WiFi-based Long Distance Research Articles

CSMA/PJ: A Protective Jamming Based MAC Protocol to Harmonize the Long and Short Links

WiFi-based Long Distance (WiLD) networks are promising to cover the rural and remote regions. But the explosive short-range WiFi deployments result in the long-short coexistence. Due to CSMA is ignorance of propagation delay, its carrier sensing is too short to detect long links, leading to the temporal hidden terminal problem that causes serious performance degradation and even starvation of long links. Existing methods for traditional hidden terminal problem are inefficient to cope with this problem because of the different causes. In this paper, we propose CSMA with Protective Jamming (CSMA/PJ), a new WiLD MAC protocol that solves the temporal hidden terminal problem with the minimized influence on uncontrollable short links. The key is generating protective jamming at the WiLD receiver that is sensible to the short links. By leveraging the asymmetric propagation delay of the WiLD transmitter and receiver, we make the jamming protective rather than destructive. We precisely control the jamming right before the arrivals of WiLD packets to set aside channel time for short links. We implement and evaluate CSMA/PJ on commercial devices. The experimental results show that CSMA/PJ can improve the throughput of the WiLD link by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6\times $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5 \times $ </tex-math></inline-formula> compared with the CSMA/CA and RTS/CTS methods.

A QoS-Aware Multipath Routing Protocol for Wi-Fi Based Long Distance Mesh Networks

Routing plays a crucial role in provisioning Quality of Service (QoS) over WiFi-based Long Distance (WiLD) mesh networks. Traditional routing protocols normally maintain a single optimal path between each pair of source and destination nodes. In gateway-based mesh networks, the optimal paths between gateway and other nodes often overlap and hence degrades the overall network performance significantly. Multipath routing protocols are widely used in Wireless Mess Networks (WMN) for providing QoS to various network applications. Smooth routing of real time traffic with varying QoS requirements is a challenging task. In this paper, we propose a QoS-aware hybrid multipath routing protocol which can discover multiple maximally disjoint paths between a gateway and any other node. The gateway node selects n-best paths for the source node. Before starting a given real time flow, a path selection scheme chooses the appropriate path or set of paths amongst the available discovered paths. To evenly distribute the traffic among the paths chosen, an admission control mechanism has been proposed. In case of significant change in the quality of any discovered paths, a path maintenance process induces the source node to trigger a route update process. The proposed protocol enhances the performance of real time traffic significantly. The simulation results show that the proposed protocol achieves significant improvement in different QoS parameters. With the increase in number of disjoint paths from source to destination, a substantial improvement in throughput and delay is observed.

Software Defined Wi-V2G: A V2G Network Architecture

The valley-to-peak difference in power consumption is a crucial problem in load regulation and control for a power grid. By allowing electric vehicles (EVs) to charge during off-peak hours and feed power back into the grid during peak hours, Vehicle-to-Grid (V2G) technology can help to shave the power peak. Long-distance communication is essential for data exchange between dispersed EVs and charging stations for the realization of V2G systems. However, because of the high mobility of EVs, the highvolume data transmission required and the limitations of the third-party infrastructure, it is challenging to achieve efficient and effective communication. To address these challenges, we propose a new V2G network architecture based on software-defined networking (SDN) technology. (1) We use an IEEE 802.11 WiFibased long-distance (WiLD) network with the TDMA scheme as the backhaul network, and (2) we partially replace the road side units (RSUs) with some of the WiLD nodes to provide access for, and to rapidly broadcast data to, EVs. In addition, we propose: (3) a two-stage flow table mechanism and a double roaming mechanism to address the mobility demands of V2G network terminals; and (4) a rapid data transmission scheme for communication from charging stations to EVs. A testbed was built to validate the proposed network architecture. Experimental results show that the communication time delay is in the order of milliseconds and that the reliability is higher than 99.9%.

An Efficient TDMA MAC Protocol for Multi-hop WiFi-Based Long Distance Networks

Multi-hop WiFi-based long distance (WiLD) network is considered to be a cost-effective solution for extending Internet to rural underserved areas. In such gateway-based mesh architecture, interference-free scheduling of transmission is critical in optimizing overall network performance. In this paper, we propose an efficient TDMA-based MAC protocol for gateway-based multi-hop WiLD networks for enhancing end-to-end throughput and delay performances. The possibility of collision which exists in token-based MAC protocols has been reduced significantly by employing inherent node synchronization mechanism. The proposed protocol enhances network performance by utilizing the available bandwidth through maximization of TDMA slots overlapping. It shows clear improvement over relevant MAC protocols in terms of saturation throughput as well as average end-to-end packet delay over multiple hops.

TDMA MAC Protocols for WiFi-based Long Distance Networks: A Survey

WiFi is widely being researched to use it beyond its original purpose of short-range communication. These kinds of efforts are stimulated due to its mass production and cost-effectiveness. WiFibased Long Distance (WiLD) networks envisage changing the rural communication scenario particularly in the undeveloped nations. However, CSMA/CA, the de-facto MAC protocol of WiFi, is found to be ill-suited for WiLD networks. As a result, various TDMA-based MAC protocols are proposed in the literature as an alternative to CSMA/CA. The proposed protocols have shown significant performance improvement in such scenarios. In this paper, we propose a classification framework of WiLD MAC protocols based on their major characteristics. Using the classification framework, a survey on the MAC protocols proposed for WiLD networks is presented. The distinctive features of the TDMA MAC protocols are critically examined by pointing out their strengths and weaknesses in WiLD environment. In addition, this paper puts forward some state of art open research challenges in this area.