On the performance of hybrid beamforming for millimeter wave wireless networks

The phenomenal growth in the demand for mobile wireless data services is pushing the boundaries of modern communication networks. Developing new technologies that can provide unprecedented data rates to support the pervasive and exponentially increasing demand is therefore of prime importance in wireless communications. In existing communication systems, physical layer techniques are commonly used to improve capacity. Nevertheless, the limited available resources in the spectrum are unable to scale up, fundamentally restricting further capacity increase. Consequently, alternative approaches which exploit both unused and underutilised spectrum bands are highly attractive. This thesis investigates the use of the millimeter wave (mmWave) spectrum as it has the potential to provide unlimited bandwidth to wireless communication systems. As a first step toward realising mmWave wireless communications, a cloud radio access network using mmWave technology in the fronthaul and access links is proposed to establish a feasible architecture for deploying mmWave systems with hybrid beamforming. Within the context of a multi-user communication system, an analytical framework of the downlink transmission is presented, providing insights on how to navigate across the challenges associated with high-frequency transmissions. The performance of each user is measured by deriving outage probability, average latency and throughput in both noise-limited and interference-limited scenarios. Further analysis of the system is carried out for two possible user association configurations. By relying on large antenna array deployment in highly dense networks, this architecture is able to achieve reduced outages with very low latencies, making it ideal to support a growing number of users. The second part of this work describes a novel two-stage optimisation algorithm for obtaining hybrid precoders and combiners that maximise the energy efficiency (EE) of a general multi-user mmWave multiple-input, multiple-output (MIMO) interference channel network involving internet of things (IoT) devices. The hybrid transceiver design problem considers both perfect and imperfect channel state information (CSI). In the first stage, the original non-convex multivariate EE maximization problem is transformed into an equivalent univariate problem and the optimal single beamformers are then obtained by exploiting the correlation between parametric and fractional programming problems and the relationship between weighted sum rate (WSR) and weighted minimum mean squared error (WMMSE) problems. The second stage involves the use of an orthogonal matching pursuit (OMP)-based algorithm to obtain the energy-efficient hybrid beamformers. This approach produces results comparable to the optimal beam-forming strategy but with much lower complexity, and further validates the use of mmWave networks in practice to support the demand from ubiquitous power-constrained smart devices. In the third part, the focus is on the more practical scenario of imperfect CSI for multi-user mmWave systems. Following the success of hybrid beamforming for mmWave wireless communication, a non-traditional transmission strategy called Rate Splitting (RS) is investigated in conjunction with hybrid beamforming to tackle the residual multi-user interference (MUI) caused by errors in the estimated channel. Using this technique, the transmitted signal is split into a common message and a private message with the transmitted power dynamically divided between the two parts to ensure that there is interference-free transmission of the common message. An alternating maximisation algorithm is proposed to obtain the optimal common precoder. Simulation results show that the RS transmission scheme is beneficial to multi-user mmWave transmissions as it enables remarkable rate gains over the traditional linear transmission methods. Finally, the fourth part analyses the spectral efficiency (SE) performance of a mmWave system with hybrid beamforming whilst accounting for real-life practice transceiver hardware impairments. An investigation is conducted into three major hardware impairments, namely, the multiplicative phase noise (PN), the amplified thermal noise (ATN) and the residual additive transceiver hardware impairments (RATHI). The hybrid precoder is designed to maximise the SE by the minimisation of the Euclidean distance between the optimal digital precoder and the noisy product of the hybrid precoders while the hybrid combiners are designed by the minimisation of the mean square error (MSE) between the transmitted and received signals. Multiplicative PN was found to be the most critical of the three impairments considered. It was observed that the additive impairments could be neglected for low signal-to-noise-ratio (SNR) while the ATNs caused a steady degradation to the SE performance

Hematinic effect of locust bean (Parkia biglobosa) seeds on phenylhydrazine-induced anaemia in rats

Background: Hematinic effect of the extract of locust bean seeds was investigated following Phenylhydrazine (primarily used as antipyretics) administration in wistar rats. Methods: The phytochemical, chemical and mineral constituents of the locust bean seeds were evaluated. 25 adult male wistar rats were randomly divided into 5 groups: Group 1 rats were untreated control; Group 2 received only phenylhydrazine: (negative controls); Group 3 received phenylhydrazine +100 mg/kg of extract; Group 4 received phenylhydrazine +1000 mg/kg of extract; Group 5 received  phenylhydrazine + 0.23 ml/kg of Bioferon®: phenylhydrazine (40mg/kg body weight) was administered via intraperitoneal route on day 0, with two additional doses given at 9am and 6pm, on day 1 of the experiment; the seed extracts of Parkia biglobosa and Bioferon were both administered orally for 14 days. On day 15, the rats were anesthetized by chloroform and blood was collected by direct cardiac puncture. Packed cell volume (PCV), hemoglobin (Hb), Red blood cell counts (RBC), Mean corpuscular volume (MCV), Mean concentration of hemoglobin (MCH), Reticulocytes and Mean corpuscular hemoglobin concentration (MCHC) were determined using automated machine (Sysmex apparatus of the type 8999). Results: The phytochemical analysis of the extract revealed the presence of tannis, alkaloids, flavonoid, aponin, steroid and glycosides. The chemical analysis indicated the presence of moisture, protein, crude fat, crude fibre, ash, carbohydrate, and nitrogen. The mineral contents of the extract revealed the presence of: Sodium,  Potassium, Calcium, Magnesium, Zinc, Iron, Manganese, Copper and  Phosphorus. Phenylhydrazine significantly reduced all erythrocyte parameters in group 2 rats when compared with group 1 rats (p<0.05). However, administration of the extract and Bioferon significantly increased values of all erythrocyte parameters in groups 4 and 5 rats respectively compared with group 2 rats. Conclusion: The results suggest a possible hematinic effect of the extract of locust bean seeds on the parameters of erythrocyte following phenylhydrazine administration. The observed effects of the extract could possibly be from the rich nutritional content of the P. biglobosa seeds

Towards the Assessment of Realistic Hybrid Precoding in Millimeter Wave MIMO Systems with Hardware Impairments

Funding Information: This work was supported by the University of Hertfordshire's 5‐year Vice Chancellor's Research Fellowship and by the National Research Fund, Luxembourg, under the projects ECLECTIC and 5G‐SKY. Publisher Copyright: © 2021 The Authors. IET Communications published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and TechnologyHybrid processing in millimeter wave (mmWave) communication has been proposed as a solution to reduce the cost and energy consumption by reducing the number of radio-frequency (RF) chains. However, the impact of the inevitable residual transceiver hardware impairments (RTHIs), including the residual additive transceiver hardware impairments (RATHIs) and the amplified thermal noise (ATN), has not been sufficiently studied in mmWave hybrid processing. In this work, the hybrid precoder and combiner are designed, which include both digital and analog processing by taking into account the RATHIs and the ATN. In particular, a thorough study is provided to shed light on the degradation of the spectral efficiency (SE) of the practical system. The outcomes show the steady degradation of the performance by the ATN across all SNR values, which becomes increasingly critical for higher values of its variance. Furthermore, it is shown that RATHIs result in degradation of the system only in the high SNR regime. Hence, their impact in mmWave system operating at low SNRs might be negligible. Moreover, an increase concerning the number of streams differentiates the impact between the transmit and receive RATHIs with the latter having a more severe effect.Peer reviewe

An optimal networked LiFi access point slicing scheme for internet-of-things

Light-Fidelity (LiFi) access points (APs) can be deployed anywhere to support the exponential growth of various lightweight hand-held and smart internet-of-things (IoT) devices and applications. IoT traffic is often sporadic and consists of heterogeneous bursty flows, which may affect the performance of supported wireless services. This paper develops an optimal data rate-based slicing scheme that dynamically virtualizes a networked LiFi AP downlink channel bandwidth according to the data rate demands of users and the requested services. We formulate a game optimization problem that captures the relation between three main entities: a LiFi attocellular network infrastructure provider (InP), mobile virtual network operators (MVNOs), and IoT or wireless users. A software-defined networking (SDN) controller enables the InP to reconfigure the LiFi AP downlink channel slices to MVNOs, based on their service-level agreements (SLAs) and the traffic profile of IoT services. Simulation results show that the proposed AP resources slicing scheme is promising for IoT applications