Patent Publication Number: US-11381312-B2

Title: Redundancy in a public safety distributed antenna system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of the co-pending U.S. patent application titled, “REDUNDANCY IN A PUBLIC SAFETY DISTRIBUTED ANTENNA SYSTEM,” filed on Apr. 29, 2020 and having Ser. No. 16/861,561, which is a continuation of the U.S. patent application titled, “REDUNDANCY IN A PUBLIC SAFETY DISTRIBUTED ANTENNA SYSTEM,” filed on May 12, 2017 and having Ser. No. 15/594,323, issued as U.S. Pat. No. 10,644,798, which claims the priority benefit of the U.S. provisional patent application titled, “Redundancy in a Public Safety Distributed Antenna System,” filed on May 12, 2016 and having Ser. No. 62/335,383. The subject matter of these related applications is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Public Safety communication systems employing Distributed Antenna Systems (DAS) are available. Public Safety has stringent requirements on system reliability and redundancy. A DAS typically includes one or more host units, optical fiber or other suitable transport infrastructure, and multiple remote antenna units. A radio base station is often employed at the host unit location commonly known as a base station hotel, and the DAS provides a means for distribution of the base station&#39;s downlink and uplink signals among multiple remote antenna units. The DAS architecture with routing of signals to and from remote antenna units can be either fixed or reconfigurable. 
     A DAS is advantageous from a signal strength and throughput perspective because its remote antenna units are physically close to wireless subscribers. The benefits of a DAS include reducing average downlink transmit power and reducing average uplink transmit power, as well as enhancing quality of service and data throughput. 
     Despite the progress made in public safety communications systems, a need exists for improved methods and systems related to public safety communications. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to public safety communication systems employing Distributed Antenna Systems (DAS) as part of a distributed wireless network. More specifically, the present invention relates to a DAS utilizing a software configurable network. In a particular embodiment, the present invention has been applied to the use of cross-coupled connections amongst Digital Host Units, Digital Distributed Units and Digital Remote Radios. The methods and systems described herein are applicable to a variety of communications systems including systems utilizing various communications standards. Utilizing embodiments of the present invention, fully redundant, self-monitoring, self-healing digital DAS are provided. 
     Public Safety network operators face the continuing challenge of building reliable networks. Mobility and an increased level of multimedia content for end users typically employs end-to-end network adaptations that support new services and the increased demand for broadband Internet access. One of the most difficult challenges faced by Public Safety networks is the ability to have 99.999% service availability throughout the network. Fire-fighters, Police, Homeland Security, etc. all need guaranteed communications in the event of a disaster. A high service availability system requires full redundancy of all elements/components on the communication path. 
     According to an embodiment of the present invention, a system for data transport in a Distributed Antenna System is provided. The system includes a plurality of DAUs (Digital Access Units also referred to as Hosts) which are connected to one or more BTSs (Base Transceiver Station). In another embodiment, the BTSs can be replaced with off-air signals. The off-air signals could originate from BTSs wirelessly communicating with the DAUs or via repeaters which capture a remote signal from a BTS. The plurality of DAUs are coupled to each other and operable to transport signals between the plurality of DAUs. The system also includes a plurality of DDUs (Digital Distribution Units). Each of the plurality of DDUs are in communication with one or more of the DAUs using an optical communications path. The system further includes a plurality of transmit/receive cells. Each of the plurality of transmit/receive cells includes a plurality of DRUs (Digital Remote Units also referred to as Remote Units). Each of the DRUs in one of the plurality of transmit/receive cells is in communication with one or more of the plurality of DDUs using an optical communications path (e.g., an optical fiber, which is also referred to as an optical cable and is operable to support both digital and analog signals (i.e., RF over fiber)). 
     According to another embodiment of the present invention, a system for routing signals in a Distributed Antenna System (DAS) is provided. The system includes a plurality of Base Transceiver Stations (BTS), each having one or more sectors and a plurality of BTS RF connections, or Digital connections each being coupled to one of the one or more sectors. The system also includes a plurality of local Digital Distribution Units (DDUs) located at a Local location. Each of the plurality of local DDUs is operable to route signals between the plurality of local DAUs, and coupled to at least one of the plurality of remote DRUs. The system further includes a plurality of remote DDUs located at a Remote location. The plurality of remote DDUs are operable to transport signals between the plurality of remote DRUs. The plurality of local DDUs can be coupled via at least one of Ethernet cable, Optical Fiber, Microwave Line of Sight Link, Wireless Link, or Satellite Link. 
     The plurality of local DAUs can be connected to the plurality of remote DDUs via at least one DWDM or CWDM signal and at least one optical fiber. Similarly, the plurality of remote DDUs can be connected to the plurality of remote DRUs via at least one DWDM or CWDM signal and at least one optical fiber. The plurality of remote DDUs can be coupled via at least one of Ethernet cable, Optical Fiber, Microwave Line of Sight Link, Wireless Link, or Satellite Link. In an embodiment, the plurality of remote DDUs include one or more optical interfaces. As an example, the one or more optical interfaces can include an optical input and an optical output. In some embodiments, the system also includes a server coupled to each of the plurality of remote DDUs. A single DAU port is connected to a plurality of BTSs in some implementations. 
     According to another embodiment of the present invention, a system for routing signals in a DAS is provided. The system includes a plurality of local Digital Access Units (DAUs) located at a Local location. The plurality of local DAUs are coupled to each other and operable to route signals between the plurality of local DAUs. The system also includes a plurality of remote Digital Access Units (DAUs) located at a Remote location coupled to each other and operable to transport signals between the remote DAUs and each other and a plurality of Base Transceiver Stations (BTS). The system further includes a plurality of Base Transceiver Station sector RF connections coupled to the plurality of local DAUs and operable to route signals between the plurality of local DAUs and the plurality of Base Transceiver Stations sector RF connections and a plurality of DRUs connected to a plurality of remote DAUs via at least one of a Ethernet cable, Optical Fiber, RF Cable, Microwave Line of Sight Link, Wireless Link, or Satellite Link. 
     According to another embodiment of the present invention, a Public Safety system for data transport in a Distributed Antenna System (DAS) includes a plurality of Digital Access Units (DAUs), Digital Distribution Units (DDUs) and Digital Remote Units (DRUs). The plurality of DAUs are coupled to each other and operable to transport digital signals between the plurality of remote DAUs. The system also includes a plurality of Digital Distribution Units. Each of the plurality of DDUs is in communication with a plurality of DAUs using an electrical communications path. The system further includes a plurality of transmit/receive cells. Each of the plurality of transmit/receive cells includes a plurality of DRUs. Each of the DRUs in one of the plurality of transmit/receive cells is in communication with one of the plurality of DDUs using an optical communications path. Redundancy of the Public Safety system is achieve by cross connecting the optical fibers amongst the plurality of DAU, DDU and DRUs. 
     Numerous benefits are achieved by way of the present invention over conventional techniques. For instance, embodiments enable the routing redundancy at the remote location. Additionally, embodiments provide for redundancy in the context of DAS-based architectures for public safety communication systems. These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating the basic structure of a digital access unit (DAU) according to an embodiment of the present invention; 
         FIG. 2  is a block diagram according to one embodiment of the invention showing the basic structure of a DAU with an integrated repeater functionality on the primary and secondary inputs; 
         FIG. 3  is a block diagram according to one embodiment of the invention showing the basic structure of an integrated DAU with repeater functionality on one of the inputs; 
         FIG. 4  is a block diagram according to one embodiment of the invention showing the basic structure of a digital distribution unit (DDU); 
         FIG. 5  is a block diagram illustrating a digital remote unit (DRU); 
         FIG. 6  is a block diagram illustrating the public safety system architecture that ensures redundancy in the network according to an embodiment of the present invention; 
         FIG. 7  is a block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Public Safety Digital DAS architecture; 
         FIG. 8  is a block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Public Safety Analog (RF over Fiber) DAS architecture; 
         FIG. 9  is a block diagram according to one embodiment of the invention showing the basic structure of the cross connection architecture fed by a base transceiver station (BTS) on the primary path and from an off-air BTS in the secondary path; 
         FIG. 10  is a block diagram according to one embodiment of the invention showing the basic structure of the cross connection architecture fed by a primary BTS and a secondary BTS; in this embodiment, a plurality of DRUs are fed from DDU  1  and DDU  2 ; 
         FIG. 11  is a block diagram according to one embodiment of the invention showing the basic structure of the cross connection architecture fed by a primary off-air BTS and a secondary off-air BTS, the repeater DAU has embedded repeater functionality; 
         FIG. 12  is block diagram according to one embodiment of the invention showing a redundant DRU in hot standby mode and connected to the primary DRU via an optical bypass switch and RF bypass switch; 
         FIG. 13  is a block diagram illustrating feed and host redundancy according to an embodiment of the present invention; 
         FIG. 14  is a block diagram illustrating DDU main feed redundancy, local feed redundancy, and aggregation of the main and local content according to an embodiment of the present invention; 
         FIG. 15  is a block diagram illustrating feed to DRU redundancy according to an embodiment of the present invention; 
         FIG. 16  is a block diagram illustrating DRU main feed redundancy, local feed redundancy, and aggregation of a main and local content according to an embodiment of the present invention; 
         FIG. 17  is a block diagram illustrating redundancy utilizing multiple DRUs according to an embodiment of the present invention; 
         FIG. 18  is a simplified block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Digital Public Safety Digital DAS architecture; 
         FIG. 19  is a simplified flowchart illustrating a method for selecting a primary or secondary feed according to an embodiment of the present invention; and 
         FIG. 20  is a block diagram illustrating uplink redundancy according to one embodiment of the present invention showing the basic structure of a full redundancy digital DAS architecture; 
         FIG. 21  is a block diagram illustrating DDU uplink signal redundancy to a main headend and a local headend; 
         FIG. 22  is a block diagram illustrating uplink signal redundancy from a single DRU to a primary DDU, a secondary DDU and a local headend; 
         FIG. 23  is a block diagram illustrating uplink signal redundancy from dual redundant DRUs to a primary DDU and a secondary DDU; 
         FIG. 24  is a block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Public Safety Digital DAS architecture; and 
         FIG. 25  is a block diagram according to one embodiment of the present invention showing the basic structure of a full redundancy digital DAS architecture. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     A distributed antenna system (DAS) provides an efficient means of utilization of base station resources. The base station or base stations associated with a DAS can be located in a central location and/or facility commonly known as a base station hotel. The DAS network comprises one or more digital access units (DAUs) that function as the interface between the base stations, the digital distribution units (DDUs) and the digital remote units (DRUs). The DAUs can be collocated with the base stations. The DRUs can be daisy chained together and/or placed in a star configuration and provide coverage for a given geographical area. The DRUs are typically connected via the DDUs to the DAUs by employing a high-speed optical fiber link. This approach facilitates transport of the RF signals from the base stations to a remote location or area served by the DRUs. 
       FIG. 1  is a block diagram illustrating the basic structure of a local digital access unit (DAU)  100  according to an embodiment of the present invention. In this embodiment, two BTSs are connected to a local DAU  100  via a primary port  114  and a secondary port  116  for each band. In some embodiments, the primary port  114  and the secondary port  116  can be a first RF input port and a second RF input port respectively. The local DAU  100  encompasses primary and secondary RF section per band that provide primary and secondary interface. The optical output feeds a plurality of DDUs. If the primary feed  118  or secondary feed  120  is off-air, then an RF section with a duplexer along with a power amplifier for the Rx path to the remote BTS and a low noise amplifier for the Tx path from the remote BTS, and multi-channel, digital, agile band-pass filters with adjustable pass bandwidth is applied for that feed as described in additional detail in relation to  FIG. 3 . 
       FIG. 1  depicts a local DAU  100 , also referred to as a host or host unit. In accordance with an embodiment of the present invention, each DAU is fed from a Primary BTS  102  and a Secondary BTS  104  or, as illustrated in  FIG. 2 , an off-air signal. An off-air signal references a wireless signal from a remote BTS. As an example of an off-air signal, a Primary BTS  102  could be located in the same building as the DAU, providing the primary feed  118 . A Secondary BTS  104  could be located remotely, for example, several miles away from the DAU, to provide for redundancy. In this example, the Secondary BTS  104  would provide the secondary feed. If the BTS that provides the primary feed fails, then the local DAU  100  will switch to the secondary feed  120  as described more fully below. In another implementation, two BTSs could be collocated with the local DAU  100 , with one of the BTSs operating in hot standby mode. Similar use of off-air pickups can be implemented as discussed below. 
     The BTS or off-air signal is coupled to the local DAU  100  via an RF connection or a digital connection. The local DAU  100  communicates with a plurality of Digital Distribution Units (DDUs) via an optical feed  130 . As illustrated in  FIG. 1 , the local DAU  100  can accommodate multiple frequency bands. In some embodiments, one primary RF section may be used for each frequency band. 
     In the embodiment illustrated in  FIG. 1 , the local DAU  100  includes dual RF sections: a primary RF section  106  at the 700 MHz band and a secondary RF section  108  at the 700 MHz band. These dual RF sections are utilized to receive dual inputs illustrated as the primary feed  118  and secondary feed  120 . Thus, the multi-level system redundancy provided by embodiments of the present invention includes redundancy provided by redundant RF sections in each of the DAUs. 
     In some cellular systems, the local DAU  100  would receive multiple bands as appropriate for a cellular system, for example, one or more of 150 MHz, 450 MHz, 700 MHz, 800 MHz, 900 MHz, etc. In some Public Safety (PS) implementations, a single band is utilized, whereas in other PS implementations, multiple bands are utilized. As an example,  FIG. 1  illustrates an optional primary RF section  110  at the 800 MHz band and an optional secondary RF section  112  at the 800 MHz band. Thus, the illustrated local DAU  100  includes dual RF sections per band. Primary and secondary feeds will be provided to the optional band(s) as appropriate. 
     The particular bands illustrated in  FIG. 1  are not intended to limit the present invention but to provide exemplary bands that can be utilized according to embodiments of the present invention. In this embodiment, one of the primary RF sections is designated as a primary and the other primary RF section is designated as a secondary. Although primary and secondary RF sections are illustrated in  FIG. 1 , the present invention is not limited to this implementation and a tertiary RF section can be utilized, as well as additional RF sections if the number of redundant sections is greater than three. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
     In an embodiment in which multiple bands are utilized, e.g., both 700 MHz and 800 MHz bands, the feeds at these bands can be combined in a DSP unit  122 . In some embodiments the DSP unit  122  can be a field programmable gate array (FPGA) configured with digital signal processing logic. The DSP unit  122  can provide a combined digital data stream that is output by the local DAU  100 , broadcast to the DDUs  602 , and then broadcast to the DRUs  604  as illustrated in  FIG. 6 . As an example, the primary feed  118  at 700 MHz could be combined with the secondary feed  126  at 800 MHz if the primary RF section  110  at 800 MHz has failed. 
     One feature of embodiments of the present invention is the ability to route Base Station radio resources among the DAUs or group(s) of DAUs. In order to route radio resources available from one or more Base Stations, it is desirable to configure the individual router tables of the DAUs in the DAS network. This functionality is provided by embodiments of the present invention. 
     The DAUs are networked together as illustrated in  FIG. 7  to facilitate the routing of signals among multiple DAUs. The DAUs support the transport of the RF downlink and RF uplink signals between the Base Station and the various DAUs. This architecture enables the various Base Station signals to be transported simultaneously to and from multiple DAUs. PEER ports are used for interconnecting DAUs in some embodiments. 
     The DAUs have the capability to control the gain (in small increments over a wide range) of the downlink and uplink signals that are transported between the DAU and the base station (or base stations) connected to that DAU. This capability provides flexibility to simultaneously control the uplink and downlink connectivity of the path between a particular Remote DAU (or a group of DAUs) and a particular base station sector. 
     The digital data streams  128  output by the local DAU  100  to the plurality of DDUs are the same data stream in some embodiments. These digital data streams  128  enable the content to be provided to multiple DDUs for subsequent distribution to DRUs. The digital data streams  128  output by the local DAU  100  can be the digital data stream based on the primary feed  118  or the digital data stream based on the secondary feed  120 . The digital data stream can be output from the local DAU using at least a first digital optical output port  130  connected to a primary DDU and a second digital optical output port  132  connected to a secondary DDU. 
     In operation, both RF sections are operational. Both the primary feed  118  and the secondary feed  120  are processed inside the DSP logic  122  and two digital data streams are produced. The DSP unit  122  then decides which digital data stream will be utilized for transmission. The default setting can be transmission of the primary digital data stream. Additional description related to redundant operation is provided in relation to  FIGS. 13-17 . 
       FIG. 2  depicts a repeater Digital Access Unit (DAU)  200 , also referred to as a host or host unit, which has an embedded repeater functionality. In this embodiment, two off-air feeds are connected to a repeater DAU  200  via a primary port  114  and secondary port  116  for each band. The DAU with an integrated repeater functionality encompasses a primary RF section  206  and a secondary RF section  208  per band that provide a primary and a secondary interface. The repeater function is provided by a duplexer  210  along with a power amplifier  214  for the Rx path to the primary remote BTS  202  and a low noise amplifier  212  for the Tx path from the remote BTS, and multi-channel, digital, agile band-pass filters with adjustable pass bandwidth. If the primary or secondary feed is from a collocated Base Station, then an RF section without a duplexer, power amplifier for the Rx path, and low noise amplifier for the Tx path is applied for that feed as described in additional detail in relation to  FIG. 3 . 
     In accordance with embodiments of the present invention, each repeater DAU  200  is fed from a Primary remote BTS  202  and a secondary Remote BTS  204 . The BTS or off-air signal is coupled to the DAU via an RF connection or a digital connection. The repeater DAU  200  has an embedded duplexer  210 , Low Noise Amplifier  212  and Power Amplifier  214 . This facilitates the communication with remote BTSs or an off-air signal source over large distances in which signals are weaker than from collocated BTSs. If the mixed signal feeds are delivered to a DAU, local Base Station and off-air (remote Base Station), two types of RF sections are implemented. 
       FIG. 3  depicts a Digital Access Unit (DAU)  300 , also referred to as a host or host unit, operable to receive mixed signals. In this embodiment, mixed signal feeds are delivered to a DAU—Primary Base Station  102  and off-air (remote Base Station)  204  feeds are connected to an integrated DAU  300  via a primary port  114  and secondary port  116  for each band. The integrated DAU  300  encompasses a primary RF section  106  and a secondary RF section  208  per band, that provide primary and secondary interfaces. The optical output  130  feeds a plurality of DDUs. For the remote BTS  204  feed RF section  208  with a duplexer  210  along with a power amplifier  214  for the Rx path to the remote BTS  204  and a low noise amplifier  212  for the Tx path from the remote BTS  204 , and multi-channel, digital, agile band-pass filters with adjustable pass bandwidth is applied. For feed from a collocated Base Station  102  RF section  106  without a duplexer, power amplifier for the Rx path, and low noise amplifier for the Tx path is applied. 
     In this embodiment, for the off-air feed/secondary remote BTS  204 , an RF section  208  with a duplexer  210 , power amplifier  214 , and low noise amplifier  212  is used, while for the feed from a collocated Base Station, an RF section  106  without a duplexer, power amplifier, and low noise amplifier is used. The integrated DAU  300  communicates with a plurality of Digital Distribution Units (DDUs) via an optical feed  130 . As illustrated in  FIG. 2 , the repeater DAU  200  can accommodate multiple frequency bands. In some implementations, the repeater functionality can be provided separately, although this repeater functionality is illustrated as embedded in  FIGS. 2 and 3 . 
       FIG. 4  depicts a Digital Distribution Unit (DDU)  400 . The DDU  400  routes optical signals between the plurality of DAUs and a plurality of DRUs. In accordance with the present invention, each DDU  400  is fed from a Primary DAU  402  and Secondary DAU  404 . The DDU  400  is coupled to the plurality of DAUs via optical connections  406 . The DDU  400  communicates with a plurality of Digital Remote Units (DRUs) via an optical feed. As illustrated in  FIG. 3 , the DDU  400  can accommodate interfacing to multiple primary and secondary DAUs. The DDU  400  distributes the BTS or Off-air signals to a plurality of DRUs. 
     The DDU  400  receives the primary data stream  418  and the secondary data stream  420  from the redundant set of the primary DAU  402  and the secondary DAU  404  and redistributes signals based on either or both of the primary data stream  418  and the secondary data stream  420  to a network of DRUs. As illustrated in  FIG. 4 , the primary data stream  418  is received from a primary DAU  402  in the Main Headend  410 . A first input port  430  is coupled to the first digital optical output port of the primary DAU  402 . The secondary data stream  420  is received from a secondary DAU  404  in the Main Headend  412 . A second input port  432  is coupled to the first digital optical output port of the secondary DAU  404 . 
     As illustrated in  FIG. 4 , the DDU  400  provides a larger number of optical outputs  408  for delivery of data streams  428  to the DRUs than the number of data streams received at the DDU  400 . This enables a system architecture in which a small number of DAUs and DDUs interoperate with a large number of DRUs. The DDU  400  receives the data stream from the DAU and redistributes the data stream to multiple DRUs. In some embodiments, the DDU  400  has 16 optical ports  414 , with two utilized to receive the primary data stream  418  and the secondary data stream  420  and  14  utilized as output ports to provide data streams to the DRUs. At least a first output port and a second output port of the optical ports  414  are utilized to provide redundancy for the data streams to the DRUs. In other embodiments, including the embodiment illustrated in  FIG. 4 , two optical ports are utilized to receive the primary data stream  418  and the secondary data stream  420  from the Main Headend  410 . Further, two optical ports are utilized to receive the Local Headend primary local data stream  422  and the Local Headend secondary local data stream  424  from the Local Headend, with 12 optical ports utilized to provide data streams  128  to the DRUs. 
     In the illustrated embodiment, the Local Headend  412  can represent a local municipality service that operates on the same or a different band than the entity represented by the Main Headend  410 . The DAUs at the Local Headend  412  can provide additional data streams that can be received by the DDU  400 , aggregated with the data stream received from the Main Headend  410 , and delivered to the DRUs. As an example, the primary data stream  418  from the Main Headend and the primary data stream  422  from the Local Headend could be processed in a DSP unit  430 . In some embodiments, the DSP unit  430  can be an FPGA configured with digital signal processing logic. The DSP unit  430  can generate a combined stream and the combined stream can be transmitted to the DRUs. In addition to distribution or rebroadcasting of a data stream from a small number of DAUs, or host units, to a larger number of DRUs, the DDU  400  can aggregate additional data streams locally at the location where it is positioned, thereby providing augmentation of services for a particular area. 
       FIG. 5  depicts a Digital Remote Unit (DRU)  500  which contains a 700 MHz band RF section  502  and an 800 MHz band RF section  504  that deliver the BTS Tx signal  506  to the antenna and receives the User Rx signal  508  from the antenna, according to an embodiment of the present invention. The DRU  500  is interconnected with a plurality of DDUs. The DRU  500  translates the RF Rx signals to digital signals for transport to the BTS and translates the digital Tx signals from the BTS to RF signals for broadcasting over the antenna. In accordance with the present invention, each DRU  500  is fed from a Primary DDU  510  and a Secondary DDU  512 . The DRU  500  is coupled to the plurality of DDUs via optical connections  514 . As illustrated in  FIG. 5 , the DRU  500  can accommodate interfacing to multiple frequency band RF transceivers. The DRU  500  consists of a plurality of RF sections and a multiplexer  516  to facilitate interconnection  518  to a RF antenna. 
     The DRU  500  receives a primary data stream  520  and a secondary data stream  522  from the Primary DDU  510  and the Secondary DDU  512 . In  FIG. 6 , for example, DDU- 1  and DDU- 3  in TD  1   612  provide the primary data stream  520  and the secondary data stream  522  to DRU-T 1 . A DSP unit  524  processes the received data streams to provide outputs to the RF section(s), which can be implemented at different bands as needed to provide the RF output for the leaky coaxial cable, for example, in a tunnel, or a station antenna, either directional or omnidirectional. In some embodiments, the DSP unit  524  can be an FPGA configured with digital signal processing logic. 
       FIG. 6  depicts one embodiment of a Public Safety system architecture  600 . The plurality of DAUs  602  feed a plurality of DDUs  604  that in turn feed a plurality of DRUs  606  (which can also be referred to as remote units). In accordance with the present invention, a plurality of DAUs  602  are interconnected with a plurality of DDUs  604  that feed a plurality of DRUs  606 . As illustrated in  FIG. 6 , at RF Headend  1   608  there is a collocated a primary and secondary DAUs  610 . Similarly at TD  1   612  there is collocated a primary and secondary DDU  614 . The primary and secondary DDUs feed a plurality of DRUs  606 . The DRUs  606  are connected to antennas  616  that provide coverage to a fixed remote location. 
     The system illustrated in  FIG. 6  includes 3 RF Headend sites, 6 Tunnel Distribution (TD) sites, and Station Distribution (SD) equipment. In this configuration, 126 DRUs for tunnels coverage and 56 DRUs for station coverage are utilized. It should be noted that TD and SD equipment can be integrated with Headend sites. As illustrated, the unit count is redundant DAUs: 8; Digital Distribution Units: 32; and DRUs: 182. 
     The 3 RF Headend sites are fed by different base station resources. Referring to RF Headend  1   608 , a pair of redundant DAUs  610  are represented by Host- 1  and Host- 2 . The pair of redundant DAUs  610  provides a data stream  618  to multiple, redundant DDUs  614 , which are also arranged in pairs. Each pair of redundant DDUs  614  provides the data stream  618  to multiple DRUs. Thus, the single line between Host- 1  and DDU- 1   620  represents a set of four redundant lines connecting DAU- 1  and DAU- 2  to DDU- 1  and DDU- 2 . The single line between DDU- 1  and DDU- 2  to DRU-T 1   622  represents a set of two redundant lines connecting DDU- 1  and DDU- 2  to DRU-T 1 . Thus, the optical fibers illustrated in  FIG. 6  are exemplary and simplified and not intended to limit the number of connections provided between elements. In this implementation, TD  1   612  includes DDU 1 -DDU- 4 , TD  2  includes DDU- 5 -DDU- 8 , and the like. In  FIG. 6 , the set of DDUs, DDU- 1  and DDU- 2  feed DRU-T 1 -DRU-T 14 . The other Tunnel Distribution sites TD  2  through TD  24  provide data streams to DRU-T 15  through DRU-T 126 . 
       FIG. 7  depicts a Digital Public Safety system  700  that includes multiple cross connections between DAUs, DDUs and DRUs. The primary feed  118  and secondary feed  120  are networked via a cross connection between the DAUs  706 , a cross connection between the DDUs  708  (DDU 16 ) and a cross connection between the DRUs  710  (hd 37   s ). Redundancy in coverage is achieved by overlapping antenna radiation patterns  712 . The secondary units/elements  716  work in parallel, so that should any of the primary units/elements  714  fail, secondary units/elements  716  are ready to carry on the task with a minimum switchover time. Performance of the primary units/elements  714  and the secondary units/elements  716  is monitored and information is used by decision-making logic to automatically reconfigure system units/elements, if failure is detected. Cross connection between system units/elements provide an operational system resilient to simultaneous multi-point failures. As described more fully below, embodiments of the present invention provide redundancy at several levels, including multiple, redundant DAUs at the Main Headend  718 , multiple, redundant RF sections in each DAU, multiple, redundant DDUs at the Secondary Headend  720 , and the like. 
     Referring to  FIG. 7 , in the illustrated embodiment, the primary feed  118  and secondary feed  120  are split between multiple DAUs. As discussed in relation to  FIG. 1 , the primary DAU  722  and the secondary DAU  724  have redundant RF sections (for each band served), that enable reception of the primary feed  118  and the secondary feed  120  by the DAUs. The primary DAU  722  and the secondary DAU  724  are cross connected by cross connection  706  at the digital/baseband level. The primary DAU  722  provides content in a form of data stream to the secondary DAU  724 , and secondary DAU  724  provides content to the primary DAU. The primary DAU  722  and the secondary DAU  724  are cross connected  708  to a primary DDU  726  and a secondary DDU  728  as depicted in  FIG. 7 . The primary DDU  726  and the secondary DDU  728  are also use a cross connection between the DRUs  710 , DRU- 1   730  and a second DRU- 2   732 . The DRUs achieve redundancy by having overlapping antenna radiation patterns  712  with other DRUs. 
     The high service availability is achieved by 1:1 redundancy, which can also be considered as dual modular redundancy. Each element in the network (except DRU) has a secondary unit. Secondary units/elements  716  work in parallel, so that should any of the primary units/elements  714  fail, secondary unit(s) is/are ready to carry on the task with a minimum or reduced switchover time. Performance of the primary units/elements  714  and the secondary units/elements  716  is monitored and information used by decision making logic to automatically reconfigure system units/elements, if failure is detected. Cross connection between system units/network elements provide operational systems resilient to simultaneous multi-point failures. Some embodiments of the present invention provide system availability of up to and exceeding 99.999% availability, for example, in an implementation for 700 MHz Radio Systems. 
     As illustrated in  FIG. 7 , the primary DAU  722  receives, at the primary RF section (RF-P), the primary feed  118  from the splitter/combiner  734 . The primary DAU  722  also receives, at the secondary RF section (RF-S), the secondary feed  120  from a second splitter/combiner  736 . The splitter/combiner  734  and the second splitter/combiner  736  enable the primary feed  118  and the secondary feed  120  to be received at both the primary DAU  722  and the secondary DAU  724 . Both the primary feed  118  and the secondary feed  120  are processed in by a DSP unit in each of the DAUs. A first DSP unit  723  in the primary DAU  722  generates a primary data stream  738  and a second DSP unit  725  in the secondary DAU  724  generates a secondary data stream  740  and either the primary data stream  738  or the secondary data stream  740  is selected as discussed herein. In between the Main Headend  718  and the Secondary Headend  720 , as well as between the Secondary Headend  720  and the Tunnel/Station Distribution  742 , multiple optical fibers can carry either the primary feed  118  or the secondary feed  720  depending on whether the primary feed  118  or the secondary feed  120  is selected by the first DSP unit  723  in the primary DAU  722  and the second DSP unit  725  in the secondary DAU  724 . 
     Cross connection  706  of the DAUs at the digital level is provided as illustrated in  FIG. 7 . The first DSP unit  723  in the primary DAU  722  is connected to the second DSP unit  725  in the secondary DAU  724  and vice versa. The connection of the first DSP unit  723  and the second DSP unit  725  enables operation in the event of failure of both RF sections in one of the DAUs. As discussed in additional detail in relation to  FIG. 13 , if both RF sections in the primary DAU  722  fail, the primary feed  118  or secondary feed  120  received at the secondary DAU  724  can be delivered to the first DSP unit  723  of the primary DAU  722  through the cross connection  706  between the first DSP unit  723  and the second DSP unit  725 . As a result, failure of both RF sections in one of the DAUs can be compensated for through the cross connection  706  at the DSP unit level. 
     Referring to  FIGS. 7 and 13 , the cross connection  706  is implemented, in an embodiment, by connections from the primary DAU  722  to the secondary DAU  724  and from the secondary DAU  724  to the primary DAU  722 . As described herein, these are digital connections between the FPGA/DSP sections of the DAUs. Referring to  FIG. 13 , the connection between the first DAU and the second DAU is provided by primary data stream  1334  from the primary integrated DAU  1302  that is received by ASP 2   1333  in the second integrated DAU  1304 . The connection between the second DAU and the first DAU is provided by secondary data stream  1336  from the secondary integrated DAU  1304  that is received by ASP 2   1332  in the first integrated DAU  1302 . 
     Fiber redundancy between the Main Headend  718  and the Secondary Headend  720  is provided by embodiments of the present invention as illustrated in  FIG. 7 . For example, the primary DAU  722  outputs the primary data stream  738 . The primary DAU  722  can include a first digital optical output port connected to a first input port on the primary DDU  726  and a second digital optical output port connected to a first input port on the secondary DDU  728 . The secondary DAU  724  outputs the secondary data stream  740 . The secondary DAU can include a first digital optical output port connected to a second input port on the primary DDU  726  and a second digital optical output port connected to a second input port on the secondary DDU  728 . In the example configuration, the output from each DAU is transmitted on two fibers, one fiber connects a DAU to the primary DDU  726  and a second fiber connects the DAU to the secondary DDU  728 . In a default mode, for example no failures, the primary feed  118  is processed by the primary DAU  722  and the secondary DAU  724  and the primary data stream  738  and secondary data stream  740  both transmit data associated with the primary feed  118  providing redundancy for the primary feed  118 . In the default mode both DDUs then transmit the primary data stream  738  to the DRUs. 
     If one of the primary RF sections fails in a DAU, the DSP unit associated with the failed RF section can switch to provide the secondary feed  120  generated from the secondary RF section as the data stream. In the example embodiment, if the primary DDU  726  receives a primary data stream  738  and a secondary data stream  740  with different feeds, the logic in the DSP unit  727  of the primary DDU  726  can be configured to select a data stream to transmit to the DRUs based on one or more signal characteristics. 
     In  FIG. 7 , the dots below the DDUs  746  in the Secondary Headend and the dots below the DRUs  744  represent implementations in which additional DDUs and additional DRUs are utilized. Examples of such implementations were discussed previously in relation to  FIG. 6 . Examples would include implementations in which additional DRUs are provided in tunnels, additional bands are utilized, and the like. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
     In the system illustrated in  FIG. 7 , the set of DRUs, DRU- 1   730  and DRU- 2   732 , receive redundant digital data streams from the primary DDU  726  and the secondary DDU  728  using cross connection between the DRUs  710 . DRU- 1   730  includes a first input port coupled to a first output port of the primary DDU  726  and a second input port coupled to the first output port of the secondary DDU  728 . DRU- 2   732  includes a first input port coupled to a second output port of the primary DDU  726  and a second input port coupled to the second output port of the secondary DDU  728 . DRU- 1   730  and DRU- 2   732  process the digital data streams and provide RF signals using an RF output port to antennas A 1  and A 2  respectively. A 1  and A 2  are arranged such that their antenna coverage areas produce overlapping antenna radiation patterns  712 . Thus, redundancy is achieved through overlapping coverage, which enables the system cost to be reduced (for systems in which the number of remote units is much greater than the number of hosts and distribution units) in comparison with systems that would utilize redundant remotes. If one of the DRUs fails, then coverage in the area covered by the failed DRU will be provided by the other DRU. 
       FIG. 24  is a block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Public Safety Digital DAS architecture.  FIG. 24  illustrates a system  2400  configured to interface directly with a primary backhaul connection  2402  and a secondary backhaul connection  2404 . The system  2400  includes many of the features described in relation to  FIG. 7  that provide redundancy in a digital public safety system including cross connections between the DAUs, DDUs, and DRUs. Accordingly, the discussion provided in relation to  FIG. 7  is applicable to the system illustrated in  FIG. 24  as appropriate. System  2400  replaces the primary DAU and the secondary DAU with a primary baseband unit (BBU)  2406  and a secondary BBU  2408 . Each BBU includes a microprocessor section  2410  and a DSP unit  2412  to process the signals required to interface with the DDUs in the secondary headend  720  and the backhaul connections. The BBUs at the main headend  2410  include output ports that connect to the input ports on the DDUs at the secondary headend  720 . In some implementations, the BBU/DDU interface may use a standard such as OBSAI (Open Base Station Architecture Initiative), CPRI (Common Public Radio Interface) and/or ORI (Open Radio Interface). 
       FIG. 8  depicts an Analog Public Safety system that includes multiple cross connections between Main Hubs, Secondary Hubs and Remote Units (RUs). The primary feed  118  and secondary feed  120  are networked via a cross connection  802  between the main Hubs, a second cross connection  804  between the Expansion Hubs and a third cross connection  806  between the RUs (Remote Units). Redundancy in coverage is achieved by overlapping antenna radiation patterns  712 . The secondary units/elements  816  work in parallel, so that should any of the primary units/elements  814  fail, secondary unit(s) is/are ready to carry on the task with a minimum switchover time. Performance of the primary and secondary units/elements is monitored and this information is used by decision-making logic to automatically reconfigure system units/elements, if failure is detected. Cross connection between system units/elements provide operational systems resilient to simultaneous multi-point failures. As described more fully below, embodiments of the present invention provide redundancy at several levels, including multiple, redundant Main Hubs at the Main Headend  718 , multiple, redundant RF sections  848  and Optical Modules  850  in each Main Hub, multiple, redundant Expansion Hubs at the Secondary Headend  720 , multiple, redundant Optical modules  850  and Remote Unit Drive modules  852  in each Secondary Hub, and the like. 
     Referring to  FIG. 8 , in the illustrated embodiment, the primary feed  118  and the secondary feed  120  are split between multiple Main Hubs. The primary main hub  822  and the secondary Main Hub  824  have redundant RF sections  848  (for each band served), that enable reception of the primary feed  118  and the secondary feed  120  by the Main Hubs. The primary main hub  822  and the secondary Main Hub  824  are cross connected  804  to a primary expansion hub  826  and a secondary expansion Hub  828  over primary and secondary Optical Modules  850 , as depicted in  FIG. 8 . The primary expansion hub  826  and the secondary expansion Hub  828  are also cross connected  806  to multiple RUs, RU-A 1   830  and RU-A 2   832 , over primary and secondary Remote Unit Drive modules  852  in the Expansion Hubs and primary and secondary optical section  854  in the RU-A 1   830 . In another embodiment, the RU-A 2   832  optical front end is comprised of an optical switch  856  that performs selection between primary and secondary optical signals, and an optical section  854  that transfers the optical signal back to RF. The RUs achieve redundancy by having overlapping antenna radiation patterns  712  with other RUs. 
       FIG. 9  depicts a Public Safety System  900  that is fed by a combination of a Local BTS  902  and a remote BTS  904 . The remote BTS  904  is the secondary feed  120  for the Public Safety architecture. The interconnection between the DAUs and the DDUs  924  as well as between the DDUs  924  and the DRUs  926  demonstrates the 1:1 redundancy of the system  900 . To better illustrate the redundancy capability; any failure of either a BTS, a RF connection, a fiber, a DAU, a DDU or a DRU will be accommodated by re-routing the signals through alternative paths. 
     Referring to  FIG. 9 , redundancy of the feed is provided by a primary feed  118  from the above ground base station  902  and an off-air secondary feed  120  from the above ground tower  906 . Redundancy of the host units, for example DAUs, each with redundant RF sections, and cross connection at the digital level  908  is provided in the RF Headend  1   910 . TD- 1   912  provides a set of redundant distribution units fed with dual fiber link, thereby providing fiber link redundancy. Redundancy at the remote locations is provided by DRUs fed with dual fiber link, adding additional fiber link redundancy. 
     Referring to  FIG. 9 , two different feeds are utilized for the primary feed  118  and the secondary feed  120 : a base station  902  feed and off-air directional antenna  914  pickup from a macro tower  906 . Because of the differing nature of the feeds, different types of RF sections are utilized as illustrated in the integrated DAU  300  in  FIG. 3 . The DSPs of the primary integrated DAU  916  and the secondary integrated DAU  918  are interconnected as discussed in relation to  FIG. 7 . 
     Primary and secondary optical fibers  920  carry the data streams from the primary integrated DAU  916  and the secondary integrated DAU  920  in the RF Headend  1   910  to the DDUs in the secondary headend TD- 1   912 . In this implementation, the primary optical fibers  922  from the primary integrated DAU  916  connect to four DDUs  924  in TD- 1   912 . The DDUs  924  then replicate the data streams and deliver or rebroadcast them to the 28 DRUs  926 . 
     In the embodiment illustrated in  FIG. 9 , the secondary feed  120  is provided to the primary integrated DAU  916  and the secondary integrated DAU  918 . Due to the mixed signal type feed in this embodiment (e.g., from the Base station and/or from off-air) the Host unit will have two types of RF modules. As illustrated in  FIG. 3 , for the off-air feed, the integrated DAU unit will have an RF module with a power amplifier and a low noise amplifier. For the Base Station feed, the integrated DAU unit will have an RF module without the PA and LNA. 
       FIG. 10  depicts a Public Safety System  1000  that is fed by a combination of two Local BTSs. The secondary BTS  1002  is in hot swappable standby mode. Redundancy is provided at the base station level (set of redundant BTSs  1002 ,  1004 ), at the Headend  1010  level (set of redundant host units, primary DAU  1006  and DAU  1008 , each with redundant RF sections and cross connection at the digital level), at the secondary headend  1012  level (redundant distribution units, DDU  924 , fed with dual fiber link=&gt;fiber link redundancy), and at the remote level (DRU  926 , fed with dual fiber link=&gt;fiber link redundancy). Since the feeds are provided from base stations, the host units can both be a local DAU  100  as illustrated in  FIG. 1 . 
       FIG. 11  depicts a Public Safety System  1100  that is fed by off-air signals  1102  from a combination of two remote BTSs. Redundancy is provided in a manner similar to that discussed in relation to  FIG. 10 . Redundant donor directional antennas  1104  pointing to different donor sites receive RF signals. Redundant host units  1106 ,  1108  as illustrated by repeater DAU  200  in  FIG. 2 , each with redundant RF sections, and cross connection at digital level, receive the RF signals and utilize the integrated repeater function to amplify the received RF signals. Redundant distribution units, DDU  924 , fed with dual fiber link provide fiber link redundancy. Redundancy at the remote units, DRU  926 , is provided by feeding the remote units with a dual fiber link to provide additional fiber link redundancy. 
       FIG. 12  depicts a Public Safety System  1200  utilizing a primary DRU  1202  and hot swappable secondary DRU  1204 . In the redundant system illustrated in  FIG. 7 , each of the system elements is implemented in a redundant manner: Main Headend with redundant hosts; Secondary Headend with redundant DDUs; and Tunnel/Station Distribution with DRUs having overlapping coverage areas to provide redundancy at the DRUs.  FIG. 12  illustrates another possible implementation in which, rather than utilizing overlapping coverage areas, a redundant secondary DRU  1204  is utilized at the remote level to provide redundancy. 
     In the embodiment illustrated in  FIG. 12 , redundancy is provided in situations, for example, applications that emphasize backup protection, in which the benefit provided by redundant DRUs outweighs the additional system cost associated with the redundant DRUs. In this implementation, 1:1 redundancy is provided in a hot standby mode. In default operation, the secondary DRU  1204  is active, but it is not processing the signal received by the primary DRU  1202 . Additional description of this operation is provided in relation to  FIG. 17 . 
     According to embodiments of the present invention, architectures including a variation of a Dual Modular Redundancy (DMR) are utilized in which duplicated elements work in parallel, so that should any of the system elements/components fail, another element/component is ready to carry on system tasks with a reduced or minimum switchover time. Embodiments of the present invention utilize Active Redundancy systems in which performance of the key elements is monitored and information is used by decision-making logic to automatically reconfigure the system components if failure is detected. 
       FIG. 13  is a block diagram of a public safety system  1300  illustrating feed and host redundancy according to an embodiment of the present invention. The primary feed  118  and secondary feed  120  are delivered to the primary integrated DAU  1302  and the secondary integrated DAU  1304  via a splitter/combiner  1306  such that they are fed to a redundant RF section  1308  in the primary integrated DAU  1302  and a second redundant RF section  1310  in the secondary integrated DAU  1304 . As illustrated in  FIG. 13 , both primary integrated DAU  1302  and secondary integrated DAU  1304  have both primary and secondary RF sections at one or more bands (e.g., 700 band and 800 band). In some embodiments, the primary integrated DAU  1302  and/or the secondary integrated DAU  1304  are quad-band units, providing primary and secondary RF sections at two bands. Thus, the primary feed  118  is provided to primary RF section  1320  and secondary RF section  1313  and the secondary feed  120  is provided to primary RF section  1311  and secondary RF section  1322 . Both of the primary feed  118  and secondary feed  120  are translated into the digital domain and processed inside the DSP Unit  1312  in each of the DAUs. The primary integrated DAU  1302  utilizes the digital signal processing functionality provided by the DSP Unit  1312  to implement two decision points: monitoring and/or selection of primary feed  118  or secondary feed  120  provided by the primary BTS  1314  or the secondary source  1316 , and monitoring and/or selection of a primary/secondary feed from the secondary integrated DAU  1304  received over a fiber connecting the DAUs  1318  (e.g., the secondary integrated DAU  1304 ) in case the primary feed  118  or the secondary feed  120  is not available due to primary host failure. One of skill in the art will understand that the fiber connecting the DAUs  1318  corresponds to cross connection  706  in  FIG. 7 . 
     In default operation, considering the primary host (primary integrated DAU  1302 ), both the primary feed  118  processed by the primary RF section  1320  and the secondary feed  120  processed by the secondary RF section  1322  are converted to digitals signals using the ADCs  1324  and presented to Automated Selection Point  1   a  (ASP 1   a )  1326 . The switch represented by the logic implementing ASP 1   a    1326  is set such that the digital signal associated with the primary feed  118  is passed through ASP 1   a    1326  by default. The digital signal passed by ASP 1   a    1326  is then combined with the optional digital signal passed through a second ASP 1   b    1328  receiving digital signals at the optional 800 MHz band. Thus, ASP 1  logic is provided for each band that is implemented in the hosts. 
     A splitter  1330  is utilized to provide a copy of the combined signal, local data stream  1334 , to Automated Selection Point  2  (ASP 2 )  1333  of the secondary integrated DAU  1304 . If the combined signal provided by ASP 2   1332  of the primary integrated DAU  1302  is suitable for broadcast, the switch represented by the logic implementing ASP 2   1332  passes the combined signal for delivery to the DDUs. Similar operation is carried out concurrently or simultaneously in the secondary integrated DAU  1304 , which also receives the primary feed  118  and the secondary feed  120 . Modifications from default operation are also provided by embodiments of the present invention. 
     At the first decision point, an Automated Selection Point  1   a  (ASP 1   a )  1326  passes the primary feed  118  (signal) or switches to the secondary feed  120  (signal) output by the secondary RF section  1322  if loss of primary feed  118  (signal) is detected (e.g., which could result from primary BTS  1314  or primary RF section  1320  failure). Thus, measurements of the digital signals output by the ADCs  1324  coupled to each of the primary RF section  1320  and the secondary RF section  1322  made at the ASP 1   a    1326  enable ASP 1   a    1326  to pass the primary feed  118  (signal) as a default or switch to the secondary feed  120  (signal) if the quality of the primary feed  118  (signal) is below a threshold. Thus, if the performance of the primary feed is below a threshold, then ASP 1   a  can switch to the secondary feed, which can then be passed to splitter  1330 . 
     At the second decision point, a second Automated Selection Point (ASP 2 )  1332  passes the local data stream  1334  or switches to an external data stream  1336  provided by a secondary host (secondary integrated DAU  1304 ) if loss of the local data stream  1334  is detected (e.g., which could result, for instance, from both RF sections or ADC/DAC circuit failure). In an embodiment, ASP 2   1332  will pass the local data stream  1334  as a default. 
     In an embodiment, if failure (e.g., performance below a threshold) of both primary RF section  1320  and second RF section  1322  occurs, resulting in loss of output from ASP 1   a    1326  (assuming no signal at the second band), no signal will be received at splitter  1330 . In this embodiment, ASP 2   1332  will thus select the external data stream  1336  for rebroadcasting if the quality of the local data stream  1334  is below a threshold. The external data stream  1336  is an output of ASP 1   a    1327  in the secondary integrated DAU  1304 . Thus, digital content from the secondary integrated DAU  1304  is delivered as external data stream  1336  to ASP 2   1332  in the primary integrated DAU  1302 , and, in turn, to primary fibers  1338 . The primary fibers are connected to one or more digital optical output ports  1348 . The one or more digital optical output ports include a first digital optical output port connected to a primary DDU and a second digital optical output port connected to a secondary DDU. 
     Accordingly, digital cross connection between the RF sections of the DAUs is provided by embodiments as previously discussed in relation to  FIG. 7 . As a result, the system  1300  is able to maintain the signal on both the primary fibers  1338  and secondary fibers  1340  to the primary and secondary DDUs respectively. Thus, embodiments of the present invention enable operational signals on either or both primary fibers  1338  and secondary fibers  1340  to be maintained, even in the event of failure of the RF sections and/or DSP unit in either the primary integrated DAU  1302  or the secondary integrated DAU  1304 . In some implementations, the ASP 1   a    1326  or ASP 1   b    1328  or ASP 2   1332  switching time is less than a few seconds, for example, less than 2 sec. 
     In  FIG. 13 , the 800 MHz band is illustrated as optional. If the 800 MHz band is utilized, the DSP unit  1312  receives primary and secondary data streams for both bands from the primary and secondary RF sections associated with each band. In the illustrated embodiment, the DSP unit  1312  receives a primary 800 MHz data stream  1342  and a secondary 800 MHz data stream  1344 . The 800 MHz band includes the second Automated Selection Point  1  (ASP 1   b )  1328  that passes the primary 800 MHz data stream  1342  or switches to the secondary 800 MHz data stream  1344  output by the secondary RF section  1346  if loss of the primary data stream  1342  at the 800 MHz band is detected. Data streams representing different bands are aggregated and then delivered to the second Automated Selection Point (ASP 2 )  1332  that passes the local data stream  1334  or switches to an external data stream  1336  provided by a secondary host (secondary integrated DAU  1304 ) if loss of the local data stream  1334  is detected. 
     In both the primary integrated DAU  1302  and the secondary integrated DAU  1304 , the primary and secondary streams are provided to the DSP unit  1312 . If the primary integrated DAU  1302  fails such that the redundant RF section  1308  has failed and the primary integrated DAU  1302  loses both data streams, the system  1300  can provide self-healing. The system  1300  can use the data stream produced by the DSP unit  1312  in the secondary integrated DAU  1304  (e.g., the primary RF Section data stream) and can deliver this data stream to the DSP unit  1312  in the primary integrated DAU  1302 . The system can transmit the data stream to the primary DDUs after passing the data stream through ASP 2   1332  in the DSP unit  1312  in the primary integrated DAU  1302 . The same data stream will be provided by the second integrated DAU  1304  to the secondary DDUs. Accordingly, both the primary and secondary data streams can be maintained on the fiber connecting the DAUs  1318  (Main Headend) and the DDU units (Secondary Headend). If the primary data stream is produced by the DSP unit  1312  in the secondary integrated DAU  1304 , then this primary data stream is provided to the DSP unit  1312  in the primary integrated DAU  1302  for transmission to the Secondary Headend. If the secondary data stream is produced by the DSP unit  1312  in the secondary integrated DAU  1304 , then this secondary data stream is provided to the DSP unit  1312  in the primary integrated DAU  1302  for transmission to the Secondary Headend. It should be noted that the discussion provided in relation to the operation of primary integrated DAU  1302  is applicable to secondary integrated DAU  1304  as appropriate. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
     All of the components in  FIG. 13  may be active and operating in parallel to provide redundancy. The ASP points can be rerouting signals based on monitoring conditions of the system. ASP points can be monitoring any data associated with the digital domain. In addition to monitoring the power of the digital signals, the I/Q content of the signal can be analyzed to determine the quality of the primary feed  118  and/or the secondary feed  120 . Thus, monitoring and analysis of the feeds is not limited to complete loss of signal (e.g., cutting of primary feed  118 ), but can include metrics related to the quality of the signals. 
       FIG. 20  is a block diagram illustrating uplink redundancy according to one embodiment of the present invention showing the basic structure of a full redundancy digital DAS architecture. Multiple uplink primary data streams are received on the primary fibers  1338  and secondary fibers  1340  from the primary and secondary DDUs, respectively. In the illustrated embodiment, the uplink data streams received at the primary integrated DAU  1302  from multiple DDUs include a primary data stream carrying the primary uplink feed for the 700 MHz Band, P 1 P  2002 ; a primary data stream carrying the secondary uplink feed for the 700 MHz Band, P 1 S  2004 ; a primary data stream carrying the primary uplink feed for the 800 MHz Band, P 2 P  2006 ; and a primary data stream carrying the secondary uplink feed for the 800 MHz Band, P 2 S  2008 . Further, the uplink data streams received at the secondary integrated DAU  1304  from multiple DDUs include a secondary data stream carrying the primary uplink feed for the 700 MHz Band, S 1 P  2010 ; a secondary data stream carrying the secondary uplink feed for the 700 MHz Band, S 1 S  2012 ; a secondary data stream carrying the primary uplink feed for the 800 MHz Band, S 2 P  2014 ; and a secondary data stream carrying the secondary uplink feed for the 800 MHz Band, S 2 S  2016 . 
     DSP Unit  1312  is configured to implement ASP 1   c    2018 . ASP 1   c    2018  passes a data stream carrying the primary uplink feed by default (P 1 P  2002 , P 2 P  2006 , S 1 P  2010 , S 2 P  2014 ). ASP 1   c    2018  can be configured to monitor the data stream carrying the primary uplink feed and switch to a data stream carrying the secondary uplink feed (P 1 S  2004 , P 2 S  2008 , S 1 S  2012 , S 2 S  2016 ) if loss of primary uplink feed is detected (primary optical path loss, or primary hdDDU failure) The outputs of ASP 1   c  can be summed  2024  to create a local uplink data stream  2020  and passed to ASP 2   b    2022 . 
     The local uplink data stream  2020  is split by the DSP unit  1312  at ASP 2   b    2022  and a copy of the local uplink data stream  2020  is transmitted to the secondary integrated DAU  1304 . ASP 2   b    2022  can include logic that monitors the local uplink data stream  2020  and controls the output using a switch. If a characteristic of the local uplink data stream  2020  does not meet a signal or data stream threshold, ASP 2   b    2022  can select a backup uplink data stream  2026  from the secondary integrated DAU  1304 . In some embodiments, ASP 2   b    2022  can receive data related to the integrity of the local uplink data stream  2020  from ASP 1   c    2018 . The uplink data stream output from ASP 2   b    2022  is delivered to the appropriate RF section by a splitter/combiner  2028 . The uplink data stream is further split at ASP 1   a    1326  and ASP 1   b    1328  and transmitted to both the 700 MHz primary RF section  1320  and the 700 MHz secondary RF section  1322  and the 800 MHz primary RF section  1345  and the 800 MHz secondary RF section  1346  respectively. In some implementations, ASP 1   a    1326  may receive a status for the redundant RF section and select an RF section to receive the upstream signal using a switch. The RF Switch (RF SW-PP)  2030  passes a primary RF signal from the primary integrated DAU  1302 , or switches to an RF signal from the secondary primary integrated DAU  1304  if the primary RF signal is lost. RF SW-SP  2032  passes a primary RF signal from the secondary integrated DAU  1304 , or switches to a secondary RF signal from the primary integrated DAU  1302  if the primary RF signal is lost. Both RF switches RF signal is deliver the RF signal to the associated Base Station. 
       FIG. 14  is a block diagram illustrating DDU  400  fiber (feed) redundancy and aggregation capability according to an embodiment of the present invention. In the default mode of operation, the digital distribution unit (DDU)  400  receives the primary digital data stream  418  and the secondary digital data stream  420  from the primary host unit (primary DAU  402 ) and the secondary host unit (Secondary DAU  404 ) located at the Main Headend  410  location, which can be referred to as the primary data stream  418  and the secondary data stream  420 . A main Automated Selection Point  3   a  (ASP 3   a )  1402  passes the primary data stream  418  by default or switches to the secondary data stream  420  if loss of the primary data stream  418  is detected (e.g., which could result from the primary host (primary DAU  402 ) failing or failure of the primary fiber optic cable  1406  connecting the host and the DDU). 
       FIG. 14  illustrates local content represented by a primary local data stream  422  and a secondary local data stream  424  from a Local Headend  412 . Thus, the DDU  1400  has the capability to receive and aggregate local content converted to a digital data stream (for example, at the 700 MHz or the 800 MHz bands). If local content is present, for example, from a separate municipality represented by the local headend, then a local ASP 3   b    1404  receives the data streams at small form factor port (SFP)  3  and SFP 4  and passes the primary local data stream  422  by default or switches to the secondary local data stream  424  if loss (e.g., operation below a threshold) of the primary local data stream  422  is detected. A combiner  1408  sums the data streams provided by the main ASP 3   a    1402  and/or the local ASP 3   b    1404  for delivery of aggregated data to the DRUs. 
     It should be noted that in the implementation illustrated in  FIG. 14 , both the primary and secondary DDUs have similar functionality. The processing conducted inside the DSP unit  1412  in the DDUs can be remotely updated/reconfigured. The ASP points are rerouting signals based on monitoring conditions of the system. ASP points can be monitoring any data associated with the digital domain. In addition to monitoring the quality of the digital data streams, the I/Q content associated with the signal can be analyzed to determine the quality of the primary feed  118  and the secondary feed  120 . The logic implementing ASP 3  can provide switching times in millisecond range. 
       FIG. 21  is a block diagram illustrating DDU uplink signal redundancy to the main headend and the local headend feed. The DDU  1400  receives an uplink digital data stream generated by DRUs over a plurality of fiber optic connections  2102  connected to a plurality of input ports  2104 . The plurality of input ports  2104  are coupled to the DSP unit  1412 . In some embodiments, the DSP unit  1412  can include logic that processes the uplink digital data stream generated by the DRUs. The DSP unit  1412  includes a summer  2106  that combines the uplink digital data streams coming from multiple DRUs. Next, the DSP Unit  1412  delivers the uplink digital data stream to a splitter  2108  that separates the uplink digital data stream into two signals, a first uplink digital data stream  2110  for the main headend  410  and a second uplink digital data stream  2112  for the local headend  412 . The main ASP 3   a    1402  splits the first uplink digital data stream  2110  for simultaneous transmission over the primary optical path  2114  and the secondary optical path  2116  to the Main Headend. Local ASP 3   b    1404  splits the second uplink digital data stream  2112  for simultaneous transmission over the primary optical path  2118  and the secondary optical path  2120  to the local headend  412 . 
       FIG. 15  is a block diagram illustrating fiber to remote redundancy according to an embodiment of the present invention.  FIG. 15  illustrates elements of the digital remote unit (DRU)  1500  and redundancy provided at the DRU. The DRU  1500  receives the primary digital data stream  520  and the secondary digital data stream  522  from the digital distribution units primary DDU  510  and secondary DDU  512 . The primary digital data stream  520  and the secondary digital data stream  522  are received at a primary optical port  1512  and a secondary optical port  1514  respectively. An Automated Selection Point  4   a  (ASP 4   a )  1502  passes the primary digital data stream  520  or switches to the secondary digital data stream  522  if loss of primary digital data signal is detected (which could result, for example, from failure of the primary DDU  510  or the primary fiber optic cable  1504  failing). Similar processing can be performed for optional bands that are utilized as well as summing as appropriate. The RF sections  1530  translate the digital signal to the analog domain for subsequent broadcast through the broadcast media, including a leaky coaxial cable or a station antenna, after multiplexing as appropriate. 
     Implementation of the DSP unit  1524  using an FPGA enables the processing conducted by the DSP unit  1524  to be remotely updated/reconfigured as appropriate. The ASP points are rerouting signals based on monitoring conditions of the system. ASP points can be monitoring any data associated with the digital domain. In addition to monitoring the quality of the digital data streams, the I/Q content associated with the signal can be analyzed to determine the quality of the primary feed  118  and the secondary feed  120 . Additionally, switching times for the ASP 4   a    1502  in the DRU  1500  are on the order of the millisecond range. 
     In  FIG. 15  optional primary and secondary data streams  1506  at a second (e.g., 800 MHz) band are illustrated. Thus, the DRU  1500  has the capability to receive and aggregate content at different bands (for example, at the 700 MHz or the 800 MHz bands). If the optional band is present, for example, from a separate municipality, then a second ASP 4   b    1510  receives the data streams at SFP 3  and SFP 4  and passes the primary data stream in the optional band or switches to the secondary data stream in the optional band if loss of the primary data stream in the optional band is detected. A combiner  1508  sums the data streams provided by the main ASP 4   a    1502  and/or optional band second ASP 4   b    1510  for production of aggregated data at the DRUs. 
       FIG. 16  is a block diagram illustrating redundancy at a remote unit, DRU  1500 , through local aggregation according to an embodiment of the present invention.  FIG. 16  shares similarities with  FIG. 15  and description provided in relation to  FIG. 15  is applicable to  FIG. 16  as appropriate. The DRU  1500  has ability to receive and aggregate local content converted to a digital data stream  1602  (for example, at the 700 MHz or the 800 MHz bands). Thus, the DRU  1500  provides an alternative approach for local content aggregation that can supplement or be utilized in place of local content aggregation that is performed at the DDU. Implementation of the DSP unit  1524  using an FPGA enables the processing conducted by the DSP unit  1524  to be remotely updated/reconfigured as appropriate. 
       FIG. 16  illustrates local content represented by a primary local data stream  1610  and a secondary local data stream  1612  from a Local Headend  1608 . Thus, the DRU  1500  has the capability to receive and aggregate local content converted to a digital data stream  1602  (for example, at the 700 MHz or the 800 MHz bands). If local content is present, for example, from a separate municipality, then the second ASP 4   b    1510  receives the data streams at SFP 3  and SFP 4  and passes the primary local data stream  1610  or switches to the secondary local data stream  1612  if loss of the primary local data stream  1612  is detected. A combiner  1508  sums the data streams provided by the main ASP 4   a    1502  and/or the local second ASP 4   b    1510  for production of aggregated data at the DRUs. 
       FIG. 22  is a block diagram illustrating DRU uplink signal redundancy to a primary DDU, a secondary DDU and a local headend. DRU  1500  receives RF signals from an antenna  2202 . Signals are processed inside band/channel dedicated RF sections  1530 , and then translated to baseband and transmitted to analog to digital converters (ADCs)  2204 . The ADCs  2204  convert the baseband signals to an uplink digital data stream and are coupled to the DSP unit  1524 . The DSP unit  1524  sums  2206  the uplink digital data streams coming from the ADCs  2204  coupled to the DSP Unit  1524 . Next, the DSP Unit  1524  delivers the summed uplink digital data streams  2214  to a splitter  2208  that separates the summed uplink digital data streams into two signals, a first uplink digital data stream  2210  for the DDUs and a second uplink digital data stream  2212  for the local headend  1608 . The first ASP 4   a    1502  splits the first uplink digital data stream  2210  for simultaneous transmission over the primary optical path  2216  to the primary DDU  510  and the secondary optical path  2218  to the secondary DDU  512 . The Second ASP 3   b    1510  splits the second uplink digital data stream  2212  for simultaneous transmission over the primary optical path  2220  and the secondary optical path  2222  to the local headend  1608 . 
       FIG. 17  is a block diagram illustrating redundancy utilizing multiple DRUs according to an embodiment of the present invention. As described below, a redundant DRU  1704  is implemented with integrated dual optical bypass switches  1706  and RF bypass switches  1708 . In some implementations, the optical bypass switches may be replaced with optical splitters/combiners. As an alternative to substantially overlapping antenna coverage areas as illustrated in  FIG. 7 , the implementation illustrated in  FIG. 17  provides redundant DRUs for applications in which the additional cost of the redundant DRU  1704  is justified by the additional backup protection provided by the use of the redundant DRU  1704 . It should be noted that combinations of the architectures in  FIGS. 7 and 17  can be implemented in which redundant DRUs are utilized in conjunction with overlapping antenna coverage areas. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
     As illustrated in  FIG. 17 , the primary DRU  1702  receives the primary data stream  520  and the secondary data stream  522  from a primary DDU  510  and a second DDU  512 . In default mode, the primary data stream  520  is processed through the DSP unit  1524  in the primary DRU  1702 , converted to an RF signal in the RF section  1710  of the primary DRU  1702 , and broadcast through leaky coaxial cable or a station antenna  1712 . During normal operation, the secondary DRU  1704  is active, but does not receive the primary data stream  520  and the secondary data stream  522 , which are delivered to the primary DRU  1702  by the optical bypass switches (OBSs)  1706 . During normal operation, the primary DRU  1702  monitors the primary data stream  520  and the secondary data stream  522 , operating using the primary data stream  520  as a default in some implementations. If the primary data stream  520  fails, then the primary DRU  1702  can switch to using the secondary data stream  522  as discussed in relation to ASP 4   a    1502  of the primary DRU  1702  as discussed in relation to  FIGS. 15 and 16 . 
     In the event that the primary DRU  1702  fails, the OBSs  1706  and the RF bypass switch (RFBS)  1708  will shift to the bypass position. The OBSs  1706  in this bypass position will switch to redirect and/or deliver the primary data stream  520  and the secondary data stream  522  to the secondary DRU  1704 , which receives them at input ports  1714  coupled to the automatic selection point  4   a  (ASP 4   a )  1502  of the secondary DRU  1704 . In the embodiment illustrated in  FIG. 17 , the OBSs  1706  are integrated into the primary DRU  1702  along with the RFBS  1708 . The secondary DRU RF output  1716  is provided to RFBS  1708 , which, in the bypass position, outputs the RF signal received from the secondary DRU  1704  rather than the primary DRU RF output  1720  from the multiplexer  1718  of the primary DRU  1702 . As a result, the secondary DRU RF output  1716  is directed to leaky coaxial cable or a station antenna  1712  or other suitable broadcast equipment. Thus, in this mode of operation, the optical signals will be delivered to the input ports  1714  of the secondary DRU  1704  and the RF signal from the secondary DRU  1704  will be delivered to the leaky coaxial cable or station antenna  1712 . 
       FIG. 23  is a block diagram illustrating uplink signal redundancy from dual redundant DRUs to a primary DDU and a secondary DDU. Primary DRU  1702  receives RF signals from an antenna  2302 . If the primary DRU  1702  is operational, the uplink signals are processed as discussed in relation to DRU  1500  in  FIG. 22 . If the primary DRU  1702  fails, RFBS  1708  and the OBSs  1706  will switch to the bypass position and the uplink signals will shift to the secondary DRU  1704 . 
       FIG. 18  is a simplified block diagram according to one embodiment of the invention showing the basic structure of a full redundancy Digital Public Safety Digital DAS architecture  1800 . As illustrated in  FIG. 18 , the architecture  1800  shares some similarities with  FIG. 7 , the description of which is applicable to  FIG. 18  as appropriate. The primary feed  118  and the secondary feed  120  are split between multiple hosts. 
     Fiber redundancy between the Main Headend  1802  and the Secondary Headend  1804  is provided by a first fiber connection  1806  between the primary host  1812  and the primary DDU  1814  as well as a second fiber connection  1808  between the secondary host  1816  and the secondary DDU  1818 . For redundancy, a third fiber connection  1810  between the primary DDU  1814  and the secondary DDU  1818  is provided. In case of failure of the primary DDU  1814 , the primary/secondary stream provided by the host units will be transmitted from the DSP block  1820  of the functioning DDU to the DSP block  1820  of the failed DDU. 
     In a similar manner, redundancy at the tunnel/station distribution  1822  is provided by a fourth fiber connection  1824  between the primary DDU  1814  and the primary DRU  1826 , a fifth fiber connection  1828  between the secondary DDU  1818  and the secondary DRU  1830 , and a fiber connection between the DSP block  1820  of the primary and secondary DRUs. In case of failure of one of the DRUs, the signal from the working DRU can be routed to the failed DRU for broadcast through the antenna of the failed DRU. 
       FIG. 19  is a simplified flowchart illustrating a method for selecting a primary or secondary feed according to an embodiment of the present invention. As an example, the method can include processing RF signals at a DAU. First, the DAU receives a primary RF signal and a secondary RF signal ( 1902 ). The primary and secondary RF signals may be received from a local BTS or a remote BTS over a wired or wireless connection. In some implementations, the RF signal may be received over the air from a remote BTS. Next, the DAU will translate the primary and the secondary RF signals to the digital domain ( 1904 ). In some implementations, the DAU may use an FPGA to implement an ADC. In other implementations, the DAU may use a separate ADC to translate the primary and secondary RF signals to the digital domain. The DAU receives the primary RF signal as a digital primary feed and the secondary RF signal as a secondary digital feed at an automated selection point  1   a  (ASP 1   a ) ( 1906 ). 
     In some implementations, ASP 1   a  will output the primary feed by default. ASP 1   a  will determine if the primary feed is above a threshold value ( 1908 ). The ASP 1   a  can monitor digital signal characteristics or analyze the digitized RF signal to determine a threshold value. ASP 1   a  outputs the primary feed if it is above the threshold value ( 1912 ). If the primary feed is below a threshold value, ASP 1   a  will output the secondary feed ( 1910 ). Next, the output from ASP 1   a  is combined with other frequency bands present at the DAU ( 1914 ). 
     The combined output can be transmitted to a secondary DAU and a second ASP, ASP 2  ( 1916 ). The DAU receives a secondary DAU feed at ASP  2  ( 1918 ) and ASP 2  determines if the primary feed is still above a threshold value ( 1920 ). If the primary feed is above a threshold value, ASP 2  outputs the primary feed ( 1922 ) for transmission using an optical port. If ASP 2  determines the primary is below a threshold value, ASP 2  outputs the secondary DAU feed ( 1924 ) for transmission using an optical port. 
     It should be appreciated that the specific steps illustrated in  FIG. 19  provide a particular method of selecting a primary or secondary feed according to an embodiment of the present invention. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in  FIG. 19  may include multiple sub-steps that may be performed in various sequences as appropriate to the individual step. Furthermore, additional steps may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives. 
       FIG. 25  is a block diagram according to one embodiment of the present invention showing the basic structure of a full redundancy digital DAS architecture  2500 . The architecture  2500  includes an RF Headend  2538  that is fed by a combination of a 700 MHz Band BTS  2502  and an 800 MHz Band BTS  2504 . The 700 MHz Band BTS  2502  outputs a 700 MHz feed  2516  to a splitter/combiner  2506 . The 800 MHz Band BTS  2504  outputs an 800 MHz feed  2518  to a second splitter/combiner  2520 . The splitter/combiner elements create a primary feed and a secondary feed for each frequency and is coupled to four DAUs, a 700 MHz primary DAU  2508 , a 700 MHz secondary DAU  2510 , an 800 MHz primary DAU  2512 , and an 800 MHz secondary DAU  2514 . 
     The 700 MHz primary feed  2522  is received at an input port on the 700 MHz primary DAU  2508 . As described above, the DAU creates a primary digital data stream that includes the 700 MHz primary feed  2522 . The 700 MHz primary DAU  2508  also receives a primary digital data stream from the 800 MHz primary DAU  2512  over a first optical fiber connection  2530 . The 700 MHz primary DAU  2508  combines the digital data streams as discussed above in  FIG. 13  and transmits a primary digital data stream over optical fiber connections  2534  to a plurality of DRUs  2536 . The 700 MHz secondary feed  2524  is received at an input port on the 700 MHz secondary DAU  2510 . As described above, the DAU creates a secondary digital data stream that includes the 700 MHz secondary feed  2524 . The 700 MHz secondary DAU  2510  also receives a secondary digital data stream from the 800 MHz secondary DAU  2514  over a second optical fiber connection  2532 . The 700 MHz secondary DAU  2510  combines the digital data streams as discussed above in  FIG. 13  and transmits a secondary digital data stream over optical fiber connections  2534  to the plurality of DRUs  2536 . 
     It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. 
     Table 1 is a glossary of terms used herein, including acronyms. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Glossary of Terms 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 ADC 
                 Analog to Digital Converter 
               
               
                 BTS 
                 Base Transceiver Station 
               
               
                 CDMA 
                 Code Division Multiple Access 
               
               
                 CWDM 
                 Coarse Wave Division Multiplexing 
               
               
                 DAU 
                 Digital Access Unit 
               
               
                 DDC 
                 Digital Down Converter 
               
               
                 DDU 
                 Digital Distribution Unit 
               
               
                 DNC 
                 Down Converter 
               
               
                 DRU 
                 Digital Remote Unit 
               
               
                 DSP 
                 Digital Signal Processing 
               
               
                 DUC 
                 Digital Up Converter 
               
               
                 DWDM 
                 Dense Wave Division Multiplexing 
               
               
                 FPGA 
                 Field-Programmable Gate Array 
               
               
                 PA 
                 Power Amplifier 
               
               
                 RF 
                 Radio Frequency 
               
               
                 RRH 
                 Remote Radio Head 
               
               
                 RRU 
                 Remote Radio Head Unit 
               
               
                 UMTS 
                 Universal Mobile Telecommunications System 
               
               
                 WCDMA 
                 Wideband Code Division Multiple Access 
               
               
                 WLAN 
                 Wireless Local Area Network