The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Song Chong - One of the best experts on this subject based on the ideXlab platform.

  • opportunistic underlay transmission in multi carrier cognitive radio systems
    Wireless Communications and Networking Conference, 2009
    Co-Authors: Kyuho Son, Song Chong, Bang Chul Jung, Dan Keun Sung
    Abstract:

    Underlay transmission in cognitive radio enables a secondary (unlicensed) system to utilize a frequency band of primary (licensed) system as long as the unlicensee interferes less than a certain threshold with the licensee. The secondary system needs to carefully consider not only its own channel to achieve a capacity gain by this sharing spectrum in multi-carrier systems, but also the interference channel to reduce interference at the primary receiver. In this paper, we formulate a capacity maximization problem of the secondary system under an interference-Power constraint as well as a conventional transmit-Power constraint, and propose an optimal Power Allocation policy in which we exploit a two-dimensional frequency-selectivity on both channels. Through extensive simulations, we compare the performance of optimal Power Allocation policy with that of Equal Power Allocation policy and further investigate the effect of the primary's Power Allocation policy on the performance of the secondary system. Numerical results show that the optimal Power Allocation policy can achieve a higher capacity in more frequency-selective channels, compared to an Equal Power Allocation policy. Interestingly, a water-filling policy for the primary system also gives additional opportunities to the secondary system than the Equal Power Allocation policy.

  • downlink resource Allocation in multi carrier systems frequency selective vs Equal Power Allocation
    IEEE Transactions on Wireless Communications, 2008
    Co-Authors: Song Chong
    Abstract:

    This paper revisits Equal Power Allocation from the viewpoint of asymptotic network utility maximization (NUM) problem in multi-carrier systems. It is a well-known fact that the Equal Power Allocation is near optimal to the sum capacity maximization problem in high SNR (signal-to-noise ratio) regime, i.e., optimal water-filling approximates to Equal Power Allocation in that case. Due to this property together with its simplicity, the Equal Power Allocation has been adopted in several researches, but its performance in other problems has not been clearly understood. We evaluate the suitability of Equal Power Allocation in NUM problem which turns into various resource sharing policies according to utility functions. Namely, our conclusion is that in frequency selective channels, the Equal Power Allocation is near optimal for efficiency-oriented resource sharing policy, but when fairness is emphasized, its performance is severely degraded and thus frequency-selective Power Allocation is necessary. For this, we develop a suboptimal subcarrier and frequency-selective Power Allocation algorithm for asymptotic NUM problem using the gradient-based scheduling theory and compare the performance of Equal Power Allocation and the developed algorithm. Extensive simulation results are presented to verify our arguments.

  • downlink resource Allocation in multi carrier systems frequency selective vs Equal Power Allocation
    World of Wireless Mobile and Multimedia Networks, 2007
    Co-Authors: Song Chong
    Abstract:

    In this paper, dynamic subcarrier and Power Allocation problem is considered in the context of asymptotic utility maximization in multi-carrier systems. Using gradient-based resource Allocation, we formulate an optimization problem involving subcarrier and transmit Power Allocation for each time slot, and propose an optimal algorithm solving the problem. Since the optimal algorithm is impractical due to its complexity, a simple suboptimal algorithm is also proposed based on generalized Benders decomposition. Furthermore, we identify the performance of Equal Power Allocation policy by showing that Equal Power Allocation is not always near optimal in general utility maximization problem and characterizing the optimality condition of Equal Power Allocation. This result not only justifies the use of our dynamic Power Allocation, but also generalizes the performance of Equal Power Allocation, which is well-known to be approximately optimal to the sum capacity maximization problem in high SNR (signal-to-noise ratio) regime. Our algorithms and analysis are verified through extensive simulations.

Matthew R. Mckay - One of the best experts on this subject based on the ideXlab platform.

  • secure transmission with artificial noise over fading channels achievable rate and optimal Power Allocation
    IEEE Transactions on Vehicular Technology, 2010
    Co-Authors: Xiangyun Zhou, Matthew R. Mckay
    Abstract:

    We consider the problem of secure communication with multiantenna transmission in fading channels. The transmitter simultaneously transmits an information-bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate and use it as the objective function to optimize the transmit Power Allocation between the information signal and the artificial noise. Our analytical and numerical results show that Equal Power Allocation is a simple yet near-optimal strategy for the case of noncolluding eavesdroppers. When the number of colluding eavesdroppers increases, more Power should be used to generate the artificial noise. We also provide an upper bound on the SNR, above which, the achievable secrecy rate is positive and shows that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained.

  • secure transmission with artificial noise over fading channels achievable rate and optimal Power Allocation
    arXiv: Information Theory, 2010
    Co-Authors: Xiangyun Zhou, Matthew R. Mckay
    Abstract:

    We consider the problem of secure communication with multi-antenna transmission in fading channels. The transmitter simultaneously transmits an information bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate, and use it as the objective function to optimize the transmit Power Allocation between the information signal and the artificial noise. Our analytical and numerical results show that Equal Power Allocation is a simple yet near optimal strategy for the case of non-colluding eavesdroppers. When the number of colluding eavesdroppers increases, more Power should be used to generate the artificial noise. We also provide an upper bound on the signal-to-noise ratio (SNR) above which the achievable secrecy rate is positive and show that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained.

  • Physical layer security with artificial noise: Secrecy capacity and optimal Power Allocation
    3rd International Conference on Signal Processing and Communication Systems, ICSPCS'2009 - Proceedings, 2009
    Co-Authors: Xiangyun Zhou, Matthew R. Mckay
    Abstract:

    We consider the problem of secure communication in wireless fading channels in the presence of non-colluding passive eavesdroppers. The transmitter has multiple antennas and is able to simultaneously transmit an information bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form lower bound for secrecy capacity, which is used as the objective function to optimize transmit Power Allocation between the information signal and the artificial noise. Our analytical and numerical results show that Equal Power Allocation is a simple and generic strategy which achieves near optimal capacity performance. We also find that adaptive Power Allocation based on each channel realization provides no or insignificant capacity improvement over Equal Power Allocation.

  • analytical performance of mimo svd systems in ricean fading channels with channel estimation error and feedback delay
    IEEE Transactions on Wireless Communications, 2008
    Co-Authors: Shi Jin, Matthew R. Mckay, Wai Ho Mow, Xiqi Gao, Iain B Collings
    Abstract:

    This paper analyzes bit error rate (BER) and outage probability of singular value decomposition-based multiple-input multiple-output systems with channel estimation error and feedback delay over uncorrelated Ricean fading channels. By utilizing marginal unordered and ordered eigenvalue distributions of complex noncentral Wishart matrices, we derive exact closed-form expressions on the average system performance and high signal- to-interference-plus-noise ratio (SINR) approximations on the individual eigen-subchannels, respectively, under the assumption of Equal Power Allocation. Our expressions apply for various modulation formats and arbitrary numbers of transmit and receive antennas. Our results show that in low-to-moderate SINR regimes, both the BER and the outage probability increase with channel estimation error, feedback delay and the Ricean K-factor at a polynomial rate that is inversely proportional to the difference between the numbers of transmit and receive antennas. We also show that, with channel estimation error and feedback delay, the diversity orders of the BER and outage probability are zero and an irreducible error floor exists at high SINR.

Dan Keun Sung - One of the best experts on this subject based on the ideXlab platform.

  • opportunistic underlay transmission in multi carrier cognitive radio systems
    Wireless Communications and Networking Conference, 2009
    Co-Authors: Kyuho Son, Song Chong, Bang Chul Jung, Dan Keun Sung
    Abstract:

    Underlay transmission in cognitive radio enables a secondary (unlicensed) system to utilize a frequency band of primary (licensed) system as long as the unlicensee interferes less than a certain threshold with the licensee. The secondary system needs to carefully consider not only its own channel to achieve a capacity gain by this sharing spectrum in multi-carrier systems, but also the interference channel to reduce interference at the primary receiver. In this paper, we formulate a capacity maximization problem of the secondary system under an interference-Power constraint as well as a conventional transmit-Power constraint, and propose an optimal Power Allocation policy in which we exploit a two-dimensional frequency-selectivity on both channels. Through extensive simulations, we compare the performance of optimal Power Allocation policy with that of Equal Power Allocation policy and further investigate the effect of the primary's Power Allocation policy on the performance of the secondary system. Numerical results show that the optimal Power Allocation policy can achieve a higher capacity in more frequency-selective channels, compared to an Equal Power Allocation policy. Interestingly, a water-filling policy for the primary system also gives additional opportunities to the secondary system than the Equal Power Allocation policy.

  • performance of voip in hsdpa based on an adaptive Power Allocation scheme
    Wireless Communications and Networking Conference, 2006
    Co-Authors: Young Ik Seo, Dan Keun Sung
    Abstract:

    In the HSDPA system, code multiplexing in one TTI is required to transmit packets for multiple VoIP users. This paper proposes an adaptive Power Allocation (APA) scheme for code multiplexing. The proposed APA scheme adaptively allocates the transmit Power to each user in downlink according to the user's link status. The user capacity in the HSDPA system based on the proposed APA scheme is compared with that of the conventional Equal Power Allocation (EPA) scheme through simulation. The simulation results show that the user capacity of HSDPA based on the proposed APA scheme is 136, compared to 75 of the conventional EPA scheme

Mischa Dohler - One of the best experts on this subject based on the ideXlab platform.

  • distributed adaptive Power Allocation for wireless relay networks
    International Conference on Communications, 2007
    Co-Authors: Branka Vucetic, Zhendong Zhou, Mischa Dohler
    Abstract:

    In this paper, we consider a 2-hop wireless relay network. We explore transmit Power Allocation among the source and relays to maximize the received SNR at the destination. We consider two relaying protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and calculate the respective Power Allocations for both uncoded and coded system. For a 2- hop relay system with one relay node, we derive a closed-form Power Allocation solution and based on it we propose a relay active condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in an idle state. For a system with more than one relay nodes, general closed-form Power Allocation solutions based on the extact SNR expression are not tractable, so we calculate a SNR upper bound and derive a sub-optimum Power Allocation solution based on this bound. The simulation results show that for a 2-hop relay channel, the proposed adaptive Power Allocation (APA) scheme can bring the system a considerable SNR gains compared to the Equal Power Allocation scheme. This gain will be further monotonically increased as the number of relays increases.

  • distributed adaptive Power Allocation for wireless relay networks
    IEEE Transactions on Wireless Communications, 2007
    Co-Authors: Branka Vucetic, Zhendong Zhou, Mischa Dohler
    Abstract:

    In this paper, we consider a 2-hop wireless diversity relay network. We explore transmit Power Allocation among the source and relays to maximize the received signal to noise ratio (SNR) at the destination. We consider two relay protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and design the respective Power Allocations for both uneeded and coded systems. For a 2-hop relay system with one relay node, we derive a closed-form Power Allocation solution and, based on it, we propose a relay activation condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in the idle state. For a system with more than one relay node, general closed-form Power Allocation solutions based on an exact SNR expression are difficult to derive; we hence, calculate a SNR upper bound and derive a sub-optimum Power Allocation solution based on this bound. The simulation results show that for a 2-hop diversity relay channel with one relay node the proposed adaptive Power Allocation (APA) scheme yields about 1- 2 dB SNR gains compared to the Equal Power Allocation. This SNR gain increases monotonically as the number of relays increases

Maged Elkashlan - One of the best experts on this subject based on the ideXlab platform.

  • artificial noise aided secure transmission in large scale spectrum sharing networks
    IEEE Transactions on Communications, 2016
    Co-Authors: Yansha Deng, Lifeng Wang, Syed Ali Raza Zaidi, Jinhong Yuan, Maged Elkashlan
    Abstract:

    We investigate beamforming and artificial noise generation at the secondary transmitters to establish secure transmission in large scale spectrum sharing networks, where multiple noncolluding eavesdroppers attempt to intercept the secondary transmission. We develop a comprehensive analytical framework to accurately assess the secrecy performance under the primary users’ quality of service constraint. Our aim is to characterize the impact of beamforming and artificial noise generation (BF&AN) on this complex large scale network. We first derive exact expressions for the average secrecy rate and the secrecy outage probability. We then derive an easy-to-evaluate asymptotic average secrecy rate and asymptotic secrecy outage probability when the number of antennas at the secondary transmitter goes to infinity. Our results show that the Equal Power Allocation between the useful signal and artificial noise is not always the best strategy to achieve maximum average secrecy rate in large scale spectrum sharing networks. Another interesting observation is that the advantage of BF&AN over BF on the average secrecy rate is lost when the aggregate interference from the primary and secondary transmitters is strong, such that it overtakes the effect of the generated AN.

  • artificial noise aided secure transmission in large scale spectrum sharing networks
    arXiv: Information Theory, 2016
    Co-Authors: Yansha Deng, Lifeng Wang, Syed Ali Raza Zaidi, Jinhong Yuan, Maged Elkashlan
    Abstract:

    We investigate beamforming and artificial noise generation at the secondary transmitters to establish secure transmission in large scale spectrum sharing networks,where multiple non-colluding eavesdroppers attempt to intercept the secondary transmission. We develop a comprehensive analytical framework to accurately assess the secrecy performance under the primary users' quality of service constraint. Our aim is to characterize the impact of beamforming and artificial noise generation on this complex large scale network. We first derive exact expressions for the average secrecy rate and the secrecy outage probability.We then derive an easy-to-evaluate asymptotic average secrecy rate and asymptotic secrecy outage probability when the number of antennas at the secondary transmitter goes to infinity. Our results show that the Equal Power Allocation between the useful signal and artificial noise is not always the best strategy to achieve maximum average secrecy rate in large scale spectrum sharing networks. Another interesting observation is that the advantage of beamforming and artificial noise generation over beamforming on the average secrecy rate is lost when the aggregate interference from the primary and secondary transmitters is strong, such that it overtakes the effect of the generated artificial noise.