Power Efficient Communication Research Articles

A frequency-agile retrodirective tag for large-scale sub-terahertz data backscattering

Backscattering is a promising power-efficient communication technique providing sustainable wireless links with a low carbon footprint. This approach is a critical enabler for dense IoT networks, which are forecast to grow to 41 billion by 2025. However, existing backscatter designs are limited to the sub-6 GHz bands or narrowband operation in the millimeter-wave regime; therefore, they fail to concurrently support many interference-free low-power users. Enabling a frequency-agile wideband backscatter design in the sub-terahertz offers a two-pronged advantage for densely deployed backscatter networks: spatial reuse enabled by directionality and frequency multiplexing enabled by the large available bandwidth. We present the first sub-THz backscatter architecture that operates above 100 GHz. Our design relies on a detailed understanding of reciprocity in leaky-wave devices and offers a realistic joint localization and communication protocol for sub-THz backscatter networks.

A Machine Learning Approach for Path Loss Prediction Using Combination of Regression and Classification Models.

One of the key parameters in radio link planning is the propagation path loss. Most of the existing methods for its prediction are not characterized by a good balance between accuracy, generality, and low computational complexity. To address this problem, a machine learning approach for path loss prediction is presented in this study. The novelty is the proposal of a compound model, which consists of two regression models and one classifier. The first regression model is adequate when a line-of-sight scenario is fulfilled in radio wave propagation, whereas the second one is appropriate for non-line-of-sight conditions. The classification model is intended to provide a probabilistic output, through which the outputs of the regression models are combined. The number of used input parameters is only five. They are related to the distance, the antenna heights, and the statistics of the terrain profile and line-of-sight obstacles. The proposed approach allows creation of a generalized model that is valid for various types of areas and terrains, different antenna heights, and line-of-sight and non line-of-sight propagation conditions. An experimental dataset is provided by measurements for a variety of relief types (flat, hilly, mountain, and foothill) and for rural, urban, and suburban areas. The experimental results show an excellent performances in terms of a root mean square error of a prediction as low as 7.3 dB and a coefficient of determination as high as 0.702. Although the study covers only one operating frequency of 433 MHz, the proposed model can be trained and applied for any frequency in the decimeter wavelength range. The main reason for the choice of such an operating frequency is because it falls within the range in which many wireless systems of different types are operating. These include Internet of Things (IoT), machine-to-machine (M2M) mesh radio networks, power efficient communication over long distances such as Low-Power Wide-Area Network (LPWAN)-LoRa, etc.

Power efficient UAV-assisted FSO communication: novel 4-PAM optical pulse generation and performance analysis in foggy environment

Power efficient UAV-assisted FSO communication: novel 4-PAM optical pulse generation and performance analysis in foggy environment

Cooperative Hybrid Networks with Active Relays and RISs for B5G: Applications, Challenges, and Research Directions

Among the recent advances and innovations in wireless technologies, reconfigurable intelligent surfaces (RISs) have received much attention and are envisioned to be one of the enabling technologies for beyond 5G (B5G) networks. On the other hand, active (or classical) cooperative relays have played a key role in providing reliable and power-efficient communications in previous wireless generations. In this article, we focus on hybrid network architectures that amalgamate both active relays and RISs. The operation concept and protocols of each technology are first discussed. Subsequently, we present multiple use cases of cooperative hybrid networks where both active relays and RISs can coexist harmoniously for enhanced rate performance. Furthermore, a case study is provided which demonstrates the achievable rate performance of a communication network assisted by either an active relay, an RIS, or both, and with different relaying protocols. Finally, we provide the reader with the challenges and key research directions in this area.

Joint Design of Long-Term Base Station Activation and Short-Term Beamforming for Green Wireless Networks

Base station (BS) activation is a widely-used approach to alleviate the system power cost for device maintenance. However, frequently switching on/off BSs may also introduce extra power and signaling costs, which motivates us to limit the BS switching frequency when performing BS activation. To address this, we study a problem of joint long-term BS activation and short-term beamforming (J-LTBA-STBF) in a network where multiple multi-antenna BSs cooperatively serve multiple single-antenna users. LTBA means that each BS’s active/inactive switching frequency is properly controlled to yield relatively stable BS-user association and limited switching power, while STBF lies in that due to the low cost of refreshing beamformers, the transmit beamformers are allowed to be updated frequently to maximally lower the transmit power. Following the idea, two efficient algorithms are designed, according to the data amount they request to start running, to optimize the active BSs and the BS transmit beamformers in multiple adjacent time slices. Consequently, the transmit, maintenance and switching powers can be well balanced to facilitate power-efficient communications. Numerical results validate the efficacies of the algorithms.

Performance Analysis of MIMO Heterogeneous Wireless Sensor Networks

Wireless Sensor Networks (WSN) are widely used in remote applications related to defence and healthcare. A network with nodes having different capabilities like sensing, various computational capabilities, power-efficient communication, and a varied sensing range is called a heterogeneous wireless sensor network. Heterogeneous wireless sensor networks using MIMO wireless channels are more useful for energy-efficient multi-channel communication. MIMO applications in wireless sensor networks have the potential to enhance throughput, reduce End-to-End Delay, improve packet delivery ratios, and conserve energy in wireless sensor networks. Its implementation needs to be carefully considered in light of the specific deployment conditions and resource constraints of the network, considering proper antenna design, synchronisation mechanisms, and energy-efficient algorithms. This paper presents a comparative performance analysis of MIMO wireless sensor networks and traditional wireless sensor networks without MIMO for various Quality of Service parameters like Packet Delivery Ratio, End to End Delay, Throughput and Residual energy. The research work shows that the application of MIMO in Wireless Sensor Networks enables sensor nodes to collaborate effectively, leading to improved reliability and coverage, and also increases the network's lifetime by conserving energy in resource-constrained sensor nodes through the preservation of Residual Energy.

Time-Frequency Domain Non-Orthogonal Multiple Access for Power Efficient Communications

We propose a power efficient non-orthogonal multiple access (NOMA) scheme suitable for Internet of Things (IoT) and device-to-device (D2D) communications. OFDM-based power-domain NOMA (PD-NOMA) is one of the promising approaches to achieve simultaneous connections of massive devices. Nevertheless, the problem of high peak-to-average power ratio (PAPR) is a major challenge, since power amplifier (PA) efficiency is a critical factor for IoT and D2D devices consisting of low-cost hardware components. This paper overcomes this problem by introducing time-frequency domain NOMA (TF-NOMA), where OFDM and DFT-spread OFDM (DFT-s-OFDM) are superposed over the time-frequency domain. By utilizing the low PAPR property achieved by DFT-precoding, TF-NOMA can efficiently reduce the PAPR of the downlink signal transmitted by the base station (BS) as well as the uplink signals of the devices located far from BS. As a result, the proposed TF-NOMA can operate with higher PA efficiency than the conventional OFDM-based PD-NOMA. Furthermore, the insertion of DFT-precoding with the aim of PAPR reduction also enhances the error propagation resistance due to the resulting Gaussian mixture signal property. Throughout the mathematical analysis and computer simulations, we demonstrate that TF-NOMA achieves better error rate performance than the conventional PD-NOMA with significant improvement of PA efficiency.

LoRaline: A Critical Message Passing Line of Communication for Anomaly Mapping in IoV Systems

The importance of road safety is felt nowadays more than ever, where various technologies, including self-driving cars, have become abundant. Nowadays, it has more demand to build autonomous and electrical vehicles with information retrieval systems within the received sensory data not only from the local sensors but also the online and live streaming data over networks. To increase road safety dissemination of critical information, including the possibility of an obstacle or danger being in the middle of the road, automotive navigation and control systems are required. A novel method is proposed to make this critical communication possible over a specially designed vehicular ad-hoc network, where natural or urban barriers can prevent signal propagation. The network is implemented using the LoRaWAN interface and SX127x LoRa Radio module. The SX1272MB2xAS is fitted with the SX1272 transceiver, which, added to a high-performance FSK /OOK RF transceiver modem, features the LoRa™ long-range modem providing highly power-efficient communication. For this aim, two new mechanisms have been proposed. The first mechanism enables the nodes to receive data from a suggested communication link. In contrast, the second mechanism is designed to extract vital information such as establishing the connection, closing the connection, successful data transmission, errors, etc. The findings demonstrate that the proposed mechanisms have successfully enabled LoRaWAN to operate in IoV environment. The evaluation reveals that metrics such as battery consumption and covering range outperform similar technologies. Finally, this paper proposes a message-passing strategy based on Belief Propagation (BP) which provides more accurate marginal probabilities to overcome the low data rate as a foundation for our future work.

Performance evaluation of MIMO DFT-Spread WR-OFDM system for spectrum efficiency and power efficiency

ABSTRACT It is important to design a spectrum-efficient and power-efficient wireless communication system, which is the main design target in cellular and wireless communication engineering. Basically, to make it, the desired system must have a low peak-to-average power ratio (PAPR), low-level of out-of-band (OOB) power emission and can provide a high throughput. In this paper, we propose a high-throughput cellular communication system, namely Discrete Fourier Transform-Spread Windowing and Restructuring Orthogonal Frequency Division Multiplexing (DFT-Spread WR-OFDM), which has considerably low PAPR and low OOB power emission for upcoming next-generation beyond 5G (B5G) and 6G cellular communication systems. High PAPR is still one of the challenging issues for the MIMO-OFDM system. The proposed system is an effective arrangement of DFT-Spreading and windowing techniques to reduce PAPR and OOB power emission, respectively. Multiuser diversity is obtained using localized subcarrier mapping. We take advantages of spatial multiplexing to enhance the data throughput significantly. Additionally, frequency-domain equalization (FDE)-minimum mean squared error (MMSE) is used to combat the inter-symbol interference (ISI) effect. Simulation results verify that the suggested system considerably lowers PAPR and OOB power emission compared to the conventional systems. Furthermore, the proposed scheme shows better bit error rate (BER) performance over the MIMO Rayleigh fading channel environment. Simulation results also confirmed that the channel capacity of our suggested system is better than the conventional multi-carrier systems.

RCS-OFDM enabling full brightness control with power-efficient visible-light communication.

In this Letter, we report a novel optical orthogonal frequency division multiplexing (O-OFDM) scheme that provides power-efficient communication and effective brightness control. The proposed scheme exploits the anti-symmetry property of asymmetrically clipped O-OFDM (ACO-OFDM) and signal reversal, doubling the linear dynamic range and enabling full brightness control. It also generates less nonlinear distortion compared with the conventional ACO-OFDM and does not need additional pulse modulations required in previous work. Following detailed descriptions of the proposed scheme with simulation results, a proof-of-concept demonstration showing the full brightness control maintaining the benefits of the power-efficient ACO-OFDM communication scheme is presented. To the best of the authors' knowledge, this is the first experimental demonstration showing the feasibility of O-OFDM-based dimming control.

Power Efficient Communications Employing Phase Sensitive Pre-Amplified Receiver

The receiver sensitivity is a very important metric in optical communication links operating at low received signal powers. Phase sensitive optical amplifiers (PSAs) can amplify optical signals without excess noise, thus providing a fundamental sensitivity improvement of 3 dB when employed as a pre-amplifier compared to conventional erbium doped fiber amplifiers (EDFA). In this letter, we investigate, both theoretically and experimentally, the sensitivities achieved using power efficient multi-dimensional modulation formats such as M-ary pulse position modulation format (M-PPM) and M-PPM combined with quadrature phase shift keying (QPSK) along with a near-noiseless PSA pre-amplified coherent intradyne receiver. We find that at high signal to noise ratios (SNRs) corresponding to low bit-error-rates (BER), M-PPM+QPSK results in the best sensitivity, which is improved with the order M, while at low SNRs corresponding to high BER (~14% where 100% overhead forward error correction codes (FEC) would be needed to recover the data), QPSK is the most sensitive format, while at the same time providing the best spectral efficiency. We report experimental sensitivities of 2.1 photons per information bit (PPB) at a pre-FEC BER = 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> using 64-PPM+QPSK and assuming 7% FEC, and 0.8 PPB at a pre-FEC BER = 0.14 using QPSK and assuming 100% FEC.

Design and Study of an mmWave Wearable Textile Based Compact Antenna for Healthcare Applications

In this study, the design of a compact and novel millimeter wave cotton textile-based wearable antenna for body-centric communications in healthcare applications is presented. The free space and on-body antenna performance parameters for the proposed antenna at 60 GHz are investigated and analyzed. The antenna is based on a 1.5 mm thick cotton substrate and has an overall dimension of 7.0 × 4.5 × 1.5 mm3. In free space, the antenna is resonant at 60 GHz and achieves a wide impedance bandwidth. The maximum gain at this resonant frequency is 6.74 dBi, and the radiation efficiency is 93.30%. Parametric changes were carried out to study the changes in the resonant frequency, gain, and radiation efficiency. For body-centric communications, the antenna was simulated at 5 different distances from a three-layer human torso-equivalent phantom. The radiation efficiency dropped by 24% and gradually increased with the gap distance. The antenna design was also analyzed by using 10 different textile substrates for both free space and on-body scenarios. The major benefits of the antenna are discussed as follows. Compared to a previous work, the antenna is very efficient, compact, and has a wide bandwidth. In BCWCs for e-health applications, the antenna needs to be very compact due to the longer battery life, and it has to have a wide bandwidth for high data rate communication. Since the antenna will be wearable with a sensor system, the shape of the antenna needs to be planar, and it is better to design the antenna on a textile substrate for integration into clothes. The antenna also needs to show high gain and efficiency for power-efficient communication. This proposed antenna meets all these criteria, and hence, it will be a good candidate for BCWCs in e-health applications.

Optimal Design of LEMoNet for Environmental Monitoring of Data Centers

Half of the electrical power in today’s data centers (DCs) is consumed by cooling units, but much is wasted due to over-cooled or under-utilized servers. Environmental monitoring using Data Center Wireless Sensor Networks (DCWSNs) plays a central role in detecting and mitigating hotspots or over-cooling conditions. These networks often include thousands of sensors and require a reliable and power-efficient communication protocol. The Low Energy Monitoring Network (LEMoNet) is a two-tier DCWSN protocol that features Bluetooth Low Energy (BLE) for sensor communication in the first tier and leverages multi-gateway packet receptions in its second tier. This research studies the performance of LEMoNet in different DC topologies through the development of an analytical model. The model solves a multi-objective optimization problem to calculate two design parameters. The first parameter is the optimal number of gateways and an optimal location for each one. The second parameter is an optimal transition (TX) power for each sensor, subject to the application requirements. Evaluation results show that the optimal design includes one gateway on every other row. Also, the model reduces 65% of the sensors’ power consumption via TX power optimization while Packet Reception Rate (PRR) is kept up at the level of 95%.

Compact and Wideband PIFA Design for Wireless Body Area Sensor Networks

The specific advantage of fractal geometry to realize compact antenna features is exploited in this work for the design of a miniaturized Planar Inverted-F Antenna configuration with a large bandwidth. The conventional quadrilateral radiating element of a Planar Inverted-F Antenna is replaced by a Minkowski pre-fractal-based shape, thus increasing the resonant wavelength without affecting the overall antenna dimensions. Consequently, with the new design, a physically smaller antenna can achieve the same resonant frequency of a larger conventional configuration. Measured as well as simulated reflection coefficient and radiation patterns are presented to validate the assumptions. The impedance bandwidth of the antenna (2.19 to 2.52 GHz) covers the ISM band with a boresight gain of 1.5–2 dB over the entire band. Furthermore, to demonstrate the miniaturization effect, a successful comparison is provided with an identically sized, conventional square Planar Inverted-F Antenna design. The proposed antenna design can be usefully adopted for power-efficient communications in the framework of Wireless Body Area Sensor Networks.

Low Complexity Modified Viterbi Decoder with Convolution Codes for Power Efficient Wireless Communication

Low Complexity Modified Viterbi Decoder with Convolution Codes for Power Efficient Wireless Communication

A Robust and Efficient Fault-Resilient RadHard ADPLL

The high pace emergence in semiconductor technologies and associated application demands have revitalized industries to explore power efficient, stable and fault tolerant digital communication solutions, particularly for time critical applications operating at higher frequency ranges. Thus strengthening low cost CMOS digital design with Radiation Hardened by Design (RHBD) approach can be of paramount significance compared against the high cost Radiation Hard by Process (RHBP) approach. With this motivation, in this paper a novel and robust All-Digital-Phase Locked Loop (ADPLL) design has been developed for frequency synthesis. Our ADPLL design model encompasses multiple novelties and contributions including Feedback-Divider-Less-Counter (FDLC) based ADPLL, predictive phase-frequency detection (PFD), enhanced Time to Digital Converter (TDC) to detect next-edge occurrence of the reference clock that reduces locking period and complexity. The predictive PFD applies a phase-prediction scheme that delays the clock-edges of the reference frequency with a calibrated amount that it always aligned towards the expected frequency clock edge. It makes TDC to be narrow enough to cover the reference and oscillator jitter. Our proposed ADPLL design applied a narrow range converter (TDC) that assist phase-error prediction, correction and phase detection. The reference clock delay facilitates accurate timing relationship estimation with the variable frequency and hence performs retuning of the variable clock to reduce locking period and reduce noise. The ADPLL design has exhibited satisfactory performance for the frequency synthesis with reference frequency of 20MHz and the synthesis frequency of 2.4 GHz meeting radiation hardened features. The simulation results has revealed that the proposed Rad Hard ADPLL design can be a potential solution for space communication systems by maintaining low jitter of 340ps and power consumption of 371.7mW, as the narrow range TDC designed can detect sample radiation induced impulse noise of 20ns, 1mV and correct it.

Wearable IMU-Based System for Real-Time Monitoring of Lower-Limb Joints

Recent advances in micro-electromechanical systems technology have enabled the evolution of miniature, low-power, and high-performance inertial motion sensors that are commonly found in most present-day smart gadgets. Furthermore, high-speed and power-efficient communication and computing technologies may enable these sensors to potentially pave the way for home-based remote monitoring and assessment of human health in the imminent age of new technologies such as Smart Home, internet-of-things, and internet-of-everything. Continuous monitoring of lower-limb joints in a wearable platform is such an application that may potentially enable the tele-rehabilitation of patients with motor impairment, gait abnormalities, and joint injuries through quantitative rather than observational analysis of gait health. In this work, we designed, implemented, and validated a two-stage sensor fusion algorithm to estimate lower-limb joint angles in real-time. The drift in the cumulatively integrated gyroscope data was estimated in real-time using a gradient descent approach that was subsequently used to correct the inclination of the sensors. The roll and pitch angles thus obtained for each sensor mounted above and below the joint were then fused in the second stage to obtain a real-time estimate of joint angle by exploiting a gradient descent method. Since the joint angles were estimated primarily from the gyroscope data and without incorporating any magnetic field measurement, the joint angles thus obtained were least affected by the external acceleration and are insensitive to magnetic disturbances. The performance of the proposed algorithm was validated with a publicly available dataset and in the presence of simulated external acceleration.

Optimization in Secure Routing and Power Efficient Communication in Wireless Adhoc Network

Security and data propagation are the two major concerns in wireless adHoc network. The optimal routing with power conservation and traffic monitoring defines the operational efficiency of the adHoc network. Wherein energy conservation and routing security are used as a measuring parameter in controlling the traffic flow, no two parameters are defined in together to optimize the route selectivity in the network. The monitoring of routing parameter in providing secure route is governed by the characteristic optimization of forwarding link and the approach of link selection. In this paper, an approach for optimal link selection for secure routing using multi attribute monitoring and controlling of traffic flow is presented. The proposed work defines a fairness factor based on multiple monitoring attribute to control the operational efficiency of the network. The multi attribute monitoring offers a more reliable and secure path in adHoc network in traffic flow modeling. The validations of the proposed approach were developed following the energy conservation and security provisioning in adHoc network.

A generalized multilevel-hybrid chaotic oscillator for low-cost and power-efficient short-range chaotic communication systems

In this paper, we present and evaluate a novel multilevel hybrid-chaotic oscillator. The proposed generalized multilevel-hybrid chaotic oscillator (GM-HCO) was created by combining a multilevel discrete function generated from user data with a continuous function having a damping factor greater than ln(2) to achieve variable rates and adaptive carrier frequencies. Improved spectral efficiency and lower complexity of the transceiver compared with differentially coherent systems were achieved by multilevel signals at the transmitter and a matched filter at the receiver. An exact analytical solution for the generalized fixed basis function and the impulse response of the matched filter were also derived. The bit error rate (BER) expression of the GM-HCO was derived for two levels. It was found that the noise performance of the proposed system was better than a hybrid chaotic system based on forward time and differential chaos shift keying (DCSK). A comprehensive set of simulations were carried out to evaluate the performance of the proposed system with chaotic communication systems in the presence of additive white Gaussian noise (AWGN). The performance of the proposed system was comparable with that of conventional communication systems. The results demonstrate that the proposed system can offer better noise performance than existing chaotic communication systems, and it also offers variable transmitter frequencies and improved spectral efficiency. Noise-like behavior of the chaotic signals provides an additional layer of security at the physical layer compared with conventional (sinusoidal) communication systems.

Performance of hybrid cellular-VLC link for indoor environments under dynamic user movement

Visible light communications (VLC) is an emerging technology that complements the existing cellular network in order to provide high throughput, secure and power efficient indoor communication system. In this paper, we analyze the performance of hybrid cellular-VLC downlink where the outdoor coverage is provided via cellular network, and the indoor coverage is provided through a VLC system. In the proposed framework, VLC access point (AP) helps to communicate the information between the base station (BTS) and user by acting as a decode-and-forward (DF) relay. The relay decodes the received signal from the base station and then uses the decoded signal to modulate the intensity of the optical transmitter. Multiple light emitting diode (LED) transmitters with rectangular deployment are considered for a VLC transmitter. The channel model for VLC link has been modeled as an integrating sphere VLC channel which includes both line-of-sight (LOS) and non-line-of-sight (NLOS) links. Further, the movement and density of people have also been considered while deriving the closed-form expressions for the outage probability and bit-error-rate (BER) for the hybrid cellular-VLC downlink. In addition, the proposed work also utilizes optimal Lambertian order (OLO) to achieve increased average received optical power through LOS path and uniform delay spread in an indoor environment. It has been shown that by using the proposed hybrid cellular-VLC downlink, it is possible to achieve significant amount of power saving (approximately 51%) at BTS as compared to direct cellular link. Finally, the dimming range is calculated for the proposed system under dimming constraint. Results show that dimming range up to 70% can be achieved in the hybrid cellular-VLC link.