The proliferation of wireless local area network (WLAN) deployments in enterprises, public areas, and homes will likely cause frequent geographical coverage overlap among multiple networks. A recent growing interest is the coordination among WLAN providers for efficient network management over a large coverage area. While radio resource management for a single WLAN has been studied extensively, little research work addresses resource management over multiple domains. When multiple WLANs co-locate in a small geographic vicinity, the lack of cooperative multi-domain resource management can cause significant performance degradation due to inter-domain interference. Unbalanced loads among multiple networks can incur congestion in a few WLANs while foregoing unused excess resources in others. Moreover, since WLANs often operate in unlicensed frequency bands shared by various public and private networks, they must cope with the dynamic RF environment involving a diverse set of interference sources. This paper introduces a new cooperative load balancing framework for multi-domain WLANs operating in an interference environment. A third-party-based architecture is proposed to facilitate fair radio resource allocation among multiple networks. The proposed third-party agent collects observed network state information from different WLANs and optimizes resource usage. Under the proposed scheme, resource utilization and co-channel interference can be adaptively balanced across the entire integrated system. The impact of other co-located interference sources in the operational environment are taken into account in the optimization process. The proposed load balancing framework for interference environments is a complement to the interference mitigation mechanisms operated at the PHY/MAC layer. Simulation results show that the proposed multi-domain load balancing scheme outperforms other schemes which do not consider interdomain interference or environmental interference.

The IEEE 802.11 and Low Rate WPAN (LR-WPAN) wireless networks can provide complimentary services and are likely to be installed within the same environments. Coexistence between the networks would be impaired, if the probability of packet collision between the networks is sufficiently large. This paper presents the results of an empirical study examining the impact of IEEE 802.11 on the LR-WPAN. The study focused on evaluating one aspect of the probability of collision: determining the interference power at which packet retransmission is likely to be required. The results from this empirical study are used to substantiate analytical models for interference suppression versus carrier frequency offset. The empirical study and analytical model are used to provide insight into the impact of adjacent channel interference from the interfering wireless service.

This paper investigates cooperative radio resource management for multiple cognitive radio networks in interference environments. The objective of this research is to manage shared radio resources fairly among multiple non- cooperative cognitive radio networks to optimize the overall performance. We emphasize the underlying predictability of network conditions and promote management solutions tailored to different interference environments. A multi-agent-system- based approach is proposed to achieve information sharing and decision distribution among multiple cognitive radio networks in a distributed manner. We address the distributed constraint optimization problem (DCOP) in cognitive radio networks and study the effectiveness of DCOP algorithms to find the optimal radio resource assignment through communications between distributed agents.

Mobile IP is a solution for mobility support in the global Internet. However, it suffers from long handoff delay. Many solutions have been proposed to reduce the handoff delay of Mobile IP. Among these solutions, Fast Handovers for Mobile IPv6 (FMIPv6) and Hierarchical Mobile IPv6 (HMIPv6) are actively developed by the Internet Engineering Task Force for future IPv6 networks. A majority of the research on performance analysis of Mobile IP handoff latency either adopts a simulation approach or is based on experimental testbeds. This paper focuses on the analytical modeling of handoff latency for the two Mobile IPv6 fast handoff protocols, FMIPv6 and HMIPv6, using IEEE 802.11-based wireless local area networks as the wireless access networks. Different from other previously proposed analytical models for handoff latency analysis, our model considers comprehensive factors from both link layer and network layer which influence the Mobile IP handoff delay. Individual analytical models for each of these factors affecting the handoff latency are developed. The outcome of this research is the probability distribution of the handoff latency occurring within a certain range based on the offered traffic load and network conditions.

The proliferation of wireless local area network (WLAN) deployments will likely cause frequent geographical coverage overlap among multiple networks. A recent growing interest is the coordination among WLAN providers for efficient network management. When multiple WLANs co-locate in a small geographic vicinity, the lack of cooperative multi- domain resource management can cause significant performance degradation due to inter-domain interference. Moreover, since WLANs often operate in unlicensed frequency bands shared by various public and private networks, they must cope with the dynamic RF environment involving a diverse set of interference sources. This paper introduces a new cooperative resource management framework for multi-domain WLANs operating in an interference environment. Under the proposed scheme, resource utilization and co-channel interference can be adaptively balanced across the entire integrated system. Simulation results show that the proposed scheme outperforms other schemes without inter-domain cooperation or without the consideration of environmental interference.

For many sensor network applications such as wild fire detection and battlefield surveillance, it is necessary to minimize energy consumption and extend system lifetime by leveraging the redundant deployment of sensor nodes while at the same time provide full sensing coverage and communication connectivity. An energy balanced stochastic based traffic distribution (SBTD) has been introduced in J. Wang and I. Howitt (2005), which has the target to prolong the network's lifetime. Thus, SBTD can be used to provide efficient communication connectivity in the future routing paradigm. This paper investigates the connectivity of the wireless sensor networks using the SBTD in a log-normal shadowing environment. Our main contributions include: (i) the effective communication coverage of nodes in the network using the SBTD is derived; (ii) the network connectivity and the parameters affecting the network connectivity are discussed and investigated; (iii) and the system accuracy using different values of the optimization parameter is discussed

Energy utilization is a challenging problem in wireless sensor networks due to the limited battery capacity in sensor nodes. This paper presents a fundamentally different design of an energy-efficient WSN, named stochastic-WSN (S-WSN). Two main energy-saving techniques are proposed: (i) optimal traffic flow and (ii) efficient scheduling and routing protocol to implement the optimal traffic flow. By using the optimal traffic flow, each sensor can decide its own activity in the routing procedure, thus, S-WSN realizes near-zero network administrative overhead. The optimal traffic flow provides a constructive approach for defining a scheduling algorithm, which keeps only a small subset of nodes awake in the network to provide connectivity while placing the majority of nodes in sleep mode. It reduces power consumption as well as operation interference. The network lifetime obtained using S-WSN provides a significant improvement as compared to using the energy balanced data propagation (EBDP) approach

Energy efficient data transmission and traffic control are essential for increasing the lifetime of wireless sensor networks (WSN). In traditional sensor networks, the optimization of the traffic distribution is restricted to a subset of the possible routes. This constraint makes achieving a global energy minimization impossible. In this paper, the stochastic based traffic distribution (SBTD) is formulated in terms of the traffic segmentation with an additional degree of freedom of the routes. It is derived based on the parametric stochastic models underlying the operational characteristics of the WSNs, whereby, the nodes' unbalanced energy consumption is balanced and the network's lifetime is prolonged. As illustrated in the paper, a WSN using the proposed optimal traffic distribution performs significantly better in conserving energy and increasing the WSN's lifetime as compared to the energy balanced data propagation (EBDP) as suggested in C. Efthymiou, et al (2004)

Energy efficiency is a major concern in wireless sensor networks (WSNs) and as such power control policies play an essential component in maximizing a network's lifetime. Optimal power control policies provide the correct trade-off in balancing packet transmission reliability within the operational environment with expanded energy based on the wireless transceiver characteristics. In this paper, an extension of an energy model previously developed for the Chipcon CC2420, an IEEE802.15.4trade device, is presented. The approach provides an extended energy model taking into account transitions energy cost between the Chipcon CC2420 operational states. The empirical testbed used to obtain the measured data is presented along with a summary of the measurements. A comparison is made between the extended model and the previous model to illustrate the importance of incorporating the transition energy requirements

Wireless sensor networks (WSN) are a subset of wireless networking applications focused on enabling sensor and actuator connectivity without the use of wires. Energy consumption among the wireless devices participating in these networks is a major constraint on the deployment for a broad range of applications enabled by WSNs. This paper introduces, for the first time, a novel methodology based on predictive protocol management with contingency planning (PPM and CP). This approach allows efficient update of the WSN operational mode in order to optimize the energy utilization based on the time varying characteristics of the radio-frequency (RF) in which the network operates.

An analytical model is derived for evaluating the effectiveness of IEEE 802.11b packet fragmentation for mitigating Bluetooth interference in an arbitrary radio propagation environment. An expression for the optimal packet fragmentation is obtained based on the analytical model. Then, based on the optimal packet fragmentation, the performance is quantified and a method for estimating the optimal fragmentation solution is presented.

Energy efficiency is a major concern in large scale wireless sensor networks. Transmit power control can provide an effective mechanism for improving energy efficiencies. In this paper, an alternative approach to power management is presented which is applicable to wireless sensor networks. The approach is based on developing power control policies which take into account the sensor network's deployment characteristics and the RF environment in which the sensor network is deployed. The method developed in the paper can be applied, in general to packet based transceivers, but the energy models developed for optimizing the transmit power are based on IEEE802.15.4/spl trade/ devices, specifically the Chipcon CC2420. As illustrated in the paper, the approach provides a straight forward method for evaluating the feasibility of a network's deployment strategy as well as provide insight into the modifications to the wireless network design to obtain greater energy efficiencies.

With detection and monitoring requirements becoming more complicated and difficult, wireless sensor networks are envisioned to revolutionize the paradigm of collecting and processing information in diverse environments, such as on Mars' in-situ exploration. However, energy utilization by sensor nodes often impacts the application's life time due to limited battery capacity. One of the problems in energy utilization is that nodes near the base station lend to die earlier than other nodes because of their higher traffic. This paper suggests an energy balanced chain (EBC) which can efficiently prolong the sensor network lifetime by actively controlling the nodes' hop distances. In EBC, we formulate the energy balance optimization problem in terms of the segmentation space. By adjusting the transmission power, nodes with higher traffic have a longer hop distance than nodes with lower traffic. Further, numerical analysis results show that EBC performs significantly better than traditional hop-by-hop transmission.

An acquisition method of long pseudo-noise (PN) sequences in direct-sequence spread spectrum (DS/SS) systems is presented. The concurrent cross correlation of locally generated auxiliary signals with the incoming PN sequence produces binary search estimates leading to an initial approximation of the input signal's PN offset. The PN receiver then uses a closed-loop subsystem to determine the true offset of the incoming PN signal. New phase estimates are generated from successive corrections of likely errors in the binary search. The acquisition scheme's average acquisition time and its variance are analytically determined. Simulation results show that the proposed acquisition scheme is faster than the conventional serial receiver. A hybrid serial/parallel PN acquisition receiver is used for comparing the acquisition performance given similar hardware complexity. The hybrid receiver used the same number of parallel correlators as used in the proposed receiver's input phase estimator. Simulation results show that the proposed system provides an improved performance under normal operating conditions.

IEEE 802.15.4 is a proposed standard addressing the needs of low-rate wireless personal area networks or LR-WPAN with a focus on enabling wireless sensor networks. The standard is characterized by maintaining a high level of simplicity, allowing for low cost and low power implementations. Its operational frequency band includes the 2.4 GHz industrial, scientific and medical band providing nearly worldwide availability; additionally, this band is also used by other IEEE 802 wireless standards. Coexistence among diverse collocated devices in the 2.4 GHz band is an important issue in order to ensure that each wireless service maintains its desired performance requirements. This paper presents a brief technical introduction of the IEEE 802.15.4 standard and analyzes the coexistence impact of an IEEE 802.15.4 network on the IEEE 802.11b devices.

Evaluating the coexistence between wireless local area networks and wireless personnel area networks is an important issue for determining usage policies for wireless devices that are collocated and sharing the same frequency spectrum. A method is presented for evaluating the impact Bluetooth piconets will have on IEEE 802.11b performance when collocated within a specific building layout. The method is centered on analytically evaluating the probability of collision between an 802.11b packet and packets from Bluetooth piconets. The analytical model is based on a parametric representation of the Bluetooth interference environment and a site specific propagation model used to estimate the received signal powers.

Direct sequence spread spectrum systems require a local replica of the pseudonoise (PN) sequence to be synchronized with the received signal's spreading code. A method is proposed to improve the PN sequence acquisition time and decrease the acquisition time variability. The proposed method is based on a binary search algorithm. At each stage of the algorithm, an auxiliary signal is used to formulate a new search region within the PN sequence, and at each stage the search region is reduced by half. The region containing the incoming PN phase is therefore obtained within O(log/sub 2/ (N+1)) steps. A closed loop coherent PN acquisition algorithm presented by Salih and Tantaratana (1996) motivated the use of the auxiliary signal, and the algorithm of Salih et al. is also used for comparison. Results indicate the algorithm presented in this paper can achieve a factor of two to three times improvement in the mean acquisition time with a significant decrease in the acquisition time variability.