Hardware, Software

Introduction to RF communication

This post introduces the basics of RF communication along with various band specifications used for wireless communication. It also covers comparison of  different bands on basis of their data rates and other parameters.

Content

  1. Introduction
  2. Available frequency Bands
  3. Types of RF communication
  4. Different wireless protocols

Introduction

Now a days, we are surrounded by a large number of wireless devices working on different protocols, on different frequency bands thus utilizing almost whole of the “Radio-wave” frequency spectrum.

Adhering to it’s high density, complete frequency spectrum can be divided into different groups and each group can be further divided into different channels.

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Considering the above distribution, most of the wireless devices works in the VHF and UHF bands. Working on such high frequencies has some of it’s renowned advantages like decreased antenna size, low interference from power devices, efficiency in propagation (low dispersion) etc.
Propagation at lower frequencies reduces dependencies on line-of-sight communication (As they get reflected from ionosphere). They are characterized by narrow bandwidth(usually 10%), higher bandwidths might reduce performance.
VLF and LF links usually carry low-rate digital signals or Morse code, while MF links are wide enough to carry voice signals. Above approximately 30 MHz, radio transmissions pass through the ionosphere, so higher frequency signals cannot propagate through ionospheric hops. They operate on line-of-sight or near line-of-sight propagation paths.
VHF and UHF support enough bandwidth to carry not only voice and data, but also video signals—including commercial television broadcasts.
Microwave frequencies are used to carry high information content signals in wide bandwidths. Wide band microwave point-to-point links carry large blocks of telephone signals, television signals, and wide band digital data. Communication satellite links are also at microwave.

For analysis of frequency domain, we usually prefer decibel scale since it allows a wide range of frequency components to be represented on a single scale!

Availability of frequency bands in India

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Radio wave frequency band extending from 9Khz to 400Ghz can be broadly divided into three bands namely permeable, semi-permeable and LOS band.
Some of the frequency ranges from above spectrum is available for general purpose use without license. Here’s the list of such unlicensed bands:

Frequency Band: 865-867 MHz

Low power RFID equipments or any other low power wireless devices or equipments
Power: Maximum transmitter output power of 1 Watt ( 4 Watts Effective Radiated Power)Carrier Bandwidth: 200 KHz
Reference: GSR 564 ( E) dated 30 July 2008

Frequency Band: 2.4-2.4835 GHz

Use : Low power equipments
Power: Maximum transmitter output power of 1 Watt ( 4 Watts Effective Radiated Power)
Carrier Bandwidth: spectrum spread of 10 MHz or higher
Reference: GSR 45E dated 28.1.2005

Frequency Band: 5.150-5.350 GHz, 5.725 – 5875
Use : Low power equipments for Cellular telecom systems including Radio Local Area Networks, Indoor applications
Power: maximum mean Effective Isotropic Radiated Power of 200mW, maximum mean Effective Isotropic Radiated Power density of 10mW/MHz in any 1 MHz bandwidth,
Carrier Bandwidth: 1MHz
Reference: GSR No 46E dated 28.1.2005

Frequency Band: 5.825 to 5.875 GHz
Use : Low power equipments
Power: maximum transmitter output power of 1 Watt ( 4 Watts Effective Radiated Power)Carrier Bandwidth: spectrum spread of 10 MHz or higher
Reference: GSR no 38E dated 19.1.2007

Frequency Band: 26.957-27.283 MHz
Use : Wireless equipments intended to be used while in motion or during halts
Power: maximum Effective Radiated Power ( ERP) of 5 Watts
Reference: GSR no 35 E dated 10.01.2007

Frequency Band: 335.7125, 335.7375,335.7625, 335.7875, 335.8125 and 335.8375MHz
Use : Low power equipments for the remote control of cranes
Power: maximum transmit power of 1mW
Carrier Bandwidth: 10 KHz
Reference

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