Abstract:
Disclosed are systems and methods for transmitting a signal. An exemplary system includes a circuit for a system having a signal source, an antenna, and a cable coupled to the signal source and the antenna. The circuit includes an amplifier having an input for coupling to the cable, and output for coupling to the antenna, and a control input. The amplifier varies output power responsive to a signal on the control input. A detector detects a DC bias on the cable. The detector has an output coupled to the control input of the amplifier.

Description:
[0001]    This application claims the benefit of U.S. Patent Application No. 60/438,991 filed on Jan. 10, 2003, which is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    This invention relates generally to systems and methods for transmitting a radio signal and, more particularly, to transmitting a radio signal with a selectable transmit power.  
           [0004]    2. Description of Related Art  
           [0005]    In wireless applications, every system presents its own set of considerations. Different site environments magnify technical differences between different hardware. For example, in wireless local area network (WLAN) applications, maximizing signal efficiencies remain somewhat of an art dictated by particularities of geography, man made structures, hardware, weather, etc. In some instances, a single preset transmit power does not meet the requirements of the application and adjustment of transmit power is desirable.  
           [0006]    When a WLAN is setup between remote users and a central station, the designer needs to select bi-directional amplifiers that have particular output strengths to provide for sufficient signal strength to cover the distance between the user and the central station. There have been attempts made by others to provide some flexibility for bi-directional amplifiers that include a dip switch adjustment on the bi-directional amplifier itself that may be set to provide the desired output. The problem is that if the user wishes to change the output level because of interference issues or other reasons, they would have to gain access to the bi-directional amplifier to change the settings or swap out the bi-directional amplifier with a new one. Neither of these alternatives is efficient or convenient to be done with any frequency.  
           [0007]    Notwithstanding the usefulness of the above-described approaches, a need still exists for adjusting the transmission power of the transmitted signal by the user without making a physical change at the bi-directional amplifier.  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide systems and methods for varying transmit power in a radio system.  
           [0009]    To achieve this and other objects of the present invention, the invention contemplates a circuit for a system having a signal source, an antenna, and a cable coupled to the signal source and the antenna, the circuit comprising an amplifier having a first input for coupling to the cable, an output for coupling to the antenna, and a second input, wherein the amplifier varies gain responsive to a signal on the second input; and a detector having an input for coupling to the cable, the detector having an output coupled to the second input of the amplifier, wherein in the amplifier is responsive to a first signal on the cable, the first signal including an RF signal, and the detector is responsive to a second signal on the cable.  
           [0010]    According to at least one embodiment of the invention, the invention includes an amplifier for a system having a signal source for a transmission signal, an antenna, and a cable coupled to the signal source and the antenna, the amplifier comprising: a sensor having a first input for coupling to the cable and an output, a transmission amplifier module having an input for coupling to the cable and an output for coupling to the antenna, the transmission amplifier module including an attenuator having a first input for receiving the transmission signal from the cable, a second input connected to the output of the sensor, and an output for communicating with the antenna; and wherein the attenuator varies the gain of the transmission signal received at the first input responsive to a signal received at the second input from the sensor based on voltage of the signal received at the amplifier to produce a desired output power level for the transmission signal.  
           [0011]    According to at least one embodiment of the invention, the invention includes a power injector for use in a system having a signal source, an amplifier, and cable, the power injector comprising: an input in communication with the signal source, an output in communication with the amplifier, an actuator for selecting an output power level, and a voltage regulator in communication with the output and the actuator, the voltage regulator has a plurality of selectable output power levels.  
           [0012]    According to at least one embodiment of the invention, the invention includes an bi-directional amplifier in communication with a signal source and an antenna, the bi-directional amplifier comprising: means for switching between receive and transmit modes, means for setting the output power level of a transmission signal based on the voltage of the transmit signal and providing a control signal, means for attenuating the transmit signal based in part on the control signal, and means for amplification of a received signal.  
           [0013]    According to at least one embodiment of the invention, the invention includes an amplifier and a power injector together as a kit and as part of a wireless system.  
           [0014]    According to at least one embodiment of the invention, the invention includes a method for setting the output power of a radio signal comprising: receiving a desired output level for the transmission, transmitting a signal having a RF component including the signal to be transmitted and a DC component representative of the transmission output level, receiving the signal, amplifying the RF component of the signal, detecting the size of the DC component and providing an attenuation control signal, attenuating the RF component of the signal to a level such that when the RF signal is transmitted it will be transmitted at the desired output level, and transmitting the RF component of the signal.  
           [0015]    Given the following enabling description of the drawings, the invention should become evident to a person of ordinary skill in the art. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. The use of cross-hatching and shading within the drawings is not intended as limiting the type of materials that may be used to manufacture the invention.  
         [0017]    [0017]FIG. 1 is a diagram of a system employing an amplifier circuit in accordance with the present invention.  
         [0018]    [0018]FIG. 2 is a diagram emphasizing a portion of the system shown in FIG. 1.  
         [0019]    [0019]FIG. 3 is a diagram emphasizing another portion of the system shown in FIG. 1.  
         [0020]    [0020]FIG. 4 is a diagram emphasizing a portion of the circuitry shown in FIG. 3.  
         [0021]    [0021]FIG. 5 is a diagram emphasizing a portion of the circuitry shown in FIG. 4.  
         [0022]    [0022]FIG. 6 is a diagram of circuitry used with that of FIG. 3.  
         [0023]    [0023]FIG. 7 is a diagram of circuitry used with that of FIG. 3.  
         [0024]    [0024]FIG. 8 is a diagram emphasizing an aspect of a system in accordance with another embodiment of the invention.  
         [0025]    [0025]FIG. 9 is a diagram emphasizing a portion of the circuitry shown in FIG. 8.  
         [0026]    [0026]FIG. 10 is a diagram emphasizing another portion of the circuitry show in FIG. 8.  
         [0027]    [0027]FIG. 11 is a diagram emphasizing another portion of the circuitry shown in FIG. 8.  
         [0028]    [0028]FIG. 12 is a diagram emphasizing another portion of the circuitry shown in FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The invention is for use as part of a system that typically includes wireless equipment  20  such as a radio modem for transmitting and receiving communication, a power injector  30 , an amplifier  40 , an antenna  28 , and cabling  22 ,  24 ,  26  connecting each of these components together as illustrated, for example, in FIG. 1. The system may be in a Wireless Local Area Network (WLAN), or Wireless Local Loop (WLL). The system may be applied to Wireless Internet Access (WIA) point-to-point and point-to-multipoint applications. This invention allows the user of the wireless equipment  20  to set the level of output power given to a transmission signal by setting the level preferably through the power injector  30  that sets a voltage for the transmission on the cable that is detected by the amplifier  40  that then adjusts the output power of the transmission based on the set voltage. The amplifier  40  preferably is a bi-directional amplifier.  
         [0030]    [0030]FIG. 1 illustrates the system having a module (or amplifier)  40  in accordance with a first preferred embodiment of the present invention.  
         [0031]    A radio modem  20  is connected to send signals to and receive signals from an RF cable  22 . The radio modem  20  includes circuitry to implement a Time Division Duplex (TDD) protocol, and to otherwise meet the user&#39;s needs.  
         [0032]    A power injector  30  passes signals between the cable  22  and a cable  24 , and superimposes a DC voltage on the RF signal on the cable  24 . The level of the DC voltage is variable by manual manipulation of a control knob  32 . The power injector  30  is typically located in a protected environment, such as a shelter or inside the building, and proximate to radio modem  20  or other wireless RF equipment.  
         [0033]    The cable  24  communicates signals between the power injector  30  and the module  40 . The module  40  amplifies RF signals received from the cable  24 , and sends the amplified signal to an antenna  28 . The module  40  is powered by the DC voltage on the cable  24 . The module  40  is mounted on the pole of antenna  28  on the exterior of a building. The module  40  may be mounted on the pole using any number of means including U-bolts, clamps, etc.  
         [0034]    Preferably, the housing for the module  40  is small and waterproof, to provide for direct mounting on the antenna  28 . The illustrated embodiment includes a housing having N-type, male, 50 Ohm connectors adapted for quick connection to standard commercially available N-type, female, 50 Ohm connectors disposed on the connecting cables.  
         [0035]    [0035]FIG. 2 illustrates the power injector  30  in more detail. A voltage regulator  34  generates four voltages: V 1 , V 2 , V 3 , and V 4 . In this example, V 1  equals 9 volts, V 2  equals 10 volts, V 3  equals 11 volts, and V 4  equals 12 volts. A control knob  32  includes a 4-to-1 switch for connecting (or applying) a selected one of voltages V 1 , V 2 , V 3 , or V 4  to the lower terminal of the inductor  36 . The voltage regulator  34  and control knob  32  may be designed to provide two or more output power levels.  
         [0036]    A capacitor  38  blocks a DC current from passing between the voltage regulator  34  and the cable  22 . An inductor  36  blocks the RF signal from passing to the regulator  34  from either cable  22  and/or  24 .  
         [0037]    [0037]FIG. 3 shows certain circuitry in the module  40 . At the time depicted in FIG. 3, the module  40  is in the transmit mode, meaning that a switch  422  transfers a signal on the cable  24  through the transmission amplifier module (or transmission pathway)  44  to the antenna  28  via switch  424 . An exemplary embodiment of the transmission amplifier  44  includes a driver amplifier  442  and a power amplifier  446  as illustrated in FIG. 3. An input of digital attenuator  444  receives the output of the driver amplifier  442 . The digital attenuator  444  attenuates the received signal from the driver amplifier  442  as dictated by a control input (or signal) from a DC level sensor (or detector)  448 , and transfers the attenuated signal to the input of the power amplifier  446 . The power amplifier  446  transfers an output signal to the antenna  28  via the switch  424 .  
         [0038]    In the receive mode, the switches  422  and  424  are in the opposite position of that depicted in FIG. 3. An exemplary receive path is illustrated in FIG. 3 and described herein is a receiving amplifier module (or path or means)  46 . A low noise amplifier (LNA)  462  receives a signal from the antenna  28 , via the switch  424 , and transfers an amplified signal to the input of a band pass filter  464 . The band pass filter  464  transfers a filtered output to the input of a low noise amplifier  466 . The low noise amplifier  466  transfers an amplified signal to the input of a band pass filter  468 . The band pass filter  468  transfers the filter output to the cable  24  via the switch  422 . As one of ordinary skill in the art will appreciate based on this disclosure, a variety of receive circuitry found in bi-directional amplifiers could be used for the receive path  46  in the illustrated bi-directional amplifier.  
         [0039]    In other words, the module  40  toggles between a transmitting mode and a receiving mode. In the transmitting mode, the switch  424  operatively connects the amplifier  446  to the antenna  28 . In the receiving mode, the switch  424  directs an antenna signal to the receive path  46 .  
         [0040]    [0040]FIG. 4 emphasizes certain circuitry in the DC level sensor  448 . The respective + input of each of comparators (means for determining the voltage level of the signal being transmitted)  4482 ,  4484 ,  4486  receives a signal from the cable  24 .  
         [0041]    The − input of the comparator  4482  receives a reference voltage substantially equal to (V 1 + V 2 )2, causing the comparator  4482  to apply a digital output U 1  to a 3:4 decoder  4488  (means for coding a signal to instruct the attenuator  444  the level of attenuation to apply to the signal being transmitted). V 1  and V 2  are two of the user selectable voltages sent from the power injector  30 , as illustrated in FIG. 2.  
         [0042]    The − input of the comparator  4484  receives a reference voltage substantially equal to (V 2 + V 3 )2, causing the comparator  4484  to apply a digital output U 2  to the 3:4 decoder  4488 . V 3  is one of the user selectable voltages sent from the power injector  30 , as illustrated in FIG. 2.  
         [0043]    The − input of the comparator  4486  receives a reference voltage substantially equal to (V 3 + V 4 )2, causing the comparator  4484  to apply a digital output U 3  to the 3:4 decoder  4488 . V 4  is one of the user selectable voltages sent from the power injector  30 , as illustrated in FIG. 2.  
         [0044]    Table 1 below shows functionality of the 3:4 decoder  4488 . The decoder  4488  produces output (Y 1 , Y 2 , Y 3 , and Y 4 ) as a function of input (U 1 , U 2 , and U 3 ).  
         [0045]    Table 1 also shows the functionality of the comparators  4482 ,  4484 ,  4486 . The comparators  4482 ,  4484 ,  4486  produce outputs (U 1 , U 2 , and U 3 ) as a function of a DC voltage on the cable  24 .  
                                                   TABLE 1                                   DC Input                                       Cable 104   U1   U2   U3   Y1   Y2   Y3   Y4                           V1   0   0   0   1   0   1   0           V2   1   0   0   1   0   0   1           V3   1   1   0   0   0   1   1           V4   1   1   1   1   1   1   1                      
 
         [0046]    One of ordinary skill in the art will appreciate that if a number other than four output power levels are provided for at the power injector  12 , that the number of comparators can be scaled up or down to correspond to the number of possible output power levels.  
         [0047]    [0047]FIG. 5 illustrates an implementation of the 3:4 decoder  4488  using digital logic components that are capable of providing the outputs shown in Table 1 for the inputs representative of the desired output power level.  
         [0048]    [0048]FIG. 6 shows additional circuitry preferably connected to an input node  402  in module  40 . A DC/DC converter  482  generates a 12 volt reference, used to generate the references applied to the − inputs of the comparators of FIG. 4. A voltage regulator  484  produces 7 volts for powering the power amplifier  446 . In other words, although the DC voltage on node  402  may vary between 9 and 12 volts, the voltage regulator  484  applies a constant voltage of 7 volts to the power amplifier  446 .  
         [0049]    [0049]FIG. 7 shows exemplary circuitry for the module  40  to control the switching of switches  422 ,  424 , including an RF power sensor  486  and a switching controller  50  having a voltage comparator  502  connected to the output of the power sensor  486 . The voltage comparator  502  provides an output to a switch controller  504  that generates a signal “T/R switch.” The signal “T/R switch” controls whether the switches  422  and  424  are in the transmit position or the receive position. An element  506  provides a transmission voltage threshold to comparator  502 . The module  40  thereby switches from transmit to receive mode automatically when the RF power is below the threshold level provided by element  506 . The voltage comparator  502 , the element  506 , and the switch control  504  together can be considered to be a switching controller  50 .  
         [0050]    The first preferred embodiment of the invention preferably incorporates protective features such as lighting protection circuitry and power surge protective circuitry to prevent damage from operational or environmental anomalies.  
         [0051]    Thus, the first preferred embodiment of the invention provides a standardized amplifier that is economical to install, and usable with a broad range of hardware and in a broad range of operational environments.  
         [0052]    [0052]FIG. 8 is a diagram illustrating another exemplary embodiment of the system in accordance with the present invention. The illustrated system includes a variable gain amplifier  441  at the input of amplifier  442  in the transmission amplifier  44 . Amplifier  441 , RF power sensor  486 ′, and gain control circuit  440  cooperate to provide a substantially constant input to the amplifier  442 .  
         [0053]    [0053]FIG. 9 illustrates a possible implementation of RF power sensor  486 ′. As one of ordinary skill in the art will appreciate, the implementation illustrated in FIG. 9 may be used for the RF power sensor  486  by eliminating the connection to the gain control  440 .  
         [0054]    [0054]FIG. 10 illustrates a possible implementation of gain control circuit  440 , which receives the output of power sensor  486 ′. Gain control circuit  440  essentially subtracts the output of RF power sensor  486 ′ from a reference voltage, and applies the subtraction result to a control input of variable gain amplifier  441 . Thus, the amplifier  441  remains at a predetermined output power level independent of the RF input power level on input node  402 . Alternatively, amplifier  442  may be omitted from this exemplary embodiment.  
         [0055]    [0055]FIG. 11 illustrates a possible implementation of the variable gain amplifier  441 . A variable attenuator AT- 110  has a control input that receives the output of the gain control circuit  440  illustrated in FIG. 10.  
         [0056]    [0056]FIG. 12 illustrates a possible implementation of switching control circuit  50 ′. As one of ordinary skill in the art will appreciate, the implementation illustrated in FIG. 12 may be used for switching control circuit  50 . A voltage comparator has a − input connected to the output from the power sensor  486 ′. The voltage comparator has a + input connected to a 10K:300 resister divider that provides a threshold to distinguish between transmitting and receiving. The circuit  50 ′ provides a two line output to transmit/receive switches  422  and  428  to switch between the transmit and receive modes depending on the output voltage. The two line output includes the signals RX-V and TX-V shown in FIG. 12. This embodiment thereby switches from transmit to receive mode automatically when RF power is below the threshold level. Alternatively, a single or pair of LED(s) may be included to indicate in which mode the module is operating in.  
         [0057]    Circuits to implement RF power sensor  486 ′, gain control circuit  440 , and variable gain amplifier  441  are described in U.S. application Ser. No. 09/524,745, of David Ge, filed Mar. 14, 2000 for SMART AMPLIFIER FOR TIME DIVISION DUPLEX WIRELESS APPLICATIONS, the contents of which are hereby incorporated by reference. These circuits collectively are means for normalizing the signal input into said attenuating means based on the voltage of the transmit signal.  
         [0058]    Numerous other embodiments are possible. For example, although a control knob has been illustrated and discussed for the DC level control knob  32  for the power injector  30 , there are numerous other ways of effecting power control. For example, power control may be adjusted with dedicated buttons or slides on or connected to the power injector  30 , or may be adjusted in response to commands originating from a conventional keyboard connected to a general purpose computer. These various ways for effecting power control are covered by mechanical actuator.  
         [0059]    Different exemplary embodiments have been described above with various components that can be grouped into functional groupings. Means for switching between receive and transmit modes includes RF power sensor  486 , switching controller  50 ,  50 ′, and switches  422 ,  424 . Means for setting the output power level of a transmission signal based on the voltage of the transmit signal and providing a control signal includes the DC level sensor  448 . Means for attenuating the transmit signal based in part on the control signal includes the attenuator  444 , and under at least one embodiment the transmission amplifier  44 . Means for amplification of a received signal includes the receiving amplifier path  46  and its illustrated embodiments. Means for setting a desired output level for the transmission signal include actuator  32  and voltage regulator  34 .  
         [0060]    Benefits, other advantages, and solutions to problems have been described above with regard to specific examples. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not critical, required, or essential feature or element of any of the claims.  
         [0061]    Additional advantages and modifications will readily occur to those skilled in the art. The preferred embodiment of the invention in its broader aspects is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or the scope of Applicants′ general inventive concept. The preferred embodiment of the invention is defined in the following claims. In general, the words “first,” “second,” etc., employed in the claims do not necessarily denote an order.  
         [0062]    As used herein “substantially” is a relative modifier intended to indicate permissible variation from the characteristic so modified. It is not intended to be limited to the absolute value or characteristic which it modifies but rather approaching or approximating such a physical or functional characteristic.  
         [0063]    Given the foregoing, it should be apparent that the specific described embodiments are illustrative and not intended to be limiting. Furthermore, variations and modifications to the preferred embodiment of the invention should now be apparent to a person having ordinary skill in the art. These variations and modifications are intended to fall within the scope and spirit of the preferred embodiment of the invention as defined by the following claims.