System Throughput Performance Research Articles

Non-Orthogonal Random Access and Data Transmission Scheme for Machine-to-Machine Communications in Cellular Networks

In order to address the signalling overhead and resource allocation problems of Machine-to-Machine (M2M) communications with non-orthogonal multiple access (NOMA), we propose a hybrid non-orthogonal random access and data transmission (NORA-DT) scheme. A novel design of NORA-DT protocol for M2M communications in cellular networks is firstly proposed. A power back-off scheme is introduced to adjust machine-type communications device (MTCD)'s target arrived power, and a closed-form analytic formula for the relation of MTCD's transmission power is derived. Based on the transmission power relation, the devices are clustered into a set of NOMA clusters. In the hybrid NORA-DT protocol, the cluster center MTCD transmits a extended preamble on behalf of the MTCDs in the same NOMA cluster on the physical random access channel (PRACH) for connection request. Base station (BS) can perfectly detect the preamble collisions in advance and schedules physical uplink shared channel (PUSCH) only to the NOMA clusters without collision. Then the MTCDs in the same NOMA clusters transmit data packets right after preamble transmission on the PUSCH to reduce the signalling overhead. By finding the optimal power allocation, we propose a low-complexity energy efficiency maximization problem for NORA-DT scheme. Due to the relation of MTCD's transmission power, we transform the problem into the function of cluster center MTCD's transmission power and solve it by difference of convex (DC) programming under the maximum transmission power constraints and minimum rate requirements at the MTCDs. A computationally efficient adaptive resource allocation scheme is finally proposed to improve the system throughput and resource usage. The optimal resource allocation between PRACH and PUSCH for any number of MTCDs can be learned by BS in advance, which avoids frequent computation. The analytic model is validated by simulation results. We demonstrate that the proposed NORA-DT scheme can significantly improve the system throughput, resource efficiency and energy efficiency performance.

Uplink Performance Improvement for Downlink-Uplink Decoupled HetNets with Non-uniform User Distribution

In the heterogeneous networks (HetNets), the downlink-uplink decoupled (DUDE) user association is a very promising technology that can employ different association strategies for uplink and downlink. The DUDE mode has great potential for improving system capacity and frequency efficiency. However, interference between the DUDE user equipment (DUDE UE), macro user equipment (MUE) and small user equipment (SUE) still needs to be considered and properly tackled. Therefore, this paper presents an optimization scheme of frequency allocation and power control to improve the communication quality of users. Firstly, the multiple region frequency allocation (MRFA) scheme is proposed for non-uniform user distribution to alleviate interference among users and allocate spectrum resources equally to dense users. This scheme is modelled as a sub-region partition problem with maximum sum rate, which can disperse densely distributed users to different sub-bands for transmission. Secondly, the convergent power control (CPC) algorithm is considered to improve the transmission performance of each user. It can converge the transmit power to the optimal transmit power for reducing interference among co-channel users when there is no disturbance in the network. The CPC algorithm can also make the signal-to-interference-plus-noise-ratio (SINR) of each active user always greater than the target threshold until the end of communication by dynamically adjusting the transmit power of users. Simulation results show that the joint scheme of MRFA and CPC achieves a higher system throughput and better user performance than existing frequency allocation schemes or power control schemes.

Performance of low level protocols in high traffic wireless body sensor networks

The rapid development of medical sensors has increased the interest in Wireless Body Area Network (WBAN) applications where physiological data from the human body and its environment is gathered, monitored, and analyzed to take the proper measures. In WBANs, it is essential to design MAC protocols that ensure adequate performance and Quality of Service (QoS). This paper investigates Medium Access Control (MAC) protocols used in WBAN, and compares their performance in a high traffic environment with respect to different QoS and network performance metrics. Such scenario can be induced in case of emergency for example, where physiological data collected from all sensors on human body should be sent simultaneously to take appropriate action. This study can also be extended to cover collaborative WBAN systems where information from different bodies is sent simultaneously leading to high traffic. OPNET simulations are performed to compare the performance of the different MAC protocols under the same experimental conditions. A new MAC scheme aiming to enhance the delay, throughput, and energy performance of the system is then proposed and compared to existing protocols, to evaluate its performance in high traffic environment.

Cooperative Non-Orthogonal Multiple Access over Log-Normal Power Line Communication Channels

In this paper, we analyze the performance of cooperative power domain non-orthogonal multiple access (NOMA) in power line communication (PLC) networks. Due to the high signal attenuation of the source to user links, a relay aids communication from the source to two users. With half-duplex transmission, the source transmits a superimposed symbol in the first phase. The relay utilizes amplify-and-forward (AF) and decode-and-forward (DF) protocol on the received superimposed signal and forwards it to the users in the second phase. We derive analytic expressions for the outage probability and the system throughput of the proposed system under a PLC log-normal channel with impulsive noise. Based on the results for AF NOMA relaying case, we analyze the system performance at high signal-to-noise ratio (SNR) and derive closed-form lower and upper bounds for the outage probability. Simulation results show an improvement in the outage probability and the system throughput performance of the AF and DF NOMA schemes compared to the NOMA without relaying transmission and conventional orthogonal multiple access scheme. Furthermore, the impact of the channel variance is highlighted in the results. It is shown that the DF NOMA has a better outage probability than the AF NOMA scheme for low channel variance scenarios (i.e., less branches and connected loads in the PLC network). However, as the channel variance increases, AF NOMA scheme has similar outage probability performance as the DF NOMA scheme. In addition, it is shown that the system throughput is enhanced when the relay employs DF relaying compared to AF relaying.

Adaptive proportional fair scheduling with global-fairness

In practical communication systems, there are always multiple subscribers competing for limited resources, such as time and frequency, hence effective user scheduling is essential to multi-user communications in achieving good system throughput and fairness performance. The conventional proportional fair (PF) scheduling achieves fairness at the cost of system spectral efficiency (SE) loss. Such fairness is of long-term feature, i.e., all the users’ scheduling probabilities become approximately the same only when the observation time is long enough. Therefore, PF cannot guarantee the fairness for subscribers who enter the system temporarily or stay in the system for a short period of time. In addition, delay requirement of real-time-service users can hardly be met with conventional PF. In order to remedy these deficiencies, we propose adaptive proportional fair (APF) scheduling algorithms. In each time slot, the infrastructure node, e.g., base station, dynamically adjusts the forgetting factor based on the variance of all the subscribers’ scheduling priorities, so that users’ scheduling weights can be adaptively updated. Our in-depth simulation results show that compared to conventional PF, APF can not only achieve both long-term and short-term fairness which we refer to global-fairness, but also obtain high system SE. Moreover, users’ delay performance can be obviously improved.

A New User Grouping and Power Allocation Scheme for Downlink Non-orthogonal Multiple Access Systems

In this paper, we propose a new user grouping and power allocation scheme based on beamforming for downlink non-orthogonal multiple access systems. The proposed user grouping scheme can effectively reduce the interference from the other user and other beams as well, and can effectively improve the weak user rate especially when the SNR is not large. In addition, a power allocation scheme that can maximize the sum capacity while satisfying a certain fairness index is proposed. From the simulation results, the user grouping and power allocation method proposed in this paper can not only improve the overall system throughput performance, but also improve the fairness of weak users.

Amplify-and-Forward Relaying Based Spectrum Sharing in Both Time and Spectrum Domains With Wireless Powered Primary User

We propose a spectral and energy efficient cooperative spectrum sharing scheme with the primary user (PU) capable of harvesting wireless energy. Along with an access point (AP) transferring wireless power to PU, a secondary source (SS) and a secondary relay (SR) can cooperatively transmit data to a secondary destination (SD) using the amplify-and-forward protocol. The interference from secondary transmissions can boost the amount of harvested energy at PU. After the wireless power transfer phase, PU transmits data to AP using the harvested energy, and meanwhile SS transmits data to SD. The SR could simultaneously forward the data of both systems to improve their communication qualities. With the energy and data cooperations from SS and SR, more energy can be harvested by PU and the data reception at AP becomes more reliable, so the throughput performance of primary system can be satisfied more easily. As a result, a fraction of spectrum could be enough for the primary system and the remaining spectrum is released to the secondary system. The optimal time and bandwidth factors are determined to maximize the throughput of secondary system under the performance constraint of primary system. The numerical results show that our proposed scheme significantly outperforms the non-cooperative scheme in terms of system throughput.

On Outage Probability and Throughput Performance of Cognitive Radio Inspired NOMA Relay System

To improve the throughput and the outage probability of the Cognitive Radio (CR) inspired system, a novel Non-Orthogonal Multiple Access (NOMA) can be deployed to adapt multiple services in 5G wireless communication. In this scheme, after the reception of the superposition coded symbol with a predefined power allocation factors from the primary source, the relay decodes and forwards with a new superposition coded symbol (i.e. allocating another power factors) to the destination. By employing twin antenna design at the relay, the bandwidth efficiency in such scheme will be improved. Assuming Rayleigh fading channels, the closed-form expressions in terms of throughput and the outage performance are derived. Through numerical results, they showed that the outage performance of the proposed scheme using a Single Antenna (SA) scheme at the relay is better than a Twin Antenna (TA) scheme because SA scheme is not affected by its own antenna interference.

Downlink Performance of Superimposed Pilots in Massive MIMO Systems

In this paper, we investigate the downlink throughput performance of a massive multiple-input multiple-output system that employs superimposed pilots for channel estimation. The component of downlink (DL) interference that results from transmitting data alongside pilots in the uplink (UL) is shown to decrease at a rate proportional to the square root of the number of antennas at the BS when the least-squares channel estimate is employed in a matched-filter precoder. The normalized mean-squared error (NMSE) of the channel estimate is compared with the Bayesian Cramer-Rao lower bound that is derived for the system, and the former is also shown to diminish with increasing number of antennas at the base station. Furthermore, we show that staggered pilots are a particular case of superimposed pilots and offer the downlink throughput of superimposed pilots while retaining the UL spectral and energy efficiency of regular pilots. We also extend the framework for designing a hybrid system, consisting of users that transmit either regular or superimposed pilots, to minimize both the UL and DL interference. The improved NMSE and DL rates of the channel estimator based on superimposed pilots are demonstrated by means of simulations.

Resource Allocation and Power Control for D2D Communication Underlaying LTE-Advanced Networks

Device-to-device (D2D) communications has proven to be efficient in improving the network performance and releasing the traffic load of base station. D2D user equipment(DUEs) can share the same LTE resources blocks with the cellular user equipment(CUEs), but it would cause severe co-channel interference. In this paper, a resource allocation and power control scheme is proposed to reduce the impact of co-channel interference. First, adopt a resource allocation scheme based on greedy algorithm on the premise of meeting the minimum rate requirements of devices, then the path loss compensation factor matrix could be calculated according to the distance between DUEs to the base station and CUEs and used to reduce the influence. Simulation results show that the proposed algorithm has better performance in D2D user access rate and system throughput.

Optimal Radio Access Technology Selection Algorithm for LTE-WiFi Network

Heterogeneous network (HetNet) comprises multiple radio access technologies (RATs) allowing a user to associate with a specific RAT and steer to other RATs in a seamless manner. To cope up with the unprecedented growth of data traffic, mobile data can be offloaded to wireless fidelity (WiFi) in a long term evolution (LTE) based HetNet. In this paper, an optimal RAT selection problem is considered to maximize the total system throughput in an LTE-WiFi system with offload capability. Another formulation is also developed where maximizing the total system throughput is subject to a constraint on the voice user blocking probability. It is proved that the optimal policies for the association and offloading of voice/data users contain threshold structures. As a policy search over the entire policy space may become computationally inefficient, we propose computationally efficient algorithms based on the threshold structures for the association and offloading of users in LTE-WiFi HetNet. Simulation results are presented to demonstrate the voice user blocking probability and the total system throughput performance of the proposed algorithms in comparison with other benchmark algorithms.

Relaying protocols for buffer‐aided energy harvesting wireless cooperative networks

Here, the authors study a buffer-aided relay system, in which the source node and the relay node are energy harvesting nodes, and the source node transmits the information to the destination node via the relay node. Both the source node and relay node are assumed to equipped with an energy buffer and can temporarily store the harvested energy; in addition, the relay node possesses a data buffer to store the received information temporarily. Particularly, the authors propose two buffer-aided energy harvesting relay protocols, namely the harvest-then-transmit (HtT) protocol and the joint link selection and power allocation (JLSPA) protocol. For the HtT protocol, the expressions of the average achievable throughput and the optimal power splitting factor are obtained in close form. For the JLSPA protocol, based on the channel state information and buffer state information, a JLSPA protocol which maximises the average achievable throughput is presented. Furthermore, for the JLSPA protocol, the bounds on average achievable rate, average data buffer size, and average delay are analysed and the throughput-delay trade-off is revealed. The simulation results show that the proposed buffer-aided relaying scheme could improve the throughput performance of energy harvesting relay system significantly.

Resource Allocation for Energy Harvesting-Powered D2D Communication Underlaying UAV-Assisted Networks

In this paper, we investigate the resource allocation problem for unmanned aerial vehicle (UAV)-assisted networks, where a UAV acting as an energy source provides radio frequency energy for multiple energy harvesting-powered device-to-device (D2D) pairs with much information to be transmitted. The goal is to maximize the average throughput within a time horizon while satisfying the energy causality constraint under a generalized harvest-transmit-store model, which results in a non-convex problem. By introducing the Lagrangian relaxation method, we analytically show that the behavior of all D2D pairs at each time slot is exclusive: harvesting energy or transmitting information signals. The formulated non-convex optimization problem is thus transformed into a mixed integer nonlinear programming (MINIP). We then design an efficient resource allocation algorithm to solve this MINIP, where D.C. (difference of two convex functions) programming and golden section method are combined to achieve a suboptimal solution. Furthermore, we provide an idea to reduce the computational complexity for facilitating the application in practice. Simulations are conducted to validate the effectiveness of the proposed algorithm and evaluate the system throughput performance.

Optimal channel selection for simultaneous RF energy harvesting and data transmission in cognitive radio networks

AbstractIn this paper, a radio frequency–powered cognitive radio network is considered, in which the secondary users are powered by a radio frequency energy harvester (rectenna). Unlike most existing works, we consider a realistic rectenna characteristic function and derive the actual amount of harvested energy and thus obtain the resulting actual energy level of the secondary users. We consider a system architecture at which simultaneous energy harvesting and data transmission for each secondary user is possible. We introduce a strategy to manage the challenge of network throughput decreasing because of the lack of the secondary users' energy via selecting the best possible channels for energy harvesting and, simultaneously, by allocating the best channels for data transmission. Therefore, we implement cognition in spectrum utilization and in energy harvesting. We show that the amount of harvested energy affects the available energy of the secondary user and, consequently, the throughput; therefore, the channel selection to maximize energy harvesting affects the network throughput. To maximize the network throughput, the Hungarian algorithm is employed, and then, an algorithm with lower complexity based on the matching theory is proposed. Finally, we compare our proposed approach with some existing benchmarks and show its high performance in energy harvesting and system throughput.

Optimal Inter-Element Spacing of FD-MIMO Planar Array in Urban Macrocell with Elevation Channel Modelling

Full Dimension multiple input multiple output (FD-MIMO) architecture employs a planar array design at the Base Station (BS) to provide high order multi-user MIMO (MU-MIMO) via simultaneous data transmission to large number of users. With FD-MIMO, the BS can also adjust the beam direction in both elevation and azimuth direction to concentrate the energy on the user of interests while minimizing the interference leakage to co-scheduled users in the same cell or users in the neighboring cells. In a typical highly populated macrocell environment, modelling the elevation angular characteristics of three-dimensional (3D) channel is critical to understanding the performance limits of the FD-MIMO system. In this paper, we study the throughput performance of FD-MIMO system with varying elevation angular spread and inter-element spacing using a 3D spatial channel model. Our results show that for a typical urban scenario, horizontal beamforming with correlated antenna spacing achieves optimal performance but by restricting the spread of elevation angles of departure, elevation beamforming achieves high array gain with wide inter-element spacing. We also realize significant gains due to spatial array processing via modelling the elevation domain and varying the inter-element spacing for both the transmitter and receiver.

A flexible resource scheduling scheme for an adaptive SCMA system

Sparse code multiple access (SCMA) is a new type of non-orthogonal multiple access technology, and it originates from low-density signature (LDS) technology. SCMA can obtain an additional coding gain through the codebook design. Combining the concepts of OFDMA and CDMA, SCMA has the advantages of high capacity, low time delay and high data rate. We propose adaptive allocation technology (AAT) and design an adaptive SCMA system. The designed system has better flexibility and adaptability than conventional OFDMA and SCMA systems. However, preventing fragmentation of physical resource blocks (PRBs) in the resource scheduling is crucial for rendering the adaptive SCMA system feasible. For this purpose, we design two optional resource scheduling schemes: resource first and user first. The theoretical derivation and simulation results demonstrate the feasibility and superiority of the proposed algorithms and schemes in terms of system throughput and packet loss rate (PLR) performance.

A coalitional game‐based integrated framework for optimal power allocation in multirelay cooperative environment

SummaryCooperative relaying has emerged as an efficient transmit strategy in wireless networks affected by fading. In multirelay scenarios, the performance of cooperative systems is heavily influenced by resource allocation among the available relays. However, in practical scenarios, a relay may not help unless the cooperation improves its own utility. To address the above problem, this paper introduces a novel integrated game‐theoretic framework that involves incentive‐based optimal power allocation among the cooperating relays. Coalition formation game has been used to model the cooperation among relays that is integrated into a Stackelberg game, for considering the benefits of source and relays jointly. The game theoretic framework has been implemented with an objective to find an optimal and stable coalition set of relays that not only maximizes their utilities but also helps the source to allocate the optimal power to the relays at the optimal price, thereby increasing its utility too. Simulation results have confirmed that the proposed game theoretic solutions achieve comparable performance in system throughput as compared with the centralized approach.

A Two-Stages Relay Selection and Resource Allocation with Throughput Balance Scheme in Relay-Assisted D2D System

Introducing relay node to Device-to-Device (D2D) technology can extend the cell coverage range and improve the system performance. In this paper, we discuss a relay-assisted D2D communication underlaying cellular network from two aspects. Firstly, we discuss relay selection problem. A two-stages relay selection and resource allocation method is proposed. The stage 1 determines the range of candidate relay UEs through an area division method. Through this way, signaling overhead and measurement overhead can be reduced. The stage 2 selects an optimal relay UE from candidate relay UEs and determines the resource allocation method using an optimal bipartite matching theory with a pretty low complexity. Secondly, we find that the two-stages method causes a throughput unbalance and resource waste problem. Therefore, throughput balance is investigated in this paper. Eight throughput balance options are discussed in details. Then, three throughput balance schemes are proposed. The two-stages method and three throughput balance schemes are evaluated by simulation. Simulation results show that the proposed two-stages method can improve the throughput of relay-assisted D2D communication with a low signaling overhead and measurement overhead. Three proposed throughput balance schemes can improve system throughput performance further.

Delay and Delay-Constrained Throughput Performance of a Wireless-Powered Communication System

In this paper, the delay and delay-constrained throughput performance of a point-to-point wireless-powered communication system is investigated. In this system, the wireless-powered node, e.g., a user equipment (UE), receives data at the same time when powered from the other node, e.g., an access point (AP), and uses the harvested wireless energy to send data to the other node. The investigation focuses on the delay performance of sending data in the downlink (DL) from the AP node to the UE node and that in the uplink (UL) from the UE node to the AP node, based on which the throughput performance on both directions when delay constraints are enforced is also studied. To this aim, the cumulative service capacity of the service process is first analyzed for both DL and UL, taking into consideration the delay caused by the nontransmission phase for the AP or UE in each charging cycle. Thereafter, a general upper bound on the delay distribution for stochastic traffic arrivals is obtained for both DL and UL, based on which the delay-constrained throughput performance is further studied. In addition, to ensure the delay performance, the required energy storage capacity and wireless charging rate are investigated. The obtained results are exemplified with two specific traffic types, and the accuracy of the analysis is validated by comparison with extensive simulation results. The analysis and results shed new light on the performance of wireless-powered communication systems.

基于二维Markov链和中继聚合方法的多跳ARQ系统吞吐量的分析

本文主要基于中继聚合的研究方法对多跳ARQ系统的吞吐量进行了分析。首先，对由一对收发节点和一个中继节点组成的两跳ARQ系统的节点状态进行了定义，通过建立二维的Markov链得到了四阶的状态转移矩阵，并因而求得两跳ARQ系统中继节点的状态转移概率。其次，在讨论由一对收发节点和N个中继节点组成的N + 1跳ARQ系统时，我们采用中继聚合将N个中继节点合并成一个超级中继并使得N + 1跳系统在原理上等效于两跳系统，从而求得N + 1跳ARQ系统中继节点的状态转移概率。最后，把多跳ARQ系统自身的状态定义为“G”和“B”，结合超级中继和直传链路的状态我们得到了多跳ARQ系统状态转移过程的八个状态，并通过稳态方程求得了多跳ARQ系统吞吐量的解析式。事实上，我们的结果也证实了多中继和多跳ARQ系统的吞吐量研究有统一的方法，有利于后续研究的统筹规划。 In this paper, we analyzed the throughput of multi-hop ARQ system based on the method of relay aggregation. Firstly, we defined the node-state of two-hop ARQ system which consisted of a pair of transceivers and one relay node, and obtained the four-state transition matrix by establishing a two-dimensional Markov chain, then obtained the state transition probability of relay nodes in two hop ARQ system. Secondly, in the N + 1-hop ARQ system composed of a pair of transceivers and N relay nodes, we used relay aggregation to merge N relay nodes into a super relay and made the N+1-hop system equivalent to the two-hop system in principle, then obtained the state transition probability of relay nodes in N + 1-hop ARQ system. Finally, we defined the state of the multi-hop ARQ system as “G” and “B”, and got eight-state of state transfer processes of multi-hop ARQ system by combining with the state of the super relay and direct channel, and obtained the analytical solution for the throughput of multi-hop ARQ systems based on the steady-state equation. In fact, it was shown that there was a unified method to study the throughput performance of multi-relay and multi-hop ARQ system.