Patent Publication Number: US-8537798-B2

Title: Coexistence mechanism for collocated WLAN and WWAN communication devices

Description:
BACKGROUND 
     Embodiments of the inventive subject matter generally relate to the field of wireless communications and, more particularly, to a coexistence mechanism for collocated WLAN and WWAN communication devices. 
     When wireless devices are in close proximity to each other, communications from one wireless device may interfere with communications from the other wireless device. For example, when wireless wide area network (WWAN) devices (e.g., Long-Term Evolution (LTE) devices) and wireless local area network (WLAN) devices operate in close proximity to each other, some frequency bands used by WWAN devices may be too close to frequency bands used by WLAN devices, resulting in interference between the WLAN and the WWAN devices. For example, in a system having an LTE device located in close proximity to a WLAN device, some frequency bands used by the LTE device (e.g., LTE band  38  and LTE band  40 ) may be very close to WLAN frequency bands (e.g., the WLAN 2.4 GHz ISM band). Furthermore, the radio protocol of one wireless device can interfere with the radio protocol of the other wireless device. 
     SUMMARY 
     Various embodiments of a coexistence mechanism for collocated WLAN and WWAN communication devices are disclosed. In one embodiment, a WLAN device of a communication system determines a WLAN communication time interval associated with the WLAN device for performing WLAN communication operations and a WWAN communication time interval associated with a WWAN device of the communication system for performing WWAN communication operations. The WLAN device is coupled with the WWAN device. A coexistence signal is provided from the WLAN device to the WWAN device to indicate the WLAN communication time interval associated with the WLAN device and the WWAN communication time interval associated with the WWAN device. It is determined, at the WLAN device, whether the WLAN communication time interval is in progress to determine whether to perform one or more WLAN communication operations. In response to determining that the WLAN communication time interval is in progress, the one or more WLAN communication operations are performed at the WLAN device. In response to determining that the WLAN communication time interval is not in progress, it is determined not to perform the one or more WLAN communication operations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments may be better understood, and numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. 
         FIG. 1  is an example conceptual diagram illustrating a coexistence mechanism for collocated WLAN and LTE devices, according to some embodiments; 
         FIG. 2  is a flow diagram illustrating example operations of a WLAN device configured to implement a time-splitting scheduling coexistence mechanism for control of the communication medium; 
         FIG. 3  is a flow diagram illustrating example operations of an LTE device configured to implement a time-splitting scheduling coexistence mechanism for control of the communication medium; 
         FIG. 4  is an example flow diagram illustrating example operations for scheduling WLAN communication in accordance with an LTE communication schedule; 
         FIG. 5A  is an example timing diagram illustrating scheduling WLAN communication in accordance with an LTE communication schedule; 
         FIG. 5B  is an example timing diagram illustrating a WLAN client station requesting WLAN packets from a remote WLAN access point; 
         FIG. 6  is a flow diagram illustrating example operations for scheduling WLAN communication in accordance with an LTE communication schedule, while implementing a time-splitting scheduling coexistence mechanism; 
         FIG. 7  is a continuation of  FIG. 6  and also illustrates example operations for scheduling WLAN communication in accordance with an LTE communication schedule, while implementing a time-splitting scheduling coexistence mechanism; 
         FIG. 8  is an example timing diagram illustrating potential time intervals for WLAN and LTE communications; 
         FIG. 9  is a flow diagram illustrating example operations for maximizing frequency separation between a WLAN device and a collocated LTE device when the WLAN device is configured as an access point; 
         FIG. 10  is a flow diagram illustrating example operations for maximizing frequency separation between a WLAN device and a collocated LTE device when the WLAN device is configured as a WLAN client station; and 
         FIG. 11  is a block diagram of an electronic system including a coexistence mechanism between collocated wireless communication devices, according to some embodiments. 
     
    
    
     DESCRIPTION OF EMBODIMENT(S) 
     The description that follows includes exemplary systems, methods, techniques, instruction sequences, and computer program products that embody techniques of the present inventive subject matter. However, it is understood that the described embodiments may be practiced without these specific details. For instance, although examples refer to a coexistence mechanism for a collocated WLAN device and a LTE device, embodiments are not so limited. In other embodiments, the coexistence mechanism described herein can be implemented for other WWAN standards and devices, e.g., WiMAX, Global System for Mobile Communications (GSM), 3G, 4G, etc. In other instances, well-known instruction instances, protocols, structures, and techniques have not been shown in detail in order not to obfuscate the description. 
     Interference between wireless radio devices (e.g., an LTE device and a WLAN device) may occur when the wireless radio devices are collocated on a common system and/or are communicating in close proximity to each other. Such interference between the collocated wireless radio devices can result in performance degradation. Existing techniques typically employ a large number of expensive RF filters with a sharp frequency roll-off (e.g., bulk acoustic wave (BAW) devices, thin film bulk acoustic resonators (FBARs), etc.) near the antennas of the wireless radio devices to filter blockers in adjacent frequency bands and unwanted out-of-band signals. However, the RF filters may not be able to completely eliminate the blockers and out-of-band signals because of practical filter limitations. For example, LTE band  40  (associated with a frequency band of 2.3 GHz-2.4 GHz) coincides with the WLAN 2.4 GHz frequency band. In this example, adding RF filters (e.g., with a sharp frequency roll-off) may filter out a substantial portion of the 2.4 GHz ISM band and, therefore, may render portions of the 2.4 GHz WLAN frequency band ineffective. Furthermore, these types of RF filters may be ineffective in rejecting LTE transmissions that can impact WLAN communications (or WLAN transmissions that can impact LTE communications). Using a large number of RF filters can also increase the cost associated with the wireless radio devices. Furthermore, in some cases (e.g., when the wireless radio devices operate in a large temperature range, such as −30° C. to +85° C.), the out-of-band signal rejection abilities of the RF filters may be degraded and hence additional processing components (e.g., filters, power amplifiers, low-noise amplifiers, etc.) may be utilized in the wireless radio devices, which further increases the implementation cost and complexity. 
     In some embodiments, a coexistence mechanism can be implemented that enables quasi-simultaneous operation of the collocated wireless radio devices. The collocated wireless radio devices can be configured to schedule communications during certain allocated communication time intervals to minimize packet collision and interference. For example, the coexistence mechanism can be implemented to enable the collocated WLAN device (operating in the 2.4 GHz frequency band) and the LTE device (operating at frequency bands that are very close to the 2.4 GHz frequency band) to operate with minimal interference. The wireless radio devices can exchange coexistence signals via a coexistence interface to indicate their respective transmission and reception activity, to schedule time intervals during which each of the wireless radio devices are permitted to communicate, and to schedule their transmission and reception time intervals to minimize interference between the wireless radio devices. The wireless radio devices can also throttle their transmissions (and/or switch to a low power state) to enable both the wireless radio devices to share the communication medium while minimizing interference between the wireless radio devices. Such a coexistence mechanism can preclude the need for expensive RF filters (and additional processing components) for minimizing interference between the wireless radio devices and can enable simultaneous operation of the wireless radio devices (when the wireless radio devices operate in adjacent frequency bands). 
       FIG. 1  is an example conceptual diagram illustrating a coexistence mechanism for collocated WLAN and LTE devices, according to some embodiments. As illustrated in  FIG. 1 , in some implementations, the LTE device  102  (e.g., which may be referred to as “LTE user equipment (UE)”) and the WLAN device  110  can be embodied on distinct integrated circuits (e.g., distinct LTE and WLAN chips) on a common circuit board (or on separate circuit boards in close proximity). In other implementations, the LTE device  102  and the WLAN device  110  can be embodied on a single integrated circuit (e.g., a system on a chip (SoC)). The LTE device  102  and the WLAN device  110  can be included within various types of electronic devices with wireless communication capabilities (e.g., mobile phones, notebook computer, tablet computers, gaming consoles, personal computers, etc). For example, the LTE device  102  and the WLAN device  110  may be collocated within a portable router. The LTE device  102  may be a wide area network (WAN) modem and the WLAN device  110  may be a local area network (LAN) bridge to another electronic device (e.g., a personal computer). The LTE device  102  and the WLAN device  110  may operate simultaneously to facilitate data transfer between the portable router and the personal computer. 
     In some implementations, the LTE device  102  comprises an LTE coexistence unit  104 , an LTE processing unit  106 , and LTE schedule information  108 . The LTE coexistence unit  104  is configured to communicate with the LTE processing unit  106 . The LTE coexistence unit  104  may also generate the LTE schedule information  108 . In some implementations, the WLAN device  110  comprises a WLAN coexistence unit  112 , a WLAN processing unit  114 , and WLAN schedule information  116 . The WLAN coexistence unit  112  can communicate with the WLAN processing unit  114 . The WLAN coexistence unit  112  may also generate the WLAN schedule information  116 . In one implementation, the WLAN processing unit  114  can be a medium access control (MAC) unit. The LTE device  102  and the WLAN device  110  communicate via an interface  120 . In one implementation, the interface  120  can be a physical interface comprising wires connecting the LTE device  102  and the WLAN device  110 . In another implementation, the interface  120  can be a bi-directional digital interface over which digital control coexistence signals can be exchanged. In another implementation, the interface  120  can be a bi-directional message-based coexistence interface over which messages comprising coexistence information are exchanged between the LTE device  102  and the WLAN device  110 . The WLAN coexistence unit  114  and the LTE coexistence unit  104  can use the interface  120  to exchange information regarding pending communications, operating frequency information, type of LTE technology being used (e.g., time division duplex (TDD) or frequency division duplex (FDD)), and other related information, as will be further described below. In some implementations, the information regarding pending communications can comprise an exact transmission and reception schedule, a future transmission and reception schedule, the periodicity of the transmission and the reception, a priority of the communications, etc. As will be described below with reference to stages A-D, the WLAN coexistence unit  112  and the LTE coexistence unit  104  can schedule communications of their respective devices to minimize interference with the collocated device. 
     At stage A, the LTE coexistence unit  104  transmits the LTE schedule information  108  to the WLAN coexistence unit  112 . The LTE schedule information  108  can indicate timing information of coexistence events such as a start time of LTE packet transmission, a start time of LTE packet reception, a transmission/reception duration, packet priority, etc. In some implementations, if the exact timing information (e.g., the start time of LTE packet transmission/reception) is not predictable, the LTE coexistence unit  104  can indicate a LTE communication slot duration and an interval within each communication slot during which the LTE device  102  is programmed to transmit (“LTE transmit interval”) and receive (“LTE receive interval”). For example, in accordance with TDD-LTE communication protocols, the LTE communication slot may be 5 ms, and each 5 ms communication slot may be partitioned into a 2 ms LTE transmit interval and a 3 ms LTE receive interval. 
     At stage B, the WLAN coexistence unit  112  determines a time interval during which only the WLAN device  110  can communicate (“WLAN allocated communication time interval”) and a time interval during which only the LTE device  102  can communicate (“LTE allocated communication time interval”). In one implementation, the WLAN coexistence unit  112  can determine the WLAN allocated communication time interval and the LTE allocated communication time interval based on knowledge of a WLAN beacon interval and an LTE frame interval. In other implementations, if the LTE schedule information  108  and/or the WLAN schedule information  116  are available, the WLAN coexistence unit  112  may take the LTE schedule information  108  and/or the WLAN schedule information  116  into consideration when determining the WLAN allocated communication time interval and the LTE allocated communication time interval. The WLAN device  110  may not communicate during the LTE allocated communication time interval and, likewise, the LTE device  102  may not communicate any LTE user data during the WLAN allocated communication time interval. This can ensure that LTE packet transmissions do not interfere with WLAN packet receptions and that WLAN packet transmissions do not interfere with LTE packet receptions. The WLAN coexistence unit  112  can also notify the LTE coexistence unit  104  of the WLAN allocated communication time interval and the LTE allocated communication time interval. 
     At stage C, the LTE coexistence unit  104  coordinates LTE transmission and LTE reception based, at least in part, on the WLAN allocated communication time interval and the LTE allocated communication time interval. As will be described with reference to  FIG. 3 , the LTE coexistence unit  104  can cause the LTE processing unit  106  to transmit LTE packets (e.g., the LTE user data) and to receive LTE packets only during the LTE allocated communication time interval. In some implementations, as will be described below, the LTE processing unit  106  may transmit the LTE packets only during the LTE allocated communication time interval but may receive LTE packets (e.g., control packets, data packets, etc.) from the LTE base station during either the LTE or the WLAN communication intervals. Furthermore, the LTE processing unit  106  may immediately transmit a response to the received LTE packets (e.g., an acknowledgement message) irrespective of whether this transmission (of the acknowledgement message) occurs during the LTE communication interval or the WLAN communication interval. The LTE processing unit  106  can transmit the response to the received LTE packets at low power to minimize interference with communications of the WLAN device  110 . In some implementations, the LTE device  102  may switch to a low power state during the WLAN allocated communication time interval. In other implementations, as will be described with reference to  FIGS. 6-8 , the LTE device  102  may receive (but not transmit) LTE packets during the WLAN allocated communication time interval. 
     At stage D, the WLAN coexistence unit  112  coordinates WLAN transmission and WLAN reception to minimize overlapping with LTE transmission and LTE reception based, at least in part, on the WLAN allocated communication time interval and the LTE allocated communication time interval. As will be described with reference to  FIG. 2 , the WLAN coexistence unit  112  can cause the WLAN processing unit  114  to transmit WLAN packets and receive WLAN packets only during the WLAN allocated communication time interval. In some implementations, when the WLAN device  110  is configured as an access point, the WLAN device  110  may switch to the low power state during the LTE allocated communication time interval. In other implementations, when the WLAN device  110  is configured as a WLAN client station as will be described with reference to  FIGS. 4-5 , the WLAN processing unit  114  may schedule its communications so that WLAN transmissions coincide with the LTE transmit interval and WLAN receptions coincide with the LTE receive interval. In other implementations, as will be described with reference to  FIGS. 6-8 , the WLAN processing unit  114  may receive (but not transmit) WLAN packets during the LTE allocated communication time interval. 
       FIG. 2  is a flow diagram (“flow”)  200  illustrating example operations of a WLAN device configured to implement a time-splitting scheduling coexistence mechanism for control of the communication medium. The flow  200  begins at block  202 . 
     At block  202 , a WLAN device configured as an access point detects a collocated LTE device. In one implementation, the WLAN device may be a portable router or mobile phone configured as an access point. With reference to  FIG. 1 , the LTE device  102  may be collocated with the WLAN device  110  and the WLAN coexistence unit  112  may detect the collocated LTE device  102 . In one implementation, the LTE coexistence unit  104  may transmit a coexistence signal to notify the WLAN coexistence unit  112  of the presence of the collocated LTE device  102 . In another implementation, the WLAN coexistence unit  112  may access a predetermined memory location to determine whether there are other communication devices collocated with the WLAN device  110 . In some implementations, the WLAN coexistence unit  112  may also receive the LTE schedule information  108  from the LTE coexistence unit  104 . For example, the WLAN coexistence unit  112  may receive an indication of when (i.e., a time instant) the collocated LTE device  102  is scheduled to transmit/receive LTE packets, a priority of the LTE packets scheduled to be transmitted/received, and/or other scheduling related information. The flow continues at block  204 . 
     At block  204 , a WLAN allocated communication time interval and an LTE allocated communication time interval are determined at the WLAN device. For example, the WLAN coexistence unit  112  can determine the WLAN allocated communication time interval and the LTE allocated communication time interval. In some implementations, the WLAN coexistence unit  112  can determine the WLAN allocated communication time interval and the LTE allocated communication time interval based, at least in part, on the LTE schedule information  108 . When determining the LTE allocated communication time interval and the WLAN allocated communication time interval, the WLAN coexistence unit  112  may also take into consideration a WLAN beacon interval, the frame structure (or frame interval) of an LTE base station (e.g., which may be referred to as “evolved NodeB” or “eNodeB” for LTE) to which the LTE device  102  is connected, a maximum duration for which the LTE device  102  can delay transmitting a response (e.g., acknowledgement messages, etc.) to the LTE base station before the LTE packet will be retransmitted, and/or other related information. The LTE coexistence unit  104  can provide the LTE schedule information  108 , the LTE frame interval, the LTE transmission/reception period, and/or other LTE related information to the WLAN coexistence unit  112  in one or more coexistence messages sent via the interface  120 . In another implementation, the WLAN allocated communication time interval and the LTE allocated communication time interval can be predefined to a default value. In another implementation, the WLAN allocated communication time interval and the LTE allocated communication time interval may be dynamically configurable. In some implementations, the WLAN coexistence unit  112  may allot an equal amount of time for the WLAN allocated communication time interval and the LTE allocated communication time interval. For example, WLAN coexistence unit  112  may determine that the WLAN allocated communication time interval and the LTE allocated communication time interval should each be 20 ms. In other implementations, the WLAN coexistence unit  112  may allot different amounts of time for the WLAN allocated communication time interval and the LTE allocated communication time interval (e.g., depending on the LTE schedule information  108 , the WLAN beacon interval, the LTE frame interval, etc.). For example, WLAN coexistence unit  112  may determine that the WLAN allocated communication time interval should be 20 ms and that the LTE allocated communication time interval should be 30 ms. As will be described below, the WLAN device  110  can coordinate its communications (e.g., WLAN packet transmissions and WLAN packet receptions) to be within the WLAN allocated communication time interval. For example, the WLAN and LTE allocated communication time intervals may be allotted such that a first 20 ms is allocated to the WLAN device  110 , the next 20 ms is allocated to the LTE device  102 , the next 20 ms is allocated to the WLAN device  110 , and so on. In other words, the WLAN allocated communication time interval and LTE allocated communication time interval can be consecutive and periodically repeating time intervals. The WLAN processing unit  114  can then ensure that the WLAN device  110  communicates during the allocated 20 ms and enters the low power state during the 20 ms time interval allocated to the LTE device  102 . The flow continues at block  206 . 
     At block  206 , a notification of the WLAN allocated communication time interval and the LTE allocated communication time interval is provided to the collocated LTE device. In one implementation, the WLAN coexistence unit  112  can provide a coexistence message via the interface  120  indicating the WLAN allocated communication time interval and the LTE allocated communication time interval to the LTE coexistence unit  104 . For example, the WLAN coexistence unit  112  may indicate that the WLAN allocated communication time interval and the LTE allocated communication time interval are 20 ms long. The WLAN coexistence unit  112  may also indicate a time instant at which the LTE allocated communication time interval is scheduled to start or a time interval after which the LTE allocated communication time interval will start. For example, the WLAN coexistence unit  112  may indicate that the LTE allocated communication time interval of 20 ms will start after 10 ms. As will be described with reference to  FIG. 3 , the LTE device  102  can coordinate its communications (e.g., LTE packet transmissions) to be within the LTE allocated communication time interval. The flow continues at block  208 . 
     At block  208 , it is determined whether the WLAN allocated communication time interval is currently in progress. For example, the WLAN coexistence unit  112  can determine whether the WLAN allocated communication time interval is currently in progress. In one implementation, the WLAN coexistence unit  112  can implement a WLAN coexistence timer to determine whether the WLAN allocated communication time interval is currently in progress. The WLAN coexistence unit  112  and/or other processing components of the WLAN device  110  can detect a trigger (based on the WLAN coexistence timer) when the WLAN allocated communication time interval begins or elapses. As described above, the WLAN processing unit  114  may be permitted to transmit or receive WLAN packets only during the WLAN allocated communication time interval. In some implementations, the WLAN coexistence unit  112  can determine whether the WLAN allocated communication time interval is currently in progress and can notify the WLAN processing unit  114  when the WLAN allocated communication time interval begins and ends. In another implementation, the WLAN processing unit  114  can itself keep track of when the WLAN allocated communication time interval begins and ends. If it is determined that the WLAN allocated communication time interval is currently in progress, the flow continues at block  210 . Otherwise, the flow continues at block  216 . 
     At block  210 , WLAN packets are exchanged with one or more WLAN stations connected to the WLAN device. The flow  200  moves from block  208  to block  210  if the WLAN coexistence unit  112  determines that the WLAN allocated communication time interval is currently in progress. During the WLAN allocated communication time interval, the WLAN processing unit  114  can receive WLAN packets from one or more WLAN stations connected to the WLAN device  110  (e.g., when the WLAN device  110  is configured as a WLAN access point). The WLAN processing unit  114  can poll the connected WLAN stations to cause the connected WLAN stations to transmit their respective WLAN packets (if any). The WLAN processing unit  114  can also transmit WLAN packets intended for the connected WLAN stations and can also transmit control messages (e.g., beacon messages, probe response messages, etc.). In one implementation, the WLAN processing unit  114  can determine (e.g., based on the WLAN schedule information  116 , based on data in a data transmit queue, etc.) a number of WLAN packets that can be transmitted before the WLAN allocated communication time interval elapses or before the WLAN device  102  is scheduled to receive a WLAN packet. The flow continues at block  212 . 
     At block  212 , it is determined whether to handoff control to the LTE device to initiate the LTE allocated communication time interval. For example, the WLAN coexistence unit  112  can determine whether to handoff control to the LTE device  102  to initiate the LTE allocated communication time interval. In one implementation, the WLAN coexistence unit  112  can access the WLAN coexistence timer to determine whether to handoff control to the LTE device  102  to initiate the LTE allocated communication time interval. In another implementation, the WLAN coexistence timer may notify the WLAN coexistence unit  112  just before the WLAN allocated communication time interval elapses. For example, based on knowledge that the WLAN device  110  requires 1 ms to transmit control messages (e.g., to one or more WLAN devices such as WLAN access points, connected WLAN stations, etc.) for switching to the low power state, the WLAN coexistence timer may indicate (e.g., to the WLAN coexistence unit  112 ) to handoff control and suspend WLAN communications 1 ms before the WLAN allocated communication time interval elapses. If it is determined to handoff control to the LTE device  102  to initiate the LTE allocated communication time interval, the flow continues at block  214 . Otherwise, the WLAN device  110  retains control of the communication medium and the flow loops back to block  210  where the WLAN device  110  can continue to communicate with the WLAN stations connected to the WLAN device  110 . 
     At block  214 , a control message is broadcast to other WLAN devices to prevent WLAN communications associated with the WLAN device. For example, the WLAN processing unit  114  can broadcast a CTS2SELF control message to other WLAN devices to prevent WLAN communications. As part of the CTS2SELF message, the WLAN processing unit  114  can also indicate a time interval (e.g., the LTE allocated communication time interval) for which the other WLAN devices should not initiate WLAN communications. For example, the WLAN processing unit  114  can set a network allocation vector (NAV) parameter in the CTS2SELF message to indicate the time interval for which the WLAN communications should not be initiated. The WLAN devices that receive the CTS2SELF message from the WLAN device  110  do not initiate WLAN communications. This can free the communication medium from WLAN communications, thus preventing interference between LTE communications and WLAN communications during the LTE allocated communication time interval. It is noted that in some implementations, on determining to handoff control to the LTE device  102 , the WLAN processing unit  114  can transmit (via the interface  120 ) a coexistence message to the LTE device  102  to indicate the start of the LTE allocated communication time interval. The flow continues at block  216 . 
     At block  216 , the WLAN device switches to a low power state. For example, the WLAN coexistence unit  112  can cause the WLAN processing unit  114  and the other processing components of the WLAN device  110  to switch to the low power state (e.g., a low power state, an idle state, etc.). The flow  200  moves from block  208  to block  216  on determining that the WLAN allocated communication time interval is currently not in progress (i.e., that the LTE allocated communication time interval is in progress). The flow  200  moves from block  214  to block  216  after the WLAN device  110  broadcasts the control message to prevent WLAN communications during the LTE allocated communication time interval. For example, because of the CTS2SELF message transmitted at block  214 , the WLAN device  110  does not transmit WLAN packets or receive WLAN packets when the WLAN allocated communication time interval is not in progress (i.e., during the LTE allocated communication time interval). From block  216 , the flow loops back to block  208  where the WLAN coexistence unit  112  determines whether the WLAN allocated communication time interval has begun (i.e., when to switch to an active power state). It is noted that on determining (e.g., based on the WLAN coexistence timer) that the WLAN allocated communication time interval will begin, the WLAN coexistence unit  112  can transmit a control message to cause the processing components of the WLAN device  110  to switch to the active power state (e.g., an awake mode, a high power state, etc.). 
     Although  FIG. 2  describes the WLAN device  110  switching to the low power state and not initiating WLAN communications during the LTE allocated communication time interval, embodiments are not so limited. In some implementations, the WLAN device  110  may be permitted to transmit messages that cannot be delayed until the WLAN allocated communication time interval begins (“emergency WLAN messages”). During the LTE allocated communication time interval, the WLAN device  110  may request the LTE device  102  for permission to transmit the emergency WLAN messages (e.g., WLAN beacon messages, high priority messages, immediate acknowledgement messages, etc.) by sending a coexistence message via the interface  120 . 
       FIG. 3  is a flow diagram  300  illustrating example operations of an LTE device configured to implement a time-splitting scheduling coexistence mechanism for control of the communication medium. The flow  300  begins at block  302 . 
     At block  302 , an LTE allocated communication time interval and a WLAN allocated communication time interval are determined at an LTE device collocated with a WLAN device. In one implementation, as described with reference to  FIG. 1 , the LTE coexistence unit  104  can receive an indication of the LTE allocated communication time interval and the WLAN allocated communication time interval from the WLAN coexistence unit  112 . As described above, the LTE allocated communication time interval and the WLAN allocated communication time interval can be successively alternating time intervals. The LTE device  102  and the WLAN device  110  may communicate during the LTE allocated communication time interval and the WLAN allocated communication time interval, respectively. The flow continues at block  304 . 
     At block  304 , it is determined whether the LTE allocated communication time interval is currently in progress. For example, the LTE coexistence unit  104  can determine whether the LTE allocated communication time interval is currently in progress. The LTE coexistence unit  104  can implement an LTE coexistence timer to determine whether the LTE allocated communication time interval is currently in progress. The LTE coexistence unit  104  and/or other processing components of the LTE device  102  may detect a trigger (based on the LTE coexistence timer) when the LTE allocated communication time interval begins or elapses. As will be described below, the LTE processing unit  106  may be permitted to transmit or receive LTE packets only during the LTE allocated communication time interval. If it is determined that the LTE allocated communication time interval is currently in progress, the flow continues at block  306 . Otherwise, the flow continues at block  312 . 
     At block  306 , LTE packets are exchanged with an LTE base station to which the LTE device is connected. The flow  300  moves from block  304  to block  306  if the LTE coexistence unit  104  determines that the LTE allocated communication time interval is currently in progress. During the LTE allocated communication time interval, the LTE processing unit  106  can receive LTE packets from the LTE base station (also known as eNodeB). The LTE processing unit  106  can also transmit LTE packets to the LTE base station. In one implementation, the LTE processing unit  106  can determine (e.g., based on the LTE schedule information  108 ) a number of LTE packets that can be transmitted/received during the LTE allocated communication time interval. The flow continues at block  308 . 
     At block  308 , it is determined whether to handoff control to the WLAN device to initiate the WLAN allocated communication time interval. For example, the LTE coexistence unit  104  can determine whether to handoff control to the WLAN device  110  to initiate the WLAN allocated communication time interval. In one implementation, the LTE coexistence unit  104  can access the LTE coexistence timer to determine whether to handoff control to the WLAN device  110  to initiate the WLAN allocated communication time interval. In another implementation, the LTE coexistence timer may notify the LTE coexistence unit  104  just before the LTE allocated communication time interval elapses to enable the LTE device  102  to prevent subsequent LTE communications during the WLAN allocated communication time interval (as will be described below). If it is determined to handoff control to the WLAN device  110  to initiate the WLAN allocated communication time interval, the flow continues at block  310 . Otherwise, the LTE device  102  retains control and the flow loops back to block  306  where the LTE device  102  can continue to communicate with the LTE base station. 
     At block  310 , an absence of LTE user data at the LTE device is indicated to the LTE base station. The flow  300  moves from block  308  to block  310  if the LTE coexistence unit  104  determines to handoff control to the WLAN device  110  to initiate the WLAN allocated communication time interval. In preparation for the start of the WLAN allocated communication time interval, the LTE processing unit  106  can prevent transmission of LTE packets from the LTE device  102  to the LTE base station and can ensure that the LTE base station does not transmit LTE messages requesting LTE packets from the LTE device  102 . The LTE processing unit  106  can transmit a control message to the LTE base station to indicate that the LTE device  102  has no LTE user data to transmit. It is noted that in some implementations, on determining to handoff control to the WLAN device  110 , the LTE processing unit  106  can transmit a coexistence message to the WLAN device  110  (via the interface  120 ) to indicate the start of the WLAN allocated communication time interval. The flow continues at block  312 . 
     At block  312 , the LTE device switches to a low power state. For example, the LTE coexistence unit  104  can cause the LTE processing unit  106  and other processing components of the LTE device  102  to switch to the low power state (e.g., by sending a control signal). The flow  300  moves from block  304  to block  312  on determining that the LTE allocated communication time interval is currently not in progress. The flow  300  moves from block  310  to block  312  on determining that the LTE allocated communication time interval will elapse and that the WLAN allocated communication time interval will begin. The LTE device  102  may not transmit LTE packets or receive LTE packets when the LTE allocated communication time interval is not in progress (i.e., during the WLAN allocated communication time interval). From block  312 , the flow loops back to block  304  where the LTE coexistence unit  104  determines whether the LTE allocated communication time interval has begun (i.e., when to switch to an active power state). In some implementations, on determining (e.g., based on the LTE coexistence timer) that the LTE allocated communication time interval will begin, the LTE coexistence unit  104  can cause the processing components of the LTE device  102  to switch to the active power state (e.g., by sending a control signal). It is noted, however, that in other implementations the LTE device  102  may be configured not to switch the low power state and may, instead, remain in the active power state during the WLAN allocated communication time interval. 
     Although  FIG. 3  describes the LTE device  102  switching to the low power state and not initiating LTE communications during the WLAN allocated communication time interval, embodiments are not so limited. In some implementations, the LTE device  102  may be permitted to transmit messages that cannot be delayed until the LTE allocated communication time interval begins (“emergency LTE messages”). During the WLAN allocated communication time interval, the LTE device  102  may request the WLAN device  110  for permission to transmit the emergency LTE messages (e.g., high priority messages, immediate acknowledgement messages, etc.) by transmitting a coexistence message via the interface  120 . 
     Also, although  FIG. 3  describes the LTE device  102  switching to the low power state and preventing all LTE communications during the WLAN allocated communication time interval, embodiments are no so limited. In some implementations, when the LTE device  102  operates in a frequency division duplex (FDD) mode (e.g., using LTE Band  7  that is very close to the 2.4 GHz ISM band), the LTE device  102  may continue to receive LTE packets from the LTE base station during the WLAN allocated communication time interval and may only prevent LTE packet transmissions during the WLAN allocated communication time interval. When the LTE device  102  operates in the FDD mode, LTE packet reception may not interfere with WLAN communications because there may be sufficient frequency separation between an LTE packet reception frequency band and the 2.4 GHz ISM band to enable interference rejection. However, when the LTE device  102  operates in a time division duplex (TDD) mode, the LTE device  102  may prevent LTE packet transmissions and LTE packet receptions during the WLAN allocated communication time interval. 
     In some implementations, if the LTE device  102  receives an LTE packet from the LTE base station during the WLAN allocated communication time interval, the LTE device  102  may wait until the LTE allocated communication time interval to transmit an acknowledgement message to the LTE base station. In another implementation, however, the LTE device  102  may request the WLAN device  110  for permission to transmit an emergency LTE acknowledgement message via the interface  120  (as described above). In yet another implementation, the LTE device  102  may transmit the acknowledgement message as an inband control message at very low power. In another implementation, on receiving the LTE packet from the LTE base station during the WLAN allocated communication time interval, the LTE device  102  may transmit (without any delay) the acknowledgement message at very low power to the LTE base station via an LTE control channel. This can help minimize interference between the LTE device  102  and the WLAN device  110 , when the LTE device transmits the acknowledgement message. 
     Furthermore, it is noted that although  FIG. 2  and  FIG. 3  describe the WLAN coexistence unit  112  determining the WLAN allocated communication time interval and the LTE allocated communication time interval, and notifying the LTE device  102  of the WLAN allocated communication time interval and the LTE allocated communication time interval, embodiments are not so limited. In some implementations, the LTE coexistence unit  104  can receive a coexistence message (e.g., from the WLAN coexistence unit  112 ) indicating the presence of the collocated WLAN device  110 . In another implementation, the LTE coexistence unit  104  can access a predetermined memory location to determine whether the WLAN device  110  is collocated with the LTE device  102 . The LTE coexistence unit  104  can be configured to determine the LTE allocated communication time interval and the WLAN allocated communication time interval. In some implementations, the WLAN coexistence unit  112  may communicate the WLAN schedule information  116  to the LTE coexistence unit  104 . The LTE coexistence unit  104  can then determine the LTE allocated communication time interval and the WLAN allocated communication time interval based on the WLAN schedule information  116  and/or the LTE schedule information  108 . Similarly as described above with reference to  FIG. 2 , in some implementations, the LTE coexistence unit  104  can also consider the WLAN beacon interval and the LTE frame interval when determining the LTE allocated communication time interval and the WLAN allocated communication time interval. The LTE coexistence unit  104  may then notify the WLAN coexistence unit  112  of the LTE allocated communication time interval and the WLAN allocated communication time interval. In another implementation, the LTE coexistence unit  104  and the WLAN coexistence unit  112  can be configured to exchange one or more coexistence messages via the coexistence interface  120  to negotiate the WLAN allocated communication time interval and the LTE allocated communication time interval. 
       FIG. 4  is an example flow diagram  400  illustrating example operations for scheduling WLAN communication in accordance with an LTE communication schedule. The flow  400  begins at block  402 . 
     At block  402 , an indication of an LTE transmit interval and an LTE receive interval associated with an LTE device is received at a WLAN device from a collocated LTE device. With reference to  FIG. 1 , in some implementations, the WLAN coexistence unit  112  can receive the indication of the LTE transmit interval and the LTE receive interval from the LTE coexistence unit  104 . Typically, the LTE device  102  may adhere to multiple communication slots and each communication slot may be split into a time interval during which the LTE device  102  can transmit (referred to herein as the “LTE transmit interval”) and a time interval during which the LTE device  102  can receive (referred to herein as the “LTE receive interval”).  FIG. 5A  is an example timing diagram illustrating scheduling WLAN communication in accordance with an LTE communication schedule.  FIG. 5A  depicts the alternating LTE transmit intervals  502 A- 502 D and LTE receive intervals  504 A- 504 D. In one implementation, the communication slot may be 5 ms, the LTE transmit interval may be 2 ms, and the LTE receive interval may be 3 ms. Referring back to  FIG. 4 , in one implementation, the WLAN device  110  can be configured as a client WLAN device and can connect to a WLAN access point. As will be described below, the WLAN processing unit  114  can schedule WLAN transmissions during the LTE transmit interval and can schedule WLAN receptions during the LTE receive interval to minimize interference with LTE transmissions and LTE receptions. The flow continues at block  404 . 
     At block  404 , it is determined whether the LTE transmit interval is currently in progress. For example, the WLAN coexistence unit  112  can determine whether the LTE transmit interval is currently in progress. To minimize interference, the WLAN coexistence unit  112  can attempt to align WLAN transmissions with the LTE transmit interval. In other words, with reference to  FIG. 5A , the WLAN processing unit  114  may transmit WLAN packets only during the LTE transmit intervals  502 A- 502 D. On determining that the LTE transmit interval is not in progress, the WLAN coexistence unit  112  may automatically determine that the LTE receive interval is in progress (since the LTE transmit and receive intervals are consecutive and alternating intervals). In some implementations (as depicted in  FIG. 4 ), on determining that the LTE transmit interval is not in progress, the WLAN device  110  can wait until the start of the next LTE transmit interval to transmit WLAN packets and to request (from the WLAN access point) for WLAN packets. In other implementations, on determining that the LTE transmit interval is not in progress, the WLAN device  110  can receive one or more WLAN packets from the WLAN access point (e.g., in response to a previously transmitted request for WLAN packets, etc.). With reference to  FIG. 4 , if it is determined that the LTE transmit interval is currently in progress, the flow continues at block  406 . Otherwise, the flow loops back to block  410 . 
     At block  406 , it is determined whether WLAN packets are available for transmission to the WLAN access point. For example, the WLAN processing unit  114  can determine whether WLAN packets are scheduled to be transmitted to the WLAN access point. In one implementation, the WLAN processing unit  114  may access the WLAN schedule information  116  to determine whether there are any WLAN packets to be transmitted to the WLAN access point. In another implementation, the WLAN processing unit  114  may access a data transmit queue to determine whether there is any data to be transmitted to the WLAN access point. If the WLAN processing unit  114  determines that WLAN packets are available for transmission to the WLAN access point, the flow continues at block  408 . Otherwise, the flow continues at block  410 . 
     At block  408 , the one or more WLAN packets are transmitted to the WLAN access point to which the WLAN device is connected. The flow  400  moves from block  406  to block  408  if the WLAN coexistence unit  112  determines that the LTE transmit interval is currently in progress and if the WLAN processing unit  114  determines that one or more WLAN packets are available for transmission. With reference to  FIG. 5A , the WLAN processing unit  114  may transmit WLAN packets during the time intervals  502 A,  502 B,  502 C, and  502 D. It is noted that, in one implementation, the WLAN processing unit  114  may transmit the WLAN packets during the LTE transmit interval irrespective of whether the LTE device  102  is transmitting an LTE packet during the same time interval. In other words, the WLAN device  110  and the LTE device  102  may simultaneously transmit a WLAN packet and an LTE packet, respectively. As depicted in  FIG. 5A , the WLAN device  110  and the LTE device  102  simultaneously transmit WLAN packet  506 A and LTE packet  508 A, respectively, during the LTE transmit interval  502 A. The WLAN device  110  and the LTE device  102  simultaneously transmit WLAN packet  506 C and LTE packet  508 B, respectively, during the LTE transmit interval  502 C. In another implementation, the WLAN processing unit  114  may transmit a WLAN packet during the LTE transmit interval only when the LTE device  102  is not transmitting an LTE packet. With reference to  FIG. 5A , the WLAN processing unit  114  transmits WLAN packet  506 B during the LTE transmit interval  502 B, when the LTE device  102  does not transmit an LTE packet. The WLAN processing unit  114  does not transmit a WLAN packet during the LTE transmit interval  502 D, when the LTE device  102  transmit LTE packet  508 C. In some implementations (e.g., when the WLAN device implements 802.11b/g communication standards), the WLAN processing unit  114  may transmit only one WLAN packet within the LTE transmit interval so that the WLAN processing unit  114  can receive (in accordance with the 802.11b/g communication standards) an acknowledgement message for each WLAN packet transmitted. As will be described below, the WLAN processing unit  114  can schedule transmission of the WLAN packet towards the end of the LTE transmit interval so that the acknowledgment message for the transmitted WLAN packet is received (at the WLAN device  110 ) during the LTE receive interval. In other implementations (e.g., when the WLAN device  110  implements the 802.11n communication standard that incorporates block-ACK mechanisms), the WLAN processing unit  114  may transmit any suitable number of WLAN packets within the LTE transmit interval. In this implementation, the WLAN processing unit  114  can determine a number of WLAN packets that can be transmitted before the LTE transmit interval elapses. For example, the WLAN processing unit  114  may determine that two WLAN packets can be transmitted before the LTE transmit interval  502 A elapses. After the WLAN packets are transmitted to the WLAN access point, the flow continues at block  410 . 
     At block  410 , it is determined whether the LTE receive interval is scheduled to begin. The flow  400  moves from block  408  to block  410  after the WLAN processing unit  114  transmits the WLAN packets to the WLAN access point. The flow  400  also moves from block  406  to block  410  if the WLAN processing unit  114  determines that there are no WLAN packets to be transmitted during the LTE transmit interval. To minimize interference, the WLAN coexistence unit  112  can attempt to align WLAN receptions with the LTE receive interval. In other words, with reference to  FIG. 5A , the WLAN processing unit  114  may transmit WLAN packets only during the LTE transmit intervals  502 A- 502 D. In determining whether the LTE receive interval (e.g., the LTE receive interval  504 A) is scheduled to begin, the WLAN coexistence unit  112  can determine whether the LTE transmit interval (e.g., the LTE transmit interval  502 A) will elapse within a predetermined time interval. In one implementation, the predetermined time interval can be configured based on an amount of time required to transmit (to the WLAN access point) a request for WLAN packets intended for the WLAN device  110 . For example, if the WLAN device  110  uses a PSPoll message to request for WLAN packets intended for the WLAN device  110 , the predetermined time interval may be equal to the transmission duration associated with the PSPoll message. If it is determined that the LTE receive interval is scheduled to begin, the flow continues at block  412 . Otherwise, the flow loops back to block  404  where the WLAN coexistence unit  112  can determine whether WLAN packets are available for transmission to the WLAN access point during the LTE transmit interval. 
     At block  412 , a request for WLAN packets intended for the WLAN device is transmitted to the WLAN access point. For example, in response to the WLAN coexistence unit  112  determining that the LTE receive interval is scheduled to begin, the WLAN processing unit  114  can query the WLAN access point to determine whether one or more WLAN packets are available for the WLAN device  110 . In some implementations, on determining that the LTE receive interval is scheduled to begin, the WLAN coexistence unit  112  can cause the WLAN device  110  to switch to a power save mode and can cause the WLAN processing unit  114  to use a power save mechanism to pull (or receive) WLAN packets from the WLAN access point. As described below, with reference to  FIG. 5B , the WLAN processing unit  114  can transmit PSPoll messages, Unscheduled Automatic Power Save Delivery (UAPSD) messages, NULL messages, etc. to request (from the WLAN access point) WLAN packets intended for the WLAN device  110 . The WLAN processing unit  114  can control when to receive the WLAN packets from the WLAN access point and can, therefore, schedule WLAN receptions to coincide with the LTE receive interval.  FIG. 5B  is an example timing diagram illustrating the WLAN device  110  requesting WLAN packets from a remote WLAN access point.  FIG. 5B  depicts the LTE transmit intervals  502 A and  502 B and the LTE receive intervals  504 A and  504 B. Just before the LTE transmit interval  502 A elapses, the WLAN device  110  transmits PSPoll message  520  to the WLAN access point to request WLAN packet, if any, from the WLAN access point. Transmitting the PSPoll message  520  just before the LTE transmit interval  502 A elapses can ensure that acknowledgement message  530  from the WLAN access point is received (at the WLAN device  110 ) during the LTE receive interval  504 A. During the LTE receive interval  504 A, the WLAN access point also transmits WLAN packets  534  (e.g., MAC service data units (MSDU)) to the WLAN device  110 . During the next LTE transmit interval  502 B, the WLAN device  110  transmits acknowledgement message  522  to the WLAN access point and (towards the end of the LTE transmit interval  502 B) transmits another PSPoll message  524  to the WLAN access point. During the next LTE receive interval  504 B, the WLAN access point transmits an acknowledgement message  536  and WLAN packets  538  to the WLAN device  110 . The WLAN device  110  transmits another acknowledgement message  526  during the next LTE transmit interval. The flow continues at block  414 . 
     At block  414 , one or more WLAN packets intended for the WLAN device are received from the WLAN access point. With reference to  FIG. 5A , the WLAN processing unit  114  may receive WLAN packets (from the WLAN access point) during the LTE receive intervals  504 A,  504 B,  504 C, and  504 D. It is noted that, in one implementation, the WLAN processing unit  114  may receive the WLAN packets during the LTE receive intervals irrespective of whether the LTE device  102  is receiving an LTE packet during the same interval. In other words, the WLAN device  110  and the LTE device  102  may simultaneously receive a WLAN packet and an LTE packet, respectively. As depicted in  FIG. 5A , the WLAN device  110  and the LTE device  102  simultaneously receive WLAN packet  510 A and LTE packet  512 A, respectively, during the LTE receive interval  504 A. In another implementation, the WLAN processing unit  114  may receive a WLAN packet during the LTE receive interval only when the LTE device  102  is not receiving an LTE packet. With reference to  FIG. 5A , the WLAN processing unit  114  receives WLAN packets  510 B and  510 C during the LTE receive intervals  504 C and  504 D respectively, when the LTE device  102  does not receive an LTE packet. The WLAN processing unit  114  does not receive a WLAN packet during the LTE receive interval  504 B, when the LTE device  102  receives LTE packet  510 B. After the WLAN packets (if any) are received from the WLAN access point, the flow loops back to block  404 , where the WLAN coexistence unit  112  continues to determine whether the LTE transmit interval is in progress. 
     It is noted that in some implementations, the WLAN device  110  may be scheduled to receive a beacon message from the WLAN access point during an LTE transmit interval. The WLAN device  110  may indicate (to the LTE device  102 ) a time interval during which the WLAN device  110  expects to receive the beacon message from the WLAN access point. For example, the WLAN device  110  may notify the LTE device  102  (e.g., by transmitting a coexistence message via the interface  120 ) that the WLAN device  110  expects to receive a beacon message every 100 ms. The LTE device  102  can reschedule the LTE communications so as not to interfere with the WLAN device&#39;s reception of the beacon message. Furthermore, in some implementations, the WLAN device  110  can communicate (to the WLAN access point) an exact schedule of the time intervals during which the WLAN device  110  is permitted to transmit/receive WLAN packets. For example, with reference to  FIG. 5A , the WLAN device  110  may indicate that it can transmit WLAN packets during the LTE transmit intervals  502 A- 502 D of the WLAN allocated communication time interval and can receive WLAN packets during the LTE receive intervals  504 A- 504 D. In another implementation, the WLAN device  110  may indicate a duration of the LTE transmit interval, a duration of the LTE receive interval, a periodicity of the LTE receive interval, and/or a periodicity of the LTE transmit interval. For example, the WLAN device  110  may indicate that it will transmit WLAN packets for 2 ms within each consecutive 5 ms interval. 
       FIG. 6  and  FIG. 7  depict a flow diagram  600  illustrating example operations for scheduling WLAN communication in accordance with an LTE communication schedule while implementing a time-splitting scheduling coexistence mechanism. The flow  600  begins at block  602 . 
     At block  602 , a WLAN device receives an indication of an LTE transmit interval and an LTE receive interval from a collocated LTE device. With reference to  FIG. 1 , in some implementations, the WLAN coexistence unit  112  can receive the indication of the LTE transmit interval and the LTE receive interval from the LTE coexistence unit  104 . In one implementation, the WLAN coexistence unit  112  can receive (from the LTE coexistence unit  104 ) a coexistence message via the interface  120  that indicates the presence of the collocated LTE device  102 . The coexistence message can comprise the indication of the LTE transmit interval and the LTE receive interval. In some implementations, the LTE coexistence unit  104  may also provide the LTE schedule information  108  to the WLAN coexistence unit  112  in a coexistence message transmitted via the interface  120 . The flow continues at block  604 . 
     At block  604 , a WLAN allocated communication time interval and an LTE allocated communication time interval are determined at the WLAN device. For example, the WLAN coexistence unit  112  can determine the WLAN allocated communication time interval and the LTE allocated communication time interval. The WLAN allocated communication time interval and the LTE allocated communication time interval may be determined based on one or more of the LTE transmit interval, the LTE receive interval, the LTE schedule information  108 , the WLAN schedule information  116 , a WLAN beacon interval, an LTE frame interval, etc. In other embodiments, the WLAN allocated communication time interval and the LTE allocated communication time interval may be predefined default values or may be dynamically configurable by the WLAN coexistence unit  112 . In some implementations, the WLAN coexistence unit  112  may allot an equal amount of time for the WLAN allocated communication time interval and the LTE allocated communication time interval. In other implementations, however, the WLAN coexistence unit  112  may allot different amounts of time for the WLAN allocated communication time interval and the LTE allocated communication time interval. As described above, the WLAN allocated communication time interval and the LTE allocated communication time interval can be consecutive and periodically repeating time intervals allotted to the WLAN device  110  and the LTE device  102  for their respective communications. For example, a 20 ms time interval may be allocated to the WLAN device  110  for WLAN transmissions and WLAN receptions. The next consecutive 20 ms time interval may be allocated to the LTE device  102  for LTE transmissions and LTE receptions. With reference to  FIG. 8 , the LTE coexistence unit  104  can indicate the LTE transmit intervals  802 A- 802 H and the LTE receive intervals  804 A- 804 H. The WLAN coexistence unit  112  can determine that the WLAN allocated communication time interval  820  and the LTE allocated communication time interval  822  each comprise four LTE transmit intervals and four LTE receive intervals. In the example shown in  FIG. 8 , the WLAN allocated communication time interval  820  comprises the LTE transmit intervals  802 A- 802 D and the LTE receive intervals  804 A- 804 D. The LTE allocated communication time interval  822  comprises the LTE transmit intervals  802 E- 802 H and the LTE receive intervals  804 E- 804 H. As will be described below, during the WLAN allocated communication time interval  820 , the WLAN processing unit  114  can schedule WLAN transmissions to coincide with the LTE transmit intervals  802 A- 802 D and can schedule WLAN receptions to coincide with the LTE receive intervals  804 A- 804 D. The flow continues at block  604 . The flow continues at block  606 . 
     At block  606 , a notification of the WLAN allocated communication time interval and the LTE allocated communication time interval is provided to the collocated LTE device. For example, the WLAN coexistence unit  112  can provide the notification of the WLAN allocated communication time interval  820  and the LTE allocated communication time interval  822  to the LTE coexistence unit  104  by transmitting a coexistence message via the interface  120 . The WLAN coexistence unit  112  may also indicate a time instant at which the LTE allocated communication time interval is scheduled to start or a time interval after which the LTE allocated communication time interval will start. The flow continues at block  608 . 
     At block  608 , it is determined whether the WLAN allocated communication time interval is currently in progress. For example, the WLAN coexistence unit  112  can determine whether the WLAN allocated communication time interval  820  is currently in progress. As described above, the WLAN processing unit  114  may be permitted to transmit WLAN packets only during the WLAN allocated communication time interval  820 . If it is determined that the WLAN allocated communication time interval  820  is currently in progress, the flow continues at block  610 . Otherwise, the flow continues at block  618  in  FIG. 7 . 
     At block  610 , it is determined whether the LTE transmit interval is currently in progress. For example, the WLAN coexistence unit  112  can determine whether the LTE transmit interval  802 A- 802 D is currently in progress in response to determining that the WLAN allocated communication time interval  820  is currently in progress. To minimize interference, the WLAN coexistence unit  112  can attempt to transmit WLAN packets during the LTE transmit interval  802 A- 802 D of the WLAN allocated communication time interval  820 . In some implementations (as depicted in  FIG. 6 ), on determining that the LTE transmit interval is not in progress, the WLAN coexistence unit  112  can determine whether the WLAN allocated communication time interval is still in progress. In other implementations, on determining that the LTE transmit interval is not in progress, the WLAN coexistence unit  112  may automatically determine that the LTE receive interval is in progress (since the LTE transmit and receive intervals are consecutive and alternating intervals). The WLAN processing unit  114  can then receive one or more WLAN packets from the WLAN access point (e.g., in response to a previously transmitted request for WLAN packets, etc.). In another implementation, on determining that the LTE transmit interval is not in progress, the WLAN device  110  can wait until the start of the next LTE transmit interval of the WLAN allocated communication time interval  820  to transmit WLAN packets and to request (from the WLAN access point) for WLAN packets. With reference to  FIG. 6 , if it is determined that the LTE transmit interval  802 A- 802 D is currently in progress, the flow continues at block  612 . Otherwise, the flow loops back to block  608 . 
     At block  612 , one or more WLAN packets are transmitted to a WLAN access point to which the WLAN device is connected. The flow  600  moves from block  610  to block  612  if the WLAN coexistence unit  112  determines that the LTE transmit interval  802 A- 802 D is currently in progress within the WLAN allocated communication time interval  820 .  FIG. 8  depicts time intervals during which the WLAN processing unit  114  could potentially transmit WLAN packets. In  FIG. 8 , the WLAN processing unit  114  could transmit WLAN packets  806 A,  806 B,  806 C, and  806 D during LTE transmit intervals  802 A,  802 B,  802 C, and  802 D, respectively. In some implementations, the WLAN processing unit  114  can determine whether one or more WLAN packets are available for transmission to the WLAN access point. If so, the WLAN processing unit  114  can determine a number of WLAN packets that can be transmitted before the LTE transmit interval of the WLAN allocated communication time interval  820  elapses. For example, the WLAN processing unit  114  may determine that only one WLAN packet can be transmitted before the LTE transmit interval  802 A elapses. It should be noted that in some implementations, the WLAN device  110  may implement the 802.11n communication standards but may be connected to a remote WLAN access point that implements an older version of the 802.11 communication standards (e.g., 802.11b/g communication standards). In this implementation, the WLAN device  110  can stop transmitting WLAN packets just before the LTE receive interval (e.g.,  804 A,  804 B,  804 C, or  804 D) begins. This can enable the remote WLAN access point to provide an acknowledgement message during the LTE receive interval (i.e., so that the WLAN device  110  can receive the acknowledgement message during the LTE receive interval). After the WLAN packets, if any, are transmitted to the WLAN access point, the flow continues at block  614 . 
     At block  614 , it is determined whether the LTE receive interval is scheduled to begin. The flow  600  moves from block  612  to block  614  after the WLAN processing unit  114  transmits WLAN packets to the WLAN access point (or if the WLAN processing unit  114  determines that there are no WLAN packets to be transmitted). As described above, in determining whether the LTE receive interval (e.g., the LTE receive interval  804 A) of the WLAN allocated communication time interval  820  is scheduled to begin, the WLAN coexistence unit  112  can determine whether the LTE transmit interval (e.g., the LTE transmit interval  802 A) will elapse within a predetermined time interval (e.g., the transmission duration associated with a PSPoll message). If it is determined that the LTE receive interval  804 A- 804 D of the WLAN allocated communication time interval  820  is scheduled to begin, the flow continues at block  616 . Otherwise, the flow loops back to block  608  where the WLAN coexistence unit  112  can determine whether the WLAN allocated communication time interval  820  and the LTE transmit interval  802 A- 802 D are currently in progress. 
     At block  616 , WLAN packets intended for the WLAN device are requested and received from the WLAN access point. To minimize interference with the LTE device  102 , the WLAN processing unit  114  can attempt to receive WLAN packets during the LTE receive interval  804 A- 804 D of the WLAN allocated communication time interval  820 .  FIG. 8  depicts time intervals during which the WLAN processing unit  114  can potentially receive WLAN packets. During the WLAN allocated communication time interval  820 , the WLAN processing unit  114  can receive WLAN packets  810 A,  810 B,  810 C, and  810 D during receive intervals  804 A,  804 B,  804 C, and  804 D, respectively. In some implementations, as depicted in  FIG. 8 , the WLAN processing unit  114  may receive WLAN packets  810 A- 810 D even when the LTE device  102  is scheduled to receive LTE packets  812 A- 812 D (i.e., simultaneous WLAN and LTE reception) during the receive intervals  804 A- 804 D. In other implementations, the WLAN processing unit  114  may receive the WLAN packets only when the LTE device  102  is not scheduled to receive an LTE packet. As described above with reference to  FIG. 5B , the WLAN processing unit  114  can query the WLAN access point (e.g., by transmitting a PSPoll message) just before the LTE transmit interval  802 A- 802 D of the WLAN allocated communication time interval  820  elapses to determine whether one or more WLAN packets (intended for the WLAN device  110 ) are available at the WLAN access point. This can ensure that the WLAN processing unit  114  receives WLAN packets (or a notification that there are no WLAN packets intended for the WLAN device  110 ) during the LTE receive intervals  804 A- 804 D of the WLAN allocated communication time interval  820 . From block  616 , the flow loops back to block  608  where the WLAN coexistence unit  112  determines whether the WLAN allocated communication time interval  820  is still in progress. 
     At block  618  of  FIG. 7 , it is determined whether the LTE transmit interval of the LTE allocated communication time interval is currently in progress. The flow  600  moves from block  608  in  FIG. 6  to block  618  in  FIG. 7  on determining that the WLAN allocated communication time interval  820  is not in progress (i.e., that the LTE allocated communication time interval  822  is in progress). For example, the WLAN coexistence unit  112  can determine whether the LTE transmit interval  802 E- 802 H of the LTE allocated communication time interval  822  is currently in progress. If it is determined that the LTE transmit interval  802 E- 802 H is currently in progress, the flow continues at block  620 . Otherwise, the flow continues at block  622 , where the WLAN coexistence unit  112  can determine whether the LTE receive interval  804 E- 804 H of the LTE allocated communication time interval  822  is in progress. 
     At block  620 , WLAN transmit operations and WLAN receive operations are suspended at the WLAN device. For example, the WLAN coexistence unit  112  can cause the WLAN processing unit  114  to suspend the WLAN transmit operations and the WLAN receive operations. If the WLAN device  110  is configured as a client WLAN device, the WLAN processing unit  114  can prevent WLAN transmissions during the LTE allocated communication time interval. Also, the WLAN processing unit  114  may not prompt (e.g., by transmitting a PSPoll message) the WLAN access point to transmit WLAN packets intended for the WLAN device  110 . In other words, the WLAN coexistence unit  112  can ensure that WLAN device  110  is not transmitting or receiving WLAN packets when the LTE device  102  is programmed to transmit LTE packets.  FIG. 8  depicts time intervals during which the WLAN processing unit  114  may be prevented from transmitting or receiving WLAN packets. In  FIG. 8 , the WLAN processing unit  114  is prevented from transmitting or receiving WLAN packets during LTE transmit intervals  802 E,  802 F,  802 G, and  802 H of the LTE allocated communication time interval  822 . The flow continues at block  622 . 
     At block  622 , it is determined whether the LTE receive interval is currently in progress. The flow  600  also moves from block  618  to block  624  if the WLAN coexistence unit  112  determines that the LTE transmit interval  802 E- 802 H of the LTE allocated communication time interval  822  is not currently in progress. If the WLAN coexistence unit  112  determines that the LTE receive interval  804 E- 804 H is currently in progress, the flow continues at block  624 . Otherwise, the flow continues at block  626  where the WLAN coexistence unit  112  can determine whether the LTE transmit interval  822  is still in progress. 
     At block  624 , WLAN packets intended for the WLAN device are received from the WLAN access point. Although the WLAN processing unit  114  may not be permitted to transmit WLAN packets during the LTE transmit interval  802 E- 802 H of the LTE allocated communication time interval  822 , the WLAN processing unit  114  may be permitted to receive WLAN packets during the LTE receive intervals  804 E- 804 H of the LTE allocated communication time interval  822 . As depicted in  FIG. 8 , the WLAN processing unit  114  can potentially receive WLAN packets  810 E,  810 F,  810 G, and  810 H during LTE receive intervals  804 E,  804 F,  804 G, and  804 H, respectively, during the LTE allocated communication time interval  822 . In some embodiments, the WLAN device  110  may be permitted to receive WLAN packets during the LTE receive intervals  804 E- 804 H of the LTE allocated communication time interval  822  only if the WLAN access point (to which the WLAN device  110  is connected) supports block acknowledgements (e.g., when the WLAN device  110  implements the IEEE 802.11n communication standard that incorporates block-ACK mechanisms). This is because when the WLAN device  110  and the WLAN access point support block-ACK, the WLAN access point does not expect to receive an acknowledgement message for each WLAN packet. The WLAN device  110 , therefore, can receive WLAN packets from the WLAN access point during the LTE receive intervals  804 E- 804 H of the LTE allocated communication time interval  822  and can transmit one acknowledgement message during the WLAN communication time interval. The flow continues at block  626 . 
     At block  626 , it is determined whether the LTE allocated communication time interval is in progress. For example, the WLAN coexistence unit  112  can determine whether the LTE allocated communication time interval  822  is in progress. If it is determined that the LTE allocated communication time interval  822  is in progress, the flow continues at block  618  where the WLAN coexistence unit  112  determines whether the LTE transmit interval  802 E- 802 H is in progress. If it is determined the LTE allocated communication time interval  822  is not in progress, the flow continues at block  608  in  FIG. 6  where the WLAN coexistence unit  112  determines whether the WLAN allocated communication time interval  820  is in progress (and the LTE allocated communication time interval  822  has elapsed). 
     Although  FIG. 6  and  FIG. 7  describe operations of the WLAN device  110  when the WLAN device  110  is configured as a WLAN client device connected to a WLAN access point, embodiments are not so limited. In implementations where the WLAN device  110  is configured as a WLAN access point, the WLAN processing unit  114  can determine or receive a notification (e.g., during the WLAN allocated communication time interval  820 ) to handoff control to the LTE device  102  to initiate the LTE allocated communication time interval  822  by transmitting a coexistence message via the interface  120 . Accordingly, as described with reference to  FIG. 2 , the WLAN device  110  can broadcast a CTS2SELF control message to other WLAN devices to prevent WLAN communication. The WLAN device  110  can switch to the low power state where it neither transmits WLAN packets nor receives WLAN packets. Also, when the WLAN device  110  is configured as a WLAN access point, the WLAN device  110  can transmit WLAN packets to one or more connected WLAN devices (at block  612 ) and can receive WLAN packets from the one or more connected WLAN devices (at block  616 ). Furthermore, in some implementations, the WLAN device  110  can communicate to the WLAN access point (if the WLAN device  110  is configured as a client station), or to connected WLAN stations (if the WLAN device  110  is configured as a WLAN access point), the time intervals during which the WLAN device  110  is permitted to transmit/receive WLAN packets. For example, the WLAN device  110  may indicate that it can transmit WLAN packets during the LTE transmit intervals  802 A- 802 D of the WLAN allocated communication time interval and can receive WLAN packets during the LTE receive intervals  804 A- 804 D. 
     Although not described with reference to  FIGS. 6-7 , the LTE device  102  can also be configured to implement operations described in the flow  600  to determine whether/when to transmit and receive LTE packets. The LTE device  102  can be configured to operate in either the TDD mode (e.g., using LTE Band  40 ) or the FDD mode (e.g., using LTE Band  7 ). The LTE coexistence unit  104  can determine the presence of the collocated WLAN device  110  (e.g., based on a coexistence message received via the interface  120 ). In some implementations, the LTE coexistence unit  104  can provide the LTE schedule information  108  to the WLAN coexistence unit  112  and can receive (via the interface  120 ) an indication of the WLAN allocated communication time interval and the LTE allocated communication time interval from the WLAN coexistence unit  112 . In another implementation, the LTE coexistence unit  104  can receive, via the interface  120 , the WLAN schedule information  116  from the WLAN device  110 . Accordingly, the LTE coexistence unit  104  can determine the WLAN allocated communication time interval and the LTE allocated communication time interval. The LTE coexistence unit  104  can then provide the indication of WLAN allocated communication time interval and the LTE allocated communication time interval to the WLAN device  110 . In yet another implementation, the LTE coexistence unit  104  can receive the WLAN communication interval from the WLAN device  110  and can accordingly determine the LTE allocated communication time interval. With reference to  FIG. 8 , the LTE device  102  can determine to communicate during the LTE allocated communication time interval  822 . The LTE coexistence unit  104  can also determine the LTE transmit intervals  802 E- 802 H and the LTE receive intervals  804 E- 804 H that fall within the LTE communication time interval  822 . 
     The LTE coexistence unit  104  can determine whether the LTE allocated communication time interval  822  is currently in progress to determine whether the LTE processing unit  106  is permitted to transmit LTE packets. If the LTE allocated communication time interval  822  is currently in progress, the LTE coexistence unit  104  can determine whether one of the LTE transmit intervals  802 E- 802 H is currently in progress. The LTE device  102  can transmit LTE packets  808 A,  808 B,  808 C, and  808 D (to the LTE base station) during the LTE transmit intervals  802 E,  802 F,  802 G, and  802 H, respectively, of the LTE allocated communication time interval  822 . In some implementations, the LTE processing unit  106  can determine whether one or more LTE packets are available for transmission to the LTE base station. If so, the LTE processing unit  106  can determine a number of LTE packets that can be transmitted before the LTE transmit interval of the LTE allocated communication time interval  822  elapses. In this implementation, the LTE processing unit  106  can stop transmitting the LTE packets just before the LTE receive interval (e.g.,  804 E,  804 F,  804 G, or  804 H) begins. This can enable the LTE base station to provide an acknowledgement message during the LTE receive interval (i.e., so that the LTE processing unit  106  can receive the acknowledgement message during the LTE receive interval). If one of the LTE transmit intervals  802 E- 802 H is currently not in progress, the LTE coexistence unit  104  may automatically determine that one of the LTE receive intervals  804 E- 804 H is in progress (since the LTE transmit and receive intervals are consecutive and alternating intervals). The LTE device  102  can receive LTE packets  812 E,  812 F,  812 G, and  812 H (from the LTE base station) during the LTE receive intervals  804 E,  804 F,  804 G, and  804 H, respectively, of the LTE allocated communication time interval  822 . 
     The LTE coexistence unit  104  can also determine whether the LTE allocated communication time interval  822  is scheduled to elapse within a predetermined time interval (i.e., whether the WLAN allocated communication time interval  820  is scheduled to begin). The predetermined time interval can be selected as a time duration required (by the LTE processing unit  106 ) to transmit a control message (to the LTE base station) indicating an absence of LTE user data for transmission to the LTE base station. On determining that the WLAN allocated communication time interval  820  is scheduled to begin, the LTE processing unit  106  can transmit the control message to the LTE base station. The LTE device  102  may not transmit LTE packets during the LTE transmit intervals  802 A- 802 D of the WLAN allocated communication time interval  820 . In some implementations, the LTE device  102  may not receive LTE packets during the LTE receive intervals  804 A- 804 D of the WLAN allocated communication time interval  820 . However, in other implementations as depicted in  FIG. 8 , the LTE device  102  may be permitted to receive LTE packets  812 A,  812 B,  812 C, and  812 D (from the LTE base station) during the LTE receive intervals  804 A,  804 B,  804 C, and  804 D of the WLAN allocated communication time interval  820 . In other words, the WLAN processing unit  114  and the LTE processing unit  106  may simultaneously receive WLAN packets and LTE packets, respectively, during any LTE receive interval. In other implementations, the LTE processing unit  106  may receive LTE packets during the WLAN allocated communication time interval  820  only if the WLAN processing unit  114  is not scheduled to receive WLAN packets. Furthermore, in some implementations, the LTE device  102  may operate in a power save mode. The LTE device  102  may indicate, to the LTE base station, the LTE transmit intervals  802 E- 802 H and the LTE receive intervals  804 E- 804 H during which the LTE device can transmit and receive LTE packets, respectively. Accordingly, the LTE base station can transmit LTE packets to the LTE device  102  during the LTE receive intervals  804 E- 804 H. 
       FIG. 9  is a flow diagram  900  illustrating example operations for maximizing frequency separation between a WLAN device and a collocated LTE device when the WLAN device is configured as an access point. The flow  900  begins at block  902 . 
     At block  902 , a collocated LTE device is detected at a WLAN device configured as an access point. In one implementation, with reference to  FIG. 1 , the WLAN coexistence unit  112  can receive a control signal (from the LTE coexistence unit  104 ) identifying the collocated LTE device  102 . For example, the control signal may be a digital signal (or a coexistence message) transmitted via the interface  120 . As another example, the control signal may be a voltage level transmitted via a physical wire. In another implementation, the WLAN coexistence unit  112  can access a predetermined location (e.g., read a flag bit) to determine whether the LTE device  102  is collocated with the WLAN device  110  and/or whether the collocated LTE device  102  is enabled. The flow continues at block  904 . 
     At block  904 , an LTE operating frequency band associated with the collocated LTE device is determined. For example, the WLAN coexistence unit  112  can determine the LTE operating frequency band associated with the collocated LTE device. In some implementations, the WLAN coexistence unit  112  can receive, as part of the control signal or the coexistence message (received at block  902 ), an indication of the LTE operating frequency band. In another implementation, the WLAN coexistence unit  112  may access a predetermined location to determine the LTE operating frequency band associated with the collocated LTE device  102 . The flow continues at block  906 . 
     At block  906 , one or more WLAN frequency channels separated from the LTE operating frequency band by at least a threshold frequency separation are identified. For example, the WLAN coexistence unit  112  can identify one or more WLAN frequency channels separated from the LTE operating frequency band by at least the threshold frequency separation. For example, the collocated LTE device  102  may use LTE band  7  associated with an LTE operating frequency band of 2.5 GHz to 2.69 GHz. If the threshold frequency separation is selected to be 68 MHz, the WLAN coexistence unit  112  can identify WLAN frequency channels  1 - 5  with WLAN operating frequencies 2.412 GHz-2.432 GHz. The flow continues at block  908 . 
     At block  908 , a target WLAN frequency channel is selected from the one or more identified WLAN frequency channels. For example, the WLAN coexistence unit  112  can select the target WLAN frequency channel from the one or more identified WLAN frequency channels. In one implementation, the WLAN coexistence unit  112  can select the target WLAN frequency channel as one with a WLAN operating frequency that is farthest from the LTE operating frequency band. With reference to the above example, if the collocated LTE device  102  uses LTE band  7 , the WLAN coexistence unit  112  may select WLAN frequency channel  1  (with WLAN operating frequency of 2.412 GHz) as the target WLAN frequency channel. In another implementation, the WLAN coexistence unit  112  can select (as the target WLAN frequency channel) any one of WLAN frequency channels with a WLAN operating frequency that is separated from the LTE operating frequency band by at least the threshold frequency separation. In selecting the target WLAN frequency channel, the WLAN coexistence unit  112  can also take interference/noise sources into consideration. For example, if the WLAN frequency channel that is the farthest from the LTE operating frequency band (e.g., the WLAN frequency channel  1 ) has a lot of noise and interference, the WLAN coexistence unit  112  may select the WLAN frequency channel  2  (or another frequency channel) as the target WLAN frequency channel. In other words, the WLAN coexistence unit  112  can select the target WLAN frequency channel to maintain an optimal balance between sufficient frequency separation from the LTE operating frequency band associated with the collocated LTE device  102  and noise/interference on the WLAN frequency channels. The flow continues at block  910 . 
     At block  910 , the target WLAN frequency channel is used for communication with one or more WLAN devices. For example, the WLAN coexistence unit  112  can cause the WLAN device  110  (e.g., the WLAN processing unit  114 ) to communicate with one or more other WLAN devices via the target WLAN frequency channel. For example, the WLAN processing unit  114  can broadcast beacon messages, advertise the existence of the WLAN device  110 , and initiate subsequent communications with other WLAN devices via the target WLAN frequency channel. From block  910 , the flow ends. 
       FIG. 10  is a flow diagram  1000  illustrating example operations for maximizing frequency separation between a WLAN device and a collocated LTE device when the WLAN device is configured as a WLAN client station. The flow  1000  begins at block  1002 . 
     At block  1002 , a collocated LTE device is detected at a WLAN device configured as a client station. For example, similarly as was described above, the WLAN coexistence unit  112  can detect the collocated LTE device  102  based on an indication (e.g., a control signal, a coexistence message, etc.) received from the LTE coexistence unit  104 , based on reading a predetermined memory location, etc. The flow continues at block  1004 . 
     At block  1004 , an LTE operating frequency band associated with the collocated LTE device is determined. For example, similarly as was described above, the WLAN coexistence unit  112  can determine the LTE operating frequency band associated with the collocated LTE device based on the indication identifying the collocated LTE device  102  (received at block  1002 ), based on reading a predetermined memory location, etc. The flow continues at block  1006 . 
     At block  1006 , one or more WLAN access points with which a WLAN communication link can be established are identified. For example, the WLAN processing unit  114  can identify one or more WLAN access points with which the WLAN device  110  can establish the WLAN communication link. The WLAN processing unit  114  can scan available WLAN access points (e.g., listen for beacon messages, exchange probe request/response messages, etc.) and can identify the WLAN access point(s) with which it can establish the WLAN communication link (e.g., based on proximity of the WLAN access point to the WLAN device  110 , shared communication parameters, etc.). The flow continues at block  1008 . 
     At block  1008 , a WLAN operating frequency associated with each of the identified WLAN access points is determined. For example, the WLAN processing unit  114  can determine the WLAN operating frequency associated with each of the WLAN access points identified at block  1006 . The WLAN processing unit  114  can read beacon messages, transmit probe request messages, receive probe response messages, etc. from each of the WLAN access points (identified at block  1006 ) to determine their respective WLAN operating frequency. For example, the WLAN processing unit  114  may determine that a first WLAN access point uses WLAN channel  1  (with operating frequency 2.412 GHz), that a second WLAN access point uses WLAN channel  3  (with operating frequency 2.422 GHz), and that a third WLAN access point uses WLAN channel  11  (with operating frequency 2.462 GHz). The flow continues at block  1010 . 
     At block  1010 , a target WLAN access point associated with a WLAN operating frequency that is farthest from the LTE operating frequency band is identified. For example, the WLAN coexistence unit  114  can select the target WLAN access point as one of the WLAN access points identified at block  1006  that is associated with a WLAN operating frequency that is sufficiently separated from the LTE operating frequency. With reference to the above example, if the collocated LTE device  102  uses LTE band  7  with an LTE operating frequency band of 2.5 GHz to 2.69 GHz, the WLAN coexistence unit  112  can select the first WLAN access point that uses WLAN channel  1 . In some implementations, the WLAN coexistence unit  112  can also take interference/noise sources into consideration when selecting the target WLAN access point. For example, if the WLAN coexistence unit  112  determines that WLAN channel  1  is subject to a lot of interference/noise, the WLAN coexistence unit  112  can select another WLAN access point associated with another WLAN operating frequency. In the above example, the WLAN coexistence unit  112  may select the second WLAN access point that uses WLAN channel  3  if WLAN channel  3  is deemed to be sufficiently separated from LTE frequency band  7 . The flow continues at block  1012 . 
     At block  1012 , the WLAN communication link is established with the target WLAN access point. For example, the WLAN processing unit  114  can exchange association request and response messages, authentication request and response messages, etc. with the target WLAN access point to establish the WLAN communication link with the target WLAN access point. From block  1012 , the flow ends. 
     Although not described with reference to  FIG. 10 , it is noted that if the WLAN coexistence unit  112  cannot identify any WLAN access point with a WLAN operating frequency that is sufficiently separated from the LTE operating frequency band and with an acceptable noise level, the WLAN coexistence unit  112  can determine not to establish a WLAN communication link with any of the available WLAN access points and can continue to scan for additional WLAN access points. 
     It should be understood that  FIGS. 1-10  are examples meant to aid in understanding embodiments and should not be used to limit embodiments or limit scope of the claims. Embodiments may perform additional operations, fewer operations, operations in a different order, operations in parallel, and some operations differently. Typically, when the WLAN device  110  (e.g., a WLAN access point or a WLAN client station) supports 802.11b/g communication standards (i.e., when the WLAN device  110  does not support block-ACK), the WLAN device  110  expects to receive an acknowledgement (ACK) message when the WLAN device  110  transmits a WLAN packet to a destination WLAN device. If the WLAN device  110  does not receive the ACK message, the WLAN device  110  may retransmit the WLAN packet at progressively lower modulation levels (e.g., at lower data rates) until the ACK message is received or until the lowest modulation level is reached. However, such a rate fallback procedure can increase the packet transmit time. In some implementations, if the WLAN coexistence unit  112  detects the LTE device  102  collocated with the WLAN device  110 , the WLAN processing unit  114  may not implement the rate fallback procedures if the WLAN device  110  does not receive the ACK message in response to a transmitted WLAN packet. In some implementations, the WLAN processing unit  114  may not implement the rate fallback procedures if it is determined that the LTE device  102  is scheduled to transmit/receive an LTE packet, or if it is determined that the LTE allocated communication time interval will start. In another implementation, the WLAN processing unit  114  may disable the rate fallback procedures on detecting the collocated LTE device  102 . The WLAN processing unit  114  may retransmit the WLAN packet at the original modulation level. In another implementation, the WLAN processing unit  114  may implement the rate fallback procedures only if the WLAN packet can be completely retransmitted at a lower modulation level within the WLAN allocated communication time interval. Otherwise, the WLAN processing unit  114  may wait until the next WLAN allocated communication time interval to retransmit the WLAN packet at the lower modulation level. This can help prevent an “avalanche” effect because of WLAN packet retransmission at progressively lower modulation levels. Preventing the rate fallback procedures can also help minimize collision between retransmitted WLAN packets and LTE packets. 
     It is also noted that in some implementations the WLAN coexistence unit  112  and the LTE coexistence unit  104  may be capable of resolving contention between the WLAN schedule information  116  and the LTE schedule information  108 . For example, using coexistence messages transmitted via the interface  120 , the WLAN coexistence unit  112  and the LTE coexistence unit  104  may resolve contention based on priority of pending WLAN and LTE communications or based on a start time of the communications. 
     Embodiments may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, embodiments of the inventive subject matter may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium. The described embodiments may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic device(s)) to perform a process according to embodiments, whether presently described or not, since every conceivable variation is not enumerated herein. A machine-readable medium includes any mechanism for storing or transmitting information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). A machine-readable medium may be a non-transitory machine-readable storage medium, or a transitory machine-readable signal medium. A machine-readable storage medium may include, for example, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of tangible medium suitable for storing electronic instructions. A machine-readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, an electrical, optical, acoustical, or other form of propagated signal (e.g., carrier waves, infrared signals, digital signals, etc.). Program code embodied on a machine-readable medium may be transmitted using any suitable medium, including, but not limited to, wireline, wireless, optical fiber cable, RF, or other communications medium. 
     Computer program code for carrying out operations of the embodiments may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on a user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN), a personal area network (PAN), or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
       FIG. 11  is a block diagram of an electronic system  1100  including a coexistence mechanism between collocated wireless communication devices, according to some embodiments. In some implementations, the electronic system  1100  may be one of a personal computer (PC), a laptop, a tablet computer, a netbook, a mobile phone, a gaming console, or other electronic devices comprising a collocated WLAN device  1112  and an LTE device  1118 . In some implementations, the LTE device  1118  and the WLAN device  1112  can be embodied on distinct integrated circuits (e.g., distinct LTE and WLAN chips) on a common circuit board (or on separate circuit boards in close proximity). In other implementations, the LTE device  1118  and the WLAN device  1112  can be embodied on a single integrated circuit (e.g., a system on a chip (SoC)). The LTE device  1118  and the WLAN device  1112  can be included within various types of electronic devices with wireless communication capabilities (e.g., mobile phones, notebook computer, tablet computers, gaming consoles, personal computers, etc). The electronic system  1100  includes a processor unit  1102  (possibly including multiple processors, multiple cores, multiple nodes, and/or implementing multi-threading, etc.). The electronic system  1100  includes a memory unit  1106 . The memory unit  1106  may be system memory (e.g., one or more of cache, SRAM, DRAM, zero capacitor RAM, Twin Transistor RAM, eDRAM, EDO RAM, DDR RAM, EEPROM, NRAM, RRAM, SONOS, PRAM, etc.) or any one or more of the above already described possible realizations of machine-readable media. The electronic system  1100  also includes a bus  1110  (e.g., PCI, ISA, PCI-Express, HyperTransport®, InfiniBand®, NuBus, etc.), and network interfaces  1104  that include one or more of a wireless network interface (e.g., a WLAN interface, a Bluetooth® interface, a WiMAX interface, a ZigBee® interface, a Wireless USB interface, etc.) and a wired network interface (e.g., an Ethernet interface, etc.). 
     The electronic system  1100  also includes a communication unit  1108 . The communication unit  1108  comprises the WLAN device  1112  and the LTE device  1118 . In some implementations, the LTE device  1118  comprises an LTE coexistence unit  1122  coupled to an LTE processing unit  1120 . The WLAN device  1112  comprises a WLAN coexistence unit  1114  coupled to a WLAN processing unit  1116 . In some implementations, as described with reference to  FIGS. 1-3 , the WLAN coexistence unit  1114  and the LTE coexistence unit  1122  can schedule their respective communications within a WLAN allocated communication time interval and an LTE allocated communication time interval respectively. In another implementation, as described with reference to  FIGS. 4-5 , the WLAN coexistence unit  1114  may schedule its communications so that WLAN transmissions coincide with an LTE transmit interval and WLAN receptions coincide with an LTE receive interval. In another implementation, as described with reference to  FIGS. 6-8 , the WLAN coexistence unit  1114  can schedule WLAN transmissions within the LTE transmit interval of the WLAN allocated communication time interval. Furthermore, as described in  FIGS. 9-10 , the WLAN coexistence unit  1114  may comprise functionality to select a WLAN frequency channel (when the WLAN device  1112  is configured as an access point) or to select a WLAN access point based on the operating frequency of the WLAN access points (e.g., when the WLAN device  1112  is configured as a client station). 
     Any one of the above-described functionalities may be partially (or entirely) implemented in hardware and/or on the processor unit  1102 . For example, the functionality may be implemented with an application specific integrated circuit, in logic implemented in the processor unit  1102 , in a co-processor on a peripheral device or card, etc. Further, realizations may include fewer or additional components not illustrated in  FIG. 11  (e.g., additional network interfaces, peripheral devices, etc.). The processor unit  1102  and the network interfaces  1104  are coupled to the bus  1110 . Although illustrated as being coupled to the bus  1110 , the memory  1106  may be coupled to the processor unit  1102 . 
     While the embodiments are described with reference to various implementations and exploitations, it will be understood that these embodiments are illustrative and that the scope of the inventive subject matter is not limited to them. In general, a coexistence mechanism for collocated WLAN and WWAN communication devices as described herein may be implemented with facilities consistent with any hardware system or hardware systems. Many variations, modifications, additions, and improvements are possible. 
     Plural instances may be provided for components, operations, or structures described herein as a single instance. Finally, boundaries between various components, operations, and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the inventive subject matter. In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the inventive subject matter.