Abstract:
A time-division communication system wirelessly receives a communication signal during receive time periods and wirelessly transfers a communication signal during transmit time periods. These communication signals have multiple receive and transmit channels. The communication system circulates the received communication signal to various filters that pass particular receive channels and that reflect other receive channels back the circulator(s). Eventually, the reflected receive channels circulate to the appropriate filters and are passed. The filters also pass transmit channels to the circulator(s) where they are circulated and reflected until they combine into the transmit communication signal.

Description:
TECHNICAL BACKGROUND 
     In a bi-directional communication system, an antenna receives a first communication signal over the air and transfers a second communication signal over the air. The antenna transfers the first communication signal to a base station, and the base station transmits the second communication signal to the antenna. The base station and antenna may also operate in a time-division manner, where the base station and antenna transmit during transmit time periods and receive during receive time periods. These transmit and receive time periods repeatedly alternate over time. 
     The transmitted and received communications signals may be comprised of multiple frequency channels where one system in the base station transmits and receives over a first frequency channel, and a second system in the base station transmits and receives over a second frequency channel. During transmit time periods, the frequency channels are combined to form the transmitted communication signal. During receive time periods, the frequency channels are separated from the received communication signal. Various devices are used to combine these frequency channels for transmission and separate these frequency channels upon reception. Resonant cavities use wave-guides to combine and separate communication signals. Unfortunately, resonant cavities are relatively large and expensive. Hybrid microwave combiners use couplers and splitters to combine and separate communication signals. Unfortunately, hybrid microwave combiners introduce unacceptable loss and are also relatively expensive. 
     OVERVIEW 
     A time-division communication system wirelessly receives a communication signal during receive time periods and wirelessly transfers a communication signal during transmit time periods. These communication signals have multiple receive and transmit channels. The communication system circulates the received communication signal to various filters that pass particular receive channels and that reflect other receive channels back to the circulator(s). Eventually, the reflected receive channels circulate to the appropriate filters and are passed. The filters also pass transmit channels to the circulator(s) where they are circulated and reflected until they combine into the transmit communication signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that illustrates a time-division communication system. 
         FIG. 2  illustrates the operation of a time-division communication system during a receive time period. 
         FIG. 3  illustrates the operation of a time-division communication system during a transmit time period. 
         FIG. 4  is a block diagram that illustrates a time-division communication system. 
         FIG. 5  illustrates the operation of a time-division communication system during a receive time period. 
         FIG. 6  illustrates the operation of a time-division communication system during a transmit time period. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed 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 below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
     Example #1 
       FIG. 1  illustrates time-division communication system  100 . Time-division communication system  100  comprises: filters  101 - 102 , circulator  105 , antenna system  107 , and communication systems  111 - 112 . Communication system  111  is coupled to filter  101 , and filter  101  is coupled to port  1  of circulator  105 . Communication system  112  is coupled to filter  102 , and filter  102  is coupled to port  2  of circulator  105 . Antenna system  107  is coupled to port  3  of circulator  105 . 
     Filter  101  comprises a band-pass filter that passes signals in a first frequency band and that blocks (reflects) signals in other frequency bands. Filter  102  comprises a band-pass filter that passes signals in a second frequency band and that blocks (reflects) signals in other frequency bands. Filters  101 - 102  effectively present low impedance to passed signals and high impedance to reflected signals. Although various frequency configurations could be used, the first frequency band and the second frequency band could be non-adjacent frequency bands or they could be adjacent frequency bands that are separated by a smaller unused guard frequency band. The frequency bands could be 10 MHz wideband channels. 
     Circulator  105  includes port  1 , port  2 , and port  3 . Circulator  105  may include additional ports although they are not required. Circulator  105  could be a magnetic circulator. Signals that enter circulator  105  through port  1  exit circulator  105  through port  2 . Signals that enter circulator  105  through port  2  exit circulator  105  through port  3 . Signals that enter circulator  105  through port  3  exit circulator  105  through port  1 . 
     Antenna system  107  comprises an antenna and possibly other components, such as an amplifier, filter, signal processor, or some other communication equipment. Antenna system  107  wirelessly receives and transmits communication signals over the air. Antenna system  107  exchanges the communication signals with port  3  of circulator  105 . 
     Communication system  111  comprises a base station, switching system, router, or some other communication equipment. Communication system  111  operates in a time-division fashion that alternates between repeating receive and transmit time periods. During the receive time periods, communication system  111  receives a receive channel in the first frequency band from filter  101 . During the transmit time periods, communication system  111  transmits a transmit channel in the first frequency band to filter  101 . 
     Communication system  112  comprises a base station, switching system, router, or some other communication equipment. Communication system  112  operates in a time-division fashion that alternates between repeating receive and transmit time periods. During the receive time periods, communication system  112  receives a receive channel in the second frequency band from filter  102 . During the transmit time periods, communication system  112  transmits a transmit channel in the second frequency band to filter  102 . 
     Communication systems  111 - 112  use the same receive and transmit time periods. Thus, communication systems  111 - 112  both transmit channels during the transmit time periods and they both receive channels during the receive time periods. These multiple receive channels must be separated for delivery to each system, and the transmit channels from each system must be combined for wireless transmission. The receive and transmit time periods alternate—possibly separated by a relatively small unused time period. Communication systems  111 - 112  could be integrated together or distributed among multiple components. Communication systems  111 - 112  may receive and transmit Wireless Interoperability for Microwave Access (WiMAX) communication signals. Communication systems  111 - 112  may receive and transmit using other synchronized protocols. 
       FIG. 2  illustrates the operation of time-division communication system  100  during a receive time period. In the receive time period, antenna system  107  wirelessly receives a receive communication signal over the air. The receive communication signal includes a first receive channel in the first frequency band and a second receive channel in the second frequency band. The receive communication signal may include additional channels, although that is not required. 
     Antenna system  107  transfers the receive communication signal to port  3  of circulator  105 . Circulator  105  circulates the receive communication signal from port  3  to port  1 . Port  1  of circulator  105  transfers the receive communication signal to filter  101 . Filter  101  passes the first receive channel in the first frequency band and transfers the first receive channel to communication system  111 . Filter  101  blocks the second receive channel in the second frequency band and reflects the second receive channel back to port  1  of circulator  105 . Circulator  105  circulates the second receive channel from port  1  to port  2 . Port  2  of circulator  105  transfers the second receive channel to filter  102 . Filter  102  passes the second receive channel in the second frequency band and transfers the second receive channel to communication system  112 . 
       FIG. 3  illustrates the operation of time-division communication system  100  during a transmit time period. In the transmit time period, communication system  111  transmits a first transmit channel in the first frequency band to filter  101 , and communication system  112  transmits a second transmit channel in the second frequency band to filter  102 . Note that the following operations with respect to the first and second transmit channels occur contemporaneously, although for clarity, the operations with respect to the first transmit channel are presented first. 
     Filter  101  passes the first transmit channel in the first frequency band and transfers the first transmit channel to port  1  of circulator  105 . Circulator  105  circulates the first transmit channel from port  1  to port  2 , and port  2  transfers the first transmit channel to filter  102 . Filter  102  blocks the first transmit channel in the first frequency band and reflects the first transmit channel back to port  2  of circulator  105 . Circulator  105  circulates the first transmit channel from port  2  to port  3 . 
     As discussed above, filter  102  received the second transmit channel from communication system  112 . Filter  102  passes the second transmit channel in the second frequency band and transfers the second transmit channel to port  2  of circulator  105 . Circulator  105  circulates the second transmit channel from port  2  to port  3 . Port  3  of circulator  105  transfers a transmit communication signal comprised of the first transmit channel and the second transmit channel to antenna system  107 . Antenna system  107  wirelessly transmits the transmit communication signal over the air. 
     Example #2 
       FIG. 4  illustrates time-division communication system  400 . Time-division communication system  400  comprises: filters  401 - 403 , circulators  405 - 406 , antenna system  407 , and communication systems  411 - 413 . For clarity, the circulator ports are not numbered on  FIG. 4 , but circulators  405 - 406  could have the same port configuration and operation as circulator  105  above. Communication system  411  is coupled to filter  401 , and filter  401  is coupled to port  1  of circulator  405 . Communication system  412  is coupled to filter  402 , and filter  402  is coupled to port  1  of circulator  406 . Communication system  413  is coupled to filter  403 , and filter  403  is coupled to port  2  of circulator  406 . Antenna system  407  is coupled to port  3  of circulator  405 . Port  2  of circulator  405  is coupled to port  3  of circulator  406 . 
     Filter  401  comprises a band-pass filter that passes signals in a first frequency band and that reflects signals in other frequency bands. Filter  402  comprises a band-pass filter that passes signals in a second frequency band and that reflects signals in other frequency bands. Filter  403  comprises a band-pass filter that passes signals in a third frequency band and that reflects signals in other frequency bands. The first frequency band and the second frequency band are non-adjacent frequency bands that are separated by another operational frequency band. The second frequency band and the third frequency band are adjacent frequency bands that are separated by a smaller unused guard frequency band. The first, second, and third frequency bands may comprise bands in the Broadband Radio Service (BRS) and/or Educational Broadband Service (EBS) spectrum. Other frequency spectrums authorized for Time Division Duplex or flexible use service may also use this technique. 
     Circulators  405 - 406  comprise magnetic circulators. Antenna system  407  comprises an antenna, band-pass filter, and low-noise amplifier. Communication system  411  transmits and receives signals in the first frequency band in a time-division mode that alternates between repeating receive and transmit time periods. Communication system  412  transmits and receives signals in the second frequency band in a time-division mode that alternates between repeating receive and transmit time periods. Communication system  413  transmits and receives signals in the third frequency band in a time-division mode that alternates between repeating receive and transmit time periods. Communication systems  411 - 413  share the same receive and transmit time periods, and thus, their respective receive channels must be separated and their respective transmit channels must be combined. Communication systems  411 - 413  may be integrated into a single base station. 
       FIG. 5  illustrates the operation of time-division communication system  400  during a receive time period. In the receive time period, antenna system  407  wirelessly receives a receive communication signal over the air. The receive communication signal includes a first receive channel in the first frequency band, a second receive channel in the second frequency band, and third receive channel in the third frequency band. 
     Antenna system  407  transfers the receive communication signal to circulator  405 . Circulator  405  circulates the receive communication signal to filter  401 . Filter  401  passes the first receive channel in the first frequency band to communication system  411 . Filter  401  reflects the second receive channel in the second frequency band and reflects the third receive channel in the third frequency band back to circulator  405 . Circulator  405  circulates the second and third receive channels to circulator  406 . 
     Circulator  406  circulates the second and third receive channels to filter  402 . Filter  402  passes the second receive channel in the second frequency band to communication system  412 . Filter  402  reflects the third receive channel in the third frequency band back to circulator  406 . Circulator  406  circulates the third receive channel to filter  403 . Filter  403  passes the third receive channel in the third frequency band to communication system  413 . 
       FIG. 6  illustrates the operation of time-division communication system  400  during a transmit time period. In the transmit time period, communication system  411  transmits a first transmit channel in the first frequency band to filter  401 , communication system  412  transmits a second transmit channel in the second frequency band to filter  402 , and communication system  413  transmits a third transmit channel in the third frequency band to filter  403 . Note that the following operations with respect to these transmit channels occur contemporaneously, but for clarity, the operations with respect to the transmit channels are presented one at a time. 
     Filter  401  passes the first transmit channel in the first frequency band to circulator  405 . Circulator  405  circulates the first transmit channel to circulator  406 . Circulator  406  circulates the first transmit channel to filter  402 . Filter  402  reflects the first transmit channel in the first frequency band back to circulator  406 . Circulator  406  circulates the first transmit channel to filter  403 . Filter  403  reflects the first transmit channel in the first frequency band back to circulator  406 . Circulator  406  circulates the first transmit channel to circulator  405 . Circulator  405  circulates the first transmit channel to antenna system  407 . 
     Filter  402  passes the second transmit channel in the second frequency band to circulator  406 . Circulator  406  circulates the second transmit channel to filter  403 . Filter  403  reflects the second transmit channel in the second frequency band back to circulator  406 . Circulator  406  circulates the second transmit channel to circulator  405 . Circulator  405  circulates the second transmit channel to antenna system  407 . 
     Filter  403  passes the third transmit channel in the third frequency band to circulator  406 . Circulator  406  circulates the third transmit channel to circulator  405 . Circulator  405  circulates the third transmit channel to antenna system  407 . Antenna system  407  wirelessly transmits a transmit communication signal comprising the first, second, and third transmit channels. 
     Note that system  400  effectively adds and additional circulator and filter to system  100  in order to support an additional transmit/receive channel. Additional circulators and filters could be added to system  400  in a similar manner to support additional transmit/receive channels. Thus, systems  100  and  400  efficiently combine and separate multiple frequency channels in a bi-directional time-division communication system.