35
CDMA TECHNOLOGY INSTRCTOR: NAZILA SAFAVI
CDMA TECHNOLOGY
INSTRCTOR: NAZILA SAFAVI
What This Course is All About?
CDMA
CDMA
odeivisionultipleccess
What is Multiple Access?
Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit
n Types of Media -- Examples: Twisted pair - copper Coaxial cable Fiber optic cable Air interface (radio signals)
n 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
Transmission
Medium
Each pair of users enjoys a dedicated,
private circuit through the transmission
medium, unaware that the other users exist.
Multiple Access: Simultaneous private use of a transmission medium by multiple, independent users.
What is a Channel?
The physical transmission medium is a resource that can be subdivided into individual channels according to different criteria depending on the technology used:
Here’s how the three most popular technologies establish channels:
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 Mult iple Access
each user uses the same frequency all the time, but mixed with different distinguishing code patterns
a channel is a unique code patternFrequency
Time
Power
FrequencyTime
Power
FrequencyTime
Power
FDMA
TDMA
CDMA
Channel: An individually-assigned, dedicated pathway through a transmission medium for one user’s information
Defining Our Terms
n 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 UPNLINK)
in 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart in 1900 MHz PCS they are 80 MHz apart
n CDMA Forward Channel the 1.25 MHz Forward Link
n CDMA Reverse Channel the 1.25 MHz Reverse Link
n 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 CHANNELCDMA
ReverseChannel 1.25 MHz
CDMAForwardChannel 1.25 M Hz
Spread Spectrum Principles
Why do we call this a “Spread Spectrum” technique?
Spread Spectrum Payoff:Processing Gain
Spread SpectrumTRADITIONAL COMMUNICATIONS SYSTEM
SlowInformation
SentTX
SlowInformationRecovered
RX
NarrowbandSignal
SPREAD-SPECTRUM SYSTEM
FastSpreadingSequence
SlowInformation
Sent
TX
SlowInformationRecovered
RX
FastSpreadingSequence
WidebandSignal
n Traditional radio communication systems transmit data using the minimum bandwidth required to carry it as a narrowband signal
n 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
n The de-spreading gives substantial gain proportional to the bandwidth of the spread-spectrum signal
n The gain can be used to increase system performance and range, or allow multiple coded users, or both
CDMA Spreading Principle:Anything We Can Do, We Can Undo
n Any data bit stream can be combined with a spreading sequence
n The resulting signal can be de-spread and the data stream recovered if the original spreading sequence is available and properly timed
n After de-spreading, the original data stream is recovered intactNote - The spread sequences actually shown are icons, not accurate or to scale
ORIGINATING SITE DESTINATION
SpreadingSequence
SpreadingSequence
InputData
(Base Band)
RecoveredData
(Base Band)
Spread Data Stream(Base Band + Spreading Sequence)
Shipping and Receiving” via CDMA
n Whether in shipping and receiving, or in CDMA, packaging is extremely important!
n Cargo is placed inside “nested” containers for protection and to allow addressing
n The shipper packs in a certain order, and the receiver unpacks in the reverse order
n CDMA “containers” are spreading codes
FedExData Mailer
FedExDataMailer
Shipping Receiving
CDMA Spreading Principle:Multiple Successive Spreadings are
Reversible
n Multiple spreading sequences can be applied in succession and then reapplied in opposite order, to recover the original un-spread data streamthe spreading sequences can have different desired properties
n All spreading sequences originally used must be available in proper synchronization at the recovering destinationNote - The spread sequences actually shown are icons, not accurate or to scale
SpreadingSequence
ASpreadingSequence
BSpreadingSequence
CSpreadingSequence
CSpreadingSequence
BSpreadingSequence
A
InputDataX
RecoveredDataX
X+A X+A+B X+A+B+C X+A+B X+ASpread-Spectrum Chip Streams
ORIGINATING SITE DESTINATION
How Many Spreading Sequences Do We Need?(Discriminating Among Forward Code Channels
n A Mobile Station, tuned to a particular CDMA frequency, receives a Forward CDMA Channel from a sector in a Base Station.
n This Forward CDMA Channel carries a composite signal made of up to 64 “forward code channels”
n Some of these code channels are “traffic channels” while other are “overhead channels” needed by the CDMA system to operate properly.
n A set of 64 mathematical codes is needed to differentiate the 64 possible forward code channels that can be contained in a Forward CDMA Channel. 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)
How Many Spreading Sequences Do We Need?(Discriminating Among Base Station
n A mobile Station is surrounded by Base Stations, all of them transmitting on the same CDMA Frequency
n Each Sector in each Base Station is transmitting a CDMA Forward Traffic Channel containing up to 64 distinct forward code channels
n A Mobile Station must be able to discriminate between different Sectors of different Base Stations and listen to only one set of code channels
n 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
n 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 of a particular base station
A B
Up to 64Code Channels
Up to 64Code Channels
How Many Spreading Sequences Do We Need?(Discriminating Among Reverse Code Channels
n The CDMA system must be able to uniquely identify each Mobile Station that may attempt to communicate with a Base Station
n A very large number of Mobile Stations will be in the market
n 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
n 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 “access channel” (explained later in this course)
RV Trafficfrom M.S.
#1837732008RV Trafficfrom M.S.
#8764349209
RV Trafficfrom M.S.
#223663748System AccessAttempt by M.S.#4348769902
(on access channel #1)
CDMA Magic Spreading Tool #1:Walsh Codes
n 64 “Magic” Sequences, each 64 chips long a chip is a binary digit (0 or 1)
n 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
n Two same-length binary strings are orthogonal if the result of XORing them has the same number of 0s as 1s
WALSH CODES # --- ------ ------ ------- ------ ------ 64 - Chip Se quen ce -- ------ ------- ------ ------ ------- ------ --
0 0 00000 00000 000 0000 000000 0000 00000000 000 0000000 0000 00 00 0000000 00 0
1 0 10101 01010 101 0101 010101 0101 01010101 010 1010101 0101 01 01 0101010 10 1 2 0 01100 11001 100 1100 110011 0011 00110011 001 1001100 1100 11 00 1100110 01 1 3 0 11001 10011 001 1001 100110 0110 01100110 011 0011001 1001 10 01 1001100 11 0 4 0 00011 11000 011 1100 001111 0000 11110000 111 1000011 1100 00 11 1100001 11 1 5 0 10110 10010 110 1001 011010 0101 10100101 101 0010110 1001 01 10 1001011 01 0
6 0 01111 00001 111 0000 111100 0011 11000011 110 0001111 0000 11 11 0000111 10 0 7 0 11010 01011 010 0101 101001 0110 10010110 100 1011010 0101 10 10 0101101 00 1 8 0 00000 00111 111 1100 000000 1111 11110000 000 0111111 1100 00 00 0011111 11 1 9 0 10101 01101 010 1001 010101 1010 10100101 010 1101010 1001 01 01 0110101 01 010 0 01100 11110 011 0000 110011 1100 11000011 001 1110011 0000 11 00 1111001 10 0
11 0 11001 10100 110 0101 100110 1001 10010110 011 0100110 0101 10 01 1010011 00 112 0 00011 11111 100 0000 001111 1111 00000000 111 1111100 0000 00 11 1111110 00 013 0 10110 10101 001 0101 011010 1010 01010101 101 0101001 0101 01 10 1010100 10 114 0 01111 00110 000 1100 111100 1100 00110011 110 0110000 1100 11 11 0011000 01 115 0 11010 01100 101 1001 101001 1001 01100110 100 1100101 1001 10 10 0110010 11 0
16 0 00000 00000 000 0011 111111 1111 11110000 000 0000000 0011 11 11 1111111 11 117 0 10101 01010 101 0110 101010 1010 10100101 010 1010101 0110 10 10 1010101 01 018 0 01100 11001 100 1111 001100 1100 11000011 001 1001100 1111 00 11 0011001 10 019 0 11001 10011 001 1010 011001 1001 10010110 011 0011001 1010 01 10 0110011 00 120 0 00011 11000 011 1111 110000 1111 00000000 111 1000011 1111 11 00 0011110 00 0
21 0 10110 10010 110 1010 100101 1010 01010101 101 0010110 1010 10 01 0110100 10 122 0 01111 00001 111 0011 000011 1100 00110011 110 0001111 0011 00 00 1111000 01 123 0 11010 01011 010 0110 010110 1001 01100110 100 1011010 0110 01 01 1010010 11 024 0 00000 00111 111 1111 111111 0000 00000000 000 0111111 1111 11 11 1100000 00 025 0 10101 01101 010 1010 101010 0101 01010101 010 1101010 1010 10 10 1001010 10 1
26 0 01100 11110 011 0011 001100 0011 00110011 001 1110011 0011 00 11 0000110 01 127 0 11001 10100 110 0110 011001 0110 01100110 011 0100110 0110 01 10 0101100 11 028 0 00011 11111 100 0011 110000 0000 11110000 111 1111100 0011 11 00 0000001 11 129 0 10110 10101 001 0110 100101 0101 10100101 101 0101001 0110 10 01 0101011 01 030 0 01111 00110 000 1111 000011 0011 11000011 110 0110000 1111 00 00 1100111 10 0
31 0 11010 01100 101 1010 010110 0110 10010110 100 1100101 1010 01 01 1001101 00 132 0 00000 00000 000 0000 000000 0000 00001111 111 1111111 1111 11 11 1111111 11 133 0 10101 01010 101 0101 010101 0101 01011010 101 0101010 1010 10 10 1010101 01 034 0 01100 11001 100 1100 110011 0011 00111100 110 0110011 0011 00 11 0011001 10 035 0 11001 10011 001 1001 100110 0110 01101001 100 1100110 0110 01 10 0110011 00 1
36 0 00011 11000 011 1100 001111 0000 11111111 000 0111100 0011 11 00 0011110 00 037 0 10110 10010 110 1001 011010 0101 10101010 010 1101001 0110 10 01 0110100 10 138 0 01111 00001 111 0000 111100 0011 11001100 001 1110000 1111 00 00 1111000 01 139 0 11010 01011 010 0101 101001 0110 10011001 011 0100101 1010 01 01 1010010 11 040 0 00000 00111 111 1100 000000 1111 11111111 111 1000000 0011 11 11 1100000 00 0
41 0 10101 01101 010 1001 010101 1010 10101010 101 0010101 0110 10 10 1001010 10 142 0 01100 11110 011 0000 110011 1100 11001100 110 0001100 1111 00 11 0000110 01 143 0 11001 10100 110 0101 100110 1001 10011001 100 1011001 1010 01 10 0101100 11 044 0 00011 11111 100 0000 001111 1111 00001111 000 0000011 1111 11 00 0000001 11 145 0 10110 10101 001 0101 011010 1010 01011010 010 1010110 1010 10 01 0101011 01 0
46 0 01111 00110 000 1100 111100 1100 00111100 001 1001111 0011 00 00 1100111 10 047 0 11010 01100 101 1001 101001 1001 01101001 011 0011010 0110 01 01 1001101 00 148 0 00000 00000 000 0011 111111 1111 11111111 111 1111111 1100 00 00 0000000 00 049 0 10101 01010 101 0110 101010 1010 10101010 101 0101010 1001 01 01 0101010 10 150 0 01100 11001 100 1111 001100 1100 11001100 110 0110011 0000 11 00 1100110 01 1
51 0 11001 10011 001 1010 011001 1001 10011001 100 1100110 0101 10 01 1001100 11 052 0 00011 11000 011 1111 110000 1111 00001111 000 0111100 0000 00 11 1100001 11 153 0 10110 10010 110 1010 100101 1010 01011010 010 1101001 0101 01 10 1001011 01 054 0 01111 00001 111 0011 000011 1100 00111100 001 1110000 1100 11 11 0000111 10 055 0 11010 01011 010 0110 010110 1001 01101001 011 0100101 1001 10 10 0101101 00 1
56 0 00000 00111 111 1111 111111 0000 00001111 111 1000000 0000 00 00 0011111 11 157 0 10101 01101 010 1010 101010 0101 01011010 101 0010101 0101 01 01 0110101 01 058 0 01100 11110 011 0011 001100 0011 00111100 110 0001100 1100 11 00 1111001 10 059 0 11001 10100 110 0110 011001 0110 01101001 100 1011001 1001 10 01 1010011 00 160 0 00011 11111 100 0011 110000 0000 11111111 000 0000011 1100 00 11 1111110 00 0
61 0 10110 10101 001 0110 100101 0101 10101010 010 1010110 1001 01 10 1010100 10 162 0 01111 00110 000 1111 000011 0011 11001100 001 1001111 0000 11 11 0011000 01 163 0 11010 01100 101 1010 010110 0110 10011001 011 0011010 0101 10 10 0110010 11 0
EXAMPLE:
Correlation of Walsh Code #23 with Walsh Code #59#23 0110100101101001100101101001011001101001011010011001011010010110#59 0110011010011001100110010110011010011001011001100110011010011001XOR 0000111111110000000011111111000011110000000011111111000000001111
Correlation Results: 32 1’s, 32 0’s: Orthogonal!!
Note: Example of orthogonality – The coordinates used to describe the position of a mobile station at a certain time: latitude (North or South of the Equator), longitude (East or West of Greenwich), altitude (relative to sea level), and time. A change in any of these magnitudes does not affect the other three, therefore they are “orthogonal”.
Correlation and Orthogonality
Correlation is a measure of the similarity between two binary strings
Code #23 0110100101101001100101101001011001101001011010011001011010010110
-(Code #23) 1001011010010110011010010110100110010110100101100110100101101001
Code #59 0110011010011001100110010110011010011001011001100110011010011001
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
-(#23)
#23
#23
#59
-(#23)
CDMA Magic Spreading Tool #2:The Short PN Sequences
n The two PN Sequences, I and Q, are 32,768 chips longTogether, they can be
considered a two-dimensional binary “vector” with distinct I and Q component sequences, each 32,768 chips long
n Each Short PN Sequence (and, as a matter of fact, any sequence) correlates with i tself perfectly if compared at a timing offset of 0 chips
n Each Short PN Sequence is special: Nearly orthogonal to a copy of itself that has been offset by any number of chips (other than 0)
IQ
32,768 chips long26 2/3 ms.
(75 repetitions in 2 sec.)
IQIQ
100% Correlation: All bits = 0
Short PN Sequence vs. Itself @ 0 Offset
IQIQ
Orthogonal: 16,384 1’s + 16,384 0’s
Short PN Sequence vs . Itself @ Any Offset
Unique Properties:
CDMA Magic Spreading Tool #3:The Long PN Sequence (User Long Code)
n Each mobile station uses a world-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
n Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete
n Portions of the Users Long Codes generated by different mobile stations for the duration of a call are not exactly orthogonal but are sufficiently different to permit re liable decoding on the reverse link
Long Code Register (@ 1.2288 MCPS)
Public Long Code Mask (STATIC)
User Long CodeSequence
(@1.2288 MCPS)
1 1 0 00 1 1 0 0 0 PERMUTED ESNAND
=SUM
Modulo-2 Addition
CDMA Code Channels in the Forward Direction
n PILOT: WALSH CODE 0 The Pilot is a “structural beacon” which
does not contain a c haracter stream. It is a timing source used in system acquisition and as a measurement device during handoffs
n SYNC: WALSH CODE 32 This carries a data stream of system
identification and parameter information used by mobiles during sy stem acquisition
n PAGING: WALSH CODES 1 up to 7 There can be from one to seven paging
channels as determined by capacity needs. They carry pages, system parameters information, and call setup orders
n TRAFFIC: any remaining WALSH codes The traffic channels are as signed to
individual users to c arry call traffic. All remaining W alsh codes are available, subject to ove rall capacity limited by noise
Pilot Walsh 0
Walsh 19
Paging Walsh 1Walsh 6
Walsh 11
Walsh 20Sync Walsh 32
Walsh 42
Walsh 37Walsh 41
Walsh 56Walsh 60
Walsh 55
Coding Process on CDMA Forward Code Channels
MTX BSC BTS (1 sector)
FECWalsh #1
Sync FECWalsh #32
FECWalsh #0
FECWalsh #12
FECWalsh #23
FECWalsh #27
FECWalsh #44
Pilot
Paging
Vocoder
Vocoder
Vocoder
Vocoder
more more more
Short PN CodePN Offset 246
Trans-mitter,
Sector X
I Q
A Forward Channel is identified by:
v its CDMA RF carrier Frequency
v the unique Short Code PN Offset of the sector
v the unique Walsh Code of the user
MSC
CDMA Code Channels in the Reverse Direction
There are two types of CDMA Reverse Channels:
n TRAFFIC CHANNELS are used by individualusers during their actual calls to transmit trafficto the BTS
• a reverse traffic channel is defined by a user-specific public or private Long Code mask
• there are as many reverse Traffic Channels asthere are CDMA phones in the world
n 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
• an access channel is defined by a user-independent public long code mask
• Access channels are paired with Paging Channels. There can be up to 32 access channels per paging channel
BTS
REG
1-800242
4444
Coding Process on CDMA Reverse Code Channels
MTX BSC BTS (1 sector)
Channel Element
Access Channels
Vocoder
Vocoder
Vocoder
Vocoder
more more
Receiver,Sector X
A Reverse Channel is identified by:v its CDMA RF carrier Frequencyv the unique Long Code PN Offset
of the individual handset
Channel Element
Channel Element
Channel Element
Channel Element
Long Code Gen
Long Code Gen
Long Code Gen
Long Code Gen
Long Code Gen
more
LongCode Long
Code LongCode
LongCode
LongCode
LongCode
MSC
CDMA’s “Magic” Spreading SequencesSummary of Characteristics & Functions
n Each CDMA spreading sequence is used for a specific purpose on the forward link and a different purpose on the reverse link
n The sequences are used to form “code channels” for users in both directions
Cell
Walsh Codes
Short PN Sequences
Long PN Sequence
Type of Sequence
Mutually Orthogonal
Near orthogonal with itself
a t any chip offset
except 0
se ctions of it a re near-orthogonal
Special Properties
64
2
1
How Many
64 chips1/19,200
sec.
32,768 chips
26-2/3 ms75x in 2
sec.
242 chips~41 days
Length
Information Carrier
supe r-reliable“Trojan horse”
Quadra ture Spreading
(Zero offset)
Data Scrambling &
Disti nguish us ers
Reverse Link
Funct ion
User ide nti ty
within cel l’s s ignal
Distinguish C ells,
Sectors & Quadrature Spreading
Data Scrambling to avoid all 1’s or 0’s
Forward Link
Function
IQ
32,76 8 chips long26-2/3 ms.
(75 repetitions in 2 sec.)
64codes
64 chips long
AND
=M odulo-2 A ddition
Basic Spreading & De-spreading Example:User’s Data Spread, Sent, Recovered
At Originating Site:n Input A: User’s Data @
19,200 bits/secondn Input B: Walsh Code #23
@ 1.2288 Mcpsn Output: Spread
spectrum signal
At Destination Site:n Input A: Received
spread spectrum signaln Input B: Walsh Code #23
@ 1.2288 Mcpsn Output: User’s Data @
19,200 bits/second just as originally sent Drawn to actual scale and time alignment
via air interface
XORExclusi ve-O R
Gate
1
Input A: Received Signal
Input B: Spreading Code
Output: User’s Original Data
Input A: User’s Data
Input B: Spreading Code
Spread Spectrum Signal
XORExclusi ve-O R
G ate
Originating Site
Destination Site
1
Spectrum Usage and System Capacity:Signal Bandwidth, Vulnerability, and Frequency Reuse
n Each wireless technology (AMPS, NAMPS, D-AMPS, GSM, CDMA) uses a specific modulation type with its own unique signal characteristics
n The total traffic capacity of a wireless system is determined largely by radio signal characteristics and RF design
n RF signal vulnerability to Interference dictates how much interference can be tolerated, and therefore how far apart same-frequency cells must be spaced
n For a specific S/N level, the Signal Bandwidth determines how many RF signals will “fit” in the operator’s licensed spectrum
AMPS, D-AMPS, N-AMPS
CDMA
30 30 10 kHz
200 kHz
1250 kHz
1 3 1 Users
8 Users
22 Users1
1
11
1
11
11
1
11
1
1
1 23
4
43
2
56
17
Typical Frequency Reuse N=7
Typical Frequency Reuse N=4
Typical Frequency Reuse N=1
Vulnerability:C/I 17 dB
Vulnerability:C/I 12-14 dB
Vulnerability:Eb/No 6 dB
GSM
17 dB = 101.7 5014 dB = 101.4 25 12 dB = 101.2 16
Relationship Between Eb/N0 And S/N
Eb =S R
Signal Power Bit Rate
= N0 =N W
Noise Power Bandwidth
=
=S R
W N
X = S N
W R
X
S R
N W
Eb
N0=
Signal to Noise
ProcessingGain
E / tB / t
=
WR
1,250,00014,400
87 1.9410 19 dB
WR
1,250,0009,600
130 2.1110 21 dB8 Kb vocoder(Full Rate)
13 Kb vocoder(Full Rate)
CDMA Advantage (13 kb vocoder at full rate)
AMPS
N-AMPS
D-AMPS
GSM
CDMA
Analog FM
Analog FM
DQPSK
GMSK
QPSK/OQPSK
30 KHz.
10 KHz.
30 KHz.
200 KH z.
1,250 K Hz.
C/I 17 dB
C/I 17 dB
C/I 17 dB
C/I 12-14 dB
Eb/N
o 6dB
Tech-nology Modulat ion Type Channel
BandwidthQuality
Indicator
S/N 17 dB
S/N 17 dB
S/N 17 dB
S/N 12 to 14 dB
S/N –13dB
S/N
17 dB = 101.7 5014 dB = 10 1.4 25 12 dB = 10 1.2 16
-13 dB = 10 -1.3 = 0.05 ~
S N
10 0.6
10 1.9= = 10 -1.3= -13 dB
Signal to NoiseProcessing Gain (W/R)
S N
X = 10 0.610 1.9
Eb N0
Reverse Link Interference Scenarios
n AMPS, N-AMPS, TDMA, and GSM systems do not use spreading. Co-channel users must be separated by distance to achieve the desired C/I ratio. Interferors are co-channel
users in distant cellsn CDMA systems use spreading and
due to their spreading gain can tolerate negative C/I.Many co-channel users can
share the same cell!However, this requires that
all users be power-controlled so their signals reach the base station at the same signal level
2
3
4
5 6
7
4
6
4
7 2
7
2
5
3
5
36
1
1
1
1
1
1
1
AMPS-TDMA-GSM
CDMA
usersTight Reverse-Link Power Control is essential in CDMA
CDMA Capacity Considerations
60 %
6%
6 %
6%
6%
6%
6%
0.2%
0.2%
0.2%
0.2%
0.2%
0.2%
0.2%
0.2%
0.2%
0.2%0.2%
0.2%
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 % 0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 03 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 % 0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %
1 X 60 = 60
6 X 6 = 36
12 X 0.2 = 2.4
18 X 0.03 = 0.54
24 X 0.01 = 0.24
TOTAL = 99.18 %
80 %
1 %
1 %
6 %
6 %
1 %
1 %
0.2%
0.1%
0.1%
0.1%
0.1%
0.1%
0.2%
0.1%
0.1%
0.1%0.1%
0.1%
0. 01 %
0. 01 %
0. 03 %
0. 01 %
0. 01 %
0. 01 %
0. 01 %0. 01%
0. 01 % 0. 01 %
0. 01 %
0. 00 %
0. 00 %
0. 01 %
0. 00 %
0. 00 %
10 0%
RURAL AREA
URBAN AREA
NEAR A HIGHWAY
Coexistence of CDMA with Other Systems
n Guard bands are needed between CDMA and other systems because CDMA increases the noise floor for those systems.
n These systems appear as noise for the CDMA system.
n No guard band is needed between adjacent CDMA systems.
260 kHzGuard Band
260 kHzGuard Band
Frequency
Power 1.77 MHz
1.25 MHzCDMA Carrier
Overlaying CDMA on an AMPS System
CDMA
1770 ÷ 30 = 59
1250 ÷ 30 = 41.7
260 ÷ 30 = 8.7
260 kHz 260 kHz1.25 M Hz No minal Bandw idth
Frequency
Power
1.77 MH z
CDMA CARRIER
n All frequencies are available for AMPS use
n Only the frequencies in the purple area are available for AMPS use
CDMA 800 MHz Cellular Spectrum Usage
n All CDMA RF carriers are 1.25 MHz. wide can serve ~22 users w/8 kb vocoder (~17 users w/13 kb vocoder)
n The cellular spectrum of one operator is 12.5 MHz. wide. You’d expect that 10 CDMA carriers would fit. However, only 9 carriers can be used operators must maintain a “token” AMPS presence for several years “guard bands” are required at the edges of frequency blocks or any
frequency boundaries between CDMA/non-CDMA signals no guard bands are required between adjacent CDMA carriers
Possible CDM A Center Freq. As signments
Channel Numbers
Forward l ink (i.e ., cell site transmits)Rev erse link ( i.e., mobile trans mits)824MHz
8 49M Hz
869MHz
8 94M Hz
otherusesA” A”A B A’ B’
1 10 10 1.5 2.5
A B A’ B’
1 10 10 1.5 2.5
9 9110231 33 3334 666667 716717 79 9 99110231 3 33334 66 666 771 671 7 7 99
~300 kHz. “gua rd bands ” possibly required if a dja cent-freque nc y signa ls are non-CDMA (AMPS, TDM A, ES MR, etc. )
CDMA 800 MHz Cellular Spectrum Usage
Order Side “A” Side “B”
1 283 384
2 242 425
3 201 466
4 160 507
5 119 548
6 78 589
7 37 630
8 1019 777
9 691 736
The above table is an example of CDMA channel allocation, in chronological order, which allows maximum CDMA channel packing.
Note: a) requires frequency coordination with non-cellular interferes
b) requires frequency coordination with A-side carrier
Deploying CDMA on the 1900 MHz band
CDMA
1770 ÷ 50 = 35.4
1250 ÷ 50 = 25
260 ÷ 50 = 5.2
260 kHz 260 kHz1.25 MHz Nominal Bandwidth
Frequency
Power
1.77 MHz
CDMA CARRIER
n All frequencies are available for non-CDMA use
n Only the frequencies in the blue area are available for non CDMA use
CDMA PCS 1900 MHz Spectrum Usage
n A, B, and C licenses can accommodate 11 CDMA RF channels in their 30 MHz of spectrum
n D, E, and F licenses can accommodate 3 CDMA RF channels in their 10 MHz of spectrum
n 260 kHz guard bands are required on the edges of the PCS spectrum to ensure no interference occurs with other applications just outside the spectrum
Gua rd B ands
Forwa rd li nk ( i.e., cell s ite transmits )Reve rse link (i.e., mobi le tra nsmits)1 850 MHz
BTA
BTA
BTA
BTA
BTA
BTA
Paired Bands
MTA BTAMTABTA MTAM TA
19 10 M Hz
1930MHz
1 990M Hz
Data Voice
A D B E F C A D B E F C
15 5101 0 1 515151 515 555 55
Licensed Licensed
Unlicense d0
Channel Numbe rs
299300 400 69 97 00 80 0 90 0 11990 29 93 00 400 699700 8 00 900 119 9
CDMA PCS 1900 MHz Spectrum Usage
1 25
2 50
3 75
4 100
5 125
6 150
7 175
8 200
9 225
10 250
11 275
493 BTAs (Basic Trading Areas) are grouped into 51 MTAs (Metropolitan Trading Area s).
The following tables are examples of CDMA channel allocation, in chronological order, which allow maximum CDMA channel packing. Each table represents the “preferred” set of CDMA channels according to J-STD-008.
PCS Band A
1 25
2 50
3 75
4 100
5 125
6 150
7 175
8 200
9 225
10 250
11 275
1 25
2 50
3 75
4 100
5 125
6 150
7 175
8 200
9 225
10 250
11 275
1 325
2 350
3 375
PCS Band B PCS Band C
PCS Band D
1 725
2 750
3 775
1 825
2 850
3 875
PCS Band E
PCS Band F
