Patent Application
20160380836
The present invention relates to automatic sensing of connections in a network, particularly in analog RF distribution networks. The present invention also relates generally to the exchange of signaling information in an RF-over-fiber link, and in particular, the exchange of signaling information over the optical transport link used in in-building distributed antenna systems (DAS) to connect head-ends to remote units.
RF distribution networks often involve connections between physically distant nodes. By way of example, in an RF-over-fiber distribution network between a DAS head-end (HE) and a DAS remote unit, head-end transceivers will typically be located on a building rooftop within line-of-sight of one or more cellular base stations, and remote units (RUs) will be distributed throughout a building. In certain installations, multiple head-ends, corresponding to different wireless service providers, may share the same RUs. Ensuring proper cabling (i.e., proper connection between the HEs and the RUs) or detecting cable connection failures in such circumstances can be challenging.
The invention is directed to a method for detecting a user connection in an RF network. Embodiments of the invention include providing a first low-speed modem DC coupled to a first node connected to a first side of a user connection; providing a second low-speed modem DC coupled to a second node connected to a second side of a user connection; and with the first low-speed modem, modulating a DC voltage onto the user connection and detecting the modulated DC voltage using the second low-speed modem.
Embodiments of the invention further include using a digital-to-analog converter (DAC) and analog-to-digital converter (ADC) pair as the first modem, and using a second digital-to-analog converter (DAC) and analog-to-digital converter (ADC) pair as the second modem. Another embodiment of the invention includes using integrated circuits implementing a dial-up modem standard as the first and second modems.
In certain embodiments, where the modems do not have full duplex capability, the first node comprises an RF output and the first low-speed modem comprises a digital-to-analog converter (DAC), and the second node comprises an RF input and the second low-speed modem comprises an analog-to-digital converter (ADC). Further, the DC voltage may be modulated onto the user connection with pulse-width modulation, where a 20% modulation represents a binary 0, an 80% modulation represents a binary 1, and a 50% modulation represents a frame bit. Additionally, a part of the modulated DC voltage detected by the second low-voltage modem may comprise a 16 bit node ID.
Embodiments of the invention also provide a method for signaling over an RF-over-fiber link at a low bit-rate without interfering with the payload signal going across the fiber. This method of providing signaling over an RF-over-fiber link having a laser, an optical fiber, and an optical detector, where the RF-over-fiber link carries an RF payload signal, includes providing a digital to analog converter in electronic communication with the bias voltage of the laser such that the bias voltage of the laser is modulated with a low bit-rate signal, such that the low bit rate signal is present optically on the optical fiber; receiving the low bit rate signal and the RF payload signal with an optical detector which converts the combined signal into an electrical combined signal; and providing a low speed analog-to-digital converter that monitors the low bit-rate signal.
In certain embodiments, the low bit-rate signal is modulated with pulse-width modulation, where a 20% duty cycle represents a binary 0, an 80% duty cycle represents a binary 1, and a 50% duty cycle represents a frame bit. Further, in certain embodiments, a part of the low bit-rate signal monitored by the low speed analog-to-digital converter comprises a 16 bit node ID.
Embodiments of the invention have certain advantages, for example, the invention allows an installer or configurer of an RF network to determine the connectivity between network nodes, because the invention enables the user to verify that the system has been connected as intended. Additionally, embodiments of the invention allow the system to make this check automatically and alert the user to the existence of cabling problems. Further, embodiments of the invention allow the system to optimize the gain of its constituent elements to balance user demands on the network and to provide maximum dynamic range and noise performance.
The ability provided by the invention to automatically determine network connectivity, and even to dynamically and automatically build network maps, obviates the need to verify connectivity via manual inspection of the system, which becomes more difficult as the number of connections increases or the connections span distances which do not allow the installer to see both ends of the connection at the same time.
Embodiments of the invention are particularly advantageous where connectivity is established in the field by the end-user because the user's eventual configuration cannot be known a priori. If the system is already in operation when connectivity is changed, determining the network topology without disturbing the operation of existing nodes can also be problematic. Embodiments of the invention are especially useful in systems that bond multiple channels together to form MIMO channels, because upper-level protocols are typically unaware that the network connection has been implemented over multiple physical channels. Embodiments of the invention described herein solve the above identified problems by automatically establishing the RF network topology.
Additionally, in an RF-over-fiber optic system, it is sometimes necessary to exchange signaling information between two nodes (e.g., a head-end and a remote unit), for example, to check connectivity, for handshaking, and other purposes. Embodiments of the invention described herein advantageously accomplish this without consuming undue amounts of bandwidth or using up the dynamic range of the RF-over-fiber link.
The invention will be more fully understood by referring to the following Detailed Description of Specific Embodiments in conjunction with the Drawings, which are embedded in the Detailed Description below.
A detailed description of preferred embodiments of the invention is set forth below.
References throughout this specification to “one embodiment,” “an embodiment,” “a related embodiment,” or similar language mean that a particular feature, structure, or characteristic described in connection with the referred to “embodiment” is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. It is to be understood that no portion of disclosure, taken on its own and in possible connection with a figure, is intended to provide a complete description of all features of the invention.
In addition, the following disclosure may describe features of the invention with reference to corresponding drawings, in which like numbers represent the same or similar elements wherever possible. In the drawings, the depicted structural elements are generally not to scale, and certain components are enlarged relative to the other components for purposes of emphasis and understanding. It is to be understood that no single drawing is intended to support a complete description of all features of the invention. In other words, a given drawing is generally descriptive of only some, and generally not all, features of the invention. A given drawing and an associated portion of the disclosure containing a description referencing such drawing do not, generally, contain all elements of a particular view or all features that can be presented is this view, for purposes of simplifying the given drawing and discussion, and to direct the discussion to particular elements that are featured in this drawing. A skilled artisan will recognize that the invention may possibly be practiced without one or more of the specific features, elements, components, structures, details, or characteristics, or with the use of other methods, components, materials, and so forth. Therefore, although a particular detail of an embodiment of the invention may not be necessarily shown in each and every drawing describing such embodiment, the presence of this detail in the drawing may be implied unless the context of the description requires otherwise. In other instances, well known structures, details, materials, or operations may be not shown in a given drawing or described in detail to avoid obscuring aspects of an embodiment of the invention that are being discussed.
Networks are commonly modeled as directed or undirected graphs. Each vertex in the graph represents a node in the network, and each edge in the graph represents a connection between nodes. Each node and edge in the graph is assigned a numeric identifier which is unique across the system.
Computational or logical modules in the system are connected via a computer network which may or may not be distinct from the analog RF network. These modules create nodes in the graph, and request node identifiers for themselves from the system's central authority (such as a database). Each module in the system may have multiple nodes, and that component will also know how those nodes are interconnected. These computational components will tell the system's central authority to establish edges between its internal nodes. Each module in the RF network (i.e., the physical network) may have one or more nodes representing the external connectors located typically on the module's front panel.
Embodiments of the invention enable detection of a connection between modules by providing a DC-coupled path from the connector on a module to a low-speed modem. Examples of low-speed modems include dial-up modem standards, for example Bell 103, V.21, and V.90. An exemplary embodiment is set forth in
In the implementation of
Alternate designs include an integrated circuit implementing a dial-up modem standard used in place of the DAC-ADC pair. Alternative embodiments employ a software implementation of the modulation (using the DAC) or demodulation (using the ADC). This alternate implementation is discussed in greater detail below.
The modem's analog I/O is low-pass filtered so that the RF signal carried on the connection (i.e., the data being transported) is significantly attenuated and does not disrupt the operation of the modem 40. Because the modem 40 is DC-coupled to the connector, it may modulate DC voltages onto the RF line which may be detected at the other end by the remote module's demodulator. The AC coupling between the RF and the connector eliminates the interference caused by the low-speed modem 40.
Using this circuitry in place, a module broadcasts information to anything that is connected to it. In certain embodiments, the information is the node ID of the node (encoded in binary) representing the connector as assigned by the central authority. One or more remote modules receive, and attempt to demodulate and decode the broadcast signal, in order to determine the ID of the broadcasting node. If a received signal has been successfully demodulated, the broadcasting node is identified, and the receiving module contacts the central authority to establish node connectivity between itself and the broadcaster. In the exemplary embodiment shown in
If the low-speed modem does not support full-duplex operation, this approach requires that only one node broadcast to a connection at a time. In the reference implementation, connectors operating as RF outputs would broadcast, and connectors operating as RF inputs would demodulate.
As long as the system is cabled such that only one RF output drives any given connection, this approach allows simultaneous detection of the connectivity for the entire system. If two broadcasters (in the reference case, the RF outputs) are connected together, the system will not detect a valid connection, as the two modulators will interfere with one another.
When the receiver detects the node ID of the broadcaster, it contacts the central authority to effect a connection represented as an edge in the graph. The only information it needs to accomplish this is the node ID of its receiver and the node ID broadcast to it. Error checking can be implemented using any suitable error-detection scheme such as parity checks, Hamming codes, or the like.
Further reduction in erroneous connections may be achieved by establishing node types for cable-detect transmitters and cable-detect receivers which are distinct from other node types in the system, so that those nodes in the system that would not be expected to establish automatic connections would not be permitted to do so.
Because this approach does not interfere with the RF performance of the system, it may be implemented continuously during system operation. This allows the system to detect service disruption caused by a failed cable, or by an unintentional act on the part of the user. It also allows the system to detect intentional changes to the network topology and react accordingly.
The arrangement for detecting a connection according to embodiments of the invention have certain advantages. For example, in an analog RF distribution network, it is beneficial to determine the connectivity between network nodes, because it enables the user to verify that the system has been connected as intended. Additionally, provision for the automatic detection of the connectivity between network nodes can alert the user to the existence of cabling problems. Additionally, embodiments of the invention also allow the system to optimize the gain of its constituent elements to balance user demands on the network and to provide maximum dynamic range and noise performance.
Non-interfering signaling of the sort described above can also be achieved in a system employing an RF-over-fiber link. Thus, alternative embodiments of the invention are directed to providing signaling over an RF-over-fiber link at a low bit-rate without interfering with the payload signal going across the fiber. This is accomplished by providing a facility for adjusting the laser's bias voltage, and circuitry at the receiving end to detect the modulated optical power level.
With these provisions, the transmit equipment applies low-level, low-speed (i.e., audio frequency or lower) modulation to the laser's bias voltage, and that signal can be detected on the receiving end by the optical power detection circuitry. As long as the modulator's carrier frequency is sufficiently low, this signal will not affect the operation of the in-band RF signal being transmitted over the fiber. It will have a small impact on the amount of dynamic range available to the signal of interest, but this can be mitigated by reducing the depth of modulation on the signaling carrier, by only transmitting signaling information during “quiet” times (such as during system initialization, or when the system is seeing a low amount of use), or both.
In a particular embodiment of
The approach described herein provides one-way transmission of low-bandwidth signaling data from the transmitter to the receiver. Conventionally, signaling over an RF-over-fiber link is accomplished by implementing high-bandwidth modulation schemes (such as wi-fi) over the fiber. Embodiments of the invention have advantages over this conventional approach because they are realized with less costly equipment, do not require wi-fi capability at both ends of the fiber optic link, and eliminate the possibility of the modulated signal interfering with the payload signal.
The sequence 200 begins with step 205, where all modules in the network with cable detection hardware transmit the node ID (i.e., in the directed graph) of each cable detection node. Step 210 indicates that the node id transmission over the cable detect hardware will be accomplished by using pulse width modulation to send a 16-bit node ID plus a frame bit.
In step 215, the cable detect transmissions may transmit additional bits to serve as an error detection function (such as a Hamming code). Step 215 is optional. In step 220, when a cable detect receiver successfully demodulates a received node ID, it will verify that the received node ID represents a cable detect transmit node in the database graph before adding it to the graph.
In step 225, if the node ID demodulated by a cable detect receiver is not a cable detect transmitter, the receiver will disregard it and continue looking for a valid node ID. In step 230, RF connections between modules within the remote unit will be fixed, and if the modules are detected in the system, the detected modules will be added to the directed graph. In steps 235 and 240, the automatic cable detect is performed over the fiber optic cables. Optical transmitters will use the same pulse width modulation (PWM) algorithm to transmit a node ID as the other cable detect hardware, but will modulate the laser bias to achieve this. Receivers will detect bias modulation with optical power detectors.
Utilizing the cable detect methods described in relation to
While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention.
This application claims the benefit of U.S. Provisional Patent Application No. 62/184,161 filed on Jun. 24, 2015, titled “AUTOMATIC ESTABLISHMENT OF ANALOG NETWORK TOPOLOGY,” and U.S. Provisional Patent Application No. 62/184,164 filed on Jun. 24, 2015, titled “OUT-OF-BAND SIGNALING OVER A FIBER OPTIC LINK,” the entire contents of which are hereby incorporated by reference herein, for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62184161 | Jun 2015 | US | |
| 62184164 | Jun 2015 | US |
