Patent Publication Number: US-2022239327-A1

Title: Apparatus supporting multi-radio coexistence

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 16/239,916, filed on Jan. 4, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The technology of the disclosure relates generally to multi-radio coexistence. 
     BACKGROUND 
     Wireless communication devices have become increasingly common in current society. The prevalence of these wireless communication devices is driven in part by the many functions that are now enabled on such devices. Increased processing capabilities in such devices means that wireless communication devices have evolved from being pure communication tools into sophisticated multimedia centers that enable enhanced user experiences. 
     In this regard, a wireless communication device may employ a variety of wireless communication technologies for enabling a variety of concurrent communication scenarios. For example, it may be necessary for the wireless communication device to support such wireless communication technologies as wireless local area network (WLAN) based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, low-rate wireless system (e.g., ZigBee) based on IEEE 802.15.4 standard, and/or Bluetooth based on the Bluetooth Special Interest Group (SIG) specification. 
     Notably, the WLAN, the low-rate wireless system, and the Bluetooth technologies are configured to transmit and receive respective radio frequency (RF) signals in the Industrial, Scientific, and Medical (ISM) band. As such, the WLAN, the low-rate wireless system, and the Bluetooth RF signals can potentially interfere with each other when communicated concurrently. Given that a WLAN transmitter typically transmits the WLAN RF signal, which also occupies a larger bandwidth of the ISM band, at a much higher power than a low-rate wireless system transmitter does, a low-rate wireless system receiver may fall victim to the stronger WLAN transmission RF signal due to receiver blocking and/or saturation, particularly when the low-rate wireless system receiver is collocated in close proximity (e.g., in a same form factor) to the WLAN transmitter. In this regard, it may be desired to protect the low-rate wireless system receiver from being interfered by WLAN and/or Bluetooth transmitters when the low-rate wireless system receiver is collocated in proximity to the WLAN/Bluetooth transmitters. 
     SUMMARY 
     Aspects disclosed in the detailed description include an apparatus supporting multi-radio coexistence. More specifically, the apparatus is configured to support coexistence between multiple transceiver circuits configured to communicate radio frequency (RF) signals in a shared RF medium, such as an Industrial, Scientific, and Medical (ISM) band. In examples discussed herein, one transceiver circuit asserts a medium access request via a standard-defined coexistence interface for communicating (e.g., transmitting and/or receiving) an RF signal in the shared RF medium regardless of whether the shared RF medium is currently occupied by another transceiver circuit. In a non-limiting example, the transceiver circuit can be configured to assert or de-assert the medium access request in response to a variety of trigger events. Depending on whether the medium access request is granted, the transceiver circuit may start communicating the RF signal in the shared RF medium in different modes. As such, it may be possible to reduce medium access delay for the transceiver circuit requesting to access the shared RF medium, while protecting the transceiver circuit currently occupying the shared RF medium from undue interruption and interference. 
     In one aspect, a multi-radio apparatus is provided. The multi-radio apparatus includes a first transceiver circuit configured to communicate a first RF signal in a shared RF medium. The multi-radio apparatus also includes a standard-defined coexistence interface coupled to the first transceiver circuit. The multi-radio apparatus also includes a second transceiver circuit coupled to the standard-defined coexistence interface. The second transceiver circuit is configured to assert a medium access request via the standard-defined coexistence interface for communicating a second RF signal in the shared RF medium in response to a first trigger event. The second transceiver circuit is also configured to communicate the second RF signal in a first mode in response to a medium access grant for the medium access request being asserted via the standard-defined coexistence interface. The second transceiver circuit is also configured to communicate the second RF signal in a second mode in response to the medium access grant for the medium access request not being asserted. The second transceiver circuit is also configured to de-assert the medium access request in response to a second trigger event. 
     In another aspect, a method for supporting coexistence between a first transceiver circuit configured to communicate a first RF signal and a second transceiver circuit configured to communicate a second RF signal in a shared RF medium is provided. The method includes asserting a medium access request for communicating the second RF signal in the shared RF medium in response to a first trigger event. The method also includes communicating the second RF signal in a first mode in response to a medium access grant for the medium access request being asserted. The method also includes communicating the second RF signal in a second mode in response to the medium access grant for the medium access request not being asserted. The method also includes de-asserting the medium access request in response to a second trigger event. 
     Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure. 
         FIG. 1A  is a schematic diagram of an exemplary existing multi-radio apparatus in which a transmitting transceiver circuit can cause undue radio frequency (RF) interference to a receiving transceiver circuit due to insufficient RF separation between the transmitting transceiver circuit and the receiving transceiver circuit; 
         FIG. 1B  is a schematic diagram providing an exemplary illustration of a standard-defined coexistence interface for mitigating RF interference caused by the transmitting transceiver circuit to the receiving transceiver circuit of  FIG. 1A ; 
         FIG. 2  is a schematic diagram of an exemplary multi-radio apparatus configured according to an embodiment of the present disclosure to support an enhanced multi-radio coexistence scheme between a first transceiver circuit and a second transceiver circuit based on a standard-defined coexistence interface; 
         FIG. 3  is a flowchart of an exemplary process that can be employed by the second transceiver circuit of  FIG. 2  to enable the enhanced coexistence scheme in the multi-radio apparatus; 
         FIG. 4  is a time sequence diagram providing an exemplary time sequence for acquiring a shared RF medium by the second transceiver circuit of  FIG. 2  to receive an RF signal; 
         FIG. 5  is a time sequence diagram providing an exemplary time sequence for acquiring a shared RF medium by the second transceiver circuit of  FIG. 2  to transmit an RF signal; and 
         FIG. 6  is a time sequence diagram providing an exemplary time sequence for acquiring a shared RF medium by the second transceiver circuit of  FIG. 2  to transmit and receive an RF signal. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
     Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Aspects disclosed in the detailed description include an apparatus supporting multi-radio coexistence. More specifically, the apparatus is configured to support coexistence between multiple transceiver circuits configured to communicate radio frequency (RF) signals in a shared RF medium, such as an Industrial, Scientific, and Medical (ISM) band. In examples discussed herein, one transceiver circuit asserts a medium access request via a standard-defined coexistence interface for communicating (e.g., transmitting and/or receiving) an RF signal in the shared RF medium regardless of whether the shared RF medium is currently occupied by another transceiver circuit. In a non-limiting example, the transceiver circuit can be configured to assert or de-assert the medium access request in response to a variety of trigger events. Depending on whether the medium access request is granted, the transceiver circuit may start communicating the RF signal in the shared RF medium in different modes. As such, it may be possible to reduce medium access delay for the transceiver circuit requesting to access the shared RF medium, while protecting the transceiver circuit currently occupying the shared RF medium from undue interruption and interference to help improve link quality. 
     Before discussing the apparatus of the present disclosure, a brief overview of a standard-defined coexistence interface between a pair of collocated transceiver circuits is first provided with reference to  FIGS. 1A and 1B . The discussion of specific exemplary aspects of the apparatus supporting multi-radio coexistence according to the present disclosure starts below with reference to  FIG. 2 . 
       FIG. 1A  is a schematic diagram of an exemplary existing multi-radio apparatus  10  in which a transmitting transceiver circuit  12  can cause undue RF interference to a receiving transceiver circuit  14  due to insufficient RF separation between the transmitting transceiver circuit  12  and the receiving transceiver circuit  14 . The transmitting transceiver circuit  12  may be a wireless local area network (WLAN) transceiver circuit configured to transmit a WLAN RF signal  16  to a WLAN receiver  18  in accordance with medium access control (MAC) layer and physical (PHY) layer specifications as defined by the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. The transmitting transceiver circuit  12  may also be a Bluetooth (BT) transceiver circuit configured to transmit a BT RF signal  20  to a BT receiver  22  in accordance to MAC layer and PHY layer specifications as defined by the Bluetooth Special Interest Group (SIG) standard. The receiving transceiver circuit  14  may be a low-rate wireless system (e.g., ZigBee) transceiver circuit configured to receive a low-rate RF signal  24  from a low-rate wireless system transmitter  26  in accordance to MAC layer and PHY layer specifications as defined by the IEEE 802.15.4 standard. 
     The transmitting transceiver circuit  12  is configured to transmit the WLAN RF signal  16  and/or the BT RF signal  20 , and the receiving transceiver circuit  14  is configured to receive the low-rate RF signal  24  in a shared RF medium  28 . The shared RF medium  28  may correspond to the Industrial, Scientific, and Medical (ISM) band occupying a 2.4-2.5 GHz RF spectrum. 
     The transmitting transceiver circuit  12  and the receiving transceiver circuit  14  are collocated in the existing multi-radio apparatus  10 . Hereinafter, a pair of transceiver circuits is referred to as being collocated when the transceiver circuits are provided in a same form factor and/or separated by 10-40 dB of RF separation. Notably, the transmitting transceiver circuit  12  may transmit at a significantly higher power than the low-rate wireless system transmitter  26  does. As a result, the WLAN RF signal  16  and/or the BT RF signal  20  may block and saturate the receiving transceiver circuit  14 . Consequently, the receiving transceiver circuit  14  may be impaired to receive the low-rate RF signal  24 . 
     To help mitigate RF interference between the transmitting transceiver circuit  12  and the receiving transceiver circuit  14  collocated in the existing multi-radio apparatus  10 , the IEEE 802.15.2 standard has defined a standard-defined coexistence interface  30 , which is also known as a two-wire coexistence interface. Hereinafter, the standard-defined coexistence interface  30  as defined by the IEEE 802.15.2 is referred to as a standard-defined coexistence interface. 
       FIG. 1B  is a schematic diagram providing an exemplary illustration of the standard-defined coexistence interface  30  for mitigating RF interference caused by the transmitting transceiver circuit  12  to the receiving transceiver circuit  14  of  FIG. 1A . In a non-limiting example, the transmitting transceiver circuit  12  is currently transmitting the WLAN RF signal  16  (not shown) and/or the BT RF signal  20  (not shown) in the shared RF medium  28  (not shown), while the receiving transceiver circuit  14  is prepared to receive the low-rate RF signal  24  (not shown) via the shared RF medium  28 . In this regard, the receiving transceiver circuit  14  provides a medium access request  32  to the transmitting transceiver circuit  12  via a first wire  34  of the standard-defined coexistence interface  30 . In a non-limiting example, the receiving transceiver circuit  14  may initiate the medium access request  32  by asserting the first wire  34  to a logical HIGH. Upon receiving the medium access request  32 , the transmitting transceiver circuit  12  may respond in a number of ways. 
     In one embodiment, the transmitting transceiver circuit  12  can suspend transmission of the WLAN RF signal  16  and/or the BT RF signal  20  immediately. Subsequently, the transmitting transceiver circuit  12  provides a medium access grant  36  to the receiving transceiver circuit  14  via a second wire  38  in the standard-defined coexistence interface  30 . In a non-limiting example, the transmitting transceiver circuit  12  may initiate the medium access grant  36  by asserting the second wire  38  to a logical HIGH. Accordingly, the receiving transceiver circuit  14  can start receiving the low-rate RF signal  24  without interference from the WLAN RF signal  16  and/or the BT RF signal  20 . Upon successful completion of receiving the low-rate RF signal  24 , the receiving transceiver circuit  14  may cancel the medium access request  32  by de-asserting the first wire  34  to a logical LOW. In response, the transmitting transceiver circuit  12  cancels the medium access grant  36  by de-asserting the second wire  38  to a logical LOW and resumes transmission of the WLAN RF signal  16  and/or the BT RF signal  20 . By immediately suspending transmission of the transmitting transceiver circuit  12 , it may be possible to reduce medium access delay of the receiving transceiver circuit  14 . However, the reduction in medium access delay may come at an expense of potential disruption to the WLAN RF signal  16  and/or the BT RF signal  20 . 
     In another embodiment, the transmitting transceiver circuit  12  can suspend transmission of the WLAN RF signal  16  and/or the BT RF signal  20  after completing current transmission. Subsequently, the transmitting transceiver circuit  12  provides the medium access grant  36  to the receiving transceiver circuit  14  via the second wire  38  in the standard-defined coexistence interface  30 . In a non-limiting example, the transmitting transceiver circuit  12  may initiate the medium access grant  36  by asserting the second wire  38  to a logical HIGH. Accordingly, the receiving transceiver circuit  14  can start receiving the low-rate RF signal  24  without interference from the WLAN RF signal  16  and/or the BT RF signal  20 . Upon successful completion of receiving the low-rate RF signal  24 , the receiving transceiver circuit  14  may cancel the medium access request  32  by de-asserting the first wire  34  to a logical LOW. In response, the transmitting transceiver circuit  12  cancels the medium access grant  36  by de-asserting the second wire  38  to a logical LOW and resumes transmission of the WLAN RF signal  16  and/or the BT RF signal  20 . In this case, the receiving transceiver circuit  14  may suffer an increased medium access delay, thus causing a potential disruption to the low-rate RF signal  24 . 
     In another embodiment, the transmitting transceiver circuit  12  may chose to ignore the medium access request  32 . Accordingly, the transmitting transceiver circuit  12  maintains the second wire  38  as the logical LOW. In this regard, the receiving transceiver circuit  14  may be denied a chance to receive the low-rate RF signal  24  in an interference-protected manner. 
     As discussed above, the standard-defined coexistence interface  30  may help mitigate RF interference caused by the transmitting transceiver circuit  12  to the receiving transceiver circuit  14  in the existing multi-radio apparatus  10 . However, depending on different ways of handling the medium access request  32 , the transmitting transceiver circuit  12  and/or the receiving transceiver circuit  14  may be subject to undue interruption in transmitting/receiving respective RF signals. Hence, it may be desired to enhance the existing multi-radio apparatus  10  to reduce medium access delay of the receiving transceiver circuit  14 , while protecting the transmitting transceiver circuit  12  from undue interruption and interference. 
     In this regard,  FIG. 2  is a schematic diagram of an exemplary multi-radio apparatus  40  configured according to an embodiment of the present disclosure to support an enhanced multi-radio coexistence scheme between a first transceiver circuit  42  and a second transceiver circuit  44  based on a standard-defined coexistence interface  46 . In examples discussed herein, the first transceiver circuit  42  can be a WLAN/BT transceiver circuit configured to communicate a WLAN/BT RF signal  48  (also referred to as “first RF signal”) in a shared RF medium  50 . The second transceiver circuit  44  may be a low-rate wireless system (e.g., ZigBee) transceiver circuit configured to communicate a low-rate RF signal  52  (also referred to as “second RF signal”) in the shared RF medium  50 . The shared RF medium  50  may be an ISM band located in the 2.4-2.5 GHz RF spectrum. 
     The first transceiver circuit  42  may be coupled to a first antenna(s)  54  via a first front-end circuit  56 , which may include a power amplifier (PA) (not shown) for amplifying the first RF signal  48  prior to being radiated by the first antenna(s)  54  and a low-noise amplifier (LNA) (not shown) for amplifying the first RF signal  48  after being absorbed by the first antenna(s)  54 . The second transceiver circuit  44  may be coupled to a second antenna(s)  58  via a second front-end circuit  60 , which may include a PA (not shown) for amplifying the second RF signal  52  prior to being radiated by the second antenna(s)  58  and an LNA (not shown) for amplifying the second RF signal  52  after being absorbed by the second antenna(s)  58 . 
     The standard-defined coexistence interface  46  is identical to the standard-defined coexistence interface  30  in  FIGS. 1A and 1B . Accordingly, the standard-defined coexistence interface  46  includes a first wire  62  and a second wire  64  that are identical to the first wire  34  and the second wire  38  in the standard-defined coexistence interface  30 , respectively. In this regard, the multi-radio apparatus  40  is configured to support the enhanced coexistence scheme between the first transceiver circuit  42  and the second transceiver circuit  44  without requiring any change to the standard-defined coexistence interface  46 . 
     The first transceiver circuit  42  is identical to the transmitting transceiver circuit  12  in  FIG. 1A . In this regard, the multi-radio apparatus  40  is able to support the enhanced coexistence scheme without requiring intrusive change in the first transceiver circuit  42 . As such, it may be possible to employ any standard-compliant WLAN/BT transceiver circuit in a plug-and-play manner, thus helping to reduce complexity and costs associated with implementation of the enhanced coexistence scheme. 
     The second transceiver circuit  44  is functionally equivalent to the receiving transceiver circuit  14  in  FIG. 1A . However, the second transceiver circuit  44  is modified from the receiving transceiver circuit  14  to incorporate additional functionalities for enabling the enhanced coexistence scheme of the present disclosure. More specifically, the second transceiver circuit  44  may be configured to enable the enhanced coexistence scheme based on a process, as discussed next in  FIG. 3 . 
       FIG. 3  is a flowchart of an exemplary process  100  that can be employed by the second transceiver circuit  44  of  FIG. 2  to enable the enhanced coexistence scheme in the multi-radio apparatus  40 . The process  100  includes the additional functionalities being incorporated into the second transceiver circuit  44  of  FIG. 2  for enabling the enhanced coexistence scheme. 
     According to the process  100 , the second transceiver circuit  44  asserts a medium access request  66  via the standard-defined coexistence interface  46  for communicating (transmitting or receiving) the second RF signal  52  in the shared RF medium  50  in response to a first trigger event (block  102 ). In a non-limiting example, the second transceiver circuit  44  can assert the medium access request  66  by toggling the first wire  62  in the standard-defined coexistence interface  46  from a logical LOW to a logical HIGH. 
     The first transceiver circuit  42 , which may be currently occupying the shared RF medium  50 , may become aware of the medium access request  66  by detecting the first wire  62  being togged to the logical HIGH. In response, the first transceiver circuit  42  may grant the medium access request  66 , either immediately or after a short delay. In a non-limiting example, the short delay can be caused by hardware implementation and/or software function calls. In addition, the short delay may also be caused as a result of the first transceiver circuit  42  attempting to complete an ongoing transmission/reception prior to yielding the shared RF medium  50  to the second transceiver circuit  44 . Accordingly, the first transceiver circuit  42  may assert a medium access grant  68 , for example, by toggling the second wire  64  in the standard-defined coexistence interface  46  from a logical LOW to a logical HIGH. The second transceiver circuit  44  may determine that the medium access request  66  is granted when the second wire  64  is toggled to the logical HIGH. 
     In this regard, the second transceiver circuit  44  is configured to communicate the second RF signal  52  in a first mode in response to the medium access grant  68  for the medium access request  66  being asserted via the standard-defined coexistence interface  46  (block  104 ). In contrast, the second transceiver circuit  44  is configured to communicate the second RF signal  52  in a second mode in response to the medium access grant  68  for the medium access request  66  not being asserted via the standard-defined coexistence interface  46  (block  106 ). 
     The second transceiver circuit  44  is further configured to de-assert the medium access request  66  in response to a second trigger event (block  108 ). The second transceiver circuit  44  may de-assert the medium access request  66  by toggling the first wire  62  in the standard-defined coexistence interface  46  from the logical HIGH to the logical LOW. Accordingly, the first transceiver circuit  42  may then toggle the second wire  64  from the logical HIGH to the logical LOW. 
     With reference back to  FIG. 2 , the first trigger event that causes the second transceiver circuit  44  to assert the medium access request  66  can include a variety of predefined events. In one example, the second transceiver circuit  44  is preparing to receive the second RF signal  52  via the shared RF medium  50 . In this regard, the first trigger event can correspond to a successful reception of a preamble/start-frame delimiter (SFD) of an incoming packet(s)  70  in the second RF signal  52 . In another example, the second transceiver circuit  44  is preparing to transmit the second RF signal  52  via the shared RF medium  50 . In this regard, the first trigger event can correspond to a successful detection of a standardized trigger event, such as an IEEE 802.15.4 MAC layer command. 
     If the first transceiver circuit  42  asserts the medium access grant  68  immediately upon detecting the medium access request  66 , the second transceiver circuit  44  is configured to communicate (transmit or receive) the second RF signal  52  in the first mode. In the first mode, the second transceiver circuit  44  may activate the PA in the second front-end circuit  60  to amplify the second RF signal  52  prior to being radiated by the second antenna(s)  58 . In this regard, the first mode may be seen as a “full-power” mode. 
     In contrast, if the first transceiver circuit  42  does not assert the medium access grant  68  immediately or within a defined delay (e.g., 200 μs) upon detecting the medium access request  66 , the second transceiver circuit  44  is configured to communicate (transmit or receive) the second RF signal  52  in the second mode. In the second mode, the second transceiver circuit  44  may deactivate the PA in the second front-end circuit  60  such that the second RF signal  52  is not amplified prior to being radiated by the second antenna(s)  58 . In this regard, the second mode may be seen as a “reduced-power” mode. Moreover, the second transceiver circuit  44  may cause the second RF signal  52  to be attenuated prior to being radiated by the second antenna(s)  58 . In a non-limiting example, the second RF signal  52  can be attenuated to a defined power level that is below a receiver saturation threshold of the first transceiver circuit  42  such that the second RF signal  52  does not interfere with the first transceiver circuit  42  when the second RF signal  52  is transmitted in a different channel from the first transceiver circuit  42 . 
     Despite being transmitted at a reduced power level, an outgoing packet(s)  72  in the second RF signal  52  may still be received by a nearby low-rate wireless system receiver (not shown). Thus, by transmitting the second RF signal  52  in the second mode, it may be possible to reduce a medium access delay for the second transceiver circuit  44  even when the first transceiver circuit  42  does not yield the shared RF medium  50  in a timely fashion. Notably, the second transceiver circuit  44  may not know whether the outgoing packet(s)  72  has been received correctly in absence of an acknowledgement (ACK) from the low-rate wireless system receiver. In this regard, the second transceiver circuit  44  may be configured to retransmit the outgoing packet(s)  72  when the first transceiver circuit  42  asserts the medium access grant  68 . 
     In the unlikely event that the first transceiver circuit  42  denies the medium access request  66 , the second transceiver circuit  44  may be configured to cause the first transceiver circuit  42  to be decoupled from the first front-end circuit  56  and the first antenna(s)  54 . The second transceiver circuit  44  may set a delay time-out timer immediately upon asserting the medium access request  66 . Accordingly, the second transceiver circuit  44  may cause the first transceiver circuit  42  to be decoupled from the first front-end circuit  56  and the first antenna(s)  54  upon expiration of the delay time-out timer. In this regard, the second transceiver circuit  44  can forcefully take over the shared RF medium at an expense of the first transceiver circuit  42 . Notably, this scenario should not happen if the first transceiver circuit  42  is configured to operate in compliance with the standard-defined coexistence interface  46 . The second transceiver circuit  44  may reset the delay time-out timer in response to the second wire  64  being asserted to the logical HIGH or upon successful reception of an ACK. 
     Given that the second RF signal  52  is often communicated with a relatively longer duty-cycle, the second transceiver circuit  44  is configured to occupy the shared RF medium  50  longer than needed. In this regard, the second transceiver circuit  44  is configured to de-assert the medium access request  66  in response to the second trigger event. 
     In one non-limiting example, the second transceiver circuit  44  can initiate a predefined time-out timer immediately when the medium access grant  68  is asserted. The predefined time-out timer may be longer than a temporal duration for transmitting/receiving an 802.15.4 packet and/or the duration for completing an MAC layer retransmission(s). In this regard, the second trigger event can correspond to an expiration of the predefined time-out timer. By de-asserting the medium access request  66  based on the predefined time-out timer, it may be possible to prevent the second transceiver circuit  44  from holding the shared RF medium  50  for an excessive length of time, thus helping data throughput on the shared RF medium  50 . 
     In another non-limiting example, the second transceiver circuit  44  acquires the shared RF medium  50  for receiving the incoming packet(s)  70  in the second RF signal  52 . In this regard, the second trigger event may correspond to a successful transmission of an ACK by the second transceiver circuit  44  in response to successful reception of the incoming packet(s)  70 . 
     In another non-limiting example, the second transceiver circuit  44  acquires the shared RF medium  50  for transmitting the outgoing packet(s)  72  in the second RF signal  52 . In this regard, the second trigger event may correspond to a successful reception of an ACK by the second transceiver circuit  44  in response to the transmission of the outgoing packet(s)  72 . 
     As discussed earlier, the second transceiver circuit  44  may assert the medium access request  66  in response to detection of the preamble of the incoming packet(s)  70 . In this regard, the second transceiver circuit  44  may be further configured to examine the destination address of the incoming packet(s)  70  to help determine whether the incoming packet(s)  70  is destined to the second transceiver circuit  44 . In case the incoming packet(s)  70  is not destined to the second transceiver circuit  44 , the incoming packet(s)  70  may be treated as an invalid incoming packet(s). Accordingly, the second trigger event can correspond to detection of the invalid incoming packet(s). 
     Some specific non-limiting examples of the enhanced coexistence scheme are now discussed in reference to  FIGS. 4-6  below. Common elements between  FIGS. 2 and 4-6  are shown therein with common element numbers and will not be re-described herein. 
       FIG. 4  is a time sequence diagram providing an exemplary time sequence  74  for acquiring the shared RF medium  50  by the second transceiver circuit  44  of  FIG. 2  to receive the second RF signal  52 . At time T 1 , the second transceiver circuit  44  detects a preamble/SFD  76  of the incoming packet(s)  70  (first trigger event) and asserts the medium access request  66  on the first wire  62 . In the meantime, the first transceiver circuit  42  is communicating the first RF signal  48  on the shared RF medium  50  (not shown). At time T 2 , the first transceiver circuit  42  asserts the medium access grant  68  on the second wire  64  and suspends communication of the first RF signal  48 . The second transceiver circuit  44 , one the other hand, may have missed at least part of the incoming packet(s)  70  and does not acknowledge reception of the incoming packet(s)  70 . As a result, a retransmitted incoming packet(s)  70 ( 1 ) may be sent and subsequently received by the second transceiver circuit  44 . In response, the second transceiver circuit  44  transmits an ACK  78  (second trigger event) at time T 3  and de-asserts the medium access request  66  at time T 4 . In response, at time T 5 , the first transceiver circuit  42  de-asserts the medium access grant  68  and resumes communication of the first RF signal  48  thereafter. 
       FIG. 5  is a time sequence diagram providing an exemplary time sequence  80  for acquiring the shared RF medium  50  by the second transceiver circuit  44  of  FIG. 2  to transmit the second RF signal  52 . At time T 1 , the second transceiver circuit  44  asserts the medium access request  66  on the first wire  62  and starts transmitting the outgoing packet(s)  72  in the second mode. In this regard, the outgoing packet(s)  72  is transmitted at a reduced power level and may not be correctly received by an intended receiver. As a result, the second transceiver circuit  44  may not receive an ACK  82  as expected. At time T 2 , the first transceiver circuit  42  asserts the medium access grant  68  on the second wire  64 . In case the second transceiver circuit  44  did not receive the ACK  82  as expected, the second transceiver circuit  44  retransmits the outgoing packet(s)  72 ( 1 ) in the first mode. At time T 3 , the second transceiver circuit  44  receives the ACK  82  (second trigger event) for the retransmitted outgoing packet(s)  72 ( 1 ). Accordingly, the second transceiver circuit  44  de-asserts the medium access request  66 . In response, at time T 4 , the first transceiver circuit  42  de-asserts the medium access grant  68  and resumes communication of the first RF signal  48  thereafter. 
       FIG. 6  is a time sequence diagram providing an exemplary time sequence  84  for acquiring the shared RF medium  50  by the second transceiver circuit  44  of  FIG. 2  to transmit and receive the second RF signal  52 . At time T 1 , the second transceiver circuit  44  receives a preamble/SFD  76  of an IEEE 802.15.4 ZigBee cluster library (ZCL) request command (first trigger event) in the incoming packet(s)  70 . Accordingly, the second transceiver circuit  44  asserts the medium access request  66  on the first wire  62 . In the meantime, the first transceiver circuit  42  is still communicating with the first RF signal  48  on the shared RF medium  50  (not shown). As a result, the second transceiver circuit  44  may not receive the incoming packet(s)  70  correctly and thus may not be able to acknowledge the incoming packet(s)  70 . At time T 2 , the first transceiver circuit  42  asserts the medium access grant  68  on the second wire  64 . Accordingly, the second transceiver circuit  44  may receive the retransmitted incoming packet(s) 70(1) and transmit the ACK  78 . Subsequently, the second transceiver circuit  44  may transmit a number of outgoing packets  72  and receive a number of corresponding ACKs  82 . The second transceiver circuit  44  may conclude a packet exchange by transmitting an IEEE 802.15.4 ZCL response packet as the final outgoing packet(s)  72  (second trigger event) and subsequently de-assert the medium access request  66  at time T 3 . In response, at time T 4 , the first transceiver circuit  42  de-asserts the medium access grant  68  and resumes communication of the first RF signal  48  thereafter. 
     Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.