1. CDMA Theory

2. CDMA Theory Unit 1
CDMA Basic Principle

3. Main Content Definitions of CDMA and How to realize
Spread spectrum modulation
Spreading codes used in CDMA
Vocoding in CDMA

4. Multiple Access Types of Media -- Examples: Twisted pair - copper
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.
Multiple Access: Simultaneous private use of a transmission medium by multiple, independent users.
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

5. Channels FDMA TDMA CDMA FDMA Frequency Division Multiple Access
Time
Power
FDMA
TDMA
CDMA
Channel: An individually-assigned, dedicated pathway through a transmission medium for one user’s information.
The transmission medium is a resource that can be subdivided into individual channels according to the technology used.
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

6. Defining Our Terms 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 Channel
1.25 MHz Forward Link
CDMA Reverse Channel
1.25 MHz 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
Forward

7. Main Content
Spread spectrum modulation

8. What is Spread Spectrum
ORIGINATING SITE
DESTINATION
Spreading
Sequence
Input
Data
Recovered
Spread Data Stream
Definition:Spread spectrum technique ,employ a transmission bandwidth that is several orders of magnitude greater than the minimum required signal bandwidth.
Sender combines data with a fast spreading sequence, transmits spread data stream
Receiver intercepts the stream, uses same spreading sequence to extract original data

9. C=B*log2(1+S/N) Spread Spectrum Principles SHANON Formula Where,
C is capacity of channel, b/s
B is signal bandwidth, Hz
S is average power for signal, W
N is average power for noise, W
It is the basic principle and theory
for spread spectrum communications.

10. CDMA Is a Spread-Spectrum System
Spread Spectrum Payoff: Processing Gain
Spread Spectrum
TRADITIONAL COMMUNICATIONS SYSTEM
Slow
Information
Sent TX
Recovered RX
Narrowband
Signal
SPREAD-SPECTRUM SYSTEM
Fast
Spreading
Sequence
Wideband Signal
Traditional technologies try to squeeze the signal into the minimum required bandwidth
Direct-Sequence Spread spectrum systems mix their input data with a fast spreading sequence and transmit a wideband signal
The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data

11. Spread Spectrum Principles
1.25 MHz
30 KHz
Power is “Spread” Over a Larger Bandwidth
MATH
HAMMER
MATH
HAMMER

12. Spread Spectrum Principles
Many code channels are individually
“spread” and then added together to
create a “composite signal”

13. Main Content
Spreading codes used in CDMA

14. Spreading Codes in CDMA
Spreading codes selection is the key of spreading
Spectrum modulation!
Spreading code chip speed：1.2288Mc/s；
Spreading code：Forward link—Walsh cod & Short PN
Reverse link —Long PN

15. Walsh Code Defination =
The Walsh function is named after Walsh, the mathematician who proved it an orthogonal function in It is expressed as Walsh (n,t), n for the serial number. The CDMA system of IS-95 is differentiated with the Walsh function.
Walsh code is an orthogonal square matrix. It is just composed of +1(0) and –1(1). H n 2n =
___ 1

16. Correlation of Walsh Code #23 with Walsh Code #59
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
WALSH CODES
# Chip Sequence
EXAMPLE:
Correlation of Walsh Code #23 with Walsh Code #59 # #
XOR
Correlation Results: 32 1’s, 32 0’s: Orthogonal!!

17. In mathematics, orthogonality is the relation of two lines atright angles to one another (perpendicularity), and the generalization of this relation into n dimensions; and to a variety of mathematical relations thought of as describing non-overlapping, uncorrelated, or independent objects of some kind.
The concept of orthogonality has been broadly generalized in mathematics, science, and engineering, especially since the beginning of the 16th century. Much of it has involved the concepts of mathematical functions, calculus, and linear algebra.

18. Correlation and Orthogonality
Code #
–(Code #23)
Code #
PARALLEL
XOR: all 0s
Correlation: 100%
(100% match)
ORTHOGONAL
XOR: half 0s, half 1s
Correlation: 0%
(50% match, 50% no-match)
ANTI-PARALLEL
XOR: all 1s
Correlation: –100%
(100% no-match)
#23
–(#23)
#59
Correlation is a measure of the similarity between two binary strings

19. Walsh Code Function in Forward Link
Sync
Pilot
FW Traffic
(for user #1)
Paging
(for user #2)
(for user #3)
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”

20. Short PN Sequences
The two Short PN Sequences, I and Q, are 32,768 chips long I Q
32,768 chips long
26 2/3 ms.
(75 repetitions in 2 sec.)
100% Correlation: All bits = 0
Short PN Sequence vs. 0 Offset
Orthogonal: 16,384 1’s + 16,384 0’s
Short PN Sequence vs. Any Offset
Unique Properties:
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)

21. Short PN Function in Forward LinkB
Up to 64
Code Channels
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.

22. Long Code Register (@ 1.2288 MCPS)
The Long PN Sequence
Long Code Register MCPS)
Public Long Code Mask
(STATIC)
User Long Code
Sequence
MCPS) 1 P E R M U T D S N
AND =
Modulo-2 Addition
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 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete.
Portions of the User Long Codes generated by different mobile stations for the duration of a call are not exactly orthogonal but are sufficiently different to permit reliable decoding on the reverse link.

23. Long PN Function in Reverse Link
RV Traffic
from M.S. # # #
System Access
Attempt by M.S. #
(on access channel #1)
The CDMA system must be able to identify each Mobile Station that may attempt to communicate with a Base Station.
A very large number of Mobile Stations will be in the market.
One binary digit sequence called the Long PN Sequence (or Long PN Code) is defined for the purpose of uniquely identifying each possible reverse code channel.
This sequence is extremely long and can be used in trillions of different ways. Each one of them constitutes a mathematical code which can be used to identify a particular user (and is then called a User Long Code) or a particular “user Reverse Traffic channel”.

24. Summary of Characteristics & Functions
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 I Q
32,768 chips long
26-2/3 ms.
(75 repetitions in 2 sec.)
64 codes
64 chips long
AND = S U M
Modulo-2 Addition
Cell
Each CDMA spreading sequence is used for a specific purpose on the forward link and a different purpose on the reverse link.
The sequences are used to form “code channels” for users in both directions.

25. Main Content
Vocoding in CDMA

26. Variable Rate Vocoder
A-to-D C O N V E R T
64 Kbps D
“Codebook” Instruction
8Kbps
MSC
Speech coding algorithms (digital compression) are necessary to increase cellular system capacity.
Coding must also ensure reasonable fidelity, that is, a maximum level of quality as perceived by the user.
Coding can be performed in a variety of ways (for example, waveform, time or frequency domain).
Vocoders transmit parameters which control reproduction of voice instead of the explicit, point-by-point waveform description.

27. Variable Rate Vocoding
CDMA uses a superior Variable Rate Vocoder
Full rate during speech
Low rates in speech pauses
Increased capacity
More natural sound
Voice, signaling, and user secondary data may be mixed in CDMA frames
DSP QCELP VOCODER
Codebook
Pitch
Filter
Formant
Coded Result
Feed-
back
20ms Sample

28. Variable Rate Vocoding
Rate Set 2 Frame Sizes
bits
Full Rate Frame
1/2 Rate Frame
1/4 Rt.
1/8 36 72
144
288
Rate Set 1 Frame Sizes 24 48 96
192
Rate set1（8KQCELP & EVRC):Rate set2（13KQCELP ):
Full rate：9.6Kbps Full rate ：14.4Kbps
Half rate：4.8Kbps Half rate ：7.2Kbps
1/4 rate：2.4Kbps 1/4 rate ：3.6Kbps
1/8 rate:1.2Kbps 1/8 rate :1.8Kbps

29. Variable Rate Voice Bit and PCM
Where is vocoder?
BTS
BSC
MSC
Analog voice
Variable Rate
PCM

30. CDMA CHANNEL STRUCTURE
CDMA Theory Unit 2
CDMA CHANNEL STRUCTURE
AND MODULATION

31. Main Content The Forward Channels in IS-95
The Reverse Channels in IS-95
New Channels in CDMA20001X

32. IS-95 Channel Structure

33. Pilot Channel
Used by the mobile station for initial system acquisition
Transmitted constantly by the base station
The same Short PN sequences are shared by all base stations
Each base station is differentiated by a phase offset
Provides tracking of:
Timing reference
Phase reference
Acquisition by mobile stations is enhanced by:
Short duration of Pilot PN sequence
Uncoded nature of pilot signal
Facilitates mobile station-assisted handoffs
Used to identify handoff candidates
Key factor in performing soft handoffs

34. Pilot Channel Generation
The Walsh function zero spreading sequence is applied to the Pilot
The use of short PN sequence offsets allows for up to 512 distinct Pilots per CDMA channel
The PN offset index value (0-511 inclusive) for a given pilot PN sequence is multiplied by 64 to determine the actual offset
Example: 15 (offset index) x 64 = 960 PN chips
Result: The start of the pilot PN sequence will be delayed 960 chips x microseconds per chip = microsecond

35. Sync Channel Used to provide essential system parameters
Used during system acquisition stage
Bit rate is 1200 bps
Sync channel has a frame duration of 26 2/3 ms
Frame duration matches the period of repetition of the PN Short Sequences
Simplifies the acquisition of the Sync Channel once the Pilot Channel has been acquired
Mobile Station re-synchronizes at the end of every call
(Acquired Pilot)
Sync Channel

36. Paging Channels
Paging Channel
Used by the base station to
transmit system overhead information
and mobile station-specific messages.
There is one paging channel per sector per CDMA carrier
The Paging Channel uses Walsh function 1
Two rates are supported: 9600 and 4800 bps

37. CDMA Forward Traffic Channels
Sync
Paging
Pilot
CDMA Cell Site
Used for the transmission of user and signaling information to a specific mobile station during a call.
Maximum number of traffic channels: 64 minus one Pilot channel, one Sync channel, and 1 Paging channel.
This leaves each CDMA frequency with at least 55 traffic channels.
Unused paging channels can provide up to 6 additional channels.

38. Quadrature Phase Shift Key (QPSK) Modulation
Convolutional
Encoding
Code Symbol
Repetition
Vocoder
Processing
Baseband Traffic
to RF Section
PCM Voice
Block
Interleaving
Data Scrambling
Power Control
Subchannel
Orthogonal
Spreading
Quadrature
Baseband
Filtering
(Symbol
Puncturing)
Walsh Function
1.2288
Mcps
19.2 ksps
from Power
Control Mux
I-Channel Pilot PN Sequence
Mcps
Baseband
Filter I Q S
Q-Channel Pilot PN Sequence
cos(2pfct)
sin(2pfct) G
A I N
The forward traffic channel is combined with two different PN sequences: “I” and “Q”
Baseband filtering ensures the waveforms are contained within the 1.25 MHz frequency range
The final step is to convert the two baseband signals to radio frequency (RF) in the 800 MHz or 1900 MHz range

39. Main Content The Forward channels in IS-95
The Reverse channels in IS-95
New Channels in CDMA20001X

40. Reverse Access Channels
4800 bps
Used by the mobile station to:
Initiate communication with the base station
Respond to Paging Channel messages
Has a fixed data rate of 4800 bps
Each Access Channel is associated with only one Paging Channel
Up to 32 access channels (0-31) are supported per Paging Channel

41. CDMA Reverse Traffic Channels
Used when a call is in progress to send:
Voice traffic from the subscriber
Response to commands/queries from the base station
Requests to the base station
Supports variable data rate operation for:
8 Kbps vocoder
Rate Set , 4800, 2400 and 1200 bps
13 Kbps vocoder
Rate Set , 7200, 3600, 1800 bps

42. Main Content The forward channels in IS-95
The reverse channels in IS-95
New Channels in CDMA20001X

43. CDMA2000-1X New Features
High speed kbps packet data capabilities;
Increased mobile standby battery life;
Total backward compatibility to reuse switch and call processing features;
Voice capacity 1.5—2times larger than IS-95
CDMA2000 1x RF Capacity

44. CDMA20001X New Technology
Forward link
Fast power control
IS-95，50Hz;IS-2000，800Hz；
Transmitting diversity
Release A OTD（orthogonal transmit diversity）;
Use variable length Walsh code, support multiple code channels for one user，adopt turbo code for error correction modulation。
Reverse link
Support pilot channel, help BTS demodulate MS;
Walsh code is used to distinguish code channels,not
orthogonal modulation;
support multiple code channels for one user，adopt turbo code for error correction modulation。
CDMA2000 1x = 1.25 MHz Radio Transmission Technology

45. 1x New Channels in Commercial Network
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 xRTT 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
For backward compatibility, channels defined in IS-95 still exist in IS-2000; IS-2000 adds many others
SCH used for high-speed data (any burst over 9600 bps). Although the standard supports the assignment of up to 2 per users, only 1is supported now; in future, support for up to 2 may be assigned.
SCCH (up to 7 of which can be assigned) are still supported in IS-2000, not likely to be used or supported
QPCH saves mobile standby battery power; enhancement to slotted mode paging
R-PCH allows base station to do timing corrections without having to guess where mobile is. Actually results in less transmit power overall.
Fundamental difference between IS-95B and IS-2000 is that a dedicated connection between a base station and mobile can exist without a fundamental channel. Also, use of reverse pilot channel enables the base station to demodulate signals from the mobile.

46. Forward Supplemental Channel (F-SCH)
Assigned for high-speed packet data (>9.6 kbps) in the forward direction; (FCH is always assigned to each call)
Up to 2 F-SCH can be assigned to a single mobile
SCH cannot exist without having a fundamental channel established
F-SCH supports Walsh code lengths of depending on data rate and chip rate(in RC3, only use chips)
SCH-1
File transfer at kbps
FCH
Voice, power control and link continuity
Mobile 1
In the example, Mobile 1 shows currently supported scenario (an FCH is always assigned for each call: data or voice). Note however, that (for now) simultaneous voice and data calls are not supported.
SCHs cannot be assigned without some other FCH being assigned as well.

47. Reverse Pilot Channel (R-PICH)
Mobile transmits well-known pattern (pilot)
Allows base station to do timing corrections without having to guess where mobile is (in search window)
Mobile can transmit at lower power, reducing interference to others

48. Reverse Supplemental Channel (R-SCH)
Used for high-speed packet data (>9.6 kbps)
Difference between F-SCH and R-SCH is in Walsh code based spreading
F-SCH supports Walsh code lengths of 4 to 128 (1xRTT) or 1024 (3xRTT) depending on data rate and chip rate
Walsh code allocation sequence is pre-determined and common to all mobiles
Users are differentiated using long PN code with user mask
Here is the first mention of variable length Walsh codes. It’s probably enough to know that Walsh code length for data calls is variable at this point. Implementation and rationale for Walsh codes of varying length is discussed later.
Note that Walsh codes are now used explicitly in the reverse direction. This is because there are now more than one reverse channel, and they need to be distinguishable from one another.

49. The End !