Abstract:
A method and apparatus that allows off-the-shelf equipment to be installed in a wide range of physical sites having a wide range of distances between a master system unit and each of a plurality of remote units. The master system unit has an integrated active combiner/splitter. The active combiner/splitter provides bi-directional gain or attenuation in each of the individual inputs/outputs to allow control of the signal level.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 60/290,247, filed on May 10, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to wireless communications, and more particularly to a method and apparatus for automatically adjusting the amount of gain or loss in a communication system in which signals are relayed between a master system unit and a remote unit in order to compensate for varied environments. 
     2. Description of the Related Art 
     Modern communications systems are an important part of our society today. One such communications system is a wireless cellular communication system. In wireless cellular communication systems, communications between users are conducted through one or more base stations. The term forward link is used to refer to communications from a base station to a subscriber station, and the term reverse link is used to refer to communications from a subscriber station to a base station. A subscriber station is the device that is used by an individual who subscribes to a communication provider for communication services. For example, a person who uses a conventional cellular telephone is a subscriber to the cellular telephone services provided by a cellular telephone service provider, such as Leap Wireless International Inc. 
     By transmitting information on a reverse link to a base station, a subscriber may communicate with people at other locations through any one of a number of communications systems, including conventional telephones, cellular telephones, or the Internet. The base station receives the information (voice or data) from the first subscriber station and routes the information to a Base Station Controller (BSC). The base station controller routes the information to a Mobile Switching Controller (MSC). The base station serving the subscriber stations sends the information back to the subscriber on the forward link. 
     As a subscriber station moves about a wireless cellular communication system, the quality of the forward and reverse links to transmit data will vary. In particular, a user of a subscriber station may move inside a building or enter an area in which signals are blocked, such as a tunnel or valley. When the user does so, the subscriber station may not be able to operate due to the low energy level in the signal that is available to and from the subscriber station. 
     One solution to this problem is to establish a relay station that can receive signals from a base station and relay (i.e., retransmit) those signals to the user&#39;s subscriber station. However, in complex structures, such as buildings having several floors and corridors, a simple relay station is not effective. Accordingly, another approach is to place a master system unit at a location from which signals to and from a base station can be transmitted and received, respectively. Signals are then communicated over a wire line to a remote unit. The remote unit transmits information received from the base station via the master system unit to subscriber stations within an area into which signals transmitted directly from the base cannot easily be received. Likewise, the remote unit receives information from subscriber stations within the area. The remote unit then communicates the information received from the subscriber stations over wire lines to the master system unit. The master system unit communicates the information over the air to the base station. 
     One significant problem with such a configuration of the master system unit and remote units is that the design and installation of such a system is expensive and complex. One of the reasons for this is that the distances between the master system unit and the remote units are not known until the installation site has been selected. Therefore, each system must be customized to the site to account for the particular physical relationship between the master system unit and the remote units. Furthermore, while it is preferable to have as many remote units coupled to one master unit as possible in order to reduce the cost of the system, there is a trade-off between the distance that a remote unit can be from the master system unit, and the number of remote units that can be connected to the master system unit. That is, the more remote units the master system unit has to drive, the shorter the cable has to be between each remote unit and the master system unit. One way to resolve this problem is to add gain (i.e., using amplifiers to boost the signal) at the master system unit and the remote units to increase the length of the wire line between the master system unit and the remote unit. However, by increasing the gain, signals will over-drive the inputs to closer remote units. Therefore, it is difficult to provide off-the-shelf integrated equipment that can be used in the wide range of physical sites in which such equipment is required to operate. 
     Accordingly, there is a need for a system that allows a master system unit to drive remote units at a greater distance while accommodating a broad range of physical configurations. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, provided is a system that allows off-the-shelf equipment to be installed in a very wide range of physical sites having a wide range of distances between a master system unit and each of a plurality of remote units. The master system unit has an integrated active combiner/splitter. The active combiner/splitter provides bi-directional gain or attenuation in each of the individual input/output ports to allow control of the signal level. 
     In accordance with another aspect of the present invention, provided is a master system unit for use in a wireless communication system. The master system unit includes an input port, an output port, a plurality of bi-directional ports, and a combiner/splitter. The combiner/splitter is coupled to the input port, the output port, and the plurality of bi-directional ports. The combiner/splitter further comprises a splitter, a combiner, a first circuit, and a second circuit. The splitter is coupled to the input port and the combiner is coupled to the output port. The first circuit includes a first attenuator coupled to the splitter and a first amplifier. The first amplifier is coupled to a duplexer which is coupled to one of the plurality of bi-directional ports and a second amplifier. The second amplifier is coupled to a second attenuator which is coupled to the combiner. The second circuit includes a third attenuator coupled to the splitter and a third amplifier. The third amplifier is coupled to a duplexer which is coupled to one of the plurality of bi-directional ports and a fourth amplifier. The fourth amplifier is coupled to a fourth attenuator which is coupled to the combiner. 
     The master system unit may further include a processor that is coupled to each attenuator. The processor receives information regarding power levels at points outside the master system unit and sets the gain of each attenuator in response to the power levels. 
     The master system unit may further include a user input port for a user to provide information to the processor. The information includes estimates of the length of wire line to be connected between the master system unit and remote units. Each estimate may be associated with one of the master system unit bi-directional ports. The processor sets the gain of each attenuator in response to the provided estimates. The master system unit may further include a modem for providing communication between the master system unit and a user or external device. The master system unit may further include a memory coupled to the processor for providing storage of data. 
     In accordance with another aspect of the present invention, provided is a method for adjusting the gain of a signal received by a master system unit. The master system unit includes a combiner/splitter for adjusting the gain of the signal comprising the steps of splitting the signal into a plurality of signals, adjusting the gain of each signal based on predetermined gain parameters, wherein the gain is adjusted by individually controlling the attenuation of each signal, amplifying and outputting each signal, receiving signals from a plurality of remote units, amplifying each signal received from the plurality of remote units, 
     adjusting the gain of each signal based on predetermined gain parameters, wherein the gain is adjusted by individually controlling the attenuation of each signal, and combining each of the signals and outputting a combined signal. 
     In accordance with another aspect of the present invention, provided is a method for installing a master system unit and a remote unit, the master system unit being coupled to the remote unit by a wire line. The method comprising the steps of estimating the length of the wire line between the master system unit and the remote unit, setting gain elements in the master system unit to a specified gain based on the initial estimate, transmitting a test signal into an RF input of the master system unit, detecting and estimating the amount of power at points in the wire line between the master system unit and remote unit, and adjusting the gain elements in the master system unit and the remote unit based on the estimate. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Understanding of the present invention will be facilitated by consideration of the following detailed description of an exemplary embodiment of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like part and in which: 
         FIG. 1  is a block diagram illustrating an in-building communication system according to the present invention. 
         FIG. 2  is a block diagram of an implementation example of a master system unit according to the present invention. 
         FIG. 3  is a schematic diagram of an implementation example of a combiner/splitter of the master system unit according to the present invention. 
         FIG. 4  is a flowchart illustrating a method for adjusting the gain of a signal received by a master system unit according to the present invention. 
         FIG. 5  is a flowchart illustrating a method for installing a master system unit and a remote unit according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates an in-building communication system  100 , which is disclosed in pending patent application entitled “In-building Radio Frequency Coverage,” Ser. No. 09/430,616, filed on Oct. 29, 1999. U.S. Pat. No. 6,501,942, which is assigned to the assignee of the present invention and which is incorporated herein by reference in its entirely as if set forth in full herein. The communication system  100  includes a base station  102  that transmits radio-frequency (RF) signals to an antenna  104 , which is preferably on top of building  106 . Preferably, the RF signal emitted by the base station  102  is a code division multiple access (CDMA) signal. 
     A master system unit  108  which is preferably located within the building  106  receives the RF signals transmitted from the base station  102 . The base station  102  and the master system unit  108  communicate over the air or via a cable by utilizing a cellular network, digital network, coaxial cable, ethernet cable, or fiber optic lines. 
     The master system unit  108  relays the received signals to remote units  110   a - 110   f  over wire lines  114 . The remote units  110  transmit the received signals to one or more subscriber stations  112  located within the building  106 . The subscriber station  112  is adapted to receive signals emitted by the base station  102 . One or more subscriber stations  112  is configured to transmit signals to a corresponding remote unit  110 , and the information in the signals is transferred to the master system unit  108  over wire lines  114 . The master system unit  108  transmits the signals comprising the information received from one or more subscriber stations  112  to the base station  102 . 
     The wire lines  114  between the master system unit  108  and each remote unit  110  may be relatively lengthy. For example, if the master system unit  108  is on top of a tall building (e.g., 40th floor) and a remote unit  110  is located on the lowest floor (e.g., 1 st  floor), the wire line  114  between the master system unit  108  and the remote unit  110  can be as long as several hundred meters. The master system unit  108  and the remote units  110  have the ability to compensate for degradation of signals that occur due to the losses experienced from the length of the wire lines  114 . In particular, the master system unit  108  and the remote units  110  can adjust the gain of signals transmitted between the master system unit and the remote units. 
       FIG. 2  is a block diagram of an implementation example of an master system unit  200  including combiner/splitter  202  and input/output ports  204 . The master system unit  200  down converts received RF signals to forward intermediate frequency (IF) signals. The forward IF signals are then transferred to remote units. The master system unit  200  adjusts the gain of the received signals by the active combiner/splitter  202 . 
     The active combiner/splitter  202  provides bi-directional gain or attenuation in each of the individual input/output ports  204  to allow adjustment of each signal level through the use of attenuators. This allows signals that are intended for use with remote units that are relatively nearby to be coupled to the wire line between the master system unit  200  and the remote unit at relatively low power level. This reduces the amount of radiation and prevents the inputs of those nearby remote units from being saturated. Alternatively, the signal output from the master system unit  200  may be coupled to the wire line between the master system unit  200  and the remote unit at a relatively high power level in order to ensure that the signal is received at a distant remote unit with sufficient power. 
     The combiner/splitter  202  is configured as an integrated active unit or as separate combiner and splitter units. In one implementation example, the combiner/splitter  202  comprises a combiner coupled to the master system unit  200 , a splitter coupled to the master system unit, a plurality of attenuators including a first plurality of attenuators coupled to the splitter and a second plurality of attenuators coupled to the combiner, a plurality of amplifiers including a first plurality of amplifiers coupled to the first plurality of attenuators and a second plurality of amplifiers coupled to the second plurality of attenuators, and a plurality of duplexers coupled to the first plurality of amplifiers, the second plurality of amplifiers, and the master system unit  200 . The schematic details of this implementation example of the combiner/splitter  202  are illustrated and described below in reference to  FIG. 3 . 
     The master system unit  200  may further include processor  206 . In this implementation, the processor  206  is coupled to the combiner/splitter  202  for setting the gain elements (i.e., attenuators) of the combiner/splitter. In one implementation example, the processor  206  adjusts the gain parameters of the combiner/splitter  202 , in response to, receiving information regarding the power levels at points outside the master system unit  200 . 
     The processor  206  automatically calibrates the amount of attenuation during an initialization process. For example, an installer transmits a test signal into an RF input of the master system unit  200 . Detectors at strategic locations in the circuit estimate the amount of power that is present at each location. The detected amount of power is communicated to the processor  206 . In response, the processor  206  determines the proper gain parameters to set gain elements (i.e., attenuators) in the remote unit and the master system unit  200 . 
     The master system unit  200  may further include memory  208 . In this implementation, the memory  208  is coupled to the processor  206  for temporary or permanent storage of data. The memory  208  is preferably volatile memory providing for the processor  206  to store data during processing. For example, the memory may be, but not limited to, a memory chip, RAM, SRAM, DRAM, EPROM, flash memory, or related memory device. The memory  208  may include more than one memory element such as two or more memory chips. 
     The master system unit  200  may further include user ports providing for a user or external device the ability to communicate information to the processor  206 . The user ports provide for connection to a cable, telephone line, network connection, or related communication connection. In one example, the user port can be a network card or modem  210 . The master system unit  200  contains all the necessary software for communicating with and processing requests or commands from a user or external device. The software may be stored in the memory  208  or a storage device located in the master system unit  200 . For example, the storage device may be, but not limited to, a hard drive, CD-ROM, DVD, optical medium, flash memory, floppy disk, or other related storage device. 
     The modem  210  communicates with the processor  206  and allows users to provide information to the processor. The information includes, but is not limited to, gain parameters, estimates of the length of wire line to be connected between the master system unit and a remote unit, master system unit control parameters, remote unit control parameters, and other system information. The user can communicate with the modem  210  using different communication mediums such as a telephone line, network connection, or the Internet. 
     For example, a user communicates with the modem  210  over a telephone line with a computer. The user connects to the modem  210  and transmits information regarding estimates of the length of wire line to be connected between the master system unit  200  and remote units. The modem  210  responds by transmitting the received information to the processor  206 . In response to the provided estimates, the processor  206  sets the gain of each attenuator by submitting new gain parameters. Additionally, a user or external device may request information from the processor  206  through the modem  210 . The requested information can include, but is not limited to, master system unit status, remote unit status, master system unit control parameters, remote unit control parameters, wire line conditions, gain parameters settings and other related system information. 
     The master system unit  200  may further include a power supply for powering the master system unit  200 , active combiner/splitter  202 , processor  206 , memory  208 , modem  210 , remote units, and other system components. The power supply is configured to supply singularly or in combination AC and/or DC current. 
       FIG. 3  is a schematic diagram of an implementation example of a combiner/splitter of the master system unit. The master system unit includes a master system unit input port  302 , a master system unit output port  330 , and master system unit bi-directional ports  320   a - 320   d . The master system unit input port  302  is coupled to the input port of splitter  304 . The splitter  304  has a plurality of splitter output ports that are each coupled to an input port of attenuators  308   a - 308   d  for receiving signals  306   a - 306   d . The output ports of the attenuators  308  are coupled to the input ports of amplifiers  310   a - 310   d . The amplifiers  310  output ports are coupled to the input ports of IF duplexers  312   a - 312   d . The IF duplexers  312  further include bi-directional ports and output ports. 
     The IF duplexers  312  bi-directional ports are coupled to the input ports of duplexers  314   a - 314   d  contained in the master system unit bi-directional ports  320   a - 320   d . The duplexers  314  provide bi-directional ports for communication with a modem and are coupled to the inputs ports of bias-Ts  316   a - 316   d . The bias-Ts  316  provide for outputting signal  318   a - 318   d  to a corresponding remote unit over wire lines. 
     The IF duplexers  312  output ports are coupled to the input ports of amplifiers  322   a - 322   d . The amplifiers  322  output ports are coupled to the input ports of attenuators  324   a - 324   d . The attenuators  324  output ports are coupled to the input ports of combiner  328 . The combiner  328  is coupled to the master system unit output port  330  and provides for generating a combined signal  332  from signals  326   a - 326   d  received from the attenuators  324 . 
     In one implementation example, during operation the master system unit input port  302  receives signal  300  which is transferred to the splitter  304 . The splitter  304  splits the signal  300  into separate signals  306 , and transfers each signal to the inputs of corresponding attenuators  308 . For example, signal  306   a  is transferred to the input of attenuator  308   a . The attenuators  308  provide for adjusting the gain of each signal by individually controlling the amount of attenuation of each signal. Initially, the amount of attenuation is based on predetermined gain parameters. The gain parameters of each attenuator can be individually changed responsive to power or system changes. The gain parameters can be in the form of decibels (dB) or other attenuation settings. In one implementation example, a processor is coupled to each of the attenuators to provide for adjusting the gain parameters of each attenuator. For example, the processor receives updated power measurement information, and in response, submits new gain parameters to one or more attenuators. 
     The attenuators  308  adjust the gain of each of the signals  306  based on predetermined gain parameters by individually controlling the attenuation of each signal. The adjusted signals are transferred to the inputs of amplifiers  310 . The amplifiers  310  amplify and output each signal to the input of IF duplexers  312 . The IF duplexers  312  output each signal from the duplexer bi-directional port to the input of duplexers  314  contained in the master system unit bi-directional ports  320 . The duplexers  314  each provide a bi-directional port for communication with a modem and transfer the signals to the inputs of the bias-Ts  316 . The bias-Ts  316  each output signals  318  to a corresponding remote unit over the wire lines. The bias-Ts  316  enable both IF and DC signals to be applied to a single wire line. The bias-Ts  316  each provide a reliable method for powering the remote units with a low-voltage DC and thus eliminates the need to install power outlets at each remote unit. The output signals  318  each include the IF signals along with a DC signal for powering a corresponding remote unit. 
     In another implementation example, remote units coupled to the master system unit transfer IF signals  318  which are received by the master system unit bi-directional ports  320 . The bias-T&#39;s  316  output the signals to duplexers  314 . The duplexers  314  transfer the signals to the duplexer bi-directional port of the IF duplexers  312 . The IF duplexers  312  output each signal from the output ports to the input of amplifiers  322 . The amplifiers  322  amplify and output each signal to the inputs of the attenuators  324 . The attenuators  324  provide for adjusting the gain of each signal by individually controlling the amount of attenuation of each signal. The adjusted signals  326  are transferred to the inputs of the combiner  328 . The combiner  328  combines signals  326  into a combined signal  332  which is transferred from the combiner to the master system unit output port  330 . 
       FIG. 4  is a flowchart illustrating a method for adjusting the gain of a signal received by the master system unit. In step  400 , the signal is split into a plurality of signals. In step  402 , the gain of each signal is adjusted based on predetermined gain parameters. The gain is adjusted by individually controlling the attenuation of each signal. In step  404 , each signal is amplified and output to a corresponding remote unit. In step  406 , signals are received from a plurality of remote units. In step  408 , each signal received from the plurality of remote units is amplified. In step  410 , the gain of each signal is adjusted based on predetermined gain parameters. The gain is adjusted by individually controlling the attenuation of each signal. In step  412 , each of the signals is combined and a combined signal is output. 
     In one implementation example, the master system unit  200  receives a signal. The combiner/splitter  202  includes a splitter that splits the signal into a plurality of signals that are transferred to a plurality of attenuators. The attenuators adjust the gain of each signal based on predetermined gain parameters by individually controlling the attenuation of each signal. The adjusted signals are each output to an amplifier. Each amplifier amplifies and outputs the signals to a plurality of remote units. The combiner/splitter  202  receives signals from the plurality of remote units. Each signal is amplified by a plurality of amplifiers and output to a plurality of attenuators. The attenuators adjust the gain of each signal based on predetermined gain parameters. The attenuators output each adjusted signal to a combiner. The combiner combines each of the signals and outputs a combined signal. 
       FIG. 5  is a flowchart illustrating a method for installing a master system unit and a remote unit. In one implementation example, referring to  FIG. 1 , the master system unit  108  is coupled to the remote unit  116  by wire line  110 . The installation method begins, in step  500 , by estimating the length of the wire line  110  between the master system unit  108  and the remote unit  116 . The length of wire lines between the master system unit and the remote units will vary depending upon placement of the remote units. For example, one remote unit may be 100 meters from the master system unit while another may be 200 meters from the master system unit. Due to losses that occur during signal transmission in the wire lines, the remote unit that is 200 meters away will need a stronger signal to be sent from the master system unit, as compared to the remote unit 100 meters away. 
     In step  502 , gain elements are set in the master system unit to a specified gain based on the initial estimate. For example, the gain elements are attenuators or other devices that provide for controlling the attenuation of signals. The gain/attenuation in each port  204  of the active combiner/splitter  202  is first estimated to be either full power (i.e., minimum attenuation) or minimum power (i.e., maximum attenuation) depending upon an initial estimate of the wire line length. During installation, an installer indicates on a terminal connected to the master system unit whether the wire line is greater than or less than a predetermined length. For example, if the length of the wire line is estimated to be greater than  150  meters, then the attenuators are reduced to a zero decibel (dB) setting. If the length of the wire line is estimated to be less than  150  meters, then the attenuation is increased to the maximum amount (e.g., 12 decibels). 
     In step  504 , a test signal is transmitted into an RF input of the master system unit. The test signal is of a predetermined level. For example, an installer can inject the signal into the RF input (e.g., input/output ports  204 ) during the installation process. In step  506 , the amount of power at points in the wire line between the master system unit and the remote unit is detected and estimated. Detectors at strategic locations in the circuit estimate the amount of power that is present at each location. The amount of power can be the instantaneous power or average power over time at each location. In step  508 , the gain elements in the master system unit and the remote unit are adjusted based on the estimate. 
     In one implementation example, the processor  206  controls the amount of attenuation of signals received by each attenuator by adjusting the gain parameters of each attenuator. During the installation process, the processor  206  automatically calibrates the amount of attenuation for each attenuator during an initialization process. The processor  206  receives estimates of the amount of power detected at different locations in the wire line. The processor  206  then determines the proper gain parameters to set the attenuators in the remote unit and master system unit  200  in response to the estimates. The processor  206  then updates the gain parameters in one or more attenuators. 
     Although this invention has been shown and described with respect to detailed embodiments, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of the claimed invention.