This article discusses test and measurement for wireless applications for ships and submarines.
Platform-based ship and submarine systems used for naval applications have various systems for different applications, including communication, radar, signal monitoring and electronic warfare. These systems operate in different frequency bands operating in audio, radio frequency (RF) and microwave ranges, covering a broad spectrum from a few Hz to GHz. Communication with submarines is difficult because radio waves do not travel well through the deep sea.
Several techniques are used to communicate with submarines. Underwater acoustic communication is used for sending and receiving messages under water. There are several ways of achieving such communication, but the most common is using hydrophones.
Very low frequency (VLF) radio waves, ranging from 3kHz to 30kHz, can penetrate seawater to depths of approximately 20 metres. Submarines that are more deeply submerged might use a buoy equipped with an antenna on a long cable. A buoy is usually raised a few metres below the surface.
A surfaced submarine can use ordinary radio communication on higher frequencies, such as high frequency (3MHz – 30MHz), very high frequency (30MHz – 300MHz) or ultra high frequency (300MHz to 3GHz), and transmit information via voice.
Srisailam Todeti, senior applications specialist, Keysight Technologies India, says “Underwater communication is difficult due to a number of factors, such as time variations of the channel, multipath propagation, strong signal attenuation and small available bandwidth. Thus, development of communication systems requires rigorous testing to ensure that these can operate under demanding environments.
“For true evaluation of the device under test (DUT), the selected test instrument should maintain high accuracy and performance against different environmental conditions. Hence, a standardised instrument can help with a better analysis.
“If required, the same test instrument can be used in systems, in place of some sub-systems. Before going to field, these systems can be tested by injecting the signals with different signal impairments in a lab. Calibration of the test setup is required to inject corrected signals into the DUT.”
Test solutions for wireless applications under the deep sea
To test and maintain the above-mentioned systems in the field, instruments such as function/arbitrary waveform generator, audio analyser, signal generator, spectrum analyser, vector network analyser, channel emulator and so on are used. Then, there are software available that help in generating and analysing custom signals.
Analogue and vector signal generators generate signals such as AM, FM, pulse, QPSK, QAM, chirp, barker modulation, antenna scan pattern and the like.
A vector network analyser is used for component characterisation, and cable and antenna testing.
SystemVue software for radar signal generation is used to generate different kinds of waveforms and to download the signals into AWG or VSG. A user can add impairments and verify DUT performance with sea clutter model impairments on signals.
Propsim is a radio channel emulator to simulate channel propagation effects on signals and test DUT injected mode in a lab setup.
Radar cross section measurement system measures the cross-section of the ship.
Some other test and measurement instruments are base station analysers (for example, BTS Master), Bluetooth and WLAN testers, cable and antenna analysers (for example, Site Master), channel emulator conformance test systems, handset one box testers, radio communication analysers, land mobile radios (for example, LMR Master), passive intermodulation analysers (for example, PIM Master), power meters and sensors, shield box signal generators, signalling testers (base station simulators) and signal analysers.
Devices in the market
Madhukar Tripathi, head – marcom and optical business, Anritsu India, says “The ultra-portable spectrum analyser MS2760A utilises non-linear transmission line technology and offers dynamic range, sweep speed and amplitude accuracy. Its size enables direct connection to almost any DUT, eliminating the need for lossy, expensive cables or antennae. It provides continuous coverage from 9kHz to 110GHz, and is great for millimetre-wave applications like 5G, 802.11ad, satellite communications, automotive radars and more. It measures channel power, adjacent channel power and occupied bandwidth.”
Anritsu’s MS2850A provides maximum analysis bandwidth of 1GHz and frequency range of 9kHz to either 32GHz or 44.5GHz. It can capture up to 24 seconds at 100MHz span using 32GB memory. Signal data can be analysed for efficient R&D of next-generation standards prior to release.
PCIe/ISB3.0 enables high-speed transfer of large captured data.
Radio communication test station MT8000A by Anritsu provides all-in-one support for RF measurements and protocol tests in sub-6GHz and millimetre-wave bands. After combining with an OTA chamber, it enables both millimetre-wave band RF measurements and beamforming tests specified by 3GPP.
Emulators for creating test environments
Propsim channel emulation solution is a radio channel emulator that enables recreating wireless channel propagation effects in a controlled lab environment. It is a one-box solution for performing a realistic and accurate emulation of all typical radio channel propagation effects, such as multi-path propagation, fast fading, dynamic delays, attenuation, noise, interference and shadowing. It enables real-time performance testing of devices and base stations. The solution emulates impairments of complex real-world radio channel conditions for accurate testing with dynamic multi-path propagation, range pathloss and blocking effects, Doppler from mobility and multi-paths, and noise and synchronous programmable interference.
Imran Baig, senior application engineer, Keysight Technologies India, says, “Propsim fulfils the requirements of both present and future wireless communication systems. It provides feature sets for radio interface testing of current cellular communication systems, such as LTE/LTE-A, WLAN, WCDMA, GSM, TD-SCDMA, etc.
“Additionally, Propsim enables testing of next-generation communication systems, such as 5G and VHF communication systems operating at 30MHz – 300MHz frequency. It includes pre-stored standard channel emulations (emulation connection diagram with channel models according to 3GPP standards).
“For basic use, the user only needs to load the emulation and adjust the power levels of Propsim. For advanced use, all versatile channel modelling tools for creating user-defined channel models and for modifying predefined standard channel models are available.”
Propsim F64 5G channel emulation solution F8800A addresses diverse test needs in 5G, 4G and WLAN 802.11ax.
Field-to-lab virtual drive testing emulates impairments of complex 3D real-world radio channel conditions to support user-defined 3D spatial scenarios and dynamic modelling of movement, arbitrary and complex test scenarios, multi-frequency and multi-RAT HetNet test scenarios, device-to-device (D2D) supporting Internet of Things (IoT) and vehicle-to-everything (V2X) scenarios, 3D antenna beam pattern model embedding, antenna array and antenna library tool for modelling arrays and beams.
Challenges and improvement areas
Communication signal standards are changing at a fast rate. Also, communication bands are overlapped into microwave frequency bands. Hence, testing DUT performance against only a particular test signal cannot give true performance. It is necessary to simulate all kinds of signals and inject these into the systems.
Latest communication radios are software-defined with fast-hopping signals up to 1000 hops per second and beyond. It would be difficult to jam these signals with wide-band jamming techniques. Research is on for developing follow-on jamming techniques, where the jammer system follows each hop of the radio. So, faster switching source and receiver looks challenging.