Patent Publication Number: US-8971256-B2

Title: Ad-hoc directional communication in contention access period

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
     The present Application for Patent claims benefit of U.S. provisional application Ser. No. 61/169,534 filed Apr. 15, 2009, and U.S. provisional application Ser. No. 61/177,411 filed May 12, 2009, and assigned to the assignee hereof and are hereby expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field 
     Certain aspects of the present disclosure generally relate to a wireless communication and, more particularly, to association between communicating devices and to ad-hoc directional communication in a contention access period. 
     2. Background 
     In emerging wireless communication standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.15.3c standard, a network coordinator scheduling (e.g., control by a piconet controller or an access point) is mandatory to access a medium for any device-to-device communication. However, efficiency of this access can be very low, particularly for data applications with very random and bursty traffic. 
     A channel time allocation (CTA), which is a time division multiplexing (TDM) based approach, can provide means to support streaming applications with high data rates. On the other hand, the use of large amount of bursty data is not well supported in the IEEE 802.15.3c standard. 
     The link budget for transmitting high data rates over 60 GHz frequency band supported by standards such as the IEEE 802.15.3c, IEEE 802.11ad and European Computer Manufacturer&#39;s Association Technical Committee 48 (ECMA-TC48) requires considerable antenna gain as well as flexibility in the orientation of end-point devices. This directional communication presents a new challenge for devices communicating with multiple peers in multiple directions. Such devices need to be informed in advance to which direction to set their antennas. However, the nature of contention-based traffic is that it is not always possible to know in advance which directions to use, since anyone of the potential peers may gain access to a medium. Several attempts and restrictions were applied in a contention access period (CAP) specified by the IEEE 802.15.3c standard, but none of them provided an efficient solution for this problem. 
     Therefore, there is a need in the art for a method to provide efficient ad-hoc peer-to-peer communication in the CAP while ensuring that antenna directions of communicating peers point to each other. Preceding this, it is desirable that peers (i.e., wireless nodes of the network) are associated with the network coordinator. 
     SUMMARY 
     Certain aspects provide a method for wireless communications. The method generally includes monitoring, by an apparatus, a medium in a contention access period (CAP) for availability of the medium for data transmission by the apparatus, after determining the medium is available for data transmission by the apparatus, obtaining the medium by transmitting, from the apparatus, a common mode signaling (CMS) frame in the CAP, and transmitting, from the apparatus, at least one data frame to another apparatus in the CAP over a wireless channel of the medium after obtaining the medium. 
     Certain aspects provide an apparatus for wireless communications. The apparatus generally includes a monitoring circuit configured to monitor a medium in a contention access period (CAP) for availability of the medium for data transmission by the apparatus, and a transmitter configured to obtain the medium by transmitting a common mode signaling (CMS) frame in the CAP, after determining the medium is available for data transmission by the apparatus, and wherein the transmitter is also configured to transmit at least one data frame to another apparatus in the CAP over a wireless channel of the medium after obtaining the medium. 
     Certain aspects provide an apparatus for wireless communications. The apparatus generally includes means for monitoring a medium in a contention access period (CAP) for availability of the medium for data transmission by the apparatus, means for obtaining the medium by transmitting, from the apparatus, a common mode signaling (CMS) frame in the CAP, after determining the medium is available for data transmission by the apparatus, and means for transmitting at least one data frame to another apparatus in the CAP over a wireless channel of the medium after obtaining the medium. 
     Certain aspects provide a computer-program product for wireless communications. The computer-program product includes a computer-readable medium encoded with instructions executable to monitor, by an apparatus, a medium in a contention access period (CAP) for availability of the medium for data transmission by the apparatus, obtain the medium by transmitting, from the apparatus, a common mode signaling (CMS) frame in the CAP, after determining the medium is available for data transmission by the apparatus, and transmit, from the apparatus, at least one data frame to another apparatus in the CAP over a wireless channel of the medium after obtaining the medium. 
     Certain aspects provide a wireless node. The wireless node generally includes at least one antenna, a monitoring circuit configured to monitor a medium in a contention access period (CAP) for availability of the medium for data transmission by the wireless node, and a transmitter configured to obtain the medium by transmitting via the at least one antenna a common mode signaling (CMS) frame in the CAP, after determining the medium is available for data transmission by the wireless node, and wherein the transmitter is also configured to transmit via the at least one antenna at least one data frame to another wireless node in the CAP over a wireless channel of the medium after obtaining the medium. 
     Certain aspects provide a method for wireless communications. The method generally includes receiving, by an apparatus, a common mode signaling (CMS) frame transmitted by another apparatus indicating access to a medium for data communication by the other apparatus in a contention access period (CAP), receiving, from the other apparatus once the access to the medium for data communication is indicated at the apparatus, at least one data frame over a wireless channel of the medium in the CAP, and transmitting, to the other apparatus, an acknowledgement that the at least one data frame is successfully received over the wireless channel of the medium in the CAP. 
     Certain aspects provide an apparatus for wireless communications. The apparatus generally includes a receiver configured to receive a common mode signaling (CMS) frame transmitted by another apparatus indicating access to a medium for data communication by the other apparatus in a contention access period (CAP), wherein the receiver is also configured to receive, from the other apparatus once the access to the medium for data communication is indicated at the apparatus, at least one data frame over a wireless channel of the medium in the CAP, and a transmitter configured to transmit, to the other apparatus, an acknowledgement that the at least one data frame is successfully received over the wireless channel of the medium in the CAP. 
     Certain aspects provide an apparatus for wireless communications. The apparatus generally includes means for receiving a common mode signaling (CMS) frame transmitted by another apparatus indicating access to a medium for data communication by the other apparatus in a contention access period (CAP), means for receiving, from the other apparatus once the access to the medium for data communication is indicated at the apparatus, at least one data frame over a wireless channel of the medium in the CAP, and means for transmitting, to the other apparatus, an acknowledgement that the at least one data frame is successfully received over the wireless channel of the medium in the CAP. 
     Certain aspects provide a computer-program product for wireless communications. The computer-program product includes a computer-readable medium encoded with instructions executable to receive, by an apparatus, a common mode signaling (CMS) frame transmitted by another apparatus indicating access to a medium for data communication by the other apparatus in a contention access period (CAP), receive, from the other apparatus once the access to the medium for data communication is indicated at the apparatus, at least one data frame over a wireless channel of the medium in the CAP, and transmit, to the other apparatus, an acknowledgement that the at least one data frame is successfully received over the wireless channel of the medium in the CAP. 
     Certain aspects provide a wireless node. The wireless node generally includes at least one antenna, a receiver configured to receive via the at least one antenna a common mode signaling (CMS) frame transmitted by another wireless node indicating access to a medium for data communication by the other wireless node in a contention access period (CAP), wherein the receiver is also configured to receive via the at least one antenna, from the other wireless node once the access to the medium for data communication is indicated at the wireless node, at least one data frame over a wireless channel of the medium in the CAP, and a transmitter configured to transmit via the at least one antenna, to the other wireless node, an acknowledgement that the at least one data frame is successfully received over the wireless channel of the medium in the CAP. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. 
         FIG. 1  illustrates an example wireless communication system in accordance with certain aspects of the present disclosure. 
         FIG. 2  illustrates various components that may be utilized in a wireless device in accordance with certain aspects of the present disclosure. 
         FIG. 3  illustrates an example transmitter that may be used within a wireless communication system in accordance with certain aspects of the present disclosure. 
         FIG. 4  illustrates an example receiver that may be used within a wireless communication system in accordance with certain aspects of the present disclosure. 
         FIG. 5  illustrates an association procedure in accordance with certain aspects of the present disclosure. 
         FIG. 6  illustrates example operations for associating a device with a piconet controller in accordance with certain aspects of the present disclosure. 
         FIG. 6A  illustrates example components capable of performing the operations illustrated in  FIG. 6 . 
         FIG. 7  illustrates an example of association flow in accordance with certain aspects of the present disclosure. 
         FIG. 8  illustrates another example of association flow in accordance with certain aspects of the present disclosure. 
         FIG. 9  illustrates example operations for ad-hoc directional transmission in a contention access period (CAP) in accordance with certain aspects of the present disclosure. 
         FIG. 9A  illustrates example components capable of performing the operations illustrated in  FIG. 9 . 
         FIG. 10  illustrates an example scenario for ad-hoc directional transmission in the CAP with no antenna-pattern training in accordance with certain aspects of the present disclosure. 
         FIG. 11  illustrates example operations for antenna-pattern training as a part of the ad-hoc directional transmission illustrated in  FIG. 9  in accordance with certain aspects of the present disclosure. 
         FIG. 11A  illustrates example components capable of performing the operations illustrated in  FIG. 11 . 
         FIG. 12  illustrates an example scenario for ad-hoc directional transmission in the CAP with antenna-pattern training in accordance with certain aspects of the present disclosure. 
         FIG. 13  illustrates an example of an empty common mode signaling (CMS) frame in accordance with certain aspects of the present disclosure. 
         FIG. 14  illustrates a structure of a physical layer (PHY) header of the CMS frame in accordance with certain aspects of the present disclosure. 
         FIG. 15  illustrates a structure of a medium access control (MAC) header of the CMS frame in accordance with certain aspects of the present disclosure. 
         FIG. 16  illustrates a structure of a fragmentation control field of the MAC header in accordance with certain aspects of the present disclosure. 
         FIG. 17  illustrates a structure of a Duration Information Element (IE) field of the CMS command frame in accordance with certain aspects of the present disclosure. 
         FIG. 18  illustrates an example of busy medium durations in the case of ad-hoc directional transmission without training of antenna patterns in accordance with certain aspects of the present disclosure. 
         FIG. 19  illustrates an example of busy medium durations in the case of ad-hoc directional transmission with training of antenna patterns in accordance with certain aspects of the present disclosure. 
         FIG. 20  illustrates an example of quasi-omni preamble reception in accordance with certain aspects of the present disclosure. 
         FIG. 21  illustrates a frame structure with long preamble for accessing the medium in the CAP in accordance with certain aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the disclosure are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the disclosure disclosed herein, whether implemented independently of or combined with any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. 
     In the following detailed description, various aspects of the disclosure may be described in the context of a wireless network or “piconet” in accordance to the IEEE 802.15 family of standards (whether adopted or proposed). While these disclosed aspects may be well suited for use with such networks in which an access point (AP) may serve as a piconet coordinator (PNC), those skilled in the art will readily appreciate that these disclosed aspects are likewise applicable for use in various other communication environments utilizing any type of access points (APs) and access terminals (ATs), including, but not limited to, networks in accordance with the IEEE 802.11 family of standards and may, in fact, allow networks in accordance with different standards to better co-exist. Accordingly, any reference to an IEEE 802.15 compliant network is intended only to illustrate the disclosed aspects, with the understanding that such disclosed aspects have a wide range of applications. 
     The teachings herein may be incorporated into (e.g., implemented within or performed by) a variety of wired or wireless apparatuses (e.g., nodes). In some aspects, a wireless node implemented in accordance with the teachings herein may comprise an access point or an access terminal. 
     An access point (“AP”) may comprise, be implemented as, or known as NodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller (“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, Basic Service Set (“BSS”), Extended Service Set (“ESS”), Radio Base Station (“RBS”), or some other terminology. 
     An access terminal (“AT”) may comprise, be implemented as, or known as an access terminal, a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment, or some other terminology. In some implementations, an access terminal may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smart phone), a computer (e.g., a laptop), a portable communication device, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium. 
     In some aspects, the node is a wireless node. Such wireless nodes may provide, for example, connectivity for or to a network (e.g., a personal area network or piconet, wide area network such as the Internet, or a cellular network) via a wired or wireless communication link. 
     Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof. 
     An Example Wireless Communication System 
       FIG. 1  illustrates an example of a wireless communication system  100  (i.e., a Piconet  1 ) in which aspects of the present disclosure may be employed. As illustrated, Piconet  1  may include a number of wireless devices  102  or “terminals”  1 A- 1 E that can communicate with one another using relatively short-range wireless links  104 . In the illustrated example, terminal  1 E acts as a PNC for Piconet  1 . Although illustrated with five devices, it should be appreciated that any number of devices (i.e., two or more) may form a wireless personal area network. 
     Each of the terminals  102  in the Piconet  1  may include, among other things, a wireless transceiver to support wireless communication and controller functionality to manage communication with the network. The controller functionality may be implemented within one or more digital processing devices. The wireless transceiver may be coupled to one or more antennas to facilitate the transmission of signals into and the reception of signals from a wireless channel. Any type of antennas may be used including, for example, dipoles, patches, helical antennas, antenna arrays, and/or others. 
     The devices in the Piconet  1  may include any of a wide variety of different device types including, for example, laptop, desktop, palmtop, or tablet computers having wireless networking functionality, computer peripherals having wireless networking capability, personal digital assistants (PDAs) having wireless networking capability, cellular telephones and other handheld wireless communicators, pagers, wireless network interface modules (e.g., wireless network interface cards, etc.) incorporated into larger systems, multimedia devices having wireless networking capability, audio/visual devices having wireless networking capability, home appliances having wireless networking capability, jewelry or other wearable items having wireless networking capability, wireless universal serial bus (USB) devices, wireless digital imaging devices (e.g., digital cameras, camcorders, etc.), wireless printers, wireless home entertainment systems (e.g., DVD/CD players, televisions, MP3 players, audio devices, etc.), and/or others. In one configuration, for example, a wireless personal area network may include a user&#39;s laptop computer that is wirelessly communicating with the user&#39;s personal digital assistant (PDA) and the user&#39;s printer in a short-range network. In another possible configuration, a wireless personal area network may be formed between various audio/visual devices in, for example, a user&#39;s living room. In yet another configuration, a user&#39;s laptop computer may communicate with terminals associated with other users in a vicinity of the user. Many other scenarios are also possible. 
     Standards have been developed, and are currently in development, to provide a framework to support development of interoperable products that are capable of operating as part of a wireless personal area network (e.g., the Bluetooth standard (Specification of the Bluetooth System, Version 1.2, Bluetooth SIG, Inc., November 2003), the IEEE 802.15 standards, etc.). The IEEE 802.15.3c standard, for example, is a high data rate wireless personal area network standard. In accordance with the IEEE 802.15.3c standard, one of the terminals within a piconet is selected as a Piconet Coordinator (PNC) to coordinate the operation of the network. For example, with reference to  FIG. 1 , the device PNC  1 E represents a PNC for the Piconet  1  in an IEEE 802.15.3c implementation. 
     As illustrated, PNC  1 E may transmit a beacon signal  110  (or simply “beacon”) to other devices of Piconet  1 , which may help the other terminals within Piconet  1  synchronize their timing with PNC  1 E. Thus, the beacon, typically sent at the beginning of every super-frame, contains information that may be used to time-synchronize the terminals in the piconet. Each terminal in the piconet, including the PNC, may reset its super-frame clock to zero at the beginning of the beacon preamble. If a terminal does not hear a beacon, it may reset its super-frame clock to zero at the instant where it expected to hear the beginning of the beacon preamble (e.g., based on previous super-frame timing). 
       FIG. 2  illustrates various components that may be utilized in a wireless device  202  that may be employed within the wireless communication system  100 . The wireless device  202  is an example of a device that may be configured to implement the various methods described herein. The wireless device  202  may be the PNC  1 E or a terminal  102  in the Piconet  1 . 
     The wireless device  202  may include a processor  204  which controls operation of the wireless device  202 . The processor  204  may also be referred to as a central processing unit (CPU). Memory  206 , which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to the processor  204 . A portion of the memory  206  may also include non-volatile random access memory (NVRAM). The processor  204  typically performs logical and arithmetic operations based on program instructions stored within the memory  206 . The instructions in the memory  206  may be executable to implement the methods described herein. 
     The wireless device  202  may also include a housing  208  that may include a transmitter  210  and a receiver  212  to allow transmission and reception of data between the wireless device  202  and a remote location. The transmitter  210  and receiver  212  may be combined into a transceiver  214 . An antenna  216  may be attached to the housing  208  and electrically coupled to the transceiver  214 . The wireless device  202  may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas. 
     The wireless device  202  may also include a signal detector  218  that may be used in an effort to detect and quantify the level of signals received by the transceiver  214 . The signal detector  218  may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device  202  may also include a digital signal processor (DSP)  220  for use in processing signals. 
     The various components of the wireless device  202  may be coupled together by a bus system  222 , which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus. 
       FIG. 3  illustrates an example of a transmitter  302  that may be used within a wireless communication system  100  that utilizes single-carrier or some other transmission technique. Portions of the transmitter  302  may be implemented in the transmitter  210  of a wireless device  202 . The transmitter  302  may be implemented in the PNC  1 E for transmitting data  304  to a terminal  102 . The transmitter  302  may also be implemented in a terminal  102  for transmitting data  304  to the PNC  1 E. 
     Data  304  to be transmitted are shown being provided as input to a mapper  306 . The mapper  306  may map the data stream  304  onto constellation points. The mapping may be done using some modulation constellation, such as binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), 8 phase-shift keying (8PSK), quadrature amplitude modulation (QAM), etc. Thus, the mapper  306  may output a symbol stream  308 , which may represents an input into a preamble insertion unit  310 . 
     The preamble insertion unit  310  may be configured for inserting a preamble sequence at the beginning of the input symbol stream  308 , and generates a corresponding data stream  312 . The preamble may be known at the receiver and may be utilized for time and frequency synchronization, channel estimation, equalization and channel decoding. The output  312  of the preamble insertion unit  310  may then be up-converted to a desired transmit frequency band by a radio frequency (RF) front end  314 . An antenna  316  may then transmit a resulting signal  318  over a wireless channel. 
       FIG. 4  illustrates an example of a receiver  402  that may be used within a wireless device  202  that utilizes a single-carrier or some other transmission technique. Portions of the receiver  402  may be implemented in the receiver  212  of a wireless device  202 . The receiver  402  may be implemented in a terminal  102  for receiving data  404  from the PNC  1 E. The receiver  402  may also be implemented in the PNC  1 E for receiving data  404  from a terminal  102 . 
     When a signal  404  is received by an antenna  406 , it may be down-converted to a baseband signal  410  by an RF front end  408 . A frame format of the received signal for single-carrier data communications typically comprises a preamble followed by a data portion. A portion of the preamble  412  may be used for channel estimation by unit  416 . Received data  414  may be processed by an equalization unit  420  employing previously computed channel estimates  418 . 
     A demapper  424  may input an equalized data stream  422  and may perform the inverse of the symbol mapping operation that was performed by the mapper  306  from  FIG. 3  thereby outputting a data stream  426 . Ideally, this data stream  426  corresponds to the data  304  that was provided as input to the transmitter  302 , as illustrated in  FIG. 3 . 
     Association of Device with Network Controller 
     Certain aspects of the present disclosure support an efficient association of an apparatus in a piconet (e.g., a device of the Piconet  100 ) with another apparatus, e.g., the piconet controller (PNC)  1 E from  FIG. 1 .  FIG. 5  illustrates a sample association procedure, and  FIG. 6  illustrates example operations  600  for associating a second apparatus (e.g., a device of a piconet) with a first apparatus (e.g., a PNC of the same piconet) in accordance with certain aspects of the present disclosure. 
     At  602 , the first apparatus may transmit quasi-omni beacons  502  in a plurality of transmit directions  504  of the first apparatus. At  604 , the second apparatus may receive the quasi-omni beacons  502 , and may determine a preferred transmit direction of the first apparatus. At  606 , the second apparatus may send Association Request Command (CMD) frames in any of association sub-contention access periods (S-CAPs)  506  using one of transmit omni-directions of the second apparatus. Each Association Request may be sent with an Immediate Acknowledgement (IACK) mode. The Association Request may also include information about a preferred receive quasi-omni direction of the second apparatus. 
     At  608 , the first apparatus may receive the previously transmitted Association Request CMD frames, and may respond, at  612 , with an IACK message to a first Association Request detected in the association S-CAP  506  using the preferred receive quasi-omni direction of the second apparatus. If the second apparatus does not receive the IACK, then the second apparatus may resend, at  610 , Association Request CMD frames using another transmit omni-direction of the second apparatus. The second apparatus may also apply back-off after each Association Request in the association S-CAP  506 . 
     Once a management entity (DME) provides Association Response information to the first apparatus, the first apparatus may include a second apparatus&#39; Association Response Indication in quasi-omni beacon transmitted to the second apparatus, and may allocate, at  614 , an association channel time allocation (CTA) for the second apparatus to complete association with the first apparatus. At  616 , the first apparatus may send an Association Response message in the allocated association CTA. The Association Response may include information about a preferred receive quasi-omni direction of the first apparatus. 
     At  618 , the second apparatus may receive the Association Response, and may send another Association Request CMD frame in a preferred direction Association S-CAP. At  620 , the first apparatus may receive the other Association Request CMD frame, and may allocate a channel time allocation period (CTAP)  512  for beam training and for data transmission. A regular contention access period (CAP)  510  may be used for a directional communication between peers (i.e., between devices of the piconet), and the CTAP  512  may be utilized for directional communication between the first apparatus (e.g., the PNC) and the second apparatus (e.g., the device), as illustrated in  FIG. 5 . It should be also noted that the second apparatus may send an announce CMD to the first apparatus over one association S-CAP, and the first apparatus may always allocate the CTA to communicate with the second apparatus. 
       FIG. 7  illustrates an example of association flow in accordance with certain aspects of the present disclosure. A DME  708  may send a MLME-ASSOCIATE.request (MLME: Media Access Control Sub-layer Management Entity) message  710  to a device (DEV)  706  to initiate DEV&#39;s association with a PNC  704 . The DEV  706  may then transmit an Association Request CMD frame  712  to the PNC  704 . The Association Request CMD frame  712 , sent in a regular S-CAP, may comprise an identification of the DEV (i.e., DEVID), as illustrated in  FIG. 7 . When the Association Request CMD frame  712  is detected, the PNC  704  may respond to the DEV with an IACK message  714 . After that, the PNC  704  may send to the DEV  706  an Associate Response CMD frame  716  to allocate an association CTA for the DEV to complete association with the PNC. The Associate Response CMD frame  716  may comprise DEV&#39;s ID and DEV&#39;s address, as illustrated in  FIG. 7 . 
     Before a time-out period  718  elapses, the DEV  706  may send to the PNC  704  a second Association Request CMD frame  724  with DEV&#39;s address. In the meantime, the PNC  704  may indicate to a DME  702  association with the DEV  706  by sending a MLME-ASSOCIATE.indicate message  720 , and the DEV  706  may confirm association with the PNC  704  by sending a MLME-ASSOCIATE.confirm message  722  to the DME  708 . The MLME-ASSOCIATE.confirm message  722  may comprise DEV&#39;s address and DEV&#39;s ID, as illustrated in  FIG. 7 . 
     The PNC  704  may respond to the detected Association Request CMD frame  724  with an IACK message  726 , and may allocate a channel time allocation period (CTAP) for beam training and data transmission. The PNC may transmit a beacon  728  to the DEV over the allocated CTAP, and the DEV may send to the DME  708  a MLME-DEV-INFO.ind massage  730  indicating a DEV&#39;s information set. An optional SYNC frame  732  may be also transmitted from the DEV to the PNC. The sequence of messages  728 - 732  may be repeated for every super-frame, as illustrated in  FIG. 7 . 
       FIG. 8  illustrates another example of association flow in accordance with certain aspects of the present disclosure. A DME  808  may send a MLME-ASSOCIATE.request message  810  to a DEV  806  to initiate DEV&#39;s association with a PNC  804 . As illustrated in  FIG. 8 , Association Request CMD frames  812  and  814  may be sent from the DEV  806  to the PNC  804 , but the PNC may not be able to detect these frames. Upon detection at the PNC  804  of an Association Request CMD frame  816  that comprises DEV&#39;s ID, the PNC may respond to the DEV with an IACK message  818 . All transmissions  812 - 818  may be performed over an association S-CAP, as illustrated in  FIG. 8 . 
     The PNC may allocate an association CTA for the DEV  806  to complete the DEV&#39;s association by transmitting a beacon  820 . The PNC may include DEV&#39;s ID and DEV&#39;s address into an Associate Response CMD frame  822  sent to the DEV over the allocated association CTA. Upon detection of this frame, the DEV  806  may respond to the PNC with an IACK message  824  also transmitted over the allocated association CTA. 
     Following the IACK message  824 , the PNC  804  may indicate to a DME  802  association with the DEV by sending a MLME-ASSOCIATE.indicate message  826 , and the DEV  806  may confirm the association with the PNC by sending a MLME-ASSOCIATE.confirm message  828  to the DME  808 . The MLME-ASSOCIATE.confirm message  828  may comprise the DEV&#39;s address and DEV&#39;s ID, as illustrated in  FIG. 8 . Then, the DEV  806  may send to the PNC  804  a second Association Request CMD frame  830  with the DEV&#39;s address. The PNC  804  may respond to the detected Association Request CMD frame  830  with an IACK message  832 , and then the PNC may allocate the CTAP for beam training and for data transmission. The transmissions  830  and  832  may be performed over a preferred direction association S-CAP. 
     The PNC may transmit a beacon  834  to the DEV over the allocated CTAP, and the DEV may send to the DME  808  a MLME-DEV-INFO.ind massage  836  indicating an information set of the DEV. An optional SYNC frame  838  may be also transmitted from the DEV to the PNC. The sequence of messages  834 - 838  may be repeated for every super-frame, as illustrated in  FIG. 8 . 
     Medium Allocation for Devices in the Network 
     One example of a media access control (MAC) is the use of a synchronized system where all devices (DEVs) within a single network (such as a piconet or a basic service set (BSS) network) may be synchronized to a common clock. A synchronization frame may be sent in every super-frame and may contain necessary information for time synchronization of DEVs in the network. Each DEV in the network may use a time stamp in the synchronization frame to reset its super-frame clock to zero at the beginning of the super-frame. 
     If a network controller (i.e., a piconet controller (PNC) or an access point (AP)) is responsible to allocate a medium for devices in the network, then the network controller may request the medium using various methods of command frame transmission in defined time slots within the super-frame (i.e., beacon period). Such allocation may be a fixed reservation, such as a channel time allocation (CTA) for the IEEE 802.15.3c standard, or a distributed reservation protocol (DRP) for the European Computer Manufacturer&#39;s Association (ECMA) standard. Allocation of the medium may be also semi-flexible where multiple devices may compete over the medium, while directional transmission may not be allowed (i.e., restricted to low rate omni-directional traffic) or may be predefined (i.e., a sectored or a directional CAP). 
     Channel time allocations (CTAs) may provide the best Quality of Service (QoS) for connections in the IEEE 802.15.3c system, but potentially CTAs may also cause coexistence problems due to hidden nodes and the presence of other networks such as the IEEE 802.11ad network. This may be because once a DEV owns a CTA, then the DEV may perform transmission without using a listen-before-talk mechanism. Therefore, in an environment where multiple physical layer (PHY) modes co-exist, the self-healing contention access mechanism may provide improved channel utilization. However, due to the directional nature of the millimeter-wave transmission supported by the IEEE 802.15.3c standard, new rules need to be introduced to allow for directional communication in the CAP. 
     Certain aspects of the present disclosure relate to a method for allowing a directional ad-hoc peer-to-peer communication within the network  100  illustrated in  FIG. 1  without any involvement of a network coordinator (such as the PNC  1 E or any access point) for medium access allocation. The peer-to-peer communication may also support antenna-pattern training and beamforming (i.e., pro-active beamforming). 
     Procedures for Accessing the Medium in Contention Access Period 
     A basic medium access mechanism during a CAP may be based on a carrier-sense multiple access with collision avoidance (CSMA/CA) approach. In order to minimize collisions, a transmitting DEV may be required to first sense that a medium is idle for a random length of time. The MAC may use clear channel assessment (CCA) capabilities of a PHY to detect whether the channel is busy or idle. 
     If there is insufficient time remaining in the CAP for the entire frame exchange sequence, then the transmitting DEV may not commence transmission of the frame. The IEEE 802.15.3c DEV may be allowed to transmit one frame at a time with a back-off being applied to every frame that is attempted during the CAP, except for an immediate acknowledgement (Imm-ACK) frame. The IEEE 802.11 DEV may be allowed to transmit one or more frames for the duration of a transmit opportunity period with the back-off being applied to every attempt for obtaining ownership of the medium. 
       FIG. 9  illustrates operations  900  for ad-hoc directional transmission in a CAP with optional training of antenna-patterns (i.e., beamforming) in accordance with certain aspects of the present disclosure.  FIG. 10  illustrates an example scenario for the ad-hoc directional transmission in the CAP with no antenna-pattern training. 
     At  905 , the DEV- 1  may monitor a medium in the CAP, such as the CAP  1000  illustrated in  FIG. 10 , for availability of the medium for data transmission by the DEV- 1 . Also, at  910 , the DEV- 2  may monitor the medium in the CAP for availability of the medium for data transmission by the DEV- 2 . At  915 , after determining the medium is available for data transmission, the DEV- 1  may obtain the medium by transmitting an empty common mode signaling (CMS) frame  1002  in the CAP. At  920 , the DEV- 2  may receive the empty CMS frame transmitted by the DEV- 1  indicating access to the medium for data communication by the DEV- 1  in the CAP. The empty CMS frame  1002  may contain only a long preamble and one or more headers, and may be transmitted omni-directionally or quasi omni-directionally. 
     At  925  and  930 , the DEV- 1  and the DEV- 2  may optionally perform antenna-pattern training (i.e., beamforming) with each other in order to determine preferred transmit and receive antenna patterns (i.e., sector or beam patterns) of the DEV- 1  and the DEV- 2 . Following the empty CMS frame and optional antenna-pattern training (i.e., beamforming), the DEV- 1  may be allowed (after a minimum inter-frame space (MIFS)  1004 ) to send, at  935 , the data frame  1006  in any modulation coding scheme (MCS) supported by the CAP PHY mode using a known preferred transmit antenna pattern. A DEV of the IEEE 802.11ad system may be allowed to send one or more data frames in any MCS supported by the CAP PHY mode for a remaining duration of a transmit opportunity period. At  940 , the DEV- 2  may receive the data frame  1006  transmitted in the CAP from the DEV- 1 . After a short inter-frame space (SIFS)  1008 , the DEV- 1  may receive an acknowledgement frame  1010  transmitted from the DEV- 2 , which confirms successful reception of the data frame  1006  at the DEV- 2 . 
     It may be assumed that the preferred transmit pattern of the DEV- 1  is known as a result of previously performed beamforming. Therefore, the DEV- 1  may use the preferred transmit pattern (i.e., sector or beam) toward the DEV- 2  for transmitting the data frame  1006 , at  935 . 
     In order to allow for better efficiency in the CAP specified by the IEEE 802.15.3c standard and since the back-off is being applied to every frame attempted during the CAP, it may be desirable to allow for standard aggregation of data frames within the CAP. 
     As illustrated in  FIG. 9 , the DEV- 1  may optionally train the DEV- 2  using a beamforming protocol with at least one level of antenna-pattern training. For certain aspects of the present disclosure, if the DEV- 1  failed to obtain the preferred transmit pattern, then the DEV- 1  may not commence transmission and may apply back-off before attempting to re-gain the medium. 
     For standards which allow bi-directional traffic within the transmit opportunity period and for standards which allow transmission of multiple data frames within the transmit opportunity period, the proposed medium access procedure in the CAP may be expanded to include a single CMS frame and an optional training sequence per DEV per transmit opportunity period. The CMS frame may be also a vanguard CMS frame, which may be transmitted from the DEV when the medium for data transmission in the CAP is obtained for the first time. The vanguard CMS frame may be employed for training of antenna patterns used for future communication. 
       FIG. 11  illustrates example operations  1100  for antenna-pattern training, which may be included as steps  925  and  930  in operations  900  for the ad-hoc directional transmission illustrated in  FIG. 9 .  FIG. 12  illustrates an example scenario for the ad-hoc directional transmission in the CAP with antenna-pattern training (i.e., beamforming) between two communicating devices. At  1110 , the DEV- 1  may perform beamforming with the DEV- 2  by sending training sequences  1206  using at least one transmit antenna pattern. Before sending the training sequences, the DEV- 1  may set a beam tracking bit in a PHY header of the transmitted empty CMS frame  1202  to ‘1’ in order to request beamforming with the other DEV (i.e., the DEV- 2  illustrated in  FIG. 12 ). 
     At  1120 , the DEV- 2  may receive the training sequences  1206  transmitted from the DEV- 1  using a plurality of receive antenna patterns. The DEV- 2  may determine at least one preferred receive antenna pattern of the DEV- 2  and at least one preferred transmit antenna pattern of the DEV- 1 . Following a short inter-frame space  1208 , the DEV- 2  may send a CMS frame  1210  in order to access the medium in the CAP. 
     At  1130 , following a minimum inter-frame space (MIFS)  1212 , the DEV- 2  may send to the DEV- 1  feedback information  1214  about a first preferred transmit antenna pattern of the DEV- 1  chosen from the at least one preferred transmit antenna pattern of the DEV- 1 . The feedback information  1214  may be transmitted using all available transmit antenna directions of the DEV- 2 . Optionally, the DEV- 2  may send to the DEV- 1  feedback information  1218  about a second preferred transmit pattern of the DEV- 1 . The DEV- 1  may sweep its receive antenna patterns during reception of the feedback information  1214  transmitted from the DEV- 2 . 
     At  1140 , following a SIFS  1220 , the DEV- 1  may determine at least one preferred receive antenna pattern of the DEV- 1  and at least one preferred transmit antenna pattern of the DEV- 2 , and may send feedback information  1222  to the DEV- 2  about the at least one preferred transmit antenna pattern of the DEV- 2 . After a MIFS  1224 , the DEV- 1  may send a data frame  1226  using the first preferred transmit antenna pattern of the DEV- 1  in any MCS supported by the CAP PHY mode. The transmitted data frame  1226  may be received at the DEV- 2  using a preferred receive antenna pattern chosen from the at least one preferred receive antenna pattern of the DEV- 2 . Following a SIFS  1228 , the DEV- 2  may send back to the DEV- 1  an acknowledgement frame  1230  using a preferred transmit antenna pattern chosen from the at least one preferred transmit antenna pattern. 
     In a Symmetric Antenna System (SAS), there may be no need for sending feedback information during training of antenna directions. Therefore, each DEV in the SAS may train its peers by sending only repetitions of training sequence in every antenna direction. In the above description of antenna-pattern training, each DEV (i.e., the DEV- 1  and the DEV- 2 ) may send a training sequence following an empty CMS frame, and each DEV may then transmit data frames in a transmit antenna direction that may be previously determined to be a preferred receive antenna direction. 
     CMS Frame Format and Channel Sensing 
     Each device in the IEEE 802.15.3c system may be required to send an empty CMS frame when trying to obtain medium access for transmitting data in a PHY mode other than CMS. The empty CMS frame may be transmitted either omni-directionally or quasi omni-directionally. As illustrated in  FIG. 13 , the empty CMS frame  1300  may comprise a Long preamble  1302 , a PHY header  1304 , a MAC header  1306 , a header check sum (HCS)  1308 , and parity bits  1310 . 
       FIG. 14  illustrates a structure of the PHY header  1304  from the CMS frame  1300  in accordance with certain aspects of the present disclosure. The PHY header  1304  may comprise: a scrambler seed identifier (ID) field  1402 , an aggregation bit  1404 , an unequal error protection (UEP) bit  1406 , a modulation coding scheme (MCS) field  1408 , a frame length field  1410 , a preamble type field  1412 , a beam tracking bit  1414 , a low latency mode bit  1416 , a pilot word length bit  1418 , a periodic channel estimation sequence (PCES) bit  1420 , and a reserved field  1422 . 
     All fields of the PHY header  1304  of the empty CMS frame  1300  may be fixed, except the beam tracking bit  1414 . The beam tracking bit  1414  may be set to ‘1’ if training sequences for beam tracking follow the current CMS frame  1300 , and may be set to zero otherwise. The frame length field  1410  may be an unsigned integer that indicates the number of octets of the MAC frame body excluding a frame check sequence (FCS) field. The frame length field  1410  may be set to zero in the empty CMS frame  1300  or may indicate duration of following one or more data frames. 
     The aggregation bit  1404  of the PHY header  1304  may be set to zero, and the UEP bit  1406  may be also set to zero. The MCS field  1408  may be set to 0b00000. The preamble type field  1412  may be set to 0b00. The low latency mode bit  1416  may be set to zero, the pilot word length bit  1418  may be set to zero, and the PCES bit  1420  may be set to zero. 
       FIG. 15  illustrates a structure of the MAC header  1306  of the empty CMS frame  1300  illustrated in  FIG. 13  in accordance with certain aspects of the present disclosure. The MAC header  1306  may comprise: a frame control field  1502 , a piconet identification (PNID) field  1504 , a destination ID (DestID) field  1506 , a source ID field (SrcID) field  1508 , a fragmentation control field  1510 , and a stream index field  1512 . 
     A DEV that listens to the medium may obtain peer information (i.e., the source ID, the destination ID and the stream index) from the MAC header previously transmitted from another DEV. Based on the information from the MAC header, the listening DEV may decide either to keep its receiver open for one or more optional training sequences and/or a following data frame, or to switch to a listening mode since a transmitting DEV may not be any of its peers and/or the listening DEV may not be the transmission destination. 
     In order to allow better efficiency in the CAP and since the back-off may be applied to every frame attempted during the CAP, certain aspects of the present disclosure support utilization of unidirectional standard aggregation data frames in the CAP. Certain aspects of the present disclosure support removing restriction of an ACK policy to an 1 mm-ACK frame and to a No-ACK (i.e., negative acknowledgement) frame, and also allow for a block ACK frame. 
     The IEEE 802.15.3 piconet networks may use the carrier-sense multiple access with collision avoidance (CSMA/CA) scheme during the CAP and time division multiple access (TDMA) during a channel time allocation period (CTAP). The CAP may provide efficient method of coexistence with other networks, including the IEEE 802.11 networks, since the CSMA/CA algorithm used in the CAP may be similar to the CSMA/CA algorithm used in the IEEE 802.11 networks, i.e. a transmitter may use a listen-before-talk mechanism. 
     A clear channel assessment (CCA) mechanism in the CAP of the current IEEE 802.15.3 system may not be robust enough to support directional transmission, which may lead to a considerable waste of power and poor co-existence. Certain aspects of the present disclosure support a modified CCA mechanism that may allow directional transmission in the CAP. 
     The PHY of the IEEE 802.15.3 system may require energy detection as a part of the CCA process. A sufficiently strong signal may result in a DEV signaling which may indicate that the medium is busy. This may improve the coexistence performance. The omni-directional (or quasi omni-directional) empty CMS frame may be used during the first part of the CCA (i.e., during listening for the Long preamble). 
     A start of a valid Long preamble sequence at a receive level equal to or greater than a defined minimum sensitivity may indicate that the medium is busy with a probability greater than 90% within 5 μs. The receiver CCA function may report in all circumstances that the medium is busy with any signal that may be 20 dB above the defined minimum sensitivity for the CMS frame. 
     If a DEV wishing to initiate transfer detects the Long preamble during its listen-before-talk period (i.e., during a back-off inter-frame space), the DEV may refrain from transmitting and may suspend its back-off counter according to a back-off algorithm. This DEV may also remain in a receive mode during the CMS frame in order to obtain peer information from the MAC header. Based on the obtained peer information, the DEV may decide whether to keep its receiver open for one or more optional training sequences and/or following data frame, or to switch to the listening mode if a transmitting device is not any of DEV&#39;s peers and/or DEV is not the transmission destination. 
     In order to obtain frame duration, the listening DEV may also decide to decode the optional training sequences and the PHY header of the following data frame, even if the listening DEV may not be the transmission destination. The listening DEV may then operate in a sleep mode for the duration of the data frame including an ACK frame in order to save power consumption. 
     There is no mechanism in the current IEEE 802.15.3c standard, such as a Network Allocation Vector (NAV), to indicate transmission duration in the CAP, i.e., to inform the listening DEV of a medium busy duration. This may lead to considerable waste of power and poor co-existence. Certain aspects of the present disclosure support adding duration indication to the CAP transmission. In one aspect, the fragmentation control field  1510  of the MAC header  1306  of the empty CMS frame  1300  illustrated in  FIG. 15  may be reallocated to indicate duration information. 
       FIG. 16  illustrates a structure of the fragmentation control field  1510  of the MAC header  1306  in accordance with certain aspects of the present disclosure. The fragmentation control field  1510  may comprise a duration field  1602 , a duration indication bit  1604 , and a reserved field  1606 . The Duration Indication (DI) bit  1604  may be set to ‘1’ to indicate that bits  0 - 12  (i.e., the duration field  1602 ) may contain duration information. The duration field  1602  may contain the time in microseconds for which the medium is busy. A maximum allocated duration may be 8 ms, which may allow for aggregated data frame of 256 KB, while still maintaining 8% frame error rate (FER) in a highest supported MCS. 
     Certain aspects of the present disclosure support a requirement that a DEV obtaining the medium for transmitting a data frame in the PHY mode other than CMS may transmit an omni-directional (or quasi omni-directional) CMS command frame before the data frame. This particular command frame may include a new duration information element (IE) in a frame payload. 
       FIG. 17  illustrates a structure of the new duration IE field  1700  of the CMS command frame in accordance with certain aspects of the present disclosure. The duration IE field  1700  may comprise an element ID field  1702 , a length field  1704 , and a duration field  1706 . The duration field  1706  may contains a time in microseconds for which the medium is busy. A maximum allocated duration may be 8 ms, which may allow for aggregated data frame of 256 KB, while still maintaining 8% frame error rate (FER) in a highest MCS. 
       FIG. 18  illustrates an example of durations  1800  and  1800 ′ indicating how long the medium may be busy for an ad-hoc directional transmission with no training in accordance with certain aspects of the present disclosure. For example, the duration  1800  may comprise a cumulative duration of an empty CMS frame  1802 , a MIFS  1804 , a data frame  1806 , a SIFS  1808 , and an ACK frame  1810 . The duration  1800  may be indicated in the empty CMS frame  1802 , while the duration  1800 ′ may be indicated in an empty CMS frame  1802 ′. 
       FIG. 19  illustrates an example of durations  1900   a  and  1900   b  indicating how long the medium may be busy for an ad-hoc directional transmission with training in accordance with certain aspects of the present disclosure. The duration  1900   a  may be indicated within an empty CMS frame  1902 , while the duration  1900   b  may be indicated within an empty CMS frame  1910 . As illustrated in  FIG. 19 , the duration period  1900   a  may comprise a cumulative duration of the empty CMS frame  1902 , a MIFS  1904 , training sequences  1906 , a SIFS  1908 , the empty CMS frame  1910 , a MIFS  1912 , a first feedback information  1914 , a MIFS  1916 , a second feedback information  1918 , a SIFS  1920 , a feedback information  1922 , a SIFS  1924 , a data frame  1926 , a SIFS  1928 , and an ACK frame  1930 . As illustrated in  FIG. 19 , the duration period  1900   b  may comprise a cumulative duration of the empty CMS frame  1910 , the MIFS  1912 , the first feedback information  1914 , the MIFS  1916 , the second feedback information  1918 , the SIFS  1920 , the feedback information  1922 , the SIFS  1924 , the data frame  1926 , the SIFS  1928 , and the ACK frame  1930 . 
     Transmission Opportunity and Slotted Access 
     As previously described, the newly proposed access methods may be applied to any contention access protocol, including the IEEE 802.11 and the enhanced distributed channel access (EDCA). This is because the suggested mechanism may define a method for device listening to a medium according to any medium access priority and timing rules in order to obtain and maintain a transmission direction from a vanguard CMS frame headers according to new rules of ad-hoc (i.e. a proactive) beamforming. 
     This mechanism may be also applied for directional data transfer during a contention-free period (CFP). In this case, a point coordinator (PC) may establish the CFP using a beacon frame. For millimeter-wave PHY, this beacon frame may be transferred using a CMS frame format, and may comply with the previously described rules for ad-hoc (i.e., pro-active) beamforming. 
     Any data transfer within the CFP may be also performed according to the previously described rules of obtaining and maintaining transmission direction, from a vanguard CMS frame header and optional training sequence in a first transmission from each DEV. 
     Quasi-Omni Transmission and Reception 
     A DEV, which may be incapable of transmitting an omni-directional CMS frame and its preferred transmit pattern is unknown, may send the CMS frame in one of its supported transmit directions each time the DEV gains control over the medium. 
     If the DEV (i.e., the DEV- 1 ) is capable of performing beamforming with another DEV (i.e. a DEV- 2 ), the DEV- 1  may set a beam tracking field in a PHY header of the CMS frame to ‘1’. The DEV- 1  may then train the DEV- 2  using the beamforming protocol with either one or two levels. In one aspect of the present disclosure, the DEV- 1  may use round-robin of supported transmit antenna directions each time the DEV- 1  gains control over the medium, while its preferred transmit pattern may be unknown. 
     A DEV, which may be incapable of transmitting an omni-directional CMS frame and its preferred transmit pattern is known, may use its preferred transmit pattern (i.e., a sector or beam) each time the DEV gains control over the medium. 
       FIG. 20  illustrates an example of quasi-omni preamble reception in accordance with certain aspects of the present disclosure. A CMS frame  2000  may be a vanguard CMS frame, which may be transmitted from the DEV when the medium for data transmission in a CAP is obtained for the first time. As illustrated in  FIG. 20 , a listening device (i.e. DEV- 1 ), which may be not omni-capable, may sweep receive directions every defined period of time (i.e., every CCA detection time period) until the listening device detects the presence of the preamble. The CCA detection time period may be 2 μs for a single carrier/high speed interface (SC/HIS) PHY and 9 μs for an audio-video (AV) PHY. 
     The sweep may be performed over all receive antenna directions of the DEV- 1  or over a set of receive antenna directions suitable for reception from its current peers. Upon detection of a Long preamble  2002  of the CMS frame  2000 , the DEV- 1  may find a working antenna direction for a particular peer. The DEV- 1  may use this working antenna direction until detecting the PHY header  2004 . The DEV- 1  may detect the PHY header  2004 , and then may proceed according the previously defined rules. 
     Accessing the Medium in Cap Using Long Preamble 
     Certain aspects of the present disclosure support utilizing a long preamble for accessing the medium in a contention access period (CAP).  FIG. 21  illustrates a frame structure  2100  with a long preamble  2102  in accordance with certain aspects of the present disclosure. The DEV trying to access the medium in the CAP may send the long preamble  2102  followed by 8-bit Duration field  2104 . The long preamble  2102  may be sent according to a single carrier (SC) transmission scheme using a base rate, and may be protected with a Hamming 12′8 code. If the medium is granted, then the DEV may be allowed to send over the regular CAP using its best direction a data packet  2108  along with a header  2106  in any modulation-coding scheme (MCS) supported by the CAP PHY mode. 
     In certain aspects of the present disclosure, it may be preferable to use a HSI MCS0 (High Speed Interface Modulation Coding Scheme 0)/AV LRP (Audio/Video Low-Rate PHY) preamble sequence for regular CAP transmission, supporting only HSI PHY/AV PHY respectively. Therefore, the long preamble  2102  may comprise the CMS/HIS MSC0/AV LRP preamble sequence. A start of the valid CMS/HIS MSC0/AV LRP preamble sequence at a receive level equal to or greater than a defined minimum sensitivity for the CMS may indicate that the medium is busy with a certain probability, for example, with the probability greater than 90% within approximately 5 μs. The receiver clear channel assessment (CCA) function may report in certain circumstances that the medium is busy with any signal approximately 20 dB above the minimum sensitivity for the CMS/HIS MCS0/AV LRP long preamble sequence. 
     If a DEV (e.g., DEV- 1 ) wishing to initiate a transfer detects the CMS/HIS MCS0/AV LRP preamble sequence during its listen-before-talk (i.e., during its back-off inter-frame space) period, the DEV- 1  may refrain from transmitting and may suspend its back-off counter according to the back-off algorithm. The DEV- 1  may also remain in receive mode in order to obtain information about the duration of the frame  2100 . After obtaining the duration information, the DEV- 1  may go to sleep mode for the duration period equal to the frame transmission (including acknowledgement) in order to save power consumption. 
     The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrate circuit (ASIC), or processor. Generally, where there are operations illustrated in Figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, blocks  602 - 620 ,  905 - 940  and  1110 - 1140 , illustrated in  FIGS. 6 ,  9  and  11  correspond to circuit blocks  602 A- 620 A,  905 A- 940 A and  1110 A- 1140 A illustrated in  FIGS. 6A ,  9 A and  11 A. 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. 
     As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. 
     The various operations of methods described above may be performed by any suitable means capable of performing the operations, such as various hardware and/or software component(s), circuits, and/or module(s). Generally, any operations illustrated in the Figures may be performed by corresponding functional means capable of performing the operations. 
     The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     The steps of a method or algorithm described in connection with the present disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in any form of storage medium that is known in the art. Some examples of storage media that may be used include random access memory (RAM), read only memory (ROM), flash memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM and so forth. A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. A storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     The functions described may be implemented in hardware, software, firmware or any combination thereof. If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. 
     Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material. 
     Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium. 
     Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims. 
     The techniques provided herein may be utilized in a variety of applications. For certain aspects, the techniques presented herein may be incorporated in an access point, an access terminal or other type of wireless device with processing logic and elements to perform the techniques provided herein.