Packet delay analysis on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks

In this paper, the average packet delay on IEEE 802.11 DCF under finite load traffic in multi-hop ad hoc networks is analyzed. We employ a Markov chain model to analyze the probability of transmission at each node in an arbitrary slot and derive the channel access delay. We model each node using an M/G/1 queue and derive the queueing delay. The model is extended from analyzing the single-hop average packet delay to evaluating the end-to-end packet delay in multi-hop ad hoc networks without assuming the traffic to be in a saturation state. To validate our analytic results, we have done extensive simulation. The analytic and the simulation results match very well.

On Minimizing Delay with Probabilistic Splitting of Traffic Flow in Heterogeneous Wireless Networks

In the paper,we propose a framework to investigate how to effectively perform traffic flow splitting in heterogeneous wireless networks from a queue point.The average packet delay in heterogeneous wireless networks is derived in a probabilistic manner.The basic idea can be understood via treating the integrated heterogeneous wireless networks as different coupled and parallel queuing systems.The integrated network performance can approach that of one queue with maximal the multiplexing gain.For the purpose of illustrating the effectively of our proposed model,the Cellular/WLAN interworking is exploited.To minimize the average delay,a heuristic search algorithm is used to get the optimal probability of splitting traffic flow.Further,a Markov process is applied to evaluate the performance of the proposed scheme and compare with that of selecting the best network to access in terms of packet mean delay and blocking probability.Numerical results illustrate our proposed framework is effective and the flow splitting transmission can obtain more performance gain in heterogeneous wireless networks.

PERFORMANCE COMPARISON OF CELL-BASED AND PACKET-BASED SWITCHING SCHEMES FOR SHARED MEMORY SWITCHES

Shared Memory (SM) switches are widely used for its high throughput, low delay and efficient use of memory. This paper compares the performance of two prominent switching schemes of SM packet switches: Cell-Based Switching (CBS) and Packet-Based Switching (PBS).Theoretical analysis is carried out to draw qualitative conclusion on the memory requirement,throughput and packet delay of the two schemes. Furthermore, simulations are carried out to get quantitative results of the performance comparison under various system load, traffic patterns,and memory sizes. Simulation results show that PBS has the advantage of shorter time delay while CBS has lower memory requirement and outperforms in throughput when the memory size is limited. The comparison can be used for tradeoff between performance and complexity in switch design.

AFAR:adaptive fuzzy ant-based routing for communication networks

We propose a novel approach called adaptive fuzzy ant-based routing (AFAR), where a group of intelligent agents (or ants) builds paths between a pair of nodes, exploring the network concurrently and exchanging obtained information to up-date the routing tables. Routing decisions can be made by the fuzzy logic technique based on local information about the current network state and the knowledge constructed by a previous set of behaviors of other agents. The fuzzy logic technique allows multiple constraints such as path delay and path utilization to be considered in a simple and intuitive way. Simulation tests show that AFAR outperforms OSPF, AntNet and ASR, three of the currently most important state-of-the-art algorithms, in terms of end-to-end delay, packet delivery, and packet drop ratio. AFAR is a promising alternative for routing of data in next generation networks.

A new constrained-send mechanism to enhance the performance of IEEE 802.11 DCF

In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To avoid collision of high access loading, a constrained-send probability is introduced at the end of each back off procedure for the station transmitting. The performance of this mechanism is analyzed based on a 2-Dimension Markov analytical model, after that the optimum constrained-send probability is derived. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both system throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.

Optimal Output Feedback Control and Stabilization for NCSs with Packet Dropout and Delay: TCP Case

This paper considers the output feedback control and stabilization problems for network control systems（NCSs） with packet dropout and input delay, and the TCP（transmission control protocol） case is mainly investigated. Specifically, whether the control signal is lost can be acknowledged by the receiver in the NCSs. The main contributions are： 1） For the finite horizon case, the ＂optimal＂output feedback control is derived by using the dynamic programming approach, and it is noted that the separation principle holds for the considered situation; 2） For the infinite horizon case, for the first time, the necessary and sufficient stabilization conditions are derived for NCSs with packet dropout and delay.

Call admission control scheme for real-time services in packet-switched OFDM wireless networks

A call admission control scheme is proposed for real-time services in packet-switched orthogonal frequency division multiplexing （OFDM） wireless cellular networks. The main idea of the proposed scheme is to use maximum acceptance ratio to maintain maximum channel utilization for real-time services according to the desired packet-level and call- level quality-of-service （QoS） requirements. The acceptance ratio is periodically adjusted by using a time discrete Markov chain and Wiener prediction theory according to the varying traffic load. Extensive simulation results show that this algorithm maintains high channel utilization, even as it guarantees packet-level and call-level QoS requirements for real-time services.

Dynamic data packing towards the optimization of QoC and QoS in networked control systems

A class of networked control systems is investigated whose communication network is shared with other applications. The design objective for such a system setting is not only the optimization of the control performance but also the efficient utilization of the communication resources. We observe that at a large time scale the data packet delay in the communication network is roughly varying piecewise constant, which is typically true for data networks like the Internet. Based on this observation, a dynamic data packing scheme is proposed within the recently developed packet-based control framework for networked control systems. As expected this proposed approach achieves a fine balance between the control performance and the communication utilization: the similar control performance can be obtained at dramatically reduced cost of the communication resources. Simulations illustrate the effectiveness of the proposed approach.