Abstract:
A remote radio head unit (RRU) system for achieving high data rate communications in a Distributed Antenna System is disclosed. The Distributed Antenna System is configured as a Neutral Host enabling multiple operators to exist on one DAS system. The present disclosure enables a remote radio head unit to be field reconfigurable and support multi-modulation schemes (modulation-independent), multi-carriers, multi-frequency bands and multi-channels. As a result, the remote radio head system is particularly suitable for wireless transmission systems, such as base-stations, repeaters, and indoor signal coverage systems.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the following U.S. Patent applications, all of which are incorporated herein by reference: 
         [0000]    
       
         
               
               
               
             
           
               
                   
               
               
                 Serial Number 
                 Filing Date 
                 Title 
               
               
                   
               
             
             
               
                 60/877,035 
                 Dec. 26, 2006 
                 Method For Baseband Predistortion 
               
               
                   
                   
                 Linearization in Multi-Channel Wideband 
               
               
                   
                   
                 Communication Systems 
               
               
                 60/925,603 
                 Apr. 23, 2007 
                 Digital Hybrid Mode Power Amplifier System 
               
               
                 60/925,577 
                 Apr. 23, 2007 
                 N-Way Doherty Distributed Power Amplifier 
               
               
                 61/012,416 
                 Dec. 8, 2007 
                 Baseband Derived RF Digital Predistortion 
               
               
                 11/961,969 
                 Dec. 20, 2007 
                 A Method for Baseband Predistortion 
               
               
                   
                   
                 Linearization in Multi-Channel Wideband 
               
               
                   
                   
                 Communication Systems. 
               
               
                 61/041,164 
                 Mar. 31, 2008 
                 An Efficient Peak Cancellation Method For 
               
               
                   
                   
                 Reducing The Peak-To-Average Power Ratio 
               
               
                   
                   
                 In Wideband Communication Systems 
               
               
                 12/108,502 
                 Apr. 23, 2008 
                 Digital Hybrid Mode Power Amplifier System 
               
               
                 61/172,642 
                 Apr. 24, 2009 
                 Remotely Reconfigurable Power Amplifier 
               
               
                   
                   
                 System 
               
               
                 12/603,419 
                 Oct. 21, 2009 
                 N-Way Doherty Distributed Power Amplifier 
               
               
                   
                   
                 with Power Tracking 
               
               
                 61/288,838 
                 Dec. 21, 2009 
                 Multi-Band Wideband Power Amplifier Digital 
               
               
                   
                   
                 Predistortion System and Method 
               
               
                 61/288,840 
                 Dec. 21, 2009 
                 Remote Radio Head Unit System with 
               
               
                   
                   
                 Wideband Power Amplifier and Method 
               
               
                 61/288,844 
                 Dec. 21, 2009 
                 Modulation Agnostic Digital Hybrid Mode 
               
               
                   
                   
                 Power Amplifier System and Method 
               
               
                 61/288,847 
                 Dec. 21, 2009 
                 High Efficiency, Remotely Reconfigurable 
               
               
                   
                   
                 Remote Radio Head Unit System and Method 
               
               
                   
                   
                 for Wireless Communications 
               
               
                 12/767,669 
                 Apr. 26, 2010 
                 Remotely Reconfigurable Power Amplifier 
               
               
                   
                   
                 System and Method 
               
               
                 61/374,593 
                 Aug. 17, 2010 
                 Neutral Host Architecture for a Distributed 
               
               
                   
                   
                 Antenna System 
               
               
                 61/382,836 
                 Sep. 14, 2010 
                 Remotely Reconfigurable Distributed Antenna 
               
               
                   
                   
                 System and Methods 
               
               
                 12/928,931 
                 Dec. 21, 2010 
                 Modulation Agnostic Digital Hybrid Mode 
               
               
                   
                   
                 Power Amplifier System and Method 
               
               
                 12/928,933 
                 Dec. 21, 2010 
                 Remote Radio Head Unit System with 
               
               
                   
                   
                 Wideband Power Amplifier and Method 
               
               
                 12/928,934 
                 Dec. 21, 2010 
                 Multi-Band Wideband Power Amplifier Digital 
               
               
                   
                   
                 Predistortion System and Method 
               
               
                 12/928,943 
                 Dec. 21, 2010 
                 High Efficiency, Remotely Reconfigurable 
               
               
                   
                   
                 Remote Radio Head Unit System and Method 
               
               
                   
                   
                 for Wireless Communications 
               
               
                 61/439,940 
                 Feb. 7, 2011 
                 Daisy Chained Ring of Remote Units for a 
               
               
                   
                   
                 Distributed Antenna System 
               
               
                 [not assigned yet] 
                 Aug. 16, 2011 
                 Neutral Host Architecture for a Distributed 
               
               
                   
                   
                 Antenna System 
               
               
                 [not assigned yet] 
                 Aug. 16, 2011 
                 Remotely Reconfigurable Distributed Antenna 
               
               
                   
                   
                 System and Methods 
               
               
                 [not assigned yet] 
                 Aug. 16, 2011 
                 Daisy Chained Ring of Remote Units for a 
               
               
                   
                   
                 Distributed Antenna System 
               
               
                   
               
             
          
         
       
     
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to wireless communication systems employing Distributed Antenna Systems (DAS). More specifically, the present invention relates to a DAS which is part of a distributed wireless network base station in which all radio-related functions that provide network coverage and/or capacity for a given area are contained in a small single unit that can be deployed in a location remote from the remaining distributed wireless network base station unit or units which are not performing radio-related functions. Multi-mode radios capable of operating according to GSM, HSPA, LTE, TD-SCDMA, UMTS and WiMAX standards with advanced software configurability are features in the deployment of more flexible and energy-efficient radio networks. The present invention can also serve multiple operators and multi-frequency bands per operator within a single DAS to reduce the costs associated with radio network equipment and radio network deployment. 
       BACKGROUND OF THE INVENTION 
       [0003]    Wireless and mobile network operators face the continuing challenge of building networks that effectively manage high data-traffic growth rates. Mobility and an increased level of multimedia content for end users requires end-to-end network adaptations that support both new services and the increased demand for broadband and flat-rate Internet access. In addition, network operators must consider the most cost-effective evolution of the networks towards 4G and other advanced network capabilities. Wireless and mobile technology standards are evolving towards higher bandwidth requirements for both peak rates and cell throughput growth. The latest standards supporting these higher bandwidth requirements are HSPA+, WiMAX, TD-SCDMA and LTE. The network upgrades required to deploy networks based on these standards must deal with the limited availability of new spectrum, leverage existing spectrum, and ensure operation of all desired wireless technology standards. The processes of scarce resource optimization while ensuring a future-proof implementation must both take place at the same time during the transition phase, which usually spans many years and thus can encompass numerous future developments. Distributed open base station architecture concepts have evolved in parallel with the evolution of the various technology standards to provide a flexible, lower-cost, and more scalable modular environment for managing the radio access evolution. Such advanced base station architectures can generally be appreciated from  FIG. 1  [PRIOR ART], which shows an architecture for a prior art Distributed Wireless Network Base Station. In  FIG. 1 ,  100  is a depiction of a Distributed Wireless Network Base Station. The Base Transceiver Station (BTS) or Digital Access Unit (DAU)  101  coordinates the communication between the Remote Radio Head Units  102 ,  103  and the Base Station Controller (BSC). The BTS communicates with multiple Remote Radio Heads via optical fiber. For example, the Open Base Station Architecture Initiative (OBSAI), the Common Public Radio Interface (CPRI), and the IR Interface standards introduced publicly-defined interfaces separating the Base Transceiver Station (BTS) or Digital Access Unit and the remote radio head unit (RRU) parts of a base station by employing optical fiber transport. 
         [0004]    The RRU concept constitutes a fundamental part of an advanced state-of-the-art base station architecture. RRU-based system implementation is driven by the need to achieve consistent reductions in both Capital Expenses (CAPEX) and Operating Expenses (OPEX), and enable a more optimized, energy-efficient, and greener base deployment. An existing application employs an architecture where a 2G/3G/4G base station is connected to RRUs over multiple optical fibers. Either CPRI, OBSAI or IR Interfaces may be used to carry RF data to the RRUs to cover a sectorized radio network coverage area corresponding to a radio cell site. A typical implementation for a three-sector cell employs three RRU&#39;s. The RRU incorporates a large number of digital interfacing and processing functions. However, commercially available RRU&#39;s are power inefficient, costly and inflexible. Their poor DC-to-RF power conversion insures that they will need to have a large mechanical housing to help dissipate the heat generated. The demands from wireless service providers for future RRU&#39;s also includes greater flexibility in the RRU platform, which is not presently available. As standards evolve, there will be a need for multi-band RRUs that can accommodate two or more operators using a single wideband power amplifier. Co-locating multiple operators in one DAS system would reduce the infrastructure costs and centralize the Remote Monitoring Function of multiple Operators on the Network. To accommodate multiple operators and multiple bands per operator would require a very high optical data rate to the RRUs which is not achievable with prior art designs. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention substantially overcomes the limitations of the prior art discussed above. Accordingly, it is an object of the present invention to provide a high performance, cost-effective DAS system, architecture and method for an RRU-based approach which enables each of multiple operators to use multi-frequency bands. The present disclosure enables a RRU to be field reconfigurable, as presented in U.S. Patent application U.S. 61/172,642 (DW-1016P), filed Apr. 24, 2009, entitled Remotely Reconfigurable Power Amplifier System and Method, U.S. Patent application U.S. Ser. No. 12/108,502 (DW1011U), filed Apr. 23, 2008, entitled Digital Hybrid Mode Power Amplifier System, U.S. Patent application U.S. 61/288,838 (DW1018P), filed Dec. 21, 2009, entitled Multi-band Wideband Power Amplifier Digital Predistortion System, U.S. Patent application U.S. 61/288,840 (DW1019P), filed Dec. 21, 2009, entitled Remote Radio Head Unit with Wideband Power Amplifier and Method, U.S. Patent application U.S. 61/288,844 (DW1020P), filed Dec. 21, 2009, entitled Modulation Agnostic Digital Hybrid Mode Power Amplifier System, and U.S. Patent application U.S. 61/288,847 (DW1021P), filed Dec. 21, 2009, entitled High Efficiency Remotely Reconfigurable Remote Radio Head Unit System and Method for Wireless Communications incorporated herein by reference. In addition, the system and method of the present invention supports multi-modulation schemes (modulation-independent), multi-carriers, multi-frequency bands, and multi-channels. To achieve the above objects, the present invention maximizes the data rate to the Remote Radio Head Unit in a cost effective architecture.  FIGS. 2 and 3  depict a low power RRU and high power RRU. The RRUs depicted in  FIGS. 2 and 3  can be extended to a multi-band and multi-channel configuration. Multi-band implies more than two frequency bands and multi-channel implies more than one output to an antenna system. Various embodiments of the invention are disclosed. 
         [0006]    An embodiment of the present invention utilizes a RRU Access Module. The objective of the access module is to de-multiplex and multiplex high speed data to achieve aggregate data rates sufficient for operation of a plurality of RRU Band Modules which are geographically distributed. An alternative embodiment of the present invention utilizes the physical separation of the RRU Band Modules from the RRU Access Module using an optical fiber cable, Ethernet cables, RF cable and any other form of connection between the modules. In an alternative embodiment, a Remote Radio Unit comprised of one or more RRU Band Modules may be collocated with the antenna or antennas. In a further alternative embodiment, the RRU Access Module can also supply DC power on the interconnection cabling. In other aspects of the invention, control and measurement algorithms are implemented to permit improved network deployment, network management, and optimization. 
         [0007]    Applications of the present invention are suitable to be employed with all wireless base-stations, remote radio heads, distributed base stations, distributed antenna systems, access points, repeaters, distributed repeaters, optical repeaters, digital repeaters, mobile equipment and wireless terminals, portable wireless devices, and other wireless communication systems such as microwave and satellite communications. The present invention is also field upgradable through a link such as an Ethernet connection to a remote computing center. 
         [0008]    Appendix I is a glossary of terms used herein, including acronyms. 
     
    
     
       THE FIGURES 
         [0009]    Further objects and advantages of the present invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0010]      FIG. 1  [PRIOR ART] is a block diagram showing the basic structure of a prior art Distributed Wireless Base Station system. 
           [0011]      FIG. 2  is a block diagram showing a multi-channel High Power Remote Radio Head Unit according to one embodiment of the present invention. 
           [0012]      FIG. 3  is a block diagram multi-channel High Power Remote Radio Head Unit according to one embodiment of the present invention. 
           [0013]      FIG. 4  is a block diagram of a Remote Radio Head Unit high level system of the present invention. 
           [0014]      FIG. 5  is a block diagram of the Remote Radio Head Unit Access Module of the present invention. 
           [0015]      FIG. 6  is a Remote Radio Head Unit Band Module according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The present invention is a novel Distributed Antenna System that utilizes a high speed Remote Radio Head Unit Access Module interconnected with Remote Radio Head Unit Band Module. 
         [0017]    An embodiment of a Remote Radio Head Unit in accordance with the invention is shown in  FIG. 2 . Fiber  1 , indicated at  200 A, is a high speed fiber cable that transports data between the BTS and the Remote Radio Head Unit. Fiber  2 , indicated at  200 B, is used to daisy chain other remote radio head units which are thereby interconnected to the BTS or DAU. The software-defined digital platform  216  performs baseband signal processing, typically in an FPGA or equivalent. Building block  203  is a Serializer/Deserializer. The deserializer portion extracts the serial input bit stream from the optical fiber  201  and converts it into a parallel bit stream. The serializer portion performs the inverse operation for sending data from the Remote Radio Head Unit to the BTS. In an embodiment, the two distinct bit streams communicate with the BTS using different optical wavelengths over one fiber, although multiple fibers can be used in alternative arrangements. The deframer  204  deciphers the structure of the incoming bit stream and sends the deframed data to the Crest Factor Reduction Algorithm  209 . The Crest Factor Reduction block  209  reduces the Peak-to-Average Ratio of the incoming signal so as to improve the Power amplifier DC-to-RF conversion efficiency. The waveform is then presented to the Digital Predistorter block  208 . The digital predistorter compensates for the nonlinearities of the Power Amplifier  221  in an adaptive feedback loop. Digital Upconverter  210  filters and digitally translates the deframed signal to an IF frequency. The Framer  204  takes the data from the two digital downconverters  206 ,  207  and packs it into a Frame for transmission to the BTS over the optical fiber  201 . Elements  211  and  212  are Analog to Digital converters that are used to translate the two analog receive signals into digital signals. The receiver comprises a diversity branch which contains a downconverter  217  and a Band Pass Filter  223 . The main branch has a receiver path comprised of a duplexer  224  and a downconverter  218 . In some embodiments, one or both downconverters  217  and  218  can have an integral uplink low-noise amplifier. 
         [0018]    The power amplifier has an output coupler for extracting a replica of the output signal in the feedback path. The feedback signal is frequency-translated by downconverter  219  to either an IF frequency or baseband and presented to an Analog to Digital converter  213 . This feedback signal is used in an adaptive loop for performing Digital Predistortion to compensate for any nonlinearities created by the power amplifier. 
         [0019]    The Ethernet cable is used to locally communicate with the Remote Radio Head Unit. Switch  226  is used to allow easy access to either the FPGA or the CPU. DC power converters  228  and  229  are used to obtain the desired DC voltages for the Remote Radio Head Unit. Either an external voltage can be connected directly into the RRU or the DC power may be supplied through the Ethernet cable. 
         [0020]    Although the description of the instant embodiment is directed to an application where a second optical fiber connection provides a capability for daisy chaining to other Remote Radio Head Units, an alternative embodiment provides multiple optical fiber connections to support a modified “hybrid star” configuration for appropriate applications which dictate this particular optical transport network configuration. 
         [0021]      FIG. 3  depicts a remote radio head unit. In at least some designs, this architecture offers benefits when the RF output power is relatively low. In the embodiment shown in  FIG. 3 , digital predistrortion and crest factor reduction are not employed as was the case in  FIG. 2 . Even though this topology shows a non-diversity configuration, a diversity receive branch can be added along with an additional transmitter path for development of a Multiple Input Multiple Output (MIMO) Remote Radio Head Unit. 
         [0022]    The Remote Radio Head Unit high level system is shown in  FIG. 4 . It comprises a Remote Radio Head Unit Access Module  400  which communicates directly with the BTS or DAU. The function of the Remote Radio Head Unit Access Module  400  is to route the high speed data (at any desired speed, e.g., such as 10 Gbps as illustrated in  FIG. 4 ) (the “Data Speed) to the multiple Remote Radio Head Unit Band Modules and allows for local communications with them via Ethernet. A backplane  401  is used to interconnect the Remote Radio Head Unit Access Module  400  with the various Remote Radio Head Unit Band Modules  402 , 403 , 404 , 405  at any speed lower than the Data Speed (e.g., less than or equal to 3 Gbps as illustrated in  FIG. 4 ). The output ports of the Remote Radio Head Unit Band Modules are combined and sent to an antenna for transmission. An alternative embodiment is described as follows. Although the description of instant embodiment is directed to applications for up to four Remote Radio Head Unit Band Modules, an alternative embodiment involves feeding a much larger quantity of Remote Radio Head Unit Band Modules with signals of various bandwidths at various frequency bands covering multiple octaves of frequency range, to support a wide range of applications including location-based services, mobile internet, public safety communications, private enterprise telecommunications and broadband, and other wireless applications. The system can in theory support an infinite quantity of RRUs. Also, the Remote Radio Head Unit Band Modules may be set up remotely to have RF power values selected based on the specific desired applications as well as location-specific radio signal propagation factors. A further alternative embodiment leverages the flexibility of the architecture shown in  FIG. 4  to provide a capability known as Flexible Simulcast. With Flexible Simulcast, the amount of radio resources (such as RF carriers, CDMA codes or TDMA time slots) assigned to a particular RRU or group of RRUs by each RRU Access Module can be set via software control to meet desired capacity and throughput objectives or wireless subscriber needs. 
         [0023]    The detailed topology of the Remote Radio Head Unit Access Module is shown in  FIG. 5 . It comprises a Small form Factor Pluggable optic transceiver (SFP)  500  which operates on two distinct wavelengths, one for communicating from the BTS to the Remote Radio Head Unit Access Module and the other for communicating in the opposite direction. The SFP contains a Laser Diode for converting the electronic signal to an optical signal and an Optical detector for converting the optical signal into an electronic signal. A multiplexer/demultiplexer  501  converts the high speed data to multiple lower speed data paths for delivery to a FPGA  502 . The multiplexer/demultiplexer  501  performs the opposite function when data is being sent back to the BTS or DAU. The framer/deframer  503  routes the data to the appropriate Remote Radio Head Unit Band Modules. An additional multiplexer/demultiplexer  506  allows for further expansion of lower speed Remote Radio Head Units. The number of Remote Radio Head units is only limited by the capability of the FPGA. Local communication with the Remote Radio Head Unit&#39;s Access Module&#39;s FPGA or the individual Remote Radio Head Unit Band Modules is via an Ethernet connection  508 . Although the description of this embodiment is mainly directed to an application where a BTS or DAU (or multiple BTS or DAU) feeds the Remote Radio Head Unit Access Module, an alternative embodiment is described as follows. The alternative embodiment is one where the digital optical signals fed to the Remote Radio Head Unit Access Module may be generated by an RF-to-Digital interface which receives RF signals by means of one or more antennas directed to one or more base stations located at some distance from the Remote Radio Head Unit Access Module. A further alternative embodiment is one where the digital signals fed to the Remote Radio Head Unit Access Module may be generated in a combination of ways; some may be generated by an RF-to-Digital interface and some may be generated by a BTS or DAU. Some neutral host applications gain an advantage with regard to cost-effectiveness from employing this further alternative embodiment. Although the optical signals fed to the Remote Radio Head Unit Access Module described in the preferred and alternative embodiments are digital, the optical signals are not limited to digital, and can be analog or a combination of analog and digital. A further alternative embodiment employs transport on one or multiple optical wavelengths fed to the Remote Radio Head Unit Access Module. 
         [0024]    The Remote Radio Head Unit Band Module is shown in  FIG. 6 . It comprises a Software Defined Digital (SDD) section  610  and an RF section  622 . An alternative embodiment employs a Remote Antenna Unit comprising a broadband antenna with RRU Band Module Combiner and multiple plug-in module slots, into which multiple RRU Band Modules intended for operation in different frequency bands are inserted. To provide an overall compact unit with low visual impact, this embodiment employs RRU Band Modules which each have a physically small form factor. One example of a suitably small form factor for the RRU Band Module is the PCMCIA module format. A further alternative embodiment employs RRU Band Modules where each has an integral antenna, and the embodiment does not require a common antenna shared by multiple RRU Band Modules. 
         [0025]    In summary, the Neutral Host Distributed Antenna System (NHDAS) of the present invention enables the use of remote radio heads for multi-operator multi-band configurations, which subsequently saves hardware resources and reduces costs. The NHDAS system is also reconfigurable and remotely field-programmable since the algorithms can be adjusted like software in the digital processor at any time. 
         [0026]    Moreover, the NHDAS system is flexible with regard to being able to support various modulation schemes such as QPSK, QAM, OFDM, etc. in CDMA, TD-SCDMA, GSM, WCDMA, CDMA2000, LTE and wireless LAN systems. This means that the NHDAS system is capable of supporting multi-modulation schemes, multi-bands and multi-operators. 
         [0027]    Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.