Diversity receiver and orthogonal frequency-division multiplex signal receiving method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a diversity receiver that receives a radio signal using a plurality of receiving antennas, and more particularly to a diversity receiver for receiving a signal that has been subjected to orthogonal frequency division multiplexing on the transmitting side.

【0002】

[Conventional technology]

Orthogonal Frequency Division Multiplex (OFDM) is known as a method for transmitting digital signals wirelessly. In this orthogonal frequency division multiplexing method, a digital signal can be efficiently transmitted by multiplexing and transmitting a digital signal using a large number of subcarriers having different frequencies. Further, in the orthogonal frequency division multiplexing method, by providing a guard interval section in front of the effective symbol section, it is possible to prevent deterioration of the reception characteristic due to intersymbol interference even when multipath occurs.

【0003】

Conventionally, an antenna switching type diversity receiver as shown in FIG. 2 has been known as a device for reducing the influence of fading due to mobile reception of a radio signal subjected to such orthogonal frequency division multiplexing.

【0004】

In the conventional diversity receiver shown in FIG. 2, the received signals received by the antennas 15 to 18 are amplified by the LNAs 19 to 22, and then input to the selector 23. The selector 23 selects one received signal based on the select signal from the demodulator 25 and inputs it to the tuner 24. The tuner 24 frequency-converts an RF (Radio Frequency) signal in a desired band into an IF (Intermediate Frequency) signal and sends it to the demodulator 25.

【0005】

Further, the tuner 24 detects the signal level of the received signal and notifies the demodulator 25 using the RSSI (Received Signal Strength Indication) signal. The demodulator 25 monitors the RSSI signal, and when the signal level falls below a predetermined threshold value, controls the selector 23 to switch the selection of the received signal. If the signal level after switching the selection is also below the threshold value, the operation for switching the selection is repeated.

【0006】

[Problems to be Solved by the Invention]

In the conventional diversity receiver, it is not possible to detect in advance whether or not the signal level of the received signal is increased by switching the selection of the received signal. Therefore, the reception state after switching may be worse than that before switching, and the signal subjected to orthogonal frequency division multiplexing may not be stably received.

【0007】

Further, when the demodulator 25 shown in FIG. 2 demodulates the digital signal transmitted by the configuration using the equalizer, the frequency characteristic changes abruptly due to the switching of the selection of the received signal, so that the received signal is equalized. The error at the time of conversion becomes large, and the possibility that a demodulation error occurs may increase.

【0008】

Further, the conventional diversity receiver requires a circuit for controlling the operation of the selector 23 shown in FIG. 2 to switch the selection of the received signal, which causes a problem that the circuit configuration becomes complicated.

【0009】

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a diversity receiver capable of stably receiving a signal subjected to orthogonal frequency division multiplexing with a simple configuration. To do.

【0010】

[Means for solving problems]

In order to achieve the above object, the diversity receiver according to the first aspect of the present invention includes a plurality of antennas for receiving radio signals subjected to orthogonal frequency division multiplexing and a reception signal simultaneously received by the plurality of antennas. A delay circuit that adds a time delay to the received signal in order to have a delay time difference between them, a received signal received by one of the plurality of antennas that is not coupled to the delay circuit, and a time delay due to the delay circuit. A mixer that synthesizes the received signal to which is added, a tuner that frequency-converts a signal in a predetermined band synthesized by the mixer into an intermediate frequency signal, and a digital signal from the intermediate frequency signal obtained by the tuner. It is characterized in that it is provided with a demodulator that demodulates the signal.

【0011】

According to the present invention, the delay circuit adds a time delay to the received signal so as to have a delay time difference between the received signals that have been subjected to orthogonal frequency division multiplexing received simultaneously by a plurality of antennas. The mixer synthesizes the received signal received by the plurality of antennas that are not coupled to the delay circuit and the received signal to which the time delay is added by the delay circuit, and uses it for demodulation of the digital signal. As a result, it is possible to obtain a received signal that is substantially the same as the received radio wave in a multipath environment without switching between a plurality of antennas, and with a simple configuration, deterioration during demodulation is reduced and stable reception is possible. ..

【0012】

More specifically, the delay circuit ensures that the delay time difference between the received signals simultaneously received by the plurality of antennas is greater than or equal to the reciprocal of the bandwidth allocated to one subcarrier in orthogonal frequency division multiplexing. , It is desirable to add a time delay to the received signal. As a result, it is possible to prevent the signal level after synthesis by the mixer from being lowered due to the frequency dip, and stable reception is possible.

【0013】

Further, the delay circuit receives signals so that the delay time difference between the received signals simultaneously received by the plurality of antennas is shorter than the length of the guard interval section in the signal transmitted by the orthogonal frequency division multiplexing method. It is desirable to add a time delay to.

【0014】

The orthogonal frequency division multiplex signal reception method according to the second aspect of the present invention is equal to or greater than the inverse of the bandwidth allocated to one subcarrier in the orthogonal frequency division multiplex method between received signals simultaneously received by a plurality of antennas. In order to have a delay time difference that becomes It is characterized by doing.

【0015】

Here, it is desirable to add a time delay to the received signals so that the delay time difference between the received signals simultaneously received by the plurality of antennas is shorter than the length of the guard interval section.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the diversity receiver according to the embodiment of the present invention will be described in detail with reference to the drawings.

【0017】

FIG. 1 is a diagram showing a configuration of a diversity receiver 100 according to an embodiment of the present invention. As shown in the figure, this diversity receiver 100 includes a plurality of antennas 1 to 4, a plurality of LNAs (Low Noise Amplifiers) 5 to 8, a plurality of delay circuits 9 to 11, a mixer 12, and a tuner 13. , A demodulator 14 and the like.

【0018】

The plurality of antennas 1 to 4 are subjected to orthogonal frequency division multiplexing (OFDM) on the transmitting side, and are for receiving RF (Radio Frequency) signals transmitted wirelessly. Antenna 1 is coupled to mixer 12 via LNA5. Antenna 2 is coupled to delay circuit 9 via LNA6. Antenna 3 is coupled to delay circuit 10 via LNA7. The antenna 4 is coupled to the delay circuit 11 via the LNA8.

【0019】

Here, the RF signals with orthogonal frequency division multiplexing received by the plurality of antennas 1 to 4 are signals for transmitting digital data using a large number of subcarriers orthogonal to each other in the symbol period. One symbol section is divided into a valid symbol section and a guard interval section. The guard interval section is a redundant signal section that is preceded by the valid symbol section in the symbol section and is a copy of the rear part of the valid symbol section.

【0020】

The plurality of LNAs 5 to 8 are provided corresponding to each of the plurality of antennas 1 to 4, and are low noise amplifier circuits for amplifying the received signal. The LNA5 sends the amplified received signal to the mixer 12. Further, the LNAs 6 to 8 send the amplified reception signal to the corresponding delay circuits 9 to 11, respectively.

【0021】

The plurality of delay circuits 9 to 11 are provided corresponding to each of the LNAs 6 to 8 and are circuits for adding a time delay to the amplified received signal. Here, when the bandwidth allocated to one subcarrier is B [Hz], each delay circuit 9 to 11 has at least the relevant band between the received signals simultaneously received by the antennas 1 to 4. A time delay is added to each received signal so that a delay time difference of 1 / B [seconds] or more, which is the reciprocal of the width, occurs. Further, the time delay added by each of the delay circuits 9 to 11 is sufficiently shorter than the length of the guard interval section.

【0022】

The mixer 12 is for synthesizing the received signal amplified by the LNA 5 and the received signal with a time delay added by each of the delay circuits 9 to 11. The mixer 12 sends a signal obtained by synthesizing each received signal to the tuner 13.

【0023】

The tuner 13 is composed of a down converter, a bandpass filter, and the like, and is for selecting and extracting a received signal that has transmitted a desired digital signal and converting it into an IF (Intermediate Frequency) signal.

【0024】

The demodulator 14 is composed of an orthogonal detector, an A / D (Analog / Digital) converter, an FFT (Fast Fourier Transform) circuit, etc., and is transmitted from an IF signal extracted by the tuner 13 by an orthogonal frequency division multiplexing method. This is for demodulating a digital signal and outputting it as demodulated data.

【0025】

The operation of the diversity receiver 100 according to the embodiment of the present invention will be described below. Orthogonal frequency division multiplexing is performed on the transmitting side, and the RF signal transmitted wirelessly is received by a plurality of antennas 1 to 4.

【0026】

The received signals received by the plurality of antennas 1 to 4 are sent to LNAs 5 to 8 and amplified. The LNA5 sends the amplified signal to the mixer 12. Further, LNA6 to 8 send the amplified signal to the delay circuits 9 to 11, respectively.

【0027】

The delay circuits 9 to 11 add a time delay to the received signals received from the LNAs 6 to 8, respectively, and then send the signals to the mixer 12.

【0028】

Here, if the received signals received simultaneously by the plurality of antennas 1 to 4 are combined without adding a time delay, the directivity characteristics of the plurality of antennas 1 to 4 have a strong directional dependence. A sufficient signal level may not be obtained depending on the direction of arrival of radio waves.

【0029】

On the other hand, if a delay time difference is generated between the received signals received simultaneously by the plurality of antennas 1 to 4, it can be regarded as substantially equivalent to the received radio wave in the multipath environment. That is, the received signal with the time delay can be equated with the delayed wave reaching the diversity receiver 100, and when the delay time is within the length of the guard interval interval, the signal is transmitted without intersymbol interference. The digital signal can be demodulated. As a result, deterioration during demodulation can be reduced, and a signal subjected to orthogonal frequency division multiplexing can be stably received.

【0030】

For example, a signal obtained by combining a sinusoidal signal having a frequency of f [Hz] and a sinusoidal signal obtained by adding a time delay of T [seconds] to the sinusoidal signal can be expressed by Equation 1.

[Number 1]

sin (2πft) + sin2πf (t + T) Note that π is the pi and t is the time variable.

【0031】

Such a composite signal is always zero for an arbitrary time variable t when the relationship shown in Equation 2 is established.

[Number 2]

2πfT = (2n + 1) π Note that n is an arbitrary integer.

【0032】

That is, the frequency component of the composite signal becomes zero at the frequency F [Hz] shown in Equation 3.

[Number 3]

F = (2n + 1) / 2T [0033]

As is clear from the above explanation, assuming that the delay time difference applied to the signals received by the two antennas at the same time is T [seconds], the frequency components of the frequency components are every frequency 1 / T [Hz] indicated by the reciprocal. A dip (frequency dip) occurs.

【0034】

Therefore, the delay circuits 9 to 11 have at least 1 / B [between the received signals received simultaneously by the plurality of antennas 1 to 4 when the bandwidth allocated to one subcarrier is B [Hz]. A time delay is added to the received signals received by each so as to have a delay time difference of [seconds]. That is, the delay circuits 9 to 11 set the time for the received signal so that the delay time difference between the received signals received simultaneously by the plurality of antennas 1 to 4 is equal to or greater than the reciprocal of the bandwidth allocated to one subcarrier. Add a delay. As a result, it is possible to prevent the signal level after synthesis by the mixer 12 from being lowered due to the frequency dip, and stable reception is possible.

【0035】

Further, if the delay time difference between the received signals received simultaneously by the plurality of antennas 1 to 4 is made sufficiently shorter than the length of the guard interval section, the delay wave due to the multipath actually arrives. A sufficient margin can be secured.

【0036】

The mixer 12 synthesizes the received signal amplified by the LNA 5 and the received signal with a time delay added by the delay circuits 9 to 11, and sends the received signal to the tuner 13.

【0037】

The tuner 13 selects and extracts a received signal in a band for transmitting a desired digital signal from the signal synthesized by the mixer 12, converts it into an IF signal, and sends it to the demodulator 14.

【0038】

The demodulator 14 demodulates a digital signal from the IF signal obtained by the tuner 13 and outputs it as demodulated data.

【0039】

As described above, according to the present invention, by synthesizing the received signals received simultaneously by the plurality of antennas 1 to 4 with a delay time difference between them, it is possible to prevent a decrease in the signal level and to prevent an orthogonal frequency. It is possible to stably receive a signal that has been subjected to division multiplexing.

【0040】

Further, according to the present invention, the selection of the received signal is not switched as in the conventional case. Therefore, the frequency characteristics of the received signal do not change abruptly, and the signal subjected to orthogonal frequency division multiplexing can be stably received. In addition, a circuit for controlling the operation for switching the selection of the received signal becomes unnecessary, and the configuration becomes simple.

【0041】

The present invention is not limited to the above-described embodiment, and various modifications and applications are possible. For example, in the above embodiment, the signal transmitted wirelessly by the four antennas 1 to 4 has been described, but the present invention is not limited to this, and consideration is given to stabilization of reception characteristics and simplification of the configuration. Then, an arbitrary number of antennas may receive a signal subjected to orthogonal frequency division multiplexing.

【0042】

Further, when a plurality of antennas 1 to 4 include an antenna for receiving a horizontally polarized RF signal and an antenna for receiving a vertically polarized RF signal, between the received signals received by both antennas. May be synthesized without having a delay time difference.

【0043】

[Effect of the invention]

As described above, according to the present invention, in order to have a delay time difference between received signals received simultaneously by a plurality of antennas, the received signals are combined after a time delay is added, and the digital signal is demodulated. To do. As a result, it is possible to stably receive a signal subjected to orthogonal frequency division multiplexing with a simple configuration.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the structure of the diversity receiver which concerns on embodiment of this invention.

[Figure 2]

It is a figure which shows the structure of the conventional diversity receiver.

[Explanation of symbols]

1 ~ 4, 15 ~ 18 antennas 5 ~ 8, 19 ~ 22 LNA 9 ~ 11 Delay circuit 12 mixer 13, 24 tuners 14, 25 demodulator 23 Selector