IEEE 802.15.4

purpose of tracking and surveillance in a terrain through random and dense deployment. Recent advancements in micro-electro mechanical system (MEMS) technology have made it possible to make these components small, powerful, and energy efficient. Very small in size, the sensor nodes are capable of gathering, processing, and communicating information to outside world through intermediate router nodes. Sensor node is the basic building block of a WSN and is a self contained modular low-cost electronic system that consists of three major functional units viz. sensing, computation and communication, packed in a small unit, about 1 inch in diameter. The sensing element monitors a variety of ambient conditions. The computation unit include data analysis and the communication unit consists of RF transmission and reception between different nodes, within the vicinity of the transmission range [3][4]. The basic objective of IEEE 802.15.4 is to support short range applications such as habit monitoring, battlefield surveillance, nuclear, biological, and chemical attack detection, industry automation, home automation and many more [3]. Such applications require a small, low-cost, highly reliable technology that offers long battery life, IEEE and ZigBee alliance [5] are working together to achieve the goal. IEEE 802.15.4 standard focuses on the specification of the lower two layers (physical and data link layer) whereas ZigBee alliance provides upper layers of the protocol stack (from network to the application layer) for interoperable data networking, security services and a WSN application. [6] This paper is organized as follows: Section II presents the literature survey. Section III gives the brief overview of IEEE 802.15.4. Experimental set-up is given in section IV. Results are discussed in section V and finally, section VI presents the conclusion.

5. Jung C, Hwang H, Sung, and Hwang G (2009), “Enhanced Markov Chain Model and Throughput Analysis of the Slotted CSMA/CA for IEEE 802.15.4 Under Unsaturated Traffic Conditions,” IEEE Transactions on Vehicular Technology, Vol. 58, no. 1, pp. 473–478.

The primary objective in WSN design is maximizing node/network lifetime, while maintaining appropriate level of data transfer. The communication of sensor nodes is more energy consuming than their computation. It is a main concern to minimize communication while achieving the desired network operation. Communication in a clear channel is an ideal case. However in reality of the shared spectrum band like the 2.4 GHz ISM band, which is used by the IEEE 802.15.4 devices, collision caused by collocating devices from multiple standards is unavoidable. As a result, sensor devices will have lower performance under interference environment since they need to waste energy on trying to communicate rather than the communication process itself. The more flexible and intelligent functionality that can adapt the system in respond to the interference environment (possible collision) could enhance the system performance leading to an optimization of the node/network lifetime.

Wireless sensor networks are an increasingly important application area for WPANs such as IEEE 802.15.4 (Callaway, Jr. 2004; Guti´errez et al. 2004). The primary objective of sensing applications running on those networks is to achieve and maintain the desired information throughput. This throughput, often referred to as the event sensing reliability, is defined as the mean number of packets received by the network sink in unit time (Sankarasubramaniam et al. 2003). In addition, many application scenarios require wireless sensor networks to op- erate with as little maintenance as possible due to high cost and, sometimes, infeasibility of maintenance activities. In such cases, maximization of network lifetime is often a secondary objective with no less importance than the primary one. This dual objective can only be achieved through activity management of both the individual nodes and the overall network. Typically, the sensor lifetime can be extended by adjusting the frequency and ratio of active and inactive periods of sensor nodes (Sankarasubramaniam et al. 2003). This approach is supported in 802.15.4 networks that operate in beacon enabled mode, since the superframe (i.e., the time interval between two successive beacons) is divided into active and inactive periods, and individual nodes are free to switch to a power-saving mode during the latter; for obvious reasons, this is often referred to as ‘sleeping’. Power saving typically involves turning off the radio subsystem which is the single greatest power consumer; in most hardware implementations, this will reduce power consumption by two to three orders of magnitude and allow prolonged operation on battery power. For example, a single AAA battery can power a radio transceiver that draws 10 mA (a fairly typical value for the current generation of sensor motes) for two years, provided that the duty cycle does not exceed 0.5% (Guti´errez et al. 2004).

In the past decade several short range wireless technologies have been developed as an answer to the increasing demand for portable and flexible connectivity. In addition to the upsurge in the deployment of IEEE 802.11 based Wireless Local Area Networks (WLANs), few complementary low-power and low- cost technologies, among which IEEE 802.15.4, are establishing their place on the market as enablers of the emerging Wireless Sensor Networks (WSNs). The IEEE 802.15.4 standard was specifically developed to address a demand for low-power, low- bit rate connectivity towards small and embedded devices. Furthermore the standard is trying to solve some problems that were inadequately taken into account by Bluetooth technology. The choice of the digital modulation scheme in IEEE 802.15.4 significantly affects the output load at the different types of devices in wireless sensor communication system. There is no universal „best‟ choice of the modulation scheme, but depending on the physical characteristics of the channel, parametric optimizations and required level of performance some will prove better fit than the others. The 802.15.4 is an IEEE standard, targeting a set of applications that require simple wireless connectivity, high throughput, very low power consumption and lower module cost.

to postpone again and perform the CCA. The issue emerges when hub recognizes occupied channel and performs another backoff process on grounds that sensor hubs may overlook data about CCA'sfailed identification and further cause’s repetitive senses [41]. The wasteful backoff procedure will bring about considerable measure of debasements in framework execution, for example, bringing down usage and additionally minimizing system throughput. There are more impediments and limitations that influence the execution of IEEE 802.15.4 MAC standard, following segment presents late related works and proposed suitable answers for upgrade CSMA/CA [44].

IEEE 802.15.4 devices can operate in either secured mode or nonsecurity mode [1]. Devices operating in the secured mode adopt AES with security services including access con- trol, data encryption, frame integrity, and sequential fresh- ness. Keys are assumed to be provided by higher layer pro- cesses, and key management and key establishment are not specified. Access control is to allow a device to select the other devices to communicate with. In IEEE 802.15.4, a de- vice maintains an access control list (ACL) from which it ex- pects to receive frames, if the access control service is pro- vided. Data encryption is achieved by using a symmetric ci- pher, that is, AES, provided on beacon payloads, command payloads, and data payloads. Frame integrity, provided on data frames, beacon frames, and command frames, is to use a message integrity code (MIC) to protect data from being modified without the key as well as to provide assurance that data come from the sender with the key. Sequential fresh- ness is to use an ordered sequence of frames to reject replayed frames by comparing the last known freshness value with the freshness value in a newly arrived frame to update the fresh- ness value or to signal a failed check message. Furthermore, several security suites are defined to achieve di ff erent pur- poses and di ff erent levels of security.

IEEE 802.15.4 standard [1] defines the protocol and interconnection of devices via radio communication in a wireless personal area network (WPAN). The standard uses CSMA/CA medium access mechanism and sup- ports star as well as peer-to-peer topologies. It provides applications such as home entertainment and control, security alarms, industrial monitoring and control, per- sonal mobile healthcare and tele-assist, etc. Two types of device called the full function device (FFD) and the reduced function device (RFD) are used in a LR-WPAN network. FFD is a fully functional device which can be a PAN coordinator, a coordinator, or just a device. RFD is a device with reduced functionality which can only func- tion as an end device. It cannot communicate with any other device in addition to coordinator. We talk about the PAN-coordinator, which acts as a coordinator for the entire WPAN. It is authorized to provide synchroni- zation services in an established network.

In IEEE 802.15.4 Body Area Networks (BAN), security solution is required for data confidentiality, authentication and integrity at low cost. But the existing solutions for WBAN either provide any one of the security features or provide all the features with high cost. In this paper, we propose to develop light-weight security architecture for IEEE 802.15.4 BAN. It consists of local sensors situated on various parts of the body which forms various clusters. The local sensor collects data from different parts of the body and transmits the data to their respective cluster head. A wireless local gateway (WLG) is deployed within the patient’s home and a hospital gateway (HG) is set in the hospital. The cluster head transmits the data securely to the WLG. At WLG, a new message is created by aggregating all messages from various clusters of a patient. A secret key is generated using Elliptic Curve Cryptography (ECC) for encryption and the encrypted message with message authentication code (MAC) is transmitted to the HG. At the destination, the doctor first authenticates the MAC and then decrypts the data with the secret key and monitors the patient’s health condition. Thus the data cannot be read by any other person, providing a secured transmission at low cost.

Wireless sensor networks based on the IEEE 802.15.4 standard have been designed to specify the physical layer (PHY) and medium access control (MAC) sublayer for low power consumption, short transmission range, and low-rate wireless personal area network (LR-WPAN) [1]. The IEEE 802.15.4 standard has three kinds of topology: star, peer-to-peer, and cluster tree topologies, which can operate on beacon- and non-beacon-enabled modes. The beacon-enabled mode has the most unique features of IEEE 802.15.4, while the beacons are used to synchronize the attached devices, to identify the per- sonal area network (PAN), and to describe the structure of the superframe.

The main features of IEEE 802.15.4 standard are network flexibility, low cost, very low power consumption, and low data rate in an Adhoc self-organizing network among inexpensive fixed, portable and moving devices. It is developed for applications with relaxed throughput requirements which cannot handle the power consumption of heavy protocol stacks. IEEE 802.15.4 defines a popular MAC standard for wireless sensor and actuator networks. With the default parameters, under medium to high load, 802.15.4 generates excessive collisions and packet losses. Low duty cycles even exacerbate the problem, because more nodes become active after long periods of sleep and contend for channel access. In this dissertation, the behavior of IEEE 802.15.4 in the beacon-enabled mode is analyzed to identify the main performance bottlenecks and apply the optimization approach of the 802.11 Idle Sense. Moreover, in this dissertation, a novel stochastic characterization of the delay and packet loss probability distribution, and energy consumption for a unclustered network topology with slotted IEEE 802.15.4 has been made. The analysis was based on the stochastic modeling using Stochastic Petri Nets modeling data packet transmission. The analysis can be used efficiently to provide a set of optimal sleep and listening times that minimize the energy consumption of the network while guaranteeing latency and reliability constraints. Compared to existing protocols that minimize only the energy consumption, our optimization is based on probability distribution and gives much better results. Thus our method can be effectively employed to ensure a longer lifetime of the network.

Recently, Kobayashi [5] et al. proposes a method energy saving by combining the IEEE 802.11with IEEE 802.15.4. If the big data packets is are sent, the method will use IEEE 802.11 for high throughput. On the other hand, if the size of data packet is small, IEEE 802.15.4 is selected to decrease energy consumption. Up until now, there have been many analysis and evaluation of energy efficient MAC protocols in WSN such as simulation and performance evaluation of energy efficient S-MAC and RI-MAC protocols [6], simulation and analysis of energy consumption for S-MAC and T-MAC protocols [7], energy consumption in mobile ad hoc networks [8]. However, none of the above evaluations consider the energy efficient between S-MAC and the IEEE 802.15.4 MAC protocols, which is worked at beacon and non-beacon enabled mode.

ditional rates to the IEEE 802.15.4 standard protocol does not require heavy changes in the hardware design, we have shown that our approach (RA + MM approach) is more energy efficient compared to the standard proto- col and to the case where only the mobility management approach is used (MM approach). In fact, simulations have demonstrated that besides the considerable im- provement in the average time of synchronization for both MM and RA + MM approaches compared to STD approach, the average remaining energy in RA + MM is higher. We have also analyzed the performance of com- municating nodes (a sender and a receiver) and have fig- ured out that the high remaining energy when using the standard protocol (STD) is due to long periods of syn- chronization loss during which nodes do not communi- cate. We have also demonstrated the energy efficiency of our approach compared to the mobility management (MM) approach. Communicating node analysis has also shown the efficiency of our approach in terms of syn- chronization time. In fact, the number of received bea- cons for both sender and receiver is higher than the av- erage beacon number. Finally, we have highlighted the impact of changing the packet interval on the network performance. This is useful for conceiving a new PHY- aware MAC layer that can tune CSMA-CA backoff pe- riods; accordingly, the packet transmission time can be tuned in order to optimize the packet delivery ratio.

In [3], the authors proposed a scheduling approach, where the CFP is always splitted into 16 mini slots. The basic idea is to exploit the fact that the GTS descriptor has a structure not fully utilized in the standard scheme and to propose a new mapping to represent nine new slots. The nodes in the PAN must be aware of this new map- ping for the GTS allocation. Following the same ideas, in [4], the authors presented a more flexible approach and proposed a CFP divided into more than 16 mini time slots for periodic real-time message allocation. This pro- posal offers tighter delay bounds and improves the GTS utilization through an off-line bandwidth allocation algo- rithm. With both approaches [3,4], it is possible to extend the GTS allocation to support applications that require a slightly higher number of slots than the original IEEE 802.15.4 specification.

Monitoring behaviour of the elderly and the disabled living alone has become a major public health problem in our modern societies. Among the various scientific aspects involved in the home monitoring field, we are interested in the study and the proposal of a solution allowing distributed sensor nodes to communicate with each other in an optimal way adapted to the specific applica- tion constraints. More precisely, we want to build a wireless network that consists of several short range sensor nodes exchanging data between them according to a communication protocol at MAC (Medium Access Control) level. This protocol must be able to optimize energy consumption, trans- mission time and loss of information. To achieve this objective, we have analyzed the advan- tages and the limitations of WSN (Wireless Sensor Network) technologies and communication protocols currently used in relation to the requirements of our application. Then we proposed a deterministic, adaptive and energy saving medium access method based on the IEEE 802.15.4 physical layer and a mesh topology. It ensures the message delivery time with strongly limited col- lision risk due to the spatial reuse of medium in the two-hop neighbourhood. This proposal was characterized by modelling and simulation using OPNET network simulator. Finally we imple- mented the proposed mechanisms on hardware devices and deployed a sensors network in real situation to verify the accuracy of the model and evaluate the proposal according to different test configurations.

Researchers have explored the sensor node energy with different modulation schemes. Chouhan et al. [3] have proposed a framework for energy consumption based design space exploration. Using this framework, the authors have explored various modulations schemes and observed that using modulations saves energy as compared to unmodulated data transmission. E. Shih, S. Cho, F. S. Lee [5] analyze both transmission time and constellation size optimization for MQAM and MFSK (both coded and uncoded), considering both transmission and circuit energy consumption. For both MQAM and MFSK, it has been shown that optimizing transmission time or, equivalently, constellation size, minimizes the total energy used for transmission of information. Sharma and Banerjee [9] has worked on Performance Analysis of narrow band and UWB Modulation Techniques using a Sensor Network Model. This paper extends the work of [12] by considering modulation techniques as performance parameter of WSNs in addition with Error control codes. Here, the three modulation types i.e. ASK, BPSK, and OQPSK, are used to find an energy minimization scheme in IEEE 802.15.4 LR- WPAN. Among these three modulation types, OQPSK has been a preferable choice for WSNs because of its less noise interference characteristics. Further, this paper is extended to the study of three most widely used modulation schemes in wireless communication systems, i.e. MQAM, MPSK and MFSK [3] along with suitable Error Correction Codes. The PSK scheme is mostly used in wireless Communication because the probability of error (P e ) or Bit Error Rate

Spectrum using BPSK operating in the frequency range of 868 MHz at a data rate of 20 Kbps, (ii) Direct Sequence Spread Spectrum using BPSK operating in the frequency band of 915 MHz at a data rate of 40 Kbps, (iii) Direct Sequence Spread Spectrum using O-QPSK operating in the frequency band of 2.4 GHz at a data rate of 250 Kbps. For analysis purposes in this work, we have considered higher data rate physical media (2.4 GHz/250 Kbps) which is an internationally used license free ISM frequency band. The specifications of IEEE 802.15.4 Zigbee transceiver operated with 2.4 GHz band is as follows: The data modulation scheme used here is Direct Sequence Spread Spectrum-Offset Quadrature Phase Shift Keying (DSSS- OQPSK). The complete block diagram of Coded IEEE 802.15.4 Zigbee RF transceiver system is shown in Figure 1. This is our proposed modified IEEE 802. 15. 4 Zigbee RF transceiver block diagram, where FEC encoder and decoder blocks are included in conventional functional block diagram. It involves spreading and modulation of input bits. In the first stage, incoming bits are grouped into four, so as to represent a Zigbee symbol. These four bits are used to select one of the 16 nearly orthogonal Pseudo random Noise (PN) sequences to be transmitted. The mapping of symbols to chips is achieved through 32-chip PN sequences shown in Table I. The PN sequences are related to each other through cyclic shifts and the successive selected PN sequences are concatenated and sent to the OQPSK modulator.

standard is very much suitable for low rate-wireless personal area network. It can be easily implied in wireless sensor network. The key focus of our study is exploring the different aspects of standard 802.15.4 low rate - personal area network. In recent times Zigbee has gained popularity in LR-WPAN. The IEEE 802.15.4 based zigbee offers an ideal specification for low data rate and low power consumption applications providing a reliable and cost effective network. These features are promising for various applications like Health care, Fire emergency, traffic management, flood detection, military application and home automation. As a future work we can add security in encryption mechanism in this standard.

Abstract. Coexistence problem is one of the most important issues in the IEEE 802.15.4 based Wireless Sensor Networks (WSNs), since the system operates on the highly populated 2.4 GHz ISM band. As a result, system performance of WSNs can be greatly impaired by the interference from over powering signal from other systems such as WLAN and Bluetooth. This paper proposes an approach based on centralized control for dynamic channel allocation. The proposed method offers multi-channel utilization with intelligent controlling mechanism in order to provide system performance enhancement in order to cope with variation of interfered environment. Based on centralized control, decision making process is performed by the network coordinator allowing such system flexibility. Simulation model has been developed and it is embedded with this proposed mechanism in order to test the system performance. To observe the system performance under the proposed method, variety of simulation scenarios are performed with the variation of two major factors affecting system performance including the size of the network topology and the scale of interference. Proposed method is evaluated and the simulation results are compared against tradition system as well as system with multi- channel utilization method with channel scheduling. The flexibility of the method proposed here allows the system to have better system performance under different test scenarios both in terms of average packet end-to-end delay and system throughput. Keywords: Wireless sensor network, IEEE802.15.4, multi-channel utilization.

cellular network. The Internet of Things describes a network of smart objects where they can communicate and share the information among each other using Internet. The smart objects are intelligent devices with inbuilt software, sensor and programs. Every smart object has a unique identification in network by their internal programs. Figure-1 shows that the internet of smart devices network is the combination of smart device applications and layered framework included IEEE 802.15.4.