Frequency Division Multiple Access Systems Research Articles

Impact of Sub-Band Correlation on SFR and Comparison of FFR and SFR

In soft frequency reuse (SFR) when the user is classified as a cell-center user based on signal-to-interference-plus-noise-ratio in a sub-band, the user retains its sub-band. On the other hand, if the user is classified as a cell-edge user, a new sub-band is allocated. We analyze the impact of correlation between the cell-center sub-band and the cell-edge sub-band for a user when the SFR technique is used in a cellular orthogonal frequency division multiple access (OFDMA) system. The coverage probability (CP) and the average rate are derived for the following two cases: 1) when the sub-bands are independent and 2) when the sub-bands are completely correlated. We show that correlation significantly decreases the edge CP and the average rate of the SFR technique, and as the power control factor increases, the impact of correlation decreases. Fractional frequency reuse (FFR) and SFR techniques are compared and it is shown that the impact of correlation on the FFR is significantly lower. Furthermore, it is also shown that the FFR provides better edge CP and average rate when compared with the SFR in single-input single-output (SISO) networks, thereby suggesting that the FFR should be preferred over SFR in cellular SISO OFDMA systems. However, for single-input multiple-output networks, the SFR provides a better average rate when compared with the FFR, especially when the sub-band correlation is not significant. Finally, the impact of log-normal shadowing has been carefully studied.

Side information embedding and detection scheme for selected mapping based single‐carrier frequency‐division multiple access systems

Selected mapping (SLM) works effectively in peak-to-average power ratio reduction for the single-carrier frequency-division multiple access (SC-FDMA) system. However, the need for side information (SI) transmission results in data rate loss and increase of the system complexity. To avoid explicit SI transmission for SLM-based SC-FDMA systems, an SI embedding and detection scheme is proposed by exploiting the block pilot symbols. Specifically, to enable SI embedding, the authors propose to represent the SI index for each data symbol in the subframe by a location set of some selected subcarriers in the block pilot symbol. For SI detection, an optimal pilot-aided maximum-likelihood SI detector is presented. As a low-complexity alternative, a suboptimal log-likelihood ratio SI detector is also proposed. In addition, the authors provide theoretical analysis of SI detection error rate and discuss the effect of the proposed scheme on channel estimation. Simulation results show that, in SLM-based SC-FDMA systems, the proposed scheme significantly outperforms existing methods in terms of both SI detection and bit error rate (BER) and achieves the same BER performance as its counterpart with perfect SI.

A Semi Blind Channel Estimation Method Based on Hybrid Neural Networks for Uplink LTE-A

The paper describes how to improve channel estimation in Single Carrier Frequency Division Multiple Access (SC-FDMA) system, using a Hybrid Artificial Neural Networks (HANN). The 3 rd Generation Partnership Project (3GPP) standards for uplink Long Term Evolution Advanced (LTE-A) uses pilot based channel estimation technique. This kind of channel estimation method suffers from a considerable loss ofbitrate due to pilot insertion; all data frame sent contains reference signal. The HANN converts data aided channel estimator to semi blind channel estimator. To increase convergence speed, HANN uses some channel propagation Fuzzy Rules to initialize Neural Network parameters before learning instead of a random initialization, so its learning phase ismore rapidly compared to classic ANN.HANN allows more bandwidth efficient and less complexity. Simulation results show that HANN has better computational efficiency than the Minimum Mean Square Error (MMSE) estimator and has faster convergence than classic Neural Networks estimators.

Jammer-Assisted Resource Allocation in Secure OFDMA With Untrusted Users

In this paper, we consider the problem of resource allocation in the orthogonal frequency division multiple access system with single source and $M$ untrusted users in presence of a friendly jammer. The jammer is used to improve either the weighted sum secure rate or the overall system fairness. The formulated optimization problem in both the cases is a mixed integer non-linear programming problem, belonging to the class of NP-hard. In the sum secure rate maximization scenario, we decouple the problem and first obtain the subcarrier allocation at source and the decision for jammer power utilization on a per-subcarrier basis. Then, we do joint source and jammer power allocation using primal decomposition and alternating optimization framework. Next, we consider fair resource allocation by introducing a novel concept of subcarrier snatching with the help of jammer. We propose two schemes for jammer power utilization, called proactively fair allocation (PFA) and on-demand allocation (ODA). PFA considers equitable distribution of jammer power among the subcarriers, while ODA distributes jammer power based on the user demand. In both cases of jammer usage, we also present suboptimal solutions that solve the power allocation at a highly reduced complexity. Asymptotically optimal solutions are derived to benchmark optimality of the proposed schemes. We compare the performance of our proposed schemes with equal power allocation at source and jammer. Our simulation results demonstrate that the jammer can indeed help in improving either the sum secure rate or the overall system fairness.

Weighted sum throughput maximisation for cooperative relay‐aided multi‐cell orthogonal frequency division multiple access cellular networks considering partial fairness

This study addresses resource allocation problem with partial fairness, considering weighted sum throughput maximisation for an orthogonal frequency-division multiple access system with half-duplex decode-and-forward relaying. In the system formulation, multi-cell co-channel interference as one of the critical factors in multi-cell processing has been taken into account and its effect on system performance is evaluated. It has been shown that the problem is in the form of combinatorial non-convex optimisation problems (NP-hard). Avoiding to solve NP-hard problem, the authors have made suboptimal solutions according to iterative methods to satisfy the system requirements in the best way. In this way, the resulting non-convex optimisation problem has been solved by dual Lagrangian decomposition, and iterative resource allocation algorithms are proposed to find solutions which satisfy Karush–Kuhn–Tucker conditions. Two resource allocation strategies based on centralised and distributed scenarios are derived to maximise the average system throughput (bit/s/Hz) considering partial fairness. Simulation results indicate that the authors’ proposed methods work better than interference threshold methods and other conventional algorithms such as single cell methods which use local information processing.

Iterative nonlinear detection for SFBC SC–FDMA uplink MIMO transmission systems

SummarySingle‐carrier frequency division multiple access (SC‐FDMA) systems with space frequency block coding (SFBC) transmissions achieve both spatial and frequency diversity gains in wireless communications. However, SFBC SC‐FDMA schemes using linear detectors suffer from severe performance deterioration because of noise enhancement propagation and additive noise presence in the detected output. Both issues are similar to inter‐symbol‐interference (ISI). Traditionally, SC‐FDMA system decision feedback equalizer (DFE) is often used to eliminate ISI caused by multipath propagation. This article proposes frequency domain turbo equalization based on nonlinear multiuser detection for uplink SFBC SC‐FDMA transmission systems. The presented iterative receiver performs equalization with soft decisions feedback for ISI mitigation. Its coefficients are derived using minimum mean squared error criteria. The receiver configuration study is Alamouti's SFBC with two transmit and two receive antennas. New receiver approach is compared with the recently proposed suboptimal linear detector for SFBC SC‐FDMA systems. Simulation results confirm that the performance of the proposed iterative detection outperforms conventional detection techniques. After a few iterations, bit‐error‐rate performance of the proposed receiver design is closely to the matched filter bound. Copyright © 2016 John Wiley & Sons, Ltd.

Blind inter carrier interference compensation in MIMO SC-IFDMA system using firefly algorithm

A mathematical formulation of the detrimental effects of carrier frequency offset (CFO) and channel on uplink MIMO single carrier frequency division multiple access system with interleaved subcarrier mapping (SC-IFDMA) is carried out, and a linear filter is derived to counteract the performance degradation, under the assumption of perfect knowledge of CFO. Later on, the assumption on CFO parameter is removed, and a blind interference cancelation scheme based on firefly algorithm is proposed. The typical structure of the interference in SC-IFDMA is utilized in developing a low complexity implementation model for the proposals. The extensive simulation study is carried out using MATLAB and the significant features of the proposals were substantiated.

Artificial Noise Aided Secrecy Information and Power Transfer in OFDMA Systems

In this paper, we study simultaneous wireless information and power transfer (SWIPT) in orthogonal frequency division multiple access (OFDMA) systems with the coexistence of information receivers (IRs) and energy receivers (ERs). The IRs are served with best-effort secrecy data and the ERs harvest energy with minimum required harvested power. To enhance the physical layer security for IRs and yet satisfy energy harvesting requirements for ERs, we propose a new frequency domain artificial noise (AN) aided transmission strategy. With the new strategy, we study the optimal resource allocation for the weighted sum secrecy rate maximization for IRs by power and subcarrier allocation at the transmitter. The studied problem is shown to be a mixed integer programming problem and thus non-convex, while we propose an efficient algorithm for solving it based on the Lagrange duality method. To further reduce the computational complexity, we also propose a suboptimal algorithm of lower complexity. The simulation results illustrate the effectiveness of proposed algorithms as compared against other heuristic schemes.

CFO mitigation for uplink SFBC SC-FDMA

To mitigate inter-carrier interference due to large carrier frequency offset (CFO) in an uplink single-carrier frequency division multiple access (SC-FDMA) system, a three-tap adaptive frequency-domain decision feedback equalizer (AFD-DFE) is designed in this paper. Our design exploits the banded and sparse structure of the equivalent channel matrix. The block recursive least squares (RLS) algorithm is used to adapt the AFD-DFE. Consequently, by exploiting the matrix structure in the frequency-domain, the complexity of the block RLS is reduced substantially when compared to its time-domain counterpart. In addition, the design is extended to space-frequency block coded (SFBC) SC-FDMA systems. We show that our proposed AFD-DFE exhibits significant performance improvement when compared to a one-tap AFD-DFE while still enjoying a low computational complexity.

Joint Spectrum and Power Allocation for D2D Communications Underlaying Cellular Networks

This paper addresses the joint spectrum sharing and power allocation problem for device-to-device (D2D) communications underlaying a cellular network (CN). In the context of orthogonal frequency-division multiple-access systems, with the uplink resources shared with D2D links, both centralized and decentralized methods are proposed. Assuming global channel state information (CSI), the resource allocation problem is first formulated as a nonconvex optimization problem, which is solved using convex approximation techniques. We prove that the approximation method converges to a suboptimal solution and is often very close to the global optimal solution. On the other hand, by exploiting the decentralized network structure with only local CSI at each node, the Stackelberg game model is then adopted to devise a distributed resource allocation scheme. In this game-theoretic model, the base station (BS), which is modeled as the leader, coordinates the interference from the D2D transmission to the cellular users (CUs) by pricing the interference. Subsequently, the D2D pairs, as followers, compete for the spectrum in a noncooperative fashion. Sufficient conditions for the existence of the Nash equilibrium (NE) and the uniqueness of the solution are presented, and an iterative algorithm is proposed to solve the problem. In addition, the signaling overhead is compared between the centralized and decentralized schemes. Finally, numerical results are presented to verify the proposed schemes. It is shown that the distributed scheme is effective for the resource allocation and could protect the CUs with limited signaling overhead.

Reduced feedback link design for device‐relaying enhanced multiple‐input single‐output orthogonal frequency‐division multiple access wireless systems

Device-relaying enhanced multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA) systems are one of the promising and cost-effective methods to satisfy data rate requirements of future wireless networks. To implement device relaying in MISO-OFDMA systems efficiently, the channel state information belonging to all links is required at the base station. However, the feedback load increases with the number of users, device-relay candidates, antennas and subcarriers. A novel scheduling and a joint feedback link design and relay selection algorithm in device-relaying enhanced downlink MISO-OFDMA systems are proposed, while reducing the feedback load significantly without sacrificing the system performance.

OFDMA 다중률 비디오 멀티캐스트 전송에서 스케줄링 방식의 장기적 성능 평가

OFDMA는 주파수와 시간 축에 따라 융통성 있는 자원 할당이 가능하고, 적응적 변조와 코딩이 가능하기 때문에 다중률 멀티캐스트 전송에 적합하다. 계층적 코딩과 달리 MDC (multiple description coding)는 비디오 스트림을 서브 스트림으로 분해와 재조립이 용이하며, 수신율에 비례하여 비디오 품질도 증가하는 특성을 가지고 있다. OFDMA 무선 또는 이동통신망에서 비디오를 다중률로 멀티캐스트 전송할때 자원 할당과 전송률에 관한 수학적 모델을 제시하고, 사용자가 느끼는 비디오 품질 인덱스인 MOS(mean opinion score)를 최대화 혹은 비례적 공평성을 극대화하는 스케줄링 방식에 대해, 평균값 분석 방법론을 통해 장기적 관점에서 비교 분석한다. 또한, 제한된 자원 내에서 일부 사용자에게 최저 품질을 보장하는 pruning 알고리즘을 제시하고, 비디오 세션 전 기간 또는 일부 기간에 최적으로 서브 스트림을 분할할 수 있음을 보인다.

Resource allocation based on cross-layer QoS-guaranteed scheduling for multi-service multi-user MIMO–OFDMA systems

Cross-layer strategies for resource allocation in wireless networks are essential to guaranty an efficient utilization of the scarce resource. In this paper, we present an efficient radio resource allocation scheme based on PHY/MAC cross layer design and QoS-guaranteed scheduling for multi-user (MU), multi-service (MS), multi-input multi-output (MIMO) concept, orthogonal frequency division multiple access (OFDMA) systems. It is about a downlink multimedia transmission chain in which the available resources as power and bandwidth, are dynamically allocated according to the system parameters. Among these parameters, we can mention the physical link elements such as channel state information, spectral efficiency and error code corrector rate, and MAC link variables, which correspond to the users QoS requirements and the queue status. Primarily, we use a jointly method which parametrizes these system parameters, according to the total power, and the bit error rate constraints. Secondly, we propose a QoS-guaranteed scheduling that shares the sub-carriers to the users. These users request several type of traffic under throughput threshold constraints. The main objective in this work is to adjust the average throughput per service of each user, according to their needs and likewise to satisfy a great number of connexions. Subsequently, we consider a model of moderated compartmentalization between various classes of services by partitioning the total bandwidth into several parts. Each class of service will occupy a part of the bandwidth and will be transmitted over a maximum number of sub-carriers. The simulation results show that the proposed strategy provides a more interesting performance improvement (in terms of average data rate and user satisfaction) than other existing resource allocation schemes, such as nonadaptive resource allocation strategy. The performances are also analyzed and compared for the two multi-service multi-user MIMO---OFDMA systems; with sub-carriers partitioning and without sub-carriers partitioning.

Iterative MMSE equalization and CFO compensation for the uplink SC‐FDMA transmission

SummarySingle‐carrier frequency division multiple access is greatly sensitive to carrier frequency offset (CFO) between transceivers. This leads to the destruction of orthogonality among subcarriers, which in turn leads to inter‐carrier interference and multiple access interference between different users. Minimum mean square error (MMSE) equalizer that uses an inverse operation on an interference matrix with a dimension equal to the number of subcarriers is normally used to invalidate CFO effects. Hence, the terminal processing complexity is very high. The proposed conjugate gradient method attempts to mitigate the higher computational complexity by iteratively evaluating the MMSE solution without direct matrix inverse operation. To further mitigate the multiple access interference, MMSE combined with parallel interference cancellation is also implemented. The analysis of the proposed method shows better performance and fast convergence in single‐carrier frequency division multiple access systems. The maximum iteration number to formulate an accurate solution is almost equal to the number of active users in the uplink access. Simulation results bring out the effectiveness of the present method compared with the existing CFO compensation schemes in terms of computational complication and system performance with large frequency offsets. Copyright © 2016 John Wiley & Sons, Ltd.

AFD-DFE using Constraint-Based RLS and Phase Noise Compensation for Uplink SC-FDMA

In this paper, we develop a constraint-based block recursive least-squares (CRLS) for an adaptive frequency-domain decision feedback equalizer (AFD-DFE) in uplink single-carrier frequency division multiple access systems. For the AFD-DFE, both the feedforward and feedback filters are implemented in the frequency domain; therefore, the CRLS complexity can be reduced substantially when compared to its time-domain counterpart by exploiting the matrix structure in the frequency domain. The performance of the CRLS algorithm is better than that of the RLS when applied to the AFD-DFE, with no increase in the computational complexity. Our designed AFD-DFE with CRLS not only enjoys a lower computational complexity when compared to the frequency-domain channel-estimate-based minimum mean square error DFE (MMSE DFE), but its performance is also better than that of the MMSE DFE with decision errors (practical case) and is close to the MMSE DFE with correct decisions (ideal case). Moreover, we iteratively compensate the transmitter and receiver phase noise using its properties in the time and frequency domains. Simulation results demonstrate the robustness of our designed AFD-DFE using CRLS.

Subcarrier Allocation and Precoder Design for Energy Efficient MIMO-OFDMA Downlink Systems

This paper studies the subcarrier allocation and precoder design problem for downlink multiple-input-multiple-output-orthogonal frequency-division multiple access systems. The criterion is to maximize the energy efficiency (EE) of the system. We adopt the time-sharing concept to allocate each subcarrier to one user, which results in a criterion similar with that of rate maximization. However, this approach does not make it possible to solve the problem for any value of the transmit power. We found that there exist gaps along the direction of total transmit power when the user selection switches for each subcarrier, which leads to a discontinuous EE function, for which quasi-concavity has to be checked. We first show that the sufficient conditions obtained for the subcarrier allocation approach are the optimal ones among all possibilities with the same transmit power. Then, we show that the proposed subcarrier allocation results in a discontinuous and quasi-concave EE function. We also give an upper bound of the EE function when the proposed sufficient conditions are not met. Finally, we propose an algorithm to find the maximal EE and its performance is illustrated by means of numerical results.

A New Swap-Based Frequency-Domain Packet Scheduling Algorithm in OFDMA System with Data Queue Size Constraints

This paper aims at the frequency-domain packet scheduling (FDPS) problem in orthogonal frequency division multiple access (OFDMA) system. Under users’ data queue size constraints, a new swap-based FDPS algorithm is proposed to achieve further improvement in system throughput. In this algorithm, the swap of physical resource blocks (PRBs) between different users is introduced to give a comprehensive view of the overall scheduling process. Moreover, the proposed algorithm optimizes the choosing method of swap candidates and always tries to select the user who can maximize the throughput improvement. Simulation results demonstrate that this new algorithm can improve the system throughput significantly as well as reduce the resource waste effectively.

Power allocation for uplink SC‐FDMA systems with arbitrary input distribution

Existing power allocation schemes for single-carrier frequency division multiple access (SC-FDMA) systems are based on the assumption of Gaussian inputs. However, in practical systems, the inputs belong to a set of finite symbol alphabets. In this reported work the power allocation problem in the uplink SC-FDMA system with arbitrarily distributed finite power inputs is considered. An optimal solution to the problem is found by using the relationship between minimum mean-square error and mutual information. Simulation results show that solution allocates power in accordance to the modulation scheme employed and achieves significant power saving compared to schemes that assume Gaussian inputs.

Coordinated Scheduling Algorithm for System Utility Maximization With Heterogeneous QoS Requirements in Wireless Relay Networks

In this paper, we focus on the radio resource management (RRM) issues in the two-hop Orthogonal Frequency Division Multiple Access (OFDMA) system with heterogeneous quality of service (QoS) requirements. To solve the RRM problem, we first propose a new two-hop frame structure to support the data relay operation from the base station to the relay station and cooperative transmission for the edge users. Then, a two-hop coordinated scheduling algorithm is proposed, which utilizes the proposed two-hop frame structure and considers the corresponding interference status. The proposed two-hop coordinated scheduling algorithm solves the RRM problem of the two-hop OFDMA system with heterogeneous QoS requirements in an iterative manner, and so maximizes the system utility.

Joint User Scheduling and MU-MIMO Hybrid Beamforming Algorithm for mmWave FDMA Massive MIMO System

The large bandwidth and multipath in millimeter wave (mmWave) cellular system assure the existence of frequency selective channels; it is necessary that mmWave system remains with frequency division multiple access (FDMA) and user scheduling. But for the hybrid beamforming system, the analog beamforming is implemented by the same phase shifts in the entire frequency band, and the wideband phase shifts may not be harmonious with all users scheduled in frequency resources. This paper proposes a joint user scheduling and multiuser hybrid beamforming algorithm for downlink massive multiple input multiple output (MIMO) orthogonal frequency division multiple access (OFDMA) systems. In the first step of user scheduling, the users with identical optimal beams form an OFDMA user group and multiplex the entire frequency resource. Then base station (BS) allocates the frequency resources for each member of OFDMA user group. An OFDMA user group can be regarded as a virtual user; thus it can support arbitrary MU-MIMO user selection and beamforming algorithms. Further, the analog beamforming vectors employ the best beam of each selected MU-MIMO user and the digital beamforming algorithm is solved by weight MMSE to acquire the best performance gain and mitigate the interuser inference. Simulation results show that hybrid beamforming together with user scheduling can greatly improve the performance of mmWave OFDMA massive MU-MIMO system.