Browsing by Author "Lee, TS"

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A beamspace diversity combiner for sector division multiple access communications
(1998)
Lee, TS
;
Lee, ZS
;
電信工程研究所
;
Institute of Communications Engineering
A beamspace-time blind RAKE receiver for sectored CDMA systems
(2001-04-01)
Lee, TS
;
Tsai, TC
;
Chen, CH
;
電信工程研究所
;
友訊交大聯合研發中心
A beamspace-time (BT) RAKE receiver is proposed for multiple access interference (MAT) suppression and multipath diversity reception in sectored wireless CDMA communications. The scheme involves three stages. First, a set of adaptive beamformers encompassing a prescribed angular sector is constructed on an antenna array, each providing effective suppression of out-of-sector MAI and reception of in-sector signal. Second, a set of adaptive correlators is attached to each beam to combat in-sector MAI. Finally, the beamspace correlator output data are combined to capture the signal multipaths coherently. The above three-stage operation is performed in a blind mode in that no training signal is needed. The only information required is the signature, timing and a rough estimate of the angle of arrival (AOA) of the desired signal.
A beamspace-time interference canceling CDMA receiver for sectored communications in a multipath environment
(2001-07-01)
Lee, TS
;
Tsai, TC
;
電信工程研究所
;
友訊交大聯合研發中心
;
Institute of Communications Engineering
A beamspace-time (BT) receiver is proposed for interference suppression and multipath diversity reception in sectored wireless code division multiple access communications. The scheme involves two stages, First, a set of adaptive space-time diversity processors, in the form of beamformer-correlator pairs, is constructed which provides effective suppression of unwanted interference and reception of signals from a prescribed spare-time region, Second, the output data obtained by these processors are maximum ratio combined to capture the signal multipath components coherently. The proposed BT receiver is blind in that no training signal is required. The only information required is the signature sequence, timing and a rough estimate of the angle of arrival of the signal for selecting the sector of interest.
A beamspace-time rake receiver for sectored CDMA systems
(2000)
Lee, TS
;
Tsai, TC
;
電信工程研究所
;
Institute of Communications Engineering
A beamspace-time (BT) RAKE receiver is proposed for multiple access interference (MAI) suppression and multipath diversity reception in sectored wireless CDMA communications. The scheme involves two stages. First, a set of diversity beamformers is constructed and then combined for each finger which provides effective reception of in-sector signals and suppression of out-of-sector MAI. Second, an adaptive correlator is attached to each combined beam to combat in-sector MAI and collect signal multipaths in a coherent manner The proposed BT RAKE receiver is blind in that no training signal is required. The only information required is the signature sequence, timing and a rough estimate of the angle of arrival (AOA) of the signal.
A decision aided CDMA receiver with partially adaptive decorrelating multi-user interference cancellation
(2003-08-01)
Lin, GJ
;
Lee, TS
;
電信工程研究所
;
友訊交大聯合研發中心
;
Institute of Communications Engineering
A CDMA receiver with enhanced multiple access interference (MAI) suppression is proposed for a pilot symbols assisted system over multipath channels. The design of the receiver involves the following procedure. First, blind adaptive correlators are constructed at different fingers based on the scheme of generalized sidelobe canceller (GSC) to collect the multipath signals and suppress MAI. A low-complexity partially adaptive (PA) realization of the GSC correlators is proposed which incorporates multi-user information for reduced rank processing. By a judiciously designed decorrelating procedure, a new GSC structure is obtained in which the MAI are decorrelated and suppressed individually. The next step is then a simple coherent combining of the correlator outputs with pilot aided channel estimation. Finally, further performance enhancement is achieved by an iterative scheme in which the signal is reconstructed and subtracted from the GSC correlators input data, leading to faster convergence of the receiver. The proposed low-complexity PA CDMA multi-user receiver is shown to be robust to multipath fading and channel errors, and achieve nearly the same performance of the ideal maximum SINR and MMSE receivers by using a small number of pilot symbols.
A decision feedback CDMA receiver with partially adaptive interference suppression
(2001)
Lin, GJ
;
Lee, TS
;
Tan, CC
;
電信工程研究所
;
Institute of Communications Engineering
A novel CDMA receiver with adaptive multiple access interference (MAI) and narrowband interference (NBI) suppression is proposed for reverse link signal reception over multipath channels. The design of the receiver involves the following procedure. First, adaptive correlators are constructed based on the generalized side-lobe canceller (GSC) scheme to collect the multipath signals and suppress strong MAI and time-varying NBI. In particular, partial adaptivity is incorporated into the GSC for reduced complexity processing. A simple combiner with channel estimation then gives the symbol decisions. In order to enhance the performance of the adaptive correlators, a decision aided scheme is introduced which subtracts the reconstructed signal from the input data of the GSC, leading to improved output SINK and convergence. The proposed CDMA receiver is evaluated through simulations, and the results show that it can outperform the conventional MMSE receiver designed for time-invariant interference.
A low complexity group-wise PIC based mixed-mode MIMO-OFDM system
(2004)
Deng, JH
;
Lin, CY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A mixed-mode MIMO-OFDM system with the reduced complexity group-wise parallel interference cancellation (G-PIC) algorithm is proposed. At the transmitter, the data stream is first demultiplexed into two groups of substreams, one with capacity constraint via the spatial multiplexing (SM) mode and the other with link quality constraint via the space-time block coding (STBC) mode. At the receiver, a reduced complexity GPIC is proposed to separate the transmitted streams from different antennas and is based on the following procedures: First, a group-wise MMSE detector and ordering strategy are designed for each group to provide reliable initial decisions for recursive PIC. Second, a recursive group-wise detector, which consists of a conventional PIC, subspace projector and reduced size NIL searcher, is developed. Simulation results show that the proposed reduced complexity G-PIC provides almost identical performance compared to the conventional BLAST and relatively lower computational load.
A low complexity partially adaptive CDMA receiver for downlink mobile satellite communications
(2003-01-01)
Lin, GJ
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A novel CDMA receiver with enhanced interference suppression is proposed for pilot symbols assisted mobile satellite systems in the presence of frequency offset. The design of the receiver involves the following procedure. First, adaptive correlators are constructed at different fingers, based on the scheme of generalized sidelobe canceller (GSC), to collect the multipath signals and suppress multi-access interference (MAI). In particular, a partially adaptive (PA) realization of the GSC correlators is proposed based on the Krylov subspace technique, leading to an efficient algorithm without the need of complicated matrix computations. Second, pilot symbols assisted frequency offset estimation, channel estimation and RAKE combining give the estimate of signal symbols. Finally, further performance enhancement is achieved by an iterative scheme in which the signal is reconstructed and subtracted from the GSC correlators input, leading to faster convergence of the receiver. The proposed low complexity PA receiver is suitable or the downlink of mobile satellite CDMA systems, and shown to outperform the conventional fully adaptive MMSE receiver by using a small number of pilot symbols. Copyright (C) 2003 John Wiley Sons, Ltd.
A low-complexity adaptive multi-beam space-time receiver for CCI/ISI cancellation over frequency selective multipath channels
(2003-05-01)
Ho, CL
;
Lee, TS
;
電信工程研究所
;
友訊交大聯合研發中心
;
Institute of Communications Engineering
A space-time (ST) receiver is proposed for combating the cochannel interference (CCI) and intersymbol interference (ISI) in a frequency-selective multipath environment. The scheme involves two stages. First, a set of adaptive beamformers pointed at a prescribed angular sector in space is constructed on an oversampled antenna array, each providing effective suppression of CCI and reception of desired signals. Second, a fractionally-spaced decision feedback equalizer (DFE) follows to eliminate the ISI left in beamformer outputs. In particular, both the beamformers and DFE can be realized in the form of a generalized sidelobe canceller (GSC) with the aid of channel estimation, and partial adaptivity is incorporated for reduced complexity processing and improved convergence. The proposed ST receiver can be employed as a multi-beam smart antenna system which is suitable for cellular communications. Computer simulations demonstrate that it can achieve nearly the same performance as the optimal ST minimum mean square error (MMSE) DFE with a much lower implementation complexity.
A low-complexity multi-user CDMA receiver with blind channel estimation and partially adaptive MAI suppression
(2003-09-01)
Lin, GJ
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
;
Department of Computer Science
A low complexity multi-user receiver with blind channel estimation and multiple access interference (MAI) suppression is proposed for a CDMA system under multipath fading and frequency offset. The design of the receiver involves the following procedure. First, a method of joint MAI suppression and channel estimation is developed based on the generalized side-lobe canceller (GSC) technique. In particular, channel estimates are obtained blindly in the form of the effective composite signature vectors (CSV) of the users. Second, a low-complexity partially adaptive (PA) realization of the receiver is proposed which incorporates reduced-rank processing based on the information of multi-user CSV's. By a judiciously designed decorrelating procedure, a new PA receiver is obtained with a much lower complexity. Finally, pilot symbols assisted frequency offset estimation and channel gain compensation give the estimate of users' symbols. Further performance enhancement is achieved by a decision aided scheme in which the signal is reconstructed and subtracted from the receiver input data, leading to significantly faster convergence. The proposed receiver is shown to be robust to multipath fading and frequency offset, and achieves nearly the same performance of the optimal maximum SINR and MMSE receivers with a much lower overhead for pilot symbols.
A multistage multi-carrier CDMA receiver with blind adaptive MAI suppression
(2001)
Deng, JH
;
Lin, GJ
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A multistage multicarrier CDMA (MSMC-CDMA) receiver with enhanced multiple access interference (MAI) suppression is proposed for a reverse link time-multiplexed pilot symbols assisted system over multipath channels. The design of the receiver involves the following procedure. First, a blind adaptive matched filter is attached to each finger to perform despreading and combat MAI. Second, channel estimation and a RAKE combiner gives the estimate of the signal. Finally, signal reconstruction is accomplished by exploiting the channel estimate, data decisions, and signal's signature. The reconstructed signal is then subtracted from the data sent to the next stage. With signal reconstruction and subtraction as stages proceed, the MSMC-CDMA receiver can achieve nearly the performance of the optimal maximum SINR (MSINR) receiver, as confirmed by simulations.
A multistage multi-carrier CDMA receiver with enhanced interference suppression
(2001)
Deng, JH
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A multistage multicarrier CDMA (MSMC-CDMA) receiver with enhanced multiple access interference (MAI) suppression is proposed. The design of the receiver involves the following procedure. First, a set of adaptive matched filters (MF) is constructed to collect multipath signals with different time delays. The tap weights of each MF are determined in accordance with the linearly constrained minimum variance (LCMV) criterion so that strong MAI can be effectively suppressed. Second, channel estimation and signal reconstruction are accomplished by exploiting pilot symbols,, decision-directed symbols and the signal's signature. Finally, a decision-directed RAKE receiver gives the estimate of the signal, which is then subtracted from the data sent to the next stage. The proposed receiver can be used in a reverse link system with time-multiplexed pilot symbols, and achieves nearly the performance of the optimal maximum SINR (MSINR) receiver.
A near-optimal low-complexity transceiver for CP-free multi-antenna OFDM systems
(2006-01-01)
Lin, CY
;
Wu, JY
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.
A partially adaptive CDMA interference canceller for multipath channels
(2000)
Lee, TS
;
Tsai, TC
;
電信工程研究所
;
Institute of Communications Engineering
An adaptive receiver with enhanced interference rejection is proposed for CDMA communications over multipath channels. The design of the receiver involves a two-stage procedure. First, an adaptive correlator bank is constructed in the form of generalized sidelobe canceller (GSC) to suppress strong interference. To reduce complexity, the partially adaptive implementation is incorporated in the design of GSC blocking matrix. Next, a maximum ratio combining of the correlator outputs is performed to constructively collect the multipath energy. Since strong MAI has been removed, channel estimation can be done accurately, leading to improved performance compared to the conventional RAKE receiver.
A sectorized beamspace adaptive diversity combiner for multipath environments
(1999-09-01)
Lee, TS
;
Lee, ZS
;
電信工程研究所
;
Institute of Communications Engineering
The beam diversity technique is effective in combating multipath fading in wireless communications. In a beam diversity system, multiple receiving branches are formed with multiple antenna beams with distinctive patterns. These beams are synthesized in such a fashion that the fading phenomena observed at different branches are nearly uncorrelated, The disadvantage of such a system is the lack of adaptivity for cochannel interference (CCI) suppression. In this paper, an adaptive beam diversity combiner is proposed for sectorized signal reception. The diversity branches are formed with several adaptive beamformers whose response patterns encompass an angular sector in the field-of-view of the receiver,With a set of judiciously chosen weight vectors, effective diversity combining can be achieved inside the sector, and out-of-sector CCI can be suppressed via nulling, Simulation results confirm the efficacy of the proposed scheme.
A space-time multi-carrier CDMA receiver with blind adaptive MAI suppression
(2002-08-01)
Deng, JH
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
;
Department of Computer Science
A space-time (ST) receiver is proposed for multiple access interference (MAI) and narrowband interference (NBI) suppression, and multipath diversity reception in wireless multi-carrier CDMA communications incorporating antenna arrays. The scheme involves three stages. First, an adaptive matched filter is attached to each finger at each antenna to combat the MAL Second, an adaptive beamformer is constructed for each finger which provides effective reception of the signal of interest (SOI) and suppression of time-varying NBI. Finally, beamformer output data from different fingers are combined to capture the signal multipath components coherently. The proposed ST receiver is shown to perform reliably under strong interference, and outperform the ST MMSE receiver with pilot symbols aided channel estimation.
Adaptive beamforming with interpolated arrays for multiple coherent interferers
(1997-03-01)
Lee, TS
;
Lin, TT
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
The spatial smoothing technique is effective in decorrelating multiple coherent interferers for an adaptive beamformer. However, it requires a configuration with identical subarrays. This paper presents an interpolation scheme to synthesize multiple virtual subarrays allowing for the use of spatial smoothing from a real array of arbitrary geometry. After interpolation, the optimum spatially smoothed subarray beamformer is constructed. A dimension recovery transformation can then be implemented to calculate the weights of the full array which will retain the interference nulls of the subarray beamformer. The efficacy of the proposed scheme is assessed through simulation. (C) 1997 Elsevier Science B.V.
Adaptive beamforming with interpolated arrays for multiple coherent interferers
(1997-03-01)
Lee, TS
;
Lin, TT
;
電信工程研究所
;
Institute of Communications Engineering
The spatial smoothing technique is effective in decorrelating multiple coherent interferers for an adaptive beamformer. However, it requires a configuration with identical subarrays. This paper presents an interpolation scheme to synthesize multiple virtual subarrays allowing for the use of spatial smoothing from a real array of arbitrary geometry. After interpolation, the optimum spatially smoothed subarray beamformer is constructed. A dimension recovery transformation can then be implemented to calculate the weights of the full array which will retain the interference nulls of the subarray beamformer. The efficacy of the proposed scheme is assessed through simulation. (C) 1997 Elsevier Science B.V.
An efficient interference cancellation scheme for CP-Free MIMO-OFDM systems
(2005)
Lin, CY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
Conventional orthogonal frequency division multiplexing (OFDM) systems use cyclic prefix (CP) to protect signal from the multipath channel induced distortions. However, the presence of CP could greatly decrease the effective data rate. In this paper, an interference cancellation scheme based on the generalized sidelobe canceller (GSC) principle is proposed for interference suppression of CP-free multiple-input multiple-output (MIMO) OFDM systems. An associated reduced complexity implementation based on the partially adaptive (PA) scheme is also proposed by exploiting the structural information of the signal and interference signature matrices. As well, we study sampling error in the proposed system. Under the block transmission model, a simple sampling error estimation method is proposed. Whenever sampling error is known, the proposed GSC equalizer can he directly applied based on the timing offsetted system model. Simulation results show that the performance of the proposed solution is almost identical to that obtained by the conventional CP-based MIMO-OFDM system under either the synchronous or asynchronous scenario.
An iterative maximum SINR receiver for multicarrier CDMA systems over a multipath fading channel with frequency offset
(2003-05-01)
Deng, JH
;
Lee, TS
;
電信工程研究所
;
友訊交大聯合研發中心
;
Institute of Communications Engineering
A robust iterative multicarrier code-division multiple-access (MC-CDMA) receiver with adaptive multiple-access interference (MAI) suppression is proposed for a pilot symbols assisted system over a multipath fading channel with frequency offset. The design of the receiver involves a two-stage procedure. First, an adaptive filter based on the generalized sidelobe canceller (GSC) technique is constructed at each finger to perform despreading and suppression of MAI. Second, pilot symbols assisted frequency offset estimation, channel estimation and a RAKE combining give the estimate of signal symbols. In order to enhance the convergence behavior of the GSC adaptive filters, a decisions-aided scheme is proposed, in which the signal waveform is first reconstructed and then subtracted from the input data of the adaptive filters. With signal subtraction, the proposed MC-CDMA receiver can achieve nearly the performance of the ideal maximum signal-to-interference-plus noise ratio receiver assuming perfect channel and frequency offset information. Finally, a low-complexity partially adaptive (PA) realization of the GSC adaptive filters is presented as an alternative to the conventional multiuser detectors. The new PA receiver is shown to be robust to multiuser channel estimation errors and offer nearly the same performance of the fully adaptive receiver.