Dongsook Kim

Optimal Stochastic Routing in Low Duty-Cycled Wireless Sensor Networks

We study a routing problem in wireless sensor networks whereby sensors are duty-cycled. When sensors alternate between on and off modes, delays encountered in packet delivery due to loss in connectivity can become a critical problem, and how to achieve delay-optimality is nontrivial. For instance, when sensors’ sleep schedules are uncoordinated, it is not immediately clear whether a sensor with data to transmit should wait for a particular neighbor (who may be on a short route) to become available/active before transmission, or simply transmit to an available/active neighbor to avoid waiting. To obtain some insight into this problem, in this paper we formulate it as an optimal stochastic routing problem, where the randomness in the system comes from random duty-cycling, as well as the uncertainty in packet transmission due to time-varying channel conditions. A similar framework has been used in prior work that results in optimal routing algorithms that are sample-path dependent, also referred to as opportunistic in some cases. We show that such algorithms are no longer optimal when duty-cycling is introduced. We develop and analyze an optimal centralized stochastic routing algorithm for this problem, and then simplify the algorithm to work with only local information. We further develop a distributed algorithm utilizing only local sleep/wake information of neighbors. This algorithm is shown to perform better than some existing distributed opportunistic routing algorithms such as ExOR.

A throughput-efficient code assignment scheme for an integrated voice/data multi-code CDMA system

In this paper, we propose an efficient code assignment scheme (CAS), namely, unfair-sharing scheme, to enhance the average throughput of non real-time data users in an integrated voice/data multi-code CDMA system. The unfair-sharing CAS allocates the maximum number of sub-codes only for one data user while assigning a single sub-code for the rest of the data users. To achieve a fair transmission for all data users, the number of sub-codes for each data user is scheduled by the round-robin method. It is shown that the proposed CAS is more efficient for non real-time data service than the conventional CAS, called a fair-sharing scheme, in terms of throughput, average power saving factor, and system utilization factor. Specifically, when a system is loaded by 20% of the maximum number of voice users and 30% of the maximum number of data users, the proposed CAS enhances the throughput approximately more than 200%.

Distributed admission control via dual-queue management

This paper introduces and studies a new queue management framework via the use of connection level information already embedded in existing data traffic. Our goal is to improve the system performance and resource utilization at times of intense network congestion. Under this framework, data packets and connection establishment packets are queued separately. Different queueing and dropping policies can then be applied to them, thus the term dual-queue management. This framework is stateless and does not require per-flow queueing or flow counting. Using examples of such policies our initial simulation shows that this scheme can lead to much higher performance and network resource utilization during severe congestion. It also leads to more robust and scalable network design. Moreover, it provides an attractive mechanism for network provisioning via parameter tuning.