Wireless Ad Hoc and Sensor Networks

Background on Networking 41where w(t) is the basic pulse of duration approximately 1 nsec, often awavelet or a Gaussian monocycle, and T f is the frame or pulse repetitiontime. In a multinode environment, catastrophic collisions are avoided byusing a pseudorandom sequence c j to shift pulses within the frame todifferent compartments, and the compartment size is T c sec. One mayhave, for instance T f = 1 µ sec and T c = 5 nsec. Data is transmitted usingdigital PPM, where if the data bit is 0 the pulse is not shifted, and if thedata bit is 1 the pulse is shifted by δ. The modulation shift is selected tomake the correlation of w(t) and w(t δ) as negative as possible. The meaningof d[/ j Ns ] is that the same data bit is transmitted Ns times, allowing forvery reliable communications with low probability of error.In addition, the power, mobility, and task management planes monitorthe power, movement, and task distribution among the sensor nodes andhelp the sensor nodes coordinate the sensing aspect while lowering theoverall power consumption. Many protocols and algorithms for WSN aredesigned by taking into account the physical layer requirements such asthe microprocessor and receiver types. This is essential to minimize thepower consumption even though incorporating the physical layer needsin the protocol design may result in a custom solution.1.5.1 Closest PeersThe following are the closest peers to a WSN. They are:Bluetooth was initiated in 1998 and standardized by the IEEE asWireless Personal Area Network (WPAN) specification IEEE802.15. Bluetooth is a short-range RF technology aimed at facilitatingcommunication of electronic devices between each otherand with the Internet, allowing for data synchronization that istransparent to the user. Supported devices include PCs, laptops,printers, joysticks, keyboards, mice, cell phones, PDAs, andconsumer products. Mobile devices are also supported. Discoveryprotocols allow new devices to be hooked up easily to the network.Bluetooth uses the unlicensed 2.4-GHz band and can transmitdata up to 1 Mbps, can penetrate solid nonmetal barriers, andhas nominal range of 10 m that can be extended to 100 m. Amaster station can service up to seven simultaneous slave links.Forming a network of these networks, for example, a piconet,can allow one master to service up to 200 slaves. Currently,Bluetooth development kits can be purchased from a varietyof suppliers, but the systems generally require a great deal oftime, effort, and knowledge for programming and debugging.Forming piconets has not yet been streamlined and is undulydifficult.