Abstract:
A method and apparatus discover hidden wireless devices in a wireless network using a directional antenna system, preventing partitioning of the wireless network. A first wireless device located in a first antenna sector is joined in response to an initial first beacon. First beacons are received from the joined first wireless device during corresponding first beacon periods. At least a second antenna sector is scanned during at least one first beacon period to listen for second beacons from a second wireless device in the second antenna sector, while remaining joined with the first wireless device. The first beacons are not received while the second antenna sector is scanned. The second wireless device is joined in response to an initial second beacon. Second beacons are then received from the joined second wireless device during corresponding second beacon periods, and the first beacons are received during the corresponding first beacon periods.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     A claim of priority is made to U.S. Provision Application No. 60/885,178, filed Jan. 16, 2007, the subject matter of which is hereby incorporated by reference. 
    
    
     BACKGROUND AND SUMMARY 
     Advancements continue to be made in wireless communications technology. For example, wireless local area networks (WLANs) and wireless personal area networks (WPANs) networks are becoming more common in homes and businesses. Such networks may include a variety of independent wireless electronic devices or terminals, which wirelessly communicate with one another. WLANs and WPANs may operate according to a number of different available standards, including IEEE standards 802.11 (Wi-Fi), 802.15 (Bluetooth) and 802.16 (WiMax), as well as the WiMedia Alliance Ultra-Wideband (UWB) standard. 
       FIG. 1  is a block diagram showing a conventional wireless network  100 , including multiple terminals configured to communicate with one another over exemplary WPAN  125 . The wireless terminals may include any electronic devices or nodes configured to communicate with one another. For example,  FIG. 1  depicts a home network in which the electronic devices include a personal computer  120 , a digital television set  121 , a digital camera  122  and a personal digital assistant (PDA)  123 . The network  100  may also include an interface to other networks, such as modem  130 , to provide connectivity of all or some of the wireless devices  120 - 123  to the Internet  140 , for example. Of course, there are many other types of wireless networks in which electronic devices communicate with one anther, including networks in manufacturing plants, medical facilities, security systems, and the like. 
     Wireless devices may communicate with one another using directional antennas, which extend transmission range. For example, recent wireless networks operate in very high frequency bands (e.g., 60 GHz), and thus use directional antennas to compensate for high path loss associated with high frequency bands. In both centralized and distributed wireless networks, wireless devices using directional antennas must align their respective antennas at the same time in order to communicate. In other words, the wireless devices must first find each other, which is accomplished by the wireless devices scanning (e.g., sweeping their antenna beams) around surrounding areas. However, the wireless devices may not discover one another unless there is pre-coordination among them to assure that they are sweeping their antenna beams at the same time. 
     Beacons are widely used to convey important control information between devices. Beacons are usually broadcast so that all devices in the transmission range of the beaconing device can receive the beacons. For example, an IEEE 802.11 access point periodically sends out beacons so that the IEEE 802.11 wireless devices around the access point can associate with the access point and communicate. As stated above, in wireless networks in which directional antennas are used, beacons may only be sent in certain directions. As a result, only a limited number of devices in proximity of the beaconing device will receive the beacons, thus making beacons less useful. The wireless devices may be pre-programmed to know the direction of each other&#39;s antennas, but this requires a protocol to coordinate the wireless devises&#39; antenna directivity, as well as beacon transmission, reception and processing. 
     In other words, wireless devices may not be able to discover and communicate with each other even though they are in the same network  100  and in proximity to one another. Such coordination or synchronization is difficult and costly to implement. However, wireless devices not having a common time-domain reference point for coordinating antenna control and/or beacon transmission will not communicate properly as a network. 
     Accordingly, it would be desirable to provide a wireless device and method of wireless communications that provides a mechanism enabling wireless devices to find and communicate with each other, particularly when the wireless devices are using directional antenna systems. 
     In one aspect of the invention, a method is provided for discovering hidden wireless devices in a wireless network using a directional antenna system, preventing partitioning of the wireless network. The method includes joining a first wireless device located in a first antenna sector in response to an initial first beacon received from the first wireless device; receiving multiple first beacons from the joined first wireless device during corresponding first beacon periods; and scanning at least a second antenna sector during at least one first beacon period of the first beacon periods to listen for second beacons from a second wireless device in the second antenna sector, while remaining joined with the first wireless device. The first beacons are not received while at least the second antenna sector is scanned. 
     The method may further include sending multiple first response beacons to the joined first wireless device in response the received first beacons. The first response beacons are not sent while scanning at least the second antenna sector. 
     The method may further include receiving an initial second beacon from the second wireless device while scanning the second antenna sector; joining the second wireless device in response to the initial second beacon; and receiving multiple second beacons from the joined second wireless device during corresponding second beacon periods. At least a portion of the first beacons continues to be received. 
     When the first beacon periods occur at different times than the second beacon periods, the method may further include receiving each of the first beacons and the second beacons. When the first beacon periods occur at the same times as the second beacon periods, the method may further include alternating between receiving the first beacons and the second beacons. 
     The method may further include sending multiple second response beacons to the joined second wireless device in response the received second beacons. When sending the first response beacons occurs at the same times as the second beacon periods, the method may further include alternating between sending the first response beacons and receiving the second beacons. When sending the second response beacons occurs at the same times as the first beacon periods, the method may further include alternating between sending the second response beacons and receiving the first beacons. 
     The method may further include scanning at least a third antenna sector during one first beacon period of the multiple first beacon periods and one second beacon period of the multiple second beacon periods to listen for third primary beacons, while remaining joined with the first wireless device and the second wireless device. The first beacons and the second beacons may not be received while the third antenna sector is being scanned. Scanning the second antenna sector may include sweeping a beam of the directional antenna system. 
     In accordance with a representative embodiment, an apparatus is provided for communicating with multiple wireless devices through a wireless network, where the apparatus is initially joined with a first wireless device located in a first antenna sector of multiple antenna sectors. The apparatus includes a directional antenna system, a transceiver and a processor. The directional antenna system is configured to communicate over the wireless network in the antenna sectors. The transceiver is configured to receive multiple first beacons from the joined first wireless device via the antenna system during corresponding first beacon periods. The processor is configured to control the antenna system to scan at least a second antenna sector of the antenna sectors during at least one first beacon period of the first beacon periods to listen for beacons from the wireless devices. The first beacons are not received while the directional antenna system is scanning, and the apparatus remains joined with the first wireless device. 
     The transceiver may receive an initial second beacon from a second wireless device located in the second antenna sector while the antenna system is scanning, enabling the apparatus to join with the second wireless device. The transceiver may also receive multiple second beacons from the joined second wireless device during corresponding second beacon periods, while continuing to receive at least a portion of the first primary beacons. The antenna system may include one of an antenna array or a steerable antenna. 
     When the first beacon periods occur at different times than the second beacon periods, the transceiver may receive each of the first primary beacons and the second primary beacons. When the first beacon periods occur at the same times as the second beacon periods, the transceiver may alternate between receiving the first primary beacons and the second primary beacons. 
     The transceiver may send multiple first response beacons to the joined first wireless device in response the received first beacons and send multiple second response beacons to the joined second wireless device in response the received second beacons. The first response beacons may not be sent while the antenna system scans the antenna sectors. When sending the first response beacons occurs at the same times as the second beacon periods, the transceiver may alternate between sending the first response beacons and receiving the second beacons. When sending the second response beacons occurs at the same times as the first beacon periods, the transceiver may alternate between sending the second response beacons and receiving the first beacons. 
     In accordance with a representative embodiment, a method is provided for enabling a secondary wireless device to discover multiple primary wireless devices through a wireless network, where activation schedules of the secondary wireless device and the primary wireless devices are not synchronized. The method includes receiving first primary beacons from a first primary wireless device in a first antenna sector and sending first secondary beacons to the first primary wireless device in response; skipping receiving the first primary beacons from the first primary wireless device; and scanning other antenna sectors and listening for additional primary beacons while skipping receiving the first primary beacons. The method also includes receiving an initial second primary beacon from a second primary wireless device in a second antenna sector while scanning the antenna sectors and sending an initial second secondary beacon to the second primary wireless device in response; and receiving second primary beacons from the second primary wireless device and sending secondary beacons to the second primary wireless device in response, in addition to receiving the first primary beacons from a first primary wireless device and sending the first secondary beacons to the first primary wireless device in response. 
     The first primary beacons may be received during a first time period and the second primary beacons may be received during a second time period. When the first time period conflicts with the second time period, the method further includes alternating receiving the first primary beacons and the second primary beacons. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a conventional wireless communications network. 
         FIG. 2  is a block diagram of representative primary devices communicating with a second device in a wireless network according to various embodiments. 
         FIG. 3  is a functional block diagram of a representative wireless device according to various embodiments. 
         FIGS. 4A-4C  are block diagrams of beacon periods of wireless devices according to an embodiment. 
         FIG. 5  is a flow chart of a wireless device discovery process according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation and not limitation, example embodiments disclosing specific details are set forth in order to provide a thorough understanding of an embodiment according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known devices and methods may be omitted so as to not obscure the description of the example embodiments. Such methods and devices are clearly within the scope of the present teachings. 
     In the various embodiments, a protocol for controlling beacons, sent and received through directional antennas of wireless devices in a wireless network, such as a WLAN or WPAN. The protocol provides wireless devices the ability to transmit beacons in a coordinated manner in a WLAN or WPAN using directional antennas. The wireless devices are thus able to exchange information via beacons, either directly or indirectly, to enable network management, data transmission and other communications, without having to previously coordinate antenna directivity or time synchronization of the wireless devices. 
       FIG. 2  is a block diagram of a representative wireless network  200 , which may be a WLAN, WPAN, or the like, according to various standards and protocols. Each representative wireless device  210 ,  220 ,  230  of wireless network  200  transmits and receives beacons through directional antennas. For example, each wireless device  210 ,  220 ,  230  may use a switching-beam antenna or a steering antenna, in order to cover a wide area by beam sweeping/switching. However, lack of coordination in beam sweeping among the wireless devices  210 ,  220  and  230  may cause hidden-node problems, effectively partitioning the network, which would otherwise be well connected. 
     In  FIG. 2 , wireless devices  210  and  230  are indicated to be primary devices and wireless device  220  is indicated to be a secondary wireless device. For purposes of discussion, the distinction between primary and secondary devices is that the primary devices (e.g., wireless device  210 ,  230 ) initiate communications over network  200  by sending beacons, indicated by shaded regions A, B, C and D, which represent antenna sectors. The secondary devices (e.g., wireless device  220 ) receive and respond to the primary device beacons. The representative primary devices  210  and  230  may be network access points, for example, and the representative secondary device  220  may include any type of device configured to communicate over the wireless network  200 , such as a personal computer, a digital television set, a digital camera and a PDA, and the like, as discussed above. 
     The location and direction of the wireless devices  210 ,  220  and  230  are not known a priori by one another. Therefore, upon powering up (or entering the network  200 ), wireless device  210 , for example, does not know the location of the other devices (e.g., wireless device  220 ) or in which direction to point its antenna to establish communications with the other devices. When primary device  210  receives no beacons after scanning for a period of time,(e.g. one superframe), it attempts to discover other wireless devices by sending beacons in each of its beams or antenna sectors.  FIG. 2  depicts wireless device  210 , as well as wireless devices  220  and  230 , as having four antenna sectors for purposes of discussion. It is understood that each of these devices may have any number of antenna sectors, without departing from the spirit and scope of the various embodiments. Also, the wireless devices  210 ,  220  and  230  do not need to know the number or locations of the antenna sectors of the other devices. 
     Wireless device  210  sends beacons in all four of its beams, indicated by shaded sector regions A-D. Wireless device  220  subsequently powers on (or otherwise enters the network  200 ) and begins scanning its corresponding antenna sectors A-D. Because wireless device  210  is actively sending beacons, wireless device  220  receives a primary beacon in its antenna sector C, sent by wireless device  210  in its antenna sector A. 
     Wireless device  220  responds by sending a secondary beacon to wireless device  210  in the opposite direction, thus joining wireless device  210 . 
     When wireless device  230  powers on (or otherwise enters the network  200 ), it also begins scanning its corresponding sectors A-D. Wireless device  230  may not be able to receive (hear) the primary beacons sent from wireless device  210 , for example, due to path loss, low signal strength, signal interference, obstructions, or the like. Accordingly, wireless device  230  will begin sending its own primary beacons in all four of its antenna sectors A-D. However, in a conventional system, wireless device  220 , which is in closer proximity to wireless device  230 , will not hear the primary beacons sent from wireless device  230  because its antenna is positioned in the opposite direction, away from wireless device  230  (e.g., in sector C of wireless device  220 ). As a result, the network  200  is partitioned, since wireless device  230  is unable to communicate with wireless devices  210  and/or  220 . 
     In order to avoid partitioning the network  200 , wireless device  220  executes a discovery algorithm, according to embodiments of the present invention, enabling wireless device  230  to join wireless devices  210  and  220  after they have established a communication session. More particularly, wireless device  220  skips transmission of its secondary beacon to wireless device  210  in order to listen for and receive beacons from new primary device(s) (e.g.,. wireless device  230 ). Wireless device  220  will send responsive secondary beacons to any new primary devices and, when necessary, alternate secondary beacon transmissions in different antenna sectors to avoid conflicts with receiving/sending beacons with wireless device  210 .  FIG. 3  is a functional block diagram of representative secondary wireless device  220 , configured to communicate with representative primary wireless devices  210  and  230 , according to various embodiments, over the wireless network  200 . Although wireless device  220  is shown and discussed in detail, it is understood that the wireless devices  210  and  230  are configured and function in substantially the same manner as wireless device  220 . It is further understood that each of the wireless devices  210 ,  220 ,  230  may function as primary or secondary devices, depending on its configuration and/or which device is sending primary beacons for discovering other wireless devices. 
     As will be appreciated by those skilled in the art, one or more of the various “parts” shown in  FIG. 3  may be physically implemented using a software-controlled microprocessor, hard-wired logic circuits, or a combination thereof. Also, while the parts are functionally segregated in  FIG. 3  for explanation purposes, they may be combined variously in any physical implementation. 
     Wireless device  220  includes transceiver  224 , processor  226 , memory  228 , and antenna system  222 . Transceiver  224  includes a receiver  223  and a transmitter  225 , and provides functionality for wireless device  220  to communicate with other wireless devices, such as wireless devices  210  and  230 , over wireless communication network  200  according to the appropriate standard protocols. 
     Processor  226  is configured to execute one or more software algorithms, including the discovery algorithm of the embodiments described herein, in conjunction with memory  228  to provide the functionality of wireless device  220 . The discovery algorithm may be software control of antenna system  222 , for example, implemented in the medium access control (MAC) layer. Processor  226  may include its own memory (e.g., nonvolatile memory) for storing executable software code that allows it to perform the various functions of wireless device  220 , discussed herein. Alternatively, the executable code may be stored in designated memory locations within memory  228 . 
     In  FIG. 3 , antenna system  222  includes a directional antenna system which provides a capability for the primary device  220  to select from multiple antenna beams for communicating with other wireless devices in multiple directions. For example, antenna system  222  may include multiple antennas, each corresponding to one antenna beam, or antenna system  222  may include a steerable antenna or antenna array that can combine multiple different antenna elements to form a beam in different directions. 
     The antenna system  222  operates various sectors corresponding to the directions in which the antenna system  222  may be directed. For example, a kth wireless device has the capability to transmit and receive signals in M k  directions or sectors. As stated above, these sectors may be generated using a sectorized antenna, which selects among M k  directional antennas of the antenna system  222 , or may be virtually formed using adaptive antenna arrays of the antenna system  222 . 
     As previously mentioned, different devices (e.g., primary devices  210 ,  230  and secondary device  220 ) may have different numbers and distributions of antenna sectors, and it is not necessary that all directions are covered by the various sectors of one device. For example,  FIG. 2  depicts an example in which the antenna system  222  of wireless device  220  defines four antenna sectors, sectors A, B, C and D. For purposes of simplifying explanation, the representative sectors A-D are evenly distributed in four quadrants surrounding wireless device  220  (as well as wireless devices  210  and  230 ) and are depicted in two dimensions. Actual sectors may have differing and/or overlapping coverage extending in three dimensions. Also, in the depicted illustrative configuration, wireless device  210  and/or  230  may include a fixed directional antenna directed to one sector, in which wireless device  220  is located. 
       FIGS. 4A ,  4 B and  4 C are block diagrams of operational time lines  410 ,  420  and  430 , which respectively correspond to signals sent and/or received by wireless devices  210 ,  220  and  230 . Each time line indicates one beacon period of corresponding superframe (not shown), according to various embodiments. 
     Each timeline  410 - 430  includes a series of consecutive blocks or time slots within a beacon period, which represent fixed periods of time associated with the beaconing process. For example, time line  410  shows a beacon period having four beacon slots, slots A-D, which correspond to antenna sectors A-D of wireless device  210 . The shaded beacon slots indicate primary beacon slots in which primary beacons are actively transmitted. The beacon slots A-D indicated by dashed lines represent the secondary/response beacon slots for the corresponding sectors, as specified in the corresponding primary beacons of wireless device  210 . Likewise, time line  430  shows beacon periods having primary and secondary beacon slots A-D corresponding to antenna sectors A-D of wireless device  230 . Time line  420  shows individual beacon slots in which wireless device  220  sends responsive beacons to each of wireless devices  210  and  230 . 
     The time slots may vary in size, without departing from the spirit and scope of the embodiments. For example, the number of slots per superframe and/or length of time of each time slot may be configured to provide unique benefits for any particular situation or to meet various design requirements. Also, antenna directivity and beacon periods have not been pre-coordinated or otherwise synchronized among the wireless devices  210 ,  220  and  230 . 
     The dashed arrows pointing downward indicate primary beacons being sent by the primary wireless devices  210  and  230  to the secondary wireless device  220 . The dashed arrows pointing upward indicate responsive secondary beacons being sent by the second wireless device  220  to the primary wireless devices  210  and  230 . As discussed above with respect to  FIG. 2 , wireless device  210  is only able to communicate with wireless device  220  in antenna sector A, due to the wireless devices&#39; relative locations. Therefore, the dashed arrows show wireless device  210  sending primary beacons and receiving secondary beacons only in sector A of timeline  410 . Likewise, wireless device  230  is only able to communicate with wireless device  220  in antenna sector C, due to the wireless devices&#39; relative locations. Therefore, the dashed arrows show wireless device  230  sending primary beacons and receiving secondary beacons only in sector C of timeline  430 . 
     Because wireless devices  210 ,  220  and  230  are not synchronized, the time periods for exchanging beacons may or may not overlap. For example,  FIG. 4A  depicts a scenario in which the timing works out, such that the primary beacons sent by wireless device  210  (time line  410 ) and wireless device  230  (time line  430 ) do not interfere with one another and do not interfere with the respective secondary beacons sent by wireless device  220  (time line  420 ). In other words, the time during which wireless device  210  sends/receives primary and secondary beacons in its antenna sector A does not overlap with the time during which wireless device  230  sends/receives primary and secondary beacons in its antenna sector C. Thus, wireless device  220  does not need to adjust its timing. 
     In contrast,  FIG. 4B  depicts a scenario in which the timing of sending primary beacons and receiving secondary beacons completely overlaps. In other words, the time during which wireless device  210  sends/receives primary and secondary beacons in its antenna sector A is the same as the time during which wireless device  230  sends/receives primary and secondary beacons in its antenna sector C. Similarly,  FIG. 4C  depicts a scenario in which the timing of sending primary beacons and receiving secondary beacons partially overlaps. In other words, the time during which wireless device  210  receives secondary beacons in its antenna sector A is the same as the time during which wireless device  230  sends primary beacons in its antenna sector C. Accordingly, in response to the scenarios of  FIGS. 4B and 4C , secondary wireless device  220  must coordinate between the primary wireless devices to maintain communications over the network  200  and to avoid partitioning after wireless device  230  has been discovered and joined to wireless devices  210  and  220 , as discussed below. 
       FIG. 5  is a flow diagram showing a process for discovering hidden nodes and coordinating beacon transmission and reception using directional antennas, according to an embodiment. The process steps of  FIG. 5  will be discussed, in part, with reference to the time lines  410 - 430  of  FIGS. 4A-4C . 
     At step S 510 , wireless device  220  enters the network  200 , for example, by powering on. It is assumed that the wireless device  210  is already on and transmitting primary beacons in slots A-D (e.g., of  FIG. 4A ) in each of its corresponding antenna sectors A-D. Wireless device  220  scans all of its sectors A-D listening for primary beacons in the beacon period slots corresponding at step S 512 . Each beacon transmitted by the primary wireless device  210  includes information, such as the number, location and/or corresponding sector number of beacon slot(s) in which the a receiving secondary wireless device should send a responsive secondary beacon. 
     When wireless device  220  does not receive a primary beacon (step S 514 : No), it continues to scan all antenna sectors, repeating step S 512 . When wireless device  220  detects a primary beacon (step S 514 : Yes), it transmits a responsive secondary beacon at step S 516 . The secondary beacon is transmitted in the antenna sector (e.g., sector C) of wireless device  220  directed toward wireless device  210 . Wireless device  220  thus joins wireless device  210 , and wireless devices  210  and  220  then continue to exchange beacons at step S 518 , maintaining a communications session between the two devices. 
     At step A 520 , wireless device  220  skips receiving a primary beacon from wireless device  210  and/or transmitting a secondary beacon to wireless device  210 . This enables wireless device  220  to scan all of its antenna sectors at step S 522  and listen for other beacons, such as a primary beacon from wireless device  230 . The timing of when wireless device  220  skips receiving/transmitting beacons may vary. The wireless device may skip receiving/transmitting beacons at regular or periodic intervals, e.g., set according to a predetermined schedule, or the wireless device may skip receiving/transmitting beacons irregularly or randomly. For example, wireless device  220  may skip receiving every other beacon (and thus transmit every other responsive beacon) to scan other antenna sectors. Alternatively, wireless device  220  may skip receiving every number of beacons (e.g., every second, third, fiftieth, etc., beacon), depending on how often it is desired for wireless device  220  to check for other wireless devices. Also, the timing of when wireless device  220  skips receiving/transmitting beacons may vary depending on the number of primary wireless devices with which it is joined. For example, if wireless device  220  is already associated with two primary wireless devices, it must periodically skip receiving/transmitting beacons with respect to both primary wireless devices in order to scan its antenna sectors at step S 52 . This may result in wireless device  220  exchanging beacons less frequency with both primary wireless devices. 
     At step S 524 , wireless device  220  determines whether it has received a new beacon (e.g., a beacon from a wireless device other than wireless device  210 ). When it has not received a new beacon (S 524 : No), wireless device  220  returns to step S 518 , continuing to exchange beacons with wireless device  210  and periodically or randomly skipping the beacon exchange at steps  5518  and  5520 . When wireless device  220  receives a new beacon (e.g., a primary beacon from wireless device  230 ) (step S 524 : Yes), it transmits a responsive beacon at step S 526  in the antenna sector in which the new beacon was received. 
     At this point, wireless device  220  learns information regarding communications with wireless device  230  based on the timing of the new beacon and information contained in the beacon. Wireless device  220  therefore knows the schedule according to which it must exchange beacons with wireless device  230 . At step S 528 , wireless device  220  compares the schedule with the original schedule of beacon exchanges with wireless device  210  and determines whether the schedules conflict. For example,  FIGS. 4B and 4C  depict scenarios in which the beacon receive/transmit schedules conflict. As discussed above,  FIG. 4B  shows that wireless device  220  would have to receive beacons from and send responsive beacons to both wireless devices  210  and  230  in the same time periods, and  FIG. 4C  shows that wireless device  220  would have to transmit a responsive beacon to wireless device  210  in the same time period that it would receive a beacon from wireless device  230 . These scenarios create conflicts because, for example, wireless device  220  would not only have to simultaneously receive/transmit beacons from different devices, but it would have to have its directional antenna pointed in different directions. 
     Therefore, when wireless device  220  determines that there is a conflict between beacon exchanges (step S 528 : Yes), it proceeds to alternate beacon exchanges with wireless device  210  and wireless device  230  at step S 532 . For example, in the illustrative scenario depicted in  FIG. 4B , wireless device  220  skips receiving a primary beacon from wireless device  210  to receive (and respond to) a primary beacon from wireless device  230 , and wireless device  220  skips receiving a primary beacon from wireless device  230  to receive (and respond to) a primary beacon from wireless device  210 . In the illustrative scenario depicted in  FIG. 4C , wireless device  220  skips sending a responsive beacon to wireless device  210  in order to receive (and respond to) a primary beacon form wireless device  230 . 
     Skipping beacon transmission/reception (e.g., to avoid conflicting timing and/or to periodically scan antenna sectors) will not effect the communication session between the wireless devices as long as successful beacon exchanges are accomplished within a predetermined timeframe set for the wireless network  200 , which is typically adjustable. When there is no conflict (step S 528 : No), wireless device  220  exchanges beacons with both wireless devices  210  and  230  without alternating between the devices at step S 530 . 
     As long as the communication session(s) continues (step S 540 : No), wireless device  220  will return to step S 520  and continue to regularly or randomly skip beacon exchanges with all associated primary wireless devices (e.g., wireless devices  210  and  230 ), adding additional wireless devices as new beacons are detected. The process ends when the communication session(s) ends (step S 540 : Yes). In various embodiments, wireless device  220  may stop scanning for additional beacons based on other criteria. For example, wireless device  220  may be programmed to discontinue sector scanning once it has joined with a predetermined number of wireless devices (e.g., four wireless devices or one in each antenna sector). 
     According to the exemplary embodiments, neighboring wireless devices, such as representative wireless devices  210 ,  220  and  230 , are able to discover one another and rendezvous, e.g., for purposes of exchanging information and/or aiming antennas, without synchronizing time schedules. Therefore, wireless devices in proximity, regardless of topology will be well connected and the network will not be partitioned. This approach can be applied, for example, to assist devices using directional antennas in locating each other. Examples are provided herein for illustration purposes and are not to be construed as limiting the scope of the teachings of this specification, or the claims to follow. 
     While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.