Patent Publication Number: US-2021168860-A1

Title: Method and apparatus for supporting wideband and multiple bandwidth transmission protocols

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/449,898 filed on Jun. 24, 2019, which issued on Feb. 16, 2021 as U.S. Pat. No. 10,925,088, which is a continuation of U.S. patent application Ser. No. 15/827,957 filed on Nov. 30, 2017, which issued on Jun. 25, 2019 as U.S. Pat. No. 10,334,626, which is a continuation of U.S. patent application Ser. No. 15/180,231 filed on Jun. 13, 2016, which issued on Dec. 12, 2017 as U.S. Pat. No. 9,844,075, which claims the benefit of U.S. patent application Ser. No. 13/529,651 filed on Jun. 21, 2012, which issued on Jun. 14, 2016 as U.S. Pat. No. 9,369,918, which claims the benefit of U.S. Provisional Application No. 61/500,788 filed on Jun. 24, 2011, U.S. Provisional Application No. 61/508,524 filed on Jul. 15, 2011, U.S. Provisional Application No. 61/607,352 filed on Mar. 6, 2012, and U.S. Provisional Application No. 61/642,048 filed on May 3, 2012, the contents of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     A wireless local area network (WLAN) in an infrastructure basic service set (BSS) mode may include an access point (AP) for the BSS and one or more wireless transmit/receive units (WTRUs) associated with the AP. The AP may access or interface with a distribution system (DS) or another type of wired or wireless network that carries traffic in and out of the BSS. Traffic to WTRUs that originates from outside the BSS may arrive through the AP and may be delivered to the WTRUs. Traffic originating from WTRUs to destinations outside the BSS may be transmitted to the AP to be delivered to the respective destinations. 
     Traffic between WTRUs within the BSS may also be transmitted through the AP where the source WTRU transmits traffic to the AP, and the AP delivers the traffic to the destination WTRU. Such traffic between WTRUs within a BSS may be peer-to-peer traffic. Such peer-to-peer traffic may also be transmitted directly between the source and destination WTRUs with a direct link setup (DLS) using an IEEE 802.11e DLS or an IEEE 802.11z tunneled DLS (TDLS). A WLAN in an independent BSS mode may not have APs and WTRUs that communicate directly with each other. 
     New spectrum is being allocated in various countries around the world for wireless communication systems such as WLANs. Such spectrum may be limited in the size and also in the bandwidth of the channels it comprises. Given the limitations of such spectrum, WLANs may only be able to support smaller bandwidths and lower data rates, as compared to high throughput (HT) and very high throughput (VHT) WLANs, such as IEEE 802.11n and current draft IEEE 802.11ac based WLANs, respectively. For example, such is the case in spectrum allocated below 1 GHz in various countries with bandwidths of 1, 2, 4, 8 and 16 MHz. Another example is the television white space (TVWS) spectrum. In addition, more than one primary bandwidth mode may be supported because sometimes only some bandwidth modes are reliable or feasible for communication because of poor wireless link conditions and also because only some bandwidth modes allow a longer range in communication. Higher bandwidth transmissions may be supported as an aggregation of multiple primary bandwidth mode channels. One such example is in the sub 1 GHz spectrum where there may be BSSs supporting and allowing operation of 2 MHz and 1 MHz bandwidth modes as the primary bandwidth modes. Higher bandwidth transmissions, (e.g., 4 MHz, 8 MHz, 16 MHz), may be supported over multiples of 2 MHz/1 MHz bandwidths. 
     The WTRUs may support an increased communication range with a robust low rate modulation and coding set with repetition in a 1 MHz mode. Also, the WTRUs may be capable of receiving in 2 MHz and 1 MHz modes. 
     SUMMARY 
     Enhanced protocols may be used to alleviate loss of spectrum efficiency in wideband transmission. The protocols may implement wideband transmission opportunity (TXOP) truncation where all of the channels involved in communication over the wideband may be released. In one scenario, a wireless transmit/receive unit (WTRU) may obtain a TXOP, (i.e., reserve a medium), for a 2 MHz bandwidth mode frame transmission with another device, (e.g., another WTRU or an access point (AP)), capable of the 2 MHz bandwidth mode and a 1 MHz bandwidth mode. The WTRU may conduct a request-to-send (RTS)/clear-to-send (CTS) frame exchange in the second bandwidth mode, and truncate the TXOP with a contention free (CF)-End frame in the first and second bandwidth modes. In another scenario, an AP may obtain a TXOP for a 2 MHz bandwidth mode frame transmission with a WTRU capable of both 2 MHz and 1 MHz bandwidth modes. 
     An AP may receive, from a WTRU, a first CF-End frame and transmit a second CF-End frame in response to the first CF-End frame. The first CF-End frame may include a duration field and a basic service set identifier (BSSID) field that includes an individual/group bit indicating whether a bandwidth value is set. The second CF-End frame may be transmitted on a primary channel and/or on one or more non-primary channels based on whether the bandwidth value is set. The individual/group bit may indicate that a scrambling sequence is included in the first CF-End frame, and may indicate that the scrambling sequence includes bandwidth information. If the individual/group bit of the BSSID field has a value of one (1), the AP may determine that the scrambling sequence of the first CF-End frame indicates a bandwidth associated with a TXOP being truncated by the WTRU. The AP may then transmit the second CF-End frame at the bandwidth indicated by the scrambling sequence of the first CF-End frame. 
     A WTRU may maintain a first and second network allocation vector (NAV) counter and receive a CF-End frame from another WTRU. The CF-End frame may indicate a truncation of a TXOP of the other WTRU. The WTRU may update the first and second NAV counters based on the received CF-End frame. Based on the updated first and second NAV counters, the WTRU may determine whether to attempt to access the medium. 
     A WTRU may maintain a TXOP holder MAC address and receive a CF-End frame from another WTRU. The CF-End frame may indicate a truncation of a TXOP of the other WTRU. The WTRU may reset the NAV counter of the WTRU based on a BSSID field in the received CF-End frame. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1A  is a diagram of an example communications system in which one or more disclosed embodiments may be implemented; 
         FIG. 1B  is a diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system shown in  FIG. 1A ; 
         FIG. 1C  is a diagram of an example radio access network and an example core network that may be used within the communications system shown in  FIG. 1A ; 
         FIG. 2  is a diagram of an example format of an IEEE 802.11 contention free (CF)-End frame; 
         FIG. 3  is a diagram of an example network in which a CF-End frame may lead to premature cancellation of a network allocation vector (NAV); 
         FIG. 4  is a diagram of example of packet exchanges of the network of  FIG. 3 ; 
         FIG. 5  is a diagram of an example CF-End frame transmission by a neighbor AP/WTRU; 
         FIG. 6  is a diagram of an example NAV reset by a receiving WTRU; 
         FIG. 7  is a diagram of an example method for transmitting a CF-End frame with a parameter set to truncate a transmit opportunity (TXOP); 
         FIG. 8  is a diagram of an example wideband TXOP protocol; 
         FIG. 9  is a diagram of an example wideband TXOP protocol; 
         FIG. 10  is a diagram of an example method for a WTRU to obtain a TXOP; 
         FIG. 11  is a diagram of an example method for a WTRU to obtain a TXOP; 
         FIG. 12A  is a diagram of an example method for an AP to obtain a TXOP; 
         FIG. 12B  is a diagram of another example method for an AP to obtain a TXOP; 
         FIG. 13  is a diagram of an example packet exchange sequence; and 
         FIG. 14  is a diagram of an example method for a WTRU/AP storing or saving the TXOP holder MAC address for the BSS in which it belongs or is associated. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  shows an example communications system  100  in which one or more disclosed embodiments may be implemented. The communications system  100  may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, and the like, to multiple wireless users. The communications system  100  may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems  100  may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like. 
     As shown in  FIG. 1A , the communications system  100  may include WTRUs  102   a ,  102   b ,  102   c ,  102   d , a radio access network (RAN)  104 , a core network  106 , a public switched telephone network (PSTN)  108 , the Internet  110 , and other networks  112 , though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like. 
     The communications systems  100  may also include a base station  114   a  and a base station  114   b . Each of the base stations  114   a ,  114   b  may be any type of device configured to wirelessly interface with at least one of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to facilitate access to one or more communication networks, such as the core network  106 , the Internet  110 , and/or the other networks  112 . By way of example, the base stations  114   a ,  114   b  may be abase transceiver station (BTS), a Node-B, an evolved Node-B (eNB), a Home Node-B (HNB), a Home eNB (HeNB), a site controller, an access point (AP), a wireless router, and the like. While the base stations  114   a ,  114   b  are each depicted as a single element, it will be appreciated that the base stations  114   a ,  114   b  may include any number of interconnected base stations and/or network elements. 
     The base station  114   a  may be part of the RAN  104 , which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, and the like. The base station  114   a  and/or the base station  114   b  may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station  114   a  may be divided into three sectors. Thus, in one embodiment, the base station  114   a  may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station  114   a  may employ multiple-input multiple-output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell. 
     The base stations  114   a ,  114   b  may communicate with one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  over an air interface  116 , which may be any suitable wireless communication link, (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, and the like). The air interface  116  may be established using any suitable radio access technology (RAT). 
     More specifically, as noted above, the communications system  100  may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station  114   a  in the RAN  104  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as universal mobile telecommunications system (UMTS) terrestrial radio access (UTRA), which may establish the air interface  116  using wideband CDMA (WCDMA). WCDMA may include communication protocols such as high-speed packet access (HSPA) and/or evolved HSPA (HSPA+). HSPA may include high-speed downlink packet access (HSDPA) and/or high-speed uplink packet access (HSUPA). 
     In another embodiment, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as evolved UTRA (E-UTRA), which may establish the air interface  116  using long term evolution (LTE) and/or LTE-Advanced (LTE-A). 
     In other embodiments, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement radio technologies such as IEEE 802.16 (i.e., worldwide interoperability for microwave access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 evolution-data optimized (EV-DO), Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), global system for mobile communications (GSM), enhanced data rates for GSM evolution (EDGE), GSM/EDGE RAN (GERAN), and the like. 
     The base station  114   b  in  FIG. 1A  may be a wireless router, HNB, HeNB, or AP, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may utilize a cellular-based RAT, (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, and the like), to establish a picocell or femtocell. As shown in  FIG. 1A , the base station  114   b  may have a direct connection to the Internet  110 . Thus, the base station  114   b  may not be required to access the Internet  110  via the core network  106 . 
     The RAN  104  may be in communication with the core network  106 , which may be any type of network configured to provide voice, data, applications, and/or voice over Internet protocol (VoIP) services to one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d . For example, the core network  106  may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, and the like, and/or perform high-level security functions, such as user authentication. Although not shown in  FIG. 1A , it will be appreciated that the RAN  104  and/or the core network  106  may be in direct or indirect communication with other RANs that employ the same RAT as the RAN  104  or a different RAT. For example, in addition to being connected to the RAN  104 , which may be utilizing an E-UTRA radio technology, the core network  106  may also be in communication with another RAN (not shown) employing a GSM radio technology. 
     The core network  106  may also serve as a gateway for the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to access the PSTN  108 , the Internet  110 , and/or other networks  112 . The PSTN  108  may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet  110  may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the Internet protocol (IP) in the TCP/IP suite. The networks  112  may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks  112  may include another core network connected to one or more RANs, which may employ the same RAT as the RAN  104  or a different RAT. 
     Some or all of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  in the communications system  100  may include multi-mode capabilities, i.e., the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU  102   c  shown in  FIG. 1A  may be configured to communicate with the base station  114   a , which may employ a cellular-based radio technology, and with the base station  114   b , which may employ an IEEE 802 radio technology. 
       FIG. 1B  shows an example WTRU  102  that may be used within the communications system  100  shown in  FIG. 1A . As shown in  FIG. 1B , the WTRU  102  may include a processor  118 , a transceiver  120 , a transmit/receive element, (e.g., an antenna),  122 , a speaker/microphone  124 , a keypad  126 , a display/touchpad  128 , a non-removable memory  130 , a removable memory  132 , a power source  134 , a global positioning system (GPS) chipset  136 , and peripherals  138 . It will be appreciated that the WTRU  102  may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. 
     The processor  118  may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a microprocessor, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, an integrated circuit (IC), a state machine, and the like. The processor  118  may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU  102  to operate in a wireless environment. The processor  118  may be coupled to the transceiver  120 , which may be coupled to the transmit/receive element  122 . While  FIG. 1B  depicts the processor  118  and the transceiver  120  as separate components, the processor  118  and the transceiver  120  may be integrated together in an electronic package or chip. 
     The transmit/receive element  122  may be configured to transmit signals to, or receive signals from, abase station (e.g., the base station  114   a ) over the air interface  116 . For example, in one embodiment, the transmit/receive element  122  may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element  122  may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element  122  may be configured to transmit and receive both RF and light signals. The transmit/receive element  122  may be configured to transmit and/or receive any combination of wireless signals. 
     In addition, although the transmit/receive element  122  is depicted in  FIG. 1B  as a single element, the WTRU  102  may include any number of transmit/receive elements  122 . More specifically, the WTRU  102  may employ MIMO technology. Thus, in one embodiment, the WTRU  102  may include two or more transmit/receive elements  122 , (e.g., multiple antennas), for transmitting and receiving wireless signals over the air interface  116 . 
     The transceiver  120  may be configured to modulate the signals that are to be transmitted by the transmit/receive element  122  and to demodulate the signals that are received by the transmit/receive element  122 . As noted above, the WTRU  102  may have multi-mode capabilities. Thus, the transceiver  120  may include multiple transceivers for enabling the WTRU  102  to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example. 
     The processor  118  of the WTRU  102  may be coupled to, and may receive user input data from, the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128  (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor  118  may also output user data to the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128 . In addition, the processor  118  may access information from, and store data in, any type of suitable memory, such as the non-removable memory  130  and/or the removable memory  132 . The non-removable memory  130  may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory  132  may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor  118  may access information from, and store data in, memory that is not physically located on the WTRU  102 , such as on a server or a home computer (not shown). 
     The processor  118  may receive power from the power source  134 , and may be configured to distribute and/or control the power to the other components in the WTRU  102 . The power source  134  may be any suitable device for powering the WTRU  102 . For example, the power source  134  may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), and the like), solar cells, fuel cells, and the like. 
     The processor  118  may also be coupled to the GPS chipset  136 , which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU  102 . In addition to, or in lieu of, the information from the GPS chipset  136 , the WTRU  102  may receive location information over the air interface  116  from a base station, (e.g., base stations  114   a ,  114   b ), and/or determine its location based on the timing of the signals being received from two or more nearby base stations. The WTRU  102  may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. 
     The processor  118  may further be coupled to other peripherals  138 , which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals  138  may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth© module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like. 
       FIG. 1C  is a system diagram of the RAN  104  and the core network  106  according to an embodiment. As noted above, the RAN  104  may employ an E-UTRA radio technology to communicate with the WTRUs  102   a ,  102   b ,  102   c  over the air interface  116 . The RAN  104  may also be in communication with the core network  106 . 
     The RAN  104  may include eNode-Bs  140   a ,  140   b ,  140   c , though it will be appreciated that the RAN  104  may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs  140   a ,  140   b ,  140   c  may each include one or more transceivers for communicating with the WTRUs  102   a ,  102   b ,  102   c  over the air interface  116 . In one embodiment, the eNode-Bs  140   a ,  140   b ,  140   c  may implement MIMO technology. Thus, the eNode-B  140   a , for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU  102   a.    
     Each of the eNode-Bs  140   a ,  140   b ,  140   c  may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in  FIG. 1C , the eNode-Bs  140   a ,  140   b ,  140   c  may communicate with one another over an X2 interface. 
     The core network  106  shown in  FIG. 1C  may include a mobility management gateway (MME)  142 , a serving gateway  144 , and a packet data network (PDN) gateway  146 . While each of the foregoing elements are depicted as part of the core network  106 , it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator. 
     The MME  142  may be connected to each of the eNode-Bs  142   a ,  142   b ,  142   c  in the RAN  104  via an S1 interface and may serve as a control node. For example, the MME  142  may be responsible for authenticating users of the WTRUs  102   a ,  102   b ,  102   c , bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs  102   a ,  102   b ,  102   c , and the like. The MME  142  may also provide a control plane function for switching between the RAN  104  and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA. 
     The serving gateway  144  may be connected to each of the eNode Bs  140   a ,  140   b ,  140   c  in the RAN  104  via the S1 interface. The serving gateway  144  may generally route and forward user data packets to/from the WTRUs  102   a ,  102   b ,  102   c . The serving gateway  144  may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs  102   a ,  102   b ,  102   c , managing and storing contexts of the WTRUs  102   a ,  102   b ,  102   c , and the like. 
     The serving gateway  144  may also be connected to the PDN gateway  146 , which may provide the WTRUs  102   a ,  102   b ,  102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a ,  102   b ,  102   c  and IP-enabled devices. An access router (AR)  150  of a wireless local area network (WLAN)  155  may be in communication with the Internet  110 . The AR  150  may facilitate communications between APs  160   a ,  160   b , and  160   c . The APs  160   a ,  160   b , and  160   c  may be in communication with STAs  170   a ,  170   b , and  170   c.    
     The core network  106  may facilitate communications with other networks. For example, the core network  106  may provide the WTRUs  102   a ,  102   b ,  102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a ,  102   b ,  102   c  and traditional land-line communications devices. For example, the core network  106  may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network  106  and the PSTN  108 . In addition, the core network  106  may provide the WTRUs  102   a ,  102   b ,  102   c  with access to the networks  112 , which may include other wired or wireless networks that are owned and/or operated by other service providers. 
     Herein, the terminology “WTRU” may include but is not limited to a station (STA), a user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, a mobile internet device (MID) or any other type of user device capable of operating in a wireless environment. When referred to herein, the terminology “AP” may include but is not limited to a base station, a Node-B, a site controller, or any other type of interfacing device capable of operating in a wireless environment. 
     A network allocation vector (NAV) protection mechanism may be used at the medium access control (MAC) layer to protect packet transmissions on the wireless medium. For the embodiments described herein, the terms device, node, or device/node may refer to, for example, a WTRU, an AP, or any other node. A NAV may be an indicator maintained by each device/node, of a time period when transmission on the wireless medium may not be initiated by the device/node. Each frame may contain a duration field that is set to a time period as defined by the MAC layer protocol. The duration field may be set to a time period corresponding to the transmission of any subsequent frames along with inter-frame spacing as required by the frame exchange sequences defined in the MAC layer protocol. A device that receives a valid frame not addressed to it, may update its NAV using the information in the duration field of the received frame if the update results in a new NAV value that may be greater than the current NAV value. 
     In a BSS, packet collisions may occur because of a hidden node. To mitigate the hidden node problem, a request-to-send (RTS) and a clear-to-send (CTS) frame exchange may be used to set the NAV appropriately in the neighborhoods of the devices engaged in a frame exchange. To obtain a transmit opportunity (TXOP) and reserve the medium, a device may transmit an RTS frame addressed to a recipient device as the first frame of a frame exchange sequence. The recipient device may respond with a CTS frame addressed to the device that transmitted the RTS frame. In this way the NAV may be set for other WTRUs in the neighborhoods of the devices to support the frame exchange sequence. The duration fields in the RTS and CTS frames may be set to protect the desired frame exchange sequence. 
     Alternatively, a CTS-to-self frame may be transmitted before a transmission requiring protection. A device may first transmit a CTS frame addressed to itself and with a duration value that protects the subsequent transmissions. This alternative may involve less overhead than other protection mechanisms. 
     WLANs with very high throughput (VHT) of greater than 100 Mbps on top of the MAC layer, for example in accordance with current draft IEEE 802.11ac, may be used to enhance system performance and achieve high data rates. VHT WLANs may include features such as wideband transmissions by aggregating channels. For example, for IEEE 802.11, a channel may be 20 MHz wide. In another example, four (4) 20 MHz channels may be aggregated for an 80 MHz wideband transmission. 
     A BSS may operate with a 20 MHz channel as a primary channel on which the devices of the BSS may camp or be associated with. In order for a device to perform a wideband transmission, it may aggregate one or more non-primary 20 MHz channels with the primary 20 MHz channel to create a desired bandwidth to support the wideband transmission. Any channel that is not a primary channel may be referred to as a secondary channel or a non-primary channel. In addition, the device may set the NAV of other devices on the non-primary channels of the aggregated channel for the wideband transmission. To set the NAV of the devices on the non-primary channels, the initiating device of the wideband transmission may conduct an RTS-CTS frame exchange on the non-primary channels with the receiving/responding device of the wideband transmission. The receiving/responding device may respond to the RTS frame from the initiating device on the one or more non-primary channels with a CTS frame if it determines that the non-primary channel is clear/idle/not-busy. For example, the receiving/responding device may respond with a CTS frame when there is no potentially interfering signal, energy, or transmission. 
     If the receiving/responding device on the one or more non-primary channels responds with a CTS frame, then the initiating device may assume that the non-primary channels are available for use and may aggregate the channels into the bandwidth for wideband transmission. If the receiving/responding device does not respond with a CTS frame on the one or more non-primary channels, or there is a failure in the reception of the CTS frame, the initiating device may assume that the one or more non-primary channels is not available for use and may not aggregate the channels into the bandwidth for wideband transmission. However, the RTS frame transmitted by the initiating device may set the NAV so that the devices in its neighborhood may not reset the NAV until a CTS timeout interval. The CTS timeout interval may include the duration from the reception of RTS from the initiating device to the start of the reception of a packet following the RTS from the initiating device. The NAV in the neighboring devices may be set as: 
       (2×SIFS)+(CTS Time)+Receiver Start Delay+(2×Slot Time),  Equation (1)
 
     where the short inter-frame spacing (SIFS) and Slot Time may be system parameters. 
     Two cases may be considered with respect to the deployment of overlapping BSS (OBSS) in the neighborhood: an OBSS case and a non-OBSS case. The OBSS case may include a scenario where the communication between the transmitting and receiving devices may interfere with a neighboring BSS, and may impact performance. 
     In a non-OBSS case, if the neighbor devices that have their NAV set by the RTS frame are in the same BSS as the initiating device that transmitted the RTS, the neighbor devices may not be able to use those channels for an off-channel DLS/TDLS operation until a CTS timeout interval. This may lead to an inefficient usage of the spectrum. In an OBSS case, if the neighbor devices that have their NAV set by the RTS frame are in an OBSS, the neighbor devices may not be able to use those channels for the duration of a CTS timeout interval, which may lead to an inefficient usage of the spectrum. 
     The inefficiency in usage of spectrum for the OBSS devices may affect basic BSS operation, for example, communication between an AP and one or more WTRUs, and their respective DLS/TDLS operation. OBSS interference may occur in dense urban deployments with the proliferation of wireless devices. This problem may be aggravated if the non-primary channel for the BSS in question is a primary channel for the OBSS. An enhanced protocol may be designed to alleviate this loss of spectrum efficiency for the devices in the OBSS. 
     In both example cases above, any WTRU that sets its NAV based on the duration field of the RTS frame may consider the medium to be busy for a CTS timeout interval, regardless of whether the medium was actually reserved with an acknowledging CTS frame. 
     In another example, a WTRU may successfully reserve the medium on a primary channel and one or more non-primary channels for a pre-determined duration of time, which may be referred to as a wideband TXOP duration. The wideband TXOP may be a TXOP for the initiating WTRU over a wideband that includes a primary channel and one or more non-primary channels. One way of reserving the medium may be performing a successful RTS-CTS frame exchange on the requested channels. The WTRUs that receive either the RTS frame, the CTS frame, or both, may set their NAVs based on a duration field contained in these frames. The medium may be reserved and the NAV may be set by any other allowed MAC protocol. The allowed MAC protocol may not include RTS-CTS. Though the medium may have been successfully reserved by the initiating WTRU for a pre-determined duration, for example, for a wideband TXOP duration, the data transmission may not last for the total wideband TXOP duration for which the medium has been reserved. In this situation, the device that may hold the TXOP, or may have reserved the medium for the wideband TXOP duration, may initiate a procedure to truncate the wideband TXOP so that the medium may be released to other devices, including those in an OBSS, on channels aggregated in the wideband transmission. 
       FIG. 2  is a diagram of an example format of an IEEE 802.11 CF-End frame  200 . The CF-End frame may include a frame control field  210 , a duration field  220 , an RA field  230 , a basic service set identifier (BSSID) field  240 , and an FCS field  250 . The frame control field  210 , the duration field  220 , the RA field  230 , and the BSSID field  240  may be included in a MAC header  260 . The BSSID may be included a timing advance (TA) field. In the CF-End frame  200 , the duration field  220  may be set to 0 and the RA field  230  may include the broadcast group address. 
     Each BSS may be uniquely identified by a BSSID. The CF-End frame may have a BSSID field  240 , and it may be, for example, a TA field that contains the BSSID of the WTRU transmitting it. Any WTRU that receives a CF-End frame may reset its NAV. This procedure for truncation of TXOP may be inadequate for truncation of wideband TXOP in VHT WLANs, since the medium may be released to all WTRUs, including those in an OBSS, on all channels in the wideband spectrum. A wideband TXOP truncation procedure to solve this problem is described herein. TXOP reservation and truncation mechanisms are described herein for multiple primary bandwidth modes as well. 
     Mechanisms for bandwidth and static/dynamic indications in the spectrum where legacy devices operate, for example, as in IEEE 802.11ac, may have to adopt signaling and protocol methods that may be constrained to support legacy compatibility. Such indications may be used in control frames, for example, in an RTS/CTS exchange for wideband TXOP reservation. In certain spectrums allocated for WLAN, for example, below 1 GHz, there may be no requirement of compatibility with legacy devices. This lack of compatibility may be exploited in designing new methods in signaling and protocol for bandwidth and static/dynamic indications. 
     The basic IEEE 802.11 CF-End mechanisms that truncate TXOP reservation may have some deficiencies. A WTRU may interpret the reception of a CF-End frame as a NAV reset, and it may reset its NAV timer to 0 at the end of the PPDU containing this frame, irrespective of whether the NAV has been set in the WTRU that transmitted the CF-End frame. This may lead to a premature cancellation of the NAV, and decreased performance due to a packet collision that may be caused by such premature NAV cancellations. 
       FIG. 3  is a diagram of an example network  300  in which the design of a CF-End frame may lead to premature cancellation of a NAV.  FIG. 3  shows a first BSS (BSS1)  310  and a second BSS (BSS2)  320 . As shown in  FIG. 3 , AP1  330  and WTRU1  340  belong to BSS1  310 ; AP2  350  and WTRU2  360  belong to BSS2  320 ; and WTRU3  370  may belong to BSS1  310  or it may belong to another overlapping BSS (OBSS) BSS3 (not shown) started by AP3  380 . WTRU3  370  may be within radio range of WTRU1  340 , WTRU2  360  and AP3  380 ; AP1  330 , AP2  350  and AP3  380  may not be able to hear each other; WTRU1  340  may be within range of AP1  330  and WTRU3  370 , while WTRU2  360  may be within range of AP2  350  and WTRU3  370 . 
       FIG. 4  is a diagram of example of packet exchanges  400  of the network of  FIG. 3 , which may lead to premature cancellation of NAV at WTRU3 due to the current design of truncation of TXOP by using CF-End frames.  FIG. 4  shows a first BSS (BSS1)  410  and a second BSS (BSS2)  420 . As shown in  FIG. 4 , AP1  430  and WTRU1  440  belong to BSS1  410 ; AP2  450  and WTRU2  460  belong to BSS2  420 ; and WTRU3  470  may belong to BSS1  410  or it may belong to another overlapping BSS (OBSS) BSS3  425  started by AP3  480 . 
     As shown in  FIG. 4 , at T=0 ms, WTRU1  440  may transmit an RTS frame  445  to reserve the medium for 3 ms, and set the NAV counter at WTRU3  480  to be 3 ms. AP1  430  may respond with a CTS frame  435 , after which the WTRU1  440  may start to transmit its data frame  447  to AP1  430 . AP1  430  may subsequently transmit an acknowledgement (ACK)  437  of the reception of the data packet. At time T=1.5 ms, AP2  450 , without being able to hear the ACK  437  transmitted by AP1  430 , may transmit an RTS frame  455  to WTRU2  460 . When WTRU2  460  receives the RTS frame  455  from AP2  450 , it may respond with a CTS frame  465  to reserve the medium for 5 ms, and may update the NAV counter at WTRU3  470  to be 5 ms. AP2  450 , after receiving the CTS frame  465  from WTRU2  460 , may start transmitting its data packet  457  for WTRU2  460 . At T=1.7 ms, WTRU1  440 , which may have finished all of its transmissions, may transmit a CF-End frame  449  to indicate truncation of its TXOP. WTRU3  470  may set its NAV=0 after receiving the CF-End frame  449  from WTRU1  440  though the current NAV at WTRU3  470  is set by WTRU2  460 , which may currently be receiving a data packet  475  after a correct medium reservation. WTRU3  470  may decide to compete for medium access, since its NAV=0 and WTRU3  470  may not sense any activity using clear channel assessment (CCA). This may lead to a collision at WTRU2  460 . WTRU2  460  may fail to receive its packets from AP2  450 , and may lead to a breakdown of the medium reservation mechanism and decreased system performance. 
     The problem of premature cancellation of NAV is expected to be more prevalent in the current and future generations of WLAN systems due to increased WLAN coverage ranges. In IEEE 802.11ah systems, for example, a WTRU may be required to have a coverage range of up to 1 km. This may lead to a much greater number of overlapping BSSs in the same area. The chance of hearing a CF-End frame that erroneously cancels NAV counters may increase with the number of OBSSs. 
     The problem of premature cancellation of a NAV may also be more prevalent in the current and future generations of WLAN systems due to lower data rates. In IEEE 802.11ah systems, for example, a WTRU may have a data rate as low as 100 kbps. Transmissions using a low data rate may lead to a longer transmission time, which may require more frequent application of a medium reservation mechanism, which in turn may lead to more frequent truncation of TXOPs and more frequent premature cancellations of NAVs at WTRUs. 
     The problem of premature cancellation of a NAV may also be more prevalent in the current and future generations of WLAN systems due to multiple operating bandwidths in OBSS. For example, in IEEE 802.11ac, 802.11af and 802.11ah systems, there may be multiple operating modes with variable, and sometimes dynamic, operating bandwidths. More frequent application of medium reservation mechanisms may provide protection of different and/or dynamic operating modes with variable bandwidths in OBSSs, which in turn may lead to more frequent truncation of TXOPs and more frequent premature cancellations of NAVs at WTRUs. 
     A method and apparatus may be used to alleviate the loss of spectrum efficiency in wideband transmission. For example, when a medium reservation is conducted by a device in a BSS over a wideband that it may not be able to use in its entirety, the method and apparatus may release unusable bandwidth. The released bandwidth may be used by devices in the same BSS for DLS/TDLS mode. Additionally, a method and apparatus may be used to alleviate spectrum usage inefficiency in an OBSS environment. The method and apparatus may be used to address the issue of wideband TXOP truncation where the channels involved in communication over the wideband may be released for WTRUs of both the current BSS and any OBSS. 
     In addition, a method and apparatus may be used for TXOP reservation and truncation for multiple primary bandwidth modes. The methods may include signaling and protocol enhancements for bandwidth and static/dynamic indications when legacy compatibility may not be a requirement or constraint. The methods may also include signaling and protocol enhancements to remedy deficiencies in the basic CF-End mechanism in IEEE 802.11 to truncate a TXOP. 
     Although the embodiments described hereafter consider the method of reserving the medium using an RTS-CTS frame exchange, it should be understood that the embodiments are not limited to these specific examples, and may be applied to any other type of frame exchange or in a different way, for example, any other MAC protocol for medium reservation and NAV setting. It should also be understood that the drawings are for illustration purposes only and may not be considered as limiting the scope of the embodiments. 
     A transmitting WTRU may be an IEEE 802.11 WTRU that initiates communication with another IEEE 802.11 WTRU. The communication may be triggered by an RTS frame or any other MAC protocol to reserve the medium and set the NAV. A receiving WTRU may be an IEEE 802.11 WTRU that is the recipient of the data being transmitted by the transmitting WTRU. A neighboring BSS may be a BSS neighboring (overlapping with or interfering with) the BSS to which the transmitting and the receiving WTRUs belong. A neighbor AP/WTRU may be an IEEE 802.11 AP/WTRU that may be a member of the neighboring BSS. The neighbor AP/WTRU may refer to an AP or any WTRU in the neighboring BSS. 
     A NAV reset may be performed by a neighbor AP/WTRU. The neighbor AP/WTRU may monitor the channels on which an RTS frame was transmitted by the transmitting WTRU. The monitored channels may include a primary channel and/or one or more non-primary channels. If the neighbor AP/WTRU does not detect any activity in the medium on any or all of those channels following the RTS frame, the neighbor AP/WTRU may free the medium for its BSS. 
     In one embodiment, the neighbor AP/WTRU may monitor these channels for a certain predefined period of time for any activity in order to determine if the medium is being used for communication on those channels. For example, the neighbor AP/WTRU may monitor the primary channel of its BSS, (i.e., the neighboring BSS), which may be a non-primary channel for the BSS of the transmitting WTRU. The neighbor AP/WTRU may monitor this channel for a CTS frame from a receiving WTRU following an RTS frame transmission from the transmitting WTRU. Alternatively, the neighbor AP/WTRU may monitor the channels on which the RTS frame was transmitted by the transmitting WTRU. 
     The neighbor AP/WTRU may or may not receive the CTS frame transmitted by the receiving WTRU in response to the RTS frame from the transmitting WTRU due to any of the following reasons. The neighbor AP/WTRU may be a hidden node to the receiving WTRU, and hence the CTS frame transmitted by the receiving WTRU may be heard by the transmitting WTRU but not the neighbor WTRU. The CTS frame of the receiving WTRU may be lost due to interference or collision. The receiving WTRU may not have responded to the RTS frame of the transmitting WTRU. 
     If a CTS frame corresponding to the RTS frame of the transmitting WTRU is not heard after a short inter-frame spacing (SIFS) duration of time, the neighbor AP/WTRU may further monitor the medium for a predetermined additional amount of time to determine if the medium is being used. For example, the neighbor AP/WTRU may monitor the medium for a duration of (SIFS+ΔT) from the reception of an RTS frame. Alternatively, the neighbor AP/WTRU may monitor the medium for an additional (SIFS+ΔT) time duration following the time when the CTS frame was expected. AT may be a predefined value or a configurable parameter. 
     If the medium is found to be idle at the end of a (SIFS+ΔT) duration from the transmission time of the RTS frame, or at the end of a (SIFS+ΔT) duration from the time a CTS frame is expected, the neighbor AP/WTRU may release the medium by resetting the NAV in any or all of the following ways. For example, the neighbor AP/WTRU may transmit a specific frame, for example a contention free (CF)-End frame with the BSS identity (BSSID) field set to its BSSID and the receiver address (RA) field set to the broadcast group address. 
       FIG. 5  is a diagram of an example CF-End frame transmission  500  by a neighbor WTRU. In the example shown in  FIG. 5 , a WTRU  505  may transmit an RTS frame  510  on a primary channel  515 , and an RTS frame  520  on a non-primary channel  525 . In this example, the WTRU  505  may receive a CTS frame  530  on the primary channel  515  after a SIFS duration  535 . If the neighbor WTRU  537  does not receive a CTS frame on the non-primary channel  525  after a (SIFS+ΔT) duration, the neighbor WTRU  537  may transmit a CF-End frame  540  on the non-primary channel  525  to reset the NAV on the non-primary channel. The WTRU  505  may transmit a data frame  550  on the primary channel  515  if the CTS frame  530  was received. 
     In another example, a new action frame may be defined or any other existing action frame may be modified to reset the NAV. At the end of a monitoring period, if the medium is found to be idle, the neighbor WTRU may transmit the new action frame, or modified existing action frame, that lets other WTRUs in its BSS reset their NAVs. 
     A NAV reset may be performed by the receiving WTRU. For example, the receiving WTRU may respond to the RTS on the channels where communication may not be possible, in such a way that the WTRUs that set their NAV based on the RTS may reset their NAVs for future communication. 
     In one example, the receiving WTRU, after receiving an RTS from the transmitting WTRU on the channels that the transmitting WTRU intends to aggregate for wideband transmission, may respond with a CTS frame on those channels where communication is possible and may respond in an alternative manner on the channels where communication may not be possible. The channels where communication may not be possible may be referred to as “non-usable channels” hereafter. 
     One alternative manner in which the receiving WTRU may respond may be by transmitting a CTS frame even on the non-usable channels. When responding on a non-usable channel, the receiving WTRU may set the Duration field to 0. Any WTRU other than the transmitting WTRU that receives a CTS frame with this Duration value may reset its NAV. Alternatively, the receiving WTRU may set the Duration field in the CTS transmitted on non-usable channels to a value that may be a short duration of time, for example T short . T short  may be a fixed value or a configurable parameter. Since any WTRU that receives a CTS may set its NAV to the value indicated in the Duration field of the CTS frame, the WTRUs/APs receiving this CTS may backoff for a short duration of time and may be able to access the medium after that. This example may apply to legacy and IEEE 802.11ac WTRUs alike. 
     In both examples described above, the transmitting WTRU may consider the channel(s) on which a CTS with a duration set to a value other than what is expected for successful communication is received as non-usable. For example, if the Duration field in the CTS frame contains a value other than (Duration field value in the RTS frame—SIFS Time—time required to transmit the CTS frame), the transmitting WTRU may consider the channel(s) on which this CTS frame was received as not available for communication. 
     In another example, a new action frame may be introduced or an existing action frame may be modified to achieve this purpose. For example, after receiving an RTS from the transmitting WTRU, the receiving WTRU may respond with a CTS on the channels where communication is possible and with the new or modified action frame on the non-usable channels. The WTRUs that receive this new or modified action frame may consider the channel(s) on which this frame was received to be free and available for communication and may reset their NAVs. The transmitting WTRU on reception of this new or modified existing action frame may consider the corresponding channel(s) as unusable. 
       FIG. 6  is a diagram of an example NAV reset  600  performed by the receiving WTRU in non-usable channels using a CTS frame with the duration field set to 0 or T short .  FIG. 6  shows a transmitting WTRU  610 , a receiving WTRU  620 , and a neighbor WTRU  630 . The transmitting WTRU  610  may be configured to communicate on a primary channel  615  and a non-primary channel  617 . The receiving WTRU  620  may be configured to communicate on the primary channel  615  and the non-primary channel  617 . The neighbor WTRU  630  may be configured to communicate on the non-primary channel  617 . The transmitting WTRU  610  may transmit an RTS frame  640  on the primary channel  615 , and an RTS frame  645  on the non-primary channel  617 . The receiving WTRU  620 , in response to the RTS frame  640 , may transmit a CTS frame  650  on the primary channel  615  after a SIFS duration  635 . In response to the RTS frame  645 , the receiving WTRU  620  may transmit a CTS frame  655  on the non-primary channel  617  after a SIFS duration  635 . The CTS frame  655  may include a Duration field set to 0 or T short . The neighbor WTRU  630  may receive the CTS frame  655  on the non-primary channel  617  and reset its NAV immediately or after T short , based on the duration indicated by the Duration field. 
     A wideband TXOP truncation may be performed. A wideband TXOP may be a TXOP for a medium reservation over one or more channels, for example on a primary channel and one or more non-primary channels. In a wideband TXOP truncation example, all or some of the channels involved in communication may be released when the communication terminates before the end of the wideband TXOP duration. A wideband TXOP truncation may allow other WTRUs/APs, including those in an OBSS, to use the medium on any of the channels of the wideband transmission. 
     The NAV may be set on the primary and non-primary channels by a device to reserve the medium for a wideband TXOP to transmit packet data. The NAV may be set using any allowed mechanism, for example, RTS and CTS frame exchange, transmitting CTS-to-self frames on the primary and non-primary channels, or by any other method such as transmitting IEEE 802.11n based non-HT duplicate packet formats where the same packet may be transmitted simultaneously on primary and non-primary channels. The device may truncate the TXOP with a CF-End frame if it has no more packet data to transmit. The CF-End frame transmitted by a device may include the BSSID of the BSS to which the device belongs or is associated with. The device may transmit a CF-End frame on each of the channels, for example the primary channel and non-primary channels. If the device transmits on a primary channel and non-primary channels, the device may use the non-HT duplicate mode where the CF-End frame may be transmitted simultaneously on the channels. Alternatively, the CF-End frame on a channel may be transmitted with a BSSID that matches the BSSID of the BSS for which the given channel is a primary channel. 
     The CF-End frame may be transmitted in a wideband packet format by a WTRU truncating its wideband TXOP where the CF-End frame may span the entire bandwidth of the primary and non-primary channels. In this example, the AP of the BSS to which the WTRU belongs may transmit a CF-End frame after an inter-frame duration, for example a SIFS, in response to the CF-End frame from the WTRU in one or more of the following ways. In a first example, the AP may transmit a CF-End frame with its BSSID on the primary channel. In a second example, the AP may transmit a CF-End frame with its BSSID on the primary and non-primary channels, for example in a non-HT duplicate format. Ina third example, the AP may transmit a CF-End frame with its BSSID on the primary channel and a CF-End frame on a non-primary channel with the BSSID of the BSS for which the non-primary channel may be the primary channel. 
     An AP/WTRU may obtain neighbor AP BSSID information. In one example, all APs in the same neighborhood may obtain neighbor AP information explicitly via a wired backbone or control signaling over the wireless interface. The neighborhood may include the same geographical area, and the APs may belong to the same subnet, for example. In another example, the APs may obtain its neighbor AP information implicitly by monitoring different channels. 
     When an AP receives a CF-End frame from a device in a neighbor BSS on the primary channel of the AP, where the BSSID in the received CF-End frame does not match the BSSID of the AP, the AP may respond by transmitting a CF-End frame after an inter-frame duration, for example, a SIFS duration, with its own BSSID on the primary channel of the AP. 
     When an AP receives a CF-End frame from a device in the same BSS on the primary channel of the AP, where the BSSID in the received CF-End frame matches the BSSID of the AP, the AP may respond by transmitting a CF-End frame after an inter-frame duration, for example, a SIFS duration, with its own BSSID on the primary channel of the AP. 
     A CF-End frame with specific parameters may be set to truncate the TXOP on both primary and non-primary channels. For example, one or more parameters of the CF-End frame may be set so that the TXOP may be truncated both on the primary and the non-primary channels efficiently and may result in better usage of the available bandwidth in both the current and the neighbor BSS. 
       FIG. 7  is a diagram of an example method  700  for transmitting a CF-End frame with a parameter set to truncate the TXOP on both the primary and non-primary channels. If a non-AP WTRU of the BSS under consideration is the TXOP holder, the non-AP WTRU may transmit one of the following to truncate its TXOP: (1) a CF-End frame with the individual/group bit in a timing advance (TA) field set to ‘0’ on the primary channel or on all primary and non-primary channels, or (2) a CF-End frame with the individual/group bit in the TA field set to ‘1’, on the primary channel or on all primary and non-primary channels. Referring to  FIG. 7 , the AP may receive a CF-End frame  710 . The AP may determine  720  whether an individual/group bit in the TA field of the CF-End frame is set to ‘ 1 ’. A CF-End frame with an individual/group bit that is set to ‘ 1 ’ may, for example, indicate truncation of the TXOP to all devices, including the OBSS devices, and/or it may indicate a bandwidth in which to transmit the CF-End frame response. If the AP determines that the individual/group bit is set to ‘ 1 ’, the AP may respond by transmitting a CF-End frame on the primary and non-primary channels  730 . For example, if the individual/group bit is set to ‘ 1 ’, the AP may respond on the same channels that the AP received the CF-End frames or on the bandwidth indicated by the received CF-End frame. When the individual/group bit is set to ‘ 1 ’, it may indicate that a bandwidth value is set, and/or that a scrambling sequence is included in the frame which signals the bandwidth value. If the AP determines that the individual/group bit is set to ‘ 0 ’, the AP may respond by transmitting a CF-End frame on the primary channel  740 . 
     In this example, the AP of the BSS to which the WTRU belongs may transmit a CF-End frame after an inter-frame duration, for example a SIFS, in response to the CF-End frame from the WTRU. Alternatively, if the AP itself is a TXOP holder, it may directly transmit a CF-End frame truncating the TXOP. In both the above cases, the AP may set one or more parameters of the CF-End frame in any or all of the following ways. The AP may transmit the CF-End frame on the primary channel and also the non-primary channels if needed. 
     The following mechanisms may be adopted independently or in any combination. For example, the AP may set the individual/group bit of the TA field in the CF-End frame to ‘ 0 ’ on the primary channel and to ‘ 1 ’ on all non-primary channels that may be released, the AP may set the individual/group bit of the TA field in the CF-End frame to ‘ 0 ’ on the primary channel, the AP may set the individual/group bit of the TA field in the CF-End frame to ‘ 0 ’ on the primary channel and to ‘ 0 ’ on all non-primary channels that may be released, the AP may set the individual/group bit of the TA field in the CF-End frame to ‘ 1 ’ on all the channels that may be released, (both primary and non-primary channels), and/or the AP may set the duration field of the CF-End frame to a non-zero value. 
     A WTRU/AP may store the TXOP holder MAC address for the BSS in which it belongs or is associated with. This MAC address may be obtained, for example, from the MAC address included in the frame that initiated a frame exchange sequence or TXOP reservation. The WTRU/AP may determine that the TXOP holder is associated with or belongs to its BSS if either the transmitter or receiver address in the frame, received or transmitted by the TXOP holder, matches the MAC address of the AP of its BSS or BSSID. The WTRU/AP may discard the stored TXOP holder MAC address for its BSS when the NAV timer is zero or is reset. The WTRU/AP may change or update the stored TXOP holder MAC address for its BSS when the NAV timer is set or updated with a new value. 
     When a non-AP WTRU or AP receives a CF-End frame from a neighbor device on the primary channel of the WTRU, where the BSSID in the received CF-End frame does not match the BSSID of the WTRU, and the individual/group bit in the TA field is set to ‘ 1 ’, the WTRU may reset its NAV and consider the medium available for communication. In a variation of this embodiment, the NAV reset may also be conditional upon whether the current NAV was not set by a TXOP holder that belongs to or is associated with its BSS. 
     When a non-AP WTRU or AP receives a CF-End frame from a neighbor device on the primary channel of the WTRU where the BSSID in the received CF-End frame does not match the BSSID of the WTRU, and the individual/group bit in the TA field is set to ‘ 0 ’, the WTRU may reset its NAV and consider the medium available for communication. In a variation of this embodiment the NAV reset may also be conditional upon whether the current NAV was not set by a TXOP holder that belongs to or associated with its BSS. 
     When an AP receives a CF-End frame from a neighbor device on the primary channel of the AP, where the BSSID in the received CF-End frame does not match the BSSID of the AP but the individual/group bit in the TA field is set to ‘ 1 ’, the AP may respond by transmitting a CF-End frame after an inter-frame duration, for example, a SIFS duration, with its own BSSID on the primary channel of the AP. In a variation of this embodiment, the AP response with a CF-End frame may also be conditional upon whether its current NAV was not set by a TXOP holder that belongs to or associated with its BSS. The AP may transmit the CF-End frame after a predetermined duration such as a SIFS, a PIFS, or any other inter-frame duration. 
     When an AP receives a CF-End frame from a neighbor device on the primary channel of the AP, where the BSSID in the received CF-End frame does not match the BSSID of the AP, and the individual/group bit in the TA field is set to ‘ 0 ’, the AP may respond by transmitting a CF-End frame after an inter-frame duration, for example, a SIFS duration, with its own BSSID on the primary channel of the AP. In a variation of this embodiment, the AP response with a CF-End frame may also be conditional upon whether its current NAV was not set by a TXOP holder that belongs to (is associated with) its BSS. The AP may transmit the CF-End frame after predetermined duration such as a SIFS, a PIFS, or any other inter-frame duration. 
     In the above CF-End frames or CF-End frame sequences, there may be a decision process in the devices that determines if the above CF-End frames or CF-End frame sequences may be accommodated in the remaining duration of the wideband TXOP. The transmission of the CF-End frames or CF-End frame sequences may be conditional on that determination of whether they may be accommodated. For example, the CF-End frames or CF-End frame sequences may not be transmitted if they cannot be accommodated within the initially reserved TXOP duration. 
       FIG. 8  is a diagram of an example method  800  for wideband TXOP truncation in an OBSS case where an AP  810  may be the TXOP holder. The AP  810  may begin a NAV-set sequence  815  on its primary channel and/or one or more non-primary channels to initiate a TXOP duration  820 . The NAV-set sequence  815  may begin after an EDCA channel access period  825 . After a SIFS duration  830 , the AP  810  may begin an initiator sequence  835 . After a SIFS duration  840 , the AP  810  may transmit a CF-End frame  845  on its primary channel and/or one or more non-primary channels to indicate truncation of the TXOP. The neighbor AP  850  may transmit a CF-End frame  855  to its BSS WTRUs, on its primary channel after a SIFS duration  860  following the reception of a CF-End frame  845  from the AP  810 . The primary channel of the neighbor AP  850  may be a communicating BSS non-primary channel of the AP  810 . The CF-End frame  855  may include the BSSID of the neighbor AP  850 . This method may aid the WTRUs on previously busy channels in both BSSs to reset their NAVs and release the medium for communication. 
       FIG. 9  is a diagram of an example method  900  for wideband TXOP truncation in an OBSS case where a WTRU  910  may be the TXOP holder. The WTRU  910  may begin a NAV-set sequence  915  on its primary channel and/or one or more non-primary channels to initiate a TXOP duration  920 . The NAV-set sequence  915  may begin after an EDCA channel access period  925 . After a SIFS duration  930 , the WTRU  910  may begin an initiator sequence  935 . After a SIFS duration  940 , the TXOP holding WTRU  910  may transmit a CF-End frame  945  on its primary channel and/or one or more non-primary channels to indicate truncation of the TXOP. The AP  950  of the BSS of this WTRU and the neighbor AP  955  may each transmit a CF-End frame  960 ,  965  after a SIFS duration  970  following the WTRU  910  CF-End frame transmission. The CF-End frame  960  and the CF-End frame  965  may each include their corresponding BSSID in the frame. This method may aid the WTRUs on previously busy channels in both BSSs to reset their NAVs and release the medium for communication. 
     A No CF-End frame method may be implemented. In this example, a VHT device, for example, a WTRU or an AP, that does not have any data to transmit before the end of the initially reserved TXOP may not transmit any CF-End frame to truncate the TXOP. This rule may be applied for VHT devices in one or more of the following scenarios in wideband transmission, or all transmissions regardless of whether they may be wideband or not. This example method may be used to achieve fairness in the medium where all the WTRUs and/or APs that set their NAVs at the beginning of the TXOP may continue to back off until the end of the actual TXOP. In this example, since a CF-End frame is not transmitted, the TXOP is not truncated and the remaining TXOP duration after data transmission may be wasted. However since no device may access the channel, a level of fairness may be achieved for all devices. 
     TXOP protection and truncation in multiple primary bandwidth modes are described below. Some WLAN systems may support multiple primary bandwidth modes of transmission. The multiple bandwidth modes may be supported because sometimes only some bandwidth modes are reliable or feasible for communication because of poor wireless link conditions. The IEEE 802.11ah standard operating in the sub 1 GHz spectrum may have BSSs that support operation of multiple primary bandwidth modes namely, 2 MHz and 1 MHz bandwidth modes. The 1 MHz bandwidth mode may be more reliable for communication and offers a longer range than the 2 MHz bandwidth mode. The devices may support an increased communication range with a robust low rate modulation and coding set with repetition, for example, MCSO-rep2, only in 1 MHz mode. It may be required that all devices are capable of receiving in 2 MHz and 1 MHz modes. Higher transmission bandwidths of 4, 8 and 16 MHz may also be supported in IEEE 802.11ah. TXOP truncation mechanisms for multiple primary bandwidth modes using the 2 MHz and 1 MHz primary bandwidth modes are described as an example for convenience. These mechanisms may apply to a general case of multiple primary bandwidth modes. 
     In a BSS supporting 2 MHz and 1 MHz primary bandwidth modes, there may be WTRUs that may only transmit or receive using the 1 MHz bandwidth mode. This may be because the WTRUs may be capable of only 1 MHz primary bandwidth mode operation, or the WTRUs may be capable of both 2 MHz and 1 MHz primary bandwidth modes of operation, but have a poor channel link with the other device they are communicating with. In this example, only 1 MHz bandwidth mode operation may be feasible for communication and 2 MHz bandwidth mode transmissions may not be received successfully. Note that the other WTRUs in the BSS may be able to communicate using both 2 MHz and 1 MHz primary bandwidth modes. 
       FIG. 10  is a diagram of an example method  1000  for a WTRU  1010  to obtain a TXOP and reserve the medium for a 2 MHz bandwidth mode frame transmission using an RTS/CTS exchange in a 1 MHz bandwidth mode and truncating the TXOP with a CF-End frame in a1 MHz bandwidth mode. In  FIG. 10 , a WTRU  1010  may reserve the medium  1015  for a 2 MHz bandwidth mode frame transmission with another device that may be capable of both 2 MHz and 1 MHz bandwidth modes. To obtain a TXOP for a 2 MHz bandwidth mode frame transmission, the WTRU  1010  may conduct an RTS-CTS exchange in the 1 MHz bandwidth mode so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may set their NAV in addition to other WTRUs. The RTS-CTS exchange may include the WTRU  1010  transmitting an RTS frame  1020  on a primary 1 MHz channel within the 2 MHz bandwidth, and receiving, after a SIFS duration  1025 , a CTS frame  1030  on the primary 1 MHz channel within the 2 MHz bandwidth in response to the RTS frame  1020 . In this example, when the WTRU  1010  has no more data to transmit, the WTRU  1010  may truncate the TXOP with a CF-End frame  1035  transmission in the 1 MHz bandwidth mode so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may reset their NAV in addition to other WTRUs. In response to such a CF-End frame transmission in the 1 MHz bandwidth mode, an AP (not shown) in a BSS may transmit a CF-End frame  1040  in the 1 MHz bandwidth mode so that all WTRUs in the BSS may reset their NAV and thus may mitigate hidden node problems. 
     Alternatively, the WTRU may truncate the TXOP with a CF-End frame transmission in the 2 MHz bandwidth mode so that the WTRUs that transmit or receive using the 2 MHz bandwidth mode may reset their NAV in addition to other WTRUs. In response to such a CF-End frame transmission in the 2 MHz bandwidth mode, an AP in a BSS may transmit a CF-End frame in the 1 MHz bandwidth mode so that all WTRUs in the BSS may reset their NAV and thus may mitigate hidden node problems. 
       FIG. 11  is a diagram of an example method  1100  for a WTRU  1110  to obtain a TXOP and reserve the medium for a 2 MHz bandwidth mode frame transmission using RTS/CTS exchange in both 1 MHz parts of the 2 MHz bandwidth and truncating the TXOP with a CF-End frame in both 1 MHz parts of the 2 MHz bandwidth. A neighbor AP or OBSS may camp on or operate on the non-primary 1 MHz part of the 2 MHz primary channel of the given BSS, using the non-primary 1 MHz part as its primary 1 MHz channel. 
     Referring to  FIG. 11 , a WTRU  1110  may reserve the medium  1115  for a 2 MHz bandwidth mode frame transmission with another device that may be capable of both 2 MHz and 1 MHz bandwidth modes. To obtain a TXOP for a 2 MHz bandwidth mode frame transmission the WTRU  1110  may conduct an RTS-CTS exchange in both 1 MHz parts of the 2 MHz bandwidth so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may set their NAV in addition to other WTRUs, in its BSS and the OBSS. 
     The RTS-CTS exchange may include the WTRU  1110  transmitting an RTS frame  1120  on the primary 1 MHz channel within the 2 MHz bandwidth, and transmitting an RTS frame  1125  on the non-primary 1 MHz channel within the 2 MHz bandwidth. After a SIFS duration,  1130 , the WTRU  1110  may receive a CTS frame  1135  on the primary 1 MHz channel within the 2 MHz bandwidth, and receive a CTS frame  1140  on the non-primary 1 MHz channel within the 2 MHz bandwidth. 
     The WTRU  1110  may then transmit its data  1145  on the 2 MHz bandwidth, and receive a response  1150  on the 2 MHz bandwidth after a SIFS duration  1155 . When the WTRU  1110  has no more data to transmit, the WTRU  1110  may truncate the TXOP with a CF-End frame transmission  1160 ,  1165  in both 1 MHz parts of the 2 MHz bandwidth or at least in the primary 1 MHz channel within the 2 MHz bandwidth, so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may reset their NAV in addition to other WTRUs, in its BSS and the OBSS, or in the 2 MHz bandwidth mode. In response to such a CF-End frame transmission an AP (not shown) in a BSS may transmit a CF-End frame  1170 ,  1175  in both 1 MHz parts of the 2 MHz bandwidth so that all WTRUs in its BSS and OBSS may reset their NAV and thus may mitigate hidden node problems. 
       FIG. 12A  is a diagram of an example method  1200  for an AP  1210  to obtain a TXOP  1215  and reserve the medium for a 2 MHz bandwidth mode frame transmission using an RTS/CTS exchange in a 1 MHz bandwidth mode and truncating the TXOP with a CF-End frame in the 1 MHz bandwidth mode. In  FIG. 12A , the AP  1210  may reserve the medium for a 2 MHz bandwidth mode frame transmission with a WTRU (not shown) that may be capable of both 2 MHz and 1 MHz bandwidth modes. To obtain a TXOP  1215  for a 2 MHz bandwidth mode frame transmission, the AP may conduct an RTS-CTS exchange in the 1 MHz bandwidth mode so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may set their NAV in addition to other WTRUs. The RTS-CTS exchange may include the AP  1210  transmitting an RTS frame  1220  on a primary 1 MHz channel within the 2 MHz bandwidth, and receiving, after a SIFS duration  1225 , a CTS frame  1230  on the primary 1 MHz channel within the 2 MHz bandwidth in response to the RTS frame  1220 . The CTS frame  1230  may be a short CTS frame. A short CTS frame may be a shortened version of the CTS frame. The short CTS frame may only include a PHY preamble, and may not include MAC layer fields. The frame format of the short CTS may comprise a short training field (STF), along training field (LTF) and a signal (SIG) field in that order. The SIG field of the short CTS frame may include an indication that the frame is a short CTS frame. The short CTS frame may include other indications or signaling requirements for the short CTS frame such as CTS ID to indicate the intended receiver of the CTS, a bandwidth when the CTS may need to indicate the available bandwidth at the receiver side within the bandwidth indicated by RTS, and a duration for NAV setting. 
     The AP  1210  may then transmit its data  1235  on the 2 MHz bandwidth, and receive a response  1240  on the 2 MHz bandwidth after a SIFS duration  1245 . When the AP  1210  has no more data to transmit, the AP  1210  may truncate the TXOP  1215  with a CF-End frame  1245  in the 1 MHz bandwidth mode so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may reset their NAV in addition to other WTRUs. 
       FIG. 12B  is a diagram of an example scenario  1250  where a neighbor AP or OBSS may camp on or operate on the non-primary 1 MHz part of the 2 MHz primary channel of the given BSS, using non-primary 1 MHz part as its primary 1 MHz channel. In this example, an AP may reserve the medium for a 2 MHz bandwidth mode frame transmission with an RTS/CTS exchange in both 1 MHz parts of the 2 MHz bandwidth and truncate the TXOP with a CF-End frame in both 1 MHz parts of the 2 MHz bandwidth. To handle such a scenario, the AP  1210  may transmit another CF-End frame  1260  simultaneously on the non-primary 1 MHz channel/part within the 2 MHz to reset the NAV for WTRUs in a neighbor BSS or OBSS. In addition, to obtain a TXOP  1215  for a 2 MHz bandwidth mode frame transmission, the AP  1210  may conduct an RTS-CTS exchange in both 1 MHz parts of the 2 MHz bandwidth so that WTRUs that transmit or receive using the 1 MHz bandwidth mode may set their NAV in addition to other WTRUs, in its BSS and the OBSS. For example, the AP  1210  may transmit an RTS frame  1270  on the non-primary 1 MHz part within the 2 MHz bandwidth, and receive a CTS frame  1280  after a SIFS duration  1225 . The CTS frame  1280  may be a short CTS frame. 
     In the above embodiments, the RTS and CTS frames transmitted in the 1 MHz bandwidth mode may include one or more indicators that indicate the transmission bandwidth mode for which TXOP or medium reservation is requested. The one or more indicators may indicate a 2 MHz or a 1 MHz bandwidth mode for which a TXOP is requested. Such indicators may be included in any part of the frame, for example, in the signal (SIG) field of the physical layer (PHY) preamble, the MAC header, or scrambling sequence used in the frame. This may be useful in scenarios where unused bandwidth may be reused. 
     In the above embodiments, the CF-End frames transmitted in the 1 MHz bandwidth mode may include one or more indicators that indicate that the TXOP being truncated is for a given bandwidth mode. The one or more indicators may indicate a 2 MHz or a 1 MHz bandwidth mode for which a TXOP is being truncated. Such indicators may be included in any part of the frame, for example, in the SIG field of a PHY preamble, the MAC header, or scrambling sequence used in the frame. This may be useful in scenarios where unused bandwidth may be reused. 
     In one embodiment of signaling bandwidth information in frames which may be used for RTS, CTS and CF-End frames, a device may set the individual/group bit in the TA field of a frame to ‘ 0 ’ to indicate a1 MHz bandwidth. Alternatively, the device may set the individual/group bit in the TA field of a frame to ‘ 1 ’ to indicate a 2 MHz or higher bandwidth, for example 4 MHz, 8 MHz, or 16 MHz, where the actual bandwidth may be signaled in combination with other indications. An example indication may include a scrambling sequence used in the frame. In such an example, 1 bit may be used to indicate static and dynamic bandwidth and 2 bits may be used to indicate 2 MHz, 4 MHz, 8 MHz, and/or 16 MHz. 
     In the above embodiments, the CF-End frames may have the individual/group bit in the TA field of the CF-End frame be set appropriately according to the mechanisms discussed earlier. 
     The RTS-CTS exchange mechanism examples in the above embodiments, when applied to wideband transmissions, for example, 4 MHz, 8 MHz, or 16 MHz, may be repeated. These wideband transmissions may be repeated using the non-HT duplicate format in each primary mode bandwidth, for example, two 2 MHz bandwidths within a 4 MHz wideband. 
     In a variation of the embodiments above, the RTS-CTS frame exchange sequence may be replaced by any other valid NAV setting frame sequence exchange such as a CTS-to-self, a short CTS-to-self frame, an initial frame, or a data packet. An initial frame may be an initiating frame such as a PSMP frame or a Null Data Packet Announcement frame for channel sounding purposes. In order to obtain a TXOP for a 2 MHz bandwidth mode frame transmission, a WTRU may transmit a CTS-to-self frame in the 1 MHz bandwidth mode so that WTRUs that only transmit or receive using the 1 MHz bandwidth mode may set their NAVs in addition to other WTRUs. In the above embodiments the RTS-CTS frame exchange may be also be replaced by an RTS-short CTS frame exchange. 
     Even though the above embodiments have been described with the 2 MHz and 1 MHz primary bandwidth modes as an example for convenience, they may be applicable to the general case of multiple primary bandwidth modes. The 1 MHz primary bandwidth mode may represent more reliable primary bandwidth modes or the most reliable primary bandwidth mode, for example, MCSO-Rep2 PHY transmission mode of 1 MHz in IEEE 802.11ah, and the 2 MHz primary bandwidth mode may represent higher primary bandwidth modes that may be less reliable for communication. An MCS02-Rep2 transmission may use BPSK modulation with ½ code rate and two times repetition. In this example, the RTS-CTS frames and the CF-End frames may be signaled in the more reliable primary bandwidth modes or in the most reliable primary bandwidth mode, for example, MCSO-Rep2 PHY transmission mode of 1 MHz in IEEE 802.11ah. 
     An 802.11ah BSS may support both 1 MHz and 2 MHz primary modes of operation. Therefore it may need some channel selection methods for the BSS. The AP may follow one or more of the following methods to establish an 802.11ah BSS. These methods may aid in the coexistence of two or more BSSs in the same neighborhood. In one example, the primary 1 MHz, 2 MHz, 4 MHz or 8 MHz channel for an 802.11ah AP may be the channel within the operating channel width of the BSS that is used to transmit 1 MHz, 2 MHz, 4 MHz or 8 MHz frames/packets, respectively. 
     A secondary 1 MHz channel for an 802.11ah AP with a 2 MHz operating channel width may be a 1 MHz channel in its operating channel width that does not overlap with its primary 1 MHz channel. A secondary 2 MHz channel in an 802.11ah BSS may be a 2 MHz subchannel adjacent to the primary 2 MHz channel that together form the primary 4 MHz channel. A secondary 4 MHz channel in an 802.11ah BSS may be a 4 MHz subchannel adjacent to the primary 4 MHz channel that together form the primary 8 MHz channel. A secondary 8 MHz channel in an 802.11ah BSS may be an 8 MHz subchannel adjacent to the primary 8 MHz channel that together form the primary 16 MHz channel. 
     An AP may scan a set of channels that are potentially affected by 802.11ah BSS operation for existing BSSs before starting an 802.11ah BSS. The AP may scan a channel for a specific duration and more than once if needed. If an AP starts an 802.11ah BSS that occupies some or all channels of any existing BSSs, the AP may select a primary channel of the new 802.11ah BSS such that a primary 2 MHz channel may be identical to the 2 MHz primary channel of any one of the existing BSSs or a primary 1 MHz channel may be identical to the 1 MHz primary channel of any one of the existing BSSs. 
     In a BSS with a 4 MHz, 8 MHz, or 16 MHz operating channel width, the selected 2 MHz primary channel, from among the channels on which no beacons are detected during scanning, may not be identical to the secondary 2 MHz channel of any existing BSSs with a 4 MHz, 8 MHz or 16 MHz operating channel width and/or may not overlap with the secondary 4 MHz channel of any existing BSSs with a 16 MHz operating channel width. In a BSS with a 2 MHz operating channel width, the selected 2 MHz primary channel, from among the channels on which no beacons are detected during scanning, may not be identical to the secondary 2 MHz channel of any existing BSSs with a 4 MHz, 8 MHz or 16 MHz operating channel width and/or may not overlap with the secondary 4 MHz channel of any existing BSSs with a 16 MHz operating channel width. In a BSS with a 1 MHz operating channel width, the selected 1 MHz primary channel, from among the channels on which no beacons are detected during scanning, may not overlap with the secondary 2 MHz channel of any existing BSSs with a 4 MHz, 8 MHz or 16 MHz operating channel width and/or may not overlap with the secondary 4 MHz channel of any existing BSSs with a 16 MHz operating channel width. 
     An AP operating in an 802.11ah BSS with a 4 MHz, 8 MHz or 16 MHz operating channel width, in response to detecting a BSS in the neighborhood whose primary channel is the secondary 2 MHz channel of the AP, may switch to 2 MHz operating channel width and/or move to a different channel set. An AP operating in an 802.11ah BSS with a 2 MHz, 4 MHz, 8 MHz or 16 MHz operating channel width, in response to detecting a BSS in the neighborhood whose primary channel is the secondary 1 MHz channel of the AP, may switch to 1 MHz operating channel width and/or move to a different channel set. 
     In a spectrum where legacy devices operate, for example, as in IEEE 802.11ac devices operating in a 5 GHz bandwidth with legacy IEEE 802.11n devices, the bandwidth and static/dynamic indications may support compatibility with legacy devices. The bandwidth and static/dynamic indications may be used in control frames, for example, in RTS and CTS exchanges for wideband TXOP reservation. Because of the constraint for legacy support, the bandwidth and static/dynamic indications for IEEE 802.11ac were designed so that the last three bits within the first 7 bits of the scrambling sequence used in a frame may be used for bandwidth and static/dynamic indications. One bit may be used for a static/dynamic indication, and two bits may be used for a bandwidth indication of 20 MHz, 40 MHz, 80 MHz or 160 MHz/80 MHz+80 MHz. To indicate that the first 7 scrambled bits are modified the individual/group bit in the TA field of the control frame, for example, an RTS frame, may be set to 1. 
     Using the three bits in the scrambling sequence for signaling may reduce the effectiveness of the scrambling function. This problem may be eliminated by exploiting the fact that in the new spectrum being allocated for a WLAN, for example, below 1 GHz as in IEEE 802.11ah, there is no requirement of compatibility with legacy devices. Two bits in the SIG field of the PHY preamble may be used for a bandwidth indication of 2 MHz, 4 MHz, 8 MHz or 16 MHz/8 MHz+8 MHz. Note that the bandwidths of IEEE 802.11ah may be obtained from IEEE 802.11ac by scaling down with a factor of 10. To indicate whether the bandwidth is Static/Dynamic an individual/group bit may be included in the TA field of the control frame, for example, the bit may be set to 1 to indicate a dynamic bandwidth and 0 to indicate a static bandwidth. 
     In another method of signaling bandwidth information for 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz, a device may set the individual/group bit in the TA field of a frame to ‘ 0 ’ to indicate a 1 MHz bandwidth. Alternatively, the device may set the individual/group bit in the TA field of a frame to ‘ 1 ’ to indicate a 2 MHz or higher bandwidth, for example, 4 MHz, 8 MHz, or 16 MHz, where the actual bandwidth may be signaled in combination with other indications, for example, in a scrambling sequence used in the frame. In this example, 1 bit may be used to indicate static and dynamic bandwidth and 2 bits may be used to indicate 2 MHz, 4 MHz, 8 MHz, and 16 MHz. 
     The WTRU/AP behavior for this solution is as follows. A WTRU/AP may set the individual/group bit in the TA field of a control frame to indicate static/dynamic bandwidth, for example, the bit may be set to 1 to indicate dynamic bandwidth and 0 to indicate static bandwidth. A WTRU/AP may set the two bits for a bandwidth indication of 2 MHz, 4 MHz, 8 MHz or 16 MHz/8 MHz+8 MHz in the SIG field of the PHY preamble of a control frame. Thus, in a wideband TXOP reservation protocol exchange, a WTRU/AP may transmit an RTS with three bits set as described above to indicate the desired bandwidth and whether it is static/dynamic. In response to this in the static case, a WTRU/AP may transmit a CTS frame including a bandwidth indication, if all of the bandwidth is available as requested in the RTS. In the dynamic case, a WTRU/AP may respond by transmitting a CTS frame including a bandwidth indication on the available channels in the bandwidth requested/indicated in the RTS frame. 
     Even though the above embodiments have been described with the 2 MHz primary bandwidth mode as an example for convenience, the embodiments may be applicable to the general case of any primary bandwidth mode. 
     Solutions are described herein that may provide a remedy for the deficiencies in the basic truncation of TXOP mechanism using CF-End frames. 
     As described in  FIG. 4 , the NAV counter at WTRU3 may be prematurely cancelled when it receives a CF-End frame from a first WTRU, although the most recent value of the NAV counter at the first WTRU may have been updated by a medium reservation frame from another WTRU that may be out of the radio range of the first WTRU.  FIG. 13  is a diagram of an example packet exchange sequence  1300  similar to the one illustrated in  FIG. 4 , however, with the enhancement such that the NAV counter at the other WTRU may no longer be cancelled prematurely due to the extra check on the duration field of the CF-End frame by the receiving WTRUs of the CF-End frame. 
       FIG. 13  shows a first BSS (BSS1)  1310  and a second BSS (BSS2)  1320 . As shown in  FIG. 13 , AP1  1330  and WTRU1  1340  may belong to BSS1  1310 ; AP2  1350  and WTRU2  1360  may belong to BSS2  1320 ; and WTRU3  1370  may belong to BSS1  1310  or it may belong to another overlapping BSS (OBSS) BSS3  1375  started by AP3  1380 . 
     As shown in  FIG. 13 , at T=0 ms, WTRU1  1340  may transmit an RTS frame  1345  to reserve the medium for 3 ms, and set the NAV counter at WTRU3  1370  to be 3 ms. AP1  1330  may respond with a CTS frame  1335 , after which the WTRU1  1340  may start to transmit its data frame  1347  to AP1  1330 . AP1  1330  may subsequently transmit an acknowledgement (ACK)  1337  of the reception of the data packet  1347 . At time T=1.5 ms, AP2  1350 , without being able to hear the ACK  1337  transmitted by AP1  1330 , may transmit an RTS frame  1355  to WTRU2  1360 . When WTRU2  1360  receives the RTS frame  1355  from AP2  1350 , it may respond with a CTS frame  1365  to reserve the medium for 5 ms, and may update the NAV counter at WTRU3  1370  to be 5 ms. AP2  1350 , after receiving the CTS frame  1365  from WTRU2  1360 , may start transmitting its data packet  1357  for WTRU2  1360 . At T=1.7 ms, WTRU1  1340 , which may have finished all of its transmissions, may transmit a CF-End frame  1349  to indicate truncation of its TXOP. In this example method, a value may be included in the duration field of the CF-End frame  1349 , which may be currently set to “0”. When WTRU1  1340  completes all transmissions and still has a TXOP remaining, it may transmit the CF-End frame  1349  with its duration field set as follows: 
       Duration_ CF -End=Remainder_TXOP−Length_ CF -End_Frame,  Equation (2)
 
     where Remainder_TXOP is the time remaining in the TXOP of which the holder is the transmitting WTRU of the CF-End frame, and Length_CF-End_Frame is the length in time of the CF-End frame. 
     WTRU3  1370  may receive CF-End frame  1349  and compare its NAV counter value to the duration value contained in the CF-End frame  1349 . If NAV Duration_CF-End, NAV is set to 0. Alternatively, NAV is set to 0 if NAV=Duration_CF-End. Otherwise, the received CF-End frame may be ignored. Note that an AP may transmit a CF-End frame with its duration field set as Duration_CF-End=Remainder_TXOP—Length_CF-End_Frame to indicate truncation of its TXOP. 
     In a second example, an additional NAV counter referred to as Previous NAV value (P_NAV) may be used in the MAC Layer of WTRUs, where P_NAV may be used to set the duration field of the CF-End frame to “Remainder_TXOP—Length_CF-End_Frame”. The P_NAV counter may be used to record previous NAV counter values which may in turn be used to prevent premature cancellation of medium reservations. By definition, P_NAV NAV. The P_NAV counter, if its value is non-zero, may follow the same count-down process as the NAV counter. 
     The AP/WTRU behavior may be as follows. When an AP/WTRU receives a packet P that contains medium reservation time T, it may compare its P_NAV, NAV values to the value of T. For example, for NAV&gt;T, if P_NAV&gt;T, ignore P. Otherwise, set P_NAV=T. In another example, for NAV=T, if P_NAV&lt;T, set P_NAV=T. Otherwise, ignore P. In yet another example, for NAV&lt;T, set P_NAV=NAV, and set NAV=T. These examples may include an adjustment for timing inaccuracies, propagation delays and clock drifts, and the like. 
     When a WTRU or AP completes all transmissions and still has TXOP left, it may transmit a CF-End frame with its Duration Field set to the value Duration_CF-End=Remainder_TXOP—Length_CF-End_Frame. When a WTRU receives a CF-End frame, it may compare its P_NAV, NAV counter values to the duration value included in the CF-End frame. 
     In a NAV&lt;Duration_CF-End example, the received CF-End frame may be ignored. For NAV=Duration_CF-End, if P_NAV #0, the WTRU may set NAV=P_NAV and set P_NAV=0. If P_NAV=0, the WTRU may set NAV=0. 
     In a NAV&gt;Duration_CF-End example, if P_NAV&gt;Duration_CF-End, the received CF-End frame may be ignored. If P_NAV=Duration_CF-End, the WTRU may set P_NAV=0. If P_NAV&lt;Duration_CF-End, the received CF-End frame may be ignored. These examples may include an adjustment for timing inaccuracies, propagation delays and clock drifts, and the like. 
       FIG. 14  is a diagram of an example method  1400  for a WTRU/AP storing or saving the TXOP holder MAC address for the BSS in which it belongs or is associated. Referring to  FIG. 14 , the WTRU/AP may obtain 1410 a transmit (Tx) and receive (Rx) MAC address of a frame from a TXOP holder. This MAC address may be obtained for example from the MAC address included in the frame that initiated a frame exchange sequence or TXOP reservation. The WTRU/AP may determine  1420  whether the TXOP holder is associated with or belongs to its BSS if either the Tx or Rx MAC address in the frame received or transmitted by the TXOP holder matches the MAC address of the AP of its BSS or BSSID. 
     The WTRU/AP may determine  1430  whether the NAV is updated if the Tx or Rx MAC address matches the MAC address of the AP or BSSID. If the NAV is updated, the WTRU/AP may determine  1440  whether the TXOP holder MAC address from the frame matches a stored MAC address. If the TXOP holder MAC address matches a stored MAC address, the WTRU/AP may determine  1450  whether the NAV timer has been reset. If the NAV timer is zero or has been reset, the WTRU/AP may discard  1460  the TXOP holder MAC address. If the TXOP holder MAC address does not match a stored MAC address, the WTRU/AP may change or update  1470  the stored TXOP holder MAC address for its BSS when the NAV timer is set or updated with a new value. 
     In an example variation of this embodiment, a WTRU/AP may also store/save and maintain the TXOP holder MAC address when the TXOP holder does not belong to its BSS. This may be separate from the saved or stored TXOP holder MAC address for its BSS. The WTRU/AP may determine that the TXOP holder is not associated with, or does not belong to, its BSS if neither the transmitter nor receiver address in the frame received or transmitted by the TXOP holder matches the MAC address of the AP of its BSS or BSSID. 
     In this example, the WTRU/AP may maintain a BSS NAV and a Non-BSS NAV. The BSS NAV may be set or updated when the TXOP holder is associated with the same BSS as the WTRU/AP. The non-BSS NAV may be set or updated when the TXOP holder is not associated with the same BSS as the WTRU/AP. The WTRU/AP may attempt to initiate medium access procedure only if both of its NAVs, BSS NAV and Non-BSS NAV timers are zero or reset. 
     The WTRU/AP behavior for this solution is described below. If a WTRU/AP receives a CF-End frame with a BSSID that does not match its own then it may not reset its BSS NAV and may reset its non-BSS NAV. If a WTRU/AP receives a CF-End frame with a BSSID that does match its own, then it may reset its BSS NAV and may not reset its non-BSS NAV. 
     In another example variation of this embodiment, if a WTRU receives a CF-End frame with a BSSID that does match its own, then it may reset its BSS NAV, and may reset its non-BSS NAV. This behavior may be implemented as part of the system design or made configurable as part of deployment or operation that is configurable by AP for the entire BSS, or configurable by WTRU/AP autonomously. Essentially, this variation of the embodiment may allow aggressive operation of devices by ignoring neighbor BSS transmissions. 
     In another example, if a WTRU/AP receives a CF-End frame with a BSSID that does not match its own, then it may not reset its NAV if the NAV was set by a TXOP holder that does belong to the same BSS. Moreover, the WTRU/AP may reset the NAV if the NAV was not set by a TXOP holder in the same BSS. Note that a WTRU/AP may store the TXOP holder address for the BSS, and therefore may know whether the current NAV was set by a TXOP holder that belongs to its BSS or not. 
     If a WTRU/AP receives a CF-End frame with a BSSID that does match its own, then it may reset the NAV if the NAV was set by a TXOP holder in the same BSS. Moreover, the WTRU/AP may not reset its NAV if the NAV was not set by a TXOP holder that belongs to the same BSS. Note that a WTRU/AP may store the TXOP holder address for the BSS and therefore may know whether the current NAV was set by a TXOP holder that belongs to its BSS or not. 
     In a variation of this embodiment, if a WTRU receives a CF-End frame with a BSSID that does match its own, then it may reset the NAV if the NAV was set by a TXOP holder in the same BSS. Moreover, the WTRU may reset its NAV if the NAV was not set by a TXOP holder that belongs to the same BSS. This behavior may be implemented as part of the system design or made configurable as part of deployment or operation that is configurable by AP for the entire BSS, or configurable by a WTRU/AP autonomously. This variation of the embodiment may allow aggressive operation of devices by ignoring neighbor BSS transmissions. 
     In all of the above proposed embodiments, a device may transmit a CF-End frame if there is sufficient time left in the TXOP duration to accommodate the CF-End frame duration and associated SIFS duration. There may be a decision process in the devices that determines if the above CF-End frames or CF-End frame sequences may be accommodated in the remaining duration of the wideband TXOP. The transmission of the CF-End frames or CF-End frame sequences may be conditional on that determination of whether they may be accommodated. For example, the CF-End frames may not be transmitted if they cannot be accommodated within the initially reserved TXOP duration. 
     In all of the above proposed mechanisms/embodiments, when a WTRU/AP receives a CF-End with a non-matching BSSID, may take further action to clear its NAV based on a check that its NAV was not set by a device in its own BSS. In all the above proposed embodiments, when an AP receives a CF-End frame with a non-matching BSSID, the AP may take further action to transmit a subsequent CF-End frame with its own BSSID based on a check that NAV was not set by a device in its own BSS. 
     In all of the above proposed embodiments, when a WTRU/AP receives a CF-End frame with a non-matching BSSID and with the individual/group bit of the TA field in the CF-End frame set to a value (0 or 1), the WTRU/AP may take further action to clear its NAV based on a check that its NAV was not set based on a transmission by a device in its own BSS. In all the above proposed embodiments, when an AP receives a CF-End frame with a non-matching BSSID and with the individual/group bit of the TA field in the CF-End frame set to a value (0 or 1), the AP may take further action by transmitting a subsequent CF-End frame with its own BSSID based on a check that its NAV was not set based on transmission by a device in its own BSS. 
     As an alternative in all the above proposed embodiments, a WTRU or AP may transmit a CF-End frame with the BSSID field that may include its own MAC address indicating the identity of the transmitter of the CF-End frame. In such an alternative, a device, may check to see if the MAC address of the transmitter of the CF-End frame matches the TXOP holder address stored in the device. If there is a match then the device receiving the CF-End frame may reset its NAV. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element may be used alone or in combination with any of the other features and elements. In addition, the embodiments described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals, (transmitted over wired or wireless connections), and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, a cache memory, a semiconductor memory device, a magnetic media, (e.g., an internal hard disc or a removable disc), a magneto-optical media, and an optical media such as a compact disc (CD) or a digital versatile disc (DVD). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, Node-B, eNB, HNB, HeNB, AP, RNC, wireless router or any host computer.