BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to mobile communications, and more specifically to base stations used in mobile communications. 
         [0002]    Mobile communications are implemented by means of appropriate network architecture.  FIG. 1  shows a high level block diagram of an exemplary mobile network architecture. In  FIG. 1 , device  102  is a wireless mobile device that can communicate with first base station  104 . Usually, a multiplexing technology is used for such access, such as, for example, Code Division Multiple Access (CDMA), Time Division Multiplexing (TDMA), etc. The network includes the first base station  104 , a second base station  106 , and a third base station  108 . Each base station  104 ,  106 ,  108  has a transmission range that defines a cell  110 ,  112 ,  114 . Any given base station transmits and receives mobile calls via the cell&#39;s antenna. Thus, a wireless mobile device located within a given cell transmits and receives call information to/from the base station associated with that cell. 
         [0003]    Each base station  104 ,  106 ,  108  communicates with, and is controlled by, a mobile switching center (MSC)  116 . The MSC  116  switches calls between the cellular network and the public switched telephone network (PSTN) and vice versa. For example, consider landline telephone  120  connected to central office (CO)  124 . The CO  124  communicates with the MSC  116 . When a user of the landline telephone  120  calls mobile device  102 , the call is routed to the MSC  116  in a well known manner. A typical MSC is aware of the cell location of all mobile phones and directs the call to the first base station  104  because the mobile device  102  is located in the first cell  110 . 
         [0004]      FIG. 2  shows a more detailed block diagram of a traditional base station  200 . The base station  200  includes a plurality of radios, such as a first radio  204 , a second radio  208 , and a third radio  212 . Each radio  204 ,  208 ,  212  generates transmission signals having a particular frequency to be transmitted to a mobile device and also analyzes/processes signals received by the base station from the mobile device. The signal generated by each radio  204 ,  208 ,  212  is first sent to a respective power amplifier (PA)  220 ,  224 ,  228  for amplification before the signal is transmitted to a mobile device. An output signal (the amplified signal) of each PA  220 ,  224 ,  228  is transmitted to an Antenna Interface Frame (AIF)  232 . 
         [0005]    In more detail, an output signal (e.g., a first output signal  236 ) is transmitted from a PA (e.g., first PA  220 ) to a transmit combiner  240  of the AIF  232 . The transmit combiner  240  combines the output signals from the PAs  220 ,  224 ,  228  into a single output signal  244 . The single output signal  244  has a power that is the summation of the powers (i.e., the signal spectra) associated with the output signal of each PA  220 ,  224 ,  228 . The output signal  244  of the transmit combiner  240  is then provided as input to a central duplexer  248  of the AIF  232 . 
         [0006]    The central duplexer  248  is a device that isolates a transmit signal path  252  from a receive signal path  256  while permitting them to share a common antenna  260 . The duplexer  248  can combine communication signals onto a single cable for transmission by the antenna  260 . The duplexer  248  can also filter the signals before sending or receiving signals to/from the common antenna  260 . The central duplexer  248  is designed for operation in the frequency band used by the receiver  256  and the transmitter  252 , and is capable of handling the output power of the output signal  244  of the transmit combiner  240 . 
         [0007]    The receive path  256  of the central duplexer  248  passes a receiver signal  264  to a receive splitter  268 . The receive splitter  268  splits the receiver signal  264  into a plurality of radio signals (e.g., radio signal  272 ) that are each associated with a corresponding radio (e.g., radio  212 ). 
         [0008]    The design of a traditional base station, such as base station  200 , has several drawbacks. First, base stations (e.g., base station  200 ) typically have a complex and costly AIF that hosts many components including the central duplexer. When additional radios and PAs are added to a base station, additional transmit combiners and receive splitters often have to be added to the AIF. 
         [0009]    Second, the duplexer is a central element whose power capacity is designed to meet the maximum capacity (equal to the maximum number of radio frequency (RF) carriers (e.g., radios)) of a base station. To illustrate, suppose an operator of a mobile network has a need to handle three carriers. The operator purchases a base station that can handle the required three carriers from a seller of base stations. At a later point in time, the operator may determine that the operator needs to add a fourth carrier to the capacity of the base station. The operator then has to upgrade the base station by purchasing an additional radio and an additional PA. The central duplexer, however, is not replaced because the duplexer in the base station has to be able to handle the maximum number of carriers of the base station. Therefore, the AIF (and therefore the base station itself) typically has a high entry cost (i.e., with initial deployments, there are costs associated with the final (i.e., maximum capacity) configuration after capacity upgrades are made) because of the cost associated with the initially deployed central duplexer. Thus, a typical operator pays for a central duplexer that can handle the maximum capacity of the base station when the operator initially purchases the base station. This traditionally results in a high, up-front cost for the operator. 
         [0010]    Third, base stations also often have separate printed circuit boards (PCBs) (also referred to as Maintenance Replaceable Units, or MRUs) for the radio, PA, and AIF. Even if one or more of the radio(s) and PA(s) are integrated into a single PCB (i.e., MRU), the AIF is typically located with a separate PCB (i.e., MRU). Therefore, someone who maintains a base station may need to have all of the PCBs (MRUs) associated with the different components of the base station. Further, when an owner of a base station decides to upgrade the base station for more capacity or other enhanced features, the owner typically has to replace multiple MRUs. 
         [0011]    Therefore, there remains a need to solve many of the shortcomings associated with traditional base stations. 
       BRIEF SUMMARY OF THE INVENTION 
       [0012]    In accordance with an aspect of the present invention, a base station includes an antenna and a plurality of integrated transceiver modules. Each integrated transceiver module includes a radio and a duplexer that connects to the radio and the antenna for transmission of and reception of communication signals. Accordingly, in one aspect of the invention, there is no centralized duplexer and the function of the duplexer is thereby “decentralized”. The integrated transceiver module therefore modularizes the base station so that all of the components of a base station can be located on a single module (e.g., one printed circuit board (PCB) or Maintenance Replaceable Unit (MRU)). The base station can be upgraded by inserting additional integrated transceiver modules into the base station. 
         [0013]    In one embodiment, each integrated transceiver module also includes a power amplifier in communication with the radio and the duplexer and configured to amplify communication signals transmitted by the radio to the duplexer. 
         [0014]    Each integrated transceiver module may be connected to the antenna via a common star point. In one embodiment, the common star point is a solder joint. Each transceiver module may also include a left handed compensator in communication with the duplexer and configured to compensate for frequency dependency of a cable connecting the duplexer and the star point. 
         [0015]    In one embodiment, the radio, power amplifier, duplexer and/or left handed compensator are manufactured using microstrip technology. The duplexer may be configured to transmit and receive communication signals of a frequency channel associated with the radio. 
         [0016]    These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a block diagram of an exemplary network including base stations and a mobile switching center; 
           [0018]      FIG. 2  is a more detailed block diagram of an exemplary base station using a central duplexer; and 
           [0019]      FIG. 3  is a block diagram of a base station RF architecture using decentral duplexers in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In accordance with an aspect of the present invention, the central duplexer is “decentralized” by having a “decentral” duplexer for every RF carrier (e.g., every radio and power amplifier (PA)). 
         [0021]      FIG. 3  is a block diagram of a base station  300  having four separate modules  304 ,  308 ,  312 ,  314 . Each module  304 ,  308 ,  312  includes a respective radio  316 ,  320 ,  324 , a respective PA  328 ,  332 ,  336 , and a separate, respective decentral duplexer  340 ,  344 ,  348 . In one embodiment, each PA  328 ,  332 ,  336  is a variable PA (e.g., the frequency and/or the power amplification provided by the PA  328 ,  332 ,  336  can be varied). Although this configuration requires additional components (i.e., a duplexer for each module  304 ,  308 ,  312 ,  314 ), the configuration is actually more cost effective than the base station shown in  FIG. 2  because it avoids up-front payment for a larger duplexer and a less powerful (e.g., less power handling) duplexer is needed for each module  304 ,  308 ,  312 ,  314 . In particular, each duplexer  340 ,  344 ,  348  handles the power associated with a single RF carrier instead of the combined power associated with all of the RF carriers (e.g., as shown with output signal  244  of  FIG. 2 ). Thus, the duplexers  340 ,  344 ,  348  required for each module  304 ,  308 ,  312  have less stringent power handling requirements than the central duplexer  248  of the AIF  232  in the configuration of  FIG. 2 . Further savings may be realized by using filter structures that are less costly but limited in power handling in one or more of the duplexers  340 ,  344 ,  348  to filter the signal(s) transmitted (or received). It should be noted that the description also applies to the fourth module  314  but is not explicitly stated because the components of the module  314  are not shown. 
         [0022]    Assume that each carrier  316 ,  320 ,  324  transmit path provides 20 W of average power and each has a Crest factor (peak to average power ratio of Modulation) of 7 dB (=factor 5). Each duplexer  340 ,  344 ,  348  then has to handle 20 W average power and 100 W peak power (20 W×5). In comparison, the central duplexer  248  shown in  FIG. 2  with 4 RF carriers has to handle 80 W average power (4×20 W) and 1600 W peak power (100 W×4 signals×4 peaks in phase) due to constructive superposition of RF signals which may occur. Thus, there is a saving in peak power by a factor of 16 (1600/100) due to the decentralized approach of  FIG. 3 . A power saving by a factor 16 is equivalent to a voltage handling saving by a factor of 4 (i.e., the square root of 16). 
         [0023]    Central duplexers are typically manufactured using cavity resonator technology. A cavity resonator is a hollow chamber whose dimensions allow the resonant oscillation of electromagnetic (or acoustic) waves. To manufacture a cavity resonator, an alumina block is typically milcutted. 
         [0024]    In one embodiment, each decentralized duplexer  340 ,  344 ,  348 , however, is instead manufactured using metamaterial filter technology. Metamaterial structures can be built using microstrip technology. Microstrip technology is typically much cheaper than milcutting an alumina (or other metal) block. Furthermore, microstrip technology is typically also used to manufacture the radio and the power amplifier. Thus, by using the decentral duplexer design, the manufacturing technology for the duplexers  340 ,  344 ,  348  becomes compatible with the manufacturing technology of the radio and the power amplifier. Further, as the efficiency of power amplifiers improves (e.g. by using switch-mode power amplifiers), the heat dissipation of power amplifiers may be reduced. As a result, in one embodiment the radio, PA and the decentral duplexer are combined on a common PCB, thereby forming a “single board”, fully integrated transceiver (fiTRX) module (shown as module  304 ,  308 ,  312 ). The construction of such a transceiver may be automated via one or more machine placing SMDs (Surface Mount Devices) on a PCB. 
         [0025]    In one embodiment, the power saving described above may reduce problems associated with the tuning of metamaterial duplexers (e.g., limited power handling capability). Specifically, tuning elements like varactors and RF switches inside metamaterial structures that are used to tune and reconfigure the structures often have to handle large voltages and larger currents if the duplexer has to handle large power RF signals. Tuning elements are typically limited in terms of current and voltage handling. Handling large currents and voltages with coaxial resonators may come at a cost of large form factors. 
         [0026]    The combination of multiple RF carriers in each module  304 ,  308 ,  312 ,  314  is implemented using filter combining technology on the transmit side (TX) and filter splitting technology on the receive side. Filter combining/splitting is implemented when the decentral duplexer passes the active transmit/receive channel (e.g., 5 MHz with the Universal Mobile Telecommunications System (UMTS) network) rather than the full band (e.g. 60 MHz in the IMT2000 band). Thus, unlike the central duplexer  248  of  FIG. 2 , which receives the entire frequency band that is going to be transmitted (via combined output signal  244  associated with radios  204 ,  208 ,  212 ) and that is received (via the antenna  260 ), each decentral duplexer only transmits and receives the active transmit/receive frequency channel associated with its radio and not the entire frequency band (e.g., associated with radios  316 ,  320 ,  324 ). Furthermore, there is no longer a need for a transmit combiner or a receive splitter (or an AIF) when using decentral duplexers. 
         [0027]    In one embodiment, filter combining and/or filter splitting (by each decentral duplexer) is achieved because the metamaterial filter structures have an impedance near infinity if the filter operates outside its passband. 
         [0028]    The decentral duplexers  340 ,  344 ,  348  of the base station  300  connect to a common star point  352 . The star point  352  connects with an antenna  356 . 
         [0029]    In one embodiment, each decentral duplexer  340 ,  344 ,  348  can be tuned over a wide frequency range (e.g. more than an octave). This may result in the base station  300  being a multiband base station. In another embodiment, the decentral duplexers  340 ,  344 ,  348  are each tuned to different frequencies and still connect to star point  352 . 
         [0030]    In one embodiment, a coaxial cable connects the decentral duplexers residing inside the fiTRX with the star point  352 . An impedance of infinity (before the coaxial cable connects the decentral duplexer to the antenna) may be transformed into non-infinity impedance (when the coaxial cable is connected) (by line transformation effects), which then violates the concept of the common star point. Specifically, at the star point  352 , at one channel one coax cable provides nominal impedance (e.g., 50 Ohms) and other cables then provide infinity. This is needed to have one 50 Ohm path for each channel. As power has to flow only one way, if other cables also provided 50 Ohms, the power from one transmitter can get backwards into another transmitter at one channel. Thus, power from one transmitter goes completely into the antenna and not backwards into the other transceivers. It is therefore beneficial to compensate the regular “right handed” behavior of classical coax cables with a “left handed” (LH) compensator. In particular, each duplexer  340 ,  344 ,  348  is in communication with a respective LH compensator  360 ,  364 ,  368 . The LH compensator  360 ,  364 ,  368  compensates for the frequency dependency of the cable (e.g., cable  372 ) from the decentral duplexer (e.g., duplexer  348 ) to the star point  352 . 
         [0031]    The LH compensator may only affect the phase of an RF signal and not its amplitude. The combination of a right handed coax cable and a left handed compensator results in transparency for multiple frequency bands. This combination can maintain an out of band impedance of infinity between the decentral duplexer  340 ,  344 ,  348  and the star point  352 . As the compensation by the LH compensator works multiple bands, fiTRXs at different frequency bands can be connected to the common star point  352 , allowing for the creation of a multiband base station  300 . The LH compensator may have applications with a multicarrier base station router (BSR). 
         [0032]    In one embodiment, the LH compensator  360 ,  364 ,  368  is located next to the corresponding decentral duplexer  340 ,  344 ,  348  inside the fiTRX and is manufactured using the same technology as is used for the decentral duplexer. In one embodiment, the star point  352  is a common solder joint connected to multiple RF cables. In another embodiment, the fiTRX  304 ,  308 ,  312  may be connected directly with the antenna  356 . 
         [0033]    Another advantage of the invention involves easier maintenance. For example, when an individual (e.g., a technician or engineer) has to perform maintenance on the traditional base station (e.g., the base station  200  shown in  FIG. 2 ), the individual has to travel with several maintenance replaceable units (MRUs), such as a replacement AIF, replacement PAs, and replacement radio cards. Even if the radio cards and the PAs are integrated in a single PCB, the individual still has to travel with a PCB of the radio cards and the PAs as well as one or more AlFs. With base station  300 , however, the number of MRUs that an individual has to travel with to repair or upgrade the base station  300  may be reduced relative to base station  200  (which typically translates into a cost savings). In particular, if each radio, PA, and duplexer are integrated onto a single PCB, then the PCB may be the only MRU needed. 
         [0034]    The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments shown and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention.
Disclosed is a base station comprising an antenna and a plurality of integrated transceiver modules. Each integrated transceiver module includes a radio and a decentral duplexer connected to the radio and the antenna for transmission of and reception of communication signals. The integrated transceiver module therefore modularizes the base station so that all of the components of a base station can be located on a single module (e.g., one printed circuit board (PCB)). The base station can be upgraded by inserting additional integrated transceiver modules into the base station.