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Advanced Concepts of CDMA SLIDE 1 Copyright Hewlett Packard © 1999
Advanced Training Version - 6th Edition
Concepts of Concepts of CDMACDMA
Advanced Concepts of CDMA SLIDE 2 Copyright Hewlett Packard © 1999
Power
Frequency
Time
FDMA
Frequency
Power
Time
TDMA
Frequency
CDMA
Power
Time
Cellular Access Cellular Access MethodsMethods
Advanced Concepts of CDMA SLIDE 3 Copyright Hewlett Packard © 1999
US Cellular Channel 384
Frequency
Amplitude
Frequency
Amplitude
AMPS
45 MHz
Forward Link
881.52 MHz836.52 MHz
Reverse Link
CDMA
45 MHz
836.52 MHz 881.52 MHz
Reverse Link Forward Link
CDMA is Also Full CDMA is Also Full DuplexDuplex
Advanced Concepts of CDMA SLIDE 4 Copyright Hewlett Packard © 1999
3
6
CDMA Reuse FDMA Reuse
11
1
1
11
11
16
22
1
45
7
Cellular Frequency Cellular Frequency Reuse PatternsReuse Patterns
Advanced Concepts of CDMA SLIDE 5 Copyright Hewlett Packard © 1999
Capacity =
(Chan BW)(Data Rate)
× (1)(S/N)
× (1)(Vaf)
(Fr)×
CDMA = (1,230,000)(9,600)
× (1)(5.01)
× (1)(.40)
(0.67)×
CDMA = 42 calls (Using 1.5 MHz BW)
AMPS = 1.5 MHz ÷ 30 kHz = 50 ChannelsCapacity = 50 Channels ÷ 7 (1/7 Frequency
Reuse)AMPS = 7 calls (Using 1.5 MHz BW)
Processing
Gain
Processing
Gain
CDMA Capacity GainsCDMA Capacity Gains
Advanced Concepts of CDMA SLIDE 6 Copyright Hewlett Packard © 1999
Interference Sources
Walsh CodeSpreading
Encoding &Interleaving
Decode & De-Interleaving
BasebandData
BasebandData
Background Noise
External Interference Other Cell InterferenceOther User Noise
9.6 kbps 19.2 kbps 1228.8 kbps 19.2 kbps 9.6 kbps
CDMA Transmitter
CDMA Receiver
1.23 MHz BW
fc
1.23 MHz BW
fc
10 kHz BW
0
10 kHz BW
0
1.23 MHz BW
fc
1.23 MHz BW
fcfc
-113 dBm/1.23 MHz
fc
Spurious Signals
Walsh CodeCorrelator
1228.8 kbps
The CDMA ConceptThe CDMA Concept
Advanced Concepts of CDMA SLIDE 7 Copyright Hewlett Packard © 1999
Received Signal
Time
Correlation = 1
Correlation = 0
Correlation = 0
Correlation = 0
What is Correlation ?What is Correlation ?
• Is a Measure of How Well a Given Signal Matches a Desired Code
• The Desired Code is Compared to the Given Signal at Various Test Times
Advanced Concepts of CDMA SLIDE 8 Copyright Hewlett Packard © 1999
CDMA
CDMA
Analog
Analog
CDMA Paradigm ShiftCDMA Paradigm Shift
• Multiple Users on One Frequency– Analog/TDMA Try to Prevent
Multiple Users Interference
• Channel is Defined by Code– Analog Systems Defined
Channels by Frequency
• Capacity Limit is SoftAllows Degrading Voice Quality to
Temporarily Increase CapacityReduce Surrounding Cell Capacity to
Increase a Cell's Capacity
Advanced Concepts of CDMA SLIDE 9 Copyright Hewlett Packard © 1999
CDMA DiversityCDMA Diversity
• Spatial Diversity– Making Use of Differences in Position
• Frequency Diversity– Making Use of Differences in Frequency
• Time Diversity– Making Use of Differences in Time
Advanced Concepts of CDMA SLIDE 10 Copyright Hewlett Packard © 1999
CDMA Spatial CDMA Spatial DiversityDiversity
• Diversity Reception:– Multiple Antennas at Base Station
Each Antenna Is Affected by Multipath Differently Due to Their Different Location
Allows Selection of the Signal Least Affected by Multipath Fading
• If Diversity Antennas Are Good, Why Not Use Base Stations as a Diversity Network?– Soft Handoff
Advanced Concepts of CDMA SLIDE 11 Copyright Hewlett Packard © 1999
MTSO
Vocoder / Selector
Base Station 2Base Station 1
Land Link
Spatial Diversity Spatial Diversity During Soft HandoffDuring Soft Handoff
Advanced Concepts of CDMA SLIDE 12 Copyright Hewlett Packard © 1999
Amplitude
Frequency
1.23 MHz BW
CDMA Frequency CDMA Frequency DiversityDiversity
• Combats Fading, Caused by Multipath• Fading Acts like Notch Filter to a Wide
Spectrum Signal• May Notch only Part of Signal
Advanced Concepts of CDMA SLIDE 13 Copyright Hewlett Packard © 1999
CDMA Time DiversityCDMA Time Diversity
• Rake Receiver to Find and Demodulate Multipath Signals
• Data is Interleaved– Spreads Adjacent Data in Time to
Improve Error Correction Efficiency
• Convolutional Encoding– Adds Error Correction and Detection
• Viterbi Decoding– Most Likely Path Decoder for
Convolutionaly Encoded Data
Advanced Concepts of CDMA SLIDE 14 Copyright Hewlett Packard © 1999
Original Data Original Data FrameFrame
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Errors/Time
Interleaved Data FrameInterleaved Data Frame
Errors/Time1 5 9 13 2 6 10 14 3 7 11 15 4 8 12 16
Errors/Time
TX
RX
1 2 3 4 5 6 7 8 9 10 11 12 13 15 1614
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Errors/Time
TX
RX
1 2 3 45 6 7 89 10 11 1213 14 15 16
1 5 9 132 6 10 143 7 11 154 8 12 16
1 2 3 45 6 7 89 10 11 1213 14 15 16
Why Interleaving Why Interleaving WorksWorks
Advanced Concepts of CDMA SLIDE 15 Copyright Hewlett Packard © 1999
Time
Frequency
Amplitude
The Rake ReceiverThe Rake Receiver
Advanced Concepts of CDMA SLIDE 16 Copyright Hewlett Packard © 1999
Output
T0
W0
T4T1 T2 T3
W1 W2 W3 W4
+
Delay Taps
Tap Weights
Antenna
Rake Receiver DesignRake Receiver Design
Advanced Concepts of CDMA SLIDE 17 Copyright Hewlett Packard © 1999
SynchronizationSynchronization
• All Direct Sequence, Spread Spectrum Systems Should be Accurately Synchronized for Efficient Searching
• Finding the Desired Code Becomes Difficult Without Synchronization
Advanced Concepts of CDMA SLIDE 18 Copyright Hewlett Packard © 1999
Reverse Link Power Reverse Link Power ControlControl
• Maximum System Capacity is Achieved if:All Mobiles are Powered Controlled to the Minimum
Power for Acceptable Signal QualityAs a result, all Mobiles are Received at About Equal
Power at the Base Station Independent of Their Location
• There are Two Types of Reverse Control:– Open Loop Power Control– Closed Loop Power Control
• Open & Closed Loop Power Control are Always Both Active !
Advanced Concepts of CDMA SLIDE 19 Copyright Hewlett Packard © 1999
Open Loop Power Open Loop Power ControlControl
• Assumes Loss is Similar on Forward and Reverse Paths
• Receive Power+Transmit Power = -73– All powers in dBm
• Example:– For a Received Power of -85 dBm
Transmit Power = (-73) - (-85) Transmit Power = +12 dBm
• Provides an Estimate of Reverse TX Power for Given Propagation Conditions
Advanced Concepts of CDMA SLIDE 20 Copyright Hewlett Packard © 1999
Closed Loop Power Closed Loop Power ControlControl
• Directed by Base Station• Updated Every 1.25 msec• Commands Mobile to Change TX
Power in +/-1 dB Step Size• Fine Tunes Open Loop Power Estimate• Power Control Bits are "Punctured"
over the Encoded Voice Data• Puncture Period is two 19.2 kbps
Symbol Periods = 103.6 usec
Advanced Concepts of CDMA SLIDE 21 Copyright Hewlett Packard © 1999
CDMA Variable Rate CDMA Variable Rate Speech CoderSpeech Coder
• DSP Analyzes 20 Millisecond Blocks of Speech for Activity
• Selects Encoding Rate Based On Activity:High Activity: Full Data Rate Encoding (9600 bps)Some Activity: Half Data Rate Encoding (4800 bps)Low Activity: Quarter Date Rate Encoding (2400
bps)No Activity: 1/8 Data Rate Encoding (1200 bps)
• How Does This Improve Capacity? – Mobile Transmits in Bursts of 1.25 ms
• System Capacity Increases by 1/Vaf
Advanced Concepts of CDMA SLIDE 22 Copyright Hewlett Packard © 1999
CDMA Frame = 20 ms
Full Rate
Half Rate
Quarter Rate
Eighth Rate
Mobile Power BurstingMobile Power Bursting
• Each Frame is Divided Into 16 Power Control Groups
• Each Power Control Group Contains 1536 Chips (represents 12 encoded voice bits)
• Average Power Is Lowered 3dB for Each Lower Data Rate
Advanced Concepts of CDMA SLIDE 23 Copyright Hewlett Packard © 1999
Base Station Variable Base Station Variable Rate VocoderRate Vocoder
• Base Stations Do Not Pulse TX Channels
• How Does the Base Station Handle Variable Rate Vocoding ?– Repeats Data Bits When Transmitting at
Reduced Rates– Repeating Data Adds 3 dB Coding Gain– Lowers the TX Power 3 dB for Each Lower
Rate
Advanced Concepts of CDMA SLIDE 24 Copyright Hewlett Packard © 1999
WalshCover
I Short Code
Q Short Code
FIR
FIR1.2288Mbps
Walsh Code Generator
I
Q
1.2288Mbps
1.2288 Mbps
1.2288 Mbps
Long Code
19.2 kbps
19.2 kbps
Vocoded Speech data
20 msec blocks
Interleaver
Power Control
Puncturing
19.2 kbps
19.2 kbps
800 bps
800 bps
P.C.MUX
9.6 kbp
s
19.2 kbps
3/4 rate
1/2 rate
14.4 kbp
s
19.2 kbps
Convolutional
Encoder Long CodeScramblin
g
Short Code Scrambler
Forward Link Traffic Forward Link Traffic Channel Physical Channel Physical LayerLayer
Advanced Concepts of CDMA SLIDE 25 Copyright Hewlett Packard © 1999
CDMA VocodersCDMA Vocoders
• Vocoders Convert Voice to/from Analog Using Data Compression
• There are Three CDMA Vocoders:– IS-96A Variable Rate (8 kbps maximum)– CDG Variable Rate (13 kbps maximum)– EVRC Variable Rate (improved 8 kbps)
• Each Has Different Voice Quality:IS-96A - moderate qualityEVRC - near toll qualityCDG - toll quality
Advanced Concepts of CDMA SLIDE 26 Copyright Hewlett Packard © 1999
12 8171
192 bits in a 20 ms Frame
Information Bits
CRCEncoder Tail Bits
9600 bpsFrame
879
96 bits in a 20 ms Frame
Information Bits
4800 bpsFrame
8
839
48 bits in a 20 ms Frame
Information Bits
Encoder Tail Bits
2400 bpsFrame
815
24 bits in a 20 ms Frame
Information Bits
Encoder Tail Bits
1200 bpsFrame
CRCEncoder Tail Bits
12 8266
288 bits in a 20 ms Frame
Information Bits
CRCEncoder Tail Bits
8124
144 bits in a 20 ms Frame
Information Bits
10
854
72 bits in a 20 ms Frame
Information Bits
820
36 bits in a 20 ms Frame
Information Bits
14400 bpsFrame
7200 bpsFrame
3600 bpsFrame
1800 bpsFrame
CRCEncoder Tail Bits
8
CRCEncoder Tail Bits
6
CRCEncoder Tail Bits
1-bit Reserved or Frame Erasure
Mixed Mode
bit
Mixed Mode
bit
Mixed Mode
bit
Mixed Mode
bit
Mixed Mode bit
Mixed Mode bit
Mixed Mode bit
Mixed Mode bit
CDMA Frame FormatsCDMA Frame Formats
1-bit Reserved or Frame Erasure
1-bit Reserved or Frame Erasure
1-bit Reserved or Frame Erasure
Advanced Concepts of CDMA SLIDE 27 Copyright Hewlett Packard © 1999
+Data In9600 bps
Data Out9600 bps
Data Out9600 bps
D D DD D DD D
+
Forward Error Forward Error ProtectionProtection
• Uses Half-Rate Convolutional Encoder• Outputs Two Bits of Encoded Data for
Every Input Bit
Advanced Concepts of CDMA SLIDE 28 Copyright Hewlett Packard © 1999
ConvolutionalEncoder
14.4 kbps
19.2 kbps
Vocoded Speech data
3/4 rate
20 msec blocks
14.4 14.4 TCH Forward Link TCH Forward Link ModificationsModifications
• Replaces 8 kbps Vocoder with a 13 kbps Vocoder (both Variable Rate)
• Effects:Provides Toll Quality SpeechUses a 3/4 Rate EncoderReduces Processing Gain
1.76 dBResults in Reduced Capacity
or Smaller Cell Sizes
Advanced Concepts of CDMA SLIDE 29 Copyright Hewlett Packard © 1999
112
2
3
4567
89
1011
CDMA System TimeCDMA System Time
• How Does CDMA Achieve Synchronization for Efficient Searching ?
Use GPS Satellite System
• Base Stations Use GPS Time via Satellite Receivers as a Common Time Reference
• GPS Clock Drives the Long Code Generator
Advanced Concepts of CDMA SLIDE 30 Copyright Hewlett Packard © 1999
Modulo-2 Addition
Long Code Output
34 12
User AssignedLong Code Mask
42 bits
4142 55
Long Code Generator
Long Code GenerationLong Code Generation
Advanced Concepts of CDMA SLIDE 31 Copyright Hewlett Packard © 1999
Long CodeGenerator
EncodedVoice Data
19.2 kbps
1.2288 Mbps
XOR
Long CodeDecimator
19.2 kbps
19.2 kbps
Long Code ScramblingLong Code Scrambling
– User's Long Code Mask is Applied to the Long Code
– Masked Long Code is Decimated Down to 19.2 kbps
– Decimated Long Code is XOR'ed with Voice Data Bits
– Scrambles the Data to Provide Voice Security
Advanced Concepts of CDMA SLIDE 32 Copyright Hewlett Packard © 1999
Long CodeDecimatedData
Long Code Scrambled Voice Data
19.2 kbps
Long CodeDecimator
19.2 kbps
19.2 kbps
800 bps
P.C.Mux
Closed Loop Power Control Bits
800 bps
Closed Loop Power Closed Loop Power Control PuncturingControl Puncturing– Long Code is
Decimated Down to 800 bps
– Decimated Long Code Controls the Puncture Location
– Power Control Bits Replace Voice Data
– Voice Data is Recovered by the Mobile's Viterbi Decoder
Advanced Concepts of CDMA SLIDE 33 Copyright Hewlett Packard © 1999
W =2
0 00 1
4W =
0 0 0 00 1 0 10 0 1 10 1 1 0
W = 01
n
n
n
n
W WW WW =
2n
Walsh CodesWalsh Codes
Advanced Concepts of CDMA SLIDE 34 Copyright Hewlett Packard © 1999
Cross Correlation
N agreements - N disagreementsN
total_number_of_digits
=
W =
0 0 0 00 1 0 10 0 1 10 1 1 0
4
0 0 0 00 0 1 1Y Y N N
2 match - 2 don't =0
Checking for Checking for OrthogonalityOrthogonality
Advanced Concepts of CDMA SLIDE 35 Copyright Hewlett Packard © 1999
What is theSpreading RateIncrease ?
EncodedVoice Data
19.2 kbps
1.2288 Mbps
1.2288 Mbps
XOR
Walsh CodeGenerator
Walsh Code SpreadingWalsh Code Spreading
Advanced Concepts of CDMA SLIDE 36 Copyright Hewlett Packard © 1999
To I/QModulator
1.2288 Mbps
1.2288 Mbps
Q Channel ShortSequence CodeGenerator
Walsh CodedData at1.2288 Mbps
I Channel ShortSequence CodeGenerator
Why Spread Again Why Spread Again with the Short with the Short Sequence ?Sequence ?– Provides a Cover to
Hide the 64 Walsh Codes
– Each Base Station is Assigned A Time Offset in its Short Sequences
– Time Offsets Allow Mobiles to Distinguish Between Adjacent Cells
– Also Allows Reuse of All Walsh Codes in Each Cell
Advanced Concepts of CDMA SLIDE 37 Copyright Hewlett Packard © 1999
chip
0 5 10 15 20 25 30
1
Pseudo-Random Sequence
0
-1
chip offset
Auto-Correlation Versus Time Offset
0 5 10 15 20 25 30
0
Auto-CorrelationAuto-Correlation
• Is a Comparison of a Signal Against Itself
• Good Pseudo-Random Patterns Have:
Strong Correlation at Zero Time Offset
Weak Correlation at Other Time Offsets
Advanced Concepts of CDMA SLIDE 38 Copyright Hewlett Packard © 1999
chip offset
Auto-Correlation VersusTime Offset with 17 dB Noise
Added
0 5 10 15 20 25 30
0
Short Code CorrelationShort Code Correlation
– Short Codes Are Designed to Have:Strong Auto-Correlation
at Zero Time OffsetWeak Auto-Correlation
at Other OffsetsGood Auto-Correlation
In Very Poor Signal-to -Noise Ratio Environments
– Allows Fast Acquisition in Real World Environment
Advanced Concepts of CDMA SLIDE 39 Copyright Hewlett Packard © 1999
Walsh Code 32
Walsh Code 0
Pilot Channel
Sync Channel
Walsh Codes 1 to 7
Walsh Codes 8-31, 33-63
Traffic Channels1 up to 55 Channels
All 0's
19.2 kbps 1228.8 kbps
1228.8 kbps
1228.8 kbps
I
Convert to I/Q & Short Code Spreading
Convert to I/Q & Short Code Spreading
Convert to I/Q & Short Code Spreading
FIR LP Filter &D/A Conversion
FIR LP Filter &D/A Conversion
FIR LP Filter &D/A Conversion
FIR LP Filter &D/A Conversion
Q
4.8 kbps
I Data
I Data
I Data
I Data
Q Data
Q Data
Q Data
Q Data
Paging Channels1 up to 7 Channels
19.2 kbps 1228.8 kbps Convert to I/Q & Short Code Spreading
Forward Link Channel Forward Link Channel FormatFormat
Advanced Concepts of CDMA SLIDE 40 Copyright Hewlett Packard © 1999
+Sum of A & BWalsh EncodedData Streams
W =20 00 1
- User A- User B
For a 0 Input,Use Code 00
Channel AVoice Data
+10
0 0 01
Channel AWalsh EncodedVoice Data
-1
+1
1 100 0 0 0 0
For a 1 Input,Use Code 11-1
+1
1 1
-1
+1
0 0
User A For a 0
Input,Use Code 01-1
+1
For a 1 Input,use code 10-1
+1
Channel BVoice DataChannel BWalsh EncodedVoice Data
+10 1 10 0
-1
+1
1 10 0 00 1 1
1
User B
10
0
-1
+2
+1
-2
Walsh Coding ExampleWalsh Coding Example
Advanced Concepts of CDMA SLIDE 41 Copyright Hewlett Packard © 1999
Original User A Voice Data+10
0 0 01
Multiply Summed Data with Desired Walsh Code
+10 1 10 0
-1
+1
1 0
+2
-1
+1
-2
User A + B Walsh Data
+2
Correlation Coefficient
-1
+1
1 1-1
+1
-2
x =
+2
-1
+1
-2
+2
-1
+1
-2
Original User B Voice Data
-1
+1
-2
+2
-1
+1
-2
= 1+2Multiply Summed Data with Desired Walsh Code
User A + B Walsh Data1
T0
T
z =ij
fi (t) f (t)j dt
= =x1-
Walsh Decoding Walsh Decoding ExampleExample
Advanced Concepts of CDMA SLIDE 42 Copyright Hewlett Packard © 1999
+Sum of A & BWalsh EncodedData Streams
Channel AWalsh EncodedVoice Data
-1
+1
1 100 0 0 0 0
Channel BWalsh EncodedVoice Data
-1
+1
1 10 0 00 1 1
-1
+2
+1
-2
Multiply Summed Data with Desired Walsh Code+2
-1
+1
1 1-1
+1
-2
x =
+2
-1
+1
-2
= 0.75-Original Data Was0 (-1), We Have Interference Now!
Original Time Delayed
What if Walsh Codes What if Walsh Codes are Not Time Aligned ?are Not Time Aligned ?
Advanced Concepts of CDMA SLIDE 43 Copyright Hewlett Packard © 1999
Uses Walsh Code 0:All 64 bits are 0
All Data into Walsh Modulator is 0
Output of Walsh Modulator is Therefore all 0's
Pilot Channel is just the Short Codes
Q
Walsh Code
0
I Short Code
Q Short Code
FIR
FIR1.2288Mbps
Walsh Code Generator
I
1.2288Mbps
1.2288 Mbps
1.2288 Mbps
All 0 inpu
t
Short Code Scrambler
WalshModulato
r
Pilot Channel Physical Pilot Channel Physical LayerLayer
Advanced Concepts of CDMA SLIDE 44 Copyright Hewlett Packard © 1999
Walsh32
Cover
I Short Code
Q Short Code
FIR
FIR1.2288Mbps
Walsh Code Generator
I
Q
1.2288Mbps
1.2288 Mbps
1.2288 Mbps
Sync Channel Message Data
Interleaver
4.8 kbp
s
1/2 rate
Convolutional
Encoder
Short Code Scrambler
2x
4.8 kbp
s
SymbolRepetition
2.4 kbp
s
1.2 kbp
s
Sync Channel Physical Sync Channel Physical LayerLayer
Advanced Concepts of CDMA SLIDE 45 Copyright Hewlett Packard © 1999
Walsh
1 to 7Cover
I Short Code
Q Short Code
FIR
FIR1.2288Mbps
Walsh Code Generator
I
Q
1.2288Mbps
1.2288 Mbps
1.2288 Mbps
19.2 kbps
Paging Channel
Long Code
19.2 kbps
Long CodeScramblin
g
Short Code Scrambler
Paging Channel Message Data
Interleaver
19.2 kbp
s
1/2 rate
Convolutional
Encoder
2x
19.2 kbp
s
SymbolRepetition
9.6 kbp
s
4.8 kbp
s
Paging Channel Paging Channel Physical LayerPhysical Layer
Advanced Concepts of CDMA SLIDE 46 Copyright Hewlett Packard © 1999
Interleaver
I Short Code
Q Short Code
1.2288Mbps
I
Q
307.2 kbps
t/2
1/2 Chip Delay28.8 kbps
20 msec blocks
Vocoded Speech Data
64-ary Modulator
1.2288 Mbps
1 of 64 Walsh Codes
Long Code
1.2288 Mbps
1.2288 Mbps
FIR
FIR
Walsh Code 1
Walsh Code 2
Walsh Code 0
Walsh Code 62
Walsh Code 63
Walsh Code 61
Convolutional
Encoder
9.6 kbps
28.8 kbps
1/3 rate
1/2 rate
14.4 kbps
28.8 kbps
Long Code Modulator
Short Code Scrambler
Reverse Link Traffic Reverse Link Traffic Channel Physical Channel Physical LayerLayer
Advanced Concepts of CDMA SLIDE 47 Copyright Hewlett Packard © 1999
Data In9600 bps
Data Out9600 bps
Data Out9600 bps
+D D DD D DD D
++ Data
Out9600 bps
Reverse Error Reverse Error ProtectionProtection
• Uses Third-Rate Convolutional Encoder
• Outputs Three Bits for Every Input Bit
Advanced Concepts of CDMA SLIDE 48 Copyright Hewlett Packard © 1999
ConvolutionalEncoder
14.4 kbps
28.8 kbps
Vocoded Speech data
1/2 rate
20 msec blocks
14.4 14.4 TCH Reverse Link TCH Reverse Link ModificationsModifications
• Replaces 8 kbps Vocoder with a 13 kbps Vocoder (both Variable Rate)
• Effects:Provides Toll Quality SpeechUses a 1/2 Rate EncoderReduces Processing Gain 1.76
dBResults in Reduced Capacity
or Smaller Cell Sizes
Advanced Concepts of CDMA SLIDE 49 Copyright Hewlett Packard © 1999
307.2 kbps
Walsh Code 1
Walsh Code 2
Walsh Code 0
Walsh Code 62
Walsh Code 63
Walsh Code 61
28.8 kbps
64-64-ary Modulationary Modulation
• Every 6 Encoded Voice Data Bits Points to One of the 64 Walsh Codes
• Spreads Data From 28.8 kbps to 307.2 kbps:
(28.8 kbps * 64 bits)/ 6 bits = 307.2 kbps)
• Is Not the Channelization for the Reverse Link
Advanced Concepts of CDMA SLIDE 50 Copyright Hewlett Packard © 1999
Why Aren't Walsh Codes Why Aren't Walsh Codes Used for Reverse Used for Reverse Channelization ?Channelization ?• All Walsh Codes Arrive Together in Time to All Mobiles From the Base Station
• However, Transmissions from Mobiles DO NOT Arrive at the Same Time at the Base Station
Advanced Concepts of CDMA SLIDE 51 Copyright Hewlett Packard © 1999
WalshModulatedVoice Data
307.2 kbps
1.2288 Mbps
1.2288 Mbps
XOR
Long CodeGenerator
Reverse Channel Long Reverse Channel Long Code SpreadingCode Spreading
• Long Code Spreading Provides Unique Mobile Channelization
• Mobiles are Uncorrelated but not Orthogonal with Each Other
Advanced Concepts of CDMA SLIDE 52 Copyright Hewlett Packard © 1999
t/2 QFIR
I Short Code
Q Short Code
1.2288Mbps
I
1/2 Chip Delay
1.2288 Mbps
1.2288 Mbps
FIR
Reverse Channel Short Reverse Channel Short Sequence SpreadingSequence Spreading
• Same PN Short Codes Are Used by Mobiles
• Short Sequence Spreading Aids Base Station Signal Acquisition
• Extra 1/2 Chip Delay is Inserted into Q Path to Produce OQPSK Modulation to Simplify Power Amplifier Design
Advanced Concepts of CDMA SLIDE 53 Copyright Hewlett Packard © 1999
I
Q
I
Q
00 01
11
01
1110
00
10
OQPSK ModulationOQPSK Modulation
• QPSK Makes one Symbol Change Every Period
• OQPSK Makes two Symbol Changes Every Period if both I and Q Data Changes
• Example Symbol Pattern is:– 00, 10, 01,11
Advanced Concepts of CDMA SLIDE 54 Copyright Hewlett Packard © 1999
Filtered Offset QPSK
Filtered QPSK
I I
Base Station Pilot Channel TX Mobile Station TX
CDMA Modulation CDMA Modulation FormatsFormats
Advanced Concepts of CDMA SLIDE 55 Copyright Hewlett Packard © 1999
Function Forward Link{Base to Mobile}
Reverse Link{Mobile to Base}
9.6 kbps Convolutional
Encoder
1/2 Rate{9600 in 19200 out}
1/3 Rate{9600 in 28800 out}
14.4 kbps Convolutional
Encoder
3/4 Rate{14400 in 19200
out}
1/2 Rate{14400 in 28800
out}
Walsh Coding Channelization
64-ary Modulation
Long CodeSpreading
Voice Privacy Channelization
Short Code Spreading
Base Station Identification
Aid Base Station
Searching
Channelization Channelization SummarySummary
Advanced Concepts of CDMA SLIDE 56 Copyright Hewlett Packard © 1999
Forward Link{Base to Mobile}
Reverse Link{Mobile to Base}
+ -High Power Transmitter-Pilot Channel-Added Time Diversity-Orthogonal Code
Channels
-Wide Range Power Control-Diversity Reception at
Base
- -Complexity of Soft Handoff
-Non-coherent Demodulation
-Limited Power-Uncorrelated Code
Channels
Link Advantages & Link Advantages & DisadvantagesDisadvantages
Advanced Concepts of CDMA SLIDE 57 Copyright Hewlett Packard © 1999
Layer 2
Multiplex Sublayer
Layer 1Physical Layer
Channel Data - 9600 bps or 14400 bps
Traffic Channel
Primary TrafficLayer 2
SignalingLayer 2Link Layer
Paging & Access Channels
Layer 3Call Processing and
Control
CDMA Multiplex CDMA Multiplex SublayerSublayer
Advanced Concepts of CDMA SLIDE 58 Copyright Hewlett Packard © 1999
CDMA Service OptionsCDMA Service Options
• Service Options Are:1- Voice Using 9600 bps IS-96-A Vocoder2- Rate Set 1 Loopback (9600 bps)3- Voice Using 9600 bps (EVRC)4- Asynchronous Data Service (circuit switched)5- Group 3 Fax6- Short Message Service (9600 bps)7- Internet Standard PPP Packet Data 8- CDPD Over PPP Packet Data9- Rate Set 2 Loopback (14400 bps)14-Short Message Service (14400 bps)32,768- Voice Using 14400 bps (CDG)
Advanced Concepts of CDMA SLIDE 59 Copyright Hewlett Packard © 1999
EIA/TIA 95-BCombines TSB-74 & J-STD-008 for a Universal Protocol
J-STD-008Not Backwards Compatible, PCS only Protocol
IS-95 Rev ABackwards Compatible with IS-95. First Deployed Protocol
IS-95 Rev 0Original System- never actually deployed.
TSB-74Cellular Protocol that adds 14400 Channel Support ARIB T53
Japan CDMASystem Cellular
Protocol
CDMA Protocol StacksCDMA Protocol Stacks
Advanced Concepts of CDMA SLIDE 60 Copyright Hewlett Packard © 1999
Ten Minutes in the Ten Minutes in the Life of a CDMA Mobile Life of a CDMA Mobile PhonePhone• Turn-on
– System Access
• Travel– Idle State Hand-Off
• Initiate Call• System Access• Continue Travel
– Initiate Soft Handoff
– Terminate Soft Handoff
• End Call
Advanced Concepts of CDMA SLIDE 61 Copyright Hewlett Packard © 1999
CDMA Turn On ProcessCDMA Turn On Process
• Find All Receivable Pilot Signals– Choose Strongest One
• Establish Frequency and PN Time Reference (Base Station I.D.)
• Demodulate Sync Channel• Establish System Time• Determine Paging Channel Long
Code Mask
Advanced Concepts of CDMA SLIDE 62 Copyright Hewlett Packard © 1999
SYNCSYNC
Sync Channel MessageSync Channel Message
• Contains the Following Data:Base Station Protocol RevisionMin Protocol Revision SupportedSID, NID of Cellular SystemPilot PN Offset of Base StationLong Code StateSystem TimeLeap Seconds From Start of System TimeLocal Time Offset from System Time Daylight Savings Time FlagPaging Channel Data RateChannel Number
Advanced Concepts of CDMA SLIDE 63 Copyright Hewlett Packard © 1999
PagingPaging
Read the Paging Read the Paging ChannelChannel
• Demodulate the Paging Channel:
Use Long Code Mask Derived from the Pilot PN Offset Given in Sync Channel Message
• Decode Messages• Register, if Required by
Base Station• Monitor Paging Channel
Advanced Concepts of CDMA SLIDE 64 Copyright Hewlett Packard © 1999
–Overhead MessagesSystem Parameters Access ParametersCDMA Channel ListExtended System ParamsExtended Neighbor List
–Other MessagesOrderChannel AssignmentData Burst
–More MessagesAuthenticationSSD UpdateFeature NotificationStatus RequestService RedirectionGeneral PageGlobal Service RedirectionTMSI Assignment
J-STD-008 Paging Messages:
Paging Channel Paging Channel MessagesMessages
Advanced Concepts of CDMA SLIDE 65 Copyright Hewlett Packard © 1999
CDMA Idle State CDMA Idle State HandoffHandoff
• No Call In Progress• Mobile Listens to New Cell• Move Registration Location if Entering
a New Zone
Advanced Concepts of CDMA SLIDE 66 Copyright Hewlett Packard © 1999
CDMA Call InitiationCDMA Call Initiation
• Dial Numbers, Then Press Send• Mobile Transmits on a Special
Channel Called the Access Channel• The Access Probe Uses a Long
Code Mask Based On:Access & Paging Channel NumbersBase Station IDPilot PN Offset
Advanced Concepts of CDMA SLIDE 67 Copyright Hewlett Packard © 1999
Interleaver
I Short Code
Q Short Code
1.2288Mbps
I
Q
307.2 kbps
t/2
1/2 Chip Delay28.8 kbps
64-ary Modulator
1.2288 Mbps
1 of 64 Walsh Codes
Access Channel Long Code
1.2288 Mbps
1.2288 Mbps
FIR
FIR
Walsh Code 1
Walsh Code 2
Walsh Code 0
Walsh Code 62
Walsh Code 63
Walsh Code 61
Long Code Modulator
Short Code Scrambler
Access Channel Message Data
Convolutional
Encoder
2x
28.8 kbp
s
SymbolRepetition
14.4 kbp
s4.8 kbp
s
1/3 rate
Reverse Link Access Reverse Link Access Channel Physical Channel Physical LayerLayer
Advanced Concepts of CDMA SLIDE 68 Copyright Hewlett Packard © 1999
CDMA Call CompletionCDMA Call Completion
• Base Answers Access Probe using the Channel Assignment Message
• Mobile Goes to A Traffic Channel Based on the Channel Assignment Message Information
• Base Station Begins to Transmit and Receive Traffic Channel
Advanced Concepts of CDMA SLIDE 69 Copyright Hewlett Packard © 1999
CDMA Soft Handoff CDMA Soft Handoff InitiationInitiation
• Mobile Finds Second Pilot of Sufficient Power (exceeds T_add Threshold)
• Mobile Sends Pilot Strength Message to First Base Station
• Base Station Notifies MTSO• MTSO Requests New Walsh
Assignment from Second Base Station• If Available, New Walsh Channel Info
is Relayed to First Base Station
Advanced Concepts of CDMA SLIDE 70 Copyright Hewlett Packard © 1999
CDMA Soft Handoff CDMA Soft Handoff CompletionCompletion
• First Base Station Orders Soft Handoff with new Walsh Assignment
• MTSO Sends Land Link to Second Base Station
• Mobile Receives Power from Two Base Stations
• MTSO Chooses Better Quality Frame Every 20 Milliseconds
Advanced Concepts of CDMA SLIDE 71 Copyright Hewlett Packard © 1999
Ending CDMA Soft Ending CDMA Soft HandoffHandoff
• First BS Pilot Power Goes Low at Mobile Station (drops below T_drop)
• Mobile Sends Pilot Strength Message• First Base Station Stops Transmitting
and Frees up Channel• Traffic Channel Continues on Base
Station Two
Advanced Concepts of CDMA SLIDE 72 Copyright Hewlett Packard © 1999
CDMA End of CallCDMA End of Call
• Mobile or Land Initiated• Mobile and Base Stop Transmission• Land Connection Broken
Advanced Concepts of CDMA SLIDE 73 Copyright Hewlett Packard © 1999
CDMA
CDMA ConclusionsCDMA Conclusions
• New Access Method– Code Based
• Designed for Use in Interfering Environment
• Uses Multipath to Improve Reception in Fading Conditions
• Has High Capacity– 6 Times Analog for 14.4 kbps Voice– 10 Times Analog for 9.6 kbps Voice