strength being sufficient, suspect the presence of interference. A spectrum analyser can be used to identify potential interference and search for the source.
• After identifying the source of the interference, consider how to resolve the interference issue. An example of a simple measurement method based on the use of free software to check wireless LAN signal strength is shown in Figure 2. Each waveform is associated with a network name (SSID) and wireless channel. For WMTS applications, the central monitor of the WMTS is equipped with a simple spectrum analyser function that enables measurement of the strength of received radio signals. If the radio signal strength in a wireless LAN or WMTS is found to be sufficient according to the results of simple measurements, but communications problems persist, the cause is assumed to be interference from radio waves emitted by other devices.
Combining a spectrum analyser with antennas, designed for use with the radio frequency band being measured, can detect and visualise radio signals that cause interference in the same frequency band, in addition to WMTS and wireless LAN radio signals. In the case where the radio strength is
sufficient but communication is compromised, a real-time spectrum analyser (RTSA) is used to capture transient and instantaneous radio frequency changes at the location where the wireless issue has occurred. It checks for both signal strength and interference. Multiple measurements are needed at different times as radio propagation conditions vary depending on the day of the week, the time of day and whether doors are open or closed. In the example shown in Figure 3, signals are
observed on channels 1, 3, 6, and 8 of the wireless LAN, but three of these channels are being overlapped by other stronger radio waves. Steep peaks due to Bluetooth devices and radio signals of unknown origin in the higher frequency range are present. These other radio signals can be
considered to be problematic, especially if the wireless LAN equipment can be moved to another place where these other radio signals disappear or are diminished, and communications improves. Once the presence of interfering
waves is confirmed, a cart with a battery-operated spectrum analyser and an antenna tuned to the frequency of the radio signals to be measured can be used to narrow down the area where the interference occurs. A laptop computer is used to control the measurement sequence and record the results. The cart is moved around according to the floor plan of the ward to measure the interference strength at several points. As the source may not be on the same floor, measurements are taken on the floors above and below as well as in adjacent buildings. The source of the interference can be identified
by pointing a highly directional antenna in various directions. Some spectrum analysers have a function to indicate the strength of the received radio signal by sound (pitch and volume), enabling an efficient search for the source to be made without a screen or data. The source of interference can be validated by turning its power off or covering it with a conductive sheet to see if the interference disappears.
Wireless standards continue to evolve to provide higher speeds and capacity. For example, devices compliant with the Wi-Fi 6E and Wi-Fi 7 standards will enable shorter transfer times for medical data and the real-time monitoring of high- precision images. Fast low-latency 5G combined, with faster wireless LAN will overcome distance limitations faced by medical devices and services. Combining 5G mobile communications with
wired optical fibre enables the exchange of high- definition images such as 4K and 8K in real time, contributing to the expansion of telemedicine. Telemedicine using this technology can also share video of patients during emergency transport and provide improved medical care in remote areas. Demonstration tests of remote surgery have also begun using robots to perform the actual procedure. With faster wireless communications, virtual
Figure 4: Real-time spectrum analysers
reality (VR), augmented reality (AR), and mixed reality (MR) technologies are becoming more prevalent. Collectively called XR, these technologies can be used for medical examinations, education, surgical support, and rehabilitation. For example, AR/XR can confirm the locations of actual patient organs and blood vessels obtained by CT and other diagnostic imaging equipment to improve surgical and educational efficiencies.
Interference is a major issue that needs to be taken care of when designing wireless networks for medical applications. As wireless technology advances and the spectrum becomes more congested, interference issues will be more problematic and will need to be mitigated through extensive testing and careful design. Anritsu offers a wide range of test equipment
and extensive experience in testing and evaluating wireless networks for medical facilities and applications, including Bluetooth and WLAN test sets, spectrum analysers, VNAs, and spectrum monitoring through to 5G, RAN and communications test systems. Furthermore, Anritsu is well positioned to deliver products to test and evaluate emerging Wi-Fi and 5G Advanced standards that will become mainstream in the years ahead. As an essential part of the IT infrastructure of a
medical facility, wireless communications looking forward will require the introduction of technology to provide, for example, fast, reliable and stable connections over short and long distances, low latency, comprehensive security, high data rates, and real time video. Anritsu offers two handheld spectrum analysers: the Field Master MS2080A, which can measure frequencies from 9 kHz to 6 GHz and has a 40 MHz RTSA bandwidth, and the Field Master Pro MS2090A, which has a frequency range of 9 kHz to over 9 GHz and a 110 MHz RTSA bandwidth. A variety of antenna are also
available from the company for interference investigation.
Figure 3: Example of radio signal conditions measured using an RTSA 33
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