Abstract:
The present invention relates to a symbol acquisition apparatus and a method thereof. The method includes: determining a first boundary according to a first preamble symbol and generating a first confidence value according to signal quality of the first preamble symbol; determining a second boundary according to a second preamble symbol and generating a second confidence value according to signal quality of the second preamble symbol; and determining a symbol boundary from the first and the second boundaries according to the first and the second confidence values.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a communication system, and more specifically, to a symbol acquisition apparatus and a method thereof. 
     2. Description of the Prior Art 
     Initially an ultra wideband (UWB) communication system was applied to military affairs. In recent years, the requirements of high-speed exchange techniques have rapidly increased. Hence, for the low-cost communication products, UWB communication systems have become more popular. In general, the bandwidth of UWB communication system is larger than 20% of the value of the related central frequency. That is, assume that the central frequency of the transmitted signal is 6 GHz and the transmitted bandwidth of the communication system is more than 1.2 GHz, and the communication system can be viewed as a UWB communication system. Compared with the signal bandwidth, 1.25 MHz, utilized by CDMA system, the UWB communication system is 1000 times bandwidth of the CDMA system. 
     The information of a traditional RF transmission is carried by a continuous wave. However, the UWB communication system utilizes a very short pulse wave to transmit information. Each pulse wave continues only about 1/10 13  second. In this way, the energy provided by the UWB communication system distributes over a very broad band, rather than being clustered around a single carrier frequency. Therefore, the energy distribution on a unit bandwidth of the UWB communication system is substantially lower than the energy distribution of the related art communication technique. However, the UWB communication system lacks good ability of piercing through an obstacle. Additionally, it is easily affected by a multi-path effect and interfered by other wireless communication system. 
     Taking IEEE 802.15.3a specification as an example, there are four preamble symbols at the front end of a received packet. A related art UWB communication system perform a cross correlation on the four preamble symbols of the front end of the packet by match filter, and determines a preamble symbol boundary according to a maximum value of the calculating results. Because the above-mentioned preamble symbols are transmitted on different bands, the UWB communication system generates symbol boundaries corresponding to the preamble symbols. However, due to the UWB communication system is easily affected by the multi-path effect, the above-mentioned calculating results may contain a plurality of peek values. In this way, the system may misjudge the position of the maximum value and further generate a wrong symbol boundary. Additionally, comparing with other wireless communication systems, the energy of the UWB communication system is distributed over a broader band. Hence, when the band utilized by the UWB communication system overlaps the surrounding band utilized by other wireless devices, the signal-to-noise ratio (SNR) will be substantially reduced, further influence signal qualities and lower the correctness of the generated symbol boundaries. 
     SUMMARY OF THE INVENTION 
     One of the objectives of the present invention is therefore to provide a symbol acquisition apparatus and a related method for determining a symbol boundary, to solve the above-mentioned problem. 
     One of the objectives of the present invention is therefore to provide a symbol acquisition apparatus and a related method for determining a symbol boundary, to utilize a plurality of symbol boundaries to determine a preferred symbol boundary. 
     One of the objectives of the present invention is therefore to provide a symbol acquisition apparatus and a related method for determining a symbol boundary, to generate a plurality of confidence values to represent the correctness of the generated symbol boundaries to determine a preferred symbol boundary. 
     One of the objectives of the present invention is therefore to provide a packet detection method for determining that the UWB communication system has received a packet when the UWB communication system properly generates a symbol boundary. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an embodiment of a symbol acquisition apparatus according to the present invention. 
         FIG. 2  is a flowchart of an embodiment of the method for determining a symbol boundary symbol according to the present invention. 
         FIG. 3  is a detailed flowchart of step  208  shown in  FIG. 2 . Please refer to  FIG. 3  and  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 1 .  FIG. 1  is a block diagram of an embodiment of a symbol acquisition apparatus  100  according to the present invention. In the present embodiment, the symbol acquisition apparatus  100  is applied to a multi-band communication system. The front end of the received signal R shown in  FIG. 1  comprises a plurality of preamble symbols, and after preamble symbols has a plurality of data symbols, wherein the preamble symbols are transmitted via different bands. According to this embodiment, the symbol acquisition apparatus  100  comprises a receiving module  20  and a control module  80 . The receiving module  20  comprises a boundary generating unit  40 , a confidence value generating unit  60  and a power detector  70 . The boundary generating unit  40  sequentially estimates four symbol boundaries SB 1 , SB 2 , SB 3  and SB 4  respectively corresponding to preamble symbols P 1 , P 2 , P 3  and P 4  according to the preamble symbols of the received signal R. The confidence value generating unit  60  respectively estimates four confidence values CFD 1 , CFD 2 , CFD 3  and CFD 4  according to the received signal R to represent signal qualities of the preamble symbols P 1 , P 2 , P 3  and P 4 , respectively. In the present embodiment, the preamble symbols P 1 , P 2 , P 3 , P 4  are transmitted via different bands, so that the signal qualities of the preamble symbols P 1 , P 2 , P 3 , P 4  are substantially different, and the detected symbol boundaries SB 1 , SB 2 , SB 3 , SB 4  are not periodical. Finally, the control module  80  selects a preferred symbol boundary from the symbol boundaries SB 1 , SB 2 , SB 3  and SB 4  according to the confidence values CFD 1 , CFD 2 , CFD 3 , CFD 4  (that is, respectively represent the signal qualities of the preamble symbols P 1 , P 2 , P 3 , P 4 ) to detect the following data symbols. 
     The boundary generating unit  40  comprises a match filter  42 , a logical circuit  44 , a sliding window adder  46  and a determining unit  48 . The preamble symbol is a known signal, and the match filter  42  performs a cross correlation operation on the received signal R and the known preamble symbol P i  to generate a plurality of correlative values Corr i,1 , . . . , Corr i,n . Please refer to the following equation for the operation theory of the match filter  42 : 
     
       
         
           
             
               
                 
                   
                     Corr 
                     
                       i 
                       , 
                       n 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         t 
                         = 
                         0 
                       
                       127 
                     
                     ⁢ 
                     
                       
                         P 
                         
                           i 
                           , 
                           t 
                         
                       
                       · 
                       
                         R 
                         
                           n 
                           - 
                           t 
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     Wherein, P i,t  denotes a t th  sampled signal of an i th  preamble symbol, and each preamble symbol comprises 128 sampled points. 
     The logical circuit  44  compares each of the correlative values Corr 1 , . . . , Corr n  with a threshold value Vth_sb. In an embodiment, if the correlative value Corr is greater than the threshold value Vth_sb, the correlative value Corr keeps the same value; otherwise (if the correlative value Corr is not greater than the threshold value Vth_sb), the correlative value Corr is set to zero. Please refer to the following equation for the operation theory of the logical circuit  44 : 
     
       
         
           
             
               
                 
                   
                     Corr 
                     
                       i 
                       , 
                       n 
                     
                   
                   = 
                   
                     { 
                     
                       
                         
                           
                             0 
                             , 
                             
                               
                                 if 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                    
                                   
                                     Corr 
                                     
                                       i 
                                       , 
                                       n 
                                     
                                   
                                    
                                 
                               
                               &lt; 
                               Vth_sb 
                             
                           
                         
                       
                       
                         
                           
                             Corr 
                             
                               i 
                               , 
                               n 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     That shows the logical circuit  44  is utilized for filtering out smaller correlative values Corr. 
     The plurality of correlative values Corr 1,1 , . . . , Corr 1,n  are sequentially sent into the sliding window adder  46 . Assume that the size of the sliding window W 1  corresponding to the adder  46  is 5, the sliding window adder  46  generates an operational value CV_sb 1,1  by summing the correlative values Corr 1,1 , . . . , Corr 1,5 . In the same manner, in the next operational time point, the sliding window adder  46  generates an operational value CV_sb 1,2  by summing the correlative values Corr 1,2 , . . . , Corr 1,6 . Please refer to the following equation showing the operation theory of the sliding window adder  46 : 
     
       
         
           
             
               
                 
                   
                     CV_sb 
                     
                       i 
                       , 
                       n 
                     
                   
                   = 
                   
                     
                       ∑ 
                       
                         u 
                         = 
                         0 
                       
                       4 
                     
                     ⁢ 
                     
                       
                          
                         
                           Corr 
                           
                             i 
                             , 
                             
                               n 
                               - 
                               u 
                             
                           
                         
                          
                       
                       2 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
           
         
       
     
     Finally, the determining unit  48  selects a maximum value from the inputted operational values CV_sb, and determines the symbol boundary SB 1  corresponding to the preamble symbol P 1  according to the position of the maximum value. Determining and obtaining the maximum value of the operational value CV_sb and determining the symbol boundary is covered within the scope of the related art and is omitted here for the sake of brevity. 
     The power detector  70  is utilized for constantly detecting the power value of each sampled point of the received signal R, and for outputting a power value Pwi when the maximum value of the operational values CV_sb i,n  is generated. The boundary generating unit  40  respectively generates different symbol boundaries SB 1 , SB 2 , SB 3  and SB 4  according to the four preamble symbols in the received signal R. Therefore, the power detector  70  then sequentially outputs four corresponding power values Pw 1 , Pw 2 , Pw 3  and Pw 4 . In the present embodiment, the confidence value generating unit  60  comprises a match filter  62 , a logical circuit  64 , a sliding window adder  66  and a determining unit  68 . In an embodiment, the operations of the match filter  62 , the logical circuit  64  and the sliding window adder  66  are substantially similar to the above-mentioned components with same name, so please refer to the above-mentioned equations (1) through (3) for descriptions about the operations of the match filter  62 , the logical circuit  64  and the sliding window adder  66 . In a preferred embodiment, the threshold value Vth_cfd utilized by the logical circuit  64  can be greater than the threshold value Vth_sb utilized by the logical circuit  44 , so that the signal qualities can be more precisely expressed. In addition, the sliding window W 1  utilized by the sliding window adder  46  can be greater than the sliding window W 2  utilized by the sliding window adder  66  to gather energy of the different patterns sufficiently. In the present embodiment, assume that the size of the sliding window W 2  corresponding to the sliding window adder  66  is 3. The sliding window adder  66  generates the operational value CV_cfd i,1  by summing the correlative values Corr i,1 , . . . , Corr i,3  in the sliding window W 2 . In the same manner, in the next operational time point, the sliding window adder  66  generates an operational value CV_cfd i,2  by summing the correlative values Corr i,2 , . . . , Corr i,4 . Finally, the determining unit  68  generates the confidence value CFD 1  corresponding to the preamble symbol P 1  according to the ratios of the maximum value of the operational values CV_cfd to the power value Pw 1 . Please note that the method for generating the power values Pw 1 , Pw 2 , Pw 3  and Pw 4  is not limited to that utilized in the present embodiment; for example, the power detector  70  can directly output a power value of each sampled point of the received signal R. The determining unit  68  then respectively selects the power values Pw 1 , Pw 2 , Pw 3  and Pw 4  detected when the operational value CV_sb is the maximum value. 
     Finally, the control module  80  selects a preferred symbol boundary from the symbol boundaries SB 1 , SB 2 , SB 3  and SB 4  according to the confidence values CFD 1 , CFD 2 , CFD 3  and CFD 4 . For example, assume that the confidence values CFD 1 , CFD 2 , CFD 3  and CFD 4  respectively are 0.75, 0.5, 0.75 and 0.82, that means the symbol boundary SB 4  has the greatest reliability than other symbol boundaries (i.e., the symbol boundary SB 4  is the most reliable). Therefore, the control module  80  selects the symbol boundary SB 4  as a preferred symbol boundary SB opt . Please note that another embodiment of the present invention can generate a preferred symbol boundary SB opt  by calculating a weighted average of the symbol boundaries SB 1 , SB 2 , SB 3  and SB 4  according to the confidence values CFD 1 , CFD 2 , CFD 3  and CFD 4 . The present invention match filters  42 ,  62  and the sliding window adders  46 ,  66  belong to the scope of a related art, therefore the related description is omitted here for the sake of brevity. 
     In addition, both of the boundary generating unit  40  and the confidence value generating unit  60  comprise the match filters  42  and  62 . Therefore, in the present invention, the two match filters  42  and  62  can be combined and the outputted correlative value Corr can be sent simultaneously to the logical circuits  44  and  64 . Similarly, logical circuits  44  and  46  can be combined, and the sliding window adders  46  and  66  can be combined according to design considerations. 
     Please refer to  FIG. 2 .  FIG. 2  is a flowchart of an embodiment of the method for determining a symbol boundary symbol according to the present invention. As shown in  FIG. 2 , an initialization step must be executed when symbol boundary detection beginning (step  202 ); for example, the time T D  is reset to 0. Next, the step  204  is to update the time T D  expanded on detecting the preamble symbol and to compare the time T D  with the predetermined time T th1  (step  206 ). When the time T D  is far more than a cycle of a preamble symbol, the operation of detecting the symbol boundary of the preamble symbol is terminated and the initialization step is then restarted; otherwise, the operational values CV_sb and CV_cfd are generated according to the sampled results of the received signal R (step  208 ) and the power of the received signal R is to be detected to generate a corresponding power value (step  212 ). Next, further determine the sequentially inputted operational values CV_sb whether comprising a maximum value or not, then a symbol boundary SB is determined according to the maximum value, and a confidence value CFD is generated according to the operational values CV_cfd and a power value Pw detected when the maximum value of the operational values CV_sb is generated. Then, the time T D  is reset to 0 (step  214 ) to re-detect a symbol boundary SB and a confidence value CFD of a next preamble symbol. Please refer to the following equation for the method for generating the confidence value: 
     
       
         
           
             
               
                 
                   
                     CFDi 
                     = 
                     
                       
                         CV_cfd 
                         MAX 
                       
                       Pwi 
                     
                   
                   , 
                   
                     i 
                     = 
                     
                       1 
                       ~ 
                       4 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
           
         
       
     
     Wherein CV_cfd MAX  denotes a maximum value of the operational values CV_cfd. Finally, when the symbol boundaries SB 1 , SB 2 , SB 3 , SB 4  and the confidence values CFD 1 , CFD 2 , CFD 3 , CFD 4  (respectively corresponding to the preamble symbols P 1 , P 2 , P 3 , P 4 ) have been generated, a preferred symbol boundary SB opt  is generated according to the symbol boundaries SB 1 , SB 2 , SB 3 , SB 4  and the confidence values CFD 1 , CFD 2 , CFD 3 , CFD 4  (step  218 ). The maximum value of the operational values CV_sb is not generated immediately when the detection of the preamble symbol(s) is just starting, therefore, in a preferred embodiment, the present invention compares a predetermined time T th2  with the time T D  (step  210 ). In this way, the probability of misjudging the maximum value of the operational values CV_sb can be reduced by utilizing the predetermined time T th2  omitting a portion of operational values CV_sb. 
       FIG. 3  is a detailed flowchart of step  208  shown in  FIG. 2 . Please refer to  FIG. 3  and  FIG. 1 . The method for determining a symbol boundary according to the present invention utilizes the match filters  42  and  62  to perform a cross correlation operation on sampled results of the received signal R and generate a plurality of correlative values (step  262 ), then utilizes the logical circuit  44  to compare each of the correlative values with the threshold value Vth_sb. If a correlative value is less than the threshold value Vth_sb, the correlative value is set to 0 (step  264 ) to reduce the possibility of misjudging the symbol boundary, and then the correlative value is transmitted to the sliding window W 1 . In the end, the sliding window adder  46  sums the correlative values in the sliding window up to generate the operational value CV_sb (step  266 ). Similarly, while step  264  is executing, the logical circuit  64  compares the correlative value and the threshold value Vth_cfd. If the correlative value is less then the threshold value Vth_cfd, the correlative value is set to 0 (step  268 ) and then the correlative value is transmitted to the sliding window W 2 . Finally, the sliding window adder  66  sums the correlative value in the sliding window to generate the operational value CV_cfd (step  270 ). It should be noted that step  264  and step  268  are independent of one another. Therefore, if step  264  sets a certain correlative value to 0, the correlative value utilized in step  268  is not influenced. After steps  266  and  270  are completed, step  208  is completed and step  210  shown in  FIG. 2  is then performed. 
     In the present embodiment, the present invention selects a symbol boundary with a higher accuracy according to confidence values, or calculates another symbol boundary by a weighted averages method to detect the following data symbols. On the other hands, the threshold values Vth_cfd and CV_cfd could also be designed to be a adjustable value or a dynamic changing value. For example, when the transmitting environment become worse, the symbol acquisition apparatus  100  changes the threshold values Vth_cfd and CV_cfd dynamically for increasing the correctness of symbol boundary acquisition. In addition, when the multi-band communication system detects corresponding symbol boundaries of several preamble symbols, the multi-band communication system determines that a packet has been received. In this way, the present invention method can also be utilized for detecting a packet. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.