Orthogonal time-frequency space(OTFS)is a new modulation technique proposed in recent years for high Doppler wireless scenes.To solve the parameter estimation problem of the OTFS-integrated radar and communications sy...Orthogonal time-frequency space(OTFS)is a new modulation technique proposed in recent years for high Doppler wireless scenes.To solve the parameter estimation problem of the OTFS-integrated radar and communications system,we propose a parameter estimation method based on sparse reconstruction preprocessing to reduce the computational effort of the traditional weighted subspace fitting(WSF)algorithm.First,an OTFS-integrated echo signal model is constructed.Then,the echo signal is transformed to the time domain to separate the target angle from the range,and the range and angle of the detected target are coarsely estimated by using the sparse reconstruction algorithm.Finally,the WSF algorithm is used to refine the search with the coarse estimate at the center to obtain an accurate estimate.The simulations demonstrate the effectiveness and superiority of the proposed parameterestimation algorithm.展开更多
In this paper, we propose a new differential space-time-frequency （DSTF） modulation for MIMOOFDM system with four transmit-antennas and arbitrary receive-antennas, which can improve the transmission rate since it ca...In this paper, we propose a new differential space-time-frequency （DSTF） modulation for MIMOOFDM system with four transmit-antennas and arbitrary receive-antennas, which can improve the transmission rate since it can adopt high order quadrature amplitude modulation （QAM） modulation. Our proposed DSTF scheme embeds some full diversity full rate （FDFR） quasi-orthogonal space-time codes （QOSTBC） with QAM modulation into the frequency intervals and adopts the differential modulation in both time and frequency domains. The simulation results demonstrate that the proposed DSTF scheme can improve transmission rate greatly. Compared with the conventional differential unitary space-time modulation （DUSTM）, it can get better transmission performance in high transmission rate for MIMO-OFDM system.展开更多
An efficient spaee-time-frequency （STF） coding strategy for multi-input multi-output orthogonal frequency division multiplexing （MIMO-OFDM） systems is presented for high bit rate data transmission over frequency s...An efficient spaee-time-frequency （STF） coding strategy for multi-input multi-output orthogonal frequency division multiplexing （MIMO-OFDM） systems is presented for high bit rate data transmission over frequency selective fading channels. The proposed scheme is a new approach to space-time-frequency coded OFDM （ODFDM） that combines OFDM with space-time coding, linear precoding and adaptive power allocation to provide higher quality of transmission in terms of the bit error rate performance and power efficiency. In addition to exploiting the maximux diversity gain in frequency, time and space, the proposed scheme enjoys high coding advantages and low-complexity decoding. The significant performance improvement of our design is confirned by corroborating numerical simulations.展开更多
We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudi...We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudinal temperature of 8. 4 μK are loaded into a one-dimensional optical lattice. Spectroscopic analysis of the1S0-3P0 transition gives a linew idth of 180 Hz measured using magnetic field-induction,w hich mixes the3P1 state w ith the3P0 state. Rabi oscillations are observed. Because of the inhomogeneous excitation among the atoms,the Rabi π-pulse excitation at 5 ms show s a near 65% excitation of atoms. The transverse velocity distribution of the atomic beam and the absolute frequencies of the four inter-combination transitions of the isotopes w as measured precisely using velocity-selective fluorescence spectroscopy. By optical injection of tw o cascade external-cavity diode lasers,a single comb line at 689 nm from an optical femtosecond laser comb is filtered and amplified w ith a 37-d B side-mode suppression and a linew idth of less than 240 Hz. We describe recent w ork on a space optical clock concerning the physical vacuum system,thermal analysis,and a permanent-magnet Zeeman slow er for a space strontium optical clock. The first six mode frequencies are obtained and the corresponding oscillation modes are described in detail. We also simulate and analyze thermal profiles for both the physical and optical units installed in the cooling system. When the injected cooling w ater has a temperature of 21℃ or28℃,the units meet operational requirements for temperatures in a space environment. Using a series of permanent magnets,a Zeeman slow er is built that can w ithstand space launching and operating conditions for the space optical clock.展开更多
基金supported by the National Natural Science Foundation of China(No.61871203)the Postgraduate Scientific Research and Innovation Projects of Jiangsu Province,China(No.KYCX23_3878)。
文摘Orthogonal time-frequency space(OTFS)is a new modulation technique proposed in recent years for high Doppler wireless scenes.To solve the parameter estimation problem of the OTFS-integrated radar and communications system,we propose a parameter estimation method based on sparse reconstruction preprocessing to reduce the computational effort of the traditional weighted subspace fitting(WSF)algorithm.First,an OTFS-integrated echo signal model is constructed.Then,the echo signal is transformed to the time domain to separate the target angle from the range,and the range and angle of the detected target are coarsely estimated by using the sparse reconstruction algorithm.Finally,the WSF algorithm is used to refine the search with the coarse estimate at the center to obtain an accurate estimate.The simulations demonstrate the effectiveness and superiority of the proposed parameterestimation algorithm.
基金This work was supported in part by the National Natural Science Foundation of China under grant No. 60572117the Natural Science Foundation of Hubei Province under grant No. 2005ABA244.
文摘In this paper, we propose a new differential space-time-frequency （DSTF） modulation for MIMOOFDM system with four transmit-antennas and arbitrary receive-antennas, which can improve the transmission rate since it can adopt high order quadrature amplitude modulation （QAM） modulation. Our proposed DSTF scheme embeds some full diversity full rate （FDFR） quasi-orthogonal space-time codes （QOSTBC） with QAM modulation into the frequency intervals and adopts the differential modulation in both time and frequency domains. The simulation results demonstrate that the proposed DSTF scheme can improve transmission rate greatly. Compared with the conventional differential unitary space-time modulation （DUSTM）, it can get better transmission performance in high transmission rate for MIMO-OFDM system.
基金This project was supported by the National Natural Science Foundation of China (60272079) and the"863"High Tech-nology Research and Development Programof China (2003AA123310)
文摘An efficient spaee-time-frequency （STF） coding strategy for multi-input multi-output orthogonal frequency division multiplexing （MIMO-OFDM） systems is presented for high bit rate data transmission over frequency selective fading channels. The proposed scheme is a new approach to space-time-frequency coded OFDM （ODFDM） that combines OFDM with space-time coding, linear precoding and adaptive power allocation to provide higher quality of transmission in terms of the bit error rate performance and power efficiency. In addition to exploiting the maximux diversity gain in frequency, time and space, the proposed scheme enjoys high coding advantages and low-complexity decoding. The significant performance improvement of our design is confirned by corroborating numerical simulations.
文摘We report on studies of an optical lattice for a strontium clock performed at the National Time Service Center. Follow-ing tw o-stage laser cooling and trapping,88 Sr cold atoms w ith population of 105 and a longitudinal temperature of 8. 4 μK are loaded into a one-dimensional optical lattice. Spectroscopic analysis of the1S0-3P0 transition gives a linew idth of 180 Hz measured using magnetic field-induction,w hich mixes the3P1 state w ith the3P0 state. Rabi oscillations are observed. Because of the inhomogeneous excitation among the atoms,the Rabi π-pulse excitation at 5 ms show s a near 65% excitation of atoms. The transverse velocity distribution of the atomic beam and the absolute frequencies of the four inter-combination transitions of the isotopes w as measured precisely using velocity-selective fluorescence spectroscopy. By optical injection of tw o cascade external-cavity diode lasers,a single comb line at 689 nm from an optical femtosecond laser comb is filtered and amplified w ith a 37-d B side-mode suppression and a linew idth of less than 240 Hz. We describe recent w ork on a space optical clock concerning the physical vacuum system,thermal analysis,and a permanent-magnet Zeeman slow er for a space strontium optical clock. The first six mode frequencies are obtained and the corresponding oscillation modes are described in detail. We also simulate and analyze thermal profiles for both the physical and optical units installed in the cooling system. When the injected cooling w ater has a temperature of 21℃ or28℃,the units meet operational requirements for temperatures in a space environment. Using a series of permanent magnets,a Zeeman slow er is built that can w ithstand space launching and operating conditions for the space optical clock.
