GB2593245A

GB2593245A - Distributed spectrum monitoring system

Info

Publication number: GB2593245A
Application number: GB2014929.0A
Authority: GB
Inventors: Thomas Durante George; Melvyn Stephen Ross Philip
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 2019-10-01
Filing date: 2020-09-22
Publication date: 2021-09-22
Anticipated expiration: 2040-09-22
Also published as: GB202014929D0; GB2593245B; WO2021064338A1; GB201914144D0

Abstract

A distributed spectrum monitoring system comprises a plurality of antennas 12 deployed in a geographically distributed array remote from a control station location 14. Each antenna 12 is operably connected to a computer controlled real-time spectrum analyser 20 via RF/optic conversion means and a fibre optic cable run 18. A synchronisation source 24 synchronises received signals in the time and frequency domains. The spectrum analysers 20 and synchronisation source 24 are networked to a master control computer 28 means all configured to be collocated at the control station location 14, such that a remote sample of the EM environment can be captured and characterised in real-time. Optionally the synchronisation source is configured to receive timing data from a GNSS receiver. The distributed monitoring system may be configured to be mobile.

Description

DISTRIBUTED SPECTRUM MONITORING SYSTEM

TECHNICAL FIELD

The invention relates to the field of electromagnetic spectrum monitoring and more specifically to a distributed spectrum monitoring system

BACKGROUND

The electromagnetic (EM) environment is becoming increasingly contested as the use of wireless communications and applications continues to grow. Therefore, it is becoming ever more desirable to be able to monitor the wider EM environment, in order to facilitate spectrum management and optimisation.

Spectrum analysers measure the amplitude versus frequency (power spectrum) of an input electrical signal and, hence, can be used to monitor the power distribution of the signal. They are primarily used to monitor or measure the power spectrum or waveform of EM signals through the incorporation of suitable transducers which convert EM signals into electrical signals. Spectrum analysis is used in many applications across many bandwidths but is particularly useful in the radio-frequency (RE) range to characterise the frequency response from RE circuits and devices. For example, it can be used to analyse noise, distortion, interference, loss and electromagnetic compatibility amongst other things.

Spectrum analysers are most commonly used in a laboratory environment to test a specific device and are generally limited to single-channel input. Monitoring the wider dynamic EM environment remains challenging and systems which utilise distributed, networked spectrum analysers tend to be bulky and expensive.

It is an aim of the invention to provide an alternative distributed spectrum monitoring system.

SUMMARY

According to the invention, there is provided a distributed spectrum monitoring system comprising: a plurality of antennas deployable in a geographically distributed array remote from a control station location, each antenna suitable for receiving a signal; each antenna being operably connected to a computer controlled real-time spectrum analyser via RF/optic conversion means and a fibre optic cable run; and a synchronisation source for synchronising received signals in the time and frequency domains; wherein the spectrum analysers and synchronisation source are networked to a master control computer means, all configured to be collocated at the control station location, such that a remote sample of the EM environment can be captured and characterised in real-time.

The use of fibre optic cable runs is more efficient than coaxial cable in terms of signal transmission speed, noise and interference resistance, dimensions, bandwidth, and losses. The conversion/modulation of the received signal and subsequent transmission through the fibre optic cable runs results in almost no signal loss even over large transmission distances, for example up to several kilometres. This allows for the spectrum analysers to be collocated and networked at the control station location and hence more easily synchronised in time and frequency by a single networked synchronisation source. The provision of a master control computer with a suitable graphical user interface (GUI) enables a single operator to manage the multiple systems in an intuitive manner, live viewing the spectrum at the different antenna positions. The system, therefore, provides for a geographically-distributed, multi-node, synchronised, real time, remote, spectrum monitoring capability.

The benefit of using the fibre optic cable runs extends up to a distance of several kilometres, however the fibre optic cable run is preferably 50-3000m and more preferably 100-2000m in length.

The synchronisation source is essential in order to ensure synchronised acquisition of signals from the plurality of antennas, thereby allowing for remote, real-time monitoring. It may operate a synchronized clock system by receiving timing data from either a Network Time Protocol (NTP) server or from a Global Navigation Satellite System (GNSS) receiver, ensuring that all clocks stay synchronized and do not drift from their accurate time. For example, a one pulse per second (1PPS) signal that is accurately distributed from the synchronisation unit to each of the spectrum analysers ensures that they all trigger their spectrum acquisition at the same time.

The antennas are generally selected to provide the parameters, such as frequency range, polarisation and radiation pattern, which are appropriate to the band of signal to be monitored and to suit the dynamic range of the system. For example, for wide area monitoring omni-directional antennas may be used. Alternatively, use of directional antennas and a large standoff allows for remote monitoring of a smaller area with higher antenna gain across a smaller area of interest.

The networking functionality at the control station location is conveniently provided by a simple Ethernet connected Local Area Network although other networking configurations are possible.

The system is designed to be modular and scalable, allowing for the number of antennas, converters and real-time analysers to be changed to meet the requirement. For example, the control station location might accommodate 3-10 computer controlled spectrum analysers, or more. This means that the computing and signal receive capacity can be varied. However, it is also possible to incorporate other signal test functionality or add a transmit capability if required. Furthermore, whilst it may be implemented as a fixed installation it has the advantage that it may alternatively be implemented as a mobile spectrum monitoring system, which can be moved and integrated into new locations. For this purpose the computers and real-time spectrum analysers may be housed in a rugged, waterproof and shockproof modular rack, which may be made from a metallic or plastics material and the fibre optic cable runs may be stored on suitable robust reels.

In use the antenna/sensor nodes are arranged in a distributed array in accordance with the specific monitoring requirement. At each antenna any RF signal received is converted or modulated to be suitable for fibre optic transmission. This conversion and transmission introduces almost no signal loss even over large transmission distances, compared to co-axial cable transmission which does introduce losses especially over large distances and higher frequencies.

At the control station location the signals are converted back into RF before entering the computer controlled spectrum analyser for real-time measurement and capture/recording, controlled by the operator through a GUI installed on the master control computer.

BRIEF DESCRIPTION OF THE DRAWING

An embodiment of the invention will be described in more detail by way of example with reference to the accompanying drawings, in which: Figure 1 illustrates a distributed spectrum monitoring system in accordance with the invention; and Figure 2 illustrates the connections to two real-time spectrum analysers in the embodiment of Figure 1.

DETAILED DESCRIPTION

Figure 1 illustrates an embodiment of a mobile distributed spectrum monitoring system 10 in accordance with the invention, in diagrammatic form. Four omnidirectional antennas 12, configured to operate in both receive and transmit and selected to cover the frequency range of interest, are positioned in a geographically distributed array, approximately 1000m from the control station location 14. Each antenna 12 is connected to a battery powered RF to fibre converter 16 via a 1 -2 metre long RF coaxial cable 32; in this case Point2Point fibre optic links S Series (available from PPM Ltd) were used to provide an operational frequency range of 10MHz to 3GHz. Each RF to fibre converter 16 is housed in a robust, waterproof plastics case 15 and is connected to a 1000m fibre optic cable run 18, the other end of which is connected to a Tektronix, RSA306b (40 MHz wide bandwidth) real-time spectrum analyser 20 through a further Point2Point fibre optic links S Series, which here acts as a fibre to RF converter, at the control station location 14.

In order to provide real-time analysis the sample rate must satisfy the Nyquist criteria i.e. it must exceed double the frequency of interest and all computation must be performed at the same rate in order to provide real-time analysis output, therefore each spectrum analyser requires significant computing power. In this embodiment each spectrum analyser is controlled by an Intel NUC C78L (Intel i7 Processor) 22.

A Steatite Embedded, EC20S-X0, synchronisation source 24 is also provided at the control station location 14. This provides accurate and stable time and frequency signals for synchronisation of the system through use of its built-in GNSS receiver, which receives timing data 25 from a GNSS transmitter 27.

The computer controlled spectrum analysers 20 and synchronisation source 24 are networked to an Ethernet connected LAN 26, which is in turn connected to a master control computer 28 via an Ethernet connection 30 and KVM switch 34.

Figure 2 illustrates the connections to the real-time spectrum analysers 20 at the control station location 14. The spectrum analysers 20 (only two shown) are housed in a robust, metallic, modular rack 36. The fibre optic cable 18 is connected to the fibre to RE converter 17, located in the modular rack, which converts the light signal back to RE. The fibre to RE converter 17 is connected directly into the real-time spectrum analyser 20 via an SF connector, thereby providing lower loss and improved ruggedness. This allows for a more reliable mobile system. The fibre to SF converter 17 is provided with power input 38. The remaining inputs to the spectrum analysers 20 are a 10 MHz Reference frequency signal 40 and a time signal 42 both from the synchronisation source 24 (both of which are connected through SF connectors) and a USB connection to the spectrum analyser's control computer 22.

In use, the environmental SF signal captured by antenna 12 is transmitted via the short length of coaxial cable 32 to its associated SF to fibre converter 16, which amplifies, conditions and converts it into an optical signal for transmission over the connected fibre optic cable run 18. At the control station location 14, the signal is converted back into an RF signal by the fibre to RE converter 17 and the optical transmission is transparent to the system.

Claims

CLAIMS1. A distributed spectrum monitoring system comprising: a plurality of antennas deployable in a geographically distributed array remote from a control station location, each antenna suitable for receiving a signal; each antenna being operably connected to a computer controlled real-time spectrum analyser via RE/optic conversion means and a fibre optic cable run; and a synchronisation source for synchronising received signals in the time and frequency domains wherein the spectrum analysers and synchronisation source are networked to a master control computer means all configured to be collocated at the control station location, such that a remote sample of the EM environment can be captured and characterised in real-time.
2. A distributed spectrum monitoring system according to claim 1 wherein the fibre optic cable runs are 50-3000m in length.
3. A distributed spectrum monitoring system according to claim 2 wherein the fibre optic cable runs are 100-2000m in length.
4 A distributed spectrum monitoring system according to any preceding claim wherein the synchronisation source is configured to receive timing data from a GNSS receiver.
A distributed spectrum monitoring system according to any preceding claim wherein the networking at the control station location is provided by an Ethernet connected Local Area Network.
6. A distributed spectrum monitoring system according to any preceding claim wherein the system comprises 3-10 computer controlled spectrum analysers.
7. A distributed spectrum monitoring system according to any preceding claim wherein the system is configured to be mobile.
8. A distributed spectrum monitoring system according to claim 7 wherein the computers and real-time spectrum analysers are housed in a robust modular rack.