Energy Efficiency Of Transmissions Research Articles

Energy Efficiency Optimization in Adaptive Transmit Antenna Selection Systems With Limited Feedback

We investigate the energy efficiency (EE) of cellular downlink transmissions with limited feedback, where the channel state information (CSI) assumed to be available at the destination is quantized and fed back to the multiantenna base station for transmitting precoding purposes. Typically, the employment of antennas with poor channel quality marginally enhances system performance but substantially consumes energy resources such as circuit power. Thus, we propose an adaptive transmit antenna selection (ATAS) scheme via setting a channel gain threshold to select transmit antennas with relatively good channel condition for reducing power resource consumption. Meanwhile, the conventional single transmit antenna (STAS) scheme is considered as a baseline. In order to improve EE while considering the impact of feedback overhead, we conduct the effective EE analysis for both ATAS and STAS schemes and show that a maximal effective EE of the proposed ATAS scheme can be achieved by jointly adjusting the channel gain threshold and transmit power. As a consequence, we propose the ergodic effective EE optimization of ATAS (eEEEO-ATAS) scheme to maximize the effective EE. Numerical simulation results demonstrate that the proposed ATAS scheme performs better than the STAS scheme in terms of effective EE.

Energy-Efficient Design for Massive MIMO With Hardware Impairments

In this paper, an energy-efficient design for massive multiple-input multiple-output (MIMO) systems is studied with the consideration of hardware impairments. The objective is to maximize the system energy efficiency of both uplink and downlink transmissions by jointly optimizing the number of antennas at the base station, the number of served users, and the transmit power. Firstly, by considering the linear distortion due to hardware impairments, the resultant channel estimation error from both distortion and noise is analyzed, following which closed-form approximations for the average achievable uplink/downlink rates are derived. Then, a massive MIMO energy efficiency optimization problem considering hardware impairments is formulated. By applying the techniques of relaxation and change of variables, an alternative optimization with build-in bisection search (AO-BS) algorithm is proposed with the quasi-concavity of the transformed objective function theoretically proved. The performance of the proposed AO-BS algorithm is validated through numerical simulations, which shows fast convergence to near-optimal solutions. Compared with existing approaches, the proposed scheme improves the system energy efficiency greatly when the hardware impairments are considered. Furthermore, the system design guideline in terms of the number of antennas, the number of served users, and the transmit power is provided.

Method for determining the parameters of the front loader electromechanical transmission

A method for calculating the traction motor of a hybrid transmission of a front-end loader is proposed. It is indicated that these vehicles are characterized by a mode of operation with multiple accelerations and decelerations, as well as alternating operations with high and low required traction force. An electromechanical transmission scheme is proposed. This scheme can be effectively used in such conditions.
 The proposed method uses the concept of the magnitude of the range of an electric motor, which can be used to select a specific electric motor that provides the required mobility of the vehicle. For a front loader with a lifting capacity of 3500 kg, a maximum speed of 40 km / h and a maximum specific thrust of 1, the main parameters of the traction motor were determined. However, for the transmission with one fixed gear ratio (EMT1), an electric motor with an excessively high power was obtained. Therefore, the determination of the characteristics of the electric motor for an electromechanical transmission with two fixed gear ratios (EMT2) was carried out. In the process of calculating this transmission, a significantly lower required engine power was obtained.
 The article provides an approximate assessment of the energy efficiency of EMT1 and EMT2 transmissions. A method to determine the efficiency of an electric motor depending on its operating mode (on the current angular speed of the shaft and torque) was used. It was determined that the EMT2 transmission has the best efficiency of the electric motor both during bulldozing operation and when driving at maximum speed.
 The general conclusion is that it is most rational to use a transmission with two fixed gear ratios. As a further direction of research, the use of computer simulation for evaluating the energy efficiency of a loader in a loading-unloading cycle is highlighted.

Improving the energy efficiency of power transmissions of a rolling stock on the basis of dynamic anisotropy of frictional contact

The analysis showed the following tendencies of development and energy efficiency of designs of gearboxes for track machines: provision of a maximum level of efficiency, removal of rupture of a stream of the passed capacity, provision of a high level of reliability, decrease of power input on gearbox work, provision of convenience, simplicity of service and steering, engine braking maintenance, and also maintenance of a relatively low cost. The above-mentioned tasks are performed by including clutch pinion gears with the built in frictional amplifier elements in an automatic gearbox, and also during the effect of dynamic anisotropy of frictional bonds. Besides a torque transfer, the clutch gear carries out a safety clutch function. That means that there is sliding at a high rotational power. Factor of strengthening of the given link is Кstr → ∞ due to occurence of dynamic anisotropy of frictional bonds. Physical and mechanical characteristics of contacting surfaces are formed in the course of dynamic interaction of roughnesses in friction units at modes of dry and boundary friction. Essential-nonlinear friction processes, interconnected with dynamic processes on the contact area, define values of target characteristics of frictional system. They can fluctuate in a very wide range. The friction factor fmp for the same friction units at preservation of constant conditions and friction parameters can vary from zero to infinity that is an essence of dynamic anisotropy of frictional bonds.

Non-Orthogonal Multiple Access Assisted Multi-Region Geocast

This paper proposes a novel location-based multi-group multicast framework, which is termed non-orthogonal multiple access (NOMA)-assisted multi-region geocast . This novel spectrum sharing framework exploits the NOMA technology to realize the simultaneous delivery of different messages to different user groups characterized by different geographical locations. The essence of the proposed framework is that the geographical information of user groups unites NOMA and multi-group multicast to enhance the spectral efficiency (SE) and the energy efficiency (EE) of wireless transmissions. Specifically, we investigate the downlink beamforming design of the proposed framework in multiple-input single-output settings. The decoding strategy for NOMA is designed and guaranteed by users’ geographical information and required quality of service. The majorization and minimization algorithm is exploited to solve the non-convex and intractable problems therein. Comprehensive numerical experiments are further provided to show that NOMA holds tremendous promise but also limitations in terms of SE and EE, compared with spatial division multiple access and orthogonal multiple access.

On the Energy Efficiency of Dual Clutch Transmissions and Automated Manual Transmissions

The main benefits of dual clutch transmissions (DCTs) are: (i) a higher energy efficiency than automatic transmission systems with torque converters; and (ii) the capability to fill the torque gap during gear shifts to allow seamless longitudinal acceleration profiles. Therefore, DCTs are viable alternatives to automated manual transmissions (AMTs). For vehicles equipped with engines that can generate considerable torque, large clutch-slip energy losses occur during power-on gear shifts and, as a result, DCTs need wet clutches for effective heat dissipation. This requirement substantially reduces DCT efficiency because of the churning and ancillary power dissipations associated with the wet clutch pack. To the knowledge of the authors, this study is the first to analyse the detailed power loss contributions of a DCT with wet clutches, and their relative significance along a set of driving cycles. Based on these results, a novel hybridised AMT (HAMT) with a single dry clutch and an electric motor is proposed for the same vehicle. The HAMT architecture combines the high mechanical efficiency typical of AMTs with a single dry clutch, with the torque-fill capability and operational flexibility allowed by the electric motor. The measured efficiency maps of a case study DCT and HAMT are compared. This is then complemented by the analysis of the respective fuel consumption along the driving cycles, which is simulated with an experimentally validated vehicle model. In its internal combustion engine mode, the HAMT reduces fuel consumption by >9% with respect to the DCT.

Secure Transmission of Delay-Sensitive Data Over Wireless Fading Channels

In this paper, throughput and energy efficiency of secure wireless transmission of delay sensitive data generated by random sources is studied. A fading broadcast model in which the transmitter sends confidential and common messages to two receivers is considered. It is assumed that the common and confidential data, generated from Markovian sources, are stored in buffers prior to transmission, and the transmitter operates under constraints on buffer/delay violation probability. Under such statistical quality-of-service constraints, effective capacity of time-varying wireless transmissions and effective bandwidth of Markovian sources are employed to determine the throughput. In particular, secrecy capacity is used to describe the service rate of buffers containing confidential messages. Moreover, energy per bit is used as the energy efficiency metric and energy efficiency is studied in the low signal-to-noise regime. Specifically, minimum energy per bit required for the reliable communication of common and confidential messages is determined and wideband slope expressions are identified. The impact of buffer/delay constraints, correlation between channels, source characteristics/burstiness, channel knowledge at the transmitter, power allocation, and secrecy requirements on the throughput and energy efficiency of common and confidential message transmissions is identified.

Three-Stage Resource Allocation Algorithm for Energy-Efficient Heterogeneous Networks

In this paper, we investigate the energy efficiency of downlink transmissions in heterogeneous networks. Our objective is to satisfy the rate requirement of users while maximizing the energy efficiency of the network. We employ the fractional frequency reuse (FFR) scheme to increase the energy efficiency of downlink transmissions and to eliminate outages for the cell-edge users. We formulate the joint cell-center boundary selection for FFR, scheduling, and power allocation problems. This formulation gives us a mixed discrete (selection of the cell-center boundary selection for FFR and scheduling) and continuous (power allocation) optimization problem which is hard to solve jointly. In order to solve this problem, we propose a three-stage resource allocation algorithm. In the first stage, we propose a dynamic method to determine the cell-center region boundaries. In the second stage, we employ the Lagrangian-directed scheduler algorithm to incorporate the rate requirements of users. The third stage solves the power allocation subproblem using the Levenberg–Marquardt method combined with dual decomposition. In order to make the base stations further reduce intercell interference, interference pricing mechanism is applied. This scheme penalizes the utility of a base station with the interference it creates. The performance of the proposed algorithm is simulated in a long-term evolution (LTE) network simulation tool. Our numerical results reveal that significant gains in terms of energy efficiency can be achieved with the proposed algorithm. The outage probability is also significantly reduced.

Energy-Efficient Frequency and Power Allocation for Cognitive Radios in Television Systems

Energy-efficient resource allocation for cognitive radios operating in television systems (TV white spaces) presents a unique challenge compared with other cognitive radios because the interference constraint is for the whole frequency band rather than per carrier. This paper presents a subchannel and power allocation protocol that maximizes the energy efficiency (EE) of transmissions from a cognitive base station operating in the TV white spaces. The system model conforms to the IEEE 802.22 standard, and the proposed two-step solution to the EE maximization problem satisfies users' minimum rate requirements and keeps the interference to the primary users in the neighboring areas below a specified threshold. The first step of the protocol is a near-optimal but low-complexity subchannel assignment. This is followed by an optimal power allocation procedure that is obtained by analyzing the Karush–Kuhn–Tucker conditions. The computational complexity of the resulting resource allocation protocol is the same as that of the least complex resource allocation protocol for orthogonal frequency division multiple access (OFDMA) downlinks in the literature. Simulation results show that our protocol achieves higher EE compared with a modified and improved version of the OFDMA protocol from the literature.

Influence of the idling torque on the energy efficiency of mechanical transmissions

A modernized method for energy calculation of mechanical transmissions is outlined. In contrast to the approach proposed in classic texts, this method takes account of idling of the transmission. A correct model is proposed for determining the energy-efficient load of a mechanical transmission.

THE OPPORTUNITIES FOR GETTING ENERGY SAVINGS IN THE HYDROSTATIC DRIVE SYSTEM

Full picture of the energy losses in a hydrostatic drive system is a picture of the power of energy losses in the system elements. Paper presents the areas of the power fields of energy losses occurring in the elements of some hydraulic systems with different structures of the hydraulic motor speed control. Proposed graphical interpretation allows analysing and comparing different hydrostatic drive systems. In many constructed and manufactured machines currently used hydrostatic drive systems or electro hydrostatic systems of varying complexity. Today, the need for energy-efficient systems forces to some extent the development and improvement of computational methods using computer aided relating to energy efficiency systems. Hydrostatic systems especially in modern machines play a very important role. Actuators, such as hydraulic motors, hydraulic cylinders is commonly used for a long time, including on machines and equipment land and marine. Unawareness of proportions of the energy, volumetric, pressure and mechanical losses in elements is often the case. Problems connected with energy efficiency are essential for improvement of functionality and quality of hydrostatic drive systems, characterised by unquestioned advantages. Energy efficiency of hydrostatic transmissions, particularly those with throttling control of the motor speed, and also efficiency of the hydraulic servomechanism systems may be in fact higher than the values most often quoted in publications on the subject.

Energy Efficiency of Fixed-Rate Transmissions with Markov Arrivals under Queueing Constraints

Energy efficiency of wireless transmissions is analyzed in the presence of Markov sources and queueing constraints. Not knowing the channel conditions, the transmitter is assumed to send the data at a fixed rate over a Rayleigh fading channel. This fixed-rate transmission is modeled as a two-state (ON/OFF) continuous-time Markov chain. Using the effective bandwidth of Markov sources and the effective capacity of the Markov fluid transmission model, a characterization of the maximum average arrival rate that can be supported in the Rayleigh fading channel under buffer constraints is given, and energy efficiency is analyzed by determining the minimum energy per bit and wideband slope expressions. The impact of queueing constraints, source and channel parameters, and fixed-rate transmissions on the energy efficiency is identified.

On the Throughput and Energy Efficiency of Cognitive MIMO Transmissions

In this paper, throughput and energy efficiency of cognitive multiple-input-multiple-output (MIMO) systems operating under quality-of-service (QoS) constraints, interference limitations, and imperfect channel sensing are studied. It is assumed that transmission power and covariance of the input signal vectors are varied, depending on the sensed activities of primary users (PUs) in the system. Interference constraints are applied on the transmission power levels of cognitive radios (CRs) to provide protection for the PUs, whose activities are modeled as a Markov chain. Considering the reliability of the transmissions and channel sensing results, a state transition model is provided. Throughput is determined by formulating the effective capacity. The first derivative of the effective capacity is derived in the low-power regime, and the minimum bit energy requirements in the presence of QoS limitations and imperfect sensing results are identified. Minimum energy per bit is shown to be achieved by beamforming in the maximal-eigenvalue eigenspace of certain matrices related to the channel matrix. In a special case, wideband slope is determined for a more refined analysis of energy efficiency. Numerical results are provided for the throughput for various levels of buffer constraints and different number of transmit and receive antennas. The impact of interference constraints and benefits of multiple-antenna transmissions are determined. It is shown that increasing the number of antennas when the interference power constraint is stringent is generally beneficial. On the other hand, it is shown that, under relatively loose interference constraints, increasing the number of antennas beyond a certain level does not lead to much increase in throughput.

Energy efficiency of a hydrostatic drive with proportional control compared with volumetric control

Abstract There are uninvestigated areas connected with behaviour of elements in hydraulic systems with different structures. Unawareness of proportions of the energy, volumetric, pressure and mechanical losses in elements is often the case. Problems connected with energy efficiency are essential for improvement of functionality and quality of hydrostatic drive systems, characterised by unquestioned advantages but also by relatively low efficiency in comparison with other types of drive. Energy efficiency of hydrostatic transmissions, particularly those with throttling control of the motor speed, and also efficiency of the hydraulic servo-mechanism systems may be in fact higher than the values most often quoted in publications on the subject. Possibility of calculating the real value of the hydraulic system overall efficiency as a function of many parameters influencing it, becomes a tool of complete evaluation of the designed system quality. The paper compares efficiencies of systems with cylinder proportional control and efficiency of the system volumetric control by a variable capacity pump. Presented are also two schematic diagrams of the investigated hydrostatic systems, their principle of operation and problems of studying losses in elements and energy efficiency of systems consisting of a feed assembly, control set and cylinder.

Inertial method for estimating the effect of lubricants’ quality on energy efficiency of chain transmissions

Inertial method for estimating the effect of lubricants’ quality on energy efficiency of chain transmissions

Energy Efficiency in the Low-SNR Regime under Queueing Constraints and Channel Uncertainty

Energy efficiency of fixed-rate transmissions is studied in the presence of queueing constraints and channel uncertainty. It is assumed that neither the transmitter nor the receiver has channel side information prior to transmission. The channel coefficients are estimated at the receiver via minimum mean-square-error (MMSE) estimation with the aid of training symbols. It is further assumed that the system operates under statistical queueing constraints in the form of limitations on buffer violation probabilities. The optimal fraction of power allocated to training is identified. Spectral efficiency-bit energy tradeoff is analyzed in the low-power and wideband regimes by employing the effective capacity formulation. In particular, it is shown that the bit energy increases without bound in the low-power regime as the average power vanishes. A similar conclusion is reached in the wideband regime if the number of noninteracting subchannels grow without bound with increasing bandwidth. On the other hand, it is proven that if the number of resolvable independent paths and hence the number of noninteracting subchannels remain bounded as the available bandwidth increases, the bit energy diminishes to its minimum value in the wideband regime. For this case, expressions for the minimum bit energy and wideband slope are derived. Overall, energy costs of channel uncertainty and queueing constraints are identified, and the impact of multipath richness and sparsity is determined.

The impact of QoS constraints on the energy efficiency of fixed-rate wireless transmissions

Transmission over wireless fading channels under quality of service (QoS) constraints is studied when only the receiver has channel side information. Being unaware of the channel conditions, transmitter is assumed to send the information at a fixed rate. Under these assumptions, a two-state (ON-OFF) transmission model is adopted, where information is transmitted reliably at a fixed rate in the ON state while no reliable transmission occurs in the OFF state. QoS limitations are imposed as constraints on buffer violation probabilities, and effective capacity formulation is used to identify the maximum throughput that a wireless channel can sustain while satisfying statistical QoS constraints. Energy efficiency is investigated by obtaining the bit energy required at zero spectral efficiency and the wideband slope in both wideband and low-power regimes assuming that the receiver has perfect channel side information (CSI). Initially, the wideband regime with multipath sparsity is investigated, and the minimum bit energy and wideband slope expressions are found. It is shown that the minimum bit energy requirements increase as the QoS constraints become more stringent. Subsequently, the low-power regime, which is also equivalent to the wideband regime with rich multipath fading, is analyzed. In this case, bit energy requirements are quantified through the expressions of bit energy required at zero spectral efficiency and wideband slope. It is shown for a certain class of fading distributions that the bit energy required at zero spectral efficiency is indeed the minimum bit energy for reliable communications. Moreover, it is proven that this minimum bit energy is attained in all cases regardless of the strictness of the QoS limitations. The impact upon the energy efficiency of multipath sparsity and richness is quantified, and comparisons with variable-rate/fixed-power and variable-rate/variable-power cases are provided.

On the Capacity and Energy Efficiency of Training-Based Transmissions Over Fading Channels

In this paper, the capacity and energy efficiency of training-based communication schemes employed for transmission over a priori unknown Rayleigh block-fading channels are studied. Initially, the case in which the product of the estimate error and transmitted signal is assumed to be Gaussian noise is considered. In this case, it is shown that bit energy requirements grow without bound as the signal-to-noise ratio (SNR) goes to zero, and the minimum bit energy is achieved at a nonzero SNR value below which one should not operate. The effect of the block length on both the minimum bit energy and the SNR value at which the minimum is achieved is investigated. Flash training and transmission schemes are analyzed and shown to improve the energy efficiency in the low-SNR regime. In the second part of this paper, the capacity and energy efficiency of training-based schemes are investigated when the channel input vector in each coherence block is subject to peak power constraints. The capacity-achieving input structure is characterized and the magnitude distribution of the optimal input is shown to be discrete with a finite number of mass points. The capacity, bit energy requirements, and optimal resource allocation strategies are obtained through numerical analysis. The improvements in energy efficiency when on-off keying (OOK) with fixed peak power and vanishing duty cycle is employed are studied.

On energy efficiency and optimum resource allocation of relay transmissions in the low-power regime

Relay links are expected to play a critical role in the design of wireless networks. This paper investigates the energy efficiency of relay communications in the low-power regime under two different scenarios: when the relay has unlimited power supply and when it has limited power supply. A system with a source node, a destination node, and a single relay operating in the time division duplex (TDD) mode was considered. Analysis and simulations are used to compare the energy required for transmitting one information bit in three different relay schemes: amplify and forward (AnF), decode and forward (DnF), and block Markov coding (BMC). Relative merits of these relay schemes in comparison with direct transmissions (direct Tx) are discussed. The optimal allocation of power and transmission time between source and relay is also studied.