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ZigBee is one of the key standards that enable low-cost and low-power wireless mesh networks. Working on top of IEEE 802.15.4 MAC/PHY standard, ZigBee defines higher layers that support reliable multi-hop wireless communications. In particular, ZigBee provides multiple routing protocols to support diverse application traffic types such as multipoint-to-point, point-to-multipoint, and point-to-point. However, there are no studies that thoroughly incorporate multiple ZigBee routing protocols. In this paper, we explore multiple unicast routing and many-to-one protocols incorporated into the ZigBee standard and compare them through extensive simulations using NS2. We discuss real-world implementation issues and introduce our implementation decisions. We also examine their suitability for different scenarios and discuss some of the improvements that can be made to the ZigBee standard routing protocols.

IEEE 802.15.4 targets low data rate communication with limited power devices and cheap wireless networking solutions. In recent years both industry and academia are attracted to IEEE 802.15.4 because of its applicability in wireless sensor networks and wireless body area networks. An important feature of IEEE 802.15.4 is its very low duty cycle operation for conserving energy consumption of sensor device. Super-frame structure of IEEE 802.15.4 defines the duty cycle of nodes. The super-frame structure is based on two parameters: beacon order (BO) and super-frame order (SO). The performance of an IEEE 802.15.4 network depends on the values of BO and SO. These values depict the energy consumption, throughput, node discovery and latency of communication. IEEE 802.15.4 uses fixed BO and SO values which can be carefully chosen to meet the network requirements. In this paper, an extensive survey of dynamic super-frame adjustment algorithms is presented. The survey focuses on beacon-enabled star topology of IEEE 802.15.4 and studies the impact of aforementioned algorithms for various applications. Also, the survey categorizes common IEEE 802.15.4 applications based on their requirements for super-frame adjustment. A brief simulation analysis is included in this survey to highlight the impact of BO and SO on the network performance.

In the context of the CYBERSENSORS integrated water management research project, we derive a numerical modelling approach for throughput estimation in an IEEE 802.15.4 wireless sensor network. We focus on the standard-compliant slotted carrier sense multiple access with collision avoidance algorithm. Our approach takes into account the number of nodes in a cluster network, as well as the transmitted packet size. The configuration examined is a chain network formed by wireless sensor nodes where the first node is the source of data packets and the last is the traffic sink. Theoretical estimations are verified using the ns-2 network simulator. We also look into the 3G communication aspects of the platform involved. Hardware implementation and simulation tools are used here to derive a number of design guidelines that will define the system's architecture.

The recent increase in the number of technologies operating in the 2.4 GHz ISM band has drawn attention towards the impact they can have on each other. In this paper, we have conducted a case study about coexistence of IEEE 802.11 and IEEE 802.15.4 which has led us to discover previously unknown interactions. We show through extensive experiments that CCA method used by a wireless device can significantly change the coexistence scenario. We also highlight the ways in which coexistence can be improved by making runtime adjustments to some MAC/PHY layer parameters and show their effectiveness. Furthermore, we propose a framework which exploits the pervasiveness and ubiquity of Wi-Fi to improve coexistence among wireless technologies in the 2.4 GHz ISM band. Our framework has the capability to detect the presence of wireless technologies operating anywhere in the 2.4 GHz ISM band and also accounts for devices whose signatures do not exist in the database. It facilitates the Wi-Fi AP to make decisions such as changing the channel or making MAC/PHY layer adjustments which are compliant with the configured coexistence policy thus improving the performance of the wireless devices. We have implemented our framework on real hardware and evaluated its performance in the presence of ZigBee.

The major challenge of real-time Wireless Sensor Networks stills the optimization of both constraints: energy consumption, to get long network lifetime and the communication delay, to meet real-time requirements. In the context of IEEE 802.15.4/ZigBee networks, the association procedure has a direct effect on building paths optimizing those constraints. In this paper, we are interested on the definition of an ideal approach of load balancing to fairly distribute energy consumption among nodes in IEEE 802.15.4/ZigBee WSNs. This approach leads to conserve energy of each node in order to extend the network lifetime. To be closer to this ideal, we propose new dynamic association/re-association approaches allowing path alternation relative to association criteria and their threshold parameters. The implementation of those approaches in NS2 simulator highlights the efficiency of cooperative and dynamic association criteria particularly the one based on the sum of the inverses of remaining energy. Indeed, this approach gives better results with regard to energy distribution according to ideal approach which leads to a longer lifetime. It also performs lower latency for real time communication.

Although the ZigBee technology is massively deployed the performance question still remains unanswered. There is a lack of serious performance evaluations and thus this paper provides a comprehensive and unbiased study of the ZigBee PRO technology. An extensive real measurement was conducted to accomplish this task. We found out a big performance gap among ZigBee implementations even though they are compliant with the ZigBee standard. The presented results and analysis could be beneficial for many wireless sensor network developers.

ZigBee is an industrial standard for wireless ad hoc networks based on IEEE 802.15.4. It has been developed for low cost, low data rate and low power consumption. ZigBee's network layer defines two routing protocols namely Ad Hoc On-demand Distance Vector and Tree Routing (TR). TR protocol follows the tree topology (parent---child) in forwarding the data packets from source nodes to the sink node. However, the source does not find rather nor the location of the sink is close to the source node or if it is not in the sub-tree. In this case it will follow the tree topology which will use a lot of hops to deliver data packets to the sink node. This paper present an improvement of TR protocol for ZigBee network and is called Improved Tree Routing (ImpTR) protocol which is computationally simple in discovering the better path to transmit data packets to the sink node, and does not need any addition in hardware. ImpTR determines the better path to the sink node depending on the tables of the neighbouring nodes, which is part of the existing ZigBee network specification. Results show that the proposed algorithm provides shorter average end-to-end delay, increase throughput, decrease the average number of hops and decrease the energy consumption from the network when compared to the original TR routing protocol.

An overview is given of the new IEEE 802.11n standard. This is the first wireless LAN standard based on MIMO-OFDM, a technique pioneered by Airgo Networks to give a significant performance increase in both range and rate relative to conventional wireless LAN. Performance results show that net user throughputs over 100 Mbps are achievable, which is about four times larger than the maximum achievable throughput using IEEE 802.11a/g. For the same throughput, MIMO-OFDM achieves a range that is about 3 times larger than non-MIMO systems. This significant improvement in range-rate performance makes MIMO-OFDM the ideal solution not only for wireless LAN, but also for home entertainment networks and 4G networks.

This paper presents a system design technique for the IEEE 802.11 Wireless Local Area Network (WLAN) considering the significant parameters namely coverage, cell/frequency planning, interference, power management and data rate. The effect of the parameters on the performance of IEEE 802.11 in terms of throughput has been discussed using measurement and numerical results. These results and concepts are extremely important not only for the system design and deployment of IEEE 802.11 WLANs but also for other indoor wireless communications systems.

Wireless sensor networks have been more and more deployed for monitoring and controlling real environments. However, because of sensor nodes’ limitations, their radios are more susceptible to noise and interference than in other wireless technologies. These are critical factors in the rigorous industrial environment, whose effects may not be the same on all channels of a sensor network. In this paper, we present some experimental studies about the characteristics of IEEE 802.15.4 channels in ISM band. We are particularly interested in the differences of implementing wireless sensor networks in academic and industrial environments. A common problem of wireless sensor network implementations is that most of them are purely academic or initially prepared in laboratory. Our study shows that it is very difficult to predict the quality and stability of the different channels in sensor networks, as the environment conditions greatly influence the network performance. Empirical approaches are suitable methods for choosing the appropriate channels to deploy WSNs in noisy environments. We conduct several tests in both laboratory and in a real world environment, particularly in an oil refinery as this is our case study in the context of the FP7 GINSENG project (Ginseng 2010).

In a tree-structured ZigBee wireless sensor network, nodes close to the root of the tree (i.e., hot-spot nodes) may exhaust their power earlier than those distant from the root due to heavy loads on packet forwarding. This hot-spot problem is inherent in tree-structured networks and may demand extra energy to recover from failures of hot-spot nodes. In this paper, the backbone-aware topology formation (BATF) scheme is proposed to alleviate the hot-spot problem. BATF utilizes power-rich nodes to form a backbone tree that does not suffer from the hot-spot problem. Each power-rich node independently initiates a ZigBee tree network that attracts associations from ZigBee-compliant devices in order to distribute packet-forwarding loads over a larger set of nodes. Issues of BATF such as the partition of address space and ZigBee-compliant routing are discussed in detail. Simulation results confirm that BATF does alleviate the hot-spot problem as it improves network lifetime as well as data collection capability. Comparisons with native ZigBee protocols show that the improvement comes from our protocol design rather than simply introducing power-rich nodes.