Abstract:
A method of communicating between a base band unit and a plurality of remote radio heads includes the steps of receiving a first signal through an antenna in a first remote radio head, transmitting the first signal to a second remote radio head through a digital radio interface, receiving a second signal through an antenna in the second remote radio head, compensating for a delay accrued in the first signal, adding the first signal and the second signal to obtain a resulting signal, and transmitting the resulting signal to a base band unit through a digital radio interface.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to wireless communications and, more particularly, to a method and system for communicating via CPRI in a distributed radio head architecture. 
     BACKGROUND 
     Wireless telecommunications systems sometimes employ the use of picocell radio nodes to augment the system&#39;s coverage area. Picocell nodes are telecommunication devices smaller than traditional base stations, or macrocell nodes, and typically have a smaller range. Picocells may be deployed in locales and situations demanding extra capacity, or in areas that experience poor signal quality with the telecommunications systems. Picocells encounter scalability issues that affect the ability to deploy them in great number, including operational overhead, network traffic management scalability, and hand-off performance. These issues are more pervasive than in a wireless system implemented with macrocells. Current distributed radio equipment solutions utilizing cascaded radios are typically cascaded over a dedicated transport media. The only traffic across the transport network may be the data exchanged between radio equipment and a controller. 
     SUMMARY 
     In one embodiment, a method of communicating between a base band unit and a plurality of remote radio heads includes the steps of receiving a first signal through an antenna in a first remote radio head, transmitting the first signal to a second remote radio head through a digital radio interface, receiving a second signal through an antenna in the second remote radio head, compensating for a delay accrued in the first signal, adding the first signal and the second signal to obtain a resulting signal, and transmitting the resulting signal to a base band unit through a digital radio interface. 
     In a further embodiment, an article of manufacture includes a computer readable medium and computer-executable instructions carried on the computer readable medium. The instructions are readable by a processor. The instructions, when read and executed, cause the processor to receive a first signal through an antenna in a first remote radio head, transmit the first signal to a second remote radio head through a digital radio interface, receive a second signal through an antenna in the second remote radio head, compensate for a delay accrued in the first signal, add the first signal and the second signal to obtain a resulting signal, and transmit the resulting signal to a base band unit through a digital radio interface. 
     In yet a further embodiment, a system for telecommunications includes a base band unit, a backhaul network, and a cascaded chain of remote radio heads. The backhaul network is coupled to the base band unit. The cascaded chain of remote radio heads includes a first remote radio head coupled to a first set of one or more antennas and a second remote radio head coupled to a second set of one or more antennas, The second remote radio head is coupled to the first remote radio head through optical fiber. The cascaded chain of remote radio heads is coupled to the backhaul network. The base band unit communicates through a digital radio interface with the first remote radio head over the backhaul network. The first remote radio head communicates through the digital radio interface with the second remote radio head. The second remote radio head is configured to receive signals from the second set of antennas and communicate the signal to the first remote radio head. The first remote radio head is configured to receive a first signal from the first set of antennas, receive a second signal from the second remote radio head, compensate for a delay accrued in the second signal, add the first signal and second signal to obtain a resulting signal, and transmit the resulting signal to the base band unit through a digital radio interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagram illustrating an example wireless communications network using picocells for facilitating mobile device access; 
         FIG. 2  is a diagram illustrating the various aspects of an example picocell device; 
         FIG. 3  is a diagram illustrating an example embodiment of a wireless communications network utilizing cascaded remote radio heads over a shared network; 
         FIG. 4  illustrates an example embodiment of a system utilizing CPRI to communicate between a cascaded chain of remote radio heads; 
         FIG. 5  is a diagram illustrating an example embodiment of upstream CPRI communication between cascaded remote radio heads, showing example signal processing; and, 
         FIG. 6  is a flowchart illustrating an example embodiment of a method of communication over a shared network. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an example wireless communications network using picocells for facilitating mobile device access. Picocells  101  are mounted on overhead, open-air cables  102  connected between utility poles  103 . Each picocell  101  provides coverage to a coverage area  104 . A mobile device in coverage area  104  will be able to communicate with the network coupled to picocells  101 . Providing continuous access to the network coupled to picocells  101  as a mobile device moves between coverage areas  104  is a goal of the wireless communications network. 
       FIG. 2  illustrates the various aspects of a picocell device. A base band unit  201  controls communication between the larger communications network and mobile devices. The radio processor  202  is configured to transmit and receive signals to and from one or more antennas  203 . Antenna  203  is the physical device that broadcasts and receives wireless signals to and from mobile devices. 
     A difficulty in providing an increasing number of picocell devices is that when creating the network, each picocell&#39;s base band unit must be provisioned, commissioned, and managed individually, in a similar fashion to base stations with larger coverage areas. However, since the picocell device&#39;s coverage area  104  is relatively small, many more picocells must be deployed for an equivalent amount of coverage. The result is that the overhead of provisioning, commissioning, and managing the picocell device must be repeated many more times when using picocell devices to cover a large area, when compared to a base stations with a larger coverage area. 
     Another difficulty when using picocells is the scalability of network traffic management as the number of picocells grows. In a long term evolution (“LTE”) wireless communications network, data links are required between every cell in a cluster in order to facilitate fast and seamless hand-off between the different cells as a mobile device moves from one coverage area to another. In addition, a data link is required to connect the picocell to the service provider&#39;s core network. As a result, the number of connections required for N nodes is on the order of magnitude of N squared. Managing an exponentially growing number of connections is a scalability problem when considering the large number of picocells required to serve a large network area. 
     A third difficulty when using picocells is that when cascading them in long chains, a mobile device travelling through multiple picocell coverage areas generates multiple hand-offs, requiring action from the network to correctly predict the movement of the mobile device and hand-off the mobile device to the next picocell coverage area. This hand-off requires time and system resources. Generally speaking, moving from one picocell coverage area to another picocell coverage area requires an inter-node hard handoff. This requires, for example, finding a new target picocell to connect to the mobile device based on estimations of the mobile device&#39;s location, speed, the original picocell&#39;s signal strength and coverage area, and the target picocell&#39;s signal strength and coverage area. Once the new target picocell is determined, the original picocell communicates a handoff order comprising the target picocell&#39;s frequency or time slot to the mobile device. The target picocell informs the communications network and the communication link between the communications network and the mobile device is established through the target picocell. A common possible side effect may be a short loss in communication, or even a dropped communication connection. Since a picocell coverage area may be small, a mobile device may experience many handoffs as it moves through many picocell coverage areas. 
     One approach to addressing some of these issues may be to utilize a remote radio head means of implementing a picocell. In such a case, base band unit  201  is separate from the combination of the radio processor  202  and the antenna  203 . The radio processor  202  in this configuration may be known as a remote radio head. In  FIG. 1 , each picocell  101  may be replaced by a remote radio head and multiple remote radio heads may be coupled to a single base station  201 . However, when configuring the system to include cascaded chains of remote radio heads coupled to a base band unit, some difficulties remain. For example, the base band unit  201  requires a data connection to each remote radio head, and the resulting data throughput requirements limit the size of cascaded chains. In addition, such connections often occur over a dedicated network line. The present invention contemplates solutions to this problem while achieving the benefits of cascaded radio heads. 
       FIG. 3  illustrates an example embodiment of the present invention for a wireless communications network  301  utilizing distributed cascaded remote radio heads over a shared network. Wireless communications network  301  may have one or more base band units  302 . Base band unit  302  may be coupled to one or more mobile network clusters  303  via a general purpose, fiber-optic backhaul network  304  and shared network  318 . Backhaul network  304  may carry general data telecommunications and/or multimedia traffic to and from networks and devices, such as cable services network  314 , core wireless network  312 , internet service network  316 , land-based service subscribers  311 , mobile devices  308 , and other networks and devices not pictured. Backhaul network  304  may comprise a fiber-optic network. Shared network  318  may comprise a fiber, electromagnetic, or hybrid transmission lines. Shared network  318  may carry general data telecommunications and/or multimedia traffic to and from devices in or in communication with cluster  303  and networks connected to backhaul network  304 . Shared network  318  may be coupled to backhaul network  304  by means of an optical switch  305 . In one embodiment, optical switch  305  may comprise an optical add/drop multiplexer. Cluster  303  may be coupled to shared network  304 . Base band unit  302  may be coupled to multiple clusters  303 . 
     Each cluster  303  may comprise one or more remote radio heads  306  cascaded in a chain topology. The one or more remote radio heads  306  may be coupled to one other through optical fiber. Each remote radio head  306  may be coupled to one or more antennas  307 . Antennas  307  send and receive wireless signals to and from one or more mobile devices  308 . 
     Cluster  303  may also be coupled to an optical node  309 . Optical node  309  may be configured to transfer signals from an optical fiber to an electromagnetic transmission line  310 . In one embodiment, electromagnetic transmission line  310  comprises a coaxial cable transmission line. Optical node  309  may be coupled to one or more land-based service subscribers  311  through electromagnetic transmission line  310 . Land-based service subscribers  311  may receive any number of services by being coupled to optical node  309 , including cable television services, voice, or data. 
     The optical fiber coupling optical switch  305 , remote radio heads  306 , and optical node  309  in conjunction with the electromagnetic transmission line  310  coupling optical node  309  and land-based service subscribers  311  may comprise a shared network  118 . 
     The wireless communications network may be coupled to a core wireless network  312  that may transmit voice, data, or other digital information. The core wireless network  312  may comprise one or more wireless or hard-wired networks. Core wireless network  312  may provide voice, data, or other digital information services to devices of wireless communications network  301 . Core wireless network  312  may provide voice, data, or other digital information connections between remote devices (not shown) coupled to core wireless network  312  and devices of communications network  301 . The core wireless network  312  may be coupled to the wireless communications network  301  through shared network  318  via an optical switch  305 . 
     Wireless communications network  301  may be coupled to a cable services network  314  that may transmit television data, telephony data, or other data services. Cable services network  314  may comprise one or more networks. Cable services network  314  may provide television data, telephony data, or other data services to land-based service subscribers  311 . Cable services network  312  may be coupled to wireless communications network  301  shared network  318  via an optical switch  305 . 
     Wireless communications network  301  may be coupled to an internet service network  316  that may transmit digital data comprising telephony, internet, multimedia, or other services. The internet service network  316  may comprise one or more networks. Internet service network  316  may provide services to land-based service subscribers  311 . Internet service network  316  may be coupled to the wireless communications network  301  through shared network  318  via an optical switch  305 . 
     In operation, a voice or data connection may be established between a node in wireless communications network  301  (or in core wireless network  312 ) and mobile devices  308 . For example, mobile device  308   a  may send a signal to wireless communications network  301  which is first received by the antennas  307   a  of a remote radio head  306   a . Other remote radio heads  306   b ,  306   c ,  306   d  may also receive through antennas  307   b ,  307   c ,  307   d  the signal from mobile device  308   a . Simultaneously, other mobile devices  308   b ,  308   c , may be transmitting to wireless communications network  301  through one or more of the remote radio heads  306 . 
     After receiving a wireless transmission from mobile device  308   a , and possibly other mobile devices  308   b ,  308   c , remote radio head  306   a  may process the received signals and transmit them via shared network  318  to the next upstream remote radio head  306   b  in the cascaded chain. Remote radio head  306   b  may have also received wireless transmissions through its antennas  307   b  from mobile devices  308   a ,  308   b ,  308   c  which are processed by remote radio head  306   b . Remote radio head  306   b  may also receive a transmission from remote radio head  306   a . Remote radio head  306   b  may add the signals received through its antennas  307   b  to the transmission from remote radio head  306   a . The resulting signal may be transmitted via shared network  218  upstream in the cascaded chain of radio heads to the next remote radio head  307   c . A similar process may occur utilizing remote radio heads  307   c  and  307   d . The resulting transmission, representing the received signals from all mobile devices  308  communicating with cluster  303 , may be added to the shared network  218 . Shared network  218  may transport the received signals to backhaul network  304  via optical switch  305 , whereupon the transmission reaches base band unit  302 . Base band unit  302  may be coupled to core wireless network  312  to provide communication to mobile devices  308 . Base band unit  302  may connect each transmitted signal through the backhaul network  304  to the appropriate destination, which may be in wireless communications network  301  or in core wireless network  312 . 
     When data is transmitted from the destination node, which may be in wireless communications network  301  or in core wireless network  312 , back to mobile devices  308 , the data may flow through backhaul network  304  to the cluster  303  by way of optical switch  305  and shared network  318 . Several such downstream data connections may be made to multiple mobile devices  308  on the cluster  303 . A single composite signal composed of the multiple downstream connections may be broadcast simultaneously on all remote radio heads  306  in the cluster  303 . Remote radio head  306   a  may receive the composite signal and broadcast it to relevant mobile devices  308  within range. The ability of a mobile device  308   a  to send and receive signals from a remote radio head  306   a  may constitute a voice or data connection with the wireless communications network  301  or core wireless network  312 . When a mobile device  308   a  moves from the coverage area of one remote radio head  306   a  to the coverage area of another remote radio head  306   b , no hand-off, hard or soft, may be necessary. When a mobile device moves from the coverage area of a cluster  303  of remote radio heads to a different cluster, an intra-node hand-off may be used instead of an inter-node hand-off. Thus, operation of wireless communications network  301  implemented with distributed radio heads may resemble the operation of a network implemented with macrocells, but with the benefits of a network implemented with picocells. 
     In addition to communicating with mobile devices  308 , communications with land-based service subscribers  311  or other subscribers connected to cluster  303  may be provided by shared network  318 . Backhaul network  304  may connect television, multimedia, internet, voice, or other data services to cluster  303 . Communications with land-based service subscribers  311  may originate in cable services network  314 , internet service network, or another provider in communication with backhaul network  304 . The television, multimedia, voice, or other data services for land-based service subscribers may  311  be transported by shared network  318  between optical switch  305  and optical node  309 . The data and services between optical node  309  and land-based service subscribers  311  may be transported by electromagnetic transmission line  310 . Communications with land-based service subscribers  311  may happen simultaneously with voice and data connections between mobile devices  308  and wireless communications network  301 . 
     A method of communication between remote radio heads  306  may comprise a digital radio interface. In one embodiment, Common Public Radio Interface (“CPRI”) may be utilized. CPRI is an interface between radio equipment control (such as base band units) and radio equipment (such as base band units). The CPRI protocol specifies transport, connectivity, and control between these communications devices, specifically for layer 1 and layer 2. The CPRI protocol does not, however, specify how to accomplish a cascaded chain of remote radio heads without the significant data requirements mentioned above in the discussion of  FIG. 1 . 
       FIG. 4  illustrates an example embodiment of a system  400  utilizing CPRI to communicate between a cascaded chain of remote radio heads. One or more remote radio heads  401   a ,  401   b ,  401   c  may be chained together using CPRI. Each remote radio head  401  may communicate with a wireless device  402  by sending and receiving wireless signals  403   a ,  403   b ,  403   c  to and from wireless device  402 . Each remote radio head  401   a ,  401   b ,  401   c  may utilize a set of one or more antennas  405   a ,  405   b ,  405   c  to send and receive wireless signals  403   a ,  403   b ,  403   c . Remote radio heads  401   a ,  401   b ,  401   c  are coupled to each other and to base band unit  404  through pairs of data links  406   a ,  406   b ,  406   c . Pairs of data links  406  may be configured to carry upstream and downstream communication, and may be physically implemented with optical fiber. Pairs of data links  406  may comprise a CPRI link. Each remote radio head  401   a ,  401   b ,  401   c  may comprise a layer 1 module  407   a ,  407   b ,  407   c . Layer 1 modules  407  may comprise any combination of hardware and/or software configurable to send and receive signals in a physical layer optical interface. Each remote radio head  401   a ,  401   b ,  401   c  may comprise a layer 2 module  408   a ,  408   b ,  408   c . Layer 2 modules  408  may comprise any combination of hardware and/or software configurable to provide means of accessing or repackaging information being transported by layer 1 modules  407 . Layer 2 modules  408  may comprise any combination of hardware and/or software configurable to implement a data link layer. A layer 1 module  407   a ,  407   b ,  407   c  may be coupled to its respective layer 2 module  408   a ,  408   b ,  408   c . Each remote radio head  401   a ,  401   b ,  401   c  may comprise a processing unit  409   a ,  409   b ,  409   c . Processing units  409  may be coupled to layer 2 modules  408  and to antennas  405 . Processing units  409  may be configured to send/receive information about wireless signals  403  to/from antennas  405 . Processing units  409  may be configured to send/receive data to/from layer 2 modules  408 , or otherwise access information being transported by layer 1 modules  407  by way of layer 2 modules  408 . Processing units  409  may be configured to process information, received or to be sent, in such a way to facilitate CPRI communication in the system  400  for between base band unit  404  and wireless device  402  through remote radio heads  401 . In one embodiment, processing units  409  may be partially implemented by the radio processor  202  of  FIG. 2 . 
     Remote radio heads  401  and base band unit  404  may comprise any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data. In certain embodiments, a remote radio head  401  or a base band unit  404  may comprise a processor, for example a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, a remote radio head  401  or a base band unit  404  may interpret and/or execute program instructions and/or process data stored in a memory. A memory be coupled to a remote radio head  401  or a base band unit  404  and may include any system, device, or apparatus configured to hold and/or house one or more memory modules. Each memory module may include any system, device or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). 
     In operation, wireless device  402  may broadcast a signal  403   c . Remote radio head  401   c  may receive the signal  403   c  through its antennas  405   c . Information about the signal  403   c  may be sent to processing unit  409   c . Processing unit  409   c  may prepare the information for transport to the remainder of the wireless network and may use layer 2 module  408   c  to package information about the signal  403   c  to be sent by layer 1 module  407   c . Information about signal  403   c  may be sent to remote radio head  401   b  through data link  406   c.    
     Remote radio head  401   b  may receive information about signal  403   c  through layer 1 module  407   b . Remote radio head  401   b  may receive signal  403   b  through its antennas  405   b . Information about signal  403   b  may be sent to processing unit  409   b . Processing unit  409   b  may access information about signal  403   c  by utilizing layer 2 module  408   b  to interface with layer 1 module  407   b . Processing unit  409   b  may process information about signal  403   c  and signal  403   b  so as to accurately present the information to base band unit  404 . Additional possible implementations of such operation of processing units  409  are given in  FIG. 5 , below. Processing unit  409   b  may use layer 2 module  408   b  to package information about signal  403   b , or post-processing information about signals  403   b ,  403   c , to be sent by layer 1 module  407   b . The information may be sent to remote radio head  401   a  through data link  406   b.    
     Remote radio head  401   a  may receive information about signals  403   b  and  403   c  through layer 1 module  407   a . Remote radio head  401   a  may receive signal  403   a  through its antennas  405   a . Information about signal  403   a  may be sent to processing unit  409   a . Processing unit  409   a  may access information about signals  403   b  and  403   c  by utilizing layer 2 module  408   a  to interface with layer 1 module  407   a . Processing unit  409   a  may process information about signals  403   a ,  403   b ,  403   c  so as to accurately present the information to base band unit  404 . Processing unit  409   a  may use layer 2 module  408   a  to package information about signal  403   a , or post-processing information about signals  403   a ,  403   b , and  403   c  to be sent by layer 1 module  407   a . The information may be sent to base band unit  404  through data link  406   a.    
       FIG. 5  illustrates an example embodiment of a system  500  of upstream CPRI communication between cascaded remote radio heads showing example signal processing. One or more remote radio heads  401   a ,  401   b ,  401   c  may be coupled together using CPRI. As noted above, each remote radio head  401  may receive a signal  503   a ,  503   b ,  503   c  through its antennas from a wireless device. Each remote radio head  401  may comprise elements for processing wireless signals  503 . For example, each remote radio head  401  may comprise a delay compensation buffer  502   a ,  502   b ,  502   c , as well as an adder  504   a ,  504   b  for adding the wireless signals  503   a ,  503   b  received through antennas to signal received from another remote radio head  401 . Each remote radio head  401  may be configured to transmit the resultant signal using the CPRI protocol upstream to the next remote radio head  401 ; or in the case of remote radio head  401   a , to the base band unit  404 . 
     In operation, remote radio head  401   c  receives a wireless signal  503   c  through its antennas (not shown). Because remote radio head  401   c  is the last remote radio head in the cascaded chain, it may simply transmit the signal to remote radio head  401   b  using the CPRI protocol. Remote radio head  401   b  does not receive the signal from remote radio head  401   c  instantaneously; there may have been some delay  505   c . Thus, the received signal  506   c  is the wireless signal  503   c  with some delay  505   c . Remote radio head  401   b  may also receive a wireless signal  503   b  from its own antennas. To correctly add the wireless signal  503   b  to the received signal  506   c , delay compensation buffer  502   b  may add an estimation of delay  505   c  to wireless signal  503   b , resulting in delay-compensated wireless signal  507   b . Delay compensation buffer  502   b  may be configured at installation, taking into account the distance between remote radio heads  401   b ,  401   c , the equipment used, and any other factors that contribute to delay. Alternatively, the delay  505   c  may be measured during installation and delay compensation buffer  502   b  set accordingly. The two signals, delay-compensated wireless signal  507   b  and received signal  506   c , may be added using digital signal bits addition. The resulting signal  508   b  may comprise wireless signals  503   b ,  503   c  adjusted for time or phase associated with delay  505   c . The resulting signal  508   b  may be transmitted using CPRI to the next upstream remote radio head  401   a.    
     Similarly, remote radio head  401   a  may receive received signal  506   b  that comprises the resulting signal  508   b  and some delay  505   b . Remote radio head  401   a  may also receive a wireless signal  503   a  from its own antennas. 
     To correctly add the wireless signal  503   a  to the received signal  506   b , delay compensation buffer  502   a  may add an estimation of delays  505   b ,  505   c  to wireless signal  503   a , resulting in delay-compensated wireless signal  507   a . Delay compensation buffer  502   a  may be configured at installation, taking into account the distance between remote radio heads  401   a ,  401   b ,  401   c , the equipment used, and any other factors that contribute to delay. Alternatively, the delays  505   b ,  505   c  may be measured during installation and delay compensation buffer  502   a  set accordingly. The two signals, delay-compensated wireless signal  507   a  and received signal  506   b  may be added using digital signal bits addition. The resulting signal  508   a  may comprise wireless signals  503   a ,  503   b ,  503   c  adjusted for time or phase associated with delays  505   b ,  505   c . The resulting signal  508   a  may be transmitted using CPRI to the base band unit  404 . 
     In one embodiment, the digital signal bits addition may be accomplished by sampling, at each remote radio head, a particularly frequency of the wireless signal with an accuracy of twelve bits. Using digital signal bits addition, three bits may be allocated for carry-over bits, resulting in the ability to cascade up to eight remote radio heads with a 1.2 Gbps fiber connection for bidirectional traffic. In a further embodiment, cascading remote radio heads may be based upon the CPRI standard, version 4. In yet a further embodiment, additional remote radio heads may be supported with a larger word size. 
       FIG. 6  is a diagram illustrating an example embodiment of a method  600  of upstream communication for a cascaded chain of remote radio heads over a shared network. Simultaneously, upstream communication with wireless mobile devices, as well as bi-directional communication with land based service subscribers, may be possible. Upstream communications may be of the form wherein a wireless device may send a signal, packet, or transmission to a device in the core wireless network through a remote radio head. Downstream communications may be of the form wherein a device in core wireless network may send a signal, packet, or transmission to a wireless device through a remote radio head. 
     For upstream mobile communications, in step  601  wireless signals may be obtained from one or more mobile devices in one more remote radio heads in a single cluster. Each remote radio head may receive the wireless signals through its own antennas. For all the remote radio head devices in a single cluster, obtaining wireless signals may happen simultaneously. In step  602 , the wireless signal may be compensated for the cumulative delay occurring in all upstream wireless signal acquisitions. The compensation may be configured at installation, taking into account the distance between the remote radio head and the downstream remote radio heads. As a result, the compensated wireless signal will have minimal time or phase differences from signals received in step  603 . If the remote radio head is at the bottom of the cascaded chain of remote radio heads, no compensation may be necessary. In step  603 , the remote radio head may receive a signal from a downstream remote radio head, the signal containing the received wireless radio signals received by all downstream remote radio heads. If the remote radio head is at the bottom of the cascaded chain of remote radio heads, the remote radio head might not receive a signal from a downstream remote radio head. In step  604 , the delay compensated wireless signal and the received signal may be added together using digital signal bits addition. In step  605 , it may be determined whether or not the top of the chain of remote radio heads has been reached. If the top of the chain of remote radio heads has been reached, then in step  606 , the resulting signal may be transmitted to the base band unit. The resulting signal in this step may represent the received signals from all mobile devices communicating with the cluster. If the top of the chain of remote radio heads has not been reached, then in step  607 , the resulting signal may be transmitted upstream to the next remote radio head via the CPRI protocol. Steps  602 - 607  may be repeated for the next upstream remote radio head. For downstream mobile communications, an inbound signal to a wireless device in communication with a cluster may be routed over the backhaul network to the appropriate cluster. The signal may be routed to each remote radio head in the cluster using a single CPRI link. The signal may be broadcast simultaneously through each remote radio head&#39;s antennas and received by the wireless device. 
     For communications with land based service subscribers, an inbound signal to a land based service subscriber coupled to an optical node, the optical node coupled to a cluster, may be routed over the backhaul network to the appropriate cluster. The signal may be transported over fiber through remote radio heads. The signal may then be routed over an electromagnetic transmission line to the target land-based service subscriber. These steps may describe a downloading process; an uploading process may be accomplished simply by reversing the order of the steps. 
     Although  FIG. 6  discloses a particular number of steps to be taken with respect to an example method  600 , method  600  may be executed with more or fewer steps than those depicted in  FIG. 6 . In addition, although  FIG. 6  discloses a certain order of steps to be taken with respect to method  600 , the steps comprising method  600  may be completed in any suitable order. For example, steps  602 - 606  may be conducted in parallel, simultaneously or at different times, at each remote radio head within the cascaded chain of remote radio heads. In addition, step  603  may be completed before completing step  602 , since both steps are independent of each other and are predicate to step  604 . 
     Method  600  may be implemented using the network of  FIG. 3 , the system of  FIG. 5 , or any other system operable to implement method  600 . In certain embodiments, method  600  may be implemented partially or fully in software embodied in computer-readable media. 
     For the purposes of this disclosure, computer-readable media may include any instrumentality or aggregation of instrumentalities that may retain data and/or instructions for a period of time. Computer-readable media may include, without limitation, storage media such as a direct access storage device (e.g., a hard disk drive or floppy disk), a sequential access storage device (e.g., a tape disk drive), compact disk, CD-ROM, DVD, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), and/or flash memory; as well as communications media such wires, optical fibers, and other electromagnetic and/or optical carriers; and/or any combination of the foregoing. 
     Although the present disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and the scope of the disclosure as defined by the appended claims.