US20160249365A1 - Offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (das) - Google Patents

Abstract

Offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS) is disclosed. In this regard, in one example, an interference signal offset circuit is provided in an RAU to offset intermodulation products leaked from a downlink path to an uplink path. An offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the intermodulation products leaked from the downlink path. A signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink signal received on the uplink path, thus offsetting the intermodulation products in the uplink signal. By providing the interference signal offset circuit in the RAU to offset the intermodulation products on the uplink path, it is possible to provide more implementation flexibility for the RAU without degrading the uplink signal.

Description

PRIORITY APPLICATION
• This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application No. 62/118,186, filed on Feb. 19, 2015, the content of which is relied upon and incorporated herein by reference in its entirety.
BACKGROUND
• The disclosure relates generally to distribution of communications signals in a distributed antenna system (DAS), and more particularly to offsetting unwanted downlink interference signals in an uplink path in a DAS resulting from a shared antenna for downlink and uplink communication in a remote antenna unit (RAU).
• Wireless customers are increasingly demanding digital data services, such as streaming video signals. Concurrently, some wireless customers use their wireless devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of DASs. DASs can be particularly useful when deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source. DASs include RAUs configured to receive and transmit communications signals to client devices within the antenna range of the RAUs.
• A typical DAS comprises head-end equipment (HEE) communicatively coupled to a plurality of RAUs. The HEE is connected to receive a variety of wireless services for distribution to the RAUs, such as wideband code division multiple access (WCDMA), long term evolution (LTE), and wireless local area network (WLAN) communications services as examples. To distribute such wireless communications services in a DAS, the wireless communications services can be provided in the form of analog RF communications signals and/or digital communications signals to the HEE of the DAS for distribution to the RAUs.
• An RAU in the DAS may be configured to support more than one type of wireless service that operates in a variety of RF spectrums and bandwidths. Downlink wireless communications signals received by the RAU are typically amplified by a power amplifier to increase the signal strengths before distributing the downlink wireless communications signals to client devices through one or more coupled antennas. However, the amplified downlink communications signals may comprise a plurality of intermodulation products. For example, these intermodulation products may be created as a result of non-linearities of the power amplifier in the downlink path. For instance, if two downlink wireless communications signals operating on 850 MegaHertz (MHz) and 870 MHz bands, respectively, are amplified by a power amplifier, a plurality of intermodulation products may be generated below the 850 MHz band (e.g., 830 MHz, 810 MHz, 790 MHz, and so on) and above the 870 MHz band (e.g. 890 MHz, 910 MHz, 930 MHz, and so on). Hence, the intermodulation products should be sufficiently isolated to prevent or reduce interferences on adjacent wireless communication channels.
• No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.
SUMMARY
• One embodiment of the disclosure relates to offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS). In DASs disclosed herein, at least one remote antenna unit (RAU) is provided. The RAU is configured to receive downlink wireless communications signals in a downlink path and distribute the downlink wireless communications signals to one or more client devices through a coupled antenna. The RAU is also configured to receive “wanted” uplink wireless communications signals from the one or more client devices on an uplink path through the coupled antenna and distribute the uplink wireless communications signals on the uplink path. By “wanted” uplink wireless communications signals, it means that these uplink wireless communications signals are received from the one or more client devices to be distributed in the DAS. Intermodulation products of the downlink wireless communications signals can be generated in the downlink path and leak over to the uplink path, thus interfering with the uplink wireless communications signals and degrading the uplink wireless communications signals. Thus, these one or more intermodulation products are interferences that may degrade the “wanted” uplink wireless communications signal and thus are “unwanted” downlink interference signals that are desired to be suppressed. For example, a downlink power amplifier that amplifies downlink wireless communications signals before the downlink wireless communications signals are distributed to client devices may generate one or more intermodulation products of the downlink wireless communications signals.
• In this regard, in DASs disclosed herein, an interference signal offset circuit is provided. The interference signal offset circuit can be associated with the RAU. The interference signal offset circuit is configured to offset the plurality of downlink intermodulation products on the uplink signal path. The interference signal offset circuit comprises at least one offset signal generation circuit and a signal summing circuit. The offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the plurality of intermodulation products associated with the downlink path. The signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink wireless communications signals received on the uplink path, thus offsetting the plurality of leaked intermodulation products in the uplink wireless communications signals. By providing the interference signal offset circuit in the RAU to offset the plurality of leaked intermodulation products on the uplink path, it is possible to provide more flexibility in implementation for the RAU without degrading the uplink wireless communications signals.
• An additional embodiment of the disclosure relates to an interference signal offset circuit in a DAS. The interference signal offset circuit comprises at least one offset signal generation circuit. The at least one offset signal generation circuit is configured to receive a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The at least one offset signal generation circuit is also configured to generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The interference signal offset circuit also comprises a signal summing circuit. The signal summing circuit is configured to receive an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path. The signal summing circuit is also configured to receive the at least one uplink interference offset signal. The signal summing circuit is also configured to generate an output uplink signal based on the received uplink signal. The signal summing circuit is also configured to combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal. The interference signal offset circuit also comprises a control circuit. The control circuit is configured to receive the output uplink signal from the signal summing circuit. The control circuit is also configured to configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.
• An additional embodiment of the disclosure relates to a method of offsetting at least one unwanted downlink interference signal from an uplink signal received in a DAS. The method comprises receiving a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The method also comprises generating at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The method also comprises receiving an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path. The method also comprises generating an output uplink signal based on the uplink signal. The method also comprises combining the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal.
• An additional embodiment of the disclosure relates to an RAU in DAS. The RAU comprises a downlink power amplifier configured to amplify a plurality of downlink communications signals received in a downlink path to generate a downlink signal in the downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal. The RAU also comprises an antenna configured to transmit the downlink signal and receive an uplink signal. The RAU also comprises a coupling device communicatively coupled to the downlink power amplifier and the antenna. The coupling device is configured to provide the downlink signal received from the downlink path to the antenna for transmission. The coupling device is also configured to provide the uplink signal received from the antenna to an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path.
• The RAU also comprises an interference signal offset circuit. The interference signal offset circuit comprises at least one offset signal generation circuit. The at least one offset signal generation circuit is configured to receive the downlink signal comprising the at least one unwanted downlink interference signal. The at least one offset signal generation circuit is also configured to generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal. The interference signal offset circuit also comprises a signal summing circuit. The signal summing circuit is configured to receive the uplink signal in the uplink path. The signal summing circuit is also configured to receive the at least one uplink interference offset signal from the at least one offset signal generation circuit. The signal summing circuit is also configured to generate an output uplink signal based on the received uplink signal and the received at least one uplink interference offset signal. The signal summing circuit is also configured to combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal. The interference signal offset circuit also comprises a control circuit. The control circuit is configured to receive the output uplink signal from the signal summing circuit. The control circuit is also configured to configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.
• 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 the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.
• It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
• The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic diagram of an exemplary distributed antenna system (DAS);
• FIG. 2 is a schematic diagram of an exemplary interference signal offset circuit that can be provided in a DAS, wherein the interference signal offset circuit comprises at least one offset signal generation circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path;
• FIG. 3 is flowchart of an exemplary interference signal offset process performed by the interference signal offset circuit inFIG. 2 for offsetting the at least one unwanted downlink interference signal in an uplink path;
• FIG. 4 is a schematic diagram of another exemplary interference signal offset circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path, based a first operation configuration to measure a first power level and a first phase of at least one downlink test intermodulation product;
• FIG. 5 is a schematic diagram of another exemplary interference signal offset circuit configured to generate at least one uplink interference offset signal to offset at least one unwanted downlink interference signal leaked from a downlink path to an uplink path, based a second operation configuration to measure a second power level and a second phase of at least one downlink intermodulation product;
• FIG. 6 is a schematic diagram of an exemplary optical fiber-based DAS that may include one or more interference signal offset circuits to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; and
• FIG. 7 is a partially schematic cut-away diagram of an exemplary building infrastructure in which an interference signal offset circuit, including the interference signal offset circuits ofFIGS. 2, 4, and 5 can be employed.
DETAILED DESCRIPTION
• One embodiment of the disclosure relates to offsetting unwanted downlink interference signals in an uplink path in a distributed antenna system (DAS). In DASs disclosed herein, at least one remote antenna unit (RAU) is provided. The RAU is configured to receive downlink wireless communications signals in a downlink path and distribute the downlink wireless communications signals to one or more client devices through a coupled antenna. The RAU is also configured to receive “wanted” uplink wireless communications signals from the one or more client devices on an uplink path through the coupled antenna and distribute the uplink wireless communications signals on the uplink path. By “wanted” uplink wireless communications signals, it is meant that these uplink wireless communications signals are received from the one or more client devices to be distributed in the DAS. Intermodulation products of the downlink wireless communications signals can be generated in the downlink path and leak over to the uplink path, thus interfering with the uplink wireless communications signals and degrading the uplink wireless communications signals. Thus, these one or more intermodulation products are interferences that may degrade the “wanted” uplink wireless communications signal and thus are “unwanted” downlink interference signals that are desired to be suppressed. For example, a downlink power amplifier that amplifies downlink wireless communications signals before the downlink wireless communications signals are distributed to client devices may generate one or more intermodulation products of the downlink wireless communications signals. In this regard, in DASs disclosed herein, an interference signal offset circuit is provided. The interference signal offset circuit can be associated with the RAU. The interference signal offset circuit is configured to offset the plurality of downlink intermodulation products on the uplink signal path. The interference signal offset circuit comprises at least one offset signal generation circuit and a signal summing circuit. The offset signal generation circuit is configured to generate at least one uplink interference offset signal based on the plurality of intermodulation products associated with the downlink path. The signal summing circuit is configured to combine the at least one uplink interference offset signal with the uplink wireless communications signals received on the uplink path, thus offsetting the plurality of leaked intermodulation products in the uplink wireless communications signals. By providing the interference signal offset circuit in the RAU to offset the plurality of leaked intermodulation products on the uplink path, it is possible to provide more flexibility in implementation for the RAU without degrading the uplink wireless communications signals.
• Before discussing examples of offsetting unwanted downlink interference signals in an uplink path in a DAS starting atFIG. 2, a discussion of an exemplary DAS that employs a communications medium to support wireless communications services to a plurality of RAUs is first provided with reference toFIG. 1. The discussion of specific exemplary aspects of offsetting unwanted downlink interference signals in an uplink path in a DAS starts atFIG. 2.
• In this regard,FIG. 1 illustrates distribution of communications services to coverage areas10(1)-10(N) of aDAS12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as radio frequency (RF) identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas10(1)-10(N) may be remotely located. In this regard, the remote coverage areas10(1)-10(N) are created by and centered on RAUs14(1)-14(N) connected to a head-end equipment (HEE)16 (e.g., a head-end controller or head-end unit or central unit). TheHEE16 may be communicatively coupled to asignal source18, for example a base transceiver station (BTS) or a baseband unit (BBU). In this regard, theHEE16 receives downlink communications signals20D from thesignal source18 to be distributed to the RAUs14(1)-14(N). The RAUs14(1)-14(N) are configured to receive the downlink communications signals20D from theHEE16 over acommunications medium22 to be distributed to the respective coverage areas10(1)-10(N) of the RAUs14(1)-14(N). In a non-limiting example, thecommunications medium22 may be a wired communications medium, a wireless communications medium, or an optical fiber-based communications medium. Each of the RAUs14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services toclient devices26 within their respective remote coverage areas10(1)-10(N). The RAUs14(1)-14(N) are also configured to receive uplink communications signals20U from theclient devices26 in their respective remote coverage areas10(1)-10(N) to be distributed to thesignal source18. The size of a given remote coverage area10(1)-10(N) is determined by the amount of RF power transmitted by the respective RAU14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of theclient device26.Client devices26 usually have a fixed maximum RF receiver sensitivity, so that the above-mentioned properties of the RAUs14(1)-14(N) mainly determine the size of their respective remote coverage areas10(1)-10(N).
• With reference toFIG. 1, the downlink communications signals20D and the uplink communications signals20U may be distributed on adjacent downlink and uplink channels (not shown). For example, the downlink communications signals20D may be distributed on an 850-870 MegaHertz (MHz) downlink channel and the uplink communications signals20U may be distributed on an 825-845 MHz uplink channel. The RF transmitter/receiver in each of the RAUs14(1)-14(N) is connected to the respective antenna24(1)-24(N) through a coupling device (not shown). The coupling device is configured to alternate between transmitting the downlink communications signals20D to the respective antennas24(1)-24(N) and receiving the uplink communications signals20U from the respective antennas24(1)-24(N). The downlink communications signals20D are amplified at each of the RAUs14(1)-14(N) by a downlink power amplifier (not shown) to increase the signal strength prior to being provided to the coupling device. Due to non-linearities of the downlink power amplifier, a plurality of intermodulation products28(1)-28(X) may be generated and associated with the amplified downlink communications signals20D. In this regard, the plurality of intermodulation products28(1)-28(X) may be leaked to anuplink path29 due to insufficient isolation by the coupling device, thus degrading the uplink communications signals20U. One solution for preventing these intermodulation products28(1)-28(X) from leaking into theuplink path29 is to employ high isolation RF filters (e.g., cavity filters) in the coupling device. However, the high isolation RF filters may lead to significant cost increase of the RAUs14(1)-14(N). However, it may be desirable to avoid using higher cost high isolation RF filters in the RAUs14(1)-14(N) due to their significant costs.
• In this regard,FIG. 2 is a schematic diagram of an exemplary interference signal offsetcircuit30. The interference signal offsetcircuit30 includes an offsetsignal generation circuit32. The offsetsignal generation circuit32 is configured to generate at least one uplink interference offsetsignal34 in anuplink path40 to offset at least one unwanteddownlink interference signal36 leaked from adownlink path38 to anuplink path40. In this regard, the offsetsignal generation circuit32 receives adownlink signal42 in thedownlink path38. Thedownlink signal42 is an amplifieddownlink signal42 generated by adownlink power amplifier44 based on a plurality of downlink communications signals46(1)-46(M). Due to non-linearities of thedownlink power amplifier44, thedownlink signal42 may comprise the at least one unwanteddownlink interference signal36 after being amplified by thedownlink power amplifier44. In a non-limiting example, the at least one unwanteddownlink interference signal36 comprises a plurality of downlink intermodulation products48(1)-48(N) generated by thedownlink power amplifier44. The plurality of downlink intermodulation products48(1)-48(N) are additional downlink signals formed at frequencies different from thedownlink signal42. For example, if thedownlink power amplifier44 received two downlink communications signals46(1),46(2) operating on 850 MHz and 870 MHz bands, respectively, the plurality of downlink intermodulation products48(1)-48(N) may exist at 830 MHz, 810 MHz, 790 MHz, and so on, as well as at 890 MHz, 910 MHz, 930 MHz, and so on.
• With continuing reference toFIG. 2, thedownlink signal42 and the at least one unwanteddownlink interference signal36 are also received by acoupling device50 and distributed to one or more client devices (not shown) via at least oneantenna52 that is communicatively coupled to thecoupling device50. Thecoupling device50 also receives a wanteduplink signal54 from the one or more client devices via theantenna52 and provides the received wanteduplink signal54 to theuplink path40. Accordingly, thecoupling device50 is configured to alternate between transmitting thedownlink signal42 and receiving the wanteduplink signal54. In a non-limiting example, thecoupling device50 may be a duplexer, a multiplexer, a hybrid combiner, or a software-defined frontend module. In another non-limiting example, thecoupling device50 may be a lower-cost ceramic filter that is unable to sufficiently isolate the at least one unwanteddownlink interference signal36. As a result, the at least one unwanteddownlink interference signal36 may be leaked from thedownlink path38 to theuplink path40. Consequently, thecoupling device50 provides anuplink signal54′, which comprises the wanteduplink signal54 and the at least one unwanteddownlink interference signal36, to theuplink path40. In this regard, the wanteduplink signal54 is generated by the one or more client devices for distribution on theuplink path40. In contrast, the at least one unwanteddownlink interference signal36 is introduced by an interferer such as thedownlink power amplifier44, thus must not be distributed on theuplink path40.
• With continuing reference toFIG. 2, the interference signal offsetcircuit30 also comprises asignal summing circuit56. Thesignal summing circuit56 is configured to receive theuplink signal54′ in theuplink path40 from thecoupling device50 and generate anoutput uplink signal58 based on theuplink signal54′. In this regard, theoutput uplink signal58 is the same as theuplink signal54′. Thesignal summing circuit56 is communicatively coupled to the offsetsignal generation circuit32 to receive the at least one uplink interference offsetsignal34. Thesignal summing circuit56 is configured to combine the at least one uplink interference offsetsignal34 with theuplink signal54′. As is further discussed inFIGS. 4 and 5, the at least one uplink interference offsetsignal34 is configured to have a matching power level and an opposing phase as the at least one unwanteddownlink interference signal36 comprised in theuplink signal54′. In this regard, the at least one unwanteddownlink interference signal36 is offset by the at least one uplink interference offsetsignal34 when thesignal summing circuit56 combines the at least one uplink interference offsetsignal34 with theuplink signal54′. Hence, theoutput uplink signal58′ comprises only the wanteduplink signal54.
• With continuing reference toFIG. 2, note that the offsetsignal generation circuit32 illustrated herein may comprise a plurality of offsetsignal generation circuits32 disposed in a parallel arrangement. Each of the plurality of offsetsignal generation circuits32 may be configured to generate the at least one uplink interference offsetsignal34 to offset at least one downlink intermodulation product among the plurality of downlink intermodulation products48(1)-48(N). In this regard, the plurality of offsetsignal generation circuits32 generates a plurality of uplink interference offset signals34, respectively.
• With continuing reference toFIG. 2, the interference signal offsetcircuit30 also comprises acontrol circuit60 communicatively coupled to the offsetsignal generation circuit32 and thesignal summing circuit56. In this regard, thecontrol circuit60 is configured to receive theoutput uplink signal58. As is further discussed inFIGS. 4 and 5, thecontrol circuit60 measures an interference signal power level and an interference signal phase of at least one downlink intermodulation product among the plurality of downlink intermodulation products48(1)-48(N). Based on the measured interference signal power level and the measured interference signal phase, thecontrol circuit60 then configures the offsetsignal generation circuit32 to generate the at least one uplink interference offsetsignal34. The at least one uplink interference offsetsignal34 then offsets the at least one unwanteddownlink interference signal36.
• In this regard,FIG. 3 is flowchart of an exemplary interferencesignal offsetting process70 for offsetting the at least one unwanteddownlink interference signal36 inFIG. 2 in theuplink path40. With reference toFIG. 3, thedownlink signal42 is received in thedownlink path38, wherein thedownlink signal42 comprises the at least one unwanted downlink interference signal36 (block72). Next, the at least one uplink interference offsetsignal34 is generated based on the received at least one unwanted downlink interference signal36 (block74). Theuplink signal54′ is received in theuplink path40, wherein theuplink signal54′ comprises the wanteduplink signal54 and the at least one unwanteddownlink interference signal36 that is leaked from thedownlink path38 to the uplink path40 (block76). Subsequently, theoutput uplink signal58 is generated based on theuplink signal54′ (block78). In this regard, theoutput uplink signal58 comprises the wanteduplink signal54 and the at least one unwanteddownlink interference signal36. Finally, the at least one uplink interference offsetsignal34 is combined with theuplink signal54′ to offset the at least one unwanteddownlink interference signal36 in theoutput uplink signal58′ (block80).
• As previously mentioned inFIG. 2, thecontrol circuit60 configures the offsetsignal generation circuit32 to generate the at least one uplink interference offsetsignal34 to offset the at least one unwanteddownlink interference signal36. In fact, thecontrol circuit60 takes two steps to configure offsetting the at least one unwanteddownlink interference signal36. In the first step, thecontrol circuit60 configures the interference signal offsetcircuit30 based on a first operation configuration. In the second step, thecontrol circuit60 configures the interference signal offsetcircuit30 based on a second operation configuration. In this regard,FIGS. 4 and 5 illustrate the first operation configuration and the second operation configuration, respectively. Common elements betweenFIGS. 2, 4, and 5 are shown with common element numbers, and thus will not be re-described herein.
• In this regard,FIG. 4 is a schematic diagram of an exemplary interference signal offset circuit30(1) configured based on the first operation configuration to measure a first power level and a first phase of at least one downlinktest intermodulation product90. The interference signal offset circuit30(1) comprises at least one offset signal generation circuit32(1), a signal summing circuit56(1), and a control circuit60(1). Thecoupling device50 is coupled to theantenna52 by a first switch (S1)92, which is kept in an open position in the first operation configuration. The signal summing circuit56(1) comprises a second switch (S2)94 and a third switch (S3)96. The signal summing circuit56(1) also comprises asignal summing point98 coupled to the second switch (S2)94 and the third switch (S3)96. Thesignal summing point98 is configured to combine the at least one uplink interference offsetsignal34 with theuplink signal54′.
• With reference toFIG. 4, thecoupling device50 receives adownlink test signal102 in thedownlink path38. Thedownlink test signal102 is an amplifieddownlink test signal102 generated by thedownlink power amplifier44 based on a plurality of downlink test communications signals104(1)-104(M). In a non-limiting example, the plurality of downlink test communications signals104(1)-104(M) may be generated by a signal generator (not shown) coupled to thedownlink power amplifier44. The plurality of downlink test communications signals104(1)-104(M) are in the same operating bands as the plurality of downlink communications signals46(1)-46(M) (not shown). Alternatively, thedownlink test signal102 may also be generated based on the plurality of downlink communications signals46(1)-46(M). Due to the non-linearities of thedownlink power amplifier44, thedownlink test signal102 comprises a plurality of downlink test intermodulation products106(1)-106(N).
• With continuing reference toFIG. 4, thecoupling device50 comprises adownlink signal filter108 and anuplink signal filter110. Given that the first switch (S1)92 is kept open according to the first operation configuration, thedownlink test signal102 passes through thedownlink signal filter108 and becomes anuplink test signal112 in theuplink path40. Thedownlink signal filter108, however, is unable to provide sufficient RF isolation to eliminate the plurality of downlink test intermodulation products106(1)-106(N) comprised in thedownlink test signal102. As a result, the plurality of downlink test intermodulation products106(1)-106(N) is leaked to theuplink path40. Given that the third switch (S3)96 is also kept open according to the first operation configuration, the at least one offset signal generation circuit32(1) is decoupled from thesignal summing point98. Therefore, theuplink test signal112, along with the plurality of downlink test intermodulation products106(1)-106(N), is received by an uplink power amplifier114 configured to amplify theuplink test signal112.
• With continuing reference toFIG. 4, the control circuit60(1) comprises anuplink signal filter116 coupled to the uplink power amplifier114. Theuplink signal filter116 receives theuplink test signal112 and selectively passes the at least one downlinktest intermodulation product90 among the plurality of downlink test intermodulation products106(1)-106(N) that is comprised in theuplink test signal112. Apower detection circuit118, coupled to theuplink signal filter116, is configured to receive and measure the first power level of the at least one downlinktest intermodulation product90 passed through theuplink signal filter116. Subsequently, acontroller120, coupled to thepower detection circuit118, receives the at least one downlinktest intermodulation product90 from thepower detection circuit118 and measures the first phase of the at least one downlinktest intermodulation product90.
• FIG. 5 is a schematic diagram of an exemplary interference signal offset circuit30(2) configured based on the second operation configuration to measure a second power level and a second phase of at least onedownlink intermodulation product130. According to the second operation configuration, the first switch (S1)92 and the second switch (S2)94 are kept open while the third switch (S3)96 is closed. By opening the second switch (S2)94, thecoupling device50 is decoupled from thesignal summing point98. By closing the third switch (S3)96, at least one offset signal generation circuit32(2) is coupled to thesignal summing point98.
• With reference toFIG. 5, the at least one offset signal generation circuit32(2) receives thedownlink signal42, which may comprise the plurality of downlink intermodulation products48(1)-48(N). The at least one offset signal generation circuit32(2) comprises anintermodulation product filter132, anadjustable power amplifier134, and anadjustable phase shifter136. Theintermodulation product filter132 is controlled by thecontroller120 to selectively pass the at least onedownlink intermodulation product130 to theadjustable power amplifier134. In a non-limiting example, the at least onedownlink intermodulation product130 passed through theintermodulation product filter132 is in the same order as the at least one downlinktest intermodulation product90. For instance, if the at least one downlinktest intermodulation product90 is a third order intermodulation product among the plurality of downlink test intermodulation products106(1)-106(N), the at least onedownlink intermodulation product130 is also a third order modulation product among the plurality of downlink intermodulation products48(1)-48(N).
• With continuing reference toFIG. 5, the at least onedownlink intermodulation product130 passes through theadjustable power amplifier134, theadjustable phase shifter136, and theuplink signal filter116 without being modified. Thepower detection circuit118 measures the second power level of the at least onedownlink intermodulation product130. Subsequently, thecontroller120 measures the second phase of the at least onedownlink intermodulation product130. Next, thecontroller120 compares the second measured power level against the first measured power level. If the second measured power level is different from the first measured power level, thecontroller120 then controls theadjustable power amplifier134 to continuously adjust the second power level until the second power level substantially matches the first power level. Furthermore, thecontroller120 controls theadjustable phase shifter136 to phase-shift the second phase to be substantially opposite of the first phase. By having the second power level substantially match the first power level and the second phase substantially oppose the first phase, the at least onedownlink intermodulation product130 is able to offset the at least one downlinktest intermodulation product90. The interference signal offset circuit30(2) is placed in a normal operation configuration by closing the first switch (S1)92, the second switch (S2)94, and the third switch (S3)96. Hence, as illustrated earlier inFIG. 2, the at least one offsetsignal generation circuit32 is able to generate the at least one uplink interference offsetsignal34 to offset the at least one unwanteddownlink interference signal36.
• The interference signal offsetcircuits30,30(1), and30(2) inFIGS. 2, 4, and 5, respectively, can be provided in other DASs as well, without limitation. For example,FIG. 6 is a schematic diagram of exemplary optical fiber-basedDAS140 that may be employed according to the embodiments disclosed herein to include an interference signal offset circuit, like the interference signal offsetcircuit30 inFIG. 2. In this embodiment, the optical fiber-basedDAS140 includes an optical fiber for distributing communications services. The optical fiber-basedDAS140 in this embodiment is comprised of three (3) main components. One or more radio interfaces, provided in the form of radio interface modules (RIMs)142(1)-142(M) in this embodiment, are provided in acentral unit144 to receive and process downlink electrical communications signals146D(1)-146D(R) prior to optical conversion into downlink optical communications signals. The RIMs142(1)-142(M) provide both downlink and uplink interfaces. The notations “1-R” and “1-M” indicate that any number of the referenced component, 1-R and 1-M, respectively, may be provided. Thecentral unit144 is configured to accept the RIMs142(1)-142(M) as modular components that can easily be installed and removed or replaced in thecentral unit144. In one embodiment, thecentral unit144 is configured to support up to twelve (12) RIMs142(1)-142(12).
• Each RIM142(1)-142(M) can be designed to support a particular type of radio source or range of radio sources (i.e., frequencies) to provide flexibility in configuring thecentral unit144 and the optical fiber-basedDAS140 to support the desired radio sources. For example, oneRIM142 may be configured to support the Personal Communication Services (PCS) radio band. AnotherRIM142 may be configured to support a 700 MHz radio band. In this example, by inclusion of theseRIMs142, thecentral unit144 could be configured to support and distribute communications signals on both PCS and Long Term Evolution (LTE) radio bands, as an example. The RIMs142(1)-142(M) may be provided in thecentral unit144 that support any frequency bands desired, including but not limited to the US Cellular band, Personal Communication Services (PCS) band, Advanced Wireless Services (AWS) band, 700 MHz band, LTE bands, Global System for Mobile communications (GSM)900, GSM1800, and Universal Mobile Telecommunication System (UMTS). The RIMs142(1)-142(M) may also be provided in thecentral unit144 that support any wireless technologies desired, including but not limited to Code Division Multiple Access (CDMA), CDMA200, 1×RTT, Evolution-Data Only (EV-DO), UMTS, High-speed Packet Access (HSPA), GSM, General Packet Radio Services (GPRS), Enhanced Data GSM Environment (EDGE), Time Division Multiple Access (TDMA), LTE, Integrated Digital Enhanced Network (iDEN), and Cellular Digital Packet Data (CDPD).
• The RIMs142(1)-142(M) may be provided in the central unit144 that support any frequencies desired, including but not limited to US Federal Communications Commission (FCC) and Industry Canada frequencies (824-849 MHz on uplink and 869-894 MHz on downlink), US FCC and Industry Canada frequencies (1850-1915 MHz on uplink and 1930-1995 MHz on downlink), US FCC and Industry Canada frequencies (1710-1755 MHz on uplink and 2110-2155 MHz on downlink), US FCC frequencies (698-716 MHz and 776-787 MHz on uplink and 728-746 MHz on downlink), EU R & TTE frequencies (880-915 MHz on uplink and 925-960 MHz on downlink), EU R & TTE frequencies (1710-1785 MHz on uplink and 1805-1880 MHz on downlink), EU R & TTE frequencies (1920-1980 MHz on uplink and 2110-2170 MHz on downlink), US FCC frequencies (806-824 MHz on uplink and 851-869 MHz on downlink), US FCC frequencies (896-901 MHz on uplink and 929-941 MHz on downlink), US FCC frequencies (793-805 MHz on uplink and 763-775 MHz on downlink), and US FCC frequencies (2495-2690 MHz on uplink and downlink).
• The downlink electrical communications signals146D(1)-146D(R) are provided to a plurality of optical interfaces, provided in the form of optical interface modules (OIMs)148(1)-148(N) in this embodiment, to convert the downlink electrical communications signals146D(1)-146D(R) into downlink optical communications signals150D(1)-150D(R). The notation “1-N” indicates that any number of the referenced component 1-N may be provided. The OIMs148(1)-148(N) may be configured to provide one or more optical interface components (OICs) (not shown) that contain optical to electrical (O/E) and electrical to optical (E/O) converters (not shown), as will be described in more detail below. The OIMs148(1)-148(N) support the radio bands that can be provided by the RIMs142(1)-142(M), including the examples previously described above. Thus, in this embodiment, the OIMs148(1)-148(N) may support a radio band range from 400 MHz to 2700 MHz, as an example.
• The OIMs148(1)-148(N) each include E/O converters to convert the downlink electrical communications signals146D(1)-146D(R) into the downlink optical communications signals150D(1)-150D(R). The downlink optical communications signals150D(1)-150D(R) are communicated over a downlink opticalfiber communications medium152D to a plurality of remote antenna units (RAUs)154(1)-154(S). The notation “1-S” indicates that any number of the referenced component 1-S may be provided. O/E converters provided in the RAUs154(1)-154(S) convert the downlink optical communications signals150D(1)-150D(R) back into the downlink electrical communications signals146D(1)-146D(R), which are provided to antennas158(1)-158(S) in the RAUs154(1)-154(S) to client devices (not shown) in the reception range of the antennas158(1)-158(S).
• E/O converters are also provided in the RAUs154(1)-154(S) to convert uplink electrical communications signals160U(1)-160U(S) received from client devices through the antennas158(1)-158(S) into uplink optical communications signals150U(1)-150U(S) to be communicated over an uplink opticalfiber communications medium152U to the OIMs148(1)-148(N). The OIMs148(1)-148(N) include O/E converters that convert the uplink optical communications signals150U(1)-150U(S) into uplink electrical communications signals162U(1)-162U(S) that are processed by the RIMs142(1)-142(M) and provided as the uplink electrical communications signals162U(1)-162U(S). Note that the downlink opticalfiber communications medium152D and the uplink opticalfiber communications medium152U connected to each RAU154(1)-154(S) may be a common optical fiber communications medium, wherein for example, wave division multiplexing (WDM) may be employed to provide the downlink optical communications signals150D(1)-150D(R) and the uplink optical communications signals150U(1)-150U(S) on the same optical fiber communications medium.
• The interference signal offsetcircuits30,30(1), and30(2) ofFIGS. 2, 4, and 5, respectively, may be provided in an indoor environment, as illustrated inFIG. 7.FIG. 7 is a partially schematic cut-away diagram of anexemplary building infrastructure170 in which an interference signal offset circuit, including the interference signal offsetcircuits30,30(1), and30(2) ofFIGS. 2, 4, and 5, respectively, can be employed. Thebuilding infrastructure170 in this embodiment includes a first (ground) floor172(1), a second floor172(2), and a third floor172(3). The floors172(1)-172(3) are serviced by acentral unit174 to provideantenna coverage areas176 in thebuilding infrastructure170. Thecentral unit174 is communicatively coupled to abase station178 to receive downlink communications signals180D from thebase station178. Thecentral unit174 is communicatively coupled toRAUs182 to receive uplink communications signals180U from theRAUs182, as previously discussed above. The downlink and uplink communications signals180D,180U communicated between thecentral unit174 and theRAUs182 are carried over ariser cable184. Theriser cable184 may be routed through interconnect units (ICUs)186(1)-186(3) dedicated to each of the floors172(1)-172(3) that route the downlink and uplink communications signals180D,180U to theRAUs182 and also provide power to theRAUs182 viaarray cables188.
• Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is no way intended that any particular order be inferred.
• It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the invention. Since modifications combinations, sub-combinations and variations of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and their equivalents.

Claims (23)

What is claimed is:

1. An interference signal offset circuit in a distributed antenna system (DAS), comprising:

at least one offset signal generation circuit configured to:

receive a downlink signal in a downlink path, the downlink signal comprising at least one unwanted downlink interference signal; and

generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal;

a signal summing circuit configured to:

receive an uplink signal in an uplink path, the uplink signal comprising a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path;

receive the at least one uplink interference offset signal;

generate an output uplink signal based on the received uplink signal; and

combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and

a control circuit configured to:

receive the output uplink signal from the signal summing circuit; and

configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.

2. The interference signal offset circuit ofclaim 1, wherein:

the at least one unwanted downlink interference signal comprises a plurality of downlink intermodulation products; and

the at least one offset signal generation circuit is configured to generate the at least one uplink interference offset signal based on at least one downlink intermodulation product among the plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.

3. The interference signal offset circuit ofclaim 2, wherein the control circuit is further configured to:

measure an interference signal power level of the at least one downlink intermodulation product among the plurality of downlink intermodulation products;

measure an interference signal phase of the at least one downlink intermodulation product among the plurality of downlink intermodulation products; and

configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal based on the measured interference signal power level and the measured interference signal phase.

4. The interference signal offset circuit ofclaim 3, wherein the at least one offset signal generation circuit is configured generate the at least one uplink interference offset signal to substantially match the interference signal power level of the at least one downlink intermodulation product and be substantially opposite in phase to the interference signal phase of the at least one downlink intermodulation product.

5. The interference signal offset circuit ofclaim 2, wherein the at least one uplink interference offset signal generated by the at least one offset signal generation circuit is configured to offset the at least one downlink intermodulation product among the plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.

6. A method of offsetting at least one unwanted downlink interference signal from an uplink signal received in a distributed antenna system (DAS), comprising:

receiving a downlink signal in a downlink path, wherein the downlink signal comprises at least one unwanted downlink interference signal;

generating at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal;

receiving an uplink signal in an uplink path, wherein the uplink signal comprises a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path;

generating an output uplink signal based on the uplink signal; and

combining the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal.

7. The method ofclaim 6, further comprising generating the at least one uplink interference offset signal to offset at least one downlink intermodulation product among a plurality of downlink intermodulation products in the received at least one unwanted downlink interference signal.

8. The method ofclaim 6, further comprising:

generating the at least one uplink interference offset signal by at least one offset signal generation circuit; and

combining the uplink signal with the at least one uplink interference offset signal by a signal summing circuit.

9. The method ofclaim 8, further comprising receiving the uplink signal from a coupling device communicatively coupled to at least one antenna, wherein the coupling device is further configured to provide the downlink signal to the at least one antenna.

10. The method ofclaim 9, further comprising:

decoupling the at least one antenna from the coupling device;

decoupling the at least one offset signal generation circuit from the signal summing circuit;

receiving a downlink test signal in the downlink path, wherein the downlink test signal comprises a plurality of downlink test intermodulation products;

receiving an uplink test signal in the uplink path, wherein the uplink test signal comprises the plurality of downlink test intermodulation products leaked from the downlink path to the uplink path; and

measuring a first power level and a first phase of at least one downlink test intermodulation product among the plurality of downlink test intermodulation products.

11. The method ofclaim 10, further comprising:

decoupling the signal summing circuit from the coupling device;

coupling the at least one offset signal generation circuit to the signal summing circuit;

providing the downlink signal to the at least one offset signal generation circuit, wherein the downlink signal comprises a plurality of downlink intermodulation products;

receiving at least one downlink intermodulation product among the plurality of downlink intermodulation products from the at least one offset signal generation circuit; and

measuring a second power level and a second phase of the at least one downlink intermodulation product received from the at least one offset signal generation circuit.

12. The method ofclaim 11, further comprising:

adjusting the second power level of the at least one downlink intermodulation product to substantially match the first power level of the at least one downlink test intermodulation product; and

adjusting the second phase of the at least one downlink intermodulation product to be substantially opposite of the first phase of the at least one downlink test intermodulation product.

13. A remote antenna unit (RAU) in a distributed antenna system (DAS), comprising:

a downlink power amplifier configured to amplify a plurality of downlink communications signals received in a downlink path to generate a downlink signal in the downlink path, the downlink signal comprising at least one unwanted downlink interference signal;

at least one antenna configured to transmit the downlink signal and receive an uplink signal;

a coupling device communicatively coupled to the downlink power amplifier and the at least one antenna, wherein the coupling device is configured to:

distribute the downlink signal received from the downlink path to the at least one antenna for transmission; and

distribute the uplink signal received from the at least one antenna to an uplink path, the uplink signal comprising a wanted uplink signal and the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path; and

an interference signal offset circuit, comprising:

at least one offset signal generation circuit configured to:

receive the downlink signal comprising the at least one unwanted downlink interference signal; and

generate at least one uplink interference offset signal based on the received at least one unwanted downlink interference signal;

a signal summing circuit configured to:

receive the uplink signal in the uplink path;

receive the at least one uplink interference offset signal from the at least one offset signal generation circuit;

generate an output uplink signal based on the received uplink signal and the received at least one uplink interference offset signal; and

combine the received at least one uplink interference offset signal with the received uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and

a control circuit configured to:

receive the output uplink signal from the signal summing circuit; and

configure the at least one offset signal generation circuit to generate the at least one uplink interference offset signal to offset the at least one unwanted downlink interference signal.

14. The RAU ofclaim 13, wherein the coupling device is selected from the group consisting of: a duplexer; a multiplexer; a hybrid combiner; and a software-defined frontend module.

15. The RAU ofclaim 13, wherein the at least one unwanted downlink interference signal comprises a plurality of downlink intermodulation products generated when the plurality of downlink communications signals is amplified by the downlink power amplifier to generate the downlink signal.

16. The RAU ofclaim 15, wherein the at least one unwanted downlink interference signal leaked from the downlink path to the uplink path by the coupling device comprises the plurality of downlink intermodulation products.

17. The RAU ofclaim 15, wherein the at least one offset signal generation circuit is configured to generate the at least one uplink interference offset signal to offset at least one downlink intermodulation product comprised in the at least one unwanted downlink interference signal.

18. The RAU ofclaim 15, wherein:

the at least one offset signal generation circuit comprises a plurality of offset signal generation circuits disposed in a parallel arrangement, each of the plurality of offset signal generation circuits configured to receive the downlink signal;

the at least one uplink interference offset signal comprises a plurality of uplink interference offset signals, each of the plurality of uplink interference offset signals configured to offset at least one downlink intermodulation product among the plurality of downlink intermodulation products.

19. The RAU ofclaim 15, wherein the at least one offset signal generation circuit comprises:

an intermodulation product filter configured to selectively pass at least one downlink intermodulation product among the plurality of downlink intermodulation products;

an adjustable power amplifier coupled to the intermodulation product filter and configured to amplify the at least one downlink intermodulation product passing through the intermodulation product filter; and

an adjustable phase shifter coupled to the adjustable power amplifier and configured to phase-shift the at least one downlink intermodulation product;

wherein the at least one offset signal generation circuit is configured to provide the amplified and phase-shifted at least one downlink intermodulation product to the signal summing circuit as the at least one uplink interference offset signal.

20. The RAU ofclaim 19, further comprising a first switch configured to couple the coupling device to the at least one antenna or decouple the coupling device from the at least one antenna.

21. The RAU ofclaim 20, wherein the signal summing circuit comprises:

a second switch configured to couple or decouple the signal summing circuit with the coupling device;

a third switch configured to couple or decouple the signal summing circuit with the at least one offset signal generation circuit;

a signal summing point coupled to the second switch and the third switch, wherein the signal summing point is configured to combine the at least one uplink interference offset signal with the uplink signal to offset the at least one unwanted downlink interference signal from the output uplink signal; and

an uplink power amplifier coupled to the signal summing point.

22. The RAU ofclaim 21, wherein:

the first switch is configured to decouple the coupling device from the at least one antenna;

the second switch is configured to couple the signal summing circuit with the coupling device;

the third switch is configured to decouple the signal summing circuit from the at least one offset signal generation circuit;

the coupling device is further configured to:

receive a downlink test signal comprising a plurality of downlink test intermodulation products; and

provide the downlink test signal as an uplink test signal in the uplink path;

the signal summing circuit is further configured to:

amplify the uplink test signal; and

provide the amplified uplink test signal to the uplink signal filter in the control circuit; and

the control circuit comprises:

an uplink signal filter configured to selectively pass at least one downlink test intermodulation product among the plurality of downlink test intermodulation products;

a power detection circuit is configured to measure a first power level of the at least one downlink test intermodulation product passed through the uplink signal filter; and

a controller is configured to receive the at least one downlink test intermodulation product from the power detection circuit and measure a first phase of the at least one downlink test intermodulation product.

23. The RAU ofclaim 22, wherein:

the second switch is configured to decouple the signal summing circuit from the coupling device;

the third switch is configured to couple the signal summing circuit with the at least one offset signal generation circuit;

the at least one offset signal generation circuit is configured to receive the downlink signal and the plurality of downlink intermodulation products comprised in the downlink signal;

the controller in the control circuit is configured to configure the intermodulation product filter in the at least one offset signal generation circuit to pass the at least one downlink intermodulation product among the plurality of downlink intermodulation products, wherein the at least one passed downlink intermodulation product is in the same order as the at least one downlink test intermodulation product passed through the uplink signal filter in the control circuit;

the power detection circuit in the control circuit is configured to measure a second power level of the at least one downlink intermodulation product passed by the intermodulation product filter in the at least one offset signal generation circuit; and

the controller in the control circuit is further configured to:

measure a second phase of the at least one downlink intermodulation product passed by the intermodulation product filter in the at least one offset signal generation circuit;

adjust the adjustable power amplifier in the at least one offset signal generation circuit to make the measured second power level to substantially match the measured first power level; and

adjust the adjustable phase shifter in the at least one offset signal generation circuit to make the measured second phase to be substantially opposite of the measured first phase.

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