POOJ ALECTURER SAS IIT& RESEARCH MOHALI WIRELESS SENSOR AGENDA y Introduction y Wireless network standards y Topologies y Synchronization y Applications y Blue tooth Vs Wi-Fi y Conclusion Introduction A wireless network operates using some sort of sensors and line of site topology where the two adjacent sensors are able to detect and interpret the messages/packets that are sent or received by the communicating terminals. The system operates using electromagnetic waves or radio waves for taking the signals from one terminal to the other. Two or more computers are said to be connected with each other when there is a possible communication with each other and called wireless when there is no wire or any physical medium used for the communication. Wireless Network Standards Before we begin our discussion, it is important to understand that a number of different wireless network standards are available. These standards were established by the IEEE (Institution of Electrical and Electronic Engineers) and are commonly called the 802.11x standards. These are presented in the following table. Different Wireless Standards Radius (Indoor) Outdoor) Depends, Loss includes # ~20 Meters OFDM DSSS OFDM MIMO ~35 Meters ~38 Meters ~38 Meters ~70 Meters ~50 Meters ~100 Meters Protocol Release Date 1997 Op. Frequency 2.4 GHz Throughput (Type) Data Rate (Max) 2 Mbit/s Modulation Technique Legacy 0.9 Mbit/s 802.11 a 802.11 b 802.11 g 802.11 n 1999 1999 2003 Sept 2008 (est.) March 2008 (est.) 5 GHz 2.4 GHz 2.4 GHz Sept 2008 (est.) 3.7 GHz 23 Mbit/s 4.3 Mbit/s 19 Mbit/s 74 Mbit/s 54 Mbit/s 11 Mbit/s 54 Mbit/s 248 Mbit/s ~120 Meters ~140 Meters ~140 Meters ~250 Meters 802.11 y 23 Mbit/s 54 Mbit/s ~5000 Meters This Table show the various protocols that are relevant to our studies and after the study of this table we can easily see the differences that have been introduced from the time to time. y OFDM: In OFDM, the sub-carrier frequencies are chosen so that the sub- carriers are orthogonal to each other, meaning that cross-talk between the sub-channels is eliminated and inter-carrier guard bands are not required. This greatly simplifies the design of both the transmitter and the receiver; unlike conventional FDM, a separate filter for each sub-channel is not required. The orthogonality also allows high spectral efficiency y DSSS: Direct-Sequence Spread Spectrum (DSSS) is a modulation technique. As with other spread spectrum technologies, the transmitted signal takes up more bandwidth than the information signal that is being modulated. y MIMO(pronounced mee-moh or mai-moh): Multiple-input and multiple- output refers to the use of multiple antennas both at the transmitter and receiver to improve the performance of radio communication systems. Topologies There are mainly three topologies that are applied in the establishment of a typical wireless network. These are Static: It is the Traditional topology that uses the wires for as the communication medium. Mobile: It is that topology that uses the microwave for the sending and receipt of data i.e. communication. Hybrid: In this topology, we find the combination of both the topologies. The wireless systems operate on the outside world and the internal communication takes place through the wires. The figure shows the functioning of a hybrid topology, it is as follows. This arrangement of the computers shows that there is a central hub connecting all the systems in a closed system and on the outer side there is a broadband modem that is connected with the outer world using wireless sensor system. The various configurations are as follows y The Point To Point Topology This is one of the most reliable topology because there is only one point of failure in this topology and that is the host itself. This topology is simple enough and requires less expertise but when it comes to operate multiple hosts the complexity increases in geometric fashion. In this topology, each sensor node needs a separate connection over a wire generally twisted pair shielded wire. Due to the use of this, the cost increases and the management become difficult. Also in this case all the information is processed by the host. y Multi drop In this topology, the bus topology was used as to reduce the number of wires. It is more reliable than the point to point topology. The main problem that is observed is that of digitization of data. In the point to point topology, digitization occurred in the host, where a single clock could be used to time stamp when the analog signals from multiple sensors were acquired. multidrop network, each sensor node puts its information onto a common medium. The single-wire connection represents a potential single-point failure. y The Web Technology It is that topology in which all the hosts must be operating and connected all the time. It is possible only when the vendors agree on a common protocol so that all the hosts can communicate with each other to server to their near system. The Figure show a typical web topology. The introduction of wireless sensor networks brought a revolution in the field of networking as they are intelligent enough that they automatically make a configuration for the reliable service. These sensors are co-operating and form a temporary configuration to replace the host and in the future, they may also become self aware. . Figure shows a typical configuration. An architecture consisting of a decoder for each channel and a direct-sequence spread-spectrum receiver can perform simultaneous sampling because the same baseband signal goes to each decoder. But the decoders represent a significant cost, power, and size limitation The web topology is the most complicated as all the hops can¶t reach at a destination. So a repeating configuration is required. Also in this case the nodes come and go at random and thus there is need to reconfigure all the systems frequently that affect the performance Synchronization Time Synchronization in wireless networks is extremely important for basic communication, but it also provides the ability to detect movement, location, and proximity. The synchronization problem consists of four parts: send time, access time, propagation time, and receive time. Three current synchronization protocol . The first is relative timing and is the simplest. It relies on the ordering of messages and events. The next method is relative timing in which the network clocks are independent of each other and the nodes keep track of drift and offset. The last method is global synchronization where there is a constant global timescale throughout the network. This is obviously the most complex and the toughest to implement. Applications Environmental monitoring Habitat monitoring Acoustic detection Seismic Detection Military surveillance Process Monitoring Structural health monitoring Health Monitoring While mainstream computers have an abundance of standards, the only official standard that has been adopted for wireless sensor networks is Wireless HART. In figure are some other standards being investigated for use by researchers in the field: ZigBee Wibree 6lowpan Blue tooth Vs Wi-Fi Bluetooth-equipped hardware devices contain a Bluetooth chip that will wirelessly connect them to the PC without any interaction necessary from the user. Bluetooth devices operate in the 2.45 Gigahertz frequency range. Other devices currently operate in this frequency range as well, including cordless phones. Bluetooth devices avoid interfering with other systems is by sending out a very weak 1 mill watt signal ² a cell phone by comparison can transmit up to 3 watts. In addition to data, up to three voice channels are available, and each device is assigned a unique 48-bit address. Connections can be point-topoint or multipoint. Bluetooth devices have a maximum transmission rate of only 1 Mbps ² up to 2 Mbps in the second generation of the technology ² of which about 20 percent of this capacity is used for data headers and handshaking information. By comparison, Wi-Fi wireless LAN adapters are much more powerful and capable of reaching data transmission rates approaching 54Mbps. The most popular Wi-Fi standard is the one used in your D-Link router, 802.11b. This version provides users with 11 Mbps transmission speeds and also operates in the 2.4 GHz band. Products based on this specification have very good range and can commonly transmit data at distances of well over 100 feet. The most recently introduced specification, 802.11g, offers users the best of both worlds by providing users with higher transmission rates yet 100 percent compatibility with existing 802.11b products. Conclusion A wireless network is collection of objects in a system operate in harmony to achieve a common objective in a controlled fashion but still independent in their respective functioning. Thus a network has more than one component, a common communication medium over which they establish relationship, perform their functions at individual level and a well defined set of rules. The scope and objective of this paper is limited to the use of wireless networks that is with special reference to the computers and acquaint you with the current trends, technologies, management, problems using them. We provide proven experience in the design, development, test and implementation of wireless sensor networks in the biochemical, telecommunications, electromechanical, and environmental industries. THANK YOU