Patent Abstract:
A method and an apparatus for bit-rate enhancement and a wireless communication system using the same are disclosed. According to the present invention, two approaches are provided for bit-rate enhancement: one is an increase of chip-rate and the other is a decrease of chip number associated with on symbol. As such, the transmission bit-rate can be enhanced significantly so as to facilitate the applications of wireless voice communications or security.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the priority benefits of U.S. provisional application entitled “Method and Apparatus for Bit-Rate Enhancement and Wireless Voice Communication Using the Same” filed on Mar. 7, 2006 Ser. No. 60/779,453. All disclosures of this application are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention generally relates to spread spectrum communications. More particular, the present invention relates to a method and an apparatus for bit-rate enhancement and a wireless communication system using the same. 
         [0004]    2. Description of Related Arts 
         [0005]    Spread spectrum communication systems spread transmitted signals over bandwidths much greater than those actually required to transmit the information. The spreading spectrum technologies have been widely used both in military and commercial wireless communication systems, and applications based on the emerging IEEE 802.15.4 standard. There are many advantages of using spread spectrum approach, and the most important ones are: (1) due to spreading gain, spread spectrum systems are very robust with respect to noise and interferences; (2) multipath fading has a much less impact to spread spectrum systems; and (3) spread spectrum systems are inherently secure. 
         [0006]    IEEE 802.15.4 standard utilizes spread spectrum technology that spreading codes are constructed to have good auto-correlation and cross-correlation properties. As such, one code can effectively differentiate itself from the other codes under noisy conditions. The ideal spreading codes are orthogonal, which means the cross-correlation between two different codes is zero. In IEEE 802.15.4 standard, the transmitted data stream is grouped into one or several bits as one symbol and mapped and spreaded, i.e., encoded into M-ary Pseudo Noise (PN) spreading codes or so-called “chips.” While operating at 2.4 GHz frequency band, 4-bit data, which are group to be one symbol, are converted into 32 chips in I-channel and Q-channel alternately in transmitter side. A mapping table of symbol-to-chip at 2.4 GHz is provided in  FIG. 1 . While operating at 868/915 MHz, one bit data, which is grouped to be one symbol, is converted into 15 chips I-channel and Q-channel alternately in transmitter side. a mapping table of symbol-to-chip at 868/915 MHz is provided in  FIG. 2 . In IEEE 802.15.4 standard, half-sine pulse waveform is utilized for chip transmission at 2.4 GHz and raised-cosine pulse waveform is utilized for chip transmission at 868/915 MHz. 
         [0007]    A diagram of half-sine pulse waveform is shown in  FIG. 3  as an example. In  FIG. 3 , the left half-sine pulse represents the chip with logic “one” and the right half-sine pulse designates the chip with logic “zero.” Each chip is provided with a period of 1 μsec when the IEEE 802.15.4-based system is operated at a bit-rate of 250 Kbps associated with a chip rate of 1M chips per second. In the corresponding receiver side, the received chips are sampled at a clock rate of, for example, 20 MHz to as to generate 20 samples per chip as shown in  FIG. 2 . 
       SUMMARY OF THE INVENTION 
       [0008]    Therefore, it is an object of the present invention to provide a method and an apparatus for bit-rate enhancement and a wireless communication system using the same such that data stream can be processed at higher rate. 
         [0009]    For achieving the above-identified object, the present invention provides a method of bit-rate enhancement in the application of a wireless communication system, the method comprising the following steps of: converting bit data to symbol data; converting the symbol date to a plurality of chips, wherein each of the plurality of chips has a period less than 1 μsec; and modulating the plurality of chips to a radio frequency signal for output. 
         [0010]    The present invention provides a method of bit-rate enhancement in the application of a wireless communication system, the method comprising the steps of: 
         [0011]    receiving a radio frequency signal; demodulating the radio frequency signal to a plurality of chips, wherein each of the plurality of chips has a period less than 1 μsec; converting the plurality of chips to symbol data; and converting the symbol data to bit data. 
         [0012]    The present invention provides a method of bit-rate enhancement in the application of a wireless communication system, the method comprising the following steps of: converting bit data to symbol data; converting the symbol data to N chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; and modulating the plurality of chips to a radio frequency signal. 
         [0013]    The present invention provides a method of bit-rate enhancement in the application of a wireless communication system, the method comprising the following steps of: receiving a radio frequency signal; demodulating the radio frequency signal to N chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; converting the N chips to symbol data; and converting the symbol data to bit data. 
         [0014]    The present invention provides an apparatus of bit-rate enhancement in a wireless communication system, the apparatus comprising: means for converting bit data to symbol data; means for converting the symbol date to a plurality of chips, wherein each of the plurality of chips has a period less than 1 μsec; and means for modulating the plurality of chips to a radio frequency signal for output. 
         [0015]    The present invention provides an apparatus of bit-rate enhancement in a wireless communication system, the apparatus comprising: means for receiving a radio frequency signal; means for demodulating the radio frequency signal to a plurality of chips, wherein each of the plurality of chips has a period less than 1 μsec; means for converting the plurality of chips to symbol data; and means for converting the symbol data to bit data. 
         [0016]    The present invention provides an apparatus of bit-rate enhancement in a wireless communication system, the apparatus comprising: means for converting bit data to symbol data; means for converting the symbol data to N chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; and means for modulating the plurality of chips to a radio frequency signal. 
         [0017]    The present invention provides an apparatus of bit-rate enhancement in a wireless communication system, the apparatus comprising: means for receiving a radio frequency signal; means for demodulating the radio frequency signal to N chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; means for converting the N chips to symbol data; and means for converting the symbol data to bit data. 
         [0018]    The present invention provides a wireless communication system of bit-rate enhancement, comprising: in a transmitter comprising: means for converting bit data to symbol data; means for converting the symbol date to a plurality of chips, wherein each of the plurality of chips has a period less than μsec; and means for modulating the plurality of chips to a radio frequency signal for output; in a receiver comprising: means for receiving the radio frequency signal; means for demodulating the radio frequency signal to a plurality of received chips, wherein each of the plurality of received chips has a period less than 1 μsec; means for converting the plurality of received chips to received symbol data; and means for converting the received symbol data to received bit data. 
         [0019]    The present invention provides a wireless communication system of bit-rate enhancement, comprising: in a transmitter, comprising: means for converting bit data to symbol data; means for converting the symbol data to N chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; and means for modulating the plurality of chips to a radio frequency signal; in a receiver, comprising: means for receiving the radio frequency signal; means for demodulating the radio frequency signal to N received chips, wherein N is less than 32 at a first bandwidth and less than 15 at a second bandwidth; means for converting the N received chips to received symbol data; and means for converting the received symbol data to received bit data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a mapping table of conventional symbol-to-chip at 2.4 GHz bandwidth; 
           [0021]      FIG. 2  is a mapping table of conventional symbol-to-chip at 868/915 MHz bandwidth; 
           [0022]      FIG. 3  is an exemplary diagram of half-sine pulse waveform; 
           [0023]      FIG. 4  is a diagram to explain conventional sampling approach; 
           [0024]      FIG. 5  schematically depicts a block diagram of a bit-rate enhancement apparatus in transmitter side in accordance with one preferred embodiment of the present invention; 
           [0025]      FIG. 6  is a schematic diagram of comparing the half-sine waveforms according to the conventional approach and the present invention; 
           [0026]      FIG. 7  schematically depicts a block diagram of a bit-rate enhancement apparatus in receiver side in accordance with one preferred embodiment of the present invention; 
           [0027]      FIG. 8  is a schematic diagram of comparing the half-sine sampling according to the conventional approach and the present invention; 
           [0028]      FIG. 9  schematically depicts a block diagram of a bit-rate enhancement apparatus in transmitter side in accordance with another preferred embodiment of the present invention; 
           [0029]      FIG. 10  schematically depicts a block diagram of a bit-rate enhancement apparatus in receiver side in accordance with another preferred embodiment of the present invention; 
           [0030]      FIG. 11  is a mapping table of symbol-to-chip at 2.4 GHz bandwidth in accordance with another preferred embodiment; and 
           [0031]      FIG. 12  is a mapping table of symbol-to-chip at 868/915 MHz bandwidth in accordance with another preferred embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0032]    Referring to  FIG. 5 , a block diagram of a bit-rate enhancement apparatus in transmitter side in accordance with one preferred embodiment of the present invention is illustrated schematically. In  FIG. 5 , a transmitter  5  includes a byte-to-symbol converter  51 , a symbol-to-chip converter  53 , a I/Q shaper  55  and a mixer  57 . The byte-to-symbol converter  51  is employed to convert bit data  50  into symbol data  52 . The symbol-to-chip converter  53  is used to convert the symbol data  52  into chips  54 . An example of symbol-to-chip mapping is shown in  FIGS. 1 and 2 . The I/Q shaper  55  is utilized to shape waveform of the chips  54  in I-channel and Q-channel to generate a baseband signal  56 . The baseband signal  56  is mixed with a carrier  58  at the mixer such that the baseband signal  56  is modulated to become a radio frequency signal for transmission over the air. When the transmitter  5  is operated at 2.4 GHz, the carrier  58  has a frequency of 2.4 GHz. When the transmitter is operated at 868/915 MHz, the carrier  58  has a frequency of 868/915 MHz. 
         [0033]    In this embodiment, the transmission bit-rate can be increased by means of chip-rate enhancement. As shown in  FIG. 5 , after the symbol data  52  are converted by the symbol-to-chip converter  53  into the corresponding chips  54 , the chip-rate thereof is increased greater than 1 MHz and the chip period is decreased less than μsec as well. By taking 2.4 GHz bandwidth and the chips  54  are transmitted in half-sine pulse waveform as an example, the period of each chip  54  is decreased to 0.4 μsec and thus the corresponding chip-rate is increased to 2.5 MHz. The waveform of the baseband signals  56  after processing of the I/Q shaper  55  is shown in the right-hand side of  FIG. 6  where the conventional waveform is shown in left-hand side of  FIG. 6 . 
         [0034]    Referring to  FIG. 7 , a block diagram of a bit-rate enhancement apparatus in receiver side in accordance with one preferred embodiment of the present invention is depicted schematically. In  FIG. 7 , a receiver  7  includes a down-converter  71 , a filter  73 , a differential demodulator  75  and a symbol detector  77 . The down-converter  71  is employed to receive a radio frequency signal  70  and convert the received radio frequency signal  70  into a baseband signal  72 . The down-converter  71  includes the converter for converting the radio frequency signals into intermediate frequency signals and the converter for converting the intermediate frequency signals into baseband signals. The filter  73  is used to convert the baseband signal  72  into the corresponding chips  74 . If half-sine pulse waveform is applied, the filter  73  is a half-sine shaping filter as an example. Because the chip-rate of the received data has been increased significantly, the filter coefficients should be modified to allow the passage of signals with broader bandwidth. Thereafter, the differential demodulator  75  is used to convert the received chips  74  into symbol data  76 . The differential demodulator  75  is used to generate a sequence of phase differences which QPSK, O-QPSK and M-ary PSk can be applied. Then, the symbol date  76  are converted by the symbol detector  77  into bit data for further processing. 
         [0035]    In this embodiment, the transmission bit-rate has been increased by means of chip-rate enhancement. As shown in  FIG. 7 , the coefficients of the filter  73  should be modified to accommodate the reception of bit-rate-enhanced radio frequency signal  70 . According to the present invention, the chips  74  generated by the filter  73  have a chip-rate greater than 1 MHz which means chip period less than 1 μsec. By taking 2.4 GHz bandwidth and the chips  74  are transmitted in half-sine pulse waveform as an example, the period of each chip  74  is decreased to 0.4 μsec and thus the corresponding chip-rate is increased to 2.5 MHz. If the differential demodulator  75  samples the chips at a sampling clock of 20 MHz, the number of samples is decrease to 8 as shown in the right-hand side of  FIG. 8  where the conventional sampled waveform is shown in left-hand side of  FIG. 8 . 
         [0036]    Referring to  FIG. 9 , a block diagram of a bit-rate enhancement apparatus in transmitter side in accordance with another preferred embodiment of the present invention is depicted schematically. In  FIG. 9 , a transmitter  9  includes a byte-to-symbol converter  91 , a symbol-to-chip converter  93 , a I/Q shaper  95  and a mixer  97 . The byte-to-symbol converter  91  is employed to convert bit data  90  into symbol data  92 . The symbol-to-chip converter  93  is used to convert the symbol data  92  into chips  94 . An example of symbol-to-chip mapping is shown in  FIGS. 11 and 12 . The I/Q shaper  95  is utilized to shape waveform of the chips  94  in I-channel and Q-channel to generate a baseband signal  96 . The baseband signal  96  is mixed with a carrier  98  at the mixer such that the baseband signal  96  is modulated to become a radio frequency signal for transmission over the air. When the transmitter  9  is operated at 2.4 GHz, the carrier  98  has a frequency of 2.4 GHz. When the transmitter is operated at 868/915 MHz, the carrier  98  has a frequency of 868/915 MHz. 
         [0037]    In this embodiment, the transmission bit-rate can be enhanced by means of decreasing the chip number of symbol-to-chip mapping. As shown in  FIG. 9 , after the symbol  92  is converted by the symbol-to-chip converter  93  into the chips  94 , the chip number of symbol-to-chip mapping is less than that of the conventional approach. At 2.4 GHz bandwidth, the chip number of chips  94  associated with each symbol  92  is decrease from 32 to 16, for example, as shown in the mapping table of  FIG. 11 . At 868/915 MHz bandwidth, the chip number of chips  94  associated with each symbol  92  is decrease from 15 to 8, for example, as shown in the mapping table of  FIG. 12 . Therefore, the symbol-to-chip converter  93  is employed to convert the symbol  92  into the corresponding chips  94  based upon the corresponding relation of symbol-to-chip mapping. The mapping relationships as shown in  FIGS. 11 and 12  are ones of many feasible examples. 
         [0038]    Referring to  FIG. 10 , a block diagram of a bit-rate enhancement apparatus in receiver side in accordance with one preferred embodiment of the present invention is depicted schematically. In  FIG. 10 , a receiver  10  includes a down-converter  101 , a filter  103 , a differential demodulator  105  and a symbol detector  107 . The down-converter  101  is employed to receive a radio frequency signal  100  and convert the received radio frequency signal  100  into a baseband signal  102 . The down-converter  101  includes the converter for converting the radio frequency signals into intermediate frequency signals and the converter for converting the intermediate frequency signals into baseband signals. The filter  103  is used to convert the baseband signal  102  into the corresponding chips  104 . If half-sine pulse waveform is applied, the filter  103  is a half-sine shaping filter as an example. Because the chip-rate of the received data has been increased significantly, the filter coefficients should be modified to allow the passage of signals with broader bandwidth. Thereafter, the differential demodulator  105  is used to convert the received chips  104  into symbol data  106 . The differential demodulator  105  is used to generate a sequence of phase differences which QPSK, O-QPSK and M-ary PSk can be applied. Then, the symbol date  106  is converted by the symbol detector  107  into bit data for further processing. 
         [0039]    In this embodiment, the transmission bit-rate can be enhanced by means of decreasing the chip number of symbol-to-chip mapping. As shown in  FIG. 10 , the chip number, associated with one symbol, of the received chips  104  is less than that of the conventional approach. Therefore, the symbol detector  107  is employed to convert the chips  104  into the corresponding symbol  106  based upon the corresponding relation of symbol-to-chip mapping. The mapping relationships as shown in  FIGS. 11 and 12  are ones of many feasible examples. 
         [0040]    Although the description above contains much specificity, it should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the present invention. Thus, the scope of the present invention should be determined by the appended claims and their equivalents, rather than by the examples given.

Technology Classification (CPC): 7