Ghada H. Badawy

Performance Characterization for IEEE 802.11p Network With Single Channel Devices

In this paper, we investigate the performance of networks built from single-channel devices that use wireless access in vehicular environment protocols. We consider several traffic combinations, each of which presents a mix of traffic classes, over control and service channels. Our results show that time switching between the channels causes synchronization of backoff processes, which increases the frame collision probability, in particular for small sizes of contention windows. We also evaluate the impact of the interruption of the backoff process by inactive channel time, which gives rise to a probability distribution with repeated tails and a coefficient of variation larger than 1. Our model can also be used to evaluate different sets of enhanced distributed channel access parameters and to select the channel duty cycle according to the policy of the network operator.

Energy Provisioning in Solar-Powered Wireless Mesh Networks

Solar-powered wireless mesh nodes must be provisioned with a solar panel and battery combination that is sufficient to prevent node outage. This is normally done using historical solar insolation data for the desired deployment location and based on a temporal bandwidth usage profile (BUP) for each deployed node. Unfortunately, conventional methodologies do not take into account the use of energy-aware routing, and therefore, the deployed system may be overprovisioned and unnecessarily expensive. In this paper, we consider this resource assignment problem with the objective of minimizing the network deployment cost for a given energy source assignment. We first propose a resource-provisioning algorithm based on the use of temporal shortest-path routing and taking into account the node energy flow for the target deployment time period. We then introduce a methodology that incorporates energy-aware routing into the resource-assignment procedure. A genetic algorithm (GA) has been developed for this purpose. Our results show the large cost savings that an energy-aware resource assignment can achieve when compared with that done using the conventional methodology. To evaluate the quality of the resource assignments, we also develop a linear programming formulation that gives a lower bound on the total network resource assignment. Our results show that significant resource savings are possible using the proposed algorithms and the potential resource assignment benefits of energy-aware routing.

Tradeoff Issues for CCH/SCH Duty Cycle for IEEE 802.11p Single Channel Devices

In this paper we investigate the ratio of dwelling time in control channel (CCH) and service channel (SCH) for single channel devices deploying WAVE (Wireless Access in Vehicular Environments) protocols. Based on analytical model for both channels and four traffic types we present tradeoffs in channel performance when CCH/SCH duty cycle is changing. Our results show that, when video traffic is absent, duty cycles smaller than 0.5 can offer satisfactory performance on CCH while running larger amount of revenue generating traffic on SCH.

Performance modeling of safety message delivery in vehicular ad hoc networks

Vehicular ad-hoc networks (VANETs) will enable a wide variety of future inter-vehicle and vehicle-to-roadside applications. These services will span a large range of functionality, such as those supporting vehicular safety, to those used for best-effort roadside advertising. To support this wide range, the IEEE 802.11p standard defines seven communication channels, consisting of a single control channel for safety applications, and six service channels which can be used for other purposes. To allow a single radio interface to support both types of applications, the standard defines a channel coordination mechanism that allows the vehicular radio to alternately access the control and service channels. When this happens it is very important that safety messages are transmitted with high reliability and low latency. Using analytical models, this paper provides a performance evaluation of vehicular safety message delivery. Our results show that the mechanism defined in the standard can satisfy the needed latency requirements, but cannot satisfy the required reliability for safety message delivery.

Traffic Scheduling for Energy Sustainable Vehicular Infrastructure

Roadside infrastructure can be used provide a wide variety of commercial services in vehicular ad hoc networks. One particular challenge is that of providing roadside radio coverage in highway locations where wired electricity is not available. In this case, roadside access points (APs) powered by renewable energy such as solar power, is a viable alternative. The cost of provisioning this type of roadside infrastructure is dependent on the average power consumption of the AP, and can be reduced by energy efficient scheduling. In this paper, we consider the problem of satisfying vehicle communication requirements while minimizing the energy needed by the roadside access point. The problem is formulated as a Mixed Integer Linear Program (MILP) which provides an upper bound for the performance of any realizable scheduling algorithm. We then propose a Nearest Fastest Set (NFS) scheduler that uses vehicle location and velocity inputs to address the problem. Results from a variety of experiments show that the proposed scheduling algorithm performs well when compared to the performance bound.

Energy Aware Provisioning in Solar Powered WLAN Mesh Networks

WLAN mesh networks are often installed to provide wireless coverage for temporary events. In these types of networks, the WLAN mesh nodes can sometimes be operated using an energy sustainable source such as solar power. Resource provisioning consists of pre-assigning each node with a solar panel and battery combination that is sufficient to prevent node outage for the duration of the deployment. This is done by assuming a temporal load profile for each node, which is then used to perform the assignment using historical solar insolation data for the desired deployment location. Unfortunately, this methodology cannot take into account the state dependencies which occur when the network uses energy aware routing, and therefore the system may be over-provisioned. In this paper we propose a methodology for WLAN mesh node resource assignment that incorporates energy aware routing into the assignment algorithm. The problem consists of determining a network-wide minimum cost resource assignment subject to satisfying the input load profile. A genetic algorithm (GA) has been developed for this purpose. Our results show the large resource savings that energy aware resource assignment can achieve when compared to that done using the conventional methodology. We also study the competitive ratio of both resource assignment schemes and show that for small traffic overloading, energy aware routing performs better than shortest path routing in networks which are provisioned using the proposed methodology.

Solar Powered WLAN Mesh Network Provisioning for Temporary Deployments

WLAN mesh networks are often installed to provide wireless coverage for temporary events. In many of these cases, the WLAN mesh nodes can be operated using an energy sustainable source such as solar power. Node resource assignment consists of provisioning each node with a solar panel and battery combination that is sufficient to prevent node outage for the duration of the deployment. In this paper we consider this resource assignment problem with the objective of minimizing the total battery cost for a given energy source assignment. A methodology and algorithms for determining this resource assignment are first given. We then study the problem in the presence of shortest path and energy aware routing. To evaluate the quality of the resource assignments, we develop a linear programming formulation which gives lower bounds on the network resource assignment. Competitive ratios for different routing algorithms are then used, which demonstrates their effectiveness. We also include the case where some of the deployed nodes are designated in advance as having a continuous power source. Our results show the resource savings which are possible using the design algorithms and the potential resource assignment benefits of energy aware routing.

Position Aware Node Provisioning for Solar Powered Wireless Mesh Networks

Solar powered wireless mesh nodes must be provisioned with a solar panel and battery combination that is sufficient to prevent node outage. When such a network is deployed, there are usually restrictions in the way the nodes can be positioned, and this results in a time-varying and node-dependent attenuation of the available solar energy. Unfortunately, conventional resource provisioning methodologies do not take into account these positional variations, and therefore the deployed system may be over-provisioned. In this paper the resource provisioning problem is considered from this point of view. A linear programming formulation is first developed which gives lower bounds on the node resource provisioning cost assignments. A provisioning algorithm is then introduced that takes positional solar energy variations into consideration. Our results show that a significant reduction in provisioning cost can be obtained using the proposed methodology when compared to the conventional case.

Secondary user VoIP capacity in opportunistic spectrum access networks with friendly scheduling

In conventional cognitive radio, the primary network usually remains unchanged. In some cases, however, the primary network operator may wish to accommodate secondary user access. In this paper, we assess the secondary user VoIP capacity when primary basestation scheduling is designed to be secondary network friendly. Friendliness is measured by the number of connections that can be supported subject to typical quality of service constraints in the presence of delay tolerant primary traffic. An offline scheduler is first derived that maximizes friendliness using an integer linear program formulation. We show that this schedule can be found using a minimum cost flow graph construction in time complexity that is polynomial in the number of time slots. Two online scheduling algorithms are then compared that achieve various levels of friendliness. The first algorithm operates by having the primary network temporally shape its residual capacity subject to satisfying its own packet deadline constraints. The second algorithm assumes virtual secondary calls and applies scheduling to both primary traffic and virtual secondary traffic. Results are presented for a variety of parameters that show the degree to which friendly scheduling can improve secondary user VoIP capacity compared to non-friendly primary scheduling.

Fair Flow Control in Solar Powered WLAN Mesh Networks

Wireless LAN mesh networks are used to provide Wi-Fi access for temporary events. In this type of application it is sometimes necessary to operate some of the mesh nodes using an energy sustainable source, such as solar power. When the network is deployed, each mesh node is equipped with a solar panel and battery combination which is sufficient to prevent network outage using an assumed traffic design profile. During post-deployment network operation however, the actual traffic flows may be different from that for which the nodes were originally provisioned. To prevent node outage, the network must flow control the inputs, and this should be done in as fair a manner as possible. In this paper we propose a mechanism for achieving fair flow control on a per-flow basis. We first formulate a bound which achieves the best max-min fair flow control subject to eliminating network outage. This bound is non-causal in that it uses knowledge of future solar insolation and traffic flows to determine the optimum flow control. The bound motivates a proposed causal flow control algorithm whose operation uses prediction based on access to on-line historical weather data. Our results show that the proposed algorithm eliminates node outage and performs very well compared to the optimum flow control bound for a variety of network scenarios.