Abstract:
Methods and apparatus for determining, e.g., selecting, communications resources, e.g., tones, to use in a communications system are described. The methods are well suited for use in Orthogonal Frequency Division Multiplexing (OFDM) systems. Devices seeking to transmit information select tones in pairs for use in transmitting the information. Each tone pair includes a tone and the corresponding image tone. By restricting a communications device to select communications frequencies in pairs, the problem of interference and reduced dynamic range at a receiver due to IQ imbalance is reduced, as compared to the case where devices may use a tone independent of the corresponding image tone for transmission purposes, since the path loss from the transmitter to the receiver is likely to be the same for both tones and the transmission power level is controlled by an individual device using both of the tones.

Description:
FIELD 
       [0001]    Various embodiments relate to wireless communications, and more particularly, to methods and apparatus for determining, e.g., selecting, communications resources, e.g., tones, to use for transmission purposes. 
       BACKGROUND 
       [0002]    In an OFDMA (Orthogonal Frequency Division Multiple Access) based system, the system frequency-time resources are often divided into small resource units which can be assigned to multiple different devices for transmission purposes. The smallest resource unit usually occupies one tone in the frequency domain and one OFDM-symbol in the time domain. Which tones devices in a communications system use for transmission purposes can have a significant effect on interference, e.g., interference caused by In-phase and Quadrature phase signal imbalance. 
         [0003]    In-phase (I) and Quadrature phase (Q) signal imbalance, commonly referred to as IQ imbalance, occurs when the In-phase and Quadrature components are not fully symmetric, e.g., either in phase or in amplitude. IQ imbalance typically occurs both at the transmitter and at the receiver. In the case of single-tone transmissions by a transmitter, the IQ imbalance manifests itself as an image tone at frequency fc−f when an intended signal is sent at frequency fc+f by a transmitter, where f C  is the frequency of the carrier signal used to modulate the baseband tone f. The image tone at frequency fc−f is an interference signal generated by the transmitter transmitting on tone fc+f. In other words, part of the energy transmitted on tone fc+f leaks to tone fc−f at the receiver. Due to the existence of this leakage, signaling or the traffic transmission in the system using frequency (fc−f), potentially transmitted from another communication device, can be corrupted. Although the leakage caused by the image tone may appear at a strength which is considerably lower than the signal on the original tone (fc+f), it can still be of considerable strength when compared to other transmissions on tone (fc−f), especially when the transmission on tone fc−f comes from another transmitter. If the problems caused by the image tone are left unmitigated, the achievable reliability of decoding/detection of signals may, and often is, reduced at a device trying to receive data on the image tone frequency. As we have discussed, this effect is more pronounced when the two baseband frequencies, e.g., (f, and −f) are simultaneously used by two different devices which are transmitting on the corresponding passband frequencies (fc+f and fc−f). 
         [0004]    Consider a communications network  100  illustrated in  FIG. 1 . The network  100  includes a number of mobile wireless terminals including WT  1   102 , WT  2   104 , WT  3   106 , WT  4   108  and WT  5   110 . The wireless terminals  102  and  104  have an established communications link (WT  1   102  to WT  2   104 ). WT  1   102  transmits information to WT  2   104  using a frequency fc−f. However there is another simultaneous communications session going on where WT  4   108  transmits information to WT  3   106  using frequency fc+f over another communications link (WT  4   108  to WT  3   106 ). The WT  4   108  is physically in closer proximity of WT  2   104  than the WT  1   102 . In such a scenario, the image frequency of fc+f appears at “fc−f” (at the receiving WT  2   104 ) and may strongly damage the information signal detection capability of WT  2   104 . Furthermore, if WT  4   108  is much closer to WT  2   104  than WT  1   102  as shown in  FIG. 1 , e.g., with the pathloss from WT  4   108  to WT  1   102  being lower, the received signal due to the image tone generated by WT  4   108  can be comparable in strength or stronger than the information signal from WT  1   102  transmitted to WT  2   104  on the same tone (fc−f). 
         [0005]    The interference caused by the image tones often results in a degradation of received signal quality at a receiver device WT  2   104 , as the signals at any given frequency can be hidden under interference signals due to the existence of image tones from signals transmitted by unintended transmitters. In a system with a centralized controller, such as a cellular system where a base station or system controller controls tone assignments, interference can be mitigated by controlling the transmit power of different signals at different tones by taking into consideration the interference which will be caused by the assignment of tones to particular devices in the overall system. 
         [0006]    In an ad hoc network, a centralized controller which controls tone assignments and transmit power in the system is normally lacking and the problem of interference due to the generation of image tones can be significant. Thus, it should be appreciated that the problem of interference caused by I/Q imbalance can be more damaging in an ad hoc network due to the arbitrary location of wireless terminals and lack of the central coordination device such as a base station. 
         [0007]    In view of the above, it should be appreciated that there is a need for methods and apparatus that allow for the determination of what communications resources, e.g., tones, should be used that would reduce, avoid or mitigate the problem of dynamic range reduction at receivers due to interference caused by the generation of image tones. It would be desirable if the methods and/or apparatus were suitable for use in ad hoc networks where a centralized controller is not available for controlling tone allocation to different devices in the system. 
       SUMMARY 
       [0008]    Methods and apparatus for determining, e.g., selecting, communications resources to use in a communications system are described. The communications resources maybe, e.g., frequencies in the form of tones. The methods and apparatus are well suited for use in Orthogonal Frequency Division Multiplexing (OFDM) systems where information may be transmitted on OFDM tone-symbols. In such a system a transmitted OFDM symbol may include signal energy placed on various tone-symbols in the OFDM symbol where the tone-symbols correspond to tones selected for use by the communications device. 
         [0009]    In accordance with one embodiment, devices seeking to transmit information select tones in pairs for use in transmitting the information. Thus, when a transmitting device selects a frequency of a tone to use for transmission purposes it also selects the frequency of the corresponding image tone to use. Individual devices select one or more tone pairs to use for communications purposes. By restricting a communications device to selecting communications frequencies in pairs, e.g., a tone and its image tone, the problem of interference and reduced dynamic range at a receiver due to IQ imbalance is reduced as compared to the case where devices may use a tone independent of the corresponding image tone for transmission purposes. Since a single device uses both the tone and the image tone, the risk that the leakage from the signal transmitted on the tone to the image tone will overwhelm the signal transmitted on the image tone frequency is avoided since the path loss from the transmitter to the receiver is likely to be the same for both tones and the transmission power level is controlled by an individual device using both of the tones. 
         [0010]    In various embodiments, communications devices communicate, e.g., transmit/receive, on a set of communications resources, e.g., OFDM tones or frequencies, available in an OFDM symbol. The frequencies are used in pairs. 
         [0011]    Nearby devices prefer, and commonly do, use different tone pairs for communications to avoid interference between each other. In some embodiments where a centralized controller does not exist, e.g., ad hoc embodiments, different devices select frequencies, e.g., tone-symbols, to use for communications purposes in a distributed manner. In accordance with one feature of various embodiments, in order to prevent or reduce the possibility of an image tone (e.g., −f 1 ) appearing stronger than an intentionally transmitted signal at the frequency (f 1 ) as noted above tone selection is made by selecting pairs of tone frequencies to use, e.g. frequencies (f 1  and −f 1 ) are treated as a tone pair and a device selects the pair of frequencies to use for transmission purposes. In such an embodiment the transmitting device will transmit information using both frequencies f 1  and −f 1  during a given transmission time period, e.g., by transmitting on tones corresponding to (fc+f 1  and fc−f 1 ), where fc is the carrier frequency, during the same symbol transmission time period. 
         [0012]    The principle of selecting a frequency tone and its image frequency tone as a resource allocation unit in wireless networks may apply to both control channels and data transmission channels. In some embodiments, multiple transmitters are only allowed to transmit in the control channels, e.g., paging channel, peer discovery channel and connection scheduling channels. In this case, each device only has to select frequency resources based on the frequency pair unit in control channels. An exemplary method for selection is to let each device first monitor the usage of tone-pairs in its interference neighborhood. A device will pick the tone-pair which is not being used by any other device (or connection) in its neighborhood to avoid collision. 
         [0013]    An exemplary method of operating a wireless communications device, in accordance with some embodiments, comprises: determining, e.g., selecting, a first set of frequency pairs in a first OFDM symbol to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency; and transmitting information in said first OFDM symbol using only said determined first set of frequency pairs. As should be appreciated, the first set of frequency pairs may include a singe pair of frequencies. However, in cases where a significant amount of data is to be transmitted the first set of frequency pairs may include multiple pairs of frequencies. In some embodiments where multiple frequency pairs are selected, some frequency pairs which are not selected may be interspaced in terms of frequency with the selected frequency pairs. Thus it should be appreciated that while frequency pairs may comprise sets of adjacent tones above the carrier frequency and below the carrier frequency, all of the tones need not be adjacent in terms of frequency. 
         [0014]    An exemplary wireless communications device, in accordance with some embodiments, comprises at least one processor configured to: determine, e.g., select, a first set of frequency pairs in a first OFDM symbol to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency, and transmit information in said first OFDM symbol using only said determined first set of frequency pairs. 
         [0015]    While described in the context of an ad hoc network, it should be appreciated that the frequency pair based tone selection method may be employed in system with centralized controllers and/or other types of systems as well. 
         [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 of various embodiments are discussed in the detailed description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0017]      FIG. 1  is a drawing of a wireless communications system. 
           [0018]      FIG. 2  illustrates a communications system in accordance with one exemplary embodiment. 
           [0019]      FIG. 3  illustrates exemplary air link communications resources which can be used to communicate information. 
           [0020]      FIG. 4  illustrates an exemplary OFDM symbol including plurality of tone-symbols, in accordance with an exemplary embodiment. 
           [0021]      FIG. 5  illustrates another exemplary OFDM symbol including various tone-symbols, in accordance with an exemplary embodiment. 
           [0022]      FIG. 6  is a flowchart illustrating an exemplary communications method in accordance with an exemplary embodiment. 
           [0023]      FIG. 7  is a drawing illustrating an exemplary peer to peer communications device, implemented in accordance with one exemplary embodiment. 
           [0024]      FIG. 8  illustrates an assembly of modules which can, and in some embodiments is, used in the wireless communications device illustrated in  FIG. 7 . 
           [0025]      FIG. 9  illustrates an exemplary OFDM time frequency grid showing time-frequency resources, where tone hopping is used, in accordance with one exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 2  illustrates an exemplary wireless peer to peer communications system  200  in accordance with an exemplary embodiment. Exemplary wireless peer to peer communications system  200  includes a plurality of wireless communications devices (device  1   202 , device  2   204 , device  3   206 , device  4   208 , device  5   210 , device  6   212 , device  7   214 , . . . , device N  218 . Some of the wireless communications devices in system  200 , e.g., device  5   210 , include an interface  222 , to the Internet and/or other network nodes. Some of the wireless communications devices in system  200 , e.g., device  1   202 , device  2   204 , device  3   206 , device  4   208 , device  6   212 , device  7   214 , and device N  218 , are mobile wireless communications devices, e.g., handheld mobile devices. 
         [0027]    The communications devices ( 202 ,  204 ,  206 ,  208 , . . . ,  218 ) support various signaling between peers, e.g., peer discovery signals, pilot signals, transmission request signals, etc., and data transmissions between peers. 
         [0028]      FIG. 3  is a drawing  300  illustrating exemplary communications resources, e.g., time-frequency resources, which can be used, for example, to communicate information by one or more devices in the system  200 . Consider an exemplary embodiment of a frequency division multiplexing system, e.g., an OFDM system. In one such system, information may be transmitted in a symbol-by-symbol manner. In one such embodiment during a symbol transmission period, available bandwidth (frequency) is divided into a number of tones, each of which can be used to carry information. 
         [0029]    In  FIG. 3 , the horizontal axis  301  represents time and the vertical axis  311  represents frequency. A vertical column represents an OFDM symbol having a duration corresponding to one symbol transmission time period. A plurality of OFDM symbols, e.g., a first OFDM symbol  312 , second OFDM symbol  314 , and OFDM symbol  320  are shown. Each of the OFDM symbols includes multiple tones (frequencies) corresponding to a given symbol transmission time period. The OFDM symbol transmission time period identified by reference number corresponds to the time used to transmit one OFDM symbol. In some embodiments, an OFDM symbol includes 113 tones. However different embodiments use other number of tones. Each small box  360  represents a tone-symbol, which is the air link resource of a single tone over a symbol transmission time period. Each of the individual tone-symbols  360  is a communications resource and has a frequency and time period associated with it as should be appreciated from the figure. 
         [0030]    Communications devices communicate with each other using one or more communications resources, e.g., the tone-symbols. In an exemplary peer to peer communications system such as system  200 , a pair of peer to peer communications devices which seeks to communicate, monitors communications resources to determine which resources the devices can use for communications purposes, e.g., frequencies not being used by other devices. During the establishment of a communications session, the pair of communications devices agrees on one or more tone-symbols which the communications devices may use for transmitting and receiving information. Thus after determining, the peer communications devices which seek to communicate are aware of the selected tone-symbols or frequencies that they will use for transmitting and/or receiving information from each other. 
         [0031]    In accordance with one aspect, a communications device  202  determines a first set of frequency pairs in a first OFDM symbol to use simultaneously for transmission purposes, the first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency. Said determination may be based on the connection identifier corresponding to the connection between the two peers or the device identifier corresponding to a peer. A pair of peer communications devices (e.g., devices  202 ,  204 ) which seek to communicate may get the same connection identifier, and thus such a pair of communications devices would know the frequency pairs on which to transmit or receive form each other. In some other embodiments device  1   202  determines the set of frequency pairs to use simultaneously for transmission, and communicate the identification information regarding the determined set of frequency pairs to the device  2   204  so that the peer device  2   204  may know where to receive the information transmitted by peer device  1   202 . 
         [0032]      FIG. 4  is used to explain how communications resources, e.g., OFDM tone-symbols, form different frequency pairs.  FIG. 4  illustrates an exemplary OFDM symbol, e.g., first OFDM symbol  400 , and distribution of communications resources therein, e.g., distribution of individual tone-symbols, included in the exemplary OFDM symbol  400 . Although in the  FIG. 4  example, OFDM symbol  400  is discussed as a first OFDM symbol, it should be appreciated that the OFDM symbol  400  can be any one of the OFDM symbols  312 ,  314 , . . . ,  320 , shown in  FIG. 3 . 
         [0033]    As shown in  FIG. 4 , the OFDM symbol  400  includes 113 tone-symbols, e.g., 1 st  tone-symbol  402 , . . . , 113 th  tone symbol  452 . In accordance with one aspect, a frequency pair corresponds to a pair of tone-symbols or tones. A pair of tones include a first tone at first frequency, e.g., fc+f 1 , and another tone at its image frequency, e.g., fc−f 1 , where fc is the carrier signal frequency used to modulate a baseband tone, e.g., f 1 , and thus producing a tone at frequency fc+f 1 . For example, the OFDM symbol  400  includes a first set of frequency pairs  460 , where the first set includes frequency pair (fc+f 1 , and fc−f 1 ). In accordance with one feature of an exemplary embodiment, a communication device can determine a set of frequency pairs such as the first set frequency pairs  460  in the OFDM symbol  400 , to use simultaneously for transmission purposes. In  FIG. 4  cross hatching is used to indicate frequency pairs included in the first set of frequency pairs  460 . The remaining tone-symbols in the OFDM symbol  400  are not shaded/cross hatched to distinguish them from tone-symbols corresponding to the frequency pairs in the first set  460 . Although in  FIG. 4  example, the first set of frequency pairs  460  is shown to include a single tone-symbol pair which forms the frequency pair (fc+f 1 , and fc−f 1 ) for simplifying the illustration, it should however be appreciated that the first set of frequency pairs  460  may include a plurality of frequency pairs in some embodiments. 
         [0034]      FIG. 5  shows another example illustrating an exemplary OFDM symbol  500 , e.g., a second OFDM symbol, and arrangement of communications resources therein, in accordance with an exemplary embodiment. Although in the  FIG. 5  example, OFDM symbol  500  is discussed as a second OFDM symbol, it should be appreciated that the OFDM-symbol  500  can be any one of the OFDM symbols  312 ,  314 , . . . ,  320 , shown in  FIG. 3 . 
         [0035]    As shown in  FIG. 5 , the exemplary second OFDM symbol  500  includes a plurality of individual tone-symbols. As illustrated, the second OFDM symbol  500  includes 113 tone-symbols, e.g., 1 st  tone-symbol  502 , . . . , 113 th  tone symbol  552 . In the  FIG. 5  example, a set of frequency pairs, e.g., second set of frequency pairs  560 , includes a plurality of tone-symbol pairs, e.g., 3 frequency pairs. The second set of frequency pairs  560  includes a first, a second and a third frequency pair. The first frequency pair having a tone at frequency fc+f 1  and another tone at its image frequency fc−f 1 , the second frequency pair having a tone at frequency fc+f 2  and another tone at its image frequency fc−f 2 , and the third frequency pair in the second set having a third tone at a third frequency fc+f 3  and a fourth tone at a fourth frequency fc−f 3  which is an image frequency of the third frequency. Thus, it should be appreciated that in some embodiments a set of frequency pairs such as second set of frequency pairs  560  can include multiple frequency pairs. It should be further appreciated that in some embodiments a single device determines the frequency pairs included in the second set of frequency pairs  560  to use simultaneously for communications purposes, e.g., for transmitting information to or receiving from a communications peer in a peer to peer communications session. 
         [0036]      FIG. 6  is a flowchart  600  illustrating the steps of an exemplary method of operating a wireless communications device, e.g., a peer to peer mobile node, in accordance with various exemplary embodiments. Although the exemplary wireless communications device could be, e.g., any of the wireless communications devices of peer to peer wireless communications system  200  of  FIG. 2 , however for the purpose of illustration, it is assumed that the wireless communications device is device  1   202 . One or more of the steps in flowchart  600 , indicated by dashed lines, are optional and are performed in some embodiments, while skipped in other embodiments. The exemplary method of flowchart  600  includes determining frequency pairs in an OFDM symbol for use in communications. 
         [0037]    Operation of the exemplary method starts in step  602 , where the wireless communications device is powered on and initialized. Operation proceeds from start step  602  to step  604 . In step  604  the wireless communications device determines a first set of frequency pairs, e.g., first set  460 , in a first OFDM symbol to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency, e.g., fc+f 1 , and a second tone at a second frequency, e.g., fc−f 1 , which is an image frequency of said first frequency. Determining the first set of communications resources, i.e., the frequency pairs, is normally performed as part of a communications establishment session where one or more communications devices monitor communications resources and identify resources which are least affected by interference or noise, for use in communications. Some interference mitigation mechanism and at some level of coordination may be employed in the system to reduce the possibility of two different transmitting devices selecting the same sets of frequencies at the same time. 
         [0038]    In some embodiments during the communications establishment session the communicating peer devices (communications peers) determine and agree on the frequency pairs to be used for communications purposes, e.g., before starting to transmit or receive. In some other embodiments, the communications device  202  communicates information indicating the determined first set of frequency pairs  460  to be used by device  202  simultaneously for transmission, to a communications peer with which the device  202  seeks to communicate. The information indicating the frequency pairs may be, e.g., resource identifiers corresponding to the determined frequency pairs. 
         [0039]    Operation proceeds from step  604  to step  606 . In step  606  the wireless communications device  202  transmits information, e.g., to a communications peer such as communications device  204 , in the first OFDM symbol  400  using only the determined first set of frequency pairs  460 . Operation proceeds from step  606  to step  608 . In step  608  the communications device  202  determines a second set of frequency pairs in a second OFDM symbol, e.g., second set  560 , to use simultaneously for transmitting to or receiving information from a communications peer in a peer to peer communications session, said second set of frequency pairs including a third tone at a third frequency and a fourth tone at a fourth frequency which is an image frequency of said third frequency. In some embodiments step  608  includes step  610  which is performed when tone hopping is implemented. In step  610 , a tone hopping function is used to determine the second set of frequency pairs  560  in the second OFDM symbol  500 . The tone hopping function is, e.g., a predetermined pattern, known to the communications devices in the system  200 . Thus when tone hopping is implemented, the devices in system  200  can determine, using the tone hopping function, how the tones are being hopped from one OFDM symbol to another OFDM symbol. 
         [0040]    In some embodiments the third tone at a third frequency is same as the first tone at the first frequency, and the fourth frequency is same as the second frequency, but in a different OFDM symbol, e.g., the second OFDM symbol. However in some embodiments the third tone at a third frequency is different from the first tone at the first frequency, and the fourth frequency is different from the second frequency. This may occur for example, when tone hopping is implemented and the first tone in the first OFDM symbol  400  is hopped to a third tone at third frequency in the second OFDM symbol, and the second tone in the first OFDM symbol  400  is hopped to a fourth tone at the fourth frequency in the second OFDM symbol. 
         [0041]    Operation proceeds from step  608  which includes step  610 , to step  612 . In step  612  the communications device  202  transmits or receives information in the second OFDM symbol. Step  612  includes steps  614 ,  616  and  618 , at least one of which is performed depending on the embodiment, as part of performing the step  612 . Thus in some embodiments the communications device  202 , in step  614  transmits information in the second OFDM symbol, said information being communicated only on the determined second set of frequency pairs. In some embodiments when step  616  is performed, the device  202  receives information in the second OFDM symbol, said information being communicated only on the determined second set of frequency pairs, e.g., from a peer communications device. Alternatively in some embodiments step  618  is performed wherein the device  202  receives information in the second OFDM symbol, transmitted by a communications peer, the second OFDM symbol including said information only on the determined first set of frequency pairs. For example, step  618  may be performed e.g., when tone hopping is not implemented, and the device  202  receives information on the determined first set of frequency pairs occurring in the second OFDM symbol. Operation proceeds from step  612  back to step  604 . While steps  608  and step  612  are shown in the  FIG. 6  embodiment, these steps may not be used in other embodiments and can therefore be considered optional in at least some embodiments. 
         [0042]      FIG. 7  illustrates an exemplary wireless communications device  700 , in accordance with an exemplary embodiment. Exemplary wireless communications device  700  is, e.g., one of the wireless communications devices of  FIG. 2 . Exemplary communications device  700  may be, and in at least one embodiment is, a mobile wireless terminal supporting peer to peer communications and implementing a method in accordance with flowchart  600  of  FIG. 6 . 
         [0043]    Wireless communications device  700  includes a processor  702  and memory  704  coupled together via a bus  709  over which the various elements ( 702 ,  704 ) may exchange data and information. Communications device  700  further includes an input module  706  and an output module  708  which may be coupled to processor  702  as shown. However, in some embodiments, the input module  706  and output module  708  are located internal to the processor  702 . Input module  706  can receive input signals. Input module  706  can, and in some embodiments does, include a wireless receiver and/or a wired or optical input interface for receiving input. Output module  708  may include, and in some embodiments does include, a wireless transmitter and/or a wired or optical output interface for transmitting output. 
         [0044]    Processor  702  is configured to determine a first set of frequency pairs in a first OFDM symbol to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency, and transmit information in said first OFDM symbol using only said determined first set of frequency pairs. In various embodiments the processor  702  is further configured to receive information in a second OFDM symbol transmitted by a communications peer, said second OFDM symbol including said information only on said first set of frequency pairs. 
         [0045]    The processor  702  is further configured to determine a second set of frequency pairs in a second OFDM symbol to use simultaneously for receiving information from a communications peer in a peer to peer communications session, said second set of frequency pairs including a third tone at a third frequency and a fourth tone at a fourth frequency which is an image frequency of said third frequency, and receive information in said second OFDM symbol, said information being communicated only on said determined second set of frequency pairs. In some embodiments the processor  702  is further configured to use a tone hopping function to determine said second set of frequency pairs. The tone hopping function is, e.g., a predetermined pattern, known to the communications devices in the system  200 . 
         [0046]    The processor  702  in various embodiments is configured to determine a second set of frequency pairs in a second OFDM symbol to use simultaneously for transmitting information to a communications peer in a peer to peer communications session, the second set of frequency pairs including a third tone at a third frequency and a fourth tone at a fourth frequency which is an image frequency of said third frequency, and transmit information in said second OFDM symbol, said information being communicated only on said determined second set of frequency pairs. In some such embodiments the processor  702  is further configured to use a tone hopping function to determine said second set of frequency pairs. 
         [0047]      FIG. 8  illustrates an assembly of modules  800  which can, and in some embodiments is, used in the communications device  700  illustrated in  FIG. 7 . The modules in the assembly  800  can be implemented in hardware within the processor  702  of  FIG. 7 , e.g., as individual circuits. Alternatively, the modules may be implemented in software and stored in the memory  704  of the wireless terminal  700  shown in  FIG. 7 . While shown in the  FIG. 7  embodiment as a single processor, e.g., computer, it should be appreciated that the processor  702  may be implemented as one or more processors, e.g., computers. When implemented in software the modules include code, which when executed by the processor, configure the processor, e.g., computer,  702  to implement the function corresponding to the module. In some embodiments, processor  702  is configured to implement each of the modules of the assembly of modules  800 . In embodiments where the assembly of modules  800  is stored in the memory  704 , the memory  704  is a computer program product comprising a computer readable medium comprising code, e.g., individual code for each module, for causing at least one computer, e.g., processor  702 , to implement the functions to which the modules correspond. 
         [0048]    Completely hardware based or completely software based modules may be used. However, it should be appreciated that any combination of software and hardware (e.g., circuit implemented) modules may be used to implement the functions. As should be appreciated, the modules illustrated in  FIG. 8  control and/or configure the wireless terminal  700  or elements therein such as the processor  702 , to perform the functions of the corresponding steps illustrated and/or described in the method of flowchart  600  of  FIG. 6 . 
         [0049]    The assembly of modules  800  includes a module corresponding to each step of the method of flowchart  600  shown in  FIG. 6 . The module in  FIG. 8  which performs or controls the processor  702  to perform a corresponding step shown in flowchart  600  is identified with a number beginning with an 8 instead of beginning with 6. For example module  804  corresponds to step  604  and is responsible for performing the operation described with regard to step  604 . Assembly of modules  800  includes a module  804  for determining a first set of frequency pairs in a first OFDM symbol, e.g., first set  460 , to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency, a module  806  for transmitting information in said first OFDM symbol using only said determined first set of frequency pairs. 
         [0050]    The assembly of modules  800  further includes a module  808  for determining a second set of frequency pairs in a second OFDM symbol to use simultaneously for transmitting to or receiving information from, a communications peer in a peer to peer communications session, said second set of frequency pairs including a third tone at a third frequency and a fourth tone at a fourth frequency which is an image frequency of said third frequency. In some embodiments the module  808  further includes a module  810  for using a tone hopping function to determine the second set of frequency pairs. In some embodiments the information regarding the tone hopping function may be, e.g., stored in the memory of the communications device  700 . 
         [0051]    The assembly of modules  800  further includes a module  812  for transmitting or receiving information in the second OFDM symbol. The module  812  can be implemented, e.g., as a transceiver module. The module  812  includes a module  814  for transmitting information in the second OFDM symbol, said information being communicated only on the determined second set of frequency pairs, a module  816  for receiving information in the second OFDM symbol, said information being communicated only on the determined second set of frequency pairs, and a module  818  for receiving information in the second OFDM symbol, transmitted by a peer communications device, said second OFDM symbol including said information only on said determined first set of frequency pairs. 
         [0052]    The modules shown in dashed line boxes, e.g., modules  814 ,  816 ,  818 , are optional, and thus one or more of these modules may be present in some embodiments while not in others. The dashed boxes indicate that although these modules are included in the assembly of modules  800  in various embodiments, the processor  702  may execute such an optional module in embodiments where the step to which these modules correspond, is performed. In some embodiments, one or more modules shown in  FIG. 8  which are included within another module may be implemented as an independent module or modules. 
         [0053]      FIG. 9  is a drawing  900  illustrating an exemplary OFDM channel represented as a time frequency grid, including time-frequency resources, where the tone hopping is implemented, in accordance with a tone hopping function. As shown horizontal axis  901  represents time and the vertical axis  911  represents frequency. Each vertical column represents an OFDM symbol having a duration corresponding to one symbol transmission time period. As discussed with regard to  FIG. 3  example, during a symbol transmission period, available bandwidth (frequency) is divided into a number of tones (each small box represents a tone-symbol), each of which can be used to carry information. 
         [0054]    In accordance with various embodiments a device determines a first set of frequency pairs  950  (tone-symbol pairs) in a first OFDM symbol, e.g., symbol  912 , to use simultaneously for transmission purposes, said first set of frequency pairs including a first tone at a first frequency and a second tone at a second frequency which is an image frequency of said first frequency. When frequency hopping is used in the system, in accordance with various embodiments, a determined set of frequency pairs hops with time from symbol to symbol. Thus in some such embodiments, to determine a second set of frequency pairs in a second OFDM symbol, e.g., second set  960  in OFDM symbol  916 , to use simultaneously for transmitting to or receiving information from a communications peer in a peer to peer communications session, the device uses a tone hopping function to determine said second set of frequency pairs  960 . The second set of frequency pairs  960  includes a third tone at a third frequency and a fourth tone at a fourth frequency which is an image frequency of said third frequency. In some embodiments the tone hopping function is known to the devices in the system  200 . It should be appreciated that the frequency hopping pattern shown in the  FIG. 9  is just exemplary, and various other variations of the frequency hopping pattern according to different frequency hopping functions being used, are possible. 
         [0055]    In accordance with various features, in a communications system such as system  200  where devices identify and use available frequency resources for communications purposes, the following measures, in some embodiments, are taken: 
         [0056]    1. When a band of frequencies are selected by a communications device for user, a tone and its image tone are selected together by the same communications device. 
         [0057]    2. In a frequency hopped system where the frequency is hopped with time, the image frequency is also synchronously hopped with the original tone. 
         [0058]    The techniques of various embodiments may be implemented using software, hardware and/or a combination of software and hardware. Various embodiments are directed to apparatus, e.g., mobile nodes such as mobile terminals, base stations, communications system. Various embodiments are also directed to methods, e.g., method of controlling and/or operating mobile nodes, base stations and/or communications systems, e.g., hosts. Various embodiments are also directed to machine, e.g., computer, readable medium, e.g., ROM, RAM, CDs, hard discs, etc., which include machine readable instructions for controlling a machine to implement one or more steps of a method. 
         [0059]    It is understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged while remaining within the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
         [0060]    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, frequency pair determination, signal transmission and/or reception steps. Thus, 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). Some embodiments are directed to a device, e.g., communications node, including a processor configured to implement one, multiple or all of the steps of one or more exemplary methods. 
         [0061]    In some embodiments, the processor or processors, e.g., CPUs, of one or more devices, e.g., communications nodes such as access nodes and/or wireless terminals, are configured to perform the steps of the methods described as being performed by the communications nodes. The configuration of the processor may be achieved by using one or more modules, e.g., software modules, to control processor configuration and/or by including hardware in the processor, e.g., hardware modules, to perform the recited steps and/or control processor configuration. Accordingly, some but not all embodiments are directed to a device, e.g., communications node, with a processor which includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. In some but not all embodiments a device, e.g., communications node, includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. The modules may be implemented using software and/or hardware. 
         [0062]    Some embodiments are directed to a computer program product comprising a computer-readable medium, e.g., a non-transitory computer-readable medium, comprising code for causing a computer, or multiple computers, to implement various functions, steps, acts and/or operations, e.g. one or more steps described above. Depending on the embodiment, the computer program product can, and sometimes does, include different code for each step to be performed. Thus, the computer program product may, and sometimes does, include code for each individual step of a method, e.g., a method of controlling a communications device or node. The code may be in the form of machine, e.g., computer, executable instructions stored on a computer-readable medium such as a RAM (Random Access Memory), ROM (Read Only Memory) or other type of storage device. In addition to being directed to a computer program product, some embodiments are directed to a processor configured to implement one or more of the various functions, steps, acts and/or operations of one or more methods described above. Accordingly, some embodiments are directed to a processor, e.g., CPU, configured to implement some or all of the steps of the methods described herein. The processor may be for use in, e.g., a communications device or other device described in the present application. 
         [0063]    While described in the context of an OFDM system, at least some of the methods and apparatus of various embodiments are applicable to a wide range of communications systems including many non-OFDM and/or non-cellular systems. 
         [0064]    Numerous additional variations on the methods and apparatus of the various embodiments described above will be apparent to those skilled in the art in view of the above description. Such variations are to be considered within the scope. The methods and apparatus 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 communications devices. In some embodiments one or more communications devices are implemented as access points which establish communications links with mobile nodes using OFDM and/or CDMA and/or may provide connectivity to the internet or another network via a wired or wireless communications link. 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.