US20070184801A1 - Radio reception apparatus and radio reception method - Google Patents

Abstract

A radio reception apparatus is a radio reception apparatus for demodulating a multicarrier signal modulated according to multicarrier modulation. It includes a plurality of antenna sections, each for receiving a multicarrier signal, a plurality of carrier selection sections, each of the carrier selection sections selecting at least one subcarrier signal for each of the antenna sections out of the multicarrier signal received by each of the antenna sections, an antenna selection section for selecting a reception antenna section from among the antenna sections based on the signal strengths of the subcarrier signals selected by the carrier selection sections, and a demodulation section for demodulating the multicarrier signal received by the antenna section selected by the antenna selection section.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of and claims the benefit of priority under 35 USC §120 from U.S. Ser. No. 10/901,202, Jul. 29, 2004 and claims the benefit of priorities from both the prior Japanese Application No. 2003-202859, filed on Jul. 29, 2003 and the prior Japanese Application No. 2004-220699, filed on Jul. 28, 2004; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• This invention relates to a radio reception apparatus and in particular to a radio reception apparatus for a multicarrier signal.
• 2. Description of the Related Art
• Diversity reception has been used as a method for coping with degradation of the communication quality caused by fading in radio communications. A diversity reception apparatus in a related art receives a multicarrier signal by a plurality of reception means through a plurality of antennas. The diversity reception apparatus finds received power for each of the multicarrier signals received by the plurality of reception means, and selects one antenna based on the received power. Further, the diversity reception apparatus demodulates the multicarrier signal received through the selected antenna. (Please see JP-A-2000-174726 (Kokai), JP-A-2001-268050 (Kokai) and JP-A-2002-261727(Kokai))
• The diversity reception apparatus in the related art selects an antenna based on the signal strength of the whole multicarrier signal. However, when an antenna is selected based on the received power of the whole multicarrier signal, if a subcarrier signal of a part of multicarrier signal has large distortion, the diversity reception apparatus cannot select an antenna with good communication quality.
SUMMARY OF THE INVENTION
• It is an object of the invention to provide a radio reception apparatus that can select an antenna with good communication quality from among antennas if a multicarrier signal has distortion.
• According to one aspect of the invention, there is provided a radio reception apparatus including: a plurality of antenna sections, each of the antenna sections receiving a multicarrier signal which is modulated according to multicarrier modulation and demodulating the modulated multicarrier signal; a plurality of carrier selection sections each of the carrier selection sections selecting at least one subcarrier signal for each of the plurality of antenna sections out of the multicarrier signal received by each of the plurality of antenna sections; an antenna selection section for selecting a reception antenna section from among the plurality of antenna sections based on signal strengths of the subcarrier signals selected by the plurality of carrier selection sections; and
• a demodulation section for demodulating the multicarrier signal received by the antenna section selected by the antenna selection section.
• According to another aspect of the invention, there is provided a radio reception method using a radio reception apparatus, including: receiving a multicarrier signal modulated according to multicarrier modulation through a plurality of antenna sections; selecting at least one subcarrier signal for each of the antenna sections out of the multicarrier signal received by each of the antenna sections based on frequency; selecting a reception antenna section from among the antenna sections based on the signal strengths of the selected subcarrier; and demodulating the multicarrier signal received by the selected reception antenna section.
BRIEF DESCRIPTION OF THE DRAWINGS
• These and other objects and advantages of the invention will become more fully apparent from the following detailed description taken with the accompanying drawings in which:
• FIG. 1 is a block diagram of a diversity radio reception apparatus100 according to a first embodiment of the invention;
• FIG. 2 is a schematic drawing to specifically show the operation of thecarrier selection sections31 to33 and theantenna selection section40 in the embodiment;
• FIG. 3 is a flowchart to show the operation of the reception apparatus100;
• FIG. 4 is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus102 according to a third embodiment of the invention.
• FIGS. 5A, 5B, and5C are schematic drawings showing carrier selection sections of a reception apparatus according a fourth embodiment of the invention;
• FIGS. 6A, 6B, and6C are schematic drawings showing carrier selection sections of a reception apparatus according a fifth embodiment of the invention;
• FIGS. 7A, 7B, and7C are schematic drawings showing carrier selection sections of a reception apparatus according a sixth embodiment of the invention;
• FIGS. 8A, 8B, and8C are schematic drawings showing carrier selection sections of a reception apparatus according a seventh embodiment of the invention;
• FIGS. 9A, 9B, and9C are schematic drawings showing carrier selection sections of a reception apparatus according an eighth embodiment of the invention;
• FIG. 10 is a schematic drawing to show carrier selection sections of a reception apparatus according a ninth embodiment of the invention;
• FIG. 11 is a block diagram to show a reception apparatus according to a tenth embodiment of the invention;
• FIG. 12 is a block diagram to show a demodulation section of a reception apparatus according to an eleventh embodiment of the invention;
• FIG. 13 is a block diagram to show a demodulation section of a reception apparatus according to a twelfth embodiment and a thirteenth embodiment of the invention;
• FIG. 14 is a block diagram to show a reception apparatus according to one aspect of the invention;
• FIG. 15 is a schematic diagram which shows a frequency characteristic of a reception signal according to fourteenth embodiment of the invention;
• FIG. 16 is a flow chart to show an example of processing operation of the radio reception apparatus as shown inFIG. 15;
• FIG. 17 is a block diagram to show internal construction of the radio reception apparatus according to the fifteenth embodiment;
• FIG. 18 is a block diagram to show an internal construction of the radio reception apparatus according to the sixteenth embodiment;
• FIG. 19 is a flow chart to show one example of processing operation of the radio reception apparatus as show inFIG. 18;
• FIG. 20 shows a data construction of the packet. As show inFIG. 20;
• FIG. 21 is a block diagram to show a construction of the radio reception apparatus according to the seventeenth embodiment;
• FIG. 22 represents a frequency characteristic of a data part of a packet which was complied with IEEE802.11a;
• FIG. 23 represents a frequency characteristic of a short preamble, which is a part of a preamble part of the packet which was complied with IEEE802.11a;
• FIG. 24 is a block diagram to show the construction of the radio reception apparatus according to the eighteenth embodiment;
• FIG. 25 is a flowchart to show an example of the processing operation according to nineteenth embodiment;
• FIG. 26 is flow chart to show an example of the processing operation according to the twentieth embodiment;
• FIG. 27 is a flow chart of the processing operation according the radio reception apparatus according to the twenty-first embodiment; and
• FIG. 28 is an view to explain the general description according the twenty-second embodiment.
DETAILED DESCRIPTION OF THE INVENTION
• Referring now to the accompanying drawings, there are shown embodiments of the invention. It is to be understood that the invention is not limited to the embodiments thereof.
• A diversity radio reception apparatus according to each embodiment of the invention selects a subcarrier signal from multicarrier signals received through a plurality of antennas. The radio reception apparatus selects an antenna based on the signal strength of the subcarrier signal, and receives signals through the selected antenna. Accordingly, the radio reception apparatus can select the antenna with good communication quality. The diversity radio reception apparatus can be used as a selection diversity reception apparatus in OFDM (Orthogonal Frequency Division Multiplexing) modulation of a radio LAN, etc
First Embodiment
• FIG. 1 is a block diagram of a diversity radio reception apparatus (simply, reception apparatus)100 according to a first embodiment of the invention. The reception apparatus100 includesantennas11 to13,signal conversion sections21 to23,carrier selection sections31 to33, anantenna selection section40, and ademodulation section50. Each of theantennas11 to13 receives the multicarrier signal modulated according to multicarrier modulation by the communicating party with the reception apparatus100. In the embodiment, the three antenna sections are provided, but two or four or more antenna sections may be provided.
• Each of thesignal conversion sections21 to23 includes an LNA (Low Noise Amplifier) for amplifying the multicarrier signal, a D/C (Down Converter) section for converting the frequency of the multicarrier signal into a base band, an A/D conversion section for converting an analog signal into a digital signal, and an FFT (Fast Fourier Transform) section for executing discrete Fourier transform for each of the multicarrier signals. The multicarrier signal passed through thesignal conversion section21 to23 is made up of a plurality of subcarrier signals different in frequency band.
• Thecarrier selection sections31 to33 are connected to thesignal conversion sections21 to23 respectively for selecting a specific subcarrier signal out of the multicarrier signal passed through thesignal conversion section21 to23 based on the frequency.
• As many signal conversion sections as and as many carrier selection sections as the number of antenna sections are provided. In the embodiment, threesignal conversion sections21 to23 and threecarrier selection sections31 to33 are provided because the number of antenna sections is three (11 to13).
• Theantenna selection section40 is connected to thecarrier selection sections31 to33 and obtains the subcarrier signals selected by thecarrier selection sections31 to33. Theantenna selection section40 selects the reception antenna section based on the signal strength of each of the subcarrier signals.
• Thedemodulation section50 demodulates the multicarrier signal received through the antenna section selected by theantenna selection section40.
• FIG. 2 is a schematic drawing to specifically show the operation of thecarrier selection sections31 to33 and theantenna selection section40 in the embodiment. Thecarrier selection sections31 to33 and theantenna selection section40 will be discussed in more detail with reference toFIG. 2.
• The graph shown in thecarrier selection section31 inFIG. 2 is a graph to show the frequencies and the signal strength of the multicarrier signal received through theantenna section11. The multicarrier signal is made up of a plurality of subcarrier signals different in frequency band. Each subcarrier signal is indicated by the dashed line in the graph. Thecarrier selection section31 selects subcarrier signals SC₁and SC₂corresponding to predetermined frequencies f₁and f₂from among the subcarrier signals. Likewise, the carrier selection section32 (33) selects the subcarrier signals corresponding to the frequencies f₁and f₂from among the subcarrier signals making up the multicarrier signal received through the antenna section12 (13). The subcarrier signals selected by thecarrier selection sections31 to33 are transmitted to theantenna selection section40.
• Theantenna selection section40 has acalculation section42 and a signalstrength comparison section44. Thecalculation section42 calculates average signal strength AV₁of the subcarrier signals SC₁and SC₂selected by thecarrier selection section31, average signal strength AV₂of the subcarrier signals selected by thecarrier selection section32, and average signal strength AV₃of the subcarrier signals selected by thecarrier selection section33.
• The signalstrength comparison section44 compares the average signal strengths AV₁, AV₂, and AV₃and selects the antenna section corresponding to the maximum average signal strength from among theantenna sections11 to13.
• In the embodiment, each of thecarrier selection sections31 to33 selects two subcarrier signals, but may select one or three or more subcarrier signals.
• FIG. 3 is a flowchart to show the operation of the reception apparatus100. To begin with, theantenna sections11 to13 receive the multicarrier signal modulated according to multicarrier modulation (S10). Next, thesignal conversion sections21 to23 convert the multicarrier signals received from theantenna sections11 to13. Accordingly, the multicarrier signal is converted into a signal made up of a plurality of subcarrier signals different in frequency band (S20).
• Each of thecarrier selection sections31 to33 selects specific subcarrier signals out of the multicarrier signal based on the frequency (S30).
• Theantenna selection section40 selects the antenna section used to receive the multicarrier signal based on the signal strengths of the subcarrier signals selected by thecarrier selection sections31 to33 (S40).
• Thedemodulation section50 demodulates the multicarrier signal received through the antenna section selected by the antenna selection section40 (S50).
• According to the embodiment, the antenna section can be selected based on the signal strengths of specific subcarrier signals on specific frequency band. Accordingly, the reception apparatus100 can select the subcarrier signals having a large effect on demodulation, for example, and can conduct communications using the antenna corresponding to the subcarrier signals having the maximum average signal strength.
• Generally, when large distortion is contained in the multicarrier signal, the antenna with large received power of the whole multicarrier signal is not necessarily the antenna with good communication quality. According to the embodiment, the average signal strength of the subcarrier signals having a large effect on demodulation in the multicarrier signal can be calculated, so that the reception apparatus100 can reliably select the antenna section with good communication quality from among theantenna sections11 to13.
Second Embodiment
• Areception apparatus101 according to a second embodiment of the invention will be discussed with reference toFIGS. 1 and 2. In the first embodiment, thecalculation section42 calculates the average signal strengths AV₁, AV₂, and AV₃of the selected subcarrier signals, and the signalstrength comparison section44 compares the average signal strengths AV₁, AV₂, and AV₃, thereby selecting the antenna section for communications. The reception apparatus of the second embodiment differs from the reception apparatus of the first embodiment in that acalculation section42 selects subcarrier signals MX₁to MX₃(not shown) having the largest signal strength forcarrier selection sections31 to33, that a signalstrength comparison section44 compares the subcarrier signals MX₁to MX₃and selects the subcarrier signal having the largest signal strength from among the subcarrier signals, and that anantenna selection section40 selects the antenna section receiving the subcarrier signal having the largest signal strength.
• In the second embodiment, the subcarrier signal having the maximum signal strength can be selected from among the subcarrier signals except the subcarrier signals in the frequency band having distortion in multicarrier signal. Accordingly, thereception apparatus101 can reliably select the antenna with good communication quality.
Third Embodiment
• FIG. 4 is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus102 according to a third embodiment of the invention. Thecarrier selection section31 in the embodiment selects pilot carrier signals PC₁and PC₂out of multicarrier signals received by anantenna section11. Thecarrier selection sections32 and33 select pilot carrier signals out of multicarrier signals received byantenna sections12 and13. Other components and the operation of thereception apparatus102 are similar to those in the first or second embodiment replacing the subcarrier signals with the pilot carrier signals.
• Generally, if the pilot carrier signal is a subcarrier signal used as the reference for correcting distortion. If the signal length of the pilot carrier signal is small, the whole multicarrier signal cannot accurately be corrected.
• Therefore, the antenna section receiving the pilot carrier signal having the maximum signal strength or the largest average signal strength is selected from among theantenna sections11 to13, whereby thereception apparatus102 can accurately correct the whole multicarrier signal received through the selected antenna section. Consequently, thereception apparatus102 can conduct good-quality communications. Further, the reception apparatus of the third embodiment has similar advantages to those of the reception apparatus of the first and second embodiments.
• In the third embodiment, the number of pilot carrier signals is two, but may be one or three or more.
Fourth Embodiment
• FIG. 5A is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus103 according to a fourth embodiment of the invention. Each of thecarrier selection sections31 to33 in the embodiment has a thresholdvalue determination section34 for determining a threshold value Th concerning the signal strength of a pilot carrier signal. The thresholdvalue determination sections34 of thecarrier selection sections31 to33 determine the same threshold value Th. Thecarrier selection section31 selects pilot carrier signals PC₁to PC₃exceeding the threshold value Th out of multicarrier signal received by anantenna section11. Thecarrier selection sections32 and33 select pilot carrier signals exceeding the threshold value Th out of multicarrier signals received byantenna sections12 and13. Other components of thereception apparatus103 are similar to those previously described with reference toFIG. 1.
• Thus, in the embodiment, the pilot carrier signals each including larger signal strength than the threshold value Th are selected from among the pilot carrier signals in the multicarrier signal. In the embodiment, only the pilot carrier signals exceeding the threshold value Th are selected and thus thecarrier selection sections31 to33 may differ in the number of selected pilot carrier signals.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the third embodiment. According to the fourth embodiment, thecarrier selection sections31 to33 exclude signals including the signal strength lower than the threshold value Th, such as a pilot carrier signal PC₄. Anantenna selection section40 can select an antenna section using the pilot carrier signal including the large signal strength with small distortion among the pilot carrier signals. Consequently, thereception apparatus103 can select the antenna with good communication quality. Particularly, it is effective when a demodulation section uses only pilot carrier signals including large signal strength for distortion correction.
• For example,FIGS. 5B and 5C provide graphs of multicarrier signals received by theantenna sections11 and12. Thecarrier selection section31 selects pilot carrier signals PC₂and PC₃out of multicarrier signal from theantenna section11. Thecarrier selection section32 selects pilot carrier signals PC₅to PC₈out of multicarrier signal from theantenna section12. The average signal strength of the pilot carrier signals PC₂and PC₃is clearly larger than that of the pilot carrier signals PC₅to PC₈. Therefore, according to the embodiment, theantenna selection section40 reliably selects theantenna section11.
• On the other hand, if the threshold value is not set, thecarrier selection section31 selects not only the pilot carrier signals PC₂and PC₃, but also pilot carrier signals PC₁and PC₄. In this case, the average signal strength of the pilot carrier signals PC₁to PC₄becomes smaller than that of the pilot carrier signals PC₂and PC₃. Therefore, the difference between the average signal strength of the pilot carrier signals PC₁to PC₄and that of the pilot carrier signals PC₅to PC₈becomes smaller than that when the threshold value is set. Therefore, for theantenna selection section40 to reliably select theantenna section11, preferably the threshold value of signal strength is provided in thecarrier selection section31.
• The embodiment is effective when good pilot carrier signals including large signal strength and pilot carrier signals including extremely small signal strength are mixed in the multicarrier signal. Particularly, it produces effect when the demodulation section uses only pilot carrier signals including large signal strength for distortion correction.
Fifth Embodiment
• FIG. 6A is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus104 according to a fifth embodiment of the invention. As shown inFIG. 6A, if it is obvious that the signal strength of multicarrier signal is large or small as a whole, thresholdvalue determination sections34 set threshold value Th to zero. Accordingly, thecarrier selection sections31 to33 select all pilot carrier signals in the multicarrier signal. Anantenna selection section40 can select an antenna based on the average signal strengths of all pilot carrier signals. For example,FIGS. 9B and 9C provide graphs of multicarrier signals received byantenna sections11 and12. As shown inFIGS. 6B and 6C, theantenna selection section40 calculates the average signal strength of pilot carrier signals PC₁to PC₄and that of pilot carrier signals PC₅to PC₈. Theantenna selection section40 selects anantenna section11 including large signal strength on the whole based on the calculation result.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment. Particularly, the embodiment is effective when the distortion difference between the pilot carrier signals in the multicarrier signal is comparatively small. That is, the embodiment is effective when the signal strengths of the pilot carrier signals are large or small on the whole.
Sixth Embodiment
• FIGS. 7A to7C are schematic drawings to showcarrier selection sections31 to33 of areception apparatus105 according to a sixth embodiment of the invention. Each of thecarrier selection sections31 to33 in the embodiment has a minimumvalue detection section35. Other components of thereception apparatus105 are similar to those previously described with reference toFIG. 1.
• The minimumvalue detection section35 detects the pilot carrier signal including the minimum signal strength among pilot carrier signals. For example, in thecarrier selection section31, the minimumvalue detection section35 detects pilot carrier signal PC₄. Thecarrier selection section31 selects the pilot carrier signal PC₄. Thus, in the embodiment, the pilot carrier signal including the minimum signal strength is selected from among the pilot carrier signals in multicarrier signal. Thecarrier selection sections32 and33 also select the pilot carrier signal including the minimum signal strength from among the pilot carrier signals in multicarrier signal.
• Anantenna selection section40 compares the pilot carrier signals selected by thecarrier selection sections31 to33 and selects the antenna section including the maximum signal strength. Accordingly, in the embodiment, the antenna section including large signal strength can be selected.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment. Particularly, the embodiment is effective when the distortion difference between the pilot carrier signals in the multicarrier signal is comparatively small. That is, the embodiment is effective when the signal strengths of the pilot carrier signals are large or small on the whole.
• For example,FIGS. 7B and 7C provide graphs of multicarrier signals received byantenna sections11 and12. Assume that the pilot carrier signal including the minimum signal strength in the multicarrier signal shown inFIG. 7B is PC₄. Assume that the pilot carrier signal including the minimum signal strength in the multicarrier signal shown inFIG. 7C is PC₅. Theantenna selection section40 compares the pilot carrier signals PC₄and PC₅. Further, theantenna selection section40 selects theantenna section11 receiving the pilot carrier signals PC₄including comparatively large signal strength.
Seventh Embodiment
• FIGS. 8A to8C are schematic drawings to showcarrier selection sections31 to33 of areception apparatus106 according to a seventh embodiment of the invention. Each of thecarrier selection sections31 to33 in the embodiment has a minimumvalue detection section35 and a minimum pilot carrier signal removal section36 (simply, removal section36). Other components of thereception apparatus106 are similar to those previously described with reference toFIG. 1.
• The minimumvalue detection section35 detects the pilot carrier signal including the minimum signal strength among pilot carrier signals. For example, in thecarrier selection section31, the minimumvalue detection section35 detects pilot carrier signal PC₄. Theremoval section36 selects pilot carrier signals PC₁to PC₃other than the pilot carrier signal PC₄. Thus, in the embodiment, signals other than the pilot carrier signal including the minimum signal strength are selected from among the pilot carrier signals in multicarrier signal. Thecarrier selection sections32 and33 also select signals other than the pilot carrier signal including the minimum signal strength from among the pilot carrier signals in multicarrier signal.
• In anantenna selection section40, acalculation section42 calculates average signal strengths AV₁, AV₂, and AV₃of the pilot carrier signals selected by thecarrier selection sections31 to33. A signalstrength comparison section44 compares the average signal strengths AV₁, AV₂, and AV₃and selects the antenna section including the maximum average signal strength.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment. Further, according to the embodiment, pilot carrier signals other than the pilot carrier signal including the minimum signal strength are selected, so that thereception apparatus106 can reliably select the antenna with good communication quality. Particularly, it is effective when a demodulation section uses only pilot carrier signals including large signal strength for distortion correction.
• The embodiment is effective when good pilot carrier signals including large signal strength and pilot carrier signals including extremely small signal strength are mixed in the multicarrier signal. The embodiment is effective when pilot carrier signals including large distortion and pilot carrier signals including small distortion are mixed in the multicarrier signal. Particularly, it is effective when the demodulation section uses only pilot carrier signals including large signal strength for distortion correction.
Eighth Embodiment
• FIG. 9A is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus107 according to an eighth embodiment of the invention. Each of thecarrier selection sections31 to33 in the embodiment has a minimumvalue detection section35, aremoval section36, and a minimumvalue detection section37. Other components of thereception apparatus107 are similar to those previously described with reference toFIG. 1.
• The minimumvalue detection section35 and theremoval section36 are similar to the minimumvalue detection section35 and theremoval section36 in the seventh embodiment. The minimumvalue detection section37 selects pilot carrier signal PC₃including the minimum signal strength from among pilot carrier signals PC₁to PC₃selected by theremoval section36. Thus, in the embodiment, the pilot carrier signal including the second smallest signal strength is selected from among the pilot carrier signals in multicarrier signal. Thecarrier selection sections32 and33 also select the pilot carrier signal including the second smallest signal strength from among the pilot carrier signals in the multicarrier signal.
• For example,FIGS. 9B and 9C provide graphs of multicarrier signals received byantenna sections11 and12. In thecarrier selection section31, the minimumvalue detection section35 detects pilot carrier signal PC₄. In thecarrier selection section31, theremoval section36 selects the pilot carrier signals PC₁to PC₃. Further, in thecarrier selection section31, the minimumvalue detection section37 selects the pilot carrier signal PC₁.
• On the other hand, in thecarrier selection section32, the minimumvalue detection section35 detects pilot carrier signal PC₈. In thecarrier selection section32, theremoval section36 selects pilot carrier signals PC₅to PC₇. Further, in thecarrier selection section32, the minimumvalue detection section37 selects the pilot carrier signal PC₅.
• Anantenna selection section40 compares the pilot carrier signals PC₁and PC₅. Accordingly, theantenna selection section40 can reliably select theantenna section11.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment. Further, thereception apparatus107 according to the embodiment can reliably select the antenna with good communication quality if the signal strength of one pilot carrier signal is extremely small and the signal strength of another pilot carrier signal is large. Particularly, it is effective when a demodulation section uses only pilot carrier signals including large signal strength for distortion correction.
Ninth Embodiment
• FIG. 10 is a schematic drawing to showcarrier selection sections31 to33 of areception apparatus108 according to a ninth embodiment of the invention. Thecarrier selection section31 selects a subcarrier signal SC_midbetween a pilot carrier signal PC₁including the smallest frequency and a pilot carrier signal PC₄including the largest frequency among subcarrier signals. Thecarrier selection sections32 and33 also select a subcarrier signal between a pilot carrier signal including the smallest frequency and a pilot carrier signal including the largest frequency among subcarrier signals. Other components of thereception apparatus108 are similar to those previously described with reference toFIG. 1.
• In anantenna selection section40, acalculation section42 calculates average signal strengths AV₁to AV₃of the subcarrier signals SC_midforcarrier selection sections31 to33. Further, a signalstrength comparison section44 compares the average signal strengths AV₁to AV₃and theantenna selection section40 selects the antenna section receiving the signal including the largest signal strength.
• Usually, a subcarrier signal PC_minincluding a smaller frequency than the pilot carrier signal PC₁including the smallest frequency and a subcarrier signal PC_maxincluding a larger frequency than the pilot carrier signal PC₄including the largest frequency do not have large effect on demodulation. Therefore, thereception apparatus108 can reliably select the antenna with good communication quality by selecting the subcarrier signal SC_mid. Further, the reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment.
Tenth Embodiment
• FIG. 11 is a block diagram to show areception apparatus110 according to a tenth embodiment of the invention. Thereception apparatus110 differs from the reception apparatus of the first embodiment in that it further includes receptionstrength measurement sections61 to63. The receptionstrength measurement sections61 to63 measure the signal strengths of multicarrier signals received throughantenna sections11 to13. The receptionstrength measurement sections61 to63 measure not only the signal strengths of pilot carrier signals, but also the whole signal strength.
• Anantenna selection section40 selects an antenna section based on the combination of the signal strengths of the pilot carrier signals selected bycarrier selection sections31 to33 and the whole signal strengths measured by the receptionstrength measurement sections61 to63. For example, theantenna selection section40 selects the antenna section with the largest sum a*AV_P+b*AV_Swhere a*AV_Pis constant a multiplied by average signal strength AV_Pof the pilot carrier signals selected by thecarrier selection sections31 to33 and b*AV_Sis constant b multiplied by whole signal strength AV_Smeasured by the receptionstrength measurement sections61 to63. That is, given weights are assigned and both the pilot carrier signal strength and the whole signal strength are used to select the antenna section.
• The reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the first embodiment. Further, in the tenth embodiment, not only the pilot carrier signals, but also other subcarrier signals can be considered for selecting the antenna section. Therefore, thereception apparatus110 can conduct high-quality communications.
• In the first to tenth embodiments, theantenna selection section40 selects the antenna section based on the signal strengths of the subcarrier signals selected by thecarrier selection sections31 to33. However, theantenna selection section40 may select the antenna section based on EVM (Error Vector Magnitude) values of the subcarrier signals selected by thecarrier selection sections31 to33. In this case, the expression “signal strength” in this specification may be replaced with “EVM value.”
Eleventh Embodiment
• FIG. 12 is a block diagram to show ademodulation section50 of areception apparatus120 according to an eleventh embodiment of the invention. After anantenna selection section40 selects an antenna section, thedemodulation section50 demodulates the multicarrier signal received through the selected antenna section. Other components of thereception apparatus120 may be similar to those previously described with reference toFIG. 1. InFIGS. 12 and 13, a plurality of signals from a signal conversion section to adistortion correction section55 indicate flows of subcarrier signals.
• Thedemodulation section50 has astrength measurement section51, a thresholdvalue judgment section52, a distortionamount calculation section53, acalculation section54, and the above-mentioneddistortion correction section55. Thedemodulation section50 receives a multicarrier signal from asignal conversion section21. Thestrength measurement section51 measures the signal strength of each pilot carrier signal in the multicarrier signal. The thresholdvalue judgment section52 has a threshold value concerning the signal strength and selects each pilot carrier signal including the signal strength equal to or larger than the threshold value.
• The distortionamount calculation section53 measures the distortion amount of the pilot carrier signal selected by the thresholdvalue judgment section52. Usually, thereception apparatus120 already knows the phase and frequency of the pilot carrier signal when the signal is transmitted from the communicating party, for example. Therefore, the distortionamount calculation section53 can calculate the phase difference between the pilot carrier signal at the transmitting time and that at the receiving time as the distortion amount.
• Thecalculation section54 calculates a distortion correction value from the distortion amount provided by the distortionamount calculation section53. For example, if the thresholdvalue judgment section52 selects a plurality of pilot carrier signals, thecalculation section54 can calculate the average value of a plurality of distortion amounts and adopt the average value as the distortion correction value.
• Thedistortion correction section55 corrects each subcarrier signal in accordance with the distortion correction amount. For example, thedistortion correction section55 restores the phase of each subcarrier signal by the phase difference calculated by thecalculation section54. After the distortion of each subcarrier signal is corrected, the multicarrier signal is sent to a decoding section (not shown).
• The pilot carrier signal including small signal strength often is distorted largely. If such a pilot carrier signal is used to make distortion correction, thedemodulation section50 cannot precisely correct the subcarrier signal. Therefore, only pilot carrier signals including the signal strength equal to or larger than one threshold value as in the embodiment, whereby it is made possible for thedemodulation section50 to precisely correct the subcarrier signal. Consequently, thereception apparatus120 can be provided with high-quality reception characteristics.
• The embodiment can be combined with any of the first to tenth embodiments, so that the embodiment can also have the advantages of any of the first to tenth embodiments. Particularly, the embodiment and the fourth embodiment are used in combination, thedemodulation section50 and thecarrier selection sections31 to33 can use the common threshold value Th.
Twelfth Embodiment
• FIG. 13 is a block diagram to show ademodulation section50 of areception apparatus121 according to a twelfth embodiment of the invention. Thereception apparatus121 differs from thereception apparatus120 of the eleventh embodiment in that acalculation section54 assigns a weight to the distortion amount using the signal strength of each pilot carrier signal and then calculates a distortion correction value.
• Thecalculation section54 acquires the signal strength of each pilot carrier signal from astrength measurement section51 and acquires the distortion amount of each pilot carrier signal (for example, the phase difference) from a distortionamount calculation section53. Thecalculation section54 assigns a weight to the distortion amount based on the signal strength and then calculates a distortion correction value. For example, thecalculation section54 multiplies the ratio of the signal strengths of pilot carrier signals by the distortion amount and further adds the results together to find the distortion correction value.
• Specifically, assume that the ratio of the signal strengths of pilot carrier signals PC1, PC2, and PC3 is 0.5:0.2:0.3 and that the phase differences between PC1 and PC2, between PC1 and PC3, and between PC2 and PC3 are 10 degrees, 20 degrees, and 30 degrees respectively. In this case, thecalculation section54 calculates (0.5/1)*10+(0.2/1)*20+(0.3/1)*30. As a result, thecalculation section54 adopts 18 degrees as the distortion correction value.
• Generally, the pilot carrier signal including small signal strength often is distorted largely and thus the higher the signal strength of the pilot carrier signal, the higher the reliability of the distortion amount. Therefore, in the embodiment, a weight can be assigned in response to the reliability of the pilot carrier signal, so that the distortion amount of any other subcarrier signal can be corrected precisely. Consequently, thereception apparatus121 can be provided with high-quality reception characteristics.
Thirteenth Embodiment
• A reception apparatus according to a thirteenth embodiment of the invention will be discussed with reference toFIG. 13. In the embodiment, acalculation section54 acquires the signal strength of each pilot carrier signal from astrength measurement section51 and acquires the distortion amount of each pilot carrier signal (for example, the phase difference) from a distortionamount calculation section53.
• Each pilot carrier signal can be represented by a vector according to the signal strength and distortion amount of the pilot carrier signal. Thecalculation section54 combines the vectors into one composite vector. Further, thecalculation section54 obtains the distortion correction value from the angle of the composite vector.
• In the embodiment, as in the twelfth embodiment, not only the distortion amount of each pilot carrier signal, but also the signal strength is considered for calculating the distortion correction value. Therefore, the reception apparatus of the embodiment has similar advantages to those of the reception apparatus of the twelfth embodiment.
• The twelfth and thirteenth embodiments may be combined with the eleventh embodiment, so that the twelfth and thirteenth embodiments can also obtain the advantages of the eleventh embodiment.
Fourteenth Embodiment
• A pilot carrier signal including a frequency near a frequency of the pilot carrier signal is selected in the fourteenth embodiment.FIG. 15 is a block diagram to show radio reception apparatus according to the fourteenth embodiment.Plural antenna sections11 to13, pluralsignal conversion section21 to23, pluralcarrier selection sections31 to33,antenna selection section40, anddemodulation section50 are provided with the radio reception apparatus as shown inFIG. 15. each of theantenna sections11 to13 receives multi-carrier signal which transmitted from the transmitter (not shown).
• The numbers ofsignal conversion sections21 to23 and thecarrier selection sections31 to33 are as same as that of theantenna sections11 to13 in accordance with the antenna sections. Three antenna sections, three signal conversion sections, and three carrier selection sections are provided withFIG. 15 as an example, but the number is not limited.
• Each of thecarrier selection sections31 to33 selects at least one sub carrier signal having frequencies each of which is respectively near the plural pilot sub carriers among multi-carrier signals which pass the corresponding signal conversion section. Thedemodulation section50 demodulates the multi carrier signal which is received at the antenna section selected in the antenna section.
• Thecarrier selection sections31 to33 selects a sub carrier signal in accordance with a characteristic graph as shown inFIG. 15. a signal waveform of the multi-carrier signals are shown in the graph in which a horizontal axis shows a frequency, and a vertical axis shows a signal strength. As shown in the graph, the multi-carrier signals have plural sub carrier signals which have different frequency bans from one another. Plural known pilot carrier signals are provided with the multi-carrier signals. (Frequency f1, f2 in the graph)
• Thecarrier selection sections31 to33 selects four sub carrier signals f1−fa, f1+fa, f2−fa, and f2+fa which are nearest from the pilot carrier signals corresponding to f1 and f2.
• The sub carrier signals selected in thecarrier selection sections31 to33 are transmitted to theantenna selection section40.
• Theantenna selection section40 hascalculation section42 and signalstrength comparison section44. thecalculation section42 calculates AV1 which is an signal strength average among sub carrier signals SC1, SC2, SC3, and SC4 which are selected by thecarrier selection section31, AV2 which is a signal strength average of the sub carrier signals selected by thecarrier selection section32, and AV3 which is a signal strength average of the sub carrier signals selected by thecarrier selection section33, respectively.
• The signalstrength comparison section44 compares the signals strength averages AV1, AV2, and AV3 and selects antenna section which has a maximum signal strength average amongantenna sections11 to13.
• According to the fourteenth embodiment, thecarrier selection sections31 to33 select four sub carrier signals, but may select no more than three sub carrier signals or no fewer than five sub carrier signals. Accordingly, the above described example, each of sub carrier signals which are nearest from the pilot carrier signal at both sides thereof are selected, but plural sub carrier signals at both sides which are nearest from the pilot carrier signal may be selected, and the sub carrier signal which are nearest from the pilot carrier signal at one side thereof may be selected. In addition, a number of pilot carrier signals which are included in the multi-carrier signal is not limited in two. Further, the sub carrier signals having a frequency except for a frequency which is nearest from the frequency of the pilot carrier signal may be selected.
• FIG. 16 is a flow chart to show an example of processing operation of the radio reception apparatus as shown inFIG. 15. First, theantenna sections11 to13 receives multi carrier signals modulated by multi carrier modulation method. (Step60) Then, each of thesignal conversion sections21 to23 converts the multi carrier signals received from theantenna sections11 to13. Thus, the multi carrier signals are converted into a signal in which sub carrier signals have a different frequency with one another. (Step62)
• Next, thecarrier selection sections31 to33 respectively select plural sub carrier signals which have a nearest frequency from the frequency of the pilot carrier signal. (Step64)
• Theantenna section40 selects an antenna section which receives the multi carrier signal on the basis of the signal strength of the sub carrier signals selected by thecarrier selection sections31 to33. thedemodulation section50 demodulates the multi carrier signals received by the antenna section selected by theantenna section40. (Step68)
• Thedemodulation section50 does not perform the demodulation until theantenna selection section40 selects the antenna. Thedemodulation section50 receives a signal indicating that theantenna selection section40 selects the antenna. After thedemodulation section50 receives the signal, thedemodulation section50 performs the demodulation. Thus, power consumption of thedemodulation section50 can be decreased. Thedemodulation section50 does not demodulate a signal having a less communication quality by mistake.
• According to the fourteenth embodiment, the antenna section can be selected on the basis of a signal strength of a certain sub carrier signal in a predetermined frequency band. In particular, it can be more effective in case that the pilot carrier signals are not inadvertently transmitted when the carrier is selected and that the antenna section selects a pilot carrier signal having large signal strength thereof which have much effect on the demodulation. In the fourteenth embodiment, even if the pilot carrier signals are not received, sub carrier signals which are near from the pilot carrier signal are selected. The sub carrier signals near from the pilot carrier signal has a high mutual relation with the pilot carrier signal with respect to a signal strength, so that the antenna section having high communication quality can be selected as well as in case the antenna section is selected on the basis of the pilot carrier signal.
Fifteenth Embodiment
• In the fifteenth embodiment, the construction of theantenna selection section40 is different from that of the fourteenth embodiment.
• FIG. 17 is a block diagram to show internal construction of the radio reception apparatus according to the fifteenth embodiment. The radio reception apparatus has a same construction of the apparatus as shown inFIG. 15 other than the internal construction of theantenna selection section40. Theantenna selection section40 as shown inFIG. 17 includes pilot adjacentcarrier extraction section35 and receptionlevel comparison section36. The pilot adjacentcarrier extraction section35, in each antenna section, selects sub carrier signal having a minimum reception strength among sub carrier signals which include a nearest frequency from the frequency of the pilot carrier signal. The receptionlevel comparison section36 includes selects an antenna section which is corresponding to the sub carrier signal having a maximum signal reception strength among the sub carrier signals extracted from the pilot adjacentcarrier extraction section35.
• The pilot adjacentcarrier extraction section35 selects a sub carrier signal having a minimum signal reception strength since the smaller the signal reception strength is, the more effective the noise is. The receptionlevel comparison section36 selects the corresponding antenna section by extracting the sub carrier signal having a maximum signal reception strength among the sub carrier signals susceptible from the effectiveness of the noise.
• Thus, in the fifteenth embodiment, the sub carrier signal having a small signal reception strength is selected and compared in stead of average of the sub carrier signal reception strength, so that the effectiveness of the noise is not receptive.
Sixteenth Embodiment
• In the sixteenth embodiment, all carrier selection sections share signal conversion section and carrier selection section.
• FIG. 18 is a block diagram to show an internal construction of the radio reception apparatus according to the sixteenth embodiment. The radio reception as shown inFIG. 18 includesplural antenna sections11 to13, asignal conversion section21 shared by each antenna section, and ademodulation section50.
• Thesignal conversion part21 includes LNA (Low Noise Amplifier) which amplifies a multi-carrier signal, a D/C (Down Converter) part which frequency-converts frequency of a multi-carrier signal into a base band, an A/D conversion part which converts an analog signal into a digital signal, and a FFT (Fast Fourier Transfer) part which carries out discrete Fourier conversion to each of multi-carrier signals. A multi-carrier signal, which passed through thesignal conversion part21, has a plurality of sub carrier signals with different frequency bands each other.
• Thecarrier selection section31 is connected to output of theFFT section27 of thesignal conversion section21. Thecarrier selection section31 includes the pilot adjacentcarrier extraction section35 and signal receptionstrength comparison section36. The pilot adjacentcarrier extraction section35 selects at least one signal among the sub carrier signals which has a nearest frequency from each frequency of plural pilot sub carrier signals among multi carrier signals input from theFFT section27. The signal receptionstrength comparison section36 selects and output a sub carrier having a minimum signal reception strength among the sub carriers extracted from the pilot adjacentcarrier extraction section35 to theantenna selection section40.
• Theantenna selection section40 includesstorage section45 in which an information of the sub carrier selected by thecarrier selection section31 is stored and reception level comparison section betweenantenna46 which can determine which antenna is selected by performing a comparison on the basis of the stored information in thestorage section45.
• First, theantenna selection section40 selects anantenna section11. Thesignal conversion section21 converts a signal received in theantenna section11. Thecarrier selection section31 selects a sub carrier having a minimum signal reception level among sub carriers which has nearest frequency from that of each of the plural pilot sub carrier. Thestorage section45 of theantenna selection section40 stores the information.
• Next, theantenna selection section40 selects theantenna section12, performs same processing as theantenna section11, and stores the information in thestorage section45 of theantenna selection section40.
• Then, theantenna selection section40 selects theantenna section13, performs same processing as theantenna section12, and stores the information in thestorage section45 of theantenna selection section40.
• The reception level comparison section betweenantenna46 selects an antenna which having a maximum signal reception level of the sub carrier selected on the basis of the information stored in the storage section of theantenna selection section40.
• FIG. 19 is a flow chart to show one example of processing operation of the radio reception apparatus as show inFIG. 18. First, theantenna selection section40 selects on of the antenna sections. (Step S71) Next, the selected antenna section receives a multi-carrier signal. (Step S72) Next, thesignal conversion section21 converts a received multi-carrier signal into a signal which includes sub carrier signals having different frequency with one another. (Step S73) Next, thecarrier selection section31 selects a certain sub carrier signal, and selects a sub carrier on the basis of a signal strength of the extracted sub carrier signal. (Step S74) Then, the information of the sub carrier signal selected by thecarrier selection section31 is stored in thestorage section45 of the antenna selection section. (Step S75)
• Next, whether or not all antenna sections complete a processing is determined (Step76), one of the antenna sections is selected and Step S71 to S76 are repeated, if the antenna section does not complete the above-processing.
• Then, the reception level comparison section betweenantennas46 selects antenna section when all antenna sections complete the processing. (Step S78)
• The multi-carrier signal received in the antenna section selected by theantenna selection section40 is transmitted to thedemodulation section50, and the demodulation processing is performed. (Step S79)
• The radio reception apparatus ofFIG. 18 has only one pair of thesignal conversion section21 and thecarrier selection section31, so that the apparatus selects the antenna sections in turn, performs the processing in thesignal conversion section21 and thecarrier selection section31, and stores the information of the sub carrier signal corresponding to each antenna section in thestorage section45. When the multi-carrier signal is transmitted in a form of the packet, the processing as show inFIG. 19 may be performed at the step that the preamble section of the packet is received before receiving the data section of the packet.
• FIG. 20 shows a data construction of the packet. As show inFIG. 20, each packet has apreamble section15 and adata section16. each of thepreamble section15 and thedata section16 is configured by the multi-carrier signal, so that in the embodiment, the processing as show inFIG. 19 is performed by the preamble section of the packet. When the antenna section is selected by thedata section16, it is a risk that gain control and correction of the transmission channel have inappropriate values. Thus, in the embodiment, unit thedata section16 of the packet is received, the selection of the antenna section, the correction of the transmission channel, and correction of the transmission channel after D/C section are performed by using the preamble section of the packet.
• Thus, in the sixteenth embodiment, all antenna sections share one pair of thesignal conversion section21 and thecarrier selection section31, so that it is not necessary to provide thesignal conversion section21 and thecarrier selection section31 with each antenna section, the internal construction of the radio reception apparatus becomes simple. Thus, it is possible to decrease the electric power consumption and to make the apparatus miniaturization. Further, the appropriate antenna section is selected by the processing as show inFIG. 19, so that an antenna section having a high communication quality may be certainly selected. Further more, the antenna section is selected on the basis of the preamble section of the received packet, so that timely processing of the received data (Real Time Processing) can be performed.
Seventeenth Embodiment
• In the seventeenth embodiment, a processing in thecarrier selection section31 is accelerated.
• FIG. 21 is a block diagram to show a construction of the radio reception apparatus according to the seventeenth embodiment. The radio reception apparatus as show inFIG. 21 have a different internal construction of the carrier selection section from that of the apparatus as show inFIG. 18.
• InFIG. 21, thecarrier selection section31 in the radio reception apparatus hasFFT section37 other thanFFT section27 within thesignal conversion section21. output signal of A/D section within thesignal conversion section21 is input into theFFT section37. the reason of theFFT37 section is as follow:
• It is necessary to perform the selection of the antenna section, a gain control of the signal received by the antenna section, and the correction of the transmission channel after D/C section in the radio reception apparatus ofFIG. 21. when the antenna is changed in thedata section16 of the packet, the gain control and the correction of the transmission channel are performed
• FIG. 22 represents a frequency characteristic of a data part of a packet which was complied with IEEE802.11a. A horizontal axis corresponds to frequency, and a vertical axis represent a signal level. It is composed of 52 pieces of sub y carriers from +26 up to −26, except for 0. Sub carriers of −21, −7, +7, +21 are pilot carriers. On one hand, Fig. represents a frequency characteristic of a short preamble, which is a part of a preamble part of the packet which was complied with IEEE802.11a. A horizontal axis corresponds to frequency, and a vertical axis represents a signal level. Unlike the data part, it is composed of 12 pieces of sub carriers of +24, +20, +16, +12, +8, +4, −4, −8, −12, −16, −20, −24, and there exists no sub carrier with a frequency component which is comparable to a pilot carrier of the data part.
• In this connection, in order to select a sub carrier with high correlation with a pilot sub carrier, selected is a sub carrier which is of the nearest frequency to each of a plurality of pilot sub carriers. That is, selected are sub carriers of −20, −8, +8, +20.
• In addition, by utilizing a characteristic of a configuration of a short preamble of Fig., electric power measurement of each sub carrier is possible with shorter time than usual. Usually, i.e., in a configuration of a data part, there is a necessity to carry out Fourier conversion with time of Tk=1/fk, inverse number of fundamental frequency fk of a sub carrier in which sub carrier number is of the nearest to 0, rather than orthogonality of OFDM, and to measure reception strength. However, in the configuration of Fig., since fundamental frequency is 4*fk, 4 times, and further, only a frequency component of its constant number multiple exists, it is possible to carry out Fourier conversion and measurement of reception strength with time of Tk/4=1/(4*fk). That is, it is possible to measure signal strength with time of ¼ multiple.
• In this embodiment, even in case that a pilot carrier does not exist in a preamble part, in packet communication, it is possible to select a carrier with a high correlation with a pilot carrier, and on the basis of signal strength of that carrier, to carry out antenna selection. By this, thecommunication apparatus101 can surely select an antenna with good communication quality.
Eighteenth Embodiment
• The eighteenth embodiment is a modification of the embodiment ofFIG. 17. The internal construction of thecarrier selection section31 is different from that of the carrier selection section as show inFIG. 21.
• FIG. 24 is a block diagram to show the construction of the radio reception apparatus according to the eighteenth embodiment. Thecarrier selection section31 in the apparatus ofFIG. 24 has a mutualrelation calculating section38 and a receptionlevel comparison section36. The mutualrelation calculating section38 calculates a mutual relation degree with a frequency of the sub carrier signal included in the multi-carrier signal. A frequency of the pilot carrier signal is unknown, so that the sub carrier signal having a frequency which is nearest from the frequency of the pilot carrier signal is extracted by calculating the mutual relation degree with a frequency which is nearest from the frequency of the pilot carrier signal.
• Thus, in the eighteenth embodiment, the subcarrier signal having a frequency which is nearest from the frequency of the pilot carrier signal can be extracted without FFT section and pilot adjacent carrier extraction section within thecarrier selection section31, so that the internal construction of thecarrier selection section31 makes simple, and the miniaturization of the apparatus and the decrease of the electric power consumption can be achieved.
Nineteenth Embodiment
• In the embodiments ofFIGS. 16 and 17, the selection of the antenna section is performed on the basis of thepreamble section15 of the packet as an example. However, according algorithm of thesignal conversion section21 and thedemodulation section50, there is an unimportant pilot carrier signal. For example, in IEEE802.11a, the pilot carrier signal is mainly used for frequency correction and phase correction, but all four pilot sub carrier signals are always necessary. Thus, there is algorithm such that the pilot carrier having a low reliability and a predetermined value smaller than a threshold value with respect to the signal reception strength of the pilot carrier is not used for the frequency correction and phase correction, that is, it is not important to use the pilot carrier having a small signal reception strength in this case for the demodulation.
• According to the nineteenth embodiment, the internal construction of the radio reception apparatus is same as that of the apparatus ofFIG. 21, so that the explanation is omitted.
• FIG. 25 is a flowchart to show an example of the processing operation according to nineteenth embodiment. The processing is as same as that ofFIG. 19 from Step S81 to step S83. Next, The sub carrier signal having a minimum value of the signal reception strength is selected among the sub carrier signals except for sub carrier signal having a value of the signal reception strength lower than the threshold value. (Step S84) Then, the processing from step S85 to step S87 are performed as same as that from step S75 to step S77 as shown inFIG. 19.
• Next, theantenna selection section40 an antenna section which has a maximum signal reception strength among the sub carrier signals stored in thestorage section45. (Step S88)
• Thus, in the nineteenth embodiment, the sub carrier signals are narrow by previously setting the threshold value, so that the processing of thecarrier selection section31 is accelerated by previously getting out of the unnecessary sub carrier signals.
Twentieth Embodiment
• The twentieth embodiment is a modification of the embodiment ofFIG. 19. whether or not the antenna section is selected is determined by a number of the sub carrier signals having a value over the threshold value.
• FIG. 26 is flow chart to show an example of the processing operation according to the twentieth embodiment. The processing from step S91 to step S97 is perform as same as that from step S81 to step S87 as shown inFIG. 25. Next, theantenna selection section40 compares a number of the sub carrier signals selected by thecarrier selection section31 and selects an antenna which has a largest number of the sub carrier signals over the threshold value. (Step S98)
• In the processing of Step S98, in case that plural antenna sections are applicable, the sub carrier signal which has a maximum signal strength value is selected by comparing a signal strength of the sub carrier signal having a minimum value among the plural antenna sections with one another.
• Further, in Step S98, the antenna section which has maximum average signal strength of the sub carrier signal selected by thecarrier selection section31 may be selected.
• Thus, according to twentieth embodiment, in case that the algorism such that the pilot carrier having a low reliability and a predetermined value smaller than a threshold value with respect to the signal reception strength of the pilot carrier is not used for the frequency correction and phase correction is used, more pilot carrier signals can be used for the frequency correction and the phase correction. In addition, in case that plural antenna sections having a maximum number of selected sub carrier signals, among the plural antenna sections, more reliable antenna section can be selected on the basis of the signal strength of the sub carrier signals selected by thecarrier selection section31. Thus, the communication quality is improved.
Twenty-First Embodiment
• According to the twenty-first embodiment, sub carrier signals included in multi-carrier signals are weighted in accordance with frequency differences between frequencies of the pilot carrier signals and frequencies of the sub carrier signals.
• FIG. 27 is a flow chart of the processing operation according the radio reception apparatus according to the twenty-first embodiment. The processing from step S101 to step S103 is as same as that ofFIG. 19. Next, with respect to each sub carrier signal, a weighted coefficient is set in accordance with the frequency difference. (Step S104) a relation between the frequencies and the weighted coefficient may be previously prepared. The smaller frequency differences between the pilot carrier signal and sub carrier signal are, the larger weighted coefficient is set.
• Next, the weighted signal reception strength is calculated by multiplying the signal reception strength with the set weighted coefficient. (Step S105) Next, the processing from step S106 to step S108 is as same as that from step S75 to step S77 as shown inFIG. 19.
• Next, theantenna selection section40 selects an antenna section which has a sub carrier signal having a maximum signal reception strength on the basis of the calculation result of the signal reception strength by the step S105. (Step S109)
• Thus, according to the twenty-first embodiment, since the sub carrier signal is weighted in accordance with the frequency differences between the pilot carrier signal and the sub carrier signal, the sub carrier signal near the frequency of the pilot carrier signal can be preferentially selected.
Twenty-Second Embodiment
• According to the twenty-second embodiment, the processing is performed in each group which holds plural subcarrier signals together as one group.
• FIG. 28 is an view to explain the general description according the twenty-second embodiment. In the twenty-second embodiment, all sub carrier signals is divided into firstsub carrier group55 in which the sub carrier signals are near the frequency of the pilot carrier signal and secondsub carrier group56 in which the subcarrier signals is far from the frequency of the pilot carrier signal.
• Eachcarrier selection section31 selects at least one sub carrier signal from the firstsub carrier group55, and selects at least one sub carrier signal from the secondsub carrier group56. Theantenna selection section40 selects an antenna section on the basis of the signal reception strength of the sub carrier signals which selected from bothsub carrier groups55,56.
• For example, thecarrier selection section31 respectively selects a sub carrier signal having a minimum signal reception strength from the sub carrier signal groups. Thus, the two selected sub carrier signals is differently weighted, and calculates the weighted signal reception strength.
• Theantenna selection section40 selects an antenna which is corresponding to the sub carrier signal having the weighted maximum signal reception strength.
• Alternatively, thecarrier selection section31 selects a sub carrier signal having a minimum signal reception strength from the firstsub carrier group55, and selects all sub carrier signals of the secondsub carrier group56. the signal reception strength of the sub carrier signal selected by the firstsub carrier group55 and the average signal reception strength of all sub carrier signals of thesub carrier group56 are respectively weighted, and thus are combined. In this case, theantenna selection section40 selects an antenna section which has a sub carrier signal having a maximum signal reception strength calculated by thecarrier selection section31.
• Thus, according to the twenty-second embodiment, the sub carrier signals are divided into plural groups. The signal reception strength are weighted and corrected in each group, so that the antenna section can be selected in a short time compared with the case that a weighted operation is performed in each sub carrier signal.

Claims (1)

1. A method for receiving radio signals with a radio receiver having a plurality of antennas, comprising:

receiving multicarrier signals which are modulated according to multicarrier modulation using the antennas;

selecting at least one subcarrier signal out of the multicarrier signal received by each antenna;

selecting a reception antenna among the plurality of antennas based on signal strengths of the subcarrier signals selected for each antenna;

demodulating the multicarrier signal received by the reception antenna;

measuring signal strength and distortion amounts of pilot signals in the multicarrier signal being received by the reception antenna; and

correcting the multicarrier signal received by the reception antenna using the measured signal strength and the distortion amounts.

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