Shairmina Shafi

Performance of a beacon enabled IEEE 802.15.4 cluster with downlink and uplink traffic

The performance of an IEEE 802.15.4 compliant network operating in the beacon enabled mode with both downlink and uplink traffic is analyzed through discrete time Markov chains and the theory of M/G/1 queues. The model considers acknowledged transmissions and includes the impact of different network and traffic parameters such as the packet arrival rate, packet size, inactive period between the beacons, and the number of stations. We investigate the nonsaturation region and outline the conditions under which the network abruptly goes to saturation. The analysis of stability of the network queues shows that the stability of the downlink queue at the coordinator is the most critical for network operation. Due to the abruptness with which the switch from nonsaturation to saturation occurs, the network operating point has to be carefully chosen according to the volume of downlink traffic. Furthermore, our model shows that certain features prescribed by the standard actually limit the performance of 802.15.4 networks.

The impact of MAC parameters on the performance of 802.15.4 PAN

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, stations 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.

Performance of IEEE 802.15.4 beacon enabled PAN with uplink transmissions in non-saturation mode - access delay for finite buffers

In this work, we derive the probability distribution of access delay and calculate throughput of a personal area network operating under the IEEE standard 802.15.4 in the beacon enabled mode. We model the network using the theory of discrete time Markov chains and M/G/1/K queues. The model considers acknowledged uplink transmission in non-saturation mode, and includes the impact of different parameters such as packet arrival rate, number of stations, the finite size of individual node buffers, packet size, and inactive period between the beacons. Our model also captures the problem of congestion at the beginning of the superframe due to multiple transmissions delayed from the previous superframe. The results show that average access delays, even for small buffer sizes, may be quite high if the throughput exceeds 50%, which can seriously affect applications with delay bounds. Values of throughput larger than 50% can be achieved at the expense of larger buffer sizes, which imposes implementation problems on devices with small memory resources.

Avoiding the Bottlenecks in the MAC Layer in 802.15.4 Low Rate WPAN

We analyze the operation of the MAC layer of an IEEE 802.15.4 compliant network cluster in the beacon enabled mode with bidirectional traffic. We identify certain issues in the standard that lead to serious performance limitations, and suggest some simple modifications of the coordinator function that allows the network to handle higher traffic loads

Cross-layer activity management in an 802-15.4 sensor network

Sensor networks operate under conflicting requirements of maintaining the desired value of information throughput while simultaneously maximizing the lifetime of individual nodes. In doing so, the characteristics of the operating environment, including the MAC and PHY layers, have to be taken into account as well. In this article we consider activity management of sensor nodes in a beacon-enabled IEEE 802.15.4-compliant network. Activity management is performed through lightweight probabilistic control of the duration of sleep and service periods of individual sensors. We present two distributed activity management policies which are capable of achieving and maintaining the desired network reliability while maximizing the lifetime of the entire network.

Maintaining reliability through activity management in 802.15.4 sensor networks

Achieving the desired data rate from a sensor network while simultaneously maximizing the lifetime of individual sensors are somewhat conflicting goals, further complicated by the fact that collisions at the MAC layer will affect both the throughput and power consumption. We address this problem in the context of a beacon enabled 802.15.4 sensor network by analytically modeling the network reliability as the function of the activity management policy and MAC layer parameters. The network coordinator monitors the throughput and adjusts the probability with which individual sensors go to sleep after sending their data. Results show that this activity management policy is able to maintain the desired data rate in a wide range of sensor network sizes and packet arrival rates at the nodes

Performance limitations of the MAC layer in 802.15.4 low rate WPAN

The recent IEEE 802.15.4 standard defines a low rate wireless personal area network which can be used to implement sensor networks. In particular, the beacon enabled mode with slotted CSMA-CA contention resolution mechanism appears suitable for deployment in simple hierarchical sensor clusters. However, a detailed analysis of the operation of the MAC layer according to the 802.15.4 standard reveals a number of issues which may potentially become performance bottlenecks and thus lead to serious performance degradation. we analyze those issues and their impact, and suggest modifications of the coordinator function that allow the network to handle higher traffic loads and thus offer much improved performance to its clients.

Real-time admission control in 802.15.4 sensor clusters

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.

Activity management through Bernoulli scheduling 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.

Admission control in 802.15.4 beacon enabled 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.