Abstract:
In accordance with the invention, a method and system relating to the rate recovery mechanism in a Wireless Local Area Network (WLAN) and Bluetooth coexistence system is provided.

Description:
BACKGROUND 
       [0001]    In today&#39;s world, the use of Wireless Personal Area Networks (WPANs) is becoming increasingly popular because of the flexibility and convenience in connectivity they provide. WPAN systems, such as those based on Bluetooth technology, provide wireless connectivity to peripheral devices and/or mobile terminals by providing short distance wireless links that allow connectivity within a specific range; for instance a 10-meter range. In contrast to WPAN systems, Wireless Local Area Networks (WLANs) provide connectivity to devices that are located within a slightly larger geographical area, such as the area covered by a building or a campus, for example. WLAN systems are based on IEEE 802.11 standard specifications, typically operating within a 100-meter range, and are generally utilized to supplement the communication capacity provided by traditional wired local area networks (LANs) installed in the same geographical area as the WLAN system. 
         [0002]    In some instances, WLAN systems may be operated in conjunction with WPAN systems to provide users with an enhanced overall functionality. However, collocation interferences arise in such instances, because of the proximity of the two transceivers. In such cases, signals being transmitted from one device typically cause the other device&#39;s receiver to saturate, thus rendering it desensitized. 
         [0003]    If both the devices (Bluetooth device and WLAN device) operate in the same unlicensed ISM band at 2.4 GHz, both the devices transmit and receive at the time and frequency thus jeopardizing effective communication at overlapping frequencies. In such instances, transmission typically has to be scheduled in such a way as to avoid simultaneous transmission. This transmission scheduling is typically performed by employing techniques known as Packet Traffic Arbitration (PTA) techniques. The PTA algorithm prevents WLAN from transmitting at certain points in time when the Bluetooth device needs to receive or transmit. For example, if a person is making a phone call through a Bluetooth headset and at the same time is uploading/downloading emails using WLAN, the PTA algorithm prevents the WLAN from transmitting when the Bluetooth needs to receive or transmit so that a clear voice is transmitted through the Bluetooth headset. 
         [0004]    An Access Point (AP) is a device that connects wireless communication devices together to form a wireless network. In standard communication protocols, Access Points send frames to the Stations (STA) and the STA send an Acknowledgement (ACK) upon successful reception of a frame. If PTA is used for WLAN Bluetooth coexistence, Bluetooth can suppress transmissions of the collocated WLAN device. The possible frames that could be suppressed are ACK frames. Typically, these frames are sent as a response to a frame from the AP. If the ACK frames are suppressed, the access point could wrongly conclude that its frame got corrupted due to a noisy channel, or weak signal, and retransmit the same frame at a lower data transmission rate. Frames with lower data rate have a higher probability of corruption by the collocated Bluetooth, making it even more likely that an AP would further reduce its data transmission rate. This ends in a spiral until the access point has reached the lowest data transmission rate. This behavior impacts the throughput of the WLAN system tremendously. 
         [0005]    A rate recovery mechanism is a means to make an AP start with higher data transmission rates once it reduces its data transmission rate because of the reception of corrupted set of frames. The rate recovery mechanism is explained as follows: When a Wireless Local Area Network Station (WLAN STA) receiving frames at a predetermined data transmission rate detects a certain number of frames transmitted from the AP at a reduced data transmission rate, the WLAN STA transmits a de-authentication frame to the AP. Due to the de-authentication frame, the AP discards information about the WLAN STA (e.g., the data transmission rate of the WLAN STA). Following the sending of the de-authentication frame, the WLAN STA resends an authentication frame and the AP starts transmitting at its highest data transmission rate. 
         [0006]    If, after reset of the data transmission rate in the AP, the initial frame is not acknowledged because of low signal strength, some APs will send the next frame at the lowest possible data transmission rate, causing the rate fallback to occur again. 
       SUMMARY 
       [0007]    In accordance with the invention, a method and system relating to the rate recovery mechanism in a Wireless Local Area Network (WLAN) and Bluetooth coexistence system is provided. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a flow diagram illustrating the sequence of steps in a method for implementing an improved rate recovery mechanism in an embodiment in accordance with the invention; 
           [0009]      FIG. 2  is a flow diagram illustrating the sequence of steps in a method for implementing an improved rate recovery mechanism according to an embodiment in accordance with the invention; 
           [0010]      FIG. 3  is a flow diagram illustrating the sequence of steps in a method for implementing an improved rate recovery mechanism when the re-association between WLAN STA and AP is performed at a low data transmission rate according to an embodiment in accordance with the invention; and 
           [0011]      FIG. 4  illustrates certain frame transmissions between a WLAN STA and an AP according to an embodiment in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Embodiments in accordance with the invention described herein provide a method and system for implementing an improved rate recovery mechanism in a WLAN and Bluetooth coexistence system. As described below, the invention provides for the functioning of Access Points (AP) that fall back to a lower data transmission rate when the initial frame exchange between an AP and the WLAN STA fails, after resetting the AP as part of a rate recovery mechanism. 
         [0013]      FIG. 1  depicts a flow diagram at  100  illustrating the sequence of method steps in an improved rate recovery mechanism in accordance with an embodiment in accordance with the invention. In conducting a wireless communication, a set of frames transmitted at a predetermined data transmission rate is exchanged between an AP and a WLAN STA in a WLAN/Bluetooth coexistence system, and the averaged signal strength of the set of frames received is determined. Should there be a failure of communication resulting in a rate fallback (AP lowering its data transmission rate to its lowest rate), the WLAN STA detects the rate failure and sends a de-authentication frame to the AP. After the de-authentication frame is sent to the AP, the WLAN STA sends a re-authentication frame and a re-association frame. In the re-association frame the WLAN STA encodes the data transmission rate (Physical Layer data transmission rate (PHY rate)) that it supports based upon the previously determined averaged signal strength. 
         [0014]    In one embodiment in accordance with the invention, as a first step  105 , a set of frames transmitted at a predetermined data transmission rate is exchanged between the AP and the WLAN STA. In a second step  110 , the WLAN STA determines the averaged signal strength of the set of frames received from the Access Point (AP). If the WLAN STA subsequently detects a data transmission rate failure in the set of frames received from the AP (step  115 ), the WLAN STA sends a de-authentication frame to the AP in step  120 . In response to the de-authentication frame, the AP discards any previous information about the WLAN STA. After sending the de-authentication frame (step  125 ), the WLAN STA then sends a re-association frame and re-authentication frame to the AP which includes the data transmission rate(s) supported by the WLAN STA at the previously averaged signal strength. This is to say that the data transmission rates supported by WLAN STA are encoded in the re-association frame. In response (step  130 ), the AP transmits at the predetermined data transmission rate(s) supported by the WLAN. Thus, by limiting the allowed data transmission rate(s), the initial frames sent from the AP after reset will be at a rate supported and acknowledged by the WLAN without further reduction of the data transmission rate by the AP. 
         [0015]    If the WLAN STA determines that it will not be able to receive frames at higher data transmission rates, it will indicate that those higher data transmission rates are not supported. However, in order to assure interoperability with a wide range of AP transmission rates, the WLAN STA includes the option to support the higher data transmission rates if the signal strength is high enough. Moreover, if the WLAN STA determines that the signal strength has increased sufficiently to enable it to receive the set of frames at the highest data transmission rates, it can re-associate with the AP and include the higher data transmission rates in the re-association frame. 
         [0016]      FIG. 2  is a flow diagram ( 200 ) illustrating the sequence of steps in a method for implementing an improved rate recovery mechanism according to an embodiment in accordance with the invention. In a first step shown at  205 , a set of frames transmitted at a predetermined data transmission rate is exchanged between an AP and a WLAN STA. As indicated in step  210 , the WLAN determines the averaged signal strength of the set of frames received from the AP. If the averaged signal strength is acceptable, an acknowledgement (ACK) is sent to the AP. If however, as indicated in step  215 , the WLAN STA detects a data transmission rate failure (an unacceptable averaged signal strength for the transmitted data rate) in the set of frames received from the AP, it will send a de-authentication frame to the AP (step  220 ) causing the AP to discard the information it has about the WLAN STA. As stated in step  225 , the WLAN then sends a re-authentication and a re-association frame to the AP which includes the data transmission rate or rates supported by the WLAN STA at the averaged signal strength. If as indicated in step  230  the WLAN determines that the AP is thereafter not transmitting at a supported data transmission rate, it will instruct the AP to discontinue the transmission. If the AP continues to transmit at a transmission rate that is higher than that which the WLAN STA can receive at the current signal strength of the frames, re-association will fail (step  235 ), and the WLAN STA will store in memory the fact that the higher data transmission rate is required. In step  240 , the WLAN sends a re-authentication frame and a re-association frame to the AP which includes an indication that the higher data transmission rate is not supported. 
         [0017]      FIG. 3  is a flow diagram illustrating the sequence of steps in a method  300  for an improved rate recovery mechanism when a re-association between WLAN STA and AP is performed at a low data transmission rate according to an embodiment in accordance with the invention. In this embodiment, in step  305  a set of frames is exchanged between the AP and the WLAN STA at a data transmission rate lower than the rate specified in a previous re-association frame sent to the AP based on a previously determined averaged signal strength. In step  310  a new averaged signal strength of the set of frames received from the AP at the lower data transmission rate is determined, and in step  315 , the new averaged signal strength is used to determine an increased data transmission rate, greater than the lower data transmission rate, at which the reception of frames will be allowed. In step  320 , a re-association frame is sent from the WLAN STA to the AP which includes the increased data transmission rate. 
         [0018]      FIG. 4  illustrates at  400  certain frame transmissions between the WLAN STA  405  and the AP  410  according to an embodiment in accordance with the invention. When the WLAN STA  405  detects a data transmission rate failure, a de-authentication frame  415  is sent to the AP  410 . AP  410  acknowledges the reception of de-authentication frame  415  by sending an acknowledgement (ACK) frame  420  to the WLAN STA  405 . Upon receiving the ACK frame  420 , WLAN STA  405  sends a re-authentication request frame  425  to the AP  410 . AP  410  acknowledges the reception of re-authentication frame  425  by an ACK frame  430  and sends the authentication response frame  435  to the WLAN STA  405 . Further, WLAN STA  405  sends re-association request frame  440  to the AP  410 . AP  410  receives the re-association request frame  440  and sends the ACK frame  445 , and also sends the association response frame  450  to the WLAN STA  405 . Within the exchange of re-association request frame  440  and association response frame  450 , both the WLAN STA  405  and AP  410  encode the data transmission rates they support. Upon receiving the association response frame  450  from the AP  410 , WLAN STA  405  acknowledges the reception of the association response frame  450  by sending an ACK frame  455  to the AP  410 . 
         [0019]    Embodiments in accordance with the invention can be applied to WLAN and Bluetooth coexistence implementations that use Packet Traffic Arbitration (PTA) and the rate recovery mechanism. Embodiments in accordance with the invention can be implemented in a BGW211 WLAN chip. 
         [0020]    The forgoing description sets forth numerous specific details to convey a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced in ways not limited to these specific details. Well-known features are sometimes not described in detail in order to avoid obscuring the invention. Other variations and embodiments are possible in light of the above teachings, and it is thus intended that the scope of invention not be limited by this detailed description, but only by the following Claims.