Abstract:
The present disclosure is a novel utility of a software defined radio (SDR) based Distributed Antenna System (DAS) that is field reconfigurable and support multi-modulation schemes (modulation-independent), multi-carriers, multi-frequency bands and multi-channels. More specifically, the present invention relates to a DAS utilizing one or more Daisy-Chained Rings of Remote Units. The present invention enables a high degree of flexibility to manage, control, enhance, facilitate the usage and performance of a distributed wireless network such as Flexible Simulcast, automatic traffic load-balancing, network and radio resource optimization, network calibration, autonomous/assisted commissioning, carrier pooling, automatic frequency selection, frequency carrier placement, traffic monitoring, traffic tagging, pilot beacon, etc. As a result, a DAS in accordance with the present invention can increase the efficiency and traffic capacity of the operators&#39; wireless network.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Patent Application Ser. No. 61/439,940, filed on Feb. 7, 2011, entitled DAISY CHAINED RING OF REMOTE UNITS FOR A DISTRIBUTED ANTENNA SYSTEM, which is hereby incorporated by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to wireless communication systems employing Distributed Antenna Systems (DAS) as part of a distributed wireless network. More specifically, the present invention relates to a DAS utilizing one or more remotely monitored and controlled digital access units configured to assign particular packet transmissions to selected ones of a plurality of remote units, which can in some embodiments be configured in a daisy-chained rings. 
     BACKGROUND OF THE INVENTION 
     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. One of the most difficult challenges faced by network operators is maximizing the capacity of their DAS networks while ensuring cost-effective DAS deployments and at the same time providing a very high degree of DAS remote unit availability. 
     In order to provide DAS network capacity which is high enough to meet short-term needs of network subscribers in specific locations yet also avoid costly and inefficient deployment of radio resources, DAS network planners prefer to employ DAS architectures and solutions which provide a high degree of dynamic flexibility. Therefore, it would be advantageous for wireless network operators to employ a DAS solution which has a high degree of flexibility to implement dynamic rearrangements based on ever-changing network conditions and subscriber needs. Also, the more future-proof a DAS deployment can be, generally the lower its life cycle cost. 
     DAS network planners and system integrators employ a wide range of innovative approaches for helping to ensure that a particular DAS deployment is as cost-effective as possible. The types of costs considered by network planners and integrators include DAS deployment or DAS installation cost, as well as operational costs including maintenance costs, emergency restoration costs and network re-arrangement costs. Rearrangement costs are particularly significant for indoor DAS applications, due to frequent changes in building use and facility needs changes. Therefore, it would be advantageous to employ DAS systems and methods which are based on as few DAS transport facilities as possible to minimize installation and/or lease costs and have self-healing capabilities to avoid the need for costly emergency restoration services. 
     In order to obtain a high degree of DAS remote unit availability, two primary conditions must be satisfied. First, the DAS remote unit itself must be inherently reliable. Second, the transport media e.g., optical fiber, must be very reliable. It is well known that electronic and/or optical connections themselves are a significant root cause of failure or reduced availability in a DAS network. Companies who maintain outdoor DAS networks have reported that a failure of outside plant optical fiber facilities is not as rare as would be desirable. Therefore, it would be advantageous to employ systems and methods which offer higher redundancy and/or self-healing features in the event of failure of a transport media connection. 
     SUMMARY OF THE INVENTION 
     The present invention substantially achieves the advantages and benefits discussed above and overcomes the limitations of the prior art discussed above by providing a distributed antenna system responsive to one or more base stations and having at least one but in some embodiments a plurality of Digital Access Units (“DAU&#39;s”), each operating to control the packet traffic of an associated plurality of Digital Remote Units (“DRU&#39;s”). In embodiments employing multiple DAU&#39;s, the DAU&#39;s can be daisy-chained linearly or in a ring configuration. Likewise, depending upon the implementation, the DRU&#39;s associated with a given DAU can be configured in either a linear or ring Daisy chain configuration. 
     The data received from the base stations is down-converted, digitized and converted to baseband with the DAU. The data streams are then I/Q mapped and framed and independently serialized, such that multiple data streams are available in parallel from the DAU. In at least some embodiments, the DAU communicates with the associated DRU&#39;s via an optical transport arrangement. It will be appreciated by those skilled in the art that, using the present invention, it is possible to configure a distributed antenna system having n base stations, each providing m RF outputs for transmission by one or more associated DAU&#39;s to o DRU&#39;s, where the only limits are imposed by the technical performance specifications of the particular DAS, such as delay. 
     By the use of a ring configuration for connecting, in at least some embodiments, the DRU&#39;s and/or the DAU&#39;s, fault tolerance is built into the system, with resulting high availability. In single DAU embodiments, each DRU is accessible through two paths, and therefore remains available even in the event of a line break. In multi-DAU embodiments, where the DAU&#39;s are linearly daisy-chained, each DRU is accessible from multiple DRU&#39;s such that even some DAU failures will not prevent system operation. In embodiments employing a ring connection for the DAU&#39;s, multiple paths exist to each DAU, and thus provide an additional level of fault tolerance as well as dynamic load balancing and resource management as discussed in greater detail hereinafter. 
     Thus, the configuration of the advanced system architecture of the present invention provides a high degree of flexibility to manage, control, enhance and facilitate the radio resource efficiency, usage, availability, and overall performance of the distributed wireless network. The present invention enables specialized applications and enhancements including Flexible Simulcast, automatic traffic load-balancing, network and radio resource optimization, network calibration, autonomous/assisted commissioning, carrier pooling, automatic frequency selection, radio frequency carrier placement, traffic monitoring, traffic tagging, and indoor location determination using pilot beacons. The present invention can also serve multiple operators, multi-mode radios (modulation-independent) and multi-frequency bands per operator to increase the efficiency and traffic capacity of the operators&#39; wireless networks. 
     Further the present invention provides a high degree of dynamic flexibility, supports dynamic re-arrangements, and provides a low life cycle cost. This advanced system architecture enables deployment of DAS networks using fewer DAS transport facilities to reduce costs, while providing self-healing features. The present invention also offers redundancy and enhanced system availability. 
     It is an object of the present invention to provide Flexible Simulcast capabilities, as disclosed in U.S. Provisional Application Ser. No. 61/382,836, entitled “Remotely Reconfigurable Distributed Antenna System and Methods,” filed Sep. 14, 2010, incorporated herein by reference and attached as Appendix A, in a high-availability ring configuration using, for example, optical fiber transport. As discussed above, the ring configuration insures that a break in any optical fiber cable will not shut down the daisy-chained network, because the downlink and uplink signals can be rerouted around the cable break to the respective DRUs. 
     It is a further object of the present invention to balance the bidirectional data rate on the optical fibers so as to increase the maximum achievable data rate during operation on the ring network of DRUs. 
     It is a further object of the present invention to provide higher transport network capacity in the event the data transport is asymmetrical between the downlink and uplink, as is typically the case for mobile broadband networks. 
     It is a further object of the present invention to provide an adaptive and automatic control for optimizing the transport media capacity on the ring. 
     It is a further object of the present invention to provide a method of summing co-channel users&#39; uplink signals in the DRU daisy chain. 
     Applications of the present invention are suitable to be employed with distributed base stations, distributed antenna systems, distributed 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 upgradeable through a link such as an Ethernet connection to a remote computing center. 
     Appendix I is a glossary of terms used herein, including acronyms. 
    
    
     
       THE FIGURES 
       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: 
         FIG. 1  is a block diagram according to one embodiment of the invention showing the basic structure and an example of a unidirectional, channelized downlink transport, one ring scenario based on having one DAU and four DRUs. 
         FIG. 2  is a block diagram in accordance with an embodiment of the invention showing the basic structure and an example of a unidirectional, channelized uplink transport, one ring scenario based on having one DAU and four DRUs. 
         FIG. 3  is a block diagram in accordance with an embodiment of the invention showing the basic structure and an example of a unidirectional, channelized uplink transport, two ring scenario based on having one DAU and eight DRUs. 
         FIG. 4  is a block diagram in accordance with an embodiment of the invention showing the basic structure and an example of unidirectional channelized uplink or downlink transport. This example of a five ring scenario comprises two DAUs and twenty DRUs.  FIG. 4  provides an example of a daisy chain ring network. 
         FIG. 5  illustrates an embodiment of a cellular network system employing multiple DRUs according to the present invention. 
         FIG. 6  illustrates an embodiment of a multi-band system employing six different services operating in different frequency channels with multiple DRUs according to the present invention. 
         FIG. 7  illustrates in block diagram form the interaction between the DAU embedded software control module and the DRU embedded software control module. 
         FIG. 8  illustrates in block diagram form an embodiment of a DAS according to an aspect of the invention, including daisy-chained DAU&#39;s. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is a novel Reconfigurable Distributed Antenna System that provides a high degree of flexibility to manage, control, reconfigure, enhance and facilitate the radio resource efficiency, usage and overall performance of the distributed wireless network.  FIG. 1  illustrates an embodiment of the Distributed Antenna System  100  that provides an example of a unidirectional, channelized downlink transport in accordance with the present invention. In  FIGS. 1-4 , a dotted line denotes a distinct subset of uplink and downlink channels identified as “A.” A dashed line denotes a distinct subset of uplink and downlink channels identified as “B.” The subset of uplink and downlink channels in A do not include those of B and vise versa. The system employs a Digital Access Unit functionality  105  (hereinafter “DAU”). The DAU  105  serves as an interface between associated base stations (BTS)  110 A-B and a plurality of digital remote units (DRU)  125 A- n , although only four DRU&#39;s are shown in  FIG. 1 . In the present description, “DRU” will be used interchangeably with Remote Radio Head Unit, or “RRU”, because of the similarity of the functions discussed herein, although those skilled in the art will recognize that a DRU communicates with a DAU, whereas an RRU communicates with a base station. In addition, those skilled in the art will recognize that a DAU is monitored and controlled by a remote network operations center (“NOC”), as indicated at bidirectional link  115  in  FIG. 1 . Such links are typically Ethernet connections or external modems, but can be any form of link suitable for remote monitoring and control. The NOC has the capability to remotely configure the DAU parameter settings which in turn configures the DRU&#39;s parameter settings. The NOC can request information from the DAUs. The DAUs can subsequently request information from the DRUs. The information requested includes but is not limited to uplink power, downlink power, optical error rate, gain settings, active carriers, etc. 
     For the downlink (DL) path, RF input signals  120 A through  120   n  are received at the DAU  105  from one or more base station units (BTS) indicated at  110 A through  110   p . The RF input signals are separately down-converted, digitized, and converted to baseband (using a Digital Down-Converter) by the DAU. Data streams are then I/Q mapped and framed and specific parallel data streams are then independently serialized and translated to optical signals using pluggable SFP modules, again by the DAU  105 . The independently serialized, parallel data streams are then delivered to different DRU&#39;s  125 A- 125   k , typically over optical fiber cable arranged, in at least some embodiments, in a ring configuration indicated at connection pairs  140 A- 145 A, or, in other embodiments, a daisy chain configuration. In addition, each DAU can support a plurality of rings with associated DRU&#39;s, where the additional rings are indicated by fiber optic pairs up through  140   o - 145   o . It will be appreciated by those skilled in the art that the number of RF inputs, DAU&#39;s and DRU&#39;s and rings is limited only by network performance factors, such as delay. In addition, as discussed in connection with  FIG. 4  herein, the DAS can be further extended by using a ring or daisy-chain of DAU&#39;s, each of which supports an arrangement of DRU&#39;s and rings as shown in  FIG. 1 . 
     One function of the DAU  105  is to determine the direction in which downlinked channels are propagated around the ring. As just one example, the embodiment shown in  FIG. 1  is configured to have downlink channels A, B, C and D propagate in a first direction, for example clockwise, and channels E, F, G, and H propagate in the counter direction, although it will be understood that the number of channels propagating in each direction need not be equal, nor adjacent, nor sequential. Likewise, the number of channels received at each DRU is assigned by the DAU and need not be equal, adjacent or sequential, but instead will typically be any configuration that optimizes network utilization. 
     Referring next to  FIG. 2 , an embodiment of an uplink (UL) path in accordance with the invention can be better appreciated. Channels received at the antenna associated with each DRU are converted into optical signals by each DRU  125 A- 125   k . Optical signals received from the DRU&#39;s are de-serialized and de-framed by the DAU  105 , and are also up-converted digitally using a Digital Up-Converter implemented within the DAU  105 . Each data stream is then independently converted to the analog domain and up-converted to the appropriate RF frequency band, still within the DAU  105  in the illustrated implementation, although this functionality can be separate. The RF signals are then delivered to the appropriate one of a plurality of BTS&#39;  110 A- 110   p . As with the arrangement shown in  FIG. 1 , the direction of propagation of each channel is controlled by the DAU, with some channels propagating in a clockwise direction and others in a counterclockwise direction. Also as discussed in connection with  FIG. 1 , while adjacent channels are shown as propagating in the same direction in  FIG. 2 , this is not required and any channel can be selected to propagate in either direction. 
     Referring again to  FIG. 1 , it will be appreciated by those skilled in the art that, in some implementations of a DAS, more than one carrier can exist in each channel, and, as such, a DRU may receive a channel comprising a signal containing two or more carriers, or a wireless operator may have more than one RF carrier per channel allocated to a single base station. This is referred to as a “composite signal”. The manner in which a composite downlink signal is managed by the present invention can be better understood with reference to  FIG. 1 . In such instances, the DAU will receive a composite downlink input signal  130  from, e.g., a first base station  110 A belonging to one wireless operator, enters the DAU  105  at the RF input port  120 A. Composite signal  130  comprises carriers A-D. A second composite downlink input signal from e.g., a pth base station  110   p  belonging to the same wireless operator enters DAU 1  at the DAU 1  RF input port  120   n . Composite signal  135  comprises carriers E-H. The functionality of the DAU  105 , and DRU&#39;s  125 A- 125   k , respectively, are explained in detail in U.S. Provisional Application Ser. No. 61/374,593, entitled “Neutral Host Architecture for a Distributed Antenna System,” filed Aug. 17, 2010, incorporated herein by reference and attached hereto as Appendix B. 
     One optical output of DAU  105  is fed to DRU  125 A, via bidirectional optical cable  140 A. A second optical output of DAU  105  is fed via bidirectional optical cable  145 A to DRU 3 . Similarly, bidirectional optical cables  150 ,  155  and  160  connect DRU&#39;s  125 A- n  in a ring configuration, such that DRU  125 A connects to DRU  125 B via cable  150 A, DRU  125 B connects to DRU  125   n  via cable  150 B, and DRU  125   k  connects to DRU  125 C, or the kth−1 DRU, via cable  150   m . This connection facilitates networking of DAU  105 , which means that all of Carriers A-H are available within DAU  105  to transport data to DRU&#39;s  125 A- k  depending on software settings within the networked DAU system. Depending upon the embodiment, the software settings within DRU  125 A are configured either manually or automatically, such that carriers A-H are present in the downlink output signal  155 A at the antenna port of DRU  125 A. The presence of all eight carriers means that DRU  125 A is potentially able to access the full capacity of both base stations feeding DAU  105 . A possible application for DRU 125 A is a cafeteria in an enterprise building during the lunch hour where a large number of wireless subscribers are gathered. 
     DRU  125 B is fed by a second optical port of DRU  125 A via bidirectional optical cable  150 A. The optical cable  150 A performs the function of daisy chaining DRU  125 A with DRU 125 B. As with DRU  125 A, the software settings within DRU  125 B are configured either manually or automatically such that Carriers A, C, D and F are present in downlink output signal  155 B at the antenna port of DRU  125 B. The capacity of DRU  125 B is set to a much lower value than DRU  125 A by virtue of its specific channel settings as controlled by DAU  105 . The individual Digital Remote Units have integrated frequency selective DUCs and DDCs with gain control for each carrier. The DAU&#39;s can remotely turn on and off the individual carriers via the gain control parameters. 
     In a similar manner as described previously for DRU  125 A, the software settings within DRU  125 C are configured either manually or automatically such that Carriers B and F are present in downlink output signal  155 C at the antenna port of DRU  125 C. Compared to the downlink signal  155 B at the antenna port of DRU  125 B, the capacity of DRU  125 C, which is also configured via its software settings, is much less than the capacity of DRU  125 B. DRU  125   n  is fed by the optical cable  150   m  connected to the second optical port of the n th −1 DRU, shown for simplicity in  FIG. 1  as DRU  125 C. The software settings within DRU  125   n  are configured either manually or automatically such that carriers A, D, E and H are present in downlink output signal  155 D at the antenna port of DRU  125   n . Typically, the capacity of DRU  125   n  is set to a much lower value than DRU  125 A, however, the relative capacity settings of each of DRU&#39;s  125 A- n  can be adjusted dynamically to meet the capacity needs within the coverage zones determined by the physical positions of antennas connected to those DRU&#39;s. As noted above, the ring connection is completed by interconnecting DRU  125 B and DRU  125   n  through optical cable  150 B. The ring configuration insures that any optical cable breaks will not shut down the daisy chained network. The downlink and uplink signals will be rerouted around the cable break to the respective DRUs. 
     The present invention facilitates conversion and transport of several discrete relatively narrow RF bandwidths. This approach allows conversion of only those multiple specific relatively narrow bandwidths which carry useful or specific information. This approach also allows more efficient use of the available optical fiber transport bandwidth for neutral host applications, and allows transport of more individual operators&#39; band segments over the optical fiber. As disclosed in U.S. Provisional Application Ser. No. 61/374,593, entitled “Neutral Host Architecture for a Distributed Antenna System,” filed Aug. 17, 2010 together with U.S. Provisional Application Ser. No. 61/382,836, entitled “Remotely Reconfigurable Distributed Antenna System and Methods”, filed Sep. 14, 2010, both assigned to the assignee of the present invention, and also referring to  FIG. 1  of the instant patent application, Digital Up Converters located within the DRU can be dynamically reconfigured as the result of commands from the NOC to transport from the DAU input to any specific DRU output any specific narrow frequency band or bands, RF carriers or RF channels which are available at the respective RF input port of either DAU. This capability is illustrated in  FIG. 1  where only specific frequency bands or RF carriers appear at the output of a given DRU. More specifically, through commands received from the NOC, the FPGA&#39;s in the DAU and one or more of the associated DRU&#39;s can be reprogrammed or reconfigured to convert and transport only the desired narrow bandwidths. 
     A related capability of the present invention is that not only can the Digital Up Converters located within each DRU be configured to transport any specific narrow frequency band from the DAU input to any specific DRU output, but also the Digital Up Converters within each DRU can be configured to transport any specific time slot or time slots of each carrier from the DAU input to any specific DRU output. The carriers and time slots are monitored by the DAU by filtering the signals and performing power detection of the individual time slots, which information can be conveyed to the NOC as desired. Then, as with the Digital Up Converters, the Field Programmable Gate Arrays (FPGA) in the DAU or DRU can be dynamically reconfigured by commands received from the NOC in a manner analogous to software programmability. The DAU detects which carriers and corresponding time slots are active. This information is relayed to the individual DRUs via the management control and monitoring protocol software. This information is then used, as appropriate, by the DRUs for turning off and on individual carriers and their corresponding time slots. 
     Data transport between the Base Station and the subscribers is typically asymmetrical, whereby the downlink data rate is higher than the uplink rate. The ring network configuration of Daisy Chained DRUs can exploit this data rate asymmetry to maximize the data transport on the optical fibers  150 A- 150   m.    
     The present invention balances the bidirectional data rate on the optical fibers so as to increase the maximum achievable data rate on the ring network of DRUs. The individual downlink channels are transmitted in a unidirectional sense along the ring network. Referring to  FIG. 1 , downlink channels A, B, C, and D are transmitted in a clockwise sense around the ring of DRU&#39;s  125 A- k . On the other hand, downlink channels E, F, G and H are transmitted in a counterclockwise sense around the ring of DRU&#39;s. Referring to  FIG. 2 , the uplink channels J, K, L and M are transmitted in a counterclockwise sense whereas uplink channels N, O, P and Q are transmitted in a clockwise sense around the ring of DRUs. If the downlink and uplink data rates were the same, there would be no advantage in the transport mechanism. However, if the data transport is asymmetrical between the downlink and uplink then a significant advantage can be gained. For example, for a factor of two difference between the downlink and uplink data rates, a 4/3 factor increase in data transport can be achieved. The larger the asymmetry between the downlink and uplink data rates, the larger will be the increase in data transport using the unidirectional channel transport mechanism around the ring. 
     Referring again to  FIG. 1 , a further embodiment in accordance with another aspect of the present invention may be better understood. In the event that there is a significant change in asymmetry between the downlink and uplink data rates and/or if there is a change in channel complement at the BTS, the Management Control module [discussed in connection with  FIG. 7  herein] which is typically comprised within each DAU is able to automatically and adaptively re-allocate data transport resources on the clockwise direction of the ring and on the counter-clockwise direction of the ring to maximize the overall transport capacity. As stated previously, the larger the degree of asymmetry between uplink and downlink data rates for a particular DAU, the higher the increase in data transport using the unidirectional channel transport mechanism around the ring. If there is more than one DAU present, in an embodiment one DAU is designated a Master DAU by the NOC, and the Management Control module located in the Master DAU makes decisions to optimize the overall transport capacity. In the event the master DAU fails, the NOC can designate another DAU as master. Alternatively, any suitable failover algorithm can be implemented. 
     Referring to  FIG. 3 , an alternative embodiment of the present invention wherein a single DAU controls a plurality of rings, each comprising a plurality of daisy-chained DRU&#39;s, can be better understood. In  FIG. 3 , two daisy-chained rings, indicated at  300  and  305 , are shown although the number of rings could be greater and is determined mainly as a matter of design preference up to limits imposed by network performance. The rings each link a plurality of DRU&#39;s  310 A- n  and  315 A- m , to a single DAU  320 . The directional flow of the data transport is shown as the dashed lines  325  and dotted lines  330 . The downlink channels available from the plurality of DRU&#39;s are divided into two subsets which flow in opposite directions around the two daisy-chained rings. The uplink channels are transported in a similar fashion. The channels are grouped into the two subsets so as to maximize the data transport to and from the DRUs. The DAU in turn communicates with one or more BTS&#39;s via RF Ports  335 A- p.    
     Heuristic algorithms may be used to allocate RF channel data in a Dual-ring DAS. For  FIG. 3 , there are two fibre rings R 1 , R 2  (clockwise and counter clockwise) and a set T of n≧2 independent RF channels Ki, 1≦i≦n (including uplink and downlink). A channel Ki requires a bandwidth of b(Ki) to transport on a fibre ring. A time-bounded algorithm exists which obtains a schedule having the optimal bandwidth allocation (i.e. the maximum aggregate bandwidth of each ring is as small as possible). A large number of advanced heuristic algorithms have been developed to solve such scheduling optimization problems. Some examples are genetic algorithm, evolutionary algorithm, greedy search, Tabu search, harmony search, simulated annealing, ant colony optimization, etc. For purposes of simplicity and clarity, a simple heuristic algorithm for two rings is described here, although the number of rings is not limited to two. 
     The algorithm begins by sorting the channels Ki decreasingly by bandwidth b(Ki). Then it schedules the channel in such a way that each channel is assigned to the ring which has the smaller aggregate bandwidth. The formal description of the algorithm follows. 
     
       
         
               
             
           
               
                   
               
             
             
               
                   Input: T = set of n independent channels Ki with required bandwidth 
               
               
                 b(Ki), 1≦ i ≦n . 
               
               
                   Output: L 1 , L 2  and D 1 , D 2 . Lj is the set of channels schedule on ring 
               
               
                 Rj , and D j  is the maximum aggregate bandwidth of ring Rj, Dj = (Σb(J), 
               
               
                 JεL j ), 1≦j≦2 . 
               
               
                   ALGORITHM (T, L, D) 
               
               
                   Step 1 (initialize Ki and D 1 , D 2 ) Sort Ki such that b(Ki)≦ b(Ki +1 ), 
               
               
                 1≦ i ≦n−1. D 1  ← 0, D 2  ← 0 . 
               
               
                   Step 2 (Schedule a channel) 
               
               
                    For i =1 to n, step 1 do 
               
               
                   If D 1  ≦ D 2 , then [ assign Ki onto L 1 , D 1  ← D 1  + b(Ki) ] . 
               
               
                     else [ assign Ki onto L 2 , D 2  ← D 2  + b(Ki) ] . 
               
               
                   
               
             
          
         
       
     
     Referring next to  FIG. 4 , a still further an alternative embodiment of the present invention may be understood. The arrangement illustrated in  FIG. 1  comprised downlink signals from two separate base stations belonging to the same wireless operator entering the DAU  105  at input ports  110 A and  110   p , respectively. In the embodiment of  FIG. 4 , a first composite signal enters a first DAU  400  at that DAU&#39;s RF input port from a base station  405 , and a second composite downlink input signal from, e.g., a second base station  410  belonging to a different wireless operator enters DAU  415  at that second DAU&#39;s RF input port. DAU  400  directly supports two rings  420  and  425 , DAU  415  directly supports two rings  430  and  435 , and a ring  440  is shared between DAU  400  and DAU  405 . Each of the rings comprises daisy-chained DRU&#39;s generally indicated at  445  and connected via, for example, fiber optic links, as discussed in connection with  FIG. 1 . It will be noted that channels A are transported in the opposite sense as channels B. The downlink channels in subset A are transported counterclockwise around each ring, whereas the channels in subset B are transported in a clockwise sense around each ring. In this embodiment, signals belonging to both the first operator and the second operator are converted and transported to the DRU&#39;s  445  on ring  440  because DAU  400  and DAU  405  are daisy-chained through the fiber optic cable  440 . This embodiment provides an example of a neutral host wireless system, where multiple wireless operators share a common infrastructure comprised of DAU  400 , DAU  415 , and DRU&#39;s  445 . All the previously mentioned features and advantages accrue to each of the two wireless operators. It will further be appreciated that, while  FIG. 4  illustrates only two DAU&#39;s linked in daisy-chain style, it is possible to daisy chain a larger plurality of DAU&#39;s, and the daisy-chained DAU&#39;s can also be configured in a ring configuration similar to the manner in which the DRU&#39;s are connected. This arranged is illustrated in  FIG. 8 , below. 
     As disclosed in U.S. Provisional Application Ser. No. 61/374,593, entitled “Neutral Host Architecture for a Distributed Antenna System,” filed Aug. 17, 2010 and again referring to  FIG. 1  of the instant patent application, the Digital Up Converters present in the DRU&#39;s of the present invention can be programmed to process various signal formats and modulation types including FDMA, CDMA, TDMA, OFDMA and others. Also, the Digital Up Converters present in the respective DRUs can be programmed to operate with signals to be transmitted within various frequency bands subject to the capabilities and limitations of the system architecture disclosed in U.S. Provisional Application Ser. No. 61/374,593, mentioned above. In one embodiment of the present invention where a wideband CDMA signal is present within, e.g., the bandwidth corresponding to a first carrier at the input port to DAU  105 , the transmitted signal at the antenna ports of DRU  125 A, DRU  125 B and DRUk will be a wideband CDMA signal which is virtually identical to the signal present within the bandwidth corresponding to that first carrier at the input port to DAU  105 . 
     As disclosed in U.S. Provisional Application Ser. No. 61/374,593, again identified above, and also referring to  FIG. 1  of the instant patent application, it is to be understood that the Digital Up Converters present in the respective DRUs can be programmed to transmit any desired composite signal format to each of the respective DRU antenna ports. As an example, the Digital Up Converters present in DRU  125 A and DRU  125 B can be dynamically software-reconfigured as described previously so that the signal present at the antenna port of DRU  125 A would correspond to the spectral profile shown in  FIG. 1  as  155 A and also that the signal present at the antenna port of DRU  125 B would correspond to the spectral profile shown in  FIG. 1  as  155 B. The application for such a dynamic re-arrangement of DRU capacity would be e.g., if a company meeting were suddenly convened in the area of the enterprise corresponding to the coverage area of DRU  125 B. 
     Referring again to  FIG. 2 , another embodiment of the Distributed Antenna System of the present invention can be better understood. As disclosed in the aforementioned U.S. Provisional Application Ser. No. 61/374,593, and also as shown in  FIG. 2 , the optical ring transport mechanism can be implemented with regard to uplink signals. As discussed previously with regard to downlink signals and by referring to  FIG. 1 , the uplink system shown in  FIG. 2  is mainly comprised of DAU  105 , together with DRU&#39;s  125 A- 125   k . In a manner similar to the downlink operation explained by referring to  FIG. 1 , the operation of the uplink system shown in  FIG. 2  can be understood as follows. 
     The Digital Down Converters present in each of DRU&#39;s  125 A- k  are dynamically software-configured as described previously so that uplink signals of the appropriate desired signal format(s) present at the receive antenna ports of the respective DRU&#39;s  125 A- 125   k  are selected based on the desired uplink band(s) to be processed and filtered, converted and transported to the appropriate uplink output port of DAU  105 . The DAU and DRUs frame the individual data packets corresponding to their respective radio signature using the Common Public Interface Standard (CPRI). Other Interface standards are applicable provided they uniquely identify data packets with respective DRUs. Header information is transmitted along with the data packet which identifies the DRU and DAU that corresponds to the individual data packet. 
     In one example for the embodiment shown in  FIG. 2 , DRU&#39;s  125 A and  125 C are configured to receive uplink signals within the Channel K bandwidth, whereas DRU  125 B and DRU  125   n  are both configured to reject uplink signals within the Channel K bandwidth. When DRU  125 C receives a strong enough signal at its receive antenna port within the Channel K bandwidth to be properly filtered and processed, the Digital Down Converters within DRU  125 C facilitate processing and conversion. Similarly, when DRU  125 A receives a strong enough signal at its receive antenna port within the Channel K bandwidth to be properly filtered and processed, the Digital Down Converters within DRU  125 A facilitate processing and conversion. The signals from DRU  125 A and DRU  125 C are combined based on the active signal combining algorithm, and are fed to the base station connected to the uplink output port of DAU  105 . The term simulcast is frequently used to describe the operation of DRU 125 A and DRU  125 C with regard to uplink and downlink signals within Channel K bandwidth. The term Flexible Simulcast refers to the fact that the present invention supports dynamic and/or manual rearrangement of which specific DRU are involved in the signal combining process for each Channel bandwidth. 
     Referring still to  FIG. 2 , the Digital Down Converters present in DRU  125 A are configured to receive and process signals within Channel J-Q bandwidths. The Digital Down Converters present in DRU  125 B are configured to receive and process signals within Channel J, L, M and O bandwidths. The Digital Down Converters present in DRU  125 C are configured to receive and process signals within Channel K and O bandwidths. The Digital Down Converters present in DRU  125   n  are configured to receive and process signals within Channel J, M, N and Q bandwidths. The respective high-speed digital signals resulting from processing performed within each of the four DRU are routed to the DAU. As described previously, the uplink signals from the four DRUs are combined within the respective DAU corresponding to each base station. 
     In summary, the Reconfigurable Distributed Antenna System of the present invention described herein efficiently conserves resources and reduces costs. The reconfigurable system is adaptive or manually field-programmable, since the algorithms can be adjusted like software in the digital processor at any time. 
     Referring next to  FIG. 5 , an alternative embodiment of the present invention may be better understood.  FIG. 5  provides a daisy chain example of a distributed antenna system (DAS). Each DRU has a coverage radius that can be adjusted based on the power transmission from that particular remote unit. The DAU controls the various DRU&#39;s transmission power and can optimize the overall coverage zone. In the illustrated embodiment, DAU  502 , again under the control of a NOC (not shown), is associated with a base station  501  and in turn interfaces with three DRU&#39;s  503 ,  504  and  505 . A user  506  with a mobile device is provided relatively uniform coverage throughout the area covered by the three DRU&#39;s. 
     Referring next to  FIG. 6 , a still further alternative embodiment may be better appreciated.  FIG. 6  shows an embodiment of a multi-band system illustrating one DAU supporting up to six different services operating at different frequency bands, with three optical rings of DRU&#39;s  1 - 60 . The input frequency bands  605 - 630  (here denoted as six frequency bands at 700, 800, 850, 1900, 2100 and 2600 MHz) are input into the DAU  600  from the BTS&#39;s (not shown). The DAU includes, among other functionalities discussed herein, an RF IN portion for each band, and a digital distribution matrix for distributing the frequency bands to a plurality of DRU&#39;s, indicated as DRU 1 -DRU 60 , daisy-chained along three separate rings  635 ,  640  and  645  for achieving the desired coverage. The frequency bands are transported to either all or a subset of DRUs. The particular number of frequency bands, DAU&#39;s, DRU&#39;s and rings is exemplary only, and can, in practice, be any number appropriate to the performance capabilities and needs of the network. 
     Referring next to  FIG. 7  that illustrates embedded software control modules, the software embedded in the DAU and DRU, which controls the operation of key functions of these devices, can be better understood. In particular, the DAU embedded software control module  700  comprises a DAU Management Control Module  705  and a DAU monitoring module  710 . The DAU Management Control Module  705  communicates with the NOC  715 , and also the DAU monitoring module  710 . One such key function is determining and/or setting the appropriate amount of radio resources (such as RF carriers, CDMA codes or TDMA time slots) assigned to a particular DRU or group of DRUs to meet desired capacity and throughput objectives. As noted previously, the NOC  715  monitors the DAS operation and sends commands to the DAU&#39;s for configuring various functions of the DRU&#39;s as well as the DAU, in at least some embodiments. 
     The DAU Monitoring module, in addition to other functions, detects which carriers and corresponding time slots are active for each DRU. The DAU Management Control module communicates with the DRU Embedded Software Control module  720  over a fiber optic link control channel via a control protocol. In an embodiment, the control protocol comprises headers together with packets of data, such that both control information and data are transmitted to the DRU&#39;s together as a message. DRU functions or features that the header would control in the DRU are typically implementation specific and can include, among other things, measuring uplink and downlink power, measuring gain of uplink and downlink, and monitoring alarms in the DRU. 
     In turn, the DRU Management Control module  725  within the DRU Embedded Software Control Module sets the individual parameters of all the DRU Digital Up-Converters  730  to enable or disable specific radio resources from being transmitted by a particular DRU or group of DRUs, and also sets the individual parameters of all the DRU Digital Down-Converters  735  to enable or disable specific radio resources from being transmitted by a particular DRU or group of DRUs. In addition, the DRU Embedded Software Control Module comprises a DRU Pilot Beacon Control Module  740 , which communicates with a DRU Pilot Beacon  745 . 
     Referring next to  FIG. 8 , an embodiment of a daisy-chained configuration of DAU&#39;s is illustrated, together with a daisy-chained configuration of DRU&#39;s. In an embodiment, a plurality of base stations  800 A- 800   n  are each associated with one of DAU&#39;s  805 A- n . The DAU&#39;s are daisy-chained, and each DAU communicates with one or more daisy-chains  810 A- 810   m  of DRU&#39;s which may or may not be arranged in a ring configuration. It will be appreciated that the DAU&#39;s can also be configured in a ring configuration, as discussed above. 
     An algorithm operating within the DAU Monitoring module which detects which carriers and corresponding time slots for each carrier are active for each DRU provides information to the DAU Management Control module to help identify when, e.g., a particular downlink carrier is loaded by a percentage greater than a predetermined threshold whose value is communicated to the DAU Management Control module by the DAU&#39;s Remote Monitoring and Control function  715 . If that occurs, the DAU Management Control module can adaptively modify the system configuration to begin to deploy, typically although not necessarily slowly, additional radio resources (such as RF carriers, CDMA codes or TDMA time slots) for use by a particular DRU which need those radio resources within its coverage area. At the same time, usually the DAU Management Control module adaptively modifies the system configuration to begin to remove, again typically slowly, certain radio resources (such as RF carriers, CDMA codes or TDMA time slots) for use by a particular DRU where that DRU no longer needs those radio resources within its coverage area. 
     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. 
     
       
         
               
             
               
               
             
           
               
                 APPENDIX I 
               
               
                   
               
               
                 Glossary of Terms 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 ACLR 
                 Adjacent Channel Leakage Ratio 
               
               
                 ACPR 
                 Adjacent Channel Power Ratio 
               
               
                 ADC 
                 Analog to Digital Converter 
               
               
                 AQDM 
                 Analog Quadrature Demodulator 
               
               
                 AQM 
                 Analog Quadrature Modulator 
               
               
                 AQDMC 
                 Analog Quadrature Demodulator Corrector 
               
               
                 AQMC 
                 Analog Quadrature Modulator Corrector 
               
               
                 BPF 
                 Bandpass Filter 
               
               
                 BTS 
                 Base Transceiver System or Base Station 
               
               
                 CDMA 
                 Code Division Multiple Access 
               
               
                 CFR 
                 Crest Factor Reduction 
               
               
                 DAC 
                 Digital to Analog Converter 
               
               
                 DAU 
                 Digital Access Unit 
               
               
                 DET 
                 Detector 
               
               
                 DHMPA 
                 Digital Hybrid Mode Power Amplifier 
               
               
                 DDC 
                 Digital Down Converter 
               
               
                 DNC 
                 Down Converter 
               
               
                 DPA 
                 Doherty Power Amplifier 
               
               
                 DQDM 
                 Digital Quadrature Demodulator 
               
               
                 DQM 
                 Digital Quadrature Modulator 
               
               
                 DSP 
                 Digital Signal Processing 
               
               
                 DUC 
                 Digital Up Converter 
               
               
                 EER 
                 Envelope Elimination and Restoration 
               
               
                 EF 
                 Envelope Following 
               
               
                 ET 
                 Envelope Tracking 
               
               
                 EVM 
                 Error Vector Magnitude 
               
               
                 FFLPA 
                 Feedforward Linear Power Amplifier 
               
               
                 FIR 
                 Finite Impulse Response 
               
               
                 FPGA 
                 Field-Programmable Gate Array 
               
               
                 GSM 
                 Global System for Mobile communications 
               
               
                 I-Q 
                 In-phase/Quadrature 
               
               
                 IF 
                 Intermediate Frequency 
               
               
                 LINC 
                 Linear Amplification using Nonlinear Components 
               
               
                 LO 
                 Local Oscillator 
               
               
                 LPF 
                 Low Pass Filter 
               
               
                 MCPA 
                 Multi-Carrier Power Amplifier 
               
               
                 MDS 
                 Multi-Directional Search 
               
               
                 OFDM 
                 Orthogonal Frequency Division Multiplexing 
               
               
                 PA 
                 Power Amplifier 
               
               
                 PAPR 
                 Peak-to-Average Power Ratio 
               
               
                 PD 
                 Digital Baseband Predistortion 
               
               
                 PLL 
                 Phase Locked Loop 
               
               
                 PN 
                 Pseudo-Noise 
               
               
                 QAM 
                 Quadrature Amplitude Modulation 
               
               
                 QPSK 
                 Quadrature Phase Shift Keying 
               
               
                 RF 
                 Radio Frequency 
               
               
                 RRH 
                 Remote Radio Head 
               
               
                 RRU 
                 Remote Radio Head Unit 
               
               
                 SAW 
                 Surface Acoustic Wave Filter 
               
               
                 UMTS 
                 Universal Mobile Telecommunications System 
               
               
                 UPC 
                 Up Converter 
               
               
                 WCDMA 
                 Wideband Code Division Multiple Access 
               
               
                 WLAN 
                 Wireless Local Area Network