Abstract:
The invention discloses a wireless communication system for calculating time of flight. The system transmits and receives a plurality of packets every a plurality of delay times. Thereafter, the wireless communication system calculates a plurality of reference times according to the delay times and processing times and then averages the reference times to obtain the time of flight. Thereby, the time of flight can be calculated more accurately.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a wireless communication system, and more particularly relates to a wireless communication system for calculating time of flight (TOF). 
         [0003]    2. Description of the Prior Art 
         [0004]    Recently, the development of the wireless communication positioning has been growing rapidly, and the wireless communication positioning has been widely applied to many applications. For example, the positioning can be applied to the navigation system, the information management of where users locate, the mobile emergency positioning (e.g. related positioning rules of E-911 legislation for phones in America), the logistics management, and the car dispatch. 
         [0005]    Time of arrival (TOA) and time difference of arrival (TDOA) are wireless positioning algorithms relative to time, and they can be applied to different kinds of wireless communication positioning, such as the global positioning system (GPS), the cell phone positioning, the ultra wide band (UWB), the ultrasonic positioning, and the like. 
         [0006]    Time of flight plays a key role of TOA and TDOA and has a great effect on the accuracy of the positioning. A general method for calculating time of flight does not takes account of the influence of the hardware structure, the interference in the wireless communication environment, and the load of the hardware system, such that the calculated result will not be accurate. 
         [0007]    Therefore, a scope of the invention is to provide a wireless communication system for accurately calculating time of flight to solve the aforesaid problems. 
       SUMMARY OF THE INVENTION 
       [0008]    A scope of the invention is to provide a wireless communication system for calculating time of flight. 
         [0009]    According to a preferred embodiment, the wireless communication system of the invention comprises a first communication module and a second communication module. The first communication module spends a first processing time transmitting and receiving each packet. And, the second communication module spends a second processing time transmitting and receiving each packet. 
         [0010]    In this embodiment, the first communication module transmits a first pilot to the second communication module. After transmitting the first pilot, the first communication module sequentially transmits N first packets each with a first delay time, wherein N is a natural number larger than 1. 
         [0011]    After receiving the first pilot, the second communication module sequentially receives the N first packets each with a second delay time. Afterward, the second communication module transmits the second pilot to the first communication module. After transmitting the second pilot, the second communication module sequentially transmits N second packets each with a third delay time. Each of N first packets is respectively corresponds to one of the N second packets. 
         [0012]    After receiving the second pilot, the first communication module sequentially receives the N second packets each with a fourth delay time. Afterward, according to N first processing times, N second processing times, N first delay times, N second delay times, N third delay times, and N fourth delay times corresponding to the N first packets and the N second packets, the first communication module calculates N reference times and averages the N reference times to obtain a time of flight (TOF). 
         [0013]    Therefore, the wireless communication system of the invention sequentially receives and transmits multiple packets every multiple delay times. According to the delay times and the processing times, the wireless communication system of the invention calculates multiple reference times and then averages the reference times to obtain the TOF. Accordingly, it can be more accurately to calculate the TOF. 
         [0014]    The advantage and spirit of the invention may be understood by the following recitations together with the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE APPENDED DRAWINGS 
         [0015]      FIG. 1  is a functional block diagram illustrating the wireless communication system according to a preferred embodiment of the invention. 
           [0016]      FIG. 2A  and  FIG. 2B  are schematic diagrams illustrating the packet transmission of the wireless communication system in  FIG. 1 . 
           [0017]      FIG. 3  is a schematic diagram illustrating the packet transmission according to another preferred embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Please refer to  FIG. 1 .  FIG. 1  is a functional block diagram illustrating the wireless communication system  1  according to a preferred embodiment of the invention. As shown in  FIG. 1 , the wireless communication system  1  comprises a first communication module  10  and a second communication module  12 . The first communication module  10  comprises a first baseband circuit  100 , a first radio frequency circuit  102 , and a first antenna  104 . The second communication module  12  comprises a second baseband circuit  120 , a second radio frequency circuit  122 , and a second antenna  124 . In this embodiment, the time of the first communication module  10  is asynchronous with the time of the second communication module  12 . 
         [0019]    The first communication module  10  spends a first processing time transmitting and receiving each packet. The first processing time comprises a first transmitting time, a first receiving time, and a first influence time, wherein the first communication module  10  spends the first transmitting time transmitting each packet; the first communication module  10  spends the first receiving time receiving each packet; and the first communication module  10  spends the first influence time on wireless environment and system load. The second communication module  12  spends a second processing time transmitting and receiving each packet. The second processing time comprises a second transmitting time, a second receiving time, and a second influence time, wherein the second communication module  12  spends the second transmitting time transmitting each packet; the second communication module  12  spends the second receiving time receiving each packet; and the second communication module  12  spends the second influence time on the wireless environment and the system load. The first processing time and the second processing time are described in the following equation 1 and equation 2: 
         [0000]        A (Process)= TxA (Process)+ RxA (Process)+Φ xA ; and  Equation 1: 
         [0000]        B (Process)= TxB (Process)+ RxB (Process)+Φ xB   Equation 2: 
         [0020]    In the equation 1 and equation 2, A(Process) represents the first processing time, TxA(Process) represents the first transmitting time, RxA(Process) represents the first receiving time, ΦxA represents the first influence time, B(Process) represents the second processing time, TxB(Proces&#39;s) represents the second transmitting time, RxB(Process) represents the second receiving time, and ΦxB represents the second influence time. 
         [0021]    Please refer to  FIG. 2A  and  FIG. 2B .  FIG. 2A  and  FIG. 2B  are schematic diagrams illustrating the packet transmission of the wireless communication system  1  in  FIG. 1 . In this embodiment, as shown in  FIG. 2A , the first communication module  10  transmits the first pilot PLa to the second communication module  12 . After transmitting the first pilot PLa, the first communication module  10  sequentially transmits three first packets Pa 1 -Pa 3  each with a first delay time Tta 1 -Tta 3 . After receiving the first pilot PLa, the second communication module  12  sequentially receives the first packets Pa 1 -Pa 3  each with a second delay time Trb 1 -Trb 3 . Afterward, as shown in  FIG. 2B , the second communication module  12  transmits the second pilot PLb to the first communication module  10 . After transmitting the second pilot PLb, the second communication module  12 , sequentially transmits three second packets Pb 1 -Pb 3  each with a second delay time Ttb 1 -Ttb 3 . After receiving the second pilot PLb, the first communication module  10  sequentially receives the second packets Pb 1 -Pb 3  each with a fourth delay time Tra 1 -Tra 3 . It should be noticed that each first packet Pa 1 -Pa 3  respectively corresponds to one of the second packets Pb 1 -Pb 3 . 
         [0022]    According to the first processing times A(Process), the second processing times B(Process), the first delay times Tta 1 -Tta 3 , the second delay times Trb 1 -Trb 3 , the third delay times Ttb 1 -Ttb 3 , and the fourth delay times Tra 1 -Tra 3  corresponding to the first packets Pa 1 -Pa 3  and the second packets Pb 1 -Pb 3 , the first communication module  10  calculates three reference times and then averages the three reference times to obtain a time of flight (TOF). It should be noticed that the number of the first and second packets can be adjusted according to practical applications. 
         [0023]    The reference time can be calculated by the following equation 3: 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 1 
                               
                               + 
                               
                                 
                                   A 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   A 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 3 
                               
                               + 
                               
                                 
                                   A 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               3 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   3 
                 
               
             
           
         
       
     
         [0024]    In the equation 3, TxA_ 1 -TxA_ 3  respectively represents the first time point when the first communication module  10  transmits the first packet Pa 1 -Pa 3 , RxA_ 1 -RxA_ 3  respectively represents the second time point when the first communication  10  receives the second packet Pb 1 -Pb 3 , and ΔT_ 1 -ΔT_ 3  represents the reference time. 
         [0025]    In this embodiment, the relation of the first delay time, the second delay time, and the second influence time is listed in the following equation 4: 
         [0000]        Trb−Tta=RxB (Process)− TxA (Process)+Φ xB   Equation 4: 
         [0026]    In the equation 4, Tta represents the first delay time, and Trb represents the second delay time. 
         [0027]    Similarly, the relation of the third delay time, the fourth delay time, and the first influence time is listed in the following equation 5: 
         [0000]        Tra−Ttb=RxA (Process)− TxB (Process)+Φ xA   Equation 5: 
         [0028]    In the equation 5, Ttb represents the third delay time, and Tra represents the fourth delay time. 
         [0029]    In this embodiment, assuming that the first delay time Tta is equal to the third delay time Ttb, the equation 6 could be obtained by subtracting the equation 5 from the equation 4 first and substituting with the equation 1 and the equation 2 later, listed as follows: 
         [0000]        Trb−Tra=B (Process)− A (Process).  Equation 6: 
         [0030]    The equation 6 is substituted into the equation 3, so as to obtain the following equation 7: 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 ΔT_ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 1 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 1 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 ΔT_ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 2 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 2 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 ΔT_ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   B 
                                    
                                   
                                     ( 
                                     Process 
                                     ) 
                                   
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 3 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 3 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               3 
                             
                           
                         
                       
                     
                      
                     
                         
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   7 
                 
               
             
           
         
       
     
         [0031]    In this embodiment, the second processing time B(Process) is estimated by a time difference between a time point after the second communication module  12  receives the first packet Pa 1 -Pa 3  and a time point before the second communication module  12  transmits the corresponding second packet Pb 1 -Pb 3 . In such a way, the equation 7 is further transformed into the following equation 8: 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 β_ 
                                  
                                 1 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 1 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 1 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 β_ 
                                  
                                 2 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 2 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 2 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 TxA_ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 T_ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 β_ 
                                  
                                 3 
                               
                               + 
                               
                                 Tra_ 
                                  
                                 3 
                               
                               - 
                               
                                 Trb_ 
                                  
                                 3 
                               
                             
                             = 
                             
                               RxA_ 
                                
                               3 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   8 
                 
               
             
           
         
       
     
         [0032]    In the equation 8, β_ 1 -β_ 3  represents the estimated time difference. 
         [0033]    Afterward, substituting the first time point TxA_ 1 -TxA_ 3  generated while the first communication module  10  transmits the first packet Pa 1 -Pa 3 , the second time point RxA_ 1 -RxA_ 3  generated while the first communication module  10  receives the second packets Pb 1 -Pb 3 , the second delay time Trb_ 1 -Trb_ 3 , the fourth delay time Tra_ 1 -Tra_ 3 , and the estimated time difference β_ 1 -β_ 3  into the equation 8, such that the reference time ΔT_ 1 -ΔT_ 3  is obtained. Further, average the reference times ΔT_ 1 -ΔT_ 3  to obtain the time of flight. 
         [0034]    Because the invention takes account of the influence of the hardware structure, the disturbance in the wireless environment, and the load of the hardware system, the calculated time of flight will be more accurate than the prior art. 
         [0035]    Please refer to  FIG. 3 .  FIG. 3  is a schematic diagram illustrating the packet transmission according to another preferred embodiment of the invention. In this embodiment, the time of the first communication module  10  of the wireless communication system  1  is synchronous with the time of the second communication module  12 . 
         [0036]    The first communication module  10  spends a third processing time transmitting each packet. The third processing time comprises a transmitting time for transmitting each packet. The second communication module  12  spends a fourth processing time receiving each packet. The fourth processing time comprises a receiving time for receiving each packet, and an influence time on the wireless environment and the system load. 
         [0037]    As shown in  FIG. 3 , the first communication module  10  sequentially transmits three packets P 1 -P 3  each with a fifth delay time Tta′ 1 -Tta′ 3 . The second communication module  12  sequentially receives packets P 1 -P 3  each with a sixth delay time Trb′ 1 -Trb′ 3 . According to the third processing time, the fourth processing time, the fifth delay time Tta′ 1 -Tta′ 3 , and the sixth delay time Trb′ 1 -Trb′ 3  corresponding to the packets P 1 -P 3 , the first communication module  10  calculates three reference times and then averages the reference times to obtain a time of flight. It should be noticed that the number of packets can be adjusted according to practical applications. 
         [0038]    The reference time is calculated by the following equation 9: 
         [0000]    
       
         
           
             
               
                 
                   
                     
 
                   
                    
                   
                     { 
                     
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 
                                   
                                     RxB 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 
                                   
                                     RxB 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 
                                   
                                     RxB 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               3. 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   9 
                 
               
             
           
         
       
     
         [0039]    In the equation 9, TxA′_-TXA′_ 3  respectively represents the first time point when the first communication module  10  transmits the packet P 1 -P 3 , RxB′_ 1 -RxB′_ 3  respectively represents the second time point when the second communication module  12  receives the packet P 1 -P 3 , ΔT′_ 1 -ΔT′_ 3  represents the reference time, TxA(Process)′_ 1 -TxA(Process)′_ 3  represents the transmitting time corresponding to the packet P 1 -P 3 , and RxB(Process)′_ 1 -RxB(Process)′_ 3  represents the receiving time corresponding to the packet P 1 -P 3 . 
         [0040]    In this embodiment, the relation of the fifth delay time, the six delay time, and the influence time is listed in the following equation 10: 
         [0000]        Trb′−Tta′=RxB (Process)′− TxA (Process)′+Φ xB′.   Equation 10: 
         [0041]    In the equation 10, Tta′ represents the fifth delay time, Trb′ represents the sixth delay time, and ΦxB′ represents the influence time. 
         [0042]    The equation 10 is substituted into the equation 9, and the equation 11 is then obtained as follows: 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     1 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     1 
                                   
                                 
                                 ) 
                               
                               - 
                               
                                 Φ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   xB 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     2 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     2 
                                   
                                 
                                 ) 
                               
                               - 
                               
                                 Φ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   xB 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 2 
                                  
                                 
                                   
                                     TxA 
                                      
                                     
                                       ( 
                                       Process 
                                       ) 
                                     
                                   
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     3 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     3 
                                   
                                 
                                 ) 
                               
                               - 
                               
                                 Φ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   xB 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               3 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   11 
                 
               
             
           
         
       
     
         [0043]    When the transmitting time TxA(Process)′_ 1 -TxA(Process)′_ 3  and the influence time ΦxB′_ 1 -ΦxB′_ 3  are equal to zero, the equation 11 is further transformed into the following equation 12: 
         [0000]    
       
         
           
             
               
                 
                   { 
                   
                     
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 1 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     1 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     1 
                                   
                                 
                                 ) 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               1 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 2 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     2 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     2 
                                   
                                 
                                 ) 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               2 
                             
                           
                         
                       
                       
                         
                           
                             
                               
                                 
                                   TxA 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 Δ 
                                  
                                 
                                     
                                 
                                  
                                 
                                   T 
                                   ′ 
                                 
                                  
                                 _ 
                                  
                                 3 
                               
                               + 
                               
                                 ( 
                                 
                                   
                                     
                                       Trb 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     3 
                                   
                                   - 
                                   
                                     
                                       Tta 
                                       ′ 
                                     
                                      
                                     _ 
                                      
                                     3 
                                   
                                 
                                 ) 
                               
                             
                             = 
                             
                               
                                 RxB 
                                 ′ 
                               
                                
                               _ 
                                
                               3 
                             
                           
                         
                       
                     
                     . 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   12 
                 
               
             
           
         
       
     
         [0044]    Afterward, substitute the first time point TxA′_-TXA′_ 3  generated while the first communication module  10  transmits the packet P 1 -P 3 , the second time point RxB′_ 1 -RxB′_ 3  generated while the second communication module  12  receives the packet P 1 -P 3 , the fifth delay time Tta′_ 1 -Tta′_ 3 , and the sixth delay time Trb′_ 1 -Trb′_ 3  into the equation 11, such that the reference time ΔT′_ 1 -ΔT′_ 3  is obtained. Finally, the reference times ΔT′_ 1 -ΔT′_ 3  are averaged to obtain the time of flight. 
         [0045]    Compared to the prior art, the wireless communication system of the invention sequentially receives and transmits multiple packets with multiple delay times. According to the delay times and the processing times, the wireless communication system of the invention calculates multiple reference times and then averages the reference times to obtain the TOF. Alternatively, because the invention takes account of the influence of the hardware structure, the disturbance in the wireless environment, and the load of the hardware system, the calculated time of flight will be more accurate than the prior art. Additionally, no matter whether the time of the first communication module is, synchronous with the time of the second communication module, the invention can be applied to both. 
         [0046]    With the example and explanations above, the features and spirits of the invention will be hopefully well described. Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teaching of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.