QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> Wireless sensor networks are very application specific and have to be developed according to the requirements of a particular problem. They are usually deployed in harsh and mobile environments, with tasks ranging from just collecting environment readings to highly crucial tasks like tracking an enemy vehicle. This means the sensor networks can monitor or sense a very wide range of parameters and tasks. However, all these measurements and events that are read by the sensors are never of equal importance. So we propose PR-MAC, which provides a scheme in which we prioritize the events that are being recognized. Our aim is to design a MAC layer protocol which would reduce the delay of transmitting high priority tasks or measurements. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> The paper proposes a MAC layer protocol called QoMOR (QoS-aware MAC protocol using optimal retransmission) that is designed to provide QoS in a decentralized network with multiple sensor (source) nodes that do not have the capability to receive acknowledgements from the sink node. A minimum data delivery probability between the sensor and sink nodes is achieved by allowing each source node to transmit each new packet an optimal number of times in every interval of time. The paper first discusses the single QoS class case and derives the maximum achievable frame delivery probability and then extends the concepts to the multiple QoS class case. It also addresses a few design optimization criteria. Simulation and numerical analysis results show that QoMOR can effectively provide QoS guarantees under distributed control without using conventional ARQ-based schemes. <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <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> BIB003 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> Rapid penetration of small, customized wireless devices and enormous growth of wireless communication technologies has already set the stage for large-scale deployment of wireless sensor networks. While the need to minimize the energy consumption has driven significant researches in wireless sensor networks, offering some precise quality of service (QoS) for multimedia transmission over sensor networks has not received significant attention. However, the emerging new applications like video surveillance, telemedicine and traffic monitoring needs transmission of wireless multimedia over sensor networks. Naturally, offering some better QoS for wireless multimedia over sensor networks raises significant challenges. The network needs to cope up with battery-constraints, while providing improved QoS (end-to-end delay and bandwidth requirement). This calls for a suitable sensory MAC protocol capable of achieving application-specific QoS. In this paper, we have proposed a new QoS-based sensory MAC protocol, which not only adapts to application-oriented QoS, but also attempts to conserve energy without violating QoS-constraints. Performance modeling, analysis and simulation results demonstrate that the proposed protocol is capable of providing lower delay and better throughput, at the cost of reasonable energy consumption, in comparison to other existing sensory MAC protocols. <s> BIB004 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> Ultra-wideband (UWB) is a physical (PHY) layer technology that promises high transmission rates, as well as high resistance to noise and multipath effects. However, the impulse-based nature of UWB, coupled with its low transmission power, makes it difficult to enable efficient detection of the signals. Consequently, conventional carrier-sensing based MAC protocols cannot be used with a UWB PHY. In this paper, we propose SASW-CR - a slotted Aloha MAC protocol for UWB networks with sliding contention window and cooperative retransmissions, which provides QoS support without the use of carrier sensing. SASW-CR utilizes the slotted-Aloha technique to avoid carrier sensing and reduce packet collisions. In addition, it makes use of differentiated contention windows to provide varying classes of QoS for different traffic classes. A cooperative retransmission technique is also introduced to improve the overall traffic throughput and reduce end-to-end delay. The efficacy of our protocol is demonstrated through simulations. <s> BIB005 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> The media access control (MAC) protocol in wireless sensor networks provides a periodic listen/sleep state for protection from overhearing and idle listening. However, many scenarios and applications exist in which sensor nodes must send data quickly to destination nodes. This paper proposes the priority-based quality-of-service MAC (PQMAC) protocol for wireless sensor networks. We use data priority levels to differentiate among data transmissions, and propose a MAC protocol based on these levels. This protocol manages scheduling by adaptively controlling network traffic and the priority level. We focused on reducing the latency of the message transmission from the source to the destination. Simulation results showed that PQMAC reduces latency problems in wireless sensor networks while maintaining energy efficiency. <s> BIB006 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> Popularity of Wireless Sensor Networks (WSNs) combined with the multimedia requirements of new applications have enabled Wireless Multimedia Sensor Networks (WMSNs) which commonly carry heterogeneous traffic. In order to deliver multiple types of traffic with different requirements in highly resource constrained sensor networks, Quality of Service (QoS) provisioning becomes unavoidable. In this work, we propose Diff-MAC; a QoS-aware and priority-based MAC protocol for WMSNs. Diff-MAC aims to increase the utilization of the channel with effective service differentiation mechanisms while providing fair and fast delivery of the QoS-constrained data. Performance evaluation results of Diff-MAC, obtained through extensive simulations, show significant improvements, in terms of latency, data delivery and energy efficiency, compared to two other existing protocols. <s> BIB007 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Comparisons <s> Enabling quality of service (QoS) applications over battery-constrained wireless sensor networks (WSNs) poses significant challenges, because of the special characteristics of such networks. Developing real-time applications for WSNs necessitates the development of new communication protocols capable of achieving application-specific QoS and at the same time save energy. In this paper, we continue our previous work on developing and improving our EQ-MAC protocol, which is designed specifically for WSNs to reduce energy consumption and provides QoS guarantees through the use of the service differentiation concept. The proposed protocol consists of two subprotocols: Classifier MAC (C-MAC) and Channel Access MAC (CA-MAC). C-MAC is responsible of classifying gathered data at sensor nodes based on its importance. The CA-MAC is an energy conserving medium access mechanism which uses a hybrid scheduling technique. CA-MAC saves energy by differentiating between control and data messages. Data messages are assigned scheduled slots with no contention (here we have to emphasize that slots are assigned only to those nodes that have data to send, this allows an efficient energy use of the Time Division Multiple Access (TDMA) slots), whereas short periodic control messages are assigned random access slots. To study the performance of the EQ-MAC protocol, we have conducted several simulation experiments on Network Simulator (NS-2) to evaluate and compare the performance of our protocol against S-MAC and Q-MAC protocols. Simulation results demonstrate that EQ-MAC outperforms the other two protocols and achieves a significant improvement in terms of the energy expenditure and delivery ratio. Under prioritized traffic, EQ-MAC is comparable to Q-MAC in average latency, while achieving less energy consumption. Copyright © 2010 John Wiley & Sons, Ltd. <s> BIB008
In Table 2 , we summarize the general aspects of the QoS-aware MAC protocols that we have discussed for WSNs. The table also presents comparisons of the discussed algorithms in two groups, namely protocols with differentiated services and application-specific protocols. The Type column shows the type of MAC mechanism(s) used in the protocol. Service Differentiation column specifies whether the protocol supports service differentiation or not whereas the Priority Assignment column presents whether the protocol assigns priorities to different traffic types and if it does whether it is static, dynamic or hybrid. The Synchronization field shows whether the protocol requires synchronization or not. The Energy-awareness column is important to show whether the protocol provides energy-awareness together with QoS provisioning which are known to be conflicting requirements. The Complexity column demonstrates the level of complexity in the execution of the protocol. Finally, the Scalability field shows how scalable the protocol is with the increased number of sensor nodes and complexity within a WSN. Most of the protocols provide random medium access, i.e., CSMA, or propose hybrid solutions such as CSMA and TDMA. We observe that instead of providing deterministic QoS guarantees, majority of the protocols follow a service differentiation approach by classifying data packets according to their type and associated network parameters at the MAC layer are tuned according to the requirements of different types. Those protocols that provide service differentiation usually assign static priorities to the traffic types since this is simpler to manage. However, dynamic priority assignment may be necessary where the priorities of different packet types may vary in time. Traffic adaptivity is usually not supported whereas most of the protocols do not require synchronization since they allow for random access. As the MAC protocols provide QoS provisioning, their complexity increases but still they should be processed by the sensor devices without any resource problems. Although WSNs are becoming popular among complex applications that require fast and efficient data delivery, energy awareness is still a major requirement and most of the protocols support energy efficient communication in the network. In terms of scalability, we observe both trends: good and weak protocols in terms of scalability but one should not forget that WSNs are composed of hundreds, thousands and even more devices and the protocols should be able to work with these numbers of nodes. As we mentioned before, performance of the MAC protocols for WSNs are highly application dependent. Therefore, we need to evaluate the performance of all surveyed protocols under the same application or simulation environment, which is quite hard to be done, in order to make accurate quantitative comparisons in terms of communication delay, delay jitter, throughput, energy efficiency, lifetime, etc. However, for those interested, please check the individual papers of these protocols for small scale qualitative comparisons between their competitors. For instance in BIB007 we compare the performance of DiffMAC with Saxena et al. MAC BIB004 and give qualitative results in terms of lifetime, delay, energy efficiency and delivery rate. Additionally, a classification of these protocols is provided in Fig. 6 . As mentioned, we observe two main trends in QoS-aware MAC protocols for WSNs: protocols that follow differentiated services approach and protocols that provide application specific QoS support. Protocols that provide service differentiation can further be classified as the protocols that provide static differentiation (i.e., static parameters are tuned at the MAC layer), protocols with dynamic differentiation where dynamic parameters are tuned at the MAC layer, such as the remaining time till the packet deadline, and the protocols with hybrid QoS support where both static and dynamic parameters are taken into account as discussed in Section 5.6. Among the protocols that we have surveyed in Section 6, BIB004  BIB005 BIB001 BIB006 BIB002 BIB003 BIB008 provide static differentiation whereas Table 2 Comparison of QoS-aware WSN MAC protocols in the literature.