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The Radio frequency (RF) fingerprinting technique makes highly secure device authentication possible for future networks by exploiting hardware imperfections introduced during manufacturing. Although this technique has received considerable attention over the past few years, RF fingerprinting still faces great challenges of channel-variation-induced data distribution drifts between the training phase and the test phase. To address this fundamental challenge and support model training and testing at the edge, we propose a federated RF fingerprinting algorithm with a novel strategy called model transfer and adaptation (MTA). The proposed algorithm introduces dense connectivity among convolutional layers into RF fingerprinting to enhance learning accuracy and reduce model complexity. Besides, we implement the proposed algorithm in the context of federated learning, making our algorithm communication efficient and privacy-preserved. To further conquer the data mismatch challenge, we transfer the learned model from one channel condition and adapt it to other channel conditions with only a limited amount of information, leading to highly accurate predictions under environmental drifts. Experimental results on real-world datasets demonstrate that the proposed algorithm is model-agnostic and also signal-irrelevant. Compared with state-of-the-art RF fingerprinting algorithms, our algorithm can improve prediction performance considerably with a performance gain of up to 15\%., Comment: This paper was accepted by IEEE INFOCOM 2023 Workshop (DeepWireless)

In reconfigurable intelligent surface (RIS)-assisted wireless communication systems, the pointing accuracy and intensity of reflections depend crucially on the 'profile,' representing the amplitude/phase state information of all elements in a RIS array. The superposition of multiple single-reflection profiles enables multi-reflection for distributed users. However, the optimization challenges from periodic element arrangements in single-reflection and multi-reflection profiles are understudied. The combination of periodical single-reflection profiles leads to amplitude/phase counteractions, affecting the performance of each reflection beam. This paper focuses on a dual-reflection optimization scenario and investigates the far-field performance deterioration caused by the misalignment of overlapped profiles. To address this issue, we introduce a novel deep reinforcement learning (DRL)-based optimization method. Comparative experiments against random and exhaustive searches demonstrate that our proposed DRL method outperforms both alternatives, achieving the shortest optimization time. Remarkably, our approach achieves a 1.2 dB gain in the reflection peak gain and a broader beam without any hardware modifications., Comment: 6 pages, 6 figures. This paper has been accepted for presentation at the VTC2023-Fall

Polyisocyanurate (PIR) foam is a robust thermal insulation material utilized widely in the modern construction. In this work, the flammability of one representative example of this material was studied systematically using experiments and modeling. The thermal decomposition of this material was analyzed through thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry. The thermal transport properties of the pyrolyzing foam were evaluated using Controlled Atmosphere Pyrolysis Apparatus II experiments. Cone calorimetry tests were also carried out on the foam samples to quantify the contribution of the blowing agent (contained within the foam) to its flammability, which was found to be significant. A complete pyrolysis property set was developed and was shown to accurately predict the results of all aforementioned measurements. The foam was also subjected to full-scale flame spread tests, similar to the Single Burning Item test. A previously developed modeling approach based on a coupling between detailed pyrolysis simulations and a spatially-resolved relationship between the total heat release rate and heat feedback from the flame, derived from the experiments on a different material in the same experimental setup, was found to successfully predict the evolution of the heat release rate measured in the full-scale tests on the PIR foam.

Millimeter wave (mmWave) communication has recently attracted significant attention from both industrial and academic communities. The large bandwidth availability as well as low interference nature of mmWave spectrum is particularly attractive for industrial communication. However, inherent challenges such as coverage and blockage of mmWave communication cause highly fluctuated channel quality. This paper explores wireless medium access control (MAC) schedulers for mmWave-based industrial wireless applications. Our objective is to design a high-performance and enhanced fairness MAC scheduling algorithm that responds rapidly to channel variations. The key contribution of our work is a method to modify the standard proportional fair (SPF) scheduler. It introduces more flexibility and dynamic properties. Compared to the SPF, our enhanced proportional fair (EPF) scheduler not only improves the priority for users in poor channel conditions but also accelerates the reaction time in fluctuated channel conditions. By providing higher fairness for all users and enhancing system robustness, it particularly adapts to the scatter-rich industrial mmWave communication environment. Through extensive performance evaluation based on the widely accepted network simulator (ns-3), we show that the new scheduler achieves better performance in terms of delivering ultra-low latency and reliable services over mmWave-based industrial communication., Comment: Accepted for publication in IEEE VTC Fall 2020

This paper proposes a dimension reduction-based signal compression scheme for uplink distributed MIMO cloud radio access networks (C-RAN) with an overall excess of receive antennas, in which users are jointly served by distributed multi-antenna receivers connected to a central processor via individual finite-capacity fronthaul links. We first show that, under quantization noise-limited operation, applying linear dimension reduction at each receiver before compressing locally with a uniform quantization noise level results in a sum capacity that scales approximately linearly with fronthaul capacity, and can come within a fixed gap of the cut-set bound. The dimension reduction filters that maximize joint mutual information are then shown to be truncated forms of the conditional Karhunen-Loeve transform, with a block coordinate ascent algorithm for finding a stationary point given. Analysis and numerical results indicate that the signal dimension can be reduced without significant loss of information, particularly at high signal-to-noise ratio, preserving the benefits of using excess antennas. The method is then adapted for the case of imperfect channel state information at the receivers. The scheme significantly outperforms conventional local signal compression at all fronthaul rates, and with complexity linear in network size represents a scalable solution for distributed MIMO C-RAN systems.

In this paper, we propose a new technique for the future fifth generation cellular network wireless backhauling. We show that hundreds of bits per second per Hertz (bits per second per Hz) of spectral efficiency can be attained at a high carrier frequency (such as 26 GHz) between large antenna arrays deployed along structures (such as lamp posts) that are close and roughly parallel to each other. Hundreds of data streams are spatially multiplexed through a short range and line of sight massive multiple input massive multiple output propagation channel thanks to a new low complexity spatial multiplexing scheme, called block discrete Fourier transform based spatial multiplexing with maximum ratio transmission. Its performance in real and existing environments is assessed using accurate ray-tracing tools and antenna models. In the best simulated scenario, 1.6 kbits per second per Hz of spectral efficiency is attained, corresponding to 80% of Singular Value Decomposition performance, with a transmitter and a receiver that are 200 and 10,000 times less complex, respectively., Comment: draft version of IEEE Globecom 2016 paper

The first measured results for massive multiple input, multiple-output (MIMO) performance in a line-of-sight (LOS) scenario with moderate mobility are presented, with 8 users served in real-time using a 100 antenna base Station (BS) at 3.7 GHz. When such a large number of channels dynamically change, the inherent propagation and processing delay has a critical relationship with the rate of change, as the use of outdated channel information can result in severe detection and precoding inaccuracies. For the downlink (DL) in particular, a time division duplex (TDD) configuration synonymous with massive MIMO deployments could mean only the uplink (UL) is usable in extreme cases. Therefore, it is of great interest to investigate the impact of mobility on massive MIMO performance and consider ways to combat the potential limitations. In a mobile scenario with moving cars and pedestrians, the massive MIMO channel is sampled across many points in space to build a picture of the overall user orthogonality, and the impact of both azimuth and elevation array configurations are considered. Temporal analysis is also conducted for vehicles moving up to 29km�h and real-time bit error rates (BERs) for both the UL and DL without power control are presented. For a 100 antenna system, it is found that the channel state information (CSI) update rate requirement may increase by 7 times when compared to an 8 antenna system, whilst the power control update rate could be decreased by at least 5 times relative to a single antenna system.

Millimeter wave (mmWave) communication is a key enabling technology with the potential to deliver high capacity, high peak data rate communications for future railway services. Knowledge of the radio characteristics is of paramount importance for the successful deployment of such systems. In this paper mmWave channel measurements are reported for a railway environment using a wideband channel sounder operating at 60GHz. Highly directional antennas are deployed at both ends of the link. Data is reported for path loss, root mean square (RMS) delay spread and K-factor. Static and mobile measurements are considered. Analysis shows that the signal strength is strongly dependent (up to 25dB) on the azimuth orientation of the directional transmit and receive antennas. A path loss exponent of n=2.04 was extracted from the Line-of-Sight measurements with optimally aligned antennas. RMS delay spreads ranged from 1ns to 22ns depending on antenna alignment. 50% of the measured K-factors were found to be less than 6dB. We conclude this is the result of ground reflections in the vertical Tx-Rx plane.

Massive MIMO has rapidly gained popularity as a technology crucial to the capacity advances required for 5G wireless systems. Since its theoretical conception six years ago, research activity has grown exponentially, and there is now a developing industrial interest to commercialise the technology. For this to happen effectively, we believe it is crucial that further pragmatic research is conducted with a view to establish how reality differs from theoretical ideals. This paper presents an overview of the massive MIMO research activities occurring within the Communication Systems & Networks Group at the University of Bristol centred around our 128-antenna real-time testbed, which has been developed through the BIO programmable city initiative in collaboration with NI and Lund University. Through recent preliminary trials, we achieved a world first spectral efficiency of 79.4 bits/s/Hz, and subsequently demonstrated that this could be increased to 145.6 bits/s/Hz. We provide a summary of this work here along with some of our ongoing research directions such as large-scale array wave-front analysis, optimised power control and localisation techniques., Comment: Presented at the IET Radio Propagation and Technologies for 5G Conference (2016). 5 pages

The first measured results for massive multiple-input, multiple-output (MIMO) performance in a line-of-sight (LOS) scenario with moderate mobility are presented, with 8 users served by a 100 antenna base Station (BS) at 3.7 GHz. When such a large number of channels dynamically change, the inherent propagation and processing delay has a critical relationship with the rate of change, as the use of outdated channel information can result in severe detection and precoding inaccuracies. For the downlink (DL) in particular, a time division duplex (TDD) configuration synonymous with massive MIMO deployments could mean only the uplink (UL) is usable in extreme cases. Therefore, it is of great interest to investigate the impact of mobility on massive MIMO performance and consider ways to combat the potential limitations. In a mobile scenario with moving cars and pedestrians, the correlation of the MIMO channel vector over time is inspected for vehicles moving up to 29 km/h. For a 100 antenna system, it is found that the channel state information (CSI) update rate requirement may increase by 7 times when compared to an 8 antenna system, whilst the power control update rate could be decreased by at least 5 times relative to a single antenna system., Comment: Accepted for presentation at the 85th IEEE Vehicular Technology Conference in Sydney. 5 Pages. arXiv admin note: substantial text overlap with arXiv:1701.08818

This paper presents achievable uplink (UL) sumrate predictions for a measured line-of-sight (LOS) massive multiple-input, multiple-output (MIMO) (MMIMO) scenario and illustrates the trade-off between spatial multiplexing performance and channel de-coherence rate for an increasing number of base station (BS) antennas. In addition, an orthogonal frequency division multiplexing (OFDM) case study is formed which considers the 90% coherence time to evaluate the impact of MMIMO channel training overheads in high-speed LOS scenarios. It is shown that whilst 25% of the achievable zero-forcing (ZF) sumrate is lost when the resounding interval is increased by a factor of 4, the OFDM training overheads for a 100-antenna MMIMO BS using an LTE-like physical layer could be as low as 2% for a terminal speed of 90m/s., Comment: 4 pages, 5 figures

The QUAdrotor Swarm ARena (QUASAR) is an experimental test bed for autonomous multi-agent unmanned aerial vehicle (UAV) control systems. The development of QUASAR is motivated by the desire to experimentally test and validate new hardware-in-the-loop multi-agent control methods. A key focus of the project is on investigating the performance comparisons between linear and nonlinear multi-agent control methods under realistic operating conditions. Preliminary numerical simulations using MATLAB/Simulink indicate that nonlinear control methods more effectively compensate for unpredictable disturbances and dynamic model uncertainty. However, the results also suggest that standard linear control methods offer the benefit of ease of implementation. In addition to the control design trade-offs, preliminary experimental results have demonstrated the practical trade-offs that exist in using different inter-agent wireless communication protocols (e.g., radio versus Wi-Fi). Ongoing research efforts include experimentally testing new hardware-in-the-loop multi-agent UAV control methods that effectively compensate for disturbances and uncertain dynamics (e.g., unmodelled wind gusts). It is expected that this research project will provide increased potential for multi-agent UAV implementation in military and civilian applications, which achieve reliable performance under the unpredictable and potentially adversarial operating conditions encountered in real-world operating conditions.

Cloud Radio Access Network (C-RAN) has attracted a worldwide attention in both academia and industry. This network architecture re-forming has been considered as a potential solution to meet the increasing capacity demands for future mobile data traffic. In addition, Network Virtualisation is a promising technique for efficient resource utilisation. This paper proposes a customisable resource virtualisation algorithm for multi user data scheduling in a Long Term Evolution (LTE) C- RAN deployment. The algorithm is based on the hypervisor specific assignment of air resources allocation between the virtual operators (VOs) dynamically, based on either joint scheduling or per cell schemes. The objective is to improve the resource allocation mechanism based on traffic conditions and a database of pre-defined services priorities. Two distinctive scenarios are considered and evaluated against standard Round Robin (RR) C-RAN scheduling technique. Simulation results show improvements in the overall traffic throughput and reduction in end-to-end delay for delay sensitive applications. In addition, an assessment of fairness guarantee is considered across all users.

The vast growth in mobile data traffic with its increasing capacity demands necessitates investigating future solutions to cope with these challenges. Network Virtualisation is considered one potential solution to simplify the current wireless networks. Recently efforts have been made to show the performance gains of different resource allocation schemes in legacy LTE air interface virtualization. Moreover Cloud — based mobile networks are anticipated to play a significant role for next generation mobile networks. This paper investigates the potential deployment benefits of a novel resource virtualization algorithm (Traffic Aware Joint Scheduling) in Cloud-RANs (C-RAN). Air interface resources are coordinated and allocated dynamically by a hypervisor among different virtual operators (VOs). Three distinctive schemes are proposed and evaluated against standard Round Robin (RR) C-RAN scheduling. Simulation results show improvements in the throughput of the mobile video traffic and reduction in end-to-end delay for delay sensitive applications. In addition, an assessment of fairness guarantee is considered across all users. Note that this paper considers the impact of the proposed schemes on the transmission/data plane.

In this paper, for the first time real-world channel measurements are used to analyse the performance of spatial modulation (SM), where a full analysis of the average bit error rate performance (ABER) of SM using measured urban correlated and uncorrelated Rayleigh fading channels is provided. The channel measurements are taken from an outdoor urban multiple input multiple output (MIMO) measurement campaign. Moreover, ABER performance results using simulated Rayleigh fading channels are provided and compared with a derived analytical bound for the ABER of SM, and the ABER results for SM using the measured urban channels. The ABER results using the measured urban channels validate the derived analytical bound and the ABER results using the simulated channels. Finally, the ABER of SM is compared with the performance of spatial multiplexing (SMX) using the measured urban channels for small and large scale MIMO. It is shown that SM offers nearly the same or a slightly better performance than SMX for small scale MIMO. However, SM offers large reduction in ABER for large scale MIMO., Comment: IEEE Vehicular Technology Conference Fall 2013 (VTC-Fall 2013), Accepted

Herein, results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurements under the EU IST SATURN project are reported. Our investigation shows that for non-line-of-sight (NLOS) cases, the average power delay profiles fit the exponentially decaying curve quite well, therefore a simple wideband model for single-input single-output (SISO) proposed in COST259 has been used in our model. Furthermore, the investigations show that the MIMO channel covariance matrix of each normalized tap of the impulse response could be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively. Based on the above results, a wideband statistical model is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, we use this model to show some capacity characteristics of Hiper-LAN/2 channels in NLOS indoor scenarios., QC 20110617

Downlink beamforming in a WLAN-type system employing access points and mobiles equipped with multiple antennas and associated receivers and transmitters are considered. The beamforming aims at maximizing the performance under constraints on transmit power or equivalent isotropic radiated power (EIRP). Solutions for the two constraints are derived and investigated using simulated and measured channels. Our simulation and experimental results shows that performance gains of 8-10dB when using four directional transmitter antennas and two receive antennas (as compared with a base-line one-transmit two-receive), are possible under both constraints. For simulated channels, a delay between channel estimation and use of the same channel of up to 10% of the (inverse of the) Doppler frequency only degrades performance some tenths of a dB. In our measurements, very small degradations are seen with delays of up to 130ms. The measurements were made under relatively stationary conditions with only occasionally moving people Two different strategies for updating the beamforming vectors: sounding and ping-pong, are also considered in the paper., QC 20110617

In this paper, we present results of 5.2 GHz wideband indoor multiple input multiple output (MIMO) channel measurementsunder the EU IST SATURN project. First we show the average power delay profile for the single input single output (SISO) channel. Furthermore, our investigation shows that for non-line-of-sight (NLOS) indoor scenarios, the MIMO channel covariance matrix of each normalized tap of channel impulse response can be be well approximated by the Kronecker product of the covariance matrices seen from the transmitter and receiver respectively.Based on the above results, a wideband statistical model for HiperLAN/2 MIMO channel is presented. Monte-Carlo simulations show reasonably good agreement between the measured data and our model. Finally, weuse this model to show the capacity characteristics of theHiperLAN/2 channel in NLOS indoor scenarios., QC 20111107

Herein, a line-of-sight (LOS) multiple input multiple output (MIMO) channel model is presented based on 5.2 GHzindoor MIMO channel measurements. The signal from the dominant direction is estimated and removed from the channel data. The residual part is shown to be Rayleigh distributed and its covariance matrix can be well approximated by theKronecker product of the covariance matrices seen from the transmitter and receiver respectively. Therefore we model the whole narrowband LOS indoor MIMO channel as a static rank one matrix plus a statistical model based on Rayleigh distribution with a multiplicative covariance structure., QC 20111107. Invited paper

A WLAN-type scenario where a base-station (access point) equipped with multiple antennas is transmitting and a mobile with only a single antenna is receiving, is considered. Three approaches are investigated: Grid-of-beams (GOB), Maximal-Ratio (MR) and equal-gain (EG) each with one of the following constraints 1) Total transmit power over all antenna elements, 2) Maximum power on any antenna element 3) Equivalent isotropic radiated power (EIRP). The median diversity gain for the MR approach was estimated to be 14.8dB, 10.6dB, and 11.4dB using constraint 1-3, respectively at 5.2GHz in a modern University building at 5-50 meter range. For GOB corresponding numbers are 9.4dB,9.4dB,2.3dB and for EG 13.9dB,13.9dB,10.3dB, respectively. These results were virtually independent of delay between channel estimation and use of the same estimate, when the delay is less than 130ms. This result was obtained although there were people moving in the environment. The diversity gain under the EIRP constraint is encouraging and shows that coverage improvements are possible even under EIRP limitations., QC 20110617

In this paper, we present results from measurements conducted by the University of Bristol.We study the channel characteristics of Multiple-Input-Multiple-Output (MIMO) indoor channel at 5.2GHz. Our investigation shows that the envelope of the channel for non-line-of-sight (NLOS) indoorsituations is approximately Rayleigh distributed and consequently we focus on a statistical descriptionof the first and second order moments of the narrowband MIMO channel. Furthermore, it is shown thatfor NLOS indoor scenarios, the MIMO channel covariance matrix can be well modeled by a Kroneckerproduct of the covariance matrices describing the correlation at the transmitter and the receiver siderespectively. A statistical narrowband model for the NLOS indoor MIMO channel based on thiscovariance structure is presented along with some simulation results., QC 20111107

A dedicated inverse Doherty amplifier is presented in this paper using commercially available 10W GaN HEMT devices. Results show that an emulated 1W peaking amplifier and a 10W carrier amplifier can be used to create a highly efficient amplification architecture. Ideal inverse active load-pull is introduced theoretically with experimental results showing good agreement with the theory. A generic characterization scan of the inverse Doherty amplifier yields state of the art drain and power added efficiency in the output power back-off. A drain and power added efficiency of 60% and 50% are obtained at 10dB output power back-off respectively with a maximum output power of 41dBm at 2.1GHz.

In this paper a new characterization method is proposed to optimize envelope tracking (ET) Radio Frequency power amplifier (RFPA) average drain efficiency in the presence of variable envelope RF signals with high peak-to-average power ratio (PAPR). The proposed method consists of measuring the input and output signal complex envelopes as well as instantaneous envelope efficiency of the tested RFPA in the presence of an original configuration of envelope and RF driving signals. The improvement of the average efficiency is obtained by optimizing the input power level of the RF driving signal only. This, results in a Nonlinear Envelope Tracking (NET) system that compensates for the efficiency drop in classic ET architectures. A drain efficiency improvement of 21 percentage points has been achieved with a class-J PA operating at 2 GHz in the presence of a Long Term Evolution (LTE) modulated signal that exhibits a PAPR of 14.4 dB while complying with the 3GPP LTE standard linearity requirements.