Abstract:
There is provided a transmitter that transmits data in a spread spectrum communications system including a spread modulation portion spreading transmitting data with a spread code, an RZ conversion portion converting the transmitting data spread to an RZ signal, and an impulse sequence conversion portion multiplying the RZ signal by an impulse sequence to convert the RZ signal to an impulse radio signal.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to transmitters, receivers, and data communications systems and methods to communicate with the use of impulse-based UWB (Ultra Wide Band) signals.  
         [0003]     2. Description of the Related Art  
         [0004]     In the spread spectrum radio communications (Spread Spectrum), there has been proposed the technique for diversifying the correlation characteristics in such a manner that the PN (Pseudorandom Noise) code used in the DS (Direct Sequence) spread system is converted into the RZ (Return to Zero) form and multiplied by the data (refer to Japanese Patent Application Publication No. 4-347943). By converting the PN code to the RZ form, outputs of the PN codes become zero only for a given period, as shown in  FIG. 1 . The PN codes include both positive and negative values, so the conversion to the RZ form results in three values, positive, negative, and zero.  
         [0005]     In recent years, attention has been focused on the UWB-IR (UWB-Impulse Radio) system that enables the large-capacity transmission and sustains multiple users. The UWB-IR system uses an impulse signal equal to or smaller than one nanosecond. The UWB-IR signals are distributed over several GHz frequencies, and can share the frequency bands without interfering with the conventional radio systems.  
         [0006]      FIG. 2  shows a configuration of a transmitter in which the data is multiplied by the PN code converted into the RZ form and the impulse sequence. The data is multiplied by the PN code in the RZ form in a first multiplier  4 , and then the data is multiplied by an impulse sequence generated in an impulse generator  3 .  
         [0007]      FIG. 3  shows signal waveforms generated in the transmitter shown in  FIG. 2 .  FIG. 3 (B) shows the signal waveform of the PN code.  FIG. 3 (C) shows the signal waveform of the PN code in the RZ form.  FIG. 3 (D) shows the signal waveform after the data shown in  FIG. 3 (A) is multiplied by the PN code in the RZ form and then spread.  FIG. 3 (E) shows the signal waveform after the spread data shown in  FIG. 3 (D) is multiplied by the impulse sequence and converted into the impulse radio signals.  FIG. 3 (F) shows the signal waveform at a receiving end.  
         [0008]     The receiving end, however, cannot specify the waveform, when receiving and demodulating the impulse radio signals shown in  FIG. 3 (E). For, example, if ‘ 1 ’ continues in the spread data shown as dotted line in  FIG. 3 (D), the receiving end cannot specify the signal waveform (namely, the signal shown in  FIG. 3 (D) in which the spread code is multiplied by the impulse radio signal. This is because when the signal multiplied by the spread code is estimated with the impulse radio signal, multiple signal patterns can be speculated as shown in  FIG. 3 (G). Accordingly, it is impossible to specify the signal waveform.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention has been made in view of the above circumstances and provides a transmitter, receiver, a data communications system, and method thereof that readily enable the spread communications with impulse radio signals.  
         [0010]     According to one aspect of the present invention, preferably, there is provided a transmitter that transmits data in a spread spectrum communications system including: a spread modulation portion spreading transmitting data with a spread code; an RZ conversion portion converting the transmitting data spread to an RZ signal; and an impulse sequence conversion portion multiplying the RZ signal by an impulse sequence to convert the RZ signal to an impulse radio signal.  
         [0011]     According to another aspect of the present invention, preferably, there is provided a receiver that receives an impulse radio signal in which an RZ signal is multiplied by an impulse sequence code including: a receiving portion having n buffers that sequentially receive at intervals of 1/n in one cycle of the RZ signal, where n is an arbitrary natural number; and a demodulation portion that demodulates an output from the buffers to be determined valid. The impulse sequence of the pulse width of picoseconds level enables the UWB communications.  
         [0012]     According to still another aspect of the present invention, preferably, there is provided a data communications system in which impulse radio signals are transmitted and received including the above-described transmitter and receiver.  
         [0013]     According to yet another aspect of the present invention, preferably, there is provided a method for transmitting data in a spread spectrum communications system including: spreading transmitting data with a spread code; converting the transmitting data spread to an RZ signal; and multiplying the RZ signal by an impulse sequence to convert the RZ signal to an impulse radio signal.  
         [0014]     According to yet another aspect of the present invention, preferably, there is provided a method for receiving an impulse radio signal in which an RZ signal is multiplied by an impulse sequence code including: sequentially receiving with n buffers at intervals of 1/n in one cycle of the RZ signal, where n is an arbitrary natural number; and demodulating an output from the buffers to be determined valid.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Preferred embodiments of the present invention will be described in detail with reference to the following drawings, wherein:  
         [0016]      FIG. 1  illustrates an RZ signal;  
         [0017]      FIG. 2  shows a configuration of a conventional transmitter;  
         [0018]      FIG. 3  shows signal waveforms generated in the conventional transmitter;  
         [0019]      FIG. 4  shows a configuration of a transmitter in accordance with a first embodiment of the present invention;  
         [0020]      FIG. 5  shows the waveforms in the transmitter in accordance with the first embodiment of the present invention;  
         [0021]      FIG. 6  is a flowchart showing a procedure of the transmitter;  
         [0022]      FIG. 7  shows a configuration of a receiver in accordance with the first embodiment of the present invention;  
         [0023]      FIG. 8  shows a configuration of the buffer provided in a receiving portion;  
         [0024]      FIG. 9  illustrates the buffer in the receiving portion;  
         [0025]      FIG. 10  illustrates the buffer in the receiving portion;  
         [0026]      FIG. 11  illustrates the buffer in the receiving portion;  
         [0027]      FIG. 12  illustrates synchronization acquisition;  
         [0028]      FIG. 13  illustrates the synchronization acquisition;  
         [0029]      FIG. 14  illustrates the synchronization acquisition; and  
         [0030]      FIG. 15  illustrates the synchronization acquisition.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     A description will now be given, with reference to the accompanying drawings, of embodiments of the present invention.  
       First Embodiment  
       [0032]     A description will be given, with reference to  FIG. 4 , of a transmitter  10  in accordance with a first embodiment of the present invention. The transmitter  10  includes a baseband processing portion  11 , a carrier wave processing portion  12 , and a transmitting portion  21 . The baseband processing portion  11  encodes and compresses a digital sound signal obtained from a codec (not shown) in a given encoding method, puts the signals together in a given block, and outputs to the carrier wave processing portion  12 . In the carrier wave processing portion  12 , the signal processed by the baseband processing portion  11  is placed on a carrier wave. The carrier wave processing portion  12  includes a modulator  13 , a spread modulator  14 , an RZ converter  15 , and an impulse sequence converter  16 . The modulator  13  modulates the data in a given modulation method such as phase modulation. The spread modulator  14  completes the spread modulation with the PN code. The RZ converter  15  converts the signal that has completed the spread modulation, to the RZ form. The impulse sequence converter  16  converts the signal in the RZ form to the impulse radio signal. The spread modulator  14  is equipped with a PN code generator  17  and a first multiplier  18 . The impulse sequence converter  16  is equipped with an impulse generator  19  and a second multiplier  20 . The output from the impulse sequence converter  16  is electrically amplified to a desired level in the transmitting portion  21  and transmitted wirelessly via an antenna.  
         [0033]     A description will now be given, with reference to a flowchart shown in  FIG. 6 , of a procedure of the carrier wave processing portion  12 . In accordance with the first embodiment of the present invention, as shown in  FIG. 4 , the modulated signal is multiplied by PN code in the first multiplier  18  (step S 1 ), and the signal that has been spread is converted into the RZ form (step S 2 ). Then, the signal that has been converted into the RZ form is multiplied by the impulse sequence to convert to the impulse radio signal (step S 3 ). The impulse ratio signal is output from the antenna after the electricity level is adjusted (step S 4 ).  
         [0034]      FIG. 5  shows the waveforms in the carrier wave processing portion  12 . The signal that has been spread shown in  FIG. 5 (B) is generated by multiplying the transmitting signal that has been modulated in the modulator  13  by the PN code in the PN code generator  17 . Then, the afore-mentioned generated signal is converted into the RZ form in the RZ converter  15  as shown in  FIG. 5 (C). The afore-mentioned signal in the RZ form is multiplied by the impulse sequence to generate the impulse radio signal as shown in  FIG. 5 (D). With respect to the impulse sequence, each phase of the impulse is adjusted according to the spread code. The impulse sequence is multiplied by the signal converted into the RZ form for the pulse-position modulation.  
         [0035]     The impulse sequence converter  16 , as shown in  FIG. 5 (D), generates the impulse radio signal in synchronization with a rising edge of the input signal. Therefore, as shown in  FIG. 3G , the receiving end may not determine the signal waveform in some cases, when the impulse radio signal is generated by multiplying the signal after the spread modulation by the impulse sequence.  
         [0036]     In contrast, in accordance with the first embodiment of the present invention, the data is converted into the RZ form after spread by the PN code. Hence, even if ‘1’ continues in the signal after spread as shown in  FIG. 5 (B), it is possible to reflect the continuous ‘1’ after the RZ conversion, as shown in  FIG. 5 (C). Despreading can be accomplished properly at the receiving end, even if the signal in the RZ form (hereinafter, simply referred to as RZ signal) is converted into the impulse radio signal.  
         [0037]     With a pulse width of the impulse sequence generated from the impulse generator  19  set to be several picoseconds, the impulse radio signal will be able to utilize a wide range of frequencies for transmission, from 3.1 GHz to 10.6 GHz, namely, the ultra wide band (UWB) communication.  
         [0038]     A description will now be given, with reference to  FIG. 7 , of a configuration of a receiver  30 . The receiver  30 , as shown in  FIG. 7 , includes a receiving portion  31 , a carrier wave processing portion  32 , a synchronization acquisition portion  33 , and a baseband processing portion  34 . The signal received from the antenna is temporarily stored in a buffer in the receiving portion  31 . The carrier wave processing portion  32  obtains the received signal from the receiving portion  31  and generates the baseband signal with the despreading operation or demodulation. The synchronization acquisition portion  33  detects a data receive timing and notifies the receive timing that has been detected to the carrier wave processing portion  32  in order to obtain the data from the signal received from the antenna. The baseband processing portion  34  performs the A/D conversion of the signal output from the carrier wave processing portion  32 , removes the influence such as phasing, determines the type of the received signal, corrects the error, and decodes the signal properly, so that the sound data is separated from other communications data. The sound data is supplied to the codec (not shown) included in a DSP (Digital Signal Processor).  
         [0039]      FIG. 8  shows a configuration of the buffer provided in the receiving portion  31 . The buffer in accordance with the first embodiment of the present invention is composed of n buffers as shown in  FIG. 8 . The signals are sequentially input into the buffers  1  through n in such a manner that one cycle of the RZ signal is divided into n, the signal received in a first 1/n segment is input into the buffer  1 , and the signal received in the subsequent 1/n segment is input into the buffer  2 .  FIG. 11  shows how the signals are input. In this manner, the buffers for receiving the signals are shifted by the 1/n segment. When the subsequent cycle starts, the signal is input into the buffer  1  again. That is to say, the buffers  1  though n receive the data in the same segment in each cycle of the RZ signal. The signals received by the buffers  1  through n are determined whether valid or invalid. The reliability in demodulation can be enhanced by using only the valid signal for demodulation.  
         [0040]     The buffers  1  through n respectively receive the signals provided in the same segment in each spread cycle. When the signal stored in any buffer corresponds to the PN code, it is determined that the synchronization has been acquired and then despreading operation is performed with the use of the output from the corresponding buffer. This facilitates the despreading operation of the spread data output in the RZ form. Furthermore, the signals are sequentially input into the n buffers at intervals of 1/n (n is an arbitrary natural number) in one cycle of the RZ signal. It is therefore possible to demodulate without establishing synchronization with the impulse radio signal.  
         [0041]     Referring to  FIG. 9 , if the received signal is unstable in rising and trailing edges and delay or misalignment occurs in signal, the waveform of transmitting signal is different from that of the receiving signal. In this case, the output from the buffer, if it is determined that the correct signal is not received, should not be used. Instead, the data can be demodulated correctly by determining that the signal received in the middle of the buffer is valid.  
         [0042]     With respect to the intervals when the buffers  1  through n receive the signal, the influence of the impulse noise can be eliminated, by setting the intervals in consideration of the afore-mentioned noise. That is to say, as shown in  FIG. 10 , the receiving intervals of the buffers  1  through n are elongated than the intervals between the occurrences of the impulse noises so that the multiple buffers may not be affected by the same impulse noise. This makes it possible to receive the data correctly.  
         [0043]     A description will now be given of the operation of the synchronization acquisition portion  33 . When the signal that has been modulated by the pulse-position modulation is transmitted and received, a reference signal, known as leader pulse, is transmitted to establish the synchronization between the transmitter and receiver prior to the data transmission. In accordance with the first embodiment of the present invention, the leader pulse signal is transmitted several times as shown in  FIG. 12 , and the receiver  30  receives the leader pulse signal to acquire the synchronization.  
         [0044]     Generally, after the synchronization is acquired, despreading operation is performed. However, as shown in  FIG. 13 , a delay occurs because the despreading operation is also performed for the leader pulse part. In accordance with the first embodiment of the present invention, only the despreading operation is performed for the data part to be received subsequent to the leader pulse part, as show in  FIG. 14 . This shortens the delay time for data recovery. The period necessary for acquiring the synchronization can be calculated with the received PN code and the number of chips corresponding to the reference code prepared in the receiver  30 . In addition, the transmitting period of the leader pulse is already known, and the period for adjusting is delayed from the accomplishment of the synchronization, as shown in  FIG. 14 . Then, the despreading operation is performed at the data receive timing.  
         [0045]     Furthermore, according to the present embodiment, one transmitting period (transmitting period of one symbol) is set to several milliseconds, and the receiver  30  acquires the synchronization each time receiving the signal. The transmitting period is configured not to become misaligned. This eliminates the necessity of acquiring the synchronization in the transmitting period. The receiver  30  again acquires the synchronization in the subsequent transmitting period. It is possible to achieve the spread spectrum communications without acquiring the synchronization.  
         [0046]     The present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and modifications may be made without departing from the scope of the present invention.  
         [0047]     The present invention is based on Japanese Patent Application No. 2004-297717 filed on Oct. 12, 2004, the entire disclosure of which is hereby incorporated by reference.