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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
ModulationWhat 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 Name Frequency Power OutputIndoor RangeOutdoor Range
Data Rate
XBee 2.4 GHz 1 mW 30 meters100 meters
250 Kbps
XBee-PRO 2.4 GHz 10 mW19 mW (EIRP)
80 meters800 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