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AN ENERGY-EFFICIENT MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS 61 Copyright © 2008 SciRes. AN ENERGY-EFFICIENT MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS 63 Copyright © 2008 SciRes. AN ENERGY-EFFICIENT MAC PROTOCOL FOR WIRELESS SENSOR NETWORKS 65 Copyright © 2008 SciRes. Abstract Swallowable body sensor networks (BSNs) are composed of sensors which are swallowed by patients and send the collected data to the outside coordinator.
Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract Conventional MAC protocols for wireless sensor network perform poorly when faced with a delay-tolerant mobile network environment. Characterized by a highly dynamic and sparse topology, poor network connectivity as well as data delay-tolerance, delay-tolerant mobile sensor networks exacerbate the severe power constraints and memory limitations of nodes. An Energy-Efficient MAC Protocol Using Dynamic Queue Management for Delay-Tolerant Mobile Sensor Networks.
1, 1-69 This subsection describes how to efficiently transmit a long message in both energy and latency. This paper proposes an energy-efficient MAC protocol using dynamic queue management (EQ-MAC) for power saving and data queue management. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.AbstractCritical infrastructure monitoring applications are rapidly increasing.
Via data transfers initiated by the target sink and the use of a dynamic queue management strategy based on priority, EQ-MAC effectively avoids untargeted transfers, increases the chance of successful data transmission, and makes useful data reach the target terminal in a timely manner. This paper proposes S-MAC, a medium-access control (MAC) protocol designed for wireless sensor networks. This method avoids the overhearing problem and is inspired by PAMAS [10], but does not require an additional channel. It can be a long series of packets or a short packet, and usually the receiver needs to obtain all the data units before it can perform in-network data processing or aggregation. Multi-hop communication is analyzed and proved more energy efficient than single-hop communication within the human body when the circuitry power is low.
Experimental results show that EQ-MAC has high energy efficiency in comparison with a conventional MAC protocol. It also achieves a 46% decrease in packet drop probability, 79% increase in system throughput, and 25% decrease in mean packet delay.
A network of these devices will collaborate for a common application such as environmental monitoring.
Per-node fragment-level fairness is reduced since sensor network nodes are often collaborating towards a single application. The downside of the scheme is that the latency is increased due to the periodic sleep of each node. It provides mechanism for collision avoidance such that interfering sensor nodes do not transmit at the same time. We expect sensor networks to be deployed in an ad hoc fashion, with individual nodes remaining largely inactive for long periods of time, but then becoming suddenly active when something is detected. 3 also shows the timing relationship of three possible situations that a sender transmits to a receiver. The coordinator collects the path-loss map and calculates the schedules, including routing, slot assignment and transmission power. In the literature, researchers have proposed different MAC protocols with features aimed at improving energy efficiency and thereby prolonging the life of sensor nodes. So the latency requirement of the application places a fundamental limit on the sleep time. Sensor MAC, Time-out MAC (T-MAC), Dynamic Sensor MAC (DSMAC), WiseMAC, Quorum-based MAC (Queen-MAC) and Traffic Adaptive Medium Access Protocol (TRAMA) are some examples of proposed MAC protocols.
S-MAC uses three novel techniques to reduce energy consumption and support self-configuration. Because there are many nodes, they will be deployed casually in an ad hoc fashion, rather than carefully positioned.
The value of this field indicates how long it will take to complete the remaining packet transmission. Other important attributes include fairness, latency, and throughput and bandwidth utilization. These attributes are generally the primary concerns in traditional wireless voice and data networks, but in sensor networks they are secondary. The effectiveness of this proposed Packet-Duration-Value-based MAC (PDV-MAC) protocol is tested via Simulation which is implemented in Visual C# and MATLAB. IntroductionCritical infrastructure monitoring has become a major research area in recent times. If it fails to receive the ACK, it will extend the reserved transmission time for one more fragment, and re-transmit the current fragment immediately. It is shown by the results obtained that the proposed MAC protocol can indeed be implemented in sensor nodes to improve energy efficiency in wireless sensor network.1. Critical infrastructure is a term used to describe assets that are essential for the functioning of a society and economy. Finally, S-MAC applies message passing to reduce contention latency for sensor-network applications that require store-and-forward processing as data move through the network.
Since sensor networks are committed to one or a few applications, application-specific code can be distributed through the network and activated when necessary or distributed on-demand. IntroductionOne fundamental function of the Medium Access Control (MAC) protocol is to avoid collisions so that interfering nodes do not transmit at the same time. We evaluate our implementation of S-MAC over a sample sensor node, the Mote, developed at University of California, Berkeley.
Techniques such as data aggregation can reduce traffic, while collaborative signal processing can reduce traffic and improve sensing quality. The experiment results show that, on a source node, an 802.11-like MAC consumes 2a€“6 times more energy than S-MAC for traffic load with messages sent every 1a€“10s. In-network processing implies that data will be processed as whole messages at a time in store-and-forward fashion, so packet or fragment-level interleaving from multiple sources only increases overall latency.
Wireless Sensor Network (WSN) consists of large number of distributed sensor nodes which are organized into multi-hop wireless networks.
Each node has one or more sensors, low-power radio, embedded processors and mostly battery powered. Such a network normally consists of a large number of distributed nodes that organize themselves into a multi-hop wireless network. It then waits for a random delay td and rebroadcasts this schedule, indicating that it will sleep in ta?’td seconds.
Each node has one or more sensors, embedded processors and low-power radios, and is normally battery operated. The random delay is for collision avoidance, so that multiple followers triggered from the same synchronizer do not systematically collide when rebroadcasting the schedule.
The monitoring can increase safety through the prevention of catastrophic failures, environmental damage, hazardous leaks, and so forth [2]. The above-mentioned applications require extremely low energy usage to maximize the deployment lifetime.
These are categorized as Low-energy critical infrastructure monitoring applications.The requirements [3] for such a network are energy efficiency, long lifetime, scalability, reliability, availability, robustness, maintainability, and security.
In addition, Carrier Sense Multiple Access (CSMA)-based MAC protocols do not require clock synchronization and global topology knowledge. Low energy is required as the sensors are normally located where power mains and the network infrastructures are not readily available. When a node joins or leaves the network dynamically it can be controlled without extra operations.
These endpoints are highly distributed in challenging environments that include cities, rural areas, forests, mountains, and below-ground monitoring locations. On the other hand, it is possible that some neighboring nodes fail to discover each other at beginning due to collisions when broadcasting schedules. The main design features for MAC protocols in a WSN include energy, latency and throughput as well as scalability.Several MAC protocols with different energy efficiency objectives have been proposed in the literature for wireless sensor networks.
The distance between the coordinator and the endpoints may vary from few meters to few kilometers. They also need to operate for long durations without human interactions.The above application space is not well served by any existing or planned standard of IEEE. As a result, an IEEE TG4k is formed as an amendment to IEEE 802.15 family to address the LECIM. On the one hand, node turns ON its radio and can communicate with its neighbours during the active part, as well as send messages queued during the sleeping part. The intentions are to facilitate low-energy operation for multiyear battery life and establish a simple and low-cost communication environment with reliable data transfer capabilities.Due to the unique features of LECIM networks, a great deal of research is required for the effective network management and operations. As stated above, sensor nodes are likely to be battery powered, and it is often very difficult to change or recharge batteries for these nodes.
Each node maintains a TDMA like frame, called super frame, in which the node schedules different time slots to communicate with its known neighbors. The timer of one node will fire first and its broadcast will synchronize all of its peers on its schedule.
On the other hand, a node turns OFF its radio during the sleeping part and cannot immediately communicate with its neighbours. As LECIM network’s battery powered endpoints must operate for years, it necessitates the needs for advanced power management of the radio. In fact, someday we expect some nodes to be cheap enough that they are discarded rather than recharged. If instead two nodes independently assign schedules (either because they cannot hear each other, or because they happen to transmit at nearly the same time), those nodes on the border between the two schedules will adopt both. So if a node receives a packet destined to another node, it knows how long it has to keep silent. In S-MAC, neighbouring nodes form virtual clusters so as to set up a common sleep schedule. In this paper, we pursue the idea of using a second, ultra-low-power radio that can be used to trigger a remote interrupt, so that a receiver can shoot up its primary radio to engage in efficient communication with the sender. The node records this value in a variable called the network allocation vector (NAV) [1] and sets a timer for it. It is noted that two neighboring nodes in two different virtual clusters wake up during the listening periods of both clusters. Another important attribute is the scalability to the change in network size, node density and topology.
Although per-hop fairness and latency are reduced, we will argue that the reduction does not necessarily result in lower end-to-end fairness and latency. Although the super frame structure is similar to a TDMA frame, it does not prevent two interfering nodes from accessing the medium at the same time.
The disadvantage is that these border nodes have less time to sleep and consume more energy than others.
Every time when the NAV timer fires, the node decrements the NAV value until it reaches zero.
The implications of S-MAC, therefore, are that throughput is reduced because only the active part of the frame is used for communication, and latency is increased as a message-driven event could occur during the sleeping period.
The traditional MAC (medium access control) protocols may fail to achieve optimal power consumption when on demand functionality is needed and the coordinator is supposed to send data at long time intervals and at a random fashion to the endpoints which spend most of the time in off mode. Besides, there is a possibility that neighboring nodes in two virtual clusters follow two different wake-up and sleep schedules; thereby resulting in more energy consumption. Dam and Langendoen [2] proposed Time-Out MAC (T-MAC) protocol to improve the weak results of S-MAC during variable traffic densities.
This is the first protocol for LECIM networks using framed slotted aloha to the best of our knowledge.The rest of the paper is structured as follows. For example, if a node only has packets to be sent to one neighbor, it cannot reuse the time slots scheduled to other neighbors.
Variable loads in sensor networks are expected, since the nodes that are closer to the sink must relay more traffic and traffic may change over time. Physical carrier sense is performed at the physical layer by listening to the channel for possible transmissions. One interesting feature of piconet is that it also puts nodes into periodic sleep for energy conservation.
An active period ends when upon waking up there is no activation event before expiration of threshold set for time-out. The scheme that piconet uses to synchronize neighboring nodes is to let a node broadcast its address before it starts listening.
If a node wants to talk to a neighboring node, it must wait until it receives the neighbora€™s broadcast.
The medium is determined as free if both virtual and physical carrier sense indicates that it is free. Yoo and Choi [3] proposed Dynamic Sensor-MAC (DSMAC), which adds a dynamic duty-cycle feature to S-MAC. The performance of the proposed MAC is analyzed and compared with related protocols in Section 6. If a node fails to get the medium, it goes to sleep and wakes up when the receiver is free and listening again. When a receiver node notices that the average one-hop latency value is high, it decides to shorten its sleep time and announces it within the SYNC period.


Related WorkAn ever increasing number of works are dealing with the protection of the sensed data in critical infrastructure monitoring applications; but, accessing the shared medium in such networks has received comparatively little attention.
After a sender node receives this sleep-period decrement signal, it checks its queue for packets destined to that receiver node. The survey in [4] covers the general ideas about using a WSN to ensure the protection of critical infrastructure. If there are packets then it doubles its duty cycle when its battery level is above a specified threshold. In [5], the authors provide an overview of the main challenges and open research issues on critical information infrastructure security.
The SYNC packet is very short, and includes the address of the sender and the time of its next sleep. In his contribution, [4] proposed the spatial TDMA and CSMA with preamble sampling protocol in which all sensor nodes are defined to have two communication channels. In [6], the authors identify the precise security requirements for distributing the symmetric keys along the one-dimensional WSN used for monitoring an extended piece of linear infrastructure such as a pipe.
The next-sleep time is relative to the moment that the sender finishes transmitting the SYNC packet, which is approximately when receivers get the packet (since propagation delays are short). The data channel is accessed using the TDMA and the control channel is accessed using CSMA. This paper also proposes lightweight key distribution schemes which could benefit applications like perimeter surveillance and pipeline monitoring. Moreover, [5] proposed a Wireless Sensor MAC (WiseMAC) for the downlink of infrastructure wireless sensor networks. This is a significant waste of energy, especially when node density is high and traffic load is heavy. WiseMAC is a novel energy efficient MAC protocol based on synchronized preamble sampling to minimize idle listening.
First, they propose a model to maximize the amount of monitoring-related data that can survive after a portion of the critical infrastructure suffers a disaster.
Another category of MAC protocol is based on scheduling wherein data transmissions are scheduled in advance to avoid contention. In such protocol, besides data transmission, nodes exchanges neighbor information periodically to schedule the transmission. In [3], a preliminary fragmentation for TG4k to improve apparent reliability of the medium is proposed. TRAMA is a TDMA-based protocol proposed by [7] to increase the utilization of classical TDMA in an energy efficient manner. It can greatly reduce energy consumption compared to transmitting all the raw data to the end node [4,5,6]. Sensor networks will be composed of many small nodes to take advantage of physical proximity to the target to simplify signal processing.
In TRAMA, contention-free “scheduled access” and contention-based “random-access” are performed alternatively.
Data transmissions take place in the scheduled access slot and neighbor information exchange is performed in a random access slot. TSCH allows the endpoints, to hop over the entire channel space in a slotted way thus minimizing the negative effects of multipath fading and interference while avoiding collisions.In [9], the authors proposed contention free low-energy link access for LECIM by distributing the access load on a slotted link.
The main advantage of TRAMA over S-MAC is the improvement in channel utilization but there is a trade-off in longer delay and higher energy consumption. In fact, it is similar to multiframe order in DSME (distributed synchronous multichannel extension) of TG4e. In this case, MAC protocols that promote fragment-level fairness actually increase message-level latency for the application. It is clear that node D should go to sleep since its transmission interferes with Ba€™s reception. In contrast, message passing reduces message-level latency by trading off the fragment-level fairness. It is easy to show that node E and F do not produce interference, so they do not need to go to sleep. The receiver periodically turns radio ON to sample for the incoming messages and if the preamble is detected, it continues listening for the normal message transfer. C is two-hop away from B, and its transmission does not interfere with Ba€™s reception, so it is free to transmit to its other neighbors like E.
Neighboring nodes are free to talk to each other no matter what listen schedules they have.
In view of the fact that more than one sender may want to send packets to a receiver at the same time, such nodes need to contend for the transmission medium to avoid collision.Furthermore, researchers have proposed other MAC protocols.
The main idea is the coordinator keeps listening to the channel and the endpoints keep sleeping. In summary, all immediate neighbors of both the sender and the receiver should sleep after they hear the RTS or CTS packet until the current transmission is over. In their approach, the communication of cluster heads uses the FDMA technology which can decrease crosstalk between different frequency and the cluster heads can identify each other. If the coordinator wants to send a unicast frame, it waits for the data packet from the desired endpoint and then sends the unicast frame piggybacked with the ACK. In [9], the authors proposed a quorum-based energy efficient MAC protocol, named Queen-MAC. In the case of the broadcast or multicast frame, the coordinator sends a sequence of wakeup calls to make an appointment about the desired frame transmission time.The main problem in many applications of LECIM is that some endpoints may sleep for years, some for months, and some for days. This paper proposed an adaptive quorum-based protocol that independently and adaptively schedules nodes wake-up times. For those endpoints who wake up and communicate very rarely and sleep majority of the time, if coordinator wants to let them to change the data rate, frame format, or any other parameters within certain time limit, then making delay in making the respective changes beyond the desired time threshold would harm the whole system.
But how the endpoints will know that coordinator want to send them the data is a challenging job especially in the case of LECIM networks where battery power is needed to work for many years.Traditional WSN MAC protocols like T-MAC [13], B-MAC [14], X-MAC [15], WiseMAC [16], and Zigbee [17] cannot satisfy all the requirements of LECIM. T-MAC does not use fixed active period but having the capability to shorten the active period if the channel is idle for a short time (TA). In the case of data, the node remains active till data reception or until the active period ends. In [12], the authors proposed a MAC protocol based on sleep schedule of sensor node dynamic duty cycle.
B-MAC utilizes low power listening (LPL) and an extended preamble to achieve low power communication. The transmitter precedes the data packet with a preamble that is equal to the longest wakeup period of any node. Moreover, if a node receives a packet destined to another node, it knows how long it has to keep silent. During the listening period if a node detects a preamble it remains active to receive the data. The node records this value in a variable called the Network Allocation Variable (NAV); and sets a timer for it. The lengthy preamble assures the sender that at some point the receiver will detect the preamble, and will become ready to receive the data. In the X-MAC, the receiver wakes up periodically to listen for the preamble and the transmitter continuously transmits strobed preambles (sends small bursts then waits for ACK then sends another preamble and so on).
The receiver needs to listen to at least two preambles and one ACK before starting the data communication with the transmitter.
WiseMAC is based on preamble sampling technique in which endpoints sample the medium with a constant period at regular intervals. If a node fails to get the medium, it goes to sleep and wakes up when the receiver is free and listening again.In this paper, a novel energy-efficient MAC protocol is proposed based on Duration Value (DV) in transmitted packets.
In WiseMAC, the access point (AP) first learns the sampling schedule of all the endpoints in the network and then start the transmission at the right moment with a wakeup preamble of minimized duration. Initially, the size of the preamble equals the wakeup interval and then it reduces the size of the preamble by knowing the sleep schedules of the neighboring endpoints. Problem DefinitionMost of the power in WSNs is consumed by the onboard transceiver in a sensor node. In beacon mode, the PNC (PAN Coordinator) transmits beacon and then waits for the data from the nodes in CAP period.
Addition of new nodes can easily be adjusted to topology changes; for example, replacing exhausted nodes in the network and adding new nodes to the network. It also supports a contention-free period (CFP) for time-sensitive data.Traditional MAC protocols mainly focus on bandwidth utilization and throughput. Whereas frame can be defined as a format of aggregated bits from a medium access control sub-layer entity that are transmitted together in time; a packet is the formatted, aggregated bits that are transmitted together in time across the physical medium. However, they lack energy conservation mechanisms, which is one of the most important requirements of LECIM.
The payload is defined as the content of a data message that is being transmitted [14].The link layer data packet is the smallest communication entity between neighbouring sensor nodes in a WSN.
Additionally contention-based protocols use CCA (clear channel assessment) to determine the status of the channel, however, this is not always guaranteed in LECIM due to the long distance among the nodes. It consists of a header field H bits long, payload of size P bits and a T bit trailer; as shown in Figure 1 below. The header field generally includes the current segment number, total number of segments in the corresponding higher layer packet, higher layer packet identifier and the source and destination identifiers.
As the downlink data which is rare but plays a very important role for network management, therefore, in this paper, we propose framed slotted aloha-based MAC using wakeup radio which mainly encompasses the downlink data communication in LECIM networks. The payload contains information bits and the trailer is composed of parity bits for error control [14].
The most common approach is to use a zero-bias Schottky voltage doublers (voltage multiplier, envelope detector), as exemplified by [18–21].
Based on results reported in this paper and the work of [16], sensor node energy consumption over a period of time,Figure 1.
In [18], the authors used the wakeup radio approach for developing a low-power MAC for WBAN. Durante and Mahlknecht [21] presented a solution with a Schottky voltage doublers followed by a programmable amplifier and integrator.
The DV is stored by every sensor node in a variable called a Network Allocation Variable (NAV). The data rate and sensitivity are high because of the amplification stage, at the expense of power consumption. The node decrements this value every time the NAV timer fires until its value becomes zero.
Other solutions, such as Pletcher and Rabaey [23], advocated a design based solely on amplifiers with high sensitivity, at the expense of power consumption.
It is also possible that a neighboring node wakes up or a new node joins in the middle of a transmission.
Suppose a node is only the neighbor of the receiver but not the sender, it will not hear the data fragment being sent to the receiver by the sender. If ACK packet is not sent by the receiver frequently, the new node may conclude, from its own carrier sense, that the medium is free.
Marinkovic and Popovici [26] developed a nanopower wakeup radio with 470?nW idle listening power.3. Based on such decision, if the node starts transmitting, the current transmission will be corrupted at the receiver.
Overview of LECIM NetworksThe purpose of TG4k group is to facilitate single point to multi-thousands of points communication for critical infrastructure monitoring. For example, suppose a neighbouring node receives an RTS from the sender or CTS from the receiver, it goes to sleep for the entire message time. It aims to address the needs of minimal network infrastructure and to collect the scheduled and event data from a large number of nonmain powered endpoints that are widely dispersed or are in challenging propagation environment. However, if the sender extends the transmission time due to fragment losses or errors, the sleeping neighbours may not immediately be aware of this transmission extension.
It supports low-energy operation which is necessary in order to maintain multiyear battery life.
The amendment wishes to minimize the network maintenance traffic and endpoint active durations.
It is however necessary to note that collisions occur at the receiver due to interference from neighbouring nodes.
The major goal is to support the monitoring of management requirements of critical infrastructure applications to enable preventive maintenance, safety, reliability, and cost reduction through operation efficiency.
It is noted also, that the research focus of the current work is on the neighbouring nodes of the receiver. The call for proposal submission was issued on May 2011 [27].The LECIM applications are set primarily in an outdoor environment. For an energy efficient wireless sensor network, a node should sleep to avoid overhearing if its NAV is not zero. The major requirements for LECIM networks are that the application data rate can be as high as 40?Kbps, it includes thousands of endpoints per main powered infrastructure, it has an asymmetric application data flow, energy conservation is maintained for endpoints, has reliable operation in dramatically changing environments, it has a large coverage area, it has a long deployment life with minimal human contact, it can cope with small and infrequent messages, it is tolerant to data latency for uplink communication, it can address supporting thousands of connected endpoints, and so forth.Two kinds of network devices are proposed for LECIM—coordinator (collector) which is typically main powered and endpoints which are battery powered.
Listening to receive possible traffic that is not sent by any node constitutes idle listening.The aim of the current work is to eliminate idle listenisng and collision. No mobility is needed for endpoints but limited portability for the coordinator is supported. Problem SolutionA schematic representation of a typical wireless sensor network, showing the operations of the proposed PDV-MAC protocol is presented in the Figure 2 below. Medium-Access Control Protocol for LECIMIn this section, we discuss our proposed MAC protocol for LECIM networks.


The receiver then generates random values corresponding to the number of its neighbouring nodes. The size of the LECIM network is very large and the scalability is one of the important issues. The values are added by the receiver to the received DV and then broadcast to its neighbouring nodes. This means, that each node in the neighbourhood of the receiving node will receive current transmission’s notification in form of different values of rDV.
Most of the major existing MACs are unsuitable for LECIM network due to various reasons [2].
IEEE 802.11 networks are optimized for computing applications that require high data rate, high duty cycle, and high performance. Proposed sensor network model.upon the exchange of RTS and CTS between the sender and receiver, the receiver generates n non-repeating integer random values corresponding to n neighbouring nodes.
Since transmission (or reception) is normally not allowed between the sender (or receiver) and its neighbours while transmission is ongoing between the sender and receiver, the energy model in Equation (1) is consequently modified to obtain Equation (3). This is achieved by eliminating terms relating to energy consumption for transmission and reception. The DV is the reported duration value of the transmitting nodes and ?i are the generated non-repeating random values for node i. Superframe Structure and Slot DesignThe superframe structure of the proposed MAC is shown in Figure 3. It contains a beacon, Emergency Access Period (EAP), Normal Access Period (NAP), and Guaranteed Access Period (GAP). ETS are used for sending emergency commands to the coordinator describing the type of emergency happened to the endpoint.
Emergency can be the problem happening to the endpoint itself like malfunctioning hardware or software and critical battery life situation. Discussion of ResultsIn this paper, the Duration Value (DV) reported by the sender is 300 ms. The number of slots in NAP can be optimized as per the network size.The length of EAP is configurable (first 2, 4, or 8 slots) and 50% of them will be used for ETS and MTS, respectively. The length of NAP as well as GAP is also configurable and depends upon the applications and number of endpoints. Energy consumption based on randomized DV and same DV (for the graph in Figure 4).Figure 4. Energy consumption by sensor nodes—randomized DV and same DV.which 10% is assumed corrupted at the receiver and must be re-transmitted. The slot length considers propagation delay (Tp), actual packet length, and nominal guard timings (GTn).
Two scenarios are presented in Table 3, namely: the proposed PDV-MAC protocol (using DV + random factor) and existing MAC protocol (with same DV). Ten random non-repeating integer values are generated in the range 1 - 100 ms, and used to obtain ten (10) randomized DV values.
This long superframe duration will result in smaller number of collisions with the expense of some delay. The consequent of this sleep schedule is that each node will wake up at different times; and normally at time when ongoing transmission would have completed. But as stated earlier that delay is not a problem in those applications, so the use of longer superframe size will result in power efficiency and data reliability. Moreover, since the focus of this work is on energy consumption by neighbouring nodes of the receiver, it is expected that transmission of packets by the neighbouring nodes of the receiver is not allowed. Hence, neighbouring nodes can either be in sleep or idle mode.In Table 6 therefore, energy consumption by the neighbouring nodes of the receiver are presented in Column 2. This short superframe duration will enable the endpoints to receive beacons quickly and transmit their data soon. In Column 3, however, the data presented in respect of energy consumption consists of the energy consumed by each node in sleep mode and energy consumed by each node in idle mode. If we use a long superframe duration and the endpoint just miss the beacon, then it will have to wait for the whole superframe to listen for the next beacon which may result in excessive delay.
It is necessary to note in this case, that the energy consumed in idle mode represents the proportion of energy consumed during the random time added to the DV in the case of the proposed PDV-MAC protocol. It is important to further note that neighbouring sensor nodes of the receiver can either be in sleep or idle mode. Since the coordinator uses main power, therefore, sending the beacons after a short interval will not affect the lifetime of LECIM network. The general MAC frame consists of the MAC header, payload also called MAC service data unit (MSDU), and MAC footer (CRC). It specifies how the rest of the frame looks, that is, it indicates the type of MAC frame being transmitted, specifies the format of the address field, and information about acknowledgment. For instance, a data frame may contain both source and destination information, while the return acknowledgment frame does not contain any address information at all. ConclusionIn this paper, a novel PDV-MAC protocol was proposed based on duration value in transmitted packets of the sender.
This flexible structure helps increase the efficiency of the protocol by keeping the packets short.
The duration value was randomized using nonrepeating randomly generated integer values corresponding to the number of neighbouring nodes of the receiver. These random values were used to obtain randomized duration values which were broadcast to the neighbouring nodes of the receiver. The efficacy of the proposed PDV-MAC protocol was tested via simulation which was implemented in Visual C# and MATLAB.
The sequence number which is 8 bits long in the MAC header matches the acknowledgment frame with the previous transmission.
The transaction is considered successful only when the acknowledgment frame contains the same sequence number as the previously transmitted frame. It is shown by the results obtained, that the proposed PDVMAC protocol can indeed be implemented to improve energy efficiency in wireless sensor networks. The first field is Sync which consists of 8 bits synchronization sequence, the second field is Receiver ID which is 16 bits long, the next is message field and in the last is 16 bits long CRC field.
Estrin, “An Energy-Efficient MAC Protocol for Wireless Sensor Networks,” Proceedings of the 21st Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2002), New York, June 2002, pp. Communication ProcessIn [32], we presented a framed slotted aloha protocol for LECIM networks. In this section, we discuss the main idea of the uplink communication and complete details of the proposed downlink communication process. For uplink communication, our proposed MAC was appropriate but for downlink (coordinator to endpoints) we found some difficulties.
Choi, “Medium Access Control with Dynamic Frame Length in Wireless Senor Networks,” Journal of Information Processing Systems, Vol. When an emergency event happens to an endpoint, it sends the emergency data packet using framed slotted aloha in the first half of the EAP period. The emergency data packet contains specific event type information, for example, malfunction or fire to an endpoint, critical battery situation, and so forth.
An endpoint also sends an emergency command when the remaining battery power reaches 10% of its capacity.The GAP period in our proposed MAC is optional and can be used for the applications where the traffic is deterministic and the number of endpoints is smaller in number. The main aim of using the GAP period is to provide predictable real-time guarantees for time-critical applications such as industrial applications, where a small delay makes a great difference in the on going process.
The coordinator announces in the beacon about the GTS allocated to the endpoints in the GAP period. Decotignie, “WiseMAC: An Ultra Low Power MAC Protocol for the Downlink of Infrastructure Wireless Sensor Networks,” Proceedings of the 9th IEEE Symposium on Computers and Communication, Alexandra, 2004, pp. Downlink CommunicationFor downlink communication, our proposed MAC uses a separate and ultra-low-power wakeup radio along with the main radio.
The wakeup radio allows the endpoints to go into deep sleep mode until they receive a special wakeup signal, after which the main radio (data channel) is invoked and is used for data transmission.
This wakeup packet is in the form of modulated wakeup signal containing addressing information in order to avoid undesired endpoint wakeups. After receiving the wakeup packet, the wake-up receiver wakes up the microprocessor and the microprocessor then interprets the command and decides about the waking up of the main radio for data communication. Only the main radios of the desired endpoint(s) wakeup and microprocessors of the rest of the endpoints go to sleep mode again. After receiving the ACK, the coordinator sends the desired data in the downlink management time slots of the next superframe using the framed slotted aloha approach as discussed above.In the case of broadcast message, the coordinator sends a wakeup call to wake up all the endpoints from sleep mode by specifying the broadcast address and then sends the desired data in the management time slots of the next superframe. Garcia-Luna-Aceves, “Energy Efficient, Collision-Free Medium Access Control for Wireless Sensor Networks,” Proceedings of ACM SenSys 2003, Los Angeles, November 2003, pp. For verification purposes, the coordinator checks the packets received from the endpoints after sending the information regarding those changes. Need of Wakeup RadioAs in LECIM, the endpoints are deployed in inaccessible regions and the battery replacement is costly and difficult, therefore, energy efficient performance is a central challenge. Several techniques have been proposed in the literature for wireless sensor networks (WSNs) to minimize the energy consumption of the transceiver by reducing the transceiver’s duty cycle. But in the case of LECIM where lifetime is required in years and the events of interest happens rarely, turning off the radio transceiver can save energy but it cripples flexibility in terms of downlink traffic.
In the case of downlink traffic where the coordinator wants to convey messages like change in data rate, topology or frame formats, the endpoints need to wake up periodically to check activity on channel. One solution is to let the endpoints wake up periodically and check the activity on the channel and if there is something for them then receive it otherwise sleep again.
As messages from coordinator to the endpoints are rare and infrequent, therefore, great amount of energy is consumed in idle listening.In order to reduce the idle listening problem, we need to increase wakeup interval and to decrease the sampling time.
Increasing the length of this wakeup interval can save energy but can lead to a huge increase in delay which in certain circumstances is unaffordable. To avoid wasting energy and reduce the delay, we propose for LECIM that each endpoint is equipped with a low power wakeup radio which monitors the communication channel continuously, while keeping the other components in deep-sleep mode. When the coordinator wants to communicate with the desired endpoint, it sends a wakeup packet containing its address. All the endpoints receive the wakeup call but only the microcontroller (MCU) of the designated endpoint triggers its main radio.
Structure of Wakeup Radio Transmitter and ReceiverWe consider the LECIM as a one-hop star topology built around a coordinator. The coordinator is typically mains powered and endpoints are power-constrained equipped with small batteries. We propose for the coordinator to be equipped with the wakeup signal transmitter used in [26] which consists of ADF7020 RF transceiver and MSP430 microprocessor. The transceiver uses frequency shift keying (FSK) mode for actual data transfer and On Off Keying mode for sending wakeup packets. Yamada, “Low Overhead MAC Protocol for Low Data Rate Wireless Sensor Networks,” International Journal of Distributed Sensor Networks, Vol. The transmitter can use any carrier frequency because there is no input filter at the wakeup receiver.
Wakeup receiver allows an endpoint’s main radio along with other components to sleep and to be awakened later.
The main building blocks include a charge pump, low-cut filter, and preamble detector and comparators.
The preamble detector is used to exclude unnecessary wakeups from common interference sources by examining whether the wakeup preamble is generated in the expected data range or not.
The optionally used second comparator checks the correctness of the preamble sequence and then generates the wakeup signal. Jain, “Energy Efficient MAC Protocol for Wireless Sensor Networks—A Review,” International Journal of Emerging Trends in Electrical and Electronics, Vol. Performance AnalysisIn this section, we present analytical expressions for our main performance metrics of interest for downlink traffic that is, power consumption and delay. Delay in general is not a problem in LECIM, but in the case of downlink traffic it becomes one of the major focuses of interest. Wake up radio approach is the best approach for achieving low latency in low data rate applications at the rate of less energy consumption.We derive power consumption and latency models for our proposed MAC and compare it with the existing MAC protocols like B-MAC, X-MAC, WiseMAC, T-MAC, and Zigbee. We use the parameters of the low power radio transceiver developed at CSEM (Swiss Center for Electronics and Micro technology) within the WiseNET project [33].
Like other asymmetric systems, in LECIM, the coordinator works as a master node connected with the main supply and all other endpoints are slaves with small batteries. For simplicity, we do not model power consumption due to retransmission and hence ignore transmission errors and collisions. The link is setup in two steps, at the first step the coordinator sends a WUC on the wakeup radio. Bouallegue, “An Energy-Latency-Efficient MAC Protocol for Wireless Sensor Networks,” International Journal of Electrical and Computer Engineering, Vol.
Vu, “An Estimation of Sensor Energy Consumption,” Progress in Electromagnetic Research B, Vol.
Pister, “System Architecture Directions for networked sensors,” ASPLOS IX Proceedings of the 9th International Conference on Architectural Support for Programming Languages and Operating Systems, Cambridge, 2000, pp.



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