This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the at...This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the attacker and the capability to defend the GNSS during navigation countermeasures.Key evaluation indicators for the jamming effect of GNSS suppressive and deceptive jamming sources are first created,their evaluation models are built,and their detection procedures are sorted out,as the basis for determining the deployment principles.The principles for collaboratively deploying multi-jamming sources are developed to obtain the deployment structures(including the required number,structures in demand,and corresponding positions)of three single interference sources required by collaboratively deploying.Accordingly,simulation and hardware-in-loop testing results are presented to determine a rational configuration of the collaborative deployment of multi-jamming sources in the set situation and further realize the full-domain deployment of an interference network from ground,air to space.Varied evaluation indices for the deployment effect are finally developed to evaluate the deployment effect of the proposed configuration and further verify its reliability and rationality.展开更多
The adaptive digital beamforming technique in the space-polarization domain suppresses the interference with forming the coupling nulls of space and polarization domain.When there is the interference in mainlobe,it wi...The adaptive digital beamforming technique in the space-polarization domain suppresses the interference with forming the coupling nulls of space and polarization domain.When there is the interference in mainlobe,it will cause serious mainlobe distortion,that the target detection suffers from.To overcome this problem and make radar cope with the complex multiple interferences scenarios,we propose a multiple mainlobe and/or sidelobe interferences suppression method for dual polarization array radar.Specifically,the proposed method consists of a signal preprocessing based on the proposed angle estimation with degree of polarization(DoP),and a filtering criterion based on the proposed linear constraint.The signal preprocessing provides the accurate estimated parameters of the interference,which contributes to the criterion for null-decoupling in the space-polarization domain of mainlobe.The proposed method can reduce the mainlobe distortion in the space-polarization domain while suppressing the multiple mainlobe and/or sidelobe interferences.The effectiveness of the proposed method is verified by simulations.展开更多
For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is ...For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.展开更多
In CDMA communication systems, all the subscribers share the common channel. The limitation factor on the system’s capacity is not the bandwidth, but multiuser interference and the near far problem. This paper models...In CDMA communication systems, all the subscribers share the common channel. The limitation factor on the system’s capacity is not the bandwidth, but multiuser interference and the near far problem. This paper models CDMA system from the perspective of mobile radio channels corrupted by additive white noise generated by multipath and multiple access interferences. The system’s receiver is assisted using different combining diversity techniques. Performance analysis of the system with these detection techniques is presented. The paper demonstrates that combining diversity techniques in the system’s receivers markedly improve the performance of CDMA systems.展开更多
Radio Frequency Interferences (RFI), such as strong Continuous Wave Interferences (CWI), can influence the Quality of Service (QoS) of communications, increasing the Bit Error Rate (BER) and decreasing the Signal-to-N...Radio Frequency Interferences (RFI), such as strong Continuous Wave Interferences (CWI), can influence the Quality of Service (QoS) of communications, increasing the Bit Error Rate (BER) and decreasing the Signal-to-Noise Ratio (SNR) in any wireless transmission, including in a Digital Video Broadcasting (DVB-S2) receiver. Therefore, this paper presents an algorithm for detecting and mitigating a Multi-tone Continuous Wave Interference (MCWI) using a Multiple Adaptive Notch Filter (MANF), based on the lattice form structure. The Adaptive Notch Filter (ANF) is constructed using the second-order IIR NF. The approach consists in developing a robust low-complexity algorithm for removing unknown MCWI. The MANF model is a multistage model, with each stage consisting of two ANFs: the adaptive IIR notch filter <i>H</i><i><sub>l</sub></i>(<i>z</i>) and the adaptive IIR notch filter <i>H</i><i><sub>N</sub></i>(<i>z</i>), which can detect and mitigate CWI. In this model, the ANF is used for estimating the Jamming-to-Signal Ratio (JSR) and the frequency of the interference (<i>w(0)</i>) by using an LMS-based algorithm. The depth of the notch is then adjusted based on the estimation of the JSR. In contrast, the ANF <i>H</i><i><sub>N</sub></i>(<i>z</i>) is used to mitigate the CW interference. Simulation results show that the proposed ANF is an effective method for eliminating/reducing the effects of MCWI, and yields better system performance than full suppression (<i>k<sub>N</sub></i>=1) for low JSR values, and mostly the same performance for high JSR values. Moreover, the proposed can detect low and high JSR and track hopping frequency interference and provides better Bit error ratio (BER) performance compared to the case without an IIR notch filter.展开更多
Intelligent reflecting surface(IRS)has been widely regarded as a promising technology for configuring wireless propagation environments.In this paper,we utilize IRS to assist transmission of a secondary user(SU)in a c...Intelligent reflecting surface(IRS)has been widely regarded as a promising technology for configuring wireless propagation environments.In this paper,we utilize IRS to assist transmission of a secondary user(SU)in a cognitive radio-inspired rate-splitting multiple access(CR-RSMA)system in which a primary user's(PU's)quality of service(QoS)requirements must be guaranteed.Without introducing intolerable interference to deteriorate the PU's outage performance,the SU conducts rate-splitting to transmit its signal to the base-station through the direct link and IRS reflecting channels.For the IRS-assisted CR-RSMA(IRS-CR-RSMA)scheme,we derive the optimal transmit power allocation,target rate allocation,and successive interference cancellation decoding order to enhance the outage performance of the SU.The closed-form expression for the SU's outage probability achieved by the IRS-CR-RSMA scheme is derived.Various simulation results are presented to clarify the enhanced outage performance achieved by the proposed IRS-CR-RSMA scheme over the CR-RSMA scheme.展开更多
Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cel-lular communication networks. In this paper, we first discuss a simple NOMA model with t...Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cel-lular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier si-multaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-in-put multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential re-search challenges.展开更多
In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access(CF-m MIMO-NOMA) system with conjugate beamforming precoder and compare against the or...In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access(CF-m MIMO-NOMA) system with conjugate beamforming precoder and compare against the orthogonal multiple access(OMA) counterpart. A novel achievable closed-form spectral efficiency(SE) expression is derived, which characterizes the effects of the channel estimation error, pilot contamination, imperfect successive interference cancellation(SIC) operation, and power optimization technique. Then, motivated by the closedform result, a sum-SE maximization algorithm with the sequential convex approximation(SCA) is proposed, subject to each AP power constraint and SIC power constraint. Numerical experiments indicate that the proposed sum-SE maximization algorithms have a fast converge rate, within about five iterations. In addition, compared with the full power control(FPC) scheme, our algorithms can significantly improve the achievable sum-SE. Moreover, NOMA outperforms OMA in many respects in the presence of the proposed algorithms.展开更多
Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this ...Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this impairment is the InterCarrier Interference (ICI) and Inter- Symbol Interference (ISI) introduced by the excessive multipath delay. Specifically, Multiple Input Multiple Output (MIMO) beamforming is helpful in cancelling such interference since it can spatially suppress some of the multipath. In this paper, we propose an ICI eliminating beamforming scheme employing a per-tone processing approach, thus with moderate computational complexity. The ISI is removed by using a simple decision feedback equalizer, while the optimal steering and combining vectors are then derived to maximize the Signal to Interference plus Noise Ratio (SINR). This method not only achieves the beamforming benefit, but also significantly alleviates the ICI. Simulation results show that the proposed algorithm can effectively reduce the system Symbol Error Rate (SER), per- mitting good performance for multipath delay profiles that would break conventional links.展开更多
The cognitive multiple input multiple output( MIMO)network can utilize radio spectrum efficiently and satisfy the demand of high data rate. In order to decrease the interference during transmission,a new interference ...The cognitive multiple input multiple output( MIMO)network can utilize radio spectrum efficiently and satisfy the demand of high data rate. In order to decrease the interference during transmission,a new interference alignment( IA) algorithm based on cognitive MIMO networks is proposed in this paper. The algorithm is realized by designing two-level pre-coding, the first-level precoding aligns the interference generated by the cognitive users( CUs) to unused sub-channels of the primary user( PU),thereby eliminating the interference of CUs to PU; the second-level precoding is used to improve the throughput of CUs. Simulation shows that the proposed IA algorithm can eliminate the interference that the CUs produce on the PU and improve the throughput of CUs spontaneously.展开更多
Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potent...Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potential approaches among the proposed solutions to resolve this issue are well explored cognitive radio(CR)technology and recently introduced non-orthogonal multiple access(NOMA)techniques.Both the techniques are employed for efficient spectrum utilization and assure the significant improvement in the spectral efficiency.Further,the significant improvement in spectral efficiency can be achieved by combining both the techniques.Since the CR is well-explored technique as compared to that of the NOMA in the field of communication,therefore it is worth and wise to implement this technique over the CR.In this article,we have presented the frameworks of NOMA implementation over CR as well as the feasibility of proposed frameworks.Further,the differences between proposed CR-NOMA and conventional CR frameworks are discussed.Finally,the potential issues regarding the implementation of CR-NOMA are explored.展开更多
The structure and trubulence phenomena of multiple shock wave /turbulent boundary layer interaction (MSW-TBLI) in a square duct were investigated using flow visualization methods and a two-component Laser Doppler Velo...The structure and trubulence phenomena of multiple shock wave /turbulent boundary layer interaction (MSW-TBLI) in a square duct were investigated using flow visualization methods and a two-component Laser Doppler Velocimeter (LDV ). First - the MSW-TBLI was visualized by schlieren photography and laser holographic interferography. Second, the time-mean and fluctuating velocities in the MSW-TBLI were explored in detail using LDV Spatial distributions of turbulence intensity,Reynolds shear stress and turbulence kinetic energy are presented.展开更多
Wireless relaying has been known to provide the improvements in link reliability, spectral efficiency, and coverage extension. In this paper, we use full duplex relays for Interference Alignment (IA) in K-users Interf...Wireless relaying has been known to provide the improvements in link reliability, spectral efficiency, and coverage extension. In this paper, we use full duplex relays for Interference Alignment (IA) in K-users Interference Channel (IC) and show K Degrees of Freedom (DOF) is achievable. In first hop, relays receive signals from transmitters and forward them to receivers in second hop. Two iteratively algorithms are proposed for computing relays function, precoder, and decoder matrices. First algorithm minimizes leakage interference at receivers that has appropriate performance at high Signal to Noise Ratio (SNR) region. Furthermore, the second algorithm has better performance at low-mediate SNR. The performance of proposed algorithms are compared with other schemes and validated with simulation in terms of achieved sum rate.展开更多
Space-time selective parallel interference cancellation(ST-SPIC) is a computationally effective approach combining multiuser detection (MUD) with antenna array technology for CDMA systems. The exploitation of signal r...Space-time selective parallel interference cancellation(ST-SPIC) is a computationally effective approach combining multiuser detection (MUD) with antenna array technology for CDMA systems. The exploitation of signal reliability is a key issue in ST-SPIC. In order to improve the reliability estimation, a pair of reliability thresholds are introduced. Then an improved selective interference cancellation algorithm is proposed to exploit the reliability accordingly. More practical space-time processing algorithms are also incorporated in the proposed ST-SPIC scheme to overcome the limitation caused by some idealised assumptions taken in the original ST-SPIC scheme. Numerical results show that the proposed ST-SPIC scheme outperforms its traditional counterpart in a CDMA microcell environment.展开更多
In this paper, we discuss and analyze an optical code division multiple access for multiple user system. Media access control implementation has been considered. For fulfilling the huge need of bandwidth services, tec...In this paper, we discuss and analyze an optical code division multiple access for multiple user system. Media access control implementation has been considered. For fulfilling the huge need of bandwidth services, technology tends to move to optical networks and three major optical systems come into existence. Code division of the optical network is most used and real concept interacted with users up to this time. Optical code division multiple access provides complete spectrum to each and every user for the time of accessing the channel. In the paper, we have proposed network architecture with optical encoder and decoder along with optical code translator which is supporting multiple user systems. We integrate the code translator with encoding and decoding of optical code to use the optical network at full extent and present the simulation validation results of 6 Gb/s 3-hop transmission by use of proposed architecture. Further, we have implemented experimentation with 6 users 3 Gb/s optical code division multiple access network. Through simulation structure, it is shown that the combination of encoding with EDFA in multiple user environment system provides improvement in bit error rate and also improves the multiple access interference. With increase of users in the network, MAI value increases and our proposed scheme controls interference in the network.展开更多
In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique....In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. The paper presents space-time coded minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. For the above structure, we have presented the estimation of BER for a MMSE DFE using computer simulation experiments. The simulation includes the effects of additive white Gaussian noise, multipath fading and multiple access interference (MAI). Furthermore, the performance is compared with standard linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard linear equalizer (LE) and RAKE receiver.展开更多
Radiolocation has been previously studied for CDMA networks, the effect of Multiple Access Interference has been ignored. In this paper we investigate the problem of Radiolocation in the presence of Multiple Access In...Radiolocation has been previously studied for CDMA networks, the effect of Multiple Access Interference has been ignored. In this paper we investigate the problem of Radiolocation in the presence of Multiple Access Interference. An extensive simulation technique was developed, which measures the error in location estimation for different network and user configurations. We include the effects of lognormal shadow and Rayleigh fading. Results that illustrate the effects of varying shadowing losses, number of base stations involved in position location, early-late discriminator offset and cell sizes in conjunction with the varying number of users per cell on the accuracy of radiolocation estimation was presented.展开更多
In this paper, rejection of multiple narrowband interferers in a binary phase shift keying modulated orthogonal frequency division multiplexing (BPSK-OFDM) system is investigated. The BPSK-OFDM system in consideration...In this paper, rejection of multiple narrowband interferers in a binary phase shift keying modulated orthogonal frequency division multiplexing (BPSK-OFDM) system is investigated. The BPSK-OFDM system in consideration operates in an additive white Gaussian noise (AWGN) channel. A cascade complex coefficient adaptive infinite impulse response (IIR) notch filter with gradient-based algorithm is used to reject the interferers. Bit error ratio (BER) performance of the system is studied and a general closed-form expression is derived assuming negligible steady-state leakage NBI and by estimating the decision variable as Gaussian distributed based on Central Limit Theorem (CLT). Dependence of the BER performance on the notch bandwidth coefficient is demonstrated by the analysis. Extensive simulation results are included to substantiate accuracy of the analysis.展开更多
This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying freq...This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying frequency in a quadriphase shift keying (QPSK) modulated direct-sequence code-division multiple-access (DS-CDMA) communication system. The QPSK DS-CDMA signals are transmitted over a frequency non-selective Rayleigh fading channel. The analysis is based on a first-order real-coefficient difference equation with respect to steady-state instantaneous frequency tracking error from which a closed-form expression that relates frequency tracking mean square error (MSE) with number of DS-CDMA active users and NBI power is obtained. Closed-form expressions for optimum notch bandwidth coefficient and step size constant that minimize the frequency tracking MSE are also derived. Computer simulations are included to substantiate the accuracy of the analyses.展开更多
基金the National Natural Science Foundation of China(Grant No.42174047 and No.42174036)the National Science Foundation Project for Outstanding Youth(No.42104034).
文摘This paper realizes the full-domain collaborative deployment of multiple interference sources of the global satellite navigation system(GNSS)and evaluates the deployment effect to enhance the ability to disturb the attacker and the capability to defend the GNSS during navigation countermeasures.Key evaluation indicators for the jamming effect of GNSS suppressive and deceptive jamming sources are first created,their evaluation models are built,and their detection procedures are sorted out,as the basis for determining the deployment principles.The principles for collaboratively deploying multi-jamming sources are developed to obtain the deployment structures(including the required number,structures in demand,and corresponding positions)of three single interference sources required by collaboratively deploying.Accordingly,simulation and hardware-in-loop testing results are presented to determine a rational configuration of the collaborative deployment of multi-jamming sources in the set situation and further realize the full-domain deployment of an interference network from ground,air to space.Varied evaluation indices for the deployment effect are finally developed to evaluate the deployment effect of the proposed configuration and further verify its reliability and rationality.
基金supported by the National Natural Science Foundation of China(6190149661871385)。
文摘The adaptive digital beamforming technique in the space-polarization domain suppresses the interference with forming the coupling nulls of space and polarization domain.When there is the interference in mainlobe,it will cause serious mainlobe distortion,that the target detection suffers from.To overcome this problem and make radar cope with the complex multiple interferences scenarios,we propose a multiple mainlobe and/or sidelobe interferences suppression method for dual polarization array radar.Specifically,the proposed method consists of a signal preprocessing based on the proposed angle estimation with degree of polarization(DoP),and a filtering criterion based on the proposed linear constraint.The signal preprocessing provides the accurate estimated parameters of the interference,which contributes to the criterion for null-decoupling in the space-polarization domain of mainlobe.The proposed method can reduce the mainlobe distortion in the space-polarization domain while suppressing the multiple mainlobe and/or sidelobe interferences.The effectiveness of the proposed method is verified by simulations.
基金supported by the National High Technology ResearchDevelopment Program of China (863 Program) (2008AA0248)
文摘For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum(DSSS) systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.
文摘In CDMA communication systems, all the subscribers share the common channel. The limitation factor on the system’s capacity is not the bandwidth, but multiuser interference and the near far problem. This paper models CDMA system from the perspective of mobile radio channels corrupted by additive white noise generated by multipath and multiple access interferences. The system’s receiver is assisted using different combining diversity techniques. Performance analysis of the system with these detection techniques is presented. The paper demonstrates that combining diversity techniques in the system’s receivers markedly improve the performance of CDMA systems.
文摘Radio Frequency Interferences (RFI), such as strong Continuous Wave Interferences (CWI), can influence the Quality of Service (QoS) of communications, increasing the Bit Error Rate (BER) and decreasing the Signal-to-Noise Ratio (SNR) in any wireless transmission, including in a Digital Video Broadcasting (DVB-S2) receiver. Therefore, this paper presents an algorithm for detecting and mitigating a Multi-tone Continuous Wave Interference (MCWI) using a Multiple Adaptive Notch Filter (MANF), based on the lattice form structure. The Adaptive Notch Filter (ANF) is constructed using the second-order IIR NF. The approach consists in developing a robust low-complexity algorithm for removing unknown MCWI. The MANF model is a multistage model, with each stage consisting of two ANFs: the adaptive IIR notch filter <i>H</i><i><sub>l</sub></i>(<i>z</i>) and the adaptive IIR notch filter <i>H</i><i><sub>N</sub></i>(<i>z</i>), which can detect and mitigate CWI. In this model, the ANF is used for estimating the Jamming-to-Signal Ratio (JSR) and the frequency of the interference (<i>w(0)</i>) by using an LMS-based algorithm. The depth of the notch is then adjusted based on the estimation of the JSR. In contrast, the ANF <i>H</i><i><sub>N</sub></i>(<i>z</i>) is used to mitigate the CW interference. Simulation results show that the proposed ANF is an effective method for eliminating/reducing the effects of MCWI, and yields better system performance than full suppression (<i>k<sub>N</sub></i>=1) for low JSR values, and mostly the same performance for high JSR values. Moreover, the proposed can detect low and high JSR and track hopping frequency interference and provides better Bit error ratio (BER) performance compared to the case without an IIR notch filter.
基金the National Nature Science Foundation of China under Grant No.61271259 and 61301123,the Chongqing Nature Science Foundation under Grant No.CTSC2011jjA40006,and the Research Project of Chongqing Education Commission under Grant No.KJ120501 and KJ120502
基金supported in part by National Natural Science Foundation of China under Grant 62071202in part by Shandong Provincial Natural Science Foundation under Grants ZR2020MF009,ZR2020MF075in part by Shandong Key Laboratory of Intelligent Buildings Technology undert Grant SDIBT202004.
文摘Intelligent reflecting surface(IRS)has been widely regarded as a promising technology for configuring wireless propagation environments.In this paper,we utilize IRS to assist transmission of a secondary user(SU)in a cognitive radio-inspired rate-splitting multiple access(CR-RSMA)system in which a primary user's(PU's)quality of service(QoS)requirements must be guaranteed.Without introducing intolerable interference to deteriorate the PU's outage performance,the SU conducts rate-splitting to transmit its signal to the base-station through the direct link and IRS reflecting channels.For the IRS-assisted CR-RSMA(IRS-CR-RSMA)scheme,we derive the optimal transmit power allocation,target rate allocation,and successive interference cancellation decoding order to enhance the outage performance of the SU.The closed-form expression for the SU's outage probability achieved by the IRS-CR-RSMA scheme is derived.Various simulation results are presented to clarify the enhanced outage performance achieved by the proposed IRS-CR-RSMA scheme over the CR-RSMA scheme.
文摘Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for the next generation cel-lular communication networks. In this paper, we first discuss a simple NOMA model with two users served by a single-carrier si-multaneously to illustrate its basic principles. Then, a more general model with multicarrier serving an arbitrary number of users on each subcarrier is also discussed. An overview of existing works on performance analysis, resource allocation, and multiple-in-put multiple-output NOMA are summarized and discussed. Furthermore, we discuss the key features of NOMA and its potential re-search challenges.
基金supported in part by the National Key Research and Development Program of China under Grant 2018YFC1314903the National Natural Science Foundation of China under Grants 61861039,61372124,and 61427801+1 种基金the Science and Technology Project Foundation of Gansu Province under Grant 18YF1GA060the Postgraduate Research&Practice Innovation Program of Jiangsu Province under Grant SJKY19_0740 and KYCX20_0709。
文摘In this paper, we investigate the downlink performance of cell-free massive multi-input multi-output non-orthogonal multiple access(CF-m MIMO-NOMA) system with conjugate beamforming precoder and compare against the orthogonal multiple access(OMA) counterpart. A novel achievable closed-form spectral efficiency(SE) expression is derived, which characterizes the effects of the channel estimation error, pilot contamination, imperfect successive interference cancellation(SIC) operation, and power optimization technique. Then, motivated by the closedform result, a sum-SE maximization algorithm with the sequential convex approximation(SCA) is proposed, subject to each AP power constraint and SIC power constraint. Numerical experiments indicate that the proposed sum-SE maximization algorithms have a fast converge rate, within about five iterations. In addition, compared with the full power control(FPC) scheme, our algorithms can significantly improve the achievable sum-SE. Moreover, NOMA outperforms OMA in many respects in the presence of the proposed algorithms.
基金Supported by the National Science Fund for Distinguished Young Scholars (No. 60725105)the National Basic Re-search Program of China (2009CB320404)+5 种基金the Program for Changjiang Scholars and Innovative Research Team in Universitythe National High Technology Research and Development Program of China (2007AA01Z288)the 111 Project (B08038)the National Natural Science Founda-tion of China (No. 60902032, 60902033, and 60702057)the Key Project of Chinese Ministry of Education (107103) the Program for State Key Laboratory of Integrated Service Networks (ISN02080001)
文摘Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from performance deterioration when the length of Cyclic Prefix (CP) is shorter than the Channel Impulse Response (CIR). The fundamental reason of this impairment is the InterCarrier Interference (ICI) and Inter- Symbol Interference (ISI) introduced by the excessive multipath delay. Specifically, Multiple Input Multiple Output (MIMO) beamforming is helpful in cancelling such interference since it can spatially suppress some of the multipath. In this paper, we propose an ICI eliminating beamforming scheme employing a per-tone processing approach, thus with moderate computational complexity. The ISI is removed by using a simple decision feedback equalizer, while the optimal steering and combining vectors are then derived to maximize the Signal to Interference plus Noise Ratio (SINR). This method not only achieves the beamforming benefit, but also significantly alleviates the ICI. Simulation results show that the proposed algorithm can effectively reduce the system Symbol Error Rate (SER), per- mitting good performance for multipath delay profiles that would break conventional links.
基金Innovation Program of Shanghai Municipal Education Commission,China(No.12ZZ126)the Program of Shanghai Normal University,China(No.DZL126)
文摘The cognitive multiple input multiple output( MIMO)network can utilize radio spectrum efficiently and satisfy the demand of high data rate. In order to decrease the interference during transmission,a new interference alignment( IA) algorithm based on cognitive MIMO networks is proposed in this paper. The algorithm is realized by designing two-level pre-coding, the first-level precoding aligns the interference generated by the cognitive users( CUs) to unused sub-channels of the primary user( PU),thereby eliminating the interference of CUs to PU; the second-level precoding is used to improve the throughput of CUs. Simulation shows that the proposed IA algorithm can eliminate the interference that the CUs produce on the PU and improve the throughput of CUs spontaneously.
文摘Recently,the increasing demand of radio spectrum for the next generation communication systems due to the explosive growth of applications appetite for bandwidths has led to the problem of spectrum scarcity.The potential approaches among the proposed solutions to resolve this issue are well explored cognitive radio(CR)technology and recently introduced non-orthogonal multiple access(NOMA)techniques.Both the techniques are employed for efficient spectrum utilization and assure the significant improvement in the spectral efficiency.Further,the significant improvement in spectral efficiency can be achieved by combining both the techniques.Since the CR is well-explored technique as compared to that of the NOMA in the field of communication,therefore it is worth and wise to implement this technique over the CR.In this article,we have presented the frameworks of NOMA implementation over CR as well as the feasibility of proposed frameworks.Further,the differences between proposed CR-NOMA and conventional CR frameworks are discussed.Finally,the potential issues regarding the implementation of CR-NOMA are explored.
文摘The structure and trubulence phenomena of multiple shock wave /turbulent boundary layer interaction (MSW-TBLI) in a square duct were investigated using flow visualization methods and a two-component Laser Doppler Velocimeter (LDV ). First - the MSW-TBLI was visualized by schlieren photography and laser holographic interferography. Second, the time-mean and fluctuating velocities in the MSW-TBLI were explored in detail using LDV Spatial distributions of turbulence intensity,Reynolds shear stress and turbulence kinetic energy are presented.
文摘Wireless relaying has been known to provide the improvements in link reliability, spectral efficiency, and coverage extension. In this paper, we use full duplex relays for Interference Alignment (IA) in K-users Interference Channel (IC) and show K Degrees of Freedom (DOF) is achievable. In first hop, relays receive signals from transmitters and forward them to receivers in second hop. Two iteratively algorithms are proposed for computing relays function, precoder, and decoder matrices. First algorithm minimizes leakage interference at receivers that has appropriate performance at high Signal to Noise Ratio (SNR) region. Furthermore, the second algorithm has better performance at low-mediate SNR. The performance of proposed algorithms are compared with other schemes and validated with simulation in terms of achieved sum rate.
文摘Space-time selective parallel interference cancellation(ST-SPIC) is a computationally effective approach combining multiuser detection (MUD) with antenna array technology for CDMA systems. The exploitation of signal reliability is a key issue in ST-SPIC. In order to improve the reliability estimation, a pair of reliability thresholds are introduced. Then an improved selective interference cancellation algorithm is proposed to exploit the reliability accordingly. More practical space-time processing algorithms are also incorporated in the proposed ST-SPIC scheme to overcome the limitation caused by some idealised assumptions taken in the original ST-SPIC scheme. Numerical results show that the proposed ST-SPIC scheme outperforms its traditional counterpart in a CDMA microcell environment.
文摘In this paper, we discuss and analyze an optical code division multiple access for multiple user system. Media access control implementation has been considered. For fulfilling the huge need of bandwidth services, technology tends to move to optical networks and three major optical systems come into existence. Code division of the optical network is most used and real concept interacted with users up to this time. Optical code division multiple access provides complete spectrum to each and every user for the time of accessing the channel. In the paper, we have proposed network architecture with optical encoder and decoder along with optical code translator which is supporting multiple user systems. We integrate the code translator with encoding and decoding of optical code to use the optical network at full extent and present the simulation validation results of 6 Gb/s 3-hop transmission by use of proposed architecture. Further, we have implemented experimentation with 6 users 3 Gb/s optical code division multiple access network. Through simulation structure, it is shown that the combination of encoding with EDFA in multiple user environment system provides improvement in bit error rate and also improves the multiple access interference. With increase of users in the network, MAI value increases and our proposed scheme controls interference in the network.
文摘In recent times, there has been growing interests in integration of voice, data and video traffic in wireless communication networks. With these growing interests, WCDMA has immerged as an attractive access technique. The performance of WCDMA system is deteriorated in presence of multipath fading environment. The paper presents space-time coded minimum mean square error (MMSE) Decision Feedback Equalizer (DFE) for wideband code division multiple access (WCDMA) in a frequency selective channel. The filter coefficients in MMSE DFE are optimized to suppress noise, intersymbol interference (ISI), and multiple access interference (MAI) with reasonable system complexity. For the above structure, we have presented the estimation of BER for a MMSE DFE using computer simulation experiments. The simulation includes the effects of additive white Gaussian noise, multipath fading and multiple access interference (MAI). Furthermore, the performance is compared with standard linear equalizer (LE) and RAKE receiver. Numerical and simulation results show that the MMSE DFE exhibits significant performance improvement over the standard linear equalizer (LE) and RAKE receiver.
文摘Radiolocation has been previously studied for CDMA networks, the effect of Multiple Access Interference has been ignored. In this paper we investigate the problem of Radiolocation in the presence of Multiple Access Interference. An extensive simulation technique was developed, which measures the error in location estimation for different network and user configurations. We include the effects of lognormal shadow and Rayleigh fading. Results that illustrate the effects of varying shadowing losses, number of base stations involved in position location, early-late discriminator offset and cell sizes in conjunction with the varying number of users per cell on the accuracy of radiolocation estimation was presented.
文摘In this paper, rejection of multiple narrowband interferers in a binary phase shift keying modulated orthogonal frequency division multiplexing (BPSK-OFDM) system is investigated. The BPSK-OFDM system in consideration operates in an additive white Gaussian noise (AWGN) channel. A cascade complex coefficient adaptive infinite impulse response (IIR) notch filter with gradient-based algorithm is used to reject the interferers. Bit error ratio (BER) performance of the system is studied and a general closed-form expression is derived assuming negligible steady-state leakage NBI and by estimating the decision variable as Gaussian distributed based on Central Limit Theorem (CLT). Dependence of the BER performance on the notch bandwidth coefficient is demonstrated by the analysis. Extensive simulation results are included to substantiate accuracy of the analysis.
文摘This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying frequency in a quadriphase shift keying (QPSK) modulated direct-sequence code-division multiple-access (DS-CDMA) communication system. The QPSK DS-CDMA signals are transmitted over a frequency non-selective Rayleigh fading channel. The analysis is based on a first-order real-coefficient difference equation with respect to steady-state instantaneous frequency tracking error from which a closed-form expression that relates frequency tracking mean square error (MSE) with number of DS-CDMA active users and NBI power is obtained. Closed-form expressions for optimum notch bandwidth coefficient and step size constant that minimize the frequency tracking MSE are also derived. Computer simulations are included to substantiate the accuracy of the analyses.