Relay Stations (RSs) can be deployed in a wireless network to extend its coverage and improve its capacity. Smart (directional) antennas can enhance the functionalities of RSs by forming the beam only towards intended receiving Subscriber Stations (SSs). In this paper, we study a joint problem of selecting a beam width and direction for the smart antenna at each RS and determining the RS assignment for SSs in each scheduling period. The objective is to maximize a utility function that can lead to a stable and high-throughput system. We define this as the Beam Scheduling and Relay Assignment Problem (BS-RAP). We show that BS-RAP is NP-hard, present a Mixed Integer Linear Programming (MILP) formulation to provide optimal solutions and present two polynomial-time greedy algorithms, one of which is shown to have a constant factor approximation ratio.

Transparent optical networks must support dynamic traffic demands and end-to-end optical transmission. We present a new physically-aware algorithm based on dynamic programming for routing and wavelength assignment in such networks that considers both linear and nonlinear impairments that accumulated along the transmission path. We show that our algorithm scales well to large networks and typically yields the lowest blocking probability when compared to several existing methods. In addition, it is flexible and can adapt to situations where either linear or nonlinear impairments dominate.

Relay stations can be deployed between mobile stations and base stations in a single-hop wireless network to extend its coverage and improve its capacity. In this paper, we exploit cooperative diversity, channel diversity and multiuser diversity gains in an OFDMA-based wireless relay network. We study a joint channel and relay assignment problem with the objective of maximizing a well-adopted utility function that can lead to a stable system. This problem turns out to be NP-hard. First, a mixed integer linear programming formulation is presented to provide optimal solutions. We then present three simple greedy algorithms to solve the problem in polynomial time, namely, Greedy-ChannelFirst, Greedy-RelayFirst and Greedy-Joint. We also perform a comprehensive theoretical analysis for the performance of the proposed algorithms. Our analytical results show the Greedy-ChannelFirst algorithm is a constant factor approximation algorithm which always provides a solution whose objective value is guaranteed to be no smaller than the optimal value multiplied by a constant less than 1; however, the other two algorithms do not provide a similar performance guarantee. Extensive simulation results have been presented to show that all three proposed algorithms perform very well on average cases.

Relay Stations (RSs) can be deployed in a wireless network to extend its coverage and improve its capacity. Smart (directional) antennas can enhance the functionalities of RSs by forming one or multiple beams only towards intended receivers. In this paper, we focus on the topology control approach for efficient communications in wireless relay networks with smart antennas. This approach precomputes an antenna pattern for each node such that an efficient network topology can be formed for future communications. The corresponding optimization problem is formally defined as the Beam Selection Problem (BSP). First, we present an Integer Linear Programming (ILP) formulation to provide optimal solutions. Then we present a Linear Programming (LP) rounding-based algorithm for the BSP and show it has a constant factor approximation ratio. We also present a simple and fast greedy algorithm to solve the problem. Extensive simulation results show that the proposed algorithms provide close-to-optimal performance.

Relay stations can be deployed in a wireless network to extend its coverage and improve its capacity. In this paper, we study a scheduling problem in OFDMA-based wireless relay networks with consideration for multi-user diversity, channel diversity and spatial reuse. First, we present a Mixed Integer Linear Programming (MILP) formulation to provide optimum solutions. It has been shown by previous research that performance of a wireless scheduling algorithm is usually related to the interference degree delta, which is the maximum number of links that interfere with a common link but do not interfere with each other. Therefore, we then show that the interference degree delta is at most 4 for any 2-hop relay network and 14 for any general h-hop (h >; 1) relay network. Furthermore, we present a simple greedy algorithm for the scheduling problem and show it has an approximation ratio of 1/(1+δ), which leads to an approximation ratio of 1/5 for the 2-hop case and 1/15} for the general case. In addition, we present three heuristic algorithms, namely, the weighted degree greedy algorithm, the Maximum Weighted Independent Set (MWIS) algorithm and the Linear Programming (LP) rounding algorithm, to solve the scheduling problem. Extensive simulation results have showed that the LP rounding algorithm performs best and always provides close-to-optimum solutions. The performance of the simple greedy algorithm is comparable to that of the other algorithms.

In this paper, we exploit cooperative diversity, channel diversity and multi-user diversity gains in an OFDMA-based wireless relay network by studying a joint channel and relay assignment problem. This problem turns out to be NP-hard. First, a mixed integer linear programming formulation is presented to provide optimal solutions. We then present a constant factor approximation algorithm and two heuristic algorithms to solve this problem in polynomial time. Extensive simulation results have been presented to justify the efficiency of the proposed algorithms.

Nodes in a cognitive radio mesh network may select from a set of available channels to use provided they do not interfere with primary users. This ability can improve overall network performance but introduces the question of how best to use these channels. This paper addresses the following specific problem: given a routing path P, choose which channels each link in P should use and their transmission schedule so as to maximize the end-to-end data flow rate (throughput) supported by the entire path. This problem is relevant to applications such as streaming video or data where a connection may be long lasting and require a high constant throughput. The problem is hard to due the presence of both intraflow and inter-flow interference. We have developed a new constant-factor approximation algorithm for this problem. If certain natural conditions on the path are met, the performance guarantee is ¼ of optimal. It has been shown by simulation results that the end-to-end throughput given by the proposed algorithm is often within 90% or better of optimal.

Wireless communications over water may suffer from serious multipath fading due to strong specular reflections from conducting water surfaces. Cognitive radios enable dynamic spectrum access over a large frequency range, which can be used to mitigate this problem. In this paper, we study how to leverage cognitive radios for effective communications in wireless networks over water. We formally define the related problem as the Overwater Channel Scheduling Problem (OCSP) which seeks a channel assignment schedule such that a "good" communication link can be maintained between every Mobile Station (MS) and the Base Station (BS) all the time. We present a general scheduling framework for solving the OCSP. Based on the proposed framework, we present an optimal algorithm and several fast heuristic algorithms. In addition, we discuss an extension to the heavy traffic load case and propose two throughput-aware scheduling algorithms. We performed simulation runs based on path loss data provided by the Advanced Refractive Effects Prediction System (AREPS) and present simulation results to justify the efficiency of the proposed scheduling algorithms.

In this paper, we explore the feasibility of using Mobile Ad-hoc Networks (MANETs) for rural public safety. First, we discuss a QoS enhancement to a standard routing protocol, Dynamic Source Routing (DSR). By incorporating a new routing metric and the available bandwidth and delay estimation algorithms with DSR, we design a new routing protocol, QoS- Aware Source Routing (QASR), to meet the QoS requirements specified by Statement of Requirements (SoR) for public safety communications. We then evaluate the performance of QASR and the well-known standard routing protocols including Ad- hoc On-demand Distance Vector (AODV) and DSR based on real public safety scenarios using the OPNET modeler at the 4.9GHz public safety spectrum band. Simulation results show that QASR significantly outperforms DSR and AODV in terms of various performance metrics.

Cognitive radios allow unlicensed wireless users to access channels that are in the licensed spectrum bands. However, in a wireless network with cognitive radios, when a licensed user becomes active on a channel in a certain area, nodes and links that were using that channel must release it, which will cause traffic failures. Simple and effective recovery schemes are needed to re-allocate available resources for the failed traffic. In this paper, we study the failure recovery in wireless mesh networks with cognitive radios. We formally formulate the corresponding problems as integer linear programming problems. By solving them, we can obtain optimal solutions. Moreover, an efficient distributed heuristic algorithm is presented for fast recovery. Simulation results show that the performance given by our distributed algorithm is close to that of the optimal solutions.

A smart adaptive antenna has multiple Degrees of Freedom (DOFs), which can be used for intended communications and interference suppression. In this paper, we study routing and scheduling in wireless backhaul networks with smart antennas. In a wireless backhaul network, a spanning tree rooted at the gateway node is usually constructed for routing. We formally define the Interference aware Tree Construction Problem (ITCP) which offers full consideration for interference impact and DOF availability, and present an algorithm to optimally solve it in polynomial time. As for scheduling, we first present a polynomial-time, optimal algorithm for a special case in which the number of DOFs in each node is large enough to suppress all potential secondary interference. An effective heuristic algorithm is then presented for the scheduling problem in the general case. Extensive simulation results have been presented to justify the efficiency of the proposed algorithms.

The demands for vehicular Internet access are proliferating. Access points (APs) can be deployed along the roadside to provide wireless coverage and network access for mobile vehicles. However, high mobility may cause frequent link breakages, which will seriously impact quality of service (QoS). In this paper, we study reliable routing for roadside to vehicle (R2V) communications in rural areas where rough terrain poses additional challenges. We propose a novel routing protocol where the stationary APs play a key role in route maintenance. The protocol includes a prediction algorithm which can predict the lifetimes of wireless links with consideration for terrain effects, as well as routing algorithms which can find stable paths for packet forwarding based on the prediction. Simulation results based on OPNET modeler and the rural roadways in the Yellowstone National Park show that the proposed protocol substantially outperforms existing ad-hoc routing protocols.

Although a large number of Internet users now enjoy high-speed access, there are still vast geographic regions where broadband services are either prohibitively expensive or simply unavailable at any price. networks paper examines the alternatives for using 2.4 GHz 802.11b (Wi-Fi) technology to provide fixed broadband access in areas where DSL and cable-based service are frequently not available. We explore the economics of offering wireless broadband service in rural areas consisting of towns, smaller remote communities as well as widely scattered users. We model a network, based on realistic demographics, equipment and operations costs, service revenues, customer demand and usage, and to calculate the life-cycle economics in terms of capital investment and profitability. We compare the cost-benefits of using the conventional Wi-Fi technology, as is typically used in metro areas today, with a novel and promising approach based on dynamically steerable beam-forming antennas to increase the coverage and capacity. Our results show that cost-effective, affordable high-speed wireless Internet access can be provided in rural and remote areas.

The paper analyses and simulates the impact of providing voice and non-voice personal communications services (PCS) on the volume of network database transactions. A number of activities in PCS, such as user mobility and call origination and delivery, require data management functions. These include mobility registration, radio channel management, service profile query, security-related functions such as authentication and privacy, and special billing arrangements. A large portion of these data management activities may be performed using elements of the intelligent network such as switches (e.g., service switching point or SSP) and network databases (e.g., service control point or SCP). The authors extend the single logical database model to include data partitioning into multiple databases. This model is helpful in case a single database is inadequate to handle all the transaction volume generated due to PCS. They give a first-cut analysis using such a model. A simulation framework is described for data management under various scenarios. This work pertains mainly to data management. In addition, qualitative effects of data partitioning on signaling traffic are outlined.>

The use of SCM (subcarrier multiplexing) transmission to deliver broadcast analog video signals within a CPN (customer premises network) as an overlay to an all-digital B-ISDN (broadband integrated services digital network) is considered. The feasibility of a proposal where the analog and digital signals are carried on different wavelengths is shown. An architecture for an optical CPN, termed H-Bus and incorporating emerging broadband SONET and ATM (asynchronous transfer mode) standards, is taken as a baseline for the delivery of switched digital, two-way voice, data, and video services. An optical overlay for the distribution of analog, broadcast video services using subcarrier multiplexing is considered. Several key alternatives associated with the delivery of broadcast video services are assessed, including signal quality, number of simultaneous channels, number of user terminals to be served, and modulation format. These issues are considered in terms of their impact on the interface with the public local exchange network and on the complexity, topology, and cost of the CPN.>

A methodology is presented for conducting strategic network planning studies under a new set of planning assumptions. The key element of the described methodology is a mathematical model of the equipment-replacement decision-making process that explicitly captures the economic impact of emerging technologies, architectures, and services. The general replacement decision model (GRDM) is a mathematical model that computes the optimal sequence of replacement times for particular pieces of telecommunications network equipment. GRDM takes information about costs and revenues and their trends in time associated with existing and emerging technologies and services and calculates the sequence of technology replacement intervals that minimizes the net present worth of expenditures associated with embedded plant and its replacements. The generality of the model supports its application to a broad range of network evolution issues, including the deployment of fiber optics and intelligent network features. An illustrative application of GRDM is presented which evaluates how the optimal economic lives of analog and digital switching equipment change as the assumed date of widespread broadband switching availability is varied.>

The potential interference of spurious, radiation from the local oscillators of direct broadcast satellite (DBS) television receivers to terrestrial 11 GHz microwave radio services is examined. Typical parameters for DBS receivers are identified and used in a computer simulation to calculate the aggregate effect of a large number of units distributed about a terrestrial repeater site. The results of the analysis show that for a local oscillator frequency of 11.2 GHz, DBS LO leakage of -70 dBW/unit, and a density of 2600/km2(1000/mi2) the cumulative interference power would be comparable to the thermal noise level of a terrestrial radio system under realistic conditions. Methods of scaling the results for other system parameters are also presented.