Monitoring system for a distributed antenna system

Abstract

A monitoring system 22 for a distributed antenna system (DAS) 10 is provided. The DAS comprises central transmitter 12 which is connected by a signal transmission network 14 to a plurality of distributed antenna devices (DAD) 16.1 to 16.n. The network comprises physical branches. Each of the DAD's is connected to a respective sub-branch 14.11 and comprises at least one antenna 18. The antenna is associated with a frequency band having a center frequency fc and an associated wavelength Ac. The monitoring system comprises a central monitoring unit (CMU) 24 which is coupled to the network 14. A monitoring device 28.1 is associated with at least one of the DAD's and permanently mounted a distance d<2λc away from the antenna of the DAD. The monitoring device comprises a controller 30, a transceiver 32 and an antenna 34. The controller being configured, upon being polled by the CMU 24 with a monitoring signal via the network and the distributed antenna device, to cause the transceiver 32 to respond by transmitting a response signal to the CMU 24 via the distributed antenna device 16.1 and the network 14.

The invention claimed is: 
     
       1. A monitoring system for a distributed antenna system comprising at least a central transmitter and a plurality of distributed antenna devices connected to the transmitter via a respective physical branch of a signal transmission network comprising a plurality of branches, each of the distributed antenna devices comprising at least one antenna which is associated with a frequency band having a centre frequency fc and a corresponding wavelength λc, the monitoring system comprising:
 a central monitoring unit which is configured to be coupled to the network; 
 at least one path diagnostic switching device configured to be connected in a branch of the network and further configured to be switched between a first state wherein it passes along branch input power received by the at least one path diagnostic switching device and a second state wherein it attenuates or diverts away from the branch at least some of the input power received by the at least one path diagnostic switching device;  
 at least one monitoring device associated with at least one of said distributed antenna devicesand permanently mounted a distance d away from the at least one antenna of the distributed antenna device, the distance d being less than 2 times λc (2λc); 
 the at least one monitoring device comprising a local controller, a transceiver and an antenna; and  
 the local controller being configured to, upon being polled by the central monitoring unit with a monitoring signal via the associated distributed antenna device and the respective branch of the network, to process the monitoring signal to measure the quality of the monitoring signal and to cause the transceiver to respond to the monitoring signal by transmitting a response signal comprising an indication of the measured quality to the central monitoring unit via the associated distributed antenna device and the network. 
 
     
     
       2. The monitoring system as claimed in  claim 1  wherein the at least one monitoring device is mounted a distance d away from the at least one antenna, the at least one antenna associated with a frequency band having a centre frequency fc and a corresponding wavelength λc, and wherein d is less than (λc/2). 
     
     
       3. The monitoring system as claimed in  claim 1  wherein the at least one monitoring device comprises a local power supply comprising at least one of a battery and an energy harvesting circuit for collecting configured to collect energy from the distributed antenna device through the antenna of the monitoring device. 
     
     
       4. The monitoring system as claimed in  claim 1  wherein the at least one monitoring device is associated with a respective unique address which is stored in a memory arrangement of the monitoring device. 
     
     
       5. The monitoring system as claimed in  claim 4  wherein the central monitoring unit comprises means for measuring the a processor configured to process a measured strength of the response signal received from the at least one monitoring device and be connected to a database for storing data relating to the unique addresses of the at least one monitoring device and at least one of data relating to the a monitored status of the associated distributed antenna device and data relating to a position of the associated distributed antenna device. 
     
     
       6. The monitoring system as claimed in  claim 1  wherein the at least one monitoring device comprises an indicator arrangement for providing a human perceivable configured to provide an indication relating to a monitored status of at least one of the associated distributed antenna device and the branch connected thereto, based on the measured quality of the monitoring signal. 
     
     
       7. The monitoring system as claimed in  claim 1  wherein the at least one monitoring device is mounted in or on the associated distributed antenna device. 
     
     
       8. The monitoring system as claimed in  claim 7  wherein the at least one monitoring device is encapsulated in a housing which is mountable on an optional a radome of the associated distributed antenna device. 
     
     
       9. The monitoring system as claimed in  claim 1  wherein the central monitoring unit is configured to be coupled to the network by a coupler to inject the monitoring signal into the network. 
     
     
       10. The monitoring system as claimed in  claim 1  wherein the monitoring signal and the response signal are at least one of a) at least 10 dB weaker than a main signal transmitted by the central transmitter and b) out of band relative to the main signal. 
     
     
       11. The monitoring system as claimed in  claim 1  comprising at least one path diagnostic switching device which is connected in a branch of the network and configured to be switched between a first state wherein it passes along the branch input power received by the switch device and a second state wherein it attenuates or diverts away from the branch at least some of the input power received by the switch device. 
     
     
       12. A distributed antenna system comprising a monitoring system as claimed in  claim 1 . 
     
     
       13. A The monitoring system as claimed in  claim 1  wherein the quality of the monitoring signal is measured by measuring the strength of the monitoring signal and wherein the indication of the measured quality comprises data relating to the measured strength. 
     
     
       14. A method of monitoring performance of a distributed antenna system comprising at least a central transmitter, at least one path diagnostic switching device, and a plurality of distributed antenna devices connected to the transmitter via a respective physical branch of a signal transmission network comprising a plurality of branches, each of the distributed antenna devices comprising at least one antenna which is associated with a frequency band having a centre frequency fc and a corresponding wavelength λc, the method comprising:
 for at least some of the distributed antenna devices, providing a respective associated monitoring device at a distance d<2λc from the at least one antenna; 
 switching the at least one path diagnostic connected in a branch of the network between a first state wherein it passes along branch input power received by the at least one path diagnostic switching device and a second state wherein it attenuates or diverts away from the branch at least some of the input power received by the at least one path diagnostic switching device; 
 transmitting from a central monitoring unit to at least one targeted monitoring device a monitoring signal via the an associated distributed antenna device and the respective branch of the network; and  
 atby the at least one targeted monitoring device, processing the monitoring signal to measure the quality of the monitoring signaland, generating a response signal comprising an indication of the measured quality and transmitting the response signal to the central monitoring unit via the associated distributed antenna device and the network. 
 
     
     
       15. The method as claimed in  claim 14  wherein the monitoring signal is addressed to the at least one targeted monitoring device by utilizing a respective unique address of the at least one targeted monitoring device. 
     
     
       16. The method as claimed in  claim 14  wherein the monitoring signal is processed by measuring the strength of the monitoring signal at the at least one targeted monitoring device. 
     
     
       17. The method as claimed in  claim 16  wherein data relating to the measured strength is sent from the at least one targeted monitoring device via the associated distributed antenna device and the network to the central monitoring unit and wherein the data is identified by the a respective unique address of the at least one targeted monitoring device. 
     
     
       18. The method as claimed in  claim 17  wherein the strength of the response signal is measured at the central monitoring unit and wherein one or more results of the measurements are utilized to monitor the status of asymmetrical up and down paths between the central monitoring unit and the at least one targeted monitoring unit. 
     
     
       19. The method as claimed in  claim 14 wherein distributed switches in the network are utilized, further comprising, by the monitoring unit, controlling distributed switches in the network to selectively to attenuate or divert power propagating to at least some of the distributed antenna devices, thereby to switch the at least some of the distributed devices out of the distributed antenna system, and wherein the switches are controlled by command signals from at least the central monitoring unit. 
     
     
       20. The method as claimed in  claim 19  wherein the monitoring signal, the response signal and the command signals are at a signal level to ensure communication and sensing between central monitoring unit, the monitoring devices and the switches devices distributed switches, but below the a level of a main signal transmitted by the central transmitter. 
     
     
       21. A monitoring system for a distributed antenna system, the monitoring system comprising:
 a central monitor configured to be coupled via a network to a plurality of antennas; and   a plurality of remote monitors associated with the plurality of antennas, the plurality of remote monitors comprising:   a first remote monitor of the plurality of remote monitors configured to, upon being polled by the central monitor with a first monitoring signal transmitted via the network and a first antenna associated with remote monitor, transmit a first response signal to the central monitor via the first antenna associated with the first remote monitor and the network; and   a second remote monitor of the plurality of remote monitors configured to, upon being polled by the central monitor with a second monitoring signal transmitted via the network and a second antenna associated with the second remote monitor, transmit a second response signal to the central monitor via the second antenna associated with the second remote monitor and the network;   wherein the first remote monitor and the second remote monitor are associated with the first and second antennas sharing a branch of the network connecting the first and second antennas to the central monitor;   wherein the central monitor is further configured to:
 in response to a determination that no first response signal has been received from the first remote monitor, label at least one of the first remote monitor or the first antenna associated with the first remote monitor as defective; and 
 in response to a determination that a signal strength of the first response signal received from the first remote monitor does not satisfy a first signal strength threshold and that a signal strength of the second response signal received from the second remote monitor does not satisfy a second signal strength threshold, determine that the branch has failed.  
   
     
     
       22. The monitoring system as claimed in claim 21 wherein the first response signal comprises a first unique identifier of the first remote monitor and the second response signal comprises a second unique identifier of the second remote monitor, and wherein the central monitor is configured to identify the first response signal using the first unique identifier and the second response signal using the second unique identifier.  
     
     
       23. The monitoring system as claimed in claim 21 wherein at least one of the first or second monitoring signal is at least one of: out of band relative to a main signal transmitted by a central transmitter of the distributed antenna system or at least 10 dB weaker than the main signal.  
     
     
       24. The monitoring system as claimed in claim 21 wherein the central monitor is further configured to, responsive to receiving the first response signal from the first remote monitor and a determination that a signal strength of the first response signal received from the first remote monitor does not satisfy a signal strength threshold, transmit an instruction to the first remote monitor to change status of the first remote monitor and provide indication of the change.  
     
     
       25. The monitoring system as claimed in claim 21 wherein the central monitor is further configured to:
 in response to a determination that no second response signal has been received from the second remote monitor, label at least one of the second remote monitor or the second antenna associated with the second remote monitor as defective.