Abstract:
Methods and apparatus are provided for optimizing a receive side subsystem of a cellular communication system with a transmit side subsystem of the system. The receive side subsystem includes one or more superconducting components, preferably a superconducting filter, coupled to an amplifier, preferably a low noise amplifier. The transmit side subsystem includes a transmitter and, preferably, a power amplifier. The system matches and balances the range or radius of the received side subsystem with the range or radius of the transmit side subsystem. As a result, the receive range and the transmit range of the system overlap. A control system configured to match and balance the subsystems is optionally provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Application Serial No. 60/277,418, entitled “Apparatus and methods for improved tower mount systems for cellular communications,” filed Mar. 19, 2001, and from co-pending U.S. Provisional Application Serial No. 60/277,419, entitled “Method and apparatus for combined receive and transmit subsystems in cellular communication systems,” filed Mar. 19, 2001, the disclosures of which are expressly incorporated herein by reference in their entireties. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of telecommunications and cellular communications, such as, e.g., cellular telephone communications. More particularly, this invention relates to telecommunications and cellular communications systems, which may include the use of tower mountable superconducting components, configured to balance received signal strength with transmitted signal strength to increase system capacity while reducing dropped and blocked calls.  
         BACKGROUND  
         [0003]    Radio frequency (RF) equipment have used a variety of approaches and structures for receiving and transmitting radio waves and other signals in selected frequency bands. The type of filtering structure used often depends upon the intended use and the specifications for the radio equipment. For example, dielectric filters may be used for filtering electromagnetic energy in the ultra-high frequency (UHF) band, such as, e.g., those used for cellular communications in the 800+ MHz frequency range. Because of an increase in the number of users utilizing a limited bandwidth, demand has increased for greater frequency selectivity than can be provided by normal or non-superconducting resonator filters, especially for RF signals in the ultra-high frequency bands that may be used for cellular communications. As a result, substantial attention has recently been devoted to the development of high temperature superconducting (HTS) RF filters for use in, for example, cellular telecommunications systems, to accomplish and optimize high frequency selectivity.  
           [0004]    Current telecommunications systems may include a receive side subsystem, such as a receiver front-end that incorporates an HTS filter system. A current, prior art telecommunications system  10  incorporating an HTS receiver front-end (not shown), an antenna array  14 , and a tower  12  is depicted in FIG. 1. Because the performance of the HTS receiver front-end is enhanced relative to a conventional, non-HTS receiver front-end, the prior art system  10  will generally be able to receive signals from a greater receive coverage area  18  than the transmit coverage area  16  for the system&#39;s  10  transmitter. It should be noted that, as drawn, the transmit coverage area  16  is shown slightly above the receive coverage area  18 . But, this separation is shown merely for purposes of drawing clarity. In practice, the coverage areas  16 ,  18  are substantially overlaid. Turning back to the technical deficiencies of the current, prior art system  10 , the end result of the larger receive coverage area  18 , relative to the transmit coverage area  16 , is that users within the receive coverage area  18  will be heard, but will not necessarily be able to receive signals due to the limited capability of the transmitter relative to the HTS receiver front-end. As a further consequence, users in the unbalanced coverage area  20  of the system  10 , i.e., where the receive coverage area  18  extends but the transmit coverage area  16  does not, are often dropped, and/or their calls are often blocked. Those of ordinary skill in the art have failed to provide an effective solution to this problem. For example, some current systems incorporating an HTS receiver front-end may address this problem by merely generating a transmit radius that is equivalent to the maximum receive radius. This is undesirable because the transmit side subsystem often does not need to operate at maximum power in order to cover an area equal to the receive radius at any one time.  
           [0005]    Thus, it is believed that those of ordinary skill in the art would find a telecommunications system that matched the transmit coverage area with the receive coverage area to be quite useful. Furthermore, it is believed that those skilled in the art would find a tower mounted communications system incorporating HTS components, wherein the system balances the transmit and receive radii, to be useful. Additionally, it is believed that a tower mounted communication system incorporating a dynamically controllable transmit side subsystem to dynamically generate a transmit radius substantially equivalent to a receive radius would be useful.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to methods and systems for transmitting and receiving telecommunications signals. More particularly, the present invention is directed to tower mounted telecommunications systems that preferably incorporate superconducting materials and that balance transmitted and received signals in order to increase the coverage area of the systems while also reducing dropped and blocked calls.  
           [0007]    In one aspect of the present invention, a method for optimizing a telecommunications system is provided. A receive side subsystem that may include an HTS receiver front-end is provided within the system. A transmit side subsystem, with may include a power amplifier, is also provided within the system. A receive coverage area of the receive side subsystem is determined. Subsequently, a power of the transmit side subsystem is adjusted in order to generate a transmit signal having a transmit coverage area that is substantially equivalent to the receive coverage area. To adjust the power of the transmit side subsystem, the power amplifier may be operated to generate the appropriate transmit signal strength.  
           [0008]    This method of the present invention may also include mounting the receive side subsystem atop a tower. Additionally, the transmit side subsystem may also be mounted atop the tower. When the receive side and the transmit side subsystems are both mounted atop the tower, the receive side subsystem and the transmit side subsystem may be enclosed in a common enclosure.  
           [0009]    A power distribution unit that is capable of adjusting the power of the transmit side subsystem may be provided. The power distribution unit may be coupled to the transmit side subsystem. The power distribution unit may also be coupled to the receive side subsystem. The power distribution unit may include a logic unit that is configured to determine the receive coverage area of the receive side subsystem, compare the receive coverage area with the transmit coverage area, and determine the proper strength of a transmit signal having a transmit coverage area substantially equivalent to the receive coverage area.  
           [0010]    The receive coverage area may be continuously monitored, and the power of the transmit side subsystem may be continuously varied in order to maintain the transmit coverage area substantially equivalent to the receive coverage area.  
           [0011]    In another aspect of the present invention, a method for optimizing a telecommunications system having a tower and a first amplifier with a power per carrier capacity is provided. The first amplifier is removed from the system. Then, an HTS receiver front-end is installed atop the tower. A second amplifier, having a power per carrier capacity of at least substantially twice the power per carrier capacity of the first amplifier, is installed.  
           [0012]    The second amplifier may be dynamically controllable. When the second amplifier is dynamically controllable, a receive signal radius of the HTS receiver front-end is determined. A transmit signal radius substantially equivalent to the receive signal radius is then generated by adjusting the power per carrier capacity of the second amplifier. The receive signal radius is continuously monitored. Additionally, the power per carrier capacity of the second amplifier is continuously varied in order to maintain the transmit signal radius substantially equivalent to the receive signal radius.  
           [0013]    In one embodiment, the power per carrier capacity of the first amplifier is not greater than substantially 20 watts, and the power per carrier capacity of the second amplifier is at least substantially 40 watts. In another embodiment, the power per carrier capacity of the second amplifier is substantially at least twice the power per carrier capacity of the first amplifier.  
           [0014]    A power distribution unit may also be installed within the system. The power distribution unit may be configured to vary the power per carrier capacity of the second amplifier. The power distribution unit may be coupled to the second amplifier. Additionally, the power distribution unit may be coupled to the HTS receiver front-end.  
           [0015]    In another aspect of the present invention, a method for optimizing a telecommunications system including a superconducting receive side subsystem having a receive coverage area is provided. A transmit side subsystem is provided within the system. The transmit side subsystem includes a power amplifier, and has a transmit coverage area. The receive coverage area of the receive side subsystem is determined. The receive coverage area is then compared with the transmit coverage area. The transmit coverage area is adjusted so that the transmit coverage area is substantially equivalent to the receive coverage area.  
           [0016]    When the receive coverage area is initially greater than the transmit coverage area, a power level of the power amplifier is increased in order to increase the transmit coverage area to an area substantially equal to the receive coverage area. When the receive coverage area is initially less than the transmit coverage area, a power level of the power amplifier is decreased in order to decrease the transmit coverage area to an area substantially equal to the receive coverage area. Additionally, when the receive coverage area and the transmit coverage area are initially substantially equal, the power level of the power amplifier is maintained.  
           [0017]    A power distribution unit may be provided within the system. The power distribution unit may include a logic unit configured to determine the receive coverage area of the receive side subsystem, compare the receive coverage area with the transmit coverage area, and determine a transmit signal strength sufficient to produce a transmit coverage area substantially equivalent to the receive coverage area. The power distribution unit may also be coupled to the receive side subsystem. Furthermore, the power distribution unit may be coupled to the transmit side subsystem.  
           [0018]    This method may also include continuously repeating the determining the receive coverage area step, comparing the receive coverage area with the transmit coverage area step, and adjusting the transmit coverage area step during the operation of the system.  
           [0019]    Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 illustrates a current, prior art telecommunications system incorporating an HTS receiver front-end that does not account for an extended coverage area of the HTS receiver relative to the smaller coverage area of the transmitter of the prior art system.  
         [0021]    [0021]FIG. 2 a  illustrates an embodiment of a telecommunications system having substantially equal transmit and receive coverage areas, according to the present invention.  
         [0022]    [0022]FIG. 2 b  illustrates another embodiment of a telecommunications system having substantially equal transmit and receive coverage areas, according to the present invention.  
         [0023]    [0023]FIG. 3 illustrates an embodiment of a flow process for a method of balancing a transmit coverage area with a receive coverage area, according to the present invention.  
         [0024]    [0024]FIG. 4 illustrates another embodiment of a flow process for a method of balancing a transmit coverage area with a receive coverage area, according to the present invention.  
         [0025]    [0025]FIG. 5 illustrates a multiple tower telecommunications system with overlapping receive and transmit coverage areas, according to the present invention.  
         [0026]    [0026]FIG. 6 shows a software generated comparison of transmit and receive capacity for a non-HTS multiple tower telecommunications system having four towers.  
         [0027]    [0027]FIG. 7 shows a software generated comparison of transmit and receive capacity for an HTS multiple tower telecommunications system having four towers.  
         [0028]    [0028]FIG. 8 shows a software generated comparison between transmit and receive capacity for the HTS multiple tower telecommunications system of FIG. 7, wherein the strength of a power amplifier of the transmit side subsystem is increased.  
         [0029]    [0029]FIG. 9 shows a software generated comparison of transmit and receive area coverage for a non-HTS multiple tower telecommunications system having four towers.  
         [0030]    [0030]FIG. 10 shows a software generated comparison of transmit and receive area coverage for an HTS multiple tower telecommunications system having four towers.  
         [0031]    [0031]FIG. 11 shows a software generated comparison of transmit and receive area coverage for the HTS multiple tower telecommunications system of FIG. 10, wherein the strength of a power amplifier of the transmit side subsystem is increased. 
     
    
     DETAILED DESCRIPTION  
       [0032]    The present invention provides systems, processes, and methods for balancing transmitted and received signals in HTS telecommunications systems in order to increase the coverage area of the systems while also reducing dropped and blocked calls.  
         [0033]    Turning to the preferred embodiments, FIG. 2 a  illustrates one telecommunications system  100  of the present invention. As shown, the telecommunications system  100  is a tower mounted system. Nevertheless, one skilled in the art will recognize that other configurations for the system  100 , such as conventional, non-tower mounted implementations, may be utilized. The system  100  includes a tower or mast  102  and a base station  150  located near the bottom of the tower  102 . An antenna or a plurality of antennas  103  is mounted towards the top of the tower  102 . In FIG. 2 a , an array/plurality of antennas  103  is illustrated. Each antenna may be dedicated to either receiving or transmitting signals. Alternatively, each antenna is used to both transmit and receive signals. Additionally, a single antenna capable of both receiving and transmitting signals may be incorporated in the system  100 , rather than the illustrated array or plurality of antennas  103 .  
         [0034]    A first transmission path  109 , which may incorporate a coaxial cable, connects the antennas  103  with a front-end subsystem  110 . The front-end subsystem  110  is preferably mounted atop the tower  102  in proximity to the antennas  103 , thereby reducing the length of the transmission path  109 , and minimizing the cable length required to connect the subsystem  110  with the antennas  103 . In an alternative embodiment, the front-end subsystem  110  may be located near or within the base station  150  rather than atop the tower  102 .  
         [0035]    The front-end subsystem  110  is preferably enclosed within an environmentally protective system housing  134 . The housing  134  is designed to isolate the electronics and components of the front-end subsystem  110  from ambient forces. Consequently, any suitable housing capable of insulating the subsystem  110  from external forces and inclement weather is usable for the housing  134 . Further, the housing  134  is mountable to the tower  102  using any suitable attachment means, such as, e.g., brackets, placement on a platform, being formed as an integral part of the tower  102 , or the like.  
         [0036]    The housing  134  protects the front-end subsystem  110 , which includes a receive side subsystem  120  and other electronics. For example, if the transmit side subsystem (not shown) is incorporated within the subsystem  110  instead of being located in the base station  150 , the housing  134  also protects a transmit filter and a power amplifier. A system having a front-end subsystem that incorporates both the receive side and transmit side subsystems is discussed herein, and illustrated in FIG. 2 b.    
         [0037]    Turning back to FIG. 2 a , the front-end subsystem  110  includes an HTS receive side subsystem  120 , such as, e.g., an HTS receiver front-end. The receive side subsystem  120  is also located within the housing  134 , and preferably incorporates both an HTS filter  122  and a low noise amplifier  124  (LNA). Although one HTS filter  122  and one LNA  124  is shown in FIG. 2 a , a plurality of HTS filters  122  and a plurality of LNAs  124  may be incorporated into the receive side subsystem  120 .  
         [0038]    The HTS filter  122  is preferably manufactured from a thin-film superconductor, although the present invention also contemplates other constructions such as thick-film superconductors. The thin-film superconductor may, for example, comprise a yttrium containing superconductor known generally as a YBCO superconductor, or, alternatively, a thallium-based superconducting compound. U.S. Pat. No. 6,083,884, entitled, “A-axis high temperature superconducting films with preferential in-plane alignment,” and U.S. Pat. No. 5,358,926, entitled, “Epitaxial thin superconducting thallium-based copper oxide layers,” disclose exemplary thin-film superconductors that may be used with the present invention. The disclosures of the &#39;884 and the &#39;926 patents are fully and expressly incorporated by reference herein. The invention is not, however, limited to a particular type or class of superconductors, i.e., any HTS superconductor that will properly filter RF signals at HTS temperatures may be used in constructing the HTS filter  122 .  
         [0039]    The receive side subsystem  120  may also incorporate a non-superconducting filter in addition to an HTS filter  122 . Such a subsystem is disclosed in co-pending and commonly assigned U.S. patent application Ser. No. 09/818,100, filed Mar. 26, 2001, and entitled, “A filter network combining non-superconducting and superconducting filters.” U.S. patent application Ser. No. 09/818,100 is fully and expressly incorporated by reference herein.  
         [0040]    The receive side subsystem  120  further includes a cryocooler  126  that is used to cool the HTS filter  122  and LNA  124 , and possibly other electronic components that may be incorporated into the receive side subsystem  120 . The cryocooler  126  included with the receive side subsystem  120  may be any suitable cryocooler, such as, e.g., a Stirling cycle cryocooler, a Brayton cycle cryocooler, a Gifford-McMahon cryocooler, a pulse tube cryocooler, and the like. Exemplary cryocoolers are disclosed in U.S. Pat. No. 6,327,862, entitled, “Stirling cycle cryocooler with optimized cold end design,” and U.S. Pat. No. 6,141,971, entitled “Cryocooler motor with split return iron.” The disclosures of the &#39;862 and the &#39;971 patents are fully and expressly incorporated herein by reference. U.S. Pat. No. 6,311,498, entitled “Tower mountable cryocooler and HTSC filter system,” also discusses cryocoolers suitable for use with the present invention. The disclosure of the &#39;498 patent is also fully and expressly incorporated herein by reference.  
         [0041]    The cryocooler  126  is thermally coupled at its cold end to a cryogenic enclosure  128  that contains the HTS components and other electronics. The cryogenic enclosure  128  is preferably a vacuum dewar. The use of a vacuum dewar for the cryogenic enclosure  128  minimizes the transfer of heat from the external environment to the inside of the cryogenic enclosure  128 .  
         [0042]    A cold stage  127  is preferably located within the cryogenic enclosure  128 . The cold stage  127  preferably contains thereon the HTS filter  122  and the LNA  124 . Optionally, other electronic components that are used in the receive side subsystem  120  may also be located upon the cold stage  127 . The cold stage  127  may have a single face, or, optionally, a plurality of faces to hold a number of HTS filters  122  and LNAs  124 . A cooling transfer segment or cold finger  125  couples the cold stage  127  with the cryocooler  126 . The cooling transfer segment  125  facilitates thermal transfer between the cold stage  127  and the cryocooler  126 .  
         [0043]    Further details of an exemplary receive side subsystem  120  suitable for use with the present invention are described in co-pending and commonly assigned U.S. application Ser. No. 10/017,147, filed Dec. 13, 2001, and entitled, “MEMS-based bypass system for use with a HTS RF receiver.” The disclosure of U.S. application Ser. No. 10/017,147 is fully and expressly incorporated by reference herein.  
         [0044]    The front-end subsystem  110  of system  100  does not include a transmit side subsystem  116 . Rather, the transmit side subsystem  116  is located within the base station  150 . The transmit side subsystem  116  includes a power amplifier  114  coupled to the transmit electronics  156 , which in turn is coupled to a power distribution unit  158 . The power amplifier  114  is also coupled to a transmitter filter  112 . The transmitter filter  112  may be a conventional, non-superconducting filter. Alternatively, the transmitter filter  112  may incorporate superconducting materials. In this alternative embodiment, suitable cryogenic components are included within the transmit side subsystem  116 , similar to the cryogenics incorporated within the receive side subsystem  120 . In an alternative embodiment, the transmit side subsystem  116  may be included within the front-end subsystem  110  rather than being placed within the base station  150 .  
         [0045]    Turning back to the embodiment illustrated in FIG. 2 a , transmit signals, as a component of a combined transmit/receive signal, are received by a first front-end multiplexer  130  within the front-end subsystem  110 . The first front-end multiplexer  130  separates out the transmit signal component of the combined signal, and delivers the transmit signal to a second front-end multiplexer  230 . The second front-end multiplexer  230  then delivers the transmit signal to the antennas  103 , via the first transmission path  109 , for broadcast into the transmit coverage area  160  of the system  100 . As will be discussed, the strength of the transmit signal, i.e., the transmit coverage area  160 , is adjusted by the system  100  such that the transmit coverage area  160  is substantially equal to the receive coverage area  180 , thereby eliminating or substantially reducing dropped calls or blocked calls within the coverage area of the system  100 .  
         [0046]    The system  100  preferably includes a second transmission path  132 . Like the first transmission path  109 , the second transmission path  132  preferably includes a coaxial cable. The second transmission path  132  connects the front-end subsystem  110  with the base station  150 . For example, the second transmission path  132  carries a combined transmit/receive signal to and from the base station  150  to the first front-end multiplexer  130 .  
         [0047]    To process a received RF signal, a RF signal received by the antennas  103  is first delivered to the second front-end multiplexer  230 , as a component of a combined transmit/receive signal, via the first transmission path  109 . The second front-end multiplexer  230  separates the receive signal from the combined signal and transmits the receive signal to the receive side subsystem  120 . Once received by the receive side subsystem  120 , the RF signal, i.e., the received signal, is filtered by the HTS filter  122  to remove any signals in unwanted frequencies, and is amplified by the LNA  124 . The filtered and amplified RF signal is then relayed to the first transmitter/receiver system multiplexer  130 .  
         [0048]    The first transmitter/receiver system multiplexer  130  delivers the received signal, as part of a combined transmit/receive signal, to the base station  150 , via the second transmission path  132 , for further processing. In the base station  150 , a base station side multiplexer  152  splits the received signal from the combined signal, and the received signal is provided to receive electronics  154  for processing. The receive electronics  154  are further coupled to a power distribution unit  158 , which will be described herein.  
         [0049]    Turning now to FIG. 2 b , an embodiment of the present invention, system  100 ( b ), that includes the transmit side subsystem  116  mounted atop the tower  102  is shown. As illustrated, the transmit side subsystem  116  is incorporated within front-end subsystem  110 ( b ). Because the transmit side subsystem  116  has been moved to a position atop the tower  102 , base station  150 ( b ) no longer contains these components. Components that are common to both system  100  and system  100 ( b ) are identified with like numbers, and reference is made to the description of these components with respect to system  100 .  
         [0050]    The multiplexers  152 ,  130 , and  230  operate to deliver received signals in a manner substantially similar as described with regard to system  100 . Because the transmit side subsystem  116  of system  100 ( b ) is located atop the tower  102  instead of within base station  150 ( b ), the operation of the multiplexers  152 ,  130 , and  230  with regard to transmit signals differs somewhat from system  100 . A transmit signal is generated by the transmit electronics  156  within the base station  150 ( b ), and is delivered to the base station side multiplexer  152 . The base station side multiplexer  152  delivers the transmit signal to the front-end subsystem  110 ( b ), via the second transmission path  132 , as part of a combined transmit/receive signal. Once received by the front-end subsystem  110 ( b ), the first front-end multiplexer  130  splits the transmit signal from the combined transmit/receive signal, and delivers the transmit signal to the transmit side subsystem  116 . The transmit side subsystem  116  amplifies and filters the transmit signal in a manner substantially similar as previously described with system  100 . The transmit side subsystem  116  then delivers the amplified and filtered transmit signal to the second front-end multiplexer  220 . The second front-end multiplexer  220  provides the amplified and filtered transmit signal, via the first transmission path and as part of a combined transmit/receive signal, to the antennas  103  for broadcast.  
         [0051]    As noted, the present invention optimizes the performance of a telecommunications system by generating substantially equal transmit and receive coverage areas. Exemplary processes of the present invention that ensure substantially equal transmit and receive coverage areas will now be discussed. It should be noted that although the following discussion refers primarily to system  100  this discussion is equally applicable to system  100 ( b ). As previously detailed, the systems of the present invention include transmit electronics  156  coupled to both the transmit side subsystem  116  and the power distribution unit  158 . The power distribution unit  158  optimizes the operation of the systems by implementing a logic process  30 , as shown in FIG. 3. It is noted that one of ordinary skill in computer programming is capable of developing a program that implements the logic process  30 . Consequently, details of a specific program for implement the logic process  30  is not discussed herein.  
         [0052]    The power distribution unit  158  preferably incorporates a logic unit (not shown) to implement and operate the logic process  30 . The logic unit may include a suitable central processing unit, a memory component suitable for storing the process  30 , which may be, e.g., read only memory (ROM), flash memory, non-volatile EEPROM, or the like, a memory component suitable for storing temporary data related to receive and transmit signal strengths, which may be, e.g., random access memory (RAM), flash memory, non-volatile EEPROM, or the like, and input/output components to communicate with the transmit electronics  156  and the receive electronics  154 .  
         [0053]    Turning to FIG. 3, the logic unit receives a received signal from the receive electronics  154 . (Step  32 ). The logic unit then determines the strength of the received signal. By determining the strength of the received signal, the logic unit also calculates the receive coverage area  180  of the system  100 . (Step  34 ). Utilizing the receive coverage area  180 , the logic unit calculates the transmit signal strength necessary to generate a transmit coverage area  160  of substantially the same area as the receive coverage area  180 . (Step  36 ). Once the logic unit determines the proper transmit signal strength to generate the desired transmit coverage area  160 , the logic unit instructs the power distribution unit  158  to transmit an appropriate instruction to the transmit electronics  156 . (Step  38 ).  
         [0054]    Upon receipt of an instruction from the power distribution unit  158 , the transmit electronics  156  generate a transmit signal, and relays the transmit signal to the power amplifier  114 . Based on the instruction received from the power distribution unit  158 , the transmit electronics  156  also adjusts the power of the power amplifier  114  to an appropriate level. (Step  38 , FIG. 3). For example, upon receipt of a command signal from the power distribution unit  158 , the transmit electronics  156  may set the power, which may be the power per carrier capacity, of the power amplifier  114  to a level adequate to amplify the transmit signal and generate a transmit coverage area  160  that will substantially match the receive coverage area  180 . The power amplifier  114  increases the signal strength of the transmit signal to the desired level, and then relays the amplified transmit signal to the transmitter filter  112 . The transmit side subsystem  116  is preferably coupled to the base station side multiplexer  152 . Accordingly, the transmit side subsystem  116  provides the base station side multiplexer  152  with the amplified transmit signal. The base station side multiplexer  152  subsequently provides the amplified transmit signal, as a component of a combined transmit/receive signal, to the first front-end multiplexer  130 , via the second transmission path  132 . Once received by the front-end subsystem  110 , the subsystem  110  processes the amplified transmit signal as previously described, and broadcasts the signal to produce the transmit coverage area  160 .  
         [0055]    Consequently, by executing the process  30  shown in FIG. 3, the power distribution unit  158  ensures that users within an area covered by the system  100  can both transmit and receive RF signals. In other words, the system  100  will produce transmit and receive coverage areas  160 ,  180  of substantially the same size.  
         [0056]    The receive coverage area  180  of the system  100  may vary during the operation of the system  100  due to a number of factors, such as, e.g., an increase in the number of users in the area or a decrease in the number of users in the area. Also, communications systems may utilize protocols that are inherently dynamic, such as, e.g., code division multiple access (CDMA) systems and the like. Accordingly, to compensate for receive coverage areas that may vary during the operation of the system  100 , the power distribution unit  158  may be further capable of continuously varying the transmit coverage area  160  to substantially match the receive coverage area  180 . To provide for a continuously variable system  100 , the power amplifier  114  of the transmit side subsystem  116  is preferably one wherein the power level may be dynamically or continuously adjusted.  
         [0057]    Turning to FIG. 4, a process  40  for varying the transmit coverage area  160  during the operation of the system  100  is illustrated. Steps  32 ,  34 , and  36  are substantially similar to these steps of process  30 , and reference is made to the discussion of these steps for process  30  as these steps apply to process  40 . Turning specifically to process  40 , the logic unit of the power distribution unit  158 , after it determines the proper transmit signal strength (Step  36 ), compares the transmit signal strength with the previous transmit signal strength. (Step  42 ). If signal strengths are equivalent, the logic unit instructs the power distribution unit  158  to maintain the transmit signal strength constant; the power distribution unit  158  subsequently relays the instruction to the transmit electronics  154 . (Step  44 ). If, however, the logic unit determines that the transmit signal strength has changed, the logic unit instructs the power distribution unit  158  to adjust the transmit signal accordingly; the power distribution unit  158  subsequently relays the instruction to the transmit electronics  154 . Here, the transmit signal strength may be decreased if the logic unit determines that the receive coverage area has been reduced. Or, the transmit signal strength may be increased if the logic unit determines that the receive coverage area has increased.  
         [0058]    The present invention also provides for a method of retrofitting existing telecommunications systems to provide a system in accordance with the present invention. In one embodiment of this method of retrofitting, the existing telecommunications system may be substantially similar to the prior art system  10  illustrated in FIG. 1. For example, the existing telecommunications system may include a power amplifier that does not exceed 20 watts of power per carrier. The existing system also includes an HTS receiver. The existing HTS receiver is preferably capable of operating at up to substantially 40 watts of power per carrier. Therefore, when this existing telecommunications system is in operation, the receive coverage area may be greater than the transmit coverage area. The problems that may result from this imbalance, such as, e.g., calls being dropped or blocked, have been previously discussed.  
         [0059]    The present invention provides for a method of retrofitting this existing telecommunications system by, first, removing the existing power amplifier from the installation. Next, a power amplifier suitable of generating at least substantially 40 watts of power per carrier is installed into the system, thereby replacing the old power amplifier. The power distribution unit  158  is also installed and added to the system, and is coupled to both the transmit and receive electronics of the system. The power distribution unit  158  is then operated to increase the possible power generated by the power amplifier to at least substantially 40 watts per carrier, thereby matching the capacity of the HTS receiver. The power distribution unit  158  implements the process  30  shown in FIG. 3 to enable the system to balance the receive coverage area and the transmit coverage area of the system. Further, the power distribution unit  158  may also implement process  40  as shown in FIG. 4 to continuously vary and adjust the power per carrier capacity of the power amplifier, thereby dynamically adjusting the transmit coverage area relative to the receive coverage area to compensate for any variations in the receive coverage area. Preferably, this retrofit method increases the transmit power of an existing telecommunications system by at least a magnitude of two.  
         [0060]    [0060]FIG. 5 illustrates a multiple tower telecommunications system  500  with overlapping receive and transmit coverage areas, according to the present invention. As shown, the multiple tower system  500  utilizes a plurality of systems  100 ( b ) that include a receive side subsystem  120  and a transmit side subsystem  116 . Both subsystems  120 ,  116  are both mounted and elevated on a tower  102 . Alternatively, the multiple tower system  500  may incorporate a plurality of systems  100 , wherein only the receive side subsystems  120  are mounted and elevated on the tower  102 . The following discussion will focus on a multiple tower system  500  that includes a plurality of systems  100 ( b ), although it will be appreciated that the discussion applies equally to a multiple tower system  500  having a plurality of systems  100 .  
         [0061]    Multiple tower system  500  provides for an overlap of transmit coverage areas  160  and receive coverage areas  180  amongst the plurality of systems  100 ( b ). The overlap of the plurality of transmit and receive coverage areas  160 ,  180  allows for an increased overall capacity for the multiple tower system  500 , in comparison to a single system  100 ( b ) in isolation. For example, the overlap between the coverage areas  160 ,  180  of the systems  100 ( b ) allows the multiple tower system  500  to “handoff” users  502  amongst the plurality of systems  100 ( b ), thereby creating an overall larger coverage area  160 , 180  for the multiple tower system  500  than would be possible for any single system  100 ( b ). Additionally, the individual systems  100 ( b ) are arrayed such that there are no gaps in any overlapping coverage areas  160 ,  180 . Any gaps in overlapping coverage areas  160 ,  180  would result in user calls being dropped when a user is within a gapped area.  
         [0062]    FIGS.  6  to  8  show software generated comparisons of transmit and receive user capacities for a non-HTS multiple tower telecommunications system having four towers, and similar comparisons for an HTS multiple tower system that implements the systems and methods of the present invention.  
         [0063]    Turning first to FIG. 6, a software generated comparison of transmit and receive user capacities is shown for a non-HTS system that has a 6 dB noise figure for the receive side subsystems and transmit side subsystems that are operating at 20 W. The transmit capacity for the non-HTS multiple tower system is shown in the top screen shot, with the light area of the screen indicating the transmit capacity range for the non-HTS system. The bottom screen shot of FIG. 6 shows the receive capacity for the same non-HTS system, with the area of overlap between the individual towers shown in the light areas. There is a gap in receive user capacity that is illustrated by the gap between the light areas in the center of the bottom screen shot. When this system is processing 36 users, the system has adequate transmit capacity. The receive capacity is limited, however, and dropped calls, or call blocking, begins occurring at 36 users because of the gap in coverage seen in the bottom screen shot of FIG. 6. Therefore, there is an imbalance between the transmit and receive capacity of this non-HTS system.  
         [0064]    Turning now to FIG. 7, software generated comparisons of transmit and receive user capacities are illustrated for an HTS multiple tower system of the present invention, such as, e.g., system  500 . Because the system incorporates HTS filters in the receive side subsystems, the noise figure for the receive side is reduced to 2 dB, assuming a 6 dB noise figure for a comparable, non-HTS system. For FIG. 7, a power level of 20 W is maintained for the transmit side subsystems. Referring to the bottom screen shot, which shows the receive user capacity for the HTS system, the reduced noise figure for the receive side subsystems results in an overlap of receive capacity for all of the individual systems of the multiple tower HTS system, i.e., there are no gaps in receive capacity. With respect to the transmit capacity of the same HTS system, however, gaps in transmit capacity begin to appear when 48 users are employing the system. The gaps in transmit capacity are represented by the dark areas between the larger, lighter areas in the top screen shot. Therefore, the performance of the HTS multiple tower system is limited on the transmit side, not the receive side.  
         [0065]    Using the systems methods of the present invention, the transmit capacity of the HTS multiple tower system is adjusted to balance the transmit and receive user capacities. With reference to the system modeled in FIG. 7, FIG. 8 illustrates software generated comparisons of the transmit and receive capacities for the system when, utilizing the systems and methods of the present invention, it is determined that the power to the transmit side subsystems may be increased to 70 W to compensate for the increased performance of the HTS receive side subsystems. The present invention is utilized to determine that the maximum transmit and receive user capacities may be increased to support 70 users without dropped or blocked calls, which in this case requires increasing the power of the transmit side subsystems to 70 W. The transmit user capacity is represented by the light areas in the top screen shot. As is seen in the bottom screen shot, all of the receive user capacities of the individual HTS systems of the multiple HTS tower systems overlap, with no gaps, when 70 users are supported.  
         [0066]    FIGS.  9  to  11  show software generated comparisons of transmit and receive coverage areas (as opposed to the user capacities shown in FIGS.  6  to  8 ) for a non-HTS multiple tower telecommunications system having four towers, and similar comparisons for an HTS multiple tower system that implements the systems and methods of the present invention. The transmit and receive coverage areas in these figures are for lightly loaded systems, i.e., approximately 21 to 25 users are using the respective systems.  
         [0067]    Turning first to FIG. 9, the transmit and receive coverage areas for a non-HTS multiple tower system that does not incorporate the systems and methods of the present invention are shown. The receive side subsystem of this non-HTS system has a 6 dB noise figure, and the transmit side subsystem is operating at 20 W. As seen in the bottom screen shot, the light area indicates the overlap of the receive coverage areas of this non-HTS system. At 25 users, the non-HTS system is limited to a receive coverage area of 15 miles, although the transmit coverage area capacity may be greater. Therefore, this non-HTS system is limited to a coverage area of 15 miles before callers are dropped or blocked due to limitations on the receive side.  
         [0068]    Turning now to FIG. 10, the transmit and receive coverage areas are shown for an HTS multiple tower system that incorporates the present invention. Due to the use of superconducting materials, the noise figure of the receive side subsystems is reduced to 2 dB, in comparison to the non-HTS system discussed with regard to FIG. 9. Because of the lower noise figure, the receive coverage area is increased compared to FIG. 9, as seen in the bottom screen shot by the lighter area.  
         [0069]    Turning now to FIG. 11, the transmit and receive coverage areas of the HTS system discussed in FIG. 10 is shown when the transmit power is increased to 70 W. The systems and methods of the present invention are used to determine that the transmit power of the transmit side subsystems may be increased to 70 W to increase the transmit coverage area, shown in the top screen shot by the lighter area, while also maintaining a receive coverage area, shown in the bottom screen shot by the lighter area, that does not have any gaps in coverage area.  
         [0070]    While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the figures and are described herein in detail. It should be understood, however, that the invention is not to be limited to the particular forms, systems, or methods disclosed. Furthermore, other aspects and embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.