Heterogeneous networks utilizing relay nodes with low transmission power becomes an important deployment scenario in 4G cellular standards. It can offer high data rate delivery as well as ubiquitous end-user experience. For such a network, an efficient mobile association and load balancing scheme is critical to achieve high system capacity and satisfactory user experience. In this paper, the main challenges for mobile association and load balancing in a heterogeneous network with relay nodes are discussed and addressed. An optimal framework that aims to maximize system capacity is presented. It considers both the relay backhaul resource usage and wireless access link resource availability. A heuristic algorithm that enables the practical implementation is proposed and evaluated. Simulation results show that the proposed mobile association and load balancing scheme outperforms the conventional schemes in a heterogeneous environment.

In the future heterogeneous wireless networks with a mixed deployment of macro BS and micro relay stations, different nodes will compete for the same radio resources for providing mobile services. This poses great challenges to radio resource management and coordination. One critical step to achieve the optimal radio resource usage is for the mobiles to connect to the access nodes that provide the best radio conditions to them. This paper proposes a new mobile association mechanism in such a heterogeneous environment that aims to provide the best service to the mobiles on both uplink and downlink while minimizing the interference level. The simulation results show that with the proposed scheme the mobile performance shall be improved compared with the traditional mobile association schemes.

In this paper, we investigate the leader following based formation control of multiple nonholonomic mobile robots. We present a new kinematics model for the leader-follower system using Cartesian coordinates rather than the commonly used polar coordinates in literature. Based on this new model and the idea of integrator backstepping, a globally stable controller is derived for the whole system. Simulation results are included to verify the efficacy of the presented new model and controller.

In this paper, we investigate the mechanism of the phenomena of swarm flocking, which can be widely observed in such as schooling fish and flocking migrate birds in nature. By combining the ideas of virtual force and nearest neighborhood law, we propose a decentralized controller to explain such phenomena. This decentralized controller can enable all swarm members to converge to a common velocity with bounded errors, no matter the swarm topology is fixed or dynamic. The advantage of this controller is that it just needs local information to achieve the stable group behavior. Simulation results are included to verify the proposed controller.

An ad hoc network is a self-organized and distributed entity consisting of a number of mobile stations (MS) without the coordination of any centralized access point. Clustering is one of the fundamental problems in ad hoc networks. In this context, we describe a distributed clustering algorithm for multihop ad hoc networks. We first propose a randomized control channel broadcast access method to maximize the worst-case control channel efficiency, based on which a distributed clustering algorithm is proposed. Both theoretical analysis and simulations indicate that the proposed clustering algorithm takes much less time and overhead to cluster a given network with more stable cluster structure, while incurring very small maintenance overhead in a dynamic network resulting from the mobility of the MS.

An ad hoc network is a self-organized and distributed entity, consisting of n mobile stations (MSs) without the coordination of any centralized access point. Initialization is one of the fundamental tasks to set up an ad hoc network, which involves assigning each of the n MSs a distinct ID number from 1 to n, distributedly. In Nakano et al. (2000), randomized initialization protocols are developed for single-hop ad hoc networks under different conditions. However, carrier sensing has not been utilized and suitable acknowledgment schemes for the algorithms are not developed. Moreover, the assumption taken by Nakano et al. about MSs being able to listen while transmitting is not valid for ad hoc networks. In this context, we describe two algorithms for initializing an ad hoc network with carrier sensing capability. First, a novel acknowledgment scheme is proposed for notifying a transmitting MS whether its transmission is successful during the initialization. Then, two distributed and randomized initialization algorithms are developed and analyzed, under the assumptions of a known and unknown number of users in the network, respectively. Both algorithms are obtained based on optimizing some key parameters to minimize the total time required to complete the initialization. Both theoretical analysis and simulations indicate that the proposed initialization algorithms outperform the existing methods, in the sense that they take much less time to complete the initialization and the average number of transmission attempts before success is much smaller.

The problem of broadcast channel access in single-hop and multihop ad hoc networks is considered. Two novel randomized and distributed channel access algorithms are developed and analyzed for single-hop and multihop networks, respectively. These algorithms are designed based on maximizing the worst-case channel efficiency, by optimizing some key parameters, including the backoff probability distribution and slot length. The proposed algorithm for single-hop networks offers significantly higher throughput than the CSMA methods when the traffic load is heavy, while still achieving good performance when the load is light or medium. The proposed algorithm for multihop networks can flexibly adapt to the traffic load, and offers much better throughput performance than the existing broadcast scheduling algorithms in light or medium load.