Chih-Min Chao

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The use of OVSF codes in WCDMA systems has offered opportunities to provide variable data rates to flexibly support applications with different bandwidth requirements. Two important issues in such an environment are the code placement problem and code replacement problem. The former may have significant impact on code utilization and, thus, code blocking(More)
In multihop wireless ad hoc networks, it is important that all mobile hosts are synchronized. Synchronization is necessary for power management and for frequency hopping spread spectrum (FHSS) operations. IEEE 802.11 standards specify a clock synchronization protocol but this protocol suffers from the scalability problem due to its inefficiency contention(More)
In the third-generation partnership project technical specification, orthogonal variable spreading factor (OVSF) codes are used as channelization codes. The use of OVSF codes can provide variable data rates to flexibly support applications with different bandwidth requirements. Most works in the literature assume that only one single OVSF code is used to(More)
Since sensor nodes are energy-constrained, energy saving is a critical issue in wireless sensor networks. By reducing the number of transmissions, data aggregation is an effective approach to save energy. In the literature, most of data aggregation protocols rely on a structured architecture to accomplish the data gathering task. Such structure-based(More)
Packet scheduling in a WCDMA system poses a new challenge due to its nature of variable bit rates and location-dependent, time-varying channel conditions. In this work, two new downlink scheduling algorithms for a WCDMA base station are proposed to support multimedia transmissions. With a credit management and a compensation mechanism, our algorithms(More)
Although multiple channels are supported in the physical layer, the IEEE 802.11 MAC layer mechanism is designed for using a single channel. Exploiting multiple channels enhances spatial reuse and reduces transmission collisions and thus improves network throughput. Designing a multi-channel MAC protocol is much more difficult than designing a singlechannel(More)