Wireless Communication Protocols

by Mike Denko, Alex Motalleb, and Tony Qian

Image taken from: http://findicons.com/icon/84804/wifi

Purpose

• Want to make an embedded application where a wired connection isn't practical, things to consider with a wireless solution:o Antennao Frequency Bando Power Consumptiono Rangeo Data Rateo Cost

Outline

1. Antennas

2. RF Modules

3. Wi-Fi

4. Zigbee

5. Bluetooth

6. Comparison

Outline

1. Antennasa. Overview

b. Antenna Theory

c. Antenna Types

d. Bandwidth & Gain

e. Terminology

2. RF Modules

3. Wi-Fi

4. Zigbee

5. Bluetooth

6. Comparison

Why are we covering antennas?

• Antennas are used in all wireless embedded systems

• Some embedded applications will require you to pick an antennao You may design a PCB that will include an antennao Having a basic understanding of how antennas work

can help you pick oneo This presentation will provide information to help you

read an antenna spec sheet

Image taken from: http://store.diyembedded.com/index.php?main_page=product_info&products_id=28

How does an antenna work?

• Converts an electrical signal into electromagnetic radiation and vice versa

• Transmissiono Radio transmitter supplies radio

frequency current to antenna terminalso Antenna radiates energy

from current in electro-magnetic waves

• Receptiono Antenna intercepts power

from electromagnetic waves to produce voltage at its terminals, that voltage is then amplified

Image taken from: http://upload.wikimedia.org/wikipedia/commons/d/da/Felder_um_Dipol.jpg

Basic Antenna Types• Omnidirectional - Radiates

in all horizontal directionso Dipole Antennas

• Semi-directional - Radiates in a horizontal arco Patch Antennaso Panel Antennaso Yagi Antennas

• Directional (Beam) - Radiates in one directiono Parabolic Disheso Grid Antennas

• More information on antenna types can be found at:o http://zaielacademic.net/networking_wireless/

wireless_antennas.htm

Patch antenna

Parabolic antenna

OmnidirectionalBasic Antenna Types

Image taken from: http://zaielacademic.net/networking_wireless/wireless_antennas.htm

DirectionalBasic Antenna Types

Image taken from: http://zaielacademic.net/networking_wireless/wireless_antennas.htm

Directional: Fresnel Zone

• Radiation from directional antenna does not travel in direct path

• Fresnel calculations can be found at: http://zaielacademic.net/networking_wireless/wireless_antennas.htm

Image taken from: http://zaielacademic.net/networking_wireless/wireless_antennas.htm

Reading Antenna Spec Sheets

Antenna BandwidthReading Antenna Spec Sheets

• Bandwidth - Difference between high and low cutoff frequencies

• Describes the range of frequencies at which an antenna can receive or transmit a signal

• Measured in hertz

• Bands located in different areas of the frequency spectrum can have the same bandwidth

Images taken from: http://www.antenna-theory.com/basics/bandwidth.phphttp://upload.wikimedia.org/wikipedia/commons/6/6b/Bandwidth_2.svg

Antenna Gain (dBi)Reading Antenna Spec Sheets

• Transmissiono Describes how well antenna turns electrical power

into electromagnetic radiation

• Receptiono Describes how well antenna turns electromagnetic

radiation into electrical power

• Defined as ratio of power produced by antenna from far away source over power produced by hypothetical isotropic antenna

• Units are decibels-isotropic (dBi)o G = 10 log 10 ( I A / I Q )

http://whatis.techtarget.com/definition/decibels-relative-to-isotropic-radiator-dBi

Image taken from: http://www.maximintegrated.com/app-notes/index.mvp/id/3622

Receive Sensitivity and Transfer Power (dBm)

Reading Antenna Spec Sheets

• Transfer Power - Total power over bandwidth

• Receive Sensitivity - The necessary radiation power needed by the receiver to pick up a signal from the transmitter

Power (dBm) Power (W)

-30 dBm 0.0000010 W

-20 dBm 0.0000100 W

-10 dBm 0.0001000 W

0 dBm 0.0010000 W

1 dBm 0.0012589 W

2 dBm 0.0015849 W

3 dBm 0.0019953 W

4 dBm 0.0025119 W

5 dBm 0.0031628 W

6 dBm 0.0039811 W

7 dBm 0.0050119 W

8 dBm 0.0063096 W

9 dBm 0.0079433 W

10 dBm 0.0100000 W

20 dBm 0.1000000 W

Image taken from http://www.mobilemark.com/engineering/antenna-theory-simplified.html

Antenna RangeReading Antenna Spec Sheets

Antenna Gain (dBi) Range (km)

0 .8714

4 2.189

7 4.368

10 8.7146

13 17.3879

16 34.693

20 87.146

24 218.9

• Frequency = 2442 Hz (Wi-Fi)• Transmitting power: 18 dBm = .06 W @ 11 Mbps• Receiving sensitivity: -90 dBm = 10^(-12) W @ 11 Mbps

Other TermsReading Antenna Spec Sheets

• Beamwidth - The width of the angle at which an antenna will accept signalso A narrower beamwidth is desirable for a directional

antenna

• Front to Back Ratio - describes how much a signal received behind the antenna is reduced compared to a signal received in the front

• Effective Aperture - Describes the effectiveness of an antenna at receiving power from radio waves

(http://en.wikipedia.org/wiki/Effective_aperture)

• More detailed information: http://www.afar.net/tutorials/antennas/

What We Covered So Far• Antenna Theory

o Transmittingo Receiving

• Basic Antenna Typeso Omnidirectionalo Directional

• How to read antenna spec sheetso Frequency Rangeo Bandwidtho Antenna Gain (dBi)o Antenna Senstivity (dBm)

• Calculated Antenna Range

• http://www.afar.net/tutorials/antennas/

Outline

1. Overview of Antennas

2. RF Modulesa. What are they?

b. RF Module Communication

c. Modulation

3. Wi-Fi

4. Zigbee

5. Bluetooth

6. Comparison

RF Modules

• Integrated circuits designed to transmit and/or receive radio signals

• Have a radio transmitter and/or receiver

• An umbrella term that includes many different pieces of hardwareo Several different wireless protocols are used among

RF Modules

Image taken from: https://www.sparkfun.com/products/10535?

RF Module Communication

• Antennas are used to transmit and receive data

• Use either wireless serial or a specific protocol

• Signals containing data or information are modulated

Image taken from: http://www.sciencedirect.com/science/article/pii/S0168169909000076

Modulation• Varying a property of a high frequency signal (carrier

signal) to send information

• Amplitude modulation and frequency modulation used in radio

• Similar modulation used in simple RF Moduleso Amplitude Shift-Keying (ASK)o Frequency Shift-Keying (FSK)o On-off keying (OOK)

• More complex modulation used for more complex protocols

Amplitude-Shift Keying (ASK)

• Changes amplitude of the transmitted signal based on the data being sent

• Assigns specific amplitudes for 1's and 0's

• On-off Keying (OOK) is a simple form of ASK

Image taken from: http://www.ele.uri.edu/Courses/ele436/labs/ASKnFSK.pdf

Frequency-Shift Keying

• Changes frequency of the transmitted signal based on the data being sent

• Assigns specific frequencies for 1's and 0's

Image taken from: http://www.ele.uri.edu/Courses/ele436/labs/ASKnFSK.pdf

Outline

1. Overview of Antennas

2. RF Communication

3. Wi-Fia. Overview

b. Bandwidth & Data Rates

c. MIMO

d. Antenna

e. Embedded Applications

4. Zigbee

5. Bluetooth

6. Comparison

Wi-Fi

• Overviewo “Wireless Fidelity”, exchanges data

wirelesslyo Wireless Local Area Networks (WLAN)

based on the IEEE 802.11 specificationsi. WLAN links two or more devices using some wireless

distribution method, and provides a connection through an access point to the wider internet.

o Internet Accessi. Wide Range (65 feet indoor, much greater outdoor)

ii. High Speed (54Mbps)

IEEE 802.11

• WLAN standards (2.4, 3.6, 5GHz)

• History (Wi-Fi)o 1997, initial speed 1 and 2 Mbpso 1999, 802.11 a/b, 20MHz bandwidth

i. a: 5GHz, high data rate, small wavelength

ii. b: 2.4GHz, 11Mbps, large effective overall range

o 2003, 802.11 g (54Mbps)o 2009, 802.11 n (MIMO), both 2.4 and 5

GHz, 54Mbps to 600Mbps, 40MHz bandwidth

Image taken from: en.wikipedia.org/wiki/File:United_States_Frequency_Allocations_Chart_2003_-_The_Radio_Spectrum.jpg

United States Partial Frequency Spectrum

Image taken from: en.wikipedia.org/wiki/File:United_States_Frequency_Allocations_Chart_2003_-_The_Radio_Spectrum.jpg

Wi-Fi Radio Technology

• High frequency allows high data rateo 802.11 a , 5GHz; 802.11 b/g, 2.4GHzo Able to change frequency

• Efficient coding techniqueso 802.11 a/g, OFDM

i. Subcarriers are orthogonal to each otherii. Eliminates the need for guard bands

o 802.11 b, CCK (complementary code keying)i. Replace the previous code in wireless digital networksii. Transfer more data per unit time for a given signal

bandwidthMore information: http://searchmobilecomputing.techtarget.com/definition/Complementary-Code-Keying

Orthogonal Subcarriers

Wi-Fi Radio Technology

• Multiple input Multiple output (MIMO)o Smart antenna technology

i. SISO: Tradition antenna configuration using one

transmitter and one receivero Transmitting multiple data streams

simultaneously and spread transmit heato WiMAX, LTE…

SISO scheme

Wi-Fi Antenna

• Omnidirectional Wi-Fi antennao Multiple directionso Routers and mobile adapterso Gain: 2 to 9 dBi

i. dBi - decibels relative to an isotropic (0 dBi) reference antennaii. dBd - decibels relative to a dipole (0 dBd) reference antennaiii. 2.15 dBi =0 dBd

• Directional Wi-Fi antennao Extend the range in one directiono High gain (above 10dBi)o More information:

http://compnetworking.about.com/od/homenetworkhardware/a/introduction-to-wifi-wireless-antennas.htm

Wi-Fi Antenna

• Exampleso Yagi Antennas (0.8 mil)

i. Extend the range of outdoor hotspots in a specific directions

ii. High gain, usually 12 dBi or higher

o Cantenna (1.2-2 mil)i. A brand name of Wi-Fi directional antennas

ii. Supports 2.4GHz signaling with gain up to 12 dBi

iii. Beamwidth of about 30 degrees

o Othersi. Backfire antennas

ii. Parabolic or dish antennas

iii. More information: http://www.radiolabs.com/Articles/wifi-antenna.html

Wi-Fi Security

• Security goals and strategieso mutual authenticationo private communicationo data integrity

• Wired Equivalent Privacy (WEP)

• IEEE 802.11i (WPA and WPA2)o WPA2: supports most new Wi-Fi deviceso Fully compatible

• Security Trade-Offo Embedded system: private/public access

Pros and ConsAdvantages• Frees network devices

from cables, allows for a more dynamic network to be grown

• Cheaper development for embedded systemo price drops

• Backwards compatible; reliable products

• Security

• High speedo 54Mbps

Disadvantages• 802.11b/g use the 2.4

GHz spectrum, which is crowded with other devices (Bluetooth... )

• 802.11n doubles the radio spectrum/bandwidth (40 MHz)

• Power consumptiono 0.5-1w, chipsetso 1-2w, wifi deviceo 4-5w, router

• Limited network range

• Security risks (configure)

Wi-Fi for Embedded System

• Control applications where wired connection are too costly or inconvenient

• Emergency applications that require immediate and transitory setup

• Mobile applications

• Camera applications

• Communication with other Wi-Fi devices

Application

• Internet Accesso Hotspots

• City-wide Wi-Fi

• Campus-wide Wi-Fi

• Direct computer-to-computer communications o Wireless ad hoc network

Outline

1. Overview of Antennas

2. RF Communication

3. Wi-Fi

4. Zigbeea. Overview

b. Data Rates, Power, & Broadband

c. Communication Protocol

d. Applications

5. Bluetooth

6. Comparison

Zigbee

• What is it?o A protocol for high level communication

over digital radios, based in IEEE 802.15.4

• Why “Zigbee”?o The name “Zigbee” refers to the dance

bees do to communicate

http://openlearn.open.ac.uk

What is Zigbee?

• Zigbee (low-power)o Specializes in using low power, low

speed, long battery life radios for transmission

• Zigbee Proo Higher power, higher range, shorter

battery life. Still compatible with regular Zigbee

Zigbee (low power)

• 250 kbits/s

• Operates at 2.4 GHz

• Up to 400 ft, unobstructed

• 45 mA transmit current

• 2.1-3.6 supply Voltage

• 250 kbits/s

• Operates at 2.4 GHz

• Up to 1 mi, unobstructed

• 295 mA transmit current

• 3.0-3.4 supply Voltage

Zigbee Pro

Antennas• U.FL

o When Size is a concerno Up to 6 GHZo Can be surface mounted or

printed on the boardo Omnidirectional

• ¼ Wave Whipo Omnidirectional

• RP-SMAo Depending on size, rated up to 18

GHz, 26.5 GHzo Omnidirectional

• More information: http://www.sparkfun.com/datasheets/Wireless/Zigbee/XBee-Datasheet.pdf

Zigbee Products

• If someone wants to build a Zigbee compliant product must have their design base on the Zigbee based stack protocol

• Zigbee Alliance, a collection of companies that publish the Zigbee standard, are in charge of design

Stack Architecture • Physical layer implemented through IEEE

802.15.4, which defines the frequency bands of operation, 2.4 GHz, 915 Mhz, 868 Mhz. o maximum length of packet, 127 bytes.

• Stack Featureso NWK – Network layer support,

mechanism to manage the networks. Meshes, routing of data, discovery and maintenance, etc.

o APS – Application support sublayer, mechanism to forward messages between devices.

o ZDO – Zigbee device object, defines the role of the node within the Zigbee network.

o SSP- Manages security protocols. Two types; residential, one NWK key and commercial, two NWK keys.

• Application Profiles- Custom software programmed by the user

Zigbee Networking

Pros and Cons

Advantages• Mesh networking allows

for longer distance communication

• With no central point failure, communication is more robust

• Low power and long life

• Low cost

Disadvantages• Smaller range than Wi-Fi

• Lower data rates than bluetooth and Wi-Fi

Applications• Because of Zigbee characteristics,

applications focus on monitoring.

• Example, Home Automationo Saves on energy bills by

monitoring temperature, motion in rooms.

o Can manage home security.

• Example, Health Careo Targeted at persons with

chronic health care issues.o Pill dispenser and monitor.o Sensor that transmit alarm calls

if triggered.

Outline

1. Overview of Antennas

2. RF Communication

3. Wi-Fi

4. Zigbee

5. Bluetootha. Overview

b. Antennas

c. Applications

6. Comparison

• Designed as a wireless cable replacement

• “Bluetooth” was the early name for the special interest group

• Uses radio waves to transmit over short distances. PAN’s of up to 164 feet

BluetoothA Quick Overview

Networks

• Piconet – One host device with up to 7 active slave devices

• Scatternet – Collection of piconets wherein host devices are master of their respective piconet, but slave to other devices

Versions• Bluetooth 1.1

o Ratified in IEEE 802.15.1 standard. Buggy but operational

• Bluetooth 1.2

o Higher data rates of 721 Kbit/s

o Adaptive frequency hopping

o Faster connection and discovery

• Bluetooth 2.0

o Introduction of EDR (Enhanced Data Rates) of 2.1 Mbits/s. Achieved by using Gaussian frequency shift keying

o Lower power consumption

o Backwards compatible with 1. versions

• Bluetooth 2.1

o Also backward Compatible.

o Extended inquiry response, provides information regarding connectivity during device inquiry.

o Secure Simple Pairing, improves pairing and connectivity of Bluetooth device and host.

• Bluetooth 3.0

o Ultra wide broadband allows for even faster data rates of up to 24 Mbit/s.

o Enhanced power control allows for very low power consumption.

• Bluetooth 4.0

o Ultra low power consumption during idle state.

Antennas• PIFA Antenna

o Printed antenna, usually about 20 to 25 mm in length

o Placed on the edge of PCBo 2.4 GHz

• Ceramic Dielectric Antennao Smaller than PIFAo Forms a concentrates electric field by wrapping

around a high-dk ceramic slab

• LMX9820/A Antennao About 14 x 10 mm in sizeo Metal shielding protects the components from the

electric field of antenna

• LMX9830 Antennao About 6 x 9 mm in sizeo Unshielded, so it cannot be placed near other

elements

Applications

• Characteristics make it ideal for short range PAN applications

• General, wireless communication between wireless devices

• Example, connectivity between wireless mouse and laptop

Outline

1. Overview of Antennas

2. RF Communication

3. Wi-Fi

4. Zigbee

5. Bluetooth

6. Comparison

Comparison

*Source: Digikey

Wifi Zigbee Bluetooth

IEEE Standard 802.11 802.15.4 802.15.1

Frequency Band 2.4, 3.6, 5 GHz 2.4 GHz 2.4 Ghz

Data Rates 54 Mbits/s 250 Kbits/s 1 Mbit/s

Power Consumption

High Very Low, Low Medium

Antennas Yagi Antenna; Cantenna

U.FL, 1/4 Wave Whip, RP-SMA

PIFA ,Ceramic Dielectric, LMX9830

Range 500 ft Outdoor 400 ft, 1 mi Outdoor

35 -300 ft Outdoor

Cost 20-80$ (module) 20-30$* 40-100$*

Application Example

Internet Access (Hotspots); Mobile Applications

Home AutomationHealthcare Monitoring

Wireless mouse, Wireless headset

ReferencesAntennas

• http://k9erg.tripod.com/theory.htm

• http://en.wikipedia.org/wiki/Radio_frequency

• http://en.wikipedia.org/wiki/Antenna_(radio)

• http://www.mobilemark.com/engineering/antenna-theory-simplified.html

• http://www.tselectronic.com/tech_notes/antenna_spec.php

• http://www.afar.net/tutorials/antennas/

• http://www.qsl.net/co8tw/vertical.htm

• http://electronics.howstuffworks.com/question490.htm

• http://zaielacademic.net/networking_wireless/wireless_antennas.htm

• http://en.wikipedia.org/wiki/Antenna_aperture

RF Modules• http://en.wikipedia.org/wiki/Rf_module

Wi-Fi• http://www.creativeworld9.com/2011/03/abstract-and-full-paper-on-wi-fi.html

• http://en.wikipedia.org/wiki/Wi-Fi

• http://compnetworking.about.com/od/homenetworkhardware/a/introduction-to-wifi-wireless-antennas.htm

• http://www.radiolabs.com/Articles/wifi-antenna.html

Zigbee• http://www.sparkfun.com/datasheets/Wireless/Zigbee/XBee-2.5-Datasheet.pdf

• http://www.lsr.com/downloads/products/330-0098.pdf

• http://www.stg.com/wireless/ZigBee_comp.html

• http://en.wikipedia.org/wiki/Zigbee

Bluetooth• http://en.wikipedia.org/wiki/Bluetooth

Questions?