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Virtual access network embedding in wireless mesh networks

Network virtualization of a wireless mesh network (WMN) is an economical way for different subscribers to customize their exclusive access networks through a common network infrastructure. The most critical task of network virtualization is virtual network embedding, which can be divided into two sub-problems: node mapping and link mapping. Although there exist approaches to virtual network embedding in wired networks, the characteristics of WMNs make virtual network embedding become a unique and challenging problem. In this paper, virtual access network embedding is studied for WMNs. To support flexible resource allocation in virtual access network embedding, each access node is designed based on orthogonal frequency division multiple access (OFDMA) dual-radio architecture. Through subcarrier allocation on each link, virtual access networks are gracefully separated from each other. To coordinate channel assignment across different links under the constraint of a limited number of orthogonal channels, a novel channel allocation algorithm is proposed to exploit partially-overlapped channels to improve resource utilization. Since the virtual access network embedding problem is NP-hard, a heuristic algorithm is developed based on an enhanced genetic algorithm to obtain an approximate but effective solution. Simulation results illustrate that the virtual access network embedding framework developed in this paper works effectively in WMNs.

Multicast Service-Oriented Virtual Network Embedding in Wireless Mesh Networks

Multicast is used in numerous real-time applications which have high demand on quality of service (QoS). When a number of multicast applications are deployed in a wireless mesh network (WMN), network virtualization technology can be used to guarantee the QoS for each application. Since wireless links are unreliable, packet loss is inevitable when the multicast service-oriented virtual networks (VNs) are embedded into a WMN. Although multicast allows the occurrence of packet loss, it is still important to ensure the packet loss rate is below a certain level for QoS guarantee. In this letter, we propose a novel approach, referred to as WELL, to settle the problem of embedding multicast VNs with reliability constraints into a WMN with lossy links. Through opportunistic rebroadcast, WELL minimizes the activation time of the VNs while satisfying their reliability constraints. Simulation results reveal that WELL dramatically outperforms both pure broadcast and unicast based solutions.

Network Virtualization for Smart Grid Communications

Information exchange is critical in smart grid for system control and management. Optical fibers are widely used in transmission grid and substations to provide high-capacity and high-reliability communications. However, due to high cost and inflexibility, optical fibers are not suitable for information transmission in distribution grid. Wireless mesh network (WMN) and power line communication (PLC) network are more appropriate for distribution grid communications. Nonetheless, both WMN and PLC technologies tend to suffer from bit error and packet loss due to interference and attenuation. It is extremely difficult to provide real-time services with low delay and high reliability in both of them. Network virtualization (NV) is a promising technology to support customized end-to-end performance of various services. In this paper, an NV-based framework is proposed for smart grid communications. In the framework, real-time services are supported by virtual networks (VNs) that are mapped to two physical networks simultaneously, i.e., WMN and PLC network. The WMN for NV is designed to adopt orthogonal frequency division multiple access as the multiple access scheme. In this way, different VNs are allocated distinct subcarriers. Concurrent transmissions in multiple subcarriers bring the benefit of additional diversity. The enhanced transmission diversity through the two networks and the allocated subcarriers contributes to the reliability guarantee of the real-time services. Since the VN mapping and subcarrier assignment problem is nondeterministic polynomial-time hard, a heuristic solution is developed to solve the problem efficiently and effectively. Simulation results reveal the effectiveness of our proposed framework.

SWIMMING: Seamless and Efficient WiFi-Based Internet Access from Moving Vehicles

Demand for Internet access from moving vehicles has been rapidly growing. Meanwhile, the overloading issue of cellular networks is escalating due to mobile data explosion. Thus, WiFi networks are considered as a promising technology to offload cellular networks. However, there pose many challenging problems in highly dynamic vehicular environments for WiFi networks. For example, connections can be easily disrupted by frequent handoffs between access points (APs). A scheme, called SWIMMING, is proposed to support seamless and efficient WiFi-based Internet access for moving vehicles. In uplink, SWIMMING operates in a “group unicast” manner. All APs are configured with the same MAC and IP addresses, so that packets sent from a client can be received by multiple APs within its transmission range. Unlike broadcast or monitor mode, group unicast exploits the diversity of multiple APs, while keeping all the advantages of unicast. To avoid possible collisions of ACKs from different APs, the conventional ACK decoding mechanism is enhanced with an ACK detection function. In downlink, a packet destined for a client is first pushed to a group of APs through multicast. This AP group is maintained dynamically to follow the moving client. The packet is then fetched by the client. With the above innovative design, SWIMMING achieves seamless roaming with reliable link, high throughput, and low packet loss. Testbed implementation and experiments are conducted to validate the effectiveness of the ACK detection function. Extensive simulations are carried out to evaluate the performance of SWIMMING. Experimental results show that SWIMMING outperforms existing schemes remarkably.

POCAM: Partially overlapped channel assignment in multi-radio multi-channel wireless mesh network

Wireless mesh network (WMN) is deemed as a promising technology to provide last few miles connectivity. Multi-radio multi-channel mesh nodes are often used to increase the chance of concurrent transmission. Although IEEE 802.11b/g standards define 11 available channels, the maximum number of non-overlapping channels is only three. Most existing channel assignment schemes are based on these non-overlapping channels. However, exploiting the partially overlapped channels can further improve the network performance. In this paper, we model the partially overlapped channels and propose a new partially overlapped channel assignment algorithm called POCAM. The POCAM algorithm stems from the measurements of commercial radios on real testbeds. The characteristics of traffic distribution in the WMN backhaul are also taken into consideration. The simulation results based on NS-3 demonstrate that POCAM achieves much better performance than the traditional channel assignment schemes which only utilize non-overlapping channels.

Network-Leading Association Scheme in IEEE 802.11 Wireless Mesh Networks

The association policy in current IEEE 802.11 networks usually considers Received Signal Strength Indication (RSSI) to be the only metric to capture access link quality. However, when a Mesh Client (MC) in IEEE 802.11-based Wireless Mesh Network (WMN) needs to be associated with the most appropriate Mesh Access Point (MAP), the quality of both the access link and the routing path in mesh backhaul should be considered. To take into account this requirement, most existing approaches rely on MAPs to provide more information for MCs such as traffic load, routing metric, airtime cost, etc. These solutions inevitably need to modify the IEEE 802.11 standard or wireless interface drivers on both MAPs and MCs, which is not feasible or flexible in actual deployment. In this paper, a network-leading association scheme is proposed for IEEE 802.11 WMNs. It is completely operated by MAPs and does not require any modification on MCs. It also adapts to the dynamic network environment and always selects the best MAP to serve an MC. Simulation results on ns-3 platform indicate that the network-leading association scheme remarkably improves the performance of IEEE 802.11 WMNs as compared with the existing approaches.

A Cross-Layer Scheme for Access Point Selection in Wireless Mesh Networks

In wireless mesh networks (WMNs), a station (STA) often has a group of candidate access points (APs) to be associated with. How to select the most appropriate AP has been an open problem. In IEEE 802.11 standards, the STA simply chooses the one with the strongest RSSI. Since this AP selection strategy can cause severe network load unbalance, many new methods have been proposed. However, these solutions mainly focus on the WLAN environment and are not applicable for WMNs. The unique wireless multi-hop backbone in WMN will introduce higher latency, which must be considered during the AP selection process. In this paper, we propose a cross-layer AP selection scheme based on the information of both link layer and routing layer aiming at reducing the network transmission delay. The problem is formulated as a nonlinear programming problem, and a heuristic search algorithm is given. Experiment results show that the cross-layer scheme can reduce the mean delay of the whole network by about 30% and can benefit real-time applications.

POCOSIM: a power control and scheduling scheme in multi-rate wireless mesh networks

Transmission power control (TPC) is a key technique in wireless networking. There are abundant works on TPC aiming at saving the energy or improving the performance of WSNs, MANETs and WLANs. However, the research on throughput-and-fairness-oriented TPC scheme represented for multi-rate wireless mesh networks is rather limited. As routers usually have stable power supply, throughput rather than energy consumption is the most crucial factor in wireless mesh networks. Therefore POCOSIM (POwer COntrol and Scheduling scheme In Multi-rate wireless mesh networks) is introduced in this paper to improve the throughput and the fairness in the context of multi-rate WMN. Traffic patterns of the system are analyzed based on a model of conflict graph, and a differential evolution based algorithm is proposed to optimize the time allocation vector. Simulations demonstrate that POCOSIM can improve the throuhgput and also can strike a balance between throughput and fairness.