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Periodic Sleep-Listen Each node goes to sleep for some time, and then wakes up and listens to see if any other node wants to talk to it.
Collision and Overhearing Avoidance Interfering nodes go to sleep after they hear an RTS or CTS packet. Timeout-MAC (T-MAC) Proposed to enhance the poor results of S-MAC protocol under variable traffic load. An Energy-efficient MAC protocol for Wireless Sensor Networks Wei Ye, John Heidemann, Deborah Estrin. CMPE280n An Energy-efficient MAC protocol for Wireless Sensor Networks Wei Ye, John Heidemann, Deborah Estrin presented by Venkatesh Rajendran.
Investigating Mac Power Consumption in Wireless Sensor Network Javier Bonny Supervised by Jun Luo. ADCA: An Asynchronous Duty Cycle Adjustment MAC Protocol for Wireless Sensor Networks GLOBECOM 2008 Yu-Chia Chang, Jehn-Ruey Jiang and Jang-Ping Sheu. 1 An Energy-efficient MAC protocol for Wireless Sensor Networks Wei Ye, John Heidemann, Deborah Estrin presented by Xiang Li.
S-MAC Sensor Medium Access Control Protocol An Energy Efficient MAC protocol for Wireless Sensor Networks.
An Energy-Efficient MAC Protocol for Wireless Sensor Networks Wei Ye, John Heidemann, Deborah Estrin -- Adapted the authors’ Infocom 2002 talk. KAIS T An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Network Tijs van Dam, Koen Langendoen SenSys’03 Ku Dara Network & Security LAB at. An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks by Tijs van Dam and Koen Langendoen Delft University of Technology The Netherlands. 1 Medium Access Control in Sensor Networks Huaming Li Electrical and Computer Engineering Michigan Technological University. 1 An Adaptive Energy-Efficient MAC Protocol for Wireless Sensor Networks The First ACM Conference on Embedded Networked Sensor Systems (SenSys 2003) November. AS-MAC: An Asynchronous Scheduled MAC Protocol for Wireless Sensor Networks Beakcheol Jang, Jun Bum Lim, Mihail Sichitiu, NC State, Fifth IEEE Inernational. 1 MAC Protocols Saurabh Ganeriwal University of California Los Angeles CS113, March 1, 2006. Robust paradigms are a necessity, particularly for emerging wireless sensor network (WSN) applications.
This situation could be highly annoying when the injured are shifted from one unit to another because static sensor nodes would need to be removed and reattached.
Transmission Timing for AcknowledgementWe have already indicated that our objective is to reduce the preamble size.
Retry TransmissionThe node can wait for a particular amount of time for the MAC acknowledgement prior to attempting a retry transmission. Possible Transfer Data Rate in the Ideal and Worst-Case ScenariosThe possible data rate can be determined using an ideal scenario and a worst-case scenario. Equation (5) shows the total time consumed for transmitting the data frame in an ideal scenario.
This paper introduces the design, implementation, and performance analysis of the scalable and mobility-aware hybrid protocol named boarder node medium access control (BN-MAC) for wireless sensor networks (WSNs), which leverages the characteristics of scheduled and contention-based MAC protocols.
2”, which is the time consumed sending and receiving the synchronization, and “2?” is the energy consumed by the sender and receiver for synchronization.During intra-communication, the node that transmits its clock to the one-hop neighbor is called the parent, and the receiving node at the one-hop neighborhood is called the child.
Wireless Body Area Networks (WBANs) consist of a limited number of battery operated nodes that are used to monitor the vital signs of a patient over long periods of time without restricting the patient’s movements. The contention-based protocols use Clear Channel Assessment (CCA) to determine the status of the channel.
In order to trigger the interrupt for MCU, we need enough energy in the receiving signal which is in the form of electromagnetic waves. Here Ptr is the transmission power, Gt is the transmitting antenna gain, Gr is the receiving antenna gain, Lp is free space path loss, R is the distance between transmitter and receiver and ? is the wavelength.We used the example of a Mica2 mote with a CC1000 radio transceiver. B-MACB-MAC utilizes low power listening and an extended preamble to achieve low power communication.
T-MACT-MAC is the improved version of S-MAC by shortening the awake period if the channel is idle. Duration field in each transmitted packet indicates how long the remaining transmission will be. Sleep and listen periods are predefined and constant which decreases the efficiency of the algorithm under variable traffic load. Suffers from early sleeping problem –node goes to sleep when a neighbor still has messages for it. Data channel uses TDMA Control channel uses CSMA Preamble sampling used to decrease idle listening time. Conflict when one node starts to send the preamble to a node that is already receiving another node’s transmission where the preamble sender is not within range. The lack of robust and efficient paradigms causes a reduction in the provision of quality of service (QoS) and additional energy consumption.
IntroductionWireless sensor networks (WSNs) are considered to be appealing event-based systems that achieve both densely deployed sensor nodes and the perception of a certain physical sensation. Keeping with the vision of faster and reliable communication, the mobile sensor nodes are the best replacement for the jumble of wires and wounded people’s concerns. Therefore, the ODFF uses an 8-byte acknowledgement frame that can reduce the substantial amount of time in the acknowledgement frame, as shown in Figure 3. In an ideal situation, the ODFF-based approach finds the free channel for sending the data on a non-beacon-enabled network.
Like contention-based MAC protocols, BN-MAC achieves high channel utilization, network adaptability under heavy traffic and mobility, and low latency and overhead. IntroductionWireless sensor networks (WSNs) have become an increasingly popular research topic in recent years. The nodes that are synchronized with the clock often use a short preamble without the target address of the node that reduces the energy consumption.Let us assume that the average energy consumed by the parent and child nodes for one work cycle is “?” and “?”, respectively. IntroductionWireless Sensor Networks (WSNs) have and will continue to play a vital role in our daily lives. In T-MAC the nodes listen to the channel for only a short time (TA) after the synchronization phase and then return to sleep mode if no data is received. Reduce idle listening by transmitting all messages in bursts of variable length, and sleeping between bursts. Sleep and listen periods are predefined and constant, which decreases the efficiency of the algorithm under variable traffic load.
In this paper, we introduce modular energy-efficient and robust paradigms that involve two archetypes: (1) the operational medium access control (O-MAC) hybrid protocol and (2) the pheromone termite (PT) model. The key objective is to consistently sense the event features while utilizing minimal energy resources, processing and storage capabilities [1,2].
Like schedule-based MAC protocols, BN-MAC reduces idle listening time, emissions, and collision handling at low cost at one-hop neighbor nodes and achieves high channel utilization under heavy network loads.
WSNs have produced promising solutions for several applications, such as intrusion detection, target detection, industrial automation, environmental monitoring, surveillance and military systems, medical diagnosing systems, and tactical systems [1].
The average short preamble reception time could be reduced because the receiving node wakes up based on the stored schedule of the neighbor nodes.
In the case of data, the node remains awake till data reception or untill the end of the awake period. T-MACNoCSMA, Contention –based GoodGives better results under variable loads Early sleeping problem. The O-MAC protocol controls overhearing and congestion and increases the throughput, reduces the latency and extends the network lifetime. To achieve this objective, a substantial amount of research has been conducted to develop the cooperative networking protocols needed to accomplish the necessary communication while achieving maximum energy efficiency. If the number of symbols increases, the transmitting node could stay for a longer time in an ideal mode. In the worst-case scenario, it should be assumed that 25% of the data packets require a retry transmission. WSNs consist of small sensor nodes disseminated in a targeted area to monitor the events for collecting the data of interest. Prolonging the lifetime of the WBAN strongly depends on controlling the energy consumption of sensor nodes.
These sensor nodes are densely deployed in the area to be monitored to sense and transmit data towards the base station. To handle this problem either we need to increase the transmitting power or the receiving antenna gain.
The transmitting node precedes the data packet with a preamble that is greater or equal to the longest wake-up period of any node. O-MAC uses an optimized data frame format that reduces the channel access time and provides faster data delivery over the medium. In addition, 80% of the sensor nodes are static and deployed inside the rooms to monitor and report the current status of the wounded. Based on our experiments, we have determined that the ideal wait time for MAC could be 30, 36, 42, 48 or 54 symbols. WSNs also experience many challenging problems, including large energy consumption, network scalability, mobility, coverage, and uniformity [2]. To achieve energy efficiency, low duty cycle MAC protocols are used, but for medical applications, especially in the case of pacemakers where data have time-limited relevance, these protocols increase latency which is highly undesirable and leads to system instability. WSNs can greatly simplify system design and operation, as the environment being monitored does not require the communication or energy infrastructure associated with wired networks [1]. For example, a patient suffering from fever triggers temperature, blood pressure, and respiration sensors at the same time.In the TDMA-based protocols nodes are assigned their own time slot, and may access the shared medium only in this time slot. In the case of WBAN we cannot increase the transmitting power above a certain limit, because of concerns over power consumption and radio interference. However using an antenna of higher gain is not practically applicable in the case of WBAN especially for implanted nodes. A node samples the medium during the listening period and if a preamble is detected it remains awake to receive the data. Decentralized sleep-listen scheduling results in different sleep and wake-up times for each neighbor of a node. These communication protocols have achieved significant improvements in terms of the different parameters correlated with each of the individual layers. In handling this disaster situation, the static and mobility-aware nodes use the semi-synchronization approach to synchronize with each other. These problems affect the lifetime of the network, increase the latency, and reduce the throughput.
In this paper, we propose a low power MAC protocol (VLPM) based on existing wakeup radio approaches which reduce energy consumption as well as improving the response time of a node. This allows for scheduling of sleep, idle listening and avoidance of collisions at the transceiver, without additional overhead. Therefore, in the case of WBAN, where the transmitting power as well as antenna gains is limited, we need to store some energy to trigger the interrupt successfully.
The purpose of using the lengthy preamble is to assure the sender that at some point during the preamble the receiver will detect the preamble, and remain awake to receive the data. The PT model provides robust routing for single and multiple links and includes two new significant features: (1) determining the packet generation rate to avoid congestion and (2) pheromone sensitivity to determine the link capacity prior to sending the packets on each link. However, these protocols experience several challenges when combined for multiple layers; these challenges include additional energy consumption, QoS, mobility, scalability, uniformity, data redundancy, congestion, lack of robustness, reliability and insufficient coverage. If the network consists of multi-hops, then a smaller number is not an ideal choice for a large-scale wireless sensor network. Unlike other hybrid MAC protocols, BN-MAC incorporates three promising models that further reduce the energy consumption, idle listening time, overhearing, and congestion to improve the throughput and reduce the latency.
The limited battery life and harsh operating conditions cause further complications, which can lead to node failure [3]. Sensor technology enables the development of small and intelligent medical sensors which can be worn on or implanted in the human body. However, conventional TDMA schemes are not suitable for WBANs because these protocols require high quality time synchronization since the clock drift may lead to disastrous consequences.Another approach is to use a radio triggered power management scheme which avoids useless wake-up periods. Without considering the transmissions and receptions, the duty cycle is at least 12.5 %, which is a considerably high value.
The state-of-the-art research in this work is based on improving both the QoS and energy efficiency.
Furthermore, the limited battery life and extreme operating conditions can cause node failure [3], which wastes additional energy [4]. The semi-synchronization approach is deployed for the nodes in regions that are following the interior communication process explained in the next section. One of the models used with BN-MAC is automatic active and sleep (AAS), which reduces the ideal listening time. Although significant research has been conducted on WSNs to maintain high communication standards (especially coverage), the issue of high power consumption remains unresolved [4]. These biosensors are capable of measuring significant physiological parameters like heart rate, blood pressure, body and skin temperature, oxygen saturation, respiration rate, electrocardiogram, etc. In this scheme a very low-power wake-up radio hardware component monitors the environment when the node enters sleep mode. Analytical Models for Power Consumption and LatencyIn this section, we provide models for latency and power consumption of VLPM and compare them to the corresponding models of B-MAC, X-MAC, TMAC and SCP-MAC. The semi-synchronization is managed by deploying the anycast methodology.The anycast methodology helps forward the sensor data to the next hop nodes. When nodes finish their monitoring process, AAS lets them automatically go into the sleep state to avoid the idle listening state. The radio is one of the major power-consuming sections of the sensor in WSNs that can be handled using energy-efficient medium access control (MAC) protocols.
The low power wake-up receiver monitors the activity on channel all the time with a very low power and keeps the MCU (Micro Controller Unit) along with main radio in sleep mode. The obtained measurements are communicated either via a wireless or a wired link to a central node, like a Personal Digital Assistant (PDA) or a microcontroller board, which may then in turn display the information on a user interface or transmit the aggregated vital signs to a medical center.
When the stand-by radio transceiver receives radio signals, it wakes the sleeping node instantly, consequently saving energy spent in previous wake-up and listen intervals.In this paper we propose a Very Low Power MAC (VLPM) protocol for WBANs. To obtain numerical results we are considering TeloseB platform with T1 CC1000 transceiver [28]. There are a few cross-layer protocols for maintaining high standards of communication, particularly coverage, but the issues of high energy consumption and improving the QoS have not been properly resolved [4]. Another model used in BN-MAC is the intelligent decision-making (IDM) model, which helps the nodes sense the nature of the environment. Several MAC protocols, introduced to reduce the energy consumption, improve the lifetime of WSNs [5]. When a node [BN or BNC (BAN Coordinator)] wants to communicate with another node, it uses the low-power radio to send a wakeup packet, which will prompt the receiver to power up its primary radio to listen for the message that follows shortly. Using a wired connection for this purpose turns out to be too cumbersome and involves a high cost for deployment and maintenance.
Finally; the QoS metrics of the O-MAC and PT paradigms are evaluated and compared with other known hybrid protocols involving the MAC and routing features.
With the proper placement of a mobile infrastructure, a wide area can be covered compared with an infrastructure-based network deploying the same number of sensors [5]. Thus, efficient bandwidth utilization and bidirectional end-to-end reliability are the focus to maintain the smooth transfer of data from a region’s nodes to the DON because they are mandatory in WSNs [16,17,18]. Based on the nature of the environment, the nodes decide whether to use the active or passive mode.
Unfortunately, most of the application-dependent [6] MAC protocols for WSNs are not energy efficient and thus do not effectively improve the lifetime of WSNs.
The wake-up packet contains the desired node’s ID along with some other information to let the targeted node to wake-up and take part in communication and let all other nodes to go to sleep mode quickly. However, the use of a wireless interface results in an emerging new technology called WBAN [7]. We categorize BAN traffic into two types: uplink (from BN to BNC) and downlink (BNC to BN).
However, the key services’ energy efficiency and the QoS provision are hurdles for robust WSNs. End-to-end reliability is acknowledged when the data from each event are reported to the DON. This decision power of the nodes further reduces energy consumption because the nodes turn off the radio of the transceiver in the passive mode.
The protocols should be scalable to adjust to changes in the network, such as the insertion of new nodes and the deletion of existing nodes [7,8]. A WBAN could be seen as a special purpose wireless sensor network with a number of additional system design requirements.
Average power consumption for each protocol can be calculated by multiplying the power consumed during the activity (transmission, reception and sleep) and its duty cycle (duration during which the concerned activity performed) as shown in Equation (5). Detailed studies in [6,7,8] show that the cross-layered approaches could result in substantial savings in terms of energy efficiency. The DON of each region forwards the collected data from the nodes in regions applying exterior communication to the base station using the IP network. The third model is the least-distance smart neighboring search (LDSNS), which determines the shortest efficient path to the one-hop neighbor and also provides cross-layering support to handle the mobility of the nodes.
The reduction in energy achieved by the MAC protocols increases the latency, particularly in multi-hop data communication [9]. A WBAN is most likely to incorporate a wearable and implantable node operating in two different frequencies.
The coordinator then assigns the resources to the node in the Res-ACK packet and receives the desired data. We have computed the Dtx and Drx for each protocol in its corresponding sections.Latency is the second performance metric of interest. As a result, several cross-layered approaches have been designed and implemented [9,10,11,12,13]. The BN-MAC also incorporates a semi-synchronous feature with a low duty cycle, which is advantageous for reducing the latency and energy consumption for several WSN application areas to improve the throughput. These design constraints must be considered when developing new MAC protocols.MAC protocols are classified into different categories, such as schedule-based, contention-based, mobility-aware, and hybrid protocols [10,11], however, many of the contention-based MAC protocols are based on sensor-MAC (S-MAC), which are designed for specific WSN applications [12]. Analytical results show that the proposed protocol outperforms both synchronized and unsynchronized MAC protocols like T-MAC, SCP-MAC, B-MAC and X-MAC in terms of energy consumption and response time.
In the case of downlink traffic the coordinator sends a wake-up packet to the node along with the resources. It is bounded by application requirements, for example, in the case of an emergency; event detection must be reported at the BNC within a few seconds.

We assume that the transmission range of the mobile and static sensor nodes is the same as that of the high-power sensor nodes. BN-MAC uses a unique window slot size to enhance the contention resolution issue for improved throughput.
The low power receiver of the BN then wakes up the processor to interpret the message and then wake-up the main radio to start the actual communication. Depending on the MAC protocol there can be a rather large difference between average latency and worst-case latency. There is still much to be gained by reconsidering the features and functionalities of the protocol layers in an integrated manner to introduce communication paradigms for efficient and reliable communication while saving energy and improving the QoS provisioning in WSNs. BN-MAC also prefers to communicate within a one-hop destination using Anycast, which maintains load balancing to maintain network reliability. The nodes, which follow contention-based mechanisms, are not required to follow the cluster.
Whether the patient is in the hospital, at home or on the move, the patient will no longer need to stay in bed, but will be able to move around freely. To the best of our knowledge, this kind of low power approach has not been considered before for WBAN.The rest of the paper is categorized into four sections. To handle these issues, this paper introduces modular energy-efficient and robust paradigms that improve the energy efficiency and QoS provisioning.
BN-MAC is introduced with the goal of supporting four major application areas: monitoring and behavioral areas, controlling natural disasters, human-centric applications, and tracking mobility and static home automation devices from remote places.
These protocols are network adaptable to allow for the insertion and removal of sensor nodes from the network. Furthermore, the data obtained during a large time interval in the patient’s natural environment offers a clearer view to the doctors than data obtained during short stays at the hospital [9].
These paradigms involve the O-MAC protocol with the PT model to build a hybrid approach by incorporating the medium access control with the network.
There are two types of communication: one is between sensor nodes and the DON, and the other is from DON to DON in the case of a greater distance of the DON from the base station.
These application areas require a congestion-free mobility-supported MAC protocol to guarantee reliable data delivery.
An example of a WBAN used for medical and non-medical applications to monitor the body function for sporting, health, entertainment, and emergency applications is shown in Figure 1 [8]. The O-MAC protocol involves the features of time division multiple access (TDMA) and carrier sense multiple access (CSMA).
Therefore, TDMA is combined with frequency division and multiple access (FDMA) to enable concurrent communication among the sensor nodes [19].
BN-MAC was evaluated using network simulator-2 (ns2) and compared with other hybrid MAC protocols, such as Zebra medium access control (Z-MAC), advertisement-based MAC (A-MAC), Speck-MAC, adaptive duty cycle SMAC (ADC-SMAC), and low-power real-time medium access control (LPR-MAC).
In the figure the game server is used for handling the non-medical applications like sports, while the other servers are used for dealing with medical related services. Section 4 presents useful analytical derivations and performance analysis of VLPM with other MAC protocols.
The O-MAC maintains the trade-off between energy efficiency and time management by introducing an optimized data frame format model. The frequency channels are recycled throughout the simulation process in the entire WSN so as to minimize the required number of frequency channels. The simulation results indicate that BN-MAC is a robust and energy-efficient protocol that outperforms other hybrid MAC protocols in the context of quality of service (QoS) parameters, such as energy consumption, latency, throughput, channel access time, successful delivery rate, coverage efficiency, and average duty cycle. However, in such protocols, node problems occur due to the presence of a tight schedule; once a node misses its schedule, then it must wait for the next turn, thus increasing the energy consumption.
Several sensors are placed in clothes, directly on the body or under the skin of a person, which measure the temperature, blood pressure, heart rate, ECG (Electrocardiography), EEG (Electroencephalography), respiration rate, SpO2 levels etc.
Consequently, the sensor nodes and DON can communicate self-reliantly without snooping each other.
Additionally, schedule-based MAC protocols are not adaptable due to changes in network topology [15].Hybrid protocols leverage the characteristics of time division multiple access (TDMA) and carrier sense multiple access (CSMA) [16].
The new features also include the anycast addressing methodology and automatic buffering because the anycast methodology helps to select the particular nodes in the 1-hop neighborhood to avoid the overhearing problem and thus reduces the additional energy consumed in the 1-hop neighborhood; furthermore, automatic buffering helps to reduce the data storage wait time.
Existing hybrid MAC protocols are based on the clustering approach [17,18], where time is divided into different time slots for each node in the cluster. The contention-based protocols also called the duty cycling protocols, such as BMAC [10], SMAC [11] and TMAC [12] etc.
Related WorkOwing to the fact that energy efficiency is a vital part of WBAN performance, recently there has been a considerable amount of research effort directed towards the development of low power energy efficient MAC protocols. The TDMA part of O-MAC is also improved because the nodes are not required to synchronize with all of the 1-hop neighborhood nodes but rather only with the particular nodes that must be used for forwarding the data to the next hop of the network.
In addition, ODFF includes the security portion to avoid the attacks encountered at the transceiver of the radio. These protocols inherit good scalability and support topology changes but they are not suitable for WBAN due to the following reasons [13].
The performance of both beacon and non-beacon mode was studied in [14] and it was concluded that non-beacon mode is better than beacon mode in terms of throughput and latency. To handle the collisions in accessing the slots at the channel, a novel randomization algorithm is introduced for energy efficiency and QoS provisioning. The bandwidth is distributed among the sensor nodes such that each neighboring sensor node uses a different frequency band. For example, sensor node “A” wants to access a slot number 5, and if slot number 5 is already occupied by node “B”, then this algorithm helps to redirect node “A” to another available empty slot to avoid the potential collision on the network. In [15] the authors supported the non-beacon mode for low data rate and asymmetric traffic. PT involves two important features: the packet generation rate, the pheromone sensitivity, which helps determine the predicted amount of pheromone, and each link’s capacity.
As a result, the PT model provides the shortest path from the source to the destination without overlap. As such, this feature provides advanced information regarding the flow of traffic that helps avoid congestion over the network. It is extremely difficult to create an effective schedule with channel reuse or a high degree of concurrency (the ideal solution is NP-hard) [19].
In addition, it is also capable of load balancing and fault tolerance in the case of route failure and possible congestion. In addition, pheromone sensitivity predicts the amount of traffic on each link and helps in forwarding the data to each link according to the capacity, which maintains load balancing. Second, TDMA requires clock synchronization, which is an important feature of several sensor applications. Therefore, O-MAC with PT maintains the state of the art in terms of energy efficiency and also develops the tradeoff between energy efficiency and time management. If this system model is deployed in a realistic environment, it could provide both operational stability and a swift recovery for critical scenarios. However, tight synchronization results in energy overhead because it necessitates recurring message exchanges.
This protocol uses heart rhythm information to perform synchronization and to improve energy efficiency, but the heart beat information is not always valid due to variations in the patient’s condition.
In the simulation platform, the state-of-the-art hybrid and individual layered configurations have been implemented to obtain a complete performance evaluation. It would also guarantee that the disaster recovery process could be accurately monitored and communicated to all staff, clearly recognizing all of the essential roles and their responsibilities using WSNs. Third, issues may arise due to frequent topology changes resulting from time-fluctuating channel conditions, such as battery outages, changes in the physical environment, and node failure.
A Dynamic TDMA protocol with focus on the dependability and power efficiency is presented in [18]. The simulation experiments and analytical performance and evaluation demonstrate that O-MAC with PT substantially improved the communication performance and outperformed other competing hybrid protocols in terms of energy efficiency and QoS parameters. In Dynamic TDMA, the coordinator assigns slots to the nodes which have buffered packets and are released after transmission. These results highlight the benefits of the novel modular energy-efficient and robust paradigm (O-MAC with PT) for deploying general scenarios as well as particular scenarios in WSNs. Fourth, it is difficult to determine the intercession relation among neighboring nodes due to different communication and radio interference ranges from each other and other interfering nodes that may not be involved with direct communication (this situation is known as interference anomaly) [20].
However, this protocol still needs some form of synchronization which is difficult to achieve, especially in the case of implanted nodes. The remainder of this paper is organized as follows: in Section 2, we present the system model for the proposed work. Fifth, during low contention, TDMA results in lower channel utilization and increased delays. In BodyMAC [19], although the authors have defined downlink and uplink sub frames for on-demand and normal traffic but for implant node they have not considered a very low power wake-up mechanism. These problems with TDMA demonstrate that TDMA is not a reasonable choice when used individually, even if an efficient TDMA schedule is used. CSMA does not need considerable setup support, such as clock synchronization and global topology information. In TaMAC [21], the authors tried to solve the idle listening and overhearing problems by taking into account the traffic information of the sensor nodes to dynamically adjust the duty cycle of the sensor nodes according to their traffic-patterns.Some of the most important design constraints of a node in medical applications are the response time along with energy efficiency.
The dynamic joining and leaving of nodes is handled efficiently without additional operations. For pacemakers and in control systems, long latencies can lead to a huge loss of human life and system instability.
However, these benefits may come at the cost of an increased amount of trial and error; a trial may face collisions when more than two nodes attempt to access the channel simultaneously, causing signal fidelity to decay at the destination. One of the possible alternatives to reduce latency and to improve energy efficiency is to use an additional low power wake-up radio hardware which is capable of reacting instantly on an event of interest and with negligible power consumption. System ModelThe disaster recovery process facilitates an effective recovery response to disaster-congested states, territories, tribes, and local dominions. Although collisions at a one-hop neighbor node can easily be reduced by using carrier sensing before transmission, carrier sensing is not controlled beyond one hop. The robust disaster recovery process provides a flexible archetype that empowers the disaster response staff to function in a cohesive and collective manner. This issue, called the hidden terminal problem, affects throughput, particularly in high-data-rate sensor applications. PicoRadio [22], one of the earliest works on wake-up radio, uses a carefully designed very low power transceiver module, which is capable of monitoring the radio environment. It also emphasizes the importance of reestablishing, regenerating and rejuvenating the social, health, natural, economic, and environmental aspects of the community and shaping a more vigorous community. In [23] the authors have shown that use of wake-up radio is very beneficial in terms of energy consumption rather than in low duty cycling protocol.
Thus, this type of recovery process requires a state-of-the-art wireless sensing paradigm that helps eliminate the various restrictions related to traditional wireless networks. The RTS frame consists of five fields include frame control, receiver address, duration, FCS and transmitter address. The CTS frame consists of four fields include frame control receiver address, FCS and duration.
We introduce the flat topology network based on our proposed paradigms for monitoring the disaster recovery situation. The network is divided into three regions, and each region is handled and controlled by a dynamic operational node (DON). Hybrid MAC protocols also experience inter-cluster communications and require tight time synchronization. These hybrid MAC protocols also use long preambles (signals used to synchronize transmission timing between two or more nodes and systems) that consume bandwidth and increase channel utilization [23]. Due to the lack of addressing mechanism in their proposed prototype, energy is wasted by waking up all the other nodes unnecessarily and hence it is not suitable for WBANs.
Each network region monitors the different events of the disaster recovery operation for the collection of the data depicted in Figure 1. In [26], the authors have proposed to attach passive RFID (Radio-frequency Identification) tags to the sensor node for conserving node energy.
In worst-case scenarios, the performance of BN-MAC will not be reduced because this protocol needs local synchronization at one-hop neighborhoods. But to activate a passive RFID tag we need to have an RFID reader to send strong radio signals. In [27] the authors proposed a radio triggered wake-up with addressing capabilities that allows the non-target nodes to go to sleep mode quickly just after interpreting the ID in the wake-up packet.
We assume that the other 10% are static sensor nodes that are already deployed for the protection of each region.
Region B monitors the performance and activities of doctors, nurses and other staff in the disaster situation so that their roles and effectiveness in responding to the disaster situation can be analyzed.
In region “B”, 50% of the nodes were assumed to be static and deployed in different parts of the hospital building, and the remaining 50% were mobile sensor nodes attached to the body of doctors, nurses and other staff. Region “C” collects updated information regarding victims who were brought into the hospital for treatment. Section 7 presents the intelligent decision-making (IDM) model to automatically place nodes into either active or passive mode. The reason for this circuit to use is that as in the WBAN the transmitting power and the receiving antenna gain is normally very limited and the chances of tissue loss and other path losses are greater.
In region “C”, 20% of the nodes are mobile sensor nodes that are attached to the body of wounded people because static sensor nodes could increase the anxiety level of those injured persons, which would be challenging for the staff to manage.
Thus the energy received from a signal by the simple radio triggered circuit may not be enough to trigger the interrupt in all the cases.Figure 2 shows the schematic of the radio triggered wake-up receiver with filter. This stand-by hardware first collects and stores the energy from the radio signals and then generates a sufficient output voltage to interrupt the MCU [24].The job of the antenna of the radio triggered circuit is to collect energy from electromagnetic waves. The incoming radio frequency activates the antenna and then the electrical energy of the antenna powers other parts of the circuit and produces an output voltage.
The use of a band filter which is made up of a resistor (Rf) and capacitors (Ch, Cl) intensifies the selecting power of the circuit to distinguish between wake-up radio signal frequency and false alarms. Research Goals, Challenges, and ContributionsOne of the key goals of introducing BN-MAC is to support the multiple application domains of WSNs. We focus on several characteristics and factors that affect the performance of existing hybrid MAC protocols and BN-MAC. The transformer makes it easier to reach the voltage threshold required for triggering an interrupt. Factors that affect energy consumption and scalability include idle listening, overhearing, congestion, and mobility.
The key challenge is determining how to integrate all of the proposed models to work as a single unit.
Mobility is also difficult to address due to limitations and constraints at the MAC layer for maintaining scalability.BN-MAC is proposed as a hybrid protocol involving a contention part and a scheduled part. The contention part is semi-synchronized [24] with a low duty cycle that helps to achieve faster access to the medium and manages the synchronization among nodes.
Since in WBAN as nodes normally work within a 3 meter range, therefore we believe that this delay will not increase more.The capacitor Cse is used to store energy. The semi-synchronous feature is preferable for several application areas to reduce latency and energy consumption and maximize throughput. As soon as the antenna receives radio signals, the energy is accumulated on Cse due to the flow of current which causes the voltage to increase across the capacitor. The wake-up signal transmitter used in our work consists of a TelosB node (using CC2420 as main radio and MSP 430 as MCU), Texas Instruments Inc.’s CC1000 radio transceiver and an optional ZHL-2010 frequency amplifier for increasing communication range as shown in Figure 3 [27]. Whenever the sensor node requires the schedule of its neighboring nodes, the sensor node uses the Anycast message mechanism because the sensor node can send a control message to only the nearest node in the group of potential receivers or may choose several nodes, depending on the situation. The CC1000 radio generates a modulated signal which has the capability to uniquely address different nodes and also to send short commands within the wake-up packet.
When the data are sent, the node uses the unicast message mechanism to forward the same data to all possible destinations. In addition, the neighbor discovery process consists of a short preamble message that consumes less energy. Third, BN-MAC discovers the presence and level of mobility of the sensor nodes within its neighbors using the received signal strength indicator (RSSI) and link quality indicator (LQI), both of which are obtained from the neighbor nodes at the time of synchronization.BN-MAC performs localized reuse time slot allocation without changing the slots of the nodes that already exist if the node intends to perform further communication. The BNC can either be a standalone device or integrated within another device such as a cell phone or a Personal Data Assistant (PDA) whose job is to obtain the data from BNs and send it onward for further processing. The BNs are battery powered sensor nodes which measure the physiological parameters and send to the BNC.
Fourth, new energy level information (ELI) algorithm is used for the dynamic selection of the coordinator, known as the boarder node (BN).
Both the BNs and BNC consists of a low power wake-up transmitter as well as a receiver.The wake-up receiver monitors the channel for activity constantly and keeps the MCU along with main radio in sleep mode. When an event of interest happens, the wake-up receiver then interrupts the MCU, which then wakes up the main radio to start communication. BN stays at the position as long as it uses its sources “energy” for performing some specific task for a definite period inside the network region then it vacates the position when the energy is reduced for the next node to become BN. In BN-MAC, the node with the highest energy level in its region will have a large probability of becoming the BN. Nodes wake-up periodically to listen for incoming packets and then decide whether to go into a sleep state or stay awake.
In the case, if no packets are destined to them the nodes then set the timer for the next wake-up and switches off its radio.
With the AAS model, sensor nodes are forced to go into the sleep state after performing the events that can prolong the lifetime of the network. This model significantly outperforms the previous sleep-wake up approaches designed for controlling the idle listening time. LDSNS is used to determine the shortest distance of the sensor node to one-hop neighbor nodes. Another problem is that if we decrease the duty cycle we will save energy but we will have to pay the penalty for latency. For time-sensitive applications like pacemakers and control systems long latencies can lead to system instability. This ability is critical because the sensor node is capable of obtaining energy from the Sun, which allows the sensor node to preserve its battery energy when automating the passive mode in an outdoor environment. To keep the network responsive, the wake-up period needs to happen frequently so that the nodes wake-up quickly and reply to the incoming messages. The mode of the sensor node is typically set manually at the time of installation according to the nature of the environment; however, the IDM model automates the sensor node to reduce the energy consumption and expand the network lifetime. Related WorkAlthough the deployment of WSNs has highly fascinated academia and industry, WSN platform has been experiencing several kinds of challenges due to many limitations and constraints.

After interpretation the MCU then decides whether to go to sleep or activate the main radio based on the address field in the wake-up packet. The necessity of multi-featured MAC protocol is of paramount importance to handle mobility based scenarios for several real time WSN applications.
Our protocol assumes two different types of wake-up and ACK packets namely WUP, Res-WUP and Imm-ACK, Res-ACK respectively. The BNC uses Res-WUP and Res-ACK by piggybacking resource allocation on wake-up and acknowledgement messages. This piggybacking becomes rather difficult and more complex when used for applications in which a message is needed to be sent out every few seconds, or even minutes.
The hybrid protocol named Z-MAC is introduced that integrates the features of both TDMA and CSMA techniques [25]. But in the case of WBAN where the traffic is low and infrequent, this piggybacking approach is more beneficial in terms of energy utilization and latency.
In Z-MAC, CSMA is used as a baseline and TDMA resolves conflicts by scheduling the channel access. In VLPM, Imm-ACK is used by the BN as well as by the BNC for simple acknowledgment without resource allocation.
The wake-up packet is sent at a special radio frequency which does not interrupt with other types of radio communication. If any node competes for accessing the channel, then the highest priority based node first gets the access to the channel. The MCUs of the non-targeted nodes process the incoming message and then turn off quickly while the MCU of the addressed node turns on its main radio for radio communication. In a highly competitive environment, the node priority scheme decreases the network congestion. Handling Downlink and Uplink TrafficIn the case of downlink traffic the BNC requests the data from the BNs.
Further, Z-MAC has another network adaptability problem because the nodes are tightly scheduled with each. As a result, Z-MAC decreases the throughput and increases excess energy consumption during the mobility.Advertisement-based MAC (A-MAC) hybrid protocol is introduced in [26] for controlling collision, overhearing and marginally idle-listening issue.
In the wake-up period, the BN wakes up for a certain amount of time to sense the channel for activity and then either goes to the sleep mode again or remains awake. This periodic wake-up and sleep approach leads to idle listening and over hearing problems.During idle listening, the transceiver of the BN remains in an active state which consumes a lot of energy.
In the meantime, if a sender wants to send a packet to that BN then the sender will have either to wait till the wake-up time of that node or will have to send a lengthy preamble followed by the desired data packet.
A-MAC also uses an advertisement message that helps the sender to inform the neighboring nodes regarding its transmission schedule. Both cases results in a huge amount of energy consumption as well as in undesirable latency. The major advantage of A-MAC protocol is to inform the nodes in advance in order to make receiver and sender ready for data transmission. In some applications of WSN this latency may not be so dangerous but in some applications such as occurrence of emergency events, this latency can lead to critical and potentially life-threatening situations.Our protocol can respond well to the above mentioned problems of traditional MAC protocols. In our proposed protocol, in the case of downlink traffic the coordinator (BNC) reads the command from the quarter it is concerned with and then acts according to the following procedure. Further, A-MAC is only designed for monitoring the surveillance applications, but it does not have enough support for mobility and real time communication.Speck MAC is a deviation of B-MAC protocol [27]. The Res-WUP contains the desired node ID along with other necessary information like resource allocation, type of data needed etc.
The Speck MAC aimed to reduce energy consumption and overhearing problem during heavy traffic. Upon receiving the Res-WUP, the wake-up receivers of all non-targeted BNs in the range go to sleep mode just after interpreting the message. However, it consumes extra energy by sending wake-up frames [28] and also experiences excess latency. In the interpretation process, only MCU is in active mode while the main transceiver remains in sleep mode.
Therefore simple message interpretation is required which is not overly expensive in terms of energy usage. First, the node is capable to calculate its energy consumption and an average sleep time before sending synchronized packets. Second, the node adjusts the duty cycle based on network conditions then announces its schedule by sending broadcast messages to neighbor nodes. Figure 6 describes the downlink communication between BNC and BN.Similarly in the case of uplink traffic emergency signal in the form of a WUP arrives from the BN to the BNC, when a life critical sensor node senses some abnormality in its relevant part of body. When the emergency event occurs, the sensor quickly triggers the wake-up transmitter, which prepares a wake-up packet by including a node ID and sends it to the coordinator. Additionally, ADC-SMAC behaves poorly in mobile environments.Low-power real-time medium access control (LPRT) protocol is proposed for actuation and wireless systems using star topology [30].
The LPRT-MAC introduces the super frame concept that uses mini slots for transmission to the base station. The MCU will then wake up its main radio if not already awake and will send Res-ACK to the destination node (BN). The BNC then process the data and forwards it onward for further necessary action to doctors, hospitals and databases. The advantage of our proposed protocol is that the wake-up signal will not interrupt the ongoing communication between the coordinator and other nodes during the transmission of the wake-up signal. Also, due to the mode always being on a low power wake-up receiver circuit, the destination is informed in time with very low power without using long preamble or without using complex synchronization. Based on the literature survey of hybrid MAC protocols, we conclude that the reported hybrid MAC protocols are not good candidates for mobility and real time applications under congested and heavy traffic network load. To support several mobility and real time applications, we have introduced BN-MAC protocol that reduces energy consumption and improves scalability. BN-MAC also controls the congestion based on LDSNS and energy aware-routing protocol (EAP) [31] to maximize the throughput, reduce the latency and prolongs the network lifetime. Performance EvaluationThis sub-section describes the evaluation of radio triggered circuit for WBAN and the analytical models used for comparing VLPM with other MAC protocols. System Model for BN-MACWe adopt an ad hoc-based network architecture that comprises sensor nodes with limited power resources and a BN with more dispensing capability and higher energy.
Evaluation of the Radio Triggered Circuit for WBANIn this section we evaluate the effectiveness of the radio triggered circuit for WBAN in terms of antenna gain, latency and lifespan for different BAN traffic scenarios. We are taking the same scenario as that described in [24] instead of taking a specific BAN chip because in our approach the radio triggered circuit makes no use of the node battery power. The WSN is divided into different regions, with each region controlled by a BN that coordinates within the given region and adjacent regions. Numerous economical BT node rev3 sensors are deployed over the battlefield area to provide a high level of coverage. The BT node rev3 is a self-directed prototyping platform based on a microcontroller, a Bluetooth radio, and ZigBee. In sleep mode all the hardware components except the interrupt controller and low power amplifier switch off.In this scenario, we assume that there exists one event per two BAN hours and the event lasts for 60 BAN seconds. The Bluetooth-enabled sensors cover short-distance communication among the troops deployed at the nearest positions, whereas ZigBee covers the long distances among troops.
We also assume that each BN uses two 2000 mAh AA batteries with an average voltage of 1.5 V, during the network life time. A small number of fixed coordinators obtain accurate positions of their troops as well as the enemy and their weapons. Each end sensor node is logically connected with a digital addressable lighting interface controller (DALIC). We computed the lifespan of the network for regular, low traffic (on-demand) and sporadic bursts of traffic as shown in Figure 8.In the case of regular traffic we assume that the BN wakes up for 200 ms (including switching time) to communicate with BNC and then goes to sleep mode for 1 BAN minute (the BN wakes up for event detection after every 60 seconds and then remains in wake-up mode for 200 ms in total to transfer the detected data to the BNC).
The DALI protocol broadcasts messages simultaneously to the address multiple devices to find their locations.
In the case of on-demand traffic, the BN remains in the sleep mode and wakes up only when the BNC requires it to send the data by sending a low power wake-up call.
To determine the exact location, the DALIC requires an active bat location (ABL) system that automatically determines the location of the objects.We also assume that all of the sensor nodes use seismic modality, and each sensor senses different events during every sampling period using a seismic frequency spectrum. We have considered multiple issues when designing region-based WSNs for a military scenario. The first consideration is that we have identified the area of the war and a possible solution. The second consideration is focused on the deployment issues of the network, such as the location of the sensor nodes determined before deployment. To save energy, the nodes typically use short-range and one-hop communication rather than long-range communication. We use a one-hop destination search to schedule and deliver data.We have focused on a combined mobility and static scenario using the ns2 network simulator in the scenario depicted in Figure 1. The command node is a heterogeneous node that obtains event information through homogenous nodes fixed in the field. Similarly, the command node forwards the collected information using the (homogenous) sensor nodes to the BN. Intra communication is used within the region, whereas intercommunication is used outside of the region. Anycast is used to exploit the knowledge of immediate channel condition in choosing the appropriate downstream neighbor on smaller time scales. Additionally, the main notion behind MAC layer anycasting is to accomplish the objectives of network layer, while invoking short-term improvement at the MAC layer, based on the local channel settings. Anycast also provides the option of specifying multiple downstream destinations to the MAC protocol. Anycast allows for increased load balancing to minimize the work load and complexity of the network for reliable data transfer. Thus, each node stores and forwards the packets to several nodes, resulting in increased energy consumption. The cross-layering support of BN-MAC successfully resolves this issue using the pheromone termite (PT) mobility model. This model is specially designed to control the scalability of WSNs and the mobility of nodes. The PT analytical model monitors the behavior of the WSN using the packet generation rate and the pheromone sensitivity over single and multiple links [32]. The PT routing model monitors the different activities of the troops and maintains a faster recovery process using the packet generation rate and pheromone sensitivity. The AAS model lets the nodes go into the sleep state after monitoring and processing the collected information. In this scenario, some of the sensor nodes are deployed in the open battlefield area, whereas some are grounded or fixed to buildings to monitor different processes, as such situations demand the sensor nodes to act differently. BN-MAC uses the IDM model to sense the nature of the environment, which allows the mode of the sensor node to be automatically switched either into the active or passive mode.
BN-MAC Protocol DesignBN-MAC is proposed with the aim of supporting multiple applications, particularly military applications, which require mobility-aware and static devices to be controlled from remote places. MAC design in WSNs is ant involved process because WSNs are based on mechanisms that are entirely different from the traditional networks. Therefore, the MAC protocols should be well organized to distribute the bandwidth fairly and be energy efficient, with appealing features that may stimulate the robust design of the communication media.
One of the key factors for introducing BN-MAC is to reduce energy consumption while addressing idle listening, overhearing, mobility, and congestion concerns. BN-MAC also shortens the latency while guaranteeing the reliability of the WSN.BN-MAC improves the existing Z-MAC, A-MAC, Speck-MAC, ADC-SMAC, and LPRT-MAC protocols by adding new features.
The mechanism of BN-MAC supports the hybrid topology that combines the features of TDMA and CSMA.
In addition, BN-MAC eliminates idle listening in each region to achieve a considerable energy saving.
Bi-directional traffic inside each region of the WSN promotes smooth data exchange and efficient use of the bandwidth.
These operations are performed once during the setup process and are not performed again until the network topology is physically changed.
In this approach, the initial costs for running these operations are balanced while achieving a better throughput and reduced energy consumption during intra- and inter-transmission.
Finding the List of One Hop-NeighborsWhen a node intends to start communication with its neighbor node after accessing the channel, the node sends an Anycast message to its one-hop neighbor nodes to obtain the details of neighboring nodes.
The process of sending the Anycast ensures that the intended neighboring nodes are able to talk with each other, even if they possess different sleeping and communication schedules. The neighbor discovery process consists of short messages (short preambles), which consume less network bandwidth and improve the throughput.Each node randomly sends a short preamble for finding the list of intended neighbor nodes using Anycast after two seconds for 15 s. This timing is used obtain maximum throughput; packet sending intervals from 1 to 10 s were considered, but the time interval of 2 s provides the maximum throughput. We have also set the packet sending time at 15 s to facilitate the successful completion of the packet sending process. The node is unable to complete the packet sending cycle when the time is less than 15 s, and when the time is greater than 15 s, the node comes into the idle situation because after finishing the packet sending task and thus waits on the channel until the level of set time is reached. We present the performance of the BN-MAC at different time intervals and packet sending durations in Figures 2 and 3. A comparison of BN-MAC and Z-MAC, the nodes of which use 30 s for the neighbor discovery process, indicates that Z-MAC has higher energy consumption.The node discovery process in BN-MAC consists of a one-hop neighbor node, but nodes are able to obtain two-hop neighbor information that is helpful for expanding cross-layering support. The two-hop information that has been obtained is also used for slot allocation, which enables the node to increase mobility because the node retains the information even when the two-hop node is moving. BN-MAC is scalable because the one-hop topological change is easy to handle; each node knows the schedule of the one-hop neighbor node. BN-MAC uses a promising time scheduler because the assigned slot does not exceed the one-hop neighborhood.
The localized time slot allocation which is used with channels to synchronize for the whole network.
It also helps the node to gather allocation information for all 1-hop and 2-hop neighbor nodes. After channel sampling, each node initially sends a short preamble message asynchronously using the Anycast approach within the one-hop neighbor node to obtain the list of one-hop neighbor nodes. When the sender receives a reply from the one-hop neighbor nodes, the sender attempts to fix the schedule with the intended one-hop neighbor nodes (nodes that are chosen for future communication) before sending the data.
These dual features of sending a short preamble asynchronously to obtain the list of neighbor nodes and fixing the schedule synchronously reduce the network overhead. When the sender completes the scheduling process with the intended nodes, the sender chooses the shortest efficient path for sending the data using the LDSNS model, as explained in [33]. The use of a short preamble message allows for reductions in overhead and latency at each hop.
The short-preamble-enabled MAC protocols have an advantage over the long-preamble-enabled MAC protocols due to their low-power duty cycle mechanism. The existing lower power listening (LPL) technique uses a long preamble and suffers from the overhearing problem, which increases energy consumption in non-targeted receivers, such as Z-MAC. In the long-preamble techniques, the node must wait until the long preamble is received before it starts receiving data and acknowledgments.
Targeted receivers are also affected because the targeted receivers have to wait until the long preamble is received, causing increased energy consumption.X-MAC uses a short preamble message to reduce the energy consumption and latency, but one disadvantage of X-MAC is that the destination address of the node is inserted into each short preamble message.
X-MAC forces all nodes to check the preamble to determine whether they are targeted nodes, which increases energy consumption and the duty cycle (wake-up process).
X-MAC is based on an asynchronous mechanism, and no schedule of neighbor nodes is maintained, making it more difficult for each node to send data without prior scheduling information.
Unlike X-MAC, BN-MAC deploys both asynchronous features for sending short preamble messages to obtain the list of one-hop neighbor nodes and synchronous features for fixing the schedule with the intended neighbors.The MAC protocol should be capable of handling spatial correlation while also adjusting to changes in the number of competing nodes [35]. When multiple nodes want to communicate with the same neighbor node within the region, BN-MAC uses a slotted contention window. Then, the nodes randomly select a slot in the contention window.The winner of the slot obtains access to the medium for communication. If multiple nodes attempt to select the same slot, BN-MAC uses sampling and randomization such that each node has an equal probability of accessing the channel. Furthermore, BN-MAC uses 256 congestion window slots, whereas the other MAC protocols use 1–32 contention windows for randomized listening before sending the preamble messages. This increased number of slots reduces congestion and latency and allows higher throughput to be obtained.
We have used different numbers of congestion window slots, with 30% of the active sensor node contenders allocated to each window slot. These experiments indicated that BN-MAC produces the maximum throughput when 256 slots are used, as shown in Figure 4. Hence, the use of 256 window slots increases the throughput considerably.Sensor nodes also perform automatic buffering within the region during intra-communication to reduce the drop rate and prolong the network lifetime. We demonstrate the process of long permeable (LPL), short permeable (X-MAC), and BN-MAC in Figure 6.X-MAC uses a short preamble with a target address to access the channel to communicate with another node.
However, all of the nodes en route will remain awake until the short preambles are received by the destination node, which results in increased energy consumption. X-MAC also has a delay of transmission for sending the packets until the receiver wakes up [36]. The BN-MAC protocol does not use the target address of the node when sending a short preamble message. Thus, all of the nodes do not continue to wait; instead, only the intended node wakes up to receive the short preamble.
In addition, BN-MAC uses an automatic packet buffering process similar to that used in [37]; this process reduces the wake-up time and increases the network lifetime.
In the automatic buffering process, the node uses a promiscuous mode that enables the node to listen to all ongoing data traffic and coordinates, if requested. Furthermore, the node saves a copy of the received packet regardless of the intended destination of the data packet until receipt of the packet is acknowledged by the destination node.
Such buffering requires a relay that is used by the saturated conditions because each node is able to cooperate in sending data packets to other buffers.
As mentioned above, a short preamble consumes less energy and prolongs the network lifetime.

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