Patent Document

PRIORITY CLAIM 
       [0001]    The present application is a continuation of, and claims the benefit of priority from, co-pending U.S. patent application Ser. No. 10/965,011 filed on Oct. 14, 2004, entitled “ENHANCED BEACON SIGNALING METHOD AND APPARATUS”, which is commonly assigned, and fully incorporated herein by reference for all purposes. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention is related to communications systems, and more particularly, to methods and apparatus for transmitting information in a multi-user communications system. 
       BACKGROUND 
       [0003]    Multiple access communications systems are common today. In such systems, multiple devices, e.g., wireless terminals, may have the ability to communicate with a base station at the same time. Multiple access communication systems are often implemented as cellular systems, where each cell normally corresponds to the coverage area of a single base station. Cells may include one or more different sectors. In sectorized cases, base stations often include different transmitters for different sectors. In addition, different sectors may use the same or different carrier frequencies. 
         [0004]    Spread spectrum OFDM (orthogonal frequency division multiplexing) multiple access, is one example of a spectrally efficient wireless communications technology. OFDM can be used to provide wireless communication services. In OFDM spread spectrum system, the total spectral bandwidth is normally divided into a number of orthogonal tones, e.g. subcarrier frequencies. In a cellular network, the same bandwidth is often reused in all the cells of the system. 
         [0005]    In various multiple access communications systems, there is a need to communicate transmitter information to wireless terminals, e.g., information indicating the carrier used by a particular transmitter, cell identification information, and/or sector identification information. While transmitting such information at extremely high power can increase the chance of detection of the transmitted information, it can lead to excessive and/or unnecessary interference, e.g., in cells or sectors several cells away from the transmitter. Dedicating huge amounts of power to transmitting transmitter information signals can also limit the amount of data that can be transmitted in a system since power allocated to transmitting the transmitter information signals may not be available for transmitting user data, e.g., text, video or speech data. 
         [0006]    In view of the above discussion, it should be appreciated there is a need for methods and apparatus directed to the problem of communicating transmitter information in a reliable and easy to detect manner while limiting the amount of signal interference generated by signals used to transmit such information and also balancing the need to allocate power to such transmission with the importance of allocating power to the transmission of user data. 
       SUMMARY 
       [0007]    The present invention is directed to methods and apparatus for implementing a communications system, e.g., an OFDM communications system, where it is important to transmit transmitter information, e.g., transmitter cell, sector and/or carrier frequency information, in addition to transmitting user data. In accordance with the present invention, narrowband, relatively high power tones are used to transmit transmitter information. These signals will be referred to herein as beacon signals. Beacon signals are transmitted using several times the transmission power used to transmit other signals, e.g. user data, communications segment assignment information, etc. In accordance with some embodiments of the present invention, beacon signals differ in per-tone power from non-beacon signals by at least a multiple of the per tone power level of the signal transmitted with the next highest transmission power level. That is, beacon signals in accordance with the present invention are transmitted with N times the power of the next highest power signal that is transmitted by the transmitter used to transmit the beacon signals, where N may be at least 10, 20, 30, 40 or more. 
         [0008]    By maintaining a relative difference in average per tone signal energy of user data and/or other control signals to the average per tone energy of a beacon signal, e.g., a difference of 20, 30, 40 or more times, the probability that a beacon signal which is the transmitted as the higher power signal can be detected reliably will be several times the probability of the data or other control signals being detected. This approach provides a high probability of beacon signal detection while avoiding having to put all or 80% or more of the available transmission power into a beacon signal. The transmission power that is not put into the beacon signal can, and in various embodiments is, used to transmit user data in parallel with the beacon signal. Thus, user data may receive more than 20% and sometimes more than even 40% or 60%, of a transmitter&#39;s maximum possible transmission power during a period, e.g., single symbol transmission period, in which a beacon signal, e.g., beacon tone, is transmitted in accordance with the invention. 
         [0009]    In accordance with the present invention, each base station sector transmitter transmits signals using a plurality of tones in parallel, e.g., over 10 but sometimes over 20, 100, 1000, or even more tones in parallel. In some embodiments the tones are evenly spaced within the frequency band used by the particular base station sector transmitter. As discussed above, concentrating more power on a tone used to transmit a beacon signal than other tones, e.g., used to transmit user data or other information, transmitting all or the majority of a base station sector&#39;s transmission power on one or more tones which comprise a beacon signal during a single transmission period, e.g., an OFDM symbol transmission period, can be wasteful. The various methods of the invention address this problem by using novel power allocations to beacon signals designed to use power efficiently while providing a high probability of detection. 
         [0010]    In accordance with the present invention, in some embodiments less than 80% of the transmitter&#39;s total available transmission power is put into a beacon signal. In some embodiments of this type, user data is transmitted at the same time as the beacon signal, e.g., using different tones, with more than 20% of the total maximum possible transmission power being allocated to the user data during the transmission of the beacon signal. The beacon signal can be transmitted into the same or a different frequency band from the user data which is transmitted at the same time as the beacon signal. The maximum possible transmission power may correspond to a physical limitation of the transmitter or a set maximum amount of power the transmitter is permitted to use. 
         [0011]    Thus, to make efficient use of the available bandwidth and available transmission power, in accordance with the present invention, in some but not all embodiments during transmission time periods in which a beacon signal is transmitted, more than 20% of the transmitter&#39;s power, and in many cases more than 30%, 40%, 50%, 60% and even sometimes more than 70% of the transmitters total transmission power is allocated to the transmission of user data while one or more tones corresponding to a beacon signal are transmitted. In such a case, where a large number of tones are used, the beacon tone power may still be several times, e.g., 20, 30, 40 or more times the maximum average per tone energy of data tones which occurs in a time period, e.g., a one second time period, which can occur anywhere in a larger 2 second transmission time period, e.g., where the beacon tone may be transmitted in the 2 second time period. 
         [0012]    Such a power allocation to the communication of user data, e.g., voice, text or image data, can be achieved, while meeting the comparatively high transmission power level requirements of a beacon signal, by limiting the number of beacon signals to a relatively small number during any one symbol transmission time period, e.g., to less than ⅕ or even less than 1/20th the number of tones used during a symbol transmission time period. Such an approach is particularly useful in systems which use a large number of tones, e.g., over 100, 500 or even 1000 tones in parallel, e.g., during each symbol transmission time period. In some OFDM embodiments of this type, some user data is transmitted in the form of modulated symbols on tones which are not used to transmit a beacon signal during the time period in which a beacon signal is transmitted. 
         [0013]    Given that the beacon signals are transmitted with relatively high power level, they can be detected using relatively simple to implement energy detection methods even in the case where precise timing and tone synchronization is not maintained between the transmitter of the beacon signal and the receiver of the beacon signal. Accurate detection of transmitted user data, given the lower power level at which it is transmitted, may and often does involve a receiver achieving symbol timing synchronization with the transmitter in terms of symbol timing. 
         [0014]    In various embodiments, the beacon signal is used to communicate transmitter information such as a cell identifier, sector identifier and/or information about a frequency band associated with the transmitter which transmitted the detected beacon signal. Such information is communicated, in most embodiments, by the beacon signal without the need for beacon signal phase to be taken into consideration. 
         [0015]    In some, but not all embodiments, a base station transmitter, e.g., a sector transmitter of a base station transmits a signal in a first period of time, e.g., an OFDM symbol transmission time period, that includes a plurality of signal tones where each signal tone corresponds to a different frequency. In one such embodiment, the transmitted signal includes a beacon signal transmitted on at least one tone and a user data signal transmitted in parallel, e.g., at the same time, with said beacon signal on tones which are not used to transmit said beacon signal. In various embodiments where this method is used the user data is transmitted by the transmitter with an average per tone power less than 1/20 of the transmission power of each tone used to transmit the beacon signal. The beacon signal may be transmitted into the same frequency band as the band used by the transmitter to communicate user data, e.g., text, voice, or images, or into a frequency band used by a transmitter of a neighboring sector or cell for transmitting user data. 
         [0016]    In some embodiments, a method of operating a base station is performed where the method includes the steps of: transmitting first signals into a first region using a set of N tones to communicate information over a first period of time, said first period of time being at least two seconds long, where N is larger than 10 (and in some cases more than 20, 100 or 1000); and transmitting during a second period of time a second signal including a set of X tones into said first region, where X is less than 5 (and where X in some cases is one), and where less than 80% (and in some embodiments less than 60%) of a maximum average total base station transmission power used by said base station transmitter to transmit signals into the first region during any 1 second period during said first period of time is allocated to said set of X tones and each one of said X tones to which power is allocated receives at least 20 times (and sometimes at least 30 or 40 times) the per tone average power allocated to tones during said any one second period. 
         [0017]    Various embodiments of the present invention are also directed to a base station which implements the above described invention. In some exemplary embodiments a base station includes: a transmitter that uses a set of N tones to communicate information into a first region, where N is larger than 10 (and in some cases larger than 20, 99, 1000); a first control module coupled to said transmitter, for controlling the transmitter to transmit over a first period of time using first signals into the first region, said first period of time being at least two seconds long; and a second control module coupled to said transmitter for controlling the transmitter to transmit during a second period of time a second signal including a set of X tones into said first region, where X is a positive integer less than 5 (and in some embodiments 1), and where less than 80% of a maximum average total base station transmission power used by said base station transmitter to transmit into the first region during any 1 second period during said first period of time is allocated to said set of X tones and where each one of said X tones to which power is allocated is at least 20 times (and sometimes at least 30 or 40 times) the per tone maximum average power allocated to tones during any one second time period in said first time period. 
         [0018]    In some embodiments, user data is allocated and transmitted using more than 20%, and in some cases more than 40 or even 60%, of a transmitter&#39;s maximum transmission power while transmitting a beacon signal. For example, a sector transmitter may put 40% of its maximum output transmission power which is permitted to be transmitted during a symbol transmission period. During the same transmission period a beacon signal may be transmitted on a tone with the beacon tone being transmitted at more than 20, or in some cases more than 40 or 60 times the power level of the user data. 
         [0019]    The methods and apparatus are well suited to OFDM implementations where multiple modulated symbols, one per tone, are transmitted in parallel during an OFDM symbol period. In such embodiments, beacon signals may be transmitted in parallel with the tones used to transmit data symbols. 
     
    
     
       BRIEF DESCRIPTION OF FIGURES 
         [0020]      FIG. 1  is a drawing illustrating exemplary base station transmitter timing relationships in accordance with methods of the present invention. 
           [0021]      FIG. 2  is a drawing illustrating exemplary per tone power relationships in an exemplary 2 nd  time interval. 
           [0022]      FIG. 3  is a drawing illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval. 
           [0023]      FIG. 4  is a drawing illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval corresponds to an embodiment where the 2 nd  time period and the third time period are fully overlapping. 
           [0024]      FIG. 5  is a drawing illustrating exemplary per tone power relationships in an exemplary 5 th  time interval. 
           [0025]      FIG. 6  is a drawing illustrating exemplary base station transmitter timing relationships in accordance with methods of the present invention. 
           [0026]      FIG. 7  is a drawing illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval corresponding to an embodiment where the 2 nd  time period and the third time period are fully overlapping. 
           [0027]      FIG. 8  is a drawing illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval corresponding to an embodiment where the 2 nd  time period and the third time period are fully overlapping. 
           [0028]      FIG. 9  shows an exemplary wireless communications system, supporting beacon signaling, implemented in accordance with the present invention. 
           [0029]      FIG. 10  illustrates an exemplary base station, alternately referred to as an access node, implemented in accordance with the present invention. 
           [0030]      FIG. 11  is a drawing of an exemplary wireless terminal (WT), e.g., mobile node, implemented in accordance with and using methods of the present invention. 
           [0031]      FIG. 12  is a flowchart of an exemplary method of operating a base station transmitter, in a frequency division multiplexed communications system, e.g., and OFDM system, in accordance with the present invention. 
           [0032]      FIG. 13  is flowchart of another exemplary method of operating a base station transmitter in a frequency division multiplexed system in accordance with the present invention. 
           [0033]      FIG. 14  is a flowchart of an exemplary method of operating a base station transmitter in a communications system in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 1  is a drawing  100  illustrating exemplary base station transmitter timing relationships in accordance with methods of the present invention.  FIG. 1  includes a horizontal axis  102  representing time and a first period of time  104 , e.g., a 2 sec interval. In some embodiments, the 1 st  period of time  104  is larger than 2 seconds. 
         [0035]    The exemplary base station transmitter, e.g., an OFDM signal sector transmitter, in an exemplary frequency division multiplexed communications system, e.g., an exemplary OFDM system, is operated to communicate information using a set of N tones over the first period of time  104  using first signals into a first region, e.g., a sector of a cell, where N is greater than 20. In some embodiments, the transmitter is a sector transmitter corresponding to one carrier frequency in a sector of a cell which uses multiple carrier frequencies. 
         [0036]    The set of N tones, e.g., 113 tones, may be a set of tones used for downlink signaling from the base station transmitter to wireless terminals, said downlink signaling including broadcast signals including beacon signals and assignments, as well as user specific signals, e.g., user specific downlink traffic channel signals including user data. During an exemplary second period of time  106 , e.g., an OFDM symbol transmission period, the transmitter is operated to transmit a second signal including a set of X tones into said first region, where X is less than 5 and where less than 80% of a maximum average total base station transmission power used by said base station to transmit signals into the first region during any one second period during said first period of time is allocated to set of X tones and each one of said X tones to which power is allocated is allocated at least 20 times the per average tone power allocated to tones during said first period of time. For example, the set of X tones during the second period of time  106  may comprise a beacon signal, and the second period of time may be an OFDM transmission time interval in a sequence of successive OFDM transmission time intervals which has been designated for beacon signals. In some embodiments, user data including at least one of voice, text and image data is communicated on at least one of the N tones transmitted during said first period of time  104 , and transmitter information including at least one of sector, cell and carrier frequency information is transmitted on at least one of said X tones during said second period of time  106 . An exemplary 1 sec interval  108  of maximum average total BS transmission power used by said base station transmitter to transmit signals into the first region is shown in  FIG. 1 . In general, the one second interval  108  of maximum power may slide or occur at different locations within the first period of time  104 .  FIG. 1  includes an exemplary fifth period of time  110 , e.g., an exemplary OFDM symbol transmission time interval during the 1 second interval  108 . 
         [0037]      FIG. 1  also includes an exemplary third period of time  112 , e.g. an exemplary OFDM symbol transmission interval. During the third period of time, the transmitter is operated to transmit a third signal into said first region including a set of Y tones, where Y≦N, each tone in said third set of tones to which power is allocated is allocated at most 8 times the average per tone power allocated to tones during said 1 second interval of time  108 . In  FIG. 1 , the third period of time  112  has the same duration as the second period of time  106 , e.g., an OFDM symbol transmission time interval. In some embodiments, the second and third periods of time ( 106 ,  112 ) overlap. In the example of  FIG. 1 , the second and third periods of time ( 106 ,  112 ) fully overlap. In some embodiments, the second and third periods of time ( 106 ,  112 ) are disjoint. In various embodiments, the transmitter is operated to modulate at least two of data control, and pilot signals on at least some of said set of Y tones during the third period of time. 
         [0038]    In some embodiments, the transmitter is operated to transmit user data using Y tones during said second period of time, said Y tones being within the set of N tones that are not included in said X tones, where Y is a positive integer greater than one, more than 20% of the total transmitter power used during said second period of time  106  being allocated to the Y tones during said second period of time  106 . In some embodiments, more than 50% of the total transmitter power used during said second period of time  106  being allocated to the Y tones. In various embodiments, transmitting user data includes transmitting modulated symbols on said Y tones, each of the Y tone tones communicating one symbol one symbol, e.g., one OFDM modulation symbol in one OFDM symbol transmission interval. 
         [0039]    In some embodiments, an exemplary fourth time period also occurs during the 1 st  period of time  104 , the fourth time period having the same duration as the 2 nd  time period and being non-overlapping with respect to the 2 nd  time period. For example, the fourth time period can be an interval used to transmit another beacon signal on a set of G tones, the beacon signal transmitted in the fourth time period being different than the beacon signal transmitted in the 2 nd  time period. 
         [0040]    Note that  FIG. 1  is not drawn to scale. For example, the duration of an OFDM symbol transmission interval is significantly smaller than shown, e.g., each OFDM symbol transmission interval, in some embodiments, being 10 micro-sec in duration. 
         [0041]      FIG. 2  is a drawing  200  illustrating exemplary per tone power relationships in an exemplary 2 nd  time interval  106 .  FIG. 2  is a plot of per tone power for 2 nd  time period  106  divided by average per tone power over one second interval  108  on vertical axis  202  vs tone index on horizontal axis  204 . The exemplary system corresponding to  FIG. 2 , uses N=50 tones (tone index 0 . . . 49)  206  for downlink signaling. The exemplary beacon signal  208  uses one tone with tone index 34 and 25 times the average per tone power over the one second interval. Thus, in this example, the tone set X includes one tone. In some embodiments, the tone set X includes two tones. This relatively high concentration of power on a narrow frequency, as shown in  FIG. 2 , makes the beacon signal  208  easy to detect and identify by WTs receiving downlink signaling. 
         [0042]      FIG. 3  is a drawing  300  illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval  106 .  FIG. 3  is a plot of per tone power for 2 nd  time period  106  divided by average per tone power over one second interval  108  on vertical axis  302  vs tone index on horizontal axis  304 . The exemplary system corresponding to  FIG. 3 , uses N=500 tones (tone index 0 . . . 49)  306  for downlink signaling. The exemplary beacon signal  307  transmitted during second time period  106  uses four tones with tone index values (7, 12, 17, 21) and 25 times the average per tone power over the one second interval for each tone, as represented by blocks ( 308 ,  310 ,  312 , and  314 ), respectively. 
         [0043]    In some embodiments, at least one said X tones, e.g., beacon tones, is transmitted at predetermined frequency, and at least one of said X tones is transmitted using a frequency having a fixed frequency offset≧0 from the lowest frequency tone in said set of N tones. For example, a carrier beacon signal may use such X tones. In some embodiments, at least one of said X tones is transmitted at a frequency which is determined as a function of at least one of a base station identifier and a sector identifier. 
         [0044]    In the example of  FIG. 2  the exemplary second signal, e.g., beacon signal, using the set of X tones, where X=1, is transmitted using 50% of the max average total base station transmission power used by said base station transmitter to transmit signals into the first region during the 1 sec interval  108 . In the example of  FIG. 3  the exemplary second signal, e.g., beacon signal, using the set of X tones, where X=4, is transmitted using 20% of the max average total base station transmission power used by said base station transmitter to transmit signals into the first region during the 1 sec interval  108 . 
         [0045]    In the examples of  FIGS. 2 and 3 , none of the N−X tones in said set of N tones are used during the second period of time  106 , as transmitter power is concentrated on the beacon signal (X tones) and not on the other (N−X) tones during this time.  FIG. 4  is a drawing  400  illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval  106 .  FIG. 4  corresponds to an embodiment where the 2 nd  time period  106  and the third time period  112  are fully overlapping.  FIG. 4  is a plot of per tone power for 2 nd  time period  106  divided by average per tone power over one second interval  108  on vertical axis  402  vs tone index on horizontal axis  404 . In the  FIG. 4  example, the 2 nd  time period  106  is the same as the third time period  112 . The exemplary system corresponding to  FIG. 4 , uses N=100 tones (tone index 0 . . . 99)  406  for downlink signaling. The exemplary beacon signal  408  transmitted during second time period  106  uses one tone with tone index=68 and 25 times the average per tone power over the one second interval for each tone. Thus, in this example, the tone set X, of the beacon signal  408 , includes one tone. In  FIG. 4  a set of Y tones, the set having 99 tones includes each of the tones in the set of N tones not in the set of X tones. Tones of the set of Y tones have 5 times, 1 time or 0.5 times the per tone power divided by the average per tone power over the 1 sec interval. For example exemplary signal  410  using tone  0  at the 5× relative power level may be part of a pilot signal, while exemplary signal  412  using tone  12  at the 1× relative power level may be part of a control signal such as an assignment, acknowledgement, timing control signal, or power control signal. Exemplary signal  414  using tone  99  at the 0.5× relative power level may be part of a downlink traffic channel signal conveying user data. 
         [0046]      FIG. 5  is a drawing  500  illustrating exemplary per tone power relationships in an exemplary 5 th  time interval  110 .  FIG. 5  is a plot of per tone power for 5 th  time period  110  divided by average per tone power over one second interval  108  on vertical axis  502  vs tone index on horizontal axis  504 . The exemplary system corresponding to  FIG. 5 , uses N=100 tones (tone index 0 . . . 99)  506  for downlink signaling. Tones shown in the example of  FIG. 5  have 2×, 1× or 0.5× the per tone power divided by the average per tone power over the 1 sec interval. For example exemplary signal component  512  uses tone  38  at the 2× power level and may be part of a control signal such as a pilot signal, an assignment signal, an acknowledgement signal, a timing control signal or a power control signal; exemplary component  510  uses tone  13  at 1× power level and may be part of a user data signal, while exemplary component  508  at 0.5× power level uses tone  9  and may be part of another user data signal. During exemplary 5 th  interval  110  shown, the total transmission power is 100% the average transmission power during the 1 sec interval  108  of max average total BS transmit power into the first region. In the example of  FIG. 5 , there are two tones with signal components of type  512  representing 4% of the total power, ninety-four tones with signal components of type  510  representing 94% of the total power, and four tones with signal components of type  508  representing 2% of the total power. In general, the total power during each 5 th  interval  110 , e.g., each OFDM symbol transmission interval, will deviate from the average power of the 1 sec interval  108 . 
         [0047]      FIG. 6  is a drawing  600  illustrating exemplary base station transmitter timing relationships in accordance with methods of the present invention.  FIG. 6  shows an exemplary variation of  FIG. 1  in accordance with the present invention. Exemplary first time period  604  of  FIG. 6  is similar or the same as exemplary first time period  104  of  FIG. 1 . Exemplary one second interval  608  of maximum average total BS transmit power of  FIG. 6  is similar or the same as interval  108  of  FIG. 1 . Exemplary second time periods ( 606 ,  606 ′) of  FIG. 6  are similar or the same as exemplary second time period  106  of  FIG. 1 . Exemplary 1 st  2 nd  time period  606  and exemplary 2 nd  2 nd  time period  606 ′ illustrate that the second time period periodically repeats during the first time period  604 .  FIG. 6  includes repetitions of the 3 rd  time period (1 st  3 rd  time period  612 , 2 nd  1 st  time period  612 ′, 3 rd  1 st  time period  612 ″ . . . . Nth 3 rd  time period  612 ′″) within the first time period  604 . Each 3 rd  time period ( 612 ,  612 ′,  612 ″,  612 ′″) is similar or the same as exemplary 3 rd  time period  112  of  FIG. 1 . In some embodiments, for each repetition of said second time period there are at least Z repetitions of said 3 rd  time period, where Z is at least 10. In some embodiments, Z is at least 400. 
         [0048]      FIG. 7  is a drawing  700  illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval  106 .  FIG. 7  corresponds to an embodiment where the 2 nd  time period  106  and the third time period  112  are fully overlapping.  FIG. 7  is a plot of per tone power for 2 nd  time period  106  divided by average per tone power over one second interval  108  on vertical axis  702  vs tone index on horizontal axis  704 . In the  FIG. 4  example, the 2 nd  time period  106  is the same as the third time period  112 . The exemplary system corresponding to  FIG. 7 , uses N=100 tones (tone index 0 . . . 99)  706  for downlink signaling. The exemplary beacon signal  708  transmitted during second time period  106  uses one tone with tone index=68 and 25 times the average per tone power over the one second interval for each tone. Thus, in this example, the tone set X, of the beacon signal  708 , includes one tone. In  FIG. 7  a set of Y tones, the set including 35 tones in the set of N tones not in the set of X tones. Tones of the set of Y tones have 5×, 1× or 0.5× the per tone power divided by the average per tone power over the 1 sec interval. For example, exemplary signal  710  using tone  0  at the 5× relative power level may be part of a pilot signal, while exemplary signal  712  using tone  12  at the 1× relative power level may be part of a control signal such as an assignment, acknowledgement, timing control signal, or power control signal. Exemplary signal  714  using tone  99  at the 0.5× relative power level may be part of a downlink traffic channel signal conveying user data. Exemplary tone  26   716  is an unused tone from the set of N tones. In this embodiment, 64 tones from the set of N−X=99 tones go unused during the second period of time  106  in the first region. In some embodiments, at least half of the N−X tones which are in said set of N tones but not in said set of X tones go unused during said second period of time in the first region. 
         [0049]      FIG. 8  is a drawing  800  illustrating another exemplary per tone power relationships in an exemplary 2 nd  time interval  106 .  FIG. 8  corresponds to an embodiment where the 2 nd  time period  106  and the third time period  112  are fully overlapping.  FIG. 8  is a plot of per tone power for 2 nd  time period  106  divided by average per tone power over one second interval  108  on vertical axis  802  vs tone index on horizontal axis  804 . In the  FIG. 8  example, the 2 nd  time period  106  is the same as the third time period  112 . The exemplary system corresponding to  FIG. 8 , uses N=100 tones (tone index 0 . . . 99)  806  for downlink signaling. The exemplary beacon signal  808  transmitted during second time period  106  uses one tone with tone index=68 and 25 times the average per tone power over the one second interval for each tone. Thus, in this example, the tone set X, of the beacon signal  808 , includes one tone. In  FIG. 8  a set of Y tones, the set including 2 tones (tone index=12 and tone index=26) in the set of N tones not in the set of X tones, are associated with signal components ( 812 ,  812 ′), respectively. In this example, tones of the set of Y tones have 1× the per tone power divided by the average per tone power over the 1 sec interval. For example exemplary signal  812  using tone  12  at the 1× relative power level may be part of a control signal such as a pilot, an assignment, acknowledgement, timing control signal, or power control signal or part of a user data signal such as a signal including voice, text, and/or user application data. Exemplary tone  26   816  is an unused tone from the set of N tones. In this embodiment, 97 tones from the set of N−X=99 tones go unused during the second period of time  106  in the first region. In some embodiments, multiple ones of the N−X tones in the set of N tones but not in the set of X tones are used during said second period of time in the first region. 
         [0050]      FIG. 9  shows an exemplary wireless communications system  900 , supporting beacon signaling, implemented in accordance with the present invention. The system  900  uses apparatus and methods of the present invention.  FIG. 9  includes a plurality of exemplary multi-sector cells, cell  1   902 , cell  2   904 , cell  3   906 . Each cell ( 902 ,  904 ,  906 ) represents a wireless coverage area for a base station (BS), (BS 1   908 , BS 2   910 , BS  3   912 ), respectively. In the exemplary embodiment, each cell  902 ,  904 ,  906  includes three sectors (A, B, C). Cell  1   902  includes sector A  914 , sector B  916 , and sector C  918 . Cell  2   904  includes sector A  920 , sector B  922 , and sector C  924 . Cell  3   906  includes sector A  926 , sector B  928 , and sector C  930 . In other embodiments, different numbers of sectors per cell are possible, e.g., 1 sector per cell, 2 sectors per cell, or more than 3 sectors per cell. In addition, different cells may include different numbers of sectors. 
         [0051]    Wireless terminals (WTs), e.g., mobile nodes (MNs), may move throughout the system and communicate with peer nodes, e.g., other MNs, via wireless links to BSs. In cell  1   902  sector A  914 , WTs ( 932 ,  934 ) are coupled to BS 1   908  via wireless links ( 933 ,  935 ), respectively. In cell  1   902  sector B  916 , WTs ( 936 ,  938 ) are coupled to BS 1   908  via wireless links ( 937 ,  939 ), respectively. In cell  1   902  sector C  918 , WTs ( 940 ,  942 ) are coupled to BS 1   908  via wireless links ( 941 ,  943 ), respectively. In cell  2   904  sector A  920 , WTs ( 944 ,  946 ) are coupled to BS  2   910  via wireless links ( 945 ,  947 ), respectively. In cell  2   904  sector B  922 , WTs ( 948 ,  950 ) are coupled to BS  2   910  via wireless links ( 949 ,  951 ), respectively. In cell  2   904  sector C  924 , WTs ( 952 ,  954 ) are coupled to BS  2   910  via wireless links ( 953 ,  955 ), respectively. 
         [0052]    BSs may be coupled together via a network, thus providing connectivity for WTs within a given cell to peers located outside the given cell. In system  900 , BSs ( 908 ,  910 ,  912 ) are coupled to network node  968  via network links ( 970 ,  972 ,  974 ), respectively. Network node  968 , e.g., a router, is coupled to other network nodes, e.g., other base stations, routers, home agent nodes, AAA server nodes, etc., and the Internet via network link  976 . Networks links  970 ,  972 ,  974 ,  976  may be, e.g., fiber optic links. 
         [0053]    BSs  908 ,  910 ,  912  include sectorized transmitters, each sector transmitter using a specific assigned carrier frequency for ordinary signaling e.g., downlink traffic signals such as user data directed to specific WT(s), in accordance with the invention. The sector transmitter&#39;s assigned carrier frequency used for ordinary signaling also conveys broadcast signals such as, e.g., assignment signals, pilot signals, and/or beacon signals, from the BS to WTs. BSs  908 ,  910 ,  910  transmit beacon signals conveying carrier information, cell identification information and/or sector identification information. In addition, in accordance with some embodiments of the invention, each base station sector transmitter transmits additional downlink signals such as, e.g., pilot signals and/or beacon signals within the carrier frequency bands assigned to adjacent cell/sector transmitters for their ordinary signaling. Such downlink signals provide information to the WTs, e.g., WT  932 , which may be used to evaluate and decide which carrier frequency to select and which corresponding base station sector/cell to use as an attachment point. The WTs, e.g., WT  932 , include receivers with the capability to process information from BSs  908 ,  910 ,  912  sector transmitters providing information on alternative carrier frequencies bands that may be used for ordinary communications, e.g., downlink traffic channel signaling, and that may be selected by the WT. 
         [0054]      FIG. 10  illustrates an exemplary base station  1000 , alternately referred to as an access node, implemented in accordance with the present invention. The BS is called an access node because it serves as a WT&#39;s point of network attachment and provides the WT access to the network. The base station  1000  of  FIG. 10  may be a more detailed representation of any of the base stations  908 ,  910 ,  912  of the system  900  of  FIG. 9 . The base station  1000  includes a sectorized receiver  1002 , a sectorized transmitter  1004 , a processor  1006 , e.g., a CPU, an I/O interface  1008 , and a memory  1010  coupled together via a bus  1012  over which the various elements may interchange data and information. The sectorized receiver  1002  includes a plurality of receivers (sector  1  receiver  1016 , sector N receiver  1020 ), each receiver coupled to a receive antenna (receive antenna  1   1018 , receive antenna N  1022 ), respectively. Each receiver ( 1016 ,  1020 ) includes a decoder ( 1024 ,  1026 ), respectively. Uplink signals from a plurality of wireless terminals  1100  (See  FIG. 11 ) are received via sectorized antenna ( 1018 ,  1022 ) and processed by sectorized receivers ( 1016 ,  1020 ). Each receiver&#39;s decoder ( 1024 ,  1026 ) decodes received uplink signals and extracts the information encoded by the WTs  1100  prior to transmission. The sectorized transmitter  1004  includes a plurality of transmitters, a sector  1  transmitter  1028 , a sector N transmitter  1030 . Each sector transmitter ( 1028 ,  1030 ) includes an encoder ( 1036 ,  1038 ), for encoding downlink data/information, and is coupled to a sector transmit antenna ( 1030 ,  1034 ), respectively. Each antenna  1030 ,  1034  corresponds to a different sector and is normally oriented to transmit into the sector to which the antenna corresponds and may be located. Antennas  1030 ,  1034  may be separate or may correspond to different elements of a single multi-sector antenna which has different antenna elements for different sectors. Each sector transmitter ( 1030 ,  1034 ) has an assigned carrier frequency band to be used for ordinary signaling, e.g., downlink traffic signaling. Each sector transmitter ( 1030 ,  1034 ) is capable of transmitting downlink signals, e.g., assignment signals, data and control signals, pilot signals, and/or beacon signals in its own assigned carrier frequency band. Each sector transmitter ( 1030 ,  1034 ), in accordance with some embodiments of the invention, also transmits additional downlink signals, e.g., pilot signals and/or beacon signals into other carrier frequency bands, e.g., the carrier frequency bands assigned to adjacent cells/sectors for their ordinary signaling. The base station I/O interface  1008  couples the base station  1000  to other network nodes, e.g., other access nodes, routers, AAA servers, home agent nodes, and the Internet. The memory  1010  includes routines  1040  and data/information  1042 . The processor  1006  executes routines  1040  and uses the data/information  1042  in the memory  1010  to control the operation of the base station  1000  including scheduling users on different carrier frequencies using different power levels, power control, timing control, communication, signaling, and beacon signaling in accordance with the invention. 
         [0055]    Routines  1040  includes a plurality of set of routines (sector  1  routines  1044 , sector N routines  1046 ), each set corresponding to a sector covered by the BS  1000 . In some embodiments, e.g., embodiments where multiple carrier frequencies are used for ordinary signaling, e.g., downlink traffic channel signaling including user data, in a single sector, additional sets of routines may exist for the sector corresponding to the different carriers corresponding to different BS sector attachment points. 
         [0056]    Exemplary sector  1  routines  1044  include communications routines  1048  and base station control routines  1050 . Communications routines  1048  perform the various communications protocols used by the BS  1000 . Base station control routines  1050  uses the data/information  1042  to control the operations of the BS  1000  including operation of sector  1  receiver  1016 , operation of sector  1  transmitter  1028 , operation of I/O interface  1008 , and implementation of methods of the present invention including beacon signaling. Scheduler module  1052  schedules users, e.g., assigning air link resources such as uplink and downlink traffic channel segments to WTs. Signaling module  1054  uses the data/information  1042  in memory  1010  to perform control of the downlink and uplink signaling in regard to sector  1  signaling. Signaling module  1054  controls sector  1  transmitter  1028  to transmit over periods of time, e.g., intervals 2 sec or longer, using downlink signals into the first sector of the cell corresponding to BS  1000 . Some of the downlink signals transmitted include downlink traffic channel signals including user data such as voice, text, and/or image information, pilot signals and other control information such as assignments, acknowledgement, timing control and power control information. Signaling module  1054  uses the sets of tones assigned to the BS  1000  including a set of N downlink tones, where N is larger than 20. Signaling module  1054  controls timing operations, e.g., OFDM symbol transmission timing operations and beacon activation timing control operations. 
         [0057]    Beacon module  1056  includes a sector  1  beacon module  1058  and an adjacent sector beacon module  1060 . Beacon module  1056  uses the data/information  1042  in memory  1010  to control the sector  1  transmitter beacon functions including beacon signal generation and transmission, in accordance with the present invention. Beacon module  1056  controls the sector  1  transmitter  1028  to transmit beacon signals during designated beacon signaling intervals, a beacon signal using a set of X tones where X is a positive number less than 5, and where the power allocated to the set of X tones of the beacon signal is less than 80% of a maximum average base station transmission power used by the base station to transmitter to transmit into sector  1  during any 1 second interval of time during a first designated time period of at least 2 seconds, the at least 2 second interval including the beacon signal, and where each one of said X tones to which power is allocated is at least 20 times the per tone average power allocated to tones during the any one second time period in the at least 2 sec long interval. 
         [0058]    Sector  1  beacon module  1058  performs control operations related to beacons signals generated and transmitted within the carrier frequency band used by sector  1  transmitter  1028  for ordinary downlink signaling, e.g., downlink signaling including user data. Adjacent sector beacon module  1060  performs operation related to beacon signals generated and transmitted within the carrier frequency band used by adjacent sectors for transmitting ordinary downlink signaling. By transmitting beacon signals in adjacent bands, a WT with a single receiver chain tuned, to a single carrier, can receive beacon signals conveying information about different potential carrier frequency BS sector attachment points while still operating on its current attachment point carrier frequency. 
         [0059]    Data/information  1042  includes a plurality of sets of data/information (sector  1  data/information  1062 , sector N data/information  1064 ). Sector  1  data/information  1062  includes data  1066 , sector information  1068 , a plurality of sets of carrier information (carrier  1  information  1070 , carrier N information  1072 ), tone information  1074 , non-beacon downlink tone information  1076 , beacon information  1078 , WT data/information  1080 , average transmitter power information  1082 , current transmitter power information  1084 , timing information  1086 , and downlink signals  1088 . 
         [0060]    Data  1066  includes user data/information received from and user data/information to be transmitted to a plurality of WTs, e.g., WTs using sector  1  of BS  1000  as a network attachment point and WTs in a communications session with a WT using sector  1  of BS  1000  as a network attachment point. Sector information  1068  includes information identifying sector  1 , e.g., specific BS sector identifiers. 
         [0061]    Carrier information (carrier  1  info  1070  and carrier N info  1072 ) includes information associated with each of the carriers used in sector  1  for downlink signaling. In some embodiments, a given sector of a cell may use multiple carriers for user data downlink signaling with each of the multiple carriers corresponding to a different alternative network attachment point. In such an embodiment, each carrier within the sector may be associated with a different BS sector transmitter, and a given sector may have multiple BS sector transmitters, e.g., multiple sector  1  transmitters  1028 . 
         [0062]    In some embodiments, e.g., an embodiment using adjacent sector beacon module  1060 , carrier information ( 1070 ,  1072 ) includes information identifying whether the carrier is the carrier used by transmitter  1028  in sector  1  for ordinary downlink signaling including user data, and beacon signals and other control signals or whether the carrier is the carrier used for user data downlink signaling by an adjacent sector in which case the sector  1  transmitter transmits beacon signals using the carrier but not user data. 
         [0063]    Carrier information ( 1070 ,  1072 ) also includes information identifying bandwidth, e.g., about which the downlink carrier is centered. Carrier information ( 1070 ,  1072 ) includes information pertaining to downlink and/or uplink carriers used in sector  1 . Downlink carrier information is used in tuning the sector  1  transmitter  1028 , while uplink carrier information is used in tuning the sector  1  receiver  1016 . 
         [0064]    Tone information  1074  includes downlink tone information  1090  corresponding to downlink signaling and uplink tone information  1092  corresponding to uplink signaling with respect to sector  1  of BS  1000 . Downlink tone information  1090  includes tone set information  1094  and power information  1096 . Tone set information  1094  includes a set of N tones, where N is larger than 20, used by the sector  1  transmitter  1028  for downlink signaling including user data, beacon signals, pilot signals, and other control signals such as assignments, acknowledgements, timing control signals, and power control signals. In some embodiments, the set of N tones is a contiguous set of tones using the bandwidth allocated for downlink signaling for the sector  1  transmitter  1028 . 
         [0065]    In some embodiments, downlink tone information  1090  includes tone hopping information, where information is mapped to logical tones and the logical tones are hopped to physical tones over time according to a periodic predetermined tone hopping sequence which may be a function of the base station and/or base station sector. Power information  1096  includes power level information including total sector transmit power allocated to the set of N tones, power level information on a per tone basis, and/or power information on an average basis. 
         [0066]    Uplink tone information  1092  includes information such as tone set information associated with the set of tones in the uplink band to which sector  1  receiver  1016  is tuned. 
         [0067]    Beacon information  1078  includes tone set information  1097  power information  1095 , and transmitter information  1093 . Tone set information  1097  includes information on a set or sets of X tones from the set of N tones, X being less than 5, where each set of X tones comprises the tones of a beacon signal. Power information  1095  includes information identifying the power level to be used on each of the N tones of the beacon signal, where each one of X tones to which power is allocated is allocated at least 20× the per tone average power allocated to tones during any one second period of time in a first period of time of at least 2 seconds, the first period including the beacon signal; power information  1095  also includes information identifying the power level to be used on the combined set of X tones comprising the beacon signal, where the power is less than 80% of a maximum average total base station transmission power used by base station sector  1  transmitter  1028  during the any one second period of time. 
         [0068]    Transmitter information  1093  includes cell identification information  1091 , sector ID information  1089 , and carrier identification information  1087 . The various types of transmitter identification information in info  1093  may be conveyed by beacon signals, e.g., by the set of X tones associated with the beacon and the time at which the sector  1  transmitter  1028  transmits the beacon in a repeating sequence of beacon signals. 
         [0069]    Non-beacon downlink tone information  1076  includes information on sets of Y tones, Y≦N, which are used to transmit non-beacon downlink signals such as user data, pilot signals, and other control signals. During different time intervals, e.g., different OFDM symbol transmission intervals, the set of Y tones may change. For example, when the OFDM transmission time interval is an interval during which a beacon signal is not transmitted, the set of Y tones may include each of the N tones. In some embodiments, during a beacon transmission interval, the set of Y tones includes 0 tones. In other embodiments, during a beacon interval, a set of N−X tones exists, and a subset of Y tones from the set of N−X tones is used to transmit user data at the same time as the beacon signal transmission. In some embodiments, the set of Y tones during the beacon transmission interval is a set of greater than 50 tones. Power information  1099  includes information identifying the power allocated to the set of Y tones and to each of the tones in the set of Y tones. In some embodiments, more than 20% of the total sector transmitter power during a beacon transmission interval is allocated to the set of Y tones during that beacon interval. In some embodiments, more than 50% of the total sector transmitter power during a beacon transmission interval is allocated to the set of Y tones during that beacon interval. 
         [0070]    WT data/information  1042  includes a plurality of sets of information (WT  1  data/info  1085 , WT N data/info  1073 ). Each set of information, e.g., WT 1  data/information  1085 , may correspond to a WT using BS  1000  sector  1  as its network attachment point. WT  1  data/info  1085  includes user data  1083  in route from/to WT  1  and resource/user/session information  1075 . User data  1083  includes voice information  1081 , text information  1079 , and image information  1077 . Resource/user/session information  1075  includes information identifying resources allocated to WT 1  such as a base station assigned identifier and allocated segments, e.g., dedicated uplink and downlink traffic channel segments. Resource/user/session information  1075  also includes information identifying users, e.g., other WTs, in communications sessions with WT 1  and routing information associated with those other WTs. 
         [0071]    Average transmission power information  1082  includes information of the sector  1  transmitter  1028  average transmission power, e.g., over a 1 sec intervals. Current transmission power information  1084  includes information on the transmission power of the sector  1  transmitter  1028  transmissions during the current OFDM symbol transmission interval including power levels of each of the tones used during the current OFDM symbol transmission interval. When the current OFDM symbol transmission interval is a beacon interval, the current transmission power information  1084  also includes information on the combined power on the set of tones comprising the beacon signal. The transmission power allocated to the tones is controlled in accordance with the methods of the invention, e.g., allocating a relatively high level of power on a per tone basis to beacon tones, in comparison to the level of power on a per tone basis allocated to user data or other non-beacon control signals. 
         [0072]    Timing information  1086  includes interval information  1071  and repetition information  1069 . Interval information  1071  includes timing structure information on transmission intervals, e.g., periods of time at least two seconds long in which sector  1  transmitter  1028  is controlled to transmit signals into sector  1 . Interval information also includes information on periods of time in which sector  1  transmitter  1028  is controlled to transmit beacon signals into sector  1  and information on periods of time during which sector  1  transmitter  1028  is controlled to transmit non-beacon signals into sector  1 . Interval information  1071  includes information such as OFDM symbol timing information, e.g., the duration of a single OFDM symbol transmission interval, and timing synchronization information, e.g., with respect to other sectors of the cell and between the downlink and the uplink. 
         [0073]    Repetition information  1069  includes information on the periodic repetition of beacon signals and/or beacon signaling intervals. Repetition information  1069  includes on structure which repeat, e.g., slots (grouping of successive OFDM symbol transmission intervals), superslots (grouping of slots), beacon slots (grouping of superlots including one beacon signal), ultra slots (grouping of beacons slots, where some beacon slots within the ultra slot include different beacon signals). 
         [0074]    Downlink signals  1088  include OFDM modulation symbols  1067 , beacon signals  1065 , non-beacon control signals  1063 , and user data signals  1061 . OFDM modulation symbols  1067  include information conveyed on a modulation symbol, e.g., data, control, and/or pilot information modulated on a symbol, the modulation symbol being conveyed by using a non-beacon tone. Beacon signals  1065  include information identifying a beacon signal to be transmitted, e.g., a beacon signal conveying transmitter information such as carrier information, sector ID information, and/or cell ID information. Non-beacons control signals  1063  include information on signals such assignments, acknowledgements, power control, timing control, and pilot signals and corresponding control segment information. User data signals  1065  include information on user signals such as downlink traffic channel segment signals and corresponding segment information. 
         [0075]      FIG. 11  is a drawing of an exemplary wireless terminal (WT)  1100 , e.g., mobile node, implemented in accordance with and using methods of the present invention. Exemplary WT  1100  may be any of the WTs ( 932 ,  934 ,  936 ,  938 ,  940 ,  942 ,  944 ,  946 ,  948 ,  950 ,  952 ,  954 ,  956 ,  958 ,  960 ,  962 ,  964 ,  966 ) of the exemplary system  900  of  FIG. 9 . 
         [0076]    WT  1100  includes a receiver  1102 , a transmitter  1104 , a processor  1106 , e.g., a CPU, 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  1136  and data/information  1138 . 
         [0077]    The processor  1106  executes the routines  1136  and data/information  1138  in memory  1110  to control the operation of the WT and implement methods in accordance with the present invention. User I/O devices  1108 , e.g., microphone, keyboard, keypad, mouse, video camera, speaker, display, etc., allow a user of the WT to input user data/information to be communicated to another WT participating in a communications session with WT  1100  and to output user data received from another WT participating in a communications session with WT  1100 . 
         [0078]    Receiver  1102  is coupled to a receive antenna  1114  through which WT  1100  can receive downlink signals from base stations, the downlink signals including beacon signals, user data signals, and non-beacon control signals such as pilot signals, timing control signals, power control signals, assignments, and acknowledgements. Receiver  1118  includes a 1 st  RF module  1118 , a first receiver chain  1120 , a digital signal processing module  1122 , an energy detection/SNR detection module  1124 , and a band selection controller  1126 . In some embodiments, e.g., some dual RF receiver chain embodiments, receiver  1102  includes a 2 nd  RF module  1128  and a 2 nd  receiver chain  1130 . 
         [0079]    1 st  RF module  1118  is tuned to a carrier signal and accepts and processes downlink signals within the carrier signals associated band. 1 st  receiver chain  1120  accepts and process the output signals from the 1 st  RF module  1118 . 1 st  RF module  1118  may include an RF filter and/or mixer circuitry. The 1 st  RF module  1118  receives a control input from the band selection controller  1126 , e.g., selecting a carrier frequency and tuning the receiver  1102  to the selection. 
         [0080]    1 ST  receiver chain  1120  includes an A/D module  1119  for performing an analog to digital conversion and a FFT/DFT (fast fourier transform/discrete fourier transform) module  1121  which performs either a FFT or a DFT on the digital signal from the A/D module  1119  output. 1 st  RF chain  1120  may also include additional filters, e.g., baseband filters. Output from the 1 st  receiver chain  1120  is input to the energy detection/SNR detection module  1124 . 
         [0081]    Energy detection/SNR module  1124  detects energy associated with each of the tones of the downlink band. Beacon signal components may be identified by their relatively high power per tone power with respect to other non-beacon tones. In some embodiments beacon signals may also be detected by SNR measurement information. Note that beacons may be detected without the need for precise timing synchronization, e.g., allowing beacons from multiple unsynchronized base station transmitters transmitted in the same carrier band to be detected and processed. 
         [0082]    Non-beacon components, e.g., lower power tones not classified as beacon tones and which have been transmitted from the attachment point base station sector, are processed by the digital signal processing module  1122 . The digital signal processing module  1122  performs symbol detection and recovery. Digital signal processing module  1122  operations includes timing synchronization operations. The digital signal processing module  1122  includes a decoder  1132  for decoding information which was encoded by the BS prior to transmission. In some embodiments, the decoder  1132  uses redundant information in the encoded signal to recover information which was lost due to the concurrent transmission of a beacon tone on the same tone used for data or a non-beacon control signal. In some embodiments, the energy detection/SNR detection module  1124  is included as part of the digital signal processing module  1122 . 
         [0083]    In some embodiments, a 2 nd  RF module  1128  and a 2 nd  receiver chain  1130  are used. The 2 nd  RF module  1128  is similar or the same as St RF module  1128 , while 2 nd  receiver chain  1130  is similar or the same as 1 st  receiver chain  1120 . In some embodiments, the 2 nd  RF module  1128  and/or 2 nd  receiver chain  1130  are simpler in complexity, e.g., in terms of the number of gates and/or operations performed, than 1 st  RF module  1118  and 1 st  receiver chain  1120 . In an embodiment with both 1 st  and 2 nd  receiver chains, the 1 st  RF module  1118  is tuned to the carrier of the base station sector attachment point transmitters allowing the reception and processing of downlink beacon signals, user data signals, and non-beacon control signals, while the 2 nd  RF module  1128  is tuned, via a band selection controller  1126  control signal to an alternate carrier band and beacon signals within that band are received and processed but no user data signals. Signaling forwarded through the 2 nd  RF module  1128  and 2 nd  receiver chain  1130  is forwarded to the energy detection/SNR detection module  1124  for beacon detection and identification, but is not forwarded to the digital signal processing module  1122  for OFDM modulation symbol information recovery operations. 
         [0084]    Transmitter  1104  is coupled to a transmit antenna  1116  through which the WT can send uplink signals including user data and requests for a change of network attachment point, to BSs. Transmitter  1104  includes an encoder  1134  for encoding data/information to be transmitted, e.g., user data. 
         [0085]    Routines  1136  includes a communications routine  1140  and wireless terminal control routines  1142 . The communications routine  1140  implements the various communications protocols used by WT  1100 . The wireless terminal control routines  1142  using the data/information  1138  control the operation of the WT  1100  including implementing methods of the present invention. Wireless terminal control routines  1142  include signaling routines  1144 , receiver controller module  1146 , and a carrier band selection module  1148 . 
         [0086]    Signaling routines  1144  include downlink signaling routines  1150  and uplink signaling routines  1152 . The downlink signaling routines  1150  control operations pertaining to the reception, recovery, and processing of downlink signals received by receiver  1102 . The uplink signaling routines  1152  control operations pertaining to the transmission of uplink signals to the BS sector network attachment point via transmitter  1104 . 
         [0087]    The downlink signaling routines  1150  include beacon module  1154  and ordinary signaling module  1156 . Beacon module  1154  controls operations pertaining to recovery, detection, and identification of beacon signals. For example, based on the signal energy level of a detected received tone exceeding a threshold level, the received tone may be identified by the beacon module  1154  as beacon component tone. Then, by operations including comparing the frequency of the beacon component tone to stored system characteristic information  1178 , the beacon module  1154  may identify the beacon signal and obtain beacon source transmitter identification information  1190  such as, e.g., carrier identification, cell identification, and/or sector identification. 
         [0088]    Ordinary signaling module  1156  controls operations pertaining to recovery, detection, and identification of data/and information conveyed on non-beacon downlink signals including modulation symbols, e.g., OFDM modulation symbols, which are processed by the digital signal processing module  1122 . Ordinary signaling module  1156  includes a user data module  1158  for controlling operations including the recovery of user data, e.g., voice, text, and or video data/information from a peer of WT  1100 . Ordinary signaling module  1156  also includes a non-beacon control module  1160  for performing control operation pertaining to the recovery and processing of non-beacon downlink control signals such as, e.g., pilot signals, timing control signals, power control signals, assignments of identifiers and segments, and acknowledgements. 
         [0089]    Carrier band selection module  1148  selects the carrier to tune the 1 st  RF module  1118 , and in some embodiments, the optional 2 nd  RF module  1128 . The carrier band selection module  1146  makes band selection decisions using detected beacon information  1166 , e.g., selecting an attachment point and/or selecting to change an attachment point and initiate a handoff. For example, the carrier band selection module  1126  may select to set to 1 st  RF module  1118  to the carrier used for ordinary signaling corresponding to the strongest received beacon signal. In embodiments, using second RF module  1128 , the carrier band selection module  1148  may select to set the 2 nd  RF module  1128  to different alternative potential carriers at different times so as to search for additional beacons to evaluate. 
         [0090]    Output selection signals from the carrier band selection module  1148  are input to the receiver controller module  1146  which signals the band selection controller  1126  in the receiver  1102  to implement the selection decisions. 
         [0091]    Data/information  1138  includes user data  1162 , user/device/session/resource information  1164 , detected beacon information  1166 , carrier frequency information  1168 , cell/sector information  1170 , downlink user data signals  1172 , downlink non-beacon control signals  1174 , uplink signals  1176 , and system characteristic information  1178 . 
         [0092]    User data  1162  includes voice, text, and/or video data information to/from a peer WT in a communications session with WT  1100 . User/device/session/resource information  1164  includes information identifying users/other WTs, e.g., peers of WT  1100  in communication sessions with WT  1100 , routing information, base station identifiers assigned to WT  1100 , and segments assigned to WT  1100 , e.g., uplink and downlink traffic channel segments. 
         [0093]    Detected beacon information  1166  includes a plurality of sets of detected beacon information (beacon  1  information  1180 , beacon N information  1182 ), each set of beacon information corresponding to a detected beacon signal. Beacon  1  information  1180  includes signal energy information  1184 , e.g., the energy level of the detected beacon tone or tones, SNR (signal to noise ratio) information  1186  of the detected beacon signal, tone information  1188 , e.g., the identified tone or tones of the detected beacon signal each tone with a corresponding energy level in info  1184 . Beacon  1  information  1180  also includes transmitter information  1190 , e.g., an identified carrier, an identified cell, an identified sector which has been determined to be associated with the source transmitter of the beacon signal. In some embodiments, multiple different beacon signals, e.g., in a sequence of beacon signals from the same base station sector transmitter are received to determine transmitter information  1190 . 
         [0094]    Carrier frequency information  1168  includes information identifying the current attachment point downlink carrier, e.g., the carrier to which 1 st  RF module  1118  is tuned. Carrier frequency information  1168  also includes information identifying the carrier frequency for uplink signaling to which the transmitter  1104  is tuned. 
         [0095]    Cell/sector information  1170  includes information identifying the current BS cell and/or sector attachment point, e.g., a cell identifier such as a value of slope in a pilot tone sequence, and a sector identifier identifying a sector type. Downlink user data signals  1172  include information from received signals including OFDM modulation symbols which have been communicated over downlink traffic channel segments to WT  1100 . Downlink non-beacon control signal  1174  include information from received signals including OFDM modulation symbols which have been communicated over downlink control channel segments, such as assignment segments, acknowledgment segments, power control segments, timing control segments, and/or pilot segments to WT  1100 . Uplink signals  1176  includes information to be conveyed on uplink channel segments to the BS sector attachment point. Uplink signals  1176  include user data conveyed on uplink traffic channel segments. Uplink signals  1176  also includes handoff request messages  1192  to initiate a handoff request, e.g., in response to a comparison of detected beacon signals. Uplink signals  1176  may also include access signals sent to establish a new wireless link with a base station sector attachment point, e.g., where the base station sector attachment point has been selected based on received and compared beacon signals. 
         [0096]    System characteristic information  1178  includes a plurality of sets of BS attachment point information (BS attachment point  1  information  1194 , BS attachment point N information  1196 ), corresponding to the different potential attachment points in the system, e.g., based on cell, sector, and/or carrier frequency. System characteristic information  1178  may be used by the beacon module  1154  when evaluating received beacon information, e.g., tone information  1188  to determine transmitter information  1190 . BS attachment point  1  information  1194  includes beacon information  1198 , timing structure information  1199 , tone information  1195 , and carrier information  1197 . Beacon information  1198  includes information used to identify the beacons transmitted by the BS attachment point  1  transmitter, e.g., tone sets used for beacon signals, transmission power levels of the beacon tones, types of beacon signals, position of beacon tones within the band of with respect to the lowest tone of the band or with respect to the carrier frequency, and/or tone hopping used by the beacon signals. Timing structure information  1199  includes timing information and/or timing relationships used by the BS attachment point  1  such as OFDM symbol timing, slot timing, superslot timing, beacon slot timing, ultra slot timing, and/or timing relationships to other BS attachment points, e.g., within the same cell. Carrier information  1197  includes information identifying the carriers used for downlink and uplink signaling and associated bandwidths. Tone information  1195  includes information identifying sets of tones associated with the downlink carrier and used to convey downlink signals, as well as any structural information associating specific tones with specific downlink segments at specific times with the timing sequence. Tone information  1195  also includes information identifying sets of tones associated with the uplink carrier and used to convey uplink signals, as well as any structural information associating specific tones with specific uplink segments at specific times with the timing sequence. 
         [0097]      FIG. 12  is a flowchart  1200  of an exemplary method of operating a base station transmitter, in a frequency division multiplexed communications system, e.g., and OFDM system, in accordance with the present invention. The transmitter may be, e.g., an OFDM signal transmitter which is a sector transmitter in the base station, and the sector transmitter may correspond to one carrier frequency in a sector of a cell which uses multiple carrier frequencies. Operation starts in step  1202  where the base station is power on and initialized and proceeds to step  1204 . In step  1204 , the base station transmitter is operated to transmit first signals into a first region, e.g., a sector of a cell, using a set of N tones to communicate information over a first period of time using first signals in a first region, said first period of time being at least 2 seconds long and N being larger than 20. 
         [0098]    Step  1204  includes sub-step  1206  and, in some embodiments, optional step  1208 . For each second period of time, steps  1206  is performed, and, in some embodiments, optional step  1208  is performed in parallel. In some embodiments, the second period of time periodically repeats during the first period of time. In step  1206 , the base station is operated to transmit during a second period of time a second signal into said first region, where X is less than 5, and where less than 80% of a maximum average total base station power used by said base station to transmit signals into the first region during any one second period of time is allocated to said set of X tones and each one of said X tones is allocated at least 20 times the per tone average power allocated to tones during any one second period. In some OFDM embodiments, the second period of time is a period of time used to transmit an orthogonal frequency division multiplexed symbol. In some embodiments, the second period of time occurs within the first period of time and the set of X tones is a subset of the set of N tones. In various embodiments, the user data including at least one of voice, text and image data is communicated on at least one of the N tones transmitted during said first period of time and transmitter information including at least one of sector, cell, and carrier frequency information is transmitted on at least one of said X tones during said second period of time. In some embodiments X is equal to one or two. In some embodiments, e.g., an embodiment without step  1208 , none of the N−X tones in said set of N tones but not in said set of X tones are used during said second period of time. In some embodiments, at least half of the N−X tones which are in the set of N tones but not in said set on X tones go unused during said second period of time in the first region. In various embodiments, multiple ones of the N−X tones in said set of X tones are used during said second period of time in the first region. 
         [0099]    In step  1208 , the base station is operated to transmit user data using Y tones during said second period of time, said Y tones being tones within said set of X tones, where Y is a positive integer greater than one, more than 20% of the total transmitter power used during said second period of time to transmit signals into the first region being allocated to the Y tones during said second period of time. In some embodiments more than 50% of the total transmitter power used during said second period of time to transmit signals into the first region is allocated to the Y tones during said second period of time. In some embodiments, said Y tones includes at least 70 tones. In various embodiments, transmitting user data includes transmitting modulated symbols on said Y tones, each of the Y tones communicating one symbol. 
         [0100]      FIG. 13  is flowchart  1300  of another exemplary method of operating a base station in a frequency division multiplexed system in accordance with the present invention. Operation starts in step  1302  where the base station is powered on and initialized and proceeds to step  1304 . 
         [0101]    In step  1304 , the base station transmitter is operated to transmit first signals into a first region using a set of N tones to communicate information over a first period of time using first signals in a first region, said first period of time being at least two seconds long, where N is larger than 20. Step  1304  includes sub-steps  1306 ,  1308 , and  1310 . In sub-step  1306 , for each second period of time, the base station transmitter is operated to transmit during a second period of time a second signal including a set of X tones into said first region, where X is less than 5, and where less than 80% of a maximum average total base station power used by said base station transmitter to transmit signals into the first region during any one second period during said first period of time is allocated to said set of X tones and each one of said X tones to which power is allocated is allocated at least 20 times the per tone average power allocated to tones during said any one second period. In sub-step  1308 , for each third period of time, the base station transmitter is operated to transmit during a third period of time a third signal into said first region including a set of Y tones, where Y≦N, each tone in said third set of tones to which power is allocated is allocated at most 8 times the average power allocated to tones during said first period of time, said third period of time having the same duration as said second period of time. In sub-step  1310 , for each fourth period of time, the base station is operated to transmit during a fourth period of time a fourth signal including a set of G tones into said first region, where G is less than 5, and where less than 80% of a maximum average total base station power used by said base station transmitter to transmit signals into the first region during any one second period of time during the first period of time is allocated to said set of G tones and each one of said G tones to which power is allocated is allocated at least 20 times the per tone average power allocated to tones during said any one second period of time. 
         [0102]    In some embodiments, the third period of time and said second period of time overlap, and the method further comprises modulating at least two of data, control and pilot signals on at least some of said set of Y tones. In some embodiments, the third period of time and the second period of time are disjoint, and the method further comprises modulating at least two of data, control and pilot signals on at least some of said set of Y tones. In various embodiments, at least one of said X tones is transmitted at predetermined fixed frequency and said at least one of said X tones is transmitted using a frequency having a fixed frequency offset≧0 from the lowest frequency tone in said set of N tones. In some embodiments, at least one of said X tones is transmitted at a frequency which is determined as a function of at least one of a base station identifier and a sector identifier. 
         [0103]    In some embodiments, for each repetition of said second period of time in said first period of time there are at least Z repetitions of said third period of time in said first period of time, where Z is greater than 10. In various embodiments Z is greater than 400. 
         [0104]    In some embodiments, the frequency of at least one of said G tones is a function of at least one of a base station identifier and a sector identifier and said at least one of G tones is not one of said set of X tones. For example, the at least one of X tones may correspond to a carrier beacon signal and the at least one of G tones may correspond to a cell/sector beacon, and the second time period and the fourth time period do not overlap. In some embodiments, the second and fourth time periods periodically repeat during the first period of time. In some embodiments, the second and fourth time periods repeat at different rates. 
         [0105]      FIG. 14  is a flowchart  1400  of an exemplary method of operating a base station transmitter in a communications system in accordance with the present invention. In some embodiments, the base station transmitter is a sector transmitter of a base station. In various embodiments, the sector transmitter corresponds to a single one of a plurality of carrier frequencies used by a sector of a base station. Operation starts in step  1402  where the base station transmitter is powered on and initialized. Operation proceeds from step  1402  to step  1404 . 
         [0106]    In step  1404 , the base station transmitter is operated to transmit a signal in a first period of time, said signal including a plurality of signal tones, each signal tone corresponding to a different frequency, said signal including a beacon transmitted on at least one tone and a user data signal transmitted in parallel with said beacon signal on tones which are not used to transmit said beacon signal, said user data having been transmitted by said first transmitter with average per tone power less than 1/20th of the transmission power of each tone used to transmit said beacon signal. 
         [0107]    Step  1404  includes sub-step  1406 . In sub-step  1406 , the base station transmitter uses the frequency of a tone in said transmitted beacon signal to convey information indicating at least one of a cell identifier, a sector identifier, and a carrier identifier. Operation proceeds from step  1404  to step  1408 . 
         [0108]    In some embodiments, the step of transmitting a signal in a first period of time includes transmitting user data on at least 100 tones and transmitting said beacon on less than 3 tones. In some embodiments at least N times the average per signal tone energy of said transmitted signal is transmitted on each of the tones in the signal used to transmit said beacon signal, where N is a positive value greater than 5, 20, 99, or 150. 
         [0109]    In various embodiments, the beacon signal is transmitted into a frequency band used by a base station located adjacent a cell in which said base station is located which is not used by said base station to transmit user data. 
         [0110]    In step  1408  the base station transmitter is operated to transmit a signal in a second period of time, which includes user data and which does not include any tones with a per tone transmission power that is more than 1/10 th  of the transmission power of each tone used to transmit the beacon signal. 
         [0111]    In one particular exemplary method of operating a base station transmitter in a frequency division multiplexed communications system in accordance with the invention, the method includes the steps of: transmitting first signals into a first region, e.g., sector, using a set of N tones to communicate information over a first period of time, said first period of time being at least two seconds long, where N is larger than 10; and transmitting during a second period of time a second signal including a set of X tones into said first region, where X is less than 5, and where less than 80% of a maximum average total base station transmission power used by said base station transmitter to transmit signals into the first region during any 1 second period during said first period of time is allocated to said set of X tones (sometime X is one or two) and each one of said X tones to which power is allocated receives at least 20 times (and sometimes 40, 60 or more times) the per tone average power allocated to tones during said any one second period. In some implementations, the first region is a sector of a cell; and said communications system is an orthogonal frequency division multiplexed system and wherein said second period of time is a period of time used to transmit an orthogonal frequency division multiplexed symbol. The particular exemplary method may include transmitting during a third period of time a third signal (e.g., a non-beacon signal) into said first region, said third signal not including said second signal, said third signal including a set of Y tones, where Y≦N, each tone in said third set of Y tones to which power is allocated at most 8 times the average per tone power allocated to tones during said first period of time. The method sometimes further includes modulating at least data, control and pilot signals on said set of Y tones. The different information may be modulated on different tones, e.g., with data being modulated on one tone or more tones, control on other tones and pilot signals on still other tones. In some implementations at least one of said X tones is transmitted at a transmission frequency which is determined as a function of at least one of a base station identifier and a sector identifier. In some implementations, for each repetition of said second period of time in said first period of time there are at least Z repetitions of said third period of time in said first period of time where Z is at least 10, but in some cases at least 20, 40 or 400. Thus, in a two second time interval, the method may involve several beacon time periods but many more time periods in which beacon signals are not transmitted, e.g., sometimes over 400 user data time periods for each beacon signal time period. Each of the second and third time periods may include one or multiple OFDM symbol transmission time periods. The second and third time periods may be the same or different in terms of duration depending on the implementation. Notably, user data signal tones are normally transmitted at ⅛ the average transmission power allocated to beacon signal tones which are transmitted at much higher power levels than the user data signal tones, e.g., 20 times or more the power level in some cases. The above described method implementations are only some exemplary implementations, and are not the only method implementations which are possible in accordance with the invention. 
         [0112]    In one exemplary embodiment, a base station transmitter for use in a communication system, includes a transmitter for transmitting signals including multiple tones, each tone corresponding to a different frequency; and a transmitter control module for controlling the transmitter to transmit a signal in a single symbol transmission time period using a plurality of signal tones that are transmitted in parallel, each signal tone corresponding to a different frequency, said control means causing user data to be transmitted on signal tones with more than 20% of the base stations transmitter&#39;s maximum possible transmission power for a symbol time period being placed on tones used to communicate user data, said signal also including a beacon signal transmitted on at least one tone on which user data is not transmitted, said beacon signal being transmitted with more than 20 times the transmission power of any of the signal tones used to transmit user data. In some implementations, the transmitter control module controls the transmitter to transmit the beacon signal in a frequency band used by an adjacent transmitter to transmit user data and which is not used by said transmitter to transmit user data, e.g., the beacon signal is transmitted into the frequency band normally used by a neighboring sector or base station transmitter for establishing communications links with WTs being serviced by the transmitter. In some cases, the second period of time occurs within said first period of time; and the X tones is a subset of said N tones. The base station in the exemplary base station embodiment being described includes stored user data including at least one of voice, text and image data to be communicated; and the first control module includes control logic for controlling the transmitter to transmit user data on at least one tone during said first period of time and to transmit user data on a plurality of Y tones which are a subset of said N tones, said Y tones not being included in said X tones during said second period of time. 
         [0113]    In yet another exemplary base station embodiment, a base station transmitter of the invention which is for use in a communication system, e.g., an OFDM communications system includes: a transmitter for transmitting signals including multiple tones, each tone corresponding to a different frequency; and a transmitter control module for controlling the transmitter to transmit a signal in a single symbol transmission time period using a plurality of signal tones that are transmitted in parallel, each signal tone corresponding to a different frequency, said control means causing user data to be transmitted on signal tones with more than 20% of the base stations transmitter&#39;s maximum possible transmission power for a symbol time period being placed on tones used to communicate user data, said signal also including a beacon signal transmitted on at least one tone on which user data is not transmitted, said beacon signal being transmitted with more than 20 times the transmission power of any of the signal tones used to transmit user data. The base station transmitter control module may include logic for controlling the transmitter to transmit said beacon signal in a frequency band used by an adjacent transmitter to transmit user data and which is not used by said transmitter to transmit user data. The transmitter may be a sector transmitter in which case the first region is a sector of a cell, In some embodiments said communications system is an orthogonal frequency division multiplexed system and the second period of time is a period of time used to transmit an orthogonal frequency division multiplexed symbol. In some base station implementations, at least one of the X tones used by the base station is transmitted at a frequency which is determined as a function of at least one of a base station identifier and a sector identifier. The base station includes control circuitry and/or logic for transmitting during a third period of time a third signal into said first region, the third signal, e.g., a user data signal, not including said second signal which may be, e.g., a beacon signal, said third signal including a set of Y tones, where Y≦N, each tone in said third set of Y tones to which power is allocated having at most 8 times the average per tone power allocated to tones during said first period of time. Thus, in such an implementation, signals corresponding to user data will be transmitted with much less power, eg., 1/20 or less of the power allocated to beacon signal tones. The base station includes a control module and/or logic for transmitting during a third period of time a third signal into said first region, aid third signal not including said second signal, said third signal including a set of Y tones, where Y≦N, each tone in said third set of Y tones to which power is allocated at most 8 times the average per tone power allocated to tones during said first period of time, said third period of time having the same duration as said second period of time, wherein for each repetition of said second period of time in said first period of time there are at least Z repetitions of said third period of time in said first period of time where Z is at least 10 and, in some cases Z is at least 400. 
         [0114]    While described primarily in the context of an OFDM system, the methods and apparatus of the present invention, are applicable to a wide range of communications systems including many non-OFDM and/or non-cellular systems. 
         [0115]    Control modules, e.g., transmission control modules, implemented in accordance with the invention may perform multiple transmission control operations. In such a case, the module includes circuitry and/or logic, e.g., stored instructions, for performing each of the control operations attributed to the control module. Thus, a single control module may multiple means, one for performing each control operation attributed to the control module. Similarly, routines may include instructions for performing multiple operations where the instructions corresponding to a particular operation represent a means for performing the operation. 
         [0116]    In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, for example, carrier band selection, digital signal processing, energy detection/SNR detection, decoding, timing synchronization, signal quality detection, etc. In some embodiments various features of the present invention 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, the present invention is 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). 
         [0117]    Numerous additional variations on the methods and apparatus of the present invention described above will be apparent to those skilled in the art in view of the above description of the invention. Such variations are to be considered within the scope of the invention. The methods and apparatus of the present invention 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 the present invention.

Technology Category: h