# Patent

## Title
Dynamic cell bonding (DCB) for radio-over-fiber (RoF)-based networks and communication systems and related methods

## Abstract

Communication devices, systems, and methods for dynamic cell bonding (DCB) for networks and communication systems are disclosed. In one embodiment, a method of operating a wireless communication system is provided. The method includes determining a first plurality of remote units in a cloud bonded to a communication session, measuring a received signal strength from each of the first plurality of remote units, and measuring a received signal strength from each of a second plurality of remote units in the cloud not bonded to the communication session. One or more of the second plurality of remote units is dynamically bonded to the communication session if the measured received signal strength of the one of the second plurality of remote units is greater than the measured received signal strength of the first plurality of remote units.

## Background
PRIORITY APPLICATION
This application is a continuation of U.S. application Ser. No. 12/705,779, filed on Feb. 15, 2010 now U.S. Pat. No. 8,275,265, the content of which is relied upon and incorporated herein by reference in its entirety, and the benefit of priority under 35 U.S.C. §120 is hereby claimed


BACKGROUND
1. Field of the Disclosure
The technology of the disclosure relates to dynamic cell bonding (DCB) and, more specifically, to the use of DCB to compensate for the bandwidth limitations of multi-mode optical fiber (MMF).
2. Technical Background
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (coffee shops, airports, libraries, etc.). Wireless communication systems communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” in order to communicate with the access point device.
One approach to deploying a wireless communication system involves the use of “picocells.” Picocells are radio frequency (RF) coverage areas having a radius in the range from about a few meters up to about 20 meters. Picocells can be provided to provide a number of different services (e.g., WLAN, voice, radio frequency identification (RFID) tracking, temperature and/or light control, etc.). Because a picocell covers a small area, there are typically only a few users (clients) per picocell. Picocells also allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.
In conventional wireless systems, picocells are created by and centered on a wireless access point device connected to a head-end controller or head-end unit. The wireless access point device includes digital information processing electronics, an RF transmitter/receiver, and an antenna operably connected to the RF transmitter/receiver. The size of a given picocell is determined by the amount of RF power transmitted by the access point device, the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the wireless client device. Client devices usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the access point device mainly determine the picocell size.
One problem that can exist with wireless communication systems is the multi-path (fading) nature of signal propagation. This simply means that local maxima and minima of desired signals can exist over a picocell coverage area. A receiver antenna located at a maximum location will have better performance or signal-to-noise ratio (SNR) than a receiver antenna located in a minimum position. In this regard, signal processing techniques can be employed to improve the SNR of wireless data transmission in such wireless communication systems. For example, special diversity can be utilized in instances involving many access points. Other signal processing techniques include Multiple Input/Multiple Output (MIMO) techniques for increasing bit rates or beam forming for SNR, or wireless distance improvement. These techniques involve multiple antennas separated by a distance such that individual RF channels are formed between the transmitter and receiver. This distance can be less than one (1) foot in some instances.
In addition to the factors affecting SNR, variation in bandwidth response distribution among optical fiber links can also impede wireless data transmission. For example, multi-mode optical fibers (MMF) used in providing communications links can have varying distributions of bandwidth responses thus causing varying loss responses. For example, FIGS. 1A-1C illustrate exemplary MMF bandwidth response distributions to highlight the degree to which similar MMFs having similar defined characteristics can vary in loss. FIG. 1A provides a graph 2A illustrating an exemplary bandwidth response of thirteen (13) MMFs having a 62.5 micrometer (μm) core measured in a Radio-over-Fiber (RoF) link with an eight hundred fifty (850) nanometer (nm) vertical-cavity surface-emitting laser (VCSEL) measured over a range of input frequencies extending from zero (0) to six (6) GigaHertz (GHz). An exemplary distribution of the bandwidth response 3A of the thirteen (13) MMFs in the graph 2A at five (5) GHz is also illustrated in FIG. 1A to the right of graph 2A. As illustrated in this example, the loss for all measured MMFs is approximately negative eight (−8) decibels (dB) with a relatively large standard deviation between the MMFs having similar defined characteristics. Thus, if the thirteen (13) MMFs illustrated in FIG. 1A were used in a wireless communication system, the picocells formed by each of the MMFs would have a varying loss, even in the case of equal-length MMFs. This variability results in the unpredictable behavior and operation of such wireless systems.
For comparison purposes, FIG. 1B provides a graph 2B illustrating an exemplary bandwidth response of eight (8) MMFs having a fifty (50) μm core measured in an RoF link with an eight hundred fifty (850) nm VCSEL measured over a range of input frequencies extending from zero (0) to six (6) GHz. An exemplary distribution of the bandwidth response 3B for the eight (8) MMFs at five (5) GHz is also illustrated FIG. 1B to the right of graph 2B. In this example, the bandwidth loss for all measured MMFs is approximately −2.4 dB, with a smaller standard deviation of loss when compared to the standard deviation of loss for the 62.5 μm core MMFs illustrated in FIG. 1A. However, the fifty (50) μm core MMFs provided in the example of FIG. 1B may be more expensive than the 62.5 μm core MMFs provided in the example of FIG. 1A.
Comparing the loss in the 62.5 μm core MMFs in FIG. 1A to the fifty (50) μm core MMFs in FIG. 1B, the loss variation is less pronounced for fifty (50) μm core MMFs than for 62.5 μm core MMFs. Therefore, depending on the MMF, the link loss among MMFs will have a distribution similar to that illustrated in FIG. 1C.
It would be advantageous to counteract the variations in loss caused by variations in bandwidth distribution of optical fibers used as communication links in wireless communication systems. MMFs having larger variations in bandwidth distribution may be less expensive to employ in wireless communication systems, but may result in unpredictable behavior having a deleterious effect on the operation of optical fiber enabled wireless communication systems. Therefore, it would be advantageous to counteract the variations in loss of MMFs having larger variations in bandwidth distribution among optical fibers having similar defined characteristics.
SUMMARY OF THE DETAILED DESCRIPTION
Embodiments disclosed in the detailed description include communication devices, systems, and methods for dynamic cell bonding (DCB) for networks and communication systems. In one embodiment, a method of operating an optical fiber-based wireless communication system is provided. The method comprises determining a first plurality of remote units in a cloud bonded to a communication session, measuring a received signal strength and/or a data rate from each of the first plurality of remote units, measuring a received signal strength and/or an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session, and dynamically bonding one of the second plurality of remote units to the communication session if the measured received signal strength or the estimated data rate of the one of the second plurality of remote units is greater than the measured received signal strength or the data rate of one of the first plurality of remote units.
Alternative embodiments disclosed in the detailed description include a controller for DCB for networks and communication systems. In this embodiment, the controller comprises a head end unit configured to determine a first plurality of remote units in a cloud bonded to a communication session, measure a received signal strength and/or a data rate from each of the first plurality of remote units, measure a received signal strength and/or an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session, and dynamically bond one of the second plurality of remote units to the communication session if the measured received signal strength or the estimated data rate of the one of the second plurality of remote units is greater than the measured received signal strength or the data rate of one of the first plurality of remote units.
Alternative embodiments disclosed in the detailed description include a system for DCB for networks and communication systems. In this embodiment, the system comprises a plurality of remote units, and a head end unit comprising a controller for directing a signal to the plurality of remote units, wherein the controller is configured to determine a first plurality of remote units in a cloud bonded to a communication session, measure a received signal strength and/or a data rate from each of the first plurality of remote units, measure a received signal strength and/or an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session, and dynamically bond one or several of the second plurality of remote units to the communication session if the measured received signal strength or the estimated data rate of the one of the second plurality of remote units is greater than the measured received signal strength or the data rate of one of the first plurality of remote units.
Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description that follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.



BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1A-1C are diagrams illustrating exemplary varying bandwidth distributions and losses among multi-mode optical fibers (MMFs) having similarly defined characteristics;
FIG. 2 is a schematic diagram of an exemplary generalized embodiment of an optical fiber-based wireless picocellular system;
FIG. 3 is a more detailed schematic diagram of an exemplary embodiment of the system of FIG. 2;
FIG. 4 is a schematic diagram of an exemplary embodiment of a centralized optical fiber-based wireless picocellular system that includes multiple optical fiber cables optically coupled to a central head-end unit;
FIG. 5 is a “top down” view of the system of FIG. 4, showing an exemplary extended picocellular coverage area formed by using multiple optical fiber cables;
FIGS. 6A-6C are diagrams illustrating exemplary signal strength and bit rate within an exemplary square elementary cell;
FIGS. 7A and 7B are diagrams illustrating exemplary signal strength and bit rate within an exemplary square elementary cell;
FIGS. 8A and 8B are diagrams illustrating signal strength and bit rate within an exemplary square elementary cell employing dynamic cell bonding (DCB);
FIG. 9 is an illustration of a hardware configuration for practicing a two-by-two (2×2) Multiple Input/Multiple Output (MIMO) communication processing scheme in accordance with exemplary embodiments described herein;
FIG. 10 is a flowchart of DCB in accordance with exemplary embodiments described herein;
FIG. 11 is an illustration of a hardware configuration for practicing a four-by-four (4×4) MIMO communication processing scheme in accordance with exemplary embodiments described herein;
FIG. 12 shows a schematic representation (not to scale) of the refractive index profile of a cross-section of the glass portion of an exemplary embodiment of multimode optical fiber disclosed herein wherein the depressed-index annular portion is offset from the core and is surrounded by an outer annular portion; and
FIG. 13 is a schematic representation (not to scale) of a cross-sectional view of the optical waveguide fiber of FIG. 12.



DETAILED DESCRIPTION
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the concepts may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.
There is described below, in exemplary and non-limiting embodiments, embodiments that include communications devices, systems, and methods for dynamic cell bonding (DCB) for Radio-over-Fiber (RoF)-based networks and communication systems. In one embodiment, a method of operating an optical fiber-based wireless communication system is provided. The method comprises determining a first plurality of remote units in a cloud bonded to a communication session, measuring a received signal strength and/or a data rate from each of the first plurality of remote units, measuring a received signal strength and/or an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session, and dynamically bonding one or several of the second plurality of remote units to the communication session if the measured received signal strength or the estimated data rate of the one of the second plurality of remote units is greater than the measured received signal strength or the data rate of one of the first plurality of remote units.
In accordance with exemplary embodiments disclosed herein, DCB can be employed in a dense (i.e., separated by several meters) grid of antennas to compensate for link loss variation due to the use of multi-mode optical fibers (MMFs) in the system. As discussed more fully below, DCB can equalize link loss for different optical fibers and mitigate fading effects. This can result in an increase in the coverage area with maximum bit rate in a radio-over-multi-mode-fiber picocellular system.
DCB can be performed continually and/or periodically to measure the signal strengths of remote units near to remote units involved in a Multiple Input/Multiple Output (MIMO) communication session. When it is determined that switching the operation of a remote unit currently utilized in a communication session to a nearby unutilized or underutilized remote unit not bonded to the communication session can result in greater signal strength or a faster data rate, the operation of the two remote units is dynamically swapped. This swapping is referred to herein as “dynamic cell bonding” or, more simply, “dynamic bonding.” As a result of the dynamic bonding, the remote unit previously engaged in the MIMO communication session is subsequently unbonded from the MIMO communication session.
More specifically, in accordance with exemplary embodiments described below, a picocell infrastructure can be utilized to achieve wireless transmission gains by combining the separate single antennas (fed by single optical link) at remote units of neighboring cells by signal processing from a central location. Specifically, in a relatively dense grid of antennas, DCB can be utilized to compensate for the bandwidth limitations of MMFs. As discussed more fully below, a network based on low-bandwidth MMF with DCB has even slightly better coverage than a fixed-cell network where only the highest-bandwidth MMFs are used.
Before discussing exemplary embodiments of an MMF network employing DCB, FIGS. 2-5 are provided to discuss examples of an optical fiber-based wireless communication system which may employ the fiber optic array cables and other systems and methods described herein to enable wireless communication.
FIG. 2 illustrates a schematic diagram of an exemplary embodiment of an optical fiber-based wireless picocellular system 10 employing MMF. The optical fiber-based wireless picocellular system 10 is also referred to herein as “system 10.” The system 10 in this embodiment includes a head-end unit 12, a plurality of transponder units or remote antenna units 14, or simply “remote units 14.” At least one optical fiber radio frequency (RF) communication link 16 optically couples the head-end unit 12 to each remote unit 14. The head-end unit 12 may be any type of controller or control system, or any other device or system that can control communications directed to and from the remote units 14, as described in more detail below. As also discussed in detail below, the system 10 facilitates the formation of a picocell 18 substantially centered about remote unit 14 and extending in a generally conical form away from an associated remote unit 14. The plurality of remote units 14 forms a picocellular coverage area 20. While illustrated as covering separate and distinct regions of space, picocellular coverage areas associated with different remote units may intersect and overlap. The head-end unit 12 is adapted to perform or to facilitate any one of a number of RoF applications, such as radio frequency identification (RFID), wireless local area network (WLAN) communication, or cellular phone service, as examples. Shown within the picocell 18 is a client device 22 in the form of a computer. The client device 22 may be any device capable of receiving and transmitting RF communications and signals. The client device 22 includes an antenna system 24 (e.g., a wireless card) adapted to receive and/or send electromagnetic RF signals.
FIG. 3 is a detailed schematic diagram of an exemplary embodiment of system 10 of FIG. 2. In an exemplary embodiment, the head-end unit 12 includes a service unit 26 that provides electrical RF service signals for a particular wireless service or application. In an exemplary embodiment, the service unit 26 provides electrical RF service signals by passing (or conditioning and then passing) such signals from one or more outside networks 28, as described below. In a particular example embodiment, this includes providing WLAN signal distribution as specified in the Institute of Electrical Engineers (IEEE) 802.11 standard, i.e., in the frequency range from 2.4 to 2.5 GigaHertz (GHz) and from 5.0 to 6.0 GHz. In another exemplary embodiment, the service unit 26 provides electrical RF service signals by generating the signals directly. In another exemplary embodiment, the service unit 26 coordinates the delivery of the electrical RF service signals between client devices within the picocellular coverage area 20.
The service unit 26 is electrically coupled to an electrical-to-optical (E/O) converter 30 that receives an electrical RF service signal from the service unit 26 and converts it to a corresponding optical signal, as discussed in greater detail below. In an exemplary embodiment, the E/O converter 30 includes a laser suitable for delivering sufficient dynamic range for the RoF applications described herein, and optionally includes a laser driver/amplifier electrically coupled to the laser. Examples of suitable lasers for the E/O converter 30 include, but are not limited to, laser diodes, distributed feedback (DFB) lasers, Fabry-Perot (FP) lasers, and vertical cavity surface emitting lasers (VCSELs).
The head-end unit 12 also includes an optical-to-electrical (O/E) converter 32 electrically coupled to the service unit 26. The O/E converter 32 receives an optical RF service signal and converts it to a corresponding electrical signal. In an example embodiment, the O/E converter 32 is a photodetector, or a photodetector electrically coupled to a linear amplifier. The E/O converter 30 and the O/E converter 32 constitute a “converter pair” 34.
In accordance with an exemplary embodiment, the service unit 26 includes an RF signal modulator/demodulator unit 36 for modulating/demodulating RF signals, a digital signal processing unit (“digital signal processor”) 38, a central processing unit (CPU) 40 for processing data and otherwise performing logic and computing operations, and a memory unit 42 for storing data, such as data to be transmitted over a WLAN.
The remote unit 14 includes a converter pair 44, wherein the E/O converter 30 and the O/E converter 32 therein are electrically coupled to an antenna system 24 via an RF signal-directing element 46, such as a circulator. The signal-directing element 46 serves to direct the downlink and uplink electrical RF service signals, as discussed below. In accordance with an exemplary embodiment, the antenna system 24 includes one or more patch antennas, such as disclosed in U.S. patent application Ser. No. 11/504,999, filed Aug. 16, 2006 entitled “RADIO-OVER-FIBER TRANSPONDER WITH A DUAL-BAND PATCH ANTENNA SYSTEM,” and U.S. patent application Ser. No. 11/451,553, filed Jun. 12, 2006 entitled “CENTRALIZED OPTICAL-FIBER-BASED WIRELESS PICOCELLULAR SYSTEMS AND METHODS,” both of which are incorporated herein by reference in their entireties.
The optical fiber RF communication link 16 includes a downlink optical fiber 48D having a downlink optical fiber input end 50 and an output end 52, and an uplink optical fiber 48U having an uplink optical fiber input end 54 and an output end 56. The downlink and uplink optical fibers 48D and 48U optically couple the converter pair 34 at the head-end unit 12 to the converter pair 44 at the remote unit 14. Specifically, the downlink optical fiber input end 50 is optically coupled to the E/O converter 30 of the head-end unit 12, while the output end 52 is optically coupled to the O/E converter 32 at the remote unit 14. Similarly, the uplink optical fiber input end 54 is optically coupled to the E/O converter 30 of the remote unit 14, while the output end 56 is optically coupled to the O/E converter 32 at the head-end unit 12.
In accordance with an exemplary embodiment, the optical fiber-based wireless picocellular system 10 employs a known telecommunications wavelength, such as eight hundred fifty (850) nanometers (nm), one thousand three hundred (1300) nm, or one thousand five hundred fifty (1550) nm. In another exemplary embodiment, the system 10 employs other less common but suitable wavelengths such as nine hundred eighty (980) nm.
Exemplary embodiments of the system 10 include using multi-mode optical fiber for downlink and uplink optical fibers 48D and 48U. The particular type of optical fiber depends on the application of the system 10. For many in-building deployment applications, maximum transmission distances typically do not exceed three hundred (300) meters (m). The maximum length for the intended RoF transmission needs to be taken into account when considering using multi-mode optical fibers for the downlink and uplink optical fibers 48D and 48U. For example, it has been shown that a one thousand four hundred (1400) MHz/km multi-mode optical fiber bandwidth-distance product is sufficient for 5.2 GHz transmission up to three hundred (300) m.
In an exemplary embodiment, the system 10 employs fifty (50) μm multi-mode optical fiber (MMF) for the downlink and uplink optical fibers 48D and 48U, and E/O converters 30 that operate at eight hundred fifty (850) nm using commercially available VCSELs.
The system 10 also includes a power supply 58 that generates an electrical power signal 60. The power supply 58 is electrically coupled to the head-end unit 12 for powering the power-consuming elements therein. In an exemplary embodiment, an electrical power line 62 runs through the head-end unit 12 and over to the remote unit 14 to power the E/O converter 30 and the O/E converter 32 in the converter pair 44, the optional RF signal-directing element 46 (unless the RF signal-directing element 46 is a passive device such as a circulator), and any other power-consuming elements (not shown). In an exemplary embodiment, the electrical power line 62 includes two wires 64 and 66 that carry a single voltage and that are electrically coupled to a DC power converter 68 at the remote unit 14. The DC power converter 68 is electrically coupled to the E/O converter 30 and the O/E converter 32 in the converter pair 44, and changes the voltage or levels of the electrical power signal 60 to the power level(s) required by the power-consuming components in the remote unit 14. In an exemplary embodiment, the DC power converter 68 is either a DC/DC power converter, or an AC/DC power converter, depending on the type of electrical power signal 60 carried by the electrical power line 62. In an exemplary embodiment, the electrical power line 62 includes standard electrical-power-carrying electrical wire(s), e.g., 18-26 American Wire Gauge (AWG) used in standard telecommunications and other applications. In another example embodiment, the electrical power line 62 (dashed line) runs directly from the power supply 58 to the remote unit 14 rather than from or through the head-end unit 12. In another example embodiment, the electrical power line 62 includes more than two wires and carries multiple voltages.
In an example embodiment, the head-end unit 12 is operably coupled to one or more outside networks 28 via a network link 72.
With reference to the optical fiber-based wireless picocellular system 10 of FIGS. 2 and 3, the service unit 26 generates an electrical downlink RF service signal SD (also referred to herein as “electrical signal SD”) corresponding to its particular application. In an exemplary embodiment, this is accomplished by the digital signal processor 38 providing the RF signal modulator/demodulator unit 36 with an electrical signal (not shown) that is modulated onto an RF carrier to generate a desired electrical signal SD.
The electrical signal SD is received by the E/O converter 30, which converts this electrical signal into a corresponding optical downlink RF signal SD′ (also referred to herein as “optical signal SD′”), which is then coupled into the downlink optical fiber 48D at the downlink optical fiber input end 50. In an exemplary embodiment, the amount of power provided to antenna system 24 is varied to define the size of the associated picocell 18 (FIG. 2), which in example embodiments range anywhere from about a meter across to about twenty meters across.
The optical signal SD′ travels over the downlink optical fiber 48D to the output end 52, where it is received by the O/E converter 32 in the remote unit 14. The O/E converter 32 converts the optical signal SD′ back into the electrical signal SD, which then travels to the RF signal-directing element 46. The RF signal-directing element 46 then directs the electrical signal SD to the antenna system 24. The electrical signal SD is fed to the antenna system 24, causing it to radiate a corresponding electromagnetic downlink RF signal SD′′ (also referred to herein as “electromagnetic signal SD′′”).
Because the client device 22 is within the picocell 18, the electromagnetic signal SD′′ is received by the antenna system 24 of the client device 22, which may be part of a wireless card, or a cell phone antenna, for example. The antenna system 24 converts the electromagnetic signal SD′′ into an electrical signal SD in the client device 22 (the electrical signal SD is not shown therein). The client device 22 then processes the electrical signal SD, e.g., stores the signal information in memory, displays the information as an e-mail or text message, etc.
In an exemplary embodiment, the client device 22 generates an electrical uplink RF signal SU (not shown in the client device 22), which is converted into an electromagnetic uplink RF signal SU′′ (also referred to herein as “electromagnetic signal SU′′”) by the antenna system 24.
Because the client device 22 is located within the picocell 18, the electromagnetic signal SU′′ is detected by the antenna system 24 of the remote unit 14, which converts this signal back into the electrical signal SU. The electrical signal SU is directed by the RF signal-directing element 46 to the E/O converter 30, which converts this electrical signal SU into a corresponding optical uplink RF signal SU′ (also referred to herein as “optical signal SU′”), which is then coupled into the uplink optical fiber input end 54 of the uplink optical fiber 48U. The optical signal SU′ travels over the uplink optical fiber 48U to the output end 56, where it is received by the O/E converter 32 at the head-end unit 12. The O/E converter 32 converts the optical signal SU′ back into the electrical signal SU, which is then directed to the service unit 26. The service unit 26 receives and processes the electrical signal SU, which in an example embodiment includes one or more of the following: storing the signal information, digitally processing or conditioning the signals, sending the signals on to one or more outside networks 28 via the network links 72, and sending the signals to one or more client devices 22 in the picocellular coverage area 20. In an example embodiment, the processing of the electrical signal SU includes demodulating the electrical signal SU in the RF signal modulator/demodulator unit 36, and then processing the demodulated signal in the digital signal processor 38.
FIG. 4 is a schematic diagram of an exemplary embodiment of an optical fiber-based wireless picocellular system 200 according the disclosure. The optical fiber-based wireless picocellular system 200 is also referred to herein as the “system 200.” The system 200 is similar to the system 10 as described above and illustrated in FIGS. 2 and 3, but includes multiple optical fiber cables 202 optically coupled to a central head-end station 204. The central head-end station 204 includes a number of E/O converter arrays 206 and a corresponding number of O/E converter arrays 208, arranged in pairs in converter array units 210, with one converter array unit 210 optically coupled to one optical fiber cable 202. Likewise, the system 200 includes a number of downlink multiplexers 212 and uplink multiplexers 214, arranged in pairs in multiplexer units 216, with one multiplexer unit 216 electrically coupled to one converter array unit 210. In an exemplary embodiment, a controller 215 is electrically coupled to each multiplexer unit 216 and is adapted to control the operation of the downlink and uplink multiplexers 212 and 214 therein. Here, the term “array” is not intended to be limited to components integrated onto a single chip as is often done in the art, but includes an arrangement of discrete, non-integrated components.
While described above with reference to the operation of a single remote unit 14, in accordance with exemplary embodiments disclosed below, remote units 14 are grouped into clouds of remote units 14 for use in DCB. As used herein, a “cloud” refers to a set comprising all remote units 14 each associated with one another in such a way that each may be counted when determining the number of nodes (NumNodes) available for the purposes of performing DCB. As described more fully below, a cloud may be further defined, for example, as the set of all remote units 14 physically linked to the same access point. For example, a plurality of remote units 14 forming a cloud may be used in combination with diversity antennas on client devices 22 (FIG. 2) to provide a Multiple-Input/Multiple-Output (MIMO) configuration. MIMO is the use of multiple antennas at both the transmitter and receiver to improve communication performance to maximize the performance of a system, such as the system 200. Such an arrangement can be used to achieve an increased bit rate at the same antenna power level. It achieves this by employing higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity (reduced fading).
Each E/O converter array 206 is electrically coupled to the downlink multiplexer 212 in the corresponding multiplexer unit 216. Likewise, each O/E converter array 208 is electrically coupled to the uplink multiplexer 214 in the corresponding multiplexer unit 216. Service units 218 are each electrically coupled to both the downlink and uplink multiplexers 212 and 214 within each multiplexer unit 216. Respective downlink and uplink optical fiber cables 220 and 222 optically couple each converter array unit 210 to a corresponding optical fiber cable 202. In an example embodiment, the central head-end station 204 includes connector ports 224 and optical fiber cables 202 include connectors 226 adapted to connect to the connector ports 224. In an exemplary embodiment, the connectors 226 are Mechanical Transfer (MT) connectors, such as the UNICAMTM MTP connector available from Corning Cable Systems LLC, Hickory, N.C. In an example embodiment, the connectors 226 are adapted to accommodate the electrical power line 62 connected to the connector port 224.
FIG. 5 is an illustration of a “top down” view of the system 200, showing an extended picocellular coverage area 20 formed by using multiple optical fiber cables 202 as might, for example, be spread across a floor of a building or other structure in a generally planar manner. A grid 228 is superimposed over the resultant array of remote units 14. In the exemplary embodiment shown, the remote unit 14 is located at each intersection of every two generally orthogonal grid lines to form a regularly distributed array of the remote units 14. In an example embodiment, the system 200 supports anywhere from two remote units 14 to hundreds of remote units 14, to even thousands of remote units 14. The particular number of remote units 14 employed is not fundamentally limited by the design of the system 200, but rather by the particular application.
The system 200 operates in a manner similar to the system 10 as described above, except that instead of the remote units 14 being disposed in a single optical fiber cable 202, they are distributed over two or more optical fiber cables 202 through the use of corresponding two or more converter array units 210. The electrical signals SD from the service units 218 are distributed to each multiplexer unit 216. The downlink multiplexers 212 therein convey electrical signals SD to one, some, or all of the converter array units 210, depending on which remote units 14 are to be addressed by which service unit 218. The electrical signals SD are then processed as described above, with the downlink optical signals SD′ being sent to one, some, or all of remote units 14. The uplink optical signals SU′ generated by the client devices 22 in the corresponding picocells 18 return to the corresponding converter array units 210 at the central head-end station 204. The optical signals SU′ are converted to electrical signals SU at the receiving converter array unit(s) 210 and are then sent to the uplink multiplexers 214 in the corresponding multiplexer unit(s) 216. The uplink multiplexers 214 therein are adapted (e.g., programmed by the controller 215) to direct the electrical signals SU to the service unit(s) 218 that require(s) receiving electrical signals SU. The receiving service units 218 process the electrical signals SU, which as discussed above in an exemplary embodiment includes one or more of: storing the signal information; digitally processing or conditioning the signals; sending the signals on to the one or more outside networks 28 via the network links 72; and sending the signals to one or more client devices 22 in the picocellular coverage area 20.
FIGS. 6-8 discussed below are provided in order to illustrate examples of implementing DCB in a MIMO communication session. In this regard, FIGS. 6A-6C are illustrations of exemplary disparaging that can occur in maximum bit rates achievable by the client device 22 of the system 200 operating within one or more picocells bounded by four remote units 14 forming a square elementary cell 230, as an example. With reference to FIG. 6A, the grid 228 corresponds to the grid 228 of FIG. 5. At each intersection of grid lines is a node 232 corresponding to the position of a remote unit 14. As used herein, references to a “node 232” may be used interchangeably with references to the “remote unit 14” associated with the node 232. For purposes of explanation, nodes 232 active in a communication session are designated as “node 232A.” More specifically, nodes 232 initially active in a MIMO communication session prior to the performance of DCB as described in accordance with reference to exemplary embodiments described herein are referred to as “node 232A” (see FIG. 9). Nodes 232 not bonded to a communication session but included in a cloud that includes nodes that are bonded to the communication session are referred to as “node 232C.” Returning to FIG. 6A, the four nodes 232A active in a communication session forming the square elementary cell 230 are surrounded by other adjacent nodes 232C. The eight adjacent nodes 232C are candidate nodes that can be utilized in a DCB scenario. In the simulation illustrated in FIG. 6A, each square elementary cell 230 has an a=five (5) meter (m) period.
FIG. 6B is an illustration showing the maximum bit rate achievable by a client device 22 within an exemplary square elementary cell 230 of a 4×4 MIMO system. In this example, the square elementary cell 230 has a period of a=5 m. There is assumed a path loss exponent of 4.0 and a shadow fading parameter of 3.5 dB. It is further assumed that each client device antenna system 24 is onmidirectional. Gaussian distribution for the fiber loss is assumed with σ=3 dB. Lastly, it is assumed that each MMF utilized to communicate with each remote unit 14 at each node 232A is a 62.5 μm fiber and is selected to be in the top 5% of bandwidth compared to other MMFs having the same characteristics. It is evident that, when utilizing the top five percent (5%) of MMFs from a random distribution of MMFs, up to approximately ninety four percent (94%) of the square elementary cell 230 is covered at the maximum bit rate. This result is further illustrated in FIG. 6C where there is plotted the percentage of the cell area coverage (% of cell area) for each bit rate (bit rate, Mb/s).
FIGS. 7A and 7B illustrate the percentage of coverage at varying bit rates for a square elementary cell 230 having the same dimensions and operating with the same parameters as in FIG. 6B with one exception. Specifically, in this example, each MMF utilized to communicate with each remote unit 14 at each node 232A is randomly selected so as to mirror the distribution of characteristics across all MMFs of the same or similar type. As a result, the MMFs utilized in the present example have a lower-bandwidth on average than do those utilized with reference to FIGS. 6B and 6C. The resulting increased variability in the quality of individual MMFs thus selected is reflected in the decreased percentage of the cell area covered at the maximum bit rate. Specifically, as seen in FIGS. 7A and 7B, the cell area covered at the maximum bit rate drops considerably to less than 80%. Note that in the exemplary embodiments of FIGS. 6A, 6B, 7A, and 7B, the same four (4) nodes 232A bonding the square elementary cell 230 are utilized as bonded to an RoF communication session.
In an exemplary embodiment in accordance with the disclosure, DCB is utilized to increase the percentage of a cell area covered at the maximum bit rate. In accordance with the simulated results illustrated in FIGS. 8A and 8B, it is possible to achieve results superior to those illustrated in FIGS. 6B and 6C even while utilizing the MMFs employed in FIGS. 7A and 7B. As described more fully below, DCB is employed to expand the set of nodes 232 that may be utilized in, for example, the 4×4 MIMO situation illustrated in FIG. 6A. Specifically, instead of merely using remote units 14 associated with the four nodes 232A forming the square elementary cell 230, each of the remote units 14 associated with the eight adjacent nodes 232C may be dynamically swapped, or “bonded”, with one of the four nodes 232A when it is determined that doing so would increase the percentage of the square elementary cell 230 within which the maximum bit rate can be achieved. As described more fully below, in an exemplary embodiment, this determination is made based, in part, upon which remote units 14 associated with nodes 232 belonging to the cloud of nodes 232 including adjacent nodes 232C exhibit the best signal-to-interference (S/I) and S/N ratios.
With continued reference to FIG. 8A, there is illustrated the cell area coverage using a random distribution of MMFs (as in FIGS. 7A and 7B) but employing DCB. The results are illustrated in FIGS. 8A and 8B, where it is demonstrated that the performance of the system when DCB is employed increases such that nearly one hundred percent (100%) of the square elementary cell 230 enjoys a maximum bit rate.
An exemplary embodiment of a method by which DCB can be performed in accordance with the disclosure is described with reference to FIG. 9 and the flowchart of FIG. 10. With reference to FIG. 9, there is illustrated a hardware configuration for a 2×2 MIMO scenario engaged in a communication session with, for example, a client device 22 (not shown), whereby multiple antenna systems 24 each at one of a number of remote units 14 and a corresponding number of antennas at the client device 22 engage in a communication session. In the exemplary illustrated configuration in FIG. 9, the system 200 (FIG. 4) operates to select two (2) of the five (5) nodes 232 each associated with a remote unit 14 exhibiting, for example, the highest measured received signal strength and/or data rate. In exemplary embodiments, all of the nodes 232 are presumed to be distributed in a generally planar manner such as across a floor of a building.
In this example, as illustrated in FIG. 10, the process of DCB begins with a first node 232A′ already selected, though in practice it need not be (block 300). As illustrated, node 232A′, located at center, is hardwired to service unit 26 and remains in a selected state throughout DCB. Next, beginning at N=1, the signal strength at each remote unit 14 corresponding to each of the four (4) other nodes is measured. Note that, in this example, the number of possible nodes from which to chose when performing DCB is five (5). As the node 232A′, located at center, is always selected, there remain four (4) possible other nodes 232 that can be utilized. Node 232A′, at center, is darkened to indicate that it is selected. As a result, the total possible number of nodes (NumNodes) in the present example is four (4) (total number of nodes (5)−number of nodes always activated (1)=4). The process proceeds to measure the signal strength of each of the remaining four (4) nodes 232. To achieve these measurements, a computing device, such as the CPU 40, queries the received signal strength from a client device 22 via the remote unit 14 corresponding to N=1 (block 302). The CPU 40 stores the measured signal strength corresponding to N=1 in memory, such as in memory unit 42 (block 304).
Next, a check is performed to see if N=NumNodes (block 306). As noted above, in the present example, NumNodes=4. As a result the comparison of N, having a value of “1,” does not equal NumNodes (equal to “4”). As a result, N is increased by one (block 308) and the process of measuring the signal strength of the other nonmeasured nodes continues once again (block 302). After three more iterations, it will be determined that N is equal to NumNodes.
Next, processing continues to select those remote units 14 corresponding to measured nodes, numbering NumNodes in total, having the highest signal strength (block 310). Because the present example is a 2×2 MIMO configuration in which only two nodes are utilized at any one time and, further, because the node 232A′, located at center, is always selected, this block requires that only the remote unit 14 corresponding to the node with the single highest associated value be selected. In the present example, the node 232A′ selected is the node directly to the left of center node 232A′. As a result, the CPU 40 instructs the 4×1 switch receiving an input signal from the service unit 26 to direct or otherwise transmit the signal to the node 232A′ at left of center (block 312). As a result, in the present example, the nodes 232C remain as adjacent, unutilized and unbonded nodes.
Next, MIMO signal processing is performed (block 314). During MIMO signal processing, data is transmitted to and received from the client device 22 via the selected remote units 14 having the highest measured signal strength.
Note that thus far there has been described only the first iteration of blocks by which the first number of remote units 14 are selected for use in MIMO processing (block 300 to block 314). After the initial selection of nodes is performed, a decision to perform dynamic cell bonding is made (block 316). Dynamic cell bonding is the process by which the nodes utilized in MIMO communication (e.g., two (2) nodes in 2×2 MIMO processing, four (4) nodes in 4×4 MIMO processing, etc.) are periodically, in a dynamic fashion, reassessed to determine the optimal configuration and utilization of the nodes. In the present example, if a determination is made to perform DCB, the process continues to block 302. As described above, the received signal strengths of all four (4) nodes (not including the central node 232A′) are again measured and, if necessary, a node 232C is chosen to replace the operation of node 232A′. This newly selected node 232C is then dynamically bonded with the communication session to become an active node 232A′ while, in approximate synchronicity, the formerly activated node 232A′ is unbounded from the communication session. If a decision is made to forgo DCB, the process terminates (block 316).
In an alternative exemplary and non-limiting embodiment, a data rate of a remote unit 14 can be used in addition to or in lieu of antenna signal strength in FIG. 10. In this regard, the data rate of remote units 14 proximate to the selected center node 232A′ can be used to provide a MIMO configuration and to determine dynamic cell bonding in FIG. 10. Data rate is another measure of the performance of a remote unit 14. Thus, in the embodiment of FIG. 10, the remote units 14 totaling NumNodes with the highest data rates can be used to provide the active nodes 232A for the MIMO configuration (blocks 302-312 in FIG. 10). Further, the data rate of nodes 232A selected for the MIMO configuration in FIG. 10 can also be used to determine communication performance and thus if an active node 232A should be selected for release in a dynamically bonded communication session. In this regard, the processing at block 316 in FIG. 10 can use the measured data rates of the active nodes 232A to reassess whether any of the active nodes 232A should be replaced with unbounded nodes 232C. In this regard, the measured estimated data rate(s) of nodes 232C, i.e., estimated based on the measured signal strength of nodes 232C, is compared with the data rate(s) of active nodes 232A. An estimated data rate is used to determine the performance of unbonded nodes 232C, because unbonded nodes 232C are not part of the communication session in this embodiment. As used herein, reference to “measured estimated data rate” refers to the process of determining an estimated data rate for an unbonded node 232C. If the estimated data rate(s) of unbonded nodes 232C are greater than the data rate(s) of active nodes 232A, as previously described above, such unbonded node(s) 232C can be chosen to replace the operation of active node(s) 232A and be dynamically bonded with the communication session to become an active node 232A (block 316 in FIG. 10).
FIG. 11 is an illustration of a hardware configuration for a 4×4 MIMO scenario. In the exemplary illustrated configuration, the system 200 (FIG. 4) operates to select four (4) of the best nine (9) nodes each associated with a remote unit 14. Note that, in the example, four nodes 232A′ have been initially chosen as exhibiting the highest signal strength. Once again, the node 232A′, located at center, is always activated so that the total number of nodes available for DCB (NumNodes) is equal to eight (8). Thus, when DCB is performed, N will cycle from one (1) to eight (8) as the signal strength of each node is measured.
The rapidity with which DCB occurs may vary. DCB may be configured to be performed at time intervals ranging from hours to minutes to seconds and even to subsecond intervals. When utilizing MMF at high bandwidths, the transmission quality of the fiber is unstable. In addition, the position of the client device 22 can move thus altering the remote units 14 being utilized for MIMO communication. Further, the temperature of the lasers used and the state of the physical couplings along a MMF can both change over time. As a result, it is beneficial to periodically perform DCB as described in accordance with exemplary embodiments herein.
In addition, the flowchart of FIG. 10 describes the process of DCB for a single client device 22. In practice, it is likely that DCB will be performed in serial fashion for each client device 22 engaged in MIMO communication via the system 200. It is therefore evident that the amount of time required to perform DCB on a plurality of client devices 22 is dependent upon, at least, the number of client devices 22 and the number of nodes (NumNodes) at which a signal strength must be measured. As a result, the degree of periodicity of DCB may be bounded, in part, by factors including, but not limited to, the number of client devices 22 and the number of nodes (NumNodes) at which a signal strength must be measured.
As noted above, a “cloud” refers to a set comprising all remote units 14 each associated with one another in such a way that each may be counted when determining NumNodes for the purposes of performing DCB. In the exemplary embodiments described above with reference to FIGS. 9 and 11, the cloud is defined by the specific nodes physically connected to the service unit 26. Specifically, all nodes physically connected to a single service unit are deemed to be in the same cloud. In other exemplary embodiments, clouds may be defined logically, such as when based upon geographic proximity. In such instances, when nodes are regularly distributed across, for example, floors of a building, nodes which reside on adjacent floors but which are otherwise aligned vertically may be included in the same cloud. In another exemplary embodiment, for any given first node, all other nodes belonging to the same cloud as the first node may be defined as being within the line of sight from the first node where line of sight distance d can be found from the following equation:




  
    
      P
      TX
    
    +
    
      20
      ⁢
      
        
      
      ⁢
      
        log
        10
      
      ⁢
      
        c
        
          
            
          
          ⁢
          
            4
            ⁢
            
              
            
            ⁢
            π
            ⁢
            
              
            
            ⁢
            
              fd
              0
            
          
        
      
    
    +
    
      10
      ⁢
      
        
      
      ⁢
      n
      ⁢
      
        
      
      ⁢
      
        log
        10
      
      ⁢
      
        
          d
          0
        
        d
      
    
  
  =
  
    P
    noise
  




where PTX is the transmitter antenna power in dBm, Pnoise is the thermal noise power (equals −92 dBm for the bandwidth of 16.6 GHz), c is the speed of light, f is the operation radio frequency (e.g. 2.4 or 5.2 GHz), n is the path loss exponent determined experimentally and d0 is a reference distance outside of the Fraunhofer region of the antenna. Typically, d0=1 m is assumed.

Regardless of the manner in which one or more clouds are defined, each cloud and a unique identifier of each remote unit included in the cloud must be determined and recorded. In an exemplary embodiment, a configuration is performed during which information regarding each cloud and a unique identifier of each remote unit included in the cloud is stored, for example, in memory unit 42 and available to CPU 40.
As used herein, it is intended that terms “fiber optic cables” and/or “optical fibers” include all types of single mode and multi-mode light waveguides, including one or more bare optical fibers, loose-tube optical fibers, tight-buffered optical fibers, ribbonized optical fibers, bend-insensitive optical fibers, or any other expedient of a medium for transmitting light signals. An example of a bend-insensitive, or bend resistant, optical fiber is ClearCurve® Multimode fiber commercially available from Corning Incorporated. Suitable fibers of this type are disclosed, for example, in U.S. Patent Application Publication Nos. 2008/0166094 and 2009/0169163.
Bend resistant multimode optical fibers may comprise a graded-index core region and a cladding region surrounding and directly adjacent to the core region, the cladding region comprising a depressed-index annular portion comprising a depressed relative refractive index relative to another portion of the cladding. The depressed-index annular portion of the cladding is preferably spaced apart from the core. Preferably, the refractive index profile of the core has a parabolic or substantially curved shape. The depressed-index annular portion may, for example, comprise a) glass comprising a plurality of voids, or b) glass doped with one or more downdopants such as fluorine, boron, individually or mixtures thereof. The depressed-index annular portion may have a refractive index delta less than about −0.2% and a width of at least about 1 micron, said depressed-index annular portion being spaced from said core by at least about 0.5 microns.
In some embodiments that comprise a cladding with voids, the voids in some preferred embodiments are non-periodically located within the depressed-index annular portion. By “non-periodically located” we mean that when one takes a cross section (such as a cross section perpendicular to the longitudinal axis) of the optical fiber, the non-periodically disposed voids are randomly or non-periodically distributed across a portion of the fiber (e.g. within the depressed-index annular region). Similar cross sections taken at different points along the length of the fiber will reveal different randomly distributed cross-sectional hole patterns, i.e., various cross sections will have different hole patterns, wherein the distributions of voids and sizes of voids do not exactly match for each such cross section. That is, the voids are non-periodic, i.e., they are not periodically disposed within the fiber structure. These voids are stretched (elongated) along the length (i.e. generally parallel to the longitudinal axis) of the optical fiber, but do not extend the entire length of the entire fiber for typical lengths of transmission fiber. It is believed that the voids extend along the length of the fiber a distance less than about 20 meters, more preferably less than about 10 meters, even more preferably less than about 5 meters, and in some embodiments less than 1 meter.
The multimode optical fiber disclosed herein exhibits very low bend induced attenuation, in particular very low macrobending induced attenuation. In some embodiments, high bandwidth is provided by low maximum relative refractive index in the core, and low bend losses are also provided. Consequently, the multimode optical fiber may comprise a graded index glass core; and an inner cladding surrounding and in contact with the core, and a second cladding comprising a depressed-index annular portion surrounding the inner cladding, said depressed-index annular portion having a refractive index delta less than about −0.2% and a width of at least 1 micron, wherein the width of said inner cladding is at least about 0.5 microns and the fiber further exhibits a 1 turn, 10 mm diameter mandrel wrap attenuation increase of less than or equal to about 0.4 dB/turn at 850 nm, a numerical aperture of greater than 0.14, more preferably greater than 0.17, even more preferably greater than 0.18, and most preferably greater than 0.185, and an overfilled bandwidth greater than 1.5 GHz-km at 850 nm.
50 micron diameter core multimode fibers can be made which provide (a) an overfilled (OFL) bandwidth of greater than 1.5 GHz-km, more preferably greater than 2.0 GHz-km, even more preferably greater than 3.0 GHz-km, and most preferably greater than 4.0 GHz-km at an 850 nm wavelength. These high bandwidths can be achieved while still maintaining a 1 turn, 10 mm diameter mandrel wrap attenuation increase at an 850 nm wavelength of less than 0.5 dB, more preferably less than 0.3 dB, even more preferably less than 0.2 dB, and most preferably less than 0.15 dB. These high bandwidths can also be achieved while also maintaining a 1 turn, 20 mm diameter mandrel wrap attenuation increase at an 850 nm wavelength of less than 0.2 dB, more preferably less than 0.1 dB, and most preferably less than 0.05 dB, and a 1 turn, 15 mm diameter mandrel wrap attenuation increase at an 850 nm wavelength, of less than 0.2 dB, preferably less than 0.1 dB, and more preferably less than 0.05 dB. Such fibers are further capable of providing a numerical aperture (NA) greater than 0.17, more preferably greater than 0.18, and most preferably greater than 0.185. Such fibers are further simultaneously capable of exhibiting an OFL bandwidth at 1300 nm which is greater than about 500 MHz-km, more preferably greater than about 600 MHz-km, even more preferably greater than about 700 MHz-km. Such fibers are further simultaneously capable of exhibiting minimum calculated effective modal bandwidth (Min EMBc) bandwidth of greater than about 1.5 MHz-km, more preferably greater than about 1.8 MHz-km and most preferably greater than about 2.0 MHz-km at 850 nm.
Preferably, the multimode optical fiber disclosed herein exhibits a spectral attenuation of less than 3 dB/km at 850 nm, preferably less than 2.5 dB/km at 850 nm, even more preferably less than 2.4 dB/km at 850 nm and still more preferably less than 2.3 dB/km at 850 nm. Preferably, the multimode optical fiber disclosed herein exhibits a spectral attenuation of less than 1.0 dB/km at 1300 nm, preferably less than 0.8 dB/km at 1300 nm, even more preferably less than 0.6 dB/km at 1300 nm.
In some embodiments, the numerical aperture (“NA”) of the optical fiber is preferably less than 0.23 and greater than 0.17, more preferably greater than 0.18, and most preferably less than 0.215 and greater than 0.185.
In some embodiments, the core extends radially outwardly from the centerline to a radius R1, wherein 10≦R1≦40 microns, more preferably 20≦R1≦40 microns. In some embodiments, 22≦R1≦34 microns. In some preferred embodiments, the outer radius of the core is between about 22 to 28 microns. In some other preferred embodiments, the outer radius of the core is between about 28 to 34 microns.
In some embodiments, the core has a maximum relative refractive index, less than or equal to 1.2% and greater than 0.5%, more preferably greater than 0.8%. In other embodiments, the core has a maximum relative refractive index, less than or equal to 1.1% and greater than 0.9%.
In some embodiments, the optical fiber exhibits a 1 turn, 10 mm diameter mandrel attenuation increase of no more than 1.0 dB, preferably no more than 0.6 dB, more preferably no more than 0.4 dB, even more preferably no more than 0.2 dB, and still more preferably no more than 0.1 dB, at all wavelengths between 800 and 1400 nm.
FIG. 12 shows a schematic representation of the refractive index profile of a cross-section of the glass portion of an embodiment of a multimode optical fiber 500 comprising a glass core 420 and a glass cladding 400, the cladding comprising an inner annular portion 430, a depressed-index annular portion 450, and an outer annular portion 460. FIG. 13 is a schematic representation (not to scale) of a cross-sectional view of the optical waveguide fiber of FIG. 12. The core 420 has outer radius R1 and maximum refractive index delta Δ1MAX. The inner annular portion 430 has width W2 and outer radius R2. Depressed-index annular portion 450 has minimum refractive index delta percent Δ3MIN, width W3 and outer radius R3. The depressed-index annular portion 450 is shown offset, or spaced away, from the core 420 by the inner annular portion 430. The annular portion 450 surrounds and contacts the inner annular portion 430. The outer annular portion 460 surrounds and contacts the annular portion 450. The clad layer 400 is surrounded by at least one coating 510, which may in some embodiments comprise a low modulus primary coating and a high modulus secondary coating.
The inner annular portion 430 has a refractive index profile Δ2(r) with a maximum relative refractive index Δ2MAX, and a minimum relative refractive index Δ2MIN, where in some embodiments Δ2MAX=Δ2MIN. The depressed-index annular portion 450 has a refractive index profile Δ3(r) with a minimum relative refractive index Δ3MIN. The outer annular portion 460 has a refractive index profile Δ4(r) with a maximum relative refractive index Δ4MAX, and a minimum relative refractive index Δ4MIN, where in some embodiments Δ4MAX=Δ4MIN. Preferably, Δ1MAX>Δ2MAX>Δ3MIN. In some embodiments, the inner annular portion 430 has a substantially constant refractive index profile, as shown in FIG. 12 with a constant Δ2(r); in some of these embodiments, Δ2(r)=0%. In some embodiments, the outer annular portion 460 has a substantially constant refractive index profile, as shown in FIG. 12 with a constant Δ4(r); in some of these embodiments, Δ4(r)=0%. The core 420 has an entirely positive refractive index profile, where Δ1(r)>0%. R1 is defined as the radius at which the refractive index delta of the core first reaches value of 0.05%, going radially outwardly from the centerline. Preferably, the core 420 contains substantially no fluorine, and more preferably the core 420 contains no fluorine. In some embodiments, the inner annular portion 430 preferably has a relative refractive index profile Δ2(r) having a maximum absolute magnitude less than 0.05%, and Δ2MAX<0.05% and Δ2MIN>−0.05%, and the depressed-index annular portion 450 begins where the relative refractive index of the cladding first reaches a value of less than −0.05%, going radially outwardly from the centerline. In some embodiments, the outer annular portion 460 has a relative refractive index profile Δ4(r) having a maximum absolute magnitude less than 0.05%, and Δ4MAX<0.05% and Δ4MIN>−0.05%, and the depressed-index annular portion 450 ends where the relative refractive index of the cladding first reaches a value of greater than −0.05%, going radially outwardly from the radius where Δ3MIN is found.
Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. These modifications include, but are not limited to, extension to MIMO configurations extending beyond 2×2 MIMO or 4×4 MIMO to, for example, 2×3 MIMO, 4×6 MIMO, 8×8 MIMO and the like. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. It is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

## Claims

1. A method of operating a wireless communication system, comprising:
(a) determining a first plurality of remote units in a cloud bonded to a communication session;
(b) measuring at least one of a received signal strength and a data rate from each of the first plurality of remote units;
(c) measuring at least one of a received signal strength and an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session;
(d) dynamically bonding one of the second plurality of remote units to the session if the at least one of the measured received signal strength and the estimated data rate of the one of the second plurality of remote units is greater than the at least one of the measured received signal strength and the data rate of one of the first plurality of remote; and
(e) unbonding the one of the first plurality of remote units from the communication session, wherein
the communication session is comprised of a Multiple Input/Multiple Output (MIMO) session.

2. The method of claim 1, wherein the first plurality of remote units in the cloud is coupled to a service unit, and the second plurality of remote units in the cloud is coupled to the service unit.

3. The method of claim 2, wherein the first plurality of remote units in the cloud are within a line of sight of each other and wherein the second plurality of remote units in the cloud are within the line of sight.

4. The method of claim 2, wherein dynamically bonding the one of the second plurality of remote units to the communication session is repeated for each of the second plurality of remote units.

5. The method of claim 2, wherein dynamically bonding the one of the second plurality of remote units and unbonding the one of the first plurality of remote units from the communication session are repeated approximately every predetermined period of time of less than one second.

6. A controller comprising:
a head-end unit communicatively coupled to and configured to conduct a communication session with a first plurality of remote units and a second plurality of remote units;
where the head-end unit is configured to:
(a) determine the first plurality of remote units in a cloud bonded to a communication session;
(b) measure at least one of a received signal strength and a data rate from each of the first plurality of remote units;
(c) measure at least one of a received signal strength and an estimated data rate from each of the second plurality of remote units in the cloud not bonded to the communication session;
(d) dynamically bond one of the second plurality of remote units to the communication session if at least one of the measured received signal strength and the estimated data rate of the one of the second plurality of remote units is greater than the at least one of the measured received signal strength and the data rate of one of the first plurality of remote units; and
(e) repeat dynamically bonding the one of the second plurality of remote units to the communication sessions and unbonding the one of the first plurality of remote units to the communication session approximately every predetermined period of time of less than one second.

7. The controller of claim 6, wherein the communication session is comprised of a Multiple Input/Multiple Output (MIMO) session, and wherein the head-end unit is further configured to unbond the one of the first plurality of remote units from the communication session.

8. A system, comprising:
a plurality of remote units; and
a head-end unit communicatively coupled to and configured to conduct a communication session with a first plurality of remote units and a second plurality of remote units comprising a controller for directing a signal to the plurality of remote units,
wherein the head-end unit is configured to:
(a) determine the first plurality of remote units in a cloud bonded to the communication session;
(b) measure at least one of a received signal strength and a data rate from each of the first plurality of remote units;
(c) measure at least one of a received signal strength and an estimated data rate from each of a second plurality of remote units in the cloud not bonded to the communication session; and
(d) dynamically bond one of the second plurality of remote units to the communication session if at least one of the measured received signal strength and the estimated data rate of the one of the second plurality of remote units is greater than at least one of the measured received signal strength and the data rate of one of the first plurality of remote units, wherein
the first plurality of remote units and the second plurality of remote units are coupled to a service unit.

9. The system of claim 8, wherein the head-end unit is configured to repeat dynamically bonding the one of the second plurality of remote units to the communication session for each of the second plurality of remote units.

10. The system of claim 8, wherein the first plurality of remote units in the cloud are within line of sight of each other and wherein the second plurality of remote units in the cloud are within the line of sight.

11. The system of claim 8, wherein the head-end unit is further configured to unbond the one of the first plurality of remote units from the communication session, and wherein the communication session is comprised of a Multiple Input/Multiple Output (MIMO) session.

12. The system of claim 8, wherein the head-end unit is configured to repeat dynamically bonding the one of the second plurality of remote units to the communication session and unbonding the one of the first plurality of remote units from the communication session approximately every predetermined period of time.