The authors study the design of heterogeneous two-tier wireless sensor networks (WSNs), where one tier of nodes is more robust and computationally intensive than the other tier. The authors find the ratios of densities of nodes in each tier to maximise coverage and network lifetime. By employing coverage processes and optimisation theory, the authors show that any topology of WSN derived from r...

Two-tier network structure is usually used to lighten the energy consumption in Wireless Multimedia Sensor Networks (WMSNs) for large scale surveillance application. Previous methods for target tracking in two-tier WMSNs mostly focused on reducing energy cost to prolong lifetime of the networks without considering the effect of visual target tracking. This paper presents a collaborative multi-t...

The ability to accurately determine the geographic location of an arbitrary IP address has potential in many applications. Previous methods that are based on observing the relationship between network delay and physical distance are inaccurate. Methods based on delay similarity are more accurate but inefficient because they require information on a large number of landmark nodes near the destin...

A learner's performance does not rely only on the representation language and on the algorithm inducing a hypothesis in this language. Also the way the induced hypothesis is interpreted for the needs of concept recognition is of interest. A exible methodology for hypothesis interpretion is ooered by the philosophy of a learner's second tier as originally suggested by Michalski (1987). Here, the...

In today's competitive markets, firms try to reduce their supply cost by selecting efficient suppliers using different techniques. Several methods can be applied to evaluate the efficiency of supplier base. This paper develops generalized network data envelopment analysis models to examine the efficiency of two-tier supplier bases under cooperative and non-cooperative strategies where each tier...

When the sensor field is too large in self-organization clustering, energy inefficiency may result when cluster-heads broadcast an Advertisement Message over the sensor field area. Limiting the transmission range of the Advertisement Message is a requirement in this case. Detrimentally, when the transmission range is limited, Advertisement Message non-receiving nodes can be generated due to sel...

High-resolution images with wide field of view are important in realizing many applications of wireless multimedia sensor networks. Previous works that generally use multi-tier topology and provide such images by increasing the capabilities of camera sensor nodes lead to an increase in network cost. On the other hand, the resulting energy consumption is a considerable issue that has not been se...

While mobile ad-hoc networking (MANET) research has received a considerable attention in recent years, the majority of them have focused on single-tier (e.g., ground) and homogeneous (e.g., same radio for every node) MANET. Few have investigated the potential implications of multi-tier and heterogeneous natures of MANET on the design and performance of MANET protocols in a systematic manner. Fo...

Hierarchical organizations in general boost overall system scalability. Some existing research work organizes peers into different hierarchical structures. In these systems, the top-tier overlay is either a completely-connected graph or a CHORD ring. These overlays can achieve good routing latency ( ) 1 ( O or ) (log O ), where n is the number of groups. However, each node has to keep a large n...

Solid State Disk technologies are increasingly replacing high-speed hard disks as the storage technology in high-random-I/O environments. There are several potentially I/O bound services within the typical LHC Tier-2 in the back-end, with the trend towards many-core architectures continuing, worker nodes running many single-threaded jobs and storage nodes delivering many simultaneous files can ...