1. CDMA Technology Overview
Lesson 2 – Spectrum Usage and System Capacity

2. Spectrum Usage and System Capacity: Signal Bandwidth, Vulnerability and Frequency Reuse
Each wireless technology (AMPS, NAMPS, D-AMPS, GSM, CDMA) uses a specific modulation type with its own unique signal characteristics
The total traffic capacity of a wireless system is determined largely by radio signal characteristics and RF design
RF signal vulnerability to Interference dictates how much interference can be tolerated, and therefore how far apart same-frequency cells must be spaced
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
10 kHz
200 kHz
1250 kHz 1 3
1 Users
8 Users
22 Users 2 4 5 6 7
Typical Frequency Reuse N=7
Typical Frequency Reuse N=4
Typical Frequency Reuse N=1
Vulnerability:
17 dB dB
6 dB
GSM
17 dB = 50
14 dB = 25
12 dB = 16

3. Relationship Between Eb/N0 and S/N
Signal Power
Bit Rate S R
E / t
B / t
Noise Power
Bandwidth N W
Eb =
N0 = = = =
Signal to Noise S R N W Eb N0 = S R W N X S N W R X = =
Processing
Gain W
1,250,000
8 Kb vocoder
(Full Rate) 10
2.11 = =
130 = =
21.1 dB R
9,600 W
1,250,000
13 Kb vocoder
(Full Rate) 10
1.94 = = 87 = =
19.4 dB R
14,400

4. Þ S/N Advantage of CDMA 10 0.6 10 -1.34 10 1.94
AMPS
N-AMPS
D-AMPS
GSM
CDMA
Analog FM
DQPSK
GMSK
QPSK/OQPSK
30 KHz.
10 KHz.
200 KHz.
1,250 KHz.
17 dB dB
6dB
Tech-nology
Modulation Type
Channel Bandwidth
Quality
Indicator
17 dB
12 to 14 dB
–13.4 dB
S/N
17 dB = 50
14 dB = 25
12 dB = 16
-13.4 dB = = S N Þ
10 0.6 =
-13.4 dB
Signal to Noise
Processing Gain (W/R) X
Eb N0 1 22

5. Overlaying CDMA on an AMPS System
Each CDMA Channel: MHz ÷ 30 kHz = 41.7 = ~41 AMPS channels
Each Guard Band: kHz ÷ 30 kHz = = ~9 AMPS channels
260 KHz
1.25 MHz Nominal Bandwidth
Frequency
Power
1.77 MHz
CDMA CARRIER
41 AMPS channels
9 AMPS
channels
CDMA
AVAILABLE
885 KHz
Minimum Separation between AMPS/TDMA and CDMA center frequency:
(1,250 kHz ÷ 2) kHz = 885 kHz
TOTAL: MHz ÷ 30 kHz = 59 AMPS channels
GUARD
BAND

6. 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
869
894
other
uses A” A B A’ B’ 1 10
1.5
2.5
991
1023
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 ~22 users w/8 kb vocoder (~17 users w/13 kb vocoder)
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

7. Deploying CDMA on the 1900 MHz Band

8. 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
Paired Bands
MTA
BTA
1910
1930
1990
Data
Voice D E F C 15 5 10
Licensed
Unlicensed
Channel
Numbers
299
300
400
699
700
800
900
1199
A, B, and C licenses can accommodate 11 CDMA RF channels in their 30 MHz of spectrum
D, E, and F licenses can accommodate 3 CDMA RF channels in their 10 MHz of spectrum
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

9. Overlaying CDMA on the 1900 MHz Band
Each CDMA Channel: MHz ÷ 50 kHz = 25 channels
Each Guard Band: kHz ÷ 50 kHz = = ~5 channels
TOTAL: MHz ÷ 50 kHz = = ~ 35 channels
260 KHz
1.25 MHz Nominal Bandwidth
Frequency
Power
1.77 MHz
CDMA CARRIER
Just as with the CDMA on AMPS overlay, a GUARD ZONE is also needed
GUARD
BAND

10. Number of Voice Channels (As AMPS Channels Are Converted to Digital)
TDMA
13 kbps
CDMA
8 kbps
Number of Voice Channels
Number of CDMA Carriers 1 2 3 4 5 6 7 8 9
200
150
100 50

11. CDMA Frequency Channel Assignment at 800 MHz Cellular
IS-95 RECOMMENDS TO START CDMA DEPLOYMENT
WITH EITHER THE PRIMARY OR THE SECONDARY CHANNEL 1
334
667
991
1023
333
666
715
799
716
Channel
Numbers
A Band
B Band A’ A” B’
1013 31 73
115
157
199
241
283
384
426
468
510
552
594
636
691
777
CDMA A-Band Carriers
CDMA B-Band Carriers 8 7 6 5 4 3 2 9 * **
* 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

12. CDMA Frequency Clearing: A-band (N=7 Reuse Pattern)
To deploy a CDMA carrier centered on AMPS/TDMA Channel 283, AMPS/TDMA Channels 254 through 312, inclusive, must be cleared from the CDMA coverage area
The CDMA channel is implemented, centered on AMPS/TDMA Channel The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 253 and 313

13. CDMA Frequency Clearing: B-band (N=7 Reuse Pattern)
To deploy a CDMA carrier centered on AMPS/TDMA Channel 384, AMPS/TDMA Channels 355 through 413, inclusive, must be cleared from the CDMA coverage area
The CDMA channel is implemented, centered on AMPS/TDMA Channel The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 354 and 414

14. Overlay Guard Zone Deployment
AMPS Only Cells
approx 19 channels per sector
CDMA & AMPS Cells
approx 16 channels per sector
one CDMA channel/carrier/frequency
( ) ÷ 21 = 2.8 = ~3 AMPS channels must be cleared per sector in the CDMA & AMPS area and in the Guard Zone to make room for the first CDMA channel/carrier/frequency
The Guard Zones are needed between CDMA and other systems because CDMA increases the noise floor for those systems
AMPS Only Cells (GUARD ZONE)
approx 16 channels per cell

15. Other Technologies: Avoiding Interference
In conventional radio technologies, the desired signal must be strong enough to override any interference
AMPS, TDMA and GSM depend on physical distance separation to keep interference at low levels
Co-channel users are kept at a safe distance by careful frequency planning
Nearby users and cells must use different frequencies to avoid interference 2 3 4 5 6 7 1
AMPS-TDMA-GSM
Figure of Merit: C/I
(carrier/interference ratio)
AMPS: +17 dB
TDMA: +14 to 17 dB
GSM: +12 to 14 dB

16. Other Technologies: Avoiding Interference
In conventional radio technologies, the desired signal must be strong enough to override any interference
AMPS, TDMA and GSM depend on physical distance separation to keep interference at low levels
Co-channel users are kept at a safe distance by careful frequency planning
Nearby users and cells must use different frequencies to avoid interference 2 3 4 5 6 7 1
AMPS-TDMA-GSM
Figure of Merit: C/I
(carrier/interference ratio)
AMPS: +17 dB
TDMA: +14 to 17 dB
GSM: +12 to 14 dB

17. CDMA: Using a New Dimension
All CDMA users occupy the same frequency at the same time! Frequency and time are not used as discriminators
CDMA operates by using CODES to discriminate between users
CDMA interference comes mainly from nearby users
Each user is a small voice in a roaring crowd -- but with a uniquely recoverable code
Transmit power on all users must be tightly controlled so their signals reach the base station at the same signal level
Figure of Merit: Ec/Io, Eb/No
(energy per chip [bit] / interference [noise] spectral density)
CDMA: Ec/Io -17 to -2 dB
CDMA: Eb/No ~+6 dB

18. Convolutional Encoder R=1/2 K=9 Power Control Decision
The Network View
Convolutional Encoder R=1/2 K=9
Symbol Repetition
Packet
Routing
9600 bps 4800 bps 2400 bps 1200 bps
T-1
64 kbs PCM
Block Interleaver
19200 sps 9600 sps 4800 sps 2400 sps
19.2 Ksps
Long Code
PN Generator
Mcps
Decimator ¸64
M U X
Data Scrambling
Walsh Code Wt
User Address
Mask (ESN)
I PN +Dt
Q PN +Dt
Up- Conversion
S I other users
S Q other users
Correlator
C o m b i n e r
Block De-Interleaver
Viterbi
Decoder
Voice
Coding
Switching
BCN
Unch.
PN +Dt
CDSU
800 Hz
HPA
LNA IF RF
BTU/ STU
De- modulation
Modulation
Down
Conversion
MTX
BSC
BTS
Power Control Decision

19. S The Handset View Receiver Transmitter Antenna symbols chips RF
Duplexer &
Bandpass
Filters IF
BPF
Mixer
LNA
Local
Oscillator
(Synthesized)
Traffic Correlator
PN Generator
Walsh Generator
Vocoder
Search Correlator (Pilots)
Walsh =0
CPU &
Control
Algorithms
Conv. Encoder
& Symbol Rep.
Block
Interleaver
Orthogonal
Modulator
Data Burst
Randomizer
Direct Seq.
Spreading
Quadrature
Baseband
Filtering
Power
Amplifier
Antenna
Receiver
Transmitter
voice bits
audio
symbols
chips RF LO
Open Loop Pwr Control
message
bits
message bits
LONG CODE Generator
Transmit Gain Adjust: Closed Loop Pwr Control S
Viterbi
Decoder

20. Lesson Review What is the C/I ratio (in decibels) for GSM users?
12 – 14 dB
Processing Gain (W/R) is
the rate of bit rate to bandwidth
the rate of bandwidth to bit rate
all of the above
none of the above
The rate of bandwidth to bit rate
Frame Error Rate (FER) is a better performance measurement that Bit Error Rate (BER)?
True

21. Lesson Review, continued
All CDMA RF carriers
are 1.25 MHz wide
can serve ~ 22 users with a 8kb vocoder
can serve ~ 17 users with a 13kb vocoder
all of the above
none of the above
As the number of voice channels increase, the number of AMPS carriers decrease.
True
Long Code PN generation occurs in the
MTX
BSC
BTS