Abstract:
A radio communications system in which a desired signal can be accurately discriminated from interfering signals, even when signals from a plurality of transmitters are received simultaneously, is provided. A transmitter for this system communicates information using signals which are repeated over predetermined periods. A pulse generator generates pulses having a predetermined repetition period based on an information bit to be communicated. Transmission means transmit the pulses generated by the pulse generator. Pulse amplitude alterating means control the amplitude of the pulses to be transmitted by the transmitting means in accordance with a predefined pattern under the control of a control unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application claims priority to Japanese Priority Document JP 2001-247993, filed in the Japanese Patent Office on Aug. 17, 2001, the entire contents of which are incorporated herein by reference to the extent permitted by law.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a radio communications system, a transmitter, a receiver, a radio transmission method, a radio reception method and a computer program therefor.  
           [0004]    2. Description of Related Art  
           [0005]    [0005]FIGS. 8A and 8B schematically show a radio communications system for communicating information using impulse signals. A transmitter  101  uses an impulse signal sequence comprising consecutive impulses having a predetermined impulse period as shown in FIG. 8B to communicate information to a receiver  102 . Examples of such an information communicating method using an impulse signal sequence include Ultra Wide Band (UWB) communications systems and the like. UWB communications systems communicate information by transmitting impulse signals at predetermined repetition periods. In other words, a base band communication is performed using a signal comprising pulse sequences having a very narrow pulse width (e.g., 1 ns (nanosecond) or less). The occupied bandwidth is on the order of GHz and is such that the value obtained by dividing the occupied bandwidth by the center frequency thereof (e.g., 1 GHz to 10 GHz) is approximately 1. The above-mentioned bandwidth is much greater than bandwidths ordinarily used for wireless LAN communications employing W-CDMA®, CDMA2000®, SS (Spread Spectrum), OFDM (Orthogonal Frequency Division Multiplexing) technologies and the like.  
           [0006]    UWB communications schemes are characteristic in that, due to the low power spectral density properties thereof, they hardly interfere with other radio communications systems. Therefore, there are expectations for UWB communications as a technology capable of overlaying frequency bands used by existing radio communications systems. Further, because ultra wide bandwidths are used, UWB communications is viewed as a promising technology which could realize ultra high-speed radio communications on the order of 100 Mbps in its application to personal area network (PAN) technology.  
           [0007]    In communicating information using the impulse signals mentioned above, the amplitude of each of the impulses constituting the impulse signals are handled by a transmitter and a receiver as being constant.  
           [0008]    [0008]FIGS. 9A through 9I explain a UWB communications scheme which is an example of a method of communicating information using an impulse signal sequence. In UWB communications, 1 bit of information to be communicated from a transmitting end is transmitted using several impulses. Namely, 1 bit of information  501  (FIG. 9A) is directly spread using a predetermined spreading code  502  (FIG. 9B), and is thereafter converted into a spread signal  503  (FIG. 9C). Corresponding to its value of 0 or 1, the spread signal  503  is converted into a very fine impulse sequence and is transmitted as a transmission signal  504  by way of an antenna. FIG. 9E is an enlarged view of a portion  504 - 1  showing the first few pulses of the transmission signal  504 . As is apparent therefrom, in UWB schemes, the amplitude of each transmitted pulse is uniform.  
           [0009]    On a receiving end, a signal, which is the transmission signal  504  onto which noise is superimposed, is received as a received signal  505  (FIG. 9F). The received signal  505  is despreaded using a predetermined despreading code  506  (FIG. 9F). In other words, the received signal  505  is detected with a correlator, and a correlator output  507  (FIG. 9H) is obtained. A spreading code is integrated in the correlator output  507 , and the correlator output  507  becomes an integrated signal  508  (FIG. 9I).  
           [0010]    Problems associated with radio communications systems using conventional impulse signals are explained below. FIG. 10 shows an arrangement of a radio communications system in which each of receivers  202  and  204  receives a signal from a plurality of transmitters  201  and  203 . In this case, when a condition arises whereby the transmitters  201  and  203  happen to start transmission at an identical pulse position, each of the receivers  202  and  204  simultaneously receives pulses from the transmitters  201  and  203 . If there is a large power difference between the pulses from the desired (relevant) transmitter and the pulses from an interfering transmitter, the pulses with greater power is received due to the “Capture Effect.” On the other hand, when the power difference between the desired transmitter and the interfering transmitter is small, neither of the pulses are received and both pulses are lost.  
           [0011]    Especially in a PAN, because a base station is often absent, it is rare for transmission power control at the transmitter to be performed. Therefore, the closer a transmitter is to a receiver, the greater the power of the received pulse becomes. Thus, when the interfering transmitter is at a position closer to the receiver than the desired transmitter is, due to the capture effect mentioned above, only interfering pulses are received.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention addresses such an issue as presented above, and provides a transmitter, a receiver and a radio communications system for performing transmission using an impulse signal sequence, wherein the transmitter, receiver and radio communications system are capable of accurately discriminating between an interference signal and a desired signal even when signals from multiple transmitters are received at once.  
           [0013]    In order to overcome the issue presented above, the present invention comprises certain characteristics as described hereinafter.  
           [0014]    In a radio communications system which communicates information using an impulse signal sequence comprising impulses having a predetermined impulse period, one aspect of the present invention is that a transmitter for such a system comprises: impulse signal sequence generating means for generating an impulse signal sequence based on a spread signal obtained by spreading an information bit to be communicated using a spreading code; control means for controlling the amplitude of the impulse signal sequence generated by the impulse signal sequence generating means mentioned above in accordance with a predefined pattern; and transmission means for transmitting the impulse signal sequence received from the impulse signal sequence generating means and whose amplitude has been controlled.  
           [0015]    In relation to what is described above with respect to one aspect of the present invention, the impulse signal sequence generating means may be such that it comprises a transmission data processing section, a transmission buffer, a pulse forming section, an amplifier, and a pulse generator. Further, the control means may comprise a control unit and pulse amplitude altering means.  
           [0016]    In a radio communications system which communicates information using impulse signal sequences comprising impulses having a predetermined impulse period, a second aspect of the present invention is that a receiver for such a system comprises: radio reception means for receiving a radio signal including an impulse signal sequence whose impulse amplitude is altered in accordance with a predefined pattern, and for obtaining a correlated output signal of the radio signal and a spreading code; amplifying means for amplifying the correlated output signal mentioned above; and control means for controlling the amplifying operation of the amplifying means mentioned above according to a predefined pattern.  
           [0017]    In relation to what is described above with respect to the second aspect of the present invention, the radio reception means may be such that it comprises reception means, and a correlator. Further, the amplifying means may comprise an amplifier, and the control means may comprise a control unit and an amplification factor alteration processing section.  
           [0018]    In a radio communications system which communicates information using an impulse signal sequence comprising impulses having a predetermined impulse period, a third aspect of the present invention is that a receiver for such a system comprises: radio reception means for generating a correlated output signal of a radio signal including an impulse signal sequence, whose impulse amplitude is altered based on a predefined pattern, and a spreading code; a weighting processing section for weighting an information value, which is generated from the correlated output signal mentioned above; and control means for controlling the weighting operation of the weighting processing section mentioned above based on a pattern corresponding to the predefined pattern mentioned above.  
           [0019]    In relation to what is described above with respect to the third aspect of the present invention, the radio reception means may be such that it comprises, for example, reception means, a correlator, an integrator, and an A/D converter. Further, the control means may comprise a control unit and a weighting alteration processing section.  
           [0020]    According to the present invention, even in cases where pulses from a plurality of transmitters are received simultaneously, the desired pulses can be accurately discriminated from interfering pulses, and thus therein lies an advantage in that appropriate processing can be performed with respect to the received signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    The invention disclosed herein will become better understood as a detailed description is made of the preferred embodiments with reference to the appended drawings in which:  
         [0022]    [0022]FIG. 1 is a schematic view illustrating a first embodiment of the present invention.  
         [0023]    [0023]FIG. 2 is a schematic view illustrating a second embodiment of the present invention.  
         [0024]    [0024]FIG. 3 shows the configuration of a transmitter  801  according to an embodiment of the present invention.  
         [0025]    [0025]FIG. 4 shows the configuration of a receiver  901  according to an embodiment of the present invention.  
         [0026]    [0026]FIG. 5 shows the configuration of a receiver  1001  according to an embodiment of the present invention.  
         [0027]    [0027]FIG. 6A through FIG. 6I are time charts illustrating procedures of a communications scheme of the first embodiment of the present invention.  
         [0028]    [0028]FIG. 7A through FIG. 7I are time charts illustrating the procedures of a communications scheme of the second embodiment of the present invention.  
         [0029]    [0029]FIG. 8A and FIG. 8B are schematic views illustrating a radio communications system using an impulse signal sequence.  
         [0030]    [0030]FIG. 9 illustrates procedures of a communications scheme using an impulse signal sequence.  
         [0031]    [0031]FIG. 10 illustrates problems associated with a conventional communications scheme using an impulse signal sequence. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]    First, an outline of the present embodiments will be described. One characteristic of the embodiments described herein is that they change the amplitude of pulses to be transmitted according to a predefined pattern. FIG. 1 illustrates a first embodiment of the present invention, and FIG. 2 illustrates a second embodiment of the present invention. In FIGS. 1 and 2, the X-axis represents time (t) and the Y-axis represents voltage (V).  
         [0033]    In the first embodiment shown in FIG. 1, the amplitude of each pulse (a to j in FIG. 1) to be transmitted is altered according to a predefined pattern. In FIG. 1, the amplitudes of pulses b, c, e, h and i are smaller than those of pulses a, d, f, g and i.  
         [0034]    In the second embodiment shown in FIG. 2, the amplitudes of a plurality of impulses (A to H in FIG. 2) to be transmitted are altered in groups in accordance with a predefined pattern.  
         [0035]    The example shown in FIG. 2 illustrates an impulse signal sequence after an alteration of the amplitudes is performed in accordance with the predefined pattern mentioned above. The amplitudes of the pulses included in areas B, C, E, H and J are set to be smaller than those of the pulses included in areas A, D, F, G and I. By thus altering the amplitudes of the pulses to be transmitted in groups, each group comprising a plurality of pulses, a situation in which only interference pulses are received due to the “Capture Effect” may be avoided. It is noted that various methods of grouping a plurality of pulses may be adopted. For example, units by which amplitude alteration is performed may be defined as: a predetermined number of consecutive pulses; a plurality of pulses which correspond to the length of several spreading codes; one transmission frame; or any other arbitrary definition of a unit as may be deemed appropriate.  
         [0036]    [0036]FIG. 3 illustrates the configuration of a transmitter  801  of the radio communications system of the present embodiments. In FIG. 3, a transmission data processing section  802  converts an inputted information bit into a spread signal using a predetermined spreading code. A transmission buffer  803  temporarily stores the spread signal. A pulse generator  804  reads out the spread signal and generates a corresponding pulse sequence. Transmission means  805  comprises an RF circuit and the like, and outputs the pulse sequence across the air by way of an antenna  808 . A control unit  806  controls the timing of signal processing and the like at each of the sections mentioned above.  
         [0037]    Further, the pulse generator  804  has a pulse forming section  804 - 1  that generates a pulse sequence based on the spread signal from the transmission buffer  803 , and an amplifier  804 - 2  that amplifies this pulse sequence. A pulse amplitude altering section  807  is connected to the amplifier  804 - 2 . The pulse amplitude altering section  807 , under the control of the control unit  806 , controls the amplification factor of the amplifier  804 - 2  according to a predefined amplitude pattern, and alters the amplitude of the pulses using one of the two methods mentioned above. In practice, the control unit  806  may comprise a central processing unit (CPU), and the CPU may follow instructions of a program stored in a storage device not shown in drawing (for example, an EEPROM (Electrically Erasable Programmable Read-Only Memory) and the like), and accordingly control the amplification factor of the amplifier  804 - 2  in accordance with a predefined amplitude pattern. The above-mentioned pulse altering operation includes an operation where the amplitude is equal to 0, in other words, where no pulse is transmitted.  
         [0038]    [0038]FIG. 4 shows a first configuration of a receiver of the radio communications system according to an embodiment of the present invention. A receiver  901  according to the first configuration has a configuration which is suitable for processing a pulse sequence whose pulse amplitude is altered pulse by pulse. In FIG. 4, reception means  902  comprise an RF circuit and the like, and receives a pulse sequence from the transmitter  801  by way of an antenna  909 . A correlator  903  calculates a correlated value between a pulse from the reception means  902  and a reference pulse, and thereafter sends the calculated result to an amplifier  904 . The amplifier  904  amplifies the output from the correlator  903 . An integrator  905 - 1  integrates the amplified pulse. An A/D converter  905 - 2  converts the integrated pulse into a digital signal. A received signal processing section  906  performs channel-decoding on the digital signal. A control unit  907  controls the timing of signal processing and the like at each of the sections mentioned above.  
         [0039]    The receiver  901  of the present embodiment further has an amplification factor alteration processing section  908 . The amplification factor alteration processing section  908  alters the amplification factor of the amplifier  904  under the control of the control unit  907 . This control operation will be described later. In practice, the control unit  907  may comprise a CPU, and the CPU may follow instructions from a program stored in a storage device not shown in drawing (for example, an EEPROM and the like), and accordingly control the amplification factor of the amplifier  904 .  
         [0040]    [0040]FIG. 5 shows a second configuration of a receiver in the radio communication system according to an embodiment of the present invention. A receiver  1001  of the second configuration has an appropriate configuration to process a pulse sequence whose amplitudes are altered by units of several pulses which correspond to the length of a spreading sequence length (for example, a pulse sequence corresponding to an information bit of 1 bit). In FIG. 5, reception means  1002  comprising an RF circuit and the like receive a pulse sequence from the transmitter  801  of FIG. 3 by way of an antenna  1009 . A correlator  1003  calculates a correlated value between the pulse from the reception means  1002  and a reference pulse and sends the calculated result to an integrator  1004 - 1 . The integrator  1004 - 1  integrates several pulses corresponding to the spreading sequence length. An A/D converter  1004 - 2  converts the integrated output into a digital signal. A weighting processing section  1005  performs weighting processing on the output in which pulses corresponding to the spreading sequence length are integrated. A received signal processing section  1006  performs channel-decoding and the like on the weighted signal. A control unit  1007  controls the timing of signal processing and the like at each of the sections mentioned above.  
         [0041]    The receiver  1001  further has a weighting alteration processing section  1008 , which performs a control function whereby a weighting value used by the weighting processing section  1005  is altered under the control of the control unit  1007 . Th control function will be mentioned below. In practice, the control unit  1007  may comprise a CPU, and the CPU may follow instructions from a program stored in a storage device not shown in drawing (for example, an EEPROM), and accordingly operate to alter the weighting value in accordance with a predefined amplitude pattern.  
         [0042]    Procedures of a radio communications scheme according to a first embodiment of the present invention are described below with reference to FIGS. 3, 4, and  6 A to  6 I.  
         [0043]    In a radio communications scheme for communicating information using an impulse signal sequence, 1 bit of information to be communicated from a transmission end is transmitted by way of a plurality of impulses. In other words, the bit of information data  601  (FIG. 6A) to be communicated is directly spread using a predetermined spreading code  602  (FIG. 6B) at the transmission data processing section  802  to be converted into a spread signal  603  (FIG. 6C). In accordance with the binary value of the spread signal  603 , the spread signal  603  is converted at the pulse generator  804  into a very fine pulse sequence. Thereafter, the pulse sequence is transmitted as the transmission signal  604  (FIG. 6D) by the transmission means  805 .  
         [0044]    In addition, with respect to the modulation method of the transmission signal  604  of the present embodiment, the explanation given above is such that it supposes a bi-phase modulation method which uses phase changes as the binary information of the impulse signal. However, a pulse position modulation method may also be applied in which a signal whose timing of generation of impulses is slightly offset corresponding to the binary information of a spread signal. Such a method is disclosed in PCT application publication number WO96/09694 which corresponds to published Japanese translation publication number 10-508725.  
         [0045]    Here, in converting the spread signal  603  into a pulse sequence, the amplitude of each pulse is altered by the pulse amplitude altering means  807  in accordance with a predefined pattern. This pulse amplitude altering processing includes such a processing wherein the amplitude is 0, in other words, wherein the pulse is not transmitted.  
         [0046]    [0046]FIG. 6E is an enlarged view of a portion  604 - 1  of the transmission signal  604  corresponding to the first few pulses thereof. As can be seen from this drawing, in the first embodiment, the amplitude of each pulse is altered in accordance with the predetermined pattern and the transmission signal  604  is transmitted thereafter.  
         [0047]    On the receiving end, a signal in which a noise signal is superimposed onto the transmitted signal is received as a received signal  605  (FIG. 6F) by the reception means  902  by way of the antenna  909 . The received signal  605  is despreaded using a predefined despreading code  606  (FIG. 6G). In other words, the received signal  605  is detected by the correlator  903 , and a correlated output  607  (FIG. 6H) is thereby obtained.  
         [0048]    When no amplification factor altering process is performed at the amplifier  904  at the next stage, signals such as those shown in FIG. 6H are sent to the integrator  905 - 1 , where a spreading code is integrated to obtain an integrated output  608  (FIG. 6I). The integrated output  608  is inputted to the A/D converter (or a comparator)  905 - 2 , and judging of the received data is performed.  
         [0049]    On the other hand, because the control unit  907  is informed, in advance, of the pattern used on the transmission end (FIG. 6D), the control unit  907 , by way of the amplification factor alteration processing section  908 , is capable of controlling the amplification factor of the amplifier  804 - 2  in accordance with this pattern. In this case, the integrator  905 - 1  receives a signal in which the amplitude of each pulse is substantially unaltered as shown in FIG. 9H.  
         [0050]    According to the first embodiment of the present invention described above, because the amplitude of each pulse is altered using a predetermined amplitude pattern before they are transmitted, it becomes possible to accurately discriminate the desired pulse from interfering pulses even when pulses from a plurality of transmitters are received simultaneously, thus making it possible to perform appropriate weighting on the received pulses. Therefore, the desired signal may be received in an appropriate manner.  
         [0051]    Procedures of a radio communications scheme using an impulse signal sequence according to a second embodiment of the present invention is described below with reference to FIGS. 3, 5, and  7 A to  7 I.  
         [0052]    In a radio communications scheme according to the present embodiments, 1 bit of information to be communicated from a transmission end is transmitted by way of a plurality of impulses. In other words, information bit data  701  (FIG. 7A) to be communicated is directly spread at the transmission data processing section  802  using a predetermined spreading code  702  (FIG. 7B) to be converted into a spread signal  703  (FIG. 7C). In accordance with the binary value of the spread signal  703 , the spread signal  703  is converted at the pulse generator  804  into a very fine pulse sequence. Thereafter, the pulse sequence is transmitted as a transmission signal  704  (FIG. 7D) by the transmission means  805 .  
         [0053]    With respect to the modulation method of the transmission signal  704  of the present embodiment, the explanation given above is such that it supposes a bi-phase modulation method which uses phase changes as the binary information of the signal. However, a pulse position modulation method may also be applied in which a signal, whose timing of generation of the impulses is slightly offset corresponding to the binary information of a spread signal, is used. Such a method is disclosed in PCT application publication number WO096/09694 mentioned above.  
         [0054]    Here, in converting the spread signal  703  into a pulse sequence, the amplitude of each pulse is altered by the pulse amplitude alteration means  807  in accordance with a predefined pattern. The pulse amplitude alterating process here includes an operation where the amplitude is set to 0, in other words, where the pulse is not transmitted.  
         [0055]    [0055]FIG. 7E is an enlarged view of a portion  704 - 1  of the transmission signal  704  corresponding to the first few pulses thereof. As can be seen from this drawing, in the second embodiment, the amplitudes of a plurality of pulses (in this case, a number of pulses corresponding to the spread sequence length) are altered in accordance with the predetermined pattern and they are transmitted thereafter.  
         [0056]    On the receiving end, a signal in which noise is superimposed on the transmission signal  704  is received as a received signal  705  (FIG. 7F) by the reception means  1002  via the antenna  1009 . The received signal  705  is despreaded using a predefined despreading code  706  (FIG. 7G). In other words, the received signal  705  is detected by the correlator  1003 , and a correlated output  707  (FIG. 7H) is obtained.  
         [0057]    The correlated output  707  is integrated by the integrator  1004 - 1  in an amount corresponding to the spreading code length, and thus an integrated output  708  (FIG. 7I) is obtained. The A/D converter (or comparator)  1004 - 2  receives the integrated output  708  and performs judging of the received data.  
         [0058]    When no weighting processing as mentioned above is performed at the weighting processing section  1005  at the next stage, a signal, which is the integrated output  708  shown in FIG. 7I converted into a digital signal, is sent to the received signal processing section  1006 .  
         [0059]    Because the control unit  1007  is informed, in advance, of the pattern used on the transmission end (FIG. 7D), the control unit, by way of the weighting alteration processing section  1008 , is capable of controlling the weighting processing at the weighting processing section  1005  in accordance with this pattern. In this case, the received signal processing section  1006  receives a signal whose amplitude by units corresponding to the spreading sequence length is substantially unaltered.  
         [0060]    At this point, the output from the correlator  1003  is compared with the pattern mentioned above. In accordance with the comparison result thereof, weighting of the estimated accuracy of the bit judgment of the received pulse is performed. In other words, when the amplitude of the received pulse is significantly greater than the expected amplitude, it is judged that this bit is affected by interference, and processings, such as concluding that a bit judgment of 0 or 1 is impossible, are performed.  
         [0061]    According to the second embodiment of the present invention described above, because the amplitudes of the pulses are altered before transmission by units corresponding to the length of the spreading sequence in accordance with a predefined pattern, even in cases where pulses from a plurality of transmitters are simultaneously received, the desired pulse may be accurately discriminated from interfering pulses. Thus, appropriate weighting of the received pulses becomes possible.  
         [0062]    In the examples above, the configurations of the transmitter and the receiver were such that a CPU serves as the control units  806 ,  907  and  1007 , and performs control functions and the like based on a program stored in an EEPROM. However, the present invention is not limited thereto. For example, a program-storing medium on which the program is stored may be installed to the transmitter and the receiver, and control functions may be performed by the transmitter and the receiver.  
         [0063]    The computer program-storing medium mentioned above is not limited to packaged media such as a flexible disk, a CD-ROM, or a digital versatile disk but also includes, for example, a semiconductor memory or a magnetic disk onto which a computer program is temporarily or permanently stored. Further, as to means for storing a program onto these program-storing media, wired or radio communications means such as a local area network (LAN), the Internet, a digital communications satellite or the like may be used to download the program, and the program may be written on a program-storing medium. Further, a communications unit such as a router or a modem may mediate the storing process.  
         [0064]    Thus, since the invention disclosed herein may be embodied in other specific forms without departing from the spirit or general characteristics thereof, some of which forms have been indicated, the embodiments described herein are to be considered in all respects illustrative and not restrictive. The scope of the invention is to be indicated by the appended claims, rather than by the foregoing description, and all changes which come within the meaning and range of equivalents of the claims are intended to be embraced therein.