Unit I: Introduction

TOPICS Fundamentals of Wireless Communication Technology The Electromagnetic Spectrum Radio propagation Mechanisms Characteristics of the Wireless Channel MANETs and WSNs concepts and architectures Applications of Ad Hoc and Sensor networks Design Challenges in Ad hoc and Sensor Networks.

Fundamentals of Wireless Communication Technology Transmitting/receiving voice and data using electromagnetic waves in open space. Information from sender to receiver is carried over a well defined channel.

Fundamentals of Wireless Communication Technology Each channel has a fixed frequency bandwidth & capacity (bit rate). Different channels can be used to transmit information in parallel and independently.

Electromagnetic Spectrum X rays and gamma rays are not used due to practical concerns Radio waves are easy to generate and most widely used.

Electromagnetic Spectrum Band Name Frequency Wavelength Application Extremely Low Frequency (ELF) 30 – 300 Hz 10,000 – 1000 Km Power line frequencies Voice Frequency (VF) 300 – 3,000 Hz 1,000 – 100 Km Telephone communication Very Low Frequency (VLF) 3 – 30 KHz 100 – 10 Km Marine communication Low Frequency (LF) 30 – 300 KHz 10 – 1 Km Medium Frequency (MF) 300 – 3000 KHz 1000 – 100 m AM broadcasting High Frequency (HF) 3 – 30 MHz 100 – 10 m Long distance aircraft/ship communication Very High Frequency (VHF) 30 – 300 MHz 10 – 1 m FM broadcasting Ultra High Frequency (UHF) 300 – 3000 MHz 100 – 10 cm Cellular telephone Super High Frequency (SHF) 3 – 30 GHz 10 – 1 cm Satellite communication, Microwave links Extremely High Frequency (EHF) 30 – 300 GHz 10 – 1 mm Wireless local loop

Electromagnetic Spectrum VLF, LF, MF bands – ground waves or surface waves SHF band – space wave VHF band – sky wave

Radio Propagation mechanism Reflection – dimension of an object is larger than wavelength of radio wave Scattering – dimension of an object is smaller than wavelength of radio wave Diffraction – dimension of an object is comparable to the wavelength of radio wave

Characteristics of the wireless channels Path loss Fading Interference Doppler shift

Path loss Ratio of power of the transmitted signal to the power of same signal received by receiver. Dependent on radio frequency used and nature of terrain Path loss models – Free space & Two ray Free space – no attenuation of signals, only direct path Pr = Pt Gt Gr (/4πd)2 Two ray – direct path & Reflected path Pr = Pt Gt Gr (ht hr/d2)2

Fading Fluctuations in signal strength when received at the receiver. Types – (1) Fast/small scale fading (2) slow/large scale fading. Fast fading – rapid fluctuations in amplitude, phase or multipath delays. Slow fading – objects partially absorb the transmissions Counter measure – Diversity & Adaptive modulation

Interference Types : (1) ACI (2) CCI (3) ISI Interference Counter measure ACI Guard band CCI Usage of directional antennas, dynamic channel allocation ISI Adaptive equalization

Doppler Shift Change in frequency when transmitter and receiver are mobile in nature. Higher frequency – when both move towards Lower frequency – when both move away

Applications of Ad hoc Networks Military applications (Secure & Cost) Communication among group of soldiers Communication among military objects (fleets of air planes or warships) Collaborative & Distributed computing (Reliability & Economic) Communication among group of people in conference Emergency operations Search & rescue, crowd control and commando operations Wireless mesh networks (Self organization & maintenance) Residential zones Highways Business zones Civilian regions University campuses Wireless sensor networks Hybrid wireless networks