Evaluating medium access control protocols for wireless sensor networks

Abstract Wireless sensor networks (WSNs) offer us a potential for greater awareness of our surroundings, collecting, measuring, and aggregating parameters beyond our current abilities, and provide an opportunity to enrich our experience through context-awareness. As a typical sensor node is small with limited processing power, memory, and energy resources, in particular, these WSNs must be very energy-efficient for practical deployment. Medium access control (MAC) protocols are central to the energy-efficiency objective of WSNs, as they directly control the most energy consuming part of a sensor node: communications over the shared medium. This thesis focuses on evaluating MAC protocols within the WSN domain by, firstly, surveying a representative number of MAC protocols and their features. Secondly, three novel MAC protocols are proposed, one for layered contention-based access, one for layered scheduled access, and one for cross-layer contention-based access. Thirdly, a novel energy consumption model is proposed, and fourthly, a holistic MAC protocol evaluation model is proposed that takes into account application emphasis on performance metrics. The MAC protocols are evaluated analytically. In addition, the layered contention-based MAC protocol has been implemented and measured, and the cross-layer contention-based protocol operating over an impulse radio-ultra wideband (IR-UWB) physical layer has been verified by simulations with relevant physical layer characteristics. The energy consumption evaluation model proposed is straightforward to modify for evaluating delay, and it can reuse state transition probabilities derived from throughput analysis. The holistic application-driven MAC protocol evaluation model uses a novel single compound metric that represents a MAC protocol's relative performance in a given application scenario. The evaluations have revealed several significant flaws in sensor MAC protocols that are adapted to sensor networking from ad hoc networks. Furthermore, it has been shown that, when taking sufficient details into account, single hop communications can outperform multi-hop communications in the energy perspective within the feasible transmission ranges provided by sensor nodes. The impulse radio physical layer introduces characteristics to MAC protocols that invalidate traditional techniques which model the physical layer in terms of simple collisions. Hence, these physical layer characteristics have been modelled and included in the analysis, which improves the level of agreements with simulated results

Ad hoc LTE method for resilient smart grid communications

Abstract LTE network is a good choice for delivering smart grid demand response (DR) traffic. However, LTE connectivity is not pervasively available due to smart meter improper positioning, limited of coverage, or base station software or hardware failures. In this paper, a solution is introduced to overcome issues relating to lack of LTE base station connectivity for user equipment (UE) considered as remote terminal units, i.e. communication interfaces connected to smart meters. The solution is an ad hoc mode for the LTE-Advanced UE. The ad hoc mode is applied to reach a relay node that is the nearest UE with base station connection. DR traffic is delivered between clusters of UEs and a relay node using multi-hop communications. Analytical Markov chain models and a Riverbed Modeler network simulation model are implemented to illustrate the functionalities and the performance when DR traffic is delivered with varying transmission power levels. A detailed physical layer propagation model for device-to-device communications, a static resource allocation in time domain, hybrid automatic repeat request retransmissions, and a capability for a UE to receive uplink transmissions are modeled both analytically and in the simulator. Both the disjoint analysis and simulations show that all packets are successfully transmitted at most with the fourth transmission attempt and the average network delay is low enough to support most of the smart grid DR applications (139.2–546.6 ms)

Impact of shared LTE network high typical traffic loads on smart grid demand response schemes

Abstract Smart grid (SG) demand response (DR) programs and their management attain higher importance as distributed energy generation becomes more popular in households due to reducing prices of small-scale renewable energy generation equipment. The use of public telecommunications infrastructure is a good candidate for enabling DR communications over SGs, but the LTE networks become excessively congested during peak hours and the SG DR traffic delivery can be degraded. The network simulations evaluate traffic volumes, delivery ratios, and delays of various traffic types, including SG DR communications, when an LTE macrocell network capacity is exceeded by an increased amount of typical traffic types (Skype video call, FTP, Yotube video stream, and HTTP). The results show that the SG DR traffic can be delivered, maintaining satisfactory communications performance also in a highly loaded network conditions. The QoS class of SG DR traffic transmitted in downlink direction can even be considered to be lowered below the QoS of typical traffic types

Shared LTE network performance on smart grid and typical traffic schemes

Abstract This paper investigates the possibility of delivering distinct smart grid (SG) demand response (DR) applications in a highly loaded LTE network. In a shared LTE network, the proportion of SG DR traffic is relatively low when compared to typical traffics such as voice over IP, Skype video call, FTP, Youtube video stream, and HTTP. The quality of service (QoS) requirements for the SG DR traffics have to be fulfilled by maintaining the network delays and the packet delivery ratios within certain limits, while not causing significant hindrance to the typical traffics. The Riverbed Modeler network simulations are performed using detailed physical layer propagation models, detailed LTE functionality, and a suburban topology. In the simulation scenarios, three distinct DR applications generate varying amounts of SG DR traffic to the LTE network while the LTE capacity is exceeded by the typical traffics. The results illustrate that satisfactory performance for the SG DR traffics can be maintained due to the constant traffic characteristics and relatively low traffic amount that facilitates the scheduling of channel resources. Typically, the more a DR application generates traffic the higher hindrance it causes for the typical traffics other than the voice over IP that applies the QoS class of highest priority

Simulating LoRaWAN:on importance of inter spreading factor interference and collision effect

Abstract The paper introduces a LoRaWAN simulation model implemented for the Riverbed Modeler (former OPNET modeler suite). First, the key components of the developed simulator solution are detailed. Then, the results of the simulator’s validation for several test scenarios are presented. The developed simulator is used to investigate the effect of collision models on the results of LoRaWAN performance simulation. Specifically, the three models are studied: a baseline — implying loss off all colliding packets, an intra spreading factor (SF) with capture effect, and intra/inter SF with capture effect. The simulations verify that the results of the baseline model are in line with that for pure Aloha, while the two other demonstrate up to two-three fold higher delivery ratio. The obtained results illustrate the substantial impact of the collision model on the accuracy of simulations and motivate the need for further practical studies for the collision and interference mechanisms within a LoRaWAN network. Based on the results obtained through simulations, several drawbacks related to the use of strictly periodic traffic in LoRaWAN networks are noted

The effect of multiple access categories on the MAC layer performance of IEEE 802.11p

Abstract The enhanced distributed channel access (EDCA) mechanism enables IEEE 802.11p to accommodate differential quality of service (QoS) levels in vehicle-to-vehicle (V2V) communications, through four access categories (ACs). This paper presents multi-dimensional discrete-time Markov chain (DTMC) based model to study the effect of parallel operation of the ACs on the medium access control (MAC) layer performance of ITS-G5 IEEE 802.11p. The overall model consists of four queue models with their respective traffic generators, which are appropriately linked with the DTMCs modeling the operation of each AC. Closed-form solutions for the steady-state probabilities of the models are obtained, which are then utilized to derive expressions for key performance indicators at the MAC layer. An application for a highway scenario is presented to draw insights on the performance. The results show how the performance measures vary among ACs according to their priority levels, and emphasize the importance of analytical modeling of the parallel operation of all four ACs