Computer Science Department University of Virginia Gang Zhou 1 Spread Spectrum and CC2420.

11

Computer Science DepartmentUniversity of Virginia

Gang Zhou <[email protected]>

Spread Spectrum and CC2420

22

Group Presentation Gang ZhouOutline Outline

Spread Spectrum TheorySpread Spectrum Theory Definition of Spread Spectrum, DSSS and FHSSDefinition of Spread Spectrum, DSSS and FHSS Basic Principle of DSSSBasic Principle of DSSS Performance in the Presence of InterferencePerformance in the Presence of Interference

CC2420 RadioCC2420 Radio Main featuresMain features IEEE 802.15.4 Frame FormatIEEE 802.15.4 Frame Format Modulation and Spreading ProcessModulation and Spreading Process

Tinyos and MicaZTinyos and MicaZ TinyOS Module WrappingTinyOS Module Wrapping MicaZ HardwareMicaZ Hardware

33

Group Presentation Gang ZhouDefinition of Spread SpectrumDefinition of Spread Spectrum

SS is a transmission technique in which a pseudo-SS is a transmission technique in which a pseudo-noise code, independent of the information data, noise code, independent of the information data, is employed as a modulation waveform to is employed as a modulation waveform to “spread” the signal energy over a bandwidth “spread” the signal energy over a bandwidth much greater than the signal information much greater than the signal information bandwidth. At the receiver the signal is bandwidth. At the receiver the signal is “despread” using a synchronized replica of the “despread” using a synchronized replica of the pseudo-noise code.pseudo-noise code. A transmission techniqueA transmission technique Data independent PN codeData independent PN code Spread the energy in transmitter sideSpread the energy in transmitter side Despread the energy in receiver sideDespread the energy in receiver side

44

Group Presentation Gang ZhouDSSS and FHSSDSSS and FHSS

DSSSDSSS A pheudo-noise sequence pnA pheudo-noise sequence pntt generated at the generated at the

modulator, is used in conjunction with an M-ary PSK modulator, is used in conjunction with an M-ary PSK modulation to modulation to shift the phase of the PSK signalshift the phase of the PSK signal pseudorandomly.pseudorandomly.

FHSSFHSS A pseudo-noise sequence pnA pseudo-noise sequence pntt generated at the generated at the

modulator is used in conjunction with an M-ary FSK modulator is used in conjunction with an M-ary FSK modulator to modulator to shift the carrier frequency of the FSK shift the carrier frequency of the FSK signalsignal pseudorandomly. pseudorandomly.

We focus on DSSS since MICAZ uses DSSS.We focus on DSSS since MICAZ uses DSSS.

55

Group Presentation Gang ZhouBasic Principle of DSSSBasic Principle of DSSS

Input:Input: Binary data dBinary data dtt with symbol rate R with symbol rate Rss = 1/T = 1/Tss Pseudo-noise code pnPseudo-noise code pntt with chip rate R with chip rate Rcc = 1/T = 1/Tcc (an integer (an integer

of Rof Rss))

Spreading:Spreading: Multiply dMultiply dt t with PN sequence pnwith PN sequence pnt t

The effect of multiplication is to spread the baseband The effect of multiplication is to spread the baseband bandwidth Rbandwidth Rss of d of dtt to the bandwidth of R to the bandwidth of Rcc..

Despreading: the received baseband signal rxDespreading: the received baseband signal rxbb is is multiplied with the PN sequence pnmultiplied with the PN sequence pnrr:: If pnIf pnrr = pn = pntt, the recovered data is produced on d, the recovered data is produced on drr. To . To

multiply is to despread.multiply is to despread. If pnIf pnrr ≠ pn ≠ pntt, no despreading action. , no despreading action.

66

Group Presentation Gang ZhouPerformance in the presence of Performance in the presence of interferenceinterference

Received signal: rxReceived signal: rxbb = tx = txbb + i = d + i = dtt . pn . pntt + i + i

ddr r = rx= rxbb . pn . pntt = d = dtt . pn . pntt . pn . pntt + i . pn + i . pntt

pnpntt . pn . pntt = +1 for all t = +1 for all t

ddrr = d = drr + i . pn + i . pntt

Hence:Hence:The data signal is reproducedThe data signal is reproduced

The interference signal is spreaded, that is, energy The interference signal is spreaded, that is, energy spreaded. spreaded.

77

Group Presentation Gang Zhou

The essence behind the interference rejection The essence behind the interference rejection capability of a spread spectrum system is that:capability of a spread spectrum system is that: The useful signal (data) gets multiplied twice by the The useful signal (data) gets multiplied twice by the

PN sequencePN sequence But the interference signal gets multiplied only onceBut the interference signal gets multiplied only once

The spread spectrum signal has a lower power The spread spectrum signal has a lower power density than the directly transmitted signal.density than the directly transmitted signal. Compared with the direct signal, the spread spectrum Compared with the direct signal, the spread spectrum

signal looks like noise signal, weak and energy signal looks like noise signal, weak and energy spreaded. spreaded.

The spread spectrum signal is resistant to:The spread spectrum signal is resistant to: InterferenceInterference Multipath fadingMultipath fading

88





99

Group Presentation Gang ZhouMain featuresMain features

DSSS baseband modem with 2 Mchips/s and 250kbps DSSS baseband modem with 2 Mchips/s and 250kbps effective data rateeffective data rate

Q-QPSK with half sine pulse shaping modulationQ-QPSK with half sine pulse shaping modulation 128 (RX) + 128 (TX) byte data buffering128 (RX) + 128 (TX) byte data buffering Low current consumption (RX: 19.7 mA, TX: 17.4 mA)Low current consumption (RX: 19.7 mA, TX: 17.4 mA) Low supply voltage (2.1 – 3.6 V) with on-chip voltage Low supply voltage (2.1 – 3.6 V) with on-chip voltage

regulatorregulator Programmable output powerProgrammable output power 16 available frequency channels (IEEE 802.15.4 16 available frequency channels (IEEE 802.15.4

standard)standard) Fc = 2450 + 5 (k-11) MHz, k = 11, 12, …, 26Fc = 2450 + 5 (k-11) MHz, k = 11, 12, …, 26

Hardware MAC encryptionHardware MAC encryption

1010


High sensitivity (-94 dBm)High sensitivity (-94 dBm) High adjacent channel rejection (39 dB)High adjacent channel rejection (39 dB) High alternate channel rejection (46 dB)High alternate channel rejection (46 dB)

1111

Group Presentation Gang ZhouIEEE 802.15.4 Frame FormatIEEE 802.15.4 Frame Format

Synchronization Header:Synchronization Header:Preamble sequence is 4 bytes of 0x00 (length configurable)Preamble sequence is 4 bytes of 0x00 (length configurable)The Start of Frame Delimiter is set to 0xA7 (content The Start of Frame Delimiter is set to 0xA7 (content configurable)configurable)A synchronization header is always transmittedA synchronization header is always transmitted

1212


Length Field:Length Field:Means the number of bytes in the MPDUMeans the number of bytes in the MPDUThe most significant bit is reserved, so the maximum value is The most significant bit is reserved, so the maximum value is 127127

1313


1414


Frame Check Sequence:Frame Check Sequence:FCS is calculated over MPDUFCS is calculated over MPDUFCS is automatically generated and verified by hardware, if FCS is automatically generated and verified by hardware, if enabled.enabled.The FCS polynomial is: xThe FCS polynomial is: x1616 + x + x1212 + x + x55 + 1 + 1

1515


Acknowledge Frame:Acknowledge Frame:If AUTOACK is enabled, an acknowledge frame is transmitted If AUTOACK is enabled, an acknowledge frame is transmitted for all incoming frames accepted by the address recognition for all incoming frames accepted by the address recognition with the acknowledge request flag set and a valid CRC.with the acknowledge request flag set and a valid CRC.The acknowledge frame is transmitted 12 symbol (hardware The acknowledge frame is transmitted 12 symbol (hardware switch time) periods after the last symbol of the incoming switch time) periods after the last symbol of the incoming frame.frame.

1616

Group Presentation Gang ZhouModulation and Spreading ProcessModulation and Spreading Process

The general modulation process (3 steps)The general modulation process (3 steps) Step 1:Step 1: Each byte is divided into two symbols, 4 bits Each byte is divided into two symbols, 4 bits

each. The least significant symbol is transmitted first. each. The least significant symbol is transmitted first. Step 2:Step 2: Each symbol is mapped to one out of 16 pseudo- Each symbol is mapped to one out of 16 pseudo-

random sequences, 32 chips each.random sequences, 32 chips each. Step 3:Step 3: The chip sequence is then transmitted at 2 The chip sequence is then transmitted at 2

MChips/s, with the least significant chip transmitted first MChips/s, with the least significant chip transmitted first for each symbol.for each symbol.

1717


Step 2: Step 2: Each symbol is mapped to one out of 16 pseudo-Each symbol is mapped to one out of 16 pseudo-random sequences, 32 chips each.random sequences, 32 chips each.

1818


Step 3: Step 3: The chip sequence is then transmitted at 2 MChips/s, with The chip sequence is then transmitted at 2 MChips/s, with the least significant chip transmitted first for each symbol.the least significant chip transmitted first for each symbol. The chip sequences are modulated onto the carrier using Q-The chip sequences are modulated onto the carrier using Q-

QPSK with half-sine pulse shaping.QPSK with half-sine pulse shaping. Even-indexed chips are modulated onto the in-phase (I) carrier.Even-indexed chips are modulated onto the in-phase (I) carrier. Odd-indexed chips are modulated onto the quadrature-phase Odd-indexed chips are modulated onto the quadrature-phase

(Q) carrier.(Q) carrier.

1919


A question: Does CC2420 uses A question: Does CC2420 uses strictstrict DSSS? DSSS? I guess the answer is no! (I may be wrong.)I guess the answer is no! (I may be wrong.) My reason:My reason:

In CC2420, chip sequences are used to represent the In CC2420, chip sequences are used to represent the data, while in DSSS, PN codes are used to multiply data, while in DSSS, PN codes are used to multiply the data, rather than to replace the data.the data, rather than to replace the data.

Then another question: Then another question: How to despread the data out from the received How to despread the data out from the received

signal?signal?

2020





2121

Group Presentation Gang ZhouTinyOS Module WrappingTinyOS Module Wrapping

Generic Comm

AM

CC2420Control

SpiByte

RandomLFSR

BackoffEncoding

DataControl(Freq,Power,etc )

CC2420RadioM

CC2420RadioC

HPLCC2420M

Read/Write CC2420 Registers/Commands

Transfer to/from TXFIFO/RXFIFO

Hardware Specific

High Speed Timer

Generic Comm

AM

CC2420Control

SpiByte

RandomLFSR

BackoffEncoding

DataControl(Freq,Power,etc )

CC2420RadioM

CC2420RadioC

HPLCC2420C

Read/Write CC2420 Registers/Commands

Transfer to/from TXFIFO/RXFIFO

Hardware Specific

High Speed Timer

HPLCC2420C

HPLCC2420M

TimerC

TimerM

MSP430TimerM

MSP430ClockM

HPLUSART0M

HPLCC2420C

HPLCC2420M

TimerC

TimerM

MSP430TimerM

MSP430ClockM

HPLUSART0M

Telos (TI MSP430)HPLCC2420C

HPLCC2420M

TimerC

TimerM

HPLClockHPLUARTM

HPLCC2420FIFOM

HPLCC2420C

HPLCC2420M

TimerC

TimerM

HPLClockHPLUARTM

HPLCC2420FIFOM

MicaZ (AVR)

2222

Group Presentation Gang ZhouMicaZ HardwareMicaZ Hardware IEEE 802.15.4/ZigBee compliant RF transceiverIEEE 802.15.4/ZigBee compliant RF transceiver

2.4 to 2.4835 GHz, a globally compatible ISM band2.4 to 2.4835 GHz, a globally compatible ISM band

Direct sequence spread spectrum radio which is resistant to Direct sequence spread spectrum radio which is resistant to RF interference and provides inherent data securityRF interference and provides inherent data security

250 kbps data rate250 kbps data rate

Runs TinyOS 1.1.7 and higher, including Crossbow’s reliable Runs TinyOS 1.1.7 and higher, including Crossbow’s reliable mesh networking stack software modulesmesh networking stack software modules

Plug and play with Plug and play with allall of Crossbow’s sensor boards, data of Crossbow’s sensor boards, data acquisition boards, gateways, and softwareacquisition boards, gateways, and software

2323

Group Presentation Gang ZhouReferencesReferences MPR/ MIB User’s Manual, MPR/ MIB User’s Manual, www.xbow.comwww.xbow.com IEEE 802.15.4 Standard, IEEE 802.15.4 Standard,

http://www.ieee802.org/15/pub/TG4.htmlhttp://www.ieee802.org/15/pub/TG4.html Ir. J. Meel, Spread Spectrum (SS), Ir. J. Meel, Spread Spectrum (SS), www.denayer.bewww.denayer.be Joe Polastre, IEEE 802.15.4: Platforms, Progress, and TinyOS, Joe Polastre, IEEE 802.15.4: Platforms, Progress, and TinyOS,

http://webs.cs.berkeley.edu/retreat-6-04/joep-nest-2004-sprinhttp://webs.cs.berkeley.edu/retreat-6-04/joep-nest-2004-springretreat-802154.pptgretreat-802154.ppt

Thanks! Any question?Thanks! Any question?

Date post:	19-Dec-2015
Category:	Documents
View:	213 times
Download:	0 times

Computer Science Department University of Virginia Gang Zhou 1 Spread Spectrum and CC2420.

Documents