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

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.

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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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 of  claim 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.