QoS-aware MAC protocols for wireless sensor networks: A survey <s> IEEE 802.15.3/802.15.4 and extensions <s> This document gives the motivation for the ZigBee alliance and explains the physical, medium access and routing layers of ZigBee. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> IEEE 802.15.3/802.15.4 and extensions <s> IEEE 802.15.4 slotted carrier-sense multiple access with collision avoidance (CSMA-CA) adopts periodic sleeping for energy efficiency support. However, such a periodic sleeping mechanism, especially with contention-based medium access, tends to cause additional sleep delay due to heavy contention. In this letter, we propose a priority-based scheme, comprising frame tailoring and priority toning, in order to relax such a problematic delay and guarantee time-bounded delivery of high priority packets in event-monitoring networks. <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> IEEE 802.15.3/802.15.4 and extensions <s> In beacon-enabled mode, IEEE 802.15.4 is ruled by the slotted CSMA/CA Medium Access Control (MAC) protocol. The standard slotted CSMA/CA mechanism does not provide any means of differentiated services to improve the quality of service for timecritical events (such as alarms, time slot reservation, PAN management messages etc.). In this paper, we present and discuss practical service differentiation mechanisms to improve the performance of slotted CSMA/CA for time-critical events, with only minor add-ons to the protocol. The contribution of our proposal is more practical than theoretical since our initial requirement is to leave the original algorithm of the slotted CSMA/CA unchanged, but rather tuning its parameters adequately according to the criticality of the messages. We present a simulation study based on an accurate model of the IEEE 802.15.4 MAC protocol, to evaluate the differentiated service strategies. Four scenarios with different settings of the slotted CSMA/CA parameters are defined. Each scenario is evaluated for FIFO and Priority Queuing. The impact of the hiddennode problem is also analyzed, and a solution to mitigate it is proposed. <s> BIB003 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> IEEE 802.15.3/802.15.4 and extensions <s> Abstract In sensor networks, data packets transmitted by different devices in home networking and industrial applications maintain different levels of importance. In this paper, we propose two mechanisms for IEEE 802.15.4 sensor networks to provide multi-level differentiated services which are required by each and every device. Mathematical model based on the discrete-time Markov chain is presented and is analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of the variation of contention window size and backoff exponent for service differentiation on 802.15.4 sensor networks. From the results, we derive that contention window size is more affective than backoff exponent on the saturation throughput while backoff exponent is more affective than contention window size on the average delay of every device. Simulation results are given to verify the accuracy of the numerical model. <s> BIB004 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> IEEE 802.15.3/802.15.4 and extensions <s> In wireless sensor network, IEEE 802.15.4 should operate in beacon-enabled mode in order to schedule periodic sleep and wake up to minimize energy consumption. In beacon enabled mode QoS is supported by using guaranteed time slots(GTS). However maximum number of GTS node cannot exceed seven, and the number is not sufficient for wireless sensor network which have high node density. In this paper, we present QoS support mechanism in beacon enabled mode using CSMA/CA back-off time. Our algorithm have compatibility with IEEE 802.15.4 Standard, which means that there is no need to change hardware to support QoS on existing network. We will analysis the performance of our algorithm to design QoS parameters. <s> BIB005
Besides discussing the QoS-aware MAC protocols designed for WSNs, in this section we discuss the state of the art in related MAC layer standards. The aim of IEEE 802.15.3  standard is to develop an ad hoc MAC layer for high data rate wireless personal area networks (WPANs) and a physical layer that can reach up to 20Mbps. The standard is geared towards handling voice, images and file transfers and it has an operational transmission range of approximately 10 m. Basically, the standard is specified for higher data rate scenarios and does not address the requirement of energy efficiency or other QoS requirements in WSNs. The IEEE 802.15.4 standard BIB001  , which is used as a basis for the ZigBee, WirelessHART, and MiWi specifications, has been originally designed for low-rate WPANs. The standard is then adopted by WSNs, interactive toys, smart badges, remote controls and home automation, operating on license-free ISM bands. IEEE 802.15.4 is intended as a specification for low-cost, low-powered networks with no critical concerns about throughput and latency. Therefore, QoS issues have not been the main concern in the original specification. Later, the IEEE 802.15.4a Task Group was created with the goal of defining a new physical layer, which is able to provide higher data rates and high-accuracy ranging capabilities. New releases of the standard focus on using UltraWide Band (UWB) and chirp signals as alternative physical layer technologies to overcome the bandwidth limitations. UWB can achieve bit rates varying approximately between 0.1 Mbps and 26 Mbps. However, besides higher data rates, other QoS issues, such as latency, reliability, are not addressed in the specification. Instead, there exists a number of studies to improve the performance of IEEE 802.15.4 MAC standard in terms of QoS support BIB004 BIB002 BIB003 BIB005 . Since they mainly adopt similar strategies, we believe that, surveying one of the examples will be sufficient to understand the basics of QoS support in 802.15.4 MAC. In BIB004 , authors derived an extension for IEEE 802.15.4, beacon enabled slotted CSMA-CA standard to provide service differentiation among sensor nodes based on their application-specific level of importance. Two mechanisms are proposed to realize service differentiation: variable contention window size and variable backoff exponent. A mathematical model based on the discrete-time Markov chain is also presented to evaluate the throughput, delay and packet drop probability performance of the modified 802.15.4 standard. Advantages and disadvantages: Since it is a service differentiation add-on scheme proposed for a well-known MAC protocol, it can be widely used in all IEEE 802.15.4 compatible sensor devices. However, priorities can only be assigned to sensor nodes statically beforehand which makes this proposal inappropriate for multi-modal sensor networks.