Normally,in the downlink Network-Coded Multiple Access(NCMA)system,the same power is allocated to different users.However,equal power allocation is unsuitable for some scenarios,such as when user devices have differen...Normally,in the downlink Network-Coded Multiple Access(NCMA)system,the same power is allocated to different users.However,equal power allocation is unsuitable for some scenarios,such as when user devices have different Quality of Service(QoS)requirements.Hence,we study the power allocation in the downlink NCMA system in this paper,and propose a downlink Network-Coded Multiple Access with Diverse Power(NCMA-DP),wherein different amounts of power are allocated to different users.In terms of the Bit Error Rate(BER)of the multi-user decoder,and the number of packets required to correctly decode the message,the performance of the user with more allocated power is greatly improved compared to the Conventional NCMA(NCMA-C).Meanwhile,the performance of the user with less allocated power is still much better than NCMA-C.Furthermore,the overall throughput of NCMA-DP is greatly improved compared to that of NCMA-C.The simulation results demonstrate the remarkable performance of the proposed NCMA-DP.展开更多
Due to the limited uplink capability in heterogeneousnetworks (HetNets), the decoupled uplinkand downlink access (DUDA) mode has recently beenproposed to improve the uplink performance. In thispaper, the random discon...Due to the limited uplink capability in heterogeneousnetworks (HetNets), the decoupled uplinkand downlink access (DUDA) mode has recently beenproposed to improve the uplink performance. In thispaper, the random discontinuous transmission (DTX)at user equipment (UE) is adopted to reduce the interferencecorrelation across different time slots. By utilizingstochastic geometry, we analytically derive themean local delay and energy efficiency (EE) of an uplinkHetNet with UE random DTX scheme under theDUDA mode. These expressions are further approximatedas closed forms under reasonable assumptions.Our results reveal that under the DUDA mode, there isan optimal EE with respect to mute probability underthe finite local delay constraint. In addition, with thesame finite mean local delay as under the coupled uplinkand downlink access (CUDA) mode, the HetNetsunder the DUDA mode can achieve a higher EE witha lower mute probability.展开更多
Traditional cellular network requires that a user equipment(UE) should associate to the same base station(BS) in both the downlink(DL) and the uplink(UL). Based on dual connectivity(DC) introduced in LTE-Advanced R12,...Traditional cellular network requires that a user equipment(UE) should associate to the same base station(BS) in both the downlink(DL) and the uplink(UL). Based on dual connectivity(DC) introduced in LTE-Advanced R12, DL/UL decouple access scheme has been proposed, which is especially suitable for heterogeneous networks(Het Nets). This paper is the pioneer to take the DL/UL decouple access scheme into consideration and develop a novel resource allocation algorithm in a two-tier Het Net to improve the total system throughput in the UL and ease the load imbalance between macro base stations(MBSs) and pico base stations(PBSs). A model is formulated as a nonlinear integer programming, and the proposed algorithm is a sub-optimal algorithm based on the graph theory. First, an undirected and weighted interference graph is obtained. Next, the users are grouped to let users with large mutual interferences to be assigned to different clusters. Then, the users in different clusters are allocated to different resource blocks(RBs) by using the Hungarian algorithm. Simulation results show that the proposed algorithm can provide great promotions for both the total system throughput and the average cell edge user throughput and successfully ease the load imbalance between MBSs and PBSs.展开更多
Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influ...Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influence of natural wind pressure to analyze the stope face differential pressure, gob air leakage field distribution and gas migration regularity theoretically. Established a two-dimensional physical model with one source and one doab, and applied computational fluid dynamics analysis software Fluent to do numerical simulation, analyzed and contrasted to the areas of gob air leakage on size and gas emission from gob to working face on strength when using the downlink ventilation and uplink ventilation. When applied downward ventilation in stope face, the air leakage field of gob nearly working face, and the air leakage intensity were smaller than uplink, this can effectively reduce the gas emission from gob to working face; when used downlink ventilation, the air leakage airflow carry the lower amount of gas to doab than uplink ventilation, and more easily to mix the gas, reduced the possibility of gas accumulation in upper comer and the stratified flows, it can provide protection to mine with safe and effective production.展开更多
For logging while drilling(LWD)systems,it is necessary to adjust the working state of the downhole tools in real-time according to different operating conditions.In this paper,on the basis of the characteristics of LW...For logging while drilling(LWD)systems,it is necessary to adjust the working state of the downhole tools in real-time according to different operating conditions.In this paper,on the basis of the characteristics of LWD systems,a mud pressure-apperceived downlink system was examined.For the design of this system,a signal acquisition and processing board was created based on a piezoelectric ceramic sensor to acquire the mud pressure signal.The error sources of the downlink command sending process were analyzed,and an error accumulation compensation processing algorithm was proposed to improve the recognition success rate of the downhole system.Moreover,to reduce noise interference on the characteristics of the mud impulse signal,a fi ltering algorithm was proposed based on the empirical mode decomposition method,and the success rate of instruction issuance was determined by identifying feedback instructions.Field tests were conducted to further improve the system,the results of which suggested that the system had good mud adaptability,high recognition success rate,and a certain application value.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
Long Range Wide Area Network(LoRaWAN)has been developed to meet the requirements for the enormous device-to-device communication of Inter-net of Things(IoT)networks,which consist of a large number of participating dev...Long Range Wide Area Network(LoRaWAN)has been developed to meet the requirements for the enormous device-to-device communication of Inter-net of Things(IoT)networks,which consist of a large number of participating devices spread over large coverage areas with low data rates and low power con-sumption.It supports communications in both directions,uplink,and downlink directions.However,the downlink communication in the current LoRaWAN raises the bottleneck issue at gateways due to the used gateway selection algo-rithm.This paper proposes a novel gateway selection algorithm based on the duty cycle time-off values for the existing gateways,Duty Cycle Gateway Selection(DCGS),to direct acknowledgment packets as downlink traffic towards the most suitable gateway.Thus,the proposed system avoids subsequent retransmission of previously sent traffic that leads to excessive traffic overloading the network.The proposed system avoids exhausting a gateway duty cycle with downlink traffic by distributing the downlink traffic among available gateways based on the duty cycle time off.DCGS is evaluated using FloRa and INET frameworks in the well-known network simulator OMNeT++.The result shows the superior perfor-mance of the proposed approach over the existing Signal-to-Noise ratio(SNR)based selection mechanism.It clearly indicates that the DCGS maintains a better confirmed packet delivery rate while reducing number of retransmissions,colli-sions,and power consumption.展开更多
A full-duplex optical passive access scheme is proposed and verified by simulation, in which hybrid 64/16/4-quadrature amplitude modulation(64/16/4QAM) orthogonal frequency division multiplexing(OFDM) optical signal i...A full-duplex optical passive access scheme is proposed and verified by simulation, in which hybrid 64/16/4-quadrature amplitude modulation(64/16/4QAM) orthogonal frequency division multiplexing(OFDM) optical signal is for downstream transmission and non-return-to-zero(NRZ) optical signal is for upstream transmission. In view of the transmitting and receiving process for downlink optical signal, in-phase/quadrature-phase(I/Q) modulation based on Mach-Zehnder modulator(MZM) and homodyne coherent detection technology are employed, respectively. The simulation results show that the bit error ratio(BER) less than hardware decision forward error correction(HD-FEC) threshold is successfully obtained over transmission path with 20-km-long standard single mode fiber(SSMF) for hybrid downlink modulation OFDM optical signal. In addition, by dividing the system bandwidth into several subchannels consisting of some continuous subcarriers, it is convenient for users to select different channels depending on requirements of communication.展开更多
In this paper, the performance of a 60 GHz radio over fiber(Ro F) system with 4/16/64 quadrature amplitude modulation(QAM) orthogonal frequency division multiplexing(OFDM) downstream signals is studied. Delivery of 10...In this paper, the performance of a 60 GHz radio over fiber(Ro F) system with 4/16/64 quadrature amplitude modulation(QAM) orthogonal frequency division multiplexing(OFDM) downstream signals is studied. Delivery of 10 Gbit/s M-ary QAM(MQAM) OFDM signals through the 20-km-long single-mode fiber(SMF) is complicated in terms of intensity modulation and direct detection(IM/DD). Using self-homodyne method, the beating of two independent light waves generating the millimeter-wave at the photodetector can be down-converted to baseband in the electrical domain. Meanwhile, three kinds of sub-carrier arrangement schemes are compared and discussed, and the simulation results show that lower peak-to-average power ratio(PAPR) can be obtained adopting the adjacent scheme. At bit error rate(BER) of 10^(-3), the receiver sensitivity using 4QAM-OFDM sub-carrier signal is almost enhanced by 4 dB and 9 dB compared with those of 16 QAM-OFDM signal and 64 QAM-OFDM signal.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
A study on the zero-forcing beamforming （ZFBF） scheme with antenna selection at user terminals in downlink multi-antenna multi-user systems is presented. Simulation results show that the proposed ZFBF scheme with re...A study on the zero-forcing beamforming （ZFBF） scheme with antenna selection at user terminals in downlink multi-antenna multi-user systems is presented. Simulation results show that the proposed ZFBF scheme with receiver antenna selection （ZFBF-AS） achieves considerable throughput improvement over the ZFBF scheme with single receiver antenna. The results also show that, with multi-user diversity, the ZFBF-AS scheme approaches the throughput performance of the ZFBF scheme using all receiver antennas （ZFBF-WO-AS） when the base station adopts semi-orthogonal user selection （SUS） algorithm, and achieves larger throughput when the base station adopts the Round-robin scheduling algorithm. Compared with ZFBF-WO-AS, the proposed ZFBF-AS scheme can reduce the cost of user equipments and the channel state information requirement at the transmitter （CSIT） as well as the multiuser scheduling complexity at the transmitter.展开更多
This paper investigates the downlink capacity distribution and the outage probability of the interested area of maximum ratio transmission-selection combining(MRT-SC) scheme in the distributed antenna system(DAS).Comp...This paper investigates the downlink capacity distribution and the outage probability of the interested area of maximum ratio transmission-selection combining(MRT-SC) scheme in the distributed antenna system(DAS).Composite fading channels are assumed,which include path loss,lognormal shadowing and multi-path Rayleigh fading.Analytical approximations of the capacity's cumulative distribution function(CDF),the outage capacity,the mean capacity,and the outage probability of the interested area are derived by means of moment generation function(MGF) and Gauss-Hermite series expansion based approaches.The influence of antenna number,path loss exponent,and shadowing standard deviation on the capacity distribution are investigated.The simulation results agree with the analytical approximations well,and thus the analytical approximations are able to substitute the time-intensive Monte Carlo simulation for further investigation.展开更多
When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportu...When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportunities.Because of the assumptive prior knowledge about the time-frequency locations of primary downlinks and uplinks,this procedure is usually not considered in the design of cognitive radios.In this paper,a cooperative method is proposed for the downlink/uplink identification of time-division duplex-based orthogonal frequency-division multiple access systems.In this method,the power level of the primary link is extracted as the key feature,which also contributes to the subsequent cognitive behaviours.The effects of the primary and secondary systems and the effects of the detection parameters on the identification accuracy are all analysed in detail.The simulation results show that the proposed method can identify the primary links precisely and quickly with low complexity.展开更多
To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be rob...To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be robust to imperfect CSI.A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed.The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI.Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance.In addition,the effect of spatial correlation on the performance of the proposed algorithm is also simulated.展开更多
Long Term Evolution (LTE) Carrier Aggregation (CA) was introduced by the Release-10 3GPP specifications. CA allows aggregation of up to 5 cells for a terminal;both downlink (DL) CA and uplink (UL) CA are supported by ...Long Term Evolution (LTE) Carrier Aggregation (CA) was introduced by the Release-10 3GPP specifications. CA allows aggregation of up to 5 cells for a terminal;both downlink (DL) CA and uplink (UL) CA are supported by the 3GPP specifications. However, the first commercial deployments focus on the aggregation of two cells in the downlink. The benefits of LTE CA are increased terminal peak data rates, aggregation of fragmented spectrum and fast load balancing. In this paper, we analyze different strategies of DL scheduling for LTE CA including centralized, independent and distributed schedulers, we provide the corresponding simulation results considering UE data rate limitations and different traffic models. Also, we compare the performance of a single LTE carrier with LTE CA using the same total bandwidth.展开更多
This paper investigates a unmanned aerial vehicle(UAV)deployment problem in a non-orthogonal multiple access(NOMA)system,where the UAV is deployed as an aerial mobile base station to transmit data to two ground users....This paper investigates a unmanned aerial vehicle(UAV)deployment problem in a non-orthogonal multiple access(NOMA)system,where the UAV is deployed as an aerial mobile base station to transmit data to two ground users.An optimization problem is formulated by deploying the UAV for maximizing the sum rate of the two users.In order to solve the optimization problem,the feasible solution region is first reduced to a line segment between two users.Then,the optimization problem is simplified to a univariate problem,which can be solved by derivation under a certain situation,and the corresponding analytical solution is also provided.Moreover,a generalized algorithm,which considers 2 situations,is proposed to further determine the optimal UAV’s location.Specifically,four cases are discussed in the first situation.Extensive simulations are depicted to demonstrate effectiveness of the proposed algorithm and its superiority over the benchmarks in maximizing the two users’sum rate.展开更多
A robust scheme is proposed to jointly optimize transmit/receive beamformers for Mul-tiple Input Multiple Output(MIMO) downlinks where the available Channel State Information(CSI) at Base Station(BS)(CSIBS) is imperfe...A robust scheme is proposed to jointly optimize transmit/receive beamformers for Mul-tiple Input Multiple Output(MIMO) downlinks where the available Channel State Information(CSI) at Base Station(BS)(CSIBS) is imperfect.The criterion is to minimize the sum Mean Square Error(sum-MSE) over all users under a constraint on the total transmit power,which is a non-convex and non-linear problem.Observing from the first order optimization condition that the optimal trans-mit/receive beamformers are mutually dependent,the transmit/receive beamformers for each user are updated iteratively until the sum-MSE is minimized.Simulation results indicate that the proposed scheme can effectively mitigate the system performance loss induced by imperfect CSIBS.展开更多
The sum rate maximization beamforming problem for a multi-cell multi-user multiple-input single-output interference channel(MISO-IC)system is considered.Conventionally,the centralized and distributed beamforming solut...The sum rate maximization beamforming problem for a multi-cell multi-user multiple-input single-output interference channel(MISO-IC)system is considered.Conventionally,the centralized and distributed beamforming solutions to the MISO-IC system have high computational complexity and bear a heavy burden of channel state information exchange between base stations(BSs),which becomes even much worse in a large-scale antenna system.To address this,we propose a distributed deep reinforcement learning(DRL)based approach with lim⁃ited information exchange.Specifically,the original beamforming problem is decomposed of the problems of beam direction design and power allocation and the costs of information exchange between BSs are significantly reduced.In particular,each BS is provided with an inde⁃pendent deep deterministic policy gradient network that can learn to choose the beam direction scheme and simultaneously allocate power to users.Simulation results illustrate that the proposed DRL-based approach has comparable sum rate performance with much less information exchange over the conventional distributed beamforming solutions.展开更多
A novel scheme which can realize high-speed optical signals transmission and reception by using 4-pulsed amplitude modulation (4-PAM) and demodulation in 10 Gb/s passive optical access systems with different bandwidth...A novel scheme which can realize high-speed optical signals transmission and reception by using 4-pulsed amplitude modulation (4-PAM) and demodulation in 10 Gb/s passive optical access systems with different bandwidth optical Bessel filter (OBF) is introduced. In this scheme, a PAM sequence generator module, an M-ary pulse generator module and one Mach-Zehnder intensity Modulator (MZM) are employed for generating the 10 Gb/s optical 4-PAM signals. And then, the generated optical 4-PAM signal achieves transmission over 20 km single mode fiber (SMF) for downstream (DS) access links application. Finally, the optical 4-PAM signal after transmission is directly detected and demodulated. We measure time-domain sequential waveform curves, optical spectrum curves, and eye-diagrams, and analyze the receiver sensitivity of 10 Gb/s 4-PAM signals before and after transmission. The received performance of the optical 4-PAM signals after transmission over 20 km single mode fiber (SMF) with different bandwidth OBF has also been analyzed.展开更多
In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The prop...In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The proposed scheme uses the time-reversed version of the channel impulse responses （CIR） obtained from the transmitted signal at base uplink to pre-process the station. By exploiting the weak correlations of fading channels for different user ends （UE）, it is helpful to alleviate the multi-user interference （MUI） and co-channel interference （CCI）. Moreover, the application of the TR technique in a multiple input-single output （MISO） configuration can reduce the delay spread of the channel impulse response, and mitigate inter-symbol interference （ISI）. The UE can be simplified by canceling the iteration operation. Thus the data detection of the proposed scheme is rather simple as compared with the traditional IDMA, the complexity and computational load of UE is decreased substantially, and the proposed scheme provides a great deal of privacy and security to mobile users.展开更多
文摘Normally,in the downlink Network-Coded Multiple Access(NCMA)system,the same power is allocated to different users.However,equal power allocation is unsuitable for some scenarios,such as when user devices have different Quality of Service(QoS)requirements.Hence,we study the power allocation in the downlink NCMA system in this paper,and propose a downlink Network-Coded Multiple Access with Diverse Power(NCMA-DP),wherein different amounts of power are allocated to different users.In terms of the Bit Error Rate(BER)of the multi-user decoder,and the number of packets required to correctly decode the message,the performance of the user with more allocated power is greatly improved compared to the Conventional NCMA(NCMA-C).Meanwhile,the performance of the user with less allocated power is still much better than NCMA-C.Furthermore,the overall throughput of NCMA-DP is greatly improved compared to that of NCMA-C.The simulation results demonstrate the remarkable performance of the proposed NCMA-DP.
基金supported in part by the National Key R&D Program of China under Grant 2021YFB 2900304the Shenzhen Science and Technology Program under Grants KQTD20190929172545139 and ZDSYS20210623091808025.
文摘Due to the limited uplink capability in heterogeneousnetworks (HetNets), the decoupled uplinkand downlink access (DUDA) mode has recently beenproposed to improve the uplink performance. In thispaper, the random discontinuous transmission (DTX)at user equipment (UE) is adopted to reduce the interferencecorrelation across different time slots. By utilizingstochastic geometry, we analytically derive themean local delay and energy efficiency (EE) of an uplinkHetNet with UE random DTX scheme under theDUDA mode. These expressions are further approximatedas closed forms under reasonable assumptions.Our results reveal that under the DUDA mode, there isan optimal EE with respect to mute probability underthe finite local delay constraint. In addition, with thesame finite mean local delay as under the coupled uplinkand downlink access (CUDA) mode, the HetNetsunder the DUDA mode can achieve a higher EE witha lower mute probability.
基金supported by the National Natural Science Foundation General Program of China under Grant No.61171110the National Basic Research Program of China under Grant No.2013CB329003
文摘Traditional cellular network requires that a user equipment(UE) should associate to the same base station(BS) in both the downlink(DL) and the uplink(UL). Based on dual connectivity(DC) introduced in LTE-Advanced R12, DL/UL decouple access scheme has been proposed, which is especially suitable for heterogeneous networks(Het Nets). This paper is the pioneer to take the DL/UL decouple access scheme into consideration and develop a novel resource allocation algorithm in a two-tier Het Net to improve the total system throughput in the UL and ease the load imbalance between macro base stations(MBSs) and pico base stations(PBSs). A model is formulated as a nonlinear integer programming, and the proposed algorithm is a sub-optimal algorithm based on the graph theory. First, an undirected and weighted interference graph is obtained. Next, the users are grouped to let users with large mutual interferences to be assigned to different clusters. Then, the users in different clusters are allocated to different resource blocks(RBs) by using the Hungarian algorithm. Simulation results show that the proposed algorithm can provide great promotions for both the total system throughput and the average cell edge user throughput and successfully ease the load imbalance between MBSs and PBSs.
文摘Aiming at the issue that mass of gas emission from mining gob and the gas exceeded in working face, gob air leakage field and gas migration regularity in downlink ventilation was studied. In consideration of the influence of natural wind pressure to analyze the stope face differential pressure, gob air leakage field distribution and gas migration regularity theoretically. Established a two-dimensional physical model with one source and one doab, and applied computational fluid dynamics analysis software Fluent to do numerical simulation, analyzed and contrasted to the areas of gob air leakage on size and gas emission from gob to working face on strength when using the downlink ventilation and uplink ventilation. When applied downward ventilation in stope face, the air leakage field of gob nearly working face, and the air leakage intensity were smaller than uplink, this can effectively reduce the gas emission from gob to working face; when used downlink ventilation, the air leakage airflow carry the lower amount of gas to doab than uplink ventilation, and more easily to mix the gas, reduced the possibility of gas accumulation in upper comer and the stratified flows, it can provide protection to mine with safe and effective production.
文摘For logging while drilling(LWD)systems,it is necessary to adjust the working state of the downhole tools in real-time according to different operating conditions.In this paper,on the basis of the characteristics of LWD systems,a mud pressure-apperceived downlink system was examined.For the design of this system,a signal acquisition and processing board was created based on a piezoelectric ceramic sensor to acquire the mud pressure signal.The error sources of the downlink command sending process were analyzed,and an error accumulation compensation processing algorithm was proposed to improve the recognition success rate of the downhole system.Moreover,to reduce noise interference on the characteristics of the mud impulse signal,a fi ltering algorithm was proposed based on the empirical mode decomposition method,and the success rate of instruction issuance was determined by identifying feedback instructions.Field tests were conducted to further improve the system,the results of which suggested that the system had good mud adaptability,high recognition success rate,and a certain application value.
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supporting this work by Grant Code:(22UQU4331076DSR01).
文摘Long Range Wide Area Network(LoRaWAN)has been developed to meet the requirements for the enormous device-to-device communication of Inter-net of Things(IoT)networks,which consist of a large number of participating devices spread over large coverage areas with low data rates and low power con-sumption.It supports communications in both directions,uplink,and downlink directions.However,the downlink communication in the current LoRaWAN raises the bottleneck issue at gateways due to the used gateway selection algo-rithm.This paper proposes a novel gateway selection algorithm based on the duty cycle time-off values for the existing gateways,Duty Cycle Gateway Selection(DCGS),to direct acknowledgment packets as downlink traffic towards the most suitable gateway.Thus,the proposed system avoids subsequent retransmission of previously sent traffic that leads to excessive traffic overloading the network.The proposed system avoids exhausting a gateway duty cycle with downlink traffic by distributing the downlink traffic among available gateways based on the duty cycle time off.DCGS is evaluated using FloRa and INET frameworks in the well-known network simulator OMNeT++.The result shows the superior perfor-mance of the proposed approach over the existing Signal-to-Noise ratio(SNR)based selection mechanism.It clearly indicates that the DCGS maintains a better confirmed packet delivery rate while reducing number of retransmissions,colli-sions,and power consumption.
基金supported by the National Natural Science Foundation of China(No.61107064)the Chongqing University Innovation Team Founding(No.KJTD201320)the Chongqing Science and Technology Commission Foundation(No.cstc2016jcyjA 1233)
文摘A full-duplex optical passive access scheme is proposed and verified by simulation, in which hybrid 64/16/4-quadrature amplitude modulation(64/16/4QAM) orthogonal frequency division multiplexing(OFDM) optical signal is for downstream transmission and non-return-to-zero(NRZ) optical signal is for upstream transmission. In view of the transmitting and receiving process for downlink optical signal, in-phase/quadrature-phase(I/Q) modulation based on Mach-Zehnder modulator(MZM) and homodyne coherent detection technology are employed, respectively. The simulation results show that the bit error ratio(BER) less than hardware decision forward error correction(HD-FEC) threshold is successfully obtained over transmission path with 20-km-long standard single mode fiber(SSMF) for hybrid downlink modulation OFDM optical signal. In addition, by dividing the system bandwidth into several subchannels consisting of some continuous subcarriers, it is convenient for users to select different channels depending on requirements of communication.
基金supported by the National Natural Science Foundation of China(No.61107064)the Bayu Scholars Founding,the Chongqing University Innovation Team Founding(No.KJTD201320)+3 种基金the Chongqing Science and Technology Commission Foundation(Nos.cstc2014jcyj A40046,cstc2016jcyj A1233 and cstc2016jcyj A0246)the Chongqing 2011 Collaborative Innovation Center Project(Chongqing Education Department(2016)No.40)the Chongqing Graduate Scientific Research Innovation Project(Nos.CYS15225 and CYS16225)the Science and Technology Special Funds in Wanzhou District
文摘In this paper, the performance of a 60 GHz radio over fiber(Ro F) system with 4/16/64 quadrature amplitude modulation(QAM) orthogonal frequency division multiplexing(OFDM) downstream signals is studied. Delivery of 10 Gbit/s M-ary QAM(MQAM) OFDM signals through the 20-km-long single-mode fiber(SMF) is complicated in terms of intensity modulation and direct detection(IM/DD). Using self-homodyne method, the beating of two independent light waves generating the millimeter-wave at the photodetector can be down-converted to baseband in the electrical domain. Meanwhile, three kinds of sub-carrier arrangement schemes are compared and discussed, and the simulation results show that lower peak-to-average power ratio(PAPR) can be obtained adopting the adjacent scheme. At bit error rate(BER) of 10^(-3), the receiver sensitivity using 4QAM-OFDM sub-carrier signal is almost enhanced by 4 dB and 9 dB compared with those of 16 QAM-OFDM signal and 64 QAM-OFDM signal.
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supported by the National Natural Science Foundation of China (60496314)the National High Technology Research and Development Program of China (2006AA01Z266).
文摘A study on the zero-forcing beamforming （ZFBF） scheme with antenna selection at user terminals in downlink multi-antenna multi-user systems is presented. Simulation results show that the proposed ZFBF scheme with receiver antenna selection （ZFBF-AS） achieves considerable throughput improvement over the ZFBF scheme with single receiver antenna. The results also show that, with multi-user diversity, the ZFBF-AS scheme approaches the throughput performance of the ZFBF scheme using all receiver antennas （ZFBF-WO-AS） when the base station adopts semi-orthogonal user selection （SUS） algorithm, and achieves larger throughput when the base station adopts the Round-robin scheduling algorithm. Compared with ZFBF-WO-AS, the proposed ZFBF-AS scheme can reduce the cost of user equipments and the channel state information requirement at the transmitter （CSIT） as well as the multiuser scheduling complexity at the transmitter.
文摘This paper investigates the downlink capacity distribution and the outage probability of the interested area of maximum ratio transmission-selection combining(MRT-SC) scheme in the distributed antenna system(DAS).Composite fading channels are assumed,which include path loss,lognormal shadowing and multi-path Rayleigh fading.Analytical approximations of the capacity's cumulative distribution function(CDF),the outage capacity,the mean capacity,and the outage probability of the interested area are derived by means of moment generation function(MGF) and Gauss-Hermite series expansion based approaches.The influence of antenna number,path loss exponent,and shadowing standard deviation on the capacity distribution are investigated.The simulation results agree with the analytical approximations well,and thus the analytical approximations are able to substitute the time-intensive Monte Carlo simulation for further investigation.
基金supported by the National Natural Science Foundation of China under Grants No. 60832008,No. 60902001
文摘When coexisting with dual-link primary systems,secondary systems in cognitive radios should first distinguish between the primary downlinks and uplinks in order to efficiently explore their respective spectrum opportunities.Because of the assumptive prior knowledge about the time-frequency locations of primary downlinks and uplinks,this procedure is usually not considered in the design of cognitive radios.In this paper,a cooperative method is proposed for the downlink/uplink identification of time-division duplex-based orthogonal frequency-division multiple access systems.In this method,the power level of the primary link is extracted as the key feature,which also contributes to the subsequent cognitive behaviours.The effects of the primary and secondary systems and the effects of the detection parameters on the identification accuracy are all analysed in detail.The simulation results show that the proposed method can identify the primary links precisely and quickly with low complexity.
基金the National Natural Science Foundationof China(No.60572156)
文摘To reduce the performance deterioration induced by imperfect channel state information(CSI) in correlated multiple input multiple output(MIMO) downlink,the linear transmit/receive filters should be optimized to be robust to imperfect CSI.A sub-optimization algorithm based on minimizing sum MSE conditional on available imperfect CSI estimates subject to a per-user power constraint is proposed.The algorithm adapts the existing MMSE algorithm from uncorrelated single-user MIMO system with perfect CSI to correlated MIMO downlink with imperfect CSI.Simulation shows that the suboptimal algorithm can effectively mitigate the performance loss induced by imperfect CSI and has a good convergence performance.In addition,the effect of spatial correlation on the performance of the proposed algorithm is also simulated.
文摘Long Term Evolution (LTE) Carrier Aggregation (CA) was introduced by the Release-10 3GPP specifications. CA allows aggregation of up to 5 cells for a terminal;both downlink (DL) CA and uplink (UL) CA are supported by the 3GPP specifications. However, the first commercial deployments focus on the aggregation of two cells in the downlink. The benefits of LTE CA are increased terminal peak data rates, aggregation of fragmented spectrum and fast load balancing. In this paper, we analyze different strategies of DL scheduling for LTE CA including centralized, independent and distributed schedulers, we provide the corresponding simulation results considering UE data rate limitations and different traffic models. Also, we compare the performance of a single LTE carrier with LTE CA using the same total bandwidth.
基金the National Natural Science Foundation of China(No.61702258,61901211)the Natural Science Foundation of Jiangsu Province(No.BK20170766).
文摘This paper investigates a unmanned aerial vehicle(UAV)deployment problem in a non-orthogonal multiple access(NOMA)system,where the UAV is deployed as an aerial mobile base station to transmit data to two ground users.An optimization problem is formulated by deploying the UAV for maximizing the sum rate of the two users.In order to solve the optimization problem,the feasible solution region is first reduced to a line segment between two users.Then,the optimization problem is simplified to a univariate problem,which can be solved by derivation under a certain situation,and the corresponding analytical solution is also provided.Moreover,a generalized algorithm,which considers 2 situations,is proposed to further determine the optimal UAV’s location.Specifically,four cases are discussed in the first situation.Extensive simulations are depicted to demonstrate effectiveness of the proposed algorithm and its superiority over the benchmarks in maximizing the two users’sum rate.
基金the National Natural Science Foundation of China(No.60572156)
文摘A robust scheme is proposed to jointly optimize transmit/receive beamformers for Mul-tiple Input Multiple Output(MIMO) downlinks where the available Channel State Information(CSI) at Base Station(BS)(CSIBS) is imperfect.The criterion is to minimize the sum Mean Square Error(sum-MSE) over all users under a constraint on the total transmit power,which is a non-convex and non-linear problem.Observing from the first order optimization condition that the optimal trans-mit/receive beamformers are mutually dependent,the transmit/receive beamformers for each user are updated iteratively until the sum-MSE is minimized.Simulation results indicate that the proposed scheme can effectively mitigate the system performance loss induced by imperfect CSIBS.
基金supported by the joint research project with ZTE Corporation under Grant No.HC-CN-2020120002.
文摘The sum rate maximization beamforming problem for a multi-cell multi-user multiple-input single-output interference channel(MISO-IC)system is considered.Conventionally,the centralized and distributed beamforming solutions to the MISO-IC system have high computational complexity and bear a heavy burden of channel state information exchange between base stations(BSs),which becomes even much worse in a large-scale antenna system.To address this,we propose a distributed deep reinforcement learning(DRL)based approach with lim⁃ited information exchange.Specifically,the original beamforming problem is decomposed of the problems of beam direction design and power allocation and the costs of information exchange between BSs are significantly reduced.In particular,each BS is provided with an inde⁃pendent deep deterministic policy gradient network that can learn to choose the beam direction scheme and simultaneously allocate power to users.Simulation results illustrate that the proposed DRL-based approach has comparable sum rate performance with much less information exchange over the conventional distributed beamforming solutions.
文摘A novel scheme which can realize high-speed optical signals transmission and reception by using 4-pulsed amplitude modulation (4-PAM) and demodulation in 10 Gb/s passive optical access systems with different bandwidth optical Bessel filter (OBF) is introduced. In this scheme, a PAM sequence generator module, an M-ary pulse generator module and one Mach-Zehnder intensity Modulator (MZM) are employed for generating the 10 Gb/s optical 4-PAM signals. And then, the generated optical 4-PAM signal achieves transmission over 20 km single mode fiber (SMF) for downstream (DS) access links application. Finally, the optical 4-PAM signal after transmission is directly detected and demodulated. We measure time-domain sequential waveform curves, optical spectrum curves, and eye-diagrams, and analyze the receiver sensitivity of 10 Gb/s 4-PAM signals before and after transmission. The received performance of the optical 4-PAM signals after transmission over 20 km single mode fiber (SMF) with different bandwidth OBF has also been analyzed.
基金the Nature Science Founding of China under Grant. No. 60496313National Basic Research Program of China under Grant No. 2007CB310604.
文摘In this paper, we propose a downlink transmission and receiving scheme for interleave-division multiple access （IDMA） system based on time-division duplexing （TDD） mode and time-reversal （TR） technique. The proposed scheme uses the time-reversed version of the channel impulse responses （CIR） obtained from the transmitted signal at base uplink to pre-process the station. By exploiting the weak correlations of fading channels for different user ends （UE）, it is helpful to alleviate the multi-user interference （MUI） and co-channel interference （CCI）. Moreover, the application of the TR technique in a multiple input-single output （MISO） configuration can reduce the delay spread of the channel impulse response, and mitigate inter-symbol interference （ISI）. The UE can be simplified by canceling the iteration operation. Thus the data detection of the proposed scheme is rather simple as compared with the traditional IDMA, the complexity and computational load of UE is decreased substantially, and the proposed scheme provides a great deal of privacy and security to mobile users.
