FIELD OF THE INVENTION

Embodiments of the present invention generally relate to a system and method for monitoring the operational condition of a radio distribution network of a Distributed Antenna System (“DAS”).

BACKGROUND

When transmission or retransmission of radio frequency (RF) signals is desired, such as signals from cellular networks, WiFi, LTE systems, public safety systems, and others, inside or within a specific area or location such as building, an underground subway station, a basement, a parking lot, a stadium, and others, a signal source is used to transmit the RF signals. These signal sources include, for example, a Base Transceiver Station (BTS), a Small Cell, a Signal Booster (or BDA or Repeater), a Fiber DAS (distributed antenna system), and/or an equivalent signal source. The output port or ports of the signal source are connected to a radio distribution network which may be defined as an arrangement of passive elements (power splitters, couplers, circulators, etc.) that are used to distribute signals to antennas positioned throughout the specific area, for example, the interior of a building.

The connection between the signal source and the antennas can be implemented through a distribution network that can include physical and/or wireless connections, and the signal distribution network may or may not use splitters or couplers to distribute the signals to each antenna. In this manner, the signals generated or amplified by the signal source are received and radiated by the antennas to provide radio frequency (“RF”) coverage in all of the areas of the desired or specific area, enabling Downlink communication (from the signal source to the terminal units (“TUs”)) of the signals from the source to all terminal units located in that specific area or space. The terminal units may include cell phones, tablets, IoT devices, walkie talkies, or other receiver or transceiver device that can communicate using one or more of the RF signals from the signal source.

FIG. 1illustrates a known radio communication system including a signal source101, a transmission line109, an antenna port or connector103, an antenna105, and a terminal unit107. In the Uplink direction (from the terminal units to the signal sources), the antennas, that are distributed throughout the specified or desired area or space, receive the signals that are emitted or transmitted by the terminal units, and through use of the same distribution network that allows communication in the Downlink direction, these signals transmitted by the TUs reach the signal source, which allows communication to be established between the TUs and the signal source in the Uplink direction.

A problem experienced by all of these systems relates to the inability of the signal sources and of the administrators of such radio communication systems to determine if any of the antennas (e.g., an antenna inside a building) has been disconnected or damaged, or if the functionality of the antenna has been altered in any manner. In general, signal sources may have the capability of determining whether the distribution network has been disconnected, but they are not fully aware and do not have the capability to control or monitor the operational status of the devices at the other end of the distribution network. For example, the signal sources cannot control or monitor the operation or performance of antennas distributed inside a building.

The use of signal boosters as signal sources in a public safety application serves to illustrate the problem with the prior art.FIG. 2illustrates a known radio communication system with a point of anomaly. A signal booster (illustrated as a signal source201) may be equipped with incident and reflected power meters, such that in the event that the coaxial connector coupled to the output port of the signal booster becomes disconnected, the power meter can detect reflected power, which would mean that due to a no load condition (e.g., open port) or mismatched impedance, the signal power is being reflected and returned to the signal booster through the transmission line209. The detection of the reflected power would indicate that there is an operational malfunction within the distribution network (e.g., there is a fault or point of anomaly such as a short circuit211), which allows the signal booster to generate an alarm, for example a VSWR alarm, to alert the system administrator that the distribution network is not operating properly and that there will be potential problems with the emission of radio signals all over the entire area of interest, and consequently, that TUs may be left without coverage by not establishing a proper link with the signal booster.

FIG. 3illustrates a known radio communication system with a point of anomaly and experiencing loss of signal due to transmission line attenuation.FIG. 3shows a signal booster being used as a signal source301, a long transmission line309, and a point of anomaly311(e.g., a short circuit). Now, detection of reflected signal power is directly linked to the attenuation experienced by the signal from the time it is reflected (reflection may be generated by a disconnection of the coaxial cable, by an impedance problem/mismatch in the transmission line, or by a short circuit) until the time the reflected signal is received by the power meter in the signal booster. When the reflection occurs at the output connector of the signal booster (for example, if someone disconnects the coaxial output connector of the signal booster), the reflection is measured without any attenuation and is easily detectable. On the other hand, if the reflection occurs along a certain stretch of the transmission line, for example by an impedance mismatch at some point inside a coaxial cable, then the reflected signal returns back from the coaxial cable to the signal booster. If the reflected signal, as it makes its way back to the signal booster, is attenuated as a result of the travel distance between the point of reflection and the signal booster (which is almost if not always the case, as all transmission lines introduce losses that translate into attenuation of the signals), then it can be very difficult for the signal booster to detect such reflected signal, which means that in effect the signal booster loses its ability to detect anomalies in the distribution network.

FIG. 4illustrates a known radio communication system including a signal booster used as a signal source401, a transmission line409, a power splitter413, an operational antenna405, and a point of anomaly411. The ability to detect points of anomaly is further impaired when the distribution network includes signal splitters or signal couplers, which are components used to split signals and feed them to two or more coaxial cables, because these signal splitting components (e.g., power splitters, couplers, taps, etc.) further attenuate the signals (both incident and reflected signals) and because due to their design or manufacture, they oftentimes absorb the signals after the signals are reflected and returned back to the splitting device output port. As a result of the use of these splitting components, the signal reflected from a point of anomaly is prevented from ever reaching the signal booster, preventing the signal booster from detecting anomalies beyond the splitting or signal coupling components.

Another problem with indoor distribution systems is the inability to determine the location of the TUs. When a TU transmits an uplink (“UL”) signal, that signal is received by at least one of the indoor antennas, it travels through the distribution network to the signal source, as all the UL signals received by all the indoor antennas do, which makes the signal source unable to determine where a particular TU is located within the specific coverage area. By contrast, in a scenario where the intended coverage area is outdoors, many signal sources may receive the same UL signal from a specific TU and an analysis of power received from the TU can be performed in the time domain, which means that it would be possible to determine the location of a TU located outdoors through dimensional analysis.

There are different solutions to provide indoor location of the TUs, but those solutions require the installation of software or firmware on the TU so that the TU can send specific information to the signal source, which might then be used to provide a dimensional location of the TU. Other solutions to provide indoor location of the TUs require the installation of additional hardware in the TU and/or at the indoor location, such as but not limited to, RFID, beacons and others, which provides the signal source with the ability to provide a dimensional location of the TU based on information received from the additional hardware. All of the present solutions require additional software and/or firmware and/or hardware to be incorporated at or with the Terminal Unit, or hardware installed at the indoor area for the Terminal Unit to interact with the hardware.

A brief description of solutions that have been applied to the problem of detecting anomalies that may exist in the signal distribution systems follows. A first existing solution is the placement of VSWR alarms at the signal source output. This existing method is the most basic for detecting anomalies in the signal distribution network (distribution network, antennas, splitters, couplers, etc.) and it is limited by the attenuation experienced by the signals when reflected from the point of anomaly (broken coaxial cable, unplugged connector, antenna disconnected or damaged, short circuit, among others) until they reach the output port of the signal source. SeeFIG. 3.

A second existing solution implements granularity of the signal sources. With the goal of being able of exerting better control over each indoor antenna (and monitoring each antenna), and with the objective of obviating the losses that are introduced by the distribution networks, among other improvements, another existing solution involves providing signal sources with a higher level of granularity, meaning that each signal source manages a very small number of antennas which are connected to the signal source through very short paths of distribution media (e.g., short jumpers of coaxial cable), allowing any reflected signal to be detected by the signal source. The problem with this alternative existing solution is that it requires installation of a large number of signal sources, which causes a negative impact on the overall cost of the system, making this solution unviable for many systems. This solution is illustrated inFIG. 5, which shows a side by side comparison of a more conventional radio distribution network having a signal source501, several power splitters513and indoor antennas505, with a granular system having each signal source from the set of signal sources521connected to a corresponding antenna in the set of antennas525through short paths.

A third existing solution involves positioning couplers and/or other devices or components within the passive distribution network to monitor the VSWR reflected from the antennas. In this case many units are placed within the distribution network to constantly measure the VSWR of the cables and antennas. One limitation of this solution is that measuring the VSWR only provides an indication of how the network impedance is compensated, but does not reveal any information related to modifications or changes to the distribution network that result in changes to the signal propagation indoors. For example, if a third party replaces a original coaxial cable or transmission line in the distribution network for another transmission line with the same characteristic impedance but with different attenuation specifications, then the VSWR may not change and may not be indicative of any problems within the distribution network, the new additional losses introduced in the distribution network (due to the new transmission line attenuation specifications) may cause the signals to be further attenuated, affecting the resulting propagation of signals at the indoor location, which would also constitute a failure of the system.

A fourth existing solution involves connecting or embedding devices with antennas which detect through use of RFID, current sensing, current consumption, among others, if the antennas are connected to the passive distribution network. This type of solution allows the system owner or administrator to verify that all antennas are connected, but the disadvantage of these systems is that they do not provide an indication of VSWR or changes in the network and/or faults that modify the indoor propagation pattern.

With respect to a determining the location of a terminal unit positioned indoors, some solutions are based on specific software and/or firmware and/or hardware installed on the TU and/or the indoor location, wherein such software/firmware/hardware reads TU information such as, but not limited to, GPS location, and determines whether such information is transmitted to the signal source for dimensional location calculations. The limitation of these solutions is that their effectiveness depends on such software and/or firmware and/or hardware installed on the TU and/or at the indoor location, which increases the cost of the overall system and makes the system less fault tolerant, as the system performance will be dependent on additional system variables, reducing the system reliability. Further, in some cases these type of systems are limited in terms of performance due to the limited availability of external information, such as but not limited to, GPS signals present in the indoor location of the TU.

Therefore, in view of these disadvantages, there is a need in the art for an improved system and method to detect and report the location of points of anomaly of a radio distribution network of a radio communication system and to detect the location of terminal units within an indoor coverage area.

SUMMARY

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. Rather than specifically identifying key or critical elements of the invention or to delineate the scope of the invention, its purpose, inter alia, is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

The present disclosure relates to the detection of points of anomaly in a radio communications system and to the determination of the location of terminal units within an indoor signal coverage area. In exemplary implementation of the present disclosure, a communication system may include a signal source for transmitting downlink signals and receiving uplink signals to and from an indoor signal coverage area; a distributed antenna system interposed between the signal source and the indoor signal coverage area, the distributed antenna system having a master unit connected to at least one remote unit through a distribution network; and at least one antenna, connected to and corresponding to the at least one remote unit, for transmitting and receiving the downlink signals and the uplink signals to and from terminal units within the indoor coverage area. The master unit and the remote unit may be configured to detect the location of points of anomaly within the communication system. Further, the master unit may be configured to detect the location of terminal units within the indoor coverage area based on information provided by the at least one remote unit.

The following description and the annexed drawings set forth in detail certain illustrative aspects of the invention. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following description of the invention when considered in conjunction with the drawings.

