Patent Publication Number: US-2007116096-A1

Title: Impulse signal acquisition method and apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority from Korean Patent Application No. 2005-111864 filed Nov. 22, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      Methods and apparatuses consistent with the present invention relate to acquiring an impulse signal, and more particularly, to the acquisition of an impulse signal having a wide cell from an impulse signal used for transmitting and receiving data in an ultra wide band (UWB) communication system and then acquiring an impulse signal having a narrow cell inside the impulse having the wide cell.  
      2. Description of the Related Art  
      Unlike existing narrow band communications for transmitting data together with carrier waves with a base band signal, recent UWB wireless technology is used to transmit data using ultra-short base band pulses reaching several nano-seconds without carrier waves.  
       FIG. 1A  is a block diagram of a related art UWB communication system which performs a serial search to acquire an impulse signal.  
      Referring to  FIG. 1A , a received signal is multiplied by a template signal output from a time hopping (TH) code generator  120  by a multiplier  110  and then applied to a correlator  130 . A signal y output from the correlator  130  is compared with a threshold value ξ by a comparator  140 . If the signal y is smaller than the threshold ξ, the signal y is applied to an acquisition controller  150 . If the signal y is larger than the threshold value ξ, a serial search process shown in  FIG. 1B  is performed to acquire an impulse signal.  
       FIG. 1B  is a view illustrating a serial search process for acquiring an impulse signal.  
      As shown in  FIG. 1B , in a case where a received signal and a template signal do not synchronize with each other due to two cells, the acquisition controller  150  controls the TH code generator  120  to delay the template signal by one cell and then by another cell so as to synchronize the template signal with the received signal.  
      Here, an operation of acquiring the template signal synchronized with the received signal is performed using a sub-nanosecond cell.  
      Also, in an uncertainty region of 20 nanoseconds (ns), an impulse acquisition is tested 20 times in the unit of 1 ns cell. Additionally, in a case where the uncertainty region is 1 microsecond (μs) and a cell is 0.25 ns, 4000 cells are required. Thus, 4000 tests must be performed. An average impulse acquisition time for acquiring an impulse radio (IR)-UWB signal is 500 ms to about 1 second.  
      As described above, in the related art, a large number of tests are required for acquiring an impulse signal. Also, a large amount of time is required for acquiring the impulse signal, which increases power consumption.  
     SUMMARY OF THE INVENTION  
      Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above.  
      The present invention provides an impulse signal acquisition method and apparatus for acquiring an impulse signal having a wide cell from an impulse signal used for transmitting and receiving data in an UWB communication system and then acquiring an impulse signal having a narrow cell inside the impulse signal having the wide cell.  
      The present invention also provides an impulse signal acquisition transmitter comprising an impulse generator which varies a pulse width of an impulse signal used for transmitting data according to a predetermined control signal to generate the impulse signal, and a controller which applies a pulse width control signal used to vary the pulse width of the impulse signal to the impulse generator.  
      The impulse generator may generate an impulse signal having a narrow cell or an impulse signal having an N-times wider cell than the narrow cell according to the pulse width control signal.  
      If a pulse width of the impulse signal having the narrow cell is 1 ns, a pulse width of the impulse signal having the wide cell is 2 ns.  
      According to another aspect of the present invention, there is provided an impulse signal acquisition transmitter comprising a first impulse generator which generates a first impulse signal having a first pulse width; a second impulse generator which generates a second impulse signal having a second pulse width; an N th  impulse generator which generates an N th  impulse signal having an N th  pulse width; a switch which switches one of the first, second, and N th  impulse generators according to a predetermined control signal to generate an impulse signal; and a controller which controls the switch so as to generate the impulse signal.  
      The first, second, and N th  impulse generators may generate impulse signals which have narrow or wide cells.  
      According to another aspect of the present invention, there is provided an impulse signal acquisition receiver comprising an impulse generator which varies a pulse width according to a predetermined control signal to generate an impulse signal to be multiplied by a received signal; a comparator which compares the received signal with a threshold value; and a controller which applies a pulse width control signal which varies the pulse width to the impulse generator and shifts a phase of the impulse signal so as to synchronize the impulse signal with the received signal.  
      The impulse generator may generate an impulse signal having a narrow cell or an impulse signal having an N-times wider cell than the narrow cell according to the pulse width control signal.  
      According to another aspect of the present invention, there is provided an impulse signal acquisition receiver comprising a first impulse generator which generates a first impulse signal having a first pulse width; a second impulse generator which generates a second impulse signal having a second pulse width; an N th  impulse generator which generates an N th  impulse signal having an N th  pulse width; a switch which switches one of the first, second, and N th  impulse generators to generate an impulse signal to be multiplied by a received signal; a comparator which compares the received signal with a threshold value; and an acquisition controller which controls the switch to generate the impulse signal and shifts a phase of the impulse signal so as to synchronize the impulse signal with the received signal.  
      The impulse signal acquisition receiver may further include: a pseudo number (PN) code generator which generates a PN code for coding the impulse signal; and a switch which switches the PN code generator to one of the first, second, and N th  impulse generators according to control of the acquisition controller.  
      The first, second, and N th  impulse generators may generate impulse signals which have narrow cells or wide cells.  
      According to another aspect of the present invention, there is provided an impulse signal acquisition method comprising transmitting a preamble packet which includes an impulse signal; receiving the preamble packet and acquiring a received signal from the preamble packet using an impulse having a wide cell; and acquiring a received signal using an impulse having a narrow cell inside the impulse having the wide cell.  
      In the transmitting, the impulse signal may be an impulse signal having a wide cell or an impulse signal having a narrow cell.  
      In the receiving, the preamble packet may include a first preamble packet which includes an impulse signal having a wide cell and a second preamble packet which includes an impulse signal having a narrow cell.  
      The received signal may be compared with a threshold value, and if the received signal does not synchronize with the impulse signal, a phase of the impulse signal may shift so as to synchronize the impulse signal with the received signal.  
      A pulse width of the impulse signal having the narrow cell may be 1 ns, and a pulse width of the impulse signal having the wide cell may be 2 ns.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other aspects of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which:  
       FIG. 1A  is a block diagram of a related art UWB communication system which performs a serial search to acquire an impulse signal;  
       FIG. 1B  is a view illustrating a serial search process for acquiring an impulse signal;  
       FIG. 2A  is a view illustrating an impulse signal acquisition method according to an exemplary embodiment of the present invention compared with a related art impulse signal acquisition method;  
       FIG. 2B  is a view illustrating a structure of preamble packet data transmitted and received in an UWB communication system to which an impulse signal is applied according to an exemplary embodiment of the present invention;  
       FIG. 2C  is a graph illustrating an impulse signal having a wide cell and an impulse signal having a narrow cell;  
       FIG. 3  is a view illustrating parameters different from a cell width of an impulse signal;  
       FIG. 4  is a block diagram of a transmitter of an impulse signal acquisition apparatus according to an exemplary embodiment of the present invention;  
       FIG. 5  is a block diagram of a transmitter of an impulse signal acquisition apparatus according to another exemplary embodiment of the present invention;  
       FIG. 6  is a block diagram of a receiver of an impulse signal acquisition apparatus according to an exemplary embodiment of the present invention;  
       FIG. 7  is a block diagram of a receiver of an impulse signal acquisition apparatus according to another exemplary embodiment of the present invention; and  
       FIG. 8  is a view illustrating a process of acquiring an impulse signal according to an exemplary embodiment of the present invention.  
       FIG. 9  is a graph illustrating acquisition times required for acquiring an impulse signal having a wide cell and an impulse signal having a narrow cell. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION  
      Certain exemplary embodiments of the present invention will be described in greater detail with reference to the accompanying drawings.  
      In the following description, same drawing reference numerals are used for the same elements even in different drawings. The matters defined in the description such as a detailed construction and elements are nothing but the ones provided to assist in a comprehensive understanding of the invention. Thus, it is apparent that the exemplary embodiments of the present invention can be carried out without those defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
       FIG. 2A  is a view illustrating an impulse signal acquisition method according to an exemplary embodiment of the present invention compared with a related art impulse signal acquisition method. As shown in  FIG. 2A , in the impulse signal acquisition method according to the exemplary embodiments of the present invention, an impulse signal is acquired using a 2-ns cell, and then an impulse signal is acquired using a 1 ns cell inside the 2 ns cell.  
      Thus, in the related art impulse signal acquisition method, 20 tests are performed to acquire an impulse signal in a 20-ns uncertainty region. However, in the impulse signal acquisition method according to the exemplary embodiments of the present invention, the 2-ns cell is used. Thus, 10 tests are performed to acquire an impulse signal. 2 tests are performed with respect to the impulse signal in the 2-ns cell using the 1-ns cell. As a result, 12 tests are performed in the 20-ns uncertainty region.  
       FIG. 2B  is a view illustrating a structure of preamble packet data transmitted and received in a UWB communication system to which an impulse signal is applied according to an exemplary embodiment of the present invention.  
      As shown in  FIG. 2B , the preamble packet data according to the present exemplary embodiment includes a first preamble packet which includes impulses with wide cells and a second preamble packet which includes impulses with narrow cells.  
      For example, the first preamble packet may comprise a plurality of 2-ns cells, and the second preamble packet may include 1-ns cells.  
      Here, an impulse signal p(t) can be obtained using a Gaussian quadratic function shown in Equation 1:  
               p   ⁡     (   t   )       =           4     3   ⁢   a   ⁢     π           ⁡     [     1   -       [     t   a     ]     2       ]       ⁢     exp   ⁡     [       -     1   2       ⁢       (     2   a     )     2       ]                 (   1   )             
 
 wherein ‘a’ is 0.125 ns in a narrow cell but 0.25 ns in a wide cell. 
 
      Accordingly, waveforms of impulse signals with respect to the narrow cell of 0.125 ns and the wide cell of 0.25 ns obtained using Equation 1 are shown in  FIG. 2C . As shown in  FIG. 2C , a width of a wide cell is two times a width of a narrow cell.  
      Also, Table 1 below shows cell widths and parameters, and  FIG. 3  shows parameters different from the cell widths.  
                       TABLE 1                       Parameter   Sign   Basic Value                  Frame duration   T f     100 ns       Chip Duration   T c     10 ns       # Chip in One Frame   N f     10       Cell Width   T cell     2a       Period of TH Code   N c     16       Uncertainty Region   T p     N c  * T f  = 1600 ns       # Cells in the Uncertainty Region   N   T p /Tb               6400(Tcell 0.25), 3200(0.5)                  
 
       FIG. 4  is a block diagram of a transmitter of an impulse signal acquisition apparatus according to an exemplary embodiment of the present invention.  
      Referring to  FIG. 4 , the transmitter includes an information source unit  410 , a controller  412 , a spreading unit  414 , an impulse generator  416 , a PN code generator  418 , and a transmitter (Tx) antenna  420 .  
      The information source unit  410  stores data to be transmitted, and the controller  412  controls the impulse generator  416  to generate impulses of an impulse signal having a 2-ns or 1-ns cell width, the impulse signal being used to transmit the data.  
      The spreading unit  414  spreads the data with a PN code according to a control signal of the controller  412 .  
      The impulse generator  416  generates a variable impulse signal having a 2-ns or 1-ns cell width according to a pulse width control signal of the controller  412 .  
      The Tx antenna  420  transmits an impulse signal for the data in a wireless manner.  
       FIG. 5  is a block diagram of a transmitter of an impulse signal acquisition apparatus according to another exemplary embodiment of the present invention.  
      Referring to  FIG. 5 , the transmitter according to the present exemplary embodiment includes an information source unit  410 , a controller  412 , a spreading unit  414 , a switch  510 , a first impulse generator  512 , a second impulse generator  514 , . . . , and N th  impulse generator  516 , a PN code generator  418 , and a Tx antenna  420 .  
      The information source unit  410 , the spreading unit  414 , the PN code generator  418 , and the Tx antenna  420  are as described in the previous exemplary embodiment and thus will not be described herein.  
      The transmitter according to the present exemplary embodiment includes impulse generators which generate impulse signals which have different pulse widths and selectively switches the impulse generators to generate an impulse signal having a corresponding pulse width.  
      The switch  510  switches one of the first impulse generator  512 , the second impulse generator  514 , . . . , and the N th  impulse generator  516  according to a control signal of the controller  412 .  
      The first impulse generator  512  generates a first impulse signal having a first pulse width, for example, a 2-ns-cell.  
      The second impulse generator  514  generates a second impulse signal having a second pulse width, for example, a 1-ns cell.  
      The N th  impulse generator  516  generates an N th  impulse signal having an N th  pulse width.  
       FIG. 6  is a block diagram of a receiver of an impulse signal acquisition apparatus according to an exemplary embodiment of the present invention. Referring to  FIG. 6 , the receiver includes a Receiver (Rx) antenna  602 , a multiplier  604 , an impulse generator  606 , a correlator  608 , a comparator  610 , a validation unit  612 , an acquisition controller  614 , a switch  616 , and a PN code generator  618 .  
      The Rx antenna  602  receives data from a transmitter.  
      The multiplier  604  multiplies a received signal by an. impulse signal and then outputs the multiplication result.  
      The impulse generator  606  generates a varied impulse signal according to a pulse width control signal of the acquisition controller  614 .  
      The correlator  608  detects a preamble and a sync word signal using an auto-correlation method.  
      The comparator  610  compares a signal y applied from the correlator  608  with a threshold value ξ. If the signal y is smaller than the threshold value ξ, the comparator  610  transmits a cell shift signal to the acquisition controller  614 . If the signal y is larger than or equal to the threshold value ξ, the comparator  610  transmits a false alarm signal to the acquisition controller  614  through the validation unit  612 .  
      The acquisition controller  614  applies a control signal for shifting a phase of an impulse signal to be generated and a pulse width control signal for generating an impulse signal having a varied pulse width to the impulse generator  606  according to the cell shift signal applied from the comparator  610 . When the received signal and the impulse signal synchronize with each other, the acquisition controller  614  controls the switch  616  to input the received signal as input data.  
      The PN code generator  618  generates a PN code for coding the received signal.  
       FIG. 7  is a block diagram of a receiver of an impulse signal acquisition apparatus according to another exemplary embodiment of the present invention. Referring to  FIG. 7 , the receiver includes an Rx antenna  602 , a multiplier  604 , a first impulse generator  710 , a second impulse generator  712 , . . . , and an N th  impulse generator  714 , a first switch  720 , a second switch  730 , a correlator  608 , a comparator  610 , a validation unit  612 , an acquisition controller  614 , a switch  616 , and a PN code generator  618 .  
      The Rx antenna  602 , the multiplier  604 , the correlator  608 , the comparator  610 , the validation unit  612 , the switch  616 , and the PN code generator  618  are as described in the previous exemplary embodiment and thus will not be described herein.  
      The receiver according to the present exemplary embodiment includes impulse generators which generate impulse signals which have different pulse widths and selectively switches the impulse generators to generate an impulse signal having a corresponding pulse width.  
      The first impulse generator  710  generates a first impulse signal having a first pulse width, for example, a 2-ns cell.  
      The second impulse generator  712  generates a second impulse signal having a second pulse width, for example, a 1-ns cell.  
      The Nth impulse generator  714  generates an N th  impulse signal having an N th  pulse width. The first switch  720  switches one of the first impulse generator  710 , the second impulse generator  712 , . . . , and the N th  impulse generator  714  according to a control signal of the acquisition controller  614 .  
      The second switch  730  switches the PN code generator  618  to one of the first impulse generator  710 , the second impulse generator  712 , . . . , and the N th  impulse generator  714  according to the control signal of the acquisition controller  614  to insert a PN code into each impulse signal.  
       FIG. 8  is a view which illustrates a process of acquiring an impulse signal according to an exemplary embodiment of the present invention.  
      For understanding of the exemplary embodiment of the present invention, a receiver will be described as an example.  
      When a signal as shown in (a) of  FIG. 8  is received through the Rx antenna  602 , the acquisition controller  614  applies a pulse width control signal for generating an impulse signal having a wide cell as shown in (b) of  FIG. 8  to the impulse generator  606 . The signal received through the Rx antenna  602  is also an impulse signal having a wide cell.  
      Thus, the impulse generator  606  generates the impulse signal having the wide cell shown in (b) of  FIG. 8  according to the pulse width control signal.  
      The impulse signal having the wide cell is multiplied by the received signal by the multiplier  604  and then applied to the correlator  608 .  
      A signal y output from the correlator  608  is compared with a threshold value ξ by the comparator  610 .  
      If the received signal shown in (a) of  FIG. 8  and the impulse signal shown in (b) of  FIG. 8  do not synchronize with each other due to one cell, the comparator  610  outputs a cell shift signal for shifting the cell to the acquisition controller  614 .  
      The acquisition controller  614  applies a pulse width control signal for shifting the impulse signal by one cell according to the cell shift signal to the impulse generator  606 .  
      The impulse generator  606  generates an impulse signal which shifts by one cell so as to synchronize with the received signal as shown in (c)  FIG. 8 .  
      If the received signal received through the Rx antenna  602  is a received signal having a narrow cell as shown in (d) of  FIG. 8 , the acquisition controller  614  of the receiver generates an impulse signal having a narrow cell.  
      Thus, the impulse generator  606  generates an impulse signal having a narrow cell as shown in (e) of  FIG. 8 .  
      If the received signal and the impulse signal do not synchronize with each other by one cell, the acquisition controller  614  shifts the impulse signal by one cell to generate an impulse signal.  
      Thus, the impulse generator  606  generates an impulse signal having a narrow cell, the impulse signal synchronizing with the received signal, as shown in (f) of  FIG. 8 .  
      Acquisition times required for acquiring an impulse signal having a wide cell and an impulse signal having a narrow cell are shown in  FIG. 9 . As shown in  FIG. 9 , a mean acquisition time required for acquiring an impulse signal having a wide cell is much shorter than a mean acquisition time required for acquiring an impulse signal having a narrow cell.  
      As described above, according to the exemplary embodiments of the present invention, an acquisition time required for acquiring an impulse signal used for transmitting and receiving data can be reduced. Thus, a number of tests performed for acquiring the impulse signal can be reduced. Also, power consumption can be reduced so as to reduce energy. Efficiency of transmitting and receiving the data can be improved.  
      The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments of the present invention is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.