Patent Publication Number: US-2007099677-A1

Title: Data transfer method and transceiver thereof

Description:
BACKGROUND  
      The invention relates in general to wireless communication, and in particular, to a data transfer method and transceiver thereof.  
      IEEE 802.11 Wireless Local Area Network (WLAN) deploys Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme as the data, access method. In CSMA/CA scheme the transmission media is shared by every station including every wireless client and AP in the network. Any station wishing to transmit must detect the condition of the radio channel in advance. The station may transmit data if the radio channel is free. If the channel is already occupied by a data transmission, the station has to wait until the channel is released again. The station employs a timer, referred as network allocation vector (NAV), to count the remaining time of the ongoing data transmission, such that it can attempt to send a frame after NAV is zero. The duration of channel occupation is referred as “Busy Medium” period.  
      To prevent two stations sending frames simultaneously, CSMA/CA scheme employs a random backoff counter at each station to further delay a random period so that data collision of the two stations is minimized. The station can attempt to transmit a frame upon elapse of the random backoff period.  
       FIG. 1  illustrates a system diagram of a wireless network, comprising first station STA 1 , second station STA 2 , third station STA 3 , reception coverage  10 , reception coverage  12 , and reception coverage  14 ,.  
      Referring to  FIG. 1 , if reception coverage  10  of the first station STA 1  includes the second station STA 2  but not the third station STA 3 , a problem known as “hidden node” may occur when both stations STA 1  and STA 3  transmit data to station STA 2  simultaneously, and station STA 2  may receive corrupted data.  
      On the other hand, if the reception coverage  10  of the first station STA 1  includes both stations STA 2  and STA 3  when station STA 1  only wishes to communicate with station STA 2 , the first station STA 1  may detect the unwanted data from station STA 3 , and trigger the CSMA/CA mechanism, resulting in power waste for receiving the corrupted data, further delay due to network allocation vector counter and random backoff counter, and performance degradation.  
      Thus a data transfer method and transceiver circuit for wireless communication is proposed.  
     SUMMARY  
      The present invention is directed to a data transfer method and transceiver circuit for wireless communication.  
      According to one embodiment of the invention, the transceiver comprises an antenna, and a receiving module. The antenna receives first data. The receiving module is coupled to the antenna, receives the first data, compares a source address of the first data with a desired address, determines first signal strength of the first data if the source address matches the desired address, and adjusts receiver sensitivity of the transceiver based on the first signal strength.  
      In accordance to another embodiment of the invention, a data transfer method comprises receiving first data, comparing a source address of the first data with a desired address, determining first signal strength of the first data if the source address matches the desired address, and adjusting receiver sensitivity of the transceiver based on the first signal strength. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more fully understood from the detailed description, given hereinbelow, and the accompanying drawings. The drawings and description are provided for purposes of illustration only and, thus, are not intended to be limiting of the present invention.  
       FIG. 1  illustrates a system diagram of a wireless network.  
       FIG. 2  is a block diagram of an exemplary transceiver in the invention.  
       FIG. 3  is a flowchart of an exemplary data transfer method of the invention, incorporating the transceiver in  FIG. 2 .  
       FIG. 4  plots Signal-to-Noise Ratio (SNR) against Packet Error Rate (PER) of data, according to an embodiment incorporating the wireless system in  FIG. 2  and the data transfer method in  FIG. 3 .  
       FIG. 5  plots Signal-to-Noise Ratio (SNR) against Packet Error Rate (PER) of data, according to an embodiment incorporating the wireless system in  FIG. 2  and the data transfer method in  FIG. 3 . 
    
    
     DETAILED DESCRIPTION  
      For simplicity, while this disclosure of the invention is incorporated into an IEEE 802.11 Wireless Local Area Network (WLAN) under Infrastructure Mode, the circuitry and method disclosed may also find application in Adhoc Mode or other systems, and those skilled in the art may make modifications where appropriate based on the principle of the invention.  
       FIG. 2  is a block diagram of an exemplary transceiver in the invention, comprising antenna  200 , amplifier  202 , data detection module  204 , and receiving module  206 . Antenna  200  is coupled to amplifier  202 , subsequently to data detection module  204  and receiving module  206 .  
      Antenna  200  receives first data Dr from remote station  22  via a transmission channel, then delivers to amplifier  202 . Remote station  22  may be an access point. Amplifier  202  amplifies first data Dr by amplifier gain G, and in turn passes to receiving module  206  and data detection module  204 .  
      Data detection module  204  detects first data Dr through carrier sense (CS) or energy detection (ED), and enables receiving module  206  upon detection. Data detection module  204  may be an energy detector comparing channel energy in the transmission channel against an energy detection threshold Eth, such that the presence of first data Dr can be identified if the channel energy exceeds energy detection threshold Eth. Energy detection threshold Eth is adjustable to a required receiver sensitivity of receiver  20 .  
      Receiving module  206  receives and demodulates first data Dr to the first data Dr, with a data frame format compliant with Media Access Control (MAC) layer in IEEE  802 . 11  specification, in which a source address of remote station  22  is specified. Receiving module  206  then compares the source address of the first data with a desired address, determines first signal strength of the first data if the source address matches the desired address, and adjusts receiver sensitivity of the transceiver to a target sensitivity based on the first signal strength.  
      The desired address is the address of remote station  22 . The signal strength may be measured in Received Signal Strength Indicator (RSSI), a measure of received signal strength at antenna  200 .  
      Receiving module  206  may include a lookup table  2060  (LUT) containing lookup signal strength and corresponding lookup sensitivity. The target sensitivity is decided through looking up the lookup signal strength of lookup table  2060  with the first signal strength, and find the corresponding lookup sensitivity as the target strength.  
      Data detection module  204  sets energy detection threshold Eth that the signal strength of data Dr must meet to achieve target packet error rate Pe. If the signal power is lower than energy detection threshold Eth, the minimum achievable packet error rate Pr will be increased to exceed packet error rate Pe. The receiver sensitivity may be adjusted by altering energy detection threshold Eth of the data detection circuit, or by altering reception gain G of amplifier  202 .  
       FIG. 3  is a flowchart of an exemplary data transfer method of the invention, incorporating the transceiver in  FIG. 2 .  
      Upon initialization in step S 300 , data transfer method  40  determines if transceiver  20  wishes to transmit data Dt to remote station  22  in step S 302 . Since in CSMA/CA transmission scheme, transceiver  20  detects requests access to a transmission channel prior to data reception.  
      In step S 304 , the receiver sensitivity of transceiver  20  is maximized prior to data transmission to remote station  22 , such that transceiver  20  can detect Busy Medium in the transmission channel, if any, is present before transmitting data Dt in step S 306 .  
      Next in step S 308 , data detection module  204  determines if antenna  200  receives data Dr from the transmission channel. In absence of data Dr data transfer method  40  loops back to step S 302 , so that transceiver  20  may transmit data Dt to request transmission channel again. If data Dr is received at antenna  200 , passed through amplifier  202  to receiving module  206  to continue step S 310 .  
      In step S 310 , receiving module  206  retrieves the source address from data Dr, and compares the source address with a desired address corresponding to remote station  22 . Match of the source address and the desired address suggests transceiver  20  picking up correct data Dr from remote station  22 , thus data transfer method  40  continues at step S 312 , otherwise it routes back to step S 302 .  
      In step S 312 , since transceiver  20  has obtained the correct data Dr, receiving module  206  determines signal strength Sr (first signal strength) of data Dr, thereby adjusting receiver sensitivity of transceiver  20 .  
      In step S 314 , receiving module  206  decides a target sensitivity corresponding to signal strength Sr based on lookup table  2060 . If the target sensitivity exceeds the receiver sensitivity, data transfer method  40  moves to step S 316 , if the target sensitivity is less than the receiver sensitivity, data transfer method  40  continues at step S 318 , the target sensitivity is just the receiver sensitivity, data transfer method  40  loops back to step S 302 .  
      In step S 316 , the receiver sensitivity is increased, such that data Dr from remote station  22  can be detected at a lower packet error rate. The receiver sensitivity may be increased via rising energy detection threshold Eth, or lowering amplifier gain G of amplifier  202 . Upon completion of step S 316 , data transfer method  40  circles back to step S 302 , such that transceiver  20  receives subsequent data Dr with higher receiver sensitivity.  
      In step S 318 , the receiver sensitivity is decreased,  400402 so that data beyond remote station  22  cannot be detected. The receiver sensitivity may be decreased via lowering energy detection threshold Eth, or increasing amplifier gain G of amplifier  202 .  
       FIG. 4  plots Signal-to-Noise Ratio (SNR) against Packet Error Rate (PER) for the first data Dr in transceiver  20 , according to an embodiment incorporating the wireless system in  FIG. 2  and the data transfer method in  FIG. 3 .  FIG. 4  shows an exemplary method of receiver sensitivity adjustment by altering energy detection threshold Eth, and comprises window  400 , window  402 , window  404 , threshold  410 , threshold  412 , threshold  414 , threshold  416 , and signal  420 .  
      Energy detection threshold window  402  represents a threshold range adjustable by energy detection threshold Eth, such that only signal strength Sr of received data Dr exceeding which can be detected by data detection module  204 . As energy detection threshold Eth approaches threshold  410  direction (leftwards), signal strength Sr has to be stronger to be recognized in data detection module  204 , i.e. data Dr with weaker signal strength Sr are ignored, less data Dr are detectable in transceiver  20 , and lower receiver sensitivity is resulted in. Accordingly, if energy detection threshold Eth is moved towards threshold  414  direction, more data Dr become detectable in transceiver  20 , leading to higher receiver sensitivity.  
      Upon initialization in step S 300 , energy detection threshold Eth is set at threshold  412  and amplifier gain G is fixed, method  40  determines transfer mode of transceiver  20  in step S 302 , maximizes the receiver sensitivity by altering energy detection threshold Eth to threshold  414 , such that more data Dr become detectable in step S 304 , transmitting data Dt in step S 306 , determines if antenna  200  receives data Dr in step S 308 , compares the source address with the desired address in step S 310 , detects signal strength Sr at threshold  416 , determines threshold  416  (signal strength Sr) is higher than threshold  414  (energy detection threshold Eth) in step S 314 , adjusts the receiver sensitivity to lower by altering energy detection threshold Eth towards threshold  416  in step S 318 , then loops back to transfer mode detection in step S 302 .  
       FIG. 5  plots Signal-to-Noise Ratio (SNR) against Packet Error Rate (PER) for the first data Dr in transceiver  20 , according to an embodiment incorporating the wireless system in  FIG. 2  and the data transfer method in  FIG. 3 .  FIG. 5  shows an effect of adjusting receiver sensitivity by altering amplifier gain G, and comprises window  500 , window  502 , window  504 , threshold  510 , threshold  512 , threshold  514 , gain  520 , gain  522 , gain  524 , signal strength  530 , signal strength  532 , signal strength  534 , and achievable PER  540 .  
      Referring to  FIG. 5 , gain  520  is lower than gain  522 , subsequently lower than gain  524 . Data Dr has a achievable PER  540 , and Signal strength Sr has to exceed energy detection threshold Eth to be detected by data detection module  204 . As amplifier gain G approaches gain  520  direction (rightwards), signal strength moves towards energy detection threshold Eth, i.e. data Dr become weaker, less data Dr are detectable in transceiver  20 , and lower receiver sensitivity is resulted in. Accordingly, if amplifier gain G is moved towards threshold  524  direction, more data Dr become detectable in transceiver  20 , leading to higher receiver sensitivity.  
      Upon initialization in step S 300 , energy detection threshold Eth is set at threshold  512  and amplifier gain G is at gain  522 , method  40  determines transfer mode of transceiver  20  in step S 302 , maximizes the receiver sensitivity by altering amplifier gain G to gain  524 , such that more data Dr become detectable in step S 304 , transmitting data Dt in step S 306 , determines if antenna  200  receives data Dr in step S 308 , compares the source address with the desired address in step S 310 , detects signal strength  534  at gain  524 , determines signal strength  534  (gain  524 ) is stronger than threshold  512  (energy detection threshold Eth) in step S 314 , adjusts the receiver sensitivity to lower by altering amplifier gain G towards gain  520  in step S 318 , then loops back to transfer mode detection in step S 302 .  
      In yet another embodiment of the invention incorporating the wireless system in  FIG. 2 , the data transfer method in  FIG. 3 , the receiver sensitivity adjustment in  FIGS. 4 and 5 . Method  40  sets Energy detection threshold Eth at threshold  512  and amplifier gain G at gain  522  in step S 300 , determines transfer mode of transceiver  20  in step S 302 , maximizes the receiver sensitivity by altering amplifier gain G to gain  524  and energy detection threshold Eth to threshold  414 , such that more data Dr become detectable in step S 304 , transmitting data Dt in step S 306 , determines if antenna  200  receives data Dr in step S 308 , compares the source address with the desired address in step S 310 , detects signal strength Sr, determines threshold  616  (signal strength Sr) is higher than threshold  512  (energy detection threshold Eth) in step S 314 , adjusts the receiver sensitivity to lower by altering amplifier gain G towards gain  520  and energy detection threshold Eth towards threshold  416  in step S 318 , then loops back to transfer mode detection in step S 302 .  
      While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.