DBPSK/DQPSK CCK - Home | College of Engineering and ...cs.uccs.edu/~gsc/pub/master/pjfong/UCCS...
Transcript of DBPSK/DQPSK CCK - Home | College of Engineering and ...cs.uccs.edu/~gsc/pub/master/pjfong/UCCS...
.11 tech. OVW 1
Module contents
Technologies overview
Spread SpectrumDirect Sequence
Frequency Hopping
ModulationDBPSK/DQPSK
CCK
.11 tech. OVW 2
OSI Reference Model: Phy
Network Oper. SystemNetwork LayerGuarantees delivery data
DriversLLC Layersend/receive data
LAN ControllerMAC Layerdata into/out frame
MODEMPhysical Layerframe into/out phy frame
Physical LayerPhysical Layer
IEEE: MAC LayerIEEE: MAC Layer
IEEE: LLC LayerIEEE: LLC Layer
Network LayerNetwork Layer
.11 tech. OVW 3
Wireless LAN TechnologiesWireless LAN Technologies
InfraredInfrared Spread SpectrumSpread
SpectrumNarrow BandNarrow Band
Direct SequenceDirect
Sequence FrequencyHopping
FrequencyHopping
Wireless LAN technologies(overview)
.11 tech. OVW 4
Wireless LAN technologies(Infrared)
low power infrared light as the carrierNo license requiredVery restricted mobility, limited coveragehigh data rate (10 Mbps, 16 Mbps)Line-of-Sight Infrared
no objects in the path between two stations
Diffuse Infrareduses reflections to set-up wireless link
.11 tech. OVW 5
Wireless LAN technologies(Narrow Band)
Dedicated band (18 GHz)License required
ISM band (915 MHz, 2.4 GHz, 5.8 GHz)unlicensed (special modulation)extremely low output power i.e. limited coveragehigh data rate (up to 10 Mbps) on short distance
Europe - DECT band (1.8 GHz)based on voice standard
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• 915 MHz only in the Americas (region 2)• 2.4 GHz for global availability (region 1,2,3)
1 2 3 4 6 8 10 20 30 40 60 100GHz
123
ISM Frequency AllocationsWorldwide
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Wireless LAN technologies(Spread Spectrum)
Unlicensed usage (ISM band)No line of sight requirement (indoor)High link reliabilityBuilt-in transmission securityTwo techniques used:
Direct SequenceFrequency Hopping
Standard RadioTransmission
Spread SpectrumTransmission
Frequency Spectrum (MHz)
2400 2500
PowerPower
FrequencyFrequency
88 103 2400FM Band
.11 tech. OVW 8
Module contents
Technologies overview
Spread SpectrumDirect Sequence
Frequency Hopping
ModulationDBPSK/DQPSK
CCK
.11 tech. OVW 9
Multiple Access MethodsMultiple users share the available spectrum
FREQUENCY
TIME
User 3User 2User 1
• Multiple users sharethe same frequencychannel sequentially
• Time slot sequencerepeats over and over
TDMA
TIME
FREQUENCY
CODE
CDMAalso known as “Spread Spectrum”
User 3User 2User 1
• Channel is “spread” over wide frequencyband
• Many users share the same frequencyband at the same time
• Each user is assigned a unique “code”to identify and separatethem
FREQUENCY
TIME
FDMA
1 2 3
Each user assigned adifferent frequency -like ordinary radio
.11 tech. OVW 10
Spread Spectrum TechnologiesDS vs. FH
Direct SequenceEach symbol is transmitted over multiplefrequencies at the same timeVery efficient (no overhead)Higher speed than FH at comparabledistancesSystem capacity (multiple channels)higher than FH
Frequency HoppingSequential use of multiple frequenciesHop sequence and rate will vary“End hop waste time”
COMPLETE WAVEBAND ALLOCATED
Time
Time
.11 tech. OVW 11
Spreading: Information signal (I.e. a “symbol”) is multiplied by a unique,high rate digital code which stretches (spreads) its bandwidth beforetransmission.Code bits are called “Chips”.Sequence is called “Barker Code”
Source andChannelCoding
RFModulator
CodeGenerator
X
Multiplier
Code Bits (Chips)
Digital Signal (Bits)
FrequencySpectrum
f
“Spread” FrequencySpectrum
f
Spread Spectrum TechnologiesDirect Sequence transmitter
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Spread Spectrum TechnologiesWhat happens during “spreading”
X
=
“symbol”
“Barker” sequence
Result of multiplication
Symbol time ts“1” “0”
Chiptime tc
Due to the multiplication of asymbol with Barker code, the“rate-of-change” increases witha factor 11This means that cycle rateincreases from 1 MHz to 11MHz
In terms of spectrum thismeans that after RFmodulation the signal is spreadfrom 2 MHz bandwidth to 22MHz bandwidth
2 Mhz 22 Mhz
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At the receiver, the spread signal is multiplied again by a synchronizedreplica of the same code, and is “de-spread” and recoveredThe outcome of the process is the original “symbol”
RFDemodulator
Channeland
SourceDecoding
CodeGenerator
X
Multiplied
Code Bits (Chips)
De-SpreadSignal
f
“Spread” FrequencySpectrum
f
Digital Signal (Bits)
Spread Spectrum TechnologiesDirect Sequence receiver
.11 tech. OVW 14
Spread Spectrum TechnologiesDe-spreading
Data
:11 chip code
Direct SequenceSpread Spectrum
Signal
+11
-11
+1
-1
Symboltime
When the incoming signal is de-spread, it results in either apositive (+) or a negative (-)“spike”
These “spikes” arrive at intervalsequal to the symbol time
A positive spike represents a “1”symbol, a negative spikerepresents a “0” symbol
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Spread Spectrum TechnologiesDirect Sequence receiver - effect of echoes
echo
echo
peak
Symboltime
Echoes may arrive at thereceiver, fluctuations can benoticed at positions other than atthe symbol time boundaries
These fluctuations are ignored asthe receiver will only interpret thespike at the synchronizationpoints (separated from each otherby the symbol time)
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Module contents
Technologies overview
Spread SpectrumDirect Sequence
Frequency Hopping
ModulationDBPSK/DQPSK
CCK
.11 tech. OVW 17
ModulationDBPSK (Differential Binary Phase Shift Keying)
I
Q
Bit Input Phase Change (+jω)0 01 π
Table 1, 1 Mb/s DBPSK Encoding Table.
.11 tech. OVW 18
I
Q
Dibit pattern (d0,d1)d0 is first in time Phase Change (+jω)
00 001 π/211 π10 3π/2 (-π/2)
Table 1, 2 Mb/s DQPSK Encoding Table
ModulationDQPSK (Differential Quadrature Phase Shift Keying)
.11 tech. OVW 19
CCK = Complementary Code KeyingIEEE 802.11 standard for high speed11 and 5.5 Mbps data ratesOutstanding high multi-path performanceOutstanding low-SNR performanceSeamless interoperability with existing DSMaintains QPSK chips at 11 MHz chip rateMaintains 3 frequency channelsFCC and MKK regulations satisfied
CCKTurbo 11 Mb approach
.11 tech. OVW 20
Data bits are encoded to a symbol which istransmitted in the form of 8 chipsFor Data-Rate = Medium Encoding means:
mapping 2 data bits to I or Q channel (in-Phase,Quaternary Phase)mapping 2 data bits to one of 4 ComplexCodewords
For Data-Rate = High Encoding means:mapping 2 data bits to I or Q channel (in-Phase,Quaternary Phase)mapping 6 data bits to one of 64 ComplexCodewords
Codewords are complex complementarycodes selected from a code set
CCKHow it works
5.5 MBpsCCK
8 chips
2 bits encoded to4 complex code words; 2-QPSK
11 MBpsCCK
8 chips
6 bits encoded to64 complex code words; 2-QPSK
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Pick One of 4 ComplexCodes *
MUX1:8
2
DATAIN
I OUT
Q OUT
1.375 MHz8 chips clocked with 11 MHz
11 MHz
1
1
Data Rate = 4 bits/symbol * 1.375 MSps = 5.5 MBps
Scrambler
1
1 *= Code Set:747B47B78B7BB8B7see next slide
CCKOperating at medium speed
.11 tech. OVW 22
Pick One of 64 ComplexCodes
MUX1:8
6
DATAIN
I OUT
Q OUT
1.375 MHz11 MHz
1
1
Data Rate = 8 bits/symbol * 1.375 MSps = 11 Mbps
Scrambler
1
1
Code Set is defined by formula:
},,,,
,,,{1213132141
4214314321
)()()()(
)()()(
ϕϕϕϕϕϕϕϕϕϕ
ϕϕϕϕϕϕϕϕϕϕ
jjjjj
jjj
eeeeeeeec
+++++
+++++++
−−
=
CCKHow it works
.11 tech. OVW 23
Bit-rates:
The 11 chips Barker sequence in Standard DSSS carries one symbol clocked at1MHz, which results in a symbol rate of 1Msymbol/sec.
The 8 chips sequence in CCK clocked at 1 MHz, results in a symbol rate of 1.375Msymbol/sec (I.e. 11/8)
At date rate = medium, 4 data bits are mapped on one symbol, which results in 5.5Mbps (I.e. 1.375 * 4)
At date rate = high, 8 data bits are mapped on one symbol, which results in 11Mbps (I.e. 1.375 * 8)
CCKData rates and symbol rates
.11 tech. OVW 24
11 MBpsCCK
5.5 MBpsCCK
802.11 DSSS QPSK2MBpsBarkerQPSK
802.11 DSSS BPSK1 MBpsBarkerBPSK
11 chips
1 MSps
1 bit used toBPSK code word
11 chips
1 MSps
2 bits used to QPSK code word
8 chips
1.375 MSps
2 bits encoded to4 complex code words; 2-QPSK
8 chips
1.375 MSps
I, Q I, QI, QI, Q
6 bits encoded to64 complex code words; 2-QPSK
CCKFrom DSSS BPSK to 11 Mbps CCK
.11 tech. OVW 25
Module summary
Technologies overview
Spread SpectrumDirect Sequence
Frequency Hopping
ModulationBQPSK/BQPSK
CCK