Browsing by Author "Liu, Jen-Hsi"

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Joint Relay Selection and Scheduling Algorithm for Inter-Piconet Communications in Millimeter Wave Wireless Personal Area Networks
(2011)
Liu, Jen-Hsi
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Chao, Hsi-Lu
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資訊工程學系
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Department of Computer Science
Beamforming technique is used in IEEE 802.15.3c networks to avoid high propagation attenuation and path loss, and improve the overall system throughput by exploiting spatial channel reuse. In this paper, we introduce the necessity and design challenges of inter-piconet communications. Based on our observation, we propose a joint design of relay selection and scheduling. For relay selection, we define "interference-free", "concurrence-restricted extent", and "concurrence index" for properly selecting relays to improve the degree of spatial channel reuse. The designed scheduling consists of two phases: intra-piconet flow scheduling and inter-piconet flow scheduling. After performing phase 1 operations, intra-piconet flows are scheduled and the total required channel time is known. The phase 2 operations are to use the least channel time extension to schedule all inter-piconet flows. We evaluate our algorithm through simulations. The results show that the joint algorithm performs well and does achieve its objectives.
Performance Enhancement of Contention-Based Bandwidth Request Mechanism in IEEE 802.16 WiMAX Networks
(2010)
Chou, Shih-Fan
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Liu, Jen-Hsi
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Chao, Hsi-Lu
;
Guo, Tzu-Chi
;
Liu, Chia-Lung
The IEEE 802.16 standard is a promising technology for 4G mobile networks. Though supporting versatile service classes, best effort (BE) service class is expected to dominate WiMAX networks, due to operational simplicity. One of bandwidth request mechanisms that subscriber stations (SS) can utilize to issue bandwidth requests (BW-REQ) for BE connections is contention-based random access. An SS starts a timer T16 when transmitting a BW-REQ. If getting a grant before timer expiration, the SS transmits data packets at the allocated time slots; otherwise it performs truncated binary exponential backoff process for BW-REQ retransmission. The default value of T16 is one frame time. However, T16 impacts on contention and request collision significantly. In the paper, we develop an analytical model for T16 timer setting. Besides, we derive analytical expressions for the average number of tries per BW-REQ and the average packet delay. We compare the theoretical results of fixed and adjustable timers. The results show that adjusting timer reduces both the number of collision and the average packet delay.