Contention-free Medium Access Research Articles

TMPAD: Time-Slot-Based Medium Access Control Protocol to Meet Adaptive Data Requirements for Trusted Nodes in Fog-Enabled Smart Cities

The popularity of fog-enabled smart cities is increasing due to the advantages provided by modern communication and information technologies, which contribute to an improved quality of life. Wireless networks make them more vulnerable when the network is under malicious attacks that cause a collision in the medium. Furthermore, diverse applications of smart cities demand a contention-free medium access control (MAC) protocol to meet adaptive data requirements. In this work, a time-slot-based medium access control protocol to meet adaptive data requirements (TMPAD) for IoT nodes in fog-enabled smart cities is proposed. TMPAD proposes a trust mechanism to differentiate malicious and legitimate data requests. In addition, it accommodates more legitimate data-requesting nodes to transfer their data during a session by applying the technique for order performance by similarity to ideal solution (TOPSIS) and 0/1 knapsack algorithm. The performance of TMPAD is compared with well-known techniques such as first come first serve (FCFS), shortest job first (SJF), and longest job first (LJF) in different prospective scenarios. The results show that TMPAD scrutinizes more data-requesting nodes in slot allocation, allowing more data transmission in a session, with better mean trust value, as compared to other algorithms.

CAMELAMA: Cooperative awareness and spaceborne monitoring enabled by location-assisted medium access

In beaconing systems such as AIS or ADS-B, used by ships and aircraft, each node periodically broadcasts its navigational state to nearby nodes to increase traffic safety. Nowadays, these beacons are also used as a source for satellite-based global traffic monitoring. This dual use imposes competing needs on the medium access control protocol as the size of the collision domains varies by a large factor between the use cases. Even the subproblem of solely avoiding terrestrial nodes’ packets to collide from the perspective of a receiving satellite is not trivial to solve if the satellite’s collision domain spans multiple hops in the terrestrial network. Based on ideas of the LAMA protocol, we propose CAMELAMA, a novel contention-free medium access control protocol for position awareness beaconing. Our low-overhead approach uses neither forwarding of node state nor handshakes but only the navigational data that is shared between the terrestrial nodes anyway. CAMELAMA provides local cooperative awareness while at the same time desynchronizing transmissions within a satellite’s collision domain even in terrestrially disconnected topologies. In a simulation-based performance evaluation we find that CAMELAMA outperforms SO-TDMA (the MAC protocol of AIS) and also scales better with respect to high node densities.

Intra- and inter-cluster link scheduling in CUPS-based ad hoc networks

While control and user (data) plane separation (CUPS) through clustering improves the scalability of ad hoc networks in comparison to flat topologies, it introduces additional challenges for resource scheduling when contention-free medium access is employed. This paper addresses intra- and inter-cluster link scheduling problem in multi-channel ad hoc networks employing CUPS architecture. We first describe the CUPS architecture. Then, we present a novel intra- and inter-cluster link scheduling mechanism over the CUPS architecture. We propose a link scheduling strategy that is responsive to instant communication demands and available resources as a non-linear optimization problem, which is then reduced to a linear form by eliminating non-linearities in order to simplify the problem definition and enhance optimizer performance. The results of the optimizer show that the run time cost of the optimization function drastically increases by the parameter size growth. Therefore, we propose an iterative solution to decrease the running time. The adaptation of the iterative history-based approach makes the solution feasible and ensures near-optimal satisfaction and efficiency.

Cluster-Based Beaconing Process for VANET

In this paper we introduce the Cluster-Based Beacon Dissemination Process (CB-BDP) that aims to provide vehicles with a local vehicle proximity map of their vicinity. Based on this map, safety applications can be used for accident prevention by informing drivers about evolving hazardous situations. The CB-BDP is designed under the two following objectives. First, since it is used for safety applications, we want the map to be detailed and accurate as much as possible. Second, we want the map to be coordinated with nearby vehicles, thereby allowing synchronized and coordinated reactions of nearby vehicles to evolving hazardous situations. We design a cluster based aggregation–dissemination beaconing process that uses an optimized topology to distribute the vehicle proximity map. The topology is adaptive and robust in order to meet the challenging VANET conditions. An accurate and detailed map results in a heavy load of beacon messages. Our proposed scheme deals with this problem by integrating a contention-free medium access control (MAC) strategy for reliable communication.

Dynamic channel reservations for wireless multihop communications

Providing real-time service in an energy efficient manner in wireless multihop networks is an important and challenging problem. However, existing medium access control schemes are either over-coordinated (fixed-schedule-based schemes) or under-coordinated (prioritized contention-based schemes), failing to address this problem efficiently. This paper introduces a new medium access scheme, called FrugalMAC, aiming to provide timely, ondemand, and contention-free medium access by relying on a progressive, dynamic reservation mechanism coupled with reservation vectors. A node sleeps whenever the channel is not needed for data communication and slot reservation. In addition, FrugalMAC employs reservation pipelining and an admission control mechanism to support end-to-end real-time stream delivery. We have implemented a prototype of FrugalMAC in our sensor network testbed. Our preliminary results show that FrugalMAC has high energy efficiency and effectively supports timeliness.

Measurement-based link scheduling for maritime mesh networks with directional antennas

The proliferation of wireless transceivers and the availability of the unlicensed band has given a boost to the deployment of wireless networks, with IEEE802.11/WiFi being the major driver in this arena. In this research, we consider a wireless mesh network designed for long-distance communication with a typical deployment scenario of a maritime mesh network. This network uses an antenna system made up of multiple fixed-beamwidth antennas. Compared to most other directional antenna schemes which use directional antenna for transmission and omni-directional antenna for reception, our system uses directional antennas for both transmission and reception where a pair of transmitter-receiver antennas needs to be aligned and have an acceptable channel quality before transmission can take place. Through efficient use of directional antennas for both transmission and reception, and spatial reuse in transmission, we are able to realize a high-capacity mesh network. In this paper, we present a practical approach to achieve contention-free medium access, namely, a measurement-based link-scheduling algorithm. We evaluate the performance of the link-scheduling algorithm using simulations and show that it is able to exploit the spatial diversity provided by the directional antennas to outperform comparable schemes for wireless mesh networks. We also briefly discuss implementation issues to demonstrate the viability of the approach.

A distributed MAC scheme to achieve QoS in ad hoc networks

Real-time applications introduce new requirements on wireless networks and impose quality thresholds on parameters like delay, jitter, throughput, and packet loss in order to run smoothly. This paper addresses this issue by presenting a MAC scheme that offers real-time applications the opportunity to reserve transmission time based on their QoS requirements for contention-free medium access. Our scheme, which is called EDCA with Resource Reservation (EDCA/RR), operates in a fully distributed manner, is compatible with IEEE 802.11, and provides both prioritized and parameterized QoS. In this study, we have extended EDCA/RR to handle reservation collisions and, through extensive simulations, we show that our proposal can handle multiple reservations as well as uninformed stations that lie outside the transmission range of both the transmitter and the receiver while providing QoS guarantees. We compare EDCA/RR with EDCA and our results show that, as the traffic in the network increases, EDCA/RR succeeds providing the required service to QoS-demanding applications whereas EDCA fails in this task. In addition, when the medium is lossy we show that, not only does EDCA/RR give better service to real-time traffic, but also to contending non-real-time traffic.

Extending EDCA with distributed resource reservation for QoS guarantees

In this paper we describe how the contention-based medium access mechanism of 802.11e, EDCA, can be enhanced in order to allow stations to reserve medium access for their real-time applications with QoS requirements. We present our proposed scheme, which is called EDCA with resource reservation (EDCA/RR), and describe how it can be extended in order to be used in wireless multi-hop networks. EDCA/RR operates in a completely distributed manner and manages to provide deterministic, contention-free medium access, making it an attractive scheme for wireless networks.

Efficient silence suppression and call admission control through contention-free medium access for VoIP in WiFi networks

In view of the rapidly growing trend of migrating customers from traditional wired phones to mobile phones and then to VoIP services in the recent past, there is a tremendous demand for wireless technologies to support VoIP, specially on WiFi technologies which have already matured commercially. This has put forth great research challenges in the area of wireless VoIP. In this article we have addressed two core issues, efficient silence suppression and call admission control, in QoS provisioning for VoIP services in WiFi networks. In this connection we present a QoS-aware wireless MAC protocol called hybrid contention-free access (H-CFA) and a VoIP call admission control technique called the traffic stream admission control (TS-AC) algorithm. The H-CFA protocol is based on a novel idea that combines two contention-free wireless medium access approaches, round-robin polling and TDMA-like time slot assignment, and provides substantial multiplexing capacity gain through silence suppression of voice calls. The TS-AC algorithm ensures efficient admission control for consistent delay bound guarantees and further maximizes the capacity through exploiting the voice characteristic so that it can tolerate some level of non-consecutive packet loss. We expose the benefits of our schemes through numerical results obtained from simulations.

An enhancement to the IEEE 802.11e EDCA providing QoS guarantees

One of the challenges that must be overcome to realize the practical benefits of ad hoc networks is quality of service (QoS). However, the IEEE 802.11 standard, which undeniably is the most widespread wireless technology of choice for WLANs and ad hoc networks, does not address this issue. In order to support applications with QoS requirements, the upcoming IEEE 802.11e standard enhances the original IEEE 802.11 MAC protocol by introducing a new coordination function which has both contention-based and contention-free medium access methods. In this paper, we consider the contention-based medium access method, the EDCA, and propose an extension to it such that it can be used to provide QoS guarantees in WLANs operating in ad hoc mode. Our solution is fully distributed, uses admission control to regulate the usage of resources and gives stations with high-priority traffic streams an opportunity to reserve time for collision-free access to the medium.

Analysis of IEEE 802.11e for QoS support in wireless LANs

The IEEE 802.11e medium access control protocol is an emerging standard for wireless local area networks providing quality of service. An overview of this standard based on the current draft is presented on this article. We analyze the enhancements in 802.11 standard. The new hybrid coordination function of the IEEE 802.11e with its contention-based and contention-free (controlled) medium access control schemes is evaluated. The capability to provide QoS support is discussed by means of simulations.