Abstract:
A modular high power, low passive intermodulation, active, universal, distributed antenna system interface tray that includes one or more front-end RF frequency duplexers instead of a high power, low passive intermodulation attenuator to achieve superior FIM performance. A cable switch matrix allows for the use of the system among varying power levels and accomplishes the above in a modular architecture.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to distributed antenna systems in telecommunications networks. 
         [0003]    2. Description of the Prior Art 
         [0004]    The modular design of a high power, low Passive InterModulation (PIM), base station management interface for Distributed Antenna System (DAS) applications in telecommunications networks is designed for use in the telecommunication industry. A typical deployment of a Base Telecommunication Station (BTS) in the telecommunication industry is designed for high Radio Frequency (RF) power input signals. The high RF power signal provides the necessary RF power to provide both coverage and capacity in a telecommunications network and is often associated with a macro-network solution that supports high RF power antennas. In a DAS deployment, however, the goal of the network solution is to add coverage and capacity to an area where the antenna RF signal is weak or cannot be accessed, for example inside a tunnel, a stadium or an airport; that is, either in a building or outdoor. Also, DAS deployments are typically used in areas where the antennas are in close proximity to the public (UE). As a result, the RF power of the antenna must be kept low to meet minimum radiated emissions standards determined by the Federal Communications Commission (FCC). Therefore, DAS deployments utilize a low RF power signal that is used in conjunction with low RF power antennas. The RF signal is also required to have very low levels of PIM. PIM levels that are too high can cause interference in the low RF power signals in the antenna receive (Rx) path, resulting in a multitude of issues inside telecommunication networks. To this end it becomes necessary to have an interface between the BTS and the DAS that can adjust the signal input RF power level from the BTS to signal output RF power levels that are harmonious with the requirements of a DAS while inducing very low PIM levels into the attenuated RF signal. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention satisfies the requirement of providing an interface between the BTS and the DAS that can adjust the signal input RF power level from the BTS to signal output RF power levels that are harmonious with the requirements of a DAS while inducing very low PIM levels into the attenuated RF signal. This is done in a modular format that can be applied over varying signal RF frequency inputs and signal RF power levels with very low PIM. The invention provides active DAS tray monitors and regulates user defined BTS input power to the desired threshold level. This invention saves significant space compared to “passive” DAS trays. 
         [0006]    The present invention is a modular design of a high power, low PIM-BTS management interface for DAS applications in telecommunications networks. The invention includes RF duplexed modules that attenuate high RF power input signal (up to 100 W) typical of a BTS to a lower RF power output signal with very low PIM suitable for use in a DAS. The modular design allows for up to 12 separate BTS RF input signals, at different RF frequencies and signal RF power levels, to be attenuated to meet the lower RF power output signal levels required for DAS networks in a single, industry standard, 19″ rack, 4 U enclosure, for example. 
         [0007]    The modular design of a high power, low PIM, active, universal DAS interface tray demonstrates several unique features and benefits including, but not limited to, the functionality to attenuate both high and low power RF input signals from a BTS, via a cable switch matrix located on the RF module, to low and high RF power DAS output signals with low PIM. The low PIM requirement is realized through a front-end RF frequency signal duplexer, instead of a high power (up to 100 W), low PIM attenuator. The modular design supports up to twelve different RF modules with various RF frequencies and RF power levels that are configured via the cable switch matrix in a single standard 19″ tack, 4 U enclosure. All the modules are completely independent and can be field configurable to meet the demands of particular BTS and DAS network requirements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic block diagram for a single duplex RF module of the present invention. 
           [0009]      FIG. 2  is an isometric view of a partially populated 19″ rack, 4 U main chassis capable of supporting up to twelve RF modules, a main chassis and a supervisor Control/Power Supply Unit (PSU) module of the invention. 
           [0010]      FIG. 3  is an isometric view of the RF module with cable switch matrix for configuring the unit for high or low BTS input power, and front-end duplexer to maintain a PIM RF power signal. 
           [0011]      FIG. 4  is a front view of fully populated main chassis showing the twelve RF modules and the Supervisor Control/PSU module installed. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    The present invention is a modular configuration of a high power, low passive intermodulation, active, universal distributed antenna system interface tray. It will be referred to herein as “the device.” The device functions by attenuating the input power signal of a BTS to a lower power RF output signal level that can be utilized in a DAS network solution. The device can function with a variety of input BTS signal power levels, adjustable via a cable switch matrix, and frequencies. The device can also provide noise and gain adjustment of the uplink path of the RF signal. The device generates an attenuated RF output signal power level that is specified by the user via a software graphical user interface (GUI) from the BTS input signal frequency band with very low PIM characteristics. The functionality of the device can be repeated in a plurality of RF modules that can be of various frequencies and power levels within the main chassis. The example of 12 RF modules will be described herein but the invention is not limited to the use of that specific number of modules. The frequency is adjusted by the front end duplexer of the module, and the power level can be adjusted via a cable switch matrix at the front of the module. The device can support all wireless frequency bands, all power levels from BTS (from 100 mW to 100 W), all DAS power levels (0 dBm to +36 dBm), and all wireless protocols (e.g. GSM, CDMA, LTE, W-CDMA, etc.). The device includes three main parts: the RF module, the main chassis and the Supervisor Control/PSU module. 
         [0013]    Referring now to  FIG. 1 , an embodiment of the RF module portion of the device is shown in a block diagram. The RF module itself includes three main parts with distinct functionality, a front-end duplexer, a downlink section and an uplink section. 
         [0014]    Referring now to  FIG. 3 , the first part of the RF module is the front-end duplexer module. The front-end duplexer of that module allows for transmit and receive RF signals to share a common antenna port. Therefore, the front-end duplexer acts as the first element that the transmit signal from the BTS encounters and the last element the receive signal encounters before returning to the BTS. The front-end duplexer provides the function of providing the low PIM interface for transmit signal entering the device. The low PIM interface is important due to the fact that in a duplexed system, transmit and receive signals share a common antenna interface. Transmit signals have a much higher RF power level than the receive signals especially in the application that the device is intended to support in a network architecture. Passive intermodulation in the transmit path can cause interference and signal noise in the receive signal that will prevent the network from functioning properly, thus for the device, the front-end duplexer provides an important role in the functionality of the device in a DAS network. The duplexer is realized in the device via a cavity filter configured to enable low PIM functionality at the high power levels required by the DAS network. 
         [0015]    The second part of the RF module is the downlink (DL) functionality section. The DL section of the device provides the stepped attenuation of the transmit signal that transforms high power BTS signal input in a low power transmit signal that can be used by the DAS network. Prior to the transmit signal reaching the input port of the DL section, the signal is processed through a cable switch matrix. Referring to  FIG. 3 , the cable switch matrix is a manual set of cable jumpers that are configured on the front panel of the RF module. The cable jumpers are set based on the known input RF power generated by the BTS. For high power signals, the cable jumpers are set to route the transmit signal from the front-end duplexer to a 10 dB power coupler. The functionality of the coupler is to terminate a portion of the RF power into a 50-ohm termination resistor. The termination resistor absorbs the excess RF power from the transmit signal and allows the signal to then be routed to a DL portion containing a series of stepped attenuators that further reduce the RF power level of the signal. The stepped attenuator can be used or bypassed, depending on the input RF power level and the desired output RF power level. The output power level is controlled via a software GUI and can be configured by the user for the DAS network. Each of the individual RF modules in the device can be individually configured and controlled. The cable switch matrix can also be used to bypass the coupler and the termination resistor. This functionality allows for lower power RF input signals from the BTS to be supported in the DAS network. The bypassing of the coupler and the termination resistor allow for transmit signal power from the front-end duplexer to be in the same range prior to the input of the step attenuator function of the DL section. The cable switch matrix provides a user-friendly interface for configuring the individual RF modules based on the input power from the BTS. 
         [0016]    The third part of the RF module, referenced in  FIG. 3 , is the uplink (UL) functionality. The UL section receives the uplink signal from the DAS network back to the BTS via the front-end duplexer and the common antenna port. The UL provides a noise detection function of the uplink signal received from the DAS network and, via a low noise amplifier section, the UL can add gain to the receive signal prior to transmission to the BTS. The fixed gain of the system can be set based on the desired performance of the network. The noise detection is an important parameter in the overall performance of the network as it is used to provide an alarm to the network that the noise level in the system is above the desired threshold, which noise level may result in adverse performance of the network. The UL gain and noise detection functionality are effective functions of the device as used in the network architecture. The UL also provides UL power measurement within the frequency band of operation, which can be very useful for plotting spectrum on the GUI. 
         [0017]    The RF module functions are all powered and controlled by the Supervisor Control/PSU module, which is shown in  FIG. 2 . The Supervisor Control/PSU module provides all the control functions for the required attenuation of the DL path, UL noise detection and UL gain. It also supplies all the power required for the individual modules as well as the power and speed of fans in the main chassis. All functions in the Supervisor/PSU module are controlled via software that can be adjusted through a software GUI by the end user. The software uses a local area network (LAN) connection as the interface into the Supervisor Control/PSU module. The signals from the Supervisor Control/PSU module are transmitted out to the individual modules and information is received back via a backplane printed circuit board assembly (PCBA) mounted in the main chassis. Signals are switched and routed via the backplane such that each module can be controlled and configured independently of the other modules providing maximum flexibility and variety. 
         [0018]    An embodiment of the main chassis is shown in  FIG. 4 . The main chassis is the final primary unit of the device. The main chassis includes mechanical structure to support the RF modules and the Supervisor Control/PSU module. The main chassis contains the backplane PCBA as well as the fans used to actively cool the system. The main chassis is designed in such a way that the spacing of input common antenna connector ports do not interfere with each other as the mating connector cable assembly is installed.  FIG. 2  shows the functionality of this feature. It allows for the BTS input cable to be installed/uninstalled without having to remove or disconnect the surrounding modules. The main chassis also utilizes a staggered rail input system to prevent the modules from being installed in the wrong/incorrect orientation, and allows for ease of installation by hand. This provides the user with a distinctly unique installation system that prevents the improper installation of the modules in a user friendly manner. The main chassis is also frequency band/power level/air interface agnostic. Any of the module slots in the main chassis can be used by any frequency band/power level/air interface without affecting the performance of the system or the DAS network. All of the main chassis functionality may be established in a 4 U (7″ tall), 19″ rack system. The ability to support multiple independent modules in the size of main chassis is an advantage of the device. 
         [0019]    The present invention has been described with reference to a specific embodiment but is not intended to be so limited. The scope of the invention is defined by the appended claims.