Browsing by Author "Li, Chi-Fang"

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A closed-form approximation for capacity of multiuser MIMO broadcast systems: A virtual user approach
(2008)
Wang, Li-Chun
;
Yeh, Chu-Jung
;
Li, Chi-Fang
;
交大名義發表
;
National Chiao Tung University
Besides delivering high data rates in a point-to-point scenario, multi-input multi-output (MIMO) antenna techniques can broadcast personalized data to multiple users in the point-to-multipoint scenario. Zero-forcing beamforming (ZFB) is a suboptimal but simple MIMO broadcast technique, which basically decouple the MIMO channel into many parallel single-input single-output (SISO) channels. In this article, we first derive the closed-form expression for the sum rate of the ZFB MIMO broadcast system with random user selection. Secondly, under the condition with finite users, we develop a virtual user approach approximation method for estimating the sum rate of the ZFB MIMO broadcast system with exhaustive user selection. Our results indicate that the proposed analysis method can accurately estimate the optimal sum-rate throughput of ZFB.
Cell search in WCDMA under large-frequency and clock errors: Algorithms to hardware implementation
(2008-03-01)
Li, Chi-Fang
;
Chu, Yuan-Sun
;
Ho, Jan-Shin
;
Sheen, Wern-Ho
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電信工程研究所
This paper proposes a complete cell-search solution for real-world handset operations in the wide-band code-division multiple-access system. Large-frequency and clock errors are induced at initial search due to an inaccuracy of crystal oscillators within handsets and could cause fatal performance degradation. In addition to a primary search algorithm for achieving essential pseudo-noise code acquisitions, an enhanced algorithm combining frequency offset compensation, random sample per frame, and sample point reordering is proposed to achieve fast initial search even while an inaccuracy is up to 12 ppm. After a series of trade-off between performance and complexity, two search bins in the first stage are adopted to mitigate possible errors in each bin and make the enhanced schemes become effective. In final, the complete solution is presented with alternative algorithms: a primary one and an enhanced one. The solution is implemented with the flexibility for switching algorithms in different searches and using low-power methods for the sake of handsets' working time. Its core area is 3.8 x 3.8-mm(2) in a 3.3-V 0.35-mm CMOS technology, and the power consumption is 35.6 and 67 mW for the primary and enhanced algorithms, respectively.
Coverage enhancement for OFDM-based spatial multiplexing systems by scheduling
(2007)
Wang, Li-Chun
;
Chiu, Cheng-Wei
;
Yeh, Chu-Jung
;
Li, Chi-Fang
;
交大名義發表
This paper proposes a low-complexity coverage-oriented subcarriers assignment (COSA) algorithm which can efficiently assign the subchannels to enhance the coverage reliability of the orthogonal frequency division multiplexing (OFDM) based spatial multiplexing systems in the multiuser environment. Motivated by the increasing popularity of OFDM and the multi-input multi-output (MIMO) technique, how to use the multiuser and the frequency diversity simultaneously to improve the coverage reliability of the diversity-deficient multiplexing system is an essential issue. Because the total available transmit power is split uniformly across transmit antennas in the OFDM-based spatial multiplexing systems, increasing the number of transmit antennas leads to a smaller signal-to-noise ratio (SNR) per degree of freedom. Thus we propose the COSA algorithm to enhance the coverage performance of this system. Besides, by means of order statistics and Glivenko-Cantelli Theorem, we develop an analytical expression for the link outage probability and cell coverage reliability of the OFDM-based spatial multiplexing systems when using COSA, respectively.
Coverage performance analysis of multiuser MIMO broadcast systems
(2008)
Wang, Li-Chun
;
Yeh, Chu-Jung
;
Li, Chi-Fang
;
交大名義發表
;
National Chiao Tung University
We consider the downlink of a multiuser multi-input multi-output (MIMO) broadcast channel under a single cell structure. To study the achievable link coverage performance of zero-forcing beamforming (ZFB) and zero-forcing dirty-paper coding (ZF-DPC) when the channel state information (CSI) is available to the transmitter. First we develop analytical closed-form expressions for the link outage probability and coverage reliability of baseline ZFB and ZF-DPC when no multiuser scheduling involved. We find that the coverage performance of ZFB can only approach to that of the weakest link of ZF-DPC under predetermined required SNR and outage probability. Secondly, for exploring the achievable cell coverage, we discuss the strongest link performance of both broadcast beamforming schemes under multiuser scheduling. Under a framework of analysis for ZF-DPC and simulation for ZFB, we show that a soft coverage enhancement can be easily done by using scheduling techniques without extra hardware power consumption.