RF Basicsby

Raoul van BergenField Application Engineer EmbeddedDigi International GmbH Dortmund

raoul.van.bergen@digi.com

Wireless Communication Basics

RF Basics• Basic Communication System

– Transmitter and Receiver

Transmitter Receiver

RF BasicsBasic Communication System

– Transmitter and Receiver– Transmitting Antenna

Transmitter ReceiverAntenna 1

RF BasicsBasic Communication System

– Transmitter and Receiver– Transmitting Antenna– Receiving Antenna

Transmitter ReceiverAntenna 1 Antenna 2

RF BasicsBasic Communication System

– Transmitter and Receiver– Transmitting Antenna– Receiving Antenna– Environment

Transmitter ReceiverAntenna 1 Antenna 2

Environment

RF BasicsMaximizing Range

Transmitter ReceiverAntenna 1 Antenna 2

RF Essentials

Maximizing Range– Increase Transmitter (TX) Power

• Government Regulated• Low-powered Applications

Increase Power ReceiverAntenna 1 Antenna 2

RF EssentialsMaximizing Range

– Increase Transmitter (TX) Power– Increase Receiver (RX) Sensitivity

• Specified in dBm• Every 6 dB doubles the range LOS• Every 12 dB doubles range indoors / urban

environments

IncreasePower

ImproveRX Sensitivity

IncreaseGain

IncreaseGain

RF BasicsMaximizing Range

– Increase Transmitter (TX) Power– Increase Receiver (RX) Sensitivity– Increase Antenna Gain

• More gain equates with more focusing of energy• Antenna cables should be as short as possible

IncreasePower

ImproveRX Sensitivity

IncreaseGain

IncreaseGain

RF Basics

Basic Communication System– Transmitter and Receiver– Transmitting Antenna

• Focused energy

RF Basics

Basic Communication System– Transmitter and Receiver– Transmitting Antenna– Receiving Antenna

• Focused energy

RF Basics

Antenna Gain– Government-imposed power

restrictions– Omnidirectional

RF Basics

Antenna Gain– Directional

RF BasicsMaximizing Range

– Increase Transmitter (TX) Power– Improve Receiver (RX) Sensitivity– Increase Antenna Gain– Clear the Environment of obstructions

• Visual (Linear) line-of-sight vs. RF (Radio) line-of-sight

IncreasePower

ImproveRX Sensitivity

IncreaseGain

IncreaseGain

Clear theEnvironment

RF Basics

Fresnel Zone– Football-shaped path

FresnelZone

RF BasicsFresnel Zone

– Football-shaped path– Acceptable = 60% of Zone 1 + 3 meters– Raise antennas to help clear the zone

RF Basics

Fresnel Zone– Football-shaped path– Acceptable = 60% of Zone 1 + 3 meters– Raise antennas to help clear the zone– Formula

RF BasicsFresnel Zone Diameters

RangeDistance

868 MHz ModemsRequired Fresnel

Zone Radius

2.4 GHz ModemsRequired Fresnel

Zone Radius

1 m 0,29 m 0,18 m

3 m 0,51 m 0,31 m

10 m 0,93 m 0,56 m

30 m 1,61 m 0,97 m

100 m 2,94 m 1,77 m

300 m 5,09 m 3,06 m

1600 m 11,76 m 7,07 m

8000 m 26,29 m 15,81 m

16000 m 37,18 m 22,36 m

Importance of Frequency Selection

• Geographic Deployment– Worldwide versus Regional

• RF Performance– Range– RF Penetration– Antenna Considerations

License-Free Bands

2.4 GHz

315 MHz420 MHz900 MHz5.7 GHz

900 MHz433 MHz

433 MHz868 MHz5.7 GHz

915 MHz

Regulatory Bodies

• FCC (United States)• IC (Canada)• ETSI (Europe, some APAC)• C-Tick (Australia• Telec (Japan)• Anatel (Brazil)

Rates and Ranges

Range

Pe

ak

Da

ta R

ate

Closer Farther

Slo

wer

Fas

ter

UWB Wireless Data Applications

Wireless Video Applications

IrDA

802.11g

802.11b

802.11a

2.5G/3G

Bluetooth™

ZigBee™Data

Transfer

Wireless Networking

Wi-Fi®

Cellular

NodesNodes and Rates

• Modem– Modulate / Demodulate

Radio Modem Operation

Wireless Communication BasicsWhat is modulation?

– The process by which a parameter (amplitude, frequency or phase of a sinusoidal signal) of a higher frequency carrier wave is altered in accordance with the baseband message signal.

– Transforms the message signal into a form that is suitable for transmission over the channel.

– The transmitter uses the baseband message signal to modulate a carrier and transmit it over the channel.

Radio Modem OperationTwo types of spread spectrum used in modern

Radios

1.FHSS- Frequency Hopping Spread Spectrum• Transmitter rapidly hops from one channel to the

next in a pseudo-random fashion, avoiding long-term interference.

• Receiver follows transmitter• Some Digi Products use FHSS

– 24XStream 2400 2480

• Price-to-Performance Value

• High Receiver Sensitivity

• Low Power Consumption

• FCC (U.S.A.), IC (Canada), • ETSI (Europe) Approved

XStreamKey Features

Best Value OEM RF Modules 2.4GHz

XStream (2.4 GHz)Best Value OEM RF Modules

Specifications

Indoor/urban Range up to 180 m

Outdoor line-of-sight Range up to 16 km

Transmit Power Output 50 mW (17 dBm)

Receiver Sensitivity -105 dBm @9600 bps

Operating Frequency 2.45-2.46 GHz

Operating Voltage 5V (OEM) 7-18 (Boxed)

RF Data Rate 9600 or 19200 bpsInterface Packages Available

Radio Modem OperationTwo types of spread spectrum used in modern Radios

2. DSSS- Direct Sequence Spread Spectrum• Each bit is represented by N, shorter segments, called chips.• Increases over-the-air rate by a factor of N, widening the spectrum• Correlator in receiver examines the chips and maps chips back to bits,

while simultaneously spreading undesired signals• Processing gain, 10*log(chip_rate/bit_rate)• Some Digi products

use DSSS– XBee– XBee-Pro– All WiFi

enabledproducts

Digi RF Products Packaged (Boxed)

Modules (Embedded)

DigiRF Products

• XBee• XStream• XTend• XPress• XCite• Digi Mesh

Product Brand Specs

Product Name Frequency Power OutputIndoor RangeOutdoor Range

Data Rate

XBee 2.4 GHz 1 mW 30 meters100 meters

250 Kbps

XBee-PRO 2.4 GHz 50 mW100mW (EIRP)

100 meters1200 meters

250 Kbps

9XTend 900 MHz 1 Watt 900 meters64 kilometers

115 Kbps

9XStream 900 MHz 100 mW 450 meters32 kilometers

19.2 Kbps

24XStream 2.4 GHz 50 mW 180 meters16 kilometers

19.2 Kbps

9XCite 900 MHz 4 mW 90 meters300 meters

38.4 Kbps

Digi RF Modules