Contention-free Protocol Research Articles

SCMAC: A Slotted-Contention-Based Media Access Control Protocol for Cooperative Safety in VANETs

Vehicular ad hoc networks (VANETs) can improve the safety during the traffic by enabling cooperative communication among the vehicles. The media access control (MAC) protocol should be well designed so that cooperative messages can be exchanged efficiently and reliably. Because vehicles move fast on the road, the network topology changes rapidly, which makes it harder to design the MAC protocol. This article introduces SCMAC, a slotted-contention-based time-division multiple access MAC protocol. SCMAC combines the advantages of the contention-based protocols and the contention-free protocols, and hence, can accommodate different traffic densities and channel conditions. Each time slot is divided into two periods: 1) reservation period (RP) and 2) transmission period (TP) in the protocol. Nodes compete in the RP to confirm whether the channel can be used before the transmission can take place in the TP. Analysis and simulation results are also presented to evaluate the performance of SCMAC in various scenarios. The results show that SCMAC can adapt different traffic densities and channel conditions and can provide more real time and efficient services compared to the other protocols.

Cross-layer cluster-based energy-efficient protocol for wireless sensor networks.

Recent developments in electronics and wireless communications have enabled the improvement of low-power and low-cost wireless sensors networks (WSNs). One of the most important challenges in WSNs is to increase the network lifetime due to the limited energy capacity of the network nodes. Another major challenge in WSNs is the hot spots that emerge as locations under heavy traffic load. Nodes in such areas quickly drain energy resources, leading to disconnection in network services. In such an environment, cross-layer cluster-based energy-efficient algorithms (CCBE) can prolong the network lifetime and energy efficiency. CCBE is based on clustering the nodes to different hexagonal structures. A hexagonal cluster consists of cluster members (CMs) and a cluster head (CH). The CHs are selected from the CMs based on nodes near the optimal CH distance and the residual energy of the nodes. Additionally, the optimal CH distance that links to optimal energy consumption is derived. To balance the energy consumption and the traffic load in the network, the CHs are rotated among all CMs. In WSNs, energy is mostly consumed during transmission and reception. Transmission collisions can further decrease the energy efficiency. These collisions can be avoided by using a contention-free protocol during the transmission period. Additionally, the CH allocates slots to the CMs based on their residual energy to increase sleep time. Furthermore, the energy consumption of CH can be further reduced by data aggregation. In this paper, we propose a data aggregation level based on the residual energy of CH and a cost-aware decision scheme for the fusion of data. Performance results show that the CCBE scheme performs better in terms of network lifetime, energy consumption and throughput compared to low-energy adaptive clustering hierarchy (LEACH) and hybrid energy-efficient distributed clustering (HEED).

A Novel Pure Limited Queueing Model for IEEE 802.11 Contention-Free Networks

IEEE 802.11 point coordination function (PCF) protocol plays a fundamental and core role for other contention-free protocols such as IEEE 802.11e HCCA. In PCF, each station transmits at most one packet upon polled. Existing theoretical studies on PCF either reconstruct complicated queueing models that are not easily extended for heterogeneous traffic, or convert the PCF system into an exhaustive queueing system that are difficult to understand. This paper propose applying the classic pure limited queueing model for performance analysis to overcome existing methods' drawbacks. The proposed model is naturally consistent with the semantics of the PCF protocol and therefore it is most easy to understand and simpler than existing models. The derived theoretical expressions are exactly same to the existing results that are already verified by extensive simulations.

Efficient Cluster Mobility Support for TDMA-Based MAC Protocols in Wireless Sensor Networks

Node mobility is a key feature of using Wireless Sensor Networks (WSNs) in many sensory applications, such as healthcare. The Medium Access Control (MAC) protocol should properly support the mobility in the network. In particular, mobility is complicated for contention-free protocols like Time Division Multiple Access (TDMA). An efficient access to the shared medium is scheduled based on the node's local neighborhood. This neighborhood may vary over time due to node movement or other dynamics. In scenarios including body-area networking, for instance, some clusters of nodes move together, creating further challenges but also opportunities. This article presents a MAC protocol, MCMAC, that provides efficient support for cluster mobility in TDMA-based MAC protocols in WSNs. The proposed protocol exploits a hybrid contention-free and contention-based communication approach to support cluster mobility. This relieves the protocol from rescheduling demand due to frequent node movements. Moreover, we propose a listening scheduling mechanism to avoid idle listening to mobile nodes that leads to a considerable energy saving for sensor nodes. The protocol is validated by performing several experiments in a real-world large-scale deployment including several mobile clusters. The protocol is also evaluated by extensive simulation of networks with various scales and configurations.

A New Delay Analysis for IEEE 802.11 PCF

The contention-free protocols can provide strict quality of service and have been receiving growing attention. The IEEE point coordination function (PCF) protocol is a very basic and important contention-free protocol. However, its existing performance analysis method is tedious and complicated. This paper proposes applying the classic M/G/1 vacation model to analyze the delay performance of the PCF in a straightforward manner, thereby avoiding reconstructing a new analysis model as done in previous research. Compared with related work, our method is simpler and more scalable and our results are more general. Simulations show that our analytical results are very accurate for both homogeneous and heterogeneous traffic.

Energy-efficient transmissions for bursty traffic in underwater sensor networks

In Underwater Sensor Networks (UWSNs), sensor nodes have limited energy resource and consume a lot of power during message transmission. Since expensive transmitting power consumption is an inevitable feature of underwater acoustic transmission, to extend network operation time, it is desirable for nodes to avoid energy wastage resulting from transmission collisions. Enabling nodes to use multiple channels in a contention–free way helps reduce transmission collisions. To the best of our knowledge, when nodes have bursty traffic loads, existing UWSN multi–channel solutions do not support contention–free transmission while available UWSN single–channel contention–free protocols generally suffer from low utilisation. In this paper, we propose a contention–free multi–channel MAC protocol for UWSNs that work well even when nodes experience uneven and bursty traffic loads. Simulation results verify that the proposed protocol conserves energy and is extremely suitable for a heavy–loaded environment.

Minimum delay routing for wireless networks with STDMA

STDMA emerges as a promising channel access technique for providing Quality of Service (QoS) guarantees in multi-hop ad hoc networks such as community mesh and sensor networks. The contention-free channel access combined with spatial reuse of the channel provide significant benefits in the energy/throughput trade-off. On the other hand, the time-multiplexed communication introduces extra delay on the packets when relayed by intermediate nodes. Hence in large wireless sensor networks or mesh networks, where data is routed over several hops before reaching the data sink, STDMA protocols may introduce high end-to-end latency due to the reservation-based access policy. We argue that a suitable routing protocol specifically designed for reservation-based Medium Access Control (MAC) protocols can alleviate their high-latency drawback. Following this argument, we propose first such routing algorithms working on top of a generic STDMA MAC protocol. First, we consider routing with data fusion and present our GreenWave routing idea. We show that our algorithm significantly reduces the end-to-end delay when compared to routing over the shortest-hop paths. Second, we consider routing without data fusion, by taking into account the effect of congestion along the paths on the end-to-end delays. We provide a QIP formulation of the problem, and present a lower bound and a heuristic algorithm to bound the optimal solution. Based on the centralized heuristic algorithm, we propose a distributed, dynamic routing protocol GreenWave routing with Congestion and Flow control (GWCF), which uses a novel congestion and flow control technique utilizing the underlying contention-free protocol. We show by simulations that GWCF routing significantly improves the end-to-end delay while increasing the network throughput when compared to routing over shortest paths.