CDMA

1. CDMA System
Course Name
cdma2000 Systems

2. Contents
The characteristics of mobile
communications
CDMA migration from 2G to 3G
CDMA spectrum usage
CDMA Codes
CDMA Channels
The advantage of CDMA
cdma2000 -1x

3. Characteristics of Mobile
Communication
• Mobility：
– flexible and convenient ， global personal
communication
• Poor environment and conditions ：
– Co-channel interference, multi-path(space and
time)shadow effect and delay, power change and
other noise
• Multiple MS and channels：
– Interference, near and far effect
• Limit of frequency resources
• Reliability is important
– registration, handoff, switching

4. Communications System
AMPS: Advanced Mobile Phone System
TACS: Total Access Communication System
GPRS: General Packet Radio Services
11GG 22GG 33GG
Analog
cellular
DDiiggiittaall cceelllluullaarr DDiiggiittaall cceelllluullaarr
VVooiiccee VVooiiccee //ddaattaa VViiooccee // hhiigghh ssppeeeedd ddaattaa
AAMMPPSS CCDDMMAA 11XXRRtttt CCDDMMAA22000000
TTAACCSS GGSSMM GGPPRRSS WW__CCDDMMAA
8800’’ 11999922 11999999 22000011 22000033

5. CDMA Evolution Paths
2Mbps
153.6kbps
CDMA
1xRTT
CDMA
1xEV-DV
CDMA
IS-95
CDMA
1xEV-DO
CDMA
3x 5x
2G 2.5G 3G
9.6kbps

6. CDMA-Its History & Status

7. CDMA-Its History & Status
 1993, the first CDMA standard IS-95 was issued;
 In 1995, CDMA technology was put into
commercialization in Hong Kong and America on
large scale;
 In April, 2001, China Unicom began to construct
CDMA networks—the largest in the world (about
70Million line now);
 At present, CDMA commercial networks are
established in about 40 countries or area, almost
20% of all users in the world.

8. CDMA Subscriber Growth History:
Sept.1997 through Sept.2003

9. CDMA 800 MHz Cellular
Spectrum Usage
Possible CDMA
Center Freq. Assignments
Channel
Numbers
Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)824
MHz
849
MHz
869
MHz
894
MHz
other
usesA” A”A B A’ B’
1 10 10 1.5 2.5
A B A’ B’
1 10 10 1.5 2.5
991
1023
1
333
334
666
667
716
717
799
991
1023
1
333
334
666
667
716
717
799
~300 kHz. “guard bands” possibly required if adjacent-
frequency signals are non-CDMA (AMPS, TDMA, ESMR, etc.)
• All CDMA RF carriers are 1.25 MHz. wide
– Can serve ~20 users /8 kb vocoder

10. CDMA PCS 1900 MHz
Spectrum Usage
Guard Bands
Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)
1850
MHz
B
T
A
B
T
A
B
T
A
B
T
A
B
T
A
B
T
A
Paired Bands
MTA BTAMTABTA MTAMTA
1910
MHz
1930
MHz
1990
MHz
Data Voice
A D B E F C A D B E F C
15 51010 1515151515 555 55
Licensed Licensed
Unlicensed
0
Channel
Numbers
299
300
400
699
700
800
900
1199
0
299
300
400
699
700
800
900
1199

11. CDMA Frequency Channel
Assignment at 800 MHz Cellular
1
334
667
991
1023
333
666
715
799
716
Channel
Numbers
A Band B Band A’A” B’
1019 37 78 119 160 201 242 283 384 425 466 507 548 589 630 691 777
CDMA A-Band Carriers CDMA B-Band Carriers
8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 9 9 8
* ***
* Requires frequency
coordination with non-cellular
interferers
** Requires frequency
coordination with A-band
carrier
A Band Primary Channel 283
A Band Secondary Channel 691
B Band Primary Channel 384
B Band Secondary Channel 777
736

12. Multiple Access
Each pair of users
enjoys a dedicated,
private circuit through
the transmission
medium, unaware that
the other users exist.
Since the beginning of telephony and radio,
system operators have tried to squeeze the
maximum amount of traffic over each circuit. Transmission
Medium• Types of Media -- Examples:
– Twisted pair - copper
– Coaxial cable
– Fiber optic cable
– Air interface (radio signals)
Advantages of Multiple Access
–Increased capacity: serve more users
–Reduced capital requirements since fewer
media can carry the traffic
–Decreased per-user expense
–Easier to manage and administer

13. Multiple Access Schemes
Power
Power
Power
FDMA
TDMA
CDMA
• FDMA Frequency Division Multiple
Access
– Each user on a different frequency
– A channel is a frequency
• TDMA Time Division Multiple Access
– Each user on a different window
period in time (“time slot”)
– A channel is a specific time slot on a
specific frequency
• CDMA Code Division Multiple Access
– A channel is a unique code pattern
– Each user uses the same frequency
all the time, but mixed with
different distinguishing code
patterns

14. Frequency Reuse
CDMA (IS-95)
frequency reuse = 1
TDMA (IS-136)
frequency reuse = 7

15. Terms & Definitions
• CDMA Channel or CDMA Carrier or CDMA Frequency
– Duplex channel made of two 1.25 MHz-wide bands of electromagnetic
spectrum, one for Base Station to Mobile Station communication (called the
FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base
Station communication (called the REVERSE LINK or the UPLINK)
– In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart
– In 1900 MHz PCS they are 80 MHz apart
• CDMA Forward & Reverse Channel
– 1.25 MHz Forward / Reverse Link
• CDMA Code Channel
– Each individual stream of 0’s and 1’s contained in either the CDMA Forward
Channel or in the CDMA Reverse Channel
– Code Channels are characterized (made unique) by mathematical codes
– Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic
channels
– Code channels in the reverse link: Access and Reverse Traffic channels
45 or 80 MHz
CDMA CHANNEL
CDMA
Reverse
Channel
1.25 MHz
CDMA
Forward
Channel
1.25 MHz

16. Walsh Codes
• 64 Sequences, each 64 chips long
– A chip is a binary digit (0 or 1)
• Each Walsh Code is Orthogonal to all other Walsh
Codes
– This means that it is possible to recognize and
therefore extract a particular Walsh code from a
mixture of other Walsh codes which are “filtered
out” in the process
– Two same-length binary strings are orthogonal if
the result of XORing them has the same number
of 0s as 1s

17. Short PN Sequences
• The two Short PN Sequences, I and Q, are 32,768
chips long
• Together, they can be considered a two-dimensional
binary “vector” with distinct I and Q component
sequences, each 32,768 chips long
• Each Short PN Sequence (and, as a matter of fact, any
sequence) correlates with itself perfectly if compared
at a timing offset of 0 chips
• Each Short PN Sequence is special: Orthogonal to a
copy of itself that has been offset by any number of
chips (other than 0)

18. The Long PN Sequence
• Each mobile station uses a unique User Long Code Sequence
generated by applying a mask, based on its 32-bit ESN, to the
42-bit Long Code Generator which was synchronized with
the CDMA system during the mobile station initialization.
• Generated at 1.2288 Mcps, this sequence requires 41 days, 10
hours, 12 minutes and 19.4 seconds to complete.
Long Code Register
(@ 1.2288 MCPS)
Public Long Code Mask
(STATIC)
User Long Code
Sequence
(@1.2288 MCPS)
1 1 0 0 0 1 1 0 0 0 P E RMU T E D E S N
AND
=S UM
Modulo-2 Addition

19. Coding Process on CDMA
Forward Channels
WALSH
19
BTSPilot Walsh 0
Walsh 19
Paging Walsh 1
Walsh 6
Walsh 11
Walsh 20
Sync Walsh 32
Walsh 42
Walsh 37
Walsh 41
Walsh 56
Walsh 60
Walsh 55
PN OFFSET 116BTS
PN OFFSET 226BTS
PN OFFSET 510BTS
S
PN
372
x
x
x
PN OFFSET
ANALOG
SUM/MUX
PN OFFSET 372

20. CDMA Code Summary
Walsh Codes
Short PN
Sequences
Long PN
Sequences
Type of
Sequence
Mutually
Orthogonal
Orthogonal with
itself at any time
shift value
except 0
near-orthogonal
if shifted
Special
Properties
64
2
1
How
Many
64 chips
1/19,200 sec.
32,768 chips
26-2/3 ms
75x in 2 sec.
242 chips
~41 days
Length
Orthogonal
Modulation
(information carrier)
Quadrature
Spreading
(Zero offset)
Distinguish users
Reverse Link
Function
User identity
within cell’s
signal
Distinguish Cells
& Sectors
Data Scrambling
to avoid strings
of 1’s or 0’s
Forward Link
Function

21. CDMA Advantages
• Spread Spectrum
• Soft & Softer Handoff
• Rake Receiver
• Variable Rate Vocoder
• High quality voice
• Power Control
• Coverage
• Simple Network Planning
• Green Handset
• Smooth migration to 3G and the operator’s
benefit is protected at the most

22. Spread Spectrum (1)
S(f)
ff0
Before spreading
Signal
S(f)
ff0
After spreading
Signal
S(f)
ff0
After despreading
signal
Interfering noise
f
S(f)
f0
Before despreading
Signal
Interfering noise

23. Spread Spectrum(2)
Radio
Channel
Channel Coding
(SS)
Carrier
Modulation
DS-PN
Source
Coding
Transmit
Antenna
Radio
Channel
Channel
Coding
(SS)
Carrier
Modulation
DS-PN
Source
Coding
Transmit
Channel
Decoding
Carrier
Demodulation
DS-PN
Source
Decoding
Receive
Channel
Decoding
Carrier
Demodulation
DS-PN
Source
Decoding
Receive
Antenna
A B

24. Spreading Spectrum (3)
“Principle of Using Multiple Codes”
Spreading
Sequence
A
Spreading
Sequence
B
Spreading
Sequence
C
Spreading
Sequence
C
Spreading
Sequence
B
Spreading
Sequence
A
Input
Data
X
Recovered
Data
X
X+A X+A+B X+A+B+C X+A+B X+A
Spread-Spectrum Chip Streams
ORIGINATING SITE DESTINATION

25. Spread Spectrum (4)

26. Advantages of Spread
Spectrum
Avoid interference arising from jamming
signal or multi-path effects.
Covert operation:Difficult to detect
Achieve Privacy: Difficult to demodulate,
Noise like signal.
Impossible to Eavesdrops on the signal
expect using the same PN sequence

27. Soft & Softer Handoff
Connection first and disconnection
afterwards in handoff.
High quality of service and effective
reduction of call drops.
Softer handoff: same BS &
frequency, between different sectors.
Soft handoff: adjacent cells of
the same frequency.
BSC
BSC MSC

28. Rake Receiver (1)
d1
d2
t t t
d3
transmission
receiving
Raker combination
noise

29. Rake Receiver (2)
Correlator 1
Correlator 2
Correlator 3
Search Correlator
Combiner
To De-Interleaver,
Viterbi Decoder
Multipath Delay
Components
( 150 ms > Dt > 1ms)
Rake receiver can isolate
multipath spaced > 1 chip length.

30. Rake Receiver (3)
• Handset uses combined outputs of the three traffic
correlators ―rake fingers‖
• Each finger can independently recover a particular
PN offset and Walsh code
• Fingers can targeted on delayed multipath
reflections, or even on different BTSs
• Searcher continuously checks pilots

31. Intelligent Vocoder

32. High Quality Voice(1)
Voice quality
64k
PCM
present
GSM
8k
CDMA
13k
CDMA
8k EVRC
CDMA

33. High Quality Voice(2)
High quality Voice??
Voice activity Technology

34. Power Control
Autonomous power control
On the Uplink tells the MS to vary it’s transmitted power inversely with
the power level it receive from the BS.
Direct power control
On the Uplink measures Eb/No at the base station and sends power
Control Bits over the Downlink to the MS to instruct the MS to
either increase or decrease its transmit power.
Downlink power control
Attempts to use minimum power needed to meet to a Frame Error Rate
(FER) threshold at the MS s.

35. Coverage
• The coverage radius is 2 times of
standard GSM.
• Coverage of 1000 km2: GSM
needs 200 BTS 's, while CDMA
requires only 50.
• Under the same coverage
conditions, the number of BTS 's
is greatly decreased

36. Simple Network Planning
Simple project design &
convenient capacity expansion
1
3
2
4
3
2
4
2
4
4
1
2
3
1
4
2
3
1
4
1
1
1
1
1
1 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Simple project design &
convenient capacity expansion

37. Green Handset
Systems
M ean
transmission
power
M ax
transmission
power
GSM 125 mW 2W
CDM A 2 mW 200mW
Low transmission power:
Accurate power control, handoff
control, voice activation

38. Functions of the CDMA
Reverse Channels
• There are two types of CDMA Reverse
Channels:
– TRAFFIC CHANNELS are used by
individual
users during their actual calls to transmit
traffic
to the BTS.
– ACCESS CHANNELS are used by mobile
stations not yet in a call to transmit
registration requests, call setup requests, page
responses, order responses, and other
signaling information

39. Coding Process on CDMA
Reverse Channels
• Each mobile is uniquely identified by the User Long
Code, which it generates internally.
• All mobile stations transmit simultaneously on the
same 1.25 MHz wide frequency band.
• Any nearby BTS can dedicate a channel element to
the mobile station and successfully extract its signal.
• Mobile stations also use the other CDMA spreading
sequences, but not for channel-identifying purposes.
• Short PN Sequences are used to achieve phase
modulation.
• Walsh Codes are used as Orthogonal Modulation to
give ultra-reliable communications recovery at the
BTS.

40. Benefits of the cdma2000 1x
Standards
• Increased mobile standby battery life (via Quick
Paging Channel)
• Total backward compatibility to reuse switch
and call processing features
• 2-3 dB better coverage
• High speed 153.6 kbps packet data capabilities
• cdma2000 1x = 1.25 MHz Radio Transmission
Technology

41. Backward Compatible with
IS-95 Air Interface
IS-95 mobiles are supported in the IS-
2000 standard for 1xRTT:
• No need to change any RF infrastructure
• Capacity improvements will not be
realized until most IS-95 subscribers
disappear

42. Channel List: 1xRTT vs. IS-95
• IS-95B built on the IS-95A channels, and introduced two new channels
– Fundamental channel was the same as IS-9A traffic channel
– Supplemental code channels assigned to support rates above 14.4Kbps
• IS-2000 1xRTT continue to build on the IS-95 channels
– IS-95 channels continue to be supported in IS-2000 to support IS-95
mobiles
Pilot channel
Sync channel
Paging channel Access channel
Forward Traffic Channel Reverse Traffic Channel
Fundamental channel Fundamental channel
Supplemental Code channel (F-SCCH) Supplemental Code channel (R-SCCH)
Supplemental channel (F-SCH) Supplemental channel (R-SCH)
Quick Paging channel (F-QPCH) Reverse Pilot channel (R-PICH)
IS-95B
1xRTT
IS-95A
Forward Reverse

43. Discriminating Among Forward
Code Channels
• A Mobile Station receives a Forward Channel from a sector
in a Base Station.
• The Forward Channel carries a composite signal of up to 64
forward code channels.
• Some code channels are traffic channels and others are
overhead channels.
• A set of 64 mathematical codes is needed to differentiate the
64 possible forward code channels.
– The codes in this set are called “Walsh Codes”
SyncPilot
FW Traffic
(for user #1)
Paging
FW Traffic
(for user #2)
FW Traffic
(for user #3)

44. Discriminating Among Base
Station
• A mobile Station is surrounded by Base Stations, all of them transmitting on
the same CDMA Frequency.
• Each Sector in each Base Station is transmitting a Forward Traffic Channel
containing up to 64 forward code channels.
• A Mobile Station must be able to discriminate between different Sectors of
different Base Stations.
• Two binary digit sequences called the I and Q Short PN Sequences (or Short
PN Codes) are defined for the purpose of identifying sectors of different
base stations.
• These Short PN Sequences can be used in 512 different ways in a CDMA
system. Each one of them constitutes a mathematical code which can be
used to identify a particular sector.
A B
Up to 64
Code Channels
Up to 64
Code Channels

45. Example of cdma2000 1x
Network

46. Structure of a Typical CDMA
system