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We present a simulation framework for evaluating the performance of cooperative reconfigurable intelligent surface (RIS) based systems, which may ultimately deploy an arbitrary number of RISs to overcome adverse propagation-related effects, such as cascaded fading. The physical model underlying the proposed framework considers the (optional) presence of a dominant signal path between the source and RIS, and then between each subsequent stage of the communication link to the destination. Accompanying the dominant signal component is a non-isotropic scattered signal contribution, which accounts for angular selectivity within the cascaded RIS stages between the source and destination. The simulation of the time-correlated scattered signal, reflected by the illuminated reflective elements, is achieved using autoregressive modelling. As a by-product of our analysis, significant insights are drawn which enable us to characterize the amplitude and phase properties of the received signal, and the associated complex autocorrelation functions (ACFs) for the product of multiple Rician channels. For both single and cooperative RIS systems, the outage probability (OP), and important second-order statistics, such as the level crossing rate (LCR) and average outage duration (AOD), are analyzed for a variety of system configurations, accounting for practical limitations, such as phase errors. It is shown that by using multiple RISs cooperatively, the AOD is reduced at a lower signal-to-noise-ratio (SNR) compared to single RIS-assisted transmission under the same operating conditions. Lastly, increased channel variations (i.e., higher maximum Doppler frequencies) are shown to decrease the AOD in the case of absent phase errors; yet, this improvement is not observed when phase errors are present.

This paper presents a framework for achieving machine learning (ML)‐assisted direction‐of‐arrival (DoA) accuracy enhancement using a millimetre‐wave (mmWave) dynamic aperture. The technique used for the enhanced DoA estimation accuracy leverages an over‐sized lens‐loaded cavity antenna connected to a single RF chain in the physical layer and a computational method in the computational layer of the framework. It is shown for the first time that by introducing a reconfigurable mode‐mixing mechanism inside the over‐sized lens‐loaded cavity hardware, a greater number of spatially orthogonal radiation modes can be achieved giving rise to many cavity states. If the best cavity state is determined and selected by means of design exploration using a contemporary ML‐assisted antenna optimisation method, the computational DoA estimation accuracy can be improved. The mode‐mixing mechanism in this work is a randomly oriented metallic scatterer located inside an over‐sized constant−ϵ r lens‐loaded cavity, connected to a stepper motor that is electronically controlled by inputs from the computational layer of the presented framework. Measurement results in terms of near‐field radiation mode scans are included in this study to verify and validate that the proposed ML‐assisted framework enhances the DoA estimation accuracy. Moreover, this investigation simultaneously provides a simplification in the physical layer implementation of mmWave radio hardware, and DoA accuracy enhancement, which in turn lends itself favourably to the adoption of the proposed framework for channel sounding in mmWave communication systems.

Direction of arrival (DoA) estimation plays a crucial role in channel characterization and is a critical step to execute the necessary beam-shaping operations needed from antennas present within a wireless environment. Conventional DoA estimation frameworks rely on array-based topologies, making use of the phase difference information between the individual channels to retrieve the DoA data. Recently, the idea of computational imaging has been shown to offer a promising solution to conventional raster-scan-based techniques. This is mainly due to the physical layer compression facilitated by special types of compressive apertures (or surfaces) that leverage the idea of synthesizing quasi-orthogonal radiation patterns (modes) to probe and encode the scene information in an indirect manner and compress it into a single channel (or a reduced number of channels). The application of computational imaging to the channel characterization problem is intriguing. Yet, a system level of knowledge of the design parameters, which are key to understanding the development of compressive surfaces for computational DoA estimation, is far from comprehensive. In this paper, we demonstrate different techniques to synthesize spatio-temporally incoherent field patterns, a key requirement for computational DoA estimation, and provide a study of the different system level parameters needed to design such antennas. We show that by increasing the orthogonality of the radiated modes (and thus reducing the information redundancy), a single-channel compressive antenna can retrieve the DoA pattern of multiple far-field sources even under a signal-to-noise ratio (SNR) level of as low as 0 dB, without the necessity to use a multi-channel physical architecture.

In this study, we explore the impact of a two-handed grip on the coverage of ahandset featuring three antenna arrays operating in the n257 frequency band of 26.5 GHz - 29.5 GHz. We focus on beam steering, which is effectively implemented using the antenna arrays and multi-bit phase shifters to provide quasi-omnidirectional coverage. We investigate how different hand grips impact the handset’s coverage region, including clockwise (CW) and anti-clockwise (ACW) rotation of the handset. Our findings reveal that, for the CW two-handed grip, beam steering significantly increased the coverage region (in which gain is greater than 0 dBi) from 19.7% to 42.2% of the spherical region surrounding the handset when 3-bit phase shifters are used for analogue beam steering. Similarly, for the ACW two-handed grip, coverage was increased from 10.2% to 36.9% with 3-bit beam steering. Cumulative distribution function (CDF) performance for effective isotropic radiated power (EIRP) is also considered for the handset in free space,along with both grip orientations. It is once again shown that beam steering offers a significant performance increase; however, it is also shown that introducing the user’s hand grip degrades the performance. Additionally, this paper investigates the impact of varying the phase shifter resolution used to actuate beam steering on the coverage of the handset. We found that increasing the resolution increases the number of possible steering angles at each array, thereby increasing the percentage coverage of the handset. However, we also note that the relationship between resolution and coverage plateaus around 3 bits. Overall, our study highlights the importance of beam steering in improving coverage and signal strength for handsets operating in the n257 frequency band. By exploring the impact of different hand grips and phase shifter resolution, we provide valuable insights into designing future handsets that can better serve users in various settings.

This paper presents a handset antenna array that operates within approved millimetre-wave 5G (mmWave) 3GPP n257 band 26.5-29.5 GHz and provides quasi-omnidirectional radiation characteristics. The paper showcases a 4 x 1 linear antenna array that is placed into 3 distinct locations within a handset for testing against a numerical hand model which allows simulation of the effects of a user in a specific handset holding scenario. Blockages can cause significant degradation of the performance of the antenna, however, the optimized antenna locations presented in this work were capable of reasonable gain coverage with 52% coverage for gain values greater than 0 dBi. These results were achieved using a 3-bit phase shifter and have been verified by simulations, while single 4x1 array characteristics were confirmed by far-field measurements. Beam steering characteristics of these arrays are thoroughly investigated, showcasing how signal coverage can be improved in the event of a blockage. Study was also carried out into the effectiveness of increasing the size of multi-bit phase shifters and it is shown how this improvement is negligible beyond a certain point.

This paper investigates the impact of a left-handed grip on the coverage of a handset featuring three antenna arrays operating in the n257 frequency band (26.5 GHz - 29.5 GHz). As in previous work, beam steering is implemented using the antenna arrays and multi-bit phase shifters to provide quasi-omnidirectional coverage. The results are compared to coverage data found in previous work for a handset held with a right-handed grip, and a handset in free space. It was found that, for a left-handed grip, beam steering increased the coverage region (in which gain is greater than 0 dBi) from 22% to 57% of the spherical region surrounding the handset through the use of 3-bit phase shifters. This is similar to the increase from 23% to 52% coverage achieved when beam steering was implemented for a right-handed grip in previous work [1]. This paper also investigates the impact of varying the size of multi-bit phase shifters used to actuate beam steering on the coverage of the handset. Increasing the number of bits available to the phase shifters increases the number of possible steering angles at each array, which increases the percentage coverage of the handset. This relationship between available bits and coverage starts to plateau around 3 bits.

New constraints based on practical hardware are introduced in Compressive Sensing (CS) based rectangular antenna array thinning technique. In a standard CS array sparsity enforcement, antenna elements are considered as ideal point sources which does not comply with the practical hardware. It also does not consider the impact of mutual coupling of neighbouring antenna elements on the impedance mismatch. In this work, we propose a combination of constraints based on physical antenna array specifications, mutual coupling and practical antenna element radiation performance in the CS based array thinning enforcement. Analytical modelling along with a design example is presented and discussed. Array performance based on full--wave electromagnetic simulations show the reliability of the proposed approach.

In this study, an ultra-wideband (UWB) monopole antenna with a dynamically reconfigurable notch band, along with the associated RF-triggered power management unit (PMU) that enables the dynamic reconfigurability, are presented. The UWB monopole antenna has a rectangular slot which hosts a J-shaped stub, electrically connected with the radiator using one PIN diode switch. When the diode is OFF, the monopole antenna has a UWB characteristic, while when it is turned ON a frequency notch is created at 5.6 GHz. The diode is fed from a PMU that consists of a rectenna and a DC-to-DC active booster. When the rectenna that consists of a patch antenna and a rectifier receives a −11 dBm or higher 5.6 GHz signal, it rectifies the RF signal into a sufficiently high DC voltage. The rectified DC voltage is applied to the cascaded DC-to-DC booster as enabling signal, and the booster provides at its output terminal sufficient DC power to actuate the PIN diode and thus dynamically reconfigure the UWB antenna. The dynamically reconfigurable notch band is created immediately in response to the reception of an external, −11 dBm RF signal at 5.6 GHz, and it disappears in real time immediately after the external RF signal is removed. 13 12 2046 2052