Abstract:
Wireless devices, e.g., in a cognitive radio network, discover and use locally available usable spectrum for communication. Beacon signaling facilitates available spectrum discovery, spectrum usage coordination, and device identification. A wireless terminal, which may have entered a new area and powered up, monitors to detect for the presence of beacon signals in a communications band. When the wireless terminal fails to detect a beacon, the wireless terminal assumes that the spectrum is available and transmits its user beacon signal thereby providing notification of its presence in the area to other wireless terminals. The wireless terminal maintains a coordinated timing relationship between its beacon transmit interval and beacon detect interval, which are performed on an ongoing basis. The combination of beacon TX interval and beacon monitoring interval represents a small fraction of total time, allowing for power conservation. The coordinated timing relationship, known to peers, facilitates efficient peer-peer communications session establishment.

Description:
RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/758,011 filed on Jan. 11, 2006, titled “METHODS AND APPARATUS FOR USING BEACON SIGNALS FOR IDENTIFICATION, SYNCHRONIZATION OR ACQUISITION IN AN AD HOC WIRELESS NETWORK”, U.S. Provisional Patent Application Ser. No. 60/758,010 filed on Jan. 11, 2006, titled “METHODS AND APPARATUS FOR FACILITATING IDENTIFICATION, SYNCHRONIZATION OR ACQUISITION USING BEACON SIGNALS”, U.S. Provisional Patent Application Ser. No. 60/758,012 filed on Jan. 11, 2006, titled “METHODS AND APPARATUS FOR USING BEACON SIGNALS IN A COGNITIVE RADIO NETWORK”. U.S. Provisional Patent Application Ser. No. 60/863,304 filed on Oct. 27, 2006, U.S. Provisional Patent Application Ser. No. 60/845,052 filed on Sep. 15, 2006, and U.S. Provisional Patent Application Ser. No. 60/845,051 filed on Sep. 15, 2006, each of which is hereby incorporated by reference and all of which are assigned to the assignee hereof. 
     
    
     FIELD  
       [0002]     The present invention is directed to methods and apparatus for signaling in wireless communication and, more particularly, to methods and apparatus for using beacon signals for detecting spectrum availability in a radio network, e.g., a cognitive radio network.  
       BACKGROUND  
       [0003]     Wireless spectrum is an expensive and valuable resource but significant portions of spectrum often go unused. The concept of cognitive radio allows wireless devices to discover and use locally available and usable spectrum for communication. The wireless device should be able to sense its environment, including its location, and then be able to alter its communication parameters, including power and carrier frequency, so as to dynamically reuse available spectrum. A key technical challenge of cognitive radio is to detect the availability of the spectrum in a robust and power efficient manner. For example, when a terminal just powers up or moves into a new area, the terminal may not have knowledge of the communication parameters or even technologies that maybe currently used in the vicinity of the geographical area. The detection method has to be robust, e.g., against various uncertainties including the lack of timing and frequency synchronization. Power efficiency has great impact on the battery life of the terminals and is thus another important issue in wireless systems.  
         [0004]     In view of the above discussion, it should be appreciated that there is a need for new and improved ways for detecting spectrum availability in a radio network.  
       SUMMARY  
       [0005]     In accordance with various embodiments, before a wireless terminal starts to use a spectrum band, the wireless terminal is to scan a spectrum band to determine whether the spectrum band is available for use. The step of scanning includes searching for a beacon signal in the spectrum band.  
         [0006]     In one exemplary embodiment, a beacon signal includes a sequence of beacon signal bursts in a spectrum band, each beacon bust including one or more beacon symbols. A beacon symbol is transmitted using a beacon symbol transmission unit. A beacon signal burst includes one or more beacon symbols with the number of beacon symbols occupying a small fraction of the beacon symbol transmission units of the beacon symbol burst, e.g., ±10%. In some exemplary orthogonal frequency division multiplexing (OFDM) systems, each beacon symbol is a single tone over an OFDM symbol period. In some exemplary orthogonal frequency division multiplexing (OFDM) systems, each beacon symbol is a single tone over a small number, e.g., one, two, three or four, OFDM symbol periods. A beacon signal burst, in some embodiments, includes one or more tones e.g., a single tone or a small number of tones such as two three or four tones, which are used to convey beacon symbols over a small number of transmission symbol time periods, e.g., one or two symbol transmission time periods. The beacon signal bursts are transmitted in an intermittent (i.e., non-continuous) manner so that there are a number of symbol periods between a first and a second beacon signal bursts. Successive beacon signal bursts may, and sometimes do, use different tones for the beacon symbols according to a predetermined or pseudo random tone hopping sequence.  
         [0007]     In accordance with various embodiments, a beacon signal can be used to carry a small amount of information. In an exemplary OFDM system, information can be contained in the frequency of the tone(s) of the beacon symbol in a given burst, the time interval between successive bursts, and/or the tone hopping sequence. The information carried by the beacon signal, in various embodiments, includes at least one of the following about the transmitter: the identifier, the type, the priority level, the current transmission power value, and maximum power information, e.g., the maximum power that the transmitter is capable of transmitting.  
         [0008]     If the wireless terminal has not detected any beacon signal in the step of searching for a beacon signal, then, in some embodiments, the spectrum band is available to be used by the terminal. Otherwise, in one embodiment, the wireless terminal is not allowed to use the spectrum band.  
         [0009]     If the wireless terminal determines that a candidate spectrum band is available for use, the wireless terminal may start to use the spectrum, e.g., transmitting/receiving data or control signals or establishing peer-to-peer communication sessions with another wireless terminal. In one embodiment, the transmission power of the wireless terminal is a function of the type or the priority level of the wireless terminal.  
         [0010]     In accordance with one aspect of various embodiments, while the wireless terminal is using the spectrum, the wireless terminal transmits its own user beacon signal in the spectrum band. The user beacon signals transmitted by different wireless terminals may be, and sometimes are, different from each other with information carried by the beacon signals. In one embodiment, wireless terminals are of different service priority levels and correspond to different user beacon signals.  
         [0011]     In accordance with another aspect of various embodiments, while the wireless terminal is using the spectrum, the wireless terminal listens to the spectrum and attempts to detect a beacon signal, which may be sent by another wireless terminal. The wireless terminal may continuously be in the listening mode (i.e., on time) for a time interval of a few symbol periods. The on time is followed by an off time during which the terminal is in a power saving mode and does not receive any signal, e.g., turn off the receive modules. Alternatively, the wireless terminal may continuously be in the listening mode while the wireless terminal is using the spectrum.  
         [0012]     In one embodiment, when a first wireless terminal detects the presence of a user beacon signal from a second wireless terminal, irrespective of whether the first wireless terminal is currently using the spectrum band or not, the wireless terminal needs to compare the priority level. If the priority level of the second wireless terminal is higher, the first wireless terminal considers the spectrum band unavailable for use. Moreover, the first wireless terminal shall stop using the spectrum band if the first wireless terminal is currently using the spectrum band, so that higher priority users or services can use the spectrum band without the interference from the first wireless terminal. If the priority level of the second wireless terminal is lower, the first wireless terminal considers the spectrum band available for use. If the first wireless terminal has not been using the spectrum, the first wireless terminal may start to transmit its own user beacon signal. In some embodiments, the first wireless terminal derives the timing and/or frequency of the second wireless terminal from the detected beacon signal, and then uses that information to determine the timing and/or frequency to transmit its own user beacon signal. Assuming that the second wireless terminal is also listening to detect a user beacon signal, advantageously, the above synchronization helps the user beacon signal of the first wireless terminal to be received by the second wireless terminal, so that the second wireless terminal will stop using the spectrum.  
         [0013]     In accordance with another aspect of various embodiments, the wireless terminal estimates the path loss between the wireless terminal and the corresponding transmitter of the detected beacon signal. The estimation can be, and sometimes is, based on the received power of the beacon signal. If the path loss is sufficiently great, e.g., greater than a predetermined level, then the wireless terminal can use the spectrum band.  
         [0014]     In accordance with various embodiments, in a geographic area, if any communication mode e.g., wireless terminal or base station, is in a data session in a spectrum band, then the node is required to transmit a node beacon signal in the spectrum band. In the data session, the mode may be transmitting or receiving control or data signals. In the area, different modes may co-exist, with each wireless terminal using at least one of a variety of services, such as cellular phone, wireless local loop, digital television, etc., which may be supported by different technologies.  
         [0015]     An exemplary method of operating a wireless communications devices, in accordance with various embodiments includes: monitoring during a first period of time to detect at least a portion of a beacon signal including at least one beacon signal in a first communications band; and when a beacon signal portion including at least one beacon symbol is not detected during said first period of time, transmitting a first signal during a second period of time following said first period of time. An exemplary wireless communications device in accordance with various embodiments includes: a beacon detections module for detecting receipt of at least one beacon symbol communicated in a first communications band; a transmitter; and a transmission control module for controlling signal transmission as a function of an output of said beacon detection module, said transmission control module controlling said transmitter to transmit a first signal during a second period of time following a first period of time when a beacon signal portion including at least one beacon symbol is not detected during said first period of time.  
         [0016]     While various embodiments have been discussed in the summary above, it should be appreciated that not necessarily all embodiments include the same features and some of the features described above are not necessary but can be desirable in some embodiments. Numerous additional features, embodiments and benefits are discussed in the detailed description which follows. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  illustrates an exemplary cognitive radio network in a geographic area implemented in accordance with various embodiments.  
         [0018]      FIG. 2  illustrates a ladder diagram of an exemplary method of using beacon signals to control the use of the spectrum band in a cognitive radio network implemented in accordance with various embodiments.  
         [0019]      FIG. 3  illustrates different exemplary beacon signals, e.g., system and/or user beacon signals, implemented in accordance with various embodiments.  
         [0020]      FIG. 4  illustrates an example of utilizing timing synchronization information implemented in accordance with various embodiments.  
         [0021]      FIG. 5  illustrates a flowchart of a method used by an exemplary wireless terminal implemented in accordance with various embodiments.  
         [0022]      FIG. 6  illustrates one embodiment of monitoring for beacon signal bursts and transmitting a beacon burst in accordance with a predicted beacon monitoring interval.  
         [0023]      FIG. 7  illustrates a detailed illustration of an exemplary wireless terminal implemented in accordance with various embodiments.  
         [0024]      FIG. 8  comprising the combination of  FIG. 8A  and  FIG. 8B  is a drawing of a flowchart of an exemplary method of operating a wireless communications device, e.g., a wireless terminal such as a mobile node, in accordance with various embodiments.  
         [0025]      FIG. 9  is a drawing of an exemplary wireless terminal, e.g., mobile node, implemented in accordance with various embodiments.  
         [0026]      FIG. 10  is a drawing of a flowchart of an exemplary method of operating a wireless communications device in accordance with various embodiments.  
         [0027]      FIG. 11  is a drawing of an exemplary wireless terminal, e.g., mobile node, implemented in accordance with various embodiments.  
         [0028]      FIG. 12  is a drawing of a flowchart of an exemplary method of operating a wireless communications device in accordance with various embodiments.  
         [0029]      FIG. 13  is a drawing of an exemplary wireless terminal, e.g., mobile node, implemented in accordance with various embodiments. 
     
    
     DETAILED DESCRIPTION  
       [0030]      FIG. 1  illustrates an exemplary cognitive radio communication network  100  implemented in accordance with various embodiments. Two wireless terminals, namely a first wireless terminal  102  and a second wireless terminal  104  are present in a geographic area  106 . A system terminal  105 ; e.g., including a system beacon transmitter, is included in some embodiments. Some spectrum band is available to be used by the two terminals for the purpose of communication, e.g., peer-to-peer communication.  
         [0031]     In a cognitive radio network, there is usually no network infrastructure. Various described novel methods, apparatus and features may be used in various radio networks but are particularly well suited for use in networks where infrastructure is limited or lacking e.g., in a cognitive radio network where a wireless terminal may need to discover the information about the network. The wireless terminals may not have a common timing or frequency reference. Indeed, in such a network, the wireless terminals need to figure out whether a given spectrum band is available to be used by the wireless terminal in the current geographic area. A key idea of cognitive radio is to let a wireless terminal sense its environment and discover available spectrum. Spectrum availability is a function of the environment.  
         [0032]      FIG. 2  illustrates a ladder diagram  200  of an exemplary method of using beacon signals to control the use of the spectrum band in a cognitive radio network implemented in accordance with various embodiments.  
         [0033]     The vertical axis  201  represents time. There are three exemplary terminals, WT A  202 , WT B  204  and WT C  206  in this exemplary cognitive radio network. Assume that initially none of the wireless terminals ( 204 ,  206 ,  208 ) are powered on.  
         [0034]     First, wireless terminal A  202  is powered on. Before wireless terminal A  202  can use the spectrum band, it first scans the band to search for user beacon signals ( 208 ). Since wireless terminal A  202  is the only active terminal in the area, it does not detect any user beacon signal. Thus, wireless terminal A  202  determines that the spectrum band is available for use ( 210 ). Wireless terminal A  202  starts to use the spectrum ( 212 ). Wireless terminal A  202  broadcasts its user beacon signal to show its presence ( 214 ).  
         [0035]     At a later time, wireless terminal B  204  is powered on. Before wireless terminal B  204  can use the spectrum band, it first scans the band to search for user beacon signals ( 216 ). Wireless terminal B  204  detects the user beacon signal sent by terminal A ( 218 ). Wireless terminal B  204  furthermore learns, e.g., from the detected beacon signal or another broadcast channel of wireless terminal A, that wireless terminal A is available for peer-to-peer communication ( 220 ). So wireless terminal B  204  determines to use the spectrum ( 222 ). Wireless terminals A and B ( 202 ,  204 ) set up a peer-to-peer session ( 224 ). Since both wireless terminals ( 202 ,  204 ) are active, they both broadcast user beacon signals ( 228  and  226 ), respectively. In some embodiments, either wireless terminal broadcasts its own user beacon signal. In other embodiments, the two terminals ( 202 ,  204 ) determine the priority level of their sessions and use that to determine the user beacon signals to be sent. For example, the session priority level is the maximum priority level of either terminal.  
         [0036]     At a later time, wireless terminal C  206  is powered on. Before wireless terminal C  206  can use the spectrum band, it first scans the band to search for user beacon signals ( 230 ). Wireless terminal C  206  detects the user beacon signal sent by wireless terminal A  202  and/or by wireless terminal B  204  ( 232 ). Wireless terminal C  206  furthermore learns, e.g., from the detected beacon signal or another broadcast channel of wireless terminal A or B, that there is an ongoing session ( 234 ). Wireless terminal C  206  also learns the priority levels of detected beacon signals and compares them with its own priority level ( 236 ). If the priority level of wireless terminal C  206  is lower, then wireless terminal C  206  determines that the spectrum band is not available ( 238 ); otherwise wireless terminal C  206  may start to transmit its own user beacon signal. In such a case, both wireless terminals A and B ( 202 ,  204 ) will detect the user beacon signal from wireless terminal C  206 , and have to stop/suspend their session and stop using the spectrum.  
         [0037]     In accordance with various embodiments, a beacon signal includes a sequence of beacon signal bursts in a spectrum band, each beacon signal burst including one or more beacon symbols. A beacon symbol is transmitted using a beacon symbol transmission unit. A beacon signal burst includes a small number of beacon symbols, with the number of beacon symbols occupying a small fraction of the beacon symbol transmission units of the beacon signal burst. In some exemplary OFDM systems, a beacon symbol is a tone over an OFDM symbol period. In some exemplary OFDM systems, a beacon symbol is a tone over a small number, e.g., one, two, three, or four of successive, OFDM symbol periods. In some embodiments, a beacon signal burst includes one or more tones, e.g., a single tone or a small number such as two, three or four tones, which are used to convey beacon symbols, over a small number of transmission symbol periods, e.g., one or two symbol periods. The wireless transmitter transmits the beacon signal bursts in an intermittent (i.e., non-continuous) manner so that there are a number of symbol periods between a first and a second beacon signal bursts.  FIG. 3  illustrates in drawing  300  and  350  exemplary beacon signals in an exemplary OFDM system.  
         [0038]     In drawing  300  the horizontal axis  302  represents time and the vertical axis  304  represents frequency. A vertical column represents each of the tones in a given symbol period. Each small box  306  represents a tone-symbol, which is a single tone over a single transmission symbol period. In drawing  350  the horizontal axis  352  represents time and the vertical axis  304  represents frequency. A vertical column represents each of the tones in a given symbol period. Each small box  356  represents a tone-symbol, which is a single tone over a single transmission symbol period. A minimum transmission unit in the OFDM symbol is a tone-symbol. In this exemplary embodiment, a beacon symbol transmission unit is an OFDM tone-symbol.  
         [0039]     The beacon signal includes a sequence of beacon signal bursts, which are transmitted sequentially over time, each beacon symbol burst including one or more beacon symbols. A beacon signal burst, in various embodiments, includes a small number of tones which convey beacon symbols, e.g., a single tone, over a small number of transmission symbol periods, e.g., one or two symbol periods. Drawing  300  of  FIG. 3  shows four small black boxes ( 308 ,  310 ,  312 ,  314 ), each of which represents a beacon symbol. In this case, a beacon symbol uses the air link resources of one tone-symbol. In another exemplary embodiment, a beacon symbol uses one tone transmitted over two consecutive symbol periods and uses the air link resource of two OFDM tone-symbols.  
         [0040]     The beacon symbol tone or tones of the beacon signal may vary (hop) from one burst to another. In accordance with various embodiments, the tone-hopping pattern, including the tones used for the beacon symbol or symbols and the inter-burst interval, of the beacon signal are, in some embodiments, a function of the transmitter, e.g., a terminal, and can be used as an identification of the transmitter or an identification of the type to which the transmitter belongs, or to indicate the transmission power or the power capability of the terminal.  
         [0041]     Different user beacon signals are, in some embodiments, different from each other in at least one of the following ways: the periodicity of the beacon signal bursts, the tone or tones used for the beacon symbols in a beacon signal burst, and the hopping pattern of the beacon symbol tones used in successive beacon signal bursts.  
         [0042]     For example,  FIG. 3  shows two exemplary beacon signals ( 324 ,  374 ). Consider that first beacon signal  324  is a first user beacon signal is sent by a first wireless terminal and includes beacon signal burst ( 316 ,  318 ,  320 ,  322 ) and beacon symbols ( 308 ,  310 ,  312 ,  314 ), respectively. The second beacon signal  374  sent by a second wireless terminal includes beacon signal bursts ( 366 ,  368 ,  370 ,  372 ) and beacon symbols ( 358   360 ,  362 ,  364 ), respectively. The upper portion  300  shows a user beacon signal  324  sent by one wireless terminal, and the lower portion  350  shows another user beacon signal  374  sent by another wireless terminal. In the example, the two beacon signals have the same periodicity, but different tone hopping sequences. Specifically, the tones of the exemplary first wireless terminal beacon signal  324  follow a first slope, and the tones of the exemplary second wireless terminal user beacon signal  374  follow a second slope, where the first slope is greater than the second slope.  
         [0043]     In some embodiments exemplary system beacon signals, e.g., beacon signals from base stations and/or fixed location beacon transmitters, follow a first slope or first set of slopes and exemplary user beacon signals follow a second slope or second set of slopes, the first slope being different from the second slope and/or the first set of slopes being non-overlapping with the second set of slopes.  
         [0044]     In one exemplary embodiment, suppose that a high priority service, e.g., law enforcement or fire department service, and a low priority service, e.g., general data service, share the spectrum band. Most of time, the high priority service does not have any activity, during which the spectrum band can be used entirely by the low priority service. However, when the high priority service needs to use the spectrum, it is desired that the low priority service shall stop. The sessions associated with the low priority service shall be terminated. To achieve this objective, in accordance with various embodiments, terminals associated with different service levels use different user beacon signals, e.g., to signal different priority levels.  
         [0045]     Consider an exemplary embodiment. When the wireless terminal is scanning the spectrum band for availability, or when the wireless terminal has already been in a communication session using the spectrum band, the wireless terminal shall keep on searching for user beacon signals. If the wireless terminal detects the presence of a user beacon signal with higher priority than its own, then the wireless terminal considers the corresponding spectrum band as unavailable for use. The wireless terminal shall terminate the communication session, if any, and may proceed to scan another candidate spectrum band. This results in clean spectrum band to be used by high priority terminals or services.  
         [0046]     Drawing  400  of  FIG. 4  illustrates one embodiment of monitoring for beacon signal bursts implemented in accordance with various embodiments. The wireless terminal listens to the spectrum band and attempts to detect a user beacon signal, which may be sent by a different wireless terminal. The wireless terminal may continuously be in the listening mode for a time interval of a few symbol periods, which is called on time. The on time ( 402 ) is followed by an off time ( 406 ) during which the wireless terminal is in a power saving mode and does not receive any signal. In the off time, the wireless terminal may completely turn off the receive modules. When the off time  406  ends, the wireless terminal resumes to the on time  404  and starts to detect for beacon signals again. The above procedure repeats.  
         [0047]     In some embodiments, the length of an on time interval is shorter than that of an off time internal. In one embodiment, an on time interval is less than or equal to ⅕ of an off time interval. In one embodiment, the length of each of the on time intervals are the same, and the length of each of the off time intervals are also the same.  
         [0048]     The length of an off time interval depends, in some embodiments, on the latency requirement for a first wireless terminal to detect the presence of another (second) wireless terminal if the second wireless terminal is actually present in the vicinity of the first wireless terminal. The length of an on time interval is determined so that the first wireless terminal has a great probability of detecting a least one beacon signal burst in the on time interval. In one embodiment, the length of the on time interval is a function of at least one of the transmission duration of a beacon signal burst and the duration between successive beacon signal bursts. For example, the length of the on time interval is at least the sum of the transmission duration of a beacon signal burst and the duration between successive beacon signal bursts.  
         [0049]      FIG. 5  illustrates a flowchart  500  of an exemplary method of operating a wireless terminal used by an exemplary first wireless terminal implemented in accordance with various embodiments. Operation of the exemplary method starts in step  501 , where the first wireless terminal is powered on and initialized, and proceeds to step  502 .  
         [0050]     In step  502 , the exemplary first wireless terminal may start by scanning the spectrum band to search for user beacon signals. Then, in step  504 , the first wireless terminal checks whether a user beacon signal from a second wireless terminal has been detected. If the answer is NO, then operation proceeds from step  504  to step  516 , where the first wireless terminal determines that the spectrum is available for use. Otherwise, the first wireless terminal has found a beacon signal and operation proceeds from step  504  to step  506 , where the first wireless terminal compares the priority level of the detected user beacon signal with its own priority level. In step  508 , the first wireless terminal checks whether the detected beacon has higher priority level than its own priority level. If the answer is NO, then operation proceeds from step  508  to step  516 , where the first wireless terminal determines that the spectrum is available for use. Otherwise, operation proceeds from step  508  to step  510 . In step  510  the first wireless terminal determines the path loss from the first wireless terminal to the second wireless terminal.  
         [0051]     In one embodiment, the beacon signal carries the information about the transmission power of the second wireless terminal. Then the first wireless terminal can determine the path loss from the transmission power and the received power measured by the first wireless terminal. In a special case where each of the beacon signals are sent at the same power level, the beacon signal itself does not have to carry the information about the transmission power of the second wireless terminal. The first wireless terminal can determine the path loss from the known, e.g., predetermined beacon level, transmission power and the received power measured by the first wireless terminal. Operation proceeds from step  510  to step  512 .  
         [0052]     In step  512 , the first wireless terminal determines whether the path loss is sufficiently high e.g., in relation to a predetermined stored path loss level. If the answer is yes, then operation proceeds from step  512  to step  516 . In step  516  the first wireless terminal determines that the spectrum is available for use. Otherwise, operation proceeds from step  512  to step  514 , where the first wireless terminal determines that the spectrum is not available for use.  
         [0053]     Once the first wireless terminal determines that the spectrum is available for use in step  516 , the first wireless terminal may use the spectrum to establish communication links, e.g., peer-to-peer communication. Operation proceeds from step  516  to step  518  in which the first wireless terminal starts to use the spectrum including transmitting its own user beacon signal. Meanwhile, the first wireless terminal shall periodically be in the on time mode, e.g., with respect to receiver operation, and scan the spectrum band to search for user beacon signals as indicated by step  502 .  
         [0054]     Usually the terminals in the cognitive radio network not have a common source from which each of the terminals can derive synchronization information. In accordance with a feature of various exemplary embodiments, the wireless terminals use the timing and/or frequency information derived from a system beacon signal transmitted by a special transmitter, e.g., transmitted by a fixed location system terminal including a beacon transmitter. The fixed location system terminal may or may not be coupled to other network nodes, and may or may not include additional wireless functions in addition to transmitting the beacon signal. In some embodiments, the fixed location system terminal&#39;s sole function is to transmit a system beacon signal to be used as a reference by wireless terminals. Advantageously, the terminals now have a common timing and/or frequency reference, thereby being synchronized with each other. To elaborate, drawing  600  of  FIG. 6  illustrates an example of utilizing timing synchronization information implemented in accordance with various embodiments.  
         [0055]     The horizontal axis  601  represents time. A second wireless terminal transmits its user beacon signal  608 , which includes a sequence of beacon signal bursts,  602 ,  604 ,  606 , and so on. Now, suppose that a first wireless terminal is powered on and detects those beacon bursts. Assume that the first wireless terminal has higher priority level than the second terminal, and that the first wireless terminal intends to use the spectrum.  
         [0056]     The first wireless terminal predicts the on time intervals of the second wireless terminal&#39;s receiver, during which the second wireless terminal monitors for other user beacon signal. The prediction is a function of the estimated timing of the detected beacon burst  602 ,  604  and  606 . For example, in  FIG. 6 , the on time interval of a terminal starts from a time instance that has known time offset  612  from the beginning of a beacon signal burst sent by the same wireless terminal. Therefore, once the first wireless terminal has determined the timing of the beacon bursts of the second wireless terminal transmitter, it is possible to determine the timing of the second wireless terminal receiver from the known relationship.  
         [0057]     Rather than sending its user beacon signal at a randomly chosen time instance, in the exemplary scenario show in  FIG. 6 , the first wireless terminal chooses to transmit ( 614 ) at the time during which the second wireless terminal is listening ( 610 ). The second wireless terminal detects the user beacon signal sent by the first wireless terminal, and then decides to stop using the spectrum band because its priority level is lower.  
         [0058]     Note that in the absence of the above synchronization, it may take much longer time for the second wireless terminal to detect the user beacon signal sent by the first wireless terminal. Otherwise, the second wireless terminal may need to stay in the listening mode for a much longer time interval in order to reduce the latency of detection. The synchronization thus helps the wireless terminals to detect beacon signals much more rapidly and in a more power efficient manner.  
         [0059]      FIG. 7  provides a detailed illustration of an exemplary wireless terminal  700  implemented in accordance with various embodiments. The exemplary wireless terminal  700 , depicted in  FIG. 7 , is a detailed representation of an apparatus that may be used as any one of wireless terminals  102  and  104  depicted in  FIG. 1 . In the  FIG. 7  embodiment, the wireless terminal  700  includes a processor  704 , a wireless communication interface module  730 , a user input/output interface  740  and memory  710  coupled together by bus  706 . Accordingly, via bus  706  the various components of the terminal  700  can exchange information, signals and data. The components  704 ,  706 ,  710 ,  730 ,  740  of the wireless terminal  700  are located inside a housing  702 .  
         [0060]     The wireless communication interface  730  provides a mechanism by which the internal components of the wireless terminal  700  can send and receive signals to/from external devices and another terminal. The wireless communication interface  730  includes, e.g., a receiver module  732  and a transmitter module  734 , which are coupled via a duplexer  738  with an antenna  736  used for coupling the wireless terminal  700  to other terminals, e.g., via wireless communications channels.  
         [0061]     The exemplary wireless terminal  700  also includes a user input device  742 , e.g., keypad, and a user output device  744 , e.g., display, which are coupled to bus  706  via the user input/output interface  740 . Thus, user input/output devices  742 ,  744  can exchange information, signals and data with other components of the wireless terminal  700  via user input/output interface  740  and bus  706 . The user input/output interface  740  and associated devices  742 ,  744  provide a mechanism by which a user can operate the wireless terminal  700  to accomplish various tasks. In particular, the user input device  742  and user output device  744  provide the functionality that allows a user to control the wireless terminal  700  and applications, e.g., modules, programs, routines and/or functions, that execute in the memory  710  of the wireless terminal  700 .  
         [0062]     The processor  704  under control of various modules, e.g., routines, included in memory  710  controls operation of the terminal  700  to perform various signaling and processing as discussed below. The modules included in memory  710  are executed on startup or as called by other modules. Modules may exchange data, information, and signals when executed. Modules may also share data and information when executed. In the  FIG. 7  exemplary embodiment, the memory  710  of wireless terminal  700  includes a signaling/control module  712  and signaling/control data  714 .  
         [0063]     The signaling/control module  712  controls processing relating to receiving and sending signals, e.g., beacon signals, user data signals, messages, etc., management of state information storage, retrieval, processing, scanning, transmission control, priority determination, path loss determination device identification, user identification, and spectrum availability determination. Signaling/control data  714  includes state information, e.g., parameters, status and/or other information relating to operation of the terminal. In particular, the signaling/control data  714  includes various configuration information  916 , e.g., configuration information of type, priority level, transmission power, transmitter power capability, etc. of the terminal. The module  712  may, and sometimes does, access and/or modify the data  714 , e.g., update the configuration information  716 . The module  712  also includes module  711  for scanning a spectrum band to search for system beacon signal in the band; module  713  for transmitting user beacon signal; module  715  for comparing the priority levels of different user beacon signals; module  717  for determining path loss.  
         [0064]      FIG. 8  comprising the combination of  FIG. 8A  and  FIG. 8B  is a drawing of a flowchart  800  of an exemplary method of operating a wireless communications device e.g., a wireless terminal such as a mobile node, in accordance with various embodiments. The wireless communications device is, e.g., a portable wireless communications device, which may be operated off battery power. The wireless communications device is, e.g., wireless terminal  900  of  FIG. 9 .  
         [0065]     Operation starts in step  802 , where the wireless communications device is powered on and initialized and proceeds to step  804 . In step  804 , the wireless communications device monitors, during a first period of time, to detect at least a portion of a beacon signal including at least one beacon symbol in a first communications band.  
         [0066]     Operation proceeds from step  804  to step  806 . In step  806 , the wireless communications device makes a decision as to whether or not to transmit a first signal based on the result of said monitoring, said first signal including at least one of a beacon symbol and user data. In some embodiments the first signal is a beacon signal. In some embodiments, said user data includes at least one of text data, audio data, image data, game data, and spread sheet data.  
         [0067]     Step  806  includes sub-steps  808 ,  810 ,  812 ,  814 , and  816 . In sub-step  808 , the wireless communications device determines if a beacon signal portion including at least one beacon symbol was detected in the monitoring of step  804 . If a beacon symbol portion was detected operation proceeds from step  808  to one of alternative sub-steps  810  and  812 . If a beacon symbol was not detected, operation proceeds from step  808  to step  814 , where the wireless communications device decides not to transmit a signal during a second period of time which follows said first period of time.  
         [0068]     In sub-step  810 , the wireless communications device decides to transmit a signal in response to said detected beacon signal portion. In alternative, sub-step  812 , the wireless communications device decodes information communicated by the detected beacon signal portion. Operation proceeds from sub-step  812  to sub-step  816 . In sub-step  816 , the wireless communications device decides whether or not to transmit said first signal based on information included in said decoded information. In various embodiments, sub-step  816  includes one or more of sub-steps  818  and  820 . In sub-step  818 , the wireless communications device decides as a function of type information included in said decoded information. In various embodiments, the type information indicates whether or not a second band is allowed to be used for peer to peer communications. In some embodiments, the type information identifies a second band which is allowed to be used for peer to peer communications. In sub-step  820 , the wireless communications device decides as a function of device identification information included in said decoded information. In some such embodiments, the device identification information identifies at least one of the wireless communications device and a user that is currently using the wireless communications device.  
         [0069]     Operation proceeds from step  806 , via connecting node A  822 , to step  824 . In step  824 , the wireless communications device proceeds differently depending upon whether or not the decision of step  806  was to transmit. If the decision was to transmit, then operation proceeds from step  824  to step  826 . If the decision was not to transmit, then operation proceeds from step  824 , via connecting node B  828 , to step  804 , where additional monitoring is performed.  
         [0070]     In step  826 , the wireless communications device transmits at least a portion of said first signal during a second time period. In some embodiments, the first signal is transmitted in a second band which-is the same as the first communications band. For example, the received beacon signal portion and the first signal, e.g., transmitted beacon signal portion may correspond to peer nodes in a peer to peer communications network and both of the peer nodes may be using the same frequency band for user beacon signaling. In some other embodiments, the first signal is communicated in a second band which is different from the first communications band. For example, the received beacon signal portion may be communicated from a base station or fixed beacon signal transmitter using a different communications band than the band into which the communications device transmits its user beacon-signaling. In some such embodiments, the first and second communications bands are separated and disjoint in the frequency domain. In various embodiments, the first and second communications bands are different size frequency bands.  
         [0071]     In some embodiments, step  826  includes sub-step  830 , in which the wireless communications device transmits at least one beacon symbol. For example, the at least one beacon symbol is a single beacon symbol or a small number of beacon symbols in a beacon burst, e.g., with the beacon symbols occupying&lt;10% of the beacon symbol transmission units of the beacon burst.  
         [0072]     Operation proceeds from step  826  to one of steps  832  and  834 . In step  832 , the wireless communications device transmits user data, e.g., during a third time period, into a third communications band, said third time period following said second time period. For example, during the second time period the wireless communications device transmits at least a portion of the first signal including at least one beacon symbol, e.g., to identify its presence, and during the third time period, the wireless communications device transmits user data to a peer. In various embodiments, the third frequency band is the same as the second frequency band. For example, the wireless communications device may transmit both a user beacon signal and user data for peer to peer communications into the same frequency band. In some other embodiments, the second frequency band is different from the third frequency band. For example, there may be distinct frequency bands for user beacon signals and for user data signals.  
         [0073]     Operation proceeds from step  832  to step  834 . In step  834 , the wireless communications device monitors during a fourth time period to detect at least a portion of an additional beacon signal from another wireless communications device, e.g., from a peer in a peer to peer communications network. Step  834  includes, in some embodiments, sub-step  836 . In sub-step  836 , the wireless communications device monitors a second frequency band, different from said first frequency band, for at least a portion of an additional beacon signal.  
         [0074]      FIG. 9  is a drawing of an exemplary wireless terminal  900 , e.g., mobile node, implemented in accordance with various embodiments. Exemplary wireless terminal  900  may be any of the exemplary wireless terminals ( 102 ,  104 ) of system  100  of  FIG. 1 .  
         [0075]     Exemplary wireless terminal  900  includes a receiver module  902 , a transmitter module  904 , a processor  906 , user I/O devices  908 , and memory  910  coupled together via a bus  912  over which the various elements may interchange data and information. Memory  910  includes routines  914  and data/information  916 . The processor  906 , e.g., a CPU, executes the routines  914  and uses the data/information  916  in memory  910  to control the operation of the wireless terminal  900  and implement methods.  
         [0076]     Receiver module  902 , e.g., an OFDM receiver, is coupled to receive antenna  903  via which the wireless terminal receives signals from other wireless communications devices, e.g., other wireless terminals and/or system terminals such as base stations and/or fixed location beacon transmitters. Received signals include, e.g., beacon signals from wireless terminals, beacon signals from system nodes, and handshaking signals and user data signals from wireless terminals, e.g., in peer-to-peer communications.  
         [0077]     Transmitter module  904 , e.g., an OFDM transmitter, is coupled to transmit antenna  905 , via which the wireless terminal  900  transmits signals to other wireless communications devices, e.g., peer nodes. In some embodiments, the same antenna is used for receiver module  902  and transmitter module  904 , e.g., with the receiver and transmitter modules ( 902 ,  904 ) being coupled to the antenna via a duplexer module. Signals transmitted by the transmitter module  904  include, e.g., a first signal such as a beacon signal or beacon signal portion including at least one beacon symbol. Other signals transmitted by transmitter module  904  include peer-to-peer communication session establishment signals and user data signals.  
         [0078]     User I/O devices  908  include, e.g., microphone, keypad, keyboard, switches, camera, speaker, display, etc. User I/O devices  908  allow a user of wireless terminal  900  to input data/information, access output data/information, and control at least some functions of the wireless terminal  900 .  
         [0079]     Routines  914  include communications routines  918  and wireless terminal control routines  920 . The communications routines  918  implement various communications protocols used by the wireless terminal. Wireless terminal control routines  920  include a beacon detection module  922 , a beacon based decision module  924 , a beacon signaling decoding module  926 , a beacon signal generation module  928 , a control module  930  and a wireless terminal beacon detection module  932 .  
         [0080]     Beacon detection module  922  detects receipt of one or more beacon symbols communicated in a first communications band. Beacon based decision module  924  determines whether or not to transmit a first signal based on an output of the beacon detection module  922 , said output being a function of whether or not a beacon symbol was detected during a time period, said first signal including at least one of a beacon symbol and user data. Beacon signaling decoding module  926  decodes information communicated by a detected beacon signal portion at least one detected beacon symbol being part of said detected beacon signal portion. In some embodiments, the beacon based decision module  924  makes the decision whether or not to transmit a first signal based on decoded information generated by the decoding performed by the beacon signal decoding module. In some embodiments, the beacon based decision module  924  makes a decision not to transmit a signal during a second time period which follows a first time period when at least a portion of a beacon signal including a beacon symbol is not detected by said beacon detection module during the first period of time. In some embodiments, the beacon based decision module  924  makes the decision whether or not to transmit a signal based on type information included in the decoded information, said type information indicating that a second band is allowed to be used for peer-to-peer communications. In some embodiments, the beacon based decision module  924  makes the decision whether or not to transmit a signal based on device information included in the decoded information.  
         [0081]     Beacon signal generation module  928  generates beacon signals, said generated beacon signals communicating an identifier used to identify at least one of: i) said wireless communications device and ii) a user that is currently using said wireless communications device. Control module  930  controls the band in which the receiver and transmitter operate. Control module  930  includes a user data transmission control module  931 . In some embodiments said receiver and transmitter are controlled to use the same band in a time division multiplexed basis. In some embodiments, the receiver is controlled to use a first communications band and the transmitter is controlled to use a second communications band, said first and second communications bands being different bands. In some embodiments, the first and second communications bands are separated and disjoint in the frequency domain but have a predetermined relationship. In some such embodiments, the first and second communications bands are different size frequency bands.  
         [0082]     User data transmission control module  931  controls the transmission of user data into a third communications band during a third period. In some embodiments, the third time period follows a second time period, said second time period being a time period during which at least a portion of said first signal is transmitted, said first signal including at least one beacon symbol. In some embodiments, the third communications band is the same as the second communications band. In some embodiments, the third communications band is different from the second communications band.  
         [0083]     Wireless terminal beacon detection module  932  detects beacon symbols from other wireless communications devices during a fourth period of time, at least a portion of said fourth period of time being different from a time period during which said beacon detection module  922  is operated. The other wireless communications devices are, e.g., peer nodes in a peer to peer communications network. In some embodiments, the wireless terminal beacon detection module  932  monitors a second communications band, said second communications band being a different frequency band than said first communications band.  
         [0084]     Data/information  916  includes detected beacon signal information  934 , information recovered from decoded beacon signal portions (information recovered from a decoded beacon signal portion corresponding to a 1 st  beacon signal  936 , . . . , information recovered from a decoded beacon signal portion corresponding to an Nth beacon signal  938 ), transmission decision information  940 , device identification information  950 , user identification information  952 , first signal information  954 , current time period information  960 , receiver frequency band selection information  962 , transmitter frequency band selection information  964 , peer to peer network communication session information  966  and system data/information  968 .  
         [0085]     Information recovered from a decoded beacon signal portion corresponding to a 1 st  beacon signal  936  includes, in some embodiments, one of more of type information  942  and identification information  944 . The type information  942  is, e.g., frequency band type designation information. The type information  942  may, and sometimes does indicate that the band type is designated to be used for peer-peer communications. The identification information  944  is, e.g., device identification information and/or user identification information.  
         [0086]     Information recovered from a decoded beacon signal portion corresponding to a N th  beacon signal  938  includes, in some embodiments, one of more of type information  946  and identification information  948 . The type information  946  is, e.g., frequency band type designation information. The identification information  948  is e.g., device identification information and/or user identification information.  
         [0087]     First signal information  956  includes, in some embodiments, one or more of beacon symbol information  956  and user data  358 . Beacon symbol information  956  includes, e.g., information identifying the beacon transmission units used to convey beacon symbols, e.g., within beacon bursts of the beacon signal included in the first signal, tone hopping pattern information, and/or time information corresponding to the beacon symbols. User data  958  includes data information such as voice data, other types of audio data, image data, text data, file data, etc. of the first signal, e.g., corresponding to data symbols of the first signal.  
         [0088]     System data/information  968  includes timing/frequency structure information  970 , beacon decoding information  976 , decision criteria information  978  and beacon encoding information  980 . Timing/frequency structure information  970  includes frequency bands&#39; information  972  and time periods&#39; information  974 . Frequency bands&#39; information  972  includes information identifying a plurality of different frequency bands, which are at times used by the wireless terminal. Frequency bands&#39; information  372  also includes information relating beacon signals to frequency bands. In some embodiments, different bands are used for different purposes. For example, one frequency band, in some embodiments, is used for beacon signaling and another frequency band is used for user data signaling. In some embodiments, at least some frequency bands are used for multiple purposes, e.g., user data beacon signaling and wireless terminal beacon signaling. In some embodiments, the same band is used, at different times for different purposes, e.g., a frequency band typically used for wireless communications via a base station, in some embodiments, is at times, used for peer-to-peer communications. Time periods&#39; information  974  includes, e.g., information identifying in a timing structure when the wireless terminal should receive beacon signals, transmit beacon signals and communicate user data signals to a peer node.  
         [0089]     Beacon decoding information  976 , e.g., information mapping various potential detected beacon signals to recovered information, e.g., frequency band type designation information, device ID information, user ID information, and/or priority level information, is used by beacon signal decoding module  926  to recover information ( 936 , . . .  938 ), e.g., when processing beacon symbol information  934 .  
         [0090]      FIG. 10  is a drawing of a flowchart  1000  of an exemplary method of operating a wireless communications device in accordance with various embodiments. The wireless communications device is, e.g., a portable wireless terminal such as a mobile node which may be operated using battery power. The wireless communications device is, wireless terminal  1100  of  FIG. 11 . Operation starts in step  1002 , where the wireless communications device is powered on and initialized. Operation proceeds from start step  1002  to step  1004 . In step  1004 , the wireless communications device monitors during a first period of time to detect at least a portion of a beacon signal including at least one beacon symbol in a first communications band. In some embodiments, a beacon signal portion communicates an identification value. For examples, the identification value can be one of a device identifier and a user identifier.  
         [0091]     Then, in step  1006  operation proceeds differently depending upon whether or not at least a portion of a beacon signal including at least one beacon symbol was detected in step  1004 . If a beacon signal portion was detected, operation proceeds from step  1006  to step  1004  to monitor during another first period of time. However, if a beacon signal portion was not detected, then operation proceeds from step  1006  to step  1008 .  
         [0092]     In step  1008 , the communications device transmits a first signal, e.g., at least a portion of second beacon signal including at least one beacon symbol, during a second period of time following said first period of time. In some embodiments, the first signal is transmitted into the first communications band. In some embodiments said second period of time has a fixed time relationship with said first period of time. In various embodiments, the second period of time has a predetermined time offset from the start of the first period of time.  
         [0093]     Then, in step  1010 , the wireless communications device transmits user data. The first signal is, in some embodiments, transmitted prior to the user data transmission during non-overlapping time periods. In various embodiments, the user data is also transmitted in the first communications band. Operation proceeds from step  1010  to step  1012 . In step  1012 , the wireless communications device monitors for a response to said user data transmission from another device which with said wireless communications device is communicating on a peer to peer basis.  
         [0094]      FIG. 11  is a drawing of an exemplary wireless terminal  1100 , e.g., mobile node, implemented in accordance with various embodiments. Exemplary wireless terminal  1100  may be any of the exemplary wireless terminals ( 102 ,  104 ) of system  100  of  FIG. 1 .  
         [0095]     Exemplary wireless terminal  1100  includes a receiver module  1102 , a transmitter module  1104 , a processor  1106 , user I/O devices  1108 , and memory  1110  coupled together via a bus  1112  over which the various elements may interchange data and information. Memory  1110  includes routines  1114 , and data/information  1116 . The processor  1106 , e.g., a CPU executes the routines  1114  and uses the data/information  1116  in memory  1110  to control the operation of the wireless terminal  1100  and implements methods.  
         [0096]     Receiver module  1102 , e.g., an OFDM receiver, is coupled to receive antenna  1103  via which the wireless terminal  1100  receives signals from other wireless communications devices. Receiver module  1102  receives beacon signal portions, e.g., transmitted in a first communications band. Receiver module  1102  also receives session establishment signals and user data signals from peers, as part of peer-peer communications sessions.  
         [0097]     Transmitter module  1104 , e.g., an OFDM transmitter, is coupled to transmit antenna  1105 , via which the wireless terminal  1100  transmits signals to other wireless communications devices, e.g., peer nodes. In some embodiments, the same antenna is used for receiver module  1102  and transmitter module  1104 , e.g., in conjunction with duplex module. Transmitted signals include beacon signals, communications session establishment signals and user data signals as part of a peer-peer communications session.  
         [0098]     User I/O devices  1108  include, e.g., microphone, keypad, keyboard, switches, camera, speaker, display, etc. User I/O devices  1108  allow a user of wireless terminal  1100  to input data/information, access output data/information, and control at least some functions of the wireless terminal  1100 , e.g., attempt to establish a peer-peer communications session.  
         [0099]     Routines  1114  include communications routines  1118  and wireless terminal control routines  1120 . The communications routines  1118  implement various communications protocols used by the wireless terminal  1100 . Wireless terminal control routines  1120  include a beacon detection module  1122 , a transmission control module  1124 , a first signal, e.g., beacon signal portion, generation module  1126 , a beacon symbol generation module  1127 , a beacon information detection module  1128 , a frequency band control module  1130 , a user data transmission control module  1132 , and a response detection module  1134 .  
         [0100]     Beacon detection module  1122  detects the receipt of beacon symbols communicated in a first communications band. Transmission control module  1124  controls signal transmission as a function of an output of the beacon detection module  1122 . The transmission control module  1124  controls the transmitter module  1104  to transmit a first signal during a second period of time following a first period of time when a beacon signal portion including at least one beacon symbol is not detected during said first period of time. In some embodiments, the second period of time has a fixed time relationship with the first period of time, e.g., a predetermined time offset with respect to the start of the first period of times.  
         [0101]     First signal generation module  1126  generates first signals. For example, an exemplary first signal is a beacon signal portion such as a beacon signal burst including at least one beacon symbol. Beacon symbol generation module  1127  generates beacon symbols, e.g., beacon symbols which are included in generated beacon symbol portions. For example, a beacon symbol is a relatively high power symbol with respect to a data symbol from the transmission perspective of the wireless terminal, facilitating easy detection. For example, the average transmission power difference between a beacon symbol and a data symbol are, in some embodiments, at least 10 dBs. In some embodiments, each of the generated beacon symbols has the same transmission power level. In some embodiments, each generated beacon symbol has the same phase, while generated data symbols may, and generally do have different phase, e.g., as part of a QPSK, QAM16, QAM256, etc. constellation.  
         [0102]     Beacon information detection module  1128  determines an identification value communicated by a detected portion of a beacon signal. The identification value is, e.g., one of a device identifier and a user identifier.  
         [0103]     Frequency band control module  1130  controls the band in which the receiver module  1102  and transmitter module  1104  operate. In some embodiments, the receiver module  1102  and transmitter module  1104  are controlled to use the same band in a time division multiplexed basis, e.g., with respect to a peer-peer communications session.  
         [0104]     User data transmission control module  1132  controls transmission of user data in addition to said first signal in said first communications band. In some embodiments, the first signal is transmitted prior to said user data and the user data transmission control module  1132  control transmission of said user data to occur in a transmission time period which does not overlap with transmission of said first signal. In various embodiments, the user data transmission control module  1132  controls the transmission of user data so that user data is transmitted into the first band, e.g., the same band into which the wireless terminal is transmitting its beacon signal.  
         [0105]     Response detection module  1134  detects a response to the user data transmission from another device with which said wireless terminal device is communicating on a peer to peer basis. The response is, e.g., user data from the peer node and/or control information. Control information is, e.g., handshaking information, session establishment information, session termination information, session maintenance information, power control information, timing control information, frequency band information, etc.  
         [0106]     Data/information  1116  includes receiver frequency band selection information  1136 , current time information  1138 , transmitter frequency band selection information  1140 , beacon detect/failure to detect flag  1142 , detected beacon signal information  1144 , detected beacon signal portion identification information  1146 , device identification information  1148 , user identification information  1150 , generated first signal information, e.g., generated beacon signal, information  1152 , user data to be transmitted  1154 , detected response information from a peer  1156 , and system data/information  1158 .  
         [0107]     Receiver frequency band selection  1136  and transmitter frequency band selections  1140  are outputs of the frequency band selection module  1130  and used by the wireless terminal in controlling the receiver module  1102  and transmitter module  1104  tuning. Beacon detect/failure to detect flag  1142 , e.g., a single bit output, from beacon detection module  1122 , is used by the transmission control module  1124  in making beacon transmission decisions in accordance with the system beacon signaling rules.  
         [0108]     Detected beacon signal information  1144  includes information recovered by beacon signal detection module  1122  corresponding to a detected beacon signal, e.g., a set of identified beacon transmission units conveying beacon symbols, a pattern of beacon symbols, a slope associated with detected beacon symbols, etc. Detected beacon signal portion identification information  1146  is an output of beacon information detection module  1128  and is, e.g., a device identifier or user identifier, which identifies the source of the detected beacon signal.  
         [0109]     Generated first signal information, e.g., generated beacon signal information  1152  corresponds to the first signal generated by first signal generation module  1126  and includes, e.g., information defining a beacon signal burst including, e.g., beacon symbol tone identification information, null tone identification information, beacon burst duration information, and beacon burst timing information.  
         [0110]     User data to be transmitted  1154  includes, e.g., voice, other audio data, image data, text, and/or file data intended for a peer to be communicated under the control of user data transmission control module  1132 , e.g., at the appropriate time, e.g., during a user data interval, in an implemented timing structure. Detected response information from peer  1156  is an output of response detection module  1134 .  
         [0111]     System data/information  1158  includes timing/frequency structure information  1160 , beacon encoding information  1168 , and beacon decoding information  1170 . Timing/frequency structure information  1160  includes frequency bands&#39; information  1162 , time periods&#39; information  1164  and time periods&#39; relationship information  1166 .  
         [0112]      FIG. 12  is a drawing of a flowchart  1200  of an exemplary method of operating a wireless communications device in accordance with various embodiments. The wireless communications device is, e.g., a portable wireless terminal such as a mobile node which may be operated using battery power. The wireless communications device is, e.g., wireless terminal  1300  of  FIG. 13 . Operation starts in step  1202 , where the wireless communications device is powered on and initialized and proceeds to step  1204 . In step  1204 , the wireless communications device receives at least a portion of a beacon signal including at least one beacon symbol from another communications device. Operation proceeds from step  1204  to step  1206 . In step  1206 , the wireless communications device makes a signal transmission decision based on priority information communicated by said received beacon signal portion. The priority information indicates, e.g., one of a device priority, user priority and session priority.  
         [0113]     Priority information may be, and sometimes is, coded using a plurality of beacon symbols included in said beacon signal portion. In some such embodiments, priority information is coded at least partially by positions of beacon symbols in a set of beacon symbol transmission units used to communicate said beacon signal portion. In some embodiments, priority information is coded at last partially based on changes in beacon symbol positions in a set of beacon symbol transmission units used to transmit said beacon signal portion over a time period including multiple beacon symbol transmission time periods. In some such embodiments, the beacon symbol transmission units in a set of beacon symbol transmission units correspond to a predetermined tone hopping pattern corresponding to the priority level to be communicated. In various embodiments, a unique beacon symbol pattern is used to communicate a top priority beacon indicating a higher priority than all other beacons used to communicate priority information.  
         [0114]     In some embodiments, making a transmission decision includes deciding not to transmit user data when said priority information indicates a higher priority than a priority associated with said wireless communications device. In some embodiments, making a transmission decision includes deciding to transmit user data when said priority information indicates a lower priority than a priority associated with said wireless communications device.  
         [0115]     Making a transmission decision may, and sometimes does, include deciding to transmit user data at a transmission power level which is determined as a function of the received priority level and a received power level of the received beacon signal portion. In some embodiments, the transmission power level of the wireless communications device is reduced when the received beacon signal portion indicates a higher priority level than a priority Level indicated by a previously received beacon signal portion that was used to control transmission power. In some embodiments, the transmission power level of the wireless communications device is reduced when the received beacon signal portion indicates a lower priority level than a priority level indicated by a previously received beacon signal portion that was used to control transmission power.  
         [0116]     Next, in step  1208 , operation proceeds differently depending upon the signal transmission decision of step  1206 . If the signal transmission decision indicates that user data should be transmitted, then operation proceeds from step  1208  to step  1210 . If the signal transmission decision indicates that user data should not be transmitted, then operation proceeds from step  1208  to step  1204 , where the wireless communications device is operated to receive another at least a portion of a beacon signal including at least one beacon symbol.  
         [0117]     In step  1210 , the wireless communications device is operated to transmit at least a portion of beacon symbol e.g., a beacon signal burst or a plurality of beacon signal bursts. In various embodiments, the transmitted portion of a beacon signal identifies at least one of said wireless communications device and a user that is using said wireless communications device to transmit user data. In some embodiments, the transmitted beacon signal portion communicates priority information corresponding to said wireless communications device. Operation proceeds from step  1210  to step  1212 . In step  1212 , the wireless communications transmits user data. Operation proceeds from step  1212  to step  1214 .  
         [0118]     In step  1214 , the wireless communications device monitors for an additional signal portion including at least one beacon symbol, e.g., said additional signal portion being a portion of a beacon symbol that communicates a higher priority than the priority associated with the wireless communications device. Operation proceeds from step  1214  to step  1216 . In step  1216 , the wireless communications device determines if said additional portion was received during a predetermined period of time.  
         [0119]     IF it is determined that said additional portion was not received then operation proceeds from step  1216  to step  1218 , where the wireless communications device transmits a signal. Operation proceeds from step  1218  to step  1214  for additional monitoring for another predetermined period of time.  
         [0120]     Returning to step  1216 , if it is determined that said additional portion was not received then operation proceeds from step  1216  to step  1204 , where the wireless communications device is operated to receive another at least a portion of a beacon symbol including at least one beacon symbol.  
         [0121]      FIG. 13  is a drawing of an exemplary wireless terminal  1300 , e.g., mobile node, implemented in accordance with various embodiments. Exemplary wireless terminal  1300  may be any of the exemplary wireless terminals ( 102 ,  104 ) of system  100  of  FIG. 1 .  
         [0122]     Exemplary wireless terminal  1300  includes a receiver module  1302 , a transmitter module  1304 , a processor  1306 , user I/O devices  1308 , and memory  1310  coupled together via a bus  1312  over which the various elements may interchange data and information. Memory  1310  includes routines  1314  and data/information  1316 . The processor  1306 , e.g., a CPU, executes the routines  1314  and uses the data/information  1316  in memory  1310  to control the operation of the wireless terminal  1300  and implement methods.  
         [0123]     Receiver module  1302 , e.g., an OFDM receiver, is coupled to receive antenna  1303  via which the wireless terminal receives signals from other wireless communications devices. Receiver module  1302  receives signals from other communication devices including at least a portion of a beacon signal including at least one beacon symbol. Received signals include beacon signals and user data signals from peer nodes.  
         [0124]     Transmitter module  1304 , e.g., an OFDM transmitter, is coupled to transmit antenna  1305 , via which the wireless terminal transmits signals to other wireless communications devices, e.g., peer nodes. In some embodiments, the same antenna is used for receiver module  1302  and transmitter module  1304 , e.g., in conjunction with a duplex module. Transmitter module  1304  transmits signals including beacon signal portions and user data in accordance with decisions of the signal transmission decision module  1322 . In various embodiments, the transmitted portion of a beacon signal including at least one beacon symbol identifies at least one of: i) wireless communications device  1300  and ii) a user that is using wireless terminal  1300  to transmit user data.  
         [0125]     User I/O devices  1308  include, e.g., microphone, keypad, keyboard, switches, camera, speaker, display, etc. User I/O devices  1308  allow a user of wireless terminal  1300  to input data/information access output data/information, and control at least some functions of the wireless terminal  1300 , e.g., attempt to establish a peer-to-peer communication session.  
         [0126]     Routines  1314  include communications routines  1318  and wireless terminal control routines  1320 . The communications routines  1318  implement various communications protocols used by the wireless terminal  1300 . Wireless terminal control routines  1320  include a transmission decision module  1322 , a beacon signal generation module  1324 , a monitoring module  1326 , a control module  1328 , a transmission power control module  1330 , and a beacon signal information detection module  1332 .  
         [0127]     Transmission decision module  1222  makes a signal transmission decision based on priority information communicated by the received beacon signal portion. The priority information indicates, e.g., one of a device priority, a user priority and a session priority. Transmission decision module  1322  includes a priority based control module  1334 . Priority based control module  1334  prevents transmission of user data when the received priority information indicates a higher priority than a priority associated with said wireless terminal  1300 . In various embodiments, the priority based control module  1334  enables user data transmissions when the received priority information indicates a lower priority than a priority associated with the wireless terminal  1300 .  
         [0128]     Beacon signal generation module  1324  generates beacon signal portions, a generated beacon signal portion including at least one beacon symbol. Some beacon signal portions are referred to a beacon burst signals.  
         [0129]     Control module  1328  controls monitoring module  1326  to monitor for an additional beacon signal portion including at least one beacon symbol following the transmission decision module  1322  making a signal transmission decision. In some embodiments, if an additional beacon signal portion communicating a higher priority than said priority associated with wireless terminal  1300  is not received in a predetermined period of time, the transmission decision module  1322  makes a decision to transmit a signal.  
         [0130]     Transmission power control module  1330  controls a user data transmission power level as a function of at least one of the received priority level and a received power level of the received beacon signal portion. Transmission power control module  1330  includes a transmission power reduction module  1336 . Transmission power reduction module  1336  reduces the transmission power level when the received beacon signal portion indicates a higher priority than a priority level indicated by a previously received beacon signal portion that was used to control transmission power.  
         [0131]     Beacon signal information detection module  1332  determines priority information from a set of beacon symbols included in a received beacon signal portion, said priority information being encoded over a plurality of beacon symbols. In some embodiments, the priority information is coded at least partially by positions of beacon symbols in a set of beacon symbol transmission units used to transmit a beacon signal portion. In various embodiments, the priority information is coded at least partially based on changes in beacon symbol positions in a set of beacon symbol transmission units used to transmit a beacon signal portion. In some embodiments, the priority information is coded at least partially based on changes in beacon symbol positions in a set of beacon symbol transmission units used to transmit a beacon signal portion over a period of time including multiple beacon symbol transmission time periods. In various embodiments, the beacon symbol positions a set of beacon symbol transmission units correspond to a predetermined tone hopping pattern corresponding to the priority level to be communicated in some embodiment, a unique beacon symbol pattern is used to communicate a top priority indicating a higher priority than all other beacons used to communicate priority information.  
         [0132]     Data/information  1316  includes received beacon signal portion information (received beacon signal port  1  information  1338 , . . . , received beacon signal portion N information  1340 ), transmission decision information  1342 , user data to be transmitted  1344 , current priority associated with the wireless terminal  1346 , user data transmission power level information  1348 , priority level information associated with the received beacon signal portions (priority associated with received beacon signal portion  1   1350 , . . . , priority associated with received beacon signal portion N  1352 ), generated beacon signal portion information  1354 , and beacon signal decoding information  1356 .  
         [0133]     Received beacon signal portion  1  information  1338  includes beacon symbol information  1358  and priority information  1360 . Priority information  1370  includes at least one of device priority information  1362 , user priority information  1364 , and session priority information  1366 .  
         [0134]     Received beacon signal portion N information  1340  includes beacon symbol information  1368  and priority information  1370 . Priority information  1360  includes at least one of device priority information  1372 , user priority information  1374 , and session priority information  1376 .  
         [0135]     Transmission decision  1342  is an output of transmission decision module  1322 , indicating whether or not WT  1300  is permitted to transmit. User data to be transmitted  1344  is, e.g., voice, other audio data, image data, text data, file data, etc. that WT  1300  intends to transmit to a peer in a peer-peer communications session, if authorized.  
         [0136]     Current priority associated with the wireless terminal  1346  indicates the current priority level associated with WT  1300 , used by priority based control module  1334  for comparisons. In some embodiments, the current priority of a wireless terminal can, and sometimes does change over times, e.g., as a function of session information and/or user identification information.  
         [0137]     Priority associated with received beacon signal portion  1   1350  and priority associated with received beacon portion N  1352  correspond to received beacon signal portions ( 1338 , . . . , 1340 ) respectively, and are used by transmission decision module  1322 .  
         [0138]     Generated beacon signal portion information  1354 , e.g., information corresponding to a beacon signal burst including a set of beacon symbols and a set of intentional nulls, is an output of beacon signal generation module  1324 .  
         [0139]     User data transmission power level information  1348  includes power level adjustment information  1378 , e.g., information indicating an amount of power reduction to be implemented in response to a beacon signal detected of higher priority.  
         [0140]     Beacon signal decoding information  1356  includes beacon symbol position information  1380  and tone hopping pattern/priority level information  1382 . Beacon signal decoding information  1356  is used by beacon signal information detection module  1332  when processing beacon symbol information, e.g., info  1358 , of one or more received beacon signal portion to obtain priority information being conveyed by the beacon signals, e.g. one or more of device priority information  1362 , user device priority information  1364 , and session priority information  1366 .  
         [0141]     While described in the context of an OFDM TDD system, the methods and apparatus of various embodiments are applicable to a wide range of communications systems including many non-OFDM, many non-TDD systems, and/or many non-cellular systems.  
         [0142]     In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods, for example, generating a beacon signal, transmitting a beacon signal, receiving beacon signals, scanning for beacon signals, recovering information from received beacon signals, determining a timing adjustment, implementing a timing adjustment, changing a mode of operation, initiating a communication session, comparing priority levels of user beacon signals, determining path loss, determining a reference from a fixed location beacon transmitter, etc. In some embodiments various features are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, various embodiments are directed to a machine-readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above-described method(s).  
         [0143]     Numerous additional variations on the methods and apparatus described above will be apparent to those skilled in the art in view of the above descriptions. Such variations are to be considered within scope. The methods and apparatus of various embodiments may be, and in various embodiments are, used with CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes. In some embodiments the access nodes are implemented as base stations which establish communications links, with mobile nodes using OFDM and/or CDMA. In various embodiments the mobile nodes are implemented as notebook computers, personal data assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of various embodiments.