On Orthogonal Frequency Division Multiple Access Research Articles

Performance Analysis of QoS-Oriented OFDMA Protocol Based on IEEE 802.11ax for Cognitive Radio Network

To improve the quality of service (QoS) on the internet of medical things, a cognitive radio (CR) protocol based on orthogonal frequency division multiple access (OFDMA) is proposed, named CR-OFDMA. In this protocol, we divide a complete channel into multiple orthogonal subchannels and enhance the subchannel assignment scheme, which achieves QoS improvement under consideration of priority and fairness. Furthermore, we improve spectrum resource utilization by fully utilizing the remaining subchannels, feedback slots, and backoff slots. Then, a two-dimensional Markov model is established to describe the dynamic characteristics of the protocol operation, where the backoff stage and the backoff counter value constitute the system state. By establishing the traffic conservation equations for the system operation, the transmission probability and collision probability are calculated, and expressions of system throughput, channel utilization, and fairness index are derived. Finally, numerical results validate the advantages of CR-OFDMA.

Computation rate maximization in multi-user cooperation-assisted wireless-powered mobile edge computing with OFDMA

In the era of Internet of Things (IoT), mobile edge computing (MEC) and wireless power transfer (WPT) provide a prominent solution for computation-intensive applications to enhance computation capability and achieve sustainable energy supply. A wireless-powered mobile edge computing (WPMEC) system consisting of a hybrid access point (HAP) combined with MEC servers and many users is considered in this paper. In particular, a novel multiuser cooperation scheme based on orthogonal frequency division multiple access (OFDMA) is provided to improve the computation performance, where users can split the computation tasks into various parts for local computing, offloading to corresponding helper, and HAP for remote execution respectively with the aid of helper. Specifically, we aim at maximizing the weighted sum computation rate (WSCR) by optimizing time assignment, computation-task allocation, and transmission power at the same time while keeping energy neutrality in mind. We transform the original non-convex optimization problem to a convex optimization problem and then obtain a semi-closed form expression of the optimal solution by considering the convex optimization techniques. Simulation results demonstrate that the proposed multi-user cooperation-assisted WPMEC scheme greatly improves the WSCR of all users than the existing schemes. In addition, OFDMA protocol increases the fairness and decreases delay among the users when compared to TDMA protocol.

Optimal Resource Allocation for NOMA Wireless Networks

The non-orthogonal multiple access (NOMA) method is a novel multiple access technique that aims to increase spectral efficiency (SE) and accommodate enormous user accesses. Multi-user signals are superimposed and transmitted in the power domain at the transmitting end by actively implementing controllable interference information, and multi-user detection algorithms, such as successive interference cancellation (SIC), are performed at the receiving end to demodulate the necessary user signals. Although its basic signal waveform, like LTE baseline, could be based on orthogonal frequency division multiple access (OFDMA) or discrete Fourier transform (DFT)-spread OFDM, NOMA superimposes numerous users in the power domain. In contrast to the orthogonal transmission method, the non-orthogonal method can achieve higher spectrum utilization. However, it will increase the complexity of its receiver. Different power allocation techniques will have a direct impact on the system’s throughput. As a result, in order to boost the system capacity, an efficient power allocation mechanism must be investigated. This research developed an efficient technique based on conjugate gradient to solve the problem of downlink power distribution. The major goal is to maximize the users’ maximum weighted sum rate. The suggested algorithm’s most notable feature is that it converges to the global optimal solution. When compared to existing methods, simulation results reveal that the suggested technique has a better power allocation capability.

Energy-Efficient Joint Task Offloading and Resource Allocation in OFDMA-Based Collaborative Edge Computing

Mobile edge computing (MEC) is an emergent architecture, which brings computation and storage resources to the edge of mobile network and provides rich services and applications near the end users. The joint problem of task offloading and resource allocation in the multi-user collaborative mobile edge computing network (C-MEC) based on Orthogonal Frequency-Division Multiple Access (OFDMA) is a challenging issue. In this paper, we investigate the offloading decision, collaboration decision, computing resource allocation and communication resource allocation problem in C-MEC. The delay-sensitive tasks of users can be computed locally, offloaded to collaborative devices or MEC servers. The goal is to minimize the total energy consumption of all mobile users under the delay constraint. The problem is formulated as a mixed-integer nonlinear programming (MINLP), which involves the joint optimization of task offloading decision, collaboration decision, subcarrier and power allocation, and computing resource allocation. A two-level alternation method framework is proposed to solve the formulated MINLP problem. In the upper level, a heuristic algorithm is used to handle the collaboration decision and offloading decisions under the initial setting; and in the lower level, the allocation of power, subcarrier, and computing resources is updated through deep reinforcement learning based on the current offloading decision. Simulation results show that the proposed algorithm achieves excellent performance in energy efficient and task completion rate (CR) for different network parameter settings.

Efficient Resource Allocation for Wireless-Powered MIMO-NOMA Communications

Wireless-powered communication (WPC) is a promising technology for varied smart network applications in the industrial, commercial, and security sectors. It employs a large number of connected low-powered user equipments (UEs) in which the harvested energy from electromagnetic radiations is used for signal transmission. However, efficient resource allocation schemes are still required to optimize the performance of WPC networks over limited power and spectrum environments. In this paper, a new approach of wireless-powered multiple-input multiple-output non-orthogonal multiple access (WP-MIMO-NOMA) is designed by employing harvest-then-transmit protocol with joint time-split and power control (TS-PC) techniques to optimize the network performance and lifetime with affordable complexity. We derive the sum rate, UEs’ rates, and rate region expressions based on power-domain NOMA and successive interference cancellation (SIC) decoding. An optimal joint TS-PC (OJTS-PC) scheme is proposed to maximize the network sum rate with enhanced user-fairness under constrained harvested energy level, uplink transmit power, and minimum UE’s rate. Besides, a near-optimal greedy TS-PC (GTS-PC) algorithm is designed to reduce computational efforts significantly. For comparison, we derive the rate expressions for the reference WP-MIMO-OMA system based on orthogonal frequency-division multiple access (OFDMA) and time-division multiple access (TDMA). Numerical results validate the effectiveness of proposed resource allocation schemes in terms of realized sum rate, UE’s rate, and user-fairness without scarifying the limited power of far UEs. This will prolong the lifetime of WPC networks operating over constrained power and bandwidth resources.

Dynamic Algorithm for Interference Mitigation Between Cells in Networks Operating in the 250 MHz Band

The growing demand for Internet of Things (IoT) applications in agribusiness increases the necessity of reliable and secure connectivity in rural areas. Thus, in the particular case of Brazil, some initiatives aim to take advantage of frequency bands dedicated to limited private services. For instance, cellular networks based on orthogonal frequency-division multiple access (OFDMA) in 250 MHz bands require specialized adaptations because the interference between cells increases when these systems operate in the Very High Frequency (VHF) band. This work presents an analysis based on a reliable simulation of interference mitigation in OFDMA systems at 250 MHz using a network simulator. The simulator is calibrated with data obtained in the field by an extensive and rigorous drive test. Therefore, the analysis is based on a comparison of traditional frequency reuse schemes with a machine learning approach based on deep reinforcement learning (DRL) to reduce inter-cell interference. The numerical results indicate that the DRL approach outperforms the traditional frequency reuse (FR) schemes in four different typical agribusiness scenarios.

Joint power and subcarrier allocation for SWIPT in cognitive relay system

In this paper, we study power and subcarrier allocation in decode-and-forward (DF) cognitive relay network based on orthogonal frequency division multiple access (OFDMA) technology, in which power splitting (PS) is used for the secondary users (SUs) supporting simultaneous wireless information and the power transfer (SWIPT). We attempt to maximize the energy efficiency (EE) of the secondary system subject to the constraints of minimum system rate, maximum transmission power and minimum harvested energy. The optimal power allocation (OPA) algorithm is proposed to determine the optimal solution of relay transmission power, power splitting ratio and subcarrier allocation. To tackle the original non-convex optimization problem, the Dinkelbach method is used for fractional programming and the problem is decomposed into two solvable sub-problems. The Lagrangian dual algorithm is utilized to determine the optimal transmission power and the power splitting ratio. The Hungarian algorithm is then introduced to determine the optimal subcarrier allocation. Compared with some existing algorithms, the simulation results show that the proposed OPA scheme is able to achieve higher energy efficiency when certain communication quality is required.

User Selection and Resource Allocation Algorithms for Multicarrier NOMA Systems on Downlink Beamforming

In this paper, we propose user grouping, subcarrier allocation, and bit allocation schemes in multicarrier nonorthogonal multiple access (NOMA) systems on downlink beamforming to reduce the total transmit power while considering the data-rate and the error-rate constraints of practical modulation types. Power control is also considered. In this system, each subcarrier can be assigned to multiple users for data transmission. Each subcarrier is allocated to a cluster that contains groups of two users for data transmission. A subset of subcarriers is assigned to the same cluster for sharing. The system is based on orthogonal frequency division multiple access (OFDMA), in which a primary user (PU) is more important than a secondary user, and we ensure that all assigned subcarriers transmit data to the PU in the system. In the proposed schemes, the user-grouping operation is performed first and the subcarrier allocation along with the bit loading and power assignment are performed subsequently based on the user-grouping results. The simulation results obtained using the proposed schemes in conjunction with the nonorthogonal multiple access to allocate bits, subcarriers, and transmit power show that the proposed schemes outperform the conventional OFDMA system in terms of transmit power.

An Efficient Resource Allocation Algorithm for OFDM-Based NOMA in 5G Systems

Non-orthogonal multiple access (NOMA) has become the key technology in the future 5G wireless networks. It can achieve multi-user multiplexing in the transmit power domain by allocating different power, which can effectively improve the system capacity and spectral efficiency. Aiming at the problem of high computational complexity and improving system capacity in non-orthogonal multiple access (NOMA) based on orthogonal frequency division multiple access (OFDMA) for 5G wireless cellular networks, this paper proposes an improved low complexity radio resource allocation algorithm for user grouping and power allocation optimization. The optimization model is established with the goal of maximizing system capacity. Through the step-by-step optimization idea, the complex non-convex optimization problem is decomposed into two sub-problems to be solved separately. Firstly, all users are grouped based on the greedy method, and then the power allocation is performed on the sub-carriers of the fixed group. Simulation results show that the proposed algorithm has better system capacity than the existing state-of-the-art algorithms and reduced complexity performance.

Multiple BSSs Association Based Spatial Clustering Group Access Protocol for Next Generation WLAN

The next generation Wireless Local Area Network (WLAN) IEEE 802.11be regards Extremely High Throughput (EHT) as its core technology goal, among which multi-band capability and AP cooperation technology are regarded as its key technologies. However, the existing research on Orthogonal Frequency Division Multiple Access (OFDMA) protocol does not consider the multi-band capability and AP collaboration technology of IEEE 802.11be, so the improvement of system performance is limited and does not meet the EHT requirement. Especially when the nodes in overlapping coverage area have a large number of traffic, it is more important to improve the throughput of nodes in overlapping coverage area. In order to improve the throughput of nodes in overlapping coverage area, this paper proposes a spatial clustering group OFDMA protocol associated with multiple Basic Service Sets (BSSs). The protocol allows nodes in overlapping coverage area to be associated with multiple BSSs at the same time by using multi-band capability, that is, multi-association; Using AP collaboration technology allows nodes to perform parallel backoff with channels on multiple BSSs to improve access efficiency. Nodes in the overlapping coverage area are associated with the channels of multiple BSSs for parallel backoff. Node completed backoff and successfully accessed triggers a spatial clustering group (SCG) with close to its spatial location. OFDMA mode is used by SCG to access and transmit, thus increasing the access opportunities of nodes within overlapping coverage, thereby improving the throughput. The simulation results show that using the SCG-OFDMA protocol proposed in this paper associated with two BSSs, its throughput of nodes within overlapping coverage can achieve 353.41% higher than the IEEE 802.11ax protocol and 558.33% higher than the OMAX protocol respectively.

Spectrum allocation by wave based adaptive differential evolution algorithm

Resource allocation is very important in mobile communication. This paper studies the assignment of spectrum in cellular networks operated on orthogonal frequency division multiple access (OFDMA) system. Both network utility and fairness among all linked users are taken to measure quality of service in cellular networks. The problem is expressed as a maximization optimization model. Wave based adaptive differential evolution (WADE) algorithm is proposed to for spectrum allocation. The WADE algorithm adapts algorithmic parameters in wave propagation manner to accelerate convergence process of the algorithm. Simulation results show that WADE is more efficient than other compared algorithms. Moreover, it is effective to allocate spectrum resources in OFDMA-based cellular networks.

Performance Analysis of the IEEE 802.11ax MAC Protocol for Heterogeneous Wi-Fi Networks in Non-Saturated Conditions.

The IEEE 802.11ax standard, which realizes multi-user transmission based on orthogonal frequency division multiple access (OFDMA), has been highlighted as a key technology to meet high future demand for Wi-Fi systems. Since this standard is still being developed, performance analysis through mathematical modeling is of paramount importance; however, existing studies have several limitations. Firstly, most of these consider only the saturation network throughput, whereas for 802.11ax in particular, the access delay of the nodes needs to be studied carefully, since they no longer acquire the medium independently but depend solely on the access point’s (AP’s) schedule. Secondly, since the network performance may be affected to a greater extent by legacy nodes than by 802.11ax nodes, it is desirable to consider various heterogeneous cases of networks with existing legacy nodes. In this paper, a new analytical framework for the 802.11ax MAC protocol is provided. Markov-chain-based models are developed to represent the behavior of the 802.11ax nodes, and both non-saturated traffic conditions and co-existence with the legacy nodes are considered. Through both analysis and MATLAB simulations, it is shown that the proposed model accurately evaluates the throughput and the delay performance under various network conditions.

OFDMA Based QoS-Oriented Guarantee Novelty Multiple Access Protocol

The next generation wireless local area network (WLAN) 802.11ax standards committee takes high quality of service(QoS) guarantee as one of important technology goals of the next generation WLAN. As a result of a variety of wireless traffics, so the requirements of the QoS must also be varied. However, the existing media access control(MAC) protocol based on orthogonal frequency division multiple access(OFDMA) can’t support QoS diversification and high requirement well. To solve this problem, this paper presents a QoS-oriented OFDMA MAC for the next generation WLAN. On one hand, for backward compatibility consideration, continue to use four priority traffics of 802.11e in this protocol; on the other hand, the introduction of QoS-oriented priority scheduling algorithm to support future wireless traffic feature which is QoS of diversification and high requirements. Finally, through the simulation, the system effective throughput of the proposed QoS-OFDMA MAC is 57.8% and 59% higher than the OFDMA MAC of the sequential scheduling algorithm and the OFDMA MAC of the proportional fairness algorithm.

Design Framework for Optimizing Maintenance Efficiency in OFDMA-PONs Supporting Wireline–Wireless Convergence

Recently, a novel passive optical network (PON) has been proposed based on orthogonal frequency division multiple access (OFDMA) technology. The OFDMAPON provides the opportunity for the convergence of wireline and wireless services. Moreover, virtual subcarrier scheduling can be achieved by virtualization, thus hiding the difference of heterogeneous multiplexing methods in the OFDMA-PON supporting wireline and wireless services. In the multi-segment OFDMA-PON topology, each segment is connected to a distribution fiber. If all distribution fibers are under maintenance simultaneously, the service continuity will be disrupted, thus necessitating an appropriate virtual subcarrier scheduling scheme. In this paper, by migrating the traffic of virtual subcarriers during each maintenance batch, only a partial set of distribution fibers is maintained, leaving the remaining ones to fully support the operation. We formulate the problem aiming to minimize the number of maintenance batches while guaranteeing an acceptable scheduling period. The NPhard problem, feasibility conditions, and lower bound are analyzed. We also design a novel virtual subcarrier scheduling algorithm to solve the problem. Simulations show that the heuristic solution well matches the lower bound with a high convergence ratio of 93%. The optimal scheduling period is also determined.

A MAC layer protocol for a bandwidth scalable OFDMA PON architecture

A medium access control (MAC) layer protocol for passive optical networks (PONs) based on orthogonal frequency division multiple access (OFDMA) is proposed in this paper. The protocol is able to exploit statistical multiplexing to offer an efficient bandwidth control with greater flexibility and granularity to the bandwidth allocation, hence, providing high performance measured in terms of throughput, delay and jitter. The main recommendations of the proposed MAC are described in accordance to the physical layer features of the architecture named Bandwidth Scalable OFDMA PON (BS-OFDMA PON). Simulation results show that the proposed architecture based on tree topology is able to provide triple-play services to 32 optical network units (ONUs) and transmission rates above 33 Gb/s per wavelength.

Multi-Cluster based Dynamic Channel Assignment for Dense Femtocell Networks

This paper proposes a novel channel assignment scheme called multi-cluster based dynamic channel assignment (MC-DCA) to improve system performance for the downlink of dense femtocell networks (DFNs) based on orthogonal frequency division multiple access (OFDMA) and frequency division duplexing (FDD). In order to dynamically assign channels for femtocell access points (FAPs), the MC-DCA scheme uses a heuristic method that consists of two steps: one is a multiple cluster assignment step to group FAPs using graph coloring algorithm with some extensions, while the other is a dynamic subchannel assignment step to allocate subchannels for maximizing the system capacity. Through simulations, we first find optimum parameters of the multiple FAP clustering to maximize the system capacity and then evaluate system performance in terms of the mean FAP capacity, unsatisfied femtocell user equipment (FUE) probability, and mean FAP power consumption for data transmission based on a given FUE traffic load. As a result, the MC-DCA scheme outperforms other schemes in two different DFN environments for commercial and office buildings.

QoE-driven multi-user scheduling and rate adaptation with reduced cross-layer signaling for scalable video streaming over LTE wireless systems

The scarcity of the available radio spectrum coupled with the growing popularity of bandwidth intensive mobile video applications poses a huge challenge to network operators. The solution of over-provisioning the network is not economical; hence, an appropriate strategy for scheduling and resource allocation among the users in the system is of crucial importance. This work focuses on scheduling multiple video flows on the downlink of a wireless system based on orthogonal frequency division multiple access (OFDMA), such as Long-Term Evolution (LTE) and LTE-A (LTE-Advanced) standards. We propose a joint multi-user scheduling and multi-user rate adaptation strategy providing an appropriate trade-off between efficiency and fairness, while ensuring high quality of experience (QoE) for the end users. We consider Scalable Video Coding (SVC) which facilitates the truncation of bit streams, thus allowing graceful degradation of video quality in the event of wireless channel variations or network congestion. The proposed scheduler utilizes QoE-aware priority marking, where video layers are mapped to priority classes and targets at minimizing delay bound violations for the most important priority classes under congestion. In order to reduce congestion, we propose multi-user rate adaptation at the MAC layer via a novel dynamic filtering policy for QoE-based priority classes. Simulation results show that the proposed approach delivers to the end users a similar QoE as delivered by the state-of-the-art cross-layer approaches, where extensive cross-layer signaling, additional video rate adaptation modules at the core network, and frequent link probing from the wireless access network to the rate adaptation modules are required. The latter approaches are not implemented in real systems due to the aforementioned drawbacks, while our approach can be implemented without major modifications in the standard behavior of existing networks and equipment. The proposed framework can deliver delay-sensitive traffic as well as delay-tolerant best-effort traffic.

Multichannel Analysis of Cell Range Expansion and Resource Partitioning in Two-Tier Heterogeneous Cellular Networks

Cellular heterogeneous networks (HetNets) can improve capacity by offloading users from congested macro cells to lightly loaded small cells through biased association known as cell range expansion (CRE). However, the offloaded (range-expanded) users must be protected from macro interference through time/frequency resource partitioning. In this paper, we develop an analytical framework to evaluate the performance gain due to CRE further supported by resource partitioning in two-tier (macro-pico) networks with multichannel downlinks, e.g., those based on orthogonal frequency division multiple access (OFDMA). By exploiting the flexibility in subchannel allocation offered by OFDMA, frequency-domain resource partitioning is proposed in which the macro tier is muted on a fraction of total subchannels, which are allocated exclusively to range-expanded pico users. The load perceived by a base-station is a key factor in determining its interference contribution over the network and is directly affected by user offloading and resource partitioning. Thus, the analysis of such systems must incorporate cell load. While previous studies mostly rely on full-load assumption, in this paper, we properly characterize cell load as the function of user density, association bias and resource partitioning fraction. We then, evaluate the performance in terms of average user data rate over the entire network, and also investigate the optimal choice of association bias and resource partitioning fraction.

OFDMA-based network-coded cooperation: design and implementation using software-defined radio nodes

Benefits of network coding towards enhancing communication quality, both in terms of robustness or data transmission rates, make it a significant candidate as a future networking technology. Conventionally, network coding is mostly used in wired infrastructures, where transmission errors between nodes are negligible. Capturing the provided benefits of network coding via straightforward extension from wired networks to wireless networks is not trivial. In addition to the challenges introduced through the wireless channel impairments, we can also capture the spatial diversity gain provided by the broadcast nature of the wireless channels. In this work, we design and implement a network-coded cooperation (NCC) system that operates in real time through the use of software-defined radio (SDR) nodes for the first time in the literature. We specifically target wireless networks. Our system is based on orthogonal frequency division multiple access (OFDMA) that provides a practical means to enable high transmission rates through the use of narrowband subcarriers. The developed testbed is composed of three source nodes, a relay node and two destination nodes. The transmission of the proposed NCC-OFDMA system is completed in two phases; the broadcast and the relaying phases. Multiplexing of source nodes’ signals is achieved through OFDMA technique. In the broadcast phase, an OFDMA signal is transmitted to relay and destination nodes. In the relaying phase, the relay node first detects the OFDMA signal, generates network-coded symbols, and then transmits these symbols to destination nodes. At the end of these two phases, the destination nodes determine the source nodes’ signals by using network decoders. The destination nodes make use of both the uncoded and network-coded symbols, which are received in broadcast and relaying phases, respectively. Destination nodes then perform network decoding. Through real-time bit error rate and error vector magnitude measurements, we show that the NCC-OFDMA system can significantly improve the communication quality and robustness, while enabling data transmission between multiple users, as known from theoretical analyses. Some features of this implemented NCC-OFDMA system have the potential to be included in 5G standards, due to the improved radio resource usage efficiency.

A Transformed Conflict Graph-Based Resource-Allocation Scheme Combining Interference Alignment in OFDMA Femtocell Networks

To deal with ever-growing wireless services and to increase network throughput, it has been proposed to deploy femtocells with frequency reuse based on orthogonal frequency-division multiple access (OFDMA). However, the interference poses big challenges, particularly for dense deployment scenarios. The resource allocation with joint consideration of subchannel assignment and interference alignment (IA) is different from the traditional problems. First, we need to select the users to perform IA since the number of participant users is limited by the feasibility constraint, and the interference power levels are different due to the path loss. Second, IA increases the degrees of freedom (DoFs) while occupying the additional signal dimension of the participant user; hence, the entirety of the participants in IA require more subchannels compared with the nonparticipants when each of the users transmits the same number of streams. In this paper, we propose a transformed conflict graph-based resource-allocation scheme, where the users are selected according to the effect of IA on the requirement under the feasibility constraint. Then, the subchannel assignment can be modeled as a classical color problem. Extensive simulations show that our scheme can approximate the optimal scheme in a small network and effectively improve the satisfactory ratio of users compared with the scheme without IA in dense femtocell networks.