Wireless as Enabler of Innovation in 21st Century Health and Social Care

This paper overviews new and emerging wireless technologies that could positively impact on the lives of the elderly or disabled, as Social Care users of Assistive Technology (AT) for ‘independent living’. Novel Internet of Things (IoT) radio systems and wireless locating systems being researched at The University of Sheffield are discussed in the context of Social Care technology use-cases

Antenna Beam Steering Without Phase Shifters – an ‘Old’ Technique Revisited

Antenna arrays are of perennial interest and relevance to RF wireless system designers, indeed the rise of 5G is showing their importance is only growing. Most implementations of linear arrays use phase shifters to feed the array and hence form the main-lobe beam. In the 1960s, a technique using RF switches and Fourier analysis was discovered to be a viable alternative to phase shifters - called the Time Modulated Array (TMA). Little modern research has been conducted in this area, despite its likely cost-effective implementation and technical relevance. This paper presents a brief overview of the TMA, followed by our work into prediction and control of the RF harmonic levels in TMAs. The effect of RF ramping on the switching waveform is analysed first, followed by a novel way of reducing the carrier fundamental (due to the Fourier DC term) produced by TMAs. Finally, a novel RF transistor cascode fast switch is introduced, using 3 gain states, to pragmatically implement the reduction of the carrier fundamental. The transistor cascode in the TMA utilizes binary logic control interfaces, rather than analogue control interfaces, for hardware efficiency. Early simulation results are included

Portable and low cost channel sounding platform for VHF / UHF IoT propagation research

This paper presents work into realising a cost-effective and portable platform to support Internet of Things (IoT) propagation research at VHF and UHF. The sounding receiver uses a low cost RTL-SDR, Raspberry Pi and touchscreen. The platform runs dedicated channel sounding DSP algorithms written in Python. The resulting platform is a portable and convenient propagation measurement tool, covering 27MHz to 1.7GHz. Initial results from a city measurement campaign at 71MHz and 869.525MHz are presented, showing channel response and interference

Computed microtomography visualization and quantification of mouse ischemic brain lesion by nonionic radio contrast agents.

AIM: To explore the possibility of brain imaging by microcomputed tomography (microCT) using x-ray contrasting methods to visualize mouse brain ischemic lesions after middle cerebral artery occlusion (MCAO). ----- METHODS: Isolated brains were immersed in ionic or nonionic radio contrast agent (RCA) for 5 days and subsequently scanned using microCT scanner. To verify whether ex-vivo microCT brain images can be used to characterize ischemic lesions, they were compared to Nissl stained serial histological sections of the same brains. To verify if brains immersed in RCA may be used afterwards for other methods, subsequent immunofluorescent labeling with anti-NeuN was performed. ----- RESULTS: Nonionic RCA showed better gray to white matter contrast in the brain, and therefore was selected for further studies. MicroCT measurement of ischemic lesion size and cerebral edema significantly correlated with the values determined by Nissl staining (ischemic lesion size: P=0.0005; cerebral edema: P=0.0002). Brain immersion in nonionic RCA did not affect subsequent immunofluorescent analysis and NeuN immunoreactivity. ----- CONCLUSION: MicroCT method was proven to be suitable for delineation of the ischemic lesion from the non-infarcted tissue, and quantification of lesion volume and cerebral edema

The meta distribution of the SIR for LoRaWANs with power control

To reduce energy consumption, a device in a LoRa (Long Range) wide area network (LoRaWAN) needs to adjust its transmit power according to the distance from its tagged Gateway (GW). It is important to measure the performance of the LoRaWANs uplink with power control. In this paper, we focus on the analysis of the coverage probability and the meta distribution of the signal-to-interference ratio (SIR) for a LoRaWAN uplink with fractional power control (FPC). The LoRaWAN uplink is analysed based on the Poisson point process (PPP). We present the possible reductions in transmit power of devices whilst ensuring that the received signal power is greater than the receiver sensitivity. We derive the coverage probability of a LoRaWAN uplink, and show how power control influences it. Finally, utilizing the meta distribution of SIR, the fine-grained information of the LoRaWAN is revealed. The results show that the power control greatly increases the successful probability of edge-devices with little effect on the probability of inner-devices if an appropriate FPC coefficient is chosen. This is because the LoRa signal can be demodulated at a very low required SIR threshold

Constant envelope transceivers in millimetre-wave massive MIMO: EVM and link budget considerations

RF 30 GHz ray-tracing simulation results are presented from a conceptual Massive-Multiple Input Multiple Output (M-MIMO) propagation model in an urban canyon. The usage of Constant Envelope (CE) RF signals is evaluated in both propagation ray-rich and ray-sparse scenarios. Multiple mobile terminals are simulated each employing single carrier Phase Shift Keying (PSK). It is found that once an operational link budget is achieved CE transmitters have negligible effect on a received Error Vector Magnitude (EVM). Finally it is found that the EVM is a function of both richness of propagation rays as well as the relative proximities of mobile users. A worst-case EVM of circa 25% is observed when terminals are separated by 1m reducing to circa 5% when terminals are separated by more than 4m

A portable 28-GHz channel sounder platform and measurement results from close-to-ground field tests

This article describes a novel, bespoke, and low-cost 28-GHz RF TX and RX front end design that has been combined with a commercial Software-Defined Radio and Raspberry Pi controller to realize a portable propagation measurement system for the 28-GHz band. The complete sounder system can resolve an impulse from RX powers down to −107 dBm (3-dB impulse SNR) and the sounder TX can generate a signal of −8 dBm. Therefore, using 20-dBi antennas supports path-loss (PL) measurements of 139 dB. The sounder can resolve time-domain reflections to 33 ns in a channel measurement bandwidth of 60 MHz, producing both time-domain and frequency-domain results. The complete sounding system has been used to perform close-to-ground RF channel measurements, with propagation loss models and time-domain impulses extracted. Close-to-ground measurement is an underreported area of propagation research that is relevant for novel use-cases, such as in military applications or for mobile device-to-device communications. A key initial finding from the trials is that the PLs for 28-GHz indoor and outdoor links at circa 70 cm above ground seem close to that of free space, with very few strong reflections with delays exceeding 33 ns

IoT focused VHF and UHF propagation study and comparisons

As the market for internet of things (IoT) is growing and due to Ofcom's decision to reassign parts of the very high frequency (VHF) spectrum in the UK for IoT use, a propagation study has been conducted using the newly released VHF spectrum and the currently commercially operated ultra-high frequency (UHF) spectrum, in order to compare and contrast the suitability of the VHF spectrum for IoT use. The authors conducted their study in a number of different environments (rural, suburban, urban and dense urban), with measurement equipment deployed in a manner suitable for a portable IoT use case. Results are presented in comparison to other propagation studies available in the literature and widely used propagation models such as the Hata model. Shadowing and noise are also measured and examined. It is found that current propagation models do not provide adequate predictions within the considered use case, but found it is possible to calculate log-distance based models that provide good predictions. Path-loss is found to be constantly lower at VHF than UHF, but radio frequency noise is consistently higher. The newly released spectrum is found to be suitable for IoT deployments in all the examined environments

Cost-effective design of polarization and bandwidth reconfigurable millimeter-wave loop antenna

A singly fed reconfigurable circular loop antenna is proposed for millimeter-wave (mmWave) communication systems. This antenna’s distinctive feature lies in its capacity to adjust both polarization and bandwidth characteristics, a capability made possible by the strategic integration of two PIN diodes. These diodes are engineered to function in various modes, allowing for three distinct polarization states and accommodating two distinct bandwidths. A meticulous alignment of these PIN diodes enables the utilization of a single DC bias network as a highly effective RF choke, which simplifies the design and reduces the associated losses. Additionally, a planar biasing network that consists of coplanar strip-lines (CPS) has been employed eliminating the need for lumped elements. The simple and totally planar configuration offers a choice of right-hand circularly polarized (RHCP) radiation or left-hand circularly polarized (LHCP) radiation at 28 GHz. This is accompanied by impedance matching and axial ratio (AR) bandwidths of 12.9% and 8%, respectively, over the same frequency range with a gain of 7.5 dBic. Moreover, when the PIN diodes are unbiased, the antenna offers linear polarization (LP) over two narrow bandwidths at 27 GHz and 29 GHz featuring a maximum gain of 7.2 dBic. Therefore, the proposed configuration offers three operating modes: wide-band RHCP, wide-band-LHCP, and LP over dual narrow bands. Significantly, simulated results closely align with the measured outcomes, affirming the robustness and accuracy of this design

Receive mode time modulated antenna array incorporating subsampling -theoretical concept and laboratory investigation

An eight element Subsampling Time Modulated Array (STMA) operating in receive mode with a carrier at 2.4 GHz is presented and demonstrated using bespoke Radio Frequency (RF) hardware. Each STMA cell incorporates subsampling functionality, with the sampling frequency significantly below the carrier frequency and requiring minimal additional hardware. By using this concept, the hardware required for a receiver incorporating an antenna array can be reduced and costs saved. STMA design equations and architecture strategies are presented, and a prototype hardware demonstrator is introduced. Laboratory measurements confirm that a received radiated signal, arranged to use the fundamental or a harmonic beam pointed at the radiating source, can be resolved from the subsampled intermediate frequency (IF) output. The concept demonstration hardware provides a measured array conversion gain of 11.4 dBi on the boresight beam, 7.8 dBi on the first positive and 11.3 dBi on the first negative harmonic beams, as resolved at the final combined IF output. The array IF output Signal to Noise and Distortion ratio is 69 dB. The dependence of array sidelobe level performance on STMA sampling switch rise time is also uncovered, though good performance with real, imperfect, hardware is still obtained