Qing-An Zeng

DyXY: a proximity congestion-aware deadlock-free dynamic routing method for network on chip

A routing algorithm, namely dynamic XY (DyXY) routing, is proposed for NoCs to provide adaptive routing and ensure deadlock-free and livelock-free routing at the same time. New router architecture is developed to support the routing algorithm. Analytical models based on queuing theory are developed for DyXY routing for a two-dimensional mesh NoC architecture, and analytical results match very well with the simulation results. It is observed that DyXY routing can achieve better performance compared with static XY routing and odd-even routing

Performance analysis of a preemptive and priority reservation handoff scheme for integrated service-based wireless mobile networks

We propose an analytical model for integrated real-time and non-real-time services in a wireless mobile network with priority reservation and preemptive priority handoff schemes. We categorize the service calls into four different types, namely, real-time and non-real-time service originating calls, and real-time and non real-time handoff service request calls. Accordingly, the channels in each cell are divided into three parts: one is for real-time service calls only, the second is for non-real-time service calls only, and the last one is for overflow of handoff requests that cannot be served in the first two parts. In the third group, several channels are reserved exclusively for real-time service handoffs so that higher priority can be given to them. In addition, a realtime service handoff request has the right to preempt non-real-time service in the preemptive priority handoff scheme if no free channels are available, while the interrupted non-real-time service call returns to its handoff request queue. The system is modeled using a multidimensional Markov chain and a numerical analysis is presented to estimate blocking probabilities of originating calls, forced termination probability, and average transmission delay. This scheme is also simulated under different call holding time and cell dwell time distributions. It is observed that the simulation results closely match the analytical model. Our scheme significantly reduces the forced termination probability of real-time service calls. The probability of packet loss of non-real-time transmission is shown to be negligibly small, as a non-real-time service handoff request in waiting can be transferred from the queue of the current base station to another one.

Cost-Function-Based Network Selection Strategy in Integrated Wireless and Mobile Networks

Wireless and mobile networks have experienced great success over the past few years. However, any single type of wireless and mobile network cannot provide all types of services, e.g., wide coverage and high bandwidth. An integrated wireless and mobile network is introduced by combining these different types of wireless and mobile networks, which can provide more comprehensive services. In an integrated wireless and mobile network, a mobile terminal that is equipped with heterogeneous network interfaces is capable of accessing all the available networks. Therefore, how to select a desired network is an important issue for the integrated wireless and mobile network. Although some network-selection strategies have been proposed, most of them are designed to meet a users individual needs, such as the bandwidth, the access fee, or the power consumption. The system performance also has not been touched. In this paper, we propose a cost-function-based network selection (CFNS) strategy in an integrated wireless and mobile network from a systems perspective, which also considers a users needs. We also analyze the system performance of the proposed network-selection strategy by using a theoretical model and extensive simulations. The results obtained show that the proposed network-selection strategy affects multiple system parameters, which needs to be handled carefully.

An analytical model for information retrieval in wireless sensor networks using enhanced APTEEN protocol

Wireless sensor networks are a new class of ad hoc networks that will find increasing deployment in coming years, as they enable reliable monitoring and analysis of unfamiliar and untested environments. The advances in technology have made it possible to have extremely small, low powered sensor devices equipped with programmable computing, multiple parameter sensing, and wireless communication capability. Because of their inherent limitations, the protocols designed for such sensor networks must efficiently use both limited bandwidth and battery energy. We develop an M/G/1 model to analytically determine the delay incurred in handling various types of queries using our enhanced APTEEN (Adaptive Periodic Threshold-sensitive Energy Efficient sensor Network protocol) protocol. Our protocol uses an enhanced TDMA schedule to efficiently incorporate query handling, with a queuing mechanism for heavy loads. It also provides the additional flexibility of querying the network through any node in the network. To verify our analytical results, we have simulated a temperature sensing application with a Poisson arrival rate for queries on the network simulator ns-2. As the simulation and analytical results match perfectly well, this can be said to be the first step towards analytically determining the delay characteristics of a wireless sensor network.

Modeling and efficient handling of handoffs in integrated wireless mobile networks

We propose and analyze two handoff schemes without and with preemptive priority procedures for integrated wireless mobile networks. We categorize the service calls into four different types, namely, originating voice calls, originating data calls, voice handoff request calls, and data handoff request calls and we assume two separate queues for two handoff services. A number of channels in each cell are reserved exclusively for handoff request calls. Out of these channels, few are reserved exclusively for voice handoff request calls. The remaining channels are shared by both originating and handoff request calls. In the preemptive priority scheme, higher priority is given to voice handoff request calls over data handoff request calls and can preempt data service to the queue if, upon arrival, a voice handoff request finds no free channels. We model the system by a three-dimensional Markov chain and compute the system performance in terms of blocking probability of originating calls, forced termination probability of voice handoff request calls, and average transmission delay of data calls. It is observed that forced termination probability of voice handoff request calls can be decreased by increasing the number of reserved channels. On the other hand, as a data handoff request can be transferred from a queue of one base station to another, there is no packet loss of data handoff except for a negligibly small blocking probability.

Performance analysis of mobile cellular radio system with priority reservation handoff procedures

Studies a queueing scheme of calls in cellular radio systems where priority is given to handoff calls by assigning several channels exclusively for them. The remaining channels are shared by both the originating and handoff calls. In this scheme both the originating and handoff calls make their own queues. A handoff call queues up if on arrival it finds no idle channels. An originating call also queues if on arrival it finds that the number of available channels is less than or equal to that of the reserved channels. Important performance measures of the system such as forced termination probability, and queue lengths are obtained. Solutions for some special systems such as ones with a queue only for the handoff calls and without queues for any calls were also investigated.<<ETX>>

Channel allocation and medium access control for wireless sensor networks

Recent developments in sensor technology, as seen in Berkeleys Mica2 Mote, Rockwells WINS nodes and the IEEE 802.15.4 Zigbee, have enabled support for single-transceiver, multi-channel communication. The task of channel assignment with minimum interference, also named as the 2-hop coloring problem, allows repetition of colors occurs only if the nodes are separated by more than 2 hops. Being NP complete, development of efficient heuristics for this coloring problem is an open research area and this paper proposes the Dynamic Channel Allocation (DCA) algorithm as a novel solution. Once channels are assigned, a Medium Access Control protocol must be devised so that channel selection, arbitration and scheduling occur with maximum energy savings and reduced message overhead, both critical considerations for sensor networks. The contribution of this paper is twofold: (1) development and analysis of the DCA algorithm that assigns optimally minimum channels in a distributed manner in order to make subsequent communication free from both primary and secondary interference and (2) proposing CMAC, a fully desynchronized multi-channel MAC protocol with minimum hardware requirements. CMAC takes into account the fundamental energy constraint in sensor nodes by placing them in a default sleep mode as far as possible, enables spatial channel re-use and ensures nearly collision free communication. Simulation results reveal that the DCA consumes significantly less energy while giving a legal distributed coloring. CMAC, our MAC protocol that leverages this coloring, has been thoroughly evaluated with various modes in SMAC, a recent protocol that achieves energy savings through coordinated sleeping. Results show that CMAC obtains nearly 200% reduction in energy consumption, significantly improved throughput, and end-to-end delay values that are 50-150% better than SMAC for our simulated topologies.

A Novel Decision Strategy of Vertical Handoff in Overlay Wireless Networks

In an overlay wireless network, a mobile user can connect to different radio access networks if it is equipped with appropriate network interfaces. When the mobile user changes its connection between different radio access networks, a vertical handoff occurs. Most existing vertical handoff decision strategies are designed to meet individual needs that may not achieve a good system performance. In this paper, we propose and analyze a novel vertical hand-off decision strategy that considers the performance of the whole system. The performance comparison of the proposed vertical handoff decision strategy and existing strategy shows that the proposed strategy is better in the blocking probability of vertical handoff calls

Novel MAC Layer Handoff Schemes for IEEE 802.11 Wireless LANs

Handoff in the IEEE 802.11 wireless LANs (WLANs) occurs whenever the mobile station (STA) changes its association from one access point (AP) to another owing to poor link quality. In a WLAN, small coverage areas of APs create frequent handoffs. Previous studies have shown that the typical handoff latency is high enough to hamper the service quality of multimedia streams like VoIP (voice over IP). In this paper, a novel scheme to reduce the handoff latency is proposed by using inter-AP communication to receive the probe response(s). Another adaptive scheme to enhance the quality of service (QoS) for multimedia streams during handoff is presented which builds upon the first scheme and adaptively distributes the total handoff latency. Through extensive simulations, we prove that our adaptive scheme decreases handoff latency significantly and achieves both fast and smooth hand-off that multimedia applications entail.

Performance evaluation of medium access control for multiple-beam antenna nodes in a wireless LAN

We consider the medium access control (MAC) protocol design for nodes in a wireless LAN that use a wide-azimuth switched beam smart antenna system comprised of a multiple beam antenna array. The one-hop performance of carrier sense multiple access (CSMA) as well as slotted aloha for such a system is presented analytically and through simulation. The problem of synchronization of multiple beams in CSMA is investigated in our analysis. Our results show that, under heavy offered load conditions, CSMA is a good choice with nodes that have multiple-beam smart antennas, despite the performance loss due to the beam synchronization, providing a stable throughput that approaches unity and is invariant to fluctuations in the offered load. Slotted Aloha, on the other hand, is capable of higher peak throughput in a narrow range of offered loads as more switched beams are employed, but performance drastically reduces beyond optimum offered loads. We also introduce a method, expanded receive rule (ERR), whereby the tight synchronization among different beams of a receiver node in CSMA is relaxed, which is observed to provide better throughput. Finally, we also present performance results for a 4-way-handshake-type carrier sense mechanism using multiple beam antennas.