Wireless Communication Technology Essentials

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 Frequency Extremely Low Frequency (ELF) Band Name Wavelength 10,000 1000 Km Application 30 300 Hz 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 Marine communication 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) Extremely High Frequency (EHF) 3 30 GHz 10 1 cm Satellite communication, Microwave links Wireless local loop 30 300 GHz 10 1 mm

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 P Pr r = P = Pt t G Gt t G Gr r ( ( /4 d) Two ray direct path & Reflected path P Pr r = P = Pt t G Gt t G Gr r (h (ht t h hr r/d /d2 2) )2 2 /4 d)2 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 ACI CCI Counter measure Guard band Usage of directional antennas, dynamic channel allocation Adaptive equalization ISI

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