Patent Publication Number: US-8971462-B2

Title: Channel quality determining circuit and related method thereof

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a channel quality determining circuit and related method thereof, and more particularly, to a circuit that determines a channel quality of a signal transmitting channel according to a header of a packet and related method thereof. 
     2. Description of the Prior Art 
     General local area network (LAN) systems include a specific signal transmitting frequency band. Since some of the frequency bands are free for use, overlapped bands may be utilized by some different LAN systems for transmitting signals. For example, center frequencies of the signal transmitting frequency bands in Bluetooth (BT) system and wireless local area network (WLAN) system are substantially at 2.4 GHz. Thus, if the BT system and the WLAN system are working simultaneously, the transmitted signals may probably interfere with each other. More specifically, since a working bandwidth of a channel in the BT system is 1 MHz and there are 79 channels ranging from 2402 MHz to 2480 MHz, while the operational frequency band of the WLAN system is within a range from 2412 MHz to 2484 MHz, the channels utilized by the two communication protocols described above are substantially overlapped. In a case where the WLAN system is currently working, if the BT system also wants to transmit data via a working frequency band overlapped with the working frequency band of the WLAN system, the signal transmission quality of the WLAN system is affected. Similarly, the working WLAN system also has a severe interfere to the BT system. Thus, how to enable a plurality of different wireless transmitting systems whose operational frequency bands are overlapped with each other to quickly determine an available channel to avoid using an interfered channel is an issue to be solved in the pertinent field. 
     SUMMARY OF THE INVENTION 
     Therefore, one of the objectives of the present invention is to provide a circuit that determines a channel quality of a signal transmitting channel according to a header of a packet and related methods thereof, in order to determine an available channel quickly. 
     According to a first exemplary embodiment of the present invention, a channel quality determining circuit is provided. The channel quality determining circuit comprises a receiving circuit and a determining circuit. The receiving circuit is utilized for receiving a header of at least one packet transmitted in a signal transmitting channel. The determining circuit is coupled to the receiving circuit, for determining if a channel quality of the signal transmitting channel satisfies a predetermined quality standard according to the header of at least one packet. 
     According to a second exemplary embodiment of the present invention, a channel quality determining method is provided. The channel quality determining method comprises the step that: receiving a header of at least one packet transmitted in a signal transmitting channel; and determining if a channel quality of the signal transmitting channel satisfies a predetermined quality standard according to the header of at least one packet. 
     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 diagram illustrating an exemplary embodiment of a channel quality determining circuit according to the present invention. 
         FIG. 2  is a diagram illustrating a packet format of a Bluetooth transmitting data. 
         FIG. 3A  is a signal timing diagram of an ideal header in a Bluetooth packet according to the present invention. 
         FIG. 3B  is a timing diagram of powers corresponding to the peak and the trough of the ideal header shown in  FIG. 3 . 
         FIG. 4A  is a signal timing diagram illustrating a header in an interfered Bluetooth packet according to the present invention. 
         FIG. 4B  is a timing diagram of powers each corresponding to one half cycle of the interfered header shown in  FIG. 4 . 
         FIG. 5  is a flowchart illustrating an exemplary embodiment of a channel quality determining method according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Basically, a BT system is a frequency-hopping system, and may use an adaptive frequency-hopping (AFH) technology to avoid the interference from a signal within a constant frequency band. 
     In general, a device including a BT system may perform a software code for obtaining Bit-Error-Rate (BER) statistics. However, in order to obtain a correct channel quality analysis, the statistics should be derived from a huge number of packets in a long period of time. For example, if obtaining the statistic of each one of 79 channels in the BT system costs one second, the AFH mechanism would need 79 seconds to finish obtaining statistics of all channels. 
     Therefore, in order to accelerate the process of determining the quality of a channel, the present invention proposes a channel quality determining circuit  100 , as shown in  FIG. 1 .  FIG. 1  is a diagram illustrating an exemplary embodiment of a channel quality determining circuit  100  according to the present invention. The channel quality determining circuit  100  includes a receiving circuit  101 , a determining circuit  102  and a timer  103 . Please note that  FIG. 1  further shows a basic architecture diagram of a BT receiver for illustrating the spirit of the present invention more clearly. Therefore,  FIG. 1  further shows an analog-to-digital converter (ADC)  104 , a filter  105 , a phase detector  106 , a phase difference calculating circuit  107 , a down-sampling circuit  108 , a frequency offset compensation (FOC) circuit  109 , a slicer  110 , a frequency offset estimation circuit  111 , an access code identification circuit  112  and a synchronization circuit  113 . As the interconnection of above-mentioned components is shown in  FIG. 1 , further description is omitted here for brevity. 
     Moreover, the main function of the BT receiver shown in  FIG. 1  is to convert a received analog intermediate frequency signal Sif into a digital output signal Sd, wherein the ADC  104  is utilized for converting an analog intermediate frequency signal into a digital intermediate frequency signal, and the filter  105  is utilized for performing digital filtering upon the digital intermediate frequency signal to generate a filtered digital signal, and the phase detector  106  is utilized for performing phase detection upon the filtered digital signal, the phase difference calculating circuit  107  is utilized for calculating the difference between phases of adjacent sampling points, the access code identification circuit  112  is utilized for confirming the access code of the received signal, the synchronization circuit  113  is utilized for performing time-domain synchronization upon the received signal, the frequency offset estimation circuit  111  is utilized for estimating the offset frequency of the received signal, the FOC circuit  109  is utilized for compensating the frequency of the received signal according to the estimated offset frequency generated by the frequency offset estimation circuit  111 , and the slicer  110  is utilized for determining binary bits to generate the digital output signal Sd. The receiving circuit  101  is coupled to the FOC circuit  109  for receiving a header of at least one packet output by the FOC circuit  109 , wherein the at least one packet is transmitted via a signal transmitting channel. The determining circuit  102  is coupled to the receiving circuit  101  for determining if a channel quality of the signal transmitting channel satisfy a predetermined quality standard according to the header of the at least one packet. The timer  103  is coupled to the receiving circuit  101  and the generating circuit  102 , and used for counting a predetermined time period when the receiving circuit  101  starts operating. When the receiving circuit  101  receives the header of the at least one packet before the predetermined time period counted by the timer  103  expires, the determining circuit  102  determines if the channel quality of the signal transmitting channel satisfies the predetermined quality standard according to the header of the at least one packet. When the receiving circuit  101  fails to receive any headers from the signal transmitting channel when the predetermined time period counted by the timer  103  expires, the determining circuit  102  further determines that the channel quality of the signal transmitting channel fails to satisfy the predetermined quality standard. 
     Please refer to  FIG. 2 , which is a diagram illustrating a packet format  200  of a BT transmitting data. Generally, the packet format  200  includes an access code  201 , a header  202  and a payload  203 , wherein the access code  201  is utilized for indicating if the packet is the one that should be received by the BT system. That is, the access code  201  is for identification. The header  202  mainly carries data such as digital transmitting address, data type, etc. For example, the packet transmits images, voice or other types of digital data. The payload  203  is the actual data that is transmitted. Moreover, in one packet, the access code  201  and the header  202  are generated by shifting Gaussian Frequency Shift Keying (GFSK) modulation, while the payload  203  is generated by shifting GFSK modulation or Differential Phase Shift Keying (DPSK) modulation. When the payload  203  is transmitted at a basic rate (BR), it is generated by shifting GFSK modulation, and when the payload  203  is transmitted at an enhanced data rate (EDR), it is generated by shifting DPSK modulation. In other words, no matter whether the BT packet is transmitted at BR or EDR, the header  202  is generated by shifting GFSK modulation. 
     Since the GFSK modulation is a constant envelope modulation. Therefore, within a transmitting time T of the header  202 , the receiving circuit  101  of the channel quality determining circuit  100  of the present invention samples at a plurality of time points t 0 , . . . , tn after the phase of the received BT signal has been compensated by the FOC circuit  109  (i.e., the output of the FOC circuit  109 ), and generates a header quality (HQ) parameter according to the powers S 2 (0), . . . , S 2 (n) respectively corresponding to the obtained sampling points. The determining circuit  102  determines if the channel quality of the signal transmitting channel satisfies the predetermined quality standard according to the header quality parameter HQ of the header  202  of the packet. In this exemplary embodiment, the header quality parameter HQ may be expressed by following equation (1): 
     
       
         
           
             
               
                 
                   
                     HQ 
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                       wherein 
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                   53 
                 
               
               
                 
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     Furthermore, the transmitting time T of the header  202  of a BT packet is generally 54 us, and the signal cycle of the header  202  is generally 2 us. Thus, within the transmitting time T of the header  202 , a peak or trough occurs every 1 us (i.e., each half cycle), theoretically, wherein the peak represents bit data “1”, and the trough represents bit data “−1”. After the peak power or trough power is sampled, the power of the bit data “1” and the power of the bit data “−1” should be a constant value. Therefore, the header  202  of a BT packet includes 54 samples, theoretically. For brevity, the constant value may be normalized as 1, as shown in  FIG. 3A  and  FIG. 3B .  FIG. 3A  is a signal timing diagram of the header  202  in an ideal BT packet according to the present invention, and  FIG. 3B  is a timing diagram of powers corresponding to the peak and the trough of the header  202  shown in  FIG. 3A . The curve  302  is a voltage variation curve of the ideal header  202 , and the curve  304  is the power of the sampling points. 
     However, when a BT packet suffers from interference (e.g., the BT packet is interfered with the signal generated from the nearby WLAN system), the header  202  of the BT packet will not present a wave with a constant envelope, and the time difference between the peak and the trough is not equal to an ideal half cycle. In other words, when a BT packet suffers from interference, the signal output from the FOC circuit  109  loses Gaussian filtering characteristics, so the synchronization timing and the best sampling timing of the header  202  of the BT packet will be shifted, causing that the powers each being sampled in a half cycle are not a constant value, as shown in  FIG. 4A  and  FIG. 4B .  FIG. 4A  is a signal timing diagram illustrating a header  202  in an interfered BT packet according to the present invention.  FIG. 4B  is a timing diagram of powers each corresponding to one half cycle of the header  202  in the interfered BT packet shown in  FIG. 4A . The curve  402  is a voltage variation curve of the interfered header  202 , and the curve  404  represent powers corresponding to the sampling points. 
     As described above, in order to determine if the channel quality of the signal transmitting channel satisfies the predetermined quality standard, regarding each BT packet, the receiving circuit  101  chooses a ratio between a maximum power max n   arg (S 2 (n)) and a minimum power min n   arg (S 2 (n)) from the sampled powers to generate a header quality parameter HQ. Therefore, in an ideal situation (i.e., when the signal transmitting channel is not interfered (as shown by the situation in  FIG. 3A  and  FIG. 3B ), the maximum power max n   arg (S 2 (n)) is substantially equaled to the minimum power min n   arg (S 2 (n)), so the value of the header quality parameter HQ is roughly 0 dB. When the signal transmitting channel is interfered (as shown by the situation in  FIG. 4A  and  FIG. 4B ), the maximum power max n   arg (S 2 (n)) is not equal to the minimum power min n   arg (S 2 (n)), so the value of the header quality parameter HQ exceeds 0 dB. Therefore, the determining circuit  102  may determine if the signal transmitting channel is capable of being utilized for transmitting a BT packet according to a predetermined value (e.g. 10 dB). Moreover, when the header quality parameter HQ is not smaller than the predetermined value, the determining circuit  102  determines that the channel quality of the signal transmitting channel does not satisfy the predetermined quality standard, and therefore controls the AFH mechanism to avoid using this channel. On the contrary, when the header quality parameter HQ is smaller than the predetermined value, the determining circuit  102  determines that the channel quality of the signal transmitting channel satisfies the predetermined quality standard, and therefore transmits a BT packet via this channel. 
     In view of above description directed to the characteristics of the channel quality determining circuit  100 , one can readily know that, with a properly configured predetermined value of the determining circuit  102 , the channel quality of a signal transmitting channel basically may be determined by only using the header  202  of a BT packet. In other words, the channel quality of the 79 signal transmitting channels utilized by the BT system may all be determined by utilizing headers  202  of respective 79 BT packets. In this way, the channel quality of a signal transmitting channel can be determined quickly. Of course, it is not meant to be a limitation of the present invention that one channel quality of a signal transmitting channel is only determined by one header  202  of a BT packet. In order to improve the channel quality determination accuracy, headers  202  of a plurality of BT packets may be utilized for determining the channel quality of one signal transmitting channel, which also falls within the scope of the present invention. For example, supposing that the transmitting time of each BT packet is 625 us, the shortest time required by the present invention for determining the channel quality of all 79 signal transmitting channels utilized by the BT system is 79*625 us (about 50 ms). 
     Moreover, in some special situation (e.g., a signal transmitting channel is interfered with a strong and long lasting signal), the BT receiver may not receive any BT packets from the signal transmitting channel at all, so the timer  103  of the channel quality determining circuit  100  of the present invention is utilized for counting the predetermined time period. When the receiving circuit  101  receives a BT packet before the predetermined time period counted by the timer  103  expires, the determining circuit  102  performs the determining operation described above. When the predetermined time period counted by the timer  103  expires but the receiving circuit  101  fails to receive any BT headers from the signal transmitting channel, the determining circuit  102  further determines that the channel quality of the signal transmitting channel fails to satisfy the predetermined quality standard, and controls the AFH mechanism to switch to a next signal transmitting channel for detect the channel quality continually. Please note that implementing the timer  103  by hardware is not meant to be a limitation of the present invention. Alternatively, the timer  103  may be implemented by software. Briefly summarized, the channel quality determining circuit  100  of the present invention is capable of detecting channel qualities of the respective signal transmitting channels in the BT system quickly and accurately. 
     The operation of the channel quality determining circuit  100  in the exemplary embodiment mentioned above may be further illustrated by a channel quality determining method  500 , as shown in  FIG. 5 .  FIG. 5  is a flowchart of an exemplary embodiment of the channel quality determining method  500  according to the present invention. For clearly illustrating features of the present invention, the following description of the channel quality determining method  500  is detailed along with the description of the channel quality determining circuit  100  of the present invention; however, the disclosed exemplary embodiments are not meant to be limitations to the scope of the present invention. The channel quality determining method  500  includes following steps: 
     Step  501 : Set the number of header quality parameters HQ by 0, and start receiving a BT packet from a current signal transmitting channel and counting a predetermined time period; 
     Step  502 : Determine if a BT packet is received. If yes, go to step  503 ; otherwise, go to step  510 ; 
     Step  503 : Calculate a header quality parameter HQ of the BT packet, and adds 1 to the number of header quality parameters HQ. Go to step  504 ; 
     Step  504 : Determine if the header quality parameter HQ is smaller than a predetermined value. If yes, go to step  505 ; otherwise, go to step  512 ; 
     Step  505 : Determine that the channel quality of the current signal transmitting channel satisfies a predetermined quality standard, and record the determining result. Go to step  506 ; 
     Step  506 : Determine if the number of header quality parameters HQ is equal to a predetermined number. If yes, go to step  507 ; otherwise, go to  502 ; 
     Step  507 : Determine if the channel quality of the current signal transmitting channel satisfies the predetermined quality standard according to determining results of the predetermined number that are generated in step  505  and step  512 ; 
     Step  508 : Set the number of header quality parameters HQ by 0; 
     Step  509 : Switch to a next signal transmitting channel to start receiving a BT packet and re-counting the predetermined time period. Go to step  502 ; 
     Step  510 : Determine if the predetermined time period expires. If yes, go to step  511 ; otherwise, go to step  502 ; 
     Step  511 : Determine that the channel quality of the current signal transmitting channel fails to satisfy the predetermined quality standard. Go to step  509 ; 
     Step  512 : Determine that the channel quality of the current signal transmitting channel fails to satisfy the predetermined quality standard, and record the determining result. Go to step  506 . 
     First of all, before the BT receiver wants to receive a BT packet from a current signal transmitting channel, the receiving circuit  101  sets the number of header quality parameters HQ corresponding to the current signal transmitting channel by 0, wherein the number of header quality parameters HQ is a predetermined number. Meanwhile, the timer  103  starts to count the predetermined time period when the BT receiver starts to receive a BT packet. In step  503 , when the BT receiver receives a BT packet, the receiving circuit  101  calculates the header quality parameter HQ of the received BT packet according to equation (1) described above, and adds 1 to the number of header quality parameters HQ. When the determining circuit  102  determines that the channel quality of the current signal transmitting channel satisfies a predetermined quality standard according to the header quality parameter HQ, the determining result is recorded first (step  505 ). On the contrary, when the determining circuit  102  determines that the channel quality of the current signal transmitting channel fails to reach the predetermined quality standard, the determining result is also recorded first (step  512 ). Then, the determining circuit  102  determines if the number of header quality parameters HQ is equal to the predetermined number (step  506 ). If the number of the header quality parameters HQ fails to reach the predetermined number, the channel quality determining circuit  100  performs steps  502 - 506  repeatedly until the number of header quality parameters HQ reaches the predetermined number. 
     In order to improve the accuracy of determining the channel quality of a signal transmitting channel, the determining circuit  102  in step  507  determines if the channel quality of the current signal transmitting channel satisfies the predetermined quality standard according to determining results of the predetermined number that are generated in step  505  and step  512 . In other words, only when all the determining results of the predetermined number show that the channel quality of the current signal transmitting channel satisfies the predetermined quality standard, the determining circuit  102  determines that the channel quality of the current signal transmitting channel is really capable of being utilized for transmitting BT packets. However, this is not meant to be a limitation of the present invention. In other exemplary embodiments, the determining circuit  102  may be designed to determine that the channel quality of the current signal transmitting channel is really capable of being utilized for transmitting BT packets when more than half (or any certain number) of determining results of the predetermined number show that the channel quality of the current signal transmitting channel satisfies the predetermined quality standard. 
     After the channel quality of the current signal transmitting channel is determined, the channel quality determining circuit  100  switches to the next signal transmitting channel (step  509 ) and repeats steps  502 - 508  for determining the channel quality of the next signal transmitting channel. 
     In step  502 , when the receiving circuit  101  fails to receive a BT header, the receiving circuit  101  is still waiting for expiration of the predetermined time period. If the receiving circuit  101  fails to receive any BT headers from the current signal transmitting channel when the predetermined time period expires, the determining circuit  102  directly determines that the channel quality of the signal transmitting channel fails to satisfy the predetermined quality standard (step  511 ). The reasons are already detailed in above paragraphs. Next, the AFH mechanism of the BT receiver switches to the next signal transmitting channel to keep detecting the channel quality. On the contrary, when the receiving circuit  101  receives a BT header during the predetermined time period, the flow goes to step  503  and following steps to determine the channel quality of the current signal transmitting channel. Therefore, by performing steps  501 - 512  revealed in the channel quality determining method  500 , the channel quality determining circuit  100  may determine the channel qualities of the respective signal transmitting channels of the BT system quickly and accurately. 
     In summary, the header  202  that has not been decoded into digital data signal of the received BT packet is utilized by the present invention for determining if the channel quality of the signal transmitting channel satisfies the predetermined quality standard. Since a fewer number of BT packets are utilized in the present invention and the time required for decoding the received BT packets into digital data signals is saved, the channel quality determining circuit  100  of the present invention is capable of determining if the channel quality of the signal transmitting channel satisfies the predetermined quality standard quickly. 
     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.