The Experts below are selected from a list of 17757 Experts worldwide ranked by ideXlab platform
Fan Wei - One of the best experts on this subject based on the ideXlab platform.
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random pilot and data access for massive mimo spatially correlated rayleigh fading channels
arXiv: Signal Processing, 2019Co-Authors: Junyuan Gao, Fan WeiAbstract:Random access is necessary in crowded scenarios due to the limitation of pilot sequences and the intermittent pattern of device activity. Nowadays, most of the related works are based on independent and identically distributed (i.i.d.) channels. However, massive multiple-input multiple-output (MIMO) channels are not always i.i.d. in realistic outdoor wireless propagation environments. In this paper, a device grouping and pilot set allocation algorithm is proposed for the uplink massive MIMO systems over spatially correlated Rayleigh fading channels. Firstly, devices are divided into multiple groups, and the channel covariance matrixes of devices within the same group are approximately orthogonal. In each group, a dedicated pilot set is assigned. Then active devices perform random pilot and data access process. The mean square error of channel estimation (MSE-CE) and the spectral efficiency of this scheme are derived, and the MSE-CE can be minimized when collision devices have non-overlapping angle of arrival (AoA) intervals. Simulation results indicate that the MSE-CE and spectral efficiency of this protocol are improved compared with the traditional scheme. The MSE-CE of the proposed scheme is close to the Theoretical Lower Bound over a wide signal-to-noise ratio (SNR) region especially for long pilot sequence. Furthermore, the MSE-CE performance gains are significant in high SNR and strongly correlated scenarios.
Yijin Zhang - One of the best experts on this subject based on the ideXlab platform.
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Artificial-Noise-Aided Secure Transmission With Directional Modulation Based on Random Frequency Diverse Arrays
IEEE Access, 2017Co-Authors: Jinsong Hu, Shihao Yan, Jiangzhou Wang, Feng Shu, Jun Li, Yijin ZhangAbstract:In this paper, a random frequency diverse array-based directional modulation with artificial noise (RFDA-DM-AN) scheme is proposed to enhance physical layer security of wireless communications. Specifically, we first design the RFDA-DM-AN scheme by randomly allocating frequencies to transmit antennas, thereby achieving 2-D (i.e., angle and range) secure transmissions, and outperforming the state-of-the-art 1-D (i.e., angle) phase array (PA)-based DM scheme. Then we derive the closed-form expression of a Lower Bound on the ergodic secrecy capacity (ESC) of our RFDA-DM-AN scheme. Based on the Theoretical Lower Bound derived, we further optimize the transmission power allocation between the useful signal and artificial noise (AN) in order to improve the ESC. Simulation results show that: (1) our RFDA-DM-AN scheme achieves a higher secrecy capacity than that of the PA-based DM scheme; (2) the Lower Bound derived is shown to approach the ESC as the number of transmit antennas N increases and precisely matches the ESC when N is sufficiently large; and (3) the proposed optimum power allocation achieves the highest ESC of all power allocations schemes in the RFDA-DM-AN.
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artificial noise aided secure transmission with directional modulation based on random frequency diverse arrays
arXiv: Information Theory, 2016Co-Authors: Shihao Yan, Jiangzhou Wang, Feng Shu, Yijin ZhangAbstract:In this paper, we propose a novel directional modulation (DM) scheme based on random frequency diverse arrays with artificial noise (RFDA-DM-AN) to enhance physical layer security of wireless communications. Specifically, we first design the RFDA-DM-AN scheme by randomly allocating frequencies to transmit antennas, thereby achieving two-dimensionally (i.e., angle and range) secure transmissions, and outperforming the state-of-the-art one-dimensional (i.e., angle) phase array (PA) based DM scheme. Then we develop the closed-form expression of a Lower Bound on the ergodic secrecy capacity (ESC) of our RFDA-DM-AN scheme. Based on the Theoretical Lower Bound derived, we further optimize the transmission power allocation between the useful signal and artificial noise (AN) in order to enhance the ESC. Simulation results show that 1) our RFDA-DM-AN scheme achieves a higher secrecy capacity than that of the PA based DM scheme, 2) the Lower Bound derived is shown to approach the ESC as the number of transmit antennas N increases and precisely matches the ESC when N is sufficiently large, and 3) the proposed optimum power allocation achieves the highest ESC compared with other power allocations in the RFDA-DM-AN.
Deniz Gunduz - One of the best experts on this subject based on the ideXlab platform.
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audience retention rate aware caching and coded video delivery with asynchronous demands
IEEE Transactions on Communications, 2019Co-Authors: Qianqian Yang, Mohammad Mohammadi Amiri, Deniz GunduzAbstract:Most of the current literature on coded caching focus on a static scenario in which a fixed number of users synchronously place their requests from a content library, and the performance is measured in terms of the latency in satisfying all of these requests. In practice, however, users start watching an online video content asynchronously over time, and often abort watching a video before it is completed. The latter behavior is captured by the notion of audience retention rate , which measures the portion of a video content watched on average. In order to bring coded caching one step closer to practice, asynchronous user demands are considered in this paper by allowing user demands to arrive randomly over time, and both the popularity of video files, and the audience retention rates are taken into account. A decentralized partial coded delivery (PCD) scheme is proposed, and two cache allocation schemes are employed; namely homogeneous cache allocation (HoCA) and heterogeneous cache allocation (HeCA), which allocate users’ caches among different chunks of the video files in the library. Numerical results validate that the proposed PCD scheme, either with HoCA or HeCA, outperforms conventional uncoded caching as well as the state-of-the-art decentralized caching schemes, which consider only the file popularities, and are designed for synchronous demand arrivals. An information-Theoretical Lower Bound on the average delivery rate is also presented.
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audience retention rate aware caching and coded video delivery with asynchronous demands
arXiv: Information Theory, 2018Co-Authors: Qianqian Yang, Mohammad Mohammadi Amiri, Deniz GunduzAbstract:Most results on coded caching focus on a static scenario, in which a fixed number of users synchronously place their requests from a content library, and the performance is measured in terms of the latency in satisfying all of these demands. In practice, however, users start watching an online video content asynchronously over time, and often abort watching a video before it is completed. The latter behaviour is captured by the notion of audience retention rate, which measures the portion of a video content watched on average. In order to bring coded caching one step closer to practice, asynchronous user demands are considered in this paper, by allowing user demands to arrive randomly over time, and both the popularity of video files, and the audience retention rates are taken into account. A decentralized partial coded caching (PCC) scheme is proposed, together with two cache allocation schemes; namely the optimal cache allocation (OCA) and the popularity-based cache allocation (PCA), which allocate users' caches among different chunks of the video files in the library. Numerical results validate that the proposed PCC scheme, either with OCA or PCA, outperforms conventional uncoded caching as well as the state-of-the-art decentralized caching schemes, which consider only the file popularities, and are designed for synchronous demand arrivals. An information-Theoretical Lower Bound on the average delivery rate is also presented.
Jean Armstrong - One of the best experts on this subject based on the ideXlab platform.
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Theoretical Lower Bound for indoor visible light positioning using received signal strength measurements and an aperture based receiver
Journal of Lightwave Technology, 2017Co-Authors: Heidi Steendam, Thomas Q Wang, Jean ArmstrongAbstract:Indoor visible light positioning (VLP) using signals transmitted by lighting LEDs is a topic attracting increasing interest within the research community. In the recent years, VLP techniques using a range of receiver structures and positioning algorithms have been described. In this paper, we analyze the performance of a VLP system, which uses an aperture-based receiver and measurements of received signal strength. An aperture-based receiver has a number of receiving elements, each consisting of a photodiode and an associated aperture. It has been shown that receivers of this form can be designed which are compact and provide both a wide overall field-of-view and good angular diversity. As a result, they can efficiently extract position-related information from light transmitted by nondirectional LEDs. In our approach, we correlate the signals at the outputs of the photodiodes with a set of reference signals. The resulting observations include information on the received signal strength as well as the angle-of-arrival, and are used to directly estimate the receiver's position. In order to assess the performance of positioning algorithms based on this approach, we derive the Cramer–Rao Lower Bound on the position estimate. We show that the Cramer–Rao Bound depends on the selected reference signal, and that subcentimetre to centimetre accuracy can be obtained, using only a limited number of nondirectional LEDs.
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Theoretical Lower Bound for indoor visible light positioning using received signal strength measurements and an aperture based receiver
Journal of Lightwave Technology, 2017Co-Authors: Heidi Steendam, Thomas Q Wang, Jean ArmstrongAbstract:Indoor visible light positioning (VLP) using signals transmitted by lighting LEDs is a topic attracting increasing interest within the research community. In the recent years, VLP techniques using a range of receiver structures and positioning algorithms have been described. In this paper, we analyze the performance of a VLP system, which uses an aperture-based receiver and measurements of received signal strength. An aperture-based receiver has a number of receiving elements, each consisting of a photodiode and an associated aperture. It has been shown that receivers of this form can be designed which are compact and provide both a wide overall field-of-view and good angular diversity. As a result, they can efficiently extract position-related information from light transmitted by nondirectional LEDs. In our approach, we correlate the signals at the outputs of the photodiodes with a set of reference signals. The resulting observations include information on the received signal strength as well as the angle-of-arrival, and are used to directly estimate the receiver's position. In order to assess the performance of positioning algorithms based on this approach, we derive the Cramer–Rao Lower Bound on the position estimate. We show that the Cramer–Rao Bound depends on the selected reference signal, and that subcentimetre to centimetre accuracy can be obtained, using only a limited number of nondirectional LEDs.
Junyuan Gao - One of the best experts on this subject based on the ideXlab platform.
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random pilot and data access for massive mimo spatially correlated rayleigh fading channels
arXiv: Signal Processing, 2019Co-Authors: Junyuan Gao, Fan WeiAbstract:Random access is necessary in crowded scenarios due to the limitation of pilot sequences and the intermittent pattern of device activity. Nowadays, most of the related works are based on independent and identically distributed (i.i.d.) channels. However, massive multiple-input multiple-output (MIMO) channels are not always i.i.d. in realistic outdoor wireless propagation environments. In this paper, a device grouping and pilot set allocation algorithm is proposed for the uplink massive MIMO systems over spatially correlated Rayleigh fading channels. Firstly, devices are divided into multiple groups, and the channel covariance matrixes of devices within the same group are approximately orthogonal. In each group, a dedicated pilot set is assigned. Then active devices perform random pilot and data access process. The mean square error of channel estimation (MSE-CE) and the spectral efficiency of this scheme are derived, and the MSE-CE can be minimized when collision devices have non-overlapping angle of arrival (AoA) intervals. Simulation results indicate that the MSE-CE and spectral efficiency of this protocol are improved compared with the traditional scheme. The MSE-CE of the proposed scheme is close to the Theoretical Lower Bound over a wide signal-to-noise ratio (SNR) region especially for long pilot sequence. Furthermore, the MSE-CE performance gains are significant in high SNR and strongly correlated scenarios.
