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Introduction to RF design
Mexico – June 2008Mike Claassen
Agenda
• Part I: Getting Acquainted with the CC Portfolio– Overview of a Low Power Wireless System
• Overview of the TI Low Power Wireless Portfolio• Features of the CC2500/CC1100 Radios• Tools Overview: Packet Sniffer, RF Studio, RF Toolsticks
– Hands On – Performing a Simple Tx/Rx using the CC2500 and the RF Studio Software Design Tools
• Typical MSP430 / CC2500 Radio Connection• Overview of the RF Studio Sotware• Running a simple Tx/Rx while monitoring the CC2500 Radio Status
State Machine– Overview and Hands-On: Intermediate Radio Features
• Adding Variable Packet & Address Filtering• Adding GDO / GPIO Interrupts
– Overview and Demo of Advanced Radio Features• Frequency Hopping• Wake on Radio Power Profile
Agenda - Continued
• Part II: Getting Acquainted TI Stack Offering– Comparison of 802.15.4, SimpliciTI, and Zigbee Stacks
• Features and Benefits• What is right for your application• Device offering
– SimpliciTI Overview• SimpliciTI Components• Typical Network Topologies• Typical Payload Overview
– Hands On: Using SimpliciTI to Communicate End Device to End Device in a Typical Network
– Overview and Hands On: Adding an Access Point – Overview of the Zaccel Integrated Zigbee Modem– Hands On – Using Zaccel in a Zigbee Network
• Part III: Hardware Considerations for a LPW Design
Introduction to a Low Power Wireless System
• Definitions
• Radio Modulation Schemes
• Radio Frequency Spectrum
• Network Types
• Low Power RF Components
• Tools
Agenda
Definitions
RF Power Definitions
• dBm – power referred to 1 mW
PdBm=10log(P/1mW)0dBm = 1mW20 dBm = 100mW30 dBm = 1W-110dBm = 1E-11mW = 0.00001nW
50 Ω load : -110dBm is 0.7uV
• dBc – power referred to carrier
• Rule of thumb:
• 6dB increase => twice the range• 3dB increase => roughly doubles the
dbm power
dBm to Watt
About dBm and W
– Voltage Ratio aV = 20 log (P2/P1) [aV] = dB
– Power Ratio aP = 10 log (P2/P1) [aP] = dB
– Voltage Level V‘ = 20 log (V/1µV) [V‘] = dBµV
– Power Level P‘ = 10 log (P/1mW) [P‘] = dBm
e.g. 25mW max. allowed radiated power in the EU SRD bandP‘ = 10 log (25mW/1mW) = 10 * 1.39794 dBm ~ 14 dBm
dBm Typicals
dBm level Power Notes80 dBm 100 kW Typical transmission power of FM radio station with 30-40 miles range
60 dBm 1 kW Typical combined radiated RF power of microwave oven elements
36 dBm 4 W Typical maximum output power for a Citizens' band radio station(27 MHz) in many countries
30 dBm 1 W Typical RF leakage from a microwave oven - Maximum output power for DCS 1800 MHz mobile phone
27 dBm 500 mW Typical cellular phone transmission power
20 dBm 100 mW Bluetooth Class 1 radio, 100 m range (maximum output power from unlicensed FM transmitter). Typical wireless router transmission power.
4 dBm 2.5 mW Bluetooth Class 2 radio, 10 m range
0 dBm 1.0 mW Bluetooth standard (Class 3) radio, 1 m range
−10 dBm 100 µW Typical maximum received signal power (−10 to −30 dBm) of wireless network
−70 dBm 100 pW Typical range (−60 to −80 dBm) of Wireless received signal power over anetwork
−127.5 dBm 0.178 fW Typical received signal power from a GPS satellite
For more information: http://en.wikipedia.org/wiki/DBm
Radio Definitions
• PERPacket Error Rate, % of packets not received successfully
• SensitivityLowest input power with acceptable link quality (typically 1% PER)
• Deviation/separationFrequency offset between a logic ‘0’ and ‘1’ using FSK modulation
• Blocking/selectivityHow well a chip works in an environment with interference.
Radio Modulation Schemes
Wireless Communication Systems
Low Frequency Information Signal
(Intelligence)
High Frequency Carrier
Modulator Amplifier
Transmitter
Communication Channel
Amplifier Demodulator (detector)
Output transducer
Receiver
Amplifier
Modulation and Demodulation
digitalmodulation
digitaldata analog
modulation
radiocarrier
analogbasebandsignal
101101001 Radio Transmitter
synchronizationdecision
digitaldataanalog
demodulation
radiocarrier
analogbasebandsignal
101101001 Radio Receiver
Source: Lili Qiu
Clock and Data Recovery
• Data is asynchronous, no clock signal is transmitted. • Clock is recovered (trained) with the preamble.
Received Data Train
1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 0 0 1 1 0 0 1 0 1 0
Expected Preamble
4 clocks 2 clocks 1 clock
Recovered Clock Bit Time
Modulation Methods
• Starting point: We have a low frequency signal and want to send it at a high frequency
• Modulation: The process of superimposing a low frequency signal onto a high frequency carrier signal
• Three modulation schemes available:1. Amplitude Modulation (AM): the amplitude of the carrier varies
in accordance to the information signal2. Frequency Modulation (FM): the frequency of the carrier varies
in accordance to the information signal3. Phase Modulation (PM): the phase of the carrier varies in
accordance to the information signal
Digital Modulation – ASKThe modulation of digital signals is known as Shift KeyingAmplitude Shift Keying (ASK/OOK):
– Pros: simple, duty cycling (FCC), lower transmit current– Cons: susceptible to noise, wide spectrum noise
• Rise and fall rates of the carrier's amplitude can be adjusted to reduce the spectrum noise at low to medium data rates
• This is called Shaped OOK– Example: Many legacy wireless systems
1 0 1
t
Source: Lili Qiu
•Signal Space Diagram• Each axis represents a ‘symbol’
• OOK has two basis functions: sinusoid & no sinusoid
• OOK has two symbols: carrier & no carrier
• Distance between symbols predicts BER
10
Digital Modulation - FSKFrequency Shift Keying (FSK):
– Pros: Less susceptible to noise– Cons: Theoretically requires larger
bandwidth/bit than ASK– Popular in modern systems– Gaussian FSK (GFSK) has better
spectral density than 2-FSK modulation, i.e. more bandwidth efficient
1 0 1
t
1 0 1
Source: Lili Qiu
FSK modulation
FrequencyfcFc-df Fc+df
DIO=low DIO=high
Frequency deviation
Frequency separation= 2 x df
1
0
Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’
• Each basis function is ‘orthogonal’
• Distance between symbols predicts BER
Digital Modulation - PSK
Phase Shift Keying (PSK):– Pros:
• Less susceptible to noise• Bandwidth efficient
– Cons: Require synchronization in frequency and phase complicates receivers and transmitter
t
1 10
Source: Lili Qiu
10
Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’
• Each basis function is ‘orthogonal’
• Distance between symbols predicts BER
Digital Modulation – QPSK/OQPSKQuadrature Phase Shift Keying
– Pros: Symbol represents two bits of data– Cons: Phase in the signal can jump as
much as 180O causing out of band noise
Offest Quadrature Phase Shift Keying– Pros: Offsetting the signal limits the phase
jump to no more than 90O
http://en.wikipedia.org/wiki/Phase-shift_keying
2CA
1α
2α
2CA
11
10
00
01
Digital Modulation - MSKMinimum Shift Keying (MSK):
– Pros: Difference in Frequency is Half the bit rate– Very bandwidth efficient – Reduced Spectrum noise
– Cons: Require synchronization in frequency and phase complicates receivers and transmitter
– Example: IEEE 802.15.4 / ZigBee
t
1 10 0
10
Signal Space Diagram / Signal Constellation• Each axis represents a ‘symbol’
• Each basis function is ‘orthogonal’
• Distance between symbols predicts BER
Radio Frequency Spectrum
Electromagnetic Spectrum
Source: JSC.MIL
SOUND LIGHTRADIO HARMFUL RADIATION
VHF = VERY HIGH FREQUENCYUHF = ULTRA HIGH FREQUENCYSHF = SUPER HIGH FREQUENCY EHF = EXTRA HIGH FREQUENCY
4G CELLULAR56-100 GHz
2.4 GHzISM band
ISM bands315-915 MHz
UWB3.1-10.6 GHz
ISM/SRD Bands
The 2400–2483.5 MHz band is available for license-free operation in most countries
• 2.4 GHz Pros– Same solution for all markets without SW/HW alterations– Large bandwidth available, allows many separate channels
and high datarates– 100% duty cycle is possible– More compact antenna solution than below 1 GHz
• 2.4 GHz Cons– Shorter range than a sub 1 GHz solution (with the same
current consumption)– Many possible interferers are present in the band
The “World-Wide” 2.4 GHz ISM Band
2.4 GHz ISM-band devices
Source: Eliezer & Michael, TI
• Due to the world-wide availability of the 2.4GHz ISM band it is getting more crowded day by day
• Devices such as Wi-Fi, Bluetooth, ZigBee, cordless phones, microwave ovens, wireless game pads, toys, PC peripherals, wireless audio devices and many more occupy the 2.4 GHz frequency band
Power
Microwave oven
Cordless Frequency802.11b/g
• The ISM bands under 1 GHz are not world-wide
• Limitations vary a lot from region to region and getting a full overview is not an easy task– Sub 1GHz Pros
• Better range than 2.4 GHz with the same output power and current consumption (assuming a good antenna – not easy for a limited space)
– Sub 1GHz Cons• Since different bands are used in different markets it is
necessary with custom solutions for each market• More limitations to output power, data rate, bandwidth etc. than
the 2.4 GHz • Duty cycle restrictions in some regions• Interferers are present in most bands
Sub 1GHz ISM Bands
Sub 1GHz ISM bands• 902-928 MHz is the main frequency band
• The 260-470 MHz range is also available, but with more limitations
• The 902-928 MHz band is covered by FCC CFR 47, part 15
• Sharing of the bandwidth is done in the same way as for 2.4 GHz: • Higher output power is allowed if you spread your transmitted power and
don’t occupy one channel all the timeFCC CFR 47 part 15.247 covers wideband modulation
• Frequency Hopping Spread Spectrum (FHSS) with ≥50 channels are allowed up to 1 W, FHSS with 25-49 channels up to 0.25 W
• Direct Sequence Spread Spectrum (DSSS) and other digital modulation formats with bandwidth above 500 kHz are allowed up to 1W
• FCC CFR 47 part 15.249• ”Single channel systems” can only transmit with ~0.75 mW output power
Frequency Spectrum AllocationUnlicensed ISM/SRD bands:• USA/Canada:
– 260 – 470 MHz (FCC Part 15.231; 15.205)– 902 – 928 MHz (FCC Part 15.247; 15.249)– 2400 – 2483.5 MHz (FCC Part 15.247; 15.249)
• Europe:– 433.050 – 434.790 MHz (ETSI EN 300 220)– 863.0 – 870.0 MHz (ETSI EN 300 220)– 2400 – 2483.5 MHz (ETSI EN 300 440 or ETSI EN 300 328)
• Japan:– 315 MHz (Ultra low power applications)– 426-430, 449, 469 MHz (ARIB STD-T67)– 2400 – 2483.5 MHz (ARIB STD-T66)– 2471 – 2497 MHz (ARIB RCR STD-33)
ISM = Industrial, Scientific and MedicalSRD = Short Range Devices
Short-Range Wireless
Different Value Drivers for Different Applications
1000m
•Headsets•PC Peripherals•PDA/Phone
• Building Automation• Residential Control • Industrial • Tracking • Sensors• Home Automation / Security• Meter Reading
Data Rate (bps)
100k 1M 10M10k1k
Range
100m
10m
1m
ZigBee/802.15.4
•PC Networking•Home Networking•Video Distribution
Wi-Fi/802.11
Proprietary Low Power Radio•Gaming•PC Peripherals•Audio•Meter Reading•Building Mgmt.•Automotive
UWB•Wireless USB•Video/audio links
Sub 1GHz Product Selection
2.4GHz Portfolio
Stack Considerations
Physical
MAC
App
Software Stack Considerations
2.4 GHz/ ISM Band Radio Data
Preamble Sync Word Radio Payload (Max 255 Bytes)** Physical
Layer
Proprietary Radio – CC2500/CC1100
Length
Field*
Address
Field*
RSSI
LQI*
CRC 16
Check
Data Payload
(Max 60 Bytes)
Proprietary Stack
Up to 64 Bytes
2-24 Bytes 2or4 Bytes 1 Byte 1 Byte 0-60 Bytes 2 Bytes 2 Bytes
MAC
Layer
* Optional Settings for the radio – activating these settings drops the useable payload** Requires monitoring at refill of the 64Byte Tx Buffer
2.4G / ISM Band Radio Data
Preamble Sync Word Radio Payload (Max 64 Bytes)
Physical
MRFI
Layer
SimpliciTI Example – CC2500/CC1100
Length
Field
Address
Field Off
RSSI
LQI
CRC 16
Check
Data Payload
(Max 60 Bytes)
Custom Application
Up to 50 Bytes
2-24 Bytes 2or4 Bytes 1 Byte 0 – 61 Bytes 2 Bytes 2 Bytes
Destination
Address
MAC
LayerSource
Address
Port
Data
Device
Info
TractID
Info
4 Bytes 4 Bytes 1 Byte 1 Byte 1 Byte 0 to 50 Bytes
SimpliciTI
Payload
2.4G Radio Data
Synchronization
Header
Radio Specific
HeaderRadio Payload (Max 127 Bytes) Physical
Layer
Frame
Control
Sequence
Number
Address
Info
Frame
Check
Command
Payload
802.15.4 OSI Layers
Frame
Control
Sequence
Number
Address
Info
Frame
Check
Beacon
Payload
Frame
Control
Sequence
Number
Address
Info
Frame
Check
Data
Payload
Frame
Control
Sequence
Number
Frame
Check
MAC
Layer
Data Frame
Command Frame
Beacon Frame
ACK Frame
2 Bytes 1 Byte 0-20 Bytes <= 104B 2 Bytes
2.4G Radio Data
Synchronization
Header
Radio Specific
HeaderRadio Payload (Max 127 Bytes) Physical
Layer
Zigbee Stack on 802.15.4
Frame
Control
Sequence
Number
Address
Info
Frame
Check
Payload
<= 104BMAC
Layer802.15.4 Frame
2 Bytes 1 Byte 0-20 Bytes <= 104B 2 Bytes
Network Layer (NWK)
Application Layer (APS)
Zigbee Device
Object 0
Application
Object 1
Application
Object xxxSecurity
Service
Provider
Network Types
Network Types
Data pathPoint to Point
Network Types
Data pathStar
Network Types
Data pathMesh
Network Types
Data pathMesh
Which Protocol?
Radio HardwareProprietary
SimpliciTI 802.15.4 Zigbee
Best Suited Topology
Point to Point Point to PointStar Network
Star Network
Source & DestinationFair
Medium
CC2520CC2530
Mesh
Addressing Destination Source & Destination
Source & Destination
Code Size Minimal <1k Good < 4k Large < 64k
Complexity Low Medium Low - Zaccel
Target Devices
CC25x0CC11x0
CC25x0CC11x0
CC2480
Low Power RF Components
Basic Building Blocks of an RF System• RF-IC
– Transmitter– Transceiver– System-on-Chip (SoC);
typically transceiver with integrated uC
• Crystal– Reference frequency for the
LO and the carrier frequency
• Balun– Balanced to unbalanced– Converts a differential signal
to a single-ended signal or vice versa
• Impedence Matching• Filter
– Used if needed to pass regulatory requirements / improve selectivity
• Antenna
RF-ICBalun
& Match
Filter
Crystal
Antenna(50Ω)
RF-ICs Examples• Transmitter
– CC1050, CC1150, and CC2550
• Transceiver – CC1100, CC2500, CC2400, and CC2420
• System-on-Chip (SoC) – Transceiver with a built-in micro controller– CC1110, CC2510, CC2430
Crystals• Provides reference frequency for Local Oscillator (LO) and
the carrier frequency• Important characteristics:
– Tolerance[ppm], both initial spread, aging & over temperature
– Price, often a price vs. performance trade-off– Size
• Various types:– Low Power crystals (32.768 kHz)
• Used with sleep modes on e.g. System-on-Chips – Crystals
• Thru hole• Tuning fork• SMD
– Temperature Controlled Crystal Oscillators (TCXO)• Temperature stability – some narrowband applications
– Voltage Controlled Crystal Oscillators (VCXO)– Oven Controlled Crystal Oscillators (OCXO)
• Extremely stable
Balun & Matching
Balun and matching towards antenna
Differential signal out of the chip
Single ended signal
Dig
ital I
ntef
ace
6 G
DO
0
7 C
Sn
8 XO
SC
_Q1
9 AV
DD
10 X
OSC
_Q2
SI 2
0
GN
D 1
9
DG
UA
RD
18
RBI
AS
17
GN
D 1
6
Antennas, commonly used
• PCB antennas– Little extra cost (PCB)– Size demanding at low frequencies– Good performance possible– Complicated to make good designs
• Whip antennas– Expensive (unless piece of wire)– Good performance– Hard to fit in may applications
• Chip antennas– Expensive– OK performance– Small size
Notes on Antennas
• The antenna is VERY important if long range is important
• A quarter wave antenna is an easy and good solution, but it is not small (433 MHz: 16.4 cm, 868 MHz: 8.2 cm)– You can “curl up” such an antenna and make a helical
antenna. This is often a good solution since it utilizes unused volume for a product.
• If you need long range and have limited space, then talk to an antenna expert !
Extending the Range of an RF System
1. Increase the Output power– Add an external Power
Amplifier (PA)
2. Increase the sensitivity– Add an external Low Noise
Amplifier (LNA)
3. Increase both output power and sensitivity– Add PA and LNA
4. Use high gain antennas– Regulatory requirements
need to be followed
RF-IC Balun & Match
2/1 Switch2/1 Switch
LNA
PA Filter
Crystal
Antenna(50Ω)
Adding an External PACC2420EM PA DESIGN• Signal from TXRX Switch pin level shifted and
buffered– Level in TX: 1.8 V, level for RX and all other
modes: 0V• CMOS & GaAs FET switches assures low RX
current consumption• Simpler control without external LNA
– No extra signal is needed from MCU to turn off LNA in low power modes
RF_P
TXRX_SWITCH
RF_N
CC2420
BALUN
TX/RX Switch
ANT
TX/RX Switch
PA
LP filter
TX path
RX path
Controllogic and
biasnetwork
19.7 mA19.7 mARX current
580 meter230 meterLine of Sight Range
-93.1 dBm-94 dBmSensitivity
9.5 dBm0 dBmOutput power
30.8 mA17.4 mATX current
CC2420EM w/PA
CC2420EM
19.7 mA19.7 mARX current
580 meter230 meterLine of Sight Range
-93.1 dBm-94 dBmSensitivity
9.5 dBm0 dBmOutput power
30.8 mA17.4 mATX current
CC2420EM w/PA
CC2420EM
Radio Range – Free Space Propagation
• How much loss can we have between TX and RX?• Friis’ transmission equation for free space propagation:
or
– Pt is the transmitted power, Pr is the received power– Gt is the transmitter, Gr is the receiver antenna gain– Lambda is the wavelength– d is the distance between transmitter and receiver, or the range
22
2
)4( dGGPP rtt
r πλ
=dGGPP rttr log204
log20 −⎟⎠⎞
⎜⎝⎛+++=πλ
d = λ PtGtGr4π Pr
Radio Range – ”real life”
• How much loss can we really have TX to RX?
• 120 dB link budget at 433 MHz gives approximately 2000 meters (Chipcon rule of thumb)
• Based on the emperical results above and Friis’equation estimates on real range can be made
• Rule of Thumb:– 6 dB improvement ~ twice the distance– Double the frequency ~ half the range (433 MHz longer range
than 868 MHz)
Important Factors for Radio Range
• Antenna (gain, sensitivity to body effects etc.)
• Sensitivity
• Channel Selectivity
• Output power
• Radio pollution (selectivity, blocking, IP3)
• Environment (Line of sight, obstructions, reflections, multi-path fading)
Development Tools and EVMs
SimpliciTI: eZ430 RF-2500
Zigbee: eZ430-RFZACC06
MSP430FG4619 Exp Board
CC2500EMK
USB FET
SOC: Smart RF 05EB
CC2500EMKLCD (SPI)
CC2511
USB
UARTJOYSTICK
POTMETER
Debug interface
IO jumpersJumpers for current measurements
BUTTONS
LED
Flash (SPI)
EMK Adapter
Interface with the MSP430 SmartRF05EB + CCMSP-EM + CCxxxxEM
MSP430F2618
32KHz XTAL
Slot for high
speed XTAL
SPI Modes
BSL interface
JTAG
interface
EM Connector
MSP430
ports
CC2500EMK
CC2520 Development kit
CC2520 DK: • 2 boards with the MSP430F2618 • 3 EMs + antennas (the small RF) boards• 3 EBs with LCD and USB (CC2511)• Packet Error Rate software
(runing on the MSP)• Smart RF studio• Packet sniffer (ZigBee) – March
CC2520 EMK:• 2 CC2520 EMs + 2 antennas
Software (free of charge for MSP430):• ZigBee stack (March 08)• IEEE 802.15.4 MAC• SimpliciTI – (March 08)
CC2520 EM
Free Design Tools – Packet Sniffer
http://www.ti.com/litv/zip/swrc045g
Free Design Tools – RF Studio
http://focus.ti.com/docs/toolsw/folders/print/smartrftm-studio.html
Software Stacks – Zigbee Z-Stack• Z-Stack™ is compliant with the ZigBee® 2006 specification and supports multiple
platforms including the CC2430 System-on-Chip and the CC2420 and MSP430 platform.
• Z-Stack also has support for CC2431 which enables users to create ZigBee applications that can change behavior based on the nodes current location in the network.
• The Z-Stack has been awarded the ZigBee Alliance's golden unit status by the ZigBee test house TÜV Rheinland and is used by thousands of ZigBee developers world wide.
• Z-Stack version 1.4.3 supports the application feature called SimpleAPI. This API was designed from the point of view of the application developer rather than the ZigBeespecification but it still provides a ZigBee Compliant Platform (ZCP). This is a good way for application developers to quickly build ZigBee-based wireless mesh networked applications. Two sample applications are provided to illustrate the use of the SimpleAPI, a sensor data collection network application and a home automation network application. The project file for the sample applications is in the Samples\SimpleApp.
• Z-Stack is well suited for:– Monitoring and control applications – Wireless sensor networks – Home and building automation – Alarm and security – Asset tracking – Applications where interoperability is required – Applications that require a free world wide ISM band (2.4 GHz)
http://focus.ti.com/docs/toolsw/folders/print/z-stack.html
Free Software Stacks - SimpliciTI
http://focus.ti.com/docs/toolsw/folders/print/simpliciti.html
Introduction to Low Power Wireless Devices
Questions?
Mike ClaassenTexas Instruments