Abstract:
A multi-channel fixed wireless terminal ( 14 ) is implemented using a gain controller ( 34 ) for controlling the gain of each of a plurality of transmission channels. The gain controller ( 34 ) includes an averager ( 62 ) for receiving and averaging gain control signals ( 58   a-   58   d ) for each of multiple transmission channels to generate an average gain control signal ( 48 ). In addition, differentiators ( 70   a-   70   d ) generate respective differential gain control signals ( 74   a-   74   d ) for the multiple transmission channels from the respective gain control signals ( 58   a-   58   d ) for the multiple transmission channels and the average gain control signal ( 48 ). A plurality of adjustable amplifiers ( 72   a-   72   d ) controlled by the respective plurality of differentiators ( 70   a-   70   d ) amplify signals transmitted over the multiple transmission channels and input thereto to maximize respective signal to noise ratios of the signals. Through implementation of the gain controller ( 34 ), the multi-channel fixed wireless terminal ( 14 ) may be implemented with only a single transmitter ( 38 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to wireless communications systems, and more particularly to channel power control in a fixed multi-line wireless terminal. 
     2. Description of Related Art 
     In many parts of the world, it is expensive or difficult to run copper wire or fiber optic cable to homes and businesses to provide local phone service. A wireless local loop telephone system enables service providers to service such areas without the need for cable and its associated costs. 
     In a wireless local loop system, telephones and other terminal equipment at a customer site are connected to a fixed wireless terminal (FWT). The fixed wireless terminal communicates with the public switched telephone network (PSTN) through a wireless radio link, thereby enabling basic telephone service to be provided to customers who would not otherwise have access to telecommunications services, at a fraction of the cost of a traditional wire line infrastructure. Because wireless local loop systems provide telecommunications system operators with the benefits of rapid deployment, large coverage area, large capacity, and lower operating and maintenance costs, digital wireless telephone networks may be deployed rapidly and economically in developing countries which lack sufficient land-line infrastructure. 
     In a multi-line fixed wireless terminal, multiple channel units share a common transmitter. The transmitter controls the transmit power of each channel unit based on power level commands received from the base station(s) servicing the FWT. More specifically, each individual channel unit provides the transmitter with a set of baseband I land Q modulation signals, as well as a power control signal to control the attenuation of the transmit power level of each individual channel unit. 
     Adjusting the power levels of the respective channel units in a multi-line FWT is problematic. One possible way to independently adjust the transmit power of each individual channel unit requires performing all power adjustments at baseband prior to combining the individual transmit baseband channels. However, with such an approach, if all individual channel units were requested to reduce their power to a minimum level, the signal to noise ratio would be reduced to unacceptably low levels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments thereof when taken together with the accompanying drawings in which: 
     FIG. 1 is a block diagram of a wireless local loop telecommunications system of the type in which a multi-line fixed wireless terminal of an embodiment in accordance with the present invention is implemented; 
     FIG. 2 is a block diagram showing the components of the multi-line fixed wireless terminal of FIG. 1 in more detail; 
     FIG. 3 is a block diagram showing the components of a composite gain adjuster located within the multi-line fixed wireless terminal of FIG.  2  and of a preferred embodiment in accordance with the present invention; and 
     FIG. 4 is a block diagram showing the components of a composite gain adjuster located within the multi-line fixed wireless terminal of FIG.  2  and of another preferred embodiment in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings in which like numerals reference like parts, FIG. 1 shows a wireless local loop digital cellular communications system  10 . As shown, terminal equipment units  12   a-   12   d  are coupled to a multi-line fixed wireless terminal (FWT)  14  at input ports  16   a-   16   d . The terminal equipment units  12   a-   12   d  may be telephones, fax machines, modems, or other customer provided equipment, or customer premise equipment (CPE). The input ports  16   a-   16   d  are typically implemented with, for example, RJ-11 jacks or other jacks from the RJ family of jacks registered with the Federal Communications Commission, such as RJ-12 and RJ-45 jacks, or with other types of connectors, to connect, for example, a twisted-pair copper cable between the terminal equipment units  12   a-   12   d  and the fixed wireless terminal  14 . While the embodiment shown in FIG. 1 shows four input ports  16   a-   16   d , the number of input ports, and therefore channels available through the FWT  14 , may vary. 
     The multi-line FWT  14  is coupled to an antenna  18  for transmitting radio frequency signals  20  to a base station  22 , and is typically mounted in a convenient location in a building or home so that it remains fixed in relation to the location of base station  22 . The radio frequency signals  20  ordinarily conform to an air interface standard, such as the industry standard IS-95 for code division multiple access (CDMA) cellular communications systems. The base station  22  ultimately communicates user voice or data signals to the public switched telephone network (PSTN)  24  after it receives signals from the FWT  14  so that customers using the telephones  12   a-   12   d  may place calls to other telephones connected to the PSTN  24 . 
     In digital cellular communications systems, such as the system  10 , it is desirable that each subscriber unit, such as the telephones  12   a-   12   d , transmits signals to the base station  22  at the minimum power level required to ensure adequate reception of the signals at the base station, while simultaneously enhancing call quality by minimizing signal interference, maximizing system call capacity, and improving the life of the batteries in the respective telephones  12   a-   12   d.    
     During a normal telephone call on the CDMA system  10 , the base station  22  will instruct either the FWT  14  or the appropriate one of the subscriber units, such as the telephone  12   a , at a rate of 800 times per second to adjust the transmit power of the subscriber unit using closed loop power control. The closed loop power control is automatically executed while a call is in progress to ensure that the base station  22  always receives signals from the subscriber unit at the desired signal level. 
     FIG. 2 shows the multi-line FWT  14  in more detail. The multi-line FWT  14  includes three main component sections: A Radio Frequency section  30 , a digital section  32 , and a composite gain adjust section  34 . The RF section  30  contains RF components necessary for providing the wireless link between the telephones  12   a-   12   d  and the base station  14 . Specifically, the RF section  30  includes a receiver  36  and a transmitter  38 . The receiver  36  is for receiving a radio signal  40  from the base station  14  via the antenna  18 , converting it into a baseband receive signal  42 , and outputting the baseband receive signal  42  to a baseband splitter  44 , which then splits the baseband receive signal into individual channel baseband receive signals  42   a-   42   d  that are each capable of being processed by the digital section  32 . 
     The transmitter  38  is for accepting a composite baseband transmit signal  46  and a composite gain adjust signal  48  from the composite gain adjust section  34 , converting these signals  46  and  48  into a transmit radio signal  49 , and transmitting the transmit radio signal  49  to the base station  22  via the antenna  18  at a power level determined by the composite gain adjust section  34  in a manner to be described in more detail below. 
     The digital section  32  includes individual digital control sections  50   a-   50   d  for each of the respective telephones  12   a-   12   d . The control sections  50   a-   50   d  include respective telephone interfaces  52   a-   52   d  and microprocessors  54   a-   54   d . The microprocessors  54   a-   54   d  are each for receiving a broadband receive signal, intended for a corresponding one of the telephones  12   a-   12   d , from the receiver  36  via the splitter  44 , converting the broadband receive signal to an audio signal, and transmitting the audio signal to a corresponding one of the telephone interfaces  52   a-   52   d . Each of the microprocessors  54   a-   54   d  is also for receiving the audio signal transmitted from a telephone microphone from a corresponding one of the telephones  12   a-   12   d , through a corresponding one of the telephone interfaces  52   a-   52   d , and converting the received audio signals to baseband transmit signals  56   a-   56   d  with a fixed gain. Each of the generated baseband transmit signals  56   a-   56   d  is then transmitted to the composite gain adjust section  34  to be combined into a composite baseband transmit signal  46  for output to the transmitter  38 . 
     In addition, the microprocessors  54   a-   54   d  in the digital section  32  are also for extracting power control request information present in the baseband receive signals  42   a-   42   d , interpreting the information, and using the information to generate gain adjust signals  58   a-   58   d  that are input into the composite gain adjust section  34  for use in setting the gain for the transmitter  38  at a desired level to satisfy power control requests received from the base station  22 . 
     The composite gain adjust section  34  according to the preferred embodiment enables the FWT  14  to support multiple telephone lines, also referred to in this description as channels, by enabling the single RF section  30  to be integrated with the multiple digital control sections  50   a-   50   d . In the composite gain adjust section  34 , a baseband transmit signal combiner  60  is for receiving the generated baseband transmit signals  56   a-   56   d  from the respective individual control sections  50   a-   50   d , and generating the composite baseband transmit signal  46 , which is input into the transmitter  38 . 
     In addition, a composite gain averager  62 , which can be realized through implementation of, for example, a simple opamp non-inverter averaging circuit, is for receiving the gain adjust signals  58   a - 58   d  from the individual control sections  50   a - 50   d , and for generating the composite gain adjust signal input  48  for the transmitter  38 . The composite gain adjust section  34  thereby enables the software of individual control sections, such as the control sections  50   a-   50   d , to be compatible, as each of the microprocessors  54   a-   54   d  thinks that it has complete control of the transmitter  38  during a call completed with the telephone corresponding to the particular microprocessor. 
     FIG. 3 shows the components of the composite power adjust section  34  in more detail. As shown, the baseband transmit signal combiner  60  includes channel gain adjusters realized by, for example, opamp difference amplifiers, and including respective gain adjust sections  70   a-   70   d  and amplifier sections  72   a-   72   d . The gain adjust sections  70   a-   70   d  are for receiving the generated composite gain signal from the gain adjust averager  62 , as well as channel IF gain signals from the respective microprocessors  54   a-   54   d , and for calculating difference signals  74   a-   74   d  indicative of differences between the composite gain signal  48  and each of the respective individual channel IF gain signals  58   a-   58   d  to set the gain of the amplifier sections  72   a-   72   d . The gain adjust sections  70   a-   70   d  are also for receiving a DC voltage corresponding to 0 dB gain for biasing the respective amplifier sections  72   a-   72   d.    
     The amplifier sections  72   a-   72   d  are for amplifying or attenuating the respective channel baseband transmit signals  56   a-   56   d , which are formed from separate quadrature baseband I and Q signals. Signal summers  78   a  and  78   b  are for receiving the respective amplified/attenuated baseband I and Q signals from the amplifier sections  72   a-   72   d , and for generating respective composite I and Q transmit signals  46   a ,  46   b  from the I and Q signals from each of the individual channels. The resulting composite transmit I and Q signals  46   a  and  46   b  are then output to the transmitter  38 . 
     Operation of the composite gain adjust section  34  will now be described with reference to FIGS. 2 and 3. If the FWT  14  is supporting two calls on, for example, telephones  12   a  and  12   b , and the base station  14  is instructing the call on the telephone  12   a  to increase its transmit power, and the call on the telephone  12   b  to decrease its power, both power control requests cannot be simultaneously satisfied without the composite gain adjust section  34  of the preferred embodiment because the transmit path for both calls is through the same RF section  30 , and because the transmit power level adjustment is executed by the transmitter  38  in the RF section. The composite gain adjust section  34  facilitates independent channel power level adjustment by creating, at the transmit baseband signal combiner  60 , the composite baseband transmit signal  46 , which is composed of each of the individual baseband transmit channel signals  56   a-   56   d  (one for each active call) summed in a manner that adjusts the levels of each of the individual baseband transmit channel signals to the proper level relative to the other baseband transmit channel signals. The composite gain adjust section  34  can therefore pass the single composite baseband transmit signal  46  to the transmitter  38  while still enabling the transmitter  38  to independently adjust channel power levels. 
     The RF section  30  transmits the composite baseband transmit signal  46  at a power level that is an average of all requested individual call levels. While the gain setting corresponding to the average power level may not be correct for any of the individual channels, the baseband level of each of the individual channels is adjusted prior to the transmit baseband combiner  60  combining the baseband transmit signals  56   a-   56   d  so that each individual call is transmitted at its correct power level. The baseband signal levels are adjusted in such a manner because it is desirable to maintain the signal levels at baseband as high as possible to maintain a high signal to noise ratio, and to enable as much power adjustment and attenuation as possible to be performed at IF and RF frequencies within the transmitter  38 . 
     Operation of the composite gain adjust section  34  will now be further illustrated by way of the following example. If the multi-line FWT  14  is supporting four active calls, with the base station  22  instructing three of the calls to transmit at a power level of 10 dBm, and the fourth call at a power level of 14 dBm, the average transmit level desired, P avg , is: 
     
       
           P   avg =(10+10+10+14)/4=11 dBm 
       
     
     Therefore, the gain of the transmitter  38  will be adjusted to a power level of 11 dBm for each channel. However, the composite gain adjust section  34  is designed so that the level of each of the individual channels is adjusted by the gain adjust sections  70   a-   70   d  of the opamp difference amplifiers by taking the difference between the desired channel gain and the composite gain: 
      Ind. gain for channel  N= (gain for desired channel  P   out )−(gain for  P   avg =11 dBm) 
     For the first three calls, the gain required to achieve an output power level of 11 dBm would be the gain of the first three calls set as follows: 
     
       
         Ind. gain for ch. 1=(gain for ch. 1 P out =10 dBm)−(gain for  P   avg =11 dBm)=−11 dBm 
       
     
     Therefore, while the appropriate gain P out  for channel 1 is 10 dBm, the composite gain adjust section  34  determines that the level of the individual baseband signal  56   a  needs to be reduced by 1 dB prior to the baseband transmit signal combiner  60  combining all of the baseband transmit signals  56   a-   56   d . This is because the gain of the transmitter  38  will be 1 dB too high, as the transmitter gain will be adjusted for P avg =11 dBm. The baseband levels for each of the individual baseband transmit signals  56   b-   56   d  for channels 2-4 are similarly adjusted by the composite gain adjust section  34  as follows: 
     
       
         Ind. gain for ch. 2=(gain for ch. 2  P   out =10 dBm)−(gain for P avg =11 dBm)=−1 dB 
       
     
     
       
         Ind. gain for ch. 3=(gain for ch. 3  P   out =10 dBm)−(gain for P avg =1 dBm)=−11 dB 
       
     
     
       
         Ind. gain for ch. 4=(gain for ch. 4  P   out =14 dBm)−(gain for P avg =11 dBm)=+3dB 
       
     
     For each of the channels, the desired individual output power equals the sum of P avg  and the individual gain for that channel: 
     
       
         Power out for ch. 1=11 dBm+(−1 dBm)=10 dBm 
       
     
      Power out for ch. 2=11 dBm+(−1 dBm)=10 dBm 
     
       
         Power out for ch. 3=11 dBm+(−1 dBm)=10 dBm 
       
     
     
       
         Power out for ch. 4=11 dBm+(+3 dBm)=14 dBm 
       
     
     Therefore, individual gain control is maintained while enabling a single transmitter to be implemented in a multi-channel FWT. As a result, the footprint of the FWT is reduced. In addition, the overall manufacturing cost of the FWT is reduced, as only a single transmitter is required. 
     While the above-discussed composite gain adjuster is a preferred embodiment in accordance with the present invention, the power adjuster can also be configured to determine the maximum desired power level of each individual call and to use the maximum desired power level to set the gain for the multi-line FWT. Such a configuration may be useful, for example, if the individual channel voltage controlled amplifiers were only capable of attenuation and could not boost signal levels. 
     Referring to FIG. 4, the power adjuster could be alternatively configured to enable two independent gain averagers  62   a ,  62   b , the former being for IF gain adjustment and the latter being for RF gain adjustment, to replace the single IF gain averager  62  in the embodiment shown in FIGS. 2 and 3 and described above. Such a configuration could be applied in, for example, a CDMA-based system in which the subscriber unit or FWT must be capable of adjusting its transmit power over a wide range of output levels, such as a 75 dB range for IS-95 protocol. Because such a wide gain variation is difficult to achieve in a single variable attenuator, the individual IF and RF gain adjusters  62   a ,  62   b  may be implemented as a result. The FIG. 4 block diagram shows an alternative embodiment including the separate gain adjusters  62   a ,  62   b  for receiving respective IF and RF gain signals  80   a-   80   d  and  82   a-   82   d , and for generating separate composite IF and RF gain adjust signals  84   a  and  84   b  input both directly to the transmitter  38  and also to the gain adjust sections  70   a-   70   d . All other components are identical to those in the embodiment shown in FIG.  3 . 
     In view of the foregoing discussion, it should be appreciated that the composite power adjuster of the above-discussed embodiment in accordance with the present invention enables each channel microprocessor in a multi-line FWT with only a single transmitter to think that it is in complete control of the transmitter by facilitating compatibility among channel software microprocessors. In addition, the composite software adjuster of the above-discussed embodiment in accordance with the present invention can be fully implemented using hardware components, and therefore does not require DSP or microprocessor intervention to achieve closed loop power control for multiple channel units. 
     While the above description is of the preferred embodiment of the present invention, it should be appreciated that the invention may be modified, altered, or varied without deviating from the scope and fair meaning of the following claims.