Browsing by Author "Ho, CL"

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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.
An OSIC based reduced-rank MIMO equalizer using conjugate gradient algorithm
(2003-09-01)
Ho, CL
;
Lin, GJ
;
Lee, TS
;
資訊工程學系
;
電信工程研究所
A reduced complexity multiple-input multiple-output (MIMO) equalizer with ordered successive interference cancellation (OSIC) is proposed for combating intersymbol interference (ISI) and cochannel interference (CCI) over frequency-selective multipath channels. It is developed as a reduced-rank realization of the conventional MMSE decision feedback equalizer (DFE). In particular, the MMSE weight vectors at each stage of OSIC are computed based on the generalized sidelobe canceller (GSC) technique and reduced-rank processing is incorporated by using the conjugate gradient (CG) algorithm for reduced complexity implementation. The CG algorithm leads to a best low-rank representation of the GSC blocking matrix via an iterative procedure, which in turn gives a reduced-rank equalizer weight vector achieving the best compromise between ISI and CCI suppression. With the dominating interference successfully cancelled at each stage of OSIC, the number of iterations required for the convergence of the CG algorithm decreases accordingly for the desired signal. Computer simulations demonstrate that the proposed reduced-rank MIMO DFE can achieve nearly the same performance as the full-rank MIMO MMSE DFE with an effective rank much lower than the dimension of the signal-plus-interference subspace.
Block based symbol detection for high rate space-time coded systems
(2004)
Ho, CL
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
Institute of Communications Engineering
A new block based symbol detection scheme is proposed for a class of high data rate space-time coded systems reported in the literature. We here adopt the vertical Bell labs layered space-time (V-BLAST) detection algorithm to defect the transmitted symbols at the receiver end, since it yields reasonable trade-off between performance and computational complexity with respect to the optimal maximum likelihood detection. By exploiting the distinctive structures resulting front the space-time block coded systems, we show that the associated V-BLAST detection can be performed in a block-by-block manner: in each iteration stage, a block of symbols is simultaneously defected. Compared with the conventional symbol-by-symbol based V-BLAST, the block based detection tends to reduce computations and decoding delays since it involves less iterations. Computer simulations show that the proposed block based symbol detection can achieve nearly the same performance of the symbol-by-symbol based one.
Path-time coding for downlink multi-user CDMA over multipath channels
(2003)
Ho, CL
;
Wu, JY
;
Lee, TS
;
電信工程研究所
;
友訊交大聯合研發中心
A new BLAST MIMO transceiver is proposed for the downlink of high data rate CDMA systems over frequency-selective multipath channels. We consider the scenario in which multiple antennas are used at both the base station (BS) and each mobile station (MS). The high data-rate stream is first demultiplexed into multiple substreams, which are then encoded across different paths and time delays by a set of "path-time" encoders for achieving path diversity, and spread by a set of precoders designed to suppress the multiple access interference (MAI) and equalize the multipath channels without the use of channel information. These coded substreams are transmitted simultaneously by multiple antennas for an increased spectral efficiency. At each MS, the received data is passed through a simple matched filter (MF) with a modified code sequence to blindly suppress the residual ISI. A multi-user detection scheme is then employed to separate the mutually interfering signals from the multiple transmit antennas and restore the diversity gain due to path-time coding (PTC). The proposed scheme can effectively provide spatial multiplexing and diversity gain at the same time. Moreover, significant enhancement in performance can be achieved at the receiver by incorporating suitable iterative interference cancellation strategies.