Abstract:
An improved filter amplifier for wireless communication is provided. The filter amplifier comprises a talk-in and talk-out booster. The booster utilizes a single local oscillator to down-convert a received signal for filtering and up-convert the received signal for further amplification. A combining unit including amplifier and isolator is operable to receive the filtered signal and amplify and combine the signal. The use of isolators allows for combining signals without interference. The booster amplifier filter unit is designed for use in low reception areas including tunnels and office buildings.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates to the amplification of wireless communication signals, and more specifically to an improved channel booster amplifier.  
         BACKGROUND  
         [0002]    In recent years, the uses of wireless communications methods have exploded. These include the use of cellular telephones, pagers, trunking radios and other such systems. While these systems are increasingly more reliable and easy to use, there are still many areas where the coverage of wireless communications systems fail. These include the interior of buildings, the inside of tunnels, and other areas where wireless communications signals cannot penetrate reliably. Various techniques have been employed to try to enhance communications inside of buildings and tunnels and other areas where wireless communications fail. However, these attempts have met with mixed success because they are often bulky and unable to adapt to a wide range of communication needs. What is needed is a compact and efficient way of filtering and boosting wireless communication signals such that they can be used in areas where coverage is not optimal.  
         SUMMARY OF THE INVENTION  
         [0003]    Accordingly, it may be appreciated that a need has arisen for an improved channel booster amplifier for wireless communications. In accordance with the teachings of the present invention, an improved channel booster amplifier is provided that substantially eliminates or reduces the disadvantages and problems associated with conventional devices.  
           [0004]    In one embodiment an improved filter amplifier for wireless communication is provided. The filter amplifier comprises a talk-in and talk-out booster. The booster utilizes a single local oscillator to down-convert a received signal for filtering and up-convert the received signal for further amplification. A combining unit including amplifier and isolator is operable to receive the filtered signal and amplify and combine the signal. The use of isolators allows for combining signals without interference. The booster amplifier filter unit is designed for use in low reception areas including tunnels and office buildings.  
           [0005]    The present invention provides various technical advantages over conventional filters. For example, the present invention provides isolation between amplification and combining of signals thus reducing signal loss through interference. Second, the filter and booster of the present invention uses easy to use cards which can be used in either the talk-in or talk-out direction. Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    For a more complete understanding of the present invention and the advantages thereof, reference is made to the following descriptions taken in conjunction with the following figures, in which like reference materials represent like parts and in which:  
         [0007]    [0007]FIG. 1 illustrates a communication system in accordance with the teachings of the present invention;  
         [0008]    [0008]FIG. 2 illustrates a booster/amplifier in accordance with the teachings of the present invention;  
         [0009]    [0009]FIGS. 3 a  and  3   b  illustrate the components of the booster and amplifier in accordance with the teachings of the present invention;  
         [0010]    [0010]FIG. 4 illustrates the combiner and associated amplifiers in accordance with the teachings of the present invention;  
         [0011]    [0011]FIG. 5 illustrates a band pass filter in accordance with the teachings of the present invention; and,  
         [0012]    [0012]FIG. 6 illustrates signal strength adjustment system in accordance with the teachings of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]    [0013]FIG. 1 is a block diagram of a wireless communication system  100  in accordance with the teaching of the present invention. The present invention is not to be limited to such an illustration; however, the illustration is instructive for purposes of invention discussion. To those skilled in the art it is known that such a communication system can be adapted to many different uses. In FIG. 1 is a communication system  100 . In one embodiment, communication system  100  is a trunking radio system used by municipalities to communicate between emergency vehicles. In this system, a first vehicle  102  with antenna  104  receives and sends communications to a second vehicle  122 . The communication can be transferred through one or more antenna systems  110 . In this system, each vehicle uses one channel to transmit communication signals and a second channel to receive communication signals. Communication signal  106  is the communication signal between first vehicle  102  and antenna  110 . Communication relayed by antenna  110  to first vehicle  102  is communication signal  108 . In FIG. 1, second vehicle  122  is inside a tunnel. Normally, second vehicle  122  would not be able to receive the communication from first vehicle  102  because the tunnel blocks the signals. To help this situation, an antenna  116  is mounted outside tunnel  124 . Included downstream from the antenna is a band pass filter  118 . The band pass filter  118  is coupled to booster amplifier  119 , which is coupled to one or more radiating cables  120  that run inside the tunnel. Radiating cable  120  is essentially a long cable antenna. System  100  operates as a fully duplex system supporting both incoming and outgoing communications.  
         [0014]    In operation, first vehicle  102  sends a communication signal to second vehicle  122 . The communication signal is transmitted from first vehicle  102  as communication signal  106  and is relayed by antenna  110  to antenna  116  as communication signal  112 . Antenna  116  receives communication signal  112  and sends it to band pass filter  118 , which filters out any frequency outside the expected range of received communication. Then the communication signal is passed to booster amplifier  119  where the signal is filtered and boosted sufficiently to be sent over radiating cable  120 . As the signal is sent over radiating cable  120 , second vehicle  122  receives the signal. Also, second vehicle  122  can transmit a communication signal by broadcasting to radiating cable  120  through booster amplifier  119 , through band pass filter  118  to which filters out signals outside the expected transmittal range. The filtered communication is sent to antenna  116 . Antenna  116  broadcasts communication signal  114  to antenna  110 . Antenna  110  broadcasts the communication signal where it is received by first vehicle  102  as communication signal  108  at antenna  104 . Such actions can then occur back and forth as necessary. Antenna  110  is not always needed. The necessity of antenna  110  depends on the location of first vehicle  102  and the strength of the transmitted signal. In some embodiments, first vehicle  102  directly communicates with antenna  116 . In a typical trunking radio system, there are separate channels for receiving and transmitting. Typically, there are  8  channels for receiving and  8  channels for transmitting. An individual is assigned a certain transmit and receive set.  
         [0015]    [0015]FIG. 2 is a block diagram of booster amplifier  119  with antenna in accordance with the teachings of the present invention. Illustrated is antenna  116  that is coupled to a duplexer  202 . Duplexer  202  sends signals received by antenna  116  to low noise amplifier band pass filter  204  which is coupled to a talk-in booster  206  which filters and amplifies the communication signal. Talk-in booster  206  is coupled to a second low noise amplifier unit  208 . Low noise amplifier unit  208  couples to a second duplexer  210  which has as one output the radiating cable  120 . Signals received from second low noise amplifier unit  208  are sent over radiating cable  120  which is typically placed in a tunnel or the like. Duplexer  210  also is coupled to a low noise amplifier band pass filter that is operable to receive signals from radiating cable  120  and duplexer  210 . Low noise amplifier unit  212  is coupled to a talk-out multi-channel booster  214  which in turn is connected to low noise amplifier unit  216  which is coupled to first duplexer  202  which in turn couples to antenna  116 .  
         [0016]    In operation, communication signals received by antenna  116  are sent to duplexer  202  where they are then relayed to the talk-in side of booster amplifier  200 . The communication signals are amplified and band pass filtered to clean up the communication signal at low noise amplifier band pass filter  204 . Next, multi-channel booster filter  206  filters and boosts the communication signal. The filtering and boosting is done in an intermediate frequency range that requires talk-in booster  206  to include means for down converting the radio frequency signal to an intermediate frequency signal. This will be described in further detail in conjunction with FIG. 3 a . The output of talk-in booster  206  will be a radio frequency signal that will then be boosted by low noise amplifier  208  and sent to duplexer  210  to be routed to radiating cable  120  for transmitting to cars or personnel inside of a tunnel, building or other areas where wireless communications fails. The operation of talk-out side is for most purposes similar. A signal is sent from inside the tunnel to cable  120  which inputs to duplexer  210  which will then send the communication signal to low noise amplifier band pass filter  212  for filtering and amplification. That signal is then sent to talk-out booster amplifier  214  where it is both boosted and amplified in an intermediate frequency and then converted back to a radio frequency signal for boosting by low noise amplifier  216 . The signal is then sent to duplexer  202  where it is routed to antenna  116  for communication outside the tunnel.  
         [0017]    [0017]FIG. 3 a  illustrates in more detail talk-in booster  206  and amplifier  208 . Talk-in booster  206  includes a splitter  302  that is coupled to band pass filter  304  that in turn is coupled to a mixer  308 . Mixer  308  is coupled to a local oscillator  306  as well as a crystal filter  310 . The output of crystal filter  310  is then supplied to a second mixer  312  that is also coupled to local oscillator  306 . Second mixer  312  outputs to amplifier  313  that then outputs to combiner  314 . The output of combiner  314  is to duplexer  210 .  
         [0018]    In operation, a communication signal is received from duplexer  202  via antenna  106 . In one embodiment, the communication signal may comprise one or more communication channels. If that is so, splitter  302  will split out the communication signal into one or more different communication channels. All processing between splitter  302  and combiner  314  is identical for each signal. Therefore, the discussion of one signal will suffice for discussion of all signals. In a typical trunking radio system, eight (8) signals are outputted from the splitter  302 . Each channel will then output to band pass filter  304  where it is filtered within a narrow range. Then, mixer  308  will mix the signal from the band pass filter with the signal from the local oscillator. This will down convert the signal to an intermediate frequency range. When the signal is in the intermediate frequency range, it is then filtered by crystal filter  310 . After filtering, the second mixer again mixes the intermediate frequency signal with the signal from local oscillator  306  in order to convert it back to the original frequency. By providing a single local oscillator  306 , to run both mixers  308  and  312 , any error in the local oscillator is compensated for. Thus, there is no frequency drift. The local oscillator is synthesizer controlled and programmable. This allows for changes in the frequency of the local oscillator. This provides technical advantages over systems that use multiple local oscillators to control one or more mixers. Also, by converting to an intermediate frequency mode before filtering helps increase the efficiency of the filtering. The signal is then sent to an amplifier where it is then amplified by amplifier  313  and then all the different signals are combined together by combiner  314  and sent to duplexer  208 .  
         [0019]    [0019]FIG. 3 b  illustrates the same system as FIG. 3 a  except on the talk-out side. In this example, talk-out booster  214  is illustrated. A signal from duplexer  310  is received by splitter  316  to be split into the number of signals necessary. The signal is then filtered by band pass filter  318  and converted to an intermediate frequency by mixer  320  and is then filtered by crystal filter  324  and mixed by mixer  326  back to the original frequency. One local oscillator  322  provides a signal to both first and second mixers  320  and  326 . The signal is then amplified by an amplifier  327  and combined by combiner  328  to be sent to duplexer  202  for sending over antenna  116 . Again, the use of a single local oscillator compensates for an error in the oscillator is an advantage. If there is an error in local oscillator it is repeated in both mixers so it is compensated for. Also, one local oscillator reduces cost and size of necessary components. Secondly, by having similar components in both the talk-in and talk-out directions, the circuitry for the booster can be integrated in a single card that can be easily used and re-used in the system of the present invention. Finally, the output of talk-in booster  206  and talk-out booster  214  are the same for each channel, regardless of the input signal.  
         [0020]    [0020]FIG. 4 illustrates the combiner in accordance with the teaching of the present invention. FIG. 4 illustrates combiner  314  although the same information would also be applicable to combiner  328 . Illustrated is an amplifier  313  coupled to an isolator  402 . The amplifier-isolator pair are reproduced for as many signals that are input to combiner  314 . Amplifier  313  receives a signal from second mixer  312  and amplifies that signal which will then go through an isolator that helps to reduce interference between the signals entering into combiner  314 . In the absence of isolator  402 , the signals for each of the different frequencies tend to interfere with each other and create intermodulations between the signals making the communication difficult to receive. If the signals are first combined and then amplified the required amplifier would be a very high power amplifier. The use of an amplifier for each channel allows a lower power amplifier to be used saving power and reducing thermal problems. The providing of isolator  402  between the amplifier  313  and the combiner  314  increases the isolation between each input into the combiner  314  and prevents interference between adjacent signals.  
         [0021]    [0021]FIG. 5 illustrates band pass filter  304  in accordance with the teachings of the present invention. This information would also apply to band pass filter  318 . A pin attenuator  500  receives a signal from splitter  302 . The pin attenuator  500  attenuates and sends the signal to band pass filter  502  which filters and then sends the signal to low noise amplifier  504  for amplification. The signal is sent to a second filtering stage  506  for filtering before sending to the first mixer  308 .  
         [0022]    In operation, the communication signal from the signal goes to pin attenuator  500  in order to attenuate the signal. The amount of attenuation depends upon a number of factors and is done to avoid too much gain in the system. The signal is then band pass filtered by band pass filter  502  and amplified to some extent by low noise amplifier  504 . Finally, the signal is again band pass filtered to remove any signals outside the expected received range and the signal is sent to mixer  308 .  
         [0023]    [0023]FIG. 6 illustrates an attenuation and amplification adjustment system in accordance with the teachings of the present invention. Illustrated is pin attenuator  500  coupled to band pass filter  502 , low noise amplifier  504  and second filtering stage  506 , as discussed in FIG. 5. First mixer  308  couples to crystal filter  310  and second mixer  312 , which in turn couples to power amplifier  208 . All of these components have been previously discussed. In this embodiment, a received signal strength indicator (RSSI)  600  is coupled between first mixer  308  and second mixer  312 . RSSI measures the strength of the received signal and sends this information to microprocessor  602 . Microprocessor  602  then compares the received signal strength to predetermined thresholds. If the signal strength is below a certain first threshold, it is assumed no signal is received and any amplification is turned off at low noise amplifier unit  208  to conserve power. When the signal strength meets or exceeds the first threshold, amplification is activated. If the signal strength is higher then a second threshold, pin attenuator  500  can be used to attenuate the received signal. If this was not done, distortion of the received signal could occur. Microprocessor  602  is also operable to control the settings of local oscillator  306  to adjust local oscillator  306  to the correct frequency for the channel to be filtered.  
         [0024]    While the invention has been particularly shown and described in the foregoing detailed description, it will be understood by those skilled in the art that various other changes in form and detail may be made without departing from the spirit and scope of the invention.