A survey of communication/networking in Smart Grids

Advances in low-power and low-cost sensor networks have led to solutions mature enough for use in a broad range of applications varying from health monitoring to building surveillance. The development of those applications has been stimulated by the finalization of the IEEE 802.15.4 standard, which defines the medium access control (MAC) and physical layer for sensor networks. One of the MAC schemes proposed is slotted carrier sense multiple access with collision avoidance (CSMA/CA), and this paper analyzes whether this scheme meets the design constraints of those low-power and low-cost sensor networks. The paper provides a detailed analytical evaluation of its performance in a star topology network, for uplink and acknowledged uplink traffic. Both saturated and unsaturated periodic traffic scenarios are considered. The form of the analysis is similar to that of Bianchi for IEEE 802.11 DCF only in the use of a per user Markov model to capture the state of each user at each moment in time. The key assumptions to enable this important simplification and the coupling of the per user Markov models are however different, as a result of the very different designs of the 802.15.4 and 802.11 carrier sensing mechanisms. The performance predicted by the analytical model is very close to that obtained by simulation. Throughput and energy consumption analysis is then performed by using the model for a range of scenarios. Some design guidelines are derived to set the 802.15.4 parameters as function of the network requirements.

https://biblio.ugent.be/publication/437281/file/794715.PDF

Performance Analysis of Slotted Carrier Sense IEEE 802.15.4 Medium Access Layer

In this paper, we analyze the performance limits of the slotted CSMA/CA mechanism of IEEE 802.15.4 in the beacon-enabled mode for broadcast transmissions in WSNs. The motivation for evaluating the beacon-enabled mode is due to its flexibility for WSN applications as compared to the non-beacon enabled mode. Our analysis is based on an accurate simulation model of the slotted CSMA/CA mechanism on top of a realistic physical layer, with respect to the IEEE 802.15.4 standard specification. The performance of the slotted CSMA/CA is evaluated and analyzed for different network settings to understand the impact of the protocol attributes (superframe order, beacon order and backoff exponent) on the network performance, namely in terms of throughput (S), average delay (D) and probability of success (Ps). We introduce the concept of utility (U) as a combination of two or more metrics, to determine the best offered load range for an optimal behavior of the network. We show that the optimal network performance using slotted CSMA/CA occurs in the range of 35% to 60% with respect to an utility function proportional to the network throughput (S) divided by the average delay (D).

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A comprehensive simulation study of slotted CSMA/CA for IEEE 802.15.4 wireless sensor networks

Wireless Sensor Networks (WSNs) represent a very promising solution in the field of wireless technologies for industrial applications. However, for a credible deployment of WSNs in an industrial environment, four main properties need to be fulfilled, i.e., energy efficiency, scalability, reliability, and timeliness. In this paper, we focus on IEEE 802.15.4 WSNs and show that they can suffer from a serious unreliability problem. This problem arises whenever the power management mechanism is enabled for energy efficiency, and results in a very low packet delivery ratio, also when the number of sensor nodes in the network is very low (e.g., 5). We carried out an extensive analysis-based on both simulation and experiments on a real WSN-to investigate the fundamental reasons of this problem, and we found that it is caused by the contention-based Medium Access Control (MAC) protocol used for channel access and its default parameter values. We also found that, with a more appropriate MAC parameters setting, it is possible to mitigate the problem and achieve a delivery ratio up to 100%, at least in the scenarios considered in this paper. However, this improvement in communication reliability is achieved at the cost of an increased latency, which may not be acceptable for industrial applications with stringent timing requirements. In addition, in some cases this is possible only by choosing MAC parameter values formally not allowed by the standard.

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A Comprehensive Analysis of the MAC Unreliability Problem in IEEE 802.15.4 Wireless Sensor Networks

The IEEE 802.15.4 protocol proposes a flexible communication solution for low-rate wireless personal area networks including sensor networks. It presents the advantage to fit different requirements of potential applications by adequately setting its parameters. When enabling its beacon mode, the protocol makes possible real-time guarantees by using its guaranteed time slot (GTS) mechanism. This paper analyses the performance of the GTS allocation mechanism in IEEE 802.15.4. The analysis gives a full understanding of the behavior of the GTS mechanism with regards to delay and throughput metrics. First, we propose two accurate models of service curves for a GTS allocation as a function of the IEEE 802.15.4 parameters. We then evaluate the delay bounds guaranteed by an allocation of a GTS using network calculus formalism. Finally, based on the analytic results, we analyse the impact of the IEEE 802.15.4 parameters on the throughput and delay bound guaranteed by a GTS allocation. The results of this work pave the way for an efficient dimensioning of an IEEE 802.15.4 cluster.

/pdf/gts-allocation-analysis-in-ieee-802-15-4-for-real-time-3rpk521fbi.pdf

GTS allocation analysis in IEEE 802.15.4 for real-time wireless sensor networks

The operation of a personal area network, operating under the IEEE Standard 802.15.4 in the beacon enabled mode, is analyzed using the theory of discrete time Markov chains and M/G/1/K queues. The model includes the impact of different parameters such as packet arrival rate, number of stations, station's buffer size, packet size, and inactive period between the beacons. We have derived several important performance parameters such as probability of access, probability that medium is idle, queue length distribution in the device, and probability distribution of the packet service time. Some important conclusions regarding the implementation of 802.15.4 networks and compatible network devices are outlined.

The impact of MAC parameters on the performance of 802.15.4 PAN

Performance limitations of the MAC layer in 802.15.4 low rate WPAN

The problem of admission control is considered in a beacon-enabled 802.15.4 network. The network coordinator decides to admit or reject a new node on the basis of the analytical model of the packet service time, using the number of nodes in a cluster, packet arrival rate and packet size as independent variables. Simulation experiments confirm the validity of the chosen admission control algorithm, which is shown to provide a slightly conservative estimate with respect to the ideal condition.

Real-time admission control in 802.15.4 sensor clusters

The activity of individual nodes in a sensor network has to be managed in order to meet the simultaneous goals of maximizing the network lifetime and achieving the desired information throughput at the network sink. In this work we investigate the interaction of activity management with the CSMA-CA-based MAC layer in a beacon enabled IEEE 802.15.4-compliant network cluster. Activity management is performed through Bernoulli scheduling of service and sleep periods, which gives better results than the traditional, exhaustive and I-limited scheduling of the active and sleep periods. We derive the event reliability at the cluster coordinator as the function of physical layer parameters, data link layer parameters, Bernoulli scheduling parameter, and the probability distribution of sleep period. Based on the centralized analytical model, we derive distributed algorithm for calculating sleep parameters and demonstrate that the proposed distributed activity management policy is capable of achieving and maintaining the desired network reliability while maximizing the network lifetime.

Activity management through Bernoulli scheduling in 802.15.4 sensor clusters

The problem of admission control at the sensor cluster coordinator is considered in a beacon enabled 802.15.4 network. The admission control algorithm is based on analytical modeling of the packet service time, using the number of nodes in a cluster, packet arrival rate, and packet size as independent variables. Simulation experiments confirm the validity of the chosen admission control algorithm, which is shown to provide a slightly conservative estimate with respect to the ideal condition.

Shairmina Shafi

Papers

The impact of MAC parameters on the performance of 802.15.4 PAN

Performance limitations of the MAC layer in 802.15.4 low rate WPAN

Real-time admission control in 802.15.4 sensor clusters

Activity management through Bernoulli scheduling in 802.15.4 sensor clusters

Admission control in 802.15.4 beacon enabled clusters