Abstract:
A communication system is supplied for filtering and attenuating a receive signal in between a bi-directional antenna system and a bi-directional base station system. In the communication system, a first circulator is configured to receive a receive signal from a first bi-directional link coupled to the bi-directional antenna system and circulate the receive signal to a first uni-directional link. A signal processing system is configured to receive the receive signal from the first uni-directional link, filter and attenuate the receive signal, and transfer the receive signal to a second uni-directional link. A second circulator is configured to receive the receive signal from the second uni-directional link, circulate the receive signal to a second bi-directional link coupled to the bi-directional base station system, receive a transmit signal from the second bi-directional link, and circulate the transmit signal to a third uni-directional link. Additionally, the first circulator is configured to receive the transmit signal from the third uni-directional link and circulate the transmit signal to the first bi-directional link coupled to the bi-directional antenna system.

Description:
TECHNICAL BACKGROUND 
     A base station is connected to an antenna by a feedline. The feedline is bidirectional and can be comprised of a variety of different signal processing components. In operation, a base station&#39;s antenna receives and transmits wireless communication signals over the air. A communication signal is received by the antenna and the signal is transferred to the base station by way of the feedline. The antenna also receives interference/noise from various sources such as other base stations and other antennas as well as various other sources. During installation a test signal is inserted into the feedline to determine the loss of the feedline. 
     OVERVIEW 
     Generally described, a communication system is supplied for filtering and attenuating a receive signal in between a bi-directional antenna system and a bi-directional base station system. In an example, a first circulator is configured to receive a receive signal from a first bi-directional link coupled to the bi-directional antenna system and circulate the receive signal to a first uni-directional link. A signal processing system is configured to receive the receive signal from the first uni-directional link, filter and attenuate the receive signal, and transfer the receive signal to a second uni-directional link. A second circulator is configured to receive the receive signal from the second uni-directional link, circulate the receive signal to a second bi-directional link coupled to the bi-directional base station system, receive a transmit signal from the second bi-directional link, and circulate the transmit signal to a third uni-directional link. Additionally, the first circulator is configured to receive the transmit signal from the third uni-directional link and circulate the transmit signal to the first bi-directional link coupled to the bi-directional antenna system. A method of operating a communication system to filter and attenuate a receive signal in between a bi-directional antenna system and a bi-directional base station system is also provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a communication system. 
         FIG. 2  is a flow diagram illustrating a method of operating a communication system. 
         FIG. 3  is a block diagram illustrating a communication system. 
         FIG. 4  is a flow diagram illustrating a method of configuring a communication system. 
         FIG. 5  is a flow diagram illustrating a method of operating a communication system. 
         FIG. 6  is a flow diagram illustrating a method of operating a communication system. 
         FIG. 7  is a block diagram illustrating a communication system. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a block diagram illustrating communication system  100 . Communication system  100  is configured to filter and attenuate signals exchanged between antenna system  101  and base station system  105 . Communication system  100  includes antenna system  101 , circulator  102 , signal processing system  103 , circulator  104 , and base station system  105 . 
     Antenna system  101  and circulator  102  communicate over communication link  110 . Circulator  102  and signal processing system  103  communicate over communication link  111 . Signal processing system  103  and circulator  104  communicate over communication link  112 . Circulator  104  and base station system  105  communicate over communication link  113 . Circulator  104  and circulator  102  communicate over communication link  114 . Thus, antenna system  101  and base station system  105  communicate over the links and components described above. 
     Antenna system  101  comprises an antenna and possibly other components, such as an amplifier, filter, signal processor, or other communication equipment. Antenna system  101  is a bi-directional antenna system that can receive signals from communication system  106  as well as transmit signals to communication system  106 . Throughout the remainder of the descriptions of  FIGS. 1 and 2 , signals that antenna system  101  receives from communication system  106  will be referred to as receive signals and signals that antenna system  101  transmits to communication system  106  will be referred to as transmit signals. Antenna system  101  exchanges wireless receive and transmit signals with communication system  106  over communication link  115 . Antenna system  101  exchanges receive and transmit signals with circulator  102  over communication link  110 . 
     Circulator  102  comprises circuitry that receives, circulates, and transfers signals. For example, circulator  102  comprises three ports—ports  1 ,  2 , and  3 . A signal that enters circulator  102  via port  1  is circulated to port  2  and exits circulator  102  via port  2 . Likewise, a signal that enters circulator  102  via port  2  is circulated to port  3  and exits via port  3  and a signal that enters circulator  102  via port  3  is circulated to port  1  and exits via port  1 . To further illustrate, in  FIG. 1  port  1  could be where communication link  110  and circulator  102  interface, port  2  could be where communication link  111  and circulator  102  interface, and port  3  could be where communication link  114  and circulator  102  interface. 
     Circulator  102  exchanges receive and transmit signals with antenna system  101  over communication link  110 . Circulator  102  circulates and transfers a receive signal to signal processing system  103  over communication link  111 . Circulator  102  receives a transmit signal from circulator  104  over communication link  114 . Additionally, circulator  102  circulates and transfers the transmit signal to antenna system  101  over communication link  110 . 
     Signal processing system  103  comprises components that filter and attenuate a signal. Signal processing system  103  receives a receive signal from circulator  102  over communication link  111 . Signal processing system  103  also transfers a receive signal to circulator  104  over communication link  112 . 
     Circulator  104  comprises circuitry that receives, circulates, and transfers signals. For example, circulator  104  comprises three ports—ports  1 ,  2 , and  3 . A signal that enters circulator  104  via port  1  is circulated to port  2  and exits circulator  104  via port  2 . Likewise, a signal that enters circulator  104  via port  2  is circulated to port  3  and exits via port  3  and a signal that enters circulator  104  via port  3  is circulated to port  1  and exits via port  1 . To further illustrate, in  FIG. 1  port  1  could be where communication link  112  and circulator  104  interface, port  2  could be where communication link  113  and circulator  104  interface, and port  3  could be where communication link  114  and circulator  104  interface. 
     Base station system  105  comprises components that receive and transmit signals. Base station system  105  receives a receive signal from circulator  104  over communication link  113 . Base station  105  also transfers a transmit signal to circulator  104  over communication link  113 . 
     Communication links  110 - 114  comprise wired communication links. Communication links  110  and  113  comprise bi-directional links. Communication links  111 ,  112 , and  114  comprise uni-directional links. Communication link  115  comprises a wireless communication link. 
       FIG. 2  is a flow diagram illustrating a method of operating communication system  100  to filter and attenuate a signal in between antenna system  101  and base station system  105 . Communication system  100  receives signals from communication system  106  and transmits signals originating from base station system  105  to communication system  106 . In step  201 , circulator  102  receives a receive signal from antenna system  101  over communication link  110 . Circulator  102  then circulates and transfers the receive signal to signal processing system  103  over communication link  111 . 
     In step  202 , signal processing system  103  receives the receive signal from circulator  102  over communication link  111 . After receiving the receive signal, signal processing system  103  filters the receive signal. For example, signal processing system  103  may contain a band-pass filter. Also after receiving the receive signal, signal processing system  103  attenuates the receive signal. Signal processing system  103  may filter and attenuate the receive signal in any order. Signal processing system  103  transfers the receive signal to circulator  104  over communication link  112 . 
     In step  203 , circulator  104  receives the receive signal from signal processing system  103  over communication link  112 . Circulator  104  circulates and transfers the receive signal to base station system  105  over communication link  113 . Also in step  203 , circulator  104  receives a transmit signal transferred from base station system  105  over communication link  113 . Circulator  104  circulates and transfers the transmit signal to circulator  102  over communication link  114 . In step  204 , circulator  102  receives the transmit signal from circulator  104  over communication link  114 . Circulator  102  also circulates and transfers the transmit signal to antenna system  101  over communication link  110 . Note, communication system  100  uses time-division duplex to separate receive and transmit signals. 
       FIG. 3  is a block diagram illustrating communication system  300 . 
     Communication system  300  is configured to filter and attenuate signals in between antenna  302  and base station  313 . Communication system  300  includes antenna system  301 , circulator  305 , signal processing system  306 , circulator  310 , base station  313 , lightning arrestor  314 , and bias-T element  315 . 
     Antenna system  301  and lightning arrestor  314  communicates over communication link  326 . Lightning arrestor  314  is electrically coupled to bias-T element  315 . Bias-T element  315  communicates with circulator  305  over communication link  320 . Circulator  305  and signal processing system  306  communicate over communication link  321 . Signal processing system  306  and circulator  310  communicate over communication link  322 . Circulator  310  and base station  313  communicate over communication link  323 . Circulator  310  and circulator  305  communicate over communication link  324 . Thus, antenna  302  and base station  313  communicate over the links and components described above. 
     Antenna system  301  comprises antenna  302 , band-pass filter  303 , and low-noise amplifier  304 . Antenna  302 , band-pass filter  303 , and low-noise amplifier  304  are connected by electrical circuitry. Antenna  302  comprises a bar, dipole, patch, parabolic dish, array, or some other type of antenna. Band-pass filter  303  comprises circuitry that filters signals by allowing frequencies within a certain range to pass and rejecting frequencies outside of that range. Low-noise amplifier  304  comprises circuitry that amplifies signals. Throughout the remainder of the descriptions of  FIGS. 3-7 , signals that antenna system  301  receives from communication system  316  will be referred to as receive signals and signals that antenna system  301  transmits to communication system  316  will be referred to as transmit signals. Antenna system  301  receives receive signals from communication system  316  over communication link  325  as well as transmits transmit signals to communication system  316  over communication link  325 . Additionally, antenna system  301  exchanges receive and transmit signals with lightning arrestor  314  over communication link  326 . 
     Lightning arrestor  314  comprises circuitry that helps to prevent damage to electronic instruments within communication system  300  by limiting the rise in voltage when communication system  300  is struck by lightning. Lightning arrestor  314  is electrically coupled to bias-T element  315 . Bias-T element  315  comprises circuitry that inserts power into communication link  326  as well as adds and removes signaling over communication link  326 . Bias-T element  315  communicates with circulator  305  over communication link  320 . Lightning arrestor  314  and bias-T element  315  are typically placed near base station  313  or integrated within base station  313 . 
     Circulator  305  receives a receive signal from bias-T element  315  over communication link  320 . Circulator  305  circulates and transfers the receive signal to signal processing system  306  over communication link  321 . Additionally, circulator  305  receives a transmit signal from circulator  310  over communication link  324 . Circulator  305  circulates and transfers the transmit signal to bias-T element  315  over communication link  320 . 
     Signal processing system  306  comprises band-pass filter  307 , bypass circuit  308 , and gain element  309 . Band-pass filter  307 , bypass circuit  308 , and gain element  309  are connected by electrical circuitry. Band-pass filter  307  comprises circuitry that filters signals by allowing frequencies within a certain range to pass and rejecting frequencies outside of that range. Bypass circuit  308  comprises circuitry that allows signals to bypass gain element  309 , if needed. Gain element  309  comprises circuitry that inserts loss or adds gain to signals. Band-pass filter  307  filters a receive signal on the way to bypass circuit  308 . If bypass circuit  308  receives a bypass signal, then bypass circuit  308  transfers the receive signal to circulator  310  over communication link  322 . If bypass circuit  308  does not receive a bypass signal, then bypass circuit  308  transfers the receive signal to gain element  309 . Gain element  309  inserts loss or adds gain to the receive signal before transferring the receive signal to circulator  310  over communication link  322 . 
     Circulator  310  receives a receive signal from signal processing system  306  over communication link  322 . Circulator  310  circulates and transfers the receive signal to base station  313  over communication link  323 . Additionally, circulator  310  receives a transmit signal from base station  313  over communication link  323 . Circulator  310  circulates and transfers the transmit signal to circulator  305  over communication link  324 . Base station  313  receives the receive signal from circulator  310  over communication link  323 . Base station  313  also transfers a transmit signal to circulator  310  over communication link  323 . Although shown separately, circulator  305 , signal processing system  306 , and circulator  310  may be integrated within base station  313 . 
     Communication links  320 - 324  and  326  comprise wired communication links. Communication links  320 ,  323 , and  326  comprise bi-directional links. Communication links  321 ,  322 , and  324  comprise uni-directional links. Communication link  325  comprises a wireless communication link. 
       FIG. 4  is a flow diagram illustrating a method of configuring communication system  300 . In step  401 , a test signal is inserted into communication system  300  at a location between antenna  302  and band-pass filter  303 . In step  402 , the test signal is measured at a location on communication link  323  to determine the total loss present in communication system  300 . For example, the total loss of communication system  300  could be −4 dB. Additionally, low-noise amplifier  304 , which adds approximately 13 dB of gain to communication system  300 , is bypassed during this measurement so as to not interfere with the determination of the total loss of communication system  300 . 
     In step  403 , a determination is made as to whether or not there is too much interference/noise in communication system  300 . If a determination is made that there is not too much interference in communication system  300 , then, in step  404 , communication system  300  is not altered. However, if a determination is made that there is too much interference in communication system  300 , then, in step  405 , circulator  305 , signal processing system  306 , and circulator  310  are inserted in communication system  300  at a location between antenna system  301  and communication link  323 . Signal processing system  306  will introduce a known quantity of additional loss into communication system  300 . For example, signal processing system  306  will introduce −5 dB of loss into communication system  300 . 
     In step  406 , the amount of loss that gain element  309  needs to insert into communication system  300  to offset the gain inserted by low-noise amplifier  304 , the total loss of the system, and the loss introduced by signal processing system  306  is determined. In step  407 , gain element  309  is set so that the total loss in communication system  300  is equal to 0 dB. For example, if low-noise amplifier  304  inserted a gain of 13 dB, the total loss of the system was −4 dB, and signal processing system  306  inserted a loss of −5 dB, then gain element  309  would need to be set to insert −4 dB of loss into communication system  300  to create a net loss of 0 dB. 
     Another additional concern pertaining to communication system  300  is that low-noise amplifier  304  may stop functioning. In that case, the loss in communication system  300  will again become unbalanced. Using the example above to illustrate, when the 13 dB of gain from low-noise amplifier  304  is removed from communication system  300  the resulting total loss will now be −13 dB. In response, bypass circuit  308  may receive a signal to bypass gain element  309 , which would remove the loss added by gain element  309  earlier. For example, the −4 dB of loss inserted into communication system  300  by gain element  309  would be removed thereby leaving only −9 dB of loss left in communication system  300 . 
       FIG. 5  is a flow diagram illustrating a method of operating communication system  300  to filter and attenuate a receive signal transferred from antenna system  301  to base station  313 . In step  501 , antenna  302  receives a receive signal. Band-pass filter  303  filters the receive signal. Low-noise amplifier  304  amplifies the receive signal. Antenna system  301  transfers the receive signal to circulator  305  through lightning arrestor  314  and bias-T element  315  and over communication links  320  and  326 . 
     In step  502 , circulator  305  receives the receive signal from bias-T element  315  over communication link  326 . Circulator  305  circulates and transfers the receive signal to signal processing system  306  over communication link  321 . In step  503 , signal processing system  306  receives the receive signal. Band-pass filter  307  filters the receive signal. 
     In step  504 , bypass circuit  308  either receives a bypass signal or bypass circuit  308  does not receive a bypass signal. If bypass circuit  308  does receive a bypass signal, then, in step  505 , the gain element is bypassed and the bypass circuit  308  transfers the receive signal to circulator  310  over communication link  322 . If bypass circuit  308  does not receive a bypass signal, then, in step  506 , gain element  309  receives the receive signal. Gain element  309  also receives a user input. Gain element  309  inserts loss into the receive signal based on the user input. Gain element  309  transfers the receive signal to circulator  310  over communication link  322 . 
     In step  507 , circulator  310  receives and circulates the receive signal. Circulator  310  transfers the receive signal to base station  313  over communication link  323 . In step  508 , base station  313  receives the receive signal from circulator  310  over communication link  323 . 
       FIG. 6  is a flow diagram illustrating a method of operating communication system  300  to transmit a transmit signal transferred from base station  313  to antenna system  301 . In step  601 , base station  313  transmits a transmit signal to circulator  310  over communication link  323 . In step  602 , circulator  310  receives the transmit signal from base station  313  over communication link  323 . Circulator  310  circulates and transfers the transmit signal to circulator  305  over communication link  324 . 
     In step  603 , circulator  305  receives the transmit signal from circulator  310  over communication link  324 . Circulator  305  circulates and transfers the transmit signal to antenna system  301  through lightning arrestor  314  and bias-T element  315  and over communication links  320  and  326 . In step  604 , antenna system  301  receives the transmit signal from circulator  305  over communication links  320  and  326 . Low-noise amplifier  304  passes the transmit signal to band-pass filter  303 . Antenna  302  transmits the transmit signal to communication system  316  over communication link  325 . 
       FIG. 7  is a block diagram illustrating communication system  700 . Communication system  700  is configured to filter and attenuate signals in between antenna  702  and base station  713 . Communication system  700  includes antenna system  701 , circulator  705 , signal processing system  706 , circulator  710 , base station  713 , lightning arrestor  714 , bias-T element  715 , and bias-T element  716 . Communication system  700  is similar to communication system  300  except that in communication system  700  bias-T element  715  is further connected to bias-T element  716  by communication link  725 . Additionally, communication link  723  (communication link  323  in communication system  300 ) also includes bias-T element  716 , lightning arrestor  711 , and bias-T element  712 . 
     Bias-T element  712  adds DC voltage and signaling to the transmit signal sent from base station  713  to antenna  702 . The DC voltage is used to power various components of antenna system  701 , such as low-noise amplifier  704 . Bias-T element  716  removes the DC voltage added to the transmit signal so that the added DC voltage does not pass through circulators  710  and  705  as well as signal processing system  706 . Bias-T element  715  reinserts the DC voltage into the transmit signal once the transmit signal reaches communication link  720 . Bias-T element  716  also adds and removes signaling over communication link  725 . Bias-T element  716  may be located within the same component box as circulator  705 , circulator  710 , and signal processing system  706 . 
     Note that signal processing systems  306  and  706  effectively provide a way to insert additional loss into a received signal without affecting a signal that is transmitted by communication systems  300  and  700  respectively. Moreover, signal processing systems  306  and  706  provide a way for an operator of communication systems  300  and  700  to determine the amount of loss to insert into the received signal. Signal processing systems  306  and  706  also allow the operator to remove any loss that had been previously inserted into the received signal. 
     The above description and associated figures teach the best mode of the invention. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Those skilled in the art will appreciate that the features described above can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.