CDMA Technology Overview Lesson 2 – Spectrum Usage and System Capacity

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: C/I @ 17 dB C/I @ 12-14 dB Eb/No @ 6 dB GSM 17 dB = 101.7 @ 50 14 dB = 101.4 @ 25 12 dB = 101.2 @ 16

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

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. C/I @ 17 dB C/I @ 12-14 dB Eb/No @ 6dB Tech-nology Modulation Type Channel Bandwidth Quality Indicator S/N @ 17 dB S/N @ 12 to 14 dB S/N @ –13.4 dB S/N 17 dB = 101.7 @ 50 14 dB = 101.4 @ 25 12 dB = 101.2 @ 16 -13.4 dB = 10-1.34 @ 0.046 = S N Þ 10 0.6 10 1.94 = 10 -1.34 -13.4 dB Signal to Noise Processing Gain (W/R) X Eb N0 1 22

Overlaying CDMA on an AMPS System Each CDMA Channel: 1.250 MHz ÷ 30 kHz = 41.7 = ~41 AMPS channels Each Guard Band: 260 kHz ÷ 30 kHz = 8.7 = ~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) + 260 kHz = 885 kHz TOTAL: 1.77 MHz ÷ 30 kHz = 59 AMPS channels GUARD BAND

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

Deploying CDMA on the 1900 MHz Band

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

Overlaying CDMA on the 1900 MHz Band Each CDMA Channel: 1.250 MHz ÷ 50 kHz = 25 channels Each Guard Band: 260 kHz ÷ 50 kHz = 5.2 = ~5 channels TOTAL: 1.77 MHz ÷ 50 kHz = 35.4 = ~ 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

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

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

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 283. The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 253 and 313

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 384. The first usable AMPS/TDMA Channels (outside of the Guard Zone) are Channels 354 and 414

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 ( 42 + 9 + 9 ) ÷ 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

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

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

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

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 1.2288 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

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

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

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