JP2006121161A - Ofdm signal receiver and composite receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive OFDM signal receiver capable of obtaining high performance without the need for using a plurality of expensive broadband filters which hardly provide high performance characteristics. <P>SOLUTION: The OFDM signal receiver is constituted in such a way that high performance and inexpensive narrow band filters 120, 121 are connected in parallel in a band limit section 111. The band limit section 111 can thereby compensate a cause to deterioration caused in a frequency band where pass bands of the filters 120, 121 are overlapped by utilizing the algorithm of an OFDM demodulation system. Thus, the OFDM receiver which uses the inexpensive high performance narrow band filters without the need for using the plurality of expensive broadband filters which hardly provide high performance characteristics can easily obtain high performance for various characteristics such as a passing loss, an in-band ripple, a noise suppressing amount, a temperature characteristic, and a VSWR. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an OFDM (Orthogonal Frequency Division Multiplexing) signal receiver and the like, and more particularly to an OFDM signal receiver and a composite receiver that perform band limitation appropriately when receiving a wideband signal.

  In recent years, even in mobile communication systems, studies have been made to increase system capacity in order to provide a throughput of 100 Mbps or more over a wide range of coverage (radio wave arrival area). For example, a radio bandwidth is 100 MHz or more. A study using a mobile communication system has also been reported. In general, in a wideband signal receiver, an analog / digital conversion unit (hereinafter referred to as an AD conversion unit) performs sampling (that is, oversampling) in the AD conversion unit in consideration of power consumption, device volume, cost, etc. of logic components. Number) is difficult to take large. For this reason, a system in which a noise signal that is turned back by sampling by the AD conversion unit enters the signal band is likely. Therefore, it is essential to provide an analog band limiting filter having a steep frequency characteristic in the wideband signal receiver.

  In mobile communication systems, a filter having excellent frequency selectivity, for example, a SAW (Surface Acoustic Wave) filter using a surface vibration wave of a piezoelectric element is generally used as a band limiting filter. There are many. In the SAW filter, generally, an IDT (Inter Digital Transducer: crossed finger electrode) can be expressed by weighting the shape of sin (πbt) / (πbt). Here, b is the bandwidth and t is the time. Therefore, since the insertion loss increases as the bandwidth b increases, the wideband SAW filter has a larger passage loss than the narrowband filter. Further, in order to obtain a wide band characteristic in the SAW filter, it is necessary to use a device having a large electromechanical coupling coefficient. However, since the electromechanical coupling coefficient and the temperature coefficient are generally in a trade-off relationship, a wide band is required. The filter increases the gain (passage loss) and the amount of temperature change at the center frequency.

  In general, a wideband filter has a larger specific band than a narrowband filter. In a wideband filter having a large ratio band, the impedance change in the band is greatly different even with the same L and C constants. Therefore, in order to obtain a desired performance over the entire frequency band, compared with a narrowband filter, There are problems such as deterioration of out-of-band suppression amount, impedance characteristics, or in-band ripple for suppressing noise and the like. Furthermore, the wideband band limiting filter has a large variation in band characteristics, and the yield is lower than that of the narrowband filter, resulting in an increase in the cost of the wideband signal receiver. Therefore, in order to obtain a required out-of-band suppression amount in the wideband signal receiver, it is necessary to connect a plurality of band limiting filters (for example, SAW filters) in series. Furthermore, it is necessary to add a plurality of amplifiers to compensate for the loss of the band limiting filter.

  Various techniques relating to a broadband signal receiver in which a plurality of such band limiting filters and amplifiers are connected have been reported. FIG. 17 is a block diagram showing an example of a conventional filter serial type broadband signal receiver in which a plurality of band limiting filters and amplifiers are connected in series. This filter series type broadband signal receiver automatically performs an antenna 2002, a front-end unit 2003 that amplifies the input signal with low noise and converts it into an IF frequency, a band limiting unit 2001, and an AD conversion unit so that input signals are constant. In addition, an AGC (Automatic Gain Control) unit 2004 for adjusting the gain, an AD conversion unit 2005 for converting an analog signal into a digital signal, a signal processing unit 2006 for demodulating the digital signal, and the like are provided. Further, the band limiting unit 2001 has a configuration in which a plurality of filters 2011a, 2011b, and 2011c and a plurality of amplifiers 2010a, 2010b, and 2010c are connected in series.

  Also known is a technique for performing OFDM signal processing using FFT (Fast Fourier Transform) processing (see, for example, Patent Document 1). FIG. 18 is a configuration diagram illustrating an example of a conventional wideband signal receiver that performs processing of an OFDM signal using FFT processing. 18 that are the same as those in FIG. 17 are denoted by the same reference numerals. The wideband signal receiver of FIG. 18 is similar to the technique disclosed in Patent Document 1, and includes a front end unit 2003, a wideband filter 2111 and a band limiter having a notch filter 2112 that gives sharp attenuation to a specific frequency. Unit 2101, an AD conversion unit 2005, and an OFDM signal processing unit 2106 that has functions of orthogonal demodulation processing, FFT processing, and channel estimation processing and performs processing of an OFDM signal. Details of the OFDM method are reported in Non-Patent Document 1 and Non-Patent Document 2 below.

  Next, the operation of the band limiting unit 2101 in FIG. 18 will be described. The output of the wideband filter 2111 for extracting the band of the OFDM signal converted into the IF frequency band is input to the notch filter 2112 configured by ceramic, LC, etc., and the analog adjacent interference component of the OFDM signal that cannot be removed only by the wideband filter 2111 is obtained. The notch filter 2112 is used for removal. In general, the notch filter 2112 affects the phase in the OFDM band, but in the case of OFDM, the phase change is compensated by equalization or delay detection demodulation processing, so that the effect of the phase is virtually eliminated. have.

  Another technique for performing OFDM signal processing using FFT processing is also known (see, for example, Patent Document 2). FIG. 19 is a block diagram showing another example of a conventional wideband signal receiver that processes an OFDM signal using an FFT processing function. In FIG. 19, the same components as those in FIG. 17 are denoted by the same reference numerals, and redundant description is omitted. The wideband signal receiver of FIG. 19 includes a front end unit 2003, an orthogonal demodulation unit 2207 that performs orthogonal demodulation processing, an AD conversion unit 2005, and an OFDM signal processing unit 2206 that includes an FFT processor, an unnecessary component remover, and a demodulation processor. It is the composition provided with.

Next, the band limiting operation of the wideband signal receiver shown in FIG. 19 will be described. The FFT processor 2211 performs fast Fourier transform on the output signal of the AD conversion unit 2005 to convert the time axis into the frequency axis. After the FFT processing, the desired wave and the interference wave can be easily separated, and the unnecessary component remover 2212 operates to remove unnecessary components other than the desired wave signal.
JP 2000-13357 A JP 2003-143103 A ITU-RS contribution (TG11 / 3) Television Society Research Report Vol.17, No.54, p7-12, BCS 93-33 (Sep.1993)

  However, since the filter serial type broadband signal receiver as shown in FIG. 17 includes a plurality of expensive broadband filters and filter loss compensating amplifiers, the circuit scale increases and the cost increases and the power consumption increases. There are problems such as. Furthermore, since a plurality of broadband filters having a large gain temperature drift and a large temperature change amount at the center frequency are connected in series, there is a problem that reception performance is likely to deteriorate due to temperature fluctuation. Further, in the wideband receiver as shown in FIG. 18, it is difficult to suppress wideband out-of-band noise by the notch filter 2112. Further, in the wideband receiver as shown in FIG. 19, it is necessary to prevent the influence of a noise signal that is turned back by sampling in the AD conversion unit 2005. In order to increase the number of oversampling, an AD conversion unit 2005 capable of high-speed sampling and a signal processing unit 2006 capable of high-speed processing are required. In the AD conversion unit 2005 and the signal processing unit 2006, power consumption increases as the sampling speed and signal processing speed increase, and the circuit scale and cost also increase. For this reason, there are problems such as an increase in power consumption of the broadband signal receiver and an increase in circuit scale and cost.

  Further, in the wideband receiver described in Patent Document 2, the characteristics of the band limiting filter are moderated, and the AD converter performs an operation of inputting a signal (noise) other than the desired wave. The resolution is degraded. For this reason, since it is necessary to use a high-resolution AD conversion unit that is expensive and consumes a large amount of power, there are problems such as a further increase in power consumption and a further increase in circuit scale and cost.

  The present invention has been made in view of such points, and without using a plurality of wideband filters that are expensive and difficult to obtain high-performance characteristics, pass loss, in-band ripple, noise suppression amount, temperature characteristics It is an object of the present invention to provide an inexpensive OFDM signal receiver and composite receiver that can realize high performance with respect to VSWR (Voltage Standing Wave Rate) and the like.

  An OFDM signal receiver according to the present invention includes an analog signal receiving means for receiving a high-frequency analog signal, an analog / digital converting means for converting the analog signal received by the analog signal receiving means into a digital signal, and an analog / digital converting means. And a digital signal processing means for performing OFDM demodulation processing on the digital signal received from the analog signal receiving means, wherein the analog signal receiving means includes a band limiting unit for synthesizing the received signal of the analog signal by connecting a plurality of filters having different pass bands in parallel. The structure to be provided is taken.

  Further, in the OFDM signal receiver according to the present invention, the band limiting unit includes a matching circuit for matching impedance when distributing and combining a plurality of filters on its input side and output side. take.

  Further, in the OFDM signal receiver according to the present invention, the band limiting unit arbitrarily varies the level of the analog signal and the phase of the analog signal in the path of at least one filter. A configuration including at least one of the variable phase circuits is adopted.

  Further, in the OFDM signal receiver according to the present invention, the band limiting unit adopts a configuration in which a plurality of filters having different pass bands are configured in the same device, and the pass delay amount of each filter is made equal.

  An OFDM signal receiver according to the present invention includes an analog signal receiving unit that receives a high-frequency analog signal, a plurality of analog-digital conversion units that convert the analog signal received by the analog signal receiving unit into a digital signal, Digital signal processing means for performing OFDM demodulation processing on each digital signal received from the analog-digital conversion means, and the analog reception means outputs each analog signal output from a plurality of filters having different passbands, A band limiting unit for inputting to each of the plurality of analog / digital conversion means is provided, and the digital signal processing means is a parallel / serial converter that synthesizes digital signals input from the plurality of analog / digital conversion means by parallel / serial conversion processing. Configuration with converter Take.

  In the OFDM signal receiver according to the present invention, the band limiting unit adopts a configuration for synthesizing analog signals so that the pass bands of a plurality of filters having different pass band characteristics do not overlap. Furthermore, the band limiting unit adopts a configuration that allows arbitrary selection of filters having different pass bands for synthesizing analog signals. Moreover, a composite receiver can also be comprised by the OFDM signal receiver of the said invention.

  According to the OFDM signal receiver of the present invention, the band limiting unit of the analog receiving means connects a plurality of filters having different passbands in parallel to synthesize an analog signal, so a high-performance and inexpensive narrowband filter is used. Band limitation. As a result, a high-performance and inexpensive OFDM signal receiver can be realized. Further, since the band limiting unit of the analog receiving means includes one or both of a variable gain circuit and a variable phase circuit in the path of at least one filter, in addition to the effects of the invention, the characteristics of the filter may vary. It is possible to avoid a frequency band in which the gain greatly decreases.

  Further, according to the OFDM signal receiver of the present invention, the band limiting unit configures a plurality of filters having different pass bands in the same device, and equalizes the pass delay amount of each filter. Therefore, in addition to the effects of the present invention, it is possible to realize an OFDM signal receiver that is easy to adjust analog signals and that is small and inexpensive.

  Further, according to the OFDM signal receiver of the present invention, the band limiting unit of the analog signal receiving unit passes the signal through the parallel circuit of a plurality of filters having different pass bands, and each signal is sent to each analog / digital conversion unit. You are typing. Further, the parallel / serial converter of the digital signal processing means synthesizes signals by parallel / serial conversion processing. Therefore, in addition to the effect of the present invention, there is no need for adjustment even when a narrow band filter is used, so that it is possible to realize an OFDM signal receiver that is high performance and easy to manufacture.

  Further, according to the OFDM signal receiver of the present invention, the band limiting unit synthesizes the two outputs so that the pass bands of a plurality of filters having different pass band characteristics do not overlap. Therefore, in addition to the effects of the present invention, even if a large number of filters are provided, the AD conversion means can be integrated into two. Furthermore, according to the OFDM signal receiver of the present invention, it is possible to select filters with different passbands to be combined in the band limiter, so that in addition to the effects of the above invention, the OFDM signal receiver and other types of reception It is possible to share the bandwidth limiter of the receiver, and as a result, it is possible to construct a compact, high-performance and inexpensive OFDM signal receiver and composite receiver.

  The OFDM signal receiver of the present invention includes a band limiting unit that synthesizes signals via a plurality of filters having different pass bands, and this band limiting unit is configured so that a high-performance and inexpensive narrow band filter is connected in parallel. The configuration was In this way, by using a configuration in which narrowband filters are connected in parallel, by using the OFDM demodulation method algorithm, the band limiting unit compensates for characteristic deterioration factors that occur in the frequency band where the bands overlap. It is characterized by. Thereby, a high-performance and inexpensive OFDM signal receiver can be realized.

  Hereinafter, some embodiments of an OFDM signal receiver according to the present invention will be described in detail with reference to the drawings. In the drawings used in the embodiments described below, the same components are denoted by the same reference numerals, and redundant description will be omitted as much as possible.

<Embodiment 1>
FIG. 1 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 1 of the present invention. The OFDM signal receiver shown in FIG. 1 includes an analog receiver 101, an analog / digital converter (AD converter) 102, a digital signal processor 103, and an antenna 104. The digital signal processing unit 103 has various functional units necessary for OFDM demodulation, such as an orthogonal demodulation functional unit 103a, an FFT functional unit 103b, and a channel estimation unit 103c. Further, the analog reception unit 101 is a front-end unit 110 that amplifies an input signal with low noise and converts it to an IF frequency, a band limiting unit 111 that suppresses a noise signal outside the desired signal band, and an input of the AD conversion unit 102 An AGC unit 112 that automatically adjusts the gain so that the signal is constant is provided.

  FIG. 7 is a characteristic diagram of the filter according to Embodiment 1 of the present invention, in which the horizontal axis represents frequency (MHz) and the vertical axis represents gain (dB). The band limiting unit 111 illustrated in FIG. 1 includes, for example, a filter 120 and a filter 121 having different pass characteristics as illustrated in FIG. 7 in parallel, and a signal input to the band limiting unit 111 is received by each of the filters 120 and 121. It is comprised so that it may synthesize | combine via. Since the filters 120 and 121 have different pass bands, it is only necessary to match the impedance between the input and output, and the filters 120 and 121 do not need to be provided with elements for equal power distribution and equal power synthesis.

  An OFDM signal received from the antenna 104 is input to the analog reception unit 101 to perform gain conversion, frequency conversion, and band limitation. Then, the output signal of the analog receiving unit 101 is converted into a digital signal by the AD conversion unit 102, and OFDM demodulation processing is performed by the digital signal processing unit 103. Here, the band limiting unit 111 in the analog receiving unit 101 changes the level and phase characteristics of the output signal in the frequency band where the filters 120 and 121 overlap with the same gain. Further, when the pass delay characteristics of the two filters 120 and 121 are different, signals of two waves that are temporally different within the same band are output from the band limiting unit 111.

  However, in the OFDM system, gain change and phase change can be estimated by channel estimation using a pilot signal for each subcarrier, so even if the gain and phase characteristics in the band change, the OFDM demodulation process Compensate. For this reason, the influence of the characteristic deterioration that occurs in the frequency band where the band is overlapped by the band limiting unit 111 is substantially eliminated. Further, in the OFDM system, a multipath (delay time) within a guard interval is compensated by using a guard interval function which is a redundant portion provided between signals in order to prevent a multibus failure. Therefore, if the delay time difference between the plurality of filters 120 and 121 falls within the guard interval, the influence of the delayed wave generated by the difference between the delays of the two filters 120 and 121 is eliminated.

  As described above, in the OFDM signal receiver according to Embodiment 1 of the present invention, the band limiting unit 111 is configured to connect the band limiting unit 111 in parallel with a high-performance and inexpensive narrowband filter. The deterioration factor that occurs in the frequency band where the passbands of the filters 120 and 121 overlap can be compensated using the algorithm of the OFDM0 demodulation method. In this way, the OFDM signal receiver according to the first embodiment uses a high-performance and inexpensive narrow-band filter without using a plurality of wide-band filters that are expensive and difficult to obtain high-performance characteristics. By configuring the limiting unit 111, it is possible to easily realize high performance of various characteristics such as pass loss, in-band ripple, noise suppression amount, temperature characteristics, and VSWR.

  In FIG. 1, the number of filters of the band limiting unit 111 is two in parallel, but the same effect can be obtained even if three or more filters are arranged in parallel. In FIG. 1, the band limiting unit 111 does not include a matching circuit for performing impedance matching to distribute and combine a plurality of filters. However, even if such a matching circuit is added, the OFDM of FIG. The same effect as a signal receiver can be exhibited.

  FIG. 8 is a block diagram showing a configuration of an OFDM signal receiver to which a matching circuit is added as an application example of the OFDM signal receiver according to Embodiment 1 shown in FIG. In the OFDM signal receiver shown in FIG. 8, matching circuits 1101 and 1102 are added to the input and output sides of the filters 120 and 121 in the configuration shown in FIG. Here, the matching circuits 1101 and 1102 operate so that there is no reflected wave with respect to components whose impedances are connected to the three terminals, respectively.

  In the OFDM signal receiver of FIG. 1, the AGC unit 112 is connected to the output side of the band limiting unit 111. However, the AGC unit 112 has no signal quality degradation due to distortion, and the AD conversion unit 102 If the gain can be adjusted so that the input signal becomes constant, the same effect can be obtained even when connected to the input side of the band limiting unit 111. Further, in the OFDM signal receiver of FIG. 1, quadrature demodulation processing is performed in the digital signal processing unit 103. Even if an analog quadrature demodulation unit is disposed in front of the AD conversion unit 102, the same effect can be obtained. Can do. Further, in the OFDM signal receiver of FIG. 1, the band limiting unit 111 is placed after the frequency changing unit. However, in a fixed channel system, the same effect can be obtained before the frequency converting unit.

<Embodiment 2>
FIG. 2 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 2 of the present invention. The OFDM signal receiver according to the second embodiment shown in FIG. 2 adds a variable phase circuit 201 and a variable gain circuit 202 to the band limiter 211 in addition to the OFDM signal receiver according to the first embodiment shown in FIG. Circuit configuration. In the OFDM signal receiver of FIG. 2, the variable phase circuit 201 operates to arbitrarily change the phase of the output signal of the filter 120, and the variable gain circuit 202 arbitrarily changes the level of the output signal of the variable phase circuit 201. To work. Further, the output signal of the variable gain circuit 202 is combined with the output signal of the filter 121 and input to the AGC unit 112.

  Next, the operation of the OFDM signal receiver in the second embodiment configured as shown in FIG. 2 will be described with reference to the characteristic diagrams of the filters 120 and 121 and the band limiting unit 211. FIG. 9 is a characteristic diagram of the filter 120 of the band limiting unit 211 according to Embodiment 2 of the present invention, and FIG. 10 is a characteristic diagram of the filter 121 of the band limiting unit 211 according to Embodiment 2 of the present invention. FIG. 11 is a characteristic diagram of the filter 120 and the filter 121 of the band limiting unit 211 according to Embodiment 2 of the present invention, and FIG. 12 is a band limiting unit having a drop frequency band according to Embodiment 2 of the present invention. FIG. 13 is a characteristic diagram of the band limiting unit 211 having no drop frequency band according to the second embodiment of the present invention. In these characteristic diagrams, the horizontal axis indicates frequency (MHz) and the vertical axis indicates gain (dB).

  The filter 120 in the band limiting unit 211 in FIG. 2 has, for example, frequency-gain characteristics as shown in FIG. The filter 121 has frequency-gain characteristics as shown in FIG. 10, for example. Therefore, if the characteristics of the filter 120 in FIG. 9 and the characteristics of the filter 121 in FIG. 10 are overlapped to narrow the frequency range, the frequency-gain characteristics as shown in FIG. 11 are obtained. In addition, when signal synthesis is simply performed in the band limiting unit 211 in FIG. 2, for example, there may be a characteristic having a drop frequency band as shown in FIG. In the characteristic diagram of FIG. 12, the gain is greatly reduced when the frequency is in the vicinity of the (fa + 20) MHz band. In the OFDM system, when such a gain drop occurs, the signal level of the subcarrier in the band where the gain falls is lowered and the required signal CN ratio (carrier-noise ratio) cannot be obtained. The communication quality of subcarriers in the band where the frequency drops is deteriorated. This degrades the overall reception performance of the FDM signal receiver.

  The drop in gain as shown in FIG. 12 occurs because the phases of the filter 120 and the filter 121 are combined in opposite phases in the band A where the gains of the filter 120 and the filter 121 shown in FIG. 11 are at the same level. It is a phenomenon. That is, since filters of different materials generally have different pass delay characteristics, the amount of phase change (that is, the slope of the phase change) within a predetermined band (here, the entire received signal band) is different. For this reason, when filters made of different materials are configured in parallel, the amount of change in phase differs, so that a frequency band in which the phase is reversed in a certain frequency period is generated.

  Therefore, when the gain drops as shown in FIG. 12, the gains of the filter 120 and the filter 121 are adjusted by adjusting the variable phase circuit 201 or the variable gain circuit 202 in the circuit shown in FIG. As shown in FIG. 13, by adjusting the phase relationship so that the phase relationship is reversed in the frequency band where the gain difference between the filter 120 and the filter 121 is such that the phase relationship is not reversed in the frequency band of the same level. Thus, it is possible to obtain a frequency-gain characteristic without a drop in the gain. Although slight gain fluctuations occur in FIG. 13, the reception performance of the FDM signal receiver does not deteriorate as long as the required CN ratio is obtained.

  Further, by adjusting the variable gain circuit 202 in FIG. 2 to equalize the pass gains of the filter 120 and the filter 121, the CN ratio of all subcarriers can be made constant. This makes it possible to obtain stable reception characteristics even under conditions where fading occurs.

  As described above, the OFDM signal receiver according to the second exemplary embodiment of the present invention has a configuration in which the variable phase circuit 201 or the variable gain circuit 202 is placed on the output side of the filters 120 and 121 in the band limiting unit 211 and is variable. By adjusting the phase circuit 201 or the variable gain circuit 202, it is possible to prevent generation of a frequency band in which the gain drops greatly in the combined output of the filter 120 and the filter 121. As described above, the OFDM signal receiver according to the second embodiment can realize the band limiting unit 211 that does not have the frequency band in which the gain is greatly reduced even if the filter characteristics vary, thereby realizing a high-performance OFDM signal receiver. It becomes possible to do.

  In the OFDM signal receiver of FIG. 2, the variable phase circuit 201 and the variable gain circuit 202 are placed on the output side of the filter 120. However, the present invention is not limited to this, and the phase difference between the filter 120 and the filter 121 can be varied. Needless to say, even if the variable phase circuit 201 and the variable gain circuit 202 are provided on the input side of the filter 120, the same effect can be obtained. In the OFDM signal receiver of FIG. 2, the variable phase circuit 201 and the variable gain circuit 202 are arranged in this order on the output side of the filter 120. If the phase difference between the filter 120 and the filter 121 can be varied, the variable phase circuit 201 The circuit 201 and the variable gain circuit 202 may be arranged in the reverse order.

<Embodiment 3>
FIG. 3 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 3 of the present invention. The OFDM signal receiver of the third embodiment is an example in which the plurality of filters 320 and 321 in the band limiting unit 311 are configured as the same device in the OFDM signal receiver of the second embodiment described above. In FIG. 3, the filter 320 and the filter 321 are configured in the filter device 301 and are the same material.

  In general, the delay characteristic of a SAW filter is determined by the material of the filter and the configuration of the IDT, and mainly depends on the material. When filters of the same material are configured in parallel, there is almost no delay time difference between signals passing through the same band in a plurality of filters. Further, since the amount of change in phase is equal between the filter 320 and the filter 321, the phase difference is substantially constant even in the overlapping frequency band. Even when the materials of the filter 320 and the filter 321 are the same, the gain is greatly reduced when the phase relationship between the filter 320 and the filter 321 is opposite in phase as in the case where the materials of the filter are different, but compared with the case where the materials are different. Adjustment that does not cause a drop can be easily performed. Further, the configuration of the filter as in Embodiment 3 is similar to that of the antenna duplexer, and the same method can be used in the manufacturing method of the OFDM signal receiver. A receiver can be manufactured.

  As described above, the OFDM signal receiver according to Embodiment 3 of the present invention has a large gain in the combined output of the filters by configuring the plurality of filters 320 and 321 in the band limiting unit 311 with the same device. As a result, it is easy to make adjustments so as not to generate a frequency band in which the filter falls, and manufacture of the filter can be realized by an already established manufacturing method. As described above, the OFDM signal receiver according to Embodiment 3 of the present invention is easy to perform adjustment and can realize a small and inexpensive band limiting unit. Therefore, the OFDM signal receiver is high performance, small and inexpensive. Can be configured.

<Embodiment 4>
FIG. 4 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 4 of the present invention. The OFDM signal receiver according to the fourth embodiment shown in FIG. 4 is the same as the OFDM signal receiver according to the first embodiment described above, except that a signal that has passed through a plurality of filters in the band limiter 411 is -This is an example of a composition that is synthesized by serial conversion processing. Therefore, the AGC units 112a and 112b, the AD conversion units 102a and 102b, and the digital signal processing unit 403 are branched into two systems. The AGC units 112a and 112b perform the same operation as the AGC unit 112 in FIG. 1, and the AD conversion units 102a and 102b also perform the same operation as the AD conversion unit 102 in FIG.

  In FIG. 4, the band limiting unit 411 inputs the input signal to the filters 120 and 121 having different pass characteristics. The output signal of the filter 120 is level-converted by the AGC unit 112a and input to the AD conversion unit 102a. Similarly, the output signal of the filter 121 is level-converted by the AGC unit 112b and input to the AD conversion unit 102b. The output signals of the AD conversion units 102a and 102b are respectively input to two systems of the digital signal processing unit 403.

  The digital signal processing unit 403 performs orthogonal demodulation processing on the signals input from the AD conversion units 102a and 102b by the orthogonal demodulation processors 451 and 452, and then performs FFT processing by the FFT processors 453 and 454, respectively. Further, the output signals of the FFT processors 453 and 454 are subjected to phase and gain compensation by the channel estimator 455 only for the selected subcarriers, and are input to the P / S processor 456. Then, the P / S processor 456 performs parallel / serial conversion processing on the selected subcarrier signal.

  Next, the operation of the OFDM signal receiver according to Embodiment 4 configured as shown in FIG. 4 will be described. FIG. 14 is a characteristic diagram of a received signal according to Embodiment 4 of the present invention, where the horizontal axis represents frequency (MHz) and the vertical axis represents received signal level (dBm). FIG. 15 is a characteristic diagram of the filters 120 and 121 of the band limiting unit 411 according to Embodiment 4 of the present invention, where the horizontal axis indicates frequency (MHz) and the vertical axis indicates filter gain (dB). ing.

  For example, the OFDM signal as shown in FIG. 14 is input to the band limiting unit 411 in FIG. As shown in FIG. 14, the OFDM signal has subcarriers a, b, c, d, e, f, g, and h. Further, the filters 120 and 121 in the band limiting unit 411 have characteristics as shown in FIG. 15, for example. That is, the filter 120 operates to suppress frequency bands other than the subcarriers a, b, c, and d, and the filter 121 operates to suppress frequency bands other than the subcarriers e, f, g, and h.

  In P / S processor 456, subcarriers a, b, c, and d are selected from FFT processor 453, and subcarriers e, f, g, and h are selected from FFT processor 454 and combined. As a result, the P / S processor 456 can demodulate the received signal using the narrowband filters 120 and 121. Furthermore, since the output signals of the filters 120 and 121 are not synthesized by the analog receiver 101, there is no need for adjustment because there is no drop in gain associated with the inversion of the phase of the output signal. Further, since the signal level is also divided by dividing the signals input to the AD conversion units 102a and 102b by frequency, the resolution of each AD converter 102a and 102b can be lowered.

  As described above, the OFDM signal receiver according to Embodiment 4 of the present invention combines the signals that have passed through the narrow-band filters 120 and 121 in the band limiting unit 411 with the P / S processor 456. Even if a plurality of narrow-band filters 120 and 121 are used, phase adjustment can be eliminated. As described above, the OFDM signal receiver according to the fourth embodiment does not need to be adjusted even if a narrow band filter is used, so that an OFDM signal receiver having high performance and easy manufacture can be realized. Is possible.

<Embodiment 5>
FIG. 5 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 5 of the present invention. The OFDM signal receiver of the fourth embodiment shown in FIG. 5 is an example in which a plurality of filters in the band limiting unit 511 are combined into two outputs in the OFDM signal receiver of the fourth embodiment described above. It is. In FIG. 5, the band limiting unit 511 inputs the input signal to filters 520, 521, 522, and 523 having different pass characteristics. The output signals of the filters 520 and 521 are combined, subjected to level conversion by the AGC unit 112a and input to the AD conversion unit 102a. Similarly, the output signals of the filters 522 and 523 are level-converted by the AGC unit 112b and input to the AD conversion unit 102b.

  Next, the operation of the OFDM signal receiver of Embodiment 5 configured as shown in FIG. 5 will be described. FIG. 16 is a characteristic diagram of the filters 520, 521, 52, and 523 of the band limiting unit 511 according to Embodiment 5 of the present invention, where the horizontal axis represents frequency (MHz) and the vertical axis represents filter gain (dB). Is shown. For example, an OFDM signal as shown in FIG. 14 is input to the band limiting unit 511. Note that the OFDM signal shown in FIG. 14 has subcarriers a, b, c, d, e, f, g, and h.

  Since the filters 520, 521, 522, and 523 in the band limiting unit 511 in FIG. 5 have characteristics as shown in FIG. 16 and do not synthesize filters having adjacent pass bands, phase inversion is performed on two output signals. There will be no drop in gain (level). Therefore, it is not necessary to adjust the phase between the filters as in the case of the fourth embodiment.

  As described above, the OFDM signal receiver according to Embodiment 5 of the present invention combines two signals so as not to combine adjacent filters in the band limiting unit 511 having a plurality of filters. By doing so, two AD converters can be provided regardless of the number of filters. As described above, in the OFDM signal receiver according to the fifth embodiment, two AD conversion units can be provided even if a plurality of filters are provided. Therefore, the OFDM signal receiver is small, high-performance, and easy to manufacture. Can be realized.

<Embodiment 6>
FIG. 6 is a block diagram showing a configuration of a composite receiver including an OFDM signal receiver according to Embodiment 6 of the present invention. The OFDM signal receiver according to the sixth embodiment shown in FIG. 6 is the same as the OFDM signal receiver according to the first embodiment described above, except that a switch 601 is newly provided in the band limiting unit 611 and the OFDM signal is processed by the digital signal processing unit 603 This is an example having a narrowband signal demodulation processing function (for example, a demodulation processing function of CDMA (Code Division Multiple Access)).

  In FIG. 6, the switch 601 can select whether or not to combine the passing signal of the filter 120 with the output signal of another filter. The digital signal processing unit 603 can select OFDM demodulation and CDMA demodulation by selecting and operating a switch 610 provided therein.

  Next, the operation of the OFDM signal receiver according to the sixth embodiment configured as shown in FIG. 6 will be described. When a broadband OFDM signal is received, a broadband signal including the pass band of the filter 120 is input to the digital signal processing unit 603 by connecting the switch 601. Then, the digital signal processing unit 603 can demodulate the received broadband OFDM signal by selecting the OFDM demodulation processing by the switch 610. When a narrow-band CDMA signal is received, the pass band signal of only the filter 121 is input to the digital signal processing unit 603 by disconnecting the switch 610. At this time, since signal synthesis is not performed, there is no generation of phase, gain change, and delay wave in the band due to synthesis. Next, the digital signal processing unit 603 can demodulate the received narrowband CDMA signal by selecting the CDMA demodulation processing by the switch 610.

  As described above, the composite receiver including the OFDM signal receiver according to the sixth embodiment of the present invention includes the switch 601 in the band limiting unit 611, so that a wideband OFDM signal and a narrowband other scheme are provided. Can be shared by the band limiter 611. As described above, the OFDM signal receiver according to the sixth embodiment constructs a compact, high-performance, and inexpensive composite receiver by sharing the band limiting unit of the OFDM signal receiver and the receivers of other systems. It becomes possible. In addition, although the switch is used in the circuit configuration of the OFDM signal receiver shown in FIG. 6, the circuit configuration is not limited to the switch and can control the synthesis of the filter (for example, a variable gain circuit). The same effect as described above can be exhibited.

  As described above, the OFDM signal receiver according to the present invention configures a band limiting unit by paralleling high-performance and inexpensive narrow band filters, and an OFDM demodulation method algorithm is used to determine the degradation factor generated in the band limiting unit. By using and compensating, a high-performance and inexpensive OFDM signal receiver can be realized. Therefore, the OFDM signal receiver of the present invention can be effectively used in the fields of mobile communication systems and terrestrial digital broadcasting.

1 is a block diagram showing a configuration of an OFDM signal receiver according to Embodiment 1 of the present invention. Block diagram showing a configuration of an OFDM signal receiver according to a second embodiment of the present invention Block diagram showing a configuration of an OFDM signal receiver according to a third embodiment of the present invention Block diagram showing a configuration of an OFDM signal receiver according to a fourth embodiment of the present invention Block diagram showing a configuration of an OFDM signal receiver according to a fifth embodiment of the present invention Block diagram showing a configuration of an OFDM signal receiver according to a sixth embodiment of the present invention FIG. 6 is a characteristic diagram of the filter according to the first embodiment of the present invention. 1 is a block diagram showing a configuration of an OFDM signal receiver to which a matching circuit is added as an application example of the OFDM signal receiver according to Embodiment 1 shown in FIG. The characteristic diagram of the filter of the band limiting unit according to the second embodiment of the present invention The characteristic diagram of the filter of the band limiting unit according to the second embodiment of the present invention Filter of band limiting unit and filter characteristic diagram according to Embodiment 2 of the present invention Characteristic diagram of band limiting unit having drop frequency band according to embodiment 2 of the present invention FIG. 6 is a characteristic diagram of a band limiting unit having no drop frequency band according to the second embodiment of the present invention. The characteristic view which shows the received signal which concerns on Embodiment 4 of this invention Filter of band-limiting unit and filter characteristic diagram according to embodiment 4 of the present invention The characteristic diagram of the filter of the band limiting unit according to the fifth embodiment of the present invention Configuration diagram showing an example of a conventional filter series type broadband signal receiver in which a plurality of band limiting filters and amplifiers are connected in series Configuration diagram showing an example of a conventional wideband signal receiver that performs processing of an OFDM signal using an FFT processing function The block diagram which shows the other example of the conventional wideband signal receiver which processes an OFDM signal using a FFT processing function

Explanation of symbols

101 Analog receiving unit 102, 102a, 102b AD conversion unit 103, 403, 603 Digital signal processing unit 103a Orthogonal demodulation function unit 103b FFT function unit 103c Line estimation unit 104 Antenna 110 Front end unit 111, 211, 311, 411, 511, 611 Band limiting unit 112, 112a, 112b AGC unit 120, 121, 320, 321 Filter 201 Variable phase circuit 202 Variable gain circuit 301 Filter device 451, 452 Quadrature demodulation processor 453, 454 FFT processor 455 Line estimator 456 Parallel Serial conversion processor 601 switch 1101, 1102 matching circuit

Claims (8)

An analog signal receiving means for receiving a high-frequency analog signal;
Analog / digital conversion means for converting the analog signal received by the analog signal receiving means into a digital signal;
Digital signal processing means for performing OFDM demodulation processing on the digital signal received from the analog-digital conversion means,
The said analog signal receiving means is equipped with the band restriction | limiting part which synthesize | combines the received signal of an analog signal by connecting the several filter from which a pass band differs in parallel, The OFDM signal receiver characterized by the above-mentioned.   2. The OFDM signal reception according to claim 1, wherein the band limiting unit includes a matching circuit for matching impedance when distributing and combining the plurality of filters on its input side and output side. Machine.   The band limiting unit includes at least one of a variable gain circuit that arbitrarily changes the level of the analog signal and a variable phase circuit that arbitrarily changes the phase of the analog signal in the path of at least one filter. The OFDM signal receiver according to claim 1 or 2.   4. The band limiting unit according to claim 1, wherein a plurality of filters having different pass bands are configured in the same device, and the amount of pass delay of each filter is made equal. OFDM signal receiver. An analog signal receiving means for receiving a high-frequency analog signal;
A plurality of analog-digital conversion means for converting the analog signal received by the analog signal receiving means into a digital signal;
Digital signal processing means for performing OFDM demodulation processing on each digital signal received from the plurality of analog-digital conversion means,
The analog receiving unit includes a band limiting unit that inputs each analog signal output from a plurality of filters having different passbands to each of the plurality of analog-digital conversion units,
The OFDM signal receiver, wherein the digital signal processing means includes a parallel / serial converter that synthesizes digital signals input from the plurality of analog / digital conversion means by parallel / serial conversion processing.   6. The OFDM signal receiver according to claim 5, wherein the band limiting unit synthesizes an analog signal so that pass bands of a plurality of filters having different pass band characteristics do not overlap.   The OFDM signal receiver according to claim 1, wherein the band limiting unit can arbitrarily select filters having different pass bands for synthesizing analog signals.   A composite receiver comprising the OFDM signal receiver according to claim 7.

Images