A new quadrature coded OFDM system is proposed. The transmitted data symbols are grouped in such format that the in phase side and the quadrature side of the symbols are arranged in opposite order. By analysis an...A new quadrature coded OFDM system is proposed. The transmitted data symbols are grouped in such format that the in phase side and the quadrature side of the symbols are arranged in opposite order. By analysis and simulation, the performance of the new system can be improved greatly, as well as the harmful influences on the system owing to frequency offset can be reduced effectively, which can combat the disadvantages of OFDM system.展开更多
The position decoding accuracy and the spatial resolution of positron emission tomography detectors are greatly influenced by the performance of the two-dimensional position map,including the gain uniformity of photom...The position decoding accuracy and the spatial resolution of positron emission tomography detectors are greatly influenced by the performance of the two-dimensional position map,including the gain uniformity of photomultiplier tube (PMT),the baseline offset of the PMT signals and the accuracy of analogue to digital converter (ADC).In this work,a PMT-quadrant sharing detector was designed.Two data acquisition platforms are employed to conduct the influence factors on the two-dimensional position map performances,one was that the waveforms of the PMT signals were scanned by the sequence acquisition mode based on the oscilloscope of LeCroy waveRunner 204MXi-A,and another was a self-developed high speed ADC data acquisition module.Results show that the event decoding positions were concentrated on the PMT with higher gain,the position map was distorted at the baseline offset of signal,and the cross-line artifacts were caused by the insufficient ADC sampling bit for a larger size position map.All the parameters need be adjusted properly to stabilize a real system,and the flexible oscilloscope platform can be used to design the detector block and the other platform with high ADC accuracy.Likely,the electrical circuit with a proper ADC accuracy adjusts the PMT gains and baseline offsets.展开更多
Power offset is zero-order term in the capacity versus signal-to-noise ratio curve. In this paper, approximate analysis of power offset is presented to describe MIMO system with uniform linear antenna arrays of fixed ...Power offset is zero-order term in the capacity versus signal-to-noise ratio curve. In this paper, approximate analysis of power offset is presented to describe MIMO system with uniform linear antenna arrays of fixed length. It is assumed that the number of receive antenna is larger than that of transmit antenna. Spatially Correlated MIMO Channel is approximated by tri-diagonal toeplitz matrix. The determinant of tri-diagonal toeplitz matrix, which is fitted by elementary curve, is one of the key factors related to power offset. Based on the curve fitting, the determinant of tri-diagonal toeplitz matrix is mathematically tractable. Consequently, the expression of local extreme points can be derived to optimize power offset. The simulation results show that approximation above is accurate in local extreme points of power offset. The proposed expression of local extreme points is helpful to approach optimal power offset.展开更多
This paper presented an automatic gain control （AGC） circuit suitable for FM/cw ladar. The proposed architecture was based on two-stage variable gain amplifier （VGA） chain with a novel DC offset canceller circuit,...This paper presented an automatic gain control （AGC） circuit suitable for FM/cw ladar. The proposed architecture was based on two-stage variable gain amplifier （VGA） chain with a novel DC offset canceller circuit, which contained an improved Gilbert cell and a Gm-C feedback loop. To keep the VGA with a linearity in dB characteristic, an improved exponential gain control circuit was introduced. The AGC was implemented in 0.18 gm standard CMOS process. Simulation and measurement results verified that its gain ranged from -20 dB to 30 dB, and band- width ranged from 100 kHz to 10 MHz. Its power consumption was 19.8 mW under a voltage supply of 3.3 V.展开更多
文摘A new quadrature coded OFDM system is proposed. The transmitted data symbols are grouped in such format that the in phase side and the quadrature side of the symbols are arranged in opposite order. By analysis and simulation, the performance of the new system can be improved greatly, as well as the harmful influences on the system owing to frequency offset can be reduced effectively, which can combat the disadvantages of OFDM system.
基金Supported by in part by Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP200800031071)National Natural Science Foundation of China (No. 10975086)the National High Technology Research and Development Program (863 Program) of China (No. 2006AA020802)
文摘The position decoding accuracy and the spatial resolution of positron emission tomography detectors are greatly influenced by the performance of the two-dimensional position map,including the gain uniformity of photomultiplier tube (PMT),the baseline offset of the PMT signals and the accuracy of analogue to digital converter (ADC).In this work,a PMT-quadrant sharing detector was designed.Two data acquisition platforms are employed to conduct the influence factors on the two-dimensional position map performances,one was that the waveforms of the PMT signals were scanned by the sequence acquisition mode based on the oscilloscope of LeCroy waveRunner 204MXi-A,and another was a self-developed high speed ADC data acquisition module.Results show that the event decoding positions were concentrated on the PMT with higher gain,the position map was distorted at the baseline offset of signal,and the cross-line artifacts were caused by the insufficient ADC sampling bit for a larger size position map.All the parameters need be adjusted properly to stabilize a real system,and the flexible oscilloscope platform can be used to design the detector block and the other platform with high ADC accuracy.Likely,the electrical circuit with a proper ADC accuracy adjusts the PMT gains and baseline offsets.
文摘Power offset is zero-order term in the capacity versus signal-to-noise ratio curve. In this paper, approximate analysis of power offset is presented to describe MIMO system with uniform linear antenna arrays of fixed length. It is assumed that the number of receive antenna is larger than that of transmit antenna. Spatially Correlated MIMO Channel is approximated by tri-diagonal toeplitz matrix. The determinant of tri-diagonal toeplitz matrix, which is fitted by elementary curve, is one of the key factors related to power offset. Based on the curve fitting, the determinant of tri-diagonal toeplitz matrix is mathematically tractable. Consequently, the expression of local extreme points can be derived to optimize power offset. The simulation results show that approximation above is accurate in local extreme points of power offset. The proposed expression of local extreme points is helpful to approach optimal power offset.
基金Supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China(No.2012ZX03004008)
文摘This paper presented an automatic gain control （AGC） circuit suitable for FM/cw ladar. The proposed architecture was based on two-stage variable gain amplifier （VGA） chain with a novel DC offset canceller circuit, which contained an improved Gilbert cell and a Gm-C feedback loop. To keep the VGA with a linearity in dB characteristic, an improved exponential gain control circuit was introduced. The AGC was implemented in 0.18 gm standard CMOS process. Simulation and measurement results verified that its gain ranged from -20 dB to 30 dB, and band- width ranged from 100 kHz to 10 MHz. Its power consumption was 19.8 mW under a voltage supply of 3.3 V.
