Abstract:
A concurrent control method for a communication device embedded with Wi-Fi Direct includes dynamically adjusting a target beacon transmission time (TBTT) of a Wi-Fi Direct connection according to a time difference between the TBTT of the communication device and a nearest TBTT of a wireless local area network access point (WLAN AP) and whether a channel for the Wi-Fi Direct connection and a channel for the WLAN connection are different.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a concurrent control method for a communication device embedded with Wi-Fi Direct, and more particularly, to a concurrent control method to handle network scheduling and power saving when the communication device acts as a peer-to-peer (P2P) group owner and at the same time connects with a conventional wireless local area network (WLAN) access point (AP). 
         [0002]    Wi-Fi Direct is a wireless communication protocol that allows Wi-Fi devices to communicate with each other without connecting to a traditional WLAN AP, which increases connectivity and a great number of P2P applications. Wi-Fi Direct is simply a software-only protocol and can be built into any Wi-Fi device. With a growing demand for Wi-Fi Direct application, the scenario of two or more protocols coexistence, e.g. a legacy WLAN protocol such as IEEE 802.11a/g/n coexisting with Wi-Fi Direct, or a 3G/4G protocol coexisting with Wi-Fi Direct, is applied in kinds of communication devices as laptops, smart phones and multimedia devices which are embedded with Wi-Fi Direct. 
         [0003]    Please refer to  FIG. 1 , which is a diagram of a wireless network  10 , including a WLAN AP  100 , a communication device  102  which is embedded with a legacy WLAN protocol and Wi-Fi Direct as a laptop, and devices  104 ,  106  and  108  as a TV, a projector, or a digital camera. The left half of the wireless network  10  illustrates a traditional WLAN where the communication device  102  is a client station of a base service set (BSS) and can access the internet through the WLAN AP  100 . The right half of the wireless network  10  illustrates a P2P network where the communication device  102  is a P2P group owner acting as an AP and connects with the devices  104 ,  106  and  108  as P2P client devices. The communication device  102  can access the internet through the WLAN AP  100  and use P2P services at the same time. In addition, the communication device  102  may connect with a Bluetooth embedded device or may access 3G/4G network and also use P2P services at the same time. 
         [0004]    Timing synchronization function (TSF) is specified in IEEE 802.11 WLAN standards to achieve timing synchronization by periodically exchanging timing information through beacons. An AP in a BSS transmits beacons periodically to all client stations in the same BSS and each beacon includes a timestamp, which indicates the value of a TSF timer of the AP, and a beacon interval, which indicates the distance between two beacons. Beacons are sent at every target beacon transmission time (TBTT). Each client station in the BSS also maintains a local TSF timer counting in increments of microseconds, so they can miss a beacon and still remain roughly synchronized with the TSF timer of the AP. Upon receiving a beacon, a client station sets its local TSF timer to the timestamp included in the received beacon if the timestamp is later than its local TSF timer. 
         [0005]    Please refer to  FIG. 2 , which is a diagram of beacon transmission of the communication device  102 , illustrating beacons sent to P2P client devices and beacons received from the WLAN AP  100  in the condition that the P2P network and the BSS of the WLAN AP  100  operate on different channels, e.g. channel  3  and channel  11 . As shown in  FIG. 2 , the communication device  102  establishes the P2P network first and connects to the WLAN AP  100  later. Since the communication device  102  acts as an AP, it periodically sends beacons to the P2P client devices  104 ,  106  and  108  at every TBTT and sends broadcast/unicast frame (if any) after TBTT. After the connection with the WLAN AP  100  is established, the communication device  102  starts to listen to beacons from the WLAN AP  100  at TBTTs of the WLAN AP  100 . 
         [0006]    Note that, in the case of the communication device  102  implemented by a single MAC/PHY solution, the communication device  102  has to switch between channels if the established P2P network and the BSS of the WLAN AP  100  operates on different channels. However, as shown in  FIG. 2 , when TBTT of the WLAN AP  100  is close to TBTT of the communication device  102 , the communication device  102  is unable to switch from channel  3  to channel  11  to receive beacons from the WLAN AP  100  because it needs time to send beacons and broadcast frames to P2P client devices. As a result, the connection with the WLAN AP  100  may be suffered from the increasing of buffered packet delay time due to the lost of WLAN AP&#39;s beacon. On the other hand, if the communication device  102  switches from channel  3  to channel  11  to listen to beacons and broadcast frames sent from the WLAN AP  100 , P2P network performance degrades due to information leakage. 
         [0007]    Therefore, when the WLAN AP establishes the WLAN connection with the communication device  102  by using a channel different from the communication device uses to establish P2P network, it is hard to do fast network scheduling on an overlapping period of the broadcast frames of the communication device  102  and the WLAN AP  100 . 
         [0008]    Please refer to  FIG. 3 , which is a diagram of beacon transmission of the communication device  102  in the condition that the P2P network and the BSS of the WLAN AP  100  operate on the same channel, e.g. channel  6 . Similar to the illustrated in  FIG. 2 , the communication device  102  establishes the P2P network first and then connects to the WLAN AP  100 . As shown in  FIG. 3 , TBTT of the WLAN AP  100  is far away from TBTT of the communication device  102 , and the communication device  102  has to wake up to listen beacons during each period of the power saving mode of a P2P group owner. Thus, power consumption increases. Besides, if the communication device  102  is also embedded with a TDMA-based protocol, TBTT of the communication device  102  may collide with an important time slot when it communicates with a TDMA-based communication device after the P2P network is established. 
         [0009]    Therefore, concurrent operation of Wi-Fi Direct and a traditional WLAN protocol or a TDMA-based protocol is a major consideration to improve Wi-Fi Direct application. 
       SUMMARY OF THE INVENTION 
       [0010]    It is therefore a primary objective of the claimed invention to provide a concurrent control method for a communication device embedded with Wi-Fi Direct. 
         [0011]    According to an embodiment of the present invention, A concurrent control method for a communication device embedded with Wi-Fi Direct includes dynamically adjusting a target beacon transmission time (TBTT) of a Wi-Fi Direct connection according to a time difference between the TBTT of the communication device and a nearest TBTT of a wireless local area network access point (WLAN AP) and whether a channel for the Wi-Fi Direct connection and a channel for the WLAN connection are different. 
         [0012]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a diagram of a wireless network according to the prior art. 
           [0014]      FIG. 2  and  FIG. 3  are diagrams of beacon transmission of a communication device embedded with a legacy WLAN protocol and Wi-Fi Direct. 
           [0015]      FIG. 4  is a flowchart of a process according to an embodiment of the present invention. 
           [0016]      FIG. 5  and  FIG. 6  are diagrams of beacon transmission of a communication device using the process of  FIG. 4 . 
           [0017]      FIG. 7  is a flowchart of a process according to an embodiment of the present invention. 
           [0018]      FIG. 8  is a flowchart of a process according to an embodiment of the present invention. 
           [0019]      FIG. 9  and  FIG. 10  are diagrams of beacon transmission of a communication device using the process of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, electronic equipment manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . .” Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0021]    Please refer to  FIG. 4 , which is a flowchart of a process  40  according to an embodiment of the present invention. The process  40  is utilized in a communication device embedded with at least a WLAN protocol, e.g. IEEE 802.11a/g/n and Wi-Fi Direct, such as the communication device  102  in  FIG. 1 . The process  40  is performed under a condition that when the communication device acts as a P2P group owner, first establishes a Wi-Fi Direct connection (also called P2P connection) with P2P client devices and later establishes a WLAN connection with a WLAN AP. After the WLAN connection is established, the communication device performs the process  40  to control concurrent operation of the WLAN protocol and Wi-Fi Direct, for improving network scheduling and reducing power consumption as illustrated in  FIG. 2  and  FIG. 3 . The process  40  comprises the following steps: 
         [0022]    Step  400 : Start. 
         [0023]    Step  402 : Measure a time difference D between a TBTT of the communication device and a nearest, TBTT of the WLAN AP for timing synchronization of the communication device. 
         [0024]    Step  404 : Check whether a channel for the Wi-Fi Direct connection and a channel for the WLAN connection are different. If yes, perform  406 ; else, perform Step  412 . 
         [0025]    Step  406 : Check whether the time difference D is less than a threshold TH 1 . If yes, perform Step  408 ; else, perform Step  418 . 
         [0026]    Step  408 : Shift a time synchronization function (TSF) timer of the communication device by a first shift value to make a time difference between TBTT of the communication device and TBTT of the WLAN AP greater than the threshold TH 1 . 
         [0027]    Step  410 : Send a first message including the timestamp of the TSF timer of the communication device to a P2P client device for updating a TSF timer of the P2P client device, wherein the first message to the P2P client device is sent prior a first shifted beacon. 
         [0028]    Step  412 : Check whether the time difference D is larger than a threshold TH 2 . If yes, perform Step  414 ; else, perform Step  418 . 
         [0029]    Step  414 : Shift a TSF timer of the communication device by a second shift value to make a time difference between TBTT of the communication device and TBTT of the WLAN AP less than the threshold TH 2 . 
         [0030]    Step  416 : Send a second message including the timestamp of the TSF timer of the communication device to a P2P client device prior to sending the first shifted beacon, to update a TSF timer of the P2P client device. 
         [0031]    Step  418 : End. 
         [0032]    Please note that, the process  40  is preferred to be utilized in the communication device (as the P2P group owner) which has a beacon interval identical to the beacon interval of the WLAN AP. In order to realize the process  40 , please also refer to  FIG. 5  and  FIG. 6 , which are diagrams of beacon transmission of the communication device performing the process  40 , including beacons sent to P2P client devices and beacons received from the WLAN AP, based on different condition that the channel for the Wi-Fi Direct connection and the channel for the WLAN connection are different or the same. The beacon interval of the communication device and the beacon interval of the WLAN AP are the same, e.g. 100 ms. 
         [0033]    As shown in  FIG. 5 , since the Wi-Fi Direct connection and the WLAN connection are established on different channels, the communication device has to enter a power saving mode (relative to the P2P network) to switch channel to establish the WLAN connection. As shown in  FIG. 6 , since the Wi-Fi Direct connection and the WLAN connection are on the same channel, the communication device can directly establish the WLAN connection without switching channel. As a P2P group owner, the communication device knows its own beacon interval and its local TSF timer. During the establishment of WLAN connection (that is, the period that communication device enters the connected phase), the communication device can obtain information about the value of TSF timer of the WLAN AP and the beacon interval of the WLAN AP, and performs the process  40 . 
         [0034]    The process  40  is described in detail as follows. According to Step  402 , the communication device measures a time difference between a TBTT of the communication device and a nearest, TBTT of the WLAN AP for timing synchronization of the communication device, denoted as D as shown in  FIG. 5 . Please note that, the communication device can measure the time difference D in advance without waiting until actual TBTT of the WLAN AP because TBTT of the WLAN AP can be derived according to the TSF timer of the WLAN AP, which is known to the communication device during the establishment of WLAN connection. 
         [0035]    Then, the communication device can compare the time difference D with at least one threshold to determine whether shifting a time synchronization function (TSF) timer of the communication device. Specifically, according to Step  404 , the communication device checks whether the channel used for the Wi-Fi Direct connection and the channel used for the WLAN connection are different. When the used channels are different, according to Step  406 , the communication device further checks whether the time difference D is less than a threshold TH 1 . The threshold TH 1  can be the minimum time difference the communication device requires for switching channels, such as switching from channel  3  to channel  11  as illustrated in  FIG. 5 . If the time difference D is less than the threshold TH 1 , the communication device will not be able to switch to other channel to receive a beacon from the WLAN AP; in opposite, if the time difference D is larger than the threshold TH 1 , the communication device has enough time to switch channel to receive a beacon from the WLAN AP and there is no problem to do network scheduling of Wi-Fi Direct and WLAN. 
         [0036]    On the other side, when the channel used for the Wi-Fi Direct connection and the channel used for the WLAN connection are the same, according to Step  412 , the communication device further checks whether the time difference D is larger than a threshold TH 2 . The threshold TH 2  can be the maximum time difference between the two TBTTs which makes the communication device to have a least acceptable efficiency of power consumption. If the time difference D is larger than the threshold TH 2 , the TBTT of the WLAN AP may be far away from a nearest, earlier TBTT of the communication device and out of the Wi-Fi Direct connected phase so that the communication device has to wake up to receive a beacon when it is already in the power saving mode. In opposite, if the time difference D is smaller than the threshold TH 2 , the communication device may have much time staying in the power saving mode and get better efficiency of power consumption. 
         [0037]    Briefly, according to Steps  402 ,  404  and  406 , the communication device determines whether TBTT of the communication device and TBTT of the WLAN AP are too close to switch channel; and according to Steps  402 ,  404  and  412 , the communication device determines whether TBTT of the communication device and TBTT of the WLAN AP are too far away to maintain acceptable efficiency of power consumption. 
         [0038]    Steps  408 ,  410 ,  414  and  416  carry out the essential concept of the present invention, that is, to shift the TSF timer of the P2P group owner and inform the P2P client devices in advance. 
         [0039]    When the measured time difference D is less than the threshold TH 1 , according to Step  408  and Step  410 , the communication device shifts its TSF timer by a first shift value to make a time difference between TBTT of the communication device and TBTT of the WLAN AP greater than the threshold TH 1 , and the communication device sends a first message including the timestamp of its TSF timer to a P2P client device for updating a TSF timer of the P2P client device, wherein the first message to the P2P client device is sent prior a first shifted beacon, so that the P2P client device can receive beacons at shifted TBTTs. The first message may be a beacon or a probe response. By using Step  408  and Step  410 , the communication device as the P2P group owner has enough time to finish broadcast to all the P2P client devices and then switches to receive a beacon from the WLAN AP. Please note that, the communication device can shift its own TSF timer earlier or later, as long as enough time for switching between channels is provided. 
         [0040]      FIG. 5  illustrates the effect of the process  40 . In  FIG. 5 , TBTTs of the communication device and TBTTs of the WLAN AP after the WLAN connection is established are numbered in sequence as TBTT 0 , TBTT 1 , TBTT 2 , etc. As shown in  FIG. 5 , the process  40  is performed after the communication device enters the WLAN connected phase, and as a result, the time difference D is measured, different channels (channel  3  and channel  11 ) for the Wi-Fi Direct connection and the WLAN connection is detected, the TSF timer of the communication device is shifted later so that new TBTT 1  is later than the original time, and two probe responses are sent to different P2P client devices before the new TBTT 1  when the first shifted beacon will be sent. Therefore, each P2P client device receives a probe response which announces that the TSF timer of the P2P group owner is shifted, and thereby the P2P client device is able to update its own TSF timer accordingly. In another embodiment, the communication device can also carry the timestamp of the shifted TSF timer in a beacon, and can send this beacon as soon as possible after the WLAN connection is established, e.g. send a beacon as the first message at TBTT 1 , in place of the probe response. 
         [0041]    On the other hand, when the measured time difference D is larger than the threshold TH 2 , Step  414  and Step  416  are performed. The communication device shifts its TSF timer by a second shift value to make a time difference between TBTT of the communication device and TBTT of the WLAN AP less than the threshold TH 2 , and prior to sending the first shifted beacon, the communication device sends a second message including the timestamp of its TSF timer to the P2P client device, for updating the TSF timer of the P2P client device. The second message may be a beacon or a probe response. The communication device can shift its own TSF timer earlier or later, as long as the time difference between TBTT of the communication device and TBTT of the WLAN AP is as close as possible, to be able to stay in a longer power saving phase and have lower power consumption. 
         [0042]    In a preferred embodiment of Step  404 , based on the condition that the beacon interval of the communication device and the beacon interval of the WLAN AP are the same, the communication device shifts its TSF timer to make zero time difference between TBTT of the communication device and TBTT of the WLAN AP. That is, TBTT of the communication device and TBTT of the WLAN AP are aligned, which helps the communication device to have the maximum time staying in the power saving mode. 
         [0043]      FIG. 6  also illustrates the effect of the process  40 . As shown in  FIG. 6 , the process  40  is performed after the communication device enters the WLAN connected phase and the time difference D is measured, identical channel (channel  6 ) for the Wi-Fi Direct connection and the WLAN connection is detected, the TSF timer of the communication device is shifted later so that new TBTT 1  is later than the original time, and two probe responses are sent to different P2P client devices before the new TBTT 1 . Therefore, each P2P client device is able to update its own TSF timer according to the received probe response. In another embodiment, the communication device can also carry the timestamp of the shifted TSF timer in a beacon and can send this beacon as the second message at TBTT 1 , in place of the probe response. 
         [0044]    Please note that a beacon is a broadcast message to all the P2P client devices and a probe response is a unicast message. The P2P client device has to reply an acknowledgement or non-acknowledgement with respect to a received probe response. Therefore, it is better to use a probe response as the message carrying the timestamp of the TSF timer since the communication device can make sure that the P2P client device indeed receives information of the shifted TSF timer or not, according to the acknowledgement. In another embodiment, the communication device can send both a beacon and a probe response, for increasing the opportunity for the P2P client device to update its TSF timer. 
         [0045]    The process  40  is one of embodiments of the present invention, performed based on that the beacon interval of the communication device as a P2P group owner and the beacon interval of the WLAN AP are the same. However, the beacon interval of the communication device may not always be the same as the beacon interval of the WLAN AP; one of them may change its own setting, or the communication device may handover to connect with another WLAN AP using a different beacon interval. Therefore, those skilled in the art can make alteration and modification accordingly. 
         [0046]    Please refer to  FIG. 7 , which is a flowchart of a process  70  according to an embodiment of the present invention. The process  70  covers a larger scope including the process  40  of  FIG. 4  since whether the beacon interval is identical or different is taken into account. The process  40  is also utilized in a communication device as the communication device  102  in  FIG. 1 , and is performed for controlling concurrent operation of the traditional WLAN protocol and Wi-Fi Direct. The process  70  comprises the following steps: 
         [0047]    Step  700 : Start. 
         [0048]    Step  702 : Determine whether a beacon interval of the communication device and a beacon interval of a WLAN AP are the same. If yes, perform the process  40 ; else, perform Step  704 . 
         [0049]    Step  704 : Check whether a channel for the Wi-Fi Direct connection and a channel for the WLAN connection are different. If yes, perform  706 ; else, perform Step  714 . 
         [0050]    Step  706 : Find out if next TBTT of the communication device and the next TBTT of the WLAN AP will get collision in advance. In another word, to find out a time difference D between the next TBTT of the communication device and the next TBTT of the WLAN AP is less than a threshold TH 1 . 
         [0051]    Step  708 : Shift a TSF timer of the communication device by a third shift value so that TBTT of the communication device is apart from TBTT of the WLAN AP as far as possible. 
         [0052]    Step  710 : Send a third message including the timestamp of the TSF timer of the communication device to a P2P client device prior to sending the first shifted beacon, to update a TSF timer of the P2P client device. 
         [0053]    Step  712 : Go back to Step  706  to look for next TBTT collision point. 
         [0054]    Step  714 : Find out if next TBTT of the communication device and the next TBTT of the WLAN AP will get separation in advance. In another word, to find out a time difference D between the next TBTT of the communication device and the next TBTT of the WLAN AP is larger than a threshold TH 2 . 
         [0055]    Step  716 : Shift a TSF timer of the communication device by a fourth shift value so that the communication device has the maximum time staying in a power saving mode. 
         [0056]    Step  718 : Send a fourth message including the timestamp of the TSF timer of the communication device to a P2P client device prior to sending the first shifted beacon, to update a TSF timer of the P2P client device. 
         [0057]    Step  720 : Go back to Step  714  to look for next separated TBTT point. 
         [0058]    The process  70  is taken while a Wi-Fi Direct connection is established prior a WLAN connection, wherein the WLAN connection is established between the communication device and the WLAN AP and the Wi-Fi Direct connection is established between the communication device as a P2P group owner and a P2P client device. After the WLAN connection is established, according to Step  702 , the communication device determines whether its own beacon interval is the same as the beacon interval of the WLAN AP. When the beacon intervals are the same, the communication device performs the process  40 ; otherwise, according to Step  704 , the communication device will check whether a channel for the Wi-Fi Direct connection and a channel for the WLAN connection are different and selectively perform Step  706  to Step  712 ; else, perform Step  714  to Step  720 . 
         [0059]    When the channel for the Wi-Fi Direct connection and the channel for the WLAN connection are different, according to Step  706 , the communication device find out if next TBTT of the communication device and the next TBTT of the WLAN AP will get collision in advance. If found then according to Step  708  and Step  710 , the communication device shifts its own TSF timer by a third shift value so that TBTT of the communication device is apart from TBTT of the WLAN AP as far as possible, and prior to sending a first shifted beacon, the communication device sends a third message including the timestamp of its TSF timer, which can be a beacon or a probe response, to the P2P client device. As a result, the communication device has enough time to switch channel and gets a better performance of network scheduling, and the P2P client device can update its own TSF timer according to the received beacon or probe response. Once finish the TSF shift adjustment, go back to Step  706  to find out next TBTT collision in advance. 
         [0060]    When the channel for the Wi-Fi Direct connection and the channel for the WLAN connection are the same, according to Step  714 , the communication device find out if next TBTT of the communication device and the next TBTT of the WLAN AP will get separation in advance. If found then according to Step  716  and Step  718 , the communication device shifts its own TSF timer by a fourth shift value to make the communication device have the maximum time staying in the power saving mode and have the minimum power consumption, and prior to sending the first shifted beacon, the communication device sends a fourth message including the timestamp of its TSF timer, which can be a beacon or a probe response, to the P2P client device to update the TSF timer of P2P client device. Similarly, the fourth shift value may be generated according to the time difference D, the beacon interval of the communication device and the beacon interval of the WLAN AP. 
         [0061]    The idea of concurrent control for Wi-Fi Direct and a legacy WLAN protocol can also be used when the communication device embedded with Wi-Fi Direct is further embedded with a TDMA-based protocol, such as Bluetooth, 3G or 4G protocol. Please refer to  FIG. 8 , which is a flowchart of a process  80  according to an embodiment of the present invention. The process  80  comprises the following steps: 
         [0062]    Step  800 : Start. 
         [0063]    Step  802 : Check whether a beacon is expected to be collided with traffic on a reserved time slot of the coexistent communication device while a Wi-Fi Direct connection is established prior the TDMA based connection. If yes, perform Step  804 ; else, perform Step  808   
         [0064]    Step  804 : Shift a TSF timer of the communication device to make TBTT corresponding to the beacon apart from the reserved time slot. 
         [0065]    Step  806 : Send a fifth message including the timestamp of the TSF timer of the communication device to a P2P client device prior to sending the first shifted beacon, to update a TSF timer of the P2P client device. 
         [0066]    Step  808 : End 
         [0067]    According to Step  802 , when a Wi-Fi Direct connection is established prior a WLAN connection, the communication device checks whether a beacon sent to the P2P client device is expected to be collided with traffic on a reserved time slot used by the communication device, i.e. whether a TBTT collides with a reserved time slot. The reserved time slot can be a Bluetooth SCO (synchronous Connection-Oriented) reserved time slot for voice transmission, for example. 
         [0068]    Usually, traffic of the TDMA-based communication device is given a higher priority than traditional WLAN/Wi-Fi Direct transmission since the TDMA-based communication device uses dedicated uplink/downlink resources, which is contention-free, and traditional WLAN/Wi-Fi Direct is contention-based. When the communication device knows that the beacon is expected to collide with traffic on the reserved time slot, according to Step  804 , the communication device shifts its TSF timer by a fifth shift value, to make the TBTT apart from the reserved time slot. And prior to sending the first shifted beacon, the communication device sends a fifth message including the timestamp of its own TSF timer to a P2P client device, to update the TSF timer of the P2P client device. The fifth message can also be a beacon or a probe response. 
         [0069]    Please refer to  FIG. 9  and  FIG. 10 , which are diagrams of beacon transmission and TDMA transmission in a communication device embedded with Wi-Fi Direct and a TDMA-based protocol.  FIG. 9  and  FIG. 10  illustrate the effect of the process  80  of  FIG. 8 . As shown in  FIG. 9 , the communication device shifts its TSF timer later and sends probe responses as the fifth messages to two P2P client devices before sending the first shifted beacon. As shown in  FIG. 10 , the communication device sends a beacon as the fifth message. In another embodiment, the communication device can also sent both a beacon and probe responses, to increase the opportunity for the P2P devices to update the TSF timer and thus improve performance of the Wi-Fi Direct connection. 
         [0070]    In conclusion, through the above concurrent control processes, when the communication device embedded with Wi-Fi Direct and legacy WLAN sends beacons to P2P client devices after the WLAN connection is established, the communication device considers the channels used for Wi-Fi Direct connection and the WLAN connection and the time difference between TBTT of the communication device and TBTT of the WLAN AP, and therefore network scheduling and power consumption are greatly improved. 
         [0071]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.