Huei-Wen Ferng

Connection-wise end-to-end performance analysis of queuing networks with MMPP inputs

A systematic method for link/connection-wise end-to-end performance evaluation in queueing networks receiving heterogeneous Markov-modulated Poisson processes (H-MMPPs) is proposed. The method consists of (i) connection-wise nodal performance analysis; (ii) tagged departure process analysis; and (iii) moment matching. For the tagged departure process of an H-MMPPs/G/1 queue, we propose two decomposition schemes to approximate the output process of a tagged traffic stream which is mixed with other traffic streams. A moment matching method is further proposed to emulate the tagged output process as a two-state MMPP. The adjacent down-stream node along a reference connection can be then modeled as an H-MMPPs/G/1 queue. Recursively performing (i)‐(iii), the end-to-end performance of a reference connection is obtained. The methodology developed in this paper can be applied to packet-switched high-speed networks, especially to asynchronous transfer mode (ATM) networks.

Departure Processes of BMAP/G/1 Queues

A unified approach is applied to analyze the departure processes of finite/infinite BMAP/G/1 queueing systems for both vacationless and vacation arrangements via characterizing the moments, the z-transform of the scaled autocovariance function of interdeparture times CP(z), and lag n (n≥1) covariance of interdeparture times. From a structural point of view, knowing departure process helps one to understand the impact of service mechanisms on arrivals. Through numerical experiments, we investigate and discuss how the departure statistics are affected by service and vacation distributions as well as the system capacity. From a practical perspective, output process analysis serves to bridge the nodal performance and connectionwise performance. Our results can be then used to facilitate connection- or networkwise performance analysis in the current high-speed networks.

Energy-Efficient Routing Protocol for Wireless Sensor Networks with Static Clustering and Dynamic Structure

Due to limited energy of sensor nodes in a wireless sensor network, an energy-efficient routing protocol with static clustering and dynamic structure (ERP-SCDS) is proposed in this paper. Utilizing virtual points in a corona-based wireless sensor network, static clusters with dynamic structures are formed in ERP-SCDS. Moreover, next-round cluster heads are selected in advance to avoid a deadlock when the old cluster heads die. Finally, a simple relay node selection mechanism instead of a complicated multi-hop route discovery algorithm is further designed for ERP-SCDS. Integrating these mechanisms enables ERP-SCDS to form balanced cluster sizes to prolong the network lifetime. Via simulations, we demonstrate that ERP-SCDS significantly outperforms LEACH, HEED, and Hausdorff previously proposed in the literature.

Design of Novel Node Distribution Strategies in Corona-Based Wireless Sensor Networks

Considering coverage, efficiency, and durability, three nonuniform node distribution strategies for a corona-based wireless sensor network (WSN) are proposed in this paper. To derive lower bounds on sensor nodes in coronas, we investigate the optimal node placement based on coverage. We then prove the feasibility of balanced energy depletion for a primitive geometric node distribution (GND) and a primitive energy proportional node distribution (EPND). Applying the optimal node placement and GND enables us to propose the first strategy (Strategy I) to reach completely balanced energy depletion. Combining the optimal node placement, EPND, and a simple switch scheduling, the second strategy (Strategy II) and the third strategy (Strategy III) are designed for a uniform-width corona model and a nonuniform-width corona model, respectively. Although balanced energy depletion may not be reached, Strategy II achieves the longest network lifetime and Strategy III requires the fewest sensor nodes among the three strategies. Finally, the performance investigation done by both analytical and simulation approaches exhibits the superiorities of the proposed strategies over the two closest strategies in the literature in terms of number of sensor nodes, network lifetime, and residual energy.

Using priority, buffering, threshold control, and reservation techniques to improve channel-allocation schemes for the GPRS system

Taking a comprehensive approach, we investigate effects on the channel allocation for the general packet radio service (GPRS) system caused by priority strategy, buffering, threshold control on the buffer, and channel reservation. Moreover, four new dynamic channel-allocation schemes based on various combinations of these techniques are proposed and analyzed using the Markov chain approach. Analytical results obtained include blocking/forced-termination/dropping probabilities, cost-function definition based on the above metrics, and (mean) delay times. Through numerical examples, we demonstrate that: 1) priority and threshold control are efficient strategies to differentiate the quality of service (QoS) between a new voice call and a handoff voice call; 2) buffering allows more admitted rates of voice calls or data packets, but increases the delay time; and 3) channel reservation may directly improve a specific service, but it degrades performance of other services much. At last, better schemes suitable for the GPRS system are suggested after a thorough comparison of system performance.

A dynamic resource reservation scheme with mobility prediction for wireless multimedia networks

To reduce the call blocking probability (CBP) and call dropping probability (CDP) of real-time and non-real-time traffic in wireless multimedia networks, resource reservation is frequently employed to achieve both the above-mentioned goal as well as to avoid long latency of path rebuilding. However, pure resource reservation may lead to inefficient resource utilization and increase of CBP and CDP due to frequent handoff in wireless networks. To reduce unnecessary resource reservation, the prediction of moving direction can be incorporated to enhance the pure resource reservation. Therefore, a dynamic resource reservation scheme with mobility prediction is proposed in this paper. In this scheme, a resource request with available range rather than a fixed resource request is specified by each traffic to make the reservation scheme flexible. Using simulation results, we show that mobility prediction can dynamically adjust resource reservation and effectively enhance system resource utilization. Moreover, the available interval of resource request gives flexibility to resource reservation which also improves the system performance.

Uplink capacity enhancement for an integrated HAPS-terrestrial CDMA system

The integration of a high altitude platform station (HAPS) with existing terrestrial communication systems would be beneficial as several kinds of wireless services can be easily extended into remote areas. In this letter, we first examine the uplink capacity of a sharing-band overlaid HAPS-terrestrial code division multiple access (CDMA) system and an improved version using a doughnut-like cell model. Numerical results indicate that the uplink capacity is poor under both the proposals due to serious inter-system interference. To mitigate this problem, a ring structure is proposed for HAPS when integrated with a terrestrial cellular system

Designing a fair scheduling mechanism for IEEE 802.11 wireless LANs

A fair scheduling mechanism called distributed elastic round robin (DERR) is proposed in this letter for IEEE 802.11 wireless LANs operated in a distributed manner. To quantify the fairness, we not only derive its fairness bound, but also observe the fairness through ratios of throughput and weight using a simulation approach. By numerical comparisons among DERR, distributed deficit round robin (DDRR), and IEEE 802.11e, we demonstrate that DERR outperforms the other two mechanisms in performance and fairness.

A secure routing protocol for wireless sensor networks with consideration of energy efficiency

Focusing on the issues of security and energy efficiency, we present an energy-efficient secure routing protocol for wireless sensor networks (WSNs). With the location and energy-aware characteristics for routing, our protocol gives a better delivery rate, energy balancing, and routing efficiency. In addition, the proposed security mechanism ensures the data authenticity and confidentiality in the data delivery. Evaluating the proposed protocol through both simulation and analysis, we show that our proposed protocol can significantly outperform the closest routing protocol and security mechanism.

Path-wise performance in a tree-type network: Per-stream loss probability, delay, and delay variance analyses

This paper deals with path-wise performance analysis rather than a nodal one to enrich results previously obtained in the literature under simple but unsatisfactory assumptions, e.g., Poisson processes. First deriving the per-stream loss probability, delay, and delay variance of an isolated queue with multi-class input streams modeled by heterogeneous two-state Markov-modulated Poisson processes (MMPPs), we then propose simple and novel decomposition schemes working together with an input parameter modification scheme to (approximately) extract the per-stream output process for a lossy queue receiving MMPPs under a general service time distribution. The novelty of the decompositions is that they can be easily implemented based on a lossless queueing model. Through numerical experiments, we show that the accuracy in estimating the per-stream output process using such schemes is good. These decomposition schemes together with the input parameter modification scheme and a moment-based fitting algorithm used to fit the per-stream output as a two-state MMPP make analysis of path-wise performance viable by virtually treating each node in isolation along a path to get performance measures sequentially from the source node en route to the destination node.