To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios,this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal...To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios,this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal frequency division multiple access(OFDMA)and non-orthogonal multiple access(NOMA).The idea of this protocol is that OFMDA is used to divide the entire frequency field into multiple orthogonal resource units(RUs),and NOMA is used on each RU to enable more users to access the channel and improve spectrum efficiency.Based on the protocol designed in this paper,in the case of imperfect successive interference cancellation(SIC),the probability of successful competition subchannels and the outage probability are derived for two scenarios:Users occupy the subchannel individually and users share the subchannel.Moreover,when two users share the channel,the decoding order of the users and the corresponding probabilities are considered.Then,the system throughput is obtained.To achieve better outage performance in the system,the optimal power allocation algorithm is proposed in this paper,which enables the optimal power allocation strategy to be obtained.Numerical results show that the larger the imperfect SIC coefficient,the worse the outage performance of weak users.Compared with pure OFDMA and NOMA,OFDMA-NOMA-RA always maintains an advantage when the imperfect SIC coefficient is less than a specific value.展开更多
A non-cooperative game is proposed to perform the sub-carrier assignment and power allocation for the multi-cell orthogonal frequency division multiple access(OFDMA) system.The objective is to raise the spectral eff...A non-cooperative game is proposed to perform the sub-carrier assignment and power allocation for the multi-cell orthogonal frequency division multiple access(OFDMA) system.The objective is to raise the spectral efficiency of the system and prolong the life time of user nodes.This paper defines a game player as a cell formed by the unique base station and the served users.The utility function considered here measures the user's achieved utility per power.Each individual cell's goal is to maximize the total utility of its users.To search the Nash equilibrium(NE) of the game,an iterative and distributed algorithm is presented.Since the NE is inefficient,the pricing of user's transmission power is introduced to improve the NE in the Pareto sense.Simulation results show the proposed game outperforms the water-filling algorithm in terms of fairness and energy efficiency.Moreover,through employing a liner pricing function,the energy efficiency could be further improved.展开更多
In this paper, the 40-Gbps orthogonal frequency division multiple access(OFDMA) technology enabled by subcarrier allocation in the form of integrated architecture for the intra-cell is proposed in the downlink transmi...In this paper, the 40-Gbps orthogonal frequency division multiple access(OFDMA) technology enabled by subcarrier allocation in the form of integrated architecture for the intra-cell is proposed in the downlink transmission passive broadband optical access system. The data-carrying subcarriers in the inverse fast Fourier transform/fast Fourier transform(IFFT/FFT) size of1 024 points are successfully divided into three sub-channels,in which each sub-channel has 256 useful subcarriers, by using adaptive dynamic bandwidth allocation(DBA). Taking the inherent advantages of M-ary quadrature amplitude modulation(MQAM)modulation mechanism into account, the performance of the absolutely identical MQAM format over the different sub-channels for the downstream OFDMA-passive optical network(PON) is investigated based on the intensity modulation direct detection(IMDD) system by simulations. The results show that three parallel4 QAM or 16 QAM or 64 QAM OFDMA data, which are transmitted over three sub-channels, is more suitable for different sub-channel allocations, respectively. In addition, comparing with single port4/16/64 QAM OFDM over the same access system, the receiver sensitivity economizes – 0.6 d Bm, 0.6 d Bm, 4.6 d Bm at the bit error rate(BER) value of 10-3 respectively.展开更多
Call Admission Control (CAC) is one of the key traffic management mechanisms that must be deployed in order to meet the strict requirements for dependability imposed on the services provided by modern wireless network...Call Admission Control (CAC) is one of the key traffic management mechanisms that must be deployed in order to meet the strict requirements for dependability imposed on the services provided by modern wireless networks. In this paper, we develop an executable top-down hierarchical Colored Petri Net (CPN) model for multi-traffic CAC in Orthogonal Frequency Division Multiple Access (OFDMA) system. By theoretic analysis and CPN simulation, it is demonstrated that the CPN model is isomorphic to Markov Chain (MC) assuming that each data stream follows Poisson distribution and the corresponding arrival time interval is an exponential random variable, and it breaks through MC's explicit limitation, which includes MC's memoryless property and proneness to state space explosion in evaluating CAC process. Moreover, we present four CAC schemes based on CPN model taking into account call-level and packet-level Quality of Service (QoS). The simulation results show that CPN offers significant advantages over MC in modeling CAC strategies and evaluating their performance with less computational complexity in addition to its flexibility and adaptability to different scenarios.展开更多
A system model based on joint layer mechanism is formulated for optimal data scheduling over fixed point-to-point links in OFDMA ad-hoc wireless networks. A distributed scheduling algorithm (DSA) for system model op...A system model based on joint layer mechanism is formulated for optimal data scheduling over fixed point-to-point links in OFDMA ad-hoc wireless networks. A distributed scheduling algorithm (DSA) for system model optimization is proposed that combines the randomly chosen subcarrier according to the channel condition of local subcarriers with link power control to limit interference caused by the reuse of subcarrier among links. For the global fairness improvement of algorithms, a global power control scheduling algorithm (GPCSA) based on the proposed DSA is presented and dynamically allocates global power according to difference between average carrier-noise-ratio of selected local links and system link protection ratio. Simulation results demonstrate that the proposed algorithms achieve better efficiency and fairness compared with other existing algorithms.展开更多
A resource allocation problem considering both efficiency and fairness in orthogonal frequency division multiple access (OFDMA) systems is studied. According to the optimality conditions, a downlink resource allocat...A resource allocation problem considering both efficiency and fairness in orthogonal frequency division multiple access (OFDMA) systems is studied. According to the optimality conditions, a downlink resource allocation algorithm consisting of subcarrier assignment and power alloca- tion is proposed. By adjusting the tradeoff coefficient, the proposed algorithm can achieve different levels of compromise between efficiency and fairness. The well-known classic resource allocation policies such as sum-rate maximization algorithm, proportional fairness algorithm and max-rain algorithm are all special cases of the proposed algorithm. Simulation results show that the compromise between efficiency and fairness can be continuously adjusted according to system requirements.展开更多
Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes includin...Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes including relay selection and resource allocation using hierarchical modulation (HM) to fully exploit the radio resources in cellular networks where user equipments (UEs) relay for each other.The relay selection procedure considers both the channel conditions and the energies left in relays to make the cooperative communications behave better.To mitigate the spectrum efficiency loss due to the half-duplex mode,the bits of relayaided UE and its relay (which is also a UE) are transmitted simultaneously in one sub-channel using HM to improve the utilization efficiency of sub-channels.Besides,time resources are used effectively with the adaptively changed proportion of the two sub-frames divided for relay transmission.Simulation results show that the proposed schemes can improve the spectrum efficiency compared with the traditional schemes.展开更多
To improve the total throughput of the uplink orthogonal frequency division multiple access system,a low complexity hybrid power distribution(HPD) combined with subcarrier allocation scheme is proposed.For the fairn...To improve the total throughput of the uplink orthogonal frequency division multiple access system,a low complexity hybrid power distribution(HPD) combined with subcarrier allocation scheme is proposed.For the fairness mechanism for the subcarrier,the inter-cell interference is first analyzed to calculate the capacity of the multi-cell.The user selects the subcarrier with the largest channel gain.Based on the above subcarrier allocation scheme,a new kind of HPD scheme is proposed,which adopts the waterfilling-power-distributed scheme and the equal-power-distributed scheme in the cell-boundary and the cellcenter,respectively.Simulation results show that compared with the waterfilling-power-distributed scheme in the whole cell,the proposed HPD scheme decreases the system complexity significantly,meanwhile its capacity is 2% higher than that of the equal-powerdistributed scheme over the same subcarrier allocation.展开更多
The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on m...The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on maximizing the system throughput and spectral efficiency.As the green radio is essential in 5G and future networks,the energy efficiency becomes the major concern.In this paper,we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes.Specifically,we employ the advanced multi-antenna technology in a multiple input-multiple output(MIMO)system.The first scheme is based on transmit spatial diversity(TSD),in which the vector channel with the highest gain between the base station(BTS)and specific antenna at the remote terminal(RT)is chosen for transmission.The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput.The space-division multiple-access(SDMA)scheme assigns single subcarrier simultaneously to RTs with pairwise“nearly orthogonal”spatial signatures.In the fourth scheme,we propose to design the transmit beamformers based on the zero-forcing(ZF)criterion such that the multi-user interference(MUI)is completely removed.We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.展开更多
A quality of service(QoS) guaranteed cross-layer resource allocation algorithm with physical layer, medium access control(MAC) layer and call admission control(CAC) considered simultaneously is proposed for the ...A quality of service(QoS) guaranteed cross-layer resource allocation algorithm with physical layer, medium access control(MAC) layer and call admission control(CAC) considered simultaneously is proposed for the full IP orthogonal frequency division multiple access(OFDMA) communication system, which can ensure the quality of multimedia services in full IP networks.The algorithm converts the physical layer resources such as subcarriers, transmission power, and the QoS metrics into equivalent bandwidth which can be distributed by the base station in all three layers. By this means, the QoS requirements in terms of bit error rate(BER), transmission delay and dropping probability can be guaranteed by the cross-layer optimal equivalent bandwidth allocation. The numerical results show that the proposed algorithm has higher spectrum efficiency compared to the existing systems.展开更多
In this paper, we propose optimum and sub-optimum resource allocation and opportunistic scheduling solutions for orthogonal frequency division multiple access (OFDMA)-based multicellular systems. The applicability, ...In this paper, we propose optimum and sub-optimum resource allocation and opportunistic scheduling solutions for orthogonal frequency division multiple access (OFDMA)-based multicellular systems. The applicability, complexity, and performance of the proposed algorithms are analyzed and numerically evaluated. In the initial setup, the fractional frequency reuse (FFR) technique for inter-cell interference cancellation is applied to classify the users into two groups, namely interior and exterior users. Adaptive modulation is then employed according to the channel state information (CSI) of each user to meet the symbol error rate (SER) requirement. There then, we develop subcarrier-and-bit allocation method, which maximizes the total system throughput subject to the constraints that each user has a minimum data rate requirement. The algorithm to achieve the optimum solution requires high computational complexity which hinders it from practicability. Toward this suboptimum method with the reduced to the order of O(NIO, the total number of subcarriers end, we complexity propose a extensively where N and K denote and users, respectively. Numerical results show that the proposed algorithm approaches the optimum solution, yet it enjoys the features of simplicity, dynamic cell configuration, adaptive subearrier-and-bit allocation, and spectral efficiency.展开更多
This article presents downlink initial synchronization and cell identification algorithms for long term evolution (LTE) of third-generation (3G) mobile communication systems, which are based on synchronization cha...This article presents downlink initial synchronization and cell identification algorithms for long term evolution (LTE) of third-generation (3G) mobile communication systems, which are based on synchronization channel (SCH) and cell specific pilot symbols, respectively. The key features of the proposed scheme are: it can improve performance of the frequency synchronization through oversampling of the SCH, it can support a large number of target cells by modulating a cell-specific pilot sequence over two symbols within a subframe, and it can guarantee cell identification performance by maximally ratio combining the frequency domain differential cross-correlation. Simulations show that the proposed scheme has a potential use in 3G LTE.展开更多
This article studies the coarse flame synchronization of orthogonal frequency division multiplexing access-time division duplex (OFDMA-TDD) systems and proposes a new method to improve coarse frame synchronization p...This article studies the coarse flame synchronization of orthogonal frequency division multiplexing access-time division duplex (OFDMA-TDD) systems and proposes a new method to improve coarse frame synchronization performance. The new method utilizes the user equipment to user equipment (UE-UE) interference, which is usually considered as a specific challenge for time division duplex (TDD) and also as implicit frame boundary information to enhance coarse frame synchronization performance. Numerical results show the synchronization performance is imoroved bv the new method.展开更多
Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observation...Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observations,it is preferable to formulate PPP-RTK functional models based on original(undiferenced and uncombined)observations.While there exist many variants of the undiferenced and uncombined PPP–RTK models,a unifed theoretical framework needs developing to link these variants.In this contribution,we formulate a class of undiferenced and uncombined PPP-RTK functional models in a systematic way and cast them in a unifed framework.This framework classifes the models into a code-plus-phase category and a phase-only category.Each category covers a variety of measurement scenarios on the network side,ranging from small-,medium-to large-scale networks.For each scenario,special care has been taken of the distinct ionospheric constraints and the diference between Code Division Multiple Access(CDMA)and Frequency Division Multiple Access(FDMA)signals.The key to systematically formulating these models lies in how to deal with the rank defciency problems encountered.We opt for the Singularity-basis(S-basis)theory,giving rise to the full-rank observation equations in which the estimable parameters turn out to be the functions of original parameters and those selected as the S-basis.In the sequel,it becomes straightforward to derive for each scenario the user model as it,more or less,amounts to the single-receiver network model.Benefting from the presented theoretical framework,the relationships and diferences between various undiferenced and uncombined PPP-RTK models become clear,which can lead to the better use of these models in a specifc situation.展开更多
This paper describes an optimal power allocation scheme for orthogonal frequency division multiple access two-way relay networks with physical network coding. The aim is to enhance the achievable sum rate of the termi...This paper describes an optimal power allocation scheme for orthogonal frequency division multiple access two-way relay networks with physical network coding. The aim is to enhance the achievable sum rate of the terminals for a constrained total transmit power. Convex optimization is used to derive a closed-form solution for the power allocation between the relay node and the two terminals. This reduces the variable dimensionality of the objective function for the power assignment problem among multiple carriers when the total transmit power is constrained. This solution is then used to derive the optimal power control scheme. This method reduces the implementation complexity compared with the traditional resource allocation scheme. Numerical and simulation results show that the approach achieves almost the optimal sum rate and outperforms the fixed power assignment method with less computational load in various scenarios.展开更多
This paper presents an in-depth analysis of the interference strength and required guardband width between coexistent users for distributed orthogonal frequency division multiple access (OFDMA). In dynamic spectrum ...This paper presents an in-depth analysis of the interference strength and required guardband width between coexistent users for distributed orthogonal frequency division multiple access (OFDMA). In dynamic spectrum access networks, the cross-band interference between spectrally adjacent users is considered harmful with frequency guardbands inserted between spectrum blocks to eliminate the interference. However, the strength of the cross-band interference depends heavily on the user heterogeneity in different OFDM configurations. The cross-band interference due to the three user heterogeneity artifacts of power heterogeneity, sampling rate heterogeneity, and symbol length heterogeneity is investigated to determine the required guardband width. Analytical and simulation results show that the greater user heterogeneity requires larger guardbands with the sampling rate heterogeneity having the greatest effect. These results can be used to assist the design of spectrum allocation strategies.展开更多
A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first ob- tained based ...A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first ob- tained based on the received training signals at each user's prescribed subcarder positions. Then, the re- ceived training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were used to reliably estimate each user's CFO. The CFO estimator performance was evaluated by the bit error rate per- formances of the CFO compensation-based receivers at the base station. Simulations show that with this optima CFO compensation receiver, the performance gain with the esti- mated CFO values is approximately 3 dB better at the 0.1% bit error rate than the initial CFO estimates.展开更多
Efficient radio resource allocation is essential to provide quality of service (QoS) for wireless networks. In this article, a cross-layer resource allocation scheme is presented with the objective of maximizing sys...Efficient radio resource allocation is essential to provide quality of service (QoS) for wireless networks. In this article, a cross-layer resource allocation scheme is presented with the objective of maximizing system throughput, while providing guaranteed QoS for users. With the assumption of a finite queue for arrival packets, the proposed scheme dynamically a/locates radio resources based on user's channel characteristic and QoS metrics derived from a queuing model, which considers a packet arrival process modeled by discrete Markov modulated Poisson process (dMMPP), and a multirate transmission scheme achieved through adaptive modulation. The cross-layer resource allocation scheme operates over two steps. Specifically, the amount of bandwidth allocated to each user is first derived from a queuing analytical model, and then the algorithm finds the best subcarrier assignment for users. Simulation results show that the proposed scheme maximizes the system throughput while guaranteeing QoS for users.展开更多
Distributed multipoint systems (DMS) are important and timely for the move to future broadband wireless communication systems. Traditional studies on DMS have mainly focused on the issues with the spatial division m...Distributed multipoint systems (DMS) are important and timely for the move to future broadband wireless communication systems. Traditional studies on DMS have mainly focused on the issues with the spatial division multiple access such as precoding techniques, which only consider a narrowband case. This paper addresses the downlink radio resource management of the orthogonal frequency division multiple access DMS (OFDMA-DMS), including power allocation between users or subcarriers, and distributed antenna selection. Signal models with incoherent and coherent transmitters are built. To maximize the system throughput, for the incoherent transmitter case, a strategy based on the iterative water-filling power allocation is proposed to approach the optimality. As for the coherent case, where coherent additions of the signal could occur at the users, the problem is transformed into an integer programming which is solvable. Numerical results show that the gain from the coherent transmitter is promising. And to achieve a near-optimal solution, only part of the DA ports will be used, which have better channel conditions.展开更多
This paper reports an investigation of the carrier frequency offset (CFO) compensation in the uplink of the orthogonal frequency division multiple access (OFDMA) system with interleaved subcarrier assignment. The ...This paper reports an investigation of the carrier frequency offset (CFO) compensation in the uplink of the orthogonal frequency division multiple access (OFDMA) system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.展开更多
基金funded in part by the National Natural Science Foundation of China under Grant 61663024in part by the Hongliu First Class Discipline Development Project of Lanzhou University of Technology(25-225305).
文摘To address the problems of network congestion and spectrum resources shortage in multi-user large-scale scenarios,this paper proposes a twice random access OFDMA-NOMA-RA protocol combining the advantages of orthogonal frequency division multiple access(OFDMA)and non-orthogonal multiple access(NOMA).The idea of this protocol is that OFMDA is used to divide the entire frequency field into multiple orthogonal resource units(RUs),and NOMA is used on each RU to enable more users to access the channel and improve spectrum efficiency.Based on the protocol designed in this paper,in the case of imperfect successive interference cancellation(SIC),the probability of successful competition subchannels and the outage probability are derived for two scenarios:Users occupy the subchannel individually and users share the subchannel.Moreover,when two users share the channel,the decoding order of the users and the corresponding probabilities are considered.Then,the system throughput is obtained.To achieve better outage performance in the system,the optimal power allocation algorithm is proposed in this paper,which enables the optimal power allocation strategy to be obtained.Numerical results show that the larger the imperfect SIC coefficient,the worse the outage performance of weak users.Compared with pure OFDMA and NOMA,OFDMA-NOMA-RA always maintains an advantage when the imperfect SIC coefficient is less than a specific value.
基金supported by the National Natural Science Foundation of China(60972059)the Fundamental Research Funds for the Central Universities of China(2010QNA27)+2 种基金China Postdoctoral Science Foundation(20100481185)the Ph.D.Programs Foundation of Ministry of Education of China(20090095120013)the Talent Introduction Program and Young Teacher Sailing Program of China University of Mining and Technology
文摘A non-cooperative game is proposed to perform the sub-carrier assignment and power allocation for the multi-cell orthogonal frequency division multiple access(OFDMA) system.The objective is to raise the spectral efficiency of the system and prolong the life time of user nodes.This paper defines a game player as a cell formed by the unique base station and the served users.The utility function considered here measures the user's achieved utility per power.Each individual cell's goal is to maximize the total utility of its users.To search the Nash equilibrium(NE) of the game,an iterative and distributed algorithm is presented.Since the NE is inefficient,the pricing of user's transmission power is introduced to improve the NE in the Pareto sense.Simulation results show the proposed game outperforms the water-filling algorithm in terms of fairness and energy efficiency.Moreover,through employing a liner pricing function,the energy efficiency could be further improved.
基金supported by the National Natural Science Foundation of China(61771082 61801065+3 种基金 61871062)the China Scholarship Council(201908500139)the Science and Technology Research Program of Chongqing Municipal Education Commission(KJQN201800615KJQN201800609)
文摘In this paper, the 40-Gbps orthogonal frequency division multiple access(OFDMA) technology enabled by subcarrier allocation in the form of integrated architecture for the intra-cell is proposed in the downlink transmission passive broadband optical access system. The data-carrying subcarriers in the inverse fast Fourier transform/fast Fourier transform(IFFT/FFT) size of1 024 points are successfully divided into three sub-channels,in which each sub-channel has 256 useful subcarriers, by using adaptive dynamic bandwidth allocation(DBA). Taking the inherent advantages of M-ary quadrature amplitude modulation(MQAM)modulation mechanism into account, the performance of the absolutely identical MQAM format over the different sub-channels for the downstream OFDMA-passive optical network(PON) is investigated based on the intensity modulation direct detection(IMDD) system by simulations. The results show that three parallel4 QAM or 16 QAM or 64 QAM OFDMA data, which are transmitted over three sub-channels, is more suitable for different sub-channel allocations, respectively. In addition, comparing with single port4/16/64 QAM OFDM over the same access system, the receiver sensitivity economizes – 0.6 d Bm, 0.6 d Bm, 4.6 d Bm at the bit error rate(BER) value of 10-3 respectively.
基金Supported by the National Natural Science Foundation of China (No. 61271421)the Education Department of Henan Province (No. 2011GGJS-002 and No. 12A510023)
文摘Call Admission Control (CAC) is one of the key traffic management mechanisms that must be deployed in order to meet the strict requirements for dependability imposed on the services provided by modern wireless networks. In this paper, we develop an executable top-down hierarchical Colored Petri Net (CPN) model for multi-traffic CAC in Orthogonal Frequency Division Multiple Access (OFDMA) system. By theoretic analysis and CPN simulation, it is demonstrated that the CPN model is isomorphic to Markov Chain (MC) assuming that each data stream follows Poisson distribution and the corresponding arrival time interval is an exponential random variable, and it breaks through MC's explicit limitation, which includes MC's memoryless property and proneness to state space explosion in evaluating CAC process. Moreover, we present four CAC schemes based on CPN model taking into account call-level and packet-level Quality of Service (QoS). The simulation results show that CPN offers significant advantages over MC in modeling CAC strategies and evaluating their performance with less computational complexity in addition to its flexibility and adaptability to different scenarios.
文摘A system model based on joint layer mechanism is formulated for optimal data scheduling over fixed point-to-point links in OFDMA ad-hoc wireless networks. A distributed scheduling algorithm (DSA) for system model optimization is proposed that combines the randomly chosen subcarrier according to the channel condition of local subcarriers with link power control to limit interference caused by the reuse of subcarrier among links. For the global fairness improvement of algorithms, a global power control scheduling algorithm (GPCSA) based on the proposed DSA is presented and dynamically allocates global power according to difference between average carrier-noise-ratio of selected local links and system link protection ratio. Simulation results demonstrate that the proposed algorithms achieve better efficiency and fairness compared with other existing algorithms.
文摘A resource allocation problem considering both efficiency and fairness in orthogonal frequency division multiple access (OFDMA) systems is studied. According to the optimality conditions, a downlink resource allocation algorithm consisting of subcarrier assignment and power alloca- tion is proposed. By adjusting the tradeoff coefficient, the proposed algorithm can achieve different levels of compromise between efficiency and fairness. The well-known classic resource allocation policies such as sum-rate maximization algorithm, proportional fairness algorithm and max-rain algorithm are all special cases of the proposed algorithm. Simulation results show that the compromise between efficiency and fairness can be continuously adjusted according to system requirements.
基金Sponsored by the National Natural Science Foundation of China(Grant No.60832009)Beijing National Sciences Foundation(Grant No.4102044)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.BUPT2009RC0119)the National Hi-Tech Research and Development Programof China(863Program)(Grant No.2009AA01Z246)
文摘Cooperative transmission is a promising way to improve system performance in orthogonal frequency division multiple access (OFDMA) based cellular networks.This paper proposes two heuristic cooperation schemes including relay selection and resource allocation using hierarchical modulation (HM) to fully exploit the radio resources in cellular networks where user equipments (UEs) relay for each other.The relay selection procedure considers both the channel conditions and the energies left in relays to make the cooperative communications behave better.To mitigate the spectrum efficiency loss due to the half-duplex mode,the bits of relayaided UE and its relay (which is also a UE) are transmitted simultaneously in one sub-channel using HM to improve the utilization efficiency of sub-channels.Besides,time resources are used effectively with the adaptively changed proportion of the two sub-frames divided for relay transmission.Simulation results show that the proposed schemes can improve the spectrum efficiency compared with the traditional schemes.
基金supported by the National Basic Research Programof China (973 Program) (2007CB310601)the Major Science-Technology Project of Next Generation Wireless Mobile Communication Network (2009ZX03004-001)
文摘To improve the total throughput of the uplink orthogonal frequency division multiple access system,a low complexity hybrid power distribution(HPD) combined with subcarrier allocation scheme is proposed.For the fairness mechanism for the subcarrier,the inter-cell interference is first analyzed to calculate the capacity of the multi-cell.The user selects the subcarrier with the largest channel gain.Based on the above subcarrier allocation scheme,a new kind of HPD scheme is proposed,which adopts the waterfilling-power-distributed scheme and the equal-power-distributed scheme in the cell-boundary and the cellcenter,respectively.Simulation results show that compared with the waterfilling-power-distributed scheme in the whole cell,the proposed HPD scheme decreases the system complexity significantly,meanwhile its capacity is 2% higher than that of the equal-powerdistributed scheme over the same subcarrier allocation.
文摘The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on maximizing the system throughput and spectral efficiency.As the green radio is essential in 5G and future networks,the energy efficiency becomes the major concern.In this paper,we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes.Specifically,we employ the advanced multi-antenna technology in a multiple input-multiple output(MIMO)system.The first scheme is based on transmit spatial diversity(TSD),in which the vector channel with the highest gain between the base station(BTS)and specific antenna at the remote terminal(RT)is chosen for transmission.The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput.The space-division multiple-access(SDMA)scheme assigns single subcarrier simultaneously to RTs with pairwise“nearly orthogonal”spatial signatures.In the fourth scheme,we propose to design the transmit beamformers based on the zero-forcing(ZF)criterion such that the multi-user interference(MUI)is completely removed.We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.
基金supported by the National Natural Science Foundation of China(61271235)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions-Information and Communication Engineering
文摘A quality of service(QoS) guaranteed cross-layer resource allocation algorithm with physical layer, medium access control(MAC) layer and call admission control(CAC) considered simultaneously is proposed for the full IP orthogonal frequency division multiple access(OFDMA) communication system, which can ensure the quality of multimedia services in full IP networks.The algorithm converts the physical layer resources such as subcarriers, transmission power, and the QoS metrics into equivalent bandwidth which can be distributed by the base station in all three layers. By this means, the QoS requirements in terms of bit error rate(BER), transmission delay and dropping probability can be guaranteed by the cross-layer optimal equivalent bandwidth allocation. The numerical results show that the proposed algorithm has higher spectrum efficiency compared to the existing systems.
文摘In this paper, we propose optimum and sub-optimum resource allocation and opportunistic scheduling solutions for orthogonal frequency division multiple access (OFDMA)-based multicellular systems. The applicability, complexity, and performance of the proposed algorithms are analyzed and numerically evaluated. In the initial setup, the fractional frequency reuse (FFR) technique for inter-cell interference cancellation is applied to classify the users into two groups, namely interior and exterior users. Adaptive modulation is then employed according to the channel state information (CSI) of each user to meet the symbol error rate (SER) requirement. There then, we develop subcarrier-and-bit allocation method, which maximizes the total system throughput subject to the constraints that each user has a minimum data rate requirement. The algorithm to achieve the optimum solution requires high computational complexity which hinders it from practicability. Toward this suboptimum method with the reduced to the order of O(NIO, the total number of subcarriers end, we complexity propose a extensively where N and K denote and users, respectively. Numerical results show that the proposed algorithm approaches the optimum solution, yet it enjoys the features of simplicity, dynamic cell configuration, adaptive subearrier-and-bit allocation, and spectral efficiency.
基金the Cooperative Research between Beijing University of Posts and Telecommunications and TD Tech Ltd. and the National Natural Science Foundation of China (60302025).
文摘This article presents downlink initial synchronization and cell identification algorithms for long term evolution (LTE) of third-generation (3G) mobile communication systems, which are based on synchronization channel (SCH) and cell specific pilot symbols, respectively. The key features of the proposed scheme are: it can improve performance of the frequency synchronization through oversampling of the SCH, it can support a large number of target cells by modulating a cell-specific pilot sequence over two symbols within a subframe, and it can guarantee cell identification performance by maximally ratio combining the frequency domain differential cross-correlation. Simulations show that the proposed scheme has a potential use in 3G LTE.
文摘This article studies the coarse flame synchronization of orthogonal frequency division multiplexing access-time division duplex (OFDMA-TDD) systems and proposes a new method to improve coarse frame synchronization performance. The new method utilizes the user equipment to user equipment (UE-UE) interference, which is usually considered as a specific challenge for time division duplex (TDD) and also as implicit frame boundary information to enhance coarse frame synchronization performance. Numerical results show the synchronization performance is imoroved bv the new method.
基金This work was partially funded by the National Natural Science Foundation of China(Grant Nos.41774042,42174034)the Key Research and Development Plan of Hubei Province(Grant No.2020BHB014)+1 种基金the Scientifc Instrument Developing Project of the Chinese Academy of Sciences(Grant No.YJKYYQ20190063)The frst author is supported by the CAS Pioneer Hundred Talents Program。
文摘Technique PPP-RTK combines the advantages of both the Precise Point Positioning(PPP)and the Real-Time Kinematic(RTK)positioning.With the emergence of multi-frequency Global Navigation Satellite System(GNSS)observations,it is preferable to formulate PPP-RTK functional models based on original(undiferenced and uncombined)observations.While there exist many variants of the undiferenced and uncombined PPP–RTK models,a unifed theoretical framework needs developing to link these variants.In this contribution,we formulate a class of undiferenced and uncombined PPP-RTK functional models in a systematic way and cast them in a unifed framework.This framework classifes the models into a code-plus-phase category and a phase-only category.Each category covers a variety of measurement scenarios on the network side,ranging from small-,medium-to large-scale networks.For each scenario,special care has been taken of the distinct ionospheric constraints and the diference between Code Division Multiple Access(CDMA)and Frequency Division Multiple Access(FDMA)signals.The key to systematically formulating these models lies in how to deal with the rank defciency problems encountered.We opt for the Singularity-basis(S-basis)theory,giving rise to the full-rank observation equations in which the estimable parameters turn out to be the functions of original parameters and those selected as the S-basis.In the sequel,it becomes straightforward to derive for each scenario the user model as it,more or less,amounts to the single-receiver network model.Benefting from the presented theoretical framework,the relationships and diferences between various undiferenced and uncombined PPP-RTK models become clear,which can lead to the better use of these models in a specifc situation.
基金Supported by the Fundamental Research Funds for the Central Universities (No. K50510010027)
文摘This paper describes an optimal power allocation scheme for orthogonal frequency division multiple access two-way relay networks with physical network coding. The aim is to enhance the achievable sum rate of the terminals for a constrained total transmit power. Convex optimization is used to derive a closed-form solution for the power allocation between the relay node and the two terminals. This reduces the variable dimensionality of the objective function for the power assignment problem among multiple carriers when the total transmit power is constrained. This solution is then used to derive the optimal power control scheme. This method reduces the implementation complexity compared with the traditional resource allocation scheme. Numerical and simulation results show that the approach achieves almost the optimal sum rate and outperforms the fixed power assignment method with less computational load in various scenarios.
基金Supported in part by the National High-Tech Research and Development (863) Program of China(Nos. 2006AA10Z261,2006AA10A301,and 2007AA100408)
文摘This paper presents an in-depth analysis of the interference strength and required guardband width between coexistent users for distributed orthogonal frequency division multiple access (OFDMA). In dynamic spectrum access networks, the cross-band interference between spectrally adjacent users is considered harmful with frequency guardbands inserted between spectrum blocks to eliminate the interference. However, the strength of the cross-band interference depends heavily on the user heterogeneity in different OFDM configurations. The cross-band interference due to the three user heterogeneity artifacts of power heterogeneity, sampling rate heterogeneity, and symbol length heterogeneity is investigated to determine the required guardband width. Analytical and simulation results show that the greater user heterogeneity requires larger guardbands with the sampling rate heterogeneity having the greatest effect. These results can be used to assist the design of spectrum allocation strategies.
基金Supported by the National Key Basic Research and Development (973) Program of China (No. 2007CB310601)
文摘A carrier frequency offset (CFO) estimator was developed based on an interference cancellation scheme for an orthogonal frequency division multiplex access uplink. An initial CFO estimate was first ob- tained based on the received training signals at each user's prescribed subcarder positions. Then, the re- ceived training signals were compensated by using the initial CFO estimates in the frequency domain and the multi-user interferences were estimated. Finally, the interference-cancelled training signals were used to reliably estimate each user's CFO. The CFO estimator performance was evaluated by the bit error rate per- formances of the CFO compensation-based receivers at the base station. Simulations show that with this optima CFO compensation receiver, the performance gain with the esti- mated CFO values is approximately 3 dB better at the 0.1% bit error rate than the initial CFO estimates.
基金the National Natural Science Foundation of China (60632030)the Hi-Tech Research and Development Program of China (2006AA01Z283, 2006DFA11050)
文摘Efficient radio resource allocation is essential to provide quality of service (QoS) for wireless networks. In this article, a cross-layer resource allocation scheme is presented with the objective of maximizing system throughput, while providing guaranteed QoS for users. With the assumption of a finite queue for arrival packets, the proposed scheme dynamically a/locates radio resources based on user's channel characteristic and QoS metrics derived from a queuing model, which considers a packet arrival process modeled by discrete Markov modulated Poisson process (dMMPP), and a multirate transmission scheme achieved through adaptive modulation. The cross-layer resource allocation scheme operates over two steps. Specifically, the amount of bandwidth allocated to each user is first derived from a queuing analytical model, and then the algorithm finds the best subcarrier assignment for users. Simulation results show that the proposed scheme maximizes the system throughput while guaranteeing QoS for users.
基金supported by the Key Project (2009ZX03003-008-01)the National Natural Science Foundation of China (60772112)+2 种基金the Hi-Tech Research and Development Program of China (2009AA011802)the Beijing Science and Technology Committee (2007B053)the Program for NCET-10-0242 and Qualcomm Company
文摘Distributed multipoint systems (DMS) are important and timely for the move to future broadband wireless communication systems. Traditional studies on DMS have mainly focused on the issues with the spatial division multiple access such as precoding techniques, which only consider a narrowband case. This paper addresses the downlink radio resource management of the orthogonal frequency division multiple access DMS (OFDMA-DMS), including power allocation between users or subcarriers, and distributed antenna selection. Signal models with incoherent and coherent transmitters are built. To maximize the system throughput, for the incoherent transmitter case, a strategy based on the iterative water-filling power allocation is proposed to approach the optimality. As for the coherent case, where coherent additions of the signal could occur at the users, the problem is transformed into an integer programming which is solvable. Numerical results show that the gain from the coherent transmitter is promising. And to achieve a near-optimal solution, only part of the DA ports will be used, which have better channel conditions.
基金the Specialized Research Fund for the Doctoral Program of Higher Education,Ministry of Education,China (No. 20030003039)
文摘This paper reports an investigation of the carrier frequency offset (CFO) compensation in the uplink of the orthogonal frequency division multiple access (OFDMA) system with interleaved subcarrier assignment. The presence of CFOs between the transmitters and the uplink receiver will destroy the orthogonality among the different subcarriers, resulting in inter-carrier interference and multiuser interference. This paper proposes a pseudoinverse CFO compensation method based on the signal structure. The proposed method can compensate the CFOs of all users simultaneously and isolate the signals from all users at the same time. Compared with the existing CFO compensation methods, the new method provides a considerable signal-to-noise ratio gain on the bit error rate performance and has a relatively low implementation complexity.