Abstract:
An improved enhancer is disclosed which uses a switch matrix to increase the isolation between two antennas. For either an reverse link or forward link communication, the enhancer has a first antenna for receiving an incoming signal, and a receiver sub-system that amplifies and converts the incoming signal from the first antenna to a first predetermined frequency band. The enhancer further has a demodulator coupled to the receiver sub-system for demodulating the converted signal, and detecting timing information thereof. Also contained in the enhancer is a transmitter sub-system operable with the receiver sub-system that converts the signal from the receiver subsystem to a second predetermined frequency band and further amplifies the signal. After the signal is thus enhanced, a second antenna is used for further transmitting the amplified signal from the transmitted sub-system. The switch matrix controls connection switching among the first antenna, the second antenna, the transmitter sub-system, and the receiver sub-system, wherein the connection switching of the switch matrix is made based on the timing information detected by the demodulator and based on whether the incoming signal comes from a terminal or a base transceiver station.

Description:
BACKGROUND OF THE INVENTION 
   The present disclosure relates generally to communication radio hardware and software, and more particularly, to the repeater or enhancer used in wireless communication systems. 
   A repeater or enhancer is a radio apparatus that is used in wireless communication systems to boost or enhance radio signal strength in order to extend the radio coverage. An enhancer typically includes a donor antenna, a service antenna, and an electronic circuit that performs signal reception, amplification, and re-transmission. For the forward link (or down link) communications from a base transceiver station (BTS) to a terminal such as a mobile station, an enhancer receives a signal from the BTS through the donor antenna, enhances and re-transmits the signal to the intended terminals with the service antenna. Similarly for the reverse link (or up link) communications from the terminal to the BTS, the enhancer receives a signal from the terminal through the service antenna, enhances and re-transmits it to the BTS using the donor antenna. As such, the enhancer merely stands in a radio path between the BTS and the terminals, and receives and transmits the radio signals at the same time. 
   It is understood that typically the transmitted signal level is much higher than the received signal level. Since the enhancer receives and transmits signals at the same time, an effective isolation mechanism is required between the donor and service antennas. Furthermore, if the BTS and terminals employ time division duplex technology (TDD) for both the forward and reverse link communications, the enhancer needs to know the exact timing for the TDD switching in order to implement a mechanism to connect the donor antenna to an input port of the corresponding receiver circuit, and similarly, the service antenna to an output port of the transmitter circuit during the forward link communications. Likewise, the TDD switch timing helps to appropriately connect the service antenna to the input port of the receiver circuit and the donor antenna to the output port of the transmitter circuit during the reverse link communications. 
   In the conventional art, several methods for improving the isolation mechanism of a enhancer have been proposed. For example, Qi Bi et al (U.S. Pat. No. 5,835,848) discloses a method using a feedback signal whose amplitude and phase are adjusted in response to the amplitude and phase of a sampled input signal when the normal output of the enhancer is turned off for a short period of time so the sampled input is the leakage signal. The information extracted is then used in the normal operation to cancel out the leakage. This method can be classified as an active noise cancellation method and needs sophisticated hardware and software implemented in the enhancer. 
   In another example, Hideto Oura (U.S. Pat. No. 6,115,369) discloses another method where the transmission and receiver times are allocated at different time slots. This method is classified as a store-then-transmit method. Its drawback is that the enhancer will not be transparent to the BTS and terminals, and the data throughputs between the BTS and terminals are reduced at least by half. 
   Stefan Kallander et al (U.S. Pat. No. 5,603,080) discloses a method where a high radio frequency used between the BTS and enhancer is first converted at a first converter into a low frequency, which is capable to transmit over cable to a second converter where the low frequency signal is converted into the high radio frequency, which is then transmitted to the terminals. This method requires two converters that locate separately and a transmission media between them. 
   What is needed is an efficient method for determining the TDD switch timing and an improved method and system that provides more signal isolation between the donor and service antennas to avoid oscillation. 
   SUMMARY OF THE INVENTION 
   This disclosure provides an improved enhancer, which uses a switch matrix to increase the isolation between two antennas. For either a forward or reverse communication, the enhancer has a first antenna for receiving an incoming signal, and a receiver sub-system that amplifies and converts the incoming signal from the first antenna to a first predetermined frequency band. The enhancer further has a demodulator coupled to the receiver sub-system for demodulating the converted signal, and detecting timing information thereof. Also contained in the enhancer is a transmitter sub-system operable with the receiver subsystem that converts the signal from the receiver sub-system to a second predetermined frequency band and further amplifies the signal. After the signal is thus enhanced, a second antenna is used for further transmitting the amplified signal from the transmitted sub-system. The switch matrix controls connection switching among the first antenna, the second antenna, the transmitter sub-system, and the receiver subsystem based on the timing information detected by the demodulator and based on whether the incoming signal comes from a terminal or a base transceiver station (BTS). 
   In another example of the present disclosure, the switch matrix is further enhanced by including four controlled amplifiers to attenuate signal leakage from the switches of the switch matrix. The controlled amplifier can be a low noise amplifier, a power amplifier, or even a double pole single throw switch. 
   In another example of the present disclosure, a synthesizer is used to produce local oscillator frequencies for use by the receiver sub-system and the transmitter sub-system. The synthesizer can also be enhanced by including several pairs of switches and amplifiers arranged in such a way to further isolate local oscillator frequencies generated by the synthesizer. 
   One example of the enhancer disclosed is an enhancer using time division duplex technology, and contains a donor antenna and a service antenna. The donor antenna is designed to be a patch antenna facing the BTS direction, while the service antenna can be a dipole antenna lying on the same plane as the patch antenna. Both the patch and dipole antennas have a null point in their radiation patterns along the vertical direction so that such an arrangement will maximize their mutual isolation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a schematic of an enhancer according to one example of the present disclosure. 
       FIG. 2  illustrates a variation of the enhancer of  FIG. 1  incorporating band pass filters in the switch matrix thereof according to one example of the present disclosure. 
       FIG. 3  illustrates another variation of the enhancer of  FIG. 1  incorporating controlled amplifications in the switch matrix thereof according to one example of the present disclosure. 
       FIG. 4  illustrates another variation of the enhancer of  FIG. 1  incorporating controlled amplifications and additional switches in the switch matrix thereof according to one example of the present disclosure. 
       FIG. 5  illustrates another variation of the enhancer of  FIG. 1  incorporating controlled amplifications and additional switches in the switch matrix thereof according to another example of the present disclosure. 
       FIG. 6  illustrates another variation of the enhancer of  FIG. 1  incorporating additional controlled switches in the switch matrix thereof according to one example of the present disclosure 
       FIG. 7  illustrates a physical layout design of a donor antenna and service antenna according to one example of the present disclosure. 
       FIG. 8  illustrates a mechanism for assigning two locally generated frequencies for two mixers of the enhancer of  FIG. 1  according to one example of the present disclosure. 
       FIG. 9  illustrates a enhancer implemented with a modulator subsystem according to another example of the present disclosure. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  illustrates a schematic of an enhancer  10  according to one example of the present disclosure. The components of the enhancer includes a donor antenna  12 , a service antenna  14 , a switch matrix  16 , a receiver sub-system  18 , a transmitter sub-system  20 , a demodulator subsystem  21  which contains a demodulator  22 , an analog-to-digital converter (ADC)  24 , and a base band module (DSP)  26 , and a synthesizer sub-system  28 . The switch matrix  16  is controlled by switch signals that are derived from the TDD switch timing information provided by the DSP  26 . Essentially, the switch matrix  16  makes appropriate connection arrangements for forward and reverse link communications to “switch in” corresponding either the donor antenna or the service antenna on one hand, and the receiver sub-system or the transmitter sub-system on the other hand. For example, Table 1 illustrates the expected connections for the input port A for the receiver sub-system  18  and the output port B for the transmitter sub-system  20 . 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Switch port connection 
             
           
        
         
             
                 
               Forward link 
               Reverse link 
             
             
                 
                 
             
           
        
         
             
               Receiver input port A 
               Donor Antenna 
               Service Antenna 
             
             
               Transmitter output port B 
               Service Antenna 
               Donor Antenna 
             
             
                 
             
           
        
       
     
   
   Taking a forward link communication session as an example, when the enhancer powers up, the switch matrix  16  connects the donor antenna  12  to the receiver input port (e.g., port A) by default. It is understood that control mechanisms may be implemented to sweep only a carrier frequency band of the entire operating spectrum of the receiver subsystem at a time in order to “lock in” an incoming signal at its best receiving condition. One or more criteria can be set up to decide which carrier frequency band should be selected, and such criteria may include the considerations for the strength of the signal, the signal-to-noise ratio after demodulation by the demodulator sub-system  21 , and the traffic loading of the carrier frequency band. When such a carrier frequency band is determined, the donor antenna  12  is tuned to receive the incoming signal at this carrier frequency band. When the receiver sub system  18  receives the incoming signal from the donor antenna  12 , the signal goes through a first band pass filter  30  to eliminate other signals that are not in a desired frequency band. The survived signal is further amplified by a low-noise amplifier (LNA)  32  and down converted to an intermediate frequency (IF) through a mixer  34 , which provides a locally generated frequency such as LO 1  or LO 2 . The signal is then further filtered by a second filter  36  (e.g., another band pass filter), and further amplified to a desired level by a second amplifier  38  operating at the intermediate frequency (e.g., an adjustable gain amplifier (AGC 1 )) such that the signal level falls into an acceptable operation range of the demodulator  22  and the ADC  24 . It is further understood that the incoming signal is continuously monitored by base band module  26 , and if the quality of the received incoming signal is not satisfactory (e.g., the signal-to-noise ratio drops below a threshold value), the enhancer scans another carrier frequency band in order to use a new carrier frequency. 
   On the transmitter sub-system side, connecting from the output of the AGC 1 , the signal is first amplified through another adjustable gain amplifier  40  (e.g., AGC 2 ), and up-converted into a radio frequency through another mixer  42  using a locally generated frequency such as the local oscillator frequency LO 1  or LO 2 . Thereafter, the signal is further amplified through a power amplifier (PA)  44  and another band pass filter  46 , and eventually sent out to the predetermined terminal through the service antenna. As such, the radio signal from the BTS has been boosted through the enhancer  10 , and further sent to the terminal. The synthesizer module  28  provides all the local oscillator frequencies (IF, LO and LO 2 ) needed for the demodulation and signal conversions (e.g., up/down conversions). With the procedure similar to selecting the best receive carrier frequency between BTS and enhancer, the receiver sub-system  18  also continuously scans or sweeps a carrier frequency band of the operating spectrum thereof to find an “ideal” frequency band for transmitting outgoing signals. One consideration for determining such an ideal frequency band is the noise level of such a frequency band. Another consideration is to keep the separation between the carrier frequency band used by the receiver sub-system  18  and the carrier frequency band used by the transmitter sub-system  20  for transmission as far apart as possible. As such, the incoming and outgoing signals are isolated to the maximum, thereby reducing signal oscillation therebetween. 
   The demodulator sub-system  21  plays a role in determining switching timing information between the reverse link and forward link communication sessions. The demodulator  22  demodulates the IF signal from the output of the receiver sub-system into an analog base band signal, and the ADC  24  further converts the analogue base band signal into a digital signal. The base band module  26  performs a synchronization function, and determines the TDD switch timing information from the digital signal. A searching algorithm is employed in the DSP to search and obtain the TDD switch timing information. The search algorithm may vary depending on communication protocols used with the particular wireless system in which the enhancer is integrated therein. For example, if the protocol used has a dedicated synchronization channel, the starting timing of the TDD forward link can be determined by searching correlation peak with the dedicated synchronization channel. After the synchronization is achieved, the TDD switch timing information can be obtained by demodulating the information contained in the synchronization channel. For example, if the total TDD time frame is fixed, the synchronization channel can contain the information indicating the ratio between the forward and reverse links, from which the starting timing for the reverse link is then derived. 
   The dedicated synchronization channel can be a virtual channel that may be mapped into a variety of physical channels so long as the mapping mechanism is predefined in the protocol and known to the enhancer. For example, the synchronization channel can be a short period of data burst transmitted before every TDD frame, or one of the co-channels that is transmitted with other traffic channels. 
   In addition, the BTS carrier frequency can be obtained at the same time during the synchronization. This is done by sweeping the relevant frequency spectrum, and at each frequency point, the base band module searches the correlation peak. It is understood that a correlation peak exists only when the enhancer is tuned to the correct BTS carrier frequency. 
   With the TDD switch timing information on hand, the switch matrix is fully controlled wherein, during the forward link, the donor antenna is connected to the receiver input port (port A in  FIG. 1 ) and service antenna is connected to the transmitter output port (port B in FIG.  1 ). On the other hand, during the reverse link, the donor antenna is connected to the transmitter output port and the service antenna is connected to the receiver input port. 
   As shown in  FIG. 1 , two mixers/local oscillators (LOs), LO 1  and LO 2 , may be used in the enhancer. This also provides a frequency different from the BTS carrier frequency for the communication link between the enhancer and the terminal. 
   One benefit of using a different frequency is that the isolation between the enhancer&#39;s donor and service antennas can be further improved. For example, if the BTS carrier frequency is f 1 , one can use f 2  (wherein f 2  differs from f 1 ) for the link between the enhancer and terminals provided there is sufficient separation between f 1  and f 2 . 
   This concept of separating the frequency bands to isolate signals feeding into the donor and service antennas can be further improved by incorporating filters with the switch matrix  16 .  FIG. 2  is the switch matrix integrated with two band pass filters according to another example of the present disclosure. For example, a first band pass filter  50  can be implemented with the service antenna  14  so that signals on f 1  can pass while signals on f 2  are to be rejected. Similarly, a second band pass filter  52  can be added to screen the signals before they reach the donor antenna  12  so that f 2  signals will pass but f 1  signals will be blocked. Therefore, during a forward link communication, there are few f 2  signals feeding back into the donor antenna  12 , while on the reverse link, there are few f 1  signals feeding back into the service antenna  14 . 
   Another benefit of using different frequencies at the donor and service antenna is that, as mentioned above, the enhancer can scan the available operating spectrum and determine which frequency band corresponds to a minimum interference, and then use that particular frequency for the link between the enhancer and the terminals/BTSs to ensure signal quality and to reduce interference. 
   Referring back to  FIG. 1 , in order to select appropriate frequencies for the mixers  34  and  42 , and after f 2  is determined, LO 1  and LO 2  are given as follows in one example of the present disclosure:
 
 LO   1 = f   1 − IF;  
 
 LO   2 = f   2 − IF  
 
and the assignment of LO 1  and LO 2  to the mixer  34  and mixer  42  has to ensure that for either the forward link or reverse link communications, the two mixers are using different LOs. Table 2 below illustrates such a mutual exclusivity in assigning the LOs.
 
   
     
       
             
           
             
             
             
           
             
             
             
           
         
             
               TABLE 2 
             
           
           
             
                 
             
             
               LO1 and LO2 selection table 
             
           
        
         
             
                 
               Forward link 
               Reverse link 
             
             
                 
                 
             
           
        
         
             
               Mixer1 
               LO2 
               LO1 
             
             
               Mixer2 
               LO1 
               LO2 
             
             
                 
             
           
        
       
     
   
   Referring to  FIG. 3  where controlled amplifications are added in the switch matrix to reduce the coupling between antennas through the switch matrix itself. Low noise amplifiers  60  and  62  are added in the receiver paths from antennas to port A (switch  65 ), and power amplifiers  64  and  66  are added in the transmitter paths from port B (switch  68 ) to antennas. The gains of the amplifiers are controlled by the base band module through, for instance, their power down pins (PD). During the forward link period, LNA 1   60  and PA 2   64  will be activated while LNA 2   62  and PA 1   66  will be de-activated (powered down). So, any leakage from switch  68  will be further attenuated by the de-activated PA 1   66 , while any leakage from switch  70  will be further attenuated by the de-activated LNA 2   62 . Similarly, during the reverse link period, LNA 2   62  and PA 1   66  will be activated while LNA 1   60  and PA 2   64  will be de-activated (powered down). So, any leakage from switch  68  will be further attenuated by the de-activated PA 2   64 , while any leakage from switch  69  will be further attenuated by the de-activated LNA 1   60 . The improvement for the isolation of the switch matrix is equal to the gain difference between the active and de-active amplifiers. 
   Referring to  FIG. 4  where the LNA 1   60  and LNA 2   62  of  FIG. 3  are replaced by controlled switch  72  and switch  74 . During the forward link period, switch  72  will be on and PA 2   64  will be activated while switch  74  is off and PA 1   66  will be de-activated (powered down). So, any leakage from switch  68  will be further attenuated by the de-activated PA 1   66 , while any leakage from switch  70  will be further attenuated by the turned-off switch  74 . Similarly, during the reverse link period, switch  74  is turned on and PA 1   66  will be activated while switch  72  is turned off and PA 2   64  will be de-activated (powered down). Any leakage from switch  68  will be further attenuated by the de-activated PA 2   64 , while any leakage from switch  69  will be further attenuated by the turned-off switch  72 . The improvement for the isolation of the switch matrix is equal to the gain difference between active amplifier PA and turned-off switch. 
   Referring to  FIG. 5 , PA 1   64  and PA 2   66  in  FIG. 3  can be replaced with controlled switch  76  and switch  78 . The isolation of the switch matrix is then improved by the gain difference between the active amplifier LNA and the turned-off switch. 
   Referring to  FIG. 6 , another embodiment of  FIG. 3  is to replace all amplifiers with controlled switches. During the forward link period, switch  80  and switch  82  will be on while switch  84  and switch  86  will be off. During the reverse link period, switch  84  and switch  86  are turned on while switch  80  and switch  82  are turned off. The isolation of the switch matrix is thus improved by using the additional controlled switches. 
   Appropriate physical design and construction of the donor antenna and service antenna can also maximize antenna isolation, thereby improving the reception to both the BTS and terminals. 
   The local oscillator frequencies for mixer 1  and mixer 2  can be selected differently for forward and reverse links as indicated in Table 2.  FIG. 7  illustrates a mechanism for feeding appropriate locally generated frequencies to the mixers through a switch matrix  90  with controlled gain amplifiers. The switch matrix  90  has four switches  92 ,  94 ,  96  and  98 , and four amplifiers A 1  through A 4 . During the forward link, the switch matrix  90  is configured that LO 2  and connected to mixer 1   34  and LO 1  is connected to mixer 2   42 . The amplifiers A 2  and A 3  are activated while amplifiers A 1  and A 4  are de-activated (powered down). During the reverse link, the switch matrix is configured that LO 1  and connected to mixer 1   34  and LO 2  is connected to mixer 2   42 . The amplifiers A 1  and A 4  are activated while amplifiers A 2  and A 3  are de-activated (powered down). As such, the LO in the desired switch paths are amplified by the active amplifiers and the leakages in un-desired switch path are attenuated by the de-activated amplifiers. The isolation between LO 1  and LO 2  is improved by the same amount as the gain difference between active and de-active amplifiers. 
     FIG. 8  illustrates an enhancer  100  implemented with an improved modulator sub-system  102  according to another example of the present disclosure. This enhancer  100  is almost the same as the enhancer  10  ( FIG. 1 ) except for an expanded modulator sub-system  102 . The expanded modulator sub-system  102  is similar to the modulator sub-system  21  of  FIG. 1  except it has added several additional components to be integrated into the enhancer  100  for injecting information from the enhancer into the signal path and further sending same out to the BTs and terminals. The additional components of the expanded modulator subsystem  102  includes a modulator  104  and a switch  106  between the receiver and transmitter subsystems, and a digital-to-analog converter  108 . In summary, whenever the enhancer  100  needs to send information to the BTS or terminals, the switch  106  connects the modulator to the transmitter sub-system. As such, the information generated in the based band module  26  will be sent out from the modulator  104  to the transmitter sub-system. The information that the enhancer sends out can be any of the following: the forward or reverse signal quality indication, interference level, hardware status or alarm, power down or frequency change request, or acknowledge to messages that are sent from BTS or terminals to the enhancer. 
     FIG. 9  illustrates a design of the donor antenna and service antenna according to one example of the present disclosure. Assuming the enhancer  10  is hanging on a wall or post  110 , the donor antenna  12  is designed to be a patch antenna facing the BTS direction, while the service antenna  14  can be a dipole antenna lying on the same plane as the patch antenna. Both the patch and dipole antennas have a null point in their radiation patterns along the vertical direction so that such an arrangement as shown in  FIG. 3  will maximize their mutual isolation. 
   The above disclosure provides several different embodiments, or examples, for implementing different features of the disclosure. Also, specific examples of components, and processes are described to help clarify the disclosure. These are, of course, merely examples and are not intended to limit the disclosure from that described in the claims. 
   While the disclosure has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the disclosure.