JP2000174726A - Diversity receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the diversity receiver of simple constitution which can obtain sufficient diversity effect even in the case of a frequency selective phasing transmission line. SOLUTION: Plural antennas 11 and 12, an antenna switch 2 switching the plural antennas 11 and 12 and selecting and outputting a reception signal from the antenna, reception circuits 31-33 converting the reception signals corresponding to the plural antennas 11 and 12 into intermediate frequency signals and base band signals and outputting them, a sub-carrier separation part 34 separating and converting the respective output signals of the reception circuits 31-33 into respective auxiliary carriers, a detector 35 removing phase fluctuation owing to the transmission of the sub-carrier signal and outputting the base band signal after detection, a minimum sub-carrier level detection part 71 comparing the voltage value or electric value of the base band signal after detection and detecting the lowest value and an antenna selection part 81 controlling the antenna switch in accordance with the value detected by the minimum sub-carrier level detection part 71 are installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for transmitting and receiving signals digitally modulated by a modulation method having a plurality of subcarriers, such as orthogonal frequency division multiplexing (OFDM), and is spatially separated. The present invention relates to a diversity receiver for receiving the digitally modulated signal by a plurality of antennas.

[0002]

2. Description of the Related Art In the field of mobile communication, digitalization of wireless communication is progressing from the viewpoint of improving confidentiality, affinity with ISDN networks and computers, and effective use of frequency resources.

[0003] As a modulation system of digital mobile radio communication, for example, phase shift keying such as π / 4 shift QPSK is often used as in a digital cellular telephone (PDC) or a personal handy phone (PHS) in Japan. Furthermore, recently, there has been an increasing demand for high-speed wireless transmission of data having a large amount of information such as images as well as voice.

Generally, to increase the data transmission rate, it is necessary to increase the modulation rate (baud rate), 64QAM or 256QA.
There are three methods of multi-level modulation represented by M and the like and parallel transmission using a plurality of carriers (multi-carriers). Of these, the higher modulation rate is the cause of intersymbol interference when radio waves on multiple propagation paths with different delay times are received at the same time, such as ghost interference in television, resulting in significant deterioration in transmission quality. An equalizer is indispensable for the receiver. Next, multi-level modulation is performed by one step for securing a desired error rate.
The transmission energy per bit, that is, the transmission power standardized by the bit rate is required more and the characteristic with respect to the interference wave is inferior, so that it is not suitable for mobile communication. On the other hand, the parallel transmission by the multicarrier does not have the above problem.
In particular, orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”)
Multi-carrier parallel transmission, which is referred to as "multi-carrier parallel transmission", has the advantage that the required bandwidth of the transmission signal is equal to the bandwidth when the modulation speed is increased, and that an equalizer is unnecessary or can be simplified. For this reason, in standardization of digital television broadcasting, multimedia high-speed wireless access systems, and wireless LANs (local area networks), the adoption of the standards has been determined or studied.

FIG. 10 is a power spectrum diagram showing a power spectrum of a transmission signal by OFDM, and shows an example in which the number of subcarriers (subcarriers) is four. In FIG. 10, f ₁ , f ₂ , f ₃ , and f ₄ indicate the first, second, third, and fourth subcarrier frequencies, respectively, and the frequency intervals are generally equal. f _c is the center frequency of the band. Then, on the transmission side, the data to be transmitted is divided into four equal parts, or the serial data to be transmitted is subjected to serial / parallel conversion to 4 bits, and is converted into serial data having a 1/4 bit rate on each of the four channels. . The first, second, third, and fourth subcarriers are subcarrier signals modulated by the data of these four channels. The subcarrier signals are added and combined, frequency-converted to a transmission frequency, amplified to a required power, and transmitted as a transmission signal. Note that the signal processing of the modulation and the addition / synthesis is realized by the inverse discrete Fourier transform or the inverse fast Fourier transform. On the contrary, the separation of the subcarrier signal on the receiving side is realized by the discrete Fourier transform or the fast Fourier transform. General. The detailed principle of these is described in, for example, Chapter 8 of the literature (supervised by Iwao Sasase, "Next-Generation Digital Modulation / Demodulation Technology", published by Trikeps Co., Ltd.). It is shown that the subcarrier signal separation processing is performed on the receiving side by the fast Fourier transform.

By the way, since fading occurs in mobile communication, transmission quality (error rate in digital communication) is significantly deteriorated. For this reason, the base station compensates for transmission quality degradation due to fading by diversity reception received by two or more antennas and a receiving circuit (branch). For example, JP-A-9-284191 discloses a configuration of an OFDM signal diversity receiver. Diversity receivers used in mobile communication base stations such as cellular phones, including the diversity receiver disclosed in the publication, employ a post-detection combining diversity system. However, the post-detection combining diversity system has a receiving circuit for each antenna, which complicates the configuration and increases the manufacturing cost, so that terminal devices requiring small size and low power consumption, small offices and homes are required. It is not preferable to use it for consumer equipment used inside. From such a viewpoint, a base station of a digital cordless telephone or the like often employs a simple diversity system called antenna switching diversity or a system called antenna selection diversity.

Next, a conventional diversity transceiver will be described. FIG. 11 is a block diagram showing a conventional diversity receiver using an antenna selection and antenna switching diversity system. In FIG. 11, 11
Is a first antenna, 12 is a second antenna, 2 is an antenna switch, 31 is a frequency converter for converting and amplifying a high frequency signal received by the antenna 11 or 12 to an intermediate frequency signal, and 32 is a frequency converter 31 An automatic gain control amplifier (AGC amplifier) for automatically amplifying an intermediate frequency signal output from the AGC amplifier and maintaining the output amplitude substantially constant, and 33 is an intermediate frequency signal amplified by the AGC amplifier 32 Is converted into a baseband signal by a phase reference signal that is asynchronous with the carrier of the received signal. The detector 5, which obtains the baseband signal after detection by the detector 5, compares the detected baseband signal obtained by the detector 35 with an appropriate threshold to determine the transmitted data, and Determination unit for outputting as data, 8
Reference numeral 0 denotes an antenna selection unit that controls the antenna switch 2 according to the received signal strength converted from the set gain of the AGC amplifier 32. Note that, as the detector 35, specifically, a synchronous detector or a delay detector is used. In the case of a modulation method having no information in amplitude such as QPSK, the AGC amplifier 3
In some cases, a limiter amplifier is used instead of 2. Many limiter amplifier integrated circuits generally have an RSSI output terminal, and the received signal strength is obtained as the RSSI terminal voltage. Although the configuration of the signal processing has been described above, an analog / digital conversion circuit is usually provided at the output of the quasi-synchronous detector 33 or at the output of the AGC amplifier 32 to convert the signal into a digital signal. Alternatively, the above signal processing is often realized by a programmed digital signal processor (DSP).

Next, the operation of the diversity receiver configured as described above will be described with reference to FIGS. FIG. 12A is a timing chart showing fading characteristics of the first antenna 11, and FIG.
FIG. 12B is a timing chart illustrating fading characteristics of the second antenna 12, FIG. 12C is a timing chart illustrating a received burst signal, and FIG.
13 is a timing chart showing the relationship between the fading and the threshold in FIG. 1, FIG. 13 (b) is a timing chart showing the relationship between the fading and the threshold in the second antenna 12, and FIG. FIGS. 14A and 14B are frequency characteristic diagrams showing the frequency characteristics of the propagation path.

In the case of the antenna selection diversity, first, the antenna selection unit 80 controls the antenna switching unit 2 and switches the antennas during the period in which the information such as the synchronization bit is not included in the received signal. Detect the received signal strength and compare them. Then, the antenna is switched to the antenna having the higher received signal strength to receive the signal for a predetermined period. For example, when a received wave is a burst signal called a time slot like a time division multiple access system (TDMA) such as PHS, the antenna is switched as shown in FIGS. In FIG. 12C, 91;
Reference numerals 92 and 93 denote first, second and third received burst signals, respectively. The hatched portion of each received burst signal is a preamble period in which information for synchronization is not included. Further, in the figure, the symbol ◎ means that the antenna is selected. First, the antenna is switched in the preamble portion of the first burst signal, and the first antenna 1
The received signal strengths at the first and second antennas 12 are compared. In the case of this example, since the signal strength at the first antenna 11 is higher, the signal is received by the first antenna 11 during the period indicated by the thick line with an arrow in the figure. Next, the second,
The same operation is performed for the third burst signal, and the second antenna 12 and the first antenna 11 are respectively selected and received. When the fading fluctuation is relatively slow as described above, there is a high probability that the antenna having the higher received signal strength is connected to the entire burst signal.

Next, in the case of the antenna switching diversity, first, the antenna selector 80 detects the received signal strength and compares it with a preset threshold value.
If the received signal strength falls below the threshold value, the antenna is switched to the other, and if the received signal strength exceeds the threshold value, reception is performed for a predetermined period without switching. For example, when a received wave is a burst signal called a time slot like a time division multiple access system (TDMA) such as a PHS, the antenna is switched as shown in FIGS. In FIG. 13C, 91;
Reference numerals 92 and 93 denote first, second and third received burst signals, respectively. The hatched portion of each received burst signal is a preamble. In the figure, a circle indicates that the antenna was continuously selected without switching, and a square indicates that the antenna was switched to the other immediately thereafter. First, it is assumed that the first antenna 11 is connected before the arrival of the first burst signal. Then, in the preamble portion of the first burst signal, the received signal strength is compared with the threshold value while the first antenna 11 remains. In the case of this example, since the received signal strength at the first antenna 11 exceeds the threshold value, no switching occurs, and the signal is continuously received by the first antenna 11. Next, in the case of the second burst signal, the preamble is continuously received by the first antenna 11, and the received signal strength is compared with a threshold value. This time, since it is below the threshold value, switching occurs, switching to the second antenna 12 is performed, and the second burst signal is received by the second antenna 12. Then, in the third burst signal, the signal is continuously received by the second antenna 12 in the preamble, and the received signal strength is compared with a threshold value. This time again falls below the threshold value, so switching occurs, switching back to the first antenna 11 again, and the third burst signal is received by the first antenna 11. The antenna switching diversity has a slightly worse characteristic than the antenna selection diversity, but requires at most one antenna switching in the preamble portion. On the other hand, in antenna selection diversity, switching may occur twice in the preamble portion. Therefore, antenna switching diversity is effective when the preamble is short.

When radio waves of a plurality of propagation paths having different delay times arrive at the same time, frequency selective fading occurs, and the frequency characteristics of the propagation paths become non-uniform.
In this case, the transfer characteristics change greatly depending on the frequency,
The received signal is subject to distortion. However, when the spread of the delay time (delay dispersion) is sufficiently smaller than the reciprocal of the transmission band, the frequency characteristics become substantially uniform within the transmission band.
Therefore, when fading is relatively slow and a narrow-band signal is transmitted, the error rate of the transmitted data is lower as the signal strength is higher, so that the signal is received in a branch considered to have good communication quality.

[0012]

However, in the above-mentioned conventional diversity receiver, in the case of a frequency selective fading propagation path whose delay dispersion is not negligible as compared with the reciprocal of the transmission band, the error rate of the transmission data is reduced. The higher the signal strength, the lower the signal strength. For example, when the OFDM signal in FIG. 10 is transmitted through a propagation path having a frequency characteristic as shown by a broken line in FIG. 14, the received OFDM signal is as shown by a solid line in FIG. In general, the error rate of transmission data becomes 10 to several tens of times when the received signal strength decreases by 3 dB, and rapidly deteriorates. For example, the error rate corresponds to FIG. 14A (Table 1) and FIG. (Table 2).

[0013]

[Table 1]

[0014]

[Table 2]

Therefore, if the received signal strengths of the subcarrier signals are different as described above, the error rate of the transmission data greatly differs for each subcarrier signal. Error rate is dominated. For example, in FIG. 14, (a) has a slightly higher average received signal strength than (b), but (b) has a better overall error rate. For this reason, the conventional diversity receiver in which antenna selection and antenna switching are performed based on the received signal strength of the entire signal has a problem that the antenna selection and antenna switching are not properly performed, and the diversity gain is reduced. .

This diversity receiver is required to have a simple configuration and to obtain a sufficient diversity effect even in the case of a frequency selective fading propagation path.

An object of the present invention is to provide a diversity receiver having a simple configuration capable of obtaining a sufficient diversity effect even in the case of a frequency selective fading propagation path.

[0018]

SUMMARY OF THE INVENTION In order to solve the above problems, a diversity receiver according to the present invention is a diversity receiver for receiving a signal having a plurality of orthogonal frequency division multiplexed or frequency division multiplexed subcarriers. A plurality of antennas, an antenna switching device for selecting and outputting a reception signal from the antenna by switching the plurality of antennas, and a reception signal supplied from the antenna switching device to convert a reception signal corresponding to the plurality of antennas into an intermediate frequency signal A receiving circuit for converting and converting the intermediate frequency signal into a baseband signal and outputting each; a subcarrier separating unit for separating and converting each output signal of the receiving circuit into a subcarrier signal corresponding to each subcarrier; A detector that outputs a baseband signal after detection by removing phase fluctuations caused by transmission of a subcarrier signal or a baseband signal after detection. A voltage value or a power value of the band signal is compared, a minimum subcarrier level detection unit that detects the lowest value, and an antenna selection unit that controls the antenna switch according to the value detected by the minimum subcarrier level detection unit Is provided.

As a result, it is possible to obtain a diversity receiver having a simple configuration capable of obtaining a sufficient diversity effect even in the case of a frequency selective fading propagation path.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A diversity receiver according to a first aspect of the present invention is a diversity receiver for receiving a signal having a plurality of subcarriers subjected to orthogonal frequency division multiplexing or frequency division multiplexing. An antenna, an antenna switch for switching and selecting a plurality of antennas to select and output a received signal from the antenna, and receiving signals supplied from the antenna switch, converting received signals corresponding to the plurality of antennas into an intermediate frequency signal, A receiving circuit that converts the intermediate frequency signal into a baseband signal and outputs each; a subcarrier separating unit that separates and converts each output signal of the receiving circuit into a subcarrier signal corresponding to each subcarrier; A detector that removes phase fluctuations and outputs a detected baseband signal, and a subcarrier signal or a detected baseband signal. Comparing the value or the power value, a minimum subcarrier level detection unit that detects the lowest value, and having an antenna selection unit that controls the antenna switch according to the value detected by the minimum subcarrier level detection unit The antenna selection or switching is performed by the minimum level in the subcarrier signal that is dominant in the error rate of the entire received signal, and the antenna selection or switching is appropriately performed so that the error rate characteristic is improved. This has the effect of switching.

A diversity receiver according to a second aspect of the present invention is a diversity receiver for receiving a signal having a plurality of subcarriers subjected to orthogonal frequency division multiplexing or frequency division multiplexing, wherein a plurality of antennas and a plurality of antennas are provided. An antenna switch for switching and selecting and outputting a received signal from an antenna; receiving signals supplied from the antenna switch, converting received signals corresponding to a plurality of antennas into an intermediate frequency signal, and converting the intermediate frequency signal to a baseband signal And a sub-carrier separation unit that separates and converts each output signal of the reception circuit into a sub-carrier signal corresponding to each sub-carrier, and detects and removes phase fluctuation due to transmission of the sub-carrier signal. Detector that outputs post-baseband signal, and voltage value or power value of subcarrier signal or post-detection baseband signal An error rate detector for estimating the transmission data error rate from the error rate detector, and an antenna selector for controlling the antenna switch in accordance with the value estimated by the error rate detector. The selection or switching of the antenna is performed based on the value obtained by directly estimating the rate, and the effect is that the selection or switching of the antenna is performed appropriately so as to improve the error rate characteristics.

A diversity receiver according to a third aspect is the diversity receiver according to the first aspect,
A switching circuit disposed between the antenna switching device and the receiving circuit, a transmitting circuit for outputting a transmission signal connected to one terminal, and a receiving circuit connected to the other terminal; When transmitting to the partner station, the switching circuit is controlled so as to transmit using the antenna selected in the receiving period, and has an effect that the error rate characteristics at the time of transmission are improved similarly to the time of reception.

A diversity receiver according to a fourth aspect is the diversity receiver according to the second aspect,
A switching circuit disposed between the antenna switching device and the receiving circuit, a transmitting circuit for outputting a transmission signal connected to one terminal, and a receiving circuit connected to the other terminal; When transmitting to the partner station, the switching circuit is controlled so as to transmit using the antenna selected in the receiving period, and has an effect that the error rate characteristics at the time of transmission are improved similarly to the time of reception.

A diversity receiver according to a fifth aspect of the present invention is the diversity receiver according to the first or third aspect, wherein the antenna selection unit detects the value detected by the minimum subcarrier level detection unit every time a plurality of antennas are switched. Is switched to the antenna whose detected value is the largest, and the switching is maintained for a predetermined period. The antenna expected to have the lowest data error rate among all the antennas is selected. This has the effect that the same good characteristics as the selection diversity can be obtained after detection.

A diversity receiver according to a sixth aspect of the present invention is the diversity receiver according to the second or fourth aspect, wherein the antenna selection section stores a value estimated by the error rate detection section every time a plurality of antennas are switched. However, the antenna is switched to the antenna whose estimated value is the smallest, and the switching is maintained for a predetermined period.
An antenna which is expected to have the lowest data error rate among all the antennas is selected, and has such an effect that good characteristics similar to selection diversity after detection can be obtained.

According to a seventh aspect of the present invention, in the diversity receiver according to the first or third aspect, the antenna selecting section determines a value detected by the minimum subcarrier level detecting section and a switching threshold value. In comparison, when the detected value falls below the switching threshold value, the antenna is switched and the switching is maintained for a predetermined period, and a good diversity effect can be obtained with a small number of antenna switching times. Has an action.

The diversity receiver according to claim 8 is the diversity receiver according to claim 2 or 4, wherein the antenna selector compares the value estimated by the error rate detector with the switching threshold. When the estimated value exceeds the switching threshold, the antenna is switched, and the switching is maintained for a predetermined period. This has the effect that a good diversity effect can be obtained with a small number of antenna switching. Have.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. (Embodiment 1) FIG.1 is a block diagram showing a diversity receiver according to Embodiment 1 of the present invention.
The case where communication is performed by M is shown.

In FIG. 1, a first antenna 11, a second antenna 11,
Antenna 12, antenna switching unit 2, frequency conversion unit 3
1. AGC amplifier 32, quasi-synchronous detector 33, detector 3
5. Since the determination unit 5 is the same as that in FIG. 11, the same reference numerals are given and the description is omitted. Reference numeral 34 denotes a discrete Fourier transform unit (DF) as a subcarrier separating unit for separating and converting the baseband signal output from the quasi-synchronous detector 33 into a plurality of subcarrier signals corresponding to each subcarrier of OFDM.
T) and 6 are parallel / serial converters for collecting received data obtained for each subcarrier, and 71 is to compare the voltage value or power value of the detected baseband signal of each subcarrier and detect the lowest value. , A minimum subcarrier level detector 81 that outputs the received signal strength of the subcarrier converted from the set gain of the AGC amplifier 32, and a minimum subcarrier level detector 81 according to the received signal strength of the minimum level subcarrier of the minimum subcarrier level detector 71. A frequency converter 31, an AGC amplifier 32, and a quasi-synchronous detector 33 constitute a receiving circuit. In addition,
Specifically, a synchronous detector or a delay detector is used as the detector 35. The discrete Fourier transform unit 34 performs a discrete Fourier transform operation for the number of samples equal to the number of subcarriers for each symbol period. FIG. 1 shows an example in which the number of subcarriers and the number of samples are four. The signal processing configuration has been described above. However, as described in the background art, the output of the quasi-synchronous detector 33 or the AGC amplifier 32
An analog-to-digital converter is provided at the output of the converter to convert it to a digital signal, and the subsequent processing is performed by a digital circuit or a digital signal processor (DSP) programmed with the above signal processing. This is desirable because it becomes easier.

The operation of the diversity receiver configured as described above will be described with reference to FIGS. FIG. 2A shows OFDM in the first antenna 11.
FIG. 2B is a frequency characteristic diagram illustrating a spectrum of a transmission signal according to OFDM.
FIG. 3A is a timing chart showing fading characteristics in the first antenna 11, and FIG. 3B is a timing chart showing fading characteristics in the first antenna 11.
FIG. 3 is a timing chart showing fading characteristics in FIG.
(C) is a timing chart showing a received burst signal.

In FIG. 1, first, an antenna selection unit 81
Controls the antenna switch 2 and switches the first antenna 11 and the second antenna 12
(That is, the minimum subcarrier level detected and notified by the minimum subcarrier level detector 71). Then, the antenna is switched to the antenna having the higher minimum subcarrier level, and reception is performed for a predetermined period. For example, when the power spectrum of the received signal at the time of the switching is as shown in FIG. 2, the second antenna 12 transmits the second subcarrier signal, and the second antenna 12 transmits the first subcarrier signal. Is the minimum subcarrier level. In this case, the minimum subcarrier level in the first antenna 11 is higher.
Therefore, the antenna selection unit 81 selects the first antenna 11, switches the antenna switch 2 to the first antenna 11 side, and holds it for a predetermined period or until the next antenna switching. In many digital wireless systems, a signal is often transmitted as a burst signal in a unit called a time slot, and a period in which information such as a synchronization bit called a preamble is not provided at the head of the time slot. FIGS. 3A and 3B show an operation example when such a burst signal is received, and the curve in the figure shows the fluctuation of the received signal strength due to fading for each subcarrier signal. In FIG. 3C, 91, 9
Reference numerals 2 and 93 are first, second and third received burst signals, respectively. The hatched portion of each received burst signal is the preamble. Further, in the figure, the symbol ◎ means that the antenna is selected. First, the antenna is switched in the preamble portion of the first burst signal, and the minimum subcarrier levels of the first antenna 11 and the second antenna 12 are compared. In the case of this example, the minimum subcarrier level in the first antenna 11, that is, the signal strength of the second subcarrier is higher than the second antenna 1
2, that is, higher than the signal strength of the third subcarrier, and is received by the first antenna 11 during the period indicated by the thick line with an arrow in the figure. Next, the same operation is performed for the second and third burst signals,
The second antenna 12 and the first antenna 11 are selected and received, respectively. And antenna 11 or 12
Are amplified and frequency-converted by the frequency converter 31, the AGC amplifier 32, and the quasi-synchronous detector 33 via the antenna switch 2, and the discrete Fourier transformer 34
After being separated into respective subcarrier signals, the signal is detected by a detector 35, converted into a baseband signal after detection, converted into reception data by a determination unit 5, and then converted into serial data by a parallel / serial conversion unit 6. Is output.

Although the receiving operation has been described above, in the case where transmission and reception are performed alternately at the same frequency by TDD (Time Division Duplex) as used in PHS, an antenna selected and used at the time of reception is used as a partner. It may be used in the next transmission period to the station. In this case, a transmission / reception switching circuit (not shown) is inserted between the antenna switch 2 and the frequency converter 31.
A configuration may be adopted in which a transmission circuit (not shown) is connected to the circuit. That is, the transmission circuit may be connected to one terminal of the switching circuit, and the reception circuits 31 to 33 may be connected to the other terminal. If such a configuration is used for a base station or a base unit of a cordless telephone, a transmission diversity effect can be obtained without performing diversity on the mobile station side required to be small and lightweight.

In the present embodiment, the minimum subcarrier level detecting section 71 is configured to detect the voltage value or the power value of the baseband signal after detection.
The voltage value or the power value of the baseband signal may be detected. In particular, in the case of a modulated signal by phase shift keying such as BPSK or QPSK, signal processing is performed using phase information such as phase delay detection, that is, a phase value corresponding to the ratio between the in-phase component and the quadrature component of the baseband signal. Therefore, the amplitude of the output of the detector 35, that is, the information of the voltage or power of the subcarrier signal is not output. Even in such a case, the above configuration can be used. In this embodiment, the antenna selection diversity has been described as shown in FIG.
1 is temporarily stored in a storage device (not shown), the antenna switch 2 is controlled by the control signal read from the storage device, and the storage content of the storage device is updated at a constant period. In this case, the selection and the switching of the antenna are held for a predetermined period. Furthermore, in the present embodiment, the multiplexing method has been described as an orthogonal frequency division multiplexing method, but the present invention is not limited to this, and can be applied to a general frequency division multiplexing method.

As described above, in the present embodiment, the reception signal is supplied from the antenna switch 2 and the plurality of antennas 1
The received signals corresponding to 1 and 12 are converted into intermediate frequency signals,
Receiving circuits 31, 32, and 33 for converting the intermediate frequency signals into baseband signals and outputting the converted signals;
3, a subcarrier separation unit 34 for separating and converting each output signal into a subcarrier signal corresponding to each subcarrier, and a detector 35 for removing a phase variation due to transmission of the subcarrier signal and outputting a detected baseband signal. , A minimum subcarrier level detector 71 for comparing the voltage value or the power value of the detected baseband signal and detecting the lowest value, and an antenna switch 2 according to the value detected by the minimum subcarrier level detector 71. And the antenna selection unit 81 that controls the error rate characteristic, it is possible to select or switch the antenna at the minimum level among the subcarrier signals that are dominant in the error rate of the entire received signal. Can be appropriately selected or switched so that the frequency is improved even in the case of the frequency selective fading propagation path. It is possible to obtain a minute diversity effect. In addition, as with the conventional antenna switching and antenna selection diversity, only one system is required for the receiving circuit. Therefore, an excellent diversity receiver having excellent characteristics even in a multicarrier transmission system such as OFDM can be easily configured.

(Embodiment 2) FIG. 4 is a block diagram showing a diversity receiver according to Embodiment 2 of the present invention.

In FIG. 4, the first antenna 11, the second antenna
Antenna 12, antenna switching unit 2, frequency conversion unit 3
1, the AGC amplifier 32, the quasi-synchronous detector 33, the discrete Fourier transform unit 34, the detector 35, the determination unit 5, and the parallel / serial converter 6 are the same as those in FIG. I do. Reference numeral 72 indicates the received signal strength of each subcarrier from the voltage value or power value of the detected baseband signal of each subcarrier and the gain set by the AGC amplifier 32, and calculates the error rate of the received data theoretically estimated from this. An error rate estimator for estimating the error rate of the entire OFDM signal by averaging all subcarriers,
2 is an antenna selection unit that controls the antenna switch 2 according to the output of the antenna switch 2. Although the configuration of the signal processing has been described above, an analog / digital conversion circuit is provided at the output of the quasi-synchronous detector 33 or the output of the AGC amplifier 32 to convert the signal into a digital signal as in the first embodiment. Is preferably performed by a digital circuit or a digital signal processor (DSP) in which the above signal processing is programmed, since adjustment without adjustment and integration into an integrated circuit are facilitated. In this case, the error rate estimating unit 72 makes a table of the relationship between the received signal strength and the data error rate theoretically obtained from the noise figure and the modulation format of the receiving circuit, and reads out the stored data in a memory. Can be easily realized.

The operation of the diversity receiver configured as described above will be described with reference to FIG. FIG.
FIG. 5A is a spectrum diagram showing a power spectrum in the first antenna 11, and FIG. 5B is a spectrum diagram showing a power spectrum in the second antenna 12.

In FIG. 4, first, the antenna selection unit 82
Controls the antenna switch 2 and switches the first antenna 11 and the second antenna 12
, The estimated value of the error rate of the received data obtained by the error rate estimating unit 72 is fetched and compared. Then, the antenna is switched to the antenna whose estimated value of the error rate is lower, and reception is performed for a predetermined period. For example, the power spectrum of the received signal at the time of the above switching is in the state shown in FIGS. 5A and 5B, and the estimated error rates for FIGS. 5A and 5B are shown in (Table 3) and (Table 4). ), The estimated error rate of the first antenna 11 is lower, so that the antenna 11 is selected, and the antenna switch 2 is connected to the first antenna 11 side.

[0039]

[Table 3]

[0040]

[Table 4]

The signal received by the antenna 11 or 12 is amplified and frequency-converted by the frequency converter 31, the AGC amplifier 32, and the quasi-synchronous detector 33 via the antenna switch 2, and is converted by the discrete Fourier transformer 34. After being separated into each subcarrier signal, it is detected by a detector 35 and converted into a baseband signal after detection. After being converted into received data by a determination unit 5, it is converted into serial data by a parallel / serial conversion unit 6. Is output.

As described above, according to the present embodiment, data is received in the branch having the lowest data error rate estimated from the received signal strength of each subcarrier. Therefore, it is received in the branch where the communication quality is expected to be the best. Particularly, in the present embodiment, since the data error rate of the entire OFDM signal is directly estimated, a branch having the best communication quality is more reliably selected, and a good diversity gain is obtained. Further, as in Embodiment 1, when used for TDD, a configuration may be adopted in which a transmission circuit is connected to perform transmission diversity.

(Embodiment 3) FIG. 6 is a block diagram showing a diversity receiver according to Embodiment 3 of the present invention, showing a case where communication is performed by OFDM.

In FIG. 6, the first antenna 11, the second antenna
Antenna 12, antenna switching unit 2, frequency conversion unit 3
1, the AGC amplifier 32, the quasi-synchronous detector 33, the discrete Fourier transform unit 34, the detector 35, the determination unit 5, the parallel / serial converter 6, and the minimum subcarrier level detector 71 are the same as those in FIG. The reference numerals are used and the description is omitted. Reference numeral 81 denotes an antenna selection unit including a comparison unit 83 and an antenna switching control unit 84. Here, the comparison unit 8
3 compares the received signal strength of the minimum level subcarrier of the minimum subcarrier level detector 71 with a preset threshold value. Then, the antenna switching control unit 84
When the comparison result in the comparing unit 83 indicates that the received signal strength of the sub-carrier of the minimum level falls below the preset threshold value, the antenna is switched to the other antenna. The antenna switch 2 is controlled so as to perform the operation.

The operation of the diversity receiver configured as described above will be described with reference to FIG. FIG.
FIG. 7A is a timing chart showing fading characteristics of the first antenna 11, FIG. 7B is a timing chart showing fading characteristics of the second antenna 12,
FIG. 7C is a timing chart showing the received burst signal.

When the received wave is a burst signal in time slot units, the antenna is switched as shown in FIGS. 7 (a) and 7 (b). In FIG. 7C, reference numerals 91, 92, and 93 denote first, second, and third reception burst signals, respectively. The hatched portion of each received burst signal is a preamble. In the figure, a circle indicates that the antenna was continuously selected without switching, and a square indicates that the antenna was switched to the other immediately thereafter. First, it is assumed that the first antenna 11 is connected before the arrival of the first burst signal. Then, in the preamble portion of the first burst signal, the received signal strength of the subcarrier of the minimum level while the first antenna 11 is kept is compared with the above threshold value. In this example, the minimum level of the first antenna 11 is the second subcarrier, but since the received signal strength of the second subcarrier exceeds the threshold value, the antenna switching does not occur. Instead, it is continuously received by the first antenna 11. Next, in the second burst signal, the first antenna 11 continues in the preamble.
, And the received signal strength of the minimum level subcarrier is compared with a threshold value. This time, the first subcarrier is at the minimum level and is below the threshold as indicated by the square in the figure, so that switching occurs and switches to the second antenna 12, and thereafter the second burst signal is 2 is received by the second antenna 12. Then, in the third burst signal, the signal is received by the second antenna 12 continuously in the preamble, and the received signal strength of the subcarrier of the minimum level is compared with the threshold value. The one with the minimum level is the first subcarrier, but since it is still below the threshold value, switching occurs, switching back to the first antenna 11 and the third burst signal to the first antenna 11 Received.

As described above, in this embodiment, the number of times of antenna switching in the preamble portion can be at most one, as in the case of the antenna switching diversity described in the conventional diversity receiver. On the other hand, in the diversity receivers of Embodiments 1 and 2, switching may be performed twice. Therefore, the present embodiment is effective when the preamble is short. Further, similarly to Embodiments 1 and 2, when used for TDD, a configuration may be adopted in which transmission diversity is performed by connecting a transmission circuit.

(Embodiment 4) FIG. 8 is a block diagram showing a diversity receiver according to Embodiment 4 of the present invention, showing a case where communication is performed by OFDM.

In FIG. 8, the first antenna 11, the second antenna
Antenna 12, antenna switching unit 2, frequency conversion unit 3
1, the AGC amplifier 32, the quasi-synchronous detector 33, the discrete Fourier transform unit 34, the detector 35, the determination unit 5, the parallel / serial converter 6, and the error rate estimator 72 are the same as those in FIG. And the description is omitted. Reference numeral 82 denotes an antenna selection unit including a comparison unit 85 and an antenna switching control unit 86. Here, the comparing unit 85 compares the error rate estimation value of the entire OFDM signal output from the error rate estimating unit 72 with a preset threshold value. The antenna switching control unit 86 switches the antenna to the other if the error rate estimation value of the entire OFDM signal in the error rate estimation unit 72 exceeds the preset threshold value as a result of the comparison in the comparison unit 85. , The antenna switch 2 is controlled so as to receive the signal for a predetermined period without switching.

The operation of the diversity receiver configured as described above will be described with reference to FIG. FIG.
9A is a timing chart illustrating fading characteristics of the first antenna 11, FIG. 9B is a timing chart illustrating fading characteristics of the second antenna 12,
FIG. 9C is a timing chart showing the received burst signal.

When the received wave is a burst signal in time slot units, the antenna is switched as shown in FIGS. 9 (a) and 9 (b). In FIG. 9C, reference numerals 91, 92, and 93 denote first, second, and third received burst signals, respectively. The hatched portion of each received burst signal is a preamble. In the figure, a circle indicates that the antenna (here, the first antenna 11) has been continuously selected without switching, and a square indicates that the antenna has been switched to the other immediately after. . First, it is assumed that the first antenna 11 is connected before the arrival of the first burst signal. Then, in the preamble portion of the first burst signal, the error rate estimation value is compared with the threshold value while the first antenna 11 remains. In the case of this example, since the error rate estimated value is below the threshold value, no switching occurs and the signal is continuously received by the first antenna 11. Next, in the second burst signal, the first antenna 1 continues with the preamble.
1 is received. Since the threshold value is exceeded this time as indicated by the symbol □ in the figure, switching of the antenna occurs to switch to the second antenna 12, and thereafter the second burst signal is received by the second antenna 12. . Then, the third burst signal is continuously received by the second antenna 12 as a preamble. This time again, the error rate estimation value exceeds the threshold value, so that switching occurs, switching is again made to the first antenna 11, and the third burst signal is received by the first antenna 11 hereinafter.

As described above, in the present embodiment, as in Embodiment 3, the number of times of antenna switching in the preamble portion can be at most one. Therefore, the present embodiment is also effective when the preamble is short, and switches the antennas by estimating the entire error rate, so that better characteristics can be obtained than in the third embodiment. Embodiments 1, 2, and 3
Similarly to the above, when used for TDD, a configuration may be adopted in which a transmission circuit is connected to perform transmission diversity.

[0053]

As described above, the diversity receiver according to the first aspect of the present invention is a diversity receiver for receiving a signal having a plurality of orthogonal frequency division multiplexed or frequency division multiplexed subcarriers. A plurality of antennas, an antenna switching device for switching between the plurality of antennas to select and output a reception signal from the antenna, and a reception signal supplied from the antenna switching device to convert the reception signals corresponding to the plurality of antennas into an intermediate frequency signal. A receiving circuit that converts the intermediate frequency signal into a baseband signal and outputs each of them; a subcarrier separating unit that separates and converts each output signal of the receiving circuit into a subcarrier signal corresponding to each subcarrier; A detector that removes phase fluctuations due to signal transmission and outputs a detected baseband signal, and a subcarrier signal or a detected baseband signal. A minimum subcarrier level detection unit that compares the voltage value or the power value of the input signal and detects the lowest value, and an antenna selection unit that controls the antenna switch according to the value detected by the minimum subcarrier level detection unit. By having, since it is possible to select or switch the antenna by the minimum level in the subcarrier signal dominant in the error rate of the entire received signal,
The antenna selection or switching can be appropriately performed so that the error rate characteristic is improved, and the advantageous effect that a sufficient diversity effect can be obtained even in the case of a frequency selective fading propagation path is obtained. As in the case of the conventional antenna switching and antenna selection diversity, only one receiving circuit is required, so that an excellent diversity receiver having good characteristics can be easily formed even in a multicarrier transmission system such as OFDM. The effect is obtained.

According to the diversity receiver of the present invention, a diversity receiver for receiving a signal having a plurality of subcarriers subjected to orthogonal frequency division multiplexing or frequency division multiplexing, wherein a plurality of antennas and a plurality of An antenna switch that switches antennas to select and output a received signal from the antenna, and a received signal supplied from the antenna switch, converts received signals corresponding to a plurality of antennas into an intermediate frequency signal, and bases the intermediate frequency signal on the base. A receiving circuit that converts each output signal to a band signal, a subcarrier separation unit that separates and converts each output signal of the receiving circuit into a subcarrier signal corresponding to each subcarrier, and removes phase fluctuation due to transmission of the subcarrier signal. A detector that outputs a baseband signal after detection, and a subcarrier signal or a voltage value or a baseband signal after detection. An error rate detection unit for estimating a transmission data error rate from a force value, and an antenna selection unit for controlling an antenna switch according to the value estimated by the error rate detection unit. Since the selection or switching of the antenna can be performed based on the directly estimated value, the selection or switching of the antenna can be appropriately performed so as to improve the error rate performance, and it is sufficient even in the case of the frequency selective fading propagation path. In addition, the advantageous effect that various diversity effects can be obtained is obtained, and the receiving circuit can be one system as in the conventional antenna switching and antenna selection diversity.
The advantageous effect that an excellent diversity receiver having good characteristics can be easily configured even in a multicarrier transmission system such as OFDM can be obtained.

According to the diversity receiver of the third aspect, in the diversity receiver of the first aspect, the transmission is arranged between the antenna switch and the reception circuit, and outputs a transmission signal to one terminal. A circuit is connected, and a switching circuit having a receiving circuit connected to the other terminal is provided, and the antenna selecting unit controls the switching circuit to transmit by the antenna selected in the receiving period when transmitting to the communication partner station. By doing so, an advantageous effect is obtained that the error rate characteristic at the time of transmission is improved similarly to that at the time of reception.

According to the diversity receiver of the fourth aspect, in the diversity receiver of the second aspect, the transmission is arranged between the antenna switch and the receiving circuit, and outputs a transmission signal to one terminal. A circuit is connected, and a switching circuit having a receiving circuit connected to the other terminal is provided, and the antenna selecting unit controls the switching circuit to transmit by the antenna selected in the receiving period when transmitting to the communication partner station. By doing so, an advantageous effect is obtained that the error rate characteristic at the time of transmission is improved similarly to that at the time of reception.

According to the diversity receiver set forth in claim 5, in the diversity receiver set forth in claim 1 or 3, the antenna selection unit is detected by the minimum subcarrier level detection unit every time a plurality of antennas are switched. By storing the detected value, switching to the antenna whose detected value is the largest, and maintaining the switching for a predetermined period, the antenna expected to have the lowest data error rate among all the antennas is selected, An advantageous effect that good characteristics similar to selection diversity can be obtained after detection is obtained.

According to the diversity receiver set forth in claim 6, in the diversity receiver set forth in claim 2 or 4, the antenna selection unit sets the value estimated by the error rate detection unit every time a plurality of antennas are switched. By switching to the antenna having the smallest estimated value and maintaining the switching for a predetermined period, the antenna expected to have the lowest data error rate among all the antennas is selected, and after detection, An advantageous effect that good characteristics similar to selection diversity can be obtained.

According to the diversity receiver set forth in claim 7, in the diversity receiver set forth in claim 1 or 3, the antenna selection unit includes a value detected by the minimum subcarrier level detection unit and a switching threshold value. When the detected value falls below the switching threshold value, the antenna is switched, and the switching is maintained for a predetermined period, whereby a favorable diversity effect can be obtained with a small number of antenna switching times. The effect is obtained.

According to the diversity receiver set forth in claim 8, in the diversity receiver set forth in claim 2 or 4, the antenna selection unit sets the value estimated by the error rate detection unit and the switching threshold value. In comparison, when the estimated value exceeds the switching threshold, the antenna is switched, and the switching is maintained for a predetermined period, thereby obtaining an advantageous effect that a good diversity effect can be obtained with a small number of antenna switching. can get.

[Brief description of the drawings]

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

2A is a spectrum diagram showing a power spectrum of a first antenna. FIG. 2B is a spectrum diagram showing a power spectrum of a second antenna.

3A is a timing chart showing fading characteristics of a first antenna. FIG. 3B is a timing chart showing fading characteristics of a second antenna. FIG. 3C is a timing chart showing a received burst signal.

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

5A is a spectrum diagram showing a power spectrum in a first antenna. FIG. 5B is a spectrum diagram showing a power spectrum in a second antenna.

FIG. 6 is a block diagram showing a diversity receiver according to a third embodiment of the present invention.

7A is a timing chart showing fading characteristics in a first antenna; FIG. 7B is a timing chart showing fading characteristics in a second antenna;

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

9A is a timing chart showing fading characteristics of a first antenna. FIG. 9B is a timing chart showing fading characteristics of a second antenna. FIG. 9C is a timing chart showing a received burst signal.

FIG. 10 is a power spectrum diagram of a transmission signal of an orthogonal frequency division multiplexed signal (OFDM signal).

FIG. 11 is a block diagram showing a conventional diversity receiver.

FIG. 12A is a timing chart showing fading characteristics in a first antenna; FIG. 12B is a timing chart showing fading characteristics in a second antenna; FIG. 12C is a timing chart showing a received burst signal.

13A is a timing chart showing fading characteristics of a first antenna. FIG. 13B is a timing chart showing fading characteristics of a second antenna. FIG. 13C is a timing chart showing a received burst signal.

14A is a frequency characteristic diagram showing the frequency characteristics of the propagation path, and FIG. 14B is a frequency characteristic diagram showing the frequency characteristics of the propagation path.

[Explanation of symbols]

2 Antenna Switch 5 Judgment Unit 6 Parallel / Serial Conversion Unit 11 First Antenna 12 Second Antenna 31 Frequency Conversion Unit (Reception Circuit) 32 Automatic Gain Control Amplifier (AGC Amplifier) (Reception Circuit) 33 Quasi-Synchronous Detector ( Receiving circuit) 34 Discrete Fourier transform section (subcarrier separating section) 35 Detector 71 Minimum subcarrier level detecting section 72 Error rate estimating section 81, 82 Antenna selecting section

Claims (8)

[Claims] 1. A diversity receiver for receiving a signal having a plurality of subcarriers subjected to orthogonal frequency division multiplexing or frequency division multiplexing, comprising: a plurality of antennas; and a reception signal from said antenna by switching said plurality of antennas. An antenna switch for selecting and outputting a signal received from the antenna switch, converting the received signals corresponding to the plurality of antennas to an intermediate frequency signal, and converting the intermediate frequency signal to a baseband signal. A sub-carrier separation unit that separates and converts each output signal of the reception circuit into a sub-carrier signal corresponding to each of the sub-carriers, and detects and removes phase fluctuation due to transmission of the sub-carrier signal. A detector for outputting a post-baseband signal; and a voltage value or electric power of the subcarrier signal or the post-detection baseband signal. It has a minimum subcarrier level detection unit that compares values and detects the lowest value, and an antenna selection unit that controls the antenna switch according to the value detected by the minimum subcarrier level detection unit. And diversity receiver. 2. A diversity receiver for receiving a signal having a plurality of subcarriers subjected to orthogonal frequency division multiplexing or frequency division multiplexing, comprising: a plurality of antennas; and a reception signal from said antenna by switching said plurality of antennas. An antenna switch for selecting and outputting a signal received from the antenna switch, converts the received signals corresponding to the plurality of antennas into an intermediate frequency signal, and converts the intermediate frequency signal into a baseband signal. A sub-carrier separating unit that separates and converts each output signal of the receiving circuit into a sub-carrier signal corresponding to each of the sub-carriers, and detects and detects a phase variation caused by transmission of the sub-carrier signal. A detector for outputting a post-baseband signal; and a voltage value or electric power of the subcarrier signal or the post-detection baseband signal. Diversity receiver characterized in that it comprises an error rate detection unit that estimates a transmission data error rate from the value, and an antenna selection unit to control the antenna switching equipment according to the value estimated by the error rate detecting unit. 3. A switching circuit disposed between the antenna switching device and the receiving circuit, wherein a transmitting circuit for outputting a transmitting signal is connected to one terminal, and the receiving circuit is connected to the other terminal. The diversity receiver according to claim 1, wherein the antenna selection unit controls the switching circuit so that, when transmitting to a communication partner station, transmission is performed by an antenna selected in a reception period. 4. A switching circuit disposed between the antenna switching device and the receiving circuit, wherein a switching circuit for outputting a transmission signal is connected to one terminal, and the receiving circuit is connected to the other terminal. 3. The diversity receiver according to claim 2, wherein the antenna selection unit controls the switching circuit so that, when transmitting to a communication partner station, transmission is performed by an antenna selected in a reception period. 5. The antenna selection unit stores a value detected by the minimum subcarrier level detection unit every time the plurality of antennas are switched, and switches to the antenna whose detected value is the largest. 4. The diversity receiver according to claim 1, wherein the switching is maintained for a predetermined period. 6. The antenna selection section stores a value estimated by the error rate detection section every time the plurality of antennas are switched, switches to an antenna having the smallest estimated value, and switches the antenna. The diversity receiver according to claim 2 or 4, wherein is maintained for a predetermined period. 7. The antenna selection section compares a value detected by the minimum subcarrier level detection section with a switching threshold, and when the detected value falls below the switching threshold, The diversity receiver according to claim 1 or 3, wherein the antenna is switched, and the switching is maintained for a predetermined period. 8. The antenna selection section compares a value estimated by the error rate detection section with a switching threshold,
5. The diversity receiver according to claim 2, wherein the antenna is switched when the estimated value exceeds the switching threshold, and the switching is maintained for a predetermined period.