Abstract:
A method for wireless communication, including positioning a first plurality of slave transceivers within a region and positioning a second plurality of slave transceivers within the region in positions spatially separated from the positions of the first plurality of slave transceivers. The method further includes receiving at the first plurality and at the second plurality of slave transceivers a reverse radio frequency (RF) signal generated by a mobile transceiver within the region and generating respective first and second slave signals responsive thereto. The method also includes conveying the first and second slave signals separately to a base transceiver station (BTS) external to the region, and processing the first and second slave signals conveyed to the BTS so as to recover information contained in the reverse RF signal generated within the region.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. application Ser. No. 09/596,955, filed on Jun. 16, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to communication networks, and specifically to cellular communication networks operating in enclosed spaces, which are cut off from cellular signals originating external to such spaces.  
         BACKGROUND OF THE INVENTION  
         [0003]    In cellular communications systems there are typically regions where the coverage is difficult or incomplete, for example, within metal-framed structures, or underground. Methods for improving the coverage in regions such as these are known in the art.  
           [0004]    In one system known in the art, a repeater is used between a base station transceiver subsystem (BTS) which is able to receive signals in a closed environment, such as a tunnel closed off to transmissions from the BTS. The system down-converts a high radio-frequency (RF) signal from the BTS to an intermediate frequency (IF) signal. The IF signal is then radiated by a cable and an antenna in the closed environment to a receiver that is also located in the closed environment. The receiver up-converts the IF signal to the original RF frequency. Such systems may be used with vehicles moving through a tunnel to enable passengers in the vehicle who would otherwise be cut off from the BTS to receive signals.  
           [0005]    In accordance with another system known in the art, a plurality of repeater systems are used between a plurality of BTSs. The systems are used in association with an environment that is closed off to transmissions from the BTSs. Each repeater system down-converts an RF signal from a respective BTS to an IF signal. The IF signal is then transferred by a cable in the closed environment to one or more respective receivers in the closed environment. Each receiver up-converts the IF signal to the original RF frequency. Such systems are used with vehicles moving between overlapping regions in a tunnel, each region covered by one of the BTSs via its repeater system. Thus, passengers in the vehicle who would otherwise be cut off from one or more of the BTSs are able to receive signals from at least one of the BTSs throughout the tunnel.  
           [0006]    In yet another system known in the art, a distributed antenna array is used within a region where reception is difficult. The performance of the antenna array is enhanced by generating signal diversity within the array. Each antenna in the array has a differential time delay applied to signals that it receives, thus generating received signal diversity. The differentially-delayed signals are preferably down-converted to an intermediate frequency and are then transferred out of the region via a cable.  
           [0007]    Another system known in the art uses a wireless repeater comprising first and second spatially-separated antennas. Both antennas receive a signal from a transmitter, and the signal received by the second antenna has a time delay added to the original signal. The two signals are summed to form one aggregate signal, which is transmitted from a third antenna. A receiver of the aggregate signal is able to reconstruct the signals received by the first and second antennas.  
           [0008]    Notwithstanding the above systems for providing coverage in areas where reception is difficult, problems of coverage in such areas continue to exist. The problems are exacerbated by the fact that even when signals in the areas can be detected, the signal quality is in many cases marginal. In other cases, signal levels of a transmission in an area of difficult coverage may vary strongly from moment to moment, so that while at initiation of the transmission the level may be more than adequate, during the course of transmission the level may become less than adequate. There is thus a need for an improved method for detection of signals in difficult reception areas. There is also a continuing need, as demands on cellular networks increase, to increase the capacity of a network without significant increase in the bandwidth requirements of the network.  
         SUMMARY OF THE INVENTION  
         [0009]    It is one aspect of the disclosed method and apparatus to provide improved signal/noise ratio in a cellular transmission network. It is a further aspect of the disclosed method and apparatus to improve the capacity of a network. It will be recognized by those skilled in the art that there are many other aspects of the disclosed method and apparatus which are not made explicit at this time.  
           [0010]    In preferred embodiments of the present invention, a group of stationary cellular transceivers, herein termed slave units, are distributed within a region that cannot be conveniently served by a base station transceiver subsystem (BTS). The slave units act as first repeaters for signals from the BTS. Typically, the region is an interior of a building, or an open region where reception of signals from the BTS is poor due to distance from the station or radiation shadowing by a structure between the BTS and the region. The slave units communicate via radiated signals (such as radio frequency (RF) signals) with a mobile transceiver (such as a mobile cellular telephone) in the region. The group of slave units is divided into a first and a second sub-group, having generally equal numbers of stationary transceivers in each sub-group.  
           [0011]    The slave units of the first sub-group are separated spatially from the slave units of the second sub-group. The spatial separation is most preferably at least enough so that a signal received by the first sub-group and a signal received by the second sub-group, from one transmission of the mobile transceiver, are distinguishable. The signals are typically distinguishable in terms of amplitude, or phase, or time of arrival, or a combination of these or other signal parameters. Thus, the slave units of one of the sub-groups can function as diversity receivers with respect to the slave units of the other subgroup, which function as main receivers.  
           [0012]    RF signals received by each sub-group of slave units from the mobile transceiver, referred to herein as reverse signals, are down-converted to intermediate frequency (IF) signals. The IF signals are then transferred from the region to a master unit, which acts as a second repeater, by one or more cables. IF signals from the main sub-group of slave units are transferred to a main-master sub-unit of the master unit. This main-master sub-unit up-converts the IF signals to main-reverse RF signals. Similarly, IF signals from the diversity sub-group of slave units are transferred to a diversity-master sub-unit, comprised in the master unit. The diversity-master sub-unit up-converts the IF signals to diversity-reverse RF signals. The main-reverse and diversity-reverse RF signals are transmitted by cable and/or over the air separately to the BTS. The BTS demodulates, recovers, and analyzes the information contained in the separate reverse RF signals. Maintaining the recovered RF signals as separate main-reverse and diversity-reverse signals gives an improvement in signal/noise ratio of up to 3 dB and improves reverse carrying capacity, compared to systems which combine the two types of signal before analysis in the BTS.  
           [0013]    In some preferred embodiments of the present invention, forward RF signals from the BTS are received by the main-master sub-unit, and are down-converted therein to IF signals. The IF signals are transferred to the first and second sub-groups of slave units, and a delay is added to the IF signal transferred to one of the sub-groups. The IF signals are up-converted to forward RF signals in the slave units, and the RF signals, comprising delayed and non-delayed forward RF signals, are radiated from the units. The mobile transceiver receives both signals. Because of the time delay introduced into one of the signals, the mobile transceiver receives both signals as a composite signal comprising information contained in the first signal and in the second delayed signal. Most preferably, the information is demodulated and recovered in the mobile transceiver. This information is then used to regenerate an optimal representation of information conveyed in the original forward RF signals.  
           [0014]    There is therefore provided, according to a preferred embodiment of the present invention, a method for wireless communication, including:  
           [0015]    positioning a first plurality of slave transceivers within a region;  
           [0016]    positioning a second plurality of slave transceivers within the region in positions spatially separated from the positions of the first plurality of slave transceivers;  
           [0017]    receiving at the first plurality and at the second plurality of slave transceivers a reverse radio frequency (RF) signal generated by a mobile transceiver within the region and generating respective first and second slave signals responsive thereto;  
           [0018]    conveying the first and second slave signals separately to a base station transceiver subsystem (BTS) external to the region; and  
           [0019]    processing the first and second slave signals conveyed to the BTS so as to recover information contained in the reverse RF signal generated within the region.  
           [0020]    Preferably, the region is generally unable to receive signals transmitted over the air from the BTS.  
           [0021]    Preferably, conveying the first and second slave signals separately to the BTS includes orthogonally polarizing the signals.  
           [0022]    Preferably, receiving at the first plurality and at the second plurality of slave transceivers the reverse RF signal generated by the mobile transceiver and generating respective first and second slave signals includes down-converting the reverse RF signal so as to generate respective first and second intermediate frequency (IF) signals, and conveying the first and second slave signals separately to the BTS includes up-converting the respective IF signals in a master unit to recover the first and second slave signals.  
           [0023]    Preferably, the method includes:  
           [0024]    conveying a forward RF signal from the BTS to a master unit;  
           [0025]    down-converting the forward RF signal to a forward IF signal;  
           [0026]    splitting the forward IF signal into a first and a second IF signal;  
           [0027]    delaying the second IF signal;  
           [0028]    conveying the first and delayed second IF signals to the first and second plurality of slave transceivers respectively;  
           [0029]    processing the first and delayed second IF signals to recover the forward RF signal and a delayed forward RF signal respectively; and  
           [0030]    transmitting the forward RF signal and the delayed forward RF signal to the mobile transceiver.  
           [0031]    There is further provided, according to a preferred embodiment of the present invention, apparatus for wireless communication, including:  
           [0032]    a first plurality of slave transceivers and a second plurality of slave transceivers, which first and second pluralities are spatially separated from one another within a region, and which first and second pluralities of slave transceivers are adapted to receive a radio frequency (RF) signal generated by a mobile transceiver within the region and to generate respective first and second slave signals responsive to the RF signal;  
           [0033]    a first master unit, which receives and processes the first slave signal from the first plurality of slave transceivers and conveys the processed first signal to a base station transceiver subsystem (BTS); and  
           [0034]    a second master unit, which receives and processes the second slave signal from the second plurality of slave transceivers and conveys the processed second signal to the BTS separately from the processed first signal, such that information contained in the RF signal is recovered by processing the first and second processed signals received by the BTS.  
           [0035]    Preferably, the region is generally unable to receive signals transmitted over the air from the BTS.  
           [0036]    Preferably the apparatus includes a polarizing antenna coupled to the first and second master units, which antenna conveys the processed first signal and the processed second signal separately to the BTS as orthogonally polarized signals.  
           [0037]    Preferably, the first and second plurality of transceivers include respective first and second down-converters which generate the first and second slave signals as respective first and second intermediate frequency (IF) signals, and the first master unit includes a first up-converter which recovers the processed first signal from the first IF signal, and the second master unit includes a second up-converter which recovers the processed second signal from the second IF signal.  
           [0038]    Preferably, the first master unit includes:  
           [0039]    a down-converter which converts a forward RF signal received from the BTS to a forward IF signal; and  
           [0040]    a splitter which splits the forward IF signal into a first and a second forward IF signal,  
           [0041]    and the second master unit includes a delay unit which delays the second forward IF signal,  
           [0042]    and the first plurality of slave transceivers includes respective pluralities of up-converters which recover the forward RF signal from the first forward IF signal and which transmit the forward RF signal to the mobile transceiver, and  
           [0043]    the second plurality of slave transceivers includes respective pluralities of up-converters which recover a delayed forward RF signal from the delayed second forward IF signal and which transmit the delayed forward RF signal to the mobile transceiver.  
           [0044]    The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings, in which: 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0045]    [0045]FIG. 1 is a schematic block diagram showing an area coverage system, according to one embodiment of the present invention;  
         [0046]    [0046]FIG. 2 is a schematic block diagram of a slave transceiver comprised in the area coverage system of FIG. 1, according to one embodiment of the disclosed method and apparatus; and  
         [0047]    [0047]FIG. 3 is a schematic block diagram showing apparatus for conveying signals between a base station transceiver subsystem and a master unit comprised in the system of FIG. 1, according to one embodiment of the present invention 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0048]    Reference is now made to FIG. 1, which is a schematic block diagram showing an area coverage system  10 , according to one embodiment of the present invention. A building  14  is substantially closed off to electromagnetic radiation from a base station transceiver subsystem (BTS)  42  external to the building. A mobile transceiver  16  within the building, such as an industry-standard mobile telephone, emits a radio frequency (RF) signal, herein termed a reverse-RF signal, receivable by BTS  42 . In accordance with one embodiment, the RF signal emitted by mobile transceiver  16 , herein also termed the reverse-RF transmitted signal, is a code division multiple access (CDMA) signal operating at an industry-standard chip rate, although the principles of the present invention are also applicable to other coding and transmission schemes.  
         [0049]    A first sub-group of slave transceivers  12 , herein also termed main slave transceivers, and a second sub-group of slave transceivers  11 , herein also termed diversity slave transceivers, are positioned within building  14 . Main slave transceivers  12  are most preferably connected in a star configuration, by one or more passive or active splitter/combiners  20 . Alternatively, slave transceivers  12  are connected in a daisy chain or a hybrid star-daisy chain configuration. Similarly, diversity slave transceivers  11  are most preferably connected in a star configuration, by one or more passive or active splitter/combiners  18 . Alternatively, slave transceivers  11  are connected in a daisy chain or a hybrid star-daisy chain configuration. Slave transceivers  11  and  12  are coupled to their respective splitter/combiners by cables  21 .  
         [0050]    Slave transceivers  11  are separated spatially from slave transceivers  12 , but otherwise the slave transceivers are all substantially similar in construction and operation. The following is a description of the operation and construction of suitable slave transceivers as given in a U.S. patent application Ser. No. 09/430,616, entitled “In-Building Radio Frequency Coverage,” filed Oct. 29, 1999, which is assigned to the assignee of the present application and whose disclosure is incorporated herein by reference.  
         [0051]    [0051]FIG. 2 is a schematic block diagram of one of the slave transceivers  11 ,  12  (either a diversity slave transceiver  11  or a main slave transceiver  12 ) according to one embodiment of the disclosed method and apparatus. Each slave transceiver  11 ,  12  comprises a bias-T filter  92 , which receives an intermediate frequency forward (IF-FWD) signal and a local oscillator reference signal (LO-REF) from master unit  44  via cables  21 . Properties of the IF-FWD and LO-REF signals are described hereinbelow. Filter  92  also receives a DC and/or an AC power signal such as a 60 Hz rectangular or sinusoidal wave from master unit  44  via cables  21 . Most preferably, filter  92  is arranged so that coupling or decoupling one of slave transceivers  11 ,  12  from cables  21  does not significantly affect operation of the other slave units.  
         [0052]    Filter  92  acts as a port, splitting off the power signal to power each slave transceiver  11 ,  12  either directly or via an optional power supply  96 , and transferring the IF-FWD and LO-REF signals received from master unit  44  to a triplexer  100 . Triplexer  100  filters and separates the IF-FWD signal and the LO-REF signal, so that the IF-FWD signal follows a forward path  91  and the LO-REF signal follows a path  93 . Preferably, path  93  comprises a pre-amplifier  118  which transfers the LO-REF signal via a narrow-band crystal filter  122  to a phase locked loop (PLL) oscillator  124 . Oscillator  124  generates a reconstituted local oscillator signal in each slave transceiver  11 ,  12  by multiplying LO-REF by an integer. This reconstituted local oscillator signal has a frequency identical to that of a local oscillator signal originally synthesized by local oscillator  36  of master unit  44 . The reconstituted local oscillator signal is input to a splitter  126 , and from the splitter the signal is input to a mixer  104  and a mixer  140 . The power level of the LO signal input to the splitter is preferably set as required to drive mixers  104  and  140 . Alternatively, a PLL oscillator  124 A and a PLL oscillator  124 B are placed in path  93  after splitter  126 , instead of oscillator  124  before the splitter. Oscillators  124 A and  124 B operate substantially as oscillator  124 .  
         [0053]    Path  91  comprises a preamplifier  102 , which receives frequencies centered on IF-FWD from triplexer  100 . The IF-FWD signal is then amplified before it is input to a variable delay  103 . Delay  103  preferably comprises a surface acoustic wave (SAW) delay device. The SAW delay device delays signals in path  91  by a time of the order of 500 ns. Most preferably, the time delay is set to be at least half a chip rate of CDMA signals received by the master unit  44 . The time delay provided by delay  103  is preferably set on installation of each slave transceiver  11 ,  12 , or alternatively the time delay is set by a remote control modem  98 , whose function is described in more detail below.  
         [0054]    The signal from delay  103  is coupled to the input of mixer  104 . Mixer  104  up-converts the IF-FWD signal received, using the reconstituted local oscillator signal, to regenerate a master RF signal received by master unit  44 . The regenerated RF signal is amplified in an RF amplifier  106  and filtered in a band-pass filter  108 . The amplifier and filter together provide an RF signal at a level suitable for coupling to the input of a variable-gain amplifier  110  and an RF power amplifier  112 . Power amplifier  112  generates an RF power output signal corresponding to the original master signal received by master unit  44 , which power signal is transferred via an isolator  114  to increase the voltage standing wave ratio. The power signal is input to an RF duplexer  116  which acts as a port. Duplexer  116  routes the power signal to a four-way splitter  144 , to which up to four slave antennas  23  are coupled and which radiate the RF power signal.  
         [0055]    Antennas  23  also receive a slave RF signal from mobile transceiver  16 . The slave signal is routed via RF duplexer  116  along a reverse path  95  to a low noise pre-amplifier  142 . The pre-amplifier is most preferably constructed from very-low-noise components by methods known in the art. A mixer  140  uses the reconstituted local oscillator signal received from splitter  126  and the output signal of pre-amplifier  142  to down-convert the slave RF signal to an intermediate frequency signal IF-REV. The IF-REV signal is amplified by an amplifier  138  feeding a band-pass filter  136 . The filter  136  and amplifier  138  together operate to generate an IF-REV signal substantially free from unwanted sidebands, such as those produced in mixer  140 .  
         [0056]    The IF-REV signal output of filter  136  is preferably output to a variable delay  137 . Delay  137  preferably comprises a SAW device that delays signals in path  95  by a time of the order of 2 ms. The time delay provided by SAW device  137  is preferably set on installation of each slave transceiver  11 ,  12 . Alternatively, the time delay is set by remote control modem  98 . The signal from delay  137  is routed through an amplifier  134 , a variable-gain amplifier  130 , and a power amplifier  128  to triplexer  100 .  
         [0057]    Alternatively, delay  137  is not present in the slave transceivers  11 ,  12 , and the IF-REV signal output of filter  136  is routed directly to amplifier  134 . The output of amplifier  128  is sampled by an automatic gain control (AGC) circuit. The output is used to adjust the gain of variable-gain amplifier  130 , so that the level of the amplified IF-REV signal is maintained at a level consistent with a link budget. Triplexer  100  routes the output of amplifier  128  via filter  92  to the master unit  44 .  
         [0058]    Preferably, the remote control modem  98  is able to receive and decode control signals originating from the master unit  44 . Most preferably, the control signals are utilized to set and/or read parameters of elements within slave transceiver  11 ,  12 , such as the gains of amplifiers  110  and  130  and the delay time of delay  103 , and/or levels of signals within the slave unit. Preferably, the control signals are transmitted as modulated signals on a base frequency within a range of approximately 280 MHz to approximately 500 MHz, although any other base frequency which is receivable by modem  98  and which does not interfere with the operation of slave transceivers  11 ,  12  and master unit  44  may be used. Preferably, parameters affecting the operation of each slave transceiver  11 ,  12 , such as gains of amplifiers  110  and  130 , are preset when each slave transceiver  11 ,  12  is set up, so that each slave transceiver  11 ,  12  is able to operate independently. Most preferably, the overall signal gain, from port to port, for path  91  and for path  95  is set to be of the order of 10-60 dB for each path.  
         [0059]    Returning to FIG. 1, the spatial separation between slave transceivers  11  and slave transceivers  12  is sufficient so that when transceiver  16  makes a transmission, the reverse-RF signal received by the sub-group of slave transceivers  11  is distinguishable from the reverse-RF signal received by the sub-group of slave transceivers  12 . For example, the received signals may differ in amplitude, or in phase, or in time of arrival, or in a combination of these or other signal parameters. Thus, main slave transceivers  12  receive the RF signal from mobile transceiver  16  as a main-reverse RF signal, and diversity slave transceivers  11  receive the RF signal from transceiver  16  as a diversity-reverse RF signal.  
         [0060]    As described above, slave transceivers  11  and  12  operate by mixing the received reverse-RF signal with a local oscillator signal, thus down-converting the received RF signal to an intermediate frequency (IF) signal, as is known in the art. The IF signals from main slave transceivers  12  are transmitted as main-IF signals from building  14 , via splitter/combiner  20  and a cable  46 , to a main-master sub-unit  24  comprised in a master unit  44 . It should be noted that the coupling of the main-master sub-unit  24  to the main slave transceivers  12  may be accomplished in any manner that distributes the signals from the main-master sub-unit  24  to the main slave transceivers  12  and provides the signals from the main slave transceivers  12  to the main-master sub-unit  24 . Likewise, any such coupling may be provided between the diversity slave transceivers  11  and a diversity-master sub-unit  22 .  
         [0061]    Main-master sub-unit  24  comprises an IF-duplexer  32 , which transfers the main-IF signals to an up-converter  34  in the main-master sub-unit. In up-converter  34  the main-IF signals are mixed with a local oscillator (LO) signal, generated by a local oscillator  36  most preferably comprised in main-master sub-unit  24 , in order to recover the main-reverse RF signal received by main slave transceivers  12 . The recovered main-reverse RF signal is then transmitted to BTS  42 , preferably via a cable connection  48 . Alternatively, the recovered main-reverse RF signal is transmitted to BTS  42  via a wireless connection. Methods for down-conversion and up-conversion of a transmitted RF signal as described hereinabove are known in the art, and a detailed description of one such method is also given in the above-mentioned U.S. Patent Application. It will be appreciated that slave transceivers  11  and  12  and master unit  44  act respectively as first repeaters coupled to a second repeater, for the purpose of transferring signals to the BTS from the building.  
         [0062]    The IF signals from diversity slave transceivers  11  are transmitted as diversity-IF signals from building  14 , via splitter/combiner  18  and a cable  49 , to diversity-master sub-unit  22  comprised in master unit  44 . Diversity-master subunit  22  comprises an IF-duplexer  26 , which transfers the diversity-IF signals to an up-converter  30  comprised in the diversity-master sub-unit. In up-converter  30  the diversity-IF signals are most preferably mixed with the local oscillator signal generated by LO  36 , in order to recover the diversity-reverse RF signal received by diversity slave transceivers  11 . The recovered diversity-reverse RF signal is then transmitted to BTS  42 , preferably via a cable connection  52 . Alternatively, the recovered diversity-reverse RF signal is transmitted to BTS  42  via a wireless connection. It will be appreciated that the diversity-reverse RF signal is transmitted separately from the main-reverse RF signal to BTS  42 , so that no degradation of signal/noise occurs by combining the two reverse RF signals, and so that reverse carrying capacity of the network is improved.  
         [0063]    Main-master sub-unit  24  also comprises a down-converter  38 , which receives a forward-RF signal from BTS  42 . Preferably the forward-RF signal is transferred from BTS  42  to down-converter  38  by a cable connection  50 . Alternatively, the forward-RF signal is transferred from the BTS to the down-converter  38  by a wireless connection. Down-converter  38  most preferably utilizes the LO signal from LO  36  to produce the IF-FWD signal. The IF-FWD signal is transferred to a splitter  40 , which splitter divides the IF-FWD signal into a first and a second substantially similar IF-FWD signal. The first IF-FWD signal is transferred via duplexer  32  and splitter/combiner  20  to transceivers  12 , wherein the BTS forward-RF signal is recovered by up-conversion.  
         [0064]    The second IF-FWD signal is transferred via a cable  41  to duplexer  26 . In the course of cable  41  there is a delay unit  28 , most preferably formed from a surface acoustic wave filter acting as a delay generator. Alternatively, delay unit  28  may comprise any standard delay unit which is able to add a time delay to the forward-IF signals transmitted from splitter  28 . Most preferably, the delay added by delay unit  28  is of the order of at least twice the chip period of the modulated RF signal transmitted by transceiver  16 . The delayed IF-FWD signal is transferred via duplexer  26  and splitter/combiner  18  to diversity slave transceivers  11 , wherein a delayed forward-RF signal is recovered by up-conversion.  
         [0065]    Mobile transceiver  16  receives both the recovered forward-RF signal transmitted from transceivers  12  and the recovered delayed forward-RF signal transmitted from transceivers  11 . The forward-RF signal and the delayed forward-RF signal are then utilized to derive an optimal forward-RF signal transmitted from BTS  42 , using methods known in the art. For example, if the RF signal is a CDMA pilot RF signal, generated by the BTS for tracking mobile transceivers, mobile transceiver  16  is able to demodulate and recover the pilot signals by identifying strong multipath arrivals with a searcher comprised in the transceiver. Alternatively, optimal signals can be recovered by non-CDMA systems which are able to tolerate delays of the size described hereinabove, and/or which can implement appropriate delays. For example, a GSM system requires a delay of the order of 8 μs.  
         [0066]    [0066]FIG. 3 is a schematic block diagram showing apparatus for conveying signals between BTS  42  and master unit  44 , according to one embodiment of the present invention. A duplexer  154  is connected to cable connections  48  and  50 , so that the forward-RF signal and the main-reverse RF signal are multiplexed. The multiplexed RF signal is coupled to a first polarizing port of a polarizing antenna  156 . A second polarizing port, orthogonal to the first port, is coupled to the diversity-reverse RF signal. Thus, antenna  156  is able to transfer the multiplexed and diversity-reverse RF signals as substantially separate signals. A polarizing antenna  160 , generally similar in operation to antenna  56 , is coupled to BTS  42 , so that the BTS is able to transmit forward-RF signals to master unit  44 , and is able to receive separate main-reverse and diversity-reverse RF signals.  
         [0067]    It will be appreciated that the scope of the present invention includes regions other than buildings closed off to electromagnetic radiation. Such regions comprise areas which are out of range of a base station transceiver subsystem due to distance from the station, or areas which are in a radiation shadow due to, for example, topography of the area, or because of a structure such as building intervening between the area and the station.  
         [0068]    It will thus be appreciated that the preferred embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.