the phase of the received signal amplified by NA6 to NA8. For example, the phase shifters 9 to 11
Defines the amount of phase shift corresponding to the amplitude of the signals generated by the triangular wave generators 12 to 14, that is, the magnitude of the signal voltage, and shifts the phase of the received signal.

The plurality of triangular wave generators 12 to 14 generate signals having a substantially triangular signal waveform (voltage waveform) and a predetermined period. The signals generated by the triangular wave generators 12 to 14 are supplied to the phase shifters 9 to 11, respectively.

The mixer 15 is for synthesizing the signal amplified by the LNA 5 and the reception signal whose phase has been shifted by each of the phase shifters 9-11.
The mixer 15 combines a signal obtained by combining the received signals,
Send to tuner 16.

The tuner 16 includes a down converter, a band-pass filter, and the like. The tuner 16 selects and extracts a received signal that has transmitted a desired digital signal, and outputs an IF (Intermed) signal.
iateFrequency (intermediate frequency) signal.

The demodulator 17 has a quadrature detector, an A / D (Anal
og / Digital converter, FFT (FastFourier Transfor)
m) It is constituted by a circuit and the like, for demodulating a digital signal transmitted by the orthogonal frequency division multiplexing method from the IF signal extracted by the tuner 16 and outputting the demodulated data as demodulated data.

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.

The received signals received by the plurality of antennas 1 to 4 are sent to LNAs 5 to 8 and amplified.
The LNA 5 sends the amplified signal to the mixer 15. Also,
The LNAs 6 to 8 send the amplified signals to the phase shifters 9 to 11, respectively.

The phase shifters 9 to 11 define the phase shift amounts based on the oscillation signals having the triangular voltage waveforms generated by the triangular wave generators 12 to 14, respectively, and each of the LNs
After the phases of the received signals received from A6 to A8 are shifted, they are sent to the mixer 15.

The mixer 15 combines the reception signal amplified by the LNA 5 and the reception signal whose phase has been shifted by the phase shifters 9 to 11, and sends it to the tuner 16.

The tuner 16 selects and extracts a reception signal in a band for transmitting a desired digital signal from the signal synthesized by the mixer 15, converts the signal into an IF signal, and sends the IF signal to the demodulator 17.

The demodulator 17 demodulates a digital signal from the IF signal obtained by the tuner 16 and outputs the demodulated data as demodulated data.

For example, if the signal level of the received signal received by any one of the plurality of antennas 1 to 4 is particularly higher than the signal level of the received signal received by another antenna, The signal level is almost the same as the level of the signal received by the antenna having the higher reception level.

On the other hand, if the signal levels of the signals received by two or more of the plurality of antennas 1 to 4 are high and substantially the same, when the received signals are combined by the mixer 15, Depending on the phase relationship and the status (profile) of the multipath, a difference occurs in the signal level after the combination.

The phase shifters 9 to 11 include a triangular wave generator 12
The amount by which the phase of the received signal is shifted (the amount of phase shift) is defined in accordance with the amplitude of the signal having a triangular voltage waveform generated in to, that is, the magnitude of the signal voltage. As a result, the amount of phase shift in the phase shifters 9 to 11 fluctuates periodically. Therefore, even if the signal level of each received signal before synthesis is constant, the signal level of the signal synthesized by the mixer 15 is periodically changed. To fluctuate.

At this time, for example, in an environment without multipath, if the signal levels of the received signals received by the plurality of antennas 1 to 4 are the same, the signal output from the LNA 5 and the signal passed through each of the phase shifters 9 to 11 When the signals have the same phase, the signal level is quadrupled by the combination. Thereby, the reception characteristics of the signal subjected to the orthogonal frequency division multiplexing are improved, and the signal can be stably received.

Also, depending on the phase relationship between the signal output from the LNA 5 and the signal passing through the phase shifters 9 to 11, the received signals may cancel each other due to the combination, and the signal level may become zero. In this case, a demodulation error occurs.

Therefore, the period in which the phase shift amounts in the phase shifters 9 to 11 fluctuate, that is, the triangular wave generators 12 to 14
The period of the signal (triangular wave) generated at is made shorter than the depth of time interleaving performed for transmitting the digital signal on the transmission side. Note that the time interleaving depth indicates the degree to which symbols adjacent to each other in a digital signal before interleaving on the transmitting side are separated on the time axis after interleaving. As a result, it is possible to easily correct the error by dispersing the demodulation error, suppress deterioration of the reception characteristics, and stably receive the signal subjected to the orthogonal frequency division multiplexing.

Further, since a signal obtained by synthesizing the received signals received by the plurality of antennas 1 to 4 is used for demodulating the digital signal, the reception level of the signal received by each of the antennas 1 to 4 changes with time. Therefore, even when the antenna having the highest reception level changes, it is possible to suppress a decrease in the signal level after the synthesis,
The receiving characteristics can be improved.

As described above, according to the present invention,
The signals received by the plurality of antennas 1 to 4 are combined with a phase difference therebetween. At this time, the signal level of the received signal can be periodically changed by periodically changing the phase shift amount of the received signal and synthesizing the received signal. As a result, it is possible to prevent the signal level of the received signal from remaining low for a long time, to appropriately demodulate the transmitted digital signal, and to stabilize the signal subjected to the orthogonal frequency division multiplexing. Can be received.

Further, according to the present invention, the selection of the received signal is not switched as in the prior art. Therefore, the frequency characteristic of the received signal does not change suddenly, and the signal subjected to orthogonal frequency division multiplexing can be received stably. Further, a circuit for controlling the operation for switching the selection of the reception signal is not required, and the configuration is simplified.

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

In the above-described embodiment, the description has been made assuming that signals having a triangular voltage waveform are generated by the triangular wave generators 12 to 14 to control the amount of phase shift in each of the phase shifters 9 to 11. It is not limited to this. That is, for example, to control the amount of phase shift in each of the phase shifters 9 to 11, such as a sine wave generator that generates a signal having a sine waveform, in order to periodically change the amount of phase shift in the phase shifters 9 to 11. May be generated.

[0044]

As described above, according to the present invention, in order to have a phase difference between received signals simultaneously received by a plurality of antennas, the received signals are shifted in phase and then combined. And demodulate the digital signal. This makes it possible to stably receive signals subjected to orthogonal frequency division multiplexing with a simple configuration.

[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 diagram illustrating a configuration of a conventional diversity receiver.

[Explanation of symbols]

 1-4, 18-21 Antenna 5-8, 22-25 LNA 9-11 Phase shifter 12-14 Triangular wave generator 15 Mixer 16, 27 Tuner 17, 28 Demodulator 26 Selector

Claims (6)

[Claims] A plurality of antennas for receiving a radio signal subjected to orthogonal frequency division multiplexing; a phase shifter for shifting a phase of a reception signal received by the plurality of antennas; A mixer that combines a reception signal received by a signal not coupled to the shifter and a reception signal whose phase has been shifted by the phase shifter, and performs frequency conversion on a signal in a predetermined band synthesized by the mixer. A diversity receiver, comprising: a tuner serving as an intermediate frequency signal; and a demodulator for demodulating a digital signal from the intermediate frequency signal obtained by the tuner. 2. The apparatus according to claim 1, further comprising a periodic signal generator configured to generate a signal having a predetermined period, wherein the phase shifter defines a phase shift amount according to an amplitude of the signal generated by the periodic signal generator, thereby receiving the signal. The diversity receiver according to claim 1, wherein the phase shift amount is periodically changed. 3. The period of a signal generated by the periodic signal generator is shorter than a depth of time interleaving performed for transmitting a digital signal on a transmission side. The diversity receiver as described. 4. The diversity receiver according to claim 2, wherein the periodic signal generator generates a signal whose voltage waveform has a substantially triangular shape. 5. A digital signal transmitted by an orthogonal frequency division multiplexing method, wherein received signals received by a plurality of antennas are shifted in phase and then combined, and the combined signal of a predetermined band is converted into an intermediate frequency by frequency conversion. Demodulating the orthogonal frequency division multiplexed signal. 6. The method according to claim 1, wherein the amount of phase shift at the time of shifting the phase of the received signal is changed in a cycle shorter than the depth of time interleaving performed for transmitting the digital signal on the transmitting side. An orthogonal frequency division multiplexed signal receiving method according to claim 5.