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M. Sawahashi - One of the best experts on this subject based on the ideXlab platform.
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variable Spreading Factor ofcdm with two dimensional Spreading that prioritizes time domain Spreading for forward link broadband wireless access
IEICE Transactions on Communications, 2005Co-Authors: Noriyuki Maeda, Yoshihisa Kishiyama, Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes the optimum design for adaptively controlling the Spreading Factor in Orthogonal Frequency and Code Division Multiplexing (OFCDM) with two-dimensional Spreading according to the cell configuration, channel load, and propagation channel conditions, assuming the adaptive modulation and channel coding (AMC) scheme employing QPSK and 16QAM data modulation. Furthermore, we propose a two-dimensional orthogonal channelization code assignment scheme to achieve skillfully orthogonal multiplexing of multiple physical channels. We first demonstrate the reduction effect of inter-code interference by the proposed two-dimensional orthogonal channelization code assignment. Then, computer simulation results show that in time domain Spreading, the optimum Spreading Factor, except for an extremely high mobility case such as for the fading maximum Doppler frequency of f D = 1500 Hz, becomes SF Time = 16. Furthermore, it should be decreased to SF Time = 8 for such a very fast fading environment using 16QAM data modulation. We also clarify when the channel load is light such as C mux /SF = 0.25 (C mux and SF denote the number of multiplexed codes and total Spreading Factor, respectively), the required average received signal energy per symbol-to-noise power spectrum density ratio (E s /N 0 ) is reduced as the Spreading Factor in the frequency domain is increased up to say SF Freq = 32 for QPSK and 16QAM data modulation. When the channel load is close to full such as when C mux /SF = 0.94, the optimum Spreading Factor in the frequency domain is SF Freq = 1 for 16QAM data modulation and SF Freq = 1 to 8 for QPSK data modulation according to the delay spread. Consequently, by setting several combinations of Spreading Factors in the time and frequency domains, the near maximum link capacity is achieved both in cellular and hotspot cell configurations assuming various channel conditions.
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variable Spreading Factor ofcdm with two dimensional Spreading that prioritizes time domain Spreading for forward link broadband wireless access
Vehicular Technology Conference, 2003Co-Authors: Noriyuki Maeda, Yoshihisa Kishiyama, Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes the optimum design for adaptively controlling the Spreading Factor in orthogonal frequency and code division multiplexing (OFCDM) with two-dimensional Spreading according to the cell configuration, channel load, and propagation channel conditions, assuming the adaptive modulation and channel coding (AMC) scheme employing QPSK and 16QAM data modulation. Furthermore, we propose a two-dimensional channelization code assignment scheme to achieve skillfully orthogonal multiplexing of multiple physical channels. Computer simulation results elucidate that bit-interleaving in the frequency domain is superior to chip-interleaving especially for a full channel load because bit-interleaving exhibits a large randomization effect of burst errors, while still maintaining code orthogonality. In time domain Spreading, the optimum Spreading Factor, except for an extremely high mobility case such as for the fading maximum Doppler frequency f/sub D/ = 1500 Hz, becomes SF/sub Time/ = 16, and it should be decreased to SF/sub Time/ = 8 for such a very fast fading environment using 16QAM modulation. When the channel load is light such as C/sub mux//SF = 0.25 (C/sub mux/ and SF denote the number of multiplexed codes and total Spreading Factor, respectively), the required average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) is reduced as the Spreading Factor in the frequency domain is increased up to say SF/sub Freq/ = 32 for QPSK and 16QAM modulation, respectively (Note that, nevertheless, 16QAm modulation under such a lighter channel load condition is replaced by QPSK modulation together with two fold the channel load as 16QAM to achieve the same information bit rate). Meanwhile, when the channel load is close to full such as when C/sub mux//SF = 0.94, the optimum Spreading Factor in the frequency domain is SF/sub Freq/ = 1 for 16QAM modulation and SF/sub Freq/ = 1 to 8 for QPSK modulation according to the delay spread. Consequently, by setting several combinations of Spreading Factors in the time and frequency domains, the near maximum link capacity is achieved both in cellular and hot-spot cell configurations assuming various channel conditions.
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Variable Spreading Factor Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM)
Multi-Carrier Spread-Spectrum & Related Topics, 2002Co-Authors: Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes Variable Spreading Factor — Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) as the most promising forward link wireless access method in broadband packet wireless transmission using an approximate 50 – 100 MHz bandwidth. OFCDM is originally based on multicarrier CDMA where the Spreading sequence is multiplied in the frequency domain, and OFCDM employing VSF can flexibly realize near optimum wireless access with higher link capacity by adaptively changing the appropriate Spreading Factor, SF, in the frequency domain based on the cell structure and radio link conditions such as the delay spread. Furthermore, by establishing the Spreading Factor of SF = 1, i.e., no Spreading mode, VSF-OFCDM can be used as orthogonal frequency division multiplexing (OFDM). Simulation results demonstrate that, while SF = 1 (OFDM) achieves higher link capacity than SF > 1 in an isolated-cell environment, OFCDM with the optimized SF value over 1 achieves approximately 1.4 times higher capacity compared with OFDM in a multi-cell environment associated with the advantageous one-cell frequency reuse. Consequently, VSF-OFCDM can provide seamless deployment of broadband packet wireless access with high link capacity, that is, OFDM in an isolated-cell environment such as hot spot areas or indoor offices, and OFCDM with the adaptively optimized SF value over 1 in a multi-cell environment such as cellular systems according to the radio link conditions such as measured delay spread, by only changing the Spreading Factor.
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Optimum channel coding rate and Spreading Factor values achieving one-cell frequency reuse in downlink VSF-spread OFDM packet radio access
VTC-2005-Fall. 2005 IEEE 62nd Vehicular Technology Conference 2005., 1Co-Authors: Yoshihisa Kishiyama, Nobuhiko Miki, Naoto Ohkubo, Hiroyuki Atarashi, M. SawahashiAbstract:This paper investigates the optimum minimum coding rate of a very-low-rate Turbo coding and Spreading Factor value that achieves one-cell frequency reuse in Variable Spreading Factor (VSF)-Spread Orthogonal Frequency Division Multiplex- ing (OFDM) radio access in the downlink. Simulation results show that the optimum minimum coding rate is approximately R = 1/5 to 1/9 to obtain a clear additional coding gain from random code Spreading. Moreover, by applying hybrid ARQ with packet combining, the required Spreading (repetition) Factor value can be decreased by the time diversity gain associated with soft-com- bining, compared to the case without ARQ. Accordingly, we show that the Spreading Factor of 8, 4, and 2 is necessary in addition to Turbo coding with R = 1/8 when the maximum number of retrans- missions in hybrid ARQ with packet combining is 0, 1, and 3 times, respectively, in order to achieve one-cell frequency reuse at the required residual packet error rate of 10 -3 for a cell radius of 1 km with 46-dBm transmission power in a 10-MHz channel bandwidth. Furthermore, for a large cell radius such as greater than 2 km, a large Spreading Factor of greater than 16 is required to mitigate the influence of background noise under such noise limited conditions. I. INTRODUCTION
Xiao-dong Wang - One of the best experts on this subject based on the ideXlab platform.
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Universal Model for the Maximum Spreading Factor of Impacting Nanodroplets: From Hydrophilic to Hydrophobic Surfaces.
Langmuir : the ACS journal of surfaces and colloids, 2020Co-Authors: Yi-bo Wang, Xiao-dong Wang, Yan-ru Yang, Yi-feng Wang, Shu-rong Gao, Min ChenAbstract:Using molecular dynamics (MD) simulations, we investigate impact behaviors of water nanodroplets on hydrophilic to hydrophobic surfaces with static contact angles ranging from 21 to 148° in a wide Weber number range of 15-90, aiming to understand how the surface wettability influences the maximum Spreading Factor of nanodroplets. We show that the existing macroscale and nanoscale models cannot capture the influence of surface wettability on the maximum Spreading Factor. We demonstrate that the failure is attributed to the rough estimation of the Spreading velocity during the Spreading stage, which is assumed to be a constant value in these models. We show that the Spreading velocity strongly depends on both the surface wettability and the Weber number. After scaling with the impact velocity, we obtain a universal function of the Spreading velocity with respect to the static contact angle and the Weber number. We employ this function to modify the expression of viscous dissipation and develop a new model of the maximum Spreading Factor. We verify that the model is in excellent agreement with the MD simulations regardless of hydrophilic and hydrophobic surfaces, with the mean relative deviation ranging from 0.88 to 4.75%. We also provide evidence to support the fact that incorporating the influence of surface wettability by modifying viscous dissipation is more reasonable than by modifying surface energy for nanodroplet impact.
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The Maximum Spreading Factor for Polymer Nanodroplets Impacting a Hydrophobic Solid Surface
The Journal of Physical Chemistry C, 2019Co-Authors: Yi-bo Wang, Xiao-dong Wang, Yan-ru Yang, Min ChenAbstract:We investigate the impact behaviors of nanoscale polymer droplets on a solid surface via molecular dynamics (MD) simulations. The maximum Spreading Factor is focused on understanding the energy dissipation mechanism during impact. Our simulations show that the macroscale model for blood droplets and the nanoscale models for water droplets cannot capture the simulated maximum Spreading Factor of nanoscale polymer droplets. We demonstrate that viscous dissipation for nanoscale polymer droplets stems from the velocity gradients in both the impact and the Spreading direction, whereas for macroscale blood droplets and nanoscale water droplets, only the velocity gradient in the impact direction contributes to it. With the consideration of different dissipation mechanism, we propose a modified expression of viscous dissipation and develop a new model to predict the maximum Spreading Factor of nanoscale polymer droplets. By comparing the model predictions with MD simulations, we show that the new model can captur...
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the maximum Spreading Factor for polymer nanodroplets impacting a hydrophobic solid surface
Journal of Physical Chemistry C, 2019Co-Authors: Yi-bo Wang, Xiao-dong Wang, Yan-ru Yang, Min ChenAbstract:We investigate the impact behaviors of nanoscale polymer droplets on a solid surface via molecular dynamics (MD) simulations. The maximum Spreading Factor is focused on understanding the energy dis...
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variable Spreading Factor orthogonal polyphase codes for constant envelope ofdm cdma system
Wireless Communications and Networking Conference, 2006Co-Authors: Yingming Tsai, Guodong Zhang, Xiao-dong WangAbstract:Novel orthogonal polyphase codes with constant envelope design for OFDM-CDMA system are proposed in the paper. The proposed codes can support large number of users and variable Spreading Factor like Hadamard codes. Proposed orthogonal polyphase codes not only have better periodic auto- and cross correlations than Hadamard codes but also have constant envelope properties which is preferred for uplink/reverse link transmission. New transmitter and receiver architecture and MMSE receiver are proposed for the OFDM-CDMA system using the proposed polyphase codes. Simulation results show that OFDM-CDMA system using proposed polyphase codes has better PAPR and BER performance than OFDM-CDMA system using Hadamard codes and OFDMA system
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WCNC - Variable Spreading Factor orthogonal polyphase codes for constant envelope OFDM-CDMA system
IEEE Wireless Communications and Networking Conference 2006. WCNC 2006., 2006Co-Authors: Yingming Tsai, Guodong Zhang, Xiao-dong WangAbstract:Novel orthogonal polyphase codes with constant envelope design for OFDM-CDMA system are proposed in the paper. The proposed codes can support large number of users and variable Spreading Factor like Hadamard codes. Proposed orthogonal polyphase codes not only have better periodic auto- and cross correlations than Hadamard codes but also have constant envelope properties which is preferred for uplink/reverse link transmission. New transmitter and receiver architecture and MMSE receiver are proposed for the OFDM-CDMA system using the proposed polyphase codes. Simulation results show that OFDM-CDMA system using proposed polyphase codes has better PAPR and BER performance than OFDM-CDMA system using Hadamard codes and OFDMA system
Hiroyuki Atarashi - One of the best experts on this subject based on the ideXlab platform.
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variable Spreading Factor ofcdm with two dimensional Spreading that prioritizes time domain Spreading for forward link broadband wireless access
IEICE Transactions on Communications, 2005Co-Authors: Noriyuki Maeda, Yoshihisa Kishiyama, Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes the optimum design for adaptively controlling the Spreading Factor in Orthogonal Frequency and Code Division Multiplexing (OFCDM) with two-dimensional Spreading according to the cell configuration, channel load, and propagation channel conditions, assuming the adaptive modulation and channel coding (AMC) scheme employing QPSK and 16QAM data modulation. Furthermore, we propose a two-dimensional orthogonal channelization code assignment scheme to achieve skillfully orthogonal multiplexing of multiple physical channels. We first demonstrate the reduction effect of inter-code interference by the proposed two-dimensional orthogonal channelization code assignment. Then, computer simulation results show that in time domain Spreading, the optimum Spreading Factor, except for an extremely high mobility case such as for the fading maximum Doppler frequency of f D = 1500 Hz, becomes SF Time = 16. Furthermore, it should be decreased to SF Time = 8 for such a very fast fading environment using 16QAM data modulation. We also clarify when the channel load is light such as C mux /SF = 0.25 (C mux and SF denote the number of multiplexed codes and total Spreading Factor, respectively), the required average received signal energy per symbol-to-noise power spectrum density ratio (E s /N 0 ) is reduced as the Spreading Factor in the frequency domain is increased up to say SF Freq = 32 for QPSK and 16QAM data modulation. When the channel load is close to full such as when C mux /SF = 0.94, the optimum Spreading Factor in the frequency domain is SF Freq = 1 for 16QAM data modulation and SF Freq = 1 to 8 for QPSK data modulation according to the delay spread. Consequently, by setting several combinations of Spreading Factors in the time and frequency domains, the near maximum link capacity is achieved both in cellular and hotspot cell configurations assuming various channel conditions.
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variable Spreading Factor ofcdm with two dimensional Spreading that prioritizes time domain Spreading for forward link broadband wireless access
Vehicular Technology Conference, 2003Co-Authors: Noriyuki Maeda, Yoshihisa Kishiyama, Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes the optimum design for adaptively controlling the Spreading Factor in orthogonal frequency and code division multiplexing (OFCDM) with two-dimensional Spreading according to the cell configuration, channel load, and propagation channel conditions, assuming the adaptive modulation and channel coding (AMC) scheme employing QPSK and 16QAM data modulation. Furthermore, we propose a two-dimensional channelization code assignment scheme to achieve skillfully orthogonal multiplexing of multiple physical channels. Computer simulation results elucidate that bit-interleaving in the frequency domain is superior to chip-interleaving especially for a full channel load because bit-interleaving exhibits a large randomization effect of burst errors, while still maintaining code orthogonality. In time domain Spreading, the optimum Spreading Factor, except for an extremely high mobility case such as for the fading maximum Doppler frequency f/sub D/ = 1500 Hz, becomes SF/sub Time/ = 16, and it should be decreased to SF/sub Time/ = 8 for such a very fast fading environment using 16QAM modulation. When the channel load is light such as C/sub mux//SF = 0.25 (C/sub mux/ and SF denote the number of multiplexed codes and total Spreading Factor, respectively), the required average received signal energy per symbol-to-background noise power spectrum density ratio (E/sub s//N/sub 0/) is reduced as the Spreading Factor in the frequency domain is increased up to say SF/sub Freq/ = 32 for QPSK and 16QAM modulation, respectively (Note that, nevertheless, 16QAm modulation under such a lighter channel load condition is replaced by QPSK modulation together with two fold the channel load as 16QAM to achieve the same information bit rate). Meanwhile, when the channel load is close to full such as when C/sub mux//SF = 0.94, the optimum Spreading Factor in the frequency domain is SF/sub Freq/ = 1 for 16QAM modulation and SF/sub Freq/ = 1 to 8 for QPSK modulation according to the delay spread. Consequently, by setting several combinations of Spreading Factors in the time and frequency domains, the near maximum link capacity is achieved both in cellular and hot-spot cell configurations assuming various channel conditions.
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Variable Spreading Factor Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM)
Multi-Carrier Spread-Spectrum & Related Topics, 2002Co-Authors: Hiroyuki Atarashi, M. SawahashiAbstract:This paper proposes Variable Spreading Factor — Orthogonal Frequency and Code Division Multiplexing (VSF-OFCDM) as the most promising forward link wireless access method in broadband packet wireless transmission using an approximate 50 – 100 MHz bandwidth. OFCDM is originally based on multicarrier CDMA where the Spreading sequence is multiplied in the frequency domain, and OFCDM employing VSF can flexibly realize near optimum wireless access with higher link capacity by adaptively changing the appropriate Spreading Factor, SF, in the frequency domain based on the cell structure and radio link conditions such as the delay spread. Furthermore, by establishing the Spreading Factor of SF = 1, i.e., no Spreading mode, VSF-OFCDM can be used as orthogonal frequency division multiplexing (OFDM). Simulation results demonstrate that, while SF = 1 (OFDM) achieves higher link capacity than SF > 1 in an isolated-cell environment, OFCDM with the optimized SF value over 1 achieves approximately 1.4 times higher capacity compared with OFDM in a multi-cell environment associated with the advantageous one-cell frequency reuse. Consequently, VSF-OFCDM can provide seamless deployment of broadband packet wireless access with high link capacity, that is, OFDM in an isolated-cell environment such as hot spot areas or indoor offices, and OFCDM with the adaptively optimized SF value over 1 in a multi-cell environment such as cellular systems according to the radio link conditions such as measured delay spread, by only changing the Spreading Factor.
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Optimum channel coding rate and Spreading Factor values achieving one-cell frequency reuse in downlink VSF-spread OFDM packet radio access
VTC-2005-Fall. 2005 IEEE 62nd Vehicular Technology Conference 2005., 1Co-Authors: Yoshihisa Kishiyama, Nobuhiko Miki, Naoto Ohkubo, Hiroyuki Atarashi, M. SawahashiAbstract:This paper investigates the optimum minimum coding rate of a very-low-rate Turbo coding and Spreading Factor value that achieves one-cell frequency reuse in Variable Spreading Factor (VSF)-Spread Orthogonal Frequency Division Multiplex- ing (OFDM) radio access in the downlink. Simulation results show that the optimum minimum coding rate is approximately R = 1/5 to 1/9 to obtain a clear additional coding gain from random code Spreading. Moreover, by applying hybrid ARQ with packet combining, the required Spreading (repetition) Factor value can be decreased by the time diversity gain associated with soft-com- bining, compared to the case without ARQ. Accordingly, we show that the Spreading Factor of 8, 4, and 2 is necessary in addition to Turbo coding with R = 1/8 when the maximum number of retrans- missions in hybrid ARQ with packet combining is 0, 1, and 3 times, respectively, in order to achieve one-cell frequency reuse at the required residual packet error rate of 10 -3 for a cell radius of 1 km with 46-dBm transmission power in a 10-MHz channel bandwidth. Furthermore, for a large cell radius such as greater than 2 km, a large Spreading Factor of greater than 16 is required to mitigate the influence of background noise under such noise limited conditions. I. INTRODUCTION
Yang Yang - One of the best experts on this subject based on the ideXlab platform.
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maximally flexible assignment of orthogonal variable Spreading Factor codes for multirate traffic
IEEE Transactions on Wireless Communications, 2004Co-Authors: Yang YangAbstract:In universal terrestrial radio access (UTRA) systems, orthogonal variable Spreading Factor (OVSF) codes are used to support different transmission rates for different users. In this paper, we first define the flexibility index to measure the capability of an assignable code set in supporting multirate traffic classes. Based on this index, two single-code assignment schemes, nonrearrangeable and rearrangeable compact assignments, are proposed. Both schemes can offer maximal flexibility for the resulting code tree after each code assignment. We then present an analytical model and derive the call blocking probability, system throughput and fairness index. Analytical and simulation results show that the proposed schemes are efficient, stable and fair.
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nonrearrangeable compact assignment of orthogonal variable Spreading Factor codes for multi rate traffic
Vehicular Technology Conference, 2001Co-Authors: Yang YangAbstract:In UTRA systems, orthogonal variable-Spreading-Factor (OVSF) codes are used to support different transmission rates for different users. In this paper, we first define an index for measuring the flexibility of an assignable code set. Based on this flexibility index, a single-code assignment scheme, namely nonrearrangeable compact assignment (NCA), is proposed for accommodating multi-rate traffic. NCA can offer maximal flexibility to the resulting assignable code set after each code assignment. As a result, it gives better blocking, throughput and fairness performance when compared to random assignment (RA) scheme.
Alagan Anpalagan - One of the best experts on this subject based on the ideXlab platform.
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effect of carrier frequency offset on the ber performance of variable Spreading Factor ofcdm systems
International Conference on Communications, 2008Co-Authors: Lamiaa Khalid, Alagan AnpalaganAbstract:In this paper, the effect of frequency offset on the performance of downlink OFCDM systems with variable Spreading Factors is investigated. The bit error rate of downlink VSF-OFCDM is analyzed taking into account the effect of carrier frequency offset when subcarrier grouping is used. An analytic expression of the SINR for downlink OFCDM with frequency offset using BPSK modulation is derived for the case of maximal ratio combining receiver. Numerical results show that, when the total Spreading Factor is fixed to 32, the VSF-OFCDM system with higher frequency domain Spreading Factor is more sensitive to frequency offset than that with lower frequency domain Spreading Factor. Our results also show that, as the number of users increases, the degradation of the BER performance is more pronounced with the higher frequency domain Spreading Factor since more subcarriers are present in each group.
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ICC - Effect of Carrier Frequency Offset on the BER Performance of Variable Spreading Factor OFCDM Systems
2008 IEEE International Conference on Communications, 2008Co-Authors: Lamiaa Khalid, Alagan AnpalaganAbstract:In this paper, the effect of frequency offset on the performance of downlink OFCDM systems with variable Spreading Factors is investigated. The bit error rate of downlink VSF-OFCDM is analyzed taking into account the effect of carrier frequency offset when subcarrier grouping is used. An analytic expression of the SINR for downlink OFCDM with frequency offset using BPSK modulation is derived for the case of maximal ratio combining receiver. Numerical results show that, when the total Spreading Factor is fixed to 32, the VSF-OFCDM system with higher frequency domain Spreading Factor is more sensitive to frequency offset than that with lower frequency domain Spreading Factor. Our results also show that, as the number of users increases, the degradation of the BER performance is more pronounced with the higher frequency domain Spreading Factor since more subcarriers are present in each group.
