Considering a multi-user Downlink scenario, this paper studies transmit antenna selection (AS) for uniform rectangular arrays (URA). A key contribution of this work is the investigation of the trade-off between AS and the array directivity (or gain), and its impact on spectral efficiency (SE) and energy efficiency (EE). In this context, to improve EE of the system, a directivity-aware transmit AS and power allocation problem is formulated and solved using a sequential approach. For AS, two schemes are proposed: Block selection (BS) and L´evy flight based binary particle swarm optimization (LFBPSO), while for power allocation, an iterative quadratic transform method is employed in combination with Dinkelbach algorithm for EE maximization. The performance of the AS schemes is evaluated with respect to SE, EE and computational complexity. The results show that the array directivity varies with the subset of selected antennas and has a direct impact on the performance of the AS schemes in terms of achievable SE and EE. Furthermore, AS without considering the directivity can incur a loss in the array gain of up to 2 dB in a λ/2 spaced array. The results also show that LFBPSO outperforms other AS schemes with respect to SE and EE. Finally, another important contribution of this work is the experimental validation of the impact of array directivity on the AS process. This is demonstrated by replacing the isotropic antenna array with a measured 4×8 uniform rectangular array of patch antennas in the simulation framework.

Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising technology for enabling seamless wireless connectivity, particularly in environments characterized by non-line-of-sight (NLoS) propagation and signal blockages. To enhance performance in such scenarios, densely deployed RIS configurations is a promising solution. In this context, this paper investigates the impact of inter-element spacing on the gain and the energy efficiency (EE) of RIS-assisted communication system. Unlike previous works, we formulate the received signal model that incorporates the array directivity and show how the array gain varies with the change in the inter-element spacing. The performance of the standard (where the spacing is half of the wavelength) and dense RIS (where the spacing is less than half of the wavelength) configurations is compared in terms of, 1) beam pattern and array gain while considering quantized and unquantized phase shifts, 2) variation in the number of RIS elements, and 3) the trade-off between EE and array gain. Results reveal that while dense RIS offers slightly improved array gain compared to standard RIS, it incurs higher power consumption and reduced EE.

Uniform planar arrays (UPAs) are widely employed in practical systems, yet the study of antenna selection for UPAs remains limited. In particular, the interplay between selected antenna subsets and directivity has been overlooked in the existing literature. This paper addresses this by exploring how different subsets of selected antennas affect directivity and developing effective antenna selection strategies for UPA with a rectangular lattice. Our findings reveal that different subsets of selected antennas can lead to significantly different values for directivity, influencing selection outcomes compared to scenarios where directivity is not considered. Furthermore, we propose and compare four antenna selection strategies: 1) Column Selection (RS), 2) Row Selection (CS), 3) Full Aperture Greedy Selection (FAGS), and 4) Hybrid Initialization Binary Particle Swarm Optimization (HBPSO). With careful initialization of the particles, HBPSO achieves a spectral efficiency performance close to exhaustive search and surpasses other strategies. Moreover, incorporating directivity into the selection process significantly affects the performance of these strategies.

This paper characterises the impact of horizontally induced vibration on the antenna's channel response due to fast vehicle manoeuvres or the side push of wind during the overtaking of a large vehicle on a motorway at millimetre wave (mmWave) frequencies. The resultant misalignment perturbs the point of observation, which produces Doppler shifts. A new composite antenna and channel model, including horizontal vibration within the antenna mounting, is developed by measuring the scattering parameters (S21) at discrete intervals of time using a vector network analyser (VNA) that generates a swept tone with a radio frequency (RF) measurement bandwidth of 2GHz centred at 25.5GHz. The S21 over discrete intervals of time represents the channel time-frequency transfer function which is utilised to generate the Doppler variant transfer function and the Doppler power spectrum after post-processing at a vibration frequency below 100Hz. It is proven experimentally that the induced Doppler power is directly proportional to the probability density function (PDF) of the Doppler Shifts. This indicates that Doppler shifts with high probabilities of occurrence have higher Doppler powers. For example, a Doppler shift ≤2000Hz having a PDF = 0.6 or above arrives with a higher power of up to −20dBm as compared to the Doppler shift of ±4000Hz, which has a lower PDF = 0.1 and Doppler powers ≤−25dBm.

Owing to the shorter wavelength in the millimeter-wave (mmWave) spectrum, miniaturized antennas can receive power with a higher efficiency than UHF bands, promising sustainable mmWave-powered Internet of Things (IoT) devices. Nevertheless, the performance of a mmWave power receiver has not been compared, numerically or experimentally, to its sub6-GHz counterpart. In this article, the performance of mmWave-powered receivers is evaluated based on a novel wearable textile-based higher order mode microstrip antenna, showing the benefits of wireless power transmission (WPT). First, a broadband antenna is proposed maintaining a stable wearable measured bandwidth from 24.9 to 31.1 GHz, over threefold improvement compared to a conventional patch. The proposed antenna has a measured 8.2 dBi co-polarized gain with the highest thickness-normalized efficiency of a wearable antenna. When evaluated for compact power receivers, the measured path gain shows that WPT at 26 GHz outperforms 2.4 GHz by 11 dB. A rectenna array based on the proposed antenna is then evaluated analytically showing the potential for up to$6.3\times $higher power reception compared to a UHF patch, based on the proposed antenna’s gain and an empirical path-loss model. Both use cases demonstrate that mmWave-powered rectennas are suitable for area-constrained and large-area wearable IoT applications.

Autonomous vehicles require vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communication. Fifth-generation (5G) and beyond wireless networks enable such infrastructure through beamforming techniques at millimetre-wave (mm-wave) frequencies. This paper characterises the impact of antenna beamwidth on the Doppler shift, cross-polarisation ratio (XPR) and the channel attenuation for the 26GHz mm-wave V2I line-of-sight (LoS) channel. It is proven that the received Doppler power spectrum is proportional to the probability density function (PDF) of the Doppler Shift. This indicates that Doppler power reduces with the Doppler shift. It has also been established that a wider antenna half power beamwidth (HPBW) of 20° instead of 17° reduces the XPR by 20dB whilst increasing the channel attenuation by 10dB in a mm-wave LoS channel with dynamic blockage. Therefore, a trade-off between the XPR and channel attenuation can be introduced by employing different antenna HPBWs.

This paper investigates the effects of antenna vibration occurring due to suspension variation during the movement for vehicle-to-infrastructure (V2I) communication by developing a two dimensional (2D) model. With highly directional antennas fitted on a car's rear bumper and at a base station (BS), different beamwidths from 10° to 50° are investigated for a moving vehicle at 70mph. The gain sensitivity of the radiation pattern and the micro-Doppler shift are modelled for suspension variations between 5cm and 20cm. The analysis has been performed based on the observed angle of arrivals (AoA) at the receiver antenna in the elevation plane. The gain sensitivity represents the BSs’ main lobes' misalignments and receiver antennas’ radiation patterns at 26GHz. The results reveal a significant impact on gain sensitivity during the first 200m of movement away from the BS. Furthermore, the total Doppler shift increases due to the micro-Doppler with vertical displacements from the suspension variation. However, this can be mitigated if the beamwidth increases relative to the link budget or the BS height increases. The 2D model is validated by utilising accelerometer data recorded whilst the vehicle is moving at 70mph on a motorway, by extracting the displacements and computing the gain sensitivity.

In this paper, a Virtual Drive Testing (VDT) methodology for a MIMO LTE Vehicle to Infrastructure (V2I) urban scenario is proposed and compared with actual road drive tests. We have developed a unique and generic radio performance analysis process based on 3D ray traced channel models, theoretic or measured antenna patterns, RF channel emulation and hardware-in-the-loop radio measurements. A 3D ray-tracing channel model is used to predict the spatial and temporal multipath ray components of the radio propagation channel between an LTE BS and the vehicle. Measured LTE vehicular antenna patterns were then applied using a spatial and polarimetric convolution process. The resulting channels were streamed into a Keysight PropSim F8 channel emulator, which was programmed to communicate with the multi-channel LTE BSs emulator and a Samsung S5 mobile client performing a handover procedure. The VDT emulation method proposed in this paper is shown to be reliable and repeatable and the accuracy of the emulated throughput agreed well with real measurements for MIMO operation.

Ray tracing is a useful tool to model the spatial and temporal propagation parameters of electromagnetic radiation. The model can normally improve by the channel sounding. However, discrepancies may arise between the channel sounding and ray-tracing model due to it needs a wide bandwidth to differentiate the incoming signals, also the antenna radiation pattern may change dramatically over this wide frequency span. To overcome this limitation, in this paper, the sparse deconvolution will be used to test and improve data measurements from real environments. Good results are obtained that shows that Cauchy-Gaussian model can differentiate between two different signals that has 0.5m distances offset for 200 MHz and 0.8m for 150 MHz theoretically. Then, comparison between the measured data using the basic Inverse Discrete Fourier Transform and the Cauchy-Gaussian model for two different scenarios shows that signals arrival in time cannot adequately determined using only Inverse Discrete Fourier Transform technique at 150 MHz, while on the contrary, the Cauchy-Gaussian model can still discriminate between them.

This paper presents 3D radiation pattern analyses for omnidirectional (dipole) and directional (patch) antennas for various body locations encompassing wrist orientations and chest positions when mounted on a body phantom. In addition to analysing the directivities and relative efficiencies at 2.44GHz for different body positions, the study considers Sector and Slice analysis of the radiation patterns. In Sector analysis, the directivity is averaged for 12 azimuth-elevation sectors, while in Slice analysis, it is averaged for 28 azimuth sectors over the full elevation. It is shown that the antenna efficiency due to body blockage can be as low as 23% relative to the chest position efficiency, and directivities ranges from 5.4 to 10.5dBi for the antennas at different orientations. The Sector analysis identifies highest average signal levels, which are between table and door height for the dipole and above door height for the patch. The Slice analysis, which doesn't account for access point or user heights, shows average directivities that peak at 5.1 and 4.4dBi for the dipole and patch antenna, respectively. Using these antennas as part of a switch diversity system would improve the average directivity by approximately 7dBi in regions of low signal levels, and hence are potentially useful for wristbands and smart clothing.

In this paper, the antenna performance for the 5.2 GHz 802.11n network is compared for four different access points with 3 antenna configurations based on the simulated throughput derived from measurements and a ray-tracing model in a two-storey house. The aim here is not only outline a methodology for access point performance that taking account the user equipment orientation, MIMO data streams that can be supported yielding a total throughput metric, but also ascertain the accuracy of the ray tracing model. In order to demonstrate this, two commercial access points are compared with two alternative antenna configurations: an orthogonal array of dipoles and a linear array of vertical dipoles. Radiation patterns, directivity and polarization mix are presented for all access points. Physical layer throughput is computed for all modulation and coding based on the measured spectral responses and simulated channel matrix. Results show the orthogonal dipole array has the best overall performance with the average throughput of 137 Mbps while vertical dipole array works worst with 106 Mbps. The ray tracing model produce results within 8% of differences and more importantly provide the same performance ranking order.

Diffraction is known to have a major influence on the propagation performance of a wireless communications link especially in lower frequency bands and hence the diffraction in millimetre wave band needs to be emphasized. In this paper, we propose a single material characterisation measurement in a controlled indoor environment at the centre frequency of 40GHz. In addition, measurement results are presented in three distinct regions, line of sight (LOS), penumbra and umbra for a more comprehensible observation. Different materials with approximately same dimension are tested. The movement of the material under test through a direct ray path is investigated. Analysis shows that concrete experiences the greatest attenuation compared to other materials under test. The proposed results show significant agreement with the Knife Edge Diffraction theory. It also can be concluded that there is a significant diffracted field in umbra regions.

This paper analyses the theoretic throughput and coverage for a multi-element in-home Wireless Local Area Network (WLAN) in the 5 GHz band. In particular we study the impact of regulatory transmit power constraints on the relative performances of beamforming and antenna selection at the access point. A novel methodology is applied based on part measurement and part simulation. In home results are provided for standard 802.11n multiple-input multiple-output (MIMO) deployments. Results show that beamforming is particularly affected by regulatory transmit power constraints. For long-range links beamforming data throughputs are reduced by more than 50%. The average data rate in our test home reduces by 14.3% when regulatory constraints are applied to the beamforming system. For antenna selection the regulatory limits result in an 8.9% reduction in average throughput. Furthermore, we show that for long range links the average data rate is improved by 50% when the antenna selection is used in place of beamforming. Although antenna selection uses single stream MIMO more frequently than beamforming, the latter performs better when multiple spatial streams are used. Beamforming is shown to work best in the easy and medium-range channels.

The design of conformal antenna arrays has historically been carried out by warping suitable planar antenna arrays to the desired radius of curvature. There has been little investigation into the effects of characteristic antenna performance on conformal array performance as the radii of curvature is varied. This paper presents a Variable Geometry Conformal Antenna Array Test Rig, designed to allow the investigation of the performance of a variety of antenna types (cavity slot, patch, etc) in a controlled environment. This approach allows direct comparisons to be drawn between each set of antenna elements in the test rig, and also simplifies the model space for Finite Difference Time Domain (FDTD) modelling, allowing an additional comparison between measured antenna pattern and coupling measurements and modelled results. In this paper measurements of Conformal Cavity Slot antenna elements and Dual Feed Dual Patch antenna elements are presented.

This paper evaluates the theoretic performance of single-user multi-stream beamforming for heterogeneous LTE-A urban deployments (i.e. Macro and Pico cells). The work investigates the impact of six different Base Station (BS) antenna configurations on system level capacity. Our standard configuration assume 8 BS and 8 User Equipment (UE) antenna elements. To enhance capacity the BS antenna number was increased to 12 and 16. A 3D laser-scanned database for the city of Bristol (UK) was used as input to the 3D channel propagation model along with measured 3D complex voltage and polarimetric antenna patterns for the individual BS and UE antenna elements. More than 50,000 ray-traced Pico and Macro cellular links per BS configuration were investigated to ensure statistical relevance. Our analysis quantifies the capacity of an 8×8 Single-User Multiple-Input-Multiple-Output (SU-MIMO) solution in realistic urban heterogeneous environments. Results address the system level benefits of increasing the number of BS antenna elements as well as the sensitivity of capacity to vertical and horizontal spatial element configurations.

Passive communications based on modulated backscatter can dramatically extend the lifespan of wireless sensor networks. Because wireless passive sensor networks reduce the dependence on the batteries, they have great potential to be used in body sensing applications. In a typical sensor network deployment, multiple passive sensor nodes modulate a common carrier. The superimposed reflected signals can be resolved by using Code division multiple access (CDMA) principles. In practical systems however, a strong carrier component will leak to the receiver, causing offset to the constellation points and as a result it will destroy cross correlation properties of the CDMA codes. To address this problem, we propose a code shift modulation instead of vanilla CDMA. We develop maximum likelihood receiver and analyse its performance. Since the complexity of ML detection strategy scales exponentially with the number of sensors, we develop a reduced complexity detection technique based on Probabilistic Data Association (PDA). We demonstrate via numerical simulations that our reduced complexity detector approaches the ML performance.

This paper evaluates the impact of antenna patterns in heterogeneous LTE-Advanced networks. The propagation channel between each BS and UE is modelled as the spatial and polarimetric convolution of the antenna patterns with the spatial and temporal multipath components from a 3D outdoor ray-tracer. An LTE-Advanced physical layer simulator is used to determine the user performance in pico-cells and macro-cells for non-line-of-sight links. The received bit mutual information rate abstraction method is employed to determine the optimal physical layer throughput based on analysis of all available modulation and coding schemes. Packet error rate, throughput, link correlation and channel capacity are studied for pico-cellular and macro-cellular users. Results show that measured antenna patterns along with their orientations strongly influence user performance in an LTE-A network.

Ray tracing is a technique often used to model indoor and outdoor environments. In order to improve the parameters used in ray tracing, measurements from channel sounding can be employed to test algorithms and build more accurate models of the channel. However, channel sounding can be limited as the antenna radiation pattern may change dramatically over a wide frequency span. As a consequence, discrepancies may arise between measurement by channel sounding and simulation by ray-tracing model. To overcome this limitation, in this paper sparse deconvolution will be adopted as a method to test and improve data measurements from real environments. Initial measurements are performed in a controlled (anechoic) environment where the sources of radiation can be specifically defined and show the effect of reduction in bandwidth on accuracy of the signal estimation. Comparisons are made between the Inverse Discrete Fourier Transform technique for processing the measured data and that using the Cauchy-Gaussian model. Good results are obtained for two different scenarios and it is shown that the Cauchy-Gaussian model requires less than half the bandwidth of the impulse response method using only IDFT.

This paper analyses the throughput and coverage of an in-home wireless LAN in the 5GHz band. A novel approach is proposed based on part measurement, part simulation. The spatial and temporal characteristics of typical in-home channels are modelled using 3D ray tracing and combined with measured and appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed across 10 rooms in a virtual test house for all modulation and coding schemes. To accelerate the simulation process a received bit information rate abstraction technique is applied. Results are given for a standard 802.11a deployment. The benefits of 3x3 MIMO are then compared against the deployment of a Wireless Mesh Network (WMN). In the latter case meshing is performed using low cost single antenna radios. Relative to the benchmark SISO system, 3x3 MIMO is shown to improve the average throughput by 123%. Given four randomly deployed mesh points, the mesh solution improves the average throughput by 31%. Importantly, for the test house under consideration the MIMO solution improves connectivity by just 3%, while the mesh network offers 100% (whole home) connectivity. The mesh network (using 4 additional mesh points) is shown to support high definition video for 90% of the links, compared to 71% with 3x3 MIMO. Results confirm that mesh networks benefit the weaker links, while MIMO boosts the stronger links.

Recently there have been proposals to extend MIMO processing to the elevation dimension in addition to the azimuth direction. To accurately assess the promised gains of these "3D-MIMO" techniques, a channel model is needed that accurately accounts for the elevation angles of the rays. In addition it would be desirable for the 3D channel model to be a simple extension of an already defined 2D channel model to allow for ease of implementation and to assist the 3GPP standardization effort in the 3D MIMO area. In this paper we propose an extension of the ITU 2D channel model to 3D by adding a distance dependent elevation spread based on observations from ray tracing. Through system-level simulations we observe that the behavior of 3D MIMO is greatly impacted by the modeling of the 3D channel.

In this paper we analyze measurements of short range ultra-wideband (UWB) multiple input multiple output (MIMO) transmission. 2 × 2 near field UWB measurements were undertaken in an anechoic chamber using a Medav UWB MIMO channel sounder. Channel characteristics were recorded for transmitter to receiver separations of 0.1 m to 0.7 m. Two independent channels were achieved, and channel capacity is twice as high as capacity of a single channel.

An ultra-wideband (UWB) antenna array is designed to satisfy given constraints in a (large) contiguous frequency range. Space limitations are tight in many applications and it is often infeasible to design the antenna array with preferred element spacings of λ/2 at the centre frequency. In this study, the authors compare uniform linear UWB antenna arrays and non-uniform reduced-aperture UWB antenna arrays with more compact element spacings following a geometric progression. The authors analyse and discuss performance degradations with respect to irregularly spaced monopoles. The manufactured non-uniform linear UWB antenna arrays are characterised by measurements in an anechoic chamber. The results are correlated with the arrayfactor and compared with measured data of uniform linearly spaced monopoles in the time and frequency domains. It is found that a compact non-uniform linear UWB array with element spacings following a geometric progression can be designed such that its main lobe performs very close to that of a uniform linear array, with an antenna array size reduction of 23.6% for a seven-element non-uniform linear UWB array.

In this paper the throughput and packet error rate for an in-home 802.11n network is theoretically derived for two different types of 3x3 antenna configurations. Our first configuration assumes the use of three low directivity omni-dectional elements. The second arrangement makes use of three orthogonally orientated directional elements. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is computed for all modulation and coding schemes using a received bit information rate abstraction technique. The theory shows that directional antennas outperform the omni-directional devices in most cases. Directional elements show increased sensitivity to orientation, however for 83% of locations and orientations they still result in throughput enhancement. Directional antennas provide a 33% improvement in average data rate for random client orientations, improving to 52% with optimum alignment to the multipath.

Throughput and packet error rate are analysed in a home environment for two different 3×3 wireless LAN solutions. A 3×3 EBF approach (using three radio chains) is compared with a reduced cost 2×2 architecture (using two radio chains). In the 2×2 solution the optimum antenna pair is selected from the same set of three antennas at the AP and client. The impact of directional, as well as omni- directional, antenna elements is considered. The spatial and temporal characteristics of the in-home channels are modelled using 3D ray tracing and combined with appropriately orientated complex polarmetric patterns for each antenna element. Physical layer throughput is calculated for all modulation and coding schemes and (for the 2×2 case) all possible antenna combinations using a novel received bit mutual information rate abstraction technique. Results show that antenna number, pattern and orientation all play a key role in determining the performance of an 802.11n system. As expected, 3×3 EBF outperforms the 2×2 solution; however, with optimum antenna selection the performance of 2×2 EBF is competitive, especially when directional antennas are used at low signal to noise ratios. For distant rooms, 3×3 EBF is only 15% better (in terms of throughput) than 2×2 EBF when directional antennas and dynamic antenna selection are applied. 2×2 EBF with omni antennas results in a 45% reduction in throughput (compared with 3×3 EBF).