Patent Publication Number: US-9838984-B2

Title: Power control method and system for wireless networks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/901,547, filed on Nov. 8, 2013, the entire content of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     Examples described herein are generally related to high-capacity wireless networking via power control. 
     BACKGROUND 
     The indoor radio environment is often dominated by computing devices having wireless capabilities that communicatively couple to other such devices having wireless capabilities and/or to an access point of a wireless local area network (“WLAN”) using wireless technologies such as the Institute of Electrical and Electronic Engineers (IEEE) 802.11™ WLAN family of specifications (e.g., sometimes referred to as “Wi-Fi®”). Also, wireless technologies designed to operate in a 60 GHz communication band, such as IEEE 802.11ad (e.g., sometimes referred to as “WiGig®”) may allow wireless capable devices to replace wired interconnects with high speed and relatively short range wireless interconnects via a process typically referred to as wireless docking. The high speed and relatively short range wireless interconnects using wireless technologies such as WiGig may allow wireless devices to wirelessly dock with devices having one or more input/output devices such as a display, a keyboard, a network interface card, a mouse or a storage device. In some examples, once wirelessly docked, the wireless device may utilize the one or more input/output devices in a same manner as when connected to a wired or physical docking station. 
     In various embodiments, it may be advantageous to enhance the efficiency and performance of wireless local area network (WLAN) deployments, for instance in situations that include dense network environments with large numbers of access points and stations. A WLAN employing such enhancements may be known as a high efficiency WLAN (HEW). In such situations, a transmitter that transmits at an excessively high power level may interfere with unintended receivers that are farther away than the intended receiver. Dense network environments may benefit from transmission power control for improved spectral reuse and concomitant capacity improvements. 
     Therefore, a need exists to provide improved spectral reuse and concomitant capacity improvements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example of wireless communications. 
         FIG. 2  illustrates an example of wireless communications. 
         FIGS. 3A-3C  illustrate examples of processes. 
         FIG. 4  is a diagram of an IEEE 802.11 header as known in the art. 
         FIG. 5  illustrates an example of interference. 
         FIG. 6  illustrates an example of a block diagram for an apparatus. 
         FIG. 7  illustrates an example of a device. 
     
    
    
     DETAILED DESCRIPTION 
     Request to Send (RTS) and Clear to Send (CTS) are components of a mechanism used by the IEEE 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem. A node wishing to send data initiates the process by sending an RTS frame. The destination node replies with a CTS. Any other node receiving the RTS or CTS frame should refrain from sending data for a predetermined time, thus solving the hidden node problem. The amount of time the node should wait before trying to get access to the medium is indicated in both the RTS and the CTS frame. The RTS frame contains the amount of time that the other nodes should wait. The wait time is often called the back-off time. The duration field within the RTS frame indicates the amount of time in microseconds needed to transmit data or management+CTS+ACK+SIFS interval. The CTS frame includes a duration field with the amount of time in microseconds, obtained by the previous RTS minus time need to transmit CTS and its short interframe space (SIFS) interval. When combined with an ACK, any wireless node overhearing the exchange of RTS/CTS will cease to transmit during this period. 
     Examples are generally directed to improvements for wireless and/or mobile devices to improve overall capacity in an area that is densely populated with wireless communication devices. The wireless technologies are associated with Wi-Fi or WiGig. These wireless technologies may include establishing and/or maintaining wireless communication links through various frequency bands to include Wi-Fi and/or WiGig frequency bands, e.g., 2.4, 5 or 60 GHz. These wireless technologies may also include wireless technologies suitable for use with mobile devices or user equipment (UE) capable of coupling to other devices via a WLAN or via a peer-to-peer (P2P) wireless connection. For example, mobile devices and the other device may be configured to operate in compliance with various standards promulgated by the Institute of Electrical and Electronic Engineers (IEEE). These standards may include Ethernet wireless standards (including progenies and variants) associated with the IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements Part 11: WLAN Media Access Controller (MAC) and Physical Layer (PHY) Specifications, published March 2012, and/or later versions of this standard (“IEEE 802.11 Standard”). 
     In some examples various IEEE standards associated with the IEEE 802.11 Standard such as IEEE 802.11a/b/g/n, IEEE 802.11ac or IEEE 802.11ad may be utilized by mobile devices or other devices to establish or maintain WLAN and/or P2P communication links and/or establish wireless communications with each other (e.g., wireless accessing). These other devices may have one or more input/output devices to possibly be used by mobile devices upon wirelessly access. The other devices may include wireless access capabilities and may include, but are not limited to, a docking device, a smart phone, a smart television, smart audio speakers, a notebook computer, a tablet computer, a netbook computer, other small computing devices (e.g., Ultrabook™ device—Ultrabook is a trademark of Intel Corporation in the U.S. and/or other countries), desktop computer, a workstation computer, a server, a handheld gaming device, a gaming console, a handheld media player or a media player console. The one or more input/output devices may either be integrated with the other devices or may be coupled via one or more wired and/or wireless connections. 
       FIG. 1  illustrates a configuration  100  useful for distributed transmission power control in accordance with an embodiment of the present disclosure. Configuration  100  includes a Wi-Fi enabled mobile device  102  and a base station  104  configured to communicate with mobile device  102 . Base station  104  may be further communicatively coupled to other mobile devices  102  or to a wide area network such as the Internet (not illustrated in  FIG. 1 ). Mobile device  102  and base station  104  together form a master pair that acquires a Wi-Fi channel and can share the Wi-Fi channel with other devices. Coverage area  112  indicates the limit of the wide-range RTS area captured by mobile device  102 , and coverage area  114  indicates the limit of the wide-range CTS area captured by base station  104 . 
     Configuration  100  further includes a Wi-Fi enabled mobile device  106  and a base station  108 , which together form a slave pair that has at least one member within the combined coverage areas  112 ,  114  controlled by the master pair  102 ,  104 . 
     The master pair broadcasts requirements such as transmission power limits for channel sharing. Slave pairs that want to share the channel with the master pair receive the broadcasts and check the requirements within the broadcasts. The requirements are described below in further details in connection with  FIG. 5  and Equations (1)-(8). If the slave pairs can meet the requirements set by the master pair, then the slave pairs are allowed to access the channel. 
     Configuration  100  may support multiple schemes as set or determined by the master pair. For example, one scheme supported by configuration  100  is for the master pair  102 ,  104  to limit interference from other sources within coverage areas  112 ,  114  to be at or below a predetermined threshold. 
       FIG. 2  illustrates a configuration  200  useful for distributed transmission power control in accordance with an embodiment of the present disclosure. Configuration  200  includes a Wi-Fi enabled mobile device  202  and a base station  204 , which together form a master pair that acquires a Wi-Fi channel and can share the Wi-Fi channel with other devices. Coverage area  212  indicates the limit of the wide-range RTS area captured by mobile device  202 , and coverage area  214  indicates the limit of the wide-range CTS area captured by base station  204 . 
     Configuration  200  further includes a Wi-Fi enabled mobile device  206  and a base station  208 , which together form a first slave pair that exists within the coverage areas  212 ,  214  controlled by the master pair  202 ,  204 . In comparison to configuration  100 , configuration  200  further includes a Wi-Fi enabled mobile device  222  and a Wi-Fi enabled mobile device  224 , which together form a second slave pair that exists within the coverage areas  212 ,  214  controlled by the master pair  202 ,  204 . The second slave pair  222 ,  224  represents additional capacity that is available due to the embodiments described herein. 
     Configuration  200  is able to support a distributed transmission power control (TPC) scheme. For example, the master pair  202 ,  204  may reserve a channel by exchanging full-power RTS/CTS messages. The reserved coverage provides protection within the coverage areas  212 ,  214  for the master and slave communication links. 
     The broadcasted power control requirements and/or rules enable low-power, short-range transmissions for slave pairs within coverage areas  212 ,  214 . Each slave pair within the coverage areas  212 ,  214  wishing to communicate will use a low-power RTS/CTS message exchange to reserve the channel for its short-range communications. The power is sufficiently low such that the interference to other slave pairs is not significant. 
     Consequently, the spatial reuse of the network increases. Namely, the HEW pairs (e.g., master pairs and multiple slave pairs) may simultaneously utilize the same time-frequency resource with a corresponding huge spectrum efficiency improvement in high-density deployment. 
       FIG. 3A  illustrates a scenario  300  using a RTS/CTS mechanism that is useful for distributed transmission power control in accordance with an embodiment of the present disclosure. Scenario  300  includes timeline  302 , which illustrates a message exchange by a HEW resource sharing master pair, the master pair including a first terminal and a second terminal. Messages illustrated above and adjacent to timeline  302  represent messages sent by the first terminal and received by the second terminal. Messages illustrated below and adjacent to timeline  302  represent messages sent by the second terminal and received by the first terminal. Messages are separated in time by a short inter-frame space (SIFS), which is a brief time required by a terminal to sense an end of a frame and to start transmitting. SIFS are not labeled in  FIG. 3A  for sake of clarity. Except for blocks  304 ,  314  and  320 , which denote contention periods, the relative height that each message extends above or below from timeline  302  qualitatively corresponds to a signal strength of the corresponding transmission. Heights are not depicted to scale. 
     Scenario  300  further includes a set  312  of a plurality of timelines  312 - 1  . . .  312 - n  illustrating a message exchange by a HEW resource sharing slave pairs. For co-existence, both the master pair (e.g., master pair  202 ,  204 ) and the slave pairs use the RTS/CTS mechanism so that the master pair can reserve the channel from the legacy devices and the slave pairs can share the channel without collisions. 
     Embodiments in accordance with the present disclosure include a Request for Open Sharing (ROS) and a Confirmation of Open Sharing (COS), which are new Media Access Control (MAC) messages for broadcasting the necessary information of resource sharing and distributed TPC. Usage of ROS and COS will be illustrated with respect to  FIGS. 3A-3C . 
     The ROS and COS messages act to reserve, for use by low power slave pairs, the transmit opportunities (TXOP) within reception range of the ROS and COS messages. TXOP is known as a time-space resource in the wireless channel. Each slave pair within such range will send its RTS/CTS messages with reduced power so that the master pair is not affected. The RTS/CTS may be further optimized for HEW, such as by usage of higher modulation schemes with attendant less signal overhead due to shorter distance, although legacy RTS/CTS may also be used. 
     Each slave pair corresponding to timelines  312 - 1  . . .  312 - n  should not transmit within a shared transmission opportunity (TXOP) slot if the channel is already reserved by a legacy device other than the master pair or by another slave pair. 
     The slave pairs will not send full-power RTS/CTS packets, which would otherwise affect nearby legacy devices, e.g., by causing the legacy devices to refrain from transmitting during a contention period. Omitting the full-power RTS/CTS reduces overhead at a cost of reliability of slave pair communication. Namely, channel reservation for all low-power pairs within coverage areas  212 ,  214 , which prevents legacy interferences, is done only by the master pair  202 ,  204 . Because of the short range of the low-power slave pairs, the protection provided by the master pair  202 ,  204  is usually adequate. However, slave pair corresponding to timelines  312 - 1  . . .  312 - n  may nevertheless perform RTS/CTS packets at a reduced power level. 
     Referring again to  FIG. 3A , timeline  302  includes a contention period  304  during which the master pair  202 ,  204  make sure there are no other master pairs or legacy devices within coverage areas  212 ,  214  that want to communicate at that time. At the conclusion of contention period  304 , the transmission opportunity (TXOP)  305  begins. TXOP  305  includes an RTS/CTS message exchange, followed by an ROS/COS message exchange. ROS/COS are new messages that are described below in greater detail. Thereafter follows an aggregation of MAC protocol data units (A-MPDU), and followed by a block acknowledgement (BA). 
     At the conclusion of contention period  304  begins a period of time denoted as Legacy NAV (RTS)  306 . NAV is known as a network allocation vector. At the conclusion of the CTS message begins a period of time denoted as Legacy NAV (CTS)  308 . The periods of time Legacy NAV (RTS)  306  and Legacy NAV (CTS)  308  are computed and tracked by each terminal that has received the respective RTS or CTS message, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium has been reserved by the RTS/CTS exchanges. 
     At the start of the A-MPDU message through the end of the BA message is a period of time  310  denoted as HEW Open-to-Sharing Vector (OSV), during which the master pair may communicate in a low-power mode. During HEW OSV period  310 , low-power slave pairs P 1 (Tx, Rx) . . . Pn(Tx, Rx) may also begin communicating. The period of time HEW OSV  310  is computed and tracked by each terminal that has received the ROS and/or COS messages, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium is available for low-power usage. HEW OSV is described below in further detail in accordance with an embodiment of the present disclosure. 
     During OSV period  310 , the plurality of timelines  312 - 1  . . .  312 - n  is active to handle low-power slave communications. For example, timeline  312 - 1  for slave pair  1  (P 1 ) begins with a contention period, e.g., contention period  314 . During contention period  314 , the slave pair (P 1 ) waits for the low-power channel to be available. At the conclusion of contention period  314 , the low-power pair P 1  exchange RTS/CTS messages, and then the low-power transmitter sends its own A-MPDU message, followed by a BA from the message receiver. A small range NAV (RTS)  316  period of time begins after contention period  314 . A small range NAV (CTS)  318  period of time begins after the CTS message. 
     Timelines for other low-power pairs (e.g., Pn) proceed substantially the same as for timeline  312 - 1 , except that the contention period (e.g., contention period  320 ) may be different to make sure that there is no contention with other low-power pairs within range of Pn. 
       FIG. 3B  illustrates a scenario  340  using modified mechanism that is useful for distributed transmission power control in accordance with an embodiment of the present disclosure. Scenario  340  is similar to scenario  300 , except with respect to timeline  342 . Timeline  342  includes a request-to-transmit (RTX) and clear-to-transmit (CTX) message pair between a master pair P 0 (Tx, Rx), which combine and replace the same information as the RTS/CTS and ROS/COS message pairs of timeline  302  in scenario  300 . At the conclusion of the RTX/CTX message pair, the A-MPDU message may begin. 
     At the conclusion of contention period  304  begins a period of time denoted as Legacy NAV (RTX)  346 . At the conclusion of the CTX message begins a period of time denoted as Legacy NAV (CTX)  348 . The periods of time Legacy NAV (RTX)  346  and Legacy NAV (CTX)  348  are computed and tracked by each terminal that has received the respective RTX or CTX message, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium has been reserved by the RTX/CTX exchanges. 
     At the start of the A-MPDU message through the end of the BA message is a period of time  350  denoted as HEW OSV, during which the master pair may communicate in a low-power mode. During HEW OSV period  350 , low-power slave pairs P 1 (Tx, Rx) . . . Pn(Tx, Rx) may also begin communicating. The period of time HEW OSV  350  is computed and tracked by each terminal that has received the RTX and/or CTX messages, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium is available for low-power usage. Other detail of scenario  340  is substantially the same as scenario  300 . 
       FIG. 3C  illustrates a scenario  360  using another modified mechanism that is useful for distributed transmission power control in accordance with an embodiment of the present disclosure. Scenario  360  is similar to scenario  300  and scenario  340 , except with respect to timeline  363 . Timeline  363  illustrates a super-frame  367 , which uses less overhead data transfer than timeline  342  or timeline  302 . Super-frame  367  includes one ROS/COS message exchange  371 , and a period of time  365  marked as N Open-for-Sharing TxOP, which in turn includes a plurality of shared TxOP  372 - 1  . . .  372 - n , with 2≦n≦N, N a positive integer, and may be referred to collectively as shared TxOP  372 . An individual but unspecified TxOP may be referred to as shared TxOP  372 - n . As illustrated in  FIG. 3C , N=4. 
     Timing within each of shared TxOP  372 - n  may be substantially identical. Timing within shared TxOP  372 - 2  is illustrated in greater detail as a representative example. Timing within shared TxOP  372 - 2  includes timeline  362 . Timeline  362  includes contention period  304 , a full-power RTS/CTS message pair, an A-MPDU message interval and a BA message, which have been individually described above in reference to timelines  302  and/or  342 . 
     Shared TxOP  372 - 2  further includes a legacy NAV (RTS) period  366  that commences after contention period  304 , and a legacy NAV (CTS) period  368  that commences after the CTS message. The periods of time Legacy NAV (RTS)  366  and Legacy NAV (CTS)  368  are computed and tracked by each terminal that has received the respective RTS or CTS message, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium has been reserved by the RTS/CTS exchanges. 
     At the start of the A-MPDU message through the end of the BA message is a period of time  370  denoted as HEW OSV period  370 , during which the master pair may communicate in a low-power mode. During HEW OSV period  370 , low-power slave pairs P 1 (Tx, Rx) . . . Pn(Tx, Rx) may also begin communicating. The period of time HEW OSV  370  is computed and tracked by each terminal that has received the ROS and/or COS messages, e.g., by way of a countdown timer in each respective terminals, which indicates how far into the future the medium is available for low-power usage. 
     The remainder of the timing of shared TxOP  372 - 2  includes a plurality  312  of transmitter/receiver slave pairs, which is substantially identical to the corresponding portion of  FIG. 3A-3B . 
     In accordance with an embodiment of the present disclosure, the COS message includes information that is used to implement transmission power control. The information includes a TPC Backoff Level (R backoff   dB ), which is an indication of a desired reduction of transmission power level, by a communication partner, from a full transmission power level. TPC Backoff Level may be sent by a receiver to a transmitter for recommending a transmission power. The transmitter may take this feedback into account for calculating an actual transmission power. 
     The COS message information may further include a reference modulation and coding scheme (MCS) level (M reference ), which is an indication of the MCS level used for calculating TPC backoff value. A receiver may send the reference MCS level information to a transmitter. The receiver suggests an MCS associated with the TPC backoff level. In other words, the TPC backoff level is for the targeted reference MCS level. 
     R backoff   dB  and M reference  are used to provide feedback from the receiver to the transmitter for power control and link rate adaptation. The transmitter may decide the actual power and MCS according to the feedback and other factors. 
     In accordance with an embodiment of the present disclosure, the ROS message includes information that is used to implement transmission power control. The information in the ROS message includes the Current Full Transmission Power Level (P Full   dBm ) which is used as reference value to estimate the path loss. This parameter specifies the transmission power level of the packet carrying the parameter so that each receiver can estimate the path loss using the parameter and the received signal strength. 
     The ROS message may further include an Interference Threshold of Admission (T dBm ), which is an allowed interference level seen by the devices of the master pair. T dBm  informs nearby devices that the master pair can tolerate an interference level below T dBm . If the master pair will use bi-directional traffic, then T dBm  may apply to both nodes of the master pair. If the master pair will use only one-way traffic, then T dBm  may apply only to the receiver of the master pair. T dBm  sets an upper limit of the transmission power of nearby slave device. 
     Transmission of the new messages described herein, e.g., ROS/COS, and the period of time denoted as HEW OSV, may be accomplished by use of known wireless communication protocols such as Wi-Fi. Wi-Fi is a frame-based communication protocol.  FIG. 4  illustrates an IEEE 802.11 frame format  400  as known in the art. A transmitted signal conforming to frame format  400  may be referred to as a packet. Frame format  400  may be divided into a twelve-byte preamble field  411 , a four-byte physical layer convergence procedure (“PLCP”) header field  412 , and a variable-length protocol data unit (“PDU”) field  413 . PDU field  413  may be further subdivided into a thirty-byte header field  421 , a variable-length payload field  422 , and a four-byte frame check sequence (“FCS”) field  423 . Payload field  422  may vary in length between zero and 2,312 bytes. Therefore, the minimum length for frame format  400  is fifty bytes when the payload field  422  is of zero length. Payload field  422  may be used to transport the new messages such as ROS/COS. 
     After potential slave pairs receive the ROS/COS messages, the potential slave pairs evaluate the admission rules for the purpose of checking the admission of resource sharing. Evaluation by the slave pairs is described below and in  FIG. 5 , assuming bi-directional traffic for the master pair. 
     A process for evaluating emission rules includes calculating maximum transmission powers of the transmitter and receiver of the slave pair, respectively. The maximum power is limited by the interference threshold set by the two master pair devices, in accordance with Equations (1) and (2).
 
 P   st   dBm =min( T   mt   dBm   +h   mt-st   dBm   ,T   mr   dBm   +T   mr-st   dBm )  (1)
 
 P   sr   dBm =min( T   mt   dBm   +h   mt-sr   dBm   ,T   mr   dBm   +T   mr-sr   dBm )  (2)
 
     In Equation (1), P st   dBm  is the maximum transmission power of slave transmitter in dB scale, T mt   dBm  is the tolerable interference threshold of the transmitter of the master pair in dB scale, h mt-st   dBm  is the path loss between master transmitter and slave transmitter, and h mr-st   dBm  is the path loss between master receiver and slave transmitter. 
     In Equation (2), P sr   dBm  is the maximum tolerable power at the slave receiver in dB scale, h mt-sr   dBm  is the path loss between master transmitter and slave receiver, and h mr-sr   dBm  is the path loss between master receiver and slave receiver. 
     Next, the process for evaluating emission rules includes estimating the signal to interference noise ratio (estimated SINR, or eSINR) in order to check the link efficiency, in accordance with Equations (3) and (4).
 
 e SINR st   dB   =P   sr   dBm   −h   st-sr   dBm   −I   st   dBm   (3)
 
 e SINR sr   dB   =P   st   dBm   −h   st-sr   dBm   −I   sr   dBm   (4)
 
     In Equation (3), I st   dBm  is the power level of non-slave interference plus noise at the slave transmitter, in a dB scale. In Equation (4), I sr   dBm  is the power level of non-slave interference plus noise at the slave receiver, in a dB scale. 
     If the estimated SINR meets the pre-defined rate threshold for the link, then the potential slave pair will try to reuse the time and/or frequency resource by a reduced power. 
     For the master pair, the parameters R backoff   dB  and T dBm  are used in evaluating a signal to interference noise ratio in accordance with Equations (5) and (6) below. 
     
       
         
           
             
               
                 
                   
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     In Equations (5)-(8), SINR mt,target   dB  and SINR mr,target   dB  are the target SINR values at the master transmitter and receiver, respectively. N is the estimated number of slave pairs. I mr   Linear  and I mt   Linear  are the power levels of non-slave interference plus noise at master receiver and transmitter in linear scale, respectively. SINR mr,degradation   dB  is the performance degradation allowed in the master pair. 
     The master pair decides to share a transmission resource (e.g., TXOP, time or frequency slot, etc.) according to following conditions: 
     First, in a low density environment, the power control and spatial reuse do not bring a significant gain since not enough slave pairs join the shared channel. Therefore, the master pair initially may detect the density of transmitters and receivers. Collision rate of CSMA/CS may be used as a good indicator for density detection. 
     Second, since the interference from the slave pairs reduce the quality of the master&#39;s channel, the master pair needs to have a channel quality above a predetermined threshold, such that the interference can be tolerated. The evaluated channel gain, SINR, and power backoff values can be good indicators for the master pair to evaluate the channel quality. 
     Embodiments in accordance with the present disclosure make use of new control variables and mechanisms. When conventional one-way traffic is assumed, some embodiments may reduce complexity and maximize backward compatibility by making the following simplifications: 
     First, the master pair may use conventional RTS/CTS to acquire a channel or TXOP. 
     Second, the master pair may share the acquired channel or TXOP with slave pairs by sending an announcement packet, e.g., the COS packet. The announcement packet may be sent by the transmitter of the master pair to the slave pairs. The announcement packet may further include an indication of the reduction of power level of subsequent data packets with respect to the power level of the announcement packet, or the power level of the current regulation region. The regulation region refers to geographical area (e.g., usually a country) covered by a regulatory regime on radio transmissions (e.g., Federal Communication Commission (FCC) regulations in the United States). A tolerable interference level may be implicitly specified in a specification, or may explicitly specified by the announcement packet. 
     Third, within the shared TXOP, all of the slave pairs use the same power level and conventional CSMA to access the shared channel. The power level can be deduced from the announcement packet. For example, the power level may be the same as the master pair&#39;s data packet or a predetermined level below (in dBs) the master&#39;s power level. Using the CSMA, a slave device may hold its transmission if the transmission would cause an above-threshold interference to existing receive devices. 
     Embodiments in accordance with the present disclosure provide a distributed TPC process that may be used to improve the performance of WLAN communication systems. Embodiments provide an improved process for simultaneous transmission for spatial reuse and backward compatibility with legacy Wi-Fi devices. 
       FIG. 6  illustrates a block diagram for a first apparatus. As shown in  FIG. 6 , the first apparatus includes an apparatus  600 . Although apparatus  600  shown in  FIG. 6  has a limited number of elements in a certain topology or configuration, it may be appreciated that apparatus  600  may include more or less elements in alternate configurations as desired for a given implementation. 
     Apparatus  600  may be usable as Wi-Fi enabled mobile device  102 , base station  104 , slave Wi-Fi enabled mobile device  106  and/or base station  108  illustrated in  FIG. 1 . 
     The apparatus  600  may comprise a computer and/or firmware implemented apparatus  600  having a processor circuit  620  arranged to execute one or more components  622 - a . It is worthy to note that “a” and “b” and “c” and similar designators as used herein are intended to be variables representing any positive integer. Thus, for example, if an implementation sets a value for a=5, then a complete set of components  622 - a  may include modules  622 - 1 ,  622 - 2 ,  622 - 3 ,  622 - 4  or  622 - 5 . The embodiments are not limited in this context. 
     According to some examples, apparatus  600  may be part of a mobile device that may be capable of operating in compliance with one or more wireless technologies such as those described in or associated with the IEEE 802.11 standards. For example, the mobile device having apparatus  600  may be arranged or configured to wirelessly couple to a Wi-Fi access point or another Wi-Fi communication device. 
     In some examples, as shown in  FIG. 6 , apparatus  600  includes processor circuit  620 . Processor circuit  620  may be generally arranged to execute one or more components  622 - a . The processor circuit  620  can be any of various commercially available processors, including without limitation an AMD® Athlon®, Duron® and Opteron® processors; ARM® application, embedded and secure processors; IBM® and Motorola® DragonBall® and PowerPC® processors; IBM and Sony® Cell processors; Qualcomm® Snapdragon®; Intel® Celeron®, Core (2) Duo®, Core i3, Core i5, Core i7, Itanium®, Pentium®, Xeon®, Atom® and XScale® processors; and similar processors. Dual microprocessors, multi-core processors, and other multi-processor architectures may also be employed as processor circuit  620 . According to some examples processor circuit  620  may also be an application specific integrated circuit (ASIC) and components  622 - a  may be implemented as hardware elements of the ASIC. 
     According to some examples, apparatus  600  may include a receive component  622 - 1 . Receive component  622 - 1  may be executed by processor circuit  620  to receive Wi-Fi probe responses and/or other communication messages in accordance with embodiments of the present disclosure. 
     In some examples, apparatus  600  may also include a gather component  622 - 2 . Gather component  622 - 2  may be executed by processor circuit  620  to gather identification information from one or more devices capable of wirelessly communicating with the mobile device. Gather component  622 - 2  may gather identification information included locations of Wi-Fi access points and/or other Wi-Fi devices and at least temporarily store the gathered identification information with ID information  623 - a . According to some examples, gather component  622 - 2  may maintain ID information  623 - a  in a data structure such as a lookup table (LUT). 
     In some examples, apparatus  600  may also include a link component  622 - 4 . Link component  622 - 4  may be executed by processor circuit  620  to determine link conditions (e.g., interference, collisions, etc.) between the mobile device and the one or more devices based on a technique utilizing the Wi-Fi frequency band. Information associated with operation of or measurements by link component  622 - 4  may be stored as QoS information  622 - 4   a . According to some examples, distance information  622 - 4   a  may be maintained in a LUT or other type of data structure. 
     In some examples, apparatus  600  may also include a protocol component  622 - 3 . Protocol component  622 - 3  may be executed by processor circuit  620  in order to communicate on a protocol level or layer with other devices. For example, protocol component  622 - 3  may interpret incoming messages, may gather and/or analyze data such as link conditions that may be needed to practice the embodiments, and may formulate outgoing messages in accordance with the protocols described herein. 
     According to some examples, apparatus  600  may also include an identify component  622 - 5 . Identify component  622 - 5  may be executed by processor circuit  620  to identify the given device from among the one or more devices based on predetermined criteria. 
     Included herein is a set of logic flows representative of example methodologies for performing novel aspects of the disclosed architecture. While, for purposes of simplicity of explanation, the one or more methodologies shown herein are shown and described as a series of acts, those skilled in the art will understand and appreciate that the methodologies are not limited by the order of acts. Some acts may, in accordance therewith, occur in a different order and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all acts illustrated in a methodology may be required for a novel implementation. 
       FIG. 7  illustrates an embodiment of a device  600 . In some examples, device  700  may be configured or arranged for wireless communications in a wireless network. Device  700  may implement, for example, a Wi-Fi access point, a storage medium and/or a logic circuit  770 . The logic circuit  770  may include physical circuits to perform operations described for other apparatus. As shown in  FIG. 7 , device  700  may include a radio interface  710 , baseband circuitry  720 , and computing platform  730 , although examples are not limited to this configuration. 
     The device  700  may implement some or all of the structure and/or operations for apparatus, storage medium  700 / 900  and/or logic circuit  770  in a single computing entity, such as entirely within a single device. The embodiments are not limited in this context. 
     Radio interface  710  may include a component or combination of components adapted for transmitting and/or receiving single carrier or multi-carrier modulated signals (e.g., including complementary code keying (CCK) and/or orthogonal frequency division multiplexing (OFDM) symbols and/or single carrier frequency division multiplexing (SC-FDM symbols) although the embodiments are not limited to any specific over-the-air interface or modulation scheme. Radio interface  710  may include, for example, a receiver  712 , a transmitter  716  and/or a frequency synthesizer  714 . Radio interface  710  may include bias controls, a crystal oscillator and/or one or more antennas  718 - f . In another embodiment, radio interface  710  may use external voltage-controlled oscillators (VCOs), surface acoustic wave filters, intermediate frequency (IF) filters and/or RF filters, as desired. Due to the variety of potential RF interface designs an expansive description thereof is omitted. 
     Baseband circuitry  720  may communicate with radio interface  710  to process receive and/or transmit signals and may include, for example, an analog-to-digital converter  722  for down converting received signals, a digital-to-analog converter  724  for up converting signals for transmission. Further, baseband circuitry  720  may include a baseband or physical layer (PHY) processing circuit  726  for PHY link layer processing of respective receive/transmit signals. Baseband circuitry  720  may include, for example, a processing circuit  728  for medium access control (MAC)/data link layer processing. Baseband circuitry  720  may include a memory controller  732  for communicating with MAC processing circuit  728  and/or a computing platform  730 , for example, via one or more interfaces  734 . 
     In some embodiments, PHY processing circuit  726  may include a frame construction and/or detection module, in combination with additional circuitry such as a buffer memory, to construct and/or deconstruct communication frames (e.g., containing subframes). Alternatively or in addition, MAC processing circuit  728  may share processing for certain of these functions or perform these processes independent of PHY processing circuit  726 . In some embodiments, MAC and PHY processing may be integrated into a single circuit. 
     Computing platform  730  may provide computing functionality for device  700 . As shown, computing platform  730  may include a processing component  740 . In addition to, or alternatively of, baseband circuitry  720  of device  700  may execute processing operations or logic for other apparatus, a storage medium, and logic circuit  770  using the processing component  730 . Processing component  740  (and/or PHY  726  and/or MAC  728 ) may comprise various hardware elements, software elements, or a combination of both. Examples of hardware elements may include devices, logic devices, components, processors, microprocessors, circuits, processor circuits (e.g., processor circuit  720 ), circuit elements (e.g., transistors, resistors, capacitors, inductors, and so forth), integrated circuits, application specific integrated circuits (ASIC), programmable logic devices (PLD), digital signal processors (DSP), field programmable gate array (FPGA), memory units, logic gates, registers, semiconductor device, chips, microchips, chip sets, and so forth. Examples of software elements may include software components, programs, applications, computer programs, application programs, system programs, software development programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, functions, methods, procedures, software interfaces, application program interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. Determining whether an example is implemented using hardware elements and/or software elements may vary in accordance with any number of factors, such as desired computational rate, power levels, heat tolerances, processing cycle budget, input data rates, output data rates, memory resources, data bus speeds and other design or performance constraints, as desired for a given example. 
     Computing platform  730  may further include other platform components  750 . Other platform components  750  include common computing elements, such as one or more processors, multi-core processors, co-processors, memory units, chipsets, controllers, peripherals, interfaces, oscillators, timing devices, video cards, audio cards, multimedia input/output (I/O) components (e.g., digital displays), power supplies, and so forth. Examples of memory units may include without limitation various types of computer readable and machine readable storage media in the form of one or more higher speed memory units, such as read-only memory (ROM), random-access memory (RAM), dynamic RAM (DRAM), Double-Data-Rate DRAM (DDRAM), synchronous DRAM (SDRAM), static RAM (SRAM), programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), flash memory, polymer memory such as ferroelectric polymer memory, ovonic memory, phase change or ferroelectric memory, silicon-oxide-nitride-oxide-silicon (SONOS) memory, magnetic or optical cards, an array of devices such as Redundant Array of Independent Disks (RAID) drives, solid state memory devices (e.g., USB memory, solid state drives (SSD) and any other type of storage media suitable for storing information. 
     Computing platform  730  may further include a network interface  760 . In some examples, network interface  760  may include logic and/or features to support network interfaces operated in compliance with one or more wireless broadband technologies such as those described in one or more standards associated with IEEE 802.11 such as IEEE 802.11ad. 
     Device  700  may be, for example, user equipment, a computer, a personal computer (PC), a desktop computer, a laptop computer, a notebook computer, a netbook computer, a tablet computer, other small computing devices, a smart phone, embedded electronics, a gaming console, a server, a server array or server farm, a web server, a network server, an Internet server, a work station, a mini-computer, a main frame computer, a supercomputer, a network appliance, a web appliance, a distributed computing system, multiprocessor systems, processor-based systems, or combination thereof. Accordingly, functions and/or specific configurations of device  700  described herein, may be included or omitted in various embodiments of device  700 , as suitably desired. In some embodiments, device  700  may be configured to be compatible with protocols and frequencies associated with IEEE 802.11 Standards for WLANs and/or for wireless docking, although the examples are not limited in this respect. 
     Embodiments of device  700  may be implemented using single input single output (SISO) antenna architectures. However, certain implementations may include multiple antennas (e.g., antennas  718 - f ) for transmission and/or reception using adaptive antenna techniques for beamforming or spatial division multiple access (SDMA) and/or using multiple input multiple output (MIMO) communication techniques. 
     The components and features of device  700  may be implemented using any combination of discrete circuitry, application specific integrated circuits (ASICs), logic gates and/or single chip architectures. Further, the features of device  700  may be implemented using microcontrollers, programmable logic arrays and/or microprocessors or any combination of the foregoing where suitably appropriate. It is noted that hardware, firmware and/or software elements may be collectively or individually referred to herein as “logic” or “circuit.” 
     It should be appreciated that the exemplary device  700  shown in the block diagram of  FIG. 7  may represent one functionally descriptive example of many potential implementations. Accordingly, division, omission or inclusion of block functions depicted in the accompanying figures does not infer that the hardware components, circuits, software and/or elements for implementing these functions would be necessarily be divided, omitted, or included in embodiments. 
     A logic flow may be implemented in software, firmware, and/or hardware. In software and firmware embodiments, a logic flow may be implemented by computer executable instructions stored on at least one non-transitory computer readable medium or machine readable medium, such as an optical, magnetic or semiconductor storage. The embodiments are not limited in this context. 
     Some examples may be described using the expression “in one example” or “an example” along with their derivatives. These terms mean that a particular feature, structure, or characteristic described in connection with the example is included in at least one example. The appearances of the phrase “in one example” in various places in the specification are not necessarily all referring to the same example. 
     Some examples may be described using the expression “coupled”, “connected”, or “capable of being coupled” along with their derivatives. These terms are not necessarily intended as synonyms for each other. For example, descriptions using the terms “connected” and/or “coupled” may indicate that two or more elements are in direct physical or electrical contact with each other. The term “coupled,” however, may also mean that two or more elements are not in direct contact with each other, but yet still co-operate or interact with each other. 
     In some examples, an example system may include a processor component and memory coupled to the processor component. The system may also include a radio coupled to the processor component and one or more antennas coupled to the radio. The system may also include wireless logic to be executed on the processor component to process reception of a high-power request for open sharing (ROS) signal by a master wireless receiver from a master wireless transmitter and to process transmission of a high-power confirmation of open sharing (COS) signal to the master wireless transmitter, the high-power COS signal comprising an indication of a desired reduction of transmission power level from high power by the master wireless transmitter. The system may also include a timer initiated by the high-power COS signal, the timer to indicate a period of time when the master wireless transmitter and master wireless receiver are enabled for low-power communication. 
     According to some examples of the system, the master wireless receiver to transmit the high-power COS signal to a slave wireless transmitter and to a slave wireless receiver, the timer to indicate a period of time when the slave wireless transmitter and slave wireless receiver are enabled for low-power communication. 
     According to some examples of the system, the high-power COS signal comprises a reference modulation and coding scheme (MCS) level. 
     According to some examples of the system, the high-power ROS signal comprises a current full transmission power level of the master wireless transmitter. 
     According to some examples of the system, the high-power ROS signal comprises an allowed interference level that the master wireless receiver is able to tolerate. 
     According to some examples of the system, the high-power COS is used by a slave processor to calculate at least one of a maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the system, the slave processor is further to calculate a signal to interference noise ratio at the slave wireless receiver by use of the maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the system, the slave wireless transmitter and the slave wireless receiver operate by reusing a time and frequency resource at reduced power based upon the signal to interference noise ratio at the slave wireless receiver. 
     According to some examples of the system, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a density of transmitters and receivers that can provide a sufficiently strong signal to the master wireless transmitter and master wireless receiver exceeds a predetermined threshold. 
     According to some examples of the system, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a quality of low-power communication exceeds a predetermined threshold. 
     According to some examples of the system, the ROS signal is combined with a request to transmit (RTX) signal, and the COS signal is combined with a clear to send (CTS) signal. 
     According to some examples of the system, the ROS signal is transmitted less frequently than a request to transmit (RTX) signal, and the COS signal is transmitted less frequently than a clear to send (CTS) signal. 
     In some examples, an example apparatus may include a processor component and a wireless transceiver to receive a wireless signal from a computing device. The apparatus may also include wireless logic to be executed on the processor component to process reception of a high-power request for open sharing (ROS) signal by a master wireless receiver from a master wireless transmitter and to process transmission of a high-power confirmation of open sharing (COS) signal to the master wireless transmitter, the high-power COS signal comprising an indication of a desired reduction of transmission power level from high power by the master wireless transmitter. The apparatus may also include a timer initiated by the high-power COS signal, the timer to indicate a period of time when the master wireless transmitter and master wireless receiver are enabled for low-power communication. 
     According to some examples of the apparatus, the master wireless receiver to transmit the high-power COS signal to a slave wireless transmitter and to a slave wireless receiver, the timer to indicate a period of time when the slave wireless transmitter and slave wireless receiver are enabled for low-power communication. 
     According to some examples of the apparatus, the high-power COS signal comprises a reference modulation and coding scheme (MCS) level. 
     According to some examples of the apparatus, the high-power ROS signal comprises a current full transmission power level of the master wireless transmitter. 
     According to some examples of the apparatus, the high-power ROS signal comprises an allowed interference level that the master wireless receiver is able to tolerate. 
     According to some examples of the apparatus, the high-power COS used by a slave processor to calculate at least one of a maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the apparatus, the slave processor further to calculate a signal to interference noise ratio at the slave wireless receiver by use of the maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the apparatus, the slave wireless transmitter and the slave wireless receiver operate by reusing a time and frequency resource at reduced power based upon the signal to interference noise ratio at the slave wireless receiver. 
     According to some examples of the apparatus, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a density of transmitters and receivers that can provide a sufficiently strong signal to the master wireless transmitter and master wireless receiver exceeds a predetermined threshold. 
     According to some examples of the apparatus, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a quality of low-power communication exceeds a predetermined threshold. 
     According to some examples of the apparatus, the ROS signal combined with a request to transmit (RTX) signal, and the COS signal combined with a clear to send (CTS) signal. 
     According to some examples of the apparatus, the ROS signal transmitted less frequently than a request to transmit (RTX) signal, and the COS signal transmitted less frequently than a clear to send (CTS) signal. 
     In some examples, an example computer-readable storage medium comprises instructions that, when executed, cause a controller to process reception of a high-power request for open sharing (ROS) signal by a master wireless receiver from a master wireless transmitter, to process transmission of a high-power confirmation of open sharing (COS) signal to the master wireless transmitter, the high-power COS signal comprising an indication of a desired reduction of transmission power level from high power by the master wireless transmitter, and to maintain a timer initiated by the high-power COS signal, the timer to indicate a period of time when the master wireless transmitter and master wireless receiver are enabled for low-power communication. 
     According to some examples, the computer-readable storage medium further includes instructions that, when executed, cause a controller to process transmission of the high-power COS signal to a slave wireless transmitter and to a slave wireless receiver, the timer to indicate a period of time when the slave wireless transmitter and slave wireless receiver are enabled for low-power communication. 
     According to some examples of the computer-readable storage medium, the high-power COS signal comprising a reference modulation and coding scheme (MCS) level. 
     According to some examples of the computer-readable storage medium, the high-power ROS signal comprising a current full transmission power level of the master wireless transmitter. 
     According to some examples of the computer-readable storage medium, the high-power ROS signal comprising an allowed interference level that the master wireless receiver is able to tolerate. 
     According to some examples of the computer-readable storage medium, the high-power COS used by a slave processor to calculate at least one of a maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the computer-readable storage medium, the slave processor further to calculate a signal to interference noise ratio at the slave wireless receiver by use of the maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the computer-readable storage medium, the slave wireless transmitter and the slave wireless receiver to operate by reusing a time and frequency resource at reduced power based upon the signal to interference noise ratio at the slave wireless receiver. 
     According to some examples of the computer-readable storage medium, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a density of transmitters and receivers that can provide a sufficiently strong signal to the master wireless transmitter and master wireless receiver exceeds a predetermined threshold. 
     According to some examples of the computer-readable storage medium, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a quality of low-power communication exceeds a predetermined threshold. 
     According to some examples of the computer-readable storage medium, the ROS signal combined with a request to transmit (RTX) signal, and the COS signal combined with a clear to send (CTS) signal. 
     According to some examples of the computer-readable storage medium, the ROS signal transmitted less frequently than a request to transmit (RTX) signal, and the COS signal transmitted less frequently than a clear to send (CTS) signal. 
     In some examples, an example method may include receiving a high-power request for open sharing (ROS) signal by a master wireless receiver from a master wireless transmitter, transmitting a high-power confirmation of open sharing (COS) signal to the master wireless transmitter, the high-power COS signal comprising an indication of a desired reduction of transmission power level from high power by the master wireless transmitter, and timing by use of a timer derived from the high-power COS signal, the timer to indicate a period of time when the master wireless transmitter and master wireless receiver are enabled for low-power communication. 
     According to some examples of the method, further comprising transmitting the high-power COS signal to a slave wireless transmitter and to a slave wireless receiver, the timer to indicate a period of time when the slave wireless transmitter and slave wireless receiver are enabled for low-power communication. 
     According to some examples of the method, the high-power COS signal comprising a reference modulation and coding scheme (MCS) level. 
     According to some examples of the method, the high-power ROS signal comprising a current full transmission power level of the master wireless transmitter. 
     According to some examples of the method, the high-power ROS signal comprising an allowed interference level that the master wireless receiver is able to tolerate. 
     According to some examples of the method, the high-power COS used by a slave processor to calculate at least one of a maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the method, the slave processor further to calculate a signal to interference noise ratio at the slave wireless receiver by use of the maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the method, the slave wireless transmitter and the slave wireless receiver to operate by reusing a time and frequency resource at reduced power based upon the signal to interference noise ratio at the slave wireless receiver. 
     According to some examples of the method, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a density of transmitters and receivers that can provide a sufficiently strong signal to the master wireless transmitter and master wireless receiver exceeds a predetermined threshold. 
     According to some examples of the method, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a quality of low-power communication exceeds a predetermined threshold. 
     According to some examples of the method, the ROS signal combined with a request to transmit (RTX) signal, and the COS signal combined with a clear to send (CTS) signal. 
     According to some examples of the method, the ROS signal transmitted less frequently than a request to transmit (RTX) signal, and the COS signal transmitted less frequently than a clear to send (CTS) signal. 
     In some examples, an example apparatus may include means for receiving a high-power request for open sharing (ROS) signal by a master wireless receiver from a master wireless transmitter, means for transmitting a high-power confirmation of open sharing (COS) signal to the master wireless transmitter, the high-power COS signal comprising an indication of a desired reduction of transmission power level from high power by the master wireless transmitter, and means for timing by use of the high-power COS signal, the timer to indicate a period of time when the master wireless transmitter and master wireless receiver are enabled for low-power communication. 
     According to some examples, the apparatus further comprises means for transmitting the high-power COS signal to a slave wireless transmitter and to a slave wireless receiver, the timer to indicate a period of time when the slave wireless transmitter and slave wireless receiver are enabled for low-power communication. 
     According to some examples of the apparatus, the high-power COS signal comprising a reference modulation and coding scheme (MCS) level. 
     According to some examples of the apparatus, the high-power ROS signal comprising a current full transmission power level of the master wireless transmitter. 
     According to some examples of the apparatus, the high-power ROS signal comprising an allowed interference level that the master wireless receiver is able to tolerate. 
     According to some examples of the apparatus, the high-power COS is used by a slave processor to calculate at least one of a maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the apparatus, the slave processor further to calculate a signal to interference noise ratio at the slave wireless receiver by use of the maximum transmission power of the slave wireless transmitter and a maximum tolerable power at the slave wireless receiver. 
     According to some examples of the apparatus, the slave wireless transmitter and the slave wireless receiver to operate by reusing a time and frequency resource at reduced power based upon the signal to interference noise ratio at the slave wireless receiver. 
     According to some examples of the apparatus, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a density of transmitters and receivers that can provide a sufficiently strong signal to the master wireless transmitter and master wireless receiver exceeds a predetermined threshold. 
     According to some examples of the apparatus, the master wireless transmitter and master wireless receiver are enabled for low-power communication if a quality of low-power communication exceeds a predetermined threshold. 
     According to some examples of the apparatus, the ROS signal combined with a request to transmit (RTX) signal, and the COS signal combined with a clear to send (CTS) signal. 
     According to some examples of the apparatus, ROS signal transmitted less frequently than a request to transmit (RTX) signal, and the COS signal transmitted less frequently than a clear to send (CTS) signal. 
     It is emphasized that the Abstract of the Disclosure is provided to comply with 37 C.F.R. Section 1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single example for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed examples require more features than are expressly recited in each claim Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed example. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate example. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein,” respectively. Moreover, the terms “first,” “second,” “third,” and so forth, are used merely as labels, and are not intended to impose numerical requirements on their objects.