Browsing by Author "Sheen, Wern Ho"

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Resource scheduling with directional antennas for multi-hop relay networks in Manhattan-like environment
(2007)
Lin, Shiang-Jiun
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Sheen, Wern Ho
;
Fu, I-Kang
;
Huang, Chia-chi
;
電信工程研究所
Multi-hop relay (MR) networks have been proposed for user throughput improvement, coverage extension and/or capacity enhancement to the traditional mobile cellular networks. In particular, an MR network is being standardized by the IEEE 802.16j Task Group as an amendment to the IEEE 802.16e standard. This paper investigates the issue of resource scheduling for the IEEE 802.16j MR network in the Manhattan-like environment. New scheduling methods are proposed for the MR network with directional antennas equipped at both the base station and relay stations. Simulation results show that the system throughput can be dramatically increased by the proposed methods as compared to the system with omnidirectional antennas.
Transmitter-Based Pre-Processing for OFDM-CDMA Forward-Link Systems with Two-Dimensional Spreading
(2006)
Kuo, Chih-Cheng
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Sheen, Wern Ho
;
Chang, Chung-Ju
;
Hsiao, Chang Lung
;
電信工程研究所
Transmitter-based signal pre-processing is investigated for the two-dimensional (2-D) OFDM-CDMA (orthogonal frequency division multiplexing, code division multiple access) forward link systems, aiming to increase the system sum-capacity and shift the signal processing complexity of a mobile unit to the base station. For the non-selective failing channels, the optimum pre-processing that achieves the maximum ergodic sum-capacity is obtained by applying the principle of multi-user water filling under the condition of zero multiple access interference (MAI). For the selective fading channels, on the other hand, three sub-optimum methods including ZF (zero-forcing) with power normalization, MMSE (minimum mean square error), and the newly proposed ZF with multi-user water filling are investigated under the constraint of total transmit power. Numerical results show that: (i) The new pre-processing outperforms the traditional other two in terms of achievable sum-capacity. (ii) 2-D spreading pattern should be adapted to the channel conditions so as to minimize MAI and thus maximize the sum-capacity. In this regard, 2-D spreading has advantage over the 1-D one. (iii) The fewer the users scheduled at a time, the higher the system capacity; a result obtained from exploiting the multi-user diversity.