QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <s> Recent advances in wireless technology have brought us closer to the vision of pervasive computing where sensors/actuators can be connected through a wireless network. Due to cost constraints and the dynamic nature of sensor networks, it is undesirable to assume the existence of base stations connected by a wired backbone. In this paper, we present a network architecture suitable for sensor networks along with a medium access control protocol based on earliest deadline first. <s> BIB001 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <s> We present an innovative MAC protocol (Q-MAC) that minimizes the energy consumption in multi-hop wireless sensor networks (WSNs) and provides quality of service (QoS) by differentiating network services based on priority levels. The priority levels reflect application priority and the state of system resources, namely residual energy and queue occupancies. The Q-MAC utilizes both intra-node and inter-node arbitration. The intra-node packet scheduling is a multiple queuing architecture with packet classification and weighted arbitration. We also introduce the power conservation MACAW (PC-MACAW) - a power-aware scheduling mechanism that, together with the loosely prioritized random access (LPRA) algorithm, govern the inter-node scheduling. Performance evaluation are conducted between Q-MAC and S-MAC with respect to two performance metrics: energy consumption and average latency. Simulation results indicate that the performance of the Q-MAC is comparable to that of the S-MAC in non-prioritized traffic scenarios; when packets with different priorities are present, Q-MAC supiors in average latency differentiation between the classes of service, while maintaining the same energy level as that of S-MAC <s> BIB002 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <s> This paper presents a new prioritized medium access control protocol (PSIFT) that improves the performance of event-driven wireless sensor networks by suppressing the redundant reports of sensor nodes in proximity. This suppression of similar reports results in low collision probability, shorter delay and accurate detection of events by the sink. PSIFT is a CSMA-based MAC protocol that provides traffic differentiation by varying the inter frame space and contention window size for each traffic class. We also introduce the new report suppression mechanism based on the broadcast nature of wireless transmission in PSIFT. This mechanism works very efficiently in large-scale, event-driven wireless sensor networks. Simulation results show that the new PSIFT MAC protocol can bring significant improvement in delay performance of the networks. When the sensing range grows up to transmission range, PSIFT can reduce the latency as much as three times in delivering reports as compared to the existing IEEE802.11 MAC protocol. <s> BIB003 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <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> BIB004 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <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> BIB005 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <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> BIB006 </s> QoS-aware MAC protocols for wireless sensor networks: A survey <s> Priority assignment <s> This paper introduces I-MAC, a new medium access control protocol for wireless sensor networks. I-MAC targets at improving both channel utilisation and energy efficiency while taking into account traffic load for each sensor node according to its role in the network. I-MAC reaches its objectives through prioritized and adaptive access to the channel. I-MAC performances obtained through simulations for different network topologies, scenarios and traffic loads show significant improvements in energy efficiency, channel utilization, loss ratio and delay compared to existing protocols. <s> BIB007
Priority assignment methods that imply the criteria of differentiation need to be identified carefully in order to achieve fair and effective QoS support. Since the correctness and accuracy of the assigned priorities affect the QoS support significantly, overall performance of the QoS mechanisms highly depends on it. As mentioned in Section 2.1, reservation-less DiffServ model is in the scope of this paper and priority assignment methods in DiffServ are divided into three categories: 1. Static priority assignment: If the priority is assigned once the packet is created and never changes until its destination, it is called as static priority assignment. Decision parameters for static priority assignment can be listed as follows: Traffic class: Packets can be prioritized based on the type of traffic like real-time, non-real-time, best effort. Accordingly, delay and loss bounded real-time packets will have higher priority whereas non-realtime and best effort packets have lower BIB005  . Source type: QoS mechanism can specify set or sets of sensor nodes or sinks which generate more important data than others and assign all network entities a priority. Consequently, the node which generates the packet also gives the priority of itself to its packets, i.e. packet inherits the priority of its creator. Priorities of the entities can be given based on the sensor type, observed area characteristics, distance to center or sink BIB006 . Data delivery model: There are four types of data delivery models in WSNs as discussed in Section 4.1. Priority of the packets can be selected based on the associated data delivery model. For example, event-driven data might have higher priority than periodic messages in case of an intrusion detection application BIB004 . 2. Dynamic priority assignment: Contrary to the static priority assignment, packet priorities may vary during delivery. There are several criteria proposed for dynamic prioritization: Remaining hop count: In a multihop WSN, remaining number of hops to the destination of the packet can be used as a parameter for packet prioritization. One of the ideas behind this parameter is minimizing the delay deviations between the packets generated by the sensor nodes which have different distances to the sink. Also, as the distance that the packet will travel increases, it becomes more vulnerable to deadline miss, dropping and link failure. Hence, packets which will traverse more hops are given higher priority. Traversed hop count: The number of traversed hops can be used for prioritization since losing, dropping or missing the deadline of a packet which has traversed more hops will be waste of more network resources than the one which has traversed less hops. Therefore, giving higher priorities to the more invested packets in terms of network resources increases the network lifetime and channel utilization. Moreover, relatively further sensor nodes from the sink usually have smaller chance to deliver their packets and suffer from high latencies. Hence, speeding up the packet as it gets closer to the sink also provides fairness among sensor nodes in terms of packet delivery ratio and latency. Examples of such dynamic priority assignment schemes can be found in BIB003 BIB002 . Packet deadline: The closer a packet is to miss its deadline, the higher priority it should have, since the packet will be useless after its deadline. In this way, waste of network resources can be prevented BIB001 . Remaining energy: Increasing the priority of the packets as the remaining energy of the generating or relaying sensor node decreases, extends the lifetime of the sensor node by preventing the energy waste caused by idle listening. Examples of protocols that provide differentiation based on remaining energy are presented in BIB007 BIB002 . Traffic load: Forwarding loads of the sensor nodes can change depending on their position or role (leaf node, relay node, cluster head) in the network. Giving higher priority to the sensor nodes that have relatively heavier forwarding load can decrease the packet dropping ratio caused by buffer overflow. Besides its role in the network, proportional buffer load of the sensor node can be an indicator of the traffic load also BIB007 BIB002 . 3. Hybrid priority assignment: Priority of the packets can be determined in a hybrid manner by considering both static and dynamic decision criteria. Moreover, by giving certain weights to these criteria, importance degree of the packet can be calculated more precisely and mapped to a priority level.