Abstract:
Methods and apparatus are provided for clear channel assessment in the Wifi network. In one novel aspect, different clear channel assessment (CCA) threshold value is set for intra-BSS and inter-BSS frames during the counting down process. A CCA procedure senses the radio channel and determines if the radio channel is busy or idle during the backoff period by comparing the signal level value of detected fames with the CCA threshold value. The counting down will be suspended if the radio channel determined to be busy. If the detected frame is inter-BSS frame, the CCA threshold value is raised. If the signal level of the detected frames is lower than the inter-BSS CCA threshold for inter-BSS fames, the radio channel is considered idle. The counting down process is resumed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 from U.S. Provisional Application No. 62/036,162, entitled, “CCA IMPROVEMENT FOR SUPPORTING OPERATOR BSS” filed on Aug. 12, 2014; the subject matter of which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosed embodiments relate generally to wireless communication, and, more particularly, to CCA improvement for supporting operator BSS. 
       BACKGROUND 
       [0003]    Wifi networks have seen exponential growth across organizations in many industries. High-density wireless networks are increasingly in demand. Many new technologies have been adopted, such as multiple input multiple output (MIMO) technology. In a traditional Wifi network deployment, the deployment of Access point (AP) of a basic service set (BSS) is carefully planned to minimize BSS overlapping. With the increasing deployment of Wifi network, overlapping BSS Wifi network has become unavoidable. For example, Wifi networks managed by multiple operators operate at the same location, such as an outdoor public Wifi network overlapping with each other and highly likely to overlap with some indoor privately managed Wifi networks. In such scenarios, the multiple managed Wifi networks, each run by independent operators, would likely overlapping each other in the coverage areas. The current Wifi standard uses carrier sense multiple access with collision avoidance (CSMA/CA) to allow multiple mobile stations to access the network without collision. When there are data frames to be sent, a mobile station starts the backoff procedure and performs clear channel assessment (CCA) procedure before it can access the network. If the medium is determined to be busy at any time during the backoff stage, the backoff procedure is suspended. The wireless communications device only resumes the backoff procedure when the channel is sensed to be idle for a DIFS period or EIFS. The channel is assessed to be idle if the measured received signal level for the channel is smaller than a CCA threshold. In the current Wifi standard, the same CCA threshold applies to all sensed traffic of the channel. In a high-density OBSS deployment, it would prolong the access procedure because the transmissions from different networks are all likely to contribute to the measured signal level of the radio channel. 
         [0004]    To improve efficiency and the access procedure, improvement and enhancement are required for CCA. 
       SUMMARY 
       [0005]    Methods and apparatus are provided for clear channel assessment in a Wifi network. In one novel aspect, different clear channel assessment (CCA) threshold value is set for intra-BSS and inter-BSS frames. The wireless communications device, preparing for data transmission, starts a backoff procedure with a counting down process. A wireless communications device starts the CCA procedure sensing the radio channel and determines if the radio channel is busy or idle during the backoff period. The wireless communications device decodes the detected frames and determines whether the frame is an intra-BSS frame or an inter-BSS frame. The CCA threshold value is adjusted based on the determined frame type. In one embodiment, if the detected frame is an inter-BSS frame, the CCA threshold value is raised. The CCA procedure compares the signal level of the detected frames with the inter-BSS CCA threshold. If the signal level of the detected frames is lower than the inter-BSS CCA threshold, the radio channel is considered idle. The counting down process is resumed if the radio channel is idle for a DIFS/EIFS period. In one embodiment, the inter-BSS is determined based on the BSS color in SIG-A field. In another embodiment, the inter-BSS is determined by the MAC address. 
         [0006]    Further details and embodiments and methods are described in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The accompanying drawings, where like numerals indicate like components, illustrate embodiments of the invention. 
           [0008]      FIG. 1  illustrates exemplary wireless networks using intra-BSS and inter-BSS CCA thresholds in accordance with embodiments of the current invention. 
           [0009]      FIG. 2  illustrates an exemplary diagram of a wireless communications device setting different CCA threshold based on the type of the detected frame in accordance to embodiments of the current invention. 
           [0010]      FIG. 3  illustrates an exemplary diagram of the access process for the wireless communications device when the detected frames are intra-BSS frames in accordance with embodiments of the current invention. 
           [0011]      FIG. 4  illustrates an exemplary diagram of the access process for the wireless communications device when the detected frames are inter-BSS frames in accordance with embodiments of the current invention. 
           [0012]      FIG. 5  illustrates detailed steps for the wireless communications device to determine whether detected frames are intra-BSS or inter-BSS frames in accordance with embodiments of the current invention. 
           [0013]      FIG. 6  illustrates an exemplary flow chart for a wireless communications device to set different CCA threshold value based on the type of detected frames for the counting down procedure in accordance with embodiments of the current invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Reference will now be made in detail to some embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
         [0015]      FIG. 1  illustrates an exemplary wireless network  100  using intra-BSS and inter-BSS CCA thresholds in accordance with embodiments of the current invention. Wireless communications system  100  includes one or more wireless networks, and each of the wireless communication network has fixed base infrastructure units, such as wireless communications devices  105  and  106 . The base unit may also be referred to as an access point, an access terminal, a base station, or by other terminology used in the art. Each of the wireless communications stations  105  and  106  serves a geographic area. The geographic area served by wireless communications stations  105  and  106  overlaps. 
         [0016]    Wireless communications devices  101  and  102  in the wireless network  100  are served by base station  105 . Other wireless communications device, such as wireless communication device  103 ,  107  and  108 , are served by a different base station  106 . 
         [0017]    In one novel aspect, the wireless communications device sets different CCA threshold for intra-BSS frames and inter-BSS frames. For example, wireless communications device  101  in the overlapping BSS system receives signals from both intra-BSS stations/devices, such as wireless communications device  103 , and inter-BSS stations, such as wireless communications station  106 . The wireless communications device first uses the initial CCA threshold to detect the traffic. Once a frame is detected and decoded frame, the wireless communications device determines whether the frame is an intra-BSS frame or an inter-BSS frame based on predefined rules. Different CCA threshold is set based on the determination of intra/inter-BSS frame. The inter-BSS CCA threshold is higher than the intra-BSS threshold. 
         [0018]      FIG. 1  further shows simplified block diagrams of wireless stations  101  and base station  102  in accordance with the current invention. 
         [0019]    Base station  102  has an antenna  126 , which transmits and receives radio signals. A RF transceiver module  123 , coupled with the antenna, receives RF signals from antenna  126 , converts them to baseband signals and sends them to processor  122 . RF transceiver  123  also converts received baseband signals from processor  122 , converts them to RF signals, and sends out to antenna  126 . Processor  122  processes the received baseband signals and invokes different functional modules to perform features in base station  102 . Memory  121  stores program instructions and data  124  to control the operations of base station  102 . Base station  102  also includes a set of control modules, such as inter-BSS handler  125  that carry out functional tasks to configure, execute and communicate with the wireless communications device  101  inter-BSS CCA threshold related tasks. 
         [0020]    Wireless communications device  101  has an antenna  135 , which transmits and receives radio signals. A RF transceiver module  134 , coupled with the antenna, receives RF signals from antenna  135 , converts them to baseband signals and sends them to processor  132 . RF transceiver  134  also converts received baseband signals from processor  132 , converts them to RF signals, and sends out to antenna  135 . Processor  132  processes the received baseband signals and invokes different functional modules to perform features in mobile station  101 . Memory  131  stores program instructions and data  136  to control the operations of mobile station  101 . 
         [0021]    Wireless communications device  101  also includes a set of control modules that carry out functional tasks. A radio-channel-sense handler  191  senses a radio channel in accordance with a first predetermined rule with a first threshold. In one embodiment, the first predetermined rule is a backoff procedure as defined in the 802.11 standard. A detected frame handler  192  decodes the detected frame and determines whether it is an intra-BSS or an inter-BSS. In one embodiment, detected frame handler  192  further determines whether the inter-BSS frame is an OBSS frame. A threshold handler  193  sets different CCA threshold based on the determined frame type. In one embodiment, threshold  194  handler sets the CCA threshold to be an intra-BSS threshold or an inter-BSS threshold based on the determined frame type. In one embodiment, threshold  193  handler further determines if the CCA threshold is the OBSS threshold or the inter-BSS threshold based on the frame type. A count down handler  194  performs the modified counting down procedure based on the CCA threshold set by threshold handler  193 . 
         [0022]      FIG. 2  illustrates an exemplary diagram of a wireless communications device setting different CCA threshold based on the type of the detected frame in accordance with embodiments of the current invention. A wireless communications device preparing to send a first frame starts the backoff procedure. At step  201 , the wireless communications device detects a second frame with a signal level higher than a first CCA threshold on the radio channel during the backoff process. In one embodiment, the first CCA threshold is set to −82 dbm. At step  202 , the wireless communications device suspends the counting down counter of the backoff procedure. At step  211 , the wireless communications device decodes the detected second frame and determines whether it is an inter-BSS or intra-BSS frame. In one embodiment, the wireless communications device determines the inter/intra-BSS type by decoding an embedded identifier, for example a BSS color in a signal field (SIG-A) in the PHY header. The BSS color indicates whether the detected second frame is an inter-BSS or intra-BSS frame. In another embodiment, the wireless communications device decodes the MAC header of the detected second frame to get the embedded BSSID or the MAC address. The wireless communications device determines whether the detected second frame is an inter/intra-BSS frame based on the BSSID or the MAC address. If step  211 , the wireless communications device determines the detected second frame is an intra-BSS frame, the wireless communications device moves to step  221  and determines the CCA results as being busy. If step  211  determines the detected second frame is an inter-BSS frame, the wireless communications device moves to step  212 . At step  212 , based on the determined frame type, the wireless communications device sets the second CCA threshold value to be the inter-BSS level. In one embodiment, the second CCA threshold is −62 dbm. At step  203 , the wireless communications device compares the detected second frame&#39;s signal level with the second CCA threshold value set at step  212 . The wireless communications device at step  221  determines the channel sense results. If the detected signal level is greater or equal to the second CCA threshold value, the radio channel is determined to be not idle. If the detected signal level is smaller than the CCA threshold value, the radio channel is determined to be idle. If the channel is determined to be idle, the communications device resume the counting down process and transmits the first frame when the counting down process ends. 
         [0023]      FIG. 3  illustrates an exemplary diagram of the access process for the wireless communications device when the detected frames are intra-BSS frames in accordance with embodiments of the current invention. Two different CCA threshold levels are set for the wireless communications device in a BSS system. CCA threshold level  301  is an intra-BSS CCA threshold level. CCA threshold level  302  is an inter-BSS CCA threshold level. The inter-BSS CCA threshold level is higher the intra-BSS CCA threshold level. At step  311 , in preparing for sending a data frame  322  on the radio channel, a wireless communications device starts the backoff procedure by starting the counting down procedure. The wireless communications device senses the radio channel during the backoff period. The signal level  351  is lower than the CCA threshold level  301 . The wireless communications device continues with the counting down process. At step  312 , data frame  321  was transmitted on the radio channel. At step  313 , the wireless communications device gets the signal level measurement results of the detected data frame  321 . The measured signal level becomes signal level  352 . Signal level  352  is higher than CCA intra-BSS threshold level  301 . At step  313 , the wireless communications device suspends the count procedure and starts to decode the detected data frame. 
         [0024]    In one novel aspect, the wireless communications device determines whether the detected data frame is an intra-BSs frame or inter-BSS frame. In one embodiment, the wireless communications device decodes SIG-A in the PHY header and gets an identifier of a BSS, BSS color. In another embodiment, the wireless communications device decodes the MAC header. In one example, as shown in  FIG. 3 , the wireless communications device determines at step  314 , that the detected frame is an intra-BSS frame. The counting down procedure continues to be suspended. At step  315 , the transmission of the data frame  321  ends. Subsequently, the measured signal level drops back to signal level  353 , which is lower than the intra-BSS CCA level  301 . The wireless communications device continues sensing the radio channel for DIFS or EIFS period. At step  316 , the DIFS or EIFS period expires with the signal level lower than the CCA level  301 . The wireless communications device determines that the radio channel has been idle for the DIFS/EIFS period. At step  316 , the wireless communications device resumes the counting down procedure. At step  317 , the counting down procedure completes while the signal level stays below CCA threshold level  301 . At step  317 , the wireless communications device sends its data frame  322 . 
         [0025]      FIG. 4  illustrates an exemplary diagram of the access process for the wireless communications device when the detected frames are inter-BSS frames in accordance with embodiments of the current invention. Two different CCA threshold levels are set for wireless communications device in an overlapping BSS system. CCA threshold level  401  is an intra-BSS CCA threshold level. CCA threshold level  402  is the inter-BSS CCA threshold level. At step  411 , in preparing for sending a frame on the radio channel, the wireless communications device starts the backoff procedure and starts the counting down procedure. The wireless communications device senses the radio channel during the back off period. The signal level  451  is lower the CCA threshold level  401 . The wireless communications device continues with the counting down. At step  412 , a data frame  421  is transmitted on the radio channel. At step  413 , the wireless communications device gets the signal level measurement results for the frame  421 . The measured signal level becomes signal level  452 . Signal level  452  is higher than CCA intra-BSS threshold level  401 . At step  413 , the wireless communications device suspends the count procedure and starts to decode the frame  421 . 
         [0026]    In one novel aspect, the wireless communications device determines whether the detected frame is an intra-BSS frame, or an inter-BSS frame. In one example, at step  413 , the wireless communications device determines that the detected frame is an inter-BSS frame. The wireless communications device updates the CCA threshold level to inter-BSS CCA level  402 . If the signal level of the frame  421  is lower than the newly updated CCA threshold level, the radio channel is determined to be idle. The wireless communications device resumes the backoff procedure in accordance with a second predefined rule. In one embodiment, the second predefined rule is to resume the counting down process if the medium is determined to be idle for DIFS/EIFS period. At step  413 , the wireless communications device continues sensing the radio channel for DIFS or EIFS period. At step  414 , the DIFS or EIFS period expires with the signal level lower than the CCA level  402 . At step  414 , the wireless communications device resumes the counting down procedure. At step  416 , the counting down procedure completes. At step  416 , the wireless communications device sends its data frame  422 . At step  415 , the transmission of inter-BSS frame  421  ends. In accordance with the embodiments of the current invention, the transmission of frame  422  overlap with inter-BSS frame  421 . 
         [0027]      FIG. 5  illustrates detailed steps for the wireless communications device to determine whether detected frames are intra-BSS or inter-BSS frames in accordance with embodiments of the current invention. At step  501 , the wireless communications device detects frames on the radio channel. At step  502 , the wireless communications device decodes the detected second frames. In one embodiment, the wireless communications device decodes the MAC header to get the BSSID or the MAC address at step  511 . In another embodiment, at step  512 , the wireless communications device decodes a unique identifier in the frame header of the detected second frame. The BSS color indicates the received frames are from inter BSS or intra BSS. At step  503 , the wireless communications device determines whether the frame is an intra-BSS or inter-BSS frame based on the result from step  511  or  512 . If step  503  determines the detected frames are intra-BSS frames, the wireless communications device moves to step  521  and sets the CCA threshold value to an intra-BSS threshold. If step  503  determines the detected frames are inter-BSS frames, the wireless communications device moves to step  522  and sets the CCA threshold value to an inter-BSS threshold. The inter-BSS threshold is higher than the intra-BSS threshold. 
         [0028]      FIG. 5  further illustrates detailed frame structures to determine whether the detected second frame is an intra-BSS frame or an inter-BSS frame. In one embodiment, by decoding the MAC address  511  of the corresponding transmitting wireless communications device, the wireless communications device may obtain the BSSID of the transmitting device, and thereby, determines whether the second frame is an intra-BSS frame or an inter-BSS frame. In another embodiment, a unique ID is decoded from the frame header. In one embodiment, the frame header is the BSS color in the SIG-A field in PHY  522 . In one embodiment, globally reserved bits  523  in SIG-A field are used to indicate whether the second frame is an intra-BSS frame or an inter-BSS frame. In another embodiment, one or more bits  524  in SIG-A field are overloaded. In this embodiment, a reserved bit in the SIG-A field is used to indicate whether the one or more SIG-A bits are overloaded. If the reserved is set, the one or more bits SIG-A bits are overloaded to indicate whether the second frame is an intra-BSS frame or an inter-BSS frame. 
         [0029]      FIG. 6  illustrates an exemplary flow chart for a wireless communications device to set different CCA threshold value based on the type of detected frames for the counting down procedure in accordance with embodiments of the current invention. At step  601 , the wireless communications device senses a radio channel in accordance with a first predetermined rule with a first threshold of a sensing value, wherein the first pre-determined rule including a counting down process. At step  602 , the wireless communications device detects a frame with a receiving signal level higher than the first threshold. At step  603 , the wireless communications device suspends the counting down process. At step  604 , the wireless communications device determines whether the frame is an inter-BSS or intra BSS frame in accordance with an identifier embedded in the frames. At step  605 , the wireless communications device raises the sensing value to a second threshold if the frame is an inter-BSS frame and comparing the receiving signal level of the frame with the second threshold. At step  606 , the wireless communications device resumes the counting down process if the receiving signal level is less than the second threshold, wherein the second threshold is higher than the first threshold. At step  607 , the wireless communications device transmits the frame when the counting down process completed. 
         [0030]    Although the present invention has been described in connection with certain specific embodiments for instructional purposes, the present invention is not limited thereto. Accordingly, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the claims.